JP2018167751A - Rear wheel steering device and vehicle - Google Patents

Abstract

To provide a rear wheel steering device which can efficiently convert a motion, suppress power consumption during position movement of a rod, and reduce size of an electric motor, and a vehicle using the same.SOLUTION: A rear wheel steering device includes a rod movably supported in an axial direction and changes the direction of rear wheels according to movement of the rod in the axial direction. The rod is a rod of an electric actuator. A drive part of the electric actuator comprises: an electric motor generating rotational torque; a differential reduction gear reducing rotational speed; a speed-increasing gear increasing the rotational speed; and a motion conversion mechanism including a ball screw mechanism converting rotational motion into linear motion of the rod.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rear wheel steering apparatus and a vehicle using the same.

  In order to improve the running stability when the car is moving straight or turning, the toe angle of the rear transportation can be adjusted according to the traveling state of the automobile or the vehicle having the mechanism for steering the rear wheels in addition to the mechanism for steering the front transportation. Automobiles equipped with changing mechanisms are being put into practical use.

  For example, Patent Literature 1 and Patent Literature 2 disclose a rear wheel steering device that steers rear transportation according to a steering angle of a front wheel when a driver steers steering. This rear wheel steering device is provided with a linear motion actuator on each of the left and right rear wheels, and the left and right rear wheels can be independently steered by this linear motion actuator. Therefore, this rear wheel steering device uses the command signal from the host control device to steer the rear wheels in the same phase or in opposite phase with respect to the steering angle of the front wheels in order to improve the running stability when the vehicle turns. Alternatively, the toe angle can be adjusted by shifting the steering angle of the left and right rear transportation in order to improve the running stability when the vehicle goes straight.

  In Patent Document 1, the steering housing is fixed to the vehicle body (chassis). However, in Patent Document 2, linear actuators are provided on the left and right rear wheels, and one of the steering housings is mounted on the vehicle body (chassis). The other is connected to the knuckle arm.

  Patent Document 3 discloses a rear wheel steering device that integrally steers left and right rear wheels. This steering device includes a steering housing fixed to a vehicle body (chassis), a rear wheel steering shaft (rod) supported so as to be movable in the axial direction of the steering housing, a pair of tie rods connected to both ends thereof, Equipped with a knuckle arm corresponding to the tie rod. Then, the steering angle of the left and right rear wheels is changed by driving the rear wheel steering shaft (rod) in the axial direction.

JP2015-202826A JP 2009-173192 A Japanese Patent Laid-Open No. 10-278834

  The motion conversion mechanism of the rear wheel steering device uses a bolt / nut fitting mechanism, and a trapezoidal screw (a screw whose thread has a trapezoidal cross section) is often used for this bolt / nut fitting mechanism. . In the rear wheel steering apparatus of Patent Documents 1 to 3, trapezoidal screws are exemplified as the motion conversion mechanism. A trapezoidal screw having a lead angle smaller than the friction angle is an irreversible motion conversion mechanism that can convert a rotational motion into a linear motion but cannot convert a linear motion into a rotational motion. Therefore, even when an external force is applied to the tire, the position of the actuator rod does not shift. Further, power consumption is not required other than the movement of the position of the actuator rod, and energy consumption can be suppressed.

  However, the efficiency of converting the rotational motion of the trapezoidal screw into a linear motion is about 25%, which is never an efficient motion conversion mechanism. When the general efficiency of the planetary gear speed reducer is set to 90%, for example, in the rear wheel steering apparatus such as Patent Document 1, the efficiency between the electric motor output and the rod output is calculated to be about 22.5%. Therefore, a large torque is required when the position of the actuator rod is moved, and the size of the electric motor increases.

  Therefore, in view of the above problems, the present invention provides a rear wheel steering device capable of efficient motion conversion, suppressing power consumption when the position of the rod is moved, and reducing the size of the electric motor, and the same. A vehicle using the vehicle is provided.

