GB2281624A - Engine crankshaft position determination - Google Patents
Engine crankshaft position determination Download PDFInfo
- Publication number
- GB2281624A GB2281624A GB9315758A GB9315758A GB2281624A GB 2281624 A GB2281624 A GB 2281624A GB 9315758 A GB9315758 A GB 9315758A GB 9315758 A GB9315758 A GB 9315758A GB 2281624 A GB2281624 A GB 2281624A
- Authority
- GB
- United Kingdom
- Prior art keywords
- engine
- correction factor
- crankshaft
- stored
- measured
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
- G01D18/002—Automatic recalibration
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
- G01D5/247—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains using time shifts of pulses
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Combined Controls Of Internal Combustion Engines (AREA)
Abstract
Apparatus and method for detecting the position of an engine crankshaft comprises a plurality of markers 12, 14, 16 nominally equally spaced around the flywheel 10 of the engine and a position sensor 18 to detect passage of the markers. A control unit 20 is arranged to measure the time between the passage of successive markers past the sensor and from these times calculate correction factors which can be used to compensate for any inaccuracies in the angular positioning of the markers on the flywheel. <IMAGE>
Description
Engine Management Systems
The present invention relates to engine management systems, and in particular to an improved method of, and apparatus for, determining the position of an engine crankshaft.
The use of a flywheel mounted toothed wheel and variable reluctance sensor to measure the position of a spark ignition engine crankshaft for the purpose of controlling ignition timing is well known and in common use. It has been propose that this method could be used to detect the presence of engine misfire. The small time differences which need to be aetected in order to achieve a reliable misfire detection system require an improvement in the accuracy of crankshaft position sensing over that which can be achieved with known systems such as those described above. Although it has been suggested that the increased accuracy can be obtained by reducing the manufacturing tolerances of the components of known systems, the accuracy required is high and has proved hard to achieve.
Accordingly the present invention provides a method of controlling an engine comprising the steps of providing a plurality of angularly spaced marker means at or close to respective notional positions on a member rotatable with the crankshaft, measuring the times at which the marker means pass a predetermined position as the crankshaft rotates, calculating expected times, corresponding to the measured times, from the notional positions of the marker means, and calculating from the measured and expected times correction factors to be used in calculations involving the positions of the marker means.
This enables the engine management system to operate on the assumption that the marker means are accurately positioned and to correct any measurements involving the position of the marker means to account for the difference between their actual position and their nominal positions, which would normally be equally spaced around the member on which they are mounted.
The method preferably further incluaes the step of checking the rate of change of the speed of rotation of the crankshaft to prevent the use of measurements made when said rate of change is greater than a predetermined value. This enables the correction factors to be calculated accurately using a relatively simple algorithm.
Preferably the method includes the step of checking operating parameters of the engine to prevent the use of measurements taken when the engine is operating outside a predetermined range of those parameters. Those parameters may include engine load or engine speed. This enables checks to be made that the engine is running normally without the need for a high degree of accuracy.
The method preferably further comprises the step of checking for engine misfire to avoid the use of measurements made when the engine is misfiring.
Preferably the time measurements are repeated a number of times and the average measured time for each marker means is used to calculate the correction factors.
A correction factor may be calculated for each of a plurality of ranges of position of the crankshaft, and each of said ranges of position may correspond to a region of the rotatable member between a respective adjacent pair of marker means being in said predetermined position.
The correction factors are preferably stored in memory such that they can be updated by repeating the measurements, and the method preferably further comprises the step of updating at least one of the the stored correction factors using a newly measured correction factor.
The method preferably further comprises the step of comparing a newly calculated correction factor with one already stored in memory and rejecting the newly calculated correction factor if it differs from the stored one by more than a predeterminea amount. This can help prevent errors occurring in the updating process.
The updating is preferably effectea by replacing the stored correction factor by a value between the stored correction factor and the newly calculated correction factor. This can prevent large sudden changes in the stored value of the correction factor which could be erroneous.
The step of calculating the expected times preferably includes an adjustment for the rate of change of speed of rotation of the crankshaft as indicated by the measured times. This is because, even though the measurements are likely to be made over a relatively short period of time, the rate of change of speed can be high enough to make an assumption of constant speed impractical.
