EP1192346B1 - Method of monitoring an internal combustion engine that is operated with an excess of air - Google Patents

Description

The invention relates to a method for monitoring both with homogeneous air-fuel mixture as well as with a high excess air to form a stratified air-fuel mixture operable internal combustion engine, in particular an internal combustion engine with direct injection according to claim 1, first part (see EP-A-887 533).

To the fuel consumption of motor vehicles with Otto engine Drive to reduce further, come more often Internal combustion engines are used which are operated with a lean mixture become. There are two basic operating modes distinguished.

In the lower load range, the internal combustion engine with a heavily stratified cylinder charge and high excess air operated (stratified charge operation). This is due to a late one Injection into the compression stroke, just before the ignition point reached. The internal combustion engine is doing while avoiding throttling losses largely unthrottled operated. To reduce the NOx raw emissions, a high exhaust gas recirculation rate sought.

In the upper load range, the internal combustion engine with homogeneous Cylinder charge operated. The injection is already done during the intake stroke to a good mixing to get from fuel and air. The sucked air mass is according to the torque request of the driver via a Throttle valve adjusted. The required injection quantity is calculated from the air mass and the speed 'and u.a. about corrects the lambda control.

The injection of the fuel takes place either in conventionally in the suction tube or directly in the or the cylinders of the internal combustion engine (direct injection).

From WO 99/18343 is a method and a device for monitoring an internal combustion engine with direct injection of fuel and / or broader throttle free Load control known. This will be an estimate of the fuel mass calculated, the per cycle in a cylinder as the actual fuel mass is the deciding factor Predictive value for the value of the actual indexed Torque's. The estimate of the fuel mass is calculated on the basis of an air ratio, that of a arranged in the exhaust tract of the internal combustion engine Oxygen sensor is detected. Depending on this estimate for the fuel mass is an estimated value for the indexed Torque of the internal combustion engine calculated. On Emergency running of the internal combustion engine is controlled when the Estimated value and a target value of the indicated torque a fulfill given condition.

In a known method (DE 42 32 974 A1) for controlling an internal combustion engine is a setpoint over the Air mass flow to be adjusted torque in a device determined for torque specification. An estimate of one ignition angle normalized actual torque is either derived from the measurement signal of a torque sensor or from the air mass flow sucked into the combustion chambers. On Adjustment of an ignition angle depends on the deviation of the setpoint from the normalized estimate of Torque.

a) eine geschichtete Verbrennung mit lambda >> 1,

b) eine homogene Verbrennung mit lambda >1

c) eine homogene Verbrennung mit lambda = 1

und eine Momentenregelung mit Erfassen des IST - Drehmoments der Brennkraftmaschine. EP-A-0 887 533 (Figure 23) discloses a control of a direct injection internal combustion engine in three types of combustion:

a) stratified combustion with lambda >> 1,

b) homogeneous combustion with lambda> 1

c) homogeneous combustion with lambda = 1

and a torque control with detecting the actual torque of the internal combustion engine.

The object of the invention is a method for controlling specify an internal combustion engine of the type mentioned, which makes it possible, even in case of error too high Torque the internal combustion engine in a safe operating condition to control.

This object is achieved by the features of patent claim 1 solved. Advantageous embodiments of the invention are in specified in the dependent claims.

The invention is characterized in that during operation the internal combustion engine with stratified charge λ >> 1 or with homogeneous air-fuel mixture λ> 1 that of the internal combustion engine indicated torque or one to this Torque proportional size is constantly detected and the values thus obtained are compared with a maximum allowable value become. If too high a torque is detected, it becomes immediate switched to the operating state homogeneous mode λ = 1. In this operating range then known and proven torque monitoring measures are activated. This results in a simple realization in existing Monitoring systems.

Is too high torque in this operating condition (TQI) are detected, runflat reactions are activated with limited functionality a further journey of the vehicle allow for troubleshooting in the workshop. Thus is a high availability of the vehicle even in case of failure given a too high torque.

