Valve for controlling fluids

[0002] This application is a 35 U.S.C. 371 application of PCT/DE 01/00122, filed on Jan. 13, 2001.

[0003] 1. Field of the Invention

[0004] The invention relates to a valve for controlling fluids and more particularly to such a valve especially useful in a fuel injection system.

[0005] 2. Description of the Prior Art

[0006] From European Patent Disclosure EP-0 477 401 A1, a valve is known in which an actuating piston of a valve member is disposed displaceably in a stepped bore of the valve housing, in a part of the stepped bore that has a small diameter. A larger piston movable by a piezoelectric actuator is disposed in a part of the stepped bore having a larger diameter. Between the two pistons, a hydraulic pressure chamber filled with a pressure medium is embodied, so that a hydraulic boost of a motion of the piezoelectric actuator occurs. That is, when the large piston is moved a certain distance by the piezoelectric actuator, the actuating piston of the valve member executes a stroke lengthened by the boosting ratio of the piston diameter, since the piston of the piezoelectric actuator has a larger surface area than the actuating piston of the valve member.

[0007] In such valves, 3/2-way control valves are also used, as disclosed for instance in U.S. Pat. No. 5,738,075. Such 3/2-way control valves can be embodied as seat-slide or seat-seat valves. Here the pressure is carried from a rail, for instance, by means of a controllable piston via a pressure chamber and a booster piston to a control chamber, from which the fuel is injected into the combustion chamber. In the nonactuated state, the pressure chamber is connected to a leak fuel line, so that leak fuel pressure prevails in the pressure chamber. However, upon a switchover of the 3/2-way control valve, regardless of the type of valve (seat-slide or seat-seat valve), a communication briefly occurs between the high-pressure region and the leak fuel region. The result is a so-called diversion surge into the leak fuel line. This hinders the relief of the control chamber of the valve until the valve has sealed off the opening to the high-pressure region.

[0008] The valve for controlling fluids according to the invention has the advantage that a diversion surge to the leak fuel line of this kind does not occur. It is prevented by disposing a slide element upstream of the seat of the control valve. The slide element is disposed in the opening direction immediately before the piston region with which the piston takes its seat on the valve seat. Depending on the stroke path of the slide element, this makes a delayed opening of the passage between the inflow line and the pressure chamber, but enables an immediate closure of the passage between the inflow line and the pressure chamber. Thus at any instant upon switchover of the control valve, it can be assured that there will be no communication between the inflow line and the leak fuel line. Because of the provision of the slide element, the stroke path of the piston for opening the communication between the inflow line and the pressure chamber is at least equal to but advantageously greater than a stroke path for closing or opening a passage between the pressure chamber of the control valve and the leak fuel line. As a result, the diversion surge into the leak fuel line can advantageously be prevented. Also advantageously, upon switchover of the control valve, the relief of the control chamber is no longer hindered, since because of the slide element, sealing off from the high-pressure region occurs immediately.

[0009] In an especially advantageous way, the slide element of the piston is embodied cylindrically. As a result, on the one hand simple production of the slide element can be achieved, and on the other, this makes an overall simple design of the control valve possible.

[0010] Advantageously, the piston of the control valve is embodied in two parts. As a result, a seat-slide valve with a pressure chamber disposed between the two parts can be realized. Especially advantageously, the control valve is embodied as a force-compensating valve. The guide diameter at the valve seat then is equivalent to the diameter of the slide element.

[0011] Also advantageously, the piston of the stepped bore is embodied in one piece. As a result, a 3/2-way seat-slide valve can be used as an outlet valve.

[0012] Preferably, the valve for controlling fluids is embodied as a 3/2-way seat-slide valve or as a 3/2-way seat-seat valve.

[0013] Overall, with the valve of the invention, an unambiguous function of a control valve without a diversion surge from the high-pressure inlet region into the leak fuel line can thus be achieved. By varying the stroke lengths or stroke paths of the slide element at the valve seat or the stroke length for closing/opening the communication with the leak fuel line, the overlap at the leak fuel slide element can be optimized.

