EP2076667B1 - Method and device for monitoring a fuel injection system - Google Patents

Description

State of the art

The invention relates to an apparatus and a method for monitoring a fuel injection system.

From the DE 195 20 300 For example, a method for detecting a leak in a common rail system is known. There, an actuating element for influencing the rail pressure is acted upon by a control signal and checks whether the pressure changes as expected. If this is not the case, leakage is detected. From the EP 1088 980 It is known to change the injection time point and besbeachten the exhaust gas mixture.

Disclosure of the invention Advantages of the invention

The device according to the invention and the method according to the invention with the features of the independent claims has the advantage over the prior art that it provides reliable and simple fault detection in the area of fuel metering and is essentially independent of the injection components used. Ie. The procedure can be used both in common-rail systems, as well as in pump-nozzle systems, and also in conventional distributor injection pumps or series pumps. Furthermore, the method and the device in any injectors in common rail systems, ie in solenoid valve injectors and / or piezoelectric actuators can be used. It is particularly advantageous to monitor the control of the start of injection or of the injection position, since the prior art only provides insufficient monitoring devices for this purpose.

A monitoring of the start of injection is advantageous because the start of injection has both an influence on the performance of the internal combustion engine, as well as on the consumption of the internal combustion engine. Furthermore, errors or tolerances at the start of injection also affect the exhaust emissions.

In diesel internal combustion engines, the start of injection is usually controlled in order to inject fuel into the cylinders at desired times or desired piston positions of the diesel internal combustion engine. If there are errors or tolerances, so that too early or too late injected, so this is not recognized in conventional injection systems. Such defects may occur in the area of the control unit, the injection system, d. H. the injectors and / or the sensor elements that detect, for example, the start of injection and / or the position of the internal combustion engine occur. Such changes in the start of injection could, among other things, result in a change in the emission behavior, the driving behavior or the noise emission.

It is particularly advantageous if only the change in the measured values between a first value and at least one second value is checked. It is preferably checked whether this change in the measured value lies in an expected window, ie it is checked whether the change in the measured value is greater than a lower threshold and less than an upper threshold. If the change in the measured value is within the window, error-free operation is detected and an error is detected outside the window. By evaluating the change due to a change in the manipulated variable, other error influences that have an effect on the fuel injection can be eliminated. Ie. by a targeted influencing of the manipulated variable and a subsequent evaluation of the change, which is caused by this change in the manipulated variable, other causes of error can be safely excluded and the error can be better assigned. In particular, the error of the detection of the sensor signals, the determination of the manipulated variable in the control unit and / or the actuator, which performs the injection can be assigned. The fact that the relationships between changes in the measured variable are determined, an even better assignment than by evaluation of the change is possible.

The measured variable used is preferably the rotational speed or a variable which is the torque which is provided by the internal combustion engine. Alternatively, it can also be provided that the angular acceleration or another variable derived from the speed signal and / or an angle signal is used as the measured variable. Furthermore, it is advantageous if the measured variable is determined from a structure-borne noise signal or a combustion chamber pressure signal.

Brief description of the drawings

• Figur 1 ein Blockdiagramm der wesentlichen Elemente,
• Figur 2 verschiedene Signale über dem Einspritzbeginn aufgetragen und
• Figur 3 ein Flussdiagramm des erfindungsgemäßen Verfahrens.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following descriptions. Show it

• FIG. 1 a block diagram of the essential elements,
• FIG. 2 plotted different signals over the beginning of injection and
• FIG. 3 a flow chart of the method according to the invention.

Embodiments of the invention

In FIG. 1 the device according to the invention is shown as a block diagram. With 100 an internal combustion engine is designated, which is associated with at least a first sensor 110 and a controller 120. The sensor 110 acts on a control unit 130 with a signal N and the control unit 130 in turn also acts on the controller 120 with a drive signal A. Furthermore, the control unit 130 processes the output signal of a second sensor 140.

The illustrated internal combustion engine 100 is preferably a self-igniting internal combustion engine. The first sensor 110 detects a signal N which corresponds to the rotational speed of the internal combustion engine. Depending on the embodiment of the procedure according to the invention, different variables can be determined on the basis of the speed signal. Thus, for example, be determined by filters, such as a differentiation, a bandpass filter or a discrete Fourier transform, the angular acceleration or other derivatives of the speed signal. These signals can be supplied instead of the speed signal N of the control unit 130.

As an alternative to this signal, it is also possible to detect other signals which characterize the torque output by the internal combustion engine. For example, based on a structure-borne sound signal or a combustion chamber pressure signal, a variable can be determined and used as a signal that characterizes the torque output by the internal combustion engine. Furthermore, further sensors may be provided, which may be provided with further sizes which characterize the operating state of the internal combustion engine. Such sensors are, for example, temperature sensors and / or pressure sensors which detect the temperature of the internal combustion engine, the pressure of the fuel and / or other variables.

The actuator 120 is preferably an injector that includes a solenoid valve or a piezoactuator. Instead of such a controller, other actuators that affect the fuel metering, can be used. In particular, a pump-nozzle unit, a distributor pump or a series pump can be provided. Depending on the drive signal provided by the control unit 130, the actuator of the internal combustion engine measures a certain amount of fuel at a specific point in time or at a specific position of the crankshaft of the internal combustion engine. It is provided, for example, that the start of energization of the solenoid valve determines the beginning of the injection and the end of the energization determines the end of the injection. Depending on the configuration of the actuator or its actuator can also be provided that the beginning of the energization determines the end and the end of the energizing the beginning of the metering. The difference between the start of energization and the end of the energization essentially determines the energization duration or the duration of the metering and thus the injected fuel quantity. The control unit 130 determines the drive signal based on the signals of the first sensor and the second sensor 140.

