DE102011010068A1 - Method for controlling combustion engine of motor car during coasting of combustion engine, involves selecting deceleration fuel cut off rotation speed to terminate thrust shutdown of engine based on currently expected dragging torque - Google Patents

Abstract

The method (10) involves determining expected dragging torque for a combustion engine (12) during coasting of the combustion engine. A deceleration fuel cut off (DFCO) rotation speed is selected (16) based on the currently expected dragging torque to terminate a thrust shutdown of the combustion engine. The determination of the expected dragging torque and selection of the rotation speed are stably repeated. The expected dragging torque over a time delay element is taken into account during the selection of the DFCO speed. Independent claims are also included for the following: (1) a control unit for controlling a combustion engine (2) a computer program product having a set of instructions to perform a method for controlling a combustion engine (3) a signal sequence with machine-readable statements having a set of instructions to perform a method for controlling a combustion engine.

Description

The invention relates to a method for controlling an internal combustion engine, a control unit, a computer program product, a computer program and a signal sequence, with the aid of which an internal combustion engine can be operated, wherein it is particularly possible to perform a fuel cut in the internal combustion engine of a motor vehicle.

When a fuel supply is interrupted in an internal combustion engine of a motor vehicle with the drive train coupled (fuel cutoff), for example when the driver of the motor vehicle releases an accelerator pedal, the internal combustion engine is no longer operated in train operation but in overrun operation. The torque present in the drive train and in the internal combustion engine results essentially from the inertia of rotating components and not from a combustion of a fuel in the internal combustion engine. Due to one of the drive direction of the internal combustion engine and the driveline opposing drag torque, for example by friction and / or connected torque consumers, the speed of the engine in overrun is always reduced and the speed of the motor vehicle is delayed. Thus, the speed of the internal combustion engine does not decrease in overrun to the extent that the internal combustion engine is strangled, takes place at a predefined DFCO speed (DFCO: "Deceleration Fuel Cut-Off") an automatic termination of fuel cut, even with a non-actuated accelerator pedal the fuel is supplied to the internal combustion engine. The DFCO speed is set so high that a stalling of the internal combustion engine is safely avoided.

There is a need to reduce the fuel consumption of an internal combustion engine.

It is an object of an embodiment of the invention to show measures that allow low fuel consumption of an internal combustion engine.

The object is achieved by the features of the independent claims.

An embodiment of the invention relates to a method for controlling an internal combustion engine, comprising the steps of determining an anticipated drag torque for the internal combustion engine during a coasting operation of the internal combustion engine and selecting a DFCO speed n _DFCO to end a _fuel cut of the internal combustion engine as a function of the currently expected drag torque wherein the determination of the expected drag torque and the selection of the DFCO speed is repeated constantly.

The DFCO speed for ending the overrun fuel cutoff of the internal combustion engine is not set once or at the occurrence of a specific event, but again and again determined depending on the currently present drag torque. The DFCO speed can be varied continuously, taking into account dynamically changing boundary conditions such that the DFCO speed is minimized without risking stalling the engine due to the applied drag torque, so that only a small amount of power is required to stall to prevent the internal combustion engine with coupled drive train. This allows low fuel consumption of the internal combustion engine and leads to a reduction of CO ₂ emissions.

Repeating the determination of the expected drag torque and the selection of the DFCO speed is in particular independent of events that affect the internal combustion engine, the powertrain and / or torque consumers. Repetition is particularly independent, that is, without a separate external signal setting a new DFCO speed and / or triggers a new determination of the DFCO speed. For example, the method can be repeated continuously after a predefined period of time, which can be constant or variable during the operation of the internal combustion engine. Preferably, the predefined time period in a cold start phase is shorter than after reaching a predefined operating temperature of the internal combustion engine. As a result, for example, an increased drag torque due to friction effects in the cold start phase can be taken into account in a fuel-saving manner.

