Planetary gear transmission systems or components – Planetary gearing or element
Reexamination Certificate
2002-08-12
2004-06-01
Lewis, Tisha D (Department: 3681)
Planetary gear transmission systems or components
Planetary gearing or element
C475S340000, C475S338000
Reexamination Certificate
active
06743148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a planetary gear set for use in a transmission apparatus, such as an automatic transmission and the like, and, more particularly, to a carrier structure of a planetary gear set of a Ravigneaux type, a double-pinion type, or the like, having pairs of pinion gears that mesh with each other.
2. Description of Related Art
In typical transmission apparatuses, such as automatic transmissions and the like, a planetary gear set that forms a speed change mechanism is disposed around an input shaft of the transmission apparatus, an output shaft thereof, or an intermediate shaft connected to the input shaft and the output shaft, or around an axis of these shafts if the shafts are coaxially disposed. Friction members of clutches, brakes and the like for controlling the engagement and disengagement of a sun gear, a carrier and a ring gear provided as speed-changing elements with respect to an input or output member or a case are less, subject to constraints in a mount position. Therefore, the friction members are disposed between or around the planetary gear set due to an apparatus layout relationship. The brake friction members, in particular, are often disposed at an outer periphery of the planetary gear set because an outer peripheral side thereof is supported to the case of the transmission apparatus.
An inside diameter of the sun gear as a component element of the planetary gear set disposed around the aforementioned shaft, whose shaft diameter is determined in accordance with a transfer torque capacity, is restricted by the outside diameter of the shaft due to the aforementioned placement relationship. Therefore, if the apparatus is designed for higher torque, the inside diameter of the sun gear is increased, and therefore, the outside diameter of the entire planetary gear set correspondingly increases. Therefore, if friction members of friction engagement elements are disposed at an outer periphery of the planetary gear set, the outside diameter of the mechanism including the friction members becomes even greater. As a result, the placement becomes very difficult in apparatuses whose outside diameter dimensions are restricted, such as automatic transmissions installed in vehicles.
In a high torque-transferring planetary gear set, it is advantageous to increase the number of pinions in order to reduce the torque load on each pinion from the viewpoint of securing durability. However, as the number of pinions is increased, it becomes more difficult to provide a rigid carrier that supports the pinions. Obtaining a rigid carrier is even more difficult because the carrier, supporting the pinions via shafts, receives torsional moments caused by reaction forces based on the intermeshing. If the rigidity of the carrier is reduced due to the aforementioned circumstances, the carrier causes an improper gear mesh due to its deformation, thus giving rise to problems of reduction in durability, occurrence of gear noises, etc.
In the case of an ordinary simple planetary gear, the number of pinions is small (normally, three to five), and the support span of the carrier supporting the pinion is also short, so that it is relatively easy to provide a rigid planetary carrier against the aforementioned torsional force. However, if the number of pinions (normally, six to ten in three to five sets) is small as in the case of a double-pinion type planetary gear, the inter-gear space for inserting bridge members that bridge two opposite end walls of the carrier in the direction of an axis thereof is considerably restricted. If the axis length of the pinions is great as in the case of a Ravigneaux-type planetary gear, the axis length of the bridge members becomes great, so that it becomes even more difficult to provide a sectional area of the members that is sufficient to secure torsional rigidity.
With regard to a planetary carrier that supports pairs of pinion gears, a conventional technology that is considered effective to secure rigidity of the carrier is disclosed in Japanese Patent No. 2852816. This technology adopts a carrier structure in which a cup-shaped first support member is connected by welding in a two-story fashion to a cup-shaped second support member having an outer peripheral flange portion. A base wall of the first support member serves as a support portion for the two types of pinions, and a base portion of the second support member serves as another support portion for the short pinions. A peripheral wall of the second support member is partially cut and raised inwardly so as to form another support portion for the long pinions. A peripheral wall of the first support member is partially cut away to expose outer peripheries of the long pinions to an outer peripheral side of the carrier for the purpose of meshing with the ring gear.
The conventional-art Ravigneaux-type planetary carrier has a structure in which the two cup-shaped support members are connected and the carrier as a whole has a box shape, and therefore is considered effective to secure rigidity. However, the long pinion-supporting portion is a tongue-like portion formed by cutting up a peripheral wall portion. Therefore, due to this structure, the tongue-like portion has a cantilever structure in which the portion is supported only at an end side thereof by the flange portion Hence, it is assumed that the rigidity for the long pinion support is low, and it can be said that the above-described structure is not altogether suitable to a high-capacity planetary gear set.
Furthermore, the structure in which the long pinions are exposed by cutting out a portion of the peripheral wall of the cup-shaped member so as to secure a mesh can be adopted in a case where the pinion diameter is small. However, if this structure is adopted in a case where the pinion diameter is increased in order to secure a capacity and a durability of the planetary gear set that are suitable for a high-output and high-speed design, it becomes necessary to reduce the sun gear diameter. Thus, a suitable gear ratio setting becomes difficult. If a gear ratio setting is made so as to avoid a reduction of the sun gear diameter, the outside diameter of the carrier becomes great, so that the entire size of the planetary gear set becomes large. Thus, weight and size reductions will be impeded.
SUMMARY OF THE INVENTION
The invention thus provides a planetary gear set that makes it possible to dispose many pinions whose outside diameter is larger relative to the sun gear diameter while providing a rigid carrier. The invention also provides a carrier structure that, in an arrangement where friction members, such as clutches, brakes, etc., are disposed at an outer peripheral side of a planetary gear set, prevents an increase in the radial dimension of the apparatus while providing transfer torque capacities of the planetary gear set and the friction members. The invention also improves the rigidity of a carrier of a planetary gear set that supports a combination of pairs of pinion gears, and to thereby provide a planetary carrier that allows an arrangement of an increased number of pinion gear pairs and improves the durability of the planetary gear.
In order to achieve the foregoing, the invention is a planetary gear set with a plurality of pinions meshing with a sun gear and a carrier that shaft-supports the pinions, wherein the carrier has an annular peripheral wall that extends entirely around outer peripheries of the plurality of pinions, wherein the annular peripheral wall has thin-wall portions formed by recesses in a radially inner side at a circumferential-direction position corresponding to a position of the pinions.
This construction makes it possible to obtain a planetary gear set in which many pinions, whose pinion diameters are great relatively to the sun gear diameter, are disposed with an annular peripheral wall sufficient to maintain a rigidity of the carrier. Furthermore, because it becomes possible to provide an arrangement of many pinions which does not degrade the rigidity of
Hayabuchi Masahiro
Hiramoto Yukio
Iida Tatsuya
Kasuya Satoru
Katou Hiroshi
Aisin AW Co. Ltd.
Lewis Tisha D
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