U.S. patent application number 11/466894 was filed with the patent office on 2008-02-28 for method for detecting steady-state and transient air flow conditions for cam-phased engines.
Invention is credited to Frank Ament, David B. Brown.
Application Number | 20080047257 11/466894 |
Document ID | / |
Family ID | 39112069 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080047257 |
Kind Code |
A1 |
Ament; Frank ; et
al. |
February 28, 2008 |
Method for detecting steady-state and transient air flow conditions
for cam-phased engines
Abstract
A particulate filter regeneration method for an internal
combustion engine system is provided. The method includes:
receiving an outlet temperature signal corresponding to a
temperature at an outlet of a particulate filter; receiving an
oxygen signal corresponding to an oxygen level in exhaust flowing
from said particulate filter; and controlling at least one of
airflow and fuel based on said oxygen level such that said outlet
temperature is within a desired range.
Inventors: |
Ament; Frank; (Troy, MI)
; Brown; David B.; (Brighton, MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21, P O BOX 300
DETROIT
MI
48265-3000
US
|
Family ID: |
39112069 |
Appl. No.: |
11/466894 |
Filed: |
August 24, 2006 |
Current U.S.
Class: |
60/286 ; 60/295;
60/297 |
Current CPC
Class: |
F01N 3/023 20130101 |
Class at
Publication: |
60/286 ; 60/295;
60/297 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Claims
1. A system for controlling regeneration of a particulate filter,
comprising: an outlet temperature sensor that senses a temperature
at an outlet of the particulate filter and that generates a
temperature signal based on said outlet temperature: an air fuel
sensor that senses an oxygen level in exhaust flowing from the
particulate filter and generates an oxygen signal based on said
oxygen level; and a control module that receives said outlet
temperature signal and said oxygen signal and controls regeneration
of said particulate filter based on said outlet temperature signal
and said oxygen signal.
2. The system of claim 1 wherein said temperature sensor senses a
substrate temperature at said outlet of said particulate
fitter.
3. The system of claim 1 wherein said temperature sensor senses a
gas temperature flowing through said outlet of said particulate
filter.
4. The system of claim 1 wherein said control module controls at
least one of airflow and fuel to maintain a desired oxygen level in
said exhaust, wherein said desired oxygen level is defined by a
control band, and wherein said control band is defined by a
plurality of selectable ranges for a plurality of selectable
temperatures.
5. The system of claim 4 wherein said selectable temperatures are
between five hundred and nine hundred degrees Celsius and said
selectable ranges are between zero and ten percent oxygen.
6. The system of claim 1 wherein said control module estimates an
accumulation of soot in said particulate filter and controls
regeneration based on said estimation.
7. The system of claim 6 further including an inlet exhaust
temperature sensor that senses a temperature of exhaust flowing
into said particulate filter and generates an exhaust temperature
signal based on said temperature of exhaust flowing into said
particulate fitter and wherein said control module initiates
regeneration by commanding engine operation such that said exhaust
temperature flowing into said particulate filter is above a soot
light-off threshold.
8. The system of claim 1 wherein when said temperature signal
indicates a temperature above a selectable threshold, said control
module controls regeneration based on said oxygen signal and said
temperature signal.
9. The system of claim 8 wherein said threshold is five hundred
degrees Celsius.
10. A particulate filter regeneration method for an internal
combustion engine system, comprising: receiving an outlet
temperature signal corresponding to a temperature at an outlet of a
particulate filter, receiving an oxygen signal corresponding to an
oxygen level in exhaust flowing from said particulate filter; and
controlling at least one of airflow and fuel based on said oxygen
level such that said outlet temperature is within a desired
range.
11. The method of claim 10 further comprising estimating an
accumulation of soot in said particulate filter and wherein said
step of controlling is performed if said estimated accumulation
exceeds an accumulation threshold.
12. The method of claim 11 further comprising receiving a
temperature signal corresponding to an inlet temperature of said
particulate filter and controlling at least one of airflow and fuel
to said engine such that said inlet temperature is above a soot
light-off threshold when said estimated accumulation exceeds an
accumulation threshold.
13. The method of claim 10 wherein said receiving comprises
receiving an outlet temperature signal corresponding to a
temperature of particulate filter substrate at said outlet of said
particulate filter.
