JP2002234457A - Controlling device for electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controlling device for an electric power steering device comparing a motor electric current estimated value found by computing with an actual motor electric current value for monitoring an operating condition of a driving system. SOLUTION: A motor electric current command value Ir(s) as a control target value of a motor output is inputted to a feed-forward compensator 51 to be inputted to a control object (motor) 50 via an adder 52 and an addition element 53. A motor electric current value Id(s) of the control object 50 can be computed according to a predetermined computing equation on the basis of the motor electric current command value Ir(s). The computed motor electric current value Id(s) is used as a motor electric current estimated value Ied(s) to be compared with the motor electric current value Id(s) (actual electric current value i), and when a difference e between them exceeds a previously set value, it is determined that a failure occurs in the driving system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for an electric power steering device.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle detects a steering torque and a vehicle speed generated in a steering shaft by operating a steering wheel, and drives a motor based on the detected signal to drive a steering force of the steering wheel. Is to assist. The control of such an electric power steering device is performed by an electronic control circuit. The outline of the control is based on the steering current detected by the torque sensor and the current supplied to the motor based on the vehicle speed detected by the vehicle speed sensor. Is calculated, and the current supplied to the motor is controlled based on the calculation result.

That is, the electronic control circuit supplies a large steering assist force when the detected vehicle speed is zero or low speed when the steering wheel is operated to generate a steering torque, and the detected vehicle speed is If the speed is fast, the motor current command value which is the control target value of the motor output is calculated according to the steering force of the steering wheel and the vehicle speed so as to supply a small steering assist force,
By performing the current feedback control so that the difference between the motor current command value, which is the result of this calculation, and the actual current value actually flowing to the motor becomes zero, an optimum steering assist force according to the running state can be provided.

[0004]

However, in the control device of the above-mentioned conventional electric power steering device,
In the calculation of the motor current command value Ir, the steering torque and the vehicle speed are used as parameters, and the rotation speed of the motor is not taken into account. Therefore, even if the motor drive circuit is normal, it is erroneously determined that an abnormal current is flowing through the motor. We may make a decision.

That is, as shown in FIG. 8, the actual current value i flowing through the DC motor has a characteristic that it decreases as the rotation speed increases because a back electromotive force is generated in accordance with the rotation speed of the motor.

On the other hand, the motor current command value Ir is determined on the basis of the steering torque and the vehicle speed, and the rotational speed of the motor is not taken into account. Therefore, if the effect of the back electromotive force generated by the rotation of the motor is not compensated by the current feedback control, The difference between the motor current command value Ir and the actual current value i of the motor becomes large, which causes an inconvenience of erroneously determining that an abnormal current is flowing through the motor.

When the battery voltage and the characteristic constant of the motor fluctuate, the control characteristics deteriorate and the motor current command value Ir increases.
And the actual current value i of the motor becomes large, which causes an inconvenience of erroneously determining that an abnormal current is flowing through the motor.

An object of the present invention is to solve the above-mentioned disadvantages.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the invention of claim 1 provides a steering assisting force to a steering mechanism based on at least a steering torque generated in a steering shaft and a detected vehicle speed. A motor current command value calculating means for calculating a motor current command value which is a control target value of a motor output based on a detected steering torque and a detected vehicle speed in a control device of an electric power steering device for controlling an output of a given motor. Motor current estimated value calculating means for calculating an estimated value of the motor current based on the motor current command value; motor current detecting means; and a difference between the calculated motor current estimated value and the detected motor current value. And a monitoring means for detecting a failure of the drive system based on the control system.

When the difference between the calculated motor current estimated value and the detected motor current value exceeds a predetermined allowable value, the monitoring means determines that the drive system has failed. Means.

[0011]

Embodiments of the present invention will be described below. FIG. 1 is a view for explaining the outline of the configuration of an electric power steering apparatus suitable for carrying out the present invention. The steering wheel is connected to a tie rod 8. The shaft 2 is provided with a torque sensor 3 for detecting a steering torque of the steering handle 1. A motor 10 for assisting the steering force is connected to the shaft 2 via a clutch 9 and a reduction gear 4.

