EP1687523B1 - Injection unit and injection method for an internal combustion engine - Google Patents

Description

The present invention relates to an injection system and a method for operating an injection system for an internal combustion engine according to the preamble of claim 1 or of claim 7.

Such injection system and such injection method are for example from DE 100 15 740 A1 or the DE 101 04634 A1 known. In this known technique, an injector assembly includes at least one servo-injector operable by a piezoelectric actuator to cause movement of a servo-valve nozzle body (nozzle needle) toward an opening of an injection passageway between a nozzle space to initiate an injection process by depressurizing a control space the servo injection valve and a combustion chamber of the respective internal combustion engine is provided.

An essential advantage of using a servo-injection valve actuated by means of a piezoelectric actuator is that with a comparatively small stroke of the piezoelectric actuator, it is possible to achieve a stroke of the nozzle body that is independent of it, generally many times greater (stroke translation). In addition, this results in the advantage that the movement of the nozzle body for opening and closing the injection passage is driven by the pressure of the fuel, which is ready for injection into the combustion chamber anyway under relatively high pressure standing in the region of the injection valve. For the activation of the Injector therefore satisfies a piezoelectric actuator with a comparatively small stroke and comparatively low actuator force.

As a rule, a piezoelectric actuator has a stack of piezo elements lying on top of one another, which rapidly changes its length when an electrical voltage is applied, to an extent dependent on the voltage, among other things. Piezoelectric ceramics suitable for this purpose are known in great variety, for example as lead zirconate titanate ceramics, and are of particular interest for use in injection valves, above all because of their high rate of change and their high piezoelectric forces.

However, since the length of the piezoelectric actuator does not depend exclusively on the applied voltage, but is also subject to manufacturing tolerances and a dependence on the temperature of the actuator, in the construction of a actuated by a piezoelectric actuator servo injection valve, a more or less large gap in the path of effect Actuator provided to a control valve body, which serves as a tolerance range for unwanted deviations and / or changes in the actuator length.

On the one hand, this so-called tolerance gap in the piezo-actuated injection valve should be as small as possible in order to maximize the usable stroke of the actuator and, on the other hand, should be as large as possible in order to avoid, in all possible operating states, a change in the length of the piezoelectric actuator caused by the operation exceeds the tolerance gap and so, without the actuator is driven, already actuated the control valve. In the latter regard, for example, a particularly important thermally driven expansion of the piezoelectric ceramic at elevated actuator temperature, as may occur in particular during operation of the internal combustion engine under certain circumstances. Accordingly, the tolerance gap can hardly be dimensioned in practice "optimal".

If the tolerance gap due to a temperature increase of the actuator can be exceeded and thus the fuel from the pressure accumulator via a pressure line to the control chamber fuel via the control valve in the virtually pressureless (compared to the fuel system pressure in the pressure accumulator) Leakage line can be released, so there is still one further problematic. Namely, when the internal combustion engine is to be started in "hot state", z. B. after a previous prolonged operation with subsequent shutdown of the engine, it may be considerably more difficult or delayed due to the release of fuel from the control room in the leakage line of the pressure build-up in the pressure accumulator. The construction of a certain minimum system pressure, which is typically some 100 bar, however, is necessary in order to realize any injection from the nozzle chamber into the combustion chamber.

From the DE 199 05 340 C2 a method and an arrangement for presetting and dynamic tracking piezoelectric actuators is known in which for this purpose the piezoelectric actuator, a DC voltage is supplied, which is optionally superimposed on a pulsed drive voltage. This DC component then determines a new rest position of the actuator and can thus be used to set the idle and for tracking the idle stroke during operation.

From the DE 37 42 241 A1 a piezo control valve is known which consists of a piezo actuator arranged in a housing and a valve. By a hydraulic clearance compensation element within the control valve possible changes in length of the reference system are automatically compensated, so that with the same working stroke of the piezo actuator member always a same stroke is ensured on the valve. A disadvantage of these two approaches to solve the above-mentioned problem of the associated effort in the field of electronic devices for controlling the injector or in the injector itself.

