EP0411321B1 - Method for controlling the measuring of fuel in a diesel engine - Google Patents

Description

State of the art

The invention relates to a method and a device for controlling the fuel metering in a diesel internal combustion engine according to the preambles of the independent claims.

Such a method for controlling the fuel metering in a diesel internal combustion engine is known from DE-A-37 29 771. In the process there, the amount of fuel to be injected in the part-load range is taken from multi-dimensional maps. The fuel quantity to be supplied to the internal combustion engine is controlled with these values. In the full load range, the output signal of a lambda probe is compared with a target value. If the output signal of the lambda probe exceeds the specified target value, the amount of fuel to be injected is limited accordingly. The control has no influence on the fuel quantity in the full load range. This device has the disadvantage that the control of the fuel quantity depends only on the operating state (start, Lecrlauf, full load, partial load) and on a few operating parameters such as speed, accelerator pedal position and the desired torque of the internal combustion engine. This device can lead to impermissible exhaust gas emissions in certain operating states.

Object of the invention

The object of the invention is to improve the dynamics of the internal combustion engine in a method for controlling the fuel metering of the type mentioned at the beginning, to minimize the exhaust gas emissions which occur, with the least possible use of additional sensors. This object is achieved by the features characterized in claims 1 and 16.

Advantages of the invention

The method and the device with the features of the independent claims has the advantage over the prior art that in certain operating ranges the fuel quantity is only controlled and in other operating ranges the pilot values act together with the controller output signal on the fuel quantity. Further advantageous refinements of the invention result from the measures specified in the dependent claims.

drawing

Zin embodiment of the invention is shown in the drawing and is explained in more detail in the following description. Figure 1 shows schematically the fuel metering in a diesel engine. FIG. 2 shows several possibilities of how the air quantity Q1 is calculated on the basis of different sizes. A flow diagram of the control logic is shown in FIG. The control parameter specification is explained in more detail in FIG. FIG. 5 shows a particularly advantageous embodiment of controller 60. FIG. 6 shows the individual operating areas of the diesel internal combustion engine.

Description of the embodiment

A diesel internal combustion engine is identified by 100 in FIG. This internal combustion engine receives fuel via a fuel pump 110 and fresh air via an intake pipe 120. The exhaust gases are discharged via the exhaust line 130. Sensors 140 on the fuel pump 110 obtain a signal SB which indicates the start of spraying or a fuel quantity signal MI which corresponds to the quantity actually injected. Sensors 150 are arranged in the intake pipe 120 and record the intake air quantity Q1, the pressure P1 and / or the temperature T1 of the air drawn in by the internal combustion engine. Sensors 160 on the internal combustion engine detect, among other things, the cooling water temperature TW. Other sensors 170 sense speed n or torque Md. A lambda signal is obtained in the exhaust pipe by means of a sensor 180.

The amount of fuel supplied to the internal combustion engine 100 essentially depends on the output signal M of the minimum selection 15. A device 20 generates an additional or replacement signal in special operating conditions. The minimum selection 15 receives a signal from a driving behavior map 30 and a sum point 40. The output signal of the driving behavior map 30 essentially depends on the rotational speed n and the driver pedal position 190. Instead of the driving behavior map 30, the output signal of a driving speed controller can also be used. The summation point 40 combines the output signals of a pilot control map 50 and a controller 60. The output signal of the pilot control map 50 can also be influenced by adaptation controllers 54, 56. An air quantity signal Q1, a speed signal n and possibly further quantities serve as input quantities for the pilot control map 50.

When the switch 70 is closed, the controller output signal MR reaches the summation point 40, via a switch to the adaptation controllers 54, 56 or to the pilot control map 50. The position of the switch 70 depends on the output of the control logic 62. By means of a control parameter specification 72, the control parameters of the controller 60 can be adapted as a function of various operating parameters (control deviation, speed and various quantity signals). The control deviation between the desired lambda value and the actual lambda value at the difference point 74 serves as the input for the controller 60. In the figures, the desired lambda value is denoted by λS and the actual lambda value by λI. The lambda setpoint comes from a setpoint specification 76, which calculates the setpoint depending on different variables such as speed n, cooling water temperature TW or start of injection 58. To improve the control dynamics, it can be advantageous to route the signals that identify the speed n and the start of injection 58 via a respective DT element (77, 78). The actual lambda value is measured by a lambda probe 180 arranged in the exhaust pipe 130.

