EP0941400B1 - Liquid control valve - Google Patents

Abstract

The invention relates to a liquid control valve which is provided, for its operation, with a bonding chamber (30) filled with liquid and placed between a piston (21) of a piezoelectric actuator (32) and a piston (25) that actuates a valve member. In order to compensate for liquid loss occurring in a bonding chamber when briefly exposed to high pressure in each cycle of operation, the pressure differential existing in the low pressure chambers (18, 22) between, on the one hand, the bonding chamber (30) and, on the other hand, the piston surfaces (31) of the piezoelectric actuator (32) and the surfaces of the piston (25) that actuates the valve member, the surfaces being in both cases turned to the side opposite the bonding chamber (30), is used during the return stroke of the actuator piston (31) to have a refilling completed along slots (35, 36) without using any valve. This type of valve is intended for use in fuel injection systems of internal combustion engines for vehicles.

Description

State of the art

The invention relates to a valve for controlling liquids according to the preamble of claim 1. Such a valve is known from DE-C-195 19 192. There, the valve member has a piston part, referred to as the primary piston, which is arranged in a bore of a secondary piston of larger diameter, which is moved by the piezo actuator. Both pistons delimit a hydraulic space in such a way that when the secondary piston is moved by the actuator by a certain distance, the primary piston of the valve member is moved by a distance increased by the transmission ratio of the stepped bore cross-sectional areas against the actuating movement of the secondary piston. The valve member, the primary piston, the secondary piston and the piezo actuator lie one behind the other on a common axis. The hydraulic space is separated from an adjacent low-pressure space by guides of primary pistons and secondary pistons with guide gaps. These are intended to ensure temperature compensation by maintaining complete filling of the hydraulic space.

However, due to the leakage current taking place there, these gaps produce a loss of fluid, particularly when the pressure in the hydraulic space is increased by an actuation, which can have a negative effect on the accuracy of the control of the actuation phases of the valve.

Advantages of the invention

The valve according to the invention with the characterizing features of claim 1 with the dimensioning of the gaps has the advantage that the valve remains optimally functional and the required filling volume is always produced with high guidance accuracy and low leakage losses in the operating phases of the valve.

An advantageous embodiment of the invention takes place according to claim 2, in which only a part of the length of the piston determines the connection between the low-pressure space and the coupling space for refilling criteria and a remaining part of the piston provides the length required to achieve a to ensure exact guidance of the pistons. This is further improved according to claim 3, the piston being provided with only a short gap length l _w close to the coupling space and according to claim 4, where the liquid from the low-pressure space flows unthrottled via the pressure medium channel to very close to the gap l _w can be

An essential improvement of the refilling according to the invention results from claim 5 in that a certain pressure which is higher than the ambient pressure is set in the low-pressure rooms. This results in an increase in the pressure gradient favoring the refilling of the coupling space towards the coupling space, this pressure being provided in accordance with claim 12.

drawing

Several embodiments of the invention are shown in the drawing and explained in more detail in the following description. FIG. 1 shows a fuel injector in section, FIG. 2 shows a first embodiment of a piston arrangement on a coupling space with liquid make-up, FIG. 3 shows another type of piston, FIG. 4 shows a modification of the piston type according to FIG. 3, and FIG. 5 shows another modification of a piston type 3, FIG. 6 shows a diagram of the refilling time, FIG. 7 shows a design with three pistons and FIG. 8 shows an injection system with the fuel injection valve according to the invention.

