GB1563176A - Hall effect position sensor magnetic circuit - Google Patents

Description

(54) HALL EFFECT POSITION SENSOR MAGNETIC CIRCUIT (71) We, MOTOROLA, INC., a corporation organised and existing under the laws of the State of Delaware, United States of America, of 1303 East Algonquin Road, Schaumburg, Illinois 60196, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention generally relates to internal combustion ignition systems and, more particularly, to an interruptable magnetic circuit for a Hall effect sensing circuit of an ignition system.

A Hall effect device produces an electrical output voltage directly proportional to the vector product of an input current density and an input magnetic flux density. The output voltage of a Hall effect device, called the Hall voltage, may be varied by controlling the flux density passing through such a device.

The apparatus supplying the magnetic flux to the Hall effect element may be thought of as a magnetic circuit comprising various magnetic circuit elements and operating and conforming with well-known magnetic circuit principles.

Application of Hall effect devices to automotive ignition system sensing apparatus requires having a moving ferrous vane which shunts the magnetic flux away from a Hall effect element, thereby providing an interruption in the magnetic flux passing through the Hall effect element and consequently changing the Hall voltage output of said element. The change in the Hall voltage is processed through electrical circuitry which provides the timing signals for the automotive ignition system.

Hall effect sensing circuits have previously been used in ignition systems for internal combustion engines. The timing signals used to control the ignition circuitry of an internal combustion engine are required to be precise. The degree of precision required for said ignition timing signals is determined in a Hall effect sensor system to a large extent by the accuracy with which the flux through the Hall effect element is shunted by the moving ferrous vane. The ferrous vanes are usually mounted on the periphery of a member rotatably mounted on the distributor shaft of an aautomotive distributor apparatus.

The Hall sensing device is mounted so that the vanes may be rotated through the air gaps in said Hall sensing device in synchronism with the distributor shaft providing Hall voltages representative of sensor on and off states.

The amount of flux passing through the air gaps in a Hall effect sensor of the type described above is reduced by fringing flux, which effectively provides an alternative path to the desired magnetic path and thereby reduces the flux density in the air gap and consequently the ratio between the sensor on and off Hall voltage levels.

A further problem encountered in using a Hall effect sensor in a shunt magnetic circuit is that it is difficult to obtain a rapid change of flux as the moving vane enters the air gap. The Hall voltage does not change sharply from an on or off state to the other state. This is due not only to leakage flux but to the fact that the flux passes through an air gap area which has flux distributed along the direction of motion of the vane leading edge. The flux is not shunted immediately by the vane but a certain number of mechanical degrees must be traversed by the vane before the flux through the gap is switched from an on to an off (shunted) condition, and conversely from an offto an on (shunted) condition.

Consequently, the need for an inexpensive, simple magnetic circuit for a Hall effect sensor in an ignition system having high flux density concentrations and fine angular resolution capabilities has been recognised as an important factor in improving the accuracy of automotive ignition systems using Hall effect sensors.

According to one aspect of the present invention there is provided a magnetic circuit, interruptable by a high permeability vane movable in a given direction, for a Hall effect sensing circuit in an ignition system of an internal combustion engine, said circuit comprising: a permanent magnet having a first pole face and a second elongate pole face, the major axis of said second elongate pole face oriented perpendicularly to the direction of the vane movement; a pole piece having a portion to which is affixed the firs pule face of said permanent magnet, said pole piece having an arm extending therefrom in a direction parallel to the direction from said first to said second permanent magnet pole faces, said arm including a portion having a predetermined configuration such that minimal surface area of said arm portion faces said permanent magnet, said arm having an elongate pole face thereon with its major axis oriented perpendicularly to the direction of the vane movement; a flux concentrator having first and second projections extending therefrom, each projection having an elongate face portion with its major axis oriented perpendicularly to the direction of the vane movement, the face portion of the first projection being spaced apart and aligned opposite the pole face of the arm portion of the pole piece and the face portion of the second projection being spaced apart and aligned opposite the second pole face of the permanent magnet, thereby forming air gaps for passage of said vane, the pole face of said arm and the second pole face of the permanent magnet being positioned for simultaneous magnetic shunting by the movement of a leading edge of said vane in said given direction between said air gaps.

