WO2004079385A1 - Hall effect sensor - Google Patents

Hall effect sensor Download PDF

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Publication number
WO2004079385A1
WO2004079385A1 PCT/IB2004/000637 IB2004000637W WO2004079385A1 WO 2004079385 A1 WO2004079385 A1 WO 2004079385A1 IB 2004000637 W IB2004000637 W IB 2004000637W WO 2004079385 A1 WO2004079385 A1 WO 2004079385A1
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WO
WIPO (PCT)
Prior art keywords
gear wheel
monitoring
sensor
toothed gear
tooth
Prior art date
Application number
PCT/IB2004/000637
Other languages
French (fr)
Inventor
Vincent Hiligsmann
Original Assignee
Melexis Nv
Priority date (The priority date 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 date listed.)
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Publication date
Application filed by Melexis Nv filed Critical Melexis Nv
Priority to EP04718356.1A priority Critical patent/EP1604219B1/en
Publication of WO2004079385A1 publication Critical patent/WO2004079385A1/en

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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
    • 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
    • G01D5/24471—Error correction
    • G01D5/2448—Correction of gain, threshold, offset or phase control
    • 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
    • G01D5/14—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 the magnitude of a current or voltage
    • G01D5/142—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 the magnitude of a current or voltage using Hall-effect devices
    • G01D5/147—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 the magnitude of a current or voltage using Hall-effect devices influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/07—Hall effect devices

Definitions

  • the present invention relates mainly to a Hall effect sensor and in particular for a Hall effect sensor used for monitoring the position of ferrous gear wheels.
  • a Hall effect sensor can be used to detect the presence or absence of a tooth on a gear wheel. This is achieved by placing a Hall element between a biasing magnet and the gear wheel to measure variations in magnetic flux as the gear wheel turns.
  • the output of the Hall element is input to a processing means which compares the output of the Hall element to a set of threshold parameters and thus outputs a binary signal indicative of the presence or absence of a tooth.
  • threshold parameters There are typically a pair of threshold parameters: a rising signal becoming greater than the first threshold parameter indicating the presence of a tooth; and a falling signal dropping below the second threshold parameter indicating the absence of a tooth or vice-versa dependant on the relative orientation of the magnet and the Hall sensor.
  • Such sensors are often used to monitor the position of the CAM and crankshafts in a modern gasoline or diesel internal combustion engine.
  • the performance requirements demanded of such a sensor in automotive applications are dictated by the timing accuracy and repeatability needed to ensure that the emissions generated by the engine are within legal limits.
  • a further requirement for automotive applications is that of accommodating variations in mechanical tolerance. Such variations include changes in effective diameter of the gear wheel caused by temperature or manufacturing tolerance, and tooth to tooth variation caused by mechanical or material variations. Additionally variations can be caused by drift in the voltage supplied to the sensor by the engines battery.
  • Hall sensors use averaging techniques to determine the average variation in flux between teeth and thus calculate a best fit pair of threshold parameters and track long term variations in these parameters. Such systems are limited since the best fit pair of threshold parameters may not be optimal for a large percentage of the teeth on the gear wheel.
  • a method of monitoring a toothed gear wheel comprising the steps of: positioning a Hall element adjacent to the gear wheel to detect variations in magnetic flux as the gear wheel rotates; comparing the output of the Hall element to a set of threshold parameters and thus outputting a binary signal indicative of the presence or absence of a tooth, wherein different threshold parameters are provided for different teeth.
  • This method allows account to be taken of variation between teeth thus allowing for more accurate tracking of the gear wheel position.
  • a biasing magnetic flux is provided.
  • the biasing flux may be provided by permanent or temporary magnetisation of the gear wheel or by the provision of a permanent magnet or electromagnet on the opposite side of the Hall element to the gear wheel.
  • the different threshold parameters provided for each tooth are individual pairs of threshold parameters and most preferably, each pair of individual threshold parameters is optimised.
  • the output of the Hall element is compared to the threshold parameters by a processing means and most preferably, the processing means monitors the output change of the Hall element associated with each individual tooth over time and uses long term averaging to calculate optimised threshold parameter pairs for each individual tooth.
  • the processing means recalculates optimised threshold parameter pairs for each individual tooth subsequent to each time that particular tooth is detected. This recalculation compensates for inaccuracies caused by temperature variation or long term drift.
