Method for operating a spark-ignition internal combustion engine

Abstract

Method for controlling the operation of a spark-ignition internal combustion engine (1), wherein the intake air is compressed by means of a compressor of an exhaust gas turbocharger (5) and an electric charger (11) depending on the operating range of the internal combustion engine (1) and is controlled by at least one throttle valve (TH), wherein the closing time (ES) of at least one intake valve (15) is adjusted depending on the operating range of the internal combustion engine (1), and wherein exhaust gas is diverted past the exhaust gas turbine (8) of the exhaust gas turbocharger (5) by means of a bypass valve (WG) depending on the operating range of the internal combustion engine (1), characterized in that the internal combustion engine (1) is operated at idle and / or at partial load in the Miller cycle with the throttle valve (TH) at least partially closed, the bypass valve (WG) open, and the electric charger (11) deactivated, and in the event of a load request (L), the following steps are carried out sequentially: a) De-throttle the intake air by opening the throttle valve (TH); a1) Check whether the internal combustion engine (1) can meet the load requirement (L); b) if the test in step a1) shows that the load requirement (L) cannot yet be met: closing the bypass valve (WG) of the exhaust gas turbine (8); b1) Check whether the internal combustion engine (1) can now meet the load requirement (L); c) if the test in step b1) shows that the load requirement (L) cannot yet be met: terminating the Miller cycle by readjusting the closing time (ES) of at least one intake valve (15); c1) Check whether the internal combustion engine (1) can now meet the load requirement (L); d) if the test in step c1) shows that the load requirement (L) cannot yet be met: switching on the electrically driven charger (11).

Description

[0001] The invention relates to a method for operating a spark-ignition internal combustion engine, wherein the intake air is compressed by means of a compressor of an exhaust gas turbocharger and an electric charger depending on the operating range of the internal combustion engine and is controlled by at least one throttle valve, wherein the closing time of at least one intake valve is adjusted depending on the operating range of the internal combustion engine, and wherein exhaust gas is diverted past the exhaust gas turbine of the exhaust gas turbocharger by means of a bypass valve depending on the operating range of the internal combustion engine.

[0002] It is well known that, when high load requirements arise from idle or low-load operation, measures are taken to provide the desired target drive torque. These measures are usually aimed at providing high load very quickly and are essentially carried out in parallel. The disadvantage is that this results in relatively high fuel consumption and / or emissions.

[0003] Methods for controlling the operation of a spark-ignition internal combustion engine using the Miller cycle are known from the prior art, particularly during idle and / or at partial engine load. It is also known to reduce disadvantages of the Miller cycle, such as power loss due to reduced cylinder charge when the engine is under load, through various measures.

[0004] DE 10 2011 122 442 A1 describes a method for operating an internal combustion engine in which combustion air is compressed using an exhaust gas turbocharger with variable turbine geometry, and the intake valve is closed before a piston in the cylinder reaches bottom dead center. To avoid efficiency losses during transient engine operation as a result of an increase in exhaust gas enthalpy due to the retardation of the ignition angle and combustion, an electrically driven charger or e-booster is connected. Furthermore, it is provided that a bypass valve of the exhaust gas turbine of the exhaust gas turbocharger is adjusted depending on the load, and that the closing time of an intake valve is adjusted depending on the load. DE 10 2012 018 692 A1 also provides that the closing time of an intake valve is adjusted depending on the load, and a bypass valve of a turbocharger is closed for a predefined period of time.

[0005] The object of the invention is to provide a simple method for controlling the operation of an internal combustion engine under a load requirement, whereby fuel and emissions can be reduced compared to known methods.

[0006] Based on a method mentioned at the outset, this object is achieved according to the invention in that the internal combustion engine is operated at idle or at partial load in the Miller cycle with at least partially closed throttle valve, open bypass valve and deactivated electric charger and in the event of a load request, the following steps are carried out one after the other: a) De-throttle the intake air by opening the throttle valve; a1) Check whether the internal combustion engine can meet the load requirement; b) if the test in step a1) shows that the load requirement cannot yet be met: closing the exhaust turbine bypass valve; b1) Check whether the engine can now meet the load requirement; c) if the test in step b1) shows that the load requirement cannot yet be met: terminating the Miller cycle by adjusting the closing time of at least one intake valve; c1) Check whether the internal combustion engine can now meet the load requirement; d) if the test in step c1) shows that the load requirement cannot yet be met: switching on the electrically driven charger.

