The subject invention relates to engines and, more particularly, to apparatus for countering unbalanced forces generated in engines and harnessing power from an engine""s crankshaft to drive accessory apparatuses.
Over the years, perhaps due to declining fossil fuel reserves and other economic factors, designers have been challenged to develop engines that are lighter and compact, more fuel efficient, more reliable, and easier to maintain than prior engines. To address such challenges, engine designers must develop new solutions to old problems that have confronted engine designers for years. One such problem involves the need to minimize vibrations created during the engine""s cycle. This need almost universally encompasses all types of engine designs the engine""s cycle. This need almost universally encompasses all types of engine designs regardless of their specific applications and tends to be very important in most, if not all, engines that employ reciprocating pistons.
Within an engine structure, forces are created by the inertia of their moving parts and by the varying gas pressures in the engine cylinders. Such forces tend to result in deflections in the structural members of the engine. Thus, vibrations of varying amplitudes and frequencies are developed throughout the engine structure and are transmitted to a support frame through the engine mounts and ultimately to various other components attached to the frame. These vibratory motions must be controlled to avoid malfunction, mechanical failure and/or excessive engine noise.
Piston reciprocation is one of the main causes of engine vibration. Each piston has a mass and inertia and, as it reciprocates within a cylinder, it applies a force to the engine structure that lies along the cylinder axis. One method employed in the past to counterbalance such piston forces involved adding a counterweight to the crankshaft to provide an inertia force in a direction that is opposite to the direction of the piston force. However, the use of such counterweights alone proved to be an ineffective method for balancing the inertia forces generated by the piston, because the counterweights themselves created additional unbalanced forces during rotation of the crankshaft.
Thus, various other counterbalance configurations have been developed in an effort to address those shortcomings. One prior method involved the use of counter-rotating counterbalances that were timed and so proportioned such that the components of their centrifugal forces in a first direction resulting from their rotation would be additive and in opposition to the piston forces to achieve a desired balance, while the components of their centrifugal forces in a second direction would be in opposition to each other so as to cancel each other out. However, the components and drive arrangements for effecting such counter-rotation of counterweights typically occupied a significant amount of space within the engine and can add undesirable weight to the engine.
U.S. Pat. No. 3,415,237 to Harkness purported to solve the above-mentioned problems associated with driving counterbalances within a single cylinder four stroke engine. That patent teaches that counterweights located external to the engine crankcase are driven through a gear arrangement attached to the camshaft. However, such arrangement was not particularly well-suited for use in multiple cylinder engines.
The designers of multiple cylinder engines must also attempt to compensate for forces known as xe2x80x9ccouplesxe2x80x9d that are generated during the combustion cycles. A couple comprises forces that want to turn the engine about its vertical axis. In multiple cylinder engines, it is desirable for the pistons in one engine bay to not reach the top of their respective strokes at the same time that the pistons in an adjacent bay are reaching their respective top strokes. If they do, engine vibration may be exacerbated. Thus, multiple cylinder engines are designed to achieve xe2x80x9ceven firingxe2x80x9d between the cylinders. However, because the pistons create forces in different directions and because the axes along which those forces lie are separated from each other (i.e., not coaxial), couples are generated which, if left unbalanced or uncountered can lead to more engine vibration.
U.S. Pat. No. 4,632,072 to Brogdon discloses a balancing arrangement for a multiple cylinder combustion engine. In that engine, a pinion gear is coaxially attached to each axial end of the crankshaft. Each pinion gear includes a counterweight that is radially spaced from the crankshaft axis of rotation. At least one idler pinion gear is rotatably mounted to the engine housing and is in meshing engagement with one of the pinion gears attached to the crankshaft. Each idler pinion includes a weighted portion spaced from its axis of rotation. Both the counterweights and the weighted portions of the idler pinions are angularly spaced from each other by a predetermined amount so that, during rotation of the crankshaft, the centrifugal force vectors of the crankshaft counterweight and idler pinion weighted portions cancel the primary moment (couple) generated by the piston reciprocation acting on axially spaced positions along the crankshaft.