Instead of the lambda signal, an exhaust gas temperature signal TA or a torque signal Md can also be regulated to a predetermined target value. The input variables of the pilot control map then differ depending on the controlled variable.

The device described works as follows: The internal combustion engine 100 receives fuel from the fuel pump 110 in accordance with the quantity signal M. In general, this quantity signal M is determined by the minimum selection 15.

The device 20 determines the amount of fuel M in certain operating states such as start, idling. The minimum selection 15 selects the smaller of the signals at its two inputs out. At one input there is a MW volume signal that characterizes the driver's wish. The driver's request is specified by the pedal value transmitter 190 or by a vehicle speed controller, not shown. Depending on the output signal of the pedal value transmitter 190 and the speed n, the driving behavior map 30 outputs the desired quantity MW. At the second output of the minimum selection 15 there is a second quantity signal which is composed of the output signals of the pilot control map 50 and the controller 60.

The pilot control map 50 outputs a quantity signal MV as a function of the speed n and the output signal Q1 of an air quantity detection 55. The air quantity detection 55 can be designed as an air quantity meter or, as shown in FIG. 2, can calculate the air quantity Q1 on the basis of various sizes. The output signal of the pilot control map 50, which can be combined multiplicatively with the output signal of the adaptive controller 54 or additively with the output signal of the adaptive controller 56, acts continuously on the quantity signal M.

The pilot control makes a rough adjustment of the fuel quantity M without a settling time. The controller 60 is only switched on, preferably at full load, in certain operating states and then corrects the pilot control quantity MV. The output signal MR of the controller 60, which depends on the difference between the actual value and the output signal setpoint specification 76, only determines the quantity signal M when the switch 70 is closed, that is to say the controller 60 is switched on. A flowchart of the control logic 62 for actuating the switch 70 is shown in more detail in FIG.

An adaptation of the feedforward control is possible through the overlaid control loop. For this purpose, the output signal of the controller 60 is passed to the inputs of the adaptive controllers 54 and 56 or a further input of the pilot control map 50 when the switch 70 is closed. Since the lambda signal can be recorded continuously, it is suitable especially for fast, easy adaptive control. The adaptive control prevents smoke peaks and improves engine elasticity. The adaptation compensates for the influence of the fuel temperature. A fuel temperature sensor is no longer necessary.

The pre-control values can be adapted in different ways. The output signal of the pilot control map is, depending on the output signal MR of the controller 60, multiplicatively corrected by the adaptation controller 54 and / or by the adaptation controller 54 additively.

Depending on the position of the switch, the output signal of the controller MR reaches the adaptation controllers 54 or 56. If the internal combustion engine is operated in operating areas in which additive errors preferably have an effect, the output signal of the controller 60 reaches the adaptation controller 56. The latter then determines an additive variable , this is then added to the output signal MV of the pilot control map 50 in all operating ranges. This is the case, for example, when only a small amount of fuel is supplied to the internal combustion engine.

On the other hand, if the internal combustion engine is operated in operating ranges in which multiplicative errors preferably have an effect, the output signal of the controller 60 reaches the adaptation controller 54. The latter then determines a multiplicative variable by which the output signal MV of the pilot control map 50 is then multiplied in all operating conditions. This is the case, for example, when a large amount of fuel is supplied to the internal combustion engine.

In a particularly advantageous embodiment, the output signal of the controller 60 can be routed directly to the pilot control map 50. As a result, the values stored in the pilot control map 50 can be changed depending on the controller output signal.

Good control dynamics can be achieved by using a connection of the lambda controller 60 to a precontrol. Since the pilot control remains in operation, the safety of the system is increased in the event of a probe failure.

The output signal of the setpoint specification 76 essentially depends on the speed n. The influence of engine heating on the exhaust gas composition can be corrected via the cooling water temperature TW, or a corresponding measured variable. Furthermore, by detecting the start of injection 58, its influence on the exhaust gas composition can be taken into account. The dynamic influence of speed n and start of injection 58 can be taken into account by DT elements.

At low driving speeds, especially at v = 0, the setpoint is shifted towards lower quantities or the control parameters are changed accordingly. This avoids that when the vehicle is at a standstill, by pressing the accelerator pedal, the speed increases steeply and inadmissible smoke emissions occur.

