JPH028940B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power steering device for an automobile capable of performing both two-wheel steering and four-wheel steering, and in particular, a pair of power cylinders for steering both front wheels of a left-right symmetrical configuration, A pair of power cylinders for steering both rear wheels with a symmetrical structure, a tie rod that connects the knuckle arms of both front and rear wheels, and a power cylinder for steering both front wheels in accordance with the amount of handle operation are controlled. The present invention relates to a power steering device equipped with a hydraulic servo.

In this case, in order to keep the steering angle ratio of the steering wheel and the wheels constant at all times and to synchronously turn the front and rear wheels during four-wheel steering, a switching valve is installed between the front and rear wheel steering power cylinders at its normal position. controls the steering of only the power cylinders for steering both front wheels, and in the switching position, directly controls the steering of one of the power cylinders for steering both front and rear wheels, and uses the discharge hydraulic pressure of the power cylinder to control the steering of the other side. When the power cylinders for steering both wheels are connected to control steering, a 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, there is a difference in pressure receiving area equal to the cross-sectional area of the piston rod between the high-pressure side oil chambers of the power cylinders on both sides, so a compression force corresponding to this differential pressure is applied. As a result, there is a risk that the tie rods of the steering mechanism may buckle and fail, and this drawback is particularly noticeable in automobiles where the maximum axle load is large, such as a self-propelled crane that lifts and moves a load.

The present invention addresses this problem by providing a constant position between the front and rear power cylinders for steering both front and rear wheels, in which only the front power cylinders for steering both wheels are controlled, and a position for steering only the front power cylinders for steering both front and rear wheels. A switching valve is connected, which has a switching position that directly controls the steering of one of the power cylinders and controls the steering of the other power cylinder for steering wheels on both sides using the discharge hydraulic pressure of the power cylinder, and the pressure is always low. The present invention is characterized in that a relief valve device that switches the maintained relief set pressure to a 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.

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 4a and 4b to both ends of the front wheel 2 via king pins 3, respectively, and turns the front wheel axles. The rear ends of the knuckle arms 5a and 5b on both sides 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. The wheel steering mechanism has the same configuration as this with a completely symmetrical arrangement, and has rear wheels 8a and 8b on both sides.
are power cylinders 9a and 9b arranged symmetrically on the left and right sides, respectively.
At the same time, the steering of both rear wheels is linked by a tie rod 10.

In FIG. 1, reference numeral 11 indicates a rotary joint for an oil path 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,
The tank T, the relief valve 13 of the entire pump system, the switching valve 14, etc. are installed on the vehicle body side, and the swivel joint 1
The flow priority valve 18, check valve 19, hydraulic servo 20, relief valve 44, etc. shown above 1 are mounted on the crane swivel base, except for the tank T.

The hydraulic servo 20 has a valve outer cylinder that sets the discharge flow rate to the oil passage 23 or 24 in conjunction with left and right rotation of the handle 22 on the driver's seat, and a feedback cylinder 26 that is linked to a motor 25 that is driven according to the discharge flow rate. comprising a control valve 27 consisting of a spool to be controlled;
Hydraulic pressure passing through the motor 25 flows through the oil path 28 or 29.
It is supplied to the power cylinder side. Therefore, the 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 flow priority valve 18 that is controlled by the pressure of pilot oil passages 31 and 32 before and after the control valve is inserted in the middle of a hydraulic pressure supply path 30 from the hydraulic pump 12 to the control valve 27, and the flow priority valve 18 is 2
A regulated flow rate is supplied to 7, and a surplus flow rate is supplied to hydraulic equipment such as a crane swing motor (not shown) through an oil line 33, so that a single hydraulic pump is used to supply a power steering system and other hydraulic systems. work 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 34 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 at the normal position (neutral position). Further, the left and right cylinder chambers of rear wheel steering power cylinders 9a and 9b are connected in parallel to the A and B ports of the switching valve 14 via oil passages 35 and 36, respectively.

The relief valve device includes a relief valve 44 connected to a hydraulic pressure supply path 30 from the hydraulic pump 12 to the hydraulic servo 20 via a flow priority valve 18 and capable of switching high or low relief setting pressure, and a drain oil path 45 connected to the hydraulic servo. It includes a solenoid valve 49 which is selectively connected to either the return oil path 39 to the tank T or the hydraulic pressure supply path 30.

The solenoid valve 49 is connected to the drain oil passage 4 of the relief valve 44.
A switch 46 on the crane swivel table issues a signal 47 or 48 to switch the switching valve 14 in the normal position (neutral position) to the right or left switching position. At this time, the signal causes the drain oil passage 45 to be switched to the upper position in the drawing, where it is connected to the hydraulic pressure supply passage 30 from the hydraulic pump.

