Proposed Efficiency Rating for an Optimized Automatic Transmission 960425
Increased concern for improving fuel mileage in today's vehicles has focused attention on powertrain component efficiencies. Currently, no efficiency standards exist for automatic transmissions but, uniform testing procedures do exist. Consequently, vehicle and transmission manufacturers have no basis for comparing transmission-to-transmission performance. In addition, manufacturers have no design targets from which to critique their product. This paper addresses this issue by developing an overall transmission efficiency rating. This rating is based upon average transmission operational torques and speeds, the percent time of operation in each gear for a representative duty cycle, and representative efficiencies at these conditions based on test data obtained from a cross section of current production transmissions.
The test sample will highlight 4 and 5 speed automatic transmission configurations including those with internal-external, gerotor, hypocycloid and variable displacement vane type pumps, two and three pass torque converters, various combinations of clutch packs, bands, and torque converter lock up strategies.
A comparison of the contribution of the pump, torque converter and gearbox to the overall transmission efficiencies is provided along with a discussion of speed versus torque dependent losses associated with the gearbox. The best of the above components will be integrated into a hypothetical “optimized” 5 speed automatic transmission configuration with torque converter lockup in 3rd, 4th, and 5th gears to achieve an efficiency rating of 76 9% or 85 8% without including idle time.