Hi,
Quote:
Originally Posted by UTpiper
. . . What is the difference in terms of impact on mpg when the ICE engages at these slower speeds rather than at 42 miles per hour?
Even when I keep my speed below 40 miles per hour for an entire trip, when I come to a stop I still feel the ICE shut down after a couple of seconds. Again, how does this differ from the actions of the ICE at and above 42 miles per hour?
. . .
How long does it take (in terms of minutes or miles) for the Prius to reach proper operating temperature? . . .
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Excellent questions and in an area some of us in Prius_Technical_Stuff have been investigating. First let's address the 42 miles per hour speed threshold for a warmed-up Prius.
Below 42 miles per hour, the Prius will use electric mode with the ICE off if there is enough battery charge and the requested speed and slope are within limits. Otherwise, the Prius will use the ICE and if needed, put more energy in the battery. So below 42 miles per hour, the Prius will cycle between electric vehicle and ICE modes:
The key is the Prius needs to be warmed up and there in lies the rub. Let me share Ken's description of the NHW20 and some NHW11 warm-up stages:
Quote:
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Originally Posted by ken
S1: up to 40C ICE runs for warming up
S2: 41-70C ICE shutdown for coasting
S3: 71C and above Can not coast with ICE off until after reaching 56 km/hr (~35 miles per hour)
Can coast with ICE off if 56 km/hr reached
Idling below 4 km/hr for several seconds enables S4
S4: 71C and above ICE shutdown for coasting below 42 miles per hour or stopped
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Here is an example showing this in operation:
In the case of my NHW11 03 Prius, the rules are different:
S1: up to 40C
ICE runs for warming up at no less than 1200 rpm.
S2: 41-70C
After exceeding 56 km/hr (~35 miles per hour), coasting allows drop to 900 rpm.
S3: 71C and above
Coasting after reaching 56 km/hr (~35 miles per hour) allows ICE shutdown below 42 miles per hour.
Allows stop transition to S4
S4: 71C, down to 60C and above
Stop allows ICE shutdown.
Coasting below 42 miles per hour allows ICE shutdown
The following chart shows recent data from my NHW11:
Some of us in Prius_Technical_Stuff are looking at ICE thermister circuits that will allow NHW11s and possibly some NHW20s to achieve S4 operation quickly and avoid falling below the S4 mode in slow-speed, cold weather operation. However, it is a work in progress.
http://hiwaay.net/~bzwilson/prius/pri_temp.html
BTW, one of the other members is doing some experiments with pre-heating the intake air. The theory is this accelerates ICE warm-up and the less-dense air reduces pumping losses. It is an experiment in progress.
Bob Wilson