JPH0124114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power steering device for an automobile that uses hydraulic pressure to reduce steering force.

A normal power steering device has a control valve that mechanically detects the rotation of the input shaft connected to the steering wheel and switches the control valve, and the switching operation of this control valve selectively controls the power cylinder installed at the tip of the input shaft. Pressure oil is supplied to the steering link to change the direction of the wheels in proportion to the rotation of the input shaft.

Especially in automobile power steering devices,
To ensure safety, the tip of the input shaft is connected to the piston of the power cylinder via a ball screw assembly so that the input shaft can be operated even if hydraulic assist force cannot be obtained due to a failure in the hydraulic system. Mechanically connected.

By the way, the control valve that controls the direction of the pressure oil sent to the power cylinder by the rotation of the input shaft is linked to the movement of the input shaft as well as the actual movement of the piston on the output side, and is now subject to feedback control. Because of this, there are significant restrictions on its installation, and its placement is usually limited to areas where the input shaft connects to the power cylinder. In addition, in order to perform such mechanical feedback control, the structure of the control valve is extremely complex, and in particular, the hydraulic pressure is controlled in response to the ground resistance of the wheels, which changes depending on the traveling speed.
In a speed-sensitive power steering system that always obtains optimal steering force, the structure of the control valve has to be even more elaborate, which makes maintainability and safety poor, and it is also expensive. It had the disadvantage of becoming.

On the other hand, from the perspective of pursuing comfort and safety in automobiles, there will be a stronger demand for control to obtain optimal steering force according to various driving conditions, and this is where microcomputers are used. The present applicant has developed a power steering system that enables optimum steering force to be obtained under all driving conditions.
57-134363).

To explain this based on FIG. 1, an input shaft 2 connected to a handle 1 is connected to a piston 4 of a power cylinder 3 as a hydraulic actuator.

In this case, the piston 4 is connected to the input shaft 2 via a ball screw assembly (not shown), and the piston 4 slides inside the cylinder 3 depending on the rotational direction and speed of the input shaft 2.

A rack 5 is provided on the side of the piston 4.
A sector gear 6 meshes with this rack 5, and as the piston 4 moves, a steering link (not shown) is driven via a pitman arm 7 which is interlocked with the sector gear 6.

The piston 4 moves due to the input rotation of the input shaft 2, and in order to assist this movement with hydraulic pressure, oil chambers 8A and 8B separated on both sides of the piston 4 are provided with
Pressure oil is selectively controlled and supplied from the pump P by the PS control valve 9.

The control valve 9 is an electromagnetic valve whose operation is controlled by a microcomputer 10 to which the rotational direction, rotational force, or rotational speed of the input shaft 2 is input, and the control load on the output side is fed back.

Here, reference numeral 11 denotes a load sensor attached to the input shaft 2, which is composed of a strain gauge or the like that detects rotational force and direction of rotation by detecting twist of the input shaft 2. 12 is a magnetic pickup for similarly detecting the rotational speed of the input shaft 2.

These detection signals are then amplified and
Input interface 1 with signal waveform processing function
4 to the arithmetic control section 15 of the microcomputer 10.

The calculation control unit (CPU) 15 performs calculations based on these inputs, selects the stored value from the storage unit (ROM) 16 in which optimal values corresponding to the operating conditions are stored in advance, and outputs the stored value to the output interface 17.
The signal is output to the control valve 9 via the control valve 9.

The control valve 9 is composed of a solenoid valve, and the switching direction and switching amount are controlled based on an input signal, and the amount of pressure oil sent to the left and right oil chambers 8A and 8B of the power cylinder 3 is controlled.

When operating the handle 1 to rotate the input shaft 2 in either direction, a reaction force proportional to the operating load applied to the piston 4 of the power cylinder 3 is generated on the input shaft 2, so this is used as the operating force for operating the handle. This operating force (rotational force and direction of rotation) is detected by the load sensor 11 attached to the input shaft 2, and at the same time the input rotational speed is detected by the pickup 12. input to the microcomputer 10.

Since the optimal value corresponding to the input signal is set in advance in the storage unit 16, the arithmetic control unit 15 reads it out, performs predetermined signal waveform processing and amplification at the output interface 17, and then outputs the control valve 9. Enter.

