EP1511932A1 - Injection valve - Google Patents

Abstract

The invention relates to an injection valve for injecting fuel, comprising a valve housing (1) inside of which a drive unit (15) controls the movement of a valve needle (5) that is pretensioned by a spring (11). The injection valve also comprises a main chamber (27), which is provided inside the valve housing, is filled with fuel and accommodates the valve needle (5), and comprises a hydraulic bearing for the drive unit (15). The aim of the invention is to provide a simple hydraulic bearing. To this end, the hydraulic bearing has a hydraulic chamber (29) that is connected to the main chamber (27), whereby fuel serves as the operating substance of the hydraulic bearing.

Description

description

Injector

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

Such an injection valve is known from DE 198 54 508, the valve needle being designed to open outwards and axially pressure-effective surfaces of the valve needle and the housing being designed such that when the pressure of the fluid changes, the same axial length change on the valve needle and on occur in the valve housing. It is also possible to adjust the areas on the valve needle so that the pressure of the fluid does not cause any 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 off from one another by means of a sealing ring and a drain.

All pressure forces are compensated in order to keep the valve needle free of pressure forces overall. For example, due to the pressure-loaded surface of the valve plate of an outward-opening injector, when the fuel pressure is high, a high pressure force acting in the opening direction acts, which is advantageously compensated for by a second pressure-loaded surface which generates a pressure force of the same amount acting in the opposite direction. With such a compensation, there are no longer any restrictions with regard to the valve plate diameter and the needle diameter.

Furthermore, it is generally known that in a high-pressure injection valve (High Pressure Direct Injection, HPDI) for direct-injection lean engines with a piezoelectric multilayer actuator as the drive element in addition to the fuel yet another resource is required for the hydraulic bearing in the injector. It is known that automatic compensation of all thermal as well as all length changes caused or caused by pressure effects of the piezo element is possible. This means that expensive alloys with low thermal expansion (eg Invar) can be dispensed with when choosing the material, and much cheaper steel with higher strength and easier machinability can be used. On the drive side, all moving parts are held against the system with little force, so that there is no stroke loss due to gaps. For an outward opening piezoelectrically driven injector, the hydraulic length compensation is implemented by a hydraulic chamber filled with oil. However, this requires a complex hermetic seal of the operating medium, for example silicone oil, against the pressurized fuel, which is often realized by a metal bellows.

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

According to the invention, this is achieved in an injection valve with the features of claim 1. An injector principle has been implemented that does not require any additional equipment for the hydraulic bearing. The fuel fills the hydraulic chamber of the valve via at least one annular gap, which ensures the length compensation.

The hydraulic chamber to which the fuel pressure is applied is advantageously very stiff in order to be able to absorb very high compressive and tensile forces in the short term, as is required when the valve is opened and closed quickly. This allows the injector to close about 5 - 10 times as quickly as if it was reset by a

Return spring alone according to the state of the art. At the same time, the losses in the valve needle stroke are lige expansion of the valve needle due to a high restoring force acting through the return spring avoided.

According to the invention, the fuel pressure-related forces on the valve needle can be set in a targeted manner. For example, a closing force caused by the fuel pressure could be set. This would ensure that the valve needle closes the valve securely even if the return spring is broken.

By suitable routing of the fuel lines, the fuel flows past the drive unit and, for example, the multilayer actuator and cools the piezoceramics. Another advantage is therefore the improved temperature behavior of the injector. Direct injection into the combustion chamber exposes the injector to high temperatures. Modern injection concepts also provide for multiple injections. The development is moving towards continuous injection rate shaping. Concepts with 5 injections per cycle are already being discussed. This creates additional waste heat. Cooling of the injector is therefore advantageous, even if no temperature problem has yet occurred in the case of injectors according to the prior art with silicone oil as the operating medium of the hydraulic bearing.

Temperature expansions, aging and setting effects mean that the absolute position of the piezo unit, but also the relative position to the valve housing, changes. Typical values are up to a few 10 μm, but are always significantly smaller than 100 μm. The hydraulic chamber must be at least high enough to compensate for all changes in length to be expected during its service life. In order to be able to form an abutment that is as rigid as possible, on the other hand, the hydraulic chamber must be designed as little as possible. A typical height of the hydraulic chamber of 200 to 500 μm is therefore preferred. In order to facilitate the filling of the hydraulic chamber with fuel, it is provided that the hydraulic chamber is connected via a cross line to a fuel supply line opening into the main chamber.

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

An exemplary embodiment of the injection valve according to the invention is described below; the only FIG. shows the injector in simplified form in a schematic longitudinal section.

