Abstract:
In one embodiment a sensor assembly has a magnetostrictive (MR) element in a sensor housing. The MR element has a sensing part engaged with a wire coil and a frusto-conical sealing part juxtaposed with a fluid the pressure of which is to be sensed.

Description:
I. FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to magnetostrictive (MS) stress sensors. 
       II. BACKGROUND OF THE INVENTION 
       [0002]    Magnetostrictive (MS) stress sensors can be used to measure stress such as might be generated within the sensor by fluid pressure. Typically, an MS stress sensor includes a MS core made from material, such as nickel/iron alloy, and a coil that surrounds the core for establishing magnetic flux within the core. The flux loop continues trough the medium on the exterior of the coil. A ferromagnetic carrier, either MS or non-MS, is used to provide an improved return path for the magnetic flux as it circles the coil through the core and the carrier. The permeability of the MS core, and thus the impedance of the coil, is a function of the stress applied to the core. The coil impedance therefore provides a signal that represents the magnitude of stress within the core and, hence, the magnitude of the physical quantity causing the stress, such as fluid pressure action on the core. 
       SUMMARY OF THE INVENTION 
       [0003]    In one embodiment a sensor assembly has a magnetostrictive (MS) element in a sensor housing. The MS element has a sensing part engaged with a wire coil and a frusto-conical sealing part juxtaposed with a fluid the pressure of which is to be sensed. 
         [0004]    The sealing part and sensing part can be unitary with each other. In some implementations the sealing part defines an end, the fluid is in a fluid chamber, and no structure is interposed between the fluid chamber and the end of the sealing part. In other implementations the sealing part defines an end separated from the fluid by a bridge defined by the sensor housing. 
         [0005]    Non-limiting embodiments of the MS element can include a threaded part, with the sensing part being between the threaded part and the sealing part and with the parts of the MS element being made from a unitary piece of MS material. The sensing part may define a cylindrical outer periphery, and the coil can be wound around the periphery. Or, the sensing part can define a cylindrical outer periphery and a through hole, and the coil is wound through the through hole. 
         [0006]    The sensing part defines an outer diameter and the sealing part defines a base that can have the same diameter as the sensing part. Or, the sensing part can define an outer diameter that is different than the diameter of the base. 
         [0007]    In another aspect, a sensor assembly includes a unitary magnetostrictive (MS) element having a sensing part engaged with a wire coil and a tapered sealing part juxtaposable with a source of stress. The wire coil carries a signal generated in the sensing part representative of stress in the sensing part caused by the source of stress. 
         [0008]    In still another aspect, a sensor is disclosed for outputting a signal representative of stress caused by a source of stress. The sensor has magnetostrictive (MS) means including a non-tapered sensing part and a tapered sealing part, and signal means configured for carrying a signal representative of stress in the sensing part of the MS means. 
         [0009]    The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a system in accordance with one non-limiting embodiment of the present invention; 
           [0011]      FIG. 2  is a partial cross-sectional view of a first embodiment of the MR sensor assembly, showing the sealing part of the MR element in contact with the fluid chamber; 
           [0012]      FIG. 3  is a cross-sectional of an alternate embodiment in which the sealing part of the MR sensor is separated from the fluid chamber by a bridge; 
           [0013]      FIG. 4  is a side view of a the sensor assembly showing an integrated sensor core with bolt head, threaded part, sensing part, and sealing part; 
           [0014]      FIGS. 5 and 6  show alternate configurations of the sensing part of the assembly for holding the excitation coil; and 
           [0015]      FIGS. 7 and 8  show alternate sensor core configurations. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Beginning with  FIG. 1 , a general, non-limiting implementation of an MS stress sensor  10  is shown. The MS stress sensor  10  can be coupled to a source of pressure, such as to a fluid container  12 , with the MS stress sensor  10  having the ability to sense fluid pressure in the fluid container  12  in accordance with principles below. Without limitation, the fluid container  12  may be, e.g., a vehicle fuel rail, an engine combustion chamber, etc., although present principles are not limited to any particular fluid (liquid or gas) application. The core of the sensor  10  is made of a magnetostrictive material such as, e.g., nickel/iron alloys, pure nickel, terfenol, galfenol. Preferred non-limiting materials include maraging steel (steel with about 18% nickel content) and nickel-iron alloys with 30%-70% nickel content. 
