JP6279367B2 - Power steering device - Google Patents

Description

  The present invention relates to rack end stopper control of a power steering apparatus.

  In the electric power steering apparatus, there is an increasing demand for rack end stopper control for limiting the output of the steering assist force in the vicinity of the rack end in order to eliminate the abutting sound at the rack end. As this rack end stopper control, Patent Literature 1 is disclosed.

JP 2008-290525 A

  In Patent Document 1, the steering angular speed is reduced by multiplying a gain in the vicinity of the rack end or inverting the sign to output an auxiliary torque in a direction opposite to the steering assist force. However, when the rack end stopper control is started, the steering assist force decreases, and the turning of the steered wheels becomes insufficient with respect to the steering of the steering wheel, and the twist amount of the torsion bar increases. As a result, the steering assist force increases, and the steering angular speed may not be reduced as expected.

  As described above, in the power steering apparatus, it is a problem to effectively reduce the steering angular velocity near the rack end.

The present invention has been devised in view of the above-described conventional problems. One aspect of the present invention is that when the turning angle is near the rack end and the steering wheel is steered in the cutting direction, the steering angular speed is The damping signal is calculated so as to increase as it increases, so that the basic assist command signal in the cutting direction is maintained or decreased when the turning angle is near the rack end and the steering wheel is steered in the cutting direction. A limiter process is performed.

  According to the present invention, in the power steering apparatus, the steering angular speed can be effectively reduced near the rack end.

Schematic which shows the power steering apparatus in embodiment. The control block diagram of ECU in embodiment. The graph which shows the start conditions of rack end stopper control.

  Hereinafter, an embodiment of a power steering device according to the present invention will be described in detail with reference to FIGS.

[Embodiment]
FIG. 1 is a schematic diagram illustrating a power steering apparatus according to the first embodiment. In the power steering apparatus shown in FIG. 1, a basic steering mechanism is constituted by a steering wheel 1, a steering shaft (steering shaft) 2, a pinion shaft 3, and a rack shaft 4. In this steering mechanism, when the steering wheel 1 is rotated by the driver, the steering torque of the steering wheel 1 is transmitted to the pinion shaft 3 via the steering shaft 2, and the rotational motion of the pinion shaft 3 is transmitted to the rack shaft. The left and right steered wheels (not shown) that are converted into the linear motion 4 and coupled to both ends of the rack shaft 4 are steered. In other words, the rack shaft 4 is formed with rack teeth that mesh with the pinion shaft 3, and a conversion mechanism that converts the rotation of the steering shaft 2 into a steering operation by meshing the rack teeth with the pinion shaft 3 is configured. The

  The pinion shaft 3 is provided with a steering torque sensor TS (for example, a resolver) that detects the steering angle of the steering wheel 1. A motor rotation angle sensor (for example, a resolver or IC) that detects the steering torque signal of the steering torque sensor TS and the rotation angle of the rotor of the electric motor M, a control device (hereinafter referred to as an ECU) based on the motor rotation angle signal of the MAS, vehicle speed information, etc. The electric motor M is driven and controlled by a motor control circuit (not shown). A steering assist force is applied from the electric motor M to the rack shaft 4 via the speed reducer 5. The electric motor M is provided with a speed reducer 5 on its output shaft, and the rotation of the electric motor M is converted into a linear motion of the rack shaft 4 while being decelerated.

  In addition, the steering mechanism is provided with a steering angle sensor AS (for example, an MR element or an IC).

  Next, the control of the ECU will be described based on the block diagram shown in FIG.

  First, the steering torque calculator 11 calculates the steering torque based on the steering torque signal of the steering torque sensor TS. The steering shaft 2 is divided in the axial direction into an input shaft on the steering wheel 1 side and an output shaft on the rack shaft 4 side. The input shaft and the output shaft are coaxially connected to each other via a torsion bar (not shown). As a result, the input shaft and the output shaft can rotate relative to each other with torsional deformation of the torsion bar. The steering torque sensor TS includes a first angle sensor that detects a rotation angle on the input shaft side and a second angle sensor that detects a rotation angle on the output shaft side, and outputs from the first angle sensor and the second angle sensor. Based on the signal, the steering torque calculation unit 11 calculates the steering torque signal by calculating the twist amount of the torsion bar.

