Abstract:
The present invention relates to a fuel level system for an automobile, and more particularly, to a fuel level system for use in informing a driver of the amount of remaining fuel in a fuel tank of an automobile using gasoline, light oil, gas or the like, wherein a flowing electric current is increased in a contact of a level sender unit. The fuel level system of the present invention comprises a level sender unit installed in a fuel tank of the automobile, a fuel gauge, and a resistor installed inside or outside the level sender unit within the fuel level system to increase an electric current flowing through a contact of the level sender unit.

Description:
RELATED APPLICATIONS  
         [0001]    The present disclosure relates to subject matter contained in Korean Application No. 10-2002-0076850 filed on Dec. 5, 2002 and No. 10-2003-0060920 filed on Sep. 1, 2003, which are herein expressly incorporated by reference its entireties.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to a fuel level system for an automobile, and more particularly, to a fuel level system for use in informing a driver of the amount of remaining fuel in a fuel tank of an automobile using gasoline, light oil, gas or the like, wherein an electric current flowing through a contact of a level sender unit is increased so as to eliminate contact resistance resulting from silver sulfide, silver oxide or other foreign materials generated due to corrosion in the contact of the level sender unit, thereby preventing wrong indication of a fuel gauge due to the contact resistance in the contact and more accurately providing the driver with information on the amount of remaining fuel.  
           [0004]    2. Description of the Prior Art  
           [0005]    Generally, an automobile is equipped with a fuel level system for informing a driver of the amount of remaining fuel in a fuel tank of the automobile. The fuel level system detects the amount of remaining fuel and then operates a fuel gauge disposed on an instrument panel on the side of a driver&#39;s seat.  
           [0006]    [0006]FIG. 1 is a sectional view schematically showing of a conventional fuel level system for an automobile, and FIG. 2 is a circuit diagram showing one example of the conventional the fuel level system. As shown in the figures, the conventional fuel level system comprises a level sender unit  20  that is installed in a fuel tank  10  and provided with a level resistor  21 ; a pivotable bar  22  with a movable piece connected to the level resistor  21  of the level sender unit  20  via a contact to change the resistance of the level resistor  21 ; and a float  23  capable of operating the bar  22  in an interlocked manner.  
           [0007]    An ECU  30  receives a voltage drop signal corresponding to the amount of remaining fuel in the fuel tank  10  from the level sender unit  20  and utilizes the signal as an operation factor for checking whether evaporated gas leaks out. The ECU  30  performs the function of converting information on the check results into a pulse width control signal and sends the pulse width control signal to a fuel gauge  40 .  
           [0008]    Then, the fuel gauge  40  receives the pulse width control signal from the ECU  30  or the voltage drop signal directly from the level sender unit  20 , and indicates the amount of remaining fuel in the fuel tank  10  in a graphical manner or using a pointer.  
           [0009]    The operational relationship among the above components will be described hereinafter with reference to FIG. 2.  
           [0010]    First, the ECU  30  comprises a pull-up resistor  31 , and the pull-up resistor  31  and the level resistor  21  of the level sender unit  20  are connected in series via the contact of the movable piece connected to the bar  22 . When a 5V constant-voltage power source  32  within the ECU  30  is applied to and energizes the serial circuit, the value of voltage drop (VL) corresponding to the amount of remaining fuel in the fuel tank  10  occurs in the level resistor  21 .  
           [0011]    Then, an AD converter  33  in the ECU  30  measures the value of the voltage drop through a monitoring resistor  34  and sends a pulse width control signal corresponding to the value of the voltage drop to the fuel gauge  40  so that the amount of remaining fuel can be indicated to a driver.  
           [0012]    Meanwhile, as shown in FIG. 3, it is possible to employ a pull-down resistor  35  connected directly to the level resistor  21  instead of the pull-up resistor  31  and to connect the AD converter  33  to the pull-down resistor  35 . However, even in this case, the operational relationship is the same.  
           [0013]    [0013]FIGS. 4 and 5 are circuit diagrams showing other examples of the conventional fuel level system for an automobile. In these examples, the conventional fuel level system only comprises the level sender unit  20  and a microcomputer-type fuel gauge  40  without such an ECU  30 . There is a difference in that the microcomputer-type fuel gauge  40  in FIG. 4 contains a microcomputer  41  and a pull-up resistor  42  in FIG. 4, whereas the microcomputer-type fuel gauge  40  in FIG. 5 contains the microcomputer  41  and a pull-down resistor  43 .  
           [0014]    Additionally, there has been used a fuel level system employing a cross coil-type or bimetal-type gauge as shown in FIG. 6. In this case, the voltage of 12V of a battery in the automobile may be applied to the gauge  50 , or a 5˜12V constant-voltage power source  51  may be independently connected to the gauge  50 . Alternatively, the ECU  30  may be connected in parallel to use information on determination of the amount of remaining fuel upon control of leak of evaporated gas.  
