Power transmission mechanism

Abstract

A power transmission mechanism (S1, S1A, S2) comprises: an input shaft (2); an output shaft (3); and a clutch (4) that is provided on a power transmission path (P) between the input shaft (2) and the output shaft (3). A speed increasing mechanism (9) is provided between the input shaft (2) and the clutch (4) on the power transmission path (P), and a speed reducing mechanism (10) is provided between the output shaft (3) and the clutch (4) on the power transmission path (P).

Description

Power transmission mechanism

[0001] The present invention relates to a power transmission mechanism.

[0002] In a power transmission mechanism that transmits rotational power, a clutch is sometimes provided on the power transmission path. For example, a power transmission mechanism incorporated in a machine tool engages the clutch during processing to transmit rotational power for processing, and disengages the clutch when processing is not being performed. Also, in a power transmission mechanism incorporated in a steer-by-wire steering system of a vehicle, the clutch is disengaged while the steered wheels are steered by steer-by-wire control. On the other hand, when the steer-by-wire control is stopped for some reason, the clutch is engaged, and the steering wheel and the steered wheels are mechanically connected. Patent Document 1 discloses a related technology.

[0003] JP 2004-75051 A

[0004] In a power transmission mechanism that transmits and interrupts rotational power by engaging and disengaging a clutch, backlash in the clutch can cause backlash in the rotational direction between the input shaft and output shaft of the power transmission mechanism. In a steering system, this backlash can lead to a deterioration in the steering feel of the steering wheel and degradation of vehicle dynamics, and in a machine tool, it can reduce the positional accuracy of the tool or workpiece, resulting in poor machining accuracy. On the other hand, increasing the machining accuracy of the clutch to reduce backlash increases the cost of the clutch.

[0005] An object of the present invention is to reduce backlash in the rotational direction between an input shaft and an output shaft in a power transmission mechanism that transmits and cuts off rotational power by connecting and disconnecting a clutch.

[0006] A power transmission mechanism according to one aspect of the present invention includes an input shaft, an output shaft, and a clutch provided on a power transmission path between the input shaft and the output shaft, wherein a speed increasing mechanism is provided on the power transmission path between the input shaft and the clutch, and a speed reducing mechanism is provided on the power transmission path between the output shaft and the clutch.

[0007] According to the power transmission mechanism, it is possible to reduce backlash in the rotational direction between the input shaft and the output shaft.

[0008] Fig. 1 is a perspective view showing a vehicle steering system equipped with a power transmission mechanism according to a first embodiment. Fig. 2 is a perspective view showing a main part of the power transmission mechanism of Fig. 1. Fig. 3 is a cross-sectional view of a main part of the power transmission mechanism of Fig. 1. Fig. 4 is a cross-sectional view of a main part according to a modified example of the power transmission mechanism of Fig. 1. Fig. 5 is a perspective view showing a vehicle steering system equipped with a power transmission mechanism according to a second embodiment.

[0009] Hereinafter, power transmission mechanisms according to several embodiments will be described with reference to the drawings. In the following description, components having the same functions as those already described will be denoted by the same reference numerals and will not be described again.

[0010] 1 to 3, a power transmission mechanism S1 according to this embodiment is applied to a steer-by-wire steering system 1A for a vehicle. The power transmission mechanism S1 includes an input shaft 2, an output shaft 3, and a clutch 4.

[0011] The input shaft 2 is a steering shaft 2. A steering wheel (not shown) is attached to the input end of the steering shaft 2, and the steering force of the driver is input to the steering shaft 2 via the steering wheel. The steering shaft is also called a column shaft.

[0012] The output shaft 3 is mechanically connected to a steering gear box, which is a steering mechanism 5. The output shaft 3 is mechanically connected to a pinion gear shaft 7 of the steering gear box via an intermediate shaft 6. The intermediate shaft 6 is mechanically connected to the output shaft 3 and the pinion gear shaft 7 via a Cardan joint, respectively.

[0013] The clutch 4 is provided on a power transmission path P between the input shaft 2 and the output shaft 3. When the clutch 4 is in an engaged state, it transmits rotational power between the input shaft 2 and the output shaft 3, and when it is in a disengaged state, it interrupts the transmission of rotational power between the input shaft 2 and the output shaft 3. In the example shown, the clutch 4 is a friction-type electromagnetic clutch. When not energized, the friction plates are pressed by the biasing force of an internal spring, and the clutch 4 is in an engaged state. When energized, the electromagnetic force generated by an internal coil releases the pressure on the friction plates against the biasing force of the spring, and the clutch 4 is in a disengaged state.