In particular, the DFCO speed n _{DFCO is} above a limit speed n ₀ , below which the engine stalled at the expected drag torque, in particular for f _DFCO / n ₀ 1.00 <n _DFCO / n ₀ ≤ 1.40, preferably 1 , 02 <n _DFCO / n ₀ ≤ 1.20, and more preferably 1.05 <n _DFCO / n ₀ ≤ 1.10. The DFCO speed can thus be far enough above the limit speed that with sufficient certainty stalling of the engine is avoided, the DFCO speed is also close enough to the limit speed to provide the lowest possible fuel consumption at the end of the fuel cut.

Preferably, in the case established, a torque flow provided by the internal combustion engine can be periodically coupled Torque consumer, in particular a compressor for an air conditioner, used for determining the expected drag torque, the proportion of the drag torque of the torque consumer in the coupled state. A sawtooth-shaped course of the selected DFCO speed is thereby avoided, so that the risk of multiple short-term switching on and off of the fuel cutoff is avoided.

Particularly preferably, the portion of the drag torque of the torque consumer in the uncoupled state is determined for the portion of the drag torque determined by the periodically selectable torque consumer, if the periodically engageable torque consumer is decoupled over a predefined minimum period. As a result, a final and / or prolonged uncoupling of the torque consumer in the determination of the expected drag torque can be considered in good time.

In particular, the average absorbed power of the periodically engageable torque consumer is adjusted by pulse width modulation of the period of the coupling. Due to the variable period of coupling of the torque consumer during a predefined interval, an average power of the torque consumer can be adjusted without complicated control, whereby the accordingly changing drag torque can be taken into account in determining the DFCO speed in a manner favorable for the operation of the motor vehicle.

Preferably, the expected drag torque via a time delay element, in particular PT1 element, is taken into account in the selection of the DFCO speed. Sudden impulses for an increased drag torque, for example by switching on an electrical load with a coupled alternator, which have only such a short pulse width that a stalling of the internal combustion engine is not to be feared, can be filtered out by the time delay element, for example in the form of a low-pass filter. without an unnecessary termination of fuel cut.

In particular, in the case of a reducing drag torque, the expected drag torque via a ramp member, in particular an I-member, is taken into account when selecting the DFCO rotational speed. This avoids that a particularly unanticipated short-term uncoupling of a torque consumer and / or a failed reading for a portion of the current drag torque leads to too low a DFCO speed, while still a just allowed reduction in the DFCO speed, for example via a controller with integrative Share, can be tracked.

Particularly preferred is a signal for coupling and / or uncoupling a torque consumer, in particular turbocharger, and / or a signal for switching on and / or off an electrical load in determining the expected drag torque taken into account before a complete coupling and / or uncoupling of the torque consumer and / or a complete switching on and / or off the electrical load is done. This enables a forward-looking determination of the DFCO speed, for example in the form of a feed-forward control.

In particular, for selecting a DFCO rotational speed n _DFCO, a base rotational speed n _B and an offset rotational speed Δn which varies as a function of the currently anticipated drag torque are used. Thus, for example, the base speed can be used for standard conditions and, in the event that unusual boundary conditions make a more accurate determination of the DFCO speed different from the base speed appear promising, a dynamic continuous adjustment of the DFCO speed by adjusting the offset Speed can be performed.

The basic rotational speed n _B preferably corresponds essentially to the DFCO rotational speed n _DFCO with minimum drag torque or with maximum drag torque. The basic speed can thereby define a barrier for the DFCO speed, which need not be undershooted or exceeded during overrun operation, so that starting from the basic speed for determining the DFCO speed only an addition or a subtraction with the calculated offset Speed needs to be done, whereby the required electronic circuit technology can be simplified.

A further embodiment of the invention relates to a control unit for controlling an internal combustion engine, in particular for carrying out the method which is embodied and developed as described above, comprising an input port for reading in information about the expected drag torque for the internal combustion engine, a computer unit for determining a current to be expected drag torque for the internal combustion engine from the information read and to select a DFCO speed n _DFCO to end a _fuel cut of the internal combustion engine as a function of the currently expected drag torque and one with a Fuel supply of the internal combustion engine connectable output port to complete the overrun fuel cutoff of the internal combustion engine by supplying fuel to the internal combustion engine. This allows a low fuel consumption of the internal combustion engine. The control unit can in particular be designed and developed further as explained above with reference to the method.

