JPH082432A - Power steering device - Google Patents

Abstract

PURPOSE:To provide a power steering device at low cost, capable of providing adequate steering force with simple structure. CONSTITUTION:A bypass valve 10 is arranged between left and right cylinder chambers C1, C2 of a power cylinder C for generating steering auxiliary force by oil discharged from an oil pump P, supplied through a servo valve V. The bypass valve 10 has a spool 16 slidably fit within a valve hole 14, and during non-operation, the spool shuts out between the cylinder chambers C1, C2, and when lateral acceleration exceeds a set value, the spool 16 is moved to communicate between both cylinder chambers C1, C2, and oil is bypassed from the cylinder chamber on the high pressure side to that on the low pressure side. Since if the steering angle is the same, lateral acceleration is increased with increase in speed, when quick steering is conducted during driving at high or medium speed, excessive lightening of the steering wheel is prevented, and suitable steering feeling can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering system, and more particularly to a power steering system capable of obtaining an appropriate steering force according to a change in lateral acceleration generated in a vehicle.

[0002]

2. Description of the Related Art A power steering system switches a control valve (servo valve) according to an input applied to a steering wheel to introduce pressure oil discharged from an oil pump into one chamber of a power cylinder. The other cylinder chamber is communicated with the tank and the oil in this chamber is circulated to operate the power cylinder to apply a steering assist force to the steered wheels. Such a power steering is required to have a characteristic of generating a steering assist force as large as possible so as to reduce the force required to operate the steering wheel when the ground contact resistance of the tire is large, such as when stationary or running at low speed. On the other hand, at the time of high speed traveling, in order to impart appropriate rigidity to the steering wheel and improve straight running stability, it is required that the steering assist force be as small as possible.

In order to obtain the above preferable steering force characteristics, there is already known a vehicle speed sensitive type power steering in which the steering force is controlled according to changes in the traveling speed of the vehicle. There are various types of vehicle speed-sensitive power steering systems. For example, the flow control valve controls the flow rate of pressure oil supplied to the power cylinder via a servo valve according to changes in vehicle speed. Type power steering, or a reaction force pressure control type power steering in which a hydraulic pressure controlled by a reaction force control valve is applied to a hydraulic reaction force chamber to generate a steering reaction force is used. The flow rate control type power steering has a problem that the range in which the steering force can be controlled is relatively narrow, and the reaction force control type power steering can obtain a preferable steering force. Since a complicated mechanism such as a force control valve and a reaction force receiving portion is required, the cost is high and the friction is large.

Further, a power steering of a type which controls a flow rate in accordance with a change in vehicle speed is further provided with a sensor for detecting a lateral acceleration generated in the vehicle body at the time of turning, so that in addition to information such as vehicle speed, a lateral direction is detected. A power steering system in which the steering force is controlled according to changes in acceleration has already been proposed (Japanese Patent Laid-Open No. 57-66071). The power steering described in this publication increases the lateral acceleration generated in the vehicle body when the front wheels change direction from the middle to the latter half of the steering when the vehicle steers rapidly during medium- and high-speed traveling. Since the tire receives the acceleration, the reaction force of the tire increases and the torsion amount of the torsion bar increases. As a result, the power assist increases, the handle becomes too light, and the feeling becomes unstable. There is one that was made for the purpose of eliminating the drawback.

In the basic structure of the conventional power steering system described above, the flow control valve 2 for controlling the oil discharged from the hydraulic pump 1 is provided with an electromagnetic solenoid 7, and the flow control valve 2 is operated by energizing the electromagnetic solenoid 7. , Control valve (servo valve)
It is designed to control the flow rate of the working oil sent to the No. The current flowing through the electromagnetic solenoid 7 is
Control based on a vehicle speed signal of a vehicle speed sensor 9 for detecting a traveling speed of the vehicle, a signal of a steering angular velocity sensor 10 for detecting a rotational angular velocity of a steering wheel SW during steering, a signal of a lateral G sensor 11 for detecting a lateral acceleration of a vehicle body, and the like. Circuit 8
Controlled by the control signal. With the above configuration of the power steering, the steering angular velocity sensor 1 can be used when performing rapid steering while traveling at a medium speed or higher.
By combining the information from 0 and the lateral G sensor 11,
The steering force at the start of steering is relatively light, and the steering characteristics become heavy in the latter half of the steering, so that a favorable steering feeling can be obtained.

