DE102019130705B4 - Method for operating an internal combustion engine and engine control device - Google Patents

Abstract

A method for operating an internal combustion engine is provided in which, in the event that knocking is detected (12) in a cylinder of the internal combustion engine, an ignition timing for the cylinder is shifted (16) by a predefined standard value to a later point in time (18) whether an increase in cooling of the cylinder and/or a fuel/air mixture fed into the cylinder is possible, and in the event that the increase in cooling is possible, a cooling capacity for cooling by a predefined capacity increment is increased (20) and essentially at the same time an ignition point for the cylinder is shifted to an earlier point in time by a predefined ignition angle increment (22), the cooling being increased by means of water injection. In the event that knocking in the cylinder is no longer detected (24), the cooling capacity is reduced, and after all previously made increases in cooling capacity have been reversed, the ignition timing for the cylinder is shifted to an earlier point in time until a predefined starting value for the ignition timing is reached or knocking is detected in the cylinder.

Description

The invention relates to a method for operating an internal combustion engine and an engine control device with the aid of which knocking in a cylinder of the internal combustion engine of a motor vehicle can be avoided.

In order to achieve the highest possible efficiency in an internal combustion engine, the maximum cylinder pressure during combustion of a fuel/air mixture in the cylinder should be just after top dead center. Unfavorable ignition of the fuel/air mixture in the cylinder can occur, particularly when the combustion engine requires a high level of performance and/or the ignition point is too early Cylinder pressure curve occur, which can lead to damage.

Out of EP 2 700 804 A1 In the event of knocking in a cylinder of an internal combustion engine of a motor vehicle, it is known to inject water into the cylinder and/or to shift an ignition point for the cylinder to a later point in time.

DE 10 2017 130 377 A1 discloses a method of operating an internal combustion engine. Depending on whether water injection conditions are met, water is injected, namely into an exhaust manifold or into cylinders. Furthermore, an ignition timing is determined based on the knock magnitude.

Out of U.S. 2013/0 180 502 A1 , out of DE 10 2015 208 359 A1 and from DE 10 2014 204 509 A1 further prior art is known.

There is a constant need to operate an internal combustion engine with a high level of efficiency, essentially without knocking.

It is the object of the invention to indicate measures that enable efficient operation of an internal combustion engine with little knocking.

The object is achieved according to the invention by a method having the features of claim 1 and an engine control device having the features of claim 7.

Preferred configurations of the invention are specified in the dependent claims and the following description, each of which individually or in combination can represent an aspect of the invention.

According to the invention, a method for operating an internal combustion engine is provided in which, in the event that knocking is detected in a cylinder of the internal combustion engine, an ignition point for the cylinder is shifted by a predefined standard value to a later point in time, it is checked whether an increase in a Cooling of the cylinder and/or a fuel/air mixture fed into the cylinder is possible, and in the event that the increase in cooling is possible, a cooling capacity for the cooling is increased by a predefined power increment and essentially at the same time an ignition timing for the Cylinder is shifted to an earlier point in time by a predefined ignition angle increment. The increase in cooling is realized by means of water injection.

In the event that knocking in the cylinder is no longer detected, the cooling capacity is reduced. The previously shifted ignition point is initially retained when the cooling capacity is reduced. When the knocking that has occurred has disappeared again, the cooling capacity can first be reduced in order to reduce an unnecessarily high flow rate of a coolant, in particular water. As a result, pump performance for conveying the coolant can be reduced. An improvement in the situation that caused knocking can first be used by suddenly or gradually reducing the cooling capacity to the original value before knocking. For example, the cooling that has taken place over a certain period of time can have the result that the temperature of an inner cylinder wall has been reduced over the long term, as a result of which the risk of knocking occurring has also been reduced over the long term during subsequent operation. The increased cooling capacity is no longer required in this situation.

After any previously made increases in cooling capacity have been reversed, the ignition timing for the cylinder is rescheduled to an earlier point in time. An improvement in combustion achieved by the previously increased cooling capacity in the cylinder can be used by shifting the ignition point to an earlier point in time. As a result, the internal combustion engine can be operated particularly close to the knock limit. If knocking is detected earlier during the spark timing shift, the method may be restarted.

