Claims:We Claim:
1. A supercharger, said supercharger comprising at least:
a shaft (100) and a rotor (102); characterized in that

said shaft (100) comprises at least a first member (103) and a second member (105), said first member (103) and said second member (105) co-axial to one another, and said rotor (102) comprises at least a boss (106) attached to body of said rotor (102), said boss co-axial to body of said rotor (102);

said first member (103) adapted to be in rotational engagement with said body of said rotor (102) via said boss (106), while second member 105 rotates within the body of said rotor (102).

2. The supercharger of claim, wherein said boss (106) is integrated with said rotor (102).
, Description:Field of the invention
[0001] This invention relates to the field of a supercharger.

Background of the invention
[0002] A supercharger is used to increase the mass of air supplied to an engine. To compress air, supercharger makes use of a pair of rotors. These rotors are coupled to the shaft which transfer power from the pulley / gears to the rotors. These rotors are made of aluminum to minimize weight and inertia, and shafts are made of steel to have optimal strength. The shaft is connected to the rotor through an interference fit. However, since the thermal expansion of aluminum is almost twice that of steel, at high operating temperatures, the interference between the shaft and rotor reduces. To compensate, if the interference at room temperature is increased, the stress on the rotor increases greatly and in many cases beyond the elastic limit of the rotor. Hence there is a need to join supercharger rotor to shaft which can transfer torque at high operating temperature.

Brief description of the accompanying drawing
[0003] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0004] FIG. 1 illustrates supercharger.

Detailed description of the embodiments
[0005] FIG. 1 illustrates supercharger. The supercharger comprises at least a shaft 100 and a rotor 102. The shaft 100 comprises at least a first member 103 and a second member 105, the first member 103 and the second member 105 are co-axial to one another. The rotor 102 comprises at least a boss attached to body of the rotor 102, the boss being co-axial to the body of the rotor 102. The first member 103 is adapted to be in rotational engagement with the body of the rotor 102, while second member 105 rotates within the body of said rotor (102). The shaft 100 may be made of steel while rotor 102 may be made of aluminum.
[0006] The working of the shaft 100 and rotor 102 arrangement will be explained in further detail. The supercharger is driven by the engine. As the shaft 100 of the supercharger rotates, the rotor 102 that is attached to the shaft 100 also rotates. The rotation of the rotor 102 causes fresh air to be sucked into the supercharger, where the air is compressed before the compressed air is sent to the inlet port of the engine. The shaft 100 and rotor 102 are in rotational engagement with one another. The shaft 100 and the rotor 102 may have a dual interference fit. The shaft 100 and the rotor 102 have two interference zones for rotational engagement. In the first zone, the shaft 100 interferes with the rotor 102 and it expands less, hence the expansion of the shaft 100 is restricted, as the rotor 102 prevents any further expansion of the shaft 100. Thereby, the interference reduces as temperature increases during working of the supercharger. In the second zone, the boss of the rotor 102 interferes with the shaft 100. So as temperature of the rotor 102 increases the interference increases. Alternately the shaft 100 which may comprise a bore, and a coupling element made of the same material as the shaft. The coupling element is inserted into shaft 100 with an interference fit. The combined engagement of shaft 100 and rotor 102 at the first zone and the second zone will satisfy the operation of supercharger at different operating temperatures.
[0007] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of type of oil pump used. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.