Abstract:
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.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from U.S. Provisional Serial No. 60/234,906, filed Sep. 26, 2000, and is incorporated herein in its entirety by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to the balancing of various inertia forces on an V-type engine. In particular, the present invention relates to the balancing of the inertia forces on a two (2) cylinder V-type internal combustion engine.  
           [0004]    2. Description of Related Art  
           [0005]    [0005]FIG. 1 illustrates the principal inertia forces of first order acting on a dual V-type engine. In this example, the crankshaft position is defined such that the crankpin is positioned in a symmetry plane φ between Cylinder  1  and Cylinder  2 , as shown in FIG. 1. Each cylinder includes a piston that is connected to a connecting rod. The connecting rods for the pistons are connected to a common crankpin. There are two pairs of inertia forces acting on the cylinders. Forces P 1  and Q 1  act on Cylinder  1  and forces P 2  and Q 2  act on Cylinder  2 . Forces P 1  and P 2  are parallel to the y axis and rotate in the same direction and at the same speed as the crankshaft. Forces Q 1  and Q 2  are oriented at an angle +2α and −2α, respectively, relative to forces P 1  and P 2 . Forces Q 1  and Q 2  rotate against the direction of the crankshaft but at the same speed. 2α is less than 90°. All of these forces have the same magnitude.  
           [0006]    The forces P 1  and P 2  can be easily balanced by an opposite counterweight W 1  rotating in the same direction as the crankshaft around the center C. The forces Q 1  and Q 2  can be reduced into force components Q 1 (x) and Q 2 (x) aligned along the x axis and force components Q l (y) and Q 2 (y) aligned along the y axis. The force components Q 1 (y) and Q 2 (Y) can be balanced by an opposite counterweight W 2  turning around the center C opposite to the crankshaft rotation but at the same speed. The connecting rods are usually attached to the common crankpin with a small offset a, as shown in FIG. 2. As such, the force components Q 1 (x) and Q 2 (x) induce a moment that can be balanced by a pair of counterweights W 3  with an offset a′. The counterweights W 3  pivot around the axis in the same direction and at the same speed as the counterweight W 2 . The counterweight W 3  are offset at an angle of +90° and −90° respectively relative to the counterweight W 2 . The Z axis is parallel to the crankshaft axis but otherwise can be positioned anywhere. The size of the counterweights W 3  can be reduced by increasing the offset a′.  
           [0007]    There are several approaches commonly used today for balancing two cylinder V-type engines. A common way to accomplish this is to choose an angle equal or close to a 90° angle between the cylinder center axis such that the components Q 1 (y) and Q 2 (y) disappear or neutralize each other (2α=90°) according to FIG. 1. The inertia forces P 1  and P 2  can be balanced with the counterweight W 1  attached to the crank webs and the mass moment induced by the pair of forces Q 1 , and Q 2  and the offset a between the connecting rods can be balanced with the counterweight W 3 . A perfect balancing of the mass forces of the first order can be accomplished and the pair of connecting rods can be attached to the same crankpin. A 90° angle, however, requires relatively large engine dimensions. These large engine sizes, however, are not acceptable for many applications. In motorcycle applications, for instance, a 90° angle design is impractical when the crankshaft axis is orientated either in the vehicle driving direction or crosswise.  
           [0008]    In such applications, a V-type engines with a cylinder angle notedly smaller than 90° is necessary. Another approach for balancing the inertia forces for the engines is necessary. The connecting rods of each cylinder may be attached to two separate crankpins with an offset between the pins. The degree of the offset has to match the difference between the actually chosen cylinder angle and 90°. There are two notable disadvantages associated with this approach. First, the separated crankpins markedly increase the distance between the pair of connecting rods. This considerably enhances the induced mass moment. Second, the two crankpin design requires an intermediate crank web for coupling the two pins. Thus, the distance between the crankshaft bearings is comparatively large since three crank webs and two crankpins have to be accommodated between the bearings. This considerably reduces the stiffness of the crankshaft considerably and limits the engine design for use in low and medium speed and power applications.  
           [0009]    For high-performance motorcycle engines, dual V-type engines are used. The engines have cylinder angles well below 90° and have a common crankpin for both connecting rods. These engines can be balanced by arranging a separate balance shaft parallel to the crankshaft. Due to the crank webs, however, the distance between the crankshaft and the balance shaft is relatively large. This induces an additional unbalance (mass moment) which itself has to be balanced by further counterweights. These counterweights preferably should be arranged far away from the crankshaft and balance shaft to keep the counterweights as low as possible. For example, the counterweights can be arranged in the cylinder head. This design, however, may require additional components, which makes the engine more expensive, causes higher friction losses and enhances noise emissions.  
         OBJECTS OF THE INVENTION  
         [0010]    It is an object of the present invention to provide an arrangement for balancing the inertia forces and moments of an engine that overcome the above-described deficiencies.  
           [0011]    It is another object of the present invention to provide an arrangement for balancing the inertia forces and moments of a high performance dual V-type engine.  
           [0012]    It is another object of the present invention to provide an arrangement for balancing the inertia forces and moments of a high performance dual V-type engine preferably for motorcycle applications.  
           [0013]    It is yet another object of the present invention to provide an arrangement for balancing the inertia forces and moments of an engine that can be used to power engine accessories.  
