JP2012045978A - Steering device for vehicle - Google Patents

Abstract

There is provided a vehicle steering apparatus that can eliminate the need for rotation prevention and that can be suitably used particularly when a rear wheel is steered.
A mechanical connection between a steering member and a turning mechanism A1 is broken. The first screw shaft 37 and the second screw shaft 44 provided on a part of the steered shaft 6 are opposite to each other. A first ball nut 38 that engages with the first screw shaft 37 via a first ball 39 is rotationally driven by the first electric motor 21. A second ball nut 45 engaged with the second screw shaft 44 via a second ball 46 is rotationally driven by the second electric motor 22. The rotation direction R1 of the first ball nut 38 and the rotation direction R3 of the second ball nut 45 are opposite to each other.
[Selection] Figure 2

Description

  The present invention relates to a vehicle steering apparatus.

  A pair of ball nuts respectively engaged with a right screw and a left screw formed on the rack shaft, an electric motor disposed between the pair of ball nuts, and a pair capable of connecting the rotor of the electric motor to the pair of ball nuts There has been proposed an electric power steering device including a clutch (see, for example, Patent Document 1). In Patent Document 1, either one of the pair of clutches is selectively connected, and either a right-hand screw or a left-hand screw is alternatively driven via a ball nut corresponding to the clutch that has been connected. To do. As a result, the steering shaft is moved in the axial direction in a direction that matches the steering direction, and power assist is performed.

Further, a groove extending in the axial length direction is provided on the peripheral surface of the rack shaft on the opposite side of the rack teeth, and a detent body slidingly contacting the groove is provided in the guide body that supports the rack shaft so as to be movable in the axial direction. An electric power steering device has been proposed (see, for example, Patent Document 2).
Moreover, an electric power steering apparatus has been proposed that includes first and second electric motors that drive the steered shafts via corresponding first and second ball screw mechanisms, respectively (see, for example, Patent Document 3). .

JP-A-6-144246 (summary) JP 2001-18812 (FIGS. 3, 4, 22nd paragraph, 30th-31st paragraph) JP 2009-292331 A (FIG. 2, 14th paragraph)

  In Patent Documents 1 and 3, in order to move the rack shaft (steering shaft) in the axial direction along with the rotation of the ball nut, it is necessary to stop the rotation of the rack shaft. It is necessary to provide a structure for preventing rotation. In addition, for example, it is necessary to adopt a detent structure in which the cross section of the rack bar has a D shape, and the cross section of the rack bush that supports the rack bar has the same D shape.

  By the way, in the vehicle steering apparatus that performs the turning using the ball screw mechanism, the end of the rack shaft (the turning shaft) (the connecting portion with the tie rod) receives a radial load due to the road surface reaction force. Bend and deform. In particular, in a cargo handling vehicle such as a forklift, when the rear wheel is a steered wheel, the maximum steered angle is as large as about 80 °, for example. Therefore, the radial load is also increased, and the deflection of the rack shaft is also increased.

  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 eliminate the need for rotation prevention and that can be suitably used particularly when the rear wheels are steered. Is to provide.

  In order to achieve the above object, the present invention provides a vehicle steering device (1) in which the mechanical connection between the steering member (2) and the steering mechanism (A1) is cut off. , 64) and a turning shaft (6) supported so as to be movable in the axial direction (X1) through the first turning shafts which are provided on a part of the turning shaft and are mutually reverse screws separated in the axial direction. A screw shaft (37), a second screw shaft (44), a first ball nut (38) engaged with the first screw shaft via a first ball (39), and the second screw shaft (37). A second ball nut (45) engaged with the screw shaft via a second ball (46), a first electric motor (21) for rotationally driving the first ball nut, and the second The rotation direction (R3, R4) of the ball nut is opposite to the rotation direction (R1, R2) of the first ball nut. A second electric motor for rotating (22) to provide a vehicle steering apparatus having a (claim 1).

  According to the present invention, since the first ball nut and the second ball nut are rotationally driven in directions opposite to each other, the first screw shaft and the second screw shaft that are reverse screws are used as the first ball nut. The rotational forces received from the nut and the second ball nut are offset. Therefore, since the force which rotates a turning shaft does not arise, the rotation detent structure of a turning shaft can be abolished. For example, the structure etc. which make the cross section of a turning shaft into D shape, and stop a turning shaft using the rack bush which has the cross section of D shape similarly can be abolished.

