JP2004098841A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress or avoid a change in torque to be transmitted to an operator by suppressing or avoiding right-and-left asymmetry in steering burden (steering torque). <P>SOLUTION: A torque integration part 16 integrates a torque detected value Ts over a preset time. A steering angle average value computation part 15 finds an average value for a steering angle θ over a preset time. An offset computation part 17 divides a torque integrated value by the steering angle average value to find a neutral point offset (an offset value) OF for the torque detected value Ts. A subtraction part 12 subtracts the offset OF from the torque detected value Ts to find a steering torque value T1 that the neutral point offset is corrected. An actual torque dead zone detection part 22 detects the range of the steering torque value T1 where a motor current value Im is held to be zero, as an actual torque dead zone. An addition part 24 corrects the actual torque dead zone to be eliminated to find a steering torque value T2 after corrected. In accordance with the steering torque value T2, a target current value for an electric motor M is set. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device configured to transmit a driving force generated by an electric motor to a steering mechanism to assist steering.
[0002]
[Prior art]
2. Description of the Related Art An electric power steering apparatus that assists steering by mechanically transmitting a driving force of an electric motor to a steering mechanism has been conventionally used. The electric motor is controlled based on a target current value set according to the steering torque applied to the steering wheel, whereby a steering assist force corresponding to the steering torque is given to the steering mechanism.
[0003]
The characteristic of the target current value with respect to the steering torque is called an assist characteristic. In general assist characteristics, a steering torque range near zero is defined as a torque dead zone, and a target current is set to zero for a steering torque value within the torque dead zone, while a steering torque value outside the torque dead zone is set for a steering torque value outside the torque dead zone. Is set to increase the absolute value of the target current value in accordance with the steering torque within a range up to a predetermined upper limit value. Thus, the greater the steering torque, the greater the steering assist force is given to the steering mechanism, and a better steering feeling is obtained.
[0004]
In addition, since the torque dead zone is provided in the assist characteristic, the steering wheel does not rotate even when the torque sensor for detecting the steering torque has a slight output error.
[0005]
[Patent Document 1]
JP-A-10-278818
[0006]
[Problems to be solved by the invention]
However, in the torque dead zone, the steering assist is not performed, so that the manual torque performance of the system is exposed. For this reason, torque fluctuations caused by, for example, uneven engagement of rack and pinion, cogging torque of the electric motor, and the like included in the steering mechanism may be transmitted from the steering wheel to the driver, and the steering feeling may be impaired.
[0007]
This problem is improved by increasing the accuracy of managing the meshing portion of the rack-and-pinion and the cogging torque of the electric motor, but increases the number of manufacturing steps and increases the cost.
Further, regardless of whether or not the torque sensor itself has an output error, when the steering wheel is operated to the right and when the steering wheel is operated to the left, the steering load (steering torque) of the driver is not always equal, A so-called left-right difference occurs. For example, there is a case where a left-right difference in steering load occurs due to a left-right difference in vehicle weight or a left-right difference in suspension rotation efficiency. In this case, the driver often feels a left-right difference in the steering load in a large steering angle range such as when turning. In addition, there is a case where a right-left difference in steering load occurs due to a right-left difference in mechanical operation efficiency of the electric power steering device itself. In this case, the driver often feels a left-right difference in the steering load in a small steering angle range such as when traveling straight ahead.
[0008]
Therefore, a first object of the present invention is to provide an electric power steering device capable of suppressing or eliminating a left-right difference in a steering load (steering torque).
A second object of the present invention is to provide an electric power steering device capable of suppressing or eliminating torque fluctuation transmitted to a driver with an inexpensive configuration and improving the steering feeling.
[0009]
Means for Solving the Problems and Effects of the Invention
In order to achieve the above object, the invention according to claim 1 provides a steering mechanism (3) for controlling a driving force of an electric motor (M) controlled according to an operation amount of an operation member (1) for steering a vehicle. ) For assisting the steering by transmitting the steering torque to the operating member, wherein the steering torque detecting means (5) for detecting the steering torque applied to the operating member; and a torque detection value which is a detection value of the steering torque detecting means. A torque integrating means for integrating a predetermined time to obtain a torque integrated value; a steering angle detecting means for obtaining a steering angle of the operating member; and a predetermined time for the steering angle detected by the steering angle detecting means. A steering angle average value calculating means (15) for calculating an average value over the range, and a torque integrated value obtained by the torque integrating means and a steering angle average value obtained by the steering angle average value calculating means. An electric power steering apparatus which comprises a middle point deviation correcting means (12,17,18) for correcting the midpoint displacement of the steering torque detection means. It should be noted that the alphanumeric characters in parentheses indicate corresponding components and the like in embodiments described later. Hereinafter, the same applies in this section.