[0006]

With the configuration of the conventional power steering described in the above publication, it is possible to obtain a preferable steering force as a vehicle speed sensitive power steering, but the control circuit, the lateral G sensor, etc. Since it is composed of various sensors, a power steering body, and the like, there is a problem that the cost is significantly higher than that of a normal power steering.

The present invention has been made to eliminate the above-mentioned drawbacks. With a very simple structure, lateral acceleration can be sensed to obtain the same preferable steering characteristics as those of the conventional vehicle speed sensitive power steering. It is intended to provide costly power steering.

[0008]

The power steering system according to the present invention is the same as the power steering system for a normal power steering system in which pressure oil discharged from an oil pump is supplied to a power cylinder via a servo valve to generate a steering assist force. A bypass valve is provided between both cylinder chambers of the cylinder to operate when the lateral acceleration generated in the vehicle body exceeds a predetermined value so that the two cylinder chambers communicate with each other.

[0009]

When a large lateral acceleration is generated in the vehicle body when a sudden steering operation is performed during traveling at medium and high speeds, the lateral G sensor detects the lateral acceleration in the conventional structure and the flow is performed via the controller. The control valve was operated to control the steering force to be large. However, in the power steering according to the present invention, when the lateral acceleration exceeds a predetermined value, the bypass valve is activated to operate the high pressure side cylinder chamber and the low pressure side cylinder. By communicating with the chamber and bypassing the oil in the high pressure side cylinder chamber to the low pressure side, the assist force generated by the power cylinder is reduced and the steering force sensed by the driver is increased.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a hydraulic circuit diagram of a power steering (generally indicated by reference numeral 1) according to an embodiment of the present invention. The power steering 1 is a control valve (servo valve) V and a power cylinder C as conventionally well known. It has and. The control valve V is an oil pump P, an oil tank T, and a power cylinder C, which are caused by the relative displacement of the input / output shaft caused by the rotation operation of a steering handle (not shown).
The flow paths are switched to the cylinder chambers C ₁ and C ₂ on both the left and right sides of the. At the neutral position of the control valve V, the oil discharged from the oil pump P and sent to the control valve V passes through the control valve V and returns to the oil tank T, and the cylinder chambers C on the left and right of the power cylinder C are provided. _{Since 1} and C ₂ also communicate with the oil tank T, these left and right cylinder chambers C ₁ and C ₂
No pressure difference is generated between them and the power cylinder C does not operate. When the steering handle is operated and the control valve V is switched, the oil discharged from the oil pump P is supplied to _one cylinder chamber C ₁ or C ₂ of the power cylinder C via the control valve V, and the other cylinder. Since the chamber is communicated with the oil tank T, the power cylinder C is operated by the pressure difference between the left and right cylinder chambers C ₁ and C ₂ , and a steering assist force is generated.

Further, in the power steering 1 according to this embodiment, the left and right cylinder chambers C ₁ of the power cylinder C,
A bypass valve 10 that communicates between C ₂ is provided. In this bypass valve 10, as shown in an enlarged view in FIG. 2, a spool 16 is slidably fitted in a valve hole 14 formed inside a valve housing 12. In the chambers 22 and 24 between the wall surfaces at both ends of the valve hole 14 and the end surfaces of the spool 16, the springs 18 and 20 are respectively provided.
Is arranged and presses the spool 16 from both sides to hold it at its neutral position. Bypass valve 10
Is arranged laterally with respect to the traveling direction of the vehicle, as will be described later. Therefore, when a lateral acceleration is generated in the vehicle body, the spool 16 has an amount corresponding to the biasing force of the springs 18 and 20. , Is moved in the direction in which the lateral acceleration acts.

