JPH03159876A - Rear wheel steering device of four-wheel steered car - Google Patents

Abstract

PURPOSE:To enhance the steering characteristics and the safety by installing a rear-wheel neutrality locking mechanism, which is disengaged by supply of pressure oil, in a part of a rear-wheel steering side link mechanism including a hydraulic power cylinder. CONSTITUTION:A rear-wheel steering device 10 is equipped with a hydraulic power cylinder 3 as a steering link mechanism 1 for steering of the rear wheels, and thereby steering displacement information on the front wheel side is transmitted to the rear-wheel steering drive system in the form of hydraulic signals. On the other hand, the steering displacement on the rear wheel side (rod moving amount of power cylinder 3) is fed back to a control valve 12 for rear-wheel steering via a tension cable 4. In a part of the steering link mechanism 1, a rear-wheel neutrality locking mechanism 60 is installed, which restrains motions of the power cylinder 3, locks the rear wheels in the neutral position, and is disengaged by supply of pressure oil. A proprietary motor pump 80 is used as oil pressure source to this locking mechanism 60.

Description

[Detailed Description of the Invention] [Field of Application for Industry L] The present invention is particularly suitable for obtaining tight turning ability at low speeds by steering the rear wheels in the opposite direction in conjunction with the front wheels by steering operation. This invention relates to an improvement of a rear wheel steering device for a four-wheel steering vehicle.

[Conventional technology]

In recent years, turning the rear wheels in the opposite direction or the same direction according to the amount of steering (steering amount) of the front wheels can improve turning ability at low speeds and driving stability at medium and high speeds. Four-wheel steering vehicles are attracting attention.

For example, when driving at low speeds, the front wheels are steered with a large steering angle. At this time, the front and rear wheels are steered in opposite phases (reverse direction steering) to minimize the vehicle's turning radius and improve turning performance. It is particularly suitable for application to long vehicles such as trucks.

Rear wheel steering devices for this type of four-wheel steering vehicle are disclosed, for example, in Japanese Patent Application Laid-open Nos. 59-128054 and 1989-128054;
1-143769 Publication, Utility Model Eft-53271
Various types of hydraulic devices have been proposed in the past, including hydraulic devices disclosed in Japanese Patent Application Laid-Open No. 81-87885. especially,
In a hydraulic system, the rear wheels are steered in the desired direction by selectively supplying oil T1 controlled to a predetermined pressure by a servo valve, etc. to the left and right chambers of the hydraulic cylinders used to steer the rear wheels. It can be steered, and compared to mechanical devices that mechanically connect the front and rear wheels with a connecting shaft, it has operational and structural advantages such as a large lh degree. It was something.

[Problem to be solved by the invention]

However, the conventional device described above still has advantages and disadvantages in terms of both structure and operational performance, and there is still room for improvement for practical use. For example, this type of rear wheel steering device requires the minimum number of structural parts, improves the workability and assembly of each part, reduces manufacturing costs, and improves the efficiency of hydraulic piping and electrical wiring. Can be placed,
Furthermore, various drive controls can be performed easily and appropriately, and there are sufficient measures to ensure that the rear wheels are locked in a state where steering is not possible during medium or high speed driving or in the event of a failure of the hydraulic system or electrical system. desired.

In particular, what is needed in response to these demands is that the rear wheels can be appropriately steered in conjunction with the front wheel steering operation, which is difficult to steer when driving at low speeds, and that There is a rear wheel steering control system structure that ensures safety during high-speed running and during failures, and it is desirable to take these points into consideration and take some measures that can satisfy the above-mentioned requirements.

