JP2012101674A - Electric power steering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate steering torque in an electric power steering system that estimates the steering torque by using a difference between a detection value of a steering angle sensor and a value based on a detection value of a motor rotation angle sensor.SOLUTION: The electric power steering system including an electric motor 13 connected to a steering shaft and a control device for driving the electric motor depending on the steering torque comprises: the steering angle sensor 15 for detecting a steering angle at each predetermined period; a motor rotation angle detection sensor means 14 for detecting a motor rotation angle of the electric motor at each predetermined period; and a steering torque estimation section means 32 for estimating the steering torque on the basis of a difference between the rotation angle and steering angle of a portion, to which the electric motor is connected, of the steering shaft, computed on the basis of the motor rotation angle. The steering torque estimation section corrects this steering angle on the basis of the motor rotation angle when this steering angle and the previous steering angle, which are detected by a steering angle detection means at an arbitrary time, are equal to each other.

Description

  The present invention relates to an electric power steering apparatus.

  The electric power steering device detects a steering torque applied to a steering shaft (steering shaft) by a torque sensor, and applies a steering assist force corresponding to the steering torque to the steering shaft by an electric motor. Therefore, if the torque sensor fails, the steering assist force cannot be set. In order to solve this problem, there is one that estimates the steering torque based on the torsion angle of the torsion bar incorporated in the steering shaft and the spring constant of the torsion bar, and controls the drive of the electric motor according to the estimated steering torque. (For example, patent document 1). In the invention according to Patent Document 1, the torsion is based on the detection value of the steering angle sensor provided on one end side of the torsion bar and the detection value of the motor rotation angle sensor of the electric motor provided on the other end side of the torsion bar. The torsion angle of the bar is calculated.

JP 2005-219573 A

  However, the steering angle sensor often has lower resolution (detection sensitivity) than the motor rotation angle sensor, and if a difference between a value based on the detection value of the steering angle sensor and a value based on the detection value of the motor rotation angle sensor is taken. In fact, even when there is no difference, a minute value that can be detected by the motor rotation angle sensor but cannot be detected by the steering angle sensor is included as the difference. Therefore, if the steering torque is estimated based on the difference between the value based on the detection value of the steering angle sensor and the value based on the detection value of the motor rotation angle sensor, and the steering assist force is set according to this steering torque, There is a possibility that a portion where the assist force is excessive or insufficient is generated.

  The present invention has been made in view of the above background, and in an electric steering device that estimates a steering torque using a difference between a detected value of a steering angle sensor and a value based on a detected value of a motor rotation angle sensor, It is an object to accurately estimate the steering torque and set an appropriate steering assist force.

  In order to solve the above problems, the present invention is connected to a steering shaft 3 coupled to a steering wheel 2, a coupling mechanism 5 that steers a tire 4 in accordance with the rotation of the steering shaft, and the steering shaft. An electric power steering apparatus 1 having an electric motor 13 and a control means 19 for driving the electric motor in accordance with a steering torque acting on the steering shaft, and a steering angle detecting means for detecting a steering angle at predetermined intervals. 15, motor rotation angle detection means 14 for detecting the motor rotation angle of the electric motor at predetermined intervals, and the rotation angle of the portion of the steering shaft to which the electric motor is connected calculated based on the motor rotation angle; Steering torque estimating means 32 for estimating the steering torque based on the difference from the steering angle, the steering torque estimating means being detected at any time by the steering angle detecting means. If it and the previous steering angle detected in the previous cycle at the time of detecting the current steering angle and the steering angle equal to, and corrects the current steering angle based on the motor rotation angle.

  According to this configuration, when a small rotational displacement that cannot be detected by the steering angle sensor occurs in the steering shaft, the detection value of the steering angle sensor is corrected based on the detection value of the motor rotation angle sensor, and the estimation of the steering torque is performed. Accuracy can be increased.

  In another aspect of the present invention, when the current steering angle is different from the previous steering angle, the steering torque estimating means determines the motor rotation angle when the current steering angle is detected as a reference motor rotation angle. When the nth steering angle is detected when the nth steering angle detected after the current steering angle is detected is equal to the current steering angle continuously from the time when the current steering angle is detected. The difference between the detected nth motor rotation angle and the reference motor rotation angle is added to the nth steering angle.

  According to this configuration, the detection value of the steering angle sensor can be corrected by a simple method.