  Further, the first electric motor is arranged so as to cancel out the rotational force received by the first screw shaft from the first ball nut and the rotational force received by the second screw shaft from the second ball nut. And a control device (19) for simultaneously driving and controlling the second electric motor (claim 2). In this case, the first electric motor and the second electric motor are simultaneously driven to rotate the first ball nut and the second ball nut in opposite directions, thereby losing the force for rotating the steered shaft. Combing is substantially possible.

  In addition, the first electric motor includes a first rotor (28) fitted to the outer peripheral surface of the first ball nut so as to be able to rotate along with the first ball nut, and the second electric motor includes the second ball. A second rotor (34) fitted to the outer peripheral surface of the nut so as to be able to rotate together, and a gap (S) between the first rotor and the opposite ends (291, 351) of the second rotor. May be provided (Claim 3). In this case, contact between the first rotor and the second rotor rotating in opposite directions can be avoided.

  Further, both ends of the steered shaft are connected to left and right rear wheels (3) as steered wheels via tie rods (7), respectively, and the amount of the gap (S1) is the maximum deflection of the steered shaft. When this occurs, there is a case where it does not become zero (claim 4). In this case, contact between the first rotor and the second rotor is avoided by the gap even when maximum deflection occurs in the steered shaft. Therefore, the present invention can be suitably used for a vehicle steering apparatus having a rear wheel as a steered wheel, for example, a vehicle steering apparatus for a cargo handling vehicle such as a forklift.

  The bush (63, 64) includes an inner peripheral surface (63a, 64a) fitted to an outer peripheral surface (61, 62a) of the end portion (61, 62) of the steered shaft. The peripheral surface and the outer peripheral surface of the end of the steered shaft may be cylindrical surfaces that coincide with each other (claim 5). As described above, the force for rotating the steered shaft is offset by the first and second electric motors. Therefore, the shape of the end portion of the steered shaft and the bush supporting the end portion can be simplified. Further, the rotation of the steered shaft can be reliably suppressed with the frictional force of the bush.

  In addition, in the above, the numbers 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.

It is a mimetic diagram showing a schematic structure of a steering device for vehicles concerning one embodiment of the present invention. It is a schematic sectional drawing of a steering mechanism. It is sectional drawing which follows the III-III line of FIG. It is sectional drawing which follows the IV-IV line of FIG.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, the vehicle steering apparatus 1 constitutes a so-called steer-by-wire system in which mechanical coupling between a steering member 2 such as a steering wheel and a steered wheel 3 is released.
The operation of the steering actuator 4 including, for example, a brushless electric motor, which is driven according to the rotation operation of the steering member 2, is converted into a linear motion in the vehicle width direction of the steering shaft 6 supported by the housing 5, Steering is achieved by converting the linear motion of the steered shaft 6 into the steered motion of the left and right steered wheels 3 for steering.

  In forklifts and other cargo handling vehicles, the steered wheels 3 are often rear wheels, and in that case, it is necessary to ensure the maximum steered angle of the steered wheels 3 as high as about 80 °, for example. When the turning angle is large, a great radial load is applied from the steered wheels 3 to both ends of the steered shaft 6 as a road surface reaction force, so that the steered shaft 6 tends to bend greatly. In the present embodiment, description will be made in accordance with the case where the steered wheels 3 are rear wheels. As will be described later, the present invention can be suitably used for such a type of rear wheel steering. However, it goes without saying that the present invention can be applied to a vehicle steering apparatus in which the steered wheels 3 are front wheels.

  The driving force (rotational force of the output shaft) of the steering actuator 4 is applied to the axial direction X1 (vehicle) of the steered shaft 6 by a motion conversion mechanism (for example, a ball screw mechanism) provided in association with the steered shaft 6. It is converted to linear motion in the width direction. The linear motion of the steered shaft 6 is transmitted to the tie rods 7 provided so as to protrude from both ends of the steered shaft 6 and cause the knuckle arm 8 to rotate. Thereby, the turning of the steered wheel 3 supported by the knuckle arm 8 is achieved.

The steered shaft 6, the tie rod 7, the knuckle arm 8, and the like constitute a steered mechanism A1 for steering the steered wheels 3. The housing 5 that supports the steered shaft 6 is fixed to the vehicle body via a bracket or the like (not shown).
The steering member 2 is connected to a rotating shaft 9 that is rotatably supported with respect to the vehicle body. A reaction force actuator 10 for applying an operation reaction force to the steering member 2 is attached to the rotary shaft 9. The reaction force actuator 10 includes an electric motor such as a brushless motor having an output shaft integrated with the rotary shaft 9.

