U.S. patent application number 10/350503 was filed with the patent office on 2004-07-29 for method for controlling emissions.
Invention is credited to Ament, Frank.
Application Number | 20040144363 10/350503 |
Document ID | / |
Family ID | 32712807 |
Filed Date | 2004-07-29 |
United States Patent
Application |
20040144363 |
Kind Code |
A1 |
Ament, Frank |
July 29, 2004 |
METHOD FOR CONTROLLING EMISSIONS
Abstract
A method is provided for controlling emissions in a parallel
hybrid motor vehicle that includes an electric propulsion system in
parallel with a combustion propulsion system. In accordance with
one embodiment of the invention, manifold absolute pressure (MAP)
is monitored in the intake manifold of the combustion propulsion
system. The electric propulsion system is engaged to reduce the MAP
to a predetermined pressure, and then fueling and combustion of the
combustion propulsion system are initiated only after the MAP is
reduced to a pressure less than the predetermined pressure.
Inventors: |
Ament, Frank; (Troy,
MI) |
Correspondence
Address: |
CHRISTOPHER DEVRIES
General Motors Corporation
Legal Staff, Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
32712807 |
Appl. No.: |
10/350503 |
Filed: |
January 24, 2003 |
Current U.S.
Class: |
123/399 ;
123/478; 180/65.25; 180/65.27; 180/65.28; 180/65.285; 60/716 |
Current CPC
Class: |
B60W 10/08 20130101;
B60W 2710/0605 20130101; B60W 20/00 20130101; F02D 41/064 20130101;
F02D 41/047 20130101; F02N 11/04 20130101; Y02T 10/62 20130101;
B60W 2710/0616 20130101; B60W 20/20 20130101; F02D 2200/0406
20130101; B60W 20/15 20160101; B60K 6/48 20130101; B60W 2510/0671
20130101; B60W 10/06 20130101; Y02T 10/6286 20130101; B60W
2710/0644 20130101; Y02T 10/6221 20130101 |
Class at
Publication: |
123/399 ;
123/478; 060/716 |
International
Class: |
F02D 001/00 |
Claims
1. A method for controlling emissions in a parallel hybrid motor
vehicle including an electric propulsion system in parallel with a
combustion propulsion system, the combustion propulsion system
having an intake manifold, the method comprising the steps of:
monitoring manifold absolute pressure in the intake manifold of the
combustion propulsion system; engaging the electric propulsion
system to reduce the manifold absolute pressure to a predetermined
pressure; and initiating fueling and combustion of the combustion
propulsion system only after the manifold absolute pressure is
reduced to a pressure less than the predetermined pressure.
2. The method of claim 1 wherein the step of engaging the electric
propulsion system comprises the step of powering the combustion
propulsion system to achieve a predetermined combustion propulsion
system RPM.
3. The method of claim 1 further comprising the step of terminating
the step of engaging after the step of initiating fueling and
combustion.
4. The method of claim 1 wherein the step of initiating fueling and
combustion comprises the steps of: controlling an amount of air
supplied through the intake manifold to the combustion propulsion
system; and controlling an amount of fuel supplied to the
combustion propulsion system.
5. The method of claim 4 wherein the step of controlling an amount
of fuel injected comprises the step of controlling pulse width and
frequency of injection of fuel by a fuel injector positioned to
inject fuel into the combustion propulsion system.
6. The method of claim 1 further comprising the steps of:
continuing to monitor the manifold absolute pressure; monitoring
torque demand on the combustion propulsion system; increasing the
amount of fuel and the amount of air supplied to the combustion
propulsion system in response to increases in monitored torque
demand; and terminating the step of increasing and reengaging the
electric propulsion system in response to the manifold absolute
pressure reaching the predetermined pressure.
7. The method of claim 6 further comprising the step of terminating
the step of re-engaging when the combustion propulsion system is
able to supply the torque demand without the manifold absolute
pressure exceeding the predetermined pressure.
