DE10325018B4 - A method of controlling the transition from a first mode of direct fuel injection gasoline engine to a second mode of operation - Google Patents

Abstract

Method for controlling the transition from a first operating mode of a direct-injection gasoline engine (46) to a second operating mode, wherein upon reaching a predetermined switching threshold (S1, S2) a fuel-air mixture in the cylinders of the gasoline engine (46) for the two Operating modes homogeneous operation and lean operation is reloaded, and wherein the switching threshold (S1, S2) to the quality of the combustion of the fuel-air mixture in the cylinders is adaptable, characterized in that the adaptation by evaluating a speed gradient (D) takes place and a determined therefrom Value for the switching threshold (S1, S2) is used to control subsequent switching operations of the two modes, and upon detection of a poor combustion after the transition to lean operation, the first switching threshold (S1) is raised for the next transition to lean operation, increasing the first switching threshold (S1) Luftm in lean operation is increased by a predetermined value, and that stored on successful switching the last found value for the increased air mass threshold (S1) ...

Description

The invention is based on a method for controlling the transition from a first operating mode of a gasoline direct injection gasoline engine to a second operating mode, according to the preamble of claim 1.

It is already known that in gasoline engines, in which the position of the throttle valve and thus the supply of fresh air mass is electronically controlled, the fuel-air mixture in the cylinders of the gasoline engine from a homogeneous operation to a lean operation, for example, stratified operation or HCCI operation is reloaded. By switching to the stratified operation, which is possible in particular at partial load, the fuel consumption can be reduced in this way. If, on the other hand, more power is required from the engine to accelerate the vehicle, for example, the system is automatically switched back to homogeneous operation.

However, it has been found that the switching between the two modes does not always take place in the desired manner. It can come when switching to speed or torque changes that cause unwanted jerking of the vehicle. For various causes such as engine parameters, tolerances, wear, contamination of the throttle valve, valves, etc. are conceivable. In stratified operation, the cause is often due to insufficient charge movement due to insufficient air mass. In homogeneous operation, on the other hand, the cause may be considered to be an excessively high exhaust gas recirculation rate or too late an ignition.

Up to now, these problems have either not been taken into account when switching to the second operating mode or, in the case of a bad transition, switching to the stratified operation has been blocked.

From the DE 198 59 424 A1 a fuel injection method for an internal combustion engine is known, wherein an injection is carried out alternatively in a homogeneous normal operation or in an inhomogeneous stratified operation. In this case, a characteristic variable for knocking is detected on at least one cylinder of the internal combustion engine in inhomogeneous stratified operation. Switching from at least one of the inhomogeneous stratified operation to homogeneous normal operation is performed when the detected characteristic size of the one cylinder satisfies a predetermined first criterion. In addition, a characteristic curve is established in which a switchover between the homogeneous normal operation and the inhomogeneous stratified operation is carried out as a function of at least one engine-specific parameter, preferably rotational speed and load and shifting at least a part of the characteristic curve in response to the fact that an operating point for the inhomogeneous shift operation is provided, is detected and the detected characteristic size of the one cylinder fulfills a predetermined criterion, preferably with regard to knock intensity or knock frequency.

In the DE 196 31 986 A1 a controller is described for a fuel direct injection fueled internal combustion engine having an electronic control unit that switches in dependence on at least one operating variable between an operation of the fuel injection in the stratified or homogeneous mode. Further, the air supply of the internal combustion engine is influenced and in the switching between these modes an adjusting element, preferably the throttle defined, in particular discontinuously adjusted, so that the torque of the internal combustion engine before and after the switching is substantially equal.

The invention has for its object to improve in a working with direct fuel injection gasoline engine switching between two modes so that the transition to the second mode is virtually neutral in torque and yet the fuel-efficient stratified operation is possible. This object is achieved with the features of claim 1.

In the method according to the invention for controlling the transition from a first operating mode to a second operating mode having the features of claim 1, there is the advantage that the switching threshold is not constant, as has hitherto been customary, but is always adapted to at least one operating parameter of the gasoline engine , It is particularly advantageous that the quality of the combustion of the fuel-air mixture in a cylinder of the gasoline engine is monitored by evaluating the speed gradient as an essential operating parameter. By forming a speed gradient, the quality of the combustion can be easily assessed. If, for example, the speed drops during the transition to the stratified operation, then this is a clear indication of a bad combustion, so that the switching threshold must be adjusted accordingly. If, on the other hand, the speed gradient approaches zero, then it can be assumed that the combustion is correct in both operating modes and no disturbing torque change occurs when switching to the second operating mode. From the quality of the combustion, a switching threshold can be determined and stored for the different operating modes, which is adapted continuously and then for one subsequent switching is available as the current switching threshold.

