Abstract:
A fuel supply system for a direct injection gasoline engine can be used in a variable fuel pressure system without using a large pulsation absorber and, as a result, is inexpensive and can be easily reduced in size. The fuel supply system for a direct injection gasoline engine includes a single-cylinder high-pressure pump, a resonator for suppressing the pressure pulsation of high-pressure fuel supplied from the high-pressure fuel pump, and a high-pressure variable regulator for variably changing the pressure of the high-pressure fuel. The fuel-supply system directly injects the high-pressure fuel into the cylinders of the engine through injectors.

Description:
FIELD OF THE INVENTION 
     The present invention relates to fuel supply equipment used in a variable fuel pressure system and, particularly, to fuel supply equipment for a direct injection gasoline engine, which comprises a single-cylinder high-pressure fuel pump and directly injects high-pressure fuel into the cylinders of an engine. 
     BACKGROUND OF THE INVENTION 
     Diesel engine technology is widely known as an example of an engine technology where the fuel is injected into its cylinders, which is so called “in-cylinder injection engine” or “direct injection engine”. For spark ignition (gasoline) engine also, in-cylinder injection type has recently been proposed. For such in-cylinder injection engines, it is required that the fuel pressure pulsation should be small enough to achieve stable injection as well as the fuel injection pressure should be sufficiently high. 
     Therefore, a single-cylinder high-pressure fuel pump which is simple in structure, produced at a low cost and compact is already known. 
     Since the single-cylinder high-pressure fuel pump has only one plunger, it generates a larger pulsation width in the fuel pressure than a multi-cylinder high-pressure fuel pump does. Therefore, a metal bellows type or metal diaphragm type pulsation absorber is provided in a fuel supply system to absorb the pulsation. 
     FIG. 8 is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine disclosed by Japanese Laid-open Patent Application No. 9-310661, for example. In this fuel supply system for a direct injection gasoline engine, the pressure of fuel (gasoline) stored in a fuel tank  70  is increased to a low level by a low-pressure fuel pump  71  and then the fuel is supplied to a high-pressure fuel pump  73  by a low-pressure pipe  72 . The high-pressure fuel pump  73  further increases the pressure of the fuel to a high level by the reciprocating motion of a plunger  75  driven by the cam shaft  74  of an unshown engine and discharges the fuel from an outlet port  76 . This outlet port  76  is connected to a common rail  79  through a high-pressure check valve  77  and a high-pressure pipe  78 . High-pressure fuel stored in the common rail  79  is supplied to injectors  81  attached to the respective cylinders  80  of the engine through branch passages  82 . 
     This common rail  79  is connected to a metal bellows type pulsation absorber  85 . This metal bellows type pulsation absorber  85  is constituted such that a barrel portion is composed of metal bellows  85   a,  an opening at one end of the metal bellows  85   a  is closed by an end plate  85   b,  a peripheral portion at the other end of the metal bellows  85   a  is connected to the end surface  85   c  of the absorber by welding or the like, a closed space is formed inside the metal bellows  85   a,  and gas such as nitrogen or argon is charged into this closed space. The pressure pulsation of high-pressure fuel to be applied to the end plate  85   b  is absorbed by the expansion and contraction of the metal bellows  85   a  so that the pressure pulsation of the high-pressure fuel supplied into the common rail  79  is absorbed. 
     FIG. 9 is a sectional view showing the configuration of a high-pressure fuel supply system  10 D equipped with a metal diaphragm type pulsation absorber. The high-pressure fuel supply system  10 D comprises a high-pressure fuel pump  11 , a low-pressure damper  14  provided in an inlet passage  12  connected to an inlet port side of the high-pressure fuel pump  11  and equipped with metal bellows  14   a,  a high-pressure damper  90  provided in an outlet passage  15  connected to an outlet port side of the high-pressure fuel pump  11  and equipped with a metal diaphragm  90   m,  and a high-pressure check valve  17  arranged on a downstream side of the high-pressure damper  90 , all of which are integrally arranged in a casing  100 . 
     The high-pressure pump  11  pressurizes the low pressure fuel supplied from the unshown fuel inlet port through the inlet passage to a high pressure level and discharges it to the outlet passage  15  by utilizing the plunger  112  which is arranged in a cylinder  111  in such a manner it can reciprocate and is driven by a cam  19  whose rotational speed is a half of an unshown engine&#39;s crank speed. 
