JPH04303070A - Rear-wheel steering system in vehicle - Google Patents

Abstract

PURPOSE:To expand an area wherein rectilinear stability is secured, in the case wherein a steering characteristic is set as such one as having a yaw-rate characteristic item. CONSTITUTION:A steering ratio thetaS is determined by a steering characteristic of thetaS=-C1.thetaH+C3.Y, by way of example. Among them, thetaH is a handwheel steering angle, Y a yaw rate and C1, C2 the control gain, respectively. A yaw- rate characteristic item functions as a component for increasing a phase quantity, and a steering angle characteristic item functions as a component for decreasing the phase quantity. At an area, where a rear-wheel slip angle betahas exceeded beta1, namely, a corresponding relationship between this slip angle betaand a cornering power CP comes to a non-linearity, the control gain C2 is made larger or the control gain C1 is made smaller, through which each phase quantity of rear wheels is increased.

Description

[Detailed description of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering system for a vehicle which steers both the front wheels and the rear wheels.

0004

2. Description of the Related Art In a rear wheel steering system for a vehicle, rear wheel steering is controlled based on preset steering characteristics. Japanese Unexamined Patent Publication No. 57-44568 discloses a vehicle in which the steering characteristic is set to include a yaw rate characteristic term. This yaw rate characteristic term acts to converge the yaw rate when it occurs, that is, it functions as a component that increases and corrects the same phase amount, contributing to improving the stability of the vehicle. I will do it.

[0006]

[Problem to be solved by the invention] Yawray in steering characteristics
It has been found that in a vehicle having a characteristic term of 100 mm, the amount of in-phase is insufficient during a turn when the lateral G acting on the vehicle body becomes considerably large, which is not preferable in terms of ensuring sufficient stability of the vehicle.

When we investigated the cause of this problem, we found that it was caused by the characteristic of the correspondence between the slip angle of the rear wheels and the cornering power. In other words, the correspondence between the slip angle and the cornering power is such that as the slip angle increases, the cornering power initially increases almost linearly, and then the cornering power increases as the slip angle increases. The degree of increase in - starts to decrease and eventually reaches a peak value, and once the peak value is passed, the cornering power decreases as the slip angle increases.

On the other hand, increasing the same phase amount is to increase the slip angle of the rear wheels and increase the cornering power of the rear wheels, but as mentioned above, the peak cornering power If the relationship between slip angle and cornering power becomes non-linear from a point slightly before this value, even if the slip angle is increased by the same amount, the cornering power will only increase slightly. Therefore, when increasing the in-phase amount according to the yaw rate characteristic term, even if this does not become a problem in the region where the slip angle is small, if the slip angle increases to the region where the slip angle becomes nonlinear, the yaw rate will increase. Cornering power is insufficient due to the in-phase amount increase due to the characteristic term, and as a result, sufficient stability of the vehicle cannot be ensured.

[0012] Therefore, an object of the present invention is to provide a rear vehicle that can further expand the running range in which the stability of the vehicle can be ensured, assuming that the steering characteristic includes a yaw rate characteristic term. An object of the present invention is to provide a wheel steering device.

[0014]

[Structure of the Invention] In order to achieve the above-mentioned object, the present invention compensates for the insufficient cornering power in a region where the correspondence relationship between the slip angle of the rear wheels and the cornering power is non-linear. Therefore, increasing means for increasing the amount of in-phase is provided.

[0016]

According to the present invention, the insufficiency of the in-phase amount is compensated for by the action of the increasing means, so that the area in which vehicle stability is ensured can be further expanded. In addition to the yaw rate characteristic term, the steering characteristic may include a characteristic term for reducing the same phase amount to reduce the same phase amount in order to balance ensuring turning performance.

In order to increase the in-phase amount by the increasing means,
For example, this can be achieved by increasing the control gain of the yaw rate characteristic term or by decreasing the control gain of the in-phase amount reduction characteristic term. Note that whether or not the relationship between the slip angle and the cornering power is in a nonlinear region can be determined based on the vehicle speed and the steering angle.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 12 indicates left and right front wheels, 16 indicates left and right rear wheels, and the left and right front wheels 12 are linked to each other by a front wheel steering mechanism 14. A handle 30 is linked to the front wheel steering mechanism 14, and the front wheels 12 are steered left and right by left and right operations of the handle 30 (the front wheel steering angle is shown as θF). Further, the left and right rear wheels 16 are connected to each other by a rear wheel steering mechanism 18.
The left and right rear wheels are simultaneously steered to the right or left (the rear wheel steering angle is shown as θR).

