WO2001001066A1

WO2001001066A1 - Linear displacement sensor

Info

Publication number: WO2001001066A1
Application number: PCT/US2000/015747
Authority: WO
Inventors: Ronald Jay Wolf; John Edward Jockel
Original assignee: American Electronic Components
Priority date: 1999-06-28
Filing date: 2000-06-08
Publication date: 2001-01-04
Also published as: AU5473000A

Abstract

A non-contact sensor (20) for providing an electrical output signal as a linear function of a displacement of an object, such as a brake pedal in an automotive application. The sensor (20) includes a magnetic flux responsive element (25) and a pair of spaced apart magnets (22, 24) defining air gaps therebetween. The sensor (20) is configured such that relative movement of a magnetic flux responsive device (25) in a direction parallel to the magnetic axis (26) of the magnets (22, 24) provides a linear electrical output signal. An important aspect of the invention is that the magnetic flux responsive sensor (25) is subjected to a constant magnetic field (30) irrespective of the air gaps between the flux responsive sensor (25) and the magnets (22, 24). Accordingly, such a configuration provides a relatively constant linear output.

Description

LINEAR DISPLACEMENT SENSOR

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to a non-contact position sensor and more particularly to a magnetic sensor for measuring the displacement of an object, such as a brake pedal in an automobile, and providing a corresponding linear electrical output signal.

2. Description of the Prior Art:

Various contact type sensors are known in the art which provide an indication of the displacement of an object, such as a brake pedal. Such contact type sensors normally include electromechanical potentiometers, formed from, for example, a thick film resistor and a movably mounted precious metal electrical wiper, adapted to be mechanically coupled to the brake pedal such that the relative position of the brake pedal relative to the resistor varies linearly in accordance with the displacement of the brake pedal. Such sensors are thus able to provide an electrical signal that is a linear function of the displacement of the brake pedal.

There are various problems with such contact type sensors. For example, such contact type sensors are subject to wear. In particular, the wipers are known to move back and forth and contact the thick film resistor a relatively large number of times over the expected life-time of the sensor; perhaps millions of times. This moving action causes localized reductions of the thickness of the thick film resistor. Since the resistance of such thick film resistors is a function of the cross- sectional area of the film, the reduction of the film thickness will change the local resistance value in that portion of the resistor which experiences the greatest amount of wear, which, in turn, can cause drift in the output over time which effects the calibration and linearity of the sensor.

There is another problem associated with contact type sensors. For example, in automotive applications, when the engine is running at a nearly constant speed, engine induced vibration can cause additional localized wear in the thick film resistor which, as discussed above, can effect the calibration and linear output of the sensor. Thus, there is a need for a sensor for measuring displacement and generating an electrical signal as a linear function of the displacement of an object, such as a brake pedal in an automotive application which does not have the problems associated with it as contact type sensors.

SUMMARY OF THE INVENTION

Briefly, the present invention relates to a non-contact sensor for providing an electrical output signal as a linear function of a displacement of an object, such as a brake pedal in an automotive application. The sensor includes a magnetic flux responsive element and a pair of spaced apart magnets defining air gaps therebetween. The sensor is configured such that relative movement of a magnetic flux responsive device in a direction parallel to the magnetic axis of the magnets provides a linear electrical output signal. An important aspect of the invention is that the magnetic flux responsive sensor is subjected to a constant magnetic field irrespective of the air gaps between the flux responsive sensor and the magnets.

Accordingly, such a configuration provides a relatively constant linear output. In an alternative embodiment of the invention, a single horseshoe magnet may be implemented. The principles of the present invention are also applicable to magnets having other configurations such as, circular magnets, arcuate magnets, as well as, multiple pole magnets to provide various output wave forms, depending on the application.

DESCRIPTION OF THE DRAWINGS

These and other objects of the present invention are readily understood with reference of the following drawings and attached specification wherein: FIG. 1 is a perspective view of a non-contact linear magnetic sensor in accordance with the present invention. FIG. 2 is an exploded perspective view of the sensor illustrated in FIG.

1.

FIG. 3 is a sectional view of the sensor illustrated in FIG. 1; shown with the spring uncompressed.

FIG. 4 is similar to FIG. 3 but shown but shown with the spring compressed.

FIG. 5 is a simplified view of the sensor in accordance with the present invention, illustrating the flux lines between the spaced apart magnets.

FIG. 6 is a graphical representation illustrating the displacement as a function of output voltage for the sensor illustrated in FIG. 5. FIG. 7 is a simplified representation of an alternate embodiment of the present invention utilizing a single horseshoe type magnet.

FIG. 8 is a graphical representation of the output voltage as a function of magnetic flux density in gauss for the sensor illustrated in FIG. 5.

FIG. 9 is an alternate embodiment of the invention utilizing arcuate magnets.