           [0014]    It is another object of the present invention to provide an arrangement for balancing the inertia forces and moments of an engine using multiple counterweight assemblies, wherein each counterweight assembly includes at least a pair of counterweights. Each of counterweight of the pair of counterweights is mounted on a separate balance shaft.  
           [0015]    Additional objects and benefits of the present invention will be apparent in view of the figures and below described embodiments of the invention.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention is directed to an arrangement of an internal combustion engine that balances the various inertia forces acting on the engine during operation. The internal combustion engine in accordance with the present invention includes at least one pair of cylinders. The cylinders are preferably arranged at an angle with respect to each other to form a V-type engine configuration. Each cylinder contains a piston movably mounted therein and connected to a common crank pin of a crankshaft by means of a pair of connecting rods. The movement of these pistons and the connecting rods during operation generate the inertia forces on the engine, which may reduce operating efficiency, as described above in connection with the prior attempts to balance engines. In accordance with the present invention, the internal combustion engine includes a plurality of counterweight assemblies that counterbalance the forces generated during engine operation.  
           [0017]    A first counterweight assembly is operatively connected to the crank webs of the crankshaft. The first counterweight assembly includes at least a pair of first counterweights. A first counterweight is associated with each crankweb. The first counterweights rotate about an axis that extends through the crankshaft, which operates the pistons. It is contemplated each of the first counterweights may be integrally formed with its corresponding crank web.  
           [0018]    The internal combustion engine in accordance with the present invention further includes a second counterweight assembly for balancing forces acting on the engine. The second counterweight assembly is spaced from the crankshaft and the first counterweight assembly. The second counterweight assembly preferably includes at least a pair of second counterweights and mounting assemblies for securing the each of the second counterweights within the engine. The second counterweights are preferably mounted on separate shafts that are located in the crankcase and driven by the crank shaft. The location of the second counterweights aids in the balancing of the forces generated during operation of the engine without increasing the size of the engine. It is contemplated that each of the second counterweights may be located on one side of the axis extending through the crankshaft.  
           [0019]    The present invention, however, is not limited to this arrangement; rather, it is contemplated that the second counterweights may be located on opposite sides of the crankshaft axis. A plane E extends between the cylinders. The plane intersects the axis of the crankshaft at a centerpoint. One of the second counterweights is preferably located on one side of the plane and the other of the second counterweights is located on an opposite side of the plane. The second counterweights are arranged within the engine such that a line that extends through a center of mass of each of the second counterweights also extends through or near the centerpoint.  
           [0020]    The internal combustion engine in accordance with the present invention also includes a third counterweight assembly for balancing forces acting on the engine. The third counterweight assembly is also spaced from the crankshaft and the first counterweight assembly. The third counterweight assembly preferably includes at least a pair of third counterweights, which are mounted to the engine crankcase with a suitable mounting assembly, such as for example a mounting or balance shaft. The second counterweights are preferably located on the same side of the axis of the crankshaft, but on opposite sides of the plane.  
           [0021]    In accordance with the present invention, it is contemplated that one or more of the counterweights may be secured to the same mounting or balance shaft. For example, one of the third counterweights and one of the second counterweights may share a common mounting assembly. With this arrangement, the third counterweight is spaced from and positioned at angle with respect to the second counterweight. This reduces weight and the number of components required to balance the engine. With this in mind, it is contemplated that certain counterweights may be combined. For example, one of the third counterweights may be formed as a single unit with one of the second counterweights. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:  
         [0023]    [0023]FIG. 1 is a schematic illustration of the inertia forces acting on a dual V-type engine having a common crankpin;  
         [0024]    [0024]FIG. 2 is a cross sectional view of a V-type engine between a pair of cylinders illustrating an embodiment of the present invention;  
         [0025]    [0025]FIG. 3 is a diagram illustrating the orientation of the second and third counterweight assemblies with respect to the crankshaft and the centerpoint for the V-type engine of FIG. 2;  
         [0026]    [0026]FIG. 4 is a diagram illustrating a variation of the orientation of the second and third counterweight assemblies with respect to the crankshaft and the centerpoint for the V-type engine of FIG. 2;  
         [0027]    [0027]FIG. 5 is a cross sectional view, similar to FIG. 2, illustrating another embodiment of the present invention;  
         [0028]    [0028]FIG. 6 is a side schematic view illustrating the orientation of the counterweights of the second counterweight assembly with respect to the crankshaft and the pair of cylinders;  
         [0029]    [0029]FIG. 7 is a cross sectional view, similar to FIG. 2, illustrating yet another embodiment of the present invention; and  
         [0030]    [0030]FIG. 8 is a side schematic view illustrating the orientation of the counterweights of the second counterweight assembly with respect to the crankshaft and the pair of cylinders of the V-type engine of FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    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.  
         [0032]    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.  
         [0033]    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.  
         [0034]    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.  
         [0035]    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.  
         [0036]    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 φ 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.  
         [0037]    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 +90° /−90 ° relative to the counterweight  14 , whereby the sign (+/−) 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 .  
         [0038]    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.  
         [0039]    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.  
         [0040]    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 .  
         [0041]    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.  
         [0042]    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.  
         [0043]    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.