JPH02293267A - Rear-wheel steering gear for four-wheel steering vehicle - Google Patents

Abstract

PURPOSE:To improve a small sharp turning property in a simple structure by installing a rear-wheel steering control valve as a rotary valve in a gap with a feedback shaft out of a rear-wheel side steering link mechanism on the output shaft of a displacement take-off shaft. CONSTITUTION:Pressure oil being controlled with its supply according to a car speed is fed to a cylinder 12 constituting a rear-wheel steering displacement transfer control mechanism 14, and it is made to flow back via a fixed restrictor 13a of a piston 13, thereby determining a moving position of the piston 13 through size of a flow rate. In this piston 13, an input shaft 20 of front-wheel steering displacement information is coupled through a spline free of movement, and a notch groove 22 making a transfer play stroke variable is provided at the other end, and it is engaged with an engaging means 23 of an output shaft 21 with a play stroke conformed to a position of the piston 13 and transmitted to a rotary control valve 15, while it is fed back from a feedback shaft 32 via a torsion bar, steering rear wheels via a power cylinder. Thus, constitution is simplifiable and, what is more, a small sharp turning property is improved in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is suitable for use in 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 paper relates to improvements to rear wheel steering devices for four-wheel steering vehicles. [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 has been developed to improve the ability to turn around at low speeds, and to improve turning ability during medium and high speed driving. Four-wheel steering vehicles that can improve driving stability are attracting attention. For example, when driving at low speeds, the front wheels are steered with a large steering angle. At this time, by setting the steering directions of the front and rear wheels in opposite phases (reverse direction steering), the vehicle's turning radius is minimized and the turning (small turning) performance is improved. It is particularly suitable for application to long-length vehicles such as trucks. As a rear wheel steering device for this type of four-wheel steering vehicle, for example, Japanese Patent Laid-Open No. 59
- Publication No. 128054, JP-A-59-14376t
Publication No. e, Publication of Utility Model Publication No. 81-53271, Japanese Patent Application Publication No. 1987-61
-Including hydraulic devices shown in Publication No. 878flS, etc.
Various proposals have been made to date. Especially in hydraulic equipment,
By selectively supplying hydraulic pressure controlled to a predetermined pressure using a servo valve, etc. to the left and right chambers of the hydraulic cylinders used to steer the rear wheels, the rear wheels can be steered in the desired direction. Compared to a mechanical device in which the front and rear wheels are mechanically connected by a connecting shaft, it had the advantage of a greater degree of freedom in terms of movement and structure. [Problems to be solved by the invention] However, the conventional device described above still has advantages and disadvantages in terms of both structure and operability, and there is still room for improvement in terms of practical use. For example, this type of rear wheel steering system requires the minimum number of component parts, unitizes each part to improve workability and assembly, and reduces manufacturing costs.In addition, hydraulic piping and electrical It is desired that wiring, etc., can be arranged efficiently and in alignment, that various drive controls can be performed easily and appropriately, and that there are sufficient measures against failures. What is needed in response to these demands is a control system structure that can appropriately steer the rear wheels in conjunction with the front wheel steering operation accompanying the steering operation. In other words, when the rear wheels are steered in conjunction with the steering operation of the front wheels, the starting point of the rear wheel steering operation and its maximum steering angle are adjusted and controlled depending on the vehicle speed, and the steering is controlled from the front wheel side to the rear wheel side. It is desirable to have a configuration that allows transmission of steering requests with some play, and that allows efficient transmission of steering information to the rear wheel steering control valve.
