JPH10278827A - Return control device for electric power steering - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a return control device for an electric power steering that can reduce a sense of incongruity that occurs when performing return control and can eliminate insufficient return of a steering wheel. An electric motor that drives an assist motor to add an assist torque to a steering torque based on an assist command value determined by an output of a torque sensor for detecting a steering torque of a steering wheel and an output of a vehicle speed sensor. In the power steering system, when the rotation direction of the assist motor 40 is different from the input direction of the steering torque, the polarity determination unit 53 determines that the steering wheel is in the return state, and adds the return command value to the assist command value. The device has a low-pass filter 6
1, an output value from the low-pass filter 61 and a return command value are input, and the output is added to the assist command value.
A shaping means 60 comprising an operator 62 is provided.

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 in which, when a steering wheel of an automobile is operated, an assist torque is added to the steering torque to improve the operability. About.

[0002]

2. Description of the Related Art Various types of electric power steering systems for automobiles have been conventionally proposed. Among them, as shown in FIG. 5, an output of a torque sensor for detecting a steering torque of a steering wheel and an automobile are disclosed. A predetermined assist command value (current command value) determined by an output of a vehicle speed sensor that detects the vehicle speed of the vehicle drives an assist motor via a drive circuit to add the assist torque to the steering torque, thereby improving the operability of the steering wheel. There is a method of improving the quality.

In such an electric power steering system, a return control device shown in FIG. 5 has also been developed as a return control device for improving the characteristics when the cut-in steering wheel is returned in the reverse direction, that is, the return property of the steering wheel. ing. That is, for example, when the rotation direction of the assist motor obtained from the motor rotation speed estimated and calculated from the current detection value of the assist motor and the terminal voltage of the motor is different from the input direction of the steering torque obtained from the torque sensor. The return of the steering wheel is improved by determining that the steering wheel is in the return state by the polarity determination means and adding the return command value determined from the vehicle speed of the vehicle to the assist command value.

However, the region in which the return control is desired to be performed is limited to a specific region of the steering torque and the motor rotation speed, whereas the above-mentioned conventional return control device of the electric power steering is not necessary. Since the return control is also performed in the area, there is a problem that the following steering feeling is uncomfortable. That is,

First, as shown in FIG. 6, when the steering torque is sufficiently large, that is, when the output of the torque sensor is larger than necessary, a return command value is output to effect return control. A slight steering back of the steering wheel (when the steering wheel is not largely steered in a straight line or the like) causes a phenomenon that a so-called steering wheel is removed.

As shown in FIG. 7, when the steering torque is extremely small, that is, when the output of the torque sensor is a very small value, the error of the torque sensor has a great effect on the output value. It becomes difficult, and the output direction of the return command value is mistakenly controlled in the reverse direction,
Alternatively, a malfunction such as overshoot may be performed.

[0007] Similarly, as shown in FIG. 7, the estimated motor rotation speed estimated value includes an error, and the error has a large effect at a low speed rotation. When the estimated value is low, the error makes it difficult to determine by the polarity determining means,
There is a case where the output direction of the return command value is erroneously returned to the reverse direction to perform the control.

Further, as shown in FIG. 8, when the return of the steering wheel is sufficiently fast, that is, when the estimated motor speed is high, a return command value more than necessary is output and the return control becomes too effective, so that the steering wheel May return too much and overshoot.

Therefore, in order to solve these problems,
The present inventors have intensively researched and developed various kinds of limiters such as a torque sensitive limiter and a motor speed sensitive limiter as shown in FIG. 9 and take out a return command value only in a necessary area and add it to an assist command value. By doing so, a return control device has been devised that reduces various discomforts that occur when performing the return control.

That is, a torque upper limiter and a torque lower limiter are respectively provided as torque sensitive limiters. In the case of FIG. 6, when the output value of the torque sensor is equal to or more than a predetermined value by the torque upper limiter, a return command value is set. The output is not output to prevent the so-called steering wheel from being removed by a slight turning back of the steering wheel during snake keeping. In the case of FIG. 7, the output value of the torque sensor is set to a predetermined value by the torque lower limiter. When the value is equal to or less than the value, the return command value is not output, so that the influence of the error of the torque sensor is eliminated and the malfunction of the return control is prevented.

