The Effect of Vehicle Electrification on Transmissions and the Transmission Market
It is clear that the electrification of on-highway vehicles is now very much a reality. But what are the implications for transmissions, and the transmission market, as governments, OEMs, suppliers and customers all strive for lower CO2 emissions/fuel costs?
From a technical perspective, there is a broad range of possible configurations for OEMs and suppliers to consider, when thinking about vehicle electrification. Whilst we cannot evaluate all of these possibilities in such a short article, what we can do is look at some of the broader market trends which are emerging, during this ‘embryonic’ period. Let us start by looking at the implications for the different types of electrified vehicle:
For Electric Vehicles (EVs), there are many simple reduction transmissions/systems, which are available for the OEMs to use. However, the volumes for EVs are not expected to represent a
significant share of the global market (see graph below). In this respect they do not yet pose a threat to the existing transmission suppliers/ supply chain. Having said that, the high torques available from electric motors are making EVs increasingly attractive to customers, for
sporty/performance applications. For the moment, most of these vehicles use single-speed transmissions, but IHS Automotive does expect multi-speed transmissions to be used in the future.
At the other end of the electrification spectrum we have the stop-start vehicles, and the slightly more complicated mild hybrids. Here we have much higher volumes to consider, but for these applications conventional transmission technologies will be used, in most cases.
Usually, an additional sensor is all that is required to confirm when the transmission is in neutral, for the stop-start operation. Most non-manuals also need some way to maintain oil pressure, usually in the form of an electric oil pump, or an oil storage system. Manual transmissions will also be offered on mild hybrids, particular in Europe, some of which will switch to e-clutches.
With so much investment in the existing supply chain and production equipment, leading to high levels of inertia, this slow ‘evolution’ of an existing technology is a story we have seen many times, in the automotive industry.
But the most interesting question arises when we consider the full hybrids. Despite their current low share, this is an important part of the market, and involves much more complex powertrain systems which always require some kind of transmission. For the full hybrids, OEMs have to ask themselves: ‘Should we retain conventional transmissions, or should we develop/use some kind of Dedicated Hybrid Transmission (DHT)?’ For some, the costs involved in developing a DHT are prohibitive, at this stage, whilst for others the need to build up knowledge and experience is paramount.
As the first OEM to bring full hybrids to the market, Toyota initially offered products which featured a CVT or a DHT, but they quickly dropped the P210 CVT in favour of the DHTs. And with the significant volumes which they have been able to achieve, have stuck with that technology ever since.
Fast forward to 2016, and we now have many more full hybrids using DHTs (or ‘EVTs’ in the IHS terminology), but we also have many using ‘standard’ transmission types, as well. These typically feature some kind of add-on electric motor, to achieve a cost-effective modular strategy.
As you can see from the following graph, IHS Automotive is currently forecasting about 5 million EVTs (= DHTs) per year, by 2028, which represents just 5 % of the global market.
In the following sections, we review some of the transmission systems already employed in full hybrids, including those OEMs who have already invested in DHTs:
Hybridised AMT Transmission
Despite their relatively simple, and cost-effective design, AMTs are not generally used for full hybrid applications. At first sight, the torque infill available from an electric motor may appear to be attractive. But in reality, the electric motors are not usually able to provide enough torque between the lower gears, where the torque interruption is most obvious to customers. Of those systems in use, the PSA MCPH4 is probably the best known example, but this will be phased out in favour of an automatic transmission, as PSA launches its new PHEV applications. Suzuki is also known to be working on an AMT-based full hybrid system, although it may have been delayed, or possibly even dropped.
Hybridised CVT Transmissions
Another early adopter of full hybrid technology was Honda, with CVT-based systems, although these have recently been replaced by DCT/ DHT-based systems. In the last few years, Subaru has started to offer full hybrids, based on the TH58 CVT from Fuji Heavy Industries. And more recently, Jatco has seen its CVTs used in Nissan hybrid applications. But despite only being favoured by a few OEMs, the volumes for full hybrid CVT systems are expected to rise.
Hybridised DCT TransmissionsThe volumes for DCTs in full hybrids are rising quite significantly, and are being used by many different OEMs. The VW Group is already using the transverse DQ400, and will soon launch a hybrid version of the longitudinal DL382. Porsche has already used the ZF 7DT75 in the 918 Spyder hybrid, with more Porsche applications expected in the future, using the recently announced ZF 8DT. Hyundai has recently launched DCT-based full hybrids, using its D6KF1.
Many other OEMs, particularly in China, will be launching similar applications in the next few years, whilst here in Europe Getrag is offering OEMs a broader range of hybridised DCTs. IHS Automotive also expects that Daimler will offer DCT-based hybrids on its various FWD (i.e. MFA platform) applications, whilst Volvo/Geely is known to be developing a DCT-based hybrid system, for its smaller CMA platform applications.
Hybridised Automatic Transmissions
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, with only a modest increase in package length. OEMs like Hyundai and Daimler have already embraced this technology, whilst suppliers like Aisin, Jatco and ZF are also supplying automatics to many OEMs such as BMW, Nissan and Volvo. Other OEMs are, of course, expected to follow using similar systems.
Dedicated Hybrid Transmissions
The design and structure of DHTs, which are characterized by having the electric motor/s fully integrated into the transmission, is just as varied as the number of potential hybrid configurations.
The Aisin/Toyota DHTs are the most established in the market, making up the majority of all DHTs manufactured to date, and are based around a planetary gearset. In these applications, one input of the planetary gearset is driven by the combustion engine, the second input is driven by the electric motor, giving a variable speed drive at the output to connect to the wheels.