An electronic control circuit 13 for controlling the power steering device is provided with an ignition key 1 from a battery 14.
Power is supplied via 1. The electronic control circuit 13 calculates a motor current command value Ir based on the steering torque detected by the torque sensor 3 and the vehicle speed detected by the vehicle speed sensor 12, and calculates the calculated motor current command value (hereinafter referred to as a current command value). ) The current control value E supplied to the motor 10 is controlled based on Ir.

The clutch 9 is controlled by an electronic control circuit 13. The clutch 9 is connected in a normal operation state, and is disconnected when the electronic control circuit 13 determines that the power steering device has failed and when the power is off.

FIG. 2 is a block diagram showing the configuration of the electronic control circuit 13. In this embodiment, the electronic control circuit 13 is mainly composed of a CPU.
The functions executed internally by the program are shown. For example, the phase compensator 21 does not indicate the phase compensator 21 as independent hardware, but indicates a phase compensation function executed by the CPU. The electronic control circuit 13
It is needless to say that these functional elements can be constituted by independent hardware (electronic circuits) without using a CPU.

Hereinafter, functions and operations of the electronic control circuit 13 will be described. The steering torque signal input from the torque sensor 3 is phase-compensated by the phase compensator 21 to enhance the stability of the steering system, and is input to the current command value calculator 22. Also,
The vehicle speed detected by the vehicle speed sensor 12 is also a current command value calculator 2
2 is input.

The current command value calculator 22 calculates the motor 10 by a predetermined formula based on the input torque signal, vehicle speed signal, estimated motor angular speed ω, and other parameters.
A current command value Ir, which is a control target value of the current supplied to the motor, is calculated.

Reference numeral 30 denotes a control unit which obtains a current control value E by using the current command value Ir as an input signal and drives a motor to be controlled. Conventional control units include, for example, a comparator, a differential compensator,
The current feedback control is constituted by a proportional operation unit and an integral operation unit so that the actual current value i actually flowing to the motor coincides with the motor current command value Ir. In the present invention, the control unit 30 is robust. The control unit performs control. This will be described in detail later.

The current control value E output from the control unit 30 is supplied to a motor drive circuit 41 to drive the motor 10. The actual current value i of the motor 10 is
And is fed back to the control unit 30.

FIG. 3 shows an example of the configuration of the motor drive circuit 41. The motor drive circuit 41 converts the current control value E input from the control unit 30 into a PWM signal (pulse width modulation signal) and a current direction signal, and converts the current control value E into FET1 to FE.
T4 and an FET gate drive circuit 45 for opening and closing the gates thereof. The boost power supply 46 is an FET
1. Power supply for driving the high side of FET2.

The PWM signal is an H bridge-connected FE.
T (field effect transistor) switching element FET1
The duty ratio of the PWM signal (time ratio for turning on / off the gate of the FET) is determined by the absolute value of the current control value E calculated by the control unit 30.

The current direction signal is a signal for instructing the direction of the current supplied to the motor, and is determined by the sign (positive or negative) of the current control value E calculated by the control unit 30.

FET1 and FET2 are switching elements whose gates are turned ON / OFF based on the duty ratio of the PWM signal, and are switching elements for controlling the magnitude of the current flowing through the motor. Also, FET3
And FET4 have their gates turned on or off based on the current direction signal described above (when one is on, the other is OF)
F), which is a switching element for switching the direction of the current flowing through the motor, that is, the rotation direction of the motor.

When FET3 is conductive, current flows through FET1, motor 10, FET3 and resistor R1, and a positive current flows through motor 10. Also, FET
4 is conducting, the current will flow through FET2, motor 1
0, the current flows through the FET4 and the resistor R2, and a negative current flows through the motor 10.