A high-pressure injector or the injection valve has a valve seat 3 in an injector housing 1. A diameter of the sealing line di is typically 3-5 mm in a fuel injection valve. The valve seat 3 is kept closed in the basic state by a valve disk 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 basic state, an injection nozzle 9 formed by the valve seat 3 and the valve plate 7 on the end face on the housing 1, is ensured by a tensioned compression spring 11 with a typical spring force (F _s ) of approximately 150 N. The compression spring is clamped between a base plate 13 of a drive unit 15 and a section of the inner wall of the valve housing 1. The valve needle 5 is rigidly connected to the base plate 13, for example via a weld seam. The fuel is fed into an interior of the valve housing 1 through a line bore 17 provided in the injector housing 1. The drive unit 15 is arranged in the upper part of the injector housing 1. This is formed from a piezoelectric multilayer actuator using low-voltage technology (PMA) 19, a Bourdon tube 21, a hydraulic piston 23 and the base plate 13. The tubular spring 19 is welded to the hydraulic piston 23 and the base plate 13, so that the multilayer actuator 19 is under a mechanical pressure prestress stands. Electrical connections 25 of the drive unit 15 are led out of the housing 1, as described below. By the hydraulic piston 23, the interior of the valve housing in a Hauptka mer 27, which in particular receives the PMA 19, and a hydraulic chamber 29 is separated. Above the hydraulic chamber 29, the drive unit 15 is connected to the injector housing 1 by means of a metal bellows 31 with a hydraulic or effectively pressure-effective diameter d ₅ . The interior of the valve housing 1 is thus closed with respect to the surroundings. The interior is additionally connected to the line bore 17 in the area of the metal bellows 31 via a cross line 33.

In the basic state when the fuel pressure p _κ of typically 100-300 bar is applied, very large resulting pressure forces act on the base plate 13 and the hydraulic piston 23 (E _D = p _κ ^# π * (dι-d5 ² ) / 4, from which approximately can result in a compressive force of F _D = 1000-5000 N. However, this increases in the pressure balance if di = ds is selected. The pressure compensation does not have to be mathematically exact, but only sufficiently precise, as described below. With typical dimensions of the injection valve, a change in the fuel pressure from ^" 100 to 300 bar with a deviation of the pressurized areas by 1 mm ² from the ideal state of compensation already results in an additional force (F _D ) of about 20 N, around which 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 open the valve unintentionally. On the other hand, this additional force (F _D ) can also Increase spring force (F _s ), making opening the valve more difficult. With increasing size of this undesired additional force (F _D ) the precise control of the injection process becomes more difficult. Particularly modern concepts with multiple injection can then hardly be realized. Preferably at least: F _s > 5 * F _D , in particular F _s > 10 _* F _D. The hydraulic piston 21 is sealed by a first and a second narrow clearance fit 35, 37 with a larger diameter d ₃ and a smaller diameter d into the correspondingly designed injector housing 1 and forms the annular hydraulic chamber 29 with the corresponding inner wall sections of the injector housing 1. Typically when installing the injector, the height of the hydraulic chamber h _{κ is set} to at least 100 - 500 μm. The hydraulic chamber 29 is used, for example, to compensate for thermal changes in the length of the drive unit 15 and / or the valve needle 5 relative to the injector housing 1, caused by the aging effects of the PMA 19 in the injector (for example, typical time periods t> 1 s), if these slow changes in length occur , an unimpeded 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 can take place over the narrow sealing gaps of the clearance fits 35, 37 of the hydraulic piston 23. These slow changes are thus compensated for by a change in the height of the hydraulic chamber 29.

However, the sealing gaps between the hydraulic piston 23 and the valve housing 1 must at the same time be dimensioned so tightly that no significant fluid exchange between the hydraulic chamber 29 and the surrounding fuel-filled interior of the injector, in particular the main chamber, occurs within typical injection times (0 ms <t <5 ms) 27 can occur. The height of the hydraulic chamber h should not change by more than 1 - 2 μm due to leakage. In order to be able 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 required, depending on the size of the spring force F _s . With a typical pressure-effective area A _κ = π «(d ₃ ² -d ₄ ² ) /. of approximately 240 mm ² (assumption: d ₃ = 18 mm, d ₄ = 4 mm) the mean pressure in the hydraulic chamber changes compared to the fuel pressure by Δp = 200 N / Ä _κ <10 bar. The fluid flow through the maximum eccentric sealing gap is calculated according to

Q _L = 2.5 »π« (d ₃ + d ₄ ) h ³ »Δp / (12 * η« l) with: viscosity of petrol: η = 0.4 mPa * s; Gap height: h = 2 μm;

Length of the sealing surfaces: 1 = 10 mm

Injection time: t_ = 5 ms

Q _L = 28.8 mm ³ / s; ΔV = Q _L * 5 * 10 ^{~ 3} s = 0.144 mm ³ ; With Δx = ΔV / A _{R there} is Δx = 0.6 μm as a stroke loss due to the leakage flow during the injection time under the assumptions made above.

