ELECTRIC POWER STEERING APPARATUS

Abstract

An electric power steering apparatus that includes a torque sensor to detect a steering torque, a current command value calculating section to calculate a current command value, a motor to generate a steering assist torque applied to a steering mechanism, and a motor control section to driving-control the motor based on the current command value, including: a steering angle estimating calculating section to vary a front-wheel weight X of a front-wheel estimated steering angle and a rear-wheel weight Y of a rear-wheel estimated steering angle corresponding to a running state of the vehicle and calculate a four-wheel estimated steering angle based on the front-wheel weight X and the rear-wheel weight Y.

Claims

1-11. (canceled)

12. An electric power steering apparatus that comprises a torque sensor to detect a steering torque which is inputted into a steering mechanism of a vehicle, a current command value calculating section to calculate a current command value based on at least said steering torque, a motor to generate a steering assist torque applied to said steering mechanism, and a motor control section to driving-control said motor based on said current command value, comprising: a steering angle estimating calculating section to vary a front-wheel weight X of a front-wheel estimated steering angle and a rear-wheel weight Y of a rear-wheel estimated steering angle corresponding to a running state of said vehicle and calculate a four-wheel estimated steering angle based on said front-wheel weight X and said rear-wheel weight Y (X+Y=1.0), wherein in a case that said running state of said vehicle is an acceleration running or a deceleration running, said electric power steering apparatus further comprises: an acceleration and deceleration calculating section to calculate an acceleration and deceleration estimated value from a vehicle speed; and an acceleration and deceleration sensitive-table to calculate said front-wheel weight X and said rear-wheel weight Y based on said acceleration and deceleration estimated value.

13. The electric power steering apparatus according to claim 12, wherein said acceleration and deceleration calculating section comprises a differential section to differentiate said vehicle speed, or a memory unit to store a previous value of said vehicle speed and a subtracting section to subtract said previous value from a present value.

14. The electric power steering apparatus according to claim 12, wherein said acceleration and deceleration sensitive-table sets said front-wheel weight X equivalent to said rear-wheel weight Y near a zero value of said acceleration and deceleration estimated value, and makes said front-wheel weight X larger in an acceleration running and a deceleration running.

15. The electric power steering apparatus according to claim 13, wherein said acceleration and deceleration sensitive-table sets said front-wheel weight X equivalent to said rear-wheel weight Y near a zero value of said acceleration and deceleration estimated value, and makes said front-wheel weight X larger in an acceleration running and a deceleration running.

16. The electric power steering apparatus according to claim 12, wherein in a case that said running state of said vehicle is a rough road running, said electric power steering apparatus further comprises: a road surface estimated value calculating section to calculate a road surface estimated value from four-wheel speeds of said vehicle; and a road surface estimated value sensitive-table to calculate said front-wheel weight X and said rear-wheel weight Y based on said road surface estimated value.

17. The electric power steering apparatus according to claim 16, wherein said road surface estimating calculating section calculates a variation of a vehicle speed in each of wheels from said four-wheel speeds, and calculates said road surface estimated value by judging said rough road running from a maximum acceleration or a maximum deceleration.

18. The electric power steering apparatus according to claim 16, wherein said road surface estimated value sensitive-table sets said front-wheel weight X equivalent to said rear-wheel weight Y near a zero value of said road surface estimated value, and makes said rear-wheel weight Y larger when said road surface estimated value is a predetermined value or more.

19. The electric power steering apparatus according to claim 17, wherein said road surface estimated value sensitive-table sets said front-wheel weight X equivalent to said rear-wheel weight Y near a zero value of said road surface estimated value, and makes said rear-wheel weight Y larger when said road surface estimated value is a predetermined value or more.

20. The electric power steering apparatus according to claim 12, wherein in a case that said running state of said vehicle is a slalom steering driving, said electric power steering apparatus further comprises: a steering angular velocity sensitive-table to calculate said front-wheel weight X and said rear-wheel weight Y from a motor angular velocity estimated value.

21. The electric power steering apparatus according to claim 20, wherein said steering angular velocity sensitive-table sets said front-wheel weight X equivalent to said rear-wheel weight Y in an area that said motor angular velocity estimated value is small, and makes said front-wheel weight X larger when said motor angular velocity estimated value is a predetermined value or more.

22. The electric power steering apparatus according to claim 12, wherein in a case that said running state of said vehicle is an acceleration running, a deceleration running, a rough road running, a slalom steering driving, an average value of a four-wheel estimated steering angle est1 which is calculated in said acceleration running and said deceleration running, a four-wheel estimated steering angle est2 which is calculated in said rough road running, and a four-wheel estimated steering angle est3 which is calculated in said slalom steering driving, is set as said four-wheel estimated steering angle.

