Abstract:
In an internal combustion engine, the fuel is conveyed by an electrically driven fuel pump. The intake side of this pump is connected to a fuel tank and its outlet side is connected to a pressure region. A prerun of the electrically driven fuel pump may be performed before the startup of the internal combustion engine. In order to increase the service life of the fuel pump, an actual pressure (pactual) in the pressure region may be detected by a pressure sensor and the execution of the prerun be a function of at least the signal of the pressure sensor.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method of operating an internal combustion engine, in which the fuel is conveyed by an electrically driven fuel pump, whose intake side is connected to a fuel tank and whose outlet side is connected to a pressure region, and in which a prerun of the electrically driven fuel pump may be performed before the internal combustion engine is started, an actual pressure in the pressure region being detected by a pressure sensor and the execution of the prerun being a function of at least the signal of the pressure sensor. 
   BACKGROUND INFORMATION 
   In a conventional method, the fuel is conveyed from a fuel tank into a pressure region by an electrical fuel pump. A fuel injector is connected to this region. This injector is in turn positioned in an intake manifold of the internal combustion engine. In this manner, the fuel may reach the intake manifold via the fuel injector and from there reach the combustion chambers of the internal combustion engine. A further method of the type initially cited is known from internal combustion engines which operate using gasoline direct injection. In these internal combustion engines, the fuel is conveyed by an electrical fuel pump, which is also referred to as a “presupply pump,” from the fuel tank into a pressure region, and from there reaches a high-pressure fuel pump (“main supply pump”), which is generally mechanically driven. This pump conveys the fuel further into a common fuel line (“rail”). Multiple injectors are connected to this rail, and the fuel is stored at high pressure therein. The injectors each inject the fuel directly into the corresponding combustion chambers of the internal combustion engine. 
   If the electrical fuel pump and the pressure region positioned downstream from it are configured as a “constant-pressure system,” the pressure region is connected via a mechanical pressure regulator to the fuel tank. In normal operation, the electrically driven fuel pump conveys the fuel continuously and at the maximum output rate. In the known internal combustion engines and/or the known methods, any quantity of fuel which is not sprayed into the intake manifold by the fuel injector in systems having intake manifold injection, and which is not conveyed further by the high-pressure pump in systems having gasoline direct injection, flows back into the fuel tank via the mechanical pressure regulator. 
   Since the electrically driven fuel pump runs continuously at the maximum output rate, it is ensured that the pressure in the pressure region always remains at the desired level, even if the maximum possible quantity of fuel is demanded by the fuel injector and/or the injectors. 
   Demand-controlled fuel systems are also known. These are also constant-pressure systems, in which the pressure in the pressure region is set to a constant value through the activation of a mechanical pressure regulator. The fuel pump is therefore no longer activated fully, i.e., continuously at maximum output, but rather only according to the demand of the internal combustion engine. The excess quantity of fuel flows back into the tank via a mechanical pressure regulator. The adjustment of the conveyance output to the instantaneous operating point of the internal combustion engine causes a savings in fuel, since the drive output of the electrically driven fuel pump may be reduced in many operating ranges of the internal combustion engine. 
   During startup of the internal combustion engine, sufficient pressure must be provided in the pressure region of the fuel system so that the fuel reaches the combustion chambers of the internal combustion engine in the desired manner. Typically, it is assumed that the pressure of the fuel in the pressure region falls to ambient pressure after the internal combustion engine is shut off. In order to be able to achieve a desired pressure for starting the internal combustion engine, at least the quantity of fuel necessary for compressing the fuel to the desired pressure must therefore be conveyed. The expansion of the fuel system during the pressure buildup must also be taken into consideration. In some known methods, the operating time of the fuel pump, which is driven at constant output, during the prerun is a function of the period of time which has passed since the internal combustion engine was shut off. 
   Using the shutoff time of the engine, a fuel system pressure, the number of pump preruns which have already occurred, etc., for example, as criteria for requiring a fuel pump prerun is described in German Published Patent Application No. 199 61 298. 
   German Published Patent Application No. 100 14 550 describes the possibility of controlling the fuel pressure during the prerun on the basis of a pressure sensor by changing the speed of the fuel pump. 