Description of the embodiments

The valve according to the invention is used in a fuel injection valve, the essential parts of which are shown in section in FIG. 1. This injection valve has a valve housing 1, in which a valve needle 3 is guided in a longitudinal bore 2, which can also be preloaded in the closing direction in a known manner, not shown here, by a closing spring. On her one At the end, the valve needle is provided with a conical sealing surface 4, which cooperates with a seat 6 on the tip 5 of the valve housing projecting into the combustion chamber, from which injection openings lead out into the interior of the injection valve, here the one surrounding the valve needle 3 under injection pressure Connect the standing fuel-filled annular space 7 to the combustion chamber so as to carry out an injection when the valve needle has lifted off its seat. The annular space is connected to a further pressure space 8, which is constantly connected to a pressure line 10, via which fuel under injection pressure is supplied to the fuel injection valve from a high-pressure fuel reservoir 9. This high fuel pressure also acts in the pressure chamber 8, and there on a pressure shoulder 11, via which the nozzle needle can be lifted from its valve seat in a known manner under suitable conditions.

At the other end of the valve needle, it is guided in a cylinder bore 12 and includes with its end face 14 a control pressure chamber 15 which is constantly connected via a throttle connection 16 to an annular chamber 17 which, like the pressure chamber 8, is always connected to the high-pressure fuel accumulator stands. Axially from the control pressure chamber 15, a bore having a throttle 19 leads off to a valve seat 20 of a control valve 21. A valve member 22 of the control valve interacts with the valve seat, which in the raised state establishes a connection between the control pressure chamber 15 and a low pressure chamber 18, which is constantly connected a relief room is connected. Arranged in the low-pressure chamber 18 is a compression spring 24 which loads the valve member 22 in the closing direction and acts on the valve member 22 on the valve seat 20, so that this connection of the control pressure chamber 15 is closed in the normal position of the control valve. Since the front surface of the valve needle 3 is larger in the area of the control pressure chamber than the surface of the pressure shoulder 11, the same fuel pressure in the control pressure chamber that also prevails in the pressure chamber 8 now holds the valve needle 3 in the closed position. If the valve member 22 is lifted off, however, the pressure in the control pressure chamber 15 decoupled via the throttle connection 16 is relieved. If the closing force is now missing or reduced, the valve needle 3 opens quickly against the force of a closing spring and, on the other hand, can be brought into the closed position as soon as the valve member 22 comes back into the closed position, since from this point on the throttle connection 16 is the original high fuel pressure then quickly rebuilds in the control pressure chamber 15.

The control valve according to the invention has a piston 25 intended for its actuation, which acts on the valve member 22 and can be actuated by a piezo actuator 32 (not shown in detail). The piston 25 is tightly guided in a guide bore 28 arranged in a housing part 26 of the fuel injection valve and, as can be seen in FIG. 2, delimits, with its end face 29, a coupling space 30 which on its opposite wall has an actuator piston 31 with a larger diameter in a bore 65 is completed, which is part of the piezo actuator 32 and which can also be non-positively coupled to the piezo actuator 32 by a spring washer 66 arranged in the coupling space 30. The actuator piston can be returned together with the piezo actuator 32 in another suitable manner. Both pistons 25 and 31 are tightly guided in their bores. Due to the different piston surfaces of the two pistons 25 and 31, the coupling space 30 serves as a translator space by translating a design-related small stroke of the piezo actuator piston 31 into a larger stroke of the piston 25 actuating the control valve 21. When the piezo actuator 32 is excited, the piston 25 is adjusted such that that the valve member 22 lifts from its seat 20. This results in a relief of the control pressure chamber 15, which in turn causes the valve needle 3 to open.

2 shows the coupling space 30 and the two pistons 25 and 31 detached from the valve housing 1. There are provided in the housing part 26 of the low pressure spaces 18 on the side of the piston 25 and a low pressure space 33 on the side of the piston 31 remote from the coupling space 30. The cylinder bores for the pistons 25 and 31 have gaps 35 and 36 of a width s ₁ and s ₂ , via which the low-pressure spaces 33 and 18 are connected to the coupling space 30. The length of the gap 35 is denoted by l ₁ and that of the gap 36 by l ₂ and the diameter of the piston 31 is d ₁ and that of the piston 25 is d ₂ .

