JP2010188909A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for promptly reacting for control loss of a steering wheel. <P>SOLUTION: The electric power steering device 1 controlling the steering assist force corresponding to at least steering torque includes wheel speed detection sensors 16l, 16r detecting the wheel speed of right and left front wheels 7l, 7r, a yaw rate sensor 14 detecting the yaw rate of a vehicle body, an actual wheel speed gap setting part 32 setting the gap of the wheel speed of the right and left front wheels 7l, 7r detected by the wheel speed detection sensors 16l, 16r as the actual wheel speed gap, a turning origination wheel speed gap setting part 33 setting the wheel speed gap between the right and left front wheels 7l, 7r that originate turning of the vehicle body as the turning origination wheel speed gap based on the yaw rate detected by the yaw rate sensor 14, and an auxiliary reaction force torque setting part 24 correcting the steering assist force based on the gap between the actual wheel speed gap and the turning origination wheel speed gap. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus, and more particularly to a technique for setting an optimum auxiliary steering force to prevent the steering wheel from being removed even when a disturbance due to a road surface condition is applied.

  2. Description of the Related Art An electric power steering apparatus that generates a steering assist force by an assist motor and reduces a driver's steering operation is widely known. In such an electric power steering apparatus, not only the steering assist force is set based on the steering torque, the steering angle, the vehicle speed, etc. applied by the driver's steering operation, but also based on the motion state quantity of the vehicle body such as the yaw rate. In some cases, for example, Patent Literature 1 discloses a correction for adding an assist reaction torque to the steering assist force. According to this, the deflection suppression performance when a disturbance such as a cross wind acts on the vehicle is enhanced, and the running stability of the vehicle is improved.

JP-A-11-147482

  However, when the steering assist force is corrected based on the yaw rate, there is a problem that the auxiliary reaction force torque cannot be generated in a situation where the yaw rate has not yet occurred. For example, if a disturbance caused by the road surface condition such as when either the left or right wheel gets on an obstacle or the friction coefficient of the road surface is different between the left and right wheels, there is a difference in the road surface reaction force that the left and right wheels receive. Occurs. As a result, the steering wheel is removed, but the yaw rate is generated after the vehicle body starts to turn. Therefore, an appropriate auxiliary reaction torque cannot be generated at the moment when the steering wheel is removed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric power steering apparatus capable of quickly responding to a handle.

  In order to solve the above-mentioned problem, the first invention is a wheel speed detecting means for detecting the wheel speed of the left and right front wheels (7) in the electric power steering device (1) for controlling the steering assist force according to at least the steering torque. (16), a yaw rate detection means (14) for detecting the yaw rate of the vehicle body, and a first wheel speed setting for setting a difference between the wheel speeds of the left and right front wheels detected by the wheel speed detection means as a first wheel speed difference. Means (32); and second wheel speed setting means (33) for setting a wheel speed difference between the left and right front wheels caused by turning of the vehicle body as a second wheel speed difference based on the yaw rate detected by the yaw rate detecting means. And steering assist force correcting means (24) for correcting the steering assist force based on the difference between the first wheel speed difference and the second wheel speed difference.

  The left and right front wheels caused by disturbance by comparing the actual wheel speed difference between the left and right front wheels (first wheel speed difference) with the wheel speed difference between the left and right front wheels (second wheel speed difference) caused by turning based on the yaw rate. The wheel speed difference can be estimated. Therefore, the steering assist force is corrected based on this wheel speed difference between the left and right front wheels caused by the disturbance, so that the steering wheel can be prevented from being removed.

It is a mimetic diagram showing the electric power steering device concerning an embodiment. It is a block diagram which shows the steering control apparatus which concerns on embodiment. It is a block diagram which shows the auxiliary reaction force torque setting part of FIG. It is a flowchart which shows the setting procedure of auxiliary reaction force torque. It is a data map which shows an auxiliary reaction force torque base value. It is a data map which shows an auxiliary reaction force torque correction value.

  Hereinafter, an embodiment in which an electric power steering device of the present invention is applied to a vehicle steering device will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram schematically illustrating a power steering apparatus according to an embodiment.

  As shown in FIG. 1, the electric power steering apparatus 1 includes a pinion 4 that is integrally connected to a steering wheel 2 via a steering shaft 3, and a pinion 4 that meshes with the pinion 4 and can reciprocate in the vehicle width direction. A rack and pinion mechanism having a rack shaft 5 is provided. Both ends of the rack shaft 5 are connected to a knuckle arm 8 that supports left and right front wheels 7 as steering wheels via tie rods 6, and the left and right front wheels 7 rotate according to the rotation operation of the steering wheel 2. It is to be steered. An assist motor (electric motor) 9 is coaxially mounted on the rack shaft 5, and the driver's manual steering force is reduced by the assist force generated by the assist motor 9.

