FR2770259A1 - PROCESS FOR CONTROL OF THE SWITCHING OF THE COMBUSTION OF AN INTERNAL COMBUSTION ENGINE WITH IGNITION CONTROL BY DIRECT INJECTION - Google Patents

Abstract

According to this method of controlling the switching between homogeneous operation and stratified operation, pre-set motor control parameters are calculated for the homogeneous operation and for the stratified operation and, following a switching instant, are set. application for the operation each time following cylinders It is each time the cylinder ZYL1, ..., ZYL4 for which the calculation of the engine control parameters valid for the current operation has been carried out completely to its end which is switched on the modified motor control parameters for the next operation.

Description

The invention relates to a method for controlling the switching of the

  combustion of a direct-ignition internal combustion engine with direct injection between homogeneous operation and stratified operation, according to which prefixed engine control parameters are calculated for homogeneous operation and for stratified operation and, as a result of a switching instant, are implemented for the

  each time following cylinders.

  To significantly reduce fuel consumption and at the same time reduce the emission of harmful substances into the exhaust gas, direct fuel injection is considered a decisive step in the case of internal combustion ignition engines ordered. Unlike the usual injection into the intake manifold, direct injection allows different operating modes thanks to the free choice of the injection time. In the case of a very early injection in the intake stroke, there is a large homogenization of the filling and therefore a homogeneous operation which is used for maximum exploitation of the air, at full load and partly also at start-up when cold and in heating mode, as well as in particular for homogeneous operation at partial load. In the case of a late injection instant during the compression stroke, a more or less strongly marked stratified filling arrangement is obtained, and therefore a stratified operation which is widely used in partial load operation with an extremely lean mixture. The instants of ignition can also be chosen in different ways (see for this purpose the AVL Session "Engine and environment" 1997, "Direct injection in controlled ignition - a draft of the system taking into account

of the whole ", pages 255 to 271).

  For the purification of exhaust gases from such internal combustion engines, NOx accumulation catalysts have a high potential for extracting nitrogen oxides while at the same time oxidizing hydrocarbons and carbon monoxide. It is known that in this case an accumulation of sulfur can occur in the NOx adsorber, which is contained even in a fuel low in sulfur, and desulfurization is thus necessary, this being subject to engine regulation. thermal type. This regeneration of the accumulation catalyst takes place, in the homogeneous operation of the engine, with an enriched mixture. Attention is drawn in this regard to the AVL Session "Engine and environment" 1997, "New developments in the catalytic aftertreatment of exhaust gases from lean-mixture engines", pages -26. Thus, in the case of direct injection, it is often necessary to switch between the two modes, namely the stratified operation and the homogeneous operation, for example when the setpoint value provided for the torque delivered by the engine is modified or when the accumulation catalyst must be regenerated. For each of the two modes, it is each time different parameters of control of the engine which are valid, for example an injection instant and a different ignition instant, as has already been explained previously. Although the injection instant and the ignition instant can be calculated in a synchronized manner with respect to the crankshaft and are then each time valid after switching respectively for homogeneous operation and stratified operation, a However, the simultaneous switching of all the engine cylinders can result in torque jumps and

  even has misfires for at least one cylinder.

  This is why the invention aims to design a switching control method so that there is an uninterrupted switching between the homogeneous operation and the stratified operation.

  without failures or bad combustion.

  To this end, the subject of the invention is a process, of the generic type defined in the introduction, characterized in that it is each time the cylinder for which the calculation of the engine control parameters valid for the operation in progress has been carried out completely at its end, which is switched to the control parameters

  engine modified for the following operation.