The present invention also provides apparatus for controlling an engine comprising a plurality of angularly space marker means at or close to respective notional positions on a member rotatable with the crankshaft, timing means for measuring the times at which the marker means pass a predetermined position as the crankshaft rotates, control means arranged to calculate expected times, corresponding to the measured times, from the notional positions of the marker means, and calculate from the measured and expected times a correction factor to be used in calculations involving the positions of the marker means.
The apparatus can be arranged to carry out the method of the invention as described bove.
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
Figure 1 is a diagrammatic representation of apparatus according to the present invention,
Figure 2 is a map of engine speed and engine load used in the operation of the present invention, and
Figure 3 is a graph showing correction used in the method of the invention for changing crankshaft speed.
Referring to Figure 1 a flywheel 10 of a V6 engine has three markers 12, 14, 16, which are nominally equally spaced at 1200 intervals round the flywheel 10. Although the markers 12, 14, 16, are positioned as accurately as possible they are not exactly in their nominal positions.
A position sensor 18 is mounted close to the flywheel 10 to detect when one of the markers 12, 14, 16, passes it.
The markers are arranged such that one of them passes the position sensor 18 as each of the cylinders passes top dead centre. Using the normal firing order of 1, 4, 2, 5, 3, 6, the first marker 12 will pass the position sensor at top dead centre for cylinders 1 and 5, the second 14 for cylinders 3 and 4, and the third 16 for cylinders 2 and 6.
The position sensor 18 is connected to a control unit 20 which forms part of an engine management system, and is arranged to check for engine misfire, using a known algorithm, based on the times at which the markers 12, 14, 16, pass the position sensor 18.
In order to determine the factors required to correct for the difference between the actual positions of the markers 12, 14, 16, and their nominal positions, the control unit first checks that the engine is operating in a region where misfire can easily be detected without a high level of accuracy in the measurement of crankshaft speed. This can be seen from Figure 2 which is a graph of engine load against engine speed. The shaded area 22, where engine speed is low but engine load is high, indicates conditions under which misfire can easily be detected. This is because in this region the firing of each cylinder produces a relatively large force on the crankshaft, and the time between cylinders firing is relatively long.
Therefore a misfire will have a substantial effect on the speed of rotation of the crankshaft, which will be easy to detect.
The control unit then checks that the engine speed is not varying by more than a predetermined amount. This is so that, in the calculation of the error factor it can be assumed that the speed is constant, which makes the calculation simple.
The control unit then checks that the engine is not misfiring. This is again so that the calculations can assume that the engine is running steadily.
Over a predetermined period, for example 10 crankshaft revolutions, the control unit measures and records the values of the times T1, T2 and T3, which are the times between the first and second markers 12, 14, the second and third markers 14, 16, and the third and first markers 16, 12, passing the position sensor as shown on
Figure 1.
The control unit then calculates the average for each of the times T1, T2 and T3 by summing the values measured and dividing by the number of readings taken. ie using the equation
T1/10 = T1 where T1' is the mean value of T1.
Correction factors xl, x2 and x3 are then calculated using the equations
x1 = (T1' + T2' + T3')/(3T1') x2 = (T1 + T21 + T3')/(3T2') x3 = (T1' + T2 + T3')/(3T3')
These correction factors are compared with those already stored in memory and if they differ from the stored values by more than a predetermined amount they are rejected.
Otherwise they are used to update those in memory. This is done using a tuneable filter as described in the equation
new value = f.xn + (l-f).stored value where f = a constant between 0 and l,and
n = 1, 2 or 3.
These correction factors are therefore the factors which, when multiplied by the measured times, would produce the predicted times. They are used to correct the measured times of the markers 12, 14, 16, passing the position sensor 18, and the corrected times are used in the misfire detection algorithm so that misfire can be detected accurately under all engine operating conditions.
