JP6387657B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to an electric power steering control apparatus that is provided in an electric power steering system that assists a steering operation of a vehicle performed by a driver with a motor and controls the system.

  The electric power steering control device of Patent Literature 1 estimates a load from a steering torque and an assist torque command value, and sets a target steering torque from the estimated load. Then, an assist torque command value is calculated from the deviation between the steering torque and the target steering torque so that the steering torque matches the target steering torque.

JP 2013-52793 A

  Since the torque required for steering increases when the frictional force of the steering system mechanical element to be controlled increases, in the technique of Patent Document 1, the assist torque command value must be increased when the frictional force of the steering system mechanical element increases. Since the assist torque command value is also used for load estimation, when the assist torque command value increases, the estimated load becomes a high value.

  Due to the influence of this frictional force, the target steering torque at the time of steering increases under the cutting condition, and the steering torque increases accordingly. Further, under the return condition, the steering torque becomes zero before the steering wheel angle returns to 0 degrees due to the influence of the frictional force. Therefore, the handle angle restoration performance deteriorates, and in order to return the handle angle to 0 degrees, the driver needs to cut the handle.

  In particular, since the road surface reaction force is small on a low μ road, the influence of the frictional force of the steering system mechanical element is relatively greater than when the road surface μ is not low. Therefore, on low-μ roads, the steering torque under cutting conditions is particularly increased compared to when the frictional force is small, and the handle angle resilience is particularly worse than when the frictional force is small. End up.

  In addition, since the self-aligning torque is smaller during low-speed driving compared to high-speed driving, the influence of the frictional force of the steering system mechanical elements is relatively greater during low-speed driving than during high-speed driving. Become. For this reason, the steering torque under the cutting condition is increased even when traveling at a low speed as compared with when traveling at a high speed, and the restoring property of the steering wheel angle is deteriorated.

  Thus, conventionally, when the frictional force of the steering system mechanical element itself changes, or when the influence of the frictional force of the steering system mechanical element relatively changes due to a change in the road surface μ or a change in the vehicle speed, the steering feeling Has changed.

  The present invention has been made based on this situation, and an object of the present invention is to provide an electric power steering system that can realize a steering feeling that is robust against a relative change in the influence of the frictional force of a steering system mechanical element. It is to provide a control device.

  The above object is achieved by a combination of the features described in the independent claims, and the subclaims define further advantageous embodiments of the invention. Further, the reference numerals in parentheses described in the claims indicate the correspondence with the specific means described in the embodiments described later as one aspect, and limit the technical scope of the present invention. is not.

In order to achieve the above object, the present invention provides a torque applied to a torsion bar based on a torsion angle of a torsion bar provided in a part of a torque transmission path for transmitting the rotation of a vehicle handle to a steered wheel An electric power steering system comprising: a torque detector (4) for detecting a steering torque, and a motor (6) for generating an assist torque for assisting the operation of the steering wheel when the steering wheel is steered by the operation of the steering wheel. An electric power steering control device (100, 200, 300) provided in (1) for controlling an assist torque by controlling a motor, a load estimation unit (110) for estimating a road load, and a load estimation unit Based on the road load estimated by the vehicle, a pre-correction target steering torque that is a target value before correction of the steering torque is determined. A fixed part (120), a steering angle detection part (11) for detecting a steering angle that is a rotation angle of a member that rotates as the steering wheel is operated, and a target steering before correction based on the steering angle detected by the steering angle detection part A target correction unit (130, 230, 330) for correcting the torque to determine the target steering torque, and a command value determination unit (170, 180) for determining the assist torque command value from the deviation between the target steering torque and the steering torque. The target correction unit includes upper and lower limit determination units (231, 232, 335, 336, 337, 338) for determining a lower limit torque and an upper limit torque of the target steering torque based on the steering angle, and target steering before correction. torque restriction unit restricts at lower torque and an upper limit torque upper limit determination section has determined that the target steering torque (the 233), and wherein a call with a.

  According to the present invention, the assist torque command value is determined from the deviation between the target steering torque and the steering torque. The target steering torque is determined by correcting the target steering torque before correction determined based on the road load based on the steering angle. Since the influence of the frictional force generated in the steering system mechanical element on the steering torque changes according to the steering angle, the target steering torque before correction determined based on the road load is corrected based on the steering angle as in the present invention. Thus, it is possible to reduce the change in the influence of the frictional force generated in the steering system mechanical element. Therefore, it is possible to realize a steering feeling that is robust against the relative change in the influence of the frictional force of the steering system mechanical element.

It is a figure showing the schematic structure of the electric power steering system 1 which concerns on 1st Embodiment. It is a block diagram which shows the component with which EPSECU100 of 1st Embodiment is provided. It is a figure which illustrates the target steering torque production | generation map with which the target torque production | generation part 123 of FIG. 2 is provided. It is a figure which illustrates the relationship between steering angle (theta) and steering torque Ts at the time of controlling by the target steering torque Tid1 before correction | amendment. It is a figure explaining the time change waveform of the value which each part of the hysteresis correction | amendment part 160 outputs. 6 is a Lissajous waveform representing a change in value d3 with respect to a change in steering angle θ in FIG. It is a Lissajous waveform illustrating the change of Tid1, Tid2, Tid3, and Tid with respect to the steering angle θ. In 1st Embodiment, it is a figure which compares and shows the Lissajous waveform at the time of controlling by Tid1 and Tid, respectively. It is a block diagram which shows the component with which EPSECU200 of 2nd Embodiment is provided. It is an example of the lower limit map with which the lower limit determination part 231 of FIG. 9 is provided. In 2nd Embodiment, it is a figure which compares and shows the Lissajous waveform at the time of controlling by Tid1 and Tid, respectively. It is a block diagram which shows the component with which EPSECU300 of 3rd Embodiment is provided. In 3rd Embodiment, it is a figure which compares and shows the Lissajous waveform at the time of controlling by Tid1 and Tid, respectively.

