Different types of counter-balance weight for hermetic reciprocating compressor

In order to have a better understanding on the design of counter-balance weight, extensive time has been spent on the study of some existing designs commonly used in the industry.

Caulking-Type Balancing Weight
This design is currently used in a series of compressors, and because of its easy availability, it is used as one of the base designs to compare with the new balancing weight. In this design, Caulking Pins are used to fasten the Crank Weight onto the Crank Weight Base. The required number of Crank Weights can be varied to suit the different inertial loads exerted with different model of compressors. Thus for this design, it has the advantage of using the same Crank Weight Base and Crank Weight for different models of compressors. However, this design requires 2 die sets for the production of the parts; one for the Crank Weight Base and the other for the Crank Weight. The design may also involve many parts, especially in the case of volumetric displacement 9.1cm3 and 10.0cm3, which is undesirable for assembly process.

Folding-Type Balancing Weight
In this design, the part is being pressed out and then bent along the fold line. Caulking is then performed to force material into the small hole to hold the folded portion in place. This design reduces the total number of parts required by eliminating the need for caulking pins as required in the caulking-type counter-balance weight. However, this design is found to be patented [1] in the Europe and North America market, and thus cannot be used for the design in this project. This design is currently used in Japan domestic market only.

Welding-Type Balancing Weight
The last type of counter-balance weight observed is the welding-type balancing weight. This design is used in one of the competitor’s compressors. The design is quite similar to the caulking type balancing weight except that the crank weights are spot-welded to the crank weight base instead of caulking. This can help to reduce the number of parts required by eliminating the need for the caulking pins. However, the application of this design is unknown.

The assembly method of the respective types of Counter-Balance Weight to the crankshaft is to be noted. For the caulking- and folding-type balancing weight, they are attached onto the eccentric portion of the crankshaft by interference force fitting, whereas fasteners, such as screws and dowel pins, are used for the welding-type balancing weight. The former will cause formation of slivers during interference force fitting, which is undesirable for quality issue and it also requires higher machining precision, and thus increases the manufacturing cost. The latter will incur additional cost on the fasteners. These existing methods of coupling counter-balance weight to the crankshaft are not cost effective enough, and the formation of the slivers has to be eliminated. Therefore, an alternative way of coupling the balancing weight to the crankshaft has to be explored.