14. The method of claim 10 wherein said receiving comprises
receiving an outlet temperature signal corresponding to a
temperature of gases flowing from said outlet of said particulate
filter.
15. The method of claim 10 wherein said desired range for said
outlet temperature is between five hundred and nine hundred degrees
Celsius.
16. The method of claim 10 wherein said oxygen level is controlled
to be within a desired range for a given outlet temperature.
17. The method of claim 16 wherein said desired range for said
oxygen level is between zero and ten percent oxygen.
18. The method of claim 10 wherein said step of controlling at
least one of airflow and fuel based on said oxygen level continues
as long as soot is available to be burned.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to vehicle engine systems, and
more particularly to detecting a state of air flow delivered to a
cylinder of an engine.
BACKGROUND OF THE INVENTION
[0002] Engines combust a mixture of air and fuel (air/fuel) to
drive a piston in a cylinder. The downward force of the piston
generates torque. A throttle controls air flow delivered to the
cylinders. By determining the amount of air ingested by the
cylinders, the fuel mass can be calculated and a proper air/fuel
mixture can be delivered to the cylinders to obtain the desired
air-fuel ratio and torque.
[0003] Air flow delivered to the cylinders can be measured using a
mass air flow (MAF) sensor. The MAF sensor measures the air flow
across the throttle. During steady-state air flow conditions, the
air flow measured across the throttle provides an accurate
estimation of the fresh air flow delivered to the cylinders.
Because the MAF sensor measures air flow across the throttle and
not the air into the cylinders, it is most accurate during
steady-state conditions, and is less accurate during transient
conditions (e.g., when additional air must flow across the throttle
to increase the manifold absolute pressure (MAF), or when the mass
of airflow must be reduced to reduce the MAF).
[0004] Air flow can be estimated using a speed density calculation,
which is typically based on MAF, engine RPM, as well as intake air
temperature and pressure. The speed density calculation is only an
approximation that is valid as tong none of the parameters that are
not explicitly accounted for in the calculation varies. However,
because the not accounted for parameters do vary over a period of
time while driving the vehicle, the speed density calculations are
only accurate for a short period of time and need to be adjusted
over time. In order to maintain the accuracy of the speed density
calculations during transient conditions, the MAF sensor is used
during stead state conditions to correct speed density
calculation.
[0005] In engines without variable cam phasing (VCP) or variable
cam timing (VCT), if the mass of fresh air entering the cylinder
changes (i.e., is transient) there is a corresponding increase or
decrease in MAF. This indicates that the mass of air is either
being accumulated or depleted in the intake manifold. During such
transient conditions, the speed density calculation is used to
determine the mass air flow entering the cylinders. The
determination of whether the mass air flow is steady-state or
transient can be made by means such as that described in commonly
assigned U.S. Pat. No. 5,423,208, the disclosure of which is
incorporated herein by reference. The control module uses the
appropriate method of estimating the mass air flow into the
cylinder based on the air flow state.
[0006] However in engines with VCP or VCT, changes in cam position
can occur without changing the MAF while causing the MAF sensor
reading to change by a large amount. This occurs because the VCP or
VCT system allows varying amounts of residual exhaust gas back into
the intake manifold, which replaces the fresh air mass in the
manifold. As a result, more or less air flows through the throttle
and the air flow is transient. Traditional air flow
transient/steady-state detection methods, like that disclosed in
U.S. Pat. No. 5,423,208 will see no change in MAF and incorrectly
determine that the air flow is steady-state.
SUMMARY OF THE INVENTION
[0007] Accordingly, the present invention provides an air flow
state determining system that determines a mass air flow into a
cylinder of an engine having a cam phaser. The system includes a
first module that determines whether an air flow state is one of
steady-state and transient based on a cam phaser position. A second
module determines the mass air flow using one of a mass air flow
sensor signal and a speed density relationship based on whether the
mass air flow state is one of steady-state and transient.
[0008] In other features, the system further includes a third
module that processes the cam phaser position using a first order
linear model and calculates an updated intermediate value based on
a cam phaser position. The air flow state corresponding to cam
phaser motion is determined based on the updated intermediate
value. The air flow state is determined based on a difference
between the updated intermediate value and a previous intermediate
value.
