ok, thanks for the advice

 

Great post. This is first I've read of anyone pushing the FEH to its maximum limit. I pull a 1500# travel trailer, mostly on flat ground and it is more than fine, but it is good to know what the extreme is.


Can you relate your experience with respect to engine braking with a heavy trailer and a steep grade?

 

I will say it is ILLEGAL to tow over 1000 pounds with any vehicle WITHOUT trailer brakes.

You NEED trailer brakes for anything larger than a jet ski with a hybrid.

The engine is specifically low compression and lower torque than a "normal" engine for optimized MPG.

THERE IS NEARLY ZERO ENGINE BRAKE ABILITY WITH THE FEH...

Electric dynamo (regenerative) braking is well, strong... using the larger 93 HP motor as a generator... making electricity slows you tremendously... if that electricity has some place to go. So for half to one mile going downhill you can dump about 20kw (26 brake HP) into the battery pack...

After that period, you can dump some amount of kw from the "wheels" generator into the smaller starter generator, making the smaller generator a motor, and that motor turns the engine at 4000 rpm without fuel... basically wasting some energy to slow you.
But the engine is so eficient and low compression it does not put up much resistance.

And the slower your speed, the less the resistance effect...
Under 25 mph you have almost zero engine brake effect.

USE TRAILER BRAKES AND ADJUST THEM TO JUST BARELY NOT LOCK UP!

In my super duty truck, pulling a light trailer, I can safely adjust the trailer brakes to assisit in panic stops only, to save wear on the trailer. You dont have that wiggle room with a FEH. It has trouble stopping itself on steep grades.

 

Thanks. I have 10" electric brakes on my trailer. I was just curious as to what sequence the FEH goes through to simulate compression braking.

 

Excellent information. I run into a situation similar to trailer towing, while descending mountain roads with 3000-4000 vertical feet of elevation loss in 5-10 miles. At the start of the descents, "engine" braking is available in the form of regeneration. But soon the battery is full to the controlled capacity, and the FEH is then mostly dependent on the friction brakes.

The use of "D" or "L" involves some consideration. The important difference is that, on the '09 FEH at least, the engine will almost always be engaged in "L", while it is free to shut off and go into ev mode if the conditions are right and it's in "D".

For a descent that will not fill up the battery, it's best to just leave it in "D" and use the brake pedal. This will maximize the energy stored which is then available for boost on more level or uphill ground. If it's below the EV speed, the engine will be off (unless it's needed to heat the exhaust system etc).

But for an "engine" braking descent that will exceed the battery capacity, it's better to have it in "L". Having it in L engages the gas motor, and even though it won't be using gas (usually) since you're off the throttle, having all the engine parts flailing around will help slow the vehicle. Put another way, having it in "L" delays filling up the hybrid battery, and so either preserves storage capacity, or leaves less braking to be done with the friction brakes.

However, as gpsman1 said, the slower you go the less "engine" braking is available, whether or not the battery is full. So on our descents, we just end up on the friction brakes. The faster the descent, the less time the friction brakes have to dissipate the resulting heat. Fortunately on these backroads we can go down as slow as we need to, to allow the brakes time to remain relatively cool.

This is similar to when we did this mountain travel with a heavily loaded '79 Chev Impala station wagon. With only a 3-spd automatic, it had virtually no engine braking at slow speeds. So we used to have to stop for half an hour partway down descents to let the brakes cool off.

For the FEH at highway speeds, wind resistance, plus regeneration, plus "engine" braking usually suffice. But a heavy trailer with no brakes of its own, on a long steep grade could result in a "runaway train" situation.

 

what have you towed?

 

Well, I can tell that John (gpsman1) has pulled a few miles. I tow a 16,000 pound 5th wheel with a F350 dually that has 400 HP and 800 ft-lbs of torque. That engine uses a turbo compression brake that engages on long descents but even that setup is "iffy" on long downgrades here in the Smokies and out west in the Rockies.

We are looking to get a 20,500 pound trailer and I have started looking for a Freightliner M2-122 medium duty truck. The one I am hunting for has a Detroit Diesel DD13 with 450 HP and 1,450 ft-lbs of torque. After pulling for years, like John, you figure out that torque counts when pulling and the FEH does NOT have the capacity to pull a heavy trailer safely.

Even more important than getting a load moving is STOPPING IT. That is why my dually is getting sold. I have the gain set to max out (10.0) on my trailer and use them on long downgrades as well as the engine compression brakes and reserve the truck brakes for an emergency but I have had one too many close calls even then. The new truck will have a Jacobs brake switched from the dash and with a 13 liter engine, I will be able to use the engine alone on steep downgrades to keep everything under control.

That is why I said what I did about safety and the life you save might be mine. Rent a U-Haul truck, put your stuff inside and rent a trailer to TOW your FEH to where you are going. Their large trucks are designed to safely haul a load and tow a small vehicle like your FEH without any problems

If someone wants to kill themselves by towing in a dangerous way, fine, go ahead but they can't control what happens when things get out of shape on a tow vehicle and then they can hurt someone else and THAT is where I have a problem.

Tow smart, tow safe and make it home with everyone in one piece.

 

Nothing. The important point is that the FEH can stress the brake capacity on long steep downgrades even without towing anything.

 

http://www.cleanmpg.com/forums/showthread.php?t=39151.

OMG MUST READ THIS

 

http://www.cleanmpg.com/forums/showthread.php?t=39151.

OMG MUST READ THIS