EP1215388A2 - Method and system for controlling an internal combustion engine - Google Patents

Abstract

The method is carried out by a system, so that the signal emanating from the sensor arranged in the exhaust stretch determines an actual value specific to each cylinder, which is compared to a desired value. Resulting from this comparison, control signals are specifiable for the individual cylinder control of the fuel and/or the amounts of air.

Description

State of the art

The invention relates to a method and a device for controlling an internal combustion engine according to the General terms of the independent claims.

Such a method and such a device for Control of an internal combustion engine is, for example, off known from DE 195 27 218. There is one procedure and one Device for regulating the smooth running of a Internal combustion engine described in which each cylinder Internal combustion engine a control deviation and a regulator assigned. Each regulator gives, starting from the assigned control deviation, a cylinder-specific Control signal before.

The aim of this procedure is to help the individual Equal amount of fuel allocated to cylinders. Differences in the metered amount of fuel between the individual cylinders are balanced. The In the event that, although all cylinders are the same Fuel quantity is metered and / or all cylinders that contribute equal torque to the total torque that different amounts of air are metered to individual cylinders to get. This has the consequence that with individual cylinders increased exhaust emissions, especially particle emissions, occur. These increased emissions can Technology can only be reduced in the whole Injection quantity and / or the mean of the cylinder-specific fuel quantities reduced so far is that emissions are minimized. This Volume reduction leads to a reduction in the performance of the Internal combustion engine.

Advantages of the invention

By means of the method according to the invention and the device according to the invention.

In that, starting from a signal, one in the exhaust tract arranged sensor determined cylinder-specific actual values and be compared with a target value, and that starting from the comparison of control signals to the individual cylinder Control of the fuel and / or air quantity can be predetermined, exhaust emissions can be significantly reduced, whereby the power output of the internal combustion engine is not is affected.

Sensors are preferably used which have a signal provide that the oxygen concentration in the exhaust gas characterized, or a signal representing the pressure in the exhaust gas characterized.

The lambda values, ie the Oxygen concentrations, all cylinders equal. Both the injected and the manipulated variable can be used Amount of fuel as well as the amount of air supplied for example by means of an individual cylinder Exhaust gas recirculation is adjustable, can be used. in the The following is the procedure using the example of Fuel quantity described.

It is particularly advantageous if the procedure with a smooth running control according to the prior art is combined.

According to the invention, it was recognized that a particularly simple Signal processing consists in that the signal of the im Exhaust tract arranged sensor with at least two Filter media with different frequencies can be filtered is, based on the filtered signal at least two frequency-specific actual values, a setpoint and frequency-specific control deviations can be determined.

A particularly meaningful signal results when the Provision of the frequency-specific quantities the output signal of the sensor arranged in the exhaust tract by means of at least two bandpasses with adjustable Center frequencies can be filtered, the center frequencies are integer multiples of the camshaft frequency.

Realizations are of particular importance in the form of a computer program with program code means and in the form of a computer program product with program code means. The computer program according to the invention has Program code means to complete all steps of the perform the inventive method if that Program on a computer, in particular a control device for an internal combustion engine of a motor vehicle becomes. In this case, the invention is represented by an in program stored in the control unit, so that this control unit provided with the program in the same The invention represents how the method for its Execution the program is suitable. The invention Computer program product has program code means that are stored on a computer-readable medium in order to to carry out the method according to the invention if that Program product on a computer, especially one Control device for an internal combustion engine of a motor vehicle is performed. In this case, the invention realized by a disk so that the The inventive method can be carried out if that Program product or the data carrier in a control unit for an internal combustion engine, in particular of a motor vehicle is integrated. As a data carrier or as Computer program product can in particular be an electrical one Storage medium are used, for example Read-only memory (ROM), an EPROM or an electrical one Permanent storage such as a CD-ROM or DVD.

Advantageous and expedient configurations and Further developments of the invention are in the subclaims characterized.

The procedure according to the invention is described below the embodiment shown in the drawing explained. FIG. 1 shows a block diagram of the device according to the invention, Figure 2 is a detailed Representation, Figure 3 is a representation of the target and Actual value.

The procedure according to the invention is described below on Example of a self-igniting internal combustion engine Exhaust gas turbocharger and 4 cylinders described. The invention but is not on self-igniting internal combustion engines limited. It can also be used in other types of Internal combustion engines are used. In this case replace corresponding components. In particular, the Invention also in internal combustion engines with others Number of cylinders and / or in internal combustion engines without Exhaust gas turbochargers are used.

In FIG. 1, the internal combustion engine is 100 characterized. You will get air through a fresh air line 118, a compressor 115 and an intake line 110 fed. The exhaust gases from the internal combustion engine pass through an exhaust pipe 120 and a turbine 125 into one Exhaust pipe 128. Turbine 125 drives the compressor 115 via a shaft, not shown.

