JP4470283B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device, and more particularly to an electric power steering device that improves the return characteristics of a steering mechanism during low-speed traveling.
[0002]
[Prior art]
The electric power steering device drives and controls a steering assist motor coupled to the steering mechanism based on the steering torque detected by the torque sensor and the vehicle speed detected by the vehicle speed sensor, and gives the steering assist force to the steering mechanism. In general, when the vehicle is traveling at low speed, the steering assist force by the steering assist motor is set to be large so that the steering wheel can be operated lightly. At high speeds, the steering assist force by the steering assist motor is reduced or reduced to zero. The steering assist motor is controlled so that the steering wheel operation is set to be heavy and the vehicle can travel safely.
[0003]
When the driver operates the steering wheel and the vehicle passes a curve, the steering device receives a force that causes the tire to return to the neutral point, that is, the linear traveling position, by a reaction force that the tire receives from the road surface. For this reason, when the driver finishes passing the curve, if the driver releases his hand from the steering wheel, the steering device will naturally return to the neutral point due to the reaction force received from the road surface, and the steering wheel will rotate in the opposite direction. To do. Such an operation is generally called “handle return”.
[0004]
[Problems to be solved by the invention]
In the conventional electric power steering device, the rotation of the steering assist motor is transmitted to the steering mechanism via the reduction gear mechanism. There is a disadvantage that the steering wheel is not properly returned during driving, that is, the steering mechanism does not return properly.
[0005]
As a countermeasure, the steering angle is detected by using a steering angle sensor provided on the steering shaft, and the steering assist motor is driven to control the steering mechanism to return to the neutral point, that is, the position where the vehicle travels linearly. Although it is necessary, due to the steering angle sensor mounting error and the steering mechanism assembly error, the position where the steering angle detected by the steering angle sensor is zero and the position where the steering mechanism runs straight (neutral point) are not necessarily the same. do not do. The object of the present invention is to solve the various problems described above.
[0006]
[Means for Solving the Problems]
The present invention solves the above problems, and the invention of claim 1 includes at least a steering torque detecting means, and is coupled to the steering mechanism based on a current command value calculated based on the detected steering torque. Detects the steering angle input to the steering shaft in an electric power steering device that drives and controls the steering assist motor Output rudder angular velocity A rudder angle sensor to A vehicle speed sensor for detecting the vehicle speed; Neutral point estimating means for estimating a neutral point of the steering mechanism, and control means for calculating a current command value of the steering auxiliary motor so as to return the steering mechanism to the estimated neutral point, and driving and controlling the steering auxiliary motor; The neutral point estimation means includes a first neutral point estimation degree estimated by fuzzy inference using the detected rudder angular velocity as input, and a second estimated by fuzzy inference using the detected steering torque as input. The third neutral point estimated by fuzzy inference using the duration of the state where the product of the neutral point estimate, the first neutral point estimate and the second neutral point estimate is not zero, and the detected vehicle speed as inputs. It is a neutral point estimation means that estimates the neutral point of the steering mechanism based on the estimation degree It is characterized by.
[0007]
And The control means is a first parameter that defines the current of the steering assist motor at the time of returning the steering wheel estimated by fuzzy inference using the neutral point information estimated by the neutral point estimating means, and a dead band at the time of returning the steering wheel. The current command value of the steering assist motor is corrected by the correction current command value at the time of returning the steering wheel calculated based on the second parameter that defines the width and the gain corresponding to the vehicle speed. .
[0009]
Furthermore, the steering mechanism may employ a rolling rack and pinion mechanism.
[0010]
If a rack and pinion mechanism is used, an elastic body may be interposed in the transmission mechanism from the pinion shaft to the steering assist motor shaft. If a rolling rack and pinion mechanism is used, steering assistance is provided from the pinion shaft. An elastic body may be interposed in the transmission mechanism up to the motor shaft.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[Outline of configuration of electric power steering apparatus]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining the outline of the configuration of an electric power steering apparatus 10 suitable for carrying out the steering wheel return control of the present invention.
[0012]
The steering wheel shaft 12 to which the steering handle 11 is attached is coupled to a tie rod 18 of a steering wheel via a reduction gear 27, universal joints 16a and 16b, and a rolling rack and pinion mechanism 17. The steering wheel shaft 12 is provided with a steering angle sensor 13 for detecting a steering angle and a torque sensor 14 for detecting a steering torque. A steering assist motor 25 for assisting a steering force is provided with a clutch 26 and a reduction gear 27. Via the steering shaft 12.
