DE19626690B4 - Method and device for monitoring a fuel metering system of an internal combustion engine - Google Patents

Abstract

method for monitoring a fuel metering system of an internal combustion engine, in particular a common rail system, characterized in that for detection from errors in the field of fuel injection evaluated a signal will that be a uniform Combustion in the cylinders of the internal combustion engine indicates, wherein an error in the field of fuel injection is detected when the instantaneous speed value in the overrun mode increases inadmissibly.

Description

State of the art

The The invention relates to a method and a device for monitoring a fuel metering system according to the preambles of the independent claims.

Such a method and apparatus monitoring of a fuel metering system are known from the US 52 41 933 A known. There, a method and apparatus for monitoring a high pressure circuit in a common rail system are described. In the device described there, the pressure in the rail is regulated. If the manipulated variable of the pressure control loop is outside a predefinable range, the device detects errors.

Of Further devices are known in which starting from the pressure in the rail is closed on the presence of an error. there the pressure is compared with lower and upper limits, and on Error detected when the pressure is outside the specified value range lies. A disadvantage of these arrangements is that an error only is detected at a strong pressure drop.

From the DE 42 43 178 A1 For example, a method and a device for monitoring a fuel metering system of an internal combustion engine are known. With the method described therein leaking injectors are detected, through which fuel constantly enters the combustion chambers. In order to detect such leaking injectors, after the start of the internal combustion engine ignition takes place in all cylinders, without a Ansteuersig signal for injection is specified. If a speed increase indicative of combustion, this is due to a leaking injector.

adversely In this approach, it is that errors during operation the internal combustion engine can not be detected. Occurs during the Operation of the internal combustion engine an error, it can not be recognized. This can damage or destroy the Internal combustion engine lead.

From the DE 40 35 958 A1 is a device for detecting dropouts known. In this case, it is monitored whether an increase in speed takes place after an injection or an ignition. If this is not the case, a misfire is detected as a missing ignition or insufficient combustion.

The DE 36 15 547 A1 shows a device for detecting a malfunctioning cylinder of a multi-cylinder internal combustion engine. For this purpose, the difference between a minimum value and a maximum value of the instantaneous speed is formed. This difference is referred to as a speed fluctuation and is calculated to each cylinder of the internal combustion engine. An error is detected when the speed variation of one of the cylinders deviates from the average of the cylinders. Furthermore, errors are detected when the fluctuation is smaller than a threshold.

The US 4,499,876 A shows a device for monitoring an internal combustion engine. Again, the instantaneous speed is evaluated. The speed change during combustion in a cylinder is evaluated. If this speed change exceeds a certain value for a cylinder, an error is detected.

The US 4,697,561 A describes a conventional misfire detection in which, based on the speed change during an injection, an error is detected.

The post-published DE 195 36 109 A1 shows a method for detecting a leak, in which a temperature sensor and / or a pressure sensor is used in the combustion chamber of the internal combustion engine. If the signal of such a sensor in a cylinder deviates from a predetermined value, an internal leak is detected.

Object of the invention

Of the Invention is the object of a device and a method of monitoring a fuel metering system of the type mentioned as possible easy and safe to recognize mistakes. This task is done by in independent claims marked features solved.

Advantages of the invention

through the method according to the invention and the device according to the invention can Error in the metering system In particular, the error to a permanent fuel injection in individual combustion chambers led, be detected safely and easily. In particular, defective Injectors are reliably detected in common-rail systems.

advantageous and appropriate embodiments and further developments of the invention are characterized in the subclaims.

drawing

The invention will be explained below with reference to the embodiments shown in the drawing. Show it 1 a block diagram of the device according to the invention, 2 plotted the course of the speed signal over time t and 3 a flowchart of an embodiment of the method according to the invention.

Description of an embodiment

In the following, the device according to the invention is shown using the example of a self-igniting internal combustion engine, in which the fuel metering is controlled by means of solenoid valves. In the 1 illustrated embodiment relates to a so-called common rail system. However, the procedure according to the invention is not limited to these systems. It can be used in all systems where the appropriate fuel metering takes place.

With 100 is an internal combustion engine referred to, which has a suction line 105 Fresh air is supplied and via an exhaust pipe 110 Gives off exhaust gases.

In the illustrated internal combustion engine is a four-cylinder internal combustion engine. Each cylinder of the internal combustion engine is an injector 120 . 121 . 122 and 123 assigned. The injectors are powered by solenoid valves 130 . 131 . 132 and 133 Metered in fuel. The fuel passes from a so-called rail 135 over the injectors 120 . 121 . 122 and 123 in the cylinders of the internal combustion engine 100 ,

The fuel in the rail 135 is from a high pressure pump 145 brought to an adjustable pressure. The high pressure pump 145 is via a solenoid valve 150 with a fuel pump 155 connected. The fuel pump is connected to a fuel tank 160 in connection.