[0010]
According to the present invention, the torque detection value is integrated over a predetermined time (for example, about 5 seconds), and the average value of the detection values of the steering angle detection means over the predetermined time is obtained. Then, based on these, the midpoint deviation of the steering torque detecting means is corrected. That is, the midpoint deviation of the steering torque detecting means is detected and corrected in real time at every predetermined time.
Therefore, by controlling the electric motor based on the steering torque value corrected for such a midpoint deviation, the load state of the vehicle (ride state, load state of the load, the position of the center of gravity, etc.) and the mechanical mechanism of the steering mechanism are controlled. The difference between the left and right steering torques caused by the dynamic operating efficiency can be eliminated, and a good steering feeling can be realized.
[0011]
The electric power steering device includes a target current value setting means (13) for setting a target current value of the electric motor based on the steering torque value subjected to the midpoint deviation correction by the midpoint deviation correction means. It is preferable to further include a motor driving means (20) for driving the electric motor based on the target current value set by the target current value setting means.
In addition, the midpoint deviation correction means calculates a midpoint deviation amount (offset value) of the steering torque detection means based on a value obtained by dividing the torque integrated value by the steering angle average value. 17) and a subtraction means (12) for subtracting the midpoint deviation calculated by the midpoint deviation calculation means from the steering torque value detected by the steering torque detection means.
[0012]
With such a configuration, the larger the steering angle is, the smaller the estimated amount of the midpoint deviation is estimated. In the large steering angle range, the value of the torque integrated value does not accurately reflect the midpoint deviation, but by calculating the amount of the midpoint deviation as described above, the midpoint deviation correction in the large steering angle region is performed. Is suppressed.
In this configuration, the steering angle average value accurately represents the steering angle range (small steering angle range or large steering angle range), and the divisor used for calculating the amount of deviation of the center point is not set to zero. In addition, it is preferable that the steering angle average value calculating means calculates an average value of absolute values of the steering angles detected by the steering angle detecting means.
[0013]
If the divisor at the time of calculating the midpoint deviation amount is too small, the calculated midpoint deviation amount becomes large. Therefore, the steering angle average value calculating means calculates the absolute value of the steering angle having an absolute value equal to or larger than a predetermined value. It is preferable to extract only the value and obtain the average value.
In addition, the above-mentioned middle point deviation amount calculating means calculates the middle point deviation amount only when the ratio of the right turn (or left turn) time in the predetermined time is within a predetermined range (for example, 20% to 80%). It is preferable to update the midpoint deviation amount by performing the operation. This is because the center point deviation amount cannot be obtained unless the operation member is operated left and right.
[0014]
On the condition that the vehicle speed is maintained at a predetermined value (for example, 10 km / h) or more during the predetermined time, the torque integration means integrates the torque detection value over the predetermined time, and sets the steering angle. It is preferable that the average value calculating means calculates an average value of the steering angles over the predetermined time. This is because it is considered that the correction of the midpoint deviation using the torque integrated value and the steering angle average value cannot be performed accurately while the vehicle is stopped.
According to a second aspect of the present invention, based on the detected torque value when the drive current of the electric motor is zero, an actual torque dead zone that is a range of the steering torque in which the drive current of the electric motor is maintained at zero is detected. 2. The electric motor according to claim 1, further comprising: an actual torque dead zone detecting means (22), and a dead zone elimination correcting means (24) for correcting the torque detection value so as to eliminate the actual torque dead zone. It is a power steering device.
[0015]
According to this configuration, the actual torque dead zone, which is the actual torque dead zone, is detected based on the detection value of the steering torque detection means, and the actual torque dead zone is eliminated. That is, even near the middle point of the steering torque, the electric motor is driven based on a target current value other than zero. As a result, for example, it is possible to prevent torque fluctuations caused by the meshing accuracy of the rack and pinion mechanism and the cogging torque of the electric motor from being transmitted to the driver via the operation member, and it is possible to improve the steering feeling. In addition, for example, a change in the steering torque can be suppressed or eliminated only by the program processing, so that a large increase in cost is not required.
