JP5224525B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that assists the operation of a steering member such as a steering wheel using a motor in an automobile or a ship.

  An electric power steering device is used to reduce the steering force of the steering wheel and give a comfortable steering feeling to the driver. The electric power steering device generates an assist force that reduces the steering force of the steering wheel using a motor. The steering shaft is provided with a steering force sensor that senses a driver's steering operation. The computer that controls the electric power steering judges the steering operation of the driver based on the detection information from the steering force sensor, further determines the necessary assist force from the vehicle state information such as the vehicle speed, and operates the motor To generate the optimal assist force.

  The mainstream steering mechanism that gives the steering angle to the front wheels is a rack and pinion type. A steering shaft is connected to a steering wheel, which is a part that is actually operated by the driver. The steering shaft transmits the operation of the steering wheel by the driver to the steering gear box. In the steering gear box, the pinion gear and the rack are engaged with each other. The steering shaft is connected to the pinion gear. When the driver rotates the steering wheel, the pinion gear rotates, and the rack moves to the left and right according to the rotation direction of the pinion gear. The left and right movement of the rack is transmitted to the knuckle arm via the tie rod, and a steering angle is given to the front wheels.

  Electric power steering devices using a motor include a method of assisting a steering shaft and a method of assisting a rack in a steering gear box. In the former electric power steering device, the rotation of the motor is decelerated by a reduction mechanism composed of a worm gear, and the torque is increased before being transmitted to the steering shaft. In the latter electric power steering apparatus, the rotation of the motor is transmitted to the rotation of the nut of the ball screw mechanism, and the rotation of the nut is converted into a linear motion in the axial direction of the screw shaft coupled to the rack. The linear movement of the screw shaft in the axial direction assists the movement of the rack in the left-right direction.

In the former power steering apparatus, an electric power steering apparatus using a ball screw instead of a worm gear has been proposed (see Patent Document 1). In the electric power steering apparatus using this ball screw, a moving cylinder is coaxially arranged around the steering shaft, and a rotating cylinder is further coaxially arranged around the moving cylinder. A first ball screw mechanism is provided between the rotating cylinder and the moving cylinder, and a second ball screw mechanism is provided between the moving cylinder and the steering shaft. The rotating cylinder is driven to rotate by a hollow motor disposed outside the rotating cylinder. The rotation of the rotating cylinder is converted into a linear motion in the axial direction of the moving cylinder by the first ball screw mechanism. The linear motion of the moving cylinder is converted into the rotational motion of the steering shaft by the second ball screw mechanism. Thus, torque that assists steering is applied from the hollow motor to the steering shaft.
JP 2004-210066 A

  However, the conventional electric power steering device has a structure in which a moving cylinder and a rotating cylinder are arranged coaxially around the steering shaft, and a hollow motor is arranged outside the rotating cylinder. Tends to be large. When the outer diameter of the electric power steering device is increased, the driver's feet are pressed. In addition, since a dedicated hollow motor is required, it is difficult to reduce the noise and improve the reliability of the motor. Furthermore, since it is necessary to process the ball rolling grooves inside and outside the moving cylinder that is long in the axial direction and to incorporate a large number of balls into the ball rolling grooves, it becomes extremely difficult to process and assemble.

  Accordingly, an object of the present invention is to provide a feasible steering shaft assist type electric power steering device using a ball screw.

  In order to solve the above-described problem, the invention according to claim 1 is a first screw shaft connected to the steering member, and a second screw shaft connected to the motor and arranged in parallel with the first screw shaft. A first nut that linearly moves in the axial direction of the first screw shaft with the rotational movement of the first screw shaft, and the first nut with the rotational motion of the second screw shaft. A second nut that linearly moves in the axial direction of the second screw shaft, and the lead of the second screw shaft and the second nut is the lead of the first screw shaft and the first nut. And an electric power steering device in which the first nut moves linearly with the linear movement of the second nut.

  According to a second aspect of the present invention, in the electric power steering apparatus according to the first aspect, the first nut and the first nut are arranged so that the first nut linearly moves with the linear movement of the second nut. A connecting member for connecting the second nut is provided.

