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One of the leading transmission technology capabilities in the world, specifically for transmission performance and efficiency was developed at Southwest Research Institute (SwRI). These capabilities include:

• Efficiency evaluation services

• Component and assembly modeling

• Transmission optimization

These capabilities encompass manual and automatic transmissions and transaxles and automatic transmission components.

For the past five years, SwRI has conducted efficiency testing and created performance maps of more than 59 transmissions and their components from different manufacturers around the world. It is expected that for the foreseeable future, we will continue to test and model approximately 15 to 20 transmissions per year.

Based upon discussions with more than 75% of the transmission manufacturers around the world, it is believed that SwRI has conducted more efficiency tests and modeled more transmissions than any other facility in the world. It is generally acknowledged that SwRI's awareness of real-world transmission characteristics and performance capabilities is extremely broad and comprehensive and is considered one of the leaders in this field.

SwRI is routinely asked to assist manufacturers to better understand how their product relates to the best-of-class transmissions from around the world, to provide recommended efficiency targets and areas for improvements, and to evaluate new transmission concepts. Staff members have authored technical papers about automatic and manual transmission efficiencies and pump comparisons.

In general, losses within an automatic transmission are distributed as follows:

• Pump—20

• Converter-locked—25

• Gearbox—55

Because the pump and gearbox losses are quite large, significant efforts have been expended to develop ways to improve these component efficiencies.

Pump Losses

• Variable displacement devices

• Fluid recirculation

• Improved volumetric efficiency by reducing rotating part clearances

• Reduced filter restrictions

• Operation at higher speeds

Gearbox Losses

• Differentiating between torque and speed dependent effects

• Reducing clutch pack drag

• Investigating the effects of drum windage and ATF churning through sensitivity testing and evaluation

SwRI Transmission Projects

The following are the various transmission-related projects conducted at SwRI that assist manufacturers in transmission improvement programs.

• Pump, converter and transmission efficiency testing and evaluation

• Transmission endurance testing and evaluation

• Steady-state and transient hot testing and evaluation

• Cold testing and evaluation

• Transaxle barrel thermal gradient

• Shock and vibration testing and evaluation

• Noise testing and evaluation

• Failure mode analysis

• Electromagnetic testing of transmission control modules

• Electronic control module strategy investigations

• Friction material development

• Clutch pack drag testing and evaluation

• Seal testing and evaluation

• Automatic transmission fluid effects

• Shift feel evaluations

• Slow shift transmission investigation

• Powerflow and kinematic analysis

• Pump, converter, and transmission modeling

• Gear tooth analysis

• Value analysis

• Sensitivity testing and evaluation

• Transaxle torque steer testing and evaluation

• Torque converter shudder testing and evaluation

• Torque converter lockup clutch damper characteristics

• Pump development

• Material development

• Component–component production variation

• Clutch pack thermal modeling

• Clutch pack kinematic model

• Pump math model

SwRI has been involved in transmission related activities for more than 25 years and has conducted more than 2 million hours of various types of transmission testing and evaluation.

Transmission Efficiency Testing and Modeling

SwRI routinely conducts efficiency testing and evaluation for various sized transmissions and creates mathematical models of the losses within the transmission. These models are three-dimensional response surfaces of torque losses as a function of input torque and input speed conditions. The response surfaces are complex, varying from transmission to transmission, and involve the use of statistical techniques in their creation. An example of a typical gearbox response surface is shown below.

The response surfaces created are based on efficiency results. Efficiency testing and evaluation of automatic transmissions is particularly challenging because it involves observing across a wide range of conditions (such as high torque-low speed and low torque-high speed) and operating modes, all of which are particularly difficult on electrical equipment. In addition, efficiency testing and evaluation requires precision instrumentation and control to obtain realistic performance information.

Testing and evaluation services are conducted at SwRI to 575 HP while maintaining the following conditions.
 

Transmission and torque converter testing conducted at SwRI is performed on specially designed test stands having large, high-speed DC dynamometers and 0.25% accurate in-line torque transducers connected to the input and output of the test article. DC dynamometers are required motoring and absorbing devices that must be used to test transmissions to allow uninterrupted testing in both the engine driving and driveline driving modes.

