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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
On schedule
of about 4.1 percent per year. Manufacturing Efficiency Market
Ahead of RM cost benefits penetration
The technology assessments
Dual-clutch transmissions
conducted by the agencies to inform
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. a u to m a t i c t ra n s m i ss i o n s ( ATs)
1 US. EPA & NHTSA. EPA/NHTSA Final June 2016. https://www3.epa.gov/otaq/
Rulemaking to Establish 2017 and Later climate/regs-light-duty.htm#2017-2025 U.S.
dominated the vehicle market (>75%
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
2016. https://www3.epa.gov/otaq/climate/ Analysis. Aug 2012. Accessed June 2016.
otherwise transmission efficiency had
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
spans improves efficiency and perfor- clamping forces on the belt/chain (as trends report,4 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 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
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 % o f t h e m a r ke t s i n c e 2 0 1 0.
the 1980s. By 2000, all automatics CVTs have seen a huge increase in Although the number of gear ratios
had lockup capabilities. Thus, dual market share in the last three years: an has increased in both manuals and
clutch transmissions (DCT) are likely estimated 22.6% of new, non-hybrid automatics, the rate of increase is
the main example of automatic cars and 11.8% of non-hybrid trucks higher for automatics.
transmission technology without were equipped with a CVT in 2015,
lockup reported in the trends report. about twice the market share in 2012.
Historical estimates of costs
Unfortunately, EPA does not (yet) The share of planetary gear systems
and benefits
track DCT production, so the data used in Toyota and Ford hybrid
gathered for the trends report did not vehicles, commonly referred to as The National Academy of Sciences
separate DCT into a distinct category. electric CVTs (e-CVTs), has remained (NAS) 2002 report5 estimated that
(EPA acknowledges that data incon- relatively constant between 2% and a 5-speed AT would see a 2%–3%
sistencies for DCTs represent an area 3% since 2007. Thus, all of the growth fuel consumption reduction over a
of future improvement in the trends in CVTs is attributable to increased 4-speed AT at a cost of $70–$154.
Table 3. Historical estimates of transmission technology costs and benefits as compared to the 2017-2025 rulemaking.
NAS 2002 NHTSA 2008–2011 EPA/NHTSA 2017–2025
BENEFIT COST BENEFIT COST BENEFIT COST Relative to
5-speed AT 2%–3% $70–$154 2%–3% $73–$160 1.1%–$1.6% $70 4-speed AT
6-speed AT 1%–$2% $140–280 1%–$2%, $146–291 0.7%–$0.8% ($81) 5-speed AT
8-speed AT — — 1%–$2% — 4.8%–$5.7% $47 6-speed AT
Aggressive Shift Logic 1%–3% $0–$70 1%–3% $0–$70 5.1%–7.0% $22 No ASL
DCT 3%–5% $70–$280 3%–5% $73–$291 5.7%–12.6% ($176)–$28 4-speed AT
CVT 4%–8% $140–$350 4%–8% $146–$364 6.0%–8.7% — 4-speed AT
Adv CVT 0%–2% $350–$840 0%–2% $364–874 — — CVT
NB: The agencies assumed that an 8-speed AT would only be applied to a 6-speed AT vehicle with towing requirement, all other vehicles transition
from 6-speed DCT to 8-speed DCT. DCT effectiveness and cost estimates include both wet- and dry-clutch.
5 Transportation Research Board and
National Research Council. Effectiveness
and Impact of Corporate Average Fuel
Economy (CAFE) Standards. Washington,
DC: The National Academies Press, 2002.
doi:10.17226/10172.
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 3TRANSMISSIONS
More speeds continue the trend of would be additional benefits from EPA/NHTSA 2017–2025
greater efficiency: a 6-speed AT switching to a 7-speed or 8-speed AT. PROJECTIONS: MARKET
will give 1%–2% fuel consumption PENETRATION, COSTS,
benefit over a 5-speed AT. Since The rapid increase in computational AND BENEFITS
this transmission was estimated to power in onboard computers and the
development of the Lepelletier gear In the agencies’ analyses, aggressive
cost an additional $140–$280 and
set has led to levels of transmission shift logic (ASL) and early torque
would require complex controls, NAS
technology adoption well beyond co nve r te r l o c k u p ( E TC L ) we re
2002 predicted 6-speed ATs in 2015
what was expected in 2002 and in combined in the models with
to be limited to luxury/performance
the 2008–2011 NHTSA rulemaking. automatic transmissions (“improved
vehicles. As shown in Figure 1, today
For the 2017–2025 rulemaking, the automatic transmission control”—
6-speed ATs occupy more than
agencies estimated that dual-clutch I ATC ) . T h e l o g i c b e h i n d t h a t
50% of the market, and 7-speed+
automated manual transmissions decision was that their addition
automatics and non-hybrid CVTs take
(DCTs/AMTs) and conventional ATs requires only minor physical modi-
up the next two largest shares.
with more gears and aggressive shift fications and calibration software.
CVTs were estimated to have 4%–8% logic (ASL) would both be relatively DCTs use clutches instead of torque
fuel consumption reduction (relative to inexpensive: an 8-speed AT with ASL converters, and are thus considered
a 4-speed AT) at a cost of $140–$350 would cost only $58 more than a automated manual transmissions.
in NAS 2002, but would be limited conventional 4-speed AT for a 11% As such, only ASL is applied to DCTs
by consumer acceptance issues and or more reduction in fuel consump- in the agencies’ models.
