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Increasing compression ratio (CR) is one of the most fundamental ways to improve engine efficiency, but the CR of practical spark ignition engines is limited by knock and spark retard at high loads. A variable CR mechanism could improve efficiency by using higher CR at low loads, and lower CR (with less spark retard) at high loads. This paper quantifies the potential efficiency benefits of applying variable CR to a modern downsized, boosted gasoline engine. Load sweeps were conducted experimentally on a multi-cylinder gasoline turbocharged direct injection (GTDI) engine at several CRs. Experimental results were compared to efficiency versus CR correlations from the literature and were used to estimate the fuel economy benefits of 2-step and continuously variable CR concepts on several engine/vehicle combinations, for various drive cycles.

Wet clutch packs are widely used in today’s automatic transmission systems for gear-ratio shifting. The frictional interfaces between the clutch plates are continuously lubricated with transmission fluid for both thermal and friction management. The open clutch packs shear transmission fluid across the rotating plates, contributing to measurable energy losses. A typical multi-speed transmission includes as many as 5 clutch packs. Of those, two to three clutches are open at any time during a typical drive cycle, presenting an opportunity for fuel economy gain. However, reducing open clutch drag is very challenging, while meeting cooling requirements and shift quality targets. In practice, clutch design adjustment is performed through trial-and-error evaluation of hardware on a test bench. The use of analytical methodologies is limited for optimizing clutch design features due to the complexity of fluid-structure interactions under rotating conditions.

A new generation of a planetary-gear-based automatic transmission system is designed with an increasing number of ratio steps. It requires synchronous operation of one or more wet clutches, to achieve a complex shift event. A missed synchronization results in drive torque disturbance which may be perceived by vehicle occupants as an undesirable shift shock. Accurate knowledge of clutch behaviors in an actual vehicle environment is indispensable for achieving precise clutch controls and reducing shift calibration effort. Wet clutches are routinely evaluated on an industry-standard SAE#2 tester during the clutch design process. While it is a valuable tool for screening relative frictional behaviors, clutch engagement data from a SAE#2 tester do not correlate well with vehicle shift behaviors due to the limited reproducibility of realistic slip, actuator force profiles, and lubrication conditions.

An analytic model of powertrain efficiency on a drive cycle was developed and evaluated using hundreds of cars and trucks from the US EPA ‘Test Car Lists’. The efficiency properties of naturally aspirated and downsized turbocharged engines were compared for vehicles with automatic transmissions on the US cycles. The resulting powertrain cycle efficiency model is proportional to the powertrain marginal energy conversion efficiency K, which is also its upper limit. It decreases as the powertrain matching parameters, the displacement-to-mass ratio (D/M) and the gearing ratio (n/V), increase. The inputs are the powertrain fuel consumption, the vehicle road load, and the cycle work requirement. They could be modeled simply with only minor approximations through the use of absolute inputs and outputs, and systematic use of scaling. On the Highway test, conventional automatic transmission vehicles of moderate performance achieve between 25% and 30% powertrain efficiency.

A step-ratio automatic transmission alters torque paths for gearshifting through engagement and disengagement of clutches. It enables torque sources to run efficiently while meeting driver demand. Yet, clutch thermal energy during gearshifting is one of the contributors to the overall fuel loss. In order to optimize drivetrain control strategy, including the frequency of shifts, it is important to understand the cost of shift itself. In a power-on upshift, clutch thermal energy is primarily dissipated during inertia phase. The interaction between multiple clutches, coupled with input torque truncation, makes the decomposition of overall energy loss less obvious. This paper systematically presents the mathematical analysis of clutch thermal energy during the inertia phase of a typical single-transition gearshift. In practice, a quicker shift is generally favored, partly because the amount of energy loss is considered smaller.

Progress in the design and application of the magneto-elastic torque sensor to automotive drivetrain systems has taken the technology from the concept level to the point where it is considered production feasible. The latest generation of the sensors shows promising results regarding both the capabilities and applications to powertrain controls. Sensor designs, electronics and packaging layout are maturing. Well-defined component specifications and requirements are becoming available. The sensor utilities for real-time shift analysis and friction element control are established through vehicle-level investigation to demonstrate the production feasibility of the technology for transmission torque sensing.

