What exactly is engine braking?
06-17-2008, 03:16 PM
#11
Contributors
Join Date: Mar 2004
Location: New Orleans, LA USA
Posts: 4,672
Likes: 0
Received 0 Likes
on
0 Posts
My Ride: E90 M3
Model Year: 2011
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, 04:35 PM
#12
Members
Join Date: Sep 2005
Posts: 168
Likes: 0
Received 0 Likes
on
0 Posts
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, 05:19 PM
#13
Members
Join Date: Nov 2007
Location: Houston, Texas
Posts: 56
Likes: 0
Received 0 Likes
on
0 Posts
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, 05:57 PM
#14
Senior Members
Join Date: Jun 2007
Location: Atlanta, GA
Posts: 1,845
Likes: 0
Received 1 Like
on
1 Post
My Ride: 2008 535i:
(8/07 Build) Metallic Bronze, Beige NASCA Leather, Ventilated Seats, Sport Pkg, Cold Wxr Pkg, Logic-7 Sound, HUD, Night Vision, PDC, Split Rear Seats, NAV, Premium Pkg, Comfort Access, HD Radio, Sport Auto Trans
Current mods: M-Aero Kit, JB4, Motorcepts 6000k HID Foglamps
Umnitza ICE-Lite 10w LED 6000k AE's
1992 Camaro RS:
Fully Restored w/Custom Interior, 5.0L V8, T-tops, OEM Z28 Foglamps, Inst Cluster, & Spoiler, Custom Sound, Too many engine mods to list
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, 07:56 PM
#15
Contributors
Join Date: Oct 2004
Location: So Cal, USA
Posts: 14,776
Likes: 0
Received 0 Likes
on
0 Posts
My Ride: 545iSMGSilver GrayAuburn Dakota LeatherLogic 7 Premium SoundSports Package
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, 08:03 PM
#16
Members
Join Date: Nov 2007
Location: Houston, Texas
Posts: 56
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by pukka' post='604690' date='Jun 17 2008, 08:57 PM
The laws of physics are always at play.
06-18-2008, 03:50 PM
#18
Senior Members
Join Date: Jun 2007
Location: Atlanta, GA
Posts: 1,845
Likes: 0
Received 1 Like
on
1 Post
My Ride: 2008 535i:
(8/07 Build) Metallic Bronze, Beige NASCA Leather, Ventilated Seats, Sport Pkg, Cold Wxr Pkg, Logic-7 Sound, HUD, Night Vision, PDC, Split Rear Seats, NAV, Premium Pkg, Comfort Access, HD Radio, Sport Auto Trans
Current mods: M-Aero Kit, JB4, Motorcepts 6000k HID Foglamps
Umnitza ICE-Lite 10w LED 6000k AE's
1992 Camaro RS:
Fully Restored w/Custom Interior, 5.0L V8, T-tops, OEM Z28 Foglamps, Inst Cluster, & Spoiler, Custom Sound, Too many engine mods to list
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, 04:26 PM
#19
Contributors
Join Date: Mar 2004
Location: Long Island, NY
Posts: 2,303
Likes: 0
Received 1 Like
on
1 Post
My Ride: 2008 535i: June 6th start build, complete June 17th, at NY Port July 5th, at dealer July 10th, took delivery Friday July 13- Plantimum Bronze/Natural Brown Leather/Light Poplar, Sport Package, Sport Auto, Active Steering, Premium Package, CWP & PDC. Dinan Performance Software 384hp & 421 ft/lbs.
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, 05:04 PM
#20
Members
Join Date: May 2008
Location: SoCal BABY!!
Posts: 114
Likes: 0
Received 0 Likes
on
0 Posts
My Ride: 2007 Chevy 3500 DRW: 7" lift, 35" tires, PPE stage 7, MBRP turbo-back, back-up camera, trac bars, Bilsteins. Pine air freshener.
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.