[Means to solve the problem]

In order to meet such demands, the rear wheel steering device for a four-wheel steering vehicle according to the present invention selects a hydraulic pressure source from the rear wheel side via a rear wheel steering control valve depending on the vehicle speed and the amount of steering displacement on the front wheel side. A power cylinder for rear wheel steering controls the steering of the rear wheel side steering link mechanism using pressure oil supplied to the rear wheel, and a power cylinder attached to the - part of the link mechanism that normally locks the rear wheels in a neutral position and uses pressure oil to control the rear wheel steering link mechanism. The rear wheel lock mechanism is equipped with a rear wheel neutral position locking mechanism that is unlocked by supplying water to enable steering of the rear wheels, and selectively supplies pressure to this locking mechanism depending on various vehicle running conditions. It is equipped with a hydraulic power source.

[Effect]

According to the present invention, the hydraulic pressure source for locking the rear wheels is driven during low-speed driving, and the locked state of the rear wheels in the neutral position is released by the supply of pressure oil. It is possible to control the rear wheels in the required state according to the rudder operation, and the hydraulic power source for the rear wheels is stopped during medium or high speed driving or in the event of a failure of the hydraulic system or electric system. As a result, the rear wheels can be properly and reliably locked in the neutral position by the opening/link mechanism, and the rear wheel steering control system can be rendered inactive.

〔Example〕

Figures 1 to 7 show an embodiment of the rear wheel steering device for a four-wheel steering vehicle according to the present invention. The link mechanism (only the rear wheel side is indicated by code 1) is equipped with an oil power cylinder 2,
3, and only the front wheel steering displacement information is transmitted as a hydraulic signal to the rear wheel steering drive system, and the rear wheel steering displacement (power cylinder 3 rod movement motor) is controlled by a tension cable. 4, the rear wheel steering position 10 is also equipped with a feedback signal system 5 that feeds back to the control system (rear wheel steering control pulse 12 to be described later).
I will explain about it. Here, 6.7 is an oil pump for supplying oil to the front and rear power cylinders 2 and 3, 8 is an oil tank, and pressure oil from the front wheel pump 6 is transferred to the front wheel side through hydraulic piping 6a. A well-known front wheel side power steering device is configured in which the oil is guided to the power cylinder 2 and returned to the oil tank 8 through the return pipe 6b. 9 is an on-vehicle battery, and in FIG. 1, hydraulic piping is shown as a double line, and electrical wiring is shown as a solid line. In this embodiment, the oil pumps 6 and 7 are dual pumps driven simultaneously by an automobile engine (not shown); however, the present invention is not limited to this, and the front and rear wheels may be configured with independent hydraulic systems. Any pump that can be used will suffice.

Further, as shown in FIGS. 1 and 5, the rear wheel steering device 10 in this embodiment is a rear wheel steering device that transmits steering displacement information on the front wheel side to the rear wheel side with a required amount of play. The threat position transmission mechanism 1l and the displacement amount transmitted by this transmission mechanism 11 with a certain play stroke are used to switch and control the extraction passage from the oil pump 7, which is the rear wheel side hydraulic pressure source, to control the rear wheel steering power steering I'nd 3. The rear wheel steering control hub 12 is operated as appropriate.

Here, the displacement transmission mechanism l1 for rear wheel steering will be briefly explained with reference to FIGS. (
The human power shaft 21 is connected to the input shaft 20 (which may be a part of the steering system such as the steering handle 2a) to transmit power, and 21 is an output shaft which is disposed in rotation with the input shaft 20 and serves as a positioning shaft. Then, the human power shaft 20 has a lever inside the casing 13.
A cylindrical member l4, which is held in a single rotation nf capacity and supported in a rotational movement D (d) relative to the output vehicle 21J-, is connected in the rotational direction by spline connection.

As shown in the sixth factor, a cutout groove 22 is formed in a part of this cylindrical member l4 at L7 such that the groove width has a predetermined transmission play stroke QC. In addition, in order to form the 9J notch groove 22, the cylindrical member 14 is divided into parts and integrated by screws or the like as shown at 14A and 14B in FIG. 14, the dimensions of each part are set so that it does not move in the axial direction within the casing l3.

