JPH11198832A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic type power steering device using an electric motor whereby a steering wheel oscillating phenomenon during the steering operation is eliminated and the feeling in the steering operation is enhanced. SOLUTION: A differential pressure sensor 60 senses the differential pressure between the supply pressure in a supply passage 43 fed from a hydraulic pump 40 driven by an electric motor 75 and the pressure in the high pressure side cylinder chamber of a power cylinder 30 during the steering operation. A controller 73 works with sensing signals given by this sensor 60 and sets a hysteresis on the motor driving voltage when the differential voltage between the pressure on the high pressure side of the power cylinder 30 and the supply pressure is decremental from the specified value and also the motor driving voltage when the differential pressure is incremental from a condition lower than the specified value.

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 for reducing the steering force of a steering wheel of an automobile or the like, and more particularly to a power steering apparatus which achieves low fuel consumption by using an oil pump driven by an electric motor as a power source. It concerns the device.

[0002]

2. Description of the Related Art There are a hydraulic steering system and an electric steering system. In many hydraulic systems, the oil pump is driven by the engine.In this system, the oil pump is always driven by the engine even during straight running, which does not require assistance. There is a problem with large losses.

On the other hand, the electric type has the advantage that the oil pump is not required and the electric motor is started and power assisted only when necessary. In the case of an electric power steering device, the assist direction is mechanically determined with respect to the operation of the steering wheel, whereas in the case of the electric power steering device, it is necessary to rotate the electric motor forward and backward in accordance with the operation direction of the steering wheel. There is.

Therefore, an electric motor is used as a power source,
2. Description of the Related Art There has been known a power steering apparatus that activates an electric motor only when necessary to drive an oil pump to achieve low fuel consumption. This power steering device communicates the supply passage of the pressure oil to the oil supply / discharge port of one of the two left and right cylinder chambers of the power cylinder by the relative rotation of the input shaft and the output shaft, A direction switching valve for communicating the oil supply / discharge port of the other cylinder chamber of the power cylinder to the discharge passage, an oil pump for discharging pressure oil according to the rotation speed to the supply passage, and an electric motor for driving the oil pump. And detects the pressure difference between the high pressure side of the power cylinder and the supply pressure, and controls the electric motor according to the pressure difference.

[0005]

In the conventional power steering apparatus described above, an oscillation phenomenon may easily occur immediately after the steering wheel is turned. The cause is that when the differential pressure is small, the motor drive voltage is increased to increase the supply pressure flow rate, and when the differential pressure is large, the motor drive voltage is reduced to reduce the supply pressure flow rate and reduce the differential pressure -Because it is a control system for the motor drive voltage.

That is, when the steering is not performed, the motor driving voltage is zero and the electric motor is stopped, but the pressure difference in the non-steering state is maintained by the pressure of the pressure oil in the supply passage. When the steering wheel is turned in such a state, the differential pressure between the high pressure side of the power cylinder and the supply pressure decreases, and the motor drive voltage gradually increases to increase the supply pressure flow rate. The motor drive voltage tends to decrease due to the increase, and the supply pressure flow rate decreases.

Since the motor drive voltage also fluctuates due to the fluctuation of the differential pressure in the process of reaching the motor maximum drive voltage, when the steering wheel is turned, an oscillation phenomenon that the weight becomes lighter or heavier occurs. Also, when the steering wheel is returned after the steering wheel is turned, the same phenomenon occurs because the motor driving voltage is controlled to drop along the locus of the differential pressure-motor driving voltage when the steering wheel is turned, and the steering feeling is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulic power steering apparatus for an electric motor which eliminates a steering wheel oscillation phenomenon during steering and improves steering feeling.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the gist of the present invention is to provide an input shaft and an output shaft which are rotatable relative to each other, and supply of pressure oil by relative rotation between the input shaft and the output shaft. A direction switching valve that communicates the passage with one cylinder chamber of the power cylinder and communicates the other cylinder chamber of the power cylinder with a discharge passage; and an oil that discharges pressure oil according to a rotation speed to the supply passage by driving an electric motor. Pump and
A differential pressure detector for detecting a differential pressure between a cylinder chamber on the high pressure side of the power cylinder and the supply pressure of the supply passage; and a detection signal from the differential pressure detector for detecting a difference between the high pressure side of the power cylinder and the supply pressure. A motor drive voltage when the pressure decreases below a predetermined value and a controller for setting hysteresis to the motor drive voltage when the differential pressure increases from a state lower than the predetermined value.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, reference numeral 10 denotes a rack and pinion type gear housing. In the rack and pinion type gear housing 10, an input shaft 11 and an output shaft 12 are rotatably housed on the same axis, respectively.
The output shaft 12 and the output shaft 12 are connected to each other via a torsion bar 13 so as to be relatively rotatable. The input shaft 11 is connected to a steering handle 14 as shown in FIG.

