JP2004330840A - Steer-by-wire type steering system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steer-by-wire type steering system simplifying a lock mechanism. <P>SOLUTION: The steer-by-wire type steering system (S) is equipped with a steered drive means (2) steered-driving a steered wheel (4), a steering wheel (1), a steering resistance applying means (19) applying on the steering wheel, and drive control means (20, 23) drive-controlling the steering resistance applying means. The steering resistance applying means consists of a motor (M) and the drive control means has a shortcircuit means (232) which sets an armature coil of the motor into the shortcircuit state when an ignition switch is turned off or the like. Electromagnetic brake is actuated on the motor by the shortcircuit of the armature coil, and locking of the steering wheel is electrically simply performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steer-by-wire steering system in which a steering wheel and a steered wheel are not mechanically connected.
[0002]
[Prior art]
2. Description of the Related Art In a steering system of a vehicle such as an automobile, when a driver of the vehicle steers a steering wheel, a front wheel or the like of the vehicle is steered, and a traveling direction of the vehicle changes. In the case of a conventional steering system, a transmission system from the steering wheel to the steered wheels is mechanically connected via a plurality of shafts, links, and the like. This is the same even when a power steering device or the like is interposed between the two.
[0003]
However, as disclosed in Patent Documents 1 and 2 and the like, a steering system using a steer-by-wire system that does not mechanically connect a steering wheel to a steered wheel has been proposed. In this steering system, a steering amount of a steering wheel is electrically detected, a control unit (ECU) calculates a steering angle of a steered wheel based on the detection signal, and drives an actuator mechanically independent of the steering wheel. By controlling, the steered wheels are steered. When such a steer-by-wire is employed, the arrangement of various devices constituting the steering system, the degree of freedom in design, and the like are expanded, and it is easy to reduce the size of the entire steering system.
[0004]
[Patent Document 1]
JP 2001-106111 A [Patent Document 2]
JP-A-2003-2224
[Problems to be solved by the invention]
By the way, when such a steer-by-wire steering system is employed, the steering wheel and the steered wheels are not mechanically connected, so that when the main power supply of the vehicle (such as an ignition switch of the vehicle) is turned off, the steering operation is performed. The steering wheel and the steered wheels are free. That is, only the steering wheel can freely rotate with respect to the steered wheels. Therefore, for example, when the driver turns off the ignition switch and gets off the vehicle, the steered wheels hardly displace due to the resistance between the steered wheels and the steering wheel, and no reaction force acts on the steering wheel. Therefore, even if the driver only touches the steering wheel, the steering wheel turns slightly. As a result, the correspondence between the steering amount of the steering wheel and the turning angle of the steered wheels is shifted from when the ignition switch is turned off. If this deviation is within a range assumed in advance, it is easy to return to the OFF state when the ignition switch is turned on again. However, as described above, since the steering wheel is lightly steered, only the steering wheel is largely rotated, and a situation in which the above-mentioned deviation exceeds an assumed range is expected. When the ignition switch is turned on again after such a situation has occurred, the driver feels a sense of discomfort unlike the case where the center position of the steering wheel is turned off.
[0006]
The present invention has been made in view of such circumstances, and provides a steer-by-wire steering system that can suppress unintentional rotation of a steering wheel even when a power switch is turned off or the like. The purpose is to:
[0007]
Means for Solving the Problems and Effects of the Invention
The inventor of the present invention has conducted intensive studies to solve this problem, and as a result, even when the power is turned off or the like, the steering wheel is free to operate by short-circuiting the armature coil of the drive motor that applies the steering resistance to the steering wheel. The inventors came up with the idea that rotation and the like can be suppressed, and developed this to complete the present invention.
That is, a steer-by-wire steering system according to the present invention includes a steering drive unit that steers the steered wheels of a vehicle, a steering wheel that is steered by a driver of the vehicle, and steering at least in accordance with a driving state of the vehicle. A steer-by-wire steering system comprising: steering resistance applying means for applying resistance to the steering wheel; and drive control means for controlling the driving of the steering resistance applying means in accordance with the driving situation of the vehicle.
The steering resistance applying means includes a motor main shaft that rotates in conjunction with the steering amount of the steering wheel, a field forming a magnetic field, and an armature coil in which a magnetic flux extending from the field is linked. The drive control means comprises a short-circuit means for short-circuiting the armature coil, the drive control means comprising a short-circuit means for changing the magnetic flux linked to the armature coil by rotation of the motor main shaft, and driving the steering resistance applying means. When the control is completed, the short-circuit means is operated.
[0008]
According to the steer-by-wire steering system (hereinafter, simply referred to as “steering system” as appropriate) of the present invention, when the drive control means is normally operated (ie, in the ON state), the steering resistance is applied to the steering wheel by the steering resistance applying means. Is given. Specifically, the drive motor constituting the steering resistance applying means exerts an appropriate reaction force (steering resistance) in the direction opposite to the steering direction of the steering wheel. Thus, even with steer-by-wire, the driver of the vehicle obtains a steering feeling similar to that of a conventional steering system in which the steering wheel to the steered wheels are mechanically connected. When the driver steers the steering wheel against the steering resistance, the steering driving means is driven in accordance with the steering amount, and the steered wheels are displaced to a desired steering angle.