The motor current detection circuit 42 detects the magnitude of the positive current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. I do. The detected motor actual current value i is input as feedback to the control unit 30 (see FIG. 2).

The above-described electronic control circuit is configured such that when the steering wheel is operated and the steering torque is generated, the detected steering torque is large, and if the detected vehicle speed is zero or low, the current command is issued. When the value Ir is set to be large and the detected steering torque is small and the detected vehicle speed is fast, the current command value Ir is set to be small, so that an optimum steering assist force according to the traveling state can be given.

Next, the control section 30 of the present invention will be described. Before that, the configuration of the conventional current feedback control section 30f will be described first.

FIG. 4 is a block diagram showing the configuration of a conventional feedback control system by using a transfer function, wherein 23 is a comparator, 24 is a differential element (KDs), and 25 is a proportional element (Kp).
), 26 are integral elements (Kt / s), 27 is an adder, and the feedback control section 30f is composed of the above circuit elements. Reference numeral 29 denotes a motor to be controlled, 29a is a proportional constant (K), 29b is a motor element (L is an inductance of the motor, R is an internal resistance of the motor, s is a Laplace operator, and 1 / ( Ls + R) indicates the motor element).

In FIG. 4, the back electromotive force Ke ω is applied to the input side of the controlled object via the adder 28. This is equivalent to the effect of the back electromotive force generated by the rotation of the motor. This shows that the back electromotive force generated by the rotation of the motor appears in the current control value on the input side. Here, Ke is the back electromotive force constant of the motor, ω is the angular velocity of the motor, and ωa is the angular acceleration of the motor.

In this control system, the current command value Ir is used as an input signal, and the actual current value i actually flowing through the motor to be controlled is fed back to the input signal to obtain the differential value, proportional value, and The current control value E is obtained by adding the integral values. The motor to be controlled is driven by the current control value.

However, in the conventional feedback control system, there is a possibility that the stability of the system may be lost with respect to a change such as a change in battery voltage or a change in temperature.

Therefore, in the present invention, the control unit 30 is constituted by a robust control system shown in FIG. 5 instead of the above-mentioned conventional feedback control system, so that the response characteristics of the control system are maintained and the fluctuation of the battery voltage is maintained. The system stability is ensured even when there are fluctuation factors such as temperature and temperature change.

FIG. 5 is a block diagram showing the configuration of the robust control system as a transfer function. Numeral 50 denotes a motor to be controlled. If the inductance L of the motor, the internal resistance R of the motor, and the Laplace operator are s, the motor element is represented by 1 / (Ls + R).

Reference numeral 51 denotes a feedforward compensator for defining a response characteristic of the motor current value Id (s) to the current command value Ir (s). Where Ln is the design value of the motor inductance, Rn is the design value of the internal resistance of the motor,
2 is a time constant and s is a Laplace operator.

An adder 52 adds the output r (s) of the feedforward compensator 51 and the output of a filter 57 described later. The output da (s) of an adder 56 described later is added through the filter 57. Is fed back to the unit 52,
It is added to the controller output r (s). Thereby, the control target 5
The fluctuation of 0 and the fluctuation of the back electromotive force generated by the rotation of the motor are compensated.

Numeral 53 denotes an adder element which adds a back electromotive force Ke ω generated by the rotation of the motor to the input side of the control object.
To the motor current value Id (s), and the back electromotive force Ke ω appears in the motor current value Id (s).
Is equivalently shown. Here, Ke is the back electromotive force constant of the motor, and ω is the angular velocity of the motor. The output of the addition element 53 is a current control value E that defines the current supplied to the motor.

Numeral 55 is a circuit element indicating the reverse characteristic of the desired motor characteristic. In this embodiment, a mathematical model of the electric characteristic excluding the term of the back electromotive force is adopted in order to prevent the effect of the back electromotive force of the motor. Ln and Rn are design values of the inductance of the motor, design values of the internal resistance of the motor, and s is a Laplace operator.

