Mild hybrids (MHEV) (also known as smart hybrids, power-assist hybrids, battery-assisted hybrid vehicles or BAHVs) are generally cars with an internal combustion engine (ICE) equipped with a minimally extended battery and an auxiliary electric combined motor and generator in a parallel hybrid configuration that is not enough for an electric-only mode of propulsion but does allow the engine to be stopped whenever the car is coasting, braking, or stopped, and then restarted once power is required again. Mild hybrids may employ regenerative braking and some level of power assist to the internal combustion engine.[1] [2] [3]
The mild hybrid's electric motor provides greater efficiency through the use of a single device that is essentially an integrated starter/alternator sometimes known as a generator-motor unit. A typical mild-hybrid setup uses a belt-powered generator-motor unit driven off the engine to supply power to a small battery. The generator is also powered through regenerative braking, enabling power that would otherwise be dissipated as heat to be recaptured and recovered for use in powering the vehicle. The small power assist generated by mild-hybrid systems can help supplement the internal combustion engine in low-speed situations or handle the demands of engine start/stop functionality. Vehicles equipped with a mild-hybrid system typically see anywhere from a 0.4 to 1.7 km/l improvement in fuel economy relative to comparable models without the technology.[4]
These contain two different energy recovery systems.
The Mercedes-Benz C-Class (W206), Mercedes-AMG SL 43 (R232), the Mercedes-AMG CLE 53, and the petrol Mercedes C254/X254 have both an electrically assisted turbocharger and a motor–generator unit (MGU-H).[5] [6]
There is doubt on whether mild hybrids should be classified as hybrid or have EV (electric vehicle) in their MHEV abbreviation as they cannot be powered only by electricity at any time.[7] Their emissions reduction is often so low that the impact on environment is negligible and may be seen as greenwashing.[8]
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.[9] 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).[10]
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.[11]
Toyota sold mild hybrid versions of the Toyota Crown executive sedan between 2001 and 2003 and the mid-size Crown Sedan between 2002 and 2008 in the Japanese domestic market.[12] [13] These models combined a BAS hybrid system with the standard straight-6 petrol engines for increased fuel economy. Toyota now sells a full hybrid version of the Crown under their brand name Hybrid Synergy Drive.
MINI and BMW have start and stop, and some with regenerative braking, in all of their vehicles sold in Europe running 4-cylinder engines with manual transmissions.[14] Citroën proposes a stop and start system on its C2 and C3 models.[15] The concept-car C5 Airscape has an improved version of that, adding regenerative braking and traction assistance functionalities, and ultracapacitors for energy buffering.[16]
In 2004 VW brought two mild hybrid concept cars to Shanghai for the Challenge Bibendum.[17]
Suzuki has announced the Suzuki Baleno with integrated SHVS-technology in 2016 on the new Suzuki HEARTECT platform. Suzuki has had experience with this mild-hybrid technology in their Suzuki Ciaz.
Most hybrids use gasoline engines, but some use Diesel engines, such as the Hyundai 1.6.[18] In 2021 Land Rover started selling the Range Rover Sport D350, which runs on the 3.0-litre D300 Ingenium Diesel engine.[19] [20] [21] [22] [23]
The Genesis G90 and Genesis GV80 Coupe offer mild hybrid options with an electric supercharger.[24] [25]