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Some cold weather, block heater data

  #1  
Old 01-09-2008, 09:06 AM
bwilson4web's Avatar
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Wink Some cold weather, block heater data

Hi folks,

Here is some data recorded in December on a 32F day:

The major time units are 5 minute intervals, 300 seconds, and the minor intervals are one minute, 60 seconds. MG2 rpm is directly proportional to the vehicle speed.

INITIAL WARMUP (first 7.5 minutes)

The block heater after an hour brings the ICE block temperature up about 30C relative to the 0C ambient. MG1 receives a little heat and MG2 gets the least. Once the ICE starts, the cold coolant from other parts of the block dips the temperature down but it quickly recovers at the ICE idles. In my area, this is a little less than $.03 of electricity.

During the warm-up phase, I shift the car into "N" at every opportunity since this results in the lowest, mass air-flow and fuel consumption. As the coolant temperature comes up, the mass air-flow decreases as the engine can run at more efficient fuel burn levels.

Once the coolant of the North American NHW11 (2003) Prius reaches 70C, the various warm-up states [email protected] discussed are available. For example, speeds above 35 mph allow the ICE to auto-shutdown all the way down to 0 mph or when the energy required is low enough that the battery can handle it. But the final, warm-up state change occurs when the ICE auto-shutdowns while the car is stopped. My route includes opportunities for this final state-change.

NORMAL HYBRID MODE (7.5 to 21 minutes)

During this mode, the car is driven like any other, fully warmed up hybrid. Specific to the Prius, I try to avoid 39-45 mph by either speeding up or slowing down. This Prius specific control law avoids transition through 42 mph that separates ICE ON/OFF mode versus ICE ALWAYS ON mode. If you reset the MFD mileage indicator, you'll see typically 55 MPG. This phase ends when I exit the Interstate and regenerative braking slows my speed down as I enter the business district where my office is located.

COOL DOWN (21-29 minutes)

Having entered the business district, I keep the speeds in the 25-35 mph range to maximize EV mode. This uses any excess battery charge to maximize my MPG. Extra NiMH battery charge can be lost by the 'self-discharge' so use this energy is a good return on investment. Given the excessive ICE run times during warm-up, there is plenty of energy to put a charge on the battery.

Questions? Comments?

Bob Wilson

ps. I would expect most hybrids share similar characteristics to a greater or lessor extent.
 

Last edited by bwilson4web; 01-09-2008 at 09:20 AM.
  #2  
Old 01-09-2008, 10:40 AM
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Default Re: Some cold weather, block heater data

Are you saying you can't get EV for the first 7.5 minutes, or you don't have any opportunity for it? With 3 hours of 400w block heater in my FEH at -10'C I can get EV in about 90 seconds, or 0.70 mile down the road.
 
  #3  
Old 01-09-2008, 10:52 AM
bwilson4web's Avatar
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Wink Re: Some cold weather, block heater data

Originally Posted by gpsman1 View Post
Are you saying you can't get EV for the first 7.5 minutes, or you don't have any opportunity for it? With 3 hours of 400w block heater in my FEH at -10'C I can get EV in about 90 seconds, or 0.70 mile down the road.
Correct but this is limited to the North American, 2001-2003, NHW11 model Prius. The European and Asian versions do not have the HC converter that is unique to this vehicle and apparently requires the coolant to reach 70C before any form of EV operation occurs. Once it reaches 70C and the final warm-up stages, coolant can go as low as 60C before the ICE comes on and stays on to rewarm the coolant.

I also have a thermistor hack that I can use to trick the coolant reading to indicate 70C once the coolant reaches 40C. This was quite successful last winter but I didn't have any block heater data to compare with the hack. From what I can tell, once the ICE reaches 40C, the vehicle works quite nicely in hybrid mode.

This winter, I have a block and separate transaxle heater and am trying to get enough cold weather data to evaluate their respective impacts. As you can see, the block heater cuts out some of the warm-up but not a whole lot. I have some data that suggests the transaxle heater is helpful too but not enough to give quantitative values. I already know the thermistor hack is effective but needed to be able to compare and contrast the different approaches.

Bob Wilson
 
  #4  
Old 01-09-2008, 11:20 AM
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Default Re: Some cold weather, block heater data

I'm going to do a similar "hack" with my car, now that I have a clearer understanding of the FEH, and I'm 4,000 miles from out of warranty.

I have found 3 "tiers" of rules for EV. While I don't the exact rules nailed down, the rules for sure change based on outdoor ambient temperature.

approximate values:
When OAT is below 15'F, no EV until cylinder head temp is over 224'F.
When OAT is between 15'F and 45'F, EV is enabled above 201'F.
When OAT is above 45'F, EV is possible with CHT in the high 100's.

I'm sure that 201'F and 224'F are magic numbers.
I've not had enough warm weather to nail down the 3rd, lowest number.
What I'm not sure of, is what is triggering these numbers.
( as I never know the exact outdoor temp, etc... )

The rule that never changes is the water temp one. 140'F is the hard deck to enter EV. No 140, no EV. Once in EV, you can keep EV down to 125'F. Always, no matter the weather. One or two people have said they had EV at 124 and 123'F. I'll bet this is latency in the meter, or calibration issues, and not an actual value, but is pretty darn close to what I've seen in 3 years. In 3 years, my car has never broken the 140/125 rule.

So back to this thread, with the EBH I get my engine to 100-104'F, and then it hits 140'F within 90 seconds after that, if I start driving right away, and don't have any cabin heat turned on. So now, there is no big incentive for me to park with a very low SOC for the night. A paradox has evolved, since starting the car lowers SOC by 5% to 9%, and I need 42% SOC to enter EV mode. The car does discharge only during the first 30 seconds, sometimes longer, after a "cold" start.
 
  #5  
Old 01-09-2008, 11:28 AM
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Default Re: Some cold weather, block heater data

Originally Posted by gpsman1 View Post
. . . A paradox has evolved, since starting the car lowers SOC by 5% to 9%, and I need 42% SOC to enter EV mode. The car does discharge only during the first 30 seconds, sometimes longer, after a "cold" start.
It looks to be about 45-50 seconds in my Prius and is associated with the catalytic converters, specificly the O(2) sensors, getting hot enough to provide mixture trim. If I punch the accelerator, it will spin up the ICE but otherwise, I'm in an electric car with a light pedal until the O(2) sensors start trimming the mixture.

Bob Wilson
 
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