23. The electric power steering apparatus according to claim 22, wherein said four-wheel estimated steering angles est1, est2 and est3 are weighted with Xt, Yt and Zt (Xt+Yt+Zt=1.0), respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the accompanying drawings:

[0022] FIG. 1 is a configuration diagram showing a general outline of an electric power steering apparatus;

[0023] FIG. 2 is a block diagram showing a general configuration example of a control system of the electric power steering apparatus;

[0024] FIG. 3 is a block diagram showing a configuration example of a control system of the electric power steering apparatus having a conventional handle-returning control function;

[0025] FIG. 4 is a block diagram showing a configuration example of the present invention;

[0026] FIG. 5 is a block diagram showing a configuration example of a steering angle estimating section;

[0027] FIG. 6A, FIG. 6B and FIG. 6C are diagrams for explaining an estimation of a four-wheel estimated steering angle;

[0028] FIG. 7 is a schematic diagram for explaining a steering angle estimation;

[0029] FIG. 8 is a block diagram showing a configuration example (Example 1-1) of a weighting section in a steering angle estimating calculating section;

[0030] FIG. 9 is a block diagram showing a configuration example of a correction gain calculating section;

[0031] FIG. 10A and FIG. 10B are schematic diagrams for explaining an operation of a vehicle slip judging section;

[0032] FIG. 11 is a block diagram showing a configuration example of the vehicle slip judging section;

[0033] FIG. 12 is a characteristic diagram showing an operation example of a vehicle slip judging;

[0034] FIG. 13A and FIG. 13B are schematic diagrams for explaining an operation of a driving-wheel slip judging section;

[0035] FIG. 14 is a block diagram showing a configuration example of the driving-wheel slip judging section;

[0036] FIG. 15 is a block diagram showing a configuration example of a handle-returning control section;

[0037] FIG. 16 is a characteristic diagram showing one example of a steering angle sensitive-table;

[0038] FIG. 17 is a characteristic diagram showing one example of a vehicle speed sensitive-table;

[0039] FIG. 18 is a characteristic diagram showing one example of a steering angular velocity sensitive-table;

[0040] FIG. 19 is a flowchart showing an operation example of the present invention;

[0041] FIG. 20 is a flowchart showing an operation example of the steering angle estimating calculating section;

[0042] FIG. 21 is a flowchart showing an operation example of the correction gain calculating section;

[0043] FIG. 22 is a flowchart showing an operation example of the handle-returning control section;

[0044] FIG. 23 is a diagram showing merits and demerits in view of a variety of evaluation viewpoints, such as a responsibility, for a steering angle estimating method in various running states of an actual running vehicle;

[0045] FIG. 24 is a block diagram showing a configuration example (Example 2-1) of the steering angle estimating section in acceleration and deceleration running;

[0046] FIG. 25 is a block diagram showing a configuration example of an acceleration and deceleration calculating section;

[0047] FIG. 26 is a characteristic diagram showing one example of an acceleration and deceleration sensitive-table;

[0048] FIG. 27 is a block diagram showing a configuration example (Example 2-2) of the steering angle estimating section in a rough road running;

[0049] FIG. 28 is a block diagram showing a configuration example of a road surface estimating section;

[0050] FIG. 29 is a characteristic diagram showing one example of a road surface estimated value sensitive-table;

[0051] FIG. 30 is a block diagram showing a configuration example (Example 2-3) of the steering angle estimating section in a slalom steering running;

[0052] FIG. 31 is a characteristic diagram showing one example of a motor angular velocity sensitive-table;

[0053] FIG. 32 is a block diagram showing a configuration example (Example 2-5) of the steering angle estimating section which can be applied to all of running states; and

[0054] FIG. 33 is a block diagram showing a modification example (Example 2-6) of the configuration shown in FIG. 32.

MODE FOR CARRYING OUT THE INVENTION

[0055] An electric power steering apparatus of the present invention does not need to have a steering angle sensor and prevents from an incorrect output by calculating a front-wheel estimated steering angle from a front-wheel left and right wheel speeds, calculating a rear-wheel estimated steering angle from a rear-wheel left and right wheel speeds, calculating a four-wheel estimated steering angle by varying weights of the front-wheel estimated angle and the rear-wheel estimated angle in response to a running state such as acceleration and deceleration running, and correcting a certainty of a four-wheel estimated steering angle by using the front-wheel estimated angle, the rear-wheel estimated angle and the four-wheel speeds, a vehicle speed and a motor angular velocity estimated value, or correcting an output of the control by using the four-wheel estimated steering angle.

[0056] Further, in the present invention, a configuration having the above functions is applied to a handle-returning (active return) control.

[0057] Embodiments according to the present invention will be described with reference to the drawings in detail. In the present embodiment, it is described in an example that is applied the present invention to the handle-returning control.

[0058] FIG. 4 shows a configuration example of the present invention corresponding to FIG. 3, there are newly provided a steering angle estimating section 100 which inputs the vehicle speed Vel, four-wheel speeds (front-wheel left and right wheel speeds, rear-wheel left and right wheel speeds) Vw and a motor angular velocity estimated value m, and calculates a four-wheel estimated steering angle est and a correction gain CG; a handle-returning control section 150 which inputs the vehicle speed Vel, the motor angular velocity estimated value m, the four-wheel estimated steering angle est and the correction gain CG, and calculates and outputs a handle-returning control value HRC; and an adding section 160 which adds the handle-returning control value HRC to a current command value Iref1, and corrects the current command value Iref1.

