JP2002316654A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an erroneous fail determination operation occurred at starting of an engine in an electric power steering device that gives steering assist force to a steering mechanism using a motor as a drive source. SOLUTION: This device has a fail determination circuit 31 that stops driving of the motor 13 when an abnormal state of a vehicle is detected. The circuit 31 starts fail determination when the engine speed reaches a fixed number and on-state of the engine is detected.

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 apparatus for assisting steering by transmitting torque generated by an electric motor to a steering mechanism.

[0002]

2. Description of the Related Art An electric power steering apparatus that assists a driver in operating a steering wheel by transmitting an output torque generated by an electric motor to a steering mechanism has been used. In the electric power steering apparatus, a failure determination function for performing necessary processing (fail safe processing) such as stopping the steering assist when determining abnormality (fail) of various devices such as a computer is provided. .

Conventionally, the failure determination function has started the determination from the time when an ignition switch is turned on.

[0004]

For this reason, when the battery voltage is lowered at the time of cranking at the time of starting the engine, it is sometimes erroneously determined that the battery voltage has dropped due to deterioration of the battery. Also, by repeatedly turning on and off the ignition switch, the computer repeatedly reads the rising edge of the vehicle speed pulse. There was something to do.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electric power steering apparatus capable of preventing an erroneous fail determination operation that occurs when the engine is started.

[0006]

SUMMARY OF THE INVENTION An electric power steering apparatus according to the present invention comprises an engine state detecting means for detecting an on state of the engine based on whether or not the engine has reached a certain number of revolutions, and an abnormality of the vehicle. Failure detection means (31) for stopping the driving of the electric motor (13) if the state is detected, and the failure determination means detects when the engine state is detected by the engine state detection means, This is to start the fail judgment.

According to the above-described configuration, the on-state of the engine is detected based on the engine speed, and when the on-state of the engine is detected, the fail judgment is started. I can't. Therefore, a voltage drop that is not abnormal during cranking is not determined to be abnormal. Further, if an erroneous failure is determined due to a decrease in the battery voltage, a time lag occurs until the normal assist (steering assist) force is restored even when the voltage returns to normal, and the steering wheel becomes heavy during that time, but such an inconvenience is also eliminated. Further, if an erroneous fail determination is made due to the repeated turning on and off of the ignition switch, the assist force will not work properly until the engine returns to normal or the engine is restarted, but such inconveniences are avoided.

Further, the electric power steering apparatus of the present invention further includes a parking brake state detecting means for detecting a state of the parking brake, and the failure judging means detects the off state of the parking brake by the parking brake state detecting means. When it is detected, it is preferable to start the fail determination regardless of whether or not the engine ON state is detected. According to the first aspect of the invention, when the vehicle starts immediately after the engine is started, a fail determination cannot be made during the engine start determination. Therefore, in order to further enhance safety, when the parking brake off state is detected, the failure determination is started immediately.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a conceptual diagram showing a basic configuration of the electric power steering device. This electric power steering device is provided in association with a steering mechanism 1 of a vehicle, and is a device for applying a steering assist force. The steering mechanism 1 includes a steering wheel 2 operated by a driver, a steering shaft 3 connected to the steering wheel 2, a pinion 4 provided at the tip of the steering shaft 3, and a rack gear unit meshing with the pinion 4. 5a and a rack shaft 5 extending in the left-right direction (vehicle width direction) of the vehicle.

Tie rods 6 are respectively connected to both ends of the rack shaft 5, and the tie rods 6 are respectively connected to knuckle arms 7 that support front left and right wheels FL and FR as steering wheels. 8 indicates a kingpin. According to this configuration, when the steering wheel 2 is operated and the steering shaft 3 is rotated, the rotation is transmitted to the pinion 4.
And by the rack shaft 5, the motion is converted into a linear motion along the left-right direction of the vehicle. This linear motion is converted into rotation of the knuckle arm 7 around the king pin 8, whereby
The front left and right wheels FL and FR are steered.

The steering shaft 3 is divided into an input shaft 3A connected to the steering wheel 2 and an output shaft 3B connected to the pinion 4. The input shaft 3A and the output shaft 3B are connected by a torsion bar 9 that twists according to the direction and magnitude of the steering torque applied to the steering wheel 2. In connection with the torsion bar 9, a torque sensor 10 for detecting the direction and magnitude of the steering torque by detecting the relative angular displacement between the input shaft 3A and the output shaft 3B is arranged. Further, a steering angle sensor 11 that detects the turning angle of the steering mechanism by detecting the rotation angle of the output shaft 3B is provided in relation to the output shaft 3B.

An electric motor 13 is coupled to either the output shaft 3B or the rack shaft 5 via a speed reduction mechanism 12.
The torque generated by the electric motor 13 is reduced at a predetermined reduction ratio by the reduction mechanism 12 and transmitted to the steering mechanism 1 as a steering assist force. In connection with the electric motor 13, a motor drive circuit 30 for driving the electric motor 13 and a current detection circuit 14 for detecting a current (motor current) actually flowing through the electric motor 13 are provided.

The electric motor 13 is provided with an electronic control unit (E
CU) 20. The electronic control unit 20 determines a target current value of the electric motor 13 based on the steering torque T detected by the torque sensor 10, the turning angle θ detected by the steering angle sensor 11, and the like. The electric motor 13 is feedback-controlled so that the target current flows with reference to the signal. The electronic control unit 20 includes a target current value setting unit 22 that determines a target current value i according to the magnitude and direction of the steering torque T and the turning angle θ.

