JP2005271877A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of realizing a natural steering characteristic when wheels are returned using a simple control method. <P>SOLUTION: In the steering device provided with an actuator M capable of controlling a wheel steering angle ϕ of the wheels W, W in the vehicle, the wheel steering angle ϕ is controlled based on a wheel steering angle ϕ1 at at least returning of the wheel and a phenomenon that the wheels W, W are returned to a neutral position by self aligning torque is duplicated at returning of the wheel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement of a steering device.

  This type of steering device has been proposed by the applicant, for example. Generally, a rack having both ends connected to wheels, two pinion gears for driving the rack, and one end connected to one pinion gear and the other. It consists of a steering shaft whose end is connected to the steering wheel, a motor that is an actuator that is connected to the other pinion gear, and a control unit that controls the torque generated by the motor. The control unit controls the torque generated by the motor in accordance with the traveling speed of the vehicle to assist the driver in operating the steered wheels (see, for example, Patent Document 1).

  In the above steering device, when the vehicle turns to a straight traveling state after turning, that is, when the wheel tries to return to the neutral state from the state where the wheel steering angle is maintained, the so-called wheel return is performed. Sometimes, the motor is controlled according to the control amount obtained by adding the return command value determined by the vehicle speed to the assist command value determined based on the vehicle speed and the steering torque. This eliminates the feeling and lack of return of the steering wheel.

In another steering device, the self-aligning torque generated on the wheel at the time of returning the wheel is calculated, and torque is generated in the motor to compensate for the friction torque of the power steering device itself facing the self-aligning torque to perform the return control. There are also suggestions to improve.
JP-A-10-278827 (from page 4, left column, line 18 to page 5, left column, line 28, FIG. 1) Japanese Patent No. 3353770 (from page 3, right column, line 40 to page 5, left column, line 2; FIG. 1)

  The above-described conventional steering device is a useful technique in that, as described above, the steering wheel can be returned to the neutral position at the time of return by the control at the time of return of the steered wheel, and the driver does not feel uncomfortable. .

  However, the technique of Japanese Patent Laid-Open No. 10-278827 is a concept that realizes smooth steering characteristics by gradually attenuating a return command for returning the steering wheel to the neutral position when the self-aligning torque becomes small. Although the control itself is not so complicated, it does not realize a natural steering characteristic by the self-aligning torque, and the technology of Japanese Patent No. 3353770 detects or calculates the self-aligning torque. Calculate the friction torque of the power steering device itself and the effect on the torque due to the moment of inertia of the motor, etc., which are harmful when the steering wheel returns to the neutral position by self-aligning torque. Torque is generated to the motor so as to remove the influence of This is a concept that requires a lot of parameters to be detected, and the control thereof is complicated. Furthermore, even when calculating the self-aligning torque, the control is also complicated, and the control is not always based on actual measurement values. Since it is not always done, it does not realize natural steering characteristics.

  Therefore, the present invention was devised in order to improve the above-described problems, and the object of the present invention is to provide a power steering system that uses a simple control method and can realize natural steering characteristics when returning to the wheel. Is to provide a device.

  In order to achieve the above object, in a steering apparatus including an actuator capable of controlling the wheel steering angle of a wheel in a vehicle, the wheel steering angle is controlled based on at least the wheel steering angle when the wheel returns.

  Further, in a steering apparatus having an actuator capable of controlling the wheel steering angle of a wheel in a vehicle, the wheel steering angle is determined based on the wheel steering angle when the wheel returns and the travel distance from the wheel return when the wheel returns. Control.

  According to the present invention, it is possible to realize a natural change in the wheel steering angle when the wheel returns to the neutral position by the self-aligning torque. That is, the return condition of the wheels is improved, and natural steering characteristics can be realized.

  Since the wheel steering angle is controlled, the wheel can be reliably returned to the neutral position. That is, the harmful effect of the wheel returning too much or insufficiently returning is eliminated.

  In addition, the control is based on the concept of faithfully reproducing the phenomenon that the wheels are returned to the neutral position by the self-aligning torque, so there is no need to bother to calculate and detect the self-aligning torque. Fewer parameters are required. Therefore, the control is also simplified.

  In addition, when the mileage required when the wheel returns to the neutral position is also included in the control, the phenomenon that the wheel is returned to the neutral position due to self-aligning torque can be faithfully reproduced, and more precisely It is possible to realize a change in the wheel steering angle when the wheel returns to the neutral position by the self-aligning torque, thereby realizing more natural steering characteristics.

