EP0857867A1 - Method and apparatus for detecting leaks - Google Patents

Abstract

The method of identification is carried out in a fuel supply system, in which the fuel is delivered from at least one pump from a low pressure region in a high pressure region, and the pressure is determinable in the HP region with at least one pressure sensor. At least two pressure values (P1, P2) at different time points are determined, and emanating from the pressure values a fuel balance is produced, and as a result of the balance faults can be identified. In the fuel amount balance in addition also taken in to account are at least one delivery amount (MF), an injection amount (ME), a return amount (MR) and/or a pressure regulating amount (MD). The delivery amount is specifiable, depending on at least one rpm (N) and a pressure value (P).

Description

State of the art

The invention is based on a method and a device to detect a leak in a fuel supply system in an internal combustion engine of the type of the main claims.

In motor vehicles with an internal combustion engine, the Fuel from an electric fuel pump Fuel tank promoted and via fuel lines fed to the injectors. Excess fuel arrives usually via a return line into the fuel tank back. In internal combustion engines with high pressure injection, especially in internal combustion engines with auto-ignition, another follows the fuel pump Pump that has a very high pressure in a high pressure area generated, which is connected to the injectors. Such fuel supply systems run the risk of that in the event of a defect in an injector Fuel injected into the corresponding combustion chamber becomes. This is commonly referred to as internal leakage.

Leakage to the outside is also possible in the case of Fuel enters the engine compartment under high pressure.

It is therefore proposed, for example, in DE-OS-31 26 393 that means are provided that are continuously printing measure in the high pressure area of the fuel supply system, wherein the pressure in the accumulator drops below a predetermined one Value leads to an error detection. There with one In such a case, fuel is constantly injected into the engine would, in the known device after detection of a Fault, the engine is switched off or the fuel requirement completed. With such an approach, only Leakages are detected in which a relatively large amount of fuel get lost. This detects minor leaks Establishment not.

The inventive device with the features of Main claims has the advantage over the known that the entire high pressure fuel supply system for leaks can be monitored and not only recognized whether an injector is constantly open, but that one too Leakage is visible to the outside. It is particularly advantageous the simplicity of the procedure according to the invention, since the procedure according to the invention has no further sensors needed.

drawing

An embodiment of the invention is in the drawing shown. 1 shows a block diagram of the fuel metering system, Figure 2 plotted the pressure over time t and FIGS. 3, 4 and 5 each show a flow chart to illustrate the procedure according to the invention.

Description of the embodiment

In Figure 1 are those for understanding the invention required components of a fuel supply system an internal combustion engine with high pressure injection shown.

The system shown is usually called a common rail system designated. At 10 is a fuel tank designated. This is via a fuel supply line with a filter 15, a pre-feed pump 20, a shut-off valve 25, a high-pressure feed pump 30 with a rail 35 in connection. In the fuel supply line is between the high pressure feed pump 30 and the rail 35 a pressure control valve 40 or a pressure relief valve arranged. Means this valve is a high pressure area with a low pressure area, especially the supply line with a Return line 45 connectable. Via the return line 45 the fuel gets back into the tank 10.

The lines between the high pressure pump 30 and the rail 35 or the pressure control valve, the rail and the lines between Rail 35 and the injectors is used as a high pressure area designated. The area in front of the high pressure pump 30 to Tank 10 is referred to as the low pressure area.

The shut-off valve 25 can be actuated by means of a coil 26. Accordingly, the valve 40 can be actuated by means of a coil 41. A sensor 50 is arranged on the rail 35. With this Sensor 50 is preferably a pressure sensor, which provides a signal that corresponds to the fuel pressure in the rail corresponds. The rail 35 is connected via a line the individual injectors 61 to 66 in connection. The injectors comprise solenoid valves 71 to 76 by means of which the Fuel flow is controllable through the injectors. Furthermore the injectors each have a connection the return line 45 in connection.

The output signal of the pressure sensor 50 and the output signals further sensors 80 reach a control unit 100 which in turn the solenoid valves 71 to 76, the coil 26 of the pre-feed pump, the coil 41 of the pressure control valve 40 and controls the high pressure feed pump. Detect the sensors 80 for example the speed N of the internal combustion engine, the driver request FP, which is preferably by means of an accelerator pedal position transmitter is determined, as well as various temperature values, such as the temperature T of the fuel.

This facility works as follows. The pre-feed pump 20, designed as an electric fuel pump or mechanical pump can be, promotes the fuel that is in the fuel tank 10 is via a filter 15 for High pressure feed pump 30. The high pressure feed pump 30 delivers the fuel into the rail 35 and builds up pressure there. Usually in systems for spark ignition internal combustion engines Pressure values from about 30 to 100 bar and at self-igniting internal combustion engines pressure values of about 400 achieved up to 2000 bar.

Between the high pressure feed pump 30 and the pre-feed pump 20 is a shut-off valve 25 that is arranged by the control unit 100 is controllable to interrupt the fuel flow.

