Save Charge for Going up steep hills

You can use Charge Mode in anticipation.

 

The same amount of power is required to get the car up the hill at the same speed, regardless of whether it comes out of your battery or your fuel tank.

At low speeds, you might see some efficiency gain from EV due to the higher low speed torque, but at higher speeds I suspect it will be a wash.

I experimented with this on a recent trip that took me through the mountains of West Virginia and Pennsyvania. I found that I needed to run EV going up some hills to make room for recharging on the subsequent downhills. Other than that, at highway speeds I just left the car in HV mode unless I needed regenerative braking, then it was EV and B mode on the downhill. I found that keeping the engine RPM below about 3000 RPM when climbing provided reasonable speed control and the instantaneous MPG didn't drop significantly.

 

I may be missing something. Try what?

Did you mean inefficiently?

 

It needs the same amount of mechanical energy delivered to the wheels. I think OP is instead counting 'fuel' before conversion to mechanical energy. We do know that the Gen3 ICE is less efficient at this conversion at high power levels, as shown on its BSFC chart. Gen3's chart is flatter / broader than Gen2's chart, but I don't recall seeing a Gen4 or Prime chart.

I.e. intentionally flog the Prius, while having the BNW draft behind it. (I remember Green Human John doing this with a VW TDI too, out on the open highway). I'm not taking such biased tests as definitive.

 

Perhaps I'm not understanding the points you are trying to make. You noted that ICE are most efficient at light load, which I don't think is the case. Low RPM and big throttle opening are efficient because they minimize pumping losses, so I follow the low RPM discussion.

On a recent long road trip with cruise on, level ground, various speeds, I don't recall seeing the ICE running as low as 1200 unless I was going below about 45 mph. At 73 mph by GPS, it was typically 1800-2000 rpm, which is still farily low speed. About 55 mpg indicated by the car at that speed.

Why wasn't the engine at 1200 rpm, if that is the most efficient speed?

I would be interested in a link to this event, so we can see exactly what they did and the results.

 

Humm, but steep uphill also uses a lot more EV power as well. If I use EV on a steep uphill, I will lose precious EV miles. I would rather be able to drive 35 miles on the flat road than using the same battery power going 15 miles of uphills. I need to perform the balancing act.

 

So I take it there is no reference for the BMW experiment, nor thoughts on the engine speed that the Prime actually runs.

Asking for further information is now considered trolling, I assume.

 

No, that isn't even close. The Gen3 engine is most efficient at around 2000 RPM, but has declines only a few percent out at 4000 RPM. See the BSFC chart here:

2010 Prius 2ZR-FXE engine efficiency map | PriusChat

He is not at risk here.

 

I'll agree with that. My turbocharged 2.0L VW TDI was pretty much a dog at 1200 RPM. They set the car up for boost at about 1700 RPM, so about that range it developed a lot of torque. Below that, gutless. I generally needed to be above 55 mph just to run in 6th gear. 60 mph on that car top gear, 1780 RPM.

The newer Corvettes will get over 30 mpg highway in top gear, and if I recall they run at about 1500 RPM.

By comparison, highway tractors (Class 8 trucks) with 12-14 liter turbo-diesels typically run in the 1200-1400 RPM range, depending on gearing.

Back in the days before computers, variable valve timing, turbos, etc, the optimum fuel economy point was generally specified as the max torque point.

 

There may be a troll here but it isn't @jb in NE

 

Thanks. Prius 17.2 mpg? I didn't think that was possible - foot on the brake and gas at same time? And, they never specified how they measured the fuel consumption - calibrated meters, dash display, etc.

Interesting exercise, but I don't see a lot of scientific rigor in that one.

And, if this were repeatably true, then manufacturers would not be abandoning larger engines for smaller boosted engines to improve fuel economy. The Ford 2.7L twin turbo in the F-150, for example. Ford small SUV's and even Mustangs with the 2.0L EcoBoost, as another example.

 

The scientific rigor? I think it was just off-camera chatting up the craft service girls...

But seriously that's rather my point. They came up with a number that might be believable, but at least now we can correctly identify the most popular account of a BMW outscoring a Prius in an economy test.

Edit: maybe imperial gallons? I can't remember TG's convention for units.

 

Thanks. Now that really was one of the stupidest things I've seen those knuckleheads come up with. There are so many things wrong, I wouldn't know where to start.