JPS58170668A - Power steering gear for automobile - Google Patents

Abstract

PURPOSE:To obtain operating pressure necessary for four-wheel steering and prevent the tie rod of a steering mechanism from being buckled and damaged in two-wheel steering, by changing the set pressure of a relief valve for the two- wheel steering or the four-wheel steering. CONSTITUTION:A hydraulic servomechanism 20 supplies pressurized oil from a hydraulic pump 12 to power cylinders 7, 9 to steer wheels. A changeover valve 14 is energized through a switch 46 to connect only the front wheel power cylinders 7a, 7b or the front and rear wheel power wheels 7a, 7b, 9a, 9b to the hydraulic servomechanism 20 to steer two or four wheels. At the same time, a solenoid valve 49 is energized through the switch 46 to open or close the drain passage 45 of a relief valve 44 to change its set pressure. In the two-wheel steering, the set pressure is lowered not to apply excessive pressure to the power cylinders 7a, 7b so that a tie rod is prevented from being buckled and damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power steering system for an automobile capable of performing both two-wheel steering and four-wheel steering, and particularly to a power steering system that is symmetrically arranged to steer both front and rear wheels separately. A tie rod that connects the cylinder and the knuckle arms of each wheel on both sides,
The present invention relates to a power steering device equipped with a hydraulic servo that controls expansion and contraction of the power cylinder according to the amount of steering wheel operation.

In this case, the steering angle ratio between the steering wheel and the wheels is always kept constant,
Moreover, in order to synchronously turn the front and rear wheels during four-wheel steering, a switching valve is installed between the front and rear wheel steering cylinders.
In the normal position, only the power cylinders for steering both front wheels are telescopically controlled, and in the switching position, one of the power cylinders for steering both front and rear wheels is directly telescopically controlled. When connected so that the power cylinder for steering both wheels on both sides is telescopically controlled by the discharge hydraulic pressure of
Four-wheel steering requires higher hydraulic pressure than two-wheel steering. However, when two-wheel steering is performed with this high hydraulic pressure, there is a difference in pressure receiving area between the high pressure side oil chambers of the power cylinders on both sides, which is similar to the cross-sectional area of the piston rod, so the compression force is applied according to this differential pressure. As a result, there is a risk that the tie rods of the steering mechanism may buckle and break, and this drawback is particularly noticeable in automobiles where the maximum axle load is large, such as a self-propelled crane that lifts a load and travels.

As described above, the present invention connects the switching valve between the front and rear wheel steering power cylinders, and also provides low pressure and high pressure relief valves that connect the operating circuits of all power cylinders to the tank. A means for emitting a signal when the switching valve is switched to the switching position and a device for receiving the signal and stopping the low pressure relief function of the relief valve are provided, so that the low pressure relief valve is operated only when only the front wheels are steered. In particular, the steering angle ratio between the steering wheel and the wheels is always constant, and the front and rear wheels are synchronously turned during four-wheel steering, thereby preventing buckling and damage to the steering mechanism in vehicles with high maximum axle loads. It is something.

An embodiment of the present invention applied to an all-wheel drive type self-propelled crane will be described below with reference to the drawings. The front wheel steering mechanism at the front of the vehicle body 1 connects the front wheel axles of both front axles 4m and 4b to both ends of the front axle 2 via king pins 6, respectively, as shown in FIG. 2, and turns the front wheel axles. Both side knuckle arms 5a, 5
The rear ends of b are connected by a tie rod 6, and the front ends of each knuckle arm and the front axle 2 are connected by power cylinders 7g and 7b arranged symmetrically. The steering mechanism has the same configuration as this, with a completely symmetrical arrangement, and the rear wheels 8a and 8b on both sides are steered by power cylinders 9a and 9b, respectively, arranged symmetrically, and the steering of the rear axles on both sides is controlled by tie rods. It is linked to 10.