[0014] Depending on the intended application, an optimal slide ratio can be formed of the various stroke lengths. The overlap should be selected such that no significant valve delays occur, yet it is still assured that no diversion surge into the leak fuel line will occur.

[0015] In the drawing, two exemplary embodiments of the invention are shown. The exemplary embodiments are explained in further detail in the ensuing description. Shown are:

[0016] FIG. 1, a schematic sectional view through a fuel injection valve in a first exemplary embodiment of the present invention; and

[0017] FIG. 2, a schematic fragmentary sectional view through a fuel injection valve in a second exemplary embodiment of the present invention.

[0018] In the exemplary embodiment shown in FIG. 1, the valve of the invention is used in a pressure-boosted common rail injector. The valve of the invention is embodied here as a 3/2-way seat-slide control valve 1.

[0019] In FIG. 1, a fuel injection valve in a first exemplary embodiment of the present invention is shown. The fuel injection valve includes the 3/2-way control valve 1. The control valve 1 comprises an actuating or control element 2 and a first piston 3 and a second piston 4. A known magnetic controller or a known piezoelectric actuator can for instance be used as the control element 2.

[0020] The first piston 3 comprises a plurality of piston portions 3athrough 3e. A first piston portion 3ais embodied cylindrically and is connected to the control element 2. This is followed by a second piston portion 3b, embodied in concave form, which in an appropriate position of the piston 3 opens a first passage at the valve seat 10. Adjacent to the second piston portion 3bis the third piston portion, embodied as a slide element 3c. The third piston portion 3cis disposed directly at the valve seat 10 or at the first passage. The piston 3 also includes a widening, fourth piston portion 3dand a further cylindrical, fifth piston portion 3e. The fifth piston portion 3eis disposed in a pressure chamber 6 disposed between the first piston 3 and the second piston 4.

[0021] The second piston 4 comprises a slide element 4aand a base body 4b. When the control valve 1 is not actuated, the piston 4 is kept in the open position by a spring 9, so that a second passage 5 between the pressure chamber 6 and a leak fuel line 8 is open. As a result, in the nonactuated state, the leak fuel pressure prevails in the pressure chamber 6.

[0022] In the control valve 1 shown in FIG. 1, a guide diameter d₁of the first piston 3 is equal to the slide diameter d₂of the second piston 4. The control valve 1 is thus constructed as a force-compensating valve.

[0023] The pressure chamber 6 also communicates with a booster piston 11 via a line 19. The booster piston 11, embodied in multiple stages, is kept in its outset position via a restoring spring 12 and with its smaller piston diameter, it communicates with a control chamber 15. The control chamber 15 is filled with fuel via a filling valve 13 and a fuel line 14. Via an injection nozzle 16, prestressed by a spring 17, the fuel is fed into a combustion chamber, not shown.

[0024] The mode of operation of the fuel injection valve will now be described. Upon actuation of the control element 2, the piston 3 is moved onward in the direction of the pressure chamber 6 from its valve seat. Upon opening of the seat, however, a communication is not immediately established between the inflow line 7 from the rail and the pressure chamber 6; instead, a slide height h₂of the slide element 3cmust be overcome first, before this communication is established. As a consequence of the motion of the piston 3 in the direction of the pressure chamber 6, the piston 4 is closed, counter to the spring force of the spring 9. In this process, a stroke length h₁at the slide element 4amust be overcome. Since according to the invention the stroke length h₂of the slide element 3cis greater than or at least equal to the stroke length h₁at the piston 4, it is thus assured that no communication between the inflow line 7, in which high pressure prevails, and the leak fuel line 8 will occur.

[0025] Once the piston 3 has covered the stroke length h₂in the direction of the pressure chamber 6, the pressure chamber 6 communicates with the high-pressure inflow line 7, so that counter to the pressure of the restoring spring 12, a high pressure is applied to the booster piston 11. This high pressure is transmitted, because of the different diameters of the booster piston 11, to the fuel-filled control chamber 15. As a result, via the pressure shoulder 18 provided at the injection nozzle 16, the force of the spring 17 is overcome, and the fuel is injected into the combustion chamber, not shown.

