DE102008002240A1 - Pressure sensor checking method for fuel injection system of diesel internal-combustion engine of motor vehicle, involves determining closing duration of injection valve to switch-over valve from opened condition to closed condition - Google Patents

Abstract

The method involves attaching an accumulator to a pressure sensor, and connecting a controllable injection valve e.g. electromagnetic valve, to the accumulator. The pressure is exerted to fuel, and the injection valve for the injection of fuel is controlled in an opened condition. A closing duration (SD) of the injection valve is determined in order to switch-over the injection valve from the opened condition to a closed condition, where failure of the sensor is determined based on the closing duration. Expected pressure (PRe) in the accumulator is determined from the closing duration. Independent claims are also included for the following: (1) a computer program having a set of instructions for performing a method for checking a pressure sensor of a fuel injection system of a motor vehicle (2) a fuel injection system for a motor vehicle.

Description

State of the art

The The invention relates to a method for checking a pressure sensor of a fuel injection system in particular of a motor vehicle according to the preamble of claim 1. The invention also relates to a corresponding computer program and a corresponding control unit and a corresponding fuel injection system.

From the DE 10 2004 028 891 A1 a method for operating an internal combustion engine is known in which the pressure at which the fuel is injected via an injection valve into the combustion chamber of the internal combustion engine is measured by means of a pressure sensor. By a corresponding control of the injection valve, a pressure is determined which corresponds to the pressure actually acting on the fuel. The measured pressure and the actual pressure are compared with each other to conclude that the pressure sensor malfunctions.

As has been explained, it is in the known method for Determining the actual pressure required, to control the injection valve accordingly. This is with effort connected and can lead to disruption of the operation.

Disclosure of the invention

Of the Invention is based on the object, a method of the initially to create that kind, in a simple way and without a Influencing the operation of a review the pressure sensor allowed for malfunction.

The The invention solves this problem by a method according to Claim 1. The object is in a computer program, a control unit and a fuel injection system of the type mentioned in the corresponding Way solved.

According to the invention assumed a fuel injection system, the one with fuel filled accumulator having associated with it a pressure sensor is, and connected to the at least one controllable injection valve is. Pressure is applied to the fuel in the accumulator and the injector is for an injection of Fuel controlled in an open state.

It has shown that the closing time is a characteristic Size of the injection valve represents. Especially has been shown to have a known relationship between the closing time of the Injector and the existing pressure accumulator, the fuel acting pressure exists.

at the invention, the closing time is determined, which is the Injector needed to open from its to pass into its closed state. Dependent on This closing time will then indicate a malfunction closed the pressure sensor.

The Invention has the advantage of being a simple verification allows the pressure sensor to malfunction, without requiring an influence on the operation required is. In particular, malfunctions of the pressure sensor be recognized, without requiring special controls the injector required are. Instead, it is sufficient in the invention, to determine the closing time to make it without special Expenditure on the existing in the accumulator, the fuel to close acting pressure. Based on this pressure can then Again, without any special effort a possible malfunction be recognized by the pressure sensor.

at An advantageous development of the invention is the closing time an expected pressure derived in the accumulator, it is from the pressure sensor a measured pressure in the accumulator measured, and it will be the expected pressure and the measured pressure compared. On In this way it is possible to malfunction the pressure sensor only recognizable by conversions and comparisons.

Especially It is advantageous if the relationship between the closing time of the injection valve and the pressure in the accumulator as a characteristic is stored. In addition, this characteristic of be dependent on a drive duration, which is the time duration that determines the injector in its open Condition is maintained.

at a further advantageous embodiment of the invention is a Actuator end, which represents the time from which the injection valve is no longer held in its open state is, it is determined a splash, which is the time represents, in which the injection valve fully closed is, and it will depend on the closing time determined by the drive end and the injection end. In this way it is possible to turn the closing time only through calculations, so without much effort to investigate.

It is particularly advantageous if the injection end from a transition to a in wesentli Chen constant pressure in the pressure accumulator is derived. Alternatively or additionally, it is advantageous if the injection end is derived from a strike, for example, a valve needle in a valve seat. This represents simple and reproducible possibilities for determining the end of the injection. As has been explained, the duration of closure and, consequently, a malfunction of the pressure sensor can be derived with the aid of the injection end.

Further Features, applications and advantages of the invention result from the following description of exemplary embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features form for itself or in any combination the subject of the invention, independently from its summary in the claims or their relationship and regardless of theirs Formulation or representation in the description or in the drawing.

1 shows a schematic block diagram of an embodiment of a method according to the invention for checking a pressure sensor of a Kraftstoffeinspitzsystems, and 2 shows a schematic diagram for use in the method of 1 ,

at A fuel injection system uses fuel with the help of a Injection valve injected into a combustion chamber of an internal combustion engine. at the injection valve may preferably be a so-called piezoelectric actuator or alternatively also an electromagnetic Act valve. As an internal combustion engine may preferably be a multi-cylinder Diesel internal combustion engine for a motor vehicle for use come, al ternativ but also a mehrzylindriger, if necessary Direct injection automotive gasoline engine.

The Fuel injection system has a pressure accumulator (the so-called Rail), to which the injection valves of the individual cylinders connected are. In the operation of the internal combustion engine is on in this pressure accumulator contained fuel a predetermined high pressure (the so-called Rail pressure). If one of the injectors is opened, so fuel is from the accumulator via the injector injected into the combustion chamber of the associated cylinder.

The Injection of fuel is by an electric control unit controlled and / or regulated. In particular, the controller determines depending on the operating variables of the Internal combustion engine for each of the cylinders which are currently up to date required injection quantity and the associated injection time of the fuel. These sizes are provided by the controller for each injection in a control start and a Driving time converted. About electrical circuits is the associated to the cylinder injection valve in Time of Ansteuerbeginns transferred to an open state and kept in this state for the drive time.

The amount of fuel actually injected into the combustion chamber is very much of the pressure acting in the accumulator on the fuel Pressure influences. The bigger the one on the fuel acting pressure is, the more fuel will be within it Driving duration injected into the combustion chamber. This on the fuel pressure applied in the accumulator is provided by a pressure sensor (the so-called rail pressure sensor) measured. For this purpose, the pressure sensor preferably with the pressure accumulator or alternatively with a be connected to the injectors.

To check the functionality of the pressure sensor is the following, in the 1 schematically illustrated method provided. This method is realized as a computer program and is executed by a computing device present in the control unit of the fuel injection system.

A starting point of the method are the two variables already mentioned, namely the actuation start AB and the actuation time AD. These two sizes are called the block 11 illustrated control and / or regulation of the fuel injection system provided. From the control start AB and the drive time AD is from a block 12 calculates the drive end AE. In this drive end AE is that time in which the control of the injection valve is terminated and the injection valve is thus no longer held in its open state.

The The aforementioned control variables relate to a certain injection of fuel by means of a particular Injection valve in the associated cylinder of the internal combustion engine.

Becomes now the injection valve according to the aforementioned control variables controlled, this does not mean that the injection valve exactly at the end of the control period AD, ie at the time of Ansteuerendes AE, abrupt and complete of his open goes into its closed state. Instead the injection valve needs a finite period of time, namely the closing time SD, from the time of the Ansteuerendes AE to move from its open to its closed state.

The time at which the injector completely in its closed state überge is referred to as Spritzende SE and can be determined in different ways. Thus, it is preferably possible to measure the injection end SE by means of the pressure sensor, namely as a transition from a variable pressure curve to a substantially constant pressure in the pressure accumulator due to the now closed injection valve. Since only a point in time and no pressure is determined in this case with the pressure sensor, a malfunction of the pressure sensor essentially does not lead to a falsification of the determined time. Alternatively or additionally, it is possible to determine the spigot end SE by means of a knock sensor or the like, which detects the striking of, for example, the valve needle in its valve seat when closing the injection valve. In the case of an electromagnetic injection valve, another possibility is to detect the injection end SE inductively.

These investigation possibilities of the splash SE are in the 1 generally as a block 13 shown.

The timing of the drive end AE and the timing of the splash end SE are one block 14 supplied, which calculates the closing duration SD of the injection valve from these variables. This closing time SD is the time difference between the drive end AE and the subsequent injection end SE.

It has been found that the closing duration SD represents a characteristic size of an injection valve. In particular, there is a known relationship between the closing duration SD of an injection valve and the pressure currently present in the pressure accumulator and acting on the fuel. This is in the 2 shown. There, the closing duration SD is plotted against the pressure PR acting on the fuel. The third variable in the diagram is the 2 also considered the drive time AD.

According to the 2 results for a certain drive time AD a substantially linear relationship between the closing time SD and the pressure acting on the fuel pressure PR. Thus, the greater the pressure PR acting on the fuel, the longer the closing time SD which the injection valve requires in order to change over from the time of the control end AE into its closed state, ie to the injection end SE.

That in the diagram of 2 The map shown can be determined in advance using an intact injection valve and an intact pressure sensor and stored in the control unit of the fuel injection system.

In the process of 1 the diagram becomes the 2 to the effect that a block 15 the closing time SD from the block 14 and the drive time AD from the block 11 is fed, and that in this block 15 then based on the diagram of the 2 from the mentioned input variables, the associated pressure in the pressure accumulator is determined. This output is from the block 15 as expected pressure PRe provided.

