EP2754878A1

EP2754878A1 - Method of operating a combustion engine

Info

Publication number: EP2754878A1
Application number: EP13151336.8A
Authority: EP
Inventors: Gianvito Coppola; Joachim Paul; Sebastian-Paul Wenzel; Roberto SARACINO
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2013-01-15
Filing date: 2013-01-15
Publication date: 2014-07-16

Abstract

A method of operating a combustion engine is described. The combustion engine comprises a cylinder, a piston, an injection valve and a pressure sensor, wherein the cylinder and the piston delimit a combustion chamber. The method comprises injecting fuel with the injection valve into the combustion chamber according to an energizing time (ET), measuring a pressure signal in the combustion chamber with the pressure sensor, determining a first course (51) of a value (Vb1) of an integrated heat release plateau depending on the pressure signal for several energizing times (ET), determining a second course (52) of the value (Vb1) for several energizing times (ET) after a given running time of the combustion engine, evaluating a first and a second offset point (OP1, OP2) of the first and the second course (51, 52), and evaluating a corrected energizing time (ETcorr) depending on the first and the second offset point (OP1, OP2).

Description

Prior Art

The invention relates to a method of operating a combustion engine. The invention also relates to a control unit for operating a combustion engine and to a combustion engine comprising such a control unit.
E.g. US 2010/0121555 A1 discloses a combustion engine comprising a pressure sensor for measuring a pressure signal in a combustion chamber of the combustion engine. Furthermore, the combustion engine comprises an injection valve for injecting fuel into the combustion chamber. Based on the measured pressure signal, a point of injection is determined and then used for influencing the amount of fuel injected into the combustion chamber.
It is an object of the invention to improve the prior art systems.