[0013]
The electronic control circuit 20 that controls the electric power steering device is supplied with power from the battery 21 via the ignition key 22. The electronic control circuit 20 is composed of a CPU, calculates a current command value based on the steering torque detected by the torque sensor 14 and the vehicle speed detected by the vehicle speed sensor 23, and the steering assist motor based on the calculated current command value. The electric current supplied to 25 is controlled. In addition, the CPU of the electronic control circuit 20 also performs neutral point calculation, handle return control, and other calculation control related to the handle return described below.
[0014]
The clutch 26 is controlled by the electronic control circuit 20, and the clutch 26 is engaged in a normal operation state. When the electronic control circuit 20 determines that the electric power steering device has failed and the power is OFF. Separated.
[0015]
FIG. 2 is a cross-sectional view showing a configuration of a main part of the rolling rack and pinion mechanism 17 described above. In FIG. 2, 31 is an input shaft, and the rotation of the steering wheel shaft 12 is transmitted to the input shaft 31 via the universal joints 16a and 16b. A pinion shaft 32 is coaxially attached to the lower portion of the input shaft 31 so as to be rotatable.
[0016]
The pinion shaft 32 is supported by bearings 33 a and 33 b arranged inside the gear box 30. Pinion teeth 32a are formed on the outer periphery of the pinion shaft 32, the rack teeth 34a of the rack shaft 34 mesh with the pinion teeth 32a, and the rack shaft 34 is displaced in the axial length direction (front and back direction in FIG. 2) to tie rod 18 ( 1), a desired steering angle is given to a steered wheel (not shown).
[0017]
In order to properly maintain the meshing relationship between the rack teeth 34 a of the rack shaft 34 and the pinion teeth 32 a of the pinion shaft 32, a pressure pad portion 35 described below is provided, and the rack shaft 34 is directed toward the pinion shaft 32 with a predetermined pushing force. Pressing with pressure. The pressure pad portion 35 is provided in a substantially cylindrical housing 30 a that protrudes from the gear box 30 in a direction orthogonal to the axial direction of the pinion shaft 32.
[0018]
The pressure pad portion 35 includes a roller 36, a needle bearing 37, a pin shaft 38, a bearing holder 39, a pad 40, a coil spring 41, and an adjusting screw 42. A pin shaft 38 is held by a bearing holder 39 disposed in the housing 30 a, and a roller 36 is rotatably supported by the pin shaft 38 via a needle bearing 37.
[0019]
The roller 36 is in rolling contact with the outer peripheral surface 34 c of the rack shaft 34 opposite to the side where the rack teeth 34 a are formed, and the opposite side is in rolling contact with the pad 40. A coil spring 41 is disposed between the pad 40 and the adjustment screw 42, and the pad 40 presses the roller 36 toward the rack shaft 34 by the elastic force of the coil spring 41.
[0020]
With the above configuration, the thrust screw 42 is rotated and moved in the axial direction, thereby adjusting the pressing force of the coil spring 41 toward the rack shaft 34 via the pad 40 and the roller 36, and the rack teeth 34a and the pinion teeth. The meshing state with 32a can be set appropriately. According to such a rolling pinion rack mechanism, even when a high load is applied between the pinion and the rack, an appropriate meshing state is maintained, and the conduction efficiency can be greatly improved.
[0021]
FIG. 3 is a partial cross-sectional view showing configurations of the steering assist motor 25 and the worm gear reduction mechanism. The feature of this configuration is that in the worm gear mechanism including the worm wheel 51 and the worm 52 used for the speed reduction mechanism of the motor 25, the rotation shaft 25a and the worm shaft 52a of the steering assist motor 25 are not shown. However, the worm shaft 52a is configured to be movable in the axial direction. Reference numeral 50 denotes a casing of the worm gear mechanism.
[0022]
In this configuration, rubber pads 54, which are elastic bodies, are disposed between the flange portions 52c at both ends of the worm shaft 52a and the worm bearing 53. Reference numeral 55 denotes a bush inserted between the worm bearing 53 and the rubber pad 54.
