Patent Publication Number: US-6213082-B1

Title: Drive arrangement for a two-cycle engine

Description:
This invention relates to a drive arrangement for a two-cycle engine. 
     As is known, various types of drive arrangements have been provided for driving reciprocating pistons in internal combustion engines. In some cases, the pistons have been driven off a crank shaft. In other arrangements, such as described in U.S. Pat. No. 5,669,340, a piston/cylinder arrangement employs a gear arrangement for reciprocating piston rods for the engine. In such constructions, the gear teeth of the meshing gears can be worn over time. As a result, the efficiency of the engine and the operability of the invention can diminish over time. 
     Accordingly, it is an object of the invention to provide a drive arrangement for a piston of a two-cycle engine which is of improved construction. 
     It is another object of the invention to improve the life of a drive arrangement for the piston of a two-cycle engine. 
     Briefly, the invention is directed to an engine having a drive shaft for rotation about a longitudinal axis thereof and at least one reciprocally mounted piston disposed radially of the shaft and is particularly directed to a drive arrangement for driving the piston off the rotation of the drive shaft. 
     The drive arrangement includes a multi-lobe drive cam which is mounted on the rotatable shaft for rotation with the shaft about the axis of the shaft, a piston rod which extends radially of the shaft for rectilinear reciprocation and a roller mounted on the piston road in abutment with the drive cam for reciprocating the piston rod in synchronism with the rotation of the drive cam. Still further, a spring means is provided for biasing the piston rod towards the drive shaft. The piston rod is connected to the piston at an end opposite the rotatable shaft for reciprocation of the piston in a combustion chamber. 
     In accordance with the invention, a drive force is transferred between the drive cam and the roller mounted on the piston rod in an efficient manner. In this respect, during operation of the engine, the piston comes under compression for only about ¼ of the cycle of the engine. Further, the pressure of compression increases only towards the end of this ¼ cycle. The multi-lobe drive cam is thus shaped so that the maximum forces which are transferred between the drive cam and roller occur only over a small portion of a lobe. 
     The use of the multi-lobe drive cam eliminates a need for a crankshaft and/or gears between the drive shaft and piston rod and permits reciprocation of the piston rod in a rectilinear manner. 
     Should wear occur in a roller which abuts against the drive cam, the roller which is removably mounted on the piston rod can be readily replaced from time to time. 
    
    
     These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the drawings wherein: 
     FIG. 1 illustrates a cross-sectional view of a drive arrangement constructed in accordance with the invention for a two-cycle engine; 
     FIG. 2 illustrates a view of the drive cam-to-piston arrangement employed in the drive arrangement of FIG. 1; 
     FIG. 3 illustrates as enlarged developed view of a lobe of the drive cam; and 
     FIG. 4 illustrates a roller of modified construction for engaging the drive cam. 
    
