I have a question, i note that in some instances, the PDK does provide engine braking although in most it simply disconnects and coasts along. Does anyone know under what circumstances it provides compression braking?
I note that when i pull out of our work parking area and head down the hill in first, the engine is providing back pressure to slow it down. I also think, under some circumstances, when using manual mode it slows down also.
I declare this subject an epic failure (as my son would say).
Sorry Harold, I think most of us are still in control of our gear changes!
Disclaimer: I know nothing specifically about PDK
Most computer controlled gearbox shifts (whether double clutch or slush boxes) have several map program which work off things like throttle action, car speed, yaw sensors and steering wheel inputs. They are used to determine if the car is being driven aggressively or gently, and change the throttle response accordingly. In my steptronic BM gearbox (which is getting very old tech now) it knows the difference between coasting on the highway and going down a steep hill. In the first, it will just coast along when you let off the throttle. In the second, it will Lock to converter and sometimes even shift down to provide engine braking. Same goes for if you start driving in a spirited manner - it holds gears longer and locks the converter.
Now...to PDK... Porsche will have spent squillions working out shift maps based on the mixed driving they would expect a car to see, as processing power has exploded since my BM box was built. And that's why sometimes it will hold and sometimes it will coast.
The steptronic gearbox came with a ten page owners manual because it was new at the time. I hate to say this....have you read the manual?
I see its a 2013 911S ? I would ask the guys at porsche as it is I hope still in warranty, but I concur with Coastr, as my 933 had me thinking I had problems as the behavior of the box seemed inconsistant, only to find it was the owner not being as cleaver as the as the Tiptronic ECU computer..
Having said that I would still ask the Techs at Prosche, also google recalls ..
I would be interested to know what you find.
The coasting feature is a fuel saving feature I would try it in Sport/Sport Plus and I hazard it will not coast in N. I never drive in anything other than S/SP mode so will try it out when back in Melbourne and report to you Harold.
Harold drove the car today and only got it coasting in non sports / sports plus mode. Also I believe I needed to be in 7th gear to get it to work. Non of the other modes coasted. I will pay more attention tomorrow and let you know.
Quotes source post: 90862
I have since found out the tiptronic boxes are very similar to the steptronic boxes - see
http://en.wikipedia.org/wiki/ZF_5HP_transmission
- it doesn't list the 993 so I'm not sure if they are a ZF box as well, but the 996/Boxster Tips are the same as Audi/BMW/VW transmissions. I assume different computers and maps and things though, tuned for the different engines. The 993 Tip is I believe a ZF 4HP.
The PDK is also a ZF gearbox - the 7DT.
Based on all that, although the PDK is a completely different design, I'd say the thinking and development stretch all the way back to the first tiptronic.
I also found out today that it doesn't take steering angle into consideration, it actually measures the difference in rotational speeds of the front wheels. If you fit a different size front wheel (i.e., spacesaver) and the wheels spin at different rates, the transmission can behave oddly, as it always thinks you're going around a corner, and you don't want to change up. Same goes if you have a dead wheel sensor on one side, that can cause transmission fault codes.
http://pap.porsche.com/pap/filestore/991-c2-catalogue.default.302ccba9-042b-4edd-9115-80c33502c771.pdf
P26 ; "when the situation allows" I suspect is the correct reverse logic answer Harold
P26 ; "when the situation allows" I suspect is the correct reverse logic answer Harold[/quot
I agree. I read some where it stated "under some circumstances" seems the same specific explanation. Maybe it lost its definition in translation to English?
The fact is , the factory is making decisions it feels are in the best interests of the driver.
And as we know , all those guardian angels are to prevent the average dentist/dentist's wife from biting off more than he/she can chew!
Harold, your car will coast when Auto Stop/Start is active as well. If you do not drive the car in Sports/+ modes and leave it in default settings it will coast. Push the A button in the centre console (to disable Stop/Start) and it will not coast in any mode.
