Power transmission mechanism

Abstract

This aims to reduce the cost of the field core used in the electromagnetic clutch incorporated between the speed-increasing mechanism and the speed-reducing mechanism in the power transmission path between the input shaft and the output shaft. [Solution] The electromagnetic clutch 4 includes a flange member 19 attached to the field core 22 of the electromagnet 10, a retaining ring 20 attached to the inner circumference of the casing 18 to restrict the movement of the flange member 19 to one axial side, and an elastic member 21 that biases the field core 22 to one axial side relative to the casing 18. The flange member 19 protrudes radially outward from the outer cylindrical portion 22b of the field core 22. The annular side wall portion 18a of the casing 18 restricts the movement of the annular bottom portion 22c extending between the inner cylindrical portion 22a and the outer cylindrical portion 22b of the field core 22 or the flange member 19 to the other axial side.

Description

Technical Field

[0001] The present invention relates to a power transmission mechanism in which an electromagnetic clutch is incorporated in a power transmission path between an input shaft and an output shaft.

Background Art

[0002] Conventionally, in power transmission mechanisms such as the steer-by-wire system of a vehicle and a machine tool, there are some that transmit and cut off rotation by a clutch. In this type of power transmission mechanism, play between the input shaft and the output shaft may occur due to play in the clutch, which can have an adverse effect on the operation and accuracy of the system. Therefore, it is preferable to suppress such play. As a countermeasure, a speed increasing mechanism is provided between the input shaft and the clutch, and a speed reducing mechanism is provided between the clutch and the output shaft (Patent Document 1).

[0003] In the power transmission mechanism disclosed in Patent Document 1, worm gears are respectively adopted for the speed increasing mechanism and the speed reducing mechanism. When the clutch is in the connected state, the play in the rotational direction of the clutch is reduced to a value multiplied by the reciprocal of the speed increasing ratio of the speed increasing mechanism and transmitted to the input shaft, while it is reduced to a value multiplied by the speed reducing ratio of the speed reducing mechanism and transmitted to the output shaft. Therefore, compared with the play in the rotational direction of the clutch, the play in the rotational direction between the input shaft and the output shaft is reduced. Further, since the clutch is provided in the speed increasing section on the power transmission path where the rotation is speeded up between the speed increasing mechanism and the speed reducing mechanism, the torque capacity required for the clutch is reduced, and it is also possible to reduce the size of the clutch. As the clutch, an electromagnetic clutch is adopted. The electromagnetic clutch is configured such that when the electromagnet is in the non-excited state, the friction plate is pressed against the driven side by the spring force and enters a connected state where rotation is transmitted from the driving side to the driven side, and when the electromagnet is in the excited state, the friction plate is attracted to the rotor on the driving side and enters a disconnected state where the rotation transmission from the driving side to the driven side is blocked, and it is a friction type one.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] International Patent Publication No. 2024 / 176325 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the power transmission mechanism disclosed in Patent Document 1, the field core of the electromagnet of the electromagnetic clutch is directly connected to the casing in order to fix the electromagnet to the casing. The field core integrally comprises an inner cylinder portion, an outer cylinder portion, an annular bottom portion extending between the inner and outer cylinder portions, and a flange portion projecting radially outward from the outer cylinder portion and the annular bottom portion. The field coil is arranged between the inner and outer cylinder portions. On one side of the field core, the flange portion and the annular bottom portion form a coplanar end face along the radial direction. It is necessary to bring this end face of the field core into axial contact with the annular side wall of the casing and fix the flange portion to the annular side wall by fastening or the like.

[0006] The field core used in small electromagnetic clutches is made of iron-based material, and its overall shape can be forged. However, during forging, it is difficult to punch the flange portion straight and uniformly in the radial direction from the outer cylinder and annular bottom portion, resulting in a forged flange portion that does not conform to the shape of the casing. Therefore, post-processing is required to finish the end face of the forged field core to a radially flat surface by machining, which incurs additional costs.

[0007] In light of the above background, the problem that this invention aims to solve is to reduce the cost of the field core provided in the electromagnetic clutch incorporated between the speed-increasing mechanism and the reduction mechanism in the power transmission path between the input shaft and the output shaft. [Means for solving the problem]

[0008] To achieve the above objectives, this invention provides an input shaft, an output shaft, an electromagnetic clutch for transmitting and interrupting rotation on a power transmission path between the input shaft and the output shaft, a speed-increasing mechanism provided between the input shaft and the electromagnetic clutch on the power transmission path, and a reduction mechanism provided between the output shaft and the electromagnetic clutch on the power transmission path, wherein the electromagnetic clutch comprises an electromagnet, a friction plate attracted axially to the electromagnet, and a casing housing the electromagnet, the electromagnet comprises a field core and a field coil attached to the field core, and the field core comprises an inner cylinder portion, an outer cylinder portion, and the space between the inner cylinder portion and the outer cylinder portion. A power transmission mechanism is adopted in which the field coil is disposed between the inner cylinder and the outer cylinder, and the electromagnetic clutch further comprises a flange member attached to the field core, a retaining ring attached to the inner circumference of the casing to restrict the movement of the flange member to one axial side, and an elastic member that biases the field core to one axial side relative to the casing, wherein the flange member protrudes radially outward from the outer cylinder, and the casing has an annular side wall portion that restricts the movement of the annular bottom or the flange member to the other axial side.