<First Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. An electric power steering system 1 shown in FIG. 1 assists an operation of a handle 2 by a driver by a motor 6.

  The handle 2 is fixed to one end of a steering shaft 3 that is an input shaft. A torque sensor 4 is connected to the other end of the steering shaft 3, and an intermediate shaft 5 is connected to the other end of the torque sensor 4.

  The torque sensor 4 is a sensor for detecting the steering torque Ts, and corresponds to a torque detector in the claims. The torque sensor 4 has a torsion bar that connects the steering shaft 3 and the intermediate shaft 5, and detects the torque applied to the torsion bar based on the torsion angle of the torsion bar.

  The motor 6 assists the steering force of the handle 2, and a worm gear is provided at the tip of the rotating shaft, and this worm gear meshes with a worm wheel provided on the intermediate shaft 5. Thereby, the rotation of the motor 6 is transmitted to the intermediate shaft 5. On the contrary, when the intermediate shaft 5 is rotated by the operation of the handle 2 or the torque input from the road surface, the rotation is transmitted to the motor 6 and the motor 6 also rotates.

  The other end of the intermediate shaft 5 opposite to the end to which the torque sensor 4 is connected is connected to the steering gear box 7. The steering gear box 7 is configured by a gear mechanism including a rack and a pinion gear (not shown), and the teeth of the rack mesh with a pinion gear provided at the other end of the intermediate shaft 5. Therefore, when the driver turns the handle 2, the intermediate shaft 5 rotates, thereby moving the rack to the left and right. Tie rods 8 are attached to both ends of the rack, and the tie rods 8 reciprocate left and right together with the rack. As a result, the direction of the steered wheels 10 changes when the tie rod 8 pulls or pushes the knuckle arm 9 ahead.

  The steering shaft 3 is provided with a steering angle sensor 11 that detects the rotation angle of the steering shaft 3. The rudder angle sensor 11 corresponds to a steering angle detector in the claims.

  Since the steering shaft 3 rotates integrally with the handle 2, the angle detected by the steering angle sensor 11 means the steering angle θ. The steering angle θ is represented by a positive value on the left or right and a negative value on the other side, assuming that the angle when the vehicle goes straight is 0 degree. A signal indicating the steering angle θ is input to the EPS ECU 100. A vehicle speed sensor 12 for detecting the vehicle speed Vc is also provided at a predetermined part of the vehicle. A signal indicating the vehicle speed Vc is also input to EPSECU 100.

  With this configuration, when the driver rotates the handle 2, the rotation is transmitted to the steering gear box 7 via the steering shaft 3, the torque sensor 4, and the intermediate shaft 5. Then, in the steering gear box 7, the rotation of the intermediate shaft 5 is converted into a left-right movement of the tie rod 8, and the left and right steered wheels 10 are steered by the movement of the tie rod 8.

EPSECU 100, which is an electric power steering control device, operates with electric power from a vehicle battery (not shown). The EPS ECU 100 calculates an assist torque command value Ta ^* based on the steering torque Ts detected by the torque sensor 4, the steering angle θ detected by the steering angle sensor 11, and the vehicle speed Vc detected by the vehicle speed sensor 12. Calculate. Then, by driving the motor 6 based on the assist torque command value Ta ^* , the assist torque for assisting the driver's turning force on the handle 2 is controlled.

  FIG. 2 shows components included in EPSECU 100. The EPS ECU 100 includes a load estimation unit 110, a pre-correction target determination unit 120, a target correction unit 130, a subtraction unit 170, a servo controller 180, and a current feedback unit 190.

The load estimation unit 110 includes an adder 111 and a low-pass filter 112. The adder 111 adds the assist torque command value Ta ^* and the steering torque Ts. The high frequency noise is removed from the added value by the low pass filter 112. The value output from the low-pass filter 112 is an estimated value of the road load. Hereinafter, this estimated value is referred to as an estimated load Tx.

  Usually, it is known that a driver is driving mainly by relying on steering reaction force information of 10 Hz or less. For this reason, the low-pass filter 112 passes a frequency component of 10 Hz or less, for example.

  The pre-correction target determination unit 120 includes an absolute value generation unit 121, a code generation unit 122, a target torque generation unit 123, and a multiplication unit 124.

  The estimated load Tx output from the load estimation unit 110 is input to the absolute value generation unit 121 and the code generation unit 122. The absolute value generation unit 121 generates an absolute value of the estimated load Tx. On the other hand, the code generation unit 122 includes a code function, and generates 1 if the input estimated load Tx is a positive value, and generates −1 if the estimated load Tx is negative.