[0016]
In addition, since the midpoint deviation is corrected with respect to the detection value of the steering torque detection means, an undesired steering assist force is applied to the steering mechanism or the operation member is moved carelessly due to the detection error of the steering torque. I can't.
The actual torque dead zone detecting means may detect the actual torque dead zone based on the steering torque value after the correction of the midpoint deviation.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electric configuration of the electric power steering device according to the first embodiment of the present invention. A steering torque applied to a steering wheel 1 as an operation member is transmitted to a steering mechanism 3 via a steering shaft 2. The driving force generated by the electric motor M is mechanically transmitted to the steering mechanism 3 as a steering assist force via a gear mechanism or by a direct drive method.
[0018]
The steering mechanism 3 includes a pinion gear connected to the steering shaft 2 and a rack that meshes with the pinion gear and is supported so as to be movable in the left-right direction of the vehicle. Wheels are steered.
The steering shaft 2 is divided into an input shaft 2A connected to the steering wheel 1 and an output shaft 2B connected to the steering mechanism 3. The input shaft 2A and the output shaft 2B are connected to a torsion bar 4. Are connected to each other. The torsion bar 4 generates a twist according to the steering torque applied to the steering wheel 1, and the direction and amount of the twist are detected by a torque sensor 5. The detected torque value Ts output from the torque sensor 5 is input to the controller 10 (electronic control unit).
[0019]
The controller 10 includes, in addition to the output signal of the torque sensor 5, a steering angle sensor 6 for detecting a steering angle θ of the steering wheel 1 and a vehicle speed sensor for detecting a vehicle speed V of a vehicle equipped with the electric power steering device. 7 are also input.
The controller 10 sets a target current value according to the torque detection value Ts output by the torque sensor 5 and the vehicle speed V detected by the vehicle speed sensor 7, and controls the motor driver 20 based on the target current value, An appropriate drive current is given to the electric motor M. As a result, a steering assist force corresponding to the steering torque and the vehicle speed V is given to the steering mechanism 3.
[0020]
The controller 10 includes an offset value generation unit 11 that generates an offset value (middle point deviation amount) OF for performing a midpoint deviation correction on the torque detection value Ts by a program process performed by a microcomputer provided therein; A subtraction unit 12 that subtracts the offset value OF generated by the offset value generation unit 11 from the torque detection value Ts and outputs a steering torque value T1 (= Ts−OF) corrected for a midpoint deviation; And a target current value setting unit 13 that sets a target current value for driving the electric motor M based on the steering torque value T1 and the vehicle speed V generated by the control unit.
[0021]
The offset value generation unit 11 calculates a steering angle average value calculation unit 15 that calculates an average value Zave of detection values of the steering angle sensor 6 over a predetermined time (for example, 5 seconds), and calculates a torque detection value Ts over the predetermined time. A torque integrating section 16 for integrating to obtain a torque integrated value Zt; and an offset value OF based on the steering angle average value Zave determined by the steering angle average value calculating section 15 and the torque integrated value Zt determined by the torque integrating section 16. An offset value calculation unit 17 to be obtained and an offset value storage unit 18 for storing and holding the offset value OF obtained by the offset value calculation unit 17 are provided. Both the steering angle average value calculating unit 15 and the torque integrating unit 16 require that the vehicle speed sensor 7 detects a vehicle speed V equal to or higher than a predetermined vehicle speed (for example, 10 km / h), that is, that the vehicle is in a running state. , The steering angle average value Zave and the integrated torque value Zt are calculated.
[0022]
The steering angle average value calculation unit 15 calculates the average value of the absolute value | θ | of the steering angle detected by the steering angle sensor 6, and the absolute value of the steering angle | θ | 1 degree) or more, the detection value θ of the steering angle sensor 6 is used for the average value calculation.
FIG. 2 is a diagram for explaining the operation of the target current value setting unit 13, and shows a relationship (assist characteristic) between the steering torque value T and the target current value. As the steering torque value T, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The target current value is a positive value when the electric motor M is to generate a steering assist force for rightward steering, and is negative when the electric motor M is to generate a steering assist force for leftward steering. Value.
