Electric power steering apparatus

Abstract

[Problem] An object of the present invention is to provide an electric power steering apparatus that suppresses a handle vibration (noisy sound) being caused by a handle inertia and a spring nature of a torsion bar and improves a steering feeling, without changing of the gain of the PI control. [Means for solving the problem] The present invention is an electric power steering apparatus that assist-controls a steering by driving a motor with a current command value calculated based on at least a steering torque, comprising a vibration-damping compensating section that calculates a vibration-damping compensation command value for suppressing a vibration of a handle based on a motor velocity of the motor, wherein the current command value is corrected by the vibration-damping compensation command value.

Claims

1. An electric power steering apparatus that assist-controls a steering by driving a motor with a current command value calculated based on at least a steering torque, comprising: a vibration-damping compensating section that calculates a vibration-damping compensation command value for suppressing a vibration of a handle based on a motor velocity of said motor, wherein said vibration-damping compensating section comprises a motor velocity-sensitive table 1 for converting said motor velocity into a trapezoidal-wave type vibration-damping compensation value 1 and a band pass filer (BPF) to output a vibration-damping compensation value 2 by BPF-filtering said vibration-damping compensation value 1, wherein a zero-cross point of said vibration-damping compensation value 1 is coincident with a zero-cross point of said motor velocity, wherein a zero-cross point of said vibration-damping compensation value 2 is prior to said zero-cross point of said motor velocity, wherein said current command value is corrected by said vibration-damping compensation command value obtained at least in part from the vibration-damping compensation value 2, and wherein vibration amplitude of said motor near said zero-cross point of said motor velocity is suppressed.

2. The electric power steering apparatus according to claim 1, wherein said vibration-damping compensating section comprises a velocity-sensitive table 2 corresponding to said motor velocity, and a vibration-damping compensation value 3 is outputted by converting a vibration-damping compensation value 2 using said velocity-sensitive table 2.

3. The electric power steering apparatus according to claim 2, wherein said vibration-damping compensating section further including a torque-sensitive gain section to output a vibration-damping compensation value 4 by multiplying a gain 1 sensitive to said steering torque with said vibration-damping compensation value 2 or 3.

4. An electric power steering apparatus according to claim 3, wherein said vibration-damping compensating section further including a vehicle speed-sensitive gain section to output said vibration-damping compensation command value by multiplying a gain 2 sensitive to a vehicle speed with said vibration-damping compensation value 4.

5. The electric power steering apparatus according to claim 1, wherein said vibration-damping compensating section further including a torque-sensitive gain section to output a vibration-damping compensation value 4 by multiplying a gain 1 sensitive to said steering torque with said vibration-damping compensation value 2 or 3.

6. An electric power steering apparatus according to claim 5, wherein said vibration-damping compensating section further including a vehicle speed-sensitive gain section to output said vibration-damping compensation command value by multiplying a gain 2 sensitive to a vehicle speed with said vibration-damping compensation value 4.

7. The electric power steering apparatus according to claim 1, wherein the vibration damping compensation value 1 is the trapezoidal-wave type in a time domain.

8. The electric power steering apparatus according to claim 1, wherein the vibration damping compensation value 1 is converted into the vibration damping compensation value 2 by performing the BPF filtering to the vibration-dampening compensation value 1 of a trapezoidal waveform in a time domain.

9. An electric power steering apparatus that assist-controls a steering by driving a motor, through a reduction mechanism, with a current command value calculated based on at least a steering torque, comprising: a vibration-damping compensating section that calculates a vibration-damping compensation command value for suppressing a vibration of a handle based on a factor of a steering angle velocity and a gear ratio of said reduction mechanism, wherein said factor is a multiplied value of said steering angle velocity and said gear ratio, and said vibration-damping compensating section comprises a motor velocity-sensitive table 1 for converting said factor into a trapezoidal-wave type vibration-damping compensation value 1 and a band pass filer (BPF) to output a vibration-damping compensation value 2 by BPF-filtering said vibration-damping compensation value 1, wherein a zero-cross point of said vibration-damping compensation value 1 is coincident with a zero-cross point of said multiplied value of said steering angle velocity and said gear ratio, wherein a zero-cross point of said vibration-damping compensation value 2 is prior to said zero-cross point of said multiplied value of said steering angle velocity and said gear ratio, wherein said current command value is corrected by said vibration-damping compensation command value obtained at least in part from the vibration-damping compensation value 2, and wherein vibration amplitude of said motor near said zero-cross point of said multiplied value of said steering angle velocity and said gear ratio is suppressed.

10. The electric power steering apparatus according to claim 9, wherein said vibration-damping compensating section comprises a velocity-sensitive table 2 corresponding to said steering angle velocity, and a vibration-damping compensation value 3 is outputted by converting a vibration-damping compensation value 2 using said velocity-sensitive table 2.