The drive cycle average powertrain efficiency of current US vehicles is studied by applying a first principles model to the EPA Test Car List database. The largest group of vehicles has naturally aspirated engines and six speed planetary automatic transmissions, and defines the base technology level. For this group the best cycle average powertrain efficiency is independent of vehicle size and is achieved by the lowest power-to-weight vehicles. For all segments of the EPA test, the fuel required per unit of vehicle work (the inverse of powertrain efficiency), is found to increase linearly with a basic powertrain matching parameter. The parameter is (D/M)(n/V), where D is engine displacement, M vehicle mass, and (n/V) the top gear engine speed over the vehicle speed. The fuel consumption penalties in the City segments due to powertrain warm-up, aftertreatment warm-up, stop-and-go operation, and power-off operation are estimated.

Vehicle certification data are used to study the effectiveness of the major powertrain technologies used by car manufacturers to reduce fuel consumption. Methods for differentiating vehicles effectively were developed by leveraging theoretical models of engine and vehicle fuel consumption. One approach normalizes by displacement per unit distance, which puts both fuel used and vehicle work in mean effective pressure units, and is useful when comparing engine technologies. The other normalizes by engine rated power, a customer-relevant output metric. The normalized work/power is proportional to weight/power, the most fundamental performance metric. Certification data for 2016 and 2017 U.S. vehicles with different powertrain technologies are compared to baseline vehicles with port fuel injection (PFI) naturally aspirated engines and six-speed automatic transmissions.

Generally within engineering design, the current emphasis is on biasing the development process towards increased virtual prototyping and reduced “real” prototyping. Therefore there is a requirement for more CAE based automated optimisation, Design of Experiments and Design for Six Sigma. The main requirements for these processes are that the model being analysed is parametric and that the solution time is short. Prediction of gear whine behaviour in automatic transmissions is a particularly complex problem where the conventional FEA approach precludes the rapid assessment of “what if?” scenarios due to the slow model building and solution times. This paper will present an alternative approach, which is a fully parametric functionality-based model, including the effects of and interactions between all components in the transmission. In particular the time-varying load sharing and misalignment in the planetary gears will be analysed in detail.

The effect of friction modifiers on the low-speed frictional properties of automatic transmission fluids (ATFs) was investigated by scanning force microscopy (SFM). A clutch lining material was covered by a droplet of test ATF, and a steel tip was scanned over the sample. The scanning speeds were varied from 0.13 to 8.56 mm /sec, and the frictional force was deduced from the torsion of the SFM cantilever. A reduction in dynamic friction due to the addition of the friction modifier was clearly observed over the entire speed range. This indicates that the boundary lubrication mechanism is dominant under this condition, and therefore surface-active friction modifiers can effectively improve the frictional characteristics. The friction reduction was more pronounced at lower sliding speeds. Thus addition of friction modifiers produced a more positive slope in the μ-ν (friction vs. sliding speed) plots, and would contribute to make wet clutch systems less susceptible to shudder vibrations.

Automatic transmissions equipped with Modulated Torque Converter Clutches (MTCC) require an effective combination of automatic transmission fluid (ATF) - friction material in order to maintain frictional integrity. However, in this study, thermal analysis has shown that ATFs can interact chemically with a friction material used in the MTCC under service conditions, potentially affecting the frictional characteristics. A technique was developed to evaluate friction material degradation. The results of this study showed that the friction material my be chemically altered by static aging in certain ATFs at elevated temperatures. The statically aged friction material samples exhibited thermal analysis signatures which were similar to identical material degraded during dynamometer and fleet vehicle tests. These vehicle tests resulted in deterioration in friction characteristics and experienced shudder.

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.

As part of the International Lubricant Standardization and Approval Committee's (ILSAC) goal of developing a global automatic transmission fluid (ATF) specification, members have been evaluating test methods that are currently used by various automotive manufacturers for qualifying ATF for use in their respective transmissions. This report deals with comparing test methods used for determining torque capacity in friction systems (shifting clutches). Three test methods were compared, the Plate Friction Test from the General Motors DEXRON®-III Specification, the Friction Durability Test from the Ford MERCON® Specification, and the Japanese Automotive Manufacturers Association Friction Test - JASO Method 348-95. Eight different fluids were evaluated. Friction parameters used in the comparison were breakaway friction, dynamic friction torque at midpoint and the end of engagement, and the ratio of end torque to midpoint torque.

Imbalances of an automatic transmission have a direct impact on NVH. To measure those imbalances, one needs to overcome two hurdles: (1) Phase uncertainty of individual component imbalance due to clutch indexing; (2) Imbalance separation of transmission from other systems, such as driveshaft and engine crank, connected to the transmission. To attack those issues, an algorithm has been developed which can deal with the phase issue caused by clutch engagement, and separate transmission imbalance at the system level without individually measuring other system imbalances. The method has been verified with several vehicle programs in both vehicle and dynamometer tests.

Ford recently introduced an industry first Modular Hybrid Transmission (MHT) in the Model U concept vehicle at the 2003 North American International Auto Show. The MHT is a full function hybrid system (i.e. capable of electric drive) that utilizes a modular approach to leverage high volume conventional driveline components to create a lower-cost hybrid system [1]. In the MHT, the torque converter of a conventional automatic transmission is removed and in its place is packaged a single high voltage electric machine and an engine disconnect clutch. Advanced controls are used to enable hybrid functions. A critical element in the development of the MHT is the ability to replicate the functions of the torque converter without compromise to the vehicle drivability. In this paper, the control of four transmission functions in the MHT will be discussed: 1) transmission engagement, 2) vehicle launch, 3) power-on up-shift and 4) coast downshift.

There is continued demand for cost and weight reduction as well as for improved process control in the production of P/M planetary carriers. After a brief review of sinter brazing as the primary process for the joining of P/M carrier components, capacitor discharge (CD) welding is introduced as a promising alternative. The processing of carriers by CD welding is described and the possibilities of advanced process control offered by this technology are reviewed. Subsequently, the micro-structure and mechanical properties of CD welded carriers are analyzed. Actual application validation data for ultimate and torsional fatigue as well as ultimate axial loading are presented for a two piece carrier produced from a P/M body and a stamped sheet metal spider as launched in the Ford Motor Company 5R55 transmission. Finally the processes of sinter-brazing and CD welding are compared, specifically the mechanical performance and manufacturing costs.

Ratcheting Devices are often used in automatic transmissions to provide a unidirectional power flow to achieve specific gear functions. These devices consist of two members that rotate relative to each other and a locking mechanism between these two rotating parts. In order to meet certain gearshift needs, the ratcheting device performs a combined overrun and engagement function. In both modes the components experience high-speed rotation and are subjected to significant impact forces. The high impact forces between the components may cause damage on the parts and the device may fail to function as intended. It is important to understand the dynamic behaviors of these ratcheting devices and the key design factors affecting their performances under various operating conditions. Vehicle tests and/or laboratory tests are often conducted to investigate the dynamic performance of these devices.

Conventional automatic transmissions (AT) use wet friction components, such as plate clutches and band brakes to engage gears or change speed ratios during vehicle operation. The quality of engagements and ratio changes depends greatly on the frictional characteristics of the friction components, which are typically evaluated with industry standard SAE #2 test machines. These inertia absorption-type dynamometer test stands energize a friction component with prescribed level of apply force and load of inertia flywheels rotating at a specified speed until the friction elements are brought to a stop. During the slip, apply force, engagement torque, and rotating speed are digitally recorded for visual evaluation of dynamic engagement behavior. The shape of the dynamic torque curve during the engagement is known to affect AT shift quality. When many curves are generated, it becomes intractable to quantify torque curve shape differences.

The International Lubricant Standardization and Approval Committee (ILSAC) ATF subcommittee members have compared the two oxidation bench test methods, Aluminum Beaker Oxidation Test (ABOT) and Indiana Stirring Oxidation Stability Test (ISOT), using a number of factory-fill and service-fill ATFs obtained in Japan and in the US. In many cases, the ATFs were more severely oxidized after the ABOT procedure than after the same duration of the ISOT procedure. The relative severity of these two tests was influenced by the composition of the ATFs. The bench test oxidation data were compared with the transmission and the vehicle oxidation test data.

In a step-ratio automatic transmission system, wet friction components are widely utilized to alter planetary gear configurations for automatic shifting. Thus, their engagement characteristics have a direct impact on shift quality or drivetrain NVH. A vehicle design process can benefit from predictive friction component models that allow analytical shift quality evaluation, leading to reduced development time. However, their practical application to shift analysis is seldom discussed in the literature although there are many references available for friction component modeling itself. A successful shift analysis requires a balance of model complexity, predictability and computational efficiency for a given objective. This paper reviews three types of friction component models found in today's open literature, namely, first principle based, algebraic, and empirical models. Model structure, assumptions, computational efficiency, and utilities are discussed.