An elastic member 11 made of, for example, a spiral spring or the like is coupled to the end of the rotating shaft 9 on the side opposite to the operation member 2 with the vehicle body. The elastic member 11 returns the steering member 2 to the straight steering position by the elastic force when the reaction force actuator 10 is not applying torque to the steering member 2.
In order to detect the operation input value of the steering member 2, a steering angle sensor 12 for detecting the steering angle θ _h of the steering member 2 is provided in association with the rotary shaft 9. The rotating shaft 9 is provided with a torque sensor 13 for detecting a steering torque T applied to the steering member 2. On the other hand, in relation to the steered shaft 6, a steered angle sensor 14 for detecting the steered angle δ _W (tire angle) of the steered wheels 3 is provided.

In addition to these sensors, a vehicle speed sensor 15 for detecting the vehicle speed V, a vertical acceleration sensor 16 serving as a rough road condition detecting sensor for detecting a vertical acceleration G _Z of the vehicle body 60, for detecting the lateral acceleration G _y of the vehicle A lateral acceleration sensor 17 and a yaw rate sensor 18 for detecting the yaw rate γ of the vehicle are provided.
The detection signals of the sensors 12 to 18 are input to a control device 19 as vehicle control means including an electronic control unit (ECU) including a microcomputer.

The control device 19 sets a target turning angle based on the steering angle θ _h detected by the steering angle sensor 12 and the vehicle speed V detected by the vehicle speed sensor 15, and the target turning angle and the turning angle sensor 14 are set. Based on the deviation from the turning angle δ _W detected by the above, the steering actuator 4 is driven and controlled (steering control) via the drive circuit 20A.
On the other hand, the control device 19 reacts via the drive circuit 20B so that an appropriate reaction force in the direction opposite to the steering direction of the steering member 2 is generated based on the detection signals output from the sensors 12-18. Drive control (reaction force control) of the force actuator 10 is performed.

  With reference to FIG. 2, the middle portion of the steered shaft 6 is inserted into a cylindrical housing 5. Between the inner peripheral surface 5a of the housing 5 and the turning shaft 6 inserted into the housing 5, first and second electric motors 21 and 22 as turning actuators, and first and second electric motors. First and second ball screw mechanisms 23 and 24 are arranged as motion conversion mechanisms for converting the respective output rotations of the motor 21 into axial movements of the steered shaft 6.

  As shown in FIG. 2, the first and second end portions 61 and 62 of the steered shaft 6 are slidably supported by cylindrical first and second rack bushes 63 and 64, respectively. . As shown in FIG. 3, the outer peripheral surface 61a of the first end 61 of the steered shaft 6 and the inner peripheral surface 63a of the first rack bush 63 are formed in cylindrical surfaces that match each other. As shown in FIG. 4, the outer peripheral surface 62 a of the second end portion 62 of the steered shaft 6 and the inner peripheral surface 64 a of the second rack bush 64 are formed in cylindrical surfaces that match each other. Between each of the rack bushes 63 and 64 and the steered shaft 6, a holding force by appropriate friction that suppresses the rotation of the steered shaft 6 works.

  Referring to FIG. 2 again, the housing 5 is configured by combining a first housing 81 and a second housing 82. Specifically, an annular first flange 83 provided at the end of the first housing 81 and an annular second flange 84 provided at the end of the second housing 82 are abutted with each other. . The first housing 81 and the second housing 82 are coupled to each other by fastening the first and second flanges 83 and 84 using the fastening screw 85.

The first electric motor 21 and the second electric motor 22 constituting the steering actuator are arranged side by side in the axial direction X1 in the housing 5 constituted by combining the first and second housings 81 and 82. Has been.
The first electric motor 21 rotates through a pair of bearings 26 and 27 to the first stator 25 fixed to the inner peripheral surface 81 a of the first housing 81 and the inner peripheral surface 81 a of the first housing 81. And an annular first rotor 28 held in a possible manner. The first rotor 28 includes an annular first rotor core 29 and a first permanent magnet 30 fitted to the outer peripheral surface 29 a of the first rotor core 29 so as to be able to rotate together.

  The second electric motor 22 rotates through a pair of bearings 32 and 33 on the second stator 31 fixed to the inner peripheral surface 82 a of the second housing 82 and the inner peripheral surface 82 a of the second housing 82. And an annular second rotor 34 held in a possible manner. The second rotor 34 has an annular second rotor core 35 and a second permanent magnet 36 fitted to the outer peripheral surface 35a of the second rotor core 35 so as to be able to rotate together.

