EP1525383A1

EP1525383A1 - Method for converting a fuel quantity into a torque

Info

Publication number: EP1525383A1
Application number: EP03787310A
Authority: EP
Inventors: Christian Birkner; Johannes Feder; Rainer Hirn; Achim Przymusinski
Original assignee: Siemens AG
Current assignee: Continental Automotive GmbH
Priority date: 2002-07-30
Filing date: 2003-07-08
Publication date: 2005-04-27
Also published as: US7096111B2; WO2004016932A1; US20040181332A1; JP2005534863A; DE10234706B4; DE10234706A1

Abstract

The invention relates to a method for converting a fuel quantity (MF) into a torque (TQ) in an internal combustion engine. According to said method, the efficiency (H) of the internal combustion engine is determined at the actual operating point, before the conversion, as a ratio of actual torque (TQ) to actual fuel quantity (MF), and the desired torque (MF) is determined from the efficiency (H) and the fuel quantity (MF).

Description

description

Method for converting an amount of fuel into a torque

The invention relates to a method for converting a target fuel quantity into a target torque in an internal combustion engine.

Torque-based control structures are increasingly being used in internal combustion engines. Structures of this type process all the performance requirements imposed on the internal combustion engine in the form of torque requirements, suitably link these torque requirements to an overall torque depending on the operating point, and use them to generate a value for a fuel quantity that the internal combustion engine can use to carry out the requested operation, i.e. to meet the torque requirements. In the case of diesel internal combustion engines, the fuel quantity can be a fuel mass, for example, which is to be injected into the combustion chambers of the internal combustion engine by means of an injection system.

Such torque-based structures have the advantage that further functionalities can be easily integrated with regard to their performance requirements for the internal combustion engine. If, for example, an internal combustion engine is to be adapted for operation with an air conditioning system, then only the torque request made by an air conditioning system has to be additionally taken into account when generating the total torque in the torque-based structure. The structures mentioned therefore give great flexibility in adapting a control system to a given internal combustion engine model.

This applies in particular since the implementation of the total torque present at the end of the torque-based structure in parameters for the fuel supply, for example in parameters for the control of an injection system, is highly engine-specific. A characteristic map is customary here, which determined the optimum fuel mass from a torque request for the respective operating point, since this parameter was previously the only parameter to be varied in an injection system. The map used here is also referred to as the main map because of its central function.

With the advent of injection systems that use largely freely controllable injectors fed from pressure accumulators, not only the fuel mass, but also an almost freely selectable variation of injection processes can now be used for a single combustion process. However, previous main characteristic fields are no longer sufficient to control such injection systems, which permit a large number of degrees of freedom; instead, complex linked map sets are used.

From this increasing complexity of converting a requested total torque into a fuel quantity, the problem arises that, accordingly, converting a fuel mass into a torque becomes increasingly difficult. Such conversions, as are required in the method of the type mentioned, occur, for example, when fuel quantity limit values, for example a maximum quantity of fuel that can be emitted by an injection system, have to be converted into a target torque in order to use them in a conventional manner to be able to take into account the torque-based control structure. Another example of a fuel quantity limit value that often has to be converted into a torque during operation can be found in soot limitation functions, as are standard for modern diesel internal combustion engines. Depending on the operating parameters, such functions output a maximum fuel mass which, to avoid undesirable soot formation, does not exceed may be. In order to integrate such functions into a torque-based control structure, a target fuel mass must be converted into a target torque.

In the prior art, this could be done by a map that is inverse to the main map. However, with the increasing complexity of the main map mentioned, such an inversion is only possible with great effort or only to a limited extent.

The invention is therefore based on the object of developing a method of the type mentioned at the outset such that the conversion of fuel quantity into torque can be carried out in a computationally economical manner and, in particular, the requirement of invertible main characteristic maps can be dropped.

According to the invention, this object is achieved in that, before the conversion to the current operating point, the efficiency of the internal combustion engine is determined as the ratio of the actual torque and the actual fuel quantity, and the target torque is determined from the efficiency and the target fuel quantity.