   In this method, the conveyance output of the electrically driven fuel pump during the prerun is tailored to the particular demand. This demand is defined by the signal provided by the pressure sensor. If the pressure sensor signals that the pressure in the pressure region is lower than desired, the electrical fuel pump is activated accordingly. In contrast, if the pressure sensor signals that the pressure in the pressure region already corresponds to the desired pressure, the electrical fuel pump remains switched off. 
   SUMMARY 
   It is an object of the present invention to provide a method such that the internal combustion engine may start even more reliably and, at the same time, the prerun of the electrically driven fuel pump may be as short as possible. 
   This object may be achieved in a method such that the electrical fuel pump is initially operated at maximum output during a prerun. 
   An example embodiment of the method according to the present invention may provide that it may be ensured that the pressure of the fuel in the pressure region necessary for an optimum start of the internal combustion engine is reached as rapidly as possible during the prerun, and the electrical fuel pump may only be activated for the shortest possible time. This may facilitate and accelerate starting the internal combustion engine, since the fuel pressure necessary for this purpose is reached very rapidly. 
   In an example embodiment, the execution of the prerun may be a function of whether a prerun has already been performed in the current operating cycle. In this manner, a prerun of the electrical fuel pump may be prevented from being executed after a vehicle in which the internal combustion engine is installed is briefly switched off and started. This also may avoid the electrical fuel pump from being put into operation unnecessarily. 
   Furthermore, a prerun of the electrical fuel pump may be executed if the actual pressure is at least equal to a specific value or lower than a specific value and/or the prerun may be ended if the actual pressure reaches or exceeds a specific value. This procedure may also shorten the operating time of the electrical fuel pump. 
   Alternatively or additionally, it is possible for the prerun of the electrical fuel pump to be ended if the duration of the prerun reaches or exceeds a specific value. This may prevent the electrical fuel pump from running too long if it is impossible to build up pressure in the fuel system (therefore, this provides a type of “safety cutoff”). In the event of cold external temperatures, the batteries which supply the electrical fuel pump may also be prevented from being overloaded by an excessively long prerun of the electrical fuel pump. 
   A possibility of reaching the maximum output during the prerun of the electrical fuel pump which is easy to implement is for the output of the fuel pump to be influenced by a PI regulator as a function of the difference between the detected pressure and a setpoint pressure in the pressure region, and by a precontroller as a function of the setpoint pressure, and for the integrator of the PI regulator to be initialized as follows for a prerun of the electrical fuel pump: maximum possible activation output minus normal precontrol output minus activation output of the P component of the PI regulator. 
   As an alternative, it is possible for the output of the fuel pump to be influenced by a PI regulator as a function of the difference between the detected pressure and a setpoint pressure in the pressure region and by a precontroller as a function of the setpoint pressure and, for a prerun of the electrical fuel pump in the precontroller, for an additional prerun precontrol output to be added to the normal precontrol output in such a manner that the overall precontrol output is initially at a maximum. This may be implemented using software and may ensure that the pressure in the pressure region is built up at maximum rate. However, this method may simultaneously prevent an overshoot occurring after the end of the prerun of the electrical fuel pump. This is a concern if the integrator of the PI regulator is initialized using a relatively high value. Because the activation of the electrical fuel pump at maximum output is caused by the precontroller in this case, an initialization of this type is not necessary. 
   In a refinement to this procedure, the additional precontrol output may be produced by giving the value zero to the input of a low-pass filter at the beginning of the prerun of the electrical fuel pump and the low-pass filter may be initialized using the following value: maximum possible activation output minus normal precontrol output. In this case, as above, the normal precontrol output is understood as the precontrol output which results from the instantaneous setpoint pressure in the pressure region of the fuel system. Such a method may be implemented using software. Through the low-pass filter, the electrical fuel pump is initially operated at maximum output. The additional precontrol output is therefore initially at maximum (it corresponds to the difference of maximum possible activation output and normal precontrol output) and then falls to zero following an exponential function. 
   In this case, the time constant of the low-pass filter may be a function of the difference between the actual pressure and the setpoint pressure in the pressure region. In this case, the setpoint pressure may be a value which is not subjected to a limitation of the maximum gradients, as is typical. If the difference between actual pressure and setpoint pressure is very large, the additional precontrol output decays relatively slowly to zero. If the difference is small, the decay occurs more rapidly. 