11. The electric power steering apparatus according to claim 10, wherein said vibration-damping compensating section further including a torque-sensitive gain section to output a vibration-damping compensation value 4 by multiplying a gain 1 sensitive to said steering torque with said vibration-damping compensation value 2 or 3.

12. The electric power steering apparatus according to claim 11, wherein said vibration-damping compensating section further including a vehicle speed-sensitive gain section to output said vibration-damping compensation command value by multiplying a gain 2 sensitive to a vehicle speed with said vibration-damping compensation value 4.

13. The electric power steering apparatus according to claim 9, wherein said vibration-damping compensating section further including a torque-sensitive gain section to output a vibration-damping compensation value 4 by multiplying a gain 1 sensitive to said steering torque with said vibration-damping compensation value 2 or 3.

14. The electric power steering apparatus according to claim 13, wherein said vibration-damping compensating section further including a vehicle speed-sensitive gain section to output said vibration-damping compensation command value by multiplying a gain 2 sensitive to a vehicle speed with said vibration-damping compensation value 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIG. 1 is a diagram illustrating a configuration example of a general electric power steering apparatus;

(3) FIG. 2 is a block diagram showing an example of a control system of the electric power steering apparatus;

(4) FIG. 3 is a block diagram showing a configuration example (the first embodiment) of the present invention;

(5) FIG. 4 is a characteristic diagram showing a characteristic example of the torque-sensitive gain section;

(6) FIG. 5 is a characteristic diagram showing a characteristic example of the vehicle speed-sensitive gain section;

(7) FIG. 6 is a flow chart showing an operational example (the first embodiment) of the present invention;

(8) FIG. 7 is a time chart showing an operation example of the BPF which is used in the present invention;

(9) FIG. 8 is a diagram showing the effects of the present invention;

(10) FIG. 9 is a characteristic diagram showing another characteristic of the velocity-sensitive table;

(11) FIG. 10 is a block diagram showing a configuration example (the second embodiment) of the present invention; and

(12) FIG. 11 is a flow chart showing an operational example (the second embodiment) of the present invention.

MODE FOR CARRYING OUT THE INVENTION

(13) The present invention suppresses a handle vibration (noisy sound) being caused by a handle inertia and a spring nature of a torsion bar and improves a vibration that a driver feels uncomfortable and a steering feeling.

(14) Accordingly, an electric power steering apparatus according to the present invention performs a band pass filer (BPF)-process for a table output value (a vibration-damping compensation value 1) determined by a velocity-sensitive table corresponding to a motor velocity, or performs the BPF-process through the velocity-sensitive table corresponding to a factor (the steering angle velocity*the gear ratio) of a steering angle velocity (a differential component of the steering angle θ) by obtaining the steering angle velocity by differentiating the steering angle θ detected by the steering angle sensor and a gear ratio of a reduction mechanism obtained in advance. The present invention calculates a vibration-damping compensation command value by multiplying the output value (a vibration-damping compensation value 2) of the BPF with a gain due to the steering torque and again due to the vehicle speed. Further, the present invention corrects the calculated vibration-damping compensation command value by subtracting from the current command value of the steering assist, and suppresses the handle vibration by driving the motor with a corrected current command value. The factor of “the steering angle velocity*the gear ratio” is equivalent to the motor velocity ω.

(15) According to the electric power steering apparatus of the present invention, since the vibration-damping compensation command value is calculated by means of the velocity-sensitive table and the BPF by inputting the motor velocity or the factor of the steering angle velocity and the gear ratio, the vibration-damping compensation command value generates only at a steering active-return time, and it is possible to suppress the influences into another controls and the steering feeling to the minimum.

(16) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(17) FIG. 3 shows a configuration example (the first embodiment) of the present invention corresponding to FIG. 2, the present invention newly provides a vibration-damping compensating section 40. The vibration-damping compensating section 40 corrects the current command value Iref1 by subtraction-inputting a vibration-damping compensation command value VCc calculated in the vibration-damping compensating section 40 based on the motor velocity ω into a subtracting section 32C and compensates the vibration of the handle. That is, in the present invention, the current command value Iref1 and the compensation signal CM are addition-inputted into the addition/subtraction section 32C, the vibration-damping compensation command value VCc calculated in the vibration-damping compensating section 40 is subtraction-inputted into the addition/subtraction section 32C, and obtains the current command value Iref2 by correcting the current command value Iref1 described above. The operations after the current command value Iref2 are the same in FIG. 2.

(18) Further, the compensation due to the compensation signal CM in the compensation signal generating section 34 is not always necessary.

