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Technical Paper

Determining Physical Properties for Rotating Components Using a Free-Free Torsional FRF Technique

2011-05-17
2011-01-1663
This paper presents a test methodology to determine the physical properties of stiffness and damping for powertrain rotating components using a free-free torsional frequency response measurement. The test methodology utilizes free-free boundary conditions and traditional modal test techniques applied to symmetric rotating components with substantially large bounding masses of known inertia. A modal test on the rotating component is executed by mounting accelerometers on opposing tangential bosses in the same direction on each of the inertial masses and impacting one of the bosses with a modal hammer to acquire frequency response functions (FRF's). Physical properties are then extracted from the FRF's using fundamental vibration relationships for an assumed two degree of freedom system. Stiffness and damping values for a variety of hollow tube carbon fiber drive shafts and a comparable steel-aluminum shaft are reported using the methodology presented.
Technical Paper

Gen2 GF6 Transmission Hardware and Controls Updates

2011-04-12
2011-01-1428
In an effort to increase fuel economy and improve shift quality - the GF6 family of General Motors transmissions has been analyzed for potential enhancements. The focus of this analysis was to improve fuel economy, while increasing downshift responsiveness, and manual mode sport delays. This paper describes a variety of the hardware philosophy changes, and control methods which have contributed to the next generation of GM clutch-to-clutch 6-speed transmissions. These changes to hardware and controls have led to a composite fuel economy improvement of 4.5% with no changes to shift or torque-converter scheduling. In addition, the downshift responsiveness has been significantly improved to reduce delay times by approximately 50% while virtually eliminating the dependency on engine torque reductions - ultimately allowing for stacked downshifts to progress with minimal, if any, time between shifts. Additionally, “tap shift” delays have been significantly decreased to levels near 150 ms.
Technical Paper

Effects of Base Stocks on Lubricant Aeration

2011-04-12
2011-01-1210
Aeration properties of lubricants is an increasing concern as the design of powertrain components, specifically transmissions, continue to become more compact leading to smaller sumps and higher pressure requirements. Although good design practices are the most important factors in mitigating the aeration level of the fluid, the fluid properties themselves are also a contributing factor. This paper investigates the aeration properties of specific base oils commonly used to formulate modern transmission fluids using the General Motors Company Aeration Bench Test found in GMN10060. The test matrix includes thirteen different fluids representing a cross-section of base oil types, manufacturers, and viscosity grades. Per the procedure found in GMN10060, the bench test measures the aeration time, de-aeration time, and percent maximum aeration of the fluid at three temperatures, 60°C, 90°C, and 120°C. In the end, the results are compared with four commercially available transmission fluids.
Technical Paper

Seal Testing in Aerated Lubricants

2011-04-12
2011-01-1209
Typical seal immersion testing in lubricants does not aerate the lubricant as typically seen during normal operation of a transmission or axle. This paper will discuss a new test apparatus that introduces air into transmission fluids and gear oils during seal immersion testing. The seal materials selected for the testing are from current vehicle applications from several different material families. The test results compare the standard properties: change in tensile strength, elongation, hardness, and volume swell. Several tests were completed to investigate and refine the new testing method for seal compatibility testing with transmission fluids and gear oils. Initial results from the first data sets indicate that lubricant aeration helps improve test repeatability. In addition to aeration, the test results explore appropriate fluid immersion temperature for repeatability and appropriate test duration.
Technical Paper

Transmission Algorithm Development using System Simulation (Virtual Vehicle)

2011-04-12
2011-01-1233
Due to the multitude of external design constraints, such as increasing fuel economy standards, and the increasing number of global vehicle programs, developers of automotive transmission controls have had to cope with increasing levels of system complexity while at the same time being forced by the marketplace to improve system quality, reduce development costs, and improve time to market. General Motors Powertrain (GMPT) chose to meet these challenges through General Motors Company's Road-to-Lab-to-Math (RLM) strategy, particularly the Math-based method of a virtual vehicle simulation environment called System Simulation. The use of System Simulation to develop transmission control algorithms has enabled GMPT to improve product quality and reduce development times and costs associated with the dependence on physical prototypes. Additionally, System Simulation has facilitated the reuse of GMPT controls development assets, improving overall controls development efficiency.
Technical Paper