A further embodiment of the invention relates to a computer program product with program code means which are stored on a computer-readable data carrier in order to carry out the method which can be developed and developed as described above, if the computer program product on a computer, in particular a control unit, the as described above and can be further developed, is executed. This allows a low fuel consumption of the internal combustion engine.

A further embodiment of the invention relates to a computer program with coded instructions for carrying out the method, which can be embodied and developed as described above, when the computer program is executed on a computer, in particular a control unit which can be developed and developed as described above becomes. This allows a low fuel consumption of the internal combustion engine. The computer program may in particular be stored on the computer program product described above, for example a floppy disk, CD-ROM, DVD, memory, a computer unit connected to the Internet. The computer program may in particular be designed as a compiled or uncompiled data sequence, which is preferably based on a higher, in particular object-based computer language, such as, for example, C, C ++, Java, Smalltalk, Pascal, Turbo Pascal.

A further embodiment of the invention relates to a signal sequence with computer-readable instructions for carrying out the method, which may be embodied and developed as described above, when the signal sequence is processed by a computer, in particular a control unit which may be configured and developed as described above becomes. This allows a low fuel consumption of the internal combustion engine. The signal sequence can in particular be generated with the aid of the computer program described above and / or with the aid of the computer program product described above. The signal sequence can be provided as electrical impulses and / or electromagnetic wave and / or optical impulses wireless or wired.

Another aspect of the invention relates to an apparatus for controlling an internal combustion engine, comprising means for determining an anticipated drag torque for the internal combustion engine during a coasting operation of the internal combustion engine and means for selecting a DFCO speed n _DFCO to terminate a _fuel cut of the internal combustion engine depending on the current expected drag torque, whereby the determination of the expected drag torque and the selection of the DFCO speed is constantly repeated.

The DFCO speed for ending the overrun fuel cutoff of the internal combustion engine is not set once or at the occurrence of a specific event, but again and again determined depending on the currently present drag torque. The DFCO speed can be varied continuously, taking into account dynamically changing boundary conditions such that the DFCO speed is minimized without risking stalling the engine due to the applied drag torque, so that only a small amount of power is required to stall to prevent the internal combustion engine with coupled drive train. This allows low fuel consumption of the internal combustion engine and leads to a reduction of CO ₂ emissions.

An embodiment of the apparatus further comprises selection means, which are formed, a DFCO speed n _DFCO above a limit speed n ₀ , below which the internal combustion engine ( 14 ) at the anticipated drag torque, wherein in particular for n _DFCO / n ₀ 1.00 <n _DFCO / n ₀ ≤ 1.40, preferably 1.02 <n _DFCO / n ₀ ≤ 1.20, and particularly preferred 1.05 <n _DFCO / n ₀ ≤ 1.10. The DFCO speed can thus be far enough above the limit speed that with sufficient certainty stalling of the engine is avoided, the DFCO speed is also close enough to the limit speed to provide the lowest possible fuel consumption at the end of the fuel cut.

An embodiment of the apparatus further provides, to use means for determining an expected drag torque, which are formed in which in the determined case of a periodically connectable to the torque flow provided by the internal combustion engine torque consumer, in particular a compressor for an air conditioner, for determining the expected towing torque to use the proportion of the drag torque of the torque consumer in the coupled state. A sawtooth shape of the selected DFCO speed is thereby avoided, so that the risk of a multiple short-term switching on and off the fuel cut is avoided.

In a further embodiment of the apparatus, means are provided for determining an expected drag torque, which are designed to use the portion of the drag torque of the torque consumer in the uncoupled state for the portion of the drag torque determined by the periodically selectable torque consumer when the periodically engageable torque consumer disconnected over a predefined minimum period. As a result, a final and / or prolonged uncoupling of the torque consumer in the determination of the expected drag torque can be considered in good time.

Furthermore, an embodiment is proposed, the means for adjusting the average recorded power of the periodically engageable torque consumer by pulse width modulation of the period of the coupling. Due to the variable period of coupling of the torque consumer during a predefined interval, an average power of the torque consumer can be adjusted without complicated control, whereby the accordingly changing drag torque can be taken into account in determining the DFCO speed in a manner favorable for the operation of the motor vehicle.