  • the senor contains a set of stored threshold parameter pairs allowing detection of teeth to commence as soon as the sensor is switched on.
  • a set of stored threshold parameter pairs may comprise a single pair of threshold parameters or may alternatively comprise a number of threshold parameter pairs.
  • the stored parameter pairs may be a standard stored set of parameters, used each time the sensor is switched on or they may be the optimised individual parameter pairs in use the last time the sensor was switched off.
  • the sensor may have a multiple modes and may select one particular stored set of threshold parameters from a number of stored sets of threshold parameters when it is in a particular mode.
  • the optimised individual threshold parameters are stored as deviations from the standard stored set of parameters. Deviations from a stored threshold are preferably stored digitally and are converted to an analogue voltage when applied to the stored threshold parameters. As the maximum size of a deviation is likely to be smaller in value than the threshold parameter itself, this reduces the amount of data storage space required for variations in the threshold parameter pairs and additionally allows conversion between analogue threshold parameters and their stored digital equivalents to run more quickly. Furthermore, if there is a data storage failure, only the deviations from the stored threshold parameters are lost. This allows monitoring to continue, if less accurately, until either the sensor is able to recalculate optimised parameters or until the sensor is repaired or replaced. /
  • the processing means In order that the processing means is able to use the correct individual threshold parameters for each tooth, it should either be provided with information indicating the number of teeth on a particular gear wheel or alternatively it should be operative to be able to calculate the number of gear teeth on a given gear wheel 5 by analysing the output of the Hall element for repeating patterns.
  • the sensor selects a reference tooth to enable synchronisation of the individual threshold parameters with the teeth on the gear wheel.
  • the sensor is able to synchronise the individual threshold parameters with a gear wheel having fewer teeth than the maximum number of threshold parameters that the 10 sensor can store.
  • the senor is adapted to operate in accordance with the method of the first aspect of the present invention and the sensor may incorporate any or 20 all of the features described in relation to the first aspect of the invention as appropriate.
  • the processing means and the data storage means are incorporated in a single integrated circuit and most preferably the Hall element is additionally incorporated in a single integrated circuit with the processing means and the data storage means.
  • the senor may be connected to an engine controller and used to monitor the position of a gear wheel in an engine.
  • the sensor is adapted to output information related to the position of the gear wheel to the engine controller and is additionally adapted to receive control signals from the engine controller.
  • the sensor may automatically offset one or more individual threshold parameters by a particular value or the sensor may switch from one mode to another mode.
  • Figure 1 shows a Hall sensor according to the present invention in use to monitor the position of a gear wheel and a plot representing the output of the Hall sensor and the variation in magnetic flux density as the gear wheel turns;
  • FIG. 2 is a block diagram showing the components of the Hall sensor of figure 1.
  • a Hall sensor 102 is placed between a magnet 104 and a ferrous gear wheel 106.
  • the gear wheel 106 is turning in a clockwise direction, as it turns a succession of teeth 108 pass close to the Hall sensor 102.
  • the flux emanating from the magnet 104 will become attracted to the lower reluctance path provided by the ferrous gear tooth 108 and thus the magnetic flux density in the vicinity of the Hall sensor 102 increases.
  • Changes in the effective diameter of the gear wheel 106 or other mechanical or material variations between the individual teeth 108 mean that the peaks in line 110 are not constant from tooth to tooth.
  • the size of the peaks or at least the relative size of the peaks associated with adjacent teeth 108 should however vary little with each subsequent rotation.
  • the Hall sensor 102 is embodied by a single integrated circuit and comprises a Hall element 202, a processing means 204, and a data storage means 206.
  • the Hall element 202 generates a voltage in response to and proportional to the local magnetic flux density, this voltage is input to the processing means 204.
  • the processing means 204 monitors the output of the Hall element 202 and compares the output to a set of individual threshold parameter pairs for each tooth 108 stored in the data storage means 206.
  • the output of Hall element 202 rises above the first threshold parameter of a threshold parameter pair, the output of the processing means 204 becomes high.
  • the output of the processing means 204 becomes low.
  • the processing means then proceeds to compare the output of the hall element 202 to the first threshold parameter of the threshold parameter pair associated with the next tooth 108.