  Further, the rudder angular velocity calculation unit 13 calculates a rudder angular velocity, which is the rotation speed of the steering shaft, based on the rudder angle signal of the rudder angle sensor AS. Here, the steering torque signal and the steering angular velocity signal may be calculated either inside or outside the ECU, but the ECU receives a steering torque signal, a steering angle signal, and a steering angular velocity signal. It is assumed that there is a steering angle signal receiver and a steering angular speed signal receiver.

In the damping signal calculation unit 14, when the steering angle signal is not less than a first predetermined angle set in advance and the steering wheel 1 is steered in the cutting direction, the electric motor M is steered in the cutting direction. A damping signal that is a damping force with respect to the force is calculated. The damping signal is calculated so as to increase as the steering angular velocity signal calculated by the steering angular velocity calculation unit 13 increases.

  Here, the damping signal is calculated by PID control, for example. That is, the PID calculation is performed based on the deviation between the steering angular velocity signal and the steering angular velocity setting value for each steering angle set in the damping signal calculation unit 14, and the damping signal is calculated. Thereby, the damping torque according to a steering condition can be provided.

  An example of the start condition of the rack end stopper control in the damping signal calculation unit 14 is shown in FIG. As shown in FIG. 3, the horizontal axis indicates the steering angle, the vertical axis indicates the steering angular velocity, the broken line indicates the rack end, and the hatched portion indicates the rack end stopper control range. As shown in FIG. 3, the rack end stopper control is started at a lower steering angular speed as the steering angle is closer to the rack end.

  In addition, when the limiter processing unit 15 determines that the steering angle signal is equal to or greater than the second predetermined angle set in advance, the limiter processing is performed on the steering torque signal. Here, the limiter process is performed so as to maintain or gradually decrease the magnitude of the steering torque signal.

  The first predetermined angle set in the damping signal calculation unit 14 and the second predetermined angle set in the limiter processing unit 15 may be the same or different values.

  The basic assist command signal calculation unit 16 calculates a steering assist force based on the steering torque signal output from the limiter processing unit 15.

  The phase compensation calculation unit 17 compensates for the phase difference from when the steering wheel 1 is rotated until the steering assist force is applied by the electric motor M, and improves the response of EPS. Since the control of the phase compensation calculation unit 17 is not directly related to the present invention, a detailed description is omitted.

  When the steering angular velocity is high when the steering wheel 1 is returned, the damping processing unit 18 gives a damping amount, and suppresses the steering wheel 1 from returning too much to steer the vehicle. Since the control of the damping processing unit 18 is not directly related to the present invention, a detailed description is omitted.

  The adder 19 adds the output of the basic assist command signal calculator 16, the output of the phase compensation calculator 17, the output of the damping signal calculator 14, and the output of the damping processor 18. Then, the motor torque command calculation unit 20 calculates the motor torque based on the signal added by the addition unit 19.

In the conventional rack end stopper control, since the reaction force of the steered wheels is used, there is a problem that the rudder angular velocity is not sufficiently reduced on a road surface with a low friction coefficient μ. According to the power steering apparatus of the first embodiment, since the damping process is performed with sensitivity to the steering angular speed , even if the friction coefficient μ of the road surface is small, the damping torque is effectively applied and the steering angular speed is reduced. It is possible to reduce the butt shock of the handle.

In addition, since the limiter process is performed on the basic assist command signal according to the turning angle, it is possible to suppress excessive assist in the cutting direction when the steering angular speed decreases near the rack end and the damping signal decreases accordingly. . In particular, the amount of shake of the torsion bar increases near the rack end, and the basic assist command signal increases accordingly. Therefore, by applying a limiter process to the basic assist command signal, the excessive assist can be effectively suppressed. it can.

