Metal working – Method of mechanical manufacture – Valve or choke making
Reexamination Certificate
2000-01-24
2001-01-16
Cuda Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Valve or choke making
C029S890100, C451S430000
Reexamination Certificate
active
06173494
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a valve assembly, especially for a fuel-injection valve for an internal-combustion engine and comprised of a valve ball and a conical valve seat, to a method of making the valve assembly and particularly the valve seat and to an apparatus for carrying out that method. The invention is particularly directed to the improvement in the valve seat for a ball valve so as to increase the sealing effectiveness where the basic conical configuration of the valve seat is imparted thereto by a machining operation.
BACKGROUND OF THE INVENTION
Ball valves cooperating with conical valve seats are used, for example, with fuel-injection valves for internal-combustion engines and the valve assembly formed by the valve ball and the seat can be provided in very small dimensions with the conical seat being formed in a machine operation and by grinding. As a rule, in the past, the conical seat has been so made that a line contact is formed between the conical surface and the grinding tool.
When conical seats are made in this fashion, it is found that in transverse cross section planes, i.e. cross sections in planes perpendicular to the axis of the conical seat or ground surface, there are deviations of that surface from a perfect circle. These deviations are referred to herein as shape deviations and when the valve assembly is used as a fuel-injection valve of the type described, such shape deviations can exceed 1 &mgr;m from the mean diameter and can be sufficient to give rise to leakage even when the valve is intended to be closed. It will be understood that a mean diameter of such a conical valve seat can be several millimeters. The leakage rates which result have been found to be detrimental to the operation of the internal-combustion engine.
OBJECTS OF THE INVENTION
It is, therefore, the principal object of the present invention to provide an improved valve assembly, especially a ball-valve assembly having a conical seat for a valve ball, whereby this drawback is avoided and leakage is minimized.
It is also an object of the invention to provide an improved seal for a ball-type valve, especially a fuel-injection valve for an internal-combustion engine whereby leakage through the closed valve is eliminated or materially reduced by comparison with earlier systems.
Still another object of the invention is to provide an improved sealing arrangement for a ball-type valve utilizing a conical seat so that the greatest sealing effectiveness is possible between the valve ball and the valve seat so that this sealing effectiveness is achieved with metal valve assemblies, i.e. assemblies in which both the valve seat and the valve ball are metal, for ceramic valve assemblies in which both the valve seat and the valve ball are composed of ceramics, and hybrid valve assemblies where one of the sealing members is composed of metal and the other of a ceramic.
It is also an object of the invention to provide an improved valve assembly for the purposes described whereby drawbacks of earlier valve assemblies are obviated.
It is also an object of the invention to provide an improved method of making the valve assembly and an improved apparatus for carrying out that method.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are attained, in accordance with the invention with a conical valve seat which has been subjected to a finish grinding to form in the conical surface an annular seating surface of circular-arc segmental cross section in an axial plane such that the radius of this seating surface, i.e. the radius of the circular arc is greater than the radius of the valve ball and the depth of the trough-shaped seating surface is at least equal to the shape deviations of the conically-ground valve seat so that along the trough-shaped seating surface those deviations are eliminated.
More particularly the valve seat can comprise a body formed with a conical cavity centered on an axis and having a machined conical surface with shape deviations from the circular in transverse cross section, the conical surface being formed with an annular finish-ground seating surface of circular-arc-segmental shape in axial section engageable by the ball valve and having a radius of curvature greater than a radius of the ball valve, the seating surface constituting a trough in the conical surface of dimensions sufficient to eliminate the shape deviations along the seating surface.
Because of the circular-arc-shaped seating surface or trough formed in the conical surface and which has a width which is very small by comparison to the width of the conical surface as a whole, the direct contact between the ball and the trough can be limited. Elimination of shape deviations from the circular in this region or their reduction to a value of less than 0.1 &mgr;m can prevent or limit leakage. The leakage rate reduction has been found to be particularly pronounced when these principles are applied to a hybrid valve, where the ball is composed of metal or ceramic and the seat is composed of ceramic or metal, although significant improvements are obtained when both the seat and the valve are composed of either metal or ceramic. With a sealing arrangement of the invention for a fuel-injection valve whose mean diameter of the valve seat may be several millimeters, the width of the trough-shaped seating surface is preferably 200 to 500 &mgr;m. The trough-shaped seating surface should have a surface roughness of less than 0.1 &mgr;m Ra. At its deepest point, the circular-arc trough-shaped seating surface has a depth in the range of 2 to 10 &mgr;m.
The invention further includes a method of making a sealing seat between a valve ball and a conical valve seat, especially for such fuel-injection nozzles of internal-combustion engines. In this method, a valve body with a conically-ground valve seat is clamped in a rotating workpiece holder while a cylindrical grinding tool for the fine grinding of the trough-shaped seating surface is engaged in a tool holder in an insert which allows radial movement of the grinding tool. The tool holder is rotated about an axis having an angle of attack of 1 to 10° with respect to the rotation axis and workpiece holder and by pressing the tool holder toward the workpiece holder and/or the workpiece holder toward the tool holder, the workpiece and tool are maintained in contact along the edge of the tool at its end face all around the periphery of the conical seat.
The tool holder and the workpiece holder are rotated in opposite senses to form the annular circular arc segmental trough-shaped contact surface in the conical valve seat with a radius of the seating surface greater than the radius of the ball and a depth of the trough sufficient to eliminate the shape deviations at least in the deepest regions of the trough.
Because the tool holder is rotated at a predetermined angle of attack to the rotation axis of the workpiece holder, no oscillating movements or swinging movements arise between the workpiece and the tool which could create shape deviations of the type which are removed by the formation of the trough.
The rotation of the tool and the workpiece in opposite senses generates the annular trough-shaped contact surface with the circular arc configuration in axial planes.
It has been found to be advantageous to hold the grinding stone in a flexible insert in the tool holder, the flexible insert allowing pressing forces between the tool holder and workpiece, radially compensatory movements of the grinding stone which can follow eccentric movements of the conically-ground valve seat to ensure that the grinding stone will contact the valve seat over the entire periphery of the latter at all times. This, of course, ensures the elimination of the shape deviations during the fine grinding of the seating surface.
According to a feature of the invention, the grinding stone is set into a synthetic resin shaft forming the flexible insert and which is received with a radial play of 100 to 300 &mgr;m in the tool holder. The rearward
Cuda Rosenbaum I
Dubno Herbert
Ernst Thielenhaus KG
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