EP1203875B1 - Method for overpressure protection of internal combustion engine - Google Patents

Description

The invention relates to a method for protecting an internal combustion engine against overpressure, wherein the pressure in at least one cylinder of the internal combustion engine is measured. Furthermore, the invention relates to an apparatus for carrying out such a method.

In recent years, increasing demands for improved performance and better fuel economy have resulted in the specific performance of internal combustion engines steadily increasing. The specific power is defined as the ratio between the power and the weight of the internal combustion engine. As a consequence of this increase, the pressures in the cylinders have increased enormously and reach levels at which mechanical stress reaches the limits of the material. It is therefore important to design the internal combustion engines so that the worst-case pressure within a cylinder remains within safe limits.

• einem Fehler im oberen Totpunkt aufgrund einer ungenauen Anbringung des Schwungrades;
• Kopfzwischenräume;
• Toleranzen des Injektionssystems.

This is usually achieved by careful calibration of the fueling strategy. Such conventional control strategies for peak pressure must be set with significant safety factors. One reason for this is that the tolerances occurring during engine production lead to considerable variations, which, for example for diesel engines, can mean a difference of 20 bar in the maximum cylinder pressure. typically, These variations from engine to engine are the result of the following factors:

• a top dead center error due to inaccurate flywheel mounting;
• Head gaps;
• Tolerances of the injection system.

The pressure difference from engine to engine of up to 20 bar has several negative consequences. For the engine designer, who needs to achieve the desired performance, the required 20 bar peak pressure safety limit necessitates the use of more material mass or more expensive materials, which increases the unit cost of the engine. For the consumer, the 20 bar difference in large power variations can result from engine to engine, so that some consumers receive vehicles that are inferior to similar engines.

Against this background, it was an object of the present invention to ensure the protection of an internal combustion engine against overpressure in the cylinders at reduced production costs and at the same time to reduce the power fluctuations between the same engines.

This object is achieved by a method having the features of claim 1 and a device having the features of claim 7. Advantageous embodiments are contained in the subclaims.

Methods in which the pressure in a cylinder is measured are known for various purposes. For example, US Pat. No. 4,397,285, US Pat. No. 4,549,513, US Pat. No. 4,846,128, US Pat. No. 4,063,238 and US Pat. No. 5,676,113 use the measured pressure to control the ignition timing in order to determine the performance of the engine to increase. It is further known from US 5,284,114, US 4,706,628 and US 4,732,126 to determine the location of the peak pressure within the cylinders and, in response thereto, to control the ignition timing and the fuel parameters. Finally, it is known from US 4 516 401 and US 4 483 146 to control the compressor of turbocharger engines by feedback of the cylinder pressure.

DE 197 05 463 A1 discloses a method and a device for controlling an internal combustion engine, in which the injection quantity is reduced until the maximum combustion chamber pressure reaches the threshold value.

JP 08 158 926 discloses a method for preventing a maximum gas pressure in the combustion chamber of an internal combustion engine, wherein an injection timing signal is generated as a function of a pressure difference.

The solution of the above object is achieved according to the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

The peak pressure is understood below to mean the greatest in-cylinder pressure occurring during an engine cycle.

The method ensures that a maximum value of the cylinder pressure which is to be regarded as the load limit is not constantly monitored by monitoring the peak pressure in at least one cylinder and by exceeding the predetermined threshold value by the peak pressure the fuel introduction and / or fuel combustion predetermined by the engine control is suitably modified. The threshold value at which the process becomes active is 5 to 20%, preferably approximately 10%, below the still permissible maximum value of the internal cylinder pressure.

The fuel introduction and / or the fuel combustion can be modified in particular by modifying the quantity of fuel supplied to the internal combustion engine, the ignition time of the air-fuel mixture and / or the fuel injection time. The aforementioned control variables can be used to influence the pressure development in the cylinder chamber in a targeted manner. Thus, for example, a reduction in the amount of fuel supplied results in a corresponding reduction in the peak pressure in the corresponding cylinder.

Preferably, the modification of the amount of fuel consists only of a reduction in the amount of fuel calculated by the engine controller. That is, the method of the present invention can at best reduce, but never increase, the amount of fuel "normally" provided by the engine control for delivery. Such a reduction of the amount of fuel satisfies the intended purpose to limit the pressure in the cylinder chamber.

