Abstract:
An installation mechanism for installing in an outer wall of a fluid flow passage a temperature sensor equipped with a thermal sensitive device and a cylindrical casing retaining the thermal sensitive device. The installation mechanism a mount base to be joined to the fluid flow passage, an attachment to be secured to the cylindrical casing, a hollow fastener to be placed around the cylindrical casing through a gap. The fastener is designed to be rotated to press a shoulder of the attachment into constant engagement of a tapered wall thereof with a seat of the mount base to fasten the cylindrical casing to the mount base. A shield disposed to close the gap to avoid the intrusion of foreign objects into between the cylindrical casing and the fastener, thereby ensuring the removal of the fastener to dismount the temperature sensor from the fluid flow passage.

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
       [0001]    The present application claims the benefits of Japanese Patent Application No. 2007-49737 filed on Feb. 28, 2007, the disclosure of which is totally incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field of the Invention 
         [0003]    The present invention relates generally to an installation mechanism for a temperature sensor working to measure the temperature of fluid, and more particularly to such a mechanism designed to ensure ease of removal of the temperature sensor from a fluid flow passage. 
         [0004]    2. Background Art 
         [0005]      FIG. 19  illustrates an example of one of conventional temperature sensors which is used as an exhaust gas temperature sensor to measure the temperature of exhaust gas emitted from a heat engine such as an automotive internal combustion engine. 
         [0006]    The exhaust gas temperature sensor  500  includes a protection tube  507 . A nipple  506  is disposed to be rotatable about the protection tube  507  and movable in a lengthwise direction of the protection tube  507 . The nipple  506  is threadable with a boss  601  secured to an outer wall of an exhaust pipe  600  extending from the engine. The protection tube  507  has a rib  505  joined to an end thereof. The installation of the exhaust gas temperature sensor  500  in the boss  601  is achieved by placing the protection tube  507  in the boss  601 , and fastening the nipple  506  into the boss  601  to bring a top end thereof into contacting abutment with the rib  505 , thereby pressing the rib  505  against the inner wall of the boss  601 . 
         [0007]    When the exhaust gas temperature sensor  500  is secured to the exhaust pipe  600 , it will exposed partially to outside the exhaust pipe  600  or the atmospheric air. This may cause foreign objects to intrude into a gap  514  between the inner periphery of the nipple  506  and the outer periphery of the protection tube  507 , which locks the nipple  506  and the protection tube  507  together. Such locking will result in a difficulty in loosening the nipple  506  to remove the exhaust gas temperature sensor  500  from the exhaust pipe  600 . 
         [0008]    For example, Japanese Patent First Publication No. 2002-122486 discloses the above type of temperature sensor. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore a principal object of the invention to avoid the disadvantages of the prior art. 
         [0010]    It is another object of the invention to provide an improved structure of a temperature sensor designed to minimize mechanical vibrations transmitted thereto and ensure the durability thereof. 
         [0011]    According to one aspect of the invention, there is provided an installation mechanism for a temperature sensor designed to install a temperature sensor in an outer wall of a fluid flow passage and ensure ease of removal of the temperature sensor from the fluid flow passage. The temperature sensor is equipped with a thermal sensitive device and a cylindrical casing which has a length and retains the thermal sensitive device. The installation mechanism comprises; (a) a mount base to be joined to the outer wall of the fluid flow passage, the mount base having a seat; (b) an attachment that is secured to the cylindrical casing of the temperature sensor and has a first and a second wall; (c) a hollow fastener which is to be placed around the cylindrical casing through a gap between an inner periphery of the hollow fastener and an outer periphery of the cylindrical casing to be rotatable about the outer periphery of the cylindrical casing and movable in a lengthwise direction of the cylindrical casing, the gap leading to outside the fastener through an opening between the fastener and the cylindrical casing, the fastener being designed to be rotated to press the first wall of the attachment into constant engagement of the second wall with the seat to fasten the cylindrical casing to the mount base so as to have the thermal sensitive device exposed to inside the fluid flow passage; and (d) a shield disposed to close at least the opening of the gap. Specifically, the shield works as a barrier or seal to block the intrusion of foreign objects into the gap between the cylindrical casing and the fastener, thereby avoiding undesirable locking of the cylindrical casing and the fastener, which ensures the ease of removal of the fastener or the temperature sensor from the fluid flow passage. 
