Uphill vs. downhill makes the biggest difference

[PriusRos]

Let me start by saying that I am still under the first 1,000 miles in my new Gen III so the car might not be fully "broken in" (although I'm not sure that I believe in a break-in period for the car, only for the driver) but I am finding that my experience so far is similar to Consumer Reports' findings and my FE is not showing much of an improvement over my Gen II.

My daily commute is a 4-5 mile drive (depending on which route I take) to and from the Metro station. In the morning, the first mile is mainly uphill, and then it's more downhill for the rest of the way. In the evening, it's not exactly reversed because I usually take a slightly different route, the shorter one, but it still involves about 2-3 miles mainly uphill, followed by a mile downhill. I'm not talking mountainous terrain or San-Francisco-style hills - just slight inclines up and down. There are a lot of lights on both routes, but it's busier and I usually have to stop more frequently in the morning.

Up to now I hadn't paid much attention to whether the mileage was better in one direction vs. the other. All I know is my overall average mpg (including longer highway trips) was only around 44mpg in my Gen II. For my Gen III, I've had two fill-ups so far, and am averaging around 45.

Anyway, for the past few days I've been resetting my Trip B meter at the beginning of each trip in the morning and the evening. I have found that my for morning commute, which is more downhill, I can get 47-51mpg on the display. The last part of the drive consists of climbing ramps in the garage in EV mode. However, on my evening trip, no matter how hard I try, I am only getting 36-40 mpg! That's a big difference, and would account for my overall mediocre FE.

I have also observed this for longer highway trips (about 30 miles each way). In one direction, the displayed showed 63mpg. However, on the return trip, it went down to 55mpg (this was the average for both directions because I hadn't reset the meter for the return trip). Again, I believe the difference was due to the the topography. Sometimes I can't even tell whether I'm going uphill or downhill, except by looking at the mpg display and knowing how hard I am pressing the gas pedal.

P.S. I realize that my topic title could be considered "No-duh", but I haven't seen a specific thread on this topic before!

[bwilson4web]

For what is worth:


I'm a great believer in route planning. Have you used Google Earth or Google maps to find alternate routes that may allow slower speeds ascending the hill(s)?

It would be especially helpful if you could give some Google Earth coordinates of your route (we don't need your home address but say a corner.) Then start a daily log from a reset trip meter. This may give some clues to how to approach a hilly commute.

Thanks,
Bob Wilson

[PriusRos]

Originally Posted by bwilson4web

For what is worth:


I'm a great believer in route planning. Have you used Google Earth or Google maps to find alternate routes that may allow slower speeds ascending the hill(s)?

It would be especially helpful if you could give some Google Earth coordinates of your route (we don't need your home address but say a corner.) Then start a daily log from a reset trip meter. This may give some clues to how to approach a hilly commute.

Thanks,
Bob Wilson

Thanks, Bob. I've varied my route for precisely this reason. I usually use the longer route in the morning because I found that I was getting better mpg than I was on the shorter route -- both because it has slightly longer time to warm up and because there is more downhill. However, coming home, there is an even longer uphill climb at the beginning of the trip if I use that route, so I take the shorter one.

I'm will probably stay with the morning route since that seems to be doing well mpg-wise and actually is slightly faster although it's longer because there's more main road, but there are a few other variations I can try for my evening trip home and will keep a log of the results.

[DetPrius]

I have observed the same thing over a longer drive. I work from home nearly 100% of the time but a few weeks had to go into to work for the first time with my 2010 Prius. My mileage on the 33 mile drive going in was very good, as in something like 64 mpg on the car. I reset the B trip meter for the drive home and was well under 60. I also felt on the way home I was doing more uphill stretches than on the way in. I had never noticed this in my previous car when I drove in 5 days a week. I looked up the elevation of the "from" and "to" locations and found they were almost 600 feet apart in elevation. This is only from one observation but I believe the elevation difference can add up quickly. It probably affects non-hybrids as well but not as much as the hybrid since it has been optimized to maximize mileage and anything working against this goal is felt.

[Rokeby]

PriusRos,

You have come upon two of the fundamental truths underlying getting
really good FE:
* route and topography make a difference. Sub truth; out-going
routes and returning routes for best FE are usually different. Good hills
have short, steep climbs and long, low-angle declines.
* one way FE figures are not truly indicative of overall FE. You have to
look at the round trip to get meaningful numbers.

Originally Posted by PriusRos

... The last part of the drive consists of climbing ramps in the garage
in EV mode. However, on my evening trip, no matter how hard I try, I
am only getting 36-40 mpg! That's a big difference, and would account
for my overall mediocre FE...

I am speaking from Gen II experience, but I believe it is relevant to
the Gen III in this situation.

Recognizing that your home-going trip is a long uphill climb leads to
the beginnings of bringing your MPG numbers up. That said, pulling
your car up the garage ramps in EV probably has a significant
contribution to your low going-home FE. The car draws heavily on
power from the HV battery during the start-up engine/catalytic
converter warm-up period. It can easily result in SOC falling 10 or
15%. Rolling down the ramps in regen does not recoup this drop. You
may also notice that even though you are in regen, the engine is
running, even though it is making no contribution to the movement of
the car and wasting gas.

Finally, it will take quite a few miles to recover the SOC. During this
time the Power Split Device PSD will be diverting power through MG2
rather than directly to the wheels for the most efficient propulsion.

Just something to consider as you find what works best in your
specific driving environment.

