Patent Publication Number: US-2010116253-A1

Title: Controller for fuel pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2008-287104 filed on Nov. 7, 2008, the disclosure of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a controller for a fuel pump which pumps up a fuel in a fuel tank and supplies the fuel to an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     A conventional fuel supply apparatus is provided with a pressure regulator at an outlet of a fuel pump which pumps up a fuel in a fuel tank. The fuel pump is driven at a constant speed and discharges the fuel in a constant quantity. The pressure regulator adjusts a pressure of fuel discharged from the fuel pump at a constant pressure. The adjusted fuel is supplied to a fuel injector. 
     In this case, since the fuel pressure is configured to be able to discharge the fuel corresponding to a maximum fuel consumption of the engine, the discharge quantity of the fuel pump is usually larger than a fuel consumption of the engine. An excessive fuel is returned to the fuel tank by the pressure regulator, and the fuel corresponding to the fuel consumption is supplied to the fuel injector. Thus, usually, the fuel pump continues to discharge the fuel more than necessary, which wastes an excessive electricity of the fuel pump and deteriorates fuel economy. 
     JP-2008-19755A describes that a target discharge quantity of a fuel pump is computed in accordance with a driving condition of the engine, a target rotational speed is derived from the target discharge quantity, and an actual rotational speed of the fuel pump is adjusted to the target rotational speed. 
     However, it is unavoidable that a characteristic of discharge quantity relative to the rotational speed of the fuel pump largely varies with age. For example, since the fuel discharged from the fuel pump is filtered by a fuel filter, a pressure loss of the fuel filter is a factor which decreases the discharge quantity of the fuel pump. As a using period of the fuel filter becomes longer, the fuel filter is gradually clogged and the pressure loss of the fuel filter becomes gradually large. Thus, it is unavoidable that the discharge quantity (fuel quantity supplied to the fuel injector through the fuel filter) is gradually decreased with an increase in pressure loss even if the rotational speed of the fuel pump is unchanged. 
     Besides, as a using period of the fuel pump becomes longer, a sliding portion of each part is gradually worn away and a fuel leakage in the fuel pump is gradually increased, so that a pump efficiency is deteriorated. Thus, it is unavoidable that the discharge quantity is gradually decreased with a deterioration in pump efficiency even if the rotational speed of the fuel pump is unchanged. 
     Conventionally, in view of the decrease in discharge quantity, in order that the fuel corresponding to the maximum fuel consumption of the engine can be supplied even when the lifetime of the fuel pump and the fuel filter has passed, the target discharge quantity and the target rotational speed are established to be high, supposing a maximum pressure loss of the fuel filter and a maximum deterioration in fuel pump at the end of lifetime thereof. Even though the pressure loss of the fuel filter and the deterioration degree of the fuel pump are normally less than that at the end of lifetime thereof, the fuel pump excessively discharges the fuel by the target discharge quantity and at the target rotational speed for the end of lifetime thereof. A large part of the fuel is not supplied to the fuel injector and is returned to the fuel tank by the pressure regulator. That is, the fuel pump wastes the excessive electricity to deteriorate the fuel economy. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above matters, and it is an object of the present invention to provide a controller for a fuel pump which can restrict a usual discharge quantity and can improve a fuel economy. 
     According to the present invention, a controller for a fuel pump, which pumps up a fuel in a fuel tank by the fuel pump, filtrates the fuel by a fuel filter and supplies the fuel to an internal combustion engine. The controller includes a filter evaluating means for evaluating a pressure loss of the fuel filter and a control means for controlling a discharge quantity of the fuel pump by controlling a rotational speed of the fuel pump. The control means corrects the rotational speed of the fuel pump in accordance with the pressure loss of the fuel filter evaluated by the filter evaluating means so as to correct the discharge quantity of the fuel pump in accordance with the pressure loss. Thereby, the target discharge quantity and the target rotational speed of the fuel pump are defined in accordance with the actual pressure loss of the fuel filter. Thus, the normal discharge amount of the fuel pump can be reduced, compared with the case that the fuel pump excessively discharges the fuel by the target discharge quantity and at the target rotational speed for the end of life time of the fuel pump. The electricity for the fuel pump is saved and the fuel economy is improved. 
