JP2000321155A - Power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power steering apparatus by which a steering torque is detected precisely without being influenced by a temperature change, which prevents a drop in a steering feeling by giving a proper steering auxiliary force and whose costs can be reduced. SOLUTION: A torque sensor 1 in which a change amount from the detection reference value of an electromagnetic variable according to a change in a steering torque is used as an output value is provided. An actuator 25 which is used to generate a steering auxiliary force is provided. When the magnitude of the output value of the torque sensor 1 is at a set value of higher, the steering auxiliary force according to the output value is generated. The detection reference value is corrected according to the time difference between a point of time when the output value of the torque sensor 1 rises and a point of time when a value corresponding to the output of the actuator 25 rises.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a torque sensor for detecting a steering torque according to a change in an electromagnetic variable,
The present invention relates to a power steering device that applies a steering assist force in accordance with the steering torque, and is particularly suitable for a case where the electromagnetic variable fluctuates due to a temperature change.

[0002]

2. Description of the Related Art A torque sensor having an output value of a change from a detection reference value of an electromagnetic variable corresponding to a change of a steering torque, and an actuator for generating a steering assist force are provided. When the size is more than the set value,
Conventionally, a power steering device that drives the actuator so as to generate a steering assist force according to the output value has been used.

[0003]

If the detection reference value deviates, there is a problem that the steering torque cannot be accurately detected and the steering feeling is degraded. For example, a torque sensor that changes a magnetic resistance of a magnetic circuit through which a magnetic flux generated by a coil passes according to a steering torque and detects a steering torque based on a change in a coil output corresponding to the change in the magnetic resistance is used. In such a torque sensor, when there is a temperature change, the inductance of the coil changes, so that the detection reference value changes. In order to compensate for the change in the detection reference value due to such temperature change, a dedicated magnetic circuit for detecting only the change in the detection reference value due to the temperature change is provided, and the change in the detection reference value is canceled. ing. However, when such a dedicated magnetic circuit is provided, there is a problem that the configuration becomes complicated and the cost increases.

An object of the present invention is to provide a power steering device that can solve the above-mentioned problem.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a torque sensor that outputs a change amount of an electromagnetic variable according to a change in steering torque from a detection reference value, an actuator for generating a steering assist force, and Means for driving the actuator so as to generate a steering assist force according to the output value when the magnitude of the output value of the torque sensor is equal to or greater than a set value. Means for obtaining a corresponding value; means for obtaining a time difference between a rising time point of the output value of the torque sensor and a rising time point of a value corresponding to the output of the actuator; and correcting the detection reference value according to the time difference. And means for performing the following. According to the above configuration, the steering assist force generating actuator is driven when the magnitude of the output value of the torque sensor becomes equal to or greater than the set value. When there is no deviation in the detection reference value, the output value of the torque sensor when the actual steering torque is zero becomes zero. When there is a deviation in the detection reference value, the output of the torque sensor when the actual steering torque is zero. The value is not zero. Therefore, there is a difference between the time when the actual steering torque is zero and the time when the magnitude of the output value of the torque sensor reaches the set value between the case where there is no deviation in the detection reference value and the case where the actual steering torque is zero. The time from when the actual steering torque is zero to when the magnitude of the output value of the torque sensor reaches the set value is the time when the output value of the torque sensor rises and the time when the value corresponding to the output of the actuator rises. Corresponding to the time difference. Since the time difference corresponds to the deviation of the detection reference value, the detection reference value can be corrected according to the time difference.

Means for obtaining a steering direction, and means for storing a correspondence between the time difference, the steering direction, and a correction value obtained in advance are provided, and a correction value obtained from the obtained time difference, the steering direction, and the stored correspondence. It is preferable to correct the detection reference value by the following. As a torque sensor, when the magnitude of the output value corresponds to the magnitude of the steering torque, and the sign of the output value corresponds to the steering direction, if there is a deviation in the detection reference value, the actual steering torque is reduced. When the value is zero, the output value of the torque sensor is not a midpoint value but a value in a right steering state or a left steering state. When the output value of the torque sensor indicates a value in the right steering state due to the deviation, when performing left steering, the time difference is larger than when there is no deviation, and when performing right steering, the time difference is greater than when there is no deviation. Is also smaller. Also, when the output value of the torque sensor indicates a value in the left steering state due to the deviation, when performing left steering, the time difference is smaller than when there is no deviation, and when performing right steering, the time difference does not vary. It will be larger than the case. Therefore, if the correction value of the detection reference value corresponding to the time difference and the steering direction is obtained in advance and the correspondence is stored, if the time difference and the steering direction are obtained at the time of the actual steering, the steering is performed in either the left or right direction. Even if
The deviation of the detection reference value can be corrected by the correction value obtained from the stored correspondence.