An adder 56 calculates the difference between the output of the circuit element 55 and the output of the adder 52, that is, the difference between the desired motor control characteristic and the actual control characteristic based on the controller output. The output da (s) of the adder 56 is represented by the following equation (1).

[0038]

(Equation 1)

From equation (1), it can be seen that the output da (s) of the adder 56 is the sum of the variation of the controlled object and the back electromotive force.
Here, L and R are the inductance of the motor to be controlled, the internal resistance of the motor, Ln and Rn are the design values of the inductance of the motor, the design values of the internal resistance of the motor, s is the Laplace operator, and Ke ω is the inverse. The electromotive force, K, is a constant.

Reference numeral 57 denotes a filter for stabilizing the operation of a control system that feeds back the output da (s) of the adder 56, and its characteristic is represented by Q (s). In this embodiment, a primary low-pass filter is used, and the filter characteristic Q in FIG.
(s) = 1 / (T1s + 1) shows an example of the filter characteristic Q (s) expressed by a transfer function. Here, T1 is a time constant, and s is a Laplace operator.

By feeding back the output of the filter 57 having the characteristic Q (s), the fluctuation of the controlled object and the back electromotive force are suppressed, and the characteristic is matched with the characteristic of the defined mathematical model. Hereinafter, this will be described.

When the output of the filter 57 is fed back, the motor current value Id (s) is expressed by the following equation (2).

[0043]

(Equation 2)

In the equation (2), Pn (s) is a mathematical model of motor characteristics. Δ (s) is calculated by the following equation (3).
Is defined by Here, Δ (s) is a perturbation component when the difference between the mathematical model and the actual characteristic is represented using a multiplicative perturbation model.

[0045]

(Equation 3)

When the filter characteristic Q (s) is approximately 1, equation (2) can be represented by the following approximate equation (4), and the motor current value Id (s) can be obtained.

[0047]

(Equation 4)

Output r (s) of feedforward compensator
Can be expressed by the following equation (5) obtained by multiplying the current command value Ir (s) by the characteristic (Lns + Rn) / (T2s + 1) of the feedforward compensator. Where T2 is a time constant and s
Is the Laplace operator.

[0049]

(Equation 5)

Therefore, the approximate expression (4) representing the motor current value Id (s) is obtained by substituting the expression (5) into r (s) of the approximate expression (4). Can be represented.
The approximate expression (6) showing the motor current value Id (s) is expressed by the characteristic Q
Cutoff frequency 1 / 2π · T2 of filter with (s)
Is established up to.

[0051]

(Equation 6)

On the other hand, as a sufficient condition for a control system subjected to multiplicative perturbation to be stable, there is a minimum gain theorem shown in the following equation (7).

[0053]

(Equation 7)

Here, T (s) is a complementary sensitivity function when the controlled object and its mathematical model match, that is, a transfer characteristic when Ln = L, Rn = R, and K = 1 in FIG. is there. In this embodiment, since T (s) = Q (s), the time constant T1 of the filter 57 having the characteristic Q (s) is determined so as to satisfy the following equation (8).

[0055]

(Equation 8)

In this embodiment, the range of Δ (s) defined by the above equation (3) is determined in consideration of the expected inductance L of the motor, the internal resistance R, and the variation range of the constant K.
If the time constant T1 of the filter 57 having the characteristic Q (s) is determined so that the above equation (8) is satisfied in the entire range of (s), robust stability can be ensured.

According to the above study, the control system shown in FIG. 5 is equal to or lower than the cutoff frequency of the characteristic Q (s) of the filter 57 (1).
/ 2π · T2), it can be further represented by the equivalent block diagram shown in FIG. 6A, and further simplified as shown in the equivalent block diagram shown in FIG. 6B.
That is, the inverse of the mathematical model is given to the numerator of the characteristic equation of the feedforward compensator 51 in FIG. 5, and the time constant T2 larger than the filter time constant T1 is given to the denominator. Response characteristics can be realized.

