Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-10-22
2002-06-11
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S467000
Reexamination Certificate
active
06401691
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims priority from Japanese patent application Nos. Hei 10-300809, filed Oct. 22, 1998 and Hei 11-124904, filed Apr. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel supply system which relieves fuel pressure pulsations in a fuel line of an internal combustion engine such as a direct injection engine which directly injects fuel into a cylinder.
2. Description of Related Art
According to a direct injection engine, it may inject fuel into a highly pressurized cylinder at a compression stroke. Therefore, pressure of fuel supplied to an injector is set higher than that of a conventional engine which injects fuel into an intake port having a low pressure.
The fuel is intermittently discharged to a common high pressure fuel pipe at a fuel discharge pump, such as a fuel injection pump, by a plunger which is driven by a cam to reciprocate. Accordingly, high pressure pulsation is generated in fuel in the high pressure fuel pipe according to the shape of the cam. In addition, the pressure in the high pressure fuel pipe is temporarily reduced because each one of a plurality of injectors connected to the common high pressure fuel pipe intermittently opens its valve respectively to inject fuel. As a result, pressure pulsations having high pressure and low pressure are generated in fuel flowing in the high pressure fuel pipe, and proceed in the high pressure fuel pipe as pressure waves.
Accordingly, whether the pressure pulsation having high pressure or the pressure pulsation having low pressure is at a fuel supply port of an injector when the injector opens its valve changes fuel injection quantity even if the injector opens its valve at the same timing.
Such injection quantity fluctuation caused by the pressure pulsation in the high pressure fuel pipe is also generated on the conventional engine which injects fuel into the intake port as long as a plurality of injectors are connected to a common fuel pipe to receive fuel. In order to solve this problem, JP-U-57-100,693 discloses a pressure relaxation device, that is a pressure damper.
However, an injection pressure of the injector and a fuel pressure in the fuel line for the direct injection engine are higher than those for the conventional engine. Therefore, such injection quantity fluctuation for each one of the injectors for the direct injection engine may be greater.
If a conventional pressure damper comprising a soft damping member, such as a diaphragm or a bellows, is applied to a high pressure fuel pipe of the direct injection engine, the damping member may be easily broken because the fuel pressure in the high pressure fuel pipe of the direct injection engine is high. In that case, sufficient durability and reliability can not be obtained. If a full accumulator is employed in order to relieve the pressure in the high pressure fuel pipe of the direct injection engine, the whole apparatus is increased in size and cost because the accumulator itself is large and expensive.
According to a V-type engine, single fuel line is separated into two pipes toward two banks and joined together at their ends to form a loop. According to such loop-shaped fuel line, a crests or troughs of the pressure waves progressing in the respective separated fuel pipes may meet at the joint of the pipes. In that case, the pressure pulsation is magnified by summating respective crests or respective troughs, and a big pressure wave progresses in the fuel line in a reversed direction.
Furthermore, the pressure pulsation is magnified by resonance when a pressure pulsation frequency approaches a natural frequency of the fuel line.
Such magnified pressure pulsations may cause further fluctuation of the injection quantity.
JP-A-10-73,062 discloses an apparatus which absorbs the vibration by a resonator. However, the resonator makes the structure complicated and expensive. Furthermore, the pressure pulsation in a wide range of the frequency can not be prevented by absorbing pressure pulsation in a certain range of the frequency because the engine rotation speed always varies and the generated pressure pulsation and frequency also vary.
Further, JP-A-9-170514 discloses an accumulator injection apparatus for a diesel engine having a common-rail for cylinders at a part of a fuel passage connecting a high pressure supply pump and fuel injection valves for respective cylinders, and having an orifice at an inlet or outlet of the common-rail to prevent the fuel pressure pulsation. However, if such apparatus is applied to a direct injection engine using gasoline, vapors are prone to remain in the fuel because the diameter of the orifice is very small. As a result, it is difficult to supply small amount of fuel precisely according to the reducing injection quantity during the lean burn. Furthermore, the small diameter of the orifice may be clogged by a foreign object.
SUMMARY OF THE INVENTION
The present invention is made in light of the foregoing problem, and it is an object of the present invention to provide a fuel supply system which reduces pressure pulsation in a high pressure fuel pipe and which has high durability and reliability.
According to an aspect of the present invention, when a high pressure portion of a pressure wave in a high pressure pipe reaches an inlet of a damping chamber formed in a pressure relaxation device, a valve provided at the inlet of the damping chamber opens to receive and hold the high pressure portion in the damping chamber.
Accordingly, the pressure around the inlet is reduced, and a reflection of the high pressure portion in a reverse direction is prevented.
Then, when a low pressure portion of the pressure wave reaches the inlet of the damping chamber, the high pressure portion held in the damping chamber is gradually released via a restricted orifice. Accordingly, the pressure of the low pressure portion increases, and a reflection of the low pressure portion in a reverse direction is prevented.
Thus, the pressure pulsation generated in fuel in the high pressure pipe is reduced, and an injection quantity for a valve opening unit time of the injector becomes constant. Accordingly, it becomes possible to reduce a fluctuation of the injection quantity even if the engine speed is changed.
Furthermore, the pressure relaxation device includes the damping chamber, the valve for opening/closing the inlet of the damping chamber, an elastic member for applying a spring force to the valve, and the restricted orifice which bypasses the valve. Accordingly, a breakage is prevented even if the fuel pressure is high in the high pressure pipe, and high reliability is obtained because of a high durability of the system.
Furthermore, the pressure relaxation device may be formed as an extended high pressure pipe, thereby facilitating to reduce its size. Therefore, the fuel supply system or the engine itself is not increased in size by providing the pressure relaxation device.
According to another aspect of the present invention, the restricted orifice is formed in the valve. Accordingly, manufacturing the restricted orifice is facilitated.
According to another aspect of the present invention, the restricted orifice is formed as a gap between a valve body and a valve seat by a spacer which prevents a fully closed state. Accordingly, it is not necessary to bore a hole.
According to another aspect of the present invention, the restricted orifice is formed in the valve seat on which the valve body abuts.
According to another aspect of the present invention, when a high pressure portion of a pressure wave transmitted in the fuel in the high pressure fuel pipe reaches an inlet of a damping chamber formed in a pressure relaxation device, a flexible bag enclosing a high pressure gas is slightly deformed to absorb the high pressure portion of the pressure wave. Further, when a low pressure portion reaches the inlet of the damping chamber, the flexible bag returns to its
Aoyama Katsuhiko
Imamura Toshio
Kanehara Kenji
Kawano Takanobu
Nakase Yoshihiro
Miller Carl S.
Nippon Soken Inc.
Nixon & Vanderhye PC
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