         [0012]    In the preferred mode of the invention, the shield is of a hollow cylindrical shape. The shield may have a flange placed in engagement with the fastener, thereby enhancing the avoidance of intrusion of foreign objects into between the cylindrical casing and the fastener and holding the body thereof from being deformed and displaced toward the thermal sensitive device when subjected to mechanical vibrations. 
         [0013]    The shield may be disposed between the fastener and the cylindrical casing so as to occupy whole of the gap. 
         [0014]    The shield may alternatively be disposed to occupy a portion of the gap including the opening. 
         [0015]    The shield may be made of a collection of fibers, thereby facilitating ease of insertion of the shield into the gap through its elasticity and permitting the shield to expand elastically within the gap to enhance the degree of sealing of the gap. 
         [0016]    The fastener may have formed therein a chamber that is a portion of the gap and exposed to the opening. The shield is at least partially fit in the chamber. This holds the body thereof from being deformed and displaced deep into the gap when subjected to mechanical vibrations. 
         [0017]    The distance between an inner periphery of the chamber and an outer periphery of the cylindrical casing is greater than that between an inner periphery of the fastener and the outer periphery of the cylindrical casing in a portion of the gap other than the chamber. This ensures the installation of the shield with a flange. 
         [0018]    The fastener may also have a second chamber formed in the inner periphery thereof of the chamber. The second chamber is so designed to have a diameter greater than that of the chamber. The shield is fit in both the chamber and the second chamber. 
         [0019]    The fastener may be designed to be joined to the base mount threadably. The attachment may be made of a hollow cylinder which has an annular shoulder defining the first wall and a tapered surface defining the second wall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only. 
           [0021]    In the drawings: 
           [0022]      FIG. 1  is a partially sectional view which shows an installation mechanism for installing a temperature sensor in an exhaust pipe of an engine according to the invention; 
           [0023]      FIG. 2  is a sectional view which illustrates a mount base secured to an exhaust pipe of an engine according to the invention; 
           [0024]      FIG. 3  is a longitudinal sectional view which shows a temperature sensor and a portion of an installation mechanism according to the invention; 
           [0025]      FIG. 4  is a longitudinal sectional view which shows an assembly of a fastener and a shield of an installation mechanism of the invention; 
           [0026]      FIG. 5  is a longitudinal sectional view which represents how to assemble a shield and a fastener of an installation mechanism of the invention; 
           [0027]      FIG. 6  is a longitudinal sectional view which shows the first modification of a shield of an installation mechanism; 
           [0028]      FIG. 7  is a longitudinal sectional view which shows the first modification of a fastener of an installation mechanism; 
           [0029]      FIG. 8  is a longitudinal sectional view which shows the second modification of a fastener of an installation mechanism; 
           [0030]      FIG. 9  is a longitudinal sectional view which shows the second modification of a shield of an installation mechanism; 
           [0031]      FIG. 10  is a longitudinal sectional view which shows the third modification of a shield of an installation mechanism which is designed to be fit in the fastener, as illustrated in  FIG. 9 ; 
           [0032]      FIG. 11  is a longitudinal sectional view which shows the fourth modification of a shield of an installation mechanism which is designed to be fit in the third modification of a fastener; 
           [0033]      FIG. 12  is a longitudinal sectional view which shows a modification of the shield of  FIG. 11 ; 
           [0034]      FIG. 13  is a longitudinal sectional view which shows a modification of an installation mechanism which is a combination of the shield of  FIG. 4  and the fastener of  FIG. 11 ; 
           [0035]      FIG. 14  is a longitudinal sectional view which shows a modification of the shield of  FIG. 13 ; 
           [0036]      FIG. 15  is a longitudinal sectional view which shows the fifth modification of a shield of an installation mechanism which is designed to be fit in the fastener of  FIG. 4 ; 
           [0037]      FIG. 16  is a longitudinal sectional view which shows a modification of an installation mechanism which is a combination of the shield of  FIG. 15  and the fastener of  FIG. 11 ; 
           [0038]      FIG. 17  is a longitudinal sectional view which shows the sixth modification of a shield of an installation mechanism which is designed to be fit in the fastener of  FIG. 4 ; 
           [0039]      FIG. 18  is a schematic view which shows a temperature sensor of the invention which is installed in an exhaust pipe of automotive vehicle; and 
           [0040]      FIG. 19  is a partially sectional view which shows an example of a conventional installation mechanism for installing a temperature sensor in an exhaust pipe of an engine. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    Referring to the drawings, particularly to  FIGS. 1 to 3 , there is shown an exhaust gas temperature sensor  1  which is to be installed in an exhaust pipe  200  of an internal combustion engine, as demonstrated in  FIG. 18 , to measure the temperature of exhaust emissions flowing through the exhaust pipe. 
