Quote:
Originally Posted by orange4boy
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Bob has done this hack and probably knows the emissions angle.
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I don't have emissions data. I live in a state that has no emissions testing and those machines are expensive. The only way to really know is to have an emissions tester and run controlled tests. Sad to say, this leaves me with 'analysis' and that gets to be a little wordy. Regardless this shows the effect and my thoughts:
Experimentally I've found that spoofing the thermostat can occur at just about any coolant temperature BUT at or below 30C, the engine is likely to stall-out or run rough. Triggering the 70C spoof at 40C works without engine running problems.
STARTUP FUEL FLOW
The following chart shows injector timing during warm-up of our NHW11:
The first 30 to 45 seconds the engine is heating up the catalytic converter. Since this is the primary emissions treatment device, this must proceed. This seems to be the prime directive for manual starts but thereafter, there is a distinct drop in fuel consumption. If the car is in gear, there was another distinct drop at 145 seconds, which may simply correspond to finishing an initial charge on the traction battery. Regardless, the catalytic converter is already warmed up.
HYDROCARBON CAPTURE DEVICE
The first device in the exhaust system is a hydrocarbon (HC) capture device that engages when the car is manually started. It has linkages (that can corrode and lock up) that operates a valve to direct the exhaust stream through a path to capture the startup HCs. If the catalytic converter is known to be at operating temperature, the HC is not needed. But manual starts appear to activate the linkages for this device until the catalytic converter operation can be confirmed, an estimated 5-10 seconds.
It appears that when the linkage has the valve closed, the control laws keep the engine running but lets us draw traction battery power to move the car. By parking near the exit of my work parking lot so I can see the on coming traffic on the road, I've timed my startup and with gentle accelerator, successfully achieved 35-40 mph on traction battery while the engine remains at warm-up idle. Once I hear the engine speed up to take the load, I can, traffic permitting, shift into "N" and see MPGs of 35-45 MPG.
Holding off an spoofing the thermistor to 40C allows the normal HC operation to operate as designed.
SIMILARITY TO NHW20 WARM-UP
Ken@Japan shared this warm-up profile on his Japanese NHW20, 2004 Prius, which does not have a thermos, warm-up bottle:
This is my warm-up profile from the NHW11, 2003 Prius:
Our ZVW30, 2010 Prius, has a similar warm-up profile to the Ken's NHW20. This
suggests that auto-stop and start during the engine warm-up does not adversely impact warm-up emissions. This is distinctly different from a manual stop and start that seems to invoke other engine start-up, control laws.
SPOOFING ICE STOP AND COOLANT TEMPERATURE
Up until about 50C, the NHW11 engine can be 'tricked' into auto-stop by holding the brake hard at a stop, shifting into "R", and pulsing the accelerator. This trick causes the engine to stop and shifting into "N" leaves it stopped ... say at a light. When ready to proceed, I shift into "D" and the engine auto-starts and I'm off. But while the engine is off, the coolant temperature continues to rise.
Within the first ~15 seconds, there is a 3-4C rise in coolant temperature. The heat from the cylinders and exhaust manifold continues to flow through the engine block and warm the coolant. After about a minute (takes a long light,) the temperature slowly begins to go down.
What this tells me is the lowest engine idle provides substantially more heat than what it takes to warm-up the engine (not counting Canadian and Yankee winter temperatures!) Having the engine auto-stop during warm-up AFTER the catalytic converter is warmed up appears to optimally warm-up the engine block and coolant.
CONCLUSION
The gold standard is to use an emissions tester during warm-up and measure the emissions. However, the warm-up control laws of the Japanese NHW20; some obscure auto-stop tricks in the NHW11; and supporting observations suggest a thermostat hack that triggers at 40C is likely to be OK.
Bob Wilson
ps. If anyone knows how I can get or rent a portable, emissions tester for a reasonable price, please let me know. I'm loath to market a thermistor hack without credible data showing it does not impact vehicle emissions.
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