How do Hybrid Cars Work?

Nice and Straightforward!

Is it really necessary to explain how do hybrid cars work?

The answer for me is YES - yes, I need to understand how they work to help inform my buying decision. I don't want to get blinded by all the green PR and end up with a hybrid more in name than body!

When I started to look seriously at buying an all-electric car, I must admit that hybrids were not really on my shopping list. BUT - then I looked at what electric cars are available now and I started to realise that a combustion-engine/electric motor hybrid may be the best option for low-emission and high MPG motoring - until at least 2012/2013.

While there is a lot of talk around plug-in hybrids at the moment - again - there isn't really many on the market. So, that brought me back to the types of hybrids you find in forecourts across the country at the moment - hybrids like the Toyota Prius, Honda Insight or Ford Fusion.

how do hybrid cars work

One of the things I couldn't help notice was that there has been a LOT of hype surrounding Hybrids over the past number of years. It became fashionable to own one and even be seen in one with celebrities showing up to red carpet events in a Toyota Prius!

What I was interested in however, was just finding out more about how hybrid cars work. Even though I'm studying Mechanical Engineering - I'm not really interested in a very technical explanation - just the sort of explanation that will help me decide if buying a hybrid car is a good idea at the moment and what I should look out for.

So, in starting my research, I had the following questions on my mind:

Just why did the motor industry bring out hybrids in the first place?

What are the main components that make a hybrid car different from a standard car?

How do hybrid cars work differently from standard cars?

Let's start with the first question:

1. Just why did the motor industry bring out hybrids in the first place?

Look around you - there are lots of different hybrids on the market today. Some of these models wear their hybrid badge proudly - like the Toyota Prius - while others are a lot more discrete. You will find hybrid family cars, hybrid sports cars, hybrid SUVs - even some hybrid minivans!

When we look at the history of the hybrid car, we see that they have been around for a long time. However, modern hybrids really only started to make an appearance on our roads in the 1990's. The Toyota Prius first made an appearance in Japan in 1997. It's stated aim was to reduce carbon emissions in urban areas (the cars were propelled by a zero-emmission electric motor in city-jams when you were driving under 15mph).

how do hybrid cars work

Both the Prius and Honda Insight made their first appearance in the USA in the early 2000's. From what I can tell - California emission standards around that time welcomed these hybrid cars enthusiastically, leading to the Toyota Prius eventually becoming US car of the year in 2004. Miles per gallon (MPG) were not really a concern at that time in the US as gas was considered too cheap to be concerned, although that was changing fast.

So, in answer to my first question - modern hybrids came into being in order to lower tailpipe emissions in built-up areas, then they got adopted enthusiastically in the US in the early 2000's. They also seemed to become mixed up with the whole climate-change debate - you could visibly show that you cared (if you had the cash!) by owning one of these hybrids.

Since the early days - the laws of many countries have demanded that car manufacturers have a higher average MPG across their model range. An easy way to do that is to introduce a hybrid model into your range. The higher MPG of e.g. your hybrid Porsche will drag up the average across the range.

Now, onto my second question:

2. What are the main components that make a hybrid car different from a standard car?

OK, so the "hybrid" part of the hybrid car refers to a combination of electric motor propulsion system and standard combustion-engine propulsion system. For the most part, these hybrids are petrol/electric - but some diesel/electric hybrids are in development (while diesel cars have lower Carbon Monoxide emissions than petrol, they typically have higher Carbon Dioxide emissions than petrol. That level of polluting is not really desirable in built-up cities like Tokyo, so we have found Japanese manufacturers concentrate on petrol hybrids up to now).

Now - this is the easy part , listing the components of a Petrol/electric hybrid car (the harder part comes later - figuring out how they all work together!). The components are:

Combustion engine - A hybrid car has an engine like the one you will find in standard cars. However, the engine on a hybrid is often smaller as part of the power requirement will be taken up by the electric motor (although the Prius engine was 1.5 litres up to 2009 and was then upgraded to 1.8 litres - so much for the theory, manufacturers will always give the punters what they want!). They will usually work on the more efficient Atkinson Cycle instead of the Otto Cycle.

