JPS63258270A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To prevent a battery to be exhausted during the travel of a vehicle by providing solenoid valves, to which a current is intermittently applied by means of valve control means, on the way of pressure passages intercommunicating a rear wheel steering cylinder in a rear wheel steering mechanism to a pump. CONSTITUTION:Between a hydraulic pump 32 and a spool valve 26, branch passages 34a, 34b are connected through fail safe type solenoid valves 36a, 36b. The valves 36a, 36b are provided with spools 82a, 82b for opening/closing the branch passages 34a, 34b. On the spools 82a, 82b, there are provided solenoids 86a, 86b connected to the positive electrode of a battery 84, and moreover, the solenoids 86a, 86b are connected to the collectors of transistors 88a, 88b. In the case that a current is applied to the solenoids 86a, 86b, the branch passages 34a, 34b are blocked against energizing force of coil springs 80a, 80b, while in the case that the current isn't applied to the solenoids 86a, 86b, the branch passages 34a, 34b are opened by means of the energizing force of the coil spring, thereby intermittently supplying an oil pressure to a rear wheel steering cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a four-wheel system for a vehicle in which when the front wheels are steered by a steering operation via a steering mechanism, the rear wheels are also steered at the same time. It relates to a steering device.

(Prior Art) When the front wheels are steered by a steering operation performed via a steering wheel, the rear wheels are also steered by the rear wheel steering mechanism as the front wheels are steered, thereby: 2. Description of the Related Art A four-wheel steering device is known that improves the drivability of a vehicle by steering the vehicle with reduced side slip of the rear wheels.

One of the rear wheel steering mechanisms in such a four-wheel steering device is a knuckle arm that supports the left and right rear wheels in a steerable manner and is connected by a connecting shaft, and pressure is applied to a rear wheel steering cylinder arranged on this connecting shaft. Some vehicles steer the rear wheels by supplying and discharging oil and moving the connecting shaft in the width direction of the vehicle. In such a rear wheel steering mechanism, two hydraulic chambers partitioned by a piston fixed to a connecting shaft are formed in the rear wheel steering cylinder, and one end of each is connected to the two hydraulic chambers. The other ends of the oil supply passage and the oil return passage are opened to an oil reservoir via a spool valve. A hydraulic pump is interposed in the oil supply passage, and the hydraulic oil pumped from the oil reservoir is sent through the oil supply passage to the two hydraulic chambers in the rear wheel steering cylinder according to the valve arrangement of the spool valve. Pressure oil is supplied to one of the two hydraulic chambers, and pressure oil from the other of the two hydraulic chambers is returned to the oil reservoir through an oil return passage.

In addition, as a four-wheel steering device, for example,
As described in Publication No. 168, the vehicle speed is such that the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, that is, the steering ratio, is changed in accordance with the vehicle speed detected by a vehicle speed sensor. A steering wheel having a sensitive steering ratio characteristic has been proposed. In a four-wheel steering system having such a vehicle speed-sensitive steering ratio characteristic, when the vehicle is traveling at a relatively low speed, the front wheel steering state and the rear wheel steering state usually have an opposite phase relationship. When the vehicle is running at a relatively high speed, the front wheel steering state and the rear wheel steering state are assumed to have the same phase relationship. The steering ratio is set. When the steering ratio is set so that the front wheel steering state and the rear wheel steering state are in an opposite phase relationship, the vehicle tends to oversteer, and the turning performance is improved. When the steering ratio is set so that the front wheel steering state and the rear wheel steering state have the same phase relationship, the vehicle tends to understeer, and driving stability is improved. It will be done.

By the way, in a four-wheel steering system having a vehicle speed-sensitive steering ratio characteristic as described above, a situation may occur where the vehicle speed detected by the vehicle speed sensor differs from the actual vehicle speed due to a failure of the vehicle speed sensor. In this case, for example, even though the vehicle is running at a relatively high speed, the front wheel steering state and the rear wheel steering state are in an opposite phase relationship. ratio is set, or even though the vehicle is running at a relatively low speed.
There is a possibility that a steering ratio is set in which the front wheel steering state and the rear wheel steering state have the same phase relationship.

