JP2007190938A - Steering system for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve practicality of a steering system for realizing steering of a wheel producing a steering amount according to the operation amount of a steering operating member by an operation of an actuator. <P>SOLUTION: A target motor rotary angle θ* of the actuator corresponding to a steering angle of the target wheel is determined based on an operation angle δ of the steering operating member. Steering speed of the wheel is limited by correcting the target motor rotary angle θ* based on set upper limit speed so that the steering speed of the wheel may not exceed the set upper limit speed. More particularly, an upper limit motor rotary angle θ<SB>limit</SB>corresponding to the steering angle of the wheel when steering is performed at the set upper limit speed is determined (S6) after determining the target motor rotary angle θ* (S2), whether or not the steering speed is required to be limited is decided by comparing the target motor rotary angle θ* with the upper limit motor rotary angle θ<SB>limit</SB>(S7), and when the limit is required, the target motor rotary angle θ* is corrected to the upper limit motor rotary angle θ<SB>limit</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle steering system that realizes steering of a wheel having a steering amount corresponding to an operation amount of a steering operation member by actuation of an actuator.

In general, when the vehicle is stopped or traveling at a considerably low speed, a large force is required to steer the wheel in a so-called stationary state or a state close thereto. The load on the steering source that performs the steering and the assist source that assists the steering of the wheels is large. Regarding a steering system for dealing with this, there is a technique as described in the following patent document. The technology described in Patent Literature 1 will be briefly described. The technology described in Patent Literature 1 is a steering system including an automatic steering device for automatically parking a vehicle without depending on a steering operation by a driver. Is a technique for preventing overloading of the turning source by stopping the turning source that is turning the wheel when the wheel is stopped. In addition, the technique described in Patent Document 2 is such that the front wheels are steered according to the operation of a steering operation member (hereinafter sometimes simply referred to as “operation member”), and the rear wheel is rearranged based on the steering amount of the front wheel. In a steering system equipped with a four-wheel steering device that steers wheels using a steering source, the steering system is miniaturized by preventing the rear wheels from turning at least when the vehicle is stopped. .
JP 2001-1930 A Japanese Patent No. 2707771

  In recent years, a part of the system called variable gear ratio steering (VGRS), that is, a system provided with a function capable of changing the ratio of the wheel turning amount to the operation amount of the operation member is partly known. Has begun to be adopted in vehicles. In addition, a steer-by-wire (SBW) type steering system, that is, a system in which wheels are steered only by a driving force from a steered source irrespective of an operating force applied to an operating member has been studied. Even in the steering system that realizes the steering of the wheel having the steering amount corresponding to the operation amount of the operation member by the operation of the actuator, when the wheel is steered in a stationary state or a state close thereto, the above-described operation is performed. There is a problem. In the VGRS system, for example, when an assist source for assisting the steering of the wheel is provided, the load on the assist source becomes large. In the SBW system, the load on the steering source becomes large. Thus, these steering systems such as VGRS and SBW still leave sufficient room for improvement in order to improve practicality. This invention is made | formed in view of such a situation, and makes it a subject to improve the practicality of the steering system which determines the steering amount of the wheel according to the operation amount of an operation member so that change is possible.

  In order to solve the above-described problems, a vehicle steering system according to the present invention includes an actuator and a control device that controls the actuator based on an operation amount of the steering operation member. A steering system including a steering device that realizes steering of a wheel serving as a steering amount, wherein the control device controls the actuator so as to limit a steering speed of the wheel within a set upper limit speed. It has a speed limiting part.

  According to the vehicle steering system of the present invention, it is possible to reduce the steering force required to steer the wheel by limiting the steering speed of the wheel, for example, the burden on the system. It becomes possible to reduce. By having such advantages, the vehicle steering system of the present invention is a highly practical system.

Aspects of the Invention

  In the following, some aspects of the invention that can be claimed in the present application (hereinafter sometimes referred to as “claimable invention”) will be exemplified and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is merely for the purpose of facilitating the understanding of the claimable inventions, and is not intended to limit the combinations of the constituent elements constituting those inventions to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiments, etc., and as long as the interpretation is followed, another aspect is added to the form of each section. In addition, an aspect in which some constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention.

  In each of the following items, the item (1) corresponds to the item (1), and the item (9) and the limitation by the technical features of the item (11) are added to the item (1). Claim 1 or Claim 2 with the limitation by the technical feature of (2) is added to Claim 3, and the limitation by the technical feature of (5) is added to any one of Claims 1 to 3. The present invention is limited to claim 4, to which one of claims 1 to 4 is limited by the technical features of (8), to claim 5 and to any one of claims 1 to 5. Claims (12), which are limited by the technical features, correspond to Claim 6 respectively.

(1) a steering operation member;
A steering device that includes an actuator and a control device that controls the actuator based on an operation amount of the steering operation member, and realizes wheel turning with a steering amount corresponding to the operation amount of the steering operation member A vehicle steering system comprising and
The vehicle steering system according to claim 1, wherein the control device includes a turning speed limiting unit that controls the actuator so as to limit a wheel turning speed within a set upper limit speed.

  The aspect described in this section is an aspect in which, even when a fast steering operation is performed, the wheel is not steered at the turning speed corresponding to the operation speed of the operation member, but is steered within the set upper limit speed. For example, in order to steer a wheel having a high steering speed when the vehicle is stopped or traveling at a considerably low speed, the wheel such as a driving force by a steering source that steers the wheel is steered. Therefore, the steering force necessary for this needs to be a large force. However, according to the aspect described in this section, the necessary turning force is reduced by limiting the turning speed of the wheels. In the VGRS system, for example, when an assist source for assisting the steering of the wheel is provided, the assist source can be reduced in size, and in the SBW system, the steering source can be reduced in size. Due to such advantages, the steering system according to the aspect described in this section is highly practical.