[0014] The clutch 4 is housed in a casing, and the casing has a notch 8A, which is a weakened portion, formed in the casing. The notch 8A is provided in a position near a flexible coupling 8B, which will be described later.

[0015] A speed-increasing mechanism 9 is provided between the input shaft 2 and the clutch 4, and a speed-reducing mechanism 10 is provided between the clutch 4 and the output shaft 3. In the illustrated example, the speed-increasing mechanism 9 and the speed-reducing mechanism 10 are each constructed using a worm gear. Note that each worm gear may have a known built-in backlash suppression mechanism. The backlash suppression mechanism suppresses backlash of the worm gear by urging the worm toward the worm wheel using the elastic restoring force of a spring. This makes it possible to sufficiently suppress backlash in the speed-increasing mechanism 9 and the speed-reducing mechanism 10.

[0016] The speed-increasing mechanism 9 is composed of a reducer arranged to increase the rotation of the input shaft 2 and output it, and the speed-reducing mechanism 10 is composed of a reducer arranged to reduce the rotation and output it to the output shaft 3. Specifically, the speed-increasing mechanism 9 includes a worm wheel 9A and a worm shaft 9B on which a worm that meshes with the worm wheel 9A is formed. The speed-reducing mechanism 10 includes a worm wheel 10A and a worm shaft 10B on which a worm that meshes with the worm wheel 10A is formed. The rotation shaft of the worm wheel 9A of the speed-increasing mechanism 9 is the input shaft 2 of the power transmission mechanism S1, and the rotation shaft of the worm wheel 10A of the speed-reducing mechanism 10 is the output shaft 3 of the power transmission mechanism S1.

[0017] The worm shaft 9B of the speed-increasing mechanism 9 is connected to one of the rotating shafts of the clutch 4 via a flexible coupling 8B, which is a weak part. The other rotating shaft of the clutch 4 is a worm shaft 10B of the reduction mechanism 10. The flexible coupling 8B can transmit rotational power between the worm shaft 9B of the speed-increasing mechanism 9 and one of the rotating shafts of the clutch 4 while allowing for eccentricity, angular deviation, and runout between them. In the illustrated example, the flexible coupling 8B is a slit-type flexible coupling, but other types of flexible couplings, such as a disk-type or Oldham-type, may also be used.

[0018] In the power transmission mechanism S1, a power transmission path P from the input shaft 2 to the output shaft 3 is formed from the worm wheel 9A and worm shaft 9B of the speed increasing mechanism 9, the worm wheel 10A and worm shaft 10B of the speed reducing mechanism 10, and the clutch 4.

[0019] The speed-increasing mechanism 9, the clutch 4, and the reduction mechanism 10 are arranged in this order along a direction perpendicular to the steering shaft 2, i.e., a direction perpendicular to the longitudinal direction of the vehicle. The speed-increasing mechanism 9, the clutch 4, and the reduction mechanism 10 are also arranged along a direction perpendicular to the output shaft 3. That is, as shown by the thick dashed line in Figure 1, the power transmission path P passing through the power transmission mechanism S1 is crank-shaped, bending at approximately right angles at the speed-increasing mechanism 9 and the reduction mechanism 10, and the steering shaft 2 and the output shaft 3 are arranged offset in the vehicle width direction.

[0020] 1, in the steer-by-wire steering system 1A, a worm shaft 9B of the speed increasing mechanism 9 is connected to the output shaft of a reaction motor 11. The reaction motor 11 generates a steering reaction force on the input shaft 2 while the clutch 4 is disengaged and steer-by-wire control is being executed. The output of the reaction motor 11 is decelerated and torque amplified by the speed increasing mechanism 9 and transmitted as a steering reaction force to a steering wheel attached to the input shaft 2.

