Patent Publication Number: US-2011048377-A1

Title: Fuel supplying system of lpi engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2009-0079450 filed on Aug. 26, 2009, the entire contents of which are incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel supplying system of a liquid propane injection (LPI) engine, and more particularly to a fuel supplying system of an LPI engine that is capable of improving maintainability and workability. 
     2. Description of Related Art 
     An LPI engine includes an LPI fuel pump feed therein so as to realize stability of fuel supplying performance when forcedly feeding fuel thereto. 
     That is, the fuel pump is mounted inside a fuel tank, and liquid-state LPG fuel that is forcedly fed is injected by an injector. 
     The LPI engine is suitable for corresponding to strict emission regulations, and can improve engine starting in winter while inducing an emission output reduction of the engine. 
     As shown in  FIG. 2 , a conventional fuel supplying system of LPI engine includes a fuel tank  10  in which a fuel pump  12  is mounted for feeding liquid-state fuel to an engine  20 , a fuel supply line  30  with one end thereof connected to the fuel pump  10  and the other end thereof connected to an injector connected to the engine  20 , and a fuel return line  40  with one end thereof connected to the engine  20  and the other end thereof connected to the fuel tank  10 . 
     The fuel supplied from the fuel pump  12  is injected to a combustion chamber through the fuel supply line  30  and the injector sequentially, and residual fuel is returned to the fuel tank  10  through the fuel return line  40 . 
     Meanwhile, a cut-off valve  32  for blocking fuel supply in case of engine stop and a temperature sensor  34  for detecting temperature of the fuel are mounted at the fuel supply line  30 . 
     Further, a pressure detecting sensor  49  for detecting pressure of the fuel and a regulator unit  48  for maintaining pressure of the fuel within a predetermined pressure range are mounted at the fuel return line  40 . 
     However, in case of malfunction of the fuel pump, after the high-pressure LPG fuel is extracted from the fuel tank by a gas extractor, the fuel tank must be cut open to replace the pump and the tank should then be patched, since the conventional LPI fuel pump is mounted inside the LPI fuel tank for feeding fuel to the engine. 
     In the case, the gas extraction is only allowed in a designated facility that complies with safety restrictions resulting in a long waiting time for customers. 
     Therefore, labor for extracting the gas is increased, and thereby customers have complaints, particularly taxi drivers. 
     Further, parts and cost of materials for compensating for noise, vibration, and harshness (NVH) of the fuel pump repair are heavy. 
     Further, since many parts are welded inside the fuel tank, thermal distortion occurred at a plate of the tank, and scale resulting in deterioration of durability of the fuel pump are generated in a welding process. 
     In addition, a problem occurs in that site workers evade the repairing and checking of the LPI fuel tank due to safety questions and unpleasant feeling caused by inhalation of gas. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention are directed to provide a fuel supplying system of a liquid propane injection (LPI) engine having advantages of improving performance of maintainability and workability. 
     In an aspect of the present invention, the fuel supplying system of a liquid propane injection (LPI) engine, may include a fuel tank for storing fuel, a main fuel pump connected to the fuel tank and disposed at the exterior of the fuel tank, a fuel supply line connecting the main fuel pump and the engine to supply fuel from the main fuel pump to the engine, and a fuel return line connecting the engine and the interior of the fuel tank to return fuel from the engine to the interior of the fuel tank, wherein a sub-fuel pump is provided to the interior of the fuel tank and connected to the fuel supply line through a sub-fuel pump connecting pipe, the sub-fuel pump being operated when a predetermined condition is satisfied. 
     The sub-fuel pump connecting pipe may be connected to an exhaust pipe disposed at the interior of the fuel tank, and the sub-fuel pump connecting pipe and the exhaust pipe may be connected to the fuel supply line through a one-way check valve disposed at a downstream side of a joining position of the sub-fuel pump connecting pipe and the exhaust pipe. 
     The predetermined condition may be satisfied when pressure of the interior of the fuel tank is lower than a predetermined pressure. 
     The one-way check valve may prevent backflow of the fuel into the fuel tank. 
     The fuel supplying system may further include a regulator unit at a downstream side of the main fuel pump. 
     In another aspect of the present invention, the fuel supplying system of an LPI engine may include a fuel tank for storing fuel, a main fuel pump connected to the fuel tank and disposed at the exterior of the fuel tank, a fuel supply line connecting the main fuel pump and the engine to feed fuel from the main fuel pump to the engine, and a fuel return line connecting the engine and the fuel tank to return fuel from the engine to the interior of the fuel tank, and a sub-fuel pump disposed inside the fuel tank and connected to the fuel supply line through a sub-fuel fuel pump connecting pipe, wherein the main fuel pump is operated while driving, and the sub-fuel pump is operated under a predetermined condition. 
     The predetermined condition may be satisfied when pressure of the interior of the fuel tank is lower than a predetermined pressure. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a fuel supplying system of LPI engine according to an exemplary embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing a conventional fuel supplying system of LPI engine. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram showing a fuel supplying system of a liquid propane fuel (LPI) engine according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , a fuel tank  100 , a regulator unit  200 , and an engine are connected to each other through a fuel supply line S and a fuel return line R so as to feed liquid-state fuel in the fuel tank  100  to the engine via the regulator unit  200 , and then unused liquid-state fuel is returned to the fuel tank  100  through the regulator unit  200 . 
     The regulator unit  200 , as a conventional device, maintains supply pressure of the liquid-state fuel supplied to the engine. 
     Further, a fuel return line R connecting the engine and the fuel tank  100  is connected to the regulator unit  200  so as to return unused fuel to the fuel tank  100 . 