Reference numeral 23 denotes an engaging stage F, which is provided on the output shaft 21-H so as to be inserted into the notched groove 22 described above, and whose portion in contact with the side edge of the groove consists of a sleeve 23b fitted into a spherical bearing 23a. A predetermined amount of play is provided until the engagement means 23 comes into contact with the side edge of the notched groove zz of the cylindrical member l4. Therefore, when the cylindrical member 14 is rotated concavely within the casing 13 by the manual shaft 20, the input shaft 20 side remains until the groove side edge comes into contact with the engagement means 23 facing the notch groove 22. The rotation on the input shaft 20 side is then transmitted to the output shaft 2l side, and as a result, the rear wheel steering angle relative to the front wheel steering angle becomes as shown in the characteristic curve shown in Fig. 7. Change. And according to this structure,
With a simple structure, the rear wheel steering angle can be controlled to a desired state, and the vehicle can function as a four-wheel steered vehicle. Further, in the above-described structure, the displacement 11 by a person or the output shaft 20.
A cylindrical member l4 that responds to the vehicle speed is provided on the shaft 7, and a mechanism is provided between the cylindrical member 14 and the output shaft 21 to connect the driver with a predetermined play, making it easy to take out displacement. It has a simple structure and is easy to incorporate into a vehicle.

Further, to explain the schematic structure of the rear wheel steering device ♂tlO illustrated in this embodiment using FIG. 1, FIG. In the rear wheel steering control mechanism unit 1, in which the rear wheel steering control valve 12 for switching the hydraulic circuit to the side power cylinder 3 is arranged in parallel on the displacement extraction sleeve (20.21),; Ij + control valve l2 is , an output shaft 2l, a feedback shaft 32 connected to the output shaft 2l through a torsion bar 31 so as to be relatively rotationally displaceable, a sleeve portion 21a provided at the shaft end, and a rotor 33. The structure and operation of this valve 2 are well known, and it switches the oil passage between the pump 7 (P) and the tank 8 (T) and the rear wheel cylinder chambers CI and C2.

Further, 34 is a coil spring which is wound around the shaft 1- in a state in which the engagement pins 34a and 34b protruding from the output shaft 21 and the valve body 35 are sandwiched in the space on the left side of the cylindrical member l4 in the casing 13; A centering spring mechanism 36 is provided that always rotates the control valve l2 back to the absolute position (neutral position). Furthermore, the other end of the tension cable 4 of the feedback signal system 5, one end of which is connected to the arm 5a provided on a part of the rear wheel link mechanism 1, is connected to the other end of the tension cable 37 to determine the actual position of the rear wheel. Displacement take-out shaft (20
．． 21) is provided on a sleeve 37a which is movably mounted on the feedback shaft 32 disposed on the same axis L as the sleeve 37a and the feedback shaft 3.
A well-known magnetic clutch 38 is provided between the two members and is configured to selectively connect these two members.

This means that the control system is always controlled by the feedback signal system! /
J#I, By connecting when a change is necessary, a feedback signal transmission system that can always adjust the deviation between the rear wheel side and the control pulse l2 and absorb suspension movement is obtained. In addition, 37b in FIG. 1 is a spring for absorbing backlash that biases the lever 37 to a certain position.

In addition, in the wooden embodiment, this mechanism unit 30 includes:
Cylindrical member 1 constituting rear wheel steering displacement transmission control mechanism 11
4. The centering spring mechanism 36, the rotary rear wheel steering control valve l2, and the electromagnetic clutch 38 are coaxially arranged together with the feedback shaft 32 of the feedback signal system 5 as a displacement extraction shaft, and the output shaft 20, 2
1. This structure simplifies the overall configuration and improves the ease of assembling the mechanical unit 30.

