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03-18-2008 09:46 PM #1
- Join Date
- Oct 2006
Many people including myself have wondered why the tow capacity is only 1,000 pounds for the '05 - '08 FEH/MMH. Ford doesn't give a reason why the regular 2.3L gas Escape is rated for 1,500 pounds which is more than FEH/MMH, but now I think it all comes down to engine torque, the eCVT transaxle and the HV battery.
The Scangauge ( http://scangauge.com/ ) has clearly identified that engine LOAD goes to 99% and requires electric motor assist with any kind of torque demand at low RPM's. This occurs without towing any weight, so we must conclude it is very hard to tow any additional weight without constantly calling on electric motor assist. Now that I've had time to study my '05 FEH, I can see this constant assist if not controlled by the driver or driving in the mountains, could overheat the electric motors, electric components and the HV battery. The systems have built in safety measures to shut these components down when they get to hot, but your left with a gas engine with very little torque at low RPM's.
The electrical assist will allow the HV battery State of Charge (SoC) to drop below the normal lower limits on acceleration demands and provide needed temporary electric motor torque. However, there is a point the electronic control module can't allow the battery SoC to drop to a point the gas engine does not have enough battery Soc to restart the engine. This would put electric motor assist at a point where it is no longer available and all acceleration would be at a dangerous level with the low RPM torque of the Atkinson Cycle gas engine in our FEH/MMH. There would be no way for the engine to get to the higher RPM and higher torque range quick enough for fast acceleration if needed. Remember, the electric torque allows the Atkinson engine to increase RPM's to a point it has the torque to no longer need electric motor assist.
I'm sure Ford designed the FEH/MMH to handle 1,000 pounds for towing, but when these limits are way over exceeded, I can see possible operational problems with the present design.