Abstract:
An apparatus for damping torsional vibration in a shaft, having a plurality of retainer pockets spaced from each other in the direction of the shaft&#39;s axis of rotation and connected for contemporaneous rotation with the shaft, and a plurality of disks each disposed within one of the retainer pockets, each retainer pocket having a circular track wall, each disk being free to shift perpendicular to the shaft&#39;s axis of rotation to engage and move along the circular track wall in response to the vibration, wherein each circular retainer pocket has a center that is at a predetermined radial offset distance relative to the shaft&#39;s axis of rotation and the respective radial offsets are angularly spaced from each other about the shaft&#39;s axis of rotation.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a torsional vibration damper, and, more particularly, to a torsional vibration pendulum damper for an internal combustion engine crankshaft. 
     BACKGROUND OF THE INVENTION 
     In a typical reciprocating internal combustion engine useful work is performed by combustion-generated expanding gases acting on a piston inside a cylinder, which, by causing movement of the engine&#39;s solid parts, imparts rotational motion to the engine&#39;s crankshaft. In multi-cylinder internal combustion engines a crankshaft&#39;s rotational motion is generated by discrete periodic power stroke pulses from individual cylinders. Superimposed on the crankshaft&#39;s rotation is an oscillatory or back-and-forth motion associated with periodic cylinder firings during a power stroke pulse of each cylinder, as such, the crankshaft&#39;s rotation is typically not absolutely smooth. Such oscillatory motion, i.e. torsional vibration, may be detrimental not only to a perceived smoothness of an engine, but, by possibly disturbing valve event timing, may also negatively affect an engine&#39;s performance. Various design dampers have been used to quell such vibrations. 
     Pendulum dampers that incorporate small masses of varying size to absorb and release vibrational energy antiphase with crankshaft vibration and impulse are known in the industry. The basic principle behind such designs is that as crankshaft rotational speed increases, energy is absorbed by a pendulum mass, but as the rotational speed decreases energy is released back into the crankshaft. Typical of such solutions is the use of heavy-metal inserts associated with a damping medium floating in smooth bores incorporated into crankshaft counterweights. In such a case the heavy-metal inserts surrounded by the damping medium achieve a damping effect in response to vibration energy transmitted by the crankshaft (See U.S. Pat. No. 6,026,776). One drawback of such solutions is the need for special fabrication and assembly of the subject crankshaft. 
     The present invention provides a torsional vibration damper that does not require internal damping medium and is suited for simple connection to a shaft which requires no special fabrication or assembly. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus for damping torsional vibration in a shaft. The apparatus has a plurality of retainer pockets spaced from each other along the shaft&#39;s axis of rotation and connected for contemporaneous rotation with the shaft. The apparatus additionally has a plurality of disks where each disk is disposed within one of the retainer pockets. Each retainer pocket has a circular track wall, and each disk is free to shift perpendicular to the shaft&#39;s axis of rotation to engage and move along the circular track wall in response to the vibration. Each circular retainer pocket has a center that is at a predetermined radial offset distance relative to the shaft&#39;s axis of rotation and the respective radial offsets are angularly spaced from each other about the shaft&#39;s axis of rotation. 
     The apparatus may be attachable to the shaft via a central hub member extending through a central opening in each disk. Said apparatus may be used for damping torsional vibration in a crankshaft of a motor vehicle engine. 
     It should be understood that the detailed description and specific examples which follow, while indicating preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a typical multi-cylinder motor vehicle internal combustion engine. 
         FIG. 2  is an elevational view of a disk pendulum vibration damper according to the invention. 
         FIG. 3  is a side view the disk pendulum vibration damper according to the invention. 
         FIG. 4  is a cross-sectional view of the disk pendulum vibration damper according to the invention taken along line A-A of  FIG. 2 . 
         FIG. 5  is an elevational view of a circular retainer pocket and a circular weighted disk within the pocket showing a constituent portion of the disk pendulum vibration damper according to the invention. 
         FIG. 6  is an enlarged view of a circular area C of the circular retainer pocket and circular weighted disk shown in  FIG. 5  providing details of a relationship between a crankshaft rotation axis, center of a circular retainer pocket, and a center of the circular retainer pocket&#39;s respective weighted disk according to the invention. 
