JP5478027B2 - Rear wheel steering device - Google Patents

Description

  The present invention relates to a rear wheel steering device used for a vehicle such as an automobile, and more particularly to a rear wheel steering device that performs rear wheel steering (rear wheel toe angle) control according to the behavior of the vehicle in a feedback compensation manner.

  By providing a linear displacement actuator such as a hydraulic cylinder device or an electric linear actuator at the connecting part of the suspension link supporting the left and right rear wheels with the lateral link or trailing link body, and driving the linear displacement actuator to extend and contract There are known rear wheel steering devices that individually change the steering angles (toe angles) of the left and right rear wheels (for example, Patent Documents 1 and 2).

  In such a rear wheel steering device, the control target value of the rear wheel steering angle is set and set so that, for example, the rear wheel toe-out state during acceleration and the rear wheel toe-in state during braking are set according to the state of the vehicle. The control deviation, which is the difference between the control target value and the turning angle (actual steering angle) detected by the turning angle sensor, is calculated, and the linear displacement actuator is controlled in a feedback compensation manner so that the control deviation approaches zero. Things have been done.

  Some linear displacement actuators are a combination of an electric motor and a feed screw mechanism. When the feed screw mechanism is driven by the electric motor, the feed screw mechanism is linearly displaced in accordance with the amount of rotation of the electric motor. There is something that steers the wheel.

This linear displacement actuator exhibits a self-locking function that self-holds the steered state at that time even when the electric motor is not supplied with current due to the screw action of the feed screw mechanism.
Japanese Patent Publication No. 8-25482 Japanese Patent Laid-Open No. 9-30438

  When the feedback compensation type control is based on P (proportional) control as in PID control, a deviation in which the actual steering angle does not coincide with the control target value in a steady state, that is, a steady deviation remains. It cannot be avoided. In a state where there is such a steady deviation, the controller continues to supply energy to the linear displacement actuator even though the control amount that is the actual steering angle (position) does not change. For example, when the linear displacement actuator is an electric type, the controller continues to pass a current through the electric actuator.

  In contrast, a linear displacement with a self-locking function that self-holds the steered state at the time even when the electric motor does not supply current, such as a linear displacement actuator that is a combination of an electric motor and a feed screw mechanism. In the actuator, continuing to supply current to the electric motor in a steady deviation state is a wasteful consumption of electric power (energy).

  The problem to be solved by the present invention is that, in a rear wheel steering device using a linear displacement actuator having a self-locking function that is self-holding, wasteful energy consumption under a steady deviation state is obtained without impairing rear wheel steering control. It is to lose.

  A rear wheel steering device according to the present invention is a rear wheel steering device for steering control of the left and right rear wheels of a vehicle, the steering driving means for steering each rear wheel and self-holding the steering state, Steering angle detecting means for detecting the turning angle of each rear wheel, vehicle state detecting means for detecting the state of the vehicle, and rear wheel turning angle according to the vehicle state detected by the vehicle state detecting means Rear wheel turning angle control target value setting means for setting the control target value of the vehicle, the control target value set by the rear wheel turning angle control target value setting means, and the turning detected by the turning angle detection means Feedback control means for controlling the steered drive means in a feedback compensation manner so that the control deviation, which is the difference from the angle, approaches zero, and whether or not the control deviation is within a set allowable steady deviation range. The control deviation is within the range of allowable steady-state deviation. When the control deviation is outside, the feedback compensation control by the feedback control means is permitted, and when the control deviation is within the range of the allowable steady deviation, the feedback compensation control by the feedback control means is prohibited, and the steering Stop control means for performing stop control for stopping energy supply to the drive means.

  In the rear wheel steering apparatus according to the present invention, preferably, the stop control unit cancels the stop control when the control target value set by the steering angle control target value setting unit changes, and the feedback The feedback compensation control by the control means is permitted.

  The rear wheel steering device according to the present invention preferably has an external force related state detection means for detecting a state variable that causes an external force acting on the steering drive means, and the stop control means detects the external force related state detection. The allowable steady deviation is set according to the state variable detected by the means.

