JP2009226972A - Geometry varying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a geometry varying device using a simple mechanism for producing a proper steering geometry corresponding to a vehicle speed. <P>SOLUTION: The geometry varying device includes: a housing 10 rotatable around a king pin axis relative to a vehicle body for supporting wheels; a knuckle arm 11 provided on the housing; a tie-rod 70 having one end connected to a steering gear box 60 and the other end connected via a joint 71 to the knuckle arm; a joint drive mechanism 100 for changing the steering geometry between a parallel geometry side and an ackerman geometry side with the displacement of the knuckle arm relative to the joint; and a control means 160 for driving the joint drive mechanism depending on an speed increase of a vehicle to change the steering geometry from the ackerman geometry side to the parallel geometry side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a geometry variable device that varies the geometry of a steering system that steers the wheels of a vehicle such as an automobile.

A steering device that steers the left and right front wheels of a vehicle such as an automobile generally converts the rotation of the steering wheel into a linear motion in the vehicle width direction by a steering gear box, and pushes and pulls the knuckle arm of the housing via a tie rod, Steer by rotating the wheel around the kingpin axis.
Patent Document 1 describes a steering angle control device in which, in such a steering device, the knuckle arm length is made variable to prevent the wheel and the vehicle body from interfering with each other during a large turning and suspension stroke.
Japanese Patent Laid-Open No. 3-176282

The parallel geometry with the left and right wheels having the same angle of cut and the Ackermann geometry that cuts the inner turning wheel larger than the turning outer wheel as the concept of the geometrical arrangement (geometry) of each component set in the steering device It has been known.
Ackerman Geometry is designed to turn right and left so that each wheel turns around a common point with the aim of turning smoothly without causing side slippage when turning at extremely low vehicle speeds where the centrifugal force can be ignored. The angle difference is set. However, in high-speed turning where the centrifugal force cannot be ignored, it is desirable for the wheels to generate a cornering force in a direction that balances the centrifugal force, and it is preferable to use a parallel geometry rather than an Ackermann geometry.

Since a vehicle steering apparatus can generally only have a fixed single steering geometry, it is often set to an intermediate geometry between an Ackermann geometry and a parallel geometry. However, in this case, the difference in steering angle between the left and right wheels is insufficient in the low speed range, the steering angle of the outer wheel is excessive, and the steering angle of the inner wheel is excessive in the high speed range. If there is an unnecessary bias in the tire lateral force distribution between the inner and outer wheels in this way, it will cause deterioration of fuel consumption due to deterioration of running resistance and early tire wear, and the smooth use of cornering due to the inefficient use of inner and outer wheels. Is damaged.
Therefore, if the steering geometry can be changed according to the vehicle speed, it can be closer to the Ackermann geometry at low speeds, and closer to parallel geometry at high speeds, without increasing driving resistance and smooth turning at low speeds and high speeds. It is possible to achieve both cornering performance at the same time.
On the other hand, for example, in a steer-by-wire type steering device that steers the left and right steered wheels by independent actuators, the steering angle difference between the left and right wheels can be set relatively freely according to the vehicle speed. In this case, since it is necessary to steer the wheels with the left and right actuators, it is required to use an actuator with excellent output and responsiveness, and it is necessary to perform precise control, so the device becomes complicated and expensive. Is inevitable.
An object of the present invention is to provide a geometry variable device capable of obtaining an appropriate steering geometry according to the vehicle speed by a simple mechanism.

The present invention solves the above-described problems by the following means.
According to the first aspect of the present invention, there is provided a housing capable of rotating about a kingpin axis with respect to a vehicle body and housing a hub bearing for supporting a wheel, a knuckle arm provided in the housing, and one end portion of which is a steering gear box. A tie rod connected to the knuckle arm via a joint that is swingable at the other end, and the kingpin shaft when the knuckle arm and the joint are relatively displaced and viewed from the vehicle front-rear direction. The joint drive mechanism that changes the steering geometry between the parallel geometry side and the Ackermann geometry side by changing the distance from the joint to the joint, and the joint drive mechanism is driven according to the speed of the vehicle, and according to the speed increase The steering geometry to the Ackermanzi Is changed from cytometry side to the parallel geometry side, a geometry variable device and a control means for changing the Ackerman geometry side the steering geometry from the parallel geometry side in accordance with the speed reduced.

