JPS5897563A - Power steering device - Google Patents

Abstract

PURPOSE:To eliminate an imcomplete return of a spool so that the spool may be surely returned to a neutral position, by applying alternate current to the spool so that the spool vibrates at a dither frequency. CONSTITUTION:When a spool 21 does not completely return even though a solenoid 22 is deenergized, a steering signal through an OR circuit 38 becomes null so that an inverter 39 reverses this signal, and therefore, an AND circuit 37 issues a high level signal since a valve position sensor 35 also issues a unit signal, thereby an oscillating circuit 41 is energized for applying alternate current to solenoid coils 33A, 33B through an amplifier 40. As the result, the spool 21 is vibrated at a dither frequency by the solenoid coils 33A, 33B, and therefore, clogging of, for example, dust causing the imcomplete return of the spool 21 is eliminated due to the dither vibration, thereby the spool 21 is pushed back toward a neutral position under the resilient force of a spring 24, 25.

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 is attached to the steering wheel.
It has a control pulp that mechanically detects and switches the rotation of the connected input shaft, and the switching operation of this control pulp selectively supplies pressure oil to the power cylinder installed at the tip of the input shaft. The direction of the wheels is changed through the steering link in proportion to the rotation of the input shaft.

In particular, in automobile power steering systems, in order to ensure safety, the tip of the input shaft is positioned so that the tip of the input shaft is aligned with the piston of the power cylinder so that steering operations can be performed even if hydraulic assist force cannot be obtained due to a failure of the hydraulic system. Mechanically interconnected via a ball and screw assembly.

By the way, the control pulp that controls the direction of the pressure oil sent to this power cylinder by the rotation of the input shaft is
Since the movement of the input shaft is linked to the actual movement of the piston on the output side, and feedback control is performed, there are significant restrictions on its installation, and it is usually installed at the connection part of the input shaft to the power cylinder. are placed in a limited manner. In addition, in order to perform such mechanical feedback control, the structure of the control valve is extremely complex. In the case of a speed-sensitive type 7 (power steering device), the structure of the control pulp must be made even more elaborate, which results in poor maintainability, poor safety, and high cost. There was a drawback.

On the other hand, control to obtain the optimum steering force according to various driving conditions will be required from the perspective of pursuing comfort and safety of automobiles (this is why the 76 microcomputer was developed). A power steering device that can always obtain optimal steering force under all driving conditions was developed by the applicant in patent application No. 56-1919.
It has been proposed as No. 6.

To explain this based on FIG. 1, an input shaft 2 connected to a hand 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 and a ball (not shown).
The piston 4 is connected to the cylinder 3 depending on the rotational direction and speed of the input shaft 2.
slide inside.

A rack 5 is provided on the side surface of the piston 4, and 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 that is linked to the sector gear 6. It has become.

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

This control pulp 9 is connected to a microcomputer 1 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.
This is an electromagnetic valve whose operation is controlled by 0.

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 input to the calculation II 111 section 15 of the microcomputer 10 via input interfaces 14 each having amplification and signal waveform processing functions.

The calculation control unit (CPU) 15 performs calculations based on these inputs, selects the stored value from the storage unit (ROM) 16 which stores the optimum value corresponding to the operating conditions in advance,
It is output to the control pulp 9 via the output interface 17.

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

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 optimum value corresponding to the input signal is preset 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 outputs it to the control pulp 9. input.

Therefore, the control pulp 9 feeds the required amount of pressure oil into 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 ff8A, 8B is on the side of the tank T). )
In this case, when the medium speed is low and the turning resistance of the wheels is large,
The load sensor 11 detects that the torsion angle of the input shaft 2 is large, so it increases the oil pressure supplied to the power cylinder 3, 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 switching amount of the control valve 9 increases so as to increase the .

As a result, an operation to move the piston 4 using the input shaft 2 is performed in the oil chamber 8A or 8B corresponding to the operating load.
The steering wheel is assisted by hydraulic pressure, so the steering wheel can be operated easily and with an appropriate operating feel.

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, thereby stopping the supply of pressure oil to the power cylinder 3.

In other words, you can also get feedback input at the same time.
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, in this power steering device, the PS control valve 9 exists independently, so if the return to the neutral state is not performed smoothly due to dust in the hydraulic oil, the steering wheel will return to the neutral position. An extremely dangerous situation occurs in which pressure oil is supplied to the power steering 3 even though it has been returned to its original position.