[0009]
Next, it is assumed that the power supply or the control is turned off by an ignition switch or the like, and the drive control by the drive control means is terminated. In this state, the steering resistance does not act on the steering wheel. However, when the steering wheel is steered in this state, the motor main shaft associated therewith is rotated. Then, the linkage magnetic flux that exits from the field and links to the armature coil changes with time, and an electromotive force is generated in the armature coil by electromagnetic induction according to the time change rate.
Here, in the case of the steering system of the present invention, the armature coil constituting the drive motor of the steering resistance applying means is short-circuited by the short-circuit means. For this reason, an exciting current flows through the armature coil, and an electromagnetic force acts in a direction that prevents a change in linkage magnetic flux. That is, a braking action is generated in a direction that prevents rotation of the steering wheel and the like.
[0010]
As described above, in the steering system of the present invention, even when the above-described drive control is completed, the braking action is naturally generated due to the rotation of the steering wheel, and the steering wheel is substantially locked to the steered wheels. , And the situation in which the phase between the two is shifted unexpectedly is avoided. Moreover, miniaturization and cost reduction can be easily achieved as compared with the case where a mechanical lock mechanism or the like is provided.
[0011]
By the way, the brake acting on the steering wheel at the end of the drive control becomes stronger as the time rate of change of the interlinkage magnetic flux is larger. Therefore, it is preferable that the steering resistance applying means includes a speed reducer between the drive motor and the steering wheel for reducing and transmitting the power from the drive motor to the steering wheel. When viewed from the steering wheel side, the rotation amount of the motor main shaft is increased with respect to the steering amount of the steering wheel, so that a larger brake acts on the steering wheel. Of course, in order to enhance the braking action, a high-performance magnet such as a rare earth magnet may be used for the field, or the number of turns of the armature coil may be increased.
[0012]
The drive motor in the present invention may be a direct current (DC) motor or an alternating current (AC) motor. One example is a brushless motor. When the rotor rotating together with the main shaft of the motor is a field, the stator becomes an armature, but the combination may be reversed. The field of the drive motor is not limited to a permanent magnet, but may be a field coil. However, a permanent magnet is preferable from the viewpoint of miniaturization and power saving. The armature coil has a single phase or three or more phases depending on the type of the drive motor. For example, in the case of the DC brushless motor, the armature coil generally has three or more phases.
[0013]
The steering handle is not limited to a well-known circular steering wheel, but may be a reciprocating steering lever or the like. In response to this, the steering amount of the steering wheel becomes the steering angle or the linear steering displacement. In any case, the steering amount is a directional displacement (the steering angle and the like are the same). The amount of steering is detected by a rotation angle sensor, a potentiometer, or the like, and an electrical detection signal is transmitted to the drive control means.
[0014]
The steering drive means may use, for example, a ball screw or a rack and pinion, or may use a hydraulic actuator. As a basic structure, a conventional electric / hydraulic power steering device can be used.
The drive control means includes, for example, an electronic control unit (ECU) and a drive circuit device for driving a drive motor of the steering resistance applying means. The driving state of the vehicle is, for example, vehicle speed, ON / OFF of an ignition switch, and the like. This drive control means may control not only the steering resistance applying means but also the steering drive means.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in more detail with reference to embodiments.
FIG. 1 shows the overall configuration of a steer-by-wire steering system S (hereinafter, referred to as “steering system S”) according to an embodiment of the present invention.
The steering system S includes a steering wheel 1 (steering handle), a steering actuator 19 (steering resistance applying means) for applying a reaction force (steering resistance) and a returning force to the steering wheel 1 via a shaft 10, and A steering drive circuit 23 that drives a steering actuator 19, an electronic control unit (ECU) 20 that controls the steering drive circuit 23, and a steering actuator 2 (a steering device) that drives the front wheels 4 that are the steered wheels by motor similarly to the electric power steering. Rudder driving means), a knuckle arm 9, a tie rod 8, a steering rod 7, and a steering gear 3 interposed between the front wheel 4 and the steering actuator 2, and a steering controlled by the ECU 20 to drive the steering actuator 2. Drive circuit 22.
[0016]
The ECU 20 and the steering drive circuit 23 correspond to the drive control means in the present invention. A vehicle speed signal is input from an external vehicle speed sensor 14 to the ECU 20, a steering angle signal is input from a steering angle sensor 11 including a rotary encoder or the like attached to the steering wheel 1, and the ECU 20 is attached to a housing of the steering gear 3. A turning angle signal is input from a turning angle sensor 13 including a potentiometer and the like. The computer in the ECU 20 sends a command for operating the steering actuator 19 and the steering actuator 2 to the steering drive circuit 23 and the steering drive circuit 22 based on these input signals.
