JP2000335432A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always secure a standby flow, and improve feeling and responsiveness while energy saving effect is sufficiently exhibited by communicating an accumulator connected to a surplus flow side port with a control part connected to a control flow side port at the time of rest steering and in the case of a large steering angle. SOLUTION: In the neutral position of steering, the respective variable throttles 4-7 of a control part C1 are opened, so that a fluid supplied from a control flow port 2 of a divider D to a supply passage 8 is returned as a standby flow through the respective variable throttles 4-7 to a tank T. As another control part C2 is closed, a surplus flow passed through an unloader valve U is all supplied to an accumulator A. On the other hand, at the time of rest steering and in the case of a large steering angle, one of variable throttles 14, 15 of the control part C2 is opened, so that the pressure fluid stored in the accumulator A is joined to the supply passage 8 through a short circuit passage 18 and a connecting passage 19. Accordingly, power shortage of a power cylinder 9 can be eliminated.

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 is linked to an engine and drives a power cylinder with a discharge fluid of a low discharge pump whose discharge amount is determined depending on the number of revolutions.

[0002]

2. Description of the Related Art Since a device for driving a power cylinder with a discharge fluid of a low discharge pump linked to an engine is cheaper than an electric power steering, a fluid power steering device has recently attracted attention again. However, in a power steering apparatus using a low-discharge pump linked to an engine, the discharge fluid of the pump must be continuously supplied as a standby flow rate to a control unit which is an open center in order to improve the responsiveness. Therefore, energy loss has become a problem. Therefore, in order to minimize this energy loss, a device in which a valve is connected between the low discharge pump and the control unit has been conventionally known.

In this conventional device, the load pressure increases during stationary operation or at extremely low speeds, and a large flow is supplied to the power cylinder in response to the increase. Also, during small steering angle steering or straight running of a vehicle that does not turn the steering wheel,
As the load pressure decreases, a small flow is supplied to the power cylinder in response to the decrease.

[0004]

There are two types of conventional devices as described above in view of their control characteristics. One of them is shown in FIG. 5, in which the pump discharge amount gradually increases as the load pressure increases to reach a specified flow rate. But,
This type of device has a problem that its responsiveness is not good. FIG. 6 shows another type. The response shown in FIG. 6 is improved as is apparent from the drawing. However, this time, there was a problem that the feeling deteriorated. SUMMARY OF THE INVENTION An object of the present invention is to provide a power steering device having a good feeling and responsiveness while sufficiently exhibiting an energy saving effect.

[0005]

According to a first aspect of the present invention, there is provided a low discharge pump which is linked to an engine and whose discharge amount is determined depending on the number of revolutions thereof, and a discharge amount from the low discharge pump which is controlled by a control flow port. A priority divider that distributes the flow to the excess flow port, a first control unit connected to the control flow port, a power cylinder whose output is controlled by the first control unit, and an accumulator connected to the excess flow port. Connecting this accumulator to the first control unit side,
And a second control unit for interrupting the connection.
The second control unit is configured to connect the accumulator to the first control unit when the steering is stationary or when the steering angle is large.

According to a second aspect of the present invention, an unloader valve is provided between the priority divider and the accumulator. The unloader valve connects the excess flow port of the priority divider to the accumulator at a normal position, and the upstream port at a switching position. Is communicated to the tank, and the normal position is maintained until the maximum pressure stored in the accumulator is reached, and when the maximum pressure is reached, the switching position is switched to the switching position.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A low-discharge pump P of the first embodiment shown in FIG. 1 is of a type which is linked to an engine (not shown) and whose discharge amount depends on the engine speed. Say. The low discharge pump P is connected to the priority divider D. The priority divider D has an inflow port 1, a control flow port 2 and a surplus flow port 3, and the inflow port 1 is connected to the low discharge pump P.
Is communicated to. The priority divider D as described above supplies a constant control flow rate of the discharge amount of the pump P to the control flow port 2 side preferentially, and supplies a surplus flow rate not less than the control flow rate to the surplus flow port 3 side. I do.

The control flow port 2 is connected to a first control unit C1. Although the specific configuration of the first control unit C1 is not shown, the first control unit C1 is integrally formed with the second control unit C2. That is, the first and second control units C1 and C2
A rotary spool is provided in the sleeve, and the sleeve and the rotary spool rotate relative to each other in accordance with the steering angle to exert a control function.

The first control unit C1 forms a bridge circuit with four variable apertures 4 to 7 formed by combining the above-mentioned convex portions and concave portions. However, the first control unit C1
Is an open center, and when the steering wheel (not shown) is maintained at the neutral position, each of the variable apertures 4 to
7 is opened. A concave portion and a convex portion are alternately formed on each of the sleeve and the rotary spool, and the variable aperture 4 is determined by the amount of wrap between the concave portion and the convex portion.
-7 are determined. Then, when the steering wheel is maintained at the neutral position as described above, in order to open the variable diaphragms 4 to 7, the concave portion and the convex portion must have an underlap relationship.