The concept according to the invention therefore no longer attempts to carry out the conversion of torque into fuel quantity in inverted form in the moent-based structure, but instead uses a determination of the efficiency of the internal combustion engine, this efficiency being understood as a ratio of torque to fuel quantity, ie not a power output by the internal combustion engine is taken into account. Based on this efficiency, as it is at the current operating point, the fuel quantity can be easily converted into torque without having to convert to complex characteristic maps. This reduces the storage space for such identifiers. At the same time, the conversion time or the computational effort required for this can be reduced. In the simplest case, the efficiency can be calculated by dividing the torque delivered at the last injection time by the amount of fuel supplied to the internal combustion engine. This calculation method can be refined in the form of an extrapolation of the efficiency, which inferred from the efficiency, as it was previously, to the efficiency at the next calculation time. Of course, any extrapolation method is suitable for the invention, which is why it is preferred that an extrapolation of the efficiency is used to determine the target torque. An extrapolation is usually particularly easy to carry out if it is a linear extrapolation. Therefore, one is particularly preferred.

Linear extrapolations regularly provide good results if they are measured in terms of the course of the extrapolating functionality, ie an efficiency curve, in the range of validity of a linear approximation of the curve. This means that extrapolation may only take place over areas in which the efficiency curve deviates only comparatively ^• slightly from a linear curve.

However, since the efficiency of an internal combustion engine changes depending on the fuel mass supplied (and depending on other operating parameters, such as operating temperature, etc.), it may sometimes be necessary to convert a quantity of fuel that is very different from the fuel mass that is used in the this simple calculation method leads to an incorrect value. In internal combustion engines, the efficiency usually increases from low fuel masses to a medium fuel mass and then decreases again. If the internal combustion engine is now operated with a low fuel mass and a torque is to be calculated for a high fuel mass, this can be said

Calculation scheme a sometimes intolerable error set. For such cases, it is expedient that an efficiency curve is used to determine the efficiency, which curve shows the maximum ratio of torque and fuel quantity as a function of the fuel quantity. Such a curve can also be used to achieve a precise determination of the target torque for the target fuel quantity, eg. B. in which the efficiency of the current fuel mass is calculated and a suitable efficiency curve is selected. A selection of the suitable efficiency curve then takes into account the parameters of the internal combustion engine that go beyond the fuel mass; These can be, among other things, speed, operating temperature of the internal combustion engine, position of a charging device (eg turbine charger), intake air temperature, ambient air pressure, fuel quality, etc.

Instead of selecting a suitable efficiency curve, it is of course also possible to work with a standard efficiency curve that requires certain standard operating conditions. With this simplification, the memory requirement for converting a ^• fuel mass into a torque is further reduced.

In order to increase the accuracy of the conversion in this simplified variant, the ratio of the actual torque and the actual fuel quantity can be compared at the current operating point and with the efficiency displayed by the efficiency curve (applicable for standard operating conditions) and the efficiency curve depending on the result of this comparison be modified so that the target torque is then determined using the modified efficiency curve. This approach combines the advantages of a very precise determination of the target torque for the desired target fuel quantity with the advantages that only a single efficiency curve has to be kept in a memory. In the modification, a variety of manipulations can be carried out on the efficiency curve, for example multiplication by a fuel mass-dependent factor or the like. It is particularly simple and yet surprisingly precise to make the difference between the calculated and displayed efficiency when comparing and to modify the efficiency curve by exactly this difference in the modification move. The underlying assumption that operating parameters deviating from the standard operating conditions essentially lead to a shift in the efficiency curve has been found to be suitable for most applications.

In a combination of the above-mentioned extrapolation approach with the use of efficiency curves, an extrapolation is always used when the actual fuel mass differs only slightly from the target fuel mass to be converted. If the difference lies above a certain threshold value and thus an extrapolation is too faulty, an efficiency curve is used. This combination combines computational economy with high accuracy. A further development of the method is therefore preferred, in which extrapolation is carried out to determine the target torque if a difference between the actual fuel quantity and target fuel quantity is below a certain threshold value, and in which the target quantity is otherwise determined. Torque the (modified) efficiency curve is generated and used.

A frequent application, in which a target fuel quantity has to be converted into a target torque, arises, as already mentioned, in a soot limitation function of a diesel engine. The method can be used there with particular advantage. It is therefore preferable that the target fuel quantity is an operating point-dependent, maximum fuel quantity which is determined by a predefined soot behavior of the internal combustion engine, and when exceeded If there is an impermissible generation of soot by the internal combustion engine at the operating point.

The invention is explained in more detail below by way of example with reference to the drawing. Show:

1 is a block diagram for a torque-based control structure with a conversion of a target fuel quantity into a target torque,

2 shows an alternative embodiment of the conversion of FIG. 2,

3 shows a torque curve that can be used when converting a target fuel quantity into a target torque, and

4 shows the course of an extrapolation of an efficiency for converting a target fuel quantity into a target torque.