1 and 2, the input shaft 11 and the output shaft 12 are provided with an inner valve 19 and an outer valve 20, respectively, which constitute a direction switching valve 17, and the direction switching valve 17 is connected to the input shaft 11 and the output shaft. The supply port 21 is rotated by two cylinder ports 2 by relative rotation with respect to the cylinder port 2.
2 and 23, and the other is connected to the discharge port 24.
It is designed to communicate with

When the directional control valve 17 is in a neutral state, the supply port 21 is closed by a first land 19a formed on the inner valve 19, and when the directional control valve 17 is operated, the supply port 21 is connected to the cylinder ports 22 and 23. The center close valve communicating with one of the two and the second land 19b formed in the inner valve 19 when in the neutral state opens to the discharge port 24, and the oil flows into the cylinder ports 22 and 23 when the direction switching valve 17 is operated. And a center open valve for controlling the pressure of the pressure.

A pinion tooth 25 is provided at the tip of the output shaft 12.
Are formed, and the rack teeth 2 meshing with the pinion teeth 25 are formed.
The rack shaft 27 having the groove 6 is slidably housed in the gear housing 10. The rack teeth 27 shown in FIG.
As shown in the figure, the piston 31 of the power cylinder 30 for assisting the steering torque is connected. The power cylinder 30 has left and right cylinder chambers 30a and 30b partitioned by a piston 31. The left and right cylinder chambers 30a and 30b are connected to the two cylinder ports 2a and 2b.
2 and 23 respectively.

Reference numeral 40 denotes a plunger type or vane type oil pump. The discharge side of the oil pump 40 supplies the pressure of the oil discharged through the check valve 41 to the supply passage 4.
3 is connected to supply to the supply port 21 of the direction switching valve 17 and the differential pressure detector 60.

The differential pressure detector 60 is, as shown in FIG.
The case housing 61 includes a spool housing 62 fitted into the case housing 61, a spool valve 63 and a differential transformer 64.

A sliding hole 65 is provided in the case housing 61.
The sliding hole 65 is provided with a spool valve 63.
Are slidably fitted. The spool valve 63 includes a shaft 66 and a plunger 67. The plunger 67 divides the sliding hole 65 into a first pressure chamber 70 and a second pressure chamber 71, and the first pressure chamber 70 has a supply passage. The second pressure chamber 71 communicates with the cylinder ports 22 and 23 via a shuttle valve 72. This shuttle valve 72
The ball 72a disposed in the passage is the cylinder port 2
The cylinder port 2 moves due to the pressure difference between
The higher one of the pressures 2 and 23 communicates with the second pressure chamber 71.

A spring 69 is provided in the second pressure chamber 71.
And presses the plunger 67 toward the first pressure chamber 70. One end of a shaft 66 of the spool valve 63 penetrates the spool housing 62, and a core 68 constituting a part of the differential transformer 64 is attached to one end of the shaft 66. The differential transformer 64 detects the movement of the spool 68 by detecting the movement of the core 68 by a change in electromotive force generated in a secondary winding (not shown). As shown in FIG. 4, the output signal S of the differential transformer 64 is input to the controller 73 as the differential pressure ΔP between the supply passage 43 and the high pressure side of the cylinder ports 22 and 23 increases. I have.

A drive circuit 74 is connected to the controller 73, and the drive circuit 74 is connected to an electric motor 75 for driving the oil pump 40.

