Rollable enveloped worm with two curve profile

Details Rollable enveloped worm with two curve profile Rollable enveloped worm with two curve profile

1999-07-13

2001-06-19

Herrmann, Allan D. (Department: 3682)

Machine element or mechanism

Gearing

Directly cooperating gears

C029S893310, C029S893320, C074S458000

Reexamination Certificate

active

06247376

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a rollable enveloped worm for engaging a gear with non-intersecting axes of rotation making an angle of approximately 90° with respect to one another for use in moving a closure member with respect to a portal through a barrier, such as a vehicle window drive system.
BACKGROUND OF THE INVENTION
In drive systems of the past, the outside diameter of a worm gear was constrained to be equal to the shaft or bearing diameter for ease of assembling through a bearing for a vehicle window drive system. The worm gear typically was rotatively driven by a drive motor and was used to drive a driven gear. The torque capacity of the worm gear was much less than that obtainable with an enveloped worm gear. The torque capacity of a worm gear is limited by having a primary or single contact tooth which contacts a mating tooth of the driven gear. Prior known enveloped worm gears have required that the teeth be specially machined and therefore are of limited application in vehicles requiring mass produced parts using conventional manufacturing techniques. Prior attempts have been made to use a conventional roll manufacturing technique to generate a multi-contact worm gear; however, such designs produced contact points where the gear teeth of the drive gear contacted mating teeth of driven gear situated on an arc which was concentric about the axis of the driven gear. This had the disadvantage of causing the multiple teeth to contact the driven teeth at a single contact location on the driven gear resulting in increased wear at that contact point, thereby reducing the useful life of the driven gear.
If a drive gear is used in a situation requiring driven movement in both a counter clockwise and clockwise direction both sides of each tooth are used to drive the load. Often times, the torque or load experience by the gear is not the same in both rotational directions. For example, when a passenger is seated on a power seat of a vehicle, a maximum load is experienced when the passenger raises the seat, while a minimum load is experienced when the passenger lowers the seat.
Prior known systems have provided a worm gear having teeth with sides which define pressure angles that are the same on both sides. When such a worm gear is used in a multi-torque environment, the gear experiences a maximum bending stress which is not balanced, and requires the motor to be of a capacity which can handle the maximum bending stress associated with the largest load.
SUMMARY OF THE INVENTION
The present invention provides a multi-tooth contact worm with an outside diameter which is not constrained to be equal to the shaft bearing diameter for ease of assembling through a bearing. The present invention starts with an eight millimeter, nine millimeter, or ten millimeter shaft, which when rolled provides outside teeth that exceed the shaft diameter by some amount allowing more teeth to be in contact with the drive gear. The extra envelopment of the present invention can be used to achieve an overall smaller package size for competitive advantage. The fact that the outer bearing is placed at the end of the shaft allows the teeth to be a larger diameter than the shaft bearing diameter. Preferably, the present invention simultaneously rolls the bearing groove with the worm, since the centroid of the enveloped teeth must be located with the gear centerline.
The present invention provides a drive system and method for manufacturing a multi-contact drive gear having improved torque capacity while enabling the gear to be manufactured using roll manufacturing techniques.
The present invention provides an increase in torque carrying capacity by preferably providing eight to twelve tooth contact between the drive gear and the driven gear. Maximizing the number of teeth in conjugate working contact between the worm gear and the worm wheel, and reducing the tooth height on both the worm gear and worm wheel provides the maximum bending strength for the individual teeth. Decreasing the worm gear tooth height allows a larger diameter core area for a given worm shaft size. This increases the capacity of the worm gear to resist bending forces. The present invention also provides a smaller diameter worm gear for a given speed reduction. More teeth in working contact allows the tangential force at the pitch diameter to be higher permitting a smaller pitch radius gear to handle a given torque. The present invention also provides a larger number of teeth in contact to increase the total gear mesh strength while allowing use of thinner teeth which are more resilient and can distribute the load while accepting greater errors in pitch match. More numerous, thinner teeth provide averaging of error and permits continued function even when one or two teeth are damaged thereby improving reliability of the worm gear system.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.


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