production cost. Advanced CVTs, with tion. DCTs would be even cheaper
The agencies used two levels of
toroidal friction elements or cone-and- and more efficient than comparable
ASL. Level 1, essentially downspeed-
ring, were estimated to have 0%–2% ATs. EPA/NHTSA also considered
ing, involves earlier upshift (i.e.,
benefit over a conventional (belt) CVT, consumer acceptance issues for
at l owe r r p m d u r i n g a cce l e ra -
at a cost of $350–$480; these are able DCTs and CVTs. CVT driveability
tion). Level 2 (“shift optimization”)
to handle higher torques, essentially issues were expected to continue
requires constant monitoring of all
opening up heavier vehicle classes to to plague consumers, while the
gear options and selecting the gear
CVT implementation. agencies assumed that better control
that puts the engine in the most
algorithms would mostly eliminate
For its 2008–2011 rulemaking, 6 efficient operating zone. Level 2
DCT consumer acceptance issues
NHTSA largely accepted the NAS ASL is expected to come with driver
and DCTs would replace CVTs and
2002 report estimates without acceptability dilemmas—including
most ATs by 2025.7
change, although NHTSA found there shift busyness—despite the progress
that is being made in making shifting
smoother and less noticeable (e.g.,
Table 4. Rulemaking projected market share, costs, and benefits of considered transmission technologies
2025 Direct Fuel consumption
2021 2025 Manufacturing Cost reduction Relative to
Aggressive shift logic — — $22 5.1%–7.0% no tech
Early torque converter lockup — — $20 0.4%–0.5% no tech
High efficiency gearbox 44% 95% $163 4.3%–5.7% no tech
6-speed AT 7% 0% -$11 1.7%–2.3% 4-speed AT
8-speed AT 30% 35% $47 4.8%–5.7% 6-speed AT
6-speed DCT 12% 0% -$176 (dry), -$124 (wet) 5.7%–8.1% 4-speed AT
8-speed DCT 42% 56% -$24 (dry), $28 (wet) 9.7%–12.6%* 4-speed AT
6-speed MT 5% 4% $173 2.0%–2.5% 5-speed MT
CVT — — — 6.0%–8.7%** 4-speed AT
* 8-speed DCT shows a 3.9%–4.7% improvement over 6-speed DCT, and costs $153 more.
**CVT benefit was calculated in EPA’s Lumped Parameter Model,7 and is not in the rulemaking.
7 “Lumped Parameter Model (LPM) for Light-
6 U.S. NHTSA. Light Truck Fuel Economy Duty Vehicles.” EPA OTAQ: Transportation
Standard Rulemaking, MY 2008–2011. March and Climate. Feb 23, 2016. Accessed June
2006. Web. June 2016. http://www.nhtsa. 2016. https://www3.epa.gov/otaq/climate/
gov/fuel-economy lpm.htm
4 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17TRANSMISSIONS
through more available gears). The much so that they project 6-speed today some wet-clutch DCTs have
agencies assumed that suppliers can ATs will be virtually eliminated by mostly overcome this problem with
minimize these issues by MY 2017, 2025 (although 6-speed MTs are on-demand hydraulic systems). It was
and they noted that if the problems projected to maintain a 4% market also assumed that, because there is
persist, effectiveness may be lower share in 2025). no torque converter, DCTs would
and costs may be higher. The Level likely be paired with engines with
2 ASL fuel consumption reduction is The effectiveness of a 6-speed AT is high low-speed torque or with trans-
relative to a transmission without any relative to a 4-speed AT, and incorpo- missions that have shorter gear ratios
previously implemented ASL. Level 2 rates a 7% improvement in gearbox to match the torque multiplication of
ASL is expected to improve efficiency efficiency that would accompany a a torque converter.
over Level 1 by 4%–5%, at virtually no switch to 6-speed AT. An 8-speed AT
additional cost. was applied after 6-speed AT only to Despite improvements in automatic
vehicles with towing requirements transmission and dual-clutch trans-
Locking the torque converter in (minivans, midsize and large trucks). mission efficiency, the agencies
ATs (and CVTs) eliminates slip to The reported effectiveness of an consider manual transmissions to
improve fuel economy. However, 8-speed is relative to a 6-speed. exhibit the most efficient energy
at lower vehicle speeds, torsional Relative to a 4-speed AT, an 8-speed transfer due to low internal gear
energy is harder to dampen, and it AT shows 6.5 %– 7.8% reduction in losses, minimal hydraulics, and
can create shaking or shuddering fuel consumption. actuation energy input from the
as it passes through the vehicle. driver. Of course, the driver may not
Thus, early torque converter lockup The incremental direct manufac- select the optimum gear for best fuel
(ETCL) and partial lockup require turing cost (DMC) for 8-speed ATs economy, so on the official test cycles
upgraded materials to withstand from 6-speed is $47. Note that the advanced automatic transmissions
higher loads. For the rulemaking, agencies predict a net savings of $11 usually provide better fuel economy.
“early lockup” is considered to occur in switching from the older 4-speed
at lower speeds than conventional design to a 6-speed Lepelletier AT. More gear ratios (usually overdrive
lockup strategies. As before, driver Thus, switching from a 4-speed to an gears) permit the engine to operate
acceptability (driveability, noise, 8-speed AT results in a DMC of $36. in the optimum efficiency range more
vibration and harshness) is key to often. However, proper stepping of
Vehicles with no towing requirement
successful implementation. the ratios is important to driver sat-
were modeled as having an 8-speed
isfaction and acceptability. For the
Reduction of mechanical friction DCT after a 6-speed DCT. The
2017–2025 rulemaking, the agencies
drives the improvements in gearbox effectiveness of 8-speed DCTs
assumed the number of gear ratios
efficiency. A number of strategies are over 4-speed ATs is 9.7%–12.6%,
increases from 5 to 6 in manual trans-
available for reducing gearbox friction, and 5.7%–8.1% for 6-speed DCTs
missions. For reference, 6-speed and
and all are generally applicable to over 4-speed ATs. Note that in the
5-speed manuals (MT) are estimated
any type of transmission. The fuel 2011 Ricardo study cited in the
to occupy 2.78% and 0.76% of the
consumption reduction of a high rulemaking, the effectiveness values
market, respectively, in 2015.
efficiency gearbox (HEG) compared include high efficiency gearbox.
