During my normal drive to work I'm always thinking about better times on when to use EV and not to (specifically if I have a section where I can kill the whole battery). So I thought I'd throw this out for discussion.

Is it always better to use Electric Mode instead of Gas?

My thinking is that the answer is actually no. It is obviously better to run in EV acclerating from the line (no matter what I would think), but is it better to hold the car at say 28-30 mph in EV and kill the battery? I don't think it is actually better to do that esp if the drive is flat or slightly downhill. The reason for this is that if you have a moderate uphill (say 3% grade or more) after that (and perhaps at a higher speed limit than 25 or 30) then I think the engine really works harder to acclerate the car up the hill and recharge the battery.

This senerio occurs early in my drive, so on cool days I don't have the ability to put the car into EV at that point in the drive. On the days where I can't put it into EV at 30 mph, when I make the turn off the small road onto the bigger, faster, uphill road it appears that I get much better gas mileage up that hill (say 30 mpg vs 20 mpg) and on the small road I am still getting 50+ mpg (vs infinate).

Just throwing the thoughts out there. I'm not sure if I explained the senerio well enough - let me know if I need to clarify.

Anyone else have thoughts?

 

Interest that you bring this up, I have similar feelings. My FEH is a 2008.

On my drive to drop off the kids at school, I have a 1 mile section with a single stop sign in the middle. I used to keep the FEH in EV for the entire section, but I found that as a result I had to use a lot of gas to get the SOC back up. I have found my overall MPG to be better if I accelerate a bit, and then back off to keep the MPG around 45-50. The SOC doesn't drop, and overall I think it is better.

My FEH really does poorly when trying to gain back the SOC used in EV (or the "start up" electric assist mode).

 

I guess it really depends on what your overall goal is. If you are purely looking at MPG then the argument might be made to use gas more in certain situations over EV. If you are looking at emissions then EV will probably be a more attractive choice. I try to balance the two fairly well on my commute and switched up my route to/from work and my child's school so that I can maximize EV and MPG and not leave me at a place where I am constantly fighting to build back up SOC. One thing to do is to watch your SOC right before it crosses the 40 to 39.9 threshold because that is where you take a big hit and thus cause yourself to have to use a lot of power to build back up the SOC. If you drop out of EV before you go below 40 you prevent the vehicle from kicking you out of EV. This is where you make a lot of savings in terms of SOC management. I may not explain that very well however because I am not as technical as many on these boards.

 

Would that be 30 MPH for pre 2009 engines?

 

This is a great thread. It really reminds me that every trip is different BUT trying new things on the same route can work to your advantage. I've too found that on one of my 2 mile straightaway it's better to have gassed up the hill (this part of the route is down hill but I have to go up that hill first) than to slow down and EV up the hill. This leaves me with more batt power to coast and EV the full 2 mile straightaway. Just my 2 cents.

 

I have just a few simple rules for driving the FEH:

- Use EV for initial startup to a few mph (basically "ease into" the throttle), then ICE at 1800- 2000rpm to accelerate to <40mph, then bump to EV mode for as long as possible.
- The moment you know you will need to stop soon, coast
- Any time you fall below target speed, use ICE at 1800-2000rpm to accelerate to target.
- On hills, accelerate to 40mph with ICE, then bump to EV just before crest of hill. Use regen braking to keep at or below 40mph on the down side.

I don't have a scan gauge or a nav system, so just use the rules above to get the most I can from the car without having to think about it too much.

I like to use cruise control in EV mode because it's so easy to push too hard and start the ICE. I use cruise control on highway driving until I hit a hill, then I go manual to keep the rpms from spiking too high.

On my '09 FWD FEH the above rules net me 48+mpg for trips longer than 5mi. I have a 2.5mi commute and I am just able to net 40mpg (because of ICE startup/warmup waste) in the summer. This will be my first winter with the car and I expect to lose a lot of mileage, already seeing it happen.

RayP

 

I live where during the winter months the temps can be minus 20 or even much lower. My eco hit, summer 8L/100km goes to 12.5L/100km in winter. I'm retired, so no commute and often, summer and winter, short drives, which also contributes to a lower econ. Still, I greatly enjoy my AWD 07 FEH, and it still beats a Subaru (I think?) which was our 2nd choice when wife and I were shopping.

 

This is only true for the very initial startup, and is debatable even then given the way the hyrbrid transmission works. After that it's almost always better to accelerate with the ICE. Remember that the battery must be charged by the ICE, so what you are looking for is overall best conversion of the gasoline's energy into forward motion and battery charge. ICE efficiency is best at higher outputs, around 75%, and it's under these conditions that acceleration and battery charging is the most efficient. You're not at 75% when cruising, only accelerating. So for best efficiency:

- Accelerate with the ICE
- Cruise in EV

Ultimately the need for the ICE to be on at all times above 40mph, plus wind drag of course, are the reasons highway FE is worse than city.

RayP

 

Always better? No. But usually.

Observations in my 2005 FEH.
Higher ICE load = higher fuel efficiency.

Mine runs most often at 89% to 99% load as displayed on a SG.
This is possible with the eCVT keeping the car always in the "highest gear" with lowest RPM possible, under nearly all conditions.

When going up a steep grade, the FEH will use battery assist if speed is less than 40 MPH, but not at speeds over this. Above 40, and the ICE simply ramps up. I noticed this while towing on I70 over the Colorado Rockies. If I got in the truck lane and let my speed drop below 40 MPH, my battery SOC hit the floor. If I kept it over 40 MPH, my battery stayed at 53% SOC and wouldn't budge. The ICE jumped up to 5000+ RPM to do all the work.
Load on my ICE was at 99% constantly for hour after hour when towing.
MPG was a "decent" 19 MPG for towing a 3200 pound box trailer.

Using Pulse & Glide will net higher MPG in the city. Use gas power to get up to speed ( anything less than 40-42 ) as quickly as possible, then drop into EV and coast for as long as possible, hopefully to the next stop sign or light without using gas or battery power. Use EV assist to get over small camel humps in the road as needed. Driving with your battery pack on the lower charge side will net higher MPG than driving around with your pack fully charged. Lower charge state, in general, allows higher amperage of regen, all other things being equal. Your gas engine will charge a lower battery more quickly, than a fuller one as well. Time savings = gas savings.

Pay attention to how much TIME your gas engine is off. I can net 54 MPG indefinately in city driving. Simple task is keeping the engine off as much time as possible. I can travel 24 miles around town in 1 hour. My gas engine will be on for as few as 12 minutes per hour. ( This generally means you are not running A/C or heater. )

HTH,
-John

 

I should probably get a ScanGauge but I think watching it would increase my driving stress, and I don't need that driving in the Bay Area. I seem to be able to get 40+mpg in mixed driving, about 50/50 city/fwy, just using the simple rules I published in this thread. Your point about keeping SOC low is good and seems to correlate with my experience w/o SG. I don't fully agree with your equation above, since I've seen curves for Atkinson cycle engines (likely Prius) that show best FE at around 75% load, but maybe the FEH is tuned differently?

One point I keep trying to make is that accelerating on EV is bad. Your "camel bumps" are probably an exception, as it is probably not good to start the ICE, run it for a second, then bump it off again just to make it up a little bump. It naturally happens for low SOC, but you have no choice. Just always keep in mind that any time the ICE is RUNNING it needs to be WORKING.

RayP