Considering these points, it is necessary to take some measures that can satisfy the above-mentioned requirements. [Means for Solving the Problems] In order to meet such demands, the rear wheel steering device for a four-wheel steered vehicle according to the present invention uses a piston that moves within a cylinder using a hydraulic signal that is proportionally controlled according to the vehicle speed. A displacement transmission control mechanism for rear wheel steering that transmits the amount of steering displacement on the front wheel side to the rear wheel side with variable play according to the piston movement position; and an input shaft that is rotated by the steering operation on the front wheel side. The power cylinder for rear wheel steering controls switching of the hydraulic passage from the rear wheel hydraulic power source according to the amount of displacement obtained by the displacement output shaft arranged coaxially with this and the displacement transmission control mechanism. The control valve is provided as a rotary valve on the output shaft of the displacement take-out shaft and between the feedback shaft from the rear wheel side steering link mechanism. be. [Operation] According to the present invention, by moving the piston within the cylinder using a hydraulic signal controlled according to the vehicle speed, the groove side of the engagement means on the output shaft side facing the notch groove formed in the piston is moved. A rotary valve for rear wheel steering that can obtain a rotation range up to the edge as variable play and is provided between the output shaft and a feedback shaft coaxially connected to the feedback shaft so as to be rotatable. The control valve allows steering control of the rear wheels according to the steering displacement information of the front wheels. (Embodiment) FIGS. 1 to 10 show an embodiment of a rear wheel steering device for a four-wheel steering vehicle according to the present invention. In this embodiment, as shown in FIG. The steering link mechanism for wheel steering (only the rear wheel side is indicated by the symbol l, and the front wheel side is not shown) is independently driven by hydraulic power cylinders 2 and 3, and steering displacement information on the front wheel side is provided. This signal is sent to the rear wheel steering drive system as a hydraulic signal, and the rear wheel steering displacement (the amount of rod movement of the power cylinder 3) is controlled by the tension cable 4 (Mw valve 15 for rear wheel steering, which will be described later).
) A rear wheel steering device 10 having a configuration that is also equipped with a signal system 5 that provides feedback to the vehicle will be described. Here, 6
, 7 is an oil bomb for supplying pressure oil to the front and rear wheel side power cylinders 2 and 3, 8 is an oil tank, and the pressure oil from the front wheel side bomb 6 is guided to the front wheel side power cylinder 2 through a hydraulic pipe 6a. A well-known front wheel side power steering device is constructed in which the oil is returned to the oil tank 8 through a return pipe 6b. 9 is an on-vehicle battery, and in FIG. 9, hydraulic piping is shown as a double line, and electrical wiring is shown as a single solid line. In this embodiment, the oil pumps 6 and 7 are dual pumps that are simultaneously driven by an automobile engine (not shown); however, the present invention is not limited to this, and the oil pumps 6 and 7 may be oil pumps in which the front and rear wheels are configured with independent hydraulic systems. It may be. Further, as shown in FIGS. 8(a) and 9, the rear wheel steering device 10 in this embodiment has a motor l driven according to the vehicle speed.
At la, there is a motor pump 1l as a hydraulic power source that can proportionally control the supply flow rate of pressure oil by a pump mechanism in the oil reservoir 1lb, and a motor pump 11 on the discharge side (MP
), one chamber 12a (left chamber in FIG. 1) is connected to the cylinder 1, and the other chamber 12b (right chamber in FIG. 1) is connected to the pressure oil return side (MT) of the motor pump 11.
A piston 13 having a fixed throttle 13a that communicates between the cylinder side chambers 12a and 12b is movably supported in the cylinder l2, and steering displacement information on the front wheel side is transmitted according to the movement position of the piston 13 in the cylinder l2. A displacement transmission control mechanism 14 for rear wheel steering selectively transmits data to the rear wheels with a required variable play, and hydraulic pressure from an oil pump 7, which is a rear wheel hydraulic pressure source, according to the amount of displacement obtained by this control mechanism 14. It is provided with a rear wheel steering control valve 15 that performs passage switching control and operates the rear wheel steering power steering 3 as appropriate. Here, the motor bomb l1 is a current from the battery 9 obtained by calculating and amplifying the signal from the vehicle speed sensor l6 by the signal controller 17a and the power controller 17b, and is selectively activated only when the vehicle speed is 20K or less. It is configured to be driven and controlled to supply the required pressure oil supply flow rate. As the proportional flow rate supply means using the motor bomb 11 and the like mentioned above, as shown in FIG. 8(b), an electromagnetic proportional flow control valve l8 having a variable throttle 18a that is opened and closed by a controller according to a signal from a vehicle speed sensor l6 is used. In this case, the front wheel side pump 6