[0007] The Miller cycle is an operating process for an internal combustion engine in which the intake valve closes "too early" compared to the Otto cycle. This reduces the air charge and the final compression pressure, but the compression and thus the expansion ratio remain the same. This increases the efficiency of internal combustion engines.

[0008] The closing of the bypass valve described in step b) is carried out in addition to the de-throttling of the intake air if step a) is not sufficient to meet the load requirement.

[0009] Furthermore, the termination of the Miller cycle described in step c) by readjusting the closing time in addition to steps a) and b) - i.e. de-throttling the intake air and closing the bypass valve of the exhaust turbine - is only carried out if steps a) and b) are not sufficient to meet the load requirement.

[0010] Finally, the electrically driven charger is switched on in addition to these according to step d) - but only if the combination of steps a), b) and c) is still not sufficient to meet the load requirement.

[0011] It is essential that each of the measures a) to d) is carried out step by step one after the other and that after each of the measures a), b), c) it is checked whether the drive torque provided by the internal combustion engine is already sufficient to meet the load requirement.

[0012] Thus, performance-enhancing measures are implemented step by step and according to a predetermined sequence, which on the one hand ensure that the load requirement is met and on the other hand avoid a sudden increase in fuel consumption - especially in the case of gasoline internal combustion engines - and / or emissions, especially in the case of diesel internal combustion engines.

[0013] One embodiment of the invention provides that during or after at least one of the steps mentioned, it is checked whether there is a risk of abnormal combustion.

[0014] An example of abnormal combustion is knocking combustion. In this case, strong pressure fluctuations occur in the combustion chamber, significantly accelerating the chemical reactions that already begin in the unburned mixture during the compression stroke. After combustion is initiated by the ignition spark, the remaining unburned mixture (end gas) is further compressed by the propagating flame and thus heated to such an extent that the ignition limit is exceeded, and spontaneous auto-ignition finally occurs in the end gas. This almost isochoric combustion leads to steep pressure gradients that propagate in the form of pressure waves in the combustion chamber and produce the familiar knocking or ringing noise. Another undesirable and abnormal combustion process is glow ignition.It is triggered by extremely hot zones in the walls surrounding the combustion chamber, so-called "hot spots" – for example, combustion residues – which are significantly above the autoignition temperature of the fuel-air mixture. While knocking combustion only occurs after the ignition spark initiates combustion, glow ignition can occur earlier. The pressure waves that occur during both knocking combustion and glow ignition can cause mechanical material damage, and the thermal stress can also lead to melting of the piston and cylinder head.

[0015] Abnormal combustion processes can be detected, for example, using knock sensors.

[0016] To prevent abnormal combustion, the invention provides that, if the risk of abnormal combustion is detected, a further check is performed to determine whether engine braking is present. If this is the case, the ignition angle is adjusted from an advanced ignition angle for engine braking to an ignition angle for normal engine operation. A check is then performed to determine whether the risk of abnormal combustion still exists.

[0017] If the risk of abnormal combustion persists, the invention further reduces the compression ratio to the lowest possible value. The compression ratio can be reduced, for example, by adjusting the piston stroke—in particular, by adjusting the length of the connecting rod connecting the piston and the crankshaft.

[0018] The success of this measure can then be assessed and investigated to determine whether the risk of abnormal combustion still exists. A further advantageous embodiment of the invention provides for the ignition timing to be retarded as an additional measure if it turns out that the previous measures are insufficient.

[0019] Even when preventing abnormal combustion, the measures are carried out sequentially, with an additional measure being taken if the previous measures prove to be insufficient.

[0020] In a further development of the invention, it is provided that at least one exhaust gas aftertreatment device is checked to see whether it has the required operating temperature and - if the operating temperature is not yet reached - the internal combustion engine is operated at maximum volumetric efficiency, minimum compression ratio and the latest possible ignition point.

[0021] To protect the exhaust gas turbocharger, one embodiment of the invention provides for the exhaust gas temperature to be determined at the inlet of the exhaust gas turbine, and for the exhaust gas turbine bypass valve to be opened if the exhaust gas temperature at the inlet of the exhaust gas turbine exceeds a defined maximum value for the respective operating point. Alternatively or additionally, it can be provided for the charge air temperature to be determined at the outlet of the exhaust gas turbocharger's compressor, and for the exhaust gas turbine bypass valve to be opened if the charge air temperature at the outlet of the compressor exceeds a defined maximum value for the respective operating point.

