EP1511932B1 - Injection valve - Google Patents

Description

The present invention relates to an injection valve according to the preamble of claim 1.

Such an injection valve is known from DE 198 54 508, wherein the valve needle is designed to open outwardly and axially pressure-effective surfaces of the valve needle and the housing are designed so that when changing the pressure of the fluid, the same axial length change to the valve needle and the valve housing occur. In addition, it is possible to adjust the surfaces on the valve needle so that the pressure of the fluid causes no force on the return spring or the valve seat. The drive chamber, in which the drive unit is arranged, and the fluid chamber, in which the valve needle and the return spring are arranged, are reliably sealed against each other by means of a sealing ring and a drain.

The compensation of all pressure forces takes place in order to keep the valve needle as a whole free of pressure forces. For example, due to the pressure-loaded surface of the valve disk of an outwardly opening injector at high fuel pressure, a high acting in the opening direction compressive force, which is advantageously compensated by a second pressure-loaded surface which generates a force acting in the opposite direction of the same amount. With such a compensation, there are no further restrictions with regard to the valve disk diameter and the needle diameter.

Furthermore, it is well known that in a high-pressure direct injection (HPDI) injector for direct injection lean-burn engines having a piezoelectric multilayer actuator as a driving element in addition to the fuel Yet another resource for the hydraulic bearing in the injector is needed. It is known that an automatic compensation of all thermal and all caused by setting effects of the piezoelectric element or pressure-related changes in length is possible. This can be dispensed with in the choice of materials on expensive alloys with low thermal expansion (eg Invar) and much cheaper steel with higher strength and easier machinability can be used. On the drive side, all moving parts are held under low force to plant, so that no lifting losses caused by gaps. For an outwardly opening piezoelectrically driven injector, the hydraulic length compensation is realized by a hydraulic chamber filled with oil. However, this requires a complex hermetic seal of the equipment, such as silicone oil, compared to the pressurized fuel, which is often realized by a metal bellows.

Also, from WO 00/17507 an injection valve is known in which a hydraulic interrupter between valve needle and piezo actuator is filled with fuel through an annular gap, which also ensures the length compensation.

The object of the present invention is to provide a powerful injection valve with a simple hydraulic bearing.

This is achieved according to the invention in an injection valve having the features of patent claim 1. An injector principle is realized which requires no additional resources for the hydraulic bearing. In order to facilitate the filling of the hydraulic chamber, the fuel over two opposite annular gaps fills the hydraulic chamber of the valve, which ensures the length compensation.

Advantageously, the hydraulic pressure applied to the hydraulic chamber is designed to be very stiff in order to be able to absorb very high compressive and tensile forces in the short term, as is required in the rapid opening and closing of the valve. Thus, the injection valve can close about 5 - 10 times as fast as a provision by a return spring alone according to the prior art. At the same time, the losses in Ventilnadelhub by the disadvantageous Elongation of the valve needle due to a high force acting by the return spring restoring force avoided.

According to the invention, the fuel pressure-related forces can be adjusted specifically to the valve needle. For example, a fuel pressure related closing force could be adjusted. This would ensure that the valve needle closes the valve safely even with a broken return spring.

By a suitable guidance of the fuel lines, the fuel flows past the drive unit and, for example, to the multilayer actuator and cools the piezoceramics. Another advantage is therefore the improved temperature behavior of the injector. The direct injection into the combustion chamber exposes the injector to high temperatures. In addition, modern injection concepts provide for multiple injections. The trend is towards continuous injection rate molding. Concepts with 5 injections per cycle are already discussed. This creates additional waste heat. Therefore, a cooling of the injector is advantageous, even if no temperature problem has occurred in injectors according to the prior art with silicone oil as the operating means of the hydraulic bearing.

Temperature expansions, aging and setting effects cause the absolute position of the piezo unit, but also the relative position to the valve housing to change. Typical values are up to a few 10 μm, but are always significantly smaller than 100 μm. The hydraulic chamber is to be realized at least so high that it can compensate for any changes in length expected during the service life. On the other hand, in order to be able to form an abutment which is as stiff as possible, the hydraulic chamber is to be made as low as possible. Preferably, therefore, a typical height of the hydraulic chamber of 200 to 500 microns is selected.

Further advantageous embodiments of the invention can be found in the further dependent claims.