Further, by configuring the control system as described above, the fluctuation due to the back electromotive force generated by the rotation of the motor is compensated.

As shown in FIG. 6, the response speed can be set within an arbitrary range determined by a time constant T2 which is larger than the time constant T1 of the filter having the characteristic Q (s).
Practically sufficient response characteristics can be realized.

Further, unlike the conventional current feedback control system, as shown in the equation (2), the characteristic Q (s) is changed with respect to the fluctuation of the battery voltage, the resistance between the motor terminals and the motor torque.
This has an important advantage that the design performance can be maintained up to the cutoff frequency of the filter and the safety can be ensured as shown in Expression (6).

Next, detection of a failure in the drive system of the electric power steering device will be described. As described above in the problem to be solved by the invention, if the effect of the back electromotive force and the fluctuation of the control target are not sufficiently compensated, the difference between the motor current command value Ir and the actual current value i of the motor increases. .

Therefore, if the motor current command value Ir is simply compared with the actual current value i of the motor and the difference exceeds a set value, it is determined that a failure has occurred in the drive system. May be erroneously determined to be a failure even though is operating normally.

Therefore, in the present invention, a fault in the drive system is detected by the method described below for the robust control system described above. When the drive train is not out of order,
As described above, since the motor current is controlled as expressed by the equation (6), the estimated value Ied (s) of the current flowing to the motor is calculated by the following equation (9). (Referred to as a current estimation value). When the drive system fails, Expression (6) does not hold.

[0064]

(Equation 9)

Then, as shown by the following equation (10),
When the absolute value of the difference e between the estimated motor current value Ied (s) and the motor current value Id (s) exceeds a preset value ER, it is determined that a failure has occurred in the drive system.

[0066]

(Equation 10)

Referring to FIG. 5, the configuration of the failure monitoring unit will be described. In FIG. 5, the failure monitoring unit 60 determines the motor current estimated value I
The calculator 61 includes a calculator 61 for calculating and estimating ed (s) and a comparator 62. The calculator 61 calculates and estimates a motor current estimated value Ied (s) based on the motor current command value Ir (s). , The comparator 62 compares the estimated motor current value Ied (s) with the motor current value Id (s), and determines the difference e as a predetermined allowable value ER
When the value exceeds, an error signal indicating that a failure has occurred in the drive system is output.

As described above, the motor current estimated value Ied (s) is the same as the motor current estimated value calculated by the approximation formula (9) when the drive system is in a normal state. ) (Actual current value) uses the actual current value i which is obtained by detecting the actual current flowing through the motor by the motor current detection circuit 42 (see FIG. 2).

FIG. 7 is a flowchart for explaining the monitoring operation of the failure monitoring unit 60 executed by the CPU of the control unit 30. In the monitoring operation described below, a sample value is repeatedly extracted at predetermined time intervals, and processing such as calculation and determination is performed.

First, the current command value calculator 22 (see FIG. 2)
From the motor current command value Ir (step P
1) An estimated motor current value Ied is calculated based on the read motor current command value Ir (step P2). Next, an actual motor current value i is detected by the motor current detection circuit 42 (see FIG. 2) (step P3).

The estimated motor current value Ied and the actual motor current value i
Then, it is determined whether or not the absolute value e of the difference exceeds a predetermined allowable value ER (step P4). If the absolute value e does not exceed the allowable value, the counter is reset (step P5). Also,
If it exceeds the allowable value, the counter is incremented by 1 (step P6).

It is determined whether or not the count value of the counter exceeds a predetermined value (step P7). If not, it is determined that the value is normal and the process returns to the main routine. If it exceeds the specified value, it is determined that a failure has occurred, the failure flag is set to 1, a warning is displayed, and preparations are made for transition to another failure processing routine (not shown) (step P8), and the process returns to the main routine. .