[0021] Furthermore, worm shaft 10B of reduction mechanism 10 is connected to the output shaft of steering motor 12. While clutch 4 is disengaged and steer-by-wire control is being executed, steering motor 12 generates a driving force to output shaft 3 for steering the steered wheels. The output of steering motor 12 is reduced in speed and torque amplified by reduction mechanism 10, and transmitted to output shaft 3 as a steering driving force. The steering driving force is input to pinion gear shaft 7 of the steering gear box via intermediate shaft 6. While steer-by-wire control is stopped and clutch 4 is engaged, reaction motor 11 and steering motor 12 function as a driving force source for the power steering mechanism.

[0022] The steering gearbox, which is the steering mechanism 5, includes a pinion gear formed on a pinion gear shaft 7 and a rack gear formed on a rack bar (not shown) inside the steering gearbox. When the pinion gear shaft 7 rotates, the rotational motion is converted into linear motion by the meshing of the pinion gear and the rack gear, and the converted linear motion moves the rack bar in its axial direction. As the rack bar moves axially, a steering drive force is transmitted to the knuckle arms of the hub carriers of the steered wheels via tie rods 13 attached so as to be able to swing on both ends of the rack bar, and the steered wheels are turned.

[0023] As shown in Figures 1 and 2, the steering shaft 2, which is the input shaft 2, is built into a steering column 14. The steering column 14 is attached to the vehicle body via a first bracket 15. A tilt mechanism is built into the first bracket 15. The tilt angle of the steering column 14 can be adjusted by operating a tilt lever 16. A case for the speed-up mechanism 9 is attached to the front end of the steering column 14. The case for the speed-up mechanism 9 is attached to the vehicle body via a second bracket 17. The tilt center axis of the steering column 14 is provided in the second bracket 17.

[0024] Reaction motor 11 is configured integrally with reaction motor ECU (Electrical Control Unit) 18, which controls reaction motor 11. Steering motor 12 is configured integrally with steering motor ECU 19, which controls steering motor 12. Reaction motor ECU 18 and steering motor ECU 19 are connected to a vehicle communication network so that they can communicate with each other. In addition to clutch 4, various sensors such as a torque sensor built into steering column 14 are connected to reaction motor ECU 18. Reaction motor ECU 18 calculates the angle required for steering based on detection values ​​of various sensors, such as the torque detected by the torque sensor, information on the vehicle's running state, etc., and transmits the calculation result to steering motor ECU 19, which controls steering motor 12 via steering motor ECU 19.

[0025] Reaction motor ECU 18 and steering motor ECU 19 communicate with each other to determine whether or not there is an abnormality in steering system 1A. If reaction motor ECU 18 and steering motor ECU 19 determine that there is no abnormality in steering system 1A, they disengage clutch 4 and execute steer-by-wire control. In steer-by-wire control, reaction motor ECU 18 causes reaction motor 11 to generate a steering reaction force on input shaft 2, and steering motor ECU 19 causes steering motor 12 to steer the steered wheels. At this time, reaction motor 11 and steering motor 12 are mechanically separated.

[0026] On the other hand, if, for example, one of reaction motor 11 and turning motor 12 does not operate normally, reaction motor ECU 18 or turning motor ECU 19 determines that an abnormality has occurred in steering system 1A and stops steer-by-wire control. Then, for example, reaction motor ECU 18 engages clutch 4 to mechanically connect the steering wheel to the steered wheels. At this time, the operation of the ECU that has malfunctioned is stopped, and the power steering function is realized by controlling the normal one of reaction motor 11 and turning motor 12. For example, if reaction motor 11 does not operate normally, turning motor ECU 19 generates a steering reaction force on input shaft 2 and steers the steered wheels using only turning motor 12. If turning motor 12 does not operate normally, reaction motor ECU 18 generates a steering reaction force on input shaft 2 and steers the steered wheels using only reaction motor 11.

[0027] The effects of the power transmission mechanism S1 according to this embodiment will be described.

