HIGH-ACCURACY IMEP COMPUTATIONAL TECHNIQUE USING A LOW-RESOLUTION ENCODER AND A CUBIC SPLINE INTEGRATION PROCESS

• US 20110208404A1
• Filed: 02/25/2010
• Published: 08/25/2011
• Est. Priority Date: 02/25/2010
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Dagci, Oguz H., Javaherian, Hossein, Haskara, Ibrahim
• Granted Patent: US 8,700,287 B2
• Time in Patent Office: Days
• US Class Current: 701/102
• CPC Class Codes: F02D 2041/286 comprising means for signal processing
• CPC Class Codes: F02D 2200/1004 Estimation of the output torque
• CPC Class Codes: F02D 35/023 by determining the cylinder pressure
• CPC Class Codes: F02D 41/1497 With detection of the mechanical response of the engine

Abstract

A method for computing indicated mean effective pressure (IMEP) in an internal combustion engine using sparse input data. The method uses a cubic spline integration approach, and requires significantly lower resolution crankshaft position and cylinder pressure input data than existing IMEP computation methods, while providing calculated IMEP output results which are very accurate in comparison to values computed by existing methods. By using sparse input data, the cubic spline integration method offers cost reduction opportunities for a manufacturer of vehicles, engines, and/or electronic control units, through the use of lower cost sensors and the consumption of less computing resources for data processing and storage.

Claims

1. A method for computing mean effective pressure in an internal combustion engine, said method comprising:

determining a set of geometric parameters for the engine, including stroke, connecting rod length, piston area, and cylinder volume;

defining a sampling resolution for a series of sampling events, said sampling resolution being an amount of crankshaft rotation between the sampling events;

computing and storing a volume array, said volume array containing combustion chamber volume as a function of crankshaft position for each crankshaft position corresponding to the sampling resolution;

computing and storing arrays of first and second derivatives of the combustion chamber volume with respect to crankshaft position, evaluated at each crankshaft position corresponding to the sampling resolution;

defining a first function f, where f is a function of cylinder pressure and the first derivative of combustion chamber volume with respect to crankshaft position;

defining a second function M, where M is a function of the first function f, the sampling resolution, and a previous value of M;

defining a cubic spline function S, where S is a function of the first function f, current and previous values of the second function M, the sampling resolution, and a previous value of S;

running the engine;

initializing a cycle by evaluating the volume array, the first and second derivative of volume arrays, the first function f, the second function M, and the cubic spline function S, where all arrays and functions are evaluated at a crankshaft position of bottom dead center at the beginning of a cycle;

taking a cylinder pressure measurement at each crankshaft position corresponding to the sampling resolution;

storing the cylinder pressure measurement for a current sampling event for calculation purposes;

calculating the first function f based on the cylinder pressure measurement for the current sampling event and the first derivative of volume array;

computing the second function M and the cubic spline function S for the current sampling event;

storing values of the first function f, the second function M, and the cubic spline function S for the current sampling event and a previous sampling event;

continuing to measure cylinder pressure and calculate the first function f, the second function M, and the cubic spline function S, as long as the crankshaft position has not reached bottom dead center upon completion of one full crankshaft rotation from initiation of the cycle; and

outputting mean effective pressure for an engine cycle as a final value of the cubic spline function, and initializing a new cycle, when the crankshaft position reaches bottom dead center upon completion of one full crankshaft rotation from initiation of the cycle.

2. The method of claim 1 wherein the first function f is defined by the equation:

3. The method of claim 2 wherein the second function M is defined by the equation:

4. The method of claim 3 wherein the cubic spline function S is defined by the equation:

5. The method of claim 1 wherein the sampling resolution is three degrees or greater of crankshaft rotation.

6. The method of claim 1 wherein the sampling resolution is six degrees or greater of crankshaft rotation.

7. The method of claim 1 further comprising using the calculated value of mean effective pressure in an engine controller to control operation of the engine.

8. A method for computing and using indicated mean effective pressure in an internal combustion engine, said method comprising:

determining a set of geometric parameters for the engine, including stroke, connecting rod length, piston area, and cylinder volume;

defining a sampling resolution for a series of sampling events, said sampling resolution being an amount of crankshaft rotation between the sampling events;

computing and storing a volume array, said volume array containing combustion chamber volume as a function of crankshaft position for each crankshaft position corresponding to the sampling resolution;

computing and storing arrays of first and second derivatives of the combustion chamber volume with respect to crankshaft position, evaluated at each crankshaft position corresponding to the sampling resolution;

defining a first function f, where f is a function of cylinder pressure and the first derivative of combustion chamber volume with respect to crankshaft position;