In FIG. 1, reference numeral 11 indicates a rotary joint for an oil line or an electric circuit installed between the vehicle body 1 and a crane swivel platform (not shown) that is rotatably supported on the vehicle body 1. Illustrated hydraulic pump 12° tank T, relief valve 13 for the entire pump system. Switching valve 14. Shuttle valve 15. Balance piston type low pressure relief valve 16. Shuttle valves 17 and the like are mounted on the vehicle body side, and a flow priority valve 18 is shown above the rotary joint 11. Check valve 19° Hydraulic servo 20. The high pressure relief valve 21 and the like are installed on the crane slewing base side, except for the tank T.

The hydraulic servo 20 has a valve outer cylinder that sets the discharge flow rate to the oil passage 26 or 24 in conjunction with the left and right rotation of the handle 22 on the driver's seat, and a motor 25 that is driven according to the discharge flow rate to provide feedback 26. It is equipped with a control valve 27 that is similar to the spool to be controlled, and the hydraulic pressure via the motor 25 is connected to the oil path 2.
8 or 29 to the power cylinder side. Therefore, the amount of oil corresponding to the rotation angle of the handle 220 is always supplied to the power cylinder side.

In the illustrated case, a pilot oil passage 3 is installed between the hydraulic pump 12 and the hydraulic pressure supply oil passage 60 to the control valve 27 before and after the control valve.
A flow priority valve 18 controlled by pressures 1 and 32 is inserted, and a regulated flow is supplied to the control valve 27, and an oil line 66 is supplied to hydraulic equipment (not shown) such as a crane swing motor.
Surplus flow is supplied through the hydraulic pumps, allowing one hydraulic pump to perform the work of the power steering system and other hydraulic systems at the same time.

The left cylinder chambers of the front wheel steering power cylinders 7a and 7b are connected in parallel to the oil passage 29, and the oil passage 64 connecting the right cylinder chambers of both power cylinders in parallel is connected to the tandem center type electromagnetic switching valve 14. It is connected to the oil passage 28 in the normal position. In addition, a rear wheel steering power cylinder 9a is connected to the A and B boards of the switching valve 14 via oil passages 35 and 36, respectively.
, 9b are connected in parallel to each other.

The oil passage 37 into which the low pressure relief valve 16 is inserted is the oil passage 28.2.
9 via the shuttle valve 15, and the oil passages 35 and 36.
The tip of the pilot oil passage 68 connected to the valve via the shuttle valve 17 is connected to the vent chamber of the balanced piston type low pressure relief valve 16. For this reason, the power series for rear wheel steering is
When the working oil pressure (pressure signal) of a and 9b acts on the pilot oil passage 68 via the shuttle valve 17, the function of the low pressure relief valve 16 is stopped and the oil pressure of the oil passage 37 exceeds the set pressure of the high pressure relief valve 21. Even if it rises, the low pressure relief valve will not open. The illustrated high pressure relief valve 21 is connected between the return oil passage 69 and the pilot oil passage 62 of the control valve 27,
The set pressure of the high pressure relief valve is also lower than the set pressure of the relief valve 16 of the entire pump system.

Next, the effects of the present invention will be explained. With the switching valve 14 in the normal position shown in the figure, when the handle 22 is rotated, for example, to the left, the control valve 27 is switched to the lower position in the figure, and the cough control valve cooperates with the motor 25 to adjust the handle rotation angle. The corresponding amount of pump discharge oil is supplied to the oil passage 28, and the oil pressure acts on the chamber 111 on the right side of the piston of the power cylinders 7a and 7b via the switching valve 14, while the oil passage 29 is connected to the tank T. From there, the front wheel 4a is connected to the tie rod 6.

4b is turned to the left and the handle 22 is rotated to the right, the control valve 27 is switched to the upper position in the diagram, and conversely, the oil passage 29 becomes the high pressure side and the oil passage 28 becomes the low pressure side. , the chamber on the left side of the piston of the power cylinder becomes the high pressure side, and the front wheel turns to the right as shown by the chain line in FIG.