  The estimated load Tx determined as an absolute value by the absolute value generation unit 121 is input to the target torque generation unit 123. In addition, the vehicle speed Vc is also input to the target torque generator 123. The target torque generation unit 123 includes a target steering torque generation map illustrated in FIG. This target steering torque generation map is a map representing the relationship between the estimated load Tx and the pre-correction target steering torque Tid1 every 20 Km / h. As for the relationship between the estimated load Tx and the pre-correction target steering torque Tid1 at any vehicle speed Vc, the pre-correction target steering torque Tid1 increases logarithmically as the estimated load Tx increases. The target torque generator 123 obtains the absolute value of the pre-correction target steering torque Tid1 by linearly interpolating the map of FIG. 3 based on the input vehicle speed Vc and the estimated load Tx.

  The multiplier 124 multiplies the absolute value of the pre-correction target steering torque Tid1 obtained by the target torque generator 123 by a value of 1 or −1 generated by the code generator 122. The value after multiplication is the target steering torque Tid1 before correction.

  In the first embodiment, instead of inputting the target steering torque Tid1 before correction to the subtracting unit 170, a target correcting unit 130 is provided, and the final target steering torque Tid is corrected by correcting the target steering torque Tid1 before correction. And

  The reason why correction is performed by the target correction unit 130 will be described. FIG. 4 shows the relationship between the steering angle θ and the steering torque Ts when the uncorrected target steering torque Tid1 is directly input to the subtraction unit 170 in a situation where the steering angle θ is steered so as to have a sin waveform. FIG. In FIG. 4, the solid line indicates normal time, the alternate long and short dash line indicates that the friction of the steering system mechanical element increases compared to the normal time, the broken line indicates that the friction of the steering system mechanical element increases compared to the normal time, and the low μ road ( In this case, the friction coefficient μ = 0.2). The steering system mechanical element means a mechanical part that constitutes a torque transmission path from the steering shaft 3 to the steering wheel 10.

  Since the graph of FIG. 4 is a graph that is substantially point-symmetric with the origin at the center, the following description will be given taking an example in which the steering angle θ is a positive value. In the first quadrant of the graph of FIG. 4, it can be seen that the steering torque Ts in the cutting state is increased by increasing the friction, as can be seen by comparing the normal time and the friction increasing time.

  Further, when the steering wheel is returned, that is, when the steering angle θ decreases, normally, the steering torque Ts becomes zero when the steering angle θ is about 4 degrees, whereas when the friction increases. The steering torque Ts is 0 at about 10 degrees. And the waveform at the time of friction increase from the waveform at the time of normal time has a shape which swelled below in the 4th quadrant. From this, it is understood that when the friction is increased, the restoring property of the handle is deteriorated. Therefore, it is necessary to steer when turning the steering angle θ back to 0 degrees.

  The waveform of the broken line in the case where the friction is increased and the road is low μ has a shape swelled further downward in the fourth quadrant than the waveform of the one-dot chain line in which the friction is increased. This is because the tire lateral force when the steering wheel is steered easily reaches the limit, and the restoring force from the tire side is reduced. Since the restoring force is small, the steering torque becomes lower than usual, or the fourth quadrant, that is, steering that is turned on when returning is required.

  As shown in FIG. 4, when the friction increases or the road surface μ decreases, the steering torque Ts changes, so that the steering feeling changes. Although not shown in FIG. 4, the self-aligning torque with respect to the same steering wheel angle is smaller than that during high-speed driving when traveling at low speeds. The relationship with the steering torque Ts changes. However, it is not preferable for the driver to change the feeling of steering by increasing the frictional force, road surface reaction force, and vehicle speed Vc of the steering system mechanical elements. Therefore, the target correction torque 130 before correction is not input to the subtraction unit 170 as it is, but is corrected by the target correction unit 130.

  The target correction unit 130 includes an adder 131 and a target correction torque generation unit 140. The target correction torque generation unit 140 includes an adder 141 corresponding to an addition unit, a steering angle reference target correction unit 150, and a hysteresis correction unit 160.

  The steering angle reference target correction unit 150 includes an absolute value generation unit 151, a code generation unit 152, a target torque correction unit 153, and a multiplication unit 154. The absolute value generator 151 receives the steering angle θ detected by the steering angle sensor 11 and generates an absolute value of the steering angle θ. The steering angle θ detected by the steering angle sensor 11 is also input to the code generation unit 152. The sign generation unit 152 includes a sign function, and generates 1 if the input steering angle θ is a positive value, and generates −1 if the input steering angle θ is a negative value.

  The target torque correction unit 153 includes a correction torque generation map. This correction torque generation map is a map showing the relationship between the steering angle θ and the steering angle reference correction torque Tid2. The corrected torque generation map has an input value different from the target steering torque generation map of FIG. 3, but the tendency of the output value with respect to the input value is the same. That is, the correction torque generation map is a map that outputs a larger steering angle reference correction torque Tid2 as the steering angle θ increases. Further, the relationship in which the steering angle θ and the steering angle reference correction torque Tid2 are determined is stored for a plurality of vehicle speeds Vc, and the steering angle reference correction torque Tid2 increases as the vehicle speed Vc increases. Same as map. The target torque correction unit 153 obtains an absolute value of the steering angle reference correction torque Tid2 by linearly interpolating the correction torque generation map based on the vehicle speed Vc and the steering angle θ.

