Abstract:
A liquid level detecting device for detecting liquid level contained in a tank includes a float and an arm that moves in a prescribed manner when liquid level changes, a permanent magnet for forming a magnetic field, a hall IC for generating an electric signal in response to the motion of the magnetic field, a rotary member linked with the arm and the permanent magnet for moving the magnetic field relative to the hall IC as the float and the arm move, a terminal member for connecting the hall IC to an outside control circuit; and a mold body including a resinous holder for holding the hall IC and the terminal member. The resinous holder includes a sheath for insulating the hall IC from heat and mechanical stress generated when the mold body is formed.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is based on and claims priority from Japanese Patent Applications: 2005-307530, filed Oct. 21, 2005; 2005-353885, filed Dec. 7, 2005; 2006-157831, filed Jun. 6, 2006; 2006-205306, filed Jul. 27, 2006; and 2006-214928, filed Aug. 7, 2006, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a liquid level detecting device that detects the level of liquid contained in a tank and a method of manufacturing such a liquid level detecting device. In particular, the present invention relates to a fuel level gauge for detecting the level of fuel contained in a fuel tank of a vehicle.  
         [0004]     2. Description of the Related Art  
         [0005]     Such a liquid level detecting device usually equipped with a magnetic sensor to detect the level of liquid contained in a tank. The liquid level detecting device includes a body, a float, a rotary member rotatable with respect to the body, an arm that is linked with the float and the rotary member to convert a vertical motion into a rotating motion, a permanent magnet mounted on the rotary member and a magnetic sensor, as disclosed in JP-A-2004-251780, its counterpart US 2004/0163467 A1, JP-A-2004-152546, JP-A-2005-10047 or its counterpart US 2005/0083045 A1.  
         [0006]     The magnetic sensor is mounted in the body to detect magnetic flux density of the magnetic field that is formed by the permanent magnet. The body includes electric terminals that connect the magnetic sensor with an outside unit and various electric parts such as lead wires, capacitors and resistors. The electric terminals and the electric parts are insert-molded into a resinous member to protect them from vibration and other environmental hazards.  
         [0007]     However, it is difficult to reduce the size of the above liquid level detecting device because of using the lead wires and common type capacitors and resistors. Although chip capacitors and chip resistors are effective to reduce the size of the device, it is difficult to mount in the device without mechanical damage because of a high molding pressure applied to the chip capacitors.  
       SUMMARY OF THE INVENTION  
       [0008]     Therefore, an object of the invention is to provide a compact liquid level detecting device.  
         [0009]     According to a feature of the invention, a liquid level detecting device for detecting liquid level contained in a tank includes a first member moving in a prescribed manner when liquid level changes, field means for forming a magnetic field, an electronic circuit for generating an electric signal in response to motion of the magnetic field, a second member linked with the first member and the field means for moving the magnetic field relative to the electronic circuit as the first member moves, a terminal member for connecting the electric circuit to an outside control circuit; and a mold body including a resinous holder for holding the electric circuit and the terminal member, wherein the resinous holder includes a case for insulating the electronic circuit from heat and mechanical stress when the mold body is formed.  
         [0010]     In the above liquid level detecting device, the first member may include a float disposed in liquid and an arm that links the float with the second member. In this case: the field means may include a permanent magnet; the second member may include a rotary member that carries the permanent magnet; and the mold body may include a hollow shaft for rotatably supporting the rotary member at its outer periphery and accommodating the case inside thereof.  
         [0011]     In the above liquid level detecting device: the electronic circuit may be a hall IC; and the electronic circuit may further include a chip capacitor connected to the terminal member to protect the electronic circuit from electric noises. In this case: the terminal member may include at least a first terminal, a second terminal and a pair of chip mounts for mounting the chip capacitor to be connected across the first terminal and the second terminal; and the terminal member, the chip capacitor and the electronic circuit may be integrated into the resinous holder to form a detecting unit that is covered with resinous material to form the mold body. In this case: the detecting unit may include a protecting cover that covers the chip capacitor; and the resinous holder may also have a dented portion in which the chip capacitor is disposed and fixed to the terminal member.  
