Gas fuel supply system

1. A gas fuel supply system for supplying gas fuel to an internal combustion engine, comprising:

a fuel supply passage for supplying the gas fuel to an injector; and

source pressure control means for controlling pressure of the gas fuel supplied to the injector through the fuel supply passage by using pressure in an intake pipe such that the differential pressure between the pressure of the gas fuel supplied to the injector and the pressure in the intake pipe increases as the pressure in the intake pipe increases.

2. The gas fuel supply system as defined in claim 1 , wherein the injector is provided in the intake pipe.

3. The gas fuel supply system as defined in claim 1 , wherein the source pressure control means comprises a diaphragm type regulator provided in the fuel supply passage, and a pressure supplying passage which connects a diaphragm chamber of the regulator to the intake pipe.

4. The gas fuel supply system as defined in claim 3 , wherein a throttle valve is provided in the intake pipe for adjusting an amount of intake air, and the pressure supplying passage connects the diaphragm chamber of the regulator to a downstream side of the throttle valve in the intake pipe.

5. The gas fuel supply system as defined in claim 4 , wherein the regulator is a two-stage type regulator comprising a high-pressure regulator and a low-pressure regulator disposed at a downstream side of the high-pressure regulator, and the pressure supplying passage connects respective diaphragm chambers of the high-pressure regulator and the low-pressure regulator to the intake pipe.

6. The gas fuel supply system as defined in claim 4 , wherein the regulator is a two-stage type regulator comprising a high-pressure regulator and a low-pressure regulator disposed at a downstream side of the high-pressure regulator, and the pressure supplying passage connects a diaphragm chamber of the low-pressure regulator to the intake pipe.

7. The gas fuel supply system as defined in claim 4 , wherein the regulator comprises a valve element for opening and closing a passing hole for the gas fuel, a diaphragm to which the valve element is connected, a decompression chamber defined in a front side of the diaphragm for receiving the gas fuel which passes the passing hole, a diaphragm chamber defined in a back side of the diaphragm, and an adjustment spring for urging the diaphragm in such a direction that the valve element opens the passing hole, wherein pressure in the diaphragm chamber acts to move the valve element in an opening direction, and pressure in the decompression chamber acts to move the valve element in a closing direction.

8. The gas fuel supply system as defined in claim 1 , wherein the source pressure control means comprises a flow rate control valve which is provided in the fuel supply passage and comprises a valve element for opening and closing a passing hole for the gas fuel, a pressure receiving part connected to the valve element, a pressure applied chamber defined in a back side of the pressure receiving part, and an adjustment spring for urging the valve element in a closing direction, wherein the pressure in the pressure applied chamber acts to move the valve element in an opening direction, and a pressure supplying passage connects the pressure applied chamber of the flow rate control valve to the intake pipe.

9. The gas fuel supply system as defined in claim 8 , wherein a throttle valve is provided in the intake pipe for adjusting an amount of intake air, and the pressure supplying passage connects the pressure applied chamber of the flow rate control valve to a downstream side of the throttle valve in the intake pipe.

10. The gas fuel supply system as defined in claim 9 , wherein a regulator for decompressing the pressure of the gas fuel to a predetermined pressure is provided in the fuel supply passage, and the flow rate control valve is provided in a downstream side of the regulator in the fuel supply passage.

11. A gas fuel supply system comprising:

a regulator for decompressing gas fuel and supplying the decompressed gas fuel to an injector provided in an intake pipe of an internal combustion engine; and

a throttle valve provided in an upstream side of the injector in the intake pipe,

wherein the regulator comprises:

a valve element for opening and closing a passing hole for the gas fuel;

a diaphragm to which the valve element is connected;

a decompression chamber defined in a front side of the diaphragm for receiving the gas fuel which passes the passing hole;

a diaphragm chamber defined in a back side of the diaphragm; and

an adjustment spring for urging the diaphragm in such a direction that the valve element opens the passing hole,

wherein pressure in the diaphragm chamber acts to move the valve element in an opening direction, and pressure in the decompression chamber acts to move the valve element in a closing direction,

wherein the diaphragm chamber of the regulator is connected to a downstream side of the throttle valve in the intake pipe, such that the differential pressure between pressure of the gas fuel supplied to the injector and pressure in the intake pipe increases if the pressure in the intake pipe increases.

12. A method for supplying gas fuel to an injector of an internal combustion engine having a throttle valve for adjusting an amount of intake air which is provided in an intake pipe, comprising a step of controlling pressure of the gas fuel supplied to the injector by using pressure in the intake pipe which is generated in a downstream side of the throttle valve such that the differential pressure between the pressure of the gas fuel supplied to the injector and the pressure in the intake pipe increases if the negative pressure in the intake pipe decreases.