         [0042]    The exhaust gas temperature sensor  100 , as clearly shown in  FIG. 3 , includes generally a thermal sensitive device  10  and a casing  20 . The exhaust gas temperature sensor  100  is, as can be seen in  FIG. 1 , installed in the exhaust pipe  200  through a installation mechanism  30  to have the thermal sensitive device  10  exposed to the exhaust gas flowing through the exhaust pipe  200 . 
         [0043]    The thermal sensitive device  10  includes a temperature transducer  101  such as a thermistor, in-sheath pin wires  102  serving as conductors extending electrically from the temperature transducer  101 , and a protective cover  103  surrounding the temperature transducer  101 . 
         [0044]    The protective cover  103  is made of a metallic hollow cylinder with a bottom. The protective cover  103  is fitted on an outer periphery of a top end of a hollow sheath pin  104 . The sheath pin  104  has the in-sheath pin wires  102  disposed therein to protect them. 
         [0045]    The thermal sensitive device  10  is coupled with the casing  20  through the sheath pin  104 . The casing  20  consists of a protection tube  107  and a cylindrical attachment  105 . The protection tube  107  serves as a hollow casing which has disposed therein the sheath pin  104  and connectors  108  to which the in-sheath pin wires  102  are joined. 
         [0046]    The cylindrical attachment  105  has a center through hole and a boss  105   a  formed on an upper end, as viewed in  FIG. 3 , thereof. The protection tube  107  is made of a metallic hollow cylinder and fit on the boss  105   a  of the cylindrical attachment  105 . The protection tube  107  is welded or brazed to the boss  105   a . The sheath pin  104  is inserted into the center through hole of the attachment  105  and welded or brazed to establish a firm joint therebetween. 
         [0047]    The connectors  108  are joined at lower ends thereof to the in-sheath pin wires  102  and at upper ends thereof to leads  109 . The leads  109  are disposed at ends thereof in an upper end of the protection tube  107  and embraced by a flexible protection tube  112 . The leads  109  are to be coupled electrically to a controller (not shown) to transmit a sensor output indicating the temperature of exhaust gas, as sensed by the thermal sensitive device  10 , to the controller. 
         [0048]    The installation mechanism  30  includes a nipple  106  and a boss  201 . The nipple  106  serves as a fastener. The boss  201  serves as a mount base. 
         [0049]    The nipple  106  is made of a cylindrical member with a center hole  160  which has a size enough to permit the protection tubes  107  and  112  to pass therethrough. The protection tube  107  is disposed in the nipple  106 . The center hole  160  is shaped to have the inner diameter which creates an air gap  114  of a distance L 1  between the inner peripheral wall of the center hole  160  and the outer peripheral wall of the protection tube  107 . This permits the nipple  106  to move a longitudinal direction of the protection tube  107  and rotate within the protection tube  107 . The nipple  106  has a flange  106   a  and an external thread  106   b  formed beneath the flange  106 , as viewed in  FIG. 3 . 