If the system includes means for identifying the firing strokes of individual cylinders then the system described above can be refined by calculating a correction factor for each cylinder, and the misfire algorithm can be used to establish which of the cylinders is misfiring. The correction factors are calculated as described above except that the times between two adjacent markers passing the sensor 18 are given two separate designations depending on which cylinder is at top dead centre at the start of the period. Thus the time between the first and second markers 12, 14, passing the position sensor during the firing stroke of cylinder 1 is designatea T1, and the time between the same two markers 12, 14, passing the position sensor during the firing stroke of cylinder 5 is designated T5.Periods T3 and T4 are similarly defined for the times between the second and third markers 14,16 passing the position sensor 18 during the firing strokes of cylinders 3 and 4, and periods T2 and T6 for the third and first markers 16, 12 and cylinders 2 and 6. Average measurements for these periods T1' to T6' are then calculated from measurements over 10 engine cycles, and correction factors calculated using the equation Xn = (T11 + T2 + T3 + T4' + T5' + T61) (6Tn ) for n = from 1 to 6.
This enables a specific correction factor to be calculated and used during the firing stroke of each cylinder thus providing a high degree of accuracy in timing measurements.
In a further refinement of the invention the system can be arranged to compensate for a change in crankshaft rotation speed during measurement of the times T1 to T6, and thereby provide more accurate correction of subsequent measured times. To achieve this the six time periods T to T6 as described above are measured over a total period short enough for any speed changes to be approximately linear, and the average rate of change of those time periods over that total period is calculated.
This can be done by measuring the values of T1 to T6 in a single engine cycle, ie two revolutions of the crankshaft, and then the value of T1 at the beginning of the next engine cycle, which will be denoted by T1,2. An average rate of change of time per firing stroke R can then be calculated using the equation R = (T1,2 - T1)/6 Since T1 and T1,2 are measured using only one marker the rate of change calculated will not be affected by errors in marker positioning.
The predicted values P1 to P6 for the measured times
T1 to T6 are then calculated as follows: P =T n 1 + (n-l)R for n + from 1 to 6 as shown in Figure 3.
The correction factors that would, when multiplied by the measured times, produce the predicted times, are then calculated as follows xn = Pn/Tn for n = from 1 to 6.
In a further variation of the methods described above, rather than taking the measurements whilst the engine is in the region of operating conditions as shown by the shaded area 22 in Figure 2, they can be taken when the engine is in over-run ie in the shaded area 24 when the engine load is negative. In this region the engine management system is arranged so that no fuel is injected, so there is no chance of misfire during measurement. Also the engine speed is unlikely to be changing quickly, and if it is, the change can easily be datected as described above.
Claims (26)
1. A method of controlling an engine comprising the
steps of:
providing a plurality of angularly space marker
means at or close to respective notional positions
on a member rotatable with the crankshaft,
measuring the times at which the marker means pass a
predetermined position as the crankshaft rotates,
calculating expected times, corresponding to the
measured times, from the notional positions of the
marker means, and
calculating from the measured and expected times
correction factors to be used in calculations
involving the positions of the marker means.
2. A method according to claim 1 further including the
step of checking the rate of change of the speed of
rotation of the crankshaft to prevent the use of
measurements made when said rate of change is
greater than a predetermined value.
3. A method according to claim 1 or claim 2 further
including the step of checking operating parameters
of the engine to prevent the use of measurements
taken when the engine is operating outside a
predetermined range of those parameters.
4. A method according to any foregoing claim wherein
the time measurements are repeated a number of times
and the average measured time for each marker means
is used to calculate the correction factors.
5. A method according to any foregoing claim wherein a
correction factor is calculated for each of a
plurality of ranges of position of the crankshaft.
6. A method according to claim 5 wherein each of said
ranges of position corresponds to a region of the
rotatable member between a respective adjacent pair
of marker means being in said predetermined position.
7. A method according to any foregoing claim wherein
the correction factors are stored in memory such
that they can be updated by repeating the
measurements.
8. A method according to claim 7 further comprising the
step of updating at least one of the stored
correction factors using a newly measured correction
factor.
9. A method according to claim 8 further comprising the
step of comparing a newly calculated correction
factor with one already stored in memory and
rejecting the newly calculated correction factor if
it differs from the stored one by more than a
predetermined amount.
