Patent Publication Number: US-2011050249-A1

Title: Electric current measuring device with increased mechanical strength for installation

Description:
CROSS REFERENCE TO RELATED DOCUMENT 
     The present application claims the benefit of priority of Japanese Patent Application No. 2009-200047 filed on Aug. 31, 2009, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1 Technical Field of the Invention 
     The present invention relates generally to an electric current measuring device which is to be installed, for example, in automotive vehicles such as passenger automobiles or autotrucks to sense or measure electric current being charged into or discharged from a storage battery mounted in the vehicle. 
     2 Background Art 
     Japanese Patent First Publication No. 2008-39571 teaches a current sensor equipped with a current measuring circuit which is disposed on a middle portion of a bus bar and retained inside a case. Some of automotive vehicles have two ground lines extending from a minus (−) terminal of a storage battery mounted in an engine compartment to both a body of the vehicle and an engine. The measurement of electric current flowing from the battery in such a type of vehicle requires installation of the current sensor near the minus terminal of the battery and monitoring of current flowing through the two ground lines. 
     The bus bar of the current sensor, as disclosed in the above publication, is made of a flat strip. Therefore, when the bus bar is joined to the terminal of the battery directly or indirectly through a bracket, it will be cantilevered by the terminal of the battery, which may result in an increased possibility of breakage thereof. 
     SUMMARY OF THE INVENTION 
     It is therefore a principal object of the invention to provide an improved structure of a current measuring device designed to have mechanical strength great enough to withstand unwanted deformation or breakage thereof. 
     According to one aspect of the invention, there is provided an electric current measuring device designed to measure current flowing between a battery and a harness. The current measuring device comprises: (a) a first securement member which is to be secured electrically to a terminal of the battery; (b) a second securement member to which the harness is to be secured electrically; (c) a bus bar including the first and second securement members; (d) a resistor disposed between the first and second securement members, the resistor being formed one of integrally with or separately from the bus bar; (e) a circuit board having installed thereon a current measuring circuit which works to measure current flowing through the resistor as a function of the current flowing between the battery and the harness based on a potential difference between two points defined on a current flow path extending through the resistor; and (f) a case which is located between the first and second securement members and in which the resistor and the circuit board are disposed. The bus bar is made of a plate strip with a bend which has a bent cross section traversing a length of the plate strip. For example, the bend is formed by at least a side edge portion of the plate strip which is bent in a direction traversing the length of the plate strip. In the preferred mode of the invention, at least one of the first and second securement members of the bus bar has the bend. 
     The formation of the bend results in an increase in mechanical strength of the bus bar or the one of the first and second securement members. This minimizes undesirable deformation or damage of the bus bar or the case when the current measuring device is joined to the terminal of the battery. The one of the first and second securement portions also undergoes a less degree of deformation, thus resulting in a decrease in looseness of the one of the first and second securement portions when joined to the battery or the harness using, for example, a screw and also in stability of electric contact to the battery or the harness. This decreases the loss of supplying electric power to, for example, an engine starter to secure the startability of an engine mounted in an automotive vehicle. The decrease in deformation of the bus bar also permit the bus bar to be made of a thinner plate as long as it is required to secure the same degree of mechanical strength of the bus bar, thus permitting the current measuring device to be reduced in weight as a whole. The bend of the bus bar may be used to avoid an error in joining of the current measuring device to the battery and also used as a stopper to stop the current measuring device from turning undesirably. The bend of the bus bar may also serve to guide movement of the first securement portion, for example, in the case where the first securement portion is joined to the battery through an electrical lead or bracket. The formation of the bend results in an increased area of the bus bar from which the heat dissipates, thus improving the cooling ability of the bus bar without use of radiator fins. This results in a decrease in change in temperature of the bus bar, which improves the accuracy in measuring the current flowing from the battery or alternatively permits the current measuring device to be made by economical material as long as the current measurement accuracy is kept unchanged at a required level. 
