Arrangement for mass balancing a V-type internal combustion engine

An arrangement of an internal combustion engine is disclosed that balances the various inertia forces acting on the engine during operation. A plurality of counterweight assemblies are provided that counterbalance the forces generated during engine operation. A first counterweight assembly rotates about the crankshaft axis. Second and third counterweight assemblies are provided that are spaced from the crankshaft axis and the first counterweight assembly. The first, second and third counterweight assemblies combine to counteract and balance the inertia forces generated during operation of the engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The arrangement for mass balancing a V-type internal combustion engine according to the present invention will now be described with reference to the embodiments shown in the accompanying drawings. The mass balancing arrangement will be disclosed in connection with a pair of cylinders. It is contemplated that each pair of cylinders will include a similar mass balancing arrangement disclosed herein. In these embodiments, the present invention is applied to a four-cycle, two-cylinder V-type internal combustion engine having a common crank pin for both connecting rods. There is a 72° cylinder angle between the cylinder axis of the two cylinder. Other cylinder angles greater or less than 90° are contemplated. Furthermore, the present invention is not limited to four cycle engines; rather, any other type of V-type engine, e.g. two cycle engines, or four, six and/or eight cylinder engines are considered to be well within the scope of the present invention. The engines disclosed herein are capable of being used in personal watercraft, motorcycles, all terrain vehicles, snow mobiles, other vehicles and boats, and outboard motors for various boats. A first embodiment of the present invention will be described in connection with FIGS. 2 and 3 . The engine includes a crankshaft 1 rotatably mounted in a crankcase 2 . A crank pin 3 is coupled to a pair of crank webs 4 and 5 . A pair of connecting rods 6 and 7 are attached on one end to the crank pin 3 and on the other end to pistons 8 and 9 , respectively. The pistons 8 and 9 are slidably fitted in cylinder bores 10 and 11 . A plane E extends between the cylinders, as shown in FIG. 2 . The engine further includes a first counterweight assembly having at least two counterweights 12 and 13 . The counterweights 12 and 13 are formed as part of the crank webs 4 and 5 , respectively, as shown in FIG. 2 . The present invention, however is not limited to counterweights that are integrally formed as part of the crankwebs. It is contemplated that the counterweights can be formed as separate components that are secured to the crankwebs. The first counterweight assembly and in particular the counterweights 12 and 13 correspond to the counterweight W 1 . The engine further includes a second counterweight assembly having at least two counterweights 14 and 15 mounted on two separate balance shafts 16 and 17 . The second counterweight assembly and in particular the counterweights 14 and 15 correspond to the counterweight W 2 . The axis of the balance shafts 16 and 17 are aligned parallel to the crankshaft axis. In FIGS. 2 and 3 , the balance shafts 16 and 17 are located on opposite sides of the crankshaft axis. The balance shafts 16 and 17 are driven by the crankshaft 1 via toothed wheels 181 , 182 , 191 , and 192 with a gear ratio of 1:1. The balance shafts 16 and 17 rotate in a direction opposite to the direction of rotation of the crankshaft. Since the counterweights 14 and 15 of the second counterweight assembly are not rotating around the crankshaft axis, the counterweights 14 and 15 are specially positioned in order to balance the mass force components Q 1 (y) and Q 2 (y). This special position is defined by a connecting line L intersecting the crankshaft axis exactly at its center point C, as shown in FIGS. 2 and 3 or near the center point C, as shown in FIG. 4 . The L is defined as a connecting line between the points S N , which are orthogonal projections of the centers of mass S to the axis of the balance shafts 16 and 17 . The center point C is defined as intersecting point of the plane E and the crankshaft axis. The counterweights 14 and 15 follow the lever relationship rule referring to the center point C where the line L acts as a lever. The counterweights 14 and 15 balance the force components Q 1 (y) and Q 2 (y) and have to match the same requirements described previously in FIG. 1 in order to balance the mass forces of first order. Since the crankshaft position in FIG. 2 is the same as shown in FIG. 1 (crankpin positioned in the plan &phgr; between the pair of cylinders) the counterweights 14 and 15 and their centers of mass S respectively have to be positioned exactly on the opposite side of the crankshaft axis referring to the crankpin, as shown in FIG. 2 . The engine further includes a water pump 20 having a water pump shaft 21 , a propeller 22 and a water pump housing 23 , as shown in FIG. 2 . The water pump shaft 21 is driven via the toothed wheels 191 and 24 with a gear ratio of 1:1. The water pump shaft 21 rotates in a direction opposite to the crankshaft rotation. The axis of the water pump shaft 21 and the balance shaft 16 are coaxially aligned. The engine further includes a third counterweight assembly having additional counterweights 25 and 26 that are located on the shafts 21 and 16 . The third counterweight assembly and in particular the additional counterweights 25 and 26 correspond to the counterweight W 3 . The counterweights 25 and 26 of the third counterweight assembly balance the mass moment induced by the force components Q 1 (x) and Q 2 (x). The counterweight 25 is positioned at an angle of &plus;90° /−90 ° relative to the counterweight 14 , whereby the sign (&plus;/−) depends on the orientation of