The speed signal n and a signal corresponding to the intake air quantity Q1 serve as the input variable for the pilot control map 50. FIG. 2 shows several options for obtaining such a signal Q1. In FIG. 2a, the computer 502 calculates the air quantity Q1 from the pressure P1 and the temperature T1 in the intake line. The absolute pressure or the differential pressure to the air pressure can be used as the pressure P1. The control system reacts faster if the temperature signal T1 of a slow temperature sensor is pre-controlled as a function of the pressure signal P1.

To reduce the number of sensors, one of the sensors for pressure or temperature can be dispensed with. It is particularly advantageous if only the air temperature T1 is measured with a fast sensor and the course of the pressure from the measured one Course of the temperature is derived. The steady-state initial value of the derived pressure is formed by a map 503 as a function of speed n and the injected fuel quantity MI. A correction of the basic level of the air temperature, which increases as the engine heats up, is approximated via an existing measurement of the cooling water temperature. The compression of the charge air quickly leads to an increase in temperature, so that the error regarding the real boost pressure is not significant.

Figure 2b shows another possibility. The quantity of air sucked in by the internal combustion engine can be obtained by means of a simulation 504 from the injected fuel quantity MI and the acceleration of the internal combustion engine, the derivation 506 of the rotational speed n over time. This simulation can only be used with the activated lambda control, since it only requires a limited accuracy as a pilot control.

FIG. 3 shows a flow chart of the control logic 62 and the control parameter specification 72. After the engine 600 has started 600, the controller 60 is initially switched off 602, the switch 70 is open. The controller output signal MR has the value zero 604. If the quantity request MW, output signal of the driving behavior map 30, is greater than the output signal of the pilot control map MV and / or if the actual lambda value is less than the lambda target value 606, the controller is switched on 608, the switch 70 is closed.

If the quantity request MW is smaller than the controller output signal MR 610 but is still larger than the output signal of the pilot control map MV 612, the output signal of the controller MR is frozen 614. This means that the output signal of the controller is temporarily stored. If the quantity request MW is greater than the controller output signal MR 610, the controller remains switched on 608. If the quantity request increases again after a short time, the controller resumes 608 if the actual lambda value is too rich with the frozen controller output signal.

If the desired quantity is smaller than the controller output signal but larger than the output signal of the pilot control map, then a counter is set 616 to zero and increased 618 in certain periods of time. If query 620 detects that the desired quantity increases in the meantime via the controller output signal MR, the controller is switched on again 608. If the desired quantity MW falls below the output signal MV of the pilot control map 622, the controller is switched off 602 and the controller output MR is set to zero 604. If the counter does not exceed a threshold S, it is increased again by one. If, on the other hand, it exceeds the threshold S 624, the frozen output signal is modified 626. By tracking the controller or by calculating the respective initial value, there is a jump-free detachment when the controller 60 is switched on.

The control parameters, i. H. the P and I components of the PI controller can be controlled as shown in FIG. 4. A kinked gain characteristic of the controller, depending on the sign of the control deviation, is particularly advantageous. A different amplification is particularly advantageous when starting from partial load 701, as long as the measured lambda value is greater than the lambda setpoint 702 (negative control deviation) and the quantity MR desired by the controller is smaller than the quantity MV output by the pilot control map. If, for the first time after partial load operation 701, the quantity request MW is between the value 703 determined by the pilot control map and the value determined by the lambda controller, then a lower gain 706 is selected for the careful approximation to the smoke limit. Then a higher gain is selected for both positive and negative control deviations.

The following modification is used for fast controllers: A low gain is selected when a small control deviation, the difference between the actual lambda value and the desired lambda value is less than a threshold S 704, signals that only a small amount is added may. A high gain 707 is chosen in all other cases. Especially at higher gears, the acceleration behavior is improved by the higher gain.

The following alternatives are also possible, with variable controller parameters 716, for influencing the control parameters: For example, the control parameters can be coupled to the fuel quantity MI via a differentiator 709. Upon acceleration, the derivation of the speed is greater than a threshold, the switch 714 is closed and the gradient 710 of the lambda signal influences the control parameters. The increase in volume through the pilot control is slower in higher gear.