A torque-based structure for determining the amount of fuel to be supplied to an internal combustion engine is shown in FIG. 1 as a block diagram. The torque-based structure 1 determines a fuel mass MF from various input variables, which is a parameter for an injection system of a diesel engine. The torque-based structure 1 not only specifies the value of the fuel mass MF, but also how it is to be delivered with a specific injection course, i.e. how the fuel mass MF should be distributed over pre, main and post injections.

The torque-based structure 1 has a torque calculation unit 2 as the core element, which calculates an overall torque TQ, which is required by the internal combustion engine, from a wide variety of input variables. The input variables of the Torque calculation unit 2 essentially include torque requirements that are suitably linked depending on the operating parameters P, which torque calculation unit 2 also receives. The structure and function of such a torque calculation unit 2 are known to the person skilled in the art.

The value for the torque TQ output by the torque calculation unit 2 is then converted in a main characteristic diagram 3 into the value for the fuel mass MF and into the parameters mentioned for controlling the injection process. When applying the torque-based structure 1 to an internal combustion engine model, essentially only the main characteristic diagram 3 has to be adapted accordingly, since only here do the motor conditions of the internal combustion engine model come into play.

The torque calculation unit 2 processes various torque requests on the input side. The most important of these is a torque request TQ-DRV from an accelerator pedal sensor 4, which represents the torque requested by the driver of a vehicle equipped with the internal combustion engine. The torque calculation unit 2 also takes into account external torque requests 5, which flow to the torque calculation unit 2 in the block diagram of FIG. 1 in the form of a torque request TQ-EXT. Such external torque requirements 5 can, for example, be requirements of external power consumers, such as air conditioning systems or the like. act. A cruise control system is also an example of an external torque request 5.

The concept of the torque-based structure 1 provides for the torque calculation unit 2 to be supplied with torque requests only. Now there are individual functions that do not issue a torque request, but one

Fuel mass limit. This is, for example, a soot limitation unit 6 or a torque ^' Limiting unit 7, which output both values for fuel masses which (at the current operating point) must not be exceeded due to exhaust gas or engine conditions. The fuel mass limit values MF-SM and MF-TQ output by these units can now not simply be supplied to the torque calculation unit 2, since these cannot process values for fuel masses. It is therefore imperative to convert these fuel mass limit values into torque limit values. For the conversion, an efficiency calculation module 8 is provided in the torque-based structure of FIG. 1, which contains the value for the fuel mass MF, as it is output by the main characteristic diagram 3, and the value for the torque TQ, which is output by the torque calculation unit 2. The efficiency calculation module 8 converts these two values, torque TQ and fuel mass MF, into an efficiency H in a manner still to be described, which efficiency efficiency by a simple multiplication in a multiplier 9 enables the fuel mass limit values MF-SM or MF-TQ in implement the corresponding torque limit values TQ-SM or TQ-MAX. These can then be fed to the torque calculation unit, so that the function of the soot limitation unit 6 and the torque limitation unit 7, which in the block diagram of FIG. 1 exemplarily represent functions that output a fuel mass value, in the torque-based structure 1 in a simple manner Can be taken into account.

Fig. 2 shows a block diagram of a possible implementation of the efficiency calculation module 8 in detail. It first calculates the ratio of torque TQ and fuel mass MF in a multiplier 10 and thus outputs one as efficiency H. Then there is a delay in a delay element 11 by one calculation cycle, so that on the output side of the delay element 11 there is the efficiency of the penultimate calculation cycle. This is symbolized in FIG. 2 by the addition (n-1). With this efficiency H, the conversion of the target fuel quantities in the form of the fuel mass limit values MF-SM and MF-TQ into target torque values in the form of the torque limit values TQ-SM and TQ-MAX is then carried out in multiplier 9. The concept of the implementation of the efficiency calculation module 8, which is laid down in the block diagram in FIG. 2, therefore provides for the efficiency from the previous calculation cycle to be used for the current conversion of the target fuel mass into the target torque.

The efficiency calculation module 8 can also be implemented in other ways. This makes it possible to fall back on an efficiency curve 12 as shown in FIG. 3. The efficiency curve 12 of FIG. 3, which shows the efficiency as a ratio of torque TQ and fuel mass MF over the fuel mass MF, shows the maximum efficiency H that the internal combustion engine can achieve with the respective fuel mass. Since the efficiency H naturally depends on the operating parameters of the internal combustion engine - for example, the operating temperature is the

'' Internal combustion engine is a significant influencing variable -, the efficiency curve 12 applies only to certain standard operating parameters. Outside of these operating parameters, the efficiency will regularly be lower for a given fuel mass. It is also conceivable that, for certain areas, operating conditions that deviate from the standard operating parameters can sometimes achieve higher efficiency.