The ignition point for the cylinder is shifted to an earlier point in time until a predefined starting value for the ignition point is reached point is reached or knocking is detected in the cylinder. This prevents the ignition point from being shifted beyond the originally intended initial value, which may be speed-dependent and/or load-dependent. In spite of the advance of the ignition timing, knocking can be avoided.

By shifting the ignition timing to a later point in time, knocking can generally be effectively prevented. As a predefined standard value, the crankshaft angle can be increased by an amount ΔKW ⁺ of 0.5°<ΔKW ⁺ ≦5.0°, in particular 1.5°≦ΔKW ⁺ ≦4.5° and preferably ΔKW ⁺ ≦3.0±0.5 be shifted to a later point in time, the predefined standard value preferably being selected differently depending on the current operating behavior of the motor vehicle engine. As a result, a higher standard value can be selected for carrying out the method at an operating point which is regarded as critical and a lower standard value for carrying out the method at an operating point which is regarded as less critical. However, this can also shift the maximum cylinder pressure during combustion to a later point in time, which is further away from top dead center, which reduces the efficiency and the efficiency of the operation of the internal combustion engine of a motor vehicle. This can be at least partially compensated for by increasing the cooling capacity. This exploits the knowledge that at the moment when the cooling capacity is increased, the predefined standard value for the standard shift in the ignition point to a later point in time can be too large. The predefined default value is dimensioned in particular for the case that further cooling is not possible, so that the knocking is safely eliminated as quickly as possible. However, if further cooling is still possible, the cooling can make a contribution to preventing knocking, which contribution makes it possible to shift the ignition timing to an earlier point in time, which correlates with this contribution. The actually intended shifting of the ignition point by the predefined standard value at a later point in time is at least partially reversed by the predefined ignition angle increment if the cooling was increased. As a result, the ignition angle can only be shifted to a later point in time to the extent that is absolutely necessary, taking into account the effect of the increased cooling. The safety-oriented shifting of the ignition point to a later point in time by the standard value is at least partially reversed in the case of additional cooling by the ignition angle increment in order to be able to limit the shift in the ignition angle to the extent necessary to avoid knocking, so that an efficient Operation of an internal combustion engine is enabled with little knocking.

The cooling capacity can be increased in particular without a stored correction data field. As a result, it is not necessary to correct and/or use an ignition map, as a result of which the ignition point and/or the cooling capacity can be regulated correspondingly quickly. As a result, the number of knock events occurring in the cylinder can be reduced. It is also possible to use fuels that have a lower knock resistance, for example fuels with an octane number of less than 98 RON. Since knocking is at least partially avoided by increasing the cooling capacity and thus less or not at all due to a shift in the ignition point, the prevention of knocking can be done almost without a significant power reduction of the internal combustion engine.

The cooling capacity can be increased in particular depending on the selected predefined ignition angle increment, which is preferably selected differently depending on the current operating behavior of the motor vehicle engine. Depending on the current operating behavior of the motor vehicle engine, an amount ΔKW- of 0.5°≤ ΔKW ^- ≤ 4.0°, in particular 1.0°≤ ΔKW ^- ≤ 3.0° and preferably ΔKW ^- ≤ 2 .0 ± 0.5° can be specified. The amount ^ΔKW− of the predefined ignition angle increment for shifting the ignition point to an earlier point in time is particularly preferably smaller by a difference of at least 0.5° than the amount ΔKW ⁺ of the predefined standard value for shifting the ignition point to a later point in time. The ignition point can be shifted to an earlier point in time, in particular in several partial steps, as long as the cooling capacity can still be increased. To increase the cooling capacity, the flow rate of the coolant can be increased by 3% to 10%, in particular by 4% to 7% and preferably by 5%±0.5%, based on the maximum flow rate at the selected ignition angle increment. This makes it possible to moderately utilize the available maximum possible increase in the flow rate for shifting the ignition point to an earlier point in time without having to fear unstable overshooting of the control of the ignition point with the aid of the adjustment of the cooling capacity. Increasing the flow rate and shifting the ignition point to an earlier point in time can, in particular, be repeated several times to control an operating point that is particularly close to the knock limit.