To actuate the valve member 22, the piezo actuator 32 is excited and the actuator piston 31 is subsequently adjusted. This leads to an increase in pressure in the coupling space 30, which in turn results in an adjustment of the piston 25 together with the valve member 22. Because of the different diameters of the pistons, the piston 25 moves further than the actuator piston 31. The pressure increase in the coupling space leads to leakage losses in the coupling space fluid via the leakage gaps between the pistons 25 and 31 and their guidance in the bores. However, the time in which there is a high pressure in the coupling space for actuating the valve member is short in comparison to the times, the load pauses which lie in between.

So that the coupling space 30 is not pumped empty over the gaps 35 and 36 in the event of a high pressure in the coupling space that arises during the work of the valve, the invention makes it possible, in the load pauses, to achieve a rapid refilling of the coupling space 30 in order to compensate for any loss of fluid that has occurred, even at relatively low pressures in the low-pressure spaces 18 and 33. This is favored by the fact that the actuator piston moves back with the piezo actuator when not energized. This is advantageously supported if the actuator piston is subjected to a restoring force towards the piezo actuator, which is preferably provided by the spring 57 which is supported in the coupling space.

• d = mittlerer Kolbendurchmesser in mm
• s = Spaltgröße in µm
• l = Dichtspaltlänge in mm,
• n = die Anzahl der Dichtspalte bzw. Kolben und
• V₀ = das Ausgangsvolumen des Kopplungsraumes in mm³ sind,

besser noch ein Verhältnis: $$\frac{{\text{n · d · s}}^{\text{3}}}{{\text{V}}_{\text{0}}\text{.l}}\text{≥ 8}$$ For this refilling, the two pistons 25 and 31 and their guides have to be designed geometrically in a special way in order to achieve an optimal working capacity of the arrangement and a repeated production of the filling volume of the coupling space 30. A geometric ratio according to the following equation should be aimed for as a leak rate characteristic: $$\frac{{\text{n · d · s}}^{\text{3}}}{{\text{V}}_{\text{0}}\text{.l}}\text{≥ 4}$$ wherein

• d = average piston diameter in mm
• s = gap size in µm
• l = sealing gap length in mm,
• n = the number of sealing gaps or pistons and
• V ₀ = the initial volume of the coupling space in mm ³ ,

better still a ratio: $$\frac{{\text{n · d · s}}^{\text{3}}}{{\text{V}}_{\text{0}}\text{.l}}\text{≥ 8}$$

From such a ratio, the fastest possible refill is given without tolerances, in particular in columns 35 and 36, having a greater influence on the duration of the refill. It follows from the above relationship that the gap and the piston diameter tend to be large and the initial volume and the length of the sealing gaps are to be chosen small. However, this leak rate characteristic value of ≥ 8 should not be chosen too large, since otherwise the leak rate will become too large and the coupling function, ie the hydraulic stiffness of the coupling space filling volume and thus the stroke, will decrease. In order to keep the stiffness of the coupling space 30 necessary for switching the valve as large as possible, the output volume V _{0 of} the coupling space must be as small as possible.

For reasons of guiding accuracy and the gap geometry to be kept constant, the gaps 35 and 36 should not be too large and the piston lengths l ₁ and l ₂ should not be chosen too small for the two pistons 25 and 31 and the characteristic value should nevertheless be selected $\frac{{\text{n · d · s}}^{\text{3}}}{{\text{V}}_{\text{0}}\text{.l}}$ ≥ 4, then can be used for the pistons 25 and 31 types, as shown in Figures 3, 4 and 5 and in which the hydraulically effective sealing gap length is reduced, ie is limited to a short length defining the above characteristic value.

A piston 37 is shown in FIG. 3, the length dimension 1 of which is interrupted twice by ring grooves 38 and 39 in order to obtain guide parts which are far apart in the case of a short sealing gap length, as a result of which the guide accuracy is increased. The gap lengths lying between the annular groove 39 and 38, the low pressure chamber 18 or 43 and the coupling chamber 30 are shorter than the original total length of the piston. This results in a more favorable geometric ratio for the filling according to the above formula for the leakage rate value with very good guidance accuracy.