         [0012]     In the above liquid level detecting device: the resinous holder may have a base portion for protecting the terminal member from molding pressure when the mold body is formed in a molding die; an adhesive agent may be disposed between the resinous holder and the chip capacitor; and a resinous material may be filled in the dented portion.  
         [0013]     In the above liquid level detecting device: the case may include a sheath that extends perpendicular to the terminal member; the terminal member may have an adhesive coating at a portion in contact with the resinous holder, and the resinous holder may have a ring-shaped projection at a portion thereof surrounding the terminal member. In this case: the resinous holder may have a dented portion at a side of the sheath behind the electronic circuit to be supported by a pin projecting from a die when the detecting unit is molded into the mold body by a molding die; the resinous holder may have a projecting portion from a side of the sheath behind the electronic circuit to be supported by a molding die when the detecting unit is molded into the mold body by the molding die.  
         [0014]     Another object of the invention is to provide an improved method of manufacturing a compact liquid level detecting device without damage.  
         [0015]     According to another feature of the invention, a method of manufacturing the above constructed liquid level detecting device includes the steps of molding the terminal member with resinous material to form an integrated unit of the resinous holder having the case and the terminal member, electrically connecting a chip element to the terminal member so that the chip element can be supported by the terminal member, thereby forming a detecting unit, and molding the detecting unit with resinous material to form the mold body.  
         [0016]     In the above method: a step of filling resinous material between the chip element and the resinous holder is added before the step of molding the detecting unit; the step of molding the terminal member may further include a step of forming a dented portion for exposing the terminal member so as to connect the chip element to the terminal member; the step of molding the terminal member may further include a step of forming a base portion behind the dented portion so that the resinous holder can be supported by a mold die at the base portion in the step of molding the detecting unit; a step of covering adhesive agent at a portion of the terminal member in contact with the resinous holder may be added before the step of molding the terminal member; a step of inserting the electronic circuit into the case may be added before the step of electrically connecting. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings:  
         [0018]      FIG. 1  is a schematic diagram illustrating a liquid level detecting device according to the first embodiment of the invention;  
         [0019]      FIG. 2  is a cross-sectional view of the liquid level detecting device shown in  FIG. 1  cut along line II-II;  
         [0020]      FIG. 3  is a cross-sectional view of the liquid level detecting device shown in  FIG. 1  cut along line III-III;  
         [0021]      FIG. 4  is a schematic diagram illustrating magnetic flux distribution around a permanent magnet shown in  FIG. 2 ;  
         [0022]      FIG. 5  is an enlarged view of a terminal member shown in  FIG. 2  viewed from direction indicated by arrow V;  
         [0023]      FIG. 6  is a cross-sectional view of the terminal shown in  FIG. 5  cut along line VI-VI;  
         [0024]      FIG. 7  is a cross-sectional longitudinal view of a detecting unit shown in  FIG. 2 ;  
         [0025]      FIG. 8  is a cross-sectional longitudinal view of a body shown in  FIG. 2 ;  
         [0026]      FIG. 9  is a circuit diagram of a fuel level gauge connected with a combination meter;  
         [0027]      FIG. 10  illustrates a variation of the detecting unit shown in  FIG. 7 ;  
         [0028]      FIG. 11  is an enlarged view of a portion of the detecting unit shown in  FIG. 10  encircled by a one-dot chain line that is indicated by arrow XI;  
         [0029]      FIG. 12  illustrates a variation of the terminal shown in  FIG. 5 ;  
         [0030]      FIG. 13  is a cross-sectional view of the terminal shown in  FIG. 12  cut along line XIII-XIII;  
         [0031]      FIG. 14  is a circuit diagram of a variation of the fuel level gauge shown in  FIG. 9 ;  
         [0032]      FIG. 15  illustrates a variation of the fuel level gauge shown in  FIG. 9 ;  
         [0033]      FIG. 16  is a cross-sectional view of a liquid level detecting device according to the second embodiment of the invention;  
         [0034]      FIG. 17  is a cross-sectional longitudinal view of a detecting unit;  
         [0035]      FIG. 18  illustrates a variation of the liquid level detecting device according to the second embodiment;  
         [0036]      FIG. 19  illustrates a molding die for manufacturing the variation of the liquid level detecting device according to the second embodiment; and  
         [0037]      FIG. 20  illustrates a molding die for manufacturing another variation of the liquid level detecting device according to the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     Some preferred embodiments according to the present invention will be described with reference to the appended drawings.  
