[OT] Engine braking

[Jordi Sayol]

On 30/07/13 21:02, Andrei Alexandrescu wrote:
> On 7/30/13 11:35 AM, Walter Bright wrote:
>> On 7/30/2013 11:18 AM, Andrei Alexandrescu wrote:
>>> Thanks for this anecdote. It's at the very best circumstantial. (With
>>> the engine
>>> off, the oil pump wasn't even started!)
>>
>> The oil pump is driven by the crankshaft, so if the engine is turning,
>> the oil pump is. (There are some highly specialized race engines with an
>> electric oil pump, but that is highly unlikely here.)
>>
>> I was told by U-Haul that when towing a car long distance, you couldn't
>> just put the manual transmission in neutral. You had to take the
>> driveshaft out, because the transmission was designed to circulate the
>> oil based on the front shaft turning, not the back shaft. It would sieze
>> after a while if you only turned the back shaft.
> 
> So that invalidates the anecdote.

I feel guilty...

> 
>> I also pointed out the "hammering" effect of alternately forward driving
>> then back driving the rotating parts, as the parts forcefully take up
>> the slack of hysteresis.
> 
> I guess any brisk adjustment of throttle would be unadvisable, one direction or another (i.e. releasing the clutch with a large difference in rotation). Back driving, however, happens as soon as one just lifts the foot off the pedal - the inertia of the car pushes on the engine.
> 
>> I also pointed out the effect of unburned gas from backdriving washing
>> oil off of the cylinder walls causing undue wear. This definitely
>> happens with carbureted cars, but with modern fuel injection the fuel is
>> shut off when backdriving.
> 
> That's my understanding as well. With fuel injection, essentially backdriving is rolling on zero gas consumption while preserving some mechanical energy - aweee-sooome.
> 
> 
> Andrei
> 

-- 
Jordi Sayol