The valve 150 includes a coil 152 , The solenoid valves 130 . 131 . 132 and 133 contain coils 140 . 141 . 142 and 143 , each by means of a power amplifier 175 can be energized. The final stage 175 is preferably in a control unit 170 arranged, which is also the coil 152 controls.

Furthermore, a sensor 177 provided the pressure in the rail 135 detected and a corresponding signal to the controller 170 passes.

Between the high pressure pump 145 and the rail 135 is a pressure control valve or a pressure relief valve 190 arranged. The pressure relief valve 190 is between the connecting line between the high pressure pump 145 and the rail 135 and a return line 195 arranged. About the return line 195 returns fuel to the reservoir 160 , The pressure control valve 190 can from the controller 170 be controlled and is in the presence of a corresponding drive signal, the connection between the rail 135 and the return line 195 and thus the reservoir 160 free.

With 180 is a sensor called the markers on a rotating shaft 185 scans. The rotating shaft is preferably the crankshaft or other rotating shaft coupled to the crankshaft, such as the camshaft or the starter ring gear. The number of markings corresponds to the number of cylinders. The marks on the rotating shaft 185 be from the giver 180 sampled.

This device works as follows. The fuel pump 155 conveys the fuel from the reservoir via the valve 150 to the high pressure pump 145 , The high pressure pump 145 builds in the rail 135 a predetermined pressure. Usually, in systems for spark-ignition internal combustion engines Pressure values of about 30 to 100 bar and achieved in auto-ignition internal combustion engine pressure values of about 1000 to 2000 bar.

By energizing the coils 140 to 143 become the corresponding solenoid valves 130 to 133 driven. The drive signals for the coils set the start of injection and the end of injection of the fuel through the injectors 120 to 123 firmly. The control signals are determined by the controller depending on various operating conditions, such as the driver's request, the speed and other variables.

at a common rail system can be a continuous injection of an injector with balanced mass balance in the rail not easily safe be recognized. This can occur, for example, when the solenoid valve permanently energized or the injector is stuck or a leak having. This can lead to an undesired pressure increase in lead a cylinder and until the engine destruction range, if the cylinder peak pressures or the permissible temperatures exceeded become.

The marks on the rotating shaft 185 be from the giver 180 sampled. The speed is recorded by a time measurement between the markings. Two speed values are determined per combustion.

In 2 Instantaneous speed values N (i) and the actual speed N are plotted against the time t. In a combustion cycle, the speed increases from a minimum value to a maximum value and then drops back to the minimum value. Each process repeats this process. If the markings are arranged appropriately, then there is a measuring interval before combustion and a measuring interval after combustion. The location of the marks is indicated by a dot in 2 shown.

Based on the distance of the previous two pulses, which are triggered by the markings, results in a speed value. The in the control unit 170 The present speed in each case assumes a lower value before combustion in a cylinder and a high value after combustion. The high value is based on a successful combustion. The actual speed increases when burning in a cylinder. Subsequently, a speed drop occurs during compression.

Due to the selected arrangement of the speed sensor 180 . 185 This speed fluctuation also occur in the signal N (i) used by the control unit. If one cylinder more fuel is metered than the other cylinder, this has the consequence that the speed increase in this cylinder is much higher than in the other cylinders.

According to the invention Leak detection in common rail systems by means of a misfire detection. At a misfire detection is monitored by various signals, whether there is a uniform combustion in all cylinders. For this purpose, a signal is evaluated, which is a uniform combustion displayed in all cylinders of the internal combustion engine. Dodge this Signal from its expected value, leakage is detected. It is particularly advantageous if only then recognized for errors when the signal deviates several times from its expected value.

to Misfire detection is usually monitored, whether a cylinder makes a smaller contribution to the work of the Internal combustion engine contributes. According to the invention is a Leakage detected when a cylinder is overpowering. The methods for evaluation in a misfire detection and the Leak detection correspond. They are essentially different only in that to Leak detection an increased Injection and in the misfire detection too small amount be detected.

at a possible embodiment For leakage detection, the speed increase during combustion is monitored. Alternative or supplementary can increase the speed also other signals are used. Usually, the misfire detection monitors this speed increase to see if he has a specific Threshold exceeds. If this is not the case, that is the speed increase is too low, then a dropout, this means an insufficient Combustion or a missed ignition, detected. Especially at low loads or in overrun is the normal misfire detection switched off, because all cylinders only a very small or no Contribute to the torque. This operating conditions is no or only a very small increase in speed before.

In However, this operating area can be monitored whether the labor contribution a cylinder larger than a maximum allowable Is worth. If such becomes inadmissible high speed detected, so is a leaking injector to go out there, usually In the thrust no injection and thus no combustion takes place.