The invention according to claim 2 is characterized in that the joint drive mechanism relatively displaces the joint relative to the knuckle arm substantially along a tangential direction of the joint locus when the tie rod swings during a suspension stroke. The geometry variable device according to claim 1.
According to a third aspect of the present invention, the joint drive mechanism determines the amount of steering to the toe-out side of the wheel when the suspension strokes to the bump side as the steering geometry changes from the Ackermann geometry side to the parallel geometry side. The geometry variable device according to claim 1 or 2, wherein the geometry variable device is increased.

According to the present invention, the following effects can be obtained.
(1) By changing the steering geometry by relatively changing the knuckle arm and the joint, the joint drive mechanism does not have to do the work of steering the wheel substantially, so an actuator with a small output can be used. In addition, an increase in unsprung weight can be suppressed by downsizing the actuator.
By controlling such a joint drive mechanism according to the vehicle speed, high responsiveness is not required as in the case of controlling according to a steering operation, for example, so that the actuator itself and its control can be simplified. can do.
By changing the steering geometry to the parallel geometry side on the high speed side and to the Ackermann geometry side on the low speed side, the tire drag can be reduced to reduce running resistance and improve fuel consumption and tire wear. it can. In addition, smooth turning is possible and steering response can be improved.
(2) By changing the joint relative to the knuckle arm substantially along the tangential direction of the joint trajectory when the tie rod swings during the suspension stroke, the toe change during straight travel accompanying the displacement of the joint is prevented, Straight running stability can be secured.
(3) Linear stability of the vehicle during high-speed driving by increasing the amount of steering to the toe-out side of the wheel when the suspension strokes to the bump side according to the geometric change from the Ackermann geometry side to the parallel geometry side Can be improved. Further, by reducing the amount of steering toward the toe-out side at the time of bumping during low speed running, the steering response of the vehicle can be further enhanced and the behavior can be made agile.

  An object of the present invention is to provide a geometry variable device capable of obtaining an appropriate steering geometry according to the vehicle speed by a simple mechanism. The present invention provides a joint drive device that raises and lowers a ball joint of a tie rod end with respect to a knuckle arm to increase the vehicle speed. In response, the steering geometry was changed from the Ackermann geometry side to the parallel geometry side.

Embodiments of the geometry variable device to which the present invention is applied will be described below.
The geometry variable device according to the embodiment is provided, for example, in a front suspension of a four-wheeled vehicle such as a passenger car that steers left and right front wheels.
FIG. 1 is a perspective view of a front suspension provided with a geometry variable device according to an embodiment as viewed from an obliquely lower side on the front side of a vehicle.
The front suspension 1 is, for example, a McPherson strut type, and includes a housing 10, a lower arm 20, a strut 30 and the like. Further, the front suspension 1 is further provided with a brake rotor 40, a drive shaft 50, a steering gear box 60 (not shown in FIG. 1, refer to FIG. 4), a tie rod 70, a joint drive device 100, and the like.

The housing 10 is a portion that houses a hub bearing that rotatably supports a hub to which a vehicle wheel (steering wheel) W (see FIG. 4) is attached. The housing 10 includes a knuckle arm 11, a ball joint 12, and the like.
The knuckle arm 11 is a portion to which the tie rod 70 is swingably connected. The knuckle arm 11 protrudes to the front side of the housing 10 and is formed integrally with the housing 10 body.
The ball joint 12 is a portion to which the lower arm 20 is swingably connected, and is provided at the lower end of the housing 10.

  The lower arm 20 is a suspension arm that is swingably connected to the vehicle body and the housing 10 and is disposed substantially along the vehicle width direction. The end of the lower arm 20 on the vehicle body side is swingable with respect to the vehicle body about a rotation axis substantially along the front-rear direction. The end of the lower arm 20 on the housing 10 side is connected to the ball joint 12 of the housing 10.

