Electric power steering apparatus

Abstract

An electric power steering apparatus that drives and controls a motor which applies an assist torque to a steering system of a vehicle and has a function switching between an assist mode and an automatic mode, including a torsion bar torsional angle calculating section to calculate a torsion bar torsional angle based on a torque information, an output-side column shaft relative angle generating section to output an output-side relative angle from an electrical angle signal of the motor, an actual handle angle calculating section to calculate an actual handle angle based on the torsion bar torsional angle and the output-side relative angle, a resonance filter to obtain an estimated handle angle in a hands-off state from the output-side relative angle, and a hands-on/off judging section to judge a hands-on state when a time that a deviation angle between the actual handle angle and the estimated handle angle is equal to or more than a predetermined angle is continued for the predetermined time or more.

Claims

1. An electric power steering apparatus that comprises a torsion bar to a column shaft coupled to a handle, drives and controls a motor which applies an assist torque to a steering system of a vehicle by a current command value and has a function switching between an assist mode and an automatic mode, comprising: a torsion bar torsional angle calculating section to calculate a torsion bar torsional angle based on a torque information relate to said torsion bar, an output-side column shaft relative angle generating section to output an output-side relative angle from an electrical angle signal of said motor using a predetermined computing expression, an actual handle angle calculating section to calculate an actual handle angle based on said torsion bar torsional angle and said output-side relative angle, a resonance filter to obtain an estimated handle angle in a hands-off state from said output-side relative angle, and a hands-on/off judging section to judge a hands-on state when a time that a deviation angle between said actual handle angle and said estimated handle angle in said hands-off state is equal to or more than a predetermined angle is continued for a first predetermined time or more.

2. The electric power steering apparatus according to claim 1, wherein said hands-on/off judging section judges a hands-off state when a time that said deviation angle is smaller than said predetermined angle is continued for a second predetermine time or more after judging said hands-on state.

3. The electric power steering apparatus according to claim 1, wherein said torque information relate to said torsion bar is a column shaft angle relate to said handle or a torsional torque relate to said torsion bar.

4. The electric power steering apparatus according to claim 3, wherein said torsion bar torsional angle calculating section is a torsion bar torsional angle computing section to input said torsional torque and compute said torsion bar torsional angle by dividing said torsional torque by a spring constant of said torsion bar.

5. The electric power steering apparatus according to claim 3, wherein said torsion bar torsional angle calculating section is a torsion bar torsional angle generating section to input a torque sensor detection input-side column angle and a torque sensor detection output-side column angle and generate said torsion bar torsional angle using a spring constant of said torsion bar.

6. The electric power steering apparatus according to claim 1, wherein said output-side column shaft relative angle generating section performs an anti-rollover process to said electrical angle signal and outputs said output-side relative angle by said predetermined computing expression.

7. The electric power steering apparatus according to claim 6, wherein said predetermined computing expression is multiplied said electrical angle signal by an electrode pairs number of said motor and a reduction ratio of said reduction mechanism.

8. The electric power steering apparatus according to claim 1, wherein said resonance filter reproduces a resonance of said handle when a steering is steered from said output-side column shaft in an actual apparatus and has a characteristic that said estimated handle angle in said hands-off state which is obtained by inputting said output-side column angle is substantially same as said actual handle angle.

9. The electric power steering apparatus according to claim 8, wherein said resonance filter is a second order or higher low pass filter (LPF).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIG. 1 is a configuration diagram showing a general outline of an electric power steering apparatus;

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

(4) FIG. 3 is a diagram showing a mechanism of a steering shaft (a column shaft) of a column-type steering;

(5) FIG. 4 is a model diagram for analyzing a force applying to the steering shaft (the column shaft);

(6) FIG. 5 is a mechanism diagram showing a relationship among a torsion bar, a handle angle and an output-side column angle;

(7) FIG. 6 is a diagram showing an installation example of sensors and a relationship between the column angle and the handle angle;

(8) FIG. 7 is a block diagram showing a configuration example of a manual input judging section according to the present invention;

(9) FIG. 8 is a block diagram showing a part of a configuration example in a case of inputting a torsional torque;

(10) FIG. 9 is Bode diagrams showing a characteristic example of a resonance filter used in the present invention;

(11) FIG. 10 is a block diagram showing a configuration example of a hands-on/off judging section;

(12) FIG. 11 is a time chart showing one example of a steering system angle characteristic in a case of a hands-on state;

(13) FIG. 12 is a time chart showing one example of the steering system angle characteristic in a case of a hands-off state; and

(14) FIG. 13 is a time chart showing another example of the steering system angle characteristic in a case of a hands-off state.