In this case, even if either of the oil passages 28 and 29 becomes the high pressure side, the high pressure side oil passage is connected to the low pressure relief valve 1 through the shuttle valve 15.
6, and since no oil pressure acts on the pilot oil passage 68, the maximum pressure of the operating circuit of the power cylinders 7m, 7b is regulated to the set pressure of the low pressure relief valve 16. Therefore, the knuckle arm 5a is adjusted based on the difference in the pressure receiving areas on both sides of the pistons of the power cylinders 7a and 7b, that is, the difference between the extension force and the contraction force of the two power cylinders.

Even if a compressive force is applied to the tie rod 6 through the tie rod 5b, there is no risk of the tie rod being buckled and damaged.

Furthermore, when the switching valve 14 is switched to the right position in the figure and the handle 22 is turned to the left to set the oil passage 28 to the high pressure side as described above, the oil passage 65 becomes the high pressure side via the switching valve 14. Hydraulic pressure acts on the chambers on the left side of the pistons of the power cylinders 9a and 9b, turning the rear wheels 8m and 8b to the left, and at the same time, the oil pressure on the chambers on the right side of the pistons of both power cylinders sequentially flows through the oil passage 66 and the switching valve 14. ．． Power cylinder 7a via oil passage 34
.

7b is supplied to the chamber on the right side of the piston, and the front wheel 4&.

Turn 4b to the left. Conversely, if you turn the handle 22 to the right and set the oil passage 29 to the high pressure side, the power cylinder 7a,
Hydraulic pressure acts on the chamber on the left side of the piston 7b to turn the front wheel to the right, and at the same time, the hydraulic pressure is applied to the chamber on the left side of the piston 7b.
The hydraulic pressure discharged to the switching valve 14. It acts on the chamber on the right side of the piston of the power cylinder 91.9b through the oil passage 66 to turn the rear wheel to the right.

In this case, the amount of oil that expands and contracts the pair of left and right power cylinders in the same direction and the amount of oil discharged from both power cylinders are not only equal, but the front and rear power cylinders have the same configuration, and the knuckle arms of both wheels are different. Because they are connected by tie rods, the front and rear wheels are arranged parallel to each other, allowing the vehicle to travel diagonally.

Furthermore, if the switching valve 14 is switched to the left position in the figure, the steering wheel 22 can be operated to turn the front and rear wheels in opposite directions at the same angle, thereby significantly reducing the turning radius of the vehicle. it is obvious.

In the case of this four-wheel steering, one of the front and rear power cylinders is directly driven by the pump discharge hydraulic pressure, and the other power cylinder is driven by the discharged hydraulic pressure, so the amount of oil required for four-wheel steering is reduced to two wheels. Same as in the case of steering, no-turn steering can be performed in the same way in either case, but the pump discharge oil pressure must be increased in accordance with the sum of the surface energy required for steering the front and rear wheels. ．． 66 becomes the high pressure side, and the oil pressure is sent to the pilot oil path 6 through the shuttle valve 17.
8 and deactivates the low pressure relief valve 160 as described above. Therefore, the maximum oil pressure of the power cylinder operating circuit is regulated by the high pressure relief valve 21, making it possible to increase the oil pressure necessary for four-wheel steering.

In this case, even if there is a difference in the front and rear axle loads, the difference in the front and rear wheel steering forces based on this difference is relatively small, so the difference in the expansion and contraction force between the power cylinders 7m and 7b on both sides and between 9a and 9b due to the increase in oil pressure is small, the compressive force acting on the front and rear tie rods 6.10 is similar to that in two-wheel steering, and there is no risk of buckling and damaging the tie rods.

Although one embodiment has been described above, the device for stopping the low-pressure IJ leaf function of the low-pressure relief valve during four-wheel steering is not limited to the configuration shown in Fig. 1;
It can also be done as shown in the figure.