On the other hand, as a motor speed-sensitive limiter,
A motor rotation speed lower limiter and a motor rotation speed upper limiter are provided. In the case of FIG. 7, the motor rotation speed lower limiter does not output a return command value when the rotation speed of the assist motor is lower than a predetermined value. In this case, the return control value is not output when the rotation speed of the assist motor is equal to or more than a predetermined value by the motor rotation speed upper limiter in the case of FIG. This prevents the return control from working and prevents the steering wheel from returning too much and overshooting.

[0012]

However, this return control device for an electric power steering still has the following problems.

For example, as shown in FIG. 3, when the steering wheel (handle) is gradually returned to near neutral, the return command value added to the assist command value is a torque-sensitive limiter and a motor speed-sensitive limiter. However, only the necessary area is taken out, but the output is turned into a pulse-like ON / OFF signal because it is discriminated by the polarity discriminating means, and the return control by this is also pulse-like and transmitted to the steering wheel as a rugged feeling. There was a problem that the returning operation of the steering wheel was uncomfortable.

When the steering wheel returns to near neutral and the so-called self-aligning torque becomes extremely small, the return command value is turned off in a pulsed manner, so that no return control is performed, and the steering wheel is no longer operated. There was still a problem that shortage of return did not occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce a sense of incongruity generated when performing return control by a simple configuration and to eliminate insufficient return of a steering wheel. It is an object of the present invention to provide a return control device of an electric power steering that can perform the control.

[0016]

Means taken to solve the problem according to the first aspect of the present invention will be described with reference to symbols used in the embodiment, which will be described as "detecting steering torque of steering wheel 10". According to a predetermined assist command value determined by the output of the torque sensor 20 and the output of the vehicle speed sensor 30 for detecting the vehicle speed, the assist motor 40 is driven to add the assist torque to the steering torque, thereby improving the operability of the steering wheel 10. In the electric power steering system, when the rotation direction of the assist motor 40 and the input direction of the steering torque are different from each other, the steering wheel 10 is determined to be in the return state by the polarity determination means 53. By adding the return command value determined by the output to the assist command value, Regarding the return control device of the electric power steering for improving the return of the steering wheel 10, a low-pass filter 61 provided on the output side of the polarity discriminating means 53 and receiving the return command value is provided. A shaping means 60 comprising an OR operator 62 to which both an output value and a return command value divided just before the low-pass filter 61 are input and whose output is added to the assist command value is provided. Control device for an electric power steering. "

The output of the OR operator 62 in the shaping means 60 is, as shown in FIG. 1, an input 1 to which a return command output from the polarity discriminating means 53 is divided and directly input, and a low-pass filter. Input 2 input via 61
And the values are as shown in Table 1 and the time chart of FIG. In other words, the pulse waveform output from the polarity discriminating means 53 becomes the waveform of the OR output shown in FIG.

[Table 1]

Therefore, according to the first aspect of the present invention, the shaping means 60 composed of the low-pass filter 61 and the OR operator 62 is provided, as shown in FIG.
When the return command output from the polarity discriminating means 53 is on, the return command value rises quickly, while when the return command is off, the return command value gradually changes based on the time constant of the low-pass filter 61. Because of the reduction, it is possible to smooth the entire return control.

Further, even after the steering wheel 10 (the steering wheel) has returned to near neutral and the self-aligning torque has almost disappeared, it is possible to gradually return and control the last little in accordance with the time constant of the low-pass filter 61. It is.

In the present invention, the shaping means 60 is provided to smooth the return command value output as an on / off signal in a pulsed manner. By providing the torque-sensitive limiter 51 or the motor rotation speed-sensitive limiter 52, it is possible to further eliminate the uncomfortable feeling of the steering feeling of the steering wheel 10.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First, an electric power steering system will be described with reference to FIGS. In FIG. 2, when the steering wheel 10 is operated, the steering torque is transmitted to the input shaft 11a of the gear case 11, and drives the rack 12 via the pinion at the lower end of the output shaft 11b. This rack 12 changes the direction of wheels 14 via a steering link 13.

