WO1994019598A1

WO1994019598A1 - Device for opening and closing a through-hole in a housing

Info

Publication number: WO1994019598A1
Application number: PCT/DE1994/000213
Authority: WO
Inventors: Andreas Kappel; Randolf Mock; Hans Meixner
Original assignee: Siemens Aktiengesellschaft
Priority date: 1993-02-26
Filing date: 1994-02-28
Publication date: 1994-09-01
Also published as: DE4306072C2; DE4306072A1

Abstract

A device is disclosed for opening and closing a through-hole in a housing. It is not possible to prepare an optimum mixture with electromagnetically controlled injection valves, as the mass inertia of their movable parts and the intrinsic inductivity of the electromagnet allow only minimum opening and closing times of about 1 to 2 ms. The minimum opening time determines however the smallest dosable amount of fuel, so that in particular in instationary states of operation of the engine and during idle running considerable dosing errors are inevitable. The object of the invention is to create an injection valve which allows very short opening and closing times even at high operation frequencies. The disclosed injection valve contains in particular a piezoactuator (P) arranged in a housing (VG), a stroke transformer which consists of a pressure piston and an alternating piston (DK, HK), a valve lifter (VS) linked to the alternating piston (HK) and a closing spring (SF) which presses the valve disk (VT) in the state of rest against the valve gasket (VD). The compensation chamber (AK) in communication with the hydraulic chamber (KA) through a ring-shaped gap (SP) located between the alternating piston (HK) and the housing (VG) is filled with a medium under overpressure. Since a membrane (M) transfers the overpressure accumulated in the compensation chamber (AK) to the hydraulic fluid (FL), no gas bubbles that could reduce the operating frequency of the valve can be formed there. The invention has applications in fuel injection valves and in check valves for water hammer injection systems.

Description

Device for opening and closing a passage opening in a housing

The operating behavior of an internal combustion engine depends crucially on the quality of the mixture spreading. For example, the pollutant emissions and the fuel consumption of the engine can be significantly reduced by metering the fuel to the intake air in accordance with the respective operating state. This applies in particular to a motor vehicle internal combustion engine equipped with a regulated three-way catalytic converter. The catalyst used to reduce pollutant emissions only works in a very small air ratio range with high efficiency. In order to ensure a maximum degree of conversion, the air / fuel ratio in any operating state of the engine may therefore only deviate by a few percent from a target value representing the respective optimum.

Electromagnetically driven injection valves do not allow optimal mixture preparation, since they allow only minimal valve opening and closing times of approximately 1 to 2 ms due to the inertia of the moving parts and the self-inductance of the electromagnet. However, the minimum opening time determines the smallest amount of fuel that can be metered, so that it is not possible to maintain the correct air ratio λ, particularly in the stationary operating states of the engine, in the part-load range and in the course with the injection valves currently available on the market. In order to avoid considerable incorrect metering, valves are therefore required whose opening and closing times are in the range of approximately 0.1 to 0.2 ms.

The principle of pressure surge injection is based on the conversion of kinetic energy into pressure energy caused by the rapid closing of a shut-off valve. As a result of Abrupt deceleration of the fuel flowing in the flywheel line of a pressure surge injection system creates a pressure wave which propagates at the speed of sound up to an injection nozzle designed in the manner of a pressure relief valve, where it causes the fuel to be injected.

With the aid of the pressure surge injection technology, high injection pressures and very good aerosols can also be generated with a fuel supply designed primarily on the low pressure technology side. It is also particularly suitable for applications in modern stratified charge engines, since it enables direct injection and ensures a high speed of the jet front of the fuel-air mixture in the combustion chamber. With the pressure surge injection, the emission of gaseous pollutants and the fuel consumption of two-stroke and

Four-stroke engines are significantly reduced and their torque curve is improved. However, these advantages cannot be fully exploited in practice, since the response time of the shut-off valves used in conventional systems, which is in the range of 1 to 2 ms, is too large by a factor of 10.

The invention is based on the object of a compactly constructed, reliable and low-wear device for opening and closing an existing device in a housing

Specify passage opening. The device should have very good dynamic properties and enable very short opening and closing times, even at high operating frequencies. This object is achieved according to the invention by a device according to claim 1.