   Furthermore, the setpoint pressure in the pressure region may be a function of the temperature in a region of the internal combustion engine, at least for the prerun of the electrical fuel pump. If the internal combustion engine is warm, possibly existing vapor bubbles may be compressed by an elevated pressure in the pressure region. If the internal combustion engine is cold, in contrast, the prerun time may be shortened with this example embodiment. 
   The present invention also relates to a computer program which is suitable for performing the method above when it is executed on a computer. In this case, the computer program may be stored in a memory, e.g., in a flash memory, a ferrite RAM, etc. 
   Furthermore, the present invention relates to a control and/or regulating unit for operating an internal combustion engine in which the fuel is conveyed by an electrically driven fuel pump, whose intake side is connected to a fuel tank and whose outlet side is connected to a pressure region. In order to improve the start quality of the internal combustion engine and to reduce the exhaust gas emissions during starting, the control and/or regulating unit may include a memory in which a computer program of the type above is stored. 
   Furthermore, the present invention relates to an internal combustion engine including a fuel system, which includes a fuel tank, an electrically driven fuel pump, whose intake side is connected to the fuel tank and whose outlet side is connected to a pressure region, a prerun of the electrically driven fuel pump being executable before starting the internal combustion engine, and a pressure sensor being provided which detects an actual pressure in the pressure region, and the execution of the prerun being a function of at least the actual pressure. In order to improve the start quality of the internal combustion engine and to reduce the exhaust gas emissions during starting, the internal combustion engine may include a control and/or regulating unit of the type above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an internal combustion engine including an electrical fuel pump. 
       FIG. 2  is a flow chart which illustrates a method of executing a prerun of the electrical fuel pump from  FIG. 1 . 
       FIG. 3  is a flow chart which illustrates a method of determining the activation output of the electrical fuel pump for the prerun in  FIG. 2 , the method including a precontroller and a PI regulator. 
       FIG. 4  is a flow chart which illustrates a first possibility for determining the activation output of the electrical fuel pump for the prerun in detailed form. 
       FIG. 5  is a flow chart similar to  FIG. 4 , which illustrates another possibility for determining the activation output of the electrical fuel pump for the prerun. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , an internal combustion engine is indicated as a whole by reference number  10 . It includes multiple combustion chambers, only one of which is illustrated in  FIG. 1 , using reference number  12 . Combustion chamber  12  may be connected to an intake manifold  16  via an intake valve  14 . A fuel injection device  18  is positioned in intake manifold  16 . A throttle valve  20  and an air mass meter  22 , implemented as a hot film sensor (“HFM sensor”) are also located upstream from fuel injection device  18  in the intake manifold. Combustion chamber  12  may be connected to an exhaust gas pipe  26  via an outlet valve  24 . A fuel-air mixture in combustion chamber  12  may be ignited by a spark plug  28 . This spark plug is activated by an ignition system  30 . 
   Fuel injection device  18  is part of a fuel system  32 . This system includes a fuel tank  34 , from which an electrically driven fuel pump  36  conveys the fuel into a fuel line  38 , which leads to fuel injection device  18 . Fuel line  38  is connected to an overflow valve  40  downstream from electrically driven fuel pump  36 . A line (without reference number) leads from this valve to an ejector pump  42 , which is arranged in the region of fuel tank  34 . 
   The fuel pressure existing in fuel line  38  is detected by a pressure sensor  44 . This sensor supplies appropriate signals to a control and regulating unit  46 , which also receives signals from HFM sensor  22  and a speed sensor  48 , which picks up the speed of a crankshaft  50  of internal combustion engine  10 . Furthermore, signals from a temperature sensor  52 , which detects the temperature of an engine block of internal combustion engine  10 , are supplied to control and regulating unit  46 . A position sensor  54 , which detects the position of an ignition key  56 , is also connected to control and regulating unit  46 . Electrically driven fuel pump  36 , overflow valve  40 , ejector pump  42 , and pressure sensor  44  may be implemented as one module in fuel tank  34 . 
   On the output side, control and regulating unit  46  activates, among other things, ignition system  30 , throttle valve  20 , and fuel injection device  18 . Furthermore, the activation output of electrical fuel pump  36  is also set by control and regulating unit  46 . This is performed by activating a clock module  58 , which outputs a pulse duty factor. The activation output of electrically driven fuel pump  36  is thus varied via pulse width modulation (PWM). 
   For starting internal combustion engine  10  (i.e., as soon as the ignition is switched on), the procedure is as follows, as illustrated in  FIG. 2 : after a starting block  60 , it is queried in a block  62  whether a prerun of electrical fuel pump  36  has already occurred in the current operating cycle and whether an actual pressure pactual detected by pressure sensor  44  is lower than a limit value G 1 . The start in block  60  is initiated when a specific position of ignition key  56  is detected by position sensor  54 . The query as to whether a prerun of electrical fuel pump  36  has already occurred in the current operating cycle is performed by checking a bit B 1 . This check provides the result “false” if a prerun of electrical fuel pump  36  has already occurred in the current operating cycle. 
   If one of the two conditions or both conditions are not fulfilled in block  62 , no prerun is executed. In contrast, if both conditions are fulfilled, clock module  58  is activated in block  64  and electrical fuel pump  36  is put into operation. The activation output, whereby electrical fuel pump  36  is activated, is calculated according to a method which is described in greater detail below in connection with  FIGS. 3 to 5 . 
   In block  66 , bit B 1  is set, indicating that a prerun of electrical fuel pump  36  was executed in the current operating cycle. As long as a prerun of the electrical fuel pump is being executed, a bit B 2  is set. In block  68 , it is queried whether actual pressure pactual of the fuel in fuel line  38  is greater than or equal to a limit value G 2 . In the present case, both limit values are identical. However, limit values G 1  and G 2  may also be different. In addition, it is queried in block  68  whether period tekp, which corresponds to the operating time of electrical fuel pump  36  during the prerun, is greater than or equal to a limit value G 3 . When one of the two conditions is fulfilled, the prerun of electrical fuel pump  36  is ended in block  70 . In order to save calculating time, the conditions for a prerun of the electrical fuel pump are no longer calculated when the internal combustion engine is in normal operation. This is also determined by querying an appropriate bit. 
   In the internal combustion engine illustrated in  FIG. 1 , the activation output of electrical fuel pump  36  is determined as a function of, among other things, actual pressure pactual and a setpoint pressure pset in a combination including a PI regulator and a precontroller. The setpoint value for the pressure in fuel line  38  is primarily a function of the current operating parameters of internal combustion engine  10 , e.g., of the temperature of internal combustion engine  10  detected by temperature sensor  52 , the speed of crankshaft  50  detected by speed sensor  58 , the air charge detected by HFM sensor  22 , and the position of ignition key  56  detected by position sensor  54 . The pressure in fuel line  38  is set by an appropriate variation of the voltage (and consequently the speed and/or the torque) of fuel pump  36 . The determination of the activation output of electrical fuel pump  36  is illustrated in a more general form in  FIG. 3 : 
   Subsequently, actual pressure pactual in fuel line  38  is detected in block  74 . The corresponding signal is provided by pressure sensor  44 . In actual pressure detector  74 , the voltage signal provided by pressure sensor  44  is averaged over ten measurement values and this average voltage value is converted into a raw pressure value via a pressure-voltage characteristic curve of pressure sensor  44 . The raw pressure value is filtered in a block  76 , from which actual pressure pactual results, and this pressure value pactual is supplied to a PI regulator (block  78 ). 
   The signals of HFM sensor  22 , speed sensor  48 , temperature sensor  52  (and possibly, for example, also position sensor  54  of ignition key  56  or signals resulting therefrom) are used in a block  80  to calculate a setpoint pressure pset. This pressure is also supplied to PI regulator  78 . In accordance with the difference between setpoint pressure pset and actual pressure pactual, a regulator output rgl is determined in PI regulator  64 , in normal operation of internal combustion engine  10 . This output is produced in the form of a specific pulse duty factor, as is typical for pulse width modulation. Setpoint pressure pset and the signals of sensors  22 ,  48 ,  52 , and  54  are also used, however, in block  82  for generating a precontrol output vsl. 
