TORSION DAMPING MECHANISM FOR A SUPERCHARGER

Abstract: An intake manifold (18) for an engine (10) includes a Roots-type supercharger (26) having a torsion damping mechanism (54) for reducing audible gear tooth rattle of timing gears (72,74) which prevent contact of meshed lobes (28c,29a) of the supercharger rotors (28,29). The damping mechanism includes a drive member (90), having an annular band portion (90d) for maintain­ ing the shape of an annular member (98) formed of rela­ tively soft elastomeric material which is fixed for rotation with the drive member via lugs (90e). The member (98) includes three arcuate slots (98d) each defining forward and reverse direction stops (98e,98f) for limiting movement of pins (94) slidably disposed at one end in the slots and fixed at the other end to the gear (74). A torsion spring (96) of low rate resiliently connects the annular member to the pins for reducing the audible gear tooth rattle. Member (98) is snugly con­ strained against deformation by the annular band (90d) and audible impacts of the stops (98e,98f) is mitigated by the soft material of the annular member (98).

Description: Field of the Invention This invention relates to a torsion damping mechanism. More specifically, the invention relates to a torsion damping mechanism for reducing audible noise of timing gears in a backflow-type supercharger driven by an internal combustion engine. Background of the Invention Rotary blowers of the backflow-type, particularly Roots-type blowers, are characterized by noisy operation. Roots-type blower noise may be roughly classified into two groups: solid borne noise caused by clashing and clanging of components subjected to fluctuating loads, and fluid borne noise caused by fluid flow characteristics such as rapid changes in fluid velocity. The invention of this application is concerned with solid borne noise caused by timing gear rattle and with secondary noise caused by a spring damper. The timing gears of the Roots-type blowers, such as the blower disclosed in U.S. Patent 4,638,570, may produce an objectionable gear rattle when the meshed teeth of the gears are substantially unloaded. Such unloaded conditions occur during non-supercharging, low engine speed modes of operation. The gear rattle may be mitigated by a damper having a low torque transmitting capacity, low rate spring which is made flexibly operative only during such modes of operation by forward and reverse stops. However, objectionable secondary noise may be cause by impacts of the forward and reverse stops due to abrupt movement of the engine throttle and/or rough low speed engine operation, and by impacts of the reverse stop during engine shut-down. EP-A-344945 is article 54 (3) EPC state of the art and relates to a super charger with torsion damping. The subject matter of EP-A-344945 can be said to comprise: a torsion damping mechanism adapted to be rotatably interposed between first drive means rotatably driven in one direction by positive torque from a periodic combustion engine and a second drive means for driving a first gear in constant mesh with a second gear; annular means disposed for rotation about an axis and fixed to one of the drive means, the annular means including an annular member, the annular member including a plurality of circumferentially spaced apart and generally arcuate-shaped slots each having first and second ends respectively defining stops in the one direction and in the opposite direction of rotation; axially extending pins each having one end loosely received by one of the slots and the other end fixed to the other drive means; and spring means for flexibly transmitting positive torque between the drive means and operative in a static state of the mechanism to position the pins closer to the second stops than the first stop. Further, US-A-2963006 relates to a two cycle super charged internal combustion engine featuring a blower having repective rotors. The shaft of one rotor is connected by a first gear with a second gear on the shaft of the other rotor to assure that the rotors will operate in timed unison and mesh properly as they rotate. The first gear carries a fitting which is bolted to it and provided with a cross pin to receive the bifurcated end of a driving quill. Via said quill the blower is driven. Summary of the Invention An object of this invention is to provide a durable, low cost spring damper which negates objectional rattle noise produced by unloaded gears and which is free of objectionable secondary noise. Another object of this invention is to provide a torsion damping mechanism which reduces timing gear rattle in a Roots-type blower driven by a periodic combustion engine and which damper prevents objectionable secondary noise during periods when the engine throttle is being abruptly moved, when the engine is being shut-down, and/or when engine is operating roughly at low speeds. According to a feature of the invention, a torsion damping mechanism is adapted to be rotatably interposed between a first drive rotatably driven in a forward direction by a torque from a periodic combustion engine and a second drive for driving a first gear in constant mesh with a second gear. The mechanism is characterized by annular means disposed for rotation about an axis and fixed to one of the drives, the annular means including an annular member formed of elastomeric material having a hardness in the range of 50-80 shore D durometer and an outer shell banded about the annular member and formed of a rigid material relative to the annular member, the annular member including a plurality of circumferentially spaced apart and generally arcuate-shaped slots each having first and second ends respectively defining stops in the forward direction and in the reverse direction; axially extending pins each having one end loosely received by one of the slots and the other end fixed to the other drive; and spring means for flexibly transmitting