The first control unit C1 as described above connects the inflow point a connected to the control flow port 2 of the priority divider D via the supply passage 8 to the variable throttles 4 and 5.
Connected to The connection point b is a variable aperture 4
And 6 and also communicates with one pressure chamber 9a of the power cylinder 9. Connection point c
Is connected to the variable throttles 5 and 7 and also communicates with the other pressure chamber 9 b of the power cylinder 9. Further, the outflow point d is connected to the variable throttles 6 and 7 and also communicates with the tank T via the return passage 10.

When the steering wheel is turned to the right, for example, the apertures of the variable diaphragms 4 and 7 become large,
Although the apertures of the variable apertures 5 and 6 are small, the variable apertures 5 and 6 are closed at the time of stationary steering or a large steering angle. When the steering wheel is turned to the left, which is opposite to the above, the apertures of the variable apertures 5 and 6 become large, and the apertures of the variable apertures 4 and 7 become small. 7 closes.

Therefore, when the steering wheel is turned to the right, the control flow rate supplied from the control flow port 2 passes through the supply passage 8 → point a → variable throttle 4 → point b, and the pressure of one of the power cylinders 9 It is supplied to the chamber 9a. At this time, the other pressure chamber 9 of the power cylinder 9
The fluid flowing out of b is returned to the tank T via point c → variable throttle 7 → point d → return passage 10. On the other hand, when the steering wheel is turned to the left, the control flow supplied from the control flow port 2 is supplied to the other pressure chamber 9b of the power cylinder 9 via the supply passage 8 → point a → variable throttle 5 → point c. Supplied to At this time, the fluid flowing out of one pressure chamber 9a of the power cylinder 9 is returned to the tank T via the point b → the variable throttle 6 → the point d → the return passage 10.

The excess flow port 3 of the priority divider D is connected to an accumulator A via an unloader valve U. The unloader valve U applies a spring force of the spring 11 to one end of the spool, and applies a pressure downstream of the unloader valve U, that is, a pressure on the accumulator A side, to the pilot chamber 12 at the other end. When the unloader valve U is in the normal position (A) by the action of the spring 11, the excess flow port 3 and the accumulator A are directly connected.

On the other hand, when the pressure in the pilot chamber 12 overcomes the spring force of the spring 11, the unloader valve U switches to the switching position (b). At this switching position (b), the surplus flow port 3 is connected in parallel to the accumulator A and the tank T.
The check valve 13 functions and the accumulator A
Backflow to the surplus flow port 3 is prevented.

The unloader valve U switches to the switching position (b) when the pressurized fluid is stored to the full capacity of the accumulator A.
In order to switch the unloader valve U to the switching position (b) as described above, the following is performed. That is, when the pressure when the pressurized fluid is stored to the full capacity of the accumulator A acts on the pilot chamber 12 side, the pilot chamber 1
The pressure receiving area on the two sides is determined. Therefore, if the pressurized fluid is stored to the full capacity of the accumulator A as described above, the unloader valve U is switched to the switching position (b). Thus, accumulator A
Then, when the pressure fluid is stored to fill its capacity,
The reason for switching to the switching position (b) is to reduce an excess flow rate to the tank T to minimize energy loss.

The accumulator A as described above is also connected to the second control section C2. That is, the second control unit C2 and the unloader valve U are connected to the accumulator A in parallel. The second control unit C2 also forms a bridge circuit with the variable apertures 14 to 17. However, these variable apertures 14 to 17 are closed centers, the variable apertures 14 and 15 located on the upstream side are gradually opened in accordance with the steering angle, and the variable apertures 16 and 17 located on the downstream side are always open. It keeps it closed. The variable apertures 14 to 1
In order to make 7 a closed center, the concave portion and the convex portion must have an overlapping relationship.

On the other hand, an inflow point e on the upstream side of the variable throttles 14 and 15 is connected to an accumulator A and an unloader valve U.
A short-circuit path 18 is connected between points f and g on the downstream side of 15. The short-circuit path 18 is connected to the communication path 19
Through the supply passage 8.

Next, the operation of the first embodiment will be described.
When the steering wheel is almost kept at the neutral position as in the case of straight running of the vehicle, the variable throttles 4 to 7 of the first control unit C1 are open, so that the supply is supplied from the control flow port 2 to the supply passage 8. The fluid is returned to the tank T via each of the variable throttles 4 to 7 as a standby flow rate. The reason why the standby flow rate is secured in this way is to maintain good responsiveness of the power cylinder 9. Then, the priority divider D can set the control flow rate flowing out of the control flow port 2 to some extent freely. If this control flow rate is sufficiently reduced, the energy loss on the first control unit C1 side can be reduced. . Further, in the first embodiment, various conditions are determined so that the control flow rate is sufficiently reduced.