  The first ball screw mechanism 23 surrounds the first screw shaft 37 formed on a part of the steered shaft 6 and the first screw shaft 37, and rotates together with the first rotor 28. Ball nuts 38 and a number of first balls 39 in a row. The first ball 39 includes a helical screw groove 40 (female screw groove) formed on the inner periphery of the first ball nut 38 and a helical screw groove 41 formed on the outer periphery of the first screw shaft 37. (Male thread groove).

  The outer peripheral surface 38 a of the first ball nut 38 is fitted to the inner peripheral surface 29 a of the first rotor core 29 so as to be able to rotate together. Further, the axial relative movement of the first ball nut 38 and the first rotor core 29 is restricted. Specifically, the first ball nut 38 is screwed to the first step portion 42 formed on the inner peripheral surface 29 a of the first rotor core 29 and the inner peripheral surface 29 a of the first rotor core 29. It is sandwiched between the first screw member 43.

  The second ball screw mechanism 24 includes a second screw shaft 44 formed on a part of the steered shaft 6 and a second screw shaft that surrounds the second screw shaft 44 and rotates together with the second rotor 34. Ball nuts 45 and a number of second balls 46 in a row. The second ball 46 includes a helical screw groove 47 (female screw groove) formed on the inner periphery of the second ball nut 45 and a helical screw groove 48 formed on the outer periphery of the second screw shaft 44. (Male thread groove).

The first screw shaft 37 and the second screw shaft 44 are formed in reverse threads. For example, when the first screw shaft 37 is a left-hand screw, the second screw shaft 44 is a right-hand screw. In addition, when the first screw shaft 37 is a right-hand screw, the second screw shaft 44 is a left-hand screw.
The second ball nut 44 is fitted to the inner peripheral surface 35a of the second rotor core 35 so as to be able to rotate together. Further, the relative movement of the second ball nut 45 and the second rotor core 35 in the axial direction is restricted. Specifically, the second ball nut 45 is screwed to the second step portion 49 formed on the inner peripheral surface 35 a of the second rotor core 35 and the inner peripheral surface 35 a of the second rotor core 35. It is sandwiched between the second screw member 50.

  The opposite end portions 291 and 351 of the first rotor core 29 and the second rotor core 35 as the opposite end portions of the first and second rotors 28 and 34 face each other in the axial direction X1. The gap amount S1, which is the amount of the gap S between the end portion 291 of the first rotor core 29 and the end portion 351 of the second rotor core 35, is maximum on the steered shaft 6 that supports the rear wheels as the steered wheels 3. It is set so that it does not become zero when bending occurs.

The control device 19 sets a target turning angle based on the steering angle θ _h detected by the steering angle sensor 12 and the vehicle speed V detected by the vehicle speed sensor 15. Further, the control device 19 configures the steering actuator 4 via the drive circuit 20A based on the deviation between the target turning angle and the turning angle δ _W detected by the turning angle sensor 14. The drive control (steering control) is performed on the first electric motor 21 and the second electric motor 22 so that the first rotor 28 and the second rotor 34 simultaneously rotate in opposite directions.

For example, when the first rotor 28 rotates in the rotation direction R1, the second rotor 34 rotates in the rotation direction R3 opposite to the rotation direction R1. When the first rotor 28 rotates in the rotation direction R2, the second rotor 34 rotates in the rotation direction R4 opposite to the rotation direction R2.
As a result, the first ball nut 38 and the second ball nut 38 are rotated in directions opposite to each other. Since the first screw shaft 37 and the second screw shaft 44 are opposite to each other, the rotational force received by the first screw shaft 37 from the first ball nut 38 and the second screw shaft 44 are the second screw shafts. The rotational force received from the ball nut 45 is offset.

  Therefore, since the force which rotates the turning shaft 6 integral with the 1st and 2nd screw shafts 37 and 44 does not arise, the rotation prevention structure of the turning shaft 6 can be abolished. That is, the first and second end portions 61 and 62 of the rack shaft as the steered shaft 6 may be a simple round shape such as a circular cross section, and the first and second ends of the steered shaft 6. As the first and second rack bushes 63 and 64 that support the portions 61 and 62, those having a simple cross-sectional shape whose inner peripheral surface 63a is a cylindrical surface can be used.