Accordingly, it is an object of the present invention to provide an injection system and an injection method for an internal combustion engine, in which the detrimental to the operation of the injection system or the internal combustion engine effects of the tolerance gap in the servo injection valve exceeding length change of the piezoelectric actuator can be reduced or eliminated.

This object is achieved by an injection system according to claim 1 and a method for operating an injection system according to claim 7. The dependent claims relate to advantageous developments of the invention.

It is essential for the invention that in the injection system, the leakage line is provided with a controllable valve which inhibits the fuel flow in the leakage line in a controlled state or that in the injection method, an optional inhibition of the fuel flow is provided in the leakage line. When exceeding the tolerance gap by one of the actual piezo control independent length change of the actuator, hereinafter also referred to as "actuator overhang" for short, can be mitigated by the fuel flow inhibition, the negative effects of this situation in a relatively simple manner or even eliminated. If there is an actuator protrusion and the flow of fuel in the leakage line is inhibited, this results in a pressure increase in the leakage line between the location of the escapement and the leakage output of the servo injection valve. This makes it possible, on the one hand, to prevent the nozzle body from being displaced unintentionally (without active actuation of the actuator) in the direction of an opening of the injection passage by the actuator projection, which is of importance, in particular, during operation of the internal combustion engine. On the other hand, the problem of the hot start of the internal combustion engine due to the delayed system pressure build-up (in the case of temperature-induced actuator overflow) can thus be eliminated, since the pressure increase in the leakage line considerably accelerates the pressure build-up in the pressure accumulator.

Another advantage of the solution according to the invention is that it can be easily realized in the context of retrofitting, as this essentially only a modification of the leakage line arrangement, for. B. by installing another, controllable valve, and a comparatively simple modification or addition of the engine control electronics is required in which in practice often already existing sensor devices for detecting operating conditions of the internal combustion engine and / or the injection system can be advantageously shared.

Advantageously, with the invention, a steady driving readiness of a vehicle operated by means of an internal combustion engine even with possibly occurring Aktorüberstand be ensured in injectors, said hydraulic solution can be used not only in the starting phase of the internal combustion engine but also during operation to "catch" about an operational change in length of the actuator.

Of course, the measures according to the invention can be used in combination with the measures already implemented so far, such. B. with the above-mentioned active electrical adjustment or tracking of the actuator idle stroke ("active piezo contraction") or a cooling of the internal combustion engine.

In one embodiment, it is provided that the injector arrangement comprises a plurality of servo-injection valves, which are connected via the pressure line arrangement to the pressure accumulator shared for this plurality of servo injection valves. Such injection systems per se are known as so-called storage injection systems, in which work is generally carried out with very high injection pressures (for example in the range of a few 100 bar to about 1,600 bar). Such systems are known as common-rail systems (for diesel engines) and HPDI injection systems (for gasoline engines).

If the injector assembly comprises a plurality of servo-injectors, as is usually the case, then each of the plurality of leak lines could be provided with its own controllable fuel-flow-blocking valve. However, since fuel flow inhibition in the leakage line hardly affects the proper operation of a servo injection valve connected thereto in which there is no actuator overflow, it is possible to have a Simplification thereby achieve that the leakage lines of these plurality of servo-injection valves are merged and the fuel flow inhibition is provided in the merged leakage line part, so z. B. the controllable valve is arranged only in this merged leakage line part.

A simple operation of the control valve results when the piezoelectric actuator acts via a plunger on a valve body of the control valve, wherein the tolerance gap between the actuator and plunger or between the plunger and the valve body can be provided.

The effect of the fuel flow inhibition in the leakage line can be made particularly large by blocking the flow of fuel in the controlled state of the controllable valve, d. H. is completely inhibited.

In an embodiment, the injection system further comprises an electronic injection control unit for operating the injector assembly and for driving the controllable valve. In this case, the functions of the actual injection control and the control of the controllable valve for fuel flow inhibition are advantageously summarized. In this case, operating parameters needed in particular for controlling the controllable valve can be used or derived directly from the injection control.