(19) The vibration-damping compensating section 40 comprises a velocity-sensitive table 41 to input the motor velocity ω and output a trapezoidal-wave type vibration-damping compensation value VC1 at before and behind zero of the motor velocity ω, a band pass filter (BPF) 42 to band-pass filter the vibration-damping compensation value VC1 from the velocity-sensitive table 41, a torque-sensitive gain section 43 to multiply a gain Gt corresponding to the steering torque Th with the vibration-damping compensation value VC2 from the BPF 42, and a vehicle spped-sensitive gain section 44 to multiply a gain Gv corresponding to the vehicle speed Vel with the vibration-damping compensation value VC3 from the torque-sensitive gain section 43 and to output a vibration-damping compensation command value VCc.

(20) The torque-sensitive gain section 43 has a characteristic for the steering torque Th as shown in FIG. 4. The torque-sensitive gain Gt holds a constant gain till a predetermined torque value 1 (0.5 Nm in this embodiment), increases from the predetermined torque value 1 to a predetermined torque value 2 (1.0 Nm in this embodiment) and holds a constant value at equal to or more than the predetermined torque value 2. That is, the characteristic is that is small value when the steering torque Th is small, gradually increases from a value (the predetermined torque value 1) and saturates at a value (the predetermined torque value 2). Thus, it is possible to easily get more effects in a state when the handle vibration is great (the steering torque detecting the torsion angle is great).

(21) Further, the vehicle speed-sensitive gain section 44 has a characteristic for the vehicle speed Vel as shown in FIG. 5. The vehicle speed-sensitive gain Gv holds a constant gain till a predetermined vehicle speed 1 (50 kph in this embodiment), increases from the predetermined vehicle speed 1 to a predetermined vehicle speed 2 (100 kph in this embodiment) and holds a constant value at equal to or more than the predetermined vehicle speed 2. That is, the characteristic is that is small value when the vehicle speed Vel is low, gradually increases from a value (the predetermined vehicle speed 1) and saturates at a value (the predetermined vehicle speed 2). Thus, it is possible to easily get more effects in a vehicle speed state when the handle vibration is great.

(22) Further, arrangement of the torque-sensitive gain section 43 and the vehicle speed-sensitive gain section 44 may be alternative.

(23) In such a configuration as described above, the operation example will be described with reference to a flow chart of FIG. 6.

(24) First, the steering torque Th is inputted (Step S1), the vehicle speed Vel is inputted (Step S2), and the current command value Iref1 is calculated in the current command value calculating section 31 (Step S3).

(25) The vibration-damping compensating section 40 inputs the motor velocity ω (Step S10) and obtains the vibration-damping compensation value VC1 corresponding to the motor velocity ω in the velocity-sensitive table 41 (Step S11). Next, the vibration-damping compensating section 40 inputs the vibration-damping compensation value VC1 into the BPF 42 and performs a BP-filtering process (Step S12), inputs the BP-filtering processed vibration-damping compensation value VC2 into the torque-sensitive gain section 43, and multiply the gain Gt corresponding to the steering torque Th with vibration-damping compensation value VC2 (Step S13). The gain-processed vibration-damping compensation value VC3 is inputted into the vehicle speed-sensitive gain section 44 (Step S14), and the vibration-damping compensation command value VCc multiplied with gain Gv corresponding to the vehicle speed Vel is outputted (Step S15).

(26) Further, the compensation signal generating section 34 generates the compensation signal CM due to the convergence 341, the inertia 342 and the SAT 343 and outputs the compensation signal CM as described above (Step S20).

(27) Furthermore, the orders of the calculation of the current command value Iref1 (Steps S1 to S3), the calculation of the vibration-damping compensation command value VCc (Steps S10 to S15) and the generation of the compensation signal CM (Step S20) are optionally changeable.

(28) The current command value Iref1, the vibration-damping compensation command value VCc and the compensation signal CM which are obtained as described above, are inputted into the addition/subtraction section 32C and are addition/subtraction-processed therein, and the current command value Iref2 is generated (Step S30). The current command value Iref2 is limited in the current limiting section 33 and then is current-controlled in the PI control section 35 as described above (Step S31), and the motor 20 is drive-controlled through the PWM control section 36 and the inverter 37 (Step S32).

(29) The motor velocity ω vibrates with a sine-wave as shown in FIG. 7(A), the velocity-sensitive table 41 has a characteristic to output a trapezoidal-wave type vibration-damping compensation value VC1 before and behind zero of the motor velocity ω when the motor velocity ω is inputted into the velocity-sensitive table 41. Therefore, the vibration-damping compensation value VC1 outputted from the velocity-sensitive table 41 is a trapezoidal-wave as shown in FIG. 7(B). The vibration-damping compensation value VC1 outputted from the velocity-sensitive table 41 is inputted into the BPF 42, only the intermediate frequency component that a high frequency component (e.g. 20 Hz or more) and a low frequency component (e.g. 5 Hz or less) are removed, passes, and the vibration-damping compensation value VC2 is outputted as shown in FIG. 7(B).

