JPH0523987B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels.

As this type of four-wheel steering device, for example,
"Vehicle steering device" disclosed in Publication No. 55-91457
There are inventions related to This invention changes the steering ratio of the front wheels and rear wheels depending on the vehicle speed, and at low speeds, the front wheels and rear wheels are steered in opposite phases, and at high speeds, these wheels are steered in the same phase. According to this feature, when steering at low speeds, for example when the vehicle is turning, the minimum turning radius is reduced and turning performance is improved, and when steering at high speeds, for example when changing lanes on a highway. Sometimes a quick change of course is achieved. However, since this steering device is configured to perform steering control by mechanically interlocking the rotational movement of the steered wheels with the front wheels and the rear wheels, there is a drawback that a large operating force must be applied to the steered wheels.

On the other hand, according to Japanese Patent Application Laid-open No. 57-11173, the actuator is equipped with a servo valve that is electrically driven by a command circuit via a servo amplifier, and a hydraulic actuator that is controlled by the servo valve. This is a "vehicle with two sets of steerable wheels" that controls the steering of the rear wheels according to the front wheel steering angle, vehicle speed, etc. input to the command circuit by coupling the rear wheel steering linkage to the rear wheel steering linkage. An invention related to a "steering angle control method" is disclosed.
According to this invention, the drawbacks of the mechanically controlled steering device disclosed in the above-mentioned publication are solved. However, in this invention, because it is necessary to make the steering angle of the rear wheels correspond accurately to the target steering angle, so-called feedback control is performed in which displacement of the actuator is detected by a potentiometer and fed back to the servo amplifier. Therefore, there are always disadvantages peculiar to feedback control, such as a delay in the response of the rear wheels to the steering of the front wheels and hunting when the rear wheels are steered.

The present invention solves the above-mentioned problems in conventional four-wheel steering devices, and performs steering control of the rear wheels by open control without feedback, and also solves the problems that generally occur in open control. Regarding the accumulation of control errors, feedback control is performed to eliminate the errors only when the steering angle of the front or rear wheels is "0", that is, when the vehicle is traveling straight without active steering. As a result, optimal rear wheel steering characteristics corresponding to the front wheel steering angle etc. are always obtained during turning, and rapid and stable control that does not cause steering delay or hunting of the rear wheels is realized.

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 shows the overall configuration of a four-wheel steering system for a vehicle according to the present invention. A steering system 2 that steers left and right front wheels 1, 1 includes a steering wheel 3 and A rack and pinion mechanism 4 that converts into linear reciprocating motion, left and right tie rods 5, 5, and a knuckle arm 6, which transmit the operation of the mechanism 4 to the front wheels 1, 1 and steer them.
It consists of 6.

On the other hand, a rear wheel steering device 8 for steering the left and right rear wheels 7, 7 includes a rear wheel operating rod 9 in the left and right direction slidably held on the vehicle, and tie rods 10 at both left and right ends of the rod 9, respectively. The rear wheels 7 have left and right knuckle arms 11, 11 connected to each other through a shaft 10, and the rear wheels 7, 7 are steered by the axial movement of the operating rod 9. And the operating rod 9 has a rack 12.
A pinion 1 is formed and meshes with the rack 12.
3 is a pair of bevel gears 15,
16 and pinion shaft 17, the rear wheels 7, 7 are steered in accordance with the amount of rotation of the pulse motor 14.

Further, the rear wheel operating rod 9 passes through the power cylinder 18, and a piston 19 that partitions the inside of the cylinder 18 into left and right hydraulic chambers 18a and 18b is fixed to the operating rod 9.
Hydraulic passages 21a and 21b led from a control valve 20 provided around the pinion shaft 17 are connected to the a and 18b, respectively, and a pump 23 driven by the control valve 20 and a motor 22 is connected to the a and 18b, respectively. A hydraulic pressure supply passage 24 and a return passage 25 are provided between them. here,
The control valve 20 is connected to the pulse motor 1
4, the hydraulic pressure supplied from the pump 23 via the hydraulic pressure supply passage 24 is applied to one of the hydraulic chambers 18 of the power cylinder 18 according to the direction of the rotational force.
a or 18b, and acts to return the hydraulic oil in the other hydraulic chamber 18b or 18a to the pump 23 via the return passage 25. Therefore, the pulse motor 14 operates the bevel gears 15, 16,
When the operating rod 9 is moved in the axial direction via the pinion shaft 17, pinion 13 and rack 12,
The hydraulic pressure introduced into the power cylinder 18 assists the movement of the operating rod 9 via the piston 19.

