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This paper presents a newly developed integrated powertrain control system. The system coordinates the controls between engine and transmission to optimize powertrain operation for drive quality and fuel economy. This new control system uses the desired engine power as the common load variable for both engine and transmission control instead of throttle as is used in conventional powertrain controls. The main advantages to this control system are improved fuel economy and drive quality. Other advantages and a brief description of the control system will be described in more detail in the following discussion.

The Hydra-Matic 6T70 is General Motors first model of a new, two-variant front wheel drive (FWD) six speed automatic transmission family. The second variant is a higher capacity model, the 6T75. The transmission was co-developed with Ford Motor Company. The 6F50 is the Ford variant that aligns with the GM 6T70 transmission. Approximately eighty five percent of the hardware is shared or common between the GM and Ford transmission variants. Ford will also have a higher capacity variant the 6F55 to align with the GM 6T75. The first GM application is the Saturn Aura for the 2007 Model Year. The Ford Edge and Lincoln MKX in MY 2007 will be the first applications for the 6F50. While the Hydra-Matic and Ford FWD six-speed family was designed with two variants in mind, the designed in modularity requires only changes to the second and third axis and case housings depending on specific torque requirements. This modular design enables a tremendous amount of part sharing.

An automatic transmission control system for clutch-to-clutch shifting systems has been developed. This enables the new General Motors Powertrain families of rear- and front-wheel drive transmissions to meet stringent cost, mass, and packaging reqiurements, while providing driveability and fuel economy improvements over the four- and five-speed transmissions that they replace. The design team utilized several new technologies and methods to robustly engineer a control system that allowed excellent first time capability and reduced calibration intensity. Innovative technical approaches were developed in several key mechatronics areas.

The Hydra-Matic 6L80 is General Motors first model of a new, four-variant, rear wheel drive (RWD) six speed automatic transmission family. The four variants are the 6L45, 6L50, 6L80 and 6L90. The new, high performance 6L80 will debut in 2006 model year performance vehicles, including the Chevrolet Corvette C6 and new Cadillac STS-V and XLR-V. By 2007, GM expects to use the RWD six speed family in as many as 25 different car, truck and SUV models in RWD, 4WD and all-wheel drive configurations. While the Hydra-Matic RWD six-speed family was designed with four variants, the built in modularity requires only two different basic diameters of parts and “flexing” on part width (length) depending on specific torque requirements. This built in modular design enables a tremendous amount of part sharing and part scaling. Modularity minimizes engineering resources, improves investment and piece cost, speed to market and allows for a wide bandwidth of vehicle and engine applications.

An integrated approach to modeling end of useful life of an automatic transmission fluid (ATF) has been developed. The flexible fluid life model allows either predictive or real-time calculations of the end of useful fluid life under different transmission design strategies and customer driver behaviors as reflected in operating temperatures, shift characteristics, fluid volume and fluid distribution throughout the transmission. An estimation of remaining useful fluid life is monitored using two metrics, namely bulk oxidation, as a general indicator of fluid quality, and frictional degradation, as an indicator of shift quality. As operating conditions increase in severity, ATF is subjected to conditions that may shorten its life. Using the developed technique, ATF useful life can be better predicted.

Since the mid-1990's, original equipment manufacturers (OEMs) of automobiles have been implementing torque converter clutches in automatic transmissions with a continuous, controlled slip mode, in order to improve the fuel economy of their vehicles. These Continuously Slipping Torque Converter Clutches (CSTCCs) are prone to an undesirable phenomenon commonly called shudder. This phenomenon has been attributed to specific shapes or slopes in the friction coefficient versus sliding speed curve of the fluid/clutch interface. Here, a method is explained that was developed to be able to screen fluids for shudder tendency, both in fresh and used states. Also included is a description of the reason for implementing CSTCCs, some background on shudder, and supporting data showing how the test method can distinguish between fluids that have different shudder tendencies.

Implementation of engine turnoff at idle is desirable to gain improvements in vehicle fuel economy. There are a number of alternatives for implementation of the restarting function, including the existing cranking motor, a 12V or 36V belt-starter, a crankshaft integrated-starter-generator (ISG), and other, more complex hybrid powertrain architectures. Of these options, the 12V belt-alternator-starter (BAS) offers strong potential for fast, quiet starting at a lower system cost and complexity than higher-power 36V alternatives. Two challenges are 1) the need to accelerate a large engine to idle speed quickly, and 2) dynamic torque control during the start for smoothness. In the absence of a higher power electrical machine to accomplish these tasks, combustion-assisted starting has been studied as a potential method of aiding a 12V accessory drive belt-alternator-starter in the starting process on larger engines.

