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Transaxle Endurance Testing

Project Brief

To assist manufacturers with reliable data, Southwest Research Institute (SwRI) has developed a 720-second endurance cycle for a 10-second, 0–60 mph accelerating vehicle. The 720-second cycle is representative of city traffic, uphill, forced downshift, and stop-and-go driving, and contains no periods of steady-state operation. As the cycle progresses, the shift becomes increasingly more demanding.

Each 720-second cycle is proportional to 24.5 miles of operation. Completion of 2,040 cycles represents the number of shifts and associated transmission/transaxle wear that would occur in 50,000 miles of operation.

During evaluation, time to shift is monitored as a measure of transmission/transaxle health. In addition, as many as eight transaxle/transmission pressures are monitored, as well as solenoid actuation signals, various temperatures, input and output torques, and input and output speeds. At prescribed intervals, fluid samples are taken and gravimetric, particle count, and acid number tests are performed as early indicators of impending failures.

Exhaustive post-component measurements are made to quantify component wear rates. The measurements include:

• Shaft-bushing outer diameters

• Bushing inner diameters and wear pattern

• Friction plate thickness and condition

• Steel plate thickness, flatness, and condition

• Clutch pack clearances (under load)

• Kick-down drum slot clearances

• Gear teeth mesh contact patterns and distress

• Input shaft, axial endplay

• Output shaft backlash

• Bearing race brinelling, false brinelling, spalling, overtemperature

• Pump gear-housing clearance

• Pump gear-gear tooth clearance

• Torque converter double-D contact

• Shaft seal wear

• Seal deterioration

Evaluation of both automatic and manual transaxles is performed. For manual transmissions and transaxles, an automatic hydraulic-actuated cylinder system engages the special 5-speed, double-H pattern and simultaneously engages and disengages the clutch as required.

The SwRI powertrain stand is configured to accept the entire transaxle-type powertrain, along with the actual engine electrical wiring and control circuitry. The engine is mounted in the stand with provisions for an external coolant water recirculation loop, exhaust system incorporation, and auxiliary fuel pumping.

Throttle position and control are achieved through a fully digital system to attain control of speed setting, throttle position, or ramp rates. Operating modes are based on torque, speed, throttle position, or manifold vacuum with setpoint accuracy of 0.005 percent F.S.

The throttle actuator is a DC motor and gear head with an adjustable slew rate of 0.1–1.0 sec. and a maximum torque of 80 in.-lb with a throttle link range of 0.5–5.0 inches.
The engine and transaxle are physically separated with an in-line torque transducer between them to provide actual input transaxle torque values. The transaxle or transmission is mounted on a headstand and driven by shafting that extends from the engine. For transaxles, the output is through half-shaft and vehicle CV joints to include actual vehicle efficiencies.

Output from the half-shaft are two in-line torque transducers. The torque transducers connect to two speed-increasing 2:0:1 gearboxes whose outputs are rigidly connected to eliminate differential speed effects. Output from the connected gearboxes is to a 250-hp eddy-current dynamometer which functions to provide aerodynamic and parasitic drag effects imposed on the vehicle, along with braking to the powertrain.

For more information about our drivetrain engineering capabilities and past performance briefs, or how you can contract with SwRI, please contact Douglas Fussner at dfussner@swri.org or (210) 522-3972.

drivetrain.swri.org

| Design and Development | Engine, Emissions & Vehicle Research Division | SwRI Home |

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012