Disclosure of the Invention

The invention solves this object by a method according to claim 1. As well, the invention solves this object by a control unit according to claim 8.
The method according to the invention comprises the steps of: injecting fuel with the injection valve into the combustion chamber according to an energizing time, measuring a pressure signal in the combustion chamber with the pressure sensor, determining a first course of a value of an integrated heat release plateau depending on the pressure signal for several energizing times, determining a second course of the value for several energizing times after a given running time of the combustion engine, evaluating a first and a second offset point of the first and the second course, and evaluating a corrected energizing time depending on the first and the second offset point.
The invention is able to adjust the energizing time for injecting fuel into the combustion chamber in real-time. This adjustment is carried out depending on the pressure signal within the combustion chamber and therefore based on the actual conditions of the combustion engine. With the invention, a drift of the energizing time due to changes of a device, e.g. due to changes of the performance of the injection valve, over the lifetime of the combustion engine can be compensated. In doing so, the adjustment is carried out for the respective individual item of the combustion engine.
It is advantageous to evaluate an actual energizing time depending on the first course and to evaluate the corrected energizing time depending on the actual energizing time and the first and the second offset point. The actual energizing time may be determined depending on e.g. the rotational speed of the crankshaft and/or depending on the driver's command and/or depending on the current load of the combustion engine or the like. Thus, the corrected energizing time is determined based on the normal evaluation of the actual energizing time.
In an embodiment of the invention, the value of the integrated heat release plateau depends on a heat release rate signal which is derived from the pressure signal. As an example, the heat release rate signal may be evaluated using a so-called "schnelles Heizgesetz (fast heating rule)". This embodiment allows fast calculations and facilitates the real-time adjustment of the energizing time.
In a further embodiment of the invention, the corrected energizing time may be calculated according to the following equation: ETcorr = ETact + OP2 - OP1. This calculation may be carried in real-time for adjusting the fuel to be injected.
Figure 1 shows a schematic block diagram of an embodiment of a combustion engine according to the invention, figure 2 shows a schematic time diagram of operating parameters of the combustion engine of figure 1, figures 3a to 3c show schematic diagrams of operating parameters of the combustion engine of figure 1, figure 4 shows a schematic flow diagram of a method according to the invention, figures 5 shows a schematic diagram of a value Vb1 depicted over an energizing time ET for an individual item of the combustion engine of figure 1, and figure 6 shows a schematic flow diagram of a method according to the invention.
In figure 1, one cylinder 10 of a number of cylinders of an internal combustion engine is shown. The combustion engine may be a diesel engine or a gasoline engine and may have e.g. four or six cylinders.
In the cylinder 10, a piston 11 is movable in an up- and down direction as shown by arrow 12. The piston 11 is coupled by a connecting rod or the like to a crank shaft 13 so that the up- and down movement of the piston 11 is converted into a rotation of the crank shaft 13 as shown by arrow 14.
The cylinder 10 and the piston 11 delimit a combustion chamber 16. An injection valve 17 is allocated to the cylinder 10 such that fuel may be injected into the combustion chamber 16 by the injection valve 17. Furthermore, a pressure sensor 18 is allocated to the cylinder 10 such that the pressure in the combustion chamber 16 may be measured by the pressure sensor 18.
The combustion engine may comprise further sensors, e.g. a sensor assigned to the crank shaft 13 for measuring a rotational speed signal N and/or a crank angle ϕ of the crank shaft 13, and so on. Furthermore, the combustion engine may comprise known functions, e.g. an exhaust gas recirculation, a turbo-charger, a fuel-tank ventilation and the like, with additional sensors.
A control unit 20, in particular a computer with a computer program, is assigned to the combustion engine. The control unit 20 generates an injection signal TI which is forwarded to the injection valve 17 for driving the injection valve 17 into a state in which fuel is injected by the injection valve 17. The pressure sensor 18 generates a pressure signal P which corresponds to the pressure measured in the combustion chamber 16 and which is input to the control unit 20. Furthermore, a number of other signals IN, OUT are input to the control unit 20 and/or are output from the control unit 20. E.g. the rotational speed signal N is forwarded to the control unit 20.
Figure 2, firstly, shows an exemplary injection signal TI of a single engine cycle which is depicted over the crank angle ϕ of the crank shaft 13. It is noted that the crank angle ϕ of the crank shaft 13 is similar to and may therefore be replaced by the time t.
The injection signal TI comprises a pilot injection PI and a main injection MI. The injection signal TI may, in a modified embodiment, comprise further pilot and/or main injections.
The course of the injection signal TI of the pilot injection PI or the main injection MI corresponds to the movement of a valve needle within the injection valve 17. At the beginning, the valve needle starts from a closed position and is moved into an open position in which the fuel is injected into the combustion chamber 16. After an energizing time ET, the valve needle is moved back into its closed position. Among others, the amount of injected fuel depends on the energizing time ET during which the injection valve 17 is in its opened position. As an example, the energizing time ET is shown in figure 2 in connection with the main injection MI.
Secondly, figure 2 shows an exemplary pressure signal P which is depicted over the crank angle ϕ of the crank shaft 13. The pressure signal P corresponds to the injection signal TI and therefore to a single engine cycle.
