Patent Publication Number: US-6668774-B1

Title: Non-contacting apparatus for determining relative rotary position of two elements

Description:
TECHNICAL FIELD 
     The present invention relates to mechanisms for determining relative angular position between two coaxially-related elements; more particularly, to mechanisms for continuously determining the instantaneous angular relationship between a camshaft pulley and a camshaft in a cam phaser apparatus for an internal combustion engine; and most particularly, to apparatus for making such instantaneous determination without contact between the two coaxially-related elements. 
     BACKGROUND OF THE INVENTION 
     In apparatus including first and second elements having coaxial relative rotation therebetween about a mean angular position, the need arises to determine changes in the relative angular position in either direction. An especially demanding application is one in which both elements are being simultaneously rotated on a common shaft. Just such a situation occurs in variable cam phasing systems for internal combustion engines. The angular relationship between the camshaft pulley and the camshaft itself is variable and must be determined at all times, but conveying a signal from the rotating apparatus via prior art means is difficult and cumbersome. 
     One known approach is to use a conventional position sensor, resistive or otherwise, mounted on the rotating cam phaser, and to convey a signal to an engine control module (ECM) via slip rings. This solution is expensive to implement and is prone to failure. 
     Another known approach is to use digital Hall-effect proximity sensors to detect the passing of timing features on each of the elements. By measuring the time interval therebetween, the angular relationship can be inferred. This solution, while theoretically sound, is complicated to implement because the angular velocity of the engine can vary within a single revolution of the cam phaser, causing an error in the apparent time phase measurement. 
     What is needed is a simple, inexpensive, and reliable means for determining the phase relationship of first and second coaxially mounted rotatable elements in an assembly, especially a cam phaser. 
     It is a principal object of the present invention to provide a simplified and reliable measurement of the phase relationship of such elements. 
     It is a still further object of the invention to provide such measurement proximately and without electrical connection to the assembly. 
     SUMMARY OF THE INVENTION 
     Briefly described, apparatus in accordance with the invention includes a Hall-effect magnetic field strength sensor disposed coaxially adjacent to an assembly having first and second coaxially-related elements oscillatingly-rotatable about a mean angular relationship therebetween. One of the elements is provided with a threaded axial bore or stud, and the other of the elements is provided with a longitudinally-splined axial bore. A pin having threads on a first end and splines on the second end is matingly disposed on both the threads and splines, respectively, of the two coaxially-related elements. A permanent magnet is mounted on an end of the pin adjacent the Hall-effect sensor, creating a magnetic response therein. As the angular relationship between the two elements changes, the pin turns with the splined element. However, the turning pin is simultaneously displaced axially of the assembly by the threads, thus displacing the magnet with respect to the sensor and thereby changing the intensity of the field experienced by the sensor. Thus, the sensor output is a continuous signal representing the intensity of magnetic field which is directly proportional to the relative angular position of the two elements. Because the magnet and sensor are coaxially disposed, rotation of the magnet, as occurs, for example, in a cam phaser application, is irrelevant. In such an application, the sensor signal is provided to an engine control module for continuous monitoring and control of the advance and retard timing of engine intake valve opening and closing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic cross-sectional view of a first embodiment of an apparatus in accordance with the invention; 
     FIG. 2 is a schematic cross-sectional view of a second embodiment of an apparatus in accordance with the invention; 
     FIG. 3 is a schematic cross-sectional view of a third embodiment of an apparatus in accordance with the invention; 
     FIG. 4 is a cross-sectional view of a prior art vane-type cam phaser; and 
     FIG. 5 is a cross-sectional view of a vane type cam phaser in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 through 3, first element  10  and second element  12  are disposed coaxially on axis  14 . First element  10  is formed of a non-ferromagnetic material, for example, a polymeric resin, aluminum, or certain stainless steels. First element  10  is provided with a first axial well  16  having a thin bottom wall  18 . Second element  12  is provided with a second axial well  20  having a bottom wall  22 . Coaxially disposed closely adjacent well bottom wall  18  but not in contact with element  10  is a ratiometric Hall-effect sensor  24 , a semiconductor device which produces a voltage proportional to the local magnetic field strength. One such device is the A3515LUA, available from Allegro Microsystems, Inc., Worcester, Mass. 01615, USA. Sensor  24  may be connected to a control means  26 , for example, an engine control module. 
     Extending into both wells  16  and  20  and axially moveable therein is a pin  28 , splined along one end portion and threaded along the opposite end portion. The only differences among the embodiments shown in FIGS. 1-3 is the male/female relationships of the threads and splines and their placement in either element  10  or element  12 . All are equivalent in function in accordance with the invention. 