There Fuel in an internal leakage, such as a leaking Injector, constantly gets into the cylinder, the ignition can already before the top dead center. In this case, the combustion does not contribute Speed increase at. The additional fuel is followed by one delayed Combustion, which is the usual Misfire corresponds. According to the invention is therefore monitored in all operating conditions, whether the speed is inadmissible increases or whether the speed increase is less than a threshold value is. Once the speed increase outside a predetermined window is located, is detected on dropouts or errors. The thresholds, which define the window within which a dropout is detected are preferably in a map depending on the speed N and the cooling water temperature TW stored.

In 3 is shown with reference to a flow chart an embodiment of the method according to the invention. In step 300 is the speed value N (2 · Z) before the current combustion, ie detected during compression. Then in step 310 the speed value N (2 × Z + 1) is detected after the current combustion.

In step 320 the mean value NAM of the speed increases is calculated. This calculation is preferably carried out according to the following formula.

in this connection Z corresponds to the number of cylinders of the internal combustion engine at the size k is it is a variable. The values N (k) are respectively around the instantaneous speed values. The value NAM is the same as two Engine cycles, that is over 2 × Z burns, averaged speed increases.

In the next step 330 the threshold value SW is specified as a function F of the rotational speed N and the cooling water temperature TW. This threshold value SW indicates by what value the current speed increase NAA can deviate from the average speed increase NAM before an error is detected.

In the next step 340 the current value NAA for the speed increase of the current combustion is determined. This is done according to the following formula: NAA = N (2 * Z + 1) - N (2 * Z)

The subsequent query 350 checks whether the difference between the current speed increase NAA and the average speed increase NAM is greater than the threshold value SW. If this is the case, the speed increases after combustion to an impermissibly high value, so in step 360 an error counter FZ increased by 1. An error is detected if an instantaneous speed value rises inadmissibly. In particular, an impermissible increase in the instantaneous speed value is detected when the instantaneous speed value deviates by more than a threshold from an average speed value.

The subsequent query 365 checks whether the error counter FZ is greater than a threshold ZS. If this is the case, in step 370 detected on a faulty injector. Through the steps 360 and 365 It is achieved that not every inadmissible increase in the speed leads to an error detection and thus to an emergency shutdown of the internal combustion engine. In a simplified embodiment, these steps may also be omitted.

Recognizes the query 350 in that the difference NAA-NAM is not greater than the threshold value SW, the query follows 380 this checks whether the idle state LL is present. If this is not the case, then step immediately follows 390 , If this is the case, then in step 385 checks whether the difference NAA - NAM is smaller than the threshold SW. If this is the case then it will also be in step 360 the counter FZ increases. If this is not the case, then step follows 390 , In step 390 The values for the speeds of the previous metering are overwritten with the values of the current metering.

In this embodiment, it is checked whether the rotational speed after combustion is excessively strong increases. If this is the case, then errors are detected. In a preferred embodiment, it is only then recognized for errors and appropriate measures initiated when several times an error has occurred.

at A further embodiment provides that it is checked whether in each case at the same Cylinder an error has occurred. In this case, the defective Injector can be detected.

In an advantageous embodiment, it is provided that tighter limits are used in overrun. This means that the threshold SW in step 330 depending on whether the overrun operation is present or not different limit values are selected. In overrun mode, smaller values are specified for the threshold value SW. This means in overrun operation, even a lesser increase in speed results in error detection.

Claims (9)

A method for monitoring a Kraftstoffzumesssystems an internal combustion engine, in particular a common rail system, characterized in that is evaluated to detect errors in the fuel injection a signal indicative of a uniform combustion in the cylinders of the internal combustion engine, wherein an error in the Fuel injection is detected when the instantaneous speed value in the overrun operation increases inadmissible. Method according to claim 1, characterized in that that one inadmissible long injection and / or an impermissibly large amount of injected fuel is recognized. Method according to one of the preceding claims, characterized characterized in that an error is detected if at least one Cylinder of the internal combustion engine provides an excessive work performance. Method according to one of the preceding claims, characterized characterized in that an error is detected when a current one Speed value not allowed increases. Method according to claim 4, characterized in that that starting from at least two rotational speed values, a speed change is determined. Method according to claim 5, characterized in that that an inadmissible Rise of the current speed value is detected when the speed change by more than a threshold of a mean speed change differs. Method according to one of the preceding claims, characterized characterized in that an error is recognized only when the Signal deviates several times from the expected value. Method according to one of the preceding claims, characterized characterized in that a defective injector is detected. Device for monitoring a Kraftstoffzumesssystems an internal combustion engine, in particular a Common rail system, characterized in that means are provided are used to detect errors in the field of fuel injection Evaluate a signal that a uniform combustion in the cylinders indicates the internal combustion engine, the means being an error in the field detect the fuel injection when the current speed value in overrun mode inadmissible increases.