JP2010179678A - Device for estimating road surface friction coefficient - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly estimate a road surface friction coefficient even immediately after a startup. <P>SOLUTION: This device includes an ignition on IG, a straight advance determination part 22 for determining a straight advance according to the signals of the steer angle θs of front wheels and a vehicle speed V, an actuator drive control part 23 for controllably steering rear wheels to toe-in or toe-out by a straight advance determination, a load calculation part 25 for calculating a load during a rear wheel steering as an integrated current value, and a road surface friction coefficient estimating part 26 for obtaining an estimated road surface friction coefficient μr from a map 27 according to the load. In an automobile in which a certain level of road surface friction coefficient can be set before the driver operates the automobile, a large jump of the road surface friction coefficient between that road surface fiction coefficient and the road surface friction coefficient obtained after steering can be suppressed, and a vehicle control is performed using the road surface friction coefficient, the vehicle control can be smoothly performed from the startup to the initial steering. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a road surface friction coefficient estimating device used when estimating a state quantity of a vehicle.

  Conventionally, when estimating a vehicle body slip angle or the like which is a state quantity of a vehicle, road surface μ (road surface friction coefficient) information has become important, but it is very difficult to directly measure the road surface friction coefficient. Therefore, the value is estimated. For example, the difference between the estimated yaw rate or lateral G estimated by the observer and the actually measured yaw rate or lateral G is estimated using the method of least squares, or the steering torque (electric There is a method based on a method of estimation based on a power steering torque sensor detection value (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-12160

  In the case of the above structure, it is necessary to actually steer with the steering wheel, and there is a problem that the road surface friction coefficient cannot be estimated when going straight. Therefore, an initial value is set as the calculated value of the road surface friction coefficient, but it is conceivable to set a high friction coefficient of a normal dry road surface as the initial value.

  However, when starting on a straight road surface having a low friction coefficient, if a high friction coefficient is set as an initial value, the control value of the road surface friction coefficient does not match the actual value at the first steering. When a low friction coefficient is estimated according to steering, there is a problem that it may be difficult to smoothly control the vehicle due to a large jump from the previous high friction coefficient to the low friction coefficient. It was.

  In order to solve such problems and make it possible to estimate an appropriate road surface friction coefficient immediately after starting, in the present invention, the rear wheels (5L, 5R) can be driven at least toe-in or toe-out. A steering device (10), a straight traveling determination means (22) for determining a straight traveling state, a rear wheel load detecting means (24, 25) for detecting a load of the rear wheel steering device (10), and the rear wheel (5L) , 5R) is toe-in or toe-out at a predetermined turning angle at least once, and the road surface friction coefficient is estimated according to the load of the rear wheel steering device (10) during the toe-in or toe-out. And an estimation means (26).

  In particular, when it is determined that the vehicle is in the straight traveling state, the front road surface friction coefficient may be estimated.

  Thus, according to the present invention, it becomes possible to set a certain road surface friction coefficient before the driver operates, and a jump with a large road surface friction coefficient between the road surface friction coefficient obtained after steering is performed. Is suppressed. Therefore, in the automobile in which the vehicle control is performed using the road surface friction coefficient, the vehicle control at the first steering after the start can be smoothly performed. In particular, by using a map, a map can be created by calculation on an experimental basis, and the road surface friction coefficient can be easily obtained.

It is a schematic block diagram of the motor vehicle V to which the rear-wheel steering apparatus to which this invention was applied is applied. It is a principal part control block diagram based on this invention. It is a flowchart which shows control. (A) is a figure which shows the state which steered the rear wheel to the toe-in side, (b) is a figure which shows the state which steered the rear wheel to the toe-out side. It is a figure which shows the map of the road surface friction coefficient with respect to an electric current integrated value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an automobile V to which a rear wheel toe angle variable control device 10 as a rear wheel steering device to which the present invention is applied is applied. In the description, for the wheels and members arranged for them, that is, tires, electric actuators, etc., subscripts L or R indicating left and right are attached to the numerals, respectively, for example, rear wheel 5L (left), For example, the rear wheel 5R (right) is referred to as the rear wheel 5. In addition, the vehicle body 1 is used as a reference for front and rear, left and right, and top and bottom.

  As shown in FIG. 1, the vehicle V includes front wheels 3L and 3R to which tires 2L and 2R are mounted, and rear wheels 5L and 5R to which tires 4L and 4R are mounted, and these front wheels 3L and 3R. The rear wheels 5L and 5R are suspended from the vehicle body 1 by left and right front suspensions 6L and 6R and rear suspensions 7L and 7R, respectively.

