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India is the sixth largest producer of commercial vehicle in the world. According to the statistical analysis, India produces more than 3.9 million units of commercial vehicle per year (htt). All vehicles, aircraft and water craft included, requires transmission system in order to enable torque and speed conversion. Transmissions are distinguished in accordance with their function and purpose for e.g. gearboxes, steering boxes and power take-offs. (Harald Nauheimer, 2011)
The transmission system consists of clutch, gear box, propeller shaft which transmits the torque from the gear box to the rear axle through a differential gear to distribute the final torque to the driving wheels. (H.Bayrakceken, 2007)
The functions of the transmission system are:
- 1.
To disconnect the engine from the road wheels when desired.
- 2.
To connect the engine to the driving wheels without shock.
- 3.
To vary the leverage between the engine and the driving wheel.
- 4.
To vary the engine speed permanently in a fixed ratio.
The transmission system consists of a union joint, pinion bearings and planetary gears. Failure in the transmission system components covers one fourth of the on road automobile failures (Harald Nauheimer, 2011). Failures due to Manufacturing and design, maintenance, raw material and user originated ones are some of the other common failures that are observed in the automobile (H.Bayrakceken, 2007). The possible faults that are observed in the system are on a) the universal joints which are situated on either side of the propeller shaft, b) faults at the Gear box, c) in the differential and d) on the pilot bearing which is coupled on to the pinion gear. In this paper the failures that the authors have simulated on the vehicle transmission system are given in Table 2.
Table 2. Combination of faults under investigation
| AGC | All good condition |
| BB | Broken pilot bearing |
| DP | Damaged pinion |
| PP | Pitted pinion |
| FSJ | Faulty star joint |
| PPFSJ | Pitted pinion faulty star joint |
Gears form a major part of the transmission system in the heavy vehicles. The common faults that are observed are tooth failure, pitting and wear. These damage types limit the load capacity of the gear wheels. The major factors affecting the performance are: