JP2002255054A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering operability (steering feel) at the time of abnormality of a torque sensor. SOLUTION: A device calculates an alternate assist command current Ie* according to previously stored map data (Fig. 5) in an alternate assist control is this embodiment. In the map, though a so-called 'dead band' is set in the vicinity of an origin, the alternate assist command current Ie* is set approximately in proportion to a steering wheel angular velocity dθ. An upper limit is set for the alternate assist command current Ie* and in this map, a ratio β/α of a maximum of the alternate assist command current Ie* for a maximum value α an assist command current Ia* at the time of the normality is set to be approximately 1/5. By calculating the alternate assist command current Ie* according to the map and outputting it to a PI control unit, problems that the steering feel of heaviness is rapidly or excessively provided at the time of the abnormality or that steering cannot be easily done at the time of stationary steering or quick steering can be effectively solved or eased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor for applying an auxiliary torque to a steering mechanism of a vehicle, a torque sensor for detecting the magnitude and direction of a steering torque T applied to a steering wheel, and driving control of the motor. The present invention relates to an electric power steering device having a motor control device.

[0002]

2. Description of the Related Art In a conventional electric power steering apparatus, for example, an assist command current is determined in accordance with a steering torque T and a vehicle speed V, and a motor control device controls an actual motor current to match this assist command current. A device controlled by PI control or the like is generally known. As shown in FIG. 7, for example, when an abnormality in a torque sensor is detected, an alarm device is automatically activated to report the abnormality to a driver in a predetermined manner. At the same time, there is a device that stops the power supply to the motor and changes the steering system of the steering mechanism to a manual steering operation.

[0003]

[0005] However, in the case of full manual steering, even when abnormal, the steering feeling is heavy,
In particular, there is a problem that the steering is hard to be performed at the time of stationary steering or sudden steering. Further, the change of the steering method as described above must be performed instantaneously, and therefore, immediately after the change of the steering method to the full manual steering or the like, a great uncomfortable feeling occurs in the steering feeling. Therefore, a means that can alleviate such discomfort even slightly is expected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has as its object to be able to continue supplying any amount of assist torque for steering when the torque sensor is abnormal, and An object of the present invention is to realize an electric power steering apparatus with high operability, which can alleviate the above-mentioned uncomfortable feeling even slightly.

[0005]

Means for Solving the Problems, Functions and Effects of the Invention In order to solve the above-mentioned problems, the following means are effective. That is, the first means includes a motor for applying an assist torque to the steering mechanism of the vehicle to assist the steering, a torque sensor for detecting the magnitude and direction of the steering torque T applied to the steering wheel, and driving control of the motor. In an electric power steering device having a motor control device, an abnormality detecting means for detecting an abnormal state of the torque sensor, and automatic control switching means for switching at least a part of the drive control to an alternative control method when the abnormal state is detected. , Motor or steering wheel rotational angular velocity d
and alternative control execution means for executing an alternative control method based on θ.

As such an alternative control method, for example, a control method using the rotational angular velocity dθ of the steering wheel and its differential value (d ² θ) as input parameters is conceivable. In particular, when the measurement accuracy, response performance, and the like in the current sensing technology are taken into account, the former rotational angular velocity d
Although it is often advantageous to use θ, in general, according to the above-described first means of the present invention, by using these physical quantities as input parameters, appropriate or best assistance can be provided as an emergency alternative. It is possible to generate torque.

In addition, when the steering angle is large, or when the driver tries to return the steering wheel, a road surface reaction force (self-aligning torque) can be obtained. Often sufficient. That is,
According to the above-described first means of the present invention, as an emergency alternative means, it is possible to generate an auxiliary torque that is more than a certain level effective. Therefore, according to the first means of the present invention, when the torque sensor is abnormal, it is possible to continue to supply the assist torque for steering at all, and therefore, the electric power steering which can alleviate the above-mentioned uncomfortable feeling even slightly. The device can be realized.

The above abnormal state includes a recoverable temporary abnormal state. Accordingly, in such a case, the control may return to the original control method. The present invention is effective irrespective of whether or not such a normal return of the control method is performed.

The second means is a substitute control execution means of the first means, and calculates a torque value having an upper limit and substantially proportional to the rotational angular velocity dθ as the value of the auxiliary torque. That is. That is, this means is to determine the presence or absence of the driver's steering intention, the left-right direction, and the strength thereof from the rotational angular velocity dθ of the motor or the steering wheel. It is possible to generate and apply torque.

However, the value dθ is equal to or proportional to the value of the difference (change amount) of the rotation angle θ of the steering wheel during each detection cycle or between each control cycle of the predetermined control to be executed. And can be determined by a predetermined difference operation or a predetermined differential operation.

The upper limit of the value of the auxiliary torque is provided to prevent the steering wheel from being turned too much, or the rotational angular speed dθ is simply determined by the driver's intention of steering. This is because the ratio is not always proportional. It is desirable that the upper limit value be changed according to the vehicle speed for substantially the same reason as in the prior art. That is, the upper limit is set to be higher as the vehicle speed is lower.