  According to a third aspect of the present invention, there is provided the electric power steering apparatus according to the second aspect, wherein the rolling element rolling groove has a pair of opposing side wall portions and a bottom portion and extends in the longitudinal direction inside the pair of side wall portions. A rolling member circulation including a raceway member including a load rolling element rolling groove that is sandwiched between the pair of side wall portions so as to be movable in a longitudinal direction of the raceway member and faces the rolling element rolling groove of the raceway member. A moving block having a path and a second nut, a plurality of rolling elements arranged in the rolling element circulation path of the moving block, and provided at both longitudinal ends of the track member, And a support portion that rotatably supports the second screw shaft, wherein the connecting member connects the moving block and the first nut.

  According to a fourth aspect of the present invention, in the electric power steering apparatus according to the third aspect, a base to which the track member is attached, and a support bracket that is attached to the base and rotatably supports the first screw shaft. And.

  By arranging the second screw shaft connected to the motor in parallel with the first screw shaft connected to the steering member, an electric power steering device using a ball screw can be realized, and the driver It is possible to arrange the motor and the second screw shaft in a direction where there is a space so as not to compress the foot of the. Furthermore, since a commercially available motor can be used instead of a dedicated hollow motor, the motor can be quiet and the reliability can be improved. Since the reduction ratio can be increased by increasing the difference between the leads of the first screw shaft and the second screw shaft, the output of the motor can also be reduced.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the overall configuration of the electric power steering apparatus. This electric power steering apparatus is of a steering shaft assist type that assists the steering shaft 1. A steering shaft 1 that transmits the operation of the steering wheel 2 by the driver to the steering mechanism 3 is connected to the steering wheel 2 that is a steering member.

  The steering gear 6 of the steering mechanism 3 includes a pinion gear 4 connected to the end of the steering shaft 1 and a rack 5 that meshes with the pinion gear 4 and moves in the left-right direction as the pinion gear 4 rotates. The rack 5 is accommodated in the housing 7 so as to be movable in the vehicle lateral direction. Tie rods 8 for connecting the rack 5 to the knuckle arm 9 are attached to the left and right ends of the rack 5. A hub 11 that is a mounting portion of the front wheel 10 is supported by a knuckle arm 9. A steering angle is given to the front wheel 10 by pushing or pulling the knuckle arm 9. When the steering wheel 2 is rotated, the pinion gear 4 is rotated. Then, the rack 5 moves to the left or right according to the rotation direction of the pinion gear 4. The movement of the rack 5 is transmitted to the knuckle arm 9 through the tie rod 8 and a steering angle is given to the front wheel 10.

  The electric power steering apparatus causes the steering shaft 1 to exert an assist force by the motor 28. A steering force sensor 29 is provided on the steering shaft 1. The control unit 61 determines a steering operation by the driver based on information from the steering force sensor 29, further determines a necessary assist force from information such as a vehicle speed from the traveling state detection sensor 30, and drives the motor 28. It outputs to the drive circuit 28a. The drive circuit 28a supplies a current to the motor 28, and operates the motor 28 to exert an optimum assist force. The electric power used by the motor 28 is supplied from the battery. Torque generated in the motor 28 is transmitted to the steering shaft 1 via the transmission mechanism 62.

  The steering shaft 1 is rotatably supported inside a housing 63 attached to the vehicle body. The housing 63 is attached to the vehicle body such that the internal steering shaft 1 is inclined rearward and upward in the passenger compartment.

  FIG. 2 is a perspective view of the transmission mechanism 62 inside the housing 63. The transmission mechanism 62 is a combination of a first ball screw mechanism 14 and a second ball screw mechanism 17 that are vertically arranged in two stages. The screw shaft 12 of the upper first ball screw mechanism 14 and the screw shaft 15 of the lower second ball screw mechanism 17 are parallel to each other. The axis of the first screw shaft 12 and the axis of the second screw shaft 15 are separated from each other by a predetermined distance, and they do not intersect each other. The first screw shaft 12 is connected to the steering shaft 1, and the second screw shaft 15 is connected to the motor 28.

  The lead of the first screw shaft 12 is set larger than the lead of the second screw shaft 15. For example, the lead of the first screw shaft 12: the lead of the second screw shaft 15 = 30 to 50: 1. A first ball screw nut 13 that is a first nut is fitted to the first screw shaft 12. A second ball screw nut 16 that is a second nut is fitted to the second screw shaft 15. As shown in FIG. 4, the first ball screw nut 13 and the second ball screw nut 16 are connected by a connecting member 33. When the motor 28 is rotated, the second screw shaft 15 is rotated. The rotation of the second screw shaft 15 is transmitted to the first screw shaft 12 via the first and second ball screw nuts 13 and 16. The rotation of the second screw shaft 15 is transmitted to the first screw shaft 12 after being reduced to 1/30 to 50, for example.

  As shown in FIGS. 2 and 3, the transmission mechanism 62 has an elongated rectangular base 18. A pair of support brackets 19 a and 19 b that rotatably support the first screw shaft 12 are attached to both ends of the base 18 in the length direction. The first screw shaft 12 is supported by support brackets 19a and 19b via bearings 20 and 21 so as to be rotatable about its axis.

  On the outer peripheral surface of the first screw shaft 12, a spiral ball rolling groove 12a (see FIG. 5) of a predetermined lead is processed. Since the ball 22 as a rolling element rolls, the surface of the ball rolling groove 12a is finished smoothly and with high strength.

  As shown in FIG. 2, a wheel connecting shaft 25 is coupled to one end of the first screw shaft 12. The center line of the first screw shaft 12 coincides with the center line of the wheel connecting shaft 25. A cylindrical wheel holding portion 26 is provided at the tip of the wheel connecting shaft 25. A plurality of attachment holes 26a are formed in the wheel holding portion 26 in the circumferential direction. The steering wheel 2 is fixed to the wheel holding portion 26 by passing the mounting screw through the mounting hole 26 a and screwing it into the steering wheel 2 attached to the wheel holding portion 26.

  The pinion gear 4 is connected to the other end of the first screw shaft 12 via a universal joint or the like. The rotation angle of the first screw shaft 12 is detected by a steering angle sensor 27 such as an encoder. Since the first screw shaft 12 is connected to the steering shaft 1, the rotation angle of the first screw shaft 12 is equal to the rotation angle of the steering wheel 2.

  FIG. 5 shows a detailed view of the first ball screw nut 13 fitted to the first screw shaft 12. The first ball screw nut 13 includes a nut body 31 in which a load ball rolling groove 31 a is processed on an inner peripheral surface, and a pair of end caps 32 provided at both ends of the nut body 31. Since the ball 22 rolls, the surface of the loaded ball rolling groove 31a is finished smoothly and with high strength. In the nut body 31, a ball return passage 31b penetrating in the axial direction of the nut body 31 is opened to circulate the ball 22. The end cap 32 is formed with a direction changing path 32a that scoops up the ball 22 rolling on the ball rolling groove 12a of the first screw shaft 12 and leads it to the ball return path 31b. A ball circulation path composed of a loaded ball rolling path, a direction changing path 32a, and a ball return path 31b between the ball rolling groove 12a of the first screw shaft 12 and the loaded ball rolling groove 31a of the nut body 31. A plurality of balls 22 are arranged and accommodated.

  When the first screw shaft 12 is rotated, the first ball screw nut 13 fitted to the first screw shaft 12 via the ball 22 moves in the axial direction. At the same time, the ball 22 circulates in the ball circulation path. The ball 22 that rolls on the load ball rolling path rolls up to one end of the load ball rolling path, and then scoops up into the direction changing path 32a of the end cap 32, passes through the ball return path 31b, and then the opposite end cap 32. To the other end of the original load ball rolling path. In addition to the above-mentioned end cap type ball circulation path, a return pipe type or deflector type ball circulation path can be used as the ball circulation path.

