Abstract:
A multi-cylinder reciprocating-piston engine with two crankshafts located generally end-to-end with respect to each other and with power output ends of the crankshafts located adjacent each other and mechanically interconnected with each other so they rotate at equal speeds but in opposite directions. Pairing of oppositely moving pistons reduces engine vibration. The crankshafts may be coaxial or offset radially from each other. Power from the engine is delivered from the adjacent power output ends of the crankshafts.

Description:
BACKGROUND OF INVENTION  
         [0001]    The present invention relates to a reciprocating piston engine, and particularly to an internal combustion engine including a pair of counter-rotating crankshafts.  
           [0002]    Conventional multi-cylinder high speed internal combustion engines small enough for use in automobiles, motorcycles, and smaller applications typically utilize a single crankshaft connected to all the pistons through connecting rods. One end of the crankshaft is connected to deliver power from the engine through a clutch or torque converter. Such a crankshaft may include counterweights to balance the pistons and connecting rods, and must have sufficient torsional stiffness to withstand the torque developed by the engine. The rotating mass of the crankshaft, particularly at high speeds, results in gyroscopic forces that can significantly affect the handling characteristics of vehicles, particularly motorcycles, in which such engines are used. Any imbalance in such an engine can result in significant vibration. The engine&#39;s crankcase and cylinder block structures must therefore be sturdy enough to absorb such vibrations as well as the torque and power developed by the engine in operation.  
           [0003]    In order to minimize the gyroscopic effects of a crankshaft, it has been known in the past to provide a pair of counter-rotating side-by-side crankshafts in an engine, with each crankshaft connected to each piston by at least one connecting rod, as shown in Hammerton, U.S. Pat. No. 5,435,232, and Wittner, U.S. Pat. Nos. 5,682,844 and 5,873,333, for example. Wittner discloses such an engine that the inventor claims is desirable for motorcycles because the crankshafts are located close together, resulting in a relatively narrow engine. Such engines, however, are of complex and costly construction.  
           [0004]    What is desired, then, is an engine that can safely operate at high speeds, without the undesired gyroscopic effects and problems of vibration found in previously known engines, and that is not overly complex.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention supplies an answer to the aforementioned shortcomings of previously known engines, by providing an engine in which a pair of counter-rotating crankshafts are aligned generally end-to-end.  
           [0006]    In one preferred embodiment of such an engine, a plurality of cylinders are arranged generally in line with each other, with a respective piston disposed reciprocatingly within each cylinder, and with each piston connected with a respective one of the counterrotating crankshafts.  
           [0007]    In one preferred embodiment of the invention the crankshafts are located coaxially with respect to each other.  
           [0008]    In another preferred embodiment of the invention gears mounted on the adjacent ends of the crankshafts are meshed with each other to provide for opposite rotation of the crankshafts.  
           [0009]    The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a simplified side elevational view of a motorcycle, showing in broken line the location of an engine according to the present invention together with a transmission attached thereto.  
         [0011]    [0011]FIG. 2 is a simplified isometric view from the upper right rear of an engine embodying the present invention, together with an associated clutch and transmission.  
         [0012]    [0012]FIG. 3 is a simplified right side elevational view of the engine and transmission shown in FIG. 2.  
         [0013]    [0013]FIG. 4 is a simplified sectional view of the engine shown in FIGS. 2 and 3, taken along line  4 - 4  of FIG. 2, showing a crankshaft timing gear train.  
         [0014]    [0014]FIG. 5 is a simplified right side elevational sectional view of an engine which is an alternative embodiment of the present invention, together with a transmission driven by the engine.  
         [0015]    [0015]FIG. 6 is a sectional view of the engine shown in FIG. 5, taken along line  6 - 6  in FIG. 5.  
         [0016]    [0016]FIG. 7 is a simplified isometric view taken from the upper right rear of an engine which is another alternative embodiment of the present invention.  
         [0017]    [0017]FIG. 8 is a simplified front elevational view of the engine shown in FIG. 7.  
