Power transmission device

Abstract: A power transmission device with a housing (2) including first and second housing component members (3A,3B). The first and second component members (3A,3B) are fixed by bolts (6). Each bolt (6) extends through a central portion of a planetary gear (72) of a planetary gear mechanism (7). The planetary gear (72) is rotatably supported on the housing (3) through the bolts (6).

Description: This invention relates to a power transmission device suited to be used as, for example, a center differential for four-wheel drive vehicles. In general, a power transmission device used as a center differential for four-wheel vehicles includes a housing having a plurality of housing component members fixed by bolts, and a planetary gear mechanism and a differential gear mechanism which are disposed on a rotational axis of the housing. A drive torque inputted from an engine into the planetary gear mechanism is transmitted to the differential gear mechanism through the housing and further to the front and rear wheel sides from one pair of side gears of the differential gear mechanism (see Japanese Patent Unexamined Publication (Kokai) No. Hei 7-117516). The conventional power transmission device is large in part number, complicated in construction, and heavy in weight. It would be desirable to decrease the number of component parts. SE 507 150 C discloses a power transmission for a four wheel drive vehicle with a transverse engine. A planetary gear set is provided, to allow direct drive mode and crawl mode. The planetary gear is mounted on a stab shaft which is embedded in a carrier. As a result of hard study with a hope to satisfy the above demand, the inventor of the present invention found that the bolts for fixing the housing component members can be used also as support pins for rotatabl y supporting the planetary gears of the planetary gear mechanisms, thereby enabling to omit the support pins. The present invention accomplished based on this finding is as set out in claim 1. It is preferred that the housing includes a first and a second housing component members, the first housing component member being provided thereon with the sun gear and said planetary gear of the planetary gear mechanism, the second housing component member being provided therein with the differential gear mechanism. It is also preferred that the differential gear mechanism includes plural pairs of the element gears, and each of the element gear pairs is arranged in parallel to the rotational axis and away from each other in a circumferential direction of the housing. It is also preferred that the planetary gear mechanism includes a plurality of the planetary gears, and the bolt rotatably supporting each of the planetary gears is disposed between each pair of the element gears. In that case, the planetary gears and the element gear pairs may be arranged on a circumference about the rotational axis. It is preferred that the second housing component member is formed on an end face thereof, which end face is faced with the first housing component member, with a plurality of recesses for rotatably receiving therein the sun gear and the planetary gear. The housing may further include a third housing component member disposed between the first housing component member and the second housing component member. Exemplary embodiments of the present invention will now be described with reference to the accompanying drawing, in which: Fig. 1 is a sectional view taken on line B-B of Fig. 2, showing one embodiment of the present invention; Fig. 2 is a sectional view taken on line A-A of Fig. 1; Fig. 3 is a sectional view taken on line D-D of Fig. 4, showing another embodiment of the present invention; and Fig. 4 is a sectional view taken on line C-C of Fig. 3. Figs. 1 and 2 show a power transmission mechanism 1 according to one embodiment of the present invention. This power transmission mechanism 1 is used as a center differential for four-wheel drive vehicles. The power transmission mechanism 1 can also be applied to other ways of use such as, for example, a rear differential. The power transmission device 1 includes a differential case 2. This differential case 2 is fixed to a vehicle body (not shown). A housing 3 is disposed within the differential case 2. Opposite end portions of the housing 3 are rotatably supported on the differential case 2 through bearings 4, 5. This housing 3 is comprised of a first and a second housing component member 3A, 3B which are divided by a plane vertical to a rotational axis L of the housing 3. Those two housing component members 3A, 3B are in abutment with each other with axes thereof held in alignment and they are fixed by a plurality of bolts 6. The bolts 6 are arranged in parallel to the rotational axis L on outer peripheral sides of the housing component members 3A, 3B and equally spacedly in a circumferential direction of the housing 3. The bolts 6 are allowed to extend through the first housing component member 3A and threadingly engaged with the second housing component member 3B. Accordingly, when the bolt 6 is tightened, the housing component members 3A, 3B are fixed to each other. Although the bolts 6 used in this embodiment are three, they may be two, or four or more. A planetary gear mechanism 7 is disposed within the casing 2. The planetary gear mechanism 7 includes a sun gear 71, a plurality of planetary gears 72 and an inner gear 73. The sun gear 71 and the planetary gears 72 are disposed on the housing 3, while the inner gear 73 is disposed on the differential case 2. That is, the housing component member 3A is formed on an end face 31 (see Fig. 4) thereof, which end face is faced with the housing component member 3B, with circular recesses 32, 33. The recess 32 is disposed at a central portion