The target current value i is given to the subtraction section 28 as a target current value of the electric motor 13. The subtraction unit 28 calculates a deviation between the target current value i and the motor current I detected by the current detection circuit 14, and calculates the deviation from the motor control unit 29.
Give to. The motor control unit 29 performs PI (proportional integration)
A PI control unit for performing a control operation, a duty setting unit for determining a duty for PWM (pulse width modulation) control based on an output of the PI control unit, and a pulse width drive signal having a duty set by the duty setting unit And a pulse width control unit that generates

The motor drive circuit 30 is composed of a bridge circuit or the like that operates based on the pulse width drive signal. The motor drive circuit 30 is provided with a mechanism (for example, a relay contact) for turning off the drive of the electric motor based on the fail determination signal. FIG. 2 is a block diagram for explaining the function of the fail determination circuit 31 that outputs a fail determination signal to the motor drive circuit 30 when a failure state is detected.

The fail judging circuit 31 is constituted by a computer operated by software, and all or a part of its functions are realized by executing a program recorded on a recording medium such as a program ROM. . The fail determination circuit 31 receives an ignition key state signal (FIG. 2, A) and an engine ON signal (FIG. 2, C) from an engine control computer (not shown) in order to determine the start time of the failure determination. At the same time, a parking brake on / off signal (FIG. 2, B) is input.

The engine-on signal is a signal generated in the engine control computer when the detected rotation speed of the engine tachometer reaches a certain value. The "constant value"
If is set too small, the reading ability of the engine control computer cannot keep up, and the possibility of erroneous fail determination increases. If the value is set too large, fail determination cannot be performed even after normal rotation of the engine, which is dangerous. Therefore, a value slightly smaller than the idling rotation speed, for example, about 300 rotations / minute is set.

Further, the failure determination circuit 31 has an ECU abnormality signal as a criterion for performing a failure determination,
A vehicle speed signal, a battery voltage signal, and the like are input. Then, a fail determination signal for turning off the electric motor drive at the time of a failure is output from the fail determination circuit 31 to the motor drive circuit 30. FIG. 3 is a flowchart illustrating a fail-safe processing procedure performed by the fail determination circuit 31.

The fail determination circuit 31 confirms whether or not the ignition key has been turned on after the ACC (accessory) is turned on (step S).
1, S2). When the ignition is turned on, a determination is started as to whether an engine-on signal is input (step S3). The fail determination circuit 31 determines whether the parking switch has been turned off before the engine-on signal is input (step S4). If the parking switch is turned off, the process proceeds to step S7 to start a fail determination even if the engine is not turned on (step S8). This is because the vehicle may start before the engine starts normally, and in this case, it is dangerous if a fail determination cannot be made. Therefore, when the parking switch is turned off, the failure determination is started without waiting for the input of the engine-on signal.

If the parking switch has not been turned off (NO in step S4) and an engine-on signal has been input (step S5), the flow advances to step S7 to start a failure determination. If the failure determination is started, it is determined whether or not a failure state is established (step S8). If the failure state is established, a normal fail-safe process is performed (step S9). For example, the power supply voltage is monitored, and if the power supply voltage falls below a certain value, it is determined that an abnormal situation has occurred, and a fail determination signal is output to the motor drive circuit 30. When receiving an abnormal signal (for example, output during runaway) from the electronic control unit 20, the motor drive circuit 30
Outputs a fail determination signal.

As described above, the failure determination circuit 3
1 starts the fail determination when an engine-on signal is input (after the engine is started). Therefore, the failure determination is not started until the engine-on signal is input (except when the parking switch is turned off). As a result, for example, even if the battery drops due to cranking of the starter motor at the time of engine start, an erroneous fail determination is eliminated. Further, even if the ignition switch is repeatedly turned on, it is not necessary to determine that the vehicle speed has been input and to make a false erroneous determination.

Although the embodiment of the present invention has been described above, the embodiment of the present invention is not limited to the above-described embodiment, and various changes can be made within the scope of the present invention. is there.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic configuration of an electric power steering device of the present invention.

FIG. 2 is a block diagram for explaining a function of a fail determination circuit 31;

FIG. 3 is a flowchart for explaining a fail-safe processing procedure performed by a fail determination circuit 31;

[Explanation of symbols]

 Reference Signs List 1 steering mechanism 2 steering wheel 3 steering shaft 3A input shaft 3B output shaft 4 pinion 5 rack shaft 10 torque sensor 11 steering angle sensor 12 reduction mechanism 13 electric motor 14 current detection circuit 20 electronic control unit 22 target current value setting unit 28 subtraction unit 29 Motor control unit 30 Motor drive circuit 31 Fail judgment circuit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B62D 127: 00 B62D 127: 00 137: 00 137: 00 F term (Reference) 3D032 CC32 DA03 DA15 DA23 DA49 DA64 DA65 DA94 DB06 DC01 DC02 DC34 DD02 DD10 DD17 DE09 EA01 EB11 EC23 GG01 3D033 CA11 CA13 CA16 CA17 CA20 CA21 CA31

Claims (2)

[Claims] 1. An electric power steering apparatus for applying a steering assist force to a steering mechanism using an electric motor as a drive source, wherein an engine state detecting means detects an on state of the engine based on whether or not the engine has reached a certain number of revolutions. And, when an abnormal state of the vehicle is detected, it has a failure determination means for stopping the drive of the electric motor, the failure determination means, when the engine state detection means detects the ON state of the engine, An electric power steering apparatus for starting a fail determination. 2. A parking brake state detecting means for detecting a state of a parking brake, wherein the fail judging means detects an on state of the engine when the parking brake state detecting means detects an off state of the parking brake. 2. The electric power steering apparatus according to claim 1, wherein a fail determination is started regardless of the presence or absence of the power steering.