         [0018]    [0018]FIG. 9 is a simplified right side elevational view of the engine shown in FIG. 7.  
         [0019]    [0019]FIG. 10 is a simplified sectional view of the engine shown in FIGS. 7, 8 and  9 , taken along line  10 - 10  in FIG. 9.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings which form a part of the disclosure herein, in FIG. 1 a motorcycle  10  includes a frame  12  supported by a front wheel  14  mounted in a front fork  16  mounted steerably on the front of the frame  12  and controlled by handlebar  18 . The frame  12  supports an operator&#39;s seat  20 . A driving rear wheel  22  is mounted on a swing arm  24  and driven by a chain  26  that is powered by an engine and transmission combination  28 , shown schematically in broken line. It will be understood that instead of a chain  26 , there might be a shaft drive, belt drive, or other final drive mechanism.  
         [0021]    Referring next to FIG. 2, an engine  30  is shown in greatly simplified form, with a cylinder block  31  and a cylinder head  33  shown in phantom outline and with engine valves omitted, so that the other moving parts of the engine may be seen more clearly.  
         [0022]    Associated with the engine  30  are a clutch  32  and a transmission  34 , connected to an engine output shaft  35 . In the engine and transmission combination  28  as shown in the engine output shaft  35  is tubular, i.e., a torque tube connected drivingly as a power input to the clutch  32 , while a separate shaft located within the torque tube delivers power from the clutch into the transmission  34 .  
         [0023]    A starter and suitable drive gearing may be provided in a housing  38 . A final drive sprocket  42  for the chain  26  is driven by the transmission  34 .  
         [0024]    It is of principal importance that the engine  30  includes two oppositely rotating crankshafts aligned longitudinally with respect to each other. That is, the crankshafts are arranged generally end-to-end rather than alongside each other, with a rear crankshaft  44  and a front crankshaft  46  supported in suitable bearings (not shown) and rotating oppositely with respect to each other. The front and rear crankshafts  46  and  44  are coaxially aligned with each other along a single axis of rotation  47 , as may be seen in FIGS. 2-3. The driving or power output ends of the crankshafts  44  and  46  thus face each other and are closely adjacent to each other at the middle of the length of the engine  30 .  
         [0025]    A pair of pistons, a front or number one piston  48  and a number two piston  50 , are connected to the front crankshaft  46  by respective connecting rods  52  and  54 . It may be seen that the respective crank throws of the crankshaft  46  are opposed, separated by  180  degrees of crankshaft rotation, so that the number one piston  48  is at top dead center while the number two piston  50  is at bottom dead center, as shown in FIG. 2.  
         [0026]    A number three piston  56  and a number four piston  58  are similarly connected to the rear crankshaft  44  by respective connecting rods  60  and  62 . The crank throws of the rear crankshaft  44  are also opposed to each other, and are in phase with those of the front crankshaft  46 . The number three piston  56  is thus at top dead center when the number one piston  48  is at top dead center, and the number four piston  58  is at bottom dead center at the same time, as shown in FIG. 2. The crankshafts are shown having been rotated 180° in FIG. 3, with the pistons  48 ,  50 ,  56 , and  58  being at the opposite ends of their respective strokes.  
         [0027]    A front crankshaft output gear  64  is fastened to the power output end of the front crankshaft  46  so as to be driven by and rotate with the front crankshaft  46 . A rear crankshaft output gear  66  is similarly fastened to the power output end of the rear crankshaft  44 , a small distance apart from the front crankshaft output gear  64 , so as to be driven by and rotate with the rear crankshaft  44 . It may be seen that the front crankshaft output gear  64  is larger in diameter than the rear crankshaft output gear  66 .  