  The struts 30 are provided on the strut fixing portion provided on the upper side of the engine room side of the vehicle body and on the upper portion of the housing 10. The strut 30 includes a suspension spring that is a coil spring and a shock absorber that is inserted on the inner diameter side thereof, and expands and contracts according to the stroke of the suspension. The upper end of the strut 30 is supported so as to be rotatable with respect to the vehicle body via a strut upper mount 31 (see FIG. 4). The lower end portion of the strut 30 is connected to the upper end portion of the housing 10 via a bracket 32.

The brake rotor 40 is a disk-shaped member that is fixed to the hub and rotates with the wheels. The brake rotor 40 generates braking force by being sandwiched between brake pads by a brake caliper (not shown).
The drive shaft 50 is a rotating shaft that transmits a driving force from the differential gear side (not shown) to the hub side, and is provided with constant velocity joints at both ends so that it can swing according to the stroke or turning of the suspension. Yes.

  The steering gear box 60 includes a rack and pinion mechanism that converts the rotational motion of the steering wheel and the steering shaft into linear motion along the vehicle width direction of the steering rack.

  The tie rod 70 is a shaft-like member provided between the steering gear box 60 and the left and right housings 10. The end of the tie rod 70 on the steering gear box side is connected to the steering rack. The end of the tie rod 70 on the housing 10 side is connected to the knuckle arm 11 via a ball joint 71.

The ball joint 71 includes a ball stud 72, a socket 73 (see FIG. 2), and the like.
The ball stud 72 includes a ball 74 and a stud 75. The ball 74 is a spherical portion held by the socket 73. The socket 73 is provided on the upper surface portion at the end of the tie rod 70. The stud 75 is a cylindrical shaft-shaped portion that protrudes upward from the ball 74 and is a trapezoidal screw shaft having a male trapezoidal screw 76 formed on the outer peripheral surface thereof. A spline shaft portion 77 (see FIG. 2) is formed at the end of the stud 75 on the side opposite to the ball.

The joint driving device 100 is fixed to the tip of the knuckle arm 11 and relatively displaces the ball joint 71 in the vertical direction with respect to the knuckle arm 11. Note that this relative displacement direction is arranged substantially vertically along the tangential direction of the locus of the ball joint 71 of the tie rod 70 during the suspension stroke.
FIG. 2 is a schematic cross-sectional view of a connection portion between the joint drive device 100 and the ball joint 71.
FIG. 3 is a block diagram illustrating a configuration of a control system of the joint drive device 100.
The joint drive device 100 includes a casing 110, a motor 120 (see FIG. 1), a worm gear 130, a worm wheel 140, a vehicle speed sensor 150, a geometry setting unit 160, a control amount setting unit 170, a motor control unit 180, and the like.

The casing 110 is a member in which each component of the joint drive device 100 is accommodated and held. Further, the casing 110 is formed with an opening 111 into which the stud 75 of the ball stud 72 is inserted substantially along the vertical axis from below. A female trapezoidal screw 112 to be combined with the trapezoidal screw 76 of the stud 75 is formed on the inner peripheral surface of the opening 111.
The motor 120 is an actuator that serves as a power source for the joint drive device 100, and its rotation shaft is arranged substantially horizontally. The motor 120 is, for example, a stepping motor (synchronous motor) that operates in synchronization with supplied pulse power and has a positioning function.

The worm gear 130 is connected to the output shaft of the motor 110.
The worm wheel 140 is rotatably supported around a rotation axis provided concentrically with the central axis of the stud 75 of the ball stud 72 and is driven by the worm gear 130. A spline hole is formed in the central portion of the worm wheel 140. The spline shaft 77 of the ball stud 72 is inserted into the spline hole, and is splined. Thereby, the ball stud 72 is in a state where relative rotation around the central axis is prohibited with respect to the worm wheel 140 and relative displacement along the central axis direction is allowed.