The front wheel steering mechanism 14 and the rear wheel steering mechanism 18 are mechanically linked via an intermediate shaft 52 constituting a linkage mechanism. The front wheel steering angle θF is transmitted to the rear wheel steering mechanism 18 via the intermediate shaft 52. is transmitted to the rear wheel steering mechanism 18 with a steering ratio of . That is, although the steering ratio θS is expressed as θR/θF, by changing the steering ratio by the steering ratio changing means 20, even if the front wheel steering angle θF is the same, the rear wheel steering angle θR can be arbitrarily changed. It is subject to change. Note that although the steering ratio changing mechanism 20 itself is known, an example thereof will be described in detail later.

The steering ratio changing mechanism 20 is controlled by a control unit U configured using, for example, a microcomputer. This control unit U determines a target steering angle of the rear wheels from a predetermined steering ratio θS obtained based on preset steering characteristics, and while looking at the output of the sensor 28 that detects the steering ratio, The steering ratio changing mechanism 20 is feedback-controlled so that the actual steering angle θR of the rear wheels 16 becomes the target steering angle.

In the embodiment, the steering characteristics are set using the vehicle speed, steering angle, and yaw rate as parameters. Therefore, the control unit U includes each sensor, which detects the vehicle speed V. Signals from a sensor 24, a sensor 25 that detects the steering wheel angle θH, a sensor 26 that detects the yaw rate Y, and a sensor 28 that detects the steering ratio θS are input.

The steering characteristics in this embodiment are as follows: steering ratio θS
is set to be determined based on the following equation (1). θS=-C1・θH+C2・Y...(1)

[
In the above equation, C1·θH is a steering angle characteristic term serving as a characteristic term for reducing the same phase amount, C2·Y is a yaw rate characteristic term, and C1 and C2 are the control gains thereof. In this steering characteristic equation, the sign "+" means an increase in the amount of same phase, and the sign "-" means a decrease in the amount of same phase. Therefore, the steering angle characteristic term becomes a component for decreasing the phase amount, and the yaw rate characteristic term becomes a component for increasing the phase amount.

In the embodiment, C1 and C2 are functions f(V, θ) whose parameters are vehicle speed V and steering angle θH, respectively.
H), g(V, θH). In other words, the above equation (1) becomes the following equation (2). θS=-f(V, θH)+g(V, θH)・Y
(2) The function f(V, θH) is set as shown in FIG. 5, and g(V, θH) is set as shown in FIG. 6, for example.

FIG. 7 shows the correspondence between the slip angle β of the rear wheels and the cornering power CP. As is clear from Fig. 7, when the slip angle is increased from 0, β and C decrease until the cornering power reaches β1.
The relationship with P is almost linear, but becomes non-linear after β1. Then, CP reaches its peak value at β2, and after β2, CP decreases nonlinearly. Therefore, it is understood that at the point in time when β1 is exceeded, in order to obtain the required increase in cornering power, the degree of increase in the slip angle β should be made larger than in the linear region. However, the slip angle is determined by the cornering power.
It is meaningless to make it larger than β2, which is the peak value of CP.

A flowchart showing a control example of the present invention in FIG.
In the following explanation, P indicates a step. First, in P1, signals from each sensor are input, and then in P2, the rear wheel slip angle β is determined with reference to a map set based on, for example, the vehicle speed V and the steering wheel angle θH.

At P3, the slip angle β determined at P2
It is determined whether or not the slip angle is greater than or equal to the slip angle β1 shown in FIG. When the determination in P3 is YES, in P4 a correction coefficient A (>1) is determined based on the slip angle β. Next, in P5, the corrected control gain C2 is determined by multiplying the control gain C2 of the yaw rate characteristic term by the correction coefficient A. As a result, the corrected control gain C2 is increased, resulting in in-phase amount increasing correction.

After P5, in P6, the steering ratio θS is determined based on the above equation (1) or (2), and then in P7, the rear wheel steering angle θR is determined to correspond to the steering ratio θS. The steering ratio changing mechanism 20 is controlled so that.