The present invention aims to solve this problem, 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 dither oscillate when a handlebar neutral position signal is input and the PS control valve is switched in one direction to prevent return failure. This is to ensure that the system is released and returns to the neutral position.

Hereinafter, embodiments of the present invention will be described based on the drawings.

In FIG. 2, the electromagnetic PS control valve 9 is
A spool 21 is slidably housed in the valve body 20, and a drive rod 23 of a solenoid 22 is connected to the end of the spool 21, thereby switching the spool 21 left and right.

The valve body 20 includes a high pressure boat P on the hydraulic pump side,
Two low pressure ports T on the reservoir side and operating ports A and B located between these and connected to the oil chambers 8A and 8B of the power cylinder 3 are formed between them, and the spool 21
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 by the three lands C1, C2, and C3 formed in the figure, and when the spool 21 is switched to the right, the high pressure boat Pressure oil from P to operating port A (
At this time, operating port B is connected to low pressure port T), and conversely, when the spool 21 is switched to the left, pressure oil from high pressure port P is connected to operating port B (operating port A is connected to low pressure port T). Send each.

Spring chambers 26 and 27 are formed at both ends of the spool 21 and have neutral return springs 24 and 25 interposed therein.

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

The solenoid 22 has two coils 33A and 33B, and an excitation current from the microcomputer 10 (see FIG. 1) is supplied through circuits 34A and 34B. For example, when the coil 33A is excited, the spool 21 is moved to the left. When the coil 33B is excited, it is also 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 an AND circuit 37.

The valve position sensor 35 outputs a high level signal "'1" when the valve is at a position other than the neutral position, and the output switches to a low level "0" at the neutral position.

Signal circuits 34A, 34 from the microcomputer 10
Both outputs of B are taken out to the OR circuit 38, and the inverter 3
9 to the AND circuit 37.

When a 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 "O" when the steering wheel is in the neutral position.

Therefore, the AND circuit 37 determines that both human power signals are
'', that is, only when the valve spool 21 is switched to one side and the solenoid 22 is not receiving a steering signal, its output switches to the high level 111 II.

An oscillation circuit 41 operated by the output of this AND circuit 37
is provided, and this oscillation output is applied to the solenoid coils 33A and 33B via an amplifier 40. 42A, 42
B is a backflow prevention diode.

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

In this case, the valve position sensor 35 detects the displacement of the spool 21 and outputs 1°' to the AND circuit 37;
Since the output of 4A is 1'', the other input of the AND circuit 37 becomes 0'° due to the inverter 39, so the AND
The 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 not switched to the neutral position, the spool 21 becomes malfunctioning due to, for example, dirt in the oil, even though the solenoid 22 is de-energized. Since the steering signal through the OR circuit 38 is O° and the inverter 39 inverts it, the
Since the output of the valve position sensor 35 is also 1'', the O circuit 37 outputs a high level signal, which activates the oscillation circuit 41 and applies an alternating current to the solenoid coil 33A133B via the amplifier 840. .

As a result, the spool 21 is connected to the solenoid coils 33A, 3
3B causes an oscillation action, and when the dirt or other blockage that was causing the return failure is 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 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 (p), and two valve position sensors are also provided. Of course, the control of the PS control valve 9 is not necessarily performed by a microcomputer, but it is sufficient to include a control circuit that senses steering operation and outputs a signal.

As described above, according to the present invention, when the spool returns poorly, an alternating current is applied to the solenoid coil to apply an excitation force to the spool to return it to the neutral position.
It is possible to reliably prevent the danger of the pressurized cylinder 7 continuing to be supplied to the power cylinder with the control valve being switched even though the handle is in the neutral position.

[Brief explanation of the drawing]

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...P
S control valve, 10... microcomputer, 11... load sensor, 21... spool, 2
2... Solenoid, 33A, 33B... Coil, 3
5... Valve position sensor, 37... AND circuit, 3
8...OR circuit, 41...oscillation circuit.

Claims (1)

[Claims] A means for detecting the load and rotation direction of the input shaft connected to the steering wheel, an IIJI11 circuit that outputs a steering signal based on this detected value, and a signal from this control circuit that switches to the hydraulic actuator of the steering system. A power steering device comprising an electromagnetic control valve that selectively supplies pressure oil, comprising means for detecting that the control pulp 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: control means for applying an alternating current to a solenoid coil to vibrate the spool when the pulp spool is not in a neutral position.