         [0039]     A liquid level detecting device according to the first embodiment of the invention will be described with reference to  FIGS. 1-15 .  
         [0040]     As shown in  FIGS. 1 and 2 , the liquid level detecting device according to the first embodiment of the invention is used as a fuel level gauge  1  that is fixed to a fuel tank to detect the level A 1  of fuel A. The fuel level gauge  1  includes a float  2 , an arm  3 , a rotary member  4 , a body  5 , a permanent magnet  6 , a detecting unit  7 , etc.  
         [0041]     The float  2  is made of a resinous member whose specific gravity is arranged to float on the fuel. The arm  3  is made of a metal (e.g. stainless steel) rod whose outside diameter is D 1  and connected between the float  2  and the rotary member  4 . As the level of the fuel moves up or down, the float  2  with an end of the arm  3  moves up and down. Accordingly, the other end of the arm  3  rotates the rotary member  4 .  
         [0042]     The rotary member  4  has a cylindrical inner wall  41 , which rotatably receives a hollow shaft  51  of the body  5 , a pair of holder members  42 , which supports a portion of the arm  3 , and a through hole  43 , which receives an end of the arm  3 . A ring-shaped groove  52  is formed on the periphery of the shaft  51  to carry a circlip or snap ring  53 , thereby fixing the rotary member  4  to the shaft  51  of the body  5 .  
         [0043]     The holder members  42  are formed on a surface of the rotary member  4  behind the body  5 . The holder members  42  have a semi-cylindrical inside wall whose inside diameter D 2  is a little smaller than the outside diameter of the arm  3  and a mouth  42   a  whose width W is smaller than inside diameter D 2 . The holder members  42  are formed so that the center axis of the hole defined by the semi-cylindrical inside wall thereof can be aligned with each other. The through hole  43  is formed to be parallel to the cylindrical inside wall  41  of the rotary member  4 . The inside diameter of the through hole  43  is equal to or a little smaller than the outside diameter of the arm  3 . The center axis of the through hole  43  extends to cross the center axis of the hole defined by the semi-cylindrical inside wall of the holder member  42 .  
         [0044]     The body  5  includes the detecting unit  7 , as shown in  FIG. 7 .  
         [0045]     The permanent magnet  6  is a cylindrical ferrite-made permanent magnet disposed inside the rotary member  4  to be coaxial with the hole defied by the inside wall  41  of the rotary member  4 . As shown in  FIG. 4 , the permanent magnet  6  is magnetized and polarized so that the magnetic flux thereof flows in a radial direction of the inside wall  41 . The permanent magnet  6  is insert-molded in the resinous portion of the rotary member  4 , which also includes the holder members  42 .  
         [0046]     The detecting unit  7  is comprised of a hall IC  70 , a terminal member  8  that connects the hall IC  70  with an outside unit, a pair of chip capacitors  9  and a chip holder  10  that has a sheath  13  for holding the hall IC  70  therein. The sheath  13  extends perpendicular to the terminal member  8  and is disposed inside the hollow shaft  51 , so that the hall IC  70  is positioned in the magnetic flux M of the permanent magnet  6 . The hall IC  70  includes signal, ground and power leads  71 - 73 , a hall element and an amplifying circuit. The hall IC  70  provides a hall voltage signal that is proportional to the magnetic flux density at its signal lead  71  when it is given a magnetic field. The hall voltage signal is amplified by the amplifying circuit before it is transmitted to a control circuit  21  ( FIG. 9 ).  