Determined based on the signals from various sensors 80 the control unit 100 control signals for application of the solenoid valves 71 to 76 of the injectors 61 to 66. By opening and closing the solenoid valves 71 to 76 the beginning and end of fuel injection into the Internal combustion engine controlled.

The pressure of the fuel is measured by means of the pressure sensor 50 detected in the rail 35 and thus in the high pressure area. Outgoing The control unit 100 calculates a signal from this value to act on the pressure control valve 40. Preferably the pressure is increased by actuating the pressure control valve 40 a predeterminable value regulated, which among other things by operating conditions the internal combustion engine depends, which means of the sensors 80 are detected.

If errors occur, the fuel supply can be switched off with the Shutoff valve 25 are prevented. Furthermore, if something is recognized Error, the valve 40 controlled so that the pressure in the Rail 35 drops. Furthermore, the valves 71 to 76 are activated in such a way that that they remain closed and therefore no injection he follows.

Leakage can occur in these systems. Here comes Fuel from the high pressure range on the one hand Injectors in the internal combustion engine and / or over a leak in the engine compartment of the vehicle. Such leaks in the engine compartment or an injector that is not working correctly be recognized safely.

To detect a leak in the high pressure area, a Volume balance of the high pressure area, especially the Rails 35 considered. This can be a volume balance and / or create a mass balance. In the illustrated The fuel masses are considered in the exemplary embodiment. However, the corresponding fuel volumes can also be used consider.

To create a fuel quantity balance, the fuel masses flowing into the rail and the fuel masses flowing out of the rail are considered. The following equation 1 applies: V E * P = M F - M E - M R - M D - M L

With a point are the derivatives over time or the changes within a period of the corresponding Sizes marked.

With MF is the delivery mass, which from the high pressure pump 30 in the high pressure area is promoted. This mass is present in control unit 100. It essentially depends on the speed N of the internal combustion engine, the pressure P in the rail from.

ME is the injection mass that comes from the rail injected into the internal combustion engine via the injectors becomes. This amount is in the control unit. It essentially depends on the control of the injectors.

MR is the return mass that is given by the injectors gets back into the tank via line 45. This Return mass is composed of the control mass MS, which is required to control the injectors and the Leakage mass MLD, which is a loss in the range of Injectors. The return mass comes through the line 45 also back into the tank. This mass is in the Control unit usually does not exist before and must therefore be learned will. Alternatively, it can also be provided that operating states be selected in which this mass is known.

The size MD is the pressure control compound from the pressure control valve 40 from the high pressure area in the Tank is returned to the pressure P in the high pressure range to keep at its predetermined value.

The size ML is the leakage mass. This is the size you are looking for. The procedure does not differentiate between an internal leak in which fuel is over defective injector gets into the combustion chamber, and one external leakage, with fuel in particular in the engine compartment of the motor vehicle arrives.

In Figure 1, the mass flows are at the corresponding Places marked with arrows.

The sizes V and E are constants of the fuel and the Metering system. The size V is essentially determined by the volume of the high pressure area, which results from the Rail, line and injector volume. In the Size E go among other things the fuel density and that Compressibility module of the fuel.

The values P2 and P1 are two pressure values the fuel pressure in the rail at two different times, the change in size is based on the Relate the difference between these two times.

The pressure P in the rail is plotted over time t in FIG. Arrows mark the start of each injection designated. The pressure P in the rail decreases with each injection and then increases to its original value. in the steady state pressure reaches between two injections always the same for the same position of the crankshaft Value. To determine the mass balance over the time interval between times t1 and t2 at which the Pressure P1 and P2 is measured, the mass flows are integrated.

It is particularly advantageous if the two times t1 and t2 a fixed angular distance between two injections that includes a full injection. This corresponds to a 4-cylinder engine 180 ° crankshaft. If you look at a complete metering, the sizes MF and ME can be stored in maps.

The return mass MR is preferably learned in a state in which there is no fault, and depending on operating parameters, like the speed N and the pressure P in the rail stored in a map.

Because the mass MD drained from the pressure control valve into the tank is, usually not known, will be during defined the pressure control valve after checking for leakage controlled. This means on the one hand it can be completely closed or be completely open. It must be in the open State the mass MDM, which results in the open state, be known.

Equation 2 then applies to the leakage mass ML. ML = MF - ME - MR - MD - V E * (P2 - P1)

The procedure according to the invention is shown in FIG a flow chart. In a first step 310 the test process is initialized. To do this a specific control signal is applied to the pressure control valve.

Is the relationship between the control signal for the pressure control valve 40 and the mass MD not known, so it will Pressure control valve controlled so that there is a defined Condition. For example, the pressure control valve 40 controlled so that it is completely closed. In this In this case, the value for MD is zero. Will the pressure control valve 40 controlled so that it is completely open, so the mass MD assumes the value MDM.

Is the relationship between the control signal for the Pressure control valve 40 and the mass MD known, it does not have to can be controlled in a defined manner. In this case it is the corresponding one Read MD value from a map.

The initialization of the test program can, for example as part of the inspection of the system in the workshop. Furthermore, it can be provided that the reviews in fixed time intervals and / or after the expiry of a predetermined number of engine revolutions is carried out.

