JP2857903B2 - Electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric power steering device for an automobile or the like.

2. Description of the Related Art As an electric power steering device for an automobile, an electric motor for assisting a steering force, a motor drive circuit thereof, a current detection circuit for detecting a current flowing through the motor, and a steering wheel are provided. A target value calculating means for calculating a target value of the current of the motor based on the steering force; and a PWM for outputting a PWM signal to the motor drive circuit based on the target value of the current and the actually measured value of the current detected by the current detection circuit. There is known one provided with conversion means.

In such a power steering device, it is necessary to take safety measures such as judging failures of various sensors and actuators and stopping the device.
The output of each sensor is detected, and failure diagnosis is performed.

With respect to the sensor, a failure can be determined based on the presence or absence of the output or deviation from the normal range. However, regarding the motor current detection circuit, which is one of the most important parts in the electric power steering device, there is a difference between the actual current flowing to the motor and the motor control circuit because the motor control circuit forms a feedback loop. Even if it occurs, it is very difficult to judge this as a failure. For this reason, not all operations processed by the output of the current detection circuit, that is, normal motor control and fail-safe related to the motor, are not established, which poses a serious safety problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric power steering apparatus that can solve the above-described problem and can reliably determine a failure in a motor current detection circuit.

Means for Solving the Problems An electric power steering apparatus according to the present invention includes an electric motor for assisting a steering force, a motor drive circuit thereof, a current detection circuit for detecting a current flowing through the motor, and a steering wheel. Target value calculating means for calculating a target value of the current of the motor based on the steering force to be supplied; and outputting a PWM signal to the motor drive circuit based on the target value of the current and the actually measured value of the current detected by the current detection circuit. An electric power steering apparatus comprising: a PWM conversion means; a first calculation means for obtaining a PWM duty by calculation independently from an actual measured value of a current from a target current value; A second calculating means for obtaining a PWM duty by calculation; and a current detecting circuit based on a difference between the PWM duty obtained by the two calculating means. In which and a fault diagnosis means for diagnosing the fault.

Preferably, the first calculating means calculates the PWM duty from the target value of the current, the measured value of the power supply voltage of the motor, and the measured value of the rotation speed of the motor.

If no failure has occurred in the current detection circuit of the motor, that is, if the actual current value flowing through the motor is equal to the actual measurement value of the motor current by the motor current detection circuit, the PWM duty obtained by the first arithmetic means and the second arithmetic means P required by
There is no difference from the WM duty.

If a failure occurs in the motor current detection circuit, that is, if there is a difference between the actual current value of the motor and the measured current value, the first
The PWM duty obtained by the calculating means is independent of the measured value of the current, and the PWM duty obtained by the second calculating means is based on the measured value of the current.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

The power steering apparatus includes a DC motor (1) for assisting a steering force, a motor drive circuit (2), a current detection circuit (3) for detecting a current flowing through the motor (1), and a steering force applied to a steering wheel ( Torque sensor (4) for detecting the torque), a vehicle speed sensor (5) for detecting the speed of the vehicle, and a motor drive circuit based on the outputs of the torque sensor (4), the vehicle speed sensor (5) and the current detection circuit (3). A control device (6) for controlling (2) is provided. The control device (6) is constituted by, for example, a microcomputer, and a target value calculating means (7) for calculating 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). A control element calculating means (8) for outputting a motor control signal based on the current target value and the actually measured value of the current detected by the current detection circuit (3);
Also provided is a PWM conversion means (9) for PWM-converting this control signal and outputting the PWM signal to the motor drive circuit (2). Since the configuration of the power steering apparatus so far is known, a general description is omitted.

The power steering device includes a power supply voltage sensor (10), a motor rotation speed sensor (11), a first calculating means (PWM duty calculating means) (12), Two calculation means (PWM duty calculation means) (13) and a failure diagnosis means (14) are added.

The power supply voltage sensor (10) detects a power supply voltage of the motor (1), that is, a battery voltage. The rotation speed sensor (11) detects the rotation speed of the motor (1).

Two operation means (12) (13) and failure diagnosis means (1
4) is provided in the control device (6). The first calculating means (12) is independent of the actual measured value of the current from characteristic elements such as the target current value, the power supply voltage and the rotation speed of the motor (1).
Calculate the PWM duty. The second calculating means (13) calculates the PWM duty from the target value of the current and the actually measured value of the current. This PWM duty is obtained through the control element calculation means (8). Failure diagnosis means (1
4) diagnoses a failure of the current detection circuit (3) based on the difference between the PWM duty calculated by the first calculating means (12) and the PWM duty calculated by the second calculating means (13). That is, when the difference is larger than a predetermined value, it is determined that a failure has occurred.

If no failure has occurred in the current detection circuit (3), that is, if the actual current value flowing through the motor (1) is equal to the actual measurement value of the motor current by the current detection circuit (3), the first calculation means (12) calculates the current. There is no difference between the calculated PWM duty and the PWM duty obtained by the second calculating means (13).

