WO2009075151A1 - Damping force control apparatus - Google Patents

Damping force control apparatus Download PDF

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Publication number
WO2009075151A1
WO2009075151A1 PCT/JP2008/070372 JP2008070372W WO2009075151A1 WO 2009075151 A1 WO2009075151 A1 WO 2009075151A1 JP 2008070372 W JP2008070372 W JP 2008070372W WO 2009075151 A1 WO2009075151 A1 WO 2009075151A1
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WO
WIPO (PCT)
Prior art keywords
section
damping coefficient
damping
unsprung
sprung
Prior art date
Application number
PCT/JP2008/070372
Other languages
French (fr)
Inventor
Hiroki Kambe
Jin Hozumi
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Toyota Jidosha Kabushiki Kaisha
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Publication of WO2009075151A1 publication Critical patent/WO2009075151A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/016—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/016—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input
    • B60G17/0161—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input mainly during straight-line motion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/016—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input
    • B60G17/0165—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input to an external condition, e.g. rough road surface, side wind
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/018—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by the use of a specific signal treatment or control method
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/019—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by the type of sensor or the arrangement thereof
    • B60G17/01908—Acceleration or inclination sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2202/00—Indexing codes relating to the type of spring, damper or actuator
    • B60G2202/30—Spring/Damper and/or actuator Units
    • B60G2202/32—The spring being in series with the damper and/or actuator
    • B60G2202/322—The spring being in series with the damper and/or actuator the damper being controllable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
    • B60G2400/10—Acceleration; Deceleration
    • B60G2400/102—Acceleration; Deceleration vertical
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
    • B60G2400/20—Speed
    • B60G2400/204—Vehicle speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
    • B60G2400/25—Stroke; Height; Displacement
    • B60G2400/252—Stroke; Height; Displacement vertical
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
    • B60G2400/90—Other conditions or factors
    • B60G2400/91—Frequency
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/10—Damping action or damper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/10—Damping action or damper
    • B60G2500/11—Damping valves
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2600/00—Indexing codes relating to particular elements, systems or processes used on suspension systems or suspension control systems
    • B60G2600/02—Retarders, delaying means, dead zones, threshold values, cut-off frequency, timer interruption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2600/00—Indexing codes relating to particular elements, systems or processes used on suspension systems or suspension control systems
    • B60G2600/70—Computer memory; Data storage, e.g. maps for adaptive control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2800/00—Indexing codes relating to the type of movement or to the condition of the vehicle and to the end result to be achieved by the control action
    • B60G2800/16—Running
    • B60G2800/162—Reducing road induced vibrations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2800/00—Indexing codes relating to the type of movement or to the condition of the vehicle and to the end result to be achieved by the control action
    • B60G2800/90—System Controller type
    • B60G2800/91—Suspension Control
    • B60G2800/916—Body Vibration Control

