Abstract:
A method for determining a fluid level value in a fluid tank of an internal combustion engine equipped with a discrete level sensor is provided. The discrete level sensor is configured for generating a first electrical signal when a fluid level is above or equal to a first predetermined fluid level threshold value and generating a second electrical signal when the fluid level is above or equal to a second predetermined fluid level threshold value. The second predetermined fluid level threshold value is greater than the first predetermined fluid level threshold value. The method includes monitoring a number of occurrences of the first electrical signal and of the second electrical signal over a time interval. The fluid level in the fluid tank is calculated as a function of the number of occurrences of the first and of the second electrical signals over the time interval.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to British Patent Application No. 1110996.4, filed Jun. 28, 2011, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to an internal combustion engine, particularly an internal combustion engine of a motor vehicle, equipped with a fluid tank and a discrete level sensor. 
       BACKGROUND 
       [0003]    Internal combustion engines are conventionally equipped with a variety of fluid tanks, for example a fuel tank or an urea tank containing urea solution used in the exhaust gas treatment system, for which it is desirable to monitor to some degree the level of the fluid within. Continuous fluid level sensors have widely been used for detecting the level of fluid in a tank. They work by continuously measuring a level within a specified range and determining the exact amount of fluid in the tank as a function of the measured level. Unfortunately these sensors are relatively expensive. As alternative to continuous sensors, discrete level sensors could also be used. Discrete level sensors provide information on the level of fluid in the tank by simply indicating whether the fluid in the tank is above or below predetermined level threshold values. Discrete level sensors are therefore less precise since they are unable to detect the precise level of fluid between two level threshold values. Also when used in internal combustion engines they present additional problems. During transitory driving states of the vehicle, i.e., for example, during acceleration or deceleration, discrete level sensors provide level indications which are often misleading. In those situations the fluid in the tank is sloshed around and the level threshold values are randomly exceeded so that the sensor provides conflicting information regarding the actual level of the fluid in the tank. This is even truer when the discrete level sensors are used, for example, to detect the level of urea in urea tanks. Such tanks normally have a relatively flat and wide parallelepiped shape and small movements of the vehicle are enough to cause the fluid to slosh in the tank and to randomly exceed or fall below various threshold level values. 
         [0004]    In view of the above, it is at least one object of an embodiment herein to provide a method to determine in a substantially precise way the fluid level in a fluid tank equipped with a discrete level sensor. 
         [0005]    Another object of an embodiment herein is to provide a method for determining a fluid level which is substantially reliable even in transitory driving conditions. 
         [0006]    Another object of an embodiment herein is to achieve the above mentioned objects in a simple, rational and inexpensive way without using complex devices and by taking advantage of the computational capabilities of an Electronic Control Unit (ECU) of the vehicle. 
         [0007]    These objects are achieved by a method, by an engine, by a computer program and computer program product, by an electromagnetic signal, and by an automotive system having the features recited in the independent claims. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0008]    In greater details, an embodiment herein discloses a method for determining a fluid level value in a fluid tank of an internal combustion engine equipped with a discrete level sensor, wherein the discrete level sensor is configured for:
       generating a first electrical signal when a fluid level is above or equal to a first predetermined fluid level threshold value (LT 1 ),   generating at least a second electrical signal when the fluid level is above or equal to a second predetermined fluid level threshold value (LT 2 ), the second predetermined fluid level threshold value (LT 2 ) being greater than the first predetermined fluid level threshold value (LT 1 ), and wherein the method comprises the steps of:   monitoring a number of occurrences of the first and of the second electrical signal over a time interval; and   calculating the fluid level in the fluid tank ( 500 ) as a function of the monitored number of occurrences of the first electrical signal and of the monitored number of occurrences of the second electrical signal over the time interval.       
 
         [0013]    In this way, the level of fluid in a tank equipped with a discrete level sensor can be precisely calculated as a function of the signals generated by the sensor, and a reliable and precise information on the fluid level in the fluid tank can be obtained even in transitory conditions of the vehicle. 
         [0014]    According to an embodiment, the fluid level in the fluid tank is calculated as a weighted average of the predetermined fluid level threshold values, each threshold value being weighted by the number of occurrences of the corresponding electrical signal. 
         [0015]    In this way it is possible to determine the fluid level by using a simple calculation which can be easily implemented using the capabilities already present in the ECU of an internal combustion engine. 
         [0016]    According to another embodiment, a fluid level threshold value is disregarded in the calculation of the fluid level if the corresponding monitored number of occurrences is below a predetermined occurrence threshold value 
         [0017]    The methods of the various embodiments can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the methods described above, and in the form of a computer program product comprising the computer program. 