In the simplest variant of the method, the pressure in only one cylinder of a multi-cylinder internal combustion engine is measured and assumed as representative of all cylinders of the engine. According to one embodiment of the method, however, the pressure in a plurality of cylinders, in particular in each cylinder bank of the internal combustion engine and / or in each cylinder of the internal combustion engine can be measured. This further increases the accuracy and safety of the overpressure protection.

Furthermore, the method may also differentiate with respect to the modification of the fuel introduction and / or the fuel combustion between the cylinders. In the simplest case, the fuel introduction and / or the fuel combustion is modified in the same way for all cylinders of the engine. Preferably, however, the variables mentioned are modified separately for each cylinder bank and / or for each cylinder of the internal combustion engine. In this way, critical pressures limited to certain cylinders can be selectively controlled in these cylinders without unnecessarily impairing the performance of the unaffected cylinders.

In principle, the method according to the invention intervenes only when a fuel introduction and / or fuel combustion is predetermined by the engine control, which leads to a pressure in the engine which exceeds a predetermined threshold value. When the threshold value is exceeded, the method according to the invention becomes active and influences the fuel introduction and / or fuel combustion in the sense of a reduction of the pressure values. In order nevertheless to come as close as possible to the conditions sought by the engine control, it is advantageously attempted to reduce the peak pressure in the engine Keep the cylinder as close as possible to the maximum permissible limit of the maximum value. However, as soon as the engine control system prescribes fuel introduction and / or combustion, which would lead to lower pressure values, these new specifications are executed immediately.

The invention also relates to a device for carrying out a method of the type described above, which includes a peak pressure regulator, which is connected on the input side with at least one arranged in a cylinder of the engine pressure sensor and the output side with a control device for fuel introduction and / or fuel combustion. The peak pressure regulator is further configured to modify fuel injection and / or fuel combustion when the peak pressure in the cylinder exceeds a predetermined threshold, the modification being such that the peak pressure in the cylinder remains below a maximum pressure, the threshold being 5 to 20%. is smaller than the Mamimalwert and the fuel injection and / or the fuel combustion are modified so that the peak pressure in the cylinder as close to the maximum value (P _max ) is, as long as not lower pressure values are controlled by the engine control. With such a device, the above-explained advantages of the method according to the invention can be achieved.

Fig. 1

schematisch das erfindungsgemäße Verfahren an einem Vierzylindermotor;

Fig. 2a-f

sechs verschiedene Anordnungsmöglichkeiten für Sensoren und Regeleinrichtungen zur Durchführung des erfindungsgemäßen Verfahrens;

Fig. 3

ein Flussdiagramm des Verfahrensablaufes;

Fig. 4

Kraftstofffluss und zugehörigen Druck im Zylinder beim Stand der Technik;

Fig. 5

Kraftstofffluss, zugehörigen Druck im Zylinder und Regelungsmodi bei Durchführung des erfindungsgemäßen Verfahrens.

In the following, the invention will be explained by way of example with the aid of the figures. Show it:

Fig. 1

schematically the inventive method on a four-cylinder engine;

Fig. 2a-f

six different possible arrangements for sensors and control devices for carrying out the method according to the invention;

Fig. 3

a flowchart of the process flow;

Fig. 4

Fuel flow and associated pressure in the cylinder in the prior art;

Fig. 5

Fuel flow, associated pressure in the cylinder and control modes in carrying out the method according to the invention.

In Figure 1, the control system according to the invention for an internal combustion engine is shown schematically, which may be both a gasoline engine and a diesel engine. In particular, diesel engines benefit from the method of the invention because they are subject to greater pressure variations within the cylinder and the maximum peak pressures are much higher than in gasoline engines.

FIG. 1 shows four cylinders 1 of an internal combustion engine arranged one behind the other in a known manner. In each cylinder 1, a pressure sensor 3 is arranged, via which the pressure prevailing in the cylinder pressure is measured and reported to a peak pressure regulator C. Such peak pressure regulators C, C ', C' ', C' '' are provided separately for all cylinders of the engine.

The output of regulator C acts on actuators of the fuel injection system. These include the injectors 2 and possibly also the fuel pump. The mainly controlled variable is the amount of injected fuel F _q for each cylinder. This variable can be controlled individually for each cylinder or jointly for several or for all cylinders. Alternatively, the timing of the injection (F _tim for a diesel engine) or the spark timing control (for a gasoline engine) may be controlled instead of or together with the amount of the injected fuel F _q .