  In another aspect of the present invention, the direction of the steering torque is compared with the direction of the steering angular velocity based on the steering angle, and the case where the directions of the steering torque and the steering angular velocity are the same is determined as a forward state, Steering state detection means 36 for determining a return state when the steering torque and the steering angular velocity contradict each other, and the control means is calculated based on the steering torque in the forward state. The damper amount calculated based on the steering angular velocity is subtracted from the basic assist amount, and in the return state, the damper amount is added to the basic assist amount. Further, instead of comparing the direction of the steering torque and the direction of the steering angular velocity, the forward state and the return state are determined by comparing the direction of the steering torque and the direction of the motor rotational angular velocity based on the motor rotational angle. Also good.

  According to this configuration, it is possible to improve the steering feeling by adding the damper amount according to the steering state to the steering assist force.

  With the configuration as described above, in the electric steering apparatus that estimates the steering torque using the difference between the values based on the detected values of the steering angle sensor and the motor rotation angle sensor, the steering torque is accurately estimated and appropriate steering assist is obtained. You can set the force.

Schematic explanatory view showing a power steering device according to an embodiment The block diagram which shows the control apparatus of the power steering apparatus which concerns on embodiment The figure which shows the relationship between steering angular velocity and steering torque, and a steering state Flow chart showing the target current setting procedure by the controller Flow chart showing calculation procedure of estimated steering torque by steering torque estimation unit Graph showing the corrected steering angle θs ′ The graph which shows the steering torque of the power steering device which concerns on embodiment

  Hereinafter, an embodiment in which the present invention is applied to a rack and pinion type power steering apparatus for a vehicle will be described in detail with reference to the drawings.

<Schematic configuration of steering device>
As shown in FIG. 1, a power steering device 1 includes a steering shaft (steering shaft) 3 connected to a steering wheel 2 and a rack-and-pinion type connecting mechanism that connects the steering shaft 3 and left and right front wheels 4. And 5. The steering shaft 3 is provided with a universal joint 6 at an appropriate place, and a pinion 7 constituting the connection mechanism 5 is integrally connected to an end portion on the side opposite to the steering wheel 2 side. The coupling mechanism 5 is engaged with a pinion 7 and is provided with a rack shaft 8 that can be reciprocated in the vehicle width direction, and a tie rod 10 that is coupled to both ends of the rack shaft 8 and that is coupled to the knuckle 9 of the left and right front wheels 4. And. Thereby, the left and right front wheels 4 are steered in accordance with a manual rotation operation of the steering wheel 2.

  An electric motor 13 is connected to the steering shaft 3 via a speed reducer 12. The electric motor 13 applies a driving force as a steering assist force to the steering shaft 3 via the speed reducer 12. The speed reducer 12 includes a worm (not shown) connected to the output shaft of the electric motor 13 and a worm wheel (not shown) connected to the steering shaft 3 and meshing with the worm, and the reduction ratio becomes D. Yes. The electric motor 13 is provided with a motor rotation angle sensor 14 for detecting the motor rotation angle. The motor rotation angle sensor 14 may be a known rotary encoder or resolver.

  A steering angle sensor 15 is provided at a portion of the steering shaft 3 on the steering wheel 2 side, and a torque sensor 16 is provided at a portion between the steering angle sensor 15 and the speed reducer 12. The steering angle sensor 15 is a sensor that detects a steering angle corresponding to the rotation angle of the steering wheel 2, and may be a known rotary encoder, resolver, or potentiometer. The torque sensor 16 detects a steering torque applied to the steering shaft 3 (torque applied to the steering shaft 3 by the driver via the steering wheel 2), and is a known torsion bar type torque sensor or magnetostrictive torque sensor. It may be. When the torsion bar type torque sensor is used, it is necessary to divide the steering shaft 3 into two and to connect the two steering shafts 3 by the torsion bar constituting the torque sensor 16.

  The electric motor 13 is driven and controlled by a control device (ECU: electric control unit) 17. As shown in FIG. 2, the control device 17 includes a CPU, a ROM, a RAM, and the like. The control unit 18 executes a program stored in the ROM, and a detection value detected by each sensor by the control unit 18. A drive circuit 20 for PWM-controlling the electric motor 13 based on the calculated motor control signal (PWM control signal) is provided. The drive circuit 20 is a bridge circuit of switching elements, generates a motor voltage corresponding to the motor control signal, and drives the electric motor 13 by flowing a motor current I corresponding to the steering torque. The control unit 18 includes a steering angle θs from the steering angle sensor 15, a sensor steering torque Ts from the torque sensor 16, a motor rotation angle θm from the motor rotation angle sensor 14, and a vehicle speed sensor provided at an appropriate position of the vehicle. The vehicle speed V from 21 is input.

