Contributed by Bob Chabot
Electrification Energizes the Transmission Market
It's clear that the electrification of vehicles is now very much a reality. But what are the implications — for transmissions and the transmission market — as OEMs, suppliers, service professionals and customers strive for lower CO2 emissions/fuel costs?
The choice of transmissions for hybrids is dependent on the type of vehicle architecture. P0 and P1 are the current architectures in operation. Newer P2 hybrids, which utilize twin clutch transmission systems that can work with 48-Volt architectures, are just beginning to appear in some new OEM platforms. P3 and P4 architectures are under development and targeted for introduction by 2025. They feature innovations such as double shafts suitable for transverse engines, regenerative braking, axle electric drive motors and additional transmission ratios. (Image — Equipment and Tool Institute)
OEMs and Suppliers Consider a Broad Range of Possible Configurations
“The possibilities for electrification by OEMs and suppliers in vehicle transmissions is in an ‘embryonic’ state,” says Chris Guile, a principal analyst with IHS Automotive. “Possible implications span different types of electrified vehicles — from conventional automobiles to full-on electric vehicles (EVs).”
For EVs, there are many simple reduction transmissions/systems, which are available for the OEMs to use, although IHS Automotive says volumes for EVs are not expected to represent a significant global market threat to existing transmission suppliers or the supply chain for some time. Currently limited to single-speed transmissions, the researcher says that may change as multi-speed transmissions emerge and are offered in the near future.
At the other end of the electrification spectrum we have stop-start vehicles, and the slightly more complicated mild hybrids. Here we have much higher volumes to consider. However, current investment in the existing supply chain and production equipment has a high level of inertia, which will slow ‘evolution’ beyond applying conventional transmission technologies. The shift is also hampered by the economics of providing an additional sensor to confirm when the transmission is in neutral (for the stop-start operation), the need for an electric oil pump or oil storage system to maintain oil pressure, and a switch to e-clutches for some inbound mild hybrids.
“Full hybrids have more interest from OEMs than the other types,” Guile shared. “Despite their current low market share, this is where the interest of automakers and suppliers is focused. Although an important part of the market, it also poses a dilemma to OEMs.”
IHS Automotive is currently forecasting that by 2028, Electrically Variable Transmissions (also known as Dedicated Hybrid Transmissions) will dominate the full hybrid vehicle market. (Image — IHS Automotive)
The Status Quo
Full hybrid vehicles involve much more complex powertrain systems that require some kind of transmission. For instance, OEMs have to decide at some point, based on market penetration, whether to retain Conventional Variable Transmissions (CVTs) or develop/use some kind of more efficient Dedicated Hybrid Transmission (DHT).
The development costs involved are prohibitive for some automakers, especially those just beginning a program. Others still need to build up knowledge, experience and market share before transitioning. In addition, there are no guarantees of success, as there is no reliable way to predict how real customers will react to a new transmission system and its driving feel.
Currently, there are only a few transmission systems used in electrified vehicles. Guile provided a short list or them:
- Hybridized Automated Manual Transmissions (AMTs) — Despite relatively simple and cost-effective design that use electro-hydraulic mechanisms, AMTs are not generally used for full hybrid applications. Although the torque infill available from an electric motor may appear to be attractive, in reality, electric motors are not usually able to provide enough torque between the lower gears. This torque interruption very obvious and bothersome to customers.
- Hybridized Continuously Variable Transmissions — Early adopters of full hybrid technology, such as Toyota or Honda, have typically employed CVTs early in their development programs and then switched to more efficient technologies. Toyota and Honda both began with CVTs, but moved to DVTs sooner than other OEMs. Both built up significant volumes and have stuck with that technology ever since. In contrast, Nissan and Subaru have both begun full hybrids programs, based on CVT applications. According to Guile, “Expect the volumes for full hybrid CVT systems to rise in the short term, despite the limited number of OEMs using them. After that, who knows?”
- Hybridized Dual Clutch Transmissions (DCTs) — The volumes for DCTs in full hybrids are also rising quite significantly, and are being used by many different OEMs. “In addition to the VW Group, Daimler, Volvo, Getrag and others with transverse and/or longitudinal DCTs, look for the use of DCTs in China to ramp up significantly,” Guile noted.
- Hybridized Automatic Transmissions (HATs)— Full hybrids based on classic automatic transmission designs are also growing significantly. “One reason for this is the ease with which the torque converter can be replaced by an electric motor and clutches,” Guile explained. “OEMs like Hyundai and Daimler have already embraced this technology, whilst suppliers like Aisin, Jatco and ZF are also supplying automatics to BMW, Nissan, Volvo and others.
- Dedicated Hybrid Transmissions — “The structure of DHTs is characterized by having the electric motor(s) fully integrated into the transmission,” Guile stated. “But design is just as varied as the number of potential hybrid configurations.” Based around a planetary gearset, in these applications, one input of the planetary gearset is driven by the combustion engine, while the second input is driven by the electric motor, giving a variable speed drive at the output to connect to the wheels. Recently, DHTs have also taken on another name, Electrically Variable Transmissions (EMTs).
