Injector seat that includes a coined seal band

A fuel injector apparatus and method for use in a fuel injection system of an internal combustion engine that includes a body, a valve seat, closure member, and an orifice plate. The valve seat comprises the intersection of two angled surfaces before assembly of the fuel injector. During assembly of the fuel injector, a member presses against the edge of the sealing surface of the valve seat to create an oblique third sealing surface or sealing band that is coined into the valve seat. The sealing band provides an improved seal between the valve closure member and the valve seat which operates to prevent leakages of fuel in the fuel injector.

FIELD OF INVENTION

The present invention relates to a method and apparatus used to coin a valve seat in a fuel injector during assembly of the fuel injector to improve leakage and seating between the closure member and the valve seat in the fuel injector.

BACKGROUND

The metal to metal seal formed in a valve between a valve closure member and a valve seat determines the accuracy at which the fluid flowing through the valve is controlled. Leakage results when the surfaces between the valve closure and the valve seat do not mate correctly. This leakage is detrimental in systems where precise flow control is desired. Similarly, the amount of gasoline leakage from a fuel injector has an effect on evaporative emissions. Government legislation has reduced the amount of automotive evaporative emissions so customers are requiring more stringent fuel injector leakage.

A valve seat is typically a ground hardened conical seat (Rc>55). The valve closure member is also of a similar material and hardness. This conical valve seat and valve closure member must have low roundness in order to produce a tight seal to prevent leakage. One method used to produce low seat roundness resulting in a tight seal between the closure member and the valve seat is grinding. Grinding greatly influences the accuracy and reliability of the fluid valve, however, the roundness tolerances for low leakage rates are in sub micron range. As a result, grinding becomes an extremely expensive manufacturing procedure. Such activities will increase manufacturing costs and therefore there exists a need for alternate procedures that are less costly and desirable.

Another method for manufacturing a closure member and valve seat applies an axial compressive load to force the closure member against the seat, coining the closure member to the seat. The method described in U.S. Pat. No. 5,081,766 produces a valve assembly that is capable of accurate and reliable fluid metering yet avoids expensive tolerance control on surface finishing and part dimensioning. The method disclosed by this patent involves the inclusion of an additional step in the assembly process, a coining step, but eliminates the necessity for stricter tolerances on surface finish and part dimensioning. Accordingly, reconfiguration of existing manufacturing equipment and processes requires merely adding the coining step to reduced leakage through the injector. This coining step however does not involve the use of a coining die to coin the part. Rather the coining step involves the application of axial compressive load to force a rounded distal end of the closure member against a conical surface of the seat so that the coining action occurs as an annular zone of surface contact between the closure member and the seat. The force of application is preferably conducted in a particular manner so that the closure member is neither irreversibly bent or buckled by the coining step. This step is conducted during the assembly process so that neither the solenoid nor the spring which are the operating mechanism in the completed injector has an influence on the result of coining.

It would be beneficial to develop a method and apparatus to form a better seal between the closure member and the seat using part materials and initial geometry configuration when a closure member first contacts valve seat during assembly of the fuel injector to assure improved seal and manufacturing cost savings.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of this invention, a fuel injector for an internal combustion engine, comprising: a body having an inlet, an outlet and a longitudinal axis entering therethrough; a valve assembly regulating the flow of fuel to a combustion chamber wherein a closure member rests on a valve seat in a closed position to prohibit the flow of fuel, the valve seat having an upstream surface meeting a down stream surface to form a sealing edge; a sealing band coined into the sealing edge upon the axial movement downwards of an assembly member onto a sealing surface of the valve seat; and an orifice disk having at least one orifice for allowing fuel to pass from valve assembly to the combustion chamber when closure member is biased into an open position.

In accordance with another aspect of this invention, A method of lowering leakage rates in a fuel injector, the fuel injector having a body with a first end and a second end disposed along a longitudinal axis, a body having an inlet, an outlet and a longitudinal axis entering therethrough; a valve assembly regulating the flow of fuel to a combustion chamber wherein a closure member rests on a valve seat in a closed position that prohibits the flow of fuel; an orifice disk having at least one orifice for allowing fuel to pass from valve assembly to the combustion chamber when closure member is biased into an open position, the method comprising: providing a sealing surface of the valve seat having an upstream surface meeting a down stream surface to form a sealing edge; coining the sealing surface of the valve seat to create a sealing band onto the sealing edge prior to assembly of the fuel injector;

displacing a closure member axially downwards onto the sealing surface of the valve seat to seal the valve seat; directing the fuel to flow towards the longitudinal axis; and diverting the fuel through the at least one orifice of the orifice disk.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring toFIG. 1, a solenoid fuel injector10comprising a generally tubular metal body20having a longitudinal axis B-B extending therethrough, an elongated metal armature tube30disposed coaxial with axis within metal body20where downstream end of armature tube30is affixed to a closure member40, guide member50, an annular valve seat60for mating with closure member40, and a metal orifice disc member70for dispensing a quantity of fuel that is to be combusted in an internal combustion engine (not shown).

