Power transmission device for vehicle

Abstract

In a power transmission device for a vehicle, a boss portion of a clutch guide, which is an input-side rotation member of a clutch unit, includes: a spline portion spline-connected to a small-diameter portion at one end of a center shaft which is an input shaft; and a fitting portion that extends further from the spline portion in an axial direction to contact the outer circumference of a medium-diameter portion of the center shaft. A recess functioning as a torque fuse is formed in the medium-diameter portion of the center shaft corresponding to the fitting portion. When the center shaft is severed or disconnected at the recess, the medium-diameter portion of the severed cut center shaft can still remain within the fitting portion, so that appropriate centering can be secured and stable self-propulsion of the vehicle can be secured without unwanted misalignment of the axis of rotation of the clutch.

Claims

1. A power transmission apparatus for a vehicle, comprising: an input shaft to which is transmitted rotary motion from a drive source; a clutch for transmitting rotary motion of the input shaft by disconnectably connecting drive power transmission; and an output shaft connected to the clutch, characterized in that the input shaft is spline-connected at one end thereof to an input-side rotation member of the clutch for rotating together with the input-side rotation member of the clutch, in that the input-side rotation member of the clutch includes a boss portion that includes a spline portion spline-connected to the one end of the input shaft, and a fitting portion extending further from the spline portion in an axial direction into contact with an outer periphery of the input shaft, and in that a portion of the input shaft that corresponds to the fitting portion has a recess formed therein for functioning as a torque fuse.

2. The power transmission apparatus for a vehicle as claimed in claim 1, which is a differential mechanism for distributing rotation of a drive shaft, to which is transmitted the rotary motion from the drive source, to left and right wheels, and wherein the differential mechanism includes: a driving bevel gear rotatable integrally with the drive shaft; a driven bevel gear meshing with the driving bevel gear; a center shaft extending in a direction intersecting the drive shaft and rotatable integrally with the driven bevel gear; left and right clutch units disposed to left and right of the center shaft; and left and right output shafts for transmitting outputs of the left and right clutch units to the left and right wheels, respectively, wherein the center shaft includes: a middle large-diameter portion; left and right medium-diameter portions located to left and right of the large-diameter portion; and left- and right-end small-diameter portions adjoining the left and right medium-diameter portions, the driven bevel gear being fixed to the large-diameter portion, wherein the input shaft is the center shaft, the clutch is the left or right clutch unit, and the output shaft is the left or right output shaft, wherein the boss portion of the input-side rotation member of the clutch is spline-connected to the small-diameter portion of the center shaft, and wherein the recess functioning as the torque fuse is formed in the medium-diameter portion of the center shaft.

3. The power transmission apparatus for a vehicle as claimed in claim 1, wherein the recess functioning as the torque fuse is formed in correspondence with a portion of the fitting portion adjoining the spline portion.

4. The power transmission apparatus for a vehicle as claimed in claim 2, wherein the recess functioning as the torque fuse is formed in correspondence with a portion of the fitting portion adjoining the spline portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a sectional view showing an embodiment of a power transmission device for a vehicle of the present invention which is constructed as a differential mechanism; and

(2) FIG. 2 is an enlarged sectional view of portions pertaining to a left clutch unit in the embodiment of the power transmission device.

DESCRIPTION OF EMBODIMENTS

(3) An embodiment of a power transmission device for a vehicle (vehicular power transmission device) of the present invention shown in FIG. 1 is constructed as a differential mechanism 10 for distributing rotation of a drive shaft 1 to left and right wheels (not shown). The drive shaft 1 is connected to a not-shown propeller shaft so that rotary motion is transmitted from a not-shown drive source (engine) to the drive shaft 1. The differential mechanism 10 includes: a driving bevel gear 2 rotatable integrally with the drive shaft 1; a driven bevel gear 3 meshing with the driving bevel gear 2; a center shaft 4 disposed to extend in a direction intersecting the drive shaft 1 and connected to the driven bevel gear 3 for integral rotation with the driven bevel gear 3; clutch units 5 and 6 disposed to the left and right of the center shaft 4; and left and right output shafts 7 and 8 for transmitting respective outputs of the clutch units 5 and 6 to the left and right wheels (not shown), respectively. The center shaft 4 is supported by a case of the differential mechanism 10 via tapered roller bearings 11 and 12.

(4) The center shaft 4 is constructed to generally include a middle large-diameter portion 4a constituting a middle part of the center shaft 4, medium-diameter portions 4b located to the left and right of the large-diameter portion 4a, and left- and right-end small-diameter portions 4c adjoining the medium-diameter portions 4c. The driven bevel gear 3 is fixed to the large-diameter portion 4a to rotate the entire center shaft 4. The left- and right-end small-diameter portions 4c each have a plurality of spline teeth formed therein at intervals along the circumference thereof and are spline-connected to input-side rotation members of corresponding ones of the clutch units 5 and 6 for rotating together with the input-side rotation members.