[0023]
The target current value has a positive value for a positive steering torque value T, and has a negative value for a negative steering torque value T. When the steering torque value T is a small value in the range of -α to α (for example, α = 0.4 Nm) (torque dead zone), the target current value is set to zero. The absolute value of the target current value is set to decrease as the vehicle speed V detected by the vehicle speed sensor 7 increases. As a result, a large steering assist force can be generated during low-speed running, and the steering assist force can be reduced during high-speed running.
[0024]
In this embodiment, the steering torque value T1 corrected for the above-mentioned midpoint deviation is used as the steering torque value T used for setting the target current value.
FIG. 3 is a diagram for explaining a process performed by the offset value generation unit 11. The torque sensor 5 ideally outputs a torque detection value proportional to the steering torque value T applied to the steering wheel 1, but a left-right difference occurs depending on the load state of the vehicle and the like. That is, although the steering torque is zero, the detected torque value Ts takes a positive or negative value. The torque detection value Ts at this time is obtained by the offset value generation unit 11 as the offset value OF.
[0025]
When the offset value OF is zero, that is, the relationship between the detected torque value Ts when the midpoint deviation is not corrected and the steering torque value T1 used for calculating the target current value is as shown by a broken line in FIG. When the offset value OF is a value other than zero (for example, a negative value), as a result of the calculation in the subtraction unit 12, the relationship between the torque detection value Ts and the steering torque value T1 for calculating the target current value is determined. , And as shown by the solid line in FIG.
[0026]
FIG. 4 is a flowchart for explaining the generation processing of the offset value OF by the offset value generation unit 11. First, in order to determine whether the vehicle is running at a predetermined vehicle speed (10 km / h in this example) or more, it is determined whether the vehicle speed V is equal to or higher than the predetermined vehicle speed (step S1). If the vehicle speed V is lower than the predetermined vehicle speed, a plurality of parameters t, ta, Zt, and Zθ described later are each initialized to zero (step S11), and the process returns.
[0027]
If the vehicle speed V is equal to or higher than the predetermined vehicle speed, it is determined whether the time (integrated time) t (second) during which the steering angle detection value θ and the torque detection value Ts are integrated has reached a predetermined time (5 seconds in this example). It is determined (step S2). When the integration time t reaches the predetermined time (NO in step S2), the steering angle θ is a positive value (that is, a value when the steering angle is turned rightward from the steering angle midpoint) in the integration time t. The integration time (positive integration time) ta in the state is within a certain range (4 seconds>ta> 1 second in this example, that is, 20 to 80% of the total integration time (5 seconds in this example)). It is determined whether or not (step S3). If the positive side integration time Ta is not a value within the certain range, the parameters t, ta, Zt, and Zθ are each initialized to zero (step S11), and the process returns.
[0028]
If the accumulated time t has not reached the predetermined time (YES in step S2), it is determined whether the steering angle θ is within a certain steering angle range (1 degree>θ> -1 degree in this example), that is, the absolute value of the steering angle. It is checked whether the value | θ | is less than a fixed value (1 degree in this example) (step S4). If the steering angle θ is a value outside the fixed steering angle range (NO in step S4), it is further determined whether the steering angle θ is a positive value, that is, whether θ ≧ 1 degree (step S5). ). If the steering angle θ is θ ≧ 1 degree, the calculation cycle f (second) is added to the positive integration time ta (step S6), and further, the calculation cycle f is added to the integration time t (step S7).
[0029]
On the other hand, if the steering angle θ is less than 1 degree (NO in step S5), the calculation cycle f is not added for the positive integration time ta, but is added only for the integration time t. Is performed (step S7).
In the following step S8, the torque detection value Ts in the current cycle is added to the torque integrated value Zt, and the absolute value | θ | of the steering angle in the current cycle is added to the steering angle integrated value Zθ, and the routine returns.
[0030]
On the other hand, when it is determined in step S3 that the positive integration time ta is within a certain range, that is, while integrating the torque integrated value Zt and the steering angle integrated value Zθ over a predetermined time, the positive integration time ta is determined. When steering to the right (right side) and the negative side (left side) is performed at a certain ratio, the offset value OF is obtained.
