JPH0147346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for controlling the flow rate of hydraulic oil for power steering of a vehicle according to vehicle speed.

In order to reduce steering force in automobiles, the installation rate of power steering, which uses hydraulic pressure to power-assist wheel turning operations, is increasing, but wheel turning resistance generally changes with vehicle speed. However, the resistance tends to decrease as the driving speed increases, so while a large hydraulic assist force is required in the low speed driving range, it is more similar to manual steering in the high speed driving range in order to improve steering stability. It is said that a certain amount is sufficient.

Therefore, a speed-sensitive power steering system that improves high-speed stability by reducing the amount of oil supplied to the hydraulic actuator of the power steering according to the vehicle speed has been developed.
It has been proposed as a number.

Now, to explain this based on FIG. 1, hydraulic oil from a hydraulic pump 1 driven in synchronization with the engine is transferred via an orifice 2 to a hydraulic actuator 3 of the power steering, which is operated by a switching valve (not shown). (switches by sensing the current).

A first flow bypass valve 5 that bypasses a portion of the hydraulic oil from upstream of the orifice 2 and returns it to the reservoir 4.
will be provided.

This first flow bypass valve 5 responds to the differential pressure before and after the orifice 2, and when the differential pressure exceeds a certain value, it opens and returns the excess flow to the reservoir 4, thereby providing the required amount mainly in the low speed range. Hydraulic oil is supplied to the hydraulic actuator 3. In addition, the orifice 2
A second flow bypass valve 6 is provided that bypasses a portion of the hydraulic fluid from downstream of the reservoir 4 and returns it to the reservoir 4. This bypass valve 6 opens based on the output of the vehicle speed sensor 7, and as the vehicle speed increases. By increasing the valve opening degree, the bypass flow rate is increased, and the hydraulic oil flow rate to the hydraulic actuator 3 is reduced in the high speed range, creating a state similar to manual steering.

Therefore, as shown in FIG. 2, when the engine speed increases and the pump discharge amount increases to a predetermined value, the flow rate supplied to the hydraulic actuator 3 is adjusted by sensing the differential pressure across the orifice 2. When the flow rate bypass valve 5 of No. 1 is opened, the flow rate is maintained at that flow rate.

When the vehicle speed further increases (revolutions increase) and moves from a medium speed range to a high speed range, the second flow bypass valve 6 opens in accordance with the vehicle speed and bypasses the flow, so the amount of hydraulic oil supplied decreases. It is reduced to a sufficient degree to ensure maneuverability at high speeds.

By the way, in such a device, the first flow rate bypass valve 5 controls the flow rate based on the engine rotation speed that drives the hydraulic pump 1 rather than the vehicle speed, while the second flow rate bypass valve 6 controls the flow rate based on the vehicle speed. It's under control.

For this reason, for example, when climbing a winding slope using a low gear while the engine speed is high,
In reality, there is a region where the vehicle speed and engine speed are not proportional, where the vehicle speed does not increase and therefore the flow rate decreases despite the large steering resistance and the power assist force is insufficient, and accurate flow control is not possible. I can't get it.

On the other hand, even if the vehicle speed is the same, the load on the hydraulic actuator 3 fluctuates, and if the circuit pressure on the actuator 3 side fluctuates due to an increase or decrease in the load due to, for example, road surface conditions, the bypass amount of the second flow bypass valve 6 also fluctuates. , as a result, hydraulic actuator 3
There is a problem in that there is an excess or deficiency in the required flow rate, which impairs maneuverability.

The present invention focuses on such problems and improves stability in all vehicle speed ranges, especially in high-speed maneuverability, by supplying the required flow rate even when vehicle speed, engine speed, or hydraulic actuator load fluctuates. An object of the present invention is to provide a power steering flow control device that improves the performance of the power steering system.

Embodiments of the present invention will be described below with reference to the drawings.

In the present invention, as shown in FIG. 3, the second flow bypass valve 8 is interposed in a circuit 9 connecting the orifice 2 and the hydraulic actuator 3, and the drain circuit 10 of the flow bypass valve 8 includes: A pressure control valve 11 is interposed.

