Hybrid, Plug-in Hybrid, HEV, PHEV, FCHEV… What Do They Mean?

When looking at hybrid cars, you might have come across a range of different terms and acronyms used to describe them. Most of us know the basic idea behind a ‘hybrid’ car (aka one with a standard internal combustion engine, and also an electric battery which gets charged when the car is in operation), but terms like plug-in hybrid, PHEV, FCHEV and HEV have the potential to confuse matters! So this article takes a look at what each of these mean.

Basic Definitions

  • Hybrid/HEV: This is the traditional hybrid, also called a HEV. A car mainly with a combustion engine, but also with an electric battery. The car’s combustion engine will recharge the electric battery as needed, and the car will ‘switch’ between electric and engine mode to get the best fuel efficient.
  • Plug-in Hybrid/PHEV: A plug-in hybrid vehicle (also called a PHEV) takes the idea of a traditional hybrid further, by allowing for the electric battery to be charged by being plugged in. You can also switch to fully electric mode when driving it around, so you can use a PHEV as a fully EV until the battery runs out (or is re-charged), gaining the full benefit of this.
  • FCHEV: This lesser known term stands for Fuel-Cell Hybrid Electric Vehicle. In other words, it’s a hybrid car which uses hydrogen power (via a fuel cell) instead of gasoline power (via a combustion engine). The Mercedes GLC F-Cell, announced last year and due for release next year, is an example of a FCHEV.

Traditional Hybrid/HEV – in more detail

As mentioned earlier, a traditional hybrid car has both an internal combustion engine, but also an electric drivetrain (as in, electric battery power which drives the wheels forward via an electric motor). The Toyota Prius is the best known example of a HEV, having sold around 4 million units since their launch back in 1997. Since being one of the earliest ‘eco friendly’ cars sold on the mass market, a range of Hollywood celebrities have been seen driving (and promoting) the Prius – including Cameron Diaz, Jessia Alba, Harrison Ford and Orlando Bloom.

A teaser image of the Toyota Prius all-wheel drive
A teaser image of the Toyota Prius all-wheel drive

In terms of the drivetrain – also called a powertrain – there are a few types for hybrids:

  • In-parallel hybrids: the combustion engine and electrical motor are both connected to the transmission and thus can provide power (to drive the wheels) at the same time. Such hybrids use full size, standard combustion engines and a small motor and battery pack (since the electric component is supplementary, not key, to driving a hybrid car forward). These tend to be more efficient at higher, more consistent speeds – such as highway driving.
  • In-series hybrids: only the electric motor drives the drive shaft – and thus wheels – forward, in a similar way to how electric cars work. The combustion engine is not full sized, and instead it’s used more as a generator to provide power to the electric motor and/or battery pack. These tend to be more efficient at lower, less stable speeds – such as inner-city driving.
  • Power-split hybrids: these take the ‘best’ ideas from both of the above, incorporating power-split devices which allow for the power going to the drive-train to be practically separate from the power required when the driver puts their foot down on the accelerator pedal. In other words, power-split hybrids aren’t a simple ‘accelerator pedal -> power source -> drive shaft moves -> wheels move’ type flow. The power management system can instead ‘choose’ the best power source (gasoline or electric) at the best time.

Plug-in Hybrid/PHEV – in more detail

Whilst traditional hybrids do have an electric battery pack, how and why the electric power is used is not up to the driver – the hybrid car will choose for you, based on a range of factors (and naturally constrained by their original design).

However with a plug-in hybrid, the driver has ‘access’ to the rechargeable electric battery pack. This is via the plug-in recharge port within the hybrid car, which the driver can connect to a charging station. There’s then a separate fuel port for the standard gasoline based fuelling at a pump.

The Hyundai Ioniq PHEV 2018
The Hyundai Ioniq PHEV 2018

The driven can then choose whether to drive in full-electric mode (i.e. purely from the electric battery pack) or from gasoline power (i.e. via the internal combustion engine). This helps to eliminate ’range anxiety’ because when the electric power is running very low, the PHEV will just switch back to gasoline power.

It is worth noting that the electric battery within a PHEV is naturally smaller than in a full-electric BEV. For example, the Hyundai Ioniq PHEV has a 8.9 kWh battery giving a 39 mile (62.7 km) range. This compares to the Hyundai Ioniq BEV, with a 28 kWh battery and 174 mile (280 km) range.

However usually the battery pack is one of the biggest costs of a vehicle, and so the advantage of a PHEV is that they can be cheaper to buy than a full-electric car, but yet the driver still gets the benefit of pure-electric fuel for their (shorter) journeys.

Hydrogen Hybrid/FCHEV – in more detail

A lesser known term is the FCHEV, or ‘hydrogen hybrid’ – a hybrid-electric vehicle (HEV) whose power source is via fuel-cells (FC).

In other words, whilst a traditional hybrid has an electric component but is primarily fuelled via gasoline and the internal combustion engine, a FCHEV still has the electric component – but it is instead primarily fuelled via hydrogen and the fuel-cells.

To be honest though, a FCHEV is essentially just a ‘hydrogen car’. Both the Toyota Mirai and Mercedes GLC F-Cell describe their cars as having hybrid technology, despite the fact that both are considered to be pure hydrogen cars.

This is therefore a little confusing, but it’s worth remembering how hydrogen cars work. Essentially a hydrogen car produces power via fuel cells, but then everything after that is the same as an electric car. So whilst a purely-electric car naturally isn’t a hybrid because everything (including its power source – aka the battery pack) is electric, a hydrogen car is a split between its power source (hydrogen) and the drive train (electric) – hence describing it as a FCHEV/hydrogen hybrid is potentially appropriate.

If/when hydrogen car technology matures, however, it will be interesting to see whether they continue with the current ‘hybrid’ style design.

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