Patent Application
20160107680
The present invention relates to an electric power steering control unit that PI-controls a current command value calculated based on at least a steering torque, and provides a steering system of a vehicle with a steering assist force generated by a motor, and in particular to an electric power steering control unit that compresses in a case that the vibration of the vibration compressing object, such as a steering wheel (handle), the current command value and a motor speed, continues during a predetermined time or more than the predetermined time within a scope of a predetermined frequency and further improves a steering feeling for a driver.
An electric power steering apparatus that energizes a steering apparatus of a vehicle by using a rotational torque of a motor as an assist torque, applies a driving force of the motor as the assist torque to a steering shaft or a rack shaft by means of a transmission mechanism such as gears or a belt through a reduction mechanism. A conventional electric power steering apparatus (EPS) performs a feedback control of the motor current in order to accurately generate a torque of an assist force. The feedback control adjusts a current supplied to the motor so that a difference between a steering assist command value (a current command value) and a detected motor current value becomes small, and the adjustment of the current applied to the motor is generally performed by an adjustment of a duty ratio of a pulse width modulation (PWM) control.
A general configuration of a conventional electric power steering apparatus will be described with reference to
The control unit 30 mainly comprises a CPU (or an MPU or an MCU), and general functions performed by programs within the CPU are shown in
Functions and operations of the control unit 30 will be described with reference to
Further, a compensation signal CM from a compensation section 34 is added in the adding section 32A, and the compensation of the system is performed by the addition of the compensation signal CM so as to improve a convergence, an inertia characteristic and so on. The compensation section 34 adds a self-aligning torque (SAT) 343 and an inertia 342 in an adding section 344, further adds the result of addition performed in the adding section 344 and a convergence 341 in an adding section 345, and then outputs a result of addition performed in the adding section 345 as the compensation signal CM.
Furthermore, as shown in
The CPU (micro-computer) in such the electric steering apparatus generates the voltage control command for controlling the motor by the PI control as stated above. The gains of the PI control are adjusted to accommodate values in accordance with the kinds of the vehicles.
When the gain of the PI control becomes greater, a noisy sound and a vibration due to the noises occur. In this connection, it is necessary to limit not to occur the vibration and the noisy sound. However, if the gain of the PI control is limited, the frequency characteristic of the current control falls and it is impossible to improve the responsibility of the steering assist. Further, even if the gain of the PI control is sufficiently decreased, it is impossible to perfectly avoid the vibration in a vicinity of a resonance frequency of the steering system and a comfortable feeling is not necessarily obtained.
In order to dissolve such problems, for example, an electric power steering apparatus disclosed in Japanese Published unexamined Patent Application No. 2006-188183 A (Patent Document 1) is proposed. That is, the electric power steering apparatus of Patent Document 1 comprises a vibration detecting means detects the vibration of the steering members, and a gain changing means for falling either one of the proportional gain and the integration gain of the PI control when the vibration of the steering members is detected by the vibration detecting means.
However, since the electric power steering apparatus disclosed in Patent Document 1 does not extract the vibration wave-form for the handle vibration compression, it is necessary to calculate and process for all frequency range. Therefore, there is a problem that the processing capacity becomes large. Further, since the extraction of the handle vibration wave-form is carried out by a differential peak-hold processing or the like and the gain is changed as the vibration continuation when an inter-peak value exceeds a predetermined threshold, it is necessary to accurately detect the inter-peak distance. Accordingly, there is a problem that the calculation capacity becomes large.
Furthermore, as the vibration components, although there are the vibrations of the current command value, the motor speed and so on except for the torque of the handle (steering wheel), the countermeasure for the vibration is not entirely disclosed in Patent Document 1.
The present invention has been developed in view of the above-described circumstances, and an object of the present invention is to provide an electric power steering control unit that detects the vibration components of the vibration compressing object such as the handle and current command value based on an expression of Fourier series of which calculation capacity is small, changes a gain of the PI control section at only a time when the vibration of the predetermined frequency continues during the predetermined time or more than the predetermined time and compresses the vibration, and improves the steering feeling.
The present invention relates to an electric power steering control unit that PI-controls a current command value calculated based on at least a steering torque, and drive-controls a motor by means of a control command value which is PI-controlled and assist-controls a steering, comprising: a vibration detecting section to detect a vibration of a vibration compressing object and outputs a vibration signal; a continuation-time judging section to output a continuation signal when said vibration signal continues equal to or more than a predetermined time; and a gain setting section to change a gain of said PI-control based on said continuation signal; wherein a vibration compressing of said vibration compressing object is performed in a continuation of a predetermined frequency of said vibration signal and being equal to or more than said predetermined time.