         [0047]     The terminal member  8  is made of a conductive metal and has a signal terminal  81 , a ground terminal  82 , a power terminal  83 , a pair of fixing holes  84  and two pairs of chip mounts  85 , as shown in  FIG. 5 . The terminals  81 ,  82 ,  83  are respectively connected to the three leads  71 - 73  of the hall IC  70 . The signal terminal  81  is connected with the signal lead  71 , the ground terminal  82  is connected with the ground lead  72  and the power terminal  83  is connected with the power lead  83 . Such connection is made by means of welding, soldering or mechanical clamping. The other end of terminal member  8  projects from the body  5  to be connected with the outside control circuit  21  shown in  FIG. 9  at the other end via a connector (not shown) and a wire harness (not shown).  
         [0048]     The power terminal  83  receives electric power to drive the hall element and the amplifying circuit. The signal terminal  81  transmits the hall voltage signal to the control circuit  21 . That is, a driving voltage is applied to the hall element via the power terminal  83  and the power lead  73  thereby generating a hall voltage signal if a magnetic field is formed around the hall element. The hall voltage signal is amplified by the amplifying circuit, which is driven by power supplied thereto via the power terminal  83  and the power lead  73 , and sent to the control circuit  21  via the signal terminal  81  and the signal lead  71 .  
         [0049]     The magnetic flux density of the magnetic flux passing through the hall element of the hall IC  70  changes as the fuel level A 1  changes and the rotary member  4  rotates. Therefore, the hall voltage signal changes, and the output signal of the hall IC  70  changes. Then, the level A 1  of the fuel is calculated from the output signal of the hall IC  70 .  
         [0050]     As shown in  FIG. 5 , the first pair of chip mounts  85  projects in parallel with the terminals  81 ,  82 ,  83  into a space formed between the ground terminal  82  and the signal terminal  81 , and the second pair of chip mounts projects in parallel with the terminals  81 ,  82 ,  83  into a space formed between the ground terminal  82  and the power terminal  83 .  
         [0051]     As shown in  FIGS. 6 and 7 , a portion of the terminal member  8  is dented to form the mounts  85 , onto which epoxy resin is applied to form a protecting cover  91  in order to protect the chip capacity  9  and solder  92  from heat of molding. The detecting unit  7  is formed when the terminal member  8 , the hall IC  70  and the chip capacitors  9  are connected each other, and the chip holder  10  is fixed thereto. The chip holder  10  is fixed to the terminal member  8  to hold the chip capacitors  9 . The chip holder  10  is made of a heat resistive material such as polyphenylene sulfide (PPS) and has a chip holding portion  11 , a base portion  12  and a sheath portion  13 .  
         [0052]     After the hall IC  70  is soldered to the terminal member  8 , the chip holder  10  is fixed to the terminal member  8  at the fixing holes  84  by means of thermal adhesion or press-fitting. Thereafter, the chip capacitors  9  are soldered to the chip mounts  85  so that the chip capacitors  9  can be held by the chip holder  10 .  
         [0053]     As shown in  FIG. 8 , the detecting unit  7  is insert-molded with resinous material to form the body  5 . In the meantime, the chip holder  10  is supported by a molding die at the base portion  12  thereof, so that the chip capacitors  9  can be held by the chip holding portion  11  of the chip holder  10 . Because the chip capacitors  9  are held by the chip holding portion  11 , the chip capacitors  9  are prevented from being damaged by a high molding pressure during the insert-molding. The terminal member  8  is also supported by the chip holder  10  against the molding pressure. Therefore, the terminal member  8  is prevented from bending or deforming, so that the chip capacitors  9  can be protected from mechanical stresses. Further, the hall IC  70  is protected from molding heat by the sheath portion  13 .  