[0028] (1) The power transmission mechanism S1 includes an input shaft 2, an output shaft 3, and a clutch 4 provided on a power transmission path P between the input shaft 2 and the output shaft 3. A speed-up mechanism 9 is provided on the power transmission path P between the input shaft 2 and the clutch 4, and a speed-reduction mechanism 10 is provided on the power transmission path P between the output shaft 3 and the clutch 4. Therefore, when the clutch 4 is in an engaged state, the play in the rotational direction of the clutch 4 is reduced by a value multiplied by the inverse of the speed-up ratio of the speed-up mechanism 9 and transmitted to the input shaft 2, and the play is reduced by a value multiplied by the reduction ratio of the reduction mechanism 10 and transmitted to the output shaft 3. If the play in the rotational direction of the clutch 4 is 20° around the center of rotation, the speed-up ratio of the speed-up mechanism 9 is 20 / 1, and the reduction ratio of the reduction mechanism 10 is 1 / 20, the play between the input shaft 2 and the output shaft 3 is reduced to 1°. In this way, according to the power transmission mechanism S1, even when a clutch 4 with a large backlash in the connected state is used, it is possible to reduce the backlash in the rotational direction between the input shaft 2 and the output shaft 3.

[0029] Furthermore, according to the power transmission mechanism S1, the clutch 4 is provided in the section of the power transmission path P where the rotation speed is increased between the speed-up mechanism 9 and the speed-down mechanism 10, so that the transmission torque required of the clutch 4 can be reduced and the clutch 4 can be made smaller.

[0030] (2) In the power transmission mechanism S1, the input shaft 2 is the steering shaft 2, and the output shaft 3 is mechanically connected to the vehicle's steering mechanism 5. That is, the power transmission mechanism S1 constitutes a part of the vehicle's steering system 1A. The power transmission mechanism S1 can reduce play in the rotational direction between the input shaft 2 and the output shaft 3, thereby reducing the play felt by the driver through the steering operation and improving the steering feel of the driver. In addition, it can also reduce errors in the steering angle of the steered wheels, improving the vehicle's dynamic performance.

[0031] (3) In the event of a frontal collision, the front of the vehicle may be crushed, causing the steering gear box to move rearward relative to the vehicle body. In a conventional steering mechanism, when the steering gear box moves rearward, the collision load is transmitted to the steering shaft 2 via the intermediate shaft 6, causing the steering wheel to move rearward relative to the vehicle body.

[0032] In contrast, in the power transmission mechanism S1, the speed-up mechanism 9, the clutch 4, and the reduction mechanism 10 are arranged in a direction perpendicular to the steering shaft 2, i.e., perpendicular to the vehicle longitudinal direction. Therefore, the steering shaft 2 and the output shaft 3 are offset in the vehicle width direction. (Hereinafter, the portion of the power transmission mechanism S1 where the speed-up mechanism 9, the clutch 4, and the reduction mechanism 10 are aligned is also referred to as the laterally extending portion.) Therefore, even if a collision load is input to the output shaft 3 during a frontal collision, the laterally extending portion rotates or deforms, preventing the collision load from being directly transmitted to the steering shaft 2. This suppresses rearward movement of the steering wheel, thereby improving occupant protection performance. Note that the extension direction of the laterally extending portion is not limited to a direction perpendicular to the steering shaft 2. In other embodiments, the speed-up mechanism 9, the clutch 4, and the reduction mechanism 10 may be arranged in a direction that intersects the steering shaft 2 at an angle other than a right angle in a plan view. In this case, the steering shaft 2 and the output shaft 3 are disposed offset in the vehicle width direction, so that the same effect can be obtained.

[0033] (4) In the power transmission mechanism S1, a flexible coupling 8B, which is a weak part, is provided on the power transmission path P between the speed increasing mechanism 9 and the clutch 4. In addition, a notch 8A, which is a weak part, is formed in the casing of the clutch 4 in a position near the flexible coupling 8B. Therefore, when a collision load is input to the output shaft 3 in the event of a frontal vehicle collision, the casing breaks starting from the notch 8A and the flexible coupling 8B deforms. This more reliably reduces the load input to the steering shaft 2 and further suppresses rearward movement of the steering wheel in the event of a vehicle collision, thereby further improving occupant protection performance.

[0034] (5) The power transmission mechanism S1 includes a flexible coupling 8B that deforms due to a collision load input to the output shaft 3 during a vehicle frontal collision. The flexible coupling 8B can transmit rotational power while in a deformed state as long as the amount of deformation is within an allowable range. Therefore, with the power transmission mechanism S1, after a vehicle frontal collision, the steerable wheels can be steered by operating the steering wheel, improving limp-home performance.