  The multiplication unit 154 multiplies the absolute value of the steering angle reference correction torque Tid2 determined by the target torque correction unit 153 by the value of 1 or −1 generated by the code generation unit 152. The value after multiplication is the steering angle reference correction torque Tid2.

  The hysteresis correcting unit 160 includes a subtracting unit 161, a limiting unit 162, a subtracting unit 163, a previous value holding unit 164, and an amplifying unit 165.

  The subtracting unit 161 calculates the value held by the previous value holding unit 164 from the current value θ (n) of the steering angle θ that is sequentially input, that is, the previous value θ (n−1) of the steering angle θ and the value d3. The difference from the previous value d3 (n-1) is subtracted. Hereinafter, the subtracted value is d2. This value d2 is input to the limiting unit 162.

  The limiting unit 162 has an upper limit value and a lower limit value whose absolute value is the same as the upper limit value and opposite in sign, and the value d2 input from the subtracting unit 161 is between the upper limit value and the lower limit value. In this case, the value d2 is output as it is. The value output by the limiting unit 162 is assumed to be d3. If the input value d2 is greater than or equal to the upper limit value, the upper limit value is output as d3. If the input value d2 is equal to or lower than the lower limit value, the lower limit value is output as d3.

  The subtracting unit 163 subtracts the value d3 output from the limiting unit 162 from the current value θ (n) of the steering angle θ. The previous value holding unit 164 holds the value subtracted by the subtracting unit 163. Let the held value be d1. The value d1 held by the previous value holding unit 164 is output to the subtraction unit 161 when the steering angle θ is input to the subtraction unit 161 next time. Based on the next steering angle θ, the value d1 held by the previous value holding unit 164 is a value calculated using the previous steering angle θ (n−1). The amplifying unit 165 amplifies the value d3 output from the limiting unit 162 with a preset gain Kh. The value after amplification is the hysteresis correction torque Tid3. The hysteresis correction torque Tid3 determined in this way becomes constant at a predetermined hysteresis torque when the steering angle θ changes, and changes to the hysteresis torque of the opposite sign when the direction of change of the steering angle θ is reversed, and then remains constant. Become.

FIG. 5 is a diagram for explaining a time change waveform of the steering angle θ, the values d1, d2, d3, and the hysteresis correction torque Tid3 when steering is performed so that the time change of the steering angle θ becomes a sin waveform. The value d3 (n) can be transformed as shown in Equation 1 below. In Equation 1, Guard () represents a restriction within a predetermined range, for example, ± 1 deg, n represents a current value, and n−1 represents a value before one calculation cycle.
(Formula 1) d3 (n) = Guard (d2 (n))
= Guard (θ (n) -d1 (n))
= Guard (θ (n) − (θ (n−1) −d3 (n−1)))
= Guard (θ (n) −θ (n−1) + d3 (n−1))

  From the last line of Equation 1, it can be seen that the value d3 (n) is accumulated every time the change of the steering angle θ from one calculation cycle is within the limit range. Therefore, within the limit range, the same change as the steering angle θ (n) is shown. In the time change waveform of FIG. 5, the waveform of d3 such as a section between times t0 to t1 and t2 to t3 corresponds to this.

  When the value in Guard () reaches the upper limit value or the lower limit value, the upper limit value or the lower limit value is maintained. In the time change waveform of FIG. 5, the waveform of d3 such as a section between times t1 to t2 and t3 to t4 corresponds to this.

  If the change of the value d3 with respect to the steering angle θ is expressed from the change of the steering angles θ and d3 shown in FIG. 5, a Lissajous waveform as shown in FIG. 6 is obtained. That is, the value d3 is constant at a limit value that is an upper limit value or a lower limit value. When the direction is reversed, the value d3 becomes the same value as the steering angle θ up to the limit value of the opposite sign, and when the limit value of the opposite sign is reached, It becomes constant at the limit value.

  When this value d3 is multiplied by the gain kh, the hysteresis correction torque Tid3 is obtained. Therefore, the Lissajous waveform of the hysteresis correction torque Tid3 shown in FIG. 7 has the same shape as the waveform of FIG.

  Returning to FIG. The adder 141 adds the steering angle reference correction torque Tid2 output from the steering angle reference target correction unit 150 and the hysteresis correction torque Tid3 output from the hysteresis correction unit 160. The added value Tid2 + Tid3 corresponds to the correction torque in the claims.

  This value Tid2 + Tid3 is added to the pre-correction target steering torque Tid1 by the adder 131. The value after addition by the adder 131 is the final target steering torque Tid.

  FIG. 7 is a Lissajous waveform that illustrates changes in the target steering torque Tid1, the steering angle reference correction torque Tid2, the hysteresis correction torque Tid3, and the target steering torque Tid with respect to the steering angle θ described above.

  As shown in the upper left figure, when the steering angle θ increases, the pre-correction target steering torque Tid1 increases as the steering angle θ increases. When the change of the steering angle θ is in the opposite direction, the target steering torque Tid1 before correction becomes smaller as the steering angle θ decreases with a smaller value than when the steering angle θ increases.