In the above-mentioned state, if the accumulator A does not sufficiently store the pressurized fluid, the unloader valve U maintains the normal position (A). That is, in this case, the acting force on the pilot chamber 12 side is
This is because it is smaller than the spring force. When the steering wheel is kept neutral, the second control unit C
Since the valve 2 is closed, all excess flow passing through the unloader valve U is supplied to the accumulator A.
Then, if the pressure fluid is stored to the full capacity of the accumulator A, the pilot chamber 12 of the unloader valve U
Since the acting force on the side overcomes the spring force of the spring 11, the unloader valve U switches to the switching position (b).

When the unloader valve U is in the switching position (b)
, The surplus flow rate via the priority divider D is returned to the tank T. At this time, the fluid stored in the accumulator A is blocked by the check valve 13 and does not flow backward.

When the steering wheel is switched left or right from the above state, the opening of the variable throttles 14, 15 of the second control unit C2 is controlled in accordance with the steering angle. However, in this embodiment, the second control unit is controlled not only when the overlapping amount of the variable throttles 14 to 17 is properly maintained and the steering wheel is maintained at neutral, but also at a small steering angle within a certain range. I try not to open C2. Therefore, when the steering angle is small, the power cylinder 9 operates with a small control flow rate supplied from the control flow port 2 of the priority divider D. Since the operation is performed with a small control flow rate, the output of the power cylinder does not increase so much. In other words, the power assisting force at this time does not increase so much. In this way, safety is maintained at the time of a small steering angle such as at the time of high-speed running.

At the time of stationary steering or a large steering angle of the steering wheel, one of the variable apertures 14 and 15 of the second control unit C2 is opened. When the variable throttle 14 or 15 of the second controller C2 is opened, the pressure fluid stored in the accumulator A joins the supply passage 8 through the short-circuit passage 18 and the communication passage 19. Therefore, the flow rate supplied from the supply passage 8 to the inflow point a is
It is the sum of the control flow supplied from the control flow port 2 of the priority divider D and the flow from the accumulator A. However, the flow rate supplied from the accumulator A is determined by the degree of opening of the variable throttles 14 and 15 of the second control unit C2, which ultimately depends on the steering angle. When the variable throttle 14 or 15 of the second control unit C2 is opened in a state where the accumulator A does not store a sufficient pressure fluid, the flow rate passing through the unloader valve U is directly supplied to the second control unit C2. And make up for the shortfall.

According to the first embodiment described above, when the vehicle is running straight or when the steering wheel is kept neutral, a small control flow rate controlled by the priority divider D is supplied from the control flow port 2 and , It will be returned to the tank as a standby flow.
As described above, since the standby flow rate is only a small control flow rate, the energy loss at this time is very small. Further, even at a small steering angle, the power cylinder 9 operates with a small control flow rate, so that the power assisting force is small. However, when the steering angle is small, a large assist force is not required from the viewpoint of safety. Therefore, it is reasonable to operate the power cylinder 9 with a small control flow rate at a small steering angle.

At the time of stationary steering or a large steering angle, the opening degree of the variable throttle 14 or 15 of the second control unit C2 is increased, so that the pressure fluid stored in the accumulator A or directly supplied from the unloader valve U. The fluid is the second
It merges with the first control unit C1 via the control unit C2. Therefore, power shortage does not occur in the power cylinder 9.

In addition, since the control flow rate is constantly supplied to the first control section C1 as a standby flow rate, good responsiveness can be maintained. Further, since the standby flow rate is constantly supplied, even if the fluid from the accumulator A joins the standby flow rate, the feeling is not impaired. Further, in the first embodiment, if the accumulator A does not sufficiently store the pressurized fluid, the unloader valve A maintains the normal position (A) by the action of the spring 11. Therefore, a predetermined flow rate is always maintained in the accumulator A, and the flow rate of the accumulator A is rarely insufficient. Even if the flow rate is insufficient, the fluid from the unloader valve U is directly supplied to the second control unit C2, so that the flow rate does not become insufficient on the power cylinder 9 side. On the other hand, if the fluid is accumulated to the full capacity of the accumulator A, the excess flow port 3 of the priority divider D communicates with the tank T, so that there is almost no energy loss.

