Abstract:
A sensor package and method of making the same is disclosed in which the sensor package includes a sensor component for electromagnetic sensing having a sensor body with a sensor tip at one end. A sensor housing having a cavity for receiving the sensor component is disposed in a substrate and is aligned with an object to be sensed. The housing further includes a snap-fit interface with the sensor component that is configured to admit and secure the sensor tip during assembly thereof. A bracket is mechanically fixable to the substrate at a first end and is in operable communication with the sensor tip at a second end. The bracket is configured to bias the sensor tip towards the object to be sensed for elimination of an internal air gap between the sensor tip and housing formed during assembly thereof.

Description:
TECHNICAL FIELD  
         [0001]    The present disclosure relates to a method and apparatus for holding a first object with respect to a second object. More particularly, the present disclosure relates to a bracket system for precisely locating a sensor relative to an object to be sensed. Still more particularly, the present disclosure relates to a bracket system, wherein interaction between the bracket and the body of the sensor results in the sensor being fixed positionally with respect to the bracket, and further results in elimination of an internal air gap between the body of the sensor and a housing in which the sensor is disposed.  
         BACKGROUND OF THE INVENTION  
         [0002]    Magnetic sensors operate on the principle of detecting magnetic flux density modulation caused by the movement of appropriately configured reluctors (or targets). The magnetic sensor must be affixed very close to the reluctor since its sensitivity decreases very rapidly with the size of the air gap between the reluctor and the magnetic sensor. In most automotive applications, for example, the air gaps are on the order of 0.3 to 1.75 mm. Over such a range of air gaps, the sensor output signal decreases more than ten times. The signal attenuation at large air gaps makes the sensor operation more prone to noise induced failures as well as less accurate in detecting the elements of the reluctor as it spins in relation to the magnetic sensor. Both of these factors are often unacceptable in critical engine control and diagnostic applications.  
           [0003]    It may at first glance appear that there would be no problem whatsoever to choose and achieve an appropriate air gap between the magnetic sensor and the reluctor. However, in the majority of production cases, the stack-up of tolerances of the many different components randomly cause internal air gaps that influence the net size of the air gap, which consequently precludes achieving, at each assembly, a precisely predetermined external air gap between the magnetic sensor and the reluctor by mere assembly of the parts. As a result, because of the random variations caused by accumulation of tolerances, mere assembly of the parts risks damaging interference between the magnetic sensor and reluctor on the one hand, and inaccurate readings associated with too large a net air gap on the other hand. To lessen all the tolerances so that mere assembly assures, at each assembly, the optimum external air gap is physically difficult to obtain and involves costs associated with manufacturing such precise parts.  
           [0004]    The majority of magnetic sensors used in automotive applications involve non-adjustable air gap placement, wherein the stack-up of tolerances results in an internal air gap that causes deviation from the optimal external air gap. For example, a rigid bracket is affixed to the body of a magnetic sensor. The magnetic sensor is placed into a sensor bore in the engine block, and the bracket is bolted, via a bolt hole in the bracket, to a threaded mounting hole in a mounting surface of the engine block. When the bracket is bolted, the length of the sensor body from the bolt hole of the bracket to the sensor tip determines the external air gap with respect to the reluctor, which air gap is affected by the stack-up of tolerances. Even though subject to tolerance related placement inaccuracy, this structural mounting methodology is used widely because of the simplicity of the hardware, and ease of assembly and service.  
           [0005]    In situations where external air gap variation cannot be tolerated, the external air gap is preset during magnetic sensor installation by means of an adjustable bracket, often referred to as a “side-mount” bracket. The adjustability of side-mount brackets resides in a bolt slot which allows for the bracket to be adjusted along the slot elongation relative to the threaded mounting hole of the mounting surface.  
           [0006]    In one form of operation of the side-mount bracket, the sensor body is placed into the sensor bore of the engine block such that the sensor tip is allowed to touch the surface of the reluctor, and then it is withdrawn a distance equal to the predetermined optimum external air gap. This method is time consuming.  
