What's a hybrid ?

I've said quite a bit here that I'm getting something Shiny soon ...

In fact, the anticipation is making me read all sorts of Stuff about hybrid cars. There's a lot of different types of vehicles out there that use electric to get them going :

Stop/Start :
These are still technically hybrids, although they will only work in hybrid when you're starting off. It's aimed at you not burning any fuel when you're sitting at traffic lights, while still being able to pull away while the engine is starting up. They have bigger batteries and as well as recharging the battery off the engine, they can recharge while you slow down. I think the idea is that you take the car out of gear at lights and the engine will turn off until you put the clutch pedal to the floor again.

It's the simplest form of hybrid but still offers up decent fuel economy gains. (And emissions but I don't personally think vehicle CO2/mile emissions are particularly significant to anything) Not convinced about the additional wear inherent in continually stopping and starting an engine, hopefully the oil and water is still circulating during the off time.

KERS :
This is what the Formula 1 cars have nowadays. It stands for Kinetic Energy Recovery System and is the next simplest form of hybrid. What will happen here is that while you brake or slow down, energy that would have gone into heating up your brake pads and discs will get harvested into a battery instead. With the F1 cars, that energy can then be pushed back into the wheels later when extra power is wanted.

I'd call these Series Hybrids as the engine always has to be turning to make the car go. A road example is the Honda CR-Z, which has a small electric motor supplementing a 1.5 litre engine. You have the better baseline economy of the 1.5 boosted to something like a 1.8 litre when you ask the car to give it. One difference between CR-Z and F1 is that the CR-Z will give the extra power when asked, whereas the F1 driver will press a button. Apart from that, they're the same.

The disadvantage is that the motor and batteries add extra weight. So whereas the CR-Z technically has more and better power available than my old Puma, it's slower to the magic 60 by over a second.

Range Extender Hybrid :
Still a Series hybrid, although this time the motor is connected directly to the wheels instead of the engine. Most of the juice comes from pure electric from the wall socket but when the battery gets low the engine fires up and recharges the battery. One big advantage there is that the engine can turn at the speed where it gives best Power vs Economy, most of the time a car engine is nowhere near that because the speed it goes is directly tied to road speed.

Sidebar - what do the Power numbers for an engine mean ?
Power : bHP - brake horse power (or PS or kW). This is the amount of energy an engine produces over a certain amount of time. When the car is moving, all sorts of things are trying to hold it back and it takes energy to overcome that. It's when Energy back = Energy forward that you get a consistent speed. Some cars have what's called an "Overdrive" 5th or 6th gear where the maximum speed is lower in top gear than in the gear below because lower engine revs = less power = less able to overcome what's holding the car back. The "Overdrive" means it's burning less fuel at cruising speed.

Power is what people look for but it only helps top speed which you are never going to do. Excess power is burned off and wasted as heat.

Torque : Nm or lb/ft. This is more interesting ... Torque is "turning power". If you've got a siezed nut you want to release or a jar cap that refuses to budge, it's irrelevant how quick you can spin the nut. Torque is the power that gets the nut or jar top moving.
High torque = lots of acceleration.

Where an electric motor helps is that it gives huge amounts of torque without any delay. The motor in the Lexus that's waiting for me gives 207Nm torque, the engine in my Focus gives 196Nm. That's more turning power in the motor as a boost than is in the Focus total and it's available at all speeds instead of just a small segment of the rev range.

Where was I ?
Range Extender Hybrids work off the motor and battery most of the time, with the battery being topped up by the engine when it needs it. The idea is that they have a long range on the battery, with you topping that up on your home electric. I'm not so sure about that, mechanical stuff works best when they're being used. If it took a while between needing the range extender engine, it's going to take time for the cobwebs to come off.

Nice idea - not convinced ... yet. We'll see how the Chevy Volt and Vauxhall Ampera do when they come out. Another issue is that you lose energy twice with the Range Extender - firstly when the generator gets it from the engine, secondly when the motor puts it on the road.

Parallel Hybrid :
This is what I'm getting. It's a car with engine and a motor, like the series and range extenders. However, either the motor or the engine can drive the wheels. Or both can join in for when you want maximum power. So you can do stuff like cruise on just the engine and then have a burst of acceleration using the engine coupled with the motor.

It's not the same as having a Big Engine, as that pulse of extra power from the motor only lasts as long as the battery does. But it gives you the power advantage of the big engine (temporarily) coupled with the economy of the small engine. The motor also adds some smoothness and refinement back in.

With the Lexus/Prius, the motor and engine are driving the front wheels through a Continuously Variable Transmission. That's like a gearbox with 1000 speeds instead of 5 or 6. What it means is that the motor and engine can go at the speed they want to go at, instead of being tied to road speed. So they'll give max power when you want it or max efficiency in the cruise.

However - all the energy ultimately comes from the engine, there's no power lead to plug in. So the ultimate economy is determined by that engine, boosted by how much the motor can scavenge.

There's a few interesting ideas coming too with the hybrids, things like :
Plug In Parallel Hybrid - just like the Prius/Lexus but you can recharge the battery at home. The Prius plug in will come with a bigger battery too, at the cost of extra weight.
Split drive - there's a Peugeot coming soon that sends engine power to the front wheels and electric power to the back. Curious as to how that will work. If it does, it could be handy - electric and engine could work to their full potential, however there's big chances for the front wheels to be spinning at a different speed to the back wheels. That tends to lead to not going in the intended direction.
Gas Turbine hybrid - Gas Turbines give great power ... but only work best inside a specific speed range. Which is perfect for Range Extender Hybrids !

Wow - I thought this was going to be a short "What's a hybrid" but it's gone Wall Of Text again. Oh well :-)