Patent Publication Number: US-7222611-B2

Title: Fuel supply apparatus and fuel pressure regulating method for internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a technology for appropriately controlling a pressure in a fuel supply passage at the time when an operation of an internal combustion engine is stopped. 
     RELATED ART 
     As a fuel supply apparatus for an internal combustion engine, there has been known a system configured such that, in order to prevent the fuel temperature rise due to excessive fuel, which is not injected to be returned to a fuel tank from a fuel injection valve through a pressure regulator on the downstream of the fuel injection valve, a fuel return passage from the fuel injection valve is eliminated, and a pressure regulator is arranged just after a fuel pump to regulate a fuel pressure (to be referred to as a non-return system). 
     Japanese Unexamined Patent Publication No. 7-293397 discloses a fuel supply apparatus of such a type, in which in order to prevent that the vapor is generated from fuel remaining in a fuel supply passage after an engine operation is stopped, a residual pressure in the fuel supply passage is held to prevent the vapor generation. 
     Further, in Japanese Unexamined Utility Model Publication No. 5-12643, a fuel pressure in a fuel supply passage after an engine operation is stopped, is lowered to the atmospheric pressure. 
     However, in the case where the residual pressure at the time when the engine operation is stopped is held as in Japanese Unexamined Patent Publication No. 7-293397, since the residual pressure is too high, the fuel leakage from the fuel injection valve occurs, so that the fuel vapor tends to be accumulated in a cylinder, resulting in the deterioration of operating performance at the engine re-starting time or the exhaust emission. 
     Further, if the fuel pressure is lowered to the atmospheric pressure at the time when the engine operation is stopped as in Japanese Unexamined Utility Model Publication No. 5-12643, the vapor tends to be generated, and the engine re-starting performance is degraded due to a delay in the fuel pressure rise at the engine re-starting time. 
     SUMMARY OF THE INVENTION 
     The present invention has an object to prevent the fuel leakage from a fuel injection valve and the generation of vapor at the time when an engine operation is stopped. 
     In order to achieve the above object, the present invention is constituted so that a bypass passage, which returns fuel in a fuel supply passage into a fuel tank, is opened, and a part of the fuel in the fuel supply passage is returned from the opened bypass passage into the fuel tank, and then, a fuel pressure in the fuel supply passage is lowered to a predetermined fuel pressure higher than the atmospheric pressure, to be regulated. 
     The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings. 
    
    
     
       BRIEF EXPLANATION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a system configuration of an internal combustion engine in a first embodiment. 
         FIG. 2  is an enlarged section view of a pressure regulating mechanism disposed in the first embodiment. 
         FIG. 3  is a time chart showing states of engine operation stopped time and engine operation re-started time in the first embodiment. 
         FIG. 4  is a diagram showing a system configuration of a fuel supply apparatus of an internal combustion engine in a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a diagram showing a system configuration of an internal combustion engine in a first embodiment. 
     In  FIG. 1 , fuel in a fuel tank  1  is sucked by an electrically operated fuel pump  2 , and the fuel discharged from fuel pump  2  is sent under pressure via a fuel supply passage  3  to a fuel injection valve  4  of each cylinder. 
     A fuel damper  5  is disposed in fuel supply passage  3 , and a fuel pressure sensor  6  detecting a fuel pressure is attached to a fuel gallery section  3 A on the downstream end. 
     Fuel injection valve  4  is an electromagnetic fuel injection valve, which is opened when the power is supplied to a solenoid thereof and is closed when the power supply is stopped, and is controlled to open according to a drive pulse signal of predetermined pulse width Ti (valve open time), sent from a control unit  7 , corresponding to an engine required fuel quantity, to inject the fuel into an engine intake passage (not shown in the figure). 
     A bypass passage  8 , which bypasses fuel supply passage  3  to return the fuel into fuel tank  1 , is connected to the upstream end of fuel supply passage  3 , that is, a portion directly above a discharge port of fuel pump  2 . On the connection point of bypass passage  8  and fuel supply passage  3 , there are disposed an open/close valve  9  switching the communication/the shutoff between fuel supply passage  3  and bypass passage  8 , and a pressure regulating mechanism  10  which regulates the fuel pressure in fuel supply passage  3  to a predetermined fuel pressure higher than the atmospheric pressure, when fuel supply passage  3  and bypass passage  8  are communicated with each other by an opening operation by open/close valve  9 . 
     Here, fuel pump  2 , bypass passage  8 , open/close valve  9  and pressure regulating mechanism  10  are disposed in fuel tank  1 . 
       FIG. 2  shows the details of open/close valve  9  and pressure regulating mechanism  10 . Open/close valve  9  comprises an electromagnetic valve provided with: a valve body  9   a  opening/closing bypass passage  8  to switch the communication/the shutoff between fuel supply passage  3  and bypass passage  8 ; a return spring  9   b  urging valve body  9   a  to be closed; and a solenoid  9   c  driving valve body  9   a  to open, and is driven to open/close by an ON/OFF operation of solenoid  9   c  based on a signal from control unit  7 . During an engine operation, open/close valve  9  is kept in a closed state by the OFF operation of solenoid  9 . Pressure regulating mechanism  10  disposed adjacent to the downstream side of open/close valve  9 , comprises: a diaphragm valve  10   a  opening/closing bypass passage  8 ; and a return spring  10   b  urging diaphragm valve  10   a  to be closed with a predetermined urging force. Here, the urging force of return spring  10   b  is set to be the magnitude at which diaphragm valve  10   a  is opened when it receives a fuel pressure lower than the fuel pressure held in fuel supply passage  3  at the time of the engine operation stop (but higher than the atmospheric pressure). 
     Control unit  7  receives, in addition to a detection signal from fuel pressure sensor  6 , an intake air amount detection signal Q from an air flow meter  11 , an engine rotation speed signal Ne from a crank angle sensor  12 , an engine cooling water temperature (to be referred as water temperature hereunder) signal Tw from a water temperature sensor  13 , an ON or OFF signal from an engine key switch  14 , and the like. 
     Then, in control unit  7  incorporating therein a microcomputer, a basic fuel injection pulse width Tp (basic valve open time) corresponding to the engine required fuel quantity, namely, a cylinder intake air amount, is calculated based on the intake air amount Q and the engine rotation speed Ne, and also, a target fuel pressure Pa of fuel pump  2  is set based on the engine rotation speed Ne and the basic fuel injection pulse width Tp. Thereafter, control unit  7  feedback controls, by a PID control or the like, a basic duty which is set based on the engine rotation speed Ne and the basic fuel injection pulse width Tp, based on the target fuel pressure Pa and the fuel pressure detected by fuel pressure sensor  6 , to obtain a control duty signal, and outputs the control duty signal to a pump drive circuit (FPCM)  15  to control fuel pump  2 , thereby performing a feedback control to obtain a target fuel pressure. 
     Thus, the fuel pressure during the engine operation is feedback controlled, and after the engine operation stop, the fuel pressure is regulated, by the control using open/close valve  9  and pressure regulating mechanism  10  according to the present invention. 
     Namely, when engine key switch  14  is turned OFF, control unit  7  supplies the power to open/close valve  9  for a predetermined period of time, to open it (shown by the chain line in  FIG. 2 ). Then, the fuel pressure held in fuel supply passage  3  at the time of engine operation stop, is applied on diaphragm valve  10   a  of pressure regulating mechanism  10  via open/close valve  9 . As described above, the valve opening force acting on diaphragm valve  10   a  by the fuel pressure at the time of engine operation stop is greater than the urging force of return spring  10   b . Therefore, diaphragm valve  10   a  is urged to open, so that the fuel passes through bypass passage  8  to be returned into fuel tank  1  (shown by the chain-lined arrows in  FIG. 2 ). Thus, when the fuel pressure is lowered so that the valve opening force applied on diaphragm valve  10   a  equals to the urging force of return spring  10   b , diaphragm valve  10   a  is closed, and the fuel pressure in fuel supply passage  3  communicating with bypass passage  8  on the upstream side of diaphragm valve  10   a  is maintained to be the predetermined fuel pressure which acts, on diaphragm valve  10   a , a force equal to the urging force of return spring  10   b . Open/close valve  9  is shut off of the power supply after the predetermined period of time, to be closed, thereby enabling the power consumption to be a minimum while maintaining the fuel pressure to be a predetermined fuel pressure Po. 
       FIG. 3  shows states of engine operation stopped time and engine operation re-started time. 
     Since the fuel pressure in fuel supply passage  3  is lowered to the predetermined fuel pressure Po after the engine operation stop, it is possible to prevent the fuel leakage from fuel injection valve  4 . Further, since the predetermined fuel pressure is higher than the atmospheric pressure, the generation of vapor can be suppressed and also a delay in fuel pressure rise at the engine operation re-started time can be suppressed, thereby satisfying the engine re-starting performance. 
     Moreover, since fuel pump  2 , bypass passage  8 , open/close valve  9  and pressure regulating mechanism  10  are disposed in fuel tank  1 , a space outside fuel tank  1  can be effectively utilized. 
       FIG. 4  shows a system configuration in a second embodiment. 
     In this system configuration, in addition to the configuration in the first embodiment, a relief valve  21  whose open/close operation can be arbitrarily controlled (for example, it is opened when the engine operation is started) and a return passage  22  returning the fuel into fuel tank  1  via relief valve  21  are disposed on the downstream side of a portion, to which fuel injection valve  4  is attached, in fuel supply passage  3 . 
     Thus, even in the case where especially, the fuel temperature becomes high so that the vapor is generated in fuel supply passage  3 , relief valve  21  is opened, thereby enabling the vapor to escape to return passage  22 . 
     The entire contents of Japanese Patent Application No. 2003-320622 filed on Sep. 12, 2003, a priority of which is claimed, are incorporated herein by reference. 
     While only a selected embodiment has been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. 
     Furthermore, the foregoing description of the embodiment according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined in the appended claims and their equivalents.