In FIGS. 3 and 4, members with the same reference numerals as in FIG. 1 indicate corresponding members.

In the embodiment shown in FIG. 3, a solenoid valve 40 which is normally energized to open is inserted into the oil passage 37 between the low pressure relief valve 16 and the tank T, and a switch 41 mounted on the crane swivel base is used. When issuing the signal 42 or 46 to switch the switching valve 14 to the right or left switching position, the magnetic valve 40
is switched to the upper position in the diagram to block the oil passage. Therefore, even if the low pressure relief valve 16 opens during four-wheel steering, the solenoid valve 40 stops its relief action.

In the embodiment shown in FIG. 4, the high pressure relief valve shown in FIG. 1 is configured as a relief valve 44 as shown in FIG. 5 which can be switched between low pressure and high pressure, and the drain oil passage 45 is normally When the switch 46 on the crane swivel table issues a signal 47 or 48 to switch the switching valve 14 to the right or left switching position, the drain oil passage 45 is connected to the tank T as shown in FIG. Hydraulic pressure supply oil line 6 from the hydraulic pump
A solenoid valve 49 is provided which is switched to the upper position in the figure where it connects to 0.

The relief valve 44 is constructed by fitting a piston valve 56, which is always biased to close by an adjustment spring 52, into a lever-shaped movable cylinder 51 which is slidably movable within a certain range within a valve housing 50. If the drain oil passage 45 communicates with the tank, the small hole 5
The movable cylinder is held at the left end position shown in the figure by the reaction force of the hydraulic pressure of the Brera Shabot 54 transmitted into the movable cylinder 51 through 1a, and when the pressure is low 91J-7, the internal pressure of the movable cylinder closes the cylinder. When the valve portion 53a of 56 opens against the elasticity of the spring 52, the Brera Chabot 54 opens.
Hydraulic pressure is relieved to the tank boat 55 through the side passage hole 51b. In addition, when the drain oil passage 45 communicates with the oil pressure supply oil passage 60, due to the difference in pressure receiving area and oil pressure on both sides of the movable cylinder 51, the movable cylinder 51 moves to the right until it engages with the stepped edge 50m of the valve housing 50. Sliding adjustment spring 52
compresses and functions as a high pressure relief valve. Note that 56 is a stopper bolt for the movable cylinder 51, and 57 is a pressure adjustment bolt for the spring 52.

According to the present invention, even if the maximum axle load of an automobile becomes large, requiring power cylinders for both wheel steering and tie rods that interlock these power cylinders to be disposed before and behind the axle, two-wheel steering and four-wheel steering can be performed. In addition, it has the effect of preventing the tie rod from being buckled and damaged due to the compression force based on the difference in the expansion and contraction forces of the power cylinders for steering both wheels during two-wheel steering.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is a plan view showing an outline of the steering mechanism, Fig. 3 is a circuit diagram of the main part of another embodiment, and Fig. 4 is a further embodiment. Fig. 5 is a longitudinal sectional front view of the relief valve. 1... Vehicle body, 2... Front axle, 4a, 4b... Front wheel, 5m, 5b... Knuckle arm, 6, 1o...
Tie rod, 8a, 8b river wheel, 7a, 7b, 9at
9 b-゛° power cylinder, 12 river hydraulic pump, 14
...Switching valve, 15.17...Shuttle valve, 16...
・Low pressure relief valve, 2o...hydraulic servo, 21...
・High pressure relief valve, 22...handle, 25...
Motor, 27... control valve. Spear 1 time + 2 Drawer 3 Illustration procedure amendment May 6, 1980 Commissioner of the Patent Office Kazuo Wakasugi 1 Indication of the case 1981 Permit Application No. 052302 2 Title of the invention Automobile power steering device 3 Supplement 1 Relationship with the person who performs the knife/1kuto Patent applicant Mr. Katokusei Sakusho R (t) Kato Seisakusho Co., Ltd. 4 Agent
Person 6 Supplement 1■-J: Increased number of inventions (1) The specification shall be amended as shown in the attached sheet. (There is no change in the content except for the matters stated in the column subject to amendment.) (2) Figures 1 and 3 from the drawings originally attached to the application are to be deleted. (3) Figures 4 and 5 in the above drawings are attached to Figure 1.
Corrected in Figure and Figure 3. Following the above, this amendment deletes the embodiment shown in FIGS. 1 and 3 from the drawings originally attached to the application, and limits the gist of the claimed invention to the invention shown in FIGS. 4 and 5. It's something you do for the sake of it. Description 1, Name of the invention Power steering device for an automobile 2, Claims A pair of power cylinders for steering both front wheels with a symmetrical configuration, and a pair of power cylinders for steering both rear wheels with a symmetrical configuration. , the tie rod that connects the knuckle arms of each wheel on both sides, and the amount of handle operation
￥5ilIlii@ In a power steering device equipped with a hydraulic servo that controls the steering of the power cylinder for wheel steering, between the front and rear power cylinders for wheel steering on both sides,
-Q% A constant position in which only the power cylinders for both wheels are controlled, and one in which one of the power cylinders for steering both front and rear wheels is directly controlled, and the discharge oil pressure of the power cylinder is used to control the steering of the other side. A relief valve device that connects a switching valve provided with a switching position for steering control of a power cylinder for wheel steering, and switches a relief valve device normally maintained at low pressure to high pressure in conjunction with switching of the switching valve. is connected to a hydraulic pressure supply path from a hydraulic pump to a hydraulic servo. A power steering device for an automobile, in particular, a pair of power cylinders for steering both front wheels in a symmetrical configuration, a pair of power cylinders for steering both rear wheels in a symmetrical configuration, and knuckles for both front and rear wheels. A tie rod that connects the arms, and a hydraulic servo that controls the steering of the front wheel cylinders for steering both front wheels according to the amount of steering wheel operation are provided. Always keep the steering angle ratio of the wheels constant,
Moreover, in order to synchronously turn the front and rear wheels during four-wheel steering, a switching valve is installed between the front and rear power cylinders for steering both wheels, and in its normal position, only the power cylinders for steering both front wheels are controlled. In addition, in the switching position, one of the power cylinders (for steering both front and rear wheels) is directly controlled, and the discharge hydraulic pressure of the power cylinder is used to control the steering of the other power cylinder for steering both wheels. When connected like this, higher hydraulic pressure is required for four-wheel steering than for two-wheel steering.However, when two-wheel steering is performed with this high hydraulic pressure, the pressure between the high-pressure side oil chambers of both power cylinders increases. Since there is a difference in the pressure-receiving area