  • the output of the processing means 204 is thus a binary signal, being high when a tooth 108 is adjacent to the Hall element 202 and low otherwise as illustrated by line 112 in figure 1.
  • the output of the processing means 204 may be monitored by external circuitry (not shown) and means are provided for connecting the output of the processing means to further circuitry (not shown). In particular, by monitoring the frequency at which the output of the processing means 204 switches, the speed of rotation of the gear wheel 106 can be calculated. In addition, if the starting orientation of the gear wheel 106 is known, the instantaneous orientation of gear wheel 106 can be calculated.
  • Values for the first and second threshold parameters are stored in the data storage means 206 wherein there are individual first and second threshold parameters stored for each individual tooth 108.
  • the threshold parameter pairs stored for each individual tooth 108 are optimised. This is achieved by taking a long term average of the value of the output of the Hall element associated with each individual tooth and thus calculating appropriate values for the individual first and second threshold parameters. The long term average value is recalculated subsequent to each detection of the particular tooth by the processing means 204.
  • the optimised threshold parameters are stored as deviations from a standard stored pair of threshold parameters.
  • the calculated deviations are stored as digital values in the data storage means 206 and are subsequently converted to analogue values and applied to the analogue voltages of the standard stored parameter pair when the particular tooth corresponding to the particular deviation is to be detected.
  • the processing means 204 When the sensor is first turned on, the processing means 204 is able to use the stored standard pair of threshold parameters to begin detection of teeth immediately. Once detection of teeth 108 has begun, the processing means 204 begins to calculate optimised individual threshold parameters for each tooth 108. It is possible, if desired, to provide more than one stored pair of threshold parameters and the sensor can then select a particular pair of stored threshold parameters to use when beginning detection of teeth 108.
  • the processing means 204 first selects an individual tooth 108 to be a reference tooth.
  • the processing means 204 to synchronise the individual optimised threshold parameter pairs with the gear teeth 108. If alternatively, the number of teeth on a gear wheel is not known, the processing means 204 first monitors the output of the Hall element 202 to detect patterns and to thus determine how many teeth 108 gear wheel 106 has. The processing means 204 then selects a reference tooth as described above. The processing means 204 is thus able to synchronise the individual optimised threshold parameter pairs with the gear teeth 108 even if the number of teeth 108 is less than the maximum number of threshold parameter pairs that can be stored.
  • Means are provided to allow signals to be input to the processing means
  • Input signals may inform the sensor of the number of teeth on a particular gear wheel, may cause the sensor to adjust the stored deviation for one or more individual parameters, or in particular may be used to switch the sensor from one mode to another mode.
  • the sensor described above is suitable for use in conjunction with an engine controller for monitoring the position of a gear wheel within an engine.
  • the engine controller may send signals to the sensor causing the sensor to alter its mode, its threshold parameters or the number of teeth on a gear wheel it is trying to detect. Additionally the engine controller may act to change the mode of the sensor, adjust the operation of the engine or output an alarm in response to signals received from the sensor.

Abstract

The invention provides an improved method of monitoring a toothed gear wheel comprising the steps of: positioning a Hall element (202) adjacent to the gear wheel (106) to detect variations in magnetic flux (110) as the gear wheel (106) rotates; comparing the output of the Hall element (202) to a set of threshold parameters and thus outputting a binary signal (112) indicative of the presence or absence of a tooth (108), wherein different threshold parameters are provided for different teeth (108). The invention further provides an apparatus (102) suitable for carrying out the above method comprising a Hall element (202), placed between a magnet (104) and a gear wheel (106) to detect variations in magnetic flux (110) as the gear wheel (106) rotates; a processing means (204), for comparing the output of the Hall element (202) to a set of threshold parameters and thus outputting a binary signal (112) indicative of the presence or absence of a tooth (108); and a data storage means (206) for storing a set of threshold parameters for each individual tooth (108).

Description

HALL EFFECT SENSOR
The present invention relates mainly to a Hall effect sensor and in particular for a Hall effect sensor used for monitoring the position of ferrous gear wheels.
