JPH0374264A - Rear wheel steering device - Google Patents

Abstract

PURPOSE:To miniaturize a motor and a battery by providing such a constitution as to steer rear wheels through physical interlock with front wheel steering, and as to conduct power steering by a difference between the steering angle by this steering and a target steering angle. CONSTITUTION:A controller 15 first calculates a target rear wheel steering angle delta from the turning angle of a steering wheel 3 and vehicle speed. Then, a deviation deltaM between a rear main steering angle deltaM to the front wheel steering angle by the turning angle of the wheel 3 through rear wheel main steering systems 13, 14, 12, 11 and a target rear wheel steering angle delta is determined. This shows a target rear wheel auxiliary steering quantity, and a controller 15 calculates the rotating quantity (target motor rotating quantity) thetaS of a motor 10 to obtain this deviation DELTAM. The controller 15 determines a motor rotating quantity instruction I to zero the deviation between this rotating quantity thetaS and a measured motor rotating quantity thetaM detected by a rotary encoder 19 according to this deviation, and supplies the instruction I to a driving circuit 16. The driving circuit 16 supplies such a driving current as to provide the motor rotating quantity corresponding to the instruction I to the motor 10 by the electric power from a battery 20.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a rear wheel steering device for a vehicle.

(Prior Art) This type of device aims to improve the turning stability and cornering performance of a vehicle by steering the rear wheels by a target steering angle determined in accordance with the front wheel steering.

Conventional devices that perform this rear wheel steering are, for example,
As seen in Japanese Patent No. 46765, it has been common practice to steer the rear wheels only by power using an electric motor or a hydraulic actuator over the entire rear wheel steering angle range.

(Problem to be Solved by the Invention) However, according to such a conventional rear wheel steering device, a large amount of power is required for rear wheel steering, and especially when this steering is performed by an electric motor, a large battery or motor is required. This was disadvantageous in terms of weight and cost.

An object of the present invention is to solve the above-mentioned problem by physically linking the rear wheels to front wheel steering and power steering only the difference between the resulting steering angle and the target steering angle. do.

(Means for Solving the Problems) For this purpose, the rear wheel steering device of the present invention provides a vehicle that, when steering the front wheels, steers the rear wheels by a target steering angle determined according to the front wheel steering. A rear wheel main steering system that mainly steers the rear wheels in conjunction with each other, and a rear wheel auxiliary steering system that power steers the rear wheels so that the deviation between the rear wheel steering angle by the main steering system and the target steering angle becomes zero. It is configured with the following.

(Operation) When steering the rear wheels by the target steering angle in response to front wheel steering, the rear wheel main steering system physically links the rear wheels with the front wheel steering to main steer the rear wheels, and adjusts the rear wheel steering angle by this main steering. The rear wheel auxiliary steering system power-steers the rear wheels so that the deviation from the target steering angle becomes zero, and as a result, the rear wheels can be steered by the target steering angle.

By the way, when steering the rear wheels, only the above-mentioned deviation is relied on the power steering, so the rear wheel steering power is small, and the battery and motor can be downsized, especially when power steering is performed using an electric motor. It is advantageous in terms of weight and cost.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the rear wheel steering system according to the present invention.

IR does not indicate left and right front wheels, 2L and 2R do not indicate left and right rear wheels. Front wheel IL.

The rear wheels 1R can be steered by a steering wheel 3 via a pinion 4 and a rack 5, and the rear wheels 2L and 2R can be steered by the stroke of a tie rod 6.

To explain the rear wheel steering system here, a pole nut 7 is screwed onto a tie rod 6, and this pole nut is supported by a base plate 8 so as not to be displaced in the axial direction. The pole nut 7 is drivingly coupled to the output shaft of an electric motor 10 via a gear set 9, and the motor 10 is mounted on the base plate 8. Further, the base plate 8 is movable in a direction parallel to the tie rods 6 and supported on the vehicle body, and a rack 11 extending in the same direction is mounted on the base plate 8. A pinion 12 is engaged with the rack 11, and this pinion 12 and another pinion 13 that is engaged with the rack 5 are rotatably supported by the vehicle body or are mounted on the steering shaft 1.
This concludes with 4.

