Half a croissant, on a plate, with a sign in front of it saying '50c'
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Micro APU Micro Hybrid Car

Start/Stop Car, with less horrible battery usage
  [vote for,

Let's compare what happens when three types of cars pull up to an intersection, stop for a light, sit around, and drive away.

For simplicity, let's assume they all have automatic transmissions. Thus, in all three cases, the driver brings the car to a halt with the brake, keeps his foot on the brake for a minute or two, then puts his foot on the gas to drive away.

In the case of a conventional car, the efficiency of the engine drops off sharply as demand on the engine decreases. When slowing down or idling, the only load on the engine is from the accessories, which are a few hundred watts at most. Thus, the efficiency as the driver slows to a halt and idles is very low. As long as the car sits still, it consumes fuel and spews out exhaust. The only positive thing is that when the driver accelerates away, no external energy is needed to get the engine going, since it was idling the whole time.

Next, consider a Micro Hybrid Car, also known as a Stop/Star Car. When the car is moving, the accessories are powered electrically, from the engine's alternator. When the driver is slowing down the car, or when the car is off, the engine is automatically turned off. When the driver puts his foot on the accelerator, the engine is automatically restarted. In between stopping and starting the engine, all power for the accessories comes from the batteries.

While Micro Hybrids obviously use less gas and produce less emissions, they are very hard on their batteries. In part, this is because in the time between an automatic engine stop and the following restart, the car's accessories consume about ten times as much energy as what's needed for engine restart alone.

Overall, they are approximately one hundred times harder on their batteries than conventional vehicles. Next generation car batteries, such as Axion's Lead- Carbon cells, can merely withstand about ten times as many charge/discharge cycles as a conventional battery.

So even though Micro Hybrids are the least expensive of all hybrid technologies, they will, apparently, be really bad for their batteries.

Now we consider a Micro Hybrid Car, with a very tiny Auxiliary Power Unit. At the same time as the car is being brought to a halt, the APU automatically starts. As soon as the APU reaches its operating speed, it takes over powering the vehicle accessories, after which the main engine shuts off.

When the traffic light turns green, and the driver hits the gas, the APU's throttle is fully opened, and power from either the APU alone, or the APU and battery together are used to start the main engine.

When the main engine's rpms are above some threshold, the APU shuts off.

Since size of the APU is carefully matched to the amount of power needed for running the accessories, it does it's primary task fuel efficiently.

And while the APU might not be able to completely cover the energy needs of the main engine's starter, it will reduce it significantly.

By eliminating drain on the battery from the accessories, and reducing drain during engine restarting, the battery life should very much extended... at least compared to a conventional Micro Hybrid Car's battery.

PS: I almost forgot to state the size! I expect that one or two horsepower ought to suffice to run all of the typical accessories, except perhaps the A/C.

goldbb, Feb 15 2013

Small model gas turbine powers a model train http://www.youtube....watch?v=w1UVvWiHqvE
[Sunstone, Feb 23 2013]

Model airplane jet turbines could be converted to direct drive https://www.google....al&client=firefox-a
Model airplanes jets are readily availble and could be modified to a gear drive for car engine accessories [Sunstone, Feb 23 2013]

Micro turbine engines http://en.wikipedia...rbine#Microturbines
[Sunstone, Feb 23 2013]

Horsepower required to run engine accessories http://mechanics.st...-belt-generally-use
[Sunstone, Feb 23 2013]

Patent for hybrid engine accessory power system http://www.google.com/patents/US7975465
[Sunstone, Feb 23 2013]

APU for powering accessories on commercial trucks http://www.comfleet.../APU/WillisAPU.html
[Sunstone, Feb 23 2013]


       [+] I think we can dispense with the A/C at stop-lights, so the only high-draw must-have is headlights. Apart from that I doubt a vehicle's needs would take more than a few tens of watts.
FlyingToaster, Feb 16 2013

       Provided the car won't be bouncing around too much, I can reccomend a type of metal halide HID bulb that draws just over two watts and will outshine any conventional headlight.
Alterother, Feb 16 2013

       [Alterother] Are you sure? If a 55 watt headlamp is 5% efficient, then 2.75 watts of that is converted to light. It's hard to outshine that using just over 2 watts.
scad mientist, Feb 16 2013

       Interesting idea. Although I tend to think that battery technology is improving enoughto deal with this, this does offer an alternative approach.   