of the end face 31 with an axis thereof held in alignment with the rotational axis L. The recesses 33, which are employed in this embodiment, are three which is equal to the number of the bolts 6. The recesses 33 are equally spacedly arranged in a circumferential direction on a circumference about the rotational axis L. The recesses 32, 33 are shielded by the housing component member 3B. The recesses 32, 33 may be formed on the end face 34 which is faced with the housing component member 3A, or they may be formed on both the end faces 31, 34. The sun gear 71 is rotatably received in the recess 32. An inner end portion of an input sleeve 9, which is disposed on the rotational axis L, is unrotatably connected to a central portion of the sun gear 71. The input sleeve 9 is rotatably supported on the housing component member 3A. Accordingly, the sun gear 71 is rotatably supported on the housing component member 3A through the input sleeve 9. The planetary gears 72 are rotatably received in the respective recesses 33. The planetary gears 72 are in mesh with the sun gear 71. Accordingly, the planetary gears 72, when the housing 3 is rotated, are rotated about their own axes and also rotated around the sun gear 71. The inner gear 73 is fixed to an inner peripheral surface of the differential case 2 with an axis thereof held in alignment with the rotational axis L. The inner gear 73 is in mesh with the planetary gears 72. Accordingly, when the sun gear 71 is driven for rotation by the input sleeve 9, the planetary gears 72 and the housing 3 are driven for rotation at a reduced speed. The three bolts 6 are arranged on the same circumference as the planetary gears 72 and on the circumferentially same positions. Those bolts 6 extend through central portions of the planetary gears 72. The planetary gears 72 are rotatably supported on the bolts 6. Accordingly, the bolts 6 are served not only as means for fixing the housing component members 3A, 3B each other but also as support pins for rotatably supporting the planetary gears 72. The support pin for rotatably supporting the planetary gears 72 are not required in this power transmission device 1. The number of parts can be reduced to that extent. An end portion of the housing component member 3A, which end portion is carried on the bearing 4, projects outside from the differential case 2, and a spline portion 3a is formed on the projected end portion of the housing component member 3A. An outer end portion of the input sleeve 9, which is projected outside from the differential case 2 and the housing component member 3A, is formed with a spline portion 9a. The spline 3a has the same size dimension as the spline portion 9a. The differential case 2 is provided on the outside thereof with a drive sleeve 10. This drive sleeve 10 is disposed on the rotational axis L and driven by an engine (not shown). One end portion of the drive sleeve 10 is faced with the input sleeve 9 in proximate relation. A spline portion 10a is formed on this end portion of the drive sleeve 10. The spline portion 10a has the same size dimension as the splines 3a, 9a. On the outside of adjacent end portions of the input sleeve 9 and the housing component member 3A, a ring sleeve 11 is movably disposed for movement in a direction of the rotational axis L. Spline hole portions 11a, 11b are formed in one and the other end portions of an inner peripheral surface of the ring sleeve 11, respectively. The spline hole portion 11a is normally engaged with the spline portion 10a of the drive sleeve 10. The other spline hole portion 11b is switched between a first position where it is not engaged with any of the spline portions 3a, 9a and a second position where it is selectively engaged with one of the spline portions 3a, 9a, depending on the position of the ring sleeve 11. That is, when the ring sleeve 11 is moved to the position (this position is hereinafter referred to as the "neutral position") of Fig. 1, the spline hole portion 11b is located between and not engaged with any of the spline portion 3a and the spline portion 9a. When the ring sleeve 11 is moved rightwardly (this position is hereinafter referred to as the "high-speed position") in Fig. 1 from the neutral position, the spline hole portion 11b is engaged with the spline portion 3a. When the ring sleeve 11 is moved leftwardly (this position is hereinafter referred to as the "low-speed position") in Fig. 1 from the neutral position, the spline hole portion 11b is engaged with the spline portion 9a. Since the spline hole portion 11b is not engaged with any of the spline portions 3a, 9a when the ring spline 11 is moved to the neutral position, the rotation of the drive sleeve 10 is not transmitted to the planetary gear mechanism 7. When the ring sleeve 11 is moved to the high-speed position, the rotation of the drive sleeve 10 is transmitted to the housing 3 through the ring sleeve 11. Accordingly, the housing 3 and the planetary gears 72 are rotated about the rotational axis L at the same speed as the drive sleeve 10. When the ring sleeve 11 is moved to the low-speed position, the rotation of the drive sleeve 10 is transmitted to the sun gear 71 through the ring sleeve 11 and the input sleeve 9. Accordingly, the housing 3 and the planetary gears 72 are rotated about the rotational axis L at a lower speed than the drive sleeve 10. A differential gear mechanism 8 is disposed within the housing component member 3B. The differential gear mechanism 3B includes one pair of side gears 81, 81 which are comprises of one pair of bevel gears, and one pair of element gears 82, 82 which are comprised of one pair of bevel gears. The pair of side gears 81,81 are rotatably supported on the housing 3 with axes thereof held in alignment with the rotational axis L. The pair of element gears 