Therefore, in the event that the vehicle speed detected by the vehicle speed sensor differs from the actual vehicle speed due to a malfunction of the vehicle speed sensor, the operation of the rear wheel steering mechanism is prohibited and only the front wheels are steered. It is necessary to make sure that the

(Problem to be Solved by the Invention) In this way, as a means for inhibiting the operation of the rear wheel steering mechanism, for example, an oil supply passage connected to two hydraulic chambers in a rear wheel steering cylinder via a spool valve. and the oil return passage are communicated by a bypass passage in which a solenoid valve is interposed, and when the operation of the rear wheel steering mechanism is prohibited, the power supply to the solenoid valve is stopped, the bypass passage is opened, and the oil return passage is opened by a hydraulic pump. It is conceivable that the pressurized oil from the oil reservoir is returned to the oil reservoir through the bypass passage and the oil return passage without being supplied to the hydraulic chamber in the rear wheel steering cylinder.

However, when a bypass passage that communicates the oil supply passage with the oil return passage, a solenoid valve interposed in the bypass passage, etc. are used as means for prohibiting the operation of the rear wheel steering mechanism, as described above. In order to ensure that only the front wheels of the vehicle are steered in the event of an accident such as a disconnection of the solenoid, the bypass passage is blocked and the rear wheel steering mechanism is disabled while the solenoid valve is energized. It is necessary to open the bypass passage and prohibit the operation of the rear wheel steering mechanism when the solenoid valve is operated and the solenoid valve is not energized. Therefore, when the vehicle is in a running state, the solenoid valve is always energized, which inconveniently increases the power consumption of the battery.

In view of these points, the present invention provides a pump means for pumping fluid to a rear wheel steering cylinder in a rear wheel steering mechanism, and a pressure passage that communicates the pump means with the rear wheel steering cylinder. , a solenoid valve that selectively takes a state in which the fluid pumped by the pump means is supplied to the rear wheel steering cylinder and a state in which fluid is prohibited from being supplied to the rear wheel steering cylinder; An object of the present invention is to provide a four-wheel steering device for a vehicle in which power consumption of a battery is reduced when power is supplied to a solenoid valve to supply power to a cylinder.

(Means for Solving the Problems) In order to achieve the above-mentioned object, a four-wheel steering device for a vehicle according to the present invention includes a front wheel steering mechanism that steers the front wheels in response to a steering operation in the vehicle, and a rear wheel steering mechanism. a rear wheel steering mechanism that steers the rear wheels by supplying fluid to the rear wheel steering cylinder in response to steering of the front wheels; and a pump that pumps fluid to the rear wheel steering cylinder. a first state in which fluid is supplied to the rear wheel steering cylinder by the pump means, the fluid being pumped by the pump means is supplied to the rear wheel steering cylinder; a solenoid valve that selectively assumes a second state that prohibits the supply of fluid to a rear wheel steering cylinder; and valve control means that causes the solenoid valve to assume the first and second states. The valve control means intermittently energizes the solenoid valve to cause the solenoid valve to assume the first state, and stops energizing the solenoid valve to cause the solenoid valve to assume the second state. It is said that

(Function) In the four-wheel steering system for a vehicle constructed as described above and according to the present invention, the four-wheel steering system for a vehicle according to the present invention is arranged in relation to the pressure passage that communicates the rear-wheel steering cylinder of the rear-wheel steering mechanism with the pump means. By intermittently energizing the solenoid valve by the valve control means, the fluid pumped by the pump means is supplied to the rear wheel steering cylinder through the pressure passage, and a four-wheel steering state of the vehicle is obtained. By stopping the energization of the solenoid valve by the valve control means, the supply of fluid from the pump means to the rear wheel steering cylinder is prohibited, and the operation of the rear wheel steering mechanism is prohibited, and the vehicle is changed from the four-wheel steering state. It is assumed that only the front wheels are steered.

