Hi folks,

This morning tried an experiment to separate warm-up mileage from the rest of my 10 mile commute. The protocol was:

• Reset MPG and trip meter before starting car
• Record MPG when coolant reached 70F (a critical temperature for North American Prius, the boundary between warm-up and normal hybrid mode)
• Clear MPG and reset trip meter
• Record MPG when arriving at work

This breaks the trip into two parts so we can clearly see the impact of cold weather operation:

1. To @70F coolant: 31.1 MPG for 1.2 miles -> 0.0396 gallons
2. end of commute: 66.7 MPG for 9.2 miles -> 0.1379 gallons
3. total: 58.6 MPG for 10.4 miles

It may make more sense to use the "cold" idiot light as the transition point although I find this to be at a significantly lower coolant temperature. Regardless of how the transition point is selected, breaking the commuting trip into a 'warm-up' phase followed by the 'commute' phase makes it much easier to understand why different driving styles and approaches are needed for each. The key is finding the boundary between 'warm-up' and 'hybrid' operating modes of the vehicle.

During warm-up, my Prius works more like a regular gas car so I maximize use of my neighborhood streets during the warm-up. In my neighborhood I can use 25 miles per hour speeds and "N" for pulse and glide. The only hybrid mode is regenerative braking so I slip into "D" when I need to slow down or brake.

Once the car has reached 70F coolant temperature, the boundary between 'warm-up' and 'hybrid' modes, I like to keep my speeds between 30-38 miles per hour and 46-55 miles per hour when possible to maximize use of the built-in, hybrid cycle. If I'm going to use speeds up to 65 miles per hour, I prefer to have at least 2 miles of highway ahead.

Finally, when I get within 1-2 miles of my destination, I like to revert to speeds of 30 miles per hour and slower to maximize EV mode into the final parking place. This often gives a significant boost to the commuting MPG and makes good use of the stored battery energy.

This profile works for the Prius and probably all Toyota and Ford hybrids. I suspect the two-mode GM hybrids will have similar performance characteristics. I don't know enough about the energy flows of the Hondas to know if they are as sensitive to the warm-up cycle as the Toyota/Ford hybrids.

GOOD LUCK!
Bob Wilson

 

My own HCH1 is EXTREMELY sensitive to load vs MPG in warm up.

I'm always very careful to minimize the load, but especially when the outside temp is near or below zero.

I start with a "nudge" just enough to get rolling the gentle 1/4 mile delcine through my subdivision while rolling in N.

At the end is a stop sign where I turn onto a half mile 35MPH street. Usually nobody behind so I'll take my time to reach 30-35MPH.

I switch back to N again in time to gently roll to a stop at the next sign.
I brake only the last 20 or so feet.

The freeway is two miles ahead.
If it's very, very cold I'll take the frontage road instead of jumping right onto the freeway.
It gives a little more warming time, rather than jumping right up to +60MPH in traffic.

Additionally,
I keep warm up time to a minimum by limited or no heater use for the 1st 15 minutes or so. Typically I'll set the direction to defrost to help keep the window clear, and fan to OFF so the compressor isn't running, loading down the engine.
If I need to clear the window I'll rotate the fan on, clearing the window then turn it off again.
The purpose is for the engine to warm just itself up first, rather than taking the extra time to warm up the cabin as well.

I know the Prius heater is technically completely different, but thought I'd toss that in for the rest of us.

I have a 50 mile (each way) commute and can usually make up for a cold start for the distance, but is always helpful to begin "on the right foot". (Or off of it)
If I had a shorter commute it would make all the difference between a good run or a bad one.

Of course my HCH1 doesn't have EV mode but how I handle the cold starts (Driving "normal" vs driving thoughtfully) can have 5-15 MPG difference.
It sounds similar to what you are finding with your EV experiments?

-Steve

 

Sounds like it would work pretty well for the TCH. It is actually pretty close to what I do now except for one difference. I live in a rural mountain community with hills and two ways into my street, one a gentle climb coming home and the other a little steeper and shorter with a dowhill bit at the end. I exit downhill in the morning via the gentle slope for engine warm-up, but come home via the steeper one as that way I have a final downhill coast for a few minutes before I shut down. That leaves me with a nice cool-down and a high SOC for the overnight period when the batteries will be the coldest.

Target speeds for the TCH are also a little different. On level, dry pavement under typical Northwest conditions with OEM Energy tires, my best speed for FE is very near 58 miles per hour. With the snow tires on, I am still trying to get the data, but I think the number is more like 55 or 54 MPH.

BTW, from recent experience gained -- if you plan to ski for several days at a mountain resort, and the hybrid will be outside, I strongly suggest that you plan your arrival to shutdown with a high SOC. I was up at Whistler recently, and my battery was almost off the scale after the long weekend. I made a mental note to check the SOC during prolonged mountain stays after that one. Fortunatelly, no problem starting.

 

Excellent! This sure has proved true this winter. The block heater helps a little but not as much as attention to warm-up.