[0022] As a further protective measure for the exhaust gas turbocharger, a variant of the invention can provide for the speed of the exhaust gas turbocharger to be determined and the bypass valve of the exhaust gas turbine to be opened when the speed of the exhaust gas turbocharger reaches a defined maximum value for the respective operating point. Furthermore, the bypass valve of the exhaust gas turbine is opened when the compressor of the exhaust gas turbocharger reaches its surge limit for the respective operating point.

[0023] The measures for protecting the exhaust gas turbocharger override step b) in claim 1.

[0024] The invention is explained in more detail below with reference to the exemplary embodiment illustrated in the figures, which schematically show: Fig. 1 shows the temporal sequence of the method according to the invention in the case of a load request; Fig. 2 shows the timing of the method according to the invention in the event of a risk of abnormal combustion; Fig. 3 a compressor map of an exhaust gas turbocharger with registered operating limits; and Fig. 4 an internal combustion engine for carrying out the method according to the invention.

[0025] The method according to the invention is suitable for Fig. 4 schematically illustrated internal combustion engines 1 with at least one cylinder 2 with an intake system 3, an exhaust system 4, and an exhaust gas turbocharger 5, the compressor 6 of which is arranged in the intake line 7 of the intake system 3 and the exhaust gas turbine 8 in the exhaust line 9 of the exhaust system 4. The exhaust gas turbine 8 can be bypassed via a bypass line 10, with a bypass valve WG (wastegate) arranged in the bypass line 10, which, in its open position, directs the exhaust gas through the bypass line 10 and, in its closed position, through the exhaust gas turbine 8. An electrically driven charger 11 is also arranged in the intake line 7. Reference numeral 12 denotes a bypass line for the electric charger 11, wherein the air flow is guided past the electric charger 11 through the bypass line 12 when the electric charger 11 is deactivated by opening the bypass valve 13 arranged in the bypass line 12.A throttle valve TH is arranged in the charge air line 14 of the intake line 7, with which the charge air can be throttled.

[0026] Reference numeral 15 denotes intake valves and reference numeral 16 exhaust valves, with which the gas exchange of the cylinders 2 is controlled. At least the closing point ES of the intake valves 15 can be adjusted via a VVT device for changing the valve timing. An ignition adjustment device 17 is provided for adjusting the ignition timing. The internal combustion engine 1 further has a device 18 for adjusting the compression ratio ε, for example a device for adjusting the length of the connecting rods. The VVT device for adjusting the valve timing, the throttle valve TH, the bypass valve WG and the electric charger 11, the bypass valve 13 for bypassing the electric charger 11, the ignition adjustment device 17 and the device 18 for adjusting the compression ratio ε are connected to an electronic control unit ECU.Furthermore, the electronic control unit (ECU) is connected to various sensors for determining the accelerator pedal position, the engine speed, the torque, the cylinder pressure, etc., as indicated by reference numeral 19. Reference numeral 20 indicates an exhaust aftertreatment device of the exhaust system 4 arranged in the exhaust line 9.

[0027] In Fig. 1 schematically shows the positions of the throttle valve Th and the bypass valve WG (wastegate) for the exhaust gas turbine 8 of the exhaust gas turbocharger 5 over time t for a load requirement on the internal combustion engine 1. Here, Th C the closed position and with Th O the fully open position of the throttle valve Th. Analogously, WG C the closed position and with WG Othe fully open position of the bypass valve WG of the exhaust gas turbine 8. Furthermore, the temporal progression of the control timing adjustment for the intake closing ES between maximum intake closing advance ES MILmax when operating the internal combustion engine 1 in the Miller cycle and the intake valve timing advance ES vol.max to achieve maximum volumetric efficiency when operating the internal combustion engine 1 in normal operation. Furthermore, Fig. 1 the power P e,SC of the electric charger 11, where P e,SC,0 the power = 0 of the deactivated electric charger 11 and with P e,SC,max the maximum power of the electric charger 11 is indicated. The arrow L indicates an increasing load requirement.

[0028] At time t0, the internal combustion engine 1 is idling or operating at low partial load. When a load demand L is present, the throttle valve Th is first moved from the closed position Th C to the fully open position Th O switched, which increases the drive torque. At the end of phase T1, a check is carried out to determine whether the internal combustion engine 1 can meet the load requirement L. If this is not the case, for example because the load requirement L increases, the bypass valve WG (wastegate) of the exhaust gas turbine 8 is moved from the open position WG in phase T2. O into the closed position WG Cswitched on and thus the entire exhaust gas is passed through the exhaust turbine 8. At the end of phase T2, it is again checked whether the internal combustion engine 1 can meet the load requirement L. If the load requirement L continues to increase and cannot be met by the previous measures, the Miller cycle is terminated as an additional measure in phase T3 and the closing time of at least one intake valve 15 or all intake valves 15 is adjusted by the advanced intake closing time ES assigned to the Miller cycle. MILmax to the inlet closing time ES assigned to normal operation vol.max reset to operate the internal combustion engine 1 at maximum volumetric efficiency. At the end of phase T3, a check is made again to determine whether the internal combustion engine 1 can now meet the load requirement L. If this is still not the case, the electrically driven charger 11 is activated in phase T4 and operated at maximum power P e,SC,maxoperated to enable higher charging. If the test after each of the phases T1, T2, or T3 shows that the load requirement L can be met, further performance-enhancing measures are unnecessary.

