Before we dive into what Hybrid Electric Vehicles (HEV) are, it’s important to understand what hybrid vehicles are. Any vehicle that has two or more distinct power sources can be called a hybrid vehicle. So technically, vehicles which use both petrol/diesel and CNG can also be termed hybrids, although we tend to use the term to define more eco-friendly transportation. So what are Hybrid Electric Vehicles? These are vehicles that combine a usual internal combustion engine as well as an electric propulsion system.
There are a lot of different types of hybrid electric vehicles as well, depending on the degree of hybridization, as well as the powertrain. With increasing fuel costs and the danger of actually running out of fossil fuels in the next couple of decades, it’s only logical that we shift to different types of engines, because we can’t depend on fossil fuels forever. So here’s all you need to know about hybrid electric vehicles!
Hybrid vehicles, rather hybrid electric vehicles, are not such a new concept as many would imagine. Back in 1901, Ferdinand Porsche, founder of the Porsche car company created the Lohner-Porsche Mixte Hybrid, the world’s first petrol and electric hybrid vehicle. It was powered by a 10-14 bhp petrol and electric motors mounted on the hub of its wheels. Quite clearly ahead of its time, the Lohner-Porsche Mixte Hybrid formed the basis for NASA’s Lunar Rover, and even inspired a lot of modern railway locomotives, in addition to being the beginning of hybrid vehicles. Unfortunately, not many shared the Ferdinand’s enthusiasm, and it wasn’t until 1997 that hybrid vehicles really caught on. This could be attributed to the general indifference to sustainable fuels, of course, but was also probably because fuel prices weren’t as worrying as they are today.
Though there were similar vehicles made in 1905, 1915 and 1931, we’d have to wait longer to see affordable hybrid vehicles. In 1997, Toyota introduced the Prius in Japan. It was the first mass produced hybrid electric vehicle, and was initially not so well received because the need for hybrids wasn’t as apparent then, but it quickly grew to be a popular car, and is now the highest selling hybrid vehicle of all time. Honda jumped into the hybrid vehicle game in 1999 with the Honda Insight, a Honda Civic sized sedan. By the new millennium, more carmakers introduced plans for hybrid vehicles, and today, they are seen as the primary segment of the future.
Pretty much all hybrid electric vehicles use the following technologies/innovations to save on fuel costs, or in some cases, bypass them entirely. Depending on the type of vehicle or the situation, HEV’s often tweak engines and internals for more power or better fuel economy.
- Electric Motor Drive/Assist: The most important part of hybrid electric vehicles are of course, the electric motors. As mentioned earlier, depending on the situation or vehicle, it is employed differently. In general, HEV’s come with smaller fuel efficient petrol engines that are assisted by the electric motor when more power is required. During low power or cruising conditions, the vehicle is powered by the electric motor, to save fuel costs. This motor is usually charged while the petrol engine is in use, or the battery pack is charged by a small generator.
- Regenerative Braking: This is a technology that converts kinetic energy of the vehicle into usable power that charges the batteries for use either then or later. Basically, the electric motor applies force to stop the wheels during braking, and the opposing energy is then used to charge batteries. In conventional vehicles, the braking mechanism applies opposing force, and energy is wasted in the form of heat by friction. So energy isn’t wasted.
- Automatic start/stop: Finally, there is automatic start/stop technology, which shuts off the engine when it is idle, and restarts it when required, thus saving fuel and reducing emissions.
Not all hybrid electric vehicles are the same. Depending on the type of powertrain and degree of hybridization, there are multiple classifications. Ostensibly, the more powerful the vehicle is, the higher the cost as well, and the same applies to the complexity of the power sources.
Types by degree of hybridization
- Mild Hybrid: As the name suggests, mild hybrids don’t depend so much on their electric motors. In simpler words, it’s primarily a petrol/diesel powered vehicle with an electric motor for savings. In these types of vehicles, the electric motors aren’t too powerful, and cannot propel the vehicle only by themselves. Mild hybrids may use techniques like regenerative braking, but since they don’t depend on the electric motor as much, it’s not necessary. Essentially, mild hybrids offer 10-15% better fuel economy figures by employing the start-stop technique, or shutting off the engine during coasting. They also transfer some of the load from electric accessories to the electric motor instead of the engine for further savings. In some situations, the electric motor is also used to provide the main engine with an extra kick during acceleration.
- Full Hybrid: Full hybrids are vehicles that can run solely either on their internal combustion engines, or their electric motors, or a combination of both. Since they are more complex and have larger battery packs, they are also more expensive. Depending on the situation, either half of the of power system is used, or in some cases, even both together. A computer decides how and where to reroute power, using a differential based power delivery system. The popular Toyota Prius uses this kind of a system, and is a full hybrid vehicle with better fuel economy figures and lower carbon emissions. Typically, the engines used here are also fuel efficient in themselves.
- Plug-in Hybrids: More of a sub category of full hybrids, plug-in hybrids are vehicles that can be plugged into an electrical outlet to be charged. Just like full hybrids, they can be run on an ‘electric only’ mode, and are favorable for the multiple modes of use. These vehicles are typically suited for longer drives, since power outlets are easily found on roadside pitstops, and even in designated charging stations in some countries.
Types by power source nature
Although most HEV’s are either fuel cell or electric motor based, there are lesser known types such as hydraulic hybrids that substitutes electric motors for hydraulic systems with hydraulic accumulators and variable displacement pumps. They aren’t used too much commercially, and some are under development as well.
- Internal combustion-Electric Hybrids
- Electric-Fuel Cell Hybrids
- Internal combustion-pneumatic Hybrids
- Internal combustion-hydraulic Hybrids
Types by powertrain
Finally, we have hybrid electric vehicles classified by how power is delivered to the drivetrain. In principle, all of them are pretty straightforward and easy to understand since the concepts are simple. Implementation, however, is quite another story.
- Parallel Hybrids: The most commonly used type of system is parallel hybrid. They have both internal combustion engines and some kind of electric motor as well. As the name suggests, in parallel systems, it is possible to run both the internal combustion engine and the electric motor simultaneously, or just one of them depending on the situation. They also employ technologies like the start-stop system and regenerative braking for maximum efficiency. One of the power sources is always idling while the other is in use exclusively, so that it can be used at a moment’s notice.
- Series Hybrids: More expensive than parallel hybrids, series hybrids use one of their power sources at a time. They’re usually better suited to extended drives, and are also called Extended Range Electric Vehicles (EREVs). They can be powered only by the electric system, and when that is exhausted, it can switch to the internal combustion engine and charge the electric motor simultaneously. Series Hybrid vehicles usually have larger battery packs, thus increasing their cost.
- Power-split Hybrids: Finally, we have power-split, or series-parallel hybrids. As the name suggests, they combine the characteristics of both parallel and series hybrids, giving you the best of both worlds. It is generally known that series hybrids are more efficient at lower speeds and parallel hybrids are more efficient at higher speeds, so power-split systems are more adaptive, changing or combining power sources according to the situation. The Toyota Prius is the best example of a power-split hybrid.
The world seems to be finally catching on to the importance of hybrid vehicles, and in the past few years, there have been rapid advances in this arena. From more powerful battery packs to more efficient engines to better hybridization, companies around the world are innovating to create systems to serve the imperative purpose of transportation, while keeping the environment in mind. A lot of countries have started offering charging stations and lower taxes on hybrid vehicles to offset their higher initial cost, to push people into taking the greener path.
In India, however, the market is far more cost-sensitive, and cars are increasing on roads day by day. It will take quite a while to make that jump to hybrids, but here’s to hoping that we follow suit and do what’s best for the world. After all, we’re from the same planet!