The first flow bypass valve 12 has a structure similar to that shown in FIG. 1, and a differential pressure responsive spool 14 is slidably housed inside a valve housing 13.
Depending on the position of this spool 14, the pump port 1
5 is divided into a supply port 16 and a bypass port 17.

Pump port 15 communicates with hydraulic pump 1 , supply port 16 communicates with hydraulic actuator 3 via orifice 2 and second flow bypass valve 8 , and bypass port 17 communicates with reservoir 4 .

The front end of the spool 14 is operated by the hydraulic pressure in front of the orifice from the hydraulic pump 1, and the rear end is operated by the hydraulic pressure after passing through the orifice 2, which is led to the rear pressure chamber 19 via the pilot passage 18. It's summery. The spool 14 is biased to the left in the figure by a spring 20 provided in the rear pressure chamber 19, so that when the amount of oil from the hydraulic pump 1 is low, the bypass port 17 is fully closed, but the amount of oil remains As the pressure difference between the front and rear ends of the spool increases, the spool is pushed back to the right against the spring 20 and the bypass port 17 begins to open. Therefore, according to this first flow bypass valve 12,
As shown in Fig. 2, the amount of oil supplied from the supply port 16 is kept at a nearly constant value regardless of the pump discharge amount.
Keep Q ₀ .

On the other hand, the second flow bypass valve 8 installed in the circuit 9 connecting the orifice 2 and the hydraulic actuator 3 has a spool 23 slidably housed inside the valve housing 21 and driven by an electromagnetic solenoid 22. , depending on the position of this spool 23,
Supplying hydraulic oil from pump port 24 to port 25
Two variable orifices 27A and 27B are formed that divide the flow into the bypass port 26 and the bypass port 26.

The pump port 24 communicates with the orifice 2, the supply port 25 communicates with the hydraulic actuator 3, and the bypass port 26 communicates with the reservoir 4 via the pressure control valve 11.

The electromagnetic solenoid 22 is connected to a calculation circuit (for example, a microcomputer) 28, which receives signals from an engine rotation speed sensor 29 and a vehicle speed sensor 30, and controls the hydraulic actuator 3.
calculates the required supply amount to the electromagnetic solenoid 22, outputs a drive signal to the electromagnetic solenoid 22, positions the spool 23,
Appropriate opening degrees are given to variable orifices 27A and 27B.

In addition, the drain circuit 1 of the second flow bypass valve 8
The pressure control valve 11 installed in the valve housing 32 has a differential pressure responsive spool 33 slidably housed inside the valve housing 32, and depending on the position of the spool 33, hydraulic oil flows from the inlet port 34 to the drain port 35. Intermittent.

Hydraulic pressure from a supply circuit 36 extending from the supply port 25 of the second flow rate bypass valve 8 to the hydraulic actuator 3 acts on the front end of the spool 33 via a pilot passage 37, and the bypass valve 8 acts on the rear end of the spool 33.
Hydraulic pressure from the bypass port 26 is guided to a rear pressure chamber 39 via a pilot passage 38 and acts thereon.

The spool 33 is biased toward the left in the figure, that is, in the valve opening direction, by a spring 40 provided in the rear pressure chamber 39.

When the negative pressure of the hydraulic actuator 3 fluctuates and, for example, the hydraulic pressure of the supply circuit 36 increases, the spool 33
is pushed back to the right against the spring 40 and squeezes the drain port 35, thereby drain circuit 1
The pressure at 0 is increased, and as a result, the pressure is kept equal to the pressure in the supply circuit 36.

Next, the operation of this device will be explained. First, the fourth
The logical judgment of the arithmetic circuit 28 will be explained with reference to the diagram.
Now, Qp=Cp・N...discharge amount of the hydraulic pump 1 proportional to engine speed N (graph A) _Q0 ...maximum flow rate maintained by the first flow bypass valve 12 (graph A) Qm=f(V )...Required flow rate to obtain the required power assist force at vehicle speed V (graph B). Then, Qp≧Q ₀ ≧Qm In other words, when the engine is running at high speed in a high-speed driving range, Qp and Qm are compared, and Qm =
The electromagnetic solenoid 2 changes the drive signal i according to the vehicle speed V as shown in graph C so that f(V)
2, move the spool 23 to the right in the diagram,
Squeeze variable orifice 27A and adjust variable orifice 2
Q ₀ is changed to Qm to expand 7B and increase the amount of bypass.
The current is divided into (Q ₀ −Qm).