  According to the rear wheel steering apparatus of the present invention, it is monitored whether the control deviation of the feedback compensation type control is within the range of the allowable steady deviation, and if the control deviation is outside the range of the allowable steady deviation, the vehicle Although feedback compensation control for rear wheel steering according to the state is performed, when the control deviation falls within the allowable steady deviation range, the feedback compensation control is prohibited and the energy supply to the steering driving means is stopped. Thereby, useless energy consumption under the steady deviation state is eliminated without impairing the rear wheel steering control, and energy saving of the rear wheel steering control is achieved.

  Below, the embodiment of the rear-wheel steering apparatus by this invention is described with reference to FIGS.

  First, a four-wheeled vehicle to which a rear wheel steering device according to the present invention is applied will be described with reference to FIG.

  The four-wheel vehicle 1 of the present embodiment includes left and right front wheels 4L and 4R and left and right rear wheels 6L and 6R. The front wheels 4L and 4R are fitted with tires 3L and 3R, respectively, suspended by the vehicle body 2 by left and right front suspensions 7L and 7R, and attached to the vehicle body 2 by knuckles 9L and 9R so as to be freely turned. The rear wheels 6L and 6 are fitted with tires 5L and 5R, respectively, suspended by the vehicle body 2 by left and right rear suspensions 8L and 8R, and attached to the vehicle body 2 by knuckles 21L and 21R so as to be turnable.

  The four-wheel vehicle 1 includes a front wheel steering device 10 that directly steers the left and right front wheels 4L and 4R by steering the steering wheel 11. The front wheel steering device 10 includes a pinion 13 that is integrally connected to a steering wheel 11 via a steering shaft 12 and a tooth portion that meshes with the pinion 13 so as to be able to reciprocate in the vehicle width direction. A rack and pinion mechanism having a rack shaft 14 is also provided. Both ends of the rack shaft 14 are connected to the left and right knuckles 9L and 9R by tie rods 15. The left and right front wheels 4L, 4R are steered (turned) when the rack shaft 14 moves in the vehicle width direction by the rotation operation of the steering wheel 11.

  The steering shaft 12 is provided with a steering angle sensor 51 for detecting the steering angle of the steering wheel 11 corresponding to the actual steering angle of the front wheels 4L, 4R. Hereinafter, it is assumed that the steering angle sensor 51 outputs a sensor signal indicating the actual front wheel steering angle.

  The four-wheeled vehicle 1 has one end connected to the vehicle body 2 and the other end connected to the knuckle 21L of the left rear wheel 6L, one end connected to the vehicle body 2, and the other end connected to the right rear. A right linear actuator 40R connected to the knuckle 21R of the wheel 6R. The left and right linear actuators 40L and 40R are electrically operated, and expand and contract by a linear operation, and individually change the turning angles of the left and right rear wheels 6L and 6R.

  The left and right linear actuators 40L and 40R are controlled by a rear wheel steering control device (ECU) 100. The rear wheel steering control device 100 is of an electronic control type including a microcomputer. The rear wheel steering control device 100 receives a sensor signal indicating the actual front wheel steering angle from the steering angle sensor 51, and the vehicle speed from the vehicle speed sensor 52 that detects the vehicle speed of the four-wheeled vehicle 1. The sensor signal indicating the yaw rate of the vehicle body 2 is input from the yaw rate sensor 53 that detects the yaw rate of the vehicle body 2, and the sensor signal indicating the lateral acceleration is input from the lateral acceleration sensor 54 that detects the lateral acceleration acting on the vehicle body 2. Then, using these sensor signals, the steering angle control target value of the left and right rear wheels is calculated in accordance with a preset rear wheel steering control law.

The rear wheel steering control device 100 converts the turning angle control target value into the control target stroke amount of the linear actuators 40L and 40R, and the linear actuators 40L and 40R from the stroke sensors 55L and 55R provided in the linear actuators 40L and 40R. The sensor signal indicating the actual stroke amount is input, and the control signal is output to each of the linear actuators 40L and 40R so that the control deviation which is the difference between the control target stroke amount and the actual stroke amount approaches zero.

