JP2003320950A - Electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric steering apparatus for improving steering feeling. <P>SOLUTION: In the electric power steering apparatus, failure in a vehicle speed sensor is detected by a step S103. When the failure in the vehicle speed sensor is detected (Yes in S105), a control vehicle speed is set by a step S111 so that a vehicle speed changes from a detection vehicle speed immediately before failure by the vehicle speed sensor to a preset 300 km/h at an acceleration of 1 G. Then, a detection speed used for an assist torque determination means is substituted with the control vehicle speed concerned by a step S115. As a result, even if the vehicle speed sensor fails, assist torque is determined by a control map based on the control vehicle speed instead of the detection vehicle speed due to the vehicle speed sensor, thus improving steering feeling. <P>COPYRIGHT: (C)2004,JPO

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 system.

[0002]

2. Description of the Related Art A motor for generating an assist torque for compensating a steering force, a torque sensor for detecting a steering torque, a vehicle speed sensor for detecting a vehicle speed, and an assist torque determined by the detected torque detected by the torque sensor. An electric power steering apparatus including a control map for each detected vehicle speed detected by the vehicle speed sensor, and an assist torque determining means for determining the assist torque by the control map based on the detected torque and the detected vehicle speed, for example, , JP 1-
There is an "electric power steering controller" disclosed in Japanese Patent No. 215667.

In the "electric power steering control device" according to this publication, a vehicle speed detector (vehicle speed sensor) is provided.
When a vehicle speed detector fails, a steering torque detector (torque sensor) is provided by providing switching means for switching the control of the steering assist force (assist force) by the variable control map (control map) to the fixed control map in the event of an abnormality in the vehicle. ), The output steering assist force from the electric motor (motor) is small when the steering torque is small, and control is possible with variable characteristics that increase as the steering torque increases.

[0004]

However, according to the "electric power steering control device" according to the patent publication, the drive current value given to the electric motor for generating the steering assist force is generated when the vehicle speed detector is abnormal. The variable control map is controlled to shift to the fixed control map by changing the variable control map according to a predetermined arithmetic process. Therefore, since the drive current applied to the electric motor is directly controlled during the transition due to such arithmetic processing, even if the steering torque fluctuates during the transition, the transition control has priority and the steering assist force by the electric motor is given. Cannot be handled flexibly. That is, there is a problem that the steering feeling may be uncomfortable during the transition from the variable control map to the fixed control map.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electric power steering apparatus capable of improving steering feeling.

[0006]

[Means for Solving the Problems and Actions and Effects of the Invention]
In order to achieve the above object, in the electric power steering apparatus according to claim 1, a motor that generates an assist torque that supplements the steering force, a torque sensor that detects the steering torque, a vehicle speed sensor that detects the vehicle speed, and A control map for determining the assist torque with respect to the detected torque detected by the torque sensor is provided for each detected vehicle speed detected by the vehicle speed sensor, and the assist torque is determined by the control map based on the detected torque and the detected vehicle speed. An electric power steering apparatus including: an assist torque determining unit that determines an abnormality of the vehicle speed sensor by the vehicle speed sensor abnormality detecting unit that detects an abnormality of the vehicle speed sensor, and an abnormality of the vehicle speed sensor by the vehicle speed sensor abnormality detecting unit. When detected, the vehicle speed sensor detects a predetermined increase in speed from the vehicle speed immediately before the abnormality detected toward the predetermined vehicle speed. When a vehicle speed sensor abnormality is detected by the vehicle speed sensor abnormality detecting means and the vehicle speed sensor abnormality detecting means, the control vehicle speed setting means sets the detection speed used for the assist torque determining means. And a vehicle speed replacing means for replacing the control vehicle speed set by the means.

