JPH0124112B2 - - 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 provides optimal control force, the structure of the control valve has to be even more elaborate, which makes maintainability and safety poor and expensive. There was a drawback.

On the other hand, control to obtain the optimum steering force according to various driving conditions will be increasingly required from the perspective of pursuing comfort and safety in automobiles, and for this reason microcomputers are being 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, 11 is a load sensor attached to the input shaft 2, which is composed of a strain gauge or the like that detects the rotational force and direction of rotation by detecting the 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 pick-up 12. input into 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 this value, 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 handle has been returned to the neutral position, pressure oil is supplied to the power cylinder 3, creating a very dangerous situation.

The purpose of the present invention is to solve this problem, that is, when the electromagnetic PS control valve remains switched when the handle is in the neutral position, the pump discharge oil is returned to the tank side and the power assist is stopped.

The present invention provides power assist by bypassing high pressure from the valve spool pump to the tank side when the PS control valve is switched in one direction while the steering wheel neutral position signal is input. It will be forcibly discontinued.

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 includes 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
are formed, and the three land portions C ₁ , C ₂ , C ₃ formed on the spool 21 make it possible for the neutral position shown in the figure to be
The hydraulic oil from the high pressure port P is returned to the low pressure port T, and when the spool 21 is switched to the right, the hydraulic oil from the high pressure port P is returned to the low pressure port T. ),
Conversely, when the spool 21 is switched to the left, the pressure oil from the high pressure port P is sent to the operating port B (the operating port A is connected to the 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 communicate with each other to the low pressure side due to leakage from the periphery of the spool 21, and do not prevent the spool 21 from moving to the left or right.

By the way, the left low pressure port T and the high pressure port P communicate with each other via a passage 29, and a normally closed solenoid valve 31 is interposed therebetween.

The solenoid 22 has two coils 33A and 3.
3B, and an excitation current from the microcomputer 10 (see Fig. 1) is supplied through 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".

From the microcomputer 10 to the signal circuit 34
Both outputs sent to A and 34B are taken out to the OR circuit 38, and are sent to the AND circuit 3 via the inverter 39.
7 is input. When the steering signal is input to 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 handle is in the neutral position.

Therefore, when both input signals are "1", the AND circuit 37
1 is switched to either one and the steering signal is not input to the solenoid 22, its output is switched to high level "1" and the solenoid valve 31 is The valve is opened by energizing the valve. Therefore, the output voltage via the pulse position sensor 35 and the inverter 39 is
An AND circuit 37 that operates based on the output of the OR circuit 38 and an amplifier 40 that amplifies the output operate the solenoid valve 31 when the valve spool 21 is not at the neutral position even though the steering signal is at the neutral position. A control means is configured to open and bypass high pressure to the low pressure port.

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 becomes "0" by the inverter 39, and therefore the AND circuit The solenoid valve 31 is de-energized while the output of the solenoid valve 37 remains at a low level.

When the steering wheel is returned from such a steering state and the steering signal is switched to the neutral signal "0", even though the solenoid 22 has been de-energized, the spool 21 may have failed to return due to, for example, dirt in the oil. If this occurs, the steering signal input to the OR circuit 38 is "0", so the inverter 39 inverts it, and as a result,
Since the output of the valve position sensor 35 is also "1", the AND circuit 37 outputs an excitation signal to the solenoid valve 31.

As a result, the solenoid valve 31 opens and short-circuits the high pressure port P to the low pressure port T.

As a result, even if the spool 21 is in the left position and fails to return, high pressure will not be supplied to the operating port B, and therefore no pressure oil will be sent to the power cylinder 3, and the power assist will stop. be. Therefore, it is possible to prevent an unexpected situation in which the direction of the wheels changes automatically against the driver's will.

In this embodiment, the solenoid 22 is provided with two coils 23A and 23B to have dual effect, but a solenoid is provided at each end of the spool 21, and two valve position sensors are also provided to prevent return failure. Solenoid valve 3 to release high pressure when
Of course, valve 1 may be opened. Further, 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 detects steering operation and outputs a signal.

As described above, according to the present invention, when the spool returns poorly, the high pressure in the operating port is released to the tank side and power assist is stopped, so the control valve remains switched even though the handle is in the neutral position. In some cases, the supply of pressure oil to the power cylinder is inevitably stopped, and the risk of unauthorized steering operation can be reliably prevented.

[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, 23A, 23B...Coil, 26,
27...Spring chamber, 29...Oil passage, 31...Solenoid valve, 35...Valve position sensor, 37...AND circuit,
38...OR 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 the control valve, comprising means for detecting that the control valve is in a switching position, means for detecting the steering signal, and a high-pressure port of the control valve. A passage communicating with the low pressure port, a solenoid valve interposed in this passage, and when the valve spool is not in the neutral position even though the steering signal is in the neutral position, the solenoid valve is opened to transfer high pressure to the low pressure port. A power steering device comprising a bypass control means.