Automatic Transmission Technology

Faced with increasing competition in world markets, today's automotive manufacturers must develop vehicles with improved powertrain performance to meet demands for increased fuel efficiency. A proven leader in automotive innovations with more than two million hours of transmission testing, Southwest Research Institute (SwRI) supports manufacturers' efforts by providing complete engineering services and precision test facilities for transmission development.

SwRI facilities include transaxle, transmission, torque converter, and powertrain dynamometer test stands.

Engineering Services

Southwest Research Institute engineers have created extensive capabilities and state-of-the-art, precision laboratories for:

• Transmission and transaxle evaluations
• Torque converter testing
• Pump evaluations
• Powertrain testing

SwRI performs highly accurate engineering analyses on automatic transmissions in the following key areas:

• Stress
• Vibration
• Noise reduction
• Materials selection
• Failure modeling
• Hydraulic system modeling
• Component evaluation
• Thermal and heat transfer computations
• Electromagnetic emissions suppression
• Statistical data processing

Facilities

Engineering investigations are supported by a comprehensive, state-of-the-art testing facility that includes:

• Dual dynamometer test stands
• Engine-driven test stand
• Torque converter test stand
• Pump stand
• Temperature-controlled environmental chambers
• Vibration shakers and shock tables
• Electromagnetic intensity anechoic chambers
• Free-field noise test site
• SAE #2 friction machines
• Destructive component testing
• Nondestructive component testing
• Hydraulic test laboratories

SwRI's facilities provide a broad range of operating conditions for environmental and efficiency testing:

• Transmission input and output torque control and measurements from 0 to 3,000 ft-lb, accurate to ±1 ft-lb.
• Transmission input and output shaft speed control with measurements from 0 to 6,000 rpm, accurate to ±1 rpm.
• External transmission component pressure control to 0.25 psi, measurements from 0 to 300 psi, accurate to ±0.1 percent.
• External transmission fluid flow control to ±0.2 gpm, measurements from 0 to 25 gpm, accurate to ±0.2 percent.
• Transmission fluid temperature control and measurements from minus 40 to 275 degrees F, accurate to ±1 degree F for measurements, ±2 degrees F for control.
• Acoustic intensity measurements from 40 to 110 dB, within ±0.5 dB.
• Relative humidity control and measurements from 10 to 99 percent RH, accurate to 3 percent.
• Random vibration application from minus 50 g to 2,000 Hz.
• Shock application from 0 to 500 g.

Transaxle and Transmission Evaluations

The SwRI transaxle and transmission test stands provide precise simulation of the following vehicle operating conditions:

• Stall
• Neutral
• Spin
• Engine driving constant input torque
• Coast driving constant output torque

Highly accurate measurements are made through the entire speed range. Input power is provided by a 225-hp-motoring, 300-hp-absorbing DC dynamometer capable of high-speed operations of up to 6,000 rpm. Outputs are connected through rigid shafting into a 320-hp-motoring, 575-hp-absorbing DC dynamometer. Both input and output dynamometers are regulated by precision closed-loop controllers.

The Institute's transaxle test stand accepts transaxles with different input-to-output shaft, vertical, and horizontal centerline dimensions. The transmission test stand is configured for automotive and light truck applications.

SwRI's transaxle test stand, capable of testing transaxles for 1.3- to 5.8-liter engines, is specifically designed to eliminate differential speed effects.

Precision transaxle testing allows SwRI engineers to observe small efficiency changes in all gears.

Torque Converter Testing

The SwRI torque converter stand allows testing the torque converter independently of the transmission, while simulating operating conditions in the transmission. The Institute tests converters for:

• Stall conditions
• Spin losses
• Engine driving constant input torque
• Coast driving constant output torque

The flywheel is mounted on a shaft assembly supported on high-speed precision bearings. The converter is supported on a simulated shaft and pump housing assembly. A separate 20-hp pump and motor provides automatic transmission fluid to the torque converter, and fluid temperatures are controlled to ±2 degrees F through a temperature range of 100 to 300 degrees F.