  The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a schematic diagram of a steering apparatus according to an embodiment. FIG. 2 is a flowchart illustrating a control procedure of the steering device according to the embodiment. FIG. 3 is a map showing the relationship between the change in the rotation angle of the motor used for the map calculation of the control of the steering device and the travel distance in the embodiment. FIG. 4 is a diagram showing a trajectory of the vehicle when the wheels return to the neutral position by self-aligning torque. FIG. 5 is a control block diagram of a motor control portion of the steering device according to the embodiment.

 As shown in FIG. 1, the steering apparatus in one embodiment basically includes a steering wheel SW, a pinion gear P1 connected to the steering wheel SW via a gear box G1, a motor M as an actuator, A pinion gear P2 connected to the motor M via a gear box G2, a rack R driven by the rotational movement of each of the pinion gears P1 and P2, and a tie rod 8 and a knuckle arm 9 to both ends of the rack R Torque sensor 1 for detecting the operating torque of the wheels W, W and the steering wheel SW, a speed sensor 2 for detecting the traveling speed of the vehicle, a rotation angle sensor 3 for detecting the rotation angle of the motor M, and a torque sensor 1, a control unit 5 that processes signals input from the speed sensor 2 and the rotation angle sensor 3 and controls driving of the motor M.

  The steering wheel SW will be described in detail below. As shown in FIG. 1, the input shaft 10 of the gear box G1 is connected to the center of the steering wheel SW, and the gear box G1 outputs the rotation of the input shaft 10 at a predetermined reduction ratio. It is transmitted to the shaft 11. A pinion gear P <b> 1 is connected to the other end of the output shaft 11. Therefore, the rotational speed of the steering wheel SW is decelerated by the gear box G1 and transmitted to the pinion gear P1, and the pinion gear P1 meshes with a rack R that is slidably attached to the vehicle.

  A torque sensor 1 is attached to the gear box G1, and the torque sensor 1 can detect an operation torque when the steering wheel SW is rotated. The torque sensor 1 may be any sensor that can measure the strain of the input shaft 10 and the output shaft 11 and can output a changed voltage, current, or the like as a signal. For example, a strain gauge or a load cell may be used. .

  On the other hand, a general thing can be used for the motor M as an actuator. For example, when it is configured as a brushless motor, although not specifically shown, the shaft M1 is rotatably inserted into the frame. And a coil wound around a core attached to the frame, and a plurality of magnets attached to the shaft M1, and the magnets are provided to face the coil and the core. The coil of the motor M is connected to the control unit 5. Although the motor M has been described as a brushless motor, other motors such as a DC brush motor and an AC motor can be used. The shaft M1 is provided with a rotation angle sensor 3 for detecting the rotation angle θ of the shaft M1 as means for detecting the wheel steering angle φ. The rotation angle sensor 3 is, for example, a resolver, a hall element, or a rotary device. An encoder or the like may be used, and the rotation angle sensor 3 is connected to the control unit 5 so that a signal that is a current or a voltage can be output to the control unit 5. Although the wheel steering angle φ may be directly detected, the motor M is mechanically coupled to the wheels W and W via the pinion gear P2 and the rack R, so that the rotation angle θ of the motor M is Since the corresponding wheel steering angle φ is uniquely determined, the rotation angle θ of the motor M can be controlled as a reference.

  Further, the shaft M1 of the motor M is connected to one end of the electromagnetic clutch D, the other end of the electromagnetic clutch D is connected to the input shaft 20 of the gear box G2, and the gear box G2 has a predetermined reduction ratio. The rotation of the input shaft 20 is transmitted to the output shaft 21. A pinion gear P2 is connected to the other end of the output shaft 21. Therefore, the rotational speed of the motor M is decelerated by the gear box G2 and transmitted to the pinion gear P2, and the pinion gear P2 meshes with a rack R that is slidably attached to the vehicle.

  As described above, when the steering wheel SW and the motor M are operated and driven, the rack R can move in the left-right direction in FIG. 1, and both ends of the rack R are connected to the tie rods 8. The end portion is connected to the wheels W and W via the knuckle arm 9. Therefore, when the rack R is moved with respect to the vehicle as described above, the wheels W and W are configured to be steered at the same steering angle, which is a so-called rack and pinion type steering mechanism. In the above description, the steering mechanism is a rack and pinion type, but it may be a ball screw type, and the link mechanism between the wheels W and W and the rack R is a so-called rack and pinion type in the present embodiment. However, other known link mechanisms such as a center arm type and a cross link type may be used.

  Next, the control unit 5 will be described. The control unit 5 is connected to the torque sensor 1, the rotation angle sensor 3, and the motor M, and is connected to a speed sensor 2 that detects the traveling speed of the vehicle.

