Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2001-01-08
2003-12-30
Solis, Erick (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S673000, C123S406240, C123S090150, C701S111000
Reexamination Certificate
active
06668812
ABSTRACT:
TECHNICAL FIELD
This invention pertains to a method of detecting and correcting air-fuel ratio or torque imbalances in individual cylinders of a three-cylinder engine or banks of three cylinders in a V6 engine using a single sensor. More specifically, this invention pertains to the use of a frequency-domain characterization of the pattern of such imbalances in detecting and correcting them.
BACKGROUND OF THE INVENTION
There is a continuing need for further refinement of air-fuel ratio (A/F) control in vehicular internal combustion engines. At present, A/F is managed by a powertrain control module (PCM) onboard the vehicle. The PCM is suitably programmed to operate in response to driver-initiated throttle and transmission gear lever position inputs and many sensors that supply important powertrain operating parameters. The PCM comprises a digital computer with appropriate processing memory and input-output devices and the like to manage engine fueling and ignition operations, automatic transmission shift operations and other vehicle functions. In the case of such engine operations, the computer receives signals from a number of sensors such as a crankshaft position sensor, and an exhaust oxygen sensor.
Under warmed-up engine operating conditions, the PCM works in a closed loop continuous feedback mode using the voltage signals from an oxygen sensor related to the oxygen content of the exhaust. The crankshaft angular position information from the crankshaft sensor and inputs from other sensors are used to manage timing and duration of fuel injector duty cycles. Zirconia-based, solid electrolyte oxygen sensors have been used for many years with PCMs for closed loop computer control of fuel injectors in applying gasoline to the cylinders of the engine in amounts near stoichiometric A/F. The PCM is programmed for engine operation near the stoichiometric A/F for the best performance of the three-way catalytic converter.
With more strict emission standards gradually phasing in, there is a need for further refinement of automotive technologies for emissions reduction. One such refinement is the use of a linear response (wide-range) A/F sensor in the exhaust pipe(s) in place of the current zirconia switching (nonlinear) oxygen sensor. Experiments have demonstrated that significant reductions in tailpipe NO
x
emissions are possible because of the more precise A/F control offered by a linear A/F sensor.
A second refinement is to increase vehicle fuel economy by diluting the air-fuel mixture with excess air (lean burn) or with exhaust gas recirculation (external EGR). The maximum benefit is achieved at the highest dilute limit. However, in a multi-cylinder engine, the limit is constrained by development of partial burns and possibility of misfire in the cylinder(s) containing the leanest mixture. This happens due to maldistribution of air, fuel or EGR in different cylinders. Thus, a new capability for the control of every cylinder air-fuel ratio by software is needed. Here, the intention would be to control only one variable (e.g., air, fuel or spark) to create uniform A/F or torque in all cylinders since only a single variable (e.g., A/F, O
2
or torque) would be measured. Clearly, single-loop feedback controllers around various sensors can operate independently to control air, fuel or spark in every cylinder.
Another motivation for all-cylinder A/F control is cost containment. For very low emission applications, fuel injectors of high precision (i.e., very small tolerances of less than 3%) are thought to be required. Achievement of this degree of tolerance, if possible at all, would be costly. A better solution would be to have a software means to compensate for the differences between fuel injectors in real-time operation of the engine. Another source of cylinder imbalances in a multi-cylinder engine is the inherent engine maldistribution due to variable breathing capacities into various cylinders. The air maldistribution can result in A/F or torque imbalances for which a software solution is sought.
Accordingly, it is seen that new emission reduction strategies for automotive gasoline engines would be enabled or enhanced by the development of a process for detecting and correcting fuel, air or spark imbalances between cylinders of a multi-cylinder engine.
SUMMARY OF THE INVENTION
In this invention, a process is provided that would balance A/F or torque amongst all cylinders of a three-cylinder engine or separately in either bank of a V6 engine. The benefits in terms of emissions reduction, fuel economy and driveability will depend on the degree of A/F or torque imbalances present in the engine and is engine dependent. In general, it is estimated that the benefit would depend on exhaust system configuration as well. For example, the benefit in a V6 engine with dual banks of unequal pipe lengths is larger when a single sensor is used for control and when fuel injectors have larger tolerances.
A principal cause, but not necessarily the sole cause, of cylinder A/F imbalances in a fuel-injected engine is differences in the delivery rates of the fuel injectors. Fuel injectors are intricate, precision-made devices, but the delivery rates of “identical” injectors may vary by as much as ±5%. Thus, the normal operation of a set of such injectors may be expected to lead to the delivery of varying amounts of fuel in the respective cylinders even when the PCM specifies identical “injector on” times. If the air flow rate or the exhaust gas recirculation rate is not varying in proportion with the fuel imbalances, there can be significant differences in A/F and/or torque among cylinders.
In a three-cylinder (or dual exhaust system V6) engine, individual cylinder maldistributions of air, fuel and EGR cause fluctuations in the instantaneous oxygen sensor voltages measured downstream at the point of confluence in the exhaust manifold. These O
2
sensor voltages are representative of the A/F of the cylinders. The actual A/F signal is periodic with the successive exhausts of the three cylinders, but the periodic pattern remains similar over prolonged engine operation especially if the pattern is due mainly to variances in fuel injector deliveries. Any arbitrary pattern of cylinder to cylinder differences in A/F ratio can be represented by a combination of simpler basic A/F patterns here referred to as “templates”. In this notation, a template consists of a unique pattern of −1, 0 and +1 units of A/F or a multiple thereof in each cylinder only. Negative and positive signs imply fuel-rich and fuel-lean A/F, respectively, and 0 implies stoichiometric A/F for a particular cylinder exhaust event. At this point the values of −1 and +1 simply indicate rich and lean A/F without regard to the magnitude of the departure of the ratio from the stoichiometric value, typically about 14.7 for most common gasoline fuels available today.
Obviously, each cylinder could experience a rich or lean A/F when the PCM is trying to control the overall A/F at the stoichiometric ratio. However, it has been determined in connection with this invention that the patterns of all possibilities are not independent of each other. It turns out that the number of independent basic patterns in this representation is equal to the number of cylinders. Specifically for a three-cylinder engine, any unknown pattern of imbalances can be reduced to a combination of three basic patterns T
1
, T
2
and T
3
shown in FIG.
1
. Referring to
FIG. 1
, template T
1
has the pattern +1, 0, −1 (i.e., lean A/F, stoichiometric A/F and rich A/F) for cylinders
1
,
2
,
3
respectively. Template T
2
is the pattern −1, +1, 0 and template T
3
is the pattern +1, +1, +1.
It has been further discovered in connection with this invention that the pattern of unknown three cylinder A/F imbalances with magnitudes (a, b, c) can be uniquely related to the above three templates by appropriate weighting factors (f
1
, f
2
, f
3
) applied to the values of the terms of each template (FIG.
1
). Thus, the kn
General Motors Corporation
Marra Kathryn A.
Solis Erick
LandOfFree
Individual cylinder controller for three-cylinder engine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Individual cylinder controller for three-cylinder engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Individual cylinder controller for three-cylinder engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3125765