[0009] According to the above configuration 1, the field core is fixed axially by the cooperation of the annular side wall of the casing, the retaining ring, the elastic member, and the flange member. Therefore, it is not necessary to integrally form the flange portion on the field core, and since axial errors are absorbed by the elastic member, high precision is not required for the attachment of the field core and the flange member. As a result, it is possible to reduce the cost of the field core by eliminating the need for post-processing to finish one side of the field core with high precision.

[0010] In the above configuration 1, configuration 2 can be adopted in which the flange member consists of a retaining ring attached to the outer circumference of the field core.

[0011] According to the above configuration 2, since a retaining ring is used for the flange member, the cost of the flange member can be reduced while making it easy to attach to the field core.

[0012] In the above configuration 1, configuration 3 can be adopted in which the flange member consists of a plate material fixed to the axial end face of the annular bottom.

[0013] According to the above configuration 3, since plate material is used for the flange member, the cost of the flange member can be reduced.

[0014] In any one of the above configurations 1 to 3, configuration 4 can be adopted in which the elastic member consists of an annular spring sandwiched between the annular bottom or the flange member and the casing.

[0015] According to the above configuration 4, since an annular spring is used for the elastic member, the annular shape is used to sandwich the elastic member axially between the annular bottom of the field core or the flange member and the casing, and to position it radially, thereby biasing the field core to one side in the axial direction.

[0016] In any one of the above configurations 1 to 4, configuration 5 can be adopted, wherein the power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, the electromagnetic clutch further has a rotor connected to the drive-side transmission shaft and a sleeve made of a non-magnetic material disposed between the drive-side transmission shaft and the rotor, the rotor has a hollow shaft portion and an annular yoke portion projecting radially from one axial side of the hollow shaft portion to the space between the field core and the friction plate, the sleeve fits into the inner circumference of the hollow shaft portion, and the drive-side transmission shaft fits into the inner circumference of the sleeve.

[0017] According to the above configuration 5, magnetic leakage from the rotor to the drive-side transmission shaft can be prevented by the sleeve when the electromagnet is excited.

[0018] In any one of the above configurations 1 to 4, configuration 6 can be adopted, wherein the power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, the electromagnetic clutch further has a rotor directly connected to the drive-side transmission shaft, the rotor has an annular yoke portion located between the field core and the friction plate, and the drive-side transmission shaft is made of a non-magnetic material.

[0019] According to the above configuration 6, magnetic leakage from the hollow shaft portion of the rotor to the drive-side transmission shaft can be further prevented.

[0020] In any one of the above configurations 1 to 6, configuration 7 can be adopted, wherein the power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, the electromagnetic clutch further has a rotor connected to the drive-side transmission shaft, the rotor has an annular yoke portion located between the field core and the friction plate, and slits are formed at multiple locations in the circumferential direction of the annular yoke portion, penetrating the annular yoke portion in the axial direction.

[0021] According to the above configuration 7, when the rotor and friction plate are attracted by the excitation of the electromagnet, a magnetic circuit is formed that reciprocates multiple times between the rotor and the friction plate, thereby improving the attraction force.

[0022] In any one of the above configurations 1 to 7, the power transmission path has a drive-side transmission shaft provided between the speed increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the speed reducing mechanism and the electromagnetic clutch. The electromagnetic clutch further has a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion positioned between the field core and the friction plate. The friction plate is arranged to be axially movable between a position in contact with the inner driver and a position in contact with the annular yoke portion. An impact absorbing member for reducing the collision sound of the friction plate is provided between at least one of the annular yoke portion and the friction plate and between the friction plate and the inner driver. The configuration 8 can be adopted.

[0023] According to the above configuration 8, the collision sound caused by the axial movement of the friction plate can be reduced, and the quietness of the electromagnetic clutch can be improved.

[0024] In any one of the above configurations 1 to 8, the power transmission path has a drive-side transmission shaft provided between the speed increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the speed reducing mechanism and the electromagnetic clutch. The electromagnetic clutch further has a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion positioned between the field core and the friction plate. The friction plate is arranged to be axially movable between a position in contact with the inner driver and a position in contact with the annular yoke portion. At least one of the drive-side transmission shaft and the driven-side transmission shaft has a stepped portion capable of restricting axial movement by axially abutting against the corresponding rotor or inner driver, which is the connecting partner. The configuration 9 can be adopted.

[0025] According to the above configuration 9, it is possible to prevent a corresponding rotor or inner driver that receives the axial movement of the friction plate from axially shifting with respect to a corresponding drive-side transmission shaft or driven-side transmission shaft by a corresponding step portion.

[0026] In any one of the above configurations 1 to 9, the power transmission path has a drive-side transmission shaft provided between the speed increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the speed reducing mechanism and the electromagnetic clutch. The electromagnetic clutch further has a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion located between the field core and the friction plate. The friction plate is arranged to be axially movable between a position where it abuts against the inner driver and a position where it abuts against the annular yoke portion. The friction plate and the rotor are spline-fitted. It is possible to adopt Configuration 10.