The measures listed in the dependent claims advantageous refinements and improvements of the method specified in claim 1 are given.

Conveniently, the solution appears to specify a limit for the transition to the stratified operation for a negatively occurring speed gradient, which may not be exceeded. This ensures that a certain speed gradient during switching is still tolerable. This is also necessary to eliminate, for example, occurring measurement tolerances.

If, on the other hand, the predetermined limit value for the rotational speed gradient is exceeded during the transition to the stratified operation, then it is assumed that there is poor combustion in the stratified operation because an insufficient air mass is present. This case can be solved in an advantageous manner by simply lifting the air mass supplied.

Furthermore, it is provided that raising the first switching threshold d. H. in this case, increase the air supply gradually, if it turns out that at the first increase the speed gradient was still too large. If the first switching threshold is successfully raised, the last found value for the increased air mass is saved. This value can then be read out of the memory and used for the further switching to the stratified operation.

If, on the other hand, poor combustion is detected in homogeneous operation, then the first switching threshold is lowered for the next transition to the stratified operation since it can be assumed that the ignition took place too late due to an excessively high air mass. The lowering of the first switching threshold is advantageously carried out by reducing the air supply, so that the ignition can be done slightly earlier. The found reduced value is stored again so that it can be used again for subsequent switching.

On the other hand, if the lowering of the switching threshold does not lead to an acceptable transition from homogeneous to stratified operation, then the transition to the stratified operation is blocked in order not to impair the ride comfort.

When switching from the stratified operation to the homogeneous operation, it is considered an advantage that in order to determine the second switching threshold, first the exhaust gas recirculation rate (EGR rate) and then the air mass are reduced to a value required for homogeneous operation. If a bad combustion is detected in the stratified operation, then the switchover takes place a little earlier at a time when the air mass is still greater. With these measures, the second switching threshold can be adapted to the operating conditions of the engine in a simple and advantageous manner.

If, on the other hand, unstable combustion is detected after switching to homogeneous operation, the EGR rate is reduced and / or the changeover is initiated a little later, when the air mass has further reduced. If the switchover is successful, the last found value for the second switchover threshold is stored and is then available for further switchover. However, if the switchover can not be carried out successfully, switching to the stratified operation is again blocked.

An embodiment of the invention is illustrated in the drawing and will be explained in more detail in the following description.

1 shows a first flowchart in which the switching is controlled from the homogeneous operation to the stratified operation,

2 shows a second flowchart in which the switching from the stratified to the homogeneous mode is controlled and

3 shows a device for controlling the switching between the two modes.

In the first flowchart according to 1 is explained in a schematic representation of the sequence of switching from a homogeneous operation in a lean operation. As a lean operation, the layered operation is exemplified. In the two operating modes, it should be noted in principle that during homogeneous operation, the fuel injected directly into the cylinders of the gasoline engine is swirled in such a way that it is homogeneously distributed in the combustion chamber. In stratified operation, on the other hand, the fuel is distributed particularly in the uppermost layer. These different fuel distributions are achieved by design measures, for example by a suitably designed combustion chamber or a corresponding injection method. The changeover to the various modes can be influenced by controlling the air mass supplied, in particular by controlling the throttle valve and also by controlling the exhaust gas recirculation rate (EGR rate). The resulting combustion of the fuel-air mixture generates a corresponding torque of the engine. When switching the In both modes of operation, the aim is that as far as possible no torque changes and thus no speed gradient arises. Since the quality of the combustion can have a decisive influence in the switching of the operating modes, it is proposed according to the invention to control the switching thresholds as a function of the quality of the combustion and to adapt it accordingly for subsequent switching operations.

In stratified operation (lean operation), the quality of the combustion is often impaired by an insufficient air mass, since the charge movement is too low. In homogeneous operation, on the other hand, the EGR rate is often too high or the ignition is too late. With the aid of the speed gradient, adaptable switching thresholds are formed for the individual operating modes in order to improve the combustion during the changeover of the operating modes. Here a clearly negative speed gradient is an indication that there is a bad combustion.

