High resolution sensor system for internal combustion engines

Abstract: A high resolution sensor for internal combustion engines has symmetric and asymmetric magnetic encoders mounted on a support plate for synchronous rotation with the engine. Hall-effect sensor devices monitor the magnetic fields of the encoders and transmit signals to an Electronic Engine Control Unit. Ignition and fuel injection timing are deduced from the positions of the magnetic encoders. The encoders are magnetized on a fixture which establishes the size, strength, and location of each pole.

Description: BACKGROUND OF THE INVENTION This invention relates generally to an ignition spark timing control system, and more particularly to a sensor system having magnetic sensing capabilities for timing the ignition to the engine shaft position. Virtually all internal combustion engines manufactured today include an electronic control unit which monitors and controls ignition timing. Functions which were once controlled through various mechanical linkages are increasingly controlled in the electronic control unit. With this control arrangement, timing of engine spark and fuel injection functions with the valve of each cylinder can be precisely controlled. This precision provides greater efficiency and responsiveness of the engine to varying conditions of operation. Distributor sensors used today typically produce one pulse, or one rising edge, for each spark plug to be fired. Many currently used distributors do not provide information required to control the fuel injection system. Further, such systems do not provide information to the electronic control unit to indicate which spark plug is being fired. In such systems, the electronic control unit controls spark advance with respect to valve and fuel injector timing by estimating engine speed between sensor signals and delaying the spark for a calculated time after a sensor signal has been received. Okada et al, in U.S. Patent 4,742,811, disclosed an ignition timing control system using three axially adjacent columns of magnets attached to a shaft. Each magnet column rotates in relation to a Hall-sensor which generates a signal at various degrees of shaft rotation. The first row of magnets is symmetrically spaced about the column. The second row is asymetrically spaced; while the third row is symmetrically spaced, but has one pulse which is differentiated from the others by very small pole reversals at the end of the pulse. Processing of these three signals through the electronic control unit provides the discrimination capability necessary to proper functioning of the system. The disposition of the magnetic columns one above the other in the Okada patent requires a substantial minimum height for the assembly described. Moreover, the twenty-four symmetrical poles in the first column indicates that each pole is subtending an angle of fifteen degrees on the circumference of the column. This rather large pulse to angle equivalence acts to limit the precision of the device function. The imprecision is overcome by the use of three magnetized columns rather than the lesser number. In the European patent application EP-A-190 639 of HITACHI, is disclosed the realization of a magnetic recording medium shaped in a rotary disk, with two tracks concentrically, but without accuracy about the disposition of the magnetic sensor facing the medium. U.S. Patent 3,373,729 to Lemen, discloses an electronic ignition system for internal combustion engines which uses a disk having a plurality of equally spaced magnets about its periphery. The disk is sawed perpendicular to its axis to form a slot having axially opposed magnets in the disk periphery on both sides of the slot. A Hall-sensor placed within the slot generates triggering signals according to the fluctuating magnetic field experienced as the disk rotates. This device, in essence, serves to replace the breaker points found in the distributor of a standard mechanically timed ignition system. Thus, this prior art eliminates the mechanical contact points together with their shortcomings, but it does not improve the accuracy of the ignition and fuel injection timing. The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limiations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter. SUMMARY OF THE INVENTION According to the present invention, this is accomplished by providing a high resolution sensor system for internal combustion engines including : a first annular magnetic encoder having an array of uniformly distributed and uniformly sized magnetic poles ; a second annular magnetic encoder having an array of magnetic poles, said first and second encoders being integral in rotation with a distributor shaft ; a first magnetic field sensor located near the rotary path of said first encoder ; a second magnetic field sensor located near the rotary path of said second encoder ; said two encoders are concentric and coaxial, disposed on a rotatable plate support ; characterized in that the angular size and the strength of the magnetic poles of said second encoder are non-uniform, that said two sensors are mounted, at appropriate radial locations to provide alignment with said two encoders respectively, on a fixed housing spaced from said rotatable support by a bearing/spacer, and that said first and second annular magnetic encoders are fixed to said rotatable support by an attachment device comprising : an annular ring having a flat area on an axial face to bear against said encoder ; an axially extending annular fin