According to a further aspect of the invention there is provided a magnetic circuit, interruptable by a high permeability vane moving in a given direction, for a Hall effect sensing circuit in an internal combustion engine ignition circuit comprising: an oblong permanent magnet having a first pole face and a second elongate pole face, said second pole face positioned on a salient portion of said permanent magnet and having its major axis perpendicularly oriented with respect to the given direction of said vane movement; a pole piece formed from a flat plate having a portion to which is affixed the first pole face of said permanent magnet and having a flat arm portion extending therefrom in a direction parallel to the direction from said first to said second permanent magnet pole faces, said flat arm positioned edgewise with respect to the permanent magnet, said flat arm having an elongate pole face on an end thereof, said elongate pole face having its major axis perpendicularly oriented with respect to the given direction of said vane movement; a flux concentrator formed from a flat plate and positioned edgewise with respect to said permanent magnet and said pole piece flat arm, said flux concentrator having first and second projection portions extending therfrom with elongate faces portions thereon oriented with their major axes each perpendicular to the given direction of said vane movement, the elongate face of the first projecting portion being spaced apart and aligned opposite the elongate pole face of the flat arm of said pole piece and the elongate face of the second projecting portion of said flux concentrator being spaced apart and aligned opposite the second pole face of the permanent magnet; said elongate face of the second projecting portion of said flux concentrator having the Hall effect element of said Hall effect sensing circuit positioned adjacent thereto to provide a magnetic flux path through said Hall effect element from said concentrator to said permanent magnet with an air gap for passage of said vane, the pole face of said arm and the second pole face of the permanent magnet being positioned for simultaneous magnetic shunting by the movement of a leading edge of said vane in said given direction between said air gaps.

An embodiment of the invention comprises an improved magnetic circuit, interruptable by a high permeability vane movable in a given direction, for a Hall effect sensing circuit in an ignition system for an internal combustion engine. The magnetic circuit includes a permanent magnet, a pole piece having an extending arm portion, and a flux concentrator spaced apart from said permanent magnet and said pole piece thereby providing an air gap for the passage of said vane. The permanent magnet has a first pole face which is affixed to the pole piece and a second elongated pole face having its major axes oriented perpendicularly to the direction of movement of the reluctor plate. The pole piece arm extends therefrom and includes a portion having a predetermined configuration such that minimal surface area of said arm portion faces said permanent magnet to reduce leakage flux.

Said arm also has a pole face thereon having an elongaged area with its major axes oriented perpendicularly to the direction of the vane movement. The flux concentrator has first and second elongated face portions thereon, each face having its major axes oriented perpendicularly to the direction of the vane movement. One face is aligned opposite the pole face of the arm portion of the pole piece and the other face is aligned opposite the second pole face of the permanent magnet. The permanent magnet may be oblong shaped and have the second elongated pole face positioned on a salient portion of said permanent magnet.

The pole piece may be formed from a flat plate with the arm portion extending therefrom perpendicularly and said arm portion edgewise disposed with respect to the permanent magnet. The flux concentrator may also be formed from a flat plate and be positioned edgewise with respect to said permanent magnet.

The invention will now be described by way of example only with particular reference to the accompanying drawings wherein: Fig. 1 is a perspective view of an automotive ignition system employing a magnetic circuit of the invention for a Hall effect sensor; Fig. 2 is an enlarged, cross-sectional perspective view taken along line 2-2 of Fig.l showing the housing containing a permanent magnet, pole piece, and flux concentrator; Fig. 3 is an enlarged perspective view of the component elements of the circuit of the invention and Fig. 4 is a plan view of the elements of the circuit of the invention together with a diagram relating the mechanical movement of the vane to the flux density in the air gap.