Definitions

  • the present invention relates to a damping force control apparatus for a vehicle which controls damping forces of shock absorbers disposed on the vehicle at positions corresponding to wheels.
  • the damping coefficient of the shock absorber is controlled a constant low damping coefficient so as to absorb the vibration of the unsprung portion by the shock absorber and suppress transmission of the vibration to the sprung section, to thereby improve ride quality.
  • FIG. 3(a) shows the relation between damping coefficient and vertical acceleration of the sprung section
  • FIG. 3(b) shows the relation between damping coefficient and longitudinal acceleration (acceleration in the front-rear direction) of the sprung section.
  • the present invention has been achieved to solve the above problems, and an object of the invention is to suppress not only a vertical vibration of a sprung section but also a longitudinal vibration of the sprung section when a vibration of an unsprung section is strong, to thereby improve ride quality.
  • the present invention provides a damping force control apparatus for a vehicle which includes a shock absorber interposed between an unsprung section and a sprung section at each wheel position of the vehicle, the shock absorber having a variable damping coefficient, and which controls the damping coefficient of 2
  • the clamping force control apparatus comprising unsprung-section vibration detection means for detecting a vibration in an unsprung-section resonance frequency band at each wheel position; and unsprung-section damping control means, operable when a level of the detected vibration in the unsprung-section resonance frequency band exceeds a reference level, for setting the damping coefficient of the shock absorber on the basis of a specific damping coefficient which minimizes a sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration of the sprung section, the specific damping coefficient being determined from a relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and a relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section.
  • the unsprung-section vibration detection means may include vertical acceleration detection means for detecting a vertical acceleration of the sprung section or the unsprung section at each wheel position; and unsprung-section vibration component extraction means for extracting a vibration component in the unsprung-section resonance frequency band from a signal representing the detected vertical acceleration.
  • the unsprung-section vibration detection means detects a vibration in an unsprung-section resonance frequency band at each wheel position.
  • the vertical acceleration detection means detects a vertical acceleration of the sprung section or the unsprung section; and the unsprung-section vibration component extraction means extracts a vibration component in the unsprung-section resonance frequency band from a signal representing the detected vertical acceleration.
  • the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient.
  • This specific damping coefficient is a damping coefficient which minimizes the sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration (acceleration in the front-rear direction) of the sprung section and which is determined from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section.
  • the damping coefficient which minimizes the sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration of the sprung section can be obtained by calculating a damping coefficient such that the square root of the sum of the square of the vertical acceleration and the square of the longitudinal acceleration assumes the minimum value.
  • the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section can be defined by arithmetic expressions or the like.
  • the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient when the level of the vibration in the unsprung-section resonance frequency band detected by the unsprung-section vibration detection means exceeds the reference level.
  • the damping coefficient of the shock absorber is set to the specific damping coefficient.
  • the damping coefficient of the shock absorber is set to a settable value closest to the specific damping coefficient.
  • the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a well-balanced manner, and ride quality is improved.
  • the damping force control apparatus further comprises specific-damping-coefficient acquisition means for acquiring, as the specific damping coefficient, a damping coefficient which minimizes the sum of vectors of the vertical acceleration of the sprung section and the longitudinal acceleration of the sprung section, from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section; and the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient acquired by the specific-damping-coefficient acquisition means, when the level of the detected vibration in the unsprung-section resonance frequency band exceeds the reference level.
  • specific-damping-coefficient acquisition means for acquiring, as the specific damping coefficient, a damping coefficient which minimizes the sum of vectors of the vertical acceleration of the sprung section and the longitudinal acceleration of the sprung section, from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of
  • the specific damping coefficient is acquired by the specific-damping-coefficient acquisition means.
  • the specific-damping-coefficient acquisition means can store the specific damping coefficient in storage means in advance, and acquire the specific damping coefficient by reading it out of the storage means.
  • arithmetic expressions or maps which represent the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section are previously stored in the storage means as relation defining data.
  • the specific-damping-coefficient acquisition means can acquire the specific damping coefficient on the basis of the relation defining data stored in the storage means.
  • the specific-damping-coefficient acquisition means can store a map or an arithmetic expression which defines the relation between the running state and the specific damping coefficient in the storage means as relation defining data, and acquire the specific damping coefficient on the basis of the relation defining data stored in the storage means.
  • the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient acquired by the specific-damping-coefficient acquisition means. Accordingly, the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a well-balanced manner, and ride quality is improved.
  • the damping force control apparatus further comprises relative position detection means for detecting a relative vertical position of the unsprung section in relation to the sprung section at each wheel position; and vehicle-height-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected relative position.
  • the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section changes depending on, for example, the forward-tilting angle of the shock absorber (an angle of the axis of the shock absorber in relation to a vertical line) and the longitudinal-principal-elastic-axis dihedral angle (an angle of the longitudinal principal elastic axis in relation to a horizontal line) of a suspension. Further, these angles change depending on the vehicle height; i.e., the relative vertical position of the unsprung section in relation to the sprung section.
  • the relative position detection means detects the relative vertical position of the unsprung section in relation to the sprung section, and the vehicle-height-responsive specific damping coefficient changing means changes the specific damping coefficient in accordance with the detected relative position.
  • the vehicle-height-responsive specific damping coefficient changing means may be configured to store in storage means relation defining data, such as a map or an arithmetic expression, which determines a specific damping coefficient corresponding to the relative vertical position of the unsprung section in relation to the sprung section, and set the specific damping coefficient corresponding to the relative vertical position of the unsprung section in relation to the sprung section, by use of the relation defining data stored in the storage means, while the vehicle is running.
  • relation defining data such as a map or an arithmetic expression
  • the relative vertical position of the unsprung section in relation to the sprung section is equivalent to the vertical position of the sprung section in relation to the unsprung section, and these expressions refer to the relative positional relation between the sprung section and the unsprung section in the vertical direction.
  • the specific damping coefficient becomes a more proper one, and the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a more well-balanced manner, and ride quality is improved.
  • the damping force control apparatus further comprises vehicle speed detection means for detecting a vehicle speed; and vehicle-speed-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected vehicle speed.
  • the vehicle speed detection means detects the vehicle speed; and the vehicle-speed-responsive specific damping coefficient changing means changes the specific damping coefficient in accordance with the detected vehicle speed.
  • the vehicle-speed-responsive specific damping coefficient changing means may be configured to store in storage means relation defining data, such as a map or an arithmetic expression, which determines a specific damping coefficient corresponding to the vehicle speed, and set the specific damping coefficient corresponding to the vehicle speed, by use of the relation defining data stored in the storage means, while the vehicle is running.
  • relation defining data such as a map or an arithmetic expression
  • the specific damping coefficient becomes a more proper one, and the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a more well-balanced manner, and ride quality is improved.
  • FIG. 1 is a schematic configuration diagram of a damping force control apparatus according to a first embodiment.
  • FIG. 2 is a simplified model diagram used for explaining specifications of a suspension device.
  • FIGS. 3(a) and 3(b) are characteristic charts showing a relation between damping coefficient and sprung-section vertical acceleration and a relation between damping coefficient and sprung-section longitudinal acceleration, respectively.
  • FIGS. 4(a) and 4(b) are characteristic charts showing a relation between damping coefficient and sprung-section vertical acceleration and a relation between damping coefficient and sprung-section longitudinal acceleration, respectively.
  • FIG. 5 is a flowchart showing an unsprung-section damping control routine according to the first embodiment.
  • FIG. 6 is a schematic configuration diagram of a damping force control apparatus according to a second embodiment.
  • FIG. 7 is a reference map for acquiring a specific damping coefficient according to the second embodiment.
  • FIG. 8 is a flowchart showing an unsprung-section damping control routine according to the second embodiment.
  • FIG. 9 is a schematic configuration diagram of a damping force control apparatus according to a third embodiment.
  • FIG. 10 is a reference map for acquiring a specific damping coefficient according to the third embodiment.
  • FIG. 11 is a flowchart showing an unsprung-section damping control routine according to the third embodiment.
  • FIG. 12 is a schematic configuration diagram of a damping force control apparatus according to a fourth embodiment.
  • FIG. 13 is a reference map for acquiring a specific damping coefficient according to the fourth embodiment.
  • FIG. 14 is a flowchart showing an unsprung-section damping control routine according to the fourth embodiment.
  • FIG. 1 schematically shows the configuration of a damping force control apparatus for a vehicle according to a first embodiment.
  • the clamping force control apparatus includes shock absorbers 10 and coil springs 20.
  • one of the shock absorbers 10 and one of the coil springs 20 are disposed between a vehicle body BD and each of a front left wheel WfI, a front right wheel Wfr, a rear left wheel WrI, and a rear right wheel Wrr.
  • the wheel W When the location (front, rear, left, and right) of a wheel is not specified, the wheel is simply referred to as the wheel W.
  • Each shock absorber 10 is interposed between a suspension member 14 and the vehicle body BD.
  • the suspension member 14 is composed of a lower arm, a knuckle, etc., and holds the wheel W so as to allow the wheel W to swing in the vertical direction in relation to the vehicle body BD.
  • the shock absorber 10 includes a cylinder 11 and a piston rod 12, which is inserted into the cylinder 11 in a vertically movable manner.
  • a lower end of the cylinder 11 is connected to the suspension member 14 (such as the lower arm).
  • An upper end of the piston rod 12 is fixed to the vehicle body BD.
  • the coil spring 20 is provided in parallel with the shock absorber 10.
  • the cylinder 11 is divided into an upper chamber R1 and a lower chamber R2 by a piston 13 that liquid-tightly slides over an inner circumferential surface of the cylinder 11.
  • variable throttle mechanism 30 is mounted on the piston 13.
  • an actuator 31 which constitutes a portion of the variable throttle mechanism 30
  • the variable throttle mechanism 30 changes, in a stepwise manner, a degree of opening of a communication passage for establishing communication between the upper chamber R1 and the lower chamber R2 of the cylinder 11 such that the degree of opening of the communication passage is switched to one of a plurality of steps; i.e., a
  • the variable throttle mechanism 30 may be of a type that continuously adjusts the degree of opening of the communication passage, which establishes communication between the upper chamber R1 and the lower chamber R2 of the cylinder 11.
  • a sprung section A All members provided above the coil spring 20 and supported by the coil spring 20 are collectively referred to as a sprung section A.
  • the vehicle body BD corresponds to the sprung section A.
  • All members provided below the coil spring 20 are collectively referred to as an unsprung section B.
  • the suspension member 14, the wheel WfI - Wrr, a brake (not shown), etc. together correspond to the unsprung section B.
  • the damping force control apparatus includes a damping force control unit 40 that controls the damping forces of the shock absorbers 10 by controlling operations of the actuators 31.
  • the damping force control unit 40 (hereinafter referred to as a damping force ECU 40) includes a microcomputer as a main constituent element, the microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and the like.
  • the actuators 31 are connected to an output interface of the damping force ECU 40.
  • Sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr are connected to an input interface of the damping force ECU 40.
  • the sprung-section vertical acceleration sensors 4IfI, 41fr, 41 rl, and 41 rr are respectively mounted to sprung sections A corresponding to the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr.
  • the sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr respectively detect sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr of the sprung sections A at the sensor mounting positions, in relation to absolute space.
  • Each of the sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr detected by the sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr becomes positive when an upward acceleration is generated in the vehicle, and becomes negative when a downward acceleration is generated in the vehicle.
  • the damping force ECU 40 calculates respective damping coefficients corresponding to the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr.
  • the damping force ECU 40 controls the damping forces of the shock absorbers 10 individually by stepwise changing the degrees of opening of the communication passages of the corresponding cylinders 11 in accordance with the damping coefficient. Damping force control for the shock absorber 10 is performed in a similar manner for each of the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr.
  • the sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr are simply referred to as a sprung-section vertical acceleration sensor 41.
  • the detected sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr are simply referred to as a sprung-section vertical acceleration Gz.
  • the unsprung section B vibrates strongly in an unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz).
  • an unsprung-section resonance frequency band for example, 8 Hz to 16 Hz.
  • Tramping of the unsprung section B can be detected by extracting an unsprung-section resonance frequency band component from a vertical acceleration signal detected by the sprung-section vertical acceleration sensor 41.
  • tramping of the unsprung section B occurs, transmission of the vibration of the unsprung section to the sprung section A can be suppressed by means of changing the damping coefficient of the shock absorber 10.
  • the vertical acceleration of the sprung section A (hereinafter referred to as the sprung-section vertical acceleration Gz) in the unsprung-section resonance frequency band can be expressed by the following Equation (1), through use of the damping coefficient C of the shock absorber 10.
  • Gz(s) s 2 K tz (K 0 K u +sC(K c +K u ))/[s 5 m 2 m l C + s 4 m 2 K u m l
  • K 0 represents a wheel rate
  • K u represents an upper support rigidity
  • K tz indicates a vertical rigidity of a tire
  • s is a Laplacian operator.
  • Vibration of the unsprung section B also causes vibration of the sprung section A in the longitudinal direction (hereinafter referred to as the "longitudinal vibration of the sprung section A").
  • the longitudinal vibration of the sprung section A can also be suppressed by means of changing the damping coefficient of the shock absorber 10.
  • a longitudinal acceleration of the sprung section A (hereinafter referred to as a sprung-section longitudinal acceleration Gx) in the unsprung-section resonance frequency band can be expressed by the following Equation (2), through use of the damping coefficient C of the shock absorber 10.
  • f(s) and h(s) are as follows:
  • K x represents a longitudinal-elastic-main-axis rigidity (a rigidity, in the longitudinal direction, of a longitudinal principal elastic axis, which represents all the members, such as a link mechanism, for connecting the wheel W to the vehicle body BD);
  • K 6 represents a rigidity of an axle carrier when it rotates about a spindle axis;
  • ⁇ represents a forward-tilting angle of the shock absorber 10 (an angle between the axis of the shock absorber 10 and a vertical line);
  • ⁇ represents a longitudinal-principal-elastic-axis dihedral angle (an angle in an upward direction of the longitudinal principal elastic axis in relation to a horizontal line);
  • H represents a vertical distance between the centroid of the axle carrier and the longitudinal principal elastic axis;
  • L represents a horizontal distance between the centroid of the axle carrier and the axis of the shock absorber 10;
  • K tx represents a longitudinal rigidity of a tire;
  • P x represents a
  • FIG. 3 and FIG. 4 show sprung-section vertical accelerations Gz and sprung-section longitudinal accelerations Gx which are calculated for two example suspension apparatuses by use of Equations (1) and (2).
  • (a) shows a relation between the damping coefficient C of the shock absorber 10 and the magnitude (absolute value) of the sprung-section vertical acceleration Gz in the unsprung-section resonance frequency band
  • (b) shows a relation between the damping coefficient C of the shock absorber 10 and the magnitude (absolute value) of the sprung-section longitudinal acceleration Gx in the unsprung-section resonance frequency band.
  • the two example suspension apparatuses have different characteristics, because the suspension apparatuses have different configurations.
  • the examples indicate that the sprung-section vertical acceleration Gz decreases when the damping coefficient C is lowered.
