Correction of systematic position-sensing errors in internal combustion engines

• US 5,117,681 A
• Filed: 10/01/1990
• Issued: 06/02/1992
• Est. Priority Date: 10/01/1990
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Motor Company
• Inventors: James, John V., Dosdall, James M.
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US07/590,729
• Time in Patent Office: 610 Days
• Field of Search: 73/117.3, 73/112, 73/116
• US Class Current: 73/114.26
• CPC Class Codes: F02D 41/009 using means for generating position or synchronisation signals
• CPC Class Codes: F02D 41/123 the fuel injection being cut-off
• CPC Class Codes: F02D 41/2432 Methods of calibration
• CPC Class Codes: F02D 41/2441 characterised by the learning conditions
• CPC Class Codes: F02D 41/2474 Characteristics of sensors
• CPC Class Codes: F02P 7/0675 with variable reluctance, e.g. depending on the shape of a tooth
• CPC Class Codes: F02P 7/0775 Electronical verniers
• CPC Class Codes: G01M 15/06 by monitoring positions of pistons or cranks
• CPC Class Codes: G01M 15/11 by detecting misfire
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G01P 3/4807 by using circuits for the detection of the pulses delivered by the ignition system of an internal combustion engine

Abstract

Systematic errors in manufacturing of position markers of an internal combustion engine position sensing system are corrected by a procedure which detects nonuniformities in the placement of the position markers using an engine coastdown without combustion in the cylinders. Since the coastdown comprises a smooth deceleration, any nonuniformities detected in the velocities calculated for individual firing intervals during the coastdown are a manifestation of nonuniformities in the position marker placement. These nonuniformities are used to calculate correction factors which are stored for use when calculating velocities during engine combustion.

Claims

1. A method for determining angular spacing corresponding to individual rotation intervals between respective predetermined points disposed on an encoder wheel driven by an internal combustion engine, said method comprising the steps of:

detecting passage of said predetermined points past a fixed location to provide a position signal at each point;

causing said engine to rotate without any combustion;

measuring the time which elapses between each consecutive pair of said position signals;

selecting a rotation interval between two of said predetermined points;

determining a total elapsed time for at least one full 360°

rotation of said encoder wheel including said selected rotation interval; and

comparing said total elapsed time with a measured time corresponding to said selected rotation interval.

2. The method of claim 1 wherein said measured time corresponding to said selected rotation interval is substantially at the center of said total elapsed time.

3. The method of claim 1 wherein said engine rotating step comprises:

accelerating said engine to a high speed under its own power; and

cutting off fuel flow to said engine to cause a coastdown in engine speed without combustion.

4. The method of claim 3 further comprising the steps of:

repeating said determining and comparing steps for said selected rotation interval during other total elapsed time periods; and

combining said comparisons to derive a ratio between the actual spacing of said selected rotation interval and its assumed spacing.

5. The method of claim 1 further comprising the steps of:

repeating said determining and comparing steps for said selected rotation interval during other total elapsed time periods; and

combining said comparisons to derive a ratio between the actual spacing of said selected rotation interval and its assumed spacing.

6. The method of claim 4 wherein said combining step includes determination of an average of said comparisons.

7. The method of claim 5 wherein said combining step comprises a least squares fit of velocity calculated over said measured time and velocity calculated over said total elapsed time.

8. A method for correcting velocity measurements for a combustion engine having a position sensing system subject to systematic errors in sensing individual intervals between predetermined rotational positions of said engine, said method comprising the steps of:

establishing engine rotation at a velocity greater than or equal to a predetermined velocity;

coasting down said engine rotation while combustion is prevented in said engine;

measuring velocity for individual intervals during said coastdown to obtain measurements containing said systematic errors;

computing an average velocity centered on a selected individual interval over a longer interval comprising an integral number of full 360°

rotation(s) of said engine; and

comparing said average velocity with said measured velocity for said selected individual interval to provide a correction factor for said selected individual interval.

9. The method of claim 8 wherein said coasting down is comprised of stopping fuel flow to said engine.

10. The method of claim 8 wherein said individual velocity measurements are obtained for a plurality of full rotations of said engine, said method further comprising the steps of:

computing an average velocity substantially centered on each respective individual interval during each full engine rotation; and

sorting said individual velocity measurements and said average velocities according to each respective individual interval for comparison to provide correction factors for each respective individual interval.

11. The method of claim 8 further comprising the steps of:

measuring velocity for individual intervals during combustion operation of said engine; and

multiplying measured velocities corresponding to said selected individual interval by said correction factor.

12. The method of claim 11 wherein a corrected velocity V'"'"'_i is given by the formula V'"'"'_i =C₁ *V_i, where C₁ is said correction factor and V_i is the uncorrected measured velocity, and wherein C₁ is determined by the formula:

##EQU7## where N is the number of individual calculations being averaged, i is an integer from 1 to N, V_i is the uncorrected velocity from the ith rotation, and ω

_i is average velocity centered on V_i.

13. The method of claim 11 wherein a corrected velocity V'"'"'_i is given by the formula V'"'"'_i =C₁ *V_i, where C₁ is said correction factor and V_i is the uncorrected measured velocity, and wherein C₁ is determined by the formula:

##EQU8## where N is the number of individual calculations being averaged, i is an integer from 1 to N, V_i is the uncorrected velocity from the ith rotation, and ω

_i is average velocity centered on V_i.