JPH02136377A - Rear wheel steering device for front/rear wheel steered vehicle - Google Patents

Abstract

PURPOSE:To improve the drivability on the slippery road face in particular by freely changing the width of the dead zone maintaining rear wheels in the neutral state in response to the state of the running road face when the steering quantity of front wheels is smaller than the preset quantity. CONSTITUTION:A rear wheel steering device B has a power cylinder 35 fed with the pressure oil from a hydraulic pump 22 via a flow dividing valve 23, and the power cylinder 35 is operated and controlled to steer rear wheels in the reverse phase so that the steering quantity of the rear wheels is increased as the steering quantity of front wheels is increased by a spool valve interlocked with a built-in cam plate. The rear wheels are kept in the neutral state in the dead zone region where the steering quantity of the front wheels is smaller than the preset value. In this case, an electromagnetic flow control valve 51 is provided on a conduit pipe P4, and it is controlled by a control circuit 53 so that the width of the dead zone is increased when the nonslippery state of the running road face is detected by a road face state detector 52 and the width of the dead zone is decreased when the slippery state is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear wheel steering device for a front and rear wheel steered vehicle that steers the rear wheels in conjunction with the steering of the front wheels.

[Prior Art] Conventionally, this type of device has been disclosed in, for example, Utility Model Application Publication No. 60-92669.
As shown in the publication, the rear wheels are steered in a direction opposite to the front wheels so that the amount of steering of the rear wheels increases as the amount of steering of the front wheels increases, and the amount of steering of the front wheels is less than a predetermined value. A dead zone corresponding to the predetermined value is provided to maintain the rear wheels in a neutral state when the vehicle is not in use, and normally, at low vehicle speeds, the front wheels are steered to a large steering angle, and as the vehicle speed increases, the front wheels are no longer steered to a large steering angle. For this reason, efforts are being made to improve the turning performance of the vehicle when running at low speeds and to prevent unstable behavior when the vehicle is running at high speeds.

In addition, when driving at medium speeds on winding roads such as those in mountainous areas, the rear wheels undergo some degree of anti-phase steering, which causes a moderate amount of vehicle yawing motion, which improves the driver's steering feel. are doing.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional device, the steering characteristics of the rear wheels are determined independently of the condition of the road surface. In other words, the dynamic characteristics of the vehicle relative to the rotation of the steering wheel differ depending on whether the vehicle is traveling on a road surface that is slippery due to water, snow, etc. or when the vehicle is traveling on a road surface with a large coefficient of friction with the tires, that is, a dry, non-slip surface. However, there was a problem in that it was difficult for the driver to drive the vehicle. In other words, when the road surface is slippery, even if the steering wheel is turned, the steering becomes less effective because the tires slip, and the vehicle tends to understeer more than when the vehicle is driving on a non-slip surface. .

Additionally, once a vehicle running on a slippery road begins to turn, the tendency to become entangled may become stronger, so it may be necessary to try to correct the vehicle's position by steering in the opposite direction (countersteer) in advance. However, even with such countersteer, the yawing moment that acts in the opposite direction to the turning due to the tires slipping is smaller than when driving on a non-slip road surface, making it difficult to correct the vehicle's posture. .

The present invention was made in order to deal with the problem described in item 1.The purpose of the present invention is to make the dynamic characteristics of the vehicle with respect to the rotation of the steering wheel as constant as possible regardless of the condition of the road surface, so that the vehicle can be driven even on slippery roads. f of front and rear wheel steered vehicles made easier to operate
& provide a wheel steering device.

[Means for Solving the Problems] In order to achieve the above object, the feature of configuration-H of the present invention is such that as the amount of steering of the front wheels increases, the amount of steering of the rear wheels increases in conjunction with the steering of the front wheels. A front and rear ll1ilin steered vehicle is provided with a dead zone corresponding to a predetermined value that steers the rear wheels in a direction opposite to the front wheels, and maintains the rear wheels in a neutral state when the amount of steering of the front wheels is less than a predetermined value. In a rear wheel steering device, there is a detection means for detecting a state of a running road surface related to slipperiness, and when the detection means detects that the running road surface is in a non-slippery state, the width of the dead zone is set and controlled to be large; A dead zone width control means is provided for controlling the width of the dead zone to be set small when the slippery state of the traveling road surface is detected by the means.