The pulse motor 14 and pump drive motor 22 are operated by signals A and B output from a controller 26, respectively, and the controller 26 receives a vehicle speed signal C output from a vehicle speed sensor 27. The front wheel steering angle signal D from the front wheel steering angle sensor 28 that detects the displacement amount of the front wheel steering member in the steering device 2, for example, the steering angle of the steering wheel 3, and the rear wheel steering device 8.
A rear wheel steering angle signal E from a rear wheel steering angle sensor 29 that detects the amount of displacement of the rear wheel steering member, for example, the stroke amount of the operating rod 9, is input.

Next, the configuration of the controller 26 will be explained with reference to FIG. 2. The vehicle speed signal C from the vehicle speed sensor 27 and the front wheel turning angle signal D from the front wheel turning angle sensor 28 are used to calculate the rear wheel turning angle. 30. The calculation unit 30 stores the characteristics of the optimum rear wheel turning angle θr with respect to the front wheel turning angle θf and the vehicle speed V as shown in FIG. A target rear wheel turning angle θr ₀ corresponding to the vehicle speed V and the front wheel turning angle θf is calculated. Here, the rear wheel steering characteristics shown in Fig. 3 are as follows:
As the front wheel steering angle θf increases, the rear wheel steering angle θr increases at a small steering ratio θr/θf and in the same phase (the front and rear wheels are steered in the same direction), and the front wheel steering angle remains constant. When the steering angle exceeds θr, the phase reverses to reverse phase (a state in which the front and rear wheels are steered in opposite directions), and at high speeds, as the front wheel steering angle θf increases, the rear wheel steering angle θr becomes large at a steering ratio θr/θf and The steering ratio θr/θf is set so that it increases in the same phase and gradually decreases when the front wheel steering angle exceeds a certain value. This is to make the minimum turning radius as small as possible when the vehicle turns at low speeds, and to realize a quick course change when changing lanes at high speeds.

The target rear wheel turning angle θr ₀ calculated by the calculation unit 30 is output as a control signal (pulse signal) A to the driver 31 of the pulse motor 14. Furthermore, when the control signal A is output, a drive signal B is output to the pump drive motor 22 shown in FIG.

The controller 26 is also provided with a comparator 32 and a steering angle "0" detection section 33 as a correction means for eliminating the accumulation of errors associated with open control. Then, an actual measurement signal E indicating the actual measured rear wheel steering angle θr outputted from the rear wheel steering angle sensor 29 is input to the comparator 32, and the steering angle "0" detection section 33 receives the front wheel steering angle θr. When the angle signal D is input and the front wheel steering angle θf indicated by the signal D is "0", the steering angle is "0".
An operating signal G is output from the detection section 33 to the comparator 32. Then, the comparator 32 operates when the operation signal G is input, and compares the comparison reference value corresponding to the preset rear wheel turning angle "0" with the measured rear wheel turning angle θr indicated by the above-mentioned actual measurement signal E. Then, a correction signal (pulse signal) H corresponding to the amount of deviation is output to the driver 31 of the pulse motor 14. Here, instead of presetting a comparison reference value corresponding to the rear wheel steering angle "0" in the comparator 32, the target rear wheel steering angle θr ₀ obtained by the calculation unit 30 is set as shown by the chain line. This may be input to the comparator 32 and compared with the actually measured rear wheel turning angle θr. This is because when the comparator 32 operates, the target rear wheel turning angle θr ₀ becomes "0".

In this embodiment, the pump 23 may be driven by an engine.

Next, the operation of the above embodiment will be explained.
When the steering wheel 3 is steered while the vehicle is running, the left and right front wheels 1, 1 are steered according to the steering direction and steering angle, and the steering angle θf and the vehicle speed V at that time are detected by the sensor 27, 28 and input as signals C and D to the rear wheel turning angle calculating section 30 of the controller 26. Then, the calculation unit 30 calculates the target rear wheel turning angle θr ₀ based on the front wheel turning angle θf and the vehicle speed V indicated by the signals C and D, and according to preset characteristics as shown in FIG. At the same time as calculating, a control signal A corresponding to the calculation is output to the driver 31. Therefore, the pulse motor 14 in the rear wheel steering device 8 rotates by the number of times corresponding to the control signal A, that is, the number of times corresponding to the target rear wheel turning angle θr ₀ , and the bevel gear 15,
16, the rear wheel operating rod 9 is moved in the axial direction via the pinion shaft 17, pinion 13 and rack 12. As a result, the rear wheels 7, 7 are steered so as to match or substantially match the target rear wheel turning angle θr ₀ . At this time, the power cylinder 18 is activated to assist the movement of the operating rod 9.