         [0028]    A camshaft drive gear train  68  extends upward above the crankshaft output gears  64  and  66  and is arranged to drive a pair of camshafts  70  and  72 , supported in suitable bearings (not shown) to operate respective valves in the cylinder head  33  of the engine  30 , shown simplified in FIG. 3, without showing actual cam and valve positions. A reduction gear set in the drive gear train  68  includes a large input gear  74 , shown meshed with the front crankshaft output gear  64 , and a small output gear  76  concentric with the large gear  74  and driven to rotate along with it. The output gear  76  drives a lower intermediate idler gear  78 , which in turn drives an upper intermediate idler gear  80 . The upper intermediate idler gear  80  is meshed with one of a pair of camshaft drive gears. The intermediate idler gears  78  and  80  are preferably supported in adjustable bearings to accommodate head height variations, wear, and backlash.  
         [0029]    In the embodiment shown, the upper intermediate idler gear  80  is meshed with a left camshaft drive gear  82 , which is fixed on the left camshaft  70 , thereby driving the left camshaft  70 . The left camshaft drive gear  82  is meshed with a right camshaft drive gear  84  of the same size, drivingly fastened to the right camshaft  72 . Thus both of the camshafts  70  and  72  rotate at the same angular velocity but in opposite directions. The upper intermediate idler gear  80  could, instead, be meshed with the right camshaft drive gear  84 , with appropriate cam design.  
         [0030]    The size difference between the large gear  74  and small gear  76  of the reduction gear and the size difference between the front crankshaft output gear  64  and the camshaft drive gears  82  and  84  are chosen to result in rotation of the camshafts  70  and  72  at one half the rotational speed of the crankshafts  44  and  46 , for an internal combustion engine  30  using a four-stroke cycle. The spindles and bearings for the camshaft drive gear train  68  may be supported on a separate gear drive tower (not shown) fastened to the cylinder block  31  and the cylinder head  73 .  
         [0031]    It will be understood that the camshaft drive gear train  68  alternatively may be driven by the rear crankshaft output gear  66 , using appropriate gear sizes.  
         [0032]    It will also be understood that instead of the camshaft drive gear train  68 , it would be possible to drive the camshafts  70  and  72  by other means such as a belt or a chain drive arrangement, or to use other valve timing and operating mechanisms (not shown).  
         [0033]    As seen best in FIGS. 3 and 4, the front crankshaft output gear  64  is meshed in driving relationship with a first engine output shaft drive gear  90 . The gear  90  is mounted drivingly on the engine output shaft  35  as, for example, by the use of mating splines within the hub of the gear  90  and on the outside of the engine output shaft  35 , although other arrangements such as a suitable drive flange and hub combination, could be used instead. Also mounted in driving relationship with the engine output shaft  35  is a second engine output drive gear  94  that is somewhat smaller in diameter than the first engine output shaft drive gear  90 . The second engine output shaft drive gear  94  is aligned with the rear crankshaft output gear  66 , but since the second engine output drive gear  94  is smaller than the first engine output shaft drive gear  90  and the rear crankshaft output gear  66  is smaller than the front crankshaft output gear  64 , there is a clearance  96  between the rear crankshaft output gear  66  and the second engine output shaft drive gear  94 , and they do not mesh with each other.  
         [0034]    As shown in FIGS. 2, 3, and  4 , a crankshaft timing idler gear  98  is supported rotatably on suitable bearings defining an axis of rotation also parallel with the crankshaft axis of rotation  47 . The crankshaft timing idler gear  98  is meshed with both the rear crankshaft output gear  66  and the second engine output shaft drive gear  94 , so that they both rotate about a driven gear axis of rotation  86 .  
         [0035]    The rear crankshaft output gear  66  is smaller than the front crankshaft output gear  64 , and the second engine output drive gear  94  is smaller than the first engine output drive gear  90 , by the same ratio of effective diameters, with the result that the crankshaft timing idler gear  98  forces the front and rear crankshafts  46  and  44  to rotate at the same angular velocity but in opposite directions. As a result, the rotational inertia and consequent gyroscopic forces of the front and rear crankshafts  46  and  44  are essentially equal and opposite to each other, canceling each other out.  
         [0036]    It will be understood that instead of the front crankshaft output gear  64  and the first engine output gear being the larger set of gears, the rear crankshaft output gear  66  and the second engine output drive gear  94  could be larger and be meshed with each other, while the crankshaft timing idler gear  98  could be meshed with the front crankshaft output gear  64  and the first engine output drive gear  90 . It would also be feasible for both of the crankshaft output gears  64  and  66  to be the same size and for the crankshaft timing idler gear to be a reduction gear pair (not shown).  