[0027] According to the above configuration 10, it is possible to reliably transmit the rotational power between the friction plate and the rotor.

Effects of the Invention

[0028] As described above, by adopting the above configuration 1, this invention can reduce the cost of the field core provided in the electromagnetic clutch incorporated between the speed increasing mechanism and the speed reducing mechanism on the power transmission path between the input shaft and the output shaft.

Brief Description of the Drawings

[0029] [Figure 1] A diagram schematically showing the overall configuration of the power transmission mechanism according to the first embodiment of this invention, and showing the electromagnetic clutch in a cross-section along the axial direction [Figure 2] A diagram showing the electromagnetic clutch according to the second embodiment of this invention in a cross-section along the axial direction [Figure 3] A partial cross-sectional view showing a modification example of the connection structure between the drive-side transmission shaft and the electromagnetic clutch according to the first embodiment or the second embodiment [Modes for carrying out the invention]

[0030] Figure 1 shows a power transmission mechanism according to a first embodiment as an example of this invention (hereinafter simply referred to as "this power transmission mechanism").

[0031] This power transmission mechanism consists of an input shaft 1, an output shaft 2, and a power transmission path 3 provided between the input shaft 1 and the output shaft 2.

[0032] Input shaft 1 inputs rotational power to this power transmission mechanism. Output shaft 2 outputs rotational power from this power transmission mechanism. Power transmission path 3 increases the speed of the rotation transmitted from input shaft 1, transmits and disconnects this increased speed rotation using an electromagnetic clutch 4, and reduces the speed of the increased speed rotation transmitted from electromagnetic clutch 4 before transmitting it to output shaft 2.

[0033] In this power transmission mechanism, the power transmission path 3 consists of a speed-increasing mechanism 5, a drive-side transmission shaft 6, an electromagnetic clutch 4, a driven-side transmission shaft 7, and a reduction mechanism 8. The speed-increasing mechanism 5 increases the speed of the rotation transmitted from the input shaft 1. The drive-side transmission shaft 6 transmits the rotation increased by the speed-increasing mechanism 5 to the electromagnetic clutch 4. The driven-side transmission shaft 7 transmits the rotation transmitted from the electromagnetic clutch 4 to the reduction mechanism 8. The reduction mechanism 8 reduces the rotation transmitted from the driven-side transmission shaft 7.

[0034] In this power transmission mechanism, the speed-increasing mechanism 5 and the reduction mechanism 8 are each composed of a worm provided on the corresponding input shaft 1 or output shaft 2 and a worm wheel provided on the corresponding drive-side transmission shaft 6 or driven-side transmission shaft 7. Although worm gears are used as examples for the speed-increasing and reduction mechanisms, other gear speed increasers and gear reducers may also be used.

[0035] When this power transmission mechanism is adopted in a steer-by-wire system for a vehicle or the like (not shown), for example, if the input shaft 1 is the steering shaft to which the steering wheel is attached, the drive-side transmission shaft 6 is connected to the output shaft of the reaction force motor, the driven-side transmission shaft 7 is connected to the steering motor, and the output shaft 2 is connected to the pinion gear shaft of the steering gearbox via the intermediate shaft, then while the electromagnetic clutch 4 is disengaged and steer-by-wire control is being performed, the output of the reaction force motor can be amplified by the speed-increasing mechanism 5 and transmitted from the input shaft 1 to the steering wheel as steering reaction force, and the output of the steering motor can be amplified by the reduction mechanism 8 and transmitted from the output shaft 2 to the pinion gear shaft as steering driving force. On the other hand, while the electromagnetic clutch 4 is disengaged and steer-by-wire control is stopped, the reaction force motor and steering motor can be used as the driving force source for the power steering mechanism.

[0036] When the electromagnetic clutch 4 is engaged, the rotational play of the electromagnetic clutch 4 is reduced to a value multiplied by the reciprocal of the speed-increasing ratio of the speed-increasing mechanism 5 and transmitted to the input shaft 1, while it is reduced to a value multiplied by the reduction ratio of the reduction mechanism 8 and transmitted to the output shaft 2. In addition, as the rotational speed is increased by the speed-increasing mechanism 5, the rotational torque decreases, and as the rotational speed is reduced by the reduction mechanism 8, the rotational torque increases.

[0037] The rotation centers of the drive side and the driven side of the electromagnetic clutch 4 are set on the same axis. Here, the direction along that axis is called the "axial direction," the direction perpendicular to that axis is called the "radial direction," and the direction around the circumference of that axis is called the "circumferential direction."

[0038] The electromagnetic clutch 4 includes an electromagnet 10, a friction plate 11 located on one axial side (right side in Figure 1) relative to the electromagnet 10, a rotor 12 positioned between the electromagnet 10 and the friction plate 11 and facing the electromagnet 10 and the friction plate 11 in the axial direction, a separation spring 13 positioned between the rotor 12 and the friction plate 11, an inner driver 14 located on one axial side relative to the friction plate 11, a sleeve 15 interposed between the rotor 12 and the drive-side transmission shaft 6, a drive-side shock absorbing member 16 positioned between the rotor 12 and the friction plate 11, a driven-side shock absorbing member 17 positioned between the friction plate 11 and the inner driver 14, a casing 18 housing the electromagnet 10, the friction plate 11, the rotor 12 and the inner driver 14, a flange member 19 attached to the outer circumference of the electromagnet 10, a retaining ring 20 attached to the inner circumference of the casing 18, and an elastic member 21 sandwiched between the electromagnet 10 and the casing 18.