The internal combustion engine is a determining quantity Actuator 150 assigned. This is the Internal combustion engine supplied with fuel. Anyone can Cylinder an individual amount of fuel metered become. This is shown in Figure 1 in that each Cylinder a quantity-determining control element 151 to 154 assigned. The individual control elements 151 to 154 are generated by a control unit 160 with control signals applied. The actuators 151 to 154 are concerned are, for example, solenoid valves or piezo actuators that control the fuel metering in the respective cylinder. It can be provided that one injector per cylinder, a distributor pump or another the injected Fuel quantity determining element affecting the cylinders alternately metering fuel is provided.

The control unit 160 also acts on another Actuator 155, which is the amount of fresh air that the Internal combustion engine is influenced. At a simplified embodiment, this actuator 155 also be omitted. Furthermore, the Control unit 160 the output signals of various sensors 170, which, for example, the environmental conditions such as Temperature and pressure values as well as the driver's request characterized.

Furthermore, control unit 170 processes signals from Sensors 180 that measure the exhaust gas composition or pressure and / or characterize the temperature in the exhaust gas. This Sensor is preferably between the engine and the turbine 125 arranged. Alternatively or in addition can the sensor 185 also after the turbine in the exhaust pipe be arranged.

The sensors 180 and 185 preferably detect a signal that characterized the oxygen concentration in the exhaust gas. Alternatively and / or additionally, it can also be provided that the pressure in the exhaust pipe upstream or downstream of the turbine is evaluated.

This facility now works as follows. The fresh air is compressed by the compressor 115 and passes through the Intake line 110 in the internal combustion engine. The Internal combustion engine is about the quantity-determining Actuator 150 metered fuel. Everyone will Cylinder depending on the control signal from the control unit 160 a cylinder-specific amount of fuel supplied. The Exhaust gases reach the turbine via the exhaust pipe and drive These arrive and then pass through the exhaust pipe 128 in the environment. The turbine 125 drives the compressor 115 via a shaft, not shown.

The control unit 160 calculates on the basis of the various input signals, especially the Driver request, the control signals to act on the Actuators 151 to 154. In a preferred An embodiment is additionally an actuating device 155 provided the air supply to the internal combustion engine controls. This can preferably be a Exhaust gas recirculation device act the amount of recirculated exhaust gas determined. One is particularly preferred Embodiment in which the single cylinder amount of air supplied is influenced. This is for example by valve control of the inputs and Exhaust valves possible.

The determination of the control signals for the control elements 151 to 155 is shown in more detail in FIG. It is in particular the calculation of the fuel quantity QK shown. When calculating the amount of air can be followed accordingly.

Elements already described in FIG. 1 are included corresponding reference numerals. The actuator 150 becomes the output signal QK of an addition point 202 acted upon. At the first input of the addition point 202, the output signal QKF is applied to a quantity specification 210. This is due to the second input of addition point 2 Output signal QKL of a multiplexer 250 on.

The quantity specification 210 processes the output signal various sensors, such as one Accelerator pedal position sensor 170a and a speed sensor 170b. Furthermore, it can be provided that the Quantity specification 210 the output signal L of a sensor 180 processed. The output signal L of the sensor 180 corresponds the oxygen concentration in the exhaust tract.

The signal L of the sensor 180 also comes to a Filter device 230, which in turn has a first controller 241, a second controller 242, a third controller 243 and one fourth controller 244 is supplied with a signal that one Control deviation corresponds. Overall, the controllers 241 to 244 referred to as controller 240. The individual controllers in turn act on the multiplexer 250 Control signals, which then cyclically as signal QKL to Add addition point 202.

Based on the various sensor signals, the Quantity specification 210 an amount of fuel QKF to be injected, which is to be fed to the internal combustion engine. That amount of QKF corresponds to the amount required to meet the Provide driver with desired torque. there the quantity control 210 contains further functions, such as an idle controller or Interventions by other control units. Furthermore quantity specification 210 can already be a smooth running control, as known from the prior art. It is also possible that a non-cylinder individual Quantity specification also takes into account a lambda signal that the Characterized oxygen concentration in the exhaust gas.

Air volume error, i.e. Deviations between the air volumes, which are fed to the individual cylinders are used by the Quantity specification 210 not taken into account. different Lambda values of the individual cylinders lead to fluctuations of the lambda signal. These are recorded and used cylinder-specific regulation used. The Filter device 230 calculates from the lambda signal L that with the sensor 180, a cylinder-specific one Control deviation between the cylinder-specific target and Actual value for the lambda signal. This individual cylinder Control deviation is the respective controller, the cylinder is assigned. It can be provided that a controller is provided for each cylinder. Alternative is it is also possible that a controller successively the cylinder-specific control deviations processed. This is particularly the case when the invention as Control program is realized. The multiplexer 250 holds these signals together to form a signal QKL that the Deviations of the individual lambda signals from a target value characterized. This signal is designed so that at the actuation of the actuating device 150 Fuel quantity is metered that the lambda signal at assumes the same value for all cylinders.