8. A method for controlling emissions after start-up in a parallel
hybrid motor vehicle including an electric propulsion system in
parallel with a combustion propulsion system, the combustion
propulsion system having an intake manifold, the method comprising
the steps of: initiating propulsion of the parallel hybrid motor
vehicle by the combustion propulsion system; monitoring manifold
absolute pressure in the intake manifold of the combustion
propulsion system; engaging the electric propulsion system in
parallel with the combustion propulsion system in response to the
manifold absolute pressure exceeding a predetermined pressure; and
maintaining the electric propulsion system engaged in parallel with
the combustion propulsion system until manifold absolute pressure
is reduced to the predetermined pressure.
9. The method of claim 8 further comprising the steps of:
monitoring torque demand on the parallel hybrid motor vehicle; and
limiting fueling of the combustion propulsion system in response to
the manifold absolute pressure reaching a predetermined pressure
before the combustion propulsion system is able to supply the
torque demand.
10. The method of claim 9 further comprising the step of
terminating the step of limiting fueling after a predetermined
time.
11. A method for controlling emissions after start-up in a parallel
hybrid motor vehicle including an electric propulsion system in
parallel with a combustion propulsion system, the combustion
propulsion system having an intake manifold, the method comprising
the steps of: initiating propulsion of the parallel hybrid motor
vehicle by the combustion propulsion system to produce a driving
torque; monitoring manifold absolute pressure in the intake
manifold of the combustion propulsion system; monitoring torque
demand on the parallel hybrid motor vehicle; adjusting fueling of
the combustion propulsion system in response to the monitored
torque demand; and in response to a sudden drop in monitored torque
demand, to avoid a rapid change in the monitored manifold absolute
pressure: maintaining fueling of the combustion propulsion system
at a level higher than necessary to produce a driving torque equal
to the monitored torque demand; and engaging the electric
propulsion system to produce a torque counter to the driving
torque.
12. The method of claim 11 wherein the parallel hybrid motor
vehicle comprises a transmission and wherein the step of engaging
the electric propulsion system comprises the step of coupling the
electric propulsion system to the transmission.
13. The method of claim 11 wherein the step of monitoring torque
demand comprises the step of monitoring signals from an accelerator
pedal sensor at a control unit.
14. The method of claim 13 wherein the step of adjusting fueling
comprises the step of sending a signal from the control unit to
adjust a throttle flap.
15. The method of claim 14 wherein the step of maintaining fueling
comprises the step of sending a further signal from the control
unit to partially close the throttle flap.
Description
TECHNICAL FIELD
[0001] This invention relates generally to a method for controlling
emissions and, more specifically, to a method for controlling
emissions by controlling cold start intake manifold pressure in a
parallel hybrid motor vehicle.
BACKGROUND OF THE INVENTION
[0002] When an internal combustion engine (ICE) in a motor vehicle
is initially started (especially in a cold climate), the interior
surfaces of the engine are cold. In addition, because the engine is
initially turning at a very low RPM, the intake manifold absolute
pressure (MAP) is near atmospheric pressure. Because liquid fuel
does not combust as easily or cleanly as gaseous fuel, it is
desirable that the fuel sprayed into and mixed with the air jet
traveling into the combustion cylinders of the engine be vaporized
in order to reduce emissions from the ICE. Unfortunately, both the
relatively high MAP and the cold condition of the engine make it
difficult to vaporize the fuel injected into the combustion
cylinders. Therefore, in order to produce the desired amount of
power at start-up and during high-torque initial accelerations
shortly after start-up when the engine is still cold, additional
(i.e., excess) amounts of fuel must be pumped into the intake
manifold to obtain a sufficient amount of vaporized fuel. All of
the additional fuel is not completely vaporized and the
incompletely vaporized fuel is not completely combusted. The
consequence of the poor fuel vaporization at startup and during
initial high-torque accelerations is increased emissions. The
excess fuel that is not completely combusted at start-up and the
period shortly after start-up creates an exhaust mixture that is
too fuel-rich to be stoichiometric at the catalytic converter, thus
leading to increased hydrocarbon and carbon monoxide emissions.
