JP2008168859A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle enabling efficient steering by reducing the outputs of actuators. <P>SOLUTION: The steering torque of a steering member 2 is transmitted to a differential mechanism 8 through a third steering shaft 7, and distributed to the input shafts 11 of steering shafts 9, 10 by the differential mechanism 8. The rotational speeds of the input shafts 11 of the steering shafts 9, 10 are reduced through corresponding transmission mechanisms 15, 16, the rotational directions thereof are converted by corresponding transmission mechanisms 17, 19, and the rotational speeds are transmitted to corresponding steered wheels 18, 20. A control part 36 assists the steering while controlling the outputs of the actuators 13, 14 so that the steering angles of inner wheels are relatively large. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a vehicle steering apparatus.

Conventionally, in a vehicle steering apparatus employing a rack and pinion mechanism, when the steering member is operated and the steering shaft is rotated, this rotation is converted into an axial movement of the rack shaft along the left-right direction of the vehicle, A steered wheel connected to each end of the rack shaft via a tie rod and a knuckle arm is steered.
During turning of the vehicle, the steered wheel (corresponding to the inner wheel) on the inside of the turn and the steered wheel (corresponding to the outer wheel) on the outside of the turn turn concentrically. Therefore, an Ackermann characteristic is usually obtained by using a link mechanism for converting the axial movement of the rack shaft into the steering rotation of the steered wheels so that the steered angle of the inner wheels becomes relatively large.

However, as shown in FIGS. 7A and 7B, in the steering device using the link mechanism 93 for converting the axial movement of the rack shaft 91 into the steering rotation of the steered wheel 92, the turning of the steered wheel 92 is changed. The greater the steering angle, the greater the energy required for steering.
Specifically, as shown in FIG. 7A, when the turning angle of the steered wheel 92 is zero, if the driving force acting in the axial direction of the rack shaft 91 is F, the steered wheel 92 is moved by the driving force F. The received turning torque P1 is obtained by multiplying the distance L (corresponding to the length of the virtual arm 97 of moment) by F × cosA between the tire center 94 and the action point 96 consisting of the joint center at the end of the swing link 95. It will be a thing. That is,
P1 = L × F × cos A
However, the angle A is an angle formed by the direction perpendicular to the virtual arm 97 with respect to the axis 98 of the rack shaft 91 when the turning angle is zero.

On the other hand, as shown in FIG. 7B, when the turning angle increases, the swing angle B of the swing link 95 increases as the turning angle increases.
The steered torque P2 received by the steered wheels 92 by the driving force F acting in the axial direction of the rack shaft 91 is obtained by multiplying the distance L by F × cos B × cos C.
P2 = L × F × cos B × cos C
However, the angle B is an angle formed by the axis 99 of the swing link 95 with respect to the axis 98 of the rack shaft 91 at the turning angle, and the angle C is the above-mentioned at the turning angle. The direction perpendicular to the virtual arm 97 is an angle with the axis 99 of the swing link 95.

In this way, even when the same driving force F is applied to the rack shaft 91, the steering torque varies depending on the turning angle. Usually, in order to obtain the same turning torque (steering force), FIG. As shown, it is necessary to increase the driving energy F of the rack shaft 91 and increase the turning energy in accordance with the increase in the turning angle.
For this reason, energy efficiency is bad, a high output is requested | required as an actuator for steering, and it is contrary to energy saving. In addition, there is a problem that tire wear is large.

Incidentally, in a four-wheel steering electric vehicle, it has been proposed to change the direction of each wheel in an arbitrary direction (see, for example, Patent Document 1).
Japanese Patent No. 29602364

On the other hand, in recent years, there has been a demand for higher output in an electric power steering apparatus that assists steering using the power of an electric motor.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a vehicle steering apparatus that can reduce the output of an actuator and perform efficient steering.

  In order to achieve the above object, the present invention provides first and second steered wheels (18, 20) that are arranged on the left and right sides of a vehicle and rotate around corresponding steering center axes (21, 22), First and second steered shafts (9, 10) that extend in the left-right direction, and first and second transmission mechanisms (17, 10) that transmit the rotation of each steered shaft to the corresponding steered wheels, respectively. 19), a differential mechanism (8) for distributing the torque of the steering shaft (7) connected to the steering member (2) to the first and second steered shafts, and a first drive mechanism for rotationally driving the corresponding steered shafts. And the first and second actuators (13, 14).