  In addition, the control of the “steering speed limiting unit” included in the control device according to the aspect of this section may employ control that limits the steering speed to zero. For example, even when a steering operation is performed, it is possible to employ a control that causes the operation member to idle so that the wheels are not steered at all. If such a control is employed, for example, when the vehicle is in a stopped state, it is possible to avoid stationary. Incidentally, in this case, since the driver recognizes the turning behavior after the vehicle starts to move, after the vehicle starts to travel, the wheels are turned so that the steering amount becomes the steering amount according to the operation amount of the operation member. If steered, the driver will not feel a great sense of incongruity.

  The steering system in the aspect of this section should just be what can change the steering speed of the wheel according to the operation speed of the operation member, for example, the VGRS system explained later, that is, the operation of the operation member, It is possible to employ a steering system that transmits to the turning operation and that can change the operation turning ratio that is the ratio of the wheel turning amount to the operation amount of the operation member. In the case of this aspect, the “steering device” in the aspect of this section is configured to include a VGRS actuator that is a main body that realizes the VGRS function, and the VGRS actuator functions as the “actuator” referred to in this section. Become. In addition, in the case of this aspect, generally, an assisting source for assisting the wheel steering is provided, and the steering force depends on the assisting force of the assisting source, so that the burden on the assisting source can be reduced. is there.

  In addition, the steering system according to the aspect of this section includes an SBW type steering system, that is, a steering as an “actuator” included in the steering device under electrical control regardless of the operating force applied to the operating member. It is also possible to employ a system that realizes wheel steering according to the operation of the operation member by the driving force of the source. In the SBW system, since the operation member and the steering device are not connected so as to be able to transmit the operation, it is possible to easily limit the steering speed. In the case of this aspect, since the turning force depends solely on the driving force of the turning source that turns the wheels, it is possible to reduce the burden on the turning source.

  (2) The control device includes a target turning amount determination unit that determines a target turning amount that is a turning amount of a target wheel based on an operation amount of the steering operation member, and the turning speed limit The vehicle steering system according to item (1), wherein the unit corrects the target turning amount based on the set upper limit speed.

  For example, the operation member corresponding to the difference between the target turning amount determined in the target turning amount determination unit and the target turning amount corrected in the turning speed limit unit It can be considered that the operation is idle by the operation amount. According to the aspect of this section, it is possible to perform appropriate steering with limited steering speed.

  (3) The target turning amount determination unit changes the operation turning ratio, which is a ratio of the wheel turning amount to the operation amount of the steering operation member, according to the traveling speed of the vehicle. The vehicle steering system according to item (2), which determines the amount.

  According to the aspect described in this section, even if the steering amount is the same, the operation amount of the operation member can be changed depending on the vehicle traveling speed, so that appropriate steering is possible.

  (4) The target turning amount determination unit determines the target turning amount so that the operation turning ratio becomes smaller as the traveling speed of the vehicle becomes higher. Steering system.

  In general, when the vehicle traveling speed is relatively low, a large turning of the wheel may be performed at the time of a U-turn or the like. It is desirable to steer the wheels relatively large. Conversely, when the vehicle traveling speed is high, large steering of the wheels is a factor that impairs the stability of the vehicle. Therefore, it is desirable to steer the wheels relatively small even when the amount of operation is large. . In other words, according to the aspect of this section, it is possible to reduce the burden on the driver for performing a large amount of operation and to ensure the stability of the vehicle operation.

  (5) The vehicle steering system according to any one of (1) to (4), wherein the set upper limit speed is set based on a traveling speed of the vehicle.

  If the running speed of the vehicle is different, the turning speed at which a large force is required for turning the wheels is also different. According to the aspect described in this section, since the set upper limit speed is set based on the traveling speed of the vehicle, for example, as the traveling speed of the vehicle changes, the turning speed is set according to the traveling speed. If the speed is controlled, the steering speed can be limited in accordance with the actual situation.

  (6) The vehicle steering system according to (5), wherein the set upper limit speed is set so as to decrease as the traveling speed of the vehicle decreases.

  The force required to steer the wheels increases as the vehicle approaches the stop state. In the aspect described in this section, since the set upper limit speed is set to an appropriate magnitude according to the traveling speed, it is possible to limit the appropriate steering speed according to the actual situation as described above.

  (7) The steering system for a vehicle according to (6), wherein the turning speed restriction unit restricts the turning speed when the running speed of the vehicle is equal to or less than a set threshold running speed.

  If the traveling speed of the vehicle is high, the wheels can be steered with a small force. That is, the aspect described in this section functions only when the steered speed limiter really wants to limit the steered speed.

  (8) The set upper limit speed is set based on a slip between a road surface and a tire contact surface determined based on a running speed of the vehicle and tire rigidity. The vehicle steering system described.

  When the wheel is steered, the tire is torsionally deformed as an elastic body, and when the amount of deformation reaches a limit, slip occurs between the road surface and the ground contact surface of the tire. Note that the slip occurs even when the turning speed is extremely low in the stopped state, and occurs at a lower turning speed as the traveling speed is lower. In the aspect described in this section, for example, the set upper limit speed can be set to a speed at which the amount of deformation of the tire is maximum and the slip between the road surface and the tire contact surface starts to occur. According to the aspect described in this section, it is possible to set the set upper limit speed to an appropriate magnitude, and it is possible to limit the appropriate steering speed in accordance with the actual situation.

