JP2016097886A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device that can perform high accuracy torque feed back control.SOLUTION: A steering wheel 2 is coupled to a first pinion shaft 14 via a column shaft 7 and an intermediate shaft 8. To a tip of the first pinion shaft 14, a first pinion 17 engaging with a first rack 18 provided in one end of a rack shaft 15 is coupled. There is provided around the column shaft 7 a first torque sensor 31 to detect steering torque. The output axis of an electric motor 19 is coupled to a second pinion shaft 21 via a reduction gear 20. To a tip of the second pinion shaft 21, a second pinion 22 engaging with a second rack 23 provided in the other end of the rack shaft 15 is coupled. Around the second pinion shaft 21, there is provided a second torque sensor 32 to detect assist torque.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electric power steering apparatus.

  Patent Document 1 discloses an electric power steering device. The electric power steering apparatus of Patent Document 1 includes an electric motor, a steering torque sensor, an actual torque sensor, a vehicle speed sensor, and an electronic control unit. The electric motor is connected to a pinion shaft (pinion shaft) via a speed reducer. The pinion shaft is connected to a steering wheel (steering handle) via an intermediate shaft (lower steering shaft) and a column shaft (upper steering shaft). A pinion is provided at the lower end of the pinion shaft. The pinion meshes with a rack provided on the rack shaft.

The steering torque sensor is a sensor for detecting a steering torque applied to the steering wheel. The steering torque sensor is disposed around the pinion shaft on the upstream side (steering wheel side) of the electric motor. The actual torque sensor is arranged around the pinion shaft on the downstream side (wheel side) from the electric motor.
The electronic control unit includes target assist torque calculation means (target torque calculation means), motor current calculation means, and PID control means. The target assist torque calculating means calculates a target assist torque to be generated on the pinion shaft downstream of the electric motor based on the vehicle speed detected by the vehicle speed sensor and the steering torque detected by the steering torque sensor. In other words, the target assist torque calculating means calculates a target value of assist torque to be applied to the pinion shaft by the electric motor.

  The motor current calculation means converts a deviation (torque deviation) between the target assist torque calculated by the target assist torque calculation means and the actual torque detected by the actual torque sensor into a current of the electric motor. The PID control means controls the electric motor current so that the torque deviation converges to zero based on the current value calculated by the motor current calculation means. That is, the PID control means performs torque feedback control so that the actual torque matches the target assist torque.

JP 2006-7931 A JP-A 64-32966

  In the electric power steering apparatus of Patent Document 1, the actual torque sensor is disposed around the pinion shaft connected to the steering wheel. For this reason, the actual torque detected by the actual torque sensor is affected by the steering torque applied to the steering wheel. Therefore, in the electric power steering apparatus of Patent Document 1, the assist torque applied to the pinion shaft by the electric motor cannot be detected with high accuracy. For this reason, highly accurate torque feedback control cannot be performed.

  An object of the present invention is to provide an electric power steering apparatus that can perform highly accurate torque feedback control.

  The invention according to claim 1 is an electric power steering apparatus (1) including a rack shaft (15) that moves in an axial direction in response to an operation of the steering member (2), the steering shaft being coupled to the steering member. (6), a first pinion shaft (14) connected to the steering shaft and having a first pinion (17), and the steering shaft are arranged separately, and a second pinion (22) having a second pinion (22). A pinion shaft (21), an electric motor (19) for rotating the second pinion shaft, a first rack (18) provided on the rack shaft and meshing with the first pinion and the second pinion, respectively A first torque sensor (31) that is disposed around the second rack (23) and the steering shaft and detects a steering torque applied to the steering member. A second torque sensor (32) disposed around the second pinion shaft and detecting an assist torque, and a target assist torque is calculated using a steering torque detected by the first torque sensor, An electric power steering apparatus including motor control means (27) for controlling the electric motor so that an assist torque detected by a two-torque sensor matches the target assist torque. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

  In this configuration, the second torque sensor is disposed around the second pinion shaft that is disposed separately from the steering shaft. Therefore, the assist torque detected by the second torque sensor is not affected by the steering torque applied to the steering member. For this reason, the second torque sensor can detect the assist torque applied to the second pinion shaft by the electric motor with high accuracy. Thereby, highly accurate torque feedback control can be performed.