         [0018]    The computer program product can be embodied as an internal combustion engine provided with a discrete level sensor and a ECU in communication with the discrete level sensor, a memory system associated with the ECU, and the computer program stored in the memory system, so that, when the ECU executes the computer program, all the steps of the method described above are carried out. 
         [0019]    The method can be also embodied as an electromagnetic signal, the signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method. 
         [0020]    An embodiment further provides a control apparatus for an internal combustion engine equipped with a fluid tank and a discrete level sensor, the control apparatus comprising an Electronic Control Unit in communication with the discrete level sensor, a memory system associated with the Electronic Control Unit and a computer program stored in the memory system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0022]      FIGS. 1 and 2  are schematic representations of an automotive system comprising an internal combustion engine; 
           [0023]      FIG. 3  is a schematic representation of a fluid tank equipped with a discrete level sensor; and 
           [0024]      FIG. 4  is a schematic representation of the method according to an embodiment contemplated herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0026]    Various embodiments contemplated herein may include an automotive system  100 , as shown in  FIGS. 1 and 2 , that includes an internal combustion engine (ICE)  110  having an engine block  120  defining one or more cylinder  125  having a piston  140  coupled to rotate a crankshaft  145 . A cylinder head  130  cooperates with the piston  140  to define a combustion chamber  150 . A fuel and air mixture (not shown) is disposed in the combustion chamber  150  and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston  140 . The fuel is provided by a fuel injector  160  and the air through an intake port  210 . The fuel is provided at high pressure to the fuel injector  160  from a fuel rail  170  in fluid communication with a high pressure fuel pump  180  that increases the pressure of the fuel received from a fuel source  190 . Each of the cylinders  125  has at least two valves  215 , actuated by a camshaft  135  rotating in time with the crankshaft  145 . The valves  215  selectively allow air into the combustion chamber  150  from the port  210  and alternately allow exhaust gases to exit through a port  220 . In some examples, a cam phaser  155  may selectively vary the timing between the camshaft  135  and the crankshaft  145 . 
         [0027]    The air may be distributed to the air intake port(s)  210  through an intake manifold  200 . An air intake duct  205  may provide air from the ambient environment to the intake manifold  200 . In other embodiments, a throttle body  330  may be provided to regulate the flow of air into the manifold  200 . In still other embodiments, a forced air system such as a turbocharger  230 , having a compressor  240  rotationally coupled to a turbine  250 , may be provided. Rotation of the compressor  240  increases the pressure and temperature of the air in the duct  205  and manifold  200 . An intercooler  260  disposed in the duct  205  may reduce the temperature of the air. The turbine  250  rotates by receiving exhaust gases from an exhaust manifold  225  that directs exhaust gases from the exhaust ports  220  and through a series of vanes prior to expansion through the turbine  250 . The exhaust gases exit the turbine  250  and are directed into an exhaust system  270 . This example shows a variable geometry turbine (VGT) with a VGT actuator  290  arranged to move the vanes to alter the flow of the exhaust gases through the turbine  250 . In other embodiments, the turbocharger  230  may be of fixed geometry and/or include a waste gate. 
         [0028]    The exhaust system  270  may include an exhaust pipe  275  having one or more exhaust after-treatment devices  280 . The after-treatment devices may be any device configured to change the composition of the exhaust gases. Some examples of after-treatment devices  280  include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx Traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and diesel particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system  300  coupled between the exhaust manifold  225  and the intake manifold  200 . The EGR system  300  may include an EGR cooler  310  to reduce the temperature of the exhaust gases in the EGR system  300 . An EGR valve  320  regulates a flow of exhaust gases in the EGR system  300 . 
         [0029]    The automotive system  100  may further include an electronic control unit (ECU)  450  in communication with one or more sensors and/or devices associated with the ICE  110 . The ECU  450  may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE  110 . The sensors include, but are not limited to, a mass airflow and temperature sensor  340 , a manifold pressure and temperature sensor  350 , a combustion pressure sensor  360 , coolant and oil temperature and level sensors  380 , a fuel rail pressure sensor  400 , a cam position sensor  410 , a crank position sensor  420 , exhaust pressure and temperature sensors  430 , an EGR temperature sensor  440  and an accelerator pedal position sensor  445 . Furthermore, the ECU  450  may generate output signals to various control devices that are arranged to control the operation of the ICE  110 , including, but not limited to, the fuel injectors  160 , the throttle body  330 , the EGR Valve  320 , the VGT actuator  290 , and the cam phaser  155 . Note, dashed lines are used to indicate communication between the ECU  450  and the various sensors and devices, but some are omitted for clarity. 
         [0030]    Turning now to the ECU  450 , this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE  110 . 
         [0031]    A fluid tank in the internal combustion engine, such as the fuel source  190  or an urea solution tank associated to the SCR  280 , can be equipped with discrete level sensors. The fluid level in the tank is generally sensed by obtaining a discrete indication, such as an electrical signal, whenever a predetermined threshold value has been reached, for example whenever the quantity of fluid in the tank exceeds a predetermined quantity. Fluid level sensors make use of various kinds of float operated mechanisms, resistance mechanisms, capacitative mechanisms, and acoustic mechanisms. A commonly used fluid level sensor is a magnetic float sensor which is very popular because of its simplicity, dependability and low cost. An example of a magnetic float discrete level sensor will now be described in more details with reference to  FIG. 3  which is a schematic representation of a fluid tank  500 , in the present example, the urea solution tank, equipped with such a sensor  510 . The sensor  510  comprises a magnetic float  513 , annularly shaped, movably supported on an exterior of a tube  511 . The float  513  is adapted to be buoyant in the fluid and to move upwards and downwards along the tube with changing the fluid level in the tank  500 . A stop element  514  is located at the top of the tube  511  to stop the magnetic float  513  from being detached from the sensor  510 . 
         [0032]    The sensor  510  further comprises a switch assembly  512  supported inside the tube  511 . The switch assembly  512  comprises a plurality of switches, each located at a different position along the tube  511 , each adapted to be magnetically activated when the magnetic float  513 , moving along the length of the tube  511 , reaches its level position. Each switch therefore corresponds to a fluid level threshold value in the tank. In  FIG. 3  four fluid level threshold values are represented but the sensors can comprise from 2 to a plurality of switches and corresponding threshold level values. 
         [0033]    The switch assembly  512  also comprises a plurality of resistors, each resistor in parallel to a switch. Whenever a switch is actuated the corresponding resistor is bypassed. A constant voltage, for example 5V, is applied to the switch assembly  512  via a constant voltage generator (not shown). The switch assembly  512  is then connected to the ECU  450  which is configured to receive an electrical signal from the sensor  510 , for example a percentage of the voltage value applied to the sensor  510 , which is a function of the number of bypassed resistors i.e., of the number of actuated switches. 
         [0034]    When the fluid in the tank reaches a certain quantity corresponding to a level threshold value, the magnetic float  513  actuates the corresponding switch and a corresponding electrical signal is generated and sent to the ECU  450 . If the fluid in the fluid tank  500  is calm the magnetic float  513  is also stable along the tube  511  and the signal received by the ECU  450  is constantly the same until the level of fluid changes. 
         [0035]    In normal operation, when the vehicle is moving, the fluid in the tank also moves around. It can be observed that in those circumstances the electrical signal produced by the sensor in a time interval, for example in the range of about 20 seconds, is not constant. The ECU  450  will actually receive a combination of electrical signals each corresponding to a level threshold value. The different electrical signals could be represented by the same signal with a different value of a characterizing parameter, i.e. frequency or amplitude. The method according to an embodiment will now be described with reference to  FIG. 4 . 
         [0036]    In particular, the actual fluid level in the fluid tank  500  can be determined by the ECU  450  by monitoring the occurrences of each electrical signal in that time interval (block  1 ). The time interval can be determined in a preliminary calibration phase and it can correspond to the time needed to fill in a dedicated buffer (not shown) in the memory system  451 . 
         [0037]    A preliminary selection can be carried on the monitored occurrences on each electrical signal (block  2 ). In particular before calculating the fluid level the threshold values having a number of occurrences below a predetermined number of occurrences threshold value can be discarded. The number of occurrences threshold value, generally very small, can be determined in a calibration phase. This additional filtering step allows discarding samples only occurring sporadically in the time interval. In his way spikes due to sloshing of the fluid are detected and discarded. 
         [0038]    The fluid level in the tank is then calculated (block  3 ) as the weighted average of the threshold level values, each weighted by the number of occurrences of the corresponding electrical signal. In particular: 
         [0000]    
       
         
           
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         [0039]    wherein L represents the calculated fluid level, This represents the threshold level values from i to z, and ni represents the corresponding number of occurrences. 
         [0040]    In case of transitory driving conditions causing sloshing of the fluid in the fluid tank  500  the signal provided by the sensor  510  can change very quickly. This occurs for example when the sensor  510  is located in a fluid tank  500  of a vehicle which is accelerating or decelerating and the fluid in tank  500  is slammed from side to side. In such circumstances the magnetic float  513  moves along the tube  511  rapidly and the signal generated by the sensor  510  changes rapidly. 
         [0041]    Even in those situations the fluid level can be calculated using the above formula. Furthermore, during the preliminary filtering step (block  2 ), spikes due to sloshing of the fluid are detected and discarded. 
         [0042]    The method described above can be repeated once the time interval elapses, or the corresponding buffer is full, so as to continuously provide information on the fluid level. 
         [0043]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.