With a full load jump, i.e. the desired quantity increases very quickly, the regulator can overshoot, which results in increased soot emissions. This undesirable additional quantity is further increased if the pilot control continues to demand an increasing quantity. This overshoot of the fuel quantity to be injected is based on the dead time and the delay time of the controlled system. This can be avoided by the following procedure. If the actual lambda value falls below the target lambda value, the output signal of the pilot control map is only output with a delay if the pilot control requests an additional quantity.

FIG. 5 shows a particularly advantageous embodiment of the controller 60. The dynamics of the controller 60 can be significantly improved by using a status controller instead of a controller 60 which has at least PI behavior. B. known from DE-A-37 31 982, where it serves to control an actuator. In Figure 5, the actual controller 60 is outlined with dash-dotted lines, the other elements are designated as in Figure 1. The controller 60 outputs a quantity signal M to the line 300 (the internal combustion engine to be controlled). The behavior of the route is essentially determined by a system dead time 301 and a delay time 302.

The quantity signal M also reaches an observer 303. In block 304, the observer calculates a first lambda value from the quantity signal M and the air quantity Q1 drawn in by the internal combustion engine. The output signal of the air quantity detection 55 serves as an air quantity signal. From this first lambda signal, the observer 302 determines a second lambda value by means of a PT1 element 306 and the output signal of a proportional element 307. A dead time element 308 generates the lambda signal of the observer from the second lambda value and the output signal of the proportional element 310.

In the comparison stage, this is compared with the measured actual lambda value. This comparison signal in turn reaches the proportional elements 307 and 310. Proportional stage 312 generates a quantity signal based on the second lambda signal. Another proportional stage 314 obtains a quantity signal based on the measured lambda signal. These two quantity signals arrive at the summation point 316, which also adds the output signal of the pilot control map 50 and the proportional element 318 to this. The integrating bypass 320 processes the difference between the desired lambda value and the actual lambda value.

The implementation of the state controller can be complex. A significant improvement in the dynamics also results from the use of a Smith predictor known per se. In the Smith predictor, the lambda signal is also observed via the quantity signal M and the air quantity Q1. The fuel quantity M to be injected is then changed on the basis of this observed lambda signal.

In addition to controlling the lambda signal, the above principle can also be used to control the torque Md or the exhaust gas temperature TA. The basic principle remains the same for all variants. An operating parameter, which can be the lambda value, the exhaust gas temperature TA or the torque Md in a particularly advantageous manner, are regulated to a predefined setpoint by specifying a corresponding fuel quantity value. The setpoint of the operating parameter depends on various operating parameters. In addition, the fuel quantity signal MR is influenced by a pilot control map 50. The pilot control map 50 determines the fuel quantity signal M in all operating states. In contrast, the controller 60 is only active in certain operating ranges. The different variants differ essentially in which

Operating ranges of the controller 60 is active. In the operating states in which the controller 60 is active, the pilot control values can be corrected adaptively.

FIG. 6 shows the relationship between engine speed n and injected fuel quantity Q as a map. Various operating states are identified in this map. The start area is marked with a, the full-load area with b and e the regulation area with e, the letter d denotes the partial-load area and the letter c the sliding area.

If the controller 60 regulates the lambda value of the exhaust gas, the controller is preferably active in the operating ranges b and d (full load and part load). In the operating ranges a, c and e, only the pilot control acts on the fuel quantity. The controller is not active in these areas. The pilot control map 50 calculates the control value for the fuel quantity depending on the air quantity. As described in FIG. 3, this can be obtained. The values in the pilot control map 50 can also be called up depending on the output signals R of a soot sensor or a soot map.

If the controller 60 is an exhaust gas temperature controller, the controller is only active in the stationary operating ranges b and c. The pilot control map 50, on the other hand, is active in all operating areas. In the operating ranges d, a and e in particular, only the pilot control map 50 has an influence on the fuel quantity.

In operating range b, the supercharger speed nL and the boost pressure PL serve as input variables for the pilot control map. In operating range c, the exhaust gas recirculation rate per stroke ARR serves as an input variable. The exhaust gas recirculation rate per stroke is advantageously derived from the mixing temperature; a temperature sensor for the fresh air, the intake air and the recirculated air are required for this.