Basically, the pressure signal P would have - without any fuel combustion - a sine-wave form due to the up- and down movement of the piston 11 which leads to an increase and a decrease of the pressure within the combustion chamber 16. In figure 2, one wave of such basic pressure signal may be identified using the dotted line.
However, due to the injection of fuel into the combustion chamber 16 and a subsequent combustion of the injected fuel within the combustion chamber 16, the pressure signal P is increased during one or more periods of time and therefore comprises deviations from the sine-wave form, i.e. one or more pressure peaks. In figure 2, a first exemplary pressure peak PP1 results from the pilot injection PI and a second exemplary pressure peak PP2 results from the main injection MI.
Thirdly, figure 2 shows a heat release rate signal HRR which is depicted over the crank angle ϕ of the crank shaft 13. The heat release rate signal HRR corresponds to the pilot injection PI and the main injection MI.
The heat release rate signal HRR may be derived from the pressure signal P. For example, the heat release rate signal HRR may be evaluated using a so-called "schnelles Heizgesetz (fast heating rule)"; reference is made e.g. to Pischinger, Kraßnig, Taucar, Sams, Thermodynamik der Verbrennungskraftmaschine, Wien, New York, Springer, 1989. According to this exemplary rule, the pressure within the combustion chamber, the volume of the combustion chamber and a so-called "kalorischer Wert (caloric value)" is used to calculate the heat release rate.
The heat release rate signal HRR may be evaluated e.g. by the control unit 20.
The heat release rate signal HRR comprises a first heat release rate peak HRRP1 which results from the pilot injection PI and the corresponding first pressure peak PP1, and a second heat release rate peak HRRP2 which results from the main injection MI and the corresponding second pressure peak PP2. The first heat release rate peak HRRP1 is located at a crank angle ϕa1 and has a value Va1 and the second heat release rate peak HRRP2 is located at a crank angle ϕa2 and has a value Va2.
Fourthly, figure 2 shows an integrated heat release signal IHR which is depicted over the crank angle ϕ of the crank shaft 13. The integrated heat release signal IHR is derived from the heat release rate signal HRR by an integration over the time t. This can be done e.g. by the control unit 20.
The integrated heat release signal IHR comprises a first integrated heat release plateau IHRP1 which results from the pilot injection PI and the corresponding first pressure peak PP1 and first heat release rate peak HRRP1. A second integrated heat release plateau may also be present but is not shown in figure 2. The first integrated heat release plateau IHRP1 is located at a crank angle ϕb1 wherein this crank angle e.g. is defined to be present in the middle of the plateau. At the crank angle ϕb1, the first integrated release plateau IHRP1 has a value Vb1. This value Vb1 may be measured as an absolute value, i.e. with reference to a zero line Vb0. Alternatively, the value Vb1 may be measured as a relative value, for example with reference to the starting plateau Vbs of the first integrated release plateau IHRP1.
Figure 3a shows a diagram in which a mass MPI of the injected fuel of the pilot injection PI is depicted over the energizing time ET of the pilot injection PI. It is assumed that in particular the fuel pressure of each fuel injection of the combustion engine is basically fixed. As can be seen from figure 3a, there is - to a large extent - a linear relationship between the mass MPI of the injected fuel and the energizing time ET according to the following equation: MPI = a·ET+b.
Elongating the linear part of this relationship, an intersection point IP is found having the following value: IP = -b/a.
Figure 3b shows a diagram in which the value Vb1 of the first integrated heat release plateau IHRP1 of the pilot injection PI is depicted over the mass MPI of the injected fuel of the pilot injection PI. It is assumed that in particular the fuel pressure of each fuel injection of the combustion engine is basically fixed. Considering as well the other operating parameters of the combustion engine to be basically fixed there is again - to a large extent - a linear relationship between the mass MPI and the value Vb1, as can be seen from figure 3b. This proportional relationship can be described by the following equation: Vb1 = c.MPI.
The extent of the proportionality is dependent on the actual settings of the operating parameters of the combustion engine.
With regard to a possible drift, it is assumed that such a drift in particular in parallel of the course in figure 3b with respect to the abscissa axis, as the running time of the combustion engine increases, may be disregarded.
Then, in figure 3c, a combination of figures 3a and 3b is shown. In figure 3c, the value Vb1 of the first integrated heat release plateau IHRP1 of the pilot injection PI is depicted over the energizing time ET of the pilot injection PI. It is assumed that in particular the fuel pressure of each fuel injection of the combustion engine is basically fixed. Due to the fact that there exists - to a large extent - a linear relationship in figures 3a and 3b, there also exists - to a large extent - a linear relationship between the value Vb1 of the first integrated heat release plateau IHRP1 and the energizing time ET. The equation which describes this relationship is therefore also a combination of the equations which describe figure 3a and figure 3b: Vb1 = a·c·ET + b·c.
According to this equation, the intersection point that is found by elongating the linear part of the relationship between the first integrated heat release plateau IHRP1 and the energizing time ET is the same intersection point that is found in figure 3a, having the value: IP = -b/a.
Figure 4 relates to a method carried out at an individual item of the combustion engine.
In a step 41, the injection signal TI at least including the pilot injection PI as shown in figure 2, is injected into the combustion chamber 16 of the combustion engine. The injected pilot injection PI has the energizing time ET. The main injection MI may also be present.