  • the sprung-section longitudinal acceleration Gx increases as a result of reduction in the damping coefficient C.
  • the damping coefficient C falls below about 1600 N-s/m
  • the sprung-section longitudinal acceleration Gx increases with a decrease in the damping coefficient C.
  • the sprung-section longitudinal acceleration Gx increases with a decrease in the damping coefficient C over the entire range of the damping coefficient C.
  • a damping coefficient Ct which minimizes the sum of vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx (thereinafter, the damping coefficient C will be referred to as a specific damping coefficient Ct) is calculated in advance.
  • the damping coefficient C When the vibration of the unsprung section B in the resonance frequency band is strong, the damping force of the shock absorber 10 is controlled through use of the specific damping coefficient Ct.
  • the sprung-section longitudinal acceleration Gx changes with vehicle height and vehicle speed.
  • the specific damping coefficient Ct is calculated in advance with the vehicle height and the vehicle speed fixed to standard values.
  • Equation (3) The sum Gt of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be expressed by the following Equation (3) as a square root of the sum of the square of the sprung-section vertical acceleration Gz calculated by Equation (1) and the square of the sprung-section longitudinal acceleration Gx calculated by Equation (2).
  • the specific damping coefficient Ct at which the square root attains the lowest value is calculated in advance and stored in the ROM of the damping force ECU 40 along with a control program. Notably, there may be stored a degree of opening of the communication passage of the variable throttle mechanism 30 at which the specific damping coefficient Ct can be obtained.
  • FIG. 5 is a flowchart showing an unsprung-section damping control routine.
  • the unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program.
  • the unsprung-section damping control routine starts when an ignition switch (not shown) is turned ON.
  • the unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
  • the damping force ECU 40 performs not only the unsprung-section damping control, but also various damping force controls in parallel.
  • the other damping force controls are common and do not characterize the present invention. Therefore, in the first embodiment, configurations for performing the other damping force controls are omitted from the configuration of the damping force control apparatus.
  • the other damping force controls include, for example, vehicle speed responsive control, anti-dive control, anti-squat control, rolling control, and anti-lift control. However, because these controls do not constitute the feature of the present invention, descriptions thereof are omitted.
  • Step S11 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S12, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing. Therefore, the signal obtained through the band-pass filtering processing is an acceleration signal corresponding to the vibration state of the unsprung section B. As a result, the tramping state of the unsprung section B can be detected.
  • a frequency component in the unsprung-section resonance frequency band for example, 8 Hz to 16 Hz
  • Step S13 the damping force ECU 40 judges whether a magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds a reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds a reference level.
  • GzO threshold value
  • Step S14 the damping force ECU 40 sets the damping coefficient C to the above-described specific damping coefficient Ct.
  • the specific damping coefficient Ct is stored in a storage device, such as the ROM, of the damping force ECU 40.
  • Step S14 the specific damping coefficient Ct is acquired by being read from the storage device. A configuration for reading and acquiring the specific damping coefficient Ct corresponds to the specific damping coefficient acquisition means of the present invention.
  • the damping force ECU 40 changes the damping coefficient of the shock absorber 10 by stepwise changing the degree of opening of the communication passage of the cylinder 11.
  • the damping force ECU 40 selects a degree of opening of the communication passage corresponding to the specific damping coefficient Ct.
  • the damping force ECU 40 stores the relation between the damping coefficient and the degree of opening of the communication passage in the storage device, such as the ROM.
  • the damping force ECU 40 sets the degree of opening of the communication passage corresponding to the specific damping coefficient Ct on the basis of the stored relation.
  • the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage to one of a plurality of degrees of opening. Therefore, when the damping force ECU 40 cannot set the degree of opening of the communication passage to a degree of opening at which the specific damping coefficient Ct is attained, the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained.
  • the variable throttle mechanism 30 may be configured to have a dedicated degree of opening of the communication passage at which the specific damping coefficient Ct can be attained, as one of the plurality of degrees of opening that can be selected, and switch the degree of opening of the communication passage to the dedicated degree of opening. Further, when the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct is attained.
  • the damping force ECU 40 ends the current execution of the unsprung-section damping control routine after setting the damping coefficient of the shock absorber 10 by the processing in Step S14.
  • the unsprung-section damping control routine is performed repeatedly at predetermined short intervals.
  • the damping force ECU 40 judges in Step S13 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required.
  • the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
  • the damping force of the shock absorber 10 is controlled based on the specific damping coefficient Ct which minimizes the sum of the vectors of the vertical acceleration and the longitudinal acceleration of the sprung section A. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction are reduced in a well-balanced manner. As a result, ride quality is improved.
  • a damping force control apparatus according to the second embodiment has the following additional configuration. That is, as shown in FIG. 6, vehicle height sensors 42fl, 42fr, 42rl, and 42rr are provided for the wheels WfI, Wfr, WrI, and Wrr so as to detect the vertical portions of the unsprung sections B in relation to the sprung section A.
  • the vehicle height sensors 42fl, 42fr, 42rl, and 42rr output to the damping force ECU 40 vehicle height signals XfI, Xfr, XrI, and Xrr representing the detected vehicle heights.
  • the vehicle height sensors 42fl, 42fr, 42rl, and 42rr are respectively provided between the sprung sections A and the unsprung sections B corresponding to the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr.
  • the vehicle height sensors 42fl, 42fr, 42rl, and 42rr respectively detect vehicle heights XfI, Xfr, XrI 1 and Xrr, which correspond to displacements from a reference vehicle height, from the relative vertical positions of the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr in relation to the vehicle body BD (the sprung sections A); i.e., the distances between the sprung sections A and the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr.
  • the signals output from the vehicle height sensors 42fl, 42fr, 42rl, and 42rr each assume a positive value when the detected vehicle height is higher than the reference vehicle height, and assume a negative value when the detected vehicle height is lower than the reference vehicle height. Damping force control for the shock absorber 10 is performed in a similar manner for each of the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. Therefore, separate descriptions will not be given for the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr.
  • vehicle height sensors 42fl, 42fr, 42rl, and 42rr are simply referred to as a vehicle height sensor 42.
  • vehicle height sensor 42 The detected vehicle heights XfI, Xfr, XrI, and Xrr are simply referred to as a vehicle height X.
  • the sprung-section longitudinal acceleration Gx changes depending on the front-tilting angle ⁇ and the longitudinal principal elastic axis dihedral angle ⁇ of the shock absorber 10.
  • the front-tilting angle ⁇ and the longitudinal principal elastic axis dihedral angle ⁇ of the shock absorber 10 change depending on the vehicle height X or, in other words, the relative position of the unsprung section B in the vertical direction in relation to the sprung section A, and are univocally determined from the relative position.
  • the front-tilting angle ⁇ of the shock absorber 10 decreases and the longitudinal principal elastic axis dihedral angle ⁇ increases.
  • the longitudinal acceleration Gx of the sprung section A in the unsprung-section resonance frequency band can be expressed by use of the damping coefficient C. Therefore, ultimately, the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle height X.
  • a map (relation defining data) defining a relation between the vehicle height X and the specific damping coefficient Ct, such as that shown in FIG.
  • the map is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle height X detected while the vehicle is running.
  • the map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle height X based on Equations (1), (2), and (3), while fixing the vehicle speed to a standard value.
  • the map is stored in the ROM of the damping force ECU 40.
  • the specific damping coefficient Ct is set to a value greater than that when the vehicle height X is higher than the reference vehicle height.
  • the relation defining data can be stored in a storage means other than the ROM.
  • FIG. 8 is a flowchart showing an unsprung-section damping control routine according to the second embodiment.
  • the unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program.
  • the unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON.
  • the unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
  • Step S21 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S22, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
  • a frequency component in the unsprung-section resonance frequency band for example, 8 Hz to 16 Hz
  • Step S23 the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
  • Step S24 the damping force ECU 40 reads the vehicle height X detected by the vehicle height sensor 42. Then, in Step S25, the damping force ECU 40 acquires the specific damping coefficient Ct corresponding to the detected vehicle height X by reference to the map defining the relation between the vehicle height X and the specific damping coefficient Ct shown in FIG. 7.
  • a configuration for changing and setting the specific damping coefficient Ct in accordance with the vehicle height X corresponds to the vehicle-height-responsive specific damping coefficient changing means of the present invention.
  • a configuration for acquiring the specific damping coefficient Ct from the map corresponds to the specific damping coefficient acquisition means of the present invention.
  • the specific damping coefficient Ct may be calculated through use of Equations (1), (2), and (3) as needed.
  • relation defining data that relate the vehicle height X to ( ⁇ , ⁇ ) are stored in storage means in advance in the form of a map or the like.
  • Values of ( ⁇ , ⁇ ) corresponding to the vehicle height X detected in Step S24 are determined from the relation defining data.
  • the determined values of ( ⁇ , ⁇ ) are substituted for Equation (2).
  • the damping force ECU 40 calculates the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx of the sprung section A.
  • the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine.
  • the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening.
  • the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained.
  • the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
  • the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle height X. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
  • the damping force ECU 40 judges in Step S23 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required.
  • the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
  • the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle height X. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved.
  • a damping force control apparatus can be configured by adding to the damping force control apparatus according to the first embodiment a vehicle speed sensor 43 that detects a raveling speed of the vehicle.
  • the vehicle speed sensor 43 is connected to the damping force ECU 40 and outputs a signal indicating the vehicle speed V to the damping force ECU 40.
  • the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle speed V.
  • a map (relation defining data) defining a relation between the vehicle speed V and the specific damping coefficient Ct, such as that shown in FIG. 10, is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle speed V detected while the vehicle is running.
  • the map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle speed V based on Equations (1), (2), and (3), while fixing the vehicle height to a standard value.
  • the map is stored in the ROM of the damping force ECU 40.
  • the specific damping coefficient Ct is set to a smaller value as the vehicle speed V increases.
  • the relation defining data can be stored in a storage means other than the ROM.
  • FIG. 11 is a flowchart showing an unsprung-section damping control routine according to the third embodiment.
  • the unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program.
  • the unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON.
  • the unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
  • Step S31 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S32, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
  • a frequency component in the unsprung-section resonance frequency band for example, 8 Hz to 16 Hz
  • Step S33 the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
  • Step S34 the damping force ECU 40 reads the vehicle speed V detected by the vehicle speed sensor 43. Then, in Step S35, the damping force ECU 40 determines the specific damping coefficient Ct corresponding to the detected vehicle speed V by reference to the map defining the relation between the vehicle speed V and the specific damping coefficient Ct shown in FIG. 10.
  • a configuration for changing and setting the specific damping coefficient Ct in accordance with the vehicle speed V corresponds to the vehicle-speed-responsive specific damping coefficient changing means of the present invention.
  • Equations (1), (2), and (3) can be stored in the storage means, and the specific damping coefficient Ct can be successively calculated through use of the equations while the vehicle is running.
  • the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine.
  • the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening.
  • the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained.
  • the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
  • the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
  • the damping force ECU 40 judges in Step S33 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required.
  • the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
  • the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved.
  • a damping control apparatus is a combination of the damping control apparatuses according to the second embodiment and the third embodiment.
  • the damping control apparatus according to the fourth embodiment can be configured by adding to the damping control apparatus according to the first embodiment the vehicle speed sensor 43 and the vehicle height sensors 42fl, 42fr, 42rl, and 42rr (hereinafter referred to as simply the vehicle height sensor 42), which detect the vertical positions of the unsprung sections B in relation to the sprung sections A for the wheel WfI, Wfr, WrI, and Wrr.
  • the vehicle height sensor 42 and the vehicle speed sensor 43 are the same as those described in the second embodiment and the third embodiment.
  • the sprung-section longitudinal acceleration Gx expressed by Equation (2) changes depending on the vehicle height X and the vehicle speed V. Therefore, the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle height X and the vehicle speed V.
  • a map (relation defining data) defining a relation between the vehicle height X and the specific damping coefficient Ct at each vehicle speed V, such as that shown in FIG.
  • the map 13 is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle height X and the vehicle speed V detected while the vehicle is running.
  • the map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle height X and the vehicle speed V based on Equations (1), (2), and (3).
  • the map is stored in the ROM of the damping force ECU 40.
  • the relation defining data can be stored in a storage means other than the ROM.
  • FIG. 14 is a flowchart showing an unsprung-section damping control routine according to the fourth embodiment.
  • the unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program.
  • the unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON.
  • the unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
  • Step S41 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S42, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
  • a frequency component in the unsprung-section resonance frequency band for example, 8 Hz to 16 Hz
  • Step S43 the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
  • Step S44 the damping force ECU 40 reads the vehicle height X detected by the vehicle height sensor 42. Then, in Step S45, the damping force ECU 40 reads the vehicle speed V detected by the vehicle speed sensor 43.
  • Step S46 the damping force ECU 40 determines the specific damping coefficient Ct corresponding to the detected vehicle height X and vehicle speed V by reference to the map defining the relation between the vehicle height X and the specific damping coefficient Ct at each vehicle speed V, shown in FIG. 13.
  • the specific damping coefficient Ct may be calculated by use of Equations (1), (2), and (3) as needed, as in the case of the above-described embodiments.
  • the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine.
  • the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening.
  • the damping force ECU 40 selects a degree of opening of the communication passage at which a clamping coefficient closest to the specific damping coefficient Ct can be attained.
  • the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
  • the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle height X and the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
  • the damping force ECU 40 judges in Step S43 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required.
  • the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
  • the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle height X and the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved.
  • the damping control apparatuses for a vehicle according to the embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the object of the present invention.
  • the tramping state of the unsprung section B is detected through extraction of a frequency component in the unsprung-section resonance frequency band from the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41.
  • a vertical unsprung acceleration sensor (not shown) can be provided so as to detect the vertical acceleration of the unsprung section B.
  • the tramping state of the unsprung section B can be detected through extraction of a frequency component in the unsprung-section resonance frequency band from a vertical unsprung acceleration signal Gz detected by the vertical unsprung acceleration sensor.
  • the band-pass filtering processing is performed with the unsprung-section resonance frequency band set to 8 Hz to 16 Hz.
  • the unsprung-section resonance frequency band can be freely changed in accordance with suspension characteristics and the like.