[0003] Under most operating conditions, once the intake valves have
heated up adequately (usually within about 60 seconds after engine
start-up), the excess fuel is no longer necessary, as the intake
valves are hot enough to properly vaporize the injected fuel. At
this time, the engine RPM is also high enough to provide a low MAP,
assisting with the fuel vaporization. Even in high torque-demand
situations, such as during acceleration, which causes the MAP to
increase, the hot intake valves are able to vaporize the fuel so
that it combusts thoroughly.
[0004] High emissions, however, can also result from rapid changes
in MAP even with the engine heated, as well as from the high MAP at
start-up. When there is a rapid drop in torque demand, such as at
the end of a rapid acceleration, the throttle closes and the MAP
will quickly drop from the high MAP consistent with the rapid
acceleration to a low MAP consistent with the lower torque demand.
Any liquid fuel left in the intake manifold after the throttle
closes rapidly flashes to a gaseous state because of the low MAP
and the hot engine components. There is usually too little of this
gaseous fuel to fully combust; the fuel-air mixture is too lean
(has too much air present) to properly and completely ignite in the
cylinder combustion chamber. The unburned fuel-air mixture is
exhausted and passes to the catalytic converter. This unburned
fuel-air mixture again leads to increases in the hydrocarbon and
carbon monoxide emissions.
[0005] Air injection reaction (AIR) systems have been employed as
one means to reduce the emissions resulting from start-up and from
the driving immediately thereafter by pumping air into the exhaust
manifold. The injected air helps provide the catalytic converter
with a stoichiometric mixture of unburned fuel and air.
Additionally, advanced engine controls and advanced fuel-swirling
devices have been used to provide a more easily ignited air/fuel
mixture for injection into the cylinders. Problems exist, however,
with both of these approaches. The AIR system is only used for
about 20 seconds at the initial start-up of the motor vehicle and
has no function thereafter in the operation of the motor vehicle.
The AIR system adds weight and complexity (and thus cost) to the
motor vehicle and yet is only functionally necessary for a short
period of time at cold start-up. The advanced engine controls and
fuel-swirling techniques also add complexity and cost to the motor
vehicle. Both of these methods help primarily with reducing
start-up and initial emissions and are largely unable to reduce
emissions in other driving situations such as conditions resulting
in rapid changes in MAP.
[0006] Presently available methods for controlling emissions during
cold start-up and in situations of rapid changes in MAP are costly
and/or ineffective. Accordingly, a need exists for an improved
emissions control method that will provide cold start intake
manifold pressure control and that can provide a reliable method of
limiting both the range of the intake manifold absolute pressure
and the rate of change of intake manifold absolute pressure in the
interests of lowered emissions throughout the operation of the
motor vehicle.
SUMMARY OF THE INVENTION
[0007] In accordance with one embodiment of the invention, a method
is provided for controlling emissions in a parallel hybrid motor
vehicle that includes an electric propulsion system in parallel
with a combustion propulsion system. Manifold absolute pressure
(MAP) is monitored in the intake manifold of the combustion
propulsion system. The electric propulsion system is engaged to
reduce the MAP measured in the intake manifold to a predetermined
pressure, and then fueling and combustion of the combustion
propulsion system are initiated only after the MAP is reduced to a
pressure less than the predetermined pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The emissions control method in accordance with the
invention will be understood after review of the following
description considered together with the drawings in which:
[0009] FIG. 1 illustrates in graphical form the effect of intake
manifold pressure on cold start fuel vaporization;
[0010] FIG. 2 schematically illustrates a parallel hybrid cold
start intake manifold pressure emission control method in
accordance with one embodiment of the invention; and