    
     Referring to FIGS. 1 and 2, the drive arrangement or transmission is mounted in a main housing  10  of an engine, such as a two-cycle engine employing a fly wheel, as described in U.S. Pat. No. 5,699,340. In this respect, the engine includes a drive shaft  11  for rotation about a longitudinal axis thereof, a rotatably mounted fly wheel  12  which rotates about the axis of the drive shaft  11 , a plurality of combustion chambers  13  (only one of which is shown in FIG. 2) disposed peripherally in the main housing  10  about the axis of the drive shaft  11 , and a plurality of compression pistons  14  (only one of which is shown). Each piston  14  is slidably mounted in a respective combustion chamber  13 . The engine also has a second plurality of chambers  15  disposed peripherally in a secondary housing  10 ′ about the axis of the drive shaft  11  with each second chamber  15  disposed opposite a combustion chamber  13 . A counter-piston  16  is slidably mounted in each second chamber  15 . 
     The drive arrangement  10  replaces the gear-based transmission and unguided piston rods of the engine described in U.S. Pat. No. 5,699,340 and includes a multi-lobe drive cam  17  which is mounted on the shaft  11  for rotation about the axis of the drive shaft  11  and a plurality of reciprocally mounted piston rods  18  which extend radially of the shaft  11 . In addition, a roller  19  is mounted on each piston rod  18  and is disposed in abutment with the drive cam  17  for reciprocating the piston rod  18  in synchronism with rotation of the drive cam  17 . 
     Referring to FIG. 2, each piston rod  18  is connected in suitable fashion to the piston  14  at the end opposite from the drive shaft  11  and serves to reciprocate the piston  14  within the combustion chamber  12 . A plurality of rollers  20  mounted in the housing  10  for guiding the piston rod  14  in a rectilinear manner relative to the drive shaft  11 . 
     The drive arrangement also includes a spring means  21  for each piston rod  18  for biasing the piston rod  18  towards the drive shaft  11 . 
     As shown in FIG. 2, the spring means  21  includes an annular cup-shaped washer  22  secured to and about the piston rod  18  via a pin  23 , a shaft guide  24  which is fixedly mounted in the housing  10  (FIG. 1) of the engine in a manner not shown and a coiled spring  25  which is disposed between the washer  22  and the shaft guide  24 . As indicated, the shaft guide  24  is disposed concentrically of the piston rod  18  and the coiled spring  25  is disposed about the piston rod  18 . 
     Referring to FIG. 2, the drive cam  17  has three radially disposed lobes  26  disposed in equi-spaced manner about the circumference of the drive cam  17 . The drive cam  17  abuts against the roller  19  mounted on each piston rod  18  at all times so that continuous contact is maintained between the cam  17  and each roller  19 . As schematically illustrated by four rollers  19 , the engine is provided with four combustion chambers  13  and the drive arrangement has four reciprocally mounted piston rods  18  for driving the pistons  14  of the each respective chamber  13 . 
     Referring to FIG. 3, the surface of the drive cam  17  is configured so that each lobe  26  is of non-symmetrical shape about a central plane P so as to avoid jamming of the drive cam  17 . Thus, before the lobe  26  of the drive cam  17  moves a piston rod  18  to the outermost position, ignition of the fuel in the gap between the compression piston  14  and the opposed counter-piston  16  takes place. After ignition, the compression piston  14  continues to move radially outwardly from the drive cam  17  via the lobe  26 . At the same time, the counter piston  16  moves in a direction away from the compression piston  16 . During this time, the gap between the two piston closes and thereafter, the compression piston  14  is retracted so as to move away from the counter piston  16 . 
     For example, with the drive cam  17  rotating in a clockwise direction as indicated in FIG. 3, the apex, or a high point, of a lobe  26  begins 5° beyond a radial reference plane P which corresponds to the ignition point in the associated combustion chamber  13 . The trailing side of the lobe  26  then continues radially inwardly in a curved manner to a circular arc which extends from a 20° position to a 60° position relative to the reference plane P. During this time, the piston rod  18  (not shown) is retracting. The circular arc merges into the leading end of the next lobe  26 ′ which has a curved surface extending radially outwardly beyond the reference plane P of the lobe to a position 5° beyond a second reference plane P′ spaced 120° from the first reference plane P. During this time, the piston rod  18  (not shown) is again moved towards the counter piston  16 . 
     As indicated in FIG. 3, a portion of the leading end of a lobe  26  may be flattened, as indicated by the dotted line, in order to change the speed of the compression stroke of the piston rod  18  and thus the compression piston  14 . 
     As indicated in FIG. 1, each roller  19  is rotatably mounted in a yoke-like end of a piston rod  18 . Alternatively, as shown in FIG. 4, each roller  19 ′ may have a serrated base  27  for removable mounting of the roller  19  in a mating recess of the piston rod  18  and a member  28  which is rotatably mounted on the base  27  and which has a textured surface for abutting the drive cam  17 . The textured peripheral surface may be provided with a wear-resistant coating or the like to enhance the useful life of the roller  19 . Further, the mounting of the base  27  in the piston rod  18  is such that the roller  19  may be removed from time to time for replacement purposes should the need arise. 
     The drive arrangement  10  is such that each piston rod  18  is able to reciprocate in a rectilinear manner radially of the axis of the drive shaft  11 . Thus, the driving force of the piston rod  18  on a piston  14  can be transferred in an efficient manner. Likewise, transfer of a driving force from the drive cam  17  to a piston rod  18  is effected in a rectilinear manner as the contact point between the drive cam  17  and the roller  19  on a piston rod  18  is maintained in a plane passing through the longitudinal axis of the drive shaft  11  and the longitudinal axis of the piston rod  18 . 
     Since the contact points between the drive cam  17  and the roller  19  are located on movable surfaces, i.e. on the rotatable cam  17  and the rotatable roller  19 , sliding friction is avoided between the drive cam  17  and roller  19  thereby increasing the useful life of each. 
     Since the drive forces transmitted by the piston rod  18  are transferred coaxially, the piston rod  18  may have a slender construction between the enlarged base of the piston rod and the piston  14 . In this respect, only compression forces are transferred through the piston rod  18 . By way of example, the distance between the contact point of the roller  19  with the drive cam  17  and the end of the combustion chamber  13  in which the piston  14  reciprocates is of a length of  1 ′ 10 ″. Thus, the piston rod  18  is of relatively long length as compared with the piston rods of a conventional internal combustion engine. However, as only coaxial compression forces are being transferred by the piston rod  18 , the extended length of the piston rod  18  is of no particular consequence from a structural point of view. Thus, the fly wheel  12  may be made of any particular diameter without introducing any skewing forces on the piston rods  18  of the driving arrangement. 
     The invention thus provides a drive arrangement which operates on a continuous basis so as to reduce wear and tear and provide a longer life to the engine. 
     The invention further provides a transmission which operates with reduced wear and longer life than a transmission employing gears as described in U.S. Pat. No. 5,669,340. Further, rather than having a rocking like motion as in the engine described in U.S. Pat. No. 5,669,340, the piston rods reciprocate in a simple reciprocating manner and can be guided with limited wear. Thus, the length of the piston rod may be extended so as to increase the lever arm for a flywheel of greater diameter. Thus, the momentum provided by the larger diameter flywheel may be readily increased.