equal to the cross-sectional area of the piston rond, there is a risk that the tie rod of the steering mechanism may buckle and break due to the compressive force corresponding to this differential pressure. This is particularly noticeable in automobiles where the maximum axle load is large, such as a crane.The present invention addresses this problem by connecting only the front power cylinders for steering both wheels between the power cylinders for steering both front and rear wheels. A constant position for steering control, and a switching position for directly controlling one of the power cylinders for steering both front and rear wheels, and controlling the steering of the other power cylinder for steering both wheels using the discharge hydraulic pressure of the power cylinder. IJ-7 is connected to a switching valve provided with a switching valve, and the IJ-7 set pressure, which is normally maintained at a low pressure, is switched to a high pressure in conjunction with switching of the switching valve.
It is characterized in that the I7-f valve device is connected to a hydraulic pressure supply path to a hydraulic pump and a hydraulic servo. An embodiment of the present invention applied to an all-wheel drive type self-propelled crane will be described below with reference to the drawings. As shown in FIG. 2, the front wheel steering mechanism at the front of the vehicle body 1 connects the front wheel axles of both front wheels 4m and 4b to both ends of the front axle 2 via king pins 6, respectively, and turns the front wheel axles. Both side knuckle arms 5a, 5
The rear ends of b are connected by a tie rod 6, and the front ends of each knuckle arm and the front axle 2 are connected by power cylinders 7a and 7b arranged symmetrically, respectively, and the rear wheels at the rear of the vehicle are steered. The mechanism has the same structure with a completely symmetrical arrangement, and the rear wheels 8a and 8b on both sides are steered by power cylinders 9a and 9b, respectively, which are symmetrically arranged, and the steering of the rear wheels on both sides is controlled by tie rods 10. It is linked by In FIG. 1, reference numeral 11 indicates a rotary joint for an oil line or an electric circuit installed between the vehicle body 1 and a crane swivel platform (not shown) that is rotatably supported on the vehicle body 1, and is shown below the rotary joint 11. Hydraulic pump 12° tank T, relief valve for the entire pump system 16. The switching valve 14 and the like are attached to the vehicle body side, and the flow priority valve 18, check valve 19, etc. are shown above the rotary joint 11. Hydraulic servo20. The relief valve 44 and the like are attached to the crane slewing base side except for the tank T. The hydraulic servo 20 has a valve outer cylinder that sets the discharge flow rate to the oil passage 26 or 24 in conjunction with the left and right rotation of the handle 22 on the driver's seat, and a motor 25 that is driven according to the discharge flow rate to provide feedback 26. It is equipped with a control valve 27 consisting of a controlled spool, and the hydraulic pressure via the motor 25 is connected to the oil path 2.
8 or 29 to the power cylinder side. Therefore, an amount of oil corresponding to the rotation angle of the handle 22 is always supplied to the power cylinder side. In the illustrated case, a pilot oil path 31 is installed before and after the cough control valve in the middle of the hydraulic pressure supply path 60 from the hydraulic pump 12 to the control valve 27.
．． A flow priority valve 18 controlled by the pressure of 62 is inserted, and a regulated flow is supplied to the control valve 27, and a surplus flow is supplied to hydraulic equipment (not shown) such as a crane swing motor through an oil line 66. The left cylinder chambers of the power cylinders 7a and 7b for steering the front wheels are connected in parallel to the oil passage 29. In addition, the oil passage 64 connecting the right cylinder chambers of the war cylinder in parallel is connected to the oil passage 28 at the normal position (neutral position) of the tandem center type electromagnetic switching valve 14. The left cylinder chamber and the right cylinder chamber of rear wheel steering power cylinders 9m and 9b are connected in parallel to boats A and B through oil passages 35 and 66, respectively. More hydraulic servo 20
An external relief valve 44 is connected to the hydraulic pressure supply path 60 to the hydraulic servo via the flow priority valve 18, and the drain oil path 45 is connected to the oil pressure return path 69 from the hydraulic servo to the tank T. It includes a solenoid valve 49 that is selectively connected to any of the hydraulic pressure supply paths 60 . The solenoid valve 49 is the drain oil passage 45 of the IJ I7-F valve 44.
is connected to the tank T as shown in the figure, and the switch 46 on the crane swivel base is in the normal position (neutral position).
