Precision Powertrain Component Testing

Automotive manufacturers are continually challenged with increasingly stringent requirements to improve fuel economy. Significant powertrain efficiency improvements can be realized by reducing internal friction. Southwest Research Institute (SwRI) identifies the energy losses associated with individual powertrain components and investigates factors affecting these losses at both assembly and component levels. With extensive experience in powertrain component development, SwRI uses precision component testing capabilities to study factors affecting performance and efficiency, such as:

  • Engine mechanical efficiency
  • Transmission fluid temperatures
  • Transmission mounting angle
  • Transmission efficiency
  • Component and assembly spin losses
  • Pumping efficiency
  • Torque steer phenomenon
  • Engine wear

SwRI friction models are often used to assess tribological interfaces between engine components. In this example, an SwRI friction model was used to accurately predict rubbing losses between the cam and follower on a 3-cylinder, DOHC engine.

Engine Mechanical Efficiency

The Institute measures mechanical efficiency to determine how much energy is required to overcome inefficiencies associated with rubbing friction and pumping of working fluids. High friction and poor air management rob an engine of precious fuel energy. Lower fuel consumption is especially critical to meet increasingly stringent Corporate Average Fuel Economy standards and to decrease use of limited fossil fuel supplies. SwRI uses experimental and theoretical techniques to reduce engine and component friction in automotive powertrains. Employing these techniques, manufacturers can significantly improve the fuel economy of tomorrow's powerplants.

This representation of component friction in a four-cylinder engine shows the effect of engine speed. SwRI has compiled friction data from a variety of engines into a comprehensive database of engine and component friction. Measured friction losses are useful when validating computational codes.

Transmission Efficiency

The Institute quantifies the torque losses within a transmission gearbox for transmission manufacturers. This information is essential for initial product development, on-going improvement, vendor manufacturing process verification, modeling, and simulations. SwRI has the motoring/absorbing dynamometers and precision in-line torque sensors necessary for efficiency testing. To determine torque losses under various test conditions, precision measurements are made with specialized equipment. Capabilities include:

Torque Control 0-4,700 ft-lb, 1 ft-lb,
0-6,370 N-m, 1.4 N-m
Speed control 0-6,000 rpm, 1 rpm
Temperature control 77-275 F, 2 F
20-140 C, 1 C

Transmission Mounting Angle

Fluid churning and windage losses are major contributions to manual transmission internal torque loss and are directly affected by the installation angle of the transmission. Varying the mounting angle on the test stand, SwRI determines the effects of mounting angle on efficiency.

Engineers measure transmission efficiency as a function of transmission mounting angle. Efficiency varies by up to one percent with five-degree mounting angle difference.

Transmission Fluid Temperatures

The internal torque losses of manual transmissions are greatly affected by fluid viscosity and temperature. The temperature effect has become particularly significant as lighter weight automatic transmission fluids have replaced heavier lube oils. Controlling fluid temperature to 2 F, SwRI determines how fluid temperature affects efficiency; a gearbox can lose as much as five percent efficiency over a 60 F range.

This plot shows transmission efficiency as a function of fluid temperature.

Transmission fluid temperature is precisely controlled during testing to assess how fluid temperature changes affect transmission torque losses.

Component, Assembly Spin Losses

To measure the torque losses associated with individual internal transmission components, SwRI evaluates the components on a special spin loss test stand, capable of speeds to 11,000 rpm. Two high-speed motors are individually controlled to simulate any combination of transmission component input and output speed conditions. Components evaluated include:

  • Clutch packs
  • Pumps
  • Overrunning clutches
  • Bands
  • Seals
  • Bearings
  • Bushings
  • Planetary gear sets

Individual transmission component torque losses are evaluated on SwRI's variable-speed, dual-motoring test stand.

The Institute tests various pump configurations, such as variable displacement and internal-external gear pumps.

Pump Testing

Because automatic transmission pumping energy accounts for as much as 40 percent of the parasitic losses associated with transmission operation, manufacturers are concentrating on reducing these losses. The Institute has extensive experience evaluating the losses associated with a variety of pumps, including gerotor, crescent, ball, variable displacement, and internal-external gear.

Precision instrumentation measures real-time fluid viscosity, flow, pump speed, torque, and pressure. During testing, numerous variables affecting pump performance are controlled, such as:

  • Fluid type
  • Pump speed
  • Outlet pressure
  • Pump displacement
  • Fluid temperature
  • Fluid viscosity
  • Recirculation flow rate
  • Pump inlet restriction

Using wheel-mounted torque meters, SwRI quantifies torque steer phenomena.

Torque Steer Phenomenon

Intrinsic to high-power front wheel drive vehicles, the torque steer phenomenon is thought to be associated with asymmetrical vehicle geometry and out-of-phase power pulsing. Under controlled laboratory conditions, SwRI tests torque steer effects at varying differential side-side wheel speeds and suspension system positions. Precise wheel angle positions are maintained by independently controlling left and right suspension component positions.

The Institute measures wear as a function of lubricant and engine operation parameters using bulk activated rings and connecting rod bearings in a test engine.

Component Wear

Using state-of-the-art radioactive tracer techniques, SwRI measures real-time wear in operating engines, drivetrains, and other mechanical components under transient and steady-state conditions. These techniques, pioneered at the Institute, provide cost-effective, accurate, real-time data, detecting minute wear changes without disassembly and physical inspection. SwRI uses surface or thin-layer activation and bulk activation techniques to produce traceable isotopes in component materials. As components wear, radioactive wear particles become suspended in the lubricant, where their activity is continuously measured.

Advantages of radioactive tracer measurement techniques include:

  • Cost-effective tests
  • Repeatable measurements
  • Real-time wear data
  • Reduces test time
  • Easily measured transients
  • Identification of cause and effect relationships
  • Association of wear with specific design parameters, fuel and lubricant characteristics, and component operating conditions

This brochure was published in September 1994. For more information about precision powertrain component testing, contact Matt Castiglione, Phone (210) 522-6831, Engine, Emissions and Vehicle Research Division, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510.

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