According to a second aspect of the present invention, the steering shaft includes a column shaft (7) to which the steering member is connected, and an intermediate shaft having one end connected to the column shaft and the other end connected to the first pinion shaft. The electric power steering apparatus according to claim 1, wherein the first torque sensor is disposed around the column shaft.
In this configuration, the first torque sensor is disposed around the column shaft. For this reason, the steering torque detected by the first torque sensor is not affected by the friction of the intermediate shaft. Thereby, the steering torque applied to the steering member can be detected with high accuracy. Thereby, more accurate torque feedback control can be performed.

A third aspect of the present invention is the electric power steering apparatus according to the first or second aspect, wherein the electric motor is connected to the second pinion shaft via a speed reducer (20).
The motor torque to be output from the electric motor is set as the target assist torque (target value), and the motor torque output from the electric motor is detected as the assist torque (control amount), and those torque deviations converge to zero. Thus, it is conceivable to perform torque feedback control. In this case, the control amount is transmitted to the rack shaft via the speed reducer and the second pinion shaft. For this reason, when the control amount is transmitted to the rack shaft, the assist torque acting on the rack shaft cannot be controlled with high accuracy because it is affected by the friction of the speed reducer.

  In the configuration of the third aspect, the torque applied from the electric motor to the second pinion shaft via the speed reducer is detected as the assist torque (control amount) by the second torque sensor. Therefore, the torque to be applied from the electric motor to the second pinion shaft via the speed reducer is set as the target assist torque (target value), and the assist torque (control amount) detected by the second torque sensor and the target assist torque are set. Feedback control can be performed so that the torque deviation converges to zero. In this case, when the control amount is transmitted to the rack shaft, it is not affected by the friction of the reduction gear. Thereby, the assist torque acting on the rack shaft can be controlled with high accuracy.

FIG. 1 is a schematic diagram showing a schematic configuration of the electric power steering apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the ECU. FIG. 3 is a graph showing an example of setting the target assist torque Ta ^{* with} respect to the phase-compensated torque Th. 4A, 4B and 4C are graphs showing the characteristics of the comparative example, FIG. 4A is a graph showing the input / output characteristics of the steering torque sensor, and FIG. 4B is a graph showing the pinion shaft by the detected steering torque and the electric motor. FIG. 4C is a graph showing the relationship between the sum of the assist torque and the detected steering torque and the actual torque detected by the actual torque sensor. 5A, 5B, and 5C are graphs showing the characteristics of the present embodiment, FIG. 5A is a graph showing the input / output characteristics of the steering torque sensor, and FIG. 5B is a graph showing the second by the detected steering torque and the electric motor. FIG. 5C is a graph showing the relationship between the assist torque applied to the pinion shaft and the assist torque detected by the second torque sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member for steering the vehicle, a steering mechanism 4 that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering by the driver. And a steering assist mechanism 5 for assisting. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6.

  The steering shaft 6 includes a column shaft 7 connected to the steering wheel 2 and an intermediate shaft 8 connected to the column shaft 7 via a first universal joint 12. The column shaft 7 includes an input shaft 9 connected to the steering wheel 2 and an output shaft 11 connected to the intermediate shaft 8. The input shaft 9 and the output shaft 11 are connected via a torsion bar 10 so as to be relatively rotatable.

  A first torque sensor 31 is disposed around the column shaft 7. The first torque sensor 31 detects the steering torque applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 9 and the output shaft 11, that is, the torsion angle of the torsion bar 10. In this embodiment, the steering torque Th detected by the first torque sensor 31 is detected as a positive value for the torque for steering in the right direction, and a negative value for the torque for steering in the left direction. It is assumed that the magnitude of the steering torque increases as the absolute value thereof is detected.

