Patent ID: 7191768

Claim:
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 negative pressure in an intake pipe such that the pressure of the gas fuel increases if the negative pressure in the intake pipe decreases, and the pressure of the gas fuel decreases if the negative pressure in the intake pipe increases; wherein the source pressure control means comprises a diaphragm type regulator provided in the fuel supply passage, and a negative pressure supplying passage which connects a diaphragm chamber of the regulator to the intake pipe; wherein a throttle valve is provided in the intake pipe for adjusting an amount of intake air, and the negative pressure supplying passage connects the diaphragm chamber of the regulator to a downstream side of the throttle valve in the intake pipe; and 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 negative pressure supplying passage connects respective diaphragm chambers of the high-pressure regulator and the low-pressure regulator to the intake pipe.