[Operation of the invention] In the present invention configured as described above, the road surface condition related to the slipperiness of the road surface on which the vehicle is running is detected by the detection means, and the dead zone control means operates according to the detection result. Therefore, when driving on a non-slip road surface, the width of the dead zone that maintains the rear wheels in a neutral state with respect to front wheel steering is set to be large, and when driving on a slippery road surface, the width of the dead zone is set to be large. The width is set and controlled to be small.

As a result, when the vehicle is traveling on a slippery road surface, compared to when the vehicle is traveling on a non-slip surface,
The rear wheels begin to be steered in a phase opposite to the front wheels for a smaller amount of steering of the front wheels, and the amount of steering of the rear wheels becomes larger for the same amount of steering of the front wheels. That is, when the vehicle is traveling on a slippery road surface, the rear wheels are more likely to be steered in the opposite phase with respect to the front wheels than when the vehicle is traveling on a less slippery road surface.

As a result, when the vehicle is running on a slippery road surface, the turning radius of the vehicle tends to be smaller than when it is running on a non-slip road surface, and the tire Understeer caused by slipping is corrected, and the steering characteristics of the entire vehicle become similar to those when driving on a slippery road surface.

Furthermore, even when the rear wheels are steered in the opposite direction (countersteer) to avoid a spin while driving on a slippery road surface, the yawing moment acting in the opposite direction to the turning direction is reduced by the grooves. This is corrected for anti-phase steering, and the vehicle's attitude is repositioned in the same way as when driving on a non-slip road.

[Effects of the Invention] As is clear from the above description of the operation, according to the present invention, by controlling the steering characteristics of the rear wheels according to the condition of the road surface, understeer and countersteer caused by the slippage of the tires on the road surface can be prevented. This eliminates the difficulty of driving the vehicle, and the dynamic characteristics of the vehicle relative to the rotation of the steering wheel can be kept constant, making it easier for the driver to drive the vehicle even when the vehicle is running on a slippery road surface.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 schematically shows the entire front and rear wheel steered vehicle according to the present invention. This front and rear wheel steering vehicle has left and right front wheels FW1. The vehicle includes a front wheel steering device A that steers the FW2, and a rear wheel steering device B that steers the left and right rear wheels RWI and RW2 in conjunction with the steering of the left and right front wheels FWI and FW2.

The front wheel steering device fA is displaced in the axial direction to control the left and right front wheels FW],
, a rack bar]-1 for steering the FW2.

The rack bar 11 has a pinion gear 12 and a lower steering shaft 13a.
, left and right tie rods 17a connected to the steering handle 15 via the bevel gear 14 and the upper steering shaft 13b, and swingably connected to rack ends 16a and 16b fixed to both ends thereof.

]-7b and the left and right front wheels W1. FW2 is connected. Lower steering shaft 1
A control valve 21 consisting of a four-way valve is installed in the middle of 3a, and the control valve 21 receives a flow from a hydraulic pump 22 to a power cylinder 24 via a branch valve 23 and a conduit P1 in response to the steering torque acting on the lower steering shaft 13a. Supplying hydraulic oil to
The discharge of hydraulic oil from the cylinder 24 to the reservoir 25 via the conduit P2 is controlled. Note that the hydraulic pump 22 is driven by an engine 26. The power cylinder 24 drives the rack bar 11 in the axial direction in response to supply and discharge of hydraulic oil, thereby assisting in steering the left and right front wheels FWI and FW2.

As shown in FIGS. 1 and 2, the rear wheel steering device B includes a relay rod 31 that is displaced in the axial direction and steers the left and right rear wheels RW and RW2. The relay rod 31 is supported by a first housing 32 supported by the vehicle body so as to be displaceable in the axial direction, and at both ends thereof, tie rods 33 a, 33 b and left and right knuckle arms are attached, as in the case of the front wheel steering device A described above. The left and right rear wheels RWI and RW2 are connected via 34a and 34b.