to a baseline AT is 4.3%–5.7% (lower Independent of other improvements Lastly, neither agency felt that CVTs
bound due to 4WD trucks with an in transmission, DCTs were estimated would be competitive within the
unimproved rear axle). to have 4%–6% improvement over 2017–2025 timeframe. Nevertheless,
ATs with same number of gear ratios. t h e L u m p e d P a ra m e t e r M o d e l
Increased numbers of gears also The agencies further split DCTs into (LPM, EPA’s model for effectiveness
increase the transmission friction, wet-clutch and dry-clutch versions. of various vehicle technologies)
costs, and weight. Thus, increasing Wet-clutch DCTs have higher torque estimated CVT effectiveness as
the number of gears may see dimin- capacity since the clutches are 6.0%–8.7%, relative to a 4-speed AT.
ishing returns. Furthermore, as cooled and hydraulically actuated.
is common for many transmission Wet clutches are also useful in Figure 2 combines the historical
technologies, increased shifting can vehicles with low-torque engines, market share from the FE Trends
lead to consumer acceptance issues where cooling is required to allow Report with projected market shares
(perceived shift busyness) as well as the clutch to be slipped over a of various transmissions from the
additional losses (due to shifting). longer period of time. The agencies EPA/NHTSA 2017–2025 rulemaking
The agencies expect 8-speed ATs to assumed that the hydraulic pump for 2021 and 2025 (identified by the
be readily available beginning in MY leads to reduced efficiency compared dotted lines). As indicated by the
2017 and widespread by MY 2025, so t o d r y - c l u t c h D C Ts ( a l t h o u g h yellow region in the lower left of
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 5TRANSMISSIONS
the figure, 4 speed transmissions 100%
(both manual and automatic) have other
90% CVT
been virtually phased out by 2015. eCVT
Similarly, 5-speed transmissions 80% 5-speed 7-speed
(red) are losing market share and manual automatic 8-speed+
70% DCT
are estimated to taper off to zero
Market Share
by 2021. Future projections are for 60%
5-speed 6-speed
8-speed+ATs and, especially, DCTs automatic automatic
50%
to dominate the market, with CVTs
tapering off to zero by 2021. 40%
6-speed
manual 8-speed+
30% automatic
CURRENT PRODUCTION COSTS 4-speed
20%
AND BENEFITS ESTIMATES automatic
6-speed
DCT
Since the rulemaking was written 10%
in 2012, numerous developments 0%
h ave o cc u r re d i n C V Ts , D C Ts , 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024 2025
a n d c o nve n t i o n a l a u t o m a t i c s . Model Year
Several of these developments
are described below. Figure 2. Market share of various transmissions by speed (color) and type (shade).
CVT = continuously variable transmission for non-hybrid cars and trucks. eCVT =
CVT hybrid vehicle continuously variable transmission. DCT = dual clutch transmission.
(Source: US. EPA. Light-Duty Automotive Technology, Carbon Dioxide Emissions, and
The typical CVT utilizes a belt Fuel Economy Trends: 1975 Through 2015. Dec 2015.)
sandwiched between pairs of cones:
essentially two variable-diameter
pulleys (Figure 3). Historically, torque
limitations hindered the adoption of
CVTs in all but the smallest vehicles. HIGH GEAR
But improvements in belt design have
dramatically increased the torque
capabilities of CVTs up to 450Nm.8
CVTs captured an estimated 18% of DRIVEN PULLEY
the entire market in 2015 and sales
include compact cars (1.0L to 1.8L)
V-BELT/PUSHBELT
all the way through large passenger
vehicles (>2.5L) 9 including the DRIVE PULLEY ELEMENT
Nissan Murano—a midsize crossover
RING BUNDLE/
SUV with a 3.5L engine. PACK
As an example of the improve-
ments, Jatco produces a CVT for LOW GEAR
small cars that has an increased
RING
gear spread, which enhances launch
and acceleration. It couples a small
Figure 3. Typical belt-driven CVT configuration (left), and typical belt design (right).11
8 “Pushbelt (Working Principle).” Bosch
Transmission Technology B.V. Accessed
June 2016. http://www.bosch.nl/ “sub-transmission” to the CVT. This the efficiency benefits from reduced
transmission_technology/en/html/5869. “sub-transmission” is an auxiliary weight and the increased gear
htm “Bosch Pushbelt – Efficiency on the
gearbox. Complexity is increased, spread, internal friction is reduced
Road.” Bosch Mobility Solutions. Video
accessed June 2016. https://www.youtube. but the overall size is reduced by by 30%.10
com/watch?v=bwKKGdU0fjU 10% and weight by 13%. In addition to
9 As but one example of several CVT
suppliers, Jatco offers CVTs suitable
for a range of vehicle sizes. “Product 10 “Jatco CVT7.” Jatco Product Information.
Information.” Jatco. Accessed June 2016. http://www.jatco.co.jp/ENGLISH/products/
http://www.jatco.co.jp/ENGLISH/products/ cvt/cvt7.html. Accessed June 2016.
6 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17TRANSMISSIONS
DCT11 CLUTCHES 1 & 2 6TH
REVERSE 5TH
As shown in Figure 4, a DCT includes
two clutches, one for each concentric
input shaft (orange, purple). The two
output shafts (countershafts, hidden)
each have a number of gears (blue-
gray) that can spin freely around their
respective output shaft. Gear selectors
(smooth gray) axially slide on the
output shafts to select a specific gear
and connect it to its output shaft,
thereby driving the output shaft. Only OUTER SHAFT
one clutch is engaged at a time, so
that only one of the countershafts
drives the final output (largest gray INNER SHAFT
1ST
gear). However, the gear selectors can
preselect gears in order to shift faster
4TH
without any torque interruption. That 3RD GEAR
2ND SELECTOR
is, while one clutch and gear selector
are engaged in a particular gear, a Figure 4. Typical DCT layout and operation.
second gear selector on the non-driv-
ing countershaft (corresponding to conventional 5-speed AT). The torque DCT packaging is a concern,
the un-clutched input shaft) engages converter improves launch behavior especially as the number of gears
the next gear. The shift occurs when and acceleration through torque increases. Odd-number-geared DCTs
the first engaged clutch disengages multiplication, but additional costs, may be easier to produce (due to
and the previously disengaged clutch complexity, length, and reduced the necessity of a reverse gear).