FIG. 10 is another alternate embodiment of the present invention utilizing a circular magnet.

FIG 11 is a plan view of the sensor illustrated in FIG. 5 illustrating the air gaps between the magnetic flux responsive element and the magnets in different positions.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a non-contact displacement type sensor for providing an electrical output signal as a linear function of displacement of an object. The non-contact sensor is particularly suitable for the automotive industry for measuring displacement of an automobile brake pedal, an EGR valve and various other automotive applications in which contact sensors are known to be used. Such non-contact sensors are not subject to wear as the contact type sensors.

In one embodiment of the invention, the non-contact displacement sensor includes a magnetic flux responsive element and a pair of spaced apart magnets, each magnet having opposing North and South magnetic poles defining a magnetic axis generally perpendicular to the North and South pole faces. In this embodiment of the invention, the sensor is adapted to measure displacement of an object in a direction generally parallel to the magnetic axes of the magnets. In particular, the relative position of the magnetic flux responsive element relative to the pole faces of the magnets, as will be discussed in more detail below, is used to provide an electrical signal as a linear function of the displacement along the magnetic axis.

An important aspect of the invention is that the air gaps (i.e distance) between the magnetic flux responsive element and the magnets in a direction generally perpendicular to the magnetic axes of the magnets is not critical. More particularly, as will be illustrated and discussed in more detail below, the magnetic flux responsive element, as long as it is inbetween the two magnets, is always subjected to a constant magnetic field. As such, the two air gaps defined between the magnetic flux responsive element and each of the magnets do not have to be equal. As such, the tolerance and the calibration of such a sensor is relatively simple, thereby reducing the overall cost of the sensor.

The invention requires movement of the magnetic flux responsive element relative to the magnet(s). Thus, either the magnet(s) can be mounted stationary and the magnetic flux responsive element movably mounted or vice versa. The principles of the invention apply to all such embodiments.

As used herein, a magnetic flux responsive device refers to all such devices which provide an electrical output signal as a function of magnetic flux. Examples of such devices are Hall effect elements both discrete, hybrid and integrated circuits including Hall effect elements, as well as magnetically variable resistor elements (MRE), magnetically variable resistor sensors (MRS), hybrid, discrete and integrated circuits including MREs. Examples of the above mentioned magnetic flux responsive elements are illustrated in commonly owned U.S Patent No. 4, 970, 463, hereby incorporated by reference.

Various embodiments of the invention are illustrated. FIG. 5 illustrates an embodiment of the invention which utilizes two spaced apart bar magnets. FIG. 7 illustrates an embodiment where a single horseshoe type magnet is utilized with the polarities as generally shown in FIG. 7. FIG. 9 illustrates an embodiment where a pair of spaced apart arcuate magnets are utilized. FIG. 10 illustrates an embodiment utilizing a circular magnet. In all such embodiments, the magnetic flux responsive element is disposed between the magnets or between opposing poles of the magnet and is subjected to a constant magnetic flux irrespective of the air gap between the magnetic flux responsive element and the magnet(s). It is contemplated that the principles of the present invention would apply to all such configurations.

Referring first to FIG. 5, a non-contact sensor in accordance with the present invention, generally identified with the reference numeral 20, includes a pair of spaced apart bar magnets 22 and 24 and a magnetic flux responsive element 25. As shown in FIG. 5, each of the bar magnets 22 and 24 is a single dipole magnet. A magnetic axis 26 is defined for each of the bar magnets 22 and 24. The magnetic axis 26 in the embodiment illustrated in FIG. 5, is generally perpendicular to the plane of the pole faces of the bar magnets 22 and 24. As shown in FIG. 5, the bar magnets 22 and 24 are generally parallel and spaced apart and are configured such that the North and South pole faces 28 and 30 of each of the bar magnets 22 and 24 lie generally in the same plane. In particular, as shown in FIG. 5, a North pole face for the bar magnet 22 is aligned on one end with a South pole face of the bar magnet 24. Alternatively, in embodiments where the bar magnets 22 and 24 are not configured so that the pole faces are in the same plane, the principles of the invention apply to the overlapping portion of the magnets.

With such a configuration, the magnetic flux, illustrated by dotted lines and generally identified with the reference numeral 30, is generally constant between the spaced apart bar magnets 22 and 24 as long as the bar magnets are generally parallel to one another as the magnetic flux responsive device 25 is moved parallel to the magnetic axis 26. As such, the air gaps or distances between the magnetic flux responsive element 25 and each of the bar magnets 22 and 24 do not necessarily have to be equal. In particular, as better shown in FIG. 7, the position of the magnetic flux responsive element 25 relative to the bar magnets 22 and 24 defines air gaps on each side of the magnetic flux responsive element 25 as indicated by the arrows 27 and 29.