In a preferred embodiment, the controllable valve is controlled depending on predetermined, in particular measured operating parameters of the internal combustion engine and / or the injection system. Such operating parameters can in particular the fuel pressure in the accumulator, the fuel pressure in the leakage line, the temperature in a region of the internal combustion engine or the injector, the speed of the internal combustion engine and their load or their control ("accelerator pedal position"), etc. include. Operating parameters which are representative of the state of individual or all piezoelectric actuators (eg for their temperature and / or rest length) can also be used with particular advantage. The latter parameters can be obtained indirectly, for example, from an electronic device for controlling the piezoelectric actuators (engine control unit), z. B. by detecting the electrical capacity of the actuators. Finally, suitable parameters can also be derived from the characteristic of the movement of the nozzle body which is often already detected (eg for injection quantity control) in response to a piezo control during operation of the injection system. To detect this characteristic, known servo injection valves of the type of interest here are often equipped with a sensor system sensitive to the position of the nozzle body.

In a preferred embodiment, a plurality of operating parameters, such as those mentioned above, are combined in an electronic evaluation and are generated from a pre-stored map drive signals for the one or more controllable valves for fuel flow inhibition in the leakage line and supplied for electronic control of these valves.

In one embodiment of the invention, it is provided that the controllable valve for fuel flow inhibition is controlled in the presence of a certain operating parameter state for the fuel flow inhibition and after a fixed predetermined (or alternatively according to one of the time course certain operating parameters dependent) period is brought back into hibernation. This state of rest can then be forced, z. B. for a fixed predetermined additional period of time (dead time) are maintained. With such measures, the fuel flow inhibition can be greatly limited in terms of time, so that in particular a retrofitted according to the invention system is not significantly affected in its normal function.

In another embodiment of the invention, it is provided that the fuel flow inhibition is designed such that a predetermined maximum pressure in the leakage line can not be exceeded. This could be realized, for example, by measuring the leakage line pressure and forcibly shutting off the fuel flow inhibition based on it when the maximum pressure is reached. Alternatively or additionally, however, there is the simple possibility of providing the relevant fuel flow inhibitor (valve) with a bypass or bypass line arranged in parallel, which automatically opens when the maximum pressure is reached and thus reliably prevents undesired overpressure in the leakage line. In this case, the avoidance of overpressure in the leakage line serves, in particular, for the protection of the relevant injection servo valves, the leakage path of which must not have too great a pressure to avoid damage (typically, for example, 3.5 bar).

Fig. 1

eine schematische Darstellung zur Erläuterung des Toleranzspalts in einem piezobetätigten Servoeinspritzventil, und

Fig. 2

eine schematische Darstellung einer Einspritzanlage, bei welcher eine Mehrzahl von Servoeinspritzventilen der in Fig. 1 dargestellten Art eingesetzt wird.

The invention will be explained in more detail below with reference to an embodiment with reference to the accompanying drawings. They show:

Fig. 1

a schematic representation for explaining the tolerance gap in a piezo-operated servo injection valve, and

Fig. 2

a schematic representation of an injection system in which a plurality of servo-injection valves of in Fig. 1 shown type is used.

In Fig. 1 is a part of a high-pressure injection servo valve for an internal combustion engine in its closed state shown schematically.

This high-pressure valve has a low-pressure region L communicating with a leakage line (not shown) and a high-pressure region H connected to a pressure accumulator via a pressure line (not shown). These two acted upon with different pressure areas L, H are separated by a control valve, which is formed by a control valve seat S and a driven by the high pressure in the high pressure region H against the control valve seat S control valve body K.

The high-pressure region H forms a control chamber, not shown, or is connected to such a control chamber, in which the prevailing pressure on the rear (upper) end of an axially movably mounted and guided nozzle body (nozzle needle) acts to a front (lower) end of this nozzle body against an injector valve seat (not shown) to urge and so close to a combustion chamber of the engine leading injection passages. Although the front end of the nozzle body is located in a nozzle space which is also under high pressure, so the nozzle body in the illustrated state of rest is still pushed down to close the injection passages, since the nozzle body downward urging force due to a relatively large sized cross-sectional area of the nozzle body at its upper end is greater than the force acting at the lower end of the nozzle body force. To initiate an injection process, the pressure in the control chamber or in the high-pressure region H is reduced in the manner described below in order to cause a movement of the nozzle body in the direction of an opening of the injection passage.