Means for obtaining a steering characteristic value corresponding to the steering speed, and means for storing a time difference, a steering direction, a steering characteristic value, and a correspondence relationship between a previously obtained correction value, and the calculated time difference and a steering direction are provided. Preferably, the detection reference value is corrected by a correction value obtained from the relationship between the steering characteristic value and the stored correspondence. The time difference changes according to the steering speed. According to this configuration, since the correction value of the detection reference value is obtained according to the time difference, the steering direction, and the steering characteristic value corresponding to the steering speed, the deviation of the detection reference value can be corrected without being affected by the steering speed.

When the steering characteristic value is equal to or greater than a predetermined upper limit value, it is preferable that the detection reference value is not corrected. Accordingly, when the steering speed is increased and the time difference is reduced, it is possible to prevent the correction accuracy of the detection reference value from being reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. The vehicle power steering apparatus shown in FIG. 1 includes a torque sensor 1 for detecting a steering torque, a housing 2, an input shaft 3, and an output shaft 4.

The input shaft 3 is rotatably supported via a bearing 5 inside the housing 2, is connected to a handle shaft 9, and a steering wheel is connected to the handle shaft 9. Its output shaft 4
Is rotatably supported via a bearing 6 inside the housing 2 and connected to wheels via, for example, a rack and pinion type steering gear. The input shaft 3 and the output shaft 4 are connected to each other via a torsion bar 8 inserted into a through hole 7 penetrating the respective shaft centers. One end of the torsion bar 8 is connected to the input shaft 3 and the handle shaft 9 via a pin 23a, and the other end is connected to the output shaft 4. A worm wheel 10 is fixed to the outer periphery of the output shaft 4, and the worm 11 meshing with the worm wheel 10 is driven by a steering assist force generating motor (actuator) 25.

A first detection ring 13 made of a magnetic material is fitted to the input shaft 3 via a sleeve 12 made of a non-magnetic material, and is fixed by pins 50. A second detection ring 14 made of a magnetic material is fixed to the output shaft 4 by press-fitting. A plurality of teeth 13a, 14a are provided on the end faces of both detection rings 13, 14 along the circumferential direction, respectively. The teeth 13a of the first detection ring 13 and the teeth 14a of the first detection ring 14 have surfaces facing each other via an air gap in the axial direction of the input / output shafts 3, 4.

A cylindrical holder 16 made of a magnetic material is inserted into the housing 2, and the detection coil 17 is held by the cylindrical holder 16. The detection coil 17 is disposed so as to cover the periphery of the opposing portions of the two detection rings 13 and 14. As shown in FIG. 2, the detection coil 17 is connected to an oscillator 22 via a resistor 21 and to a control device 23 constituted by a computer. The detection coil 17 generates a magnetic flux that passes through the mutually facing surfaces of the teeth 13a and 14a, thereby forming a magnetic circuit for torque detection.

The torsion bar 8 according to a change in the steering torque transmitted from the input shaft 3 to the output shaft 4.
Causes the first detection ring 13 and the second detection ring 14 to relatively elastically rotate about the same axis. As a result, the areas of the opposing surfaces of the teeth 13a and 14a of the detection rings 13 and 14 change, so that the magnetic resistance of the torque detection magnetic circuit changes. In accordance with this change, the output voltage value of the detection coil 17, that is, the electromagnetic variable changes. The amount of change of the electromagnetic variable from the detection reference value according to the change in the steering torque is the output value of the torque sensor 1. The magnitude of this output value corresponds to the magnitude of the steering torque, and the sign of the output value corresponds to the steering direction. The output value of the torque sensor 1 changes due to a change in inductance of the detection coil 17 according to a change in the ambient temperature.

The control device 23 includes the torque sensor 1
When the magnitude of the output value is equal to or larger than the set value, the motor 25 is driven so as to generate a steering assist force according to the output value. That is, as shown in FIG. 3, when the magnitude of the detected steering torque corresponding to the magnitude of the output value of the torque sensor 1 is smaller than the set value Tk, the output of the motor 25 is zero, and the driving stability is improved. I have. When the magnitude of the detected steering torque is equal to or greater than the set value Tk, the output of the motor 25 is increased so that the steering assist force is increased in accordance with the increase, thereby facilitating the steering. The steering assist force may be controlled in accordance with other vehicle running conditions in addition to the steering torque. For example, a vehicle speed sensor may be connected to the control device 23 so that the steering assist force is reduced as the vehicle speed increases. You may.