  As shown in the upper right diagram, the steering angle reference correction torque Tid2 increases as the steering angle θ increases. This steering angle reference correction torque Tid2 has no hysteresis width. Therefore, simply multiplying the steering angle reference correction torque Tid2 by the target steering torque Tid1 before correction reduces the ratio of the hysteresis width to the absolute amount of torque and increases the feeling of returning the steering wheel. Therefore, hysteresis correction torque Tid3 that changes the Lissajous waveform shown in the lower left diagram is added. By adding the hysteresis correction torque Tid3, the ratio of the hysteresis width to the absolute amount of torque becomes equal to or greater than the target steering torque Tid1 before correction, as shown in the lower right diagram of the final Lissajous waveform of the target steering torque Tid.

The target steering torque Tid is input to the subtracting unit 170. The subtracting unit 170 subtracts the steering torque Ts from the target steering torque Tid. That is, the subtraction unit 170 calculates a torque deviation ΔT that is a deviation between the target steering torque Tid and the steering torque Ts. This torque deviation ΔT is input to the servo controller 180. The servo controller 180 calculates the assist torque command value Ta ^* so that the torque deviation ΔT becomes zero, that is, the steering torque Ts becomes the target steering torque Tid. The subtracting unit 170 and the servo controller 180 constitute a command value determining unit in the claims.

  The servo controller 180 includes a proportional unit 181, an integrator 182, a differentiator 183, and an adder 184. The proportional device 181 multiplies the torque deviation ΔT by a gain Kp. The integrator 182 integrates the torque deviation ΔT with an integration constant Ki. The differentiator 183 differentiates the torque deviation ΔT with a differential constant Kd. Here, s is a Laplace operator, and τ is a time constant.

The assist torque command value Ta ^* is input to the current feedback unit 190 and the adder 111 described above. Current feedback unit 190, based on the assist torque command value Ta ^*, the driving voltage Vd to the motor 6 so that the assist torque corresponding to the assist torque command value Ta ^* is applied to the steering wheel 10 side than the torque sensor 4 Apply. Specifically, a target current to be energized to each phase of the motor 6 is set based on the assist torque command value Ta ^* . Then, the energizing current value Im of each phase is detected, and a desired assist torque is generated by controlling the drive voltage Vd so that the detected energizing current value Im of each phase matches the target current.

  FIG. 8 is a diagram showing a comparison of Lissajous waveforms when control is performed with the pre-correction target steering torque Tid1 and the target steering torque Tid. FIG. 8 is a diagram showing the relationship between the steering angle θ and the steering torque Ts in a situation where steering is performed so that the time change of the steering angle θ becomes a sin waveform, as in FIG. 4.

  In FIG. 8, the solid line, the short one-dot chain line, and the short broken line are the cases where the pre-correction target steering torque Tid1 is input to the subtraction unit 170 as it is. Therefore, the solid line, the short dashed line, and the short dashed line in FIG. 8 have the same shapes as the solid line, the short dashed line, and the short dashed line in FIG.

  A long one-dot chain line and a long broken line are when the target steering torque Tid is input to the subtracting unit 170. From the comparison between the short and long dashed lines, even when the friction is increased, the correction based on the steering angle θ is performed to correct the steering wheel 2, that is, the steering angle θ approaches 0 degrees. It can be seen that the steering torque Ts that opposes the returning direction under the circumstances is small.

  More specifically, for example, in the fourth quadrant where the steering angle θ is positive and the steering torque Ts is negative, an operation of returning the handle 2 to the neutral position is performed. Here, it is assumed that a right rotation operation is performed to return the handle 2 from the left to the neutral position. In order for the steering wheel 2 to return smoothly from the left position to the neutral position, it is preferable that the steering torque Ts be a value close to 0 or slightly positive until the steering wheel 2 changes from the left position to the neutral position.

  However, in the fourth quadrant, since the steering torque Ts is negative, the steering torque Ts that opposes the direction in which the handle 2 is operated is generated, and the driver returns the handle 2 to the neutral position. It is necessary to apply a force in a direction to return the handle 2 to the neutral position.

  On the other hand, the Lissajous waveform indicated by the long and short dash line has fewer portions passing through the fourth quadrant. Therefore, it can be seen that the steering wheel 2 can be smoothly returned to the neutral position by setting the target steering torque Tid1 before correction to the target steering torque Tid corrected based on the steering angle θ.

  Further, from the comparison between the long broken line and the short broken line, even in a situation where the friction increases and the road is a low μ road, similarly, by performing correction based on the steering angle θ, It can be seen that the steering torque Ts that opposes the return direction of is reduced.

As described above, according to the first embodiment described above, the assist torque command value Ta ^* is determined from the torque deviation ΔT that is the deviation between the target steering torque Tid and the steering torque Ts in the subtractor 170 and the servo controller 180. The target steering torque Tid is determined by correcting the pre-correction target steering torque Tid1 determined based on the estimated load Tx based on the steering angle θ.

  Specifically, the correction in the first embodiment is a pre-correction in which a correction torque obtained by adding a hysteresis correction torque Tid3 to a steering angle reference correction torque Tid2 that increases as the steering angle θ increases is determined based on the estimated load Tx. This is a correction to be added to the target steering torque Tid1.

  Since the influence of the frictional force generated in the steering system mechanical element on the steering torque Ts changes according to the steering angle θ, the above correction can reduce the change in the influence of the frictional force generated in the steering system mechanical element on the steering torque Ts. . Therefore, it is possible to realize a steering feeling that is robust against the relative change in the influence of the frictional force of the steering system mechanical element.