     According to another aspect of the present invention, the controller for the fuel pump is provided with a pump evaluation means for evaluating a deterioration degree of the fuel pump. The rotational speed of the fuel pump is corrected in accordance with a deterioration degree and the discharge quantity of the fuel pump is also corrected in accordance with the deterioration degree of the fuel pump. Thereby, the target discharge quantity and the target rotational speed of the fuel pump are defined in accordance with the actual deterioration degree of the fuel pump. Thus, the normal discharge amount of the fuel pump can be reduced, compared with the case that the fuel pump excessively discharges the fuel by the target discharge quantity and at the target rotational speed for the end of life time of the fuel pump. The electricity for the fuel pump is saved and the fuel economy is improved. 
     According to another aspect of the present invention, the controller is provided with a filter evaluating means for evaluating a pressure loss of the fuel filter and a pump evaluation means for evaluating a deterioration degree of the fuel pump. The target rotational speed of the fuel pump and the target discharge amount of the fuel pump are corrected in accordance with the pressure loss of the fuel filter and the deterioration degree of the fuel pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become more apparent from the following description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which: 
         FIG. 1A  is schematic views showing a fuel supply apparatus in a condition in which a fuel amount remaining in a fuel tank is large according to a first to third embodiments; 
         FIG. 1B  is schematic views showing a fuel supply apparatus in condition in which a fuel amount remaining is a fuel tank is small according to a first to third embodiments; 
         FIG. 2  is a block diagram showing a configuration of a control system; 
         FIG. 3  is a flowchart showing a target rotational speed computing routine according to the first embodiment; 
         FIG. 4  is a chart conceptually showing an example of a filter pressure loss correction amount map for computing a filter pressure loss correction amount by use of an integrated value of a discharge quantity as a parameter according to the first embodiment; 
         FIG. 5  is a chart conceptually showing a two-dimensional map for computing the target rotational speed by use of the target discharge quantity and a fuel as parameters; 
         FIG. 6  is a flowchart showing a target rotational speed computing routine according to the second embodiment; 
         FIG. 7  is a chart conceptually showing an example of a pump deterioration correction amount map for computing a pump deterioration correction amount by use of an integrated value of a rotation number as a parameter according to the second embodiment; and 
         FIG. 8  is a flowchart showing a target rotational speed computing routine according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter. 
     First Embodiment 
     Referring to  FIGS. 1A to 5 , a first embodiment will be described hereinafter. First, an entire configuration of a fuel supply apparatus pump is schematically explained based on  FIGS. 1A and 1B . A fuel tank  11  accommodates a sub-tank  12 . As shown in  FIG. 1B , when a remaining fuel quantity in the fuel tank  11  is small, a jet pump  22  gathers the fuel into the sub-tank  12 . A flange  13  supporting the sub-tank  12  through an elastic member such as a spring is fixed on the fuel tank  11 . As shown in  FIG. 1A , when a fuel level in the fuel tank  11  is higher than an upper opening of the sub-tank  12 , the fuel in the fuel tank  11  is introduced into the sub-tank  12  through the upper opening thereof so that the sub-tank  12  is filled with the fuel. 
     A fuel pump  14  is provided in the sub-tank  12 , A suction filter  15  is provided at an suction port of the fuel pump  14 . A fuel filter  16  and a pressure regulator  17  are provided at a discharge port of the fuel pump  14 . The fuel filter  16  filtrates the fuel discharged from the fuel pump  14 . The pressure regulator  17  adjusts the fuel pressure discharged from the fuel pump  14  in such a manner that the fuel pressure does not exceed a set pressure. A return pipe  18  is connected to the pressure regulator  17  for returning the excessive fuel to the fuel tank  11 . 
     The fuel filtered by the fuel filter  16  is introduced into a delivery pipe  20  through a fuel pipe  19  to distribute the fuel into a fuel injector  21  of each cylinder. The distributed fuel is injected into an intake port of each cylinder from the fuel injector  21  by a fuel injection quantity which is established in accordance with the engine driving condition. The delivery pipe  20  is provided with a fuel pressure sensor  27  detecting a fuel pressure in the delivery pipe  20 . 
