There are numerous sizes and types of balance shafts used in automobile engines. Balance shafts are used to reduce or eliminate the noises and vibrations in piston engines not otherwise balanced by conventional crankshaft counterweights. These balance shafts are sometimes called "counterbalance" shafts.
Balance shafts can be rotated in the same direction as the engine crankshaft or in the opposite direction, as required for the particular engine. Some engines require a pair of balance shafts rotating in opposite directions.
Balance shafts typically have an elongated support member and one or more bob weights. The bob weights can be positioned on the same side or on opposite sides of the support member, as required.
One conventional type of balance shaft comprises a pair of opposed bob weights positioned between a pair of bearing surfaces at the two outer ends of the shaft. The bearing surfaces are supported in bearings which allow the balance shaft to rotate in accordance with the speed of the engine. A drive snout at one end is connected to a gear which is driven by the engine which in turn rotates the balance shaft. This balance shaft is normally driven at the speed of the crankshaft of the engine and thus at twice the speed of the camshaft. The balance shaft also is rotated in the opposite direction as the crankshaft.
Several types of automobile engines are inherently unbalanced, such as 90.degree. V-6 engines, and thus need a counter rotating balance shaft. Certain engines also have second order forces which vibrate at twice the speed of the crankshaft and also need to be balanced and neutralized. It is not possible to simply rotate a conventional balance shaft at twice the crankshaft speed, however. Standard balance shafts rotated at an increased speed have a tendency to bend and wear out the support bearings.
It is thus an object of the present invention to provide an improved balance shaft for an automobile engine which can balance and neutralize engine noise and vibration forces, particularly the second order forces. It is another object of the present invention to provide a balance shaft which can rotate at twice the crankshaft speed without bending or causing excessive bearing wear.
It is still another object of the present invention to provide a balance shaft which is stiffer and lighter than traditional balance shafts and which minimizes bending when rotated at increased speeds.
Other benefits, features and advantages of the present invention will become apparent from the following description, when taken in accordance with the appended claims and accompanying drawings.