1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine, and more particularly relates to a fuel supply system including a fuel filter.
2. Description of Related Art
In a conventional fuel supply system for an internal combustion engine, as illustrated in FIG. 8 (as disclosed in Japanese Patent Publication HEI 6-129325), a fuel pressure regulator 108 is disposed in a fuel pipe 106 connecting a fuel pump 102 and a fuel injection valve 104. A high-pressure fuel filter 116 is disposed in a portion of the fuel pipe 106 between the fuel pressure regulator 108 and the fuel injection valve 104. Excess fuel is returned from the fuel pressure regulator 108 to a fuel tank 114 via a fuel-return pipe 110. A low-pressure suction filter 112 is provided to a suction port of the fuel pump 102.
However, the conventional fuel supply system has the following problems:
First, because the high-pressure fuel filter is disposed in a high-pressure portion of the fuel pipe between the fuel pressure regulator and the fuel injection valve, sealing requirements at pipe connecting portions are severe (leakage at the pipe connecting portions is not allowed because fuel leakage will seriously affect fuel injection), so the cost of piping is increased.
Second, because the high-pressure fuel filter is disposed in the portion of the fuel pipe between the fuel pressure regulator and the fuel injection valve, blockage of the high-pressure fuel filter and a change in pressure drop at the high-pressure fuel filter due to such blockage will directly affect fuel injection.
Third, because a large portion of fuel discharged from the fuel pump is returned to the fuel tank via the fuel-return pipe, and because no fuel filter is provided in the fuel-return pipe, fuel in the fuel tank is not cleaned. As a result, the suction filter is likely to cause blockage. If a coarse filter having large pores is used in the suction filter to prevent the filter from being choked, foreign particles in the fuel are not filtered, thereby advancing abrasion of the fuel pump.