1. Field of the Invention
The present invention relates to a check valve that allows one-way fluid flow in a fluid passage, especially to such a check valve for use in an outlet passage of a pump for pressurizing brake fluid therein.
2. Description of Related Art
In a conventional check valve, a ball forming a valve body is biased by a spring toward a valve seat in a direction against a fluid pressure imposed on the valve body, i.e., in a direction for closing the check valve. When the fluid pressure imposed on the ball becomes higher than a biasing force of the spring by a predetermined amount, the ball is separated form the valve seat to open the passage. Upon opening the passage, the ball takes a position where the fluid pressure balances the biasing force of the spring.
When such a check valve is installed in a downstream passage of an outlet port of a pump, the position of the ball in an open state of the check valve is not stably maintained, because the fluid pressure imposed on the ball varies according to the outlet pressure of the pump. In other words, the ball vibrates according to a pulsating pressure of the pump, and the pulsation of the pump pressure is amplified by the vibration of the ball. This has been a problem in the conventional check valve.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved check valve in which a vibration of a valve body due to pump pressure pulsation is prevented or suppressed and thereby to avoid an amplification of the pulsating pressure by the check valve.
The check valve according to the present invention is used in a fluid passage such as a bake fluid passage in an anti-lock brake system (ABS) of an automotive vehicle. The check valve is disposed at an outlet port side of a pump that pumps up the brake fluid in wheel cylinders and returns the brake fluid to a master cylinder.
The check valve is integrally formed with an elongate valve casing having a fluid passage therein. A valve seat is positioned in the fluid passage at a middle portion of the valve casing, and a valve body is disposed in contact with the valve seat. The valve body is biased by a biasing member such as a spring or a resilient rubber rod in a direction to push the valve body against the valve seat thereby to close the fluid passage. A fluid pressure is imposed on the valve body in a direction to lift the valve body from the valve seat thereby to open the fluid passage. At the open state, the valve body takes a position balancing the fluid pressure with the biasing force.
Since the fluid pressure supplied from the pump to the check valve is pulsating, the valve body is vibrated by the pulsating pressure. To suppress the valve body vibration, the biasing force is applied to the valve body in a direction slanted from a direction in which the fluid pressure is imposed on the valve body. In other words, the biasing force having a component against the fluid pressure and a lateral component is given to the valve body. On the other hand, a sidewall restricting the lateral movement of the valve body is formed in the valve casing. When the valve body is lifted from the valve seat by the imposed fluid pressure, the valve body is pushed toward the sidewall by the lateral component of the biasing force. Thus, the valve body movement is restricted and its vibration due to the pulsating pressure is suppressed. Preferably, a ceiling wall for restricting a vertical movement of the valve body is formed in the valve casing in addition to the sidewall to further restrict the valve body vibration.
The valve body may be constituted by a ball, and the biasing force may be supplied to the ball via another ball contacting the ball-shaped valve body. In this case, both balls are positioned in the valve casing so that a line connecting centers of both balls lies slantedly from the direction of the fluid pressure imposition to generate the lateral component of the biasing force. It is also preferable to form an outlet port of the fluid passage in a direction of the lateral component of the biasing force, so that the valve body is further pressed to the sidewall by the fluid flow.
The valve casing may be composed of a seat member and a cylindrical sleeve connected to the seat member. In this case, the valve seat is formed at one end of the seat member, and the fluid is introduced from another end. The biasing member and the valve body are contained in the cylindrical sleeve. A rod member having a tapered surface transferring the biasing force to the ball constituting the valve body may be interposed between the spring and the valve body.
According to the present invention, the valve body such as a ball is pushed against the sidewall by the lateral component of the biasing force when the valve takes the open position. Therefore, the vibration of the valve body due to the pulsating pressure is suppressed.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.