JPH10100914A - Control device for electric power steering device - Google Patents

Abstract

(57) Abstract: In a control device for an electric power steering device, a motor current value is detected and corrected by using an inexpensive one-way current detection circuit without newly providing a sample and hold circuit or the like. SOLUTION: This is a control device of an electric power steering device for urging a steering shaft with an auxiliary load by controlling a motor connected to an H-bridge circuit of a semiconductor element, and constitutes two arms of the H-bridge circuit facing each other. Of the pair of semiconductor elements, the semiconductor element of the first arm is driven by the PWM signal having the first duty ratio determined based on the current control value, and the semiconductor element of the second arm is connected to the first arm. Drive control means driven by a PWM signal having a second duty ratio defined by a function of the duty ratio of the first and second motors, and a motor current value is detected by a voltage between terminals of a resistor inserted in series with the first and second arms. Motor current detection means and motor current detection correction means for correcting the motor current value with the second duty ratio are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device which applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and more particularly to a motor drive circuit having an H-bridge circuit structure of a semiconductor element. The present invention relates to a control device for an electric power steering device that economically detects a motor current value in the case of:

[0002]

2. Description of the Related Art An electric power steering apparatus for energizing a steering apparatus of an automobile or a vehicle with an auxiliary load by the rotational force of a motor uses a transmission mechanism such as a gear or a belt through a speed reducer to transmit the driving force of the motor to a steering shaft or the like. An auxiliary load is applied to the rack shaft. In such an electric power steering apparatus, when the end contact lock state of the handle is held for a long time in the stationary state, or when the garage operation is repeated for a long time, a large current continuously flows through the motor, and the motor However, there is a problem that heat may be generated to cause smoke, emit odor, or burn out, which may cause an accident. Therefore, it is necessary to accurately detect the motor current value.

First, the configuration of a general electric power steering device will be described with reference to FIG. The shaft 2 of the steering handle 1 has a reduction gear 3, universal joints 4a and 4
b, connected to a tie rod 6 of a steered wheel via a pinion rack mechanism 5; The shaft 2 is provided with a torque sensor 10 for detecting a steering torque of the steering handle 1,
A motor 20 for assisting the steering force of the steering handle 1 is connected to the shaft 2 via a clutch 21 and a reduction gear 3. The control unit 30 that controls the power steering device is supplied with power from the battery 14 via the ignition key 11. The control unit 30 controls the steering torque T detected by the torque sensor 10 and the vehicle speed sensor 1.
The steering assist command value I of the assist command is calculated based on the vehicle speed V detected in step 2, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I. The clutch 21 is ON / OFF controlled by the control unit 30 and is ON (coupled) in a normal operation state.
The clutch 21 is turned off (disengaged) when the control unit 30 determines that the power steering device has failed, and when the power of the battery 14 is turned off by the ignition key 11. Although the control unit 30 is mainly composed of a CPU, a general function executed by a program in the CPU is as shown in FIG.

Here, the function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by a phase compensator 31 in order to enhance the stability of the steering system, and the phase-compensated steering torque TA is input to a steering assist command value calculator 32. Is done.
The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. Steering assist command value calculator 32
Determines a steering assist command value I, which is a control target value of the current supplied to the motor 20, based on the input steering torque TA and the vehicle speed V.
3 is attached. The memory 33 stores a steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 32. The steering assist command value I is subtracted by the subtractor 3.
0A, is input to a feed-forward differential compensator 34 for increasing the response speed, and the deviation (I-i) of the subtractor 30A is input to a proportional calculator 35,
The proportional output is input to an adder 30B and also to an integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integration compensator 36 are also added to the adder 30B, and the current control value E, which is the result of the addition in the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.