           [0007]    In another form of operation of the side-mount bracket, a gauging layer of soft, abradable material is placed onto the sensor tip, wherein the thickness of the gauging layer is equal to the optimum external air gap. The gauging layer may be either attached to the sensor body or be a part thereof, such as a protuberance, provided the sensor body is of a soft material. Now, the installer need merely place the sensor body into the sensor bore until the gauging layer touches the reluctor, and then tighten the bolt on the mounting surface to thereby hold the sensor body at this position. During initial rotation of the reluctor, a portion of the gauging layer is sacrificial to abrasion due to reluctor runout or differential thermal expansion without damage being incurred to the sensor body or the reluctor.  
           [0008]    In the event the magnetic sensor must be re-installed, an abraded gauging layer cannot again provide position location for the sensor tip, as it was formerly able to do when it was unabraded. Therefore, before dismounting the magnetic sensor, the bracket must be marked to indicate the correct position of the sensor body relative to the bracket so that when the new magnetic sensor is re-installed, its position on the bracket can be alignably sighted—not an exact procedure. Indeed, rather than try to reinstall the old, but still usable, sensor using the sighting method to reset the external air gap, a technician would rather install a new sensor having the abradable layer intact, thereby circumventing the sighting step otherwise needed to reinstall the old, but usable, sensor. This results in waste of otherwise good sensors and unnecessary expense for the customer or warranty provider.  
           [0009]    In the prior art, it is known to precisely adjust the external air gap using a threaded sensor body housing and threaded sensor bore. This structure is generally used exclusively with magnetic sensors having a single sensing element and having sensing capability unaffected by sensor rotation around its longitudinal axis. In this approach, the housing bottom is brought into touching engagement with the reluctor, and then the sensor body housing is rotated a predetermined angular amount, wherein the pitch angle of the threads raises the housing bottom a distance equal to the optimum external air gap. However, the sensor must then be inserted in the housing making sure that the sensor tip is bottomed out against the inside housing bottom to maintain the set external air gap between the outside bottom of the housing and reluctor. Otherwise, an internal air gap is created reducing the effectiveness of the sensor by altering the net air gap between the sensor tip and the reluctor. The prior art has alleviated problems associated with internal air gaps by heat staking or ultrasonic joining and then biasing the sensor tip to maintain contact with the housing bottom. These approaches prove costly and timely, as well as lacking in longevity.  
           [0010]    Accordingly, what is needed in the art is a method and apparatus for assembling a magnetic sensor which is easy and cost effective to install, and provides for automatic setting of an optimal external air gap, while eliminating any internal air gap caused by stack-up tolerances during assembly of the sensor assembly.  
         SUMMARY OF THE INVENTION  
         [0011]    A method and apparatus for assembling a magnetic sensor using snap-fit assembly and a bracket to eliminate any potential air gap as a result of the snap-fit assembly. In an exemplary embodiment, a sensor package includes a sensor component for electromagnetic sensing having a sensor body with a sensor tip at one end. A sensor housing having a cavity for receiving the sensor component is disposed in a substrate and is aligned with an object to be sensed. The housing further includes a snap-fit interface with the sensor component that is configured to admit and secure the sensor tip during assembly thereof. A bracket is mechanically fixable to the substrate at a first end and is in operable communication with the sensor tip at a second end. The bracket is configured to bias the sensor tip towards the object to be sensed for elimination of an internal air gap between the sensor tip and housing formed during assembly thereof.  
           [0012]    In another embodiment, a method for elimination of an internal air gap between a sensor body and a sensor housing during assembly thereof while maintaining an air gap between the sensor housing and an object to be sensed is disclosed. The method includes securing a housing in a substrate. The housing has a cavity defined by an open first end configured for displacement of a sensor tip of the sensor body and a second closed end aligned for electromagnetic communication with the object to be sensed when the sensor tip is proximate thereto. The bracket is configured having a first bracket component with a first opening for receiving a mechanical fastener, and a second bracket component. The second bracket component is configured to engage the sensor body and bias the sensor body toward the object when the first bracket component is biased in the same direction. The bracket is mounted upon a surface of the substrate which is parallel to a horizontal axis using the first opening for attaching and translating the bracket with respect to the substrate. The first and second bracket components are displaced relative to each other along a vertical axis. Tooth means is located on at least one of the periphery of the sensor body and a wall defining the housing cavity. The tooth means are configured to allow snap-fit connection when the sensor body is displaced in the housing cavity and the sensor tip is bottomed out against the second closed end of the housing, wherein the tooth means facilitates entry of the sensor body and limits exit with respect to the housing. The tooth means potentially allows an internal air gap after the sensor tip is bottomed out that is eliminated when the mechanical fastener is tightened down with respect to the substrate in the first opening of the bracket.  
