Self Charging Hybrid benefits??

Stubod

Hi all, just a general question really.

I understand the potential benefits of a plug in hybrid, and I understand the potential benefits of full electric, but I can't get my head around "self charging" hybrids?

Surely using an ic engine to charge a battery to power a car can't be as efficient as just using the ic engine itself? I understand there may be some "free power" generated by the braking process but surely that's a minute amount compared to the extra cost, weight and complexity?

Is it just another sales mick to enable manufacturers to meet some arbitrary emission targets? (ie like stop/start).

..or is it just me?

Ditzy_Mitzy

There are advantages to the 'self-charging', i.e. ordinary, hybrid car.  In its simplest terms, a combustion engine is most efficient when running at a constant speed and least efficient when accelerating under load or pulling away.  The engine produces most power in the second condition and least power in the first.  The less power produced, the less petrol required.  The hybrid car uses an electric motor, which produces lots of torque at low RPM, to assist the engine in conditions of heavy loading.  Energy for the motor is stored in a battery.  
The amount of electrical assistance increases or decreases depending on how much work the drivetrain is required to do.  A hybrid might pull away using the electric motor only and add in torque from the engine as the speed increases.  At constant speed the electric motor shuts down and the car runs only on petrol.  
Under heavy load, therefore, a hybrid's petrol engine does less work than a normal car's as the motor carries some of the weight.  This results in lower fuel consumption and less emissions.  The trade off is slightly higher fuel consumption under cruising conditions, as some of the engine's power is used to recharge the battery; a hybrid has a much bigger alternator than a normal car.  When the battery is charged, however, this becomes negligible.
So, to sum up, a hybrid has the ability to make its engine produce slightly more energy, and do slightly more work, in light load conditions.  This energy is stored in a battery and released at times of heavy load to reduce the work done by the engine in those conditions.  It has, in essence, a bank in which to store surplus energy.  

Grumpy_chap

I had Toyota hybrid and, for me, it was barely any more fuel efficient than the bog-standard petrol Focus I have now.
If the mix of town to main road driving was more town-based, it may have been more impressive on the fuel economy front.
The amount of time you could actually drive in the electric mode was so minimal because limits on speed, acceleration just made it impractical as an objective.  However, the battery motor is also called to assist the ICE with extra shove when on an incline for example.
The charging of the battery is essentially "free power".

DiddyDavies

Stubod said:

Hi all, just a general question really.

I understand the potential benefits of a plug in hybrid, and I understand the potential benefits of full electric, but I can't get my head around "self charging" hybrids?

A self charging hybrid would be ideal for someone who wants a hybrid vehicle but doesn't have the facilities to plug it in at their residence, someone who lives in a flat or someone who doesn't have their own private parking area where they could plug it in for example.

Stubod

DiddyDavies said:

A self charging hybrid would be ideal for someone who wants a hybrid vehicle but doesn't have the facilities to plug it in at their residence, someone who lives in a flat or someone who doesn't have their own private parking area where they could plug it in for example.

..Hi all and thanks for the replies....ref the comment above, that's not really my point as I am not totally convinced that a hybrid is significantly more economical / less emissions than a normal ic powered car. I have a colleague that has a Yaris hybrid and gets virtually the same mpg as a "standard" Yaris? The hybrid costs more, has more parts and therefore I would assume less environmentally friendly to produce?  

princeofpounds

The battery in a self-charging hybrid is not powering the whole car all the time. The car is still reliant on its ICE drivetrain much of the time, but uses electric power when ICE isn't that efficient (slow speeds, stop/start etc.).

Think of it like a mild hybrid, but with a bigger electric battery and motor, so it's not just able to assist the ICE drivetrain but fully take over at times. 

Gaming emissions is definitely part of it.