[0011] FIG. 3 illustrates in graphical form the cold start and
drive-away MAP limiting for fuel vaporization in accordance with an
embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The cold start intake manifold pressure control method in
accordance with the invention is applicable to parallel hybrid
powertrain motor vehicles. The parallel hybrid drive train motor
vehicle includes a battery-pack operated electric propulsion system
(such as an electric motor) coupled in parallel with a combustion
propulsion system (such as an internal combustion engine). For ease
of description, but without limitation, the electric propulsion
system and the combustion propulsion system will hereafter be
referred to as an electric motor and an internal combustion engine,
respectively. In accordance with the invention, during start-up and
any high-torque demand situations within a short but predetermined
time period after start-up of the internal combustion engine (ICE),
an electric motor supplements the torque that the internal
combustion engine is called upon to provide so that the manifold
absolute pressure (MAP), as measured in the intake manifold of the
ICE, remains in a predetermined MAP range. The electric motor and
internal combustion engine together provide enough combined torque
to meet driving condition. The lowered MAP provides for adequate
vaporization of fuel injected into the combustion chambers of the
internal combustion engine even under cold engine conditions so
that the cold start engine emissions are controlled. After this
predetermined amount of time has elapsed, the intake valves of the
internal combustion engine are hot enough to properly vaporize the
liquid fuel regardless of the MAP. During and after this time
period, in accordance with a further embodiment of the invention, a
control unit also regulates throttle opening and torque from the
electric motor in order to avoid rapid MAP changes that may result
in high emissions.
[0013] FIG. 1 illustrates graphically the effect of manifold
absolute pressure (MAP) as measured in the intake manifold on cold
start fuel vaporization. Fuel vapor fraction is plotted on vertical
axis 80 and injected liquid fuel pulse width (the amount of time
the fuel injector sprays fuel) is illustrated on horizontal axis
82. Lines 84, 86, 88, and 90 illustrate the resulting fuel vapor
fraction as a function of injected fuel pulse widths with intake
manifold absolute pressure [measured in kilopascals (kPa) as a
parameter]. Fuel path 92 appearing below the graph illustrates the
effect of injected fuel pulse width on resulting vaporization. For
low emission operation of the motor vehicle, it is desirable to
have an injected fuel pulse width that provides the vapor fraction
necessary to meet the demanded torque load, while being short
enough to insure that the injected fuel remains in a spray or
surface vaporization state. If the pulse width is too long, the
injected fuel does not vaporize adequately and instead is present
as surface droplets. In the extreme case, if excessive fuel is
injected (long pulse width), liquid fuel collects and becomes a
fuel puddle. Neither surface droplets nor fuel puddles combust well
and are therefore detrimental to emissions. Line 94 in FIG. 1
indicates the vapor fuel fraction necessary to meet the load
conditions. Thus, it can be seen that a MAP of about 70 kPa or less
is desirable as it allows an injected fuel pulse width short enough
to insure that the fuel path remains as spray and surface
vaporization, and not as surface droplets or fuel puddles. For
example, as line 90 illustrates, the injected fuel pulse width
required to meet the torque demand load at a MAP of 80 kPa is too
long and falls into the fuel puddle range of the fuel path. FIG. 1
also illustrates the need to control the rate of MAP change from a
higher load to a lower load. As illustrated by line 90, to meet the
load requirement at a higher MAP, such as at 80 kPa, some fraction
of the injected fuel is not vaporized. When the throttle plate is
released, there is a sudden drop in air mass, and the MAP falls to
a lower value such as 40 kPa, as line 86 illustrates. The resulting
excess fuel vapor fraction that is generated at the lower pressure
creates an uncontrolled fuel-rich mixture that passes uncombusted
through the combustion chamber and into the catalytic converter,
where it cannot be completely oxidized.
