Machine element or mechanism – Gearing – Rotary bodies
Reexamination Certificate
1999-11-09
2001-06-19
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Rotary bodies
C074S397000, C074S409000, C123S090310
Reexamination Certificate
active
06247377
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to gears, and more particularly, but not exclusively, relates to reduction of backlash in gear trains.
When the tooth of one gear mates with the gap of another gear, the gap typically provides more space than needed to accommodate the tooth. This excess space is sometimes called “lash” or “backlash.” Backlash may vary with a number of factors including radial play in the gear bearings, gear shaft eccentricity, incorrect center-to-center spacing of the gears, and the gear-to-gear variation typical of many gear manufacturing processes.
The extra space associated with backlash usually leads to significant impact loading of the gear teeth. This loading often causes excessive noise and may result in other gear train problems. For example, backlash may accelerate gear wear. Backlash reduction is of particular concern for internal combustion engine applications—especially for gear trains used with diesel engines. U.S. Pat. Nos. 5,450,112 to Baker et al., 4,920,828 to Kameda et al., 4,700,582 to Bessette, and 3,523,003 to Hambric are cited as sources of background information concerning the application of gear trains to various engines.
One way to reduce backlash is through precision machining and mounting of the gears. However, this approach is usually expensive and still may not adequately address backlash that changes over time due to wear. Another approach to reduce backlash has been the introduction of one or more scissor gears into the gear train. Generally, scissor gears have teeth which adjust in size to occupy the space available between teeth of a mating gear. U.S. Pat. Nos. 5,056,613 to Porter et al., 4,747,321 to Hannel, 4,739,670 to Tomita et al., 3,365,973 to Henden, and 2,607,238 English et al. are cited as examples of various types of scissor gears.
Backlash accommodation with a scissor gear is often limited when the scissor gear is meshed with two or more gears having different amounts of lash. Typically, the mating gear having the smallest amount of lash dictates the effective tooth size of the scissor gear; however, this size is generally inadequate to take-up the greater lash of the other mating gear or gears. One potential solution to this problem is to select mating gears which minimize the lash difference, but this “lash matching” approach is typically expensive and time-consuming. Consequently, a need remains for a gear train assembly which accommodates lash differences resulting from multiple gears meshing with a scissor gear.
One scissor gear configuration has two toothed wheels spring-biased to rotate relative to each other about a common center. For this configuration, paired gear teeth, one from each wheel, spread to occupy the available space between teeth in a mating gear. In some gear trains, loading of the tooth pairs by the mating gear becomes high enough to align each tooth pair in opposition to the spring bias. Typically, each member of the aligned pair is configured to proportionally bear this high load by being sized with the same nominal thickness. However, it has been found that random deviations from nominal are usually enough to cause one tooth or the other of each pair to bear a disproportionately high amount of the load until it has deformed enough to match the other tooth. This deformation process often subjects the gear teeth to reverse bending loads that more quickly wear-out the teeth compared to teeth subjected to unidirectional bending loads. Also, such deformation may cause greater tooth-to-tooth variation, resulting in poorer performance and a more noisy gear train. Therefore, a need exists for an anti-lash gear assembly which accommodates high loading without these drawbacks.
It has also been discovered that the knocking of heavy duty diesel engines, often attributed to combustion processes, results from high impact gear tooth noise. Typically, this noise is not sufficiently abated by conventional scissor gear configurations. Thus, a gear train is also in demand which addresses this type of noise.
SUMMARY OF THE INVENTION
The present invention relates to anti-lash gear assemblies and gear trains utilizing one or more anti-lash gear assemblies. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain features which are characteristic of the preferred embodiments disclosed herein are described briefly as follows.
In one form of the present invention, a gear train is assembled by providing a first gear and establishing a first mesh between the first gear and a second gear. The second gear is of a scissor gear configuration with an effective tooth size determined by the first mesh. A mounting position for a third gear is selected to form a second mesh with the second gear. This mounting position is determined as a function of the effective tooth size to control backlash of the second mesh.
In another form, an engine system incorporating a gear train is provided. This system includes an internal combustion engine to which first, second, and third gears are pivotally coupled. The second gear engages the first gear in a first mesh, and the third gear engages the second gear in a second mesh. The second gear is of a scissor gear configuration. This system also includes an adjustable positioning mechanism adapted to provide a range of positions of the rotational axis of the third gear relative the rotational axis of the second gear to control backlash for the second mesh. One advantage of these forms of the present invention is that lash difference between two gears meshing with a scissor gear is addressed.
In another form of the present invention, an anti-lash gear assembly is provided which includes a first gear wheel with a first number of circumferentially disposed teeth and a second gear wheel engaged to the first wheel with a spring bias configured to yielding rotate said first and second wheels relative to each other about a generally common rotational center. The second wheel defines a number of circumferentially disposed teeth each paired to a corresponding one of the first teeth. Each tooth pair has a composite thickness determined in accordance with a force acting against the bias. The first teeth each have a first circular thickness and the second teeth each have a second circular thickness nominally less then the first thickness. Generally, this thickness difference shifts loading in excess of the bias to the first wheel to reduce reverse bending loads.
In a further form of the present invention, an anti-lash gear assembly, such as a scissor gear, is provided with a high maximum bias torque to address knocking sounds of diesel engines. Generally, the maximum bias torque necessary to reduce these sounds is selected as a function of the specific engine design and expected loading. In one preferred embodiment, a maximum bias torque of at least about 100 foot-pounds is employed. In a more preferred embodiment, at least about a 200 foot-pound maximum bias torque is utilized. In a still more preferred embodiment, at least about a 500 foot-pound maximum bias torque is employed. Although generally contrary to accepted wisdom, this relatively high bias torque has been found to reduce unpleasant hammering or knocking sounds associated with some diesel engines.
In yet another form, an anti-lash gear assembly is provided that includes a first gear wheel with a first number of circumferentially disposed teeth and a first number of splines. This assembly also includes a second gear wheel with a second number of circumferentially disposed teeth and a second number of splines. The first and second splines engage each other about a generally common rotational axis and are inclined relative to this axis to rotate the first and second wheels relative to each other. The first and second teeth are paired to provide a number of composite teeth varying in size with rotation of the first and second wheels relative to each other.
In
Long Charles E.
Piraner Ilya L.
Tibbetts Dennis R.
Cummins Engine Company, Inc.
Fenstermacher David
Woodard Emhardt Naughton Moriarty & McNett
LandOfFree
Anti-lash gear assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anti-lash gear assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anti-lash gear assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492305