In internal combustion engines, power from a crank shaft is transmitted to an output shaft through a suitable transmission system. Such transmission system may include a gearing arrangement comprising a primary reduction gear as well as additional intermediate gears, input and output shafts and a clutch arrangement.
In one such transmission system, the primary driven gear is mounted or fixed on a clutch housing by suitable fastening means. The clutch housing is connected to the input shaft of the engine through the clutch plates. The primary gear is provided with torsional damper(s). The damper may comprise sets of slots, one set for placing the torsional damper springs and another set of slots for accommodating bosses provided in the clutch housing.
During a gear shift operation, especially an abrupt gear shift, torque fluctuations may cause relative rotation between the primary gear and clutch housing. The degree of such rotation depends on the severity of vibrations caused by the shock resulting when the gear change is executed by the driver but when it occurs the damper springs of the primary gear are compressed. When the shift shock is high, the springs are compressed to the extent that the bosses of the clutch housing, external to the slots in which the damper springs are located, contact the end of slots in the gear and prevent further relative rotation of the two parts thereby limiting the stroke. In such manner, the springs are stopped from becoming solid and reaching stress levels though these levels may still be high enough that spring failure may occur.
However, such a damper is not compact enough for applications where space is a constraint, for example in small motorcycles.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a torsional vibration damper which accommodates degree of shock, for example caused on a gear change, which is sufficiently compact for use in a small motorcycle.
It is a further object of the present invention to provide a damper for use in a compact setting which includes means to prevent a spring from compressing beyond a desired limit.
STATEMENT OF INVENTION
With this object in view, the present invention provides in a first aspect a transmission system having at least a driving member, at least a driven member and means to transmit torque between said driving and driven members, the means for transmitting torque including a torsional vibration damper comprising at least one damping unit arranged intermediate driving and driven members, the driving and driven member being disposed in a radial arrangement.
The damper may include a plurality of damping units comprising damping means, conveniently springs, positioned to absorb torsional shock, particularly that caused by operator gear shift in the case of an engine. Where gear shift is abrupt, this shock may be severe. The driving and driven members may take the form of gears within a transmission system. Each spring may be located within slots located within the gears, which may be a primary driven gear co-located with a cluster driving gear set. Other arrangements of gear and transmission are possible. However, the corresponding slots in driven and driving member or gear enable the spring to adopt a position intermediate the members or gears. Such an intermediate position is one selected for advantageous damping of vibrational torsion and control over the degree of relative rotation between the driving and driven members or gears.
The slots, which may be arranged in different segments of the gears, constrain movement of the springs. However, such constraint does not limit the degree of compression of the springs to reduce possibility of the spring failure when the damper is subject to torsional shock. This is the role of the limiting means which is conveniently of mechanical form.
In accordance with a second aspect of the present invention there is provided a vibration damping means including an elongate coil spring having an associated limiting means, the limiting means being elongate and incompressible during normal use, the limiting means having a length less than the length of the coil when unstressed and greater than the solid length of the coil.
The limiting means controls motion or behaviour of the spring when it is subject to compression. The limiting means may include plates or pins which contact each other and prevent further compression of the spring beyond a design limit. In this way, the limiting means may limit the stroke of the spring. The dimensions of the pins and plates are selected to avoid compression which may cause failure of the spring. Spring failure is most likely to occur where the spring has become solid, so the pins or plates may be arranged such that the compressed spring does not take up a length less than or equal to the solid length of the spring. The solid length of the spring is a characteristic of each spring and may be determined by conventional design practices.
If pins are used as the limiting means, two may be arranged in the slot and connected to the spring such that compression of the spring causes the pins to move toward each other. On contact, the pins exert opposing forces which cause spring compression to excessive levels to cease, at or before solid length of the spring is reached. The pins should have combined length selected to be greater than the solid length of the spring and may be arranged co-axially within a slot to optimize this effect. The pins may be of any suitable material but are preferably metallic or polymeric with stress failure characteristics such that excessive compression will not cause the pins to fail.
The pins may be located within a volume defined by a body of the spring. This packaging arrangement is particularly advantageous as it does not change the external dimensions of the transmission system. The limiting means could be placed externally of the body of the spring but within the slot as desired. While limiting means may be provided for each of the damping springs, this is not essential, increased benefit will be achieved if one or more of the damping springs are provided with limiting means. The vibration damper assembly allows at least two damping springs to be protected by limiting means.