(The rear wheel side bomb 7 may also be used) A control valve l
It is recommended to connect to 8. With such a configuration, 4f, the pressure oil whose supply amount is controlled according to the vehicle speed is supplied to one of the cylinder side chambers 12a and 12b constituting the rear wheel steering displacement transmission control mechanism 14, and the pressure oil is supplied to the piston 13. By returning the pressure oil to the return side via the other chamber side using the fixed throttle 13a provided, the amount of movement of the piston 13 is selected depending on whether the flow rate is large or small, and from the front wheel side according to the movement position of the piston l3. Transmission of steering information to the rear wheels can be performed with the required play stroke. That is, the rear wheel displacement transmission control mechanism 14 described above is shown in FIGS. 1 and 2(a). To explain in detail using (b) etc., 20
2l is an input shaft to which steering displacement information on the front wheel side is transmitted by being connected to the output shaft of the front wheel side power cylinder 2 (which may be part of the steering system by the steering handle 2a), etc., and 2l is this input shaft. The output shaft is arranged coaxially with 20, and this constitutes a displacement take-out shaft. And, on the input shaft 20,
The piston 13 is connected in the rotational direction and supported movably only in the axial direction by the spline connection, and a part of the piston 13 is provided with a spline connection in the axial direction as shown in FIGS. A notched groove 22 is formed in which the groove width gradually widens and opens toward one end, allowing the transmission play stroke to be varied. In order to form the notched groove 22, the piston 13 is divided into two parts as shown at 13A and 13B in the figure, and then integrated with screws. 23 is provided on the output shaft 2l so as to be inserted into the above-mentioned notched groove 22, and the part in contact with the side edge of the groove is fitted into the spherical bearing 23a so that an engaged state by appropriate line contact is obtained. the second sleeve 23b;
As is clear from Figure (b), the idle stroke until the engagement means 23 comes into contact with the side edge of the groove 22 changes depending on the position of the piston 13. Therefore, the piston l3, which is constantly urged by the spring 24 toward the pump-side chamber 12a in the cylinder 12, is affected by the pressure generated before and after the fixed throttle 13a by increasing or decreasing the flow rate of pressure oil supplied from the motor pump 1l (MP). When it moves in the axial direction by the difference, the input shaft 20 on the front wheel side uses the stroke specified by the movement position as play.
The rotation of Figure 3(a). As is clear from (b), the power is transmitted to the output shaft zl side, and as a result, the rear wheel steering angle relative to the front wheel steering angle changes as shown in the characteristic curve shown in FIG. 4, depending on the vehicle speed. According to such a configuration, the steering angle of the rear wheels can be controlled to a required state according to the vehicle speed with a simple structure, and the function as a four-wheel steering vehicle can be exhibited. In addition, in the configuration described in B, the piston 13 that responds to the vehicle speed is provided on the shaft for taking out the displacement by the output shaft 20, 21, and the piston 13 and the output shaft 21 are connected with a variable play. It is equipped with a mechanism that not only makes it easy to take out the displacement, but also has a simple structure and easy installation into a vehicle because the two functions can be easily achieved by a piston placed on the shaft. It has advantages such as being superior in terms of In addition, in this embodiment, the piston 13 for varying the play stroke described above is
Although the piston 13 is moved depending on the magnitude of the flow rate of the pressure oil, the movement of the piston 13 is obtained by the differential pressure passing through the fixed throttle 13a, so the fluctuation in the flow rate can be small, and the accuracy of the mechanism can be improved. be. Now, according to the present invention, the rear wheel steering control valve 15 is provided as a rotary valve coaxially with the piston 13 constituting the rear wheel steering displacement transmission control mechanism l4 described in E, thereby simplifying the configuration and displacing the displacement. The feature is that it is configured to ensure reliability. Here, the schematic structure of the rear wheel steering device 10 exemplified in this embodiment will be briefly explained using FIG. 1, FIG. 9, etc. This is a rear wheel steering control mechanism unit in which a rear wheel steering control valve 15 for switching the hydraulic circuit to the rear wheel side power cylinder 3 is arranged in parallel with a displacement take-out shaft (20.21) J:, and the control valve l5 is , consists of an output shaft 2l, a sleeve portion 21a provided at the shaft end of a feedback shaft 32 connected to the output shaft 2l via a torsion bar 31 so as to be relatively rotatable, and a rotor 33. The configuration and operation of this valve l5 are well known, and it switches the pressure oil passage between the bomb 7 (P) and tank 8 (T) and the rear wheel cylinder chambers CI and C2.