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Abstract

A damping force control apparatus suppresses not only a vertical vibration of a sprung section A, but also a longitudinal vibration thereof, when a vibration of an unsprung section B is strong, to thereby improve ride quality. A specific damping coefficient Ct which minimizes the sum of vectors of a sprung-section vertical acceleration and a sprung-section longitudinal acceleration is calculated in advance from a relation between a damping coefficient of a shock absorber and the vertical acceleration of the sprung section and a relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section, and the calculated specific damping coefficient Ct is stored. When a vibration in an unsprung-section resonance frequency band exceeds a threshold value, the damping coefficient of the shock absorber is set to the specific damping coefficient Ct. As a result, both the vertical vibration and the longitudinal vibration of the sprung section A can be reduced in a well-balanced manner, ride quality is improved.

Description

DESCRIPTION
DAMPING FORCE CONTROL APPARATUS
TECHNICAL FIELD
The present invention relates to a damping force control apparatus for a vehicle which controls damping forces of shock absorbers disposed on the vehicle at positions corresponding to wheels.
BACKGROUND ART
As described in, for example, Japanese Patent Application Laid-Open {kokai) No. H5-104927, there has been know a technique for controlling a damping coefficient of a shock absorber, in which a low-frequency, sprung-section resonance frequency component is removed from a detection signal of a sprung-section acceleration sensor so as to extract an unsprung-section resonance frequency component, to thereby grasp the state of vibration of the unsprung section from the extracted component. In the known technique, when the vibration of the unsprung section is not strong (when the unsprung section does not tramp), maneuvering stability is secured by means of vibration control of controlling the damping coefficient of the shock absorber to a high damping coefficient corresponding to the speed of the sprung section to thereby suppress vibration of the sprung section. When the vibration of the unsprung section is strong (when the unsprung section tramps), the damping coefficient of the shock absorber is controlled a constant low damping coefficient so as to absorb the vibration of the unsprung portion by the shock absorber and suppress transmission of the vibration to the sprung section, to thereby improve ride quality.
According to the technique disclosed in the publication, when a vibration (vertical acceleration) in the unsprung-section resonance frequency band is large, the damping coefficient is set to a low damping coefficient. However, when the damping coefficient is lowered, in some cases the ride quality becomes worse. FIG. 3(a) shows the relation between damping coefficient and vertical acceleration of the sprung section, and FIG. 3(b) shows the relation between damping coefficient and longitudinal acceleration (acceleration in the front-rear direction) of the sprung section. As can be understood from these drawings, when the damping coefficient is lowered, the vertical acceleration of the sprung section decreases; however, the longitudinal acceleration of the sprung section increases, so that the influence of a longitudinal vibration increases depending on the setting of the damping coefficient, and the ride quality deteriorates.
The present invention has been achieved to solve the above problems, and an object of the invention is to suppress not only a vertical vibration of a sprung section but also a longitudinal vibration of the sprung section when a vibration of an unsprung section is strong, to thereby improve ride quality.
In order to achieve the above-described object, the present invention provides a damping force control apparatus for a vehicle which includes a shock absorber interposed between an unsprung section and a sprung section at each wheel position of the vehicle, the shock absorber having a variable damping coefficient, and which controls the damping coefficient of 2
the shock absorber, the clamping force control apparatus comprising unsprung-section vibration detection means for detecting a vibration in an unsprung-section resonance frequency band at each wheel position; and unsprung-section damping control means, operable when a level of the detected vibration in the unsprung-section resonance frequency band exceeds a reference level, for setting the damping coefficient of the shock absorber on the basis of a specific damping coefficient which minimizes a sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration of the sprung section, the specific damping coefficient being determined from a relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and a relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section.
In this case, the unsprung-section vibration detection means may include vertical acceleration detection means for detecting a vertical acceleration of the sprung section or the unsprung section at each wheel position; and unsprung-section vibration component extraction means for extracting a vibration component in the unsprung-section resonance frequency band from a signal representing the detected vertical acceleration.
In the present invention, the unsprung-section vibration detection means detects a vibration in an unsprung-section resonance frequency band at each wheel position. For example, the vertical acceleration detection means detects a vertical acceleration of the sprung section or the unsprung section; and the unsprung-section vibration component extraction means extracts a vibration component in the unsprung-section resonance frequency band from a signal representing the detected vertical acceleration. When the level of the detected vibration in the unsprung-section resonance frequency band exceeds the reference level, the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient.
This specific damping coefficient is a damping coefficient which minimizes the sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration (acceleration in the front-rear direction) of the sprung section and which is determined from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section. The damping coefficient which minimizes the sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration of the sprung section can be obtained by calculating a damping coefficient such that the square root of the sum of the square of the vertical acceleration and the square of the longitudinal acceleration assumes the minimum value. The relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section can be defined by arithmetic expressions or the like.
The unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient when the level of the vibration in the unsprung-section resonance frequency band detected by the unsprung-section vibration detection means exceeds the reference level. In this case, preferably, the damping coefficient of the shock absorber is set to the specific damping coefficient. However, in a damping force control apparatus in which the damping coefficient of the shock absorber is changed stepwise, the damping coefficient cannot be set to the specific damping coefficient in some cases. In such a case, the damping coefficient of the shock absorber is set to a settable value closest to the specific damping coefficient.
As a result, according to the present invention, the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a well-balanced manner, and ride quality is improved.
According to another feature of the present invention, the damping force control apparatus further comprises specific-damping-coefficient acquisition means for acquiring, as the specific damping coefficient, a damping coefficient which minimizes the sum of vectors of the vertical acceleration of the sprung section and the longitudinal acceleration of the sprung section, from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section; and the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient acquired by the specific-damping-coefficient acquisition means, when the level of the detected vibration in the unsprung-section resonance frequency band exceeds the reference level.
In this invention, the specific damping coefficient is acquired by the specific-damping-coefficient acquisition means. For example, the specific-damping-coefficient acquisition means can store the specific damping coefficient in storage means in advance, and acquire the specific damping coefficient by reading it out of the storage means. Alternatively, arithmetic expressions or maps which represent the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section are previously stored in the storage means as relation defining data. In this case, the specific-damping-coefficient acquisition means can acquire the specific damping coefficient on the basis of the relation defining data stored in the storage means. Further, in the case where the specific damping coefficient is changed in accordance with a running state of the vehicle, the specific-damping-coefficient acquisition means can store a map or an arithmetic expression which defines the relation between the running state and the specific damping coefficient in the storage means as relation defining data, and acquire the specific damping coefficient on the basis of the relation defining data stored in the storage means.
When the level of the vibration in the unsprung-section resonance frequency band detected by the unsprung-section vibration detection means exceeds the reference level, the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient acquired by the specific-damping-coefficient acquisition means. Accordingly, the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a well-balanced manner, and ride quality is improved.
According to another feature of the present invention, the damping force control apparatus further comprises relative position detection means for detecting a relative vertical position of the unsprung section in relation to the sprung section at each wheel position; and vehicle-height-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected relative position.
The relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section changes depending on, for example, the forward-tilting angle of the shock absorber (an angle of the axis of the shock absorber in relation to a vertical line) and the longitudinal-principal-elastic-axis dihedral angle (an angle of the longitudinal principal elastic axis in relation to a horizontal line) of a suspension. Further, these angles change depending on the vehicle height; i.e., the relative vertical position of the unsprung section in relation to the sprung section. In view of this, in the present invention, the relative position detection means detects the relative vertical position of the unsprung section in relation to the sprung section, and the vehicle-height-responsive specific damping coefficient changing means changes the specific damping coefficient in accordance with the detected relative position.
For example, the vehicle-height-responsive specific damping coefficient changing means may be configured to store in storage means relation defining data, such as a map or an arithmetic expression, which determines a specific damping coefficient corresponding to the relative vertical position of the unsprung section in relation to the sprung section, and set the specific damping coefficient corresponding to the relative vertical position of the unsprung section in relation to the sprung section, by use of the relation defining data stored in the storage means, while the vehicle is running. Notably, the relative vertical position of the unsprung section in relation to the sprung section is equivalent to the vertical position of the sprung section in relation to the unsprung section, and these expressions refer to the relative positional relation between the sprung section and the unsprung section in the vertical direction.
As a result, according to the present invention, the specific damping coefficient becomes a more proper one, and the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a more well-balanced manner, and ride quality is improved.
According to another feature of the present invention, the damping force control apparatus further comprises vehicle speed detection means for detecting a vehicle speed; and vehicle-speed-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected vehicle speed.
The relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section changes depending on the vehicle speed. In view of this, in the present invention, the vehicle speed detection means detects the vehicle speed; and the vehicle-speed-responsive specific damping coefficient changing means changes the specific damping coefficient in accordance with the detected vehicle speed.
For example, the vehicle-speed-responsive specific damping coefficient changing means may be configured to store in storage means relation defining data, such as a map or an arithmetic expression, which determines a specific damping coefficient corresponding to the vehicle speed, and set the specific damping coefficient corresponding to the vehicle speed, by use of the relation defining data stored in the storage means, while the vehicle is running.
As a result, according to the present invention, the specific damping coefficient becomes a more proper one, and the vertical vibration of the sprung section and the longitudinal vibration of the sprung section can be reduced in a more well-balanced manner, and ride quality is improved.