[0059] As shown in FIG. 5, the steering angle estimating section 100 comprises a steering angle estimating calculating section 110 which inputs the vehicle speed Vel, the four-wheel speeds Vw and the motor angular velocity estimated value m, and calculates and outputs the four-wheel estimated steering angle est, a front-wheel estimated steering angle f and a rear-wheel estimated steering angle r, and a correction gain calculating section 120 which inputs the four-wheel speeds Vw, the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r, and calculates the correction gain CG.

[0060] As shown in FIGS. 6A, 6B and 6C, the steering angle estimating calculating section 110 (First Embodiment) calculates the front-wheel estimated steering angle f from a relation equation between the front-wheel speeds and a steering angle , and calculates the rear-wheel estimated steering angle r from a relation equation between the rear-wheel speeds and the steering angle .

[0061] The front-wheel estimated steering angle f, the rear-wheel estimated steering angle r and the four-wheel estimated steering angle est are calculated from the four-wheel speeds Vw at the steering angle estimating calculating section 110. A known method which is disclosed in, for example, Japanese Patent No. 4167959 B2 is used to calculate the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r. As shown in FIG. 7, turning radiuses of the four wheels fl, fr, rl and rr are respectively defined as Rfl, Rfr, Rrl and Rrr, the steering angles of the front wheels fl and fr are respectively defined as al and r, a wheelbase of the vehicle is defined as L, and a vehicle width is defined as E. Further, turning radiuses of a front-wheel center and a rear-wheel center are respectively defined as Rf and Rr. The wheel speeds (wheel angular speeds) of the left-front-wheel fl, right-front-wheel fr, left-rear-wheel rl and right-rear-wheel rr are defined as fl, fr, rl and rr, respectively. The steering angle of the vehicle center and the respective wheel speeds fl, fr, rl and rr have relationships shown in below Equations 1 and 2.

[00001] $\begin{matrix} _{front} = \frac{1}{2} .Math. arc .Math. .Math. \sin .Math. {\frac{4 .Math. L}{E} .Math. (\frac{_{fl} -_{fr}}{_{fl} +_{rr}})} & [Equation .Math. .Math. 1] \\ _{rear} = arc .Math. .Math. \tan .Math. {\frac{2 .Math. L}{E} .Math. (\frac{_{rl} -_{rr}}{_{rl} +_{rr}})} & [Equation .Math. .Math. 2] \end{matrix}$

[0062] As well, with respect to the 4-wheel estimated steering angle est, it is possible to increase a robust property against erroneous estimation due to a wheel speed disturbance by using an average value of the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r as in Equation 3 described below.

est=(f+r)/2[Equation 3]

[0063] Or, other than the above average value, the four-wheel estimated steering angle est can also calculate the average value of the weighted front-wheel estimated steering angle f and the weighted rear-wheel estimated steering angle r by varying a front-wheel weight X of the front-wheel estimated steering angle f and a rear-wheel weight Y of the rear-wheel estimated steering angle r depending on the vehicle speed Vel. In this case, the equation is represented by a following Equation 4.

est=(fX+rY)

X+Y=1.0[Equation 4]

[0064] In a case that the front-wheel weight X of the front-wheel estimated steering angle f and the rear-wheel weight Y of the rear-wheel estimated steering angle r are varied depending on the vehicle speed Vel, a configuration of weighting section in the steering angle estimating calculating section 110 is shown in, for example, FIG. 8 (Example 1-1). That is, the front-wheel weight X and the rear-wheel weight Y are outputted with a relationship of X+Y=1.0, from a vehicle speed sensitive table 111 which is sensitive to the vehicle speed Vel. The rear-wheel weight Y is multiplied by the rear-wheel estimated steering angle Or at a multiplying section 112, and the front-wheel weight X is multiplied by the front-wheel estimated steering angle f at a multiplying section 113. Respective multiplied results at the multiplying sections 112 and 113 are added at an adding section 114, and the added value is outputted as the four-wheel estimated steering angle est.

[0065] The vehicle speed sensitive-table 111 sets, for example, X=0.8 and Y=0.2 in a low vehicle speed. In a high vehicle speed, since the front wheels become a half-slip state at the turning and an estimating precision reduces, the rear-wheel weight Y of the rear-wheel estimated steering angle r is enlarged as X=0.2 and Y=0.8.

[0066] As well, although the front-wheel weight X and the rear-wheel weight Y are varied linearly in FIG. 8, the above values may be varied nonlinearly. Further, although the front-wheel weight X and the rear-wheel weight Y are varied based on the vehicle speed in FIG. 8, the above values may be varied depending on the steering angular velocity (Example 1-2) or the steering torque (Example 1-3).

