A Study on Effect of Various Design Parameters on Cooling of Clutch for a Continuously Variable Transmission (CVT) System of a Scooter 2014-01-2595

In scooters, the Continuously Variable Transmission (CVT) is used to transmit the power from the engine to the wheels. The CVT transmission consists of a two pulleys connected to each other through a belt. The change in the transmission ratio is achieved due to the change in the pulley diameters. A centrifugal clutch is attached to the rear pulley to transmit the power to wheels once the engaging engine speed is reached. The heat is generated due to the belt slippage and the engagement of the centrifugal clutch. Excessive heating may damage the belt, clutch and deteriorate its performance. The cooling of the belt, pulleys and the clutch is thus important for its safe operation. The cooling is achieved by the centrifugal cooling fan which forces the air over the belt, pulley and clutch. A clear understanding of the cooling system is important in designing the air flow path for clutch cooling of CVT housing. The efficiency of the cooling system depends on the quantity and direction of flow.

The work aims at the study of different design possibilities for increasing the flow through CVT housing and flow path modification within the CVT housing for reducing the clutch temperature. The work is broadly classified in to two parts, in the first part the design modification is done to increase the air flow through the CVT housing and in the second part, the flow is guided within the CVT housing to increase the cooling of the clutch housing. The objective of the work is to analyze the different flow path and to see the cooling effect of each design. The Moving Reference Frame (MRF) model was used to simulate the rotary motion of the centrifugal cooling fan. RANS K-Epsilon two equation turbulence steady state model was used to solve the 3-D numerical model. A constant heat source is assumed at the clutch inner surface and the cooling with the design modifications is evaluated.

An experimental validation is done with a defined driving cycle to validate the simulation results. The results from the experimental validation is transient whereas the simulation results are steady state, since the heat generation pattern is not uniform in experimental validation due to slippage in clutch. A relative comparison study is done to check the effect of steady state simulation results on a transient experimental evaluation.