I'm testing the Rain-X interior product for fogging this winter and it seems to work. Unfortunately, it leaves a streaky window and I can see the tracks of where the fog condensed and flowed down instead of obscuring the window. It is on the verge of being irritating but better than running the defroster.

I don't think I've ever used the electric heating elements in my Prius and I'm loath to because of the battery drain.
The first part is all but identical. I'm letting the ICE run in "N" as much as possible and only using "D" to accelerate to a coasting speed. Then at the end, I use the accumulated battery charge to limp into the parking lot.

Bob Wilson

 

The HCH-II is VERY sensitive to lower temps.

Just to make a point, let me list some of the common thresholds (at least for the current software versions, Honda's been playing with them lately especially for the northern folk):

oAT- Outside air temps
iAT - Intake air temps
cAT - Coolant temp
aBMT - Average battery module temp

If oAT at less than -12C : Limited to no Electric Assist or Regen. To obtain regen one must switch CVT to S when coasting (Similar to B in the Prius).

If iAT at 20C or better, then full electric functions begin when cAT reaches 50C. Includes EV mode, autostop, regen, assist. Until that point only Regen and Assist are active.
If iAT is less then 20C then full electric functions will begin when cAT reaches 70C. Gas engine will re-engage when cAT falls below 70C and Auto-stopped.

aBMT - If below 0C then forced regen affinity is noticeably increased. If above 90C then all electric functions will cease.

Side note:
Compared to a Gen II Prius, I've found that the HCH-II will warm up faster... but when a Prius has warmed up it will retain the optimal temp longer... especially in a glide situation. Nevertheless grille blocking and regular block heater use on both is a definite must in order to avoid precipitous fall in FE.


Cheers;

MSantos

 

the insight is also very touchy about loading the engine when it is cold. i drive through town at 25 mph for 4 miles to get to the freeway. i use MIMA to kill the regen, except when i have to stop for a light or a tourist. i can usually hit 70 mpg by the time i get to the freeway. sometimes 75 in the summer, as low as 65 in the winter.

 

i can add what i am seeing now that it's been zero for quite a few mornings recently. i have a HCHI with a 5 speed, and a 40 mile commute. i have the grill blocked and use an engine block heater.

i live in a very rural area. i am lucky in that after i crawl out of my driveway onto our road, there is no traffic. i can literally go 30-35 for the 4 miles it takes to get to the main road. with the engine heater, i see the gauge warm up at about 2-3 miles. i feather the gas so i can keep the FE climbing.

the main road into town is another 4 miles, it's 55 MPH but i can usually get away with doing 50, since there's still not much traffic, and they will pass anyhow no matter how fast i go. that gets me into town with mid 50s for FE.

after i get my coffee, my route has another few miles of 30-40 MPH, and then goes to 55. again, almost no traffic until i get within 5 miles of the town i work in. it's still mostly rural 2 lane. and goes back down to 30 through town, no stops.

with a light touch and averaging about 42 on the back roads, i have been able to post 60s every morning for the past several months, including the cold weather days. i lose a bit on the way home, which i attribute to having to start out with a cold car.

just my experience.

 

I've got another data point to share.
Another data point:

1. To @70C coolant: 27.6 MPG for 1.9 miles -> 0.0688 gallons
2. end of commute: 62.9 MPG for 8.5 miles -> 0.1351 gallons
3. total: 51.0 MPG for 10.4 miles

I'm beginning to think our various model hybrids may have a transition temperature that marks the boundary between inefficient, 'warm-up mode,' and the much more efficient 'hybrid mode.' My North American NHW11 has a well documented transition at 70C coolant temperature. Ken@Japan has listed the other warm-up stages that happen after reaching this threshold temperature.

There is some hysteresis that the coolant can go to as low as 60C before it reverts to 'warm-up mode.' In a low or no power situation in a cold wind, the ICE can cool below 60C and it will begin running the ICE again. However, it doesn't have to go back to 70C to resume 'hybrid mode' just stay above 60C. I don't know how cool it has to go before the 70C latch point is required.

During 'warm-up' my North American, NHW11 model hybrid is about as efficient as our 2001 Echo. But once 'warm-up' is over, the automatic hybrid control laws kick in and the car becomes very efficient. I suspect the same pattern but different thresholds may apply to each make and model.

Bob Wilson

 

I completely agree.

What amazes me though, is how complex this threshold mapping can be and how dynamic its behavior is as well. I have an idea of what the input parameters are but I still observe some variability in my predictions and that is most certainly attributed to further unknowns.

While attempting to understand this complex relationship through reverse engineering and experimentation is nice and fun, I would give almost anything to get a hold of the actual specifications and procedural criteria governing the software. But what the heck, sometimes it is just as exciting to do the best we can with what we've got.

Cheers;

MSantos

 

I've noticed a significant drop in FE as well even though our temps are in the 20s-30s in the morning. I don't block my grill yet. What is the best thing to use to use to block the grill and maintain engine temp?