In this way, in order to supply fluid to the rear wheel steering cylinders in order to make the vehicle adopt a four-wheel steering state, the solenoid valve is energized intermittently, thereby reducing the power consumption of the battery while the vehicle is running. The reduction will be achieved. In addition, by stopping power to the solenoid valve, the operation of the rear wheel steering mechanism is prohibited and only the front wheels are steered, so even if the vehicle speed sensor fails, the vehicle will not operate properly. Driving characteristics can be obtained.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows an example of a four-wheel steering system for a vehicle according to the present invention. In Figure 1, left and right front wheels 2L and 2
A front wheel steering mechanism 5 is provided that steers the front wheels 2L and 2R in response to steering via the steering wheel 3. A pair of knuckle members 6 are supported by the vehicle body (not shown) through 4. A pair of tie rods 8 each have one end connected to the knuckle arms 6a of these knuckle members 6, and each of the pair of tie rods 8 The steering gear mechanism 10 is constructed of a rack-and-pinion type steering gear mechanism 10 having a rack shaft 9 connected to both ends thereof. In such a front wheel steering mechanism 5, the steering force from the steering wheel 3 is transferred to the steering gear mechanism 10.
is transmitted to the tie rod 8, causing the tie rod 8 to reciprocate in the vehicle width direction, and the reciprocating movement of the tie rod 8 causes the knuckle member 6 to rotate around the joint portion 4, thereby rotating the front wheels 2L and 2R. Steering is performed.

Also, replace the left and right rear wheels 12L and 12R with the front wheels 2L and 2
A rear wheel steering mechanism 11 is provided which steers the rear wheels 12L as each wheel R is turned.
and a pair of knuckle members 16. which rotatably support 12R and are supported by the vehicle body (not shown) via the joint portion 14. A pair of tie rods 18 each having one end connected to the knuckle arm 16a of the knuckle member 16, and a rear wheel steering iron 20 each having the other end connected to both ends of the pair of tie rods 18. .

A power cylinder 22 is disposed on the rear wheel steering rod 20, and the power cylinder 22 is connected to the rear wheel steering rod 20.
It has a piston 22a fixed to the piston 22a and hydraulic chambers 22b and 22c partitioned by the piston 22a. The hydraulic chambers 22b and 22C are connected to hydraulic passages 24 and 25, respectively.
is communicated with the spool valve 26 through the
The spool valve 26 is connected to one end of each of an oil supply passage 28 and an oil return passage 29 . Oil supply passage 2
8 and the oil return passage 29 are open to an oil reservoir 30, and a hydraulic pump 32 is interposed in the oil supply passage 28. Moreover, the hydraulic pump 3 in the oil supply passage 28
2 and the spool valve 26, branches B54a and 34b formed at the other end of the bypass oil passage 34, one end of which is connected to the oil return passage 29, connect fail-safe solenoid valves 36a and 36b. connected via.

Fail-safe solenoid valves 36a and 36b
As shown in FIG. 2, the spool 82a is biased in the direction in which the coil spring 80a is compressed and the branch passage 34a is opened, and the coil spring 80b is compressed and biased in the direction in which the branch passage 34b is opened. It has a spool 82b that is energized.

The spools 82a and 82b are provided with solenoids 86a and 86b whose one ends are connected to the positive electrode of the battery 84, and the other ends of the solenoids 86a and 86b are connected to transistors 88a and 888 whose emitters are grounded, respectively.
A pulse signal Sv having a predetermined pulse width is supplied to the bases of the transistors 88a and 88b from a control unit 62, which will be described later.

When the solenoids 86a and 86b are energized, the branch passages 34a and 34b are blocked against the urging force of the coil springs 80a and 80b, and when the solenoids 86a and 86b are not energized, the coil spring 80a and the biasing force of 80b causes the branch path 34 to
a and 34b are to be opened.

In this way, by supplying the pulse signal Sv to the bases of the transistors 88a and 88b, the current A from the battery 84 is supplied to the solenoids 86a and 86b during the period ta, as shown in FIG.
During period tb, a state is alternately obtained in which the supply of current A from battery 84 is stopped. That is, solenoid 86
The coil springs 80a and 80b are not attached to the spools 82a and 82b during the period tb when the supply of current A from the battery 84 to the solenoids 86a and 86b is stopped. Although forces act on the spools 82a and 82
b is assumed to maintain a position where it closes the branch paths 34a and 34b due to its inertia.

Therefore, the fail-safe solenoid valves 36a and 36b close the bypass oil passage 34 when the pulse signal Sv is supplied from the control unit 62 to the bases of the transistors 88a and 88b, and prevent the pressure oil pumped by the hydraulic pump 32 from closing. The bypass oil passage 34 is opened when the supply of the pulse signal Sv from the control unit 62 to the bases of the transistors 88a and 88b is stopped, and the oil is pumped by the hydraulic pump 32. A valve arrangement is adopted in which pressure oil is returned to an oil reservoir 30 through an oil return passage 29 without being supplied to a spool valve 26.