[0014] FIG. 2 illustrates schematically, in accordance with an
embodiment of the invention, a parallel hybrid cold start intake
manifold pressure emission control method. Intake manifold 12
conveys air to each cylinder of an internal combustion engine (ICE)
10. In accordance with the illustrated embodiment, ICE 10 is a six
cylinder engine, although the method is applicable to an ICE with a
greater or lesser number of cylinders. Six fuel injectors 11 reside
inside the ends of intake manifold 12, each fuel injector proximate
the intake port of one of the six cylinders. Fuel pump 15 delivers
fuel to fuel injectors 11. A pressure sensor 14 is located inside
intake manifold 12 to provide measurements of the manifold absolute
pressure (MAP) in the manifold. Throttle flap 28 controls the
amount of air allowed to pass through intake manifold 12 to each
individual cylinder in ICE 10. The throttle flap rotates through a
ninety degree arc within the intake manifold, from a "closed"
position perpendicular to the air stream flow that completely
blocks air flow, to an "open" position parallel to the air stream
flow that allows an unrestricted air flow. ICE 10 delivers power to
transmission 26 which, in turn, is coupled to the drive wheels (not
illustrated) of the vehicle. Electric motor 16 draws power from
battery pack 18 and is connected to ICE 10 by coupling 20. Coupling
20 may be, for example, a system of gears, a belt drive, or the
like. Coupling 20 allows the electric motor to act as a starter
motor for ICE 10 as well as to provide power to transmission 26
either in parallel with ICE 10 or in opposition to it. Accelerator
pedal sensor 24 measures torque demand based on the position of the
accelerator pedal (not illustrated) and relays signals to control
unit 22 regarding this torque demand. Control unit 22 is configured
to receive communicatory signals from pressure sensor 14 and
accelerator pedal sensor 24, to send communicatory signals to fuel
injectors 11, and to send and receive communicatory signals to and
from ICE 10, throttle flap 28, and electric motor 16. Through these
signals control unit 22 is configured to control the frequency and
length of the injected fuel pulse width of the fuel injectors as
well as the degree to which throttle flap 28 is open. The control
unit is programmed to calculate the volume of air passing through
intake manifold 12 based on the degree to which the throttle flap
is open. Control unit 22 also is able to continuously adjust the
frequency and pulse width of the fuel injectors to match the volume
of incoming air from the intake manifold in order to create a
fuel/air mixture that meets engine demand and is also highly
efficient and low in emissions. The control unit also controls the
amount of power electric motor 16 sends ICE 10 through coupling 20.
Control unit 22 may be, for example, a stand alone processor unit,
a portion of the engine control unit, or the like.
[0015] FIG. 3 illustrates in graphical form a cold start and
drive-away MAP limiting method for fuel vaporization to control
vehicle emissions in accordance with an embodiment of the
invention. ICE rotations in revolutions per minute (RPM) divided by
twenty and MAP measured in kPa are plotted on vertical axis 30,
with time in seconds plotted on horizontal axis 32. Dotted-line 34
represents ICE RPM, solid line 36 represents intake manifold
absolute pressure, and dashed-line 38 represents fuel pulse width.
Again with reference to FIG. 2, for the first start of ICE 10 at
time T0, control unit 22 monitors the intake manifold absolute
pressure (MAP) using pressure sensor 14 while electric motor 16
begins powering ICE 10 (with throttle flap 28 closed and without
fuel being delivered to the ICE) to a high RPM, low MAP engine
rotational speed such as about 500-600 RPM. Once the control unit
senses, at time T1, through pressure sensor 14, that the MAP has
dropped below a predetermined upper pressure limit (for example, 70
kPa, represented on FIG. 3 by horizontal line 40), the control unit
causes throttle flap 28 to open partially and causes the fuel pump
to begin pumping fuel to the fuel injectors 11, which then begin
spraying fuel into the cylinders of ICE 10. Control unit 22 then
initiates combustion. As soon as ICE 10 begins combusting fuel and
powering itself, electric motor 16 stops powering the ICE. Control
unit 22 monitors torque demand based on signals from accelerator
pedal sensor 24 and adjusts both the throttle flap opening and the
fuel injectors' pulse width. At time T2, transmission 26 is shifted
into a gear and the MAP increases slightly as the throttle flap is
opened further. Time T3 represents the time at which the controller
initiates a moderate acceleration or "crowd," such as when the
motor vehicle is backed out of a garage or accelerates into
traffic. As more torque is demanded from the engine, control unit
22 increases throttle flap opening (to increase air flow to the ICE
cylinders) and increases the injected fuel pulse width, in order to
provide the cylinders with more fuel, while monitoring MAP through
pressure sensor 14. If the MAP reaches the predetermined pressure
limit (line 40) before the ICE can meet torque demand, as
illustrated at time T4 in FIG. 3, control unit 22 maintains the
opening setting of throttle flap 28 and the fuel injector pulse
width at their existing values (in order to keep MAP below the
predetermined upper pressure limit) and, at the same time, causes
electric motor 16 to provide transmission 26 (through coupling 20)
with any additional torque necessary to meet demand. The electric
motor continues supplementing the torque from the ICE until the
intake manifold MAP drops below the upper pressure limit (line 40).