The use of a compact vibrational damper arrangement for protecting the damping springs, particularly where the limiting means are arranged within the slots accommodating the damping springs, allows a greater number of torsional springs to be adopted for the same available space for the vibrational torsion damper assembly and thus more efficient damping if required.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION:
The vibrational torsion damper of the invention may be more fully understood from the following description of a preferred embodiment thereof, made with reference to the accompanying drawings in which:
Figure 1 illustrates a prior art transmission system arrangement including vibrational torsion damping means.
Figure 2 illustrates a mounting arrangement for the clutch housing and primary gear in the transmission system shown in Figure 1.
Figure 3 illustrates mounting arrangement of a cluster gear set and a primary gear according to invention.
Figure 4 illustrates the sectional view of the cluster gear according to the invention.
Figure 5 illustrates three dimensional exploded view of mounting arrangement of cluster gear and primary gear according to invention.
DESCRIPTION:
As illustrated in Figures 1 and 2, the transmission system includes a primary gear 4 connected to the crankshaft 10 of an internal combustion engine through suitable reduction ratio. Clutch housing (1) is connected to the output shaft (11) of the engine through the clutch plates and through suitable gearing. Vibrational torsion damping is achieved using springs 5, 6 and 7. Plate (8) helps retain the springs and the conical washer (3) and washer (2) between the housing (1) and primary gear (4).
Clutch housing is provided with 3 bosses (1a) projecting into slots (4a) provided in primary gear (4).
During a gear shift operation, power is transferred to the transmission. Resulting torque causes relative rotation between the primary gear (4) and clutch housing (1). The degree of this rotation depends on the severity of the shock with which the gear change is executed by the driver. When this relative rotation happens the damping springs 5, 6 & 7 are compressed. When the shift shock is high, the springs are compressed more and the bosses (1a) of the clutch housing contact the end of each corresponding slot (4a) in the gear and prevent further rotation of the two parts thereby limiting the stroke. This way the springs are stopped from becoming solid and reaching high stress levels.
In this case, the torsional damping system is built around a clutch system. It cannot be moved to any other position in the transmission system. It also requires sufficient available width in the axial direction that it is not compact enough for applications where space could be a constraint as in the case of small motorcycles.
One embodiment of the torsional damper according to the invention is shown in Figures 3, 4 and 5. In this case, a cluster driving gear (102) is connected to the output shaft of an internal combustion engine. The primary driven gear (104) is connected to the crankshaft of the engine through suitable reduction ratio.
The cluster gear (102) and the primary gear (104) have five slots (115) machined to accommodate 5 damping springs (106), each corresponding with a damping unit which, in combination, form a vibrational torsion damper for a small motorcycle. Each damping unit also includes two metallic pins 107 of hardened steel with appropriately selected metallurgical properties to resist excessive compression of the springs 106. The pins 107 each have a head of larger radius than the springs 106, and a cylindrical body of smaller radius than the springs 106. The pins 107 are placed in opposed co-axial alignment inside a volume defined by a body of each spring (106). The combined length of the two pins 107 is selected to be greater than the solid length of each spring 106 as measured in the factory. These springs 106 and metallic pins 107 are enclosed and maintained in place by a pair of cush gear plates (113). The primary gear (104), and the plates (113), are fastened together using rivets (105).
The cluster gear (102) has a circular slot (102a) cut into it, into which the lip (104a) of the primary gear can slide in a rotational way. This arrangement saves space and improves the packaging of the vibrational torsion damper.
During a gear shift operation, vibrational^ induced torque causes relative rotation between the cluster gear (102) and primary gear (104). The degree of this rotation depends on the severity of the shock with which the gear change is executed by the driver. When this relative rotation takes place, the springs 106 are compressed causing pins (107) to move towards each other. When the shift shock and consequential vibration is high, springs 106 are compressed more and the inner faces (107a) of the two pins are caused to contact each other presenting opposing forces which prevent further rotation of the two gears 102 and 104.
As the vibrational torsion damper construction is co-axial, the width of the damper assembly is kept narrow allowing a very compact design. Additionally, relatively more springs maybe packaged hence improving the torsional damping possible when compared to the prior art.