An embodiment of the injection valve according to the invention is described below; the single FIGURE shows the injection valve simplified in a schematic longitudinal section.

A high-pressure injector or the single-point valve has a valve seat 3 in an injector housing 1. A diameter of the sealing line d ₁ is typically 3 - 5 mm in the case of a fuel injection valve. The valve seat 3 is kept closed in the ground state by a valve disc 7 connected to the lower end section of a valve needle 5 (diameter d ₂ ). The valve needle 5 is arranged in the valve housing 1. The closed ground state, one formed by the valve seat 3 and the valve plate 7 frontally on the housing 1 injection nozzle 9 is ensured by a tensioned compression spring 11 with a typical spring force (F _S ) of about 150 N. The compression spring is clamped between a bottom plate 13 of a drive unit 15 and a portion of the inner wall of the valve housing 1. The valve needle 5 is rigidly connected to the bottom plate 13, for example via a weld. The fuel supply into an interior of the valve housing 1 is effected by a provided in the injector 1 line bore 17. In the upper part of the injector 1, the drive unit 15 is arranged. This is formed from a piezoelectric multilayer actuator in low-voltage technology (PMA) 19, a tube spring 21, a hydraulic piston 23 and the bottom plate 13. The tube spring 19 is welded to the hydraulic piston 23 and the bottom plate 13, so that the multilayer actuator 19 under a mechanical compression bias stands. Electrical connections 25 of the drive unit 15 are guided upward out of the housing 1, as described below. By the hydraulic piston 23, the interior of the valve housing is in a main chamber 27, which receives in particular the PMA 19, and a hydraulic chamber 29 separated. Above the hydraulic chamber 29, the drive unit 15 is connected to the injector housing 1 by means of a metal bellows 31 having a hydraulic or effective pressure effective diameter d ₅ . Thus, the interior of the valve housing 1 is closed to the environment. The interior is additionally connected in the region of the metal bellows 31 via a transverse line 33 to the conduit bore 17.

In the ground state with applied fuel pressure p _K of typically 100-300 bar act on the bottom plate 13 and the hydraulic piston 23, although very large resulting compressive forces (F _D = p _K • π • (d ₁ ² -d ₅ ² ) / 4, from which is may give about a pressing force of F _D = 1000-5000 N. However, this stands out in the pressure balance away when d = d ₅ is selected _first, the pressure equalization does not have to be carried out mathematically precise, but only in sufficient detail as described below In the case of typical dimensions of the injection valve, a change in the fuel pressure from 100 to 300 bar with a deviation of the pressurized areas of 1 mm ² from the ideal compensation state already results in an additional force (F _D ) of approximately 20 N, which is the closing force in the valve seat 3. This force can act against the spring force (F _S ) of the compression spring 11 and, in the worst case, inadvertently open the valve 13. On the other hand, this additional force (F _D ) can also be used Reinforce spring force (F _S ), thereby complicating the opening of the valve. With increasing size of this undesired additional force (F _D ), the precise control of the injection process is difficult. Particularly modern concepts with multiple injection are then hardly feasible. Preferably, at least: F _S > 5 • F _D , in particular F _S > 10 • F _D.

The hydraulic piston 23 is sealingly fitted by a first and a second tight clearance 35, 37 with a larger diameter d ₃ and a smaller diameter d ₄ in the correspondingly formed injector 1 and forms with the corresponding inner wall portions of the injector 1, the annular hydraulic chamber 29. More Way, the height of the hydraulic chamber h _{K is set} to at least 100 - 500 microns during assembly of the injector. The hydraulic chamber 29 is used, for example, to compensate for thermally induced or caused by aging effects of the PMAs 19 in the injector slow changes in length (eg typical time t> 1 s) of the drive unit 15 and / or the valve needle 5 relative to the injector 1. When these slow changes in length occur , Can take place for length compensation on the narrow sealing gaps of the clearance fits 35, 37 of the hydraulic piston 23, an unhindered fluid exchange between the hydraulic chamber 29 and the surrounding fuel-filled interior of the injector or the main chamber 27 and the transverse line 33. These slow changes are thus compensated by a change in the height of the hydraulic chamber 29.

mit:

Viskosität von Benzin:

η = 0,4 mPa•s;

Spalthöhe:

h = 2 µm;