The pressure reduction in the high-pressure region H takes place by controlled opening of the control valve formed by the valve seat S and the valve body K by means of a piezoelectric actuator P, which is surrounded by a housing G in the low-pressure region L and is provided with electrical connections A for driving it. By applying a voltage to the terminals A of the actuator P, the actuator length can be extended in the direction of the arrow VR (preferential polarization of the piezoelectric ceramic) to act on the valve body K via a plunger T. Between the actuator P and the plunger T in this case a tolerance gap d is provided which serves as a safety margin for thermal changes in length of the piezoceramic and typically z. B. has a dimension between 3 and 5 microns. Now step on the piezoelectric actuator P, z. B. due to adverse environmental influences, length changes that go beyond the extent of this gap d, the actuator P presses already in the resting state on the plunger T on the valve body K what, ultimately leading to leakage of fuel from the high pressure area H in the Low pressure range L and the connected leakage line leads. During operation of the internal combustion engine, this "actuator overhang" means an opening tendency for the servo injection valve, even if this is not actively driven electrically via the terminals A. In the case of a hot start of the internal combustion engine, this means that the pressure build-up in the accumulator can not or can not be built up quickly to an extent that is required for the beginning of the fuel injection.

However, these problems are avoided by the following with reference to Fig. 2 described construction of an injection system, in which, in particular on detection of such Aktorüberstands out the hydraulic pressure in the low pressure region L is temporarily increased.

Fig. 2 shows an injection system 10 for an internal combustion engine (not shown), comprising a pressure accumulator 12 for storing by means of a high pressure pump 14 from a fuel tank 16 in the pressure accumulator 12 funded fuel and via a pressure line assembly 18 connected to the pressure accumulator 12 injector 20 for injecting the fuel in the internal combustion engine. In the illustrated embodiment, the injector 20 consists of four servo injection valves, which are supplied via four separate pressure lines 18 from the pressure accumulator 12 provided together for this purpose with fuel.

Each of the servo-injectors is hereby referred to with reference to Fig. 1 explained design and has a control chamber and a nozzle chamber, both of which are supplied via the respective pressure line with fuel from the pressure accumulator 12, said fuel is under the provided by the high-pressure pump 14, high system pressure. Servo injection valves of this type are well known to those skilled in the art, so that can be dispensed with a more detailed explanation here.

As already related to Fig. 1 described, an injection process is initiated in each case by reducing the pressure in the control chamber of the respective servo injection valve, which is provided for this purpose with a piezoelectrically actuated control valve for releasing fuel from the control chamber into a leakage line 22.

In Fig. 2 Further, one recognizes two fuel filters 24 and 26 for coarse and fine filtering of the fuel, which is conveyed via a prefeed pump 28 to an input of the high pressure pump 14, a high pressure line 30 for promoting the pressurized system pressure from the high pressure pump 14 into the accumulator 12, a High-pressure sensor 32 for measuring the pressure in the pressure accumulator 12, a fuel return line 34 from the high-pressure pump 14 for removing excess fuel from the pump 14 to the leakage line 22 and thus further back into the fuel tank 16, and an electronic engine control unit ECU with a number of input terminals 36 and a number of output terminals 38, by means of which in a known manner operating parameters of the internal combustion engine and the injection system via the input terminals 36 are detected and evaluated and signals are generated at the output terminals 38, with which the electrical and electroni components of the system are controlled, for. B. the illustrated components 28, 14, 20th

In addition, the engine control unit ECU controls a leakage control valve 40 arranged in the combined course of the leakage line 22, with which the fuel return flow from the individual injectors depends on the detected operating parameters and by means of a suitably designed map the injector 20 can be blocked via the leakage line 22 in the fuel tank 16. The engine control unit ECU detects methods known per se by evaluating the measured operating parameters any occurring actuator overhang in one of the injectors and causes in this case a short-term driving the leakage control valve 40 for a short-term blocking of the fuel return, z. B. for a fixed predetermined period of a few seconds. This makes it possible to accelerate both the pressure build-up in the accumulator 12, which tends to be delayed in the event of an actuator overhang, during a hot start of the internal combustion engine and to intercept the internal combustion engine during an actuator overflow occurring during operation and thus to maintain proper operation.