     The metal diaphragm type pulsation absorber  90  is provided to suppress the pressure pulsation of this discharged high-pressure fuel. As shown in FIG.  9  and FIG. 10, the metal diaphragm type pulsation absorber  90  comprises a case  91  constituting one part of a high-pressure container, a plate  92  constituting the other part of the high-pressure container, and a flexible thin metal disk-like diaphragm  90   m  forming a first high-pressure chamber  93  with the above case  91  and a second high-pressure chamber  94  with the above plate  92 . The above second high pressure chamber  94  is connected via multiple through holes  96  with a recess  95  which constitutes a path between the first passage  15 P to an outlet of the high-pressure fuel pump located in the casing  100  and the second passage  15 Q to a check valve  17 . The above first high-pressure chamber  93  is filled with unshown gas from a gas filling port  97  formed in the case  91  at a predetermined pressure. This predetermined pressure is required to absorb the pulsation of the high-pressure fuel running through the second passage portion  15 Q from the first passage portion  15 P through the recessed portion  95 . 
     When pulsation occurs in the above fuel while the first high-pressure chamber  93  is filled with gas and the second high-pressure chamber  94  is filled with fuel, the diaphragm  90   m  absorbs the pressure pulsation by bending towards the case  91  and towards the plate  92  from the balance point (for example, a position having no deflection shown by a bold line in FIG. 10) where the total of the gas pressure in the first high-pressure chamber  93  and the spring force of the diaphragm  90   m  itself becomes equivalent to the average pressure of the fuel. 
     However, in the metal diaphragm type pulsation absorber  90 , since the metal diaphragm which is an expansion member expands and contracts repeatedly by an amount equivalent to the pressure pulsation of fuel with the balance point at an average fuel pressure as a center, when this fuel supply system for a direct injection gasoline engine is used in a fuel pressure variable system, the balance point changes, whereby average stress generated in the diaphragm alters, thereby causing a problem with durability. 
     For instance, when the variable range of fuel supply pressure of the fuel supply system is 5 to 10 MPa and the balance point of the metal diaphragm  90   m  is set to P 0 =7.5 MPa which is the center of the above variable range, as shown in FIG. 10, if P 0 =10 MPa, the metal diaphragm  90   m  vibrates with the balance point greatly displaced to the first high-pressure chamber  93  side and if P 0 =5 MPa, the metal diaphragm  90   m  vibrates with the balance point greatly displaced to the second high-pressure chamber  94  side. Since average stress applied to the metal diaphragm  90   m  becomes larger as the balance point displaces more from the center of the variable range, the durability of the metal diaphragm  90   m  deteriorates. 
     To prevent deterioration in the durability of the metal diaphragm, it is conceivable, for example, to reduce the volume of the first high-pressure chamber  93  so as to lessen the amount of charged gas. In this case, pulsation absorption capability becomes less. It is also possible to improve the durability of the metal diaphragm by reducing average stress to be applied to the metal diaphragm by increasing the diameter. However, in this case, the pulsation absorber becomes large in size. 
     Even when a metal bellows type pulsation absorber is used as a high-pressure damper, if fuel supply pressure is made variable, the gas charging pressure must be reduced to achieve the minimum fuel pressure and the number of pleats of the metal bellows must be increased to obtain the large expansion width of the metal bellows with the result that the system becomes large in size. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention which has been made in view of the above problems of the prior art to provide a fuel supply system for a direct injection gasoline engine which can be used in a fuel pressure variable system without using a large pulsation absorber, is inexpensive and can be reduced in size. 
     According to a first aspect of the present invention, there is provided a fuel supply system for a direct injection gasoline engine, which comprises a single-cylinder high-pressure fuel pump, a resonator for suppressing the pressure pulsation of high-pressure fuel supplied from the high-pressure fuel pump and a high-pressure variable regulator for controlling the pressure of high-pressure fuel, wherein the pressure of fuel to be injected into the cylinders of an engine from injectors is made variable, and the pressure pulsation of the fuel is suppressed. 
     According to a second aspect of the present invention, there is provided a fuel supply system for a direct injection gasoline engine, wherein the high-pressure variable regulator and the resonator are integrated with the high-pressure fuel pump. 
     The above and other objects, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     FIG. 1 is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine according to Embodiment 1 of the present invention; 
     FIG. 2 is a sectional view of a high-pressure fuel supplier according to Embodiment 1 of the present invention; 
     FIG. 3 is a diagram showing the configuration of a high-pressure variable regulator; 
     FIG. 4 is a diagram showing the configuration of another fuel supply system for a direct injection gasoline engine according to Embodiment 1 of the present invention; 
     FIG. 5 is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine according to Embodiment 2 of the present invention; 
     FIG. 6 is a sectional view of a high-pressure fuel supplier according to Embodiment 2 of the present invention; 
     FIG. 7 is a diagram showing the configuration of another fuel supply system for a direct injection gasoline engine according to Embodiment 2 of the present invention; 
     FIG. 8 is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine of the prior art; 
     FIG. 9 is a sectional view showing the configuration of another fuel supply system for a direct injection gasoline engine of the prior art; and 
     FIG. 10 is a diagram for explaining the operation of a pulsation absorber. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described with reference to the accompanying drawings. 
     Embodiment 1 
     FIG. 1 shows the configuration of a fuel supply system for a direct injection gasoline engine according to Embodiment 1 of the present invention. In FIG. 1, reference numeral  10  denotes a high-pressure fuel supplier equipped with a high-pressure fuel pump  11 ,  20  a fuel tank equipped with a low-pressure fuel pump  21 ,  30  a common rail storing the fuel supplied from the fuel tank  20  and pressurized by the high-pressure pump  11 ,  31  injectors attached to the respective cylinders of an unshown engine and connected to the common rail  30 ,  40  a high-pressure fuel passage for connecting the common rail  30  to the high-pressure fuel pump  11 , and  50  a low-pressure fuel passage for connecting the high-pressure pump  11  to the fuel tank  20 . The high-pressure fuel passage  40  and the low-pressure fuel passage  50  form a fuel passage for connecting the injectors  31  of the cylinders to the fuel tank  20 . Letter F is fuel stored in the fuel tank  20 . 
     As shown in FIG.  1  and FIG. 2, the high-pressure fuel supplier  10  comprises the high-pressure fuel pump  11 , an inlet passage  12  constituting part of the low-pressure fuel passage  50  and connected to an inlet port side of the high-pressure fuel pump  11 , a filter  13  arranged in the inlet passage  12 , a low-pressure damper  14  provided between the high-pressure fuel pump  11  and the filter  13  and equipped with metal bellows  14   a,  an outlet passage  15  constituting part of the high-pressure fuel passage  40  and connected to an outlet port side of the high-pressure fuel pump  11 , a resonator  16  which is a means of suppressing the pulsation of high-pressure fuel discharged from the high-pressure fuel pump  11  and communicates with a buffer chamber  15 S provided in the outlet passage  15 , a high-pressure check valve  17  arranged on a downstream side of the resonator  16  for maintaining the pressure of fuel in the common rail  30  to an appropriate level when the engine is suspended, a high-pressure variable regulator  18  arranged on a downstream side of the high-pressure check valve  17  for controlling the pressure of fuel to be supplied to the injectors  31  of the cylinders, a drain passage  18 D for the high-pressure variable regulator  18  and a drain passage  11 D for the high-pressure fuel pump  11 . 
     The high-pressure pump  11  pressurizes the low pressure fuel supplied from the unshown fuel inlet port through the inlet passage to a high pressure level and discharges it to the outlet passage  15  by utilizing the plunger  112  which is arranged in a cylinder  111  in such a manner it can reciprocate and is driven by a cam  19  whose rotational speed is a half of an unshown engine&#39;s crank speed. 
     Denoted by  113  and  114  are reed valves for sucking and discharging fuel, respectively. 
     A filter  22  is provided on an inlet side of the low-pressure fuel pump  21  arranged in the fuel tank  20 , and a low-pressure check valve  23  is provided on an outlet side of the low-pressure fuel pump  21 . The outlet side of the low-pressure fuel pump  21  is connected to the fuel inlet port  101  of the high-pressure fuel supplier  10  by a low-pressure pipe  24 . A filter  25  is provided in the low-pressure pipe  24 . Reference numeral  26  denotes a low-pressure regulator provided on the low-pressure pipe  24 , and  27  a low-pressure fuel return pipe for the low-pressure regulator. Reference numeral  28  represents a drain pipe for connecting the drain passage  11 D of the high-pressure fuel pump  11  to the fuel tank  20 , which is connected to a regulator drain pipe  29  for connecting the drain passage  18 D of the high-pressure variable regulator  18  to the fuel tank  20 . 
