JPH06344931A - Power steering device - Google Patents

Abstract

PURPOSE:To prevent the rise of the differential pressure in the vicinity of a neutral point and improve rigidity by suppressing the transmission of the step variation of the pressure in a feeding flow passage to a power cylinder. CONSTITUTION:A pressure sensitive bypass valve 63 which cuts off the communication of a bypass flow passage 52 according to the pressure of a feeding flow passage 21 is installed. A power steering device is constituted of a first bridge circuit 31 which is constituted of the variable throttles V1, V2, V3, and V4 for connecting a servovalve 30 with a pump and a tank 43, as semicenter open valve and the second bridge circuit 32 which is constituted of the variable throttles V5 and V6 on a pump 1 side which are connected with the pump, tank 43 and a power cylinder 100, as center closed valve and the variable throttles V7 and V8 on the tank 43 side as center open valve. After a valve 63 is operated by the throttle action of the valves V1 and V4 (V2 and V3), the valve V6 (V5) is opened, and at this time, the valve V8 (V7) has the opening area which is sufficient for the communication with the tank 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering apparatus which saves energy by reducing the flow rate supplied from a pump to a servo valve.

[0002]

2. Description of the Related Art As a power steering device of this type, Japanese Patent Application No.
There is one described in Japanese Unexamined Patent Publication No. 324121. As shown in FIG. 13, this device has a supply pump 1 for discharging hydraulic oil, and a servo valve 3 connected to the supply pump 1 via a supply passage 2. A power cylinder 8 is connected between the variable throttles 4, 5, 6, 7 of the servo valve 3 to steer the wheels in the directions distributed by the servo valve 3.

A metering orifice 9 is provided in the middle of the supply passage 2, and it operates by a pressure difference before and after the metering orifice 9. By bypassing a part of hydraulic oil from a bypass passage 10 to a tank 11, a servo valve is provided. A flow rate control valve 12 for supplying a constant flow rate of hydraulic oil is provided to the valve 3. A bypass passage 13 connected to the low pressure side of the flow control valve 12 and the tank 11 is connected to the supply passage 2 after the metering orifice 9, and the supply passage 2 is provided in the middle of the bypass passage 13. A pressure sensitive bypass valve 14 is provided for shutting off the communication between the bypass passage 13 and the tank 11 in accordance with the pressure.

An electromagnetic bypass valve 17 is arranged in parallel with the pressure sensitive bypass valve 14 to change the throttle area according to the vehicle speed.
Is provided. A bypass control valve 16 is connected between the pressure sensitive bypass valve 14 and the tank 11 of the bypass flow passage 13 and operates so as to keep a pressure difference between the supply flow passage 2 and the bypass flow passage 13 constant. Adjust the opening of.

In this tank, the opening of the bypass passage 13 is changed by the electromagnetic bypass valve 17 according to the vehicle speed, and the tank 11 is closed at low speed and opened as the vehicle speed increases.
The hydraulic oil supplied to the servo valve 3 is controlled according to the vehicle speed by controlling the flow rate flowing out to the servo valve 3. Further, when the pressure in the supply flow path 2 is low when there is no load (when traveling straight ahead), the pressure sensitive bypass valve 14 and the bypass control valve 16 are open, so the pressure after the metering orifice 9 becomes low and the flow control valve. The hydraulic fluid from the supply pump 1 is bypassed from the bypass flow passage 10 by 12.

When the pressure in the supply passage 2 rises above a predetermined level during load (steering), the pressure-sensitive bypass valve 14 shuts off the bypass passage 13 and restores the pressure after the metering orifice 9 to cause the servo control. The flow rate of the hydraulic oil supplied to the valve 3 is restored. And the bypass control valve 16
Operates so as to make the pressure difference between the bypass flow path 13 and the supply flow path 2 constant to keep the flow rate flowing out to the tank 11 per unit time constant and prevent the pressure in the supply flow path 11 from decreasing.

[0007]

However, in the above-mentioned conventional one, the pressure in the discharge passage 2 is step-changed by the operation of the load pressure sensitive valve 14, and when this pressure change is transmitted to the power cylinder 15, the assist force suddenly changes. Therefore, there is a problem that the steering feeling of the steering wheel is bad.

[0008]

SUMMARY OF THE INVENTION A power steering system according to the present invention comprises a bypass flow passage for connecting a chamber communicating with a flow control valve downstream of a metering orifice to a tank side, and a bypass flow depending on a pressure of a supply flow passage. A first bridge circuit having a pressure sensitive bypass valve that changes the throttle area of the passage, and a variable throttle provided in the flow passage that connects the servo valve to the pump and the tank; both oil chambers of the pump and power cylinder; and the tank A second bridge circuit in which a variable throttle is provided in the flow path connected to the pump. Among the variable throttles of the second bridge circuit, the variable throttle on the pump side is the center closed valve and the variable throttle on the tank side is center open. It is composed of a valve and the first
The bridge circuit's variable throttle is configured with a semi-center open valve that has a smaller opening area than the center open valve, and the center-closed valve starts to open after the pressure-sensitive bypass valve is activated by the throttle action of the semi-center open valve. At this time, the center open valve is formed so as to have an opening area sufficient to communicate with the tank, or a bypass flow passage for connecting a chamber communicating with the metering orifice downstream of the flow control valve to the tank side. , An electromagnetic bypass valve provided in the bypass flow passage for changing the throttle area according to a signal, and a pressure sensitive bypass valve provided in the bypass flow passage in parallel with the electromagnetic bypass valve for changing the throttle area according to the pressure of the supply flow passage And operates according to the pressure difference between the downstream side of the electromagnetic bypass valve and the pressure of the supply flow passage, and reduces the throttle area of the bypass flow passage. A bypass control valve that converts the servo valve to a pump and a tank, and a first bridge circuit that has a variable throttle in the flow path, and a flow path that connects both the oil chamber of the pump and the power cylinder and the tank. And a second bridge circuit provided with a variable throttle, wherein the variable throttle on the pump side of the variable throttle of the second bridge circuit is a center closed valve, and the variable throttle on the tank side is a center open valve. , The variable throttle of the first bridge circuit is composed of a semi-center open valve having a smaller opening area than the center open valve, and the center closed valve opens after the pressure sensitive bypass valve is operated by the throttling action of the semi center open valve. At the beginning, further, at this time, the center open valve has an opening area sufficient to communicate with the tank. It is obtained by forming so as to have.

