Throttle position sensor for an internal combustion engine

Abstract: An internal combustion engine throttle position sensor has a shaped dual magnet structure (212, 214) carried upon a pole piece (200) having a generally "C"-shaped cross-section, the magnets and pole piece defining a generally circular linear field which is concentric about the axis of rotation (250) of the compolete rotor. A Hall effect device (510) is located in the open portion or gap between the two magnets and is exposed to a defined field, whereby, by the use of selected geometries and particular magnet materials, a precise and yet tolerant magnetic circuit is produced.

Description: This invention relates generally to throttle position sensors and in particular to rotary position sensors which are both durable and precise for application in rugged and demanding environments, for use with an internal combustion engine. There are a variety of known techniques for angular position sensing. Optical electrical, electrostatic and magnetic fields are all used with apparatus to measure position. There are many known forms of device for using these energies for sensing. A few of the known devices are resistive contacting sensors, inductively coupled ratio detectors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, radio wave directional comparators and electrostatic ratio detectors. There are many other known detectors, too numerous to mention herein. These detection methods tend to each be valuable for one or more applications, but none meet all application requirements for all position sensing applications. Limitations arising may be due to cost, sensitivity to particular energies and fields, resistance to contamination and environment, stability, ruggedness, linearity, precision, or other factors. Transportation applications generally, and specifically automotive applications, are very demanding. Temperatures may rise to 150 degrees Centigrade or more, with road contaminants such as salt and dirt splashing upon the engine compartment, which may occur while the engine is still extremely hot from operation. At the other extreme, an engine is expected to perform in northern climates without fault, and without special preheating. Present throttle position sensors are manufactured using a resistive sensor combined with a sliding contactor structure. The sliding contact serves to "tap" the resistor element and provide a voltage proportional to position. This resistive sensor has proved to offer the greatest performance for cost in throttle position sensing applications, unmatched by any other technology to date. However, the resistive throttle position sensors are not without limitation. An automotive position sensor must endure many millions or even billions of small motions referred to in the industry as dithers. These dithers are the result of mechanical motion and vibration carried into the position sensor. Additionally, during the life of a throttle position sensor, there may be a million or more full stroke cycles of motion. In resistive sensors, these motions can affect signal quality. In spite of this shortcoming, most known throttle position sensors are resistive sensors. Over the years, efforts at improving the contactor-element interface have vastly improved the performance of these devices. Similar improvements in packaging and production have maintained cost advantage. A replacement component must be able to meet throttle position sensor performance requirements while offering similar price advantage. The combination of temperature extremes and contamination to which an automotive sensor is exposed has caused the industry to explore very rugged and durable components. One particular group of sensors, those which utilize magnetic energy, are rapidly being accepted into these demanding application. This is because of the inherent insensitivity of the magnetic system to contamination, together with durability characteristic of the components. Applying magnetic sensing to tone wheels for applications such as anti-lock braking and ignition timing has proved a relatively easy task. The impulse provided by the tone wheel is readily detected through all conditions, with very simple electronic circuitry. Magnetic throttle position sensors, particularly those using Hall effect IC detectors, are also being studied, as the industry believes these sensors will offer advantages over the present resistive technology. However, prior to the present invention, none of these sensors were able to offer the necessary combination of low cost, reliability, and precision output. Magnetic circuits offer admirable performance upon exposure to the usual moisture and dirt contaminants. However, linearity and tight tolerances are another issue. Sensors are subjected to both radial and axial forces that change the alignment of the rotor portion of the sensor with respect to the stationary portion (stator). The