In addition, 40 in FIG. 5 is a flange member that is provided on the input shaft 20h and rotates together with the cylindrical member l4, and a part of the outer periphery of the flange member is provided with a flange member having different lengths in the circumferential direction and at predetermined intervals in the circumferential direction. The first and second engaging portions 41 and 42 formed in
(only the T shown) is provided, and first and second rear wheels are mechanically engaged and disengaged from each of these engaging portions 41 and 42 by front wheel steering input to the input shaft 20. Wheel rotation 1l rudder start point detection switches 43, 44 (only one shown) are provided, and these detection switches 43. 44 controls the rear wheel steering control system to enable rear wheel steering at steering angles QA and QB (see FIG. 7), which will be described later. In other words, this type of rear wheel steering device 10 has a vehicle speed of 2.
It is preferable to activate it only when driving at a low speed of 0 km/h or less and when the steering wheel 2a is steered, and desirably keep it inactive at other times.

1. In order to perform hydraulic control of the rudder and rear wheel steering, it is desirable to put the hydraulic system and the electrical system that controls it in advance in a standby state that allows rear wheel steering, and for this purpose the timing is shifted. Two mechanical detection switches 43.44
is provided at a position where the front wheel steering state can be activated prior to rear wheel steering.

Moreover, in this embodiment, -F:. In the above-mentioned rear wheel steering control system, as shown in FIGS. A bypass passage 50a is provided from the upstream hydraulic passage of the control valve 12 to the pressure oil return passage side, and the device is designed so that the passage is always open and the passage is in a leap state when energized. An electromagnetic emergency valve 50 connected to an electric control circuit is provided, and a manual switch 51 is provided to cut off power to the emergency valve 50.
An ignition key switch 52 is provided in series in the electrical control circuit. According to this structure, the rear wheels can be steered in the required state at all times depending on the vehicle speed and the steering operation of the front wheels, and the rear wheels can also be controlled in the event of a failure in the electrical system or at the driver's request. The system can be put into a non-operating state. In other words, in the hydraulic circuit system mentioned above, in order to prevent malfunctions caused by the rear wheels being steered or the steered state being maintained when the hydraulic system or electrical system fails, the rear wheels are It is necessary to keep the supply side hydraulic piping and the return side piping of the pump 7 in communication at all times, and to maintain a state in which hydraulic pressure cannot be supplied to the rear wheel steering system.

In addition, there are requests from constructors and others to actively maintain two-wheel steering due to 13 vehicle running conditions, and it is necessary to address this.

Further, according to this embodiment, a vehicle speed control bypass valve 55 is arranged in parallel with the emergency valve 50 to selectively open and close the supply side and the return side in the hydraulic circuit system from the rear wheel side pump 7. The vehicle speed is 20km/
It is arranged so that no pressure oil is supplied to the rear wheel steering system when the condition is H or higher.

Here, 56 is attached to a speedometer etc. and the vehicle speed is 20.
Km/bl; turned off when J is 20Km/h
This is a vehicle speed switch that is turned on when: Further, 57 is a cable breakage switch that is connected in series to the vehicle speed switch 56 and is used to disable the rear wheel steering system when a breakage occurs in the cable 4 constituting the feedback signal system 5. An electromagnetic clutch 38 is connected in series with the vehicle speed control bypass valve 55 and in parallel with the vehicle speed control bypass valve 55 .

By the way, in configuring the above-mentioned rear wheel steering system NIO, it is desirable to ensure straight-line 14-wheel drive performance at high speeds and running stability on low-friction roads such as snowy roads, and when necessary, It is desirable to set the rear wheel steering system to the operating 0T1@ state and lock it when not needed to ensure the two-wheel steering state. Furthermore, one of the problems with installing the rear wheel steering stirrup mentioned above is,
There may be a loss of driving force due to a failure in the rear wheel steering drive system or a failure in the command transmission system of the rear wheel steering control system, and when such a situation occurs, the rear wheels must be locked in a neutral state. , two-wheel steering is also required.

Now, according to the present invention, in order to satisfy the above-mentioned requirements, in the rear wheel steering control system, a part of the rear wheel side steering link mechanism l always restrains the movement of the power cylinder 3, It is equipped with a rear wheel middle position locking mechanism 60 that maintains the rear wheel in a locked state in a neutral position and releases the lock by supplying oil to enable the rear wheels to be steered. A special feature is that a dedicated motor pump 80 is provided as a hydraulic pressure source for locking the rear wheels, which supplies pressure oil according to conditions.

