Why Hybrid Cars (Part 2)

Posted on Wed 06/23/2010 by


To understand why auto manufacturers would select hybrid electrical technology over a straight out electric car, you need to understand a little about electrical technology. What I hope to do here is to distill it down to a simplified version that I hope can be understood, because to explain it fully would be too technical for the average reader.

The principle of an electric motor is that it uses electrical energy to create motion.

An electric motor looks ‘somewhat’ similar to a generator, and even though both are rotary equipment, the principles are opposite.

Both have a rotor and a stator. In the rotor, both have magnets arranged around the shaft. Both also have an arrangement of electrical wiring in the stator wrapped around the rotor with a slight gap between them so the rotor can actually rotate.

In the electric motor, those wires in the stator are wrapped around a metal core, whilst in the generator, there are just the wires.

One of the principles of electricity is that if you move a magnet past a wire, a flow of electrons is induced in the wire. Conversely, if you have a magnetic field conducting material and then wrap wires around it and pass a current through those wires, then a magnetic field is induced in that material. Two different principles of the same principle, if you can see that.

It stands to reason then, if there are a lot of wires, more than the one magnet, a stronger magnetic field, and you can then move the magnet at a fast speed, then a higher current flow is induced in the wires.

Basic Generator Theory.

A group of magnets are arranged around a shaft that can rotate. These magnets are of a metal that can actually conduct a magnetic field. Wrapping wires around that metal and then passing a current through those wires induces an even larger magnetic field in that core material. If that rotor is then made to move very quickly, then a large current is induced in the many wires of the stator, thus producing electric power.

The main thing to note here is that the shaft needs to be driven. In your car, the generator is really an alternator because it produces an AC power which is then rectified to give you 12 Volts DC to operate everything that requires electrical power in your car. This alternator is driven by the engine of your car via a fanbelt, so as the engine of your car turns, then the alternator turns. In aircraft, a shaft off the jet turbine drives the alternators. In power plants, those generators are driven by turbines which in turn are driven by numerous methods like using a nuclear reaction or burning coal to produce steam, or burning Natural Gas to drive the turbine.

Basic Electric Motor Theory.

Similar wire wrapped magnetic conducting material cores are arranged around the shaft. This is the rotor.

The stator here in the electric motor however, is different. Wires are wrapped around magnetic field conducting material. While there is no electrical power applied to those wires, then the motor just does nothing.

Apply a large electric current to those wires in the stator, and this induces a large magnetic field in those series of cores. Then using the principle of like magnetic poles repelling, the rotor then rotates.

So the principle here is opposite to that of the generator.

Examples of motors would be electric fans, and on your car, windshield wipers and the starter motor. The wipers have a small motor, because the weight that is being driven is relatively small. The motor rotates while power is applied. The motor rotates in the one direction only, and when the limit of the swept area is reached, limit switches reverse the blade motion while the motor still rotates in the same direction. With a starter motor high torque is needed hence a larger motor, more wiring in the stator, and more powerful magnets in the rotor so when power is applied the motor starts, the ‘dog’ kicks in and turns over the weight of the engine enough until ignition sustains the 4 cycles, and then power is cut.

Here in the motor, a large electric current causes motion of the shaft. Electric power drives the shaft.

In the generator, a large driven motion of the shaft produces a large electric current.

Electric Motors In Cars.

The main guide here is the weight of the car and just what you then add to that car, which then increases the overall weight. With a petrol driven engined car, then a small car only requires a small engine. So something like a Toyota Yaris or a Honda Fit requires only a small engine to comfortably drive the car. However, put that same engine into a Ford Explorer, and it wouldn’t pull the skin off a custard.

The same would apply with an electric motor. A small electric motor could feasibly be used to drive a lightweight car.

However, now you have a different principle coming into play. You need a constant source of a large electrical power to supply the current flow for the stator of the motor. To supply that, you now need batteries, and a large bank of them. Can you see now how the weight is increasing. The bigger the car, the bigger the electric motor, the more batteries, and so on.

However, some of you may be thinking of the ‘perpetual motion’ possibility here.

Why not have an electric motor driving a generator. The generator provides the large electrical power needed for the motor, and the motor drives the generator, and so on. I’m afraid it’s not that simple. You need that large electric power to start the motor in the first place, and now instead of the large motor driving the car, it now also has to drive the large generator. See the point?

Each thing you add to the concept increases the weight, hence fully electric vehicles just have not become commonplace since cars were invented.

A wholly electric car now has a major drawback. The Batteries. They need to be charged to almost their full capacity all the time. Add a large generator to the mix to supply the current needed to charge them, and you add considerable weight, and you end up caught between a rock and a hard place.

So, the batteries need to be kept as close as possible to fully charged, hence the range of the car becomes the main point of interest. It’s not like getting low on fuel and pulling into a service station to fill up with gas, which might only take ten minutes or so.

Here, you are limited by the range, because it takes a lot longer to charge those batteries back up to their full capacity. To do that you need to physically connect the car to a charging point and even with the new rapid charge batteries, you are still looking at hours to get enough charge back into those batteries to resume driving.

Either way, you are replacing one form of emissions for another. There are no emissions from the electric car itself, but the charging process has emissions involved because you are using power from the grid, in the main generated from the burning of coal or natural gas, both emitting Carbon dioxide.

Then you pay to put gas in a petrol engined car, and here you are paying for the electricity you consume from the grid to charge those batteries.

Some cars are going in the fully electric direction, but these will only ever be a niche market.

The limiting factor will always be the batteries themselves. There are no lightweight batteries when you are speaking on a scale such as this. That weight alone will always mean that fully electric cars will only be small to medium, and will only have a relatively small range, and time of operation when being driven.

The cost of those batteries will again ensure that the cost of fully electric vehicles will always be totally out of proportion for vehicles of similar size and weight.

They will only ever provide a small to very small niche market, and until that battery technology can reach a stage where they can last longer, these cars will always be something that the average motorist will rarely see on the roads, let alone be able to afford one of his own.

So, now we see that fully electric vehicles are in the main, impractical.

What is needed is something that fits in between, and a Hybrid electric vehicle is now reaching that stage where it is beginning to fit into that category.

Batteries are still needed to provide the power for the electric motor, and to extend the range and provide some way of actually charging those batteries while the car is actually driving down the road, then a smaller engine is used to add to the driving force produced from the electric motor.

In this way, larger cars can be powered in this manner, negating the use of larger petrol driven engines which use considerably more fuel, and because the engine in the Hybrid is relatively small, and only operating for part of the time, then less fuel is used, hence less emissions.

This now provides the best of both Worlds.

True, these cars are still more expensive than ordinary petrol driven engined equivalents, mainly due to the exponential increase in the technology of those cars , and still with the costly factor of an expensive battery bank.

In the next post, I will detail what that technology provides in this application, and again come back to the vehicle that I had the opportunity to drive, which actually turned out to be quite an enlightening process all round.