In 1 For example, the left part refers to the homogeneous operation and the right part to the stratified operation. When switching from the homogeneous operation to the stratified operation according to 1 in position 1 a program (software program) is started, which runs in a motor control program usually as a subroutine cyclic. First, in homogeneous operation, the throttle is opened to achieve the appropriate air mass for stratified operation. From a certain air mass is in position 2 checked whether a homogeneous operation is present.

Lies according to position 2 according to the path j, a homogeneous operation, then according to position 3 To check the quality of the combustion in homogeneous operation, first the amount of the speed gradient D determined. If the amount of the rotational speed gradient D is actually smaller than the predetermined limit value G, then the program is in position via the path n 11 completed. At j (amount of the speed gradient D is larger), there is a bad combustion. The cause of the bad combustion can be a too late ignition angle, which arises at this time by an excessively high air mass. In position 4 Therefore, a threshold value S1 (first switching threshold S1) for the next switching is lowered so as to achieve more stable combustion.

The first switching threshold S1 is lowered to make the transition to the stratified operation a little earlier. In position 5 it is checked whether a predetermined maximum value M for the first switching threshold S1 has been reached. At n, the program jumps to position 11 , At j will be in position 6 decided whether switching to stratified operation should be prevented in the future. If this leads to an improved combustion in homogeneous operation at the next transitions, the new value for the first switching threshold S1 is stored and is then available for subsequent switching. In the case of unacceptable bad transitions, the transition to shiftwork will be abandoned in the future. Then the program is in position 11 finished again for this cycle.

Below is the right part of 1 explained in more detail. Was according to position 2 has been determined that there is no homogeneous operation, then the adaptation for the stratified operation is started via the path n and in position 7 the quality of the combustion of the fuel-air mixture is checked. In this case, it is examined whether the magnitude of the speed gradient D is greater than a predetermined limit G. At n, ie the quality of the combustion is acceptable, since the amount of the speed gradient D is smaller than the limit value G, is in position 11 the function ends. For switching, an adapted first switching threshold S1 is used, which essentially contains an air mass desired value, for example for the throttle position, with which the air supply to the cylinders of the gasoline engine is controllable.

Was the magnitude of the speed gradient D greater than the limit G (j, position 7 ), then poor combustion is assumed, probably due to insufficient air mass for stratified operation. According to position 8th Now the air mass threshold (first switching threshold S1) is increased for the next transition to the stratified operation. This process can be repeated several times. In position 9 a check is made as to whether a predefined maximum value M for the first switching threshold S1 has been exceeded. If this is not the case, a jump to position takes place via the path n 11 , Otherwise, at j (position 10 ) decided whether switching to the stratified operation should be prevented in the future. After that, the program is in position 11 finished again.

In the second flowchart according to 2 the switching is controlled from the stratified operation to the homogeneous operation. The program starts in position 21 , First, the EGR rate is reduced to a value that is acceptable for homogeneous operation. Subsequently, the air mass setpoint is set to the value for homogeneous operation. In position 22 is checked for homogeneous operating mode.

At n, if there is a stratified operation, the program jumps to position 29 , Here is queried whether the amount of the speed gradient D is greater than the predetermined limit G. If this is not the case, ie the speed gradient D is within the predetermined limit G, the program ends in position 33 , However, in the other case, the speed gradient D is greater than the predetermined limit value G, this may be because at this time, the air mass is too low and therefore a bad combustion was detected. That's why in position 30 the second switching threshold S2 for the air mass are changed (increased) in such a way that the switching operation takes place somewhat earlier. In position 31 it is checked whether the air mass threshold S2 exceeds a predetermined maximum value M. If an improved combustion is achieved without worsening the subsequent homogeneous combustion and without exceeding the maximum value M, this second switching threshold S2 is stored.

Will be in position 31 the maximum value M is not exceeded, then the program is in position via the path n 33 completed. If, on the other hand, the maximum value M is exceeded, then the threshold value S2 is limited to the value of the maximum value M. The program now jumps over the path j to position 32 , In position 32 a decision is made as to whether switching to stratified operation should be prevented in the future. Then the program ends again in position 33 ,

Subsequently, the left part of 2 explained in more detail. Was in position 22 If it is determined that there is a homogeneous operation, then j is in position via path j 23 checked with the aid of the speed gradient D, if there is an unstable combustion. If this is not the case, the program ends via the path n in position 33 , If an unstable combustion has been detected, ie at j the amount of the speed gradient D is greater than the predetermined limit G, is first in position 24 the threshold EGR rate checked. At n, the EGR rate threshold is lowered (position 25 ), so that will be switched in the future with a lower EGR rate. If this improves combustion, the new threshold value is saved and the program ends in position 33 ,