           [0013]    The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following brief description of the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Referring to the exemplary drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several figures:  
         [0015]    [0015]FIG. 1 is a partial perspective view of a bracket sensor system according to one embodiment of the present disclosure, shown in a typical environment of operation wherein a magnetic sensor is spaced from a reluctor a distance equal to an automatically established optimum air gap;  
         [0016]    [0016]FIG. 2 is a sectional side view of the bracket sensor assembly of FIG. 1 showing a sensor tip having no internal air gap relative to a housing in which the sensor is displaced;  
         [0017]    [0017]FIG. 3 is an enlarged partly sectional side view of FIG. 2 illustrating a snap-fit connection between the sensor and housing;  
         [0018]    [0018]FIG. 4 is an enlarged section view of FIG. 3 illustrating the snap-fit connection in more detail; and  
         [0019]    [0019]FIG. 5 is a partial side view of the bracket sensor assembly shown in FIG. 1 illustrating the sensor being biased to the bottom of the sensor housing via a bracket bolted to an engine block. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring now to the Drawings, FIGS. 1 and 2 generally depict an exemplary embodiment of a sensor probe bracket system  10  according to the present disclosure in an exemplar environment of operation, wherein the bracket system serves to locate a magnetic sensor  12  with respect to a reluctor  14 . In this regard, the magnetic sensor  12  has a sensor body  16  which includes a sensor tip  18 . The sensor tip  18  extends into a sensor bore  20  of an engine block  22 , for example, via sensor housing  24  that is spaced from the reluctor  14  a predetermined distance equal to an optimum air gap G which provides optimal sensing performance by the magnetic sensor of magnetic field variations as the reluctor spins.  
         [0021]    A sensor probe component bracket  26  (hereafter, simply “bracket”) of the sensor probe bracket system  10  is composed of a first bracket component  28  and a second bracket component  30  which lie substantially parallel with each other and are oriented parallel to a horizontal axis H and normal to the sensor bore  20  (the cylindrical axis of which is along the vertical axis V). First and second bracket components  28 ,  30  are offset from each other so that second bracket component bracket  30  can engage a first flange  32  extending from a portion of sensor body  16  extending above a second flange  34  of said housing  24 . Second flange  34  is disposed outside of port  20  and defines an opening  36  into which sensor tip  18  is initially displaced during assembly thereof. A mechanical fastener  38  such as a bolt or stud with a complementary nut secures the bracket  26  relative to a horizontal surface  40  of engine block  22  in a threaded aperture  41  of engine block  22 .  
         [0022]    Preferably, the sensor body  16  is placed trappingly into the opening  36  of the sensor housing  24  as part of the manufacturing process. In addition, the sensor body  16  is placed trappingly into a second opening  42  in second component bracket  30  as part of the manufacturing process. This not only ensures that the sensor  12  will remain permanently associated with respect to the bracket  26 , but further ensures the orientation of the sensor with respect to the bracket will be correct. The former feature facilitates installation and shipping from an assembly plant while allowing replacement, the latter feature ensures that the sensitive sensor will be properly spaced with respect to the reluctor  14  by eliminating any internal air gaps formed by the former feature. For example, the sensor body  16  may be trapped in sensor housing  24  during shipment to prevent damage to the sensor tip  18  and; the sensor body is prevented from being improperly biased by trapping the sensor body to the bracket  26  for negating incorrect placement of the bracket relative to the sensor body. It is to be understood that those ordinarily skilled in art may utilize any known modality to trap and/or permanently orient the sensor with respect to the bracket, and that the various views of the present disclosure are by way of exemplification and not limitation.  