(5) The left and right clutch units 5 and 6 each comprise a multiple plate wet clutch. In the left clutch unit 5, as shown in an enlarged view of FIG. 2, a plurality of separator plates 53 sequentially arranged at predetermined intervals in an axial direction is spline-connected to a clutch guide 51 that is the input-side rotation member of the clutch unit 5, and a plurality of friction plates 54 sequentially arranged at predetermined intervals in the axial direction is spline-connected to a clutch hub 52 that is an output-side rotation member of the clutch unit 5. The separator plates 53 and the friction plates 54 are arranged alternately in the axial direction in combinations. The clutch guide (input-side rotation member) 51 includes a boss portion 55 where a spline portion 55a is formed on its proximal portion and spline-connected to the left-end small-diameter portion 4c. The boss portion 55 also has a fitting portion 55b extending further from the spline portion 55a in the axial direction and closely contacting the outer periphery of the left medium-diameter portion 4b of the center shaft 4 fitted within the fitting portion 55b.

(6) A recess (notch, cut or hollow) 9 functioning as a torque fuse is formed, with a suitable depth, in the outer periphery of a portion (i.e., medium-diameter portion 4b) of the center shaft 4 that corresponds to the fitting portion 55b of the boss portion 55 of the clutch guide (input-side rotation member) 51. The recess 9, which is in the form of an appropriate amount of a nick, a cut or a hollow, has predetermined characteristics such that it can sufficiently withstand normal torque applied to the center shaft 4 but is fractured, broken or severed when more than predetermined torque has been applied to the center shaft 4. Formation of such a recess 9 weakens a mechanical strength of the portion (medium-diameter portion 4b) of the center shaft 4 so that the portion (medium-diameter portion 4b) of the center shaft 4 may be fractured, broken or severed due to application of more than predetermined torque (i.e., excessive torque). However, the recess 9 of the center shaft 4 is provided in a portion corresponding to the fitting portion 55b of the clutch unit 5 as noted above, and thus, when the center shaft 4 has been disconnected or severed at the recess 9 due to excessive torque, the portion of the severed shaft 4 adjacent to the large-diameter portion 4a can still remain within the fitting portion 55b of the clutch unit 5. Because the portion of the severed shaft 4 adjacent to the large-diameter portion 4a is supported by the case of the differential mechanism 10 via the tapered roller bearings 11 and 12 as noted above, axis misalignment of the shaft 4 can be avoided despite the severance or cut-off of the torque fuse. With the portion of the severed shaft 4 adjacent to the large-diameter portion 4a still remaining within the fitting portion 55b at and after the severance or cut-off of the torque fuse, appropriate centering of the axis of rotation of the clutch unit 5 can be secured so as to avoid misalignment of the axis of rotation of the clutch unit 5. In this way, the instant embodiment can secure stable self-propelled rotation at and after the cut-off the torque fuse.

(7) Note that, in the illustrated example, the recess 9 is formed or provided in positional correspondence with a portion of the fitting portion 55b adjacent to the spline portion 55a (i.e., in the neighborhood of a boundary between the fitting portion 55b and the spline portion 55a). Thus, it is possible to minimize the length of the fitting portion 55b that is required to secure stability at and after the cut-off or severance of the torque fuse. Namely, in order to secure stability (appropriate centering of the clutch's axis of rotation) at and after the severance, it is necessary that the portion of the severed shaft 4 adjacent to the large-diameter portion 4a should have more than a given necessary minimum length. However, with the position of the recess 9 in the illustrated example, the length of the portion of the severed shaft 4 adjacent to the large-diameter portion 4a still remaining within the fitting portion 55b after the cut-off of the torque fuse extends along a substantially entire length of the fitting portion 55b. Thus, the length of the fitting portion 55b can be limited to the smallest-possible or minimal length that is required to secure stability, which can significantly contribute to size reduction of the power transmission device. Needless to say, the present invention is not necessarily limited to the above-described embodiment. For example, the recess 9 may be provided in positional correspondence with a substantially middle position of the fitting portion 55b, in which case, however, it would be necessary to increase the entire length of the fitting portion 55b, e.g. to a length about two times the length of the fitting portion 55b in the illustrated example.

(8) Further, the clutch hub 52 is spline-connected to the output shaft 7 and rotatably fixed to the clutch case via a bearing 14 so that it can rotate integrally with the output shaft 7. The clutch guide 51 and the clutch hub 52, on the other hand, are supported by each other via a bearing 13 so that they are rotatable relative to each other. The plurality of separator plates 53 spline-connected to the clutch guide 51 is driven in the axial direction (rightward in FIG. 2) by a piston 56 when the clutch is in an engaged state. The clutch is brought to the engaged state by the separator plates 53 frictionally engaging the friction plates 54 in response to drive power given from the piston 53. The piston 56 is driven hydraulically and controlled to provide a necessary clutch engaging amount.

(9) Referring now back to FIG. 1, the right clutch unit 6 may be constructed in the same manner to the aforementioned left clutch unit 5 and thus will not be described here to avoid unnecessary duplication. In the right clutch unit 6, the recess 9 functioning as a torque fuse is formed in the right medium-diameter portion 4b of the center shaft 4, in the same manner as in the above-described left clutch unit 5. Note that the center shaft 4 is an input shaft for the clutch unit 5 or 6 while the output shaft 7 or 8 is an output shaft for the clutch unit 5 or 6.

(10) In the above-described embodiment, the torque fuse structure of the present invention is applied to each of the left and right clutch units 5 and 6 of the differential mechanism 10 designed for distributing rotational drive power to the left and right wheels (left and right rear wheels). However, the present invention is not so limited, and the torque fuse structure of the present invention is applicable to other types of power transmission devices. For example, the torque fuse structure of the present invention is applicable to a clutch unit for directly coupling rotation of the vehicle engine to the rear-wheel differential mechanism.