Quote:
Originally Posted by steve99
@ thambu19 how much PI is needed and where load rpm wise to maintain intake valve cleaning properties ?
another question, if you have a look at the intake cam tables at low load rpm they do a weird dance go from zero then negitive then back to zero then increase above zero. I have assumed the negitive dance was emmissions related ? |
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steve99
PFI at extremely low PWs (pulsewidths) wont really help clean the valve (like idle) because the injection duration is so short the gas fully atomizes rather quickly. What is really needed for clean up is substantial PW. I cannot tell how much PW in ms exactly because I do not know to be honest. These engine will start seeing knock at 40-50% load at speeds between 1000 and 3000rpm and higher loads at higher engine speeds so increasing the PFI% below that is always going to help valve cleaning.
Regarding the Intake cam timing I will need to make some wild assumptions shall I?
1. Generally 1200rpm to 2500rpm is the region this car would run in an FTP cylcle (one of the fuel economy test cycles)
2. Toyota wanted to go to LATE Exhaust Opening as soon as they could. So you will see Exh timing go to 40 as soon as they can. They cannot go to 40 too early in load because if they do they deteriorate the blow down of exh gases causing combustion quality issues. The reason for going late Exh opening/closing or retarded timing is for Fuel economy to get maximum expansion of the gases in cylinder.
3. With Exhaust timing so retarded the intake cannot be advanced beyond a point. If advanced it will cause the exhaust to be pushed into intake manifold during the exhaust stroke and rebreathed during intake stroke and this will increase incylinder residuals causing combustion quality issue. So by going Late Intake opening/Closing (-10) they are using a late/late strategy. Meaning open Exh late and intake Late.
4. By moving the intake late they are reducing the Dynamic Compression Ratio of the engine and this helps in reducing pumping losses (something like drag) and also helps in reducing knock.
So overall this would have been a move to maximise fuel economy. Once engine load is at 0.7 the intake is being moved to a more advanced position because
1. The throttle has maxed out in authority or in other words the throttle is almost fully open and the MAP is already 90kPa or above and the only way to get more air to flow is to change cam timing (throttle is maxed out)
2. At this time scavenging kicks in and moving intake to more advanced position helps with scavenging
3. They can simply tolerate more internal residuals at these higher loads