         [0023]    The bracket  26  automatically retains the air gap G between reluctor  14  and outside housing bottom  44  and eliminates any internal air gap between the sensor tip  18  and inside housing bottom  46  when sensor body  16  is installed in housing  24  by holding the sensor body  16  thereat via an interaction between the bracket and the sensor body, as will now be detailed with reference to FIGS. 2 through 5 according to an exemplary embodiment.  
         [0024]    [0024]FIG. 3 is an enlarged partial view of FIG. 2 detailing engagement between sensor body  16 , sensor housing  24 , and engine block  22 . Housing  24  is substantially cylindrically shaped having a first bore  50  defining opening  36  and a second bore  52  extending to inside bottom housing  46 . Housing  24  is further defined by an outside cylindrical wall  54  that extends vertically up to second flange  34  of housing  24 . Flange  34  extends past sensor bore  20  to offer support and prevent translation of sensor housing  24  toward reluctor  14 . Cylindrical wall  54  is hermetically sealed with port  20  using an O-ring  58  to bridge a gap formed therebetween. In a preferred embodiment, a circumferential channel  60  is configured in cylindrical wall  54  for retention of O-ring  58 .  
         [0025]    Bore  50  is further defined with a first tapered tooth  64  extending radially inwardly from bore  50  and tapered to facilitate entry of sensor body  16  while engaging a periphery of sensor body  16  and make difficult the exit of the sensor body from housing  24 . More specifically, first taped tooth  64  is configured to provide a snap-fit engagement between housing  24  and sensor body  16  when a periphery of sensor body is complementary configured to cooperate in snap-fit assembly with first tapered tooth  64 . For example, a periphery of sensor body may include a plurality of snap-fit connectors  66 , preferably resilient, ribs, teeth, grooves, flanges, and the like to cooperate in a snap-fit arrangement with first tapered tooth  64 . Alternatively, first tapered tooth  64  may optionally be resilient to facilitate entry of sensor body, as well, or in place of complementary snap-fit connectors  66 .  
         [0026]    Bore  52  is smaller than bore  50  yet large enough to permit translation of sensor body  16  therethrough to allow sensor tip  18  to bottom out against inside bottom housing  46 . Bore  52  forms a hermetic seal with a periphery of sensor body using a second O-ring  68  to seal a gap  70  formed between bore  52  and sensor body  16 . In a preferred embodiment, sensor body includes a circumferential channel  72  configured therein to retain O-ring  68 .  
         [0027]    The snap-fit assembly between sensor body  16  and housing  24  will be discussed below in more detail referring to FIGS. 3 and 4. In an exemplary embodiment, snap-fit connectors  66  include a second tapered tooth  74  and a third tapered tooth  76  contiguously aligned with each other. However, it will be recognized that they may be separated resulting in a larger undesired air gap after snap-fit assembly. It will be recognized that second and third tapered teeth  74 ,  76  have an opposite taper of first tapered tooth  64  to facilitate entry of sensor body  16  in bore  50  in a direction indicated by arrow  78  while substantially limiting exit of the same. Translation of sensor body in a direction opposite arrow  78  is limited by contact of horizontal surfaces  80  on first tapered tooth  64  and second tapered tooth  74 . First tapered tooth  64  further includes a vertical flat section  82  for facilitating entry of sensor body  16  while reducing mechanical failure of first tapered tooth  64  by eliminating a tip to tooth  64  that would engage teeth  74  and  76  and provide more friction therebetween.  
