H Y B R ID V E H I C L E S
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the start-stop vehicle is rarely thought of as a hybrid. During start-stop operation when the ICE is not running or stopped, it is saving fuel and tailpipe emissions. But the vehicle is still in run mode and operating off the vehicle’s 12V battery, keeping the comfort, entertainment and driver systems functional and waiting to immediately restart the ICE when needed. Most start-stop vehicles will modify the charging profile of the 12V battery by increasing the charge rate during vehicle deceleration and will use an AGM battery. The fuel savings per vehicle are low on this type of hybrid (about 1%) but it’s large enough for most manufacturers to use this form of hybridization due to its simplicity and lower initial cost. Mild Hybrid Vehicle (MHEV): The mild hybrid will have an electric motor involved in the vehicle’s drive system, but it will not propel the vehicle on its own and is only used to support the power output of ICE. The electric motor can boost the engine performance during acceleration by providing torque, eliminating the need for a traditional stator motor during start-stop operation and recuperate more energy during deceleration and braking than the mHEV can. The MHEV will have two electrical systems: a traditional 12V low voltage system and high voltage system that can range from 36V to 160V depending on the make and model. Each MHEV will have a DC-to-DC convertor to exchange energy between these systems.
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Fig. 1: There are many types of Hybrids that are now entering our shops for service and almost all the services and repairs do not have anything to do with the high voltage system. Fig. 2: This is the plug-in port for a PHEV on a Toyota Prius. Most of these plugs are standardized in North America and allow the vehicle to be plugged in at home, work or other charging location.
There are two familiar types of MHEV: The Belt-Alternator-Starter (BAS) system and the Integrated Motor Assist (IMA). The BAS is considered a bolt-on hybrid solution that can be applied to almost all vehicle platforms with few modifications. The amount of torque that a BAS system can transmit is limited by the slippage of the drive belt. The IMA MHEV made popular by Honda does not suffer from this limitation because the electric motor is connected directly to the crankshaft. GM has used the BAS, and FCA (Fiat Chrysler Automobiles) is currently using the BAS on its 48V eTorque system that is an option available to Ram 1500 trucks and Jeeps. Hybrid Vehicle (HEV) or Full Hybrid Vehicle (FHEV): The HEV will use both the electric motor and ICE to provide vehicle motion. The HEV permits full electric driving but only for short trips and will take advantage of all the mild hybrid characteristics. The HEV will have a higher high voltage battery system typically 300V to 400V. The HEV will have a more powerful electric motor than that of the mild hybrid and a more capable high voltage battery for supplying and storing more energy. Toyota and Lexus have been the leading manufacturers of HEV vehicles, but the list of HEV vehicles is much bigger in 2021 with Hyundai, Ford, Audi, Nissan, Honda, Chevrolet and Kia and others all producing HEV vehicles.
ASP | JUNE 2021
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