         [0050]    The boss  201  has, as clearly illustrated in  FIGS. 1 and 2 , an internal thread  201   a  formed in an inner periphery thereof which is engageable with the external thread  106   b  of the nipple  106 . The installation of the thermal sensitive device  10  and the casing  20  of the exhaust gas temperature sensor  100  in the exhaust pipe  200  is accomplished with the installation mechanism  30 . 
         [0051]    Specifically, the installation of the exhaust gas temperature sensor  100  in the boss  201  of the installation mechanism  30 , that is, the joint of the casing  20  to the boss  201  is achieved by bringing a tapered head  105   a  of the attachment  105  into contacting abutment with a tapered seat  201   b  of the boss  201 , and rotating the nipple  106  relative to a shield  113 , as will be described later in detail, to fasten the nipple  106  into the boss  201  while keeping the top end (i.e., the lower end, as viewed in  FIG. 3 ) of the nipple  106  placed on a shoulder  105   c  (i.e., the upper end surface, as viewed in  FIG. 3 ) of the attachment  105  until it forces the tapered head  105   b  against the tapered seat  201   b  of the boss  201 . This establishes an air-tight seat on a contact between the tapered head  105  of the attachment  105  and the tapered seat  102   b  of the boss  201  to avoid the leakage of the exhaust gas from the hole  201   c  of the boss  201  to outside the installation mechanism  30 . 
         [0052]    The flange  106   a  of the nipple  106  has a cylindrical recess or chamber  106   c  opening at the upper end thereof. The chamber  106   c  leads to the center hole  160  and is shaped to be greater in inner diameter than the center hole  160 . The chamber  106   c  is formed preferably by cutting or cold forging operations. 
         [0053]    The protection tube  107  is partially disposed in the chamber  106   c  to define an annular gap  114   a  of a distance L 2  between the outer periphery of the protection tube  107  and the inner periphery of the chamber  106   c . The distance L 2  is greater than the distance L 1 . The annular gap  114   a  opens at the upper end of the flange  106   a.    
         [0054]    The air gaps  114  and  114   a  define a cylindrical chamber within which, as illustrated in  FIG. 4 , the shield  113  is disposed. The shield  113  is made of a hollow cylindrical body and a flange  113   a  formed on an end of the cylindrical body. The hollow cylindrical body occupies the whole of the air gap  114 . Similarly, the flange  113   a  occupies the whole of the air gap  114   a . The air gap  114   a  greater in diameter than the air gap  114  serves to facilitate ease of insertion of the shield  113  into the air gap  114 . 
         [0055]    The shield  113  is made by forming materials such as metallic, ceramic, and/or asbest-free mineral material which are high in anticorrosion, thermal resistance, and formability into fibers and waving and compressing them into a hollow flanged cylindrical body. 
         [0056]    The installation of the shield  113 , the nipple  106 , and the attachment  105  on and in the exhaust gas temperature sensor  100  will be described below. 
         [0057]    First, the shield  113  and the nipple  106  are fitted in sequence on the protection tube  107  of the exhaust gas temperature sensor  100 . The attachment  105  is then joined or welded to the end of the protection tube  107 . 
         [0058]    Next, the shield  113  fit on the protection tube  107  is, as illustrated in  FIG. 5 , pushed toward the attachment  105 . Specifically, the shield  113  is forced into the nipple  106  from the upper end thereof, as viewed in  FIG. 5 , toward the thermal sensitive device  10  until it occupies the gaps  114  and  114   a  completely. This assembly is mounted in the boss  201  to install the exhaust gas temperature sensor  100  in the exhaust pipe  200  in the manner as described above. The shield  113  is designed to permit the nipple  106  to move in the lengthwise direction of the protection tube  107  and rotate about the protection tube  107 , thereby allowing the nipple  106  to be fastened into the boss  201  to install the exhaust gas temperature sensor  100  in the exhaust pipe  200 . The shield  113  is, as described above, made of a collection of fibers and fit between the protection tube  107  and the nipple  106 . This avoids the intrusion of foreign objects into the gaps  114  and  114   a  to eliminate the locking of the protection tube  107  and the nipple  106  through the foreign objects, thus settling the problem that when the nipple  106  is loosened to remove the exhaust gas temperature sensor  100  from the exhaust pipe  200 , the protection tube  112  rotates following the rotation of the nipple  106  to obstruct the removal of the temperature sensor  100 . 