engages. Basic animations of DCT efficiency come with it. However, the Several 7-speed DCTs are already on
operation are widely available.12 cost of the clutches for a DCT can the market, and their market share
be high, thus the torque converter is expected to grow. For example,
Since DCTs represent a class of does not make the transmission sig- Hyundai now includes a 7-speed
automated manual transmissions, nificantly more expensive. dry-clutch DCT option for all its
they typically do not use a torque Sonata, Elantra, and Tuscon models.16
converter, as with conventional Today, wet-clutch DCTs approach
automatics. This elimination leads to the efficiency of dry clutches due to In a report commissioned by the
launch issues. One option to solve this the expanded use of an on-demand ICCT, currently in final draft form, 17
problem is to simply include a torque hydraulic pump.15 DCTs have also seen FEV estimated the incremental cost
converter.13 Honda uses one between improvements in clutches and trans- of a 10-speed wet-clutch DCT trans-
the engine and an 8-speed DCT on the mission fluids, mainly by optimized mission over a 7-speed or 8-speed
baseline 2015 2.4-L Acura TLX.14 The friction materials and clutch pressure conventional automatic would be
DCT+torque converter combination control. These developments allow $156. Based on the total costs listed
is designed to improve the launch of micro-slip of the clutches, which in the report, the incremental cost
the DCT, and achieves a 7.4% decrease permits reduced system pressure and of a 10-speed wet-clutch DCT over
in fuel consumption (compared to a lower fuel consumption. a 7-speed dry-clutch DCT is around
$110. Thus, FEV’s estimated incremen-
Wet-clutch DCTs are also useful tal cost of a dry-clutch DCT over a
11 U.S. Patent 5167587 & U.S. Patent 7846049 for cooling the clutch in conditions comparable automatic transmission is
12 Thomas Schwenke. “Dual-Clutch where the clutch is slipped longer approximately $46. This cost increase
Transmission / Double-Clutch Gearbox for low-drag torque. Under these
(Animation).” YouTube. May 7, 2014. https:// is higher than that estimated for the
www.youtube.com/watch?v=t-oULh0I3iA. conditions, dry-clutch DCTs would 2025 rulemaking, which was actually
Accessed June 2016. simply burn out. a cost reduction of $8–$165 for
13 Robinette, D., Skrzycke, T., “A Dual Clutch
Torque Converter for Dual Input Shaft
Transmissions,” SAE Int. J. Engines, April 8, 15 Matthew Beecham. “Q&A with BorgWarner: 16 Fuel Economy. U.S. EPA OTAQ. http://www.
2013. doi:10.4271/2013-01-0232 Dual clutch transmissions.” Just Auto fueleconomy.gov. Accessed June 2016.
14 Dan Carney. “Honda’s new 8-speed DCT News & Analysis. Jan. 22, 2013. http:// 17 FEV. 2030 Passenger Car and Light
uses a torque converter.” Automotive www.just-auto.com/interview/dual-clutch- Commercial Vehicle Powertrain Technology
Engineering. Aug. 6, 2014. http://articles. transmissions_id130903.aspx. Accessed Analysis. Draft: Sept. 2015. Forthcoming
sae.org/13432/. Accessed June 2016. June 2016. report for ICCT.
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 7TRANSMISSIONS
wet-clutch and dry-clutch DCTs over Table 5. Comparison of estimated costs from rulemaking and suppliers. Source: EPA/
their conventional AT counterparts. NHTSA 2017-2025 rulemaking, FEV 2015, and FEV/EPA 201322
FEV estimated the incremental cost Cost Estimates
of a dual wet-clutch alone over a dual TECHNOLOGY BASELINE RULEMAKING FEV
dry-clutch would be $44, which is 6-speed dry-clutch DCT 6-speed AT -$127 to $26 (NAS) —
essentially on par with the estimated 7-speed dry-clutch DCT 7-/8-speed AT — $46
cost in the rulemaking of $52. Note 10-speed wet DCT 8-speed AT — $156
that FEV estimated a 10-speed DCT
8-speed wet-clutch DCT 6-speed wet-clutch DCT $153 $161*
would cost only $66 more than a
10-speed wet-clutch DCT 7-speed wet-clutch DCT — $66
7-speed DCT. This is because FEV
Wet-clutch (DCT) Dry-clutch (DCT) $52 $44
assumed 10 gear steps would be
realized by applying an advanced 8-speed AT 6-speed AT $47 $54*
connection scheme of gear wheels 6-speed MT 5-speed MT $173 $40
and synchronization units, a concept *Costs extracted from FEV/EPA 2013 report on advanced 8-speed transmissions and reduced by
different from typical DCT layouts that manufacturer learning trends as applied in the final rulemaking.
tries to solve some of the packaging
issues of 7-speed+ DCTs (albeit only gearsets are also nested to save The 9-speed ZF automatic consumes
for front-wheel drive vehicles).18 space, leading to smaller and lighter 16% less fuel than a 6 speed automatic
transmissions for the same number at the same driving speed. One
Upgrading a 6-speed manual to a of gears compared to DCTs. Thus, the innovation is that this 9-speed uses
7-speed dry-clutch DCT decreased number of gear ratios in conventional interlocking, splined dog clutches
fuel consumption by 4.1%–7.9% on automatics is increasing rapidly, up to (rather than friction clutches) to
the smaller vehicle classes modeled 10 in the upcoming Lexus application achieve faster and more efficient
by FEV. Unfortunately, the addition and Ford/GM transmission, enabling torque transfer.23 Splined dog clutches
of advanced stop/start functions both higher performance and lower have lower spin losses on clutches
and weight reduction to all other fuel consumption than the 8-speed that are not engaged.