         [0037]    In order to avoid cyclically occurring imbalances of forces which would have to be borne by the engine output drive gears  90  and  94  and the fastenings of the hubs of those gears to the engine output torque tube  35 , the number one piston  48  and number three piston  56  move reciprocally in their respective cylinders in phase with each other, and with their operating cycles in phase with each other, so that both the number one piston  48  and the number three piston  56  experience a power stroke simultaneously. Similarly, the number two piston  50  and number four piston  58  move reciprocally in phase with each other and with their power cycles in phase with each other.  
         [0038]    While there may be some unbalanced rotational inertia from the transmission itself, because its counterrotating shafts and gears may not be symmetrical and probably are not rotating at equal speeds, so that there can be some resulting net gyroscopic effect, the unbalanced rotational inertia of the transmission is very much less than that of each crankshaft, since the crankshafts are more massive, larger in diameter, and rotating at higher speeds.  
         [0039]    Because the front and rear crankshafts  46  and  44  are significantly shorter than the length of a single crankshaft for an in-line engine having the same number of cylinders as in a conventional engine, each crankshaft  46  or  44  is subjected to smaller torsional loading and is twisted less over its full length than a single longer crankshaft would be. As a result, each of the front and rear crankshafts  46  and  44  of the engine  30  can be smaller in diameter and consequently lighter in weight, using smaller bearings and thus producing less friction.  
         [0040]    Since the two pistons connected with one of the crankshafts are always moving opposite each other, the reciprocating masses of the pistons connected with each crankshaft of the engine  30  balance each other. At the same time, since the front and rear crankshafts  46  and  44  rotate in opposite directions, the lateral component of the movement of the connecting rod and crank associated with a piston on one crankshaft is opposite to and counterbalances the lateral component of movement of the corresponding engine parts associated with the same-phase piston on the opposite one of the crankshafts  46  and  44 . The result is a counterbalancing and minimization of vibration and gyroscopic effects of the entire engine, as the torque applied by each crankshaft against the block and frame of the engine balances that of the other. While in an engine having a single crankshaft the entire engine block generally oscillates angularly around the crankshaft, the engine  30  has a greatly reduced tendency to oscillate, as a result of the counterrotation of the two crankshafts  46  and  44 .  
         [0041]    Preferably, equal numbers of cylinders and their associated pistons are associated with both of the counterrotating crankshafts of such an engine, in order to provide all the available advantageous effects on engine balance. When the same even number of similar cylinders and pistons are associated with each of the counterrotating crankshafts, with the cranks arranged so that each piston moves in the opposite direction from another piston on the same crankshaft, and with each piston moving in the same direction and in the same phase of its power cycle as a counterpart piston connected with the other crankshaft, several advantages are obtained. First, the primary reciprocating masses and forces of each piston are counterbalanced by those of another piston moving in the opposite direction. Secondary rotational forces, resulting from the lateral components of acceleration and movement of each connecting rod and crank pin, are balanced by equal and opposite secondary forces of an oppositely rotating crank pin of the other of the counterrotating crankshafts and its associated connecting rod. Third, the gyroscopic forces of the pairs of counterrotating crankshafts and camshafts oppose and counterbalance one another. As a result, the engine  30  as a unit runs with very little vibration, yet needs no heavy counterweights on its crankshafts  44  and  46 . When a transmission such as the transmission  34  includes a pair of counterrotating shafts and gear sets a similar effect of balancing of gyroscopic forces within the transmission is also obtained.  
         [0042]    Nevertheless, at least a major benefit of the counterrotating crankshafts is available even without the numbers and sizes of cylinders and pistons being balanced between the two counterrotating crankshafts.  
         [0043]    It is to be understood, then, that an engine including a pair of counterrotating crankshafts according to this invention may have any desired number of cylinders and pistons and may be employed for a large variety of other end uses, such as automobiles, off-road motorcycles, boats and personal watercraft, aircraft, and other vehicles.  
