JPH04108071A - Power steering device - Google Patents

Abstract

PURPOSE:To reduce generation of cavitation so as to suppress a noise of fluid by providing constitution such that viscosity of electroviscous fluid between a valve shaft and a valve body is changed in accordance with a value of applied voltage. CONSTITUTION:A power steering device has a pressure control valve, and in this pressure control valve, a piston of a power cylinder is pressed to a right or left side to assist steering force by an assist pressure of oil in accordance with a differential rotational angle between a valve body 6 and a valve shaft 3 which are correlated by a torsion bar 7. Here, electroviscous fluid, which is used as operating oil, is supplied to the pressure control valve through a high pressure oil path 29 from a pump 13. The pressure control valve is constituted so that voltage from a power supply unit 26 can be applied to only the electroviscous fluid positioned between the valve shaft 3 and the valve body 6, and this applied voltage is controlled based on outputs from a car speed sensor 29, flow amount detecting means 20 and rotational angle sensors 22, 23.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a power steering device for a vehicle.

2. Description of the Related Art Vehicle power steering devices that utilize hydraulic pressure from hydraulic oil are known.

FIG. 7 is a cross-sectional view of the configuration of the power steering device described above.
29).

In the figure, 2 is a steering housing having a rack gear 5 therein, 2 is a piston that receives hydraulic pressure and generates an assist force, 3 is a valve shaft connected to the steering column, and 4 is a binion gear that meshes with the rack gear 5. Further, 6 is a valve body connected to the pinion gear 4 by a pin, and 7 is a torsion bar, one end of which is connected to the pinion gear 4 by a pin, and the other end connected to the valve shaft 3 by a pin. 8 is connected to the pump 13 through an inlet port provided in the valve body. Reference numeral 9 denotes an outlet port, which allows return oil from the control valve to flow back to the reservoir tank 12.

Reference numeral 10 denotes a drain oil passage provided in the valve shaft 3 and connected to the outlet port 9. 11 is a cylinder having a piston 2 inside. Reference numeral 14 denotes a communication passage for conducting hydraulic pressure of a magnitude set in the control valve section to the left oil chamber of the piston 2. Reference numeral 15 denotes a communication passage for conducting to the right oil chamber.

FIG. 8 shows the valve shaft 3. FIG. 2 is a longitudinal sectional view of a pressure control valve composed of a 6° torsion half valve body and a valve case 18. Also, Figure 9 shows the valve shaft 3.
FIG. 10 is a sectional view taken along the line B--B in FIG. 9, and FIG. 11 is a sectional view taken along the line C--C in FIG. 10.

In the figure, a plurality of shaft ports 17 are provided on the valve shaft 3, and shaft ports 17 with a return port 10 formed therein and shaft ports 17 without a return port 10 formed therein are provided alternately. Further, FIG. 12 is an enlarged view of the edge portion of the shaft port 17 indicated by 27 (-dotted chain line) in FIG.
A smooth portion called a chamfer 28 is formed in this edge portion.

FIG. 13 is a vertical cross-sectional view of the valve body 6, and FIG. 14 is a vertical cross-sectional view of the valve body 6.
FIG. 4 is a sectional view taken along line DD in FIG. 3;

In the figure, 16 is a plurality of body ports provided in the valve body 6, and the body ports 16 in which the left high pressure passage 14 is formed and the body ports 16 in which the right high pressure passage 15 is formed are provided alternately. .

A valve shaft 3 is disposed on the inner peripheral side of the valve body 6, and the piston 2 is pushed to the left or right by an assist hydraulic pressure corresponding to a rotation angle difference between the valve body 6 and the valve shaft 3.

However, in the conventional power steering device described above, the chamfer part of the pressure control valve and the body port 1
Since the assist hydraulic pressure is controlled by a throttle made up of 6 edges, the hydraulic assist amount relative to the steering amount is fixed regardless of the vehicle speed. Therefore, in order to change the hydraulic assist amount depending on the vehicle speed, it is necessary to change the hydraulic assist amount depending on the engine rotation. There were problems in that it was necessary to change the pump rotation speed, provide another control valve downstream of the pressure control valve, and open and close this control valve depending on the vehicle speed. Another problem is that cavitation occurs in the constriction section during stationary steering, and the vibrations generated when the bubbles are submerged are transmitted through the column shaft and radiated from the steering wheel, creating noise.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention supplies working hydraulic pressure discharged from a hydraulic pump to the left and right chambers in the cylinder by switching it to the left and right chambers in the cylinder using a pressure control valve to assist the steering force of the vehicle. A power steering device that uses an electrorheological fluid used as hydraulic fluid, a vehicle speed sensor that detects vehicle speed,
"Flow that detects the flow rate of electrorheological fluid flowing through a pressure control valve"
A detection means, a rotation angle sensor that detects the rotation angle difference between the valve shaft and the valve body of the pressure control valve, a vehicle speed sensor, and a flow rate detection means. The present invention is characterized by comprising a calculation means for calculating an exponent voltage, and a power supply section for applying a voltage between the valve shaft and the valve body in accordance with a voltage command signal from the calculation means.

According to the voltage value applied between the working valve shaft and the valve body, the viscosity of the electrorheological fluid between this valve shaft and the valve body is changed, and according to the vehicle speed and the rotation angle difference between the valve shaft and the valve body. assist force is generated.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, and parts equivalent to those in the example of FIG. 7 are given the same reference numerals. and,
In the example shown in FIG. 1, an electrorheological fluid whose viscosity changes depending on the applied voltage is used as the hydraulic oil. This electrorheological fluid is supplied from the pump 13 to the pressure control valve via the high pressure oil line 39.

20 is a pump rotation speed meter that measures the rotation speed of the pump 13;
A temperature sensor 21 is disposed in the high pressure oil passage 29 and measures the temperature of the electrorheological fluid, and a rotation signal from the pump rotation speed meter 20 and a temperature signal from the temperature sensor 2I are supplied to the calculation unit 25.

22 is a valve body angle sensor that detects the rotation angle of the valve body 6, and 23 is a valve shaft angle sensor that detects the rotation angle of the valve shaft 3. Angular signals from these valve body angle sensor 22 and valve shaft angle sensor 23 is supplied to the arithmetic unit 25.

Further, 24 is a vehicle speed sensor that detects the speed of the vehicle,
The vehicle speed signal from this vehicle speed sensor 24 is sent to a calculation unit 25.
supplied to

26 is a power supply unit, and this power supply unit 26 supplies the sliding member 19 and the valve shaft 3 with a voltage corresponding to a command signal from the calculation unit 25. The sliding member 19 is disposed on the inner peripheral side of the valve case 18 and is adapted to slide on the valve body 6. Moreover, 30 is an insulator formed on the inner peripheral surface of the valve case 18, and the valve case 18 and the valve body 6 are electrically insulated by this insulator 30. 31 is an insulator, and this insulator 31 is provided on the outer periphery of the valve shaft 3, and the insulator 31 electrically insulates the valve shaft 3 and the valve body 6. 32 is an insulator provided in the valve case 18, and the valve case 18 and the valve shaft 3 are electrically insulated by this insulator 32. Furthermore, 33 is also an insulator, and this insulator 33 allows the torsion bar 7 and the valve body 6 to
and are electrically insulated. Therefore, power 2 nits 2
The voltage from 6 is applied only to the hydraulic fluid located between the valve shaft 3 and the valve body 6, that is, the electrorheological fluid.

2 is a sectional view taken along the line A--A in FIG. 1, and FIG. 3 is an enlarged view of the portion indicated by 27 in FIG. 2.

Next, the operation of the example shown in FIG. 1 will be explained.

FIG. 4 is a control operation flowchart of the arithmetic unit 25, and the voltage to be applied to the pressure control valve is determined according to this flowchart.

When the engine is turned on at step 100 in FIG. 4, the process proceeds to step 101. Then, in step 101, based on the angle signals from the angle sensors 22 and 23, the angle difference between the valve shaft 3 and the valve body 6, that is, the difference in the angle between the valve body port end face during non-steering, as shown in FIG. The angular difference Δθ between the position 34 and the position 35 during steering is determined, and the vehicle speed U is calculated based on the signal from the vehicle speed sensor 24. Next step 10
In step 2, it is determined whether or not the angle difference is zero. If the angle difference Δθ is zero, it means that the vehicle is not being steered, and the process returns to step 101. In this case, that is, when the vehicle is not being steered, a constant voltage is applied from the power supply unit 26 between the valve shaft 3 and the valve body 6, and the viscosity of the hydraulic oil is kept constant. Further, since the throttle part of the pressure control valve is open-circuited, no assist hydraulic pressure is generated. In step 102, if the angular difference is not zero, the process proceeds to step 103, where the vehicle speed U is less than or equal to the predetermined low speed value U, and whether the angular difference is ○ or fluid sound, the problem angle a (the 3) or the vehicle speed U or a predetermined high speed value U is determined. If the above conditions are not met, the process returns to step 101. In step 103, vehicle speed U is less than or equal to UN, and
If the angle difference 〇 is greater than α, the process proceeds to step 104. In this step 104, the flow rate detection means, that is, the pump rotation speed meter 20. The hydraulic oil flow iQ flowing through the pressure control valve is calculated from the pump rotation speed N1 from the temperature sensor 21, etc., the hydraulic oil temperature t, and the current hydraulic oil viscosity μ, and the current throttle area A is calculated from the angular difference Δθ. be done. Then, the process proceeds from step 104 to step 105. In step 105, the required assist oil pressure P is calculated from the current vehicle speed U and the angle difference Δθ.

This assist oil pressure P changes depending on the vehicle speed U and the valve operating angle, that is, the angle difference, and the map shown in Fig. 5 (
A solid line at low speed and a broken line at high speed are applied to the arithmetic unit 25. When the assist oil pressure P is calculated in step 105, the process proceeds to step 106, where the viscosity μ of the hydraulic oil necessary to obtain the oil pressure P is calculated in consideration of the throttle cross-sectional area A at the angle difference Δθ. This viscosity μ
The calculation is performed using equation (1) which shows the relationship between the flow rate coefficient C1 which is a function of the oil pressure P, the flow rate Q, and the viscosity μ.

Here, P' is the pressure downstream of the throttle, and ρ is the density of the hydraulic oil. The flow rate Q, the throttle cross-sectional area A, and the density ρ are known, and the pressure P' is a constant value because it is the pressure of the low-pressure side oil passage from the pressure control valve to the reservoir tank. Therefore, the above (1
) is used to calculate the flow coefficient C required to set the assist pressure to P. Since the relationship between the flow rate coefficient C and the viscosity μ of the hydraulic oil is mapped and given to the calculation unit 25, the viscosity μ required to obtain the assist oil pressure P can be calculated. Next, the process proceeds to step 107, where the voltage V required to make the viscosity of the hydraulic oil μ is calculated, and a command signal is supplied to the power supply unit 26 so that the power supply unit 26 generates the voltage V. Then, in step 108, when the power supply unit 26 applies the voltage V to the electrorheological fluid, that is, the hydraulic oil, the viscosity of the hydraulic oil becomes μ. Then, the assist oil pressure becomes P, and the increase in the viscosity of the hydraulic oil suppresses the occurrence of cavitation and reduces noise.

Now, in step 103, whether the vehicle speed U or the predetermined high speed value U
If it is greater than H, the viscosity μ of the hydraulic oil is controlled in steps 104 to 108 in the same manner as described above.

However, in this case, since the vehicle speed U is greater than the predetermined high speed value Un, the assist oil pressure is controlled to be small.

In other words, the voltage value is also set to a small value so that the viscosity μ is small.

Therefore, at low speeds, the assist force is controlled to be large, and by reducing the occurrence of cavitation, fluid noise is suppressed, and at high speeds, the assist force is controlled to be small.

FIG. 6 is a partially enlarged view of another embodiment of the invention,
This corresponds to Figure 3.

In FIG. 6, the chamfer includes the first step portion 28a and the second step portion 28a.
The angle of the extension line of the first step part 28a with respect to the cylindrical surface line of the valve shaft 3 is the same as that of the second step part 28b.
It is larger than the angle b with respect to the cylindrical surface line.

The boundary line between the first step portion 28a and the second step portion 28b is a position 36 where the angle difference α, that is, the fluid sound becomes a problem.