82, 82 are rotatably supported on a pin 83 vertical to the rotational axis L. Accordingly, the pair of element gears 82, 82 are rotatable about the pin 83 and also rotatable about the rotational axis L together with the housing 3. The element gears 82, 82 are in mesh with the side gears 81, 81. Accordingly, when the housing 3 is rotated, its rotation is transmitted to the pair of side gears 81, 81 through the pin 83 and the element gears 82, 82. The rotation, which has been transmitted to one of the side gears 81, 81, is transmitted to the front or rear differential (both not shown) through an output shaft 15. The rotation, which has been transmitted to the other side gear 81, is transmitted to the rear or front differential through an output shaft 16. The relative rotation of the pair of side gears 81, 81 makes it possible to rotate the output shafts 15,16 differentially. In the power transmission device 1 thus constructed, since the bolts 6 for fixing the housing component members 3A, 3B are also used as support pins for rotatably supporting the planetary gears 72 of the planetary gear mechanism 7, there is no need to separately use the support pins for rotatably supporting the planetary gears 72. Accordingly, the number of parts can be decreased to that extent. As a result, the housing 3 can be made small in size and thus, the overall power transmission device 1 can be made small in size. Another embodiment of the present invention will now be described with reference to Figs. 3 and 4. In this embodiment, only the different portions in construction from the above-mentioned embodiment are described, and identical component parts are designated by identical reference numeral and description thereof is omitted. In a power transmission device 1' according to this embodiment, a third housing component member 3C is disposed between the housing component member 3A and the housing component member 3B. In other words, the housing 3 is comprised of the housing component members 3A, 3B, 3C which can be divided into three in a direction of the rotational axis L. The housing component member 3C is formed in a plate-like configuration. The bolts 6 extend through the housing component member 3C. Accordingly, when the bolts 6 are tightened, the housing component members 3A, 3B are pushed against opposite end faces of the housing component member 3C and the housing component members 3A, 3B, 3C are fixed to each other by the bolts 6. And the recesses 32, 33 are shielded by the housing component member 3C. In the power transmission device 1', a differential gear mechanism 8' is employed instead of the differential gear mechanism 8. The differential gear mechanism 8' includes one pair of side gear 84, 84 and three pairs of element gears 85, 85. The side gears 84, 84 are comprised of helical gears. They are rotatably arranged on the rotational axis L. Each element gear 85 is provided on one end portion thereof with a long gear portion 85a, on the other end portion with a short gear portion 85b and on an intermediate portion with a neck portion 85c. The element gears 85, 85 are arranged in parallel to the rotational axis L and supported on the housing 3 such that they can be rotated about their own axes and they can also be rotated about the rotational axis L together with the housing 3. The long gear portion 85a of each element gear 85 is in mesh, at an inner portion thereof (that portion on the side of the short gear portion 85b), with one 84 of the pair of side gears 84, 84 and at an outer portion thereof, with the short gear portion 85b of the other element gear 85. The short gear portion 85b of each element gear 85 is in mesh, at an outer portion thereof, with the long gear portion 85a of the other element gear 85. The three pairs of element gears 85, 85 are equally spacedly arranged in the circumferential direction of the housing 3. They are located away in the circumferential direction of the housing 3 with respect to the bolts 6. Especially, in this embodiment, they are located at the center of the three bolts 6, 6. In the power transmission device 1' thus constructed, since the bolts 6 and the element gear pairs 85, 85 are arranged such that they are away in the circumferential direction from the housing 3, the bolts 6 and the element gears 85 can be arranged on a same circumference. In case the bolts 6 and the element gears 6 are arranged in the same position in the circumferential direction, the former and the latter would be required to be arranged on different circumferences so that they are not interfere each other. Accordingly, the housing 3 would be enlarged in size to that extent and therefore, the power transmission device would be enlarged in size. While, the bolts 6 and the element gears 85 can be arranged on the same circumference in this power transmission device 1' and therefore, the housing 3 can be reduced in diameter and therefore, the power transmission device 1' can be made small in size. It should be noted that the present invention is not limited to the above embodiments and many changes can be made in accordance with necessity. For example, although the bolts 6 extend through the first housing component member 3A and are threadingly engaged with the second housing component member 3B in the above embodiments, it is also accepted that the bolts 6 are allowed to extend further through the other housing component member 3B and a nut is screwed to a forward end (that end which is extended through the housing component member 3B) of each bolt 6, so that the housing component members 3A, 3B (or 3A, 3B, 3C) are fixed to each other by the bolts 6 and the nuts. Of course, the bolts could also extend through the second housing component member (38) and be engaged in a threaded aperture in the first housing component member (3A).