Next, when climbing a hill, i.e. when the engine is running at high speeds in the medium to low speed range, Qp and Qm are compared and the drive signal i is changed according to R (=Qm/Qp) as shown in graph D to set Qp. The current is divided into Qm and (Qp−Qm).

In addition, when power assist is required in a medium-low speed range, that is, when the engine speed is low and the discharge amount of the hydraulic pump 1 is small, but the required flow rate of the hydraulic actuator 3 is large, the spool 23 A drive signal i is output to the electromagnetic solenoid 22 so as to move the variable orifice 27A to the left limit in the figure, fully open the variable orifice 27A, fully close the variable orifice 27B, and supply the entire flow rate to the hydraulic actuator 3.

Furthermore, when Qp=O;V>O, that is, when the hydraulic pressure of the hydraulic pump 1 runs out while the vehicle is running, an abnormality signal is output by means not shown to warn the driver.

On the other hand, in the state of the above-mentioned medium and low speed driving range, the flow rate of the hydraulic oil divided and controlled by the second bypass valve 8 may change due to the load on the hydraulic actuator 3, for example, due to an increase in the load. When the internal pressure increases and there is a risk that the oil will flow more easily to the drain circuit 10 connected to the tank and the amount of oil in the supply circuit 36 will decrease, the pressure control valve 11 of the present invention is activated.

That is, normally the spool 33 is biased by the spring 40 to open the valve, and the hydraulic oil is throttled at the drain port 35, and the pressure in the drain circuit 10 is slightly lower than the pressure in the supply circuit 36, but as described above. As the pressure in the supply port 25 increases, the spool 33 is pressed by the increased pressure in the supply circuit 36 and is pushed back to the right against the spring 40, closing the drain port 35. As a result, drain circuit 1
This prevents zero pressure oil from leaking into the tank, and as a result, a decrease in the amount of oil supplied from the second flow bypass valve 8 to the hydraulic actuator 3 is immediately suppressed.

As explained above, according to the present invention, the required flow rate can be supplied even if the vehicle speed, engine speed, or hydraulic actuator load changes using the arithmetic circuit and the hydraulic control valve. It is possible to ensure stability in terms of range steering and to make corrections for load changes in medium and low speed driving ranges.Therefore, it is possible to achieve the effect of improving steering feel in all driving ranges.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional device, FIG. 2 is a diagram of its operating characteristics, and FIG. 3 is a sectional view showing an embodiment of the present invention.
FIG. 4 is a characteristic diagram of the arithmetic circuit. 1... Hydraulic pump, 2... Orifice, 3...
Hydraulic actuator, 8... second flow bypass valve, 10... drain circuit, 11... pressure control valve,
12...first flow bypass valve, 14, 23, 3
3... Spool, 15, 24... Pump port,
16, 25... Supply port, 17, 26... Bypass port, 19, 39... Back pressure chamber, 27A, 2
7B...Variable orifice, 28...Arithmetic circuit, 2
9... Engine speed sensor, 30... Vehicle speed sensor, 34... Inlet port, 35... Drain port, 36... Supply circuit.

Claims (1)

[Claims] 1 A first bypass valve that controls the amount of oil discharged from the pump to the power steering actuator to a predetermined amount or less, and a first bypass valve that reciprocally controls the oil discharged from the first bypass valve to the power steering actuator or drain circuit. a second bypass valve equipped with a variable orifice that diverts the flow; a means for detecting engine speed; and a means for detecting vehicle speed; It is characterized by being provided with an arithmetic circuit that controls the variable orifice of the second bypass valve, and a pressure control valve that is located in the middle of the drain circuit and that increases the drain circuit pressure in accordance with the load pressure upstream of the power steering. Power steering flow control device.