E5 Here, this motor pump 80 proportionally controls the supply flow rate of pressure oil from an oil reservoir section 80b having a built-in pump section with a motor section 80a that is driven according to each persimmon running condition such as tonne speed. It is constructed as a hydraulic power source that can supply
According to the present invention, the motor pump 80, which is such an independent hydraulic power source, is connected to the rear wheel neutral position locking mechanism 60 described above.
By using it as a source of oil supply to the vehicle, it is possible to always provide a stable supply of oil, improve the reliability and performance of the lock mechanism 60 in operation-1, and also improve the reliability and performance of the lock mechanism 60 when the vehicle speed is 2.
When the speed is over 0K+*/h or when the vehicle is not being steered,
This has the advantage that the motor pump 80 can be stopped 11- to reduce unnecessary energy consumption and achieve energy savings. In particular, the rear wheel side hydraulic power source 7 is also used as the hydraulic power source for this type of rear wheel A″f locking mechanism 60,
Divided from a part of the supply path via a flow divider,
It is generally considered that pressure oil is introduced into the rear wheel steering control valve 12. The amount of pressure oil supplied to the power cylinder 3 on the rear wheel side tends to become unstable16, which poses a problem in ensuring stable steering control of the rear wheels.In contrast, the configuration according to the present invention solves this problem. This can eliminate major problems.

Here, from the motor pump 80 described above to the lock mechanism 60,
On the way to the pressure oil supply path, there is an unloading valve 63 that holds the pressure oil supply acid at a constant level, an accumulator 64 that corrects the pressure extraction on the downstream side, and an electric signal on the downstream side of the unloading valve 63. An electromagnetic rear wheel position lock control valve 62 is provided which maintains the monthly supply to the lock mechanism 60 and connects the lock mechanism 60 to the pressure oil return side by means of another electric signal. Note that the motor pump 80 is connected to a vehicle speed sensor l.
The battery 9 obtained by calculating and amplifying the signal from 6 using the signal controller 17a and the power controller 17b
With the electric current from the pump, the rotation is selectively controlled only when the vehicle speed is 20 km/h or less, and the required pressure oil supply flow rate is supplied. Further, as can be seen from FIG. 1, the hydraulic pressure from the motor pump 80 to the locking mechanism 60 is configured to be returned to the oil reservoir section 80b through a flow path.

Furthermore, since the power consumption of the motor bomb 80 and other electrical equipment is different, as is clear from the electrical control circuit shown in FIG. 54 is used as a separate circuit, and is configured to be driven by a signal from the signal controller 17a via the power controller 17b. In addition, 81 in the figure is a manual switch used when turning off the motor pump 80 manually and performing only two-wheel steering.

Here, as is clear from FIG. 2, the unloading valve 63 provided in the middle of the hydraulic flow path to the locking mechanism 60 described above is connected to a spool valve 63a that selectively connects the flow path to the tank side and a pressure sensing valve. Consisting of 63b,
When this pressure sensing valve 63b operates, it operates the spool valve 63a and partially returns the flow to the tank, thereby maintaining the supply amount of pressure oil at a constant level18. Detailed explanation will be omitted. Further, as shown in FIG. 1 and the like, this long mechanism 60 is provided with a rear wheel neutral position lock operation detection switch 61 for detecting the operating state. Furthermore, 70 in the figure is a hydraulic defect countermeasure check valve that is installed in the hydraulic pressure supply passage to the rear wheel power cylinder 3 and is used to restore the rotation to the neutral position when the rear wheels are operating in the event of a hydraulic system failure. Although it has the structure shown in the figures and FIG. 4, its explanation will be omitted here.