Two annular concave grooves 14a and 14b are formed on the inner peripheral surface of the valve hole 14, and the left and right cylinder chambers C ₁ of the power cylinder C are connected via communication passages 14c and 14d.
Each is connected to C ₂ . On the other hand, spool 16
Has a 00 annular groove 16a formed in the center thereof. At the neutral position described above, the annular concave groove 14a formed on the inner surface of the valve hole 14 by the lands 16b and 16c provided on both sides of the annular groove 16a. , 14b are closed. When the spool 16 moves in the valve hole 14 by a predetermined amount or more in response to the lateral acceleration, one of the chambers 22 and 24 accommodating the springs 18 and 20 becomes one of the left and right cylinder chambers C ₁ and C ₂ . The one cylinder chamber and the other cylinder chamber communicate with the space 26 in the annular groove 16 a formed on the outer peripheral surface of the spool 16.

The two lands 16b of the spool 16 are
For example, tapered chamfered portions 16d, 16e, 16f, 16g are formed on the outer peripheral surfaces of both ends of 16c, and these chamfered portions 16d, 16e, 16f, 16 are formed.
g and the annular groove 14a formed on the inner surface of the valve hole 14,
The variable orifices are respectively constituted by both side edge portions of 14b. Therefore, when the spool 16 moves in the valve hole 14 so that one of the cylinder chambers C ₁ and C ₂ communicates with one of the chambers 22 and 24 containing the springs 18 and 20 in the valve hole 14, 16
The chamfered portions 16d, 16e, 16f,
The opening area of the variable orifice constituted by 16g and the edge portions of the annular grooves 14a and 14b changes.

Further, inside the spool 16, an axial passage 16h penetrating the shaft portion thereof and a radial passage 16i which intersects the axial passage 16h at a right angle and is opened to the space 26 in the annular groove 16a. Between the two chambers 22, 24 accommodating the springs 18, 20 in the valve hole 14 and between these chambers 2
2, 24 and the space 26 in the annular groove 16a formed on the outer peripheral surface of the central portion of the spool 16 are in constant communication with each other. Therefore, when the spool 16 moves and one of the cylinder chambers C ₁ and C ₂ communicates with one of the chambers 22 and 24 in which the springs 18 and 20 are accommodated in the valve hole 14, this chamber is axially arranged in the spool 16. The passage 16h and the radial passage 16i communicate with the space 26 in the annular groove 16a provided in the center of the spool 16, and further the annular concave grooves 14a and 14b.
And, it communicates with the other cylinder chamber through one of the communication passages 14c and 14d. In addition, at both ends of the spool 16,
Stoppers 16j and 16k are provided respectively and regulate the movement limit of the spool 16.

The bypass valve 10 having the above structure is provided separately from the power cylinder C at the center of gravity of the vehicle.
In addition, it is ideal that they are arranged laterally with respect to the traveling direction of the vehicle. Even if it cannot be installed at the position of the center of gravity, it needs to be installed laterally with respect to the traveling direction of the vehicle, and if it is installed in the center of the vehicle, the left-right difference can be eliminated. Further, the valve housing 12 of the bypass valve 10 may be integrated with the housing of the power cylinder C and arranged laterally in order to simplify the structure and make the device compact. Also in this case, it is preferable to arrange the bypass valve 10 so as to be located at the center of the vehicle.

