JPH025623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a working fluid flow rate control device in power steering.

Power steering systems, which reduce the burden on the driver by hydraulically assisting vehicle steering operations, reduce the hydraulic assist force at high speeds because the turning resistance of the wheels decreases significantly at high speeds. Many products are designed to improve safety.

The pump that serves as the hydraulic pressure source is driven in synchronization with the engine rotation, so the discharge flow rate increases in the high rotation range,
A large amount of hydraulic fluid is supplied to the power steering hydraulic actuator, but to prevent this, we installed a flow control valve and a drooping pin type flow control device that reduces the supply flow rate as the rotation speed increases. It consists of

However, in this case, the pump rotation speed and vehicle speed do not necessarily correspond, and even when the rotation speed is high, for example when climbing a winding slope with the transmission gear position set to low gear, the steering resistance is large, so the supply flow rate is Reducing this makes the steering wheel heavier, and with top gear, etc., the vehicle speed increases even if the rotational speed is not that high, so it is necessary to reduce the supply flow rate quickly, and it is quite difficult to match these accurately. . Additionally, when the power steering load increases, the spool of the flow control valve displaces in response to this load pressure, changing the position of the drooping pin, so the supply flow rate may fluctuate depending on the load pressure. Ta. In other words, if the steering wheel was turned while driving at high speed, the drooping pin would come out and the opening of the variable orifice would increase, increasing the supply flow rate and causing a reduction in steering stability.

The present invention was proposed to solve these problems, and includes a flow rate control system that changes the opening degree depending on the transmission gear position between the pump port from the hydraulic pump and the supply port to the hydraulic actuator. A variable orifice is provided, and pressures upstream and downstream of the variable orifice are applied to both ends of the spool that controls the amount of excess flow released.
To provide a power steering flow rate control device with a simple structure and high control accuracy, which can prevent a decrease in flow rate in a high rotation and low speed range and reliably reduce power assist force in a high speed range.

In addition, the variable orifice whose opening degree changes depending on the transmission gear position is corrected according to the pump rotation speed, and the flow rate is controlled according to the vehicle speed independently of the spool that controls the bypass flow rate. The present invention provides a power steering flow rate control device that can prevent a supply flow rate from changing (increasing) due to load fluctuations (increasing).

Embodiments of the present invention will be described below based on the drawings.

In the embodiment of FIG. 1, the body 1 of the control device
is formed with a pump port 2 connected to the hydraulic pump discharge side, a supply port 3 connected to the hydraulic actuator side of the power steering via a switching valve (not shown), and a bypass port 4 that returns surplus flow to the reservoir side. and these bodies 1
are opened in the spool holes 5, respectively.

The spool hole 5 has a spool 7 that acts as a flow control valve to control the amount of excess oil released.
and a control rod 8 for making the flow path to the supply port 3 variable.

The spool 7 is pressed until it engages with the retaining ring 11 by the spring 10 of the back pressure chamber 9 to which the back pressure of the variable throttle is introduced, closing the bypass port 4, but the front pressure of the throttle applied to the left end of the spool is large. When this happens, push back the spool 7 and release the bypass port 4.
to allow some of the hydraulic oil to escape to the reservoir side.

On the other hand, a solenoid 13 operated via a control circuit 24 based on a signal from a means 23 for detecting the gear position of the transmission is arranged at the end of the movable sleeve 12 fitted into the spool hole 5.

The movable sleeve 12 is formed into a cylindrical shape with a bottom, and the cylindrical portion is provided with a port 14 that constantly communicates between the internal chamber 19 and the supply port 3, and the sleeve 12 is connected to the push rod 16 of the solenoid 13 by a spring 15 toward the supply port side. They are pressed until they touch.

The control rod 8 is integrally formed with a metering part 17 whose tip diameter is reduced in stages, and this metering part 17 enters and exits the orifice hole 20 formed in the sleeve 12 to control the opening degree of the orifice. It constitutes a variable orifice (variable aperture) 21 that changes the aperture.

The control rod 8 is attached to a piston body 30 that slides in the spool hole 5, and is biased by a spring 31 in the direction of coming out of the orifice hole 20 of the sleeve 12 until it comes into contact with a retaining ring 32.

A fixed orifice 34 for generating a pressure difference is formed in the piston body 30.

Note that the passage 22 guides the downstream pressure of the variable orifice 21 to the back pressure chamber 9 of the spool 7.

Next, the operation will be explained with reference to FIG. 2. When the flow rate fed into the pump port 2 is small, the entire amount of hydraulic oil flows from the fixed orifice 34 to the supply port 3 via the orifice hole 20.

Then, when the supply flow rate of the pump port 2 increases and the differential pressure generated at the orifice hole 20 becomes greater than a certain value, the spool 7 moves back against the spring 10 and begins to open the bypass port 4.

Therefore, some of the hydraulic oil in pump port 2 is
The orifice hole 20 is bypassed to the reservoir side.
The front and rear pressures of will be kept almost constant.

