JPH08183467A - Power steering - Google Patents

Abstract

PURPOSE: To provide a power steering receiving small shock at the time of switching voltage to be applied to an electric motor. CONSTITUTION: A power steering that assists steering by oil pressure generated by a pump 5 driven by an electric motor 4 is provided with a load detecting means 3a for detecting the load of a hydraulic power source, and a control means 1a for controlling the applied voltage target value to the electric motor 4 stepwise. The control means 1a is so constituted that the applied voltage target value is set to maintain the other applied voltage target value in the change range or less of a load detection signal changed by the change of the motor applied voltage at the time of controlling the motor applied voltage from one to the other between the adjacent step voltage of the applied voltage target value to the electric motor 4.

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. 11 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, the motor drive circuit 2 applies a voltage to the electric motor 4 to drive the electric motor 4 in accordance with the target value of the applied voltage instructed by the control unit 1, and the electric motor 4
Drives the hydraulic pump 5 to rotate to generate operating hydraulic pressure.
The control valve 6 controls the pressure of the hydraulic oil that is pressure-fed to the pipelines 6a and 6b leading to the power cylinder.

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 it, the voltage applied to the electric motor 4 is lowered by one step as shown in FIG.
The output of the electric motor 4 is reduced. And the steering wheel 7
Is operated to operate the control valve 6, 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, control is performed. The unit 1 raises the voltage applied to the electric motor 4 by one step to increase the output of the electric motor 4.

[0005]

However, in the conventional power steering apparatus, since the voltage applied to the electric motor 4 is switched in two steps as described above, there is a large difference in the voltage that can be switched. Therefore, the shock at the time of switching is large, and this is transmitted to the steering wheel 7, which deteriorates the driver's steering feeling. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power steering device that causes less shock when switching the voltage applied to the electric motor.

[0006]

A power steering device according to a first aspect of the present invention is a power steering device for assisting steering by hydraulic pressure generated by a pump driven by an electric motor, and load detecting means for detecting a load of a hydraulic pressure source. And a control unit for controlling the target voltage value applied to the electric motor in a stepwise manner based on the load detection signal from the load detection unit, the control unit adjoining the target voltage value applied to the electric motor. When controlling the motor applied voltage from one to the other among the step voltages to be set, in order to maintain the other applied voltage target value within the change range of the load detection signal that changes due to the change in the motor applied voltage,
The target value of the applied voltage is set.

In the power steering apparatus according to the second aspect of the invention, the load detecting means detects the motor current as a load detection signal.

In the power steering apparatus according to the third aspect of the invention, the load detecting means detects the hydraulic pressure of the hydraulic circuit as a load detection signal.

[0009]

In the power steering device according to the first invention,
The load detecting means detects the load of the hydraulic power source, and the control means controls the target value of the voltage applied to the electric motor in steps based on the load detection signal from the load detecting means. The control means, when controlling the motor applied voltage from one of the adjacent step voltages of the target value of the applied voltage to the electric motor to the other, within the change range of the load detection signal that changes due to the change of the motor applied voltage. Controls the target value of the applied voltage to the electric motor so that the other target value of the applied voltage is maintained. Therefore, when the voltage applied to the electric motor is increased by one step, the current flowing through the electric motor also increases, and as a result, the applied voltage is increased again by one step, and as a result, the current flowing through the electric motor is increased again. Increase ...
Even when the load does not increase due to the operation of the steering wheel, there is no possibility that the applied voltage rises to a constant voltage and the effect of controlling the applied voltage in steps disappears.

In the power steering system according to the second aspect of the present invention, the load detection means detects the motor current as a load detection signal.

In the power steering device according to the third aspect of the present invention, the load detecting means detects the hydraulic pressure of the hydraulic circuit as a load detection signal. To do.

[0012]

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 device according to the first and second inventions. 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 1a, and the electric motor 4 rotationally drives a hydraulic pump 5 to operate hydraulic pressure. Generate. The control valve 6 is a pipeline 6 leading to the power cylinder.
Controls the pressure of the hydraulic oil sent to a and 6b.

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 3a for detecting a current flowing through the electric motor 4 is connected to the motor drive circuit 2, and the detection signal thereof is input to the control unit 1a as a load detection signal. In the control unit 1a, the load detection signal is processed by the filter circuit 1b, and the voltage applied to the electric motor 4 is stepwise according to the target voltage table 1c stored in the memory based on the processed load detection signal. It is designed to be controlled.

Here, as shown in FIG. 9 (a), the load detection signal becomes large and the voltage applied to the electric motor 4 becomes 1
When stepped up (FIG. 9 (b)), the time ΔT (electric motor 4 increases) until the rotational speed of the electric motor 4 becomes balanced with the applied voltage because of the hydraulic load (FIG. 9 (c)).
Time required for the rotor to accelerate (Fig. 9 (e))
Is required, and the motor current shows a large value during that time (FIG. 9 (d)). Therefore, when the motor current is used as the load detection signal, the motor current detection signal is filtered by the filter circuit 1b to remove a sudden change in the current.

The operation of the power steering apparatus having such a structure will be described below with reference to the flow chart (FIG. 4) showing the operation. The control unit 1a always determines each section corresponding to the voltage of each step applied to the electric motor 4 which is set in the load detection signal (current flowing in the electric motor 4) (FIGS. 4S10 and S14). When the steering wheel 7 is 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 energy consumption, according to the target voltage table 1c, as shown in FIG. The voltage applied to is set to the minimum voltage (for example, 6 V) (S12 in FIG. 4) to reduce the output of the electric motor 4.

When the steering wheel 7 is operated, the control valve 6
Is activated, the hydraulic pressure is increased, the load is increased, the current flowing through the electric motor 4 is increased, and the motor current detection circuit 3a
Load detection signal is a predetermined value (eg, motor current equivalent to 8A)
Is reached and the determination section of the load detection signal changes (see S1 in FIG. 4).
6), the control unit 1a, according to the target voltage table 1c,
The voltage applied to the electric motor 4 is set in one step (for example, 2
V) The voltage is increased (S12 in FIG. 4), the voltage corresponding to the determination section is set, and the output of the electric motor 4 is increased.

Similarly, each time the electric current flowing through the electric motor 4 increases and the judgment section of the load detection signal of the motor current detection circuit 3a (for example, a motor current exceeding 2A) changes (FIG. 4S16), the control section 1a is changed. Increases the voltage applied to the electric motor 4 by one step (for example, 2 V) (see FIG. 4S
12) Then, the voltage corresponding to the determined section is set and the output of the electric motor 4 is increased. However, if the voltage applied to the electric motor 4 is raised to a constant voltage (for example, 12V) (S12 in FIG. 4), it cannot be further raised.

When the operation of the steering wheel 7 becomes small, the operating oil pressure drops, the load decreases, and the current flowing through the electric motor 4 decreases, the load detection signal of the motor current detection circuit 3a is reversed, contrary to the above. Each time the determination section (e.g., motor current equivalent to more than 2A) changes (FIG. 4S16), the control unit 1a lowers the voltage applied to the electric motor 4 by one step (e.g., 2V) and sets the voltage corresponding to the determination section. (Fig. 4
S12), the output of the electric motor 4 is decreased.

By the way, when the voltage applied to the electric motor 4 is gradually increased, even if the steering wheel 7 is not operated, the electric motor is increased due to the increase of the oil viscous resistance due to the increase of the rotational speed of the hydraulic pump 5. As the load of No. 4 increases, the current flowing through the electric motor 4 has a characteristic of increasing as shown in FIG. Therefore, when the voltage applied to the electric motor 4 is increased by one step, the current flowing through the electric motor 4 is also increased. As a result, the applied voltage is increased again by one step, and as a result, the current is applied to the electric motor 4. The current also increases again, and the applied voltage rises to a constant voltage (for example, 12V) even when the load does not increase due to the operation of the steering wheel 7, and the applied voltage is controlled in steps. There is a risk that the effect will disappear.

Therefore, in the present invention, when the motor applied voltage is controlled from one of the adjacent step voltages of the motor applied voltage target value to the other, the load detection signal (motor current) which changes due to the change of the motor applied voltage. Within the range of change in (), the motor applied voltage target value is set so as to maintain the other applied voltage target value.

FIG. 5 is a circuit diagram showing a circuit example of the control unit 1a, the motor drive circuit 2 and the motor current detection circuit 3a of the power steering device according to the first and second aspects of the invention. This circuit diagram shows the microcomputer 1 included in the control unit 1a.
From 3, the watchdog pulse for monitoring is differentiating circuit 1
4 and the diode D1 to the power supply IC10. The power supply IC 10 is adapted to give a bar reset signal to the microcomputer 13 when the watchdog pulse indicates an abnormality. Power IC
10 and the power supply IC 10 turn on / off the PN
The P-transistor Q1 constitutes a power supply circuit.

The microcomputer 13 uses a NPN transistor Q2, Q3 to turn on / off the power source of the electric motor 4 by a contact point ry1 to drive a relay drive circuit Ry1.
Turn on / off. The relay drive circuit Ry1 is connected to a power supply V _IG that is turned off when the engine is started. The microcomputer 13 is connected circuit 21 for detecting turning off of the power supply V _IG is, when the power V _IG off to stop the operation. The microcomputer 13 outputs the target value of the voltage applied to the electric motor 4 as a 4-bit digital signal, and this digital signal is converted into an analog voltage signal by the D / A converter 20 including a ladder (ladder type circuit). To be converted.

This analog voltage signal is input to the inverting input terminal of the OP amplifier 16 which constitutes a comparator. OP
The sawtooth wave generated by the multivibrator including the OP amplifier 15 is input to the non-inverting input terminal of the amplifier 16. The OP amplifier 16 outputs an NPN output signal whose output time is determined by the analog voltage signal and the sawtooth wave.
It is given to the transistor Q5, and the NPN transistor Q5 is
This output signal and the inverted PWM (Pulse Width Modurati
on) signal is applied to FET Q4.

The FET Q4 is turned on / off according to the PWM signal.
When it is turned off and turned on, a current is passed through the electric motor 4. A regenerative diode D2 for flowing a regenerative current is connected in parallel to the electric motor 4. A resistor Rs is connected between the FET Q4 and the ground, and the current flowing through the electric motor 4 is detected by the voltage across the resistor Rs. The voltage across the resistor Rs is input to the non-inverting input terminal of the OP amplifier 18 via the smoothing circuit 17, amplified, and then input to the microcomputer 13. The microcomputer 13 sets the target value of the voltage applied to the electric motor 4 in a stepwise manner by a signal representing the current flowing through the electric motor 4.

FIG. 6 is a block diagram showing the configuration of the essential parts of one embodiment of the power steering apparatus according to the first and third inventions. 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 1a, and the electric motor 4 rotationally drives a hydraulic pump 5 to operate hydraulic pressure. Generate. The control valve 6 controls the pressure of the hydraulic oil that is pressure-fed to the pipelines 6a and 6b leading to the power cylinder.

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 hydraulic pressure sensor 9 for detecting the hydraulic pressure (operating hydraulic pressure) of the hydraulic circuit is attached, for example, near the discharge port of the hydraulic pump 5, and a load detection signal corresponding to the hydraulic pressure detected by the hydraulic pressure sensor 9 is given to the control unit 1a. The control unit 1a controls the voltage applied to the electric motor 4 in a stepwise manner based on the load detection signal and according to the target voltage table 1c stored in the memory. Other configurations are the first and the first described above.
2 Since it is similar to the power steering device according to the invention,
Description is omitted.

The operation of the power steering device having such a configuration will be described below with reference to the flow chart (FIG. 4) showing the operation. The control unit 1a always determines each section corresponding to the voltage of each step applied to the electric motor 4 which is set in the load detection signal (operating oil pressure) (FIGS. 4S10 and S14), and the steering wheel 7 is When it is not operated and steering assist force is not required (operating hydraulic pressure is low),
Target voltage table 1c to reduce energy consumption
Accordingly, as shown in FIG. 8, the voltage applied to the electric motor 4 is set to the minimum voltage (for example, 6V) (see FIG. 4S1).
2) The output of the electric motor 4 is reduced.

The steering wheel 7 is operated to operate the control valve 6
Is activated, the hydraulic pressure rises, the load detection signal of the hydraulic pressure sensor 9 reaches a predetermined value (corresponding to the hydraulic pressure Pa), and the determination section of the load detection signal changes (S16 in FIG. 4), the control unit 1a In accordance with the target voltage table 1c, the voltage applied to the electric motor 4 is increased by one step (for example, 2V) (S12 in FIG. 4), the voltage corresponding to the determination section is set, and the output of the electric motor 4 is increased. Hereafter, similarly,
Each time the hydraulic pressure rises and the determination section of the load detection signal of the hydraulic pressure sensor 9 changes (S16 in FIG. 4), the controller 1a sets the voltage applied to the electric motor 4 by one step (for example, 2V).
The voltage is increased (S12 in FIG. 4), and the voltage corresponding to the determined section is set, and the output of the electric motor 4 is increased. However,
Load detection signal is a predetermined value (value exceeding working oil pressure Pb)
(S16 in FIG. 4), the voltage applied to the electric motor 4 is increased to a constant voltage (for example, 12V) (S12 in FIG. 4).
And, it can't be raised any further.

When the operation of the steering wheel 7 becomes small and the operating oil pressure drops to reduce the load, conversely to the above, every time the determination section of the load detection signal of the oil pressure sensor 9 changes (FIG. 4, S1).
6), the controller 1a sets the voltage applied to the electric motor 4 to 1
In step (for example, 2V), the voltage is lowered to set the voltage corresponding to the determination section (S12 in FIG. 4), and the output of the electric motor 4 is decreased.

By the way, when the voltage applied to the electric motor 4 is gradually increased, the operating oil pressure increases as shown in FIG. 7 due to the increase in the rotational speed of the hydraulic pump 5 even when the steering wheel 7 is not operated. There is a characteristic. Therefore, when the voltage applied to the electric motor 4 is increased by one step,
The operating oil pressure also rises, and as a result, the applied voltage is reduced to 1
The pressure is increased in steps, and as a result, the hydraulic pressure is also increased, and the applied voltage rises to a constant voltage (for example, 12V) and is applied even when there is no load increase due to the operation of the steering wheel 7. There is a possibility that the effect of controlling the voltage stepwise may be lost.

Therefore, in the present invention, when the motor applied voltage is controlled from one of the adjacent step voltages of the motor applied voltage target value to the other, the load detection signal (operating hydraulic pressure) that changes due to the change in the motor applied voltage is controlled. Within the range of change in (), the motor applied voltage target value is set so as to maintain the other applied voltage target value. In each of the above-mentioned embodiments, the voltage applied to the electric motor 4 is set to 4 steps, but needless to say, it is not limited to 4 steps and may be 3 steps or 5 steps or more.

[0032]

According to the power steering device of the first aspect of the present invention, the voltage applied to the electric motor can be changed stepwise according to the state of the load, and the shock applied when the voltage applied to the electric motor is switched. Becomes smaller.

According to the power steering apparatus of the second invention, the motor current is used as the load detection signal, so that the motor current detection circuit (load detection means) can be installed in the motor drive circuit (inside the controller). Therefore, the system can be downsized. Furthermore, no external load detection sensor is required, and no wiring is required between the sensor and the controller.

According to the power steering device of the third invention, the hydraulic pressure is used as the load detection signal to directly
It is possible to detect the load. Therefore, responsiveness and accuracy are improved.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between a motor applied voltage and a motor current.

FIG. 3 is an explanatory diagram showing a method of controlling a motor applied voltage of the power steering device according to the first and second aspects of the invention.

FIG. 4 is a flowchart showing a control operation of a motor applied voltage of the power steering device according to the first to third aspects of the invention.

FIG. 5 is a circuit diagram showing a circuit example of a control unit, a motor drive circuit, and a motor current detection circuit of the power steering device according to the first and second aspects of the invention.

FIG. 6 is a block diagram showing a main configuration of one embodiment of the power steering device according to the first and third inventions.

FIG. 7 is a characteristic diagram showing a relationship between a motor applied voltage and an operating oil pressure.

FIG. 8 is an explanatory diagram for explaining a method of controlling a motor applied voltage of the power steering device according to the first and third aspects of the invention.

FIG. 9 is an explanatory diagram for explaining the operation of the power steering device according to the first and second aspects of the invention.

FIG. 10 is an explanatory diagram for explaining a method of controlling a motor applied voltage of a conventional power steering device.

FIG. 11 is a block diagram showing a configuration example of a main part of a conventional power steering device.

[Explanation of symbols]

 1a Control unit 1b Filter circuit 1c Target voltage table 2 Motor drive circuit 3a Motor current detection circuit 4 Electric motor 5 (Hydraulic pressure) pump 6 Control valve 7 Steering wheel 9 Oil pressure sensor

Claims (3)

[Claims] 1. In a power steering device for assisting steering by hydraulic pressure generated by a pump driven by an electric motor, load detecting means for detecting a load of a hydraulic pressure source, and a load detecting signal by the load detecting means, And a control means for controlling the target voltage applied to the electric motor in a stepwise manner,
The control means, when the motor applied voltage is controlled from one of the adjacent step voltages of the target value of the applied voltage to the electric motor to the other, changes range of the load detection signal that changes due to the change of the motor applied voltage. In the following, the power steering apparatus is characterized in that the applied voltage target value is set so as to maintain the other applied voltage target value. 2. The power steering device according to claim 1, wherein the load detection means detects a motor current as a load detection signal. 3. The power steering device according to claim 1, wherein the load detection means detects the hydraulic pressure of the hydraulic circuit as a load detection signal.