[0009]

According to the above-mentioned structure of the present invention, the hydraulic fluid discharged from the pump is supplied to the servo valve after being controlled to a predetermined flow rate by the flow rate control valve which operates according to the pressure difference across the metering orifice. . When the pressure in the supply passage is low, the pressure sensitive bypass valve is fully opened, and the hydraulic oil flows into the tank. Therefore, the flow control valve further bypasses the hydraulic oil to the tank due to the low pressure on the downstream side of the flow control valve.

The pressure-sensitive bypass valve operates in response to the pressure increase in the supply passage, and when the pressure exceeds a predetermined pressure, the communication between the bypass passage and the tank is cut off, and the pressure on the downstream side of the flow control valve is restored. As a result, the flow rate bypassed to the tank by the flow control valve is reduced, and the necessary amount of hydraulic oil is supplied to the servo valve. Further, in the servo valve, the variable throttle (semi-center open valve) of the first bridge circuit is opened in the vicinity of the neutral position where the steering wheel is steered, and the working oil from the supply passage is circulated to the tank. The pump side variable throttle (center closed valve) of the second bridge circuit is closed, and both oil chambers of the power cylinder are connected to the tank via the tank side variable throttle (center open). The manual steering is performed by completely preventing the increase in the differential pressure between the two oil chambers.

During steering of the steering wheel, the pressure-sensitive bypass valve is actuated by the throttling action of the variable throttle (semi-center open valve) of the first bridge circuit, and then the center closed valve of the second bridge circuit starts to open. However, at this time, since the center open valve of the second bridge circuit still has a sufficient opening area, the differential pressure between both oil chambers of the power cylinder does not rise sharply.

According to the above-mentioned structure of claim 2,
The hydraulic fluid discharged from the pump is supplied to the servo valve after being controlled to a predetermined flow rate by a flow rate control valve that operates according to the pressure difference across the metering orifice. By increasing the throttle area of the electromagnetic bypass valve as the vehicle speed increases, the amount of hydraulic oil bypassed to the tank gradually increases, and the flow rate supplied to the servo valve decreases. The bypass control valve responds to the differential pressure between the pressure downstream of the electromagnetic bypass valve and the pressure in the supply flow path, and controls the flow rate of the hydraulic oil flowing out to the tank to control the speed without being affected by the load pressure. Supply a stable flow rate to the servo valve.

Further, in the servo valve, the variable throttle (semi-center open valve) of the first bridge circuit is opened in the vicinity of a neutral position where the steering wheel is slightly steered, and the hydraulic oil from the supply flow passage is circulated to the tank. . The pump side variable throttle (center closed valve) of the second bridge circuit is closed, and both oil chambers of the power cylinder are connected to the tank via the tank side variable throttle (center open). The manual steering is performed by completely preventing the increase in the differential pressure between the two oil chambers.

During steering of the steering wheel, the pressure-sensitive bypass valve is actuated by the throttling action of the variable throttle (semi-center open valve) of the first bridge circuit, and then the center closed valve of the second bridge circuit starts to open. However, at this time, since the center open valve of the second bridge circuit still has a sufficient opening area, the differential pressure between both oil chambers of the power cylinder does not rise sharply.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of the power steering apparatus,
Reference numeral 20 is a pump that discharges hydraulic oil according to the engine speed. Servo valve 3 that distributes and supplies hydraulic oil to power cylinder 100 via supply passage 21 to pump 20.
0 is connected.

A metering orifice 5 is provided in the middle of the supply passage 21.
0 is provided. A bypass flow passage 51 is connected to the supply flow passage 21 before the measurement orifice 50, and a bypass flow passage 52 is connected to the supply flow passage 21 after the measurement orifice 50. The flow control valve 5 is provided in the middle of the bypass flow passage 51.
3 is provided with a spool 54, and one end of the spool 54 is provided with the metering orifice 50 through the bypass flow passage 51.
The pressure of the front supply passage 21 acts, and the pressure of the supply passage 21 after the metering orifice 50 acts on the other end of the spool 54 via the bypass passage 52. A spring 55 is inserted so as to bias the spool 54 in the direction of closing the bypass flow passage 51. As a result, the opening degree of the bypass passage 51 is adjusted so that the pressure difference before and after the metering orifice 50 becomes constant, and a predetermined flow rate of hydraulic oil is supplied to the servo valve 30.

The tank 4 is provided at one end of the bypass passage 52.
3, the pressure sensitive bypass valve 63 and the bypass control valve 73 are connected in the middle of the bypass flow path 52. The pressure-sensitive bypass valve 63 is provided with a cut valve 60 in which a slit 62 for cutting off the communication of the bypass flow passage 52 is formed, and a direction in which the cut valve 60 is urged to open the bypass flow passage 52. A spring 61 is inserted in the. Then, the pressure of the supply flow passage 21 acts on one end of the cut valve 60, and the pressure of the bypass flow passage 52 acts on the other end of the cut valve 60 and the force of the spring 61 acts.