A Hall effect sensor can be used to detect the presence or absence of a tooth on a gear wheel. This is achieved by placing a Hall element between a biasing magnet and the gear wheel to measure variations in magnetic flux as the gear wheel turns. The output of the Hall element is input to a processing means which compares the output of the Hall element to a set of threshold parameters and thus outputs a binary signal indicative of the presence or absence of a tooth. There are typically a pair of threshold parameters: a rising signal becoming greater than the first threshold parameter indicating the presence of a tooth; and a falling signal dropping below the second threshold parameter indicating the absence of a tooth or vice-versa dependant on the relative orientation of the magnet and the Hall sensor.
Such sensors are often used to monitor the position of the CAM and crankshafts in a modern gasoline or diesel internal combustion engine. The performance requirements demanded of such a sensor in automotive applications are dictated by the timing accuracy and repeatability needed to ensure that the emissions generated by the engine are within legal limits. A further requirement for automotive applications is that of accommodating variations in mechanical tolerance. Such variations include changes in effective diameter of the gear wheel caused by temperature or manufacturing tolerance, and tooth to tooth variation caused by mechanical or material variations. Additionally variations can be caused by drift in the voltage supplied to the sensor by the engines battery.
To achieve the necessary accuracy known Hall sensors use averaging techniques to determine the average variation in flux between teeth and thus calculate a best fit pair of threshold parameters and track long term variations in these parameters. Such systems are limited since the best fit pair of threshold parameters may not be optimal for a large percentage of the teeth on the gear wheel.
It is therefore an object of the present invention to provide an improved Hall effect sensor.
According to a first aspect of the present invention there is provided a method of monitoring a toothed gear wheel comprising the steps of: positioning a Hall element adjacent to the gear wheel to detect variations in magnetic flux as the gear wheel rotates; comparing the output of the Hall element to a set of threshold parameters and thus outputting a binary signal indicative of the presence or absence of a tooth, wherein different threshold parameters are provided for different teeth. This method allows account to be taken of variation between teeth thus allowing for more accurate tracking of the gear wheel position.
Preferably, to increase the magnetic flux variation measured by the Hall element, a biasing magnetic flux is provided. The biasing flux may be provided by permanent or temporary magnetisation of the gear wheel or by the provision of a permanent magnet or electromagnet on the opposite side of the Hall element to the gear wheel.
Preferably, the different threshold parameters provided for each tooth are individual pairs of threshold parameters and most preferably, each pair of individual threshold parameters is optimised.
Preferably, the output of the Hall element is compared to the threshold parameters by a processing means and most preferably, the processing means monitors the output change of the Hall element associated with each individual tooth over time and uses long term averaging to calculate optimised threshold parameter pairs for each individual tooth. Advantageously, the processing means recalculates optimised threshold parameter pairs for each individual tooth subsequent to each time that particular tooth is detected. This recalculation compensates for inaccuracies caused by temperature variation or long term drift.
Preferably, the sensor contains a set of stored threshold parameter pairs allowing detection of teeth to commence as soon as the sensor is switched on. A set of stored threshold parameter pairs may comprise a single pair of threshold parameters or may alternatively comprise a number of threshold parameter pairs.
The stored parameter pairs may be a standard stored set of parameters, used each time the sensor is switched on or they may be the optimised individual parameter pairs in use the last time the sensor was switched off. Alternatively, the sensor may have a multiple modes and may select one particular stored set of threshold parameters from a number of stored sets of threshold parameters when it is in a particular mode.
Preferably, the optimised individual threshold parameters are stored as deviations from the standard stored set of parameters. Deviations from a stored threshold are preferably stored digitally and are converted to an analogue voltage when applied to the stored threshold parameters. As the maximum size of a deviation is likely to be smaller in value than the threshold parameter itself, this reduces the amount of data storage space required for variations in the threshold parameter pairs and additionally allows conversion between analogue threshold parameters and their stored digital equivalents to run more quickly. Furthermore, if there is a data storage failure, only the deviations from the stored threshold parameters are lost. This allows monitoring to continue, if less accurately, until either the sensor is able to recalculate optimised parameters or until the sensor is repaired or replaced. /
In order that the processing means is able to use the correct individual threshold parameters for each tooth, it should either be provided with information indicating the number of teeth on a particular gear wheel or alternatively it should be operative to be able to calculate the number of gear teeth on a given gear wheel 5 by analysing the output of the Hall element for repeating patterns. Preferably, the sensor selects a reference tooth to enable synchronisation of the individual threshold parameters with the teeth on the gear wheel. Most preferably, the sensor is able to synchronise the individual threshold parameters with a gear wheel having fewer teeth than the maximum number of threshold parameters that the 10 sensor can store.