         [0044]    Also of importance in this engine is the centrally-located arrangement of gears and shafts in the engine and engine block  31  and the associated transmission structures. This arrangement allows the structural components of the engine casings to be reinforced in the central portion which supports the bearings for the power output ends of crankshafts and the drive train for the camshafts, and affords significant reduction in the thickness and weight of the outer portions of the engine case structures.  
         [0045]    In FIGS. 5 and 6, another engine and transmission combination illustrates an alternative embodiment of the present concept. FIG. 5 depicts an in-line, four cylinder, four stroke internal combustion engine  108  containing reciprocating pistons  110 ,  112 ,  114 , and  116 . Pistons  110  and  112  are coupled through conventional connecting rods to drive a crankshaft  118 , and pistons  114  and  116  are similarly coupled to a second crankshaft  120 . The crankshafts  118  and  120  are displaced vertically from each other, but their axes of rotation  122  and  124  are parallel and disposed in the same vertical plane  126  (FIG. 6), and all the cylinders preferably are also aligned with each other and with the same vertical plane  126 . Pistons  110  and  114  are shown at bottom dead center positions and pistons  112  and  116  are shown at the top dead center positions.  
         [0046]    Crankshafts  118  and  120  are coupled together and timed with each other through equal-sized gears  128  and  130  meshed together on their adjacent output ends, and the two crankshafts therefore rotate at equal speeds, but in opposite directions. This counter-rotation effectively cancels nearly all gyroscopic and other internal torque forces on the engine block, and when such an engine used in a motorcycle, the elimination of gyroscopic effects significantly improves handling for turning and banking. The crankshaft output gear  128  is meshed with a transmission input drive gear  132  connected to an input shaft  134  driving a transmission  136 . An output shaft  138  and drive sprocket  140  deliver power from the transmission  136  to a drive chain such as the drive chain  26  of the motorcycle  10  shown in FIG. 1.  
         [0047]    The dual overhead camshafts  142 ,  144 ,  146 , and  148  also are provided in counter-rotating pairs. Camshafts  142  and  144  are coupled together through gears  150  and  152  to effect counter-rotation, and camshafts  146  and  148  are similarly coupled together through gears  154  and  156  for counter-rotation. Gears  150  and  154  are meshed with and driven by an idler gear  158  mounted on a shaft  160 . The idler gear  158  is meshed with and driven by a smaller gear  162  of a reduction gear pair, mounted on a shaft  164  for rotation together with the larger gear  166  of the reduction gear pair. The gear  166  is meshed with and driven by the upper crankshaft output gear  130  and is coupled with and rotates the smaller output gear  162 . The sizes of the various gears are chosen to effect a speed reduction that drives the camshafts  142 ,  144 ,  146 , and  148  at one half the crankshaft speed and coordinates operation of the engine valves  168  with movement of the pistons.  
         [0048]    As in the engine  30 , providing crankshafts and camshafts of half the total length of the engine  108  effectively reduces torsional loading imposed on each shaft and correspondingly reduces pressure applied to each. This allows for lighter weight crankshafts and camshafts and smaller bearings, contributing to a more efficient engine.  
         [0049]    The arrangement of split crankshafts and camshafts and gears also contributes significantly to the reduction of the lateral dimension of the engine case structure  170 , as evidenced in FIG. 6. For motorcycle, aircraft, and watercraft applications, this contributes beneficially to a reduction of the vehicle width and particularly the width of a motorcycle body which the operator must straddle, and improves the steering and other handling performance of the motorcycle. The engine is balanced as to both reciprocating and rotational masses without need for heavy counterbalancing. The engine operates more smoothly with fewer stresses, while affording the benefits of minimizing weight and dimensions.  