  The steered mechanism 4 includes a first pinion shaft 14 and a rack shaft 15 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 15 via a tie rod 16 and a knuckle arm (not shown). The first pinion shaft 14 is connected to the intermediate shaft 8 via the second universal joint 13. The first pinion shaft 14 rotates in conjunction with the steering of the steering wheel 2. A first pinion 17 is connected to the tip (the lower end in FIG. 1) of the first pinion shaft 14.

  The rack shaft 15 extends linearly along the left-right direction of the automobile. A first rack 18 that meshes with the first pinion 17 is formed on the first end side in the axial direction of the rack shaft 15. The rotation of the first pinion shaft 14 is converted into the axial movement of the rack shaft 15 by the first pinion 17 and the first rack 18. The steered wheels 3 can be steered by moving the rack shaft 15 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the first pinion shaft 14 via the column shaft 7 and the intermediate shaft 8. The rotation of the first pinion shaft 14 is converted into axial movement of the rack shaft 15 by the first pinion 17 and the first rack 18. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 19, a speed reducer 20, a second pinion shaft 21, a second pinion 22, and a second rack 23. The second pinion shaft 21 is disposed separately from the steering shaft 6. Therefore, the second pinion shaft 21 is not connected to the steering wheel 2. The speed reducer 20 is engaged with a worm shaft (not shown) that is integrally connected to the output shaft of the electric motor 19, meshes with the worm shaft, and is rotatably connected to the second pinion shaft 21. The worm gear mechanism includes a worm wheel (not shown).

The second pinion 22 is connected to the tip (the lower end in FIG. 1) of the second pinion shaft 21. The second rack 23 is provided on the second end side in the axial direction of the rack shaft 15. The second pinion 22 meshes with the second rack 23.
When the electric motor 19 is driven to rotate, the rotation of the electric motor 19 is transmitted to the second pinion shaft 21 via the speed reducer 20. The rotation of the second pinion shaft 21 is converted into the axial movement of the rack shaft 15 by the second pinion 22 and the second rack 23. Thereby, the steered wheel 3 is steered. That is, the steered wheels 3 are steered by rotating the second pinion shaft 21 by the electric motor 19.

  The second pinion shaft 21 includes an input shaft 24 connected to the speed reducer 20 and an output shaft 26 connected to the second pinion 22. The input shaft 24 and the output shaft 26 are connected via a torsion bar 25 so as to be relatively rotatable. A second torque sensor 32 is disposed around the second pinion shaft 21. The second torque sensor 32 detects the assist torque acting on the second pinion shaft 21 based on the relative rotational displacement amount of the input shaft 24 and the output shaft 36, that is, the torsion angle of the torsion bar 25. That is, the second torque sensor 32 detects the torque applied from the electric motor 19 to the second pinion shaft via the speed reducer 20 as the assist torque Ta.

In this embodiment, the assist torque Ta detected by the second torque sensor 32 is detected as a positive value for assist torque for rightward steering, and as a negative value for assist torque for leftward steering. It is assumed that the assist torque increases as the absolute value increases.
The electric motor 19 is controlled by an ECU (Electronic Control Unit) 27 as a motor control device. The ECU 27 receives the steering torque Th detected by the first torque sensor 31, the assist torque Ta detected by the second torque sensor 31, the vehicle speed V detected by the vehicle speed sensor 33, and the like.

FIG. 2 is a block diagram showing an electrical configuration of the ECU 27.
The ECU 27 includes a microcomputer 28 and a drive circuit 29 that is controlled by the microcomputer 28 and supplies electric power to the electric motor 19.
The microcomputer 28 includes a CPU and a memory (ROM, RAM, nonvolatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a phase compensation unit 41, a target assist torque setting unit 42, a torque deviation calculation unit 43, a PI (proportional integration) control unit 44, a PWM (Pulse Width Modulation) control unit 45, including.