(9) The steering device includes an operation conversion mechanism that converts a transmission operation of an operation amount according to the operation amount of the steering operation member transmitted to the steering device into a steering operation of a wheel,
The actuator is
A transmission ratio change actuator that is provided between the steering operation member and the operation conversion mechanism and changes a transmission ratio that is a ratio of an operation amount of a transmission operation to the operation conversion mechanism with respect to an operation amount of the steering operation member; The vehicle steering system according to any one of items (1) to (8).

  The aspect described in this section is an aspect in which the system has a VGRS function. The “transmission ratio changing actuator” in this section is a main body that realizes the VGRS function, and is a so-called VGRS actuator. The specific configuration of the transmission ratio changing actuator is not particularly limited. For example, an actuator configured to include a differential mechanism and a driving source as described later can be adopted. . In the aspect described in this section, in order to set the turning speed to 0, for example, the operation ratio is set to 0, that is, the operation member is set so that the operation amount of the transmission operation to the operation conversion mechanism becomes 0. It can be realized by making it idle. Further, the configuration of the “motion converting mechanism” in this section is not particularly limited, and includes, for example, a steered rod that connects wheels and a mechanism that moves the steered rod in the axial direction. It is possible to employ various configurations already known. As a mechanism for moving such a steered rod, for example, a rack and pinion mechanism or the like can be employed.

(10) The transmission ratio changing actuator is
(a) a first element provided so as to be capable of an operation amount corresponding to an operation amount of the steering operation member; (b) a second element provided so as to be capable of relative operation with the first element; A differential mechanism including a first element and a third element engaged with the second element; and a drive source for driving the third element, wherein the first element and the second element The vehicle steering system according to item (9), wherein the transmission ratio is changed by changing a relative movement amount with respect to the element in accordance with a driving amount of the third element.

  The mode described in this section is a mode in which the configuration of the transmission ratio changing actuator is limited. The aspect of this section has an advantage that the structure of the transmission ratio changing actuator is compact. The configuration of the “differential mechanism” in this section is not particularly limited. For example, the first element and the second element rotate relative to each other, and the third element engages with them to rotate. It is possible to use a mechanism for Specifically, a mechanism in which a bevel gear meshes, a planetary gear mechanism, a harmonic gear mechanism (sometimes called a harmonic drive mechanism (registered trademark), a strain wave gearing mechanism, a two-ring gear type, or a cup It is possible to adopt various types such as a cycloid reduction mechanism. In the aspect described in this section, in order to set the turning speed to 0, the operation of the first element may be absorbed by the operation of the third element so that the operation is not transmitted to the second element. For example, if the differential mechanism operates as described above, the third element may be driven by the drive source so that the first element idles without rotating the second element.

  (11) The vehicle steering system according to (9) or (10), wherein the motion conversion mechanism includes an assisting source for assisting a steering force of a wheel that depends on a transmission operation to itself.

  The aspect described in this section is an aspect in which the system has a power steering function in addition to the VGRS function described above. In the aspect of this section, the motion conversion mechanism is a main body that realizes the power steering function. When the mechanism is configured to include the steering rod, the motion conversion mechanism is turned by the assist force of the assisting source. It is possible to adopt a configuration that assists the movement of the rod to the left and right. That is, in the aspect described in this section, since the turning force necessary for turning the wheels is reduced, the assisting source can be reduced in size.

  (12) The steering system according to any one of (1) to (11), wherein the steering system includes a steering operation limiting device that limits an operation amount of the steering operation member without depending on a steering amount of a wheel. Vehicle steering system.

  In a general steering system, the operation amount of the steering operation member is configured to be limited when the wheel reaches the limit position of the steering. The aspect described in this section is an effective aspect in the case of such a system. For example, when the turning speed is limited to 0, it is possible to avoid rotating the operation member without limitation. . In addition, when the aspect of this section is a VGRS system, a motor as a drive source is housed in a housing, and the housing is provided with a transmission ratio change actuator structured to rotate with respect to the vehicle body. Can prevent disconnection of a cable for supplying power to the motor.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition to the following examples, the present invention is implemented in various modes including various modes modified and improved based on the knowledge of those skilled in the art, including the mode described in the above [Mode of Invention]. be able to.

<Configuration of steering system>
FIG. 1 schematically shows an overall configuration of a steering system according to an embodiment of the present invention. The steering system can be broadly divided into an operation device 10 and a steering device 12. The steering device 12 includes a steering unit 14 as an operation conversion mechanism, a VGRS actuator 16 as a transmission ratio change actuator, and an electronic control unit 18 (hereinafter sometimes abbreviated as “ECU 18”) as a control device. The steering system is a VGRS system.

  The operation device 10 includes a steering wheel 20 as a steering operation member, and a steering column 22 (hereinafter sometimes simply referred to as “column” 22). The column 22 includes a steering shaft 24 having a steering wheel 20 connected to one end thereof, and a steering tube 26 (hereinafter simply referred to as “tube 26”) as a shaft housing that rotatably holds the steering shaft 24. It is comprised including. The column 26 is fixed to the vehicle body by fixing the tube 26 to the reinforcement of the instrument panel. Further, the shaft 24 is provided with an operation angle sensor 28 that detects an operation angle δ based on the neutral position of the steering wheel 20 as an operation amount of the operation member at a connection portion of the steering wheel 20.