In a step 42, the pressure signal P is measured by the pressure sensor 18. Due to the pilot injection PI, the pressure signal at least comprises the pressure peak PP1. Then, the heat release rate signal HRR is evaluated from the pressure signal P as described above, e.g. by the control unit 20. Furthermore, the integrated heat release signal IHR is evaluated from the heat release rate signal HRR as described above, e.g. by the control unit 20. In particular, the value Vb1 at the crank angle ϕb1 of the first integrated heat release plateau IHRP1 is determined.
Step 41 and the evaluations of step 42 are repeated for different energizing times ET with the result of different corresponding values Vb1.
The above described method of figure 4 is carried out at different points in time. For example, the method of figure 4 may be carried out for a first time after a running time of e.g. one hour of the combustion engine, then for a second time after a running time of e.g. one thousand hours, then for a third time after a running time of e.g. five thousand hours, and so on. For all these points in time of the running time of the combustion engine, the obtained values Vb1 for the several energizing times ET are stored at least temporarily. For example, these operating parameters may be stored in an operating map e.g. in the control unit 20.
Figure 5 shows a diagram of the value Vb1 depicted over the energizing time ET. Insofar, figure 5 relates to figure 3c.
In figure 5, a first course 51 is shown which relates to the obtained values Vb1 for the several energizing times ET after a running time of one hour. The first course 51 is also called a nominal course. Furthermore, a second course 52 is shown in figure 5 which relates to the obtained values Vb1 for the several energizing times ET after a running time of one thousand hours. The second course 52 is also called a drifted course.
As can be seen from figure 5, the course 52 has drifted during the elapsed one thousand hours of the running time with regard to the course 51.
It is possible that the two courses 51, 52 shown in figure 5 are parallel to each other, i.e. have the same angle α1, α2. However, it is also possible that the two courses do not have the same angle α1, α2. As explained in connection with figures 3a to 3c, such deviation may be disregarded.
As explained in connection with figures 3a to 3c, there exists - to a large extent - a linear relationship between the value Vb1 of the first integrated heat release plateau IHRP1 of the pilot injection PI and the energizing time ET of the pilot injection PI. As also explained, this linear relationship may be elongated to the intersection point IP according to figure 3c.
This elongation is also carried out in figure 5 with regard to the two courses 51, 52. The first course 51 yields in an intersection point which is called a first offset point OP1 and the second course 52 yields in an intersection point which is called a second offset point OP2. As can be seen from figure 5, a difference OPD is present between the two intersection points OP1, OP2 according to the following equation: OPD = OP2 - OP1. The difference OPD is stored at least temporarily e.g. within the control unit 20.
Figure 6 relates to a method carried out during the operation of the individual item of the combustion engine.
In a step 61, the individual item of the combustion engine is operating under normal conditions. The energizing time ET for the pilot injection PI, therefore, is evaluated according to normal dependencies, e.g. depending on the rotational speed N of the crankshaft 14 and/or depending on the driver's command and/or depending on the current load of the combustion engine and so on.
The result of the evaluations of step 61 is an actual energizing time ETact which should be the basis for the actual pilot injection PI.
In order to consider the above mentioned drifting of the course 52, a step 62 is carried out. In step 62, a corrected energizing time ETcorr is calculated according to the following equation (1): $ETcorr = ETact + OP 2 - OP 1 = ETact + OPD$
This equation means in other words that the actual energizing time ETact is adjusted by the difference OPD, i.e. a parallel transition 65 is carried out from the actual energizing time ETact into the corrected energizing time ETcorr based on the two offset points OP1, OP2.
Then, in a step 63, the corrected energizing time ETcorr is used for the pilot injection PI, i.e. fuel is injected into the combustion chamber 16 according to the corrected energizing time ETcorr.
The method of figure 6 may be repeated for all pilot injections PI during the operation of the individual item of the combustion engine. In doing so, the method of figure 6 is based on figure 5. As a result, the operating parameters of the pilot injections PI, in particular the energizing time ET, are adjusted continuously.
If, then, after a running time of the combustion engine of e.g. five thousand hours, the method of figure 4 is repeated again for a third time as described above, the method of figure 6 is adapted afterwards. The method of figure 6 is then based on the first course 51 as shown in figure 5 and a third course which relates to the values of the operating parameters after five thousand hours. Alternatively, it is possible to use the second course 52 and the afore-mentioned third course together with the difference OPD shown in figure 5.
The above description of figures 5 and 6 relates to the pilot injection PI. Of course, the method of figure 6 may also be carried out in connection with any further pilot injection PI and/or any main injection MI.
The above description refers to one cylinder of a combustion engine, i.e. the cylinder 10. It is possible to carry out the described methods for every cylinder of the combustion engine. Alternatively, it is possible to apply the described methods not for all, but only for a partial number or only for one of the cylinders. In this case, the resulting adaptation of the injection signal of the applied cylinder/s may be used as a basis to evaluate an adaptation as well for the injection signals of the non-applied cylinders.
For example, it is possible to carry out the described methods for only one of the cylinders, i.e. to evaluate the offset points OP1, OP2 and/or the difference OPD for only one of the cylinders, and then to use the evaluated offset points OP1, OP2 and/or the difference OPD of the one of the cylinders for all cylinders of the combustion engine. In this case, the pressure sensor 18 must only be present in the one of the cylinders.