         [0050]    Turning to FIGS. 7, 8,  9 , and  10 , an engine  180  is a further alternative embodiment of the present invention. The engine  180  includes a cylinder block assembly including a front, or first portion  182  and a rear or second portion  184 . A first or front cylinder head  186  is fastened to the first portion  182  of the cylinder block, and a cylinder head  188  is fastened to the second portion  184  of the cylinder block. An exhaust header  190  is attached to the first, or front cylinder head  186 , and a pair of exhaust headers  192  are attached to the rear or second cylinder head  188 . An exhaust valve camshaft  194  is supported in suitable bearings in the cylinder head  186  and an exhaust valve camshaft  196  is similarly mounted in the second, or rear, cylinder head  188 . An inlet valve camshaft  198  is supported in suitable bearings in each of the cylinder heads  186  and  188 .  
         [0051]    For the sake of simplicity the cams and camshaft bearings are not shown with particularity. It will be understood that suitable camshaft covers and bearings will be attached to the cylinder head portions  186  and  188  to support and protect the camshafts.  
         [0052]    While two separate camshafts  198  and  198   a  are shown, each with a respective drive gear  224  mounted at their adjacent ends between the cylinder heads  186  and  188 , it will be understood that the camshaft may be constructed as a single camshaft  198 , if desired.  
         [0053]    As in the engine  30  described previously, the engine  180  has two oppositely-rotating crankshafts, a front crankshaft  200  and a rear crankshaft  202 , arranged end-to-end and supported for rotation in opposite directions about a common axis of rotation  204 . An engine output shaft or torque tube  206  is driven by both of the crankshafts  200  and  202  in the same manner used in the engine  30 , with a front crankshaft output gear  208  meshed with a first engine output shaft drive gear  210 . A rear crankshaft output gear  212  is smaller than the front crankshaft output gear  208 , and the diameter of a rear or second engine output shaft drive gear  214  is smaller than the first engine output shaft drive gear  210  by the same size ratio. This provides clearance  215  (FIG. 10) between the gears  212  and  214 , which are both meshed with a crankshaft timing and idler gear  216  causing the rear crankshaft  202  to rotate oppositely, but at the same angular velocity as the front crankshaft  200 .  
         [0054]    As in the engine  30 , each of the crankshafts  200  and  202  has two opposed crank throws, each connected to a respective piston, and the cranks are timed with respect to each other to have one piston at top dead center and the other piston at bottom dead center, in the same phase of their respective power cycles, simultaneously.  
         [0055]    A camshaft drive gear train  218  is located between the front and rear block portions  182  and  184  of the cylinder block assembly and includes a reduction gear pair  220 , an intermediate idler gear  221 , an upper idler gear  222 , and an inlet camshaft driven gear  224  meshed with one another and providing for rotation of the inlet camshafts  198  and  198   a  at one-half the speed of revolution of the crankshafts  200  and  202 . The exhaust camshafts  194  and  196  are driven respectively by camshaft drive gears  226  and  228 , both meshed with the inlet cam driven gear  224  to rotate oppositely and at the same speed as the inlet camshafts  198  and  198   a.    
         [0056]    The first portion  182  and second portion  184  of the cylinder block assembly define respective cylinders, with a cylinder bore axis  230  of the first portion  182 , at an appropriate angle  234  with respect to the bore axis  232  of the cylinders of the second portion  184 , to provide such alignment of the camshafts. The angle  234  between the block portions  182  and  184  also opens more desirable paths for the flow of intake air to the intake sides and the flow of exhaust gases from the outlet valve sides of the front and rear cylinder heads  186  and  188 , to make the engine  180  more efficient for use in a motorcycle.  
         [0057]    While the engines  30 ,  108 , and  180  have been shown as four-cylinder engines, it will be understood that engines with similarly counterrotating crankshafts can have as few as two cylinders or more than four cylinders, as may be desired in use of such engines in vehicles larger than motorcycles, or to power boats.  
         [0058]    It will also be understood that while the crankshafts of the engines  30  and  180  have been shown associated with a transmission input or engine output torque tube  35  or  206  in a particular arrangement, the engine power output shaft could be arranged in various other ways to deliver power from such an engine without departing from the concept of the present invention.  
         [0059]    The terms and expressions that have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims that follow.