How it Works - Full Hybrid Electric Vehicle

What Is a Full Hybrid (FHEV)?

A full hybrid electric vehicle (FHEV) is an electrified vehicle with an electric motor (eMotor) that complements an internal combustion engine (ICE). Sometimes referred to as “Hybrid Electric Vehicles” (HEV) or “self-charging hybrids,” the FHEV can operate in full EV mode, but not for long periods and significant speeds. While the eMotor can propel the vehicle alone, there is no practical electric-only range capability.

FHEV Batteries and Motor

Like ICE-only vehicles and mild hybrids (MHEVs), FHEVs have a conventional vehicle battery in a 12-volt platform to power components like lights and sensors. However, at the heart of the FHEV system is a moderately sized lithium-ion battery pack that is larger than those found in a MHEV, but smaller than those found in a plug-in hybrid (PHEV). These batteries are typically between 100- and 400-volts. The eMotor of a FHEV is also more powerful than those found in a MHEV.

FHEV Drivetrain Configurations

The FHEV drivetrain determines how the ICE and electric motor interact to move the wheels. One of the most common configurations allows the electric motor and ICE split propulsion duties. This means that the electric motor alone can power the vehicle, or the ICE engine can power the vehicle depending on the conditions. This drivetrain enables the potential for efficiency, as options for low speeds (eMotor) and high speeds (ICE) reduce energy losses.

Normal operation involves three modes seamlessly transitioning: EV-only, ICE-only, and combined EV and ICE and takes into account the driver’s demand (via the accelerator pedal) amongst other conditions to optimize the mode used at any time. During low demand, EV mode would typically be engaged. At higher loads (such as during accelerations, driving up hills or at higher speeds) the ICE would be engaged, often in combination with the eMotor. Often the driver would have no idea of the transition between both modes due to the seamless start-stop capability of the vehicle.

The Benefits of the FHEV

Since the eMotor creates more power, a FHEV can realize comparatively better fuel economy by leveraging a highly efficient and smaller ICE. Another benefit of the FHEV is regenerative braking, which is the gathering of the energy used to stop the vehicle. Much of this energy is lost in a conventional braking system via heat and wear. Regenerative braking has the secondary advantage of prolonging the life of brake pads and rotors.

Since the eMotor is used to start the vehicle, there is no need for a separate starter motor. Even though the battery is larger than that found in a MHEV, the battery is still smaller than those found in a plug-in hybrid (PHEV) and a battery electric vehicle (BEV). For this reason, FHEV batteries occupy a relatively small space.

FHEV Outlook

FHEVs can be an efficiency upgrade over ICE-only vehicles. FHEVs are ideal for consumers who want fuel efficiency without the constraints that come with charging via an external source. For example, consumers without access to a home charging infrastructure or those concerned about range and the obstacles it presents can still reap fuel efficiency benefits without going so far as a full battery electric vehicle (BEV). With that in mind, automakers are expanding and improving their FHEV offerings to meet consumer preferences around performance and comfort.

Learn more about Lubrizol’s Evogen™ e-mobility fluids for hybrid EVs.