Title of Invention

DEVICE FOR IMPROVEMENT IN PERFORMANCE OF GEAR TRAIN

Abstract

A device for reducing the noise generate^; b?y, a gear train used in driving the balancer gear comprising a primar|y driven gear (1), an idler gear (2) having an annular cavita (10) on either side, a balancer gear (3), a balancer mass (3a). a pair of scissor gears (4 and 5) both having integral lags (13) springs (6 and 7), a pin (8), a shaft (15) and circlips (11 and 12), said pin (8) being inserted in the hole of the said idler gear (2), one end of said spring (6) being held against said pin (8) in said cavity (10) of said idler gear (2), integral lug (13) of said scissor gear (4) being positioned against the otr end of the spring (6) and the entire assembly being retained by said circlips (11 and 12) on said shaft (15), said balancer gear (3) being press fitted to said balancer mass (3a).

Full Text

9 OCT 2002 FORM-2 THE PATENTS ACT, 1970 ( 39 of 1970 ) /COMPLETE SPECIFICATION SECTION 10 TITLE "A DEVICE FOR REDUCING THE NOISE GENERATED BY A GEAR TRAIN USED IN DRIVING THE BALANCER GEAR" APPLICANT BAJAJ AUTO LTD., an Indian Company, of Akurdi, Pune 411 035, Maharashtra ORGN GRANTED 9-10-2002 The following specification particularly describes the nature of the invention and the manner in which it is to be performed 628/MUM/2001 DEVICE FOR IMPROVEMENT IN PERFORMANCE OF GEAR TRAIN This invention relates to the introduction of a device to reduce the noise generated by a gear train used for driving the balancer gear of 2 and 3 wheeled vehicles. The invention is particularly applicable to the gear train containing primary driven gear, idler gear and a balancer gear used in engines working on 4 stroke principle. For simplicity of explanation, the engines described above are termed as "engines" in this specification. These engines use a balancer gear which is required for balancing the unbalanced forces created by rotation of the crankshaft There is a primary driver gear which rotates when the engine is started and the crankshaft starts rotating. This primary driver gear drives the primary driven gear which in turn drives the balancer gear through idler gear. The necessity of the idler gear is to achieve a direction of rotation for the balancer gear which is opposite to that of the crankshaft. One of the difficulties experienced with the above arrangement of the gear train is that due to inherenl unrjafahce in the balancer gear, at a particular position, there is a momentary loss of contact between the teeth of the gear pair which causes a typical noise. Yet another difficulty is that the noise as mentioned above is aggravated due to backlash. All the gear trains used for mechanical transmission of power have backlash. This is required to achieve sufficient rotational clearance between the teeth of the gears. The necessity of having a backlash need not be explained in detail since it is a known parameter in the gear design. The effect of such backlash further aggravates the noise generated in the gear train. Yet another difficulty is that the backlash varies with the manufacturing tolerances on centre to centre distance of location of gears. The backlash as explained above has a predetermined value for optimized operation of the gears. However, due to manufacturing tolerances on the center to center distance of the gear locating bores, there is likely to be an increase in the backlash which further aggravates the noise generated when the gears are rotating. The noise generated during driving of the vehicle creates nuisance to the driver. In order to avoid the noise generated due to backlash in a gear a scissor gear arrangement has been used, earlier. However, to reduce the excessive noise generated from above mentioned gear train incorporating a balancer mass, we have invented a system consisting of double scissor gear arrangement as described hereinbelow. The invention will now be explained with reference to the following figures enclosed with this complete specification: - Fig. la - Illustrates the general arrangement of the gear train as per the invention. Fig. lb - Illustrates the detailed view of double scissor gear arrangement as per the invention. Fig. 2 - Illustrates the detailed arrangement of the fitment of spring as per the invention. Fig. 3 - Illustrates the enlarged view of the gear teeth of idler gear and balancer gear in contact and balancer mass is travelling from 0 degree position towards 180 degree position through 90 degree position, as per the invention. . ' Fig. 4 - Illustrates the enlarged view of the gear teeth idler gear and balancer gear in contact while rotating and balancer mass is travelling from 180 degree position towards 0 degree position through 270 degree position as per the invention. . Fig. 5 - Illustrates the enlarged view of the gear teeth of primary driven gear and idler gear are in contact