Individual cylinder fuel control method

• US 6,314,952 B1
• Filed: 03/23/2000
• Issued: 11/13/2001
• Est. Priority Date: 03/23/2000
• Status: Expired due to Term

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Turin, Raymond Claude, Naik, Sanjeev Manubhai
• Primary Examiner(s): SOLIS, ERICK R
• Application Number:
  US09/535,006
• Time in Patent Office: 600 Days
• Field of Search: 123/672, 123/673, 123/674, 701/109
• US Class Current: 123/673
• CPC Class Codes: F02D 2041/1409 using at least a proportional, integral or derivative controller
• CPC Class Codes: F02D 2041/1415 using a state feedback or a state space representation
• CPC Class Codes: F02D 2041/1416 Observer
• CPC Class Codes: F02D 2041/1417 Kalman filter
• CPC Class Codes: F02D 2041/1426 taking into account control stability
• CPC Class Codes: F02D 2041/1433 using a model or simulation of the system
• CPC Class Codes: F02D 41/0085 Balancing of cylinder outputs, e.g. speed, torque or air-fuel ratio
• CPC Class Codes: F02D 41/1401 characterised by the control or regulation method F02D41/1473, F02D41/1477 take precedence

Abstract

An improved individual cylinder fuel control method based on sampled readings of a single oxygen sensor responsive to the combined exhaust gas flow of several engine cylinders. A model-based observer is used to reproduce the imbalances of the different cylinders and a proportional-plus-integral controller is used for their elimination. Both the observer and the controller are formulated in terms of a periodic system. The observer input signal is preprocessed such that it reflects at each point of time the deviation from the current A/F-ratio mean value calculated over two engine cycles. Therefore, transient engine operating conditions do not harm the reconstruction of the cylinder imbalances dramatically. The control algorithm features process/controller synchronization based on table lookup and a mechanism to automatically adjust the mapping between the observer estimates and the corresponding cylinders if unstable control operation is detected.

Claims

1. A control method for fueling N individual cylinders of a multi-cylinder internal combustion engine based on an output signal of an oxygen sensor positioned to respond to a combination of exhaust gases generated in the individual cylinders, the control method comprising the steps of:

sampling the oxygen sensor output signal sampling events that occur in synchronism with firing events in each of the individual cylinders;

filtering the oxygen sensor signal samples to define a nominal air/fuel ratio trajectory;

utilizing an observer model to define N state variables estimating air/fuel imbalances in each of the N different cylinders, and an additional state variable estimating a deviation of the sensed A/F ratio from said nominal air/fuel ratio trajectory;

measuring a deviation of the sensed air/fuel ratio from the nominal air/fuel ratio trajectory at each sampling event, and updating all of the state variables based on a difference between such measured deviation and the estimated deviation given by said additional state variable;

retrieving a previously stored index that associates the N state variables with corresponding individual cylinders;

fueling the individual cylinders based on the associated observer state variables using a closed-loop feedback control;

computing a control performance measure based on a sum of the indicated air/fuel ratio imbalances; and

if the performance measure indicates unstable air/fuel ratio control, identifying a new index value associating the N state variables with the individual cylinders, and storing the new index value in place of the retrieved index.

2. The control method of claim 1, wherein nominal air/fuel ratio trajectory is filtered over a plurality of engine cycles.

3. The control method of claim 1, wherein unstable air/fuel ratio control is indicated when at least a predefined increase in the performance measure is detected.

4. The control method of claim 1, wherein the observer model includes both the oxygen sensor and mixing of the exhaust gases upstream of the oxygen sensor.

5. The control method of claim 1, wherein the observer model and the closed-loop feedback control are both represented as a rotational system.

6. The control method of claim 1, wherein the step of identifying a new index value comprises the steps of:

temporarily disabling the closed-loop feedback control;

superimposing a periodic probing signal on the fuel supplied to a single cylinder over an even number of firing events under steady state operation of the engine;

monitoring the N state variables to identify a maximal response to the probing signal; and

identifying the new index value based on the identified maximal response.