Method to determine TDC in an internal combustion engine
AssigneeABB AB
InventorJarl R. Sobel
Life of this patent
Estimating the term…
Abstract
A method and apparatus for accurately determining TDC in a cylinder of an internal combustion engine. Gas pressure is measured in the cylinder relative to crank angle, giving rise to a curve of gas pressure with crank angle. An offset is found by first computing the angular position of an inflexion point of the compression pressure curve measured as a function of the crank angle, and then computing the offset as the difference between the angular position of a piston in the cylinder and a theoretical value for said angular position of the piston dependent on a known or measured flywheel angle. The value of TDC corrected by the offset is then used to calculate a value of work output such as the Indicated Mean Effective Pressure (IMEP) which may be used for diagnostic and/or control purposes.
Claims29
A method to determine a top dead center position for a piston in a cylinder of an internal combustion engine comprising one or more cylinders and a crankshaft, the method comprising:
- measuring gas pressure in at least one cylinder as a function of an angular position of the crankshaft;
- measuring an inflection point of a curve based upon the measured gas pressure during a compression stroke;
- computing a theoretical value of the inflection point based upon engine characterizing parameters;
- and
- computing an angular position of the top dead center from a difference between the measured inflection point and the computed theoretical value of the inflection point.
A method to determine an approximate value of angular position as a function of time for a piston in a cylinder of an internal combustion engine comprising one or more cylinders and a crank shaft, the method comprising:
- measuring a gas pressure in at least one cylinder as a function of time,
- computing a timing of an inflection point of a curve based upon the measured gas pressure,
- computing a theoretical value of the angular position of said piston at said inflection point, and
- estimating a crank angle of said piston as a function of time, based on said inflection point timing and said theoretical value.
A system for determining TDC of piston in a cylinder of a motor, said system comprising:
- a gas pressure sensor,
- a calculation unit operative to calculate an inflection point of a pressure curve for gas pressure in the cylinder dependent on an angular position of a crankshaft, wherein the calculation unit comprises a formula to calculate a theoretical value for position of the piston according to the formula:
-
- a
- =
- -
- 4
- (
- 1
- +
- λ
- )
-
- (
- 1
- +
- 2
-
- (
- γ
- -
- 0.0217
- )
- )
-
- (
- r
- c
- -
- 1
- )
- +
- 4
- 3
-
- (
- -
- 1
- -
- 3
-
- λ
- +
- 3
-
- λ
- 2
- )
-
- (
- 5
- +
- 4
-
- (
- γ
- -
- 0.0217
- )
- )
- (
- 1
- +
- λ
- )
- 2
-
- (
- 1
- +
- 2
-
- (
- γ
- -
- 0.0217
- )
- )
- 3
-
- (
- r
- c
- -
- 1
- )
- 2
- λ=Relation between crank radius and piston connecting rod length;
- γ=Quotient between heat capacity at constant pressure and heat capacity at constant volume (polytropic coefficient) for the compressed gas at the estimated temperature of the gas at the inflection point;
- rc=Compression ratio of the motor;
- α=theoretical inflexion point in radians.
A computer readable medium on which is stored a computer program product comprising computer code to instruct a computer or processor carry out the steps of
- measuring gas pressure in at least one cylinder as a function of an angular position of the crankshaft;
- measuring an inflection point of a curve based upon the measured gas pressure during a compression stroke;
- computing a theoretical value of the inflection point based upon engine characterizing parameters;
- and
- computing an angular position of the top dead center from a difference between the measured inflection point and the computed theoretical value of the inflection point.
A system for determining top dead center for a piston in a cylinder of an internal combustion engine comprising one or more cylinders and a crankshaft, said system comprising:
- a gas pressure sensor operative to measure gas pressure in at least one cylinder as a function of an angular position of the crankshaft;
- and
- a calculation unit operative to calculate an inflection point of a curve based upon the measured gas pressure during a compression stroke, to calculate a theoretical value of the inflection point based upon engine characterizing parameters, and to calculate an angular position of the top dead center from a difference between the measured inflection point and the computed theoretical value of the inflection point.
Dependencies are inferred from the claim text.