projecting from the flat area of said annular ring a distance proportional to the axial thickness of said encoders; at least one axially projecting stud projecting from the axial surface of said axially extending annular fin for attachment to said rotatable support. The magnetic encoders of this invention are made with a magnetizing fixture having an electrically conductive wire laid on a support in a planar serpentine path and further having magnetic field modifiers placed within the conductor loops to vary the size, strength and location of each magnetic pole formed. The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. It is to be expressly understood, however, that the drawing figures are not intended as a definition of the invention, but are for the purpose of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a fragmentary partially sectional elevation view of the sensor system. Figure 2 is a schematic plan view of the magnetic field sensors. Figure 3 is a schematic plan view of the two magnetic encoders. Figure 4 is a schematic plan view of the retainer device. Figure 5 is a sectional view of the retainer seen from line 5--5 in Figure 4. Figure 6 is a schematic plan view, from above, of the upper drive hub, the support plate, and the drive spring. Figure 7 shows a representation of the analog and digital signals detected by the magnetic field sensor from the asymmetric magnetic encoder. DETAILED DESCRIPTION In Figure 1, is shown a fragmentary partially sectioned elevation view of one embodiment of the invention. The high resolution sensing system is preferably designed to mount on an existing automobile distributor base; however, it could as well be mounted anywhere on or in the engine where it could be driven synchronously with the crankshaft or cam shaft of the engine. In this embodiment is seen the distributor shaft 1, which serves to drive the rotary member of the sensor system, protruding through the stationary distributor base 2, upon which is mounted the sensor housing 30. A high resolution magnetic encoder 10 and a low resolution magnetic encoder 15 are mounted on support plate 20 which rides on bearing/spacer 35. The encoder rings 10 and 15 are attached to the support plate using retainer ring 21 which has projecting studs 22 which protrude through holes in the support plate 20 and drive spring 40. The studs 22 of retainer 21 are upset, threaded, or otherwise secured to capture the assembly. High resolution sensor 11 and low resolution sensor 16 are mounted at appropriate radial locations to provide alignment with the high resolution magnetic encoder 10 and low resolution magnetic encoder 15, respectively. The sensors are Hall-effect transducers which provide appropriate output regardless of speed of motion. The signals generated in the sensors are transmitted to the electronic control unit of the engine. Upper drive hub 41 is coupled to the distributor shaft by which it is rotatively driven. Drive spring 40 extends from the upper drive hub 41 to the support plate 20 and provides the driving connection between the two plates. Drive spring 40 is so designed that it accommodates small vertical displacements of distributor shaft 1 without causing any relative rotation between upper drive hub 41 and support plate 20. This feature is required to avoid changes of timing which could otherwise be induced by vertical movement of the distributor shaft 1. A cover 51 is provided to protect the sensor system from damage or contamination. Optional seals 52 are provided for the interface between cover 51 and distributor shaft 1 as well as sensor housing 30 and distributor shaft 1. The seals may be O-rings or other suitable sealing devices. The cover 51 is placed on the housing 30 and secured with adhesive or other appropriate sealing means. The underside of housing 30 is filled with a castable encapsulant 50 which protects the printed wiring board and other electronics of the sensor system. High resolution sensor 11 and low resolution sensor 16 are shown schematically in a plan view in Figure 2. Here, it can be seen that the high resolution sensor consists of two Hall-effect transducers and their associated electronics. This provides high resolution by doubling the number of signals generated in the sensors in response to each magnetic pole reversal on the high resolution magnetic encoder ring 10. Only one Hall-effect transducer is used on low resolution sensor 16. Figure 3 shows a schematic plan view representative of high resolution magnetic encoder ring 10 and low resolution magnetic encoder ring 15. High resolution encoder ring 10 has a large number of magnetic poles. In the preferred embodiment, this ring will have 360 poles, but it could have more or fewer as the engine design requires. Low resolution magnetic encoder ring 15 is shown with sixteen poles, as an example, for a four-cylinder engine. There are four sharp North poles, eight intermediate South poles, and four very weak, very diffuse North poles. The four sharp North poles, one for each cylinder, are used to indicate which cylinder requires either spark or fuel. This is done by providing poles of different angular extent. For instance, it would be possible to have poles of one degree, two degrees, three degrees, and four degrees to indicate the respective cylinders to which they apply. Thus, in a four cylinder engine, the three degree magnet would correspond to the number three cylinder. Note that all timing is done on the rising edge of the magnetic pulse. Retainer ring 21 is shown in Figures 4 and 