  The steering unit 14 meshes with a housing 30 fixed to a vehicle body (specifically, a chassis), a pinion shaft 32 as an input shaft to which rotation from the operation device 10 side is input, and a pinion of the pinion shaft 32. A rack is formed, and the housing 30 is configured to include a steered rod 34 that is movable in the axial direction (the left-right direction of the vehicle). That is, the steering unit 14 is of a rack and pinion type, and the turning rod 34 is moved in the axial direction by the rotation of the pinion shaft 32. Further, both end portions of the steered rod 34 are connected to one end portions of the left and right tie rods 38 via ball joints 36, and the other end portions of the tie rods 38 are connected to the left and right ends via ball joints 40. The steering knuckle 44 that holds each of the steered wheels 42 is connected to a knuckle arm portion 46 included in each of the steering knuckles 44. Further, the steered unit 14 includes an assist mechanism 50 that assists the steered force required to steer the wheels 42, and is configured to assist the axial movement of the steered rod 34. Although not shown in detail, a ball screw (male screw) is formed on the steered rod 34, and the steered unit 14 has a bearing ball in the housing 30 and is screwed into the ball screw. And an assist motor 52 as an assisting source for rotating the ball nut. The driving force of the assist motor 52 assists the movement of the steered rod 34. Although illustration is omitted, the pinion shaft 32 includes a torsion bar, and the steering torque T can be estimated based on the twist amount of the torsion bar.

  The VGRS actuator 16 serves to transmit the rotation of the steering shaft 24 that rotates together with the steering wheel 20 to the steering unit 14. The VGRS actuator 16 has a housing 60 and an input shaft 62 that are integrally provided, and the housing 60 also rotates as the input shaft 62 rotates. The input shaft 62 is connected to the end of the steering shaft 24 opposite to the steering wheel 20 via a universal joint 64. The VGRS actuator 16 includes an output shaft 66, and one end portion of the output shaft 66 extending from the housing 60 is connected to one end portion of the intermediate shaft 68. The other end of the intermediate shaft 68 is connected to a pinion shaft 32 that is an input shaft of the steering unit 14 via a universal joint 70.

  FIG. 2 shows a side sectional view of the VGRS actuator 16 as viewed from the left side of the vehicle. The VGRS actuator 16 rotates the rotation of the input shaft 62, the input shaft 62 provided in a non-rotatable manner with respect to the housing 60, the output shaft 66 provided in a rotatable manner with respect to the housing 60, and the input shaft 62. A harmonic gear mechanism 80 that transmits to the output shaft 66 in a state where the ratio can be changed, and a VGRS motor 82 as a drive source of the harmonic gear mechanism 80 are configured. The housing 60 is generally formed in a stepped cylindrical shape, and a portion protruding toward the rear side of the vehicle is a rectangular protrusion 84, and a rectangular input shaft 62 is fitted into the protrusion 84. Thus, the housing 60 and the input shaft 62 are not rotatable relative to each other. An output shaft 66 is rotatably held on the vehicle front side of the housing 60 via a bushing 86, and a vehicle rear side of the output shaft 66 is a flange portion 88. The output shaft 66 has serrations formed on the outer periphery of the portion extending from the housing 60 on the front side of the vehicle, and the output shaft 66 is connected to the intermediate shaft 68 at the portion where the serrations are formed. Rotation is output.

  The VGRS motor 82 has a motor shaft 100, and the motor shaft 100 is rotatably held on the housing 60 by bearings 102 and 104. A plurality of permanent magnets 106 are fixed and arranged on the outer peripheral portion of the motor shaft 100 in the circumferential direction, and they constitute a rotor of the VGRS motor 82. A plurality of pole bodies 108 (in which a coil is wound around a core) are fixedly disposed on the inner surface of the housing 60 so as to face the permanent magnet 106, and each of the pole bodies 108 is connected to a stator pole. As a result, they constitute a stator. With this structure, the VGRS motor 82 is a so-called DC brushless motor. Further, although detailed description is omitted, the VGRS motor 82 includes a motor rotation angle sensor 110 (see FIG. 1) mainly composed of an encoder, and the steering wheel 20 and the steering unit 14 are in a neutral state. The rotation angle θ from the neutral position of the motor shaft 100, which is the position of the motor shaft 100, can be detected. The detected motor rotation angle θ is used for switching the energized phase of the VGRS motor 82, and for controlling the turning angle ψ of the wheel 42, which will be described in detail later.

  A cable case 116 that houses a power feeding cable 114 to the VGRS motor 82 is fixed to the outer periphery of the protruding portion 84 of the housing 60. The power feeding cable 114 is a spiral cable, and is structured to be wound or unwound by rotation of the housing 60, so that it is prevented from being abnormally loosened or pulled. Yes.

  FIG. 3 shows an exploded view of the harmonic gear mechanism 80, and the configuration and function of the harmonic gear mechanism 80 will be described with reference to this figure. The harmonic gear mechanism 80 includes a stator gear 120 as a first ring gear, a driven gear 122 as a second ring gear, a flexible gear 124 that meshes with them, and a wave generator 126 that supports the flexible gear 124 so as to be able to go around. Has been. The stator gear 120 is a ring gear with internal teeth formed, is fixed to the vehicle front side of the inner peripheral surface of the housing 60, and is not rotatable relative to the housing 60. The driven gear 122 is a ring gear in which internal teeth (the number of teeth slightly smaller than the number of teeth of the stator gear, for example, two fewer teeth) is formed. The driven gear 122 is fixed to the outer peripheral portion of the flange portion 88 of the output shaft 66 and is output. It is impossible to rotate relative to the shaft 66. The flexible gear 124 is a ring gear in which external teeth (the same number of teeth as the driven gear 122) are formed. The flexible gear 124 is made to be relatively thin so as to have flexibility. The wave generator 126 includes an elliptical cam plate 128 and a bearing 130 fitted on the outer periphery of the elliptical cam plate 128. The elliptic cam plate 128 is provided with a shaft hole at its center, and is connected to the motor shaft 100 so as not to rotate relative to the shaft hole with the vehicle front portion of the motor shaft 100 fitted therein. A flexible gear 124 is attached to the outer periphery of the bearing 130. The flexible gear 124 is deformed into an ellipse by a wave generator 126, and meshes with the stator gear 120 and the driven gear 122 at two locations on the major axis portion of the ellipse, and does not mesh with other portions.