           [0015]    Although various types of fuel level systems have been used as described above, all the fuel level systems utilize in common the contact of the movable piece and the level resistor  21  of the level sender unit  20 .  
           [0016]    Metals such as AgCu, AgPd or AgNi containing silver (Ag) are mainly used for a conductive portion of the level resistor  21  and the contact of the movable piece. At this time, the silver (Ag) and sulfur (S) contained in fuel react with each other and thus produce silver sulfide as well as silver oxide due to oxidation in the air. Such silver sulfide and silver oxide generate contact resistance in the contact. Thus, there may be a problem in that the fuel gauge of the fuel level system may not indicate a correct value.  
           [0017]    As for methods of minimizing such contact resistance, there are the following methods.  
           [0018]    First, it is possible to conceive a method by which the contact of the movable piece and the conductive portion of the level resistor are made of a material that cannot be oxidized or corroded. However, there is no feasibility because of a limitation on material technology and high costs.  
           [0019]    Second, it is possible to conceive a method by which an oxidized portion can be worn out by increasing contact pressure in the contact of the movable piece during its operation. However, there is a limitation on the durability of the contact.  
           [0020]    Finally, it is possible to conceive a method by which an electric current flowing through the contact is increased so that produced contact resistance can be eliminated due to the increased electric current.  
           [0021]    To this end, the value of pull-up or down resistance in an electronic control module and the fuel gauge is caused to be decreased and the value of level resistance of the level sender unit is also caused to be decreased. However, in order to cause the fuel gauge to more accurately indicate the amount of remaining fuel, a sufficient gap should be given between the maximum and minimum values of the level resistance. Thus, there is a limitation on the decrease in the value of the resistance.  
         SUMMARY OF THE INVENTION  
         [0022]    The present invention is contemplated to solve the aforementioned drawbacks or problems in the prior art. An object of the present invention is to provide a fuel level system for an automobile, wherein contact resistance resulting from silver sulfide, silver oxide or other foreign materials generated due to corrosion in a contact of a level sender unit is eliminated, thereby preventing wrong indication of a fuel gauge due to the contact resistance in the contact and more accurately providing a driver with information on the amount of remaining fuel.  
           [0023]    According to an aspect of the present invention for achieving the object, there is provided a fuel level system for an automobile including a level sender unit installed in a fuel tank of the automobile and a fuel gauge, comprising a resistor installed inside or outside the level sender unit within the fuel level system to increase an electric current flowing through a contact of the level sender unit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0025]    [0025]FIG. 1 is a sectional view schematically showing a conventional fuel level system for an automobile;  
         [0026]    [0026]FIG. 2 is a circuit diagram showing a first example of the conventional fuel level system;  
         [0027]    [0027]FIG. 3 is a circuit diagram showing a second example of the conventional fuel level system;  
         [0028]    [0028]FIG. 4 is a circuit diagram showing a third example of the conventional fuel level system;  
         [0029]    [0029]FIG. 5 is a circuit diagram showing a fourth example of the conventional fuel level system;  
         [0030]    [0030]FIG. 6 is a circuit diagram showing a sixth example of the conventional fuel level system;  
         [0031]    [0031]FIG. 7 is a circuit diagram showing a first embodiment of a fuel level system for an automobile according to the present invention;  
         [0032]    [0032]FIG. 8 is a circuit diagram showing a configuration for preventing an inverse electric current in the fuel level system of FIG. 7;  
         [0033]    [0033]FIG. 9 is a circuit diagram showing a second embodiment of the fuel level system for the automobile according to the present invention;  
         [0034]    [0034]FIG. 10 is a circuit diagram showing a third embodiment of the fuel level system for the automobile according to the present invention;  
         [0035]    [0035]FIG. 11 is a circuit diagram showing a fourth embodiment of the fuel level system for the automobile according to the present invention; and  
         [0036]    [0036]FIG. 12 is a circuit diagram showing a fifth embodiment of the fuel level system for the automobile according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    Hereinafter, preferred embodiments of a fuel level system for an automobile according to the present invention will be described in detail with reference to the accompanying drawings.  
         [0038]    [0038]FIG. 7 is a circuit diagram showing a first embodiment of the fuel level system for the automobile according to the present invention. The fuel level system of the present invention comprises a level sender unit  100  installed in a fuel tank of the automobile, a fuel gauge  300 , and a resistor  120  installed inside or outside the level sender unit  100  within the fuel level system to increase an electric current flowing through a contact of the level sender unit  100 .  
         [0039]    In the first embodiment shown in FIG. 7, the fuel level system comprises the level sender unit  100  that is installed within the fuel tank and includes a level resistor  110  of which a resistance value varies by means of a movable piece  111  operated in a state where it is interlocked with a float, and the resistor  120  connected in series to a side of the level resistor  110  and an ignition power source or constant-voltage power source (energizing voltage source)  130  connected in series to the resistor  120 ; and an ECU  200  that includes a pull-up resistor  220  connected in series to the level resistor  110  of the level sender unit  100  and to a power source  210 , and a monitoring resistor  230  and an AD converter  240  connected to the pull-up resistor  220 , thereby measuring the value of voltage drop due to the level resistor  110  and the pull-up resistor  220  and sending the measured value to the fuel gauge  300  through the AD converter  240 .  
         [0040]    The constant-voltage power source generally outputs a constant voltage in a range of 5 to 12V.  
         [0041]    Contact failure may sometimes occur between the level resistor  110  and the contact of the movable piece  111  that comes into contact with the level resistor  110 . In such a case, an inverse electric current may be produced toward the ECU  200  by the energizing voltage source  130 . Therefore, in order to prevent the inverse electric current, a diode  140  may be disposed between the level resistor  110  and the pull-up resistor  220 , if necessary.  
         [0042]    Further, the inverse electric current may be prevented by disposing a resistor R r    150  between a connection of a lower end of the level resistor  110  and the resistor  120  and a ground connected to the movable piece  111 , as shown in FIG. 8.  
         [0043]    [0043]FIG. 9 is a circuit diagram showing a second embodiment of the fuel level system for the automobile according to the present invention. In this embodiment, a pull-down resistor is employed in the fuel level system.  
         [0044]    In the second embodiment, the fuel level system comprises the level sender unit  100  that is installed within the fuel tank and includes the level resistor  110  of which the resistance value varies by means of the movable piece  111  operated in a state where it is interlocked with the float, and the resistor  120  of which one side is connected in series to the level resistor  110  and the other side is grounded; and the ECU  200  that includes a pull-down resistor  250  of which one side is grounded and the other side is connected in series to the level resistor  110  of the level sender unit  100 , the power source  210  connected in series to the movable piece  111 , and the monitoring resistor  230  and the AD converter  240  connected to the pull-down resistor  250 , thereby measuring the value of voltage drop due to the level resistor  110  and the pull-down resistor  250  and sending the measured value to the fuel gauge  300  through the AD converter  240 .  
         [0045]    Meanwhile, in third and fourth embodiments of the present invention shown in FIGS. 10 and 11, the technical spirit of the present invention is applied to a fuel gauge using a microcomputer.  
         [0046]    That is, although the level sender unit  100  in the third embodiment is the same as the first embodiment, the fuel level system of this embodiment is different from that of the first embodiment in that it comprises, instead of the ECU, the fuel gauge  300  which includes a pull-up resistor  320  connected in series to the level resistor  110  of the level sender unit  100  and to a power source  310  thereof, and a monitoring resistor  330  and a microcomputer  340  connected to the pull-up resistor  320 , whereby the microcomputer  340  measures the value of voltage drop due to the level resistor  110  and the pull-up resistor  320  and informs a user of the value.  
         [0047]    Even in the third embodiment, in order to prevent an inverse electric current resulting from contact failure which may sometimes occur between the level resistor  110  and the contact of the movable piece  111  that comes into contact with the level resistor  110 , the diode  140  may be disposed between the level resistor  110  and the pull-up resistor  220 , or the resistor R r    150  may be disposed between the connection of the lower end of the level resistor  110  and the resistor  120  and the ground connected to the movable piece  111 , in the same manner as the first embodiment (FIG. 10 shows a state where the diode  140  is disposed).  
         [0048]    Moreover, although the level sender unit  100  in the fourth embodiment is the same as the second embodiment, the fuel level system of this embodiment comprises, in addition to this level sender unit  110 , the fuel gauge  300  which includes a pull-down resistor  350  of which one side is grounded and the other side is connected in series to the level resistor  110  of the level sender unit  100 , the power source  310  connected in series to the movable piece  111 , and the monitoring resistor  330  and the microcomputer  340  connected to the pull-down resistor  350 , whereby measuring the value of voltage drop due to the level resistor  110  and the pull-down resistor  350  and informing the user of the value.  
         [0049]    [0049]FIG. 12 is a circuit diagram showing a fifth embodiment of the fuel level system for the automobile according to the present invention. The level sender unit  100  in this embodiment measures the value of voltage drop due to the level resistor  110  in the same manner as in the first and third embodiments, but is connected to a cross coil or bimetal gauge  370  provided with a 12V power source  360 . The ECU  200  may be connected in parallel to the level sender unit  100  to control evaporated gas, if necessary.  