Furthermore, an embodiment of the apparatus is possible, in which the means for determining an expected drag torque are formed, a signal for coupling and / or uncoupling a torque consumer, in particular turbocharger, and / or a signal for switching on and / or off an electrical load to consider the determination of the expected drag torque before a complete coupling and / or uncoupling of the torque consumer and / or a complete switching on and / or off the electrical load has been done. This enables a forward-looking determination of the DFCO speed, for example in the form of a feed-forward control.

Furthermore, an embodiment of the apparatus is possible, in which the means for determining an expected drag torque are formed, for selecting a DFCO speed n _DFCO a base speed n _B and a variable depending on the currently expected drag torque offset speed Δn to use. Thus, for example, the base speed can be used for standard conditions and, in the event that unusual boundary conditions make a more accurate determination of the DFCO speed different from the base speed appear promising, a dynamic continuous adjustment of the DFCO speed by adjusting the offset Speed can be performed.

Also, an embodiment of the apparatus is possible, in which the means for determining an expected drag torque are designed to provide a base speed n _B , which essentially corresponds to the DFCO speed n _DFCO with minimum drag torque or maximum drag torque. The basic speed can thereby define a barrier for the DFCO speed, which need not be undershooted or exceeded during overrun operation, so that starting from the basic speed for determining the DFCO speed only an addition or a subtraction with the calculated offset Speed needs to be done, whereby the required electronic circuit technology can be simplified.

The invention will now be described by way of example with reference to the accompanying drawings with reference to preferred embodiments, wherein the features shown below, both individually and in combination may represent an aspect of the invention. Show it:

1 FIG. 3 is a schematic flowchart for carrying out the method. FIG.

2 FIG. 3 is a schematic flow diagram of a partial aspect of the in 1 illustrated flowchart and

3 : a schematic diagram of a control unit for the in 1 illustrated method.

At the in 1 illustrated method 10 a determination is made 12 an expected drag torque for an internal combustion engine 14 and a selection 16 a DFCO speed for ending a fuel cut of the internal combustion engine 14 depending on the previously determined drag torque. Determining 12 of drag torque and picking 16 The DFCO speed can be repeated continuously and continuously without a separate external trigger.

Select 16 The DFCO speed can be such that first reading 18 an offset speed is performed from a map. The offset speed determines a speed difference that is added to a base speed and / or subtracted from the base speed to determine the DFCO speed. After reading 18 the offset speed is a first check 20 , whether the current drag torque in the Has reduced comparison to the previous round. For this example, the read offset speed can be compared with the read offset speed from one of the previous passes and / or with an average of the read offset speeds from several previous passes. If the drag torque should have reduced, a first adjustment takes place 22 the previous offset speed to the current speed and / or the previous DFCO speed to the currently determined DFCO speed, this first adjustment 22 in particular ramped in order to respond in the manner of a low-pass filter to sudden short-term reductions in drag torque not too sensitive.

In the event that the current drag torque has not decreased compared to the previous run, a second check is performed 24 , whether the current speed of the internal combustion engine 14 higher than the DFCO speed at maximum drag torque. In particular, the DFCO speed at maximum drag torque corresponds to the base speed, so that the current speed of the internal combustion engine 14 at the second review 24 is compared with the base speed and not with the sum of the base speed and the offset speed. If the current speed of the internal combustion engine 14 higher than the DFCO speed at maximum drag torque, it is not necessary to change the DFCO speed compared to the previous pass, so accept 26 the previous offset speed or the previous DFCO speed. If the current speed of the internal combustion engine 14 is lower than the DFCO speed at maximum drag torque, a takeover takes place 28 the current offset speed or the current DFCO speed. Finally, in the illustrated embodiment, a calculation takes place 30 the selected DFCO speed from the base speed and the offset speed selected according to the previous queries. The dynamically and continuously selected DFCO speed is used in the control of the internal combustion engine 14 Used to overrun the internal combustion engine 14 with coupled drive train 66 and accelerator pedal a fuel supply 62 to the internal combustion engine 14 turn back to a stalling of the internal combustion engine 14 to prevent by the attacking drag torque.