A power cylinder 35 for driving the lever rod 31 in the axial direction is formed within the first housing 32,
The power cylinder 35 has left and right oil chambers 35 fluid-tightly partitioned by a piston 35a fixed to the relay rod 3.
b, 35 c, each oil chamber 35 )) + 35
The relay rod 31 is driven in the axial direction in accordance with the supply and discharge of hydraulic oil to and from c. Right oil chamber 35c of power cylinder 35
A neutral return spring 36 that passes through the relay rod 31 is installed inside the spring 36.
The initial load is 7I! , P[l are applied thereto, and are supported at both ends by left and right retainers 37a and 37b, respectively. Left retainer 37 a is relay rod 3
The relay rod 3 is slidably assembled on the outer periphery of the relay rod 1.
Displacement to the left from the position in FIG. It is regulated by a stepped portion 32a formed on the inner periphery of. Right retainer 37b
is slidably assembled on the outer circumference of the relay rod 3, and displacement of the relay rod 31 from the position shown in FIG. 2 to the right is regulated by an annular stopper member 38b fixed to the relay rod 31, and A plug 39 screwed into the right end of the housing 32 restricts displacement to the right from the same position relative to the housing 32 .

A spool valve 42 that constitutes a hydraulic copying mechanism together with the power cylinder 35 is provided in the second housing 41 placed on the first housing 32 . The spool valve 42 includes a valve sleeve 42a that is slidably accommodated in the second housing 41 in an axial direction in a fluid-tight manner, and a valve spool 42b that is accommodated in the sleeve 42a so that it can slide in the axial direction. Then, valve sleeve 4-2
The supply and discharge of hydraulic oil to and from the power cylinder 35 is controlled according to the relative displacement between the valve sleeve 42a and the valve spool 42b, and the valve sleeve 42a is connected to the relay rod 3 via a lever 43.

As shown in FIGS. 2 and 3, the upper end of the lever 43 is supported by a pin 44 whose tip end is rotatably passed through the upper end of the lever 43. are the first and second housings 32.4 centered on the upper end portion.
1, it is possible to swing the loe in the left-right direction in FIG. 2.

The bottle 44 is threaded at its base onto the inner periphery of a nut member 45, and the nut member 45 is threaded onto the second housing 41 on its outer periphery. Further, a screw 46 is screwed onto the side of the second housing 41 facing the bottle 44, and the lever 43 is prevented from being removed by contacting the tip end surface of the screw 46 with the tip surface of the bottle 44. .

A convex portion 4 having a spherical outer periphery is provided at the intermediate portion of the lever 43.
3a is provided, and the convex portion 43a is fitted into a hole 42a1 formed at the tip of the valve sleeve 42a. A pin 47 is fixed to the lower end of the lever 43, and the pin 47 is slidably fitted into a groove 48a of an annular member 48 with a cross-sectional shape fixed on the outer periphery of the relay rod 31. .

Further, as shown in FIGS. 1 and 2, the spool valve 42 is connected to the supply boat 4 for controlling the supply and discharge of the hydraulic oil.
2c, discharge boat 42d and inflow and outflow ports 4.2e, 4
It is equipped with 2f. The supply boat 42c is connected to the diversion valve 23 via a conduit P3, an electromagnetic flow rate adjustment valve 51 and a conduit P4, and the discharge boat 42d is connected to the reservoir 2 via a conduit P5.
5. The inflow and outflow boats 42e and 42f are connected to the left and right oil chambers 3 of the power cylinder 35 via conduits P6 and P7.
5b and 35c, respectively.

The electromagnetic flow regulating valve 51 is composed of a valve sleeve 5], a, a valve spool 51b, an electromagnetic solenoid 51c, and a spring 51d, and the valve spool 5], b is displaced in the axial direction by controlling the supply of electricity to the electromagnetic solenoid 51c, and its supply is controlled. Boat 51. e and the outflow port 51f, the supply boat 51. Each opening degree of the throttle OF2 located between e and the discharge boat 51g is adjusted. In this case, the valve spool 51b is displaced to the left in the figure due to an increase in the amount of current supplied to the electromagnetic solenoid 51c, the opening degree of the throttle OFI decreases, and the opening degree of the throttle OF2 increases. The supply boat 51e is connected to the diversion valve 23 via a conduit P4, the outflow port 5]-f communicates with the supply boat 42c of the spool valve 42 via a conduit P3, and the discharge boat 51g communicates with a conduit P5. There is.

