Planetary gear transmission systems or components – Variable speed or direction transmission combined with... – Variable speed or direction is planetary transmission
Reexamination Certificate
1999-12-29
2001-07-10
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
Variable speed or direction transmission combined with...
Variable speed or direction is planetary transmission
C475S206000, C180S247000
Reexamination Certificate
active
06258002
ABSTRACT:
The invention is concerned with a two-stage power-split gear unit for automobiles, consisting of a casing, of an input shaft, of a planetary gear unit as an off-road gear stage, of a differential gear unit, of a first output shaft and of a second output shaft, the planetary gear unit consisting of a sun wheel, of a planet carrier with planet wheels and of a ring gear, the ring gear being connected fixedly in terms of rotation to the casing and the force flux from the input shaft to the differential gear unit taking place selectively via one of the other two members of the planetary gear unit, and the differential gear unit having compensating wheels and first and second output wheels driven by these and in each case located on the first and the second output shaft.
Power-split gear units of this type are referred to as “single offset” when they are designed with an offset output. Usually, in automobiles with all-wheel drive, they are flanged to the-longitudinally installed engine/transmission unit. The offset output is then usually that intended for the front axle. With increasingly larger and longer engine/transmission units (multi-cylinder engine, a large number of transmission speeds), it is advisable for the power-split gear unit to have as compact, in particular as short a design as possible and for the offset output to the front axle to be provided as far forward as possible.
EP 531 088 A1 discloses a power-split gear unit of this type, in which, in order in the longitudinal direction, first a planetary gear unit as an off-road gear stage, then, at some distance from this, a planetary differential, then a locking clutch and only then the output wheel for the front axle are provided. This power-split gear unit therefore has a very long build, and the rear output wheel requires a long cardan shaft to the front axle, this also being unfavorable for reasons of vibration. The distance between the off-road gear stage and the differential has a particularly adverse effect on the construction space, weight and characteristic bending frequency.
DE 41 13 965 C2 discloses a similar power-split gear unit which, following the off-road gear group, has a bevel wheel differential. This differential additionally increases the overall length, as compared with a planetary differential, without allowing the output wheel for the front axle to be transferred forward.
The object of the invention, therefore, is for a generic power-split gear unit to have as compact (in particular, short) and as vibration-resistant a design as possible and for the output wheel for the front axle to be arranged as far forward as possible.
For this purpose, according to the invention, the compensating wheels are mounted on the planet carrier of the planetary gear unit of the off-road gear stage, and the first output wheel is arranged in front of the planetary gear unit of the off-road gear stage and the second output wheel is arranged behind said planetary gear unit.
The planetary gear unit is thus combined with the differential to form a subassembly which is very short in the axial direction and which makes it possible to arrange one output wheel in front of the subassembly and one behind the latter. Hence, there is a reduction in weight and cost due to the multiple function of at least the planet carrier. Consequently, it also becomes possible to transfer the output to the front axle forward and, overall, to have a very rigid drive train.
In a first embodiment, the compensating wheels are bevel wheels which are arranged between the planet wheels of the planetary gear unit of the off-road gear stage and which mesh directly with the first and second output wheels Thus, the bevel wheels meshing with the two output wheels bridge the planetary gear unit. Since said bevel wheels are arranged between the planet wheels in a circumferential direction, the diameter of the subassembly is not appreciably increased thereby. The ratio of the torque distribution between the two output wheels can be adjusted by the choice of their number of teeth, the axis of the compensating wheels then being inclined correspondingly.
A particularly simple design with a large number of identical parts is obtained if the axes of the compensating wheels are directed radially.
In a second embodiment, the compensating wheels are spur wheels which mesh, on the one hand, with the first or second output wheel and, on the other hand, with a first intermediate wheel, and a second intermediate wheel meshes with the second or first output wheel, the first and second intermediate wheels being connected fixedly in terms of rotation to a shaft mounted in the planet carrier. This embodiment affords a great degree of freedom in the choice of the ratio of the torque distribution and makes it possible to mount the compensating wheels on that side of the planetary gear unit which faces the first output wheel.
In a particularly simple and cost-effective further development of the second embodiment, the compensating wheels are arranged coaxially relative to the planet wheels of the planetary gear unit and mesh with the first output wheel, and the first intermediate wheels are arranged between the compensating wheels.
In a third embodiment, the compensating wheels are pairs of intermeshing helically toothed spur wheel rollers, of which one meshes with the first output wheel and the other with the second output wheel, the first and second output wheels being helically toothed spur wheels. A differential (this is sometimes also referred to as a developable differential) which takes up particularly little construction space is obtained in this way. If there is an appropriate design, some locking action may also be exerted, so that there is no need for an additional differential lock.
A simplification of the third embodiment is also achieved in that the pairs of spur wheel rollers are guided, without any shaft, in the planet carrier, and in that each spur wheel roller has a clearance at the location of one of the two output wheels. This makes it possible to reduce the space requirement even further and to design the spur wheel rollers as identical parts.
The planetary gear unit for the off-road gear stage may be designed and connected up in very different ways. The gear shift may take place by the selective connection of the ring gear to either the casing or the planet carrier or by the selective connection of the input shaft to one or other member of the planetary gear unit. In one possible embodiment, the ring gear is fixed to the casing and, in order to select the off-road gear stage, a sliding sleeve is provided, of which the front end is coupled by means of first coupling teeth to the input shaft and the rear end is capable of being coupled by means of second coupling teeth to the sun wheel or to the planet carrier of the planetary gear unit, the coupling sleeve having at its front end a ring for the engagement of a shift fork. As a result, this ring can be transferred right to the front, thus reducing the overall length. The ring gear fixed to the casing makes it easier to mount and center the planetary gear unit.
In a preferred development, the planet carrier carries a hollow shaft which extends forward through the first output wheel and the front end of which is mounted in a bearing and has a radial collar which forms with the ring at the front end of the sliding sleeve a synchronizing device for the selection of the off-road gear. The advantages of synchronization are obvious. It is, as a result, achieved at a particularly low outlay in structural terms.
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Bachman & LaPointe P.C.
Marmor Charles A
Parekh Ankur
Steyr-Daimler-Puch Fahrzeugtechnik AG & Co KG
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