Transmission Breather Evaluation

Breather assembly is mounted on transmission to maintain the pressure equilibrium inside transmission. Breather allows the transmission to breathe air when the air inside transmission expands or contracts due to heating and cooling of lubricating oil during vehicle running. Breather allows the hot air to escape and cool air to enter into the transmission to prevent overheating issue. Failure of breather assembly can lead to pressure buildup inside transmission and further leading to leakage from transmission oil seals. Oil leakage through the breather assembly is governed by parameters such as opening pressure, location and orientation of breather etc. The transmission undergoes different operating conditions of input speed, load, temperature, inclination etc. Also, breather assembly is designed and positioned in such a way that there is no leakage through breather due to oil splash inside the transmission. The paper gives details of leakage issue observed at vehicle level and methodology derived to simulate on test bench. Information of vehicle level tests carried out and conditions under which leakage was observed, was used to derive a test schedule, to simulate the oil leakage issue on test rig. The transmission input speed, angle of inclination were altered during test so that the vehicle level failure is simulated on test rig. The paper also explains different trials conducted to arrive at simple and optimized design of transmission to arrest this oil leakage issue through breather. The solution proposed was again revalidated at vehicle level and results were having good correlation with rig level results. The rig level test methodology proposed in this paper can be horizontally deployed to all transmissions and subsequently lead to early capture of oil leakage issue in the development phase. Test bench validation helps to capture input early in the development time due to shorter test duration compared to vehicle level validation.