Design and Analysis of Automobile Central Differential Having Two Different Side Gear

Central differential is a geared mechanism located between the two driving axles thereby providing torque developed by engine in required ratio to both the axle. In ordinary four wheel drive vehicle, there are two differentials one in rear axle and other in front axle along with a transfer gear box in between, which converts it to four wheel drive. A four wheel drive vehicle without a central differential cannot be driven on dry, paved roads in four-wheel drive mode, as small differences in rotational speed between the front and rear wheels produces extra torque to be applied across the transmission. This phenomenon is known as "wind-up", and can cause considerable damage to the transmission or drive train. But in all wheel drive vehicle transfer gear box is replaced by central differential that transmit the power for all wheel drive (AWD), which is used in part time four wheel drive in order to reduce weight and provide optimum traction. In this thesis, a case study has been done for Maruti Suzuki Zypsy which works on the principle of four wheel drive having transfer gear box providing torque in the ratio 50:50 to rear and front axle. Literature shows that the total torque developed by engine should be divided in the ratio of 60:40 to rear and front axles which is ideal ratio for better handling and optimum level of grip. This creates a need for replacing the present transfer gear box to a modified central differential consisting two rotating side gear having different diameters mounted on front and rear side of the hub. The rear side gear drive the differential of rear axle while the front side gear will drive the differential of front axle dividing the torque developed by engine in the required ratio of 60:40 . For this CAD modeling package Creo-2 was used to model the calculated design and then analysis is done by FEM methods in ANSYS software. Then finally the performance parameters of modified automobile central differential and Transfer gear box are compared.