Originally Posted by xspirit (Post 253934)

As Gary reminds us, the '08 is different from the '09. Having the '09, my explanation and understanding of what's going on applies to it. When I use the phrase "shut off", I mean the gas engine is not running. I do not mean that I've actually turned the ignition key off.

There are four situations that need to be described:

Shifting into "L" is different if the '09 is above or below the maximum speed for ev-only operation. That limit is 63kph, or about 40mph.

Below that speed, and for the purpose of the discussion, reducing speed can be done by using the brake pedal or shifting into "L". Using just the brake pedal, and nothing special going on (like a panic stop, and above 3mph), all braking is done with the regeneration system. The engine (given it has no reason to be running such as warming up or a/c full on) will be shut off.

If, below the ev speed limit, you reduce speed by shifting into "L", and given all the caveats mentioned above etc., the engine will start up. Although it won't be using any gas, it takes some energy for all those mechanical parts to be moving around. This absorbs energy and so there will not be as much left over to send to the hybrid battery.

Now, turning to reducing speed above the ev maximum speed. Whatever else is going on, such as a/c on or off, the engine will be running above that speed. When you're coasting, it isn't consuming gas, but again having all those parts moving around requires energy that isn't going to the hybrid battery. If you use the brakes, the engine will keep turning over, at an rpm that's higher the faster you're going. Applying the brakes won't change the rpm. You'll get regeneration from using the brake pedal, but very little from the engine.

If, instead, above the ev speed limit, you shift to "L" to reduce speed, everything is the same except the engine turns over at a higher rpm. This is how the '09 simulates the engine braking of a non-hybrid. The higher the rpm, the more energy is wasted moving engine parts. I think this is why the hypermilers shift into N in this situation. So to maximize the energy available to the hybrid battery, you want to lower engine rpm, which is "D" instead of "L".

Taking these ideas on the road, I regularly drive roads with such long steepish climbs that on the way down, the hybrid battery gets filled up and I have to keep the speed under control using the brakes and/or shifting into "L".

I can compare at what point during the descents the charge gauge shows that regeneration has ended. At those points, the speed starts to build and I have to use the brakes and, if I'm not already in "L", then also shift into "L" to regulate the speed.

If I have been using "L" from the start of the descent, the point where regeneration ends is lower on the hill. This means there has been less energy being put back into the hybrid battery. It also means I have to use the mechanical brakes less, which is a good thing. Actually, I never come down the hill in "D" because the speed gets out of control right away, and using the brake pedal means I lose regeneration fairly quickly because the battery reaches capacity sooner.

I used to use "L" often to reduce speed, because I was still thinking like a non-hybrid driver. Using the transmission puts more load on the transmission and less on the brakes, and some say: "transmissions are cheaper than brakes". It's also a sign of driver skill to slow without using the brakes, as shown by slowing without the brake lights lit up. However, the hybrid is the opposite of that, and by stopping using "L", I have upped the mileage a notch.

On occasion, below the ev speed with the engine shut off, applying the brakes will cause the engine to start up. I don't know why this happens, but it's pretty rare.

Lately I've tried using the a/c to see what effect it has on the descent. I thought perhaps the FEH would just run the engine more or harder to run the a/c. In fact, doing the descent with a/c turned on, and in "L", I can get farthest down the descent without needing to use the mechanical brakes. Maybe I should try it with all the lights on and blowing the horn:-)

Now, few people with FEH's live in places where the hills are so large they will exceed the hybrid battery capacity. What matters is that it's a convenient way to test what operating mode enhances regeneration.

Originally Posted by GaryG (Post 253938)

Pre-'09's can use L to separate regen from the friction brakes at any speed. For instance, coming off the highway at 70mph, I just time L to reduce my speed.

Originally Posted by GaryG (Post 253938)

You can slow down to 6mph without using the brake pedal. Below 6mph, regen is cancelled and you are using the brake pads to stop.


Programming changed in the '09 and newer Ford Hybrids where you must use the brake pedal and judge the point between using the friction brakes and regen.

Originally Posted by GaryG (Post 253938)

Ford went back to the old way of L programming in the '13 Energi. Ford added a new mode for downhills by controlling regen to maintain your speed. For instance, if the speed limit is 35mph, you can change to this mode at 35mph, and the computer will regulate the speed by using regen on the downhill when required.

Originally Posted by xspirit (Post 253954)

Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.

Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?

In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.

Originally Posted by supersailor89 (Post 254074)

im studying Mechatronics and i will try to do something to make my FEH fully Electrical, fuel optional but id rather use a hydrogen based fuel mechanism, so powered with water and self suficient.

