JP4469065B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus.
[0002]
[Prior art]
As an electric power steering device, the output of the electric motor is transmitted to the nut of the ball screw that is coaxial with the rack shaft that is linked to the steering input shaft, and the rotation of the nut is converted into a linear motion of the rack shaft by the ball screw, and the wheel that is linked to the rack shaft There are some that assist the steering force.
[0003]
[Problems to be solved by the invention]
(1) The torsional natural frequency composed of the torsional rigidity of the rack shaft mechanically connected to the steering wheel and the inertia mass of the rotor of the electric motor deteriorates the steering wheel handle feeling. However, the torsional rigidity of the rack shaft cannot be changed from the viewpoint of strength, and the inertia mass of the rotor of the electric motor cannot be easily changed from the output side.
[0004]
(2) Cogging (pulsation) of the electric motor and vibration of the tire are transmitted to the steering wheel, which deteriorates the steering wheel handle feeling.
[0005]
(3) If the rack shaft stroke suddenly stops due to the tire climbing on the curb during steering, the electric motor will continue to rotate due to inertia even if the power supply is stopped. Exerts a large impact force on the thread groove of the ball screw provided on the rack shaft, resulting in deterioration of the function of the ball screw and deterioration of the steering wheel handle feeling such as damage to the thread groove.
[0006]
An object of the present invention is to easily change the torsional natural frequency composed of a rack shaft and a rotor of an electric motor in an electric power steering device, attenuate the cogging of the electric motor and the vibration of the tire, and reduce the torque of the electric motor. It is also to reduce the impact force of the transmission path and improve the steering wheel handle feeling.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 transmits the output of the electric motor (30) to the nut (42) of the ball screw (41) coaxial with the rack shaft (16) interlocked with the steering input shaft (12). In the electric power steering device (10) for assisting the steering force by turning the wheel connected to the rack shaft (16) by turning the rotation of 42) into a linear motion of the rack shaft (16) by the ball screw (41). The rotor side member of the motor (30) is composed of a sleeve (33) integrated with the inner periphery of the rotor (32), and a gap is formed inside the extension (36) protruding from the rotor (32) of the sleeve (33). The engaging surface of the drive member (54) is arranged so that the nut (42) can be rotated via the inner periphery of the extension portion (36) of the sleeve (33), and can be slid in the axial direction. (61) A driven portion formed on the end face of the bets (42) meshing surfaces (58) and (62) disposed opposite in the axial direction, are integrally rotationally connected inner circumference of the extension (36) of the sleeve (33) The drive member (54) and the elastic member (55) supported on the back surface between the drive member (54) and the member (57, 56) engaged with the inner periphery of the extension (36) of the sleeve (33) 54) and the nut (42) are urged in the meshing direction of their meshing surfaces (61, 62), and the meshing surface (61) of the drive member (54) and the meshing surface (62) of the nut (42) are elastic. Under the action of the elastic force of the body (55), the concave and convex meshes with each other so that they can contact and separate from each other, and the torque that the drive member (54) tries to transmit to the nut (42) is determined by the preload of the elastic body (55). When the value is less than the value, those bites urged in the meshing direction by the elastic force of the bullets (55). The surfaces (61, 62) are brought into contact with and separated from each other to absorb torque fluctuations, and when the torque exceeds the predetermined value, the meshing surfaces (61, 62) are disengaged to idle with each other. It is a thing.
[0009]
[Action]
(a) Since the meshing mechanism part of the driving part and the driven part meshed by the urging force of the projectile member is interposed in the torque transmission path from the electric motor to the rack shaft, this meshing mechanism part becomes a torque damper, and the rack shaft Therefore, the torsional rigidity can be apparently changed while securing the strength, so that the torsional natural frequency composed of the rack shaft and the rotor of the electric motor can be easily changed, and the handle feeling of the steering wheel can be improved.
[0010]
(b) Since the torque damper of (a) described above is interposed in the torque transmission path from the electric motor to the rack shaft, cogging (pulsation) of the electric motor and vibration of the tire are attenuated by this torque damper, and the steering wheel The handle feeling can be improved.