     The jet pump  22  is installed at a lower portion of the sub-tank  12  for supplying the fuel in the fuel tank  11  into the sub-tank  12 . The return pipe  18  of the pressure regulator  17  is connected to an inlet port of the jet pump  22 . The fuel in the return pipe  18  is injected into the inlet port of the jet pump  22 , which generate a negative pressure (pumping operation) in the jet pump  22 . The fuel in the fuel tank  11  is suctioned into the jet pump  22  by the negative pressure and flows into the sub-tank  12 . Thereby, as shown in  FIG. 1B , even when a remaining fuel quantity in the fuel tank  11  is small, or even when a fuel level in the fuel tank  11  is tilted, the fuel level in sub-tank  12  is kept higher than the suction port of the fuel pump  14 , so that the fuel pump  14  can suction the fuel in the sub-tank  12  stably. 
     A float  23  floating on the fuel level in the fuel tank  11  and a fuel level gauge  24  measuring a position of the float  23  as the fuel level (remaining fuel quantity) are provided outside of the sub-tank  12 . 
     As shown in  FIG. 2 , the fuel pump  14  has a pump portion  26  driven by a brushless motor  25 . The brushless motor  25  is a sensorless type brushless motor. Since the brushless motor  25  of the fuel pump  14  is immersed in the fuel, it is difficult to ensure a credibility of a position detecting sensor, such as a hall element, which detects a rotational position of a rotor. Thus, the sensorless type brushless motor is used. However, if the above problem is solved, a brushless motor having a sensor such as a hall element can be used. 
     The brushless motor  25  of the fuel pump  14  is driven by a pump driving circuit  31 . The pump driving circuit  31  is housed in the fuel pump  14 . Alternatively, the pump driving circuit  31  may be provided outside of the fuel pump  14  or the fuel tank  11 . The pump driving circuit  31  includes a feedback control circuit (feedback control means) which performs a feedback control so that an actual rotational speed of the fuel pump  14  agrees with the target rotational speed. The pump driving circuit  31  further includes a driving circuit (inverter circuit) which drives the brushless motor  25  based on the output of the feedback control circuit. A rotational speed control of the brushless motor  25  by the pump driving circuit  31  is a well known rotational speed control method, for example, the pulse-width modulation (PWM) method as shown in JP-2000-341982. 
     The pump driving circuit  31  receives a signal indicative of the target rotational speed of the fuel pump  14 , which is transmitted from an engine electronic control unit (engine ECU)  32  controlling the driving of the engine, The pump driving circuit  31  transmits a signal indicative of the actual rotational speed of the fuel pump  14  to the engine ECU  32 . According to the present embodiment, the pump driving circuit  31  is configured by a hardware circuit. Alternatively, the function of the feedback control may be realized by software. 
     The engine ECU  32  receives signals from various sensors, such as an accelerator position sensor  33  detecting an accelerator position, a crank angle sensor  34  detecting an engine speed, an airflow meter  35  detecting an intake air quantity, an intake air pressure sensor  36  detecting an intake air pressure, and the fuel pressure sensor  27 . The engine ECU  32  controls a fuel injection quantity of the fuel injector  21  and an ignition timing in accordance with the engine driving condition. 
     Furthermore, the engine ECU  32  performs a target rotational speed computing routine shown in  FIG. 3 , whereby the engine ECU  32  functions as a filter pressure loss evaluating means for evaluating a pressure loss of the fuel filter  16 . The ECU  32  corrects the rotational speed of the fuel pump  14  in accordance with the evaluated pressure loss to correct the discharge quantity of the fuel pump  14  as well. In order to realize the correction, the engine ECU  32  functions as a target discharge quantity computing means for computing a target discharge quantity by correcting an engine demand fuel quantity with a filter pressure loss correction quantity corresponding to the pressure loss of the fuel filter  16 . Further, the engine ECU  32  functions as a target rotational speed computing means for computing a target rotational speed based on the target discharge quantity. The target rotational speed is corrected in accordance with the pressure loss of the fuel filter  16  The engine ECU  32  transmits a signal indicative of the corrected target rotational speed to the pump driving circuit  31 . In this pump driving circuit  31 , a feedback control is performed in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed. The engine ECU  32  and the pump driving circuit  31  configures a control means for correcting the discharge quantity of the fuel pump  14  in accordance with the pressure loss of the fuel filter  16 . 
     In a method for evaluating the pressure loss of the fuel filter  16 , an integrated value of the fuel quantity passing through the fuel filter  16  or an integrated value of parameter relating to this fuel quantity can be used as evaluation data for the pressure loss of the fuel filter  16 . In a system in which all of the fuel discharged from the fuel pump  14  passes through the fuel filter  16 , that is, in a system in which the fuel filter  16  is disposed between the fuel pump  14  and the pressure regulator  17 , since the discharge quantity of the fuel pump  14  agrees with the fuel quantity passed through the fuel filter  16 , the integrated value of the fuel quantity passed through the fuel filter  16  is calculated by integrating the discharge quantity of the fuel pump  14 . Although the discharge quantity of the fuel pump may be computed based on the rotational speed of the fuel pump  14 , the target discharge quantity as an information of discharge amount of the fuel pump  14  can reduce a computing load. As a substituting information of the integrated value of the fuel quantity passed through the fuel filter  16 , an integrated value of a rotation number of the fuel pump  14  can be used. 
     In a case that the present invention is applied to a system in which an in-line type fuel filter is disposed between a pressure regulator and a fuel injector, the fuel quantity passed through the fuel filter becomes less than the discharge quantity of the fuel pump by the fuel quantity returned by the pressure regulator. However, since the fuel quantity passed through the fuel filter agrees with the fuel consumption of the engine, the integrated value of the fuel quantity passed through the fuel filter can be calculated by integrating the fuel consumption of the engine (fuel injection quantity). 
     Since the increase in pressure loss of the fuel filter  16  is a phenomenon which gradually occurs for a long period, an integrated value of refueling quantity measured by a fuel level gauge  24 , an integrated travel distance, or an integrated operating time of the engine can be used as the substituting information of the integrated value of the fuel quantity passed through the fuel filter  16 . After an average fuel quantity passed through the fuel filter  16  in an average driving condition is obtained, the integrated value of the fuel quantity passed through the fuel filter  16  can be evaluated based on the integrated refueling quantity, the integrated travel distance, or the integrated operating time of the engine. 
     In this case, the evaluation data of the pressure loss of the fuel filter  16  may be stored in a backup RAM which receives electric power from a battery. Generally, since a lifetime of the fuel filter  16  is longer than that of the battery, the battery is changed to new one before the fuel filter  16  is changed to new one, When the battery is removed to be changed, there is a possibility that the evaluation data of the pressure loss of the fuel filter  16  are erased. 
     According to the first embodiment, the evaluation data of the pressure loss of the fuel filter is stored in a nonvolatile memory  37 , such as EEPROM. Thereby, it is unnecessary to supply electric power to the nonvolatile memory  37  during the engine stop. Even if the battery is changed to new one, the data stored in the nonvolatile memory  37  can be hold. Besides, when the fuel filter  16  is changed to new one, the evaluation data of the pressure loss of the fuel filter  16  stored in the nonvolatile memory  37  are initialized. 
     Referring to  FIG. 3 , the target rotational speed computing routine will be described hereinafter. The target rotational speed computing routine is executed by the engine ECU  32  at a specified period during an engine operation. In step  101 , the rotational speed of the fuel pump  14  is detected based on a rotational speed signal transmitted from the pump driving circuit  31 . Then, the procedure proceeds to step  102  in which a discharge quantity of the fuel pump  14  per a computing cycle is computed based on the rotational speed of the fuel pump  14  by use of a map or a formula. As the rotational speed of the fuel pump  14  becomes higher, the discharge quantity of the fuel pump  14  per a computing cycle is increased, The discharge quantity of the fuel pump  14  per a computing cycle may be computed based on the fuel pressure in addition to the rotational speed. 
     In step  103 , a current discharge amount per a computing quantity is added to a previous integrated value of the discharge quantity stored in the nonvolatile memory  37 , so that the integrated value of the discharge amount of the fuel pump  14  from a time of shipping a vehicle until the current computing is updated and stored in the nonvolatile memory  37 . 
       Current integrated value of discharge quantity=Previous integrated value of discharge quantity+Current discharge quantity per computing cycle 
     Then, the procedure proceeds to step  104  in which a filter pressure loss correction amount corresponding to the integrated value of discharge quantity is computed based on the integrated value of the discharge amount computed in step  103  as the evaluation data of the pressure loss of the fuel filter  16 , referring to a filter pressure loss correction amount map shown in  FIG. 4 . The filter pressure loss correction amount map is preliminarily formed based on experimental data, design data, simulation results and the like. In this map, as the integrated value of the discharged amount becomes larger, the filter pressure loss correction amount becomes larger, corresponding to an increase in pressure loss of the fuel filter  16 . 
     Then, the procedure proceeds to step  105  in which a fuel quantity required by the engine, which is referred to as a required fuel quantity, is computed according to a following formula. 
       Required fuel quantity=Injection quantity of fuel injector  21 ×Engine speed/2×Number of cylinder 
     In step  106 , the filter pressure loss correction amount is added to the required fuel quantity to obtain the target discharge quantity which is corrected in accordance with the pressure loss of the fuel filter  16 . 
       Target discharge quantity=Required fuel quantity+Filter pressure loss correction amount 
     In step  107 , the target rotational speed is computed according to the target discharge quantity and the fuel pressure, referring to two-dimensional map shown in  FIG. 5  for computing the target rotational speed of the fuel pump  14 . The two-dimensional map is defined by the target discharge quantity and the fuel pressure as parameters. According to the above processing, the target rotational speed is obtained, which is corrected in accordance with the pressure loss of the fuel filter  16 . 
     Then, the procedure proceeds to step  108  in which the engine ECU  32  outputs the target rotational speed signal to the pump driving circuit  31 . The pump diving circuit  31  performs a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed. 
     According to the above described first embodiment, using the integrated value of the discharge quantity of the fuel pump  14  from a time of new vehicle as the parameter evaluating the pressure loss of the fuel filter  16 , the target discharge quantity is obtained by correcting the required fuel quantity with the filter pressure loss correction amount and the target rotational speed of the fuel pump  14  is computed based on the target discharge quantity. The target rotational speed of the fuel pump  14  is corrected in accordance with the pressure loss of the fuel filter  16 . The actual rotational speed of the fuel pump  14  is feedback controlled in such a manner as to agree with the target rotational speed. The target discharge quantity and the target rotational speed are defined in accordance with the actual pressure loss of the fuel filter  16 . Thus, the normal discharge amount of the fuel pump  14  can be reduced, compared with the case that the fuel pump  14  excessively discharges the fuel by the target discharge quantity and at the target rotational speed for the end of life time of the fuel pump  14 . The electricity for the fuel pump  14  is saved and the fuel economy is improved. 
     Besides, according to the first embodiment, the target rotational speed is computed based on the target discharge amount which is corrected in accordance with the pressure loss of the fuel filter  16 . However, the controller may be provided with a target rotational speed computing means for computing the target rotational speed of the fuel pump  14  based on the required fuel quantity or a parameter correlating thereto, a filter pressure loss correcting means for correcting the target rotational speed with the filter pressure loss amount, and a feedback control means for performing a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed corrected by the filter pressure loss correcting means. In short, the target rotational speed computed based on the required fuel quantity and the like may be corrected in accordance with the pressure loss of the fuel filter  16 . 
     Second Embodiment 
     Referring to  FIGS. 6 and 7 , a second embodiment of the present invention will be described hereinafter. However, an explanation is omitted or simplified about the substantially same portion as the first embodiment, and only the different portion is mainly explained. 
