JPH0453750B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a device for steering both the front wheels and the rear wheels of a four-wheeled vehicle such as an automobile. It relates to a four-wheel steering device that also steers the rear wheels, and in particular, it is a four-wheel steering device for a vehicle that has an improved control mechanism that sets the rear wheel steering angle in accordance with the driving condition such as the front wheel steering angle. It is related to.

(Prior art) Conventionally, the steering system for four-wheeled vehicles steers only the front wheels, and the rear wheels do not actively steer the rear wheels, although they do some toe-in or toe-out depending on the driving situation, regardless of the steering of the front wheels. It is not designed to turn the ship. However, recently, a four-wheel steering device has been proposed that steers both the front wheels and the rear wheels, and research on this type of device is being conducted.

According to the four-wheel steering system, it becomes possible to perform convenient steering, which was previously impossible, and to drive with improved steering performance, depending on various driving conditions of the vehicle. for example,
When maneuvering a vehicle at extremely low speeds, such as parallel parking or parking in a garage, by steering the rear wheels in the opposite direction to the front wheels (this is called anti-phase), it is possible to significantly change the direction of the vehicle. This makes it possible or easy to park in narrow spaces, which was previously impossible or extremely difficult. Furthermore, when steering a vehicle at extremely low speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase), the entire vehicle can be moved in parallel, making it easier to park or park the vehicle. It's often convenient.

On the other hand, when changing lanes while driving at medium to high speeds, if four-wheel steering is performed in the same phase, lateral force is applied to the front and rear wheels at the same time, making it possible to change lanes smoothly without phase lag, thereby suppressing yawing. This allows you to change lanes at high speed without fear. Furthermore, when cornering, the direction of the vehicle can be effectively changed by steering the rear wheels in opposite phases.

The four-wheel steering system for a vehicle as described above generally includes a steering system that steers the front wheels, and an actuator that drives a rear wheel steering member to drive the rear wheels, as disclosed in, for example, Japanese Patent Laid-Open No. 11173/1983. It has a rear wheel steering device that steers the wheels, and a controller that controls the rear wheel steering device. A control signal corresponding to the steering angle is output, and the actuator is actuated by the control signal. The wheel steering angle is set in accordance with the vehicle speed as well as the front wheel steering angle.)

In order to accurately steer the rear wheels according to the target rear wheel steering angle set as described above, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 57-11173,
A rear wheel turning angle sensor may be provided, and the measured rear wheel turning angle signal detected by the rear wheel turning angle sensor may be fed back to the rear wheel turning angle control system to perform so-called feedback control.

However, when such feedback control is performed, the responsiveness of the rear wheel turning angle control becomes poor, and problems occur such as the rear wheel turning not being able to follow the front wheel turning especially when a quick steering operation is performed.

(Object of the Invention) The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a four-wheel steering device for a vehicle in which the responsiveness of rear wheel steering control is sufficiently improved. It is.

(Structure of the Invention) A four-wheel steering device for a vehicle according to the present invention is provided with the above-described steering device, a rear wheel steering device, and a controller, and basically uses a measured rear wheel steering angle signal to steer the rear wheels. It employs so-called open control that does not return feedback to the angle control system, and also detects that either the front or rear wheels have been steered to a preset reference steering angle, and only when this is detected, the target rear wheel steering is performed. a regular correction means that compares the actual rear wheel turning angle with the measured rear wheel turning angle and outputs a correction signal to the actuator to reduce the deviation; and a correction means that receives the output of a starting sensor that detects the starting state of the vehicle. Until the signal is output, a correction signal is output to the actuator to reduce the deviation by comparing the target rear wheel steering angle determined by the controller and the measured rear wheel steering angle detected by the rear wheel steering angle sensor. The present invention is characterized in that it is provided with a start correction means.