[0039] The electromagnet 10 has a field core 22 and a field coil 23 attached to the field core 22.

[0040] The field core 22 seamlessly comprises an inner cylindrical portion 22a, an outer cylindrical portion 22b surrounding the inner cylindrical portion 22a radially, and an annular bottom portion 22c extending between the other axial end of the inner cylindrical portion 22a (left side in Figure 1) and the other axial end of the outer cylindrical portion 22b. The entire field core 22 is forged from an iron-based material. One side of the field core 22 consists of a forged surface that forms the axial end face of the annular bottom portion 22c and is oriented substantially radially.

[0041] The field coil 23 is positioned between the inner cylinder portion 22a and the outer cylinder portion 22b.

[0042] The flange member 19 consists of a retaining ring attached to the outer circumference of the field core 22. A retaining ring groove 22d corresponding to the flange member 19 is formed on the outer circumference of the annular bottom portion 22c. The flange member 19 protrudes radially outward from the outer cylindrical portion 22b.

[0043] The casing 18 is cylindrical with openings on both axial sides. The casing 18 has a segmented structure that allows for the incorporation of the movable and charging parts of the electromagnetic clutch 4. The casing 18 has an annular side wall portion 18a that receives the axial end face of the annular bottom portion 22c in the axial direction. On the inner circumference of the casing 18, there is a spigot portion 18b that receives the outer peripheral end of the annular bottom portion 22c in the radial direction, a retaining ring groove 18c corresponding to the retaining ring 20, and a spring seat portion 18d that receives the elastic member 21 in the axial and radial directions.

[0044] The annular side wall portion 18a restricts the axial movement of the field core 22 to the other side (left side in Figure 1). The spigot portion 18b restricts the radial movement of the field core 22. The spring seat portion 18d restricts the axial movement and radial movement of the elastic member 21.

[0045] The retaining ring 20, fitted into the retaining ring groove 18c, is located on one axial side (right side in Figure 1) relative to the flange member 19, and restricts the movement of the flange member 19 in one axial direction.

[0046] The elastic member 21 is compressed axially between the annular side wall portion 18a and the axial end face of the annular bottom portion 22c of the casing 18, and the spring force of its elastic rebound biases the field core 22 axially to one side (to the right in Figure 1) relative to the annular side wall portion 18a. This bias maintains a state in which the retaining ring groove 22d, the flange member 19, the retaining ring 20, and the retaining ring groove 18c are in contact without axial play, and the movement of the field core 22 axially to one side relative to the casing 18 is restricted. The elastic member 21 is an annular spring. For example, a coiled wave spring can be used for the elastic member 21.

[0047] The rotor 12 seamlessly comprises a hollow shaft portion 12a and an annular yoke portion 12b that protrudes radially from one axial side of the hollow shaft portion 12a (the right side in Figure 1) between the field core 22 and the friction plate 11.

[0048] A sleeve 15 is fitted to the inner circumference of the hollow shaft portion 12a. A drive-side transmission shaft 6 is fitted to the inner circumference of the sleeve 15. The drive-side transmission shaft 6, sleeve 15, and rotor 12 are fitted together in a way that allows rotational power to be transmitted from the drive-side transmission shaft 6 to the rotor 12 via the sleeve 15.

[0049] The drive-side transmission shaft 6 has a stepped portion 6a that abuts axially with the other axial end (left side in Figure 1) of the hollow shaft portion 12a. The stepped portion 6a restricts the movement of the rotor 12 to the other axial side (left side in Figure 1).

[0050] The sleeve 15 is made of a non-magnetic material such as an aluminum alloy. The rotor 12 and the drive-side transmission shaft 6 are each made of a magnetic material such as an iron-based material. Because the contact area between the rotor 12 and the drive-side transmission shaft 6 is reduced by connecting them via the sleeve 15, magnetic leakage from the rotor 12 to the drive-side transmission shaft 6 is suppressed when the electromagnet 10 is energized.

[0051] The annular yoke portion 12b has multiple slits 12c formed at various locations in the circumferential direction, penetrating the annular yoke portion 12b in the axial direction. The slits 12c are axially opposite to the friction plate 11.

[0052] A guide shaft portion 12d is formed at one axial end of the hollow shaft portion 12a, supporting the friction plate 11 in the radial direction. The guide shaft portion 12d is a spline shaft. The friction plate 11 has an inner circumference portion 11a spline-fitted to the guide shaft portion 12d. The friction plate 11 is made of a magnetic material.

[0053] The inner driver 14 is connected to the driven transmission shaft 7. The inner driver 14 has a stopper portion 14a that faces the friction plate 11 in the axial direction. The friction plate 11 is arranged to be movable in the axial direction between a position in contact with the stopper portion 14a and a position in contact with the annular yoke portion 12b.