A signal 4 for switching the switching valve 14 to the right or left switching position.
7 or 48, the signal causes the drain oil passage 45 to be switched to the upper position in the figure where it is connected to the hydraulic pressure supply passage 60 from the hydraulic pump. As shown in FIG. 3, the relief valve 44 is fitted into a valve casing 50 so as to be slidable within a certain range, and a movable cylinder 51 in the shape of a hexagon.
A piston valve 56 that is always biased to close by an adjustment spring 52 is fitted therein, and when the drain oil passage 45 communicates with the tank T, the movable cylinder 51 is inserted through the small hole 51a.
The movable cylinder is held at the left end position as shown in the figure by the reaction force of the hydraulic pressure of the pressure port 54 transmitted inside the cylinder, and the internal pressure of the movable cylinder 51 causes the valve portion 56m of the piston valve 56 to respond to the elasticity of the spring 52 during low pressure relief. When opened against the pressure, hydraulic pressure is relieved from the pressure port 54 to the tank port 55 via the through hole 51b in the side wall of the movable cylinder. In addition, the drain oil passage 45 is a hydraulic pressure supply passage 60.
If the movable cylinder 51 is connected to the stepped edge 50a of the valve housing 50 due to the difference in pressure receiving area and oil pressure on both sides of the movable cylinder 51,
compress the adjustment spring 52 by sliding it to the right until it engages the
Functions as a high pressure relief valve. This high pressure IJ-7
The set pressure of the valve is lower than the set pressure of the IJ relief valve 6 of the entire pump system. Note that 56 is a stopper bolt for the movable cylinder 51, and 57 is a pressure adjustment bolt for the spring 52. Next, the operation of the present invention will be explained. With the switching valve 14 in the normal position (neutral position) shown in the figure, when the handle 22 is rotated, for example, to the left, the control valve 27 is switched to the lower position υ in the figure, and the control valve cooperates with the motor 25 to rotate the handle 22. The amount of pump discharged oil corresponding to the rotation angle is supplied to the oil passage 28, and therefore the oil pressure acts on the chambers on the right side of the pistons of the power cylinders 7a and 7b via the switching valve 14, while the oil passage 29 is connected to the tank T. Therefore, the tie rod 6 interlocks the front wheel 4.
g, 4b to the left and the handle 22 to the right, the control valve 27 is switched to the upper position in the diagram, and the oil passage 2 is turned to the left.
9 is on the high pressure side, and the oil passage 28 is on the low pressure side, so the chambers on the left side of the pistons of the power cylinders 7m and 7b are on the high pressure side, and the front wheel 4m is on the high pressure side. 4b is turned to the right as shown by the chain line in FIG. 2. In this case, the drain oil passage 45 of the relief valve 44 is connected to the tank TK* as shown in FIG.
Since the relief set pressure of the IJ-f valve 44 is maintained at a low pressure, the maximum pressure of the operating circuit of the skeleton power cylinders 7a, 7b is regulated to this low relief set pressure. Therefore, based on the difference in the pressure receiving areas on both sides of the pistons of the power cylinders 7a and 7b, that is, the difference between the extension force and the contraction force of the power cylinders, a compression force is applied to the tie rod 6 via the knuckle arms 5m and 5b, and the main force is applied to the tie rod 6. , there is no risk of the tie rod being buckled or damaged. In addition, if the switch 46 is operated to switch the switching valve 14 to the right position in the figure in advance, and the handle 22 is turned to the left to set the oil passage 28 to the high pressure side as described above, the oil passage 28 will be opened via the switching valve 14. 65 becomes the high pressure side, and hydraulic pressure acts on the chambers on the left side of the pistons of the power cylinders 9a, 9b, turning the rear wheels 8a, 8b to the left, and at the same time turning both the power cylinders 9a, 9
The oil pressure in the chamber on the right side of the piston b is sequentially applied to the oil passage 66 and the switching valve 1.
The oil is supplied to the chambers on the right side of the pistons of the power cylinders 7a, 7b through the 4° oil passage 64, turning the front wheels 4a, 4b to the left. Conversely, when the handle 22 is turned to the right to set the oil passage 29 to the high pressure side, hydraulic pressure acts on the chambers on the left side of the pistons of the power cylinders 7a and 7b, turning the front wheels to the right, and at the same time turning the front wheels to the right. The hydraulic pressure discharged into the oil passage 64 is transferred to the power cylinder 9a via the switching valve 14 and the oil passage 66.