  In a turning mechanism that converts linear motion into rotational motion using a conventional link mechanism, there is a problem that the energy required for turning increases as the turning angle increases. On the other hand, in the present invention, the rotation of the first and second steered shafts driven by the individual actuators is transmitted to the corresponding steered wheels via the corresponding transmission mechanism, so that all the steered wheels are steered. The energy required for steering is constant in the angular range. For this reason, it is excellent in energy efficiency. The output of the actuator required for turning can be reduced and it can contribute to energy saving.

Each steered shaft includes an input shaft (11) coupled to a differential mechanism and an output shaft (12) coupled to a corresponding steered wheel, and a speed change mechanism ( 15,16) may be present (claim 2). In this case, the power of the actuator can be decelerated to achieve a required turning force and a required turning amount.
Each transmission mechanism is connected to a corresponding driven wheel (24) that rotates together with the corresponding steered wheel around the corresponding steering center axis, and is connected to the driven member so as to transmit torque, and rotates in conjunction with the corresponding steered shaft. And a drive member (23). In this case, the rotation of each steered shaft can be transmitted to the corresponding steered wheels via the drive member and the driven member.

The transmission mechanism may be any mechanism that can transmit rotation. For example, a gear mechanism, a pulley / belt mechanism, a chain / sprocket mechanism, or the like can be used.
The driven member may include a driven gear (24), and the drive member may include a drive gear (23) that meshes with the driven gear (claim 4). In this case, the transmission ratio (reduction ratio) of the transmission mechanism can be easily set.

The driven gear may include a worm wheel (24), and the drive gear may include a worm (23). In this case, reverse efficiency can be increased, and transmission of excessive input from the road surface to the steering member side can be suppressed.
A controller (36) for controlling the first and second actuators so that the turning angle (α) of the steered wheels inside the turning of the vehicle is larger than the steered angle (β) of the steered wheels outside the turning. (Claim 6). In this case, the difference in turning radius between the inner ring and the outer ring can be absorbed in the same manner as the conventional Ackermann mechanism.

  In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a control device according to an embodiment of the present invention is applied. Referring to FIG. 1, an electric power steering device (EPS) 1 includes a first steering shaft 3 connected to a steering member 2 such as a steering wheel, and a universal joint 4 connected to the first steering shaft 3. And a second steering shaft 5 as an intermediate shaft connected to each other, a third steering shaft 7 connected to the second steering shaft 5 via a universal joint 6, and a difference from the third steering shaft 7. The first and second steered shafts 9 and 10 are connected via a moving mechanism 8 so that torque can be transmitted.

Although not shown, each of the steered shafts 9 and 10 is supported by a housing so as to be rotatable via a bearing and restricted in axial movement.
Each of the steered shafts 9 and 10 includes an input shaft 11 and an output shaft 12 that are coaxially connected so as to be relatively rotatable. The input shaft 11 of each of the steered shafts 9 and 10 is connected to the differential mechanism 8.
The input shaft 11 of the first steered shaft 9 is rotationally driven by a first actuator 13 made of, for example, a coaxial brushless motor, and the input shaft 11 of the second steered shaft 10 is made of, for example, a coaxial brushless motor. The second actuator 14 is rotationally driven.

Further, a first speed change mechanism 15 is provided between the input shaft 11 and the output shaft 12 of the first steered shaft 9, and between the input shaft 11 and the output shaft 12 of the second steered shaft 10. In addition, a second speed change mechanism 16 is provided.
The output shaft 12 of the first steered shaft 9 is connected to the first steered wheel 18 through the first transmission mechanism 17 so as to be able to transmit rotation. The output shaft 12 of the second steered shaft 10 is connected to the second steered wheel 20 through the second transmission mechanism 19 so as to be able to transmit rotation.

The first steered wheel 18 is supported by the vehicle body so as to be rotatable around the first steering center shaft 21. Similarly, the second steered wheel 10 is supported by the vehicle body so as to be rotatable around the second steering center axis 22.
Each transmission mechanism 17, 19 has a worm 23 as a drive gear formed on the output shaft 12 of the corresponding steered shaft 9, 10 and a corresponding steered wheel 18, around the corresponding steering center shaft 21, 22. 20 and a worm gear mechanism provided with a worm wheel 24 as a driven gear provided so as to be able to rotate together.

