EP2766594B1 - Common rail injection system for an internal combustion engine - Google Patents

Description

The invention relates to a common rail injection system in which individual pump strokes of a high-pressure fuel pump can be selectively switched on and / or off. In other words, the invention relates to a common rail injection system with selective activation and deactivation of individual pump strokes of a high-pressure pump. in particular by means of a digital inlet valve (DIV).

Common rail injection systems are fuel injection systems for internal combustion engines, in which a high-pressure pump compresses the fuel to a high pressure level and this highly compressed fuel is introduced into a common rail. From the manifold of so-called injectors are fed, via which the highly compressed fuel is injected into the combustion chambers of the engine.

In contrast to engines with classic injection systems, such as in-line injection pumps or distributor injection pumps, which for each cylinder of the internal combustion engine has its own pressure line for supplying fuel from the injection pump to the injection nozzles of the cylinder, which are not fluidically interconnected, has the common rail injection system a common high pressure line. This makes it possible, in contrast to the classical injection systems, to control the injection time and the injection quantity independently of the angle of the crankshaft of the engine. About the common high-pressure line is applied to the injectors continuously necessary for the injection pressure. This pressure can be in a range of up to 250 MPa. The injectors function in the common rail system as electromagnetically or piezoelectrically controlled valve, via which the high-pressure fuel is introduced into the combustion chamber. In contrast to the conventional injection systems with in-line or distributor injection pumps, which permit only one injection per working stroke of the cylinder, this technique allows a plurality of injections per power stroke. This allows, for example, a pre-injection of a smaller amount of fuel through which a quieter engine operation can be achieved. By providing a post-injection after the actual main injection, for example, when using SCR catalysts (selective catalytic reduction), the nitrogen oxide content in the exhaust gas can be reduced. Also, the post-injection can be used to increase the energy content (calorific value) of the exhaust gas, so as to allow, for example, if necessary, the burn-out of a particulate filter.

In the common-rail injection system, the high-pressure pump supplies as constant a fuel pressure as possible to the distributor tube as pressure accumulator. In order to at least partially absorb the pressure peaks resulting from the pump strokes of the high-pressure pump, use is made in a common-rail injection system that the fuel, in particular diesel fuel, has a certain compressibility. In addition, the volume of the manifold serves as accumulator volume, over which pressure peaks can be equalized. In this case, pressure peaks can be better compensated, the larger the storage volume of the pressure accumulator, as a manifold, is. On the other hand, larger volumes lead to a greater inertia of the injection system, since a correspondingly high operating pressure in the entire rail system must be established. However, as far as possible compensation of the pressure peaks within the rail system is necessary in order to avoid pressure waves at the injectors, which could uncontrollably influence the fuel quantity injected into the combustion chamber. This would adversely affect the efficiency of combustion.

In order to ensure as constant a pressure supply as possible, the common-rail injection system has a fuel return from the rail system into the fuel tank. If a dependent of the operating condition of the engine pressure in the manifold constructed, excess fuel is returned via a pressure control valve in the fuel tank. This heats the fuel, which can lead to increased wear of the fuel-carrying parts. In order to avoid damage to the system, the fuel must therefore be cooled in the return from the, for which further system components, such as fuel cooler must be provided.

The high-pressure pump of the common-rail injection system must ensure a continuous supply of fuel to all injectors under all operating conditions of the engine (idle, part-load, full load). For this purpose, the performance of the high-pressure pump is designed so that more fuel can be conveyed through the high pressure pump at any time and in any operating condition of the engine, as is necessary for the operation of the internal combustion engine in the respective operating state. From this it finally follows that the high-pressure pump for the average normal operating condition is clearly oversized in order to ensure a sufficient reserve for over-promotion even in full-load operation.
However, a larger dimensioning of the high-pressure pump also means that it has a higher energy requirement, which must be provided by the internal combustion engine. This reduces the efficiency of the engine.

DE 10 2004 023 962 A1 discloses a method for driving a fuel injection system, wherein the number of delivery strokes of a high-pressure fuel pump is adjusted to the number of injections of injectors.