[0029] During the described measures for increasing the drive power of internal combustion engine 1 to meet load requirements L, a continuous or discontinuous check is performed to determine whether there is a risk of abnormal combustion. This can be done, for example, by evaluating the data from at least one knock sensor, which measures the cylinder pressure in at least one cylinder. If it is detected that there is a risk of abnormal combustion, at least one measure is taken to prevent it. Here, too, the measures are carried out sequentially, and in between—before the next measure is taken—a check is performed to determine whether the measure taken was already sufficient.

[0030] In Fig. Figure 2 shows the implementation of sequential measures to prevent abnormal combustion for an exemplary embodiment of the invention. The compression ratio ε and the ignition angle α are plotted against time t. The arrow K indicates the increasing risk of abnormal combustion, for example, a tendency to knock. At time t1 in the example shown, the internal combustion engine 1 is running at maximum compression ratio ε max and an advanced ignition angle a br,max for maximum engine braking power. If the test reveals that there is a risk of abnormal combustion occurring, such as knocking, an initial measure is taken in phase KT1 to prevent this. This consists in checking whether the ignition angle α is advanced to an optimal ignition angle α br,maxis set for engine braking, and - if this is the case - the ignition angle α is set from an advanced ignition angle for engine braking α br,max to an ignition angle α opt for normal engine operation. It is then checked whether the risk of abnormal combustion still exists. If it is determined that the risk of abnormal combustion still exists, the compression ratio ε is set to the lowest possible value ε min reduced. Now, a check is carried out again to determine whether abnormal combustion is occurring or could occur. If the danger of abnormal combustion is still acute, the ignition angle α is retarded as far as permissible, i.e., up to a limit ignition angle α COV , which is determined by a maximum permissible degree of non-uniformity or a maximum permissible coefficient of variation COV imep the indicated mean effective pressure p imepof the internal combustion engine 1. The variation coefficient COV imep the indicated mean effective pressure p imep is defined by the equation COVimep=σimeppimep⋅100, where σ imep the standard deviation of the indicated mean effective pressure p imep Usually, problems with the drivability of a vehicle powered by an internal combustion engine must be expected if the coefficient of variation COV imep the indicated mean effective pressure p imp exceeds 10%.

[0031] The performance of the exhaust aftertreatment systems also influences load demand. Therefore, at least one exhaust aftertreatment system is checked to ensure it has reached the required operating temperature. If the operating temperature has not yet been reached, the internal combustion engine is operated at maximum volumetric efficiency, minimum compression ratio, and the latest possible ignition timing.

[0032] Another criterion that influences the following of the load requirement is the protection of the exhaust gas turbocharger 5. This must be operated within a permissible range of the characteristic map.

[0033] In Fig. 3 schematically shows the characteristic map of a compressor 6 of an exhaust gas turbocharger 8, wherein the pressure ratio p2p1 between the outlet pressure p2 and the inlet pressure p1 of the compressor 6 is plotted against the volume flow v. As can be seen from Fig.3 clearly shows, the operating range of the compressor 6 is determined by the surge limit SL of the compressor 6, the maximum charge air temperature T Lmax at the outlet of the compressor 6 and the maximum speed n max of the exhaust gas turbocharger 5. Another limiting criterion of the operating range of the exhaust gas turbocharger 5 is the exhaust gas temperature T A at the inlet to the exhaust turbine 8.

[0034] If it is determined that one of these limits is exceeded - i.e. that the exhaust gas temperature T A at the inlet to the exhaust turbine 8 a defined maximum value T Amax for the respective operating point or that the charge air temperature T L at the outlet of the compressor 6 of the exhaust gas turbocharger 5 a defined maximum value T Lmax for the respective operating point, or that the speed n of the 9 exhaust gas turbocharger 5 exceeds a defined maximum value n maxfor the respective operating point, or that the compressor 6 of the exhaust gas turbocharger 5 reaches its surge limit SL for the respective operating point - the bypass valve WG of the exhaust gas turbine 8 is opened and the exhaust gas is passed through the bypass line 10 past the exhaust gas turbine 6.