Each steered wheel 18, 20 is attached to a corresponding steered wheel support member 25, 26 provided so as to be rotatable about the corresponding steering center shaft 21, 22 so as to be able to rotate together. Moreover, the worm wheel 24 of each transmission mechanism 17 and 19 is attached to the corresponding steered wheel support members 25 and 26 so as to be able to rotate together.
The differential mechanism 8 is a bevel gear type differential mechanism disposed in a differential case 27 that rotates along with the third steering shaft 7. A bevel gear 28 that rotates together with the third steering shaft 7 and a ring-shaped bevel gear 29 that rotates together with the differential case 27 are engaged with each other, and the rotation of the third steering shaft 7 is controlled by the bevel gears 28 and 29. 27 is transmitted.

The differential mechanism 8 includes two first bevel gears 30 on the input side that are rotatably supported in the differential case 27, and a second bevel gear 31 on the output side that is connected to each other via these first bevel gears 30. And a third bevel gear 32.
A steering angle sensor 33 that detects the steering angle θ of the steering member 2, a torque sensor 34 that detects the steering torque T applied to the steering member 2, and a vehicle speed sensor 35 that detects the traveling speed (vehicle speed V) of the vehicle. Is provided. The detection value of each sensor 33-35 is input into the control part 36 which consists of an electronic control unit (ECU).

Based on the detected steering torque T and vehicle speed V, the control unit 36 drives and controls the actuators 13 and 14 using a pre-stored control map, whereby the corresponding steered shafts 9 and 10 are controlled. A steering assist force is applied.
Further, the control unit 36 controls the turning angles α and β of the first and second steered wheels 18 and 20 based on the flowchart shown in FIG. That is, first, detection values of the sensors 33 to 35 are input (step S1), and based on the steering angle θ input from the steering angle sensor 33, it is determined whether or not the steering direction is the right direction (right steering). Judgment is made (step S2).

In the case of right steering (YES in step S2), based on the steering angle θ, the target value β1 of the turning angle of the second turning wheel 20 on the right side serving as the inner wheel is the first value on the left side serving as the outer wheel. The target values α1 and β1 are set so as to be larger than the target value α1 of the steered angle of the steered wheels 18 (step S3).
In the case of left steering (NO in step S2), the target value α1 of the turning angle of the first steered wheel 18 serving as the inner wheel is the target of the steered angle of the right second steered wheel 20 serving as the outer wheel. Each target value α1, β1 is set so as to be larger than the value β1 (step S4).

Specifically, the difference Δ between the target values α1 and β1 of the turning angle is set to increase as the steering angle θ increases.
Next, in step S5, target values Q1 and Q2 of the outputs of the actuators 13 and 14 are set. Specifically, first, the reference output QR of each actuator 13, 14 is determined based on the steering torque T detected by the torque sensor 34 and the vehicle speed V detected by the vehicle speed sensor 35.

The target value Q1 of the output of the actuator 13 or 14 corresponding to the turning angle of the steered wheels 18 or 20 inside the turn is set by adding the correction amount QA corresponding to the difference Δ to the reference output QR. (Q1 = Q + QA).
Further, the target value Q2 of the actuator output corresponding to the turning angle of the turning wheel outside the turn is set by subtracting the correction amount QA corresponding to the difference Δ (Q2 = Q−QA).

The controller 36 controls driving of the actuators 13 and 14 based on the target values Q1 and Q2 set in this way (step S6).
In this manner, the difference in turning radius between the turning wheel (inner wheel) on the turning inner side and the turning wheel (outer wheel) on the turning outer side is absorbed similarly to the conventional Ackermann mechanism, and at the same time, steering assist is achieved.
Referring to FIG. 3, which is a schematic diagram, the first actuator 13 includes a rotor 38 that is rotatably attached to the outer periphery of the output shaft 12, and surrounds the periphery of the rotor 38, and the inner periphery of the cylindrical housing. And a stator 39 fixed to the brushless motor. Although not shown, the second actuator 14 has the same configuration.

