Quote:
Originally Posted by daytonatrbo
I assume that some of the delayed shifts and other odd behaviors we perceive are due to this torque management. The torque output of the engine seems to be limited until the transmission fully selects a gear and locks up the TC. I think without that, and the relatively massive, low rpm torque from this engine, we would see a lot more transmission failures due to burnt up TCs and clutches.
I suspect that remapping the engine for more power, and remapping the trans for quicker shifting would result in either a very harsh shift experience, or lots more wear in the transmission.
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Here is how the system works(simplified):
The "gas pedal" map is called "driver's wish". In the DDE, the position of the pedal is converted to a 0-100% value. This value will have some real value meaning that is output torque of the engine (calculated internally by RPM, boost, etc). Then this value is send by the CAN bus and received by the transmission control module along with others. If your "driver wish" is 300(ft/bs for example, although it is calculated in Nm) but the engine is at 3000 rpm and no boost it is making only 150. At this point the TCU (TCU by it's own, not by a command by the DDE) will downshift (if possible) and unlock the TC. Once the RPM go up and boost will start to build. Once the output of the engine reaches DW the transmission will lock the TC and upshift depending on the DW. The transmission behavior is dictated by the engine output, not the other way around.
The transmission acts fine under boost and doesnt really need quicker shifts in my opinion. The problem is when off boost and the strategy to build boost quicker. 4000 RPM on 1st and 2nd gear are not the proper way to build boost.
There are not many documented transmission failures on diesels, but we'll see.
04-27-2017, 04:37 AM
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