  In addition, the vehicle V corresponds to the front wheel steering device 9 that directly steers the left and right front wheels 3L and 3R via the rack and pinion mechanism and the left and right rear suspensions 7L and 7R by steering the steering wheel 8. Left and right electric actuators 11L and 11R are provided as rear wheel steering devices respectively attached to one appropriate place. The toe angles of the rear wheels 5L and 5R can be independently changed (controlled) by driving the left and right electric actuators 11L and 11R. In this way, the rear wheel toe angle variable control as the alignment angle control means is performed. A device 10 is provided.

  The vehicle V is provided with an ECU (Electronic Control Unit) 12 for overall control of various systems, as well as a vehicle speed sensor 13, a steering sensor 14, a yaw rate sensor 15, a lateral acceleration sensor 16, and other various sensors (not shown). ), And an ignition key switch 18 is provided at an appropriate position. The detection signals from the sensors and the ignition on signal from the ignition key switch 18 are input to the ECU 12 and used for vehicle control. Note that the steering angle (amount) of the steering wheel 8 is detected by the steering sensor 14, and the turning angle of the front wheels 3 is calculated from the detected value.

  The ECU 12 includes a microcomputer, ROM, RAM, peripheral circuit, input / output interface, various drivers, and the like, and is connected to the sensors 13 to 16 and the electric actuators 11L and 11R via a communication line. Further, the ECU 12 calculates the rear wheel toe angle based on the detection results of the sensors 13 to 16 and the like, determines the displacement amount of each electric actuator 11L, 11R, and performs the toe angle control of the rear wheel 5.

  The electric actuators 11L and 11R are provided with actuator displacement sensors 17L and 17R (toe angle sensors) for detecting the positions of output rods connected to the rear suspensions 7L and 7R, respectively. The actuator displacement sensors 17L and 17R are provided. This signal is input to the ECU 12. The electric actuators 11L and 11R can extend and contract the output rod by a predetermined amount determined by the ECU 12 to accurately change the toe angles of the rear wheels 5L and 5R.

  According to the vehicle V configured in this manner, the left and right electric actuators 11L and 11R are simultaneously symmetrically displaced to freely control toe-in / to-out of both rear wheels 5L and 5R under appropriate conditions. be able to. Further, if one of the left and right electric actuators 11L and 11R is extended and the other is contracted, both rear wheels 5L and 5R can be steered left and right.

  Next, the control procedure of the rear wheel steering device will be described with reference to FIG. FIG. 2 shows a rear wheel steering control unit 21 as road surface friction coefficient estimating means that is a part of a control circuit in the ECU 12, and its block configuration is configured by an IC circuit or a CPU program. It is a good thing.

  The rear wheel steering control unit 21 includes a stop state and a straight traveling determination unit to which signals of an ignition on IG from the ignition switch 18, a steering angle θs from the steering sensor 14, and a vehicle speed V from the vehicle speed sensor 13 are input. 22 is provided. In the stop state / straight-ahead determination unit 22, when the ignition switch ON IG signal is input and it is determined that the vehicle is in the stop state or when the vehicle speed V is out (V> 0), the steering angle When θs is in a straight traveling state (θs = 0) and it is determined that the vehicle V is in a straight traveling state, a straight traveling determination signal is output to the actuator drive control unit 23.

  When the determination signal is input, the actuator drive control unit 23 outputs a control signal for turning the rear wheels 5L and 5R to toe-in or toe-out to the electric actuators 11L and 11R based on a control procedure described later. At this time, the current I flowing through the actuator drive control unit 23 is detected by the current sensor 24, and the detected current I is input to the load calculation unit 25. The current sensor 24 and the load calculation unit 25 constitute rear wheel load detection means.

  The load calculating unit 25 integrates the detected current I per unit time and outputs the current integrated value Is− to the road surface friction coefficient estimating unit 26. The road surface friction coefficient estimator 26 reads the road surface friction coefficient μr from the map 27 according to the current integrated Is value, and outputs it as the estimated road surface friction coefficient μr. For example, the ECU 12 controls the behavior of the vehicle at the first cornering by using the road surface friction coefficient μr.

  Next, the control procedure will be described with reference to the flowchart of FIG. First, in step ST1, it is determined whether or not the ignition switch 18 is on. If it is off, the process returns to step ST1. This control may be started after the accessory switch is turned on.