Referring to Fig. 1 of the drawings, an automotive ignition system assembly 10 is shown having a distributor base assembly 11, a distributor cap 12, a distributor rotor assembly 13, and a magnetic circuit housing 14. The distributor base assembly 11 and the distributor cap 12 are well-known in the art and perform the same functions as performed heretofore. Contained within the distributor base assembly 11 is a distributor shaft 15 which is rotatable about an axis in synchronism with various other mechanical components of an automotive engine, as is well-known in the art. A plate 16 is pivotal about the distributor shaft 15 and provides for advancement or retardation of the timing signals of said ignition system.

Mounted on the plate 16 is the magnetic circuit housing 14 which is positioned so that a series of vanes 17 may pass through an air gap 18. The vanes 17 extend downwardly from the peripheral portion of the distributor rotor assembly 13, which is fixed to an end of the distributor shaft 15 and rotates therewith, providing positioning of vanes 17 with respect to the magnetic circuit housing 14 in accordance with a predetermined ignition firing sequence. The vanes 17 are curved, high permeability ferrous plates of rather thin dimensions and serve to provide a shunt path for magnetic flux, as will be described hereinbelow.

Referring now to Fig. 2, the magnetic circuit housing 14 has contained therein the elements of the magnetic circuit according to the present invention. The positioning of the magnetic circuit elements with respect to the housing 14 and the positioning of the housing 14 with respect to the rotaing vane 17 is provided for by the housing.

Fig. 2 and Fig.3 show the elements of the magnetic circuit in greater detail. A permanent magnet 20 may be formed, for example, from a material such as sintered Alnico which provides a magnetic flux of sufficient strength. The permanent magnet 20 has a generally oblong configuration and has a first pole face 21 contained at one end.

At the other end of the permanent magnet 20 is a salient portion 22 having a second pole face 23 contained thereon which has a rectangular shaped area with its major axis extending perpendicularly to a line of motion 24 which indicates the direction of motion of the vane 17 past the permanent magnet second pole face 23. The permanent magnet 20 also has a flat upper surface 25 thereupon.

The permanent magnet 20 closely contacts and is affixed at the first pole face 21 to a flat portion 31 of a pole piece 30 with, for example, a soft solder. The pole piece 30 is preferably formed from a low retentivity, low carbon, cold rolled steel such as ASA 1004, 1006 or 1008 CRS 1/16th inch thick plate. An arm portion 32 is bent away from and perpendicular to the flat portion 31 of the pole pieces 30. The arm portion 32 extends over the upper surface 25 of the permanent magnet and an edge 33 of the arm portion 32 faces the upper surface 25 of the permanent magnet 20 so that minimal surface area of said arm portion 32 faces the permanent magnet 20.This orientation between the arm portion 32 and the permanent magnet 20 tends to reduce leakage flux therebetween providing for greater flux concentration in an upper air gap l8a and a lower air gap 18b of the permanent magnet and pole piece assembly.

The pole piece 30 arm portion 32 has an elongate, rectangularly shaped pole face 34 thereon. The pole piece arm 32 pole face 34 and the permanent magnet second pole face 23 lie in the same plane. The rectangularly shaped pole face 34 of the arm portion 32 also has its major axis oriented perpendicularly to the line of motion 24.

Said pole faces and the vane 17 are oriented such that vanes 17 closely pass the pole faces without touching the pole faces and the magnetic flux produced by the permanent magnet 20 is shunted through the ferrous material of the vane 17 thereby preventing a great deal of magnetic flux from crossing the upper and lower air gaps 18a, l8b.

Also held by the magnetic circuit housing 14 is a flux concentrator 40 which has a first projecting portion 41 and a second projection portion 42 extending therefrom towards respectively the pole piece pole face 34 and the permanent magnet second pole face 23. Each projection respectively has an elongate face portion 43, 44 with its major axis oriented perpendicularly to the line of motion 24 of the vane 17. The face portion 43 of the first projection is positioned opposite the pole face 34 of the arm 32 of the pole piece. The second face 44 of the flux concentrator second projection portion 42 is similarly positioned opposite the second pole face 23 of the permanent magnet 20 thereby forming air gaps 18a, 18b for passage of the vanes 17.When a vane 17 is not positioned in the air gap 18, flux flows from the permanent magnet through the pole piece 30, the flux concentrator 40, and the upper air gap 18a and the lower air gap 18b. When the vane 17 is in the air gap 18, a significantly reduced amount of flux flows through the flux concentrator 40 due to the shunting action of said high permeability vane.