  The rear wheel steering device of the present invention is a rear wheel steering device that includes a rod that is supported so as to be movable in the axial direction, and changes the direction of the rear wheel in accordance with the movement of the rod in the axial direction. A rod of an electric actuator, and a drive unit of the electric actuator includes an electric motor that generates rotational torque, a differential reducer that reduces the rotational speed, a speed increaser that increases the rotational speed, and the rotational motion of the rod And a motion conversion mechanism having a ball screw mechanism for converting into a linear motion.

  Since the ball screw mechanism is used for the motion conversion mechanism, the following advantages are obtained. The torque that rotates the screw shaft can be reduced, and the servo motor that drives the ball screw can be made smaller and lighter. The difference between the starting frictional torque and the kinetic frictional torque is small, and stick-slip does not occur, which makes mechatronics with good controllability. High feed accuracy can be easily realized. The coefficient of friction at the contact surface between the screw and the nut is small, and torque is applied to one of the screws or nuts, thereby increasing the efficiency when the axial force generated on the other nut or screw works.

  The differential reduction gear is preferably a 3K type planetary gear reduction gear including at least a sun gear, an internal gear, a planetary gear, and a carrier that supports the planetary gear so that the planetary gear can rotate. By using a 3K type planetary gear reducer, it is possible to obtain a compact and high reduction ratio. In the 3K type planetary gear device, one sun gear and one internal gear are the minimum required components. The 3K-type planetary gear device includes an A type in which two of the three basic shafts are constituted by internal gears, and a B type in which two of the three basic shafts are constituted by external gears. There is.

  The 3K type planetary gear reducer can reduce the speed reduction ratio to 40 or more. When the reduction ratio is 40 or more, the efficiency at the time of reverse input is 10% or less, and the displacement of the actuator rod hardly occurs with respect to the external force, and power consumption is almost unnecessary except for the movement of the actuator rod. .

  Even if a gear mechanism is used for the speed increaser, a belt drive mechanism may be used.

  The vehicle of the present invention uses the rear wheel steering device.

  In the present invention, even when an external force is applied to the tire, the position of the actuator rod does not shift, and power consumption is not required except when the position of the actuator rod is moved, and energy consumption can be suppressed. The efficiency between the electric motor output and the rod output can be improved while reducing the power consumption when the position of the actuator rod is moved, and the size of the electric motor can be reduced.

It is the schematic which shows the vehicle carrying the rear-wheel steering apparatus which concerns on embodiment of this invention. It is sectional drawing of the rear-wheel steering apparatus which concerns on embodiment of this invention. It is a principal part expanded sectional view of the rear-wheel steering apparatus shown in FIG. It is a graph which shows the relationship between a reduction ratio and the efficiency of a 3K type planetary gear reducer. It is a graph which shows the efficiency of a gear, and the efficiency of a 3K type planetary gear reducer. It is sectional drawing of the rear-wheel steering apparatus which used the belt mechanism for the gearbox.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 shows a vehicle 1 equipped with a rear wheel steering apparatus according to the present invention. The vehicle 1 is an automobile and includes a pair of left and right front wheels 2L and 2R and a pair of left and right rear wheels 3L and 3R.

  The front wheels 2L and 2R are steered by the movement of the steering rod 6 of the front wheel steering mechanism 5 according to the steering angle of the steering wheel 4. That is, when the driver steers the steering wheel 4, the rotation of the steering wheel 4 is transmitted to the front wheel steering mechanism 5 via the steering column 7, whereby the steering rod 6 of the front wheel steering mechanism 5 moves in the axial direction, This linear movement is transmitted through the tie rod 60, so that the directions of the front wheels 2L and 2R change integrally. A steering angle sensor 8 is provided on a steering column 7 that rotates integrally with the steering wheel 4. The outputs of the steering angle sensor 8, the vehicle speed sensor 9, and the yaw rate sensor 10 are input to an electronic control unit (ECU) 11. An ECU (engine control unit) is a microcontroller (microcomputer) that comprehensively controls engine operation control using an electrical auxiliary device.

  The rear wheels 3L and 3R are steered by the rear wheel steering devices 12L and 12R of the present invention disposed between the ball joint 19 on the knuckle arm 20 and the connecting portion 88 on the vehicle body 13, respectively. The steering angles of the rear wheels 3L and 3R are determined by the rear wheel steering control device 14 in response to a command from the electronic control unit 11 based on the traveling information of the vehicle 1, such as the steering angle sensor 8, the vehicle speed sensor 9, and the yaw rate sensor 10. Be controlled. The steering angles of the rear wheels 3L and 3R are controlled independently on the left and right.

