Description:FIELD OF INVENTION :

The field of invention is for silent sealed drives for final drive applications in 2 Wheelers. More specifically it is addressed towards a silent chain which reduces abrasion and wear and tear of the guiding surface.

BACKGROUND OF INVENTION :

The power to propel a Motorcycle is generated by IC engines which are then transmitted to rear wheel of vehicle through a powertrain, comprising a set of gears and a final transmission system predominantly made of chain-sprocket system. Typical performance requirements on chain-sprocket system include good wear life and fatigue strength. With the advent of Electric drives for two wheelers, the typical RPM range within which chain-sprocket system has to operate is considerably increased. In addition to above mentioned performance requirements, a chain-sprocket system shall be as noiseless as possible and shall operate without any abnormal strand vibration at higher speeds without much of a compromise on chain-sprocket system mass.

SUMMARY OF THE INVENTION :

The proposed chain-sprocket system consists of a chain construction that combines the advantages of noiseless operation of a silent chain and wear resistance through high contact area generation by the use of hardened bushes as in roller chain drives. The system also can optionally incorporate lubricant seals to prevent dust ingress and to maintain lubricant in functional area, thereby extending wear life of chains.

DESCRIPTION OF INVENTION WITH DRAWINGS :

Fig.1a and 1b

• An embodiment wherein some or all link plates of a silent chain are separated by one or more hardened bushes that are press fitted into the holes of the link plates that need to be separated and articulately connected to a round pin or split pins. (Fig.1a and Fig. 1b)
• An embodiment wherein the number of link plates to be used are just decided based on the load bearing capability and the length of hardened bushes are decided based on the wear resistance required.
• An embodiment wherein the link plates meshes with an involute profiled sprocket similar to a silent chain to deliver smooth drive at higher speeds but separated between each other by hardened bushes for good contact area and hence good wear resistance.
• An embodiment that enables the usage of silent chain drive with high speed reduction between the prime mover end and load end along with good wear resistance at optimal mass
• An embodiment wherein the mass of the silent chain system is optimised by using optimal number of link plates for strength and optimal length of bush (es) for wear resistance thereby avoiding the usage of more number of interleaved link plates to build required contact area with pins for wear resistance.

Fig. 2a and 2b

• An embodiment wherein rubber seals can be optionally used to seal the lubricant between two ends of the hardened bush thereby preventing external dirt ingress and extend wear life (Fig. 2a and Fig. 2b)

Fig. 3, 4a and 4b

Conventional chain Power transmission system (Fig. 3) consists of a smaller toothed entity and a larger toothed entity connected by a roller chain (Fig. 4a and Fig. 4b). One of the entities is connected to a shaft on prime-mover side and the other entity is connected to a shaft on load side. The ratio of diameters of the two entities depends on speed and torque as demanded by the application. Power is transmitted from prime mover side to load side through the media like belts, chains, ropes etc. which meshes with the entities as they rotate.
Part no Description
31 Load end
32 Prime mover end

Fig. 5 and 5a

A conventional silent chain design with many interleaved link plates guided through a pin.

DESCRIPTION OF INVENTION :

The invention typically relates to a silent chain, consisting of interleaved links. A silent chain comprises of a plurality of link plates, each having a pair of tooth parts and pin holes, stacked in the thickness direction as well as in the length direction and linked together using linking pins. Guide links are provided on the outermost sides of the link plates and are press fit to the ends of linking pins. Conventionally the guide link and link plates need to be relatively positioned to reduce wear on a chain guide surface by causing either the guide link or link plates substantially connect the guide surface.

In general, the surface speed of the entities is limited to suit the operating regime of power transmitting media through the introduction of reduction gears between the prime mover and the entity. Usage of gear box increases the cost of transmission system and also makes the system heavier and less energy-efficient in power transmission. Conventional roller Chain drive, as a power transmitting media, when transmitting power at higher linear speeds, undergoes vibrations due to chordal action resulting in noise. Silent chain design overcomes this problem but has inherent issue of higher system mass because of more number of interleaved link plates to build more area of contact with pin for higher wear life as demanded by applications like motorcycle/scooter final drive system. Also, unlike conventional roller chains, silent chain drive cannot incorporate lubricant seals to extend wear life of chain.

A conventional silent chain design (Fig. 5) has many interleaved link plates guided through a pin which are press fitted with guide plates on either ends. The profile of link plates meshes with the sprocket during power transmission. The number of link plates are decided based on tensile strength requirements and wear life requirements. Though this design is ideal for low chain tensile load and high speed applications like engine timing chain, adapting the design for drive applications such as power transmission between prime mover and rear wheel in a Motor cycle is possible only through increasing the number of link plates to meet strength and wear life requirements, thereby increasing the chain mass considerably. Hence increasing the number of link plates is not a good solution obviously. A silent chain and sprocket system is proposed for final-drive power transmission between prime mover and load wherein the issue of increase in system mass by using many interleaved link plates to increase contact area between pin and plates is overcome by press fitting a bush between selective link plates. Total length of the bushes is at least more than thrice the thickness of link plates. These link plates are separated by the bush length, thereby increasing the contact area proportionally. The bushes do not interact with sprocket and only performs the function of increasing the contact area and contact hardness. Also, the proposed design has an option of using lubricant seal at either ends of bushes in silent chain, thereby extending wear life of silent chain, which otherwise, is not possible to use in conventional silent chain design.