(Effects of the Invention) If the rear wheel turning angle is controlled by open control, control responsiveness is improved compared to the case where feedback control is performed, and the above-mentioned problems are solved. In addition, since the above-mentioned regular correction means is provided, the deviation between the target rear wheel turning angle and the measured rear wheel turning angle is reduced or eliminated each time the steering angle is adjusted to the reference steering angle, so that the control error due to open control is reduced. It does not gradually accumulate and expand. Furthermore, since the above-mentioned starting correction means is provided, even if the front or rear wheels go into a recess or run over a protruding object when parking, for example, and the basic correspondence between the two steering angles becomes incorrect, Immediately after the vehicle starts, the rear wheels are set to a steering angle that optimally corresponds to the front wheel steering angle, thereby preventing the vehicle from running abnormally when the vehicle starts.

Since the starting correction is made to continue from the time the vehicle starts until the next regular correction is applied, the rear wheel steering angle is controlled until the first regular correction is applied without the sufficient starting correction being applied. A large error remains and the vehicle does not run abnormally.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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

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 held slidably in the left and right directions on the vehicle body, 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 direction and 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 the pump drive motor 22 are operated by the signals A and B output from the controller 26, respectively, but the controller 26 also receives a vehicle speed signal C output from the vehicle speed sensor 27. A front wheel steering angle sensor 28 detects the position of the front wheel steering member in the steering device 2, for example, the steering angle of the steering wheel 3.
The front wheel steering angle signal D from
Rear wheel steering angle sensor 29 detects the stroke amount of
A rear wheel steering angle signal E from the ignition switch 31 and a pulse signal F from the ignition switch 31 are input.

Next, the configuration of the controller 26 will be explained with reference to FIG. 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 input to the rear wheel turning angle calculating section 30.
This calculation unit 30 has an optimum rear wheel steering angle θr for the front wheel steering angle θf and the vehicle speed V as shown in FIG. 3, for example.
According to this characteristic, a target rear wheel turning angle θro corresponding to the vehicle speed V and the front wheel turning angle θf indicated by the signals C and D is calculated. here,
The rear wheel steering characteristics shown in Figure 3 are such that at low speeds, as the front wheel steering angle θf increases, the rear wheel steering angle θr becomes smaller at the steering ratio θr/θf and in phase (the front and rear wheels are steered in the same direction). At the same time, when the front wheel steering angle exceeds a certain value, the phase reverses (the front and rear wheels are steered in opposite directions), and at high speeds, as the front wheel steering angle θf increases, the rear Steering ratio θr/θf with large wheel steering angle θr
The steering ratio θr/θf increases with 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 signal G carrying the target rear wheel turning angle θro calculated by the rear wheel turning angle calculation unit 30 as described above is as follows:
It is input to the driver 32 of the pulse motor 14.
The driver 32 receives this signal G and turns the rear wheels 7, 7.
A pulse signal A is output to rotate the pulse motor 14 so that the target rear wheel turning angle θro is set to the target rear wheel turning angle θro. When the pulse signal A is output, a drive signal B is output to the pump drive motor 22 shown in FIG.

On the other hand, the measured signal E indicating the measured rear wheel turning angle θr outputted from the rear wheel turning angle sensor 29 and the target signal G indicating the target rear wheel turning angle θro calculated by the calculation section 30 are sent to the comparator 33. is input. Further, the service correction operation signal H output from the steering angle sensor 34 that detects the service correction timing is input to the reset terminal of the R-S flip-flop 35, and the pulse signal F of the ignition switch 31 mentioned above is input to the R-S flip-flop 35.
It is input to the set terminal of the S flip-flop 35. H of this R-S flip-flop 35
(High) level output correction operation signal I when starting
The normal correction operation signal H is input to the OR gate 36, and the operation signal J, which is the gate output of the OR gate 36, is input to the comparator 33.

Here, the steering angle sensor 34 receives the front wheel turning angle signal D and adjusts the steering angle of the steering wheel 3 corresponding to the front wheel turning angle θf indicated by the signal D to a predetermined angle such as ±0°. Summer time H
A common correction operation signal H, which is a (High) level signal, is output. On the other hand, the R-S flip-flop 35 is
The H (High) level output of the pulse signal F is input to the set terminal, and the above-mentioned regular correction operation signal H is not input to the reset terminal (that is, L (Low)).
When the start correction operation signal I is input (level signal is input), the start correction operation signal I is output, and when the regular correction operation signal H is input to the reset terminal, the output of the start correction operation signal I is stopped.