system must include at least one bearing, and this bearing will have a finite amount of play or motion. That play results in the rotor moving relative to the stator. Unfortunately, magnetic circuits of the prior art tend to be very sensitive to mechanical motion between the rotor and stator. As noted, this motion may be in an axial direction parallel to the axis of rotation, or may be in a radial direction perpendicular to the axis, or a combination thereof. Typical magnetic circuits use one or a combination of magnets to generate a field across an air gap. The magnetic field sensor, be this a Hall effect device or a magnetoresistive material or some other magnetic field sensor, is then located in the gap. The sensor is aligned centrally within the cross-section of the gap. Magnetic field lines are not constrained anywhere within the gap, but tend to be most dense and of consistent strength centrally within the gap. Various means may be provided to vary the strength of the field monitored by the sensor, ranging from shunting the magnetic field around the gap to changing the dimensions of the gap. Regardless of the arrangement and method for changing the field about the sensor, the magnetic circuit faces several obstacles which have heretofore not been overcome. Movement of the sensor relative to the gap, which is the result of axial and radial play between the rotor and stator, will lead to a variation in field strength measured by the sensor. This effect is particularly pronounced in Hall effect, magnetoresistive and other similar sensors, where the sensor is sensitive about a single axis and insensitive to perpendicular magnetic fields. The familiar bulging of field lines jumping a gap illustrates this, in that where a Hall effect sensor is not accurately positioned in the gap it will measure the vector fraction of the field strength directly parallel to the gap. In the centre of the gap, this will be equal to the full field strength. The vector fraction perpendicular thereto will be ignored by the sensor, even though the sum of the vectors is the actual field strength at that point. As the sensor is moved from the centre of the gap, the field begins to diverge, or bulge, resulting in a greater fraction of the field vector being perpendicular to the gap. Since this will not be detected by the sensor, the sensor will provide a reading of insufficient magnitude. In addition to the limitations with regard to position and field strength, another set of issues must be addressed. A position sensor of value in the transportation industry must be precise in spite of fluctuating temperatures. In order to gain useful output, a magnet must initially be completely saturated. Failure to do so will result in unpredictable magnet performance. However, operating at complete saturation leads to another problem referred to in the art as irreversible loss. Temperature cycling, particularly to elevated temperatures, permanently decreases the magnetic output. A magnet also undergoes aging processes not unlike those of other materials, including oxidation and other forms of corrosion. This is commonly referred to as structural loss. Structural and irreversible loss must be understood and dealt with in order to provide a reliable device with precision output. Another significant challenge in the design of magnetic circuits is the sensitivity of the circuit to surrounding ferromagnetic objects. For transportation applications a large amount of iron or steel may be placed in very close proximity to the sensor. The sensor must not respond to this external influence. The prior art is exemplified by U.S. Patent No. 4 570 118. Therein, a number of difrerent embodiments are illustrated for forming the magnetic circuit of a Hall effect throttle position sensor. This patent teaches the use of a sintered samarium cobalt magnet material which is either flat, arcuate, and slightly off-axis or, in second and third embodiments, rectangular with shaped pole pieces. No discussion is provided in the aforesaid patent as to the manner in which each magnet is magnetically coupled to the other, although it appears to be through the use of an air gap formed by a plastic moulded carrier. Furthermore, no discussion is provided as to how this magnetic material is shaped and how the irreversible and structural losses will be managed. Sintered samarium cobalt is difficult to shape with any degree of precision, and the material is typically ground after sintering. The grinding process is difficult, expensive and imprecise. The device may be designed to be linear and precise at a given temperature and a given level of magnetic saturation, presumably fully saturated. However, such a device would not be capable of performing in a linear and precise manner, and not be reliable, through the production processes, temperature cycling and vibration arising in use in the transportation environment. Furthermore, devices