Figur 1

eine schematische Darstellung einer Brennkraftmaschine mit Direkteinspritzung, bei der das erfindungsgemäße Verfahren angewandt wird und

Figur 2

ein Ablaufdiagramm zum Überwachen und Steuern der Brennkraftmaschine

The invention will be explained in more detail with reference to the drawing. Show it:

FIG. 1

a schematic representation of an internal combustion engine with direct injection, in which the inventive method is applied and

FIG. 2

a flowchart for monitoring and controlling the internal combustion engine

FIG. 1 shows a rough schematic representation of a Internal combustion engine with gasoline direct injection, which depends of operating parameters both with homogeneous mixture (homogeneous with an air ratio λ = 1 or homogeneous λ> 1), as well as layered charge λ >> 1 is operable. Because of Clarity, only those parts are drawn, which are necessary for the understanding of the invention. In particular, only one cylinder is a multi-cylinder Internal combustion engine with direct injection shown.

The reference numeral 10 denotes a piston which is in a cylinder 11 limits a combustion chamber 12. In the Combustion chamber 12 opens an intake passage 13, controlled by the through an inlet valve 14, the combustion air in the Combustion chamber 12 flows. Controlled by an exhaust valve 15 branches off from the combustion chamber 12 an exhaust passage 16, in whose further course is an oxygen sensor in the form of a broadband (linear) lambda probe 17 and a NOx storage catalyst 18 is arranged.

With the signal of the lambda probe 17, the air ratio is corresponding the setpoint specifications in the different operating ranges the internal combustion engine regulated. This function takes over a known lambda control device, the preferably in a control device 21 of the internal combustion engine is integrated.

For controlling the fuel / air mixture of the internal combustion engine in the optimal lambda window during the stoichiometric Operation is the signal of one after the NOx storage catalyst 18 arranged Sauerstoffmeßaufnehmers 32 required as a guide probe. As Sauerstoffmeßaufnehmer 32 is preferably a binary lambda probe (2-point lambda probe) based on zirconium oxide ZrO2, which at one Lambda value λ = 1 with respect to its output signal a jump characteristic having. This probe signal after the NOx storage catalyst 18 arranged lambda probe 32 is also for controlling memory regeneration and adaptation model sizes such as e.g. the oxygen or NOx storage capacity used. Alternatively to the as a guide probe Also serving as an oxygen sensor 32 may be a NOx sensor be used.

The temperature of the NOx storage catalytic converter 18, which is used for and emission-optimal control of the exhaust aftertreatment system is required, by means of a temperature model from the sensor signal of a temperature sensor 33 calculated. Based on this measurement signal, catalyst heating or catalyst protection measures initiated. alternative For this purpose, the temperature of the NOx storage catalyst 18 can also be measured directly by a temperature sensor is arranged directly in the same housing.

The NOx storage catalyst serves to operate in areas with lean combustion, the required exhaust gas limit values to be able to comply. It adsorbs due to its coating the lean NOx combustion compounds in the exhaust.

To the specifically with internal combustion engines with direct injection and stratified charge NOx emissions occur To reduce internal combustion engine is an exhaust gas recirculation device intended. By adding exhaust gas to the sucked Fresh air, the combustion peak temperature is lowered, whereby the temperature-dependent nitrogen oxide emission is reduced becomes. For returning a defined partial flow of the exhaust gas therefore branches from the exhaust duct 16 in the flow direction the exhaust gas seen in front of the NOx storage catalyst 18 an exhaust gas recirculation line 19 from the downstream of a Throttle valve 20 opens into the intake passage 13. The amount of recirculated exhaust gas is by changing the duty cycle one output from the controller 21 Signals for a controllable valve 22, as a rule as exhaust gas recirculation valve, set.

The necessary for combustion in the cylinder 11 fresh air flows over an unillustrated air filter and an air mass meter 23 in the intake tract 13 to the throttle 20. This throttle valve 20 is an electric motor controlled throttle device (E-gas system), whose Opening cross section next to the operation by the driver (Driver's request) regardless of signals from the control device 21 is adjustable. This can be, for example disturbing load change reactions of the vehicle during Reduce throttle input and output as well as torque jumps at the transition from homogeneous mixture operation to Operation with stratified charge and unthrottled airway. At the same time a signal for the position of the Throttle valve 20 is output to the control device 21.

A temperature sensor 24 detects the temperature of the intake air in the intake passage 13 of the internal combustion engine and outputs a corresponding Signal to the controller 21 from. Of the Temperature sensor 24 may in a preferred embodiment be integrated into the air mass meter 23.

