U.S. patent application number 11/678094 was filed with the patent office on 2007-09-06 for disi injection timing strategy.
Invention is credited to Jon Caine, Peter Causer, Marcus Davies, Darren Jackson, Gary Peirce.
Application Number | 20070204599 11/678094 |
Document ID | / |
Family ID | 36219141 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070204599 |
Kind Code |
A1 |
Davies; Marcus ; et
al. |
September 6, 2007 |
DISI INJECTION TIMING STRATEGY
Abstract
A control strategy for a DISI engine fitted with a catalytic
converter, for reducing the light off time of the catalyst during
cold starts, which comprises setting the ignition timing for each
engine cylinder and injecting at least a proportion of the fuel,
the timing of the injection in relation to the ignition timing
being varied as a function of an engine operating condition.
Inventors: |
Davies; Marcus; (Rochester,
GB) ; Peirce; Gary; (Chelmsford, GB) ;
Jackson; Darren; (Benfleet, GB) ; Caine; Jon;
(South Woodham Ferrers, GB) ; Causer; Peter;
(Paglesham, GB) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC
FAIRLANE PLAZA SOUTH, SUITE 800, 330 TOWN CENTER DRIVE
DEARBORN
MI
48126
US
|
Family ID: |
36219141 |
Appl. No.: |
11/678094 |
Filed: |
February 23, 2007 |
Current U.S.
Class: |
60/285 |
Current CPC
Class: |
F02D 41/0255 20130101;
Y02T 10/12 20130101; F02D 41/3029 20130101; Y02T 10/26
20130101 |
Class at
Publication: |
60/285 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2006 |
GB |
0604395.4 |
Claims
1. A method for reducing light off time of a catalyst coupled
downstream of a DISI engine, comprising: setting the ignition
timing for each engine cylinder and injecting at least a proportion
of the fuel, the timing of the injection in relation to the
ignition timing being varied as a function of an engine operating
condition.
2. The method as claimed in claim 1, wherein the ignition timing
occurs during the expansion stroke.
3. The method as claimed in claim 2, wherein the timing of the
injection in relation to the ignition timing is measured from the
end of the injection to the spark timing.
4. The method as claimed in claim 3, wherein an initial proportion
of fuel is injected prior to a secondary injection.
5. The method as claimed in claim 4, wherein the initial injection
of fuel occurs during the intake or compression strokes.
6. The method as claimed in claim 5, wherein the timing of the
secondary is injection further a function of any one or more of
exhaust gas temperature, engine speed, engine coolant temperature,
engine oil temperature, throttle position, ambient air temperature,
ambient air pressure, intake air pressure, intake air temperature
and compression ratio.
7. A method for reducing light off time of a catalyst coupled
downstream of a DISI engine, comprising: injecting fuel and air
into each engine cylinder; and retarding ignition timing such that
at least a portion of said injected fuel and air exits said engine
cylinders unburned thereby raising engine exhaust gas temperature.
Description
FIELD OF INVENTION
[0001] This invention relates to direct injection spark ignition
engines and more particularly to the timing of the injection of
fuel to improve emissions.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] With a view to meeting ever more stringent emissions
legislation, rapid catalyst light-off is increasingly desirable. In
order to achieve this in direct injection spark ignition (DISI)
engines, significant levels of spark retard may be used to generate
the necessary exhaust gas temperatures.
[0003] In attempts of prior art DISI engines to retard ignition
timing, undesirable emissions and less than ideal combustion placed
a limit on the degree of retard that could be achieved, and thus
the amount of accelerated catalyst heating.
[0004] With a view to mitigating the foregoing disadvantage, the
present invention provides a control strategy for a DISI engine
fitted with a catalytic converter, for reducing the light off time
of the catalyst during cold starts, which comprises setting the
ignition timing for each engine cylinder and injecting at least a
proportion of the fuel, the timing of the injection in relation to
the ignition timing being varied as a function of an engine
operating condition.
[0005] In one embodiment of the present invention the ignition
timing occurs during the expansion stroke.
[0006] In yet another embodiment of the present invention, the
timing of the injection in relation to the ignition timing is
measured from the end of the injection to the spark timing.
[0007] In an alternative embodiment, an initial proportion of fuel
may be injected prior to the secondary injection described
above.
[0008] Alternatively, the initial injection of fuel may occur
during the intake or compression strokes.
[0009] In yet another embodiment, the timing of the secondary is
injection may be a function of any one or more of exhaust gas
temperature, engine speed, engine coolant temperature, engine oil
temperature, throttle position, ambient air temperature, ambient
air pressure, intake air pressure, intake air temperature and
compression ratio.