[0023]
According to this configuration, when a large axial force such as a kickback force is applied to the worm shaft 52a, the worm shaft 52a can move in the axial direction to release an excessive load. That is, when the worm wheel 51 is rotated by receiving a kickback from the road surface, the rotation of the worm wheel 51 is generated in the worm shaft 52 a of the worm 52 meshing with the worm wheel 51 in the elastic region (movable range) of the rubber pad 54. Until the torque overcomes the frictional force and inertial force of the steering assist motor 25, the worm shaft 52a is displaced in the axial direction and is not transmitted to the steering assist motor 25.
[0024]
That is, even when the worm wheel 51 receives kickback from the road surface and the worm wheel 51 receives rotational force, the rubber pad 54 is elastically deformed and the worm shaft 52a moves in the axial direction, and the kickback impact is applied to the rubber pad 54. Absorbed.
[0025]
According to such a structure, the kickback force does not act on the steering assist motor 25 in the movable range of the worm shaft 52a by the rubber pad 54, and it is possible to prevent the load from being concentrated on the rack and pinion mechanism. . Further, according to such a structure, the vibration damping action of the rubber pad 54 compensates for the lack of the vibration damping action, which is a drawback of the rolling rack and pinion mechanism, so that the generation of rattle noise can be prevented.
[0026]
[Handle return control]
Next, handle return control, which is a feature of the present invention, will be described. When the driver operates the steering wheel and the vehicle passes the curve, the steering device receives a force that returns the tire to the neutral point, that is, the straight running position, due to the resistance that the tire receives from the road surface. For this reason, when the driver finishes passing the curve, if the driver releases his hand from the steering handle, the steering device naturally returns to the neutral point due to the resistance received from the road surface, and the steering handle rotates in the reverse direction. . Such an operation is generally called “handle return”.
[0027]
In the electric power steering device, since the speed reduction mechanism is provided between the steering assist motor and the steering shaft, the return to the neutral point of the steering device becomes worse due to friction of the speed reduction mechanism. For this reason, it is necessary to drive the steering assist motor to control the steering device to return to the neutral point.
[0028]
In this case, as described above, the neutral point may be displaced from the position where the vehicle actually travels in a straight line, so it is necessary to estimate the neutral point where the vehicle actually travels in a straight line. In addition, since the estimated neutral point includes an error, by providing a dead band that sets the current value for driving the steering assist motor to zero within a predetermined steering angle range across the estimated neutral point, the estimated neutral point is The uncomfortable feeling during steering based on the error can be eliminated.
[0029]
Furthermore, when the error in estimating the neutral point becomes small, by setting the width of the dead band accordingly, there is no sense of incongruity during steering than when the dead band width is a fixed value. Good handle return is obtained.
[0030]
Next, a neutral point estimation method will be described. The estimation of the neutral point is based on a fuzzy reasoning method, and FIG. 4 is a diagram for explaining the configuration of the neutral point estimation unit 200 that estimates the neutral point by fuzzy reasoning. The neutral point estimation unit 200 shown in FIG. 4 shows a function executed by the CPU of the electronic control circuit 20.
[0031]
In FIG. 4, reference numeral 210 denotes a first fuzzy inference device that receives the steering angular velocity ω and outputs a neutral point estimation degree C1 related to the steering angular velocity ω. When the vehicle is traveling straight, the steering handle is not operated and the steering angular velocity ω should be zero. Therefore, the first fuzzy inference unit 210 outputs C1 = 1 when the steering angular velocity ω = 0 (zero), and the smaller value C1 (C1 <1 as the absolute value of ω increases when the steering angular velocity ω is not zero. ) Is set to output the membership function.
[0032]
Reference numeral 220 denotes a second fuzzy inference device which receives the steering torque T and outputs a neutral point estimation degree C2 related to the steering torque T. When the vehicle is traveling straight, the steering handle is not operated and the steering torque T should be zero. Therefore, the second fuzzy inference unit 220 outputs C2 = 1 when the steering torque T = 0 (zero), and the smaller value C2 (C2 <C2 <C2 <C) when the steering torque T is not zero. The membership function is set to output 1).
[0033]
In 240, an elapsed time t in which the product of the vehicle speed V and the C1 and C2 is not zero (C1 × C2 ≠ 0) is input, and the product of the vehicle speed V and the C1 and C2 is not zero (C1 × C2 ≠ 0). ) A third fuzzy inference unit that outputs a neutral point estimation degree C4 related to the elapsed time t of the state. When the vehicle is traveling straight, the higher the vehicle speed V, the higher the probability that the state is maintained, and the higher the probability that the steering handle is at the neutral point. Therefore, in the third fuzzy inference device 240, the membership is such that the higher the vehicle speed V, the higher the value of C4, and the longer the elapsed time t during which the state continues, the higher the value of C4. A function is set.