According to a second aspect of the present invention there is provided a Hall sensor for monitoring the rotation of a gear wheel comprising: a Hall element, placed between a magnet and a gear wheel to detect variations in magnetic flux as the gear wheel rotates; a processing means, for comparing the 15 output of the Hall element to a set of threshold parameters and thus outputting a binary signal indicative of the presence or absence of a tooth; and a data storage means for storing a set of threshold parameters for each individual tooth.
Preferably, the sensor is adapted to operate in accordance with the method of the first aspect of the present invention and the sensor may incorporate any or 20 all of the features described in relation to the first aspect of the invention as appropriate. Preferably, the processing means and the data storage means are incorporated in a single integrated circuit and most preferably the Hall element is additionally incorporated in a single integrated circuit with the processing means and the data storage means.
Preferably, the sensor may be connected to an engine controller and used to monitor the position of a gear wheel in an engine. Most preferably, the sensor is adapted to output information related to the position of the gear wheel to the engine controller and is additionally adapted to receive control signals from the engine controller. Typically in response to control signals received from the engine controller the sensor may automatically offset one or more individual threshold parameters by a particular value or the sensor may switch from one mode to another mode.
In order that the invention be more clearly understood, one embodiment is now described further by way of example only and with reference to the following drawings, in which: -
Figure 1 shows a Hall sensor according to the present invention in use to monitor the position of a gear wheel and a plot representing the output of the Hall sensor and the variation in magnetic flux density as the gear wheel turns; and
Figure 2 is a block diagram showing the components of the Hall sensor of figure 1. Referring to Figure 1, a Hall sensor 102 is placed between a magnet 104 and a ferrous gear wheel 106. The gear wheel 106 is turning in a clockwise direction, as it turns a succession of teeth 108 pass close to the Hall sensor 102. As a tooth 108 passes close to the Hall sensor, the flux emanating from the magnet 104 will become attracted to the lower reluctance path provided by the ferrous gear tooth 108 and thus the magnetic flux density in the vicinity of the Hall sensor 102 increases. When the wheel is turning, this leads to a periodic variation in the magnetic flux which is shown in figure 1 as line 110. Changes in the effective diameter of the gear wheel 106 or other mechanical or material variations between the individual teeth 108 mean that the peaks in line 110 are not constant from tooth to tooth. The size of the peaks or at least the relative size of the peaks associated with adjacent teeth 108 should however vary little with each subsequent rotation.
Referring to the block diagram Figure 2, the Hall sensor 102 is embodied by a single integrated circuit and comprises a Hall element 202, a processing means 204, and a data storage means 206. The Hall element 202 generates a voltage in response to and proportional to the local magnetic flux density, this voltage is input to the processing means 204. The processing means 204 monitors the output of the Hall element 202 and compares the output to a set of individual threshold parameter pairs for each tooth 108 stored in the data storage means 206.
When the output of Hall element 202 rises above the first threshold parameter of a threshold parameter pair, the output of the processing means 204 becomes high. When the output of the Hall element 202 subsequently drops below the second threshold parameter of the second parameter pair, the output of the processing means 204 becomes low. The processing means then proceeds to compare the output of the hall element 202 to the first threshold parameter of the threshold parameter pair associated with the next tooth 108. The output of the processing means 204 is thus a binary signal, being high when a tooth 108 is adjacent to the Hall element 202 and low otherwise as illustrated by line 112 in figure 1.
The output of the processing means 204 may be monitored by external circuitry (not shown) and means are provided for connecting the output of the processing means to further circuitry (not shown). In particular, by monitoring the frequency at which the output of the processing means 204 switches, the speed of rotation of the gear wheel 106 can be calculated. In addition, if the starting orientation of the gear wheel 106 is known, the instantaneous orientation of gear wheel 106 can be calculated.
Values for the first and second threshold parameters are stored in the data storage means 206 wherein there are individual first and second threshold parameters stored for each individual tooth 108.
