Gear assembly

Details Gear assembly Gear assembly

2000-03-22

2001-12-04

Estremsky, Sherry (Department: 3681)

Machine element or mechanism

Gearing

Rotary bodies

C074S432000, C192S053320

Reexamination Certificate

active

06324930

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention generally relates to gears for use in power transmission assemblies such as motor vehicle transmissions and transfer cases. More particularly, the present invention relates to a multi-piece gear assembly having reduced weight and rotational inertia which can be economically manufactured for replacement of conventional monoblock gears.
2. Discussion
Gear manufacture is a time-consuming and expensive process. Much of the cost associated with gear manufacturing arises from the cost of the gear material. Traditionally, gears are constructed from a homogeneous gear blank obtained from a billet of high alloy gear steel such as, for example, SAE 8620. While superior mechanical properties such as hardenability and fatigue strength are desirable in the gear tooth portion of such monoblock gear, these particular mechanical properties are not required throughout the remainder of the gear. In addition, when a gear is fabricated from a single material an undesirably large rotational moment of inertia results. As the rotational moment of inertia increases, so does the amount of energy required to start and stop rotation of the gear. Accordingly, a gear having a reduced rotational moment of inertia is desirable for production of an energy efficient power transmission device.
While gears having a reduced rotational moment of inertia are known in the art, such designs have certain disadvantages. For example, it is known to machine a relief into the central web portion of the gear in order to reduce its weight and rotational moment of inertia. While this method accomplishes the task of reducing the rotational moment of inertia, the overall gear design may be compromised. Specifically, the remaining web section may have been reduced to the point that subsequent heat treatment operations will cause deformation of the gear body and tooth form. This may result in a need for hard finishing of the gear form thus adding significant costs.
Other methods employed to reduce the weight and rotational moment of inertia of gears include utilization of different materials. In this regard, some composite materials such as fiber reinforced plastic, have been successful in some light duty applications. However, the heat and stress induced on the teeth of gears used in power transmission assemblies, such as motor vehicle transmissions and transfer cases, exceeds the allowable limits for most known composite materials. As such, composite gears have had only limited application in motor vehicles.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to overcome the disadvantages associated with conventional gears by providing an improved gear assembly having reduced weight and rotational moment of inertia.
It is another object of the present invention to provide a multi-piece gear assembly with the components constructed from different materials.
The present invention includes a gear assembly having a body member with an end wall interconnecting a cylindrical inner wall and a cylindrical outer wall so as to define an annular cavity. The gear assembly also includes a gear ring having a hub segment mounted on and fixed to the outer wall of the body member and a gear segment having external gear teeth. The gear assembly also includes a clutch ring that is secured to the inner and outer walls of the body member for enclosing the cavity. The clutch ring has clutch teeth adapted for engagement with a shift sleeve associated with a gearshift system for releasably coupling the gear assembly to a drive shaft.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.


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