made in accordance with the aforesaid patent are highly susceptible to adjacent ferromagnetic objects. The variation in adjacent ferromagnetic material from one engine to the next will serve to distort the field and adversely affect both linearity and precision. The open magnetic circuit not only adversely affects sensitivity to foreign objects, but also sensitivity to radiated energies, commonly referred to as Electro-Magnetic Interference (EMI or EMC). Additionally, embodiments described in the aforesaid patent are very sensitive to bearing play. The combination of an open magnetic circuit and radially narrow permanent magnet structure provides no tolerance for motion in the bearing system. This motion will be translated into a changing magnetic field, since the area within the gap in which the field is parallel and of consistent magnetic induction is very small. U.S. Patent No. 3 112 464 discloses several embodiments of a brushless Hall effect potentiometer. A first embodiment has a shaped, radially magnetized structure which varies an air gap between the magnetic structure and a casing. However, there is no provision for radial or axial motion of the magnet carried upon the rotor. Furthermore, the large magnetic structure is difficult to manufacture and relatively expensive. U.S. Patent No. 5 159 268 shows a shaped magnet structure similar to that of U.S. Patent No. 3 112 464. The structure illustrated therein suffers from the same limitations as the earlier structure. Additionally, the device of the later U.S. Patent offers no protection from extraneous ferromagnetic objects. U.S. Patent No. 5 164 668 discloses a sensor less sensitive to radial and axial play. This device requires a large shaped magnet for precision and linearity. The size of the magnet structure places additional demand upon the bearing system. The patent does not consider magnet materials, methods for compensating for irreversible and structural losses, or shielding from extraneous ferromagnetic objects. The combination of large magnet, enhanced bearing structure, and added shielding combine to make a more expensive package. Also known from the prior art is U.S. Patent No. 4 392 375. This document discloses a rotary sensor, for example for a throttle valve, in which a ferromagnetic metal type magneto-resistance element detects motion in an axial direction parallel to the axis of rotation of the sensor. It is not capable of detecting motion in a direction perpendicular to said axis of rotation. The present invention aims to overcome the aforementioned limitations of the prior art and perceived barriers to the use of a linear type throttle position sensor, by the use of a special geometry magnetic structure. According to one aspect of the invention, there is provided a rotary throttle position sensor for use with an internal combustion engine having a throttle operatively connected thereto; the rotary sensor including an assembly for providing a closed magnetic circuit including: first magnet; a second magnet; a magnetically permeable pole piece interconnecting the first and second magnets; and a varying dimension air gap defined between the first magnet and the second magnet, the first and second magnets being structured and dimensioned to provide the varying dimension air gap and to form a variable magnetic field coupled therebetween; and the assembly being coupled to the throttle and being rotatable about an axis generally parallel to the variable magnetic field coupled between the magnets so that rotation of the throttle causes rotation of the assembly; and wherein the first magnet has a first inner radial edge positioned substantially coextensive with the axis and a first outer edge radially spaced from the axis, the second magnet having a second inner radial edge positioned substantially coextensive with the axis and a second outer edge radially spaced from the axis, the first and second inner edges and the first and second outer edges of the first and second magnets, respectively, being congruent; and a magntic field sensing means is positioned in the air gap for sensing the variable magnetic field coupled between the first and second magnets, the magnetic field sensing means being positioned at a location between the first and second inner edges and the first and second outer edges of the first and second magnets. According to another aspect of the invention, there is provided a rotary throttle position sensor for use with an engine having a rotatable part to be monitored and including a shaft connected to the part and to the sensor comprising: a rotatable closed magnetic circuit assembly connected to the engine and connected to the shaft so that rotation of the part causes rotation of the magnetic circuit assembly; wherein the closed magnetic circuit assembly includes a first magnet, a second magnet, a C-shaped magnetically permeable pole piee and a varying