, 9b acts on the chamber on the right side of the piston to turn the rear wheel to the right. In this case, not only is the amount of oil that operates the left and right pair of power cylinders in the same direction equal to the amount of oil discharged from both power cylinders, but the front and rear power cylinders have the same configuration, and the distance between the knuckle arms of both wheels is the same. Because they are connected by tie rods, the front and rear wheels are arranged parallel to each other, allowing the vehicle to travel diagonally. Furthermore, by operating the switch 46 and switching the switching valve 14 to the left position in the figure in advance, the steering wheel 22 can be operated to turn the front and rear wheels in opposite directions at the same angle, thereby significantly reducing the turning radius of the automobile. This is clear from the above explanation. In the case of this four-wheel steering, one of the front and rear power cylinders is directly driven by the pump discharge hydraulic pressure, and the other power cylinder is driven by the discharged hydraulic pressure, so the amount of oil required for four-wheel steering is reduced to two wheels. Same as in the case of steering, the steering wheel can be steered in the same way in either case, but the pump discharge oil pressure must be increased in accordance with the sum of the energy required for steering the front and rear wheels. The solenoid valve 49 is switched to the upper position in the figure by a signal when switching to any switching position,
Since the relief setting pressure of the relief valve 44 has been switched to high pressure as described above, the maximum oil pressure of the power cylinder operating circuit is regulated by this high pressure relief valve 44, making it possible to increase the oil pressure necessary for four-wheel steering. do. In this case, even if there is a difference in the front and rear axle loads, the difference in the front and rear wheel steering forces based on this difference is relatively small, so the difference between the power cylinders 7a and 7b on both sides and 9a and 9b due to the increase in oil pressure
The difference in expansion and contraction forces between the front and rear tie rods 6.10 is small, and the compressive force acting on the front and rear tie rods 6.10 is similar to that in the case of two-wheel steering, and there is no risk of buckling the tie rods. According to the present invention, even if the maximum axle load of an automobile becomes large, requiring power cylinders for both wheel steering and tie rods that interlock these power cylinders to be disposed before and behind the axle, two-wheel steering and four-wheel steering can be performed. In the same way, it is possible to prevent the tie rod from buckling and breaking due to the compression force based on the difference in the expansion and contraction forces of the power cylinders for steering both wheels during two-wheel steering. Explanation Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a plan view schematically showing the steering mechanism, and Fig. 3 is a longitudinal sectional front view of the relief valve.・Front axle, 4a, 4b...front wheel, 5m, 5b...knuckle arm, 6,10...
Tie rod, 8a, 8b... Rear wheel, 7a, 7b, 9
a. 9b...Power cylinder, 12-hydraulic cylinder 7', 14
...Switching valve, 20...Hydraulic servo, 22...Handle, 25...Motor, 27...Control valve, 44...
・IJ 17-7 valve, 45...Drain oil path, 49・
··solenoid valve.

Claims (1)

[Claims] It is equipped with a symmetrically arranged power cylinder that steers both front and rear wheels separately, a tie rod that connects the knuckle arms of each wheel on both sides, and a hydraulic servo that controls expansion and contraction of the power cylinder according to the amount of steering wheel operation. In a power steering system, a switching valve is installed between the front and rear power cylinders for steering both front and rear wheels, and in its normal position, only the power cylinders for steering both front wheels are telescopically controlled, and in the switching position, both front and rear wheel steering power cylinders are One of the power cylinders for wheel steering is directly telescopically controlled, and the other power cylinder for wheel steering on both sides is connected so as to be telescopically controlled by the discharge hydraulic pressure of the power cylinder, and the operating circuits of all power cylinders are connected to the tank. A low pressure relief valve and a high pressure relief valve are provided to be connected, and a means for emitting a signal when the switching valve is switched to a switching position, and a device for receiving the signal and stopping the low pressure relief function of the relief valve are provided. A power steering device for an automobile, characterized in that a low-pressure relief valve operates only when only the front wheels are steered.