JPH08164864A - Power steering device - Google Patents

Abstract

PURPOSE: To provide a power steering device generating only a small shock at the time of switching voltage applied to an electric motor and not causing a delay in assisting steering. CONSTITUTION: This is a power steering device to carry out auxiliary steering with a hydraulic pump driven to rotate as a generating source of working hydraulic pressure by feeding back a motor rotating speed detection signal of motor rotating speed detection means 9, 10 to detect rotating speed of an electric motor 4 and controlling the electric motor 4 to rotate at target rotating speed. It is constituted to be furnished with a load detection means 3 to detect a load of the hydraulic pump 5 and to output a load detection signal and a target rotating speed deciding means 1a to decide the target rotating speed in accordance with the load detection signal of the load detection means 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a power steering system for assisting steering by using a hydraulic pump rotatably driven by an electric motor as a source of operating hydraulic pressure.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a main configuration of an example of a power steering apparatus that assists steering by using a hydraulic pump rotatably driven by an electric motor as a source of operating hydraulic pressure. In this power steering device, a motor drive circuit 2 applies a voltage to an electric motor 4 to drive the electric motor 4 in accordance with a target value of an applied voltage instructed by the control unit 1, and the electric motor 4 rotationally drives a hydraulic pump 5 to operate hydraulic pressure. Generate. This operating oil pressure is controlled by adjusting the amount of oil returned by the control valve 6 to an oil supply tank (not shown).

When the steering wheel 7 is operated and the gear device (not shown) including the pinion gear 8 provided at the lower end of the steering wheel shaft is operated, the control valve 6 is moved to the pipelines 6a and 6b leading to the power cylinder. Controls the pressure of hydraulic oil that is pumped. As a result, the power cylinder operates to generate a steering assist force in the operation direction of the steered wheels 7 according to the operation amount. A motor current detection circuit 3 that detects a current flowing through the electric motor 4 is provided between the motor drive circuit 2 and the electric motor 4, and the detection signal is input to the control unit 1 as a load detection signal. The control unit 1
The voltage applied to the electric motor 4 is controlled by this load detection signal.

In the conventional power steering apparatus having such a configuration, the control unit 1 reduces energy consumption when the steering wheels 7 are not operated and no steering assist force is required (the electric current flowing through the electric motor 4 is small). In order to suppress the voltage, as shown in FIG. 7, the voltage applied to the electric motor 4 is lowered by one step to, for example, 6 V to reduce the output of the electric motor 4.
Then, the steering wheel 7 is operated to operate the control valve 6, the operating oil pressure is increased, and the load is increased.
When the load detection signal of the motor current detection circuit 3 reaches a predetermined value due to an increase in the current flowing through the controller 1, the control unit 1 raises the voltage applied to the electric motor 4 by one step, for example, to 12V to output the electric motor 4. Is trying to increase.

[0005]

However, in the conventional power steering apparatus, when the voltage applied to the electric motor 4 is increased by one step, the electric motor 4 is operated up to an unnecessary number of revolutions as shown by the thick line in FIG. As the hydraulic pressure rises and the hydraulic pressure increases accordingly, the shock at the time of switching increases, which is transmitted to the steered wheels 7 and deteriorates the driver's steering feeling.

Further, in the hydraulic power steering system using the electric motor 4 as described above, when the rotational speed of the electric motor 4 is large and the flow rate of oil is large, the load amount with respect to the operation amount of the steering wheel 7 ( Although the motor current) increases, as described above, in order to raise the voltage applied to the electric motor 4 by one step, the steered wheels 7 are operated and the control valve 6 is actuated, the operating oil pressure is increased, and the thick line portion in FIG. As shown in, the increase in the motor current is detected after the rotational speed of the electric motor 4 is once decreased. Therefore, due to the decrease in the rotation speed of the electric motor 4,
The flow rate of oil once decreased, the increasing rate of the load amount (motor current) with respect to the operation amount of the steering wheel 7 slowed down, the detection of the motor current increase was delayed, and the steering assist was delayed.

The present invention has been made in view of the above circumstances, and provides a power steering device in which a shock when switching a voltage applied to an electric motor is small and a steering assist is not delayed. The purpose is to

[0008]

A power steering apparatus according to a first aspect of the present invention feeds back a motor rotation speed detection signal of a motor rotation speed detection means for detecting the rotation speed of an electric motor, and the electric motor outputs a target rotation speed. In a power steering device that is controlled to rotate and uses a hydraulic pump that is rotationally driven as a source of operating hydraulic pressure to assist steering, a load detection unit that detects a load of the hydraulic pump and outputs a load detection signal; Target rotation speed determining means for determining the target rotation speed based on the load detection signal of the load detecting means.

In the power steering apparatus according to the second aspect of the invention, the motor rotation speed detecting means detects the motor rotation speed based on the ripple generated in the current flowing through the electric motor.

In the power steering device according to the third aspect of the present invention, the drive circuit for the electric motor drives the electric motor P at a cycle shorter than the electric time constant of the electric motor.
It is characterized by WM driving.

[0011]

In the power steering device according to the first invention,
The load detection means detects the load of the hydraulic pump and outputs a load detection signal, and the target rotation speed determination means determines the target rotation speed of the electric motor based on the load detection signal. And
The electric motor is controlled to rotate at the target rotation speed.

In the power steering device according to the second aspect of the present invention, the motor rotation speed detecting means detects the motor rotation speed based on the ripple generated in the current flowing through the electric motor.

In the power steering device according to the third aspect of the invention, the drive circuit for the electric motor drives the electric motor by PWM at a cycle shorter than the electric time constant of the electric motor.
The current ripple generated by the PWM drive is reduced so that only the ripple due to the motor slot can be detected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the power steering device according to the present invention will be described below with reference to the drawings showing the same. FIG. 1 is a block diagram showing a main part configuration of an embodiment of a power steering apparatus according to the first to third inventions. In this power steering device, the motor drive circuit 2 applies a voltage to drive the electric motor 4 by PWM control according to the target value of the applied voltage instructed by the control unit 1, and the electric motor 4 drives the hydraulic pump 5. It is rotationally driven to generate hydraulic pressure. Then, the control valve 6 controls the hydraulic pressure distribution to the power cylinders.

When the steering wheel 7 is operated and the gear device (not shown) including the pinion gear 8 provided at the lower end of the steering wheel shaft is operated, the control valve 6 is connected to the pipelines 6a and 6b leading to the power cylinder. Controls the pressure of hydraulic oil that is pumped. As a result, the power cylinder operates to generate a steering assist force in the operation direction of the steered wheels 7 according to the operation amount.

A motor current detection circuit 3 for detecting a current flowing through the electric motor 4 is provided between the motor drive circuit 2 and the electric motor 4, and the detection signal is input to the control section 1 as a load detection signal. The detection signal output from the motor current detection circuit 3 is also input to the ripple detection circuit 9, and a ripple (proportional to the rotation speed of the electric motor 4) due to the slot of the electric motor 4 included in the detection signal is detected. . This ripple detection signal is supplied to the rotation speed detection circuit 10
Is input to the control unit 1 after being converted into a rotation speed signal representing the rotation speed of the electric motor 4.

Based on the load detection signal, the control unit 1 controls the voltage applied to the electric motor 4 by PWM (Pulse Width Modulation) so that the rotation speed signal has a predetermined value. The control unit 1 makes the cycle of the PWM pulse shorter than the electric time constant of the electric motor 4 to reduce the current ripple generated by the PWM drive, and the ripple detection circuit 9 only produces the ripple caused by the slot of the motor. Allow it to be detected. Preferably, the cycle of the PWM pulse is set to 1/10 or less of the electric time constant of the electric motor 4.

3 and 4 are waveform charts showing examples of ripples when the voltage applied to the electric motor 4 is 10V and 15V, respectively. CH1 shows the output waveform of the motor current detection circuit 3, and CH2 shows the motor current waveform. The ripple of the motor current appears at the frequency of the motor rotation speed × the number of slots. For example, when the applied voltage is 10 V (FIG. 3), from the ripple frequency of 750 Hz, the rotation speed = (750 Hz / 20 (the number of slots)) × 60 seconds = 22
It can be seen that it is 50 rpm. When the applied voltage is 15 V (FIG. 4), the rotational frequency is (1250 Hz / 20 (the number of slots)) × 60 seconds = from the ripple frequency of 1250 Hz.
It can be seen that it is 3750 rpm.

The operation of the power steering device having such a structure will be described below. When the steering wheel 7 is not operated and the steering assist force is not required (the electric current flowing through the electric motor 4 is small), the control unit 1 controls the electric motor 4 at a low rotation speed (for example, 1000 rpm) in order to suppress energy consumption. To do. As a result, the rotation speed of the electric motor 4 is kept low as shown by the thick line in FIG.

When the steering wheel 7 is operated, the control valve 6
Is activated, the hydraulic pressure increases, the load increases, the current flowing through the electric motor 4 increases, and when the load detection signal of the motor current detection circuit 3 reaches a predetermined value, the control unit 1 causes the electric motor 4 Is controlled to a high rotation (for example, 2000 rpm) (thick line in FIG. 2). When the load detection signal of the motor current detection circuit 3 is within the predetermined range, the control unit 1 controls the voltage applied to the electric motor 4 so as to keep the rotation speed at high rotation.

When the load detection signal of the motor current detection circuit 3 increases and the voltage applied to the electric motor 4 becomes approximately the battery voltage, the control unit 1 cannot increase the applied voltage any further. In this state, when the operating oil pressure increases, the motor current of the electric motor 4 increases, but the rotation speed decreases according to the motor current-rotation speed characteristic of the electric motor 4, as shown by the thick line in FIG. This indicates the output limit of the electric motor 4. When the operation of the steering wheel 7 becomes small, the operating oil pressure decreases, the load decreases, and the current flowing through the electric motor 4 decreases, the control unit 1 reverses the above-described route indicated by the bold line in FIG. The rotation speed of the electric motor 4 is controlled so as to trace.

FIG. 5 is a circuit diagram showing a circuit example of the control unit 1, the motor current detection circuit 3, the ripple detection circuit 9, and the rotation speed detection circuit 10 of the power steering device according to the first to third aspects of the invention. This circuit diagram shows the current flowing through the electric motor 4 driven by the motor drive circuit 2
The differential amplifier (motor current detection circuit 3) using 1 detects the voltage by amplifying the voltage across the resistor Rs. A ripple (proportional to the rotation speed of the electric motor 4) caused by the slot of the electric motor 4 is superimposed on this detection signal, and the ripple is extracted by the differentiating circuit 13 using the OP amplifier 12. The extracted ripple is converted into a rectangular wave by the comparator 14 to which the voltage divided by the resistors R1 and R2 is applied to the non-inverting input terminal.

The rectangular wave converted by the comparator 14 has a capacitor C1, a resistor R7 and diodes D1 and D.
The rising portion is extracted as a one-shot pulse by the differential rectification circuit 15 composed of 2. The extracted one-shot pulse is converted into a rectangular wave again by the comparator 16 to which the voltage divided by the resistors R3 and R4 is applied to the inverting input terminal. This rectangular wave is integrated by the two-stage RC integration circuit 17 and converted into a voltage according to the number of rectangular waves. The number of rectangular waves is the same as the number of ripples caused by the slots of the electric motor 4, and is proportional to the rotation speed of the electric motor 4. Therefore, the voltage corresponding to the number of the rectangular waves is a rotation speed signal proportional to the rotation speed of the electric motor 4.

This rotation speed signal has a non-reference voltage corresponding to the target rotation speed signal output by the target rotation speed determination unit 1a (the output of the motor current detection circuit 3 is directly input) provided in the control unit 1. It is input to the inverting input terminal of the OP amplifier 21 (differential amplifier) applied to the inverting input terminal, and the difference from the reference voltage is amplified and output. The reference voltage corresponding to the target rotation speed signal is adjusted by the target rotation speed determination unit 1a in the control unit 1 based on the load detection signal of the motor current detection circuit 3. The target rotation speed of the electric motor 4 is determined as shown in FIG. 9 based on the load detection signal (motor current) of the motor current detection circuit 3.

The signal output from the OP amplifier 21 after amplifying the difference between the rotation speed signal and the reference voltage is input to the inverting input terminal of the comparator 22. The sawtooth wave generated by the multivibrator 18 including the OP amplifier 19 is input to the non-inverting input terminal of the comparator 22. The comparator 22 outputs a PWM control signal whose output time is determined by the output signal of the OP amplifier 21 and the sawtooth wave, and supplies it to the motor drive circuit 2. At the inverting input terminal of the comparator 22, the voltage divided by the resistor voltage divider R6 is fed to the diode D.
3 is applied to maintain the minimum applied voltage (minimum duty of PWM) to the electric motor 4.

[0026]

According to the power steering system of the first to third aspects of the invention, the shock when switching the voltage applied to the electric motor is small, and the steering assist is not delayed.

According to the power steering device of the second and third inventions, it is not necessary to provide a motor rotation sensor for detecting the rotation speed of the electric motor, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of an embodiment of a power steering device according to the first to third inventions.

FIG. 2 is a characteristic diagram showing control characteristics of the power steering device according to the first to third aspects of the invention.

FIG. 3 is a waveform diagram showing an example of ripples superimposed on the output of the motor current detection circuit and the motor current.

FIG. 4 is a waveform diagram showing an example of ripples superimposed on the output of the motor current detection circuit and the motor current.

FIG. 5 is a circuit diagram showing a circuit example of a control unit, a motor current detection circuit, a ripple detection circuit, and a rotation speed detection circuit.

FIG. 6 is a block diagram showing a main part configuration of an example of a conventional power steering device.

FIG. 7 is an explanatory diagram showing a method of controlling a motor applied voltage of a conventional power steering device.

FIG. 8 is an explanatory diagram illustrating a relationship between a motor applied voltage and a motor rotation speed of a conventional power steering device.

FIG. 9 is an explanatory diagram showing a method of controlling a motor current and a motor target rotation speed.

[Explanation of symbols]

 1 Control Section 1a Target Rotational Speed Determining Section 2 Motor Drive Circuit 3 Motor Current Detection Circuit 4 Electric Motor 5 Hydraulic Pump 6 Control Valve 7 Steering Wheel 9 Ripple Detection Circuit 10 Rotational Speed Detection Circuit

Continuation of the front page (72) Kojin Senno 1-171 Tenjin-cho, Kodaira-shi, Tokyo Koyo Electronic Industry Co., Ltd.

Claims (3)

[Claims] 1. A hydraulic pump rotationally driven by controlling the electric motor to rotate at a target rotational speed by feeding back a motor rotational speed detection signal of a motor rotational speed detecting means for detecting the rotational speed of the electric motor. In a power steering device that assists steering as a source of operating hydraulic pressure, a load detection unit that detects the load of the hydraulic pump and outputs a load detection signal, and the target rotation speed based on the load detection signal of the load detection unit. And a target rotation speed determining means for determining the target rotation speed. 2. The power steering device according to claim 1, wherein the motor rotation speed detection means detects the motor rotation speed based on a ripple generated in a current flowing through the electric motor. 3. The power steering device according to claim 1, wherein the drive circuit of the electric motor drives the electric motor by PWM at a cycle shorter than an electric time constant of the electric motor.