INTERNAL COMBUSTION ENGINE

Field of technology

This invention relates to a method and arrangement for controlling harmful events of a reciprocating engine. Especially, this invention relates to a method and arrangement for controlling knock. The engine can be, for example, a diesel engine, a gas engine or an engine that can use a multiple of different fuels. Further, the engine can be a low-speed engine or a medium speed engine.

Prior art

Reciprocating engines are nowadays electronically controlled. In this way a good driving properties of the engine are possible, and the engine can be run on an optimal level wherein efficiency is good with low emissions. In spite of the running at the op- timal level, harmful events may occur. It is important that knock of an internal combustion engine is detected for avoiding dangerous cylinder pressures and pressure oscillations that may damage the cylinder, piston and the crank mechanism. There exist many known solutions to detect knock. The most common way is to measure the vibration levels in the vicinity of the combustion chamber. For example, EP 2189643, US 2010106392, WO 2010013663, US 2009223280, WO 2009031378 and US 2008264150 describe the use of the vibration measurements.

The aim is to avoid the knock condition and for this reason there are used threshold values to indicate the knock condition. The known solutions follow the parameter indicating the knock condition, and when the threshold value is exceeded, the knock control reacts for eliminating the knock. Although the known solutions work satisfactory, it is desirable to have a control device that can provide better quality. Short Description

The objective of the invention is to create a control arrangement that can provide better control response as the previous solutions. The objective is achieved in solutions described in the independent claims. The dependent claims describe different embodiments of the invention. Although this text mainly describes the knocking as a harmful event of the engine, the event can be another type of an undesired condition like misfiring. In the case of the other type the control arrangement is adapted to that particular type of the harmful event.

The idea of the invention is that in addition to the reaction to the knock, the opera- tion condition of the engine is defined in relation to the knock condition in order to avoid the knock beforehand and also to control the engine more flexible than in the previous solutions.

The inventive arrangement comprises a control unit that is arranged to form knock control commands to cylinder specific regulating units and is connectable to cylinder specific first sensors. The control unit is also connectable to second sensors of at least two different types. The arrangement further comprises a map for mapping values of the first sensors and the second sensors. The values of the first sensors indicate knock conditions cylinder specifically and the values of the second sensors indicate at least two variables of the engine. The map indicates also a knock area and an operation point of the engine in relation to the variables and the knock condition.

The arrangement further comprises a calculator unit and an adjusting unit 6. The calculator unit is arranged to calculate the shortest distance between the operation point and the knock area, and also arranged to calculate a gradient of the distance. The adjusting unit is arranged to form the knock control commands for regulator units of said variables as a response to the gradient for increasing the distance. Drawings

Next the invention is described in more detail with the figures of the attached drawings in which drawings

Figure 1 illustrates an example of an inventive arrangement and

Figure 2 illustrates an example of a map of the invention, and

Figure 3 illustrates an example of a diagram showing an inventive method.

Description

Figure 1 illustrates an example of an arrangement according to the invention. The control arrangement for reciprocating engines comprises a control unit 1 that is arranged to form knock control commands 8 to cylinder specific regulator units and is connectable to cylinder specific first sensors 3. The control unit is also connectable to second sensors 2 of at least two different types. The second sensors 2 measure different parameters of the engine. These parameters are not constant so they are vari- ables that can be used for controlling the engine. The variables may be, for example, manifold air pressure, manifold air temperature, main fuel injection timing, main fuel injection duration, exhaust gas recirculation, spark timing. The set of control variables is dependent on the engine and fuel system type. For example, in common rail diesel engines, manifold air pressure, manifold air temperature, main fuel injection timing and main fuel injection duration are typical choices for the variables to be measured and controlled. The first sensors 3 measure a cylinder specific parameter that indicates knock condition.

The arrangement further comprises a map or model 4 for mapping values of the first sensors 3 and the second sensors 2. The values of the second sensors indicate at least two variables of the engine. Figure 2 shows an example of the map 21 that is three-dimensional. The map 21 indicates a knock area 22 and an operation point 23 of the engine in relation to the variables (VARIABLE 1 and VARIABLE 2) and the knock condition (KNOCK INDEX). The map can be, for example, a self-organizing map. The model can be any type that is able to describe relationship between at least two signals, such as a neural network or a differential function. The knock condition axis (or vector), i.e. the knock index axis can have a scale that is based on a measurement value scale or a normalized measurement value scale (relative value scale). The knock index may represent, for example, a vibration level nearby the cylinder or pressure in the cylinder.

The arrangement further comprises a calculator unit 5 that is arranged to calculate the shortest distance 24 between the operation point 23 and the knock area 22, to be more accurate the distance 24 between the operation point 23 and the nearest knock point 25. The calculator unit is also arranged to calculate a gradient of the distance 24. The gradient comprises partial derivates in relation to the variables. In addition the arrangement comprises an adjusting unit 6 to form the knock control commands 8 to regulator units of said variables as a response to the gradient for increasing the distance. The adjusting unit can be arranged to select the largest partial derivates for forming the knock control commands. In this way it is possible to increase the dis- tance between the operation point 23 and the nearest knock point 25 fast. It also makes possible to move the operation point as little as possible, since the other variables are not changed and the small change of the variable/s having the largest partial derivate can increase the distance enough. The adjusting unit 6 can also be arranged to receive auxiliary data 10 of the engine, and also be arranged to use the auxiliary data to form the knock control commands.

It can be noted that the calculator unit 5 and the adjusting unit 6 can be arranged to form one unit 1 1 , which alternative is represented as a box with a dashed line in Figure 1. The adjusting unit may also provide diagnostic information 9 to maintenance personnel. The map or model can be arranged to be updated to take into ac- count the values of the first sensors and the second sensors. In this way the map is always up-to-date to the engines running environment and condition. An initial map or model can be based on tests run in an engine laboratory or manufacturing tests.

The invention concerns also a method for controlling knock of a reciprocating engine wherein the method comprises a step of forming knock control commands 34 to cylinder specific regulating units. The method further comprises steps of: mapping 31 values of first sensors 3 and second sensors 2, the values of the first sensors indicat- ing knock condition cylinder specifically and the values of the second sensors indicating at least two variables the engine; indicating 32 knock area 22 and an operation point 23 of the engine in relation to the variables and the knock condition; calculating 33 the shortest distance 24 between the operation point 23 and the knock area 22, and also a gradient of the distance. Said step of forming 34 the knock control commands (8) has been adapted to form the commands to regulating units of said variables as a response to the gradient for increasing the distance 24.

It is also possible that when knock occurs or is very near to occur the inventive arrangement can be arranged to determine first whether all cylinders of the engine are too close the knock area or in the knock area. In these cases general control variables of the engine are used to eliminate or reduce the knock, for example manifold air pressure, manifold air temperature and exhaust gas recirculation. Secondly the arrangement is arranged to control cylinder wise the knocking cylinders using cylinder- wise control variables, for example, main fuel injection timing, main fuel injection du- ration, spark timing, pilot fuel injection timing and pilot fuel injection duration.

The invention makes it possible to adjust one, some or all variables that are inserted into the map 4. Therefore there is great flexibility to form the control commands. The greater the distance is between the operation point and the knock area, the greater the flexibility is. Due to this there are more ways to run the engine than in pri- or art arrangements, and also taking into account load conditions in more detail. As said above when changing only the greatest partial derivate of the gradient, the control response is very fast.

There are a number of ways to achieve the inventive arrangement. Therefore it is clear that the invention is not restricted to the examples of this text, but the invention can be formed in any form within the limits of the claims.