  The control unit 5 only needs to be able to receive signals from the torque sensor 1, the rotation angle sensor 3, and the speed sensor 2 and to output a current or voltage necessary to drive the motor M. Specifically, although not shown as hardware, an amplifier for amplifying signals from the torque sensor 1, the rotation angle sensor 3 and the speed sensor 2, a converter for converting an analog signal into a digital signal, a low frequency and a high frequency It is composed of a band-pass filter for cutting components, a CPU, a storage device such as a ROM, a RAM, a crystal oscillator, and a bus system for connecting them, and a drive circuit for driving the motor M. Arithmetic processing procedures and control signal output procedures necessary for control are stored in advance in a ROM or other storage device as a program. It may be the well-known system to keep.

  In the case of the motor M as a brushless motor, the drive circuit includes, for example, a PWM circuit connected to a voltage source, a base drive circuit connected to the PWM circuit, a transistor inverter connected to the base drive circuit, and a hall A well-known device composed of a rotation logic to which an element or the like is connected can be used, and another device that can adjust the amount of current according to the type of the motor can be used.

  In the steering device configured as described above, when the driver rotates the steering wheel SW, the control unit 5 drives the motor M to drive the auxiliary torque in the same direction as the direction of rotation of the steering wheel SW. It is possible to assist the operation force to the steering wheel SW, which is a burden on the user. In other words, the present invention is embodied in a so-called power steering device that power assists the rotation operation of the driver's operation wheel SW.

  On the other hand, when no operation torque is input to the steered wheels SW after steering, that is, when the torque detected by the torque sensor 1 is 0 or near 0, the rotation angle θ detected by the rotation angle sensor 3 is detected. From the state where the wheel maintains the wheel steering angle φ corresponding to the rotation angle θ of the motor M from the self-aligning torque until the wheel returns to the neutral state. Since this is the so-called wheel return time, the following return control is performed.

  Specifically, the return control described above is controlled according to the control procedure shown in FIG. This control procedure is stored in advance in the storage device of the control unit 5 as described above.

  The control procedure will be described below. First, in step F1, the rotation angle θ of the motor M is read and temporarily stored in the storage device. The control unit 5 recognizes in which direction the wheels W and W are currently steered by the rotation angle θ of the motor M.

  In this case, the rotation angle θ is set to 0 when the wheels W and W are in the neutral position, and can take positive and negative values when the wheels W and W are steered. Specifically, the rotation angle θ is recognized every time the shaft M1 rotates in the forward direction because the rotation angle cannot be recognized when the shaft M1 of the motor M rotates 360 degrees or more due to the structure of the sensor. The process of adding 360 degrees to the rotation angle may be performed by the control unit 5. Alternatively, a measuring means for measuring the moving distance may be provided on the rack R side, and the accurate rotation angle θ of the motor M may be detected from the measured value.

  Subsequently, the process proceeds to step F2, and in step F2, it is determined whether or not the wheel is returning. As a determination method, as described above, it is determined based on signals output from the torque sensor 1 and the rotation angle sensor 3. If it is determined that the wheel is not returning, the process returns to step F1, and if it is determined that the wheel is returning, the process proceeds to step F3.

  In step F3, a map showing the relationship between the rotation angle θ from the wheel return and the travel distance X from the wheel return shown in FIG. 3 is referred to and corresponds to the current rotation angle θ of the motor M. The initial value X0 of the travel distance is determined. Here, the map showing the relationship between the rotation angle θ from the wheel return time and the travel distance X from the wheel return time will be described. If the hand is released from the steering wheel after steering, The aligning torque causes the wheel to return to the neutral position. The ideal trajectory Z of the vehicle at this time is as shown in FIG. 4, and the vehicle does not have the required travel distance until the wheel steering angle φ when the steered front wheel returns returns from φ1 to 0. There is a certain relationship between the travel distance φ1 and the required travel distance of the wheel steering angle φ.

  Theoretically, the travel distance required for the wheel steering angle φ to be strictly zero becomes infinite with only the self-aligning torque, and the steering device or the like is actually only with the self-aligning torque. Since the wheel steering angle φ is not completely zero due to the frictional resistance of the vehicle, the vehicle travels from the wheel steering angle φ until the wheel steering angle φ reaches an angle that does not impede the straight travel of the vehicle from φ1. The relationship between the practical required travel distance and the wheel steering angle φ may be the above-described constant relationship.