[0054] The driven transmission shaft 7 has a stepped portion 7a that abuts axially with one end of the inner driver 14 on one axial side (the right side in Figure 1). The stepped portion 7a restricts the movement of the inner driver 14 in one axial direction.

[0055] A separation spring 13 is sandwiched axially between the annular yoke portion 12b and the friction plate 11. The separation spring 13 is compressed axially when the friction plate 11 is attracted to the annular yoke portion 12b in the axial direction, biasing the friction plate 11 axially toward the stopper portion 14a of the inner driver 14 (to the right in Figure 1). The separation spring 13 is an annular spring. For example, a coiled wave spring can be used for the separation spring 13.

[0056] When the power supply to the field coil 23 is cut off and the electromagnet 10 is in an unexcited state, the friction plate 11 is pressed axially against the stopper portion 14a of the inner driver 14 due to the biasing force of the separation spring 13.

[0057] Furthermore, since the field core 22 is held to the rotor 12 at a predetermined degree of coaxiality by the spigot portion 18b of the casing 18, the radial gap between the outer cylinder portion 22b and the rotor 12, and the radial gap between the inner cylinder portion 22a and the rotor 12 are maintained within appropriate ranges.

[0058] Since the field core 22 is pressed axially against the retaining ring 20 on the casing 18 side by the biasing force of the elastic member 21, the air gap between the field core 22 and the rotor 12 is kept within a predetermined range so as to maintain the performance of the electromagnetic clutch 4.

[0059] Regarding the attachment of the flange member 19 to the field core 22, since the axial expansion and contraction of the elastic member 21 can absorb dimensional errors in the axial direction, post-processing to precisely finish the axial end face of the forged annular bottom portion 22c to a shape corresponding to the annular side wall portion 18a by machining is unnecessary.

[0060] Furthermore, when the friction plate 11 is attracted to the rotor 12, the rotor 12 is pushed axially away from the friction plate 11 to the other side (left side in Figure 1), but the stepped portion 6a of the drive-side transmission shaft 6 prevents the rotor 12 from shifting axially. Also, when the friction plate 11 is pressed against the inner driver 14 by the separation spring 13, the inner driver 14 is pushed axially away from the friction plate 11 to one side (right side in Figure 1), but the stepped portion 6a of the drive-side transmission shaft 6 prevents the inner driver 14 from shifting axially. For this reason, the air gap between the rotor 12 and the friction plate 11 when the electromagnetic clutch 4 is engaged is kept within a predetermined range so as to maintain the performance of the electromagnetic clutch 4.

[0061] The air gap between the field core 22 and the rotor 12, and the air gap between the rotor 12 and the friction plate 11, are controlled to be within a range of 0.1 to 1.0 mm in the axial direction.

[0062] When the field coil 23 is energized and the electromagnet 10 is energized, a magnetic circuit is formed passing through the field core 22, rotor 12, and friction plate 11. The friction plate 11 is magnetically attracted to the other axial side, moves away from the stopper portion 14a to the other axial side (left side in Figure 1), and is then attracted to the annular yoke portion 12b. At this time, because a slit 12c is formed in the annular yoke portion 12b, a magnetic circuit is formed that reciprocates multiple times between the annular yoke portion 12b and the friction plate 11, thereby improving the attractiveness between the annular yoke portion 12b and the friction plate 11.

[0063] When the electromagnet 10 is de-energized, the friction plate 11 on the drive side is pressed against the inner driver 14 on the driven side by the spring force of the separation spring 13, and the electromagnetic clutch 4 becomes connected, enabling it to transmit rotation from the drive side to the driven side. When the electromagnetic clutch 4 is connected, the rotation of the drive-side transmission shaft 6 is transmitted to the friction plate 11 via the sleeve 15, the hollow shaft portion 12a of the rotor 12 and the separation spring 13, and further transmitted to the inner driver 14 from the friction contact portion between the friction plate 11 and the stopper portion 14a, and further transmitted to the driven-side transmission shaft 7 from the connection portion between the inner driver 14 and the driven-side transmission shaft 7. Note that Figure 1 shows the electromagnetic clutch 4 in the disengaged state.

[0064] When the electromagnet 10 is energized, the friction plate 11 on the drive side is attracted to the rotor 12 on the drive side and separated from the inner driver 14 on the driven side, causing the electromagnetic clutch 4 to disengage, which blocks the transmission of rotation from the drive side to the driven side. When the electromagnetic clutch 4 is disengaged, the rotation of the drive-side transmission shaft 6 is transmitted from the sleeve 15 to the friction plate 11, but not to the inner driver 14, which is separated from the friction plate 11.

[0065] A drive-side shock-absorbing member 16 is positioned between the outer diameter side of the annular yoke portion 12b and the outer diameter side of the friction plate 11. The drive-side shock-absorbing member 16 reduces the collision noise between the friction plate 11 and the annular yoke portion 12b when the electromagnet 10 is switched from an unexcited state to an excited state.

[0066] A driven shock-absorbing member 17 is positioned between the outer diameter side of the friction plate 11 and the outer diameter side of the stopper portion 14a. The driven shock-absorbing member 17 reduces the collision noise between the friction plate 11 and the stopper portion 14a when the electromagnet 10 is switched from an energized state to a de-energized state.

