Any vehicle that has two or more sources for its driving power can be referred to as a ‘hybrid’, but carmakers are employing three general hybrid types. A mild hybrid is a vehicle driven by an internal combustion engine (ICE) that may turn itself off when the vehicle is coasting, braking or stopped in traffic, restarting as the accelerator is pressed, brake pedal is released, or the clutch is engaged. A parallel hybrid has both an ICE and one or more electric motors that work together to create wheel-turning power. A series hybrid also includes an ICE and electric motor(s), though in this case power is only delivered via the electric motor(s), with the ICE only running to charge the batteries as needed.
As the recent Frankfurt Motor Show demonstrates, virtually all major OEMs now offer (or plan to offer in the near future) models incorporating one or more of these systems, either in vehicles adapted to use hybrid systems, or in ‘dedicated’ vehicles designed from the ground up to use a hybrid propulsion solution. Cars adapted to use hybrid systems include BMW’s Mini and GM’s Malibu, while Honda’s Insight and the Toyota Prius are well-known examples of dedicated hybrids.
Turning an ICE off at idle is clearly going to save fuel, yet while the concept behind mild hybrid systems may appear simple, the working solution involves considerable complexity. A standard engine is started only once on any given journey; a mild hybrid vehicle has to be able to automatically restart its engine an unlimited number of times – this, with a minimum of intrusion and without detracting from the overall driving experience.
Since 2007, the Mini has employed BMW’s Efficient Dynamics Technologies (also offered on 1- and 5-Series models) as its mild hybrid solution. In addition to the startstop feature, it also includes brake energy regeneration and a switch point display system. Offered with all manual transmission versions, the start-stop is engaged when the car is put in neutral, the engine restarting when the clutch pedal is depressed. The so-called Intelligent Alternator Control (IAC) drives the regeneration system, channelling current developed on the overrun to the heavy-duty battery.
This is separate from the belt-driven alternator. The switch point display signals when the driver should change gear for optimum fuel economy.
Uprated parts added post-launch to second-generation Mini models with the stop-start feature include a new starter motor and alternator, which can disengage when not required, and a new, heavy-duty absorbent glass mat (AGM) battery by Varta, part of Johnson Controls. The sealed AGM battery uses glass mats saturated with boron silicate between the plates instead of a gelled or liquid electrolyte.
While the charging voltage is the same as a standard 12V car battery, the internal resistance of an AGM battery is extremely low, virtually eliminating heat build up in the battery when either under heavy charging or discharging – such as when regenerated current is delivered or when multiple engine starts are required.
Controlled Power Technologies’ Belt-driven Integrated Starter Generator (B-ISG) system also features an AGM battery. Mike Dowsett, Senior Manager, Micro Hybrids at CPT explains: “For our micro-hybrid stop-start system, the recommended battery upgrade is from a flooded lead acid battery to an AGM or valve-regulated lead acid model. They provide an energy supply that can withstand a deep discharge and rapid recharge.”
CPT’s B-ISG system has, according to Dowsett, been designed as a direct replacement for the alternator, and features very similar fittings. While the donor engine requires new calibration to reflect faster starting, including quicker crank sychronization and minor modifications to the air/fuel mix, these will result in both improved emissions and fuel economy.
“CPT SpeedStart is the highest-powered 12V B-ISG available,” claims Dowsett. “It provides 2.4kW of cranking power, which is more than most starter motors. It also provides 72Nm of torque, which when multiplied through a 3:1 belt ratio will deliver 216Nm at the crankshaft.” Dowsett goes on to say that the system can work with most larger European vehicles, even handling the compression ratio of a 2.0-litre common rail diesel. Systems that go above 12V have significantly higher hardware and integration costs, he reasons, with two voltages on a single vehicle requiring converters and other additional equipment.
GM has been offering its own belt alternator starter (BAS) system on models including the Chevrolet Malibu and Oldsmobile Aurora. While similar in concept to the CPT unit, the GM BAS replaces the conventional starter and alternator with a 36V system that controls a variety of engine functions.
Facing limited popularity, the current BAS system is due to be phased out. But development of an improved system is already well advanced, according to Brian Corbett of GM’s Hybrid and Battery Division: “The new system will go into production in calendar year 2011. We are developing the technology in-house and Hitachi will provide the lithium-ion batteries. We have not announced the manufacturing location(s) for the vehicles that will use the next-generation mild hybrid system.” The second system is expected be approximately 24% smaller and 40% lighter than the previous version, delivering up to 120V (up from the original 36V).”