However, as the pump rotation speed further increases and the flow rate increases, the flow rate to the supply port 3 increases little by little in proportion to the deflection force of the spring 10 of the spool 7, even though the bypass flow rate increases. Therefore, the fixed orifice 3 of the piston body 30
The pressure difference between the two cylinders 4 increases accordingly, and the piston body 30 is displaced while bending the spring 31, and the metering part 17 of the control rod 8 is deeply inserted into the orifice hole 20.

Incidentally, the degree of opening of this orifice hole 20 changes depending on the insertion position of the control rod 8.

For example, when the transmission gear position is low gear, the control circuit 24 does not excite the solenoid 13, and the movable sleeve 12 is stopped at the left limit by the spring 15, so that the smallest diameter part of the metering part 17 of the control rod 8 is in the orifice. It is inserted into the hole 20.

Therefore, the opening degree of the variable orifice 21 is maximized, and the flow rate to the supply port 3 is controlled to be large in the low gear position.

On the other hand, in the top gear position, the control circuit 24 maximizes the excitation current of the solenoid 13, thereby causing the push rod 16 to extend the movable sleeve 12 to a large extent.

Therefore, the large diameter portion of the metering section 17 approaches the orifice hole 20, and the variable orifice 21 approaches the orifice hole 20 accordingly.
The opening degree decreases.

Therefore, in the top gear position, supply port 3
The supply flow rate to decreases. This situation is shown in the characteristic diagram of FIG. 2, where the second and third gear positions have intermediate characteristics between the low and top gear positions.

In the low gear position, even if the engine speed (pump rotation speed) is high, the vehicle speed is low, so the required flow rate for power assist is large.On the other hand, in the top gear position, even if the engine speed is not so high, the vehicle speed is high and the required flow rate is high. By controlling as described above, it is possible to supply the required amount of hydraulic oil from low speed to high speed.

Furthermore, in relation to the pump rotation speed, as mentioned above, in the high rotation speed range, the opening degree of the variable orifice 21 decreases rapidly due to the intrusion movement of the control rod 8 itself into the orifice hole 20. The flow rate flowing to supply port 3 at is reduced. In this case, due to the relationship with the movable sleeve 12, the flow rate starts to be reduced even if the piston body 30 is slightly displaced in a high speed gear such as a top gear, compared to a low speed gear such as a low gear. In other words, the second
As shown in the figure, by reliably reducing the flow rate in the high-speed range, even more maneuverability can be ensured.

On the other hand, if the pressure downstream of the variable orifice 21 increases due to load fluctuations on the supply port 3 side, the spool 7 is returned due to the associated pressure increase in the rear pressure chamber 9, and the opening degree of the bypass port 4 is reduced. Although the pressure in the pump port 2 is increased in accordance with the load, the differential pressure across the piston body 30 does not change, so the opening degree of the variable orifice 21 is kept the same, and the supply flow rate remains the same as in the conventional drooping pin method. In addition, it is possible to prevent the increase in the amount associated with steering operation.

That is, in the present invention, the spool 7 for constant differential pressure control and the metering orifice 21 are not integrated, and the variable orifice 21 can be independently controlled regardless of the bypass flow rate.

By the way, regarding the spool 7 for differential pressure control,
Since the pump port pressure (prepressure) acts directly, the response to pressure fluctuations is extremely good, and highly accurate pressure feedback control can be performed.

As described above, according to the present invention, the variable throttle is changed according to the transmission gear position, so while the supply flow rate is reliably reduced in the high gear position and the steering stability is improved, the supply flow rate is improved in the low speed gear position. This can solve the problem of lack of power assist. Further, according to the present invention, regardless of the load fluctuation of the power steering,
The supply flow rate is always reduced in high vehicle speed ranges, further improving handling stability.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, and FIG. 2 is a flow characteristic diagram thereof. 1...Body, 2...Pump port, 3...Supply port, 4...Bypass port, 7...Spool, 8...Control rod, 10...Spring, 12...Movable sleeve, 13...Solenoid, 15...Spring, 17
... Measuring section, 20 ... Orifice hole, 21 ... Variable orifice, 23 ... Gear position detection means, 24 ... Control circuit, 30 ... Piston body, 31 ... Spring, 34
...Fixed orifice.

Claims (1)

[Claims] 1 The oil discharged from the hydraulic pump is sent from the pump port through the throttle part to the supply port communicating with the hydraulic actuator, and the excess flow is returned through the spool that opens and closes the bypass port in response to the pressure before and after the throttle. In the power steering flow control device, a means for detecting the transmission gear position is provided, and a variable orifice is formed between the pump port and the supply port, the opening degree of which decreases as the detected gear position becomes a higher gear, A piston body with a fixed orifice is provided upstream of this variable orifice, and this piston body is displaced according to the differential pressure across the fixed orifice, and a control rod protruding from the piston body is inserted into the variable orifice to control the pump port. A flow rate control device for power steering, characterized in that the pressure and the downstream pressure of the variable orifice are guided to both ends of the spool.