In DE 197 08 152 A1 a fuel injection system is described in which, in the event of imminent overpressure in a common rail, a fuel in the flow direction downstream of a high-pressure fuel pump is diverted into a low-pressure region.

DE 10 2007 059 731 A1 discloses a method for controlling a demand-based fuel pump for supplying pressurized fuel to a fuel injection system of a multi-cylinder engine. The pump includes a crankshaft driven pumping element that is fueled by an inlet control valve. There is provided a cam having an even number of pump cam lobes for generating strokes of the pumping element for pumping fuel to the system and for reducing fuel delivery by disabling a pump action of selected cam lobes when not needed maintain minimum fuel pressure in the system. The deactivated cam lobes can be selected to maintain a uniform pumping cascade of the active pump cam lobes.

EP 1 306 553 A2 describes a high-pressure fuel pump with a plurality of pump elements, which are driven by a drive shaft and each defining a working space, being assigned to a working space each of the working spaces a controllable valve means for controlling the flow rate in the working space. The pump element in the working space, to which no valve device is assigned, has the smallest diameter compared to the other pump elements.

With this in mind, it is the object of the present invention to specify a common-rail injection system which allows a sufficient pressure supply of the injection system using a dimension-minimized high-pressure pump.

The object is achieved by the features of claims 1 and 3. Advantageous embodiments of the invention are specified in the dependent claims.

The invention thus proposes a common-rail injection system for an internal combustion engine, comprising a high-pressure pump, a distributor tube and at least one injector, wherein the high-pressure pump delivers fuel for operating the internal combustion engine into the distributor tube, which communicates via the at least one fluidically connected with the distributor tube Injector is injectable into a combustion chamber of the internal combustion engine, wherein the pump stroke frequency of the high pressure pump is a multiple of the injection frequency, wherein the high pressure pump is a multi-piston pump, the injection system fluidly disposed in front of the high pressure pump having an inlet valve, by means of which the fuel flow to the individual pistons of the high pressure pump selectively for individual delivery cycles of the high-pressure pump can be interrupted, not always one and the same piston is switched load-free, but the pistons are switched alternately so load-free, that the load is evenly distributed to the piston of the multi-piston pump.

By means of the injection system according to the invention, it is possible to provide an increase in the pump stroke frequency of the high pressure pump, without this increase in frequency leads to a significant increase in wear or a reduction in the life of the pump. Compensating for the increase of the pump stroke frequencies, by providing an inlet valve upstream of the high pressure pump, it is possible to switch it off for selective delivery cycles by interrupting the fuel supply to the high pressure pump.

Thus, it can be provided, for example, that with the same piston volume of the high-pressure pump, the pump stroke frequency is doubled or multiplied. This can be achieved, for example, by doubling or multiplying the lift cams of the camshaft of the high-pressure pump. This results in the Volllastbestrieb of the engine, a corresponding multiplication of the provided fuel volume. Without the inventive provision of an inlet valve in front of the high-pressure pump, on the one hand, this would result in an excessively large fuel volume during idling or part-load operation of the engine and, on the other hand, a significantly higher wear of the high-pressure pump.

By providing an inlet valve according to the invention, pump strokes can be selectively switched load-free by the Fuel supply to the high-pressure pump is interrupted. Thus, it may be provided in the idling or part-load operation, for example, that the fuel supply to the high-pressure pump is interrupted every second pump stroke and thus the hub takes place without load. As a result, the amount of fuel delivered is reduced and excessive overfeeding is avoided. On the other hand, the load on the high pressure pump is significantly reduced, whereby the usually associated with the increase of the pump stroke frequency greater wear can be reduced.

The high-pressure pump is a multi-piston pump, and the fuel flow to the individual pistons is selectively interruptible by means of the inlet valve. As a result, in the manner already described above, the power of the pump can be multiplied in full-load operation, without requiring an increase in the pump volume. In particular, provision may be made for the fuel supply to individual pistons of the pump to be interrupted during idling and / or part-load operation of the high-pressure pump in order to reduce the delivery rate. It is provided that not always one and the same piston is switched load-free, but the pistons are switched alternately load-free. As a result, the load can be evenly distributed to the piston of the multi-piston pump and excessive wear of individual pistons is avoided. It may be provided in a further embodiment of the invention that a multi-piston high-pressure pump for each piston, a separate inlet valve is provided.