General Motors (GM) currently uses about 1000 different seals for manufacturing all of its automatic transmissions worldwide. In order to assure that these seals function correctly in service, a method of measuring seal performance with service fill automatic transmission fluids (ATFs) has to be specified. Along with this measure, a pass/fail criterion for the evaluation of seal performance is implemented. Due to the large number of seals that are utilized, it would be impractical to test each one with every fluid that is submitted for GM DEXRON®-III and/or Allison C4 certification. It is also very difficult to use production seals in testing, due to the irregular shapes and material combinations, which make measurement of the seal material properties difficult. Therefore, a revised test will be included in the DEXRON®-III and Allison C4 service fill specifications to evaluate the compatibility of service fill ATFs with a representative sample of seal materials used in production.

The rheological behavior of automatic transmission fluids (ATF) ranges from moderately shear-thinning to Newtonian. However, no commercially available ATFs are known to display shear-thickening behavior. A theoretical investigation was performed to determine if any advantages could be derived from the use of shear-thickening ATF in automatic transmission components and subsystems. A series of theoretical shear-thickening, shear-thinning, and Newtonian fluids were modeled by a power law function and compared to a reference shear-thinning ATF in simplified representations of transmission components and subsystem geometries. The results indicate that a shear-thickening ATF with zero shear viscosity, infinite shear viscosity, and power of 417 mPa-s, 6.23 mPa-s, and 1.03(dimensionless), respectively, displays optimized behavior with respect to the reference shear-thinning ATF.

General Motors plans to introduce a hybrid version of its popular light-duty full-size (Silverado/Sierra) pickup truck. Primary emphasis of the hybrid propulsion system for this truck is on maximizing fuel savings at minimum cost and without sacrificing performance or driveability. The hybrid powertrain features a novel, compact method of integrating an electric motor/generator between the largely unchanged engine and transmission. Extensive energy analysis and several unique control strategies are being used to meet the vehicle's performance, driveability, and emissions objectives. This paper will focus mainly on the powertrain integration and on powertrain controls for the hybrid propulsion system.

General Motors plans to introduce a hybrid version of its popular light-duty full-size (Silverado/Sierra) pickup truck. The program imperative of minimal vehicle architecture change drove a highly integrated powertrain solution. The hybrid powertrain features a novel, compact method of integrating an electric motor/generator between the largely unchanged engine and transmission, preserving their locations. From the targeted hybrid functions, power and energy specifications are derived. Specific design aspects and performance examples relating to the motor/generator packaging, torque converter, and overall vehicle driveabiltiy are discussed.

Rheological properties of automatic transmission fluids (ATFs) are typically characterized by their kinematic (ASTM D 445) and Brookfield (ASTM D 2983) viscosities. However, ATFs contain polymeric viscosity modifiers, which often result in non-Newtonian fluid behavior as the polymers align and stretch under the shear stresses experienced in automatic transmissions. Therefore, the standard rheological tests, which are normally run under low shear stresses, may not adequately characterize an ATF's flow properties under the operating conditions of the automatic transmission. This study was designed to characterize the rheological properties of ATFs containing different amounts of viscosity modifiers, different base oil types and different levels of permanent shear stability under the shear and temperature conditions which exist in automatic transmissions.

Active Hall Effect Sensors are used in numerous automotive applications where direction, position, and speed sensing capabilities are required. The primary usage of these devices is in the areas of engine and transmission controls as well as ABS speed monitoring systems. To reliably employ these sensors in such applications requires a thorough understanding of the device electronics and how this component interprets the magnetic fields produced by a ferromagnetic target. The traditional methods involving the construction and test of prototype sensors and targets have been costly, time consuming, and rarely resulted in a robust design. To resolve this problem General Motors Powertrain and Ansoft Corporation have jointly developed the capability to accurately model active Hall Effect Sensors.

Using standard industry tests, the oxidation stability of General Motors current factory-fill automatic transmission fluid (ATF) was compared to that of a proposed factory-fill ATF to be introduced for the 1995 Model Year. Full-scale transmission tests and Aluminum Beaker Oxidation Tests run at various temperatures showed that a proposed factory-fill fluid is substantially more resistant to oxidation than the current factory-fill ATF. Using Total Acid Number increase (Δ-TAN) as the measure of oxidation, a minimum of 35% improvement was obtained with a proposed factory fill. This improvement at least doubles the time to “perceived fluid failure” (Δ-TAN = 2.5).