  As shown in FIG. 2, the control unit 18 includes a torque sensor abnormality detection unit 31, a steering torque estimation unit 32, a torque signal switching unit 33, a steering angular velocity calculation unit 34, a base target current setting unit 35, a steering state determination unit 36, A damping compensation current setting unit 37, a target current setting unit 38, and a motor control unit 39 are provided.

  Based on the steering angle θs from the steering angle sensor 15 and the sensor steering torque Ts from the torque sensor 16, the torque sensor abnormality detection unit 31 determines the state of the torque sensor 16 as normal or failure, and determines the determination result as failure. The signal Ss is output to the torque signal switching unit 33. For example, the torque sensor abnormality detection unit 31 determines that the torque sensor 16 is out of order when the sensor steering torque Ts is not supplied even though the steering angle θs is supplied (Ts = 0).

  The steering torque estimating unit 32 estimates the steering torque applied to the steering shaft 3 based on the steering angle θs from the steering angle sensor 15 and the motor rotation angle θm from the motor rotation angle sensor 14 as the estimated steering torque, and estimates the steering. Torque Te is output to the torque signal switching unit 33. A method for estimating the estimated steering torque Te will be described later.

  Based on the failure determination signal Ss from the torque sensor abnormality detection unit 31, the torque signal switching unit 33 steers either the sensor steering torque Ts from the torque sensor 16 or the estimated steering torque Te from the steering torque estimation unit 32. The torque is selected as the torque, and the steering torque Tf is output to the base target current setting unit 35 and the steering state determination unit 36. The torque signal switching unit 33 sets the estimated steering torque Te to the steering torque Tf when the determination content of the failure determination signal Ss is failure, and the torque sensor 16 when the determination content of the failure determination signal Ss is normal. Is assumed to be normal, the sensor steering torque Ts is set as the steering torque Tf.

  The steering angular velocity calculation unit 34 generates a steering angular velocity ω by time-differentiating the steering angle θs from the steering angle sensor 15 and outputs the steering angular velocity ω to the steering state determination unit 36 and the damping compensation current setting unit 37.

  The base target current setting unit 35 refers to a predetermined base target current map set in advance on the basis of the steering torque Tf from the torque signal switching unit 33 and the vehicle speed V from the vehicle speed sensor 21, and corresponds to the corresponding base target. The current value Ib is set and output to the target current setting unit 38. The base target current value Ib corresponds to the basic assist amount.

  The steering state determination unit 36 determines the steering state based on the steering torque Tf from the torque signal switching unit 33 and the steering angular velocity ω from the steering angular velocity calculation unit 34. As shown in FIG. 3, the steering state is determined based on a positive / negative direction (forward (left) direction or reverse (right) direction) in which both the direction of the steering torque Tf and the direction of the steering angular velocity ω are neutral. When both directions are the same (the signs are both positive or negative), the steering is forward, and when the directions are different (one of the signs is positive and the other is negative), it is determined that the steering is returned. The steering state determination unit 36 outputs a steering state determination signal Sa as a determination result to the target current setting unit 38. A motor rotation angular velocity calculated from the motor rotation angle θm may be applied instead of the steering angular velocity ω.

  The damping compensation current setting unit 37 refers to a predetermined damping compensation current map set in advance based on the steering angular velocity ω from the steering angular velocity calculation unit 34 in order to set a damping compensation current value Id for damping steering. The corresponding damping compensation current value Id is set and output to the target current setting unit 38.

  The target current setting unit 38 includes a base target current value Ib from the base target current setting unit 35, a steering state determination signal Sa from the steering state determination unit 36, and a damping compensation current value Id from the damping compensation current setting unit 37. When the steering state is forward steering from the steering state determination signal Sa, the damping compensation current value Id is subtracted from the base target current value Ib, and when the steering state is return steering from the steering state determination signal Sa. Adds the damping compensation current value Id to the base target current value Ib, calculates the target current It, and outputs it to the motor control unit 39.

  The motor control unit 39 generates a PWM signal for controlling the drive circuit 20 based on the target current It from the target current setting unit 38 and controls the drive of the motor 13.

  Next, a procedure for setting the steering assist force according to the embodiment will be described with reference to the flowcharts of FIGS. 4 and 5. When the automobile starts driving, the control unit 18 receives the detection values from each sensor at a predetermined control interval (for example, 2 ms), and executes the control shown in FIGS. 4 and 5.

  First, in step S1, the control unit 18 controls the sensor steering torque Ts from the torque sensor 16, the vehicle speed V from the vehicle speed sensor 21, the steering angle θs from the steering angle sensor 15, and the motor rotation from the motor rotation angle sensor 14 at an arbitrary time. Obtain the angle θm. These values are obtained at predetermined control intervals. When it is necessary to distinguish between the current value and the previous value, the current value θs (n), the previous value θn (n−1), and the like. Are distinguished by subscripts in parentheses. The necessary previous value is held in a memory incorporated in the control device 20.