[PriusRos]

Originally Posted by Rokeby

PriusRos,



I am speaking from Gen II experience, but I believe it is relevant to
the Gen III in this situation.

Recognizing that your home-going trip is a long uphill climb leads to
the beginnings of bringing your MPG numbers up. That said, pulling
your car up the garage ramps in EV probably has a significant
contribution to your low going-home FE. The car draws heavily on
power from the HV battery during the start-up engine/catalytic
converter warm-up period. It can easily result in SOC falling 10 or
15%. Rolling down the ramps in regen does not recoup this drop. You
may also notice that even though you are in regen, the engine is
running, even though it is making no contribution to the movement of
the car and wasting gas.

Finally, it will take quite a few miles to recover the SOC. During this
time the Power Split Device PSD will be diverting power through MG2
rather than directly to the wheels for the most efficient propulsion.

Just something to consider as you find what works best in your
specific driving environment.

That's interesting. Indeed I have noticed that for my evening trip, starting with going down the ramps, I am using gas even though the car could just roll under gravity (and showing around 11mpg) and I could never understand why it's doing that. I'll stop turning on EV in the morning and see whether that makes a difference in the evening. Thanks for the tip.

[Rokeby]

PriusRos,

It may be better to come down the ramps in EV!

This is counterintuitive, but when you consider how the HSD works it
makes enough sense at least to give it a try.

Disclaimer: my experience is in my Gen II with after-market EV
switch. I hope it is relevant here.

As soon as the ICE starts, the HSD's first priority is to get the car
operating to produce minimum polution. It does this by running the ICE
rich which ultimtely leads to quick warm-up of the catalytic converter.
So, like it or not, the first minutes and miles produce very low MPGs.
One way to work with this unpleasant truth is to set things up so that
you are at least making some mileage while the MPG numbers are
low.

I don't know if there is a discretionary use EV switch in the Gen III.
If there is, engaging EV mode to get out of the garage will suppress the
engine coming on and you won't be using either fuel or SOC and your MPGs
don't take as big a hit! It works for me anyway.

As soon as you get out of the garage, drop out of EV so you don't run
down the SOC and incur the attendant recovery costs.

[PeteJE]

Thanks for sharing, I am having very similar observations - great mileage legs and horrible mileage legs. Hills are work for this car. I have a gentle long uphill to the foothills where I live (1-2 miles up up up). The top of the HSI, the last pixels where I can keep the ECO lit before the power area, yeilds me very very slow acceleration and speed. There are 2-3 stop signs and trying to keep ECO lit can only get me (very slowly) to maybe 16 - 20 mph in this 30 mph zone. I do it if no one in behind, but that is rare.

Is it better to just use the gas to get up to the speed limit in the pwr area on HSI then back off to maintain, or to do the long, slow acceleration whe ECO lit?

Can anyone shed more light on the pwr area of the HSI? What does that tell us other than lots of engine work?

I am averaging 46.8 mpg over the life (only 750 miles total - basically break in period) and now 54 mpg on my last tank reset that includes a couple of work round trips. This, honestly, has been a combo of learning technique, working hard at it, and totally blowing it off for traffic and habit at times. To me, it seems the car will get exactly as advertised on the EPA sticker - for folks like me without consistent great technique (the general public).

I had one work round trip at 60 mpg - but more miles on that trip meter quickly averaged that down. This one trip had very little traffic that forced me to worry about being too slow, or under the speed limit, etc.

My best mileage seems to come on the long, gentle freeway downgrades where I go to glide mode (no HSI bar at all).

I just share for anecdotal data points - I am anxious to learn and slowly grow my MPG. It is funny to become obsessed with MPG up at this level after driving a 5.2 Jeep V8 at 12 mpg for so long. This is the best!

[PeteJE]

There is an EV switch/mode, but discretionary is up to the car, not the driver. There are many conditions where the car does not allow it - one of them is when cold. I can never get it to work first thing after a long cooling off period.

Originally Posted by Rokeby

PriusRos,

It may be better to come down the ramps in EV!

This is counterintuitive, but when you consider how the HSD works it
makes enough sense at least to give it a try.

Disclaimer: my experience is in my Gen II with after-market EV
switch. I hope it is relevant here.

As soon as the ICE starts, the HSD's first priority is to get the car
operating to produce minimum polution. It does this by running the ICE
rich which ultimtely leads to quick warm-up of the catalytic converter.
So, like it or not, the first minutes and miles produce very low MPGs.
One way to work with this unpleasant truth is to set things up so that
you are at least making some mileage while the MPG numbers are
low.

I don't know if there is a discretionary use EV switch in the Gen III.
If there is, engaging EV mode to get out of the garage will suppress the
engine coming on and you won't be using either fuel or SOC!
As soon as you get out of the garage, drop out of EV so you don't run
down the SOC and incur the attendant recovery costs.

[bwilson4web]

Originally Posted by PeteJE

. . .
Can anyone shed more light on the pwr area of the HSI? What does that tell us other than lots of engine work? . . .

This is an area of interest for many of us who have contributed to Hobbit's thread. I've been able to map the power generated at 50%, 75% and 100% but I don't have the instrumentation to map the field, brake specific fuel consumption. This is coming but not here, yet.

There are some other aspects that have me wondering what is going on. For example, my "off the lot" performance was significantly better than recent numbers. Some of this may be lubricant related and I should have some data on that in about a month. Some may also be due to traction battery settling, a phenomena not yet throughly understood. It is an interesting time to have a new Prius.

Bob Wilson