The spool valve 26 controls the supply and discharge of hydraulic pressure to and from the hydraulic chambers 22b and 22c of the power cylinder 22 in accordance with movement of the spool 26a in the vehicle width direction. For example, when the rear wheels 12L and 12R are steered clockwise in FIG. The oil is supplied into the hydraulic chamber 22b, and the oil return passage 29 and the hydraulic passage 25 communicate with each other,
Pressure oil in the hydraulic chamber 22c is returned to the oil reservoir 30.

Furthermore, when the rear wheels 12L and 12R are steered counterclockwise in FIG. is supplied into the hydraulic chamber 22c,
In addition, the oil return passage 291 and the hydraulic passage 24 communicate with each other, and the pressure oil in the hydraulic chamber 22b is returned to the oil reservoir 30. In this way, the spool 26a in the spool pulp 26
According to the movement in the vehicle width direction, pressure oil is supplied to and discharged from the hydraulic chambers 22b and 22c of the power cylinder 22, whereby the rear wheel steering iron 20 moves in the vehicle width direction, and the rear wheel steering iron 20 moves in the vehicle width direction. 12L and 12R will be steered.

The amount and direction of movement of the spool 26a in the spool pulp 26 in the vehicle width direction are controlled in accordance with the steering angle and direction of the front wheels 2L and 2R steered by the front wheel steering mechanism 5. 12L and 12
In order to change the steering ratio of R, a pinion 38 that meshes with a rack 37 formed on a rack shaft 9 is fixed at one end, and the other end of a transmission rod 39 extending in the longitudinal direction of the vehicle is connected. A variable steering ratio mechanism 40 is arranged.

As shown in FIGS. 4 and 5, the variable steering ratio mechanism 40 has a shaft 42 rotatably supported around a central axis 01 extending in the height direction of the vehicle. A holder 44 having a bifurcated shape is fixed to one end of the holder 42 . The rotating arm 4 is attached to the holder 44 via a bin 46.
8 are connected to each other, and the center of the pin 46 coincides with a center axis 0□ which is perpendicular to the center axis O1 and extends in the vehicle width direction. Therefore, the angle of the rotation locus of the rotation arm 48 about the pin 46 with respect to the central axis O2 changes as the holder 44 rotates about the central axis O1.

One end of a link member 50 is connected to the other end of the rotating arm 48 via a ball joint, and the other end of the link member 50 is connected to the spool 26 of the spool valve 26.
a through a ball joint on the central axis Ot.

The link member 50 is slidably inserted into a through hole 52a formed in a large-diameter bevel gear 52 whose rotation center is the central axis 02. The large diameter bevel gear 52 is connected to the transmission rod 39
It is meshed with a bevel gear 54 fixed to the other end.

Therefore, when the steering wheel 3 is steered, the steering force is transmitted to the transmission rod 39 via the rack 37 and pinion 38 formed on the rack shaft 9, and the rotation of the transmission rod 39 is Accordingly, the bevel gear 54
The large-diameter bevel gear 52 rotates via the link member 5o, thereby causing the link member 5o to rotate together with the rotation arm 48.

In such a state, the rotation locus of the rotation arm 48 is aligned with the axis 4.
2 causes a tilt with respect to the central axis 02, the link member 50 is moved in the direction shown by arrow F in FIG.
is displaced in the vehicle width direction. The amount of displacement of the spool 26a is determined by the rotation locus of the rotation arm 48 about the pin 46 and the central axis 0. , that is, the rotation angle of the holder 44 about the central axis 01. For this reason, a sector gear 56 is fixed to the other end of the shaft 42 with the holder 44 fixed to one end, and the sector gear 56 receives a signal S from the control unit 62.
A worm 60 fixed to the output shaft of a pulse motor 58 is engaged with the output shaft of a pulse motor 58, which is driven and controlled by a motor.

The control unit 62 detects the vehicle speed based on a detection signal Sa from a steering angle sensor 64 that detects the steering angles of the front wheels 2L and 2R in connection with the front wheel steering mechanism 5, and the rotational speed of each of the front wheels 2L and 2R. Detection signals sbI and Sbz from the two vehicle speed sensors 66 and 67, a detection signal Sc from the engine rotation speed sensor 68 that detects the engine rotation speed, a detection signal Sd from the clutch sensor 7o that detects the engagement/disengagement state of the clutch, A detection signal Se is also supplied from a transmission sensor 72 that is provided in connection with the transmission and detects the shift position of the shift lever.

