Method of controlling engine cold restart
A method of controlling the fuel air mixture of an internal combustion engine following a cold restart includes determining a control parameter based on the value of current coolant temperature at time of current engine start, the value of coolant temperature at time of the previous engine start, a calibratable reference temperature, the total accumulated fuel mass injected during previous engine run time, the time the engine was off before the restart, and the time the engine was run after previous start. The method also includes controlling the fuel air mixture based on said control parameter.
1. A method of controlling fuel air mixture in an internal combustion engine during, and subsequent to, a cold restart, said method comprising:
a) determining a control parameter based on the following measured or modelled input parameters: coolant temperature at time of current engine start, coolant temperature at time of a previous engine start, a calibratable reference temperature, a total accumulated fuel mass injected during previous engine run time, time the engine was off before restart, and time the engine was run after previous start; and
b) controlling the fuel air mixture based on said control parameter where said control parameter is a mixture adaptation index (MAI), determined from the following equation:
M
A
I
[
g
-
1
K
]
=
(
(
T
cool
curstrt
-
T
cool
prestrt
)
abs
(
T
Ref
-
T
cool
prestrt
)
)
mfuel
prestrt
*
(
t
engoff
t
engrun
)
where Tcool curstrt is the coolant temperature at time of current engine start, Tcool prestrt is the coolant temperature at time of the previous engine start, T Ref is the calibratable reference temperature, mfuel prestrt is the total accumulated fuel mass injected during previous engine run time, t engoff is the time the engine was off before restart, and t engrun is the time the engine was run after previous start.
2. A method as claimed in claim 1 , wherein a MAI value is used to determine an offset value, indicating a relative enrichment; and in step b) the relative enrichment is used to control the fuel air mixture.
3. A method as claimed in claim 2 , wherein said relative enrichment is relative to a first start mixture.
4. A method as claimed in claim 2 , wherein subsequent to engine restart, said offset value decreases with time.
5. A method as claimed in claim 4 , wherein said offset value decays with a time constant.
6. A method as claimed in claim 4 , wherein the MAI value is determined from a stored map or table.
7. A method as claimed in claim 6 , wherein said time constant is proportional to the MAI value or said offset value.
8. A method as claimed in claim 7 , wherein said offset value is determined from said MAI value and engine run time.