Mild Hybrid

Mild Hybrid

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.

These electric motors (~20 kW or less) provide greater efficiency by replacing the starter and alternator with a single device which assists the powertrain and are called mild hybrids also don't 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.

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).