  The steering shaft 3 is provided with a steering angular velocity sensor 11 that detects the steering angular velocity ω from the steering angle of the steering wheel 2, and in the vicinity of the pinion 4, a steering torque sensor 12 that detects the steering torque T acting on the pinion 4 is provided. Is provided. A vehicle speed sensor 13 for detecting the vehicle speed V and a yaw rate sensor (yaw rate detecting means) 14 for detecting the yaw rate γ generated in the vehicle body are provided at appropriate positions on the vehicle body. In the vicinity of the left and right wheels 7l and 7r, wheel speed sensors (wheel speed detecting means) 16l and 16r for detecting the wheel speeds (rotational speeds) Vwl and Vwr of the left and right front wheels are provided.

  The output signals of the steering angular velocity sensor 11, the steering torque sensor 12, the vehicle speed sensor 13, the yaw rate sensor 14, and the wheel speed sensors 16l and 16r are controlled by a steering control device (EPS) that comprehensively controls the operation of the electric power steering device 1. -ECU) 21.

  The steering control device 21 includes a microcomputer, ROM, RAM, peripheral circuit, input / output interface, various drivers, and the like, and controls driving of the assist motor 9 based on output signals of the sensors 11 to 14 and 16. Control target value (target current It) is determined and input to the drive circuit 22 of the assist motor 9. The drive circuit 22 includes a FET bridge circuit and the like, and supplies power to the assist motor 9 based on the control target value determined by the steering control device 21, thereby controlling the output torque of the assist motor 9.

  FIG. 2 is a block diagram illustrating the steering control device 21 according to the embodiment. As shown in FIG. 2, the steering control device 21 includes an auxiliary steering torque setting unit 23, an auxiliary reaction force torque setting unit 24, a target current setting unit 25, and an output current control unit 26.

  The auxiliary steering torque setting unit 23 detects a steering wheel operation by the driver, and sets a target value of the assist torque in order to reduce the operation load according to the operation amount. The auxiliary steering torque setting unit 23 receives detection signals from the steering angular velocity sensor 11, the steering torque sensor 12, and the vehicle speed sensor 13, and an auxiliary steering torque target value that performs normal assist control based on the detection signals. Ta is set and output to the target current setting unit 25.

  The auxiliary reaction force torque setting unit 24 sets a target value of the auxiliary reaction force torque according to the vehicle behavior such as the yaw rate so as to reduce the operation load against the disturbance. The auxiliary reaction force torque setting unit 24 sets an auxiliary reaction force torque target value Tb based on output signals from the vehicle speed sensor 13, the yaw rate sensor 14, and the wheel speed sensors 16 l and 16 r, and outputs this to the target current setting unit 25. To do.

  The target current setting unit 25 is a target current for the assist motor 9 based on the auxiliary steering torque target value Ta input from the auxiliary steering torque setting unit 23 and the auxiliary reaction force torque target value Tb input from the auxiliary reaction force torque setting unit 24. It is set and output to the output current control unit 26. The output current control unit 26 controls the drive circuit 22 based on the target current It to drive the assist motor 9. Further, the output current control unit 26 performs feedback control between the actual current Ia of the assist motor 9 and the target current It.

  FIG. 3 is a block diagram showing the auxiliary reaction force torque setting unit 24. As shown in FIG. 3, the auxiliary reaction force torque setting unit (correction unit) 24 includes an auxiliary reaction force torque base value setting unit 31, an actual wheel speed difference calculation unit (first wheel speed difference calculation unit) 32, and a turn. An caused wheel speed difference calculation unit (second wheel speed difference calculation means) 33, an auxiliary reaction force torque correction value setting unit 34, and an auxiliary reaction force torque target value setting unit 35 are provided.

  The auxiliary reaction force torque base value setting unit 31 sets an auxiliary reaction force torque base value T1 based on input signals from the vehicle speed sensor 13 and the yaw rate sensor 14, and outputs this to the auxiliary reaction force torque target value setting unit 35. .

  The actual wheel speed difference calculation unit 32 calculates an actual wheel speed difference (first wheel speed difference) S_LV, which is the actual speed difference between the left and right front wheels, based on output signals from the wheel speed sensors 16l and 16r for the left and right front wheels. This is output to the auxiliary reaction force torque correction value setting unit 34.