A third means is that, in the second means, the torque value at the upper limit is set to be not more than 1/2 of the maximum value of the auxiliary torque in a normal state of the torque sensor. By setting such an upper limit value, it is possible to avoid a phenomenon (amplifying vicious cycle) in which the rotational speed of the steering wheel rises beyond the necessary limit in acceleration, so that the steering wheel is turned too much more than the steering intention. The undesirable phenomenon described above can be avoided.

The ratio of such an upper limit is preferably not more than 1/2 of the maximum value of the above-mentioned auxiliary torque in a normal state.
Although the value of this ratio somewhat depends on the type of vehicle mounted, the detailed specifications of each electric power steering device, or the target user group, it is more preferably 1/3.
The following is good. More preferably, a range of about 1/4 to 1/10 is considered as a tentative standard setting range. If this value is too large, the above-described vicious cycle may surface, which is not desirable. On the other hand, if this value is too small, the steering feeling will be hardly improved without being improved, and it will be difficult to alleviate the uncomfortable feeling. With the above means, the above-mentioned problem can be rationally solved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. However, the present invention is not limited to the embodiments described below. FIG. 1 is a schematic hardware configuration diagram illustrating a basic logical configuration of the electric power steering apparatus 100 according to the present embodiment. A controller 7 operating as a motor control device receives a vehicle speed signal from a vehicle speed sensor 6 and a torque signal relating to a steering torque T applied to a steering wheel 1 by a driver from a torque sensor 2 to detect these. The drive current of the motor 3 is controlled so that the assist torque corresponding to the value is output from the motor 3.

FIG. 2 is a control block diagram of the electric power steering apparatus 100 when the torque sensor is normal. The torque signal detected by the torque sensor 2 is input to a microcomputer (not shown) of the controller 7 in a digitized form via an interface (not shown) having an A / D converter. Thereafter, the torque signal is input to a phase compensator 70a realized by software executed by the microcomputer, where the phase compensation is performed, and then input to an assist command current setting unit 70b. The vehicle speed signal is also input to the assist command current setting unit 70b in substantially the same manner as in the related art.

FIG. 3 shows an electric power steering apparatus 10.
0 of the torque sensor during normal operation of the assist command current (Ia ^*)
6 is a graph illustrating a generation map of FIG. In the assist command current setting unit 70b, for example, as shown in FIG.
The assist command current Ia ^* (∝auxiliary torque) is calculated according to map data stored in advance.

In the PI control 70c of FIG. 2, the value of the assist command current Ia ^* calculated as described above is realized by the motor 3 based on the current value of the motor current Ir detected by the motor current detection circuit 72. as that performs feedback control (proportional-integral control), and outputs the command voltage V _n to the motor drive circuit 71. The PWM calculator 71a is
As input command voltage V _n is supplied to the motor 3,
That is, the motor drive circuit 7 is controlled so that the value of the assist command current Ia ^* calculated as described above is realized by the motor 3.
1 is electronically controlled by PWM control. As described above, when the torque sensor 2 operates normally, the motor 3 is electronically controlled as in the conventional case.

FIG. 4 is a flowchart illustrating a control processing procedure of the electric power steering apparatus 100 according to the present embodiment. Electric power steering apparatus 100 of the present embodiment
Is provided with a known or arbitrary appropriate "abnormality detecting means (not shown)" for detecting disconnection, short circuit, temporary noise, abnormal value fixing, and the like. In the processing step S01, the abnormality detecting means is provided. Based on the detection signal output by
It is determined whether or not the torque sensor 2 has an abnormality. Therefore, in the normal state where it is determined in S01 that "the torque sensor 2 operates normally", the motor 3 is electronically controlled in the same manner as in the related art according to the processing step S02 as described above.

(Control automatic switching means) However, S0
In the abnormal state where it is not determined that "the torque sensor 2 operates normally" by the step 1, the motor 3 is electronically controlled according to the processing steps S03 to S05 as follows, unlike the conventional case. That is, when the torque sensor 2 is abnormal, the control method of the motor 3 is changed as follows by S01 (automatic control switching means).

In the event of such an abnormality, first, in step S03, the assist control based on the steering torque T is stopped. In step S04, the driver is notified that an abnormality has occurred, and the process is periodically executed. Processing step S05
As a result, “alternative assist control” based on the vehicle speed V and the steering wheel angular speed dθ is performed.

(Alternative Control Executing Means) FIG. 5 is a generation map of the alternative assist command current (Ie ^* ) when the abnormality of the torque sensor of the electric power steering apparatus 100 of this embodiment is detected. Alternative assist control of this embodiment (S0 in FIG. 4)
In 5), for example, as shown in FIG. 5, the value of the alternative assist command current Ie ^* (∝auxiliary torque) is calculated according to the map data stored in advance. That is, the substitute assist command current Ie ^* corresponds (proportionally) to the value of the auxiliary torque that is substantially proportional to the rotational angular velocity dθ with an upper limit.