Lubricant Flow and Temperature Prediction in a Planetary Gearset

2011-04-12
2011-01-1235
This study introduces a method to examine the flow path of the lubricant inside a planetary gearset of an automatic transmission. A typical planetary gearbox has several load bearing elements which are in relative sliding motion to each other which causes heat to be released. The major sources of friction as well as heat are the meshing teeth between gears (sun/planet, planet/ring), thrust washers, thrust bearings and needle bearings. The lubricant performs the vital function of both lubricating these sliding interfaces and cooling these sources of heat, thereby preventing failure of the gearbox. The exact flow path that the lubricant takes inside a planetary gearset is unknown. Since the gearset is primarily splash lubricated, it is also not known how much lubricant reaches critical areas. A method is developed using computational fluid dynamic techniques to enable comprehensive flow and thermal analysis and visualization of an automatic transmission assembly.
Technical Paper

A Dual Clutch Torque Converter for Dual Input Shaft Transmissions

2013-04-08
2013-01-0232
This paper presents an alternative launch device for layshaft dual clutch transmissions (DCT's). The launch device incorporates a hydrodynamic torque converter, a lockup clutch with controlled slip capability and two wet multi-plate clutches to engage the input shafts of the transmission. The device is intended to overcome the deficiencies associated with using conventional dry or wet launch clutches in DCT's, such as limited torque capacity at vehicle launch, clutch thermal capacity and cooling, launch shudder, lubricant quality and requirement for interval oil changes. The alternative device enhances drive quality and performance at vehicle launch and adds the capability of controlled capacity slip to attenuate gear rattle without early downshifting. Parasitic torque loss will increase but is shown not to drastically influence fuel consumption compared to a dry clutch system, however synchronizer engagement can become a concern at cold operating temperatures.
Technical Paper

Automatic Transmission Rotational Inertia Effect on Shift Quality

2011-04-12
2011-01-0393
The achievable shift quality of a modern automatic transmission may be greatly affected by the equivalent rotational inertia of the gearbox and driveline components. New, more mass- and packaging-efficient higher number of gear powerflows are being developed. These new architectures often result in more components being attached to a given rotational node. The rotational speed multiplication of the components must be considered when determining their inertial torque contribution to a given speed change event. An example of this multiplication effect is presented, with a discussion of the resulting impact to shift quality disturbance. Opportunities to address the negative aspects of the higher inertial torque contribution to transmission output shaft disturbance are discussed. Coordination of engine torque control and clutch torque control is presented as a viable strategy to improve shift quality.
Technical Paper

Relative Torque Estimation on Transmission Output Shaft with Speed Sensors

2011-04-12
2011-01-0392
Automobile drivers/passengers perceive automatic transmission (AT) shift quality through the torque transferred by transmission output shaft, so that torque regulation is critical in transmission shift control and etc. However, since a physical torque sensor is expensive, current shift control in AT is usually achieved by tracking a turbine speed profile due to the lack of the transmission output torque information. A direct torque feedback has long been desired for transmission shift control enhancement. This paper addresses a “virtual” torque sensor (VTS) algorithm that can provide an accurate estimate on the torque variation in the vehicle transmission output shaft using (existing) speed sensors. We have developed the algorithm using both the transmission output speed sensor and anti-lock braking system speed sensors. Practical solutions are provided to enhance the accuracy of the algorithm. The algorithm has been successfully implemented on both FWD and RWD vehicles.
Technical Paper

Annular Nozzle in Fixed Displacement Transmission Pump

2011-04-12
2011-01-0723
General Motor's new front wheel drive six speed 6T40 automatic transmission benefits from patented technology to control high speed pump cavitation that is innovative yet cost effective. An annular nozzle is created with careful pump inlet design by integrating a conical section in the filter neck to create a jet pump to prevent high speed cavitation for almost no additional cost. Excess oil from a fixed displacement pump is used to achieve an effective increase in pressure at the inlet of the rotating group during high speed operation. Control of high speed cavitation reduces pump noise and improves line pressure control stability.
Technical Paper