It should be noted that the expected pressure PRe is not an actually existing pressure, but only the pressure which, on the basis of the present control duration AD and the determined injection end of the SE and on the basis of the diagram of the 2 Resulting connection should be present in the pressure accumulator itself.

As has been explained, the pressure in the accumulator is actually measured by the pressure sensor. This is in the 1 as a block 16 shown. The one from the block 16 output output therefore represents the measured pressure PRg in the pressure accumulator.

In a block 17 the expected pressure PRe and the measured pressure PRg are compared with each other. If a deviation of the measured pressure PRg from the expected pressure PRe is detected, which exceeds a predefinable threshold value in the positive or negative direction, it is concluded that the pressure sensor is malfunctioning. This is from the block 17 reported by means of a signal F. Preferably, the error signal F may be associated with information characterizing the significance or magnitude of the detected deviation.

As an alternative, it is possible that the block 14 determined closing time SD not using the diagram of 2 is further processed, but that from the measured pressure of the pressure sensor PRg in the pressure accumulator with the aid of the diagram of the 2 taking into account the existing activation duration AD, an associated closing duration SD * is determined. This associated closing time SD * is then compared with that of the block 14 determined closing duration SD to derive therefrom an error signal F, which in turn may be associated with a significance of the error.

Usually, in an internal combustion engine, a single pressure sensor for the pressure accumulator and a plurality of injection valves for a plurality of cylinders are present. The described method can thus be carried out for the existing pressure sensor in conjunction with each of the injection valves. In this way, there are several errors Lersignale F for the majority of injection valves.

Provided the error signals additionally the associated significances specify, the following error cases can be distinguished i) Is a significant deviation for all error signals before, it can be assumed that the pressure sensor a Malfunction. ii) Is only one of the error signals a significant deviation, it can be assumed that that the associated injection valve has a malfunction. iii) Is with all error signals no significant, but only one slight deviation, so may be due to aging Drift the pressure sensor and / or the injectors are assumed.

The Recognition of the second error case ii) brings with it the advantage That's not anymore, as hitherto for the sake of difficult Error localization usually usual, in case of an error all injectors need to be replaced, but that specifically only the defective injection valve to be replaced got to.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102004028891 A1 [0002]

Claims (11)

Method for checking a pressure sensor of a fuel injection system, in particular of a motor vehicle, wherein the fuel injection system comprises a fuel-filled pressure accumulator, which is associated with the pressure sensor, and is connected to the at least one controllable injector, and wherein the method exerted a pressure on the fuel and the Injector for injection of fuel is controlled in an open state, characterized in that a closing time (SD) is determined, which requires the injection valve to move from its open to its closed state, and in dependence on the closing time (SD) is concluded on a malfunction of the pressure sensor. The method of claim 1, wherein the closing period (SD) an expected pressure (PRe) is derived in the accumulator, wherein from the pressure sensor, a measured pressure (PRg) in the pressure accumulator is measured, and where the expected pressure (PRe) and the measured Pressure (PRg) are compared. The method of claim 1, wherein of the pressure sensor a measured pressure (PRg) is measured in the accumulator, wherein from the measured pressure (PRg) an associated closing duration (SD *) is derived, and wherein this associated closing time (SD *) and the determined closing time (SD) with each other be compared. A method according to claim 2 or claim 3, wherein the relationship between the closing duration of the injector and the pressure in the accumulator is stored as a characteristic curve, and wherein the characteristic additionally of a drive time (AD) which determines the period of time holding the injector in its open state becomes. Method according to one of the preceding claims, wherein a drive end (AE) is determined, which is the time represents, from which the injector is no longer in its open State is maintained, whereby an injection end (SE) is determined, which represents the time in which the injector is complete is closed, and wherein the closing time (SD) depending on from the drive end (AE) and the injection end (SE) is determined. Method according to claim 5, wherein the injection end (SE) from a transition to a substantially constant one Pressure in the accumulator is derived. Method according to one of claims 5 or 6, wherein the injection end (SE) from a hit, for example a valve needle is derived in a valve seat and / or at an electromagnetic injection valve is determined inductively. Method according to one of the preceding claims, the process being related to multiple injectors is carried out. Computer program for carrying out the method steps according to one of claims 1 to 8, when the computer program runs on a computing device. Control unit for a fuel injection system with a computing device and a computer program for Implementation of the method steps according to one of the claims 1 to 8 when the computer program on the computing device expires. Fuel injection system in particular for a Motor vehicle, with a control unit that uses a computing device and a computer program, wherein the computer program for carrying out the method steps according to one of the claims 1 to 8 is provided when the computer program on the computing device expires.