According to such a configuration, as described above, the members constituting the rear wheel steering system can be made into a unit, and there are also advantages such as being able to improve operational reliability. Further, reference numeral 34 denotes engagement pins 34a, 34 protruding from the output shaft 21 and the valve body 35 within the cylinder left chamber 12a.
A centering ring that always biases the control valve l5 to return to its absolute position (neutral position) using a coil spring (see Figure 5) that serves as a counter-cushion ring and is wound around the shaft with b sandwiched in between. A spring mechanism 36 is configured. Reference numeral 37 denotes a cable connection for feeding back the actual position of the rear wheel, to which the other end of the tension cable 4 of the feedback signal system 5 is connected, one end of which is connected to the arm 5a provided on a part of the rear wheel link mechanism l. The lever is provided on a sleeve 37a that is rotatably mounted on a feedback shaft 32 disposed coaxially with the displacement extraction shaft (20.21) as shown in FIGS. 1 and 7, and
A well-known electromagnetic clutch 38 is provided between the sleeve 37a and the feedback shaft 32, and is configured to selectively connect these two members. This creates a feedback signal transmission system that can constantly adjust the deviation between the rear wheels and the control pulse l5 and absorb suspension motion by separating the rear wheel steering control system from the feedback system at all times and connecting it when necessary. It's for this reason. In addition, 37b
is a spring for absorbing backlash that forces the lever 37 to a certain position. Here, in this embodiment, contrary to a general rotary valve, the sleeve 21a is placed on the input shaft side, and the sleeve 21a is placed on the output side (
The rotor 33 is connected to the feedback side (feedback side), but this is to connect the lever 37 side for connecting the cable 4 to the rotor 33 side, which has small inertia. In the wooden embodiment, the mechanism 22} 30 is a piston 13 that constitutes the displacement transmission control mechanism 14 for steering the rear wheels.
, the centering spring mechanism 36, the rotary rear wheel steering control valve 15, and the electromagnetic clutch 38 are mounted on input and output shafts 20 and 21 coaxially arranged together with the feedback shaft 32 of the feedback signal system 5 as a displacement take-out shaft. This unit configuration simplifies the overall configuration of the device and is superior in terms of ease of assembly with the mechanical unit 30, which has practical advantages. is large. Here, the output shaft 2l, rotor 33, and sleeve 21a connected via the feedback shaft 32 and torsion bar 31 described above are conventionally used as rotary flow path switching valves for front wheel side power steering devices. It is possible to repurpose the parts used, which is advantageous from a practical standpoint. Reference numeral 40 denotes a flange member which is provided on the input shaft 20 in the cylinder 12 and also serves as a spring holder for the coil spring 24 that biases the piston l3. As shown in FIG. First and second rear wheel turning start point detection switches 4 that mechanically detect the state by being selectively engaged and disengaged by front wheel turning input to the shaft 20.
3. 44, and these detection switches 43 and 44 control the rear wheel steering control system so that the rear wheels can be steered. That is, this type of rear wheel steering device 10 has a vehicle speed of 20
It is preferable to activate it only when driving at a low speed of Km/h or less and when the steering wheel 2a is steered, and desirably keep it inactive at other times. However, in order to perform rear wheel steering using hydraulic control, it is desirable to place the hydraulic system and the electrical system that controls it in advance in a standby state in which the rear wheels can be steered, and for this reason, in this embodiment, the timing is shifted. Two actuated mechanical switches are placed in positions that allow the front wheels to be turned before the rear wheels are turned. To explain this simply, as is clear from FIGS. 9 and 10, the hydraulic circuit system that constitutes the rear wheel steering device 1i10 has a mechanism that allows the rear wheels to be steered when the hydraulic system or the electrical system fails. In order to prevent malfunctions caused by steering or the steering state being maintained, the supply side hydraulic piping and the return side hydraulic piping of the rear wheel side pump 6 are always connected, so that the rear wheel rotation is maintained. An electromagnetic emergency valve 50 that maintains a state in which hydraulic pressure cannot be supplied to the steering system side is provided in the middle of the bypass pipe 50a, and when this rear wheel steering system is placed in an energized state, this communication section is cut off and the hydraulic pressure is We are trying to provide supplies. Furthermore, a manual switch 51 is also provided on this energizing circuit to put the rear wheel steering system into the operative state at the request of the driver who wants to actively maintain the two-wheel steering state depending on the driving conditions. ．． In addition, 52 in FIG. 10 is an ignition key switch, and since the power consumption of the motor pump 11 and other electrical equipment is different, the circuit is configured in a separate system with 3OA and IOA fuses 53 and 54 interposed. signal controller 1
It is configured so that it can be driven by a signal from 7a via a power controller 17b. Furthermore, 55 is a vehicle speed control bypass valve 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 pump 7, and is 20K layer 8 or higher. Sometimes it is operated so that no pressure oil is supplied to the rear wheel steering system. In addition, 56 is attached to a speedometer, etc., and is turned off when the vehicle speed is 20K or higher.
