Abstract:
A torsion damping mechanism for a rotary blower is provided that has improved durability and ease of installation into the rotary blower. A rotary blower including a torsion damping mechanism according to an embodiment of the present invention is also provided.

Description:
BACKGROUND OF THE DISCLOSURE 
   The present invention relates to a rotary blower, and more particularly, to a torsion damping mechanism (“isolator”) for reducing audible noise from the blower, and especially from the timing gears. 
   Although the present invention may be used advantageously on many different types of blowers, regardless of the manner of input drive to the blower, the present invention is especially adapted for use with a Roots-type rotary blower that is driven by an internal combustion engine. In a typical internal combustion engine used commercially for on-highway vehicles, the torque output of the engine is not perfectly smooth and constant, but instead, is generated in response to a series of individual, discrete combustion cycles. 
   A typical Roots-type blower transfers volumes of air from the inlet port to the outlet port, whereas a screw compressor actually achieves internal compression of the air before delivering it to the outlet port. However, for purposes of the present invention, the blower, or compressor, generally includes a pair of rotors, which must be timed in relationship to each other, and therefore, are driven by meshed timing gears. As is now well known to those skilled in the blower art, the timing gears are potentially subject to conditions such as gear rattle and bounce. 
   Rotary blowers of the type to which the present invention relates (either Roots-type or screw compressor type) are also referred to as “superchargers”, because they are used to effectively supercharge the intake side of the engine. Typically, the input to an engine supercharger is a pulley and belt drive arrangement that is configured and sized such that, at any given engine speed, the amount of air being transferred into the intake manifold is greater than the instantaneous displacement of the engine, thus increasing the air pressure within the intake manifold, and increasing the power density of the engine. 
   Rotary blowers of either the Roots-type or the screw compressor type are characterized by the potential to generate noise. For example, Roots-type blower noise may be classified as either of two types. The first is solid borne noise caused by rotation of timing gears and rotor shaft bearings subjected to fluctuating loads (the periodic firing pulses of the engine). The noise, which may be produced by the meshed teeth of the timing gears during unloaded (non-supercharging), low-speed operation is also referred to as “gear rattle”. The second type of noise is fluid borne noise caused by fluid flow characteristics, such as rapid changes in the velocity of the fluid (i.e., the air being transferred by the supercharger). The present invention is concerned primarily with the solid borne noise caused by the meshing of the timing gears. 
   To minimize solid borne noise, torsion damping mechanisms (“isolators”) have been developed, which can minimize the “bounce” of the timing gears during times of relatively low speed operation, when the blower rotors are not “under load”. Such torsion damping mechanisms are also referred to as “isolators” because part of their function is to isolate the timing gears from the speed and torque fluctuations of the input to the supercharger. 
   One known torsion damping mechanism is shown in  FIGS. 1 and 2  of the present application and includes an annular body adapted to be attached to a first input shaft driven by the engine through the pulley and belt drive arrangement. A second input shaft is drivingly connected to the first input shaft by the torsion damping mechanism through a plurality of pins that are received in arcuate slots in the body. Disposed between at least one of the pins and the body of the damping mechanism is a spring providing a resilient drive between the first and second input shafts, which attenuates or isolates torque fluctuations or torque spikes for preventing audible gear tooth rattle of the timing gears during non-supercharging, low engine speed modes of operation. 
   During the course of the development of a supercharger, one of the primary developmental concerns has been the durability of the torsion damping mechanism, and therefore, the ultimate service or durability life of the supercharger, in terms of the number of hours of operation, prior to any sort of supercharger component failure. Manufacturability and ease of installation are also desirable characteristics of the torsion damping mechanism to ensure, among other things, proper assembly of the supercharger. 
   BRIEF SUMMARY OF THE INVENTION 
   A torsion damping mechanism for a rotary blower is provided that is adapted to be rotatably interposed between a first drive member for driving a first gear in constant mesh with a second gear, and a second drive member rotatably driven in one direction by torque from a periodic combustion engine. The torsion damping mechanism includes a generally annular body disposed for rotation about an axis a-a and is fixed to one of the drive members. The body includes a plurality of circumferentially spaced apart bores and a plurality of circumferentially spaced apart generally arcuate-shaped slots. A cushion damper includes a plurality of cushioning members, each adapted to be received in a corresponding slot in the body. In an embodiment of the present invention, at least one of the slots includes an interference member positioned to create an interference fit between the body and the cushioning members to secure the cushioning members in the slots and inhibit movement of the cushion damper relative to the body. Axially extending first pins each have one end loosely received by one of the slots and another end fixed to the first drive member. Axially extending second pins each having one end fixedly received by the bores and another other end fixed to the second drive member. A spring is fixed at one end to the body and has a free end extending radially in cantilever fashion into at least one of the slots. The spring is interposed between the cushioning member of the one slot and the pin therein. In an embodiment of the invention, the body is provided with at least one stress-reducing feature to reduce stress in the spring. 