In the design according to FIG. 4, a piston 40 has an annular groove 41 which is arranged close to the coupling space 30 and thus defines a short effective gap length l _w . This short gap length is only included in the result value according to the above formula. The piston part following this effective gap length serves as a necessary guide part, but has no influence on the value resulting from the above formula. In this way, the favorable value for refilling during the rest periods can be achieved in a simple and safe manner.

Finally, FIG. 5 shows a piston 42 which, based on the embodiment according to FIG. 4 with a short sealing gap length, is modified in accordance with the piston 40 in that here one or more lateral grooves 43, which correspond to the annular groove 41 from FIG Remove flats 44 towards the end of the piston. With such a design, the very short gap length l _{w is} achieved, which fulfills the above requirement, and yet the guidance of the piston 42 is relatively long and therefore precise. The column width formed by the annular groove 43 and the lateral flats 44 is hydraulically so large that it is ineffective for a sealing function, and the piston part determined by its length only acts as a piston guide and is not included in the result of the leak rate characteristic value. The flattened area 44 is to be regarded as a pressure medium channel through which the annular groove 43 is supplied with pressure medium from the adjacent low-pressure space. However, this flattening can also be realized in a different form, for example as a bore or another type of channel between the annular groove 43 and the low-pressure space.

FIG. 6 shows a diagram which, on the basis of three curves 45, 46 and 47, shows the different duration of the refilling in relation to the length of time the working pressure is present in the coupling space and at different ambient pressures. A time ratio is plotted on the ordinate, which is determined by the time required to couple the coupling space to a certain pressure, for example 90% of the ambient pressure and the values of the leakage rate parameter, which arise from different parameters and two columns, ie two pistons, the pistons 25 and 31, from the above formula. It can be seen that the refilling takes place faster and more cheaply in the case of large columns, ie as the values resulting from the above formula become larger. Conversely, if the leakage rate is <4 times, there are infinite times. The pressure that prevails in the low-pressure chamber is also important. With increasing pressure there is a faster refilling.

FIG. 7 shows a design with 3 pistons, specifically with the actuator piston 31 already described and with the coupling space 30. Here, however, a piston actuating the control valve 21 is designed as a stepped piston, which is provided with two pistons 49 and 50. Accordingly, there are a total of 3 columns through which liquid can escape from the coupling space and through which the coupling space 30 must be refilled. The refilling according to the invention can also be used for such a type. It can also be used for devices with more than three pistons.

In an injection system, as is shown in simplified form in FIG. 8, one injection valve 51 is used per engine cylinder, as has already been dealt with on the basis of FIG. The injection valve 51 is connected on the one hand via a supply line 52 to a high-pressure accumulator 53 and on the other hand via a return line 54 to a low-pressure container 55 (tank). The injection system also includes a fuel pump 56, a high-pressure pump 57, an overflow valve 58, a pressure control valve 59, a pressure limiter 60, a flow limiter 61 and an electronic control device 62.

According to the invention, a pressure-maintaining valve 63 is now inserted in the return line 54, which is led from the injection valve 51 to the container 55, and is set to a pressure of 10 to 20 bar. The return line 54 must then be made correspondingly stable. In the injection valve 51, as already described, the two low-pressure spaces 18 and 34, which lie on the two sides of the actuator piston 31 facing away from the coupling space 30 and of the piston 25 actuating the valve member 22, are connected to the low pressure, and this low pressure is now achieved by the pressure control valve 63 at an elevated level of, for example Held 10 to 20 bar.

Such a measure then brings about a rapid refilling of the coupling space 30 via the columns 35 and 36 (cf. FIG. 2) according to the equation $$\text{Q =}\frac{{\text{π · d · s}}^{\text{3}}}{\text{12 · η · l}}\text{· (P0 - Pkopp)}$$ where Q is the flow rate, d the piston diameter, s the gap dimension and η the dynamic viscosity and l the leakage gap length.