Modifications and variations to the vibrational torsion damper of the invention may be understood by the skilled reader of this disclosure. Such modifications and variations are deemed to be within the scope of the invention.

WE CLAIMS :
1. A transmission system having at least a driving member, at least a driven member and means to transmit torque between said driving and driven members, the means for transmitting torque including a torsional vibration damper comprising at least one damping means arranged intermediate driving and driven members, the driving and driven member being disposed in a radial arrangement.
2. A transmission system as claimed in Claim 1, wherein the driving member and the driven member define an axial width and the damping means is located within the defined axial width.
3. A transmission system as in any preceding claim wherein the torsional vibration damper comprises at least one cylindrical compressible damping means provided for absorption of transmission shock between the driving and driven members.
4. A transmission system as in Claim 3 wherein the damping means includes limiting means to limit the degree of compression of the damping means.
5. A transmission system as in Claim 4 wherein the limiting means locates within the volume defined by the damping means.
6. A transmission system as in Claim 5 wherein the limiting means is co-located axially with the damping means.
7. A transmission system as in any one of Claims 4 to 6, wherein the limiting means comprises a plurality of members having a combined axial length greater than the solid length of the damping means.
8. A transmission system as claimed in Claim 7, wherein each of the members is a pin having a head of greater radius than the damping means and a body of smaller radius than the damping means.
9. A transmission system as in any one of Claims 4 to 8 wherein the limiting means prevents binding of the damping means, during transmission of torque.
10. A transmission system as in any one of claims 4 to 9 wherein the limiting means is formed from material with metallurgical properties for resisting excessive compressive forces.
11. A transmission system as in any of the preceding Claims wherein the driving and driven members have relative rotation.
12. A transmission system as in any of the preceding Claims wherein the damping means includes at least one coil spring.
13. A transmission system as in any of the preceding Claims wherein the damping unit is interposed within a slot provided intermediate a driving member and driven member.
14. A transmission system as in any of the preceding Claims comprising of plurality of damping units interposed between the driving and driven members.
15. A transmission system having a torque transmission assembly, an intermediate driving member, a first driven member, a second driven member, and a means to transmit torque between said first driven and the second driven members, the means for transmitting torque including a torsional vibration damper comprising at least one damping means arranged intermediate the first and the second driven members, the first and the second driven members being disposed in a radial arrangement.
16. A transmission system as in Claim 15 wherein the torsional vibration damper comprises at least one cylindrical compressible damping means provided for absorption of transmission shock between the first and the second driven members.
17. A transmission system as in Claim 15 and 16, wherein the first and the second driven members define an axial width and the damping means is located within the defined axial width.
18. A transmission system as in Claims 15 to 17, wherein the torsional vibration damper transmits torque between the first driven and the second driven members.
19. A transmission system as in Claim 15 to 17, wherein the first and the second driven members have relative motion.
20. A transmission system as in Claim 15 to 18 wherein the first and the second driven members are disposed downstream of the said torque transmission assembly.
21. A transmission system as in Claim 18, wherein the first and the second driven members are gears.
22. A transmission system as in Claims 15 to 19, wherein the first and the second driven members are a part a cluster gear.
23. A vibration damping means for use in a vehicle transmission, the damping means including an elongate coil spring having an associated limiting means, the limiting means being elongate and incompressible during normal use, the limiting means having a length less than the length of the coil when unstressed and greater than the solid length of the coil.
24. A vibration damping means as in Claim 23 wherein the limiting means locates within the volume defined by the elongate coil spring.
25. A vibration damping means as in Claim 24 wherein the limiting means is co- located axially with the damping means.
26. A vibration damping means as in any one of Claims 23 to 26, wherein the limiting means comprises a plurality of members having a combined axial length greater than the solid length of the coil spring.
27. A vibration damping means as claimed in Claim 26, wherein each of the members is a pin having a head of greater radius than the damping means and a body of smaller radius than the damping means.
28. A transmission system as substantially claimed above applied to a small two wheel vehicle.
29. A transmission system as substantially claimed above applied to a small three wheel vehicle.
Dated this the 14th day of December, 2007.
For Bajaj Auto Limited,
By its Attorney,

(ARUNACHALAM APPAJI MOHAN) (BRINDA MOHAN)