Second Embodiment
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used so far are the same as elements having the same reference numerals in the previous embodiments unless otherwise specified. Further, when only a part of the configuration is described, the above-described embodiment can be applied to the other parts of the configuration.

  The electric power steering system according to the second embodiment includes an EPS ECU 200 having the configuration shown in FIG. 9 instead of the EPS ECU 100 shown in FIG. Other configurations are the same as those of the electric power steering system 1 of the first embodiment.

  The EPS ECU 200 includes the same load estimation unit 110, pre-correction target determination unit 120, subtraction unit 170, servo controller 180, and current feedback unit 190 as in the first embodiment. A target correction unit 230 is provided instead of the target correction unit 130.

  The target correction unit 230 includes a lower limit determination unit 231, an upper limit determination unit 232, and a restriction unit 233. The lower limit determination unit 231 includes a lower limit map. FIG. 10 is an example of the lower limit map. As shown in FIG. 10, the lower limit map is a constant value at 0 km / h regardless of the steering angle θ. Except for 0 km / h, the limit torque increases as the steering angle θ increases. In the range where the steering angle θ is positive, the limit torque increases as the vehicle speed Vc increases. On the contrary, in the range where the steering angle θ is negative, the limit torque decreases as the vehicle speed Vc increases. The lower limit determination unit 231 determines a lower limit torque that is a lower limit value of the target steering torque Tid by linearly interpolating the lower limit map illustrated in FIG. 10 based on the steering angle θ and the vehicle speed Vc.

  The upper limit determination unit 232 includes an upper limit map. Although the upper limit map is not shown, it is point-symmetric with the lower limit map. The upper limit determination unit 232 linearly interpolates the upper limit map based on the steering angle θ and the vehicle speed Vc, thereby determining an upper limit torque that is an upper limit value of the target steering torque Tid. The upper limit determination unit 232 and the above-described lower limit determination unit 231 correspond to an upper and lower limit determination unit in the claims.

  Since the lower limit map and the upper limit map have a point-symmetric relationship, the sign of the steering angle θ is inverted, a value is obtained from the lower limit map, the steering angle θ, and the vehicle speed Vc, and the sign of the value is inverted and the upper limit map is inverted. Torque may be determined.

  The limiting unit 233 receives the pre-correction target steering torque Tid1. If the pre-correction target steering torque Tid1 is between the lower limit torque and the upper limit torque, the limiting unit 233 outputs the input value of the target steering torque Tid1 before correction as the target steering torque Tid. If the input pre-correction target steering torque Tid1 is equal to or lower than the lower limit torque, the lower limit torque is output as the target steering torque Tid. If the input pre-correction target steering torque Tid1 is equal to or greater than the upper limit torque, the upper limit torque is output as the target steering torque Tid.

  FIG. 11 is a diagram showing a comparison of Lissajous waveforms representing the relationship between the steering angle θ and the steering torque Ts when controlled by the target steering torque Tid1 before correction and the target steering torque Tid in the second embodiment. FIG. 11 is also a diagram showing the relationship between the steering angle θ and the steering torque Ts in a situation where steering is performed so that the time change of the steering angle θ becomes a sin waveform, as in FIGS. 4 and 8. Further, as in FIG. 8, the solid line, the short alternate long and short dash line, and the short dashed line are the cases where the target steering torque Tid1 before correction is input to the subtracting unit 170 as it is.

  A long one-dot chain line and a long broken line are when the target steering torque Tid is input to the subtracting unit 170. The short one-dot chain line and the short dashed line waveform have a large deviation from the normal waveform, which is a normal waveform, whereas the long one-dot chain line and the long dashed waveform are close to the solid waveform. Therefore, if the correction for limiting the upper limit and the lower limit of the target steering torque Tid is performed based on the steering angle θ, the steering angle can be increased even if the frictional force of the steering system mechanical element increases or the road becomes low μ. It can be seen that the characteristic of θ-steering torque Ts hardly changes.

  Therefore, in the electric power steering system of the second embodiment, the change in the friction force of the steering system machine element and the change in the road surface reaction force, that is, the influence of the friction force of the steering system machine element on the steering torque Ts is relatively It can be said that the steering feeling is robust against the increasing change.

<Third Embodiment>
Next, a third embodiment will be described. The third embodiment is an improvement over the second embodiment. The electric power steering system according to the third embodiment includes an EPS ECU 300 having the configuration shown in FIG. 12 instead of the EPS ECU 200 shown in FIG. Other configurations are the same as those of the electric power steering system of the second embodiment. The EPS ECU 300 is different from the target correction unit 230 of the second embodiment in the configuration of the target correction unit 330. Other configurations are the same as those of the EPS ECU 200 of the second embodiment.

  The target correction unit 330 also includes a restriction unit 233 provided in the target correction unit 230 of the second embodiment. In addition to these, a pseudo-differentiation unit 331, an absolute value generation unit 332, an amplification unit 333, a correction amount determination unit 334, a pre-correction lower limit determination unit 335, a subtraction unit 336, a pre-correction upper limit determination unit 337, and an addition corresponding to an addition unit A device 338 is provided.

