CFD Simulation of Transmission for Lubrication Oil Flow Validation and Churning Loss Reduction

Rapidly changing emission and fuel efficiency regulations are pushing the design optimization boundaries further in the Indian car market which is already a very cost conscious. Fuel economy can be improved by reducing moving parts friction and weight optimization.

Driveline or Transmission power losses are major factor in overall efficiency of rotating parts in a vehicle. Transmission efficiency can be improved by using low viscosity oil, reducing oil quantity and reducing churning losses in car transmission. Changes like low viscosity and reduced oil volume give rise to challenges like compromised lubrication and durability of rotating parts. This further leads to extended design cycles for launching new cars with better transmission efficiency and fuel economy into the market. Design cycle time can be reduced by using CFD simulation for oil flow validation in the early design stage.

CFD simulation of transmission is challenging due to interaction of fluid and multiple gears/shafts rotating at high speed. It is also complex as lubrication is done only by splash generated by gears and oil flow through narrow galleries further complicate the simulation. Current paper describes a CFD simulation method developed for virtual validation of lubrication and oil churning losses using Particleworks^TM software. Simulation model consists of complete transmission system with all the gears rotating, shift system, oil flow galleries and transmission housings. Input conditions to the CFD model are as per the actual test conditions. CFD Simulation model is validated by correlating it with the actual oil flow using transparent housing. Validated model is being used to carry out virtual validation for lubrication system of new design. Improved version of the CFD model is used to calculate the torque loss due to oil churning. Experience of improving oil churning losses using CFD simulation is also presented in the paper. Churning loss improvement is also validated by testing.