The threshold parameter pairs stored for each individual tooth 108 are optimised. This is achieved by taking a long term average of the value of the output of the Hall element associated with each individual tooth and thus calculating appropriate values for the individual first and second threshold parameters. The long term average value is recalculated subsequent to each detection of the particular tooth by the processing means 204.
The optimised threshold parameters are stored as deviations from a standard stored pair of threshold parameters. The calculated deviations are stored as digital values in the data storage means 206 and are subsequently converted to analogue values and applied to the analogue voltages of the standard stored parameter pair when the particular tooth corresponding to the particular deviation is to be detected.
When the sensor is first turned on, the processing means 204 is able to use the stored standard pair of threshold parameters to begin detection of teeth immediately. Once detection of teeth 108 has begun, the processing means 204 begins to calculate optimised individual threshold parameters for each tooth 108. It is possible, if desired, to provide more than one stored pair of threshold parameters and the sensor can then select a particular pair of stored threshold parameters to use when beginning detection of teeth 108.
If the number of teeth a gear wheel has is known to the sensor, the processing means 204 first selects an individual tooth 108 to be a reference tooth.
This enables the processing means 204 to synchronise the individual optimised threshold parameter pairs with the gear teeth 108. If alternatively, the number of teeth on a gear wheel is not known, the processing means 204 first monitors the output of the Hall element 202 to detect patterns and to thus determine how many teeth 108 gear wheel 106 has. The processing means 204 then selects a reference tooth as described above. The processing means 204 is thus able to synchronise the individual optimised threshold parameter pairs with the gear teeth 108 even if the number of teeth 108 is less than the maximum number of threshold parameter pairs that can be stored.
Means are provided to allow signals to be input to the processing means
(not shown) by external circuitry. Input signals may inform the sensor of the number of teeth on a particular gear wheel, may cause the sensor to adjust the stored deviation for one or more individual parameters, or in particular may be used to switch the sensor from one mode to another mode.
The sensor described above is suitable for use in conjunction with an engine controller for monitoring the position of a gear wheel within an engine. The engine controller may send signals to the sensor causing the sensor to alter its mode, its threshold parameters or the number of teeth on a gear wheel it is trying to detect. Additionally the engine controller may act to change the mode of the sensor, adjust the operation of the engine or output an alarm in response to signals received from the sensor.
It is of course to be understood that the invention is not to be restricted to the details of the above embodiment which is described by way of example only.

Claims

1. A method of monitoring a toothed gear wheel comprising the steps of: positioning a Hall element adjacent to the gear wheel to detect variations in magnetic flux as the gear wheel rotates; comparing the output of the Hall element to a set of threshold parameters and thus outputting a binary signal indicative of the presence or absence of a tooth, wherein different threshold parameters are provided for different teeth.
2. A method of monitoring a toothed gear wheel as claimed in claim 1 wherein to increase the magnetic flux variation measured by the Hall element, a biasing magnetic flux is provided.
3. A method of monitoring a toothed gear wheel as claimed in claim 2 wherein the biasing flux is provided by permanent magnetisation of the gear wheel.
4. A method of monitoring a toothed gear wheel as claimed in claim 2 wherein the biasing flux is provided by temporary magnetisation of the gear wheel.
5. A method of monitoring a toothed gear wheel as claimed in claim 2 wherein the biasing flux is provided by a permanent magnet on the opposite side of the Hall element to the gear wheel.
6. A method of monitoring a toothed gear wheel as claimed in claim 2 wherein the biasing flux is provided by an electromagnet on the opposite side of the Hall element to the gear wheel.
7. A method of monitoring a toothed gear wheel as claimed in any preceding claim wherein the different threshold parameters provided for each tooth are individual pairs of threshold parameters.
8. A method of monitoring a toothed gear wheel as claimed in claim 7 wherein each individual pair of threshold parameters is optimised.
9. A method of monitoring a toothed gear wheel as claimed in claim 7 or claim 8 wherein the output of the Hall element is compared to the threshold parameters by a processing means.
10. A method of monitoring a toothed gear wheel as claimed in claim 9 wherein the processing means monitors the output change of the Hall element associated with each individual tooth over time and uses long term averaging to calculate optimised threshold parameter pairs for each individual tooth.