Into the combustion chamber 12 protrudes a spark plug 25 and a Injection valve 26, by the contrary to the compression pressure in the combustion chamber 12 of the fuel is injected. The Promotion and provision of fuel for this injector 26 is performed by a known fuel supply system for gasoline direct injection, being of the associated Fuel circuit only a high-pressure accumulator 27 is shown, to which the individual injectors connected are.

A temperature sensor 28 detects the temperature of the internal combustion engine corresponding signal, for example via a Measurement of the coolant temperature. The speed N of the internal combustion engine is using a mark the crankshaft or a sensor wheel connected to it Sensor 29 detected. Both signals are the controller 21 for further processing, i.a. to control the Internal combustion engine with regard to the control strategy to be selected homogeneous mixture or stratified mixture.

Further control parameters necessary for the operation of the internal combustion engine are needed, such as accelerator pedal position, Signals from knock sensors, battery voltage, driving dynamics requirements etc. are also the controller 21 are supplied and are generally in the figure with the reference numeral 30 marked. About the already mentioned parameters is stored in the controller 21 by processing Control routines, etc. the load state of the internal combustion engine detected, the NOx raw emissions of the internal combustion engine and determines the degree of loading of the NOx storage catalyst. Also, the parameters are processed and processed in such a way, that in certain operating conditions of the Internal combustion engine u.a. a switching from homogeneous operation Mixture on operation with stratified charge and vice versa performed and / or initiated a recirculation of exhaust gas can be.

In addition, in the control device 21, a block 31 for Torque detection and torque monitoring provided, whose function will be explained in more detail.

Furthermore, the control device 21 is provided with a memory device 34 connected in the u.a. various Thresholds TQI_SW1, TQI_SW2, and at least one map KF1 are stored, whose meaning is based on the description of the following figure explained in more detail becomes.

In the figure 2 is shown in the form of only a schematic representation Schedule the procedure for monitoring and controlling the internal combustion engine when an inadmissibly high Torque reproduced.

Depending on whether the internal combustion engine with a layered Air-fuel mixture (air ratio λ >> 1, left Branch in Figure 2) or with a homogeneous air-fuel mixture (Air ratio λ> 1, right branch in Figure 2) operated are different monitoring mechanisms for that Torque of the internal combustion engine activated.

During operation of the internal combustion engine with a homogeneous lean air-fuel mixture is determined at lambda λ = 1 operation Torque of the internal combustion engine with a Lambda dependent Efficiency corrected. Because the optimal ignition angle at Operation of the internal combustion engine with an air ratio λ> 1, e.g. λ = 1 ... 1.4 deviates from that at λ = 1 operation is carried out an additional correction. For this purpose, the of lambda probe 17 (FIG. 1) is used.

In operation with stratified air-fuel mixture (λ >> 1) is the output from the engine torque almost only dependent on their speed and the fuel mass. For this reason, in this mode of operation Torque can be determined via a map KF1 that over The speed and the fuel mass is clamped. The the Cylinders of the internal combustion engine supplied fuel mass can in dependence of the signal of the lambda probe 17th be estimated, as for example in WO99 / 18343 is specified.

In method step S2, this is done according to the specified method determined, current torque TQI with a predetermined Value for a maximum permissible torque, namely one first threshold TQI_SW1 compared.

The first threshold TQI_SW1 is by trial on one Test bench, determined by driving tests or by simulation and is stored in the memory 34.

If the current torque TQI is less than the first threshold TQI_SW1, then either becomes method step S1 jumped back when the internal combustion engine in the operation with stratified air-fuel mixture (λ >> 1) is located (dashed line), or to the method step S3, when the internal combustion engine in the operation with homogeneous Air-fuel mixture (λ> 1) is located.

In the flowchart shown in Figure 2, the threshold applies SW1 for the current torque TQI of the internal combustion engine, Regardless of whether the operation with stratified air-fuel mixture (λ >> 1), or the operation with homogeneous Air-fuel mixture (λ> 1) is activated. It is also possible, according to the two operating modes of the internal combustion engine two different thresholds in their height provided.

The current torque TQI exceeds the first threshold TQI_SW1, so it is immediately on homogeneous operation with an air ratio λ = 1 switched and the torque monitoring method for homogeneous operation λ = 1 activated (method step S4). From operational variables for homogeneous operation at λ = 1, in particular from that of the air mass meter 23 (Figure 1) determined air mass flow LMM, the speed N and the ignition angle is the torque of the internal combustion engine In this case, it determines how it is in the already mentioned in the beginning international patent application WO99 / 183443. The determination of the current Torque and monitoring, i. the comparison with the Thresholds occur in block 31 of the controller 21st

The current torque TQI determined in a known manner is then in a step S5 with a from Driver of the vehicle driven by the internal combustion engine desired maximum torque (second threshold SW2) compared. Also the second threshold TQI_SW2 is by tests on a test bench, by road tests or determined by simulation and is stored in the memory 34. The quantity-controlled operation of the internal combustion engine (Homogenous operation λ = 1) is maintained if the current one Torque TQI below the second threshold TQI_SW2 lies. This query takes place in a waiting loop. There is no switchover to the stratified charge mode λ >> 1 or in the homogeneous mode λ> 1, even if in homogeneous operation λ = 1 no error occurs, i. the second threshold TQI_SW2 is never reached. The switching process is thus irreversible for the current driving cycle.

If the query delivers a positive result in method step S5, that is, if torque TQI exceeds second threshold value TQI_SW2, it is ensured by initiating emergency operation reactions that the internal combustion engine is brought into a safe state (method step S6).
The torque of the internal combustion engine can be limited, for example, in which the e-gas throttle valve is de-energized or there is a limitation of the speed by suppressing the injection for a certain number of cylinders. As emergency function can be carried out interventions in the ignition in addition to interventions in the filling or in the fuel supply, which on the one hand cause a limitation of the torque or acceleration, but on the other hand still allow the vehicle to continue to the next workshop.

Alternatively, the default condition for emergency operation (Query in step S 5) also configured be that the difference of the current torque and the permissible maximum value for a given period of time is integrated, starting at one point in time the current value becomes greater than the maximum value of the Torque. The condition is fulfilled when the integral is greater than another threshold. The condition can also be designed differently.

In the flow chart of Figure 2 was the erfindungssgemäße Method explained using the example of torque monitoring. In addition, it is also possible, not the torque itself, but to use a torque proportional size. Thus, e.g. in the case of operation of the Internal combustion engine with stratified charge in an advantageous Way of the internal combustion engine supplied fuel mass flow to be used.

Claims (6)

1. Method for monitoring an internal combustion engine that can be operated, depending on the operating parameters, with both a homogenous air/fuel mixture or a high excess of air under the formation of a stratified air/fuel mixture, in which case,

   during operation of the internal combustion engine with a stratified air/fuel mixture with an air ratio λ>>1 or during operation with a homogenous air/fuel mixture with an air ratio λ>1, the current value of the torque (TQI) indicated by the internal combustion engine or a variable proportional to this torque (TQI) is continuously determined,

   the current value of the torque (TQI) or the variable proportional to the torque (TQI) is compared with a first threshold value (TQI_SW1) and characterized in that

   if the first threshold value (TQI_SW1) is exceeded when operating the internal combustion engine, there is an immediate switchover to the operating mode homogeneous operation λ=1.
2. Method according to Claim 1, characterized in that

   during operation of the internal combustion engine with a homogenous air/fuel mixture with an air ratio λ=1, the current values of the torque (TQI) or variable proportional to this torque (TQI) is continuously determined,

   the current value of the torque (TQI) or the variable proportional to the torque (TQI) are compared with a second threshold value (TQI_SW2) and

   if the second threshold value (TQI_SW2) is exceeded, emergency driving measures are introduced for the motor vehicle driven by the internal combustion engine.
3. Method according to Claim 1, characterized in that
   for the emergency driving the following measures can be performed individually or in combination:

   deactivation of an e-gas throttle valve (20),

   cutting out of the injection for individual cylinders of the internal combustion engine,

   intervention in the ignition.
4. Method according to Claim 1 and 2, characterized in that the threshold values (TQI_SW1, TQI_SW2) are determined experimentally and stored in a storage device (31) of a control unit (21) controlling the internal combustion engine.
5. Method according to Claim 1 and 2, characterized in that the following applies to the threshold values (TQI_SW1, TQI_SW2): TQI_SW1 ≥ TQI_SW2
6. Method according to Claim 1 or 2, characterized in that on operating the internal combustion engine with a stratified air/fuel mixture with an air ratio λ>>1 as the variable that is proportionate to the torque that is used to feed the mass fuel flow (KST) to the internal combustion engine.

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