  Based on the output signal from the yaw rate sensor 14, the turning-induced wheel speed difference calculation unit 33 calculates a turning-induced wheel speed difference (second wheel speed difference) γ_LV that is a speed difference between the left and right front wheels caused by turning of the vehicle body. This is output to the auxiliary reaction force torque correction value setting unit 34. Here, the turning-induced wheel speed difference γ_LV refers to a wheel speed difference that occurs due to a difference in travel distance between the inner wheel and the outer wheel when the vehicle turns.

  The auxiliary reaction force torque correction value setting unit 34 calculates a wheel speed difference (disturbance-induced wheel speed difference) ΔLV caused by a disturbance based on the actual wheel speed difference S_LV and the turning-induced wheel speed difference γ_LV, and causes the disturbance. An auxiliary reaction force torque correction value T2 is set based on the wheel speed difference ΔLV. Here, the disturbance means a change in road surface unevenness and friction coefficient. For example, when one of the left and right wheels touches or rides on a convex portion of the road surface, the wheel that is in contact with the convex portion is inhibited from rotating and the wheel speed decreases, and the wheel between the other wheels A speed difference is produced. Also, when the friction coefficient of the road surface running between the left and right front wheels is different, on the road surface (low μ road) side wheel with a small friction coefficient, the wheel speed increases at the time of acceleration compared to the other, and at the time of braking The wheel speed decreases compared to the other. Since the wheel speed difference between the left and right front wheels 7 is caused by turning of the vehicle body and disturbance, the disturbance-induced wheel speed difference ΔLV is calculated by subtracting the turning-induced wheel speed difference γ_LV caused by turning from the actual wheel speed difference S_LV. Can do. The auxiliary reaction force torque correction value setting unit 34 outputs the set auxiliary reaction force torque correction value T2 to the auxiliary reaction force torque target value setting unit 35.

  The auxiliary reaction force torque target value setting unit 35 sets an auxiliary reaction force torque target value Tb based on the auxiliary reaction force torque base value T1 and the auxiliary reaction force torque correction value T2, and uses this as a target current setting unit 25. Output to.

  The processing procedure of the auxiliary reaction force torque setting unit 24 of the steering control device 21 configured as described above will be described with reference to the flowchart of FIG. FIG. 4 is a flowchart showing a procedure for setting the auxiliary reaction force torque. When the automobile starts traveling, the steering control device 21 repeatedly executes the auxiliary reaction force torque setting process of FIG. 4 at a predetermined control interval (for example, 10 ms).

  When the auxiliary reaction force torque setting process is started, the steering control device 21 uses the data map shown in FIG. 5 based on the vehicle speed V and the yaw rate γ read from the vehicle speed sensor 13 and the yaw rate sensor 14 in the auxiliary steering torque setting unit 23. The auxiliary reaction force torque base value T1 is set (S1). FIG. 5 is a data map showing the auxiliary reaction force torque base value T1. The data table shown in FIG. 5 uses a different data table depending on the detection signal from the vehicle speed sensor 13, that is, the vehicle speed V. When the vehicle speed V is high, the auxiliary reaction force torque base value T1 is large even at the same yaw rate γ. Become. In particular, when the vehicle speed V = 0, the auxiliary reaction force torque base value T1 is set to 0 regardless of the detected value of the yaw rate γ.

  Next, the actual wheel speed difference calculation unit 32 calculates the actual wheel speed difference S_LV by taking the difference between the left front wheel speed Vwl and the right front wheel speed Vwr read from the left and right front wheel speed sensors 16l and 16r (S2). ).

  Subsequently, the turning-induced wheel speed difference calculation unit 33 calculates the turning-induced wheel speed difference γ_LV by multiplying the yaw rate γ read from the yaw rate sensor 14 by the tread length L of the left and right front wheels 7 (S3). As the tread length L, a value defined for each vehicle is stored in the steering control device 21 in advance.

  Then, the auxiliary reaction force torque correction value setting unit 34 calculates the disturbance-induced wheel speed difference ΔLV by taking the difference between the actual wheel speed difference S_LV and the turning-induced wheel speed difference γ_LV, the disturbance-induced wheel speed difference ΔLV, and the vehicle speed Based on V, the auxiliary reaction force torque correction value T2 is set from the data map shown in FIG. 6 (S5). FIG. 6 is a data map showing the auxiliary reaction force torque correction value T2. The data table shown in FIG. 5 uses a different data table depending on the detection signal from the vehicle speed sensor 13, that is, the vehicle speed V. If the vehicle speed V is large, the auxiliary reaction force torque base is used even if the wheel speed difference ΔLV is caused by the same disturbance. The value T1 increases. In particular, when the vehicle speed V = 0, the auxiliary reaction force torque correction value T2 is set to 0 regardless of the detected value of the disturbance-induced wheel speed difference ΔLV.

  Next, in the auxiliary reaction force torque target value setting unit 35, the auxiliary reaction force torque base value T1 and the auxiliary reaction force torque correction value T2 are added to calculate the auxiliary reaction force torque target value Tb (S6). It is determined whether or not the force torque target value Tb exceeds the maximum value Tbmax (S7). When the auxiliary reaction force torque target value Tb exceeds the maximum value Tbmax (Yes), the auxiliary reaction force torque target value Tb is set to the maximum value Tbmax (S9). Subsequently, it is determined whether or not the auxiliary reaction force torque target value Tb is smaller than the negative minimum value (−Tbmax) (S8), and when the auxiliary reaction force torque target value Tb is smaller than the negative minimum value (Yes). The auxiliary reaction force torque target value Tb is set to the minimum value -Tbmax (S10).

  The auxiliary reaction force torque target value Tb determined in this way is added to the auxiliary steering torque target value Ta separately obtained by the target current setting unit 25, and the target current It is set based on the added value. The output current control unit 26 drives the assist motor 9 by controlling the drive circuit 22 based on the target current It.

  By performing the above processing, the wheel speed difference ΔLV between the left and right front wheels caused by disturbance is estimated, and the auxiliary reaction force torque target value Tb is set based on this disturbance-caused wheel speed difference ΔLV. Steering assist force is applied in the direction of travel. Steering of the steering wheel occurs after a difference in wheel speed between the left and right front wheels. Therefore, the steering assist force can be applied at the moment when the steering wheel is removed by applying the steering assist force based on the difference in wheel speed. Therefore, it is possible to reduce the operation burden on the driver in order to prevent the steering wheel from being removed, and it is possible to provide an operation feeling without a sense of incongruity.

  Since the wheel speed difference changes more rapidly than the yaw rate due to road-induced disturbance, the auxiliary reaction force torque is set based only on the yaw rate by setting the auxiliary reaction force torque target value Tb based on the wheel speed difference. Compared with the case where the target value Tb is set, the steering assist force can be applied to the steering wheel with better responsiveness.

  Although the description of the specific embodiment is finished as above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the present embodiment, the actual yaw rate detected from the yaw rate sensor is used to calculate the wheel speed difference caused by turning, but a standard yaw rate calculated from the steering angle, the vehicle speed, or the like may be used instead. In the present embodiment, the wheel speeds of the left and right front wheels are used to calculate the actual wheel speed difference, but the wheel speeds of the left and right rear wheels may be used.

1 .... electric power steering device, 2 .... steering wheel, 7l, 7r ... front wheel, 9 .... assist motor, 11 .... steering angular velocity sensor, 12 .... steering torque sensor, 13 .... vehicle speed sensor (wheel speed detection) Means), 14 ·· Yaw rate sensor (yaw rate detection means), 16l, 16r ·· Wheel speed sensor, 21 ·· Steering control device, 23 ·· Auxiliary steering torque setting unit, 24 ·· Auxiliary reaction force torque setting unit (steering) Assist force correction means), 25 ... target current setting unit, 26 ... output current control unit, 31 ... auxiliary reaction force torque base value setting unit, 32 ... actual wheel speed difference calculation unit (first wheel speed calculation means) ), 33 .. Turning-induced wheel speed difference calculating unit (second wheel speed calculating means), 34.. Auxiliary reaction force torque correction value setting unit, 35... Auxiliary reaction force torque target value setting unit

Claims (1)

In the electric power steering device that controls the steering assist force according to at least the steering torque,
Wheel speed detection means for detecting the wheel speed of the left and right front wheels;
A yaw rate detection means for detecting the yaw rate of the vehicle body;
First wheel speed setting means for setting a difference in wheel speed between the left and right front wheels detected by the wheel speed detection means as a first wheel speed difference;
Second wheel speed setting means for setting a wheel speed difference between the left and right front wheels caused by turning of the vehicle body as a second wheel speed difference based on the yaw rate detected by the yaw rate detection means;
An electric power steering apparatus comprising: a steering assist force correcting unit that corrects the steering assist force based on a difference between the first wheel speed difference and the second wheel speed difference.

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