When using multi-piston pumps as high-pressure pumps in common-rail injection system, the delivery of the high pressure pump can be varied over a wide range depending on the operating state of the internal combustion engine by providing an inlet valve according to the invention in front of the high pressure pump.

According to a further embodiment of the invention, it may be provided that the inlet valve is a solenoid valve or a piezoelectric valve. In particular, it can be provided that the inlet valve is a valve with a digital control (DIV, D igital I nlet V alve). This allows the integration of the control of the intake valve in the engine management of modern internal combustion engines.

In a further embodiment of the invention, it may be provided that the inlet valve is controllable via a control unit (ECU, Electonic Control U nit) of the injection system as a function of the operating state of the internal combustion engine. As a result, the delivery rate of the high-pressure pump is possible directly via the control unit of the injection system, which makes it possible to regulate the delivery rate as a function of the characteristic diagram of the engine control unit.

With the injection system according to the invention, it is possible with relatively small piston volumes of the high-pressure pump to provide significantly more powerful engines with sufficient fuel even in full-load operation. A fuel Überförderung and the associated problem of fuel heat can be reduced or even avoided. The energy consumption of the high-pressure pump can be reduced and thus the overall efficiency of the internal combustion engine can be increased.

A further advantage of the present invention is the increased conveying accuracy in the operating state of the minimum quantity delivery of the high-pressure pump or of the minimum quantity consumption of the internal combustion engine. The actual hydraulic delivery per pump stroke at the pump output always deviates slightly from the target value specified by the ECU. This deviation becomes relatively larger relative to the nominal delivery capacity of the high-pressure pump, the smaller the currently called delivery rate itself. Due to the load-free switching of individual pump strokes, the delivery deviation can advantageously be significantly reduced with minimum delivery, whereby the high-pressure side Pressure control in the common rail injection system is simplified.

A high pressure pump is provided for a common rail injection system of an internal combustion engine having a manifold and at least one injector. In this case, the high-pressure pump promotes fuel for operating the internal combustion engine in the common rail injection system, in particular in the manifold, which can be injected via the at least one fluidically connected to the manifold injector in a combustion chamber of the engine. Furthermore, the high-pressure pump has an inlet valve, which is arranged in particular in terms of flow in front of the high pressure pump, by means of which the fuel flow to the high pressure pump is selectively interruptible for individual delivery cycles of the high pressure pump.

According to a further aspect of the invention, a motor vehicle is provided which has a common-rail injection system described above or a high-pressure pump described above.

The invention further relates to a method for operating a common rail injection system for an internal combustion engine, wherein a high pressure pump delivers fuel for operation of the internal combustion engine in a manifold, which is injected via a fluidically connected to the manifold injector in a combustion chamber of the internal combustion engine, wherein the high pressure pump is operated such that the pump stroke frequency is a multiple of the injection frequency, the high pressure pump is a multi-piston pump, wherein the fuel flow to the individual pistons of the high pressure pump is selectively interrupted for individual delivery cycles of the high pressure pump, not always one and the same piston switched unloaded is, but the pistons are alternately switched so load-free, that the

Load is evenly distributed to the piston of the multi-piston pump.

As already described above, it is possible by means of the method according to the invention to provide an increase in the pump stroke frequency of the high-pressure pump, without this increase in frequency leading to a significant increase in wear or a reduction in the service life of the pump.

This allows the safe supply of fuel even larger combustion engines with relatively small-volume high-pressure pumps.

According to one embodiment of the method according to the invention, it can be provided in particular that the fuel flow to the high-pressure pump is interrupted as a function of the operating state of the engine. Thus, for example, it may be provided that the high-pressure pump is operated at a pump stroke frequency which corresponds to a multiple of the injection frequency and in part-load or idle mode part of the pump stroke cycles are switched load-free by the interruption of the fuel supply to the injection pump.