     In addition, a pressure sensor detecting fuel pressure of fuel returning to the fuel tank  100  may be mounted in the fuel return line R connected to the regulator unit  200 , and furthermore a pressure regulator may be mounted therein so as to return the fuel to the fuel tank  100  only when the fuel pressure exceeds a predetermined pressure. 
     Although not shown in the drawings, the fuel supplying system can be controlled by an ECU. 
     Further, a main fuel pump  300  is mounted at the fuel supply line S disposed between the fuel tank  100  and the regulator unit  200  so as to continuously forcedly feed the fuel in the fuel tank  100  to the engine. Herein, the main fuel pump  300  may be an external fuel pump disposed outside the fuel tank  100 . 
     Further, a pressure detecting sensor  110  may be mounted at the fuel tank  100  for detecting internal pressure of the fuel tank  100 . The pressure sensor  110  can be controlled by the ECU. 
     In addition, a sub-fuel pump  120  is mounted inside the fuel tank  100 . 
     The sub-fuel pump  120  is operated only when pressure detected by the pressure sensor  110  is less than 0.5 bar. 
     At this time, the fuel supplied from the sub-fuel pump  120  is supplied to the exterior portion of the fuel tank  100  through a sub-fuel pump connecting pipe  121 . 
     Herein, a one-way check valve  130  is provided to prevent backflow of the fuel before the fuel flows from the fuel tank  100  to the exterior thereof. 
     During the fuel supply, if the fuel supply line S is blocked or the regulator unit  200  malfunctions resulting in deterioration of the fuel flow, pressure of the fuel supply line S is greater than pressure of the sub-fuel pump  120 . 
     At this time, the fuel flows backward into the sub-fuel pump  120  through a recirculation line provided from the outlet of the main fuel pump to the inlet thereof due to the high pressure of the fuel supply line S. 
     To avoid the backflow resulting in damage to the sub-fuel pump  120 , a one-way check valve  130  preventing the backflow should be provided therewith. 
     Meanwhile, a separate exhaust pipe  122  that is diverged from the sub-fuel pump connecting pipe  121  supplies the fuel to the engine. 
     That is, the sub-fuel pump connecting pipe  121  and the exhaust pipe  122  are joined at the one-way check valve  130 . 
     Thus, the fuel in the fuel tank  100  is supplied to the main fuel pump  300  through the exhaust pipe  122  only by using internal pressure thereof, and the fuel in the fuel tank  100  is supplied to the main fuel pump  300  through the sub-fuel pump connecting pipe  121  by an operation of the sub-fuel pump  120  in the case that the internal pressure of the fuel tank  100  is less than 0.5 bar. 
     The operation of a fuel supplying system of an LPI engine according to an exemplary embodiment of the present invention will be hereinafter described in detail. 
     During driving, when pressure detected by the pressure sensor  110  is greater than 0.5 bar, the fuel flows into the main fuel pump  300  through the exhaust pipe  122  in a state in which a control valve of the fuel supply line S is disposed between the one-way check valve  130  mounted inside the fuel tank  100  and the main fuel pump  300 . 
     The main fuel pump  300  is operating continuously during driving, 
     At this time, the main fuel pump  300  pressurizes the liquid-state fuel from the fuel tank  100  by a predetermined pressure in comparison with the pressure of the fuel tank  100 . For example, a pressure of 5 bar is added to a pressure of the fuel pump  100  that is 3 bar, and thereby pressure of liquid-state fuel that is 8 bar is supplied by the fuel supply line S. 
     Meanwhile, if pressure detected by the pressure sensor  110  is less than 0.5 bar, the ECU controls the sub-fuel pump  120  disposed inside the fuel tank  100  to be operated. 
     And then, the fuel is supplied to the main fuel pump  300  through the sub-fuel pump connecting pipe  121  and the one-way check valve  130  by using a pumping operation of the sub-fuel pump  120 . 
     While the liquid-state fuel is supplied to the engine through the regulator unit  200 , a portion of the fuel is injected by the injector and ignited, and a remaining portion thereof is returned to the fuel tank  100  through the regulator unit  200  via the fuel return line R. 
     In this way, the liquid-state fuel returned through the fuel return line R is passed through the regulator unit  200  via an opened return valve, and then it is stored in the fuel tank  100 . 
     Meanwhile, the liquid-state fuel flowing into the fuel return line R is expanded according to an increase in temperature. At that time, the pressure is increased to 8 bar as described above, and then the fuel flows into the fuel tank  100  again since the pressure adjuster of the regulator unit  200  and a return valve in the fuel return line R closed are sequentially opened. 
     In case of malfunction of the main fuel pump  300 , only the main fuel pump  300  needs to be disassembled from the fuel supply line S for being repaired or replaced in a state that the control valve mounted at the fuel supply line S between the fuel tank  100  and the main fuel pump  300  is closed for a cut-off from the fuel tank  100 , and thus the repair is simplified regardless of working place. Further, because it is unnecessary to extract all the fuel from the fuel tank  100 , a loss of the fuel in the process is minimized. 
     Further, during the fuel supply, if the fuel supply line S between the main fuel pump  300  and the regulator unit  200  is blocked or malfunctions by sludge mixed in the liquid-state fuel, pressure of the fuel supply line S is greater than pressure of the sub-fuel pump  120 . However, a one-way check valve prevents backflow of the supplied liquid-state fuel in order to reduce damage to the sub-fuel pump  120 . 
     Further, because the sub-fuel pump  120  is operated only when internal pressure of the fuel tank  100  is lower than a predetermined pressure, malfunction of the sub-fuel pump  120  is minimized, and thereby longevity thereof is improved. 
     For convenience in explanation and accurate definition in the appended claims, the term “exterior” is used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.