       Of couse if you're gong to go this far, why not try and eliminate the battery all together? My wife talked about a bulldozer her dad had when she was a kid that had something they called a pony engine to start it. Basically it was a small engine that was started with a pull curd like a lawn mower. Once that was running, that engine was used to turn over the big engine: no batteries needed.   

       When you get in the car, just pull start ther APU. Maybe have it rigged to the door, so you press some lever or pedal, then pull the door closed hard, since a pull cord on the dash would look funny. Now why does the image of a pull-cord in the dash seem familiar? Did that get discussed here before? I can't imagine where else I would have seen a discussion of such a thing.
scad mientist, Feb 16 2013

       [Bigsleep], I think you should check a little more... :)
Ling, Feb 16 2013

       Well, the link refers to a 3ph ac induction motor and soft starter.
But, you are right that the dc series wound motor does have a large current at stall (start up)...could be 200A; even higher for Diesels.
Ling, Feb 16 2013

       [scad]: yeah, I'm sure. As long as you can rig the car to produce 240VAC.   

       Metal halides are significantly more effecient than halogens, but it was actually kind of a joke. The first pothole would kill the thing anyway.
Alterother, Feb 16 2013

       Are you sure you didn't mean 2 amps instead of 2 watts? 2 watts from a 240V supply would be just 8 milli-amps. I couldn't find any metal halides that drew that little current. It looks like 400W metal halides that say they draw 2A at 240V are pretty common.   

       I agree, it's too bad those aren't suitable for automotive use.
scad mientist, Feb 19 2013

       After re-thinking things and checking the back of my ballast, yes, I did mean 2 amps. 2.14, specifically. Came back here to correct myself. Please pardon my gaff.   

       It is indeed too bad, because (if my resource-verified math is correct) MH bulbs are between 7-12% effecient @ 100'. The right kind of glass reduces the effeciency by a fraction of a percent, rather than the 1-2% loss of halogens or automotive xenons. For my purposes the effective range is typically measured in inches, and the effeciency gain over incandescents or CFLs is amazing.   

       Still, a 15w MH, if such a thing existed, could probably outshine the equivalent conventional automotive headlight, at least until somebody slammed the door too hard. My HID bulbs expect dinner and a movie before they even light up, and will conk out if somebody sneezes.
Alterother, Feb 19 2013

       LED headlights, gentlemen. A bit more pricey but largely the trend.
RayfordSteele, Feb 19 2013

       How much headlight do you need while stopped at a stoplight?
lurch, Feb 19 2013

       The starter needn't be electric, it could run on compressed air, filled with a direct-drive engine- powered mechanical air compressor as the engine is running.   

       If the electric starter motor is eliminated, the remaining accessories could be powered by a deep-cycle marine-type battery that need not be constantly charged by the car's alternator; in fact, the alternator could be eliminated entirely and the battery charged while the vehicle is parked.
whlanteigne, Feb 20 2013

       Then the battery will draw off very quickly, especially if we're running 1000w metal halide headlights.
Alterother, Feb 20 2013

       //How much headlight do you need while stopped at a stoplight?//   

       Enough to see when to go again? Or enough to engage in illicit consummating activities in rural locations?
RayfordSteele, Feb 20 2013

       Model jet turbine engine(s) might work if converted to a power take off type gear drive rather than thrust, quieted enough and pedestrians and animals were protected from jet blast. I recall a car air conditioner can use 5 to 7 horsepower. Power steering pumps, alternators under a high electrical load driving a super sound system, emission control accessories, superchargers,and such could demand 20 horsepower or more gas turbine. JP4 Kerosene jet fuel may also have to be onboard in additional to auto fuel. I hope all things fall into place and somebof=dy can develop one. See links (+)
Sunstone, Feb 23 2013

       Forget scale model turbines. Jay Leno has a full-size turbine motorcycle that gets better mpg than my jeep.
Alterother, Feb 23 2013


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