Based on this configuration, the control unit 62 detects, for example, that the detection signal Sc from the engine rotation speed sensor 68 indicates that the engine rotation speed is 220 Orpm or more, and the detection signal Sd from the clutch sensor 70 indicates that the clutch is If the connected state is detected and the detection signal Se from the transmission sensor 72 indicates that the shift lever is in a shift position other than neutral, it is determined that the vehicle is in the running state.

Then, the control unit 62 compares the vehicle speed v1 indicated by the detection signal sb from the vehicle speed sensor 66 and the vehicle speed ■2 indicated by the detection signal Sbz from the vehicle speed sensor 67, and when the vehicle speed V1 and the vehicle speed ■2 match, In addition, when the vehicle speeds (1) and (2) do not suddenly change, the pulse signal Sv is supplied to the bases of the transistors 88a and 88b provided in the fail-safe solenoid valves 36a and 36b, and the vehicle speed (2) is changed. 1 and the detection signal S from the steering angle sensor 64
Based on the steering angles of the front wheels 2L and 2R indicated by a, the rear wheels 12
The steering angles of L and 12R are calculated, and a signal Sm corresponding to the calculated steering angles is supplied to the pulse motor 58 of the variable steering ratio mechanism 40. As a result, the bypass oil passage 34 is blocked,
Pressure oil that is force-fed to the oil supply passage 28 by the hydraulic pump 32 is supplied to the power cylinder 22 through the spool valve 26.
is supplied to the hydraulic chamber 22b or 22c, and
The holder 44 in the variable steering ratio mechanism 40 is rotated by a predetermined amount around the central axis OI. In such a state, a steering force on the steering wheel 3 is applied to the rack shaft 9 and the rear rack 37. pinion 3
8. By being transmitted to the large-diameter bevel gear 52 via the transmission rod 39 and the bevel gear 54, the link member 50 is rotated together with the rotation arm 48. At this time, the rotation locus of the rotation arm 48 around the pin 46 and the center axis 0
Since the angle with □ changes as the holder 44 rotates, the spool 26a is displaced in the vehicle width direction, and the spool valve 2
6, the amount of pressure oil supplied to the hydraulic chamber 22b or 22C in the power cylinder 22 is set.

In this way, the steering ratios of the rear wheels 12L and 12R are set according to the vehicle speed V1 and the steering angles of the front wheels 2L and 2R,
Based on this steering ratio, the hydraulic chamber 2 of the power cylinder 22
By supplying pressure oil to 2b or 22c, the rear wheel steering rod 20 is moved in the vehicle width direction, and the movement of the rear wheel steering rod 20 causes the knuckle member 16 to move around the joint portion 14. By rotating the rear wheels 12L and 12R, a four-wheel steering state is obtained in which the rear wheels 12L and 12R are steered at a predetermined steering ratio.

When the vehicle assumes four-wheel steering, failures and
Since the batteries 84 supply electricity to the solenoids 86a and 86b of the safe solenoid valves 36a and 36b intermittently as shown in FIG.
The power consumption of the battery 84 is significantly reduced compared to the case where electricity is constantly supplied.

Further, as described above, solenoids 86a and 8 of fail-safe solenoid valves 36a and 36b
When a pulse signal Sv is supplied from the control unit 62 to the bases of the transistors 88a and 88b so that the battery 84 is intermittently energized to the transistor 6b, the pulse signal Sv is obtained at the terminals 89a and 89b. The collector voltages of transistors 88a and 88b alternate between zero level and positive level in response to the switching action of transistors 88a and 88b.

On the other hand, if the solenoid 86a of the fail-safe solenoid valve 36a is disconnected, the transistor 88
If the collector voltage of the transistor a is constantly at zero level and the solenoid 86b of the fail-safe solenoid valve 36b is disconnected, the transistor 8
The collector voltage of 8b is constantly at zero level. Therefore, by detecting the collector voltages of the transistors 88a and 88b obtained at the terminals 89a and 89b, the solenoids 86a and 86b of the fail-safe solenoid valves 36a and 36b are activated while the vehicle is running.
and 86b can be detected.