In this generation map, although a so-called "dead zone" is provided near the origin, the value of the alternative assist command current Ie ^* is set so as to be substantially proportional to the steering wheel angular velocity dθ. However, the alternative assist command current Ie
^* Has an upper limit, and this generation map (Fig. 5)
In the above, the ratio (β / α) of the maximum value β of the alternative assist command current Ie ^* to the maximum value α of the normal assist command current Ia ^* is set to about 約.

FIG. 6 is a control block diagram when an abnormality of the torque sensor of the electric power steering apparatus 100 in this embodiment is detected. In this control block diagram, the substitute control unit 70d is a control block that implements the above-described map (FIG. 5) for generating the substitute assist command current (Ie ^* ).
0d) corresponds to the central part for implementing step S05 in FIG. That is, when the abnormality of the torque sensor 2 is detected, the torque control of the motor 3 is executed according to the following processing procedure.

The controller 7 (FIG. 1) uses a terminal voltage detection circuit 73 provided in its own device to
Is detected. Controller 7
The motor angular velocity estimator 70e, which is realized by software on a microcomputer (not shown), estimates the angular velocity dΘ of the motor 3 based on the motor terminal voltage Vr and the motor current Ir.

A steering wheel angular velocity estimator 70f realized by software on a microcomputer (not shown) of the controller 7 has a reduction ratio of the reduction gear 4 (FIG. 1) and the motor 3 estimated by the motor angular velocity estimator 70e. The angular velocity dθ of the steering wheel (the steering wheel 1 in FIG. 1) is estimated based on the angular velocity dΘ.

The substitute control unit 70d inputs the angular velocity dθ of the steering wheel 1 and the vehicle speed V, and calculates the value of the substitute assist command current Ie ^* according to the map for generating the substitute assist command current (Ie ^* ) in FIG. And PI control 70c
Output to

The PI control 70c of FIG. 6 is the same as the PI control 70c of FIG.
Performs feedback control (proportional / integral control) so that the value of the alternative assist command current Ie ^* calculated as described above is realized by the motor 3 based on the current value of the detected motor current Ir. and outputs the command voltage V _n to the PWM calculator 71a of the motor drive circuit 71. When the abnormality of the torque sensor 2 is detected, the torque control of the motor 3 is executed in accordance with the above processing procedure.

For example, by introducing the above alternative control means, the problem that the steering feeling becomes sudden or very heavy at the time of abnormality, and that the steering becomes difficult especially at the time of stationary steering or sudden steering, etc., is an effect. Is resolved or alleviated. In addition, when the torque sensor is abnormal, the assist torque for steering can be continued to be supplied to some extent, so that the uncomfortable feeling immediately after the change of the steering method can be alleviated to a small extent. Can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic hardware configuration diagram illustrating a basic logical configuration of an electric power steering apparatus 100 according to an embodiment of the present invention.

FIG. 2 is a control block diagram of the electric power steering apparatus 100 when a torque sensor is normal.

FIG. 3 is an assist command current generation map when the torque sensor of the electric power steering apparatus 100 is normal.

FIG. 4 is a flowchart illustrating a control processing procedure of the electric power steering apparatus 100.

FIG. 5 is an assist command current generation map when an abnormality of the torque sensor of the electric power steering device 100 is detected.

FIG. 6 is a control block diagram when an abnormality is detected in a torque sensor of the electric power steering apparatus 100.

FIG. 7 is a flowchart illustrating a control processing procedure at the time of detecting an abnormality of a torque sensor according to the related art.

[Explanation of symbols]

 Reference Signs List 100 ... electric power steering device 1 ... steering wheel 2 ... torque sensor 3 ... electric motor 4 ... reduction gear 5 ... rack & pinion gear 6 ... vehicle speed sensor 7 ... controller (motor control device) 71 ... motor drive circuit

Claims (3)

[Claims] 1. A motor for applying an assisting torque to a steering mechanism of a vehicle to assist steering, a torque sensor for detecting a magnitude and a direction of a steering torque T applied to a steering wheel, and a motor control for driving and controlling the motor. An electric power steering apparatus having an apparatus, wherein abnormality detection means for detecting an abnormal state of the torque sensor; and automatic control switching for switching at least a part of the drive control to an alternative control method when the abnormal state is detected. Means, and an alternative control executing means for performing the alternative control method based on the rotational angular velocity dθ of the motor or the steering wheel. 2. The electric power steering system according to claim 1, wherein the alternative control execution means calculates a torque value having an upper limit and being substantially proportional to the rotational angular velocity dθ as the value of the auxiliary torque. apparatus. 3. The electric power steering apparatus according to claim 2, wherein the torque value at the upper limit is equal to or less than の of a maximum value of the auxiliary torque in a normal state of the torque sensor.