10. A method according to claim 8 or claim 9 wherein the
updating is effected by replacing the stored
correction factor by a value between the stored
correction factor and the newly calculated
correction factor.
11. A method according to any foregoing claim further
comprising the step of checking for engine misfire
to avoia the use of measurements made when the
engine is misfiring.
12. A method according to any foregoing claim wherein
the step of calculating the expected times includes
an adjustment for the rate of change of speed of
rotation of the crankshaft as indicated by the
measured times.
13. A method substantially as hereinbefore described
with reference to the accompanying drawings.
14 Apparatus for controlling an engine comprising
a plurality of angularly spaced marker means at or
close to respective notional positions on a member
rotatable with the crankshaft,
timing means for measuring the times at which the
marker means pass a predetermined position as the
crankshaft rotates,
control means arranged to calculate expected times,
corresponding to the measured times, from the
notional positions of the marker means, and
calculate from the measured and expected times
correction factors to be used in calculations
involving the positions of the marker means.
15. Apparatus according to claim 14 wherein the control
means is arranged to check the rate of change of the
speed of rotation of the crankshaft and to prevent
the use of measurements made when said rate of
change is greater than a predetermined value.
16. Apparatus according to claim 14 or claim 15 wherein
the control means is arranged to check operating
parameters of the engine and to prevent the use of
measurements taken when the engine is operating
outside a predetermined range of those parameters.
17. Apparatus according to any one of claims 14 to 16
wherein the control means is arranged to repeat the
time measurements a number of times and use the
average measured time for each marker means to
calculate the correction factors.
18. Apparatus according to any one of claims 14 to 17
wherein a correction factors is calculated for each
of a plurality of ranges of position of the
crankshaft.
19. Apparatus according to claim 18 wherein each of said
ranges of position corresponds to a region of the
rotatable member between a respective adjacent pair
of marker means being in said predetermined position.
20. Apparatus according to any one of claims 14 to 19
wherein the control means is arranged to store the
correction factors in memory such that they can be
updated by repeating the measurements.
21. Apparatus according to claim 20 wherein the control
means is arranged to update at least one of the
stored correction factors using a newly measured
correction factor.
22. Apparatus according to claim 21 wherein the control
means is arranged to compare a newly calculated
correction factor with one already stored in memory
and reject the newly calculated correction factor if
it differs from the stored one by more than a
predetermined amount.
23. Apparatus according to claim 21 or claim 22 wherein
the control means is arranged to effect the updating
by replacing the stored correction factor by a value
between the stored correction factor and the newly
calculated correction factor.
24. Apparatus according to any one of claims 14 to 23
wherein the control means is arranged to check for
engine misfire and to avoid the use of measurements
made when the engine is misfiring.
25. Apparatus according to any one of claims 14 to 24
wherein the control means is arranged such that the
step of calculating the expected times includes an
adjustment for the rate of change of speed of
rotation of the crankshaft as indicated by the
measured times.