Further, the above-described object of the present invention is more effectively achieved by that wherein said vibration detecting section comprising: a band pass filter (BPF) to extract a predetermined frequency of said vibration compressing object; a sin-wave generating section to generate a sin-wave; a cos-wave generating section to generate a cos-wave; a first multiplying section to multiply said sin-wave with a vibration compressing object signal which is processed in said BPF; a second multiplying section to multiply said vibration compressing object signal with said cos-wave; a first integrating section to integrate a first multiplied signal from said first multiplying section; a second integrating section to integrate a second multiplied signal from said second multiplying section; a first squaring section to square a first integration signal from said first integrating section; a second squaring section to square a second integration signal from said second integrating section; and an adding section to add a first multiplied signal from said first squaring section and a second multiplied signal from said second squaring section and to output said vibration signal; or by that wherein said first integrating section and said second integrating section are initialized at a predetermined period; or by that wherein said BPF extracts a vibration frequency of 5-20 Hz; or by that wherein said vibration compressing object is said steering torque, said current command value and a motor speed of said motor; or by that wherein said gain to be changed of said PI-control is a proportional gain or an integral gain; od by that wherein said gain to be changed of said PI-control is a proportional gain and an integral gain.
According to an electric power steering control unit of the present invention, since the control unit extracts only the predetermined frequency component of the vibration compressing object, such as the steering torque, the current command value and the motor speed, with the band pass filter (BPF) and processes only the extracted frequency component, it is possible to make the capacity of the calculation process small. Further, since the control unit of the present invention bases an expression of Fourier series for the judgment of the vibration continuation and does not use the inter-peak measurement, it is possible to utilize the CPU of which calculation capacity is small and the price is cheap.
Furthermore, the control unit of the present invention determines the minimum value and the maximum value from the sampling data of the past values of the predetermine number and the present value, sets the first condition that plural output values are quite contented in a certain range, and thereafter judges, by comparing with the threshold, the second condition whether or not the predetermined time continues. Therefore, the present invention is capable of simplifying the calculation.
In the accompanying drawings:
The present invention bases an expression of the Fourier series of which calculation capacity is small, extracts only the vibration component to be necessary for compressing from a vibration compressing object such as the handle (steering wheel) and the current command value, and changes again (proportional gain, integration gain) of the PI control when the vibration continuation-time exceeds a predetermined time. According to the present invention, for the extracted frequency component, since the gain of the PI control is changed only when the vibration continues during a predetermined time, it is possible to efficiently and economically compress the vibration of the vibration compressing object with a small calculation capacity.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Although the handle vibration will be described as the vibration compressing object in the following embodiment, it is possible to similarly apply to the current command value and the motor speed and so on as the vibration compressing object.
Although the present invention extracts a frequency component for compressing the handle vibration from the steering torque, the Fourier series shown in the following expression 1 is based. The angular frequency ω[rad/s] is an angular frequency to be extracted and a predetermined period is T.
Then, if “2/T” of the expression 1 is disregarded, it is possible to obtain an amplitude component An from the following expression 2.
A
n=√{square root over (an2+bn2)} [Expression 2]
Further, if the root is removed from the expression 2 in order to simplify the calculation, the following expression 3 is established, it is possible to obtain the amplitude component An2.
A
n
2
=a
n
2
+b
n
2 [Expression 3]
The present invention will be described as abase under the above-explanation.
Besides, the compensation signal CM by means of the compensation signal generating section 34 is not essential in the present invention.
For example, it is assumed that a continuous vibration of 10 [Hz] is included in the steering torque Th. At this time, it is assumed that the continuous vibration state of 10 [Hz] is judged. The configuration of the vibration detecting section 200 is for example shown in
The sin-wave sin(ωt) is inputted into the multiplying section 204s, and the multiplied signal Ths(=Tha·sin(ωt)) with the vibration steering torque Tha is inputted into an integrating section 205s. The cos-wave cos (ωt) is inputted into the multiplying section 204c, and the multiplied signal Thc(=Tha·cos(ωt)) with the vibration steering torque Tha is inputted into an integrating section 205c. The integrating sections 205s and 205c are respectively reset to an “integrated value=0” with a predetermined period (e.g. 500 [ms]). The integration signal ITs from the integrating section 205s is inputted into a squaring section 206s and squared therein, and the integration signal ITc from the integrating section 205c is inputted into a squaring section 206c and squared therein. The respective squared values Ms and Mc are inputted into an adding section 207 and then are added, and the added value(=Ms+Mc) is outputted as the vibration signal VS.
The vibration signal VS from the vibration detecting section 200 is inputted into the continuation-time judging section 220, and the continuation-time judging section 220 outputs the continuation signal CT when the vibration signal VS continues during a predetermined time (e.g. 1.5 [sec]). The continuation signal CT is inputted into the gain setting section 230, and the gain setting section 230 outputs a gain set signal GS for changing the proportional gain Gp and/or the integration gain Gi of the PI control section 35. The PI control section 35 performs the PI control by using the newly set the proportional gain Gp and/or the integration gain Gi.
The operations except for the vibration detecting section 200, the continuation-time judging section 220 and the gain setting section 230 are the same with
In such a configuration, an operation example of the present invention will be described with reference to flow charts of
The vibration detecting section 200 inputs the steering torque Th (Step S1), and the BPF 201 within the vibration detecting section 200 extracts the vibration component of the predetermined frequency (e.g. 5-20 [Hz]) (Step S2).