[0026] Upon the return of the control valve 1, because of the stroke length of the slide element 3c, the communication between the inflow line 7 and the pressure chamber 6 is interrupted immediately, while the second passage 5 is still closed by the slide element 4a, because of the high pressure in the pressure chamber 6. Not until the spring force of the spring 9 becomes greater than the pressure in the pressure chamber 6 does the slide element 4aof the piston 4 open the passage 5, thus opening up a communication between the pressure chamber 6 and the leak fuel line 8.

[0027] Thus an unambiguous function of the control valve 1 is always assured, both upon opening and upon closing, without a diversion surge from the pressure chamber 6 into the leak fuel line 8 occurring. By the disposition of the slide element 3cupstream in the opening direction of the actual opening portion 3dof the piston 3, the disadvantages of the prior art can thus be overcome. As a result of the slide ratio h₂/h₁, an overlap of the piston 4 can be optimized depending on the application. As a rule, the overlap (h₂-h₁) is lengthened (that is, will be greater than 0), in order to assure that no surge of leak fuel will occur.

[0028] In FIG. 2, a second exemplary embodiment of a valve for controlling fluids of the invention is shown. This control valve can again be used in a fuel injection valve. Since the fuel injection valve of the second exemplary embodiment, in comparison with the first exemplary embodiment, has changes only at the control valve 1, the further parts of the fuel injection valve have not been shown in FIG. 2 or described below, since they are embodied precisely as in the first exemplary embodiment. Also in the second exemplary embodiment, the same reference numerals as in the first exemplary embodiment are used for identical parts.

[0029] The control valve 1 of the second exemplary embodiment, in contrast to the first exemplary embodiment, has only one piston 3. The piston includes a plurality of piston portions 3athrough 3e. The piston 3 again has a first cylindrical piston portion 3aand a second piston portion 3bwhich is embodied in concave form. The second piston portion 3bis adjoined by a slide element 3c, which is disposed directly at the valve seat. The piston 3 also includes a fourth, tapering piston portion 3dand a fifth, cylindrical piston portion 3e, which are connected to a control element 2. The piston 3 is disposed partly in a pressure chamber 6 and opens/closes the communication between an inflow line 7 from a rail and a booster piston (not shown) that communicates with the pressure chamber 6 via a line 19. The control valve 1 also includes a leak fuel line 8.

[0030] The mode of operation of the control valve 1 of the second exemplary embodiment is as follows. When the control element is actuated, the piston 3 is moved in the direction of the control element 2. As a result, the fourth, tapering piston portion 3dlifts away from the piston seat at the first passage at valve seat 10. However, since the slide element 3cdirectly follows the second piston portion 3b, the communication between the high-pressure inflow line 7 and the pressure chamber 6 is not opened until the edge, toward the second piston portion 3b, of the slide element 3chas moved past the valve seat 10.

[0031] Since as shown in FIG. 2 the stroke length h₂of the slide element 3cis greater than the stroke length h₁provided at the second passage 5 between the first piston portion 3aand the second piston portion 3b, it is assured that the communication between the pressure chamber 6 and the leak fuel line 8 will be closed before the communication between the inflow line 7 and the pressure chamber 6 is opened via the first passage at seat 10. Upon closure of the control valve 1, the communication between the inflow line 7 and the pressure chamber 6 is first closed, before the passage 5 between the pressure chamber 6 and the leak fuel line 8 is opened.

[0032] Thus in the second exemplary embodiment as well, a diversion surge into the leak fuel line 8 upon switchover of the control valve 1 is securely prevented. Moreover, depending on the intended use, the desired overlap (h₁-h₂) can be adjusted by the ratio of the stroke length h₂of the slide element 3cto the stroke length h₁at the second passage 5.

[0033] The above description of the exemplary embodiments of the present invention is intended solely for illustrative purposes and is not intended to limit the scope of the invention. Within the scope of the invention, various changes and modifications may be made without departing from the scope of the invention or its equivalents.