Each transmission mechanism 15, 16 includes a wave generator 40, a flex spline 41, and a circular spline 42.
The wave generator 40 is attached to the ends of the input shafts 11 of the corresponding steered shafts 9 and 10 so as to be able to rotate together. The wave generator 40 includes an elliptical cam 43 that is rotatably attached to the end of the input shaft 11 of the corresponding steered shafts 9 and 10, and a ball bearing 44 that is fitted to the outer periphery of the elliptical cam 43. Including. Although not shown, the inner ring of the ball bearing 44 is fixed to the elliptical cam 43, and the outer ring is elastically deformed via the ball.

The flex spline 41 is made of a thin cup-shaped metal elastic body, and has outer teeth 41a. The output shaft 12 is attached to a diaphragm 41b which is the bottom of the flexspline 41.
The circular spline 42 is formed of a rigid body having a ring shape and is fixed to the vehicle body. The circular spline 42 has internal teeth 42 a that mesh with the external teeth 41 a of the flex spline 41. The number of teeth of the inner teeth 42a of the circular spline 42 is increased by a plurality of, for example, two, more than the number of teeth of the outer teeth 41a of the flexspline 41.

  Referring to FIG. 4, if the wave generator 40 is rotated with the rotation of the input shaft 11, the flex spline 41 is bent into an elliptical shape by the wave generator 40. The outer teeth 41a of the flex spline 41 are engaged with the inner teeth 42a of the circular spline 42 at two positions in the long axis portion of the ellipse, and the outer teeth 41a are completely separated from the inner teeth 42a in the short axis portion. Become.

  Since the circular spline 42 is fixed, the meshing position of the external teeth 41a of the flex spline 41 and the internal teeth 42a of the circular spline 42 sequentially moves in the circumferential direction of the circular spline 42 as the wave generator 40 rotates. To go. Specifically, when the wave generator 40 rotates once in the clockwise direction, the flex spline 41 moves counterclockwise by a difference in the number of teeth, for example, two sheets, from the circular spline 42. The rotation of the circular spline 42 is output as the rotation of the output shaft 12.

  When the steering member 2 is operated, the steering torque of the steering member 2 is transmitted to the differential mechanism 8 via the first, second and third steering shafts 3, 5, 7. The first and second steered shafts 9 and 10 are distributed to the input shaft 11. The rotation of the input shaft 11 of each steered shaft 9, 10 is decelerated via the corresponding transmission mechanism 15, 16, the direction of rotation is changed by the corresponding transmission mechanism 17, 19, and the corresponding steered wheel 18, 20. Communicated. Further, the steering assist force generated by the actuators 13 and 14 controlled by the control unit 36 is applied to the corresponding turning shafts 9 and 10 to assist the steering, and as described above, the turning angle of the inner wheel is changed. The outputs of the actuators 13 and 14 are adjusted so as to be relatively large.

The conventional link mechanism 93 shown in FIGS. 7A and 7B has a problem that the energy required for turning increases as the turning angle increases.
On the other hand, in the present embodiment, as shown in FIGS. 5A and 5B, the first turning shaft 9 is rotated through the first transmission mechanism 17 including the worm gear mechanism. The worm wheel 24 as a driven gear of the first transmission mechanism 17 is configured to rotate along with the first steered wheel 18 around the first steering center shaft 21. .

  Therefore, as the worm 23 of the first steered shaft 9 rotates, the worm wheel is subjected to the driving force F applied from the worm 23 to the tangential direction of the worm wheel 24 (corresponding to the axial direction of the first steered shaft 9). A value obtained by multiplying the pitch circle radius r by 23 becomes the turning torque P, and the value of the turning torque P is constant regardless of the turning angle. That is, as shown in FIG. 6, the energy required for turning is constant regardless of the turning angle. For this reason, it is excellent in energy efficiency, the output of each actuator 13 and 14 required for steering can be reduced, and it can contribute to energy saving.

Since the speed change mechanisms 15 and 16 are interposed between the input shaft 11 and the output shaft 12 of the steered shafts 9 and 10, the power of the actuators 13 and 14 is decelerated to obtain the required steered force and the required A steering amount can be realized. Further, the independent steering of the first and second steered wheels 18 and 20 is substantially possible.
Further, since the worm gear mechanism is employed as the first and second transmission mechanisms 17 and 19 for transmitting the rotation of the respective turning shafts 9 and 10 to the corresponding steered wheels 18 and 20, a transmission ratio (reduction ratio). Etc. can be set easily. Moreover, reverse efficiency can be made high and it can suppress that the excessive input from a road surface is transmitted to the steering member 2 side.