(30) As shown in FIGS. 7(A) and (B), it is possible to advance in time (a time point t1) the vibration-damping compensation value VC2 than a time point t2 when the motor velocity ω and the vibration-damping compensation value VC1 cross zero by band-pass filtering the trapezoidal-wave type vibration-damping compensation value VC1 in the BPF 42. The component of the vibration-damping compensation value VC2 becomes the current command value (the vibration-damping compensation value VCc) for the suppression of the handle vibration, and the vibration-damping compensation value VCc is subtracted from the current command value Iref1 for the steering. Consequently, it is capable of suppressing the vibration of the motor by delaying the vibration of the motor velocity ω adjusting the timing when the motor velocity ω crosses zero.

(31) FIG. 8 shows an example of a time response of the detected torque (proportional to a torsion angle of the torsion bar) when an external disturbance torque is added at a hands-free in a state that the handle vibration easily generates with an intentional design, and compares a case (the present invention) with the vibration-damping compensation and a case (prior art) without the vibration-damping compensation. In this example, the torque sensitive-gain and the vehicle speed-sensitive gain are constant. In view of FIG. 8, it is clear that the vibration of the case with the vibration-damping compensation rapidly converges than the same of the case without the vibration-damping compensation and the vibration is effectively suppressed.

(32) Although the vibration-damping compensating section comprises the velocity-sensitive table 41 and the BPF 42 in the above first embodiment, it may use a velocity-sensitive table having a hysteresis characteristic corresponding to a direction of the motor velocity ω as shown in FIG. 9 instead of the velocity-sensitive table 41 and the BPF 42.

(33) Further, although the motor velocity ω is used as the input of the vibration-damping compensation in the first embodiment, a value which is multiplied the gear ratio of the reduction mechanism with the steering angle velocity is equivalent to a value corresponding to the motor velocity ω. Thus, the factor of the steering angle velocity and the gear ratio may be used as the input of the vibration-damping compensation. The steering angle velocity is detected by differentiate-calculating the steering angle from the steering angle sensor and the gear ratio of the reduction mechanism is determined in advance.

(34) A configuration (the second embodiment) in a case that the factor of the steering angle velocity and the gear ratio is used as the vibration-damping compensation input is shown in FIG. 10 corresponding to FIG. 3, and the “the steering angle velocity*the gear ratio” is inputted into a velocity-sensitive table 41A within the vibration-damping compensating section 40A. The velocity-sensitive table 41A is sensitive to “the steering angle velocity*the gear ratio” and is the same characteristic with the velocity-sensitive table 41 as described above (refer to FIG. 7), and the BPF 42, the torque-sensitive table 43 and the vehicle speed-sensitive table 44 are entirely the same with the first embodiment. The vibration-damping compensation command value VCc from the vibration-damping compensating section 40 is subtraction-inputted into the addition/subtracting section 32C and corrects the current command value Iref1 and suppresses the handle vibration.

(35) The operational example (the second embodiment) in the case that the factor of the steering angle velocity and the gear ratio is used as the vibration-damping compensation input is shown in a flow chart of FIG. 11 corresponding to FIG. 6. That is, the steering angle velocity and the predetermined gear ratio are inputted at the Step S10A, the vibration-damping compensation value VC1 corresponding to “the steering angle velocity*the gear ratio” is obtained at the Step S11A, and the others are the same with the first embodiment. Further, the steering angle velocity at the Step S10A may be obtained by differentiate-calculating after inputting of the steering angle θ.

(36) According to the second embodiment, it is possible to get the effects as described above and the characteristic in FIG. 8.

(37) Recently, there has been appeared the vehicles equipped with a parking support function (parking assist) that switch between the automatic steering mode and the manual steering mode. In a vehicle equipped with the parking support function, it is capable of performing the vibration-damping compensation during the operation of the steering angle control. The vibration-damping compensation according to the present invention may combine with a function to detect the vibration state.

(38) Further, the torque-sensitive gain Gt is limited to the characteristic of FIG. 4 (e.g. the increasing of non-linear), and the vehicle speed-sensitive gain Gv is limited to the characteristic of FIG. 5 (e.g. the increasing of non-linear)

EXPLANATION OF REFERENCE NUMERALS

(39) 1 handle 2 column shaft (steering shaft, handle shaft) 10 torque sensor 12 vehicle speed sensor 20 motor 30 control unit (ECU) 31 current command value calculating section 33 current limiting section 34 compensation signal generating section 35 PI control section 36 PWM control section 37 inverter 40,40A vibration-damping compensating section 41, 41A speed-sensitive table 42 BPF (band pass filter) 43 torque-sensitive gain section 44 vehicle speed-sensitive gain section 50 CAN