11. A method of monitoring a toothed gear wheel as claimed in claim 9 or claim 10 wherein the processing means recalculates optimised threshold parameter pairs for each individual tooth subsequent to each time that particular tooth is detected.
12. A method of monitoring a toothed gear wheel as claimed in any one of claims 7 to 11 wherein the sensor contains a set of stored threshold parameter pairs allowing detection of teeth to commence as soon as the sensor is switched on.
13. A method of monitoring a toothed gear wheel as claimed in claim 12 wherein the set of stored threshold parameter pairs comprises a single pair of threshold parameters.
14. A method of monitoring a toothed gear wheel as claimed in claim 12 wherein the set of stored threshold parameter pairs comprises a number of threshold parameter pairs.
15. A method of monitoring a toothed gear wheel as claimed in claim 13 or claim 14 wherein the stored parameter pairs are a standard stored set of parameters, used each time the sensor is switched on.
16. A method of monitoring a toothed gear wheel as claimed in claim 13 or claim 14 wherein the stored parameter pairs are the optimised individual parameter pairs in use the last time the sensor was switched off.
17. A method of monitoring a toothed gear wheel as claimed in claim 13 or claim 14 wherein the sensor has multiple modes and selects one particular stored set of threshold parameters from a number of stored sets of threshold parameters when it is in a particular mode.
18. A method of monitoring a toothed gear wheel as claimed in any one of claims 12 to 17 wherein the optimised individual threshold parameters are stored as deviations from the standard stored set of parameters.
19. A method of monitoring a toothed gear wheel as claimed in claim 18 wherein the deviations from a stored threshold are stored digitally and are converted to an analogue voltage when applied to the stored threshold parameters.
20. A method of monitoring a toothed gear wheel as claimed in any one of claims 9 to 19 wherein in order that the processing means is able to use the correct individual threshold parameter pairs for each tooth, it is provided with information indicating the number of teeth on a particular gear wheel.
21. A method of monitoring a toothed gear wheel as claimed in any one of claims 9 to 19 wherein in order that the processing means is able to use the correct individual threshold parameter pairs for each tooth, it is operative to calculate the number of gear teeth on a given gear wheel by analysing the output of the Hall element for repeating patterns.
22. A method of monitoring a toothed gear wheel as claimed in claim 21 wherein in order to analyse the output of the Hall element for repeating patterns the sensor selects a reference tooth to enable synchronisation of the individual threshold parameter pairs with the teeth on the gear wheel.
23. A method of monitoring a toothed gear wheel as claimed in any preceding claim wherein the sensor is able to synchronise the individual threshold parameter pairs with a gear wheel having fewer teeth than the maximum number of threshold parameters that the sensor can store.
24. A Hall sensor for monitoring a toothed gear wheel comprising: a Hall element, placed between a magnet and a gear wheel to detect variations in magnetic flux as the gear wheel rotates; a processing means, for comparing the output of the Hall element to a set of threshold parameters and thus outputting a binary signal indicative of the presence or absence of a tooth; and a data storage means for storing a set of threshold parameters for each individual tooth.
25. A Hall sensor as claimed in claim 24 wherein the processing means and the data storage means are incorporated in a single integrated circuit.
26. A Hall sensor as claimed in claim 25 wherein Hall element is incorporated in a single integrated circuit with the processing means and the data storage means.
27. A Hall sensor as claimed in any one of claims 24 to 26 wherein the sensor is connected to an engine controller and used to monitor the position of a gear wheel in an engine.
28. A Hall sensor as claimed in claim 27 wherein the sensor is adapted to output information related to the position of the gear wheel to the engine controller.
29. A Hall sensor as claimed in claim 27 or claim 28 wherein the sensor is adapted to receive control signals from the engine controller.
30. A Hall sensor as claimed in claim 29 wherein in response to control signals received from the engine controller the sensor automatically offsets one or more individual threshold parameters by a particular value.
31. A Hall sensor as claimed in claim 29 or claim 30 wherein in response to control signals received from the engine controller the sensor switches from one mode to another mode.
2. A Hall sensor as claimed in any one of claims 24 to 31 operating in accordance with the method of any one of claims 1 to 23.
PCT/IB2004/000637 2003-03-08 2004-03-08 Hall effect sensor WO2004079385A1 (en)

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