PHEV Road Trip Strategies? - Kia Niro Forum
 
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post #1 of 4 (permalink) Old 11-23-2018, 07:12 PM Thread Starter
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PHEV Road Trip Strategies?

The simplest way to drive the PHEV is to just charge the battery, go as far as you can in all-electric mode, and then start running the ICE and burning gas for the duration of the trip. Iíve been wondering if there might be a better way.

When you know that youíre going to exceed the electric range, it seems like it might make sense to drive in hybrid mode sooner rather than later, and save some of the electric range for certain kinds of driving.

On a recent 84 mile trip, one of the latter legs of the trip went up a mountain highway that requires the car to climb approximately 2000 feet over a distance of a little more than 12 miles. The previous time I drove this trip, I had zero electric range before I started the ascent, and during the last two or three miles of the climb, the ICE seemed to be struggling to maintain 70 MPH and the transmission wandered in and out of lower gears several times. But on the most recent occasion, I drove the first eight miles of my trip in electric mode, and then put the car in hybrid mode. About 40 miles later when I started the steep ascent, the gauge showed an electric range of 18 miles. I kept the car in hybrid mode for the entire ascent and it seemed to perform much better this time, even though I had about 70 pounds more weight in the car. At the top of the mountain, the electric range had dropped to 11 miles, suggesting that the electric motor had been assisting the ICE during the long climb.

After the road leveled out, I put the car back in EV mode and something surprising happened: I drove the remaining 17 miles of my trip in EV mode, and when I reached my destination, the gauge was reporting that I still had four miles of EV range. Not really sure what the explanation is for that, because I had expected the juice to run out six miles before I arrived. Just before I put the car back in EV mode, the fuel economy was somewhere around 47 MPG and when I reached my destination it had climbed to 60.0 MPG, so Iím pretty confident that the ICE didnít start again on that last leg of the trip.

Some of the strategies Iím contemplating for future trips: save the battery for climbing; use some of the battery at the outset so that it will have room to receive charge from regenerative braking later in the trip; if you expect to be in stop and go traffic, try to either save the battery for that portion, or else try to ensure that the ICE is warmed up when you are doing that kind of driving.

Wondering what other strategies people might have come up with?

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post #2 of 4 (permalink) Old 11-23-2018, 07:21 PM
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The battery is always contributing torque on climbs, no matter the mode, until it drops below some number, perhaps 15 or 20%. That is one of only two ways to get my HEV battery display to drop significantly (the other being flat roads at sub 20 mph).

Yes, if there is a mountain pass to go over, an excellent strategy is to try to get the battery to "zero" at the top, and recharge going downhill. I effectively did just that on a 15 mile scenic drive, half uphill, and half downhill - steep grades and 25 mph. Battery was almost empty at the top, and completely full at the bottom (first and only time the battery display topped out).

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post #3 of 4 (permalink) Old 11-23-2018, 08:23 PM Thread Starter
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My PHEV only picked up two miles of electric range coming down that same mountain highway the next day (in HEV mode). My experience is that the EV range goes to zero when the PHEV's battery's SOC is 20%. The first time I did this trip (when I had zero miles before I started the climb, so probably 18% to 20% SOC), I didn't think to check the SOC at the top, but I checked it after I had driven another 17 miles in HEV mode and at that point, it was only 6%. My guess is that on that first trip, I reached a point somewhere before I got to the top, where the battery stopped contributing and the ICE had to do it all.

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post #4 of 4 (permalink) Old 11-23-2018, 10:10 PM
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Part of the reason why hybrids do so much better in city driving is that wind pressure of speed is no longer consuming so much power. Consider a mountain pass that you drive over and down at 70 mph. Not so many hills (almost none) that you can go down at 70 mph and gain a lot of SOC. That is because you are pushing through a lot of air pressure at that speed consuming power.

Something to consider when conserving range is more important than time spent driving. The slower you go in any vehicle, the better the efficiency. No bottom limit on pure EV mode, they are more efficient at 10 mph than 20 mph. ICE driving appears to reach a sweet spot around 37 mph constant (ignoring pulse and glide techniques) - meeting an optimal relationship between thermal efficiency, gear ratio, and wind resistance.

One interesting point from my previous example is that my estimated range at the end of that scenic drive was exactly the same as the beginning (plus I gained SOC). Not possible of course (can't drive 15 miles without some real hit on range), but it demonstrates the possibilities of low speed driving. By the way, I came down that hill on cruise control at 25 mph, ICE never came on - 100% regen maintaining speed.

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