Hybrid designs (HEV's)

[skinny]

given that the electric motor has excellant torque characteristics to drive vehicles, and all engines are optimally run at a certain speed (for best torque (and/or power) / fuel economy), surely the best solution to integrating the two systems is in a series hybrid rather than a parallel?

in the series hybrid, the fuel motor runs (as and when needed) at a certain speed optimised for power and economy under a specific load (very easy conditions under which to optimise an engine), the power output going to a generator (again optimised to convert power at a certain rate). this generator then charges a battery off of which the electric motor runs to drive the vehicle.

As i see it, this has many advantages:
- As many parts as possible are optimised & dedicated to certain and exact performance conditions
- It is very easy to vary the components as needed, for example if you wanted a larger fuel motor and smaller battery, or if you wanted a smaller fuel motor and larger battery. you can also change the electric motor size depending on whether you want higher economoy or performance
- performance can be comparable to any modern car (including sports cars / high performance cars) instead of the usual compromise (or limit) on performance that a hybrid car usually imposes
- As peak power needed is a huge amount higher than average power, the fuel motor can be drastically downsized with no loss in performance - the system acts like a buffer
- there will also be no limit on range like pure electric vehicles as you will just fill the car up at a conventional fuel station as per normal
- low speed driving requires less energy as no power is being wasted (for example in idling or coasting in traffic, you would be using negligible amouts of enery, if any at all). you could drive in towns without the need for the fuel motor to run. similarly short runs would not require the starting of the fuel motor
- it will be a good platform for manufacturers to start investing in technology leading to pure electric vehicles, giving an opportunity to develop electric motor and battery (or alternative energy storage) technology whilst testing it in the real world. the fuel motor can then simply be phased out over time if need be
- the system and integration of the components will be simple and cheap
- the 'drivetrain' allows a wide choice of engine, including those more efficient and cleaner than petrol 4-stroke, such as relatively clean and efficient gas turbine engines
- torque characteristics of certain electric motors are perfect for vehicles, with a flat torque curve across their whole speed range up to their maximum (and often very high) speed, increasing efficiency and performance even more
- electrical braking system can directly charge up the battery instead of just converting kinetic energy supplied by the fuel into heat, thus further reducing wasted energy

I must be missing something though. why do the major hybrid electric vehicle manufacturers insist on a parallel design where a weedy little motor has to (inherently innefficiently) travel up and down the rev range, with a complicated integration of electric motor assistance when extra power is needed, the torque curves and speed range of the engine are still fundamentally flawed for vehicle use (hence the use of a 5-spd gearbox or whatever, losing more energy), and it doesn't go any of the way to producing a valid electric vehicle.

please can someone explain their choices as i simply don't get it



>>> Edited by skinny on Thursday 9th December 12:04

[annodomini2]

Easy cost, High power electric motors are generally big, heavy and expensive, modern motors are much lighter and smaller but even more expensive due to them being 'new' technology.

A petrol/diesel engine for a mass manufacturer costs at most around £500-600 per unit. (including electronics etc.)

A modern electric motor producing the same amount of power costs iro £2000-3000, before you add the power source.

Cars are all about unit cost, saving 5p on 200,000 or 300,000 cars is a lot of money, so if they were to add £1500 it would be difficult for them to justify such a hike in costs.

Plus oil companies and lack of government incentives to use electric over normal fuel.

[skinny]

i can't imagine that the honda insight for example was cheap for honda to produce either tho, didn't most governments heavily subsidise it to keep the puchase price reasonable?

also, even if this powertrain was £2000 more to the customer than a conventional set-up, this would be offset against fuel costs i would have thought...

[annodomini2]

Honda made them at a loss thats how they kept them so cheap, did it as a marketing exercise

[andytk]

As did Toyota with the Prius.

Also the leccy motors you're using are going to need some serious juice to get the power you're talking about. So you'll need ultra capacitors to supply the huge currents that you need. Big batteries simply won't hack it. I know cos I've done the sums.

Ultra capacitors are also pretty damn expensive (again cos they're a new technology)

Andy

[dilbert]

I said a couple of days back that the power to weight ratio in an electric motor will never be as good as for an internal combustion engine.

I may be proved wrong on this, but I'm sticking to it for the time being. Granted, if you're not doing that much acceleration/breaking, the motor works out pretty good. The motor might actually work out pretty close in terms of overall efficiency for long fast journeys.

I suppose I envisage a future where we're all going to be stuck up traffic in slow electric cars though!!! I suppose my argument could be self fulfilling.

To get the power out of the motor to overcome the aerodynamic drag at speed, I think it has to be so big that it seriously compromises efficiency at slow speed.

If you go the hybrid route, series or parallel you have the additional weight and inefficiency of whatever system is used to combine the power and get it to (and from) the road.

The problem I envisage with the motor is pretty physical. To get more torque you need more turns, and unless you reduce the ammount of current you feed in (reducing the overall power) the motor has to get bigger.

I'd have to check the maths on this, but if the size of the motor doubles you double the power, that's a problem. In a gas turbine (and to a similar degree a piston engine) if you double the size you square the power. I'm hoping that someone can verify that idea, it could be wrong.

I guess that's why you don't have a gas turbine driving your electric windows, or an electric motor in your fastjet. The piston engine really is a natural solution to land transport. It just needs to be electrolysed hydrogen powered.

[love machine]

Of course, I will not attempt to argue, as I am biased and merely proving my point with the fewest stats possible.

It's just some monkey hellbent on realising their invention for the glory of it. The whole mechanics/thermodynamics don't work and basically it is a total waste of time. People which follow the whole electrical car thing are blatantly idiots.

It isn't even worth further discussion IMO.

[annodomini2]

Its not impossible, the technology exists now, but a profitable production version is a few years off yet, given the cost.

[cyberface]

Having a combustion engine powering a generator, charging a chemical battery and then powering an electric motor introduces a load of inefficiencies. Every power conversion step loses a load, so the efficiency improvement of running the ICE at a steady rate would almost certainly be wiped out.

Combustible liquid fuels have great energy density compared with electric solutions. Technology just isn't there yet from what I can see - the energy density of batteries / capacitors is the problem.

Ideally we'd need:
1. Electrical storage 'battery' with comparable energy density to liquid fuel;
2. Battery doesn't require more energy to manufacture than entire lifetime energy savings versus ICE;
3. Battery is easily and cleanly disposable / recyclable at end of life;
4. Battery life is comparable to vehicle life;
5. Electric motors efficient throughout broad rev range;
6. Superconducting wires would be *really* handy for the very large currents used in electrical propulsion...

As per the 'battery' I guess there are two different approaches: either some ultra-capacitor type concept that stores shit loads of charge and can regulate the discharge, or the fuel-cell approach to generate current from chemical reactions. The fuel-cell approach, if made very efficient, would be cool but current tech has short working lifetimes and the cells cost a lot in energy to make.

I'm always sceptical of new 'solutions' that make our cars more efficient, unless I can be shown that the new technology the enable the efficiency doesn't cost more in energy / pollution terms to create than it's ever going to save. Most solar cells are a perfect example of this: don't generate any pollution in action, but the silicon purification process to make them certainly does!!!

[dilbert]

I'm always amazed by the toxicity of semiconductor manufacturing. It really is nasty, although not perhaps radioactive.

There are some new ideas for energy generation that are quite cool, obviously we're gonna need some electricity to manufacture hydrogen!

The solar/thermal idea seems pretty good, even if it is not new, and that australian convection tower seems pretty good too.