How to build a muscle car for better fuel economy?

[Ecky]

You're missing that when you are charging the batteries with your alternator, your alternator is applying a heavy load to the engine and dragging on it, causing it to burn more fuel. There's no such thing as a free lunch. The only free energy is when you capture it during deceleration, the rest is taken by loading your engine and causing it to burn more gas.

[Phoenix'97]

Originally Posted by Ecky

You're missing that when you are charging the batteries with your alternator, your alternator is applying a heavy load to the engine and dragging on it, causing it to burn more fuel. There's no such thing as a free lunch. The only free energy is when you capture it during deceleration, the rest is taken by loading your engine and causing it to burn more gas.

I still think this problem can be tackled fairly easily, unless I still have the concept all wrong.

As per my car, a rear-wheel drive V8, I have plenty of power from my engine to handle issues of drag and especially if given a camshaft to add to more torque production.

Assuming we can adapt two electric hub motors to my non-drive steering wheels, my 2-wheel rear-wheel drive now becomes an all-wheel drive. Recharging the two hub motors on the steer wheels is now the problem if I wish to use them continuously during gasoline engine operation.

I ask, why can't we add two hub generators to my drive wheels on the rear axle? For one, my V8 can handle the added weight penalty and drag from these two generators. Two, while the rear wheels are pushing the car and fighting the drag, the front wheel hub motors are also assisting by pulling the car and simultaneously fighting the drag to charge their operation.

Is there really that much loss in the tandem operation of the gasoline engine with the hub motors in this situation? If worse comes to worse, we can further augment charging by using the gasoline engine alternator which must then be a high output version! In the future, further charging can be added in the form of solar panel film on the top portion of the car.

For now, I have a hard time understanding why these two systems, the gasoline engine and front wheel hub motors, can't be used simultaneously and constantly with each other.

[Ecky]

There are conversion losses, yes. Some quick math:

-An alternator generally has something like 30-40% losses, so the greater the proportion of energy you transfer to the front wheels (powered by an alternator) the greater your losses.

-For every 10HP you add to the front wheels, you'll be adding 15HP of drag on the engine, and you'll be turning 5HP (3750 watts) of gasoline burned directly into heat.

-An extra 10HP (5 to each wheel) would therefore mean the alternator would need to dissipate 3750 watts of waste heat, and produce 7,500 watts of power, or approximately 500 amps at 15v. Your alternator is probably rated for anywhere between 60 and 110 amps, so to get 5HP to each of the front wheels, powered solely by alternators, you'd need 6-10 of the bolted to your engine.

-Alternators also are not reliable for constant loads, and will probably die quickly if used this way. Frankly, they're terrible, and have only been ignored for being as terrible as they are for as long as they have, because cars have historically had such low electrical demands and manufacturers would prefer a cheap and inefficient part that lasts "long enough".

~

You could, of course, bolt an altermotor onto the engine in place of the alternator, one that can double as a starter, produce power at high efficiency (probably 90% or greater), high voltage (meaning low amps needed, and no conversion losses) and can assist the engine during acceleration. But, you still don't want to be constantly taking power from the rear and adding it to the front, because it's still going to be lossy. At the very least, you have a 90% highly efficient altermotor producing power, and 90% efficient hub motors in the wheels, resulting in 20% of the energy produced being wasted in return for gaining full-time AWD.

Though, to be fair, adding a mechanical linkage in a traditional AWD system is going to lose 10-20% of your power and fuel economy too - this is why 4WD and AWD vehicles have lower gas mileage, all else being equal, and will even accelerate more slowly unless they're running into traction limits. These are to be avoided unless necessary.

My opinion is to abandon the idea of full-time AWD. Maybe apply power to all 4 wheels during initial acceleration and passing, and then once up to speed, let the hypothetical front hub motors just freewheel. When you slow down, use all 4 to generate power and fill your batteries.

Or, if you don't feel the need for AWD, a single altermotor on a belt to your engine will let you enjoy more efficient electricity production (saves gas and less loss = more power), greater low-end torque and acceleration on demand, and gas savings through regenerative braking. If you want to add full time electric assist, you're either going to have to charge the battery manually or accept a large fuel economy hit for transferring power to all 4 wheels all the time.

EDITED for clarity

[Phoenix'97]

Well, if I can't use the electric assist all the time then I suppose I can't use it period as there is no benefit to having it if the system can't be designed for self-sufficiency. This is why I thought using the V8 engine to help power the front hub motors while the front hub motors were doing half of the work the V8 engine is doing, would help result in such a self-sufficient system not requiring the down-time charging that is recommended.

This, at least, is what I get from reading your comment.

If this set-up is going to be troublesome then I won't bother with it for the advantages I was hoping to gain from it.

[Ecky]

So, the reason hybrid systems gain efficiency and save gas are these:

1) You replace a low efficiency alternator with a higher efficiency generator, potentially saving several mpg
2) You can capture some of your braking or slowing-down energy, which can be used to accelerate your car again, greatly improving city economy, saving your brake pads and reducing engine wear
3) You don't need to rev your engine up as much when accelerating, because you produce more power down low, which usually saves fuel and reduces engine wear. You can even gear it taller, further saving gas.
4) You get rid of unreliable alternators and starter motors, and replace them with a single more efficient device that basically will never fail

In addition to these, you *also* get a huge boost in off-the-line acceleration from the added electric torque down low, making the vehicle more fun to drive.

