Patent Application
20120216772
The invention relates to a fuel injector for injecting fuel into a combustion chamber in an internal combustion engine, in particular common rail injector.
For the introduction of fuel into a direct-injection diesel engine, use is presently made of lift-controlled common rail systems. An advantage of these is that the injection pressure is independent of load and rotational speed. Lift-controlled fuel injectors are known which have a control valve, designed as a solenoid valve or piezo valve, for controlling the pressure in a control chamber delimited by an axially adjustable injection valve element. Here, the most modern control valves are of pressure-balanced design, that is to say designed such that, in the closed state, the lowest forces possible, preferably no forces whatsoever, act in the axial direction. The use of pressure-balanced control valves permits the use of lower spring forces, low actuator forces, smaller control valve lifts and therefore faster switching times. As a result of the faster switching times, the capability to carry out multiple injections can be significantly improved.
It is also known to provide internally or externally conical valve seats in control valves of fuel injectors. In order that, in the closed state, the axially adjustable valve element of the control valve always reliably seals off, by means of its sealing region, the valve seat assigned thereto, it is the case in known fuel injectors that the guide for the valve element must be manufactured with the greatest accuracy and close pairing play. This is the case in particular if the seat angle of the internally conical or externally conical seat is selected to be relatively flat, between for example 120° and 180°. As the valve seat angle increases, the self-centering forces that act on the control valve element become lower—the flatter the seat angle, the lower is the downhill-slope force which causes the valve element to slide toward the center.
In contrast to the lower centering forces, however, flat seat angles have the advantage that the control valve exhibits less slip when it abuts against the valve seat, and therefore less wear occurs. It must however be ensured that the control valve element is guided closely and precisely. Since close and precise guides for the control valve element can however be produced only at great expense, it is sought to reach a compromise between maximum sealing action and minimum wear.
Taking the above-cited prior art as a starting point, it is the object of the present invention to specify a fuel injector having a control valve, in which the most effective possible sealing of the valve seat of the control valve is provided at the valve seat, and at the same time a comparatively cheap guide for the valve element can be realized.
The invention is based on the consideration that, in practice, it can be assumed that transverse forces act on the valve element of the control valve during operation of the fuel injector, which transverse forces cause the valve element to make contact with the guide at at least one arbitrary point at all times. Here, two extreme positions are conceivable, specifically firstly a fully tilted position in which the valve seat bears both against an upper annular edge of the guide and also, at the opposite side, against a lower annular edge of the guide, and a second extreme position in which the valve element has been displaced completely in parallel and bears against the guide along an axially extending line. The invention is also based on the assumption that the transverse forces acting on the valve element, in particular the transverse forces of a valve spring acting on the valve element, act such that the first alternative (first extreme attitude or position) is more probable, specifically that the valve element will more likely lie in the guide in a fully tilted position, and in so doing be supported both against the uppermost end of the guide and also, at the opposite side, against the lowermost end of the guide.
It can be concluded from this that the control valve should be optimized for the first extreme position, that is to say for the fully tilted valve element, preferably such that the valve element need not slip on the valve seat at all in order to interact sealingly with the valve seat, but rather provides sealing already in the fully tilted position (first extreme position).
The invention achieves this by virtue of the guide for the valve element and the geometric design and arrangement of the valve seat being realized such that an imaginary center of rotation of the valve seat is localized within the axial extent of the guide. The aim of this is to provide that said imaginary center of rotation, to be explained further below, of the valve seat and the center of rotation of the valve element which is arranged on the axial center of the guide come as close to one another as possible. This may be realized in practice by virtue of the attitude and the position of the valve guide being coordinated with the seat angle and the seat diameter.
The abovementioned imaginary center of rotation of the valve seat is formed, as per the definition, by the central point of an imaginary circle which, in a longitudinal central portion which encompasses the longitudinal central axis of the valve element, makes contact with the valve seat, preferably two surface portions of the valve seat which run at an angle with respect to one another, in a punctiform manner in each case, preferably in such a way that the imaginary circle does not intersect any of the seat surfaces. This is in turn based on the assumption that, at small tilt angles of less than 1°, the preferably conical valve seat behaves approximately in the manner of a ball. Under this assumption, therefore, the imaginary circle is the circle of rotation on which the valve element moves as it tilts. Furthermore, the invention is based on the assumption that the valve seat, by means of a valve spring force and the material elasticity, is capable of closing off a certain gap, as a result of which, with the arrangement according to the invention of the imaginary center of rotation of the valve seat, the sealing action of the control valve can be ensured in all extreme positions.
The greater the precision with which the guide is manufactured, that is to say the smaller the guide play is, the more leak-tight the control valve is also in the second, parallel-offset extreme position of the valve element.
In the first solution variant discussed above, in which the axis of rotation of the valve seat and the center of rotation of the valve element are situated as close to one another as possible in the first extreme position, the valve seat and the guide are arranged positionally fixedly relative to one another in the fuel injector.
