Thoughts on Changing Transmission Fluid

[Brandon002]

I'd like to see that original document, because what you posted states absolutely nothing about the transmission adapting to deteriorating fluids.

[JCL]

Originally Posted by Brandon002

I'd like to see that original document, because what you posted states absolutely nothing about the transmission adapting to deteriorating fluids.

I will look for it. But in the meantime, recall that we are talking about the clutch engagement time and input/output slip ratios as inputs to a modulated clutch pressure application, for a wet clutch pack. You don't think that the boundary and hydrodynamic friction characteristics are the variables we are adapting to? We are adjusting pressure, not travel position. And if we agree that we are adapting to the friction of clutch plates as they wear, isn't that friction a function of both the clutch plate surface properties and the fluid?

There is another document posted up here somewhere that talks about the x drive transfer case. That has adaptations as well. And the control strategy is exactly the same, clutch pressure is modulated based on feedback signals. In that component, when the adaptations reach their limit (no more ability to correct for fluid properties as they change from time to time) you get a light on the dash saying fluid is out of spec. Not that clutch plates are worn, but that fluid is out of spec. Exactly the same principle.

Edit: Quoted ZF transmission document: http://www.e38.org/electran1.pdf. Still looking for the original one.

[JCL]

By request, a summary of the adaptation capabilities of the ZF transmission. The easiest document to search on was the ZF patent, so here is one of the main ones. Related patents are linked on the page.

Therefore, the problem on which this invention is based is to make a method for control of a transmission of a motor vehicle available which, for each of the different influences which impair a gear shift, a separate adaptation can be carried out from which can be deduced the respective right reaction for an optimization of a subsequent gear shift.

Note that each shift is monitored, and then adaptations are calculated for an optimization of a subsequent gear shift. The system adapts, therefore, to each of the different influences which can impair a gear shift. Full details of what they measure and how those measurements are applied to the reference condition are contained in the patent. Pretty heavy reading, but some may find it interesting.

Brandon: I humbly submit that fluid condition as it changes over time is an influence which can impair a gear shift of a wet clutch pack (each clutch pack forming a shifting element). I think we agree that fluid quality over time is an influence. ZF got a patent based on adapting to each influence. Ergo, they are adapting to fluid quality, not by direct analysis of the fluid, but by measuring the performance of the fluid.

Patent linked here:

Patent US6569060 - Method for controlling a transmission of a vehicle - Google Patenter

Interesting side note again: The patent references a specific benefit of adaptive pressure control, namely that transmission manufacturing cost is reduced due to the ability to open up the manufacturing tolerance limits. Those tolerances can be opened up because the adaptive pressure control can handle wider tolerances than a 'dumb' system. We often think of modern vehicles as being much more complicated (which they are) and at the same time more precise, which would mean more demanding on things like fluid specs and quality over time. Here is a case where precision was reduced, intentionally. That intuitively fits with the transmission being more tolerant of varying fluid condition, which is where this discussion started.