In FIG. 3 shaded areas 29 and 31 represent the times electric motor
16 is supplementing the torque demand and indicate the times MAP
would exceed the predetermined upper pressure limit if it were not
for the use of the electric motor. Similarly, cross-hatched area 33
indicates the high pulse width fuel injection (with its attendant
high liquid fraction) that is avoided by the use of the electric
motor. The foregoing method, in accordance with the invention, of
preventing the MAP from exceeding a predetermined upper pressure
limit by controlling throttle flap opening and injector fuel pulse
width and using the electric motor to provide supplemental torque
necessary to meet demand continues for a predetermined amount of
time (for example, 60 seconds). Once this time period has elapsed,
the intake valves of the ICE should be hot enough to properly
vaporize the liquid fuel, regardless of MAP. The control unit then
no longer limits the fuel pump opening based on the upper MAP
limit.
[0016] In accordance with a further embodiment of the invention,
control unit 22 is also programmed to implement a second emission
control method in response to sudden drops in torque. High
emissions can result from sudden, negative changes in MAP (rapid
changes from a high MAP to a low MAP that follow a drop in torque
demand, such as after an acceleration) when the throttle flap is
abruptly closed and liquid fuel in the intake manifold, due to the
rapid pressure gradient, flashes to a gaseous state. The remaining
fuel mixture, being too lean to burn properly in the cylinders,
temporarily raises emissions. When control unit 22 senses, based on
signals from accelerator pedal sensor 24, a sudden drop in torque
demand, control unit 22 partially closes throttle flap 28 but does
not fully close it. Instead, the control unit commands electric
motor 16 to provide, through coupling 20 to transmission 26, a
torque that works counter to the torque of the internal combustion
engine. The electric motor thus creates a resistive torque in
partial opposition to the torque from ICE 10, so that the resultant
torque, the combined torque from the electric motor and the ICE, is
the amount demanded by accelerator pedal sensor 24. Because the
throttle flap is still partially open, the rapid negative change in
MAP and the high emissions that result from such a change are
avoided. This method of maintaining a throttle flap opening and
using the electric motor to provide a resistive torque may be
applied anytime during the operation of the motor vehicle when a
sudden high to low MAP change might otherwise occur, whether it is
during the predetermined startup time period or after this time
period.
[0017] Thus, it is apparent that there has been provided, in
accordance with the invention, a method for controlling emissions
in a parallel hybrid motor vehicle that fully meets the needs set
forth above. The device is reliable and provides low emissions
throughout the operation of the vehicle, not just after a cold
first engine start. Although the invention has been described and
illustrated with reference to specific embodiments thereof, it is
not intended that the invention be limited to such illustrative
embodiments. For example, the predetermined time period after
startup during which the first method of reducing emissions
operates can be tailored to suit different climates or condition.
Additionally, the MAP pressure range in which the internal
combustion engine is to operate during the predetermined time limit
can be adjusted to suit climate, fuel combustion range, and
conditions for optimum engine performance. Those of skill in the
art will recognize that many variations and modifications of such
embodiments are possible without departing from the spirit of the
invention. Accordingly, it is intended to encompass within the
invention all such modifications and variations as fall within the
scope of the appended claims.
* * * * *