Mild hybrids are generally internal combustion engines equipped with an electric machine (one motor/generator in a parallel configuration) allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly. Mild hybrids may employ regenerative brake and some level of power assist to the internal combustion engine (ICE), but mild hybrids do not have an exclusive electric-only mode of propulsion.
The electric motor (~60 kW or less) provides greater efficiency by replacing the starter and alternator with a single device which assists the powertrain. Mild hybrids do not require the same level of battery power and do not achieve the same levels of fuel economy improvement as compared to full hybrid models. One example is the 2005-07 Chevrolet Silverado, Parallel Hybrid Truck (PHT) a full-size pickup truck with a single 7 kW 3-phase electric motor mounted in the bell-housing between the engine and a conventional 4L60E transmission. Chevrolet was able to get a 10% improvement on the Silverado's city fuel efficiency by shutting down and restarting the engine on demand, and the reduction of parasitic accessory loads. However the PHT had no power assist features or all-electric "electric vehicle" (EV) capability, and very limited regenerative braking features.
Advantages and disadvantages
Compared to a full hybrid vehicle, however, mild hybrids may provide some of the benefits of the application of hybrid technologies, with less of the cost–weight penalty that is incurred by installing a full hybrid series-parallel drivetrain. Fuel savings would generally be lower than expected with use of a full hybrid design, as the design does not facilitate high levels of regenerative braking or necessarily promote the use of smaller, lighter, more efficient internal combustion engines. BMW, however, succeeded in combining regenerative braking with the "start-stop system", which is not a mild hybrid system, as it does not assist the combustion engine in their current 1-series model.
General Motors mild hybrids including the Parallel Hybrid Truck (PHT) and numerous cars and SUVs equipped with the BAS Hybrid system, often use a 36- to 48-volt system to supply the power needed for the startup motor, as well as a source of power to compensate for the increasing number of electronic accessories on modern vehicles. GM's Belt alternator starter (BAS) mild hybrid system uses a belt drive to start the internal combustion engine (ICE) through its motor–generator unit (MGU), then once started the engine drives the 14.5 kW motor-generator to charge the batteries. The BAS hybrid system also utilizes regenerative braking to replenish the system's 36 V battery and can provide moderate levels of power assist. According to the EPA, a 2009 Saturn Vue Greenline equipped with the BAS Hybrid system delivers a 27% improvement in combined fuel economy over the non-hybrid version (FWD 4cyl).
Honda's Integrated Motor Assist directly attaches a brush-less DC motor between the flywheel and transaxle, providing both assist during acceleration, and regeneration during coasting / braking. It has been produced in various voltages and power outputs, as dictated by the size and weight of the vehicle application. Models equipped with the Integrated Motor Assist include the Honda Insight (1999-2006, 2009- ), Honda Civic (2003- ), Honda Accord (2005), and CR-Z (2010- ).
During the 2008 Olympic Games in Beijing in August, Chinese automobile manufacturer Chang'an Motors supplied a number of hybrid-drive cars as taxis for the athletes and spectators. The power electronics for the "mild hybrid" drive was supplied by Infineon.
Toyota sold a mild hybrid version of the luxurious Toyota Crown beginning in 2002 only for the Japanese domestic market. Fuel economy was increased when compared with the standard 3.0 V6 petrol unit. Toyota now sells a full hybrid with an electric motor for the new 2008 Toyota Crown.
The Smart Fortwo microhybrid sold in Europe, although is not a mild hybrid.
Citroën proposes a stop and start system on its C2 and C3 models. The concept-car C5 Airscape has an improved version of that, adding regenerative braking and traction assistance functionalities, and ultracapacitors for energy buffering.
List of makes and models
- Chevrolet Silverado Hybrid (2005–2007)
- Saturn Vue Green Line (BAS Hybrid, 2007–2009)
- Saturn Aura Green Line (BAS Hybrid model 2007–2009)
- Chevrolet Malibu (BAS Hybrid model 2008–2010)
- Mercedes-Benz S400 BlueHybrid
- BMW ActiveHybrid 7
- Peugeot 308 e-HDi (from 2011, referred to by the manufacturer as micro-hybrid)
- Buick LaCrosse with eAssist (2012-)
- Buick Regal w/ eAssist (2012-)
- Buick Regal (2013 all trims in North America)
- Ferrari LaFerrari (2013-)
- Chevrolet Malibu w/ eAssist (2014-)
- Chevrolet Impala (2014 eAssist version; arriving 4th Quarter 2013)
- Honda Hybrids with Integrated Motor Assist
- "Pilot Project MOVELE: An initiative of the IDAE in favour of energy efficiency in transport" (PDF). Retrieved 2013-08-09.
- BMW EfficientDynamics - Introduction - BMW AG
- MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and Systems
- "Chinese hybrid car to use Infineon electronics" in EE Times. Retrieved July 22, 2008
- CITROEN - Stop and Start
- Green Car Congress: VW Brings Diesel Mild-Hybrid Concept to Shanghai
- List of Hybrid Cars
- Sam Abuelsamid (200-04-03). "What is a mild hybrid?". AutoblogGreen. Retrieved 2010-03-22.