         FIG. 7  is a schematic view illustrating the relationship and spacing of three retainer pockets and centers of three circular weighted disks in a disk pendulum vibration damper for a three cylinder engine according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In general the present invention is directed to a torsional vibration pendulum damper, i.e. absorber, for an internal combustion engine crankshaft. The invention may be employed with an internal combustion engine that operates with a fixed displacement, i.e. where the functioning number of cylinders is fixed, or with variable displacement. Typically the amount of an engine&#39;s functioning displacement is varied, i.e. decreased, in an effort to reduce an engine&#39;s fuel consumption by disabling the valves associated with at least one cylinder. Because, for example, a six-cylinder engine may derive sufficient power for idle or low load operation from just three of its cylinders, deactivation of three cylinders during such modes of operation is likely to reduce the engine&#39;s fuel consumption. An engine&#39;s operation on three cylinders, however, produces more vibration than in the six cylinder mode, and may therefore require supplementary damping to improve its smoothness. In the embodiment described herein the vibration absorber will be described in relation to a three cylinder engine or a three cylinder operating mode of a six-cylinder engine. It will be appreciated, however, that the invention may also be used with engines having a different number of cylinders through adjustments as will be described below. 
     Referring now to the drawings in which like elements of the invention are identified with identical reference numerals throughout,  FIG. 1  denotes a schematic cross-sectional view of a typical multi-cylinder motor vehicle engine  10 . Engine  10  has a crankshaft  20  which is rotationally driven by power stroke pulses produced by reciprocating pistons  50  via connecting rods  60 .  FIG. 2  shows a front view, while  FIG. 3  shows a side view of vibration damping apparatus  100  in accordance with the invention. Crankshaft&#39;s terminal end  25  includes threaded recess  30  for receiving complementary threaded fastener  35  with spacer or lock washer  40  for connecting vibration damping apparatus  100  to crankshaft  20  for their contemporaneous rotation (shown in  FIG. 4 ). 
     Vibration damping apparatus  100  is comprised of a plurality of weighted disks acting as pendulums and located within respective circular retainer pockets that rotate with the crankshaft. Each disk has a disk face, and the circular retainer pockets are spaced from each other along crankshaft rotation axis  120  and the disk faces are parallel to each other. The disks are preferably, but need not be, identical nor be provided with flat faces as shown in the embodiments herein. Each of the circular retainer pockets may be comprised of a one-piece molded object of an upstanding circular wall and an annular retaining wall. 
     Damping apparatus  100  shown in  FIG. 4  includes three parallel vertically upstanding circular weighted disks  112 A,  112 B and  112 C. Each disk resides within a respective circular retainer pocket  114 A,  114 B and  114 C. Circular weighted disk  112 C is located within circular pocket  114 C which is comprised of circular vertically upstanding cover wall  115 C and annular spacer insert  116 C. Circular pocket  114 B within which weighted disk  112 B resides is comprised of vertically upstanding circular isolation wall  115 B and annular spacer insert  116 B. Circular pocket  114 A within which weighted disk  112 A resides is comprised of vertically upstanding circular isolation wall  115 A and annular spacer insert  116 A. Each weighted disk  112 A,  112 B and  112 C has a respective circular opening  117 A,  117 B and  117 C, and each vertically upstanding cover wall  115 A,  115 E and  115 C has a respective circular opening  118 A,  118 B and  118 C. Damper hub  125  supports circular pockets  114 A,  114 B and  114 C and weighted disks  112 A,  112 B and  112 C by extending through circular openings  117 A,  117 B and  117 C, and through circular openings  118 A,  118 B and  118 C. Damper hub  125  includes vertically upstanding circular cover wall  125 A which closes one end of circular retainer pocket  114 A within which weighted disk  112 A resides. 
     As shown in  FIG. 4 , two adjacent circular vertically upstanding cover walls trap each weighted disk between them allowing only rotational and perpendicular movement of each disk relative to crankshaft rotation axis  120 . As additionally shown in  FIG. 4 , outer surface of vibration damping apparatus  100  may comprise pulley  28 , such as one typically used to drive via a belt (not shown) an engine accessory, e.g. an alternator or a power steering pump. Circular pockets  114 A,  114 B and  114 C are coupled to damper hub  125  with circular cross-section pins  127 . Pins  127  fit within respective apertures in each of the isolation walls  115 A,  115 B, cover wall  115 C, annular spacer inserts  116 A,  116 B,  116 C and damper hub cover wall  125 A. 