Corbett continues: “Compared to the current system, the next-gen technology will offer increased power and voltage, increased electric boost, increased regenerative braking, together with increased fuel efficiency. (The system) is a key part of GM’s environmental strategy; it’s our answer for a high-value, affordable hybrid system. It’s easy to integrate globally, offering potentially significant volume growth via broader engine and transmission application.”
Toyota’s Hybrid Synergy Drive is perhaps the most well known hybrid system. Available on a range of models, including the Prius and Lexus LX range of SUVs, the system offers familiar hybrid features, electric-only driving at low speed, regenerative braking, etc. Though while the Hybrid Synergy Drive combines petrol and electric power at the driven wheels, there are other ways to arrange a parallel hybrid.
With the upcoming launch of its HYbrid4 models, the first of which will be the Peugeot 3008, PSA Group will introduce its own parallel hybrid solution. This system is fundamentally different to other similar hybrid arrangements in that it is the first to use a diesel engine.
Further, instead of using combined petrol and electric power at the same driven wheels, the electric motor independently drives the rear wheels, effectively making this a hybrid fourwheel drive system.
Where as most other parallel hybrids locate the electric motor in close proximity to the engine, the PSA solution has the electric motor housed in the rear suspension linkage. As such, the system becomes a modular solution, meaning that a given vehicle platform does not have to be comprehensively altered in order to accommodate the new drive package, offering so-called ‘cross-range adaptation’.
According to PSA, this will allow hybrid technology to be applied to a range of vehicles, while cutting the overall cost.
In addition to claimed CO2 reductions of up to 35% over an equivalent diesel-only model, the PSA system means four-wheel drive with less complexity. The Lexus LX450h, for example, while having two separate electric motors (front and rear) has only the single petrol engine, meaning a driveshaft and transfer case is required to deliver the variable petrol-electric power to the rear axle. PSA further claims that relocating the electric motor from the engine bay to the rear axle has considerably improved vehicle weight distribution.
It is a hybrid solution that has minimal impact on production line setup, explains Eric Breton, Director of PSA Hybrid Technology Programmes: “HYbrid4 cars will be assembled on the same line as the conventional ICE versions at our Sochaux facility. To this end, some workstations will be adapted or added. The rear suspension will be provided completely assembled, with the electric motor and its wiring.
The power electronics and battery packs will be installed separately in their respective locations (under the floor of the trunk). This will allow for both maximum quality of assembly and very good cost effectiveness.”
While Peugeot is the first OEM to use a diesel engine in partnership with an electric motor, Hyundai is the first to use an LPG (liquid petroleum gas) and electric combination to create its hybrid application. The result of a $200m, 43-month development programme, this new model is also the first HEV (hybrid electric vehicle) to use lithiumion polymer (LiPoly) batteries supplied by LGChem, the company also providing the test battery packs for the GM Volt. The Elantra HEV (hybrid electric vehicle) went on sale in South Korea earlier this year, where LPG is a popular alternative to petrol. Hyundai says that it is investigating the possibility of exporting the model to other areas that have an LPG delivery infrastructure, including Australia.
Perhaps the most famous hybrid PHEV – or petrol/electric vehicle - is the Chevrolet Volt or Opel Ampera, as it is to be called in Europe. For all the talk about the Volt, GM’s Brian Corbett claims few - if any - have accurately described how the powertrain will work. “The Voltec propulsion technology used in the Volt isn’t always easily understood. It’s not a series hybrid, as these never run on electricity alone and the engine runs at a constant speed. The Volt can run on electric only and the engine does not run at a constant speed.
“After the Volt’s electric-only propulsion is depleted, the engine will start, but only to generate electric energy to drive the wheels, not charge the battery. The engine comes on to make enough electric energy to turn the wheels, because the wheels are always turning electrically. With the electric generator about half the size of the motor, you might expect there to be performance problems but that’s where the battery comes back into play, because the customer depletion point is not full depletion; by design, there’s still energy available. In peak situations, such as climbing a hill or merging into traffic, the system takes some more energy out of the battery, meaning that the system may actually come down a little below the customer depletion level.”