The high-pressure pump is a multi-piston pump, and the fuel flow to the individual pistons is selectively interrupted by means of the intake valve. In this case, the power of the pump can be multiplied in full load operation, without requiring an increase in the pump volume. In particular, provision may be made for the fuel supply to individual pistons of the pump to be interrupted during idling and / or part-load operation of the high-pressure pump in order to reduce the delivery rate. It is provided that not always one and the same piston is switched load-free, but the pistons are switched alternately load-free. As a result, the load can be evenly distributed to the piston of the multi-piston pump and excessive wear of individual pistons is avoided.

Advantageous embodiments of the common rail injection system are, as far as applicable to the high-pressure pump and the motor vehicle, also to be regarded as advantageous embodiments of the high pressure pump and the motor vehicle.

Fig. 1

zeigt eine schematische Darstellung eines erfindungsgemäßen Common-Rail-Einspritzsystems;

Fig. 2

zeigt den aus dem Profil einer Nockenwelle einer Hochdruckpumpe resultierenden Pumpzyklus;

Fig. 3

zeigt die aus der lastfrei Schaltung einzelner Pumpenhübe einer Hochdruckpumpe resultierende Förderkurve.

Hereinafter, the invention will be explained by way of example with reference to the accompanying drawings based on preferred embodiments without being limited thereto.

Fig. 1

shows a schematic representation of a common rail injection system according to the invention;

Fig. 2

shows the pumping cycle resulting from the profile of a camshaft of a high pressure pump;

Fig. 3

shows the resulting from the load-free circuit individual pump strokes of a high pressure pump delivery curve.

Fig. 1 shows a schematic representation of a common rail injection system 100 according to an embodiment of the invention. Fuel is withdrawn from a fuel tank 200 from a fuel pump 300 via a fuel line 210. Via a fuel line 310, the fuel is fed by means of the fuel pump 300 to an inlet valve 400. The intake valve 400 regulates the flow of fuel via a fuel line 410 to a high-pressure pump 500. In this case, the intake valve 400 may also be an integral part of the high-pressure pump 500. The compressed fuel is conveyed via a high-pressure line 510 to a distributor pipe (rail) 600, from where it reaches the injectors 700 via high-pressure lines 610. The compressed fuel is injected into the combustion chambers of an internal combustion engine 800 via the injectors 700. The manifold 600 is connected to the fuel tank via a fuel return line 620. Excess fuel from the manifold 600 is returned to the fuel tank via the fuel return line 620. In this case, the injection system 100 is controlled by a control device (ECU) 900, which is signal-connected via at least the injectors 700 and the inlet valve 400 via control lines 910. According to the invention, it is provided that the high-pressure pump operates at a pump stroke frequency which corresponds to a multiple of the injection frequency of the fuel injected via the injectors 700 into the combustion chambers of the internal combustion engine 900. This ensures that the high-pressure pump 500 promotes sufficient fuel into the distributor tube 600 even in the case of full-load operation of the internal combustion engine 900. In order to avoid a large over delivery of fuel into the manifold 600, the fuel flow to the high pressure pump 500 may be selectively interrupted by means of the intake valve 400 for individual pump strokes of the high pressure pump 500. As a result, these pump strokes are switched load-free and do not deliver fuel into the manifold 600. Excessive fuel return via line 620 can thereby be avoided. This also avoids excessive loading and, if necessary, accompanying increased wear of the high-pressure pump 500. The inlet valve 400 may be embodied, for example, as a digitally controllable solenoid or piezoelectric valve (ie as a DIV), which is controlled by the controller 900 as a function of the injection frequency and / or the fuel pressure in the manifold 600. As a result, the control unit receives a further characteristic which can be taken into account for the optimized control of the internal combustion engine.

Fig. 2 shows the pumping cycle resulting from profiles of camshafts of high pressure pumps. When using a 2-cam camshaft 530 to drive a pump piston of a high-pressure pump, the pump cycle curve 535 results. The stroke of the pump piston depends on the distance from the top dead center to the bottom dead center of the camshaft. The cycle from top dead center to bottom dead center and back to top dead center corresponds to a pumping cycle. Doubling the number of cams on the camshaft 540 compared to the number of cams on the camshaft 530 also results in a doubling of the pumping cycles in the pumping cycle curve 545. This results in a doubling of the delivery line for the same pump volume of a high-pressure pump.