dimension air gap forming a variable magnetic field coupled between the first and second magnets; the pole piece has two arms and a base and the first and second magnets are connected to the arms of said pole piece forming the air gap therebetween; and the interconnected first and second magnets are mounted for rotation with the pole piece about an axis; the first magnet has a first inner radial edge positioned substantially coextensive with the axis and a first outer edge radially spaced from the axis, the second magnet having a second inner radial edge positioned substantially coextensive with the axis and a second outer edge radially spaced from the axis, the first and second inner edges and the first and second outer edges of the first and second magnets, respectively, being congruent; and a stationary magnetic field sensing Hall effect device is positioned in the air gap between the first magnet and the second magnet for sensing the variable magnetic field generally parallel to the axis, the magnetic field sensing Hall effect device being positioned at a location between the first and second inner edges and the first and second outer edges of the first and second magnets. Figure 1 illustrates one practical embodiment of the sensor in a top view, with the cover removed for clarity; Figure 2 illustrates the embodiment of Figure 1 in a cross-sectional view taken along the line 2' of Figure 1; Figure 3 is a schematic view of the magnet and Hall effect device structure; Figure 4 is an alternative magnetic structure from a perspective view; Figure 5 shows the embodiment of Figure 4 in elevational view; Figure 6 illustrates the embodiment of Figure 4 in plan view; Figure 7 shows an alternative embodiment of cover in plan view; and Figure 8 is a cross-sectional view taken along the line 8-8 of Figure 7. The practical embodiment in accordance with the present invention is illustrated in plan view with cover removed in Figure 1 and in cross-section in Figure 2. The rotary sensor is designated generally by the numeral 100. The sensor includes a housing 300 and a magnetic structure or assembly 200 of arcuate periphery and generally "C"-shaped cross section, mounted to the housing. The magnetic assembly 200 includes therein a magnetically permeable pole piece 210, shaped magnets 212 and 214 defining an air gap 216, supported by a moulded rotor cup 220. The pole piece 210 is formed between and is bonded to the magnets 212 and 214 so that the air gap within the pole piece is bordered by the magnets. This use of two magnets substantially reduces loss through the air gap which otherwise occurs with only a single magnet. The closed magnetic circuit which is completed by pole piece 210 improves performance by being less sensitive to bearing play and less sensitive to external ferromagnetic objects. The closed magnetic circuit exists, for the purposes of this application, when the external flux path of the permanent magnet is confined with high permeability material, air being understood to be low permeability material. The pole piece 210, the magnets 212, 214 and the air gap 216 thus form the closed magnetic circuit The pole piece 210 further reduces the size of magnets 212 and 214 required, and may be manufactured from moulded or sintered metals. Most preferably, the pole piece 210 is formed from a sheet steel such as ANS1 430 stainless steel. As shown in Figures 1 and 2, the pole piece has a radius from an axis 250 to outer edges 261, 263. The shaped magnets 212 and 214 are preferably formed by moulding magnetic materials such as bonded ferrite. Bonded ferrite offers both a substantial cost advantage and also a significant advantage over other similar magnetic materials in structural loss due to corrosion and other environmental degradation. Other magnetic materials may be suitable, and may be determined by one skilled in the art. The magnets 212 and 214 desirably extend substantially from the outer edges 261, 263 of pole piece 210 to a region very close to or, design permitting, in line with the axis of rotation 250 of the rotor cup 220. This large extension of the magnets 212 and 214 in the radial direction greatly reduces the effects of radial motion of the magnetic structure 200. Additionally, the magnets 212 and 214 are formed with lip structures 474 and 472, as best illustrated in Figure 2. These formations extend out beyond and partially around the pole piece 210. The lips 472 and 474 serve to expand the "sweet zone" of operation of Hall effect device 510, by forcing a larger area of linear magnetic field lines to pass through the air gap between magnets 212 and 214. This larger area of linear field lines directly corresponds to greater tolerance for both radial and axial play. The moulded rotor cup 220 includes a surface designed to engage with a shaft extending, for example, from a throttle body and carrying thereon the throttle butterfly. The moulded rotor