  The configuration of the rear wheel steering device of the present invention will be described with reference to FIGS. Since the left and right rear wheel steering devices 12L and 12R have the same configuration, only the left rear wheel steering device 12L will be described, and the description of the right wheel steering device 12R will be omitted. For this reason, in the following description, the rear wheel steering device 12L is simply referred to as the rear wheel steering device 12. The rear wheel steering device 12 includes a rod 16 that is supported so as to be movable in the axial direction, and changes the direction of the rear wheel in accordance with the axial movement of the rod 16.

  The rod 16 is a rod of an electric actuator, and a drive unit 17 of the electric actuator includes an electric motor 22 that generates rotational torque, a 3K-type planetary gear reducer 23 as a differential reducer that reduces the rotational speed, A motion having a speed increasing device 90 for increasing the rotational speed decelerated by the differential speed reducer, and a ball screw mechanism 39 for converting the rotational motion accelerated by the speed increasing device 90 into a linear motion of the rod 16. A conversion mechanism 24.

  The drive unit 17 including the rod 16 is included in the housing 18. The housing 18 includes a motor storage portion 22A for storing the electric motor 22, a transmission storage portion 22B for storing the 3K type planetary gear speed reducer 23 to the speed increaser 90, and a conversion mechanism storage portion 22C for storing the motion conversion mechanism 24. With.

  As shown in FIG. 1, the rod 16 is connected to the rear wheel 3L (3R) so that the direction of the rear wheel 3L (3R) changes according to the movement in the axial direction. Specifically, the rod 16 is connected to the knuckle arm 20 via the ball joint 19. A connecting portion 88 is provided on the opposite side of the rod of the housing 18, and the housing 18 is connected and fixed to the chassis 13 (see FIG. 1) of the vehicle 1 through the connecting portion 88. When the rod 16 moves in the axial direction, the knuckle arm 20 swings around the fulcrum 21 in conjunction with this, and the direction of the rear wheel 3L (3R) changes. The connecting portion 88 has a structure in which an annular vibration-proof rubber is integrated with the inner periphery of the anti-rod side hole 89 of the housing 18.

  In this case, the electric motor 22 is disposed in parallel with the rod 16 and includes a rotor 25 and a stator 26 that applies a rotational force to the rotor 25. The rotor 25 includes a rotor shaft 28 rotatably supported by a pair of left and right rolling bearings 27 a and 27 b mounted on the housing 18, and a rotor core 29 fixed to the outer periphery of the rotor shaft 28. The rotor shaft 28 has a large-diameter shaft portion 28a housed in the transmission housing portion 22B and a small-diameter shaft portion 28b housed in the motor housing portion 22A, and is fitted from the large-diameter shaft portion 28a to the bearing 27a. The support shaft portion 28c protrudes toward the anti-motor housing portion, and the support shaft portion 28d fitted to the bearing 27b protrudes from the small diameter shaft portion 28b toward the anti-transmission housing portion side.

  For this reason, the rotor core 29 is configured by a permanent magnet that is externally fitted and fixed to the small-diameter shaft portion 28b of the rotor shaft 28 and is provided so that N stations and S poles appear alternately along the circumferential direction, for example. The stator 26 includes a stator core 30 fixed to the inner wall of the motor housing portion 22 </ b> A of the housing 18 and an electromagnetic coil 31 wound around the stator core 30. Therefore, when the electromagnetic coil 31 is energized, a rotational force is generated in the rotor core 29 by the electromagnetic force acting between the stator core 30 and the rotor core 29, and the rotor shaft 28 in which the support shaft portions 28c and 28d are supported by the bearings 27a and 27b Rotate with 29.

  As shown in FIG. 3, the 3K type planetary gear speed reducer 23 includes a sun gear 32 provided on the outer periphery of the rotor 25 and a planetary gear set 33 including a pair of planetary gears 80 and 81. The tooth 80a on the outer diameter surface of one (first) planetary gear 80 meshes with the tooth 32a on the outer diameter surface of the sun gear 32, and the other (second) planetary gear 80 has the other end in the axial direction. A planetary gear 81 is provided, and the pair of planetary gears 80 and 81 rotate together. A plurality of planetary gear sets 33 are equally arranged in the circumferential direction, and each planetary gear set 33 is mounted on a planetary gear set shaft 36 that enables rotation. That is, one end of the planetary gear set shaft 36 is fixed to the carrier 35, and the other end of the planetary gear set shaft 36 is fixed to the auxiliary carrier 91. The carrier 35 is pivotally supported by the large-diameter shaft portion 28a on the side opposite to the small-diameter shaft portion of the rotor shaft 28 via the bearing 82, and the auxiliary carrier 91 is supported by the small-diameter shaft portion side of the rotor shaft 28 via the bearing 92. Is pivotally supported by the large-diameter shaft portion 28a.

  Further, the teeth 80a on the outer diameter surface of the first planetary gear 80 mesh with the teeth 34a on the inner diameter surface of the fixed internal gear 34 fixed to the inner peripheral surface of the transmission housing portion 22B on the motor housing portion side. The teeth 81a on the outer diameter surface of the two planetary gears 81 mesh with the teeth 83a of the movable internal gear 83 that is rotatably fitted (attached) via a bearing 93 that is fitted on the carrier 35. For this reason, the movable internal gear 83 is rotatable around the axis of the rotor shaft 28.

  The motion conversion mechanism 24 includes a shaft 37 to which rotation increased by the speed increaser 90 is input, a detent mechanism 38 that prevents the rod 16 from being rotated in the axial direction, and a rotation of the shaft 37. A ball screw mechanism 39 for screwing the shaft 37 and the rod 16 so as to move the rod 16 in the axial direction is provided.

The ball screw mechanism 39 includes a screw shaft portion 39a provided at the tip portion of the rod 16, a nut portion 39b, and a ball (not shown) interposed between the screw shaft portion 39a and the nut portion 39b. The rod 16 includes a large-diameter body shaft portion 16a and a small-diameter shaft portion 16b extending from the large-diameter body shaft portion 16a toward the conversion mechanism housing portion 22C, and the anti-large-diameter shaft of the small-diameter shaft portion 16b. The screw shaft portion 39a is formed on the portion side.

  The nut portion 39b is configured at the axially central portion of the cylindrical shaft 37 that is housed in the conversion mechanism housing portion 22C. That is, the shaft 37 is composed of a nut portion 39b at the center in the axial direction and pivot support portions 37a and 37b provided at both ends, and is pivoted by a pair of bearings 41a and 41b mounted in the conversion mechanism housing portion 22C. The support portions 37a and 37b are rotatably supported. The bearings 41a and 41b are angular bearings, and support the shaft 37 so as to restrict movement in the axial direction and the radial direction in a rotatable manner. Further, a slide bearing 96 is disposed between the inner diameter surface of the pivotal support portion 37a on the main body shaft portion 16a side and the outer diameter surface of the small diameter shaft portion 16b of the rod, and the main body shaft portion 16a of the rod 16 is provided in the housing 18. It is supported by a plain bearing 43. For this reason, the slide of the axial direction of the rod 16 is possible.

  Further, a small-diameter external gear 95 is formed on the outer diameter surface of the end portion of the pivot portion 37a. The small-diameter external gear 95 is a large-diameter external gear 94 formed on the outer diameter surface of the movable internal gear 83. Is engaged. For this reason, the gearbox 90 is comprised by these. That is, the rotation of the rotor 25 is transmitted from the sun gear 32 fixed to the rotor 25 to the movable internal gear 83 via the first planetary gear 80 and the second planetary gear 81, and is output as a reduced rotation. The The rotation output from the movable internal gear 83 is a small diameter provided on the outer diameter of the large diameter external gear 94 provided on the outer diameter of the movable internal gear 83 and the shaft 37 in the motion conversion mechanism 24. The speed is increased by the external gear 95 and transmitted to the motion conversion mechanism 24.