A ceramic circuit board 50 containing varuous circuit elements is positioned within the lower air gap 18b as shown in Fig.

3. Fig. 4 shows the ceramic circuit board 50 in relationship to the line of motion 24 of the vane 17 and to the assembly of the pole piece 30 and the permanent magnet 20. A brass cap 51 affixed to ceramic circuit board 50 allows flux to pass therethrough and provides protection for a Hall effect device contained on an integrated circuit substrate.

The Hall effect device produces an output Hall voltage which is coupled to a signal processing circuit also contained on the integrated circuit substrate. The Hall voltage is directly proportional to the vector product of the current density passing through the Hall effect device and the magnetic flux density passing through the device. As a result, the output Hall voltage will be in either an on state or an off state depending upon whether an unobstructed flux is passing through the Hall effect device 52 or whether the magnetic flux is shunted by the high permeability vanes 17 being positioned within the air gap 18.

Fig. 4 shows a graphical representation of the flux density Bg in the air gap in Gauss as a function of the position in degrees of the vane leading edge 56 within the air gap. As the vane leading edge 56 moves through the air gap 18 in the direction represented by the line of motion 24, a typical prior art curve 60 shows the effects of leakage flux and of having the flux being spread out over a relatively large angular measurement. The rate of change of the flux density per mechanical degree of the prior art curve 60 is significantly less than the rate of change shown in a curve 61 which shows the performance of a magnetic circuit according to the present invention. The rate of change of flux density versus mechanical degrees provided by the present invention is much higher than that of the prior art.

Since the configuration of the present invention magnetic circuit reduces leakage flux, the peak flux density provided by the magnetic circuit of the invention has a value much higher than that provided by the prior art as may be observed from the graph in Fig. 4. Having the flux concentrated in an elongated area with its major dimension perpendicular to the direction of motion 24 of the leading edge 56 of the vanes 17 allows a rapid-change of flux with changes in mechanical position of the leading edge 56 of the vane 17. For the same reasons, as the trailing edge 57 of the vane 17 leaves the air gap 18 a high rate of change of flux density per mechanical degree is also obtained.

It is imprtant that a, high rate of flux density change per mechanical degree change be obtained in an automotive ignition system sensing circuit because the output signal obtained from the processing circuit for the Hall voltage varies due to variations in the input trigger and release voltage level of said processing circuit over a temperature range. The trigger and release points of the processing circuit may vary +100 Gauss over a range of temperatures of -30 to +125 degrees centigrade. in order to provide an ignition firing or release point within one half degree of nominal with a change of 100 Gauss, a device having a rate of change in flux density of 200 Gauss per degree is required.

The present invention provides 228 Gauss per degree to meet this requirement.

Observation of the prior art performance curve 60 shows that this performance requirement cannot be obtained.