[0011]
(c) When the rack shaft stroke is suddenly stopped, such as when the curb rides on the tire, the inertia torque is generated due to the electric motor continuing to rotate even if the power supply to the electric motor is stopped. This inertia torque is absorbed by elastic deformation of the projectile, and as a result, damage to the ball screw can be prevented, vibration noise in the transmission system can be attenuated, and the steering wheel handle feeling can be improved.
[0012]
(d) Since the nut, the drive member, and the elastic body are incorporated inside the extension portion of the sleeve and the meshing mechanism portion (torque damper) is accommodated inside the extension portion, the device configuration can be made compact.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1 is a partially cutaway front view of an electric power steering device, FIG. 2 is a schematic diagram showing a torque transmission path from the electric motor to a rack shaft and its components, and FIG. 3 is a cross-sectional view showing the main part of FIG. FIG.
[0014]
The electric power steering apparatus 10 has a housing 11 as shown in FIGS. An output shaft 14 (not shown) is connected to an input shaft 12 (steering input shaft) to which a steering wheel is coupled via a torsion bar 13, and a pinion 15 (not shown) is provided on the output shaft 14. A rack shaft 16 having a rack meshing with the rack 15 is supported on the housing 11 so as to be movable in the left-right direction. A steering torque detecting device 17 (not shown) is provided between the input shaft 12 and the output shaft 14. The steering torque detection device 17 is applied with a steering torque applied to the steering wheel to the output shaft 14, and is based on a relative rotational displacement generated between the input shaft 12 and the output shaft 14 due to elastic torsional deformation of the torsion bar 13. Is detected.
[0015]
In the electric power steering apparatus 10, both end portions of the rack shaft 16 protrude to the left and right of the housing 11, and tie rods 18 </ b> A and 18 </ b> B are connected to these end portions. The wheels can be steered. Note that one end of the rack shaft 16 is supported by the housing 11 via a rack guide (not shown) at a meshing portion with the pinion 15 and the other end via a bearing (not shown).
[0016]
In the electric power steering apparatus 10, an electric motor 30 is disposed in the housing 11 around the rack shaft 16. The electric motor 30 includes a stator (magnet) 31 fixed to the inner periphery of the housing 11, a rotor 32 in which a coil is wound around an iron core, and a sleeve 33 (rotor side member) integrated with the inner periphery of the rotor 32. ). The sleeve 33 is arranged coaxially with the rack shaft 16 at an interval on the outer periphery of the rack shaft 16, and the outer periphery of one end extension 34 (not shown) projecting to one side of the rotor 32 is a bearing 35 (not illustrated) formed of an angular ball bearing. The outer periphery of the other end extension 36 protruding to the other side of the rotor 32 is supported on the housing 11 by a bearing 37 made of a ball bearing, and is supported on both ends by these bearings 35, 37.
[0017]
In the electric power steering apparatus 10, a ball screw 41 is provided on the rack shaft 16, and a nut 42 that meshes with the ball screw 41 is disposed inside the extension portion 36 of the sleeve 33 of the electric motor 30 via a gap. The steel ball 43 is held between the screw groove 41A of the ball screw 41 and the screw groove 42A of the nut 42. Thereby, the output of the electric motor 30 is transmitted to the nut 42 via the torque damper 50, and the rotation of the nut 42 is converted into a linear motion of the rack shaft 16 by the ball screw 41.
[0018]
However, in the electric power steering apparatus 10, as shown in FIGS. 1 to 3, the torque damper 50 is interposed between the sleeve 33 and the nut 42 of the electric motor 30. The torque damper 50 is formed on the inner diameter portion of the extension portion 36 of the sleeve 33 of the electric motor 30 in order from the rear side, such as a thrust plate 51, a thrust bearing 52, a nut 42, a ball 53 (or a roller), a driving member 54, a disc spring, and the like. A spring 55, a washer 56, and a stopper ring 57 are mounted. At this time, the drive member 54 has a ring shape and includes a drive-side meshing surface 61 provided with V grooves 61A at a plurality of circumferential positions on its end surface, and the outer periphery thereof is serrated to the inner surface of the extension portion 36 in the rotational direction. They are integrally connected and slidable in the axial direction. Further, the nut 42 has a driven portion 58 at its end surface, and includes a driven-side meshing surface 62 provided with V grooves 62 </ b> A at a plurality of circumferential positions of the driven portion 58. As a result, the torque damper 50 is integrally formed with the sleeve 33 of the electric motor 30 in the rotational direction, and is formed on the drive side meshing surface 61 of the drive member 54 that is slidable in the axial direction, and the nut 42 (driven portion 58). The driven-side meshing surface 62 is disposed so as to face each other in the axial direction, and the drive member 54 is attached to the nut 42 (driven portion) by a spring 55 supported on the back by a stopper ring 57 and a washer 56 engaged with the inner periphery of the sleeve 33. 58), the meshing surfaces 61 and 62 are biased in the meshing direction via the balls 53.