When steering the front wheels using the steering wheel 3, the stroke of the rack 5 is the pinion 13, the shaft 14, and the pinion 1.
2. It is transmitted to the base plate 8 via the rack 11, and this base plate 8 is transmitted to the rear wheels 2L, 2 via the tie rod 6.
Steering R in the same direction as the front wheels. Therefore, pinion 13
, the shaft 14, the pinion 12, the rack 11, and the base plate 8 constitute a rear wheel main steering system that physically interlocks with the front wheel steering and mainly steers the rear wheels by a steering angle proportional to the front wheel steering angle. On the other hand, when the motor 10 is driven, its rotation is transmitted to the pole nut 7 through the gear set 9, and through the stroke of the Quirod 6, the rear wheels are steered in the main steering direction or back in the opposite direction, thereby performing power steering. , motor 10, gear set 9, and pole nut 7 constitute a rear wheel auxiliary steering system.

The motor 10 of the rear wheel auxiliary steering system is controlled by a controller 15 via a drive circuit 16, and the controller 15 includes a signal from a steering angle sensor 17 that detects the turning angle θ of the steering wheel 3, and a vehicle speed sensor that detects the vehicle speed V. 18 and a signal from a rotary encoder 19 that detects the rotation amount θX of the motor lO (the amount of auxiliary steering of the rear wheels Δδ by the motor). Based on this input information, the controller 15 performs the following calculation to determine how much the rear wheels should be auxiliary steered by the motor IO, and supplies the corresponding motor drive command ■ to the drive circuit 16. The circuit 16 uses electric power from the battery 20 to output a motor drive current l corresponding to the above-mentioned command I to the motor 10, and the motor assists the rear wheels in accordance with the calculation.

That is, the controller 15 first calculates the target rear wheel steering angle δ from the steering wheel turning angle θ and the vehicle speed V. Here, to derive the formula for calculating δ, the yaw rate ψ of the vehicle is expressed by the following formula using the steering wheel turning angle θ and the rear wheel steering angle δ.

However, A(V), C(V), and D(V) are functions of the vehicle speed V given by the following equation, where S is the Laplace operator.

A(v) S2+AO1mS+A02m Yaw rate ψ relative to cutting angle θ C(V) c.

S+C02(V) D(V)=D.

In order to generate it in a preferable form like S+DO2(V), (
From equations 1) and (2), the rear wheel steering angle δ may be given so as to satisfy the following equation.

Rearranging this equation (3), the rear wheel steering angle δ determined by this equation (4) is the target rear wheel steering angle in this example, and the controller 15 calculates the above equation (4) from the turning angle θ and the vehicle speed V. , determine the target rear wheel steering angle δ.

Next, the controller 15 controls the rear wheel main steering system 13.1 for the front wheel steering angle θ/N based on the steering wheel turning angle θ.
4.12.11 When the ratio of the rear wheel upper steering angle δ is K, the rear wheel main steering angle δ is expressed as K·(θ/N). and,
Deviation Δδ from the target rear wheel steering angle δ.

△δ, = δ−K・θ/N (5)
Find it by This deviation Δδ matches the rear wheel main steering angle δ with the target steering angle δ, as is clear from FIG. Represents the target rear wheel auxiliary steering amount to

The controller 15 then adjusts this target rear wheel auxiliary steering amount Δδ
The rotation amount (target motor rotation amount) θ of the motor 10 to obtain , is calculated by the following equation.

θ, 2N1・Δδ.

(6) The controller issues a motor rotation amount command ■ to zero the target motor rotation amount θ according to the deviation from the actual motor rotation amount −θ8 detected by the rotary encoder 19. = (2-S + - to Kl+) (θS-θ11
)-(7) and supplies it to the drive circuit 16.

The drive circuit 16 uses electric power from the battery 20 to generate a motor drive current 1 such that a motor rotation amount corresponding to the command I can be obtained, and supplies it to the motor 10.