The vehicle speed sensor 150 is provided in the housing 10, for example, and outputs a pulse signal corresponding to the wheel speed.
The geometry setting unit 160 includes a CPU that calculates the traveling speed of the vehicle based on the output of the vehicle speed sensor 150 and sets the steering geometry based on the calculated traveling speed.
The control amount setting unit 170 includes a CPU that sets the drive amount of the motor 120 that is a control amount based on the geometry set by the geometry setting unit 160.
The motor control unit 180 includes a drive circuit that drives the motor 120 by supplying driving pulse power to the motor 120 based on the drive amount set by the control amount setting unit 170.
The control performed by each of these setting units will be described in detail later.

Next, the steering geometry of the above-described front suspension 1 will be described.
4A and 4B are schematic views showing the steering geometry of the front suspension. FIG. 4A is a plan view of the vehicle as viewed from above, and FIG. 4B is a rear view of the vehicle as viewed from the rear side. It is a bb part arrow line view of Fig.4 (a).
In the case of the McPherson strut suspension as in the present embodiment, the kingpin shaft that is the steering axis of the wheel W connects the rotation center of the strut upper mount 31 and the rotation center of the ball joint 12 at the lower end of the housing 10. It becomes a straight line.

The kingpin shaft is provided with a kingpin inclination angle and a caster angle and is inclined.
The kingpin inclination angle is an inward inclination angle that is set such that the strut upper mount 31 is on the inner side in the vehicle width direction than the ball joint 12.
The caster angle is a rearward tilt angle set so that the strut upper mount 31 is located on the vehicle rear side with respect to the ball joint 12.

The steering geometry is when the rotation center of the ball joint 71 is on a plane that intersects the kingpin axis and the kingpin axis and includes a straight line extending in the vehicle front-rear direction (the kingpin axis and the ball joint 71 overlap in the vehicle rear view). )), The parallel geometry has the same steering angle of the inner and outer wheels.
Further, when the tie rod 70 is disposed on the vehicle front side with respect to the kingpin shaft as in the present embodiment, the ball joint 71 is disposed on the outer side in the vehicle width direction with respect to the plane described above (in the vehicle rear view). When the ball joint 71 is arranged outside the kingpin axis), the inner wheel rudder angle (toe out) becomes larger than the outer wheel rudder angle (toe out) according to the distance from this plane, and the Ackermann geometry is reached when the predetermined distance is reached. It becomes.
Therefore, in the joint drive device 100 of the present embodiment, when the ball stud 72 is displaced upward with respect to the knuckle arm 11, it approaches the Ackermann geometry, and when it is displaced downward, it approaches the parallel geometry.

FIG. 5 is a flowchart illustrating control in the geometry variable device according to the embodiment. Hereinafter, the steps will be described step by step.
<Step S01: Geometry setting>
The geometry setting device 160 sets the geometry by calculating the feed driving amount of the ball stud 72, and proceeds to step S02. The ball stud payout driving amount is set according to the traveling speed of the vehicle detected by the vehicle speed sensor 150.
FIG. 6 is a graph showing the correlation between the vehicle speed and the ball stud payout driving amount. In FIG. 6, the horizontal axis indicates the vehicle speed (the right side is high speed), and the vertical axis indicates the ball stud payout driving amount (the payout amount increases toward the upper side = the ball stud descends).

As shown in FIG. 6, in a low speed range where the vehicle speed is from zero to less than V1, the ball stud payout driving amount is zero, and the ball stud 72 is held at a predetermined initial position. At this time, the steering geometry is the Ackermann geometry.
In a medium speed range where the vehicle speed is V1 or more and less than V2, the ball stud payout driving amount increases linearly as the vehicle speed increases, and at this time, the steering geometry continuously changes from the Ackermann geometry side to the parallel geometry side. .
In a high speed range where the vehicle speed is V2 or higher, the ball stud payout driving amount is again set to a constant value, and at this time, the steering geometry is a parallel geometry.