Originally Posted by xspirit (Post 253954)

Today I tried slowing from about 40mph to a stop, by shifting into "L". There was noticeable speed retardation, and the engine was running until the speed dropped below 3mph. At that point, the engine shut off and the FEH was coasting. I had to apply the brake pedal to come to a complete stop as I was running out of space.

Other than the lower speed, which indicates recapture of the energy between 8mph and 3mph on the '09, how is this different from doing the same thing on a pre-'09?

In doing this, some energy was lost spinning the engine during the loss of speed. Had I just used the brake pedal, and stayed in "D", the engine would have been shut down the whole time, no energy would have been wasted spinning the engine, and more energy would have been recaptured through regeneration. I still don't see how this differs, except for the speed thresholds, from the pre-'09's.

Originally Posted by xspirit (Post 254030)

I used the engine braking when I needed to slow down more rapidly, rather than as a energy capture method. I found the feature useful for slower speeds downhill in the LA canyons, when the engine would stay off, the speed would be kept lower, and the charge would be maximized - until the SOC got above 60 or so, when the engine would come on. So on the 2008 it was useful for slowing down from higher speeds, or keeping the downhill speeds.

Note that on the 2008 it could be engaged without forcing the engine on, so long as the speed was below 40. On the later FEH, it would always engage the engine, although it did not always use gas to the engine.

Originally Posted by xspirit (Post 254030)

In my 06 while braking in L my engine will shut off at a slightly higher speed (35 v 30 MPH) than in D. The reverse is also true...the vehicle will stay in EV mode up to slightly higher speeds in L than in D. Under certain circumstances, there are definite advantages to selecting L in the earlier model years.

Originally Posted by GatorJ (Post 254119)

This thread should be of interest:

The low gear advantage

https://www.greenhybrid.com/discuss/...dvantage-3733/

It's an old thread and, therefore, applies to the earlier models.

Originally Posted by xspirit (Post 254121)

Therefore, wouldn't the post '08's be better suited for mountain driving or trailer towing?

Originally Posted by D-mac (Post 254124)

Not necessarily, remember the 05-08 have disc brakes all around which dissipate heat well. It's also interesting to see that on an earlier model, the rear brake pads normally wear faster than the fronts because the regen does so much of the normal braking. I haven't been able to fade the brakes even when riding them a lot at highway speeds down mountains but I suppose it's possible if you push hard enough.
Some early model drivers have had their front discs/pads rust or corrode because of non-use and wet conditions. I sometimes throw the shifter to N while braking to turn regen off and get the brakes hot to clean the pads/rotors.

Originally Posted by GatorJ (Post 254123)

In L on the early models there is a greatly reduced need to ever even engage the brake pedal when slowing. My morning commute is normally bumper to bumper in town interstate traffic. I shift into L as soon as I get on the interstate and only infrequently use the brake pedal.

Originally Posted by D-mac (Post 254124)

Not necessarily, remember the 05-08 have disc brakes all around which dissipate heat well. It's also interesting to see that on an earlier model, the rear brake pads normally wear faster than the fronts because the regen does so much of the normal braking. I haven't been able to fade the brakes even when riding them a lot at highway speeds down mountains but I suppose it's possible if you push hard enough.
Some early model drivers have had their front discs/pads rust or corrode because of non-use and wet conditions. I sometimes throw the shifter to N while braking to turn regen off and get the brakes hot to clean the pads/rotors.

Originally Posted by xspirit (Post 254161)

I thought of another aspect of this, and this consideration makes it simple for me to decide which system I prefer.

Since FEH's of any year lack really effective engine braking, and since the load on the mechanical brakes increases once the traction battery is "full", then what happens if you have a mechanical brake failure?

I realize this is vanishingly uncommon, but for my usage a brake failure would be like a runaway train and would be uniquely dangerous with an FEH. On the roads we drive, such a failure would have a high chance of being fatal. The only other "out" would be to turn into the uphill side and end up rolling.

Disc brakes can't be used as parking/emergency brakes. So cars with rear discs have little drum brake systems in the rear hubs. The earlier FEH's would be so equipped, while the later ones, with rear drums, already have rear drums.

If you're in a "runaway" situation, all you have left is the parking brake. I'd much rather have full-size rear drums in this situation than the tiny ones used as parking brakes with discs.

Rear brakes don't take much of the braking load. I've never heard of the '09+ rear drums overheating anyway, so I don't think their poorer inherent cooling compared to rear discs would become an issue to begin with. And I appreciate the option to race the engine to waste energy and reduce the load on the brakes, by shifting into "L".

Originally Posted by GatorJ (Post 254167)

Disc brakes every day of the week. The chances of "runaway" brake failure are so remote, I'll take better brake performance. It's not just cooling. it's better wet performance as well. Going to drums was strictly a cost saving measure.