The present invention relates generally to fluid driven rotary motors of the vane type which include a rotor rotatably mounted in a housing. More specifically, the present invention relates to an improved fluid driven rotary motor which includes novel means for securing the axial position of the rotor so that contact between the rotor and housing can be avoided.
Fluid driven rotary motors, and for that matter rotary compressors, of the vane type, generally comprise a housing which includes a rotor cover disposed between a pair of end plates and a cylindrical rotor, which defines opposite axial faces, rotatably mounted in the housing. The end plates may have a bore formed therein which receives the rotor in a journaled manner. The rotor is formed with a plurality of radially extending slots, each of which receives a vane in a slidable manner. The housing, rotor and vanes cooperate with one another to define a plurality of variable working volumes between the vanes. A compressed fluid is introduced into the variable working volumes through a first orifice which is formed in the housing. Likewise, the compressed fluid is exhausted through a second orifice formed in the housing. Expansion of the compressed fluid within the variable working volumes, and subsequent exhaust, causes rotation of the rotor. A drive shaft, torsionally affixed to the rotor, communicates the rotation to a tool or other apparatus.
The axial position of the rotor, with respect to the housing, is maintained so that the vanes remain in proper relation with the rotor cover. In some prior art fluid driven motors, axial displacement of the rotor has been limited by contact between the axial faces of the rotor and the end plates. Such contact frequently results in substantial wear and damage to the contacting parts as well as a loss of power output by the motor.
Typically, the spacing between the axial faces of the rotor and the end plates is maintained very small, on the order of 0.0005 inch. This close tolerance is necessary to prevent leakage of the compressed fluid between the variable working volumes, via a path across the axial faces of the rotor.
Such close spacing has at least two drawbacks. First of all, foreign particles may be carried by the compressed fluid and become lodged between an end plate and axial face of the rotor. This can exacerbate the problems of scoring and wear or even cause stalling of the rotor. Secondly, attempts to further limit the axial displacement of the rotor, so as to entirely avoid contact between the axial faces of the rotor and the housing end plates, are extremely difficult because of the limited tolerable range for axial position.
In U.S. Pat. No. 3,804,562, assigned to Atlas Copco Aktiebolag, the axial position of the rotor is adjusted by means of a set screw. The Atlas invention has the drawback that the axial position of the rotor is manually set, without the ability to see or measure the true position of the rotor with respect to each end plate. Thus, the user can only assume that the proper axial position has been achieved if, in fact, the air motor functions. Furthermore, the set screw has the possibility of loosening during operation of the motor.
In U.S. Pat. No. 4,435,140, assigned to Nippon Sohen, Inc., the axial position of the rotor in a rotary compressor, is limited by contact between the vanes and end plates. Thus, the vanes may bear the entire weight of the rotor during operation. Because the vanes and end plates are in relative rotational motion, it is expected that contact therebetween would cause substantial wear in these two portions. While such a configuration may be suitable for a rotary compressor, which can operate at relatively low rpm, it would not likely be suitable for a fluid driven rotary motor which operates at relatively high rpm. At high speeds, rapid deterioration of the vane material would be expected.