[0010] It will be appreciated that features of the invention are
susceptible to being combined in any combination without departing
from the scope of the invention as defined by the accompany
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] By way of example only, embodiments of the present invention
will now be described with reference to the accompanying drawings
wherein:
[0012] FIG. 1 is schematic section through a cylinder of a DISI
engine;
[0013] FIG. 2 is a graph showing cylinder pressure versus crank
angle in a DISI engine operated according to a first embodiment of
the present invention; and
[0014] FIG. 3 is a similar graph showing cylinder pressure in a
DISI engine operated according to a second embodiment of the
present invention.
DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0015] FIG. 1 shows a cylinder of a DISI engine 10. This is much
the same as a conventional spark ignition engine with the addition
of a high-pressure fuel injector 12 spraying fuel directly into the
cylinder. The injector 12 is controlled by an injector driver 22
that receives a signal from a central processing unit 14 (CPU). The
mixture within the cylinder is ignited by a conventional spark plug
18, controlled by an ignition system 20, again triggered by the CPU
14. Exhaust gases are then fed through an exhaust system to a
catalytic converter 16.
[0016] The catalyst needs to be operated at a minimum temperature
before it is able to treat the exhaust gases. The period of time
between the engine starting and the catalyst achieving full
operating temperature is known as the light-off period. During this
period the vehicle emissions are undesirably high. It is therefore
important to reduce this period to the shortest time possible.
[0017] This is achieved by igniting the mixture in the cylinder as
late as possible into the expansion stroke. FIGS. 2 and 3 show the
in-cylinder pressure throughout the four stroke cycle. The regions
marked A, B, C and D represent the exhaust, intake, compression and
expansion strokes respectively. The small drop early in the intake
stroke represents the opening of the inlet valve at which point the
pressure drops as fresh air is sucked in. At some point during the
induction, compression and expansion stoke, prior to ignition of
the mixture, fuel is injected via direct injector 12. During the
compression stroke the pressure rises as the piston approaches TDC.
After peak pressure the piston travels down again during the
expansion stroke and as the pressure falls the spark plug ignites
the mixture at the point Ig causing the pressure to climb to a
second peak before dropping and the cycle restarting. (This does
not, of course, prevent the spark from being fired during the
compression stroke).
[0018] By retarding the ignition point Ig well into the expansion
stroke, there is not sufficient time for the flame to ignite the
air and fuel mixture within the cylinder. Unburned fuel and air
therefore exit the cylinder with the exhaust gases. This serves to
raise the temperature of the exhaust gases since the energy
normally provided by combustion of the mixture in the cylinder has
not been imparted to the downward movement of the piston. This
function is not dependent on ignition occurring in the expansion
stroke. There are situations when the same temperature increase can
be achieved by retarding the ignition timing relative to minimum
spark for best torque (MBT) whilst it still remains in the
compression stroke.
[0019] The amount of ignition retard is dependent upon combustion
stability and the combustion concept which is related to cylinder
design and geometry.
[0020] A result of retarding the ignition is that the engine
develops less power. To compensate for this, more fuel is injected
to maintain power whilst still providing unburned mixture for
heating the exhaust gases and the catalyst 16.
[0021] In DISI engines, the timing of the injection of fuel is
critical to achieve good exhaust gas heat flux whilst minimizing
fuel flow rate and exhaust gas emissions. The relationship between
the injection and ignition timing is therefore important. Due to
the expressed desire to vary the ignition timing in order to
accelerate catalyst light-off, the present invention provides for
varying the injection timing in relation to the ignition timing
based on an operating condition of the engine. The relative timing
of the injection and ignition is measured in degrees of crank angle
from the end of the injection as the length of the injection will
itself vary during different engine operating conditions.
[0022] The relationship between injection and ignition timing need
not be constant. It is foreseeable that the crank angle separation
could vary depending on many factors, including but not limited to
exhaust gas temperature, engine speed, engine coolant temperature,
engine oil temperature, throttle position, ambient air temperature,
ambient air pressure, intake charge pressure, compression ratio
among others. The important point remains that as ignition timing
varies, the crank angle separating injection timing and ignition
timing is maintained in a predetermined functional relationship,
regardless of whether the spark is provided in the compression or
expansion strokes. This separation angle is represented by the
arrows in FIGS. 2 and 3.
[0023] FIG. 3 shows a second and preferred embodiment of the
invention in which the injection of fuel is split into two smaller
injections. This is because a single larger injection can lead to
the mixture being too rich and can restrict the degree of retard
achievable thereby limiting the heat flux to the exhaust.
[0024] Split injection allows an overall weaker mixture to be
ignited. Fuel injected at Inj1 mixes to produce a homogeneous yet
weak charge, while the latter injection Inj2 gives a localised rich
mixture in the region of the spark to allow ignition to occur. In
this embodiment, it is the second injection to create a localized
rich mixture that is timed in predetermined relation to the
variable ignition timing. While the fuel is shown as being injected
at Inj1 during the compression stroke, there is no reason why it
could not equally have been injected prior to that during the
intake stroke.
* * * * *