The second sensor 140 in particular detects variables which characterize the operating state of the vehicle or ambient conditions. In this case, in particular temperature and / or pressure variables are detected. Furthermore, it can be provided that the second sensor or the first sensor detects quantities that characterize the exhaust system of the internal combustion engine. This is it For example, the temperature or the pressure in the exhaust gas or in the intake fresh air.

Based on the various variables, the control unit 130 determines the drive signal A for the actuator 120. It may be provided that only one controller is provided, in which, based on the input variables, a manipulated variable is specified. Furthermore, a regulation can be provided which regulates, for example, the start of activation or another variable characterizing this, such as, for example, the start of injection, the start of combustion or other variables, ie. H. compares with a setpoint and depending on the deviation between the setpoint and actual value, the control signal changed accordingly until the setpoint and the actual value match.

According to the invention, it has been recognized that the fuel metering has a significant influence on the exhaust emissions. Furthermore, errors throughout the system, i. H. in the actuator, in the internal combustion engine, in the sensors 110 or in the control unit 130 effects on the fuel metering. Ie. in case of an error, the desired amount of fuel is not metered at the desired time. This in turn has effects on the behavior of the internal combustion engine, d. H. There is, inter alia, an increase in fuel consumption and / or increased exhaust emissions. Both must be reliably detected and avoided.

In FIG. 2 the relationship between the measured values M and measured value changes D for three different injection starts A is plotted. These measured values M are preferably determined from the speed increase. For example, an angular acceleration which is formed by differentiation of the speed signal can be used as the measured value. Alternatively to the angle acceleration, the result of another filtering method on the speed signal, such as bandpass filtering or discrete Fourier transform, may also be used.

A0 indicates the output value for the start of control. With this value, the actuator is usually controlled in the present operating conditions. Further, a first drive value A1 and a second value A2 entered for the control start, in which the output value A0 is reduced by a small value or increased by a small value. The measured value change D1 corresponds to the quotient of the measured value M between the state with the start of control A0 and the start of control A1 on. Accordingly, the value D2 indicates the quotient of the measured values between the operating point with the drive value A0 and the drive start A2. The value D0 assumes the value 1, since this indicates the quotient between the start of control A0 and the start of control A0.

According to the invention is now, as in FIG. 3 provided that in a first step 300, the usual in the operating state control signal output with the control start A0 and the measured value M0 is detected. In step 310, the start of control is changed to the value A1 and the measured value M1 is detected. Accordingly, in step 320, the value for the start of control is set to the value A2 and the measured value M2 is determined. The measured values used are preferably the rotational speed or variables derived from the rotational speed. As an alternative to the rotational speed, other variables that characterize the torque output by the internal combustion engine can also be evaluated.

In the subsequent step 330, the quotient D1, d. H. the quotient between the measured value M1 and the measured value M0 is determined. In step 340, the quotient D2, d. H. the quotient between the measured value M2 and M0 is calculated. In step 350, the difference V between the two quotients D1 and D2 is determined. The subsequent query 360 checks whether the difference V is smaller than a first threshold S1. If so, the program ends in step 370 with a detection for errors. If the query 360 recognizes that the difference V is not smaller than the threshold value S1, then the query 380 follows. This checks whether the difference V is greater than or equal to the second threshold value S2. If so, then an error is also detected in step 370. If this is not the case, a fault-free state is detected in step 390.

Ie. According to this exemplary embodiment, it is checked whether the difference of the quotients of measured values determined from the rotational speed lies in a specific measuring window, which is defined by the values S1 and S2, where S1 is smaller than S2. If this is the case, ie the measured values for the difference V are in this Window, is detected on a faultless and otherwise on a faulty operating state.

According to the invention, it can also be provided that further measuring points are defined, ie. H. that the control start is changed by further smaller amounts or by an amount between A0 and A1 or between A0 and A2 and the corresponding differences are calculated and evaluated accordingly.

This means that the speed changes of different injection starts are evaluated. If these measured values do not correspond to the values specified in the application, this is recognized as an error. In this case, preferably not the speed values, but speed changes between the start of control, which is usually present, and evaluated the modified start of control. It is particularly advantageous, if not the speed changes, but the ratios of the speed changes are evaluated.

In one embodiment, it may also be provided that a plurality of ratios are formed and these are likewise compared with threshold values. Ie. It is checked whether a change in the start of control results in an expected change in the speed or another measured variable. It is particularly advantageous if, instead of the rotational speed, a variable is evaluated which characterizes the torque provided by the internal combustion engine.

Claims (3)

1. Method for monitoring a fuel injection system, wherein a control variable which influences the start of injection is changed by two defined amounts and a first measurement value (M0) of a measurement variable before the change and two second measurement values (M1, M2) after the respective changes are detected, wherein two quotients (D1, D2) between the two second measurement values (M1, M2) and the first measurement value (M0) are determined, and wherein a fault is identified if the difference (V) between the two quotients (D1, D2) lies outside a measurement window.
2. Method according to Claim 1, characterized in that the measurement variable is the rotational speed or a variable which characterizes the torque provided by the internal combustion engine.
3. Device for monitoring a fuel injection system, having means which change a control variable, which influences the start of injection, by two defined values and which detect a first measurement value (M0) of a measurement variable before the change and two second measurement values (M1, M2) after the respective changes, wherein the means determine two quotients (D1, D2) between the two second measurement values (M1, M2) and the first measurement value (M0) and identify a fault if the difference (V) between the two quotients (D1, D2) lies outside a measurement window.

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