If the efficiency module now receives a value for a fuel mass MF (1) for determining the efficiency at a time (1), it first checks whether the efficiency H (MF (1)) = TQ present at the current torque TQ (1) (1) / MF (1) lies on the efficiency curve 12. The efficiency module 8 achieves this by determining the efficiency H to the fuel mass MF (1) from the curve 12 and comparing it with the calculated value. Any difference will then used to shift 13 the efficiency curve 12 into a modified efficiency curve 14.

Using the efficiency curve 14 obtained in this way, shifted by the displacement 13, the efficiency to the fuel mass limit value MF-SM (1), as it is output by the soot limitation unit 6 at the current operating point, can then be determined. 3 clearly shows that the efficiency H (MF-SM (1)) obtained in this case differs significantly from that which would be obtained with the original efficiency curve 12 due to the shift 13. As an alternative to modifying the efficiency curve 12, the shift 13 can also be applied directly to the efficiency H, which the unmodified efficiency curve 12 indicates for the fuel mass limit MF-SM (l).

The efficiency 8 determined in this way is then used in the multiplier 9 to determine the desired torque limit value TQ-SM. An analogous method is also used for the fuel mass limit value MF-TQ, the output from the Momen- ^• tenbegrenzungseinheit. 7

The approach shown in FIG. 3 to use the efficiency curve 12 in the efficiency calculation module 8 is particularly advantageous if the fuel mass at the current time MF (1), which the torque-based structure 1 provides for the internal combustion engine, differs greatly from the fuel mass limit value MF -SM or MF-TQ differentiates, so that the assumption that the fuel mass limit value has the same efficiency as the current operating point would lead to inadmissible errors in the determination of the torque limit values.

If the difference between the current value for the fuel mass MF (1) and the fuel mass limit value is only slight, in particular below a certain threshold value, the efficiency calculation module 8 dispenses with the resorted to an efficiency curve 12 and used extrapolation instead. An efficiency H (MF (1)) is determined from the fuel mass MF (1) and the current torque TQ (1) at the current time. At the next following calculation cycle (2), the same occurs for the fuel mass MF (2) and the torque TQ (2). The resulting change in efficiency (now efficiency H (MF (2)) is present) and fuel mass is used for an extrapolation, which is illustrated in FIG. 4 by an extrapolation line 15. It is therefore assumed that, due to the distance of the value for the current fuel mass MF from the current fuel mass limit value (eg MF-SM), which is below a predetermined threshold value, a linear approximation of the efficiency curve 12 shown in dashed lines in FIG. 4 is possible. The extrapolation then gives the efficiency H lying on the extrapolation line 15 to the fuel mass limit value (for example MF-SM (2)). This is then output by the efficiency calculation module 8 and used in the multiplier 9.

Claims

claims

1. A method for converting a target fuel quantity into a target torque in an internal combustion engine, characterized in that, before the conversion to the current operating point, the efficiency of the internal combustion engine is determined as a ratio of the actual torque and the actual fuel quantity and the target torque from the efficiency and the target fuel quantity is determined.

2. The method according to claim 1, characterized in that an extrapolation of the efficiency is used to determine the target torque.

3. The method according to claim 1, characterized in that an efficiency curve is used to determine the efficiency, which indicates the maximum ratio of torque and fuel quantity as a function of the fuel quantity.

4. The method according to claim 3, characterized in that the ratio of the actual torque and the actual fuel quantity is calculated at the current operating point and compared with the efficiency indicated by the efficiency curve and, depending on the result of this comparison, the efficiency curve is modified and that the determination of the target torque by means of the modified efficiency curve.

5. The method according to claim 4, characterized in that the difference between the calculated and displayed efficiency is formed in the comparison and the efficiency curve is shifted by this difference in the modification.

6. The method according to claims 2 and 4 or according to claims 2 and 5, characterized in that to determine the target torque, the extrapolation is carried out when a difference between the actual fuel quantity and the target fuel quantity below a certain threshold value lies, and that the modified efficiency curve is otherwise generated and used to determine the target torque.

7. The method according to any one of the above claims, characterized in that the target amount of fuel is a maximum amount of fuel determined by a predetermined soot behavior of the internal combustion engine, depending on the operating point.