         [0059]    The flange  113   a  of the shield  113  is fitted in the chamber  106   c  of the nipple  106 . Specifically, the flange  113   a  has the bottom placed or seated on an inner shoulder  180  formed in the nipple  106 . The bottom has a width substantially identical with a difference between the distance L 2  of the gap  114   a  and the distance L 1  of the gap  114 . This holds the shield  113  from being deformed and displaced toward the thermal sensitive device  10  when subjected to mechanical vibrations during running of the vehicle. 
         [0060]    The location where the exhaust gas temperature sensor  100  is installed in the exhaust pipe  200  is close to the ground, so that the exhaust gas temperature sensor  100  is apt to be exposed directly to water, mud, or sands and in some instances, to snow melting agent. Further, the exhaust gas temperature sensor  100  is joined directly to the exhaust pipe  200  by screwing the nipple  106  into the boss  201  of the installation mechanism  30 , so that the nipple  106  will be exposed to hot exhaust gas (e.g., 300° C. to 700° C.). Therefore, in the case of use of the exhaust gas temperature sensor  100  in automotive vehicles, it is essential for the material of the exhaust gas temperature sensor  100  to have two properties: corrosion resistance water and calcium chloride contained in the snow melting agent and heat resistance to deformation in hot environment of approximately 700° C. 
         [0061]    The shield  113  is, as described above, made of materials such as metallic, ceramic, and asbest-free mineral material which are high in anticorrosion and thermal resistance, and thus withstands severe environmental conditions where the exhaust gas temperature sensor  100  is exposed to hot exhaust gas emitted from the automotive engine. 
         [0062]    The shield  113  is, as described above, made of a collection of fibers or fabric, so that a total area of contact between itself and the outer periphery of the protection tube  107  or the inner periphery of the nipple  106  will be smaller as compared with the case where the shield  113  is made of metal. The shield  113  is, therefore, lower in friction within the gasp  114 , thus facilitating ease of insertion of the shield  113  into the gap  114 . Additionally, when the nipple  106  is removed from the boss  201  to dismount the exhaust gas temperature sensor  100  from the exhaust pipe  200 , the shield  113  does not obstruct the rotation and axial movement of the nipple  106 . 
         [0063]    It is advisable that the protection tube  107 , the attachment  105 , and the nipple  106  be made of materials identical in coefficient of linear thermal expansion with each other in order to avoid of loosening thereof arising from the exposure to thermal shock. The shield  113  is elastic, so that effects of thermal deformation i.e., expansion and contraction thereof on other parts of the exhaust gas temperature sensor  100  are low. The shield  113  is, therefore, not necessarily made of material identical in coefficient of linear thermal expansion with that of the protection tube  107 , the nipple  106 , and the attachment  105  and higher in degree of freedom of choice of materials therefor. 
         [0064]    The shield  113  is, as described above, used to seal the gaps  114  and  114   a  between the inner periphery of the nipple  106  and the outer periphery of the protection tube  107  completely, but however, may occupy only the gap  114   a , thereby minimizing the intrusion of foreign objects into the nipple  106  sufficiently. The shield  113  may be modified as discussed below. 
         [0065]      FIG. 6  illustrates the first modification of the shield  113 . The shield  113  is so shaped as to occupy the air gap  114   a  completely, but occupy the air gap  114  partially without sealing approximately a lower half of the air gap  114 . 
         [0066]    The chamber  106   c  formed in the nipple  106  may alternatively be, as illustrated in  FIG. 7 , of a frusto-conical shape in transverse section, in other words, shaped to have a tapered inner peripheral wall. The chamber  106   c  may also be shaped, as illustrated in  FIG. 8 , to have a curved inner peripheral wall. The shield  113  may be contoured to conform with the chamber  106   c  so as to occupy or seal the gap between the inner periphery of the nipple  106  and the outer periphery of the protection tube  107  completely. It is essential to shape the chamber  106   c  so that the flange  113   a  of the shield  113  engages the chamber  106   c  to stop the cylindrical body of the shield  113  from slipping deep into the air gap  114 . 
