JPH03213465A - Motor-operated power steering device - Google Patents

Abstract

PURPOSE:To perform reliable diagnosis of failure in operation by providing a means to diagnose failure in operation of a motor from the computing value of the counter electromotive voltage factor of a motor, in a motor-operated power steering device which serves to control energization of an electric motor by detection of a current flowing to the electric motor to assist a steering force. CONSTITUTION:A control device 6 of a power steering device having a DC motor 1 to assist a steering force is provided with a target value computing means 7 to compute the target value of the current of the electric motor 1 based on steering torque and a car speed. Based on a deviation between the target value and the actual measurement value of a current, flowing to the DC motor 1, detected by a current detecting circuit 3, a motor control signal is computed. In this case, a motor characteristic computing means 12 to compute the counter electromotive voltage factor and armature resistance of the motor 1 from a source voltage, a motor rotation speed, and the actual measurement value of a current is further provided. It is decided by a failure in operation diagnosing means 14 to input an output therefrom that the motor 1 is failed in operation when the electromotive voltage factor or the armature resistance is outside a given allowable range.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an electric power steering device for automobiles and the like.

BACKGROUND OF THE INVENTION An electric power steering device for an automobile includes an electric motor for assisting steering force and a control device for controlling the motor based on the steering force applied to the steering wheel. Are known.

In such power steering devices, safety measures are required to determine the failure of various sensors and actuators and stop the device. To this end, the output of each sensor is detected and failure diagnosis is performed. .

For sensors, failure can be determined by detecting their output and determining the presence or absence of a signal or deviation from the normal range. but,
In particular, with regard to actuators such as electric motors, only clear failures such as disconnections can be determined, and failures in the details are overlooked, which not only leads to complaints that the equipment does not operate properly, but also requires a great deal of time to investigate the cause. There is a problem that it is necessary.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that solves the above problems and can reliably determine a failure of an electric motor.

Means for Solving the Problems An electric power steering device according to the present invention includes an electric motor for assisting steering force, and a control device for controlling the motor based on the steering force applied to the steering wheel. In the formula power steering device, the control device includes a motor characteristic calculating means for calculating a back electromotive force coefficient of the motor, and a failure diagnosis means for diagnosing a failure of the motor from the calculated value of the back electromotive force coefficient. .

Preferably, the control device includes motor characteristic calculating means for calculating a back electromotive force coefficient and armature resistance of the motor, and a failure diagnosis means for diagnosing a failure of the motor from the calculated values of the back electromotive force coefficient and armature resistance. ing.

The back electromotive force coefficient and armature resistance of the working motor can be calculated by calculation based on the actual measured value of the motor current.

When no failure occurs in the motor, the back electromotive force coefficient is approximately constant when the temperature is constant, and when a certain failure occurs in the motor, the back electromotive force coefficient changes. If the back electromotive force coefficient changes beyond the maximum amount of change in the back electromotive force coefficient due to temperature changes within the motor's operating temperature range, or a value that has been experimentally verified and set, for example, the armature winding or magnet It can be determined that there is some sort of malfunction.

When there is no failure in the motor, the armature resistance is approximately constant when the temperature is constant, and when a certain failure occurs in the motor, the armature resistance changes. If the armature resistance changes beyond the maximum amount of change in armature resistance due to temperature changes in the motor's operating temperature range or a value set after experimental verification, for example, a malfunction of the armature winding may occur. It can be determined that

Therefore, a motor failure can be diagnosed from the calculated value of the motor's back electromotive voltage coefficient.

Furthermore, motor failure can be diagnosed based on the motor's back electromotive force coefficient and armature resistance.

Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows the electrical configuration of a portion of an electric power steering device that is related to the present invention.

The power steering device includes a DC motor (1), a motor drive circuit (2), and a motor (1) to assist steering force.
a current detection circuit (3) that detects the current flowing through the steering wheel, a torque sensor (4) that detects the steering force (torque) applied to the steering wheel, a vehicle speed sensor (5) that detects the vehicle speed, and a torque sensor (4). , vehicle speed sensor (
5) and a control device (6) that controls the motor drive circuit (2) based on the output of the current detection circuit (3).

The control device (8) is constituted by, for example, a microcomputer, and includes target value calculation means (7) that calculates a target value of the current of the motor (1) based on the outputs of the torque sensor (4) and the vehicle speed sensor (5). , control element calculation means (8) that outputs a motor control signal based on this current target value and the actual measured value of the current detected by the current detection circuit (3), and a control element calculation means (8) that outputs a motor control signal based on this current target value and the actual measured value of the current detected by the current detection circuit (3), as well as a control element calculation means (8) that converts this control signal into PWM and outputs a PWM signal to the motor. It includes a PWM conversion means (9) for outputting to the drive circuit (2). Note that the configuration of the conventional power steering device is well known, so detailed explanation will be omitted.

The power steering device is provided with a power supply voltage sensor (10), a motor rotation speed sensor (11), a motor characteristic calculation means (12), and a failure diagnosis means (13) in order to diagnose a failure of the motor (1). ing.

The power supply voltage sensor (10) detects the power supply voltage of the motor (1), that is, the battery voltage.

The rotational speed sensor (11) detects the rotational speed of the motor (1).

Motor characteristic calculation means (12) and failure diagnosis means (13)
) is provided in the control device (6). The motor characteristic calculation means (12) calculates the motor (1) as described in detail later.
The back electromotive force coefficient and armature resistance of the motor (1) are calculated from the actual measured values of the power supply voltage, rotational speed, and armature current. A fault diagnosis means (13) diagnoses a fault in the motor (1) from the calculated values of the back electromotive voltage coefficient and the armature resistance.