MODE FOR CARRYING OUT THE INVENTION

(15) A detection technology for judging whether driver's hands-on a steering (judging hands-on the steering, hands-off the steering or performing a manual input) is performed or not is existed in an electric power steering apparatus that has an assist mode to control a motor which applies an assist torque to a steering system of a vehicle when the driver steers the steering system, and an automatic mode to control the motor in response to a target steering angle which is continuously instructed by the vehicle when the vehicle autonomously runs. In the above detection, it is increasingly important to improve the detection accuracy without being affected by a disturbance noise.

(16) Instead of the conventional hands-on or hands-off judgment which is performed in a torque system, the present invention proposes a method that the hands-on or hands-off judgment is performed in an angle system in which derivative is not used. Concretely, the hands-on or hands-off judgment, that is, the manual input judgment is performed by utilizing an angle information of an assist motor of the electric power steering apparatus (EPS) which is disposed at a downstream stage of a torque sensor, estimating a handle angle by using a resonance filter (for example, a second order or higher low pass filter (LPF)) which is designed in harmony with a frequency response in the hands-off, and performing a two-stage comparison which is a comparison using an angle threshold and a comparison using a time threshold based on a deviation angle between an actual handle angle calculated from the angle information with respect to the column shaft or a torsional torque and an electrical angle signal of the motor. In the present invention, a case of hands-on the steering or one-hand-on the steering is judged as the hands-on (the manual input is performed) and a case of hands-off the steering is judged as hands-off (the manual input is not performed). The accurate hands-on or hands-off judgment is performed without using the motor angular velocity and the motor angular acceleration in which the derivative calculation is performed, and being affected by the noise relate to a free vibration system due to the torsional rigidity including the handle resonance and the like.

(17) When the output-side column shaft 2B is rotated (the rotational angle is generated) under a state that the steering system is separated from the universal joints 4a, the present invention performs the hands-on or hands-off judgment based on a phenomenon that a vibration characteristic of the input-side column shaft 2A in a case of hands-on the handle 1 is different from that in a case of hands-off the handle 1. FIG. 5 is a mechanism diagram showing a relationship among the torsion bar 23, the handle angle h and the output-side column angle c. When the torsion bar torsional angle is defined as d, a below Expression 6 is established.
h=c+d[Expression 6]

(18) FIG. 12 shows a characteristic in a case of hands-on the handle 1, that is, the actual handle angle (the input-side column angle) when the output-side column angle c is changed, with respect to a steering-forward state (t1), a steering holding state (t1t2), a steering-backward state (t2t3) and the steering holding state (t3). As well, FIG. 13 shows a characteristic in a case of hands-off the handle 1, that is, the actual handle angle (the input-side column angle) when the output-side column angle c is changed, with respect to a right-turning state (t1), the steering holding state (t1t2), a left-turning state (t2t3) and the steering holding state (t3). The characteristic difference between FIGS. 12 and 13 is caused by the torsion bar torsional angle d, and the judgment of the handle hands-off state or the handle hands-on state can be done.

(19) Embodiments according to the present invention will be described with reference to the accompanying drawings.

(20) At first, in a case that the judgment is performed by using the angle information, an arrangement relationship among the various sensors will be described, as shown in FIG. 6.