In 2 is the example of a pulse width modulation to that of the internal combustion engine 14 provided torque flow coupling torque consumers in the form of a compressor 68 for an air conditioner exemplifies how the provided by this torque consumer portion of the drag torque in the determination 12 the drag torque is taken into account. First, a first review 32 whether the torque consumer is coupled. If so, the drag torque currently provided by the torque consumer becomes the determination 12 used by the drag torque 34 , The drag torque of the torque consumer can be calculated, for example, from the current power consumption and / or output by suitable measurements. If the torque consumer is not engaged, a second check is made 36 whether the torque consumer was engaged in the previous run. If this is the case, the torque consumer has been uncoupled immediately before, so for safety's sake, first the value for the drag torque is used in the previous run 38 , Furthermore, this value is stored.

If the torque consumer was also disconnected during the previous run, a third check is made 40 whether the stored value for the drag torque is greater than zero. This is the case when the torque consumer has been disconnected only a short time ago but for safety's sake still the drag torque of the torque consumer in the coupled state for determining 12 of the drag torque is to be used. In this case, an incrementing first takes place 42 a timer and a comparison 44 of the timer with a predefined minimum period. If the value of the timer is less than the minimum period, the stored value for the drag torque of the torque consumer will be used for safety's sake 46 , If the value of the timer is not less than the minimum period, a final uncoupling of the torque consumer is detected 48 , At the same time, the drag torque provided by the decoupled torque consumer, which in most cases is zero, is used for the determination 16 at the internal combustion engine 14 used to attacking drag torque. This value is saved. Further, the timer is reset and / or initialized by setting the value of the timer to zero, for example. This can also be done in the case when at the third review 40 it is determined that the stored value for the drag torque is not greater than zero.

As in 3 presented, then the procedure 10 as a computer program 50 on a computer program product 52 be stored in the form of a data memory and as a signal sequence 54 a control unit 56 operate, the computer program product 52 also part of the control unit 56 may be, for example, as a computer unit of the control unit 56 , The control unit 56 has an input port 58 on, for example, via a CAN bus information about the on the internal combustion engine 14 to read currently attacking drag torques. Due to the over the entrance port 58 Information read in, the control unit 56 Consider a suitable DFCO speed considering dynamically changing boundary conditions. About an output port 60 can the control unit 56 a fuel supply device 62 control and / or regulate to stall the internal combustion engine 14 at a fall in the speed of the internal combustion engine 14 to avoid the DFCO speed. The internal combustion engine 14 is about a clutch 64 in overrun mode of the internal combustion engine 14 to a drive train 66 coupled, whose drag torque in the determination 12 the expected drag torque is taken into account. In particular, the drag torque of indirectly or directly with the internal combustion engine 14 preferably periodically connectable torque consumers, in particular a compressor 68 for an air conditioner and / or an alternator 70 , considered. In addition, also the drag torque of indirectly or directly with the drive train 66 connected further torque consumers 72 be taken into account.

While at least one exemplary embodiment has been described in detail in the foregoing description, it should be appreciated that a variety of variations are possible. The exemplary embodiments in the description give the skilled person a useful explanation in order to realize at least one embodiment, wherein changes in function and arrangement of the elements described in the embodiments can be made without departing from the scope of the following claims and their equivalents.

LIST OF REFERENCE NUMBERS

10

method

12

Determining an expected drag torque

14

Internal combustion engine

16

Select a DFCO speed

18

Reading an offset speed from a map

20

first check

22

first adaptation

24

second check

26

Apply the previous offset speed

28

Apply the current offset speed

30

Calculate the selected DFCO speed

32

first review

34

use the current drag torque

36

second review

38

use the previous drag torque

40

third review

42

Increment a timer

44

Comparison of the timer with a minimum period

46

continue to use the drag torque

48

recognize final uncoupling

50

computer program

52

A computer program product

54

signal sequence

56

control unit

58

input port

60

output port

62

Fuel supply means

64

clutch

66

powertrain

68

compressor

70

alternator

72

further torque consumers

Claims (14)