     Each circular weighted disk may have its outer edges slide relative to the respective circular pocket, engage and travel along the annular pocket wall, and rotate about the weighted disk&#39;s axis. The aforementioned disk&#39;s travel along the pocket wall may affect an oscillatory movement in opposition to the superimposed oscillations upon the crankshaft rotation in response to engine power stroke pulses. Each circular weighted disk may further shift relative to crankshaft rotation axis  120  to offset first order imbalances of crankshaft  20 , i.e. crankshaft center of mass imbalances from the crankshaft rotation axis. The edge of each circular disk engaging the annular pocket wall may be tapered or rounded instead of the squared shape shown in  FIG. 4 . As noted above, the invention is useful for reducing vibrations in engines having more or less than three cylinders. The total number of circular pockets and corresponding weighted disks, each residing in a respective circular pocket, may be different than the three such pockets and disks described herein as an example. 
     Circular pockets  114 A.  114 B and  114 C are mounted to damper hub  125  so that they are not coaxial with crankshaft rotation axis  120 . This may be particularly seen in the circular area B shown in  FIG. 4  and will be explained with further reference to  FIGS. 6 and 7 .  FIG. 5  illustrates a circular weighted disk, for example weighted disk  112 C received within pocket  114 C. The diameter of the disk in  FIG. 5 , which comprises the largest disk face dimension, is shown substantially the same as that of the annular recesses provided by the spacer insert. In actuality, this disk dimension will be slightly smaller, as will be described hereinafter, to allow movement of the weighted disk relative to its circular pocket.  FIG. 6  shows enlarged schematic view of circular central area C of the circular retainer pocket and the circular weighted disk shown in  FIG. 5 .  FIG. 6  is provided to show the relationship between crankshaft rotation axis  120 , the center of a circular pocket, and the center of its respective weighted disk. This relationship is similar to that of the other circular pockets with their respective weighted disks. The center of a circular pocket, which defines a circular pocket wall, is offset from crankshaft rotation axis  120  by distance R 1 . The center of the respective weighted disk, when the disk engages the circular pocket wall, is further offset from crankshaft rotation axis  120  and from the center of the respective pocket along radial line Y by distance R 2 . Both the circular pocket and the weighted disk have openings in the respective centers thereof through which the damper hub  125  extends. Distances R 1  and R 2  are calculated heuristically based on the number of functioning cylinders N in a subject engine per the mathematical relationship R 1 /R 2 =(N/2)^2. The offsets of circular pockets&#39; and of their respective weighted disks&#39; centers are thus determined to most effectively absorb a particular engine&#39;s crankshaft vibration. 
     With reference now to  FIG. 7  there is shown a schematic of the relationship between crankshaft rotation axis  120 , the centers of the circular pockets, and the respective centers of the weighted disks. It will be noted from this view that the centers of each of the respective circular pockets are equidistant in a small offset from crankshaft rotation axis  120 . However, in the case of damping apparatus  100  for a three cylinder engine there are three circular pockets, and the respective centers of the pockets are angularly equally spaced from each other about crankshaft rotation axis  120  by 120°. 
     Apertures of the respective isolation walls  115 A,  115 B, cover wall  115 C and damper hub cover wall  125 A may be spaced uniformly relative to crankshaft rotation axis  120 . Apertures  129  (shown in  FIG. 5 ) in annular spacer inserts  116 A,  116 B,  116 C, however, may be spaced non-uniformly relative to said axis in order to achieve the desired small offset of the center of the respective pocket relative to crankshaft rotation axis  120 . For expediency each pocket may be identical to other pockets and each disk may be identical to other discs utilized in vibration damping apparatus  100 . Each pocket, assuming they are identical, may be mounted with dowel pins  127  and screws  128  through rotation of 120° to achieve the 120° spacing of each pocket relative to an adjacent one, and to obtain the small offset in each pocket relative to crankshaft rotation axis  120 . 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.