  If it is determined in step ST1 that the ignition switch 18 is turned on, the process proceeds to step ST2 to determine whether the vehicle is stopped (determining whether the vehicle speed V is occurring). The determination of the vehicle speed V may be performed, for example, when a vehicle speed pulse is generated and the vehicle speed can be calculated, or when a predetermined vehicle speed (low speed) is set as a determination value and the determination value is exceeded. it can. If it is determined in step ST2 that the vehicle speed V is not output, the process proceeds to step ST4. If it is determined that the vehicle speed V is output, the process proceeds to step ST3.

  In step ST3, it is determined whether or not the vehicle is traveling straight (steered). If it is determined that the vehicle is steered, the process returns to step ST1, and if it is determined that the vehicle is not steered (straight traveling state). Proceed to step ST4. For example, when the steering angle θs is slightly generated (θs> 0), or when the steering angle θs is greater than a predetermined steering angle in consideration of play, the determination of the steering may be performed. Alternatively, the vehicle yaw rate may be used to determine that the vehicle is traveling straight when this value is equal to or less than a predetermined value.

  In step ST4, the rear wheels 5L and 5R are steered by the actuator drive controller 23 as described above. In the case of the present embodiment, for example, as shown in FIG. 4 (a), the rear wheels 5L and 5R are first driven to the toe-in side by a predetermined turning angle δr, and subsequently shown in FIG. 4 (b). In this way, the toe-out side is driven by a predetermined turning angle δr, and the toe-in / toe-out is repeated N (> = 2) times.

  In the next step ST5, the current I per unit time flowing through the electric actuators 11L and 11R during the driving in step ST4 is detected and integrated as described above, and the map shown in FIG. Is used to determine the estimated road friction coefficient μr from the current integrated value Is. When the electric energy integrated value Is is large, since the road surface friction coefficient is high, the current required for driving only the same turning angle becomes large, and the relationship shown in FIG. 5 is obtained. In the case of a proportional relationship as shown in FIG. 5, a relational expression can be set from experimental values obtained by experiments in advance. However, as shown by a two-dot chain line in FIG. The estimated road friction coefficient μr may be obtained stepwise. When this multi-section map is used, the estimated road surface friction coefficient μr can be easily obtained, and the control circuit can be simplified and the control can be performed quickly.

  Note that the drive of toe-in / toe-out in step ST4 may not be repeated N times and may be performed only once. Further, it is not necessary to perform both toe-in and toe-out steering, and the steering of only one of toe-in and toe-out may be repeated between the straight-ahead state indicated by the two-dot chain line in FIG. . Furthermore, only one of toe-in and toe-out may be steered once.

  In step ST6 following step ST5, the estimated road friction coefficient μr obtained in step ST5 is set as the initial value μ0 of the road friction coefficient. This initial value μ0 is used as a road surface friction coefficient used for vehicle behavior control in steering during subsequent cornering. As a result, it is possible to set a certain road surface friction coefficient before the driver steers, and a large jump of the road surface friction coefficient with the road surface friction coefficient obtained after steering is suppressed. Therefore, in the automobile in which the vehicle control is performed using the road surface friction coefficient, the vehicle control at the first steering after the start can be smoothly performed.

  By using the rear wheel steering device in this way, there is an advantage that the driver can operate without affecting the traveling of the vehicle in a state where the driver does not steer the steering wheel 8. In particular, the rear wheels 5L and 5R are moved in toe-in or toe-out. For example, even if the rear wheels 5L and 5R match the start timing, there is no influence on straight travel.

  Note that a plurality of maps may be prepared for the map 27 in accordance with the load difference. In that case, the present invention can be applied to a vehicle in which a load sensor is provided on a suspension or the like.

5L, 5R Rear wheel 10 Rear wheel toe angle variable control device (rear wheel steering device)
22 Stopping state and straight traveling determination unit 24 Current sensor (rear wheel load detection means)
25 Load calculation unit (rear wheel load detection means)
26 Road friction coefficient estimating section (road friction coefficient estimating means)
27 maps

Claims (2)

A rear wheel steering device capable of driving the rear wheels at least toe-in or toe-out,
A straight traveling determination means for determining a straight traveling state;
Rear wheel load detection means for detecting the load of the rear wheel steering device;
Road surface friction coefficient estimating means for setting the rear wheel to toe-in or toe-out at a predetermined turning angle at least once, and estimating a road surface friction coefficient according to the load of the rear wheel steering device at the time of toe-in or toe-out A road surface friction coefficient estimating apparatus characterized by comprising:   The road surface friction coefficient estimating device according to claim 1, wherein a road surface friction coefficient is estimated when it is determined that the vehicle is in the straight traveling state.

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