cup 220 then rotates about the axis identified as 250 in Figure 1 and carries therewith the remainder of magnetic structure 200. The moulded rotor cup 220 is retained by housing 300, seat 350, helical spring 360 and cover 310. The cover 310 engages with housing 300 and may, for example, be ultrasonically welded in place. The cover 310 is strengthened against warpage and deflection through the formation of ribs 312. Within the gap formed by magnets 212 and 214 is a hybrid circuit substrate 500 carrying thereon the Hall effect device 510. The Hall effect device 510 is desirably positioned somewhere between the outer edges 265, 267 of magnets 212 and 214 and the inner ends 511, 513 near axis 250, but not particularly close to either the edges or the ends, so as to avoid any field bulging effect. The hybrid substrate 500 may be attached by heat staking or another similar method to the housing 300. The hybrid substrate 500 additionally carries thereon electrical circuitry within tray 520. This tray 520 acts as a container into which appropriate potting compounds may be placed to provide all necessary environmental protection for the associated circuitry. The tray 520 should be electrically grounded for protection against radiated fields (EMI and EMC). The hybrid substrate 500 is electrically interconnected to electrical terminals 410 through wire bonds 530, though it is well understood that any of a large number of electrical interconnection techniques would be suitable. Electrical connector terminals 410 emerge from housing 300 at a connector body 400, for interconnection to standard mating connectors. The magnetic assemby 200 rotates about the generally central axis 250 relative to the housing 300, thereby rotating the magnets 212 and 214 together with the pole piece 210. The Hall effect device 510 is retained stationary relative to the housing 300. As best illustrated in Figure 3, the magnets 212 and 214 are shaped generally helically so as to have a relatively thicker outer end and a relatively thinner end. At the thicker ends 211 and 215, which is at the same angle of rotation of the magnetic structure 200 for both magnets 212 and 214, there is a smaller air gap 217. At the thinner ends 213 and 216, there is a correspondingly larger air gap 218. The result is generation of less magnetic induction across the gap 218, with more magnetic induction across the gap 217. Rotation of the pole piece 210 about the axis 250 results in changing field magnetic induction which is directly measured by Hall effect device 510. Proper shaping of the gap produces a linear output from Hall effect device 510. However, such a system will not perform linearly and with precision and resistance to bearing play over its life without further design considerations. In order to stabilize a magnet against irreversible losses, it is necessary, first to saturate magnets 212 and 214 and then to demagnetize the magnets by a small amount. The magnetic assembly 200 does not demagnetize evenly from magnet ends 211 and 215 to magnet ends 213 and 216, without special consideration. Absent the appropriate demagnetization, the resulting device will either lose precision as a result of temperature excursions or will lose linearity as a result of stabilizing demagnetization. Figures 4, 5 and 6 illustrate an alternative embodiment of the magnetic structure, with the rotor cup removed for clarity. Thus, the magnetic structure 450 includes a magnetically permeable pole piece 460 and two shaped magnets 464 and 466. The magnets 464 and 466 do not have the lips of the first embodiment. In every other way, this structure is designed to be a functional equivalent of the embodiment of Figures 1 to 3, with a slightly reduced "sweet zone" of operation. The magnets 464 and 466 are still tapered so as to provide changing magnetic induction with rotation. Figures 7 and 8 illustrate an alternative embodiment of cover, wherein a ferromagnetic plate 814 is shown moulded into a cover 810. The cover 810 includes reinforcing ribs 812 similar to ribs 312. The use of a ferromagnetic plate further reduces the sensitivity of position sensor 100 to external ferromagnetic objects, for those applications requiring extreme precision. For EMC and EMI considerations, plate 814 should be grounded. The apparatus for measuring angular or rotary position described herein is a low cost structure due to the minimal weight and reduced demands upon magnetic components. In addition, there are many performance advantages not heretofore obtainable, including reduced sensitivity to bearing play, resistance to contamination and environment, reduced sensitivity to externally located fields, energies and objects, durability for both full stroke motion and dithers, precision, linearity and reduced complexity. Various modifications of the above-described embodiments are possible within the scope of the invention defined by the appended claims.