Notably, there can be employed a configuration in which specific damping coefficients corresponding to combinations of the vehicle speed and the relative vertical position of the unsprung section, in relation to the sprung section are stored in storage means in the form of a map or an arithmetic expression, serving as relation defining data; and a specific damping coefficient corresponding to the vehicle speed and the vertical position is set by use of the relation defining data stored in the storage means.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic configuration diagram of a damping force control apparatus according to a first embodiment.
FIG. 2 is a simplified model diagram used for explaining specifications of a suspension device.
FIGS. 3(a) and 3(b) are characteristic charts showing a relation between damping coefficient and sprung-section vertical acceleration and a relation between damping coefficient and sprung-section longitudinal acceleration, respectively.
FIGS. 4(a) and 4(b) are characteristic charts showing a relation between damping coefficient and sprung-section vertical acceleration and a relation between damping coefficient and sprung-section longitudinal acceleration, respectively.
FIG. 5 is a flowchart showing an unsprung-section damping control routine according to the first embodiment.
FIG. 6 is a schematic configuration diagram of a damping force control apparatus according to a second embodiment.
FIG. 7 is a reference map for acquiring a specific damping coefficient according to the second embodiment.
FIG. 8 is a flowchart showing an unsprung-section damping control routine according to the second embodiment.
FIG. 9 is a schematic configuration diagram of a damping force control apparatus according to a third embodiment.
FIG. 10 is a reference map for acquiring a specific damping coefficient according to the third embodiment.
FIG. 11 is a flowchart showing an unsprung-section damping control routine according to the third embodiment.
FIG. 12 is a schematic configuration diagram of a damping force control apparatus according to a fourth embodiment.
FIG. 13 is a reference map for acquiring a specific damping coefficient according to the fourth embodiment.
FIG. 14 is a flowchart showing an unsprung-section damping control routine according to the fourth embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 schematically shows the configuration of a damping force control apparatus for a vehicle according to a first embodiment. The clamping force control apparatus includes shock absorbers 10 and coil springs 20. Specifically, one of the shock absorbers 10 and one of the coil springs 20 are disposed between a vehicle body BD and each of a front left wheel WfI, a front right wheel Wfr, a rear left wheel WrI, and a rear right wheel Wrr. When the location (front, rear, left, and right) of a wheel is not specified, the wheel is simply referred to as the wheel W.
Each shock absorber 10 is interposed between a suspension member 14 and the vehicle body BD. The suspension member 14 is composed of a lower arm, a knuckle, etc., and holds the wheel W so as to allow the wheel W to swing in the vertical direction in relation to the vehicle body BD. The shock absorber 10 includes a cylinder 11 and a piston rod 12, which is inserted into the cylinder 11 in a vertically movable manner. A lower end of the cylinder 11 is connected to the suspension member 14 (such as the lower arm). An upper end of the piston rod 12 is fixed to the vehicle body BD. The coil spring 20 is provided in parallel with the shock absorber 10. The cylinder 11 is divided into an upper chamber R1 and a lower chamber R2 by a piston 13 that liquid-tightly slides over an inner circumferential surface of the cylinder 11.
A variable throttle mechanism 30 is mounted on the piston 13. By virtue of operation of an actuator 31, which constitutes a portion of the variable throttle mechanism 30, the variable throttle mechanism 30 changes, in a stepwise manner, a degree of opening of a communication passage for establishing communication between the upper chamber R1 and the lower chamber R2 of the cylinder 11 such that the degree of opening of the communication passage is switched to one of a plurality of steps; i.e., a
ll plurality of degrees of opening. When the degree of opening of the communication passage increases in accordance with the step to which the degree of opening is switched, the damping force of the shock absorber 10 is set to a soft-side value. When the degree of opening of the communication passage decreases in accordance with the step to which the degree of opening is switched, the damping force of the shock absorber 10 is set to a hard-side value. An electric motor, for example, is used as the actuator 31. The degree of opening of the communication passage is changed by stepwise changing the rotation angle (rotation position) of the electric motor. The variable throttle mechanism 30 may be of a type that continuously adjusts the degree of opening of the communication passage, which establishes communication between the upper chamber R1 and the lower chamber R2 of the cylinder 11.
All members provided above the coil spring 20 and supported by the coil spring 20 are collectively referred to as a sprung section A. In the present embodiment, the vehicle body BD corresponds to the sprung section A. All members provided below the coil spring 20 are collectively referred to as an unsprung section B. In the present embodiment, the suspension member 14, the wheel WfI - Wrr, a brake (not shown), etc. together correspond to the unsprung section B.
The damping force control apparatus includes a damping force control unit 40 that controls the damping forces of the shock absorbers 10 by controlling operations of the actuators 31. The damping force control unit 40 (hereinafter referred to as a damping force ECU 40) includes a microcomputer as a main constituent element, the microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and the like. The actuators 31 are connected to an output interface of the damping force ECU 40. Sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr are connected to an input interface of the damping force ECU 40.
The sprung-section vertical acceleration sensors 4IfI, 41fr, 41 rl, and 41 rr are respectively mounted to sprung sections A corresponding to the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. The sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr respectively detect sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr of the sprung sections A at the sensor mounting positions, in relation to absolute space. Each of the sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr detected by the sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr becomes positive when an upward acceleration is generated in the vehicle, and becomes negative when a downward acceleration is generated in the vehicle.
The damping force ECU 40 calculates respective damping coefficients corresponding to the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. The damping force ECU 40 controls the damping forces of the shock absorbers 10 individually by stepwise changing the degrees of opening of the communication passages of the corresponding cylinders 11 in accordance with the damping coefficient. Damping force control for the shock absorber 10 is performed in a similar manner for each of the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. Therefore, separate descriptions will not be given for the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. Hereafter, the sprung-section vertical acceleration sensors 41fl, 41fr, 41 rl, and 41 rr are simply referred to as a sprung-section vertical acceleration sensor 41. The detected sprung-section vertical accelerations Gzfl, Gzfr, Gzrl, and Gzrr are simply referred to as a sprung-section vertical acceleration Gz.
Next will be described a relation between the damping coefficient C of the shock absorber 10 and vertical acceleration of the sprung section A and a relation between the damping coefficient C of the shock absorber 10 and longitudinal acceleration of the sprung section A.
When the vehicle travels over a rough road or the like, the unsprung section B vibrates strongly in an unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz). Such a vibration of the unsprung section B at the unsprung-section resonance frequency is referred to as tramping. Tramping of the unsprung section B can be detected by extracting an unsprung-section resonance frequency band component from a vertical acceleration signal detected by the sprung-section vertical acceleration sensor 41. When tramping of the unsprung section B occurs, transmission of the vibration of the unsprung section to the sprung section A can be suppressed by means of changing the damping coefficient of the shock absorber 10.
The vertical acceleration of the sprung section A (hereinafter referred to as the sprung-section vertical acceleration Gz) in the unsprung-section resonance frequency band can be expressed by the following Equation (1), through use of the damping coefficient C of the shock absorber 10. Gz(s) = s2Ktz (K0Ku +sC(Kc +Ku ))/[s5m2mlC + s4m2Kuml
+ s3C{m2 (K0 + K11 -Ktz ) + mx (K0 +KU )} + s2 Ku {Kc (mx +m2 )-Ktzm2 } -sCKt2 (Kc +Ku )-KcKuKtz ] (1 )
wherein mi represents an unsprung mass, and m2 represents a mass of the sprung section A per wheel. As shown in FIG. 2, K0 represents a wheel rate, Ku represents an upper support rigidity, Ktz indicates a vertical rigidity of a tire, and s is a Laplacian operator.
Vibration of the unsprung section B also causes vibration of the sprung section A in the longitudinal direction (hereinafter referred to as the "longitudinal vibration of the sprung section A"). The longitudinal vibration of the sprung section A can also be suppressed by means of changing the damping coefficient of the shock absorber 10. A longitudinal acceleration of the sprung section A (hereinafter referred to as a sprung-section longitudinal acceleration Gx) in the unsprung-section resonance frequency band can be expressed by the following Equation (2), through use of the damping coefficient C of the shock absorber 10.
Figure imgf000016_0001
(2)
wherein, f(s) and h(s) are as follows:
Figure imgf000016_0002
Figure imgf000017_0001
As shown in FIG. 2, parameters in the equations are as follows: Kx represents a longitudinal-elastic-main-axis rigidity (a rigidity, in the longitudinal direction, of a longitudinal principal elastic axis, which represents all the members, such as a link mechanism, for connecting the wheel W to the vehicle body BD); K6 represents a rigidity of an axle carrier when it rotates about a spindle axis; α represents a forward-tilting angle of the shock absorber 10 (an angle between the axis of the shock absorber 10 and a vertical line); β represents a longitudinal-principal-elastic-axis dihedral angle (an angle in an upward direction of the longitudinal principal elastic axis in relation to a horizontal line); H represents a vertical distance between the centroid of the axle carrier and the longitudinal principal elastic axis; L represents a horizontal distance between the centroid of the axle carrier and the axis of the shock absorber 10; Ktx represents a longitudinal rigidity of a tire; Px represents a driving stiffness; W represents a vertical load per wheel; It represents a moment of inertia of the tire and the wheel; V represents a vehicle speed; and r0 represents a steady portion of the radius of the tire under a dynamic loaded, ε represents a value obtained by dividing a dynamic loaded tire radius change amount (a change in the radius of the tire under a dynamic load) by a static loaded tire radius change amount (a change in the radius of the tire (a deformation of the tire) under a static load). In other words, ε is a value expressed by (dynamic loaded tire radius change amount/static loaded tire radius change amount). Other parameters are the same as those described for Equation (1). FIG. 3 and FIG. 4 show sprung-section vertical accelerations Gz and sprung-section longitudinal accelerations Gx which are calculated for two example suspension apparatuses by use of Equations (1) and (2). In each of the drawings, (a) shows a relation between the damping coefficient C of the shock absorber 10 and the magnitude (absolute value) of the sprung-section vertical acceleration Gz in the unsprung-section resonance frequency band, and (b) shows a relation between the damping coefficient C of the shock absorber 10 and the magnitude (absolute value) of the sprung-section longitudinal acceleration Gx in the unsprung-section resonance frequency band. The two example suspension apparatuses have different characteristics, because the suspension apparatuses have different configurations.
The examples indicate that the sprung-section vertical acceleration Gz decreases when the damping coefficient C is lowered. However, in a certain range, the sprung-section longitudinal acceleration Gx increases as a result of reduction in the damping coefficient C. For example, in the example shown in FIG. 4, when the damping coefficient C falls below about 1600 N-s/m, the sprung-section longitudinal acceleration Gx increases with a decrease in the damping coefficient C. In the example shown in FIG. 3, the sprung-section longitudinal acceleration Gx increases with a decrease in the damping coefficient C over the entire range of the damping coefficient C.
When the unsprung section B tramps because of the vehicle running over a rough road or the like, the vibration of the unsprung section B can be absorbed and the transmission of the vibration to the sprung section A can be suppressed by lowering the damping coefficient C. However, as FIG. 3 and FIG. 4 indicate, when the damping coefficient C is excessively lowered, the influence of the sprung-section longitudinal acceleration Gx becomes pronounced, resulting in deterioration of ride quality.