In a second step 320, the pressure sensor detects one first pressure value. Then in a third Step 330 read the conveying mass MF from a map. The delivery mass is preferably dependent on the speed N of the internal combustion engine, the pressure P in the rail, the Fuel temperature in the system and other sizes in one or more maps or will start from the corresponding sizes calculated.

In the subsequent step 335, the injection mass ME also dependent on the speed N, the driver's request FP as well as any other sizes, preferably from a map read out. It is particularly advantageous if as a ground signal ME, the signal in the control with which the control signals for the injectors are also calculated, is used. In addition to the sizes mentioned can also other variables characterizing the injection process are used will. These are, for example, those for pre-injection and / or the fuel masses allocated to the post-injection.

In the subsequent step 340, the return mass MR is made out read out a memory. In step 350, at the time t2 detects the second pressure value P2. In step 355 the leak mass is determined using equation 2. The subsequent one Query 360 checks whether the leakage mass ML larger than a threshold SW. If this is the case, then recognize the device detects leakage in step 370 and directs it accordingly Measures. Otherwise, the facility recognizes in step 380 the tightness of the system.

An embodiment of the learning of the return quantity MR is shown as a flow chart in FIG. In a first step 400, the mass MD is specifically set to zero in order to learn the return mass MR. This is achieved in that the pressure control valve 40 is controlled such that it remains closed and the return mass MD thus becomes zero. In a second step 410, a first pressure value P1 is recorded. The mass ME and MF is then determined in step 420, as described in FIG. 3. The second pressure value P2 is then measured in step 430. In the subsequent step 440, the mass MR is calculated according to the equation: MR = MF - V E * (P2 - P1) - ME

Then there is the query 450, which checks whether a Operating state in which there is no injection, that is, the set ME is zero. Such an operating condition exists, for example, in the so-called thrust condition. in the No overrun, so there is no fuel injection no fuel needed to control the injector. This means that the control mass MS is zero in the overrun. In this In this case, the mass MLD corresponds to the mass MR. Therefore at The presence of this state in step 460 is the mass MLD set equal to the mass MR. Is the appropriate state not before or after step 460, will step 470 the value for MR is preferably dependent on different ones Operating parameters stored in a map.

This procedure is particularly advantageous in that even small leaks with a small leakage mass, for sure be recognized. With the known leakage detection can not between a pressure drop due to a large injection quantity and a pressure drop due to a small one Leakage can be distinguished because the pressure drop at a large injection quantity can be larger than a small one Leakage. With the procedure according to the invention detect even small amounts of leakage.

FIG. 5 shows an exemplary embodiment for determining the Mass MDM shown. This mass MDM that when fully open Pressure control valve is also derived preferably learn in overrun mode and in a map save.

To learn the maximum mass MDM, the mass MD is specifically set to its maximum possible value in a first step 500. This is achieved in that the pressure control valve 40 is actuated in such a way that it is open and the MD thus reaches its maximum value MDM. In a second step 510, a first pressure value P1 is recorded. The mass ME and MF are then determined in step 520, as described in FIG. 3. The second pressure value P2 is then measured in step 530. In the subsequent step 540, the mass MDM is calculated according to the equation: MDM = MF - MLD - V E * (P2 - P1) - ME

This value depends on various operating parameters such as the speed N, the injection quantity ME and other sizes stored in a map.

Claims (8)

Method for detecting a leak in a fuel supply system an internal combustion engine, in particular an internal combustion engine with a common rail system, the fuel from at least one pump from one Low pressure area is promoted to a high pressure area and the pressure in the high pressure range with at least one Pressure sensor can be detected, characterized in that at least two pressure values (P1, P2) at different times be recorded, and that based on the pressure values a fuel quantity balance is drawn up, starting from is recognized by the fuel quantity balance for errors. A method according to claim 1, characterized in that in the fuel quantity balance in addition at least one delivery rate (MF), an injection quantity (ME), a return quantity (MR) and / or a pressure control quantity (MD). Method according to one of the preceding claims, characterized characterized in that the amount of feed (MF) depends on at least a speed (N) and a pressure value (P) can be specified is. Method according to one of the preceding claims, characterized characterized in that the injection quantity (ME) depends on at least a speed (N) and / or a driver request (FP) can be specified. Method according to one of the preceding claims, characterized characterized that the return quantity (MR) in the error-free Case is learned. Method according to one of the preceding claims, characterized characterized in that the fuel quantity balance in predetermined Intervals, in particular a predetermined number of revolutions of the engine. Method according to one of the preceding claims, characterized characterized in that when checking a pressure control valve is controlled in a defined manner. Device for detecting a leak in a fuel supply system an internal combustion engine, in particular an internal combustion engine with a common rail system, with at least one pump that delivers fuel from a low pressure area promotes in a high pressure area and at least a pressure sensor that measures the pressure in the high pressure range recorded, characterized in that means are provided the at least two pressure values (P1, P2) are different Capture points in time, and based on the pressure values Create fuel quantity balance and starting from the Detect fuel quantity balance for errors.

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