More specifically, the average steering angle Zave over the above-mentioned predetermined time is obtained by Zave = Zθ ÷ (t / f) (t / f corresponds to the number of times of integration) (step S9). Further, the offset value OF (= Zt / Zave) is obtained by dividing the torque integrated value Zt by the steering angle average value Zave (step S9). The offset value OF thus obtained is stored and held in the offset value storage unit 18 as a new offset value OF (step S10). Thereafter, the parameters t, ta, Zt, and Zθ are each initialized to zero (step S11), and the process returns.
[0031]
As described above, since the offset value OF is obtained by dividing the torque integrated value Zt by the steering angle average value Zave, the offset value OF can be reduced when the operation is performed at a large steering angle, and the small steering angle range is obtained. , The offset value OF is determined to be relatively large. In the large steering angle range, the integrated torque value Zt does not always correspond to the midpoint deviation amount of the torque detection value Ts. Therefore, the offset value OF determined as described above is determined whether the steering is performed in the large steering angle range or the small steering angle. It will have a reasonable value regardless of whether it is steered in an angular range.
[0032]
As described above, according to this embodiment, since the target current value is determined based on the steering torque value T1 corrected for the midpoint deviation, it is possible to suppress or eliminate the left-right difference in the driver's steering burden. And a good steering feeling can be realized. Moreover, since the offset value OF obtained based on the torque integrated value Zt and the steering angle average value Zave over a predetermined time (for example, 5 seconds) is updated as needed, it is possible to correct the midpoint deviation in real time, so to speak. In addition, it is possible to effectively suppress or eliminate the left-right difference in the steering torque due to the load state of the vehicle.
[0033]
FIG. 5 is a block diagram showing an electric configuration of the electric power steering device according to the second embodiment of the present invention. Parts corresponding to the respective parts shown in FIG. 1 described above are denoted by the same reference numerals in FIG. 5 as those in FIG. 1, and description thereof is omitted.
In this embodiment, the output of the motor current detection unit 21 that detects a current value (motor current value) Im flowing through the electric motor M and the steering torque value T1 after the midpoint deviation correction by the subtraction unit 12 are performed. Further, an actual torque dead zone detection unit 22 for detecting an actual torque dead zone (actual torque dead zone) is provided. The actual torque dead zone detection unit 22 detects the steering torque value T1 when the motor current value Im is zero, and thereby detects the actual range of the steering torque value T1 in which the motor current value Im is maintained at zero (the actual torque dead zone). ) Is detected. Data corresponding to the actual torque dead zone detected by the actual torque dead zone detection unit 22 is stored in the torque dead zone storage unit 23.
[0034]
FIG. 6 is a diagram for explaining data stored in the torque dead zone storage unit 23, and shows a relationship between the steering torque value T1 after the midpoint deviation correction and the motor current value Im. If it is detected that the motor current value Im is maintained at zero when the steering torque value T1 after the midpoint deviation correction takes a value within the actual torque dead zone range TL ≦ T1 ≦ TR near zero, the torque dead zone is assumed. The storage unit 23 stores a negative (left) dead zone threshold TL (<0) and a positive (right) dead zone threshold TR (> 0).
[0035]
The torque dead zone storage unit 23 stores the positive dead zone threshold value TR (positive steering threshold value TR) when the steering torque value T1 output from the subtraction unit 12 after the midpoint deviation correction is a positive value (that is, when the steering torque is rightward). Is given to the adder 24, and when the steering torque value T1 after the midpoint deviation correction is a negative value (that is, when the steering torque is to the left), the negative dead zone threshold value TL (negative value) Is given to the adding unit 24.
In the adding unit 24, one of the dead zone thresholds TR and TL is added to the steering torque value T1 after the correction of the midpoint deviation, thereby correcting the steering torque value T1 to eliminate the actual torque dead zone ( Actual torque dead zone exclusion correction) is performed. The steering torque value T2 after the actual torque dead zone elimination correction is used for setting the target current value in the target current value setting unit 13. That is, the steering torque value T2 after the real torque dead zone elimination correction is applied as the steering torque value T in the assist characteristics of FIG.
[0036]
The steering torque value T2 is eventually expressed by the following equations (1) and (2).