  When the stator gear 120 is rotated in a state where the rotation of the motor shaft 100 with respect to the stator gear 120 is prohibited, the wave generator 126 is rotated together with the stator gear 120, and the flexible gear 124 positioned therebetween is also rotated integrally therewith. Accordingly, the driven gear 122 that meshes with the flexible gear 124 also rotates in the same direction as the stator gear 120, and the driven gear 122 rotates at a ratio of 1: 1 with respect to the rotation of the stator gear 120. This ratio is a rotation ratio that is the ratio of the rotation amount of the driven gear 122 to the rotation amount of the stator gear 120, and is a basic rotation ratio (a rotation ratio that is fixed when the wave generator 126 is fixed to the stator gear 120). = 1).

  Also, consider the case where the wave generator 126 is rotated by rotating the motor shaft 100. First, in order to simplify the explanation, if the stator gear 120 is fixed, when the wave generator 126 is rotated, the flexible gear 124 is elastically deformed and rotates while moving the meshing position. Since the number of teeth of the stator gear 120 and the driven gear 122 is different, a rotational phase difference corresponding to two teeth per rotation of the wave generator 126 is generated between the stator gear 120 and the driven gear 122. If the rotation direction of the stator gear 120 and the rotation direction of the wave generator 126 are the same, the driven gear 122 is decelerated below the basic rotation ratio. On the contrary, if the rotation direction of the stator gear 120 and the rotation direction of the wave generator 126 are opposite, the driven gear 122 is accelerated to the basic rotation ratio or higher. Since the degree of acceleration and deceleration depends on the rotation speed of the wave generator 126, the rotation ratio that is the ratio of the rotation amount of the driven gear 122 to the rotation amount of the stator gear 120 is changed by changing the rotation speed of the VGRS motor 100. Can be arbitrarily changed. In this way, the harmonic gear mechanism 80 transmits the rotation of the input shaft 62 to the output shaft 66 so that the rotation ratio can be changed.

  From the structure as described above, the VGRS actuator 16 changes an operation turning ratio (transmission ratio) that is a ratio of the turning angle of the wheel 42 to the operation angle of the steering wheel 20 by changing the rotation ratio. It is said that. In the VGRS actuator 16, the stator gear 120, the housing 60 to which the stator gear 120 is fixed, and the input shaft 62 rotatably provided on the housing 60 function as a first element, and the driven gear 122 and the driven gear 122 are fixed. The output shaft 66 that functions as the second element, the flexible gear 124 that meshes with the stator gear 120 and the driven gear 122, the wave generator 126 that is mounted on the flexible gear 124, and the motor shaft 100 to which the wave generator 126 is connected. Etc. function as the third element, and the differential mechanism is configured by including these three elements.

  Further, the operating device 10 includes a lock device 150 that limits the rotation of the steering shaft 24 as a steering operation limiting device. FIG. 4 shows the structure of the locking device 150. The lock device 150 uses an electromagnetic solenoid 152 as a drive source, and includes the solenoid 152 and a lock holder 154 that is fixed to the outer periphery of the shaft 24. The lock holder 154 is fixed coaxially to the vehicle front side of the shaft 24, and a plurality of locking grooves 156 are provided at equal angular pitches on the outer periphery of the lock holder 154. The solenoid 152 has a structure in which the plunger pin 158 advances in an excited state, and is provided at a position corresponding to the lock holder 154 on the outer peripheral portion of the tube 26. In the state where the plunger pin 158 has advanced, the tip end portion of the plunger pin 158 protrudes from the pin hole 160 provided through the tube 26 and engages with one of the locking grooves 156 of the lock holder 154. ing. In the engaged state, the operation of the steering wheel 20 is restricted by restricting the rotation of the lock holder 154, that is, the rotation of the shaft 24. In addition, even when the plunger pin 158 is engaged with the locking groove 156 and the rotation in one direction is prohibited, a slight rotation in the opposite direction is allowed.

<Control by ECU>
The steering system having the structure described above is controlled by the ECU 18. The ECU 18 is mainly a computer, and detects the operation angle sensor 28, the motor rotation angle sensor 110, and the vehicle travel speed v (hereinafter sometimes abbreviated as “vehicle speed v”) described above. Various sensors such as a vehicle speed sensor 180 are connected. Incidentally, the vehicle speed sensor 180 may be configured such that the vehicle speed is acquired based on the rotational speed of each wheel 42. The ECU 18 is connected to the assist motor 52 of the assist mechanism 50, the VGRS motor 82 of the VGRS actuator 16, and the solenoid 152 of the lock device 150 via respective drive circuits (drivers). It is supposed to control the operation. The computer of the ECU 18 stores a steering control program, which will be described later, various data related to the control of the steering system, and the like.