An electric control circuit 53 for manually inputting a detection signal from a road surface condition detector 52 is connected to the g&magnetic solenoid 51c. The road surface condition detector 52 is composed of, for example, a humidity sensor, a temperature sensor, a water droplet sensor, etc., and their associated circuits, and estimates the amount of moisture on the road surface, freezing of the road surface, etc., and generates a detection signal representing the #1 friction coefficient between the tire and the road surface. Output. In addition, the road surface condition detector 5
2, a fifth wheel to which a predetermined braking force has been applied in advance is brought into contact with the road surface, and the slip state of the fifth wheel is detected by comparing the number of rotations of the fifth wheel with the vehicle speed, thereby detecting the tire and The coefficient of friction with the road surface may also be detected. Furthermore, the coefficient of friction between the tires and the road surface detected by the anti-skid device when braking the vehicle is updated and stored each time the friction coefficient is detected, and the stored Jf! A friction coefficient may also be used.

Of course, such various detection results may be used together. Based on the detection signal from the road surface condition detector 52, the electric control circuit 53 controls the energization of the electromagnetic solenoid 51c so that the amount of energization to the electromagnetic solenoid 51c decreases as the friction coefficient of the road surface decreases.

The valve spool 42b of the spool valve 42 is driven in the axial direction by a connecting rod 61 and a cam plate 62. The connecting rod 1 is supported by the second housing 41 so as to be displaceable in the axial direction, and is connected to the valve spool 4.2b by a pin 63 at one end, and formed on the lower surface of the cam play I.62 at the other end. It engages with the cam groove 62a via a pin 64 and a pawl bearing 65. The cam plate 62 is formed into a disk shape, and is rotatably supported by the second housing 44 via ball bearings 66 a, 66 b at shaft portions 62 b, 62 c formed at the center thereof. Further, the cam groove 62a formed on the lower surface of the cam plate 62 is formed in a thin spiral shape, so that the cam plate 62 can be moved from left to right when the bottle 64 and ball bearing 65 are in the position shown in FIG. 4 (reference state). When the connecting rod 61 rotates, the connecting rod 61 is displaced to both sides in the axial direction about the reference position.

As shown in FIGS. 2 and 5, a spiral spring 67 is attached to the upper surface of the cam plate 62.
The shaft portion 62c is placed so as to surround the shaft portion 62c. Stopper portions 67a are formed at the inner and outer ends of the spring 67 by bending the upper projections of the inner and outer ends of the spring 67.
, 67b are formed respectively, and both stopper portions 67
a, 67b sandwich the lever 68 fixed to the cam plate 62 and the fixing member 71 fixed to the second housing 4 with a preload applied, so that the cam plate 62 is moved by the elastic force of the spring 67. It is energized to a neutral state. In addition, in FIG. 2, the stopper parts 67a, 67b, the lever 68, and the fixing member 71 are shown rotated by 90 degrees with respect to the state (reference state) of FIG. 5.

A pair of upper and lower grooves 62d, 62 are formed on the side surface of the cam plate 62.
A pair of cables 72.73 are wound around the grooves 62d and 62e, respectively, and the cables 72.73 are connected to the cam plate 62 at each rear end.
Fixed. In addition, in FIG. 2, the fixed portions of the rear ends of the cables 72, 73 to the cam plate 62 are shown rotated by 90 degrees with respect to the state (reference state) of FIG. 5.

These cables 72 and 73 are for left and right front wheels FWI.

The cam plate 62 is rotated in conjunction with the steering of the FW 2, and as shown in FIGS. 2 and 5, the cam plate 62 is extended to the outside through entry ports 41a and 41b formed in the second housing 41, respectively. The rack end 16 a of the front wheel steering device A
, 16b.

Next, the operation of the embodiment configured as described above will be explained.

