JP2007062500A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of steering feeling at generation of abnormality. <P>SOLUTION: The electric power steering device is provided with a torque sensor 5 for detecting steering torque; a vehicle speed sensor 6; a gear position sensor 7; and a controller 10. The controller 10 is provided with a transmission position detection part 24 for detecting a transmission position based on a signal from the gear position sensor 7; an abnormality detection part 23 for detecting abnormality of the device; a control vehicle speed setting part 25 for setting a control vehicle speed used for control when the abnormality is detected according to the transmission position; and a motor current target value setting part 22 for setting a motor current target value based on the steering torque and the vehicle speed. The motor current target value setting part 22 sets the motor current target value according to the vehicle speed detected by the vehicle speed sensor 6 when the abnormality does not occur and sets the motor current target value according to the control vehicle speed set by the control vehicle speed setting part 25 when the abnormality occurs. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that assists steering by transmitting power of an electric motor to a steering mechanism of a vehicle.

Conventionally, an electric power steering device that assists steering by driving an electric motor according to a steering torque applied to a steering wheel and transmitting a driving force generated by the electric motor to a steering mechanism of the vehicle is mounted on the vehicle. Has been used.
More specifically, the electric power steering apparatus is a controller (electronic control) that sets a current target value that is a target value of a current to be supplied to the electric motor based on a torque signal from the torque sensor and a vehicle speed signal from the vehicle speed sensor. Unit). For example, the controller sets a minute torque range as a dead zone and outputs a current target value that linearly changes from zero to a predetermined upper limit value within a certain torque range. For steering torque exceeding the upper limit value of the certain torque range, the upper limit current target value is output regardless of the steering torque. By setting the current target value in this way, a larger steering assist force is generated from the electric motor as the steering torque is larger.

  The slope of the linear fluctuation of the current target value with respect to the steering torque and the upper limit value of the current target value are changed according to the vehicle speed, and so-called vehicle speed sensitive control is performed. That is, during low speed travel (including the case where the vehicle speed is zero), a large current target value is set and a large steering assist force is generated from the electric motor. On the other hand, when traveling at high speed, a small current target value is set, and the steering assist force becomes relatively small. Thereby, good steering assistance can be performed while leaving an appropriate steering reaction force in any vehicle speed range.

More specifically, a basic assist characteristic that is a basic characteristic of a current target value with respect to the steering torque is created in advance for each of a plurality of vehicle speed ranges. The controller sets a target current value corresponding to the steering torque and the vehicle speed according to the basic assist characteristics for each vehicle speed range.
On the other hand, if a failure occurs in the vehicle speed sensor that detects vehicle speed information, or if a failure such as disconnection occurs in the signal line of the vehicle speed sensor, vehicle speed sensitive control cannot be performed appropriately. Therefore, the controller executes an abnormality monitoring process for detecting an abnormality such as a vehicle speed sensor signal. When an abnormality such as a vehicle speed sensor signal is detected, the electric motor is driven based on basic assist characteristics corresponding to a constant control vehicle speed (for example, 70 km / h) which is an intermediate vehicle speed. Yes.
JP-A-8-216901

However, in this prior art, when an abnormality such as a vehicle speed signal occurs, the electric motor is driven according to the basic assist characteristic corresponding to a constant control vehicle speed, so that the assist characteristic (steering assist characteristic) is improved compared to the normal state. An obvious change appears, which may cause a significant deterioration in steering feeling.
SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can suppress deterioration of steering feeling when an abnormality occurs.

  In order to achieve the above object, an invention according to claim 1 is an electric power steering device for assisting steering by transmitting the power of an electric motor (M) to a steering mechanism (3) of a vehicle, the electric power steering. Vehicle speed detection means (6) for detecting the vehicle speed of the vehicle on which the device is mounted, abnormality detection means (23) for detecting an abnormality occurring in the electric power steering device, and transmission of the vehicle on which the electric power steering device is mounted A transmission position detecting means (24) for detecting a position and a control vehicle speed used for control when an abnormality is detected by the abnormality detecting means are set according to the transmission position detected by the transmission position detecting means. An abnormality is detected by the control vehicle speed setting means (25) and the abnormality detection means. If not, a motor drive target value corresponding to the vehicle speed detected by the vehicle speed detection means is set. If an abnormality is detected by the abnormality detection means, a control vehicle speed set by the control vehicle speed setting means is set. Motor drive target value setting means (22) for setting the motor drive target value, and motor drive means (12 to 15) for driving the electric motor based on the motor drive target value set by the motor drive target value setting means And an electric power steering device. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.

