Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-03-03
2003-05-06
Vo, Hieu T. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C701S110000, C701S102000, C701S115000, C123S435000, C123S480000
Reexamination Certificate
active
06560526
ABSTRACT:
TECHNICAL FIELD
This invention relates to cylinder-pressure based engine control using the methodology referred to as pressure-ratio management. In the context of this invention, the term “pressure ratio” refers to the ratio of the fired air-fuel mixture pressure in an engine cylinder at a given crank angle (i.e., piston position) to the pressure of a motored (no ignition) engine when the cylinder contains the same mixture at the same volume. As will be seen, the term “pressure-ratio management” refers to the use of such ratios in a programmed engine control computer to manage certain parameters affecting engine operation. More specifically, this invention relates to the use of pressure-ratio management of an internal combustion engine to detect partial-burn and misfire situations in a cylinder.
BACKGROUND OF THE INVENTION
Development of advanced engine control systems for the modern four-stroke gasoline engine is being driven by demand for higher fuel economy and increasingly stringent exhaust emission standards. Moreover, the further development of such systems is driven by requirements in the United States, for example, for on-board diagnosis (OBD II) of engine operating events that could adversely affect the catalytic converter or other emissions control equipment.
Individual-cylinder pressure-based feedback is a suitable method to optimize engine operation because engine cylinder pressure is a fundamental combustion variable that can be used to characterize the combustion process for each combustion event. For example, it has been demonstrated that optimal engine control can be maintained by monitoring the pressure in each cylinder and using that information for feedback control of spark timing, exhaust gas recirculation (EGR), air-fuel ratio (A/F), fuel balancing between cylinders, and combustion knock.
Frederic Matekunas has demonstrated (see U.S. Pat. Nos. 4,621,603; 4,622,939 and 4,624,229) that a methodology called “pressure-ratio management” can be used in computer-based, closed-loop, engine-combustion control to better manage air-fuel ratio (including fuel balance between cylinders), ignition timing and EGR dilution, respectively. The teachings of these three patents are incorporated herein by reference. Matekunas' pressure-ratio management (PRM) involves computer-based engine controls and control algorithms which are facilitated by the availability of a production-viable, reliable cylinder-pressure sensor. The PRM methods require only a signal that has a linear relationship to the cylinder pressure without knowledge of either the gain or the offset of the cylinder pressure related signal. This provides the potential of applying sensors which need not be calibrated and which may measure pressure by means which are less direct than those sensors which must be exposed to the combustion gases in the engine cylinder. Such a sensor is a non-intrusive device called the “spark-plug boss” cylinder-pressure sensor as disclosed in U.S. Pat. No 4,969,352 to Mark Sellnau. Some features of PRM will be summarized here because they can be used in combination with the processes of this invention.
PRM uses pressure data from one or more individual engine cylinders, at specified piston positions and corresponding known cylinder volumes. The data is used in the form of the ratio of the fired cylinder pressure and the “motored pressure” (i.e., the pressure that would exist in the cylinder due to the presence of an air and fuel mixture if combustion did not occur). Pressure ratio is calculated for a piston position in terms of the current crank angle position, &thgr;, in accordance with the following equation 1.
PR
(&thgr;)
=P
(&thgr;)/
P
mot
(&thgr;) (1)
Plots of fired pressure and motored pressure data for a cylinder over a range of crank angle positions before and after the top dead center position of the piston are shown in FIG.
1
A.
FIG. 1B
is a graph of pressure ratios (PR) corresponding to the pressure data of FIG.
1
A. As seen in
FIG. 1B
, the PR has unity value before combustion and rises during combustion to a final pressure ratio (FPR) which depends on the amount of heat release per unit charge mass of combustible fuel and air mixture.
The increase in the final pressure ratio is called the modified pressure ratio, MPR.
MPR=FPR
−1 (2)
The fractional rise in the pressure ratio is an estimate of the mass burn fraction in the cylinder during a single combustion event. As described in the Matekunas patents, the accuracy of the estimate is influenced only slightly by heat transfer and piston motion. Since the pressure ratio is, by definition, a ratiometric measure of cylinder pressures, PRM algorithms do not require the gain of the pressure sensor. The bias of the pressure signal (voltage) is computed using two compression samples with the assumption of polytropic behavior, which is satisfied whether or not the signal is an absolute pressure. Therefore, PRM is inherently insensitive to many of the common errors in pressure measurement. Importantly, this enables use of low-cost pressure sensors for practical implementations of the system.
Implementation of PRM (for an uncalibrated and arbitrarily biased pressure signal) requires signal sampling at a minimum of four discrete crank angle locations for which cylinder volume is known. [With an absolute pressure transducer, only a single early sample point is required. The mechanization described here is based on triggering of the pressure samples using a 24-tooth crank wheel, which provides the ability to sample at 15-degree intervals. The wheel is aligned to provide a sample at 10 degrees (ATDC).] Suitably, two samples are taken prior to significant heat release, typically 35 and 50 crank angle degrees before the top-dead-center (BTDC) position of the piston on the compression stroke, for determination of the motoring-pressure waveform (see
FIG. 1A
) and the pressure-sensor signal bias, both from polytropic relationships. A sample taken after combustion is complete, typically at the piston position characterized by 55 crank angle degrees after top dead center (ATDC), is needed to determine the FPR, which is represented as quantity B in
FIG. 1B. A
sample taken at 10 crank angle degrees ATDC (during combustion) provides the pressure ratio at this sampling point. The fractional rise in pressure ratio is an estimate of the mass-burn fraction in the cylinder in which the pressure is measured. For the 10 degree ATDC point, this is represented by the quantity A/B in FIG.
1
B and is also used by Matekunas as a PRM combustion timing parameter, referred to as PRM
10
.
PRM
10
=[PR
(
10
)−1
]/[FPR−
1] (3)
The PRM
10
timing parameter (equation 3) is a very sensitive measure of combustion phasing and is useful for minimum ignition (spark) advance for best torque (MBT) spark timing control.
PRM
10
values range between 0 and 1. For spark-ignited engines, MBT spark timing usually yields a PRM
10
value of about 0.55 with only slight sensitivity to mixture strength and engine speed. As shown in
FIG. 1B
, an exemplary value of MBT timing is spark ignition at 40 degrees BTDC. Retarded spark timing yields lower values of PRM
10
; advanced timing yields higher values of PRM
10
. Typically, a change of 0.1 in PRM
10
corresponds to 3 to 5 crank angle degrees change in spark timing. Because the mass burn rate and the slope of the PR curve are near their maximum at 10 degrees ATDC (e.g., see FIG.
1
B), the PRM
10
parameter remains a sensitive measure of combustion phasing even for high dilution ratios.
For combustion with MBT spark timing, the value of FPR is a maximum for stoichiometric mixtures with no dilution, and decreases as excess air, EGR, or residuals are increased. Therefore, FPR is useful as an indicator of total charge dilution, and is applicable to the control of mixture dilution in systems which are lean burn, use high amounts of EGR, or vary the amount of residual through variable valve train systems. For spark-ignite
Matekunas Frederic A.
Sellnau Mark C.
General Motors Corporation
Marra Kathryn A.
Vo Hieu T.
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