The phase compensation unit 41 performs processing for advancing the phase of the steering torque Th detected by the first torque sensor 31 to stabilize the system. The steering torque phase-compensated by the phase compensation unit 41 (hereinafter referred to as “phase-compensated torque Th”) and the vehicle speed V detected by the vehicle speed sensor 33 are applied to the target assist torque setting unit 42.
The target assist torque setting unit 42 sets a target assist torque Ta ^* to be applied to the second pinion shaft 21 by the electric motor 19 based on the phase-compensated torque Th and the vehicle speed V. An example of setting the target assist torque Ta ^{* with} respect to the post-phase compensation torque Th is shown in FIG. In this embodiment, the post-phase compensation torque Th is a positive value for the rightward steering torque, and a negative value for the leftward steering torque. The target assist torque Ta ^* is a positive value when the electric motor 19 should generate an assist torque for rightward steering, and a negative value when the electric motor 19 should generate an assist torque for leftward steering. It is said. The target assist torque Ta ^* is positive with respect to a positive value of the phase-compensated torque Th and negative with respect to a negative value of the phase-compensated torque Th.

When the phase-compensated torque Th is a minute value in the range of -Th1 to Th1 (torque dead zone), the target assist torque Ta ^* is set to zero. When the phase-compensated torque Th is a value outside the range of -Th1 to Th1, the target assist torque Ta ^* is such that the absolute value of the target assist torque Ta ^* increases as the absolute value of the phase-compensated torque Th increases. Is set. The target assist torque Ta ^* is set such that the absolute value thereof decreases as the vehicle speed V detected by the vehicle speed sensor 33 increases. As a result, the assist torque is increased during low speed travel, and the assist torque is decreased during high speed travel.

The torque deviation calculation unit 43 calculates a deviation (torque deviation ΔTa = Ta ^* −Ta) between the target assist torque Ta ^* set by the target assist torque setting unit 42 and the assist torque Ta detected by the second torque sensor 32. Calculate.
The PI control unit 44 converts the torque deviation ΔTa calculated by the torque deviation calculation unit 43 into a motor current value of the electric motor 19 and performs a PI (differential integration) operation on the motor current value, thereby obtaining the torque deviation ΔTa. A drive command value for converging to zero is generated. The PWM control unit 45 generates a PWM control signal having a duty ratio corresponding to the drive command value and supplies the PWM control signal to the drive circuit 29. As a result, electric power (current) corresponding to the drive command value is supplied to the electric motor 19.

The torque deviation calculation unit 43 and the PI control unit 44 constitute a torque feedback control unit. The function of this torque feedback control means controls the motor current of the electric motor 19 so that the assist torque Ta matches the target assist torque Ta ^* .
In this embodiment, the second torque sensor 32 is disposed around the second pinion shaft 21 that is disposed separately from the steering shaft 6. Therefore, the assist torque Ta detected by the second torque sensor 32 is not affected by the steering torque applied to the steering wheel 2. For this reason, the second torque sensor 32 can detect the assist torque applied to the second pinion shaft 21 by the electric motor 19 with high accuracy. Thereby, highly accurate torque feedback control can be performed.

  Furthermore, in this embodiment, the first torque sensor 31 is disposed around the column shaft 7. For this reason, the steering torque Th detected by the first torque sensor 31 is not affected by the friction of the intermediate shaft 8. Thereby, the steering torque applied to the steering wheel 2 can be detected with high accuracy. Thereby, torque feedback control with higher accuracy can be performed.

  The motor torque to be output from the electric motor 19 is set as the target assist torque (target value), and the motor torque output from the electric motor 19 is detected as the assist torque (control amount), and the torque deviation thereof becomes zero. It is conceivable to perform torque feedback control so as to converge. In this case, the control amount (assist torque) is transmitted to the rack shaft 15 via the speed reducer 20 and the second pinion shaft 21. For this reason, when the control amount is transmitted to the rack shaft 15, the assist torque acting on the rack shaft 15 cannot be controlled with high accuracy because it is affected by the friction of the speed reducer 20.

