we regard coolant temperatures below 100 degrees Celsius to be normal conditions, and
coolant temperatures above 105 degrees Celsius to be an overheat condition. When the coolant
temperature climbs above 100 degrees, the SM4 will start lowering the boost pressure to the
values in the lower row, (105 degrees), to save the engine.
In our example Boost setpoint table we have entered 250 KPA in each cell for rpm’s up to
6000 rpm.
Then, with higher rpm’s, the boost pressure will be lowered to 240 KPA at 7000 rpm. The
reasons for this can be that there is not enough fuel for a higher boost pressure at that engine
speed, or that the engine simply cannot handle a higher boost pressure at that engine speed.
At 8000 rpm we lower the boost pressure all the way down to 190 KPA, which is just above the
lowest possible boost pressure that the boost valve can control.
This is a good setup for an engine that has an active rpm range of up to about 7000 rpm, and
with a rev limit at about 8000 rpm.
If the engine does not pull any torque above 7000 rpm, it is not useful to continue with the high
boost pressure. By lowering the boost pressure all the way down to 190 KPA before going into
the rev limiter at 8000 rpm, the engine gets a safe transition into the rev limiter, thus protecting it
from potential damage.
The next step is to go into menu M5 / Boost tune and set the parameter Boost range.
Boost range is the amount of boost pressure in addition to the basic boost pressure that the
wastegate will regulate to without the boost control valve being engaged – Basic boost
pressure.
Lets say that the basic boost pressure of our wastegate is 0.85 Bar, or 85 KPA relative.
If we want the boost control valve to be able to control boost pressure to be maximum 1,5 Bar,
(150 KPA relative pressure), then we need to specify a Boost range of at least 150 – 85 = 65
KPA. In fact, Boost range is more determined by how much the boost control valve can raise
the boost from the basic boost pressure. If our boost valve is theoretically capable of raising the
basic boost by 120 KPA, that is the number we need to set Boost range to.
But things are a bit more complicated than that. One can tweak the boost control valve by
setting a higher or lower Boost range than what the boost control valve actually can regulate.
Setting Boost range lower than what the valve can regulate will make the boost control more
responsive, but at the same time the regulated boost pressure will be a bit rough.
Setting Boost range higher than what the valve actually can regulate will make the boost
control smoother, but at the same time the it will be slower in reaching the wanted Boost
setpoint. A higher value on Boost range may also make it more difficult for the boost control to
achieve the same boost pressure on all gears.
Next step is to setup the table in the menu M5 / Boost dynamic comp. Start with setting all the
cells to zero, as done in Fel!Hittar inte referenskälla. Fel!Hittar inte referenskälla.. This table
can be adjusted to make the boost regulation smoother, with the penalty of a bit less accuracy.
To Next Page
Loading...
Need help?
General