Therefore, in the first embodiment, in order to balance the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx, a damping coefficient Ct which minimizes the sum of vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx (thereinafter, the damping coefficient C will be referred to as a specific damping coefficient Ct) is calculated in advance. When the vibration of the unsprung section B in the resonance frequency band is strong, the damping force of the shock absorber 10 is controlled through use of the specific damping coefficient Ct. Notably, as described in a second embodiment and a third embodiment to be described later, the sprung-section longitudinal acceleration Gx changes with vehicle height and vehicle speed. However, according to the first embodiment, the specific damping coefficient Ct is calculated in advance with the vehicle height and the vehicle speed fixed to standard values.
The sum Gt of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be expressed by the following Equation (3) as a square root of the sum of the square of the sprung-section vertical acceleration Gz calculated by Equation (1) and the square of the sprung-section longitudinal acceleration Gx calculated by Equation (2).
Gt(s) = ^Gz(s)2 +Gx(sy (3)
The specific damping coefficient Ct at which the square root attains the lowest value is calculated in advance and stored in the ROM of the damping force ECU 40 along with a control program. Notably, there may be stored a degree of opening of the communication passage of the variable throttle mechanism 30 at which the specific damping coefficient Ct can be obtained.
Next, an unsprung-section damping control processing performed by the damping force ECU 40 will be described. FIG. 5 is a flowchart showing an unsprung-section damping control routine. The unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program. The unsprung-section damping control routine starts when an ignition switch (not shown) is turned ON. The unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
The damping force ECU 40 performs not only the unsprung-section damping control, but also various damping force controls in parallel. However, the other damping force controls are common and do not characterize the present invention. Therefore, in the first embodiment, configurations for performing the other damping force controls are omitted from the configuration of the damping force control apparatus. The other damping force controls include, for example, vehicle speed responsive control, anti-dive control, anti-squat control, rolling control, and anti-lift control. However, because these controls do not constitute the feature of the present invention, descriptions thereof are omitted.
When the unsprung-section damping control routine starts, in Step S11 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S12, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing. Therefore, the signal obtained through the band-pass filtering processing is an acceleration signal corresponding to the vibration state of the unsprung section B. As a result, the tramping state of the unsprung section B can be detected.
Next, in Step S13, the damping force ECU 40 judges whether a magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds a reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds a reference level.
When the damping force ECU 40 judges in Step S13 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band exceeds the reference value GzO, in Step S14 the damping force ECU 40 sets the damping coefficient C to the above-described specific damping coefficient Ct. The specific damping coefficient Ct is stored in a storage device, such as the ROM, of the damping force ECU 40. In Step S14, the specific damping coefficient Ct is acquired by being read from the storage device. A configuration for reading and acquiring the specific damping coefficient Ct corresponds to the specific damping coefficient acquisition means of the present invention.
The damping force ECU 40 changes the damping coefficient of the shock absorber 10 by stepwise changing the degree of opening of the communication passage of the cylinder 11. In this case, the damping force ECU 40 selects a degree of opening of the communication passage corresponding to the specific damping coefficient Ct. In other words, the damping force ECU 40 stores the relation between the damping coefficient and the degree of opening of the communication passage in the storage device, such as the ROM. The damping force ECU 40 then sets the degree of opening of the communication passage corresponding to the specific damping coefficient Ct on the basis of the stored relation. The shock absorber 10 according to the first embodiment is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage to one of a plurality of degrees of opening. Therefore, when the damping force ECU 40 cannot set the degree of opening of the communication passage to a degree of opening at which the specific damping coefficient Ct is attained, the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained.
Notably, in the first embodiment, the specific damping coefficient Ct is a fixed value calculated in advance. Therefore, the variable throttle mechanism 30 may be configured to have a dedicated degree of opening of the communication passage at which the specific damping coefficient Ct can be attained, as one of the plurality of degrees of opening that can be selected, and switch the degree of opening of the communication passage to the dedicated degree of opening. Further, when the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct is attained. As a result of the damping coefficient of the shock absorber 10 being set based on the specific damping coefficient Ct in this way, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a well-balanced manner. Therefore, ride quality is improved.
The damping force ECU 40 ends the current execution of the unsprung-section damping control routine after setting the damping coefficient of the shock absorber 10 by the processing in Step S14. The unsprung-section damping control routine is performed repeatedly at predetermined short intervals.
When the damping force ECU 40 judges in Step S13 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required. In this case, the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
In the damping force control apparatus according to the first embodiment described above, when the vibration level of the unsprung section B exceeds the reference level, the damping force of the shock absorber 10 is controlled based on the specific damping coefficient Ct which minimizes the sum of the vectors of the vertical acceleration and the longitudinal acceleration of the sprung section A. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction are reduced in a well-balanced manner. As a result, ride quality is improved.
<Second Embodiment
Next, a second embodiment of the present invention will be described. The second embodiment is identical with the first embodiment except that the specific damping coefficient Ct is changed depending on vehicle height. As compared with the damping force control apparatus according to the first embodiment, a damping force control apparatus according to the second embodiment has the following additional configuration. That is, as shown in FIG. 6, vehicle height sensors 42fl, 42fr, 42rl, and 42rr are provided for the wheels WfI, Wfr, WrI, and Wrr so as to detect the vertical portions of the unsprung sections B in relation to the sprung section A. The vehicle height sensors 42fl, 42fr, 42rl, and 42rr output to the damping force ECU 40 vehicle height signals XfI, Xfr, XrI, and Xrr representing the detected vehicle heights.
The vehicle height sensors 42fl, 42fr, 42rl, and 42rr are respectively provided between the sprung sections A and the unsprung sections B corresponding to the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr. The vehicle height sensors 42fl, 42fr, 42rl, and 42rr respectively detect vehicle heights XfI, Xfr, XrI1 and Xrr, which correspond to displacements from a reference vehicle height, from the relative vertical positions of the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr in relation to the vehicle body BD (the sprung sections A); i.e., the distances between the sprung sections A and the front-left wheel WfI, the front-right wheel Wfr, the rear-left wheel WrI, and the rear-right wheel Wrr. The signals output from the vehicle height sensors 42fl, 42fr, 42rl, and 42rr each assume a positive value when the detected vehicle height is higher than the reference vehicle height, and assume a negative value when the detected vehicle height is lower than the reference vehicle height. Damping force control for the shock absorber 10 is performed in a similar manner for each of the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. Therefore, separate descriptions will not be given for the front left wheel WfI, the front right wheel Wfr, the rear left wheel WrI, and the rear right wheel Wrr. Hereafter, the vehicle height sensors 42fl, 42fr, 42rl, and 42rr are simply referred to as a vehicle height sensor 42. The detected vehicle heights XfI, Xfr, XrI, and Xrr are simply referred to as a vehicle height X.
As shown in Equation (2) described above, the sprung-section longitudinal acceleration Gx changes depending on the front-tilting angle α and the longitudinal principal elastic axis dihedral angle β of the shock absorber 10. Moreover, the front-tilting angle α and the longitudinal principal elastic axis dihedral angle β of the shock absorber 10 change depending on the vehicle height X or, in other words, the relative position of the unsprung section B in the vertical direction in relation to the sprung section A, and are univocally determined from the relative position. For example, in the simplified model shown in FIG. 2, as the vehicle height X increases, the front-tilting angle α of the shock absorber 10 decreases and the longitudinal principal elastic axis dihedral angle β increases. Accordingly, through substituting values of (α, β) corresponding to the vehicle height X for Equation (2), the longitudinal acceleration Gx of the sprung section A in the unsprung-section resonance frequency band can be expressed by use of the damping coefficient C. Therefore, ultimately, the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle height X. In view of this, in the damping control apparatus according to the second embodiment, a map (relation defining data) defining a relation between the vehicle height X and the specific damping coefficient Ct, such as that shown in FIG. 7, is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle height X detected while the vehicle is running. The map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle height X based on Equations (1), (2), and (3), while fixing the vehicle speed to a standard value. The map is stored in the ROM of the damping force ECU 40. In the example, when the vehicle height X is lower than the reference vehicle height, the specific damping coefficient Ct is set to a value greater than that when the vehicle height X is higher than the reference vehicle height. The relation defining data can be stored in a storage means other than the ROM.
Next, the unsprung-section damping control processing performed by the damping force ECU 40 will be described. FIG. 8 is a flowchart showing an unsprung-section damping control routine according to the second embodiment. The unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program. The unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON. The unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
When the unsprung-section damping control routine starts, in Step S21 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S22, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
Next, in Step S23, the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
When the damping force ECU 40 judges in Step S23 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band exceeds the reference value GzO, in Step S24 the damping force ECU 40 reads the vehicle height X detected by the vehicle height sensor 42. Then, in Step S25, the damping force ECU 40 acquires the specific damping coefficient Ct corresponding to the detected vehicle height X by reference to the map defining the relation between the vehicle height X and the specific damping coefficient Ct shown in FIG. 7. A configuration for changing and setting the specific damping coefficient Ct in accordance with the vehicle height X corresponds to the vehicle-height-responsive specific damping coefficient changing means of the present invention. A configuration for acquiring the specific damping coefficient Ct from the map corresponds to the specific damping coefficient acquisition means of the present invention.
The specific damping coefficient Ct may be calculated through use of Equations (1), (2), and (3) as needed. For example, relation defining data that relate the vehicle height X to (α, β) are stored in storage means in advance in the form of a map or the like. Values of (α, β) corresponding to the vehicle height X detected in Step S24 are determined from the relation defining data. The determined values of (α, β) are substituted for Equation (2). Finally, through use of Equation (2) to which the values of (α, β) have been substituted, and Equations (1) and (3), the damping force ECU 40 calculates the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx of the sprung section A.