According to the first aspect of the invention, the vehicle speed sensor abnormality detecting means detects the abnormality of the vehicle speed sensor, and when the abnormality of the vehicle speed sensor is detected, the control vehicle speed setting means detects in advance from the vehicle speed detected immediately before the abnormality by the vehicle speed sensor. The control vehicle speed is set so as to change at a predetermined acceleration toward the set predetermined vehicle speed, and the vehicle speed replacing means replaces the detected speed used by the assist torque determining means with the control vehicle speed. That is, when an abnormality of the vehicle speed sensor is detected, the assist torque determination means is set to the control vehicle speed set to change at a predetermined acceleration from the vehicle speed immediately before the abnormality detected by the vehicle speed sensor to the predetermined vehicle speed set in advance. Replaces the detection speed used. As a result, even if an abnormality occurs in the vehicle speed sensor, instead of the vehicle speed detected by the vehicle speed sensor, “the vehicle speed sensor is set to transition from the detected vehicle speed immediately before the abnormality to the predetermined vehicle speed at a predetermined acceleration. Since the assist torque is determined based on the control map based on "control vehicle speed" (assist torque determining means), the motor current for driving the motor is not directly controlled even during the transition. Therefore, even if the detected torque fluctuates during the transition, the output of the assist torque from the motor can be flexibly made to correspond to the torque fluctuation, so that the steering feeling is not uncomfortable. Therefore, the steering feeling can be improved.

Further, in the electric power steering apparatus according to a second aspect of the present invention, in the control map according to the first aspect, in which the assist torque is determined with respect to the predetermined vehicle speed, the assist torque is set as the detected torque increases. Increase,
A technical feature is that the assist torque is set to a characteristic that decreases as the detected torque decreases.

According to the second aspect of the present invention, the control map is set to have a characteristic of increasing the assist torque as the detected torque increases and decreasing the assist torque as the detected torque decreases. Is detected and when the vehicle speed changes to a predetermined vehicle speed at a predetermined acceleration, the control map of the characteristic is shifted to. This allows
When the detected torque is large, for example, the assist torque increases in steering at a slow speed or when the vehicle is stopped, etc., so that the driver can easily perform steering, and when the detected torque is small, for example, in steering during lane change, etc. Since the assist torque is reduced, steering stability can be improved. Therefore,
Even if an abnormality occurs in the vehicle speed sensor, the steering feeling can be improved as described above without impairing the steering feeling.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an electric power steering apparatus of the present invention will be described below with reference to the drawings. In the following embodiments, an electric power steering apparatus provided in a vehicle such as an automobile will be described as an example of the electric power steering apparatus of the present invention.

First, the main electrical construction of the electric power steering apparatus will be described with reference to FIG. The electric power steering apparatus according to the present embodiment mainly includes the ECU 10 and the torque sensor 1.
1, a vehicle speed sensor 12, a motor M and the like.

The ECU 10 mainly uses the interface 1
4, a CPU 15, a motor drive circuit 16, and the like, based on the detected torque, the detected vehicle speed, etc. input from the torque sensor 11 and the vehicle speed sensor 12, as will be described later with reference to FIG. The motor M is controlled so that the motor M generates an assist torque that supplements the steering force. It should be noted that the CPU 15 has a semiconductor memory device (not shown) such as ROM and RAM built therein, and each control process described below is performed by the CPU 15 executing a predetermined control program stored in the semiconductor memory device. Will be realized.

The torque sensor 11 detects the torque generated between the input shaft and the output shaft. In this electric power steering device, the steering torque (detection torque) is calculated from the twist amount of a torsion bar or the like that relatively rotatably connects the input shaft connected to the steering wheel of the vehicle and the output shaft connected to the steering mechanism. It is detecting. The detected torque detected is input to the interface 14 of the ECU 10.

The vehicle speed sensor 12 detects the speed of the vehicle, and the detected vehicle speed thus detected is also input to the interface 14 of the ECU 10.

With such a configuration, the ECU
The CPU 15 constituting 10 performs a calculation for determining the current command value to be sent to the motor drive circuit 16 based on the detected torque and the detected vehicle speed input via the interface 14. Then, in the motor drive circuit 16, C
The drive current corresponding to the current command value sent from the PU 15 is output to the motor M. As a result, the motor M generates an assist torque for assisting the steering force or a torque for restoring the steering wheel.

Next, main electrical functional configurations and operations of the ECU 10 and the motor drive circuit 16 will be described with reference to FIG. As shown in FIG. 2, the ECU 10 and the motor drive circuit 16 mainly include a filter circuit 20, a phase compensation unit 21, an assist torque determination unit 22, a current command determination unit 23, a PWM circuit 25, and a motor current detection unit 2.
6, vehicle speed pulse detecting means 27, vehicle speed replacing means 28 and adding means 29.