[0067] The correction gain calculating section 120 judges a vehicle slip and a driving-wheel slip by using the front-wheel estimated steering angle f, the rear-wheel estimated steering angle r and the four-wheel speeds Vw, and calculating the correction gain CG in order to correct the certainty of the four-wheel estimated steering angle est. As shown in FIG. 9, the correction gain calculating section 120 comprises a vehicle slip judging section 121 and a driving-wheel slip judging section 122. A vehicle slip gain WSG and a driving-wheel slip gain DWG, which are calculated from the vehicle slip judging section 121 and the driving-wheel slip judging section 122, respectively, are multiplied at a multiplying section 123, and a calculation is performed such that the multiplying result is outputted as the correction gain CG.

[0068] The vehicle slip judging section 121 judges the vehicle slip by using a characteristic that a relation the front-wheel estimated steering angle fthe rear-wheel estimated steering angle r is established at a grip running maneuver as shown in FIG. 10A, and any one wheel speed of the four wheels slips as shown in FIG. 10B in a vehicle slip state and a difference the front-wheel estimated steering angle fthe rear-wheel estimated steering angle r is occurred. Further, as shown in FIG. 11, the vehicle slip judging section 121 calculates a gradual-changing amount VHJ for a vehicle slip gain at a gradual-changing amount calculating section 121-1 depending on an absolute value of the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r, transforms the gradual-changing amount VHJ for the vehicle slip gain to a vehicle slip gain WSG via an output-limiting accumulating section 121-2, and increases or decreases the vehicle slip gain WSG. In a case that the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is large, the vehicle slip gain WSG is sharply decreased, and in a case that the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is small, the vehicle slip gain WSG is gradually increased.

[0069] In the calculating of the above vehicle slip gain WSG, the feature resides in that: the vehicle slip gain WSG is sharply decreased in a case that the vehicle is slipped in a curve on a snowy road (a state that the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is large), and the vehicle slip gain WSG is gradually increased in a case that the vehicle is in the grip state (a state that the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is small) being the straight running.

[0070] As shown in FIG. 12, the gradual-changing amount VHJ for the vehicle slip gain is changed depending on the vehicle speed. Since the slip is hardly occurred in the low speed, a threshold which is compared with the absolute value of the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is larger. Since the slip tends to be occurred in the high speed, the threshold which is compared with the absolute value of the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r is smaller. The above setting is changed by a control function which uses the four-wheel estimated steering angle. Even in the high speed, the absolute value of the difference between the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r can be larger.

[0071] On the other hand, the driving-wheel slip judging section 122 judges the vehicle slip by using a characteristic that a relation the front-wheel speed Wfthe rear-wheel speed Wr is established at a driving-wheel grip running maneuver as shown in FIG. 13A, and the driving-wheel such as the front-wheel or the rear-wheel slips as shown in FIG. 13B in a slip state of the driving-wheel and a difference the front-wheel speed Wfthe rear-wheel speed Wr is occurred. From a relationship of the front-wheel left and right wheel speeds WFL and WFR, and the rear-wheel left and right wheel speeds WRL and WRR, the front-wheel speed Wf and the rear-wheel speed Wr can be calculated by following Equations 5 and 6, respectively.

Wf=(WFL+WFR)/2[Equation 5]

Wr=(WRL+WRR)/2[Equation 6]

[0072] Furthermore, as shown in FIG. 14, the driving-wheel slip judging section 122 calculates a gradual-changing amount VHD for a driving-wheel slip gain at a gradual-changing amount calculating section 122-1 depending on the difference between the front-wheel speed Wf and the rear-wheel speed Wr, transforms the gradual-changing amount VHD for the driving-wheel slip gain to a driving-wheel slip gain DWG via an output-limiting accumulating section 122-2, and increases or decreases the driving-wheel slip gain DWG. In a case that the difference between the front-wheel speed Wf and the rear-wheel speed Wr is large, the driving-wheel slip gain DWG is sharply decreased, and in a case that the difference between the front-wheel speed Wf and the rear-wheel speed Wr is small, the driving-wheel slip gain DWG is gradually increased.

[0073] In a case that the vehicle is operated with a jump start on the snowy road (a state that the difference between the front-wheel speed Wf and the rear-wheel speed Wr is large), the calculating of the above driving-wheel slip gain DWG makes the driving-wheel slip gain DWG sharply decrease. In a case that the vehicle is the grip state (a state that the difference between the front-wheel speed Wf and the rear-wheel speed Wr is small), the driving-wheel slip gain DWG is gradually increased.

[0074] The vehicle slip gain WSG and the driving-wheel slip gain DWG can adjust for respective gains from a sharp changing to a gradual changing by setting the tunable constants, and can also adjust the responsibility when correcting the four-wheel estimated steering angle est and the control output by using the four-wheel estimated steering angle est.

[0075] The handle-returning control section 150 calculates the handle-returning (active return) control value HRC by using the four-wheel estimated steering angle est and the correcting gain CG, and limits the handle-returning (active return) control value HRC when occurring the vehicle slip or the driving-wheel slip. Since the handle-returning control value HRC is calculated based on the four-wheel estimated steering angle est, the unintended handle-returning control value HRC by means of the misestimated four-wheel estimated steering angle est is outputted incorrectly when just occurring the vehicle slip or the driving-wheel slip. When occurring the vehicle slip or the driving-wheel slip, the correction gain CG is decreased and then it is possible to restrict the above incorrected output.