Further, the rear wheel neutral position locking mechanism 60 described in I-
As is clear from the figure, normally, the biasing force of the spring 66 causes the row pin 67 to engage with the engagement hole 68a formed in a part of the tie rod 68 that depicts the side 1 of the rear steering link machine. The lock pin 67 is restrained by the pressure drawing and the lock pin 67 is pulled out to release the lock. Note that this lock pin 67 is shown as a tapered pin, and by doing so, the pin can be easily taken in and taken out.

l 9 According to this configuration, when driving at low speeds, the rear wheels can be steered in the required state depending on the vehicle speed and the steering operation of the front wheels, and when driving at medium or high speeds, failures in the pressure system, electrical system, etc. can be avoided. At times, the rear wheels can be appropriately and reliably locked in the middle \1 position, and the rear wheel steering control system can be rendered inactive. That is, in order to operate the rear wheel steering system using the various electromagnetic valves and electrical switches described above, the rear wheel turning start point detection switch 43, 44 and the rear wheel middle 7 position lock operation detection switch 6l are combined. This constitutes a control system, which allows rear wheel steering control to be performed in a desired manner. To explain this simply, the engine is started with the ignition switch 52, and the F1 oil is sent to the front and rear wheel steering systems by the pump 6.7. Since the vehicle speed control bypass valve 55 is in the OFF state, the pressure oil on the rear wheel side is returned to the tank 8 side through the vehicle speed control bypass valve 55.

On the other hand, the motor pump 80 is also driven when running at low speed, and its pressure peak passes through the loading vane lever 63 and is in the off state between the neutral position lock control lever 20 and the lever 62. Pressure is accumulated in this area, increasing the oil pressure in this area.

In this state, when a steering operation is performed using the steering wheel 2a, the front wheels are steered and the input shaft 20
rotates, and at a predetermined rotation angle (QA in Figure 7), switch 4 is turned.
3 (SW-A) is turned on, the vehicle connection control bypass valve 55 is activated, the short circuit to the tank is cut off, the discharged oil is guided to the control valve l2, and the electromagnetic clutch 38 is turned on. be done. Furthermore, the number of handle rotation stitches increases compared to the concave rotation angle QA mentioned in -I2, and the predetermined angle QB
When the steering operation is performed up to the point, the switch 4 4 (SW-8) is turned on, while the neutral position lock control valve 62 is also opened, and when the high If is guided to the neutral position locking mechanism 60, the lock pin 67 is pulled out. , the rear wheels are on standby in a state where they can be steered. When the steering wheel is steered beyond the above-mentioned four-turn angle QB and beyond the stroke QC defined by the notch groove 22 in the control mechanism 11, it can be seen from FIGS. 6 and 7, etc. As is clear, the output shaft 21, which is the input side of the control valve 12, is rotated, and the valve 12 is thereby actuated, leading pressure oil to either the left or right chamber of the rear wheel power cylinder 3, thereby driving the rear wheel. While the steering is being carried out, the amount of steering is fed back from the feedback shaft 32 of the control valve l2 by the feedback signal system 5 using the tension cable 4, and is controlled to a desired operating state.

Further, when the vehicle speed becomes 20 km/h or higher, the vehicle speed switch 56 is turned off, the vehicle speed control bypass valve 55 is turned off, a flow path is formed to the tank, and the electromagnetic clutch 38 etc. are also turned off. Furthermore, motor pump 8
0 is also turned off, and the supply of pressure oil to the lock mechanism 60 is stopped.

Furthermore, if any abnormal condition occurs while driving or the electrical system or hydraulic system malfunctions, the emergency valve 50 or manual switch 51 . 81 or the like, it is preferable to put the rear wheels in a non-steered state.

By connecting switches SW-A and SW-C in parallel, even if SW-A is turned off, the rear wheel steering system remains active as long as the rear wheels are not locked in the neutral position.9 9 Four-wheel steering It is now possible to maintain the running tr in the current state.

It should be noted that the present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each part of the rear wheel steering device 10 may be modified and modified as appropriate, and various modifications may be made.