The invention enables the construction of fuel injection valves which have opening and closing times in the range of τ <0.1 ms even at high operating frequencies of f> 500 Hz. enable. With these valves, therefore, even the smallest amounts of fuel can be metered precisely and reproducibly. In addition, the very short opening and closing times a defined beam construction and demolition. The device according to the invention can in particular also be used as a shut-off valve in a pressure surge injection system.

The dependent claims relate to advantageous developments and refinements of the invention explained below with reference to the drawing. Here shows:

1, 3 and 4 embodiments of a fuel injection valve. FIG. 2 the hydraulic stroke transformer of the injection valve. FIG. 5 the pistons of the hydraulic stroke transformer. FIG. 6 the schematic structure of a pressure surge injection system. FIGS. 7 and 8 shut-off valves the pressure surge injection system

1 shows the schematic structure of a fuel injection valve, which contains a piezoelectric actuator P acting as a drive unit on a hydraulic stroke transformer DK, KA, FL, HK. To produce relatively large

Primary strokes at moderate operating voltages are particularly suitable for piezoelectric multilayer stacks, since they enable relative changes in length of approximately Δl / 1 = 1 10 "3 with drive forces of typically F = 100 to 10,000 N.

Due to the high mechanical rigidity of the piezoelectric sintered body, their electromechanical resonance is in the range from 10 to 1000 kHz, so that response times of approximately 0.001 to 0.1 ms can be achieved in principle. However, the response times that can be achieved in practical operation are longer and depend, among other things, on the electrical activation and connection of the piezo stack and on the size of the masses to be moved. Since the electrical capacitance Cp of the piezostack is typically in the range of approximately Cp = 1 to 10 μF and the internal resistance R ^ of the voltage source assigned to the stack is approximately Rj_, _ 1 to 10 Ω values, the values for the charging time constant defined by T = Cp x R _j are approximately τ = 1 to 100 με. The response times of the piezo stack are thus 1 to 2 orders of magnitude lower than those of comparable electromagnetic drives, which, in conjunction with a compact valve structure and small moving masses, enables extremely short valve opening and closing times.

The injection of the fuel K supplied via the feed line Z into an engine compartment (not shown) is carried out by lifting the valve plate VT from the valve sealing seat VD present in the housing VG. This is done by electrical control of the piezo actuator P, the axial length change of which is transmitted to the piston DK, which is sealed in a housing bore, and which thereby generates an overpressure in the chamber KA filled with a hydraulic fluid FL. If the force transmitted by the hydraulic fluid FL to the reciprocating piston HK, which is displaceably arranged in a second cylinder bore, is greater than the restoring force exerted by a closing spring SF, the plunger VS connected to the reciprocating piston HK lifts the valve plate VT from the sealing seat VD and the injection process begins. The fuel injection is ended by the electrical discharge of the piezo actuator P. As a result of the associated contraction of the actuator P, the pressure piston DK moves back down to its rest position under the force of the restoring force exerted by a strong plate spring TF, which in the Hydraulic chamber KA creates a negative pressure. Supported by the closing spring SF, the reciprocating piston HL and the plunger VS thus likewise perform a downward movement, as a result of which the valve disk VT lowers again onto the sealing seat VD.

In order to obtain a valve characteristic that is as linear as possible, the O-ring sealed valve lifter VS is only allowed to work with a defined stroke, the valve sealing seat VD and the ceiling A of the chamber AK being used as stroke-limiting stops. ken. The chamber AK filled with a medium under pressure also receives the closing spring SF, which is preferably mounted between the chamber ceiling A and a shim PS resting on a Seeger ring SR. The Seeger ring SR also serves as a bearing for the membrane M clamped between the valve tappet VS and the chamber bottom, which prevents mixing of the pressure medium present in the chamber AK with the hydraulic fluid FL emerging from the stroke transformer.

In particular, the injection valve according to the invention is characterized by the following properties and design features:

As shown in FIG. 1, the actuator P carrying out only small axial changes in length lies with its end faces on the pressure piston DK or on the support bearing PL of the housing VG. In order to largely avoid stroke losses due to the non-parallelism of the piezo end faces due to manufacturing, the bearing PL is designed in the form of a spherical washer / conical socket arrangement. The bearing PL can be attached to the housing VG or to the pressure piston DK.

The force exerted by the actuator P is transferred to the pressure piston DK, which is sealed in the hydraulic chamber KA. A commercially available sealing element, for example an O-ring OR, ensures the sealing of the pressure piston DK. However, membrane seals made of metal or rubber can also be used, since the pressure piston DK only executes the small primary stroke of a few μm generated by the actuator P.