With the help of cylinder-specific lambda control by interfering with the air measurement also air volume errors be compensated for between the individual cylinders occur, i.e. the exhaust gases of all cylinders have the same oxygen concentration. Compared to usual Quantity compensation regulations according to the prior art can clearly the exhaust gas values of the internal combustion engine be improved. This is especially the case with lower ones Speeds and large injection quantities are an advantage. Nice small deviations in the lambda value, i.e. the Oxygen concentration in the exhaust gas of a cylinder in the direction of a richer mixture lead to a sharp increase the soot emissions in this cylinder. This increased Soot emission is not the result of the somewhat lower Soot formation in a cylinder with a correspondingly lean Mixture balanced. With a cylinder-specific Lambda control can therefore have the same engine torque lower blackening number can be achieved. Alternatively lets the given moment with the same number of blackening increase. This is due to the fact that in a system without cylinder-specific lambda control the amount of fuel and so that the moment given must be lowered so far that the amount of soot is below a certain value.

In particular internal combustion engines with a turbocharger, i.e. one for compressor and one turbine are the requirements for the signal processing of the Lambda signal particularly high because the one to be evaluated Signal amplitude when using a lambda probe the turbine is very small.

There are two alternatives for the arrangement of the lambda probe to disposal. A first alternative is the lambda probe arranged in front of the turbine. This has the advantage that no mixing of the individual cylinders Exhaust gas flows through the turbine have occurred. however are in this area by opening the exhaust valves strong pressure vibrations stimulated. Compensate for this partly due to the cylinder-specific lambda differences excited vibrations on the probe signal. This is based on that described below Mode of action. Becomes a higher one in a cylinder Injection quantity injected, the corresponding one decreases Residual oxygen content in the exhaust gas and thus the output voltage the lambda probe. At the same time results from the stronger Burning a higher pressure when opening the Outlet valve. By positive cross coupling between Pressure and probe signal increases the pressure rise Sensor signal and affects the actual oxygen change opposite. This makes the measurable signal amplitude clear smaller than expected based on the pure oxygen vibration would. Another disadvantage is that an additional probe is needed.

In the second alternative, the lambda probe is behind the Turbine arranged. The advantage here is that the Interference amplitude of those caused by the combustion Pressure fluctuations in the exhaust system is smaller. adversely however, the mixing of the individual cylinders affects Exhaust gas flows out through the turbine. This also reduces this arrangement of the probe the amplitude of the measured Oxygen vibrations.

Since both when using alternative 1 and when Alternative 2 the signal to be evaluated clearly has a smaller useful amplitude than in internal combustion engines without turbocharger, is an improved signal processing for Interference suppression, especially in internal combustion engines with turbocharger, an advantage.

The heating frequency is a particularly serious disturbance To call the lambda probe. Their interference amplitude is approximately like this big, like that due to the cylinder-specific lambda differences caused vibrations. These vibrations can be compensated by fast signal preprocessing become.

3, the control deviation calculation 230 is more detailed shown. Elements already described in FIG. 2 are designated in Figure 3 with corresponding reference numerals. The output signal of the sensor 180 arrives at a Prefilter 300 to a first filter 310 and a second Filter 320. The output signal of the first filter 310 arrives at a first setpoint determination 312 and one first actual value determination 314. The output signal of the second Filter 320 arrives at a second setpoint determination 322 and a second actual value determination 324.

The output signal NWS of the first setpoint determination 312 arrives with positive sign and the output signal NWI to the first actual value determination 314 with a negative sign a node 316. In the following node 318 becomes the output signal of node 316 with linked to a weighting factor FNW. The weighted first Control deviation NWL arrives at an addition point 340 and thence to block 240.

The output signal KWS of the second setpoint determination 322 arrives with a positive sign and the output signal KWI the second actual value determination 324 with a negative sign to a node 326. In the following node 328 becomes the output signal of the node 326 linked to a weighting factor HFC. The so weighted second control deviation KWL reaches the addition point 340

The weighting factor FNW and the weighting factor FKW become provided by the weighting target 330.

The control deviation is at the output of the addition point 340 L available, which forwarded to controller 240 becomes.

Junction points 318 and 328 are a preferred embodiment of the invention. Alternatively, you can it can also be provided that the factors FNW and / or FKW otherwise, for example in filters 310 or 320, be taken into account or not taken into account.

In the illustrated embodiment, a Internal combustion engine with 4 cylinders are only two Filters provided the signal components with camshaft and Filter out the crankshaft frequency. With advantageous Embodiments can also be provided that further Frequency ranges are taken into account. In particular, can also be provided that a filter is provided which the Frequencies up to and including half the ignition frequency filter out.