and balancer mass is travelling from 0 degree position towards 180 degree position through 90 degree position, as per the invention. Fig. 6 - Illustrates the enlarged view of the gear teeth of primary driven gear and idler gear in contact while rotating and balancer mass is travelling from 180 degree position towards 0 degree position through 270 degree position as per the invention. Fig. 7 - Illustrates details of another embodiment of the gear train as per the invention. The improved device to reduce the noise generated by a gear train used for driving the balancer gear essentially comprises of parts like primary driven gear (I), idler gear (2) with two annular cavities (10), balancer mass (3 a), balancer gear (3) press fitted to balancer mass (3 a), scissor gear (4) and (5) both having integral lugs (13), spring (6 & 7) located in the annular cavity (10), circlips (11 & 12), cylindrical pin (8), bearings (14) and a shaft (15). Referring to the fig la, lb and 2, the primary driven gear (1) rotates in the direction as shown by arrows when the engine is running. The primary driven gear (1) drives the idler gear (2), which in turn drives the balancer gear (3). The idler gear (2) rotates on the shaft (15) through needle bearings (14). The idler gear (2) is assembled with two scissor gears (4) and (5) and held in position by the circlips (11) and (12). The said idler gear has two annular cavities (10) on either sides, in which spring (6) and (7) are assembled. One end of the said springs butt against cylindrical pin (8) assembled in the hole (9) provided in annular cavity (10) of the said idler gear. The other end of the said springs butt against a lug (13) integrally provided on each of the said scissor gears (4&5). The assembly of the idler gear (3) and the scissor gears (4) and (5) is done in such a way that the springs (6) and (7) are torsion loaded when assembled and the gear flanks of the idler gear and the scissor gears are not in. a straight line but have predetermined angular positions. The assembly sequence is to assemble pin (8) in the hole (9) of the idler gear (2). The spring (7) is then assembled to butt against the pin (8) and then scissor gear is assembled and retained by the circlip. This ' sequence is repeated for the spring (6) also. The torsion loading of the spring is achieved by predetermined rotation of the scissor gears with respect to the idler gear in a direction opposite to the direction of spring helix. The whole assembly is then inserted with the help of suitable tool on the engine where primary driven gear and the balancer gear are preassembled. In order to understand the reduction of noise generated by a gear train used for driving the balancer gear, it is necessary to first understand the phenomenon of generation of noise in such a system of gears. In this explanation, the terminology 'active flank' refers to the gear teeth flanks in contact in the direction of rotation and 'inactive flank' refer to the gear teeth flanks on the opposite side of the direction of rotation. Assume a situation where scissor gears(4&5) are absent and width of gear (2) is sufficient to form a gear train without scissor gear . When the center line of balancer mass (3a) is matching to 0 degree position (Refer Fig la) and this mass gets vertically lifted in the direction of rotation of gear (3), the active flanks of the gears (2) and (3) will continuously operate till the balancer mass (3a) is lifted to 180 degree position through 90 degree position. During this period, inactive flanks of the corresponding gears will not touch due to presence of backlash. As the balancer mass (3 a) rotates beyond 180 degree position, the force of gravity on the balancer mass displaces the contact between the active flanks. Further, as the rotation of the gears continue, active flanks of the gear pair will again hit and then start transferring the motion. Due to the presence of backlash, this phenomenon of active flanks coming into contact in an intermittent fashion will continue and hence create hitting noise from 180 degree position to 0 degree position through 270 degree position. Since the three gears (1,2 and 3) are in constant mesh, this phenomenon is present between gear pair of 3 and 2 and also between gear pair 2 and 1. As explained above the generation of noise is primarily because of the presence of the backlash. In the present invention, while the backlash continues to be present, the intermittent hitting of the gear flanks and subsequent noise generation is avoided by incorporation of two scissor gears as explained below. The fig 3 explains a momentary situation when the balancer mass is at 0 degree position. When the said idler gear (2) initiates the driving of the balancer gear (3), the active gear flank (20) of gear (2) drives gear flank (21) of gear (3) and are in contact with each other. This situation