Controls Development for Clutch-Assisted Engine Starts in a Parallel Hybrid Electric Vehicle

2011-04-12
2011-01-0870
In a parallel hybrid electric vehicle, higher fuel economy gains are typically achieved if significant electric drive (or engine-off) operation is possible, shifting the engine operating schedule so that it only runs at medium to high load for best efficiency. To enable efficient engine-off driving, a typical configuration will have a disconnect clutch between the engine and the rest of the driveline. In some configurations, when engine-on operation is requested the disconnect clutch is applied in conjunction with the traction motor/generator to crank the engine (i.e., a flying engine start). In this paper we describe the development of a control system for a flying engine start using an engine disconnect clutch. The clutch is located between the engine and electric motor, which is connected to the input of a multispeed transmission. We first describe an initial control algorithm evaluation using a driveline model.
Technical Paper

Effect of Flow Forces on a Flow Control Variable Force Solenoid

2011-04-12
2011-01-0394
A system level analysis was carried out on the effect of flow forces on a flow control variable force solenoid (VFS) used in automatic transmissions. Classic flow force model was reviewed as a function of the pressure difference and the solenoid current. A force balance analysis was conducted on the spool valve in the VFS, in order to study the relationship among the control current, flow forces, spring forces, and flow area. Flow bench testing was used to characterize a specific flow control VFS by both the pressure drop and solenoid current, in forward and reverse flow directions. The behavior of flow control VFS valve is significantly affected by flow forces. A sub-system level model was thus created to predict the steady-state and dynamic behavior of the flow VFS valve, which can be used in a transmission system level analysis. The modeling results were compared against experimental data to show the validity of the methodology.
Technical Paper

Model Based Torque Converter Clutch Slip Control

2011-04-12
2011-01-0396
To realize better fuel economy benefits from transmissions, car makers have started the application of torque converter clutch control in second gear and beyond, resulting in greater demand on the torque converter clutch (TCC) and its control system. This paper focuses on one aspect of the control of the torque converter clutch to improve fuel economy and faster response of the transmission. A TCC is implemented to control the slip between the pump and turbine of the torque converter, thereby increasing its energy transfer efficiency and increasing vehicle fuel economy. However, due to the non-linear nature of the torque converter fluid coupling, the slip feedback control has to be very active to handle different driver inputs and road-load conditions, such as different desired slip levels, changes in engine input torques, etc. This non-linearity requires intense calibration efforts to precisely control the clutch slip in all the scenarios.
Technical Paper

Transmission Virtual Torque Sensor - Absolute Torque Estimation

2012-04-16
2012-01-0111
Automobile drivers/passengers perceive automatic transmission (AT) shift quality through the torque transferred by the transmission. Clearly, torque regulation is important for transmission control. Unfortunately, a physical torque sensor has been too costly for production applications. With no torque measurement for feedback, controls in AT is mainly implemented in an open-loop fashion. Therefore, complicated adaptation algorithms are necessary while undesired shifts may still occur. To further simplify the controls and enhance its consistency and robustness, a direct torque feedback has long been desired in transmission control synthesis and development. A “virtual” torque sensor (VTS) algorithm has recently been developed to show a good potential in estimating relative torque along transmission output shaft using transmission output speed sensor and wheel speed sensors.
Technical Paper

Dry Dual Clutch Transmission (DCT) Thermal Model

2015-04-14
2015-01-1144
Dual Clutch Transmissions (DCT) for passenger cars are being developed by OEMs and suppliers. The driving force is the improvement in fuel economy available from manual transmissions together with the comfort of automatic transmissions. A dry clutch system (dDCT) is currently the subject of research, development, and production implementation. One of the key issues in the development of a dDCT is clutch durability. In dry clutches with current linings, above a critical temperature, the friction system starts to suffer permanent damage. In addition, the clutch friction characteristics are a function of the clutch interface temperature. Because a reliable, low-cost temperature sensor is not available for this application, the clutch control engineers rely on a good thermal model to estimate the temperature of the clutches. A thermal model was developed for dry dual clutch transmissions to predict operating temperature of both pressure and center plates during all maneuvers.
Technical Paper