  Then, replacing the above-described constant relationship between the wheel steering angle φ and the practical required travel distance with the relationship between the rotation angle θ of the motor M and the required travel distance X instead of the wheel steering angle φ, 3 is a map showing the relationship between the change in the rotation angle θ shown in FIG. 3 and the travel distance X from when the wheel returns. That is, when the magnitude of the rotation angle θ at the time of return is θ0, the required travel distance from the return time required for the rotation angle θ to change from θ0 to 0 is the distance L, The value of the travel distance X becomes X0 corresponding to when the rotation angle θ is θ0.

  That is, in this step F3, the initial value X0 of the travel distance is calculated from the map and the magnitude of the rotation angle θ when the wheel returns, and is stored in the storage device of the one-end control unit 5.

  In order to obtain the map, the vehicle to which the steering device is applied is actually run, the change of the wheel steering angle φ and the running distance X due to the self-aligning torque are measured, and the change of the wheel steering angle φ and the running are measured. What is necessary is just to obtain | require the relationship with the distance X, and also to convert into the relationship between the rotation angle θ of the motor M corresponding to the wheel steering angle φ and the travel distance X.

  Further, the map may be obtained from analysis or theoretical calculation of a suspension mechanism that affects the magnitude of the self-aligning torque.

  Then, the process proceeds to step F4 to calculate the travel distance L required until the rotation angle θ becomes zero. Since the required travel distance L is the difference between the initial travel distance X0 of the map and the travel distance X value Xe when the rotation angle θ is 0, as described above, the CPU stores it in step F3. The initial value X0 is read and the required travel distance L = Xe−X0 is calculated. The calculated required travel distance L at this time is stored in the storage device of the control unit 5.

  Further, the process proceeds to step F5. In step F5, the vehicle travel speed obtained from the signal output from the speed sensor 2 from the time of returning the wheel is integrated to calculate the travel distance LA from the time of returning the wheel. , Map calculation is performed on the magnitude θ1 of the rotation angle θ corresponding to the travel distance X1 obtained by adding the travel distance LA to the initial value X0, and the process proceeds to step F6. In this embodiment, since it is more systemically efficient to use the speed sensor 2 that would normally be mounted for a vehicle attitude control device or the like, the speed detected by the speed sensor 2 is integrated. However, the travel distance may be calculated from the wheel rotational speed and the wheel diameter by detecting the rotational speed of one or both of the wheels W and W.

  In step F6, the control unit 5 controls the drive of the motor M so that the rotation angle θ is θ1. Specifically, as shown in FIG. 5, the control in step F <b> 6 is performed by the control unit 5 giving a drive command to the motor M using the rotation angle θ of the motor M as feedback. In the block diagram shown in FIG. 5, the rotation angle θ is controlled as feedback. However, the current or voltage may be controlled as feedback. In the above description, the rotation angle θ is controlled. However, the rotation angle θ may be controlled by controlling the torque generated by the motor M.

  Further, in the above description, the control is performed based on the rotation angle θ of the motor M, but the control may naturally be performed based on the wheel steering angle φ.

  The above is the control processing procedure at the time of returning the wheel. When the driver rotates the steering wheel SW after the start of the return control, normal power assist control is performed in preference to the return control.

  Therefore, in the steering device of the present embodiment, it is possible to realize a natural change in the wheel steering angle φ when the wheels W, W return to the neutral position by the self-aligning torque. That is, the return condition of the wheels is improved, and natural steering characteristics can be realized. In other words, since the wheel return due to self-aligning torque includes friction of the steering mechanism, road surface disturbance, etc., the effects of the steering mechanism friction and road surface disturbance are compensated by controlling the wheel steering angle. It is done.

  Since the wheel steering angle is controlled, the wheel can be reliably returned to the neutral position. That is, the harmful effect of the wheel returning too much or insufficiently returning is eliminated.

  In addition, when the mileage required when the wheel returns to the neutral position is also included in the control, the phenomenon that the wheel is returned to the neutral position due to self-aligning torque can be faithfully reproduced, and more precisely The change of the wheel steering angle φ when the wheels W, W return to the neutral position by the self-aligning torque can be realized, and thereby more natural steering characteristics can be realized.

  The above-mentioned control is based on the concept of faithfully reproducing the phenomenon that the wheels are returned to the neutral position by the self-aligning torque, so there is no need to bother to calculate and detect the self-aligning torque. Fewer parameters to do. Therefore, the control is also simplified.

  Furthermore, since a large number of parameters are not required as in the prior art, there is no adverse effect such as deterioration in control accuracy and variations due to errors in detecting a large number of parameters.

