Regenerate by brake why not use from engine heat (exhaust)?

I know of no car that attempts to use brake heat, but the Gen 3 Prius does use exhaust heat to warm the coolant during engine warmup.
Toyota Global Site | Technology File

'Regenerative Braking' does not utilize the friction brakes, it is using Motor/Generator 2 to convert rotational energy to make electricity (and then store it in the Hybrid battery)

 

Some trucks can use a thermoelectric generator to make use of exhaust heat. But it is very expensive.

For the Prius, it would make far more sense to put that money into improving engine efficiency, which would leave less exhaust heat to harvest.

 

Simple answer is regenerative brakes create far far more energy than trying to harvest exhaust energy.

One idea i had was trying to use the pressure force in a shock absorber to harvest energy. There are some pretty strong forces going on when traveling down the highway.

 

'regenerative brakes' can be a misleading term. the brakes do not regenerate any energy. the vehicle uses one of the motor generators to slow it down which generates the electricity.

 

Already done by others.

 

How about a wind turbine on the roof to produce ("free") electricity to generate hydrogen for consumption in ICE?

If planes can use them turbines, so can Toyota.

 

No such thing as free energy!

On a plane, you can use the APU for emergency power and maintain speed through dropping the nose and descending (which is what it's for).

If you put a similar APU outside a Prius it would just increase the aerodynamic drag, and the engine would need to increase it's power to maintain speed. The power generated by the APU in that situation must be less than the increased engine power (1st law of Thermodynamics) .

What the Prius does is convert that kinetic energy of motion into battery energy via regenerative braking (using the PMG generator as a brake) to restore some of this energy. However it's always going to be less than the original kinetic energy due to efficiency losses.

 

Planes use them only when all the engines have failed in flight, to provide backup power to operate the controls until the plane lands. When your car engine fails, you have plenty of battery power to operate the controls until you have glided to a stop.

 

Not to mention the lawsuits when some dumbo sticks their hand in it!

 

That's true,didn't think of that! Guaranteed to have a few cases of that! Much harder to do when your plane has an engine failure at descending at 300kts!

 

OK, OK, OK, you guys have so sense of humor.

 

Course we do and I'm hoping you did too when you posted the original comment.

 

I gave you a like when I read your original post!

 

We once had a rocket surgeon ask if we could use the "little propeller" to get home if the engine died...

 

That is not an APU its an emergency hydraulic pump/power generator or RAT (Ram air turbine), most large planes control surfaces ie ailerons and elevators are hydraulically actuated, so this little turbine pump provides enough hydraulic pressure so you to still control the plane while your engine has cut off and/or if you have a electrical failures. An APU (auxiliary power unit) is an turbine power generator to provide power when the plane is stationary with its main engine off.

Kinetic energy is more linear, simple and efficient to recover vs heat energy where theirs so much variability and loss during recover unless its heavily insulated which increases weight and complexity to design.. The only thing that our car uses exhaust heat is warm up our engines faster.

 

Now seriously coming back to the issue of maximizing fuel efficiency, how come ICE air intake is not located near the driver's seat?

That way, any methane emissions from the driver would be burnt in ICE improving MPG and eliminating greenhouse emissions at the same time. I'm really disappointed Toyota engineers didn't think of that. Very easy to implement. I may want to look into it myself.

Attn Moderators: feel free to move this to the sticky thread:
Summary of proposed improvements for future versions of Prius

 

i smell the beginnings of a brilliant idea.

 

In the first place, hybrid cars do not convert heat into electricity. What they do is use gearing to put a load on an electrical generator inside the transmission, and the force required to turn the generator slows the vehicle while creating electricity which charges the battery.

Second, exhaust energy is high when the car is accelerating and very low when the car is decelerating. So when you need braking power, exhaust energy is not available. Turbocharger, use exhaust pressure (not heat) to increase vehicle horsepower. They apply a power boost when the vehicle is accelerating and not when decelerating. Perfect!

Lastly, how would you convert heat into deceleration? I can see how you can turn deceleration into heat -- it's called friction -- but how would heat be converted efficiently into deceleration?