   A rotary blower including a torsion damping mechanism according to an embodiment of the present invention is also provided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  are front and rear perspective views of a prior art torsion damping mechanism. 
       FIG. 3  is a schematic illustration of an intake manifold assembly having a positive displacement blower or supercharger for boosting intake pressure to an internal combustion engine. 
       FIG. 4  is an enlarged, fragmentary, axial cross-section of the input section of the supercharger shown schematically in  FIG. 3 . 
       FIGS. 5 and 6  are front and rear perspective views, respectively, of a torsion damping mechanism according to an embodiment of the present invention. 
       FIGS. 7 and 8  are front and rear plan views, respectively, of the torsion damping mechanism shown in  FIGS. 5 and 6 . 
       FIG. 9  is a cross-sectional view of the torsion damping mechanism shown in  FIG. 7  taken along lines  9 - 9 . 
       FIG. 10  is a rear plan view of a torsion damping mechanism body according to an embodiment of the present invention. 
       FIG. 11  is a front plan view of the torsion damping mechanism body shown in  FIG. 10 . 
       FIG. 12  is a rear plan view of a torsion damping mechanism cushion damper according to an embodiment of the present invention. 
       FIG. 13  is a side view of the cushion damper shown in  FIG. 12 . 
       FIG. 14  is a detailed view of a torsion damping mechanism spring shown received in a bore according to an embodiment of the present invention. 
       FIG. 15  is a detailed view of a torsion damping mechanism body member slot having received therein a cushioning member according to an embodiment of the present invention. 
       FIG. 16  is a detailed view of a torsion damping mechanism body anti-twist tab according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Schematically illustrated in  FIG. 3  is a portion of an internal combustion engine  10 , which may be of a periodic combustion type, such as the Otto or Diesel cycle type. The engine includes a plurality of cylinders  12  and a reciprocating piston  14  disposed within each cylinder to define an expandable combustion chamber  16 . The engine also includes intake and exhaust manifold assemblies  18 ,  20  for respectively directing combustion air to-and-from the combustion chambers via intake and exhaust valves  22 ,  24 . 
   The intake manifold assembly  18  includes a positive displacement blower or supercharger  26  of the backflow or Roots-type having a pair of rotors  28 ,  29  with meshed lobes  28   a ,  29   a . The rotors  28 ,  29  may be mechanically driven by engine crankshaft torque transmitted thereto in known manner via an unshown drive belt. The mechanical drive rotates the blower rotors  28 ,  29  at a fixed ratio relative to crankshaft speed, such that the blower displacement is greater than the engine displacement, thereby boosting or supercharging the air going to the engine combustion chambers to increase engine power. 
   The illustrated blower includes an inlet port  30  that receives an air or air-fuel mixture charge from an inlet duct or passage  32  and a discharge or outlet port  34  directing the charge to the intake valves  22  via a discharge duct or passage  36 . The intake and discharge ducts are intercommunicated via a bypass duct or passage  38  connected at openings  32   a ,  36   a  in the intake and discharge ducts  32 ,  36 , respectively. If the engine  10  is of the Otto cycle type, a throttle valve  40  preferably controls air or air-fuel mixture flow into intake duct  32  from a source, such as ambient or atmospheric air, in a well known manner. 
   Disposed within the bypass duct  38  is a bypass valve  42 , which is moved between open and closed positions by an actuator assembly  44  responsive to pressure in inlet duct  32  via a line  46  and, therefore, operative to control supercharging pressure in duct  36  as a function of engine power demand. When bypass valve  42  is in the fully open position, the air pressure in discharge duct  36  is relatively low relative to the air pressure in intake duct  32 . When the valve  42  is fully closed, the air pressure in the discharge duct is relatively high. 
