Transmissions
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WORKING PAPER 2016-17 Transmissions Authors: Aaron Isenstadt and John German (ICCT); Mark Burd and Ed Greif (Dana Corporation) Date: 29 August 2016 Keywords: Passenger vehicles, advanced technologies, fuel-efficiency, technology innovation, transmission, CVT, DCT, automatics Introduction four to five years ago.2 The ICCT is col- in the rule and how they impact laborating with automotive suppliers on cost and benefits; In 2012, the U.S. Environmental a series of working papers evaluating Protection Agency (EPA) and the • Customer-acceptance issues, technology progress and new develop- Department of Transportation’s National such as real-world fuel economy, ments in engines, transmissions, vehicle Highway Traffic Safety Administration performance, drivability, reliability, body design and lightweighting, and (NHTSA) finalized a joint rule estab- and safety. other measures that have occurred lishing new greenhouse gas and fuel since then. Each paper will evaluate: This paper provides an analysis of economy standards for vehicles.1 The transmission technology development standards apply to new passenger cars • How the current rate of progress and trends. It is a joint collaboration and light-duty trucks, model years 2012 (costs, benefits, and market pen- between ICCT, BorgWarner, Dana, the through 2025. A mid-term review of the etration) compares to projections ITB Group, and FEV. The paper relies standards will be conducted in 2017. in the rule; on data from publicly available sources Assuming the fleet mix remains • Recent technology develop- and data and information from the par- unchanged, the standards require ments that were not considered ticipating automotive suppliers. these vehicles to meet an estimated Table 1. Transmission technology compared to EPA/NHTSA 2017-2025 rulemaking. combined average fuel economy of Rapid improvements in continuously variable transmissions and conventional 34.1 miles per gallon (mpg) in model automatics have compensated for slower than projected growth in the use of dual- year 2016, and 49.1 mpg in model clutch automated manual transmissions. year 2025. The standards require an Behind RM average improvement in fuel economy of about 4.1 percent per year. On schedule Manufacturing Efficiency Market Ahead of RM cost benefits penetration The technology assessments conducted by the agencies to inform Dual-clutch transmissions the 2017–2025 rule were conducted Conventional Automatics Continuously variable transmissions 2 U.S. EPA & NHTSA. Joint Technical Support Document: Final Rulemaking for 2017-2025 BACKGROUND Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average As recently as 2007, 4- and 5-speed Fuel Economy Standards. Aug. 2012. Web. automatic transmissions (ATs) 1 US. EPA & NHTSA. EPA/NHTSA Final June 2016. https://www3.epa.gov/otaq/ dominated the vehicle market (>75% Rulemaking to Establish 2017 and Later climate/regs-light-duty.htm#2017-2025 U.S. Model Years Light-Duty Vehicle Greenhouse NHTSA. Corporate Average Fuel Economy share). Lock-up torque converters had Gas Emissions and Corporate Average Fuel for MY 2017-MY 2025 Passenger Cars and been widely used for over 20 years, but Economy Standards. Oct. 2012. Web. Jun. Light Trucks: Final Regulatory Impact otherwise transmission efficiency had 2016. https://www3.epa.gov/otaq/climate/ Analysis. Aug 2012. Accessed June 2016. regs-light-duty.htm#2017-2025 http://www.nhtsa.gov/fuel-economy not improved significantly for decades. Acknowledgements: Thanks to Keith Martin from BorgWarner Transmission Systems, Sean Osborne and Joel Kopinsky from the ITB Group and Greg Kolwich and Kiran Govindswamy from FEV for their input and reviews. © INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION, 2016 WWW.THEICCT.ORG TRANSMISSIONS These pre-2007 4- and 5-speed ATs transmission, and offers the potential thus maximizes engine efficiency. The were significantly less efficient than for smooth/quick shifts without efficient engine operation can more manual transmissions, due to losses torque interruption. One issue with than offset the inefficiencies of the in the torque converter and in the the DCT is launch performance, as continuously variable transmission, hydraulic systems inside the transmis- the vehicle must start moving while especially during low-speed urban sion. Since 2007, advances in torque engaging a single clutch. Some manu- operation, and so produce overall converter lockup and hydraulics facturers use a wet hydraulic clutch to fuel consumption reductions. CVTs have improved so much that modern solve this problem, although the need were introduced in small volumes in automatics have significantly reduced for continuous lubrication from the the United