  In this embodiment, the second torque sensor 32 detects torque applied from the electric motor 19 to the second pinion shaft 21 via the speed reducer 20 as assist torque Ta (control amount). Therefore, when the control amount (assist torque Ta) is transmitted to the rack shaft 15, it is not affected by the friction of the speed reducer 20. Thereby, the assist torque acting on the rack shaft 15 can be controlled with high accuracy.

A difference between the electric power steering device of Patent Document 1 (hereinafter referred to as a comparative example) and the above-described embodiment will be described.
4A, 4B, and 4C show the characteristics of the comparative example.
FIG. 4A is a graph showing input / output characteristics of the steering torque sensor. In FIG. 4A, the horizontal axis indicates the actual steering torque T applied to the steering wheel, and the vertical axis indicates the detected steering torque Th detected by the steering torque sensor.

  In the comparative example, the steering torque sensor is arranged around the pinion shaft connected to the intermediate shaft (lower steering shaft). Specifically, the steering torque sensor is disposed around the pinion shaft on the upstream side of the electric motor. Therefore, the detected steering torque Th detected by the steering torque sensor is affected by the friction f of the intermediate shaft. For this reason, when the steering torque T is gradually changed from zero to the positive maximum value, zero, negative maximum value, and zero, the input / output characteristics of the steering torque sensor are elliptical as shown in FIG. 4A. Draw.

FIG. 4B is a graph showing the relationship between the detected steering torque Th and the assist torque T _assist given to the pinion shaft by the electric motor. The assist torque T _assist is generated based on the detected steering torque Th affected by the friction f of the intermediate shaft. For this reason, in the comparative example, as shown in FIG. 4B, an error corresponding to the error of the detected steering torque Th occurs in the assist torque T _assist .

FIG. 4C is a graph showing the relationship between the sum (T _assist + Th) of the assist torque T _assist and the detected steering torque Th and the actual torque (detected assist torque) Ta detected by the actual torque sensor.
In the comparative example, the actual torque sensor is arranged around the pinion shaft on the downstream side of the electric motor. The motor torque output from the electric motor is transmitted to the downstream side of the electric motor in the pinion shaft through the speed reducer, and the steering torque applied to the steering wheel is transmitted through the column shaft and the intermediate shaft. The Therefore, a torque (T _assist + Th) obtained by adding the detected steering torque Th detected by the steering torque sensor to the assist torque T _assist given to the pinion shaft by the electric motor is detected by the actual torque sensor.

As described above, the detected steering torque Th includes an error due to the friction f of the intermediate shaft, and the assist torque T _assist includes an error corresponding to the error of the detected steering torque Th. Therefore, the sum (T _assist + Th) of the assist torque T _assist and the detected steering torque Th includes both errors included in these torques. For this reason, the actual torque (detection assist torque) Ta detected by the actual torque sensor includes a large error. In the comparative example, since the detection assist torque Ta including a large error is fed back, the accuracy of the torque feedback control is low.

5A, 5B, and 5C show the characteristics of the present embodiment.
FIG. 5A is a graph showing the input / output characteristics of the first torque sensor 31. 5A, the horizontal axis indicates the actual steering torque T applied to the steering wheel 2, and the vertical axis indicates the detected steering torque Th detected by the first torque sensor 31.
In the present embodiment, the first torque sensor 31 is disposed around the column shaft 7. Accordingly, the detected steering torque Th detected by the first torque sensor 31 is not affected by the friction f of the intermediate shaft 8. For this reason, as shown in FIG. 5A, the input / output characteristics of the first torque sensor 31 in this embodiment draw an ellipse that is narrower than the ellipse of FIG. That is, the first torque sensor 31 in the present embodiment can detect the steering torque applied to the steering wheel 2 with higher accuracy than in the comparative example.