The housing disclosed above forms the subject of our co-pending application 9019/78 (Serial No. 1563082) WHAT WE CLAIM IS: 1. A magnetic circuit, interruptable by a high permeability vane movable in a given direction, for a Hall effect sensing circuit in an ignition system of an internal combustion engine said magnetic circuit comprising: a permanent magnet having a first pole face and a second elongate pole face, the major axis of said second elongate pole face oriented perpendicularly to the direction of the vane movement; A pole piece having a portion to which is affixed the first pole face of said permanent magnet, said pole piece having an arm extending therefrom in a direction parallel to the direction from said first to said second permanent magnet pole faces, said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   14 is a flux concentrator 40 which has a first projecting portion 41 and a second projection portion 42 extending therefrom towards respectively the pole piece pole face 34 and the permanent magnet second pole face 23. Each projection respectively has an elongate face portion 43, 44 with its major axis oriented perpendicularly to the line of motion 24 of the vane 17. The face portion 43 of the first projection is positioned opposite the pole face 34 of the arm 32 of the pole piece. The second face 44 of the flux concentrator second projection portion 42 is similarly positioned opposite the second pole face 23 of the permanent magnet 20 thereby forming air gaps 18a, 18b for passage of the vanes 17.When a vane 17 is not positioned in the air gap 18, flux flows from the permanent magnet through the pole piece 30, the flux concentrator 40, and the upper air gap 18a and the lower air gap 18b. When the vane 17 is in the air gap 18, a significantly reduced amount of flux flows through the flux concentrator 40 due to the shunting action of said high permeability vane.

   A ceramic circuit board 50 containing varuous circuit elements is positioned within the lower air gap 18b as shown in Fig.

   3. Fig. 4 shows the ceramic circuit board 50 in relationship to the line of motion 24 of the vane 17 and to the assembly of the pole piece 30 and the permanent magnet 20. A brass cap 51 affixed to ceramic circuit board 50 allows flux to pass therethrough and provides protection for a Hall effect device contained on an integrated circuit substrate.

   The Hall effect device produces an output Hall voltage which is coupled to a signal processing circuit also contained on the integrated circuit substrate. The Hall voltage is directly proportional to the vector product of the current density passing through the Hall effect device and the magnetic flux density passing through the device. As a result, the output Hall voltage will be in either an on state or an off state depending upon whether an unobstructed flux is passing through the Hall effect device 52 or whether the magnetic flux is shunted by the high permeability vanes 17 being positioned within the air gap 18.

   Fig. 4 shows a graphical representation of the flux density Bg in the air gap in Gauss as a function of the position in degrees of the vane leading edge 56 within the air gap. As the vane leading edge 56 moves through the air gap 18 in the direction represented by the line of motion 24, a typical prior art curve 60 shows the effects of leakage flux and of having the flux being spread out over a relatively large angular measurement. The rate of change of the flux density per mechanical degree of the prior art curve 60 is significantly less than the rate of change shown in a curve 61 which shows the performance of a magnetic circuit according to the present invention. The rate of change of flux density versus mechanical degrees provided by the present invention is much higher than that of the prior art.

   Since the configuration of the present invention magnetic circuit reduces leakage flux, the peak flux density provided by the magnetic circuit of the invention has a value much higher than that provided by the prior art as may be observed from the graph in Fig. 4. Having the flux concentrated in an elongated area with its major dimension perpendicular to the direction of motion 24 of the leading edge 56 of the vanes 17 allows a rapid-change of flux with changes in mechanical position of the leading edge 56 of the vane 17. For the same reasons, as the trailing edge 57 of the vane 17 leaves the air gap 18 a high rate of change of flux density per mechanical degree is also obtained.

   It is imprtant that a, high rate of flux density change per mechanical degree change be obtained in an automotive ignition system sensing circuit because the output signal obtained from the processing circuit for the Hall voltage varies due to variations in the input trigger and release voltage level of said processing circuit over a temperature range. The trigger and release points of the processing circuit may vary +100 Gauss over a range of temperatures of -30 to +125 degrees centigrade. in order to provide an ignition firing or release point within one half degree of nominal with a change of 100 Gauss, a device having a rate of change in flux density of 200 Gauss per degree is required.

   The present invention provides 228 Gauss per degree to meet this requirement.

   Observation of the prior art performance curve 60 shows that this performance requirement cannot be obtained.