When the specific damping coefficient Ct is acquired in Step S25, subsequently, in Step S26, the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine. In this case, the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening. Therefore, when the damping force ECU 40 cannot set the degree of opening of the communication passage to a degree of opening at which the specific damping coefficient Ct is attained, the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained. Notably, when the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
As a result, the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle height X. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
On the other hand, when the damping force ECU 40 judges in Step S23 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required. In this case, the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
In the damping force control apparatus according to the second embodiment described above, the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle height X. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved. <Third Embodiment
Next, a third embodiment of the present invention will be described. The third embodiment is identical with the first embodiment, except that the specific damping coefficient Ct is changed in accordance with the vehicle speed. As shown in FIG. 9, a damping force control apparatus according to the third embodiment can be configured by adding to the damping force control apparatus according to the first embodiment a vehicle speed sensor 43 that detects a raveling speed of the vehicle. The vehicle speed sensor 43 is connected to the damping force ECU 40 and outputs a signal indicating the vehicle speed V to the damping force ECU 40.
As shown in Equation (2) described above, the sprung-section longitudinal acceleration Gx changes depending on the vehicle speed V. Therefore, the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle speed V. In view of this, in the damping control apparatus according to the third embodiment, a map (relation defining data) defining a relation between the vehicle speed V and the specific damping coefficient Ct, such as that shown in FIG. 10, is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle speed V detected while the vehicle is running. The map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle speed V based on Equations (1), (2), and (3), while fixing the vehicle height to a standard value. The map is stored in the ROM of the damping force ECU 40. In the example, the specific damping coefficient Ct is set to a smaller value as the vehicle speed V increases. The relation defining data can be stored in a storage means other than the ROM.
Next, the unsprung-section clamping control processing performed by the damping force ECU 40 will be described. FIG. 11 is a flowchart showing an unsprung-section damping control routine according to the third embodiment. The unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program. The unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON. The unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
When the unsprung-section damping control routine starts, in Step S31 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S32, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
Next, in Step S33, the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
When the damping force ECU 40 judges in Step S33 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band exceeds the reference value GzO, in Step S34 the damping force ECU 40 reads the vehicle speed V detected by the vehicle speed sensor 43. Then, in Step S35, the damping force ECU 40 determines the specific damping coefficient Ct corresponding to the detected vehicle speed V by reference to the map defining the relation between the vehicle speed V and the specific damping coefficient Ct shown in FIG. 10. A configuration for changing and setting the specific damping coefficient Ct in accordance with the vehicle speed V corresponds to the vehicle-speed-responsive specific damping coefficient changing means of the present invention. A configuration for acquiring the specific damping coefficient Ct from the map corresponds to the specific damping coefficient acquisition means of the present invention. In place of the map, Equations (1), (2), and (3) can be stored in the storage means, and the specific damping coefficient Ct can be successively calculated through use of the equations while the vehicle is running.
When the specific damping coefficient Ct is determined in Step S35, subsequently, in Step S36, the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine. In this case, the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening. Therefore, when the damping force ECU 40 cannot set the degree of opening of the communication passage to a degree of opening at which the specific damping coefficient Ct is attained, the damping force ECU 40 selects a degree of opening of the communication passage at which a damping coefficient closest to the specific damping coefficient Ct can be attained. Notably, when the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
As a result, the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
On the other hand, when the damping force ECU 40 judges in Step S33 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required. In this case, the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
In the damping force control apparatus according to the third embodiment described above, the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved. <Fourth Embodiment
Next, a fourth embodiment of the present invention will be described. A damping control apparatus according to the fourth embodiment is a combination of the damping control apparatuses according to the second embodiment and the third embodiment. As shown in FIG. 12, the damping control apparatus according to the fourth embodiment can be configured by adding to the damping control apparatus according to the first embodiment the vehicle speed sensor 43 and the vehicle height sensors 42fl, 42fr, 42rl, and 42rr (hereinafter referred to as simply the vehicle height sensor 42), which detect the vertical positions of the unsprung sections B in relation to the sprung sections A for the wheel WfI, Wfr, WrI, and Wrr. The vehicle height sensor 42 and the vehicle speed sensor 43 are the same as those described in the second embodiment and the third embodiment.
As described in the second embodiment and the third embodiment, the sprung-section longitudinal acceleration Gx expressed by Equation (2) changes depending on the vehicle height X and the vehicle speed V. Therefore, the specific damping coefficient Ct which minimizes the sum of the vectors of the sprung-section vertical acceleration Gz and the sprung-section longitudinal acceleration Gx can be calculated in advance in accordance with the vehicle height X and the vehicle speed V. In the damping control apparatus according to the fourth embodiment, a map (relation defining data) defining a relation between the vehicle height X and the specific damping coefficient Ct at each vehicle speed V, such as that shown in FIG. 13, is stored in the ROM of the damping control ECU 40, thereby allowing the specific damping coefficient Ct to be acquired from the vehicle height X and the vehicle speed V detected while the vehicle is running. The map is created by calculating, in advance, values of the specific damping coefficient Ct corresponding to different values of the vehicle height X and the vehicle speed V based on Equations (1), (2), and (3). The map is stored in the ROM of the damping force ECU 40. The relation defining data can be stored in a storage means other than the ROM.
Next, the unsprung-section damping control processing performed by the damping force ECU 40 will be described. FIG. 14 is a flowchart showing an unsprung-section damping control routine according to the fourth embodiment. The unsprung-section damping control routine is stored in the ROM of the damping force ECU 40 as a control program. The unsprung-section damping control routine starts when the ignition switch (not shown) is turned ON. The unsprung-section damping control routine is performed repeatedly at predetermined short intervals, separately for each wheel W.
When the unsprung-section damping control routine starts, in Step S41 the damping force ECU 40 reads the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. Then, in Step S42, the damping force ECU 40 extracts a frequency component in the unsprung-section resonance frequency band (for example, 8 Hz to 16 Hz) from the sprung-section vertical acceleration signal Gz through band-pass filtering processing, thereby detecting a tramping state of the unsprung section B.
Next, in Step S43, the damping force ECU 40 judges whether the magnitude Gzf of vibration of the frequency component (an absolute value of acceleration) extracted through the band-pass filtering processing exceeds the reference value GzO (threshold value). In other words, the damping force ECU 40 judges whether the vibration level of the unsprung section B exceeds the reference level.
When the damping force ECU 40 judges in Step S43 that the magnitude Gzf of the vibration in the unsprung-section resonance frequency band exceeds the reference value GzO, in Step S44 the damping force ECU 40 reads the vehicle height X detected by the vehicle height sensor 42. Then, in Step S45, the damping force ECU 40 reads the vehicle speed V detected by the vehicle speed sensor 43.
Next, in Step S46, the damping force ECU 40 determines the specific damping coefficient Ct corresponding to the detected vehicle height X and vehicle speed V by reference to the map defining the relation between the vehicle height X and the specific damping coefficient Ct at each vehicle speed V, shown in FIG. 13. Notably, instead of using the map, the specific damping coefficient Ct may be calculated by use of Equations (1), (2), and (3) as needed, as in the case of the above-described embodiments.
When the specific damping coefficient Ct is determined in Step S46, subsequently, in Step S47, the damping force ECU 40 sets the damping coefficient of the shock absorber 10 to the specific damping coefficient Ct and ends the current execution of the unsprung-section damping control routine. In this case, the shock absorber 10 is of a type in which the variable throttle mechanism 30 changes, in a stepwise manner, the degree of opening of the communication passage of the cylinder 11 to one of a plurality of degrees of opening. Therefore, when the damping force ECU 40 cannot set the degree of opening of the communication passage to a degree of opening at which the specific damping coefficient Ct is attained, the damping force ECU 40 selects a degree of opening of the communication passage at which a clamping coefficient closest to the specific damping coefficient Ct can be attained. Notably, when the shock absorber 10 is of a type that can continuously change the degree of opening of the communication passage, the degree of opening of the communication passage is set to a degree of opening at which the specific damping coefficient Ct can be attained.
As a result, the damping coefficient of the shock absorber 10 is set to an optimal specific damping coefficient Ct in accordance with the vehicle height X and the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner.
On the other hand, when the damping force ECU 40 judges in Step S43 that the magnitude Gzf of vibration in the unsprung-section resonance frequency band does not exceed the reference value GzO, the damping force ECU 40 ends the current execution of the unsprung-section damping control routine, because performance of unsprung vibration damping is not required. In this case, the damping coefficient of the shock absorber 10 is controlled to a damping coefficient set by another damping control, such as the vehicle speed responsive control.
In the damping force control apparatus according to the fourth embodiment, described above, the specific damping coefficient Ct becomes a more proper value because the specific damping coefficient Ct is acquired in accordance with the vehicle height X and the vehicle speed V. Therefore, the vibration of the sprung section A in the vertical direction and that in the longitudinal direction can be reduced in a more well-balanced manner. As a result, ride quality is further improved. The damping control apparatuses for a vehicle according to the embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the object of the present invention.
For example, in the embodiments, the tramping state of the unsprung section B is detected through extraction of a frequency component in the unsprung-section resonance frequency band from the sprung-section vertical acceleration signal Gz detected by the sprung-section vertical acceleration sensor 41. However, instead of the sprung-section vertical acceleration sensor 41 , a vertical unsprung acceleration sensor (not shown) can be provided so as to detect the vertical acceleration of the unsprung section B. The tramping state of the unsprung section B can be detected through extraction of a frequency component in the unsprung-section resonance frequency band from a vertical unsprung acceleration signal Gz detected by the vertical unsprung acceleration sensor.
Moreover, another sensor, such as a piezoelectric sensor, can be used to detect the vibration state of the unsprung section B. In the embodiments, the band-pass filtering processing is performed with the unsprung-section resonance frequency band set to 8 Hz to 16 Hz. However, the unsprung-section resonance frequency band can be freely changed in accordance with suspension characteristics and the like.

