In-Situ Measurement of Transmission Efficiency in Vehicles

SAE Recommended Practice J1540 [1] specifies test procedures to map transmission efficiency and parasitic losses in a manual transmission. The procedure comprises two parts. The first compares input and output torque over a range of speed to determine efficiency. The second measures parasitic losses at zero input torque over a range of speed. As specified in J1540, efficiency of transmissions is routinely measured on a test-stand under steady torque and speed [2] [3]. While such testing is useful to compare different transmissions, it is unclear whether the “in-use” efficiency of a given transmission is the same as that measured on the stand. A vehicular transmission is usually mated to a reciprocating combustion engine producing significant torque and speed fluctuations at the crankshaft. It is thus a valid question whether the efficiency under such pulsating conditions is the same as that under steady conditions. The main objective of this work is to develop a high-fidelity measurement technique to calculate “in-situ” transmission efficiency on a real vehicle. Transmission input torque was measured by instrumenting the flex-plate with strain gauges and appropriate telemetry. Transmission output torque was measured by instrumenting the axles with similar strain gauges and telemetry. The developed measurement system was not only capable of handling the pulsating torque and speed fluctuations of the crankshaft but also account for higher order harmonics of the torque signal in the calculation for transmission efficiency.