JPH09221048A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a superior steering feeling by a method wherein a target value of applied voltage for an electrical motor in which a value of current and a relation of value are continuously coincided to each other within a predetermined range of a motor current detected by a motor current sensing circuit is determined and then its indicating signal is outputted. SOLUTION: As a steering wheel 7 is operated to increase an operating hydraulic pressure, an electrical current flowing in an electrical motor 4 is increased. As an increasing amount of motor current sensing signal outputted by a calculation circuit 1b from a sensing signal attained under no load of a power steering device is increased to exceed a predetermined value, a target value determining section 1 makes a voltage target value applied to the electrical motor 4 to a value in which a value of the increased amount from the current under no load of sensing signal and its value relation may be coincided to each other. A low pass filter 9 may remove non-required component of a high frequency caused by sporadic variation of the motor current, smoothen a variation of this indicating signal and gives it to the motor driving circuit 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a power steering system in which a hydraulic pump driven by an electric motor is used as a source of operating hydraulic pressure to assist steering by a hydraulic cylinder, a hydraulic motor and the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an essential configuration of an example of a power steering apparatus that assists steering by using a hydraulic pump driven by an electric motor as a source of operating hydraulic pressure. This power steering device has a motor drive circuit 2 according to a target value of an applied voltage instructed by a target determination unit 1c.
Applies a voltage to the electric motor 4 to rotate it. The electric motor 4 drives the hydraulic pump 5 to discharge hydraulic oil to the control valve 6 to generate hydraulic pressure.

The control valve 6 is a pipe leading to a hydraulic cylinder (not shown) when the steering wheel 7 is operated and a gear device (not shown) including a pinion gear 6c provided at the lower end of the steering wheel shaft is operated. The pressure of the hydraulic oil sent to the lines 6a and 6b is controlled. As a result, the hydraulic cylinder operates to generate a steering assist force in the operation direction of the steered wheels 7 according to the operation amount. The hydraulic oil circulates in a hydraulic circuit including a hydraulic pump 5, a control valve 6, a hydraulic cylinder, an oil supply tank 5a and the like.

A motor current detection circuit 3 for detecting a current flowing through the electric motor 4 is connected to the motor drive circuit 2.
The motor current detection signal is input to the no-load current detection unit 1a and the arithmetic circuit 1b. The no-load current detection unit 1a detects and holds a motor current detection signal when the power steering device has no load, in consideration of the motor current that changes depending on the oil temperature, and the arithmetic circuit 1b includes the motor current detection circuit 3
Is subtracted from the motor current detection signal output by the no-load current detection unit 1a, the increase amount of the motor current detection signal from the time when the power steering device is no load to the target determination unit 1c. input. The target determination unit 1c controls the voltage applied to the electric motor 4 to be switched between high and low depending on the amount of increase of the motor current detection signal from when the power steering device has no load.

In the conventional power steering apparatus having such a configuration, the target determining unit 1c consumes energy 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). Fig. 5
As shown in, the target value of the voltage applied to the electric motor 4 is lowered to reduce the output of the electric motor 4. On the other hand, when the steering wheel 7 is operated and the control valve 6 is operated, the operating oil pressure increases. This increase in operating oil pressure increases the load on the electric motor 4, and the electric motor 4
When the amount of increase in the motor current detection signal output from the arithmetic circuit 1b reaches a predetermined value after the power steering device is unloaded, the target determination unit 1c increases.
The target value of the voltage to be applied to the electric motor 4 is increased to increase the output of the electric motor 4 and generate the steering assist force.

[0006]

However, as described above, the conventional power steering apparatus has the electric motor 4 as described above.
Since the voltage applied to is switched in two stages, there is a problem that the steering assist force changes greatly when the voltage is switched, and the steering feeling is poor.

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 having a good steering feeling.

[0008]

A power steering apparatus according to a first aspect of the present invention is a power steering apparatus which assists steering with a hydraulic pump driven by an electric motor as a source of operating hydraulic pressure. A target value of the applied voltage to the electric motor, which has a motor current detection circuit that detects a flowing current and a predetermined range of the motor current detected by the motor current detection circuit, has a magnitude and a magnitude relationship of the current that continuously match each other. Target determining means for determining and outputting the instruction signal.

In this power steering device, the motor current detection circuit detects the current flowing through the electric motor.
The target determination means is provided with a detection signal of the motor current detected by the motor current detection circuit, and determines a target value of the voltage applied to the electric motor such that the magnitude of the current and the magnitude relationship continuously match within a predetermined range. And outputs the instruction signal. As a result, the voltage applied to the electric motor changes smoothly, and the flow rate of the hydraulic oil also changes smoothly, so that the steering feeling is improved.

In the power steering apparatus according to the second aspect of the present invention, the target determining means has a low pass filter on the output side of the instruction signal.

In this power steering device, the low-pass filter removes unnecessary components of high frequency contained in the instruction signal of the target value of the voltage applied to the electric motor. As a result, unnecessary changes in the steering assist force due to sudden changes in the motor current are eliminated, changes in the voltage applied to the electric motor are smoothed, and changes in the hydraulic oil flow rate are also smoothed. Be improved.

A power steering apparatus according to a third aspect of the present invention includes a motor current change detecting means for detecting a change in the motor current detected by the motor current detecting circuit, and a change in the motor current detected by the motor current change detecting means. And an adding means for adding the output of the target determining means.

In this power steering device, the motor current change detecting means detects a change in the motor current detected by the motor current detecting circuit. The adding means adds the detected change in the motor current to the output of the target determining means. As a result, when there is a large change in the motor current during sudden steering, the voltage applied to the electric motor can be set higher depending on the magnitude of the change (steering speed). The responsiveness at the time of steering improves, and depending on the steering conditions,
Optimal control of the electric motor can be performed.

In the power steering apparatus according to the fourth aspect of the present invention, the target determining means holds the target value constant when the motor current does not reach the predetermined range. As a result, even if the motor current fluctuates up and down with a value smaller than the predetermined value, the voltage applied to the electric motor does not change, and therefore the steering assist force does not change, and the operation can be stabilized.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a power steering device according to the present invention will be described below with reference to the drawings showing the same. Embodiment 1. FIG. 1 is a block diagram showing a configuration example of a main part of an embodiment of a power steering device according to the first, second, and fourth inventions of the present invention. In this power steering device, the target determination unit 1 outputs an instruction signal of a voltage corresponding to the motor current flowing through the electric motor 4, and the low pass filter 9
However, the high frequency unnecessary component of the steering assist force due to the sudden change of the motor current included in the instruction signal is removed, and the change of the instruction signal is smoothed. The target determination unit 1 and the low-pass filter 9 constitute a target determination unit.

The arithmetic circuit 10 subtracts the output signal of the motor applied voltage detection circuit 8 described later from the instruction signal output by the low pass filter 9. The instruction signal obtained by subtracting the output signal of the motor applied voltage detection circuit 8 is the motor drive circuit 2
Given to. The motor drive circuit 2 applies a voltage to the electric motor 4 to rotate the electric motor 4 in accordance with the instruction signal.
The electric motor 4 drives the hydraulic pump 5 to discharge hydraulic oil to the control valve 6 to generate hydraulic pressure.

The control valve 6 is a pipe leading to a hydraulic cylinder (not shown) when the steering wheel 7 is operated and a gear device (not shown) including a pinion gear 6c provided at the lower end of the steering wheel shaft is operated. The pressure of the hydraulic oil sent to the lines 6a and 6b is controlled. As a result, the hydraulic cylinder operates to generate a steering assist force in the operation direction of the steered wheels 7 according to the operation amount. The hydraulic oil circulates in a hydraulic circuit including a hydraulic pump 5, a control valve 6, a hydraulic cylinder, an oil supply tank 5a and the like.

A motor applied voltage detection circuit 8 for detecting the voltage applied to the electric motor 4 is connected to the motor drive circuit 2, and its output signal is given to the arithmetic circuit 10. The arithmetic circuit 10, the motor drive circuit 2, and the motor applied voltage detection circuit 8 form a negative feedback connection.

The motor drive circuit 2 is also connected to a motor current detection circuit 3 for detecting the current flowing through the electric motor 4, and the motor current detection signal is a no-load current detection section 1a.
To the arithmetic circuit 1b. No-load current detector 1a
Represents and holds the motor current detection signal when the power steering device has no load in consideration of the motor current that changes depending on the oil temperature. The arithmetic circuit 1b outputs the motor current detection signal output by the motor current detection circuit 3. From this, the no-load current detection signal output by the no-load current detection unit 1a is subtracted, and the increase amount of the motor current detection signal from when the power steering device has no load is given to the target determination unit 1. In the predetermined range of the increase amount of the motor current from the time of no load, the target determining unit 1 sets the target of the voltage applied to the electric motor 4 in which the magnitude relationship of the current and the magnitude relationship continuously match as shown in FIG. The value is determined and the instruction signal is given to the low pass filter 9.

In the power steering apparatus having such a structure, the target determining unit 1 does not require the steering assist force because the steering wheel 7 is not operated (the electric current flowing through the electric motor 4 is when the power steering apparatus has no load). 2 is a small current), in order to suppress energy consumption and stabilize its operation, as shown in FIG. 2, the target value of the voltage applied to the electric motor 4 is kept low and constant. , The output of the electric motor 4 is reduced.

On the other hand, when the steering wheel 7 is operated and the control valve 6 is operated, the operating oil pressure increases. This increase in hydraulic pressure increases the load on the electric motor 4,
When the amount of increase in the motor current detection signal output by the arithmetic circuit 1b from the detection signal when the power steering device is unloaded increases and the current flowing through the electric motor 4 increases and exceeds a predetermined value, the target determining unit is determined. 1 is as shown in FIG.
The target value of the voltage applied to the electric motor 4 is set to a value corresponding to the increase amount of the motor current detection signal from the current when there is no load. Here, the target value of the voltage applied to the electric motor 4 is
The magnitude relationship of the increase amount of the motor current detection signal from the current when there is no load and the magnitude relationship continuously match.

When the current flowing through the electric motor 4 further increases and the amount of increase in the motor current detection signal from the current when there is no load exceeds a predetermined value, the target determining section 1 causes The target value of the voltage applied to the electric motor 4 is maintained at a constant high voltage. The low-pass filter 9 removes an unnecessary component of high frequency due to a sudden change of the motor current, which is included in the instruction signal of the target value of the voltage applied to the electric motor 4, which is given from the target determining unit 1, and removes this instruction signal. Smooth out changes.

The arithmetic circuit 10 subtracts the output signal of the motor applied voltage detection circuit 8 from the instruction signal output by the low-pass filter 9, and the instruction signal from which the output signal is subtracted is given to the motor drive circuit 2. Motor drive circuit 2
Causes the voltage applied to the electric motor 4 to reach the target value indicated by the instruction signal output by the low-pass filter 9 by this instruction signal, and drives the electric motor 4 to rotate.
The electric motor 4 drives the hydraulic pump 5 to discharge hydraulic oil to the control valve 6 to generate hydraulic pressure.

As a result, in the power steering apparatus according to the present invention, the change in the voltage applied to the electric motor 4 is made smooth and the change in the flow rate of the hydraulic oil is made smooth, so that the steering feeling is improved. Further, when the amount of change in the motor current is smaller than the predetermined value, the voltage applied to the electric motor 4 is maintained at a constant low voltage. Power does not change,
The operation can be stabilized. Further, in the steering holding state, the voltage applied to the electric motor 4 is constant at an intermediate voltage between the maximum voltage and the minimum voltage thereof, and the power mode (maximum voltage) and the standby mode (minimum voltage) that have conventionally occurred.
Hunting between the two does not occur and the steering force becomes constant. Also,
Since the voltage applied to the electric motor 4 can be raised when necessary, as required, energy consumption can be reduced.

Embodiment 2 FIG. 3 shows the first to fourth aspects of the present invention.
It is a block diagram showing an example of important section composition of an embodiment of a power steering device concerning the invention. In this power steering device, an increase amount of the motor current detection signal from when the power steering device is unloaded is given to the configuration of the power steering device described in the first embodiment by the arithmetic circuit 1b. Of the motor current change detecting circuit 12 for detecting the change of the increase amount and the arithmetic circuit 1 for adding the detection signal to the instruction signal output from the low-pass filter 9.
1 is added. The output signal of the arithmetic circuit 11 is given to the arithmetic circuit 10, and after the output signal of the motor applied voltage detection circuit 8 is subtracted, it is given to the motor drive circuit 2. The other configurations are the same as the configurations of the power steering device described in the first embodiment, and thus the description thereof will be omitted.