The operation of the power steering 1 having the above structure will be described. For example, when a steering handle (not shown) is rotated to the left during high speed traveling, the control valve V is switched, and the oil discharged from the oil pump P passes through the control valve V to the left of the power cylinder C. While being sent to the cylinder chamber C ₁ , the right cylinder chamber C ₂ communicates with the oil tank T and the oil in the cylinder chamber C ₂ is circulated, and the power cylinder is caused by the pressure difference between the cylinder chambers C ₁ and C _2. C works,
The steering wheel turns to the left. When the steered wheels change direction to the left, lateral acceleration is generated in the vehicle body to the right, and the spool 16 of the bypass valve 10 bends the spring 20 to the right in the traveling direction of the vehicle. Move in the direction. When the movement amount of the spool 16 reaches a predetermined amount or more, as shown in FIG. 3, the high pressure left cylinder chamber C ₁ is moved to the left side annular groove 14 of the inner peripheral surface of the valve hole 14.
It communicates with the chamber 22 accommodating the spring 18 on the left side via a, and further, the axial passage 16 inside the spool 16
h, the radial passage 16i, the space 26 in the annular groove 16a formed in the outer peripheral surface of the spool 16 and the right annular concave groove 14b formed in the inner peripheral surface of the valve hole 14, and the low pressure right cylinder chamber C Connected within ₂ . As a result, the high-pressure oil in the left cylinder chamber C ₁ is bypassed into the low-pressure right cylinder chamber C ₂ , and the assist force due to the operation of the power cylinder C is reduced and the steering force is increased.

Unlike the conventional power steering described in the above publication (Japanese Patent Laid-Open No. 57-66071), the bypass valve 10 of the present embodiment does not require a controller, a sensor or the like and is composed of only mechanical parts. Therefore, despite the extremely simple structure and low cost, it is possible to obtain the desired steering force by detecting the lateral acceleration generated in the vehicle and controlling the steering force. Moreover, since the steering force is controlled by detecting the lateral acceleration generated in the vehicle, the state of the vehicle that changes the lateral acceleration such as the road surface condition or tire change is directly transmitted to the driver through the steering wheel. To be done. Further, in the above-described embodiment, since the movement amount of the spool 16 increases due to the increase in the lateral acceleration and the opening area of the variable orifice increases, the input / output characteristic of the vehicle changes according to the lateral acceleration. To do. Then, normally, the lateral acceleration generated in the vehicle body increases as the vehicle speed increases if the steering angle is the same,
In this respect, the power steering 1 according to the present embodiment also has a function as a vehicle speed sensitive type.

In the above embodiment, 2 of the spool 16 is used.
By providing tapered chamfered portions 16d, 16e, 16f, 16g on the outer peripheral surfaces of both ends of the one land portion 16b, 16c,
Although the variable orifice is formed between the annular recessed grooves 14a and 14b of the valve housing 12 and the edge portion, the variable orifice is not limited to the variable orifice and is opened when the spool 16 moves in accordance with the lateral acceleration. It is sufficient that the oil in the high pressure side cylinder chamber C ₁ or C ₂ is bypassed to the low pressure side cylinder chamber. In the case of a variable orifice, chamfered portions 16d, 16e, 16f, 16g
It is also possible to obtain a desired steering force characteristic by appropriately selecting the shape.

FIG. 4 shows a bypass valve 110 provided in the power steering according to the second embodiment.
The bypass valve 110 is different from the bypass valve 10 shown in FIG. 2 in the shape of the spool 116.
The other parts have the same configuration. The spool 116 of this embodiment has a small central land 116 on the outer peripheral surface.
Two annular grooves 116n and 116p are formed on both sides of m. Two lands 116b and 116c on both end sides
In the same way as in the above-mentioned embodiment, each of the valve recesses 114a and 114b of the valve housing 112 is closed at the neutral position, and when one of the power cylinders C moves when the spool 116 moves in response to the lateral acceleration. The cylinder chamber C ₁ or C ₂ is connected to one of the chambers 122 and 124 accommodating the springs 118 and 120 in the valve hole 114 via the annular groove 114a and 114b, and the other cylinder chamber is the annular groove 114a. , 114b, two annular grooves 116n formed on the outer peripheral surface of the spool 114,
It communicates with the nearer annular groove of 116p.