Claims

[1] Method for controlling the operation of a spark-ignition internal combustion engine (1), wherein the intake air is compressed by means of a compressor of an exhaust gas turbocharger (5) and an electric charger (11) depending on the operating range of the internal combustion engine (1) and is controlled by at least one throttle valve (TH), wherein the closing time (ES) of at least one intake valve (15) is adjusted depending on the operating range of the internal combustion engine (1), and wherein exhaust gas is diverted past the exhaust gas turbine (8) of the exhaust gas turbocharger (5) by means of a bypass valve (WG) depending on the operating range of the internal combustion engine (1), characterized by that the internal combustion engine (1) is operated at idle and / or at partial load in the Miller cycle with at least partially closed throttle valve (TH), open bypass valve (WG) and deactivated electric charger (11) and in the event of a load request (L) the following steps are carried out one after the other: a) De-throttle the intake air by opening the throttle valve (TH); a1) Check whether the internal combustion engine (1) can meet the load requirement (L); b) if the test in step a1) shows that the load requirement (L) cannot yet be met: closing the bypass valve (WG) of the exhaust gas turbine (8); b1) Check whether the internal combustion engine (1) can now meet the load requirement (L); c) if the test in step b1) shows that the load requirement (L) cannot yet be met: terminating the Miller cycle by readjusting the closing time (ES) of at least one intake valve (15); c1) Check whether the internal combustion engine (1) can now meet the load requirement (L); d) if the test in step c1) shows that the load requirement (L) cannot yet be met: switching on the electrically driven charger (11). [2] Method according to claim 1, characterized by that during or after at least one step, a check is carried out to determine whether there is a risk of abnormal combustion (K). [3] Method according to claim 2, characterized by that - if the risk of abnormal combustion (K) is detected - it is checked whether the ignition angle (α) is set to an advanced ignition angle (α br,max ) is set for engine braking operation, and - if this is the case - the ignition angle (α) is adjusted from an advanced ignition angle (α br,max ) for engine braking operation to a firing angle (α opt ) for normal engine operation and checking whether there is still a risk of abnormal combustion (K). [4] Method according to claim 2 or 3, characterized by that - when the risk of abnormal combustion (K) is detected - the compression ratio (ε) is set to the lowest possible (ε min) value is reduced and it is checked whether the risk of abnormal combustion (K) still exists. [5] Method according to claim 3 or 4, characterized by that - if the risk of abnormal combustion (K) is still detected - the ignition angle (α) is further increased - preferably up to a defined limit ignition angle (α cov ) - is adjusted to late. [6] Method according to one of claims 1 to 5, characterized by that at least one exhaust gas aftertreatment device (20) is checked to see whether it has the required operating temperature and - if the operating temperature is not yet reached - the internal combustion engine (1) is shut off with an inlet closure (ES vol,max ) for maximum volumetric efficiency, minimum compression ratio (ε min ) and the latest possible ignition angle - preferably at a defined limit ignition angle (α cov ) - is operated. [7] Method according to one of claims 1 to 6, characterized by that the exhaust gas temperature (T A ) at the inlet of the exhaust gas turbine (8) and the bypass valve (WG) of the exhaust gas turbine (8) is opened when the exhaust gas temperature (T A ) at the inlet of the exhaust turbine (8) a defined maximum value (T Amax ) for the respective operating point. [8] Method according to one of claims 1 to 7, characterized by that the charge air temperature (T L ) at the outlet of the compressor (6) of the exhaust gas turbocharger (5) and the bypass valve (WG) of the exhaust gas turbine (8) is opened when the charge air temperature (T L ) at the outlet of the compressor (6) a defined maximum value (T Lmax ) for the respective operating point. [9] Method according to one of claims 1 to 8, characterized bythat the speed (n) of the exhaust gas turbocharger (5) is determined and the bypass valve (WG) of the exhaust gas turbine (8) is opened when the speed (n) of the exhaust gas turbocharger (5) reaches a defined maximum value (n max ) for the respective operating point. [10] Method according to one of claims 1 to 9, characterized by that the bypass valve (WG) of the exhaust gas turbine (8) is opened when the compressor (6) of the exhaust gas turbocharger (5) reaches its surge limit (SL) for the respective operating point. [11] Method according to one of claims 1 to 10, characterized by that step b) is overridden.

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