  Next, in step S2, the steering torque estimation unit 32 performs an estimation process of the estimated steering torque Te. The estimation steering torque Te is estimated by a subroutine shown in FIG.

As shown in FIG. 5, first, the current value θs (n) from the steering angle sensor 15 is compared with the previous value θs (n−1) held in the memory for the steering angle θs, and a change occurs. It is determined whether or not (S11). If it is determined that there is a change (Yes), the current steering angle θs (n) is set to the reference steering angle θs ₀ (S12), and the reference steering angle θs ₀ is set to the corrected steering angle θs ′ ( S13), and sets the current motor rotation angle .theta.m (n) to the reference motor angle θm ₀ (S14). Thereafter, the process proceeds to step S15.

On the other hand, in step S11, there is no change if it is determined that (No), then calculates the difference between the current motor rotation angle .theta.m (n) and the reference angular position .theta.m ₀ as variation Δθm (S17), the motor The change amount Δθm in the rotation angle is converted into a conversion change amount Δθm ′ that is a change amount in the rotation angle of the portion to which the electric motor 13 is connected via the speed reducer 12 of the steering shaft 3 (S18). The conversion is performed, for example, by dividing the change amount Δθm in the motor rotation angle by the reduction ratio D of the speed reducer 12. Then, the corrected change amount Δθm ′ is added to the reference steering angle θs ₀ to calculate the corrected steering angle θs ′ (S19). Thereafter, the process proceeds to step S15.

  In step S15, the current motor rotation angle θm (n) is converted into the rotation angle of the portion to which the electric motor 13 is connected via the speed reducer 12 of the steering shaft 3 in the same manner as in step S18. Calculate as'. In step S16, the difference between the corrected steering angle θs ′ and the converted rotation angle θm ′ is calculated, so that the electric motor 13 is detected via the portion detected by the steering angle sensor 15 of the steering shaft 3 and the speed reducer 12 of the steering shaft 3. Is calculated by calculating the torsion angle of the steering shaft 3 in the range A with respect to the portion to which the is connected, and multiplying the torsion angle by the stiffness K (N / m) in the range A to calculate the estimated steering torque Te. . When the torsion bar type torque sensor is used for the torque sensor 16, the stiffness K may be the spring constant of the torsion bar. After calculating the estimated steering torque Te as described above, the process proceeds to step 3 in FIG.

  In step S3, the damping compensation current setting unit 37 sets the damping compensation current value Id based on the steering angular velocity ω. Subsequently, in step S4, the torque sensor abnormality detection unit 31 determines normality / failure of the torque sensor 16 based on the sensor steering torque Ts and the steering angle θs (S4), and determination that the torque sensor 16 has failed. In the case where the torque signal is changed (Yes), the torque signal switching unit 33 sets the estimated steering torque Te to the steering torque Tf based on the failure determination signal Ss (S5), and in the case where the torque sensor 16 is determined to be normal (No). The torque signal switching unit 33 sets the sensor steering torque Ts as the steering torque Tf based on the failure determination signal Ss (S6).

  Subsequently, the base target current setting unit 35 sets a base target current value Ib based on the steering torque Tf and the vehicle speed V (S7), and the steering state determination unit 36 based on the steering torque Tf and the steering angular velocity ω. Whether the steering state is forward steering or return steering is determined (S8), and the target current setting unit 38 determines the target current value It based on the base target current value Ib, the steering state determination signal Sa, and the damping compensation current value Id. Is set (S9). Thereafter, the control unit 18 generates a PWM signal based on the target current value It in the motor control unit 39 and controls the motor 13 via the drive circuit 20.

  With reference to FIG. 6, the effect of correcting the steering angle θ, which is the detection value of the steering angle sensor 15, in the power steering apparatus 1 of the present embodiment will be described. As shown in FIG. 6, the resolution of the steering angle sensor 15 is an angle corresponding to four scales (for example, 1 °), and the motor rotation angle θm that is a detection value of the motor rotation angle sensor 14 is converted into an angle on the steering shaft 3. It is assumed that the resolution of the converted motor rotation angle θm ′ is an angle corresponding to one scale (for example, 0.25 °). In this case, during the period from the time t1 to the time t2, the steering angle sensor 15 cannot detect the angle change from the resolution, and the steering angle θs becomes a constant value, but the motor rotation angle sensor 14 A minute angle change that cannot be detected by the sensor 15 is detected, and the converted detection value θm ′ changes.