The relief valve 44 is arranged in a valve housing 50 as shown in FIG.
A piston valve 53, which is always biased to close by an adjustment spring 52, is fitted into a lock-shaped movable cylinder 51 that is slidably fitted within a certain range. When the movable cylinder 51 is in communication with the movable cylinder 51 through the small hole 51a, the movable cylinder is held at the left end position shown in the figure by the reaction force of the hydraulic pressure of the pressure port 54 transmitted into the movable cylinder 51 through the small hole 51a, and the movable cylinder 51 is When the valve portion 53a of the piston valve 53 opens against the elasticity of the spring 52 due to the internal pressure of
5, the hydraulic pressure is relieved. Furthermore, when the drain oil passage 45 communicates with the hydraulic pressure supply passage 30, the movable cylinder 51 slides to the right due to the difference in pressure receiving area and oil pressure on both sides until it engages with the stepped edge 50a of the valve housing 50. to compress the adjustment spring 52 and function as a high pressure relief valve. The set pressure of this high pressure relief valve is the relief valve 1 of the entire pump system.
Lower than the set pressure of 3. 56 is the movable cylinder 5
1 is a stopper bolt, and 57 is a pressure adjustment bolt for the spring 52.

Next, the operation of the present invention will be explained. Switching valve 1
4 in the normal position (neutral position) shown in the diagram,
For example, when the handle 22 is rotated to the left, the control valve 2
7 is switched to the lower position in the diagram, and the control valve is switched to the lower position in the figure.
5, the amount of pump discharge oil corresponding to the rotation angle of the handle is supplied to the oil passage 28, and the oil pressure acts on the chambers on the left side of the pistons of the power cylinders 7a and 7b via the switching valve 14, while the oil passage Since 29 is connected to the tank T, the front wheels 4a and 4b are turned to the left in conjunction with the tie rod 6, and the handle 22
When the control valve 27 is rotated to the right, the control valve 27 is switched to the upper position in the figure, and the oil passage 29 becomes the high pressure side, and the oil passage 28
is on the low pressure side, so the power cylinders 7a, 7
The chamber on the left side of the piston b becomes the high pressure side, and the front wheel 4
a and 4b turn to the right as shown by the chain lines in FIG.

In this case, the drain oil passage 45 of the relief valve 44 is connected to the tank T via the solenoid valve 49 as shown in FIG. The maximum pressure of the operating circuit of the power cylinders 7a, 7b is regulated to this low relief setting pressure. Therefore, even if a compressive force is applied to the tie rod 6 via the knuckle arms 5a, 5b based on the difference in the pressure receiving areas on both sides of the pistons of the power cylinders 7a, 7b, that is, the difference between the extension force and the contraction force of the two power cylinders, There is no risk of the tie rod buckling or breaking.

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. 35 is on 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, the chambers on the right side of the pistons of the power cylinders 9a, 9b turn. Hydraulic pressure sequentially passes through the oil passage 36, the switching valve 14, and the oil passage 34 to the power cylinders 7a and 7b.
The pistons are supplied to the right chamber of the front wheels 4a, 4.
Turn b 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 34 is transferred to the power cylinder 9 via the switching valve 14 and the oil passage 36.
It acts on the chambers on the right side of the pistons a and 9b 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 there is a tie rod between the knuckle arms of both wheels. Since the front and rear wheels are connected in parallel, the vehicle can be driven 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 vehicle. 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 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. Similarly to 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 the signal when switching to either the left or right switching position, and the relief setting pressure of the relief valve 44 is switched to high pressure as described above, so that the power cylinder operating circuit The maximum oil pressure is regulated by this high pressure relief valve 44, 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 power cylinders 7a, 7 on both sides due to the increase in oil pressure
The difference in the expansion and contraction forces between b and 9a and 9b is small, and 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.

According to the present invention, even if the maximum axle load of an automobile becomes large, requiring power cylinders for steering both wheels 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. Similarly,
Moreover, it is possible to prevent 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 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. 1...Vehicle body, 2...Front axle, 4a, 4b...Front wheel, 5a, 5b...Natsukuru arm, 6, 10
...Tie rod, 8a, 8b...Rear wheel, 7a,
7b, 9a, 9b...power cylinder, 12...
Hydraulic pump, 14...Switching valve, 20...Hydraulic servo, 22...Handle, 25...Motor, 27...
...Control valve, 44...Relief valve, 45...Drain oil path, 49...Solenoid valve.

Claims (1)

[Claims] 1. A pair of power cylinders for steering both front wheels with a symmetrical configuration, a pair of power cylinders for steering both rear wheels with a symmetrical configuration, a tie rod that connects the knuckle arms of both front and rear wheels, and a handle. In a power steering device equipped with a hydraulic servo that controls the steering of the power cylinders for steering both front wheels according to the amount of operation, a hydraulic servo for steering both front wheels is installed between the front and rear power cylinders for steering both wheels. A constant position where only the power cylinder is steered, and 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 steer the other power cylinder for steering both wheels. A relief valve device is connected to a switching valve provided with a switching position to be controlled, and switches the relief setting pressure, which is normally maintained at a low pressure, to a high pressure in conjunction with switching of the switching valve, from a hydraulic pump to a hydraulic servo. A power steering device for an automobile, characterized in that it is connected to a hydraulic supply path.