the pair of cylinders. The counterweight 26 is positioned at an angle of approximately 180° relative to the counterweight 25 . The counterweights 25 and 26 are of the same size and weight. The location of the counterweights 25 and 26 within in the engine may vary as long as the counterweights 25 and 26 are rotating around the same axis m, which is arranged parallel to the crankshaft axis, and the distance a′ is correctly adjusted to balance the mass moment induced by the pair of force components Q 1 (x) and Q 2 (x) acting on the moment arm a. The counterweights 25 and 26 may share balance shafts with the counterweights 14 and 15 . It is also contemplated that counterweights can be combined. For example, the counterweight 25 can be combined into the counterweight 14 , which would result in one big counterweight with an orientation somewhere between the original orientations of the separate counterweights. It is also contemplated to integrate the counterweight 26 into the toothed wheel 24 . The above-described geometrical relationships may vary. These relationships may be approximated; rather than being exact. Construction and design reasons may require a departure from these relationships. For example, the connecting line L might intersect the crankshaft axis in the vicinity of the center point C or even pass the crankshaft axis, as shown in FIG. 4 . In another example the axis of the water pump shaft 21 and the balance shaft 16 might not be aligned coaxially but be arranged by a little offset, as shown in FIG. 4 . The slight departure causes a slight unbalance of first order which, however, in most cases might be acceptable. It is also conceivable to omit the counterweights 25 and 26 . This, however, would produce a noticeable deterioration of the mass balancing and consequently a loss of comfort. As shown in FIG. 2 , the counterweight 26 is mounted on the water pump shaft 21 . It, however, is contemplated that the counterweight 26 may be mounted on any other shaft that meets the following requirements: it is parallel to crankshaft axis; it is approximately aligned coaxially with one of the balance shafts 16 or 17 ; and it is rotating in a direction opposite to the crankshaft rotation. For example, it is contemplated that the counterweight may be located on the shaft of an oil pump, alternator or any other kind of accessory drives. It is also contemplated that the balance shafts 16 , 17 may be used to drive the valve train or engine accessory equipment. A multifunctional arrangement of this kind is shown in the embodiment of FIG. 5 and FIG. 6 . In this arrangement, the counterweight 14 is directly mounted on the toothed wheel 182 , which turn together around the fixed balance axle 27 . It is contemplated that the axle 27 may be replaced by a balance shaft slidably pivoted in the engine housing, as shown for example in FIG. 2 . A sprocket 28 is attached to the toothed wheel 182 and drives the valve train of a first cylinder of a 4-cycle V-type engine via a timing chain. On the opposite side of the engine there is an equivalent arrangement for driving the valve train of a second cylinder of the V-type engine having a first gear wheel 194 mounted on the crankshaft 1 , a second gear wheel 193 pivoted on a fixed axle 31 and driven by the first wheel 194 , and a sprocket 32 directly attached to the wheel 193 for driving a timing chain 33 . There is no counterweight attached to the gear wheel 193 . The balancing of the mass force components Q 1 (y) and Q 2 (y) is accomplished using an additional balancing drive unit 34 as shown in FIG. 5 . This arrangement provides an advantage over the arrangement shown in FIG. 2 , where the timing chains are driven directly by the crankshaft 1 via sprockets 37 and 38 . Typically, the gear ratio between the crankshaft and the camshaft in a 4-cycle engine is 2:1. As such, the diameter of the camshaft sprocket is twice as big as the sprocket on the crankshaft. For high performance engine applications (i.e., low weight/power ratio, low size/power ratio), it is desirable to keep the diameter of the sprocket on the camshaft as small as possible. This is especially true for double overhead camshaft (“DOHC”) engines. The arrangement illustrated in FIG. 5 and FIG. 6 may be better suited for high performance applications as compared to the arrangement shown in FIG. 2 . The diameter of the sprockets 37 , 38 on the crankshaft 1 in FIG. 2 can not be reduced at will, since this would weaken the strength and stiffness of the crankshaft 1 too much. In FIG. 5 , the sprockets 28 and 32 are mounted on the intermediate gear wheels 182 and 193 . The sprockets 28 and 32 are not as limited by the dimension of the crankshaft. The diameter of the sprocket 28 can be reduced. Another embodiment of the present invention is illustrated in FIGS. 7 and 8 . It is similar to the embodiment shown in FIG. 5 . The balancing drive unit 34 , however, is omitted entirely and that the counterweight 15 is mounted directly on the gear wheel 193 . This arrangement simplifies the engine design. The connecting line L, however, passes through the crankshaft 1 away from the center point C, which results in some residual unbalance. Counterweights 25 and 26 , discussed above, and not illustrated in FIG. 5 - 8 can be added. The counterweights 25 and 26 may be attached to the gear wheels 182 and 193 . Alternatively, the counterweights 25 and 26 may be integrated directly into the counterweights 14 and 15 . This way the mass moment effected by for force components Q 1 (x) and Q 2 (x) can be reduced but not be neutralized entirely since the counterweights 25 and 26 are not turning around the same axis. As discussed above, it will be apparent to those skilled in the art that various modifications and variations may be made without departing from the scope of the present invention. Thus, it is intended that the present invention covers the modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.