According to the procedure shown in FIG. 5 described above, for example, at time t1, is held for the steering angle θs is to be differences present value and the previous value, as a reference motor rotational angle .theta.m ₀ motor rotation angle sensor .theta.m is at time t1 . Then, between time t1 of the time t2, the steering angle θs is not changed, the difference is a variation Δθm the motor rotation angle .theta.m and the reference angular position .theta.m ₀ at each time point time t2 from the time t1 is calculated The converted change amount Δθm ′, which is the converted value, is added to θs to calculate the corrected steering angle θs ′. As shown in FIG. 6, the corrected steering angle θs ′ is closer to the actual steering angle than the steering angle θs. Although the actual steering angle 3 and the actual converted motor rotation angle have a difference corresponding to the torsion angle, they tend to change following each other. Therefore, the steering angle θs is based on the detection value of the motor rotation angle sensor 14. Can be close to the true value.

  As shown in FIG. 6B, the difference obtained by subtracting the converted motor rotation angle θm ′ from the corrected steering angle θs ′ is less suppressed than the difference obtained by subtracting the converted motor rotation angle θm ′ from the steering angle θs. By using such a difference (θs′−θm ′) as the torsion angle of the steering shaft, as shown in FIG. 7, the estimated steering torque Te is suppressed from vibrating in value. When the steering assist force is set using such estimated steering torque Te, the ripple feeling of the steering assist force is reduced.

  DESCRIPTION OF SYMBOLS 1 ... Power steering apparatus, 2 ... Steering wheel, 3 ... Steering shaft, 4 ... Front wheel, 5 ... Connection mechanism, 13 ... Electric motor, 14 ... Motor rotation angle sensor, 15 ... Steering angle sensor, 16 ... Torque sensor, 17 ... Control device, 18 ... control unit, 20 ... drive circuit, 21 ... vehicle speed sensor, 31 ... torque sensor abnormality detection unit, 32 ... steering torque estimation unit, 33 ... torque signal switching unit, 34 ... steering angular velocity calculation unit, 35 ... base Target current setting unit 36 ... Steering state determination unit 37 ... Damping compensation current setting unit 38 ... Target current setting unit 39 ... Motor control unit

Claims (4)

A steering shaft coupled to a steering wheel; a coupling mechanism that steers tires according to the rotation of the steering shaft; an electric motor connected to the steering shaft; and the steering torque that acts on the steering shaft. An electric power steering apparatus having a control means for driving an electric motor,
Steering angle detection means for detecting the steering angle at predetermined intervals;
Motor rotation angle detection means for detecting the motor rotation angle of the electric motor at predetermined intervals;
Steering torque estimating means for estimating the steering torque based on a difference between a rotation angle of a portion of the steering shaft calculated based on the motor rotation angle to which the electric motor is connected and the steering angle;
When the current steering angle detected by the steering angle detection means at an arbitrary time is equal to the previous steering angle detected one cycle before the current steering angle is detected, the steering torque estimation means A power steering device, wherein the current steering angle is corrected based on a rotation angle.   When the current steering angle is different from the previous steering angle, the steering torque estimating means detects the current steering angle by using the motor rotation angle when the current steering angle is detected as a reference motor rotation angle. If the n-th steering angle detected after the current steering angle is equal to the current steering angle continuously after the current steering angle is detected, the n-th motor rotation angle detected when the n-th steering angle is detected. 2. The power steering device according to claim 1, wherein a difference between the first motor rotation angle and the reference motor rotation angle is added to the n-th steering angle. The direction of the steering torque and the direction of the steering angular velocity based on the steering angle are compared, and the case where the directions of the steering torque and the steering angular velocity are the same is determined as a forward state, and the steering torque and the steering angular velocity are A steering state detecting means for determining that the directions of the two are opposite to each other as a return state;
The control means subtracts the damper amount calculated based on the steering angular velocity from the basic assist amount calculated based on the steering torque in the forward state, and the basic amount in the return state. The power steering apparatus according to claim 1, wherein the damper amount is added to an assist amount. The direction of the steering torque and the direction of the motor rotation angular velocity based on the motor rotation angle are compared, and the case where the direction of the steering torque and the motor rotation angular velocity is the same is determined as a forward state, and the steering torque and the Steering state detection means for determining a return state when the direction of the motor rotational angular velocity is contradictory,
In the forward state, the control means subtracts the damper amount calculated based on the steering angular velocity calculated from the steering angle from the basic assist amount calculated based on the steering torque, and in the return state. In this case, the power steering device according to claim 1 or 2, wherein the damper amount is added to the basic assist amount.

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