[0009] In another feature, the system further includes a filter
module that filters the cam phaser position.
[0010] In yet other features, the system further includes a
dead-band module that adjusts the cam phaser position based on a
calibrated offset. The system further includes a minimizing module
that minimizes the cam phaser position to zero if the adjustment
results in the cam phaser position being less than zero.
[0011] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0013] FIG. 1 is a functional block diagram of an engine system
regulating using the air flow state detection control in accordance
with the present invention;
[0014] FIG. 2 is a flowchart illustrating exemplary steps executed
by the air flow state detection control according to the present
invention; and
[0015] FIG. 3 is a functional block diagram of exemplary modules
that execute the air flow state detection control of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The following description of the preferred embodiment is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses. For purposes of clarity, the
same reference numbers will be used in the drawings to identify
similar elements. As used herein, the term module refers to an
application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that
execute one or more software or firmware programs, a combinational
logic circuit and/or other suitable components that provide the
described functionality.
[0017] Referring now to FIG. 1, an engine system 10 is
schematically illustrated. The engine system 10 includes an engine
12 that combusts an air and fuel (air/fuel) mixture to produce
drive torque. Air is drawn into an intake manifold 14 through a
throttle 15. The throttle 15 regulates mass air flow (MAF) into the
intake manifold 14. The position of the throttle 15 is adjusted
based on a signal from a pedal position sensor 16 indicative of a
position of an accelerator pedal 17. Air is drawn into a cylinder
20 of the engine through an intake valve 18. Although four
cylinders 20 are illustrated, it can be appreciated that the engine
system 10 can include, but is not limited to, 2, 3, 4, 5, 6, 8, 10
and 12 cylinders.
[0018] The air is mixed with fuel and is combusted within the
cylinder 20 to reciprocally drive a piston (not shown) within the
cylinder, which rotatably drives a crankshaft 24. Exhaust is
exhausted from the cylinder through an exhaust valve 19 and into an
exhaust manifold 25. A fuel injector (not shown) injects the fuel
that is combined with the air. The fuel injector can be an injector
that is associated with an electronic or mechanical fueling system,
or another system for mixing fuel with intake air. The amount of
fuel injected by the fuel injector is regulated based on the mass
air flow into the cylinder 20 to deliver a desired air/fuel
ratio.
[0019] The opening and closing of the intake and exhaust valves 18,
19 are regulated by an intake camshaft 22 and an exhaust camshaft
23, respectively. The crankshaft 24 rotatably drives intake and
exhaust camshafts 22, 23 using a chain/belt and pulley system (not
shown) to regulate the timing of the opening and closing of the
intake and exhaust valves 18, 19, with respect to a piston position
within the cylinder 20. Although a single intake camshaft 22 and a
single exhaust camshaft 23 are illustrated, it is anticipated that
dual intake camshafts and dual exhaust camshafts may be used.
[0020] An intake cam phaser 26 and an exhaust cam phaser 27 vary an
actuation time of the intake and exhaust camshafts 22, 23,
respectively, which mechanically actuate the intake and exhaust
valves 18, 19. More specifically, the rotational position of the
intake and exhaust cam shafts 22, 23 can be advanced and/or
retarded relative to a position of the piston within the cylinder
20 to vary the actuation time of the opening and/or closing of the
inlet and/or exhaust valves 18, 19. In this manner, the timing
and/or lift of the intake and the exhaust valves 18, 19 can be
varied with respect to one another and/or with respect to a
location of the piston within the cylinder 20.
[0021] Adjustment of the intake and exhaust camshafts 22, 23 using
the intake and/or exhaust cam phasers 26, 27 can affect the MAF.
For example, when the cam phasers 22, 23 are adjusted to increase
air delivered to the cylinders 18, less exhaust residual flows into
the intake manifold 14 displacing less fresh air mass. As a result,
the mass of combustible air increases. Conversely, the intake and
exhaust cam phasers 26, 27 can be adjusted to reduce air delivered
to the cylinders 20>while increasing the exhaust gas residual
entering the intake manifold 14. As a result, there is more air
mass entering the intake manifold 14 and hence the cylinder 14.