continues till the balancer mass achieves a 180 degree position through 90 degree position. During this travel, the gear flanks (22) of Scissor gear (4) contacts the inactive flank (23) of the said balancer gear (3). The fig 4 explains a momentary situation when the balancer mass (3 a) is at 180 degree position. As the balancer mass starts rotating further and proceeds towards 0 degree position through 270 degree position, the intermittent hitting of the active flanks of the gear pair (2&3) due to gravity is prevented by the complete resting of the scissor gear flank (25) on the inactive flank (26) of the Balancer gear(3). The above explanation gives how the noise generation has been eliminated in case of a gear pair (3) and (2). The situation between gear (2) and (1) is similar only the effect of the balancer mass (3a) is indirect on primary driven gear (1) through idler gear (2). Fig 5 explains a momentary situation when the balancer mass is at 0 degree position. When the said gear (1) initiates the driving of the idler gear (2), the active gear flank (16) of primary driven gear (1) drives gear flank (17) of idler gear (2) and are in contact with each other. This situation continues till the balancer mass achieves a 180 degree position through 90 degree position. During this travel, the scisssor gear flank (19) contacts the inactive flank (18) of the said Primary driven gear (1). The fig 6 explains a momentary situation when the balancer mass (3a) is at 180 degree position. As the balancer mass starts rotating further and proceeds towards 0 degree position through 270 degree position, the intermittent hitting of the active flanks of the gear pair (1&2) due to gravity is prevented by the complete resting of the scissor gear flank (27) on the inactive flank (28) of the Primary driven gear (1). The Fig.1B illustrates arrangement wherein the gear (2) rotates on shaft (15) through bearings (14). As an embodiment of this it is possible to make gear (2) integral with shaft (15) -and this shaft and gear assembly will then rotate simtanepusly on bearings as shown in Fig.7. The scissor gears can be manufactured out of steel, any other non-ferrous metal or nylon of suitable grades. The device to reduce the noise generated by a gear train used for driving the balancer gear of 2 or 3 wheeled vehicles as described herein and as illustrated in the drawings accompanying and having variations and modifications are within the scope of the present invention. Such modification and variations are well within the knowledge skilled in the art without deviating from the scope of the invention. WE CLAIM: 1. A device for reducing the noise generate^; b?y, a gear train used in driving the balancer gear comprising a primar|y driven gear (1), an idler gear (2) having an annular cavita (10) on either side, a balancer gear (3), a balancer mass (3a). a pair of scissor gears (4 and 5) both having integral lags (13) springs (6 and 7), a pin (8), a shaft (15) and circlips (11 and 12), said pin (8) being inserted in the hole of the said idler gear (2), one end of said spring (6) being held against said pin (8) in said cavity (10) of said idler gear (2), integral lug (13) of said scissor gear (4) being positioned against the otr end of the spring (6) and the entire assembly being retained by said circlips (11 and 12) on said shaft (15), said balancer gear (3) being press fitted to said balancer mass (3a). 2. A device as claimed in Claim 1 wherein said gear train is adopted for use in 2 or 3 wheeled vehicles working on 4 stroke principle. 3. A device as claimed in Claims 1 and 2 wherein said scissor gear is made out of steel or any other non ferrous metal or nylon of suitable grades. 4. A device as claimed in Claim 1 wherein said gear (2) is integrally assembled with said shaft (15), enabling the shaft and gear assembly to rotate together on the bearings (14). 5. A device to reduce the noise generated by a gear train used for driving the balancer gear substantially as herein described with reference to the accompanying drawings. Dated this 8th day of October 2002. M K CHAKRABARTI OF L S DAVAR & CO Agent for the applicant

Documents:

658-mum-2001-claims(granted)-(9-10-2002).doc

658-mum-2001-claims(granted)-(9-10-2002).pdf

658-mum-2001-correspondence 1(3-6-2005).pdf

658-mum-2001-correspondence 2(22-3-2007).pdf

658-mum-2001-correspondence(ipo)-(8-6-2004).pdf

658-mum-2001-drawings(9-10-2002).pdf

658-mum-2001-form 1(12-7-2001).pdf

658-mum-2001-form 13(12-3-2007).pdf

658-mum-2001-form 13(2-11-2006).pdf

658-mum-2001-form 19(25-3-2004).pdf

658-mum-2001-form 2(granted)-(9-10-2002).doc

658-mum-2001-form 2(granted)-(9-10-2002).pdf

658-mum-2001-form 3-(3-8-2001).pdf

658-mum-2001-form 4(9-10-2002).pdf

658-mum-2001-form 5(9-10-2002).pdf

658-mum-2001-power of attorney(12-07-2007).pdf

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