The solenoid actuated fuel injector10is electromagnetically actuated. The electromagnetic coil100can be energized, thereby generating magnetic flux in the magnetic circuit. The magnetic flux moves armature110, armature tube30, and closure member40preferably along the axis B-B axis. A terminal80and an electrical harness connector portion90can engage a mating connector, e.g., part of a vehicle wiring harness (not shown), to facilitate connecting the solenoid actuated fuel injector10to an electrical power supply (not shown) for energizing the electromagnetic coil100. An armature110is used to axially move the armature tube30and closure member40and open it opposite spring resilient member130or to close the fuel injector10. The armature110is affixed to an upstream end of the valve armature tube30by weld and shares the longitudinal central axis B-B. The electromagnetic coil100encircles armature110.

Referring toFIGS. 2a,3, and4, the guide member50has a central circular guide hole through which the closure member40of armature tube30passes and is guided through during axial movement of the armature tube30. In the downstream end, valve seat generally includes a frusto conical surface which extends generally downstream and toward a longitudinal axis B-B. Preferably, the valve seat is60constructed of a metal such as stainless steel. A downstream end of closure member40has a convex surface that engages the conical surface of the valve seat60when the armature tube30is in closed position. Preferably the closure member40and armature tube30are constructed of metal such as stainless steel.

The sealing surface65of valve seat60includes a first seat surface60ahaving an included angle of 120° (e.g., see C2inFIG. 3), which slopes radially inwardly and downwardly toward the orifice disk150and which is also oblique to the longitudinal axis B-B. The valve seat60also includes a second seat surface60bhaving an included angle of 90° (e.g., see C1, inFIG. 3) whose downstream surface defines a gap between the closure member and the orifice disk150. The terms “inwardly” and “outwardly” refer to directions toward and away from, respectively, the longitudinal axis B-B. The gap between the closure member and the orifice disk150is disposed downstream the first and second seat surfaces60a,60bof the valve seat60. The sealing edge180, sits between the first surface60aand second surface60bof the valve seat60.

Referring toFIG. 3, before coining the geometry includes a sealing edge180of valve seat60formed by two intersecting cones of different angles: 190 with angle alpha and 200 with angle beta. A line C bisecting the included angle (alpha+beta) of the sealing edge180goes through the center of the closure member40. This geometry gives the highest ratio of coining depth to seal band width.

During assembly (not shown) of the fuel injector, the valve seat60is coined as part of a valve body assembly. The valve body assembly is held seat up on a pallet that moves through the assembly equipment on a conveyor belt. A carbide ball is used to coin the valve seat60. At the assembly stage, the carbide coining ball is held on the end of a pin with vacuum. The pin with the carbide ball on the end is raised up through the pallet and into the valve body assembly. The coining ball contacts the valve seat60and raises the valve body assembly out of the pallet. The pin with the carbide ball and valve body assembly continue to move until it reaches (without touching) a flat stop and stops. The pin is then moved slowly and sandwiches the valve seat60between the carbide ball and the flat stop. The pin continues to move until the target coining force is reached. The pin then moves back down, placing the valve body assembly on the pallet. The pallet indexes to the next station and the process is repeated. If multiple repetitions are used, the pin moves down until the valve seat60is just free of the stop, then is moved back up for the next application of coining force. Finally, once the coining process is compete, the valve seat60moves down until the valve body assembly is back in the pallet. During this process, the carbide ball does elastically deform during the repetitive hits but does not permanently deform.

The carbide coining ball presses against the sealing edge180portion of the valve seat60, and coins a third oblique surface60c(FIG. 2c) defining a sealing band170into sealing surface65of the valve seat60. Referring toFIG. 2b, this new sealing band170is located on a virtual circle that defines a sealing diameter about the longitudinal axis B. In the closed position, the closure member40prevents fuel flow through the valve seat60. In the open position, the spherical tip of the closure member40does not contact the sealing band170of the valve seat60, and thus the closure member40permits flow through the valve seat60.

As mentioned above, the armature110, armature tube30, and closure member40are axially reciprocally displaced toward and away from the valve seat60. Contact between the convex surface of the closure member40and the frusto conical surface of the valve seat60form a seal to block the flow of fluid through the orifice140. The effectiveness of the seal is determined by the tightness of the contact between the convex surface of the closure member40and the frusto conical surface of the valve seat60. Surface irregularities and misalignment between the convex surface and frusto conical surface have adverse effects on the contact tightness especially where the contact is metal to metal. To overcome these problems, the invention uses coining to remove some of the irregularities in the valve seat60, thus improving the seal. The assembly process of coining creates a seal band170of the sealing edge180of the valve seat60and is used to remove some of the irregularities in the valve seat60which improves the seal. The formation of a seal band170on the sealing edge180of the valve seat60through coining also serves to stabilize wear on the seat-needle interface by increasing the contact area between the closure member40and the valve seat60and thus reducing stress. The coining process serves to form a seal by making an oblique third contact surface that is coin fitted to the geometry of the outer surface of the valve closure member40. As a result, the leakage rates of the sealing band170are reduced.