In this way, the chamfer is attached to the first step section 28a and the second step section 28.
The reason for the configuration is as follows.

(1) With a single chamfer, the assist oil pressure increases rapidly due to the increase in viscosity. Therefore, the chamfer angle of the second stage portion 28b is made shallow, and the rise of the oil pressure with respect to the viscosity change is made gradual, thereby widening the voltage setting range for the viscosity change.

(2) If the chamfer angle is shallow, the pressure and flow rate changes in the flow direction of the hydraulic oil will be gradual, which has the effect of suppressing cavitation and reducing fluid noise.

In this way, the chamfer is set in two stages, and the angle of the chamfer is shallower in the region where the angle difference is larger than α in response to the pressure increase due to the increase in the viscosity of the hydraulic oil. can also reduce noise levels.

Note that portions other than those shown in FIG. 6 have the same configuration as the example in FIG. 1.

Effects of the Invention As described above, the present invention provides a power steering device that assists the steering force of a vehicle by selectively supplying hydraulic pressure discharged from a hydraulic pump to the left and right chambers in a cylinder using a pressure control valve. , a vehicle speed sensor that detects the electrorheological fluid used as hydraulic oil, a vehicle speed sensor that detects the vehicle speed, a flow rate detection means that detects the flow rate of the electrorheological fluid flowing through the pressure control valve, and rotation of the valve shaft and valve body of the pressure control valve. Based on the output signals from the rotation angle sensor that detects the angular difference, the vehicle speed sensor, and the flow rate detection means 9 rotation angle sensor,
calculation means for calculating the voltage to be applied to the electrorheological fluid;
a power supply unit that applies a voltage between the valve shaft and the valve body according to a voltage command signal from the calculation means, and the valve shaft and the valve according to the voltage value applied between the valve shaft and the valve body. Since the viscosity of the electrorheological fluid between the body and the body is changed,
The assist force can be controlled according to the vehicle speed and the rotation angle difference without providing another control valve downstream of the pressure control valve, and fluid noise can be suppressed by reducing the occurrence of cavitation. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the configuration of an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1, FIG. 3 is a partially enlarged view of FIG. 2, and FIG. Fig. 1 is an operation flowchart of the example, Fig. 5 is a diagram showing the relationship between differential angle and assist oil pressure, Fig. 6 is a partially enlarged view of another embodiment of the present invention, and Fig. 7 is a conventional power steering system. 8 is a vertical sectional view of the pressure control valve, FIG. 9 is a partially enlarged view of the valve shaft, FIG. 10 is a sectional view taken along line B-B in FIG. 9, and FIG. Figure 11 is a cross-sectional view taken along line C-C in Figure 10.
2 is a partially enlarged view of FIG. 11, FIG. 13 is a longitudinal cross-sectional view of the valve body, and FIG. 14 is a cross-sectional view taken along line DD in FIG. 13. 3... Valve shaft, 6... Valve body, 11
...Cylinder, 13...Hydraulic pump, 20...Pump rotation speed meter, 21...Temperature sensor, 22...Valve body angle sensor, 23...Valve shaft angle sensor, 24... Vehicle speed sensor, 25... calculation unit, 26 power supply unit, 28... chamfer, 28a.
... Chamfer first stage part, 28b... Chamfer second stage
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Claims (2)

[Claims] (1) An electrorheological fluid used as hydraulic fluid in a power steering device that assists the steering force of a vehicle by selectively supplying hydraulic pressure discharged from a hydraulic pump to left and right chambers in a cylinder using a pressure control valve; A vehicle speed sensor that detects the vehicle speed, a flow rate detection means that detects the flow rate of electrorheological fluid flowing through the pressure control valve, a rotation angle sensor that detects the rotation angle difference between the valve shaft and the valve body of the pressure control valve, and the vehicle speed. A calculation means for calculating the voltage to be applied to the electrorheological fluid based on the output signals from the sensor, the flow rate detection means, and the rotation angle sensor; A power steering device comprising: a power supply unit that applies voltage; (2) The power steering device according to claim 1, wherein the throttle section for generating pressure of the pressure control valve is a multi-stage throttle.