JPH0375385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a drive circuit for a device that controls the flow rate of hydraulic oil used in vehicle power steering according to vehicle speed.

In order to reduce steering force in automobiles, the installation rate of power steering, which uses hydraulic pressure to power assist wheel turning operations, is increasing, but wheel turning resistance generally changes with vehicle speed. However, as the resistance tends to decrease as the driving speed increases, the hydraulic assist force is required to be large in the low speed driving range, but on the other hand, in the high speed driving range, it is more similar to manual steering in order to improve steering stability. A certain amount is enough.

Therefore, a speed-sensitive power steering system has been proposed that improves high-speed stability by reducing the amount of oil supplied to the hydraulic actuator of the power steering depending on the vehicle speed or engine speed.

The one shown in FIG. 1 is disclosed in, for example, Japanese Patent Application Laid-Open No. 48-2206 and Japanese Patent Application Laid-open No. 10729-1982.
A bypass passage 5 is provided from the middle of the pipe line 3 that leads oil discharged from the hydraulic pump 1 to the power steering actuator 2 and returns to the tank 4. A bypass valve 6 installed in the bypass passage 5 is connected to the vehicle speed sensor. 7, the valve is opened in a predetermined high speed range to reduce the control flow rate to the actuator 2.

Therefore, since the hydraulic pump 1 is driven in synchronization with the engine, the flow rate supplied to the actuator 2 increases with the vehicle speed (engine rotation), and is sufficient to provide the specified power assist in the low and medium speed range. While ensuring a sufficient amount of oil, when the bypass valve 6 opens in a high speed range, the pump discharge oil is bypassed and returned to the tank 4, reducing the flow rate supplied to the actuator 2 and creating a state similar to manual steering.

In this case, the bypass valve 6 is composed of a solenoid valve,
The opening degree is gradually increased according to the output of the vehicle speed sensor 7.

For this reason, a proportional solenoid valve is used, but
The output transistor that controls the solenoid valve drive current amplifies the DC current, resulting in high power consumption and problems such as heat generation, and the proportional solenoid valve may become unstable, causing instability. Ta.

The present invention was proposed in order to solve this problem, and by controlling the solenoid valve of the flow control section while causing dither oscillation, the flow control device for power steering can be driven with high control accuracy and excellent power efficiency. The purpose is to provide circuits.

To this end, in the present invention, a flow control solenoid valve is provided in the circuit connecting the hydraulic pump driven in synchronization with the engine and the power steering actuator that operates in response to the supply of this discharged oil. In a power steering flow control device in which the valve bypasses a portion of the pump discharge oil depending on the vehicle speed, it includes a frequency-voltage conversion circuit that converts the output pulse from the vehicle speed detection means into a voltage value, and this output voltage. a pulse width modulation circuit that modulates the pulse width into a pulse width, and a means for amplifying this output pulse to drive a flow rate control solenoid valve, and the frequency-voltage conversion circuit is provided with a monostable multivibrator made of an integrated circuit. The control current value in the high vehicle speed range is obtained based on the saturation characteristics.

Embodiments of the present invention will be described below with reference to the drawings.

In the block diagram of Figure 2, 10
1 is a vehicle speed sensor that outputs a signal (pulse signal) corresponding to the vehicle speed; 11 is an amplification circuit that amplifies and shapes the waveform of the output of this vehicle speed sensor 10; and 12 is a circuit that converts a frequency signal proportional to the vehicle speed into a voltage value. 13 is an arithmetic amplification circuit that corresponds to the solenoid valve drive signal based on this voltage value; 14 is an adder circuit that adds the feedback drive value of the solenoid valve 17; 15 is the output of the adder circuit 14 16 is a power transistor that responds to this output, and based on the on/off of the power transistor 16, the current from the constant voltage power supply 18 is applied to the solenoid valve 17.
supply to.

To explain this in more detail, as shown in FIG. 3, the amplification circuit 11 amplifies the sine curve output pulse from the vehicle speed sensor 10 and shapes it into a square wave.

In this way, the frequency signal proportional to the vehicle speed is converted into a voltage value corresponding to the frequency by the next frequency-voltage conversion circuit 12. To do this, the rise and fall of the output of the amplification circuit 11 are captured. The differentiator 12A differentiates the monostable multivibrator 1 using this differentiated signal as a trigger signal.
2B is activated, and the output pulse of this monostable multivibrator 12B is smoothed by a smoother 12C.