5. From these, it is seen that magnet retainer ring 21 is annular in shape and has a "T"-cross-section. In addition, it has a plurality of projecting studs 22 which are used to secure the ring and the magnets to the thrust washer plate or support plate 20. Depending on the magnet mounting scheme employed, the retainer ring may also be made with an "L"-cross-section. The projecting studs 22 protrude through the gap between the two magnet rings 10 and 15, through support plate 20, and through drive spring 40. Drive spring 40 transmits the rotary driving force between upper drive plate 41 coupled to distributor shaft 1, and support plate 20. It also maintains firm contact between support plate 20 and bearing/spacer 35. Figure 6 shows a schematic plan view of upper drive hub 41, drive spring 40, lower drive plate, and projecting studs 22. Spring 40 is shown here as having three legs, but it could as well have been shown with more or fewer legs depending on design requirements. Figure 7 shows a schematic representation of the analog 120 and digital 130 signal resulting from one revolution of the low resolution magnetic encoder 15. The analog trace 120 represents the raw output of the Hall sensor. The digital trace 130 represents that same output after conditioning of the signal in the sensor circuitry. These traces illustrate the asymmetry which provides the discrimination that permits the proper cylinder to receive the spark signal. In this case, every other pulse subtends two degrees of angle. Pulses 122 and 126 are each two degree pulses, while pulses 124 and 128 are seven degree and twelve degree pulses, respectively. The analog, or unconditioned, signal indicates a total of sixteen poles, or eight dipoles for the full magnetic encoder ring. The digital trace 130 shows only four pulses generated by these sixteen poles. This is accomplished by the signal conditioning which is designed to only recognize positive, or North, magnetic field strengths having greater magnitudes than those of the diffuse North poles 115. Thus, the digital trace 130 only recognizes the four strong North poles 122, 124, 126, and 128. Hence, only four pulses are transmitted to the electronic control unit by the low resolution sensor circuit for each revolution of the low resolution encoder ring 15. The timing function is controlled from the rising edge of each pulse while the discrimination function is determined by the angular width of each pulse. The high resolution magnetic encoder ring 10 is, of course, turning synchronously with the low resolution magnetic encoder ring 15. Since the high resolution encoder ring 10 has 360 poles, and since it has two high resolution magnetic field sensors 11 associated with it, there are 720 pulses produced for each revolution of the high resolution encoder ring 10. This provides half degree resolution without interpolations, and even closer resolution with interpolations.

Claims: A sensor system for internal combustion engines comprising : a first annular magnetic encoder (10) having an array of uniformly distributed and uniformly sized magnetic poles ; a second annular magnetic encoder (15) having an array of magnetic poles, said first and second encoders (10,15) being integral in rotation with a distributor shaft (1) ; a first magnetic field sensor (11) located near the rotary path of said first encoder (10) ; a second magnetic field sensor (16) located near the rotary path of said second encoder (15) ; said two encoders (10,15) are concentric and coaxial, disposed on a rotatable plate support (20) ; characterized in that the angular size and the strength of the magnetic poles of said second encoder (15) are non-uniform, that said two sensors (11,16) are mounted, at appropriate radial locations to provide alignment with said two encoders (10,15) respectively, on a fixed housing (30) spaced from said rotatable support (20) by a bearing/space (35), and that said first and second annular magnetic encoders (10,15) are fixed to said rotatable support (20) by an attachment device (21,22) comprising : an annular ring (21) having a flat area on an axial face to bear against said encoders (10,15) ; an axially extending annular fin projecting from the flat area of said annular ring (21) a distance proportional to the axial thickness of said encoders (10,15) ; at least one axially projecting stud (22) projecting from the axial surface of said axially extending annular fin for attachment to said rotatable support (20). The sensor system according to claim 1, wherein it further comprises : an upper drive hub (41), coupled in rotation to said distributor shaft (1), and a drive spring (40) extending from said upper drive hub (41) to said support plate (20). The sensor system according to claim 2, wherein said drive spring (40) has an uneven number of legs. The sensor system according to claim 1, wherein said first an second magnetic field sensors (11,16) comprise Hall-effect devices together with appropriate electrical circuitry. The sensor system according to claim 1, wherein the strength of said second annular magnetic encoder (15) magnetic poles of like polarity is non-uniform. The sensor system according to claim 1, wherein the number of first magnetic field sensors (11) is two and said two sensors are placed such that the resolution of detection of pole spacing is doubled.

Inventors: SANTOS ALFRED J, SANTOS, ALFRED J.
Applicants: ROULEMENTS SOC NOUVELLE, SNR ROULEMENTS
Application year: 1991
Main classification: F02P7
IPC codes: F02D35, G01B7, F02D45, G01D5, G01P3, F02P7