         [0050]    In the first to third and fifth embodiments, a 5V constant-voltage power source is used as the power source, and a 12V ignition power source or a 5˜12V constant-voltage power source is used as the power source (energizing voltage source) applied to the resistor  120 .  
         [0051]    Hereinafter, the operation and effects of the present invention will be described with reference to FIGS.  7  to  12 .  
         [0052]    The description will be made by focusing on the operation of the first embodiment shown in FIG. 7. The power source  210  of the ECU  200  is first applied to the circuit in which the pull-up resistor  220  is connected in series to the level resistor  110  of the level sender unit  100 . Then, voltage drop corresponding to the amount of remaining fuel occurs in the level resistor  110 . This is the same as the prior art.  
         [0053]    An electric current I L1  flowing through the contact of the movable piece  111  through the circuit is calculated from 5/(R E +R L1 ), where R E  is a resistance value of the pull-up resistor  220  of the ECU  200 , and R L1  is a resistance value of the level resistor  110  corresponding to the amount of remaining fuel in the fuel tank.  
         [0054]    At this time, a flowing electric current I A  increased by means of the resistor  120  in the present invention is calculated from (energizing voltage)/(R A +R L2 ), where R A  is a resistance value of the resistor  120  and R L2  is a value obtained by subtracting R L1  from the total resistance value of the level resistor  110 .  
         [0055]    As described above, according to the present invention, it will be understood that the contact electric current flowing through the contact of the movable piece  111  and a contact portion of the level resistor  110  is increased by I A  and thus the total electric current of I A +I L  flows. The increased amplitude of the flowing electric current can be very widely adjusted depending on the setting of the value of R A . Therefore, it is possible to ensure a flowing electric current with a sufficient amplitude capable of preventing the generation of contact resistance in the contact.  
         [0056]    That is, in the circuit of the conventional fuel level system, a flowing electric current at one of an empty position (where the amount of remaining fuel is minimum) and a full position (where the amount of remaining fuel is maximum) is inevitably lower relatively than that at the other position. However, according to the present invention, a flowing lower electric current at the position in which the flowing electric current was relatively lower in the conventional fuel level system can become larger than the relatively larger electric current in the conventional fuel level system.  
         [0057]    Further, as described above, contact failure may sometimes occur between the level resistor  110  and the contact of the movable piece  111  that comes into contact with the level resistor  110 . In such a case, an inverse electric current may be produced toward the ECU  200  by the energizing voltage source  130 . Therefore, the diode  140  is disposed between the level resistor  110  and the pull-up resistor  220 , so that the inverse electric current which may flow from the energizing voltage source  130  to the ECU  200  through the resistor  120  and the level resistor  110  can be prevented.  
         [0058]    Meanwhile, in the case where the resistor R r    150  is disposed between the connection of the lower end of the level resistor  110  and the resistor  120  and the ground connected to the movable piece  111 , distributed voltages are applied to the resistor  120  and the resistor  150 . Therefore, even though contact failure occurs, a higher voltage is applied to the ECU  200 . Accordingly, the inverse electric current is prevented.  
         [0059]    Generally, when the resistance value of the resistor R r  is lower than that of the resistor  120 , the resistor R r  can perform such a function.  
         [0060]    The second embodiment is an embodiment in which the pull-down resistor is contained in the ECU and the resistor  120  is provided. In this embodiment, the amplitude of the flowing electric current I A  is calculated from (energizing voltage)/(R A +R L2 ).  
         [0061]    The third embodiment is an embodiment in which the resistor  120  is added to the fuel level system including the fuel gauge that contains the pull-up resistor and the microcomputer. In this case, it can be understood that the amplitude of the flowing electric current I A  is 12/(R A +R L2 ), which is the same as the first embodiment.  
         [0062]    Furthermore, the fourth embodiment shown in FIG. 11 is an embodiment in which the resistor  120  is added to the fuel level system including the fuel gauge that contains the pull-down resistor and the microcomputer. In this case, the amplitude of the flowing electric current I A  is (energizing voltage)/(R A +R L2 ) which is the same as the second embodiment.  
         [0063]    Finally, the fifth embodiment shown in FIG. 12 is an embodiment in which the cross coil gauge is employed. The bimetal type gauge may be employed instead of the cross coil gauge. In this case, the amplitude of the flowing electric current is calculated from (energizing voltage)/(R A +R L2 ).  
         [0064]    According to the fuel level system for the automobile, contact resistance resulting from silver sulfide, silver oxide or other foreign materials generated due to corrosion in the contact of the level sender unit is eliminated, thereby preventing wrong indication of the fuel gauge due to the contact resistance in the contact and more accurately providing a driver with information on the amount of remaining fuel.  
         [0065]    The embodiments of the present invention described above are merely examples for specifically explaining the technical spirit of the invention. Therefore, the scope of the invention is not limited to the embodiments illustrated in the accompanying drawings.