The required transient mode of operation of the valve makes it necessary to mechanically pretension the piezo actuator P with the aid of a spring element TF. A disk spring is used as the spring element TF in the exemplary embodiment shown, since it can be used to generate the required pretensioning forces in the smallest space. In terms of valve dynamics should all driven parts, in particular also the spring element TF, have the lowest possible mass. This requirement can be taken into account by using aluminum or titanium instead of steel and / or by suitable shaping of the respective parts. Since the spring mass has to be added to about a third of the mass to be driven, disc springs are preferable to the much heavier spiral compression springs. Since the plate spring TF should both generate the mechanical pretension for the piezo actuator P and also support the return of the pressure piston DK in its rest position, it is preferably between a Seeger ring with a fitting washer SR ', PS' on the pressure piston DK. and a projection of the housing wall is clamped. The opening and closing times of the valve can be largely metrized by coordinating the mechanical properties of the disc spring TF and the spiral compression spring SF used for returning the reciprocating piston HK. Coordinating the spring constants also has the advantage that the tensile stresses that occur in the hydraulic fluid FL when the valve is closed are also minimized, which in turn reduces the risk of cavitation occurring.

In principle, it would be possible to transfer the stroke generated by the actuator P directly to the valve lifter VS. However, this construction would have a number of disadvantages. Because of the rigid connection between the drive element P and the valve tappet VS, it would be very difficult to ensure sufficient tightness of the valve in the event of temperature-related length changes and manufacturing-related tolerances of the components over the desired working temperature range and at the same time also for a sufficiently high preload of the piezo stack P. In addition, a very long piezo actuator P would be required to generate the stroke of approximately 0.1 to 0.5 mm required for a large linear working range of the valve. A hydraulic valve known from EP-A-477 400 is therefore contained in the injection valve according to the invention. built-in stroke transformer with integrated adaptive tolerance compensation to amplify the actuator stroke. The step-up ratio of the stroke transformer shown in FIG. 2 is given in a good approximation by the ratio η: = (Ap / An) of the cross-sectional areas A- ^ and AJJ of pressure piston DK and stroke piston HK and can be the desired valve strokes Adjust x _H = η »X * o _β 100 μm (x _D : stroke of the pressure piston DK) within wide limits.

Compared to a purely mechanical translation

(Lever system), the hydraulic stroke transformer allows a very compact, rotationally symmetrical structure, large transmission ratios and the transmission of very large forces. Due to the small moving masses, it also exhibits good dynamic behavior. When using suitable hydraulic fluids FL, such a drive is extremely reliable and largely maintenance-free. In addition, the hydraulic power transmission enables the integration of an adaptive tolerance compensation, which makes the system insensitive to the drift phenomena caused by temperature, pressure, vibrations, etc.

As shown in FIG. 2, the mechanical tolerance compensation can be achieved in a simple manner in that the lifting piston HK is guided in a clearance fit and only the pressure piston DK is hermetically sealed by means of an O-ring OR. The gap SP remaining between the reciprocating piston HK and the cylinder bore then, given suitable dimensioning of the gap length 1 and the gap width s, then represents a large flow resistance. It leaves the thermal expansion or contraction of the hydraulic fluid FL, the housing VG or others Component-induced compensatory processes between the hydraulic fluid FL inside and outside the hydraulic chamber KA without impairing the functioning of the valve drive. Due to the gap losses occurring during the opening period of the valve (hydraulic fluid FL flowing out of the chamber KA into the oil reservoir formed by the membrane M), the valve tappet VS cannot be kept statically open for any length of time. In practice, however, this does not have a disruptive effect, since the maximum opening times of motor vehicle fuel injection valves are in the range of approximately 10 ms. In addition, the maximum opening time can be set according to the respective requirements in a wide range from a few milliseconds to a few minutes by coordinating the reciprocating piston length 1, the gap width s, the spring constant of the closing spring SF and the viscosity of the hydraulic fluid FL.

Gas bubbles in the hydraulic fluid FL of the stroke transformer would greatly reduce the maximum working frequency of the injection valve, since a new injection process could only be initiated after the gas bubbles had completely dissolved. Measures are therefore provided in the injection valve according to the invention to avoid the cavitation bubbles which are generally only triggered by tensile forces in the hydraulic fluid FL when the valve is closed.