The motor IO performs auxiliary steering of the rear wheels via the gear set 9 and the ball nut 7 according to the amount of rotation, and the rear wheel steering angle is determined by the auxiliary steering angle and the upper steering angle via the main steering system 13, 14, 12, 11. It is determined by the sum of In addition, when the front wheels are steered by the steering wheel 3, the rear wheels are controlled by the main steering system 1 as illustrated in FIG.
3.14.12.11, the main steering is performed, and in response to the main steering angle δ, the motor 1o turns the rear wheels back or further by the target auxiliary steering amount Δδ3, and adjusts the rear wheel steering angle to the target steering angle δ. Can be matched.

By the way, the rear wheel steering angle is generated in conjunction with the front wheel steering instead of relying entirely on the power steering by the motor 10, but only the deviation between this and the target steering angle (rear wheel auxiliary steering angle) is generated. Since the power is obtained through power steering by the motor 10, less power is required, and the motor 10 and battery 20 can be made smaller, which is advantageous in terms of weight and cost.

FIG. 2 shows another example of the present invention, in which the rear wheel main steering system is constructed with a wave pressure linkage instead of a gear interlocking system. That is,
Pilot cylinder 2 linked to the stroke of rack 4
1, and a rear wheel upper steering cylinder 22 that strokes the base plate 8 in the rear wheel steering direction. These cylinders 21 and 22 are interconnected by a cross pipe 23, and hydraulic fluid is sealed in the chambers of both cylinders 21 and 22 and the pipe 23.

In this example, when steering the front wheels to the right by moving the rack 4 to the left,
The pilot cylinder 21 interlocked with this moves the base plate 8 to the left via the rear wheel steering cylinder 22 using the sealed liquid, and mainly steers the rear wheels in the same phase direction as the front wheels (rightward).

In this case, the ratio of the rear wheel upper steering angle to the front wheel steering angle is determined by the inner diameter ratio of the cylinder 2L 22.

FIG. 3 shows still another example of the present invention, and in this example, based on the configuration of FIG. 1, the rear steering shaft 14 is 14a,
It is divided into two as shown by 14b, and the divided shaft 14a,
14b, JP-A-5126365, JP-A-59-
A variable steering ratio mechanism 24 as described in Japanese Patent Application Laid-open No. 92261 and Japanese Patent Application Laid-Open No. 61-163063 is interposed.

This mechanism 24 appropriately changes the ratio between the front wheel steering angle and the rear wheel upper steering angle, and is electronically controlled by the controller 15.

For this control, the controller 15 sets the above-mentioned preferred value K of the steering ratio. is calculated as follows. By setting this preferred steering ratio Ko to S-0 in the above equation (4), KO=8.
(V)/A2(V). The controller 15 controls the mechanism 24 so as to obtain this suitable steering ratio. If this is done, the above formula (5) will be obtained, and since S-0 in this formula, Δδ.

=0. Therefore, in this example, the target rear wheel auxiliary steering amount Δδ by the motor 10 is constantly zero, and the motor 10
The driving load can be further reduced. For the same reason, even in the event of a failure in which the motor 10 cannot be driven, the rear wheel main steering angle is brought close to the target rear wheel steering angle by the variable steering ratio mechanism 24, which is advantageous in terms of safety.

FIG. 4 shows yet another example of the present invention. In this example, based on the configuration shown in FIG. 1, the rear wheel auxiliary steering system is replaced with an electric motor and is operated by a hydraulic actuator 25, which provides rear wheel assistance (power). Steering is done hydraulically. The actuator 25 is provided on the base plate 8 and has a piston rod as a piston rod, and a servo valve 27 is inserted between the two chambers of the actuator and the accumulator 26. The accumulator 26 has a constant pressure stored therein by the hydraulic oil from the pump 28, and 3 4 pressure in the accumulator is used to operate the actuator 25 under the control of the servo valve 27. Servo valve 27
When the solenoid 27a is OFF, the two chambers of the actuator 25 are shut off as shown in the figure, and when the solenoid 27a is energized in one direction, the pressure corresponding to the amount of energization is applied to the actuator 25.
A pressure corresponding to the amount of current applied to the solenoid 27a during reverse direction energization is supplied to the other chamber of the actuator 25. The actuator 25 responds to the supply pressure, strokes the tie rod 6 in the corresponding direction by a corresponding distance, and can perform auxiliary steering of the rear wheels.