The specified value used to determine the count value of the counter is the motor current estimated value I
This is a value for counting the number of times that the absolute value of the difference between ed and the actual motor current value i has exceeded the allowable value to determine the occurrence of a failure. This value is used to judge that a failure has occurred when it exceeds the threshold, and is appropriately determined by experiment.

According to the fault monitoring unit described above, when comparing the estimated motor current value Ied with the actual motor current value i,
Since the robust control system compensates for the back electromotive force generated in the motor and the fluctuation of the control object, the difference between the estimated motor current value and the actual motor current value does not become abnormally large, and the drive system operates normally. Despite this, there is no risk of erroneously determining that a failure has occurred.

In the above-described embodiment, the components of the control unit are represented by transfer functions.
Any appropriate circuit element can be used as long as the circuit element has the characteristic indicated by the transfer function.

[0076]

As described above, the control apparatus for an electric power steering apparatus according to the present invention is based on the current command value input to the control system and the motor current value which is the output. Calculate the difference between the control characteristics (motor design characteristics) and the actual motor control characteristics,
Since the feedback is performed so as to correct the difference, even if the characteristic constants such as the battery voltage, the resistance between the motor terminals, and the torque constant of the motor fluctuate due to temperature and other environmental changes and other causes, the desired motor Control characteristics can be maintained, and the stability of the control system is not lost.

When the fault monitor compares the estimated motor current value obtained by the calculation with the actual motor current value, the robust control system compensates for the back electromotive force generated in the motor and the fluctuation of the control target. Therefore, the difference between the estimated motor current value and the actual motor current value does not become abnormally large, and it may be erroneously determined that a failure has occurred even though the drive system is operating normally. And the operating state of the drive system can always be accurately monitored.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating the configuration of an electric power steering device.

FIG. 2 is a block diagram of an electronic control circuit according to the present invention.

FIG. 3 is a block diagram showing an example of a configuration of a motor drive circuit.

FIG. 4 is a block diagram showing a conventional current feedback control system by a transfer function.

FIG. 5 is a block diagram showing the configuration of a control system according to the present invention as a transfer function.

FIG. 6 is a block diagram showing an equivalent circuit of the control system of the present invention by a transfer function.

FIG. 7 is a flowchart illustrating a monitoring operation of a failure monitoring unit executed by the control unit.

FIG. 8 is a view for explaining a relationship between a motor current command value and a motor actual current value with respect to a rotation speed of a motor in a control device of a conventional electric power steering device.

[Explanation of symbols]

 Reference Signs List 3 Torque sensor 10 Motor 11 Ignition key 12 Vehicle speed sensor 13 Electronic control circuit 21 Phase compensator 22 Current command value calculator 30 Control unit 41 Motor drive circuit 42 Motor current detection circuit 50 Control target (motor) 51 Feedforward compensator 52 Addition Unit 53 Addition element 55 Motor inverse characteristic circuit element 56 Adder 57 Filter 60 Failure monitoring unit 61 Computing unit 62 Comparator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D032 CC38 DA15 DA23 DA64 DB11 DC01 DC02 DC03 DD17 DD18 EC23 3D033 CA13 CA16 CA20 CA28 CA31

Claims (2)

[Claims] 1. A control device for an electric power steering device for controlling an output of a motor that applies a steering assisting force to a steering mechanism based on at least a steering torque generated in a steering shaft and a detected vehicle speed. Motor current command value calculating means for calculating a motor current command value which is a control target value of the motor output based on the detected vehicle speed; and a motor current estimated value for calculating an estimated value of the motor current based on the motor current command value. An electric motor, comprising: a calculating means; a motor current detecting means; and a monitoring means for detecting a drive system failure based on a difference between the calculated motor current estimated value and the detected motor current value. Control device for power steering device. 2. A monitor for judging that a drive system failure has occurred when the difference between the calculated estimated motor current value and the detected motor current value exceeds a predetermined allowable value. 2. The control device for an electric power steering device according to claim 1, wherein the control device is means.