Patent Publication Number: US-6655340-B2

Title: Engine with balancer for second order pitching couple

Description:
TECHNICAL FIELD 
     This invention relates to reciprocating piston engines and more particularly to a balancer for balancing a second order pitching couple in such an engine. 
     BACKGROUND OF THE INVENTION 
     In the design of an inline five cylinder engine, it was recognized that the arrangement resulted in a second order vertical pitching couple acting on the engine frame as a result of the action of crankshaft rotation and the reciprocation of the connected reciprocating masses. In order to provide a smoother running engine, it was considered desirable to provide a suitable balancer for the engine to create an opposing couple that would balance out the pitching couple developed by the operating components of the engine. 
     SUMMARY OF THE INVENTION 
     The present invention combines with the engine a balancer having dual, oppositely rotating balance shafts that create oppositely rotating unbalance couples which combine to apply a vertical pitching couple to the associated engine frame that opposes and balances the pitching couple developed in the engine rotating and reciprocating components. While the balancer has been developed for a specific five cylinder engine arrangement, it could also be utilized in other engines in which an unbalanced pitching couple is present. 
     The balancer is driven by a sprocket carried adjacent the rear end of the engine crankshaft and engaging a chain which drives first and second driven sprockets. A first balance shaft is mounted to one side of the engine frame and is directly connected with the first sprocket for rotating the balance shaft in the direction of the crankshaft at twice crankshaft speed. A second balance shaft is mounted to an opposite side of the engine frame and is indirectly connected to the second sprocket through a reversing drive for rotating the second balance shaft in a direction opposite to that of the crankshaft and at twice crankshaft speed. The balance shafts each have longitudinally-spaced, oppositely facing balance weights that develop equal and oppositely rotating unbalance couples. These couples combine to generate a vertical pitching couple equal to and opposing the second order pitching couple of the engine. 
     In a preferred embodiment, the reversing drive includes a drive gear rotatable with the second sprocket and engaging a driven gear carried on the second balance shaft. The two gears provide the reversal of direction of the balance shaft to a rotation opposite that of the crankshaft and at twice crankshaft speed. Preferably, the gears are carried by a mounting plate on fixed centers and the mounting plate is made of a ferrous material similar to the gears to maintain a relatively constant gear backlash at various operating temperatures. 
     Because of the gear drive, the balance weights of the second balance shaft are designed with smaller diameters to provide a critical mass polar moment of inertia that avoids rotational vibrations in the shaft and resulting gear tooth mismotion and rattle during operation in the range of engine speeds. For this purpose, the balance weights of the second balance shaft are made longer and of smaller diameter than the balance weights of the first balance shaft. The first balance shaft has larger diameter weights and is shorter than the second balance shaft to minimize the space occupied by the first balance shaft. 
     The chain drive includes a chain tensioner to control chain motion during engine operation. The arrangement is such that the chain, the driven sprockets and the gear components are mounted on a rear wall of the engine frame and the drive sprocket is carried on the crankshaft adjacent a rear end thereof. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front end and left side pictorial view of a five cylinder inline engine arrangement having a balancer according to the invention; 
     FIG. 2 is a pictorial view of the assembled components of the balancer shown in their positions when installed from the rear end of the engine of FIG. 1; and 
     FIG. 3 is a pictorial view of the drive portions of the balancer of FIG. 2 shown in their mounted positions on a rear wall or bulkhead of the engine. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in detail, numeral  10  generally indicates a five cylinder inline reciprocating piston internal combustion engine formed in accordance with the invention. Engine  10  has a frame  12  including a crankcase  14  conventionally mounting a crankshaft, not shown, and a cylinder block  16  internally containing cylinders, not shown, in which are reciprocated pistons connected by connecting rods with the crankshaft in a conventional manner. 