The monostable multivibrator 12B is made of an integrated circuit, and is preset so that the frequency of the trigger pulse increases as the vehicle speed increases, and when it exceeds a certain value in the high-speed range, the output pulse becomes continuous, that is, becomes saturated. By setting the output pulse width in advance, it is possible to obtain a characteristic that makes the flow rate constant in a high-speed range as shown in FIG. 4, which will be described later. Specifically, in FIG. 3, the monostable multivibrator 12B has its T
Triggered by a pulse signal applied to the terminal,
A pulse signal with a width determined by the resistor and capacitor connected to the TH and DC terminals is output from the O terminal, but the pulse train input to the T terminal is the vehicle speed signal as described above. Therefore, it is proportional to the vehicle speed, and by appropriately determining the pulse width, when the vehicle speed reaches a certain level, the output of the O terminal becomes saturated and becomes a continuous output.

The smoothed voltage is subtracted in the operational amplifier circuit 13 so that the electromagnetic valve drive current becomes 0 below the voltage value corresponding to a vehicle speed of 10 km/h. The voltage values are added in such a way that FIG. 4) is obtained.

This output value is added to the feedback drive value of the electromagnetic valve 17 in an adder circuit 14, and then compared with a triangular wave from an oscillation circuit 15A that oscillates at a predetermined frequency in a comparator 15B.

This determines the on/off duty of the power transistor 16, and therefore, this duty is ultimately proportional to the vehicle speed, and as the vehicle speed increases, the time ratio during which the power transistor 16 is on increases.

The power transistor 16 becomes conductive when the comparator 15B is turned on, and current flows through the solenoid valve 17, but this repeats intermittent high frequency, for example, 100 Hz, so the duty of the average opening drive pulse of the solenoid valve 17, i.e. Although it is proportional to the vehicle speed, there is always a slight pulsation, which prevents the electromagnetic valve 17 from becoming stuck as a so-called dither effect.

Note that the drive circuit of the present invention is not limited to use in the system shown in FIG. 1, but can be used in other power steering flow control valves.

As described above, according to the present invention, since pulse width modulation is performed to obtain the solenoid valve drive signal, the power consumption of the power transistor is reduced and the power efficiency is improved, and the solenoid valve has a dither oscillation effect. It is possible to prevent the actuation phase, eliminate hysteresis, and improve the control accuracy of flow rate with respect to speed.

Furthermore, according to the present invention, a monostable multivibrator made of an integrated circuit is provided in the frequency-voltage conversion circuit that converts the detection signal from the vehicle speed detection means into a voltage value corresponding to the frequency, and a monostable multivibrator made of an integrated circuit is provided, and Since the control current is obtained in a high vehicle speed range, a constant current value can be obtained with high precision, and the accuracy is higher than, for example, a method that combines ordinary diodes and operational amplifiers to obtain saturation characteristics. In addition, the number of parts can be reduced, space can be saved, and the circuit configuration can be simplified and the cost can be reduced.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a normal power steering flow control system, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a circuit diagram showing its details, and Fig. 4 is a diagram showing vehicle speed and solenoid valve drive. FIG. 3 is a characteristic diagram showing the relationship with current. 10...Vehicle speed sensor, 11...Width amplification circuit, 12
...Frequency voltage change circuit, 12A...Differentiator, 1
2B... Monostable multivibrator, 12C...
Smoother, 13... Arithmetic amplification circuit, 15... Pulse width modulation circuit, 16... Power transistor.

Claims (1)

[Claims] 1. A flow rate control solenoid valve is installed in the circuit connecting the hydraulic pump driven in synchronization with the engine and the power steering actuator that operates in response to the supply of this discharged oil. In a power steering flow control device that bypasses a portion of the pump discharge oil,
A frequency-voltage conversion circuit that converts the output pulse from the means for detecting vehicle speed into a voltage value, a pulse width modulation circuit that modulates this output voltage into a pulse width, and amplifies this output pulse to drive a flow rate control solenoid valve. and a monostable multivibrator made of an integrated circuit is provided in the frequency-voltage conversion circuit, and a control current value in a high vehicle speed range is obtained based on the saturation characteristics of the monostable multivibrator. Drive circuit for steering flow control device.