[bwilson4web]

Hi,

I started testing a poorly documented, power EV mode a while back with our NHW11 (2003.) I was surprised this week to discover it also exists in our ZVW30 (2010.) This is 30-40 second interval when the car starts from a 'cold soak.'

When the car first starts, the cold engine and catalytic converter generate a burst of hydrocarbon emissions. So the first priority is to get the catalytic converter hot enough to treat the hydrocarbons and get the engine warm enough to run efficiently with lower internal friction. During this 30-40 second window, both cars will draw heavily on traction battery power while severely retarding the spark and burning just 0.60-0.70 gallons per hour:

The graph shows:

• Pre-catalytic light-off - during this period, the car accelerates on traction battery power while the spark is retarded and the fuel consumption is at a fixed, rate, ~0.60-0.70 GPH. You'll notice the speed exceeded the 25 mph limit that the ZVW30 'EV mode' is liimited.
• Catalytic converters light-off - the converters reduce hydrocarbons and nitrogen oxides which is a chemical reaction that generates heat. At this point, the engine convertes to ordinary gas mode with the spark advanced and normal fuel trim.
• Coast in "N" - while the engine block is still too cool to 'auto shut,' it continues to burn fuel. But the lowest fuel rate, ~0.30 GPH, occurs when the car is coasting in "N." If your road is flat or a slight down hill, this fuel efficient glide can last some time at greater than 100 MPG.

This same pattern exists with our 2003 Prius. I suspect it may also happen in other Toyota hybrids.

As the driver, the technique is:

• park near exit, backed in - you want to start the car and pull out onto the access road. Ideally, park so you can check that all traffic is clear before starting the car.
• start and gently accelerate - once the car is in "READY," gently pull out and onto the road and continue acceleration. Watch the instanious MPG and as your speed increases, the indicated MPG will increase. The energy flow display will show power coming from the traction battery and engine power to the wheels.
• shift to "N" on MPG blip - when the cats light-off, the MPG will take a dive, ~15-20 MPG. Just shift into "N" and the MPG will once again bounce up to 100 MPG if you are travelling fast enough. At this point, a Prius is burning 0.30 GPH but the high speed from traction battery energy means the MPG is impressive.

In 2005, I first learned in "Prius Technical Stuff" that there was an initial, warm-up process unique to the 1.5L Prius. But at the time, it was an emissions related discussion comparing the NHW11's hydro-carbon converter and the NHW20's thermos. I don't remember anyone looked at it as an alternative, EV mode in part because the engine was running. No one really noticed that the fuel burn rate was fixed while the velocity could reach speeds that give very high MPG.

Bob Wilson

[bwilson4web]

Here is another chart showing a test I ran Tuesday:



Bob Wilson