1. Field of the Invention
The present invention pertains to methods and alignment fixtures for use in aligning gears which are to be disposed spaced apart on a shaft and meshed with respective driving or driven gears on a parallel shaft so that the proper mesh and a predetermined load distribution between the two sets of meshed gears may be obtained.
2. Background Art
In the art of power transmission gearing, there are numerous arrangements wherein a shaft is provided with spaced apart driving or driven gears which are meshed with respective gears mounted on an adjacent and parallel shaft. In order to provide a proper mesh, that is a mesh in which all the driving gears are actually transmitting a driving force to the respective driven gears, the gears on the respective shafts must be properly aligned so that when the teeth of one gear are in driving engagement with the associated driven gear, the teeth on the other driving gear or gears are also drivingly engaged with their respective driven gears.
In many applications of relatively large power transmission gears, it is a problem to be able to properly align the gear sets so that a substantially equal or predetermined load distribution is provided. This problem of gear tooth alignment is particularly vexatious for larger gears which, whether cut integral or arranged to be demountable from the supporting shaft, are difficult to align.
One example of relatively large power transmission gearing arrangements wherein alignment has been a problem is in the gearing for large reciprocating piston pumps and similar types of gear drives, wherein the spacing between the adjacent gears on the same shaft is such that there is no practical way to provide an alignment fixture spanning the gap between the gears and providing sufficient accuracy to assure the desired alignment.
In large drilling and well service pumps, for example, it is customary to provide a pinion or jackshaft having spaced apart integral or demountable helical gears, preferably of the opposite hand, which are respectively drivingly engaged with large driven or bull gears mounted on the pump crankshaft. A preferred arrangement of the gearing requires that the driven gears be mounted on the opposite ends of the shaft by interfitting keys or splines. In order to provide proper alignment of the gearing, it has been a practice to fix one of the driven gears on the shaft in mesh with its pinion and then loosely mount the other of the driven gears on the opposite end of the shaft and in mesh with its driving pinion. The pinion shaft is then rotated so that the loosely mounted driven gear seeks a position relative to its supporting shaft which provides proper tooth alignment. The shaft, or preferably the gear, is then removed and a keyway is cut in alignment with the keyway on the other part. The parts are then reassembled with an interfitting key so that both driven gears are fixed to their respective shaft ends and are in driven engagement with the pinions.
The time requirements and inaccuracies associated with the aforementioned technique of aligning large power transmission gears, have made it highly desirable to develop a method for aligning gears which does not require the demounting of the driving or driven gear parts after an initial assembly.
It is also important that the teeth of the other gear set, whether or not the gears are integrally mounted on their shaft, also be properly aligned with respect to each other so that prealignment of the driven gears may be obtained. In this regard prior art methods of cutting integral gears on shafts have been overly time consuming and do not assure proper alignment of the teeth on one gear with the teeth of the other gear formed on the same shaft.
For example, in cutting integral gears spaced apart on a shaft with hobs and other form cutters it has been conventional practice to place alignment marks on the shaft which are used in an effort to visually "center" the gear cutter prior to cutting the respective sets of gear teeth. This method is inaccurate due to the good chance of human error in performing the alignment process. The problems of accurately aligning certain types of cutters such as gear hobs by this technique is compounded by the nonsymmetrical shape of the cutter teeth which precludes accurate visual "sighting in" or centering methods.
Accordingly, there has been a need for improved methods for aligning heavy duty power transmission gearing whereby accurate alignment of the gearing is obtainable without the complex assembly and disassembly procedures associated with prior art techniques. In connection with developing improved methods for aligning gears which are spaced apart on a common shaft, the present invention has also provided improved fixture means particularly adapted for use in manufacturing and aligning opposed or so called double helical gear sets.