   Looking now at  FIG. 4 , therein is shown a portion of blower  26  in detail. In the illustrated configuration, blower  26  includes a housing assembly  48 , an input drive assembly  50 , and a torsion damping mechanism  52  according to an embodiment of the present invention. The housing assembly  48  includes a main housing section  54  that houses the rotors  28 ,  29 , and an input drive section  56  that define therebetween a chamber  58 . 
   The main housing section  56  includes a first drive member or shaft  60  having a right end secured to a first generally annular end member  62  and a left end secured to a timing gear of the blower (neither shown), as is known in the art. The input drive assembly  50  includes a second drive member or shaft  64  supported by anti-friction bearings  66  and  68 , a pulley  70  secured to a right end of the second shaft  64 , and a second generally annular end member  72  secured to a left end of the second shaft  64 . Pulley  70  may be driven by the previously mentioned and unshown belt, which transmits engine torque to the blower  26 . 
   During non-supercharging, low engine speed or idle speed operation, the meshed teeth of the timing gears are substantially unloaded and have been known to bounce or clash back and forth against each other through the backlash therebetween. The bounce or clash produces an objectionable noise known as gear rattle and is believed to be caused by torsionals in the supercharger drive torque provided by periodic combustion engines such as engine  10 . The resilient drive provided by torsion damping assembly  52  reduces the rattle noise below the audible range. 
   In the blower configuration illustrated in  FIG. 4 , torsion damping mechanism  52  is disposed for rotation about the common axis a-a of the shafts  60 ,  64 . Two sets of three axially extending pins  74 ,  76  connect a portion of torsion damping mechanism  52  to rotate with first and second end members  62 ,  72 , respectively. 
   In an embodiment of the present invention shown in  FIGS. 5-16 , torsion damping mechanism  52  includes a generally annular body  80  formed of a relatively hard plastic or metal material, and a cushion damper  82  secured to body  80  and formed of a relatively soft or compliant elastomeric material. Body  80  includes a central opening  84  concentric to the common axis a-a and sized to receive a first spring  86  and a second spring  87 , three circumferentially spaced apart through bores  88 , and three circumferentially spaced apart through slots  90  of generally arcuate shape interposed between the through bores  88 . Through bores  88  and slots  90  are radially spaced from and extend parallel to the common axis a-a. 
   As shown in  FIG. 4 , pins  76  are press fit at one end into second end member  72 , and are press fit at the other end into through bores  88  of the body  80 . Pins  74  are press fit at one end into first end member  62  and are slidably received at the other end by arcuate slots  90 . Pins  74  and slots  90  may be provided with an amount of radial free play therebetween to mitigate the effects of misalignment of shafts  60 ,  64  and/or components therebetween. 
   As shown in  FIGS. 5 ,  7 ,  12  and  13 , cushion damper  82  includes a webbing  91  having a central opening  92  concentric to the common axis a-a, and a plurality of cushioning members  94  interconnected by the webbing  91  and defining an end of each slot  90  when cushion damper  82  and body  80  are assembled. All of the slots  90  that receive cushioning members  94  includes an interference member  96 , such as a radially inwardly extending barb (see, e.g.,  FIGS. 11 and 15 ), which facilitates an interference fit with cushioning members  94  to secure the cushioning members  94  in slots  90  during operation of blower  26 . A raised, generally arcuate surface  98  may extend radially outwardly into slots  90  to align with a correspondingly shaped surface on a radially inner portion of cushioning members  94  to properly position the cushioning members during assembly. 
   Unlike the prior art torsion damping mechanism shown in  FIGS. 1 and 2 , the webbing  91  of cushion damper  82  according to the present invention extends over and generally covers a portion of central opening  84  of body  80 , leaving each of arcuate slots  90  unobstructed. This configuration allows each of pins  74  to be of substantially equal length—unlike the prior art design in which the pins  74  received in the arcuate slots covered by the prior art cushion damper are shorter than the pin  74  that engages the resilient drive spring. The cushion damper configuration according to the present invention permits each of pins  74  to be substantially the same length, which advantageously permits torsion damping mechanism  52  to be installed against end member  62  in any of three angular orientations. The prior art design can be installed in only one angular orientation. 