         [0054]     Then, the shaft  51  is inserted into the cylindrical inner wall  41  of the rotary member  4 , and the circlip  53  is fitted to the ring-shaped groove  52 . Subsequently, the arm  3  is inserted into the through hole  43  so that the arm  3  can rotate about the through hole  43 . Thereafter, the arm  3  is press-fitted to the inside of the holder members  42  from left in  FIG. 3 . The holder members  42  elastically deform to tightly hold the arm  3 .  
         [0055]     As shown in  FIGS. 9-11 , the fuel level gauge  1  includes a pair of chip capacitors  9  soldered to the mounts  85  of the terminal member  8  to electrically connect the terminals  81 - 83 , thereby electrically protecting the hall IC  70 . Each chip capacitor  9  is a multilayer capacitor that has a capacitor of such as 4.7 nF. One of the chip capacitors  9  has a pair of leads soldered to the first pair of chip mounts  85  that respectively project from the ground terminal  82  and the signal terminal  81 . The other chip capacitor  9  has a pair of leads soldered to the second pair of the chip mounts that respectively project from the ground terminal  82  and the power terminal  83 . In other words, the signal terminal  81  and the power terminal  83  are respectively connected to the ground via the chip capacitors  9 .  
         [0056]     If a high voltage noise signal is applied to the signal terminal  81  or the power terminal  83 , the noise signal is bypassed through the chip capacitors  9  to the ground terminal  82  without badly affecting the hall IC  70 . Therefore, the hall IC  70  is not damaged by the high voltage noise. Because the chip capacitor is much smaller than the common capacitor, the size of the fuel level gauge  1  can be made compact.  
         [0057]     As shown in  FIG. 9 , a combination meter  20  includes the control circuit  21  and a fuel meter  22 . The control circuit  21 , which includes a microcomputer, is connected to a battery  24  via an ignition switch  23  and to the fuel meter  22 .  
         [0058]     When the ignition switch  23  is turned on, the control circuit  21  starts its operation. The control circuit  21  supplies electric power to the fuel level gauge  1  via the terminal  83  to operate the hall IC  70 . The hall IC  70  sends the control circuit  21  a detection signal that corresponds to the fuel level A 1  via the signal terminal  81  to drive the fuel meter  22 .  
         [0059]     If a high voltage noise is applied to the signal terminal  81  or the power terminal  83 , the high voltage noise is discharged to the ground terminal  83  via the chip capacitors  9 . Accordingly, the high voltage noise is not applied to the hall IC  70  or an amplifier.  
         [0060]     Because the hall IC  70 , the terminal member  8  and the chip capacitors  9 , which form the detecting unit  7 , are molded with resinous material when the body  5  is formed, the fuel level gauge  1  has a high vibration proof and a high resistance to temperature change during its operation.  
         [0061]     A variation of the detecting unit  7  according to the first embodiment of the invention is shown in  FIGS. 10 and 11 .  
         [0062]     An adhesive agent  14  is filled in the space between the chip capacitor  9  and the chip holder  10  instead of the chip holding portion  11 .  
         [0063]     After the hall IC  70  is soldered to the terminal member  8 , the chip holder  10  is fixed to the terminal member  8 . Thereafter, epoxy resin or the like is applied to the chip holder  10  from right in  FIG. 10 , and the chip capacitors  9  are mounted on the chip holder  10  so that the adhesive agent  14  can be sandwiched between the chip holder  10  and the chip capacitors  9 . Subsequently, the chip capacitors  9  are soldered to the chip mounts  85  of the terminals  81 - 83 . Since the chip capacitors  9  are held by the chip holder  10  via the adhesive agent, the chip capacitors  9  can be protected from outside mechanical stress.  
         [0064]     Thereafter, epoxy resin is applied over the chip capacitors  9  and hardened to form the protecting cover  91 .  
         [0065]     The adhesive agent  14  also fills gaps between the chip capacitors  9  and terminal  8  and bonds them. Therefore, the chip capacitors  9  are also supported by the terminal member  8 .  
         [0066]     The adhesive agent can be applied to gaps between the chip capacitors  9  and the chip holder  10  even if the chip holding portion  11  remains.  
         [0067]     A variation of the terminal member  8  is shown in  FIGS. 12 and 13 . Three chip mounts  85  are formed respectively on the signal terminal  81 , the ground terminal  82  and the signal terminal  83 . The chip terminals  85  are formed on the same level as shown in  FIG. 13 . One of the chip capacitors  9  is soldered to the chip mounts  85  formed on the signal terminal  81  and the ground terminal  82 , and the other chip capacitor  9  is soldered to the chip mounts formed on the ground terminal  82  and the power terminal  83 .  
         [0068]     A variation of the fuel level gauge  1  has a hall IC  70   a  that has a pair of leads  71   a  and  73  and a terminal member that has a joint terminal  81   a , a adjusting terminal  82   a  and the power terminal. The lead  71   a  functions as the signal lead  71  and the ground lead  72 , and the joint terminal  81   a  functions as the signal terminal  81  and the ground terminal  82 . The adjusting terminal  82   a  adjusts the output signal of the hall IC  70   a  that indicates fuel level A 1  of the fuel A. The fuel level gauge  70   a  also includes a chip capacitor  9  and a chip resistor  9   a . The chip resistor  9   a  has a resistance of about 30 ohms to limit current flowing into the hall IC  70   a . The terminal member  8  and the chip holder  10  may be fixed together by means of outsert-molding.  
         [0069]     Another variation of the fuel level gauge  1  is described with reference to  FIG. 15 .  
         [0070]     The terminal member  8  that includes the terminals  81 ,  82 ,  83  and the chip holder  10  are insert-molded into the detecting unit  7  in substantially the same way described previously. An adhesive agent  16  is filled between the chip holder  10  and the chip capacitor  9 . The adhesive agent  16  is firstly put on the bottom surface of the chip capacitor  9  and brought into the dented portion  15  of the chip holder  10  to be temporally fixed thereto. Subsequently, the chip capacitor  9  is soldered to the terminals  81  and  82 . The adhesive agent  16  temporally holds the chip capacitor  9  until it is soldered to the terminals  81 ,  82  and eliminates air gaps otherwise forming between the chip capacitor  9  and the chip holder  10 . Thus, the chip capacitor  9  is protected from molding pressure during the insert-molding.  
         [0071]     The chip resistor  9   a  is also soldered to the terminals  82 ,  83  in the same manner as the chip capacitor  9 . The chip holder  10  has two base portions  12  to support the chip capacitor  9  and the chip resistor  9   a  against the molding pressure, which are the same in structure as that shown in  FIG. 7 . However, the two base portions  12  can be formed into one.  
         [0072]     After the chip capacitor  9  and the chip resistor  9   a  are soldered to the terminal member  8 , resinous material is filled into the dented portion  15  to form the protecting cover  91 . The protecting cover  91  protects the chip capacitor  9  and the chip resistor  9   a  from the molding pressure and molding temperature when the detecting unit  7  is molded into the body  5 . The dented portion  15  also prevents a melted portion of the protecting cover  15  from flowing out right after the protecting cover  15  is formed.  
         [0073]     A fuel level gauge  1  according to the second embodiment of the invention will be described with reference to  FIGS. 16-20 . Incidentally, the same reference numeral will indicate the same or substantially the same part, portion or component as the first embodiment.  
         [0074]     The fuel level gauge  1  includes a float  2 , an arm  3 , a rotary member  4 , a body  5 , a permanent magnet  6 , a detecting unit  7 , which is comprised of a hall IC  70 , a terminal member  8  that connects the hall IC  70  with an outside unit and a resinous chip holder  10 . The chip holder  10  has a sheath portion  13  that holds the hall IC  70  inside thereof. The cross section of the inside space of the sheath portion  13  is approximately the same as the cross section of the hall IC  70  to tightly hold the same.  