  In order to suppress the vibration of the screw shaft portion 39 a of the ball screw mechanism 39 at one end of the rod 16, the pivot portion 37 a that is a cylindrical portion is supported by the slide bearing 96 so as to be movable in the axial direction.

  The anti-rotation mechanism 38 includes an axially extending groove 44 formed on the inner periphery of the housing 18 and a stopper 45 having a tip portion inserted into the groove 44. The groove 44 is a stop groove whose both axial ends are closed. The stopper 45 is attached to the rod 16.

  When the rod 16 moves in the axial direction, the stopper 45 and the groove 44 move together in the axial direction together with the rod 16. When the stopper 45 comes into contact with the end surface of the groove 44, the axial movement of the rod 16 is restricted there. As described above, the stopper 45 and the groove 44 also function as a mechanical limit of the rod 16.

  A bearing 46 that rotatably supports the stopper 45 is incorporated in a connecting portion of the stopper 45 to the rod 16. Therefore, even if the tip of the stopper 45 and the inner surface of the groove 44 come into contact with each other when the rod 16 moves in the axial direction, the stopper 45 is rotated by the bearing 46, and uneven wear of the stopper 45 and the inner surface of the groove 44 is prevented. It is suppressed.

  A rotation detector 47 that detects the rotation angle of the rotor 25 is attached to the electric motor 22. As the rotation detector 47, for example, a resolver composed of a resolver rotor 47a fixed to the outer diameter of the rotor shaft 28 and a resolver stator 47b fixed to the housing 18 so as to be opposed thereto can be adopted.

  When the electric motor 22 rotates, the rotation is decelerated by the 3K type planetary gear reducer 23, and the decelerated rotation is accelerated by the speed increaser 90 and transmitted to the shaft 37, and formed on the inner diameter of the shaft 37. The nut portion 39b of the ball screw mechanism 39 rotates, and the rod 16 moves in the left-right direction according to the amount of rotation. Then, the rod 16 moves the knuckle arm 20 via the ball joint 19 shown in FIG. 1 to adjust the toe angle of the rear wheel 3L.

  A position detector 48 for detecting the axial position of the rod 16 is attached. Based on the axial position (absolute position) of the rod 16 detected by the position detector 48, the steering angle of the rear wheel 3L can be detected. The output signal of the position detector 48 is input to the rear wheel steering control device 14. As the position detector 48, for example, a device including a permanent magnet 49 fixed to the rod 16 and an analog output Hall IC 50 fixed to the housing 18 so as to face the permanent magnet 49 can be adopted.

  The position detector 48 detects the axial position (absolute position) of the rod 16 by converting the magnetic flux density detected by the Hall IC 50 into position information. If a programmable IC is used as the Hall IC 50, the absolute position accuracy can be improved by programming the relationship between the position of the rod 16 and the magnetic flux density in advance. Further, if one having two outputs from the Hall IC 50 is selected, the position can be detected in the remaining system even if one of the systems fails, and the reliability is improved.

  Although the method using the Hall IC 50 as the position detector 48 has been described, a method in which the amount of movement in the axial direction is converted into rotation and detected by a rotation angle sensor may be used, and the detection method is not limited. Alternatively, a method may be used in which the absolute position of the rod is detected from the position detector 48 when the vehicle 1 is turned on (started), and then the signal of the rotation detector 47 is counted to calculate the position.

  Here, an example of the specifications of the 3K type planetary gear reducer 23 is shown. The module is 1, the number of teeth of the sun gear 32 is 30, the number of teeth of the first planetary gear 80 is 21, the number of teeth of the second planetary gear 81 is 23, the number of teeth of the fixed internal gear 34 is 72, and the movable internal teeth When the gear 83 has 74 teeth, the reduction ratio is 51.8.

Then, the input efficiency when inputting from the sun gear 32 of the 3K-type planetary gear reducer 23 and outputting from the movable internal gear 83, and the reverse input input from the movable internal gear 83 and output from the sun gear 32 Assuming that the transmission efficiency η of the pair of gears of the constituent gears is substantially equal, the following equations 1 and 2 are calculated using the efficiency η of the gear as a parameter. Formula 1 shows the efficiency at the time of input, and Formula 2 shows the efficiency at the time of reverse input. In Equation 2, ηa, ηb, ηc, Z1, Z2, Z3, Z12, and Z11 are the same as ηa, ηb, ηc, Z1, Z2, Z3, Z12, and Z11 in Equation 1.