  Thus, feedback compensation control is performed so that the turning angles (toe angles) of the left and right rear wheels 6L and 6R become the target rear wheel turning angle (rear wheel steering angle control target value).

  As described above, in this embodiment, the feedback compensation control for the rear wheel turning is performed with the stroke amounts of the linear actuators 40L and 40R. The stroke amounts of the linear actuators 40L and 40R are substantially in a one-to-one relationship with the actual turning angles of the rear wheels 6L and 6R, and the turning is performed to detect a physical quantity representative of the turning angles of the rear wheels 6L and 6R. Stroke sensors 55L and 55R that detect the stroke amounts of the linear actuators 40L and 40R are used as the angle detection means.

  According to the four-wheeled vehicle 1 configured as described above, the left and right linear actuators 40L and 40R are displaced symmetrically with respect to each other at the same time, so that the toe-in / to-out of the left and right rear wheels 6L and 6R can be performed under appropriate conditions. Can be controlled freely below. In addition, if one of the left and right linear actuators 40L and 40R is extended and the other is contracted, the left and right rear wheels 6L and 6R can be steered left and right. For example, the four-wheeled vehicle 1 changes the rear wheels 6L and 6R to toe-out during acceleration, the rear wheels 6L and 6R to toe-in during braking, and the high-speed cornering based on the vehicle motion state grasped by various sensors. The rear wheels 6L and 6R are in phase with the front wheel rudder angle, and the rear wheels 6L and 6R are toe angle controlled (steered) in the opposite phase to the front wheel rudder angle when traveling at low speeds to control the rear wheels toe angle control. Can also be done.

  Next, a specific configuration of the rear wheel steering device of the present embodiment will be described with reference to FIGS. 2 and 3. The left and right rear suspensions 8L and 8R are of the double wishbone type. Since the left and right rear suspensions 8L, 8R have the same structure and are arranged symmetrically, the left rear suspension 8L will be described here.

  The rear suspension 8L includes the aforementioned knuckle 21L that rotatably supports the rear wheel 6L, the upper arm 22L and the lower arm 23L that connect the knuckle 21L to the vehicle body 2 so as to be movable up and down, and the turning angle (toe angle) of the rear wheel 6L. The linear actuator 40L is connected to the knuckle 21L and the vehicle body 2 and the damper 24L with a suspension spring for buffering the vertical movement of the rear wheel 5 is used.

  The upper arm 22L and the lower arm 23L have base ends connected to the vehicle body 2 via rubber bush joints 25 and 26, respectively, and tip ends connected to the upper and lower portions of the knuckle 21L via ball joints 27 and 28, respectively. One end of the linear actuator 40L is connected to the vehicle body 2 via the rubber bush joint 29, and the other end is connected to the rear portion of the knuckle 21L via the rubber bush joint 30. The damper 24L with suspension spring is fixedly connected to the vehicle body 2 at the upper end and is connected to the upper portion of the knuckle 21L via the rubber bush joint 31 at the lower end.

  By adopting such a configuration, when the linear actuator 40L is driven to extend, the rear portion of the knuckle 21L rotates outward in the vehicle width direction, so that the rear wheel 6L faces inward with respect to the vehicle traveling direction (toe-in side). ). On the other hand, when the linear actuator 40L is driven to contract, the rear portion of the knuckle 21L rotates inward in the vehicle width direction, so that the rear wheel 6L turns outward (toe-out side) with respect to the vehicle traveling direction.

  Next, the linear actuator 40L and the stroke sensor 55L will be described with reference to FIG.

  The linear actuator 40L includes a first housing 43a to which a rubber bush joint 29 on the vehicle body 2 side is attached, a housing 43 including a second housing 43b fastened to the first housing 43a by a plurality of bolts 43c, and a second housing 43b. And a telescopic rod 44 fitted in a rubber bush joint 30 on the knuckle 21L side so as to be slidable (stretchable) in the axial direction (left and right as viewed in FIG. 4).