torque between the drive means and operative in a static state of the mechanism to position the pins closer to the second stop then the first stop. Brief Description of the Drawings The supercharger and torsion damping mechanism of the present invention is shown in the accompanying drawings in which: Figure 1 schematically illustrates an intake manifold assembly having a positive displacement, backflow-type blower or supercharger therein for boosting pressure to an internal combustion engine; Figure 2 is a partial, sectional view of the supercharger; and Figures 3-5 are detailed views of a torsion damping mechanism in Figure 2. Detailed Description of the Drawings Referring first to Figure 1, therein is schematically illustrated a portion of an internal combustion engine 10 which is preferably of the 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 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 26 of the backflow or Roots-type having a pair of rotors 28,29 with meshed lobes 28a,29a. The rotors 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 at a fixed ratio relative to crankshaft speed and 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 supercharger includes an inlet port 30 receiving 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 32a,36a 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 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 or a minimum relative to the air pressure in intake duct 32. When the valve is fully closed, the air in the discharge duct is relatively high. Looking now at Figures 2-5, therein is shown a portion of blower 26 in detail. The shown portion includes a housing assembly 48, a rotor assembly 50, an input drive assembly 52, and a torsion damping mechanism 54. Damper mechanism 54 is shown in relief in Figures 2 and 4 and in section in Figure 3. The section of Figure 3 is taken along line 3-3 of Figure 4. The supercharger housing assembly includes a main housing section 56 and an input drive section 58 secured together by a plurality of bolts 60 and defining therebetween a gear chamber 62 which normally contains a lubricating oil. The main housing section 56 defines a rotor chamber 64 separated from the gear chamber by an end wall portion 56a having stepped through bores 56b,56c for supporting anti-friction bearings 66 and dynamic seals 68. Main housing section 56 also defines inlet and outlet ports 30,34 and a second unshown end wall portion for closing the left end of chamber 64 and supporting bearings similar to bearings 66. The rotor assembly 50 includes the rotors 28,29, shafts 70,71 fixed to the rotors and supported at both ends by bearings such as bearing 66, and meshed timing gears 72,74 pressed on the right ends of shafts 70,71 and operative to prevent contact of meshing rotor lobes 28a,29a. Rotors 28,29, like housing assembly 48, are preferably formed of a light-weight material, such as aluminum alloy. The rotors may include any number of lobes; herein each rotor includes three lobes 28a,29a. The lobes may be straight, as shown in Figure 1, or helical, as shown in Figure 2. A more detailed description of the main housing section and rotor assembly may be found in U.S. Patent 4,638,570 which is incorporated herein by reference. Input drive assembly 52 includes a shaft 76 supported by anti-friction bearings 78 and axially aligned with the axis of shaft 70, a dynamic seal 80, a pulley 82 secured to shaft 76 by a key 84 and nut 86, and a spring 88 leftwardly biasing the leftwardly disposed bearing 78 against a shoulder 90a to prevent bearing flutter. Shoulder 90a is defined by a sleeve portion 90b pressed on the left end of shaft 76. The sleeve portion forms part of a drive housing 90 of torsion damping mechanism 54 described further herein after. Pulley 82 is driven by the previously mentioned and unshown belt which transmits engine torque. 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 objectional 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 54 reduces the rattle noise below the audible range. Torsion damping mechanism 54 includes an annular means 92 disposed for rotation about the common axis of shaft 70,76, a set of three axially extending pins 94, and a torsion spring 96. Annular means 92 includes the drive housing 90 and an annular member 98 formed of a molded relatively soft or compliant elastomeric material. Drive member 90 is formed of a relatively hard material such as metal or thermoplastic. Member 90 includes the sleeve portion 90b, a radially outwardly extending flange portion 90c and an annular axially extending band portion 90d. Flange portion 90c includes three circumferentially spaced apart drive lugs 90e extending axially therefrom. Annular member 98 includes an outer peripheral surface 98a snugly received by band portion 90d, three circumferentially spaced apart recesses 98b receiving drive lugs 90e, a central opening 98c concentric to the common axis, and three circumferentially spaced apart through slots 98d of generally arcuate shape interposed between recesses 98b, and forward and reverse stops 98e,98f defining first and second ends of each slot. Slots 98d extend parallel to the common axis. Pins 94 are press fit at one end into bores 74a of gear 74 and are slidably received at the other end by arcuate slots 98d. Pins 94 and slots 98d may be provided with an amount of radial free play therebetween to mitigate the effects of misalignment of shafts 70,76 and/or components therebetween. The first and second ends or stops 98e,98f limit relative rotation between input and output drives respectively defined by shaft 76 and gear 74. Torsion spring 96 provides a low torque transmitting, low rate resilient drive between the input and output drives which attenuates or isolates torque fluctuations or torque spikes for preventing audible gear tooth rattle of timing gears 72,74 during non-supercharging, low engine speed modes of operation. Torsion spring 96 includes radially