What is a PHEV? Understanding Plug-in Hybrid Electric Vehicles.

Plug-in Hybrid EVs (PHEVs) are a vehicle category that unlock incredible fuel economy for day-to-day driving, and represent far more than a mid-way point between the combustion and electric worlds.

However, to take advantage of PHEVs, it's important to understand what makes them different. PHEVs are designed to continuously combine engine and electrical power, and gest the best of both power sources.

What is a PHEV? 

A PHEV combines an electric traction motor, a rechargeable battery, hybrid transmission, and an engine.

Like a Battery Electric Vehicle (BEV), a PHEV can drive on electric power alone. However, a PHEV uses a smaller battery that translates to a lower pure-electric range.

A PHEV differs from a conventional Hybrid EV (HEV) via its larger battery and the fact that its battery requires external charging between drives. And, unlike a Range-Extended EV (REEV), the engine within a PHEV is connected directly to the wheels via a hybrid transmission.

Read more about vehicle types with what is a REEV?

How a PHEV works

At first glance, a PHEV is capable of behaving like a BEV for day-to-day use. Many PHEVs are marketed based on their pure-electric capability, which can theoretically deliver silent, zero-emission driving for urban and short-distance journeys. Charging is typically carried out via a home wallbox, public charging infrastructure, or, less commonly, a standard domestic socket.

However, while being able to support shorter pure-electric trips, the real value of PHEVs comes from something else entirely: torque blending. This is the process of combining power from the traction motor and engine in real-time, which allows both the motor and the engine to operate at their most efficient "sweet spots".

This is an extension of what conventional Hybrid EVs (HEVs) do already. For passenger cars, engines are efficient at delivering the torque needed for acceleration only after their crankshafts are spinning at thousands of times per minute. HEVs take advantage of the fact that motors are efficient at delivering power at high speeds and low torques to generate that RPM.

HEVs practice torque blending for start-up and stop-go driving. Using a smaller ~2kWh battery, they maintain charge through regenerative braking and a small amount of engine power. However, beyond these conditions, HEVs fall back on relying on the engine.

By building in a larger battery that requires plug-in charge, PHEVs can torque blend for hundreds of kilometers of continuous driving, resulting in the most efficient possible use of a vehicle's fuel.

A PHEV can complete most daily commutes without engaging the combustion engine

Read more about vehicle types with what's the difference between HEV, PHEV and REEVs?

Why PHEVs matter

PHEV fuel economy and emissions performance can be comparable to that of a BEV from a lifecycle emissions perspective.

However, this does require us to look at PHEVs as something other than a middle-ground between BEVs and combustion vehicles. Unlike REEVs, the real value of PHEVs is not through their ability to provide a small amount of pure-electric range with extra combustion power kept in reserve.

Instead, efficient torque blending turns PHEVs into a distinct dual propulsion system: one which requires an incredibly sophisticated layer of software and computing power to operate in real-time, along with precise mechanical and electrical engineering.

To realize the benefit of PHEVs, however, their charge has to be maintained to ensure they can operate as an efficient dual propulsion powertrain. It also requires that automakers and policymakers ensure that the properties of PHEV powertrains are properly marketed, communicated, and regulated - not treated as a compromise or transition between pure-combustion and pure-electric mobility.

Read more about how tighter PHEV utility factor requirements will harm the auto industry.

The role that PHEVs play

PHEVs sit between conventional hybrids and fully electric vehicles - while they play an important role in the broader shift towards decarbonized mobility, they have secured their place as a long-term staple of the global vehicle park.

Rather than serving only as a transitional technology, PHEVs provide a scalable and practical solution for many markets where full electrification faces economic, infrastructure, or usage challenges.
At Horse Powertrain we understand that each country, region and town has different infrastructure barriers, that’s why we provide multiple powertrain options that suit every scenario.

Find out more about our solutions here: spotlight solutions.