When the steering wheel 15 is rotated to the right (or left),
The rotation of the steering handle 15 is transmitted to the rack bar 11 via the upper steering shaft 13b, bevel gear 14, lower steering shaft 13a, and pinion gear 12, and the bar 11 is displaced in the right (or left) direction in FIG. do. The displacement of this rack par 11 in the right (or left) direction is caused by the left and right tie rods 17a, 17
b and the left and right knuckle arms 18a, 1.8b to the left and right front wheels FW], FW2, and the front wheels FW1, FW2 are steered in the right (or left) direction. Also, it takes left and right front! FW1. In steering FW2,
A control valve 21 supplies hydraulic oil from a hydraulic pump 22 to a left (or right) oil chamber of a power cylinder 24 via a diversion valve 23 in accordance with the steering torque acting on the lower steering shaft 13 a. Since the hydraulic oil in the right (or left) oil chamber of the cylinder 24 is discharged to the reservoir 25, the power cylinder 24 presses the rack par 11 in the right (or left) direction in FIG. Assists the steering of FW2.

On the other hand, the displacement of the rack par 11 in the right (or left) direction is caused by the cable 7 via the rack end 16b (or 16a).
3 (or 72), and the same cable 73 (or 72)
) is the displacement amount of the rack par 11, that is, the left and right front wheels FW.
It is pulled forward by an amount corresponding to the steering amount of I and FW2. As a result of the cable 73 (or 72) being pulled in this way, the steering amount of the left and right front wheels FWl, FW2 is transmitted to the cam plate 62 via the cable 73 (or 72), and the cam plate 62 is connected to the spring 67. The pin 64 rotates in the counterclockwise (or clockwise) direction in FIG. 5, that is, in the clockwise (or counterclockwise) direction in FIG. is moved in the center (or circumferential) direction in response to the amount of steering, and the connecting rod 6]- is displaced in the right (or left) direction in FIG. 2 in response to the amount of steering.

By displacement of the six connecting rods in the right (or left) direction,
The valve spool 42b is displaced in the right (or left) direction in FIG.
, the hydraulic oil is supplied to the supply boat 42c of the spool valve 42 via the conduit P4, the electromagnetic flow control valve 51 and the conduit P3, and the hydraulic oil is supplied to the supply boat 42c of the spool valve 42 via the inflow/output port 42e and the conduit P6 (or the inflow/output port 42f and the conduit P7). cylinder 35
is supplied to the left oil chamber 35b (or right oil chamber 35c) of the cylinder 35, and the right oil chamber 35c (or left oil chamber 35b) of the cylinder 35 is supplied to the left oil chamber 35b (or right oil chamber 35c) of
) is discharged to the reservoir 25 through the conduit P7, the inflow/output port 42f, the discharge port 42d, and the conduit P5 (or the conduit P6, the inflow/output port 42e, the discharge port 42d, and the conduit P5). As a result, the piston 35a of the power cylinder 35 presses the relay rod 3 in the right (or left) direction in FIGS. 1 and 2 against the urging force of the spring 36. In such a case, spring 3
Since the relay rod 3 is assembled with the initial load M'CP e applied to it, the relay rod 3
1 is not displaced, and when the pressing force becomes larger than the initial load Pθ, the rod 31 starts to be displaced rightward (or leftward). When the relay rod 31 is displaced rightward (or leftward) in this way, the displacement is caused by the left and right tie rods 33a, 3
3b and the left and right knuckle arms 34a, 34b to the left and right rear wheels RWI, RW2.
2 is the left (or right) direction, that is, the left and right front wheels FWI, FW2
It begins to be steered in the opposite phase.

On the other hand, due to the displacement of the relay rod 31, the lever 43
The lower end of the groove 48a of the annular member 48 is connected to the second
When pressed in the right (or left) direction in the figure, the lever 43 swings counterclockwise (or clockwise) in FIG. 2 around the pin 44. This swinging of the lever 43 causes the valve sleeve 4 to
3a is moved to the right in FIG. 2 (
(or left) direction, and the sleeve 42a is displaced in the same direction. Then, due to the displacement of the valve sleeve 42a, the hydraulic pressure supplied to the power cylinder 35 decreases, and when the pressing force of the power cylinder 35 against the relay rod 31 matches the urging force of the spring 36, the displacement of the relay rod 31 stops. The left and right rear wheels Rw1. R.W.
The above-mentioned steering of No. 2 is also accompanied. As a result, the left and right rear wheels RW1
．． RW2 follows the shape of the cam groove 62a of the cam plate 62 and the displacement of the connecting roller 1, that is, the left and right front wheels F.
The left and right front wheels FWI according to the amount of steering of Wl and FW2.