[0019]
Therefore, in the torque damper 50, when the torque that the driving member 54 is to transmit to the nut 42 (the driven portion 58) is below a certain value determined by the preload of the spring 55, the torque damper 50 is engaged by the elastic force of the spring 55. The engagement surfaces 61 and 62 of the drive member 54 and the nut 42 (driven portion 58), which are biased in the direction, are brought into contact with and separated from each other within a range in which the balls 53 are accommodated in the V grooves 61A and 62A. The torque is transmitted while being absorbed by the elastic deformation of 55. When the torque that the drive member 54 tries to transmit to the nut 42 (driven portion 58) exceeds the above-described fixed value, the meshing surfaces 61 and 62 of the drive member 54 and the nut 42 (driven portion 58) will have their V-grooves. The balls 53 are detached from 61A and 62A and run idle, and no further torque is transmitted.
[0020]
The torque damper 50 can absorb torque fluctuations by, for example, gently setting the circumferential gradient angles of the V grooves 61A and 62A formed on the meshing surfaces 61 and 62 of the drive member 54 and the nut 42 (driven portion 58). The relative rotation angle range of the drive member 54 and the nut 42 (driven portion 58) can be expanded as appropriate, and the torsional rigidity can be easily changed.
[0021]
Hereinafter, the operation of the electric power steering apparatus 10 will be described.
(1) When the steering torque detected by the steering torque detection device 17 is lower than a predetermined value, the steering assist force is unnecessary and the electric motor 30 is not driven.
[0022]
(2) Since the steering assist force is required when the steering torque detected by the steering torque detection device 17 exceeds a predetermined value, the electric motor 30 is driven. The torque generated by the electric motor 30 is transmitted from the sleeve 33 to the nut 42 via the torque damper 50, and the rotation of the nut 42 is caused to linearly move the rack shaft 16 by the ball screw 41. Will be granted.
[0023]
(3) When the vibration of the tire is transmitted to the rack shaft 16 or the cogging (pulsation) of the electric motor 30 is generated during the operations (1) and (2) described above, these vibrations and pulsations constitute the torque damper 50. Damped by elastic deformation of the spring 55.
[0024]
(4) When the stroke of the rack shaft 16 is suddenly stopped due to the tire climbing on the curb during the steering of the above (2), the electric motor 30 tries to continue to rotate due to inertia even if the power supply is stopped. Inertia torque is generated in the sleeve 33. The inertia torque of the sleeve 33 is absorbed by the torque damper 50 and is not transmitted to the ball screw 41 or the rack shaft 16 as an impact force.
[0025]
Therefore, according to this embodiment, there are the following operations.
(1) Since the meshing mechanism portion of the drive member 54 and the nut 42 (driven portion 58) meshed by the urging force of the spring 55 is interposed in the torque transmission path from the electric motor 30 to the rack shaft 16, this meshing mechanism Since the torque damper 50 becomes a part and the torsional rigidity of the rack shaft 16 is apparently changed while securing the strength of the rack shaft 16, the torsional natural frequency composed of the rack shaft 16 and the rotor 32 of the electric motor 30 can be easily changed. This can improve the handle feeling of the steering wheel.
[0026]
(2) Since the torque damper 50 of the above (1) is interposed in the torque transmission path from the electric motor 30 to the rack shaft 16, cogging (pulsation) and tire vibration of the electric motor 30 are caused by this torque damper 50. Attenuates and improves the steering wheel handle feeling.