  FIG. 6 shows a motion guide device for guiding the second ball screw nut 16 to move linearly. In this motion guide device, the second ball screw mechanism 17 and the linear motion guide portion 39 are integrated. The motion guide device includes a track member 34 having a pair of opposing side wall portions 34a and a bottom portion 34c and having a U-shaped cross section, and a moving block 36 that moves along the longitudinal direction of the track member 34. . A mounting hole is formed in the bottom of the track member 34. The race member 34 is attached to the base by passing the bolt through the attachment hole and tightening the bolt into the screw hole of the base 18. A moving block 36 is sandwiched between the pair of side wall portions 34 a of the track member 34. The moving block 36 linearly moves along the track member 34 in the longitudinal direction of the track member 34. A ball rolling groove 34 b that is a rolling element rolling groove extending in the longitudinal direction of the track member 34 is processed inside the side wall portion 34 a of the track member 34. A ball circulation path 37 that is a two-way rolling element circulation path is provided on each of the left and right side surfaces of the moving block 36.

  As shown in FIG. 7, each ball circulation path 37 of the moving block 36 includes a load ball rolling groove 37 a that is a load rolling element rolling groove facing the ball rolling groove 34 b of the raceway member 34, and a load ball rolling. A through hole 37b parallel to the running groove 37a and a pair of U-shaped direction change paths 37c connecting the end of the load ball rolling groove 37a and the end of the through hole 37b are configured. When the moving block 36 linearly moves relative to the track member 34, the ball interposed in the loaded ball rolling path between the ball rolling groove 34b of the track member 34 and the loaded ball rolling groove 37a of the moving block 36. 40 rolls and moves. The ball 40 that has moved and moved along the load ball rolling path is lifted up to one direction changing path 37c, passes through the through hole 37b, and then returned to the load ball rolling path again from the opposite direction changing path 37c. Here, the raceway member 34 and the ball circulation path 37 of the moving block 36 constitute a linear motion guide portion 39.

  The second screw shaft 15 of the second ball screw mechanism 17 passes through the moving block 36. A ball rolling groove 15 a of a predetermined lead is processed on the outer peripheral surface of the second screw shaft 15. The lead of the second screw shaft 15 is smaller than the lead of the first screw shaft 12. Since the ball as the rolling element rolls, the surface of the ball rolling groove 15a of the second screw shaft 15 is finished smoothly and with high strength.

  Both ends of the second screw shaft 15 are rotatably supported by bearings 41 and 42 on end housings 43 and 44 which are support portions provided at both ends in the longitudinal direction of the track member 34. The second screw shaft 15 rotates about its axis. A joint 45 is attached to one end of the second screw shaft 15. A motor housing 46 to which the motor 28 is attached is provided at the end of the track member 34 in the longitudinal direction. The motor 28 is connected to the second screw shaft 15 by attaching the motor 28 to the motor housing 46 and connecting the output shaft of the motor 28 to the joint 45.

  A second ball screw nut 16 is incorporated in the moving block 36. The second ball screw nut 16 is fitted to the second screw shaft 15 penetrating the moving block 36. On the inner peripheral surface of the second ball screw nut 16, a spiral loaded ball rolling groove facing the ball rolling groove 15a of the second screw shaft 15 is processed. The second ball screw nut 16 has a ball circulation path including a loaded ball rolling groove. As with the first ball screw nut 13, various types such as a return pipe method, an end cap method, and a deflector method can be adopted as the ball circulation path. A plurality of balls are arranged in the ball circulation path. When the second screw shaft 15 is rotated, the second ball screw nut 16 moves in the axial direction, and a plurality of balls circulate in the ball circulation path of the second ball screw nut.

  As shown in FIG. 2, an L-shaped bracket 33 is coupled to the flange 13 a of the first ball screw nut 13. A moving block 36 is coupled to the lower surface of the L-shaped bracket 33. Since the second ball screw nut 16 is coupled to the moving block 36, the first ball screw nut 13 is coupled to the second ball screw nut 16 via the bracket 33 and the moving block 36.