This is a vehicle speed switch that is turned on when the vehicle speed is below m/h. 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 or the like occurs in the cable 4 constituting the feedback signal system 5. Furthermore, an electromagnetic clutch 38 is connected in series with these and in parallel with the vehicle speed control bypass valve 55. Reference numeral 60 denotes a rear wheel neutral position locking mechanism provided in the rear wheel side steering link mechanism l to restrict movement on the power cylinder 3 side, and this locking mechanism 60 includes a rear wheel neutral position locking mechanism that detects the operating state. An operation detection switch 6l is attached, and the hydraulic pressure for operating this locking mechanism 60 is led from the middle of the hydraulic piping from the rear wheel side bomb 7 via a flow divider 58, is an electromagnetic rear wheel neutral position that opens and closes the flow of pressure oil using electrical signals! A lock control valve 62 is provided. Here, 63 is an unloading valve provided upstream of the control valve 62 to maintain a constant oil pressure to the lock mechanism 60, and 64 is an accumulator downstream thereof for accumulating pressure oil. ．． Although not shown, the rear wheel neutral position locking mechanism 60 normally uses the biasing force of a spring to move the lock bin to the rear wheel side steering linkage mechanism l.
The movement is restrained by engaging the tie rod, etc. that make up the lock, and the lock pin is pulled out using pressurized oil to release the lock. Further, 65 is a check valve for preventing oil pressure failure, which is installed in the oil pressure supply passage to the rear wheel side power cylinder 3, and is used to restore the rotation to the neutral position when the rear wheels are operated in the event of a failure of the hydraulic system. In order to operate the rear wheel steering system using such various electromagnetic valves and electric switches, the rear wheel turning start point detection switch 43. 44 and a rear wheel neutral position lock operation detection switch 6l,
This allows rear wheel steering control to be performed in the desired state. That is, the engine is started with the ignition switch 52, and the pumps 6 and 7 send pressurized oil to the front and rear wheel steering systems. At this time, the pressure oil divided by the flow divider 58 passes through the unloading valve 63 and is sequentially accumulated in the 7-cumulator 64 between the neutral position lock control valves that are in the OFF state, increasing the oil pressure in this portion. Further, since the vehicle speed control bypass valve 55 is in the OFF state, the remaining pressure oil is diverted to the tank 8 side through this valve. On the other hand, pressure oil from the motor pump 11 is flowing into the valve section of the transmission control am mechanism 14. In this state, when a steering operation is performed using the steering handle 2a, the front wheels are steered, and the input shaft 20 is rotated at a predetermined rotation angle (QA in FIG. 6) with the switch 43 (SW
-A) is turned on, which causes the vehicle speed control bypass valve 5 to turn on.