(21) A Hall IC sensor 21 as an angle sensor and a 20 rotor sensor 22 of a torque sensor input-side rotor are mounted on the input-side column shaft 2A of the handle 1 side of the column shaft 2 including the torsion bar 23. The Hall IC sensor 21 outputs an AS_IS angle n of 296 period. The 20 rotor sensor 22 that is mounted to the handle 1 side closer than the torsion bar 23 outputs input-side column angle signals .sub.h1 (a first TS_IS angle) and .sub.h2 (a second TS_IS angle) of 20 period, and the input-side column angle signal .sub.h1 is inputted into an angle calculating section 50. A 40 rotor sensor 24 of a torque sensor output-side rotor is mounted on an output-side column shaft 2B of the column shaft 2, output-side column angle signals .sub.c1 (a first TS_OS angle) and .sub.c2 (a second TS_OS angle) from the 40 rotor sensor are outputted, and the output-side column angle signal .sub.n is inputted into the angle calculating section 50. Absolute angles of the input-side column angle signal .sub.h1 and the output-side column angle signal .sub.c1 are calculated from the input-side column angle signal .sub.h1 and the output-side column angle signal .sub.c1 at the angle calculating section 50, and a torque sensor detection input-side column angle th and a torque sensor detection output-side column angle tc are outputted from the angle calculating section 50.

(22) In a case that the torsional torque Tt is obtained from the torque sensor detection input-side column angle th and the torque sensor detection output-side column angle tc, when the spring constant of the torsion bar 23 is defined as Kh, the torsional torque Tr can be obtained from a below Expression 7.
Tt=Kh(thtc)[Expression 7]

(23) In a case that the hands-on or hands-off judgment is performed after the torsional torque Tt is obtained from the torque detection value, the torsional torque Tt is directly obtained from an above-described configuration of FIG. 3.

(24) The configuration of the manual input judging section according to the present invention is adapted to both a case that the torsional torque Tt is directly detected from the configuration of FIG. 3 and a case that the torsional torque Tt is obtained from the configuration of FIG. 6. At first, an embodiment in a case that the torsional torque Tt is obtained from the configuration of FIG. 6 will be described with reference to FIG. 7.

(25) The above configuration comprises a torsion bar torsional angle generating section 120 to input the torque sensor detection input-side column angle th and the torque sensor detection output-side column angle tc and generate the torsion bar torsional angle d, an output-side (OS) relative angle generating section 150 to input the electrical angle signal e of the motor from the rotational sensor 20A and output the output-side (OS) relative angle t, an adding section 121 which functions as an actual handle angle computing section, adds with the torsion bar torsional angle d and the output-side (OS) relative angle t and outputs an actual handle angle hr, a resonance filter 140 to input the output-side relative angle t and output an estimated handle angle he in the hands-off state, a subtracting section 122 to obtain a deviation angle de by subtracting the estimated handle angle he from the actual handle angle hr, and a hands-on/off judging section to judge the hands-on or the hands-off based on the deviation angle de.

(26) In the present embodiment, the torsion bar torsional angle generating section 120 obtains the torsion bar torsional angle d ((=thtc) or (=|thtc|)) based on the torque sensor detection input-side column angle th and the torque sensor detection output-side column angle tc which are shown in FIG. 6. The torsion bar torsional angle d is also obtained from the torsional torque Tt which is detected at the torque sensor section 200 shown in FIG. 3. FIG. 8 shows a configuration of the above case, the detected torsional torque Tt is inputted into the torsion bar torsional angle calculating section 120A and the torsion bar torsional angle calculating section 120A obtains the torsion bar torsional angle d by calculating a following Expression 8.
d=Tt/Kh[Expression 8]

(27) The output-side relative angle generating section 110 performs an anti-rollover process using a motor electrical angle scale (a waveform process (for example, a saw tooth wave angle signal is processed to a continuous angle signal)), and outputs the output-side relative angle t based on a following Expression 9.
t=ee(1/electrode pairs number)(reduction ratio)[Expression 9]

(28) Here, electrode pairs number is the number of electrode pairs of the motor and reduction ratio is the reduction ratio of the reduction mechanism.

(29) When tuning from the output side, a friction which is existed in the unit, a loss torque of the motor, a backlash of the spline unit of the motor shaft, inertia and a preload of the input-side bearing are related to the above process.