[0067] The shock-absorbing members 16 and 17 can be, for example, annular springs such as coiled wave springs or rubber rings such as ethylene propylene diene rubber (EPDM). Furthermore, the shock-absorbing members 16 and 17 do not need to be directly attached to the rotor 12 or inner driver 14, but can also be supported hollow from the corresponding rotor 12 or inner driver 14 via a backup plate.

[0068] This power transmission mechanism is as described above and comprises an input shaft 1, an output shaft 2, an electromagnetic clutch 4 that transmits and interrupts rotation on a power transmission path 3 between the input shaft 1 and the output shaft 2, a speed-increasing mechanism 5 provided between the input shaft 1 and the electromagnetic clutch 4 on the power transmission path 3, and a reduction mechanism 8 provided between the output shaft 2 and the electromagnetic clutch 4 on the power transmission path 3. The electromagnetic clutch 4 has an electromagnet 10, a friction plate 11 that is attracted to the electromagnet 10 in the axial direction, and a casing 18 that houses the electromagnet 10. The electromagnet 10 has a field core 22 and a field coil 23 attached to the field core 22. The field core 22 has an inner cylinder portion 22a, an outer cylinder portion 22b, and an annular bottom portion 22c extending between the inner cylinder portion 22a and the outer cylinder portion 22b. The field coil 23 is arranged between the inner cylinder portion 22a and the outer cylinder portion 22b.

[0069] This power transmission mechanism further includes an electromagnetic clutch 4 attached to a flange member 19 on the field core 22, a retaining ring 20 attached to the inner circumference of the casing 18 to restrict the axial movement of the flange member 19 to one side (right side in Figure 1), and an elastic member 21 that biases the field core 22 axially to one side relative to the casing 18. The flange member 19 protrudes radially outward from the outer cylinder portion 22b, and the casing 18 has an annular side wall portion 18a that restricts the axial movement of the annular bottom portion 22c to the other side (left side in Figure 1). As a result of having this configuration, the field core 22 is fixed axially by the cooperation of the annular side wall portion 18a of the casing 18, the retaining ring 20, the elastic member 21, and the flange member 19. Therefore, it is not necessary to integrally form the flange portion on the field core 22, and since axial errors are absorbed by the elastic member 21, high precision is not required for the attachment of the field core 22 and the flange member 19. For this reason, post-processing to finish one side of the field core 22 (the axial end face of the annular bottom portion 22c) with high precision is omitted, and the cost of the field core 22 can be reduced.

[0070] Furthermore, since this power transmission mechanism consists of a flange member 19 made of a retaining ring attached to the outer circumference of the field core 22, a general-purpose retaining ring can be used for the flange member 19, reducing the cost of the flange member 19 while making it easy to attach to the field core 22.

[0071] Furthermore, since the elastic member 21 in this power transmission mechanism consists of an annular spring sandwiched between the annular bottom 22c and the casing 18, the annular shape can be used to axially sandwich the elastic member 21 between the annular bottom 22c of the field core 22 and the casing 18, and to position it radially, thereby biasing the field core 22 axially to one side (the right side in Figure 1).

[0072] Furthermore, this power transmission mechanism has a drive-side transmission shaft 6 provided between the speed-increasing mechanism 5 and the electromagnetic clutch 4 in the power transmission path 3, and further comprises a rotor 12 connected to the drive-side transmission shaft 6 by the electromagnetic clutch 4, and a non-magnetic sleeve 15 positioned between the drive-side transmission shaft 6 and the rotor 12. The rotor 12 has a hollow shaft portion 12a and an annular yoke portion 12b that protrudes radially from one axial side of the hollow shaft portion 12a (right side in Figure 1) between the field core 22 and the friction plate 11. The sleeve 15 is fitted to the inner circumference of the hollow shaft portion 12a, and the drive-side transmission shaft 6 is fitted to the inner circumference of the sleeve 15, so that magnetic leakage from the rotor 12 to the drive-side transmission shaft 6 can be prevented by the sleeve 15 when the electromagnet 10 is excited.

[0073] Furthermore, this power transmission mechanism has a drive-side transmission shaft 6 provided between the speed-increasing mechanism 5 and the electromagnetic clutch 4 in the power transmission path 3, and the electromagnetic clutch 4 further has a rotor 12 connected to the drive-side transmission shaft 6, and the rotor 12 has an annular yoke portion 12b located between the field core 22 and the friction plate 11, and slits 12c are formed at multiple locations in the circumferential direction of the annular yoke portion 12b that penetrate the annular yoke portion 12b in the axial direction, so that when the rotor 12 and the friction plate 11 are attracted by the excitation of the electromagnet 10, a magnetic circuit is formed that reciprocates multiple times between the rotor 12 and the friction plate 11, thereby improving the attraction force.