DCT modeling prevents a separate automatic transmissions modeled in
assessment of the efficiency benefit the rulemaking.20 And, due to some Ongoing research on better friction
of DCT over conventional automatics. consumer dissatisfaction issues with m a te r i a l s h a s i m p rove d c l u tc h
some of the initial DCTs sold in the performance and reduced friction
Conventional Automatics market (discussed more below), losses, 24 leading to decreased fuel
many OEMs are focusing on improved consumption.25 The groove patterns
Conventional automatic transmissions and material in the clutch friction
automatic transmissions.2122
have also been undergoing incremen- plates are engineered to reduce
tal improvements. Unlike conventional drag, which, in addition to improving
DCTs, which must add gears for 20 Sean Szymkowski. “General Motors fuel economy, provides seamless
each expansion, the Lepelletier gear will introduct 10-speed automatic on
shifts for better performance and
eight vehicles by 2018.” GM Authority.
set design allows easier expansion delivers durability that improves the
Mar. 16, 2016. http://gmauthority.com/
of the number of gear ratios. For blog/2016/03/general-motors-will- life of the transmission.
example, a 9-speed automatic made introduce-10-speed-automatic-on-eight-
vehicles-by-2018/. Accessed June 2016.
by ZF Friedrichshafen AG (and used
21 David Sedgwick. “Once-promising dual-
by Chrysler, Jaguar Land Rover and clutch transmissions lose favor in U.S.”
Honda) uses 4 simple planetary Automotive News. Dec 7, 2015. http:// 23 “9-speed Automatic Transmission.”
www.autonews.com/article/20151207/ ZF Technology for Cars: Automatic
gearsets and 6 shift elements.19 The
OEM06/312079988/once-promising-dual- Transmission. http://www.zf.com/corporate/
clutch-transmissions-lose-favor-in-u.s. en_de/products/product_range/cars/
18 Govindswamy, K., Hellenbroich, G. and Accessed June 2016. cars_9_speed_automatic_transmission.
Ruschhaupt, J., “7-XDCT: Compact and 22 U.S. NHTSA. Corporate Average Fuel shtml. Accessed June 2016.
Cost-Efficient Dual Clutch Transmission Economy for MY 2017-MY 2025 Passenger 24 Merkel, H. “Development Trends of Friction
for Small and Mid-Size Vehicles,” SAE Int. Cars and Light Trucks: Final Regulatory Products”. BorgWarner Transmission
J. Passeng. Cars - Mech. Syst. 6(2):2013, Impact Analysis.. Aug 2012. Accessed June Systems. CTI Symposium. December 2013.
doi: 10.4271/2013-01-1271. “10-Speed Dual 2016. http://www.nhtsa.gov/fuel-economy. 25 “BorgWarner Delivers Advanced
Clutch Transmission.” FEV North America, FEV. 2030 Passenger Car and Light Technologies For New GM 8-Speed
Inc. https://www.youtube.com/watch?v=p_ Commercial Vehicle Powertrain Technology Transmission.” PR Newswire. Sep 21,
cBBRY7qhg. Video accessed June 2016. Analysis. Draft: Sept. 2015. Forthcoming 2015. http://www.prnewswire.com/news-
19 Dan Carney. “Honda’s new 8-speed DCT report for ICCT. U.S. EPA. Light-Duty releases/borgwarner-delivers-advanced-
uses a torque converter.” Automotive Vehicle Technology Cost Analysis, Advanced technologies-for-new-gm-8-speed-
Engineering. Aug. 6, 2014. http://articles. 8-Speed Transmissions: Revised Final transmission-300145826.html. Accessed
sae.org/13432/. Accessed June 2016. Report. FEV. April 2013. EPA-420-R-13-007. June 2016.
8 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17TRANSMISSIONS
Leakage from hydraulic pumps and
valves is also a major source of trans-
mission energy loss. Consequently,
there is a concerted effort among
suppliers and OEMs to improve
hydraulics (especially in combination
with start-stop).26
IMPROVEMENTS IN
DEVELOPMENT rp1 > rp2 rp1 = rp2 rp1 < rp2
Underdrive 1:1 Overdrive
DCT
Figure 5: Cross section diagram showing planetary ball tilt angle determining drive ratio.
DCTs may be ideally suited for hybrid
and electric vehicle applications (as
in the VW Jetta Hybrid and the 2017
Hyundai Ioniq). The electric motor can
provide assist during launch, eliminat-
ing the starting clutch and allowing
simpler clutches and lower cooling
requirements. 27 Several companies
co n t i n u e to m a ke i n c re m e n t a l
improvements in DCTs.28
VariGlide planetary variator29
Va r i G l i d e p l a n e t a r y v a r i a t o r
technology is a compact traction drive
Figure 6: The VariGlide planetary variator employs elasto-hydrodynamic lubrication
that employs rotating planets that can
(EHL) to transfer torque. The components and ball cam clamping features in the ring
be tilted on their axes to smoothly are shown on the right.
and continuously vary the drive ratio.
As shown in figure 5, by changing changes, and therefore the speed This mechanism of torque transfer is
the angle of tilt of each planet’s axis ratio may be continuously varied as also known as elasto-hydrodyamic
of rotation, the contact radii ratio the transmission is shifted through the lubrication (EHL). 30 At the traction
ratio range. contact there are losses that include
26 Reduced system pressure, electrohydraulic slip, side-slip and spin. Variable
pumps (Getrag), variable mechanical It is similar to a dual-ring planetary gear clamping force is provided by simple
pumps (ZF), bi-pressure pumps (GM, Aisin/
set, but the planets in the VariGlide mechanical ball cams, which enable
Toyota), and low leak solenoid valves are
some of the many approaches to reducing planetary variator are spherical rollers the correct amount of clamping force
transmission leakage. (standard bearing technology), which for the given load without the need
27 Matthew Beecham. “Q&A with BorgWarner:
transfer load through traction rather for active control.