Claims

A method of operating a combustion engine, wherein the combustion engine comprises a cylinder (10), a piston (11), an injection valve (17) and a pressure sensor (18), wherein the cylinder (10) and the piston (11) delimit a combustion chamber (16), and wherein the method comprises injecting fuel with the injection valve (17) into the combustion chamber (16) according to an energizing time (ET) and measuring a pressure signal (P) in the combustion chamber (16) with the pressure sensor (18), characterized by the steps of: determining a first course (51) of a value (Vb1) of an integrated heat release plateau (IHRP1) depending on the pressure signal (P) for several energizing times (ET), determining a second course (52) of the value (Vb1) for several energizing times (ET) after a given running time of the combustion engine, evaluating a first and a second offset point (OP1, OP2) of the first and the second course (51, 52), and evaluating (62) a corrected energizing time (ETcorr) depending on the first and the second offset point (OP1, OP2).
The method of claim 1 wherein an actual energizing time (ETact) is evaluated (61) depending on the first course (51) and wherein the corrected energizing time (ETcorr) is evaluated depending on the actual energizing time (ETact) and the first and the second offset point (OP1, OP2).
The method of one of claims 1 or 2 wherein the value (Vb1) of the integrated heat release plateau (IHRP1) depends on a heat release rate signal (HRR1, HRR2) which is derived from the pressure signal (P).
The method of one of claims 1 to 3 wherein the first course (51) and the second course (52) are determined by injecting (41) fuel for several energizing times (ET), measuring (42) the corresponding pressure signals (P) and evaluating the corresponding values (Vb1) of the integrated heat release plateau (IHRP1).
The method of one of claims 1 to 4 wherein the first and the second offset point (OP1, OP2) are evaluated by elongating the respective first and second course (51, 52).
The method of one of claims 1 to 5 wherein a difference (OPD) between the first and the second offset point (OP1, OP2) is determined.
The method of one of claims 1 to 6 wherein the corrected energizing time (ETcorr) is calculated according to the following equation: $ETcorr = ETact + OP 2 - OP 1 = ETact + OPD .$
A control unit (20) for operating a combustion engine, wherein the combustion engine comprises a cylinder (10), a piston (11), an injection valve (17) and a pressure sensor (18), wherein the cylinder (10) and the piston (11) delimit a combustion chamber (16), wherein the control unit (20) is coupled with the injection valve (17) and the pressure sensor (18), and wherein the control unit (20) is adapted to carry out the method steps of one of claims 1 to 7.
The control unit (20) of claim 7 comprising a computer and a computer program, wherein the computer program carries out the method steps of one of claims 1 to 7 when it is executed on the computer.
A combustion engine comprising the control unit (20) of one of claims 8 or 9.