An ammeter 26 for detecting the load current of the motor 25 as a value corresponding to the output of the motor 25 is connected to the control device 23. The control device 23 calculates the time difference between the rising point of the output value of the torque sensor 1 and the rising point of the load current of the motor 25 obtained from the ammeter 26, and performs steering based on the sign of the output value of the torque sensor 1. The direction is obtained, and the change speed of the magnitude of the steering torque is obtained as a steering characteristic value corresponding to the steering speed. The control device 23 stores the correspondence between the time difference, the steering direction, the steering characteristic value, and the correction value obtained in advance. The correction value can be obtained by an experiment. The correspondence is stored, for example, as a table or a function. The control device 23 stores a control program for correcting the detection reference value according to the time difference.

The flow chart of FIG.
3 shows a control procedure according to a control program stored in the control program 3.
First, the initial value of the correction value δ of the detection reference value is set to zero (step 1), and then the output value of the torque sensor 1 and the motor 25 are set.
Is read (step 2), and then the detection reference value is corrected by the correction value δ (step 3).
It is determined whether or not the magnitude T of the detected steering torque corresponding to the magnitude of the output value of the torque sensor 1 based on the corrected detection reference value is equal to or greater than the set value Tk (step 4).
If it is not equal to or greater than the set value Tk, the process returns to step 2 and the set value T
If it is equal to or greater than k, the motor 25 is driven to generate a steering assist force according to the output value of the torque sensor 1 to generate a steering assist force (step 5). Next, the rate of change dT / dt of the magnitude of the steering torque is equal to the upper limit α
It is determined whether or not this is the case (step 6). If it is not less than the upper limit α, the process returns to step 2. If it is less than the upper limit α, the output value of the torque sensor 1 rises and its ammeter Then, the time difference Δt from the rise time of the load current of the motor 25 obtained from the motor 26 is obtained (step 7), and the steering direction is obtained (step 8). Thereafter, a correction value δ of the detection reference value is obtained from the obtained time difference Δt, the changing direction dT / dt of the steering direction and the magnitude of the steering torque, and the stored correspondence (step 9). Next, it is determined whether or not to end the control based on the on / off of a key switch of the engine (step 10). If not, the process returns to step 2.

FIG. 5A shows the magnitude T of the detected steering torque corresponding to the magnitude of the output value of the torque sensor 1 and the time t.
The relationship is shown below. FIG. 5B shows the relationship between the magnitude of the load current I of the motor 25 and the time t when there is no deviation in the detection reference value. FIGS. 5 (3) and (4) show the relationship between the magnitude of the load current I of the motor 25 and the time t when there is a deviation of the detection reference value. FIG. 5C shows the case where the left steering is performed when the output value of the torque sensor indicates the value in the right steering state due to the deviation, and the case where the output value of the torque sensor is changed to the left steering state due to the deviation. When the right steering is performed in the case where the value at the time of is shown.
FIG. 5D shows the case where the right steering is performed when the output value of the torque sensor indicates the value in the right steering state due to the deviation, and the case where the output value of the torque sensor is changed to the left steering state due to the deviation. When the left steering is performed when the value at the time of is shown.

According to the above configuration, the magnitude of the steering torque corresponding to the magnitude of the output value of the torque sensor 1 is set to the set value Tk.
At this point, the steering assist force generation motor 25 is driven. When there is no deviation in the detection reference value, the output value of the torque sensor 1 when the actual steering torque is zero becomes zero. When there is a deviation in the detection reference value, the torque sensor 1 when the actual steering torque is zero. Is not zero. Therefore, there is a difference between the time when the actual steering torque is zero and the time when the magnitude of the output value of the torque sensor 1 reaches the set value Tk between the case where there is no deviation in the detection reference value and the case where there is no deviation. The time from when the actual steering torque is zero to when the magnitude of the output value of the torque sensor 1 reaches the set value Tk is the time when the output value of the torque sensor 1 rises and the time when the load current I of the motor 25 rises. Corresponding to the time difference Δt. Since the time difference Δt corresponds to the deviation of the detection reference value, the steering torque can be accurately detected by correcting the detection reference value according to the time difference Δt.

That is, when the output value of the torque sensor 1 indicates a value in the right steering state when the actual steering torque is zero due to the deviation of the detection reference value, the time difference Δt does not deviate in FIG. Compared to the case of (2), when the left steering is performed, the value increases as shown in (3) of FIG. 5, and when the right steering is performed, the value decreases as illustrated in (4) of FIG. Also,
In the case where the output value of the torque sensor indicates a value in the left steering state when the actual steering torque is zero due to the deviation of the detection reference value, the time difference Δt has no deviation of the detection reference value in FIG. As compared to the case of 2), when the left steering is performed, FIG.
As shown in (4) of FIG.
(3). Therefore, when the correction value δ of the detection reference value corresponding to the time difference Δt and the steering direction is obtained in advance and the correspondence is stored, even when the steering is performed in either the left or right direction, the time difference Δt and the steering direction are actually determined. , The deviation of the detection reference value can be corrected by the correction value δ obtained from the stored correspondence.