         [0028]    In operation and still referring to FIGS. 3 and 4, when sensor body  16  is translated in direction of arrow  78  and sensor tip  18  is bottomed out against inside bottom housing  46 , snap fit connectors  66  or preferably teeth  74  and  76  engage first tapered tooth  64  for completing a snap-fit assembly of sensor body  16  with housing  24 . However, after compressing the sensor body to the housing to complete the snap-fit assembly, an internal air gap  84  that is some portion of a ratchet pitch between first tapered tooth  64  and second and third tapered teeth  74 ,  76  results. Air gap  84  represents an amount of allowable translation of sensor body  16  after snap-fit assembly in an opposite direction of arrow  78 . Air gap  84  in turn, results in an internal air gap between sensor tip  18  and inside bottom housing  46 . It will be understood by one skilled in the pertinent art that a smaller ratchet pitch or pitch angle will limit air gap  84 . However, it is desired to eliminate the air gap  84  all together after snap-fit assembly to eliminate any internal air gap between sensor tip  18  and inside bottom housing  46  to optimize the effectiveness of sensor probe  10 .  
         [0029]    Referring now to FIG. 5, bracket  26  will be described more fully to illustrate an exemplary embodiment thereof for eliminating any internal air gap between sensor tip  18  and inside bottom housing  46  after snap-fit assembly of sensor body  16  and housing  24 . First and second bracket components  28  and  30  are connected with one another with a vertical section  86  that is substantially normal to first and second bracket components  28  and  30 . Vertical section preferably has cutout  88  (also see FIG. 1) to allow a periphery portion of flange  32  of sensor body  16  to extend therethrough. Bracket  26  having first and second bracket components  28  and  30  with vertical section  86  intermediate therebetween are preferably made of a single stock material. The single stock material is preferably stamped and composed of metal, for example, steel or aluminum. Second bracket component  30  further includes two protrusions  90  stamped therein that are diametrically opposed from each other. The two protrusions  90  are configured to engage a top surface  92  of flange  32  and thus bias sensor tip  18  at middle section thereof. Each protrusion of two protrusions  90  are diametrically opposed thus ensuring that sensor tip bottoms out against inside bottom housing  46  when mechanical fastener  38  is tightened. By tightening fastener  38  after snap-fit assembly of sensor body  16  with housing  24 , any potential air gap resulting from such snap-fit assembly is eliminated. In turn, there is an elimination of an internal air gap between sensor tip  18  and inside bottom housing  46 . It will be recognized that a suitable gap  94  is available between a bottom surface  96  of first bracket component  28  such that bracket  26  can be translated downward as shown in FIG. 5 to eliminate any air gap  84  (FIG. 4). It will be recognized that the length of vertical section  86  is configured to allow a slightly larger gap  94  than any potential air gap  84 , such that bracket  26  may be translated to negate air gap  84  caused by ratchet pitch of snap-fit assembly configuration.  
         [0030]    Now, should the magnetic sensor require servicing, it can be easily removed and a new magnetic sensor can be installed in its place, using the installation procedure outlined above. In the case of installation of a new magnetic sensor, the sensor body is assembled with the sensor housing lodged together so as to resist separation using the ratchet teeth formed in both. Consequently, the magnetic sensor can be re-installed using the snap fit to bottom out the sensor tip against the bottom of the housing until the bracket is tightened down to take up the play and resulting internal air gap between the sensor tip and housing. Thus, the same air gap can be obtained between the reluctor and outside bottom of the sensor housing because any internal air gap as a result of the stack-up tolerance between the sensor housing and sensor body is eliminated.  
         [0031]    Accordingly, the above described method and apparatus afford simple and cost effective means to assemble a sensor body with a housing and eliminating any internal air gap associated with snap-fit assembly thereof. In addition, such means of assembly and maintaining an optimum air gap between the sensor and reluctor proves to extend the longevity thereof by eliminating a biasing spring that is subject to degradation. The above described method and apparatus allows more flexibility and allows a snap-fit assembly to maintain engagement between the sensor and housing when the bracket is not mounted to an engine or transmission block and is non-functional when the bracket is mechanical fastened and biased toward the engine or transmission block. Thus, improving longevity of the snap-fit engaging means by not relying thereon after assembly to a motor vehicle. By using the snap-fit engagement and the bracket assembly in conjunction with a sensor assembly, simplicity, cost savings, and reliability can be gained.  
         [0032]    While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the apparatus and method have been described by way of illustration only, and such illustrations and embodiments as have been disclosed herein are not to be construed as limiting to the claims.