Further, the input efficiency shown in Equation 1 and the output efficiency shown in Equation 2 are shown in FIG. These efficiencies were calculated based on the parameters shown in Table 1 below.

  Generally, the efficiency η of the gear is high and is 97% or more. When η = 97%, the efficiency of the 3K type planetary gear reducer 23 at the time of input is 49%, and the efficiency at the time of reverse input is 3%. Since the reverse input is almost 0%, it is impossible to transmit the rotational motion at the time of reverse input, and even if an external force is applied from the tire as in the prior art, the displacement of the actuator rod 16 does not occur. Power consumption is not required except for position movement.

FIG. 5 shows the relationship between the reduction ratio when the gear efficiency η in the 3K type planetary gear reducer 23 is 97% and the efficiency at the time of input and reverse input. When the reduction ratio is 40 or more, the efficiency at the time of reverse input is 10% or less, and as in the case of the reduction ratio of 51.8, the position of the actuator rod 16 does not easily shift with respect to the external force. It can be seen that power consumption is almost unnecessary except for movement. FIG. 5 was calculated based on the parameters shown in Table 2 below.

  In order to use the rotation decelerated by the 3K-type planetary gear reducer 23 with a reduction ratio of 40 or more as it is for the rotational movement of the shaft 37, the electric motor 22 having a high rotational speed is required, and the feasibility is poor. Therefore, by inserting the speed increasing device 90 between the 3K type planetary gear speed reducer 23 and the shaft 37, a desired rotational speed can be obtained.

  Here, the efficiency between the electric motor output and the rod output of the 3K type planetary gear reducer 23 when the reduction ratio is 51.8 is obtained. The efficiency of the 3K type planetary gear reducer 23 is 49%, and the efficiency between the electric motor output and the rod output is 43%, assuming that the speed increaser and ball screw efficiency are 97% and 90%, which are typical values. Become. Compared to the efficiency of 22.5% between the electric motor output and the rod output in the case of the combination of the planetary gear mechanism and the trapezoidal screw of the prior art, high efficiency is obtained, and the power consumption when the position of the actuator rod 16 is moved is reduced. Therefore, the size of the electric motor can be reduced.

  In the present invention, since the ball screw mechanism 39 is used for the motion conversion mechanism 24, the following advantages are obtained. The torque for rotationally driving the screw shaft portion 39a can be reduced, and the servo motor (electric motor 22) for driving the ball screw mechanism 39 can be reduced in size and weight. The difference between the starting frictional torque and the kinetic frictional torque is small, and stick-slip does not occur, which makes mechatronics with good controllability. High feed accuracy can be easily realized. The friction coefficient at the contact surface between the screw shaft portion 39a and the nut portion 39b is small, and torque is applied to one of the screw shaft portion 39a or the nut portion 39b, thereby generating an axial force generated on the other nut 39b or the screw shaft portion 39a. Increases efficiency when working.

  For this reason, in the present invention, even when an external force is applied to the tire, the position of the actuator rod 16 does not shift, power consumption is not required except when the position of the actuator rod 16 is moved, and energy consumption can be suppressed. While maintaining the advantages of the conventional technology, the efficiency between the electric motor output and the rod output can be improved, the power consumption during the position movement of the rod of the actuator can be suppressed, and the size of the electric motor can be reduced.

  In the above embodiment, the gear mechanism is used for the speed increaser 90, but FIG. 6 shows the case where a belt drive mechanism is used as the speed increaser. The speed increaser 97 includes a large-diameter pulley 98, a small-diameter pulley 99, and a belt 100. In this case, the large-diameter pulley 98 is provided on the outer diameter of the movable internal gear 83, and the small-diameter pulley 99 is provided on the outer diameter of the shaft 37. Even with belt drive, it shows high transmission efficiency comparable to that of gears.

