JPH11255134A - Electric hydraulic power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the steering feeling of a steering handle by detecting the current of an electric motor changed according to the operating torque of the steering handle, and setting the steering threshold current and non-steering threshold current to different values according to the rotating speed of the electric motor. SOLUTION: A pump unit 20 is formed of a brush-less DC electric motor (electric motor) 21 driven by a battery and a hydraulic pump 22 driven by the electric motor 21. An ECU 30 controls the electric motor 21, detects the current by a current detecting part 21, and selects a steering mode or a non- steering mode. The rotating speed of the electric motor 21 is fed back from a rotating speed detecting means 23 to the ECU 30 to control the electric motor 21 to a desired rotating speed through a motor driving circuit 32. A steering threshold current IU and non-steering threshold current IL according to rotating speeds NU and NL are set. According to this, the steering feeling of a steering handle can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric hydraulic power steering apparatus for performing power assist using a hydraulic pump driven by an electric motor as a hydraulic source.

[0002]

2. Description of the Related Art Conventionally, in a motor vehicle (vehicle), it has been widely practiced to equip a hydraulic power steering device in order to make steering operation light. In this method, a hydraulic pump driven by a driving engine is operated, and pressure oil is supplied to a control valve and a cylinder according to operation of a steering wheel to generate an assist force.

In recent years, in order to reduce energy consumption, a hydraulic pump is operated by an electric motor powered by a battery mounted on an automobile, and the hydraulic oil generated by the hydraulic pump is supplied to a control valve and a cylinder to generate an assist force. 2. Description of the Related Art A power steering device, a so-called electro-hydraulic power steering device, has been proposed.

A first conventional example of an electro-hydraulic power steering apparatus is disclosed in Japanese Patent Application Laid-Open No. 05-278629, for example, in which a vehicle is provided with a vehicle speed sensor for detecting a vehicle speed and a steering wheel angle sensor for detecting a steering wheel angle. Equipped. Then, for example, the vehicle speed is 10 km according to the traveling state.
In the extremely low speed range of / h or less, the motor is stopped by setting the pump stop mode. In other areas, a pump operation mode is set. When the steering wheel is not operated, the motor and the pump are stopped. When the steering wheel is operated, a control signal (voltage) having a predetermined signal level (voltage) is transmitted from the control unit. When a command voltage is output, the motor is started in synchronization with the output, and power assist is performed using pressure oil generated by a hydraulic pump.

[0005] A second conventional example of an electro-hydraulic power steering apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 08-183467. This means that the motor and the hydraulic pump are always operated during traveling. That is, when the handle is not operated, the applied voltage of the motor is set low to suppress energy consumption. When the handle is operated to increase the operating oil pressure and increase the load, the motor current also increases. Therefore, when the motor current reaches a predetermined value, the applied voltage of the motor is increased stepwise to increase the motor output.

[0006]

In the above-mentioned first conventional example, since the steering angle of the steering wheel is used as the control signal, it is necessary to attach a steering angle sensor to the vehicle, which increases the cost. There is. further,
Since the on / off control of the motor is performed according to the control signal, the flow rate of the pressure oil changes abruptly when the motor starts and stops, so that there is a problem that the assist force changes abruptly and the steering feeling of the steering wheel deteriorates.

Further, in the second conventional example, the target value of the applied voltage to the motor is controlled in a step-like manner. Therefore, when the applied voltage is switched, the flow rate of the pressure oil changes suddenly as in the first conventional example. Therefore, there is a problem that a change in assist force is large and steering feeling of the steering wheel is deteriorated.

The present invention has been made in view of the above circumstances, and has as its object to eliminate the need to add a new sensor to a vehicle and to improve the steering feel of a steering wheel. To provide.

[0009]

Means taken by the present invention to solve the problem will be described with reference to the reference numerals used in the embodiments. In the electro-hydraulic power steering apparatus that drives the motor 22 and performs power assist by the hydraulic pressure generated by the hydraulic pump 22, a current of the electric motor 21 that changes according to the operating torque of the handle 11 is detected, and the current is used as a steering threshold. When the electric current becomes larger than the value current IU, the electric motor 21 is switched at a high speed by switching to the steering mode, and when the electric current becomes smaller than the non-steering threshold current IL, the electric motor 21 is switched to the non-steering mode. The motor is rotated at a low speed, and the steering threshold current IU and the non-steering threshold current IL are set.
Is set to a different value according to the rotation speed of the electric motor 21.

According to a second aspect of the present invention, a steering threshold current IU
The characteristic is that the non-steering threshold current IL is changed according to the temperature of the electric motor 21.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below with reference to FIGS. First, a handle 11, a power steering (PS) gear 12, and control valves and cylinders (not shown) shown in FIG. 2 are of a known configuration used in a hydraulic power steering apparatus.

The pump unit 20 includes a brushless DC electric motor 21 (hereinafter referred to as an electric motor 21) driven by a battery, and a hydraulic pump 22 driven by the electric motor 21. The electric motor 2
1 is provided with a Hall element (not shown) for controlling the coil current, and serves as a rotation speed detecting means 23 for detecting a rotation speed by counting signals generated by the Hall element. The hydraulic pump 22 draws oil from the oil tank and supplies pressure oil to the control valve and the cylinder, and the flow rate changes according to the rotation speed of the electric motor 21.

The ECU 30 controls the electric motor 21 and detects a current of the electric motor 21 by a current detecting section 31 to select a steering mode or a non-steering mode described later. The rotation speed of the electric motor 21 is fed back from the rotation speed detecting means 23 to the ECU 30, and the electric motor 21 is controlled to a desired rotation speed via the motor drive circuit 32. The vehicle is provided with vehicle speed detecting means 33 for detecting the vehicle speed, and the vehicle speed is input to the ECU 30.

In this embodiment, a non-steering mode when the steering wheel 11 is not operated and a steering mode when the steering wheel 11 is operated are set. That is, the rotation speed NU of the electric motor 21 in the steering mode and the rotation speed NL of the electric motor 21 in the non-steering mode are set as shown in FIG. 3 according to the vehicle speed.

In the non-steering mode, the minimum speed at which a change in steering torque can be detected as a change in motor current, that is, the electric motor 21 rotates at a low speed, supplies a small amount of oil from the hydraulic pump 22 to the cylinder, and in the steering mode. In other words, the electric motor 21 rotates at a high speed, supplies a large amount of oil from the hydraulic pump 22 to the cylinder, and generates a large assist force. When the vehicle speed is low, the rotation speeds NU and NL are set high to increase the assist force, and when the vehicle speed is high, NU and NL are set low to decrease the assist force.

The switching between the non-steering mode and the steering mode is performed by detecting the current of the electric motor 21.
That is, the current of the electric motor 21 increases and decreases as the load (torque) increases and decreases, and as the rotational speed increases and decreases. Then, a steering threshold current IU and a non-steering threshold current IL corresponding to the rotation speeds NU and NL are set. The electric motor 21 is operated in the steering mode when the current is detected to be larger than the steering threshold current IU, and is turned off when the current of the electric motor 21 is detected to be smaller than the non-steering threshold current IL. Drive in mode.

Next, the operation of the above configuration will be described with reference to FIG. (1) When the vehicle speed detecting means 33 detects the vehicle speed (point V),
Rotation speed N of electric motor 21 shown in FIG. 3 according to vehicle speed
U and NL are selected, and a steering threshold current IU and a non-steering threshold current IL shown in FIG. 4 corresponding to the rotational speeds NU and NL are set (STEP 10). When the steering wheel 11 is not operated, it is in the non-steering mode,
The electric motor 21 is rotating at the rotation speed NL shown in FIG.

(2) When the handle 11 is operated, the area of the control valve is reduced, and the PS pressure, that is, the pump discharge pressure increases. Pump discharge pressure is proportional to motor torque, and
Since the motor torque is proportional to the motor current, operating the handle 11 also increases the motor current I. This motor current I is compared with the steering threshold current IU at the rotation speed NL in STEP11.

(3) If I> IU, ie, Yes (point B), the mode is switched to the steering mode (STEP 12). Thereby, the electric motor 21 increases to the rotation speed NU shown in FIG. 3, and a large amount of oil can be supplied to the cylinder to obtain a large assist force. The motor current increases from the point B to the point C, and the steering mode operation is continued.
Returning to 0, the above-described process is repeated.

(4) When the steering is completed, the load decreases and the current also decreases. Then, in STEP 11,
If I <IU, that is, No, in STEP13, the steering threshold current IL at the rotation speed NU is compared with the steering threshold current IL.
If I> IL, that is, if No, the process returns to STEP 10 and the above-described steps are repeated.

(5) If I <IL, that is, if Yes (point D), the elapsed time in the state of I <IL is counted in STEP14. If the elapsed time does not exceed a predetermined time, for example, t seconds, the process returns to STEP10.

(6) If the condition of I <IL exceeds t seconds in STEP 14, it is recognized that the steering is completed, and S
In TEP15, the state is switched to the non-steering state. The rotation speed of the electric motor 21 decreases to the rotation speed NL shown in FIG. 3, and the current decreases from point D to point A.

According to the first embodiment, the following effects can be obtained. (1) When the steering wheel 11 is not steered, the electric motor 2
1 is switched to the non-steering mode and the vehicle is driven at a low speed, so that energy consumption can be reduced. In particular, in the case of this embodiment,
The motor rotation speed when judging the steering mode is different from the motor rotation speed when judging the non-steering mode, and the threshold currents of the steering mode and the non-steering mode at this time also depend on the motor rotation speed. Since only the motor current value has been changed, the non-steering mode can be determined with a value higher than the motor current value determined to be the steering mode. Accordingly, it is easy to set a small steering threshold value when judging the steering mode and a large non-steering threshold value when judging the non-steering mode. Energy consumption can be reduced while improving the steering feeling.