Claims: A power transmission device comprising: a housing (3) having a plurality of housing component elements (3A,3B;3A,3B,3C) which can be separated in a direction of a rotational axis (L), said housing component elements (3A,3B;3A,3B,3C) being mutually fixed by a bolt (6) extending in parallel to the rotational axis (L) ; a planetary gear mechanism (7) mounted on said housing (3), said planetary gear mechanism (7) including a sun gear (71) mounted for rotation about rotational axis (L) of said housing (3), a planetary gear (72) mounted on said housing (3) such that said planetary gear (72) can rotate not only about its own axis but also about the axis (L) of said housing (3) together with said housing (3), said planetary gear (72) being in mesh with said sun gear (71), and an inner gear (73) in mesh with said planetary gear (72); and a differential gear mechanism (8,8') mounted on said housing (3), said differential gear mechanism (8,8') including a pair of side gears (81,81;84,84) mounted for rotation about the axis (L) of said housing (3), and an element gear (82;85,85) disposed on said housing (3) such that said element gear (82;85,85) can rotate not only about its own axis but also about the axis (L) of said housing (3) together with said housing (3), said element gear (82;85,85) being in mesh with said pair of side gears (81,81;85,85) CHARACTERISED in that said bolt (6) extends through a central portion of said planetary gear (72) and said planetary gear (72) is rotatably supported on said housing (3) through said bolt (6) . A power transmission device according to claim 1, wherein said housing (3) includes a first and a second housing component member (3A,3B), said first housing component member (3A) being provided thereon with said sun gear (71) and said planetary gear (72) of said planetary gear mechanism (7), said second housing component member (3B) being provided therein with said differential gear mechanism (8;8'). A power transmission device according to claim 1 or 2, wherein said differential gear mechanism (8;8') includes plural pairs of said element gears (85,85), and each of said element gear pairs (85,85) is arranged in parallel to the rotational axis (L) and away from each other in a circumferential direction of said housing (3). A power transmission device according to any one of the preceding claims wherein said planetary gear mechanism (7) includes a plurality of said planetary gears (72), and said bolt (6) for rotatably supporting each of said planetary gears (72) is disposed between each pair of said element gears (85,85). A power transmission device according to claim 4, wherein said planetary gears (72) and said element gear pairs (85,85) are arranged on the same circumference about the rotational axis (L). A power transmission device according to any one of the preceding claims, wherein said first housing component member (3A) is formed on an end face thereof, which end face is faced with an adjacent housing component member (3B,3C), with a plurality of recesses (32,33) for rotatably receiving therein said sun gear (71) and said planetary gear (72). A power transmission device according to any one of the preceding claims wherein said housing (3) further includes a third housing component member (3C) disposed between said first housing component member (3A) and said second housing component member (3B), and said third housing component member (3C) is formed in a plate-like configuration.

Inventors: NISHIJI MAKOTO, OKUDA HIROFUMI, NISHIJI, MAKOTO, OKUDA, HIROFUMI, Nishiji, Makoto, c/o ZEXEL TORSEN S.A., Okuda, Hirofumi, c/o Konan Factory of Zexel Corp.
Applicants: BOSCH AUTOMOTIVE SYSTEMS CORP, BOSCH AUTOMOTIVE SYSTEMS CORPORATION
Application year: 1999
Main classification: B60K17
IPC codes: B60K17, F16H48