  6 is the same as that of the rear wheel steering device shown in FIGS. 2 to 3, the same members are shown in FIGS. 2 to 3 in FIG. 6. The attached reference numerals are given and their explanation is omitted. Therefore, the rear wheel steering device shown in FIG. 6 has the same effects as the rear wheel steering device shown in FIGS. 2 to 3 except for the belt drive.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be variously modified. That is, the scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. For example, as with the 3K type planetary gear reducer 23, as a reducer having a difference in efficiency at the time of input and efficiency at the time of reverse input, a hypocycloid reducer, a cycloid reducer, a ball reducer, a harmonic that similarly uses a differential. There are speed reducers, and these may be used as the differential speed reducer of the present invention.

  In the embodiment of the present invention, the electric motor 22 and the 3K type planetary gear reducer 23 are arranged on the same axis, and the movement converting mechanism 24 is arranged so that the electric motor 22 and the axis are parallel to each other. The structure has been described in which the output of the 3K type planetary gear reducer 23 is accelerated to the input of the motion conversion mechanism 24 via a gear or the like to transmit power. That is, in the above-described embodiment, an example in which the 3K-type planetary gear speed reducer 23, the speed increasing gears 90 and 97, and the motion conversion mechanism 24 are arranged in this order toward the downstream direction of the output of the electric motor 22 is shown. It was. However, in the rear wheel steering apparatus according to the present invention, the speed increasers 90 and 97, the 3K type planetary gear speed reducer 23, and the motion conversion mechanism 24 are arranged in this order in the downstream direction of the output of the electric motor 22. May be. In such a case, the 3K planetary gear speed reducer 23 and the motion conversion mechanism 24 are arranged so as to be parallel to the axis of the electric motor 22, and the output of the electric motor 22 is supplied to the 3K planetary gear speed reducer 23. A structure in which the output of the electric motor 22 is increased and transmitted by the speed increasers 90 and 97 by being connected to the input via a belt or a gear may be used.

  Alternatively, the electric motor 22, the 3K type planetary gear speed reducer 23, the planetary gear speed increaser 90, and the motion conversion mechanism 24 may be arranged side by side on the same axis. In such a case, a hollow motor having a hollow rotor can be used as the electric motor 22.

With the 3K type planetary gear reducer 23 having a reduction ratio in the range of 40 to 70, the efficiency from the electric motor output to the rod output, the rod speed 24 mm / s, and the rod thrust 3500 N when using the present invention are realized. Examples of the number of rotations of the electric motor 22 and the output of the electric motor 22 are summarized in Table 3.

Table 4 summarizes examples of combinations of planetary gear reducers and trapezoidal screws of the prior art.

  Comparing Table 3 and Table 4, it can be seen that the output of the electric motor for realizing the rod speed of 24 mm / s and the rod thrust of 3500 N can be reduced by using the present invention.

16 Rod 22 Electric motor 23 3K type planetary gear reducer 24 Motion conversion mechanism 32 Sun gear 35 Carrier 39 Ball screw mechanism 80, 81 Planetary gear 90, 97 Speed up gear

Claims (6)

A rear wheel steering device comprising a rod supported so as to be movable in the axial direction, and changing the direction of the rear wheel in accordance with the axial movement of the rod,
The rod is a rod of an electric actuator, and a drive unit of the electric actuator includes an electric motor that generates rotational torque, a differential reducer that reduces the rotational speed, a speed increaser that increases the rotational speed, and a rotational motion And a motion conversion mechanism having a ball screw mechanism for converting the motion into a linear motion of the rod.   The differential reduction gear is a 3K type planetary gear reduction gear including at least a sun gear, an internal gear, a planetary gear, and a carrier that is rotatably supported on the planetary gear. Item 4. The rear wheel steering device according to Item 1.   The rear wheel steering apparatus according to claim 2, wherein the 3K type planetary gear reducer decelerates to a reduction ratio of 40 or more.   The rear wheel steering apparatus according to any one of claims 1 to 3, wherein a gear mechanism is used for the speed increaser.   The rear wheel steering apparatus according to any one of claims 1 to 3, wherein a belt drive mechanism is used for the speed increaser.   A vehicle using the rear wheel steering device according to any one of claims 1 to 5.

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