A bypass control valve 73 is provided downstream of the pressure sensitive bypass valve 63 in the bypass passage 52.
This bypass control valve 7 is installed.
3, the throttling area is controlled according to the pressure introduced from the supply passage 21 to the bypass passage 52. That is, the bypass control valve 73 is slidably provided with a movable valve 71 that restricts the bypass flow passage 52, and the movable valve 71 is normally biased by a spring 72 in a direction to open the bypass flow passage 52.

The supply pump 20 and the tank 43 are connected by a return passage 80, and the return passage 80 is connected with an escape passage 81 connected to the bypass passage 52. The relief flow passage 81 is provided with a relief valve 82 that releases the pressure when the pressure in the supply flow passage 21 exceeds the relief pressure. The servo valve 30 is shown in FIG.
As shown in a developed view, a valve shaft 90 that is connected to the handle HD and integrally rotates, and a valve body 9 coaxially arranged on the outer circumference of the valve shaft 90.
1 and 1. And valve shaft 9
Between 0 and the valve body 91, two types of first bridge circuits 31 and second bridge circuits 32 that throttle control the hydraulic oil are alternately formed in the circumferential direction.

Variable throttles V1 and V2 are provided on the pump 20 side of the first bridge circuit 31, and variable throttle V is provided on the tank 43 side.
3 and V4 are connected to these variable diaphragms V1 and V
2, V3 and V4 are semi-center open with a distance of θ2 between the end surfaces of the valves (valve shaft 90, valve body 91) and the steering wheel HD not being steered (neutral). It is configured as a valve, and the opening area of the valve shaft 90 and the valve body 91.
7 changes according to the relative rotation angle (valve rotation angle).

Further, variable throttles V5 and V6 are formed on the pump 20 side of the second bridge circuit 32, and variable throttles V7 and V8 are formed on the tank 43 side. A power cylinder 100 that exerts an assist force is connected to the variable diaphragms V5, V6, V7, and V8, and the variable diaphragms V5, V5
V7 is connected to the left chamber 100A of the power cylinder 100, and the variable diaphragms V6 and V8 are connected to the right chamber 100B of the power cylinder 100.

Then, the variable diaphragms V5, V in the neutral state
6 is θ1 between the valves 90 and 91 as shown in FIG.
The variable throttles V7 and V8 are configured as center-closed valves that overlap each other, as shown in FIG.
It is configured as a center open valve in which the end faces of 0 and 91 are separated by θ4. Then, these opening widths θ
1, θ2, θ3, and θ4 are formed in a relationship of θ2 <θ1 <θ4 <θ3.

In the first embodiment constructed as described above, the hydraulic oil discharged from the pump 20 causes a pressure difference before and after it by the action of the metering orifice 50. When the discharge flow rate of the pump 20 increases, the pressure difference increases, and the bypass valve 54 is displaced against the spring 55. As a result, the bypass flow passage 51 is opened, and the excess flow of hydraulic oil is bypassed to the tank 43. Therefore, a constant flow rate of hydraulic oil required for assisting is delivered to the supply passage 21.

When the steering wheel HD travels straight without steering (at neutral), the variable throttles V5 and V6 (center closed valves) of the second bridge circuit 32 of the servo valve 30 are closed, so that the power cylinder 100 is connected. Is not supplied with hydraulic oil. Further, since both oil chambers 100A, 100B of the power cylinder 100 are connected to the tank 43 via variable throttles V7, V8 (center open valves), both oil chambers 100A, 100B are kept in a low pressure state. Therefore, the hydraulic fluid discharged from the pump 20 is the first
Variable apertures V1, V2, V3, V4 of the bridge circuit 31 of
It is discharged to the tank 43 through the (semi-center open valve).

The supply flow path 21 is in a low pressure state because it communicates with the tank 43 via the first bridge circuit 31. Therefore, the cut valve 60 of the pressure sensitive bypass valve 63
Is located at the left end of FIG. 1 and the slit 62 is fully open. Further, the movable valve 71 of the bypass control valve 73 operates by the pressure difference between the bypass flow passage 52 and the supply flow passage 21, and keeps the flow rate discharged to the tank 43 constant.
Therefore, the pressure in the bypass flow passage 52 is reduced by connecting the bypass flow passage 52 to the tank 43 via the slit 62 and the bypass control valve 73, and the metering orifice 50 acting on the spool 54 of the flow control valve 43.
A low pressure close to the pressure of the tank 43 acts on the latter pressure.

Therefore, the flow rate control valve 53 is provided in the bypass passage 5
1 is fully opened. Therefore, most of the hydraulic oil discharged from the pump 20 is bypassed via the bypass flow passage 51 and returned to the pump 20 via the return flow passage 80. As a result, most of the hydraulic oil is returned to the pump 20 via the bypass flow passage 51 with a small pressure loss without passing through the metering orifice 50 and the downstream supply flow passage 21 at the time of neutrality. Very low loss.

When the handlebar HD is steered and the valve shaft 90 relatively rotates relative to the valve body 91 (increases the valve rotation angle), one of the variable throttles V1, V4 (V2, V3) of the first bridge circuit 31. ), The opening area is reduced. As a result, the pressure in the supply passage 21 gradually increases. (FIG. 8) At this time, the bypass control valve 73 prevents the pressure from escaping from the bypass flow channel 52 to the tank 43 in response to the pressure increase in the supply flow channel 21. And keeps the flow rate flowing out into the tank 43 constant.