The sensors used by the controller may be any type of sensor that can give an indication of the pressure P _cyl within some or all of the cylinders. These sensors are therefore referred to below as internal cylinder pressure sensors. Typical sensors include direct in-cylinder pressure sensors such as piezoelectric or optical sensors mounted directly in the combustion chamber, or indirect in-cylinder pressure sensors such as piezoelectric sensors mounted in an ignition or glow plug or accelerometers mounted outside the combustion chamber. The output signals of the sensors can be converted in a known manner after appropriate preprocessing and calibration in pressure signals. The greater the accuracy of these pressure signals, the better the regulation according to the invention can be carried out, and the higher the benefit of the invention.

• a) ein Sensor pro Zylinder 1, ein Regler pro Zylinder;
• b) ein Sensor pro Zylinder, ein Regler pro Zylinderbank;
• c) ein Sensor pro Zylinder, ein Regler pro Motor;
• d) ein Sensor pro Bank, ein Regler pro Bank;
• e) ein Sensor pro Bank, ein Regler pro Motor;
• f) ein Sensor pro Motor, ein Regler pro Motor.

While FIG. 1 shows a system in which there is one cylinder internal pressure sensor 3 per cylinder and one peak pressure regulator C, C ', C ", C'" per sensor, the invention can also be applied to engines in which not all Cylinders are equipped with sensors. For example, only one cylinder per engine or one cylinder per cylinder bank may be equipped with a sensor for V-engines. The various configuration options are shown in FIG. 2 and include the following variants:

• a) one sensor per cylinder 1, one controller per cylinder;
• b) one sensor per cylinder, one controller per cylinder bank;
• c) one sensor per cylinder, one controller per motor;
• d) one sensor per bank, one regulator per bank;
• e) one sensor per bank, one regulator per motor;
• f) one sensor per motor, one controller per motor.

Better performance is achieved when a sensor is mounted in each cylinder. Table 1 shows which production tolerances can be compensated depending on the selected sensor configuration. 1 sensor per
... Dead-spot Head gasket interspaces Injektorencharakteristik Combustion chamber related casting / machining tolerances cylinder X X X X cylinder bank X X engine X

FIG. 3 shows a flow chart of a possible control algorithm. In block 17, the engine control calculates a conventional fuel delivery strategy based on the accelerator pedal position 11 specified by the driver as well as other sensor signals 10. The result of this calculation is the amount of fuel F _q ^d to be injected into the cylinder.

In parallel, the peak pressure P _{peak is} detected by a peak pressure _detector 13, which receives the data 12 of the cylinder _internal pressure P _cyl . This peak pressure P _peak is defined as the maximum pressure during a motor cycle. The determination happens once per engine cycle. The value P _peak is buffered in a buffer 14 until a new value overrides it. This can be done once per cycle, once per cycle, or with any other suitable sequence of steps, depending on the configuration of the pressure sensors and the number of peak pressure regulators.

In a first branch of the algorithm, the peak pressure P _{peak is} then passed to a summer in which it is subtracted from the value of the maximum permissible pressure P _max stored in block 15 in the cylinder. The difference thus formed is fed to a P _max -folgler 16. The task of this regulator is to calculate the amount of fuel to be injected in such a way that the peak pressure P _{peak is} regulated to the maximum permissible pressure P _max . Typically, this controller is a Proportional / Integral (PI) or Proportional / Integral / Derivative (PID) controller with an "anti-windup" feature for a jumpless transition from or to the original fueling strategy (blocks 18 and 19) ) to ensure. The regulator should be calibrated to avoid any pressure surplus. The output of the regulator 16 consists of a value F _q ^c for the fuel injection.

In block 18, the peak pressure P _{peak is} compared with a predetermined threshold pressure P _th , which is selected a few bar below the maximum pressure P _max . If the peak pressure remains below the threshold pressure, the original engine control strategy will not be changed. That is, according to block 20, the amount of fuel F is set equal to the fuel quantity F _q ^d predetermined by the engine control. The motor works safely well below the maximum pressure P _max , so that the pressure limiter can remain deactivated.

If the peak pressure P _peak exceeds the predetermined threshold pressure P _th in block 18 on the other hand, the motor approaches the maximum pressure P _max. According to block 19 then various measures can be taken. The reason why P _{peak is} compared to P _th and not directly to P _max is that the peak pressure regulator should be allowed to pre-plan its control actions and accordingly suppress the pressure surges which would otherwise be unavoidable in the large time delays in the system would be.