Länge der Dichtflächen:

1 = 10 mm

Einspritzzeit:

t_E = 5 ms ergibt sich

Q_L = 28,8 mm³/s; ΔV = Q_L•5•10^-3 s = 0,144 mm³;
Mit Δx = ΔV/A_K ergibt sich
Δx = 0,6 µm als Hubverlust aufgrund der Leckageströmung während der Einspritzzeit unter den oben getroffenen Annahmen.However, the sealing gaps between the hydraulic piston 23 and the valve housing 1 must at the same time be dimensioned so narrow that no appreciable fluid exchange between the hydraulic chamber 29 and the surrounding fuel-filled interior of the injector, in particular the main chamber 27, within typical injection times (0 ms <t <5 ms) can occur. The height of the hydraulic chamber h _K should be able to change by a maximum of about 1 - 2 microns due to leakage. In order to open the valve and keep it open during operation for a period of 0 ms <t <5 ms and then close it again, an average force of approximately 100-200 N is typically required, depending on the magnitude of the spring force F _s . For a typical pressure effective area A _K = π • (d ₃ ² -d ₄ ² ) / 4 of about 240 mm ² (assumption: d ₃ = 18 mm, d ₄ = 4 mm), the mean pressure in the hydraulic chamber changes the fuel pressure by Δp = 200 N / A _K <10 bar. The fluid flow through the maximum eccentric sealing gaps are calculated according to $${\mathrm{Q}}_{\mathrm{L}}\mathrm{=}\mathrm{2}\mathrm{.}\mathrm{5}\mathrm{•}\mathrm{\pi }\mathrm{•}\mathrm{(}{\mathrm{d}}_{\mathrm{3}}\mathrm{+}{\mathrm{d}}_{\mathrm{4}}\mathrm{)}{\mathrm{H}}^{\mathrm{3}}\mathrm{•}\mathrm{Ap}\mathrm{/}\left(\mathrm{12}\mathrm{•}\mathrm{\eta }\mathrm{•}\mathrm{l}\right)$$

With:

Viscosity of gasoline:

η = 0.4 mPa • s;

Gap height:

h = 2 μm;

Length of the sealing surfaces:

1 = 10 mm

Injection time:

t _E = 5 ms results

Q _L = 28.8 mm ³ / s; ΔV = Q _L • 5 • 10 ^-3 s = 0.144 mm ³ ;
With Δx = ΔV / A _K results
Δx = 0.6 μm as the stroke loss due to the leakage flow during the injection time under the assumptions made above.

The hydraulic chamber 29 has due to the compressibility of gasoline a spring action, which leads to an additional loss in the valve lift. The minimum spring rate of the hydraulic chamber 29 c _{K is} calculated according to
c _K = A _K / (χ • h _K ) with
χ = 10 ^-9 m ² / N and
h _K = 500 μm to c _K = 500 N / μm and thus results in:
Δx = ΔF / c _K = 200 N / 500 N / μm = 0.4 μm as the stroke loss of the valve due to the compressibility of gasoline.

As a result, it is shown that the maximum occurring stroke loss, which is caused by the hydraulic chamber 29, remains sufficiently small with suitable dimensioning. Overall, the drive unit 15 with the hydraulic piston 23 and the valve needle 5 form a unit which can be displaced almost unhindered with respect to the injector housing when occurring in comparison to the injection slow movements against the seat force (F _D + F _S ) between the valve seat. 3 and adjusts the valve plate 7. The length of the annular gap is relatively uncritical, with increasing length of the leakage current decreases. Since the leakage increases with the 3rd power of the gap height h, the gap height should be sufficiently small. In summary, therefore, that slow-running length changes in particular of the PMAs 19 are compensated by the hydraulic chamber 29, so that over all operating conditions and thermal loads reproducible time profiles of the valve needle and thus the injection quantities can be controlled. In the valve according to the figure, the guidance of the fuel in the injector housing is realized so that the functions of cooling the PMA 19 and the length compensation by means of the hydraulic chamber 29 can be fulfilled by means of a single fluid.