defining a second function M, where M is a function of the first function f, the sampling resolution, and a previous value of M;

defining a cubic spline function S, where S is a function of the first function f, current and previous values of the second function M, the sampling resolution, and a previous value of S;

running the engine;

initializing a cycle by evaluating the volume array, the first and second derivative of volume arrays, the first function f, the second function M, and the cubic spline function S, where all arrays and functions are evaluated at a crankshaft position of bottom dead center at the beginning of a compression stroke;

taking a cylinder pressure measurement at each crankshaft position corresponding to the sampling resolution;

storing the cylinder pressure measurement for a current sampling event for calculation purposes;

calculating the first function f based on the cylinder pressure measurement for the current sampling event and the first derivative of volume array;

computing the second function M and the cubic spline function S for the current sampling event;

storing values of the first function f, the second function M, and the cubic spline function S for the current sampling event and a previous sampling event;

continuing to measure cylinder pressure and calculate the first function f, the second function M, and the cubic spline function S, as long as the crankshaft position has not reached bottom dead center at the end of a power stroke;

outputting indicated mean effective pressure for an engine cycle as a final value of the cubic spline function, and initializing a new cycle, when the crankshaft position reaches bottom dead center at the end of a power stroke; and

using the calculated value of indicated mean effective pressure in an engine controller to control operation of the engine, including control of fuel flow to the engine.

9. The method of claim 8 wherein the first function f is defined by the equation:

10. The method of claim 9 wherein the second function M is defined by the equation:

11. The method of claim 10 wherein the cubic spline function S is defined by the equation:

12. The method of claim 11 wherein the sampling resolution is three degrees or greater of crankshaft rotation.

13. The method of claim 12 wherein the sampling resolution is six degrees or greater of crankshaft rotation.

14. A system for computing and using indicated mean effective pressure in an internal combustion engine, said system comprising:

a low-resolution crankshaft position encoder for measuring crankshaft position at a sampling resolution, where the sampling resolution is greater than one degree of crankshaft rotation;

a cylinder pressure sensor for measuring cylinder pressure at each crankshaft position corresponding to the sampling resolution; and

an engine controller configured to collect data from the crankshaft position encoder and the cylinder pressure sensor, calculate indicated mean effective pressure using a cubic spline integration algorithm, and use the calculated indicated mean effective pressure to control operation of the engine.

15. The system of claim 14 wherein the cubic spline integration algorithm includes:

determining a set of geometric parameters for the engine, including stroke, connecting rod length, piston area, and cylinder volume;

defining a sampling resolution, said sampling resolution being the amount of crankshaft rotation between sampling events;

computing and storing a volume array, said volume array containing combustion chamber volume as a function of crankshaft position for each crankshaft position corresponding to the sampling resolution;

computing and storing arrays of first and second derivatives of combustion chamber volume with respect to crankshaft position, evaluated at each crankshaft position corresponding to the sampling resolution;

defining a first function f, where f is a function of cylinder pressure and the first derivative of combustion chamber volume with respect to crankshaft position;

defining a second function M, where M is a function of the first function f, the sampling resolution, and a previous value of M;

defining a cubic spline function S, where S is a function of the first function f, current and previous values of the second function M, the sampling resolution, and a previous value of S;

running the engine;

initializing a cycle by evaluating the volume array, the first and second derivative of volume arrays, the first function f, the second function M, and the cubic spline function S, where all arrays and functions are evaluated at a crankshaft position of bottom dead center at the beginning of a compression stroke;

taking a cylinder pressure measurement at each crankshaft position corresponding to the sampling resolution;

storing the cylinder pressure measurement for a current sampling event for calculation purposes;

calculating the first function f based on the cylinder pressure measurement for the current sampling event and the first derivative of volume array;

computing the second function M and the cubic spline function S for the current sampling event;

storing values of the first function f, the second function M, and the cubic spline function S for the current sampling event and a previous sampling event;

continuing to measure cylinder pressure and calculate the first function f, the second function M, and the cubic spline function S, as long as the crankshaft position has not reached bottom dead center at the end of a power stroke; and

outputting indicated mean effective pressure for an engine cycle as a final value of the cubic spline function, and initializing a new cycle, when the crankshaft position reaches bottom dead center at the end of a power stroke.

16. The system of claim 15 wherein the first function f is defined by the equation:

17. The system of claim 16 wherein the second function M is defined by the equation:

18. The system of claim 17 wherein the cubic spline function S is defined by the equation:

19. The system of claim 14 wherein the sampling resolution is three degrees or greater of crankshaft rotation.

20. The system of claim 14 wherein the engine controller uses the calculated indicated mean effective pressure to control fuel flow to the engine.