[0022] When the intake and/or exhaust cam phasers 26, 27 remain in
a constant position, the actuation timing of the intake and exhaust
valves 18, 19 remains constant. As a result, steady-state air flow
occurs and a constant amount of air is delivered to the cylinders
20. However, when the intake and/or exhaust cam phasers are
adjusted, the actuation timing is correspondingly adjusted and the
amount of air delivered into the cylinder 20 either increases or
decreases. The resulting sudden change in air flow is typically
referred to as an air transient. An air transient that results from
a change in the camshaft position typically exists whenever the
intake and/or exhaust cam phasers 26, 27 are moved from a fixed
position.
[0023] The engine system 10 further includes an air flow sensor 30,
an engine speed sensor 31, cam phaser position sensors 32, 33, an
intake manifold air temperature sensor 34 and a MAF sensor 35. A
control module 36 receives the signals generated by the various
sensor and regulates operation of the engine system 10 based on the
air flow state detection system of the present invention. The air
flow sensor 30 measures an amount of air flowing through throttle
15 and the engine speed sensor 31 is responsive to the rotational
speed of the engine 12. The intake manifold temperature sensor 34
measures an air temperature within the intake manifold 14 and the
MAF sensor 35 measures the MAF within the intake manifold 14.
[0024] The cam phaser position sensors 32, 33 are coupled to the
intake cam phaser 26 and the exhaust cam phaser 27, respectively,
and are responsive their respective rotational positions. When the
rotational position of the intake and the exhaust cam phasers 26,
27 is adjusted, the cam phaser rotational sensors 32, 33 output a
position signal to the control module 36. The position signals can
be filtered prior to being received by or within the control module
36 using a first order lag filter to remove any high frequency
noise that may exist.
[0025] Airflow transients can occur due to changes that a
traditional air flow transient/steady state detector can detect as
well as changes in the cam phaser 26,27 position, which the
traditional transient/steady state detector does not detect.
Accordingly, the air flow state detection control of the present
invention detects whether the mass air flow is in a steady-state or
a transient state based on a signal from a traditional
transient/steady state detection control and further based on the
rotational velocity of the cam phasers 26, 27. Furthermore, the
control module 36 determines the mass air flow into the cylinders
20 based on whether the mass air flow is deemed steady-state or
transient.
[0026] Although the air flow state detection control detects
steady-state air flow and/or transient air flow based on the intake
cam phaser 26 and/or the exhaust cam phaser 27 rotational
velocities, the air flow state detection control will be based on
the rotational velocity of the intake cam phaser 26 alone being
used to detect a steady-state air flow and/or transient air
flow.
[0027] At each intake reference pulse, which is based on the engine
RPM sensor signal, the air flow state detection control determines
the intake cam position (.theta..sub.ICAM) based on the intake cam
position sensor signal. .theta..sub.ICAM can be filtered using a
first order lag filter (e.g., y=ay+(1-a)x). Proper selection of the
filter coefficient (a) enables successful sampling as slow as every
other intake reference pulse. The air flow state detection control
subtracts a calibrated offset (.theta..sub.THR) from the filtered
.theta..sub.ICAM to remove a dead-band associated with
.theta..sub.ICAM (i.e., a cam phaser adjustment value that does not
affect MAF). If the difference is less than 0, .theta..sub.ICAM is
set it to 0).
[0028] The air flow state detection control inputs .theta..sub.ICAM
into a first order model, which is provided by the following
equation:
X(k+1)=.alpha.X(k)+.beta..theta..sub.ICAM
where X is an intermediate variable, k is the current event and is
incremented each intake reference event, and .alpha. and .beta. are
pre-determined model or filter coefficients. .alpha. and .beta. are
determined using various optimization techniques, such that the
following relationship is minimized:
|[X(k)-X(k-1)]-MAF(k)-MAF(k-1)]
where MAF(k)-MAF(k-1) is the change in intake manifold pressure due
to only a change in intake cam position. If the following
relationship is true:
|X(k)-X(k-1)|>.DELTA..sub.THR
the mass air flow is transient and a transient flag is set.
Otherwise, the mass air flow is steady-state and a steady-state
flag is set.