However, the steering angle θr of the rear wheels 7, 7 is detected by the rear wheel steering angle sensor 29, and is input as an actual measurement signal E to the comparator 32 of the controller 26. It operates only when it is input, that is, when the front wheel steering angle θf is "0" and the vehicle is traveling straight. Therefore, when the operation signal G is not input during a turn, the controller 26 performs unilateral control, that is, open control, on the rear wheel steering device 8, and feeds back the measured signal E of the rear wheel steering. When used as a signal for control, there is no steering delay or hunting of the rear wheels 7, 7.

However, when the front wheel steering angle θf is "0", that is, when the steering is not performed, the operation signal G is input to the comparator 32 from the steering angle "0" detection section 33 to which the front wheel steering angle signal D is input. As a result, the comparator 32 operates and the actual measurement signal E from the rear wheel turning angle sensor 29 is compared with the reference value corresponding to the rear wheel turning angle "0". If there is a difference between the measured rear wheel turning angle θr indicated by the signal E and the reference value, a correction signal H corresponding to the amount of deviation is output to the driver 31. In other words, when the vehicle is traveling straight, feedback control is performed based on the measured signal E of the rear wheel turning angle θr, and the pulse motor 14 performs a correction operation to set the rear wheel turning angle θr to "0". As a result, even if errors are accumulated due to the open control during steering, they are resolved when the steering wheel 3 is returned to its original position, and the optimum rear wheel steering characteristics can be obtained again during the next steering operation.

Next, a second embodiment of the present invention shown in FIG. 4 will be described.

In this embodiment, as in the previous embodiment, the controller 26 includes a rear wheel turning angle calculating section 30 which receives a vehicle speed signal C and a front wheel turning angle signal D from a vehicle speed sensor 27 and a front wheel turning angle sensor 28, respectively. , a driver 31 for the pulse motor 14 to which the control signal (pulse signal) A from the calculation section 30 is input, a comparator 32 as a correction means, and a steering angle "0" detection section 33'. When the operation signal G is output from the steering angle "0" detection section 33' to the comparator 32, a correction signal (pulse signal) H is output from the comparator 32 to the driver 31. but,
In this embodiment, the signal E from the rear wheel steering angle sensor 29 is input to the steering angle "0" detection section 33' which outputs the operation signal G, and when the rear wheel steering angle θr is "0", the An operation signal G is output. Also,
In the comparator 32, a comparison reference value corresponding to the rear wheel turning angle "0" is set, and the calculation unit 3
A target signal F indicating the target rear wheel turning angle θr ₀ determined at 0 is input. Here, since the comparator 32 operates only when the rear wheel turning angle θr is "0", the measured rear wheel turning angle signal E may be inputted as shown by the chain line instead of the above comparison reference value. .

Therefore, in this embodiment, when the actual rear wheel steering angle θr is "0", that is, when the vehicle is traveling substantially straight, the feedback control is performed, and the target rear wheel steering corresponding to the front wheel steering angle θf at that time is performed. If the angle θr ₀ is not “0”, a correction operation is performed to make the rear wheel turning angle θr match the target turning angle θr ₀ .

Furthermore, in the third embodiment shown in FIGS. 5 and 6, a power cylinder 14' is used as the actuator in the rear wheel steering device 8' instead of the pulse motor in the first and second embodiments. , the left and right hydraulic chambers 14a', 14 are arranged inside the cylinder 14'.
A piston 15' partitioning into b' is connected to the rear wheel operating rod 9', and both hydraulic chambers 14a', 14
Hydraulic passages 17a' and 17b' are provided between b' and the control valve 16', respectively, and a hydraulic supply passage 19' and a hydraulic return passage 20 are provided between the control valve 16' and the hydraulic supply section 18'. is provided. Here, the power cylinder 14'
There are springs 21a' and 21b' provided therein which hold the piston 15' or operating rod 9' in a neutral position when hydraulic pressure is not applied. The control valve 16' is connected to the controller 2.
In response to the control signal A' from the power cylinder 14', supply and discharge control of hydraulic pressure to the hydraulic chambers 14a' and 14b' of the power cylinder 14' is performed in accordance with the target rear wheel turning angle θr ₀ indicated by the signal A'. Further, as in the first embodiment, the controller 26' receives signals C' and D' from the vehicle speed sensor 27' and the front wheel steering angle sensor 28'.
A calculation section 30' calculates a target rear wheel turning angle θr ₀ having characteristics as shown in FIG. 3, and a turning angle "0" detection section 3 receives the front wheel turning angle signal D'.
3", and outputs a correction signal H' when the front wheel turning angle θf is "0".