26. Apparatus substantially as hereinbefore described
with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9315758A GB2281624A (en) | 1993-07-30 | 1993-07-30 | Engine crankshaft position determination |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9315758A GB2281624A (en) | 1993-07-30 | 1993-07-30 | Engine crankshaft position determination |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9315758D0 GB9315758D0 (en) | 1993-09-15 |
| GB2281624A true GB2281624A (en) | 1995-03-08 |
Family
ID=10739671
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9315758A Withdrawn GB2281624A (en) | 1993-07-30 | 1993-07-30 | Engine crankshaft position determination |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2281624A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2073020A1 (en) * | 2007-12-21 | 2009-06-24 | Weston Aerospace Limited | Method and apparatus for monitoring the rotational speed of the shaft of a gas turbine |
| US7840370B2 (en) | 2007-12-21 | 2010-11-23 | Weston Aerospace Limited | Method and apparatus for monitoring the rotational speed of shaft |
| US8229646B2 (en) | 2007-12-21 | 2012-07-24 | Weston Aerospace Limited | Method and apparatus for monitoring gas turbine blades |
| US20130144550A1 (en) * | 2011-12-01 | 2013-06-06 | Qualcomm Incorporated | Mitigating the effect of a change in sensor calibration parameters |
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| GB2006481A (en) * | 1977-10-24 | 1979-05-02 | Philips Nv | Tachometer system |
| US4593193A (en) * | 1983-05-31 | 1986-06-03 | Rca Corporation | Apparatus and method for generating calibrated optical encoder pulses |
| US4631520A (en) * | 1984-06-08 | 1986-12-23 | Dynamics Research Corporation | Position encoder compensation system |
| GB2184305A (en) * | 1985-12-12 | 1987-06-17 | Gen Electric | Propeller speed and phase sensor |
| GB2198241A (en) * | 1986-11-07 | 1988-06-08 | Diesel Kiki Co | Spacing time measuring apparatus and method for revolution sensor |
| US4803354A (en) * | 1986-04-09 | 1989-02-07 | Hitachi Medical Corp. | Circuit for correcting output phase of rotary encoder |
| EP0310823A2 (en) * | 1987-10-01 | 1989-04-12 | Motorola Inc. | Synchronous angle counter |
-
1993
- 1993-07-30 GB GB9315758A patent/GB2281624A/en not_active Withdrawn
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2006481A (en) * | 1977-10-24 | 1979-05-02 | Philips Nv | Tachometer system |
| US4593193A (en) * | 1983-05-31 | 1986-06-03 | Rca Corporation | Apparatus and method for generating calibrated optical encoder pulses |
| US4631520A (en) * | 1984-06-08 | 1986-12-23 | Dynamics Research Corporation | Position encoder compensation system |
| GB2184305A (en) * | 1985-12-12 | 1987-06-17 | Gen Electric | Propeller speed and phase sensor |
| US4803354A (en) * | 1986-04-09 | 1989-02-07 | Hitachi Medical Corp. | Circuit for correcting output phase of rotary encoder |
| GB2198241A (en) * | 1986-11-07 | 1988-06-08 | Diesel Kiki Co | Spacing time measuring apparatus and method for revolution sensor |
| EP0310823A2 (en) * | 1987-10-01 | 1989-04-12 | Motorola Inc. | Synchronous angle counter |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2073020A1 (en) * | 2007-12-21 | 2009-06-24 | Weston Aerospace Limited | Method and apparatus for monitoring the rotational speed of the shaft of a gas turbine |
| US7840370B2 (en) | 2007-12-21 | 2010-11-23 | Weston Aerospace Limited | Method and apparatus for monitoring the rotational speed of shaft |
| US7856337B2 (en) | 2007-12-21 | 2010-12-21 | Weston Aerospace Limited | Method and apparatus for monitoring the rotational speed of the shaft of a gas turbine |
| US8229646B2 (en) | 2007-12-21 | 2012-07-24 | Weston Aerospace Limited | Method and apparatus for monitoring gas turbine blades |
| US20130144550A1 (en) * | 2011-12-01 | 2013-06-06 | Qualcomm Incorporated | Mitigating the effect of a change in sensor calibration parameters |
| WO2013082127A1 (en) * | 2011-12-01 | 2013-06-06 | Qualcomm Incorporated | Mitigating the effect of a change in sensor calibration parameters |
| CN103959072A (en) * | 2011-12-01 | 2014-07-30 | 高通股份有限公司 | Mitigating the effect of a change in sensor calibration parameters |
| JP2015510578A (en) * | 2011-12-01 | 2015-04-09 | クアルコム，インコーポレイテッド | Mitigating the effects of changes in sensor calibration parameters |
| US9625490B2 (en) * | 2011-12-01 | 2017-04-18 | Qualcomm Incorporated | Mitigating the effect of a change in sensor calibration parameters |
| CN103959072B (en) * | 2011-12-01 | 2017-06-30 | 高通股份有限公司 | Mitigate the effect of the change of pick up calibration parameter |
| KR101760780B1 (en) * | 2011-12-01 | 2017-08-04 | 퀄컴 인코포레이티드 | Mitigating the effect of a change in sensor calibration parameters |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9315758D0 (en) | 1993-09-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |
