Unitary rotational speed sensor

Abstract: Four embodiments of a reluctance type rotational speed sensor are disclosed. In the first embodiment, an annular magnet circumscribes a sensing coil having a unitary rotor nested within it, and is disposed between two elements which comprise the stator. In a second embodiment, a magnet is disposed between two halves which comprise a rotor, the entire assembly nesting within a sensing coil and being disposed between the two stator elements. In the third embodiment, the rotor carries multiple magnets in an axially opposed position with respect to teeth formed on the stator. The magnetic flux in the magnetic circuit increases and decreases as the rotor magnets alternate between aligned and non-aligned positions enabling measurement of angular speed in accordance with the increase and decrease of magnetic flux. Any of the first three embodiments may be used, with minor modifications, in environments where a rotating shaft turns within a stationary bore, or where a rotting bore turns about a stationary shaft. The fourth embodiment incorporates the features of the first three and further includes a caliper-like stator and coil assembly which may be removed for service without requiring extensive disassembly.

Description: This invention relates generally to rotational speed sensors, and more particularly to compact, unitary rotational speed sensors. Rotational speed sensors are used in many control and indicating systems. One frequently used type employs the variable reluctance principle. Common problems in such sensors in the prior art include constructing a device which will fit into compact spaces while maintaining close control over rotor-stator spacing, and providing sufficient output signal in terms of both signal amplitude and number of pulses per revolution. Prior art devices known to the inventors include those disclosed in US-A-2,462,761, US-A-3,480,812, US-A-3,596,122, US-A-3,604,966, US-A-3,649,859, US-A-4,027,753 and US-A-4,110,647. In particular, US-A-3,480,812 shows a nesting arrangement of rotor, magnet, coil and stator elements. US-A-3,649,859 discloses a reluctance-type rotational speed sensor utilizing radially extending teeth on both stator and rotor. The device known from US-A-4,027,753 comprises a sealed system. None of the above-mentioned devises, however, combine the various teachings of the present invention to obtain a significantly more compact design that is capable of greater output levels, and versatile enough for use in many environments. In the intermediate document EP-A-0 357 870 (designated States: DE, FR, GB, IT, SE) a reluctance-type rotational speed sensor is disclosed. This known speed sensor comprises a stator including two coaxial, axially spaced elements. Each of the stator elements has first and second radial portions. The first, inner radial portion of each stator element has alternating circumferentially spaced regions offering first and second magnitudes of magnetic permeability. The stator elements are in magnetic communciation with one another. A magnet is disposed between the stator elements. A rotor is arranged for rotation about an axis. This rotor, too, has alternating circumferentially spaced regions offering first and second magnitudes of magnetic permeability. The rotor, magnet and stator are arranged to form a magnetic flux path whereby a variation in a magnetic flux indicative of the rotational speed of the rotor relative to the stator is produced in the magnetic flux path upon rotation of the rotor. Means are provided for sensing this variation in magnetic flux in said flux path. According to a special embodiment the rotor can be split into two halves, sandwiching an annular magnet. In US-A-3 863 219 a measuring sensing device for detecting a rotational speed or a rotational speed change including a rotor and a stator constructed as magnet and having a coil is disclosed. The stator is constructed as an annular member with a U-shaped cross section. The coil is inserted on the inside of the U-shaped cross section. The outer leg portion of the stator carries at its free end an end-face toothed arrangement or serration opposite an end-face toothed arrangement or serration on the outer circumference of the disk-shaped rotor. The coil is used for sensing variation in magnetic flux. The present rotational speed sensor as defined in claim 1 improves upon prior art speed sensors by utilizing an axially compact design to obtain accurate measurements in a variety of environments. The flat, generally circular shape allows the sensor to measure the rotational speed of either a rotating shaft or a rotating bore. The sensor is designed to minimize the effects of eccentricities and unwanted relative movement between sensor components. For example, both radial runout and axial runout have minimal effect on the output of the sensor. Furthermore, the particular design of the magnetic circuit used by this sensor enables it to generate a high output signal for its size. The changes in flux generated by the rotor system induce alternating voltage in a coil of wire in a well known manner to produce signals representative of rotational speed. In the present speed sensor, the rotor carries circumferentially spaced magnets in an axially opposed position with respect to teeth formed on the stator. This embodiment may be used, with minor modifications, in environments where a rotating shaft turns within a stationary bore, or where a rotating bore turns about a stationary shaft. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of the sensor according to one embodiment of the speed sensor; Figure 2 is an exploded view of the components of the sensor shown in Figure 1; Figure 3 is a plan view of the rotor of the sensor used in the embodiment; Figure 4 is a sectional view of the rotor taken along the lines 12-12 in Figure 3; Figure 5 is a developed sectional view of the rotor and stator of the sensor taken with the rotor and stator in a first position; Figure 6 is a developed sectional view of the rotor and stator of the sensor taken with the rotor and stator in a second position; and Figure 7 is a sectional view of the sensor according to a modification of the embodiment; DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows one embodiment of the rotational speed sensor of the present invention. With reference to both Figure 1 and Figure 2, rotor 410 is shown having several axially extending passageways 412 circumferentially spaced about the rotor. The passageways define openings on each opposing rotor surface. Magnets 414 are retained in the passageways by use of an adhesive or by mechanical interlock. Magnets 414 are aligned so as to offer common pole faces oriented toward opposing rotor surfaces. The rotor 410 is constructed from a low magnetic permeability material such as nylon. Stator elements 416 and 418 are relatively thin members constructed from a high magnetic permeability material having slots 420. Slots 420 may be formed by piercing holes in the stator structure or by forming teeth which project from the stator structure itself. In either manner, the stator elements offer radial portions having alternating circumferentially spaced regions having first and second magnitudes of magnetic permeability. The magnets on the rotor provide a magnetic flux source and are arranged to produce a variable magnetic flux in a flux path formed around the coil 426. Coil 426 provides a means for sensing variations in magnetic flux in said flux path. The slots 420 are preferably filled with low magnetic permeability material to provide a relatively flat stator surface. The radial length of the magnets 414 is shorter than the radial length of the stator slots 420 to avoid magnetic shunting of the magnets. In addition, the circumferential width of the magnets 414 is preferably approximately the circumferential width of the stator slots 420 to permit the magnets to move into positions in which the magnetic flux path offers alternating high or low magnetic reluctance. The plastic overmolds 422 and 424 are molded and secured to the stator elements by injection molding the overmolds with the stator elements 416 and 418 incorporated in an injection molding die as inserts. During the injection molding process, plastic flows to fill the slots formed in the stator elements to form an intimately bonded structure. The stator elements 416 and 418 and the overmolds 422 and 424 are mirror images of one another permitting manufacture using the same process equipment. The stator elements 416 and 418 have flanged portions which form a cavity for receiving wire coil 426. Wire coil 426 is preferably 1300 turns of No. 39 enameled wire wound and encapsulated in bobbin 428. Retainer 430 is constructed of high magnetic permeability material and serves to maintain structural connection of the stator elements as well as establish magnetic communication therebetween. Lead wires 432 and 434 are connected to the wire coil 426 and pass through the retainer 430 and stator element 418 via strain relief 436. The air gap 438 between rotor 410 and stator elements 416 and 418 is maintained by the clamping action of retainer 430 maintaining the stator elements 416 and 418 against opposing face portions of bobbin 428. In operation, the inner most radial portions of the plastic overmold 422 and 424 may contact the hub portion 448 of rotor 410. If this occurs, very little wear will be experienced as the rotor 410 is preferably constructed from nylon filled with long fiber aramid and the plastic overmolds 422 and 424 are preferably constructed from PPS having 10% glass and 5% Teflon. A toroidal magnetic flux path is established around the coil 426 proceeding from one pole face of magnets 414 passing through the teeth of the stator element 416 radially through the stator element, axially through the retainer 430 into stator element 418 radially therethrough into the respective stator teeth and finally to the opposing pole face of magnet 414. As the rotor rotates, the rotor magnets 414 move into and out of alignment with stator teeth 421 to alternately decrease and increase the magnetic flux flowing in the flux path. The change in magnitude of magnetic flux in the magnetic flux path generates a voltage in coil 426 in accordance with known principles. The relationship between the magnets 414 and the stator slots 420 is shown in Figure 5 and Figure 6. Figure 5 illustrates the stator elements 416 and 418 having teeth 421 in aligned positions with respect to magnets 414 of rotor 410. Figure 6 illustrates the same components wherein the rotor 410 has moved to a non-aligned position. In the preferred construction of this embodiment 100 magnets are used and each stator element has 100 slots. The output voltage across leads 432 and 434 shown in Figure 1 will be an alternating voltage with an amplitude proportional to the speed of rotation and a frequency equal to the speed of rotation times the number of teeth encountered in one revolution. The elastomeric ring 440 as shown in Figure 1 provides a compliant force frictionally engaging driving shaft 442. In addition, ring 440 provides vibration isolation of the rotor relative to shaft 442. Finally, the ring 440 includes two lip portions 444 and 445 which contact plastic overmolds 422 and 424 respectively to provide a seal to keep contaminants out of the moving parts of the sensor. Friction drive of the rotor via ring 440 is the preferred drive means for the sensor; other means however, including tangs or keys engaging slots on the rotating shaft could also be used. A supplemental seal 446 may be used on either or both sides of the sensor to supplement the sealing action of lip portions 444 and 445. Figure 3 is a plan view of the rotor 410 illustrating the axially extending passageways 412 and rotor hub 448. Figure 4 is a sectional view of rotor 410 taken along the lines 12-12 in Figure 3 showing passageway 412 having a first opening on a first radially extending surface of rotor 410 and a second opening on a second radially extending surface and a portion of the passageway intermediate the openings having a smaller radial dimension so as to mechanically interlock magnet 414 formed in the passageway. The embodiment as illustrated in Figure 1 features a coil 426 radially spaced from the rotor 410 whereby the coil and rotor provide a minimal axial package size. A variation of this embodiment, as shown in Figure 7, features a coil 500 axially spaced from rotor 410 whereby the coil 500 and rotor 410 provide a minimal radial package size. The variation requires a modified stator and in all other respects is identical to the sensor of the third embodiment. As shown in Figure 7, stator elements 502 and 504 are relatively thin members constructed from a high magnetic permeability material having slots 506. Teeth (not shown) are located intermediate the slots. Plastic overmolds 508 and 510 are molded and secured to the stator elements by injection molding with the stator elements 502 and 504 incorporated in an injection molding die as inserts. Stator element 504 has a flange portion which acts in conjunction with a flange portion formed integral to overmold 510 to define a cavity for receiving wire coil 500. Retainer 514 acts in conjunction with annular magnetic flux conductor 516 to maintain stator 502 and 504 in magnetic communication with one another. A toroidal magnetic flux path is established around the coil 500 proceeding from one pole face of magnet 414 passing through the teeth of the stator element 502 radially through the stator element, axially through the retainer 514 into the annular conductor 516, radially through the annular conductor into the stator element 504, radially through the stator to the stator teeth and finally to the opposite pole face of magnet 414. All other components of the variation to the first embodiment are identical and retain identical numbers as previously described.

Claims: A rotational speed sensor comprising: a stator (416, 418; 502, 504) having alternating circumferentially spaced regions (420, 421; 506) offering first and second magnitudes of magnetic permeability; a rotor (410) arranged for rotation about an axis; and means (426; 500) for sensing variation in magnetic flux in a flux path at least partially formed by said stator; characterized by: said stator including two coaxial, axially spaced elements (416, 418; 502, 504); said stator elements (416, 418; 502, 504) having first and second radial portions; said first radial portions of said stator elements (416, 418; 502, 504) having said alternating circumferentially spaced regions (420, 421; 506) offering said first and second magnitudes of magnetic permeability; said stator elements (416, 418; 502, 504) being in magnetic communication with one another; said rotor being a low magnetic permeable rotor (410) having a plurality of circumferentially spaced magnetic flux sources (414) disposed thereon; said flux sources (414) on said rotor (410) and said circumferentially spaced regions (420, 421; 506) on said stator being arranged in axially opposed relationship to complete said magnetic flux path formed by said stator; and said magnetic flux sources (414) arranged to produce a variable magnetic flux in said flux path as said circumferentially spaced regions (420, 421; 506) on said stator elements (416, 418; 502, 504) alternate between aligned and non-aligned axially opposed