  Maintaining a frictional force between the inner peripheral surfaces 63a and 64a of the first and second rack bushes 63 and 64 and the outer peripheral surfaces 61a and 62a of the first and second end portions 61 and 62 of the steered shaft 6. By applying the force to the steered shaft 6, the rotation of the steered shaft 6 can be reliably suppressed. As a result, the conventionally used anti-rotation structure, for example, a structure in which the cross section of the steered shaft is D-shaped and a rack bush having the same D-shaped cross section is used to prevent the steered shaft from rotating can be eliminated. .

  Further, a clearance amount S1 which is an amount of the clearance S between the end portion 291 of the first rotor core 29 and the end portion 351 of the second rotor core 35 is a steered shaft 6 that supports a rear wheel as the steered wheel 3. It is set so that it does not become zero when the maximum deflection occurs in the vehicle, so a large radial load is applied to the steered shaft via the rear wheel that is the steered wheel in a cargo handling vehicle such as a forklift, Even when a great amount of bending occurs in the steered shaft, there is no problem that the first and second rotor cores 29 and 35 interfere with each other.

  The present invention is not limited to the above embodiment, and various modifications can be made.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle steering device, 2 ... Steering member, 3 ... Steering wheel, 4 ... Steering actuator, 5 ... Housing, 5a ... Inner peripheral surface of (housing), 6 ... Steering shaft, 6a ... (steering shaft) 7) Tie rod, 8 ... Knuckle arm, 21 ... First electric motor, 22 ... Second electric motor, 23 ... First ball screw mechanism, 24 ... Second ball screw mechanism, 25 ... 1st stator, 28 ... 1st rotor, 29 ... 1st rotor core, 291 ... end of (first rotor core), 34 ... 2nd stator, 35 ... 2nd rotor core, 351 ... (2nd End of the rotor core) 37 ... first screw shaft 38 ... first ball nut 38a ... inner peripheral surface (of the first ball nut) 39 ... first ball 44 ... second screw Shaft, 45 ... second ball nut, 45a ... (in the second ball nut) Surface, 46 ... second ball, 61 ... first end (of the steered shaft), 61a ... outer peripheral surface (of the first end of the steered shaft), 62 ... second (of the steered shaft) 62a ... outer peripheral surface (of the second end portion of the steered shaft), 63 ... first rack bush, 63a ... inner peripheral surface of (first rack bush), 64 ... second rack bush 64a ... (the second rack bush) inner peripheral surface, 81 ... first housing, 82 ... second housing, A1 ... steering mechanism, R1, R2, R3, R4 ... rotational direction, S ... gap, S1 ... Gap amount, X1 ... Axial direction

Claims (5)

In the vehicle steering apparatus in which the mechanical connection between the steering member and the steering mechanism is broken,
A steered shaft supported in a housing so as to be movable in the axial direction via a bush;
A first screw shaft and a second screw shaft, which are provided in a part of the steered shaft and are mutually reverse screws separated in the axial direction;
A first ball nut engaged with the first screw shaft via a first ball;
A second ball nut engaged with the second screw shaft via a second ball;
A first electric motor that rotationally drives the first ball nut;
A vehicle steering apparatus, comprising: a second electric motor that rotationally drives the second ball nut in a rotation direction opposite to a rotation direction of the first ball nut.   The first screw shaft according to claim 1, wherein the first screw shaft receives the rotational force received from the first ball nut and the second screw shaft receives the rotational force received from the second ball nut. A vehicle steering apparatus comprising a control device that simultaneously controls driving of the electric motor and the second electric motor. The first electric motor according to claim 1 or 2, wherein the first electric motor includes a first rotor that is fitted to the outer peripheral surface of the first ball nut so as to be able to rotate together.
The second electric motor includes a second rotor that is fitted to the outer peripheral surface of the second ball nut so as to be able to rotate together.
A vehicle steering apparatus in which a gap is provided between opposing ends of the first rotor and the second rotor. In claim 3, both ends of the steered shaft are respectively connected to left and right rear wheels as steered wheels via tie rods.
The vehicular steering apparatus is configured such that the amount of the gap does not become zero when maximum deflection occurs in the steered shaft. 5. The bush according to claim 1, wherein the bush includes an inner peripheral surface fitted to an outer peripheral surface of an end portion of the steered shaft,
The vehicle steering apparatus, wherein the inner peripheral surface of the bush and the outer peripheral surface of the end portion of the steered shaft are cylindrical surfaces that match each other.

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