Fig. 3 shows the resulting from the load-free circuit individual pump strokes of a high pressure pump delivery curve. there Curve 550 shows the output of a high pressure pump with a 2 cam camshaft, as with 530 in Fig. 2 is shown. Curve 570 shows the capacity of a pump of the same pump volume with a 4-cam camshaft, as in 540 in Fig. 2 is shown. The capacity 570 of the 4-cam camshaft is significantly too large for the part-load or idling operation of an internal combustion engine. Therefore, it is provided according to the invention that selectively pump cycles of a high-pressure pump are switched load-free, that is, the fuel supply to the high-pressure pump for selective pump strokes is interrupted. Shown at 560 is the delivery rate of a high pressure pump with a 4 cam camshaft in which only every second pump stroke delivers fuel and fuel delivery to the high pressure pump for the other pump strokes is interrupted by means of the present invention intake valve. It turns out that the delivery rate in this case is between the delivery rate of the 2-cam high-pressure pump of the same volume and the full delivery, ie the delivery without interrupting the fuel supply to the high-pressure pump, a volume-identical 4-cam high-pressure pump. This makes it possible to safely supply even with relatively small-volume high-pressure pumps larger internal combustion engines with fuel, whereby the efficiency of the internal combustion engine can be increased overall.

LIST OF REFERENCE NUMBERS

100

Common rail injection system

200

Fuel tank

210

Fuel line

300

Fuel pump

310

Fuel line

400

intake valve

410

Fuel line

500

high pressure pump

510

High-pressure fuel line

530

2-cam camshaft

535

Pumping cycle curve

540

4-cam camshaft

545

Pumping cycle curve

550

production curve

560

production curve

570

production curve

600

Distribution pipe (rail)

610

High-pressure fuel line

620

Fuel return line

700

injector

800

internal combustion engine

900

Control unit (ECU)

910

control line

Claims (5)

1. Common rail injection system (100) for an internal combustion engine (800), having a high-pressure pump (500), a distributor pipe (600) and at least one injector (700), wherein the high-pressure pump (500) delivers fuel for the operation of the internal combustion engine (800) into the distributor pipe (600), which fuel can be injected into a combustion chamber of the internal combustion engine (800) by means of the at least one injector (700) that is connected in terms of flow to the distributor pipe (600), wherein the pump stroke frequency of the high-pressure pump (500) is a multiple of the injection frequency, wherein the high-pressure pump (500) is a multi-piston pump, wherein the injection system (100) has a control unit (900) and, arranged upstream of the high-pressure pump (500) in terms of flow, an inlet valve (400) which can be controlled by means of the control unit (900) of the injection system as a function of the operating state of the internal combustion engine (800) and by means of which the fuel feed to the individual pistons of the high-pressure pump (500) can be selectively interrupted for individual delivery cycles of the high-pressure pump (500),
   wherein not always one and the same piston is switched into a load-free state, but characterized in that the pistons are switched alternately into a load-free state, such that the loading is distributed uniformly across the pistons of the multi-piston pump.
2. Common rail injection system according to Claim 1, characterized in that the inlet valve (400) is a solenoid valve or a piezoelectric valve.
3. Method for operating a common rail injection system for an internal combustion engine, wherein a high-pressure pump delivers fuel for the operation of the internal combustion engine into a distributor pipe, which fuel is sprayed, by injection, into a combustion chamber of the internal combustion engine by means of an injector that is connected in terms of flow to the distributor pipe, wherein the high-pressure pump is operated such that the pump stroke frequency is a multiple of the injection frequency, wherein the high-pressure pump (500) is a multi-piston pump, wherein the fuel feed to the individual pistons of the high-pressure pump is selectively interrupted for individual delivery cycles of the high-pressure pump, wherein not always one and the same piston is switched into a load-free state, but characterized in that the pistons are switched alternately into a load-free state, such that the loading is distributed uniformly across the pistons of the multi-piston pump.
4. Method according to Claim 3, characterized in that the fuel feed to the high-pressure pump is interrupted as a function of the operating state of the engine.
5. Motor vehicle comprising a common rail injection system according to one of Claims 1 and 2.

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