The function of the injection valve is now as follows: In order to start the injection process, the PMA 19 is charged via the electrical connections 25. Due to the inverse piezoelectric effect of the PMA 19 expands (typical deflection: 30 - 60 microns). In this case, the PMA is supported on the rigid hydraulic chamber 29 in order to lift the valve disk 7 against the spring force F _{S of} the compression spring 11 from the valve seat 3. Now the fuel can escape from the injection nozzle 9. The valve disk 7 is acted upon at its lower, the fuel-remote surface with the pressure of the injection chamber (not shown). As described above, the hydraulic chamber 29 is sufficiently rigid over a typical injection period. To end the injection process, the PMA 19 is discharged again via the electrical connections 25 and the PMA shortens. The hydraulic pressure (= hydraulic tension) and the spring restoring force of the compression spring 11 pull the valve plate 7 in the valve seat 3 and thus close the valve. In the end position with the valve closed, the hydraulic chamber 29 is maintained with a minimum height. The largest contribution to the restoring force comes from the hydraulic pressure bias. Due to its high rigidity and the high fuel pressure (p _K = 100-300 bar), the hydraulic chamber 29 is capable of high tensile forces (F _z = p _K • π • (d ₃ ² -d ₄ ² ) / 4 of F _z = 1000-5000 N) without appreciable change in the hydraulic chamber height h _K.

By installing a check valve in the high pressure port of the injector, the high pressure in the injector over be maintained for a longer time while the fuel pump is turned off (not shown). When the engine is restarted, the injector volume itself serves as a fuel pressure reservoir for the first injection events until the injection pump feeds the necessary fuel pressure into the injector.

Alternatively, as a drive, for example, a magnetostrictive drive can be used to actuate the valve. With a suitably constructed stroke reversal, the device described can in principle also be used for inwardly opening valves.

Claims (12)

1. Injection valve for fuel with a valve housing (1) in which a drive unit (15) controls the movement of a valve needle (5) pretensioned by a spring (11), having a hydraulic bearing for the drive unit (15) with a hydraulic chamber (29) and in the valve housing a main chamber (27) which is filled with fuel as the operating medium for the hydraulic bearing and in which the valve needle (5) is disposed, characterized in that the hydraulic bearing has a hydraulic chamber (29) which is connected in throttled condition by narrow annular gaps (35, 37) on both sides, both to the main chamber (27), and on the opposite side to part of the inner chamber of the valve housing (1), and that this part of the inner chamber is connected via a cross duct (33) to a fuel supply duct (17) entering the main chamber (27)
2. Injection valve according to claim 1, characterized in that the fuel is used for cooling the drive unit (15).
3. Injection valve according to claim 1 or 2, characterized in that the drive unit (15) is disposed in the main chamber (27).
4. Injection valve according to claim 1, 2 or 3, characterized in that the axially acting pressure surfaces of the valve needle (5) are dimensioned such that the resulting pressure forces (p_D) essentially cancel each other out, causing the resulting axially acting force (F_D) on the valve needle (5) to be minimized compared to the force (F_S) of the spring (11).
5. Injection valve according to one of the preceding claims, characterized in that a check valve is installed in a highpressure port of the injection valve.
6. Injection valve according to one of the preceding claims, characterized in that the valve needle (5) is fixed to the drive unit (15)
7. Injection valve according to one of the preceding claims, characterized in that the drive unit (15) has a hydraulic plunger (23) which in conjunction with the inner wall section of the valve housing (1) forms the hydraulic chamber (29).
8. Injection valve according to claim 7, characterized in that a height (h_K) of the hydraulic chamber (29) is approximately 200 to 500 µm.
9. Injection valve according to claim 7 or 8, characterized in that the drive unit (15) together with the hydraulic plunger (23) and the valve needle (5) form a fixed unit which can be displaced virtually unimpeded relative to the injector housing (1) in the event of slower movements occurring compared to the injection process, taking the spring forces into account.
10. Injection valve according to one of the preceding claims, characterized in that the drive unit (15) is connected to a hydraulic plunger (23) which divides the inner chamber of the housing (1) into the hydraulic chamber (29) and the main chamber (27).
11. Injection valve according to one of the preceding claims, characterized in that electrical leads (25) of the drive unit (15) are brought out of an opening in the housing (1), and that between the drive unit (15) and the housing (1) there is provided a flexible means of sealing (31).
12. Injection valve according to claim 11, characterized in that the entire inner chamber of the valve housing (1) between the means of sealing (31) and an oppositely disposed valve seat (3) is filled with the fuel.

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