The invention has sufficient industrial applications. Silent chains are currently in use for timing applications in a Motorcycle Engine wherein the chain transmits the power from crankshaft to cam shaft. The chain is smoother in operation and less noisy than a conventional roller chain or a bush chain. The link plates of silent chain engage with the sprockets gradually thereby reducing the impact noise. Silent chain type of construction is not in use for rear wheel drive application in an IC Engine powered vehicle since noise is not a concern for such vehicles. In case of Electric vehicles which are silent in its operation, usage of chain drive is restricted because of noise generated by a conventional roller or bush chain. To overcome this issue, silent chain type of construction can be used for such application. But, the wear life of silent chain is poor as compared to roller chain since, in silent chain, the bearing area is limited to number of link plates that contacts the pin and its thickness. Though the chain can meet its strength requirements, it may not meet the wear life requirement. To increase the wear life, number of link plates and (or) its thickness have to be increased, resulting in a heavier chain. Since it is desirable to keep the mass of moving components to minimum in electric vehicles to increase its range, usage of much heavier silent chain is not desirable. A new silent chain design is proposed wherein the number of link plates and hence the lacing pattern of assembly is determined only by the required tensile strength of chain as in a conventional silent chain. The need to use more link plates as demanded by wear life requirements is avoided by press fitting hardened bushes in-between the link plates, thereby increasing the bearing area without using more link plates. The mass of bush is comparatively less to link plates to be used. This construction also enables contact between pin and bush instead of pin and link plate. Since hardness profile of pin and bush can be maintained similar, the wear life also increases. The number of bushes to be used and its arrangement in the lacing is determined by the wear life requirement of the vehicle. A typical construction with 2 bushes is shown is Fig. 1. It can be one, two or more bushes with corresponding addition/deletion of link plates depending on wear life requirement.

The invention as per the disclosure is an advantageous combination of features exhibited in a conventional roller chain and a conventional silent chain advantageously modified to be used as silent chain for drive applications which is hither to unknown in prior art. This is a new industrial application thereby exhibiting a new and additional feature but which is mandatory or essential for desired drive applications. Conventionally only roller chains have been used for drive applications and not silent chains. This is because a high torque is required for drive applications. An extraordinary strength is required for drive applications of a chain when the chain is used for drive applications. Typically a conventional silent chain cannot be directly applied to a drive applications as it will suffer enormous wear and tear and hence traditionally only roller chains are used for drive applications. In this invention an attempt has thus been made to modifying the conventional silent chain and bring the advantages and features of a roller chain into the new design of the novel chain. The sufferings of conventional silent chain when applied for a drive application needs to be modified for the following reasons i.e., to increase its strength and also lower the wear and tear. One can increase the strength of silent chain by increasing the number of link plates which automatically increases the strength of chain. However increasing the number of link plates leads to increasing the weight of assembled chain and moreso cost of assembly and maintenance. Hence merely increasing the link plates in a silent chain is not a viable or desired solution. Instead the inventors have identified that the wear and strength deterioration occurs due to the smaller contact area between the pins and link plates. Hence solution is addressed towards increasing the contact area between the pins and link plates. This too can be done by increasing number of link plates which then also suffers the increase in weight, cost and assembly disadvantages. On the alternative and a simpler solution has been found by introducing bushes between the link plates which means the pins are in contact with bushes and not with link plates directly and thereby reducing the wear of pins and link plates. The novelty lies in the introduction of bushes between pin and link plates and ensuring that the wear is substantially reduced by increasing the surface area of contact whereby spreading the load across larger contact surface and diminishing the rate of wear and tear. Hence the invention relates to designing a bush fitted silent chain for drive application which is unknown in prior art.

The invention has been described as detailed above but various embodiments and variations are possible beyond the preferred embodiments disclosed in this document. All such variations and modifications as obvious to the skilled person is within the scope of this invention.
, Claims:WE CLAIM :

1. A bush fitted chain for silent drive applications comprising of a plurality of interleaved link plates guided through pins press-fitted with guide plates on either ends, whereby profile of link plates meshes with the involute profiled sprocket during power transmission and having bushes press fitted into the holes of the link plates, such that link plates are mutually spaced away from each other,

the arrangement characterised in the said bushes to increase the contact area between pins and link plates, and whereby the length of the bush is atleast more than thrice the thickness of the link plates.