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A high-pressure fuel pump includes a pressurizing chamber for pressurizing fuel, an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage, a relief passage for connecting the outlet passage located downstream of the outlet valve and the pressurizing chamb

A high-pressure fuel pump includes a pressurizing chamber for pressurizing fuel, an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage, a relief passage for connecting the outlet passage located downstream of the outlet valve and the pressurizing chamber with each other while bypassing the outlet valve. A relief valve device is provided in the relief passage and adapted to open when an internal pressure of the outlet passage becomes higher than that of the pressurizing chamber, thereby providing communication between the outlet passage and the pressurizing chamber. The relief valve includes a relief spring mechanism for pressing a relief valve to a relief valve seat. At least the relief spring mechanism among members of the relief valve device is provided outside the pressurizing chamber in the pump body.

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1. A high-pressure fuel pump comprising: a pressurizing chamber for pressurizing fuel;an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage,a relief chamber for connecting the outlet passage downstream of the outlet valve and the pressurizing chamber w

1. A high-pressure fuel pump comprising: a pressurizing chamber for pressurizing fuel;an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage,a relief chamber for connecting the outlet passage downstream of the outlet valve and the pressurizing chamber with each other, anda relief valve device configured to open when an internal pressure of the outlet passage becomes higher than that of the pressurizing chamber, thereby providing communication between the outlet passage and the pressurizing chamber via the relief chamber, wherein the relief valve device includes a relief valve, a relief valve seat for closing and opening of the relief valve, and a relief spring mechanism for pressing the relief valve to the relief valve seat;an inner wall of the relief chamber is formed by the relief valve seat and a member having a distinct structure from the relief valve seat,the relief valve seat is positioned on a pressurizing chamber side relative to the member,the relief spring mechanism is provided outside the pressurizing chamber and is exposed to fuel in the relief chamber, the relief chamber being in fluid communication with the outlet passage downstream of the outlet valve,the relief spring mechanism being structurally configured to begin to open the relief valve when a differential pressure between the pressurizing chamber and the relief chamber becomes at least 10 Mpa,the relief spring mechanism and the relief valve are positioned across the relief valve seat from each other so that the relief valve is positioned on the pressurizing chamber side relative to the relief valve seat,a diameter of an outlet valve spring is constant along a length direction of the outlet valve spring,the pressurizing chamber is formed in a body of the high-pressure fuel pump,the member has a different structure from a structure of the body of the pump, anda valve seat face of the relief valve seat has a spherical-surface shape. 2. The high-pressure fuel pump according to claim 1, wherein the fuel is pressurized in the pressurizing chamber and discharged from the outlet valve to a common rail by a plunger which is supported by a cylinder fixed to the body of the pump so as to reciprocate within the pressurizing chamber, wherein a pressure exerted by the relief spring is greater than a target pressure of the common rail. 3. The high-pressure fuel pump according to claim 1, wherein the outlet valve has been installed from the pressurizing chamber side, wherein the fuel is pressurized in the pressurizing chamber and is discharged from the outlet valve to a common rail by a plunger, anda pressure exerted by the relief spring is greater than a target pressure of the common rail. 4. The high-pressure fuel pump according to claim 1, wherein the relief chamber is open on a peripheral side face of the pressurizing chamber, wherein the fuel is pressurized in the pressurizing chamber and is discharged from the outlet valve to a common rail by a plunger, anda pressure exerted by the relief spring is greater than a target pressure of the common rail. 5. The high-pressure fuel pump according to claim 1, wherein the relief chamber is open to a top of the pressurizing chamber. 6. The high-pressure fuel pump according to claim 1, wherein the relief valve device forms an independent unit as an assembly. 7. The high-pressure fuel pump according to claim 1, wherein, in addition to the relief chamber having the relief valve device, another relief chamber having another relief valve device is provided in the high-pressure fuel pump, so that there is provided more than one relief chamber, an outlet of at least one of said another relief chamber is open at a low pressure passage in the pump. 8. The high-pressure fuel pump according to claim 7, wherein an operating pressure of said another relief valve device of said another relief chamber whose outlet is open at the low pressure passage, is set so as to be higher than that of the relief valve device of the relief chamber whose outlet is open at the pressurizing chamber. 9. A high-pressure fuel pump comprising: a pressurizing chamber for pressurizing fuel;an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage,a relief chamber for connecting the outlet passage downstream of the outlet valve and the pressurizing chamber with each other, anda relief valve device configured to open when an internal pressure of the outlet passage becomes higher than that of the pressurizing chamber, thereby providing communication between the outlet passage and the pressurizing chamber via the relief chamber, wherein the relief valve device includes a relief valve, a relief valve seat for closing and opening of the relief valve, and a relief spring mechanism for pressing the relief valve to the relief valve seat;an inner wall of the relief chamber is formed by the relief valve seat and a member having a distinct structure from the relief valve seat,the relief valve seat is positioned on a pressurizing chamber side relative to the member,the relief spring mechanism is provided outside the pressurizing chamber and is exposed to fuel in the relief chamber, the relief chamber being in fluid communication with the outlet passage downstream of the outlet valve,the relief spring mechanism being structurally configured to begin to open the relief valve when a differential pressure between the pressurizing chamber and the relief chamber becomes at least 10 Mpa,the relief spring mechanism and the relief valve are positioned across the relief valve seat from each other so that the relief valve is positioned on the pressurizing chamber side relative to the relief valve seat,the relief chamber is connected to the pressurizing chamber through an opening in a side of the relief valve device that is parallel to a movement direction of the relief valve,the pressurizing chamber is formed in a body of the high-pressure fuel pump,the member has a different structure from a structure of the body of the pump, anda valve seat face of the relief valve seat has a spherical-surface shape. 10. A high-pressure fuel pump comprising: a pressurizing chamber for pressurizing fuel;an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage,a relief chamber connecting the outlet passage and the pressurizing chamber to each other so that the outlet passage is positioned upstream of the relief chamber and the pressurizing chamber is positioned downstream of the relief chamber;a relief valve seat member positioned at an outlet side of the relief chamber in a vicinity of the pressurizing chamber and having a relief valve seat on a downstream side of the relief chamber;a relief valve positioned on the downstream side of the relief valve seat member to open and close a fuel passage formed in the relief valve seat member in cooperation with the relief valve seat;a valve rod connected to the relief valve and extending to an upstream side of the relief valve seat member through the fuel passage of the valve seat member, anda spring member positioned on an upstream side of the relief valve seat member to pull the relief valve to the relief valve seat through the valve rod, wherein an inner wall of the relief chamber is formed by the relief valve seat member and another member having a distinct structure from the relief valve seat member,the relief valve seat member is positioned on a pressurizing chamber side relative to the another member,the spring member is exposed to fuel in the relief chamber,the relief chamber is in fluid communication with the outlet passage downstream of the outlet valve,the spring member being structurally configured to begin to open the relief valve when a differential pressure between the pressurizing chamber and the relief chamber becomes at least 10 Mpa,a length of the spring member is larger than that of an outlet valve spring,the pressurizing chamber is formed in a body of the high-pressure fuel pump,the member has a different structure from a structure of the body of the pump, anda valve seat face of the relief valve seat has a spherical-surface shape. 11. The high-pressure fuel pump according to claim 10, wherein the fuel is pressurized in the pressurizing chamber and discharged from the outlet valve to a common rail by a plunger which is supported by a cylinder fixed to the body of the pump so as to reciprocate within the pressurizing chamber, wherein a pressure exerted by the relief spring is greater than a target pressure of the common rail. 12. The high-pressure fuel pump according to claim 10, wherein the outlet valve has been installed from the pressurizing chamber side, wherein the fuel is pressurized in the pressurizing chamber and is discharged from the outlet valve to a common rail by a plunger, anda pressure exerted by the relief spring is greater than a target pressure of the common rail. 13. The high-pressure fuel pump according to claim 10, wherein the relief chamber is open on a peripheral side face of the pressurizing chamber, wherein the fuel is pressurized in the pressurizing chamber and is discharged from the outlet valve to a common rail by a plunger, anda pressure exerted by the relief spring is greater than a target pressure of the common rail. 14. The high-pressure fuel pump according to claim 10 wherein the relief chamber is open to a top of the pressurizing chamber. 15. A high-pressure fuel pump comprising: a pressurizing chamber for pressurizing fuel;an outlet valve for discharging the fuel pressurized in the pressurizing chamber to an outlet passage,a relief chamber connecting the outlet passage and the pressurizing chamber to each other so that the outlet passage is positioned upstream of the relief chamber and the pressurizing chamber is positioned downstream of the relief chamber;a relief valve seat member positioned at an outlet side of the relief chamber in a vicinity of the pressurizing chamber and having a relief valve seat on a downstream side of the relief chamber;a relief valve positioned on the downstream side of the relief valve seat member to open and close a fuel passage formed in the relief valve seat member in cooperation with the relief valve seat;a valve rod connected to the relief valve and extending to an upstream side of the relief valve seat member through the fuel passage of the valve seat member, anda spring member positioned on an upstream side of the relief valve seat member to pull the relief valve to the relief valve seat through the valve rod, wherein an inner wall of the relief chamber is formed by the relief valve seat member and another member having a distinct structure from the relief valve seat member,the relief valve seat member is positioned on a pressurizing chamber side relative to the another member,the spring member is exposed to fuel in the relief chamber,the relief chamber is in fluid communication with the outlet passage downstream of the outlet valve,the spring member being structurally configured to begin to open the relief valve when a differential pressure between the pressurizing chamber and the relief chamber becomes at least 10 Mpa,the relief chamber is connected to the pressurizing chamber through an opening in a side of the relief chamber that is parallel to a movement direction of the relief valve,the pressurizing chamber is formed in a body of the high-pressure fuel pump,the member has a different structure from a structure of the body of the pump, anda valve seat face of the relief valve seat has a spherical-surface shape.