In particular, in the event that knocking is still detected in the cylinder, the steps of shifting the ignition timing for the cylinder by the predefined standard value to a later point in time, checking for an increase in cooling of the cylinder and/or in-cylinder guided fuel/air mixture is possible, and in the event that the increase in cooling is possible, increasing the cooling power for the cooling by the predefined power increment and essentially simultaneously shifting the ignition timing for the cylinder by the predefined ignition angle increment repeated earlier. If the previous control intervention is not sufficient to prevent knocking, the ignition timing can be shifted again. If the cooling capacity can still be increased in this loop run, the cooling capacity can be increased again and the shift in the ignition angle by the ignition angle increment can be reversed. If it is not possible to increase the cooling capacity, for example because a maximum cooling capacity provided for this purpose has already been reached, the ignition angle is shifted by the standard value without partial compensation being undertaken. The multiple run makes it possible to provide smaller amounts for the standard value and for the predefined power increment of increasing the cooling power and the ignition angle increment correlating with the power increment, so that a correspondingly finer regulation is possible. As a result, the internal combustion engine can be operated particularly close to the knock limit, so that the maximum cylinder pressure during combustion can be present as shortly after top dead center as possible.

It is particularly preferred that all previously made increases in the cooling capacity are simultaneously withdrawn. The energy input required to increase the cooling capacity can be reduced particularly quickly as a result. This is particularly useful if the increased cooling capacity is maintained over a longer period of time before the cooling capacity can be reduced.

In a further specific embodiment, the cooling capacity is reduced by the predefined capacity increment in each case until knocking in the cylinder is detected again or all previously made increases in the cooling capacity have been withdrawn. The cooling capacity can thereby be reduced to the same extent as it was previously increased. This makes it easier to regulate an optimal value for the cooling capacity at which the combustion engine can be operated particularly close to the knock limit. This is particularly useful if the increased cooling capacity is maintained over a rather short period of time before the cooling capacity is allowed to be reduced.

In particular, a predefined waiting time is initially awaited before the cooling capacity is reduced. This can ensure that the increase in cooling capacity can achieve an effect in the cylinder. It can be taken into account here that the increase in the cooling capacity can only influence the situation in the cylinder with a certain dead time and with a more integral control behavior. As a result, unstable oscillation of a control circuit implemented with the aid of the method can be avoided. The waiting time can be selected in particular as a function of the operating point and/or the operating behavior and/or the outside temperature or other influencing factors. For example, an operation in a
a longer waiting time at an operating point considered critical and a lower waiting time at an operating point considered less critical. A suitable waiting time t can be, for example, 0.05 s≦t≦1.0 s, in particular 0.1 s≦t≦0.7 s, preferably 0.2 s≦t≦0.5 s and particularly preferably t=0, 3 s ± 0.05 s.

The increase in cooling is realized by using water injection. Water is injected into an intake manifold in the area of an intake valve of a cylinder by means of an injector for water injection. Water injection directly into a combustion chamber of a cylinder is also conceivable. The water therefore has a cooling property, which reduces the temperature in the combustion chamber and knocking can already be avoided.

The invention also relates to an engine control device for operating an internal combustion engine with means for executing the method, which can be designed and developed as described above. The safety-oriented shifting of the ignition point to a later point in time by the standard value with the help of the engine control device is at least partially reversed in the case of additional cooling by the ignition angle increment in order to be able to limit the shifting of the ignition angle to the extent necessary to avoid knocking, so that efficient operation of an internal combustion engine with little knocking is enabled. In particular, the engine control device can be connected to a knock sensor for detecting knocking in the cylinder. In addition, the engine control device can provide a cooling capacity for cooling the cylinder and/or for cooling a fuel/air mixture for the Control cylinders using water injection. The engine control device can also be connected to an adjustment device for controlling an ignition timing in the cylinder. It is also possible for the engine control unit to store variable values for the predefined standard value for shifting the ignition point to a later point in time, the predefined power increment for increasing cooling and the predefined ignition angle increment for shifting the ignition point to an earlier point in time.

• 1: eine schematische Darstellung eines Regelkreises für ein Verfahren zum Betrieb eines Verbrennungsmotors.