Claims (9)

1. Injection unit for an internal combustion engine, comprising

   - a pressure reservoir (12) for storing fuel pumped into the pressure reservoir from a fuel tank (16) by means of a high-pressure pump (14), and

   - an injector arrangement (20), connected to the pressure reservoir (12) by means of a pressure line arrangement (18), for injecting the fuel into the internal combustion engine,

   wherein the injector arrangement (20) comprises at least one servo injection valve in which both a nozzle chamber and a control chamber are supplied with fuel from the pressure reservoir (12) via a pressure line and in which a nozzle body for opening and closing an injection passage leading from the nozzle chamber to a combustion chamber is displaceably guided, and the nozzle body is exposed at its end facing the injection passage to the pressure of the fuel in the nozzle chamber and at its opposing end to the pressure of the fuel in the control chamber,
   wherein the servo injection valve is provided with a control valve for the release of fuel from the control chamber into a fuel return line (22) leading to the fuel tank (16), which control valve may be operated by means of a piezoelectric actuator to cause a displacement of the nozzle body in the direction of an opening of the injection passage, for initiating an injection process by pressure reduction in the control chamber,
   characterised in that the fuel return line (22) is provided with a controllable valve (40) which in an actuated state blocks the fuel flow in the fuel return line (22), wherein the valve (40) is actuated depending on predefined operating parameters of the internal combustion engine and/or the injection unit and is returned to an idle state only after expiration of a predeterminable time interval.
2. Injection unit according to claim 1, wherein the injector arrangement (20) comprises a plurality of servo injection valves which are connected via the pressure line arrangement (18) to the pressure reservoir (12) used jointly for this plurality of servo injection valves.
3. Injection unit according to claim 1 or claim 2, wherein the injector arrangement (20) comprises a plurality of servo injection valves whose fuel return lines (22) are combined, whereby the combined fuel return line section is provided with the controllable valve (40).
4. Injection unit according to claim 1, 2 or 3,
   wherein the predefined operating parameters comprise the existence or non-existence of an actuator overshoot in the servo injection valve.
5. Injection unit according to any one of claims 1 to 4,
   wherein the idle state of the valve (4) after an actuation is maintained compulsorily for a stipulated fixed further time interval.
6. Injection unit according to any one of claims 1 to 5, further comprising an electronic injection control unit (ECU) for operating the injector arrangement (20) and for actuating the controllable valve (40).
7. Method for operating an injection unit (10) for an internal combustion engine, wherein the injection unit comprises:

   - a pressure reservoir (12) for storing fuel pumped into the pressure reservoir from a fuel tank by means of a high-pressure pump, and

   - an injector arrangement (20), connected to the pressure reservoir (12) via a pressure line arrangement (18), for injecting the fuel into the internal combustion engine,

   wherein the injector arrangement comprises at least one servo injection valve in which both a nozzle chamber and a control chamber are supplied with fuel from the pressure reservoir via a pressure line and in which a nozzle body for opening and closing an injection passage leading from the nozzle chamber to a combustion chamber is displaceably guided, and the nozzle body is exposed at its end facing the injection passage to the pressure of the fuel in the nozzle chamber and at its opposing end to the pressure of the fuel in the control chamber,
   wherein the servo injection valve is provided with a control valve for the release of fuel from the control chamber into a fuel return line leading to the fuel tank,
   wherein the method comprises the step of actuation of the control valve by means of a piezoelectric actuator, to cause a displacement of the nozzle body in the direction of an opening of the injection passage, for initiating an injection process by pressure reduction in the control chamber,
   characterised by a blocking of the fuel flow in the fuel return line (22), said blocking being provided depending on predefined operating parameters of the internal combustion engine and/or of the injection unit and not being lifted again until after expiration of a predeterminable time interval.
8. Method according to claim 7,
   wherein the predefined operating parameters comprise the existence or non-existence of an actuator overshoot in the servo injection valve.
9. Method according to claim 7 or claim 8,
   wherein the lifting of the blocking is compulsorily maintained for a stipulated fixed further time interval.

Images