Corbett goes on to explain that the depleted battery charge can then be replaced through regenerative technology, or alternatively, energy not used to turn the wheels can replenish the charge. But the key, Corbett says, is what the system does not do: “We don’t recharge the battery. In fact, the customer won’t recognize any of this is taking place, as their electric range indicator will remain at zero. At that point we are actually using the battery as a peak buffer, trying to recapture energy as the opportunities allow.”
General Motors has confirmed that it plans to invest $43m in its GM Subsystem Manufacturing facility, in Brownstown, Michigan, for production of the 200kg, T-shaped battery packs used in the Volt, the first case of a lithium-ion battery production centre being controlled by an OEM company.
To support this and other vehicle battery technologies, the carmaker has also opened a new $25m Global Battery Systems Lab, part of the GM Tech Center in Warren, Michigan.
As Volt production plans remain uncertain, there is time for a little last-minute lobbying. On a recent tour of GM’s Warren Technical Center, South Australia Premier Mike Rann announced that he would like to see GM’s Voletc technology appear in a version of the Holden Cruze, production of which is due to start at the GM subsidiary’s Elizabeth, Adelaide plant in 2010.
Yet there in lies the fundamental problem with the Volt. Unlike Peugeot’s HYbrid4 system, which can be adapted for use in a wide range of vehicles, the Volt is a powertrainspecific model. Although the Cruze and Volt share a similar platform and versions of the Cruze were used to test the Voltec system, those cars were highly adapted in order to accommodate the electric motor and batteries. That said, GM are considering a Holden Volt version, as part of a move to increase the choice of fuel-efficient models that use E85 biofuel and have stop-start systems.
While some OEM carmakers, battery manufacturers and even national and local governments have announced supply deals, production joint ventures and new factory builds aimed at producing lithium-ion batteries, the fact is that most hybrid vehicles use NiMH (nickel metal hydride) batteries. With Toyota (and Lexus) already having built more than two million hybrids using this battery type, PSA Group is taking the tried and tested route in using the same technology to deliver its HYbrid4 models.
All NiMH batteries use nickel as their primary material.
Another essential constituent are so-called rare earth metals (REMs), with the term ‘rare earth’ coming from the ‘uncommon oxide’ minerals first found in combination with the REM base elements. A battery pack for the Toyota Prius uses between 10 and 15kg of the REM lanthanum, together with smaller quantities of the REMs neodymium and praseodymium. In addition, the high-power magnets in the electric motor used in a hybrid vehicle require approximately 1kg of neodymium, together with small quantities of terbium and dysprosium, added to preserve magnetic characteristics at high temperatures.
Yet doubts remain over the sourcing of rare earth metals.
Estimates put Chinese production of REMs at 95% of global output, and with the Chinese government considering imposing REM export quotas, the situation could have a serious impact on hybrid vehicle production outside China. With the Toyota Prius said to be the largest single product using rare earth metals, the company is reportedly investigating alternative sources in Canada and Vietnam, while a former mine in California (Mountain Pass) is scheduled to reopen in 2012.
For the moment at least, a sustained policy of reducing export quotas has effectively created a Chinese rare earth metal monopoly.
Although the country has the capacity to supply global demand, which is rising at 10% per year, its 2009 export allocation was 38,000 tonnes – less than the total amount used by Japan in a year.
The success of the recently-released third-generation Prius has had the knock-on effect of causing a hybrid battery shortfall. While batteries for the Prius had been supplied by a joint venture between Toyota and Panasonic EV Energy, the carmaker has been forced to arrange additional battery deliveries from Sanyo Electric in order to maintain current production numbers.
The battery shortage has caused bottlenecks in production, with Prius customers waiting up to eight months for delivery. Further complicating matters, the Lexus HS250h, the premium manufacturer’s first dedicated hybrid model, has placed added demands on hybrid battery supplies.
Anticipating sales of 500 units per month, Lexus received 10,000 orders in the models’ first month of availability.
Reports suggest Toyota will start using li-ion batteries for its hybrid models in 2011, though this has yet to be confirmed. Panasonic, though, is waiting for regulatory approval to take control of Sanyo – coincidentally the world’s largest producer of rechargeable li-ion batteries.