"motor assist" obscure warm-up EV mode

This past spring, I was testing a ScanGauge when I noticed our 2003 Prius would hold the fuel consumption to 0.60 gal/hr regardless of the
accelerator and speed. I already knew the minimum, idle fuel consumption when 'cold' was 0.30 gal/hr but this fixed fuel consumption was something new. I soon verified our 2010 Prius has the same behavior.
Upon further research, there is a Toyota SAE paper that explained before the catalytic converters reach operating temperature, the Prius tries to maximize, EV mode while letting the engine run in a minimal fuel consumption mode. This means the car can accelerate to speeds of 45-50 mph using just traction battery power for the ~45 seconds it takes for the catalytic converter to become operational. My detailed write up is here:
http://www.myhybridcar.com/forums/gasoline-fuel-economy/1925-motor-assist-warm-up-ev.html#post4184
The practical effect is maximized by:
1) Don't start car until you are ready to drive, no stationary, cold idle. So try to park so you can see traffic before having to start the car. 2) Accelerate to 38-40 mph without pushing the accelerator so the engine spins faster. Watch the energy flow display and make sure the power arrow shows from the traction battery. It should take about 30 seconds to reach 38-40 mph. 3) Shift into "N" to coast in minimum fuel consumption mode, 0.30 gal/ hr, for as long as possible. 4) Shift into "D" if you need to stop or slow down for traffic. 5) Until the coolant reaches 70C (you'll need a OBD scanner like a ScanGauge) shift into "N" whenever practical and safe. Use "D" when slowing or coming to a stop.
Because of this revelation, I'm changing my warm-up protocol including parking practices. Initial data indicates this is making a significant impact but we won't really know until winter weather arrives.
Bob Wilson
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I've notice that if I block the air intake grills that the 2010 Prius will warm up faster and stay warmer for a longer time after the Prius is turned off. I've also notice that after the coolant temperature reaches 171F (77C) that it is much easier to get over an instantaneous 50 mpg energy performance from the Prius. Using the 1 minute bar FE chart I've found that from a cold start (when the gasoline engine has been turned off for more than 4 hours) for the first three to six minutes of any trip - the Prius normally gets from 15 mpg to 35 mpg - even with grill blocking, overinflated tires, a HV battery with > 50% charge, and under ideal driving conditions.
My 2010 Prius will burn 0.60 gallons per hour or more during those first few minutes to heat up the catalytic converter, charge the HV battery, and to move the car; However, If my foot is off the accelerator and the Prius is coasting downhill (+ charging the battery) during those first few minutes my Prius will burn as little as .30 gallons per hour in Drive mode.
During the winter, urban driving environments/routes (which donot require the ICE to run as often) may take the Prius up to 35 minutes before the Prius ICE coolant temperature increases from 108 F to 171 F (77C). Grill blocking in urban driving environments can help decrease the time the Prius engine needs to reach 77C signficantly - especially when the driving temperature drops below 60F and for shorter trip (<4 miles) .
For longer trips in highway driving environments (>50mph) the Prius will jump from 15C(60F) to 77C(171F) within a few minutes and grill blocking is unnecessary.
During winter, during long traffic lights when the Prius might have a 3 to 5 minute idle-stop ice cycle the coolant temperature can drop signficantly. If the ICE coolant temperatures drop too low - while waiting in traffic - the Prius ICE will automatically turn on just to keep the engine coolant warm and the MPGs will drop signficantly lower. This happen last winter when my Prius got stuck in a snow blizzard induced traffic jam and the Prius kept repeatedly turning on the ICE to keep the coolant warm while it was stuck for over 40 minutes subfreezing temperatures. Using the windshield defroster or the heater accelerated the drop of coolant temperature. For that particular 16 mile commute route the Prius got only 22 mpg ( when normally during the winter time the Prius would gets about 50 mpg on this route when its not stuck in traffic. So this represented a 56% drop in FE, Driving temperatures are crucial factor in achieving high MPGs ; in the summer time, on this same 16 mile commute route, the Prius can get about from 60 to 70 mpg! )
HTH
Walter
2010 Toyota Prius type 3, Blue Ribbon/Dark Grey, oem floormats Yokohama Avid S33 (front 50 psi/ rear 48 psi) grill blocking (100% under 60F, 50% under 80F, 0 % over 80F) ScangaugeII (FwT, SoC, RPM, GPH) Odeometer +16000 miles/ 60 mpg
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Hi,

I'm finding I can achieve 30-35+ MPG and often up to 50 MPG within the first 45-50 seconds by exploiting the catalytic converter warm-up interval. After the catalytic converters light off, mileage is dependent upon route and keeping the speed up, 35+ mph. Both Prius are responding well to this new information.

Our 2010 Prius catalytic convert comes on in less than a minute. That is the only window for aggressive use of traction battery energy to get the kinetic energy up. Then try to use higher speeds so the battery recharge overhead is a fraction of vehicle power.

Shifting into "N" as it is easy. I choose to drive both Prius as if they have manual transmissions and it works.

Bob Wilson
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