1. Field of the Invention
The present invention relates to a fluid pressure regulating device that prevents pressure increase of fluid.
2. Description of the Related Art
A fluid pressure regulating device is used to prevent pressure increase of fluid. For example, a relief valve is used to prevent pressure increase of fuel to be supplied to a fuel injector of an internal combustion engine.
Japanese laid-open patent publication No. 2002-515565 a relief valve 200 shown in FIG. 6. The relief valve 200 has a casing 110. The casing 110 has a wall surface 111 defining a casing space inside which axially extends through the casing 110. A sealing surface 114 is formed on the side of one axial end (upstream end) of the wall surface 111 of the casing 110. A hole 113 is formed between the sealing surface 114 and a fuel inlet 112. Further, a cup-shaped stopper 130 is provided on the side of the other axial end (downstream end) of the casing space. A communication hole 131 for leading fuel to a fuel outlet 116 is formed in the stopper 130. Further, a cup-shaped valve 120 is disposed between the stopper 130 and the sealing surface 114 such that the valve 120 can move (slide) along the casing space. The valve 120 has a contact surface 120a that contacts the wall surface 111 of the casing 110, and a sealing ball 121 that can contact the sealing surface 114. A spring 125 is disposed between the stopper 130 and the valve 120. The spring 125 generates an elastic force that moves the valve 120 in the direction in which the sealing ball 121 contacts the sealing surface 114. The valve 120 has a communication hole 122. A throttle element 123 is provided in the communication hole 122 on the side of the sealing surface 114 (upstream side).
The relief valve 200 operates as follows. When the pressure of fuel that flows in through the fuel inlet 112 (that is supplied to the fuel injector) exceeds a set pressure which is determined according to the elastic force of the spring 125, the valve 120 moves in the valve opening direction (upward as viewed in FIG. 6) by the fuel pressure. As a result, contact between the sealing ball 121 and the sealing surface 114 is released, and fuel led in through the fuel inlet 112 is discharged from the fuel outlet 131 via the throttle element 123 and the communication holes 122, 131. On the other hand, when the pressure of fuel that flows in through the fuel inlet 112 is reduced to below the set pressure determined according to the elastic force of the spring 125, the valve 120 moves in the valve closing direction (downward as viewed in FIG. 6) by the elastic force of the spring 125. As a result, the sealing ball 121 contacts the sealing surface 114, so that the discharge of fuel ceases. The throttle element 123 disposed in the communication hole 122 serves to weaken the force which moves the valve 120 when the valve 120 contacts the stopper 130 or the sealing surface 114.
In the relief valve 200 shown in FIG. 6, an inflow chamber (inflow fuel passage) 115 is formed on the upstream side of the contact surface 120a of the valve 120 (below the contact surface 120a as viewed in FIG. 6) by a throttle section (formed of the hole 113 and the communication hole 122) for throttling the fuel flow. Therefore, when the valve 120 moves in the valve opening direction (upward as viewed in FIG. 6), the pressure within the inflow chamber 115 increases. The pressure of fuel within the inflow chamber 115 acts upon the valve 120 as a force which moves the valve 120 in the valve opening direction (upward as viewed in FIG. 6). Therefore, even if the pressure of fuel flowing in through the fuel inlet 112 is reduced to below the set pressure determined according to the elastic force of the spring 125, the movement of the valve 120 in the valve closing direction (downward as viewed in FIG. 6) is prevented by the fuel pressure within the inflow chamber 115. In this case, the operating characteristic of the valve 120 is deteriorated, so that the pressure of the fuel flowing in through the fuel inlet 112 or the fuel to be supplied to the fuel injector decreases.
Further, an outflow chamber (outflow fuel passage) may be formed on the downstream side of the contact surface 120a of the valve 120 (upward as viewed in FIG. 6) by a throttle section (for example, formed of the communication holes 122 and 131). In this case, likewise, the pressure within the outflow chamber increases. The fuel pressure within the outflow chamber acts upon the valve 120 as a force which moves the valve 120 in the valve closing direction (downward as viewed in FIG. 6). Therefore, even if the pressure of fuel flowing in through the fuel inlet 112 exceeds the set pressure determined according to the elastic force of the spring 125, the movement of the valve 120 in the valve opening direction (upward as viewed in FIG. 6) is prevented by the fuel pressure within the outflow chamber. In this case, the operating characteristic of the valve 120 is deteriorated, so that the pressure of the fuel flowing in through the fuel inlet 112 or the fuel to be supplied to the fuel injector increases.
In this manner, if an intermediate chamber (an inflow fluid passage or an outflow fluid passage) in which the fluid is stored is provided upstream or downstream of the valve contact surface by the throttle section, the operating characteristic of the valve may be deteriorated due to the pressure of fluid within the intermediate chamber.