Method for controlling an internal combustion engine ( 14 ), comprising the steps of determining ( 12 ) of an expected drag torque for the internal combustion engine ( 14 ) during a coasting operation of the internal combustion engine ( 14 ) and Select ( 16 ) of a DFCO speed n _DFCO for ending an overrun _{fuel cutoff of} the internal combustion engine ( 14 ) depending on the currently expected drag torque, wherein the determining ( 12 ) of the expected drag torque and selecting ( 16 ) the DFCO speed is constantly repeated. Method according to Claim 1, in which the DFCO rotational speed n _{DFCO is} above a limit rotational speed n ₀ , below which the internal combustion engine ( 14 ) at the expected drag torque is, in particular for n _DFCO / n0 1.00 <n _DFCO / n ₀ ≤ 1.40, preferably 1.02 <n _DFCO / n0 ≤ 1.20 and particularly preferably 1, 05 <n _DFCO / n ₀ ≤ 1.10. Method according to Claim 1 or 2, in which, in the case ascertained, one of those of the internal combustion engine ( 14 ) provided torque flow periodically connectable torque consumer, in particular a compressor ( 68 ) for an air conditioner, for determining ( 12 ) of the expected drag torque, the proportion of the drag torque of the torque consumer ( 68 ) is used in the coupled state. Method according to Claim 3, in which, for the torque consumer which can be applied periodically ( 68 ) certain proportion of the drag torque the proportion of the drag torque of the torque consumer ( 68 ) is used in the uncoupled state when the periodically engageable torque consumer ( 68 ) is uncoupled for a predefined minimum period. Method according to Claim 3 or 4, in which the mean absorbed power of the periodically connectable torque consumer ( 68 ) is adjusted by pulse width modulation of the period of coupling. Method according to one of claims 1 to 5, in which the expected drag torque via a time delay element, in particular PT1 element, in the selection ( 16 ) of the DFCO speed. Method according to one of claims 1 to 6, wherein at a reducing drag torque the expected drag torque via a ramp member, in particular I-member, in the selection ( 16 ) of the DFCO speed. Method according to one of claims 1 to 7, wherein a signal for coupling and / or uncoupling a torque consumer, in particular turbocharger, and / or a signal for switching on and / or off an electrical load in the determination ( 12 ) of the expected drag torque is taken into account before a complete coupling and / or decoupling of the torque consumer and / or a complete switching on and / or off of the electrical load has occurred. Method according to one of Claims 1 to 8, in which for the selection ( 16 ) a DFCO speed n _DFCO a base speed n _B and a variable depending on the currently expected drag torque offset speed .DELTA.n is used. The method of claim 9, wherein the base speed n _B substantially corresponds to the DFCO speed n _DFCO at minimum drag torque or maximum drag torque. Control unit for controlling an internal combustion engine ( 14 ), in particular for carrying out the method ( 10 ) according to one of claims 1 to 10, comprising an input port ( 58 ) for reading information about the expected drag torque for the internal combustion engine ( 14 ), a computing unit for determining ( 12 ) of a currently expected drag torque for the internal combustion engine ( 14 ) from the information read and to select ( 16 ) of a DFCO speed n _DFCO for ending an overrun _{fuel cutoff of} the internal combustion engine ( 14 ) depending on the currently expected drag torque and one with a fuel supply ( 62 ) of the internal combustion engine ( 14 ) connectable output port ( 60 ) for ending a fuel cut of the internal combustion engine ( 14 ) by supplying fuel to the internal combustion engine ( 14 ). Computer program product with program code means stored on a computer-readable medium for carrying out the method ( 10 ) according to one of claims 1 to 10, when the computer program product ( 52 ) on a computer, in particular a control unit ( 56 ) according to claim 11. Computer program with coded instructions for carrying out the method ( 10 ) according to one of claims 1 to 10, when the computer program ( 50 ) on a computer, in particular a control unit ( 56 ) according to claim 11. Signal sequence with computer-readable instructions for performing the method ( 10 ) according to one of claims 1 to 10, when the signal sequence ( 54 ) from a computer, in particular a control unit ( 56 ) according to claim 11, is processed.

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