Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Reexamination Certificate
2000-01-14
2001-07-10
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
Reexamination Certificate
active
06257274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve opening and closing mechanism which is preferable to be used, for example, for opening and closing an operating fluid passageway in a wheel cylinder for expanding brake shoes of a drum brake device.
2. Description of the Related Art
Conventionally, various types of drum brake devices are used for braking the running of vehicles. These drum brake devices are classified into a leading trailing type, a two leading type, a duo-servo type, and so on, in accordance with the arrangement of brake shoes pressed against an inner circumferential surface of a substantially cylindrical drum.
A duo-servo type drum brake device is generally provided with a pair of brake shoes, which are primary and secondary shoes disposed oppositely to each other in a cylindrical drum.
The primary shoe is designed so that its entrance side in the forward rotation direction of the drum is served as an input portion while its exit side in the forward rotation direction of the drum is, for example, connected to the entrance side of the secondary shoe through an adjuster. On the other hand, the exit side of the secondary shoe is made to abut against an anchor portion mounted on a backing plate so as to receive anchor reaction force acting on the primary and secondary shoes.
Consequently, when the primary and secondary shoes are expanded and pressed against the inner circumferential surface of the drum, the anchor reaction force acting on the primary shoe is put into the entrance side of the secondary shoe. Thus, the anchor reaction force acts on the secondary shoe so as to press the secondary shoe against the inner circumferential surface of the drum. As a result, both the primary and secondary shoes act as leading shoes so that braking force with very high gain can be obtained.
The above-mentioned duo-servo type drum brake device has many advantages in comparison with the leading trailing type or two leading type drum brake device in that not only it can gain an extremely high braking force but also it can be miniaturized easily, and it can be incorporated with a parking brake easily.
Such a duo-servo type drum brake device is, however, sensitive to a change in the friction coefficient of the lining of each brake shoe. Accordingly, the duo-servo type drum brake device tends to be difficult to stabilize its braking force. A device for stabilizing the braking force is therefore needed.
Thus, the applicant of this application has made various proposals about a wheel cylinder which can control pressing force transferred to brake shoes, so that anchor reaction force is limited to a predetermined ratio relative to the fluid pressure supplied from a master cylinder in order to stabilize the braking force in a duo-servo type drum braking system. Further, the applicant of this application has an object to develop a high-performance wheel cylinder which can perform relaxation of impact at the time of quick braking and fine control of braking force.
To develop such a wheel cylinder, it is necessary and essential to develop a valve for precisely and smoothly controlling the supply of operating fluid supplied from a master cylinder. Such a valve has been therefore regarded as one of most important problems to be solved in the future.
SUMMARY OF THE INVENTION
Taking the foregoing situation into consideration, it is an object of the present invention to provide a valve opening and closing mechanism in which the quick opening and closing of a fluid passageway can be avoided. Therefore, for example, if the valve opening and closing mechanism is used in a wheel cylinder of a duo-servo type drum brake device, a sudden change in the supply of operating fluid can be prevented, and both the relaxation of impact at the time of quick braking and the fine control of the braking force can be realized.
In order to achieve the above object, according to the present invention, there is provided a valve opening and closing mechanism comprising: a cylinder having an inlet for supplying fluid pressure; a control piston which is slidably fitted to the cylinder and in which a fluid passageway for passing operating fluid supplied into the cylinder is formed at a center of the control piston so as to penetrate the control piston; a valve guide supported in a fluid chamber defined by the cylinder and the control piston, and provided with a shaft portion and a valve support portion, the shaft portion being inserted into the fluid passageway of the control piston so as to reserve a clearance for passing the operating fluid, the valve support portion being formed into a collar at a base end of the shaft portion so as to face an end surface of the control piston; and a valve assembly loosely fitted to the shaft portion of the valve guide so as to move toward the control piston with flow of the operating fluid to thereby narrow the fluid passageway of the control piston when a flow rate of the operating fluid passing through the fluid passageway of the control piston reaches a predetermined value or more; wherein a conical surface portion for gradually reducing a sectional area for passing the operating fluid when the control piston is displaced toward the fluid chamber is provided in the shaft portion of the valve guide inserted into the fluid passageway.
Preferably, in the valve opening and closing mechanism according to the present invention; the valve assembly may include an inner ring portion and an outer ring portion, the inner ring portion defining a clearance between the inner ring portion and the shaft portion so that the clearance will be a fluid passageway has a sectional area for passing the operating fluid smaller than that of the clearance between the fluid passageway of the control piston and the shaft portion, the outer ring portion being held tightly between the control piston and the valve support portion to thereby close the fluid passageway of the control piston in cooperation with the valve support portion when the quantity of displacement of the control piston toward the fluid chamber reaches a predetermined value; and the outer ring portion may abut tightly against an end surface of the control piston when the flow rate of the operating fluid passing through the fluid passageway of the control piston reaches a predetermined value or more to thereby displace the valve assembly toward the control piston, so that the fluid passageway of the control piston is switched to a mode in which the fluid passageway of the control piston communicates with the fluid chamber inside the cylinder through a clearance between the inner ring portion and the shaft portion.
According to the aforementioned configuration, when the supply of the operating fluid from the inlet to the fluid chamber in the cylinder increases suddenly so that the flow rate of the operating fluid passing through the fluid passageway of the control piston from the fluid chamber in the cylinder reaches a predetermined value or more, the valve assembly is displaced toward the control piston so as to narrow the fluid passageway of the control piston substantially. Thus, the supply of the operating fluid through the fluid passageway can be restrained.
Moreover, when the control piston is suddenly displaced toward the fluid chamber in the cylinder and the quantity of displacement of the control piston reaches a predetermined value so that the valve assembly is held between the control piston and the valve support portion of the valve guide, the fluid passageway of the control piston is closed so that the supply of the operating fluid from the fluid passageway is stopped. However, during the displacement of the control piston before the fluid passageway of the control piston is closed, the sectional area for passing the operating fluid is reduced gradually due to the conical surface portion provided in the fluid passageway of the control piston or on the shaft portion of the valve guide. Thus, there is no fear that the fluid passageway is closed at a stretch.
That is, in the aforemention
Akebono Brake Industry Co. Ltd.
Hepperle Stephen M.
Morgan & Lewis & Bockius, LLP
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