An example of the configuration of the motor drive circuit 37 will be described with reference to FIG. 5. The motor drive circuit 37 uses a field effect transistor (FE) based on a current control value E from an adder 30B.
T) FET gate drive circuit 371 as drive control means for driving each gate of FET1 to FET4, FET1 to FET4
H-bridge circuit consisting of FET4, FET1 and FET2
And a boosting power source 372 for driving the high side of the device. FET1, FET4 and resistor R2 constitute a first (or second) arm, and FET2, FET3 and resistor R1 constitute a second (or first) arm. FE
T1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir actually flowing to the motor is controlled. The FET 3 and the FET 4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and a region where the duty ratio D1 is large. Is turned on / off according to the rotation direction of the motor determined by the sign of the PWM signal. For example, FE
When T3 is conductive, current flows through FET1, motor 20, FET3, and resistor R1, and a positive current flows through motor 20. In this case, P of the duty ratio D1
When the FET1 is ON by the WM signal, it is referred to as "mode A", and when FET1 is OFF, it is referred to as "mode B". In either case, a forward current flows through the motor 20. When both FET1 and FET3 are turned off, FE
A resistor R2, a regenerative diode of FET4, a motor 2 via a regenerative diode (not shown)
0, a current in the negative direction flows through the regenerative diode of the FET 2 to form “mode C”. When the FET 4 is conducting, the current flows through the FET 2, the motor 20, the FE
The current flows through T4 and the resistor R2, and a negative current flows through the motor 20. Therefore, the current control value E from the adder 30B is also a PWM output. Also in this case, mode A, mode B, and mode C are formed as described above.

The motor current detecting circuit 38 detects the magnitude of the current in the positive or negative direction based on the voltage drop across the resistor R1, and detects the magnitude of the positive or negative current based on the voltage drop across the resistor R2. The magnitude of the current is detected. The motor current value i detected by the motor current detection circuit 38 is input to the subtractor 30A and fed back.

[0007]

The above-described motor current detection circuit 38 needs to detect currents in both directions with respect to the resistors R1 and R2, and the current detection circuit of the two-way detection type becomes expensive. There is. When an inexpensive one-way detection type current detection circuit is used, the FET gate drive circuit 37
1 and the first duty ratio D1 shown in FIG. 6A and the second duty ratio D2 shown in FIG.
When the FET 4 is controlled, an effective current Im as shown in FIG. However, when the current is measured as a drop voltage generated in the resistors R1 and R2 inserted in series with the arm by the one-way detection type current detection circuit, the current cannot be measured as shown in FIG. The current i (C) in the mode C as in D) cannot be detected, resulting in a toothless detection current. As a result, the average current of the currents i (A) and i (B) in the modes A and B is obtained. I will.
Therefore, accurate current Im cannot be detected.
That is, in one cycle of the PWM signal, the modes A to
The motor current Im actually flowing through the motor 20 through each stage of C is

## EQU1 ## Im = i (A) + i (B) + i (C). Then, the sum of the detection currents i detected by the one-way detection type current detection circuit is the following equation 2 since the current i (C) in the mode C is not detected.

[0008]

I ′ = i (A) + i (B) In order to accurately measure such a motor current Im by a one-way type current detection circuit, the sample-and-hold circuit uses a current value of mode B (B ) Is held and the current i of the mode C is held.
It is necessary to interpolate (C) and pass a low-pass filter that removes noise together with the interpolation, which inevitably increases the cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a motor current using an inexpensive one-way current detection circuit without providing an expensive circuit such as a sample and hold circuit. It is an object of the present invention to provide a control device for an electric power steering device that accurately detects and corrects a value.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a control device for an electrically conductive power steering device for energizing a steering shaft with an auxiliary load by controlling a motor having a semiconductor element connected to an H-bridge circuit. My goal is,
The semiconductor element of the first arm is driven by a PWM signal having a first duty ratio determined based on a current control value, out of a pair of semiconductor elements forming two arms facing each other of the H-bridge circuit. And a drive control means for driving the semiconductor element of the second arm with a PWM signal of a second duty ratio defined by a function of the first duty ratio, and a drive control means connected in series to the first and second arms. This is achieved by including motor current detection means for detecting a motor current value based on the voltage between terminals of the inserted resistor, and motor current detection correction means for correcting the motor current value using the second duty ratio. Further, the motor current detecting means may be a one-way current detecting means.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