By pressurizing the hydraulic fluid FL, cavitation bubbles can be completely avoided in all occurring operating states, pressures of the order of magnitude of 0.01 MPa to 1000 MPa being required depending on the application. The overpressure in the hydraulic fluid FL is advantageously generated with the aid of the chamber AK, which is connected to a compressed gas reservoir via the connection AS (see FIG. 1). Alε compressed gases come in particular inert gases such. B. argon (Ar), nitrogen (N2) or chemically less reactive Gasgemiεche such as carbon dioxide (CO2) or chlorofluorocarbons (CFCs) into consideration. The one located in the chamber AK between the valve tappet VS and the chamber bottom

Membrane M ensures that the compressed gas is not in the Hydraulic fluid FL dissolves. It also prevents the hydraulic fluid FL from leaking.

If the system is sufficiently leakproof, the chamber AK can also be separated from the gas supply under excess pressure and the connection AS can be tightly closed. The chamber AS, which is under overpressure, then performs the function of a gas pressure accumulator together with the membrane M itself.

It is also readily possible to connect the chamber AK to the pressure oil circuit of the engine, which is present. In this case, the membrane M can possibly also be omitted or replaced by a particle filter. In order to expel any gas bubbles that may still be present, it is then expedient to additionally provide a second connection serving as a drain in the chamber AK and to conduct a continuous oil flow through the chamber AK.

The injection valve can be simplified by connecting the chamber AK to the low-pressure fuel supply. In this embodiment shown in FIG. 3, no tappet seal SD is required. In addition, there is no separate fuel supply Z.

The arrangement of a compressible body (gas pressure accumulator) in the chamber AK comes into consideration when the latter is completely filled with a liquid pressure medium (fuel, oil). This measure improves the dynamic behavior of the valve, since the liquid displaced by the reciprocating piston HK only causes a slight compression of the gas pressure accumulator and does not generate excessive back pressures in the hydraulic fluid FL or counterforces on the reciprocating piston HK. Closed-cell, oil, fuel and temperature-resistant foams based on polyurethane, polyethane, polyester, natural rubber, chlorobutadiene, vinyl, polyvinyl chloride, polyimide or composite foams made from these are particularly suitable as gas pressure accumulators Components εo- like rubber bubbles. It is also possible to implement the gas pressure accumulator by means of a spring-loaded membrane integrated in the wall of the chamber AK.

Depending on the height of the overpressure generated in the chamber AK, the plate spring TF can be omitted or dimensioned weaker, since the chamber liquid already causes the pressure piston DK to return to the starting position and places the actuator P under a mechanical pretension .

A significant reduction in the mass of the pressure piston DK can be achieved by moving the plate spring TF into the hydraulic chamber KA (see FIG. 4). In order to enable fluid exchange between the chamber areas separated by the plate spring TF, compensation channels or bores must be provided on the bearing surfaces of the plate spring TF on the chamber bottom or on the pressure piston DK. Of course, it is also possible to use a pierced plate spring TF.

The proposed design measures place increased demands on the axial symmetry of the individual valve components, since otherwise the pistons DK, HK may become jammed. This applies in particular to the multiple plunger VS of the injection valve shown in FIG. 1. Such effects can largely be avoided if pistons with convexly curved side surfaces are used instead of cylindrical pistons (see FIG. 5). This measure ensures that even larger decentrations of the moving components with respect to the housing bores and guides do not impair the functioning of the valve.

An essential component of the pressure-injection injection system shown schematically in FIG. 6 is the shut-off valve AV, the opening of which is controlled by a drive element. injection process initiates. As a result, the fuel K sucked from the storage tank KR by the pressure supply unit DV via the pipeline SG is accelerated in the flywheel line SL in order to return to the storage tank KR after passing through the shut-off valve AV via the throttle DR and the pipeline RL to flow back. The rapid closing of the shut-off valve AV has the result that a pressure surge dependent on the momentary flow velocity of the fuel K in the flywheel line SL builds up, which propagates via the injection line EL to the injection nozzle ED and, when the closing pressure of the spring-loaded valve needle is exceeded, for spraying of fuel K leads. The so-called vibration damper ST serves to suppress undesired reflection pressure waves.