According to this configuration, the transmission position of the vehicle is detected, and the control vehicle speed applied when an abnormality is detected is variably set based on the detected position. Thus, for example, even when an abnormality in the vehicle speed signal is detected, the assist control according to the vehicle speed can be performed to some extent, so that deterioration of the steering feeling when the abnormality occurs can be suppressed.
The transmission position detecting means may acquire a signal from a sensor (7) for detecting a gear position of a manual transmission type vehicle. The transmission position detection means may acquire internal data (representing the transmission position) used for transmission control purposes in an automatic transmission vehicle.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention, in which an example mounted on a manual transmission type vehicle is shown. A steering torque applied to the steering wheel 1 as an operation means is mechanically transmitted to the steering mechanism 3 via the steering shaft 2. A steering assist force from the electric motor M is transmitted to the steering mechanism 3 via a speed reduction mechanism (not shown) or by a direct drive system.

  The steering shaft 2 is divided into an input shaft 2A coupled to the steering wheel 1 side and an output shaft 2B coupled to the steering mechanism 3 side. The input shaft 2A and the output shaft 2B are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the steering torque, and the direction and amount of the twist are detected by the torque sensor 5.

For example, the torque sensor 5 is configured by a magnetic sensor that detects a magnetic resistance that changes in accordance with a change in the positional relationship between the input shaft 2A and the output shaft 2B in the rotational direction. The output signal of the torque sensor 5 is input to the controller 10 (ECU).
In addition to the output signal of the torque sensor 5, the controller 10 receives a vehicle speed signal output from the vehicle speed sensor 6 and a gear position signal generated by a gear position sensor 7 that detects the position of the shift lever. The controller 10 determines a current command value as a motor drive value according to the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6, and the steering assist force according to the steering torque and the vehicle speed is used as the steering mechanism. 3, the electric motor M is driven and controlled.

  The controller 10 includes a microcomputer 11, a PWM (Pulse Width Modulation) conversion circuit 12, a motor drive circuit 13, a motor current detection circuit 14 that detects a current value flowing through the electric motor M, and a deviation calculation circuit 15. ing. The microcomputer 11 calculates a current command value based on the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6, and gives it to the deviation calculation circuit 15. The deviation calculation circuit 15 obtains a deviation between the motor current value detected by the motor current detection circuit 14 and the current command value, and gives this deviation to the PWM conversion circuit 12. The PWM conversion circuit 12 generates a PWM drive signal having a pulse width corresponding to the deviation obtained by the deviation calculation circuit 15 and inputs the PWM drive signal to the motor drive circuit 13. The motor drive circuit 13 supplies a current corresponding to the PWM drive signal to the electric motor M. Then, the driving force generated by the electric motor M is transmitted to the steering mechanism 3 as a steering assist force.

The microcomputer 11 includes a CPU (Central Processing Unit) and a memory, and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include an assist characteristic storage unit 21, a motor current target value setting unit 22, an abnormality detection unit 23, a transmission position detection unit 24, and a control vehicle speed setting unit 25.
The assist characteristic storage unit 21 stores a basic assist characteristic (assist map) in which a motor current target value corresponding to the steering torque and the vehicle speed is determined in advance.

  The motor current target value setting unit 22 applies the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6 to the basic assist characteristics stored in the assist characteristic storage unit 21 as motor drive target values. Is obtained and output as a current command value. In addition, the motor current target value setting unit 22 performs a known compensation control calculation such as so-called inertia compensation control or damping control on the target value obtained from the basic assist characteristics to obtain the motor current target value. Also good.

  The abnormality detection unit 23 detects an abnormality (failure) that occurs in the electric power steering device, and notifies the control vehicle speed setting unit 25 and the motor current target value setting unit 22 of the presence or absence of the abnormality. The detected abnormality includes a vehicle speed signal abnormality input from the vehicle speed sensor 6. More specifically, the abnormality detection unit 23 monitors, for example, an engine rotation signal output from an engine rotation sensor (not shown), and the vehicle speed continues for a predetermined time or more although there is an engine rotation signal. When the signal indicates 0 km / h, it is determined that an abnormality such as disconnection has occurred.

The transmission position detection unit 24 detects the transmission position (mission selection information) based on the gear position signal from the gear position sensor 7 and notifies the control vehicle speed setting unit 25 of the detected transmission position.
When the control vehicle speed setting unit 25 receives an abnormality occurrence notification (particularly notification of vehicle speed signal abnormality) from the abnormality detection unit 23, the control vehicle speed setting unit 25 sets a control vehicle speed according to the transmission position detected by the transmission position detection unit 24. This control vehicle speed is vehicle speed data applied to set a motor current target value when an abnormality occurs (particularly when a vehicle speed signal abnormality occurs). For example, when the transmission position is “1st speed” or “reverse”, the control vehicle speed is 10 km / h, when the transmission position is “2nd speed”, the control vehicle speed is 40 km / h, and the transmission position is “3rd speed”. The control vehicle speed in the above case is 70 km / h.

  FIG. 2 is a diagram for explaining the operation of the motor current target value setting unit 22, and shows the relationship of the motor current target value Iobj with respect to the steering torque T. For the steering torque T, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The motor current target value Iobj is a positive value when a steering assist force for rightward steering is to be generated from the electric motor M, and a steering assist force for leftward steering is to be generated from the electric motor M. Sometimes it is negative.

The motor current target value Iobj takes a positive value for a positive value of the steering torque, and takes a negative value for a negative value of the steering torque. When the steering torque is a minute value in the range (torque dead zone) of -T1 to T1 (for example, T1 = 0.4 N · m), the motor current target value Iobj is set to zero.
Further, the absolute value of the motor current target value Iobj is set to be smaller as the vehicle speed V detected by the vehicle speed sensor 6 is higher. As a result, a large steering assist force can be generated during low-speed traveling, and the steering assist force can be reduced during high-speed traveling.

  The relationship of the motor current target value Iobj with respect to the steering torque T is stored in the assist characteristic storage unit 21 as basic assist characteristics. The assist characteristic storage unit 21 stores a plurality of basic assist characteristics respectively corresponding to a plurality of vehicle speed ranges. The plurality of basic assist characteristics may be stored in the assist characteristic storage unit 21 in the form of a map for the steering torque T and the vehicle speed V.

  When an abnormality (particularly vehicle speed signal abnormality) is detected by the abnormality detection unit 23, the motor current target value setting unit 22 is not the vehicle speed V detected by the vehicle speed sensor 6, but the control vehicle speed set by the control vehicle speed setting unit 25. Is regarded as the vehicle speed, and the motor current target value is set. On the other hand, since the control vehicle speed is variably set according to the transmission position, the basic assist characteristic according to the transmission position is selected and used for setting the motor current target value.

Thus, according to this embodiment, when an abnormality occurs, the control vehicle speed is variably set according to the transmission position, so that the assist control according to the vehicle speed can be continued to some extent. Thereby, even when an abnormality occurs, it is possible to avoid that the steering feeling is significantly deteriorated.
FIG. 3 is a flowchart summarizing the operation of the motor current target value setting unit 22 and the like. If it is determined that there is no abnormality as a result of the abnormality detection process (step S1) by the abnormality detection unit 23 (NO in step S2), the vehicle speed V read from the vehicle speed sensor 6 is used as vehicle speed data for setting the motor current target value. (Step S3).

  On the other hand, if it is determined that there is an abnormality (YES in step S2), according to the transmission position detected by the transmission position detection unit 24 (step S4), the control vehicle speed is 10km / h (step S5. 1st speed or reverse), 40 km / h (step S6, second speed) or 70 km / h (step S7, third speed or higher) is used as vehicle speed data for setting the motor current target value.

  Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms. For example, in the above-described embodiment, an example in which the present invention is applied to a manual transmission vehicle has been described, but the present invention can also be applied to an automatic transmission vehicle. In this case, transmission position data used as internal data for transmission control may be taken into the electric power steering control electronic control unit (controller 10) and used to variably set the control vehicle speed when an abnormality occurs.

In the above-described embodiment, the motor current target value is used as the motor drive target value for controlling the electric motor M, but the motor voltage target value and the assist torque target value that is the target value of the steering assist force are used as the motor. It may be used as a drive target value.
In addition, various design changes can be made within the scope of matters described in the claims.

1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a figure for demonstrating a basic assist characteristic. It is a flowchart for demonstrating the variable setting of the control vehicle speed at the time of abnormality.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 5 ... Torque sensor, 10 ... Controller, 11 ... Microcomputer

Claims (1)

An electric power steering device for assisting steering by transmitting power of an electric motor to a steering mechanism of a vehicle,
Vehicle speed detection means for detecting the vehicle speed of the vehicle on which the electric power steering device is mounted;
An abnormality detecting means for detecting an abnormality occurring in the electric power steering device;
Transmission position detecting means for detecting a transmission position of a vehicle in which the electric power steering device is mounted;
Control vehicle speed setting means for setting a control vehicle speed used for control when an abnormality is detected by the abnormality detection means according to a transmission position detected by the transmission position detection means;
When no abnormality is detected by the abnormality detection means, a motor drive target value is set according to the vehicle speed detected by the vehicle speed detection means, and when an abnormality is detected by the abnormality detection means, the control vehicle speed setting means Motor drive target value setting means for setting a motor drive target value according to the set control vehicle speed;
An electric power steering apparatus comprising: motor drive means for driving the electric motor based on a motor drive target value set by the motor drive target value setting means.

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