(30) The resonance filter 140 which obtains the estimated handle angle he in the hands-off state is designed by using the reproduced data in which the resonance of the handle 1 is generated from the output-side column shaft 2B when being steered the steering on the actual apparatus, obtaining the frequency response from the measurement results of the handle angle h which is the input-side column angle and the output-side column angle c, and being in harmony with the above data and the above frequency response. The Bode diagrams which show the characteristic example of the resonance filter 140 are shown in the characteristic B (a solid line) of FIG. 9. The gain of the resonance filter 140 has a constant value up to substantially 3 [Hz], has a larger value than that of the general second-order low pass filter (LPF) shown by the characteristic A (a broken line) and has a protrusion shape between substantially 3 [Hz] and substantially 10 [Hz], and has a smaller value than that of the general second-order LPF shown by the characteristic A (the broken line) in a region that the frequency is substantially 20 [Hz] or more. The phase of the resonance filter 140 has a smaller delay than that of the general second-order LPF shown by the characteristic A (the broken line) up to substantially 20 [Hz], and has a larger delay than that of the general second-order LPF shown by the characteristic A (the broken line) in a region that the frequency is substantially 20 [Hz] or more. That is, in the actual apparatus, the bench test apparatus in which the actual vehicle is simulated or the like, the handle angle h and the output-side column angle c are measured by steering the output-side column shaft 2B in a state that the ECU is electrically energized and the hands of the driver are not in contact with the handle 1 (the hands-off state) (actually, the bench test apparatus is separated at the universal joints 4a in the electric power steering apparatus of FIG. 1, and the measurement is performed by applying the manual input). The torsional angle d is obtained from the torsional torque Tt (that is, the torsional angle d is directly obtained by the torque sensor). The handle angle h is obtained by adding the torsional angle d to the output-side column angle c (refer to the Expression 6). In the design of the resonance filter, the data of the actual vehicle or the actual data of the bench test apparatus in which the actual vehicle is simulated or the like, are used in the output-side column angle c and the handle angle h. The resonance of the handle is included in this handle angle h. Because the measurement is performed in the hands-off state, the ideal filter result he when the output-side column angle c is inputted (the estimated handle angle in the hands-off state) should be the handle angle h. In order to reproduce the resonance, the second order filter is needed. The designed resonance filter 140 is adjusted so that the estimated handle angle he in the hands-off state is in harmony with the handle angle h of the actual data. Consequently, the resonance filter 140 has a characteristic shown in FIG. 9.

(31) The waveforms of the actual output-side column angle c are shown in FIGS. 12 and 13. In contrast to the waveforms of the actual output-side column angle c, the waveforms of the actual handle angle hr are vibrated at the changing points of the steering. The noise in the estimated handle angle he in the hands-off state from the resonance filter 140 is removed by the resonance filter 140 which is designed by the tuning, and then the estimated handle angle he is inputted into the subtracting section 122.

(32) The configuration of the hands-on/off judging section 130 is shown in, for example, FIG. 10. The deviation angle de obtained at the subtracting section 122 is inputted into an absolute value calculating section 131, and the absolute value |de| of the deviation angle is inputted into an angle comparing section 132 and is compared with a predetermined angle threshold th. That is, it is judged whether a following Expression 10 is established or not.
|hrhc|=|de|th[Expression 10]

(33) In a case that the above Expression 10 is established, the angle comparing section 132 outputs an angle establishment signal AE. The angle establishment signal AE is inputted into an establishment time comparing section 133 and a non-establishment time comparing section 134. When the angle establishment signal AE continues for the predetermined time threshold T1 or more, the establishment time comparing section 133 outputs a judgment signal DS1 which shows hands-on, and the judgment signal DS1 is outputted as a judgment signal DS showing the hands-on state via an OR circuit 135. In a case that the non-establishment state in the expression 10 continues for the predetermined time threshold T2 or more after the establishment time comparing section 133 judges the hands-on state, the non-establishment time comparing section 134 outputs a judgment signal DS2 which shows the hands-off, and the judgment signal DS2 is outputted as the judgment signal DS showing the hands-off state via the OR circuit 135. The purpose that it is judged whether the hands-on state is held for the predetermined time or not will be described below. Even when the hands of the driver are in contact with the handle, it is necessary that it is not judged as the hands-off state in cases that the angle difference between the input side and the output side is not generated (for example, the road surface is flat and the vehicle runs a straight road) or the instantaneous hands-off is occurred.