[0035] <Modification> The power transmission mechanism S1 described above includes the notch 8A and the flexible coupling 8B as the weak portion, but as shown in Fig. 4, instead of the flexible coupling 8B, a small diameter portion 8C may be formed as the weak portion in the worm shaft 9B of the speed increasing mechanism 9. The small diameter portion 8C is a portion that has a locally smaller outer diameter than other portions.

[0036] In the power transmission mechanism S1A according to this modification, the small diameter portion 8C is formed between the speed increasing mechanism 9 and the clutch 4. The power transmission mechanism S1A has the same configuration as that of the first embodiment, except that the small diameter portion 8C is provided instead of the flexible coupling 8B, and therefore can obtain the above-described advantageous effects (1) to (3).

[0037] (6) In the power transmission mechanism S1A, a small diameter portion 8C, which is a weakened portion, is provided on the power transmission path P between the speed increasing mechanism 9 and the clutch 4. In addition, a notch 8A, which is a weakened portion, is formed in the casing of the clutch 4 near the small diameter portion 8C. Therefore, when a collision load is input to the output shaft 3 during a frontal vehicle collision, the casing breaks from the notch 8A and the foam shaft breaks at the small diameter portion 8C. As a result, similar to the effect of (4) above, the load input to the input shaft 2 is reduced and rearward movement of the steering wheel during a vehicle collision is suppressed, thereby improving occupant protection performance.

[0038] The flexible coupling 8B and the small diameter portion 8C may be provided at other positions on the power transmission path P between the speed-increasing mechanism 9 and the reduction mechanism 10. The section between the speed-increasing mechanism 9 and the reduction mechanism 10 extends in the vehicle width direction, with one end of the section located near the attachment point of the steering column 14 to the vehicle body and the other end of the section where the output shaft 3 is located. That is, the attachment point to the vehicle body and the input point of the collision load are spaced apart from each other in the vehicle width direction. Therefore, by providing the flexible coupling 8B and the small diameter portion 8C in the section, they can be more easily deformed or broken by the collision load in a vehicle frontal collision. For the same reason, the notch 8A may also be provided at other positions between the speed-increasing mechanism 9 and the reduction mechanism 10. Specifically, for example, the flexible coupling 8B and the small diameter portion 8C may be provided on the power transmission path P between the clutch 4 and the reduction mechanism 10. The notch 8A may be provided in a region of the casing of the clutch 4 between the clutch 4 and the reduction mechanism 10. More specifically, the flexible coupling 8B may be provided between a worm formed on the worm shaft 10B and the clutch 4. The small diameter portion 8C may also be formed on the worm shaft 10B between the worm formed on the worm shaft 10B and the clutch 4.

[0039] Second Embodiment A vehicle steering system 1B including a power transmission mechanism S2 according to a second embodiment will be described with reference to Fig. 5. In the second embodiment, only the configurations different from the first embodiment will be described, and the configurations having the same functions as the configurations already described in the first embodiment and its modified examples will be denoted by the same reference numerals, and the description thereof will be omitted.

[0040] In the power transmission mechanism S2, the clutch 4 and the reduction mechanism 10 are connected by a flexible torque transmission wire 20, and the reduction mechanism 10 is integrated with the steering gearbox. The power transmission mechanism S2 does not include an intermediate shaft 6, and therefore the output shaft 3 of the power transmission mechanism S2, i.e., the rotation axis of the worm wheel 10A of the reduction mechanism 10, is the pinion gear shaft 7 of the steering gearbox.

[0041] As in the first embodiment, the power transmission mechanism S2 includes an input shaft 2, an output shaft 3, and a clutch 4 provided on a power transmission path P between the input shaft 2 and the output shaft 3. A speed increasing mechanism 9 is provided on the power transmission path P between the input shaft 2 and the clutch 4, and a speed reducing mechanism 10 is provided on the power transmission path P between the output shaft 3 and the clutch 4. The input shaft 2 is a steering shaft 2, and the output shaft 3 is mechanically connected to a steering mechanism 5 of the vehicle. Therefore, the power transmission device according to this embodiment can achieve the effects (1) and (2) described above.

[0042] (7) In the power transmission mechanism S2, the clutch 4 and the reduction gear mechanism 10 are connected by a flexible torque transmission wire 20. Therefore, even if a collision load is input to the output shaft 3 during a vehicle frontal collision, the torque transmission wire 20 deforms, thereby suppressing the load input to the input shaft 2. This more reliably suppresses rearward movement of the steering wheel during a vehicle collision, thereby further improving occupant protection performance.