As shown in solid line in FIG. 11, the magnetic flux responsive element 25 is essentially centered between the bar magnets 22 and 24. An important aspect of the invention is even if the magnetic flux responsive element 25 is off center, as shown in dotted line in FIG. 11, the output of the magnetic flux responsive element 25 will be relatively unaffected, since the magnetic flux responsive element 25 is subject to a constant magnetic field. As such, relatively precise alignment between the magnets 22, 24 and the magnetic flux responsive element 25 is not required, thus, simplifying the calibration, construction manufacture of the non-contact sensor 20.

Another benefit of the configuration of the present invention is that the magnetic flux responsive element 25 is disposed between lateral faces 36 and 38

(FIGs. 5 and 11) of the bar magnets 22 and 24. As such, the magnetic flux responsive element 25 is primarily responsive to lateral face magnetism, for example, as indicated by the dotted lines, generally identified with the reference numeral 40.

As used herein, pole face magnetism is that flux which emanates from one pole face and returns to an opposing pole face. Lateral face magnetism is defined herein as magnetic flux emanating from one lateral face 36 and returning to an opposing lateral face 38.

FIG. 6 is a graphical illustration of the sensor output in volts on the vertical axis as a linear function of displacement, for example, in millimeters, on the horizontal axis for the embodiment illustrated in FIG. 5. The sensor output is shown in exemplary per unit values and depends specifically on the type of magnetic flux responsive elements used. FIG. 8 is similar to FIG. 6 and illustrates the magnetic flux in gauss as a function of displacement. The exemplary functions illustrated in FIGs. 6 and 8 are for an exemplary linear Hall effect device, for example, a Micronas model no. HAL 800, which provides a 0.5 to 4.5 volt output range for a 1500 gauss difference in magnetic flux and two bar magnets, for example, two (2) alnico magnets having 1500 gauss magnetic field strength, spaced apart, for example, 0.125 inches.

For the embodiment illustrated in FIG 5, is illustrated when the magnetic flux responsive element 25 is generally at one end 42, the sensor 20 will generate an output, for example, 0.5 volts. As the magnetic flux responsive element 25 moves along the magnetic axis 26, the output voltage of the sensor 20 increases and passes through a reference point of 2.5 volts (0 gauss) to a maximum of 4.5 volts at an opposing end 44 of the sensor 20.

FIG. 7, 9 and 10, represent alternate embodiments of the invention. Referring to FIG. 7, this sensor, generally identified with the reference numeral 45, illustrates a horse shoe type magnet, generally identified with the reference numeral

46. The magnet 46 includes a pair of depending legs 48 and 50 and a bight portion, generally identified with the reference numeral 50. This embodiment is similar to the embodiment illustrated in FIG. 5 except that the bar magnets are connected along one edge forming a horse shoe. The sensor 46 also includes a magnetic flux responsive element 52, disposed between the depending legs 48 and 50 of the magnet 46.

Movement of the magnet 46 relative to the magnetic flux responsive element 52 or vice versa in a direction generally parallel to the arrow 54 will cause the voltage output of the sensor 45 to vary linearly as a function of the distance of the magnetic flux responsive element 52 from one end 54 of the sensor to an opposing end 56. Another alternate embodiment of the invention is illustrated in FIG. 9.

This embodiment, generally identified with the reference numeral 58, includes a pair of spaced apart arcuate magnets 60 and 62. The radius of curvature of each of the arcuate magnets 60 and 62 is generally the same. However, the length of the circular segment of the arcuate magnets 60 and 62 is selected to span approximately 90 degrees as shown. A magnetic flux responsive elements 64 is disposed between the arcuate magnets 60 and 62. In this embodiment, the arcuate magnets 60 and 62 may be moved relative to the magnetic flux responsive element 64 or vice versa along a generally arcuate path indicated by the arcuate arrows 66 and 68. The output of the magnetic flux responsive element 64 will vary linearly, as generally illustrated in FIGs 6 and 8, as a function of the distance of the magnetic flux responsive element

64 from one end 70 of the sensor 58 to the opposing end 72 or vice versa.

An alternate embodiment is illustrated in FIG. 10 and identified with the reference numeral 76. The sensor 76 includes a generally circular magnet magnetized with four quadrature poles. Although this magnet can be implemented as a single magnet, the magnet is easier understood conceptionally by considering it as two ring magnets 78 and 80, stacked one on top of the other. Conceptually, each ring magnet 78, 80 is diametrically magnetized and stacked such that opposite poles are stacked one on top of the other. In this embodiment, a magnetic flux responsive element 82 is adapted to move within a central aperture 84 of the magnet, generally identified with the reference numeral 86, in a direction generally parallel to the arrow 87 and functions as generally shown in FIGs 6 and 8.