[0034]
When the vehicle is stopped or in a low speed region where the vehicle speed V is up to about 30 km / h, there is a high possibility that steering for parking is being performed, so the steering handle is less likely to be at the neutral point. Since parking may be performed with the direction handle turned off, if the neutral point is estimated in the low speed region, there is a high possibility that the neutral point will be mistaken. For this reason, the neutral point estimation degree C4 is set to C4 = 0 (zero) at a speed of 30 km / h or less.
[0035]
The neutral point estimation unit 200 multiplies the neutral point estimation C1 of the first fuzzy inference unit 210 and the neutral point estimation C2 of the second fuzzy inference unit 220 as inputs, and outputs an output C3. 230 and a multiplier 250 that multiplies the output C3 of the multiplier 230 and the neutral point estimate C4 of the third fuzzy inference unit 240 described above as inputs and outputs a neutral point estimate C5. Make an estimate.
[0036]
The neutral point estimation degree C5 is compared with the previous neutral point estimation degree Cm stored in the memory. When C5 ≧ Cm, that is, when the current neutral point estimation degree C5 is higher, the neutral point estimation degree C5 is stored in the memory. The degree Cm is updated with C5, and the neutral point estimation degree C5 for which the neutral point estimation degree calculated this time is determined is output as the neutral point estimation degree Cm.
[0037]
Thus, when the current neutral point estimation degree C5 is higher, the neutral point estimation accuracy can be increased by updating the previous neutral point estimation degree Cm. Hereinafter, the neutral point estimation process will be described with reference to the flowchart of FIG.
[0038]
First, the rudder angle θr detected by the rudder angle sensor 13 provided on the rudder wheel shaft 12 is read to determine whether or not it is the first detection (steps P1, P2). In the case of the first detection, the previous neutral point value θm written in the nonvolatile memory is set as the initial estimated neutral point θc, and the estimated degree Cm stored in the neutral point estimated degree memory is cleared to 0 ( Step P3). If it is not the first detection in step P2, the process of step P3 is omitted.
[0039]
The steering angular velocity ω output from the steering angle sensor 13 is read (step P4), and the difference (θ = θr−θc) between the detected steering angle θr and the estimated neutral point θc is the steering angle θ based on the estimated neutral point θc. (Step P5).
[0040]
The processing of the first fuzzy inference unit 210, that is, the neutral point estimation degree C1 is calculated with the steering angular speed ω as an input (step P6), and the processing of the second fuzzy inference unit 220, that is, the steering torque T is input. The neutral point estimation degree C2 is calculated as follows (step P7). Further, the multiplier 230 multiplies the neutral point estimation degrees C1 and C2 to obtain the neutral point estimation degree C3 (step P8), thereby improving the accuracy of the neutral point estimation.
[0041]
It is determined whether or not the neutral point estimation degree C3 is zero (step P9). If the neutral point estimation degree C3 is not zero, it is estimated that the steering handle is near the neutral point, and the duration t of the state is counted (step P10). When zero, the steering handle is presumed to be at a position other than the neutral point, and the counter for counting the duration t of the state is reset (step P11).
[0042]
The third fuzzy inference unit 240 described above is processed. That is, the vehicle speed V and the duration t are input, and the neutral point estimation degree C4 is calculated (step P12). Further, the multiplier 250 multiplies the neutral point estimation degrees C3 and C4 to obtain the neutral point estimation degree C5 (step P13), thereby improving the accuracy of the neutral point estimation.
[0043]
The previous neutral point estimate Cm stored in the memory is compared with the neutral point estimate C5 obtained by this calculation (step P14), and C5 ≧ Cm, that is, the current neutral point estimate C5 is higher. Sets the steering angle θr at that time as the estimated neutral point θc (θc ← θr), updates the steering angle θm of the neutral point stored in the nonvolatile memory with the steering angle θr (θm ← θr), and estimates the previous neutral point The estimated degree Cm stored in the degree memory is updated with C5 (Cm ← C5) (step P15).
[0044]
If C5 ≧ Cm is not satisfied in step P14, the updating process in step P15 is not performed. The neutral point estimation process is thus completed, and the process returns to the main routine.
[0045]
Next, the steering wheel return control unit executed using the result of the neutral point estimation process will be described. FIG. 6 is a diagram illustrating the configuration of the handle return control unit 400.