In the other case (position 24 , Path j) is the cause of poor combustion at too late a firing angle. This is the result of an air mass that is too high for homogeneous operation. In position 26 it is checked whether the second switching threshold S2 has not fallen below a predetermined minimum value Min. If this is not the case then it will be in position 27 lowered the switching threshold for the air mass in such a way that the switching takes place a little later. This results in a lower air mass and a previous ignition angle. Through these measures, the combustion can be stabilized and thus their quality can be improved. Then the program ends again in position 33 ,

Was against it in position 26 falls below the predetermined minimum value Min, then limited to the minimum value Min.

About the path j will now be in position 28 decided whether in the future switching to the stratified operation should be prevented. Then the program is in position 33 finished again.

3 shows a schematic representation of a device 40 to control the transition between two types of operation, in particular between the two modes of homogeneous operation and stratified operation. The device 40 is preferably formed as part of a motor control system, which by means of a software routine (program 42 ) controls the motor functions at the transition between the two modes. This program is executed cyclically in a predetermined cycle, as it was previously the case 1 and 2 has been described. Furthermore, the device 40 with a memory 43 connected, in which in addition to the determined switching thresholds S1, S2, for example, limits G for the speed gradient, maximum values M, speed values, etc. are preferably stored in tabular form. The device 40 is preferably via a bus system with a first actuator 44 for the throttle of the gasoline engine 46 and with a second actuator 45 connected to the EGR controller (Exhaust Gas Recirculation). Thus, with the help of the first actuator 44 the fresh air mass for the individual cylinders of the gasoline engine 46 and with the second actuator 45 the recirculated exhaust gas fraction (EGR rate) are controlled. Furthermore, a speed sensor 47 provided for one unit 48 provides current engine speeds, from which then the speed gradient is determined. The speed gradient is easiest by subtraction or quotient of the speed sensor 47 determined sequentially delivered speeds.

In an alternative embodiment of the invention, it is provided to apply this method to other modes of lean operation, such as HCCI operation.

Claims (8)

Method for controlling the transition from a first operating mode of a direct-injection gasoline engine ( 46 ) to a second mode, wherein upon reaching a predetermined switching threshold (S1, S2), a fuel-air mixture in the cylinder of the gasoline engine ( 46 ) is reloaded for the two operating modes homogeneous operation and lean operation, and wherein the switching threshold (S1, S2) to the quality of combustion of the fuel-air mixture in the cylinders is adaptable, characterized in that the adaptation is carried out by evaluating a speed gradient (D) and a value determined therefrom for the switching threshold (S1, S2) is used to control subsequent switching operations of the two modes, and upon detection of a poor combustion after the transition to the lean operation, the first switching threshold (S1) is raised for the next transition to lean operation, to increase the first switching threshold (S1), the air mass is increased in the lean operation by a predetermined value, and that upon successful switching the last found value for the increased air mass threshold (S1) is stored. A method according to claim 1, characterized in that for the transition from homogeneous to lean operation, a first switching threshold (S1) and for the transition from lean operation to homogeneous operation, a second switching threshold (S2) is determined. Method according to one of the preceding claims, characterized in that for the amount of the speed gradient (D), a limit value (G) is predetermined, which may not be exceeded. A method according to claim 1, characterized in that the increase of the switching threshold (S1) is repeated until the quality of the combustion in lean operation falls below the amount for the predetermined limit value (G) of the speed gradient (D). Method according to one of the preceding claims, characterized in that when detecting a bad combustion in homogeneous operation, the first switching threshold (S1) for the next transition to lean operation lowered and that upon successful switching, the new value for the switching threshold (S1) is stored. A method according to claim 5, characterized in that in an unacceptable poor transition from homogeneous to lean operation, the switch is locked in the lean mode. Method according to one of claims 1 to 3, characterized in that when switching from lean operation to homogeneous operation, first an EGR rate and then the air mass are reduced to a value required for homogeneous operation and that upon detection of a poor combustion in lean operation the switchover takes place earlier if the air mass is even greater. A method according to claim 7, characterized in that when detecting an unstable combustion after switching to the homogeneous operation, the EGR rate is reduced and / or the switchover takes place somewhat later, when the air mass has further reduced, and that upon successful switching of the new Value for the second switching threshold (S2) is stored.

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