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fuel economy

free rolling car
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I have this idea about how to make cars more fuel efficent. Have you ever notice if you are traveling along and then release the accelerator but leave it in gear the car will not travel as far as if you leave it in neutral and just coast (obviously) or if you are traveling at a certain speed and you are on just a small decline the car will, in neutral, quite happily just cruise at that speed, but if you were to be in gear the car still slows even on quite a steep hill.

my idea is simple, to allow the engine to disengage from the driving wheels when the wheels speed is greater that that at which the engine would be making them go. It would just require a racheting or sprag type clutch between the transmission and the differential (say rear wheel drive).and as soon as you need a bit of acceleration you just hit the pedal and the engine revs up engaging the clutch once again.

simple, cheap and effective and with a bit of driver thought ( not racing up to red lights etc) the engine will be allowed to just idil for a fair bit of any journey. i have experimented it myself by leaving the car in neutral when possible and can travel a fare few kilometers with the engine idilling on most journeys.

and as an added bonus the car would drive smoother without the engine breaking effect, especially at high rev. The clutch could also be locked ( via a switch and solinoid) if engines breaking effect is wanted.

thoughts?

djthearn, Jun 12 2006

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       Cruisecontrol does this.
zeno, Jun 12 2006
  

       It wouldn't "drive smoother" when you start accelerating again.   

       I think it would need some type of "suspension" connecting the two sections of the driveshaft.   

       Maybe placing it before the transmission would be a better location?
BJS, Jun 12 2006
  

       Don't we have a fuel economy here in the U.S. already?
normzone, Jun 12 2006
  

       School's out early this year.
sp. "noticed", "travelling","idle", "fair", "solenoid", "braking". And there are probably two "shift" keys on your keyboard.
Welcome to the HB.
AbsintheWithoutLeave, Jun 12 2006
  

       When the accellerator isn't fully depressed, the throttle wastes energy. The "resistance" you feel when the engine slows down the car is a result of this energy loss. Since most people don't have the accellerator fully depressed for most of their driving, the energy loss in the throttle significantly impairs fuel economy. Using something like delayed input valve closure to reduce the amount of throttling necessary could greatly improve efficiency.
supercat, Jun 12 2006
  

       When rolling down a hill in the conventional manner (with clutch engaged and therefore some degree of engine braking) surely the car's computer can (and does?) switch off all fuel (assuming fuel injection), as none whatsoever is required to keep the engine turning.   

       However, in coast mode (like in neutral, as experimented) some amount of fuel is required to keep the engine at idle.   

       This small quantity of fuel is more than the zero amount in the first paragraph - with the caveat that the engine breaking effect of that first paragraph is robbing you of useful energy.   

       How can we keep driving the engine around without suffering so much from this engine breaking effect? Answer: clever fly-by-wire valve and fuel injector control. That is, shut off all fuel as described, but also electronically open the inlet and exhaust valves, and hold them open. That way, the engine keeps turning but isn't working against any significant vacuum or compression, and the engine braking effect is greatly reduced.   

       Electronic inlet and exhaust valve control presents some challenges, but I don't see them as insurmountable.
Texticle, Jun 12 2006
  

       Simply cutting the fuel when I take my foot off the loud-pedal seems to work perfectly on my diesel.
AbsintheWithoutLeave, Jun 12 2006
  

       Maybe it could also shut off the engine while coasting, except by doing that you would not have an instant response when you "hit the pedal", but you could slow down or stop by using the momentum to start the engine, and then you could accelerate after that.
BJS, Jun 12 2006
  

       Gasoline engines require that the fuel/air mixture be within a fairly narrow range to ensure adequate combustion. Skipping fuel-injector cycles would reduce power output without wasting as much energy as the throttle, but would make operation less smooth. Delayed intake closure, from what I've read, would offer some major efficiency gains (especially with large engines run at low power levels) for a comparatively minor increase in cost.
supercat, Jun 12 2006
  

       This is a free-wheel; my mother's 1946 Rover 16 had it, and the SAAB 95 and 96 had it. Fairly widely known to exist, I would have thought.
angel, Jun 15 2006
  

       Fish. If deceleration using engine compression is not desired, the clutch pedal could be held in, or the user could shift into neutral.   

       A default behavior of the car just rolling around when no longer under positive engine load would be quite unsafe.
ed, Jun 15 2006
  
      
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