         [0017]    The MS stress sensor  10  is also electronically connected to a computer  14  which may be, without limitation, an engine control module. The computer  14  receives the signal that is output by the sensor  10  for processing the signal to, e.g., correlate the stress as indicated by the signal to a fluid pressure. Further, the computer  14  may be electronically connected to a component  16  such as a fuel pump that may be controlled by the computer  14  based on data received from the MS stress sensor  10 . 
         [0018]    A first embodiment of an MS sensor assembly is shown in  FIG. 2 . The present embodiment can be used for sensing either, relatively low pressures, or for sensing relatively high pressures depending on the strength of the selected MS core material. A strong material is understood here to be a material with high yield strength. 
         [0019]    A sensor housing  18  is shown with a fluid chamber  20  inside at least part of the housing  18 .  FIG. 2  also shows a core  22  that is made of a MS material. The core  22  embodies a frusto-conical sealing part  24  which substantially prevents fluid from leaking from the fluid chamber  20  to components discussed below. Specifically, the sealing part  24  defines an end  24   a  of the MS core  22  and no structure is interposed between the fluid chamber  20  and the end of the sealing part  24 , such that the MS core  22  functions as both a sensing element and a sealing element. It may be appreciated that the frusto-conical shape of the core  22  shown in  FIG. 2  provides a convenient and effective solution for sealing fluids under pressure and is also easier to manufacture than corresponding flat surfaces that seek to accomplish the same purpose. 
         [0020]    With more specificity regarding the above-discussed sealing feature, the housing  18  can form a frusto-conical separation wall  26  as also shown in  FIG. 2 , which closely receives the sealing part  24   a  of the core  22  to facilitate preventing fluid in the fluid chamber  20  from leaking past the core  22 . Related components to the core  22  include a coil  28  that is wound around a side  29  of an aperture in the cylindrical sensing part  30  of the core  22 . The coil  28  may induce magnetic flux in an integrated flux return path  31  upon which a magnetic flux may exist, the magnetic flux being generated by an alternating current in the coil  28 . As pressure from the fluid chamber  20  acts on the core  22  a signal indicative of flux is generated that indicates the amount of pressure currently in the fluid chamber  20 . Variations of the coil  28  will be discussed in greater detail in the descriptions below. The coil  28  may thus be supplied with AC current from a current source to generate a magnetic flux in the core  22  and then a corresponding AC voltage can provide signals representative of the changing flux in the core and, hence, the pressure in the fluid chamber. The respective roles of the current and voltage can also be reversed, that is, the coil  28  may be energized by an AC voltage source to generate a magnetic flux in the core  22  and then a corresponding AC current can provide signals representative of the changing flux in the core and, hence, the pressure in the fluid chamber. 
         [0021]    Moving to  FIG. 3 , an alternate embodiment of the MS stress sensor  10  is shown, the alternate embodiment being designed for MS stress sensors operating in relatively high pressure situations where having a sealing element of an MS core interposed directly between a fluid chamber and the rest of an MS core may damage or cause malfunction to an MS core composed of a weaker MS material. Thus, a structure for relieving some stress created by fluid pressure before the stress acts on the MS sensor element is shown in  FIG. 3 . 
         [0022]    A sensor housing  32 , which may in non-limiting embodiments include a cover  34 , is shown. The cover  34  ensures a stable and secure fit of a sensor core  40  inside the sensor housing  32  maintaining a sufficient compressive force for both, fluid sealing and minimizing airgaps in the path of the magnetic flux. The sensor housing  32  with core  40  is substantially similar to the sensor housing  18  and core  22  shown in  FIG. 2 , with the following exceptions. Distinguishing from the first embodiment, a frusto-conical separation wall  36  similar to the separation wall  26  of  FIG. 2  is shown, but in the second embodiment the separation wall  36  also includes a stress-relieving bridge  38  that is defined by the sensor housing  32  and that separates the bottom end  39  of the MS sensor element  40  from fluid  42  under pressure in the fluid chamber  44 . The stress-relieving bridge  38  advantageously reduces fluid pressure by carrying some stress away from the MS sensor element  40  before any resulting pressure acts on it. 
         [0023]    Regarding the MS sensor element  40 , it is to be understood that it includes both a coil and an MS core and that it is substantially similar to the MS sensor element described  FIG. 2 . Further, the stress-relieving bridge  38  advantageously allows the MS sensor element to be made out of any MS material, and not just one capable of functioning under relatively high amounts of pressure. Further still, as a result of force applied by fluid pressure, the cover  34  keeps the MS sensor element  40  static and in its proper position within the sensor housing  32 . 