     The bend of the bus bar may be defined by a C-shape in the cross section. This results in an increase in mechanical strength of the bus bar against bending thereof or vibrations acting thereon in a traversing direction, which minimizes the deformation or mechanical damage of the bus bar and the case. 
     The bend of the bus bar may alternatively be defined by an L-shape in the cross section. This shape is useful for avoiding the physical interference of the bus bar with any parts installed around the battery. 
     A portion of the bus bar extending outside the case and a portion of the bus bar embedded in the case are formed to have the bend. 
     The whole of the portion of the bus bar extending outside the case may be bent into a C- or L-shape to increase the mechanical strength thereof. The portion of the bus bar embedded in the case may also be bent into a C- or L-shape to increase the mechanical strength of a boundary portion of the bus bar (i.e., a portion of the bus bar placed in contact) between the case and the first securement portion, thereby minimizing a clearance around the boundary portion. 
     The bus bar may have a bottom wall and a side wall extending from an edge of the bottom wall. The bend of the bus bar may be defined by at least a portion of the bottom wall and the side wall. The portion of the bus bar embedded in the case may have a length greater than a height of the side wall that is a distance between the bottom wall of an edge of the side wall which is far from the bottom wall. This increases the mechanical strength of the boundary portion of the bus bar further. 
     The portion of the bus bar embedded in the case has a portion of the bend which is further bent. This further result in an increase in strength of a joint between the bus bar and the case. 
     The bend of the bus bar occupies an entire portion of the bus bar embedded in the case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
       In the drawings: 
         FIG. 1  is a partially sectional view which shows an electric current measuring device according to the invention which is placed in connection to a storage battery; 
         FIG. 2  is a side view of the current measuring device of  FIG. 1 ; 
         FIG. 3  is a perspective view of the current measuring device of  FIG. 1 ; and 
         FIG. 4  is a front view of the current measuring device of  FIG. 1 ; 
         FIG. 5  is a circuit diaphragm which shows a circuit structure of the current measuring device of  FIG. 1 ; 
         FIG. 6  is a front view which shows a modification of a bus bar installed in the current measuring device of  FIG. 1 ; and 
         FIG. 7  is a perspective view which shows the second modification of a bus bar installed in the current measuring device of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like parts in several views, particularly to  FIGS. 1 to 4 , there is shown an electric current measuring device  100  according to the present invention.  FIG. 1  is a partially sectional view which shows a structure of the current measuring device  100  installed on a storage battery  200  mounted in an engine compartment of an automotive vehicle.  FIG. 2  is a side view of the current measuring device  100 .  FIG. 3  is a perspective view of the current measuring device  100 .  FIG. 4  is a front view of the current measuring device  100 . 
     The current measuring device  100  includes a bus bar  110 , a circuit board  120 , a case  130 , a connector  140 , and a cover  150 . The bus bar  110  is made of a conductive material and serves as a shunt resistor. The circuit board  120  has fabricated thereon a current measuring circuit which works to monitor a potential difference between two points across the bus bar  110  along a direction in which the current flows through the bus bar  110  to measure or determine electric current flowing through the bus bar  110 . The case  130  stores the bus bar  110  and the circuit board  120  therein. The connector  140  has disposed therein a plurality of connector terminals  142  which electrically connect with the circuit board  120 . The case  130  has a chamber in which the circuit board  120  is mounted. The cover  150  is fit in the case  130  to close the chamber. 
     The bus bar  110  is of a U-shape with a turn disposed within the case  130 . The bus bar  110  has end portions one of which serves as a first securement portion  112  secured to the battery  200  to establish an electrical connection with the battery  200  and the other of which serves as a second securement portion  114  to which a harness  300  is secured electrically. The case  130  is substantially a rectangular parallelepiped and extends vertically, as viewed in  FIG. 1 , to have a given length. The case  130  is retained over one of side surfaces of the battery  200  which is closest to a terminal  202  of the battery  200  to which the current measuring device  100  is secured. The first and second securement portions  112  and  114 , as can be seen from  FIGS. 2 and 3 , lie on opposed sides of a major body of the cover  130  and extend horizontally or perpendicular to the length of the cover  130  in opposite directions. 
     The first securement portion  112  is of a C-shape in cross section. In other words, the first securement portion  112  is, as clearly illustrated in  FIG. 3 , made up of a bottom and two upright side walls extending from ends of the bottom perpendicular to the bottom. The bottom has a circular through hole  112 A formed therein. Referring back to  FIG. 1 , a metallic bracket  210  serving as a terminal clamp is fit on the minus (−) terminal  202  of the battery  200  to connect the first securement portion  112  of the bus bar  110  to the battery  200  electrically, thereby securing the current measuring device  100  to the battery  200 . The metallic bracket  210  functions as an electric lead which establishes the electric connection between the current measuring device  100  and the battery  200 . The metallic bracket  210  has on an end thereof the bolt  211  extending vertically of the metallic bracket  210 . The installation of the first securement portion  112  to the metallic bracket  210  is achieved by inserting the bolt  211  of the metallic bracket  210  through an open end of the first securement portion  112  into the hole  112 A, fastening a nut (not shown) onto the bolt  211  to retain the first securement portion  112  to the metallic bracket  210  firmly. The bottom (i.e., a strip) of the first securement portion  112  serves as a first joint surface  112 B, as illustrated in  FIG. 2 , to which the metallic bracket  210  is joined firmly. 
     The second securement portion  114  of the bus bar  110  has formed in an end thereof a circular hole through which a bolt  115  is inserted. The harness  300  is joined electrically to the second securement portion  114 . A terminal  302  is joined to the harness  300  and has a hole formed in an end portion thereof. The joint of the terminal  302  to the second securement portion  114  is achieved by inserting the bolt  115  installed on the second securement portion  113  into the hole of the terminal  302  and fastening a nut (not shown) onto the bolt  115  to fix the terminal  302  to the second securement portion  114 . An upper surface of the second securement portion  114  serves as a second joint surface  114 B, as illustrated in  FIG. 2 , to which the terminal  302  is joined firmly. 
     The case  130  is made of resin such as PPS (polyphenylene sulfide) which has greater electric insulation and thermal conductivity. A major portion of the bus bar  110  other than the first and second securement portions  112  and  114  is insert-molded with the resin in the case  130 . 
     A sectional shape of the bus bar  100  will be described below. 
     The bus bar  110  is made of a conductive strip of a given length and has at least a portion which is of a substantially C-shape in transverse cross section. Specifically, the bus bar  100 , as illustrated in  FIGS. 3 and 4 , has a C-shaped transverse cross section at least within a range including the first securement portion  113  made of a portion of the bus bar  110 . 
     In other words, at least the first securement portion  112  is, as illustrated in  FIG. 3 , made up of a bottom  410  elongated in the lengthwise direction of the bus bar  100  and upright side walls  420  extending perpendicular to the bottom  410 . Either one of the side walls  420  may be omitted. Specifically, the portion of the bus bar  110  having the C-shaped transverse cross section includes the first securement portion  112  exposed outside the case  130  and a portion of the bus bar  110  which continues from the first securement portion  112  and is embedded in the case  130 . If the length of the embedded portion of the bus bar  110  in the lengthwise direction of the bus bar  110  is defined as L 1 , and the height of each of the side walls  420  (i.e., the distance between the inner surface of the bottom  410  and the side edge of the side wall  420  in a widthwise direction of the side wall  420 ) is defined as L 2 , the length L 1  is selected to be greater than the height L 2  (L 1 &gt;L 2 ). 