   The determination of the precontrol output for a prerun of electrical fuel pump  36  may occur in various manners. The goal is to provide a desired pressure in fuel line  38  as rapidly as possible. For this purpose, electrical fuel pump  36  is to be activated using maximum output at least at the beginning of the prerun. A possibility for providing this maximum activation output at the beginning of the prerun is illustrated in  FIG. 4 . In this case, the special requirements of the prerun of electrical fuel pump  36  are taken into consideration in precontroller  82 . Firstly, however, the determination of normal regulator output rgl and normal precontrol output vsl for the normal dynamic operation of electrical fuel pump  36  (i.e., when internal combustion engine  10  is running) will be described with reference to  FIG. 4 : 
   A regulator output rgl for the dynamic operation of electrical fuel pump  36  is determined as follows: in PI regulator  78 , difference dp between setpoint pressure pset and actual pressure pactual is formed in  84 . This difference dp is fed into a proportional regulator  86  and an integrator  88 . Proportional regulator  86  provides a proportional component dpp, and integrator  88  provides an integral component dpi. Both components dpp and dpi are added in 90 and converted into regulator output rgl in block  92 . In order to prevent overload of integrator  88 , integral component dpi is delimited by limit values max and min, which are provided in memories  94  and  96 . 
   Precontrol output vsldyn for dynamic operation is determined as follows: a fuel volumetric flow vol 1  is determined from speed nmot, which is provided by speed sensor  48 , a motor constant C 1 , which is stored in a memory  98 , and relative fuel mass rk, which is provided in block  100  by multiplication in  100 . This fuel volumetric flow is the volumetric flow which reaches combustion chamber  12  through fuel injection device  18  during operation of internal combustion engine  10 . 
   A second component vol 2  is added to this fuel volumetric flow vol 1  in  102 . This volumetric flow is established in turn from a characteristic curve  104 , which is addressed using setpoint pressure pset. Fuel volumetric flow vol 2  is the volumetric flow which flows from fuel line  38  via overflow valve  40  (which may also be implemented as a pressure relief valve) to ejector pump  42  and/or back into fuel tank  34 . The sum of both components vol 1  and vol 2  provides the overall fuel volumetric flow vol to be conveyed by electrical fuel pump  36 . This sum is fed, together with setpoint pressure pset, into a characteristic map  106 , which outputs precontrol output vsldyn for dynamic operation of electrical fuel pump  36 . 
   Now regarding the determination of activation output asl during a prerun of electrical fuel pump  36 : in order to be able to initially activate electrical fuel pump  36  at maximum output during a prerun of this pump, the difference between maximum permissible activation output aslmax of electrical fuel pump  36  and precontrol output vsldyn for dynamic operation is formed in precontroller  82  if a prerun is to be executed. Maximum permissible activation output aslmax is stored in a memory  110  and is a function, for example, of clock module  58  used, which generates a pulse duty factor (the output pulse duty factor is a function of the input pulse duty factor). 
   A low-pass filter  112  is initialized using the difference formed in  108 . A time constant T of low-pass filter  112  is determined in  114  using a characteristic curve, into which difference dp between actual pressure pactual and setpoint pressure pset is fed. Setpoint pressure pset is free in this case of a gradient delimitation, while in contrast it is gradient-delimited for the determination of fuel volumetric flow vol 2  and for the use in regulator  78 . The value zero is given to the input of low-pass filter  112 . The output of low-pass filter  112  provides a precontrol output vslvor for the prerun of electrical fuel pump  36 . In  116  this output is added to precontrol output vsldyn for the dynamic operation of internal combustion engine  10  and results in total precontrol output vsl. In  118 , this output is added in turn to regulator output rgl and provides overall activation output asl. 
   Activation output asl for a prerun of electrical fuel pump  36  is determined as follows: since internal combustion engine  10  is not yet in operation during the prerun of electrical fuel pump  36  and therefore crankshaft  50  does not yet rotate, the multiplication in 100 results in the value zero. Precontrol output vsldyn for the dynamic operation of internal combustion engine  10  thus results exclusively from fuel volumetric flow vol 2  and setpoint pressure pset. In the prerun of electrical fuel pump  36 , setpoint pressure pset results from a characteristic map as a function of speed nmot and a load rl or, as in the present case, from the temperature of internal combustion engine  10 , which is provided by temperature sensor  52 . 
   However, precontrol output vsldyn determined in  106  for the dynamic operation of internal combustion engine  10  is relatively low. A condition signals that a prerun is to occur and enables low-pass filter  112 . The condition is that if a time tnse is less than a limit value gtvt, low-pass filter  112  is enabled. Due to the initialization of low-pass filter  112  using the difference between precontrol output vsldyn and maximum permissible activation output aslmax, precontrol output vslvor for the prerun of electrical fuel pump  36  initially corresponds exactly to this difference. Since this difference is added in  116  to precontrol output vsldyn for the dynamic operation, precontrol output vsl at the beginning of the prerun of electrical fuel pump  36  corresponds to maximum permissible activation output aslmax of electrical fuel pump  36 . Electrical fuel pump  36  thus initially rotates at maximum speed and maximum output, so that the pressure in fuel line  38  is built up at maximum speed. As was explained above, time constant T of low-pass filter  112  is formed as a function of the difference between setpoint pressure pset and actual pressure pactual. A large difference results in a comparatively large time constant T, while a small difference results in a correspondingly small time constant T. This means that with a large difference between pset and pactual, precontrol output vsl decays slower from the initialization value to zero than with a small difference. Since in this manner the difference between actual pressure pactual and setpoint pressure pset is to become smaller relatively rapidly during the prerun of electrical fuel pump  36 , a large integral component dpi does not built up in integrator  88  of PI regulator  78 , so that an overshoot due to the regulator is avoided when actual pressure pactual reaches setpoint pressure pset. In addition, an overflow of the integrator is prevented in that the integrator is stopped by an appropriate bit when the maximum pulse duty factor is output, but actual pressure pactual is simultaneously less than setpoint pressure pset. 
   A second possibility, using which activation output asl of electrical fuel pump  36  may be established during a prerun of electrical fuel pump  36 , is illustrated in  FIG. 5 . Those functions which may ensure that electrical fuel pump  36  is activated at maximum output at the beginning of the prerun are implemented in  FIG. 5  not in precontroller  82 , but rather in PI regulator  78 . It is to be noted at this point that those elements, blocks, and functions which may be functionally similar to elements, blocks, and functions of  FIG. 4  have identical reference numbers and are not explained again in detail in each case. 
   Similarly to  FIG. 4 , a precontrol output vsldyn for the dynamic operation of internal combustion engine  10  is determined in block  82 . Also similarly to  FIG. 4 , the difference between maximum permissible activation output aslmax of electrical fuel pump  36  and precontrol output vsldyn for the dynamic operation of internal combustion engine  10  is formed in  108 . This difference is converted in  120  into a pressure value, from which proportional component dpp, which was established in proportional regulator  86 , is subtracted in  122 . Integrator  88  is initialized using the value resulting therefrom. 
   As a result, at the beginning of a prerun of electrical fuel pump  36 , regulator output rgl, resulting from the sum of proportional component dpp and integral component dpi in  90 , i.e.,  92 , is equal to the difference between maximum permissible activation output aslmax of electrical fuel pump  36  and precontrol output vsldyn for the dynamic operation of internal combustion engine  10 . Since regulator output rgl is added in  118  to precontrol output vsldyn, an activation output asl which is equal to maximum permissible activation output aslmax results at the beginning of the prerun of electrical fuel pump  36 . As the difference between actual pressure pactual and setpoint pressure pset becomes smaller, the regulator output then falls again, so that total activation output asl is also reduced. 
   It is to be noted that the initialization of integrator  88  as illustrated in  FIG. 5  and the determination of precontrol output vslvor as illustrated in  FIG. 4  is performed each time the condition “ignition on” is detected (initialization of the engine control unit). Therefore, both steps are performed during a prerun of electrical fuel pump  36  and during a normal start of internal combustion engine  10  without a prerun. It is also to be noted that the concept of “output” used in connection with  FIGS. 3 through 5  may also be expressed in practice by a voltage value, a current value, or a pulse duty ratio.