Therefore, the control valve 9 sends the required amount of pressure oil to the oil chamber 8A or 8B of the power cylinder 3 in proportion to the magnitude and direction of the handle operating force (at this time, the other oil chamber 8A, 8B is (Connected to the tank T side.) In this case, when the vehicle speed is low and the wheel turning resistance is large, the load sensor 1
1 detects that the torsion angle of the input shaft 2 is large, so the hydraulic pressure supplied to the power cylinder 3 is increased, and when the handle rotation speed is high, the amount of pressure oil sent is increased accordingly. The microcomputer 10 controls the output value so that the amount of switching of the control valve 9 increases as the output voltage increases.

As a result, the operation to move the piston 4 using the input shaft 2 is assisted by the hydraulic pressure in the oil chamber 8A or 8B corresponding to the operating load, so the handle operation is light and easy with an appropriate operating feel. can be done.

On the other hand, when the handle 1 is fixed, the reaction force that tries to twist the input shaft 2 according to the operating load decreases, so the output value of the load sensor 11 becomes smaller, and the control valve 9 is moved to the neutral position accordingly. The power cylinder 3 is returned to the state via the microcomputer 10, and the supply of pressure oil to the power cylinder 3 is thereby stopped.

In other words, feedback input can be obtained at the same time, and when the input shaft 2 stops, the power cylinder 3 also stops operating, and the wheels are held at that switching angle.

By the way, with this power steering device,
Since the PS control valve 9 exists independently, if the return to the neutral state is not performed smoothly due to dirt etc. in the hydraulic oil,
Even though the steering wheel has been returned to the neutral position, pressure oil is supplied to the power steering wheel 3, creating a very dangerous situation.

The present invention aims to solve such problems, that is, to forcibly return the electromagnetic PS control valve to the neutral position when the handle is in the neutral position.

The present invention applies an alternating current to the solenoid coil to cause the spool to oscillate in a dither when the PS control valve is switched in one direction when a handle neutral position signal is input, thereby preventing return failure. This is to ensure that the neutral position is returned to the neutral position.

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

In FIG. 2, the electromagnetic PS control valve 9 has a spool 21 slidably housed in a valve body 20, and a drive rod 23 of a solenoid 22 is connected to the end of the spool 21, thereby controlling the spool 21 from side to side. Activate the switch to .

The valve body 20 has a high pressure port P on the hydraulic pump side, two low pressure ports T on the reservoir side sandwiching this port, and an operating port A located between these ports and connected to the oil chambers 8A and 8B of the power cylinder 3. ,B
In the neutral position shown in the figure, the hydraulic oil from the high pressure port P is returned to the low pressure port T, and the spool 21 moves to the right. When the switching occurs, the pressure oil from the high pressure port P is transferred to the operating port A (at this time, the operating port B is connected to the low pressure port T), and conversely, when the spool 21 is switched to the left, the pressure oil is transferred from the high pressure port P to the operating port A. Pressure oil is sent to each working port B (working port A is connected to low pressure port T).

A spring chamber 2 located at both ends of the spool 21 and having neutral return springs 24 and 25 interposed therein.
6 and 27 are formed.

The spring chambers 26 and 27 are connected to the low pressure side due to leakage from around the spool 21, respectively, and do not prevent the spool 21 from moving to the left or right.

The solenoid 22 has two coils 33A and 3.
3B, and an excitation current from the microcomputer 10 (see Figure 1) is supplied via circuits 34A and 34B. For example, when coil 33A is excited, spool 21 is displaced to the left, and coil 33B is excited. Similarly, it is displaced to the right.

On the other hand, a valve position sensor 35 is provided to detect the movement of the solenoid 22, and this detection signal is
Input to AND circuit 37.

In addition, the valve position sensor 35 outputs a high level signal "1" when the valve is not in the neutral position,
At the neutral position, the output switches to low level "0".

Signal circuit 34 from microcomputer 10
Both outputs of A and 34B are taken out to an OR circuit 38 and input to an AND circuit 37 via an inverter 39.

When the steering signal is input to the solenoid coil 33A or 33B, the output of the circuit 34A or 34B becomes a high level "1", and becomes a low level "0" when the steering wheel is in the neutral position.