SwRI DC dynamometers range from 225 to 300 HP in the motoring mode and 300 to 575 HP in the absorbing mode. Special shift-selectable gearboxes allow shaping of the absorbing torque speed curve to be modified for high-torque conditions at low speeds that occur in first gear with an open torque converter configuration.
 

Pump Testing

As described above, the percentage of power required to satisfy the pumping requirements of an automatic transmission can be as high as 20% of the overall. Consequently, considerable effort is involved in testing transmission pumps. SwRI has tested and modeled the performance of every type of transmission pump currently used, including:

• Internal-external crescent

• Geroter

• Hypocycloid

• Duocentric

• Variable displacement

• Ball

• External-external

Testing is performed on a special test stand configured with a 20-HP AC motor capable of speeds to 7,200 rpm, coupled to a 200 Hz variable frequency drive.

Instrumentation used during pump testing includes:

• 0.25% accurate 200 in-lb rotary transformer torque transducer

• Real-time coriolis flow meters with extremely low pressure losses

• 300°F temperature-compensated, hermetically sealed, strain gauge type 0.1% accurate pressure transducer.

Fluid conditioning is performed with auxiliary heating and cooling circuitry, including the use of low-watt-density heating elements to prevent fluid breakdown.

Pump testing and evaluation involves determining volumetric efficiency, overall efficiency, pump delivery, theoretical displacement and pumping torque. All testing and evaluation is performed at different ATF pressures and temperatures.

Pump testing and evaluation is extremely demanding and requires alignment of the pump to within 0.001 in. Confirmation of proper alignment is verified with oscilloscope traces and fast Fourier Transforms.

Clutch Pack Drag Testing and Evaluation Services

Speed-dependent losses are considered to be the area in which transmission efficiency improvements can most likely be realized, specifically in the area of clutch pack drag. Factors that affect clutch pack drag include:

• Friction material groove pattern

• Friction material groove profile

• Friction material plate flatness

• Friction material surface finish

• Separator plate surface finish

• Clutch pack clearance

• Hub centrifugal pump hole pattern

• Fluid evacuation outside the pack

To investigate these factors, SwRI has fabricated a unique clutch pack drag stand capable of simulating any input or output speed or direction of rotation to the clutch pack. The stand consists of a 20-HP AC motor capable of speeds to 10,500 rpm, a 15-HP AC motor capable of speeds to 14,500 rpm, and a 0.25% accurate, 100 in-lb rotary transformer in-line torque transducer at both ends of the clutch pack.

To simulate actual operation in the transmission, the stand contains an adjustable platform that can be tilted from 0 to 10 degrees to simulate the actual mounting angle in the vehicle. (It was found that the transmission mounting angle will affect transmission losses as a result of increased windage and churning losses.)

Information obtained from the clutch pack drag testing and evaluation is used to distribute the losses within the gearbox.

Comprehensive Transmission Services

Efficiency capability services of automatic transmissions, converters and pumps requires a specialized staff with a broad range of capabilities as follows:

• Reverse engineering

• Hydraulic and electronic controls

• Pump, converter and transmission fixture design

• Fixture fabrication

• Engine and vehicle performance

• Evaluation procedure development

• Instrumentation

• Data acquisition

• Data analysis

• Statistical capabilities

Each of these capabilities is part of the multifaceted nature of an automatic transmission's operation that must be understood and technically dealt with for successful transmission testing. For example, fixture design requires a thorough understanding of the transmission operation to allow testing of the pump and converter out of the transmission assembly while simulating necessary hydraulic inputs and outputs, lube flows, spline tooth requirements and alignments.

Fixture design requires an awareness of:

• Precision geometric tolerancing

• Surface finish requirements

• Seal gland profiles

• Bushing tolerances

• Bearing classes

• Gear tooth forms

• Materials

• Machining practices

• Surface treatments

• Welding practices

For more information about automatic transmissions capabilities at SwRI or how you can contract with SwRI, please contact Douglas Fussner at dfussner@swri.org or (210) 522-3972. 

| 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.

September 30, 2008