When the determination of P3 is NO, P4, P
The steering ratio θS at P6 is determined without performing the correction at P5 (the correction coefficient is 1). Note that the processing in P4 and P5 may be a correction such as reducing the control gain C1 of the steering angle characteristic term which is the characteristic term for reducing the in-phase amount, and the control gains of both C1 and C2 may be corrected. may also be corrected.

Next, an example of the steering ratio changing mechanism 20 and its peripheral mechanisms will be explained. As shown in Figure 2,
The rear wheel steering mechanism 18 incorporates a variable steering ratio mechanism 20 and includes a hydraulic switching valve 32, a rear wheel steering rod 34, a displacement transmitting means 36, and a hydraulic power cylinder 38. The variable steering ratio mechanism 20 includes an output rod 40, a bevel gear 42, a swing shaft member 44, a pendulum arm 46, and a connecting rod 48, and each of these members is arranged as shown in FIG. It is housed in a case 50.

The output rod 40 is supported by the case 50 so as to be able to slide in the direction of the axis L3, and by displacing the stroke in the direction of the axis L3, the output rod 40 is connected to the rear wheel steering rod 34 via the displacement transmitting means 36. is displaced in the axial direction (vehicle width direction), thereby steering the rear wheels (not shown) connected to both ends of the rear wheel steering rod 34.

The bevel gear 42 is rotatably attached to the case 50 around an axis L1 that is the same as the axis L3 of the output rod 40.
is supported by A pinion 52a at the rear end of the transmission shaft 52 that meshes with the bevel gear 42 rotates around the axis L1 as the steering wheel rotates. That is, the front wheel steering angle θF is input from the front wheel steering mechanism 14 to the rear wheel steering mechanism 18 via the transmission shaft 52.

The swing shaft member 44 has an axis L that can take a position coaxial with the axis L3 of the output rod 40 (the position shown in the figure).
2, and is fixed to the swing gear 54. This swing gear 54 meshes with a worm 58 that rotates by the drive of a servo motor 56 controlled by the control unit 22, and rotates around an axis perpendicular to the plane of the drawing that intersects the axis L2. This allows the swing shaft member 44 to be rotated at the same time.

The pendulum arm 46 is connected to the swing shaft member 44 so as to be swingable about the axis L2 of the swing shaft member 44, and the axis L4 of the pendulum arm 46 is Member 44
The connection position to the swing shaft member 44 is determined so as to pass through the intersection of the rotation axis and the axis L2 of the swing shaft member 44.

The connecting rod 48 has an axis L5 parallel to the axis L3 of the output rod 40, and the connecting rod 48 has an axis L5 parallel to the axis L3 of the output rod 40.
0, a bevel gear 42 and a pendulum arm 46. The connection to the output rod 40 is made by screwing one end of the connection rod 48 to a lever 40a fixed to the end of the output rod 40, and the connection to the bevel gear 42 is made from the axis L1 of the bevel gear 42. The other end of the connecting rod 48 is inserted through the insertion hole 42a formed in the bevel gear 42 at a distance r, and the connection to the pendulum arm 46 is made by allowing the end of the connecting rod 48 to rotate in all directions. This is accomplished by inserting the pendulum arm 46 through the insertion hole 60a of the ball joint member 60, which is provided so that it can be inserted.

Therefore, the connecting rod 48 is fixed with respect to the output rod 40, but is swingable with respect to the bevel gear 42 in the axis L5 direction (that is, the axis L3 direction), and the pendulum arm 46 For axis L4 direction (
In the illustrated state, it is slidable in a direction perpendicular to the axis L3. Note that the axis L4 of the pendulum arm 46 is tilted with respect to the direction orthogonal to the axis L3 due to the rotation of the swing shaft member 44, and the pendulum arm 46 swings in this tilted direction. In this case as well, there is a sliding component in the direction perpendicular to the axis L3, and the included angle change between L4 and the axis L5 is absorbed by the rotational action of the ball joint member 60, so that the connecting rod The component of the force transmitted to 48 in the direction perpendicular to the axis L3 is absorbed at the connection point,
Relative movement in this direction becomes possible.