Right turn T2 = Ts-OF + TR (1)
T2 = Ts-OF + TL (2)
FIG. 7 is a diagram showing a relationship between the detected torque value Ts and the steering torque values T1 and T2. When neither the correction of the center point deviation nor the correction for eliminating the actual torque dead zone is performed, the torque detection value Ts and the steering torque value to be used for the target current value calculation are in a proportional relationship indicated by a straight line L0. On the other hand, by performing the midpoint deviation correction, the relationship between the torque detection value Ts and the steering torque value T1 after the midpoint deviation correction is determined by dividing the straight line L0 along the coordinate axis of the steering torque value by the offset value OF. Follows the straight line L1 translated only by Further, when the midpoint deviation correction and the correction for eliminating the actual torque dead zone are performed on the torque detection value Ts, the relationship between the torque detection value Ts and the steering torque value T2 used for setting the target current value becomes a broken line. L2 will be followed. The broken line L2 moves the portion of Ts> OF along the straight line L1 by the positive dead zone threshold TR along the coordinate axis of the steering torque value (moves in the positive direction because TR> 0), and moves the portion of Ts <OF on the straight line L1. It is obtained by moving along the coordinate axis of the steering torque value by the negative dead zone threshold value TL (moving in the negative direction because TL <0).
[0037]
FIG. 8A shows a characteristic when the target current value is determined based on the steering torque value T1 after the correction of the midpoint deviation (in the case of the first embodiment). The torque detection value Ts and the target current value are shown. Shows the relationship with FIG. 8B shows the torque detection value Ts and the target current value when the target current value is determined based on the steering torque value T2 that has been subjected to both the midpoint deviation correction and the actual torque dead zone elimination correction (this embodiment). Shows the relationship.
As shown in FIG. 8A, when the target current value is set based on the steering torque value T1 corrected for the midpoint deviation, the range of -α ≦ T1 ≦ α becomes the torque dead zone. That is, in this steering torque range, the target current value is maintained at zero, and the electric motor M does not generate a driving force.
[0038]
On the other hand, when the steering torque value T2 corrected by the above equations (1) and (2) is given to the target current value setting unit 13, the torque dead zone is eliminated, and in any steering torque range. The electric motor M is driven, and the steering assist force is given to the steering mechanism 3.
As a result, it is possible to suppress or prevent transmission of torque unevenness caused by, for example, rack-and-pinion engagement and cogging torque of the electric motor M provided to the driver via the steering wheel 1 provided in the steering mechanism 3. can do. That is, since undesired torque fluctuation can be suppressed, the steering feeling can be improved.
[0039]
FIG. 9 is a flowchart for explaining the processing performed by the actual torque dead zone detecting unit 22. First, it is determined whether or not the vehicle speed V is equal to or higher than a predetermined vehicle speed (10 km / h in this example) (step S21). If the vehicle speed V is lower than the predetermined vehicle speed, the process returns without performing the subsequent processing.
If the vehicle speed V is equal to or higher than the predetermined vehicle speed (YES in step S21), the steering torque value T1 (= Ts-OF) obtained by correcting the current torque detection value Ts by the midpoint deviation and the positive side stored in the torque dead zone storage unit 23. It is compared with the dead zone threshold value TR, and it is determined whether the motor current value Im is equal to or less than zero (step S22). When the steering torque value T1 is larger than the positive dead zone threshold TR and the motor current value Im is equal to or less than zero, the steering torque value T1 is stored in the torque dead zone storage unit 23 as a new positive dead zone threshold TR. (Step S23). Thereafter, the process returns.
[0040]
On the other hand, if the steering torque value T1 is equal to or smaller than the positive dead zone threshold value TR or the motor current value Im exceeds zero (NO in step S22), the steering torque value T1 is stored in the torque dead zone storage unit 23. It is determined whether the threshold value is smaller than the negative dead zone threshold value TL and the motor current value Im is equal to or greater than zero (step S24). If this determination is affirmative, the steering torque value T1 is stored in the torque dead zone storage unit 23 as a new negative dead zone threshold TL (step S25). Thereafter, the process returns.
[0041]
In step S24, if the steering torque value T1 is equal to or greater than the negative dead zone threshold TL or if the motor current value Im is less than 0 (NO in step S24), the processing is performed without updating the negative dead zone threshold TL. Is returned.