When the pressure in the supply passage 21 reaches a predetermined pressure or more, the pressure sensitive bypass valve 63 is operated against the spring 61 and the opening area of the slit 62 is closed. As a result, the pressure (line pressure) in the supply flow path 21 rapidly increases (FIG. 8) and the flow rates supplied to the first and second bridge circuits 31 and 32 are increased. Further, although the pressure in the supply passage 21 sharply rises (step change (FIG. 8)) as described above due to the rotation operation of the handle HD, the variable throttles V5, V6 (center closed) of the second bridge circuit 32 The closed state of the valve) is maintained until the valve rotation angle θ1 (see FIGS. 7 and 8).
The differential pressure ΔP between the oil chambers 100A and 100B of 00 is maintained at 0. Therefore, when the valve rotation angle is θ1 or less, it is possible to prevent the differential pressure ΔP between the oil chambers 100A and 100B of the power cylinder 100 from rising, and manual steering is performed near neutral.

When the valve rotation angle exceeds θ1,
The variable diaphragm V5 (V6) of the second bridge circuit 32 starts to open. (FIGS. 5 and 7) When the variable diaphragm V5 (V6) starts to open, the variable diaphragm V8 (V7) of the second bridge circuit has an opening area sufficient to communicate with the tank 43, so that the power cylinder Both oil chambers of 100 have the same pressure as the tank 43,
The line pressure P1 at the valve rotation angle θ1 is prevented from suddenly acting on the power cylinder 100. Therefore, as shown in FIG. 9, the differential pressure ΔP of the power cylinder 100 smoothly rises according to the valve rotation angle θ. further,
As shown in FIGS. 4, 5 and 6, in order to prevent the pressure-sensitive bypass valve 63 from returning to its original state (the state shown in FIG. 1) due to the pressure in the supply passage 21 decreasing due to the opening of the variable throttle V5 (V6). Chamfers 93, 94, 9 provided on each part of 90
5, the flow rate discharged to the tank 43 is adjusted.

In the first embodiment, the relationship among the opening widths θ1, θ2, θ3, θ4 of the servo valve 30 is θ2 <θ1 <θ4 <θ3, but θ1 <θ2.
The relationship of <θ4 <θ3 may be used. A second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram of the power steering apparatus, and 20 is a pump for discharging hydraulic oil according to the engine speed. A servo valve 30 that distributes and supplies hydraulic oil to the power cylinder 100 is connected to the pump 20 via a supply passage 21.

A metering orifice 5 is provided in the middle of the supply passage 21.
0 is provided. A bypass flow passage 51 is connected to the supply flow passage 21 before the measurement orifice 50, and a bypass flow passage 52 is connected to the supply flow passage 21 after the measurement orifice 50. The flow control valve 5 is provided in the middle of the bypass flow passage 51.
3 is provided with a spool 54, and one end of the spool 54 is provided with the metering orifice 50 through the bypass flow passage 51.
The pressure of the front supply passage 21 acts, and the pressure of the supply passage 21 after the metering orifice 50 acts on the other end of the spool 54 via the bypass passage 52. A spring 55 is inserted so as to bias the spool 54 in the direction of closing the bypass flow passage 51. As a result, the opening degree of the bypass passage 51 is adjusted so that the pressure difference before and after the metering orifice 50 becomes constant, and a predetermined flow rate of hydraulic oil is supplied to the servo valve 30.

The tank 4 is provided at one end of the bypass passage 52.
3 is connected, and a pressure sensitive bypass valve 63 is connected in the middle of the bypass flow path 52. The pressure-sensitive bypass valve 63 has a cut valve 60 in which a slit 62 for blocking communication of the bypass passage 52 is formed, and a direction in which the cut valve 60 is urged to open the bypass passage 52. A spring 61 is inserted in the. And the cut valve 60
The pressure of the supply passage 21 acts on one end of the cut valve 60.
The pressure of the bypass flow passage 52 acts on the other end of the spring and the force of the spring 61 acts.

The supply pump 20 and the tank 43 are connected by a return flow passage 80, and the return flow passage 80 is connected with a relief flow passage 81 connected with the bypass flow passage 52. The relief flow passage 81 is provided with a relief valve 82 that releases the pressure when the pressure in the supply flow passage 21 exceeds the relief pressure. The servo valve 30 is shown in FIG.
As shown in a developed view, a valve shaft 90 that is connected to the handle HD and integrally rotates, and a valve body 9 coaxially arranged on the outer circumference of the valve shaft 90.
1 and 1. And valve shaft 9
Between 0 and the valve body 91, two types of first bridge circuits 31 and second bridge circuits 32 that throttle control the hydraulic oil are alternately formed in the circumferential direction.

Variable throttles V1 and V2 are provided on the pump 20 side of the first bridge circuit 31, and variable throttle V is provided on the tank 43 side.
3 and V4 are connected to these variable diaphragms V1 and V
2, V3 and V4 are semi-center open with a distance of θ2 between the end surfaces of the valves (valve shaft 90, valve body 91) and the steering wheel HD not being steered (neutral). It is configured as a valve, and the opening area of the valve shaft 90 and the valve body 91.
7 changes according to the relative rotation angle (valve rotation angle).

Variable throttles V5 and V6 are formed on the pump 20 side of the second bridge circuit 32, and variable throttles V7 and V8 are formed on the tank 43 side. A power cylinder 100 that exerts an assist force is connected to the variable diaphragms V5, V6, V7, and V8, and the variable diaphragms V5, V5
V7 is connected to the left chamber 100A of the power cylinder 100, and the variable diaphragms V6 and V8 are connected to the right chamber 100B of the power cylinder 100.