In this way, the pendulum arm 46 and the connecting rod 48 in the variable steering ratio mechanism 20 are connected so that they can move relative to each other in the direction orthogonal to the axis L3, so that the pendulum When the arm 46 rotates, the locus of the connecting point between the pendulum arm 46 and the connecting rod 48 becomes a circular locus or an elliptical locus on the outer peripheral surface of a cylinder with a radius r centered on the axis L3. .

FIG. 4 shows the case where the axis L2 of the swing shaft member 44 is tilted by θ with respect to the axis L3 of the output rod 40 (that is, the axis L4 of the pendulum arm 46 is tilted by θ with respect to the direction orthogonal to the axis L3). FIG. 4 is a diagram showing the displacement of the output rod 40 when the output rod 40 is tilted. As is clear from the figure, the pendulum arm 46
No matter which direction the pendulum arm 46 swings to the left or right, if the amount of swing is the same, the displacement of the connection point between the pendulum arm 46 and the connecting rod 48 will be S in the direction of the axis L3, and the connection point between the pendulum arm 46 and the connecting rod 48 will be S. Since the rods 48 are fixedly connected, the displacement of the output rods 40 is also S in the direction of the axis L3.

As mentioned above, the output rod 40 shown in FIG.
If the amount of swing of the pendulum arm 46 is the same, the amount of left-right displacement of the pendulum arm 46 is equal to X, but the amount of displacement However, it changes depending on the size of θ. Therefore, the rear wheel steering angle θ is relative to the front wheel steering angle θF.
The steering ratio θS, which is the ratio of R, can be set and changed by setting and changing the magnitude of the inclination θ of the swing shaft 46 by controlling the operation of the servo motor 56. moreover,
The swing shaft member 44 can be tilted not only counterclockwise as described above but also clockwise, and in this case, the direction of movement of the output rod 40 relative to the rotation of the bevel gear 42 is opposite to that in the above case. This allows the steering wheel to be steered or the rear wheels to be steered in the same phase or in the opposite phase relative to the front wheels.

The steering ratio θS set and changed by the variable steering ratio mechanism 20 is determined by the steering ratio sensor 28 attached to the swing shaft member 44, as shown in FIG. is detected based on the slope θ.

Next, parts other than the variable steering ratio mechanism 20 will be explained. First, the hydraulic switching valve 32 includes a valve housing 62 and a housing 6 inside the housing 62.
2, and a spool 64 housed so as to be displaceable in the direction of an axis L6 parallel to the axis L3 of the output rod 40. The spool 64 is displaced by the output rod 40 and the rear wheel steering rod 34 via the displacement transmission means 36. The supply of hydraulic pressure to the hydraulic power cylinder 38 is controlled by this displacement of the spool 64. In other words, when the valve housing 62 is displaced to the right from the neutral position shown in the figure, hydraulic pressure is supplied to the right oil chamber 66 of the hydraulic power cylinder 38, and when it is displaced to the left, hydraulic pressure is supplied to the left oil chamber 68 of the hydraulic power cylinder 38. be done.

The rear wheel steering rod 34 extends in the vehicle width direction parallel to the axis L3 of the output rod 40, is displaced in that direction, and is connected to both left and right ends via tie rods and knuckle arms (not shown). The displacement is performed by the hydraulic pressure of the hydraulic power cylinder 38. Further, this rear wheel steering rod 34 is provided with a centering spring 70, so that if the hydraulic system of the hydraulic switching valve 32 or the hydraulic power cylinder 38 is damaged or malfunctions and the hydraulic pressure in the hydraulic power cylinder 38 disappears, If the mechanical system of the rear wheel steering device 10 is damaged or malfunctions and the hydraulic system is opened to drain and the hydraulic pressure in the hydraulic power cylinder 38 disappears, the centering spring 70 causes the rear wheel steering rod to 34 is positioned at a neutral position, that is, a position where the rear wheels are not steered and are traveling straight, so as to provide a so-called fail-safe.

The hydraulic power cylinder 38 displaces the rear wheel steering rod 34 in the vehicle width direction by hydraulic pressure, and a piston 72 is directly fixed to the rear wheel steering rod 34. Left and right oil chambers 68, 66
Seal members 74 and 76 are provided to form the same. The seal members 74, 76 are fixed to the housing 78 of the hydraulic power cylinder 38 and are slidable with respect to the rear wheel steering rod 34. The displacement transmitting means 36 includes the output rod 3
4, the spool 64, and the rear wheel steering rod 34, and is operated in a direction to displace the spool 64 in a predetermined direction by displacement of the output rod 40,
The spool 64 is moved in the opposite direction by the displacement of the rear wheel steering rod 34 caused by the displacement of the spool 64.