The closure member40is disposed along the longitudinal axis B-B, and is movable along a plurality of positions. The closure member40includes a generally spherical tip, and the closure member40can be a needle-type or may be a ball-type assembly. The plurality of positions include an open position, (not shown) and a closed position as shown inFIG. 2b. The closure member40can be movable between a first position, so as to be in a closed configuration, and a second position so as to be in an open configuration (not shown). In the closed configuration, the closure member40contiguously engages the sealing band170of valve seat60to prevent fluid flow through the orifice140of orifice disc150. In the open configuration, the closure member40is spaced from the sealing band170of the valve seat60so as to permit fluid flow through the orifice140via a gap between the closure member40and the sealing band170of the valve seat60. In order to ensure a positive seal at the closure member40and sealing band170of valve seat60interface when in the closed configuration, closure member40can be attached to armature tube30by welds160and biased by a spring resilient member130so as to sealingly engage the sealing band170of the valve seat60. Welds160can be internally formed between the junction of the armature tube30and the closure member40. To achieve different spray patterns or to ensure a large volume of fuel injected relative to a low injector lift height, it is preferred that the spherical closure member40can be in the form of a sphere. Others skilled in the art may choose to select a valve closure member40shaped as a truncated sphere.

A valve assembly in fuel injector10traditionally includes a metal to metal seal between the moving armature assembly and a valve seat60. An armature assembly with a closure member40being held against the sealing band170surface of valve seat60by the spring resilient member130forms the seal. The contact area between the valve seat60and the closure member40is theoretically a circular band with a radius. Any irregularities or out of roundness conditions of either the valve seat60or closure member40cause the seal to leak. Coining or deforming the seal band170of the seat by either an impact on a closure member40or a carbide coining ball held against the valve seat60or by a static force on the closure member40or carbide coining ball held against the valve seat60can be used to remove some of the irregularities in the valve seat60, thus improving the seal. The formation of a seal band170on the valve seat60through coining generally 1-5 presses or hits also serves to stabilize wear on the seat-needle interface by increasing the contact area and thus reducing surface stresses. It is preferred to construct a seal band170of valve seat60with widths ranging from 0.05-0.20 mm.

In the preferred embodiment, coining depth should be greater than the amount of surface finish irregularities and roundness irregularities added together. The amount of irregularities depends on the manufacturing process. In general the more expensive the process, the less coining depth is required to remove the effect of the irregularities. Therefore it is important to use an inexpensive process and increase coining depth. The coining width is a function of the geometry of the surface being coined and the depth of the coining band. The width or surface area of the sealing band170is constrained by the range known to provide the best durability performance requirements of the fuel injector. The depth which is controlled by the geometry of the sealing edge180should be at least enough to remove the irregularities preventing a perfect seal. For example, if the sealing diameter is decreased and the sealing band width is decreased, the fuel injector will enjoy improved leak rates due to the reduction of surface area of the sealing band170thereby increasing the stress or pressure on the seal band170. However, the increased stress also causes the sealing band170to wear more quickly, decreasing the durability of the part. Therefore, there is a minimum surface area of the sealing band170required for durability. A typical turning process will yield a roundness of 0.004 mm and a surface finish on the order of 0.001 mm. Therefore, the coining depth required to perfect the seal is about 0.005 mm. If the surface is ground, the roundness is typically less than 0.0008 mm and surface finish less than 0.0002 mm which would require theoretical coining depth of 0.001 mm. When a 3 mm closure member40is coined into a 90 degree conical seat60to form a band width of 0.130 mm, the depth is theoretically 0.0014 mm depth to width ratio of 0.011. Therefore this surface would require grinding to form a seal. The geometry embodied in this invention makes coining much more efficient. With the geometry of the prototypes, coining depth is over 0.010 mm for a 0.130 width allowing a seal on seats manufactured by turning or machining with a lathe. The much higher ratio 0.08 of depth to width constitutes an advantage over current methods.

The higher depth to width ratio is afforded by coining a sealing edge180as shown inFIG. 3. The most efficient geometry for coining a ball of material into a sealing edge180is when the included angle forming the sealing edge180is bisected by a line going through the contact point of the ball and the center of the ball.

The smaller the included sealing edge180, the higher the depth to width ratio becomes. The cone angles chosen for the prototype seats, 90 & 120 degrees, were preferred to give the most transparency to the existing design in terms of flow, seal diameter and dynamic performance. Others skilled in the art may use other angles may also give the above-mentioned advantages provided the included angle forming the sealing edge180is bisected by a line going through the contact point of the carbide coining ball and the center of the carbide coining ball.

The orifice disk150is disposed proximate and downstream of the valve seat60. The orifice disk150has at least one exit orifice140disposed between the proximate and distal surfaces of the orifice disk150. The at least one exit orifice140is located on a virtual circle that defines an exit diameter about the longitudinal axis B-B.

When the closure member40is in the open position, the closure member40is raised above and separated from the sealing band170of valve seat60, forming an annular opening therebetween, allowing pressurized fuel to flow therethrough and through the at least one orifice140to an intake manifold and therefrom to a combustion chamber (not shown) for combustion. Upon moving the closure member40to the closed position, closure member40engages the sealing band170of the valve seat60, thus preventing the flow of fuel to the combustion chamber (not shown).