In the case of this example, the controller 15 controls the direction and amount of energization of the solenoid 27a, strokes the actuator 25, and feeds back a signal from the stroke sensor 29 that detects (rear wheel auxiliary steering angle) to the controller 15. .

The controller 15 determines the target rear wheel auxiliary steering amount Δδ in the same manner as described above with reference to FIG. 1, and calculates the stroke amount L5 of the actuator 25 (target actuator stroke amount) for obtaining this ΔδR using the following equation.

S N,・△δ□ The controller uses this target actuator stroke amount L
s and the actual actuator stroke amount detected by the stroke sensor 29. A solenoid drive current 1s having a direction and magnitude that makes it zero according to the deviation from the current is determined by the following equation and is supplied to the solenoid 27a.

s 2 (Kl + -□+ K3S) (15-L,
) As a result, the servo valve 27 performs auxiliary steering of the rear wheels via the actuator 25, and in response to the upward steering angle linked to the front wheel steering, the rear wheels are steered back to the target steering angle or by increasing the steering angle. Match the angle with the target rudder angle.

(Effects of the Invention) Thus, as described above, the rear wheel steering device of the present invention has a main steering system that physically links rear wheel steering with front wheel steering, and an auxiliary power steering system to adjust the excess or deficiency with respect to the target rear wheel steering angle. Since it is configured with an auxiliary steering system, the energy consumption for power steering is small, and especially when power steering is performed with an electric motor, the motor and battery can be made smaller, which is advantageous in terms of weight and cost. .

[Brief explanation of drawings]

FIG. 1 is an overall schematic plan view of a vehicle steering system showing one embodiment of the device of the present invention; FIGS. 2 to 4 are schematic plan views similar to FIG. 1 showing three other examples of the present invention, respectively; FIG. 5 is a time chart showing the relationship between the rear wheel main steering angle and the target rear wheel steering angle according to the present invention. IL, IR...Front wheel 2L, 2R...
Rear wheel 3... Steering wheel 4, 12. 13... Pinion 5, 11... Rack 7... Pole nut 8... Base plate 9
...Gear set 10...Morph 15...
Controller 16... Drive circuit 17... Rudder angle sensor 18... Vehicle speed sensor 19... Rotary encoder 20... Battery 21... Pilot cylinder 22... Rear wheel main steering cylinder 24... Steering ratio variable mechanism 25...Hydraulic rear wheel auxiliary steering actuator 27...
・Servo valve 29...stroke sensor 29 8 Procedure amendment 1. "L1" on page 16, line 7 of the specification was corrected to "L.", and the formula on line 11 of the same page was changed on December 19, 1997.

Claims (1)

[Claims] 1. Rear wheel main steering in which, during front wheel steering, the rear wheels are steered by a target steering angle determined according to the front wheel steering, in which the rear wheels are mainly steered in physical conjunction with the front wheel steering. and a rear wheel auxiliary steering system that power steers the rear wheels so that the deviation between the rear wheel steering angle by the main steering system and the target steering angle becomes zero. Device. 2. The rear wheel steering device according to claim 1, wherein the rear wheel main steering system is a mechanical interlocking system. 3. The rear wheel steering device according to claim 2, wherein a variable front and rear wheel steering ratio mechanism is inserted into the mechanical interlocking system. 4. The rear wheel steering system according to claim 1, wherein the rear wheel main steering system is a hydraulic interlock system. 5. A rear wheel steering system according to any one of claims 1 to 4, wherein the rear wheel auxiliary steering system is an electronically controlled electric system. 6. A rear wheel steering system according to any one of claims 1 to 4, wherein the rear wheel auxiliary steering system is an electronically controlled hydraulic system.