However, in this embodiment, the correction signal
H' is input to a correction valve 32' provided in the power cylinder 14', and a steering angle "0" detection section 33'' outputs the correction signal H' to this correction valve 32' and the valve 32'. The correction valve 32' constitutes a correction means for eliminating the accumulation of errors caused by open control.The correction valve 32' is connected to a communication passage 32a' that communicates the left and right hydraulic chambers 14a' and 14b' of the power cylinder 14'. Normally, the communication path 32a' is blocked off, but when the correction signal H' is inputted, the path 32a' is opened.

According to the above configuration, when the front wheel steering angle θf is not "0", that is, during steering, the power cylinder 14'
is the target rear wheel steering angle θr ₀ which corresponds to the front wheel steering angle θf obtained by the controller 26' so that the rear wheel steering angle θr is hydraulically controlled by the control valve 16'.
It operates as follows. However, when the front wheel steering angle θf is "0", the correction valve 32' opens the communication passage 32a' in response to the correction signal H'.
Since hydraulic oil freely flows in and out of the hydraulic chambers 14a' and 14b' of the power cylinder 14', the rear wheel operating rod 9' is kept neutral by the springs 21a' and 21b' regardless of the operation of the control valve 16'. It will be held in place. As a result, the control error caused by the open control of the rear wheel steering device 8' during the above-mentioned steering is eliminated by setting the rear wheels 7', 7' to the steering angle "0" when the steering is not performed. . In this embodiment, the front wheels 1',
A power cylinder 4' is also used in a steering device 2' for steering the vehicle 1'.

In each of the above embodiments, the vehicle speed sensor 27,
27' may be omitted and the rear wheel steering control may be performed in response to only the front wheel steering angle.

As described above, according to the present invention, in a four-wheel steering system for a vehicle that steers the rear wheels in response to steering of the front wheels, the steering control of the rear wheels during steering is changed to open control. At the same time, the accumulation of control errors accompanying this open control is
When not steering or actively steering,
That is, when traveling straight, the problem is resolved by corrective action using feedback control. As a result, when steering, the optimum rear wheel steering characteristics corresponding to the front wheel steering angle etc. are always obtained, and quick and stable control is performed that does not cause rear wheel steering delay or hunting, etc., and the vehicle's steering performance is improved. is significantly improved.

[Brief explanation of drawings]

Fig. 1 is an overall control system diagram of a four-wheel steering device according to the present invention, Fig. 2 is a block diagram of a controller in the first embodiment of the present invention, and Fig. 3 is an example of rear wheel steering characteristics set in the controller. FIG. 4 is a block diagram of the controller in the second embodiment of the present invention, and FIGS. 5 and 6 are an overall control system diagram and a block diagram of the controller in the third embodiment. 1, 1'... Front wheels, 2, 2'... Steering device, 7, 7'... Rear wheels, 8, 8'... Rear wheel steering device, 9, 9'... Rear wheel steering member (rear wheel operation rod), 14, 14'... actuator (14...
Pulse motor, 14'...power cylinder), 2
6, 26'... Controller, 28, 28'... Front wheel steering angle sensor, 32, 32', 33, 33', 3
3''...Correction means (32...Comparator, 32'...Correction valve, 33, 33', 33''...Steering angle "0"
Detection unit).

Claims (1)

[Claims] 1. A four-wheel steering device for a vehicle, comprising a steering device that steers front wheels, a rear wheel steering device that steers rear wheels, and a controller that controls the rear wheel steering device according to predetermined conditions, The rear wheel steering device has an actuator that operates in response to a control signal from the controller, and is configured such that the actuator changes and controls the rear wheel steering angle, and the controller is configured to control the rear wheel steering angle in a turning state. A vehicle characterized in that it is provided with a correction means that controls the actuator by open control when detecting the vehicle and outputs a correction signal to the actuator so as to perform feedback control of the actuator when a straight-ahead state is detected. 4-wheel steering device.