What exactly is engine braking?
06-17-2008 | 04:16 PM
#11
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Originally Posted by Richard in NC' post='604591' date='Jun 17 2008, 05:12 PM
Is that still true for the new sport automatic? The torque converter is redesigned and does not have the "slop" of a normal auto. I know for sure when accelerating, the tach is in lock step with the speedo (not true for most autos). I'll have to test whether I feel engine braking with it. Should be simple. Coast from 60 mph in 6th gear and then try again in 3rd gear. If the engine & speed drags down faster, it does engine brake.
Come to think of it, I've always downshifted to engine brake when driving hard (on a track, etc) with a manual tranny. With the 550i sport auto I tap down a gear or two before entering a turn. I DO feel engine braking so I THINK its the same.
Come to think of it, I've always downshifted to engine brake when driving hard (on a track, etc) with a manual tranny. With the 550i sport auto I tap down a gear or two before entering a turn. I DO feel engine braking so I THINK its the same.
06-17-2008 | 05:35 PM
#12
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The steptronic does have braking. It is called DHC (Decent hill control) I believe it is mentioned in the manual. It tries to maintain the speed downhill the same as it was when you started decending. It works even at 70 MPH in the mountains.
06-17-2008 | 06:19 PM
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Originally Posted by EBMCS03' post='604325' date='Jun 17 2008, 10:17 AM
Or the easy way to put it... the engine is dragging the car and slowing it down 
I feel my automatic 545i downshift automatically when I'm coasting after lifting off the accelerator. So, the transmission in combination with the engine are performing an engine-oriented 'braking' process?
06-17-2008 | 06:57 PM
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Previous post was spot on:
When the steptronic is in manual mode you can experience engine braking. However the computer automatically controls the shift points so its pretty difficult to really feel this effect (compared to lgoing from 4th gear to 2nd without accelerating in a true manual).
Come to think of it - the computer doesn't even allow the shifter to skip a gear at all.
06-17-2008 | 08:56 PM
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Originally Posted by markke' post='604675' date='Jun 17 2008, 06:19 PM
Actually, the basic laws of physics are at play, which cause the vehicle to slow down when acceleration stops. Wind resistance, road resistance (a friction based surface (and potentially with an incline)), weight resistance, etc. Right?
Ya. but the effects of physics vs the effects of the engine slowing down the car physics is almost null here.
06-17-2008 | 09:03 PM
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Originally Posted by pukka' post='604690' date='Jun 17 2008, 08:57 PM
The laws of physics are always at play.
06-18-2008 | 04:50 PM
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Originally Posted by zen' post='605164' date='Jun 18 2008, 02:20 PM
The 'Laws of Physics" also state that the object will gain momentum going down an incline because of the pull of gravity.
06-18-2008 | 05:26 PM
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Engine braking is caused by the internal friction of the components of the engine, the hydraulic pumping losses for circulating the oil and coolant and the resistance generated by the compression of the engine.
When you are on the gas, the power generated exceeds the above engine frictional losses and drives the car forward. When you are off the gas, in an auto or manual transmission, those frictional losses are greater than the output of engine so the engine slows down. When you are at a steady RPM, you have reached an equilibrium between power generation and frictional losses. When you take your foot off of the gas, engine braking (and other frictional losses like transmission, wheels, tire friction) slows the car down.
When you are on the gas, the power generated exceeds the above engine frictional losses and drives the car forward. When you are off the gas, in an auto or manual transmission, those frictional losses are greater than the output of engine so the engine slows down. When you are at a steady RPM, you have reached an equilibrium between power generation and frictional losses. When you take your foot off of the gas, engine braking (and other frictional losses like transmission, wheels, tire friction) slows the car down.
06-18-2008 | 06:04 PM
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Originally Posted by zen' post='605164' date='Jun 18 2008, 01:20 PM
The 'Laws of Physics" also state that the object will gain momentum going down an incline because of the pull of gravity.