  By interposing the ball 22 between the first ball screw nut 13 and the first screw shaft 12 and applying a preload to the ball, the clearance of the first ball screw mechanism 14 can be made zero. Similarly, the clearance of the second ball screw mechanism 17 can be made zero by interposing a ball between the second ball screw nut 16 and the second screw shaft 15 and applying a preload to the ball. . Since the transmission mechanism 62 in which the first ball screw mechanism 14 and the second ball screw mechanism 17 are combined has zero clearance, the transmission mechanism 62 without play is obtained.

  A stopper 50 is provided on the base 18 via a stopper support plate 48. The stopper 50 is a viscoelastic material such as urethane or rubber. The plurality of stoppers 50 are provided to face each other with a predetermined interval in the longitudinal direction of the base 18. Since the lower part of the L-shaped bracket 33 fixed to the first ball screw nut 13 abuts on the stopper 50, the movement amount in the axial direction of the first ball screw nut 13 and the second ball screw nut 16 is limited. Is done. The rotation angle of the steering wheel 2 in the clockwise direction and the counterclockwise direction is limited by the stopper 50.

  Hereinafter, the movement of the transmission mechanism when the lead of the first ball screw mechanism 14 is 30 to 50 mm and the lead of the second ball screw mechanism 17 is 1 mm, for example, will be described. In this case, when the motor 28 is rotated once, the second ball screw nut 16 advances 1 mm in the axial direction of the second screw shaft 15. Since the first ball screw nut 13 and the second ball screw nut 16 are coupled, the first ball screw nut 13 is also connected to the first screw shaft along with the linear motion of the second ball screw nut 16. Advances 1 mm in the axial direction. When the first ball screw nut 13 moves linearly, the linear motion of the first ball screw nut 13 is converted into a rotational motion, and the first screw shaft 12 rotates. Since the lead of the first ball screw mechanism 14 is 30 to 50 mm, when the first ball screw nut 13 advances linearly by 1 mm, the first screw shaft 12 rotates by 1/30 to 50 of one rotation. It will be. That is, the rotation of the motor 28 is decelerated to 1/30 to 50, and the torque of the motor 28 is amplified 30 to 50 times and transmitted to the first screw shaft 12.

  Since the first screw shaft 12 is coupled to the steering shaft 1 (the wheel coupling shaft 25 in FIG. 2), the rotation of the motor 28 is transmitted to the steering shaft 1 via a transmission mechanism. As shown in FIG. 1, the rotation of the steering shaft 1 is transmitted to the steering mechanism 3 via the steering gear 6. The torque applied from the motor 28 to the steering shaft 1 is controlled by the control unit 61. As described above, the control unit 61 is provided with the detection result of the steering torque from the steering force sensor 29, and the vehicle state, the yaw rate, the lateral acceleration, the longitudinal acceleration, etc. from the running state detection sensor 30 provided in each part of the vehicle. A detection result of a running state affecting steering is given. Further, the detection result of the steering angle from the steering angle sensor 27 is given to the control unit 61. The control unit 61 determines a control target value based on the detection result of the steering torque given from the steering force sensor 29, and the detection result of the running state given from the running state detection sensor 30 and the steering angle sensor 27. Is corrected based on the detection result of the steering angle given from, and an operation command is issued to the drive circuit 28a of the motor 28 to obtain the corrected control target value. As a result, a steering assist force according to the state of steering is applied to the steering shaft 1, and the driver operating the steering wheel 2 can experience a light and good steering feeling.

  By disposing the second screw shaft 15 connected to the motor 28 in parallel with the first screw shaft 12 connected to the steering shaft 1, the driver's feet are kept away from the driver so as not to be compressed. The motor 28 and the second screw shaft 15 can be disposed. In addition, since a commercially available motor 28 can be used instead of a dedicated hollow motor, the noise of the motor 28 can be reduced and the reliability can be improved. Furthermore, by adopting a structure in which the ball screw portion (second ball screw nut 16) and the linear motion guide portion 39 are integrated in the motion guide device that guides the second ball screw nut 16, electric power steering The device can be made more compact. Furthermore, the first screw shaft 12 is rotatably supported on the base 18 so that the mounting space can be further reduced.