The determination of the motor current value Im in steps S22 and S24 is based on the motor current corresponding to the back electromotive force generated in the motor when the electric motor M is stopped or when the motor is rotated by the reverse input from the wheels. Therefore, instead of the motor current value Im, it is determined whether the motor voltage is equal to or less than zero (in the case of step S22) or whether the motor voltage is equal to or greater than zero (in the case of step S24). You may make it determine.
[0042]
FIG. 10 is a flowchart illustrating a control routine of electric motor M by controller 10. In order to determine whether the steering is being performed, it is determined whether the torque detection value Ts is equal to the offset value OF (step S31; it may be determined whether T1 = 0). If it is determined that they are not equal to each other and therefore the steering is not being performed (the steering wheel 1 is not operated on either the left or right), the steering torque value T for setting the target current value is set to T = Ts-OF. Is performed (step S32). That is, in this case, the processing by the adding unit 24 (see FIG. 5) is omitted. A target current value is set based on the steering torque value T (Step S33). The electric motor M is controlled based on the target current value (Step S34).
[0043]
On the other hand, in step S31, when it is determined that the torque detection value Ts is not equal to the offset value OF and, therefore, steering is being performed, the sign of the corrected steering torque value T1 (= Ts-OF) in the subtraction unit 12 is used. Is determined based on the right-turning state (T1> 0, that is, Ts> OF) (step S35). In the case of the right turn state, the steering torque value T for setting the target current value is obtained by T = T2 = Ts-OF + TR (step S36), and the left turn state (T1 <0, that is, Ts <OF) is satisfied. If (NO in step S35), the steering torque value T for setting the target current value is obtained by T = T2 = Ts-OF + TL (step S37). A target current value is set based on the steering torque value T thus obtained (step S33), and the electric motor M is controlled based on the target current value.
[0044]
In this manner, control excluding the torque dead zone can be realized. In addition, since the midpoint of the steering torque is detected in real time, the automatic rotation of the steering wheel 1 does not occur in the released state.
FIG. 11 is a diagram illustrating an example of the relationship between the steering angle θ and the steering torque (the steering burden on the driver) when the steering wheel 1 is rotated left and right. The two-dot chain line shows the characteristic when the torque detection value Ts is applied to the assist characteristic in FIG. 2 without performing the correction by the subtractor 12 and the adder 24. On the other hand, the characteristics when the steering torque value T2 corrected by the subtraction unit 12 and the addition unit 24 is applied to the assist characteristics in FIG. 2 are indicated by solid lines.
[0045]
As can be understood from the comparison between these two curves, the left-right difference is eliminated by adding the offset value OF to the torque detection value Ts, and the target current value setting unit 13 is eliminated by eliminating the torque dead zone. It is understood that minute torque fluctuations (for example, see the portions indicated by reference numerals A1 and A2) in the steering torque range within the torque dead zone range in the assist characteristics according to are reduced.
The two embodiments of the present invention have been described above, but the present invention can be embodied in other forms. For example, in the above-described second embodiment, the actual torque dead zone is detected based on the steering torque value T1 obtained by applying the middle point deviation to the torque detection value Ts. May be used as it is to detect the actual torque dead zone, that is, the positive side dead zone threshold TR ′ and the negative side dead zone threshold TL ′. In this case, the following equations (1) 'and (2)' are used instead of the above equations (1) and (2).
[0046]
Right turn T2 = Ts + TR '(1)'
Left-turning T2 = Ts + TL '(2)'
Further, in the above-described embodiment, the right turn or the left turn is determined based on the sign of the steering torque value T1, but the torque detection value Ts and the offset value OF are compared in magnitude, and the right turn or the left turn is performed. May be determined.
Further, in order to eliminate torque loss due to the static friction of the steering mechanism 3 or the like, it is preferable that a dither control signal is superimposed on a control signal for driving the electric motor M, and a pseudo frictionless state is set. That is, due to the mechanical viscosity of the steering mechanism 3 and the electric motor M, there is a torque range in which the electric motor M does not operate (mechanical dead zone). If the value is within the range, the electric motor M does not operate. As a result, the stability when traveling straight ahead is poor, and the responsiveness when starting to turn the steering wheel 1 is insufficient. Such a problem is improved by superimposing the dither control signal on the control signal for driving the electric motor M.