As described above, the detected torque detected by the torque sensor 11 has the noise component removed by the filter circuit 20, and the phase compensation means 21 has advanced the phase in order to speed up the response to the torque sensor output. After that, it is input to the assist torque determination means 22. On the other hand, the detected speed detected by the vehicle speed sensor 12 is input to the vehicle speed replacing means 28 via the vehicle speed pulse detecting means 27. In the vehicle speed replacing means 28, the detected vehicle speed is replaced with the control vehicle speed by the vehicle speed replacing processing as will be described later, and the control vehicle speed concerned is the assist torque determining means 22.
Is output to.

In the assist torque determining means 22, based on the detected torque phase-compensated by the phase compensating means 21 and the control vehicle speed replaced by the vehicle speed replacing means 28,
A current value corresponding to the assist torque generated in the motor M to assist the steering force is determined. That is, as shown in FIG. 3, a control map for determining the assist torque with respect to the detected torque (steering torque) detected by the torque sensor 11 is set for each control vehicle speed (for example, 3 km / h in the example of FIG. 3,
20km / h, 60km / h, 100km / h, 180km / h, 300
6 types (km / h) are stored in the semiconductor memory device of the CPU 15, a control map suitable for the control vehicle speed is selected from these, and the assist torque for the detected torque is calculated from the selected control map. decide.

However, the control vehicle speed is 3 km / h, 20 km / h, 6
When it does not correspond to 0 km / h, 100 km / h, 180 km / h, the assist torque for the control vehicle speed is determined by performing linear interpolation calculation using the upper and lower control maps close to the control vehicle speed. Specifically, for example, when the control vehicle speed is 30 km / h, the control map of 60 km / h on the upper side close to this 30 km / h and the control of 20 km / h on the lower side close to 30 km / h of the control vehicle speed. Performs linear interpolation calculation with the map. Therefore, the assist torque required in this case is 2
The sum of the value obtained by multiplying the assist torque by the control map of 0 km / h by 0.25 and the value obtained by multiplying the assist torque by the control map of 60 km / h by 0.75. The assist torque thus determined is output to the current command determination means 23.

When the current command determining means 23 determines the current command value to be sent to the motor M based on the assist torque determined by the assist torque determining means 22, it outputs the current command value to the amplifying means 24. As a result, the current command value is amplified by the amplifying means 24 with a predetermined gain, and then converted into a pulse signal having a pulse width corresponding to the current command value by the PWM circuit 25 and output to the motor M. On the other hand, since the motor current flowing through the motor M is detected by the motor current detecting means 26, it is fed back to the adding means 29 provided in the preceding stage of the amplifying means 24.
The newly given motor current can be feedback-controlled so that the current command value and the detected value of the motor current match.

Now, the vehicle speed replacing process by the vehicle speed replacing means 28 will be described with reference to FIGS. 3 and 4. The vehicle speed replacement process is periodically performed by the CPU 15 executing a predetermined control program stored in the semiconductor memory device of the CPU 15 every 10 milliseconds by a predetermined timer interrupt or the like.

As shown in FIG. 4, in the vehicle speed replacing process, after a predetermined initialization process, a process of acquiring the detected vehicle speed is first performed in step S101. That is, as described above, the detected speed detected by the vehicle speed sensor 12 is input to the vehicle speed replacing means 28 via the vehicle speed pulse detecting means 27, and therefore a process for acquiring this is performed.

In step S103, step S101
Based on the detected vehicle speed acquired by, the determination processing of whether or not the vehicle speed sensor 12 has failed is performed. This fail determination process is performed, for example, by determining whether or not the difference between the vehicle speed detected last time (10 milliseconds before) and the vehicle speed detected this time exceeds a predetermined reference value that can change in 10 milliseconds. Be seen. If the amount of change in the detected vehicle speed does not exceed the predetermined reference value, it is not recognized that an abnormality has occurred in the vehicle speed sensor 12, and therefore the fail determination processing in step S105 is performed (N in S105).
o), the process proceeds to step S107, and processing for setting the current detected vehicle speed to the control vehicle speed is performed.

On the other hand, when the amount of change in the detected vehicle speed exceeds the predetermined reference value, it is recognized that an abnormality has occurred in the vehicle speed sensor 12, and therefore the fail determination processing in step S105 is performed (in step S105). Yes), the process proceeds to step S109, and the process of setting the control vehicle speed to a predetermined vehicle speed set in advance is performed.