In a further alternative, the precontrol values should be stored in area c as a function of the lambda value of the exhaust gas. It is particularly advantageous about the exhaust gas temperature control that this results in additional overload protection.

If the controller 60 represents a torque controller, the controller 60 can be activated in all operating ranges. The pilot control values are stored in the characteristic diagram 50 as a function of the output signal R of a soot sensor and the exhaust gas temperature. The torque is preferably measured at the output between the engine and transmission.

Claims (16)

1. Method for the provision of a fuel metering signal (M) in the case of a diesel internal combustion engine on the basis of measured variables such as the accelerator pedal position, engine speed, lambda, exhaust-gas temperature or torque, with specification of a requested fuel quantity signal (MW) as a function of the accelerator-pedal position, which signal is passed together with just one second signal to a minimum selector (15), the output signal of which, in turn, determines the fuel metering, a pilot-control characteristic map (50) specifying a pilot-control value (MV) as a function at least of the engine speed and an air quantity, and, in certain operating states, a controller (60) providing a signal (MR) with which the output signal (MV) of the pilot-control characteristic map (50) is combined by addition, the output signals (MV) of the pilot-control characteristic map (50) being adapted and/or the values stored in the pilot-control characteristic map (50) being altered, and the second signal being made up, by addition, of the adapted or unadapted output signal of the pilot-control characteristic map and the output signal (MR) of the controller (60).
2. Method according to Claim 1, characterized in that the output signals of the pilot-control characteristic map are corrected by addition and/or multiplication.
3. Method according to either of Claims 1 or 2, characterized in that one of the variables constituted by the exhaust-gas temperature, the torque or the lambda value of the exhaust gas is regulated.
4. Method according to either of Claims 1 or 2, characterized in that the controller for the lambda value of the exhaust gas is active at full load.
5. Method according to either of Claims 1 or 2, characterized in that the exhaust-gas temperature controller is active only in steady-state operating ranges.
6. Method according to either of Claims 1 or 2, characterized in that the torque controller is active in all operating ranges.
7. Method according to Claim 1 or 4, characterized in that the desired lambda value depends on the engine speed.
8. Method according to at least one of the preceding claims, characterized in that the air quantity drawn in is measured by means of an airflow meter or is calculated by means of a simulation.
9. Method according to Claim 8, characterized in that the air quantity drawn in is simulated on the basis of the derivative of the engine speed and the fuel quantity injected.
10. Method according to Claim 8, characterized in that the air quantity Q1 is calculated from the temperature T1 and the pressure P1 of the intake air, the pressure and the temperature being measured or the variation in the pressure being derived from the measured variation in the temperature or the variation in the temperature being derived from the measured variation in the pressure, the temperature signal being subjected to pilot control as a function of the pressure signal P1 in the case of a slow temperature sensor.
11. Method according to one of the preceding claims, characterized in that the output signal of the controller (60) is frozen if the quantity requested undershoots the controller output signal.
12. Method according to Claim 11, characterized in that the frozen signal is modified.
13. Method according to one of the preceding claims, characterized in that the control parameters are controlled.
14. Method according to one of the preceding claims, characterized in that a controller (60) which has at least PI action, a state controller or a Smith predictor is used as controller 60.
15. Method according to one of the preceding claims, characterized in that the output signal of the pilot-control characteristic map is delayed under certain conditions.
16. Device for the provision of a fuel metering signal (M) in the case of a diesel internal combustion engine, on the basis of measured variables such as the accelerator-pedal position, engine speed, lambda, exhaust-gas temperature or torque, with means for the specification of a desired fuel quantity signal (MW) as a function of the accelerator-pedal position, with a minimum selector (15), to which the desired fuel quantity signal (MW) can be fed together with just one second signal and the output signal of which, in turn, determines the fuel metering, a pilot-control characteristic map (50) specifying a pilot-control value (MV) as a function at least of the engine speed and an air quantity, and, in certain operating states, a controller (60) providing a signal (MR) with which the output signal (MV) of the pilot-control characteristic map (50) is combined by addition, the output signals (MV) of the pilot-control characteristic map (50) being adapted and/or the values stored in the pilot-control characteristic map (50) being altered, and the second signal being made up, by addition, of the adapted or unadapted output signal of the pilot-control characteristic map and the output signal (MR) of the controller (60).

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