The controller 73 comprises a microprocessor and a memory, and outputs the output signal S of the differential transformer 64 to the supply passage 43 and the cylinder port 22 shown in FIG.
When the output signal S1 becomes equal to or less than the output signal S1 corresponding to the differential pressure ΔP1 from the high pressure side of the motor 23 (corresponding to the time when the steering wheel 14 is steered), the drive circuit 74 drives the electric motor 75 with the motor drive voltage VM And outputs a command signal to stop the electric motor 75 when the output signal S2 becomes equal to or more than the output signal S2 corresponding to the differential pressure ΔP2.

When the command signal S from the controller 73 satisfies S1 <S <S2, the drive circuit 74 operates at a low motor drive voltage so as to keep the pressure oil in the supply passage low.
5 at low rotation, and when the command signal S satisfies S ≦ S1, the oil pump 40 is controlled by controlling the electric motor 75 at high rotation at a high motor drive voltage VM so as to supply a supply pressure required for steering assist. Drive in one direction.

Therefore, according to the present invention, the detection signal from the differential pressure detector 60 is controlled by the controller 73 to determine the difference between the motor drive voltage when the differential pressure between the high pressure side of the power cylinder 30 and the supply pressure is lower than a predetermined value. Hysteresis is set for the motor drive voltage when the pressure increases from a state lower than a predetermined value.

That is, as shown in FIGS. 4 and 5, the differential pressure ΔP between the high pressure side of the power cylinder 30 and the supply pressure is ΔP1
When the output signal S of the differential transformer 64 decreases below S1 (corresponding to turning the steering wheel), the motor drive voltage V is increased to the maximum motor drive voltage VM at once, and the supply pressure flow rate is rapidly increased. And the differential pressure ΔP decreases from ΔP1, and the output signal of the differential transformer 64 becomes S
When the motor drive voltage V increases from a state lower than 1 (corresponding to the return of the steering wheel), the motor drive voltage V is quickly reduced to a predetermined value (<VM) to set a hysteresis with a B map that reduces the supply pressure flow rate. .

The operation of the above configuration will be described. When the oil pump 40 is driven by the electric motor 75, the oil is discharged and the oil supplied to the supply passage 43 flows into the direction switching valve 17 and the differential pressure detector 60. At this time, if the steering wheel 14 is not operated and the vehicle is running straight, the input shaft 11 and the output shaft 1
2 does not generate relative rotation, the direction switching valve 17 does not operate, and the supply port 21 is connected to the cylinder port 2.
It is a closed state that does not communicate with any one of 2 and 23.

In this closed state, since the cylinder ports 22 and 23 are open to the discharge port 24, no hydraulic pressure is applied, and the second pressure chamber 7 of the differential pressure detector 60 is not operated.
No pressure acts on 1. Thereby, the differential pressure detector 60
Of the spool valve 63 is determined only by the oil pressure in the supply passage 43, and an output signal S2 corresponding to the differential pressure ΔP2 is output from the differential transformer 64 of the differential pressure detector 60 to the controller 73.
Is output, the electric motor 75 stops.

On the other hand, when the handle 14 is operated and the torsion bar 13 is twisted to rotate the input shaft 11 and the output shaft 12 relative to each other, the relative rotation of the two shafts causes the direction switching valve 17 to operate, for example. The supply port 21 communicates with one cylinder port 22 and the other cylinder port 23 communicates with the discharge port 24. When the cylinder port 22 communicates with the supply port 21, the power is supplied from the cylinder port 22 to one cylinder chamber 30 a of the power cylinder 30. The piston 31 slides by the flow rate supplied to the power cylinder 30, and the steered wheels are steered via a required link mechanism. At this time, the other chamber 30 of the power cylinder 30
The oil b is discharged from the discharge port 24 of the direction switching valve 17 to the tank.

When the direction switching valve 17 is operated and the supply port 21 communicates with one of the cylinder ports 22 and the other cylinder port 23 communicates with the discharge port 24, the oil pressure in the supply passage 43 decreases. At the same time, since the pressure from the cylinder port 22 acts on the second pressure chamber 71 of the differential pressure detector 60, the first pressure chamber 70 and the second pressure chamber 7
1 becomes smaller.