Dual clutch transmissions.” Just Auto
News & Analysis. Jan. 22, 2013. http:// than gear teeth. The carrier allows the
www.just-auto.com/interview/dual-clutch- planets to rotate about their tilting While the production capability has
transmissions_id130903.aspx. Accessed yet to be proven, the design has a
June 2016.
axes and find their equilibrium. The
input and output power are delivered number of potential benefits over
28 Ernest DeVincent. “GETRAG DCT New
Modular Platform: From 100Nm to on the same centerline (as opposed to belt CVTs. It uses roller bearings
500Nm.” Getrag. Presentation given at
spur gears), and like a planetary gear, instead of a belt to transmit loads,
7th International CTI Symposium May
the drive can be used to power-split which should be more durable. These
2013, Detroit. http://www.getrag.com/
media/products/powershift/7dct300/ or power-sum. bearings also eliminate the need for
Presentation_7DCT300.pdf “Efficient a high-pressure pump, which con-
Transmissions.” Getrag Transmission
As a traction drive, it transmits tributes to some of the benefits over
Technology. 2016. http://www.getrag.com/
en/technology/transmission_technology/ forces between the rolling surfaces
pleasure_and_consumption/efficiency_ 30 Fern Thomassy. An Engineering Approach
( b e t we e n r i n g a n d p l a n e t b a l l
and_dynamics_1.html to Simulating Traction EHL. CVT-Hybrid
29 This is a relatively new concept that operates contacts) through resistance to International Conference Mecc/Maastricht/
differently than current production CVTs. shearing of a thin film of traction fluid. The Netherlands, Nov. 17–19, 2010.
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 9TRANSMISSIONS
belt CVTs.31 The planetary CVT can
12% 11.61%
handle higher torque than belt CVTs FTP NEDC WLTC
and the same design can be used in 10.56%
both FWD and RWD applications. 10%
The VariGlide has some similarities 7.83% 7.98%
s.
8%
to the (virtually extinct) toroidal/
6.38%
ro l l e r C V T, i n t h at b o t h u s e a 6% 5.85% 5.91%
traction fluid, rather than friction, to
transmit torque. 32 Used by Nissan
4% 3.32%
(“Extroid CVT”) in the 1990s on 3.19%
several passenger cars and currently
2%
produced by Torotrak 33 for use on
heavy duty vehicles, toroidal CVTs
have largely stalled in development 0%
City Highway Combined
for light-duty vehicles. The VariGlide
has some of the same potential issues Figure 7. Fuel economy comparison with 6-speed AT
tied to the need for traction fluid,
such as spin losses and traction fluid electrification, transmissions are also CONSUMER ACCEPTANCE ISSUES
durability. According to Dana, traction upgrading to handle these changes.
Consumer acceptance issues must be
fluids have shown significant improve- Not only are hydraulic systems
considered for any new or improving
ments in both durability (resistance changing to adapt to more engine
vehicle technology. Transmissions, in
to degradation) and overall traction starting and stopping (discussed
particular, suffer from these issues,
coefficient. They continue to work above), auxiliary pumps are also
since they directly affect how the
with their OEM partners to jointly being developed. For example, FEV
engine sounds and how the vehicle
develop specifications that will sees an integrated electric motor as
feels. DCTs and CVTs generally
ultimately meet the expected “fill an option on their 7-speed+ DCTs.36
have much more pronounced issues
for life” expectations. 34 The core than improved automatics. But
technology has also been subjected Manual transmissions automatics also have some issues,
to 70,000 hours of durability testing, Manual transmissions, too, may use primarily gear “hunting” when the
which shows robustness against slip- electric clutches for reducing fuel number of gears increases.
induced damage.35 consumption and increased comfort.
A system by Schaeffler can reduce The transmissions with more gear
Electrification fuel consumption by 3.1% (idling the ratios and wider gear spread have
engine when coasting in the highest major positives in addition to better
As manufacturers roll out increasing
gear) to 8.2% (stopping the engine fuel economy: lower gears improve
numbers of vehicles equipped with
when coasting) at a direct manufac- vehicle launch, a lower ratio for the
start-stop (shutting of the engine
turing cost of $112. This system enables top gear provides quieter operation
instead of idling while stopped or
coasting start-stop for manual trans- on the highway, and more gears
coasting) and further levels of
misions; idling the engine or stopping can better maintain both lower rpm
it entirely depending on the degree for better fuel economy and higher
31 “VariGlide ® CVT Efficiency.” Dana Holding of savings.37 rpm for faster acceleration. These
Corporation. June 21, 2016. https://www. advantages have contributed to the
youtube.com/watch?v=N34pxHDoGO4&fea rapid adoption of more gear ratios in
ture=youtu.be. Video accessed June 2016.
recent years.
32 “Extroid CVT.” Nissan’s CVT Technologies.
http://www.nissan-global.com/PDF/tcvt_e.
pdf. Accessed June 2016. DCTs and CVTs have the potential for
33 “Torotrak.” Torotrak Group Products. http:// even better efficiency than ATs, but
www.torotrak.com/products-partners/ 36 “10-Speed Dual Clutch Transmission.” FEV some early models of DCTs and CVTs
products/torotraktransmissions/. Accessed North America, Inc. https://www.youtube.
June 2016.
have been criticized for poor shift
com/watch?v=p_cBBRY7qhg. Video
34 Written comment received from Dana on accessed June 2016. quality and a different “feel,” respec-
June 29, 2016. 37 Luca Ciferri. “Schaeffler touts fuel- tively, from what customers expect.
35 Dana claims over 70,000 hours of savings e-clutch for manual gearboxes.”
component durability testing for the Automotive News. June 6, 2016. http:// DCTs are losing favor with some
VariGlide. “VariGlide ® CVT Testing.” Dana www.autonews.com/article/20160606/
Holding Corporation. June 21, 2016. https:// OEM10/306069990/schaeffler-touts-fuel- manufacturers, largely due to abrupt
www.youtube.com/watch?v=DZeJ1kUiEHg&f saving--e-clutch-for-manual-gearboxes. shifting and lurching on many initial
eature=youtu.be. Video accessed June 2016. Accessed June 2016.