As described above, when the vehicle is in a four-wheel steering state,
The control unit 62 controls the vehicle speed V1 when the vehicle speed V and the vehicle speed V2 do not match, when there is a sudden change in the vehicle speed V or the vehicle speed 2, and when the vehicle speed V1 is changed even though the vehicle is actually in a running state. When vehicle speed 2 and vehicle speed 2 are both zero, it is assumed that vehicle speed sensor 66 or 67 has failed, and the supply of pulse signal Sv to the bases of transistors 88a and 88b is stopped. As a result, the bypass oil path 3
4 is opened, and the pressure oil that is force-fed to the oil supply passage 28 by the hydraulic pump 32 is returned to the oil reservoir 30 through the oil return passage 29 without being supplied to the spool valve 26. For this reason, the hydraulic chamber 22b of the power cylinder 22
The supply of pressure oil to and 22c is stopped, movement of the rear wheel steering rod 20 in the vehicle width direction is prohibited, and the front wheel 2
A state is obtained in which only L and 2R are steered.

In this way, in order to prohibit the operation of the rear wheel steering mechanism 11, each of the branch roads 34a and 34b is
By interposing the safe solenoid valves 36a and 36b, even if one of the fail-safe solenoid valves 36a and 36b fails, the branch path 3
Even if one of the branch passages 4a and 34b remains blocked, the other of the branch passages 34a and 34b is opened, and the pressure oil sent to the oil supply passage 28 by the hydraulic pump 32 is bypassed. Oil passage 34 and oil return passage 2
Since the oil is returned to the oil sump 30 through 9, it is possible to reliably shift the vehicle from a four-wheel steering state to a state where only the front wheels 2L and 2R are steered.

(Effects of the Invention) As is clear from the above description, the four-wheel steering device for a vehicle according to the present invention includes a pump means for pumping fluid to the rear wheel steering cylinder in the rear wheel steering mechanism, and Disposed in association with a pressure passage that communicates with the rear wheel steering cylinder, the fluid pumped by the pump means is supplied to the rear wheel steering cylinder, and the fluid is prohibited from being supplied to the rear wheel steering cylinder. A solenoid valve that selectively assumes a state is provided, and by intermittently energizing the solenoid valve, fluid pumped by the pump means is supplied to the rear wheel steering cylinder to obtain a four-wheel steering state of the vehicle. This makes it possible to significantly reduce the power consumption of the battery while the vehicle is running, and furthermore, it is possible to detect disconnection of the solenoid in the solenoid valve while the vehicle is running.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram schematically showing an example of a four-wheel steering system for a vehicle according to the present invention, and FIG. 2 is an illustration of a fail-safe solenoid valve used in the example shown in FIG. FIG. 3 is a diagram used to explain the current supplied from the battery to the solenoid shown in FIG. 2, and FIGS. FIG. 2 is a plan view and a rear view schematically showing the configuration of a variable steering ratio mechanism. In the figure, 2L and 2R are front wheels, 5 is a front wheel steering mechanism, 11 is a rear wheel steering mechanism, 12L and 12R are rear wheels, 26 is a spool valve, 32 is a hydraulic pump, 34 is a bypass oil passage, 3
6a and 36b are fail-safe solenoid valves, 40 is a variable steering ratio mechanism, 62 is a control unit, 66 and 67 are vehicle speed sensors, 68 is an engine rotation speed sensor, 7
0 is a clutch sensor, and 72 is a transmission sensor. Figure 2

Claims (1)

[Claims] It has a front wheel steering mechanism that steers the front wheels in response to a steering operation in the vehicle, and a rear wheel steering cylinder, and fluid is supplied to the rear wheel steering cylinder in response to the steering of the front wheels, thereby steering the rear wheels. a rear wheel steering mechanism that steers the rear wheel steering mechanism; a pump means that pumps fluid to the rear wheel steering cylinder; and a pressure passage that communicates the rear wheel steering cylinder and the pump means; Selecting a first state in which the fluid pumped by the pump means is supplied to the rear wheel steering cylinder, and a second state in which supply of the fluid pumped by the pump means to the rear wheel steering cylinder is prohibited. By intermittently energizing the solenoid valve, the solenoid valve assumes the first state, and by stopping the energization to the solenoid valve, the solenoid valve assumes the second state. A four-wheel steering device for a vehicle, comprising: valve control means for changing the state.