The shut-off valve of the pressure surge injection system shown in FIG. 7 essentially consists of the valve body VG in the form of a flow tube, a controllable closable drainage channel R and other components, the structure and mode of operation of which are already described with reference to FIGS. 1 to 5 were. Thus, the valve disk VT, by elek¬ tric actuation of the piezo actuator P through the intermediary of hydrauliεchen stroke transformer and befe¬ stigten the reciprocating plunger HK VS from Ventilεitz VD lifted and connected the ^* with the chamber AK spillway R are released. The shut-off valve allows the drain channel R to be closed very quickly, the closing times being in the range of fractions of a millisecond. As a result of the sudden deceleration of the fuel, there is a pressure surge DS, which propagates at the speed of sound and leaves the valve body VG in the direction of the injection nozzle ED.

In the embodiment of a shut-off valve shown in FIG. 8, the channel R for the fuel outflow is completely separated from the chamber AK filled with a pressurized hydraulic oil by means of an O-ring-sealed tappet bushing SD. In this case the chamber has AK a separate connection AS for an external oil pressure supply, for example the vehicle's own oil lubrication system. In this way, leakage losses in the tappet bushing and the pressure piston seal OR can be compensated for. In addition, a seal (membrane M) between the hydraulic chamber KA and the lifting transformer can be dispensed with.

The invention is, of course, not limited to the exemplary embodiments described. Thus, instead of a piezoelectric actuator, it is also possible to use electrostrictive or magneto-restrictive actuators as drive elements. All of the described embodiments have a rotationally or axially symmetrical structure. Of course, this can of course also be deviated by constructing the lifting transformer spatially distributed and connected to one another via liquid lines pressure chambers. In this case, however, a loss of functionality must be accepted.

Claims

Claims:

1. Device for opening and closing a passage opening present in a housing, characterized by a first housing chamber (KA) formed by a first bore and a first piston (DK) slidably arranged in the first bore, the first housing chamber ¬ mer (KA) is filled with a hydraulic fluid (FL), - a driving element (P) acting on the sealed-in first piston (DK), a second housing chamber (AK) filled with a medium under pressure, one the first and the second housing chamber (KA, AK) connecting a second bore, a second piston (HK) displaceably arranged in the second bore, the cross-sectional area of which is smaller than the corresponding cross-sectional area of the first piston (DK) and a plunger element ( VS), that a displacement of the second piston (HK) caused by the drive element (P) and the first piston (GK) to a rear position llelement (SF) and a closing element (VT) assigned to the passage opening.

2. Device according to claim 1, so that the housing chambers (KA, AK), the pistons (DK, HK) and the second bore each have an axially symmetrical structure.

3. Device according to claim 1 or 2, g e k e n n z e i c h n e t d u r c h a gap (SP) or channel connecting the first and the second housing chamber (KA, AK).

4. Device according to one of claims 1 to 3, characterized by a sealing element (M) resting on the wall of the second housing chamber (AK) on the drive side.

5. The device according to claim 4, a membrane (M) as a sealing element.

6. Device according to one of the claims 1 to 4, so that the medium that is under overpressure is a gas or a liquid.

7. The device according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the pressurized liquid is a hydraulic oil or a Kraftεtoff.

8. Device according to one of claims 1 to 6, so that the second housing chamber (AK) has a connection (AS) for supplying the medium under pressure and the passage opening.

9. Device according to one of claims 1 to 8, a pressure in the second housing chamber (AK) arranged in the second housing chamber (AK).

10. Device according to one of the claims 1 to 9, a piezoelectric, electrostrictive or magnetoεtrictive actuator (P) as drive element.

11. The device according to claim 10, characterized by an actuator bearing (PL) consisting of a spherical disk / conical socket arrangement.

12. Device according to one of the claims 1 to 11, g e k e n n e e i c h n e t d u r c h a spring element (TF) acting on the drive element (P) and / or the first piston (DK).

13. The apparatus of claim 12, d a d u r c h g e k e n n z e i c h n e t that the spring element (TF) is arranged in the first housing chamber (KA).

14. The apparatus of claim 12 or 13, g e k e n n z e i c h n e t d u r c h a disc spring (TF).

15. Device according to one of claims 1 to 14, d a d u r c h g e k e n e z e i c h n e t that the passage opening is connected to an inflow or outflow channel (R) for a liquid.

16. Use of a device according to one of claims 1 to 15 as a fuel injection valve.

17. Use of a device according to one of claims 1 to 15 as a shut-off valve in a Druckεtoß injection system.