It will be steered in a direction opposite to FW2.

The left and right rear wheels RWI and RW2 are steered by this control, but if the vehicle is dry and traveling on a road surface with a large coefficient of friction with the tires, that is, a non-slip road surface, the road surface condition detector 52 Since the state is detected and a detection signal representing a large coefficient of friction is supplied to the electric control circuit 53, the control circuit 53 energizes the electromagnetic solenoid 51c with a large current! I control it. As a result, the solenoid 5],c presses the valve spool 51b to the left in FIG. The oil pressure is set to be large, and most of the amount of hydraulic oil supplied to the supply port 51e is transferred from the discharge port 51g to the reservoir 2 via the conduit P5.
5, and the amount of hydraulic oil supplied from the outflow port 51f to the supply boat 4-2c of the spool valve 42 via the conduit P3 decreases. As a result, the change in the working oil pressure in the power cylinder 35 with respect to the above-mentioned displacement of the valve spool 42b changes as shown by the solid line f1 in FIG. The pressing force of the relay rod 31 is the initial load Pi of the spring 36! At this point, the left and right rear wheels RWI and RW2 begin to be steered for the first time.

The solid line a in FIG. 7 indicates the steering characteristics of the left and right rear wheels RWI, RW2. RWI.

RW2 is not steered, and the left and right rear wheels RW1 and R as shown above
A so-called dead zone is provided in the reverse phase steering control of W2. As a result, when the vehicle is running at high speed and the rotation angle of the steering wheel 15 does not become very large, the left and right rear wheels RWl and RW2 are maintained in a neutral state, and the running stability of the vehicle is improved. . Additionally, if the vehicle is running at low or medium speed and the steering wheel 15 is rotated beyond the predetermined value, the left and right front wheels FW1°FW
As the steering angle of 2 increases, the left and right rear wheels RVi/1°RW2
The steering angle of the vehicle increases, and the vehicle's turning performance improves.

In addition, in FIG. 7, the RWI of the left and right rear wheels increases as the rotation angle of the steering handle 15 increases.

The reason why the steering angle of RW2 increases in a polygonal manner is because of cam 6.
This is due to the shape of the cam groove 62a of No. 2.
By changing the shape of 2a, various left and right rear wheels RW
It is possible to realize the steering characteristics of I and RW2.

On the other hand, if the vehicle is traveling on a slippery road surface with a small coefficient of friction with the tires due to water, snow, etc., the road surface condition detector 52 detects the road surface condition and outputs a detection signal representing a small coefficient of friction. Since it is supplied to the electric control circuit 53,
The control circuit 53 controls the energization of the electromagnetic solenoid 51c with a small current. As a result, the same solenoid 5
1c is a valve spool 51. Since b is set to a position displaced to the right in Fig. 2 from the above case, the aperture OFI
of the total amount of hydraulic oil supplied to the supply port 51e is discharged from the discharge port 51g to the reservoir 25 via the conduit P5. The amount decreases, and the amount of hydraulic oil supplied from the outflow port 51f to the supply port 42c of the spool valve 42 via the conduit P3 increases. As a result, the change in the working oil pressure in the power cylinder 35 with respect to the above displacement of the valve spool 42b changes as shown by the broken line f2 in FIG. The pressing force of the relay rod 31 by the cylinder 35 is the initial load P8 of the spring 36.
It becomes larger, and from that point on, the left and right rear 1M1RWI,
RW2 will now be steered.

As a result, the left and right rear 111RWI and RW2 begin to be steered in response to a small displacement of the valve spool 42c.
Left and right rear mRWl, R with respect to the rotation angle of the steering handle 15
As for the steering characteristic of W2, as already shown by the broken line in FIG. 7, the dead zone becomes narrower, and as a result, the left and right rear wheels RWI, RW2 are largely steered for the same rotation angle of the steering wheel 15 as in the above case. It becomes like this. If the *friction coefficient of the road surface becomes even smaller, the dead zone becomes even narrower, and the steering characteristics of the left and right rear wheels RWI, RW2 change as indicated by the dashed line C in FIG.
It will change like this.