[0046]
In FIG. 6, 310 is a fuzzy inference device that receives the previously determined neutral point estimation degree Cm and outputs a parameter K that determines the magnitude of a current command value that defines the current of the steering assist motor when the steering wheel is returned. is there. If the estimation accuracy of the neutral point estimation degree Cm increases, the parameter K is gradually increased and finally set to 1.
[0047]
Further, 320 is a fuzzy inference device that outputs the parameter D for determining the width of the dead band for setting the current value supplied to the steering assist motor at the time of returning the steering wheel to zero by using the previously determined neutral point estimation degree Cm as an input. It is. If the estimation accuracy of the neutral point estimation degree Cm is increased, the parameter D is set to gradually decrease and finally become zero.
[0048]
Reference numeral 340 denotes an arithmetic unit that determines the gain G of the current command value Ir corresponding to the vehicle speed when the steering wheel is returned. A high gain parameter is output at a low vehicle speed, and a low gain parameter is output as the vehicle speed increases. Is set to
[0049]
Reference numeral 330 denotes an arithmetic unit that determines a current command value to be supplied to the steering assist motor when the steering wheel is returned, and sets the current command value Ir to the steering angle θ as shown in the illustrated characteristic. That is, the dead band width DD is obtained by multiplying the steering angle θ by a value (D × θd1) obtained by multiplying the setting value θd1 preset with respect to the steering angle θ by the parameter D output from the fuzzy inference unit. A value {(D × θd1) + θd2} obtained by adding a preset setting value θd2 is set. If the estimation accuracy of the neutral point estimation degree Cm increases, the dead band width DD gradually becomes narrower and finally becomes the width of the set value θd2.
[0050]
As a result, when the neutral point estimation degree Cm is low, that is, when the estimation error is large, the value of the parameter D increases, so the deadband width DD is set wide and the value of the parameter K decreases. The current command value Ir for returning the steering wheel is set small, and the steering wheel can be safely returned to the neutral point even if the estimation error is large.
[0051]
Further, when the neutral point estimation degree Cm is high, that is, when the estimation error is small, the value of the parameter D becomes small. Therefore, the deadband width DD is set narrow and the value of the parameter K becomes large. The current command value Ir for return is set large, and the handle can be quickly returned to the neutral point.
[0052]
The current command value Ir when the handle is returned is determined by a value (K × M) obtained by multiplying the parameter K output from the fuzzy inference unit by the coefficient M. The coefficient M determines the gradient of the current command value Ir, and is set so that the current command value Ir increases as the steering angle increases.
[0053]
FIG. 7 shows the relationship between the steering angle θ and the current command value Ir when the steering wheel is returned when the neutral point estimation degree Cm is low and high. The line (1) shows the neutral point estimation degree Cm. When the value is low, the line (2) shows the case where the neutral point estimation degree Cm is high. As is clear from FIG. 7, when the neutral point estimation degree Cm is low, the current command value Ir when returning the steering wheel is set small even if the steering angle θ is large, and even if there is an estimation error, the steering wheel is safely returned to the neutral point. When the neutral point estimation degree Cm is high, the current command value Ir at the time of returning the steering wheel is set large even if the steering angle θ is small, indicating that the steering wheel can be quickly returned to the neutral point. ing.
[0054]
The current command value Ir when the steering wheel is returned and the gain G corresponding to the vehicle speed output from the computing unit 340 are multiplied by the multiplier 350, and the corrected current command for correcting the current command value I supplied to the steering assist motor. The value Irh is output.
[0055]
By multiplying the steering wheel return current command value Ir by the gain G corresponding to the vehicle speed, the corrected current command value Irh is set small when the vehicle speed is high, so that the steering wheel can be safely returned to the neutral point. . Further, when the vehicle speed is low, the correction current command value Irh is set to be large, so that it can be returned to the steering wheel neutral point by a light steering wheel operation. Hereinafter, the processing of the above-described handle return control unit will be described with reference to the flowchart of FIG.
[0056]
First, the steering angle θr used in the neutral point estimation process and the difference (θ = θr−θc) between the steering angle θr and the estimated neutral point θc are read (steps P21 and P22). The neutral point estimation degree Cm previously obtained is input to the fuzzy inference unit 310, the parameter K is calculated, the neutral point estimation degree Cm previously obtained is input to the fuzzy inference unit 320, and the parameter D is calculated (step P23). , P24).