<Step S02: Control amount setting>
The control amount setting unit 170 calculates the target drive amount of the motor 120, which is a control amount, based on the ball stud extension drive amount obtained by the geometry setting unit 160 in step S01, and transmits the target drive amount to the motor control unit 180, step S03. Proceed to
<Step S03: Motor control>
The motor control unit 180 outputs predetermined pulse power based on the target drive amount of the motor 120 provided from the control amount setting unit 170, supplies the pulse power to the motor 120, controls the motor 120, and ends the process. As a result, the worm gear 130 drives the worm wheel 140 to rotate the spline-engaged ball stud 72 around its central axis. When the ball stud 72 rotates, the ball stud 72 is displaced relative to the casing 110 and the knuckle arm 11 along the central axis direction by the thrust generated by the trapezoidal screw.

FIG. 7 is a graph showing the inner and outer wheel steering angles in the present embodiment. In FIG. 7, the horizontal axis indicates the steering angle of the turning inner wheel toward the toe-in side, and the vertical axis indicates the steering angle of the turning outer wheel toward the toe-out side.
As shown in FIG. 7, the inner and outer wheel steering angles are equal in the parallel geometry. In the Ackermann geometry, the inner wheel rudder angle is larger than the outer wheel rudder angle, and the rudder angle difference increases as the rudder angle increases.
In the present embodiment, in the region where the vehicle speed exceeds V1 and less than V2, the steering geometry is set between the parallel geometry and the Ackermann geometry, and approaches the parallel geometry as the vehicle speed increases. As it decreases, it approaches the Ackerman geometry side.

Next, toe change (bump steer) characteristics during a stroke in the suspension device of the present embodiment will be described.
FIG. 8 is a graph showing the correlation between the suspension stroke and the toe change angle. In FIG. 8, the horizontal axis represents the suspension stroke (the right side is the contraction (bump) side, the left side is the expansion (rebound) side), and the vertical axis represents the toe change amount (the upper side is the toe-in and the lower side is the toe-out).
As shown in FIG. 8, in the present embodiment, the bump steer characteristic changes according to the change in the vehicle speed (change in the steering geometry), and the toe-out amount (bump to-out) corresponding to the contraction side stroke increases as the speed increases. . The bump toe-out amount decreases as the vehicle speed decreases, and becomes zero at a predetermined speed between V1 and V2. Further, bump toe-in occurs on the low speed side.

According to the embodiment described above, the following effects can be obtained.
(1) By moving the ball stud 72 of the ball joint 71 up and down relative to the knuckle arm 11 and changing the steering geometry, the mechanical portion of the joint drive device 100 substantially steers the wheel W itself. Therefore, the motor 120 with a small output can be used, and the structure of the speed reduction mechanism can be simplified. Further, by reducing the size of the motor 120 and the speed reduction mechanism, it is possible to suppress an increase in unsprung weight that affects the steering stability and riding comfort of the vehicle.
(2) By controlling the joint drive device 100 according to the vehicle speed, high responsiveness is not required as in the case of controlling the tie rod feed amount and pull-in amount according to the steering operation, for example. The configuration of the part and its control can be simplified.
(3) By changing the steering geometry to the parallel geometry side on the high speed side and to the Ackermann geometry side on the low speed side, the tire drag is reduced to reduce running resistance, thereby improving fuel consumption and tire wear. be able to. In addition, smooth turning can be achieved and steering response can be improved.
(4) By moving the ball stud 72 relative to the knuckle arm 11 substantially along the tangential direction of the trajectory of the ball joint 71 when the tie rod 70 swings during the suspension stroke, the straight movement associated with the displacement of the ball joint 71 is achieved. The toe change at the time can be prevented, and the straight running stability of the vehicle is not adversely affected.
(5) By increasing the steering amount of the wheels W to the toe-out side when the suspension strokes to the bump side in accordance with the geometric change from the Ackermann geometry side to the parallel geometry side, the straight running stability of the vehicle during high speed running Can be improved. Further, when the vehicle is traveling at a low speed, the amount of steering toward the toe-out side at the time of bumping is reduced, and by adopting the bump toe-in characteristic, the steering response of the vehicle can be further enhanced and the behavior can be made agile.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The configuration of the joint drive mechanism is not limited to the configuration of the embodiment described above, and can be changed as appropriate. For example, a ball spline may be used instead of the trapezoidal screw, or another mechanism may be used. Further, the actuator is not limited to the stepping motor, and feedback control may be performed using an asynchronous motor and a position sensor.
(2) Although the suspension device of the embodiment has the tie rod disposed on the front side with respect to the kingpin shaft, the present invention can also be applied to a suspension device in which the tie rod is disposed on the rear side with respect to the kingpin shaft. . In this case, the Ackermann geometry is obtained by displacing the joint inward in the vehicle width direction with respect to the kingpin axis in the vehicle rear view.
(3) The configuration of the suspension device to which the present invention is applied is not limited to the form of the embodiment and can be changed as appropriate. For example, in the McPherson strut suspension, the present invention can be applied to suspensions in which the lower arm is composed of a plurality of links, double wishbone suspension, multilink suspension, and the like.
(4) In the embodiment, the steering geometry is changed to a complete Ackerman geometry or a complete parallel geometry. However, the variable range of the steering geometry is narrower than this, and can be varied within the intermediate range between the Ackermann geometry and the parallel geometry. You may make it make it.

