Car acceleration perception by humans

That is an interesting idea but my first impression would be that the increased amount of work performed (and energy consumed) due to the intermittant acceleration would cancel out any other gains. It appears as though that energy is lost for little benefit since there is not regenerative deceleration in your vehicle, I suspect. Do you have any numbers for the efficiency of the engine based on output or based on throttle position? That may tell you at what level your engine really should operate at and how much it really varies at different power levels.

" By accelerating, the efficiency goes to near max" Can you explain this? I'm having a problem understanding how accelerating increases efficiency.

As an engine is throttled the effective expansion ratio decreases and hence efficiency. If you look at efficiency charts for an engine, they are typically peak in the 55-75% range, or about 2/3 throttle over a broad range of rpm. If you run it there you achieve max efficiency.

In the case of my car I calculate 24% normally at 75 mph and 28 when I run up and down. That difference give 28 vs 32 mpg.

Seaplaneguy

OK, not to be too argumentative but how do you imperceptibly run at 2/3 throttle?

In order to accelerate gently, you would barely be opening the throttle at all. You would never get to 2/3 throttle.

Why not just size the engine so that under normal conditions you run at 2/3 throttle.

You might be right, but I'm still having difficulty with the accelerate/decelerate cycle.

It all depend on the drive train doesn't it

If I remember right Seaplaneguy's [SPG's] project uses hydraulics & regenerative braking... In that case it would be about the control devices.

in the case of a diesel electric hybred [train] the controller determines acceleration...

Lynlych,

Yes, 2/3 throttle would be very noticeable at typical cruise RPMs, such as 2000 rpm for my car at 75 mph (about 0.04-0.05 Gs), or about where the gtechpro guy claimed where I could not notice it.

At 52 mph my car will drop out of overdrive just at the onset of lugging about 1500 rpm. In direct drive (no torque converter) it does not like to run below 1500 rpm with high torque (2/3 throttle), and starts to shake.

In fact, what would you do at 30 mph? My car only needs 4.2 hp @30 mph, and would need to run at around 200-300 rpm and 2/3 throttle. At 1500 min rpm, that is about 6-7:1 the power needed for 30 mph. (30 hp vs 4.2). Do you see the problem...it can't do it because of the power pulse / min rpm requirement.

Hence, one must look to other solutions...and that is what I am doing.

Seaplaneguy

Real driving and theoretically possible driving are two different things.

I am a very experienced driver. I've driven small cars very fast, and 5,000 gallon tankers, and drove all over Manhattan and the area in a 12'3" 24 foot box straightback Cargostar International that was weighted once as 20,000 lbs.

I felt every move all the time.

.01 and below.

All is noticed.

Compare it to walking. There is no point when you are walking that you do not experience G forces. When going up the hill they cause more pain than going down the hill.

Flying by the seat of your pants, is not a common phrase for no reason.

Speaking as one who has been a professional driver I do recommend that when you are in mixed traffic, you understand that heavy trucks driven by professionals attempting to drive efficiently do try to use gravity, and will typically go faster downhill, than up hill.

Certainly you will get better milage if you are able to operated an engine at its sweetspot.

As far as my answer to your question: all movement is felt, and there is no cut off.

Transcendian,

Thanks for the reply. .01 G seem about right and I would agree with you.

I took my mini van out and took a stop watch and accelerated at different rates. I could not notice .01, but my daughter could. I could notice .05.

A guy who makes gtechpro acceleration devices said his experience is that .05 Gs is where it is hard to tell, but as we talked he said that the smoothness of the acceleration change is key.

If you recall the derivative of acceleration is "jerk" and the "jerk" curve has to be smooth. Displacement; velocity; acceleration; jerk... third derivative of displacement... should have curved ramps or some sin function to it.

So, that requires something to smooth it out because I am giving a step function, or digital increment.

Thanks for the input.

Seaplaneguy

For the first part, you will drive all the other drivers nuts if you don't stay at the same speed in traffic.

For the second part, and I want somebody to tell me this is wrong, 'cause it is driving me nuts, I was told that modern car computers will add extra gas to the engine when you decelerate just to keep the catalytic converter up to temp. If the cat doesn't get enough gas to keep hot, it won't burn right and then it will pollute.

Jimminy Christmas, if the darn motor was running right, it wouldn't be letting usable fuel down the darn tailpipe in the first place! What's all this computer and oxygen sensor and exhaust gas recirculator stuff for then? Burn it in something that produces no helpful energy to the car? I think BMW or somebody is at least trying to make electricity from the waste heat. Let's do something like that instead of just burning extra gas to make good EPA numbers.

I don't know what BMW is doing, but I solved my converter problem by strapping an EPA administrator to the undercarriage with instructions to blow on the thing if it started to cool. My mileage went up to 85/gal overnite and the admin guy says he has a life now.