[0017]
The steering actuator 19 includes a three-phase DC brushless motor M (hereinafter simply referred to as “motor M”) as a drive motor, and a speed reducer G interposed between the motor M and the steering wheel 1.
Although not shown in detail, the motor M has a motor main shaft penetrating the center, a four-pole permanent magnet (field) disposed around the motor main shaft, and a predetermined air gap around the outer periphery. It is composed of three iron cores provided and evenly arranged, and a coil (armature coil) wound therearound. The motor main shaft and the permanent magnet form the rotor of the motor M, and the iron core and the coil form the stator of the motor M.
[0018]
The reduction gear G is composed of a planetary gear whose ring gear side is fixed to the housing. The sun gear of the speed reducer G is connected to the motor main shaft of the motor M, and the carrier that supports the planetary gear of the speed reducer G is connected to the shaft 10 on the steering wheel 1 side. As is clear from FIG. 1, the steering system on the steering wheel 1 side and the turning system on the front wheel 4 side are only electrically connected, and are not mechanically connected.
[0019]
Next, the circuit configuration of the steering drive circuit 23 will be described with reference to FIG.
The steering drive circuit 23 includes an inverter circuit 231 composed of a switching element and a short circuit 232 for short-circuiting each coil of the motor M. The inverter circuit 231 converts a direct current supplied from a battery or the like into a three-phase alternating current of a U-phase, a V-phase, and a W-phase by switching a plurality of switching elements. Thus, the U-phase, V-phase, and W-phase excitation currents are supplied to the three coils of the motor M.
[0020]
The short-circuit 232 (short-circuit means) includes a short-circuit relay R1 connected between the U-phase coil and the V-phase coil of the motor M, and a short-circuit relay R2 connected between the V-phase coil and the W-phase coil. Become.
[0021]
The operation of the short circuit 232 will be described below.
It is assumed that the driver turns off the ignition switch (IG) and gets off the vehicle. At this time, the ECU 20 issues a command to the turning drive circuit 22 to operate the short-circuit relays R1, R2, and then ends the control of the steering actuator 19. Upon completion of this control, each coil of the motor M is brought into a short-circuit state by the short-circuit relays R1, R2.
[0022]
At this time, if the driver tries to rotate the steering wheel 1 carelessly, the rotation is transmitted from the shaft 10 to the motor main shaft of the motor M via the speed reducer G. Here, each coil of the motor main shaft is in a short-circuit state by the short-circuit relays R1 and R2. For this reason, when the flux linkage of each coil changes due to the rotation of the motor main shaft, a back electromotive force is generated between the coils, an induced current flows, and an electromagnetic force in a direction that hinders the rotation of the motor main shaft is applied to the motor main shaft. Will be affected. In other words, when the driver turns the steering wheel 1 after turning off the ignition switch, a large reaction force acts on it. In addition, the rotation of the steering wheel 1 is increased in speed and transmitted to the motor main shaft by the intervention of the speed reducer G, so that the reaction force is considerably large.
[0023]
Thus, the rotation of the steering wheel 1 is hindered without intervening a mechanical lock mechanism or the like. That is, even when the control of the steering actuator 19 is in the OFF state, occurrence of a large deviation between the steering angle of the steering wheel 1 and the turning angle of the front wheels 4 is suppressed. Each timing when such control is performed is shown in FIG. 3 for reference. As described in FIG. 3, in the present embodiment, when the ignition switch is turned ON, the short-circuit relay OFF is slightly later than the control ON. Therefore, at that time, the steering wheel 1 becomes difficult to rotate. When the ignition switch is turned off, the short-circuit relay ON is slightly earlier than the control OFF. Therefore, similarly, the steering wheel 1 becomes difficult to rotate.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a steer-by-wire steering system according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a steering drive circuit in the embodiment.
FIG. 3 is a timing chart when an ignition switch is turned on / off in the embodiment.
[Explanation of symbols]
1 Steering wheel (steering wheel)
2 Steering actuator (steering drive means)
19 Steering actuator (steering resistance applying means)
20 ECU (drive control means)
23 Steering drive circuit (drive control means)
232 short circuit (short circuit)
R1, R2 Short-circuit relay M Drive motor G Reducer S Steer-by-wire steering system

Claims (2)

Turning drive means for turning the steered wheels of the vehicle;
A steering wheel steered by a driver of the vehicle;
Steering resistance applying means for applying at least a steering resistance according to a driving condition of the vehicle to the steering wheel;
A steer-by-wire steering system, comprising:
The steering resistance applying means has a motor main shaft that rotates in conjunction with a steering amount of the steering wheel, a field forming a magnetic field, and an armature coil in which a magnetic flux extending from the field interlinks. It consists of a drive motor whose magnetic flux linked to the armature coil changes by rotation of the motor main shaft,
The drive control means includes short-circuit means for short-circuiting the armature coil, and activates the short-circuit means when ending the drive control of the steering resistance applying means. . The steer-by-wire steering system according to claim 1, wherein the steering resistance applying means includes a speed reducer between the drive motor and the steering wheel for reducing and transmitting power from the drive motor to the steering wheel.

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