  The pseudo differentiating unit 331 performs pseudo differentiation on the steering angle θ using a filter. The value after pseudo differentiation means the steering speed Vs. The absolute value generation unit 332 generates an absolute value of the steering speed Vs generated by the pseudo differentiation unit 331 and outputs the absolute value to the amplification unit 333. The amplifying unit 333 amplifies the absolute value of the steering speed Vs output from the absolute value generating unit 332 with a preset gain Kg. The correction amount determination unit 334 determines a correction amount for correcting the pre-correction lower limit torque and the pre-correction upper limit torque. The correction amount determination unit 334 includes a correction amount map. The correction amount map is a map in which the value output from the amplifying unit 333 is an input value and the correction amount is an output value. In this correction amount map, the lower limit value and the upper limit value of the correction amount are determined, and the same value as the input value is output in the range of the lower limit value and the upper limit value. The correction amount determination unit 334 determines the correction amount from the correction amount map and the value output from the amplification unit 333.

  The lower limit determination unit 335 before correction is the same as the lower limit determination unit 231 of the second embodiment. However, in the third embodiment, the value determined by the pre-correction lower limit determination unit 335 is set as the pre-correction lower limit torque.

  The subtraction unit 336 subtracts the correction amount determined by the correction amount determination unit 334 from the pre-correction lower limit torque determined by the pre-correction lower limit determination unit 335. In the third embodiment, the value after subtraction by the subtraction unit 336 is the lower limit torque.

  The pre-correction upper limit determination unit 337 is the same as the upper limit determination unit 232 of the second embodiment. However, in the third embodiment, the value determined by the pre-correction upper limit determination unit 337 is set as the pre-correction upper limit torque.

  The adder 338 adds the correction amount determined by the correction amount determination unit 334 to the pre-correction upper limit torque determined by the pre-correction upper limit determination unit 337. In the third embodiment, the value after addition by the adder 338 is the upper limit torque. In the third embodiment, the pre-correction lower limit determination unit 335, the subtraction unit 336, the pre-correction upper limit determination unit 337, and the adder 338 correspond to the upper and lower limit determination units of the claims.

  The limiting unit 233 is the same as in the second embodiment. However, in the third embodiment, the range between the lower limit value and the upper limit value is wider than the second embodiment by the correction amount × 2. Further, since the correction amount increases as the steering speed Vs increases, the range between the lower limit value and the upper limit value increases as the steering speed Vs increases.

  FIG. 13 is a diagram showing a comparison of Lissajous waveforms representing the relationship between the steering angle θ and the steering torque Ts when controlled by the target steering torque Tid1 before correction and the target steering torque Tid in the third embodiment. FIG. 13 is also a diagram showing the relationship between the steering angle θ and the steering torque Ts in a situation where steering is performed so that the time change of the steering angle θ becomes a sin waveform, as in FIGS. 4, 8, and 11. . Further, as in FIGS. 8 and 11, the solid line, the short alternate long and short dash line, and the short dashed line are the cases where the pre-correction target steering torque Tid1 is input to the subtraction unit 170 as it is.

  A long one-dot chain line and a long broken line are when the target steering torque Tid corrected by the target correction unit 330 is input to the subtraction unit 170. In FIG. 11, the waveforms of the long dashed line and the long dashed line are substantially the same as the solid line, but in the third embodiment, the long dashed line and the long dashed waveform have a wider hysteresis width than the solid waveform. . Further, the hysteresis width becomes wider as the steering speed Vs becomes higher.

  When the steering speed Vs is high, the hysteresis width in the relationship between the steering angle θ and the steering torque Ts is widened. Therefore, when the driver intentionally turns back, the hysteresis width is widened. As a result, the change from the restoring force for returning the handle to the resistance force for stopping the handle becomes gradual.

  When the steering speed Vs is high, such as when the driver intentionally switches back, the steering torque Ts is switched to the opposite sign in a short time in the loop indicated by the normal Lissajous waveform. Therefore, the force that the driver receives from the handle 2 changes suddenly.

  On the other hand, in the third embodiment, when the steering speed Vs is fast, the hysteresis width in the relationship of the steering angle θ-steering torque Ts is widened, and thereby the change in the steering torque Ts becomes gentle. Accordingly, even when the steering speed Vs is fast, the force that the driver receives from the steering wheel 2 is suppressed from changing suddenly, so that the steering feeling is improved.

  Although the limit width of the limiter 233 is changed according to the steering speed Vs, the target steering torque Tid is limited according to the steering angle θ as in the second embodiment. Therefore, also in the third embodiment, the steering feeling is robust against the relative change in the influence of the frictional force of the steering system mechanical element.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following modification is also contained in the technical scope of this invention, Furthermore, the summary other than the following is also included. Various modifications can be made without departing from the scope.

<Modification 1>
For example, in the above-described embodiment, the rotation angle of the steering shaft 3 is used as the steering angle θ, which is the rotation angle of the member that rotates in accordance with the operation of the handle 2, but the member that detects the steering angle θ is the steering shaft 3. It cannot be caught. For example, the rotation angle of the intermediate shaft 5, the rotation angle of the motor 6, and the rotation angle of the steering wheel 10 may be set as the steering angle θ.