The use of a retention valve 63 is particularly recommended if the pressure difference between the pressure in the coupling chamber 30 which has dropped to about 0 bar after the actuator stroke and the ambient pressure of 1 bar until the next injection process of the internal combustion engine (for example 25 ms at an engine speed of 4800 rpm). is not sufficient for refilling the coupling space 30. With the differential pressure increased to 10 to 20 bar, the coupling space 30 can be refilled with certainty in the short time available. The advantage here is that only a single pressure control valve 63 is required per motor.

Claims (7)

1. Valve for controlling liquids, with a valve member (22), which is actuatable, counter to the force of a spring (24), by a piston (25), which, with its end, closes off a hydraulic coupling chamber (30) as a moveable wall, which hydraulic coupling chamber (30) is bounded at the other end by the end of an actuator piston (31), which has a larger diameter than that of the piston (25) and is part of a piezoelectric actuator (32), by means of the working stroke of which an increase in the pressure in the coupling chamber (30) can be produced, by means of which the piston (25) can be adjusted counter to the force of the compression spring (24), and with respective low-pressure chambers (18 and 33) on the side of the actuator piston (31) and the side of the piston (15) that actuates the valve member (32) which face away from the coupling chamber (30), in which chambers a leakage-oil pressure prevails, and with a gap (36) located between the outer circumference of the piston (25) and a guide bore (28) and a gap (35) located between an outer circumference of the actuator piston (31) and a bore (65), the said bores guiding these pistons, the gaps being dimensioned in such a way that whenever there is no pressure increase in the coupling chamber (30), the coupling chamber (30) is refilled from the low-pressure chambers via the said gaps (28 and 65) to compensate for leakage losses via these gaps into the low-pressure chambers that occur during pressure-increasing periods,
   characterized in that, for refilling, the following geometric relationship is adhered to for the length and width of the gaps, based on the largest volume occupied by the coupling chamber in the times during which there are no pressure increases: $$\frac{\mathit{\text{n}}\text{·}\mathit{\text{d}}\text{·}{\mathit{\text{s}}}^{\text{3}}}{{\mathit{\text{V}}}_{\text{0}}\text{·}\mathit{\text{l}}}\text{≥ 4, preferably ≥ 8}$$ in which V₀ is the volume of the coupling chamber (30) in mm³, n is the number of gaps that lead away from the coupling chamber (30), s is the width of the gaps in µm, l is the length of the gap in mm, and d is the mean diameter of the pistons in mm.
2. Valve according to Claim 1, characterized in that the piston (25) for actuating the valve member (22) and/or the actuator piston (31) is/are subdivided along the length of its/their guidance in the bore (28) and/or the bore (65) by at least one annular groove (38, 39, 41, 43).
3. Valve according to Claim 2, characterized in that between the coupling chamber (30) and the at least one annular groove (41, 43), a short gap length l_w is defined, which complies with the geometric relationship, and the parts of the piston located on the far side of the at least one annular groove (41, 43) are embodied as parts (40, 42) used for guidance.
4. Valve according to Claim 3, characterized in that, between the at least one annular groove (43) and the side of the piston (42) facing the low-pressure chamber (18, 34), a pressure-fluid conduit (44) is provided, by which the annular groove is supplied with pressure fluid in an unrestricted manner.
5. Valve according to one of the preceding claims, characterized in that the pressure in the low-pressure chambers can be held at a certain level, which is raised compared to the ambient pressure.
6. Injection system with a high-pressure pump, a high-pressure reservoir, and a low-pressure container, with a valve according to Claim 5, characterized in that on the low-pressure side, which is connected to the low-pressure container (55) and to the low-pressure chambers (18, 33) of the valve, a pressure-holding valve (63), which is set to a pressure of over 1 bar, is inserted into a return line (54) (Figure 8).
7. Injection system with a high-pressure pump, a high-pressure reservoir, and a low-pressure container, with a valve according to Claim 5 or 6, characterized in that the operative pressure in the low-pressure chambers (18, 33) is set to from 10 to 20 bar.