         [0024]    To further ensure that an MS sensor element remains fixed in its intended position within a sensor housing,  FIG. 4  shows a threaded part on an MS sensor core which may be used in non-limiting embodiments. More particularly,  FIG. 4  shows a unitary MS sensor core  46  that is shown outside its embodiment in a sensor housing. The MS sensor core  46  includes, from top to bottom, a hexagonal head  48 , along with a threaded part  50  which secures the core  46  in a housing through threadable engagement. Below the threaded part  50  is a sensing part  52  through which a magnetic flux permeates, and a frusto-conical sealing part  54  above a fluid cavity  56  which contains fluid under pressure. 
         [0025]    Accordingly, the sensing part  52  is between the threaded part  50  and the sealing part  54 , with the threaded part  50  engageable with a threaded hole in a sensor housing (not shown in  FIG. 4 ). Further, the MS element  46  is made from a unitary piece of MS material. Thus, the  FIG. 4  embodiment of an MS sensor core may be easily assembled while also eliminating the need for a cover because of the added threaded feature. Further still, and although a variety of means can be envisioned to secure the thread  50  to the housing (not shown), the hexagonal head  48  shown in  FIG. 4  also makes assembly of an MS stress sensor  10  easier because of its ability to secure the entire MS sensor core  46  using a tool such as a wrench. 
         [0026]      FIG. 5  shows one configuration of an MS sensor core&#39;s assembly for holding an excitation coil. The MS sensor core  58  is substantially similar in function and configuration to the MS sensor core  46  in  FIG. 4 , with the exceptions below. The MS sensor element  58  has a hexagonal head  60 , a threaded part  62 , a sensing part  64 , and a sealing part  66  that is integrated into the separation wall of a sensor housing (not shown), all the preceding parts being substantially similar in function to the hexagonal head  48 , threaded part  50 , sensing part  52 , and sealing part  54  referenced in  FIG. 4 , respectively. A fluid cavity  68  is also shown, which is to be understood to contain fluid under pressure. 
         [0027]      FIG. 5  also shows a coil  70  that is substantially similar in function to the coil  28  in  FIG. 2 . The sensing part  64  defines a cylindrical outer periphery  72  and, unlike the core  46  in  FIG. 4 , a through hole  74 .  FIG. 5  shows the coil  70  being wound through the through hole  74  plural times. As indicated by  FIG. 5 , magnetic flux  76  can permeate the core  58  and in essence is confined to closely circumscribe the through-hole  74 . Generally, if gaps of air exist within a magnetic flux path, the inductance of the coil  70  is weakened or varied as a result, which in turn weakens and/or varies the signal strength to be measured. Advantageously, the configuration of the coil  70  shown in  FIG. 5  allows for a stronger signal strength because of an air-gapless path of magnetic flux  76 , made possible by the unitary core design above. 
         [0028]    Alternatively,  FIG. 6  shows another possible configuration of an MS sensor core assembly for holding an excitation coil. The MS sensor element  78  is substantially similar to the MS sensor core  46  in  FIG. 4 . The MS sensor element  78  has a bolt head  80 , a threaded part  82 , a sensing part  84 , and a sealing part  86  that is to be integrated into the separation wall of a sensor housing (not shown), all the preceding parts being substantially similar in function to the bolt head  48 , threaded part  50 , sensing part  52 , and sealing part  54  referenced in  FIG. 4 , respectively. A fluid cavity  88  is also shown, which is understood to contain fluid under pressure. 
         [0029]      FIG. 6  also shows a coil  90  and a cylindrical outer periphery  92  defined by the sensing part  84 . The coil  90  is substantially similar in function to the coil  28  referenced in  FIG. 2 . Further, the coil  90  is wound around the cylindrical outer periphery  92  of the sensing part  84 . Distinguishing  FIG. 6  from  FIG. 5 , in  FIG. 6  the magnetic field establishes a loop of flux  94  that extend through a substantial portion of the core  78  including the threaded part  82  and the sealing part  86 , as well as the sensing part  84 . Both the threaded part  82  and the sealing part  86  are unitary with the sensing part  84  and made of the same MS material, thus allowing a uniform magnetic flux to travel through all three parts. It should also be noted that while the magnetic flux  94  loops outside the sensor core  78  in  FIG. 6 , the magnetic flux  94  still essentially does not encounter any air gaps because the outer portions of the magnetic flux  94  shown outside the sensor core  78  actually loop through a sensor housing that is not shown, the sensor housing understood to be in physical contact with the sensor core  78 . Thus, an air-gapless magnetic flux is also substantially achieved in  FIG. 6 . Moreover, the coil configuration shown in  FIG. 6  also simplifies the coil winding method compared to a method that would have to be used when winding a coil through a through hole. 