Electric motor - The electric motor on a hybrid car is easy to describe, but is very complex under the surface. This motor can drive your wheels exclusively at low speeds or will combine with the combustion-engine drive at higher speeds. It can also act as a generator to power the batteries (this is the only means for your batteries to be recharged), e.g. as your car slows it returns energy to the batteries.

Generator - The generator is a similar component to the electric motor, but its only job is to produce electrical power for the batteries.

Batteries - The batteries power the electric motor in a hybrid car - they are the equivalent of petrol in the fuel tank for a standard car.

Transmission and controls (includes "Power-split device" on the Prius) - This is a bit like the conductor in an orchestra. It's the box of tricks (how's that for a nice technical explanation) that helps your hybrid car combine the electric motor and combustion engine most efficiently for the type of driving you are doing.

OK - so far, so simple - that-s all pretty clear for me (don't know about you!).
But, I still want to know how do hybrid cars work in practice. What's happening under the bonnet when you are coasting around town? When you are on the highway?

And so onto my last question:

3. How do hybrid cars work differently from standard cars?

As I mentioned earlier, there are lots of different types of hybrids on the market at the moment - all with subtly different designs and emphasis (e.g. better acceleration or lowest possible emissions). So I thought it would be useful to examine just one model to see how do hybrid cars work differently to a standard car - and I chose - you guessed it, the Toyota Prius.

When the Prius was launched in Japan in 1997, its primary purpose was to reduce carbon emissions when driving in urban areas. To this end, its hybrid powertrain was designed to accelerate the car to 15mph on zero-emission electric power alone. As a result, you ended up with really good average MPG in built-up areas - whereas the average MPG on the highway was comparable to a standard combustion-engined car.

The drive system of the Prius is configured as a "parallel hybrid" - it's electric motor can power the car by itself, the petrol engine can power the car by itself or they can both power the car in various mixes together.

Have a look at this diagram:

how do hybrid cars work - When you start the Prius, ONLY the electric motor is required to get you going. This allows you to electric-only accelerate to 15mph. The electric motor produces 295 pound-feet of torque from 0 to 1,200 rpm, which is enough pull to get the car going without the aid of the petrol engine. Result: zero fuel consumption, zero exhaust emissions.

- Normal Driving - Lets call this either low-speed cruising or Highway cruising:

a. Low speed cruising (up to 42 mph) Electric motor only.

b. Higher-speed cruising - The car will move with a combination of combustion-engine and electric power - all of the battery electricity is also recharged by the generator at this time.

- Acceleration - Initially, the electric motor with batteries provide all power. However, the full system (including battery power) is kicked in for maxium thrust.

- Deceleration - When the you step on the brake, some brake-friction energy is routed back into the hybrid system which causes the motor to operate as a generator. This generates electricity to recharge the battery-pack.

how do hybrid cars work Now, before I get Prius owners and engineering enthusiasts complaining about how I have over-simplified all the above - I KNOW I HAVE! I've made the explanation as simple as possible to help me (and whoever else may find this section useful) with a buying decision.

In doing my research for the above, I came across many detailed technical explanations. I have simplified the above to give the "gist" of how a hybrid works. As always however, the devil is in the detail. If you want to find out the more precise detail of how the Prius and similar hybrid cars work (only if you really, really want to) - then I suggest you have a look at the following Prius Owners website - Johns Prius Website - he has done a marvellous job in remaining detailed and illustrating well (please note: this link will open another page).

In Summary.

Has my research into how do hybrid cars work helped me to decide on whether a hybrid car (e.g. Toyota Prius) is a good idea for my needs at the moment? Well - I currently drive a 2008 Peugeot 1.4 litre diesel 4 seat/4 door car. It gets about 55mpg on average. It has very low tailpipe emissions. It has very good driving feel and accelerates well. It is also cheap to service. I really don't feel that switching to a Hybrid car at this point will offer any advantages. However, my mind is very open to the new plug-in hybrids that are on the way in a couple of years. Watch this space!