A DC motor (electric motor) 45 as a drive source is accommodated in the first housing 43a. A planetary gear type speed reducer 46 and an elastic coupling (not shown) are accommodated in the second housing 43b. An output shaft 47 of the DC motor 45, speed reducer 46, is drivingly connected to the male screw member 48 A of the screw mechanism 48 sends via a resilient coupling (not shown). Nut member 48 B of the screw mechanism 48 feed is fixed mounted on the telescopic rod 44. The nut member 48B is externally threaded member 48 A and the engaged threaded engagement, moves in the axial direction by the rotation of the male screw member 48 A (left-right direction as viewed in FIG. 4).

As a result, when the DC motor 45 is driven, the rotation of the output shaft 47 is decelerated by the speed reducer 46 and transmitted to the male screw member 49A, and the rotation of the output shaft 47 is converted into a linear motion by the feed screw mechanism 48 to expand and contract. The rod 44 is linearly driven in the axial direction.

Thus, the linear actuator 40L is a linear displacement actuator in combination with the screw mechanism 48 and feed the DC motor 45, even in power interruption state in which no current is supplied to the DC motor 45, by a screw action of the feed screw mechanism 48, at that time This is a linear displacement actuator having a self-locking function for self-holding the steered state.

  The stroke sensor 55L includes a sensor housing 57 that is attached to the second housing 43b and accommodates the differential transformer 56, and a magnet 59 that is fixedly attached to the telescopic rod 44 by a bolt 58. The differential transformer 56 extends in parallel with the linear drive direction (axial direction) of the telescopic rod 44 and is disposed close to the magnet 59, and a change in differential voltage that occurs when the magnet 59 moves in the axial direction. Thus, the differential transformer type displacement measuring device that detects the expansion / contraction stroke of the expansion / contraction rod 44.

  Next, the details of the rear wheel steering control device 100 will be described with reference to FIG. The rear wheel steering control device 100 includes an input interface 101, a rear wheel turning angle control target value calculation unit 102, a control deviation calculation unit 103, a proportional control unit 104, a motor drive circuit 105, and a power interruption control unit 106. Have

  The input interface 101 receives sensor signals from the steering angle sensor 51, the vehicle speed sensor 52, the yaw rate sensor 53, the lateral acceleration sensor 54, and the left and right stroke sensors 55L and 55R.

  The rear wheel turning angle control target value calculation unit 102 determines the left and right rear wheels 6L, 6R according to a predetermined rear wheel steering angle control law in accordance with the input sensor signals (steering angle, vehicle speed, yaw rate, lateral acceleration). The turning angle control target value is calculated. The rear wheel turning angle control target value calculation unit 102 converts the turning angle control target value into a control target stroke amount (operation amount) for feedback compensation control based on the stroke amounts (control amounts) of the linear actuators 40L and 40R. , And passed to the control deviation calculation unit 103.

  The control deviation calculation unit 103 calculates the difference between the left and right rear wheels 6L and 6R by calculating the difference between the actual stroke amounts of the left and right linear actuators 40L and 40R detected by the left and right stroke sensors 55L and 55R and the left and right control target stroke amounts. Calculate the control deviation.

The proportional control unit 104 outputs the control deviation for each of the left and right linear actuators 40L and 40R from the control deviation calculation unit 103 to the motor drive circuit 105 as a proportional operation command amount by a predetermined proportional gain.

In this manner, the rear wheel turning angle control target value calculation unit 102, the control deviation calculation unit 103, and the proportional control unit 104 constitute a feedback control unit, and feedback compensation control is executed.

  The motor drive circuit 105 generates current to be supplied to the DC motors 45 of the left and right linear actuators 40L and 40R based on the left and right proportional operation command amounts by duty ratio control, and supplies current to the DC motor 45.