  The ECU 16 controls the VGRS motor 82 of the VGRS actuator 16 in order to realize the turning of the wheel 42 having a turning angle corresponding to the operation angle of the steering wheel 20, and adjusts the torsion bar twist amount of the pinion shaft 32. The assist motor 52 of the assist mechanism 50 is controlled so that the assist force according to the steering torque T estimated based on the assist torque is exhibited. More specifically regarding the control of the VGRS actuator 16, the turning angle of the target wheel 42 is determined based on the operation angle of the steering wheel 20, and the VGRS actuator 16 is adjusted so that the actual turning angle becomes the target turning angle. Control. However, in the present steering system, in order to limit the turning speed of the wheels 42 within the set upper limit speed, the target turning angle is corrected based on the set upper limit speed, and the VGRS motor 82 is set to the target turning angle. Is to control. The above control will be described in detail below.

In this control, as described above, the target turning angle ψ * is determined based on the operation angle δ of the steering wheel 20 acquired based on the detection signal of the operation angle sensor 28, and the target turning angle ψ * The wheel 42 is steered so as to become. The target turning angle ψ * is changed according to the vehicle speed v, and the rotation ratio f (v) between the stator gear 120 and the driven gear 122 corresponding to the vehicle speed v is changed as shown by the solid line in FIG. It is defined as possible. Incidentally, a broken line shown in the figure is a basic rotation ratio f _B (= 1) that is a rotation ratio in a state where the rotation of the wave generator 126 relative to the stator gear 120 is prohibited. From the relationship of FIG. 5, the rotation ratio f (v) with respect to the vehicle speed v acquired based on the detection signal of the vehicle speed sensor 180 is determined, and the target turning angle ψ * is determined based on the rotation ratio f (v). Is done. That is, the target turning angle ψ * is determined based on the operation angle δ and the rotation ratio f (v), and can be obtained by the following equation.
ψ * = δ · f (v)

Further, the turning angle of the wheel 42 is connected to the rotation amount of the stator gear 120 connected to the steering wheel 20 and the motor shaft 100 of the VGRS motor 82 as understood from the configuration of the harmonic gear mechanism 80 described above. This corresponds to the rotation amount of the driven gear 122 determined by the rotation amount of the wave generator 126. That is, the turning angle of the wheel 42 is determined by the operation angle of the steering wheel 20 and the rotation angle of the VGRS motor 82. In this steering system, the VGRS motor is applied to the input operation angle δ of the steering wheel 20. The turning angle of the wheel 42 is controlled by controlling the rotation angle 82. That is, in this control, first, the target motor rotation angle θ * corresponding to the target turning angle ψ * is determined. The target motor rotation angle θ * corresponds to an angle obtained by subtracting the amount transmitted from the steering wheel 20 to the wheel 42 in a state where the motor shaft 100 and the wave generator 126 are fixed in the target turning angle ψ *. This is an angle obtained by subtracting the rotation angle of the second element corresponding to the basic rotation ratio f _B (= 1) from the rotation angle of the second element corresponding to the rotation ratio f (v). That is, the target motor rotation angle θ * is calculated by the following equation.
θ * = δ · {f (v) −f _B }
Next, the actual motor rotation angle θ is acquired based on the detection signal of the motor rotation angle sensor 110, and the motor rotation angle deviation Δθ (= θ * −θ), which is the deviation of the actual motor rotation angle θ from the target motor rotation angle θ *. ) Is recognized, and the supply current I to the VGRS motor 82 is determined so that the motor rotation angle deviation Δθ becomes zero.

The supply current I to the VGRS motor 82 is determined in the ECU 18 according to the following PD control law based on the motor turning angle deviation Δθ.
I = K _P · Δθ + K _D · Δθ '
Here, the first term and the second term mean the proportional term component and the derivative term component in the supply current I, respectively, and K _P and K _D mean the proportional gain and the differential gain, respectively. The determined supply current I is supplied to the VGRS motor 82 via an inverter which is a drive circuit.

  The target turning angle is set so that the rotation ratio decreases as the traveling speed of the vehicle increases, as can be seen from FIG. That is, when the traveling speed of the vehicle is high, the turning amount of the wheel 42 with respect to the operation angle of the steering wheel 20 is reduced, and the stability of the vehicle operation is improved when the vehicle is traveling fast. Can do. On the contrary, when the traveling speed of the vehicle is relatively low, the steering amount of the steered wheel 42 with respect to the operation angle of the steering wheel 20 is increased, and the ease of steering operation can be improved.

As described above, in the present steering system, since the turning angle with respect to the operation angle of the steering wheel 20 is increased in the low speed range of the vehicle speed, the turning speed ω of the wheels 42 is relatively high. For example, when the vehicle is stopped or traveling at a considerably low speed and a fast steering operation is performed and the vehicle is steered at a steering speed corresponding to the operation speed, the wheel 42 is in a stationary state or a state close thereto. It will be steered. That is, the load on the assist motor 52 that assists the turning of the wheels 42 becomes large. Therefore, in order to reduce the load on the assist motor 52, ECU 16, when the traveling speed of the vehicle is less than or equal to a set threshold speed v ₀ is also performed fast steering operation, the steering speed of the wheel 42 Control is performed to _limit ω to a set upper limit speed ω _limit .

When the wheel 42 is steered, the tire of the wheel 42 is torsionally deformed. However, when the steered speed is higher than the vehicle speed, the amount of deformation of the tire exceeds the limit, and the road surface and the ground contact surface of the tire Slip occurs between the two. In this control, the set upper limit speed ω _limit is set to a speed that maximizes the amount of deformation of the tire. Incidentally, the prescribed upper speed limit omega _limit is intended to be changed according to the vehicle speed v, as shown in FIG. 6, is lowered as the vehicle speed v becomes lower, and 0 is also set the upper limit speed omega _limit in vehicle speed 0 Is done.