         [0067]      FIG. 9  illustrates the second modification of the shield  113 . The shield  113  has the inner diameter identical with the outer diameter of the protection tube  107  and the outer diameter identical with the inner diameter of the chamber  106   c . The flange  113   a  of the shield  113  has an annular lip  113   b  extending from an outer periphery thereof. The nipple  106  also has an annular chamber or groove  106   d  formed in the inner peripheral wall defining the chamber  106   c . The lip  113   b  is fit in the groove  106   d . Specifically, the shield  113  occupies the whole of the gap between the protection tube  107  and the nipple  106  completely. The engagement of the rip  113   b  with the groove  106   d  enhances the joining of the shield  113  to the nipple  106 , thereby minimizing the dislodgement of the shield  113  from the nipple  106  when the exhaust gas temperature sensor  100  is installed on the vehicle and experiencing vertical movement due to exposure to mechanical vibrations during running of the vehicle, which ensures the blocking of entry of foreign objects into the nipple  106 . 
         [0068]      FIG. 10  illustrates the third modification of the shield  113 . The shield  113  is made of an elastic disc. Specifically, the shield  113  is made to have only the flange. The nipple  106  is identical in structure with the one illustrated in  FIG. 9 . The shield  113  is fit in the groove  106   d  of the chamber  106   c  firmly through its elasticity. Specifically, the shield  113  is deformed to engage the groove  106   d . The shield  113  may alternatively be designed, like the one in  FIG. 9 , to have the rip  113   b.    
         [0069]      FIG. 11  illustrates the fourth modification of the shield  113 . The shield  113  is made of only a hollow cylindrical body. The nipple  106  is shaped not to have the chamber  106   c , as illustrated in  FIG. 3 , the shield  113  is fit only in the gap  114  between the protection tube  107  and the nipple  106 . The shield  113  may be designed, as illustrated in  FIG. 12 , to seal approximately an upper half of the gap  114 . 
         [0070]      FIG. 13  illustrates a combination of the nipple  106 , as illustrated in  FIG. 11 , and the shield  113 , as illustrated in  FIG. 4 . Specifically, the shield  113  is fit in the gap  114  with the flange  113   a  placed on the upper end surface of the nipple  106 . 
         [0071]      FIG. 14  illustrates a modification of the structure in  FIG. 13 . The shield  113  is disposed in the nipple  106  to seal approximately an upper half of the gap  114 . 
         [0072]      FIG. 15  illustrates the fifth modification of the shield  113 . The shield  113  is made of an annular disc and fit only in the gap  114   a . The nipple  106  may alternatively be shaped, as illustrated in  FIG. 16 , not to have the chamber  106   e . The shield  113  is placed on the upper end surface of the nipple  106  to seal only an inlet (i.e. an upper end) of the gap  114  between the protection tube  107  and the nipple  106 . 
         [0073]    The nipple  106  may be designed to have two or more annular grooves, like the groove  106   d  in  FIG. 9 , formed in either or both of the inner wall defining the chamber  106   c  (i.e. the gap  114   a ) and the inner wall defining the gap  114 . The grooves are shaped to extend on a plane perpendicular to the axial direction of the nipple  106 . 
         [0074]      FIG. 17  illustrates the sixth modification of the shield  113 . The flange  113   a  of the shield  113  has an inner tapered surface  113   t  facing the periphery of the protection tube  107 . The shield  113  is, as described above, made of an assembly of fibers or fabric and thus deformed due to the insertion thereof into the nipple  106 , so that the inner diameter thereof becomes slightly smaller than the outer diameter of the protection tube  107 . This may interfere with the insertion of the protection tube  107  into the shield  113  to increase a difficulty in assemble the protection tube  107  and the nipple  106  together. The inner tapered surface  113   t  eliminates such a drawback and facilitates ease of the insertion of the protection tube  107  into the shield  113 . 
         [0075]    While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include at possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.