That is, when an abnormality of the vehicle speed sensor 12 is detected in step S103, the control vehicle speed is changed from the vehicle speed detected immediately before the abnormality by the vehicle speed sensor 12 to a predetermined vehicle speed set in advance at a predetermined acceleration. The process of setting is performed by steps S109, S111, and S113.

Specifically, first, in step S109, the control vehicle speed is 300 which is a preset predetermined vehicle speed.
Determine whether it is set to km / h or higher. In the present embodiment, the predetermined vehicle speed is set to 300 km / h, but this is set by setting a vehicle speed of 300 km / h that is not detected by the vehicle speed sensor 12 during normal road surface traveling.
The special control vehicle speed is set only when the vehicle speed sensor 12 is abnormal.

At step S109, the control vehicle speed is 300.
If you cannot determine that the speed is set to more than km / h (S
No in 109), and in step S111, immediately before the occurrence of the abnormality, that is, 300 km from the previously detected vehicle speed 10 milliseconds ago.
A process for setting the control vehicle speed so that the acceleration shifts to 1 / h toward 1 / h is performed. In the case of the present embodiment, this vehicle speed replacement processing is executed every 10 milliseconds by a predetermined timer interrupt or the like, so that the control vehicle speed is accelerated by about 0.35 km / h each time step S111 is executed. When set to, acceleration of 1G can be realized. That is, in step S111, control vehicle speed = control vehicle speed +
Performs arithmetic processing of 0.35 km / h.

On the other hand, if it can be determined in step S109 that the control vehicle speed is set to 300 km / h or higher (Yes in S109), the control vehicle speed is set to 300 km / h in step S113.

In this way, steps S107, S111,
When the control vehicle speed is set in S113, the control vehicle speed set in the subsequent step S115 is replaced with the detected vehicle speed, and the replaced control vehicle speed is sent to the assist torque determining means in step S117. This completes a series of main vehicle speed replacement processing.

As a result, the detected vehicle speed detected by the vehicle speed sensor 12 is not passed to the assist torque determining means 22 as it is, but the detected vehicle speed is replaced with the control vehicle speed and is sent to the assist torque determining means 22. At 22, as described above, the process of selecting the control map and determining the assist torque can be performed based on the control vehicle speed.

That is, step S103 of the vehicle speed replacing process.
When the abnormality of the vehicle speed sensor 12 is detected by, the control vehicle speed is set in steps S111 and S113 so that the detected vehicle speed immediately before the abnormality moves to a preset 300 km / h at a predetermined acceleration of 1 G, and the step S113 is performed. Thus, the detected speed used in the assist torque determination means 22 is replaced with the control vehicle speed. As a result, the assist torque determining means 22 has a special control vehicle speed 30 that is not normally used in the control map shown in FIG.
The assist torque corresponding to the detected torque (steering torque) is determined using the control map (characteristic curve by the thick line shown in FIG. 3) corresponding to 0 km / h.

As a result, even when the control map of 300 km / h is shifted, the assist torque is determined by the control map, so that the motor current for driving the motor M should be directly controlled even during the shift. There is no.
Therefore, even if the detected torque fluctuates during the transition,
Since the output of the assist torque from the motor M can flexibly respond to the torque fluctuation, the steering feeling does not feel uncomfortable. Therefore, the steering feeling can be improved.

Further, as shown in FIG. 3, the vehicle speed sensor 12
3km / h, 20km / h, 60km / h, 100km, which is usually used as a control map (300km / h) that relates the vehicle speed to the control map used during abnormalities
/ h, 180km / h control map provided,
For example, even if the vehicle speed sensor 12 breaks down while driving at 60 km / h, the 60 km / h control map to the 100 km / h control map, the 180 km / h control map, and the 300 km
It is possible to shift to a control map of 300 km / h by making a transition at a predetermined acceleration (for example, 1 G) as described above while performing a linear interpolation calculation that is normally performed between maps such as a control map of / h.

Therefore, when a control map which is not associated with the vehicle speed is used, during the transition to the control map, the assist torque obtained by the control map and the assist torque for the vehicle speed immediately before the failure are interpolated. Since the calculation needs to be performed separately from the normal map calculation, such a calculation process is required separately, and there is a problem that the processing load of the CPU 15 due to the calculation increases.