On the other hand, as shown in FIG.
1, a torque sensor 20 detects a steering torque, a vehicle speed sensor 30 detects a vehicle speed, and an electric signal thereof is input to an electric control device (hereinafter, referred to as an ECU 50). The ECU 50 determines a predetermined assist command value (current command value) based on the input from the torque sensor 20 and the input from the vehicle speed sensor 30, transmits this to a drive circuit via each limiter, and assists the drive circuit. The motor 40 is driven.

The torque of the assist motor 40 is transmitted to the input shaft 16a of the gear case 16 via the electromagnetic clutch 15.
And drives the rack 12 via a pinion at the lower end of the output shaft 16b. Since the rack 12 is driven by the output shaft 16b of the assist motor 40 together with the output shaft 11b of the steering wheel 10, the operability of the steering wheel 10 is significantly improved.

Next, in such an electric power steering system, the return control for improving the characteristic when the cut-in steering wheel 10 is returned in the reverse direction, that is, the return property of the steering wheel 10, is performed as follows. .

First, the current value of the assist motor 40 is detected by a current detection sensor.
A terminal voltage of 0 is detected by the voltage detection sensor, and each detected value is input to the ECU 50. The ECU 50
The rotational speed of the assist motor 40 is estimated and calculated by the motor rotational speed estimation calculating means 54 from the detected current value and the motor terminal voltage value.

Further, when the rotation direction of the assist motor 40 obtained from the motor rotation speed and the input direction of the steering torque obtained from the torque sensor 20 are different from each other, the ECU 50 determines that the steering wheel 10 is in the return state. It has a polarity discriminating means 53, and when it is determined that the vehicle is in the return state, the return command value determined from the vehicle speed is added to the assist command value to improve the return property of the steering wheel 10. It is.

In this embodiment, the differential command value determined by the differential amount of the steering torque input from the torque sensor 20 and the vehicle speed input from the vehicle speed sensor 30 is added to the assist command value (current command value). This compensates for the phase lag of the control system.

In the present invention, a pulse-like return command value determined by the output value of the torque sensor 20 and the number of revolutions of the assist motor 40 is shaped into an appropriate pattern, and the control is performed to add it to the assist command value. In this embodiment, the return command value is determined based on the vehicle speed, and after the required area is extracted through the torque sensitive limiter 51 and the motor speed sensitive limiter 52 after the gain is determined, the polarity determining means 53, and is shaped by the shaping means 60 and added to the assist command value.

Here, the torque sensitive limiter 51 includes a torque upper limiter that does not output a return command value when the output value of the torque sensor 20 is equal to or more than a predetermined value, and a torque sensor 20.
When the output value of the assist motor 40 is equal to or less than a predetermined value, the motor lower limiter 52 does not output a return command value. It has both functions of a motor rotation speed lower limiter that does not output a command value and a motor rotation speed upper limiter that does not output a return command value when the rotation speed of the assist motor 40 is a predetermined value or more.

Therefore, as shown in FIG. 3, when the steering wheel (the steering wheel) is gradually returned to near neutral, the return command value added to the assist command value is the torque lower limiter of the torque sensitive limiter 51. Only the necessary area is taken out by the motor rotation speed lower limiter of the motor rotation speed sensitive limiter 52.

When the steering wheel 10 is in the returning state when the polarity discriminating means 53 determines that the rotation direction of the assist motor 40 and the input direction of the steering torque (output of the torque sensor 20) are different from each other. Since it is determined, the return command value at this time is output as a pulse-like ON / OFF signal.

This pulse-like return command value is input to the shaping means 60 at the next stage. The shaping unit 60 includes a low-pass filter 61 to which a pulse-like return command value is input, and an output value from the low-pass filter 61 and the low-pass filter 6.
An OR operator 62 to which both the return command value divided just before 1 and the return command value are input is added, and the output thereof is added to the assist command value described above.