Inside the spool 116, an axial passage 116h penetrating between both end faces and two radial passages 116r opening to spaces 126 and 127 in the two annular grooves 116n and 116p, respectively. , 116s, and the cylinder 116 C ₁ or C _{2 of} the power cylinder C moves one of the chambers 120, 122 containing the springs 118, 120 as described above. When the other cylinder chamber communicates with one of the annular grooves 116n or 116p,
The cylinder chambers C ₁ and C ₂ are connected to each other via an axial passage 116 h and a radial passage 116 r or 116 s inside the spool 116. Also, the spool 11
A vibration isolating O-ring or seal ring 116q is fitted on the outer peripheral surface of the land 116m provided at the center of the spool 6, to prevent oscillation of the spool 116 during operation. The bypass valve 110 according to this embodiment also
Similar to the bypass valve 10 of the above-described embodiment, it is necessary to dispose it laterally with respect to the traveling direction of the vehicle, and ideally, dispose at the center of gravity of the vehicle. Alternatively, the power cylinder C may be integrally installed sideways,
In particular, the central portion of the vehicle is more preferable. The power steering equipped with this bypass valve 110 can also achieve the same effect as the above-described embodiment, and in addition to that, it is possible to obtain the effect of preventing the oscillation of the spool 116.

[0021]

As described above, according to the present invention, the lateral acceleration of the vehicle exceeds a predetermined value between both cylinder chambers of the power cylinder to which the oil discharged from the oil pump is supplied via the servo valve. By providing a bypass valve that operates when the temperature becomes low and communicates between the two cylinder chambers, it is possible to obtain a low-cost power steering that can give a suitable steering force to the driver with an extremely simple configuration.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a simplified configuration of a power steering according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view showing an example of a bypass valve provided in the power steering system.

FIG. 3 is a vertical cross-sectional view showing a state when the bypass valve of FIG. 2 is in operation.

FIG. 4 is a vertical sectional view showing another example of a bypass valve.

[Explanation of symbols]

C Power cylinder C ₁ Cylinder chamber C ₂ Cylinder chamber P Oil pump V Servo valve (control valve) 1 Power steering 10 Bypass valve 12 Valve housing 14 Valve hole 14c Communication hole 14d Communication hole 16 Spool 16a Spool annular groove 16b Spool land 16c Spool land 16h Spool internal passage (axial groove) 16i Spool internal passage (radial groove) 18 Spring 20 Spring 22 Spring accommodated chamber 24 Spring accommodated chamber

Claims (4)

[Claims] 1. In a power steering system in which pressure oil discharged from an oil pump is supplied to a power cylinder via a servo valve to generate a steering assist force, a lateral acceleration of a vehicle is generated between both cylinder chambers of the power cylinder. A power steering characterized in that a bypass valve is provided to connect between both cylinder chambers when the pressure exceeds a predetermined value. 2. The power steering according to claim 1, wherein the bypass valve includes a variable orifice that changes a passage area between the cylinder chambers according to a change in lateral acceleration. 3. The bypass valve, wherein the bypass valve is disposed transversely to a traveling direction of the vehicle, a spool slidably fitted in a valve hole formed in the valve housing, and the spool. Two springs arranged on both sides of the spool to hold the spool in a neutral position in the valve hole, a communication passage opening in the valve hole and communicating the cylinder chambers in the valve hole, and a central portion of the spool. And at least one annular groove formed in the spool, an internal passage formed between the two chambers formed in the spool and accommodating the spring in the valve hole, and an internal passage that constantly communicates these chambers with the annular groove, When the spool is in the neutral position, the lands on both sides of the annular groove close the communication path to the cylinder chambers, and the spool is moved by the lateral acceleration to a predetermined level. When the above movement is made, the communication passage to one of the cylinder chambers is opened to the chamber that accommodates one spring in the valve hole, and the communication passage to the other cylinder chamber is opened to the annular groove so that both cylinders are opened. The power steering according to claim 1 or 2, wherein the rooms are communicated with each other. 4. The power steering according to claim 3, wherein a housing of the bypass valve is integrated with a power cylinder.