Claims

1. A damping force control apparatus for a vehicle which includes a shock absorber interposed between an unsprung section and a sprung section at each wheel position of the vehicle, the shock absorber having a variable damping coefficient, and which controls the damping coefficient of the shock absorber, the damping force control apparatus comprising: unsprung-section vibration detection means for detecting a vibration in an unsprung-section resonance frequency band at each wheel position; and unsprung-section damping control means, operable when a level of the detected vibration in the unsprung-section resonance frequency band exceeds a reference level, for setting the damping coefficient of the shock absorber on the basis of a specific damping coefficient which minimizes a sum of vectors of a vertical acceleration of the sprung section and a longitudinal acceleration of the sprung section, the specific damping coefficient being determined from a relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and a relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section.
2. A damping force control apparatus according to claim 1 , further comprising specific-damping-coefficient acquisition means for acquiring, as the specific damping coefficient, a damping coefficient which minimizes the sum of vectors of the vertical acceleration of the sprung section and the longitudinal acceleration of the sprung section, from the relation between the damping coefficient of the shock absorber and the vertical acceleration of the sprung section and the relation between the damping coefficient of the shock absorber and the longitudinal acceleration of the sprung section, wherein the unsprung-section damping control means sets the damping coefficient of the shock absorber on the basis of the specific damping coefficient acquired by the specific-damping-coefficient acquisition means, when the level of the detected vibration in the unsprung-section resonance frequency band exceeds the reference level.
3. A damping force control apparatus according to claim 1 or 2, wherein the unsprung-section vibration detection means includes: vertical acceleration detection means for detecting a vertical acceleration of the sprung section or the unsprung section at each wheel position; and unsprung-section vibration component extraction means for extracting a vibration component in the unsprung-section resonance frequency band from a signal representing the detected vertical acceleration.
4. A damping force control apparatus according to any one of claims 1 to 3, further comprising: relative position detection means for detecting a relative vertical position of the unsprung section in relation to the sprung section at each wheel position; and vehicle-height-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected relative position.
5. A damping force control apparatus according to any one of claims 1 to 4, further comprising: vehicle speed detection means for detecting a vehicle speed; and vehicle-speed-responsive specific damping coefficient changing means for changing the specific damping coefficient in accordance with the detected vehicle speed.
PCT/JP2008/070372 2007-12-10 2008-11-04 Damping force control apparatus WO2009075151A1 (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012117305A1 (en) * 2011-03-01 2012-09-07 Protean Electric Limited A suspension control system
US20130085617A1 (en) * 2011-09-30 2013-04-04 Siemens Aktiengesellschaft Velocity-proportional active vibration damping
WO2018036709A1 (en) * 2016-08-25 2018-03-01 Volkswagen Aktiengesellschaft Method for actuating the vibration damper of a wheel suspension
CN114056029A (en) * 2021-10-25 2022-02-18 一汽解放汽车有限公司 Vehicle shake control device and control method

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102656033B (en) 2009-12-11 2014-09-17 丰田自动车株式会社 Vehicle control device
KR102253162B1 (en) * 2014-12-02 2021-05-18 현대모비스 주식회사 Apparatus and method for control of vehicle suspension damping force

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59227515A (en) * 1983-06-07 1984-12-20 Mazda Motor Corp Suspension of automobile
US4765648A (en) * 1986-05-02 1988-08-23 Gaydon Technology Limited Suspension system for a motor vehicle
JPH05104927A (en) * 1991-08-06 1993-04-27 Atsugi Unisia Corp Vehicle suspension device
US5328202A (en) * 1991-12-19 1994-07-12 Atsugi Unisia Corporation Apparatus for controlling damping coefficient for vehicular shock absorber
DE4042520C2 (en) * 1989-04-13 1996-02-15 Mitsubishi Electric Corp Control circuit for vehicle suspension

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0784123B2 (en) * 1986-03-24 1995-09-13 株式会社日本自動車部品総合研究所 Damping force control device for shock absorber
JPH06143958A (en) * 1992-11-06 1994-05-24 Nippondenso Co Ltd Suspension control device
JP3608445B2 (en) * 1999-08-05 2005-01-12 トヨタ自動車株式会社 Vehicle damping coefficient control device
JP4421985B2 (en) * 2004-09-17 2010-02-24 本田技研工業株式会社 Road surface condition judgment method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59227515A (en) * 1983-06-07 1984-12-20 Mazda Motor Corp Suspension of automobile
US4765648A (en) * 1986-05-02 1988-08-23 Gaydon Technology Limited Suspension system for a motor vehicle
DE4042520C2 (en) * 1989-04-13 1996-02-15 Mitsubishi Electric Corp Control circuit for vehicle suspension
JPH05104927A (en) * 1991-08-06 1993-04-27 Atsugi Unisia Corp Vehicle suspension device
US5328202A (en) * 1991-12-19 1994-07-12 Atsugi Unisia Corporation Apparatus for controlling damping coefficient for vehicular shock absorber

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012117305A1 (en) * 2011-03-01 2012-09-07 Protean Electric Limited A suspension control system
US9434229B2 (en) 2011-03-01 2016-09-06 Protean Electric Limited Suspension control system
US20130085617A1 (en) * 2011-09-30 2013-04-04 Siemens Aktiengesellschaft Velocity-proportional active vibration damping
US9316283B2 (en) * 2011-09-30 2016-04-19 Siemens Aktiengesellschaft Velocity-proportional active vibration damping
WO2018036709A1 (en) * 2016-08-25 2018-03-01 Volkswagen Aktiengesellschaft Method for actuating the vibration damper of a wheel suspension
US11052720B2 (en) 2016-08-25 2021-07-06 Volkswagen Aktiengesellschaft Method for actuating the vibration damper of a wheel suspension
CN114056029A (en) * 2021-10-25 2022-02-18 一汽解放汽车有限公司 Vehicle shake control device and control method
CN114056029B (en) * 2021-10-25 2023-07-14 一汽解放汽车有限公司 Vehicle shake control device and control method

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