     According to the second embodiment, the engine ECU  32  executes a target rotational speed computing routine shown in  FIG. 6  and functions as a pump deterioration evaluating means for evaluating a deterioration degree of the fuel pump  14 , The rotational speed of the fuel pump  14  is corrected in accordance with the deterioration degree of the fuel pump  16  and the discharge quantity of the fuel pump  14  is corrected in accordance with the deterioration degree of the fuel pump  16 . In order to realize this correction, the engine ECU  32  functions as a target discharge quantity computing means for computing the target discharge quantity by correcting the required fuel quantity with the pump deterioration correction amount relating to the deterioration degree of the fuel pump  14 , a target rotational speed computing means for computing the target rotational speed of the fuel pump  14  based on the target discharge quantity, and a feedback control means for performing a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed. 
     In a method evaluating a deterioration degree of the fuel pump  14 , an integrated value of a rotation number of the fuel pump  14  or an integrated value of parameter correlating to the rotation number may be used as evaluation data of the deterioration degree of the fuel pump  14 . Since the deterioration of the fuel pump  14  gradually occurs for a long period, an integrated operation time, an integrated travel distance, or an integrated refuel quantity may be used as the substitute information of the integrated value of the rotation number. After an average rotation number per a unit operation time of the fuel pump  14  in an average driving condition, an average rotation number per a unit travel distance, or an average rotation number per a unit refuel quantity is previously obtained, the integrated value of the rotation number of the fuel pump  14  can be obtained based on the integrated operation time, the integrated travel distance or the integral refuel quantity. 
     Also in this case, the evaluation data of the deterioration degree of the fuel pump  14  is stored in the nonvolatile memory  37 . Thus, it is unnecessary to supply electricity to the nonvolatile memory  37  from the battery during the engine stop so that the evaluation data are held. Even if the battery is changed to new one, the data stored in the nonvolatile memory  37  can be held. Besides, when the fuel pump  14  is changed to new one, the evaluation data of the deterioration degree stored in the nonvolatile memory  37  may be initialized. 
     Referring to  FIG. 6 , the target rotational speed computing routine will be described hereinafter. The target rotational speed computing routine shown in  FIG. 6  is executed by the engine ECU  32  at a specified period during an engine operation. In step  201 , the rotational speed of the fuel pump  14  is detected based on a rotational speed signal transmitted from the pump driving circuit  31 . Then, the procedure proceeds to step  202  in which the rotation number of the fuel pump  14  per a computing cycle is computed based on the rotational speed of the fuel pump  14 . 
     In step  203 , a current rotation number per a computing cycle is added to a previous integrated value of the rotation number stored in the nonvolatile memory  37 , so that the integrated value of the rotation number of the fuel pump  14  from a time of shipping a vehicle until the current computing is updated and stored in the nonvolatile memory  37 . 
       Current integrated value of rotation number=Previous integrated value of rotation number+Current rotation number per computing cycle 
     Then, the procedure proceeds to step  204  in which a pump deterioration correction amount corresponding to the integrated value of the rotation number is computed based on the integrated value of the rotation number computed in step  203  as the evaluation data of the deterioration degree of the fuel pump  14 , referring to a pump deterioration correction amount map shown in  FIG. 7 . The pump deterioration correction amount map is preliminarily formed based on experimental data, design data, simulation results and the like. In this map, as the integrated value of the rotation number becomes larger, the pump deterioration correction amount becomes larger. 
     Then, the procedure proceeds to step  205  in which the required fuel quantity is computed in the same manner as step  105  of the first embodiment. In step  206 , the pump deterioration correction amount is added to the required fuel quantity so as to obtain the target discharge amount which is corrected in accordance with the deterioration degree of the fuel pump  14 . 
       Target discharge quantity=Required fuel quantity+Pump deterioration correction amount 
     Then, the procedure proceeds to step  207  in which the target rotational speed is computed in accordance with the target discharge quantity and the fuel pressure in the same manner as step  107  of the first embodiment. According to the above processing, the target rotational speed is obtained, which is corrected in accordance with the deterioration degree of the fuel pump  14 . 
     Then, the procedure proceeds to step  208  in which the engine ECU  32  outputs the target rotational speed signal to the pump driving circuit  31 . The pump diving circuit  31  performs a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed. 
     According to the above described second embodiment, using the integrated value of the rotational number of the fuel pump  14  from a time of new vehicle as the parameter evaluating the deterioration degree of the fuel pump  14 , the target discharge quantity is obtained by correcting the required fuel quantity with the pump deterioration correction amount. The target rotational speed of the fuel pump  14  is computed based on the target discharge quantity. The target rotational speed of the fuel pump  14  is corrected in accordance with the deterioration degree of the fuel pump  14 . The actual rotational speed of the fuel pump  14  is feedback controlled in such a manner as to agree with the target rotational speed. Thus, the normal discharge amount of the fuel pump  14  can be reduced, compared with the case that the fuel pump  14  excessively discharges the fuel by the target discharge quantity and at the target rotational speed for the end of life time of the fuel pump  14 . The electricity for the fuel pump  14  is saved and the fuel economy is improved. 
     Besides, according to the second embodiment, the target rotational speed is computed based on the target discharge amount which is corrected in accordance with the deterioration degree of the fuel pump  14 . However, the controller may be provided with a target rotational speed computing means for computing the target rotational speed of the fuel pump  14  based on the required fuel quantity or a parameter correlating thereto, a pump deterioration correcting means for correcting the target rotational speed with the pump deterioration correction amount, and a feedback control means for performing a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed corrected by the pump deterioration correcting means. in short, the target rotational speed computed based on the required fuel quantity and the like may be corrected in accordance with the deterioration degree of the fuel pump  14 . 
     Third Embodiment 
     Referring to  FIG. 8 , a third embodiment of the present invention will be described hereinafter. However, an explanation is omitted or simplified about the substantially same portion as the first and the second embodiment, and only the different portion is mainly explained. 
     According to the third embodiment, the engine ECU  32  executes a target rotational speed computing routine and functions as a filter pressure loss evaluating means for evaluating the pressure loss of the fuel filter  16  and a pump deterioration degree evaluating means for evaluating the deterioration degree of the fuel pump  14 . The rotational speed of the fuel pump  14  is corrected in accordance with the pressure loss of the fuel filter  16  and the deterioration degree of the fuel pump  14 , whereby the discharge quantity of the fuel pump  14  is corrected in accordance with the pressure loss of the fuel filter  16  and the deterioration degree of the fuel pump  14 . 
     The target rotational speed computing routine shown in  FIG. 8  is executed by the engine ECU  32  at a specified period during an engine operation. In steps  301 - 304 , in the same manner as steps  101 - 104  of the first embodiment, the discharge quantity of the fuel pump  14  is integrated and the filter pressure loss correction amount is computed in accordance with the integrated value of the discharge quantity. 
     In step  305 - 307 , in the same manner as steps  202 - 204  of the second embodiment, the rotational number of the fuel pump  14  is integrated and the pump deterioration correction amount is computed in accordance with the integrated value of the rotation number. 
     In step  308 , the required fuel quantity is computed in the same manner as step  105  of the first embodiment. In step  309 , the filter pressure loss correction amount and the pump deterioration correction amount are added to the required fuel quantity whereby the target discharge quantity is obtained, which is corrected based on the pressure loss of the fuel filter  16  and the deterioration degree of the fuel pump  14 . 
       Target discharge quantity=Required fuel quantity+Filter pressure loss correction amount+Pump deterioration correction amount 
     Then, the procedure proceeds to step  310  in which the target rotational speed is computed in accordance with the target discharge quantity and the fuel pressure. According to the above processing, the target rotational speed is obtained, which is corrected in accordance with the pressure loss of the fuel filter  16  and the deterioration degree of the fuel pump  14 . 
     Then, the procedure proceeds to step  311  in which the engine ECU  32  outputs the target rotational speed signal to the pump driving circuit  31 . The pump diving circuit  31  performs a feedback control in such a manner that the actual rotational speed of the fuel pump  14  agrees with the target rotational speed. 
     According to the third embodiment, since the target rotational speed can be corrected based on both of the pressure loss of the fuel filter  16  and the deterioration degree of the fuel pump  14 , both advantages of the first embodiment and the second embodiment can be obtained. 
     The present invention should not be limited to the above embodiments, but may be implemented in other ways without departing from the spirit of the invention. For example, the engine ECU is provided with a function of a feedback control means, and the pump driving circuit is configured by a simple driving circuit (inverter circuit) without the feedback function.