In piston-type positive displacement devices, an axially movable piston and a rotatable crankshaft are linked by a connecting rod which is journaled to both of them. Then the axial movement of the piston and the rotation of the crankshaft occur simultaneously one naturally being caused by the other. The cyclical reversal of the piston and connecting rod would, if not counterbalanced, create an intolerable and destructive vibration. Simultaneously, the crankpin and the connecting rod undergo movements which are other than purely axial, and these can also give rise to undesirable vibrations. The classical way to reduce these vibrations is to provide counterbalancing which by its motion and inertia provides oppositely directed force which tends to reduce the net vibratory force. Because in all engines, but especially in single-cylinder engines of practical size, it is not possible to duplicate the moving bodies and their reactions to provide precisely equal and opposite counterbalancing forces, many attempts have been made to approach a respectable compromise, but these have always been less than optimal.
In addition, the mountings of the device which are used to attach it to a base have been extensively developed for the purpose of damping the transmission of vibrations to the base.
The existence of the internal combustion engine is testimony to the acceptability of the many trade-offs which have been made to smooth its operation, and of constructions which have been built for that purpose. Still, undesirable vibrations and some engine roughness persist, and many of the existing counterbalancing devices are unsuitably bulky. Especially in small two-cycle engines where engines size must be minimized, conventional counterbalancing constructions continue to add unfavorably to the bulk of the engine. It is a useful and desirable thing to reduce engine bulk, especially when with a reduction, a smaller sized engine could be made which produces the same power for use in propelling a relatively lightweight vehicle as a bulkier engine.
Also, in any engine, it is desirable to reduce the vibration as much as possible in order to subject the engine and its parts to lesser peak stresses. Lighter-weight parts can then be used.
Among the many attempts to provide improved counter-balancing, the following United States patents appear to deserve comment: Ricardo U.S. Pat. No. 1,310,090; Ishida U.S. Pat. No. 3,528,319; Mederer U.S. Pat. No. 2,212,272; Ishido U.S. Pat. No. 3,563,223; Ljungstrom U.S. Pat. No. 2,235,160; Hintze U.S. Pat. No. 4,152,956; Berlyn U.S. Pat. No. 3,112,658; Portman U.S. Pat. No. 4,156,387; Harkness U.S. Pat. No. 3,457,804.
These intelligent efforts attest that the problem is one of long-standing, and each illustrates an attempt to improve matters. The Ricardo and Ljungstrom patents are of especial pertinence to the invention.
Another shortcoming of the internal combustion engine, or of any positive displacement piston type device is inherent in its very nature. It is based on the fact that at top dead center (TDC) and at bottom dead center (BDC), the piston exerts no torque on the crandshaft. This creates a null condition as to torque from the piston at those moments, which unless compensated for can cause roughness in operation. For this reason flywheels and other momemtum-type devices are included. The moment of inertia of such devices is important to their function--the larger the better. However, in small, lightweight engines, heavy flywheels are not tolerable. Then even the moment of inertia of the connecting rod or rods become important, but it is not particularly large. It would be a useful thing to provide the counterweight in such a way as to increase the moment of inertia and thereby to smooth out the operation of the engine near TDC and BDC.
It is an object of this invention to provide an efficient and rugged counterbalancing system which is of lesser bulk than conventional systems, and which provides complete counterbalancing, better and more complete than known system, and which because of the reduction in height which it enables, is especially suited for use in vehicles where small engines are needed, such as mopeds, motorcycles, and snowmobiles.
It is another object of this invention to provide a counterweight in such an arrangement that its moment of inertia relative to the crankshaft is comparatively large, so as to smooth out the engine's operation around TDC and BDC.
This invention is carried out in a positive displacement piston-type device such as a internal combustion engine having at least one piston, a crankshaft with an eccentric crankpin, and a connecting rod interconnecting them. A counterweight is linked to the crankshaft and is axially slidable in a axial guideway and which includes a wagging member which wags as it reciprocates.
According to one embodiment of this invention, the counterweight itself wags.
According to yet another embodiment of the invention, a connecting link wags, and transmits axial force to the reciprocating counterweight, which counterweight does not wag.