Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-02-25
2001-05-22
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C701S104000
Reexamination Certificate
active
06234149
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to systems for controlling the operation of an internal combustion having a turbocharger to thereby optimize a tradeoff between turbocharger lag and production of exhaust emissions, and more specifically to such systems including altitude (ambient air pressure) and intake manifold air temperature compensation strategies.
BACKGROUND OF THE INVENTION
Internal combustion engines having turbocharger units attached thereto are commonplace in the automotive, heavy duty truck and industrial vehicle industries. Such turbocharger units are generally responsive to at least some of the engine exhaust gas to increase air pressure in an intake manifold of the engine to thereby provide for increased intake manifold air pressure (i.e., boost pressure) and correspondingly increased engine performance. One problem that exists with turbocharged engines, however, is “turbocharger lag” which is defined for the purposes of the present invention as a time delay between the initiation of a transient event (e.g., a rapid increase in accelerator pedal position) and the stabilization (i.e., steady state condition) of turbocharger boost pressure resulting from the transient event. During such turbocharger lag conditions, overfueling of the engine typically occurs which results in the unwanted production of black smoke and other exhaust emissions. However, if fueling is reduced during such transient events, turbocharger lag time increases. Accordingly, there exists a tradeoff between turbocharger lag and the production of black smoke and other unwanted exhaust emissions.
Heretofore, one technique that designers of electronic engine control systems have used to address the problem of black smoke production (as well as the production of other unwanted exhaust emissions) during turbocharger lag conditions is a so-called electronic air fuel control (AFC) strategy. Typical AFC strategies attempt optimize the tradeoff between turbocharger lag and production of exhaust emissions, whereby a balance is struck between the two conditions resulting in acceptable levels of each. An example of one known system
10
for providing such an AFC strategy is illustrated in FIG.
1
. Referring to
FIG. 1
, system
10
includes a control computer
12
operable to interface with, and control the operation of, an internal combustion engine
14
. System
10
includes an engine speed sensor associated with engine
14
and operable to provide an engine speed signal to control computer
14
via signal path
18
. System
10
further includes a turbocharger
20
associated with engine
14
and coupled to an intake manifold
22
via conduit
24
. An aftercooler
26
is typically positioned within the intake manifold
26
and a boost pressure sensor
28
(typically a gage or absolute pressure sensor) is disposed between the aftercooler
26
and engine
14
. The boost pressure sensor
28
is operable to provide a boost pressure signal to control computer
12
, corresponding to intake manifold air pressure, or “boost” pressure, provided by turbocharger
20
, via signal path
30
. A fueling system
32
is responsive to a fueling signal provided thereto by control computer
12
on signal path
34
to supply fuel to engine
14
.
Control computer
12
includes a memory unit (not shown) having an AFC fueling strategy
36
stored therein. AFC fueling strategy
36
provides an AFC fueling signal, based on the engine speed signal provided thereto via signal path
18
and the boost pressure signal provided thereto via signal path
30
, to fueling logic block
40
via signal path
36
′. A number, P, of other engine fueling control strategies also provide fueling signals to fueling logic block
40
via a corresponding number of signal paths
38
1
-
38
p
. Examples of such other engine fueling control strategies may include one or more engine speed governors, a maximum vehicle speed limiter, and the like. In any case, fueling logic block
40
is typically operable in accordance with a “least wins” or MIN logic strategy, whereby the fueling signal provided to fueling system
32
on signal path
34
is the minimum fueling value provided to block
40
via the various signal paths
36
and
38
1
-
38
p
.
FIG. 2
illustrates one known form of the AFC block
36
of
FIG. 1
wherein AFC block
36
is implemented as a look-up table
42
stored within a memory unit (not shown) of control computer
12
. Table
42
includes a number, N, of columns corresponding to boost pressure values B
1
-B
N
and a number, M, of rows corresponding to engine speed values E
1
-E
M
. Table
42
is operable to provide an appropriate fueling value F
xy
(typically in units of mm3/stroke) based on current values of turbocharger boost and engine speed. In accordance with one known embodiment of table
42
, the fueling values F
xy
increase with increasing engine speed for each boost pressure column between B
1
and B
K
where 2<K<N, and remain constant within each boost pressure column between B
k
and B
N
. In this manner, fueling is limited to provide a minimum air-to-fuel ratio (A/F) for optimizing a tradeoff between turbocharger lag and production of exhaust emissions such as black smoke and other unwanted emissions.
While the A/F control strategy illustrated in
FIGS. 1 and 2
may effectively limit fueling to thereby optimize the tradeoff between turbocharger lag and production of unwanted exhaust emissions, it does not account for changes in absolute air pressure due to changes in altitude, nor does it account for changes in intake manifold air temperature. An equation relating air-to-fuel ratio (A/F) to intake manifold boost pressure and fueling is given by:
A/F∝=(&eegr;
v
*displ*P
man
)/(#cyl*T
man
*fueling) (1),
where &eegr;
v
is volumetric efficiency, displ is the piston displacement within each cylinder, P
man
is the absolute manifold air pressure, #cyl is the number of cylinders, T
man
is the intake manifold air temperature and fueling is a current engine fueling value. From equation (1) it can be seen that the actual A/F value is directly proportional to the absolute pressure within the intake manifold, and inversely proportional to the intake manifold air temperature.
Referring to
FIG. 3
, a plot
44
of A/F ratio vs. altitude at various boost pressure values for the prior art AFC control strategy of
FIGS. 1 and 2
is shown illustrating that as ambient air pressure decreases due to a rise in altitude, A/F decreases regardless of boost pressure. Plot
44
also includes a stoichiometric A/F value
46
(i.e., minimum A/F ratio required for complete combustion; 14.7 in this example), and further illustrates that as ambient air pressure drops significantly at very high altitudes, A/F drops well below the stoichiometric value for each of the boost pressure values illustrated. This will result in both high smoke production and poor transient performance due to significant over-fueling of the engine
14
during transient events.
One possible solution to the foregoing problem would be to use an absolute air pressure sensor in place of the commonly used gage boost pressure sensor
28
in FIG.
1
and modify table
42
of
FIG. 2
to always maintain an A/F value above stoichiometric. This solution, however, would undesirably result in inconsistent transient response depending upon altitude, and turbocharger lag would accordingly be different at different altitudes due to the decrease in allowable fueling. What is therefore needed is a system for controlling A/F to thereby consistently optimize the tradeoff between turbocharger lag and production of unwanted exhaust emissions, yet compensate for changes in ambient pressure due to changes in altitude. Such a system should ideally also provide for the ability to compensate for changes in intake manifold air temperature to thereby provide maximum control over the A/F parameter, particularly during a transient event.
SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are addressed by the present invention
Becker Lawrence H.
Bolis David A.
Edwards Ward R.
Hoehne John L.
Mills John R.
Baker & Daniels
Castro Arnold
Cummins Engine Company, Inc.
Yuen Henry C.
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