The second embodiment shown in FIG. 2 differs from the first embodiment in the second control section C2, and all other configurations are the same as those in the first embodiment. The second control section C2 of the second embodiment includes a pair of variable apertures 20, 21 having a closed center. This variable aperture 20, 2
1 has its upstream side connected to the accumulator A in parallel and its downstream side connected to the communication passage 19 in parallel. Further, the second control unit C2 thus configured is integrally formed with the first control unit C1. That is, similarly to the first embodiment, the sleeve and the rotary spool provided therein are relatively rotated to control the opening degree of one of the variable throttles 20 and 21.

The second control unit C2 as described above also increases the opening degree during stationary steering or large steering angle.
As in the embodiment, the detailed description of the operation is omitted.

The third embodiment shown in FIG.
Is different from that of the first embodiment, and all other configurations are the same as those of the first embodiment. The second control unit C2 of the third embodiment forms a bridge circuit with four variable apertures 22 to 25 of a closed center. The inflow point e of the bridge circuit is connected to the accumulator A and the unloader valve U, and the outflow point h is connected to the communication passage 19.

The variable apertures 22 to 25 described above are
When the steering wheel is turned to one side, the variable throttle 2
2 and 24 are simultaneously opened, and the variable apertures 23 and 25 are kept closed. Therefore, the fluid from the accumulator A flows into the communication passage 19 through the variable throttles 22 and 24. When the steering wheel is turned to the other side, the variable apertures 23 and 25 are simultaneously opened, and the variable apertures 22 and 25 are opened.
24 remains closed. Therefore, the fluid from the accumulator A flows to the communication passage 19 through the variable throttles 23 and 25.

In the third embodiment as described above, similarly to the first embodiment, the second control unit C2 is used when the vehicle is running straight or at a small steering angle.
Are not opened. Therefore, the power cylinder 9 operates with a small flow rate supplied from the control flow port 2. Also, at the time of stationary steering or a large steering angle, the variable throttle of the second control unit C2 is opened and stored in the accumulator A. Pressure fluid flows into the supply passage 8,
This is the same as the first embodiment.

In the fourth embodiment shown in FIG. 4, a bridge circuit is constituted by four variable apertures 22 to 25.
This is the same as the embodiment. However, in the fourth embodiment, 2
With two communication passages 26 and 27 and
The connection point i provided between 2 and 24 is connected to the communication passage 2
6 through a connection point b of the first control unit C1. Further, a connection point j provided between the variable throttles 23 and 25 communicates with a connection point c of the first control unit C1 via a communication passage 27.

That is, the fourth embodiment differs from the third embodiment in that the pressurized fluid stored in the accumulator A is directly supplied to the power cylinder 9. However, as described above, the small control flow supplied from the control flow port 2 of the priority divider D is constant,
Since the flow rate from the control unit C2 depends on the steering angle, the flow rate supplied to the power cylinder 9 ultimately depends on the steering angle. Therefore, the function is completely the same as that of the third embodiment.

[0033]

According to the power steering apparatus of the first invention, the standby flow rate can always be ensured, so that when the steering wheel is turned off, no shock is generated and the feeling is not impaired. . Also,
At the time of stationary steering or a large steering angle, the pressure fluid stored in the accumulator is supplied to the power cylinder, so that there is no response delay. According to the second invention, the fluid in the excess flow port of the priority divider can be continuously supplied to the accumulator until the pressure fluid is stored to the full capacity of the accumulator. Therefore, there is no shortage of flow rate in the accumulator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is a circuit diagram of a second embodiment.

FIG. 3 is a circuit diagram of a third embodiment.

FIG. 4 is a circuit diagram of a fourth embodiment.

FIG. 5 is a graph showing characteristics of a conventional power steering device.

FIG. 6 is a graph showing characteristics of a conventional power steering device.

[Explanation of symbols]

 P Low discharge pump D Priority divider 2 Control flow port 3 Excess double ports C1 First control unit C2 Second control unit A Accumulator 9 Power cylinder U Unloader valve

Claims (2)

[Claims] 1. A low-discharge pump associated with an engine and whose discharge amount is determined depending on the number of revolutions thereof, and a priority for distributing the discharge amount from the low-discharge pump to a control flow port side and an excess flow port side. A divider, a first control unit connected to the control flow port side, a power cylinder whose output is controlled by the first control unit, an accumulator connected to the surplus flow port side, and the accumulator connected to the first control unit side. A second control unit for connecting or disconnecting the connection, wherein the second control unit is configured to connect the accumulator to the first control unit when the steering is stationary or at a large steering angle. apparatus. 2. An unloader valve is provided between the priority divider and the accumulator. The unloader valve communicates an excess flow port of the priority divider with the accumulator at a normal position, and communicates the upstream port with the tank at a switching position. Let me
2. The power steering apparatus according to claim 1, wherein the normal position is maintained until the maximum pressure stored in the accumulator is reached, and the switching position is switched to the switching position when the maximum pressure is reached.