On the other hand, in the vehicle speed replacing process by the electric power steering apparatus according to the present embodiment, as described above, the control map used when the vehicle speed sensor 12 is in an abnormal state is associated with the vehicle speed, so that it is normally used. It is possible to obtain the assist torque between 180 km / h and 300 km / h by directly using the interpolation calculation that is performed. Therefore, as compared with the case of using a control map that is not associated with the vehicle speed, C
The processing load on the PU 15 can be reduced.

Further, the control map corresponding to the 300 km / h is set to have a characteristic that the assist torque increases as the detected torque increases and the assist torque decreases as the detected torque decreases.
Detects an abnormality of the vehicle speed sensor 12 and
By shifting to the control map of No. 3, the driver can obtain the following steering feeling. (1) When the detected torque is large, for example, the assist torque increases during steering at a slow speed or when the vehicle is stopped, etc.
The steering feeling, which is usually heavy, can be reduced. (2) When the detected torque is small or medium, the assist torque decreases in steering, for example, in a lane change, so that the steering feeling can be made heavy and the steering stability can be improved. Therefore, even if an abnormality occurs in the vehicle speed sensor 12, the steering feeling can be improved as described above without impairing the steering feeling.

In the above-described embodiment, the vehicle speed detected by the vehicle speed sensor 12 is set to 30 which is preset from the vehicle speed immediately before the abnormality.
1 as "predetermined acceleration" that changes toward 0 km / h
Although G is set, the acceleration may be such that the change in the steering force does not feel unnatural, for example, the acceleration that shifts to the control map of 300 km / h in about 2 seconds may be 4.3 G or less. As a result, similar to the above, improvement in steering feeling can be expected.

Further, in the above-described embodiment, the control map used when the vehicle speed sensor 12 is abnormal is 300 km.
Although one control map of / h was set, a plurality of control maps (for example, 200km / h, 240km / h, etc.) are set before the control map of 180km / h is changed to the control map of 300km / h.
h, 260 km / h, 280 km / h, etc.) may be set. Accordingly, during the transition from the 180 km / h control map to the 300 km / h control map, the correspondence of the assist torque to the detected torque can be set more finely, so that the steering feeling during the transition is further improved. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main electrical configuration of an electric power steering apparatus according to an embodiment of the present invention.

FIG. 2 is an ECU of the electric power steering apparatus according to the present embodiment.
It is a block diagram which shows the main electric constitutions of a motor drive circuit.

FIG. 3 is an explanatory diagram showing an example of a control map used in the assist torque determination means shown in FIG.

FIG. 4 is a flowchart showing a flow of vehicle speed replacement processing by the vehicle speed replacement means shown in FIG.

[Explanation of symbols]

10 ECU 11 Torque sensor 12 Vehicle speed sensor 15 CPU (vehicle speed sensor abnormality detecting means, control vehicle speed setting means, vehicle speed replacing means) 22 Assist torque determining means 28 Vehicle speed replacing means M Motor S103 (vehicle speed sensor abnormality detecting means) S111 (control vehicle speed setting) Means) S113 (control vehicle speed setting means) S115 (vehicle speed replacing means)

Claims (2)

[Claims] 1. A motor for generating an assist torque for compensating a steering force, a torque sensor for detecting a steering torque, a vehicle speed sensor for detecting a vehicle speed, and the assist torque for the detected torque detected by the torque sensor. An electric system that includes a control map to be determined for each vehicle speed detected by the vehicle speed sensor, and an assist torque determining unit that determines the assist torque by the control map based on the detected torque and the detected vehicle speed. A power steering apparatus, wherein a vehicle speed sensor abnormality detecting means for detecting an abnormality of the vehicle speed sensor, and when the vehicle speed sensor abnormality detecting means detects an abnormality of the vehicle speed sensor, the vehicle speed immediately before the abnormality by the vehicle speed sensor is detected. From the control vehicle, the control vehicle speed is set so that the control vehicle speed changes at a predetermined acceleration toward a predetermined vehicle speed set in advance. Setting means, and a vehicle speed replacing means for replacing the detected speed used by the assist torque determining means with the control vehicle speed set by the control vehicle speed setting means when the vehicle speed sensor abnormality detecting means detects an abnormality in the vehicle speed sensor. An electric power steering device comprising: 2. The control map in which the assist torque is determined with respect to the predetermined vehicle speed has a characteristic that the assist torque is increased as the detected torque increases and the assist torque is decreased as the detected torque decreases. It is set to 1.
The electric power steering device described.