[0047]
For example, when the vehicle is traveling straight, when the steering angle of the steering wheel 1 is small for a certain time or more, and when the steering torque is small for a certain time or more, the dither control signal is superimposed. Good.
The amplitude of the dither control signal may be within a mechanical dead zone of the electric motor M, and the frequency may be, for example, 50 to 10 Hz.
In particular, it is effective to superimpose the dither control signal in a steering mechanism capable of changing the steering gear ratio or in a steer-by-wire system having no mechanical connection between the steering wheel and the steering mechanism. In the case of a steer-by-wire system, it is preferable that a dither control signal is also superimposed on a drive control signal of a reaction force actuator for applying a steering reaction force to the steering wheel.
[0048]
Further, in the above-described embodiment, the target current value is used as the target drive value for controlling the electric motor M. May be used.
In addition, various design changes can be made within the scope of the matters described in the claims.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an electric configuration of an electric power steering device according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining an operation of a target current value setting unit, and shows a relationship between a steering torque and a target current value.
FIG. 3 is a diagram for explaining an offset value generated by an offset value generation unit.
FIG. 4 is a flowchart illustrating an offset value generation process.
FIG. 5 is a block diagram showing an electric configuration of an electric power steering device according to a second embodiment of the present invention.
FIG. 6 is a diagram showing a relationship between a steering torque value and a motor current value after the correction of the midpoint deviation.
FIG. 7 is a diagram illustrating a relationship between a detected torque value and a steering torque value.
FIG. 8A shows a characteristic when a target current value is determined based on a steering torque value after the correction of the midpoint deviation, and FIG. This shows characteristics when a target current value is determined based on a steering torque value that has undergone both corrections.
FIG. 9 is a flowchart illustrating the contents of an actual torque dead zone detection process.
FIG. 10 is a flowchart illustrating a control routine of the electric motor.
FIG. 11 is a diagram illustrating an example of a relationship between a steering angle and a steering torque (a driver's steering burden) when the steering wheel is rotated left and right.
[Explanation of symbols]
1 Steering wheel
2 Steering shaft
3 Steering mechanism
4 Torsion bar
5 Torque sensor
6 steering angle sensor
7 Vehicle speed sensor
10 Controller
11 Offset value generator
12 Subtraction unit
13 Target current value setting section
15 Steering angle average value calculation unit
16 Torque integration section
17 Offset value calculator
18 Offset value storage
20 Motor driver
21 Motor current detector
22 Actual torque dead zone detector
23 Torque dead zone storage unit
24 Adder
M electric motor
Ts Torque detection value
T1 Steering torque value after correction of midpoint deviation
T2 Steering torque value with midpoint shift correction and torque dead zone exclusion correction
V vehicle speed
Zt Torque integrated value
Zθ Steering angle integrated value
Zave steering angle average
θ steering angle
t Integration time
ta Accumulated time on the positive side (cumulative time with right turn)
OF offset value (middle point deviation amount)
f Calculation cycle
Im Motor current value
TR Positive dead zone threshold
TL Negative dead zone threshold

Claims (2)

An electric power steering device that transmits a driving force of an electric motor controlled according to an operation amount of an operation member for steering of a vehicle to a steering mechanism to assist in steering,
Steering torque detecting means for detecting a steering torque applied to the operating member;
A torque integrating means for integrating a torque detection value, which is a detection value of the steering torque detecting means, for a predetermined time to obtain a torque integrated value;
Steering angle detection means for determining a steering angle of the operating member;
Steering angle average value calculating means for calculating an average value of the steering angle detected by the steering angle detecting means over the predetermined time;
Based on the torque integrated value obtained by the torque integrating means and the steering angle average value obtained by the steering angle average value calculating means, and a midpoint deviation correcting means for correcting the midpoint deviation of the steering torque detecting means. An electric power steering device comprising: Based on the torque detection value when the drive current of the electric motor is zero, an actual torque dead zone detection unit that detects an actual torque dead zone that is a range of the steering torque in which the drive current of the electric motor is held at zero,
2. The electric power steering apparatus according to claim 1, further comprising a dead zone elimination correction unit that corrects the detected torque value so as to eliminate the actual torque dead zone.

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