As mentioned above, the principles of the present invention are suitable for various applications. One exemplary application is illustrated in FIGs. 1- 4 in which the sensor in accordance with the present invention is used as an EGR sensor, generally identified with the reference numeral 120. As shown in FIGs. 1-4, the non-contact EGR sensor includes a housing 122, for example a molded plastic housing, which includes a cover 124 (FIG. 2).

In this embodiment, the housing 122 is molded with a well 126 for receiving the various components that make-up the non-contact sensor in accordance with the present invention. For example, in this embodiment, a pair of spaced apart bar magnets 128 and 130 are rigidly secured to a plunger, generally indicated with the reference numeral 132. The plunger 132 includes a rod portion 134 and a cap portion 136.

A pair of oppositely disposed radially extending ears 133 are formed on the cap portion 136. The extending ears 133 are adapted to be received in a pair of guide slots 135 formed in the housing 122 to prevent rotation of the plunger 132 relative to the housing 122 and also stabilize axial movement of the plunger 132. A spring 138 is adapted to be received in the cap portion 136 of the plunger 132. The top 124 is formed with a central aperture 125 for receiving the plunger portion 134. The top is sealed to the housing 122 to close the well 126. An extending stud 140 (FIGs 3 and 4) is formed within the well 126. The stud 140 is used to capture one end of the spring 138. The cap portion 136 captures the other end of the spring 138. The spring 138 is used to bias the plunger 132 in a reference position as shown in FIG. 3. As force is applied to the plunger 132 in a direction of the arrow 139, the spring 138 becomes compressed as generally shown in FIG. 4. A magnetic responsive element 142 is disposed within the well 126 and configured to be received between the spaced apart magnets 128 and 130. As the plunger 132 and consequently the magnets 128 and 130 are moved so to compress the spring 138, the output voltage of the sensor 120 varies in a linear manner as shown generally in FIGs. 6 and 8. More particularly, as the brake pedal is depressed, the plunger 132 moves against the spring force of the spring 138 to compress the spring 138 to the position as shown in FIG. 4. Since the spaced apart magnets 128, 130 are attached to the plunger 132, the position of the magnetic flux responsive element 142 relative to the magnets 128 and 130 is varied which provides an electrical output signal, as discussed above, as a linear function of the displacement. Once the force on the plunger portion 134 is released, the plunger 132 under the influence of the spring 138 returns to the position as shown in FIG. 3.

The magnetic flux responsive element 142 is electrically coupled to a plurality of terminals, generally identified with the reference numeral 144. The electrical terminals 144 are suitable for mating with a suitable electrical connector 146 for connection to an external electrical circuit. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, the electronic portion of sensor in accordance with the present invention may be potted to provide protection from the environment. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

What is desired to be claimed in a Letters Patent of the United States is:

Claims

WE CLAIM:

1. A displacement sensor comprising: a pair of spaced apart magnets, each magnet having opposing North and South pole faces defining a magnetic axis perpendicular to said pole faces; and a magnetic flux responsive element disposed between said spaced apart magnets defining two air gaps for providing an output signal representative of displacement of said magnetic flux responsive element relative to said pair of spaced apart magnets, said magnets and said magnetic responsive elements configured such that said magnetic flux responsive element is subjected to constant flux irrespective of said air gaps.

2. The displacement sensor as recited in claim 1, wherein said magnetic flux responsive element is a Hall effect device.

3. The displacement sensor as recited in claim 1, wherein said magnetic flux responsive element is a magnetically variable resistor element (MRE).

4. The displacement sensor as recited in claim 1, wherein said magnetic flux responsive element is a magnetically variable resistor sensor (MRS).

5. The displacement sensor as recited in claim 1, wherein said spaced apart magnets are bar magnets.

6. The displacement sensor as recited in claim 5, wherein said spaced apart bar magnets are generally parallel to one another and said output signal represents displacement relative to an axis parallel to said magnetic axis.

7. The displacement sensor as recited in claim 1, wherein said spaced apart magnets are arcuate magnets having generally the same radius of curvature.

8. The displacement sensor as recited in claim 7, wherein said arcuate magnets span approximately 90 degrees.

9. A displacement sensor comprising: a horse shoe magnet defining depending legs and a bight portion having opposing North and South magnetic poles; and a magnetic flux responsive element disposed between said depending legs defining two air gaps for providing an output signal representative of displacement of said magnetic flux responsive element relative to said depending legs, said magnets and said magnetic responsive elements configured such that said magnetic flux responsive element is subjected to constant flux irrespective of said air gaps.

10. A displacement sensor comprising: a circular magnet having a central aperture and four quadrature poles; and a magnetic flux responsive element disposed within said central aperture, said magnetic flux responsive element and said magnet configured to provide a displacement signal as a function of axial displacement of said magnetic flux responsive element and said circular magnet.