(2) When the steering wheel 11 is steered, the electric motor 21 is promptly switched to the steering mode, and the electric motor 21 is continuously raised to the rotation speed NU. A steering feeling can be obtained. (3) Since the steering threshold current IU and the non-steering threshold current IL are set according to the vehicle speed, an optimum assist force can be obtained at both high speed and low speed.

FIGS. 5 and 6 show a second embodiment according to the first and second aspects. The difference from the first embodiment is that the temperature of the engine room in which the pump unit 20 is housed varies. In this case, the switching between the steering mode and the non-steering mode is reliably performed. When the temperature of the engine room changes, the temperature of the electric motor 21 also changes accordingly. That is, it is low in winter and high in summer. Especially when traveling on mountain roads, it becomes high.

The following relationship exists between the voltage, current and winding resistance of the electric motor 21. V = RI + KE · N where V is voltage, I is current R is resistance value of winding KE is induced voltage constant of motor N is rotation speed

Therefore, when the voltage and the rotation speed are the same,
When the temperature of the electric motor 21 (winding) is low, R is small and the current is large, and when the temperature is high, R is large and the current is small. Furthermore, when the temperature is low, the viscosity of the oil used for the hydraulic pump 22 increases, and the load on the electric motor 21 increases, so that the tendency for the current to increase increases.

Therefore, in the second embodiment, although not shown, a sensor for measuring the temperature is attached to the electric motor 21, and the steering threshold current IU and the non-steering threshold current IL are corrected from this temperature. It is something to do.

That is, as shown in FIG.
For IU and IL set in "EP10", "STEP
10A ", a correction value is added according to the measured temperature of the electric motor 21 to set IU1 and IL1.
FIG. 6 shows the threshold current. The corrected threshold currents IU1 and IL1 exhibit curves substantially parallel to IU and IL.

In the second embodiment, in addition to the effects of the first embodiment, even when the temperature of the engine room changes, the steering mode and the non-steering mode can be switched quickly and appropriately, and the optimum Thus, there is an effect that the assisting force can be obtained.

[0031]

According to the first aspect of the present invention, there is provided an electric hydraulic power steering apparatus in which a hydraulic pump is driven by an electric motor and power assist is performed by a hydraulic pressure generated by the hydraulic pump. When the current of the motor is detected and the current becomes larger than the steering threshold current, the mode is switched to the steering mode to rotate the electric motor at a high speed, and the current becomes smaller than the non-steering threshold current. In this case, the electric motor is switched to the non-steering mode to rotate the electric motor at a low speed, so that it is not necessary to add a new sensor to the vehicle, and the steering threshold current and the non-steering threshold current are Since different values are set according to the rotation speed of the electric motor, switching between the non-steering mode and the steering mode can be quickly and reliably performed, and the steering feel of the steering wheel can be improved. In which an excellent effect of being able to save energy consumption during non-steering with may improve grayed.

The steering threshold current and the non-steering threshold current according to the present invention are changed in accordance with the temperature of the electric motor. Therefore, even when the temperature in the engine room fluctuates, the steering feeling of the steering wheel is changed. This is an excellent effect that can be improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control operation according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration.

FIG. 3 is a diagram illustrating a vehicle speed and a rotation speed of an electric motor in a non-steering mode and a steering mode.

FIG. 4 is a diagram illustrating a relationship between a rotation speed of an electric motor and a threshold current in a non-steering mode and a steering mode.

FIG. 5 is a flowchart illustrating a control operation according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between a rotation speed of the electric motor and a threshold current, which are changed according to a temperature of the electric motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Handle 12 Power steering gear 20 Pump unit 21 Electric motor 22 Hydraulic pump 23 Rotation speed detection means 30 ECU 31 Current detection circuit 32 Motor drive circuit 33 Vehicle speed detection means IU Steering mode threshold current IL Non-steering mode threshold current IU1 Corrected steering mode threshold current IL1 Corrected non-steering mode threshold current

Claims (2)

[Claims] A hydraulic pump is driven by an electric motor,
In the electro-hydraulic power steering device that performs power assist by the hydraulic pressure generated by the hydraulic pump, the current of the electric motor that changes according to the operating torque of the steering wheel is detected, and the current becomes larger than the steering threshold current. When the steering mode is switched to rotate the electric motor at high speed,
When the current is smaller than the non-steering threshold current, the mode is switched to a non-steering mode so that the electric motor rotates at a low speed, and the steering threshold current and the non-steering threshold current are controlled by the electric motor. An electro-hydraulic power steering device wherein different values are set according to the rotation speed of a motor. 2. The electro-hydraulic power steering apparatus according to claim 1, wherein the steering threshold current and the non-steering threshold current are changed according to the temperature of the electric motor.