In the following, the invention is explained by way of example with reference to the attached drawing using a preferred exemplary embodiment, it being possible for the features presented below to represent an aspect of the invention both individually and in combination. It shows:

• 1 : a schematic representation of a control loop for a method for operating an internal combustion engine.

the inside 1 The illustrated control circuit 10 of an engine control device has an initial check 12 carried out with the aid of a knock sensor as to whether knocking is taking place in a monitored cylinder of an internal combustion engine of a motor vehicle. If no knocking is detected, the method represented by the control circuit 10 is not triggered and the engine control provided for normal operation remains. If the initial check 12 has shown that knocking is present, a first loop 14 is run through in the control circuit 10, in which a shift 16 of an ignition point to a later point in time by a predefined standard value takes place by an ignition angle for the ignition point to ignite of the fuel/air mixture introduced in the monitored is shifted closer to top dead center.

A check 18 then takes place as to whether cooling of the cylinder and/or of the fuel/air mixture can be increased. If this is the case, for example because no water has been injected into the cylinder or a maximum water rate provided for the water injection has not yet been reached, the cooling capacity is then increased 20 by a predefined capacity increment, with the ignition timing also being shifted 22 to an earlier point in time by a predefined ignition angle increment correlating with the predefined power increment. An ignition point that has been shifted by the standard value without taking into account a knock prevention effect achieved by the cooling can be at least partially reversed by the predefined ignition angle increment correlating with the predefined power increment, so that an unnecessarily large shift in the ignition point is avoided. If the check 18 shows that an increase 20 in the cooling capacity is no longer possible, the process steps of increasing 20 the cooling capacity and shifting 22 the ignition point by the ignition angle increment are skipped, so that when the ignition point is shifted 16 to a later point in time remains around the standard value.

A new check 24 then takes place to determine whether knocking in the cylinder is still present. If this is the case, the first loop 14 is carried out again in that the ignition timing is again shifted 16 to a later point in time by the standard value and, if necessary, the cooling output is increased 20 again and the ignition point is simultaneously shifted 22 to an earlier point in time by the Ignition angle increment is performed.

If the renewed check 24 shows that there is no knocking in the cylinder, a predefined waiting time is initially awaited and then a reduction 26 of the previously increased cooling capacity is carried out. A further check 28 then takes place to determine whether knocking is present. If this is not the case, the method can be terminated 30 and normal operation can be resumed. In this case, an adjustment of the ignition timing can be left to the regular standard engine control. However, if the further check 28 reveals that there is still knocking, the method can be carried out again with the start of the first loop 14 via a second loop 32 formed as a result. In this case, it may be that the reduction 26 in the cooling capacity was carried out too early and/or too much and the cooling capacity is again adjusted to a suitable value by running through the first loop 14, at which the knocking disappears again.

Claims (6)

Method for operating an internal combustion engine, in which, in the event that knocking is detected in a cylinder of the internal combustion engine (12), an ignition timing for the cylinder is shifted (16) to a later point in time by a predefined standard value (18), is checked whether an increase in cooling of the cylinder and/or a fuel/air mixture conducted into the cylinder is possible, in the event that the increase in cooling is possible, a cooling capacity for the cooling is increased by a predefined capacity increment (20) and in the Essentially at the same time, an ignition point for the cylinder is shifted to an earlier point in time by a predefined ignition angle increment (22), the cooling being increased by means of water injection, in the event that knocking in the cylinder is no longer detected (24) the cooling capacity is reduced (26), wherein after all previously made increases in the cooling capacity have been reversed, the ignition timing for the cylinder is shifted to an earlier point in time until a predefined starting value for the ignition timing is reached or knocking is detected in the cylinder becomes. procedure after claim 1 , in which, in the event that knocking is still detected in the cylinder (24), the steps of shifting (16) the ignition timing for the cylinder by the predefined standard value to a later point in time, checking (18) whether an increase in a Cooling of the cylinder and/or the fuel/air mixture fed into the cylinder is possible, and in the event that the increase in cooling is possible, increasing (20) the cooling power for the cooling by the predefined power increment and shifting it substantially simultaneously (22) the ignition timing for the cylinder can be repeated earlier by the predefined ignition angle increment. procedure after claim 1 or 2 , in which all previously made increases in cooling capacity are canceled at the same time. procedure after claim 1 or 2 , in which the cooling power is reduced by the predefined power increment (26) until knocking in the cylinder is detected again (28) or all previously made increases in the cooling power are withdrawn. Procedure according to one of Claims 1 until 4 , in which a predefined waiting time is initially awaited before a reduction (26) of the cooling capacity is carried out. Engine control device for operating an internal combustion engine with means for carrying out the method according to one of Claims 1 until 5 .

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