         [0075]     The terminal member  8 , which has three terminals  81 - 83 , is covered with an adhesive coating  8   a  by means of organic plating at portions thereof in contact with the chip holder  10 . The chip holder  10  has a pair of parallelly formed ring-shaped projections  10   a , each of which has a triangular cross-section, at the upper portion thereof.  
         [0076]     In manufacturing, the adhesive coating  8   a  is coated on the terminal member  8  at first. The adhesive coating  8   a  is a coating disclosed in JP-A-2001-1445, for example. Then, the terminal member  8  is insert-molded into the chip holder  10 . In the meanwhile, the adhesive coating  8   a  is chemically bonded to the resinous material of the chip holder  10  to form a diffusion zone, so that the terminal member  8  is tightly held by the chip holder  10 . Thereafter, the hall IC  70  is inserted into the sheath  13  of the chip holder  10 . Subsequently, the leads  71 - 73  of the hall IC  70  are connected with the terminals  81 - 83  of the terminal member  8  by means of fusing or clamping, so that the detecting unit  7  is formed.  
         [0077]     The detecting unit  7  is set in a molding die for forming the body  5 , which has a filling gate above the body  5 . Therefore, liquid resinous material of a high temperature flows along the pair of ring-shaped projections  10   a  after it is injected into the die until the molding is completed. Accordingly, the upper portion of detecting unit  7  is exposed to the high temperature for a long time period, so that the resinous material is completely bonded to the detecting unit  7  when the body  5  is formed.  
         [0078]     Because the hall IC  70  is accommodated in the sheath  13 , it is insulated from heat of a high temperature while the detecting unit  7  is molded into the body  5 . Because of the adhesive coating  8   a  and the ring-shaped projection  10   a , the hall IC  70  is kept from fuel even when the fuel level gauge  1  is immersed in the fuel A. Incidentally, the number of the ring-shaped projections may be changed to three or more.  
         [0079]     A variation of the fuel level gauge  1  according to the second embodiment of the invention will be described with reference to  FIGS. 18 and 19 .  
         [0080]     The chip holder  10  has a cylindrical dented portion  10   d  at the other side of the bottom of the sheath portion  13  where the hall IC  70  is accommodated.  
         [0081]     When the detecting unit  7  is set in a molding die  100 , which is comprised of an upper die and a lower die  102 ,  102 , the dented portion  10   d  is supported by a positioning pin  103  projects from the die  102 , as shown in  FIG. 19 . Accordingly, the detecting unit  7  can be molded into the body at a high precision. Reference numeral  54  indicates a hole of the body  5  through which the positioning pin  103  extends while the body  5  is being molded.  
         [0082]     The terminal member  8  is placed in grooves  107  (e.g. three grooves for terminals  81 ,  82 ,  83 ) formed between the upper die  101  and the lower die  102 .  
         [0083]     A preset amount of hot liquid of resinous material is injected through a sprue  105  and a gate  106  into a cavity  104  until the resinous material fills the cavity  104  completely. Then, the resinous material in the cavity  104  gradually cools down and hardens. When the resinous material has hardened sufficiently, the upper and lower dies  101 ,  102  are separated to unload the body  5  from the die  100 .  
         [0084]     As shown in  FIG. 20 , the chip holder  10  can have a projection  10   e  instead of the dented portion  10   d , which is to be inserted into a positioning hole  109  formed in the lower die  102  instead of the positioning pin  103 .  
         [0085]     In the liquid level detecting device described above, the hall IC  70  may be replaced by other detecting unit such as a unit including a MRE (magnetoresistance element) or a magnetodiode.  
         [0086]     In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention is to be regarded in an illustrative, rather than a restrictive, sense.