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

This shows that the ^" maximum stroke loss occurring, which is caused by the hydraulic chamber 29, remains adequately small when suitably dimensioned. Overall, the drive unit 15 together with the hydraulic piston 23 and the valve needle 5 form a unit which, as a whole, is compared slow movements occurring during the injection process can be shifted almost unhindered relative to the injector housing until the seating force (F _D + F _s ) is established between the valve seat 3 and the valve plate 7. The length of the annular gaps is relatively uncritical, the leakage flow decreasing with increasing length Since the leakage increases with the 3rd power of the gap height h, the gap height should be chosen to be sufficiently small. To summarize, slow changes in length, in particular of the Pl ^ As 19 are compensated by the hydraulic chamber 29, so that over all loading drive states and thermal loads, reproducible temporal profiles of the valve needle stroke and thus the injection quantities can be controlled. In the valve according to the FIG., The guidance of the fuel in the injector housing is implemented in such a way that the functions of cooling the PMA 19 and length compensation by means of the hydraulic chamber 29 can be performed using a single fluid.

The function of the injection valve is now as follows: To start the injection process, the PMA 19 is charged via the electrical connections 25. Due to the inverse piezoelectric effect, the PMA 19 expands (typical deflection: 30 - 60 μm). The PMA is supported on the rigid hydraulic chamber 29 in order to lift the valve plate 7 against the spring force F _{s of} the compression spring 11 from the valve seat 3. The fuel can now emerge from the injection nozzle 9. The valve plate 7 is acted upon by the pressure of the injection chamber (not shown) on its lower surface facing away from the fuel. As described above, the hydraulic chamber 29 is designed to be sufficiently rigid over a typical injection period. In order to end the injection process, the PMA 19 is discharged again via the electrical connections 25 and the ^" PMA is shortened. The hydraulic pressure tension (= hydraulic tensile force) and the spring restoring force of the compression spring 11 pull the valve plate 7 into the valve seat 3 and close In the end position with the valve closed, the hydraulic chamber 29 is maintained with a minimum height. The greatest contribution to the restoring force comes from the hydraulic pressure preload. The hydraulic chamber 29 is due to its high rigidity and the high fuel pressure (p _κ = 100 - 300 bar) able to absorb high tensile forces (F _z = p _{κ *} π • (d ₃ ² -d ₄ ² ) / 4 from F _z = 1000-5000 N) _{for a} short time without any significant change in the hydraulic chamber height h _κ

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

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

Claims

claims 1. Injection valve for fuel with a valve housing (1), in which a drive unit (15) controls the movement of a valve needle (5) biased by a spring (11), with a main chamber (27) formed in the valve housing and filled with fuel and in which the valve needle (5) is arranged and with a hydraulic bearing for the drive unit (15), characterized in that the hydraulic bearing has a hydraulic chamber (29) which is in communication with the main chamber (27), and in that the hydraulic chamber is filled with the fuel as the operating material of the hydraulic bearing. 2. Injection valve according to claim 1, characterized in that the fuel is used to cool the drive unit (15). 3. Injection valve according to claim 1 or 2, characterized in that the drive unit (15) in the Main chamber (27) is arranged. 4. Injection valve according to claim 1, 2 or 3, characterized in that the axially effective pressure surfaces of the valve needle (5) are dimensioned such that the resulting pressure forces (p _D ) essentially cancel each other out, whereby the resulting axially acting force (F _D ) on the valve needle (5) compared to the force (F _s ) of the spring (11) is kept low. 5. Injection valve according to one of the preceding claims, characterized in that a check valve is installed in a high-pressure connection of the injection valve 6. Injection valve according to one of the preceding claims, characterized in that the valve needle (5) with the drive unit (15) is fixedly connected. 7. Injection valve according to one of the preceding claims, characterized in that the drive unit (15) has a hydraulic piston (23) which, together with an inner wall portion of the valve housing (1), forms the hydraulic chamber (29). 8. Injection valve according to claim 7, characterized in that a height (h _κ ) of the hydraulic chamber (29) is approximately 200 to 500 microns. 9. Injection valve according to claim 7 or 8, characterized in that the drive unit (15) with the hydraulic piston (23) and the valve needle (5) forms a fixed unit, which is almost unhindered compared to the injector housing when compared to slower movements occurring during the injection process (1) taking into account the spring forces. 10. An injection valve according to one ^'of the preceding claims, characterized in that the drive unit (15) connected to a hydraulic piston (23) which divides the interior of the housing (1) into the hydraulic chamber (29) and the main chamber (27). 11. Injection valve according to claim 10, characterized in that the hydraulic chamber (29) is connected via a cross line (33) to a fuel supply line (17) opening into the main chamber (27). 12. Injection valve according to one of the preceding claims, characterized in that electrical leads (25) of the drive unit (15) are guided from an opening in the housing (l), and that between the drive unit (15) and the housing (1) a flexible sealing means (31) is provided. 13. Injection valve according to claim 12, characterized in that the complete interior of the valve housing (1) between the sealing means (31) and an oppositely arranged valve seat (3) is filled with the fuel. 14. Injection valve according to one of the preceding claims, characterized in that the hydraulic chamber (29) is delimited on both sides by narrow annular gaps with respect to the interior of the valve housing (1).