A 175-hp AC motor, instrumented to regulate constant torque and speed for precision closed-loop control of ±1 rpm and ±1 ft-lb, allows test stand operations to 4,500 rpm and torques to 250 ft-lb.

A strain gauge-type, in-line torque transducer, accurate to 0.25 percent, connects the motor and torque converter. Headstand bearing losses are subtracted from the motor torque to obtain actual input torque to the converter. Downstream of the converter is an in-line torque transducer accurate to 0.25-percent.

Torque converter output is fed to a 320-hp-motoring and 575-hp-absorbing dynamometer, in tandem with a 2:1 reduction gear-box, allowing speeds to 6,000 rpm and torques to 3,000 ft-lb to be achieved.

SwRI engineers analyze different torque converter performances to determine optimal transmission performance.

Pump Evaluations

The SwRI pump evaluation test stand accepts the following pump configurations:

• Vane
• Ball
• External gear
• Crescent gear
• Gerotor
• Axial piston
• Radial piston
• Centrifugal

SwRI studies overall pump efficiency and pumping torque at various pressures. Pump efficiency variations have significant effects on transmission efficiency.

Various real-time measurements of temperatures, pressures, and flows are performed along with calculations of:

• Input power
• Mechanical and volumetric efficiency
• Theoretical flow
• Output power

A 7,200 rpm, 20-hp AC motor coupled to a closed-loop, pulse-width-modulated, variable-speed drive accurate to 1 rpm supplies the stand's power. A nonobtrusive, viscosity-intensive, corriolis flowmeter provides real-time mass flow-measurements. This flowmeter's low-pressure drop allows testing of the pump through a wide pressure range.

Fluid temperatures through a range of 100 to 300 degrees F are maintained to ±2 degrees F by a separate closed-loop control heater and heat exchanger. The system incorporates the actual transmission filter, filter location, and any auxiliary pump circuitry.

Powertrain Test Stand

SwRI offers highly accurate and versatile powertrain testing, including:

• Shift feel
• Shift logic
• Hot (200 degrees F)
• Cold (minus 40 degrees F)
• Accelerated endurance

SwRI's powertrain test stand accepts the entire transaxle powertrain. Operating modes are based on:

• Torque
• Speed
• Throttle position
• Manifold vacuum

The throttle actuator has an adjustable slew rate of 0.1 to 1 sec., a maximum torque of 80 in-lb, and a throttle link range of 0.5 to 5 inches. The engine and transmission or transaxle can be physically separated to provide actual input transmission or transaxle torque values. Transaxle output through halfshaft and vehicle CV joints replicates actual vehicle efficiencies.

Differential speed effects are eliminated by connecting the transaxle halfshafts to speed-increasing 2:1 gearboxes, which have outputs connected through rigid shafting.

The aerodynamic and parasitic drag effects and powertrain braking imposed on the vehicle are provided by a 250-hp, eddy-current dynamometer connected to various-sized inertia wheels.

Support Services

SwRI provides a variety of pre- and post-test services necessary for comprehensive transmission testing, including fixture design, experiment method design, and data analysis.

Fixture Design

SwRI engineers design fixtures for pump, torque converter, transmission, and transaxle mounting. Pump and torque converter fixtures incorporate internal transmission hydraulic functions. Designs incorporate bearings, seals, splines, balance, surface finishes, geometric call-outs, material selection, and heat treatment.

The Institute staff performs comprehensive transmission support services, including pump, torque converter, and transmission fixture design and testing.

Experiment Method Design

To evaluate vehicle parameters and engine performance characteristics, SwRI engineers prepare test schedules replicating the actual operating environment for transmissions and their components. SwRI employs fractional factorial screening and Taguchi techniques to minimize experimental runs while maximizing the value of the data.

Data Analysis

SwRI engineers examine all data collected for appropriateness, accuracy, calibration, and repeatability and apply statistical methods, such as response surface modeling.

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