[0076] FIG. 15 shows a configuration example of the handle-returning control section 150. The four-wheel estimated steering angle est is inputted into a steering angle sensitive-table 151 which has a characteristic as shown in FIG. 16, and then a steering angle 1, which is outputted from the steering angle sensitive-table 151, is inputted into a multiplying section 154. The characteristic of the steering angle sensitive-table 151 to an absolute value of the four-wheel estimated steering angle est is shown in FIG. 16. That is, the steering angle 1 is gradually larger when the absolute value of the four-wheel estimated steering angle est is larger than the four-wheel estimated steering angle esta, has a peak when the absolute value of the four-wheel estimated steering angle est is equal to m, is gradually smaller when the absolute value of the four-wheel estimated steering angle est is larger than the four-wheel estimated steering angle Gm, and is zero when the absolute value of the four-wheel estimated steering angle est is larger than or equal to the four-wheel estimated steering angle estb. Further, the vehicle speed Vel is inputted into a vehicle speed sensitive-table 152 which has a characteristic as shown in FIG. 17, and an output Vel1 of the vehicle speed sensitive-table 152 is inputted into the multiplying section 154. The motor angular velocity estimated value m is inputted into a steering angular velocity sensitive-table 153 which has a characteristic as shown in FIG. 18, and an output m1 of the steering angular velocity sensitive-table 153 is inputted into a multiplying section 155.

[0077] The characteristic of the vehicle speed sensitive-table 152 is that as shown in FIG. 17, for example, the output Vel1 is sharply and nonlinearly increased when the vehicle speed Vel is larger than the low vehicle speed Vela and is gradually decreased after a predetermined peak. Further, the characteristic of the steering angular velocity sensitive-table 153 has a characteristic that the output m1 gradually and nonlinearly increases from the motor angular velocity estimated value coma for an absolute value of the motor angular velocity estimated value m as shown in FIG. 18.

[0078] The output 1 is multiplied by the output Vel1 at the multiplying section 154, the multiplied result 2 is inputted into the multiplying section 155 and is multiplied by the output m1 at the multiplying section 155, and the multiplied result HRa is inputted into a multiplying section 156 and is multiplied by the correction gain CG at the multiplying section 156. A basic control value HRb, which is obtained at the multiplying section 156, is inputted into an output-limiting processing section 157, and the handle-returning control value HRC whose output is limited, is outputted.

[0079] In such a configuration, an overall operation example will be described with reference to a flowchart of FIG. 19 and the configuration example of FIG. 4.

[0080] The vehicle speed Vel (Step S1), the four-wheel speeds Vw (Step S2) and the motor angular velocity estimated value m (Step S3) are respectively inputted into the steering angle estimating section 100. These input orders are appropriately changeable. The steering angle estimating section 100 calculates the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r based on the inputted vehicle speed Vel, the four-wheel speeds Vw and the motor angular velocity estimated value m, and calculates and outputs the four-wheel estimated steering angle est (Step S10). The steering angle estimating section 100 also calculates and outputs the correction gain CG (Step S30). The four-wheel estimated steering angle est and the correction gain CG are inputted into the handle-returning control section 150. The handle-returning control section 150 calculates the handle-returning control value based on the four-wheel estimated steering angle est (Step S50) and corrects the handle-returning control value based on the correction gain CG (Step S70). The handle-returning control value HRC is added to the current command value Iref1 at the adding section 160.

[0081] Next, in the steering angle estimating calculating section 110, an operation example of the weighting section, which weights the front-wheel weight X and the rear-wheel weight Y to the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r, respectively, will be described with reference to a flowchart of FIG. 20 and the configuration example of FIG. 8.

[0082] At first, in the steering angle estimating calculating section 110, the front-wheel estimated steering angle f is calculated (Step S11), and then the rear-wheel estimated steering angle r is calculated (Step S12). This order may be changeable. The vehicle speed Vel is inputted into the vehicle speed sensitive-table 111 of the weighting section (Step S13), and the vehicle speed sensitive-table 111 calculates the front-wheel weight X (Step S14) and the rear-wheel weight Y (Step S15) depending on the vehicle speed Vel. The front-wheel weight X is inputted into the multiplying section 113 and is multiplied by the front-wheel estimated steering angle f (Step S16), and a multiplied result f.Math.X is inputted into the adding section 114. The rear-wheel weight Y is inputted into the multiplying section 112 and is multiplied by the rear-wheel estimated steering angle r (Step S17), and a multiplied result r.Math.Y is inputted into the adding section 114. The adding section 114 adds the multiplied result f.Math.X to the multiplied result r.Math.Y and outputs the four-wheel estimated steering angle Best that is the added result (Step S18).

[0083] Besides, a calculating order of the front-wheel X and the rear-wheel Y, and a multiplying order at the multiplying sections 112 and 113 are appropriately changeable.

[0084] Next, an operation example of the correction gain calculating section 110 will be described with reference to a flowchart of FIG. 21 and the configuration examples of FIG. 9, FIG. 11 and FIG. 14.

[0085] The front-wheel estimated steering angle of (Step S31) and the rear-wheel estimated steering angle r (Step S32) are respectively inputted into the vehicle slip judging section 121 in the correction gain calculating section 120. The vehicle slip judging section 121 calculates the gradual-changing amount VHJ for the vehicle slip gain at the gradual-changing amount calculating section 121-1 depending on the absolute value of the difference between the front-wheel estimated steering angle of and the rear-wheel estimated steering angle r (Step S33), limiting-accumulates the gradual-changing amount VHJ for the vehicle slip gain at the output-limiting accumulating section 121-2, and outputs the vehicle slip gain WSG (Step S34).

[0086] The four-wheel speeds Vw is inputted into the driving-wheel slip judging section 122 in the correction gain calculating section 120 (Step S40), and the front-wheel speed Wf and the rear-wheel speed Wr are calculated based on the four-wheel speeds Vw (Step S41 and Step S42). The driving-wheel slip judging section 122 calculates the gradual-changing amount VHD for the driving-wheel slip gain depending on the absolute value of the difference between the front-wheel speed Wf and the rear-wheel speed Wr at the gradual-changing amount calculating section 122-1 (Step S43), limiting-accumulates the gradual-changing amount VHD for the driving-wheel slip gain at the output-limiting accumulating section 122-2, and outputs the driving-wheel slip gain DWG (Step S44).

[0087] The vehicle slip gain WSG and the driving-wheel slip gain DWG are inputted into the multiplying section 123, and the multiplied result of the multiplying section 123 is outputted as the correction gain CG (Step S45).

[0088] Next, an operation example of the handle-returning control section 150 will be described with reference to a flowchart of FIG. 22 and the configuration example of FIG. 15.

[0089] At first, the four-wheel estimated steering angle est is inputted into the steering angle sensitive-table 151 (Step S51), and the steering angle sensitive-table 151 outputs the steering angle 1 depending on the four-wheel estimated steering angle est (Step S52). The vehicle speed Vel is inputted into the vehicle speed sensitive-table 152 (Step S53), the vehicle speed sensitive-table 152 outputs the output Yell depending on the vehicle speed Vel (Step S54), and the output Vel1 is multiplied by the steering angle 1 at the multiplying section 154 (Step S55). Further, the motor angular velocity estimated value m is inputted into the steering angular velocity sensitive-table 153 (Step S56), and the steering angular velocity sensitive-table 153 outputs the angular velocity m1 depending on the motor angular velocity estimated value m (Step S57). The angular velocity m1 is inputted into the multiplying section 155 and is multiplied by the multiplied result 2 of the multiplying section 154 (Step S58). Then, a basic control value HRa which is the multiplied result is inputted into the multiplying section 156.

[0090] Thereafter, the correction gain CG, which is calculated at the correction gain calculating section 120, is inputted into the multiplying section 156 (Step S60) and is multiplied by the basic control value HRa (Step S61). The basic control value HRb, which is a multiplied result of the multiplying section 156, is inputted into the output-limiting processing section 157 and the output-limiting processing section 157 outputs the handle-returning control value HRC whose maximum value is limited (Step S62). The handle-returning control value HRC is inputted into the adding section 160.

[0091] In the above first embodiment, although the robustness is raised by varying the front-wheel weight X of the front-wheel estimated steering angle f and the rear-wheel weight Y of the rear-wheel estimated steering angle r depending on the vehicle speed Vel, it is possible to more accurately calculate the four-wheel estimated steering angle est by varying the front-wheel weight X and the rear-wheel weight Y depending on not only the vehicle speed but also the running state (turning road, gravel road, debris road, acceleration and deceleration and so on) of the vehicle.

[0092] FIG. 23 is a diagram showing merits and demerits when responsibilities are selected as a viewpoint in a case that various running states of an actual running vehicle are selected and a steering angle estimating method at the time. In a case that the viewpoint is responsibility and a content is turning road, high-speed slalom, and 70 [km/h], in the steering angle estimating method, the front-wheel estimated steering angle and the average estimated steering angle of the front wheels and the rear wheels obtain an extremely good evaluation, and the rear-wheel estimated steering angle obtains a bad evaluation. Similarly, in a case that the viewpoint is gravel road and the content is gravel road, free running, and 30 [km/h], in the steering angle estimating method, the front-wheel estimated steering angle and the average estimated steering angle of the front wheels and the rear wheels obtain an extremely good evaluation, and the rear-wheel estimated steering angle obtains a bad evaluation. However, in a case that the viewpoint is slip and the content is gravel road, slip running, and 30 [km/h], in the steering angle estimating method, the front-wheel estimated steering angle and the rear-wheel estimated steering angle obtain a bad evaluation, and the average estimated steering angle of the front wheels and the rear wheels obtains a slightly good evaluation. Further, in a case that the viewpoint is acceleration and deceleration and the content is test track, acceleration and deceleration running, and 0.fwdarw.100.fwdarw.0 [km/h], in the steering angle estimating method, the rear-wheel estimated steering angle obtains an extremely good evaluation, the average estimated steering angle of the front wheels and the rear wheels obtains a good evaluation, and the rear-wheel estimated steering angle also obtains a slightly good evaluation.