[0057]
The calculation unit 330 calculates the current command value Ir supplied to the steering assist motor when the steering wheel is returned (step P25), and the calculation unit 340 that calculates the gain G calculates the gain G with respect to the vehicle speed (step P26). Further, the current command value Ir is multiplied by the gain G to calculate a corrected current command value Irh at the time of returning the handle (step P27), the process is terminated, and the process returns to the main routine.
[0058]
[Electronic control circuit]
FIG. 9 is a block diagram showing a configuration of the electronic control circuit 20. The electronic control circuit 20 is composed of a CPU, and FIG. 9 is a block diagram showing its function.
[0059]
The steering torque T is input to a steering assist command value calculation unit 100 and a center response improvement unit 101 that calculate a current command value to be supplied to the steering assist motor. Each output is added by an adder 102, and the addition result is a torque control calculation. Input to the unit 103.
[0060]
The output of the torque control calculation unit 103 is input to the motor loss current compensation unit 104, and the output is input to the maximum current limiting unit 106 via the adder 105, and the maximum current value is limited and input to the current control unit 110. . The output of the current control unit 110 is input to the current drive circuit 112 via the H-bridge characteristic compensation unit 111 and drives the steering assist motor 25.
[0061]
The current value i of the steering assist motor 25 is input to the motor angular speed estimation unit 121, the current drive switching unit 122 and the current control unit 110 via the motor current offset correction unit 120, and the motor terminal voltage Vm is input to the motor angular speed estimation unit 121. Is done.
[0062]
Also, a current dither signal generation unit 130 is provided, and the output from the current dither signal generation unit 130 and the output of the motor angular acceleration estimation unit / inertia compensation unit 123 are added by an adder 131, and the addition result is an adder. In 105, the output is added to the output of the motor loss current compensator 104.
[0063]
The angular velocity ωm estimated by the motor angular velocity estimation unit 121 is input to the motor angular acceleration estimation unit / inertia compensation unit 123, the motor loss torque compensation unit 124, and the yaw rate estimation unit 125. The output of the yaw rate estimation unit 125 is input to the convergence control unit 126, and the output of the convergence control unit 126 and the motor loss torque compensation unit 124 are added by the adder 127. The details of the configuration and functions of the electronic control circuit 20 described above are disclosed in Japanese Patent Application No. 2000-154284 filed earlier by the present applicant.
[0064]
Further, a neutral point estimation unit 200 and a handle return control unit 400 are added to the electronic control circuit 20 in order to perform the control at the time of returning the handle described above.
[0065]
That is, the neutral point estimation degree Cm output from the neutral point estimation unit 200 that receives the steering torque T, the vehicle speed V, the steering angle θr, and the steering angular velocity ω is input to the steering wheel return control unit 400.
[0066]
The correction current command value Irh for correcting the current command value at the time of returning the steering wheel outputted from the steering wheel returning control unit 400 and the output of the adder 127 are added by the adder 150, and the addition result is calculated as a steering assist command value calculation. The outputs of the unit 100 and the center response improvement unit 101 are added by the adder 102, and the current command value I for assisting steering suitable for returning the steering wheel is corrected.
[0067]
In the embodiment of the present invention described above, a rolling pinion rack mechanism is employed in the electric power steering device, but this can reduce the friction of the mechanism portion as compared with the conventional pinion rack mechanism. In combination with the steering wheel return control according to the present invention, the return to the neutral point of the steering mechanism can be further improved. In addition, since the return to the neutral point is improved, it is possible to obtain an effect that the estimation accuracy of the neutral point in the steering wheel return control can be increased.
[0068]
【The invention's effect】
As described above in detail, according to the present invention, when the neutral point of the steering mechanism is estimated, the neutral point is estimated based on the detected steering angle, steering angular speed, and steering torque, and the steering mechanism is set to the estimated neutral point. The current command value of the steering assist motor is calculated so that the steering assist motor is returned to drive the steering assist motor.
[0069]
Since the neutral point is estimated using many parameters such as the rudder angle, rudder angular speed, and steering torque, and the estimated value is updated by repeated calculation, the neutral point can be estimated with high accuracy.