It is a perspective view of the front suspension provided with the Example of the geometry variable apparatus to which this invention is applied. It is typical sectional drawing of the joint drive device in the geometry variable apparatus of an Example. It is a block diagram which shows the structure of the control system of the geometry variable apparatus of an Example. It is a schematic diagram which shows the geometry of the front suspension of FIG. It is a flowchart which shows the control in the geometry variable apparatus of an Example. It is a graph which shows the correlation with the vehicle speed in the geometry variable apparatus of an Example, and a ball stud extension drive amount. It is a graph which shows the inner and outer wheel steering angle in the geometry variable apparatus of an Example. It is a graph which shows the correlation with the suspension stroke and toe change angle in the geometry variable apparatus of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front suspension 10 Housing 11 Knuckle arm 12 Ball joint 20 Lower arm 30 Strut 31 Strut upper mount 32 Bracket 40 Brake rotor 50 Drive shaft 60 Steering gear box 70 Tie rod 71 Ball joint 72 Ball stud 73 Socket 74 Ball 75 Stud 76 Trapezoid screw 77 Spline Shaft part 100 Joint drive device 110 Casing 111 Opening 112 Trapezoidal screw 120 Motor 130 Worm gear 140 Worm wheel 150 Vehicle speed sensor 160 Geometry setting part 170 Control amount setting part 180 Motor control part W Wheel

Claims (3)

A housing capable of rotating about a kingpin axis relative to the vehicle body and containing a hub bearing that supports a wheel;
A knuckle arm provided in the housing;
A tie rod having one end connected to the steering gear box and the other end connected to the knuckle arm via a swingable joint;
A joint that changes the steering geometry between the parallel geometry side and the Ackermann geometry side by changing the distance from the kingpin axis to the joint when the knuckle arm and the joint are relatively displaced and viewed from the front-rear direction of the vehicle. A drive mechanism;
The joint drive mechanism is driven according to the speed of the vehicle, the steering geometry is changed from the Ackermann geometry side to the parallel geometry side as the speed increases, and the steering geometry is changed from the parallel geometry side as the speed decreases. A geometry variable device comprising: control means for changing to the Ackermann geometry side. The joint drive mechanism is configured to displace the joint relative to the knuckle arm substantially along a tangential direction of a locus of the joint when the tie rod swings during a suspension stroke. Geometry variable device. The joint drive mechanism increases the amount of steering to the toe-out side of the wheel when the suspension strokes to the bump side in accordance with the change of the steering geometry from the Ackermann geometry side to the parallel geometry side. The geometry variable device according to claim 1 or 2.

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