That is, a failure is determined when the calculated value of the back electromotive voltage coefficient falls outside of a predetermined allowable range, or when the calculated value of the armature resistance falls outside of a predetermined allowable range.

If there is no failure in the motor (1), the back electromotive force coefficient is almost constant when the temperature is constant;
), the back electromotive force coefficient changes. If the back electromotive force coefficient changes beyond the maximum amount of change in the back electromotive force coefficient due to temperature changes within the operating temperature range of the motor (1) or a value that has been experimentally verified and set,
For example, it can be determined that there is some kind of failure in the armature winding or magnet.

If there is no failure in the motor (1), the armature resistance is almost constant when the temperature is constant, and the motor (1)
When a certain fault occurs, the armature resistance changes. If the armature resistance changes beyond the maximum amount of change in armature resistance due to temperature changes within the operating temperature range of the motor (1) or a value that has been experimentally verified and set, for example, if the armature resistance It can be determined that this is a malfunction.

Therefore, a failure of the motor (1) can be diagnosed by checking whether the back electromotive force coefficient and armature resistance of the motor (1) are within the allowable range.

Next, calculations of the back electromotive force coefficient and armature resistance will be explained with reference to FIGS. 2 and 3.

FIG. 2 shows an approximate circuit of the DC motor (1).

FIG. 3(a) shows the PWM signal, and FIG. 3(b) shows the armature current flowing through the motor (1). In addition, motor inductance is L1 motor armature resistance is R1 motor (
1) is the voltage applied to V1, the power supply voltage of the motor (1), that is, the battery voltage is E, and the armature current is 1. , the back electromotive force coefficient is 11, the rotation angle is θ, the rotation speed is ω, and the back electromotive force is e(-
, Xω). Also, the time is t, the pWM period is T,
A1 is the area where the PWM signal is on during one cycle.
, the off region is A2, and the on time, that is, the PWM duty, is Δ1.

In region A, the armature current is:

E-e.

i er(t) -(1e-"') + 1.1(o) e-"" ・・・・・・・・・・・・
... (1) In addition, it is B-R/'L, and 1. +
(0) is the armature current at 10 hours.

In region A2, the armature current is as follows.

e.

1-2(t) -f 1 e -""-"'I+1-
1(Δ1) e −B(1-Al l −−−−−
---(2) Note that i-+(Al) is the armature current when the time is 1 Δl.

Therefore, the average current 11 in areas A and A2 is
From equations (1) and (2), it is as follows.

Ding.

To 10 1.2(1) di l 11 [Δ1+ (e-BAl-1) T ■ -+ (0) (e-BA'-11 ] -e ω + [T Δi T + (e B (T A I)
l lR 1 −■,, (Δl) (e −””−” −11]
(3) In general, the time constant L/R is assumed to be sufficiently larger than the PWM period, so e-Bx-1...・・・・・・
・・・・・・・・・・・・・・・・・・ (4)
Im becomes as follows.

E-e--e.

1, - Δ1+ (T-Δ1) RT
RT EΔ1 e ω RT R E Δ1 臥−−ω (5) The RT R motor characteristic calculation means (12) calculates the back electromotive force coefficient and armature resistance based on equation (5). . In formula (5), 1. , E, Δ1/T (load time rate), and ω change with time. Also, ■, current detection circuit (3)
Therefore, E can be determined from the power supply voltage sensor (10), ω can be determined from the rotational speed sensor (11), and Δ/T can be determined from the output of the PWM conversion means (9). Therefore, in two different states, create two simultaneous equations from equation (5),
By solving this, K and R can be found. It is also possible to determine Ko and R under special conditions in which specific terms cancel out.

R is a very important component among the components that express the characteristics of the motor, and if the change is large, it can be determined that there is some kind of failure in the armature winding. In addition, K is the number of magnetic poles of the motor, 2P, the magnetic flux of each pole, Φ, and the total number of armature conductors, 2P.
When the number of internal parallel circuits between one brush is 2a, it is generally expressed as K, -PzΦ/a 2 . Therefore, if the change in K is large,
For example, it can be determined that there is some kind of failure in the armature winding or magnet.

Fault diagnosis may be performed at regular intervals, or, in a simple system, may be performed only when the system is started. Further, even if errors due to approximation are included, sufficient effects can be achieved.

In the above embodiment, a motor failure is diagnosed using the calculated value of the back electromotive voltage coefficient and the armature resistance, but it is also possible to diagnose the motor failure using only the calculated value of the back electromotive voltage coefficient.

Effects of the Invention According to the power steering device of the present invention, as described above, failure of the motor can be reliably determined.

[Brief explanation of drawings]

Fig. 1 is an electrical program diagram of the main parts of a power steering device showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an approximate circuit of a DC motor, and Fig. 3 shows a PWM signal and a motor armature. It is a graph showing electric current. (1)...DC motor, (6)...control device, (1
2)...Motor characteristic calculation means, (13)...Fault diagnosis means. Above 4

Claims (2)

[Claims] (1) In an electric power steering device that includes an electric motor for assisting steering force and a control device that controls the motor based on the steering force applied to the steering wheel, the control device An electric power steering device comprising a motor characteristic calculating means for calculating a voltage coefficient, and a failure diagnosis means for diagnosing a motor failure based on a calculated value of a back electromotive voltage coefficient. (2) The control device includes a motor characteristic calculation means for calculating a back electromotive force coefficient and armature resistance of the motor, and a failure diagnosis means for diagnosing a motor failure from the calculated values of the back electromotive force coefficient and armature resistance. The electric power steering device according to claim (1).