The time difference Δt changes according to the steering speed. That is, (1) to (4) in FIG. 6 show the relationship when the steering speed is higher than the relationship shown in (1) to (4) in FIG. 5, and in this case, the time difference Δt becomes small.
According to the above configuration, the correction value δ of the detection reference value is obtained according to the time difference Δt, the change speed dT / dt of the magnitude of the steering torque corresponding to the steering direction and the steering speed, so that the correction value δ is not affected by the steering speed. The deviation of the detection reference value can be corrected. Further, when the change speed dT / dt of the magnitude of the steering torque is equal to or greater than the upper limit α previously obtained, the detection reference value is not corrected, so that the steering speed increases and the time difference Δ
When t becomes small, it is possible to prevent the correction accuracy of the detection reference value from being lowered.

The present invention is not limited to the above embodiment. For example, as the steering characteristic value corresponding to the steering speed, a steering angle sensor may be provided to obtain a steering angle change speed, or a steering torque change acceleration or a steering angle change acceleration may be obtained.

[0022]

According to the present invention, the steering torque can be accurately detected without being affected by temperature fluctuations, and a proper steering assist force can be applied to prevent a reduction in steering feeling and reduce costs. A power steering device that can be achieved can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a power steering device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a circuit configuration of the torque sensor according to the embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the magnitude of the detected steering torque of the torque sensor according to the embodiment of the present invention and the output of the steering assist force generating motor.

FIG. 4 is a flowchart showing a control procedure of the power steering device according to the embodiment of the present invention.

5A and 5B are diagrams showing a relationship between detected steering torque and time corresponding to the magnitude of an output value of a torque sensor, and FIG. 5B shows a case where there is no deviation in a detection reference value. FIG. 3C is a graph showing the relationship between the magnitude of the load current of the motor and the time in FIG. 3C, where the detection reference value is shifted and the time difference between the rise time of the output value of the torque sensor and the rise time of the load current of the motor is large And FIG. 4D is a diagram showing a relationship between the magnitude of the load current of the motor and time when the detection reference value is shifted and the time difference is small.

FIG. 6 is a diagram showing a relationship between detected steering torque and time corresponding to the magnitude of the output value of the torque sensor when the steering speed is higher than that shown in FIG. 5 in the embodiment of the present invention; (2) is a diagram showing the relationship between the magnitude of the load current of the motor and time when there is no deviation in the detection reference value, and (3) is a rise in the output value of the torque sensor due to the deviation in the detection reference value. FIG. 4D is a diagram showing the relationship between the magnitude of the load current of the motor and the time when the time difference between the time and the rise of the load current of the motor is large. Showing the relationship between the magnitude of load current and time

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Torque sensor 23 Controller 25 Motor (actuator) 26 Ammeter

Claims (4)

[Claims] 1. A torque sensor that outputs a change amount from a detection reference value of an electromagnetic variable according to a change in a steering torque, an actuator for generating a steering assist force, and a magnitude of an output value of the torque sensor. When is equal to or more than a set value, in a power steering apparatus including means for driving the actuator, so as to generate a steering assist force according to the output value, means for obtaining a value corresponding to the output of the actuator, A means for calculating a time difference between a rising time point of the output value of the torque sensor and a rising time point of a value corresponding to the output of the actuator; and a means for correcting the detection reference value according to the time difference. Power steering device. And a means for storing a correspondence between the time difference, the steering direction, and a correction value obtained in advance. The means for obtaining the steering direction is obtained from the obtained time difference, the steering direction, and the stored correspondence. The power steering apparatus according to claim 1, wherein the detection reference value is corrected by the correction value. 3. A means for determining a steering direction, a means for determining a steering characteristic value corresponding to a steering speed, and a means for storing a correspondence between the time difference, the steering direction, the steering characteristic value, and a correction value obtained in advance. 2. The power steering apparatus according to claim 1, wherein the detection reference value is corrected by a correction value obtained from the obtained time difference, the steering direction, the steering characteristic value, and the stored correspondence. 4. The power steering apparatus according to claim 3, wherein when the steering characteristic value is equal to or greater than a predetermined upper limit, the detection reference value is not corrected.