  Further, the damping signal calculation unit 14 calculates the damping signal so as to be larger than the basic assist command signal according to the steering situation, so that the friction coefficient μ of the road surface is very small and the basic assist command signal is very high. Even if it is small, the damping torque can be effectively applied and the butt shock of the steering wheel 1 can be suppressed.

  Further, the limiter processing unit 15 reduces the steering torque signal before being input to the basic assist command signal calculation unit 16, thereby comparing the calculated basic assist command signal with a limiter process. The correction amount can be reduced. As a result, hunting due to correction control can be suppressed.

  In addition, it is possible to improve the feeling at the time of switching back by providing cutting and switching back determination with respect to the rudder angle and not providing a damping signal when the steering is rotated in the switching back direction.

  Further, usually, the vehicle is provided with a cushioning material in order to soften the collision sound when the rack end is attached. According to this embodiment, the steering angular speed can be effectively reduced in the vicinity of the rack end, so that the durability of the buffer material can be improved, and further, the cost can be reduced by omitting the buffer material.

  Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

  For example, the limiter process may set an upper limit value so that the steering torque signal does not exceed the upper limit value, may be limited by multiplying the steering torque signal by gain, or other methods may be used. .

  Here, it is the technical idea grasped | ascertained from each embodiment mentioned above, Comprising: It describes below with the effect about things other than what was described in the claim.

  2. The power steering apparatus according to claim 1, wherein a cut / return determination is provided with respect to the rudder angle, and a damping signal is not given when the steering is rotated in the return direction.

  According to this technical idea, the feeling at the time of switching back can be improved.

1. Steering wheel 2. Steering shaft (steering shaft)
DESCRIPTION OF SYMBOLS 3 ... Pinion shaft 4 ... Rack shaft M ... Electric motor AS ... Steering angle sensor TS ... Steering torque sensor MAS ... Motor rotation angle sensor 14 ... Damping signal calculating part 15 ... Limit processing part

Claims (4)

A steering shaft that rotates in accordance with a steering operation of the steering wheel, a pinion shaft provided on the steering shaft, a rack bar that has rack teeth that mesh with pinion teeth formed on the pinion shaft, and steers the steered wheels; A steering mechanism composed of
An electric motor for applying a steering force to the steering mechanism;
A control device for driving and controlling the electric motor;
A steering torque signal receiving unit provided in the control device, to which a steering torque signal generated in the steering mechanism is input;
A steering angular velocity signal receiving unit provided in the control device, to which a steering angular velocity signal that is a rotational speed of the steering shaft is input;
A steering angle signal receiving unit provided in the control device, to which a steering angle signal of the steering shaft is input;
A basic assist command signal calculation unit that is provided in the control device and calculates a basic assist command signal that is a command signal to the electric motor based on the steering torque signal;
Provided in the control device, the steering wheel is stroke steering operation direction, the steering angular velocity signal, wherein when the steering angle signal is equal to or higher than the control start threshold is a low steering angular speed closer to the rack end, in the cutting direction A calculation unit that calculates a damping signal that is a damping force with respect to the steering force of the electric motor, and a damping signal calculation unit that calculates the damping signal such that the damping signal increases as the steering angular velocity signal increases. ,
When the steering angle signal is not less than a second predetermined angle and the steering wheel is steered in the cutting direction, the basic assist command signal in the cutting direction is maintained or lowered. A limiter processing unit for performing a limiter process;
A power steering apparatus comprising:   2. The power steering apparatus according to claim 1, wherein the damping signal calculation unit calculates the damping signal such that the damping signal is larger than the basic assist command signal in accordance with a steering situation.   The power steering apparatus according to claim 1, wherein the damping signal calculation unit calculates the damping signal by PID control based on a deviation between a detected value of the steering angular speed and a set value of the steering angular speed.   The power steering apparatus according to claim 1, wherein the limiter processing unit reduces the steering torque signal before being input to the basic assist command signal calculation unit.

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