10 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17TRANSMISSIONS
DCT applications. For example, the S o m e m a n u fa c t u re r s — p r i m a r i l y with high-pressure pumps and friction,
first DCT used on the Ford Focus N i s s a n , H o n d a , To y o t a , a n d offering net efficiency improvements.
was criticized for abrupt shifts, shift Subaru—are avoiding the calibra- The CVT is an inherently lower cost
“busyness,” and poor launch.38 Poor tion challenges and perceived shift design and suppliers have managed
calibration and gear ratio selection “busyness” associated with many to keep costs low enough so that
likely explain much of these early DCTs by switching to CVTs. However, CVT sales are increasing rapidly.
challenges facing DCTs. Indeed, there CVTs also come with their share of Continued incremental development
are examples of DCTs that have been criticism. CVTs have been derided for will further reduce losses and cost.
widely praised, e.g. the 2015 VW the exact opposite behavior as DCTs.
Golf, 39 which suggests that part of With no “shifting,” CVTs can appear There is no doubt that CVTs suffer
the problem is not the hardware but as constantly revving (or constantly greater losses than DCTs and con-
software controls that are not yet not revving), with engine speed ventional ATs. Their eventual cost and
sophisticated enough. However, it seemingly uncorrelated to accel- market share, especially compared
may not be possible to remove all of erator pedal input, as consumers are to DCTs, depends on the degree to
the shift shock with dry-clutch DCTs, accustomed to. Again, calibration is which these losses are minimized and
as the high temperature variations partly at fault for this issue, but this the rate of improvement in DCTs (cost
make it difficult to control clutch effect may simply take a bit of getting and consumer acceptance).
engagement. And even wet-clutch used to. For example, Consumer
New “planetary” CVTs,42 which use
DCTs may never launch like a con- Reports recently praised the CVT
traction fluid, show promise, although
ve n t i o n a l h yd ra u l i c a u t o m a t i c used in the 2016 Honda Accord. This
they have yet to be introduced at
transmission, as they are, fundamen- evaluation suggests, again, that the
a commercial scale. Their relatively
tally, manual transmissions shifted primary problem is not the hardware,
simple design, compared to belt-
automatically. DCTs are popular in but software controls. New shifting
driven CVTs, could also mean they
Europe, as manual transmissions have logic attempts to recreate some of
are, overall, less expensive to manu-
a high market share in Europe and the shifting experience of driving
facture. However, as with all traction-
customers are used to the launch an automatic on a CVT. 41 Indeed,
drive transmissions, at the traction
quality of a manual transmission, improved drivability acceptance of
contact there are losses that include
but this familiarity is not the case in CVTs is reflected in the doubling of
slip, side-slip and spin. Improvements
the United States. Manufacturers are market share since 2012 to over 1 in
are being made to traction fluid
testing different options based on 10 trucks and 1 in 5 cars (Figure 1 and
durability and assuring “fill for life” is
their expertise: those with manual Table 2).
a prerequisite for market acceptance.
transmission experience (primarily
European-based manufacturers) are
DISCUSSION DCT
implementing DCTs, with or without
torque converters. Other improve- CVT DCTs have not taken off in the United
ments are also coming to DCTs, States as forecast due to consumer
such as electro-mechanical clutch After years of slow development, acceptance issues and difficulty in
actuation (rather than hydraulic).40 many of the solutions to problems packaging. 43 Furthermore, due to
associated with CVTs have reached
temperature constraints, it may not
a point where CVTs are now a real
38 David Sedgwick. “Once-promising dual- be possible to solve the consumer
clutch transmissions lose favor in U.S.” alternative to traditional automatics.
acceptance issues with dry-clutch
Automotive News. Dec 7, 2015. http:// Increased hydraulic pressure and
www.autonews.com/article/20151207/ DCTs. Wet-clutch DCTs are becoming
improved belts vastly expanded the
OEM06/312079988/once-promising-dual- m o re e f f i c i e n t t h a n p re d i c te d ,
clutch-transmissions-lose-favor-in-u-s. torque range of CVTs. The engine
approaching the efficiency of some
Accessed June 2016. efficiency benefits possible with CVTs
39 Mark Rechtin. “Volkswagen Golf, Ford
dry-clutch DCTs, and they benefit
finally offsets the losses associated
F-150 win car, truck of the year awards.” from reduced temperature issues
Consumer Reports. Jan 12, 2015. http:// compared to dry-clutch DCTs. Better
www.consumerreports.org/cro/ 41 Lindsay Chappell. “Nissan tweaks CVTs
news/2015/01/volkswagen-golf-ford-f- to be less CVT-like.” Automotive News.
150-win-car-truck-of-the-year-awards- July 13, 2014. http://www.autonews.com/
detroit-nactoy/index.htm. Accessed June article/20140713/OEM03/307149936/
2016. VW Golf Consumer Reports’ Road nissan-tweaks-cvts-to-be-less-cvt-like. 42 McIndoe, G., VanSelous, J., Liu, T., and
Test. Consumer Reports. http://www. Accessed June 2016. Keith Griffin. “Why David, J., “Efficiency Analysis of Multi-Mode
consumerreports.org/cro/volkswagen-golf- do today’s transmissions have so many Passenger Car Transmission Concepts
road-test.htm gears?” U.S. News & World Report. July 16, Featuring a VariGlide® CVT,” SAE Technical
40 Liu, F., Chen, L., Yao, J., Zhang, J. et al., “A 2015. http://usnews.rankingsandreviews. Paper 2016-01-1108, 2016, doi:10.4271/2016-
New Clutch Actuation System for Dry DCT,” com/cars-trucks/best-cars-blog/2015/07/ 01-1108.
SAE Technical Paper 2015-01-1118, 2015, Why_do_Todays_Transmissions_Have_so_ 43 According to BorgWarner, packaging issues
doi:10.4271/2015-01-1118. Many_Gears/. Accessed June 2016. are mainly due to the DCTs increased girth.