5 is activated, the short circuit to the tank is cut, the discharged oil is guided to the control valve l5, and the electromagnetic clutch 38 is activated.
is turned on. When the amount of rotation of the steering wheel increases and QB turns on switch 4 4 (SW-8), the neutral position lock control valve 62 opens and high pressure is guided to the neutral position locking mechanism 60, the lock pin is pulled out and the rear wheel The side is on standby so that it can be steered. Furthermore, when the handle is steered beyond the stroke QC defined by the notch groove 22 in the control mechanism 14, the output shaft 21, which is the input side of the control valve 15, is rotated, and the valve 15 is thereby actuated. Pressure oil is guided to one of the left and right chambers of the rear wheel power cylinder 3 to steer the rear wheels, and a feedback signal system 5 using the tension cable 4 changes the steering amount to the feedback shaft 32 in the control valve l5. Feedback is provided to control the desired operating state. Here, the above-mentioned steering wheel steering angle QC can be determined by changing the discharge flow rate from the motor pump 11 depending on the vehicle speed.
This changes depending on the movement position of the piston l3 of the control mechanism 14 described above, and the control valve l5 is rotationally displaced with the required play, allowing the rear wheels to be steered. In addition, when the vehicle speed becomes 20kmlb or more, the vehicle speed switch 5
6 is turned off, the vehicle speed control bypass valve 55 is turned off, a far flow path to the tank is formed, and the electromagnetic clutch 38 etc. are also turned off. In this case, it is preferable to configure the structure so that the energization to the motor bomb 11 is also turned off. ．． Furthermore, if any abnormal condition occurs while the vehicle is running, or if the electrical system or hydraulic system fails, it is preferable to use the emergency valve 50, manual switch 51, or the like to put the rear wheels in a non-steerable state. By connecting switches SW-A and S'd-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, and all four wheels It is possible to maintain running while steering. here,
What is desired when configuring the above-mentioned rear wheel steering system is to ensure straight-line driving performance at high speeds and driving stability on low-friction roads such as snowy roads, and the rear wheel steering system is only used when necessary. The system is configured to be in a standby state and an active state, and to be in a locked state when not needed to ensure two-wheel steering. Furthermore, one of the problems that arise when equipped with the above-mentioned rear wheel steering device is the loss of driving force due to a failure in the rear wheel steering drive system, and the loss of driving force in the command transmission system of the rear wheel steering control system. When something like this occurs, it is necessary to keep the rear wheels locked in a neutral state and enter a two-wheel steering state, so it is better to adopt the configuration described above. In addition, a problem in configuring the rear wheel steering device 10 described above is that it is required to position and incorporate the neutral position of this device IO side and the vehicle side, and in particular, the rear wheel steering start point detection switch, It is desirable that the positioning parts between the channels 43 and 44 and the input shaft 20 side be connected correctly to the vehicle side.
In this example, in order to solve such problems, the sixth
As shown in the figure, a neutral positioning mechanism 48 is provided in which a groove 45 is formed in a part of the outer circumference of the flange member 40, and a pawl 46 is pressed into contact with the groove 45 with a constant preload applied by a spring 47. This allows the input shaft 20 to be positioned with respect to the unit body, and is configured so that it can be easily positioned with respect to the vehicle side. Of course, this pole 46 is always movable by steering the steering wheel, but it does not hinder the movement of the input shaft 20.
Note 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 M10 may be modified or changed as appropriate, and various modifications may be considered. For example, in the embodiment described above, in order to move the piston 13 constituting the displacement transmission control mechanism for rear wheel steering, the piston 1
Although a flow control method has been described in which a fixed throttle 13a is provided in the vehicle, and a pressure difference is generated by flowing pressure oil through the fixed throttle 13a, the flow rate of which is proportionally controlled according to the vehicle speed. However, the present invention is limited to this. Instead, an electromagnetic proportional pressure control valve with a variable throttle is installed in the middle of the hydraulic passage, and a pressure control method is adopted in which pressure on the downstream side is introduced to both sides of the piston 13, and the differential pressure is used to move the piston l3. Of course, it is okay to do so. [Effects of the Invention] As explained above, the rear wheel steering device for a four-wheel steered vehicle according to the present invention includes a piston that moves within a cylinder by a hydraulic signal that is proportionally controlled according to the vehicle speed, and the piston movement position is adjusted. a displacement transmission control mechanism for rear wheel steering that transmits the amount of steering displacement on the front wheels to the rear wheels with variable play according to After controlling the switching of the hydraulic passage from the rear wheel hydraulic power source according to the displacement amount obtained by the displacement output shaft and the displacement transmission control mechanism, the power cylinder for rear wheel steering is operated as appropriate. The wheel steering control valve is provided as a rotary valve on the output shaft of the displacement take-out shaft and between the feedback shaft from the rear wheel side steering link mechanism. Despite the configuration, the steering angle of the rear wheels relative to the front wheels is variably controlled according to the vehicle speed, and steering displacement information is appropriately transmitted from the front wheels to the rear wheels. It has various excellent effects such as improving maneuverability such as tight turning when driving at low speeds. Further, according to the present invention, the rotary rear wheel steering control valve is provided coaxially with the rear wheel steering displacement transmission control mechanism that controls the transmission of steering displacement information from the front wheel side to the rear wheel side according to the vehicle speed. Because of this, the structure is not only superior in terms of ease of installation into a vehicle, but also has the advantage of being able to appropriately and reliably transmit displacement from the front wheel side to the rear wheel side. ．． Furthermore, in the present invention, the front and rear wheel side steering link mechanisms are independently driven, and the rear wheel steering device can be configured by simply adding a steering signal output section on the front wheel side, which simplifies the configuration of each part. It has the advantage of being easy to assemble, has a large degree of freedom in terms of installation space, and can achieve appropriate rear wheel steering conditions.

[Brief explanation of the drawing]

The figures show an embodiment of the rear wheel steering device for a four-wheel steered vehicle according to the present invention, FIG. 1 is a cross-sectional view of a main part of the rear wheel steering control mechanism unit that characterizes the present invention, and FIG. 2 (a) ．． 3(b) is a schematic perspective view and an enlarged view of essential parts for explaining the configuration for varying the displacement transmission play stroke, and FIG. 3(a). (b) is a cross-sectional view taken along the line ■-■ in Fig. 1 and an explanatory diagram showing its movement; Fig. 4 is a characteristic diagram showing the relationship between front and rear wheel steering angles; Figs. 5 and 6 are the same as Fig. 1. 7 is a side view of a portion of the feed pack cable connection lever,
Figure 8(a). (b) is a hydraulic circuit diagram showing the relationship between the proportional wave amount supply means and a displacement transmission control mechanism for rear wheel steering equipped with variable play, and a modification thereof; FIG. 9 is a schematic configuration diagram of the entire device; Figure 10 is the electrical circuit diagram. 1... Rear wheel side steering link mechanism, 2, 3... Front,
Power cylinder for rear wheel steering, 5... - feedback signal system, 6.7... front, rear wheel side oil pump, 8...
... Oil tank, 10 ... Rear wheel steering device, 11
-...Motor bomb, 12...Cylinder, l3.
... Piston, 14... Displacement transmission control mechanism for rear wheel steering, l5... Control valve for rear wheel steering, 16...
・Vehicle speed sensor, 18...Electromagnetic proportional flow control valve,
20. 21... Person, output shaft, 22... Notch groove, 23... Engagement means, 30... Rear wheel steering control mechanism unit 7}, 31... Torsion/ <1, 3
2... Feedback shaft, 36...φφ centering spring mechanism, 38... Electromagnetic clutch, 40...
. . . Flange portion, 41. 42 . . . One engaging portion, 43.
44...Rear wheel turning start point detection switch.

Claims (1)

[Claims] It is equipped with a piston that is moved within a cylinder by a hydraulic signal that is supplied under proportional control according to the vehicle speed, and depending on the movement position of the piston, the amount of steering displacement on the front wheel side can be selectively shifted to the rear wheel side with variable play. a displacement transmission control mechanism for rear wheel steering; a displacement output shaft comprising an input shaft rotated by the steering operation of the front wheels and an output shaft disposed coaxially therewith;
After operating a rear wheel steering power cylinder that performs switching control of the hydraulic passage from the rear wheel side hydraulic pressure source in accordance with the displacement amount obtained by the displacement transmission control mechanism and controls the steering of the rear wheel side steering link mechanism. The rear wheel steering control valve is provided as a rotary valve on the output shaft of the displacement take-out shaft and between the feedback shaft from the rear wheel side steering link mechanism. A rear wheel steering device for a four-wheel steering vehicle, characterized by: