Fuel supply system for internal combustion engine

1. A fuel supply system for supplying fuel from a fuel tank to a fuel supply piping, the system comprising:

a back pressure introducing passage provided with a pressure regulating orifice;

a fuel pump that supplies the fuel from the fuel tank to the fuel supply piping and to the back pressure introducing passage; and

a pressure regulator provided with a case, a diaphragm that partitions an inner space of the case into a fuel pressure regulating chamber and a back pressure chamber, a fuel pressure regulating port that communicates the fuel pressure regulating chamber to the fuel supply piping, a back pressure introducing port that communicates the back pressure chamber to the back pressure introducing passage, a relief port that communicates the fuel pressure regulating chamber to the fuel tank, and a relief valve that operates in accordance with a bulging degree of the diaphragm so as to open the relief port when a fuel pressure in the fuel pressure regulating chamber is larger than a relief pressure that bulges the diaphragm toward the fuel pressure regulating chamber and to close the relief port when the fuel pressure in the fuel pressure regulating chamber is not larger than the relief pressure,

wherein the relief pressure is adjusted by controlling a fuel pressure in the back pressure chamber of the pressure regulator, and

wherein the back pressure introducing passage is communicated with the fuel supply piping, and

further comprising a back pressure introducing valve that allows and interrupts a communication between the back pressure introducing passage and the fuel supply piping.

2. A fuel supply system for supplying fuel from a fuel tank to a fuel supply piping, the system comprising:

a back pressure introducing passage;

a fuel pump that supplies the fuel from the fuel tank to the fuel supply piping and to the back pressure introducing passage; and

a pressure regulator provided with a case, a diaphragm that partitions an inner space of the case into a fuel presure regulating chamber and a back pressure chamber, a fuel pressure regulating port that communicates the fuel pressure regulating chamber to the fuel supply piping, a back pressure introducing port that communicates the back pressure chamber to the back pressure introducing passage, a relief port that communicates the fuel pressure regulating chamber to the fuel tank, and a relief valve that operates in accordance with a bulging degree of the diaphragm so as to open the relief port when a fuel pressure in the fuel pressure regulating chamber is larger than a relief pressure that bulges the diaphragm toward the fuel pressure in the fuel pressure regulating chamber is not larger than the relief pressure,

wherein the relief pressure is adjusted by controlling a fuel pressure in the back pressure chamber of the pressure regulator, and

wherein the fuel pump includes:

a primary pump that supplies the fuel from the fuel tank exclusively to the fuel supply piping; and

a back pressure control pump that supplies the fuel from the fuel tank exclusively to the back pressure introducing passage.

3. The fuel supply system according to claim 2 , wherein the back pressure control pump is a centrifugal pump.

4. The fuel supply system according to claim 2 , further comprising a back pressure controller that controls the fuel pressure in the back pressure chamber of the pressure regulator.

5. The fuel supply system according to claim 4 , wherein the back pressure controller is a back pressure pump controller that controls a fuel discharging pressure of the back pressure control pump.

6. The fuel supply system according to claim 4 , wherein the back pressure controller is a pressure regulating valve that regulates the fuel pressure in the back pressure chamber of the pressure regulator.

7. The fuel supply system according to claim 2 , further comprising a return passage that returns an excessive part of the fuel, which is excessively supplied by the back pressure control pump into the back pressure chamber, to the fuel tank.

8. The fuel supply system according to claim 2 , further comprising a secondary passage that communicates the back pressure chamber of the pressure regulator to the fuel supply piping.

9. The fuel supply system according to claim 8 , further comprising a secondary passage shutting valve that is installed in the secondary passage and opens the secondary passage when the fuel pressure in fuel pressure regulating chamber of the pressure regulator is smaller than a predetermined value.

10. The fuel supply system according to claim 9 , wherein the secondary passage shutting valve is a check valve that restricts a fuel flow in the secondary passage to a direction from the back pressure chamber of the pressure regulator to the fuel supply piping and opens the secondary passage when a difference between the fuel pressure in the fuel pressure regulating chamber and the fuel pressure in the back pressure chamber of the pressure regulator is larger than a predetermined value.

11. The fuel supply system according to claim 2 , further comprising:

a relief passage that communicates the back pressure chamber of the pressure regulator to the fuel tank; and

an orifice that is installed in the relief passage.

12. The fuel supply system according to claim 1 , further comprising

a relief passage that communicates the back pressure introducing passage to the fuel tank; and

an orifice that is installed in the relief passage.

13. The fuel supply system according to claim 1 , further comprising a fuel supply controller that controls an operation of the fuel pump and an operation of the back pressure introducing valve,

wherein the fuel supply controller closes the back pressure introducing valve always before the fuel supply controller stops the fuel pump.