[0070]
In addition, a parameter that defines the current of the steering assist motor when returning the steering wheel by fuzzy inference using the estimated neutral point information as input, a parameter that defines the width of the dead band when returning the steering wheel, and the current of the steering assist motor corresponding to the vehicle speed Since the current command value of the steering assist motor is corrected using a number of parameters such as the parameter that defines the steering wheel, the accuracy of the neutral point estimate is high, and the steering mechanism can be returned with high accuracy when the steering wheel is returned. An electric power steering apparatus can be provided.
[0071]
Further, when the steering wheel return control and the rolling pinion / rack mechanism are combined, the return to the neutral point of the steering mechanism can be further improved, and an electric power steering device with a better steering feel can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an outline of a configuration of an electric power steering apparatus suitable for carrying out steering wheel return control.
FIG. 2 is a cross-sectional view showing a configuration of a main part of a rolling pinion rack mechanism.
FIG. 3 is a partial cross-sectional view showing a configuration of a steering assist motor and a reduction mechanism of the motor.
FIG. 4 is a diagram illustrating a configuration of a fuzzy inference unit that performs neutral point estimation.
FIG. 5 is a flowchart for explaining a neutral point estimation process;
FIG. 6 is a diagram illustrating a configuration of a handle return control unit.
FIG. 7 is a diagram showing a relationship between a steering angle θ and a current command value Ir when the steering wheel is returned when the neutral point estimation degree is low and high.
FIG. 8 is a flowchart for explaining handle return processing in a handle return control unit;
FIG. 9 is a block diagram showing a configuration of an electronic control circuit.
[Explanation of symbols]
10 Electric power steering device
11 Steering handle
12 Rudder axle
13 Rudder angle sensor
14 Torque sensor
16a, 16b Universal joint
17 Rolling rack and pinion mechanism
18 Tie Rod
20 Electronic control circuit
23 Vehicle speed sensor
25 Steering assist motor
26 Clutch
27 Reduction gear
30 Gearbox
31 Input shaft
32 pinion shaft
34 Rack shaft
35 Pressure pad
36 Laura
37 Needle bearing
38 pin shaft
39 Bearing holder
41 Coil spring
51 Worm wheel
52 Warm
52a Worm shaft
54 Rubber pad
200 Neutral point estimation unit
210 First fuzzy inference
220 second fuzzy inference
230 Multiplier
240 Third Fuzzy Reasoner
250 multiplier
310 Fuzzy Reasoner Outputting Parameter K
320 Fuzzy inference unit that outputs parameter D
340 Calculator for determining gain G
350 multiplier
400 Handle return control unit

Claims (5)

In an electric power steering apparatus that includes at least a steering torque detection unit and that drives and controls a steering auxiliary motor coupled to a steering mechanism based on a current command value calculated based on the detected steering torque,
A steering angle sensor that detects a steering angle input to the steering shaft and outputs a steering angular velocity ;
A vehicle speed sensor for detecting the vehicle speed;
A neutral point estimating means for estimating a neutral point of the steering mechanism,
A control means for calculating a current command value of the steering assist motor so as to return the steering mechanism to the estimated neutral point, and driving the steering assist motor;
With
The neutral point estimation means includes a first neutral point estimation degree estimated by fuzzy reasoning using the detected steering angular velocity as input, and a second neutral point estimation estimated by fuzzy reasoning using the detected steering torque as input. And a third neutral point estimate estimated by fuzzy inference with the duration of the product of the first neutral point estimate and the second neutral point estimate being non-zero and the detected vehicle speed as input. An electric power steering device characterized by being a neutral point estimating means for estimating a neutral point of a steering mechanism based on the above . The control means is a first parameter that defines the current of the steering assist motor at the time of returning the steering wheel estimated by fuzzy inference using the neutral point information estimated by the neutral point estimating means, and a dead band at the time of returning the steering wheel. second parameter defines the width, and the correction current command value at the time of return computed handle based on the gain corresponding to the vehicle speed to claim 1, characterized in that for correcting the current command value of the steering assist motor The electric power steering apparatus as described. The electric power steering apparatus according to claim 1 or claim 2, wherein the steering mechanism is a rolling type rack and pinion mechanism. The steering mechanism is a rack and pinion mechanism, an electric power according to claim 1 or claim 2, characterized in that an elastic body is interposed in the transmission mechanism from the pinion axis to the steering assist motor shaft Steering device. The steering mechanism is rolling rack and pinion mechanism, according to claim 1 or claim 2, characterized in that is interposed an elastic body during transmission mechanism from the pinion axis to the steering assist motor shaft Electric power steering device.

Images