In the already mentioned block 19, the magnitude of the fuel flow F _q ^d predetermined by the engine control ^is compared with the fuel flow F _q ^c predetermined by the slave controller 16. When P _peak comes close to P _max (ie, P _peak > P _th ) and F _q ^d > F _q ^c , protection against overpressure is necessary and the engine is operated on a fuel quantity F according to block 21, which is equal to the quantity F _q ^c calculated by the P _max follower. However, if the driver brakes, F _q ^d drops below F _q ^c and the driver regains full control (block 20: F = F _q ^d ). This is a safety criterion because the amount of injected fuel can never exceed the fuel amount of the original fuel delivery strategy. In other words, the driver always has control over the maximum fuel supply.

In block 19, the branching condition could also be evaluated with any other available quantity related to the torque, rather than the amount of fuel.

The control strategy for the peak pressure in the cylinder interior shown in Figure 3 has been on a conventional Four-cylinder 2.0-liter diesel engine tested. The maximum pressure P _max was set to 120 bar in the regulator and the threshold pressure P _th to 10 bar below the maximum pressure (that is, to 110 bar). For comparison purposes, the engine was initially operated with the peak pressure regulator switched off.

Figure 4 shows the results of this comparison, wherein the peak pressure P _peak several times by more than 10 bar exceeds the limit P _max of 120 bar. In the upper diagram of Figure 4, the peak pressure in the cylinder interior on the vertical axis and the duration of the experiment on the horizontal axis are entered. In the lower diagram, the amount of fuel that is delivered to the cylinders is entered on the same time axis in comparison with this.

In Figure 5, the results are shown when the peak pressure regulator is turned on and the same drivability (same accelerator pedal positions) is applied to the engine. The peak pressure P _{peak of} the cylinder internal pressure shown in the top diagram does not exceed the limit value P _max of 120 bar at any time.

The limitation of the fuel introduction made by the peak pressure regulator with respect to the strategy pursued by the engine control (see FIG. 4 below) can be seen from the middle diagram of FIG. It can also be seen that the peak pressure regulator is deactivated as soon as the fuel demand of the driver becomes equal to the fuel quantity predetermined by the peak pressure regulator. Due to the "anti-windup" characteristic, the fuel quantity specified by the peak pressure regulator never becomes smaller than the originally proposed fuel quantity. The bottom diagram of Figure 5 shows on the same time axis as the top two Diagrams the mode (0 = original engine control or 1 = peak pressure control) in which the fuel supply is currently being operated.

Claims (6)

1. Method for protecting against overpressure an internal combustion engine, the pressure (P_cyl) in at least one cylinder (1) of the internal combustion engine being measured, the introduction and/or combustion of fuel being modified, if the peak pressure (P_peak) in the cylinder interior exceeds a predefined threshold value (P_th), in such a way that the peak pressure subsequently remains below a maximum value (P_max), characterized in that the threshold value is 5 to 20 % less than the maximum value and the introduction and/or combustion of fuel are modified in such a way that the peak pressure in the cylinder (1) is as close as possible to the maximum value (P_max) for as long as no lower pressure values are set by the engine controller.
2. Method according to Claim 1,
   characterized in that the supplied quantity of fuel, the ignition time and/or the fuel injection time are modified.
3. Method according to one of Claims 1 or 2,
   characterized in that the modification of the supplied quantity of fuel comprises only a reduction in the fuel quantity to be supplied (F_q ^d) as calculated by the engine controller.
4. Method according to at least one of Claims 1 to 3, characterized in that the pressure in each cylinder bank and/or in each cylinder (1) of the internal combustion engine is measured.
5. Method according to at least one of Claims 1 to 4, characterized in that the introduction and/or combustion of fuel in each cylinder bank and/or in each cylinder of the internal combustion engine is modified separately.
6. Device for carrying out the method according to one of Claims 1 to 5, comprising a peak pressure regulator (C, C', C" , C"') which is connected at the input side to at least one pressure sensor (3) arranged in a cylinder (1) of the internal combustion engine, and at the output side to a control device (2) for the introduction and/or combustion of fuel, and is set up in such a way that, if the peak pressure (P_peak) in the cylinder interior exceeds a predefined threshold value (P_th), it modifies the introduction and/or combustion of fuel so that the peak pressure remains below a maximum value (P_max), the threshold value being 5 to 20 % less than the maximum value and the introduction and/or combustion of fuel being modified in such a way that the peak pressure in the cylinder (1) is as close as possible to the maximum value (P_max) for as long as no lower pressure values are set by the engine controller.

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