  The process according to the invention can also have one or more of the following particularities - the injection instant, the injection duration and the ignition instant are determined as engine control parameters, - the instant of switching is defined as a function of a setpoint provided for the air / fuel mixture ratio or air coefficient crossing a preset threshold value down or up, - the threshold values provided for switching between the stratified operation and the homogeneous operation are chosen different, - the threshold values depend on the speed of rotation, the set value provided for the air / fuel mixture ratio is determined from the ratio of the air flow measured at the fuel flow setpoint associated with the measured air flow, - to initiate switching before the switching instant, in addition to the engine control parameters provided p For operation in progress, the engine control parameters provided for the next operation are calculated additionally and, after switching all the cylinders, the calculation of the engine control parameters provided for the

  operation that has taken place is completed.

  Thus, in accordance with the invention, a synchronization of the switching takes place which is determined individually for each different cylinder of the engine. It is therefore each time that the cylinder for which the operation in progress has completely ended with the associated engine control parameters which is switched to the next operation, whether it is homogeneous combustion or stratified combustion. This prevents cylinders that are still in operation in operation from being switched over, and that fuel injection has already taken place.

  or that the charging of the ignition coil has started.

  This avoids torque jumps and misfires. Furthermore, in accordance with the invention, we define

  the condition corresponding to the switching instant.

  In order to determine the switching instant, it is observed whether a set value provided for the air / fuel mixture ratio 1 crosses downwards or upwards a determined threshold value. For this purpose, the set value provided for the air / fuel mixture ratio 1 must be calculated from the ratio of the measured air flow to the set value of the associated fuel flow. Furthermore, at the same time, before the switching instant, the engine control parameters, in particular the injection instant and the ignition instant, must be calculated both for the operation in progress and for the operation which follows. As soon as the switching instant is established, the switching of the different cylinders then takes place towards the modified operation, in the manner already described above. As soon as switching to modified operation has taken place in all cylinders, the calculation of the engine control parameters corresponding to operation in

course can then take place.

  An example of implementation of the invention is set out below in detail with reference to the drawings. We see: in Figure 1, a graph corresponding to the switching from stratified operation to the homogeneous operation of an internal combustion engine with spark ignition, direct injection and four cylinders, in Figure 2, a graph corresponding to the switching from homogeneous to stratified operation and, in Figure 3, a graph corresponding to the

  determination of the switching time.

  The intake stroke I, the compression stroke II, the expansion stroke III and the exhaust stroke IV are shown in FIG. 1 respectively for each of the cylinders ZYL1, ZYL2, ZYL3 and ZYL4. At time TU, a switching operation

  homogeneous laminate must take place.

  For cylinders 1, at the switching instant TU, the injection operation E already takes place in the compression stroke II and the charging operation L of the ignition coil occurs shortly before the end, from so that it is only after ignition Z has taken place in the following intake stroke I that this cylinder is the object of an injection operation E 'with which we pass to homogeneous operation. The cylinder 2 also remains, for the cycle shown, still in stratified operation, since before the switching time TU, the charging operation L of the ignition coil has already started and is thus caused l ignition Z for which an injection operation E is still executed in the compression stroke II. Cylinder 2 has now successfully completed stratified operation, after which switching can take place on the parameters of

  homogeneous operation motor control.

  On the other hand, for the cylinder 3, the stratified operation has already ended before the switching instant TU, so that immediately after this switching instant, the injection operation E corresponding to the homogeneous operation can take place in the admission race I which follows. This also applies to cylinder 4 for which also the stratified operation was completed at the switching time TU, so that an injection operation E corresponding to the homogeneous operation is executed

  during the admission race I which follows.

  Therefore, an injection operation which has started is always completed in the laminate operation and the ignition takes place in the laminate operation before the considered cylinder

  is switched to homogeneous operation.

  FIG. 2 shows the switching from a homogeneous operation to the stratified operation at the switching time TU. It can be seen that the cylinders 3 and 4 have completely completed the homogeneous operation when the switching is triggered, so that it is first these cylinders which are switched to the stratified operation, while the cylinders 1 and 2 still remain in operation stratified during the cycle shown, since the injection operation E has already taken place (cylinder 1) or is not

still completed (cylinder 2).