The power interruption control unit 106 is a stop control unit that stops energy supply to the linear actuators 40L and 40R serving as steering drive units, in this case, power supply. The power interruption control unit 106 determines whether or not the control deviation calculated by the control deviation calculation unit 103 is within the range of the allowable steady deviation calculated and set by the allowable steady deviation calculation unit 107, and the control deviation is determined. acceptable or outside the scope of the steady-state deviation, when the control target value calculated by the rear wheel steering angle control target value calculation unit 102 is changed to allow the above-described feedback compensation control, whereas the rear wheel steering When the control target value calculated by the angle control target value calculation unit 102 has not changed and the control deviation is within the allowable steady deviation, the feedback compensation control is prohibited, and the linear actuator 40L, The motor drive circuit 105 is instructed to stop the power supply (current) supply to the 40R.

When a power interruption command is input from the power interruption control unit 106, the motor drive circuit 105 sets the duty ratio to zero regardless of the output of the proportional control unit 104 , and stops energization of the linear actuators 40L and 40R.

  Thereby, useless energy consumption under the steady deviation state is eliminated without impairing the rear wheel steering control, and energy saving of the rear wheel steering control is achieved.

  The power interruption described above may be performed individually by the left and right linear actuators 40L and 40R, or may be performed simultaneously on the left and right linear actuators 40L and 40 only when the power interruption condition is satisfied on both the left and right sides. .

  The allowable steady deviation when the control gain is constant varies depending on the external force acting on the linear actuators 40L and 40R. On the other hand, the allowable steady deviation calculation unit 107 is detected by an external force-related state detection unit that detects a state variable that causes an external force acting on the linear actuators 40L and 40R, which is detected by the lateral acceleration sensor 54 in this embodiment. The allowable steady deviation is set according to the lateral acceleration. The allowable steady deviation is expressed by the following equation.

  Ess = K ・ αy

  However, Ess is an allowable steady deviation, αy is a lateral acceleration, and K is a constant.

Thus, linear actuators 40L, even if fluctuation allowable steady-state deviation by an external force acting on the 40R, there is no useless energy consumption under steady-state error state without impairing the rear wheel steering control, the rear wheel steering control saving Energy can be achieved.

  Next, a processing routine for rear wheel steering control according to the present embodiment will be described with reference to the flowchart shown in FIG. The processing routine is repeatedly executed at predetermined intervals by time interruption.

  First, sensor signals are input from various sensors (step S1).

Next, calculation for feedback compensation control of the turning angle of the left and right rear wheels 6L and 6R is performed using the input sensor signal according to a preset rear wheel steering control law, and the control deviation Err and the control target value δr are calculated. ^* Is calculated (step S2). The control deviation Err and the control target value δr ^* are calculated for each of the left and right linear actuators 40L and 40R. Here, for simplification of explanation, one of them will be described.

Next, it is determined whether or not the control target value δr ^* has changed (step S3). Change determination of the control target value [delta] r ^* is, whether there is a difference between the control target value [delta] r ^* of the control target value [delta] r ^* and the current front one, or if the difference may if made as to whether a predetermined value or more. When it is determined that the control target value δr ^* has changed, a duty ratio output corresponding to the control deviation Err for feedback compensation control is performed (step S4).

On the other hand, if it is determined that the control target value δr ^* has not changed, the allowable steady-state deviation Ess is calculated according to the lateral acceleration detected by the lateral acceleration sensor 54 (step S5), and the control deviation Err. Is less than or equal to the allowable steady-state deviation Ess (step S6). When the control deviation Err <the allowable steady deviation Ess is not satisfied, a duty ratio output corresponding to the control deviation Err for feedback compensation control is performed (step S4).

  On the other hand, when the control deviation Err <the allowable steady deviation Ess, an output with a duty ratio of zero, that is, a power interruption is performed (step S7).

FIG. 7 shows a time chart of the rear wheel steering control according to the present embodiment. In this time chart, the control target value δr ^* and the actual steering angle δr are shown.

At time T0, feedback compensation control is performed in which the actual steering angle δr approaches the control target value δr ^* . At time T1, the control target value δr * is the same as the previous calculation, and the actual steering angle δr and the control target value δr ^*. When the control deviation Err becomes equal to or less than the allowable steady deviation Ess, the feedback compensation control is stopped, and the power interruption for stopping the energization of the linear actuators 40L and 40R is performed.