[0029] If the steady-state flag is set, the control module 36
operates in a steady-state mode and estimates cylinder mass air
flow based on the air flow sensor 30. If the transient flag is set,
the control module 36 estimates air flow based on the speed density
approach according to the following equation:
m a = .eta. v V d P m RT o ( 1 ) ##EQU00001##
where m.sub.a is mass air into the cylinder, R is the universal gas
constant, V.sub.d is the displacement volume of the engine 12,
.eta..sub.v is the volumetric efficiency of the engine 12. T.sub.i
is the temperature of the air delivered into the intake manifold 14
and P.sub.m is the intake manifold pressure. Since R and V.sub.d
are constants for a given engine, the volume of the engine 12 can
be defined according to the following equation:
V d = .eta. v V d R ( 2 ) ##EQU00002##
Substituting V.sub.e into equation (1), mass of air into the
cylinder 20 can be defined according to the following equation:
m a = V e T i P m ( 3 ) ##EQU00003##
[0030] Referring now to FIG. 2, a flowchart illustrates exemplary
steps executed by the air flow state detection control. In step
200, control determines .theta..sub.ICAM. In step 202, control
filters .theta..sub.ICAM to provide a filtered .theta..sub.ICAM. In
step 204, control subtracts .theta..sub.THR from .theta..sub.ICAM
to remove the dead-band around the parked position. Control
determines whether .theta..sub.ICAM is less than zero in step 206.
If .theta..sub.ICAM is less than zero, control continues in step
208. If .theta..sub.ICAM is not less than zero, control continues
in step 210. In step 208, control sets .theta..sub.ICAM to
zero.
[0031] Control updates the intermediate variable X(k+1) in step
210. In step 212, control determines whether the absolute value of
the difference between X(k+1) and X(k) is greater than
.DELTA..sub.THR. If the absolute value of the difference between
X(k+1) and X(k) is greater than .DELTA..sub.THR, control continues
in step 214. If the absolute value of the difference between X(k+1)
and X(k) is not greater than .DELTA..sub.THR, control continues in
step 216. In step 214, control sets the transient flag and
estimates the cylinder mass air flow using the speed density
approach in step 218. In step 216, sets the steady-state flag. In
step 219, control determines whether the traditional or standard
transient/steady state detection control has indicated that the air
flow is steady state (SS) by setting a SS flag. If the SS flag is
set, control estimates the cylinder mass air flow using the MAF
sensor 30 in step 220. If the SS flag is not set, control continues
in step 218. In step 222 control sets X(k) equal to X(k+1) and
control ends.
[0032] Referring now to FIG. 3, exemplary modules that execute the
air flow state detection control will be described in detail. The
exemplary modules include a filter module 300, a dead-band module
302, a .theta..sub.ICAM minimizing module 304, an X updating module
306, a summer 308, an absolute value module 310, a comparator
module 312 a flag module 314 and a cylinder MAF estimating module
316. The filter module 300 and the dead-band module 302
respectively filter and remove the dead-band value from
.theta..sub.ICAM.
[0033] The .theta..sub.ICAM minimizing module 304 caps the minimum
value of .theta..sub.ICAM to zero, if .theta..sub.ICAM is less than
zero after the dead-band removal operation. The X updating module
306 determines X(k+1) based on X(k), .theta..sub.ICAM and the first
order linear model described in detail above. The summer 308
determines the difference between X(k+1) and X(k) and the absolute
value module 310 generates the absolute value of the
difference.
[0034] The comparator module 312 compares the absolute value of the
difference to .DELTA..sub.THR and outputs a first signal (e.g., 1)
if the difference is greater than .DELTA..sub.THR, and outputs a
second signal (e.g., 0) if the difference is less than
.DELTA..sub.THR. The flag module 314 sets the steady-state or
transient flag based on the output of the comparator module 312.
The cylinder MAF module 316 determines the cylinder MAF based on
either the MAF sensor signal or the speed density calculation
depending on the output of the comparator module 312 and the
condition of the standard SS flag.
[0035] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings can be implemented
in a variety of forms. Therefore, while this invention has been
described in connection with particular examples thereof, the true
scope of the invention should not be so limited since other
modifications will become apparent to the skilled practitioner upon
a study of the drawings, the specification and the following
claims.
* * * * *