A lighter weight, higher strength, more compact internal combustion engine has consistently been the goal of engine designers. Recently, the rising cost of fossil fuel has further intensified the need for an engine having such desirable characteristics since ligther weight, greater strength and reduced size can lead to greater fuel efficiency in many applications. For example, greater efficiency results when the engine is used to power a vehicle because a smaller, lighter weight engine permits an overall reduction in vehicle size and weight which translates into greater fuel economy. Unfortunately, the advanced state of engine design means that even small size or weight reductions are difficult to achieve without sacrifice of other desirable engine characteristics.
The use of a single multi-purpose gear train mounted at one end of an engine block for driving all engine accessories directly through a gear connection with the engine crankshaft is well known as illustrated in U.S. Pat. No. 3,263,663. Provision of a single drive train has numerous advantages including the reduction of parts and weight which would otherwise result if additional driving connections were made with the crankshaft. To allow lubrication of the gears and to provide mounting structure for some of the engine accessories, a housing can be provided around the gear train. Naturally, the greater number of functions which the gear cover can be designed to perform, the greater will be the weight and cost reduction potential thereof. U.S. Pat. No. 3,263,663 discloses such an unitary housing having multiple functions including shrouding the accessory gear train and providing support to a variety of engine accessories. The unitary housing of U.S. Pat. No. 3,263,663 also includes an integral engine mount which further increases the weight reducing potential of this design. However, the engine mount is spaced a substantial distance from the engine block as compared with the general size of the engine. Accordingly, a relatively large moment arm exists between the engine mount and the interface between the housing and motor block, thereby requiring greatly thickened housing walls and increased use of reinforcing webs all of which adds significantly to the weight of the unitary housing.
Other types of detachable cover plates for mounting engine accessories are known in the prior art such as disclosed in U.S. Pat. No. 2,303,093 whereby the members are designed to allow grouping of the engine accessories for driving connection with the crankshaft of the engine through a drive train encased by the detachable plate member. As illustrated in U.S. Pat. No. 2,303,093, the detachable cover plate may be provided with an exterior enlargement forming a recess within which is received a vibration controlling element mounted on the engine crankshaft outboard of the driving connection between the crankshaft and the engine accessories. U.S. Pat. No. 2,303,093 does not, however, suggest a manner whereby the detachable cover plate can be employed to perform an engine mounting or supporting function.
Engine mounts which perform an incidental shrouding function relative to the drive connection between the engine crankshaft and plural engine accessories are known as illustrated by U.S. Pat. No. 1,883,671 but such engine mounts are not disclosed for use in combination with a cover designed to completely encase a gear train extending between the crankshaft and a plurality of accessories mounted on the cover. Disclosures relating to combined mounts and shrouds have thus not suggested a gear cover design having multi-functional purposes wherein the cover portions performing the various functions cooperate in a synergistic manner to improve the strength to weight ratio of the engine.
Numerous efforts to reduce the noise produced by internal combustion engine operation have recently been pursued resulting in such concepts as disclosed in U.S. Pat. No. 3,726,365 wherein specialized structure is employed within the engine in an attempt to change the natural frequency of the engine block. While useful in some instances, the complex nature of the noise reducing structure illustrated in this patent is not practical in most commercial engine applications.
In short, the prior art has failed to disclose a multi-purpose gear cover design for an internal combustion engine which is simultaneously characterized by high strength to weight ratio, compact size and noise suppressing capability.