   Cushioning members  94  collectively define a relatively high rate resilient shock absorber for preventing audible impacts of pins  74  against body  80  due to high energy negative torque fluctuations or spikes that occur during engine shut-down, abrupt movement of the engine throttle, and/or rough engine operation at low engine speeds. Since the elastomeric material of cushioning members  94  is selected to withstand high frequency, high energy impacts of pins  74  against cushioning members  94 , an elastomer having low hysteresis may be employed, so that the material can respond to the impacts and absorb a series of high energy impacts occurring over a short period of time with minimum distortion and minimum audible noise. Acceptable performance has been obtained with materials, having a modulus of elasticity in the range of 10,000 to 40,000 psi over the normal operating range of the damping mechanism and a hardness in the range of 50 to 80 shore D durometer, preferably a range of 55 to 75. An exemplary material is Hytrel™ polyester elastomers from E.I. Du Pont de Nemours and Company. 
   First spring  86  provides a resilient drive between first and second end members  62  and  72 , which attenuates or isolates torque fluctuations or torque spikes for preventing audible gear tooth rattle of the timing gears during non-supercharging, low engine speed modes of operation. In an embodiment, first spring  86  is a torsion spring having radially extending, opposite ends or tangs  100 ,  102  interconnected by a plurality of helically wound coils (e.g., about 3.5 coils) disposed in central opening  84  of the body  80 . End  102  is retained in a bore  104  against movement relative to body  80  and cushion damper  82 . End  100  is disposed for circumferential movement in an axially open, arcuate recess  106  in an end face of body  80 , and is positioned against one of pins  74  to resiliently transmit torque in the direction of arrow A in  FIG. 8  from pin  74  to end member  62  via body  80  and pins  76 . Herein, torque in the direction of arrow A is taken as positive and in the opposite direction as negative. 
   In an embodiment, torsion damping mechanism  52  is provided with at least one spring stress-reducing feature to reduce stress in first spring  86 , which may degrade performance of mechanism  52 . One such feature is shown in  FIG. 14 , wherein the bore  104  includes a pair of side walls  108  that taper inwardly from a radially outward end wall  110  to radii  112 , which connect tapered side walls  108  to central opening  84 . Unlike the prior art torsion damping mechanism of  FIGS. 1 and 2  that includes a spring bore (not shown) having side walls that are perpendicular to the end wall with no radii between the side walls and the central opening, the embodiment of bore  104  shown in  FIG. 14  reduces stress in end  102  of spring  86  caused by manufacturing variance in the end  102 , and restriction of end  102  caused by loading of spring  86  during operation of blower  26 . 
   Another stress-reducing feature for first spring  86  is shown, for example, in  FIGS. 4 and 16 , and includes a tab  114  that extends radially inwardly into central opening  84  adjacent first spring  86 . In the prior art torsion damping mechanism shown in  FIGS. 1 and 2 , the torsion spring partially wraps around a shaft to inhibit spring twist as the spring is loaded. While contact with the shaft prevents an undesirable twisting of the torsion spring  86  during operation, this contact, unfortunately, may cause fretting of the shaft and spring, particularly if the components are not well lubricated. Contact with the shaft also increases localized stresses in the spring since the spring&#39;s movement is restricted. In contrast to the prior art, tab  114  engages first spring  86  to inhibit twisting during operation, without having the spring contact the shafts  62 ,  64 . This configuration eliminates wear on the inner diameter of the spring  86 . Additionally, since the spring  86  is allowed to float within central opening  94  without restriction, localized stresses in the spring caused by engagement with the shaft in the prior art design are eliminated. 
   To prevent gear tooth rattle, the rate of first spring  86  should be such that the natural frequency of the spring-mass system is less than one-quarter of the distributing frequency to provide acceptable isolation. By way of example only for the size supercharger disclosed herein, spring  86  has a rate of about one-third inch pound per degree of movement of end  100  relative to end  102 . The free length of a spring of such low rate would not have enough initial torque transmitting capacity to be operative in a reasonable relative rotation range such as provided by cushioning members  94 . Accordingly, spring  86  is preloaded eight degrees to provide the spring with sufficient initial torque transmitting capacity. 
   Second spring  87  is generally C-shaped having a first end received in a blind bore  116  in body  80  ( FIG. 11 ) and a second end that extends into a recess  118  ( FIG. 5 ) in an end face of body  80 , and is engageable with one of pins  74 . Second spring  87  dampens impact of the engaged pin  74  caused by torque reversals (negative torque) during operation. 
   The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.