Mountain Driving

Like normal...

B mode can be used for the mountain. All it does differently is that it purposefully wastes regen'd energy by spinning the engine so that the battery doesn't fill as quickly. If it is truly a mountain, then your battery in D mode with the brakes will probably fill up before the bottom and then you will be using regular friction brakes to slow down. Nothing wrong with that except it makes your brake life shorter towards the "normal car" territory.

 

As a general rule, I get more concerned with hills or mountains that have a 300-500 ft elevation change and ascending or descending runs approaching a mile.

CLIMBING - drive so the traction battery is not providing extra power. Discharging the battery means it will have to be charged later and charging heats the traction battery. If you can follow a heavily loaded, semi-trailer truck, it would be perfect as their power to weight ratio matches what our NHW11 Prius can handle on the engine only.

Around seconds 2400, I started a "forced charge" holding the brake and flooring the accelerator in "D". The orange line shows the forced charge voltage and the small green dots, the charging current while the dark blue and pink lines shows two of the four temperature sensors rising. By seconds 2700, the traction battery was fully charged to the maximum 80% SOC. Then I started climbing a hill in "R" as discharging the battery should be endothermic. It helped but the resistance heating of the internal battery fought this effect. But now the whole pack was much hotter, 27C went to 34C on the pink line. Even greater on the blue line, 31C to 39C. This is called "heat pumping" and puts a check of a stress on the traction battery.

DESCENDING - control speed by shifting between "B" and "D" with emphasis on "B". You want to avoid putting a charge on the traction battery as this is exothermic, it heats the battery.

I did some metrics on hill climbing with our NHW11 and on a local 8% grade hill got this data:

I found the optimum climb speed on this particular hill to be 50-55 mph which is what a loaded, semi-trailer truck will run climbing the same hill. The fuel consumption shows the engine is still providing the energy, it is not drawing power from the traction battery. But once I reach 65 mph, the car starts drawing significant energy from the traction battery. Faster speeds give the illusion of saving gas BUT it is drawing down the traction battery that has to be charged later. Worse, the subsequent charge heats the battery and that shortens the life.

I suggest getting some metrics, your own:

• traction battery fan running - if you hear it, the pack got too hot. Leave the car parked and "READY" in the shade until it stops, about 5 minutes.
• Scangauge II - program XGAUGEs to show the traction battery temperature. There are four, three in the pack and one that measures the ambient air temperature. This also gives other important metrics that can help efficient driving.
• miniVCI - more sophisticated, you'll need a windows XP system and have to modify a parameter to let it record for a longer period. It is the ultimate diagnostic tool with the ability to look at any metrics. For engineering studies, it is more useful for capturing spot values and short benchmarks.
• Android Torque - I've got a sample but am not an expert about how to get metrics for the traction battery loaded. Good people I trust have done this in the past but my current efforts, low priority, are still in progress.

GOOD LUCK!
Bob Wilson

 

Ridge running causes a lot of traction battery I/O, with attendant heat production. NHW20 cells were better at diffusing that heat than NHW11s.

What I would usually do on hills is run the air con in 'flow through' (not recirc). I believe this helps to cool the battery , and that's what you want for longevity. Not necessary in winter.

Youse guys are making me miss the little blue car

 

what happen to it?