The above-described control for limiting the turning speed will be described in more detail. When the vehicle speed v is equal to or less than the set threshold travel speed v ₀ , first, a set upper limit speed ω _limit corresponding to the vehicle speed v is determined. The upper limit motor rotation angle change amount Δθ _{limit of} the VGRS motor 82 corresponding to the change amount of the turning angle when the wheel 42 is steered at the set upper limit speed ω _limit is calculated, and in this case, from the neutral position The upper limit motor rotation angle θ _limi (= θ + Δθ _limit ) that is the motor rotation angle is determined. The calculation of the upper limit motor rotation angle change amount Δθ _limit is performed based on the operation speed of the steering wheel 20 corresponding to the set upper limit speed ω _limit . In this control, the change in the operation angle with respect to a certain minute time elapses. This is done based on the quantity Δδ. Before the calculation of the upper limit motor rotation angle variation [Delta] [theta] _limit, together with the operation angle variation .DELTA..delta is acquired, determines the upper limit operation angle variation .DELTA..delta _limit corresponding to the set upper limit speed omega _limit, they operated angle variation Based on Δδ, the upper limit operating angle change amount Δδ _limit , and the rotation ratio f (v) corresponding to the vehicle speed v described above, the following equation is used.
Δθ _limi = Δδ _limit · f (v) −Δδ · f _B

When this upper limit motor rotation angle θ _limi is smaller than the aforementioned target motor rotation angle θ *, the turning speed when the wheel 42 is turned so as to be the aforementioned target turning angle ψ * is set. It is determined that the upper limit speed ω _limit is exceeded, and the target motor rotation angle θ * is corrected to the upper limit motor rotation angle θ _limit . In this case, the motor rotation angle deviation Δθ is recognized as the upper limit motor rotation angle change amount Δθ _limit, and the supply current I to the VGRS motor 82 is determined based on the turning amount deviation Δθ based on the PD control law described above. Is done. In this way, wheel turning at the set upper limit speed ω _limit is realized.

In this control, the operation of the locking device 150 described above, more specifically, the solenoid, in detail, is performed so that the operation angle δ of the steering wheel 20 does not exceed the operation angle δ _max corresponding to the limit turning angle of the wheel 42. 152 is excited. For example, in the state where the vehicle is stopped, when the above-described control for limiting the steering speed is performed, the wheel 42 is not steered at all, and thus the steering wheel 20 can be rotated without limitation. This can be avoided by the locking device 150. In addition, if the steering operation is performed without limitation, the power supply cable 114 to the VGRS motor 82 described above may be abnormally pulled and disconnected, but the disconnection can be prevented by limiting the steering operation. Is possible. Incidentally, since the turning angle with respect to the operation angle can be changed as described above, the operation angle δ _max corresponding to the limit turning angle of the wheel 42 is the rotation ratio f (v corresponding to the vehicle speed v. ) To be determined based on.

<Steering system control program>
The steering system is controlled by executing a steering control program whose flowchart is shown in FIG. The control program is stored in a computer included in the ECU 18, and is repeatedly executed at short time intervals after the ignition switch is turned on. Hereinafter, the flow of the turning control will be described in detail with reference to the flowchart shown in FIG.

  In the turning control, first, in step 1 (hereinafter abbreviated as “S1”, the same applies to other steps), the vehicle speed v and the operation angle δ of the steering wheel 20 are acquired. Next, in S2, the rotation ratio f (v) between the stator gear 120 and the driven gear 122 is determined based on the acquired vehicle speed v, and the rotation ratio f (v) and the operation angle δ acquired in S1 are determined. Based on this, the target motor rotation angle θ * is determined. The ECU 18 (specifically, its computer) stores the map data shown in FIG. 6 of the rotation ratio f (v) with the vehicle speed v as a parameter. The rotation ratio f is referred to with reference to the map data. (v) is determined, and the target motor rotation angle θ * is determined with reference to the map data stored in the ECU 18 based on the operation angle δ and the rotation ratio f (v). Next, in S3, the actual motor rotation angle θ is acquired.

Then, in S4, whether or not the vehicle speed v is set threshold speed v ₀ within is determined. When the vehicle speed v is faster than the set threshold travel speed v ₀ , the steering speed is not limited. Therefore, in S10, the difference between the target motor rotation angle θ * determined in S2 and the actual motor rotation angle θ acquired in S3. The motor rotation angle deviation Δθ is recognized.

Further, in S4, when the vehicle speed v is within set threshold speed v _0, it is necessary to determine whether to limit the turning speed. In this case, first, in S5, the operation angle change amount Δδ is acquired from the operation angle at the previous execution of the program and the operation angle δ acquired at the current execution. Next, in S6, based on the acquired vehicle speed v, the upper limit motor rotation angle change amount Δθ of the VGRS motor 82 corresponding to the change amount of the turning angle when the wheel 42 is steered at the set upper limit speed ω _{limit. limit} is determined, and upper limit motor rotation angle θ _limit is determined based on upper limit motor rotation angle change amount Δθ _limit , operation angle change amount Δδ acquired in S5, and f (v) previously determined. The ECU 18 stores map data of the upper limit motor rotation angle change amount Δθ _{limit using} the vehicle speed v as a parameter, and the upper limit motor rotation angle change amount Δθ _limit is determined with reference to the map data. Based on the operation angle change amount Δδ, the upper limit motor rotation angle change amount Δθ _limit and the rotation ratio f (v), the upper limit motor rotation angle θ _limit is determined with reference to the map data stored in the computer.