This means that as the running road surface becomes slippery, the left and right rear wheels RWI, RW2 tend to be steered in the opposite phase to the left and right front wheels FWI, FW2, and such steering control of the left and right rear wheels RWI, RW2 increases. According to this system, understeer caused by tire slippage when a vehicle is traveling on a slippery road surface is corrected, and the vehicle can always be turned with a constant driving operation regardless of the slipperiness of the road surface.

Furthermore, when the vehicle is running on a slippery road surface, even if the steering wheel 15 is countersteered to avoid a spin, the reverse phase steering of the left and right rear wheels RWI, RW2 causes the vehicle to turn in the opposite direction. Since sufficient yawing moment can be obtained, it becomes easy to correct the vehicle's attitude.

In addition, in the above embodiment, the present invention is applied to the front wheel steering device A.
and the rear wheel steering device B are connected by cables 72, 73, and the left and right front wheels FWI, F are connected via the cables 72, 73.
This was applied to a front and rear wheel steered vehicle of the type that transmits the steering amount of W2 to the rear wheel steering device B, but like the device shown in Japanese Utility Model Application No. 60-92669 cited in the above-mentioned prior art section,
The mechanical connection between the front wheel steering device A and the rear wheel steering device B is eliminated, and instead, the steering angles of the left and right front wheels FWI, FW2 are detected by a steering angle sensor, and the left and right rear wheels are adjusted based on the detected front wheel steering angles. Calculate the target rear wheel steering angle for RWI and RW2 and achieve the same target rear wheel steering angle! The present invention may be applied to a front and rear wheel steered vehicle in which Rwl and RW2 are steered. In such a case, the left and right rear wheels RWI, RW2 may be steered using hydraulic pressure as in the device according to the above-mentioned publication, or may be steered by an electric drive means such as an electric motor.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of a vehicle equipped with a rear wheel steering device showing an embodiment of the present invention, and FIG. 2 is a longitudinal sectional front view of the same rear wheel steering device and the electromagnetic flow shown in FIG. Figure 3 is a new view taken along the line ■-■ in Figure 2, Figure 4 is a bottom view of the cam plate in Figure 2, and Figure 5 is a front view of the regulating valve. 6 is a characteristic graph of the oil pressure in the power cylinder with respect to the displacement of the valve spool shown in FIG. 2, and FIG. 7 is a graph of the steering characteristics of the rear wheels. Explanation of symbols A...Front wheel steering device, B...Rear wheel steering device, FWI
, FW2...Front wheel, RWI, RW
2...Rear wheel, 11...Rack bar-1]5...
・Steering handle, 24.35...Power cylinder,
31...Relay rod, 32.41...Housing, 36...Spring, 42...Spool valve, 43...Lever, 51...Solenoid flow rate adjustment valve, 52
... Road surface condition detector, 53 ... Electric control circuit, 61
...Connecting rod, 62...Cam play), 72.7
3... Cable. Applicant Toyota Motor Corporation Agent Patent Attorney Teru Hase (1 other person) Department b

Claims (1)

[Claims] In conjunction with front wheel steering, the rear wheels are steered in a direction opposite to the front wheels so that as the front wheel steering amount increases, the rear wheel steering amount increases, and when the front wheel steering amount is less than a predetermined value, the rear wheels are steered. In a rear wheel steering device for a front and rear wheel steered vehicle, which is provided with a dead zone corresponding to the predetermined value for maintaining the wheels in a neutral state, the device includes a detection means for detecting a state of a running road surface related to slipperiness, and a detection means for detecting a state of a running road surface related to slipperiness; Dead zone width control means for controlling the width of the dead zone to be set large when a non-slip condition of the road surface is detected, and controlling the width of the dead zone to be small when the slippery condition of the traveling road surface is detected by the detection means; A rear wheel steering device for a front and rear wheel steered vehicle, characterized in that it is provided with: