JPH0971251A - Electric power steering device and power steering control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a damage caused by the hitting of a mechanical system generated when an electric power steering(PS) is rotated to near the turning limit, and to generate a sufficiently large assist torque at the rotation starting of the steering. SOLUTION: A PS motor driving circuit 13 drives a PS motor 10 to generate the assist torque of a steering 12 by the power feeding from a power source 11. A control device 14 finds the motor rotation speed depending on a motor driving duty calculated depending on the steering torque; the power source voltage; the motor driving current; the motor winding resistance; and the counter electromotive force constant of the motor; and regulates the motor driving duty according to the level of the found motor rotation speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for a vehicle, and more particularly to an electric power steering device for controlling a steering assist force according to a steering torque of an automobile.

[0002]

2. Description of the Related Art In recent years, an electric power steering apparatus for generating a steering assist force according to a steering torque has been used for industrial vehicles such as forklifts. When this electric power steering device is used, steering characteristics are improved such that the steering wheel becomes lighter and the followability is improved, but when the steering wheel is rotated vigorously, mechanical system collision occurs at the turning limit point of the steering wheel. However, there was a drawback that it caused a great deal of damage to the mechanical system. In order to solve this problem, conventionally, a power steering device including a control circuit as shown below has been used.

FIG. 5 is a block diagram of a conventional power steering device. In this conventional device, a PS motor (power steering motor) 1 is a transistor 2A.
~ H composed of switching power devices such as 2D
The bridge circuit rotates forward and backward, which causes power assist (steering assist torque) for the steering wheel. The control signals for the transistors 2A-2D are
It is supplied from the corresponding drive circuits 3A to 3D, and these drive circuits 3A to 3D are controlled by the control circuit 4.

The torque sensor 5 detects the steering torque generated by the rotation of the steering wheel, and the control circuit 4 drives the drive circuits 3A to 3D based on the signal from the torque sensor 5.
To the control signal. At this time, the signal from the torque sensor 5 is amplified by the amplifier 6 and then limited by the correction circuit 7 so that the upper limit value and the lower limit value of the output do not exceed a certain fixed value. Therefore, the duty of the chopper signal supplied from the control circuit 4 to the H-bridge circuit.
Is limited to within a predetermined value, and the electric power supplied to the PS motor 1 is also limited to a certain value or less. As a result, the steering assist force generated by the PS motor 1 is suppressed to a certain value or less, and the occurrence of the above problem is reduced.

[0005]

However, when the above-mentioned conventional control circuit 4 is used, the duty of the control signal for controlling the drive of the PS motor 1 is always suppressed to a predetermined value or less by the correction by the correction circuit 7. Therefore, when it is desired to start the PS motor 1 by using the maximum applicable electric power with a duty of 100%, for example, when the steering wheel starts to be turned, this cannot be dealt with, and the necessary starting force is sufficiently generated. I couldn't. This adversely affects the steering performance and the feeling of steering, such as making the steering wheel very heavy.

In order to solve the above problems, the object of the present invention is to effectively prevent collision of the mechanical system at the steering wheel turning limit point when the steering wheel is rotated and to generate a sufficient steering assist force when necessary. An electric power steering device capable of preventing a mechanical trouble due to steering wheel rotation and obtaining excellent steering performance and steering feeling is provided. It is to realize at low cost without using a special device such as a rotation sensor or a steering angle sensor.

[0007]

FIG. 1 is a diagram showing the basic configuration of a power steering apparatus according to the present invention. In this figure, 10 is a PS motor (power steering motor) for applying a steering assist force (power assist force) to a steering wheel 12 of a vehicle equipped with an electric power steering system, and 11 is a PS motor. It is a power supply that supplies electric power for rotating the motor 10. 13 is
It is a PS motor drive circuit that controls the power supply from the power supply 11 based on the control signal from the control device 14 to rotate the PS motor 10 in the forward and reverse directions. Reference numeral 15 is a torque detector that detects the steering torque and outputs it as a torque signal to the control device 14. The control device 14 uses the torque detector 15
The control signal for controlling the PS motor drive circuit 13 is determined based on the torque signal from. Then, the control device 14 predicts the rotation speed of the PS motor 10 at that time based on the control signal already output, the voltage of the power supply 11, the winding resistance of the PS motor 10, the drive current, and the back electromotive force constant. To do. When the predicted rotation speed exceeds a predetermined value, the control signal to be output next is adjusted and output to the PS motor drive circuit 13. In response to this control signal, the PS motor drive circuit 13 reduces the power supplied from the power supply 11 to the PS motor 10, and the rotation of the PS motor 13 is appropriately controlled.

The PS motor drive circuit 13 can be composed of an H bridge circuit having four switching elements, and the controller 14 adjusts the duty of the chopper signal supplied to one of the four switching elements. By doing so, the switching element is switched to control the electric power supplied to the PS motor 10.

[0009]

The controller 14 controls the torque detector 1 during normal operation.
5 based on the torque signal from the PS motor drive circuit 13
Is controlled by a chopper signal to generate an auxiliary torque corresponding to the torque of the steering wheel 12. At this time, the electric power supplied to the PS motor 10 is determined by the duty of the chopper signal output from the control device 14.

However, when the rotation speed of the PS motor 10 predicted by the control device 14 is higher than a predetermined value, the duty of the chopper signal is reduced to reduce the electric power supplied to the power steering motor to increase the auxiliary torque. Reduce. The control device 14 can also perform the above control only when the steering wheel 12 rotates beyond a predetermined range.

When the above control is performed, the control device 14 controls the P
The duty of the chopper signal supplied to one switching element in the H bridge circuit that constitutes the S motor drive circuit 13 is reduced, whereby the PS from the power source 11 is reduced.
The electric power supply to the motor 10 is limited, and the steering 12
Auxiliary torque for is reduced.

By the above control, the electric power supplied to the PS motor 10 when the rotational speed of the PS motor 10 becomes too high is limited, and the auxiliary torque generated is also limited. As a result, collision of the mechanical system that occurs when the rotation of the steering wheel 12 reaches the rotational limit point can be mitigated, and damage to the mechanical system can be suppressed to a very small level. Further, in this control, when the rotation speed of the PS motor 10 is slow, such as when the steering wheel 12 starts to rotate, the duty is not limited, and thus a sufficiently large auxiliary torque can be generated at a duty of 100%.

[0013]

EXAMPLES Examples of the present invention will be described below with reference to FIGS. FIG. 2 is a block diagram of an embodiment of the present invention.

As shown in the figure, in the apparatus of this embodiment,
A PS motor (power steering motor) 20 that gives an auxiliary torque to steering of a vehicle such as a forklift equipped with an electric power steering is driven by power supply from a power supply 21. This PS motor 20 is connected to a power source 21 via an H bridge circuit 22,
The bridge circuit 22 includes four transistors 33A, 33B, 33C and 33D as switching elements,
Flywheel diode 34 connected between the collector and emitter of each of the transistors 33A to 33D
A, 34B, 34C, and 34D, and drive circuits 35A, 35B, 35C, and 35D between the base and emitter of each of the transistors 33A to 33D.
Is connected. Also, the transistors 33B and 33
Shunt resistors 36A and 36B for current detection are connected between the emitter of D and the power supply 21, respectively.

Transistor 33A of H-bridge circuit 22
To 33D are controlled by the control circuit 23 via the drive circuits 35A to 35D, respectively.
The operation of the S motor 20 is determined, and the supply of the auxiliary torque to the steering is controlled. The torque sensor 24 detects the steering torque and outputs the torque value to the control circuit 23 as a torque signal. The control circuit 23 performs the above control based on the torque signal from the torque sensor 24 and the amateur current flowing through the PS motor 20. In addition,
This amateur current is applied to the connection point 37A between the transistor 33B and the shunt resistor 36A, and the transistor 33D.
From the connection point 37B of the shunt resistor 36B to the control circuit 2
Input to 3.

The control circuit 23 has a CPU 25, and the torque signal output from the torque sensor is supplied to the amplifier 2
After being amplified by 6, it is input to the A / D port of the CPU 25. Further, the amateur currents inputted to the control circuit 23 from the connection points 37A and 37B are respectively fed to the amplifier 2
After being amplified by 7 and 28, it is input to the A / D port of the CPU 25. The CPU 25 stores an amateur resistance and a back electromotive force constant specific to the PS motor 20.
This amateur resistance is the winding resistance of the PS motor 20, and the back electromotive force constant is a constant that determines the electromotive force generated according to the motor speed of the PS motor 20. Furthermore, C
The PU 25 also stores the voltage supplied from the power supply 21 to the PS motor 20, but this voltage can also be directly detected from the power supply 21 and input to the CPU 25. Further, the current of the PS motor 20 may be measured using a current sensor, and the measured value may be input to the CPU 25.

Next, the operation of the above apparatus will be described. When a current in the direction of arrow A is applied to the PS motor 20 to rotate the PS motor 20 in the normal direction, the control circuit 23 turns on the transistor 33D by the motor normal rotation signal and supplies the chopper signal to the transistor 33A. The duty of the chopper signal is determined according to the torque signal from the torque sensor 24, and thereby the on / off of the transistor 33A is controlled and the power supply to the PS motor 20 is controlled. When the transistor 33A is turned on by this chopper signal, a current flows through the H bridge circuit 22 from the power supply 21 through the transistor 33A, the PS motor 20, the transistor 33D, and the shunt resistor 36B to the power supply 21 again. Transistor 33
When A is turned off, the transistor 33D, the shunt resistor 36B, and the shunt resistor 36 are connected from the PS motor 20.
PS motor 20 again via A and diode 34B
Current flows on the route back to. The rotation of the PS motor is controlled by switching the current route according to the chopper signal.

When the PS motor 20 is rotated in the opposite direction to the above example, the chopper signal is provided to the transistor 33C while the transistor 33B is turned on by the motor reverse signal. As a result, a current in the opposite direction to that in the above example flows through the PS motor 20, and rotation control in the opposite direction is performed.

FIG. 3 is a flow chart showing the duty control of the chopper signal by the control circuit 23. It is assumed that the control circuit 23 has already output the duty D1.

First, the CPU 25 recognizes the current torque value based on the input torque signal and the current flowing through the PS motor 20 based on the input amateur current (step S1). Next, the CPU 25 determines the duty D2 of the chopper signal to be output according to a predetermined calculation method based on the recognized torque value (step S2), and determines the already output duty D1 and the recognized amateur. Based on the current Ia, the stored voltage Ve of the power supply 21, the amateur resistance Ra of the PS motor 20 and the back electromotive force constant Ke, the rotational angular velocity W of the PS motor 20 is calculated according to the following equation (1) ( Step S3). W = (Ve · D1-Ra · Ia) / Ke (1) The above formula (1) is applied voltage Va to the PS motor 20.
Is expressed by the following equation (2). Va = Ve · D1 = Ra · Ia + Ke · W (2) The rotational angular velocity W obtained here is the rotational angular velocity of the PS motor 20 at the already output duty D1.

Subsequently, the CPU 25 determines whether the rotational angular velocity W obtained by the above method exceeds the prescribed upper limit value M (W≤M) (step S4), and the rotational angular velocity W is below the upper limit value M. If there is (step S4, YES), the duty D2 obtained in step S2 is output as the duty output value D1 (step S7) to the H bridge circuit 22 (step S8). At this time, the motor forward rotation signal or the motor reverse rotation signal is output together depending on the rotation direction of the PS motor 20, and the forward rotation or the reverse rotation of the PS motor 20 is controlled.

When it is determined in step S4 that the rotational angular velocity W exceeds the upper limit M (steps S4, N
O), the CPU 25 determines the duty D calculated in step S2.
It is determined whether 2 is smaller than the previously output duty D1 (D1> D2) (step S5). If the duty (D2) is smaller than the duty (D1) (step S5, YES), it is determined in step S2. The duty D2 is output as the output value D1 (step S7) and output (step S8).

When it is determined in step S5 that the duty D2 is equal to or greater than the duty D1 output last time (step S5, NO), the CPU 25 reduces the value of the duty output this time from the duty D1 output last time by the specified value. The value is set (step S6) and output. In step S6, the value of the duty output this time may be set to a value obtained by reducing the duty D1 output last time by a fixed ratio.

According to the above method, the number of revolutions of the PS motor 20 can be limited by limiting the duty of the control signal based on the predicted number of revolutions of the PS motor 20. Therefore, the PS motor 2
When the rotation speed of 0 is not high and it is desired to apply a large duty to the PS motor 20, the steering wheel can be rotated with a maximum duty of 100%, and the mechanical system is damaged by the high rotation of the steering wheel near the steering wheel rotation limit point. Can be prevented.

FIG. 4 is a flowchart showing a second control example different from the above control. Hereinafter, the second control will be described based on the figure, but the same steps as the steps described in the flowchart of FIG. 3 are denoted by the same reference numerals and detailed description thereof will be omitted. Here, it is assumed that the control circuit 23 stores in advance the maximum value L + of the moving distance to the right and the maximum value L− of the moving distance to the left.

First, the torque value and the motor current are input in step S1, the duty D2 is determined in step S2, and the motor rotation speed W is determined in step S3.
The PU 25 calculates the moving distance (rotation amount) L of the steering wheel (step S10). At this time, the moving distance L can be obtained by integrating the motor rotation speed W.
At this time, the moving distance to the right is represented by +, and the moving distance to the left is represented by-. Next, the calculated moving distance L
Is determined to be 0 or more (step S1
1). When the moving distance L is 0 or more (step S11, Y
ES), it is determined whether or not L is smaller than L + representing the maximum value of the movement distance to the right (step S12), and if smaller (step S12, YES), step S1 as it is
6 and if not smaller (step S12, N
O) Update L + to the current value of L (step S13)
It proceeds to step S16. When it is determined in step S11 that the moving distance L is smaller than 0 (step S11, NO), L represents the maximum value of the moving distance to the left.
-Is determined to be greater than (step S14),
If it is larger (step S14, YES), the process proceeds directly to step S16. If it is not larger (step S1)
4, NO) L- is updated to the current value of L (step S
15) Go to step S16.

In step S16, the absolute value of L + and L-
It is determined whether the sum of the absolute value of and the absolute value of is greater than or equal to the specified value. This prescribed value is set to a value close to the moving distance from the handle end to the end. When the total of the absolute values is smaller than the specified value (step S16, NO), the duty D2 obtained in step S2 is output as the output duty D1 (step S7) and output (step S8). When the sum of absolute values is equal to or greater than the specified value (step S16,
YES), L + and L- are regarded as the right end value and the left end value of the steering wheel, respectively, and the control start point L1 + in the right direction is L + -ΔL, and the control start point L1- in the left direction is L
-+ ΔL are set respectively (step S17).
Here, ΔL represents the distance from the handle end to the point where control is performed to reduce the motor rotation speed. Next, it is determined whether or not the moving distance L is larger than L1− and smaller than L1 + (step S18). If L satisfies this condition (step S18, YES), the duty D2 obtained in step S2 is set. The output duty D1 is output (step S7) (step S8). When L does not satisfy the condition of step S18 (step S18, N
O), the flow proceeds to steps S4 to S6 in FIG. 3, and when the motor rotation speed exceeds the upper limit M, duty limitation is applied.

In the above control, the state where no torque is applied to the steering wheel is regarded as the steering wheel neutral point, and the rotation limit of the steering wheel can be predicted by integrating the motor rotation speed W. Also, while the vehicle is running, the vehicle is going straight and the steering wheel position at that time is the steering wheel neutral point,
The handle end can also be calculated from that value.

[0029]

According to the present invention, if the rotation speed is too high near the handle rotation limit point when the handle is rotated, the rotation speed is limited. Therefore, the mechanical system collides with the handle rotation limit point and troubles are caused thereby. Can be effectively prevented, and a sufficient steering assist force can be generated when a large steering assist force is required such as when the steering wheel starts to rotate.