This power interruption is performed until time T2 when the control target value δr ^* changes. When the control target value δr ^* changes at time T2, feedback compensation control in which the actual steering angle δr approaches the new control target value δr ^* is resumed. At time T3, when the control target value δr ^* is the same as the previous calculation and the difference between the actual steering angle δr and the control target value δr ^* , that is, the control deviation Err again becomes equal to or less than the allowable steady deviation Ess, feedback compensation control is performed. Is stopped, and power interruption to stop energization of the linear actuators 40L and 40R is performed.

Even when the control target value δr ^* changes by a value smaller than the allowable steady deviation Ess at time T4, the feedback compensation control in which the actual steering angle δr approaches the new control target value δr ^* is resumed. At time T5, when the control target value δr ^* is the same as in the previous calculation and the control deviation Err again becomes equal to or smaller than the allowable steady deviation Ess, the feedback compensation control is stopped, and the electric power for stopping the energization of the linear actuators 40L and 40R is stopped. Is done. Thereby, it is avoided that the control deviation Err becomes large due to power interruption.

It is a whole lineblock diagram showing one embodiment of a four-wheeled vehicle to which a rear-wheel steering device by the present invention is applied. It is a perspective view which shows one embodiment of the rear-wheel sunpension structure incorporating the rear-wheel steering apparatus by this invention. It is a rear view which shows one embodiment of the rear-wheel sunpension structure incorporating the rear-wheel steering apparatus by this invention. It is a rear view which shows one Embodiment of the linear actuator and stroke sensor which are integrated in the rear-wheel steering apparatus by this invention. It is a block diagram which shows one Embodiment of the control system of the rear-wheel steering apparatus by this invention. It is a flowchart which shows the processing routine of the rear-wheel steering control by this embodiment. It is a time chart of rear-wheel steering control by this embodiment.

Explanation of symbols

4L, 4R Front wheel 6L, 6R Rear wheel 40L, 40R Linear actuator 51 Steering angle sensor 52 Vehicle speed sensor 53 Yaw rate sensor 54 Lateral acceleration sensor 55L, 55R Stroke sensor 100 Rear wheel steering angle control device 102 Rear wheel turning angle control target value calculation unit DESCRIPTION OF SYMBOLS 103 Control deviation calculating part 104 Proportional control part 105 Motor drive circuit 106 Power interruption control part 107 Permissible steady-state deviation calculating part

Claims (1)

A rear wheel steering device that controls the steering of left and right rear wheels of a vehicle,
Steering drive means for steering each rear wheel and self-holding the steered state;
A turning angle detection means for detecting a turning angle of each of the rear wheels;
Vehicle state detection means for detecting the state of the vehicle;
A lateral acceleration sensor that detects lateral acceleration acting on the vehicle body that causes external force acting on the steering drive means;
Rear wheel turning angle control target value setting means for setting a control target value of the rear wheel turning angle according to the vehicle state detected by the vehicle state detection means;
The steering drive so that a control deviation which is a difference between the control target value set by the rear wheel turning angle control target value setting means and the turning angle detected by the turning angle detection means approaches zero. Feedback control means for controlling the means in a feedback compensation manner;
When an allowable steady deviation, which is an allowable control deviation, is set according to the lateral acceleration detected by the lateral acceleration sensor , and a change amount of the control target value within a predetermined time is less than a predetermined value. The control deviation is compared with the allowable steady deviation to determine whether the control deviation is within the allowable steady deviation range, and when the control deviation is outside the allowable steady deviation range, permits the feedback compensation control by the feedback control means, when the control deviation is within the range of the allowable steady-state error, the energy supply to the steering drive means prohibits the feedback compensation control by the feedback control means was subjected to stop control for stopping, der variation within a predetermined time of the control target value is greater than a predetermined value set by the rear wheel steering angle control target value setting means In this case, a stop control means for the rambling stop control, allowing feedback compensation control by the feedback control means,
A rear wheel steering device having

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