  Further, when the map calculation is performed using the map indicating the relationship between the change in the wheel steering angle φ and the travel distance X, the calculation during the control is simplified, so that the control is further simplified.

  Furthermore, when the steering wheel SW is mechanically coupled to the wheels W and W, the steering wheel SW also follows the wheels W and W, and thus return control is performed. At the same time, the steering wheel SW can be reliably returned to the neutral position. Furthermore, since the driver can also feel that the steering wheel SW is naturally returned by the self-aligning torque, it is possible to prevent the driving vehicle from feeling uncomfortable.

  When the rotation angle θ of the motor M is continuously monitored and the wheel steering angle φ at the wheels W and W changes significantly due to some disturbance during return control, that is, when the rotation angle θ of the motor M changes significantly. If it returns to step F1 and returns control is performed from the beginning, it will become possible to deal with, for example, the case where the wheels W, W ride on curbs or small protrusions.

  In the case of the present embodiment, as described above, the steering device of the present embodiment may be controlled based on the wheel steering angle φ in addition to the control based on the rotation angle θ of the motor M. In this case, instead of the rotation angle θ and the wheel steering angle φ, the movement distance of the rack R mechanically connected to the wheels W and W, the rotation angle of the steering wheel SW, or the movement of the rack R Control may be performed by estimating the wheel steering angle φ from the distance or the rotation angle of the steering wheel SW.

  In the above-described embodiment, the steering device is embodied as a power steering device that performs power assist. However, the steering device is not based on the steering angle of the steering wheel SW but based on the wheel steering angle φ of the wheels W and W. Since control is performed, for example, a steer-by-wire steering device can be realized. Specifically, a reaction force motor for applying an operation reaction force to the operation wheel is attached to the operation wheel side, while only a motor for steering the wheel is provided on the rack side, and the wheel steering angle is set during return control. The motor to be controlled and the reaction force motor may be driven in synchronization.

  Further, in the present embodiment, the motor M is used as the actuator and the steering device is a so-called electric power steering device. However, the present invention can also be applied to a hydraulic steering device. In this case, the actuator is a hydraulic cylinder or the like. The wheel steering angle φ or the stroke of the hydraulic cylinder may be used as a reference.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

It is a schematic diagram of a steering device in one embodiment. It is a flowchart which shows the control procedure of the steering device in one embodiment. It is a map which shows the relationship between the change of the rotation angle of the motor used for the map calculation of control of the steering device in one embodiment, and travel distance. It is a figure which shows the locus | trajectory of a vehicle when a wheel returns to a neutral position by self aligning torque. It is a control block diagram of the motor control part of the steering device in one embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Torque sensor 2 Speed sensor 3 Rotation angle sensor 5 Control part 8 Tie rod 9 Knuckle arm 10,20 Input shaft 11,21 Output shaft G1, G2 Gear box P1, P2 Pinion gear M Actuator motor M1 Shaft R Rack SW Steering wheel W Wheel

Claims (8)

A steering apparatus including an actuator capable of controlling a wheel steering angle of a wheel in a vehicle, wherein the wheel steering angle is controlled based on at least the wheel steering angle when the wheel returns when the wheel returns. In a steering apparatus having an actuator capable of controlling the wheel steering angle of a wheel in a vehicle, the wheel steering angle is controlled based on the wheel steering angle when the wheel returns and the travel distance from the wheel return when the wheel returns. Steering device. The steering according to claim 1 or 2, wherein the wheel steering angle is controlled on the basis of a map indicating a relationship between a wheel steering angle from a wheel return time and a travel distance from the wheel return and a wheel steering angle at the time of return. apparatus. The steering apparatus according to claim 1 or 2, wherein a traveling distance required until the wheel steering angle becomes a neutral position from the wheel steering angle when the wheel returns is calculated, and the wheel steering angle is controlled based on the calculation result. From the map showing the relationship between the wheel steering angle from the wheel return and the travel distance from the wheel return and the wheel steering angle from the return until the wheel steering angle becomes a neutral position from the wheel steering angle at the wheel return 4. A steering apparatus according to claim 3, wherein a travel distance required for the vehicle is calculated as a map, and the wheel steering angle is controlled based on the calculation result. The steering apparatus according to any one of claims 1 to 5, wherein a wheel steering angle is controlled by controlling a torque generated by an actuator. The steering device according to any one of claims 1 to 6, wherein the actuator is a motor, and the wheel steering angle is controlled based on a rotation angle of the motor corresponding to the wheel steering angle. The steering apparatus according to any one of claims 1 to 7, further comprising a steering mechanism in which the steering wheel and the wheel are mechanically coupled.

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