[0093] In this manner, since a quality difference for the calculating method of the estimated steering angle is occurred due to the running state of the vehicle, in a second embodiment of the present invention, a configuration that the front-wheel weight X of the front-wheel estimated steering angle and the rear-wheel weight Y of the rear-wheel estimated steering angle are varied depending on the running state of the vehicle, is adopted.

[0094] In the acceleration and deceleration running, the acceleration and deceleration is estimated from the vehicle speed Vel, and the front-wheel weight X of the front-wheel estimated steering angle f and the rear-wheel weight Y of the rear-wheel estimated steering angle r are varied sensitive to the acceleration and deceleration (Example 2-1). FIG. 24 is a block diagram showing a configuration example of the weighting section of the steering angle estimating section in the acceleration and deceleration running corresponding to FIG. 8. The vehicle speed Vel is inputted into an acceleration and deceleration calculating section 200, a calculated acceleration and deceleration estimated value AS is inputted into an acceleration and deceleration sensitive-table 203, and the front-wheel weight X and the rear-wheel weight Y are calculated. The acceleration and deceleration calculating section 200 calculates the acceleration and deceleration estimated value (vehicle speed changing amount) AS from the vehicle speed Vel. As shown in FIG. 25, the acceleration and deceleration calculating section 200 has a memory unit 201 that stores a previous value. By subtracting the previous value from a present value of the vehicle speed Vel at subtracting section 202, the acceleration and deceleration estimated value AS can be calculated. The vehicle speed Vel may be differentiated. The acceleration and deceleration estimated value AS is inputted into the acceleration and deceleration sensitive-table 203, and the front-wheel weight X and the rear-wheel weight Y are calculated in accordance with a characteristic as shown in FIG. 26.

[0095] A four-wheel estimated steering angle est1 is calculated as follows. When the acceleration and deceleration estimated value AS is near zero, the four-wheel estimated steering angle est1 sets an average value of the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r by setting the front-wheel weight X equivalent to the rear-wheel weight Y. In the deceleration (the acceleration and deceleration estimated value AS<0) and in the acceleration (the acceleration and deceleration estimated value AS>0), the four-wheel estimated steering angle est1 is calculated, with the front-wheel estimated steering angle f, by increasing the front-wheel weight X (decreasing the rear-wheel weight Y).

[0096] Next, Example 2-2 that a road surface disturbance is estimated from the four-wheel speeds Vw, and the front-wheel weight X of the front-wheel estimated steering angle f and the rear-wheel weight Y of the rear-wheel estimated steering angle r are respectively varied sensitive to a road surface estimated value RS, will be described. As shown in FIG. 27, the four-wheel speeds Vw is inputted into a road surface estimated value calculating section 210, and the road surface estimated value calculating section 210 estimates a rough road based on positive and negative peak values of differences of the respective wheel speeds to the average value of the four-wheel speeds Vw. As shown in FIG. 28, the four-wheel speeds are inputted into a changing amount calculating section that comprises memory units 211 to 214 and subtracting sections 215 to 218, as described in FIG. 25. The changing amount calculating section calculates the changing amounts of the wheel speeds in the respective wheels, judges whether the vehicle runs on the rough road from the maximum acceleration and deceleration, and calculates the road surface estimated value RS. A wheel-speed vibration frequency by means of the road surface disturbance is adjusted by changing the previous value to a previous-but-one value or the like, or by changing a calculating period. The road surface estimated value calculating section 210 calculates the maximum value from absolute values of changing amounts of the respective wheel speeds, and this maximum value is set as the road surface estimated value RS.

[0097] The road surface estimated value RS is inputted into a road surface estimated value sensitive-table 220 that has a characteristic as shown in FIG. 29, and the front-wheel weight X and the rear-wheel weight Y are calculated at the road surface estimated value sensitive-table 220. That is, a four-wheel steering angle estimated value est2 is calculated as follows. When the road surface estimated value RS is near zero, the four-wheel steering angle estimated value est2 sets an average value of the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r by setting the front-wheel weight X equivalent to the rear-wheel weight Y, and when the road surface is a rough state (the road surface estimated value RS is larger than or equal to a predetermined value RS.sub.0, that is, the road surface estimated value RS is from a medium area to a large area), the four-wheel estimated steering angle est2 is calculated, with the rear-wheel estimated steering angle r, by increasing the rear-wheel weight Y (decreasing the front-wheel weight X).