         [0030]    Moving from coil configurations to sensor core configurations,  FIGS. 7 and 8  show alternate sensor core configurations.  FIG. 7  shows a sensor core configuration that has sealing and sensing parts with the same diameter at their interface with each other. 
         [0031]    A sensor housing  98  which houses the sensor core  100  is shown. The sensor core  100  is substantially similar in function and configuration to the sensor core  22  in  FIG. 2  except as noted below. A coil  102  is wound around a solid cylindrical sensing part  103  through an opening  116  that is established between the sensing part  103  and an integrated handle  103   a  that joins the sensing part  103  at upper and lower interfaces as shown. This configuration allows for increased permeability of the sensor core  100 , which in turn increases signal strength generated by a magnetic flux in the core  100 . Also, the sensor core  100  has a sealing part  104  that closely engages a separation wall  106  of the housing  98  to prevent fluid in the fluid cavity  108  from reaching other parts of the core  100 . 
         [0032]    In the configuration shown in  FIG. 7 , the sensing part  103  defines an outer diameter that is the same as that of the sealing part  104  at the interface between the two parts, with the diameter of the sealing art  104  tapering inwardly from the interface as shown. 
         [0033]    It is to be generally understood that the relevant feature of this particular embodiment is that a sensing part and a sealing part have the same base dimensions, i.e., the same cross-sectional area at their interface. While this embodiment provides a sensor core having sensing and sealing parts with the same cross-section at the interface, it is to be generally understood without limitation that the cross-section of the sealing part of a sensor core may be larger or smaller than the cross-section of the sensing part of a sensor core at the interface between the parts. 
         [0034]    Such a configuration is shown in  FIG. 8 , which depicts a sensor housing  118  that holds a sensor core  120 . The sensor core  120  is substantially similar to the sensor core  100  in  FIG. 7  with the exceptions noted below. A coil  122  can be substantially similar to the coil  28  from  FIG. 2 . 
         [0035]    Also substantially similar to previous embodiments referenced above, the sensor core  120  has a frusto-conical sealing part  124  that engages a separation wall  126  of the housing  118 . The sensor core  120  also has a sensing part  128  which is substantially similar to the sensing part  103  in  FIG. 7 . 
         [0036]    Now distinguishing from previous embodiments, the sealing part  124  defines a base  124   a  having a diameter different from the outer diameter defined by the sensing part  128 . Furthermore, the axis  136  of the sealing part  124  is offset from the axis  138  of the sensing part  128 . While sensing and sealing parts of an MS sensor core may without limitation have axes coaxial with each other, in the embodiment of  FIG. 8  it is advantageous to have the axis  136  of the sealing part  124  be offset from the axis  138  of the sensing part  128 , for the following reason. It is to be generally understood that the active portion of the sensing part  128  is the area near the coil where a magnetic flux is strongest, in particular as a result of eddy current effects. Therefore, it is advantageous to offset the axis  138  of the sensing part  128  so that the axis  136  of the sealing part  124  may be in closer proximity to the active portion of the sensing part  128  because most of the stress caused by fluid pressure in the fluid cavity  130  will be transferred along the axis  136  of the sealing part  124 . Thus, the active portion of the core  120  advantageously receives more stress from fluid pressure as a result of the axes in  FIG. 8  being offset, increasing stress-related permeability changes in the core  120 , which in turn increases signal strength generated by a magnetic flux in the core  120 . 
         [0037]    It is to be understood that a cylindrical sensing part is not the only shape that may be used in the non-limiting embodiment of a sensor core shown in  FIGS. 7 and 8 . For instance, a parallelepiped shaped sensing part may be used, having a rectangular cross-section interfacing with the circular base of a frusto-conical sealing part. Furthermore, the tops of the sensing parts in  FIGS. 7 and 8  are omitted for clarity, it being understood that a cover such as that shown in  FIG. 3  or a threaded portion such as those shown in  FIGS. 4-6  may be used in the embodiments of  FIGS. 7 and 8 . 
         [0038]    While the particular MAGNETOSTRICTIVE PRESSURE SENSOR WITH AN INTEGRATED SENSING AND SEALING PART is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.