(34) As well, in the example of FIG. 10, the absolute value of the deviation angle de is calculated and the absolute value is compared with one angle threshold th. Alternatively, the absolute value of the deviation angle de may not be calculated, and the deviation angle de may be compared with positive and negative angle thresholdsth.

(35) In such a configuration, the operation example will be described with reference to a flowchart of FIG. 11.

(36) At first, the torque sensor detection input-side column angle th and the torque sensor detection output-side column angle tc are inputted into the torsion bar torsional angle generating section 120 (Step S10), and the torsion bar torsional angle generating section 120 generates the torsion bar torsional angle d (Step S11). The torsion bar torsional angle d is inputted into the adding section 121. In a case of FIG. 8 that the torsional torque Tt shown in FIG. 3 is inputted, the torsional torque Tt is inputted into the torsion bar torsional angle calculating section 120A, and the torsion bar torsional angle calculating section 120A calculates the torsion bar torsional angle d.

(37) The motor electrical angle e is inputted into the output-side relative angle generating section 110 (Step S12), the output-side relative angle generating section 110 generates the output-side relative angle t (Step S13), and the output-side relative angle t is inputted into the adding section 121 and the resonance filter 140. Next, the adding section 121 calculates the actual handle angle hr by adding with the torsion bar torsional angle d and the output-side relative angle t (Step S14), and the resonance filter 140 processes the output-side relative angle t and calculates the estimated handle angle he (Step S15). The actual handle angle hr and the estimated handle angle he are inputted into the subtracting section 122. The subtracting section 122 calculates the deviation angle de by subtracting the estimated handle angle he in the hands-off state from the actual handle angle hr (Step S16), and the deviation angle de is inputted into the hands-on/off judging section 130.

(38) In the handle-on/off judging section 130, at first, the absolute value calculating section 131 obtains the absolute value |de| of the deviation angle de (Step S20), and the angle comparing section 132 judges whether the Expression 10 is established or not (Step S21). In a case that the Expression 10 is not established, the process is returned to the above Step S20, and in a case that the Expression 10 is established, the angle comparing section 132 outputs the angle establishment signal AE (Step S22). The angle establishment signal AE is inputted into the establishment time comparing section 133, and the duration time of the angle establishment signal AE is compared with the time threshold T1 (Step S23). When the angle establishment signal AE continues for the time threshold T1 or more, the establishment time comparing section 133 outputs the judgment signal DS1 (Step S24), and the judgment signal DS1 is outputted as the judgment signal DS via the OR circuit 135 (Step S25). After the establishment time comparing section 133 judges the hands-on state, the non-establishment time comparing section 134 judges whether the non-establishment state in the Expression 10 continues for the time threshold T2 or more or not (Step S26). When the non-establishment state continues for the time threshold T2 or more, the non-establishment time comparing section 134 outputs the judgment signal DS2 (Step S27), and the judgment signal DS2 is outputted as the judgment signal DS via the OR circuit 135 (Step S28).

(39) In the actual apparatus, the bench test apparatus in which the actual vehicle is simulated or the like, FIG. 12 shows the waveform examples of the estimated handle angle he, the actual handle angle hr and the output-side column angle c in a state that the ECU is electrically energized and the hands of the driver are in contact with the handle (the hands-on state). In FIG. 12, the steering-forward is performed up to the time point t1, the steering-holding is performed between the time point t1 and the time point t2, the steering-backward is performed between the time point t2 and the time point t3, and the steering-holding is performed after the time point t3. FIG. 13 shows the waveform examples of the respective angles with the same time scale of FIG. 12 in a state that the hands of the driver are not in contact with the handle (the hands-off state).

EXPLANATION OF REFERENCE NUMERALS

(40) 1 handle (steering wheel) 2 column shaft (handle shaft) 2A input-side column shaft (IS) 2B output-side column shaft (OS) 20 motor 23, 201 torsion bar 100 control unit (ECU) 120 input and output (IS/OS) deviation angle generating section 130 hands-on/off judging section 140 resonance filter 150 output-side (OS) relative angle generating section 200 torque sensor section