When a failure occurs in the current detection circuit (3), that is, when there is a difference between the actual current value of the motor (1) and the measured value of the current, the PWM duty obtained by the first calculating means (12) is determined by the actual measurement of the current. It is independent of the value, and the PWM duty obtained by the second calculating means (13) through the control element calculating means (8) is based on the actually measured value of the current, so that there is a difference between the two. For example, when the ratio between the actual current value of the motor (1) and the actual measured value of the current is increased due to the failure of the current detection circuit (3), that is, even though the actual current value of the motor (1) is constant, When the measured value of the current is smaller than before, the PWM duty calculated by the first calculating means (12) is obtained independently of the measured value of the current. ) Through the second
The PWM duty obtained by the calculating means (18) increases in order to increase the measured current value. Therefore, if there is a failure, the difference between the two becomes large, thereby making it possible to diagnose the failure.

Next, the calculation of the PWM duty will be described with reference to FIG. 2 and FIG.

FIG. 2 shows an approximation circuit of the DC motor (1). FIG. 3A shows a PWM signal, and FIG. 3B shows an armature current flowing through the motor (1). The motor inductance is L, the motor armature resistance is R, the voltage applied to the motor (1) is V, the power supply voltage of the motor (1), that is, the battery voltage is E, the armature current is i _e , and the back electromotive force coefficient is K. _ω , rotation angle θ, rotation speed ω, back electromotive force e
_ω (= _Kω × ω). Further, the time t, the PWM cycle T, and the area where the PWM signal is on during one cycle are A ₁ ,
The off-region is A ₂ , and the on-time, that is, the PWM duty is Δt.

In region A _1, the armature current is as follows.

Note that B = R / L, and I _e1 (0) is the armature current at time t = 0.

In region A _2, the armature current is as follows.

Note that I _e1 (Δt) is the armature current at time t = Δt.

Therefore, the average current I _a in the region A ₁ and A _2, the equation (1) and (2), as follows.

In general, the time constant L / R is assumed to be sufficiently larger than the PWM cycle, so that e- ^Bx ≒ 1 (4), and _Ia is as follows.

From Equation (5), the PWM duty Δt is as follows.

If the target current value I _M is equal to the motor armature current, equation (6) becomes as follows.

The first calculating means (12) calculates the PWM duty Δt according to equation (7). In equation (7), T, R and _Kω are constant and are known in advance. Therefore, E
From the power supply voltage sensor (10) and ω from the rotation speed sensor (1
1), by inputting each I _M from the target value computing unit (7) can be obtained Delta] t.

In the control device (6) of FIG. 1, if the control element of the control element calculation means (8) is PI (proportional integration), the PWM duty Δ1 is obtained as follows.

_{Δt = {K P (I M} -i e) + K 1 ∫ (1 M -i e) dt} T ...... (8) second calculating means (13) calculates a PWM duty Delta] t by the formula (8) . In equation (8), K _P is the control gain of the proportional element, K _I is the control gain of the integral element, and these are constant. Therefore, Δt can be obtained by inputting I _M from the target value calculation means (7) and i _e from the current detection circuit (3).

The failure diagnosis may be performed at regular intervals, or may be performed only at the start of the system in a simple system. Also, including the error due to approximation,
Effective enough.

Effects of the Invention According to the power steering device of the present invention, it is possible to reliably determine a failure in the motor current detection circuit as described above.

[Brief description of the drawings]

FIG. 1 is an electric block diagram of a main part 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 is a graph showing a PWM signal and a motor armature current. It is. (1) DC motor, (2) motor drive circuit, (3) current detection circuit, (7) target value calculation means, (9) PWM conversion means, (12) First calculation means (13) Second calculation means (14) Failure diagnosis means.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B62D 5/04 B62D 6/00

Claims (2)

(57) [Claims] 1. An electric motor for assisting a steering force, a motor drive circuit for the motor, a current detection circuit for detecting a current flowing through the motor, and a target value of a current of the motor based on a steering force applied to a steering wheel. Electric power steering, comprising: target value calculating means for calculating a current value; and PWM conversion means for outputting a PWM signal to a motor drive circuit based on the target value of the current and an actually measured value of the current detected by the current detection circuit. In the device, the calculation is performed independently from the actual value of the current from the target value of the current.
A first calculating means for obtaining a PWM duty; a second calculating means for obtaining a PWM duty by calculation from a target value of the current and an actually measured value of the current; and a second calculating means for obtaining the PWM duty.
An electric power steering apparatus comprising: a failure diagnosis unit that diagnoses a failure of a current detection circuit based on a difference in PWM duty. 2. The method according to claim 1, wherein the first calculating means calculates a target value of the current, a measured value of the power supply voltage of the motor and a measured value of the rotation speed of the motor.
The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus calculates a PWM duty.