Can someone help me to understand why you will get better mpg's when you try to deplete your battery for the last mile or so on way to your destination.

thanks!

 

maybe its as simple as the fact that if you are depleting your battery at the end of a trip, it probably means you are in EV mode, which means you aren't using any gas

 

Yes but the confusing thing is that the battery will have to be recharged at some point... presumably on the next start. So the thought would be that the system would have to run extra to recharge the battery and you'd lose the advantage.

However.... the engine will have to run for at least 30 sec on the next restart, and probably longer to heat up the water temperature.... during that time the engine is running anyway and can recharge the battery. So in the end the engine doesn't have to run an extra amount of time to get back to a charge.

 

Yeah I always assumed on the next restart (which for me is usually the next morning) the ICE is going to be running for a few minutes anyway.

The last 1/4 mile to my house is a relatively steep incline (I can't top 22-23 mph without the ICE turning on), so whenever possible I try to EV up that hill. If I have 60% of more battery (on the nav screen display), I am usually just about depleted by the time I get to the top.

 

I also live at the top of a hill that is difficult to get up in EV mode. Ideally, you want to do just that to drain the battery, and then re-charge on the trip down.

One thing that foils this plan is that when you start up in the morning the engine is cold, so the system will run the ICE until it warms up. That's the time you should be in silent running. Shifting to L helps a bit.

 

The primary reason is that the FEH always starts the gas engine upon startup. You will use gas until the engine warms up and it is likely you will provibde some charging during that time.

 

Let me, if I may (as a Toyota Camry Hybrid owner), throw out a big question mark here. If the battery is depleted at start-up (with a cold vehicle), some of the ICE's output power will be used to charge the battery, and some to propel the vehicle (unless you warm up with the vehicle stationary). When the ICE and battery are cold, neither is at its most efficient. If the battery is "full" at start-up, there is no power wastage — all of the ICE's output power goes to the wheels, either directly (mechanically) or via the two motor-generators (electrically). The question is whether it makes the most sense to do the battery charging during warm-up or later. Now, it seems to me that the best time to charge the battery is when both the ICE and the battery are working most efficiently (i.e., when they are at operating temperature), and not during warm-up. This argues against the majority opinion expressed in this thread.

Stan

 

This is not how the FEH works. During warmup from a cold start, the ICE idles with a retarded spark and rich-biased mixture. When you drive away, you are driving solely on electrical power from the HV battery. The ICE does not propel the vehicle nor charge the battery under normal circumstances. Exceptions are if you floor it during this time or if the SoC drops below about 32.5%. If you start with a fully charged battery, the SoC will drop like a rock as you drive and the warm-up idle time will be at its maximum. If you start with a depleted battery, the lower SoC limit will be reached, forcing the ICE out of the fuel-wasting idle warm-up mode. Also, when SoC is below 40% the charging current is higher, causing a higher load on the ICE and resulting improvement in BSFC, although the net benefit is minimal since you won't be able to go below 40% SoC once everything is warmed up. Ford patented this warm-up procedure as a way to reduce emissions at the expense of FE.

 

I've posted this patent link here a few times and I think Carl sees how important it is to know about this strategy during warm-up. The strategy Ford used in our FEH/MMH after the vehicle sits for about 10 minutes is not only for cold morning starts. If you learn how to slowly accelerate to speed and use FS's in "L" to build the SoC for EV driving, you'll find your average tank MPG will be better. In other words the engine will get warm sooner for EV.

If the battery SoC is high during warm-up, you didn't take advantage of EV mode while things were warmed up before you parked. This means you had a chance to increase your MPG and didn't take it.

I find it important to understand the advantages of having both, a low and high SoC during warm-up to get the best FE possible. Sometimes my Wife will drive my FEH and she always returns home with a high SoC. Most of the FE was lost while she was driving when this happens. I just take advantage of the battery SoC by letting the warm-up strategy work and build the SoC back with FS's in "L".


Very seldom do I park with more than 43% and most likely at around 41% SoC. With the HV battery that low, it will drop to like Carl said to ~32% and the warm-up strategy will stop. I know this and try to be at a speed around 40mph for FS's. Fuel is cut back during FS's, so I take a big load off the generator (MG1) charging the HV battery as I prepare to go EV as soon as I can. The RPM's will try to get carried away after the strategy stops, so you must take it real easy accelerating during this time. I try to keep under 2,000rpm if traffic permits.


Search for my post FEH warm-up for the patent link if you care to learn more about the strategy. It's posted at http://www.cleanmpg.com/ also.

GaryG

 

I've only been on GH website for about 2 months, and I can say with certainty that Carl and Gary are RIGHT ON when it comes to the FEH. I have learned a lot from their posts (as well as others). My wife is the primary 08 FEH AWD driver, and she also finishes the final drive home in EV mode to leave the SoC as low as possible. Since Ford decided that the FEH must be started each time, this is the opportune time to charge while your are getting the fWT to 153F or 143F, depending on ambient.

I know this is not the correct forum, but took the first 500+ mile trip in the FEH yesterday. I absoultely was blown away by the effect of truck drafting while monitoring the SGII. FE results were just out of sight. Drafting with my other non-hybrid vehicles while monitoring the SGII instantaneous MPG were not as dramatic. The closer the better (dah!), but even a safe distance makes a considerable difference.

Bad news. It was dark, I don't have a CB, and the truck driver didn't like being followed, and moved to the left lane, hoping I would do something. I did -> passed him slowly in the right hand lane, and aborted the Draft.

Wish I had a CB to tell him. Also wish I could have avoided the draft in 1966, but that's another story