J2716 SENT - Single Edge Nibble Transmission, Updates and Status

2011-04-12
2011-01-1034
The SAE J2716 SENT (Single Edge Nibble Transmission) Protocol has entered production with a number of announced products. The SENT protocol is a point-to-point scheme for transmitting signal values from a sensor to a controller. It is intended to allow for high resolution data transmission with a lower system cost than available serial data solution. The SAE SENT Task Force has developed a number of enhancements and clarifications to the original specification which are summarized in this paper.
Journal Article

Performance Characterization of a Triple Input Clutch, Layshaft Automatic Transmission Using Energy Analysis

2013-12-15
2013-01-9042
This paper details the design and operating attributes of a triple input clutch, layshaft automatic transmission (TCT) with a torque converter in a rear wheel drive passenger vehicle. The objectives of the TCT design are to reduce fuel consumption while increasing acceleration performance through the design of the gearing arrangement, shift actuation system and selection of gear ratios and progression. A systematic comparison of an 8-speed TCT design is made against a hypothetical 8-speed planetary automatic transmission (AT) with torque converter using an energy analysis model based upon empirical data and first principles of vehicle-powertrain systems. It was found that the 8-speed TCT design has the potential to provide an approximate 3% reduction in fuel consumption, a 3% decrease in 0-100 kph time and 30% reduction in energy loss relative to a comparable 8-speed planetary AT with an idealized logarithmic ratio progression.
Journal Article

The GM “Voltec” 4ET50 Multi-Mode Electric Transaxle

2011-04-12
2011-01-0887
The Chevrolet Volt is an electric vehicle (EV) that operates exclusively on battery power as long as useful energy is available in the battery pack under normal conditions. After the battery is depleted of available energy, extended-range (ER) driving uses fuel energy in an internal combustion engine (ICE), an on-board generator, and a large electric driving motor. This extended-range electric vehicle (EREV) utilizes electric energy in an automobile more effectively than a plug-in hybrid electric vehicle (PHEV), which characteristically blends electric and engine power together during driving. A specialized EREV powertrain, called the "Voltec," drives the Volt through its entire range of speed and acceleration with battery power alone, within the limit of battery energy, thereby displacing more fuel with electricity, emitting less CO₂, and producing less cold-start emissions than a PHEV operating in real-world conditions.
Journal Article

Dynamic Torque Characteristics of the Hydrodynamic Torque Converter

2011-05-17
2011-01-1540
The objective of this investigation is to characterize the torsional characteristics of the hydrodynamic torque converter. Analytical and experimental techniques are used to quantify the relationship between torsional oscillations imposed on the pump to those at the turbine as a function of frequency, operating point and design. A detailed model of the hydrodynamic torque converter based upon one-dimensional flow theory is used to establish fundamental torsional behavior independent of the downstream mechanical system. A simplified linear spring-mass-damper representation of the hydrodynamic torque converter is derived whose coefficients are proportional to pump speed for a particular design. A transmission dynamometer test cell with the capability to produce torsional oscillations was used to develop frequency response functions for various torque converters in a transmission, operating at steady state conditions.
Journal Article

Development of General Motors' eAssist Powertrain

2012-04-16
2012-01-1039
General Motors' (GM) eAssist powertrain builds upon the knowledge and experience gained from GM's first generation 36Volt Belt-Alternator-Starter (BAS) system introduced on the Saturn VUE Green Line in 2006. Extensive architectural trade studies were conducted to define the eAssist system. The resulting architecture delivers approximately three times the peak electric boost and regenerative braking capability of 36V BAS. Key elements include a water-cooled induction motor/generator (MG), an accessory drive with a coupled dual tensioner system, air cooled power electronics integrated with a 115V lithium-ion battery pack, a direct-injection 2.4 liter 4-cylinder gasoline engine, and a modified 6-speed automatic transmission. The torque-based control system of the eAssist powertrain was designed to be fully integrated with GM's corporate common electrical and controls architectures, enabling the potential for broad application across GM's global product portfolio.
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