As a result, as shown in the lowermost part of FIG.
When the return command value output from the polarity discriminating means 53 is on, the return command value rises quickly, while when the return command value is off, the return command value is applied to the low-pass filter 61.
Since the time constant gradually decreases based on the time constant, the entire return control can be smoothed.

Further, even after the steering wheel 10 has returned to near neutral and the self-aligning torque has almost disappeared, it is possible to perform control to gradually return the last little in accordance with the time constant of the low-pass filter 61.

In this embodiment, the input is made to the shaping means 60 after passing through the torque sensitive limiter 51 and the motor rotational speed sensitive limiter 52, but the vehicle speed is not passed through these limiters 51 and 52. May be directly input to the polarity discriminating means 53, and the output thereof may be shaped by the shaping means 60 and added to the assist command value.

In this case, there is a case where an error or a malfunction occurs due to an error of the torque sensor 20 or the assist motor 40, but at least a pulse-like ON / OFF signal output from the polarity discriminating means 53 can be removed. This makes it possible to reduce the uncomfortable feeling of the return control transmitted to the wheel 10 as a rough feeling.

[0037]

As described in detail above, according to the return control apparatus for an electric power steering according to the present invention, the return control is performed by providing the shaping means on the output side of the polarity discriminating means. This has the effect of reducing uncomfortable feeling and eliminating insufficient return of the steering wheel.

[Brief description of the drawings]

FIG. 1 is a control block diagram of an embodiment of a return control device for an electric power steering according to the present invention.

FIG. 2 is a block diagram illustrating a system according to the embodiment shown in FIG. 1;

FIG. 3 is a graph showing a state in which a return command value is output when the steering wheel is returned to the vicinity of neutral, by comparing the prior art with the present invention.

FIG. 4 is a table and a time chart showing the operation of the shaping means.

FIG. 5 is a control block diagram of a conventional return control device.

FIG. 6 is a graph showing a state in which a return command value is output during steering holding with a sufficiently large steering torque, comparing a conventional technique and an improved example.

FIG. 7 is a graph showing a state in which a return command value is output when the steering torque is extremely small, or when the return of the steering wheel is slow and the motor rotation speed is minute, by comparing the prior art and the improved example.

FIG. 8 is a graph showing a state in which a return command value is output when the return of the steering wheel is sufficiently fast, comparing a conventional technique with an improved example.

FIG. 9 is a control block diagram of a return control device in a conventional improved example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Steering wheel 20 Torque sensor 30 Vehicle speed sensor 40 Assist motor 50 Electric control device (ECU) 51 Torque sensitive limiter 52 Motor speed sensitive limiter 53 Polarity discriminating means 60 Shaping means 61 Low-pass filter 62 OR operator

Claims (3)

[Claims] An assist motor is driven by a predetermined assist command value determined based on an output of a torque sensor for detecting a steering torque of a steering wheel and an output of a vehicle speed sensor for detecting a vehicle speed, and the assist torque is converted to the steering torque. In the electric power steering system additionally improving the operability of the steering wheel, when the rotation direction of the assist motor and the input direction of the steering torque are different from each other, it is determined by the polarity determination means that the steering wheel is in the return state. By adding a return command value determined by the output of the vehicle speed sensor to the assist command value, a return control device of the electric power steering for improving the return of the steering wheel is provided on the output side of the polarity determining means. And the return command value is input. A low-pass filter, and an OR operator to which both the output value from the low-pass filter and the return command value divided just before the low-pass filter are input and the output is added to the assist command value. A return control device for an electric power steering, comprising: 2. The return control device for an electric power steering according to claim 1, further comprising a torque-sensitive limiter that does not output the return command value when the output value of the torque sensor is out of a predetermined range. 3. The electric power steering system according to claim 1, further comprising a motor rotation speed sensitive limiter that does not output the return command value when the rotation speed of the assist motor is out of a predetermined range. Return control device.