[0074] Furthermore, this power transmission mechanism has a power transmission path 3 which includes a drive-side transmission shaft 6 provided between the speed-increasing mechanism 5 and the electromagnetic clutch 4, and a driven-side transmission shaft 7 provided between the reduction mechanism 8 and the electromagnetic clutch 4. The electromagnetic clutch 4 further includes a rotor 12 connected to the drive-side transmission shaft 6 and an inner driver 14 connected to the driven-side transmission shaft 7. The rotor 12 has an annular yoke portion 12b located between the field core 22 and the friction plate 11. The friction plate 11 is arranged to move axially between a position in contact with the inner driver 14 and a position in contact with the annular yoke portion 12b. Impact absorbing members 16 and 17 are provided between the annular yoke portion 12b and the friction plate 11, and between the friction plate 11 and the inner driver 14 to reduce the collision noise of the friction plate 11. Therefore, the collision noise caused by the axial movement of the friction plate 11 when the electromagnet 10 is switched between energized and de-energized states can be reduced, and the quietness of the electromagnetic clutch 4 can be improved.

[0075] Furthermore, this power transmission mechanism has a power transmission path 3 which includes a drive-side transmission shaft 6 provided between the speed-increasing mechanism 5 and the electromagnetic clutch 4, and a driven-side transmission shaft 7 provided between the reduction mechanism 8 and the electromagnetic clutch 4. The electromagnetic clutch 4 further includes a rotor 12 connected to the drive-side transmission shaft 6 and an inner driver 14 connected to the driven-side transmission shaft 7. The rotor 12 has an annular yoke portion 12b located between the field core 22 and the friction plate 11, and the friction plate 11 is arranged to be axially movable between a position in contact with the inner driver 14 and a position in contact with the annular yoke portion 12b. Since at least one of the driving-side transmission shaft 6 and the driven-side transmission shaft 7 has a stepped portion 6a or 7a that restricts axial movement by axial abutting with the corresponding connecting partner, the rotor 12 or inner driver 14, when the electromagnet 10 is switched between energized and de-energized states, the corresponding rotor 12 or inner driver 14 that receives the axial movement of the friction plate 11 can be prevented from shifting axially relative to the corresponding driving-side transmission shaft 6 or driven-side transmission shaft 7 by the corresponding stepped portion 6a or 7a, and consequently, the air gap can be properly maintained and the performance of the electromagnetic clutch 4 can be maintained.

[0076] Furthermore, this power transmission mechanism has a power transmission path 3 which includes a drive-side transmission shaft 6 provided between the speed-increasing mechanism 5 and the electromagnetic clutch 4, and a driven-side transmission shaft 7 provided between the reduction mechanism 8 and the electromagnetic clutch 4. The electromagnetic clutch 4 further includes a rotor 12 connected to the drive-side transmission shaft 6 and an inner driver 14 connected to the driven-side transmission shaft 7. The rotor 12 has an annular yoke portion 12b located between the field core 22 and the friction plate 11. The friction plate 11 is arranged to be axially movable between a position in contact with the inner driver 14 and a position in contact with the annular yoke portion 12b. Since the friction plate 11 and the rotor 12 are spline-fitted, rotational power can be reliably transmitted between the friction plate 11 and the rotor 12.

[0077] Although it is possible to omit the spline fitting between the friction plate 11 and the rotor 12, in this case, rotational power would be transmitted only through the friction contact between the annular yoke portion 12b and the separation spring 13, resulting in inferior transmission of rotational power between the friction plate 11 and the annular yoke portion 12b when the electromagnetic clutch 4 is switched to the engaged state.

[0078] In this power transmission mechanism, an example is shown in which the flange member 19 is made of a retaining ring. However, the flange member can be provided with a mounting structure that does not require post-processing of the axial end face (forged surface) of the annular bottom that is axially supported by the annular side wall of the casing, and can be modified in various ways. As an example of such modification, a second embodiment of this invention is shown in Figure 2. In the following, only the changes from the first embodiment will be described, and the same reference numerals will continue to be used for corresponding components.

[0079] The flange member 19 of the power transmission mechanism according to the second embodiment consists of a plate fixed to the axial end face of the annular bottom portion 22c of the field core 22. For example, the flange member 19 can be made of a metal plate punched out by press working. Furthermore, as a means of fixing the flange member 19 to the axial end face of the annular bottom portion 22c, for example, means such as projection welding or brazing can be used to join the flange member 19 and the annular bottom portion 22c.

[0080] The outer circumference of the flange member 19 is fitted into the spigot portion 18b on the inner circumference of the casing 18. This fitting holds the field core 22 in a predetermined coaxial position with the rotor 12.

[0081] The annular side wall portion 18a of the casing 18 restricts the axial movement of the flange member 19 to the other side (left side in Figure 2). The elastic member 21 is sandwiched between the flange member 19 and the casing 18.

[0082] In the power transmission mechanism according to the second embodiment, a simple plate material is used for the flange member 19, thus reducing the cost of the flange member 19.

[0083] In the embodiments described above, an example was shown in which a sleeve 15 is interposed between the drive-side transmission shaft 6 and the inner circumference of the hollow shaft portion 12a of the rotor 12. However, it is also possible to omit the sleeve 15. An example of such a modification is shown in Figure 3.

[0084] The drive-side transmission shaft 6 shown in Figure 3 is made of a non-magnetic material. The drive-side transmission shaft 6 is directly connected to the inner circumference of the hollow shaft portion 12a. By modifying each of the above embodiments as shown in Figure 3, it is possible to further prevent magnetic leakage from the hollow shaft portion 12a to the drive-side transmission shaft 6 while reducing the number of parts.