But the recovery of energy from braking should not be underestimated - don't forget if you are stopping a car running at 40mph, the energy dissipated in the brakes is theoretically enough to accelerate the car back up to 40mph. You'll never recover all or even most of that, but even a chunk of it can be quite significant, especially if you are city driving and it's happening repeatedly.  So much of the electrical energy you use is not coming from the ICE (at least directly).

Nor should you underestimate the boost to efficiency you can achieve in the ICE itself when it doesn't have to operate in all driving circumstances. As noted the narrower the range the ICE has to operate in, the more efficient it can be designed. It's a big deal, in engine design terms.

Combine these two and the vehicle will be more efficient for a given amount of fuel, though maybe not as much as the mpg figures would suggest. Whether it is cost-effective is another question again.

Imagine you have 100 arbitrary units of energy in your fuel tank, 60 in terms of output from the ICE. If going straight to the wheels (assuming perfect transmission), you can travel 60 miles, let's say.

In a self-charging hybrid, maybe your ICE can now run more efficiently itself and output 70 units. Let's assume 20 of that goes into the EV system and with energy lost in conversion you end up with 16 units output. So you end up with output from both systems of 66. But then you can also recapture energy in braking, maybe 6 units that were not available in the ICE vehicle. So you end up being able to travel 72 miles on the same tank.

Those numbers are totally made up and not likely to be that proportionate, but it can give you a bit of a sense of how they can be more efficient despite including an extra energy transition where energy is lost.

Supersonos

Stubod said:

 I understand there may be some "free power" generated by the braking process but surely that's a minute amount compared to the extra cost, weight and complexity? 

It's primarily to then assist in the acceleration.  Only slightly.  But often enough to keep CO2 emissions below certain thresholds.

Stubod

..as I thought then, largely a bit of a "con" to meet some arbitrary targets?

I would think in general use any "savings" more than offset by the resources used to make and maintain the extra bits in the first place?

Ditzy_Mitzy

Stubod said:

..as I thought then, largely a bit of a "con" to meet some arbitrary targets?

I would think in general use any "savings" more than offset by the resources used to make and maintain the extra bits in the first place?

I think a lot of the problem is that full hybrids have a lot of bottom end torque and are automatic, leading most to adopt the typically modern uneconomical driving style.  The best thing to do to save petrol, which nobody seems that interested in these days, is to conserve momentum where possible.  Try to keep the car moving by anticipating hazards, slowing down early and looking out for gaps.  You know what I mean.  Older cars, which are often underpowered, encourage such a driving style.  Manual gearboxes also help with doing it, as they make engine braking and acceleration planning much easier.  
Newer cars, and newer drivers, adopt a different method: don't bother about anticipation, slam the brakes on whenever you feel like it and floor the accelerator to get back up to speed.  You see it around town; I blame diesels and their fast acceleration up to 30 mph.  Nobody bothers to look for gaps or opportunities to keep rolling, nobody cares about cornering speeds; it's all just lost in this constant need for straight line performance and the pretence that one is at Santa Pod.  It's not even a particularly fast way of driving; one can do better in a small hatchback if one pays attention.  
Hybrids, unfortunately, are king when it comes to this sort of thing.  I think that most drivers would get better economy from the things if they actually cared about how they drove them.  

dipsomaniac

Hit the nail on the head with driving style. One of the biggest wastes of energy is braking (unless you have kers)  Far too many people leave braking until the last minute or brake when they don't need to because they are not looking far enough ahead

princeofpounds

Stubod said:

..as I thought then, largely a bit of a "con" to meet some arbitrary targets?

I would think in general use any "savings" more than offset by the resources used to make and maintain the extra bits in the first place?

No, not a con - they generally are materially more efficient. When considered vs how difficult it would be to make ICE technology alone similarly more efficient, the gains are actually outstanding. Admittedly that's largely because ICE technology is so mature it's hard to make it more efficient alone. That's why car companies are actually bothering to do it at all, compared to just designing better IC engines.

As for recouping the resources used to actually make it in the first place... yeah that's a more pointed question.