In the illustrated embodiment of an internal combustion engine with four cylinders, the filters are 310 and 320 um bandpass filters, whose center frequency at Filter 310 at the camshaft frequency and filter 320, is at the crankshaft frequency.

With other cylinder numbers, there may be other band passes provided. For example, in an internal combustion engine with four or five cylinders with a bandpass the camshaft frequency and a bandpass with double Camshaft frequency that corresponds to the crankshaft frequency provided.

In an internal combustion engine with 2 * k cylinders, where k is a is a natural number, k bandpasses must be provided, the center frequencies at an integer multiple of the camshaft frequency lie.

The output signal of the sensor 180 passes through the Prefilter 300 to the bandpasses 310 and 320. This one Prefilter 300 is designed such that it is undesirable Filters out interference. The prefilter is preferably 300 formed such that it vibrates the signal, the caused by the probe heating, does not let through.

The output signal is obtained by means of bandpasses 310 and 320 of the sensor 180 separated into spectral components. For each Spectral components determine the first, second and third Actual value determination and the first, second and third Setpoint determination frequency-specific setpoints and actual values. The setpoints and actual values are calculated for the individual spectral components are preferably different.

By means of the bandpasses 310 and 320, the probe signal for the individual frequencies separately. For any frequency calculates the first actual value determination 314 and the second Actual value determination 324 a frequency-specific actual value. Accordingly, it can be provided that for each frequency first setpoint specification 312 and the second setpoint specification 320 calculates a frequency-specific setpoint. In the Junction points 316 and 326 then become the frequency-specific control deviation determined.

It is particularly advantageous if these are frequency-specific Control deviations using frequency-specific weighting factors NW and PFCs can be weighted in a frequency-specific manner. Especially It is advantageous if the weighting factors FNW and FKW be chosen so that the control loop gain for all Frequencies is set the same. This can cause a frequency-specific adjustment of the controller parameters achieved become.

The control deviations weighted or not weighted NWL and KWL are added in node 340 and the Regulator supplied. The controller corresponds to that in FIG. 1 controller 240 shown.

It is particularly advantageous with this procedure that the Controllability even with large differences in the phase position given is. Through the frequency-specific formation of the control deviation there is an increased robustness of the Controller against changes in the controlled system behavior, e.g. through changes in the area of the air system, especially in the area of intake valves, manufacturing tolerances or wear.

As an alternative to evaluating the lambda signal, a Pressure sensor can be used, the pressure in front or behind the turbine evaluates.

Claims (10)

1. A method for controlling an internal combustion engine, in which a control deviation and a controller are assigned to each cylinder of the internal combustion engine, each controller specifying a cylinder-specific control signal based on the assigned control deviation, characterized in that, starting from a signal from a sensor arranged in the exhaust tract, cylinder-specific actual values are determined and compared with a target value, and that, based on the comparison, control signals for the cylinder-specific control of the fuel and / or air quantity can be specified. 2. The method according to claim 1, characterized in that the signal of the sensor arranged in the exhaust tract can be filtered with at least two filter means with different frequencies, starting from the filtered signal at least two frequency-specific actual values, a target value and frequency-specific control deviations can be determined. 3. The method according to claim 2, characterized in that to provide the frequency-specific variables, the output signal of the sensor arranged in the exhaust tract can be filtered by means of at least two bandpass filters with adjustable center frequencies. 4. The method according to claim 1 or 2, characterized in that the center frequencies are integer multiples of the camshaft frequency. 5. The method according to at least one of the preceding claims, characterized in that the actual values and / or the target values can be predetermined differently for each frequency. 6. The method according to at least one of the preceding claims, characterized in that the control deviations can be weighted differently for each frequency. 7. The method according to at least one of the preceding claims, characterized in that the arranged in the exhaust tract sensor delivers a signal that characterizes the oxygen concentration in the exhaust gas, or a signal that characterizes the pressure in the exhaust gas. 8. A device for controlling an internal combustion engine in which each cylinder of the internal combustion engine, a control error and a controller is associated, each governor is based on the assigned control error, a cylinder-specific actuation signal, characterized in that means are provided which, starting from a signal of the Sensor arranged in the exhaust gas tract determine cylinder-specific actual values and compare them with a target value and, based on the comparison, specify control signals for the cylinder-specific control of the fuel and / or air quantity. 9. Computer program with program code means to carry out all steps of any one of claims 1 to 11 when the program is executed on a computer, in particular a control device for an internal combustion engine. 10. Computer program product with program code means, which are stored on a computer-readable data carrier, to carry out the method according to any one of claims 1 to 11, when the program product is executed on a computer, in particular a control unit for an internal combustion engine.

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