〔Effect of the invention〕

As explained above, according to the rear wheel steering device for a four-wheel steered vehicle according to the present invention, the control valve controls the amount of water from the rear wheel side hydraulic pressure source via the rear wheel steering control valve depending on the vehicle speed and the amount of steering displacement on the front wheel side. A rear wheel steering power cylinder that controls the steering of the rear wheel side steering link mechanism by selectively supplied pressure extraction, and a B4r attached to a part of the link mechanism that normally locks the rear wheels at the middle 17 position. It is also equipped with a rear wheel neutral position locking mechanism that is released by the supply of hydraulic pressure and puts the rear wheels in a state where the rear wheels cannot be steered. Since a rear wheel lock pressure source is provided, the rear wheels can be rotated in the required state according to the vehicle speed and front wheel steering action when driving at low speeds, even though it is a simple and inexpensive structure. In addition to improving maneuverability such as small turning ability, the system also properly and reliably locks the rear wheels in the neutral position during medium or high-speed driving or in the event of failures in the hydraulic system, electrical system, etc., and controls the rear wheel steering control system. It has various excellent effects in practical use, such as being able to be placed in a non-operating state.

In particular, according to the present invention, the hydraulic pressure source for the locking mechanism for locking the rear wheels in the neutral position is configured independently from the rear wheel hydraulic pressure source for the rear wheel power cylinders. Steering control on the wheel side and locking of the rear wheel in a neutral position using a locking mechanism can be performed using a stable supply of pressurized oil, eliminating unnecessary energy consumption, excellent responsiveness, and ensuring reliability in the operation L of each part. There are advantages such as being able to align the

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of the entire device showing an embodiment of the rear wheel steering device for a four-wheel steered vehicle according to the invention, Fig. 2 is a hydraulic circuit diagram of its main parts, and Fig. 3 is its electrical The circuit diagram, Fig. 4 is a schematic sectional view of the power cylinder for rear wheel steering, the steering link mechanism for the rear wheel steering 24 that locks the rear wheel center and position locking mechanism, and Fig. 5 shows the control mechanism unit for rear wheel steering. Main part cross section IA, FIG. 6 is a schematic perspective view illustrating a configuration for obtaining a displacement free stroke, and FIG. 7 is a characteristic diagram showing the relationship between front and rear wheel turning angles. 1... Rear wheel side steering mechanism, 2.3... Front, power cylinder for rear wheel steering, 6.7... Front, rear wheel side oil pump, 10... Rear wheel steering device, 1l...
...Displacement transmission mechanism for rear wheel steering, l2...Control valve for rear wheel steering, l6...Vehicle speed sensor, 20.21...
・・Person, output shaft, 30・・・・Control mechanism unit for rear wheel steering. 31...1...Shonha-, 32...
Feedback axis, 50...Emergency valve ("f1L magnetic opening/closing square), 51...Manual switch,
H, 60... Rear wheel middle and position lock mechanism, 6l...
・Rear wheel neutral position lock operation detection switch, 62...
Rear wheel middle position lock control valve, 63...Unloading valve, 64...Accumulator, 67
... Lock pin, 68 ... Tie rod, 70.
... Hydraulic pressure failure prevention check valve, 80 ... Motor pump (hydraulic source) 81 ... Manual switch. Masaki Yamakawa, 26, Agent of Isudo Jidosha Co., Ltd.

Claims (1)

[Claims] The rear wheel steering link mechanism is steered by pressurized oil that is selectively supplied from the rear wheel hydraulic power source through a rear wheel steering control valve that is activated according to the vehicle speed and the amount of steering displacement on the front wheels. A rear wheel steering power cylinder is installed in a part of the rear wheel steering link mechanism to normally maintain the rear wheels locked in the neutral position, and is unlocked by supply of pressure oil to rotate the rear wheels. The vehicle is equipped with a rear wheel neutral position locking mechanism for enabling steering, and is characterized by being provided with a rear wheel locking hydraulic source that selectively supplies pressurized oil to this locking mechanism according to various running conditions of the vehicle. Rear wheel steering device for four-wheel steering vehicles.