That is, this displacement transmission means 36 is composed of a cross lever consisting of a vertical lever and a horizontal lever, and one end A of the vertical lever is connected to the output rod 40, and the other end B is connected to the rear wheel steering. One end C of a horizontal lever is engaged with the case of the rear wheel steering device 10 fixed to the vehicle body, and the other end D of the rod 34 is engaged with the spool 64. The engaging ends A, B, C, and D are immovable in the axial direction with respect to the output rod 40, rear wheel steering rod 34, and spool 64, but are movable and rotatable in other directions. The engaging end C is engaged by a ball joint so that it can rotate but cannot move.

The stroke displacement of the output rod 40 in the direction of the axis L3 causes the rear wheel steering rod 34 to be displaced in the axial direction via the displacement transmitting means 36, thereby causing the rear wheel steering rod 34 to Although the rear wheels (not shown) connected to both ends are steered, the operating principle of the steering amount transmission is not directly related to the present invention, and is described in Japanese Patent Application Laid-Open No. 1-273772. Since it is explained in detail in , a detailed explanation thereof will be omitted. Note that the present invention is applicable to a structure in which the mechanical linkage between the front wheel steering mechanism and the rear wheel steering mechanism is cut off, that is, a structure in which the front wheel steering mechanism and the rear wheel steering mechanism are electrically linked. good.

[Brief explanation of drawings]

FIG. 1 is a simplified plan view showing the overall outline of a rear wheel steering device.

FIG. 2 is a perspective view showing details of a rear wheel steering mechanism and a steering ratio changing mechanism.

FIG. 3 is a sectional view taken along the line X5-X5 in FIG. 2;

FIG. 4 is a diagram illustrating the operating principle of the steering ratio changing mechanism.

FIG. 5 is a diagram showing the characteristics of a steering angle characteristic term as a characteristic term for reducing the same phase amount.

FIG. 6 is a diagram showing the characteristics of the yaw rate characteristic term.

[Figure 7] Figure 7 shows rear wheel slip angle and cornering power.
FIG.

FIG. 8 is a flowchart showing a control example of the present invention.

[Explanation of symbols]

12 Front wheel 14 Front wheel steering mechanism 16 Rear wheel 18 Rear wheel steering mechanism 20 Steering ratio changing mechanism 22 Control unit 24 Sensor (vehicle speed V) 25 Sensor (studder angle θH) 26 Sensor (yaw rate Y) 28 Sensor (steering ratio θS) 30 Handle 52 Intermediate shaft (linkage mechanism) θF Front wheel steering angle θR Rear wheel steering angle θS Steering ratio C1 Control gain (steering angle characteristic term)

Claims (7)

[Claims] [Claim 1] In order to converge the yaw rate, as the yaw rate increases, the amount of same phase of the rear wheels increases.
In a rear wheel steering system of a vehicle that controls rear wheel steering based on a steering characteristic having a rate characteristic term, a state in which the correspondence between the rear wheel slip angle and cornering power is nonlinear. driving area detection means for detecting that the driving area is in the nonlinear driving area; and increasing means for increasing the same phase amount of the rear wheels when the driving area detection means detects that the driving area is in the nonlinear driving area; A rear wheel steering device for a vehicle, comprising: 2. In claim 1, the steering characteristic is:
In addition to the yaw rate characteristic term, a characteristic term for reducing the same phase amount for reducing the same phase amount of the rear wheels is provided. 3. According to claim 2, the increasing means comprises:
Correction is made to increase the control gain of the yaw rate characteristic term. 4. According to claim 2, the increasing means comprises:
Correction is made so that the control gain of the characteristic term for reducing the in-phase amount is reduced. 5. The vehicle according to claim 1, wherein the driving area detecting means detects the nonlinear driving area based on vehicle speed and steering angle of the steering wheel. 6. In claim 3, the control gain of the yaw rate characteristic term controls vehicle speed and steering angle as parameters.
The function that is set as the data. 7. The vehicle according to claim 4, wherein the characteristic term for reducing the same phase amount is set as a function having vehicle speed and steering angle as parameters.