Still other arrangements have been devised to address engine vibration. For example, U.S. Pat. No. 1,855,570 to Edison, U.S. Pat. No. 2,426,875 to Hasbrouk et al., U.S. Pat. No. 2,666,418 to Gamier et al., U.S. Pat. No. 3,402,707 to Heron, U.S. Pat. No. 3,581,628 to Williams, and U.S. Pat. No. 3,667,317 to Hillingrathner disclose various means for controlling engine vibration.
Also in most modem day engine configurations and applications, a variety of ancillary components that require some form of power to function are employed. For example, many engine applications require the use of hydraulic pumps, vacuum pumps, fans, etc. Thus, it is desirable to obtain as much of that power from the engine itself, if it can be done without noticeably effecting the engine""s output. While various ancillary drive schemes, such as belts and pulleys have been employed, they are not well-suited for use in applications wherein minimization of engine size and engine weight is an important consideration.
Perhaps no industry has experienced the above-mentioned challenges more so than the aircraft industry. It is axiomatic that it is particularly desirable to have a small, lightweight, fuel efficient aircraft engine that is reliable and can be readily maintained. However, the various methods discussed above do not lend themselves well for use in such applications wherein engine size, weight and reliability may be crucial.
The engine balance apparatuses and accessory drive devices that are disclosed in U.S. Pat. No. 6,164,259 to Brogdon et al. address the above-mentioned shortcomings. In applications wherein frequent inspection is required and to reduce downtime associated with inspecting and replacing the components of such apparatus, it is desirable that such devices be easily removable and replaceable.
Thus, there is a need for an apparatus for effectively reducing engine vibration and counterbalancing forces generated within an engine that has components that may be easily detached and replaced as necessary.
There is still another need for apparatus having the above-mentioned characteristics and that is relatively compact and adds little weight to the engine when compared to prior engine balance arrangements.
Another need exists for apparatus with the above characteristics that does not require the numerous parts commonly associated with prior engine balance schemes.
Yet another need exists for the above-mentioned apparatus that is rugged and reliable and serves to transfer the thrust loads from the crankshaft to the gear assembly.
In accordance with a particularly preferred form of the present invention, there is provided a balancing apparatus for an engine having a rotating crankshaft that has a crankshaft axis. In a preferred form, the balancing apparatus includes a primary balance mass assembly that is non-rotatably and removably affixed to the crankshaft and a secondary balance mass assembly that is rotatably and removably supported on the crankshaft. In addition, a driver is attached to the crankshaft for causing the secondary balance mass assembly to rotate in a direction opposite to the direction of rotation of the crankshaft. The primary balance mass assembly includes a primary mass that is affixed to a primary hub portion and a primary cap portion that is removably attached to the primary hub portion to clamp a portion of the crankshaft therebetween and define a primary balance mass carrier. The apparatus may also include a secondary mass that is affixed to a secondary hub portion and a secondary cap portion that is removably attached to the secondary hub portion to define a secondary hole therebetween to rotatably receive another portion of the crankshaft therein. The secondary cap and secondary hub portions serve to define a second balance mass carrier.
The apparatus may include a primary gear removably and non-rotatably supported on the primary balance mass carrier and a secondary gear removably and non-rotatably supported on the secondary balance mass carrier. The secondary gear communicates with the primary gear such that rotation of the crankshaft in a first direction causes the secondary gear and the secondary balance mass carrier to rotate about the crankshaft in a secondary rotational direction opposite to the primary rotational direction.
The present invention may also comprise an engine balance mechanism that includes a crankshaft that defines a shaft axis and a primary balance mass carrier that is removably and non-rotatably attached to the crankshaft. The primary balance mass carrier has a primary balance mass thereon. The mechanism may further include a secondary balance mass carrier that is rotatably and removably received on the crankshaft. The secondary balance mass carrier has a secondary balance mass thereon. A primary gear is removably supported on the primary balance mass carrier and a secondary gear is removably supported on the secondary balance mass carrier. At least one auxiliary gear is in intermeshing engagement with the primary and secondary gears and a gear cage is coaxially supported on the crankshaft and supports auxiliary gears therein.
It is a feature of the present invention is to provide an engine balance mechanism that is readily detachable from the engine crankshaft to facilitate inspection and repair operations.
Accordingly, the present invention provides solutions to the shortcomings of prior engine balancing mechanisms and schemes. Those of ordinary skill in the art will readily appreciate, however, that these and other details, features and advantages will become further apparent as the following detailed description of the preferred embodiments proceeds.