positions with said magnetic flux sources (414). The rotational speed sensor of claim 1 wherein said means for sensing variations in magnetic flux in said flux path is a wire coil (426; 500) disposed proximate said magnetic flux path. The rotational speed sensor of claim 2 wherein said rotor (410) and said coil (426) are coaxially nested between said stator elements (416, 418). The rotational speed sensor of claim 2 wherein said coil (500) is axially spaced from said rotor (410) whereby said coil (500) and said rotor (410) provide a minimal radial package size. The rotational speed sensor of claim 2 wherein said coil (426) is radially spaced from said rotor (410) whereby said coil (426) and said rotor (410) provide a minimal axial package size. The rotational speed sensor of claim 2 wherein said alternating circumferentially spaced regions (420, 421; 506) of said stator are provided by openings (420; 506) formed in said stator elements (416, 418; 502, 504) and wherein said stator elements (416, 418; 502, 504) are formed of high magnetic permeability material. The rotational speed sensor of claim 6 wherein said openings (420; 506) are filled with a low magnetic permeability material whereby the surfaces of said stator elements (416, 418; 502, 504) are relatively flat in profile. The rotational speed sensor of claim 1 wherein said alternating circumferentially spaced regions (420, 421; 506) of said stator are provided by circumferentially spaced teeth means (421) disposed thereon and said teeth (421) are in axial opposition and close proximity to said magnetic flux sources (414) of said rotor (410). The rotational speed sensor of claim 3 further comprising retainer means (430; 514) arranged to retain said stator, coil (426; 500) and rotor (410) in a single assembly. The rotational speed sensor of claims 1, 3 and 8 further comprising: said circumferentially spaced teeth means (421) being disposed on axially opposed inner and outer radially extending surfaces of said stator elements (416, 418; 502, 504); said rotor (410) having first and second axially spaced radially extending surfaces including a plurality of circumferentially spaced passageways (412) defining a first opening on said first surface and a corresponding second opening on said second surface; each of said magnetic flux sources (414) disposed in said passageways (412) having a first pole adjacent said first opening and a second pole adjacent said second opening; said magnetic flux sources (414) disposed in said passageways (412) and said teeth means (421) of said stator being arranged in axially opposed relationship and in close proximity; and said magnetic flux sources (414) and said stator being arranged to form a magnetic flux path whereby an electrical current indicative of the rotational speed of said rotor (410) relative to said stator is induced in said coil (426; 500) upon rotation of said rotor (410) due to periodic variation of said flux path as said magnetic flux sources (414) and said teeth means (421) alternate between aligned and nonaligned axially opposed positions. The rotational speed sensor of claim 1 or 10 wherein said stator further comprises low magnetic permeability portions (420; 506) at least partially filling the spaces between the teeth (421) whereby said stator offers a relatively flat profile. The rotational speed sensor of claim 1 or 10, further comprising resilient seal means (444, 445, 446) associated with said sensor and arranged to prevent passage of fluid or contaminants from at least one direction. The rotational speed sensor of claim 1 or 10, wherein said rotor (410) is driven by a friction drive means including a resilient element (440) affixed to said rotor (410) and compliantly engaging a driving member (442). The rotational speed sensor of claims 12 and 13, wherein said friction drive means (440) and said seal means (444, 445, 446) comprise a unitary seal and drive element (440, 444, 445). The rotational speed sensor of claim 14, wherein said rotor (410) is annular and includes diametrical inner and outer edge surfaces, and wherein said unitary seal and drive element (440, 444, 445) extends along said inner edge surface of said rotor (410) and is in sealing association with at least one of said stator elements (416, 418; 502, 504). The rotational speed sensor of claims 10 and 9 further comprising said retainer means (430; 514) being arranged to provide magnetic communication between each of said stator elements (416, 418; 502, 504). The rotational speed sensor of claims 10, wherein said passageway (412) has a radial dimension intermediate said first and second opening which is smaller than either radial dimension of said first and second opening wherein said smaller radial dimension acts to form a mechanical interlock retaining said magnetic flux source (414) in said passageway (412).

Inventors: KRAMER DENNIS A, KRUSEL WILLIAM D, PECK DAVID E, PLATZER GEORGE E, KRAMER, DENNIS A., KRUSEL, WILLIAM D., PECK, DAVID E., PLATZER, GEORGE E.
Applicants: ROCKWELL INTERNATIONAL CORP, ROCKWELL INTERNATIONAL CORPORATION
Application year: 1990
Main classification: G01P3
IPC codes: G01P3