Therefore, when both input signals are "1", the AND circuit 37
1 has been switched to either one and only when the steering signal is not input to the solenoid 22, its output is switched to the high level "1".

An oscillation circuit 41 is provided which is activated by the output of this AND circuit 37, and this oscillation output is sent to an amplifier 40.
It is applied to the solenoid coils 33A, 33B via. 42A and 42B are backflow prevention diodes. That is, the AND circuit 37 operates based on the output of the OR circuit 38 via the valve position sensor 35 and the inverter 39, the oscillation circuit 41 operates based on the output, and the amplifier 40 that amplifies the oscillation output. The controller constitutes a control means that applies an alternating current to the solenoid coil 33A or 33B to vibrate the spool 21 when the valve spool 21 is not in the neutral position even though the valve spool 21 is in the neutral position.

Therefore, when a steering signal from the microcomputer 10 is input to one of the coils of the solenoid 22, for example 33A,
Based on this, the spool 21 moves to the left,
The operating port B becomes high pressure and the operating port A becomes low pressure, and pressurized oil is sent to the power cylinder 3 to power assist the steering wheel operation.

In this case, the valve position sensor 35 is connected to the spool 2.
1 is detected and outputs "1" to the AND circuit 37, but since the output of the circuit 34A is "1", the other input of the AND circuit 37 is set to "0" by the inverter 39, so the AND circuit 37 remains at a low level output, and the oscillation circuit 41 does not operate.

Suppose that when the steering wheel is returned from such a steering state and the steering signal is switched to the neutral position, the spool 21 fails to return due to, for example, dirt in the oil, even though the solenoid 22 is de-energized. Since the steering signal via the OR circuit 38 is "0" and the inverter 39 inverts it, the AND circuit 37 receives a high level signal since the output of the valve position sensor 35 is also "1". As a result, the oscillation circuit 41 is activated, and an alternating current is applied to the solenoid coils 33A and 33B via the amplifier 40.

As a result, the spool 21 is connected to the solenoid coil 3.
3A and 33B cause an oscillation effect,
The clogging caused by dirt, etc., which caused the return failure,
When removed by this dither oscillation, the spool 21 is pushed back toward the neutral position by the elasticity of the spring 24 or 25.

In this way, when the spool 21 remains displaced and fails to return, the spool 21 can be forcibly returned to the neutral state by using the excitation force generated by the dither oscillation, and this excitation spool 21 When returns to the neutral position, the position sensor 35 automatically disappears when the position sensor 35 senses this.

In addition, in this embodiment, the solenoid 22 is provided with two coils 33A and 33B to have dual effect, but a solenoid is provided at each end of the spool 21, and two valve position sensors are also provided. Of course, this is a good thing. Also,
The PS control valve 9 is not necessarily controlled by a microcomputer, but it is sufficient to include a control circuit that detects steering operation and outputs a signal.

As described above, according to the present invention, when the spool fails to return, an alternating current is applied to the solenoid coil to apply an excitation force to the spool to return it to the neutral position, so even though the handle is in the neutral position, It is possible to reliably prevent the danger of pressure oil being continuously supplied to the power cylinder while the control valve remains switched.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a conventional device, and FIG. 2 is a configuration diagram showing essential parts of the present invention. 2...Input shaft, 3...Power cylinder, 9...PS control valve, 10...Microcomputer, 11...Load sensor, 21...Spool, 22
...Solenoid, 33A, 33B...Coil, 35...
Valve position sensor, 37...AND circuit, 38...OR
Circuit, 41...Oscillation circuit.

Claims (1)

[Claims] 1 A means for detecting the load and rotational direction of the input shaft connected to the steering wheel, a control circuit that outputs a steering signal based on the detected values, and a hydraulic actuator of the steering system that is switched by the signal from this control circuit. A power steering device comprising an electromagnetic control valve that selectively supplies pressure oil to a vehicle, comprising means for detecting that the control valve is in a switching position, means for detecting the steering signal, and a means for detecting that the steering signal is in a neutral position. A power steering device characterized by comprising: a control means for applying an alternating current to a solenoid coil to vibrate the spool when the valve spool is not in a neutral position despite the fact that the valve spool is in a neutral position.