  The switching instant TU is established with reference to FIG. 3. It is assumed that the combustion is in stratified operation and that a switching to homogeneous operation must take place, because for example the engine accumulation catalyst must

  be regenerated, and then the torque TQ remains constant.

  In the engine control, the filling, i.e. the AIR LOAD air flow passing through a throttle valve in the intake manifold, is first reduced to the set value corresponding to the consistent operation. In parallel, the SOI injection instant and the IGA ignition instant in stratified operation are corrected so that the torque TQ is maintained. Furthermore, at the same time, the SOI injection instant and the IGA ignition instant corresponding to the following homogeneous combustion are

  calculated, but have not yet been implemented.

  In addition, the set value of the air / fuel mixture ratio or air coefficient 1 is calculated as follows:

MAF ZYL

SOLL IST A MFF_SP

  in which MAFZYL is the actual value of the air flow (measured) sent to the cylinder, MFF_SP is the set value of the fuel flow in stratified operation and

  1ST is the stoichiometric factor.

  As soon as lSOLL crosses a higher threshold value, for example 1.8, the switching time TU is reached and switching to the motor control parameters corresponding to homogeneous operation is triggered. As can be seen from FIG. 3, there are significant deviations for the ignition instant IGA, the injection instant SOI and the injection duration INJ. As soon as the switching has taken place in accordance with FIG. 1 for all the cylinders, the calculation of the injection instant and the ignition instant in stratified operation stops. Conversely, when it is necessary to switch from homogeneous operation to stratified operation, for example when the regeneration of the accumulation catalyst is cut off or when possibly, the torque must be modified, the air flow introduced is first of all increased, by means of the throttle valve, up to the set value in stratified operation. In parallel, here again, the injection instant and the ignition instant are corrected in such a way that the desired torque is maintained, more precisely than the torque for example.

  desired by the driver to be implemented.

  1SOLL is calculated in accordance with the above equation and, as soon as the setpoint crosses a second threshold upwards, also depending on the speed of rotation, for example 1, 4, the switching time TU 'is finds determined. The different cylinders are then switched, in accordance with FIG. 2, to the engine control parameters corresponding to the stratified operation. Calculation of the injection instant and the ignition instant during operation

  homogeneous can then be stopped.

Claims (7)

  1. Method for controlling the combustion switching of an internal combustion engine with direct injection spark ignition between homogeneous operation and stratified operation, according to which prefixed engine control parameters are calculated for homogeneous operation and for stratified operation and, following a switching instant, are applied for operation each time according to cylinders, characterized in that it is each time the cylinder (ZYL1, ..., ZYL4) for which the calculation of the motor control parameters valid for the current operation has been completed completely, which is switched to the motor control parameters modified for the following operation.   2. Method according to claim 1, characterized in that the injection instant (SOI), the injection duration (INJ) and the ignition instant (IGA) are   determined as motor control parameters.   3. Method according to claim 1 or 2, characterized in that the switching instant (TU) is defined as a function of what a set value (lSOLL) provided for the air / fuel mixture ratio (1) crosses down or up a value of prefixed threshold.   4. Method according to claim 3, characterized in that the threshold values provided for the switching between the stratified operation and the   homogeneous operation are chosen different.   5. Method according to claim 3 or 4, characterized in that the threshold values depend on the speed of rotation.   6. Method according to one of claims 3 to 5,   characterized in that the set value (lSOLL) provided for the air / fuel mixture ratio (1) is determined from the ratio of the air flow (MAF _ZYL) measured to the set value of the fuel flow   (MFFSP) associated with the measured air flow.   7. Method according to one of claims 1 to 6,   characterized in that, in order to initiate switching before the switching instant (Tu), in addition to the motor control parameters provided for the current operation, the motor control parameters provided for the following operation are calculated additionally and in that after switching all the cylinders (ZYL1, ..., ZYL4), the calculation of the engine control parameters provided for the   operation that has taken place is completed.