The first patent for a hybrid drive was filed in 1969 by four Californian engineers.

The hybrid drive is a beautiful piece of engineering, its bold, its elegance, it’s a true invention.

Before I explain how it works, i’ll need to give a bit of context.

The Basics

You’ll need to know what a transmission is, what it’s for and then I can explain a simplified model of the hybrid Drive.

The connection between Toyota engine and wheels of a Prius is an internal combustion engine or petrol engine like you find in any other car.

The power from the engine has to go to the wheels, the gears there are called the differential, quite an ingenious piece of engineering in itself but not the subject of this blog post.


Let’s just say it splits the power from the engine to the two front wheels.

Now in between the engine and the differential, that’s what we call the transmission and that’s where the Prius magic happens.

In a perfect world we would just weld in an axle and be done with it that would work from about 50 kilometers an hour below that, the engine does not have the power to drive a car.

A gasoline engine needs speed before it can produce power and at a standstill can’t even drive itself you need to disconnect it, use the starter motor to get it running, let it rev up and only then can itbe connected to the wheels, but not directly, we need some soft connection and such soft connection is called a clutch.

prius hydrid engine

Basically two millstones grinding together put some force to the wheels and excess energy as heat, lots of it.

When you reach say 50 kilometers you can lock the plates together but a normal clutch should have vaporized by then.

prius race car

So now you can drive but not very well, you see, combustion engines are really fussy about how they want to produce their energy, they don’t like fast, they don’t like slow, they demand exactly the right load and when that engine is not happy it starts burning more and more fuel with less and less output, so you put in a gearbox.

Now the speed of the engine is more or less independent of the wheels but only in distinct steps which are always too wide.

The Hybrid

There is one simple way to solve all problems completely take out the mechanic transmission and replace it by an electric generator and an electric motor.

Now the engine can run at any speed it likes and only the electric motor has to follow the speed of the wheels.

Electric motors are much less fussy than petrol engines, they produce power at standstill and at high speed but again there is a downside to this design.


If you convert energy, you lose energy as heat, in this drive you can expect to lose 15 to 20 percent of what comes in of the engine.

Now that you know some basics of transmissions we can get to the hybrid drive.

Let’s imagine we’re looking at a simple Millstone clutch, we’re thinking how can we do better, well we just replace it with a generator we don’t mount it to the car though we connect one part to one axle the other part to the other axle, just like a clutch in fact unlike the clutch, the generator gives friction which drives the car forwards.

It gives up the friction until the two parts have the same speed then friction stops.

Both parts move as if glued together like a clutch, just one difference, with a clutch it doesn’t convert friction into heat but into electricity when pulling up you might generate about 30 kilowatts of energy, that’s enough to light up a medium office building, it’s a lot of energy but what can you do with that sort of energy.

Well you build an exit motor in the drive line and any electricity that comes out the crutch you fit straight back into the motor.

And there you go the basics of the hybrid drive line.

A Closer Look

Let’s take a closer look at what’s going on when we pull up with this car at first all energy is absorbed by the generator, then pushed back in by the electric motor but while speeding up less and less energy takes the electric path while more and more is put through mechanically through the axle.

When both axles have the same speed, generation stops but now the generator acts as if it’s locked so the petrol engine connects directly to the wheels super efficient, now you think that it stops there, but no, motor and generator now switch the function the motor becomes generator converting force to electricity then feeds it back to the original generator, which is now a motor and now the axle gets speed from the engine and from the electric motor, so the engine can work at a lower speed.

It’s like a river flowing upstream, so motors and generators and generators are motors, that’s why Toyota calls them motor generators MG1 at the engine side MG2 on the other side.

I want to stress that this is not a perpetual motion machine, such machines do not exist.

The drive takes away force really torque from the outgoing axle then fits it back at a speed to the engine axle, no energy is gained from the hybrid drive and the electric drive.

For that matter, do in essence what a gearbox does exchange speed for torque or torque for speed, nothing more, you may have noticed a problem though, you cannot connect wires to a rotating coil, that’s where the planet wheel comes in.

But first let’s take a look at some electronics.

Our hybrid drive needs some electronics, the voltage of generators is all over the place, but the motors need exactly the right voltage generated frequency to run depending on the speed and load so the power has to be converted between generator and motor.

Those electronics are called the inverter by Toyota, that inverter also determines from which MG power is drawn and to which MG it is added.

The inverter has to contain a small battery to do that, three capacitors in this case but so far the hybrid drive does not need a big battery, still with all the electronics in place why not add one, there’s all kinds of tricks you can do with the battery.

For starters at traffic lights you can turn the engine off, you can pull up get to the next light without even starting the engine.

Great and city traffic when the battery is empty, only then the engine will start, then the engine will run at a pretty decent speed which is an efficient speed recharging the battery and driving the car at the same time.

Now when the battery is full the engine turns off and you’re on battery.

There’s much better use of the engine compared to a normal car.

The normal car would be either idling or working at the speed that’s way too low for efficiency the engine.

Hybrids on the other hand are either running at an efficient speed or just not running at all.

The Prius has pretty good acceleration, actually for a car with a small engine when you’re up to speed cruising along, the battery will mostly do nothing at all, remember when you convert energy you lose energy storing energy and battery only makes sense.