     Since the engine is an inline five cylinder with a 1-5-2-3-4 firing order and crankshaft pin configuration, the engine inherently develops an unbalanced secondary pitching couple operating in the vertical direction along the crankshaft axis. In order to offset this couple for a smoother running engine, a second order pitching couple balancer is provided generally indicated by numeral  18 . Removable covers  20 , shown along the right side of the engine crankcase in FIG. 1, are positioned to provide access to a portion of the engine balancer which is completely mounted within the interior of the engine  10  and so is not visible in FIG. 1 
     Referring to FIGS. 2 and 3 of the drawings, the balancer  18  includes a drive sprocket  22  which in assembly is mounted on and rotatable with the engine crankshaft adjacent a rear end thereof. Sprocket  22  engages a drive chain  24  that runs along guides  26  and  28  and is tensioned by a spring chain tensioner  30 . The chain extends laterally in either direction from the sprocket  22  and engages a first driven sprocket  32  and a second driven sprocket  34 . 
     The first sprocket  32  is directly connected to a first balance shaft  36  which includes bearing journals  38  supported in bearings not shown mounted to the left side wall of the engine frame  12 . Shaft  36  includes front and rear balance weights  40 ,  42  which are offset from the shaft axis in opposite directions so as to create an unbalance couple rotating in the direction of crankshaft rotation and at a speed twice crankshaft speed by reason of sizing of the driven sprocket  32  at half the diameter of the drive sprocket  22 . Balance shaft  36  and the connected drive sprocket  32  are supported at the rear end by a bracket  44  which in assembly is bolted to a rear wall  46  of the engine frame as shown in FIG.  3 . 
     The second driven sprocket  34  is connected with a drive gear  48  which is rotatable with the second sprocket on a shaft  50  supported by a mounting bracket  52 . Drive gear  48  engages a driven gear  54  also supported by bracket  52  with a fixed spacing from the drive gear  48 . Gear  54  is directly connected to a second balance shaft  56  which also includes bearing journals  58  supported in bearings, not shown, mounted to the right side of the engine frame  12 . Shaft  56  also carries balance weights  60 ,  62  which extend in opposite directions from the balance shaft axis and thus create when rotated a rotating unbalance couple which rotates at a speed twice crankshaft speed in a direction opposite to rotation of the crankshaft. The phasing of the balance weights on balance shaft  56  is such that the vertical forces add to one another and the lateral forces balance one another. The resulting unbalance force is a vertical rocking couple applied to the engine frame and timed in opposition to the rocking couple generated by the internal engine components so that the unbalanced engine couple is balanced by the balancer  18 . 
     In order to minimize variations in the backlash of the drive and driven gears  48 ,  54 , the bracket  52  is made of a ferrous material having a similar expansion coefficient to that of the gears. The gear center distances are thereby maintained essentially constant over a variety of operating temperatures of the engine. 
     It will be observed from the drawings that the length and diameters of the balance weights on shafts  36  and  56  are considerably different even though the rotating unbalance couples generated by the two shafts are identical. The left hand balance shaft  36  is made with shorter weights  40 ,  42  having larger diameters in order to shorten the length of the balance shaft so that it is more compact and occupies a smaller portion of the side wall of the engine for a more efficient mounting arrangement. The right hand balance shaft  56  is, on the other hand, made longer with longer balance weights  60 ,  62  having smaller diameters. This is done to reduce the polar moment of inertia of the right hand shaft below a critical mass polar moment of inertia to avoid a gear tooth mismotion or oscillation and audible gear rattle. Thus, extending the length of the shaft and balance weights with smaller diameter weights provides for a quieter drive of the rotation reversing gears and a better overall operation of the balancer. 
     While the preferred embodiment described uses a sprocket and chain drive and a gear reversing drive, equivalent components could be substituted where possible without departing from the concepts of the invention. For example, a belt could replace the chain and be connected with sprockets or gears. Other forms of reversing drives could also be employed. Thus, the terms chain, sprocket and gear as used in the claims are intended to include equivalent belt, sprocket and gear devices. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.