       FIG. 4  illustrates a circuit structure of the current measuring device  100  placed in connection to the battery  200 . The current measuring device  100  has the circuit board  120  on which a differential amplifier  10 , a differential amplifier  12 , a temperature detector  20 , a current detecting processor  30 , a voltage detecting processor  32 , a temperature detecting processor  34 , a battery SOC (State-Of-Charge) determining circuit  36 , a charge controller  40 , communication I/O circuits  50  and  52 , a CAN interface  60 , and a LIN interface  62  are fabricated. The differential amplifier  10  is connected to ends of a shunt resistor  100 ′ formed by a portion of the bus bar  110 . The differential amplifier  12  is connected to the plus (+) and minus (−) terminals of the battery  200 . The CAN interface  60  works to transmit and receive data according to a CAN protocol. The LIN interface  62  works to transmit and receive data according to a LIN protocol. The differential amplifier  10  works to amplify voltage developed across the shunt resistor  100 ′. The current detecting processor  30  works to determine electric current flowing through the shunt resistor  100 ′ based on the voltage outputted from the differential amplifier  10  and provide an output indicative thereof as a function of electric current flowing from the battery  200  to the harness  300 . The differential amplifier  10  and the current detecting processor  30  serve as the current measuring circuit. The differential amplifier  12  converts the voltage, as developed between the plus and minus terminals of the battery  200  (i.e. a battery voltage), into a selected voltage level. The voltage detecting processor  32  determines the battery voltage based on the voltage outputted from the differential amplifier  12 . The temperature detector  20  is made of a voltage divider consisting of resistors and a thermistor. The thermistor has a resistance value which changes with ambient temperature to change a fraction of voltage applied to the voltage divider. The temperature detecting processor  34  monitors the fraction of voltage outputted from the temperature detector  20  to determine the temperature of the current measuring device  100  (i.e., the temperature of the battery  200 ). The battery SOC determining circuit  36  samples the outputs from the current detecting processor  30 , the voltage detecting processor  32 , and the temperature detecting processor  34  to produce a battery state-of-charge signal. The current detecting processor  30 , the voltage detecting processor  32 , and the temperature detecting processor  34 , and the battery SOC determining circuit  36  work as a SOC sensor  38 . The charge controller  40  samples the battery state-of-charge signal, as outputted from the battery SOC determining circuit  36  to control the electric generation (i.e., an output power) of an in-vehicle electric generator  80 . Specifically, the charge controller  40  outputs a control signal to a generator controller  82  installed in the generator  80  through the communication I/O circuit  52  and the LIN interface  62  to control the power outputted by the generator  80 . The battery state-of-charge signal, as outputted from the battery SOC determining circuit  36 , is transmitted to a vehicle control system  70  through the communication I/O circuit  50  and the CAN interface  60 . The vehicle control system  70  works to perform given integrated control tasks to control operations of the engine and various in-vehicle electric loads based on the state-of-charge of the battery  200 . 
     The current detecting device  100  is, as described above, equipped with the bus bar  110  designed to partially have a rigidity-increased strip made up of a bottom wall and two side walls extending from the bottom wall (i.e., a C-shape in transverse cross section) within a range including the first securement portion  112 . This results in an increase in mechanical strength of the bus bar  110  (i.e., the first securement portion  112  formed by an end portion of the bus bar  110 ), which will minimize the unwanted deformation or mechanical damage of the bus bar  110  or the case  130  when installed near the terminal  202  of the battery  200 . 
     The decrease in deformation of the first securement portion  112  results in a decrease in looseness of the first securement portion  112  when joined to the bracket  210  through engagement of the bolt  211  with the nut and also in stability of electric contact of the first securement portion  112  to the terminal  202 , thus decreasing the loss of supplying electric power to the engine starter (not shown) to secure the startability of the engine. 
     The decrease in deformation of the first securement portion  112  also permits the bus bar  110  to be made of a thinner plate as long as it is required to secure the same degree of mechanical strength of the bus bar  110 , thus allowing the current measuring device  100  to be reduced in weight as a whole. The C-shape of the bus bar  110  (i.e., the first securement portion  112 ) may be used to avoid an error in installing the current measuring device  100  on the battery  200  and also used as a stopper to stop the first securement portion  112  from turning undesirably. The C-shape shape of the bus bar  110  also serves to guide relative movement of the bracket  210  to the first securement portion  112  when the first securement portion  112  is joined to the bracket  210  of the battery  200 . 
     The C-shape of the bus bar  110  results in an increased area of the bus bar  110  from which the heat dissipates, thus improving the cooling ability of the bus bar  100  without use of radiator fins. This results in a decrease in change in temperature of the bus bar  110 , which improves the accuracy in measuring the current flowing from the battery  200  or alternatively permits the current measuring device  100  to be made by economical material as long as the current measurement accuracy is kept unchanged at a required level. 
     The C-shape in transverse cross section of the bus bar  110  (i.e., the first securement portion  112 ) results in an increase in mechanical strength against bending thereof or vibrations acting thereon in a traversing direction, which minimizes the deformation or mechanical damage of the bus bar  110  and the case  130 . 
     The whole of a portion (i.e., the first securement portion  112 ) of the bus bar  110  extending outside the case  130  may be bent into a C-shape to increase the mechanical strength thereof. A portion of the bus bar  110  embedded in the case  130  may also be bent into a C-shape to increase the mechanical strength of a boundary portion of the bus bar  110  (i.e., a portion of the bus bar  110  placed in contact) between the case  130  and the first securement portion  112 , thereby minimizing a clearance around the boundary portion. The length L 1  of the embedded portion of the bus bar  110  in the case  130  is, as described above, set greater than the height L 2  of at least one of the side walls  420 , thereby increasing the mechanical strength of the boundary portion of the bus bar  110  further. 
     While the present invention has been disclosed in terms of the preferred embodiment 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 all possible modifications to the shown embodiment which can be embodied without departing from the principle of the invention as set forth in the appended claims. 
     For instance, the current measuring device  100  is installed on the minus (−) terminal  202  of the battery  200 , but may alternatively be joined to the plus terminal of the battery  200 . 
       FIG. 6  illustrates a modification of the bus bar  110 . Specifically, the bus bar  110  is bent into an L-shape made up of the bottom wall  410  and the side wall  420  extending vertically from either of sides of the bottom wall  410 . This shape is useful for avoiding the physical interference of the bus bar  110  (i.e., the first securement portion  112 ) with any parts installed around the battery  200 . The side wall  420  may be formed only outside the case  130  or extend into the case  130 . 
     In the above embodiment, a portion of the bus bar  110  embedded in the case  130  has substantially the same configuration as the first securement portion  112  extending outside the case  130 , but however, the embedded portion may, as illustrated in  FIG. 7 , be designed to have bends extending outwardly of the bus bar  110 .  FIG. 7  illustrates such a modification of the bus bar  110 . In  FIG. 7 , “A” indicates a portion of the bus bar  110  (i.e., the first securement portion  112 ) extending outside the case  130 . “B” indicates a portion of the bus bar  110  which continues from the first securement portion  112  and is embedded in the case  130 . The bus bar  110  has, like in the first embodiment, the side walls  110 C bent from the bottom wall  410 . Each of the side walls  110 C has a tab  110 D bent outwardly or perpendicular to the length of the bus bar  110 , thereby increasing the mechanical strength of a joint between the bus bar  110  and the case  130  and the bus bar  110  itself. Only either one of the side walls  110 C may alternatively be formed to have the tab  110 D. 
     The second securement portion  114  may also be bent, like the first securement portion  112 , into the C- or L-shape in a transverse cross section thereof, as clearly illustrated in  FIG. 3  or  6 . Alternatively, only the second securement portion may be bent into the C- or L-shape. 
     The whole of a portion of the bus bar  110  extending inside the case  130  may also be bent into the C- or L-shape in a transverse cross section thereof. The bus bar  110  is made of a conductive material and easy to bend. The whole of the bus bar  110  may, therefore, be bent into the C- or L-shape in order to increase the mechanical strength thereof. 
     The chamber of the case  130  in which the circuit board  120  is placed is closed by the cover  150 , but, may alternatively be filled with, for example, epoxy resin to encapsulate the circuit board  120 . 
     The shunt resistor  100 ′ is formed by a portion of the bus bar  110 , but may alternatively be separate from the bus bar  110  and disposed within a range where the potential difference between two points to determine the current flowing through the bus bar  110  is measured.