     Meanwhile, the fuel outlet port  102  of the high-pressure fuel supplier  10  and the common rail  30  are connected to each other by a high-pressure pipe  32 . Denoted by  33  is a fuel pressure sensor provided on the common rail  30 . A current to be applied to the coil of the above high-pressure variable regulator  18  is controlled by an unshown electronic control unit (ECU) based on the output signal of the fuel pressure sensor  33 . 
     As shown in FIG. 3, the high-pressure variable regulator  18  for controlling the pressure of fuel comprises a needle valve  1  consisting of a valve sheet  1   b  having an orifice  1   a  which is opened to a branch passage  15 K branching off from the outlet passage  15  and a needle  1   c  for opening and closing the orifice  1   a  by contacting to and separating from the valve sheet  1   b,  an unshown magnetic armature connected to the needle valve  1  integrally, an unshown spring for urging this armature downward (direction for closing the needle valve  1 ) and a coil  5  for generating a magnetic flux in a magnetic circuit comprising the armature and an unshown magnetic core, and controls the pressure of fuel discharged from the high-pressure fuel pump  11 . 
     This high-pressure variable regulator  18  urges the needle valve  1  downward by the spring, changes the magnetic flux in the magnetic circuit comprising the magnetic core and the armature corresponding to the current applied to the coil  5  based on a required pressure of the fuel, assists the spring by controlling force for urging the armature downward and adjusts the opening of the needle valve  1 . When the variable range of fuel supply pressure of the fuel supplier is 5 to 10 MPa, for example, a state having zero current applied to the coil  5  is a state where the needle valve  1  is opened most. At this point, the pressure of fuel becomes minimum at 5 MPa. When a current to be applied to the coil  5  is gradually increased, the needle valve  1  is gradually closed, and the pressure of fuel rises. When the supply current is maximum, fuel pressure is controlled to the maximum pressure of 10 MPa by urging the needle valve  1 . 
     The high-pressure variable regulator may also be of such a type that sets the pressure of the spring to a level corresponding to the maximum pressure of fuel and controls the pressure of fuel by urging the armature upward by the coil  5 . 
     The resonator  16  is a Helmholtz resonator comprising an orifice  16   a  which is opened to the buffer chamber  15 S of the outlet passage  15  at one end and a fuel control chamber  16   b  connected to an opening portion at the other end of the orifice  16   a  (see FIG.  2 ). The amplitude of fuel pressure pulsation at the resonance frequency in the outlet passage  15  that is caused by the discharge pulsation of the high-pressure pump  11  can be reduced by controlling the resonance characteristics of the resonator  16  which are determined by the volume of the fuel control chamber  16   b  and the size of the orifice  16   a.    
     The resonator  16  has a simple structure consisting of the orifice  16   a  and the fuel control chamber  16   b  and has no expansion member such as a metal diaphragm or metal bellows. Therefore, even when the range of variable fuel supply pressure of the fuel supplier is large, unlike the conventional pulsation absorber, a durability problem does not arise. 
     A description is subsequently given of the operation of the above fuel supply system for a direct injection gasoline engine. The low-pressure fuel pump  21  sucks fuel through the filter  22 , increases the pressure of the fuel to a low level and discharges the fuel. This low-pressure fuel is supplied to the fuel inlet port  101  of the high-pressure fuel supplier  10  through the low-pressure check valve  23  and the filter  25  by the low-pressure pipe  24 . At this point, when the pressure of the fuel running through the low-pressure pipe  24  exceeds a predetermined low value set by the low-pressure regulator  26 , part of the fuel in the low-pressure pipe  24  is returned to the fuel tank  20  through the low-pressure regulator  26  by the low-pressure fuel return pipe  27 , thereby controlling the pressure of fuel supplied to the high-pressure fuel supplier  10  from the fuel tank  20  to a predetermined value. 
     The fuel supplied to the inlet passage  12  of the high-pressure fuel supplier  10  is sucked by the high-pressure fuel pump  11  through the filter  13  and the low-pressure damper  14 . The high-pressure fuel pump  11  increases the pressure of the above sucked fuel to a high level, discharges the fuel from the outlet passage  15  and drains fuel leaking from a space between the plunger  112  and the cylinder  111  of the high-pressure pump  11  to the drain passage  11 D. The fuel flowing into the drain passage  11 D is returned to the fuel tank  20  through the drain pipe  29 . 
     The pulsation of the fuel supplied to the outlet passage  15  is suppressed by the resonator  16  in the buffer chamber  15 S, and then the fuel passes through the high-pressure check valve  17  and is supplied to the common rail  30  from the fuel outlet port  102  through the high-pressure pipe  32 . At this point, the pressure of the fuel running through the outlet passage  15  is controlled to a value set by the high-pressure variable regulator  18 . When the pressure of the fuel exceeds the above set value, part of the fuel in the outlet passage  15  is returned to the fuel tank  20  by the drain passage  18 D and the regulator drain pipe  29 . In this state, the injectors  31  connected to the common rail  30  inject high-pressure fuel into the respective cylinders at a fuel injection timing for each cylinder of the engine. 
     According to this Embodiment 1, the pressure pulsation of high-pressure fuel discharged from the single-cylinder high-pressure fuel pump  11  is suppressed by the resonator  16 , and the high-pressure variable regulator  18  for controlling the pressure of the high-pressure fuel is provided to control the pressure of high-pressure fuel to be supplied to the injectors  31  connected to the common rail  30 . Therefore, a fuel pressure variable type fuel supply system for a direct injection gasoline engine which is small in size and has durability can be obtained. 
     In this Embodiment 1, when the pressure of fuel in the outlet passage  15  exceeds the above value set by the high-pressure variable regulator  18 , part of the fuel in the outlet passage  15  (to be referred to as “regulator return” hereinafter) is returned to the fuel tank  20  by the drain passage  18 D and the regulator drain pipe  29 . As shown in FIG. 4, the drain passage  18 D may be connected to the inlet passage  12  to return fuel to the inlet side of the high-pressure fuel pump  11 . 
     Embodiment 2 
     FIG. 5 is a diagram showing the configuration of a fuel supply system for a direct injection gasoline engine according to Embodiment 2 of the present invention. The high-pressure variable regulator is constructed separately from the high-pressure fuel supplier. Reference numeral  60  denotes a regulator unit which is connected to the high-pressure pipe  32  for connecting the fuel outlet port  102  of a high-pressure fuel supplier  10 A having no high-pressure variable regulator to the common rail  30  and comprises a high-pressure variable regulator  61  and a filter  62  provided on an upstream side of the high-pressure variable regulator  61 . Denoted by  61 D is a drain passage for the high-pressure variable regulator  61 , and  64  a regulator drain pipe for returning regulator return to the fuel tank  20 . 
     FIG. 6 is a sectional view of the high-pressure fuel supplier  10 A according to Embodiment 2 and diagram typically showing connection between the high-pressure fuel supplier  10 A and the high-pressure variable regulator  61 . The high-pressure fuel is supplied to the high-pressure pipe  32  from the fuel outlet port  102  of the high-pressure fuel supplier  10 A, its pressure is controlled by the high-pressure variable regulator  61  provided in the high-pressure pipe  32 , and the fuel is supplied to the common rail  30 . 
     As the constituent elements of the high-pressure fuel supplier  10 A and the high-pressure variable regulator  61  are the same as those of Embodiment 1 shown in FIG.  2  and FIG. 3, their descriptions are omitted, here. 
     In this Embodiment 2, regulator return is returned to the fuel tank  20 . As shown in FIG. 7, regulator return may be returned to the fuel inlet port  101  of the high-pressure fuel supplier  10 A by a regulator drain pipe  65 . 
     As having been described above, according to the first aspect of the present invention, a single-cylinder high-pressure fuel pump, a resonator for suppressing the pressure pulsation of high-pressure fuel supplied from the high-pressure fuel pump and a high-pressure variable regulator for controlling the pressure of the high-pressure fuel are provided, the pressure of fuel to be injected into the cylinders of the engine from the injectors can be changed, and the pressure pulsation of the fuel is suppressed. Therefore, a fuel pressure variable type fuel supply system for a direction injection gasoline engine which is small in size and has durability can be obtained. 
     According to the second aspect of the present invention, since the high-pressure variable regulator and the resonator are integrated with the high-pressure pump, the system can be further reduced in size.