  FIG. 8 shows a sectional view of another example of the transmission mechanism. A moving block 52 is accommodated in the cylindrical track member 51 so as to be movable in the axial direction. The movement of the moving block 52 is guided by the ball rolling groove 51 a and the rolling element 53 on the inner peripheral surface of the track member 51, which are linear motion guide portions. A first screw shaft 54 and a second screw shaft 55 pass through the moving block 52. A first ball screw nut 56 is screwed to the first screw shaft 54, and a second ball screw nut 57 is screwed to the second screw shaft 55. By accommodating the first screw shaft 54 and the second screw shaft 55 in the cylindrical track member 51, a compact transmission mechanism can be obtained. Here, the first and second female screw portions that are screwed onto the moving block 52 with the first screw shaft 54 and the second screw shaft 55 may be formed directly by cutting or the like. Such first and second female thread portions also correspond to the first and second nuts of the present invention.

  In addition, this invention is not restricted to the said embodiment, In the range which does not change the summary of this invention, it can change variously. For example, a sliding-type screw mechanism that does not interpose rolling elements may be used for the first ball screw mechanism and the second ball screw mechanism. The electric power steering apparatus of the present invention can be applied not only to automobiles but also to ship steering mechanisms. Furthermore, in the said embodiment, although the example applied to the vehicle provided with the rack & pinion type steering mechanism was demonstrated, it is applicable also to the vehicle provided with steering mechanisms other than a rack & pinion type.

The schematic diagram which shows the whole structure of the electric power steering apparatus of one Embodiment of this invention. Perspective view of transmission mechanism Plan view of the transmission mechanism Side view of the transmission mechanism A perspective view of the first ball screw mechanism (including a partial cross-sectional view) The perspective view which shows the motion guide apparatus which integrated the 2nd ball screw mechanism and the linear motion guide part. Sectional view of the circulation path of the motion guide device Sectional view showing another example of transmission mechanism

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Steering shaft, 2 ... Steering wheel, 3 ... Steering mechanism, 4 ... Pinion gear, 5 ... Rack, 12 ... First screw shaft, 13 ... First ball screw nut (first nut), 15 ... Second Screw shaft, 16 ... second ball screw nut (second nut), 18 ... base, 19a, 19b ... support bracket, 20, 21 ... bearing, 28 ... motor, 33 ... bracket (connection member), 34 ... Track member, 34a ... side wall, 34c ... bottom, 36 ... moving block, 40 ... ball (rolling element), 41, 42 ... bearing, 43, 44 ... end housing (support), 52 ... moving block, 54 ... First screw shaft, 55 ... second screw shaft, 56 ... first ball screw nut, 57 ... second ball screw nut, 62 ... transmission mechanism

Claims (4)

A first screw shaft coupled to the steering member;
A second screw shaft coupled to the motor and disposed parallel to the first screw shaft;
A first nut that linearly moves in the axial direction of the first screw shaft in accordance with the rotational movement of the first screw shaft;
A second nut that linearly moves in the axial direction of the second screw shaft as the second screw shaft rotates.
The lead of the second screw shaft and the second nut is smaller than the lead of the first screw shaft and the first nut,
An electric power steering apparatus in which the first nut moves linearly with the linear movement of the second nut.   The electric power steering apparatus further includes a connecting member that connects the first nut and the second nut so that the first nut linearly moves with the linear movement of the second nut. The electric power steering apparatus according to claim 1. The electric power steering device further includes
A track member having a pair of side wall portions and a bottom portion facing each other and having rolling element rolling grooves extending in a longitudinal direction inside the pair of side wall portions,
The rolling member circulation path includes a load rolling member rolling groove that is sandwiched between the pair of side wall portions so as to be movable in the longitudinal direction of the race member and faces the rolling member rolling groove of the race member. A moving block having two nuts;
A plurality of rolling elements arranged in the rolling element circulation path of the moving block;
A support portion provided at both ends in the longitudinal direction of the raceway member, and rotatably supporting the second screw shaft;
The electric power steering apparatus according to claim 2, wherein the connecting member connects the moving block and the first nut. The electric power steering device further includes
A base to which the track member is attached;
The electric power steering device according to claim 3, further comprising a support bracket attached to the base and rotatably supporting the first screw shaft.

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