Claims: A rotary throttle position sensor for use with an internal combustion engine having a throttle operatively connected thereto; the rotary sensor including an assembly (200) for providing a closed magnetic circuit including: a first magnet (212); a second magnet (214); a magnetically permeable pole piece (210) interconnecting the first and second magnets; and a varying dimension air gap defined between the first magnet and the second magnet, the first and second magnets (212, 214) being structured and dimensioned to provide the varying dimension air gap and to form a variable magnetic field coupled therebetween; and the assembly (200) being coupled to the throttle and being rotatable about an axis generally parallel to the variable magnetic field coupled between the magnets so that rotation of the throttle causes rotation of the assembly; and wherein the first magnet (212) has a first inner radial edge positioned substantially coextensive with the axis and a first outer edge radially spaced from the axis, the second magnet (214) having a second inner radial edge positioned substantially coextensive with the axis and a second outer edge radially spaced from the axis, the first and second inner edges and the first and second outer edges of the first and second magnets, respetively, being congruent; and a magnetic field sensing means (510) is positioned in the air gap for sensing the variable magnetic field coupled between the first and second magnets, the magnetic field sensing means being positioned at a location between the first and second inner edges and the first and second outer edges of the first and second magnets. The rotary position sensor of claim 1, wherein the first outer edge and the second outer edge are substantially equidistant from the axis. The rotary position sensor of claim 1 or claim 2, wherein the magnetic circuit assembly is mounted so that the magnets (212, 214) rotate in planes generally perpendicular to the axis. The rotary position sensor of any of claims 1 to 3, wherein the field sensing means is a Hall effect device (510). The rotary position sensor of any of claims 1 to 4, wherein the first and second magnets (212, 214) are each shaped generally helically su as to have a relatively thicker end and a relatively thinner end. The rotary position sensor of claim 5, wherein said thicker ends of said first and second magnets (212, 214) are arranged so as to provide a narrow air gap between the magnets relative to a larger air gap between the thinner ends of the magnets. The rotary position sensor of any of claims 1 to 6, wherein the assembly (200) for providing a closed magnetic circuit is generally C-shaped in cross-section with the first and second magnets (212, 214) extending outwardly from the interconnecting magnetically permeable pole piece (210). The rotary position sensor of claim 7, wherein the pole piece (210) is formed from a material consisting of molded and sintered metals or sheet steel. The rotary position sensor of claim 7 or claim 8, wherein the first and second magnets (212, 214) are formed from moulding magnetic materials. A rotary throttle position sensor for use with an engine having a rotatable part to be monitored and including a shaft connected to the part and to the sensor comprising: a rotatable closed magnetic circuit assembly (200) connected to the engine and connected to the shaft so that rotation of the part causes rotation of the magnetic circuit assembly; wherein the closed magnetic circuit assembly includes a first magnet (212), a second magnet (214), a C-shaped magnetically permeable pole piece (210) and a varying dimension air gap forming a variable magnetic field coupled between the first and second magnets; the pole piece (210) has two arms and a base and the first and second magnets (212, 214) are connected to the arms of said pole piece forming the air gap therebetween; and the interconnected first and second magnets (212, 214) are mounted for rotation with the pole piece about an axis: the first magnet (212) has a first inner radial edge positioned substantially coextensive with the axis and a first outer edge radially spaced from the axis, the second magnet (214) having a second inner radial edge positioned substantially coextensive with the axis and a second outer edge radially spaced from the axis. the first and second inner edges and the first and second outer edges of the first and second magnets, respectively, being congruent; and a stationary magnetic field sensing Hall effect device (510) is positioned in the air gap between the first magnet and the second magnet for sensing the variable magnetic field generally parallel to the axis, the magnetic field sensing Hall effect device being positioned at a location between the first and second inner edges and the first and second outer edges of the first and second magnets. The rotary position sensor of claim 10, wherein the interconnected first and second magnets (212, 214) are mounted for rotation in planes generally perpendicular to the axis. The rotary position sensor of claim 11, wherein the first and second magnets (212, 214) have equidistant outer edges spaced radially outwardly from the axis. The rotary position sensor of claim 12, wherein said first and second magnets (212, 214) are each shaped generally helically so as to have relatively thicker ends and relatively thinner ends, and the thicker ends of the first and second magnets are arranged so as to provide a narrow air gap between the magnets relative to a larger air gap between the thinner ends of the magnets.

Inventors: CAMPBELL ROBERT J, MCCURLEY JEFFREY L, SPENCE SCOTT L, WHITE JAMES E, CAMPBELL, ROBERT J., MCCURLEY, JEFFREY L., SPENCE, SCOTT L., WHITE, JAMES E.
Applicants: CTS CORP, CTS CORPORATION
Application year: 1995
Main classification: G01D5
IPC codes: G01D5, G01B7, F02D11