Electric vehicles are continuously rising in popularity. A special variation of EVs that many users are familiar with as a concept but few really know the inner workings of, are hybrid vehicles. There are many car models and versions with this technology on the market, which might make the distinctions between the different types look rather complicated. In order to provide a better idea of which kind of hybrid might suit you best and what their respective advantages and disadvantages are, we have compiled an overview to cover the basics.
What actually is a hybrid?
Hybrid vehicles combine two different types of driving systems and consist of a mix of diesel or petrol and electric motor or fuel cell. The most common combination, and the one we are going to talk about, is combustion plus electric motor.
How are hybrid vehicles classified?
To understand the different terminology, it is important to learn the classifications. The first such distinction is to divide HEVs (hybrid electric vehicles) by motor system. There are two main types of hybrid motors systems: series hybrids and parallel hybrids.
Both parallel and series hybrids feature a petrol engine, as well as an electric motor with a rechargeable battery, inverter and transmission. However, they are configured in distinctively different ways. A series hybrid features a smaller engine than a parallel hybrid, with a larger electric motor and battery. The following will explain, why.
Series hybrids use a technique that has been around for quite some time, powering ships and locomotives. An on-board fossil fuel generator burns fuel to produce energy, which is then stored in the battery. The actual propulsion is completely electric, coming either directly from the generator or from the battery, which is charged by the generator, and regenerative braking.
Pro: The electrical system is self-sustaining and therefore can, but doesn’t have to, be externally charged. Since it primarily relies on electric power and uses less fuel, it effectively reduces emissions compared to traditional combustion engines.
Con: The large battery plus the generator are not especially cost or weight efficient.
Parallel hybrids have both an electric and a combustion engine that can operate at the same time. Depending on the power distribution, a vehicle can run on both electric and fossil fuel energy simultaneously or individually, as it is controlled via two separate drivetrains. Parallel hybrids also use regenerative braking, an energy recovery mechanism which converts the energy required to decelerate a car into a form that can be reused either immediately or stored for later, to feed the battery.
Pro: Both motors in a parallel hybrid can be comparatively small and therefore more cost and weight efficient.
Con: In comparison to the series hybrid, most parallel hybrids rely more on the combustion engine, making them less environment friendly (albeit still more than regular cars).
MHEV, FHEV, PHEV – what’s the difference?
So, we have established, that hybrid vehicle motors typically generate power through either a series or parallel system, or a combination of both. But there is also another level of distinction. Abbreviations like MHEVs, FHEVs and PHEVs don’t describe the type of motor system, but rather the distribution of combustion and electric energy in the vehicle – for example, whether the power distribution between the electric motor and combustion engine are matched, or whether one of the two is the dominant player.
Mild hybrids (MHEV = mild hybrid electric vehicle) are, as the name suggests, a more moderate type of hybrid. The electric part of the vehicle plays more of a supporting role then a lead. The main function of a mild hybrid is to recharge the battery, foremost through regenerative braking, and to kick in during start/stop and acceleration, helping to save fuel. They solely exist as parallel hybrids since the electric motor in a MHEV doesn’t give propulsion itself and can’t power the car on its own.
Pro: Mild hybrids require very small batteries because they are only used in a limited capacity. This usually means that they are less expensive and lighter.
Con: The low electric power ratio only results in minimal fuel efficiency. MHEVs therefore have limited environmental advantages.
Examples for MHEV cars: Audi Q8, Mercedes CLS 450, BMW ActiveHybrid
A full hybrid (FHEV) can be considered half an electric vehicle. Unlike mild hybrids they are able to drive solely electrical for a certain time and the electric part is equally as important as the combustion motor. Full hybrids are the basis for most series hybrids but also exist as parallel hybrids.
A special variation of the full hybrid is the plug-in hybrid (PHEV). These are equipped with large batteries and can go long distances on just electric energy. PHEVs have the ability to charge externally via a plugging into a power source.
Pro: Full hybrids, such as PHEVs, use electric energy efficiently and often. It is possible to travel comparatively long distances solely on electricity, saving fuel and therefore reducing emissions.
Con: The very large battery is rather heavy and expensive, which reflects on the overall price of the vehicles.
Examples for PHEV cars: BMW 530e, Audi A3 e-tron, Mercedes C 300 DE
As with every rule there is also the exception to it. There are further terminologies that are unique to some car manufactures and combinations of the above systems and power distributions. This overview should nevertheless be a good starting point to determine which hybrid vehicle may be a good fit for your needs, if your are interested in driving one or adding them to your fleet. Our team at Alphabet is happy to provide you any additional information you require on the subject and give you further detail on the topic.