Therefore, the spool valve 63 is connected to the first pressure chamber 7
0, the output signal S from the differential transformer 64 decreases, and as shown in FIG. 5, when the output signal S becomes equal to or less than S1, the oil pump 40 Until an output signal of a predetermined value is output from the controller 64 to the controller 73, the electric motor 75 is driven at a high motor drive voltage VM.
Driven at a high speed.

Thereafter, when the handle 14 is continuously operated, the pressure difference between the supply passage 43 and the cylinder port 22 does not become more than ΔP1, and the oil pump 40 is continuously driven at a high rotation speed. When the steering of the steered wheels is completed and the relative rotation between the input shaft 11 and the output shaft 12 stops, and the inner valve 19 and the outer valve 20 are in the neutral state,
When the supply port 21 is closed again and the pressure in the supply passage 43 increases and the output signal S from the differential pressure detector 60 becomes S2, the motor drive voltage V to the electric motor 75 is cut off and the oil pump 40 stops.

In the above operation, as shown in the flow chart of FIG. 6, the differential pressure ΔP is detected in step 80, and this differential pressure ΔP is equal to or less than ΔP1 (= the output signal S from the differential transformer 64). Is determined to be S1 or less), the processing of step 81 and subsequent steps is performed. In step 81, it is determined whether the differential pressure ΔP detected in step 80 is increasing or decreasing. When it is determined that the differential pressure ΔP is decreasing (corresponding to turning of the steering wheel), an A map is selected in step 82, a motor drive voltage V is calculated in step 84, and a motor drive voltage V is calculated in step 85. To increase the maximum motor drive voltage VM at once, and quickly increase the supply pressure flow rate.

In step 81, it is determined whether the pressure difference ΔP has increased. If it is determined that the differential pressure ΔP has increased (corresponding to the return of the steering wheel), step 8 is performed.
In step 3, the B map is selected, the motor drive voltage is calculated in step 84, the motor drive voltage is output in step 85, and the motor drive voltage is quickly reduced to a predetermined value to reduce the supply pressure flow rate.

By providing such a hysteresis for controlling the increase and decrease of the motor drive voltage V due to the decrease and increase of the pressure difference ΔP between the high pressure side of the power cylinder 30 and the supply pressure, the fluctuation of the pressure difference ΔP is reduced. Oscillation phenomena that are suppressed and become lighter or heavier when turning the handle and returning the handle can be prevented.

[0032]

As described above, according to the present invention, the hysteresis characteristic for controlling the increase and decrease of the motor drive voltage due to the decrease and increase of the pressure difference between the cylinder chamber on the high pressure side of the power cylinder and the supply pressure of the supply passage. Is provided, the oscillation phenomenon of the steering wheel during the control of the motor drive voltage is prevented, and the steering feeling is improved. In addition, there is an advantage of reducing abnormal noise when operating the steering wheel.

[Brief description of the drawings]

FIG. 1 is a control block diagram of the device of the present invention.

FIG. 2 is a sectional view of the apparatus of the present invention.

FIG. 3 is a configuration diagram of a differential pressure detector.

FIG. 4 is an output characteristic diagram of a detection signal of a differential pressure detector.

FIG. 5 shows a differential pressure-motor drive voltage map according to the present invention.

FIG. 6 is a flowchart showing a processing procedure for implementing the present invention.

[Explanation of symbols]

 Reference Signs List 11 input shaft 12 output shaft 17 direction switching valve 30 power cylinder 40 oil pump 60 differential pressure detector 73 controller 75 electric motor

Claims (1)

[Claims] An input shaft and an output shaft that are relatively rotatable;
A direction switching valve for communicating a pressure oil supply passage with one cylinder chamber of the power cylinder and communicating the other cylinder chamber of the power cylinder with a discharge passage by the relative rotation of the input shaft and the output shaft; An oil pump that discharges pressure oil according to the number of revolutions by driving a motor; a differential pressure detector that detects a differential pressure between a cylinder chamber on a high pressure side of the power cylinder and a supply pressure of the supply passage; The motor drive voltage when the differential pressure between the high pressure side of the power cylinder and the supply pressure is lower than a predetermined value and the motor drive voltage when the differential pressure increases from a state where the differential pressure is lower than the predetermined value And a controller for setting hysteresis.