To use my car again as an example, my engine is a 1L 3 cylinder with an 18,000w electric motor bolted to it. It's geared like a V6 or V8, because of its torque - I cruise on the highway around 1700rpm. When I need to pass someone, the electric motor gives me the passing power and I don't have to rev the already smaller, fuel sipping engine up to get that power, which saves gas AND reduces engine wear. Then, over the next few miles, it trickle charges the battery back up, taking a tiny percent of my cruising horsepower to slowly recharge the battery power I blew from 10 seconds of acceleration. I'm able to see 90-110mpg at highway speeds while still having a very drivable and fun car. It's no V8, mind you, but neither does it feel like any other 3 cylinder on the road.

[teoman]

If you are cruising only a flat highway at a fixed speed, then you are better not having a hybrid. As all the energy will be coming from the gasoline engine. And you are not lugging around motors and batteries.

The batteries need to be charged there is no way getting around that. (Solar will assist very very little).

If you will be sending energy from the gasoline engine to the electric motors you will have inefficiencies and you are better off just sending it to your wheels.

If you are doing stop and go or up and down hills then all this changes.


Also if you want performance a hybrid could be beneficial, it could power the front wheels while your gasoline engine powers the back wheels making it a 4 wheel drive so you have more traction.

But what you are describing is like one of those over unity machines.

[Phoenix'97]

Originally Posted by Ecky

So, the reason hybrid systems gain efficiency and save gas are these:

1) You replace a low efficiency alternator with a higher efficiency generator, potentially saving several mpg
2) You can capture some of your braking or slowing-down energy, which can be used to accelerate your car again, greatly improving city economy, saving your brake pads and reducing engine wear
3) You don't need to rev your engine up as much when accelerating, because you produce more power down low, which usually saves fuel and reduces engine wear. You can even gear it taller, further saving gas.
4) You get rid of unreliable alternators and starter motors, and replace them with a single more efficient device that basically will never fail

I am still stubborn for wanting the AWD hybrid function on my car. It is no different than how I want to build my car for when I do have fun with it, torque on demand.

Well, if two hub generators on the rear of the car are not enough for this set-up, how about also including the altermotor? When the car is braking or engaged in Decelerated Fuel Cut-Off, the front hub motors and rear generators both contribute to recharging the system as intended. I just get sick to my stomach thinking about the amount of customization that will be needed to get this to work and assuming the front wheel hub system can even work on my car.

If the system won't be AWD and self-sufficient then I see no point in having it. I don't want to have to charge up the batteries manually when I expect the system to be able to charge up while driving, that makes it all the more attractive to people such as myself. Then, not having to mess around with when the electric motors come on, they simply assist the gasoline engine throughout the entire drive, is really what I seek. With the torque that the front hub motors are able to deliver, I still have a hard time believing that this car will have trouble accelerating, especially with a V8 motor.

[Ecky]

I see no point in having rear hub motors on a RWD car in addition to an altermotor. The altermotor is already sending power to those wheels. You could just use one or other other, they do the same thing.

For AWD you could get hub motors on the front instead and use those as the only motor/generators (no need for an altermotor or anything connected to the engine) - they can apply a bit of resistance to create electricity to fill the battery and power your 12v accessories (you can then delete your alternator if you want), and add AWD acceleration for brief periods by tapping into your battery. This would make it self-sufficient, and you'd have AWD when you're trying to put power to the road, but you wouldn't be sending power through those wheels all the time, just when you need it. You'd have all of the benefits of a hybrid.

Let me restate: there is no way to assist the gas motor throughout the entire drive unless you want to charge the battery yourself, because that energy has to come from somewhere. If you're simultaneously assisting from the engine AND dragging on it at the same time, with conversion losses, overall you'll be dragging on it. Anything else would be a perpetual motion machine.

Hybrids reduce inefficiency and give you brief acceleration bursts, but any energy you send to the wheels has to be captured somewhere. They can't just pull energy from the battery forever.

[teoman]

its not that it will have trouble accelerating. The problem is that you are using your batteries and at some point they need to be recharged. Either while you are deceleration or at home. You just cannot use it full time and expect the energy to come from somewhere.

[Phoenix'97]

Originally Posted by Ecky

I see no point in having rear hub motors on a RWD car in addition to an altermotor. The altermotor is already sending power to those wheels. You could just use one or other other, they do the same thing.

For AWD you could get hub motors on the front instead and use those as the only motor/generators (no need for an altermotor or anything connected to the engine)

Let me restate: there is no way to assist the gas motor throughout the entire drive unless you want to charge the battery yourself, because that energy has to come from somewhere. If you're simultaneously assisting from the engine AND dragging on it at the same time, with conversion losses, overall you'll be dragging on it. Anything else would be a perpetual motion machine.

Originally Posted by teoman

its not that it will have trouble accelerating. The problem is that you are using your batteries and at some point they need to be recharged. Either while you are deceleration or at home. You just cannot use it full time and expect the energy to come from somewhere.

I hope I am making myself clear...

In a nutshell, can I produce enough energy to offset what the two front steering wheel hub motors only are consuming? This is why I suggested using another pair on the rear drive axle as purely generators for the front hub motors that will be pulling the car while the gasoline engine is pushing the car with it's combined torque. IF this set-up were not producing enough power, I would have to resort to using an altermotor attached to my LT1 V8.

Am I still missing the point behind your comments?

I suppose I would have to settle with the electric hub motors kicking in for stop-and-go driving, my spirited "launches", and even for conditions on the highway when I don't have enough torque up a mild grade when cruising at 1500 RPM, but I don't see why I can't have the electric assist on all the time...