The comparator 33 operates temporarily only when the operation signal J is input, and compares the target rear wheel turning angle θro indicated by the signals G and E with the measured rear wheel turning angle θr, and reduces the deviation. A correction signal K is outputted to drive the driver 32 as shown in FIG.

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 28, 27, and input as signals D and C to the rear wheel turning angle calculating section 30 of the controller 26. Based on the front wheel turning angle θf and the vehicle speed V indicated by the signals D and C, the calculation unit 30 calculates a target rear wheel turning angle θro according to preset characteristics as shown in FIG. , outputs a corresponding target signal G to the driver 32. The driver 32 generates a pulse signal A corresponding to this target signal G and inputs it to the pulse motor 14. Therefore, the pulse motor 14 in the rear wheel steering device 8 rotates by the number of times corresponding to the pulse signal A, that is, the number of times corresponding to the target rear wheel turning angle θro, and the bevel gears 15,1
6, pinion shaft 17, pinion 13 and rack 1
2 to move the rear wheel operating rod 9 in the axial direction. As a result, the rear wheels 7, 7 are steered so as to match or substantially match the target rear wheel turning angle θro. At this time, the power cylinder 18 is activated to assist the movement of the operating rod 9.

When the rear wheels 7, 7 are steered as described above, the steered angle θr is detected by the rear wheel steered angle sensor 29 and inputted to the comparator 33 of the controller 26 as an actual measurement signal E. The comparator 33 does not operate unless the operation signal J is input. Therefore, normally, unilateral control, that is, open control, is performed from the controller 26 to the rear wheel steering device 8, and when the actual measurement signal E of the rear wheel steering angle θr is fed back to perform feedback control. The steering delay and hunting of the rear wheels 7, 7 that occur do not occur.

However, when the steering wheel 3 is steered and the steering angle reaches the predetermined angle (for example, ±0°), the regular correction operation signal H is input from the steering angle sensor 34 to the OR gate 36, and the OR When the operation signal J is input from the gate 36 to the comparator 33, the comparator 33 operates and the actual measurement signal E from the rear wheel steering angle sensor 29 is output.
and the target signal G from the calculation section 30 are compared.
Then, the target rear wheel turning angle θro indicated by both signals G and E
If there is a difference between the measured rear wheel turning angle θr,
A correction signal K that reduces the deviation according to the amount of deviation.
is output to the driver 32. Therefore, the pulse motor 14 performs a correction operation so that the actual rear wheel turning angle θr matches the target rear wheel turning angle θro. As a result, the accumulation of control errors due to the open control described above is reduced or eliminated, and optimal rear wheel steering characteristics can be obtained again. Here, since the above correction operation is temporarily performed only when the steering angle of the steering wheel 3 reaches a predetermined angle, the advantages of the open control described above are essentially maintained. As explained above, in this embodiment, the front wheel turning angle sensor 28, the steering angle sensor 3
4. The OR gate 36 and the comparator 33 constitute a commonly used correction means.

Also, when starting the vehicle, the ignition switch 31
When the pulse signal F is turned on and the H (High) level output of the pulse signal F is input to the R-S flip-flop 35, the R-S flip-flop 35 outputs the starting correction operation signal I as described above. Therefore, the operation signal J is input from the OR gate 36 to the comparator 33, and the pulse motor 14 is operated to correct as described above, so that the actual rear wheel turning angle θr matches or almost matches the target rear wheel turning angle θro. be done. By correcting the rear wheel steering angle θr at the time of starting in this way, it is possible to reduce or eliminate open control errors that have accumulated during driving before the engine is stopped, and also to reduce or eliminate open control errors that have accumulated during driving before the engine stops. 1 or the rear wheels 7, 7 may fall into a recess, ride on a protruding object, or even be parked on a slope, causing the basic correspondence between the front wheels 1, 1 and the rear wheels 7, 7 to deteriorate. Even if the rear wheels are out of alignment, the rear wheels 7, 7 are immediately set to the steering angle θr that optimally corresponds to the front wheel steering angle θf when the engine is started, and the vehicle is prevented from running abnormally when starting. As explained above, in this embodiment, the ignition switch 31 constitutes a starting sensor, and the R-S flip-flop 3
5. The OR gate 36 and the comparator 33 constitute a starting correction means.