Further, according to the present invention, an electric power steering system capable of preventing mechanical troubles due to steering wheel rotation and obtaining excellent maneuverability and maneuverability is provided with a motor rotation sensor and a steering angle. It can be provided without using a special device such as a sensor. this is,
When the present invention is applied to an industrial vehicle, such as a forklift, for which a PS motor rotation sensor, a steering angle sensor, etc. are not installed in advance in the vehicle, it is not necessary to newly add a rotation sensor, a steering angle sensor, etc. It is particularly advantageous that the invention can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an electric power steering apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of an electric power steering device according to the present invention.

FIG. 3 is a flowchart showing a method of controlling a duty signal by the control circuit of this embodiment.

FIG. 4 is a flowchart showing another method of controlling the duty signal by the control circuit of this embodiment.

FIG. 5 is a diagram showing a configuration of a conventional electric power steering device.

[Explanation of symbols]

 10 PS Motor 11 Power Supply 12 Steering 13 PS Motor Drive Circuit 14 Control Device 15 Torque Detector 20 PS Motor 21 Power Supply 22 H Bridge Circuit 23 Control Circuit 24 Torque Sensor 25 CPU 26, 27, 28 Amplifier 33A to 33D Transistor 34A to 34D Fly Wheel diode 35A-35D Drive circuit 36A, 36B Shunt resistor 37A, 37B Connection point

Claims (11)

[Claims] 1. An electric power steering device for generating a steering assist force according to a steering torque of a steering of a vehicle, comprising: a power steering motor for generating the steering assist force; and an electric power from a power source to the power steering motor. A motor drive unit that supplies the power steering motor and determines a control signal that controls the motor drive unit based on the steering torque, and outputs the control signal that has already been output, the voltage of the power supply, and Predicting the rotation speed of the power steering motor based on the winding resistance of the power steering motor, the drive current, and the back electromotive force constant,
Control means for adjusting the determined control signal based on the predicted rotation speed, and controlling the motor drive means by the adjusted control signal to control the electric power supplied to the power steering motor. A power steering control device characterized by the above. 2. The control means adjusts the control signal to reduce the power supplied to the power steering motor when the rotation speed of the power steering motor exceeds a predetermined value. The power steering device according to claim 1. 3. The power steering means adjusts the control signal when the steering wheel rotates beyond a prescribed value and the rotation speed of the power steering motor exceeds a prescribed value. The power steering device according to claim 1, wherein the power supplied to the motor is reduced. 4. The power steering means comprises an H-bridge circuit having four switching elements, and the control means adjusts the duty of a chopper signal supplied to one of the four switching elements. The power steering device according to claim 1, wherein electric power supplied to the motor is controlled. 5. The control means reduces the electric power supplied to the power steering motor by reducing the duty of the chopper signal when the rotation speed of the power steering motor exceeds a predetermined value. The power steering device according to claim 4, wherein 6. A power steering control method for generating a steering assist force according to a steering torque by a power steering motor in a vehicle equipped with an electric power steering device, the step comprising: detecting the steering torque; Determining a control signal for controlling the power steering motor based on the torque, the determined control signal, the voltage supplied to the power steering motor, the drive resistance and the drive current of the power steering motor, and the back electromotive force Predicting the rotation speed of the power steering motor based on a constant, adjusting the control signal based on the predicted rotation speed, and controlling the power supplied to the power steering motor by the adjusted control signal A power steering system including steps and Grayed control method. 7. The power according to claim 6, wherein when the rotation speed of the power steering motor exceeds a predetermined value, the power supplied to the power steering motor is reduced by the control signal. Steering control method. 8. The electric power supplied to the power steering motor by the control signal when the steering of the vehicle is rotated beyond a prescribed value and the rotation speed of the power steering motor exceeds a prescribed value. The power steering control method according to claim 6, further comprising: 9. The power steering motor is driven by an H bridge circuit having four switching elements, and is supplied to the power steering motor by adjusting the duty of a chopper signal supplied to one of the four switching elements. 7. The power steering control method according to claim 6, further comprising controlling the generated electric power. 10. The electric power supplied to the power steering motor is reduced by reducing the duty of the chopper signal when the rotation speed of the power steering motor exceeds a predetermined value. The power steering control method according to claim 9. 11. The power steering control device according to claim 1, wherein the vehicle is an industrial vehicle.