Above is a cross-section image of AVL’s future Generation 2 Full Hybrid DHT, currently under development. (Image — AVL)
DHTs are the Elephant in the Full Hybrid Transmission Market
“The Aisin/Toyota DHTs combination is the longest established full hybrid transmission system in the market, accounting for the majority of all DHTs manufactured to date,” Guile emphasized. “Since 2013, Honda has offered full hybrid applications on the market that feature planetary DHTs. Although volumes are still quite low, compared to Toyota, IHS anticipates this will become Honda’s hybrid technology of choice in the longer term. Other automakers are also getting onboard with DHTs.
Back in 2006 Advanced Hybrid System 2 (a DHT) began as a joint venture between GM, Daimler and BMW. The two German OEMs quickly backed away from the project after very short production runs, preferring instead to pursue more established technologies. GM continued with the program and has subsequently developed several variants, with more expected in the future.
Ford’s HF35 DHT was first introduced into the market in 2012. It is based on a planetary gearset arrangement, which is used in several vehicle applications. Ford told IHS a revised HF45 version is under development, which will be offered in many more applications, with much higher volumes in the future.
Fiat Chrysler just announced that its new SI-EVT (Single Input, Electrically Variable Transmission) will be used first in the Chrysler Pacifica minivan. Like so many of the other DHTs, Chrysler’s iteration is based on a planetary gearset, but it uses two electric motors, both of which can be used to propel the front wheels. Other applications will follow the Pacifica.
Transmission Suppliers Demonstrate How Inertia Impacts Evolution
“Another interesting way to observe the market, is to look at the different strategies adopted by the large independent transmission suppliers,” Guile suggested. “Some, like Getrag, Jatco and ZF, have chosen to engineer variants of their standard transmission products, so they can offer the OEMs a hybrid system, complete with an electric motor and sometimes more. This contrasts with Aisin, which seems content to offer its standard automatic transmissions for OEMs to engineer into their own hybrid configurations.”
The first strategy, according to Guile, offers OEMs a simple and probably more cost-effective solution, but may limit their ability to tailor the system to their own exact requirements or strategy. The Aisin route, on the other hand, gives the OEMs much more control over the system design, but would incur higher development costs.
“What is curious to me is that most of these independent suppliers, who could probably garner greater volumes through multiple customers, have yet to bring DHTs in any volume to the market — at least so far,” Guile noted. “Is this another example of inertia in the industry, leading to evolutionary, rather than revolutionary technology trends?”
IHS Automotive is currently forecasting about 5 million DHTs (aka EVTs) per year, by 2028, which would be approximately five percent of the global transmission market. (Image — IHS Automotive)
It’s All About Having the Right Technology at the Right Time
“We can probably all think of examples where a certain technology was introduced too early to the market, resulting in low volumes and a short production run,” Guile posed. “Toyota, on the other hand, developed DHTs early for its full hybrids, and has steadily increased market penetration rates, Today, for example, more than 90 percent of Lexus and more than 30 percent of Toyota vehicles sold in Europe are now full hybrids. That’s a migrating trend.”
“Transmission suppliers are no longer standing pat,” he continued. “We are beginning to see the number of physical/mechanical gear ratios in a transmission becoming less of a defining characteristic. This is because manufactures are cascading gears to create virtual ratios (e.g. DCTs from Getrag, AVL, Punch Powertrain and others), or because some gears/operating modes rely on the electric motors only, as seen on some GKN DHTs. The number of gears/modes, which is more apparent to the vehicle driver, could end up being characterized more by the transmission control software, than the physical hardware.”
Guile shared that IHS is often asked to speculate on what might replace the hugely popular ZF 8-speed 8HP — which uses an add-on motor for hybrid applications — and in particular, how many forward speeds it would have. “I can’t help thinking that by then, something much more integrated and electrically variable (i.e. a DHT) may be more appropriate; then the number of speeds will have largely become irrelevant.”
It may not yet be the time for all OEMs to launch DHTs, but it is certainly time for them to start looking seriously at DHTs — to see where, and perhaps more importantly when, they logically fit into their electrification strategies. While DHTs are the most interesting from an engineering perspective, Guile acknowledges OEMs also have to consider if full hybrids will ever take a significant share of the market.
“Based on IHS Automotive’s current understanding of the OEMs’ productions plans, and given that most of the powertrain consultancies are already working on DHTs, we fully expect that the trend will begin to favor the DHTs, in the longer term,” Guile concluded. But the automotive market has long been known to go through evolutions, rather than revolutions,” he cautioned. “With mild hybrids offering a simple and cost-effective option for high volume applications, the question then becomes what will replace the mild hybrids — more full hybrids, or more electric vehicles?
Either way, there are no wrong answers at this stage.
[Editor's note: Visit MOTOR.com for the latest diagnostic and service insights.]