[0085] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. Accordingly, the scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0086] 1 input axis 2 Output shafts 3. Power transmission path 4. Electromagnetic clutch 5. Speed-increasing mechanism 6. Drive side transmission shaft 6a, 7a Stepped section 7. Passed side transmission shaft 8 Reduction mechanism 10 Electromagnets 11 Friction Plates 11a Inner circumference 12 rotors 12a Hollow shaft part 12b Annular yoke section 12c slit 12d Guide shaft 13 Detachment spring 14 Inner Driver 15 sleeves 16, 17 Shock-absorbing material 18 Casing 18a Annular side wall 19 Flange member 20 Retaining rings 21 Elastic members 22 Field Cores 22a Inner cylinder part 22b Outer cylinder part 22c Annular base 23 Field Coil

Claims

1. The system comprises an input shaft, an output shaft, an electromagnetic clutch for transmitting and interrupting rotation on a power transmission path between the input shaft and the output shaft, a speed-increasing mechanism provided between the input shaft and the electromagnetic clutch on the power transmission path, and a reduction mechanism provided between the output shaft and the electromagnetic clutch on the power transmission path. The electromagnetic clutch comprises an electromagnet, a friction plate attracted axially to the electromagnet, and a casing housing the electromagnet. The electromagnet comprises a field core and a field coil attached to the field core. The field core has an inner cylindrical portion, an outer cylindrical portion, and an annular bottom portion extending between the inner and outer cylindrical portions. In a power transmission mechanism in which the field coil is arranged between the inner cylinder and the outer cylinder, The electromagnetic clutch further comprises a flange member attached to the field core, a retaining ring attached to the inner circumference of the casing to restrict the movement of the flange member in one axial direction, and an elastic member that biases the field core in one axial direction relative to the casing. The flange member protrudes radially outward from the outer cylinder portion, A power transmission mechanism characterized in that the casing has an annular side wall portion that restricts the movement of the annular bottom portion or the flange member toward the other axial direction.

2. The power transmission mechanism according to claim 1, wherein the flange member comprises a retaining ring attached to the outer circumference of the field core.

3. The power transmission mechanism according to claim 1, wherein the flange member is a plate material fixed to the axial end face of the annular bottom.

4. The power transmission mechanism according to any one of claims 1 to 3, wherein the elastic member is an annular spring sandwiched between the annular bottom or the flange member and the casing.

5. The power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, The electromagnetic clutch further comprises a rotor connected to the drive-side transmission shaft and a non-magnetic sleeve disposed between the drive-side transmission shaft and the rotor. The rotor has a hollow shaft portion and an annular yoke portion that protrudes radially from one axial side of the hollow shaft portion between the field core and the friction plate, The sleeve is fitted onto the inner circumference of the hollow shaft portion, The power transmission mechanism according to any one of claims 1 to 3, wherein the drive-side transmission shaft is fitted into the inner circumference of the sleeve.

6. The power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, The electromagnetic clutch further comprises a rotor directly connected to the drive-side transmission shaft, The rotor has an annular yoke portion located between the field core and the friction plate, The power transmission mechanism according to any one of claims 1 to 3, wherein the drive-side transmission shaft is formed of a non-magnetic material.

7. The power transmission path has a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, The electromagnetic clutch further comprises a rotor connected to the drive-side transmission shaft, The rotor has an annular yoke portion located between the field core and the friction plate, The power transmission mechanism according to any one of claims 1 to 3, wherein slits are formed in the annular yoke portion at multiple locations in the circumferential direction, and the slits penetrate the annular yoke portion in the axial direction.

8. The power transmission path comprises a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the reduction mechanism and the electromagnetic clutch. The electromagnetic clutch further comprises a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion located between the field core and the friction plate, The friction plate is arranged to be movable in the axial direction between a position in contact with the inner driver and a position in contact with the annular yoke portion. The power transmission mechanism according to any one of claims 1 to 3, wherein an impact absorbing member for reducing the collision noise of the friction plate is provided between the annular yoke portion and the friction plate, and between the friction plate and the inner driver.

9. The power transmission path comprises a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the reduction mechanism and the electromagnetic clutch. The electromagnetic clutch further comprises a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion located between the field core and the friction plate, The friction plate is arranged to be movable in the axial direction between a position in contact with the inner driver and a position in contact with the annular yoke portion. The power transmission mechanism according to any one of claims 1 to 3, wherein at least one of the drive-side transmission shaft and the driven-side transmission shaft has a stepped portion that can restrict axial movement by axial abutment with the rotor or inner driver which is the corresponding connecting partner.

10. The power transmission path comprises a drive-side transmission shaft provided between the speed-increasing mechanism and the electromagnetic clutch, and a driven-side transmission shaft provided between the reduction mechanism and the electromagnetic clutch. The electromagnetic clutch further comprises a rotor connected to the drive-side transmission shaft and an inner driver connected to the driven-side transmission shaft. The rotor has an annular yoke portion located between the field core and the friction plate, The friction plate is arranged to be movable in the axial direction between a position in contact with the inner driver and a position in contact with the annular yoke portion. The power transmission mechanism according to any one of claims 1 to 3, wherein the friction plate and the rotor are spline-fitted.

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