In the present invention, as shown in FIG. 1 corresponding to FIG. 5, a one-way motor current detecting circuit 40 detects a current value i 'based on a voltage drop at resistors R1 and R2. , The current value i ′ detected at the second duty ratio D2 is corrected, and the corrected current value i is used as a feedback current. That is, in the one-way detection type current detection circuit 40 connected to the resistors R1 and R2 of the H-bridge circuit, as shown in FIG.
Is detected, and the current i 'is corrected by the correction circuit 41.
To enter. The correction circuit 41 converts the input current i ′ into F
The correction is performed based on the duty ratio D2 from the ET gate drive circuit 371, and the corrected current value i is subtracted by the subtractor 30A (FIG. 4).
Feedback). Note that the correction circuit 41
It can be handled by U software.

By the way, in the time T _{PWM of one} PWM cycle, the current can be considered to be in an equilibrium state, and the ripple of the current can be assumed to be sufficiently smaller than the effective value Ir of the current. ) Can be approximated as a solid line waveform in FIG. The waveform in FIG. 2 is obtained as a current detection value that has passed through a low-pass filter for noise reduction or digitizing anti-aliasing. Since the cutoff frequency of the low-pass filter is sufficiently lower than the frequency of PWM,
Current value detected by the motor current detecting circuit 40 i ', as in FIG. 2, the height of the area B indicated by averaged right hatched area of a region A shown in the left oblique lines in the figure at time T _PWM of 1 cycle . At this time, since the areas of the regions A and B are equal,
Holds.

[0014]

Equation 3] _{i '· T PWM = i ·} T PWM · D2 Therefore, the number of the next 4 is derived.

[0015]

I ′ = T _PWM · D2 / T _PWM · i = D2 · i From the above equation 4, the current detection value i ′ has an error with respect to the current value i to be obtained by the duty ratio D2. Therefore, the current detection value i ′ is corrected by the correction circuit 41 according to the following Expression 5, and
An effective value i of the current is obtained.

[0016]

I = i '/ D2 Accordingly, the error of the current detection value i' by the motor current detection circuit 40 can be corrected without providing the sample and hold circuit.

In the above embodiment, the H-bridge circuit is
Although the different duty ratio driving methods have been described for the upper and lower stages, the sign magnitude driving method (Japanese Patent Publication No. 3-182874) has been described.
), Simultaneous upper and lower PWM drive system (Japanese Patent Laid-Open No. 62-299)
No. 476) can be similarly applied.

[0018]

As described above, according to the control device of the electric power steering apparatus of the present invention, the motor current detection correction means for correcting the motor current detection value by the one-way current detection circuit with the second duty ratio is provided. Therefore, the error of the motor current detection value can be corrected without providing the sample and hold circuit, and the cost can be reduced without changing the function.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the principle of the present invention.

FIG. 3 is a block diagram showing an example of a conventional electric power steering device.

FIG. 4 is a block diagram showing a general internal configuration of a control unit.

FIG. 5 is a connection diagram illustrating an example of a motor drive circuit.

FIG. 6 is a time chart for explaining an operation example of the H-bridge circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 40 Motor current detection circuit 41 Correction circuit

Claims (2)

[Claims] 1. An electric power steering apparatus control device for energizing a steering shaft with an auxiliary load by controlling a motor having a semiconductor element connected to an H-bridge circuit,
The semiconductor element of the first arm is driven by a PWM signal having a first duty ratio determined based on a current control value, out of a pair of semiconductor elements forming two arms facing each other of the H-bridge circuit. And a drive control means for driving the semiconductor element of the second arm with a PWM signal of a second duty ratio defined by a function of the first duty ratio, and a drive control means connected in series to the first and second arms. An electric power comprising: motor current detection means for detecting a motor current value based on a voltage between terminals of an inserted resistor; and motor current detection correction means for correcting the motor current value with the second duty ratio. Control device for steering device. 2. The control device for an electric power steering device according to claim 1, wherein said motor current detecting means is a one-way current detecting means.