   The housing disclosed above forms the subject of our co-pending application 9019/78 (Serial No. 1563082) WHAT WE CLAIM IS: 1. A magnetic circuit, interruptable by a high permeability vane movable in a given direction, for a Hall effect sensing circuit in an ignition system of an internal combustion engine said magnetic circuit comprising: a permanent magnet having a first pole face and a second elongate pole face, the major axis of said second elongate pole face oriented perpendicularly to the direction of the vane movement; A pole piece having a portion to which is affixed the first pole face of said permanent magnet, said pole piece having an arm extending therefrom in a direction parallel to the direction from said first to said second permanent magnet pole faces, said

   arm including a portion having a predetermined configuration such that minimal surface area of said arm portion faces said permanent magnet. said arm having an elongate pole face thereon with its major axis oriented perpendicularly to the direction of the vane movement: a flux concentrator- having first and second projections extending therefrom.

   each projection having an elongate face portion with its major axis oriented perpendicularlv to the direction of the vane movement, the face portion of the first projection being spaced apart and aligned opposite the pole face of the arm portion of the pole piece and the face portion of the second projection being spaced apart and aligned opposite the second pole face of the permanent magnet, thereby forming air gaps for passage of said vane, the pole face of said arm and the second pole face of the permanent magnet being positioned for simultaneous magnetic shunting by the movement of a leading edge of said vane in said given direction between said air gaps.
2. 2. A magnetic circuit as claimed in claim I wherein the elongate pole faces of the permanent magnet second pole face and the pole piece arm and the elongate face portions of the flux concentrator are rectangularly shaped and arranged to be parallel.
3. 3. A magnetic circuit as claimed in claim I wherein a Hall effect device is positioned adjacent to the face portion of the second projection of the flux concentrator so that flux flows from the flux concentrator face portion through the Hall effect device, across the air gap. and through the permanent magnet second pole face.
4. 4. A magnetic circuit as claimed in claim I wherein the permanent magnet has an oblong configuration and wherein the second eleongate pole face is positioned at the end of a salient portion.
5. 5. A magnetic circuit as claimed in claim I wherein the permanent magnet is affixed to the pole piece portion with solder.
6. 6. A magnetic circuit as claimed in claim I wherein the pole piece is formed from a flat plate and wherein the arm is formed from a portion of said plate projecting perpendicularly from said plate.
7. 7. A magnetic circuit as claimed in claim I wherein the flux concentrator is formed from a flat plate and is positioned edgewise with respect to said permanent magnet and said pole piece arm.
8. X. A magnetic circuit, interruptable by a high permeability vane moving in a given direction, for a Hall effect sensing circuit in an internal combustion engine ignition circuit comprising: an oblong permanent magnet having a first pole face and a second elongate pole face, said second pole face positioned on a salient portion of said permanent magnet and having its major axis perpendicularly oriented with respect to the given direction of said vane movement:: a pole piece formed from a flat plate having a portion to which is affixed the first pole face of said permanent magnet and having a flat arm portion extending therefrom in a direction parallel to the direction from said first to said second permanent magnet pole faces. said flat arm positioned edgewise with respect to the permanent magnet, said flat arm having an elongate pole face on an end thereof, said elongate pole face having its major axis perpendicularly oriented with respect to the given direction of said vane movement:: a flux concentrator formed from a flat plate and positioned edgewise with respect to said permanent magnet and said pole piece flat arm, said flux concentrator having first and second prqjection portions extending therefrom with elongate face portions thereon oriented with their major axes each perpendicular to the given direction of said vane movement, the elongate face of the first projecting portion being spaced apart and aligned opposite the elongate pole face of the flat arm of said pole piece and the elongate face of the second projecting portion of said flux concentrator being spaced apart and aligned opposite the second pole face of the permanent magnet: said elongate face of the second projecting portion of said flux concentrator having the Hall effect element of said Hall effect sensing circuit positioned adjacent thereto to provide a magnetic flux path through said Hall effect element from said concentrator to said permanent magnet with an air gap for passage of said vane, the pole face of said arm and the second pole face of the permanent magnet being positioned for simultaneous magnetic shunting by the movement of a leading edge of said vane in said given direction between said air gaps.
9. 9. A magnetic circuit constructed and arranged substantially as hereinbefore described and as shown in Figures 1 to 4 of the accompanying drawings.