Then, the variable diaphragms V5, V at the neutral position
6 is θ1 between the valves 90 and 91 as shown in FIG.
The variable throttles V7 and V8 are configured as center-closed valves that overlap each other, as shown in FIG.
It is configured as a center open valve in which the end faces of 0 and 91 are separated by θ4. Then, these opening widths θ
1, θ2, θ3, and θ4 are formed in a relationship of θ2 <θ1 <θ4 <θ3.

In the second embodiment constructed as described above, the hydraulic oil discharged from the pump 20 produces a pressure difference before and after it by the action of the metering orifice 50. When the discharge flow rate of the pump 20 increases, the pressure difference increases, and the bypass valve 54 is displaced against the spring 55. As a result, the bypass flow passage 51 is opened, and the excess flow of hydraulic oil is bypassed to the tank 43. Therefore, a constant flow rate of hydraulic oil required for assisting is delivered to the supply passage 21.

When the steering wheel HD travels straight without being steered (at neutral), the variable throttles V5 and V6 (center closed valves) of the second bridge circuit 32 of the servo valve 30 are closed. Is not supplied with hydraulic oil. Further, since both oil chambers 100A, 100B of the power cylinder 100 are connected to the tank 43 via variable throttles V7, V8 (center open valves), both oil chambers 100A, 100B are kept in a low pressure state. Therefore, the hydraulic fluid discharged from the pump 20 is the first
Variable apertures V1, V2, V3, V4 of the bridge circuit 31 of
It is discharged to the tank 43 through the (semi-center open valve).

Since the supply flow passage 21 communicates with the tank 43 via the first bridge circuit 31, it is in a low pressure state. Therefore, the cut valve 60 of the pressure sensitive bypass valve 63
Is located at the left end of FIG. 2 and the slit 62 is fully open. Therefore, the hydraulic oil flowing into the bypass flow passage 52 is discharged to the tank 43 through the slit 62, so that the metering orifice 5 acting on the spool 54 of the flow control valve 43.
As for the pressure after 0, a low pressure close to the pressure of the tank 43 acts.
Therefore, the flow rate control valve 53 makes the bypass flow path 51 fully open. Therefore, most of the hydraulic oil discharged from the pump 20 is bypassed via the bypass flow passage 51 and returned to the pump 20 via the return flow passage 80.

As a result, most of the hydraulic oil is returned to the pump 20 through the bypass passages 51 and 52 having a small pressure loss at the time of neutrality, so that the energy loss of the pump 20 becomes very small. When the handlebar HD is steered and the valve shaft 90 relatively rotates (increases the valve rotation angle) with respect to the valve body 91, the first bridge circuit 3
The aperture area of one of the variable diaphragms V1 and V4 (V2 and V3) is reduced. As a result, when the pressure in the supply passage 21 gradually rises and reaches a predetermined pressure or more, the pressure sensitive bypass valve 63 is operated against the spring 61, and the slit 62
The opening area of is decreasing. Thereby, the supply channel 21
Pressure (line pressure) gradually increases. When the pressure in the supply passage 21 is further increased by steering (the valve rotation angle is increased) and the slit 62 is closed, the pressure in the supply passage 21 (line pressure) is rapidly increased (step change (FIG. 8).
Therefore, the flow rate supplied to the first and second bridge circuits 31 and 32 is increased.

Further, although the pressure in the supply passage 21 gradually rises as described above due to the rotating operation of the handle HD,
Since the closed state of the variable throttles V5, V6 (center closed valve) of the second bridge circuit 32 is maintained until the valve rotation angle θ1 (see FIGS. 7 and 8), both oil chambers 100A of the power cylinder 100 up to the angle θ1. , 100B differential pressure Δ
P is held at 0. Therefore, when the valve rotation angle is θ1 or less, both oil chambers 100A, 1A of the power cylinder 100 are
It is possible to prevent an increase in the differential pressure ΔP of 00B, and manual steering is performed near neutral.

When the valve rotation angle exceeds θ1,
The variable diaphragm V5 (V6) of the second bridge circuit starts to open. (FIGS. 5 and 7) When the variable diaphragm V5 (V6) starts to open, the variable diaphragm V8 (V7) of the second bridge circuit has an opening area sufficient to communicate with the tank 43, so that the power cylinder Both oil chambers of 100 have the same pressure as the tank 43,
Since the line pressure P1 at the valve rotation angle θ1 is prevented from suddenly acting on the power cylinder 100, FIG.
As shown in, the differential pressure ΔP of the power cylinder 100 smoothly rises according to the valve rotation angle θ. Further, as shown in FIGS. 4, 5 and 6, so that the pressure of the supply flow passage 21 is reduced by the opening of the variable throttle V5 (V6) and the pressure sensitive bypass valve 63 does not return to the original state (state of FIG. 1). The flow rate discharged to the tank 43 is adjusted by chamfering 93, 94, and 95 provided on each part of the valve shaft 90.

In the second embodiment, the relationship among the opening widths θ1, θ2, θ3, θ4 of the servo valve 30 is θ2 <θ1 <θ4 <θ3, but θ1 <θ2.
The relationship of <θ4 <θ3 may be used. Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 10 is an overall configuration diagram of the power steering apparatus according to the third embodiment, and 20 is a pump that discharges hydraulic oil according to the engine speed, and a power cylinder is provided to the pump 20 via a supply passage 21. 10
A servo valve 30 that distributes and supplies hydraulic oil to 0 is connected.

A metering orifice 5 is provided in the middle of the supply passage 21.
0 is provided. A bypass flow passage 51 is connected to the supply flow passage 21 before the measurement orifice 50, and a bypass flow passage 52 is connected to the supply flow passage 21 after the measurement orifice 50. The flow control valve 5 is provided in the middle of the bypass flow passage 51.
3 is provided with a spool 54, and one end of the spool 54 is provided with the metering orifice 50 through the bypass flow passage 51.
The pressure of the front supply passage 21 acts, and the pressure of the supply passage 21 after the metering orifice 50 acts on the other end of the spool 54 via the bypass passage 52. A spring 55 is inserted so as to bias the spool 54 in the direction of closing the bypass flow passage 51.

The tank 4 is provided at one end of the bypass passage 52.
3 is connected, and a pressure sensitive bypass valve 63 is connected in the middle of the bypass flow path 52. The pressure-sensitive bypass valve 63 has a cut valve 60 in which a slit 62 for blocking communication of the bypass passage 52 is formed, and a direction in which the cut valve 60 is urged to open the bypass passage 52. A spring 61 is inserted in the. And the cut valve 60
The pressure of the supply passage 21 acts on one end of the cut valve 60.
The pressure of the bypass flow passage 52 acts on the other end of the spring and the force of the spring 61 acts. The force of the spring 55 acts together with the opening degree.

In the bypass passage 52, an electromagnetic bypass valve 75 is arranged in parallel with the pressure sensitive bypass valve 63. The electromagnetic bypass valve 75 includes a variable throttle 76 whose throttle area is controlled by an electronic control unit 77 to which an electric signal corresponding to the vehicle speed is input. That is, the variable throttle 76 of the electromagnetic bypass valve 75 is closed when the vehicle speed is low, and the throttle area increases as the vehicle speed increases, as shown in FIG. In addition,
The electric signal input to the electronic control unit 77 is not only the vehicle speed, but also the steering angle, the steering angular velocity, the steering wheel torque, the brake signal, the shift position signal, and the LSD (Limited).
An electrical signal such as a lateral differential (Slip Differential) actuation signal or a lateral wind may be used.

Electromagnetic bypass valve 7 in the bypass flow path 52
A bypass control valve 73 is arranged on the downstream side of 5. The bypass control valve 73 is designed so that the throttle area is controlled according to the pressure introduced from the supply passage 21 to the bypass passage 52. That is, the bypass control valve 73 is slidably provided with the movable valve 71 that throttle-controls the bypass flow passage 52,
This movable valve 71 is normally bypassed by the spring 72 to the bypass passage 52.
Is held at the sliding end that opens up to the maximum.

The pump 20 and the tank 43 are connected by a return flow passage 80, and the return flow passage 80 is connected with an escape flow passage 81 connected with the bypass flow passage 52.
The relief flow passage 81 has a relief valve 82 for releasing the pressure when the pressure in the supply flow passage 21 exceeds the relief pressure.
Is provided. As shown in a developed view in FIG. 3, the servo valve 30 includes a valve shaft 90 that is connected to a handle HD and integrally rotates, and a valve body 91 coaxially arranged on the outer circumference of the valve shaft 90. It is composed by. And, between the valve shaft 90 and the valve body 91, the hydraulic oil is throttled and controlled 2.
Types of first bridge circuit 31 and second bridge circuit 3
2 and 2 are formed alternately in the circumferential direction.

Variable throttles V1 and V2 are provided on the pump 20 side of the first bridge circuit 31, and variable throttle V is provided on the tank 43 side.
3 and V4 are connected to these variable diaphragms V1 and V
2, V3 and V4 are semi-center open with a distance of θ2 between the end surfaces of the valves (valve shaft 90, valve body 91) and the steering wheel HD not being steered (neutral). It is configured as a valve, and the opening area of the valve shaft 90 and the valve body 91.
7 changes according to the relative rotation angle (valve rotation angle).

Further, variable throttles V5 and V6 are formed on the pump 20 side of the second bridge circuit 32, and variable throttles V7 and V8 are formed on the tank 43 side. A power cylinder 100 that exerts an assist force is connected to the variable diaphragms V5, V6, V7, and V8, and the variable diaphragms V5, V5
V7 is connected to the left chamber 100A of the power cylinder 100, and the variable diaphragms V6 and V8 are connected to the right chamber 100B of the power cylinder 100.

Then, the variable diaphragms V5 and V
6 is θ1 between the valves 90 and 91 as shown in FIG.
The variable throttles V7 and V8 are configured as center-closed valves that overlap each other, as shown in FIG.
It is configured as a center open valve in which the end faces between 0 and 91 are separated by θ4. Then, these opening widths θ
1, θ2, θ3, and θ4 are formed in a relationship of θ2 <θ1 <θ4 <θ3.

In the third embodiment constructed as described above, the hydraulic oil discharged from the pump 20 causes a pressure difference before and after it due to the action of the metering orifice 50. When the discharge flow rate of the pump 20 increases, the pressure difference increases, and the bypass valve 54 is displaced against the spring 55. As a result, the bypass flow passage 51 is opened, and the excess flow of hydraulic oil is bypassed to the tank 43. Therefore, a constant flow rate of hydraulic oil required for assisting is delivered to the supply passage 21.

When the steering wheel HD travels straight without being steered (at neutral), the variable throttles V5 and V6 (center closed valves) of the second bridge circuit 32 of the servo valve 30 are closed. Is not supplied with hydraulic oil. Further, since both oil chambers 100A, 100B of the power cylinder 100 are connected to the tank 43 via variable throttles V7, V8 (center open valves), both oil chambers 100A, 100B are kept in a low pressure state. Therefore, the hydraulic fluid discharged from the pump 20 is the first
Variable apertures V1, V2, V3, V4 of the bridge circuit 31 of
It is discharged to the tank 43 through the (semi-center open valve).

As described above, the supply flow path 21 is in a low pressure state because it communicates with the tank 43 via the first bridge circuit 31. Therefore, the cut valve 60 of the pressure sensitive bypass valve 63 is located at the left end of FIG. 10, and the slit 62 is in a fully opened state. Therefore, the hydraulic oil flowing into the bypass flow passage 52 is discharged to the tank 43 through the slit 62, so that the pressure after the metering orifice 50 acting on the spool 54 of the flow rate control valve 43 is a low pressure close to the pressure of the tank 43. To work. Therefore, the flow rate control valve 53 makes the bypass flow path 51 fully open. As a result, most of the hydraulic oil discharged from the pump 20 is bypassed via the bypass flow passage 51 and returned to the pump 20 via the return flow passage 80.

As a result, most of the hydraulic oil is returned to the pump 20 through the bypass passages 51 and 52 having a small pressure loss at the time of neutrality, so that the energy loss of the pump 20 becomes very small. By the way, at low speed, since the variable throttle 76 of the electromagnetic bypass valve 75 is closed by the electronic control unit 77, the hydraulic oil is guided to the pressure sensitive bypass valve 63 side and acts as described above. Then, as the vehicle speed increases, the electromagnetic bypass valve 75 of the electronic control unit 77
The variable diaphragm 76 is opened as shown in FIG. 11 according to the vehicle speed. As a result, the hydraulic oil in the bypass flow passage 52 is communicated with the tank 43 via the variable throttle 76, so that the flow rate of the hydraulic oil sent to the supply flow passage 21 is further reduced. Therefore, at high speed, the vehicle speed sensitivity is provided by the reduction of the flow rate, and the energy saving effect is produced.

When the handlebar HD is steered and the valve shaft 90 relatively rotates relative to the valve body 91 (increases the valve rotation angle), one of the variable throttles V1, V4 (V2, V3) of the first bridge circuit 31. ), The opening area is reduced. As a result, the pressure in the supply passage 21 gradually increases. (FIG. 8) At this time, the bypass control valve 73 prevents the pressure from escaping from the bypass flow channel 52 to the tank 43 in response to the pressure increase in the supply flow channel 21. And keeps the flow rate flowing out into the tank 43 constant.

When the pressure in the supply passage 21 reaches a predetermined pressure or more, the pressure sensitive bypass valve 63 is operated against the spring 61, and the opening area of the slit 62 is reduced. When the pressure in the supply passage 21 is further increased by steering (increase in valve rotation angle), the slit 62 is closed. As a result, the pressure (line pressure) in the supply passage 21 is rapidly increased as shown in FIG. (Step change) Further, although the pressure of the supply passage 21 is increased by the rotating operation of the handle HD as described above, the closed state of the variable throttles V5, V6 (center closed valve) of the second bridge circuit 32 is Since the valve rotation angle θ1 is maintained (see FIGS. 7 and 8), the power cylinder 10 is used up to the angle θ1.
The differential pressure ΔP between the two oil chambers 100A and 100B of 0 is held at 0. Therefore, when the valve rotation angle is θ1 or less, the pressure difference Δ between the oil chambers 100A and 100B of the power cylinder 100 is Δ.
It is possible to prevent the P from rising, and manual steering is performed near neutral.

When the valve rotation angle exceeds θ1,
The variable diaphragm V5 (V6) of the second bridge circuit starts to open. When the variable diaphragm V5 (V6) starts to open, the variable diaphragm V8 (V7) of the second bridge circuit is connected to the tank 43.
Since the throttle area has a sufficient area for communicating with the power cylinder 100, both oil chambers of the power cylinder 100 have the same pressure as that of the tank 43, and the line pressure P1 at the valve rotation angle θ1 rapidly increases in the power cylinder 100. Since the operation is prevented, the differential pressure ΔP of the power cylinder 100 smoothly rises according to the valve rotation angle θ as shown in FIG.
Further, the supply passage 2 is opened by the opening of the variable diaphragm V5 (V6).
In order to prevent the pressure-sensitive bypass valve 63 from returning to its original state (state of FIG. 1) due to the decrease of the pressure of No. 1, chamfers 93 provided at various parts of the valve shaft 90 as shown in FIGS.
The flow rate discharged to the tank 43 is adjusted by 94 and 95.

Further, as the vehicle speed increases, the electronic control unit 77
The throttle area A of the variable throttle 76 of the electromagnetic bypass valve 75 is opened as shown in FIG. As a result, the hydraulic oil in the bypass flow passage 52 is communicated with the tank 43 via the variable throttle 76, and the flow rate of the hydraulic oil sent to the supply flow passage 21 is reduced. Therefore, at a high speed, the flow rate of the hydraulic oil supplied to the servo valve 30 is reduced, so that the vehicle speed sensitivity is provided and the energy saving effect is produced.

As described above, not only the vehicle speed but also the steering angle, the steering angular velocity, the steering wheel torque, the brake signal, the shift position signal, the LSD (Limited Slip Dif) signal are input to the electronic control unit 77.
By using an electric signal such as a lateral (G) signal due to a lateral) operation signal and a lateral wind, it is possible to realize an optimal steering feeling according to a traveling state.