On the other hand, the oscillator 202 oscillates the frequency signal FS of the angular frequency ω(=2πf) and inputs the frequency signal FS into the sin-wave generating section 203s and the cos-wave generating section 203c. The sin-wave generating section 203s generates the sin-wave sin (ωt) (Step S3), and the cos-wave generating section 203c generates the cos-wave cos(ωt) (Step S4). The sin-wave sin(ωt) is inputted into the multiplying section 204s, and the cos-wave cos(ωt) is inputted into the multiplying section 204c. Besides, the order of the generations of the sin-wave sin(ωt) and the cos-wave cos(ωt) is arbitrary.
The multiplying section 204s multiplies the sin-wave sin(ωt) with the vibration steering torque Tha which is BPF-processed (Step S10), and the integrating section 205s integrates the multiplied signal Ths (Step S11). The integration signal ITs integrated in the integrating section 205s is inputted into the squaring section 206s and is squared in the squaring section 206s (Step S12). Similarly, the multiplying section 204c multiplies the cos-wave cos(ωt) with the vibration steering torque Tha which is BPF-processed (Step S20), and the integrating section 205c integrates the multiplied signal Thc (Step S21). The integration signal ITc integrated in the integrating section 205c is inputted into the squaring section 206c and is squared in the squaring section 206c (Step S22). Besides, the order of the integrations for the sin-wave sin(ωt) and the cos-wave cos(ωt) is arbitrary.
The respective waveforms after the multiplications in the multiplying sections 204s and 204c are shown in
The squared value Ms squared in the squaring section 206s and the squared value Mc squared in the squaring section 206c are inputted into the adding section 207 and added therein (Step S23), it is judged whether the integrating section 205c is an initialization time or not (Step S24). In a case that the integrating section 205c is judged as the initialization time, the integrating section 205c is initialized (Step S25). Thereafter, or in a case that the integrating section 205c is not judged as the initialization time, the vibration signal VS being the added value is inputted into the continuation-time judging section 220 without the initialization and it is judged whether the vibration is continued or not (Step S30). In a case that the vibration is continued, the continuation signal CT is outputted from the continuation-time judging section 220, the gain setting section 230 outputs the gain set signal GS based on the continuation signal CT and changes the proportional gain Gp and/or the integration gain Gi of the PI control section (Step S40). The changings of the proportional gain Gp and/or the integration gain Gi are performed in the directions of the falling, and they may be linear or non-linear, or may be gradually changed.
On the other hand, at the above Step S30, in a case judged that the vibration is not continuous and is temporarily, the process returns to the Step S1 and the above operations are repeated.
The judgment operation at the Step S30 is in detail performed in accordance with a flow chart of
First, the vibration signal VS being the added value is inputted as the first sampling data (y[k]) (Step S31), and is stored in the memory (not shown) (Step S32). Thereafter, the vibration signal VS is inputted till y [k−2] of the third sampling data (Step S33), at a stage in which the sampling data “y[k], y[k−1], y[k−2]” are inputted, the maximum value ymax and the minimum value ymin are determined among two past values and a present value (Step S34). Then, it is judged whether “ymin≧a·ymax” or not as a setting coefficient is “a” (Step S35). The judgment of this first condition is a discrimination whether three output values are relatively within a certain scope or not.
At the judgment of the first condition at the Step S35, in the case of “ymin≧a·ymax”, the second condition is judged whether the respective output values “y[k], y[k−1], y[k−2]” are equal to or more than a predetermined threshold yth (Step S36). In a case that the respective output values “y[k], y[k−1], y[k−2]” are more than the threshold yth, the continuation signal CT is outputted and terminated (Step S37).
At the above judgment on the first condition of the Step S35, in a case that the first condition is not established and “ymin<a·ymax”, the process is returned. Further, at the judgment on the second condition of the Step S36, in a case that any one of the “y[k], y[k−1], y[k−2]” is equal to or less than the threshold yth, the process is returned. Besides, the three sampling data are used in this embodiment, the number of the sampling of the past values are optional.
Although the vibration compressing object is the steering torque Th in the above embodiment-explanation, in the case that compresses the vibration of the current command value, the similar control is applied by inputting the current command value Iref1 or Iref2 into the vibration detecting section 200. In the case that compresses the vibration of the motor speed, the similar control is applied by inputting the motor speed signal based on the rotation sensor (e.g. resolver) or the like connected to the motor into the vibration detecting section 200. Further, it is possible to simultaneously control the steering torque Th, the current command value Iref1 or Iref2, the mot or speed as the vibration compressing object.
Furthermore, the renewal period may be equal to or more than three periods of an extracted frequency. The vibration detecting section comprises plural sections which different values are set, and in a case that either one detects the continuous vibration, it may be a continuous vibration detecting state. Further, in the detection of the continuous vibration, the latest output value is compared with a value calculated by the least squares method and so on from the past output values, it may be the continuous vibration detecting state in a case that the value is more than a rate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-142583 | Jul 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/067807 | 7/3/2014 | WO | 00 |
