Freescale Semiconductor showed off a unique hybrid powertrain that combines an air engine with an electric motor assist at the recent Society of Automotive Engineers Convergence 2012 conference in Detroit.
"It's our version of a zero emissions vehicle," Neil Krohn of Freescale Semiconductor told us. The engine and electric assist could be used to power a small vehicle.
As you can see in this video, Freescale starts the air engine with the electric motor and then employs the motor's power again when the situation calls for it. "We bring the electric motor in and overdrive the engine, so now we have an assist for acceleration," Krohn said.
The electronics used to run the hybrid powertrain include a Power Architecture microcontroller, insulated gate bipolar transistors, and gate drive ICs from Freescale, as well as a 40kW inverter from Fuji Electric.
Nothing is free. Compressing gases takes a lot of energy. The potential inside a pressure vessel is not that great compared to a lithium battery. I worked on a defense contract to develop personal power storage systems. I considered compressed air, but later found it to be cumbersome. (The joule to volume of compress air was enormous.) Even with hydrogen, I could not get the vessel size down. Let's hope they have more minds on the job to make it useful. I
I did see a car once that used a compressed hydraulic cylinder for acceleration. Every time the car stopped, it would add to the hydraulic energy. It seemed like an interesting way to go.
You have a good point there. The air motor runs off compressed air, but where does the compressed air come from? There has to be a compressor to charge the tank in the first place, which is where your concern for missing energy in the equation is right on the mark. Its the same thing as an electric car, you STILL have to charge the battery in the first place -- its just that in this case the battery is tank of compressed air. I can see that this would have to be limited to small vehicles though and short ranged ones at that, you have to have access to a compressor that can put of hundreds of psi of air. Air tanks, any pressure tank, is bulky and heavy. Even CNG powered vehicles are limited by the volume of the tanks available today -- and there you are using chemical energy to run an IC engine; with and air motor you are using only stored mechanical energy.That is why some vehicles use compressed air in regenerative braking, it is energy that can be "cheaply" harvested for short term reuse (with the inevitable thermodynamic losses, of course). But as a main driver, the loss of chemical energy makes me dubious until they explain the compression source.
Either way you look at it, only part of the system is expained and it is "zero emissions" only if you ignore the energy supplied to the system from outside. Like any electric vehicle, a compressed air vehicle, needs electricity to run a compressor to store the air. Flywheels are another example of the same kind of energy storage (admittedly without the friction losses slowing a flywheel).
There is a very fundamental loss in the use of compressed air, which is that part of the workm done in compressing the air results in a temperature rise, that is, compressing air not only raises the pressure, but also the temperature. Then, as heat is lost and the air temperature drops, there is less energy to be recovered. That is a basic and fundamental problem inherant in the use of compressed air. Using a very well insukated tank helps a bit, but the air still cools eventually, and that power iand energy are lost. So u8sing an IC-engine to drive a compressor may have some advantages, the losses through cooling of the hot air are certainly not to be ignored. On the other side, recovering braking energy through compressed air, where the stored energy will be used right away, might make a lot of sense.
This Freescale motor is an idea I have pondered for some time, but I'm not certain of why they use an electric motor. A two cylinder compressed air engine will operate without any type of starter or a transmission. Our ICEs require an optimum RPM for fuel efficiency. Why not marry the two? The ICE would run only to supply compressed air to a tank, the power train would run from the compressed air tank. The ICE would either operate at full power or be off and would be sized for whatever the maximum speed requirement of the vehicle may be. I fear I am missing something here.
Then again I'm only a professional electronics guy for the most part, but do tinker with mechanics from time to time.
Also I too use a 40KVA 400Hz 3 phase inverter at work. It weighs about 1600-1800 pounds! So 40kva in such a small package? I would love to see their design.
I don't have the power stats for this engine, Naperlou, but I do know that the big issue with compressed air engines in general is energy density (less than a lead-acid battery and about one-fifth that of a lithium-ion battery). So we're again back to the energy density issue.
I've seen compressed air engines used on city and school busses as a regenerative braking power assist. The system compressed air while the vehicle was braking and then used the compressed air to assist acceleration.
Wow. Putting aside any pragmatic issues (weight, power, efficiency, etc.) this appears to virtually run on nothing! The long sought after perpetual motion machine-? I was hoping to see more about what made it continue to run! Establish that foundational architecture and those other issues might resolve themselves thru derivative enhancements, over tests and time. But what a start-! What keeps it going?
Chuck, one thing that is pointed out in the video is the small size of the power and control electronics. I think that the car companies could probably do better than they are doing. The weight of the electric vehicles available today is still as much as an ICE driven car.
I do wonder how much power this vehicle can produce. I could see such a design being used for small utility vehicles.
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