The object is also achieved by means of a second alternative, which differs from the first alternative merely in that, here, the imaginary circle makes contact with the sealing region, which is formed on the valve element, at two spaced-apart points in a punctiform manner (and preferably does not intersect the sealing region), and in that the central point of said circle is an imaginary center of rotation of the sealing region of the valve element. In the second alternative, the sealing region and the guide are formed so as to be positionally fixed relative to one another, which may be realized by virtue of the sealing region and the guide being formed by the valve element. In the second alternative, too, it is assumed that the imaginary circle is the circle of rotation on which the valve element moves as it tilts in the closed state, that is to say when the sealing region is in contact with the valve seat. It is very particularly preferable if, in the second alternative, the sealing region is formed as an internal or external cone and, in the longitudinal sectional view of the fuel injector, two spaced-apart, linear sealing region surface portions form in each case one tangent to the imaginary circle.
It is also provided according to the invention that the central point of the imaginary circle which makes contact with the valve seat at two spaced-apart points in a punctiform manner in each case and which preferably does not intersect the seat surface, that is to say the imaginary center of rotation of the valve seat, is arranged as close as possible to the axial center, that is to say the center of rotation of the valve element in the first extreme position (contact against the upper guide edge and contact again the opposite, lower guide edge). The spacing between the central point of the circle and the axial center of the guide is very particularly preferably less than 40% of the axial guide length, in particular less than 30%, preferably less than 20%, particularly preferably less than 10% and very particularly preferably less than 5%. The same applies in the second alternative to the imaginary circle which makes contact with the sealing region at two points in a punctiform manner and which preferably does not intersect the sealing surface.
It is very particularly preferable for the central point of the imaginary circle (first or second alternative) to be arranged at the mid-point of the guide length, that is to say in the axial center of the guide, and to therefore preferably coincide with the center of rotation, mentioned numerous times above, of the valve element in the first extreme position.
If the central point of the imaginary circle (in the first or second alternative) is spaced apart axially from the axial center of the guide, it is preferable for the central point to be situated at an axial height of the guide which lies between the axial center and that end of the guide which faces toward the valve seat.
It is particularly expedient if the central point of the imaginary circle (in the first or second alternative) is arranged on a longitudinal central axis of the guide.
It is particularly expedient for the valve seat or the sealing region of the valve element to be of conical design. Here, it is alternatively possible to realize internal or external cone seats, wherein in the case of the internally conical valve seat and sealing region, the valve element interacts with internally conical surfaces, and in the case of the external cone valve seat, the valve element interacts with externally conical valve seat surfaces and sealing region surfaces.
It is very particularly expedient if the cone angle of the valve seat or of the sealing region, that is to say the angle which, in the longitudinal sectional plane, which encompasses the longitudinal central axis of the valve element, of the fuel injector, span two spaced-apart, obliquely running valve seat surface portions or sealing region surface portions which are linear in the sectional view.
In the case of the valve seat or the sealing region being formed as an external or internal cone, it is preferable for the imaginary circle to make contact with two valve seat surface portions or sealing region surface portions, which run at an angle with respect to one another, in a punctiform manner such that said surface portions form in each case a tangent to the imaginary circle, that is to say run in each case orthogonally with respect to the radius.
Each cone has an internal cone side and an external cone side, wherein internally conical valve seats or sealing regions sealingly interact with the valve element by means of their internal cone side, and external cone valve seats or external cone sealing regions sealingly interact with the valve element by means of their external cone side. It is particularly expedient for the axial guide for the valve element to be arranged on the internal cone side of the valve seat or sealing region, regardless of whether the valve seat or sealing region is an external cone or an internal cone.
A design variant is particularly expedient in which the control valve is formed as a valve which is axially at least approximately pressure-balanced when in the closed state. One possibility for this consists in the valve element being formed as a sleeve which, radially at the inside, delimits a valve chamber which is hydraulically connected to the control chamber, which valve chamber is connected to the low-pressure region when the control valve is open. It is however also possible for pin-shaped control valve elements to be designed to be axially pressure-balanced by virtue of the abovementioned valve chamber being provided in the form of an annular groove on the outer circumference of the pin.
Further advantages, features and details of the invention will emerge from the following description of preferred exemplary embodiments and on the basis of the drawings, in which:
In the figures, identical elements and elements of identical function are denoted by the same reference numerals.
A single-part or multi-part injection valve element 9 is arranged in an axially adjustable manner within an injector body. The injection valve element 9 has, at a tip (not illustrated), a closing surface by means of which the injection valve element 9 can be placed in sealing contact with an injection valve element seat formed within a nozzle body (not shown).
When the injection valve element 9 bears against its injection valve element seat, that is to say is situated in the closed position, the flow of fuel out of a nozzle hole arrangement (not shown) is blocked. In contrast, when the injection valve element is raised from its injection valve element seat, fuel can flow out of the pressure chamber 6 through the nozzle hole arrangement and into the combustion chamber of the internal combustion engine.
An upper end side 10 of the injection valve element 9 and a spring-loaded sleeve 12 which is supported axially on a restrictor plate 11 delimit a control chamber 13 (servo chamber) to which highly pressurized fuel from the pressure chamber 6 is supplied via an inflow restrictor 14 formed in the sleeve 12. The control chamber 10 is connected, via an outflow duct 15 with an outflow restrictor 16 (outflow duct 15 and outflow restrictor 16 are situated within the restrictor plate 11), to a valve chamber 17 which is delimited radially at the outside by a sleeve-shaped valve element 18 (control valve element) of a control valve 19. In the illustration of
Fuel can flow from the valve chamber 17 into the low-pressure region 8 of the fuel injector when the valve element 18, which can be actuated by an electromagnetic actuator, is raised from its valve seat 20 (control valve seat) which is formed as an internal cone and which is arranged on the restrictor plate 11, that is to say when the control valve 19 is opened. Here, the throughflow cross sections of the inflow restrictor 14 and of the outflow restrictor 15 are coordinated with one another such that, when the control valve 19 is open, there is a net outflow of fuel (control quantity) out of the control chamber 13 via the valve chamber 17 into the low-pressure region 8 of the fuel injector 1, and from there via the return line 7 into the storage vessel 3.
In the exemplary embodiment shown, the control valve 19 is designed as a valve which is pressure-balanced in the axial direction when in the closed state, wherein the valve element 18 is integrally connected, in its upper portion, to an armature plate (not illustrated) which interacts with an electromagnetic actuator (not illustrated). When the actuator is supplied with electrical current, the sleeve-shaped valve element 18 is raised from its internally conical valve seat 20, as a result of which the pressure within the control chamber 13 falls rapidly, and the injection valve element 9 moves in the axial direction, upward in the plane of the drawing, into the sleeve 12, as a result of which the injection valve element 9 is raised from its injection valve element seat and fuel can flow into the combustion chamber. To end the injection process, the supply of electrical current to the electromagnetic actuator is stopped and a closing spring (valve spring, control closing spring) (not shown) which acts in the axial direction on the valve element 18 moves the sleeve-shaped valve element 18 back onto its valve seat 20. As a result of the follow-up flow of fuel through the inflow restrictor 17, the pressure in the control chamber 13 increases rapidly, as a result of which the injection valve element 9, assisted by the spring force of a closing spring 21 which is supported on a circumferential collar (not illustrated) of the injection valve element 9, is moved in the direction of the injection valve element seat, as a result of which the flow of fuel out of the nozzle hole arrangement into the combustion chamber is stopped.
A pin 22 projects into the sleeve-shaped valve element 18 from the top downward, which pin has the task of sealing off the valve chamber 17 in the upward axial direction. The diameter of the pin 22 corresponds at least approximately to the diameter of the annular sealing line at which the valve element 18 interacts with the internally conical valve seat 20.
As can be seen from
In the longitudinal sectional plane shown which encompasses the longitudinal central axis L, an imaginary circle 26 is arranged so as to make contact with the valve seat 20 in a punctiform manner at two points P1 and P2 spaced apart in the radial direction, wherein the circle 26 does not intersect the valve seat 20. Two spaced-apart valve seat surface portions 27, 28 which enclose an internal cone angle β form in each case a tangent to the circle 26, such that the radius rs of the circle 26 is at right angles to the valve seat 20, more precisely to the valve seat surface portions 27, 28, at the points P1 and P2. The relationship β+2α=180° applies, where the angle a is the slope angle by which the valve seat surface portions 27, 28 are inclined relative to a plane running perpendicular to the longitudinal central axis L. It can be seen that the central point M of the above-described circle 26 is situated within the axial extent of the guide 24, even on the longitudinal central axis L in the exemplary embodiment shown. In the exemplary embodiment shown, the central point M, that is to say an imaginary center of rotation of the valve seat 20, coincides with the axial center 25 of the guide 24, wherein the axial center 25 constitutes a center of rotation of the valve element 18 in a first extreme position in which the valve element 18 bears both against an upper annular edge 29 of the guide 24 and also, at the opposite side, against a lower annular edge 30 of the guide.
Also shown in the drawing is the guide play S/2 between the valve element 18 and guide 23.
From the values rs (radius of the circle 26) and the slope angle α, it is possible to calculate the axial spacing x between the sealing line, that is to say at the actual seat, and the center of rotation M of the valve seat.
It can be seen that the valve element 18 is designed not in the form of a sleeve but rather as a pin which is guided in a guide 23 with the axial extent I. The central point M of a circle 26, which is arranged similarly to the exemplary embodiment according to
Situated on the outer circumference of the cylindrical, pin-shaped valve element 18 is the valve chamber 17 which is formed as an annular chamber and into which fuel from the control chamber 13 flows obliquely from the outside and, when the control valve is open, flows out downward in the axial direction to a low-pressure region 8.
The exemplary embodiment according to
In the exemplary embodiment shown, the valve chamber 17 is situated on the outer circumference of the extension 34 as an inner annular groove within the sleeve-shaped valve element 18.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 046 563.4 | Nov 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/064655 | 10/1/2010 | WO | 00 | 4/24/2012 |