     In first embodiment  30  (FIG.  1 ), well  16  is female-splined with longitudinal splines  23 , running parallel to axis  14  and pin  28  is male-splined with longitudinal splines  25  in element  10 , and well  20  is female-threaded with threads  27  and pin  28  is male-threaded with threads  29  in element  12 . 
     In second embodiment  30 ′ (FIG.  2 ), well  16  is female-threaded and pin  28  is male threaded, and well  20  is female-splined and pin  28  is male-splined. 
     In third embodiment  30 ″ (FIG.  3 ), well  16  is female-splined and pin  28  is male-splined as in embodiment  30 . Pin  28  has a threaded axial bore  32 , and well  20  is provided with a threaded stud  34  axially mounted on wall  22 . 
     In each of embodiments  30 , 30 ′, 30 ″, a permanent magnet  36  is disposed in well  16  on the end of pin  28  adjacent sensor  24 . By definition, an angular relationship with respect to axis  14  exists between elements  10  and  12 . At any given angular relationship, sensor  24  is exposed to a magnetic field produced by magnet  36  and sends a signal to control means  26  proportional to the field strength. If elements  10 , 12  are rotated with respect to each other about axis  14  to assume a different angular relationship, pin  28  must rotate with the longitudinal splined element. The rotation causes pin  28  to turn along threads  27 , 29  in the threaded element by an amount equal to the angular change between elements  10 , 12 . Magnet  36  is thereby axially displaced, according to the pitch of the threads, either toward or away from sensor  24 , depending upon the direction of relative rotation; the field experienced by sensor  24  is either increased or decreased, and the signal sent to control means  26  is either increased or decreased proportionally. The device may be readily calibrated in known fashion to relate relative angular position to signal strength. Note that, because all motions are relative to axis  14  and the magnetic field is symmetrical about axis  14 , combined rotation of elements  10 , 12  about axis  14  is irrelevant and does not affect the signal even when the sensor is stationary. 
     Referring to FIG. 4, a prior art vane-type cam phaser  50  is well known in the automotive arts for controllably altering the phase relationship between the crankshaft (not shown) and the camshaft  52  of an internal combustion engine  54 , the motion and phase of the crankshaft being transmitted to the phaser via a crankshaft pulley  56 . Phaser  50  is rotatably mounted on an end  53  of camshaft  52 . Pulley  56  is integrally assembled with phaser hub  58 , body  60 , and cover  62  which therefore rotate as a crankshaft subassembly  61  in phase according to pulley  56 . A rotor hub  64  is pressed into a recess in the end of camshaft  52 , supporting a multi-vaned rotor  66  connected to hub  64  via a hollow bolt  68  threaded into hub  64 , forming a camshaft subassembly  67  having an angular relationship to crankshaft subassembly  61 . Control hydraulic fluid in the form of pressurized engine oil flows from ports in the camshaft (not shown) axially through bolt  68 , into gallery  70 , and thence into galleries formed between vanes  72  and stator lobes (not visible in this elevational cross-sectional view) to urge rotor subassembly to a different angular position with respect to crankshaft subassembly  61 . Other mechanisms, which need not be addressed here but are well known in the art, act to urge the rotor assembly in the opposite direction as required. Thus, in normal operation of the cam phaser, there is relative rotational motion between cover  62  and bolt  64 , in both rotational directions, about a mean angular position. 
     Referring to FIG. 5, an improved cam phaser  50 ′ is shown, substantially identical in all respects to prior art phaser  50  except as shown and discussed below. A non-contacting apparatus is included in phaser  50 ′ for sensing and signaling changes in the relative angular position of subassembly  61  with respect to subassembly  67 . The embodiment shown is equivalent to embodiment  30 ′ shown in FIG.  2 . Well  20  formed in the head of bolt  68  is female-splined, and pin  28  is male splined. A new well  16  is formed in cover  62  and is female-threaded. Pin  28  is male threaded. Threads may be either right-or left-handed. A permanent magnet  36  is mounted on the outer end of pin  28 . A Hall-effect sensor  24  is mounted closely adjacent cover  62  but preferably not in contact with cover  62 , which in operation may be rotated at several hundreds or thousands of revolutions per minute. Sensor  24  is connected to engine control module  26 . Pin  28 , being spline-mounted in bolt  68 , rotates with camshaft subassembly  67  and is driven axially by threads  27  in well  16  toward and away from sensor  24 . 
     Thus, the invention provides a simple, inexpensive, reliable, non-contacting means for determining and measuring changes in angular position between first and second coaxially disposed elements. 
     While the embodiment described in FIG. 5 is shown as being equivalent to embodiment  30 ′ shown in FIG. 2, it is understood that improved cam phase  50 ′ may be shown as being equivalent to embodiment  30 ′ or  30 ″ and fall within the scope of the invention. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.