<Modification 2>
In the first embodiment, the target steering torque Tid is obtained by adding the steering angle reference correction torque Tid2 and the hysteresis correction torque Tid3 to the pre-correction target steering torque Tid1. However, the hysteresis correction torque Tid3 may not be added, and the steering angle reference correction torque Tid2 may be added to the target steering torque Tid1 before correction to obtain the target steering torque Tid.

<Modification 3>
Further, the first embodiment or the second modification may be combined with the second embodiment or the third embodiment. That is, the target correction units 230 and 330 limit the steering angle reference correction torque Tid2 or the value obtained by adding the correction torque that is the hysteresis correction torque Tid3 to the steering angle reference correction torque Tid2 to the target steering torque Tid1 before correction. Also good.

<Modification 4>
In the third embodiment, the steering speed Vs is calculated by pseudo-differentiating the steering angle θ, but is not limited thereto. For example, the rotational speed of the motor 6 may be detected and used as the steering speed Vs.

<Modification 5>
In the first embodiment described above, the hysteresis correction torque Tid3 that is constant at a predetermined torque is calculated even when the steering angle θ is changed, but is not limited thereto. The hysteresis width may be increased according to the steering angle θ by changing the gain Kh according to the steering angle θ.

  When the hysteresis width is changed according to the steering angle θ, the ratio of the hysteresis width to the absolute amount of the target steering torque Tid increases as the absolute value of the steering angle θ increases. Therefore, it is possible to adjust to a steering feel that is more preferable for the driver.

<Modification 6>
Further, in the above-described embodiment, as a method of the electric power steering system, a so-called shaft assist type configuration in which the rotation of the intermediate shaft 5 is assisted by the motor 6 has been described as an example. However, this is just an example. For example, the present invention is applicable to various assist-type electric power steering systems such as a so-called rack-assist type which assists the reciprocating motion of the tie rod 8, that is, the reciprocating motion of the rack in the steering gear box 7 with a motor. It is possible to apply.

1: electric power steering system, 100: EPSECU, 110: load estimation unit, 120: pre-correction target determination unit, 121: absolute value generation unit, 122: code generation unit, 123: target torque generation unit, 124: multiplication unit, 130: Target correction unit, 150: Steering angle reference target correction unit, 160: Hysteresis correction unit, 170: Subtraction unit 200: EPSECU, 230: Target correction unit, 300: EPSECU, 330: Target correction unit, Im: Current-carrying current value Tid: target steering torque, Tid1: target steering torque before correction, Tid2: steering angle reference correction torque, Tid3: hysteresis correction torque, Ts: steering torque, Tx: estimated load, Vs: steering speed, θ: steering angle

Claims (5)

A torque detector that detects a steering torque, which is a torque applied to the torsion bar, based on a torsion angle of a torsion bar provided in a part of a torque transmission path that transmits the rotation of the steering wheel of the vehicle to the steering wheel. 4) and
A motor (6) for generating an assist torque for assisting the operation of the steering wheel when the steering wheel is steered by the operation of the steering wheel, and provided in an electric power steering system (1),
An electric power steering control device (100, 200, 300) for controlling the assist torque by controlling the motor,
A load estimation unit (110) for estimating a road surface load;
A pre-correction target determination unit (120) for determining a pre-correction target steering torque, which is a target value before correction of the steering torque, based on the road surface load estimated by the load estimation unit;
A steering angle detector (11) for detecting a steering angle that is a rotation angle of a member that rotates in accordance with the operation of the handle;
A target correction unit (130, 230, 330) that determines the target steering torque by correcting the pre-correction target steering torque based on the steering angle detected by the steering angle detection unit;
A command value determining unit (170, 180) for determining an assist torque command value from a deviation between the target steering torque and the steering torque;
Equipped with a,
The target correction unit includes:
Upper and lower limit determining units (231, 232, 335, 336, 337, 338) for determining a lower limit torque and an upper limit torque of the target steering torque based on the steering angle;
Electric power at which the pre-correction target steering torque, limiting unit to the target steering torque limit by the lower torque and the upper limit torque the upper and lower limit determining section determines that (233), characterized that you provided with Steering control device. In claim 1,
The target correction unit (130) determines a correction torque based on the steering angle, and adds the correction torque to the pre-correction target steering torque determined by the pre-correction target determination unit, to thereby calculate the target steering torque. An electric power steering control device. In claim 2,
The target correction unit includes:
A steering angle reference target correction unit (150) for determining a steering angle reference correction torque that increases as the steering angle increases based on the steering angle;
A hysteresis correction unit (160) for applying a predetermined hysteresis torque to the change in the steering angle and determining a hysteresis correction torque for applying the hysteresis torque having an opposite sign when the direction of change in the steering angle is reversed;
An addition unit (141) that adds the steering angle reference correction torque determined by the steering angle reference target correction unit and the hysteresis correction torque determined by the hysteresis correction unit to obtain the correction torque. Electric power steering control device. In any one of Claims 1-3 ,
The upper and lower limit determining units (335, 336, 337, 338) change the upper limit torque and the lower limit torque so that a gap between the upper limit torque and the lower limit torque increases as a steering speed increases. Electric power steering control device. In any one of Claims 1-4 ,
The electric power steering control device, wherein the load estimation unit estimates the road load based on a steering torque detected by the torque detection unit and an assist torque command value for instructing the assist torque.

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