extending, opposite ends or tangs 96a,96b interconnected by a plurality of helically wound coils (herein about 3.5 coils) disposed in central opening 98c of the annular member. End 96a is retained in a blind bore 98g against movement relative to annular member 98. End 96b is disposed for circumferential movement in an axially open, arcuate recess 98h in an end face of annular member 98 and is positioned against one of pins 94 to resiliently transmit torque in the direction of arrow A in Figure 3 from annular member 98 to gear 74 via pins 94. Herein, torque in the direction of arrow A is taken as positive and in the opposite direction as negative. As previously mentioned, the primary function of spring 96 is to prevent audible gear tooth rattle of timing gears 72,74 during non-supercharging, low engine speed modes of operation. To prevent gear tooth rattle in this mode of operation, the rate of spring 96 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 96 has a rate of about one-third inch pound per degree of movement of end 96b relative to end 96a. 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 stops 98e,98f. Accordingly, spring 96 is preloaded about 14 degrees to provide the spring with sufficient initial torque transmitting capacity. The preload positions pins 94 against reverse stops 98f when the damping mechanism is in a non-torque transmitting or static state. Spring 96 also lessens the energy of impacts of the first or forward direction stops 98e and in combination with the soft material of member 98 renders such impacts inaudible. The elastomeric material of annular member 98 is selected to withstand high frequency, high energy impacts of pins 94 against stops 98e,98f. Hence, it is important to select an elastomer having low hysteresis, so that the material can respond to the impacts and absorb a series of high energy impacts occuring 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 700 to 2800 kg./cm² (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. Best performance has been obtained with Hytrel™ polyester elastomers from E. I. Du Pont de Nemours and Company. Drive member 90 constrains annular member 98 and is formed of a substantially higher strength and harder material such as metal or a hard thermoplastic. An example of such a hard thermoplastic is Victrex PEEK (polyether-etherketone) having a modulus of elasticity of about 35000 kg/cm² (500,000 psi) and obtainable from ICI (Imperial Chemical Industries) Advances Materials Business Group, Wilmington, DE 19897 U.S.A. A preferred embodiment of the invention has been disclosed herein for illustrative purposes.

Claims: A torsion damping mechanism (54) adapted to be rotatably interposed between first drive means (76) rotatably driven in one direction by positive torque from a periodic combustion engine (10) and a second drive means (74) for driving a first gear (74) in constant mesh with a second gear (72); annular means (92) disposed for rotation about an axis and fixed to one of the drive means (76), the annular means including an annular member (98) formed of elastomeric material having a hardness in the range of 50-80 shore D durometer and an outer shell (90d) banded about the annular member and formed of rigid material relative to the annular member, the annular member (98) including a plurality of circumferentially spaced apart and generally arcuate-shaped slots (98d) each having first and second ends (98e,98f) respectively defining stops in the one direction and in the opposite direction of rotation; axially extending pins (94) each having one end loosely received by one of the slots (98d) and the other end fixed to the other drive means (74); and spring means (96) for flexibly transmitting positive torque between the drive means (76,74) and operative in a static state of the mechanism to position the pins (94) closer to the second stops (98f) than the first stop. The mechanism of claim 1 in combination with a rotary blower (26) of the backflow-type comprising a housing (48); first and second meshed lobed rotors (28,29) rotatably disposed in the housing for transferring relatively low pressure inlet port air to outlet port air controllable between relatively low and high pressures; the first and second gears (74,72) respectively fixed to the first and second rotors (28,29) for preventing contact of the meshed lobes; the first drive means (76) adapted to be rotatably driven by the positive torque about the axis in one drive direction at speeds proportional to speeds of the engine (10) selectively controllable between idle and maximum speeds; the second drive means (74); and the torsion damping mechanism (54) rotatably disposed between the drive means. The mechanism of claim 1 or 2, wherein the outer shell (90d) includes a radially extending wall portion (90c) fixed to the one drive means (76). The mechanism of claim 1 or 2, wherein the outer shell (90d) includes radially inwardly extending lugs (90e) received by recesses (98b) in the annular member (98) for effecting a positive drive therebetween. The mechanism of claim 3, wherein the wall portion (90c) includes axially extending lugs (90e) received by recesses (98b) in the annular member (98) for effecting a positive drive therebetween. The mechanism of claim 1 or 2, wherein the spring means (96) is preloaded for biasing the pins (94) against the second stops (98f) when the mechanism is in the static state. The mechanism of claim 6, wherein the outer shell (90d) includes a radially extending wall (90e) portion fixed to the one drive means (76), and lugs (90e) extending therefrom and received by recesses (98b) in the annular member (98) for effecting a positive drive therebetween. The mechanism of claim 1, 2, 5 or 7, wherein the hardness is in the range of 55-75 shore D durometer.

Inventors: WOODARD, STEVEN WAYNE
Applicants: EATON CORPORATION
Application year: 1990
Main classification: F16D3
IPC codes: F16F15, F02B39, F04C29, F02B33