States in 1989. However, the gap in efficiency—in some areas hydraulic system reduces efficiency the early designs suffered from belt eliminating it entirely. somewhat. By contrast, dry DCTs use limitations, which, in addition to high an accumulator and high-pressure friction losses, restricted torque to A major breakthrough in transmis- hydraulics, which are used to shut off such an extent that the transmission sion design was the development the hydraulic system. could only be used on smaller cars. of the Lepelletier gear set system. Recent improvements in CVT controls This system enables additional gear The other major transmission type and system design have reduced combinations without increasing the is the continuously variable trans- losses and expanded the torque number of clutches and gearsets. mission (CVT). Conventionally, this capacity and ratio coverage, making Six-speed Lepelletier automatics are design uses a belt or chain to connect the CVT another strong transmission usually slightly cheaper to manufac- two pairs of concentric cones, with competitor even for larger vehicles. turer than 4-speed ATs,3 and much infinitely variable ratios between cheaper than previously-designed the maximum and minimum points. Technology history 6-speed ATs. The additional number The efficiency of the transmission is of gear ratios and increased ratio reduced by friction losses related to According to the EPA fuel economy 4 spans improves efficiency and perfor- clamping forces on the belt/chain (as trends report, manufacturers have mance by: well as high-pressure hydraulics), but been rapidly increasing the number of the system allows the engine to always transmission gear ratios. Automatic • enabling the engine to operate run at optimal speed/load points and transmissions (AT) considered by in more efficient regions of the EPA in this report were divided into speed/load curve; 70% • allowing more torque multipli- 4-5 speed cation for vehicle launch, for 6 speed 60% better performance and engine downsizing; 50% • allowing lower engine rpm in top gear, for better efficiency and less engine noise. 40% Another important development in 30% the last ten years is the dual-clutch transmission (DCT). Introduced in the European Union in 2003 on the 20% Volkswagen DQ250, a DCT is essen- 8+ speed tially a manual (layshaft) transmis- 10% CVT non-hybrid sion with the odd-numbered gears 7 speed on one shaft and the even-numbered 0% gears on a second shaft. Each shaft has its own clutch, and the gear on one shaft is disengaged at the same Figure 1. Historic market share of transmissions by number of ratios. (Source: U.S. EPA. time the gear on the other shaft is Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy engaged (see Figure 4). This design Trends: 1975 Through 2015. Dec 2015.) approaches the efficiency of a manual 4 US. EPA. Light-Duty Automotive 3 FEV. 2030 Passenger Car and Light Technology, Carbon Dioxide Emissions, and Commercial Vehicle Powertrain Technology Fuel Economy Trends: 1975 Through 2015. Analysis. Report commissioned by ICCT. Dec 2015. https://www3.epa.gov/otaq/ Forthcoming. fetrends-complete.htm 2 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17 TRANSMISSIONS Table 2. U.S. market penetration trends (cars and light trucks). (Source: U.S. EPA. Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2015.) 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015* 4–5 speed 95.7% 93.3% 86.9% 76.6% 70.7% 63.4% 48.1% 32.9% 26.3% 18.2% 10.0% 6.1% 6 speed 3% 4.1% 8.8% 14.4% 19.4% 24.5% 38.1% 52.3% 56.3% 60.1% 58.4% 57.2% 7 speed 0.2% 0.2% 1.4% 1.5% 1.8% 2.5% 2.7% 3.1% 2.8% 2.8% 3.3% 2.7% 8+ speed — — — 0.2% 0.2% 0.1% 0.2% 1.7% 2.6% 4.1% 9.5% 13.2% CVT non-hybrid 0.7% 1.3% 1.4% 5.1% 5.5% 7.3% 7.2% 8.0% 9.2% 11.8% 16.6% 18.2% CVT hybrid 0.4% 1.0% 1.5% 2.1% 2.4% 2.1% 3.8% 2.0% 2.7% 2.9% 2.3% 2.5% Manual 6.8% 6.2% 6.5% 5.6% 5.2% 4.8% 3.8% 3.2% 3.6% 3.5% 2.8% 3.6% AT w/ lockup 91.8% 91.5% 90.6% 87.1% 86.8% 85.6% 84.1% 86.5% 83.4% 80.4% 76.7% 74.0% AT w/o lockup 0.3% 0.1% 0.0% 0.0% 0.2% 0.2% 1.2% 0.3% 1.1% 1.4% 1.6% 1.7% * 2015 values are preliminary estimates. two groups: ATs with lockup torque report.) Assuming it is correct that adoption of CVTs in conventional converter (lockup bypasses the torque all 6+ speed ATs without lockup powertrains (i.e., non-hybrids). converter under certain conditions referenced in the trends report are to improve fuel economy) and ATs DCTs, then DCTs are about ~2% of the Manual transmissions (5+ gears) without lockup. Chrysler introduced transmission market in 2015. have remained between 3% and the first lockup torque converter in 4% of the market since 2010. the 1980s. By 2000, all automatics CVTs have seen a huge increase in Although the number of gear ratios had lockup capabilities.