In the power steering device having such a configuration, the motor current change detection circuit 12 changes the amount of increase in the motor current detection signal detected by the motor current detection circuit 3 when the power steering device has no load. It detects and gives the detection signal to the arithmetic circuit 11. The arithmetic circuit 11 is
The detection signal is added to the instruction signal of the target value of the voltage applied to the electric motor 4, which is output from the low pass filter 9.
The instruction signal added by the arithmetic circuit 11 is given to the arithmetic circuit 10.

Thus, in the power steering apparatus according to the present invention, the voltage applied to the electric motor 4 is changed according to the magnitude of the change (the steering speed) when the change in the motor current is large during the sudden steering. Since it can be set higher, the responsiveness at the time of sudden steering is improved, and the electric motor can be optimally controlled according to the steering condition. When the steering is performed slowly, the detection signal of the motor current change detection circuit 12 becomes substantially 0, and the motor current change detection circuit 12 and the arithmetic circuit 11 do not operate substantially. Other operations are described in Embodiment 1.
Since the operation is the same as that of the power steering device described above, the description will be omitted. In each of the above-described embodiments, the target value characteristic of the target determining unit 1 is as shown in FIG.
In the predetermined range of the motor current change amount, it is shown by a straight line connecting the minimum value and the maximum value of the target value, but it is not necessary to be a straight line, and the target value characteristic as shown by a continuous curve or polygonal line Is also good.

[0028]

According to the power steering device of the first aspect of the present invention, the steering feeling is improved. Further, in the steering holding state, the hunting between the power mode (highest voltage) and the standby mode (lowest voltage) that occurs conventionally does not occur, and the steering force becomes constant. Further, since the voltage applied to the electric motor can be increased when necessary, the energy consumption can be reduced.

According to the power steering device of the second aspect of the present invention, unnecessary changes in the high frequency steering assist force due to sudden changes in the motor current are eliminated, so the steering feel is improved.

According to the power steering device of the third aspect of the present invention, the responsiveness at the time of sudden steering is improved, and the electric motor can be optimally controlled according to the steering condition.

With the power steering device according to the fourth aspect of the present invention, when the motor current is smaller than the predetermined value, the voltage applied to the electric motor is not changed even if the motor current fluctuates up and down, so stable operation is obtained. be able to.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing characteristics of an increase amount of a motor current from when there is no load and a target value of a voltage applied to an electric motor, which is included in a target determining unit.

FIG. 3 is a block diagram showing a configuration example of a main part of an embodiment of a power steering device according to the first to fourth inventions.

FIG. 4 is a block diagram showing a configuration example of a main part of a conventional power steering device.

FIG. 5 is a characteristic diagram showing a characteristic of a change amount of a motor current from when there is no load and a target value of a voltage applied to the electric motor, which is included in a conventional characteristic determining unit.

[Explanation of symbols]

 1 Target Determining Section (Target Determining Means) 1a No-load Current Detection Section 2 Motor Drive Circuit 3 Motor Current Detection Circuit 4 Electric Motor 5 Hydraulic Pump 6 Control Valve 7 Steering Wheel 9 Low Pass Filter (Target Determining Means) 11 Computing Circuit (Adding Means) 12 Motor current change detection circuit

Claims (4)

[Claims] 1. A power steering apparatus for assisting steering using a hydraulic pump driven by an electric motor as a source of operating hydraulic pressure, wherein a motor current detection circuit for detecting a current flowing through the electric motor and a motor current detection circuit are provided. In a predetermined range of the detected motor current, the target value determining means determines the target value of the voltage applied to the electric motor, in which the magnitude relationship of the current and the magnitude relationship continuously match, and outputs the instruction signal. Characteristic power steering device. 2. The power steering apparatus according to claim 1, wherein the target determining means has a low-pass filter on the output side of the instruction signal. 3. A motor current change detecting means for detecting a change in the motor current detected by the motor current detecting circuit, and a change in the motor current detected by the motor current change detecting means is added to an output of the target determining means. The power steering device according to claim 1, further comprising: 4. The power steering apparatus according to claim 1, wherein the target determining means holds the target value constant when the motor current does not reach the predetermined range.