Hello Jdonalds,
Thanks for the writeup.
I can share my own experience too. I recently took about a 2300 mile trip in my Clarity. Except while stopped to visit with friends, where I would drive in EV mode, I did the entire trip in HV mode or HV Charge mode and the car was charged once to 100% with the 120vac charger.
I would put the car into HV mode upon startup and record fuel economy after every fill up and these numbers only include MPG for segments where the entire time the car was in HV mode including surface streets to and from freeways.. Except for one instance, the car was always in HV mode while traveling.
Before I give the numbers, these numbers are not the numbers from the Clarity. These are the numbers based on dividing the mileage on the odometer by the fuel used, and this brings up this point. Either the Odometer is off (I have to measure it one day) or the indicated fuel economy is reading high.
AC Was on for the entire trip and set at between 72 and 74, and OAT was between maybe 65 an 98 F.
On the trip, while operating in HV mode, mileage was from a low of 44.6 MPG to 54.25 MPG. (the Clarity consumption gauge was more optimistic, usually given about 10% higher MPG reading than the calculated reading) But there is more to the story. While the Owner's Manual shows a graph that suggest that the SOC will be maintained at the point where the car was put into HV mode, this did not happen for me. Over several tanks, the SOC would fall tol to half (below 58%). This means that at times, the battery was giving more current than it was getting re-supplied. In fact, the second segment where the SOC fell to 50% was also a segment northwest of Chattanooga Tennessee where there is a very long and steep grade, and on this specific segment, I decided to HV Charge back to 58% in advance of the climb, so this segment is not included in the figures above.
My driving was almost always below posted speed limits as I have a long tradition of focusing on fuel economy (First Gen Insight and Prius 3 owner, and a lot of hypermiling). In fact, the 54.25 segment (and a 53.5 mpg segment) were both recorded on my drive along the Natchez Trace Parkway from Franklin TN to Natchez MS. The speed limit is 55 on much of this segment and except for a single pass, I never exceeded 55 mph.
Highway segments were done at 65 mph (ACC mostly on) and except for Natchez Trace, almost most segments were on interstate type highways.
I would estimate that the amount of SOC used was relatively small (one bar or so for segment) but with each fillup, the SOC would be down a bar or so, so this would add maybe the equivalent of 5 miles of EV assist, and while I did not calculate it (because the actual figure was unknown) this small amount would only have slight impact on the calculated mileage (about 2% or less).
Otherwise, the car behaved as you reported. The ICE cycles on and off regularly, and by watching the instantaneous readout and the white power lines, it was easy to see that the ICE was either driving the car by itself or whether the car was only being driven by the traction motor (White bar goes much higher than current draw indicator but then creeps back down until it hits the current draw indicator, at which case, the motor would clutch back into the system, instantaneous MPG readout would fall to 38/42 mpg). At moderate highway speeds though, the ICE absolutely does not run full time. It comes on and off and it clutches and de-clutches with regularity. Using the information display, one can of course see the ICE and clutch indicators alternate).
I am guessing that the drop in SOC is just due to rounding errors of the HV program profile as it changes from ICE to EV and overshoots or undershoots the what is probably only an approximate SOC number, because even when the car is used in full HV mode for a full tank of gas, I was constantly (but very slowly) loosing SOC, so the manual is in fact incorrect in that the true SOC is not maintained as shown in the graphs depicted in the Owner's Manual, but for most shorter highway trips (100-200 miles) one would probably only loose 1 or 2 bars if the car where in HV mode from power on to power off.
Overall, I was pretty pleased with the mileage. Again, I drove the car consistent with the way I used to drive my Gen 3 Prius and Gen 1 Insight, and I had expected to have sacrificed some highway mileage when taking trips in the Clarity, but on this 2300 mile trip, I would say that I got more or less the same mileage as I got in the Prius on similar trips and driven the same speeds. The Prius normal low mpg on a similar trip would be about 44 mpg (calculated, because the Prius MPG display was also optimistic, but not nearly as much as the Clarity display is). I had some tailwind segments with the Prius of over 65 MPG, and I had some tail wind segments in the Gen 1 Insight of 85 MPG (Segment being fill to fill).
Your description of the way the car behaves in HV mode though is consistent with my own experience. Most people drive faster than I do, and my guess is that at speeds over maybe 70 mph, the ICE would probably stay on most of the time, but this is a pretty slippery car and has excellent glide characteristics, so at 65 mph, I was clearly running on battery power alone on and off, on and off.
When I would leave the highway, the ICE of course was coming on quite regularly and while sometimes it was at an idle speed, even a slight touch of the accelerator would bring on a mid-RPM drone. So this means that at least some of the mileage recorded above included some small amount of city driving (exit to friends home, off highway for meals, etc).
Clarity was very comfortable on the trip and got much better fuel economy in HV mode than I had expected, but once again, I am a very long time hybrid driver that has driving for high fuel economy for 15 years (since the original Insight, which itself was not all that great on the highway unless you drove at 55 mph with the AC off, and doing that in Texas would get you killed, or turn you into a dried tomato).
I do worry about the long term life of the ICE clutch. It picks and drops a lot on a long trip, but I only do maybe three long trips a year. It is pretty seamless though so maybe they are doing rev matching rather than just starting the engine by engaging the clutch (which would give very high wear if this were done constantly at highway speeds).
A very pleasant car to tour in though. I really my time in the car because it is far more comfortable and quiet than the Prius, and the trip comfort was what made me eventually tire of the Prius (and the Insight before that). Finally, a really comfortable hybrid.