In addition, since the turning angle of the steered wheels (inner wheels) on the inner turning side of the vehicle is larger than the steered angle (β) of the steered wheels (outer wheels) on the outer turn side, as in the conventional Ackerman mechanism, A difference in turning radius between the inner ring and the outer ring can be absorbed.
The transmission mechanisms 17 and 19 may be any mechanism that can transmit rotation. For example, other gear mechanisms, pulley / belt mechanisms, chain / sprocket mechanisms, and the like can be used.

Also, planetary gear mechanisms may be used as the transmission mechanisms 15 and 16.
Further, a differential limiting mechanism that limits the differential of the differential mechanism 8 may be provided. For example, a friction clutch as a differential limiting mechanism may be provided between the differential case 27 of the differential mechanism 8 and the second and third bevel gears 31 and 32.
In addition, various modifications can be made within the scope of the claims of the present invention.

It is a mimetic diagram of a steering device for vehicles of one embodiment of the present invention. It is a flowchart which shows the flow of the control processing in the vehicle steering device of FIG. It is a partially broken exploded perspective view of a steered shaft provided with a speed change mechanism and an actuator. It is a front view of the principal part of a transmission mechanism. (A) And (b) is a schematic diagram explaining the principle when a steered wheel is steered by rotation of a steered shaft. It is a graph which shows the relationship of the turning energy of a turning angle. (A) And (b) is a schematic diagram explaining the principle when a steered wheel is steered by the axial movement of a rack shaft in a steered mechanism using a conventional link mechanism. In the conventional turning mechanism, it is a graph which shows the relationship between turning angle and turning energy.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 2 ... Steering member, 7 ... 3rd steering shaft, 8 ... Differential mechanism, 9 ... 1st turning shaft, 10 ... 2nd turning shaft, 11 ... Input shaft, 12 DESCRIPTION OF SYMBOLS ... Output shaft, 13 ... 1st actuator, 14 ... 2nd actuator, 15 ... 1st speed change mechanism, 16 ... 2nd speed change mechanism, 17 ... 1st transmission mechanism, 18 ... 1st steered wheel, DESCRIPTION OF SYMBOLS 19 ... 2nd transmission mechanism, 20 ... 2nd steered wheel, 21 ... 1st steering center axis | shaft, 22 ... 2nd steering center axis | shaft, 23 ... Worm (drive gear. Drive member), 24 ... Worm wheel ( Driven gear, driven member), 33 ... steering angle sensor, 34 ... torque sensor, 35 ... vehicle speed sensor, 36 ... control unit, 37 ... rotor, 39 ... stator, 40 ... wave generator, 41 ... flexspline, 41a ... external teeth 42 ... circular spline, 42a ... inner teeth, 4 ... elliptical cam, 44 ... ball bearings

Claims (6)

First and second steered wheels that are arranged on the left and right sides of the vehicle and rotate around the corresponding steering center axis;
Rotatable first and second steered shafts extending in the left-right direction of the vehicle;
First and second transmission mechanisms for transmitting the rotation of each steered shaft to the corresponding steered wheels;
A differential mechanism that distributes the torque of the steering shaft connected to the steering member to the first and second steered shafts;
A vehicle steering apparatus comprising: first and second actuators that respectively rotate and drive corresponding steering shafts.   In Claim 1, each steered shaft includes an input shaft coupled to a differential mechanism and an output shaft coupled to a corresponding steered wheel, and a speed change mechanism is interposed between the input shaft and the output shaft. A steering apparatus for a vehicle.   3. The transmission mechanism according to claim 1, wherein each transmission mechanism is connected to a corresponding steered wheel around a corresponding steering center axis, and a driven member that rotates together with the corresponding steered wheel. And a driving member that rotates.   4. The vehicle steering apparatus according to claim 3, wherein the driven member includes a driven gear, and the driving member includes a driving gear that meshes with the driven gear.   5. The vehicle steering apparatus according to claim 4, wherein the driven gear includes a worm wheel, and the drive gear includes a worm.   6. The first and second actuators according to claim 1, wherein the first and second actuators are controlled so that a turning angle of a steered wheel inside the turning of the vehicle is larger than a turning angle of a steered wheel outside the turning. A vehicle steering apparatus comprising a control unit.

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