[0027]
(3) When the stroke of the rack shaft 16 is suddenly stopped, for example, when the tire curb rides up, the inertial torque due to the electric motor 30 continuing to rotate even if the power supply to the electric motor 30 is stopped. However, this inertia torque is absorbed by the elastic deformation of the spring 55. As a result, damage to the ball screw 41 can be prevented, vibration noise in the transmission system can be attenuated, and the handle feeling of the steering wheel can be improved.
[0028]
(4) Since the nut 42, the drive member 54, and the spring 55 are incorporated inside the extension portion 36 of the sleeve 33 and the meshing mechanism portion (torque damper 50) is housed inside the extension portion 36, the apparatus configuration can be made compact.
[0029]
Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration of the present invention is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. Is included in the present invention. For example, in the practice of the present invention, the meshing surfaces of the driving unit and the driven unit are not limited to meshing via balls and rollers, and the chevron tooth surface of one meshing surface is directly connected to the valley tooth surface of the other meshing surface. It is also possible to engage with the concave and convex.
[0030]
In the embodiment of the present invention, the drive unit may be integrally formed with the rotor side member, and the driven unit may be separated from the nut and slide integrally with the nut in the axial direction. In addition, torque dampers may be provided at both ends of the nut.
[0031]
【The invention's effect】
As described above, according to the present invention, in the electric power steering apparatus, the torsional natural frequency composed of the rack shaft and the rotor of the electric motor is easily changed, and the cogging of the electric motor and the vibration of the tire are attenuated. The impact force on the torque transmission path of the electric motor can also be alleviated, and the steering wheel feeling of the steering wheel can be improved.
[Brief description of the drawings]
FIG. 1 is a front view showing a partially broken electric power steering apparatus.
FIG. 2 is a schematic diagram showing a torque transmission path from the electric motor to the rack shaft and its components.
FIG. 3 is a cross-sectional view showing a main part of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 11 Housing 12 Input shaft 16 Rack shaft 30 Electric motor 32 Rotor 33 Sleeve (rotor side member)
36 Extension part 41 Ball screw 42 Nut 53 Ball 54 Drive member (drive part)
55 Spring
56 Washers (members)
57 Stopper ring (member)
58 Follower 61, 62 Mating surface 61A, 62A V groove

Claims (2)

The output of the electric motor (30) is transmitted to the nut (42) of the ball screw (41) that is coaxial with the rack shaft (16) interlocked with the steering input shaft (12), and the rotation of the nut (42) is transmitted to the ball screw (41). ) To linearly move the rack shaft (16), steer the wheel interlocked with the rack shaft (16), and assist the steering force.
The rotor side member of the electric motor (30) is composed of a sleeve (33) integrated with the inner periphery of the rotor (32), and a gap is formed inside the extension (36) protruding from the rotor (32) of the sleeve (33). The nut (42) in a rotatable manner through the
Formed on the engagement surface (61) of the drive member (54) and the end surface of the nut (42), which are integrally coupled to the inner periphery of the extension (36) of the sleeve (33) in the rotational direction and are slidable in the axial direction. A drive member (54) which is disposed so as to be opposed to the meshing surface (62) of the driven portion (58) in the axial direction and integrally coupled to the inner periphery of the extension portion (36) of the sleeve (33) in the rotational direction; The drive member (54) and the nut (42) are moved by the elastic body (55) supported on the back surface with the members (57, 56) engaged with the inner periphery of the extension (36) of the sleeve (33). Urging in the meshing direction of the meshing surfaces (61, 62),
The engagement surface (61) of the drive member (54) and the engagement surface (62) of the nut (42) engage with each other under the elastic force action of the elastic body (55) so as to be in contact with each other. ) Is less than a predetermined value determined by the preload of the projectile body (55), and is biased in the meshing direction by the resilience of the projectile body (55). These meshing surfaces (61, 62) are brought into contact with and separated from each other to absorb torque fluctuations. When the torque exceeds the predetermined value, the meshing surfaces (61, 62) are disengaged from each other. An electric power steering device characterized by being idled.   The engagement surface (61) of the drive member (54) and the engagement surface (62) of the nut (42) are provided with V grooves (61A, 62A) facing each other, and balls (53 The electric power steering apparatus according to claim 1, which engages and disengages with each other in a state where the

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