FIG. 5B is a graph showing the relationship between the detected steering torque Th and the assist torque T _assist given to the second pinion shaft 21 by the electric motor 19. In the present embodiment, the assist torque T _assist is generated based on the detected steering torque Th that is not affected by the friction f of the intermediate shaft 8. For this reason, as shown in FIG. 5B, in the present embodiment, the error of the assist torque T _assist with respect to the detected steering torque Th is smaller than that in the comparative example.

FIG. 5C is a graph showing the relationship between the assist torque T _assist and the assist torque (detected assist torque) Ta detected by the second torque sensor 32. In the present embodiment, the second torque sensor 32 is disposed around the second pinion shaft 21. Therefore, the assist torque Ta detected by the second torque sensor 32 is not affected by the steering torque T. For this reason, in this embodiment, the error of the detected assist torque Ta with respect to the assist torque T _assist is small. In other words, the second torque sensor 32 in the present embodiment can detect the _assist torque T _assist with high accuracy.

In other words, in the present embodiment, the assist torque T _assist generated based on the detected steering torque Th that is not affected by the friction f of the intermediate shaft 8 is accurately detected and fed back, so that highly accurate torque feedback control is performed. It can be performed.
As mentioned above, although embodiment of this invention was described, this invention can also be implemented with another form. For example, in the embodiment, the second torque sensor 32 is arranged around the second pinion shaft 21 so as to detect the assist torque applied from the electric motor 19 to the second pinion shaft 21 via the speed reducer 20. ing. However, the second torque sensor 32 may be arranged so that the motor torque output from the electric motor 19 can be detected as the assist torque. In this case, the target assist torque setting unit 42 may set the target value of the motor torque output from the electric motor 19 as the target assist torque.

  In the embodiment, the microcomputer 28 includes the PI control unit 44 that generates a drive control value by performing a PI calculation on the motor current value corresponding to the torque deviation ΔTa. However, instead of the PI control unit 44, a PID control unit that generates a drive control value by performing a PID (differential integral proportional) operation on the motor current value according to the torque deviation ΔTa may be used.

  In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering wheel, 4 ... Steering mechanism, 5 ... Steering assist mechanism, 6 ... Steering shaft, 7 ... Column shaft, 8 ... Intermediate shaft, 14 ... First pinion shaft, 15 ... Rack shaft , 17 ... 1st pinion, 18 ... 1st rack, 19 ... Electric motor, 20 ... Reduction gear, 21 ... 2nd pinion shaft, 22 ... 2nd pinion, 23 ... 2nd rack, 27 ... ECU, 28 ... Microcomputer , 29 ... drive circuit, 31 ... first torque sensor, 32 ... second torque sensor, 42 ... target assist torque setting unit, 43 ... torque deviation calculation unit, 44 ... PI control unit

Claims (3)

An electric power steering apparatus including a rack shaft that moves in an axial direction in accordance with an operation of a steering member,
A steering shaft coupled to the steering member;
A first pinion shaft coupled to the steering shaft and having a first pinion;
A second pinion shaft disposed separately from the steering shaft and having a second pinion;
An electric motor for rotating the second pinion shaft;
A first rack and a second rack provided on the rack shaft and meshing with the first pinion and the second pinion, respectively;
A first torque sensor disposed around the steering shaft and detecting a steering torque applied to the steering member;
A second torque sensor disposed around the second pinion shaft and detecting an assist torque;
A target assist torque is calculated using the steering torque detected by the first torque sensor, and the electric motor is controlled so that the assist torque detected by the second torque sensor matches the target assist torque. An electric power steering device including a motor control means. The steering shaft includes a column shaft to which the steering member is coupled; an intermediate shaft having one end coupled to the column shaft and the other end coupled to the first pinion shaft;
The electric power steering apparatus according to claim 1, wherein the first torque sensor is disposed around the column shaft.   The electric power steering apparatus according to claim 1 or 2, wherein the electric motor is coupled to the second pinion shaft via a reduction gear.

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