In the third embodiment, the relationship among the opening widths θ1, θ2, θ3, θ4 of the servo valve 30 is θ2 <θ1 <θ4 <θ3, but θ1 <θ2.
The relationship of <θ4 <θ3 may be used.

[0062]

As described above, according to the present invention, the center-closed valve starts to open almost at the same time as the semi-center open valve of the servo valve smoothes the throttle action,
Further, at this time, the center open valve is formed so as to have an opening area sufficient to communicate with the tank, so that the fluctuation of the flow rate (step change) at the start of the operation of the pressure sensitive bypass valve is caused in the power cylinder. It does not affect the steering feeling.

Furthermore, since it is possible to prevent an increase in the differential pressure of the power cylinder near the neutral position, it is possible to improve the feeling of rigidity near the neutral position.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a power steering apparatus according to a first embodiment.

FIG. 2 is an overall configuration diagram of a power steering apparatus according to a second embodiment.

FIG. 3 is a development view in which a half circumference portion of a servo valve is developed.

FIG. 4 is a detailed view of part A of FIG.

5 is a detailed view of a portion B of FIG.

FIG. 6 is a detailed view of a C portion of FIG.

FIG. 7 is a graph showing a relationship between a valve rotation angle θ and an opening area A of each variable diaphragm.

FIG. 8 is a graph showing the relationship between the valve rotation angle θ and the line pressure P.

FIG. 9 is a graph showing a relationship between a valve rotation angle θ and a differential pressure ΔP of a power cylinder.

FIG. 10 is an overall configuration diagram of a power steering apparatus according to a third embodiment.

FIG. 11 is a graph showing the relationship between vehicle speed and throttle area.

FIG. 12 is a graph showing characteristics of pressure and flow rate according to vehicle speed.

FIG. 13 is a diagram showing a conventional power steering apparatus.

FIG. 14 is a graph showing the relationship between the valve rotation angle θ and the pressure P of the conventional power steering apparatus.

[Explanation of symbols]

 20 pump 21 supply channel 30 servo valve 31 first bridge circuit 32 second bridge circuit 43 tank 50 metering orifices 51, 52 bypass channel 53 flow control valve 63 pressure sensitive bypass valve 70 throttle 73 bypass control valve 75 electromagnetic bypass Valve 100 Power cylinder V1 to V4 Variable throttle (semi-center open valve) V5, V6 Variable throttle (center closed valve) V7, V8 Variable throttle (center open valve)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuhisa Mori 1-1-1, Asahi-cho, Kariya city, Aichi prefecture Toyota Koki Co., Ltd.

Claims (2)

[Claims] 1. A pump for discharging hydraulic oil, a power cylinder for exerting an assist force, a servo valve for distributing and supplying hydraulic oil discharged from the pump to the power cylinders, and a supply for supplying hydraulic oil from the pump to servo valves. A power steering apparatus comprising: a flow path; a metering orifice provided in the supply flow path; and a flow rate control valve for controlling a flow rate bypassing to a tank in accordance with a pressure difference across the metering orifice. A bypass passage connecting a chamber communicating with a downstream side of the metering orifice of the valve to a tank side; and a pressure sensitive bypass valve changing a throttle area of the bypass passage according to a pressure of the supply passage, A first valve provided with a variable throttle in a passage connecting a servo valve to the pump and the tank
Of the variable throttle of the second bridge circuit, and a second bridge circuit in which a variable throttle is provided in a flow path connected to both the oil chamber of the pump and the power cylinder and the tank. Side variable throttle is a center closed valve, the tank side variable throttle is a center open valve, and the variable throttle of the first bridge circuit is a semi-center open valve with a smaller opening area than the center open valve. The center closed valve starts to open after the pressure sensitive bypass valve is actuated by the throttling action of the semi-center open valve, and at this time, the center open valve is sufficiently open to communicate with the tank. A power steering apparatus, which is formed to have an area. 2. A pump for discharging hydraulic oil, a power cylinder for exerting an assist force, a servo valve for distributing and supplying hydraulic oil discharged from the pump to the power cylinders, and a supply for supplying hydraulic oil from the pump to servo valves. A power steering apparatus comprising: a flow path; a metering orifice provided in the supply flow path; and a flow rate control valve for controlling a flow rate bypassing to a tank in accordance with a pressure difference across the metering orifice. A bypass flow path connecting a chamber communicating with the downstream side of the metering orifice of the valve to the tank side, an electromagnetic bypass valve that is provided in the bypass flow path and changes a throttle area according to a signal, and the electromagnetic bypass valve is connected in parallel with the electromagnetic bypass valve. A pressure-sensitive bypass valve that is provided in the bypass flow passage and changes the throttle area according to the pressure of the supply flow passage, and a pressure on the downstream side of the electromagnetic bypass valve. And a bypass control valve that operates according to the pressure difference in the supply flow passage to change the throttle area of the bypass flow passage, and a variable throttle is provided in the flow passage that connects the servo valve to the pump and the tank. Of the variable throttle of the second bridge circuit, and a second bridge circuit in which a variable throttle is provided in a flow path connected to both the oil chamber of the pump and the power cylinder and the tank. Side variable throttle is a center closed valve, the tank side variable throttle is a center open valve, and the variable throttle of the first bridge circuit is a semi-center open valve with a smaller opening area than the center open valve. And the center closed valve after the pressure sensitive bypass valve is operated by the throttling action of the semi-center open valve. The power steering apparatus is characterized in that the center opening valve is formed so as to have an opening area sufficient to communicate with the tank at this time when the lube starts to open.