[0098] Furthermore, the rate of the front-wheel estimated steering angle and the rear-wheel estimated steering angle may be varied sensitive to the motor angular velocity estimated value (steering angular velocity), that is, the front-wheel weight X and the rear-wheel weight Y may be varied (Example 2-3). The motor angular velocity estimated value m may be calculated from a steering angular velocity sensor or a resolver angle. FIG. 30 shows the configuration example, and the motor angular velocity estimated value m is inputted into a motor angular velocity sensitive-table 230 and the motor angular velocity sensitive-table 230 calculates the front-wheel weight X and the rear-wheel weight Y in accordance with a characteristic as shown in FIG. 31. That is, a four-wheel steering angle estimated value est3 is calculated as follows. When the motor angular velocity estimated value m is a low area (less than a predetermined value m.sub.0), the four-wheel steering angle estimated value est3 sets an average value of the front-wheel estimated steering angle f and the rear-wheel estimated steering angle r by setting the front-wheel weight X equivalent to the rear-wheel weight Y. When the motor angular velocity estimated value m is a high area which is higher than or equal to the predetermined value m.sub.0, the four-wheel estimated steering angle est3 is calculated, with the front-wheel estimated steering angle f, by increasing the front-wheel weight X (decreasing the rear-wheel weight Y).

[0099] Since there is a possibility that an output of the motor angular velocity sensitive-table 230 suddenly changes due to a sudden change of the motor angular velocity estimated value or the steering angular velocity sensor, a filter or a rate-limiting process may be added to the input signal (Example 2-4).

[0100] Further, in order to deal with all of running states, the four-wheel estimated steering angle corresponding to all of the running states may be calculated by using an average value of four-wheel steering angle estimated values which are calculated for respective running states in the acceleration and deceleration running, the rough road running and the slalom steering running with the configuration as shown in FIG. 32, with the four-wheel steering angle estimated value est1 in the above-described acceleration and deceleration running maneuver, the four-wheel steering angle estimated value est2 in the rough road running maneuver and the four-wheel steering angle estimated value est3 in the slalom steering running maneuver (Example 2-5). That is, the four-wheel steering angle estimated value est2 in the rough road running maneuver and the four-wheel steering angle estimated value est3 in the slalom steering running maneuver are added at an adding section 241, and an estimated value a which is the added result, is added to the four-wheel steering angle estimated value est1 in the acceleration and deceleration running maneuver at an adding section 240. An estimated value b, which is the added result, is inputted into a dividing section (or a multiplying section) 242, and the dividing section (or the multiplying section) 242 performs a calculation b.Math. and calculates a four-wheel estimated steering angle est4.

[0101] As shown in FIG. 33, the four-wheel steering angle estimated value est1 in the acceleration and deceleration running maneuver, the four-wheel steering angle estimated value est2 in the rough road running maneuver and the four-wheel steering angle estimated value est3 in the slalom steering running maneuver are weighted with weights Xt, Yt and Zt (Xt+Yt+Zt=1.0), respectively, and then a four-wheel estimated steering angle est5 being an average value may be calculated at a calculating section 248 (Example 2-6).

[0102] As well, in the above explanation, although the handle-returning (active return) control is described as an example, it is possible to apply to other controls (a lane keep assist which prevents from lane deviation, an active corner lamp which light is directed to a steering angle direction and so on).

EXPLANATION OF REFERENCE NUMERALS

[0103] 1 handle (steering wheel) [0104] 2 column shaft (steering shaft, handle shaft) [0105] 10 torque sensor [0106] 12 vehicle speed sensor [0107] 13 battery [0108] 20 motor [0109] 31 current command value calculating section [0110] 32 handle-returning control section [0111] 33 current limiting section [0112] 35 current control section [0113] 36 PWM-control section [0114] 37 inverter [0115] 100 steering angle estimating section [0116] 110 steering angle estimating calculating section [0117] 111 vehicle speed sensitive-table [0118] 120 correction gain calculating section [0119] 121 vehicle slip judging section [0120] 122 driving-wheel slip judging section [0121] 150 handle-returning (active return) control section [0122] 151 steering angle sensitive-table [0123] 152 vehicle speed sensitive-table [0124] 153 steering angle speed sensitive-table [0125] 200 acceleration and deceleration calculating section [0126] 203 acceleration and deceleration sensitive-table [0127] 210 road surface estimated value calculating section [0128] 220 road surface estimated value sensitive-table [0129] 230 motor angular velocity sensitive-table

ELECTRIC POWER STEERING APPARATUS

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Cpc classification

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B62D5/0466

PERFORMING OPERATIONS; TRANSPORTING

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B62D6/008

PERFORMING OPERATIONS; TRANSPORTING

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G01L5/221

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B62D5/0466

PERFORMING OPERATIONS; TRANSPORTING

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B62D15/024

PERFORMING OPERATIONS; TRANSPORTING

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B62D6/008

PERFORMING OPERATIONS; TRANSPORTING

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B62D5/0463

PERFORMING OPERATIONS; TRANSPORTING

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B62D15/025

PERFORMING OPERATIONS; TRANSPORTING

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B62D15/02

PERFORMING OPERATIONS; TRANSPORTING

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G01L5/22

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