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 11TRANSMISSIONS
control logic will also improve the the small car segments, due to their improvements to CVTs and ATs, DCTs
lurch and launch problems.44 low cost.46 are unlikely to largely replace CVTs
and ATs in the 2025 time frame, as
The need to add a wet clutch adds Changes since agency projected by EPA/NHTSA in the
$52 to the cost according to agency evaluations were conducted 2017-25 rulemaking. James Verrier,
estimates ($56 according to a recent for 2017–2025 rulemaking CEO of BorgWarner, thinks the DCT
FEV analysis 45), and degrades fuel future in the United States “will be
economy. The efficiency improve- It appears that manufacturers may
primarily the wet DCT for higher
ments to the wet clutch reduce be sticking to the transmissions they
torque applications,” such as diesels
the efficiency penalty, but at some know best. Most vehicles in Europe
and gasoline turbocharged engines.47
additional (un-quantified) cost. still use manual transmissions. DCTs,
F E V ’s re c e n t c o s t a s s e s s m e n t which are simply manual transmis-
Some, if not all, of the DCT shortfall
suggests that DCTs may be more sions shifted automatically, are
will be replaced by improvements to
expensive than assumed by the widely used by European manufac-
CVTs and conventional automatics.
agencies in the rulemaking, although turers in the United States, and their
Newer CVTs have reduced internal
still cheaper compared to conven- customers seem to be accepting
friction, wider ratio spread, and
tional automatics. them. CVT transmissions are
increased torque capacity. They will
extremely popular in Japan, as they
likely be strong competitors to DCTs
excel in the low-speed congested
Conventional AT and conventional ATs through at
conditions that dominate driving in
least 2025, especially for manufac-
Some OEMs (particularly in North Japan. Japanese manufacturers used
turers with extensive CVT expertise.
America) are sticking to designs they to use conventional automatics in
Conventional automatics can add
have experience with and relying on the United States, due to the higher
additional gear ratios in a relatively
higher-speed ATs rather than DCTs performance and torque require-
inexpensive manner and maintain a
and CVTs. Incremental improvements ments and the better fuel economy
compact size. Recent improvements
in these higher-speed automatics of conventional automatics on the
are increasing efficiency, such as
have led to efficiencies roughly on highway. However, as CVTs have
improved clutch designs and the
par with what the agencies predicted. improved to handle higher torque
use of splined dog clutches, and ATs
However, 9- and 10-speed automatics and expand the ratio spread for
largely avoid consumer acceptance
have already been introduced in better highway fuel economy, the
issues. They are likely to maintain a
the market, which have incremental Japanese manufacturers have largely
larger share of the market in 2025
efficiency improvements over the replaced conventional automatics
than projected in the rulemaking.
8-speed transmission modeled for with CVTs in the United States. The
the rulemaking. In addition, friction U.S. manufacturers are experimenting
c l u tc h e s c a n b e re p l a ce d w i t h with both CVTs and DCTs, but early SUMMARY
mechanical clutches, as on the new ZF customer acceptance issues appears In their technology analyses for the
9-speed transmission, although that to be pushing them back onto their 2025 rulemaking, EPA and NHTSA
requires faster on-board computers traditional expertise with conven- projected that DCTs would overtake
to better calibrate shifting. tional automatics. Both manufactur- conventional automatics by 2021
ing history and consumer history with and continue to increase market
Th e a g e n c i e s p ro j e c te d i n t h e the feel of a torque converter favor
rulemaking that 8-speed ATs would share through 2025. However, due
conventional automatics for the U.S. to numerous consumer acceptance
completely replace 6-speed ATs manufacturers.
by 2025. However, BorgWarner issues (which may be due primarily
believes it is likely that 6-speed ATs to calibration, rather than the actual
DCTs will certainly have a significant
will continue to be used for at least hardware), their sales have not
share of the future transmission
reached levels indicative of such a
market. However they will cost more
transition. While some of the technical
than estimated in the rulemaking,
challenges faced by DCTs are being
they may not be quite as efficient
solved, the solutions will likely make
due to the need for a wet clutch or
44 Cho, D., Gupta, R., Dai, E., McCallum, J. et a torque converter, and they will
al., “Launch Performance Optimization of 47 Richard Truett. “Ford gets the PowerShift
GTDI-DCT Powertrain,” SAE Int. J.Engines never shift quite like a conventional dual clutch transmission right, but is it too
8(3):2015, doi:10.4271/2015-01-1111. hydraulic automatic. Combined with late?” Automotive News. January 5, 2016.
45 FEV. 2030 Passenger Car and Light https://www.autonews.com/article/20160105/
Commercial Vehicle Powertrain Technology BLOG06/301059997/ford-gets-the-
Analysis. Draft: Sept. 2015. Forthcoming 46 Personal communication from BorgWarner powershift-dual-clutch-transmission-right-
report for ICCT. to ICCT, received on June 16, 2016, via email. but-is-it. Accessed June 2016.
12 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2016-17TRANSMISSIONS
them slightly more expensive and share for higher speed automatics is agencies did not explicitly predict
slightly less efficient than projected strong, putting ATs on track to meet the costs or benefits of CVTs in the
by the agencies. Although DCTs projections, and possibly to help fill in rulemaking, CVTs today appear to
remain an attractive option in terms the gap left by lagging DCTs. be on track to match the benefit
of comparative cost-effectiveness estimates available in EPA’s lumped
and efficiency, they are unlikely to When the rulemaking analyses were parameter model and they cost less
match the penetration estimates in conducted four to five years ago, than conventional automatics.
the rulemaking. CVTs were not projected to be a com-
petitive option by 2025. However, Wh i l e t h e Va r i G l i d e ® P l a n e t a r y
Conventional automatics, in general, ye a r s o f i n c re m e n t a l i m p rove - Variator was not considered in the
are matching the predicted cost ments have shown that CVTs can, overall assessments in this paper, if it
and likely exceeding the projected and are, a good alternative trans- proves successful it may offer another
benefit, due to the introduction of 9- mission. Market share has grown bump in efficiency, reduced cost, and
and 10-speed transmissions and the rapidly since 2012 and consumer improved durability.
increased efficiency of mechanical/ acceptance issues no longer seem
dog clutches. The growth in market to be plaguing CVTs. Although the
WORKING PAPER 2016-17 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 13You can also read