The above-described start correction is continued until the steering angle of the steering wheel 3 reaches the predetermined angle and the regular correction operation signal H is input to the reset terminal of the R-S flip-flop 35. Therefore, even if a long period of time passes before the first regular correction is applied after the vehicle has started, the correction at the time of starting is continued, so there is no possibility that the vehicle may run abnormally while control errors due to open control accumulate during this time. Never. Immediately after the vehicle starts, the regular correction operation signal H becomes R-.
The signal H is output to the S flip-flop 35, and even if the starting correction is terminated in a very short time, the signal H
Since the operating signal J is output from the OR gate 36 by inputting it to the OR gate 36, the regular correction is performed following the starting correction, and the control error of the rear wheel turning angle θr is immediately reduced or eliminated. .

In the above embodiment, the ignition switch 31 is used as a start sensor that detects the start of the vehicle.
However, other starting sensors include a rotational speed sensor that detects when the engine rotational speed exceeds a predetermined rotational speed, and a sensor that detects the rotation of the front wheels 1, 1 or rear wheels 7, 7. , furthermore, a sensor that detects release of the parking brake, etc. may be used.

In addition, the R-S flip-flop 3 is used as a means for continuing the start-up correction until the regular correction is applied.
Of course, known means other than 5 may be used.

Furthermore, in the above embodiment, the timing of the regular correction is set based on the steering angle of the steering wheel 3 corresponding to the steering angle of the front wheels 1, 1, but the regular correction is performed by directly detecting the front wheel steering angle. However, this may be performed when the front wheel turning angle reaches a predetermined angle or when the rear wheel turning angle reaches a predetermined angle.

[Brief explanation of drawings]

Fig. 1 is an overall control system diagram of a four-wheel steering device for a vehicle according to an embodiment of the present invention, Fig. 2 is a block diagram of a controller in the above embodiment, and Fig. 3 is a rear wheel steering characteristic set in the above controller. It is a characteristic diagram which shows an example. 1...Front wheel, 2...Steering device, 7...
Rear wheel, 8... Rear wheel steering device, 9... Rear wheel steering member (rear wheel operating rod), 14... Pulse motor, 26
...Controller, 28...Front wheel steering angle sensor,
29... Rear wheel steering angle sensor, 31... Ignition switch, 33... Comparator, 34... Steering angle sensor, 35... R-S flip-flop, 36
...OR gate.

Claims (1)

[Claims] 1. A four-wheel steering device for a vehicle, comprising a steering device for steering front wheels, a rear wheel steering device for steering rear wheels, and a controller for controlling the rear wheel steering device according to a predetermined driving condition. , the controller outputs a control signal corresponding to a preset target rear wheel steering angle according to a predetermined driving condition, and the rear wheel steering device has an actuator that operates in response to this control signal, and It is configured to drive the rear wheel steering member, detects that either the front wheels or the rear wheels are steered to a preset reference steering angle, and only when this is detected, the target determined by the controller is set. A regular correction means that compares the rear wheel steering angle with the measured rear wheel steering angle detected by the rear wheel steering angle sensor and outputs a correction signal to the actuator to reduce the deviation thereof, and a start that detects the starting state of the vehicle. After receiving the output of the sensor until the correction signal of the regular correction means is output, the target rear wheel turning angle determined by the controller is compared with the measured rear wheel turning angle detected by the rear wheel turning angle sensor. A four-wheel steering system for a vehicle, comprising: a start correction means for outputting a correction signal to the actuator to reduce the deviation.