[0043] In the power transmission mechanism S2, the clutch 4 and the speed reduction mechanism 10 are connected by the torque transmission wire 20. However, instead of or in addition to this, the speed increase mechanism 9 and the clutch 4 may be connected by a torque transmission wire. In this case, the same effects as those described above can be obtained.

[0044] The above-described embodiments and their modifications (hereinafter, "embodiments") are merely examples described to facilitate understanding of the invention. The technical scope of the invention is not limited to the specific technical matters disclosed in the above-described embodiments, but also includes various modifications, changes, alternative technologies, etc. that can be easily derived therefrom.

[0045] For example, the clutch 4 in the above-described embodiments is a disc-type friction clutch. However, the clutch 4 may be another type of friction clutch, such as a drum-type friction clutch or a cone-type friction clutch. Alternatively, the clutch 4 may be another type of clutch, such as a dog clutch, such as a roller clutch or a tooth clutch.

[0046] Although the above embodiments and the like use the speed-up mechanism 9 and the speed-down mechanism 10 that use worm gears, other types of speed-up mechanism and speed-down mechanism may also be used. The speed-up mechanism 9 and the speed-down mechanism 10 may be constructed using, for example, planetary gears or bevel gears other than worm gears. However, worm gears are advantageous in that they can achieve a large speed-up or speed-down ratio and also have the advantage of being able to incorporate the above-mentioned backlash suppression mechanism. Furthermore, the speed-up mechanism 9 and the speed-down mechanism 10 in the above embodiments and the like are single-stage speed-up and speed-down mechanisms that do not have a speed-changing function. However, the speed-up mechanism 9 and the speed-down mechanism 10 may each have a two-stage or more speed-changing function.

[0047] In the above embodiment and the like, the diameter of the worm wheel 10A of the speed reduction mechanism 10 is larger than the diameter of the worm wheel 9A of the speed increase mechanism 9 (see FIG. 3 ). That is, the reduction ratio of the speed reduction mechanism 10 is smaller than the reciprocal of the speed increase ratio of the speed increase mechanism 9. However, the relationship between the speed increase ratio and the reduction ratio is not particularly limited. The speed increase ratio and the reduction ratio may be set so that the rotation angle of the input shaft 2 and the rotation angle of the output shaft 3 match. Furthermore, the speed increase ratio and the reduction ratio may be set so that the output shaft 3 rotates less than one rotation (e.g., 0.8 rotations) or more than one rotation (e.g., 1.2 rotations) per one rotation of the input shaft 2.

[0048] In the above embodiments, examples have been shown in which the power transmission mechanism is incorporated into the steering system of a vehicle, but it goes without saying that the power transmission mechanism can be applied to other industrial machines such as machine tools, industrial robots, and construction machines.

[0049] S1, S1A, S2 power transmission mechanism, 2 steering shaft (input shaft), 3 output shaft, 4 clutch, 5 steering mechanism, 8A notch (weak part), 8B flexible coupling (weak part), 8C small diameter part (weak part), 9 speed increasing mechanism, 10 speed reducing mechanism, P power transmission path

Claims

1. an input shaft which is a steering shaft; an output shaft mechanically coupled to a steering mechanism of the vehicle; a clutch provided on a power transmission path between the input shaft and the output shaft; a speed increasing mechanism provided on the power transmission path between the input shaft and the clutch; a speed reduction mechanism provided on the power transmission path between the output shaft and the clutch; a reaction motor connected to a rotation shaft of the speed increasing mechanism on the clutch side; a steering motor connected to a rotation shaft on the clutch side of the reduction mechanism; A power transmission mechanism comprising:

2. 2. The power transmission mechanism according to claim 1, wherein the speed increasing mechanism, the clutch, and the speed reducing mechanism are arranged in a direction intersecting the steering shaft.

3. 3. The power transmission mechanism according to claim 2, further comprising a weakened portion disposed between the speed increasing mechanism and the speed reducing mechanism, the weakened portion being deformed or broken by a collision load input to the output shaft in the event of a collision of the vehicle.

4. 4. The power transmission mechanism of claim 3, wherein the weakened portion is a flexible coupling.