Next, in S7, it is determined whether or not the upper limit motor rotation angle θ _limit determined in S6 is equal to or smaller than the target motor rotation angle θ *. When the upper limit motor rotation angle θ _limit is equal to or _smaller than the target motor rotation angle θ *, it is not necessary to limit the steering speed. Therefore, in S10, the motor rotation angle deviation Δθ is equal to the target motor rotation angle θ *. It is recognized as a deviation from the motor rotation angle θ. Further, when the upper limit motor rotation angle θ _limit is larger than the target motor rotation angle θ *, it is necessary to limit the turning speed. Therefore, in S8, the target motor rotation angle θ * is corrected to the upper limit motor rotation angle θ _limit . Thus, the motor rotation angle deviation Δθ is the deviation between the upper limit motor rotation angle θ _limit and the actual motor rotation angle θ, that is, the upper limit motor rotation angle change amount Δθ _limit .

  As described above, if the motor rotation angle deviation Δθ is recognized in S8 or S10, the motor rotation angle deviation Δθ is sent to the ECU 18 in S12, and the supply current I to the VGRS motor 82 is determined. . The determined supply current I is transmitted as a command value, and one execution of the steering control program is completed.

Note that it is necessary to limit the steering speed, and after S8 is executed, a steering operation restriction control subroutine is executed in S9. This steering operation restriction control subroutine is a routine for performing the control shown in the flowchart of FIG. In this control, first, whether or not the operation angle δ acquired in S21 is larger than the operation angle δ ₀ set to a value slightly smaller than the maximum operation angle δ _max corresponding to the limit turning angle of the wheel 42. In S23, in order to prevent further steering operation, a state in which the steering operation is prohibited by the lock device 150, that is, the solenoid 152 is brought into an excited state in S23. If the operation angle δ is smaller than δ ₀ , the steering operation is not prohibited in S24, that is, the solenoid 152 is demagnetized. In the state where the lock device 150 prohibits the steering operation, if an operation for returning to the neutral position is input, it is necessary to cancel the prohibition, so that the operation to return to the neutral position is performed in S22. If it is determined that the steering operation has been performed, the steering operation is not prohibited in S24.

  The steering control program described above is repeatedly executed until the ignition switch is turned off. In the ECU 18 of the present steering system, the target turning amount determining unit is configured to include a part for executing the processes of S1 to S3 and S10, and the steering speed limiting part is included to include a part for executing the processes of S4 to S8. It is configured.

1 is a schematic diagram showing an overall configuration of a vehicle steering system that is an embodiment of the present invention. It is sectional drawing of the VGRS actuator as a transmission ratio change actuator shown in FIG. FIG. 3 is an exploded view of the harmonic gear mechanism shown in FIG. 2. It is a partial cross section figure which shows the structure of the locking device as a steering operation limiting device shown in FIG. It is the schematic which shows the relationship of the rotation ratio of the 1st element and the 2nd element with respect to the travel speed of a vehicle. It is the schematic which shows the relationship between the travel speed of a vehicle, and the setting upper limit speed of steering speed. It is a flowchart showing the steering control program performed by the electronic control unit shown in FIG. It is a flowchart which shows the steering operation restriction | limiting control subroutine performed in a steering control program.

Explanation of symbols

10: Operation device 12: Steering device 14: Steering unit (motion conversion mechanism) 16: VGRS actuator (transmission ratio change actuator) 18: Electronic control unit (control device) 20: Steering wheel (steering operation member) 28: Operation Angle sensor 52: Assist motor (assistance source) 80: Harmonic gear mechanism 82: VGRS motor (drive source) 100: Motor shaft 110: Motor rotation angle sensor 120: Stator gear (first element) 122: Driven gear (second element) 124 : Flexible gear (third element) 126: Wave generator (third element) 150: Locking device (steering operation limiting device) 180: Vehicle speed sensor

Claims (6)

A steering operation member;
A steering device that includes an actuator and a control device that controls the actuator based on an operation amount of the steering operation member, and realizes wheel turning with a steering amount corresponding to the operation amount of the steering operation member A vehicle steering system comprising and
The vehicle steering system according to claim 1, wherein the control device includes a turning speed limiting unit that controls the actuator so as to limit a wheel turning speed within a set upper limit speed. The steering device is
A wheel turning force that has an assisting source and relies on the action of transmission to itself while converting the action of transmission according to the amount of operation of the steering operation member transmitted to itself into a wheel turning action. Equipped with a motion conversion mechanism capable of assisting
The actuator is
A transmission ratio change actuator that is provided between the steering operation member and the operation conversion mechanism and changes a transmission ratio that is a ratio of an operation amount of a transmission operation to the operation conversion mechanism with respect to an operation amount of the steering operation member; The vehicle steering system according to claim 1.   The control device includes a target turning amount determining unit that determines a target turning amount that is a turning amount of a target wheel based on an operation amount of the steering operation member, and the turning speed limiting unit is The vehicle steering system according to claim 1 or 2, wherein the target turning amount is corrected based on the set upper limit speed.   The vehicle steering system according to any one of claims 1 to 3, wherein the set upper limit speed is set based on a traveling speed of the vehicle.   The vehicle steering according to any one of claims 1 to 4, wherein the set upper limit speed is set based on a slip between a road surface and a tire contact surface determined based on a running speed of the vehicle and tire rigidity. system. The vehicle steering system according to any one of claims 1 to 5, wherein the steering system includes a steering operation restriction device that restricts an operation amount of the steering operation member without depending on a steering amount of a wheel.

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