WO2001002711A1

WO2001002711A1 - Method of monitoring an internal combustion engine that is operated with an excess of air

Info

Publication number: WO2001002711A1
Application number: PCT/DE2000/002159
Authority: WO
Inventors: Martin Debusmann; Thomas Pfeufer; Lothar Rehm; Tobias Roulet; Stefan Schneider
Original assignee: Siemens Aktiengesellschaft; Daimlerchrysler Ag
Priority date: 1999-07-02
Filing date: 2000-07-03
Publication date: 2001-01-11
Also published as: EP1192346A1; EP1192346B1; DE50006419D1

Abstract

The invention relates to a method of monitoring an internal combustion engine that is operated with an excess of air. If an excessive torque (TQI) is detected during the operation of the internal combustion engine in the stratified charge mode μ⊃⊃1 or with a homogeneous air-fuel mixture μ⊃1, the engine immediately switches to the homogeneous operation state μ=1. If an excessive torque (TQI) is detected for this mode of operation, too, emergency operation modes are activated.

Description

description

Method for monitoring an internal combustion engine that can be operated with excess air

The invention relates to a method for monitoring an internal combustion engine that can be operated both with a homogeneous air-fuel mixture and with a high excess of air to form a stratified air-fuel mixture, in particular an internal combustion engine with direct injection.

In order to further reduce the fuel consumption of motor vehicles with an petrol engine, internal combustion engines that are operated with a lean mixture are increasingly used. A distinction is made between two basic operating modes.

In the lower load range, the internal combustion engine is operated with a strongly stratified cylinder charge and a large excess of air (stratified charge mode). This is achieved by late injection into the compression stroke just before the ignition point. The internal combustion engine is operated largely unthrottled while avoiding throttle losses. A high exhaust gas recirculation rate is aimed at in order to reduce the raw NOx emission.

In the upper load range, the internal combustion engine is operated with a homogeneous cylinder charge. The injection takes place during the intake stroke in order to obtain a good mixture of fuel and air. The intake air mass is adjusted according to the driver's torque request via a throttle valve. The required injection quantity is calculated from the air mass and the speed and corrected using the lambda control, among other things. The fuel is injected either in a conventional manner into the intake manifold or directly into the cylinder or cylinders of the internal combustion engine (direct injection).

WO 99/18343 discloses a method and a device for monitoring an internal combustion engine with direct fuel injection and / or largely throttle-free load control. A treasure value of the fuel mass is calculated, which is metered into one cylinder per work cycle, since the actual fuel mass is the decisive influencing variable for the value of the actual indicated torque. The treasure value for the fuel mass is calculated as a function of an air ratio, which is determined by an oxygen sensor arranged in the exhaust tract of the internal combustion engine. Depending on this treasure value for the fuel mass, a treasure value for the indicated torque of the internal combustion engine is calculated. Emergency running of the internal combustion engine is controlled when the treasure value and a target value of the indicated torque meet a predetermined condition.

In a known method (DE 42 32 974 AI) for controlling an internal combustion engine, a setpoint value of a torque to be set via the air mass flow is determined using a device for specifying the torque. A treasure value of an ignition-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. An ignition angle is adjusted as a function of the deviation of the target value from the normalized treasure value of the torque.

The object of the invention is to specify a method for controlling an internal combustion engine of the type mentioned at the outset, which makes it possible to control the internal combustion engine into a safe operating state even in the event of an excessive torque failure. This object is achieved by the features of patent claim 1. Advantageous embodiments of the invention are specified in the subclaims.

The invention is characterized in that, during operation of the internal combustion engine with stratified charge λ >> l or with a homogeneous air-fuel mixture λ> l, the torque indicated by the internal combustion engine or a quantity proportional to this torque is continuously determined and the resulting values are obtained Values are compared with a maximum permissible value. If an excessive torque is detected, the operating state is switched over to homogeneous operation λ = 1. Known and preserved torque monitoring measures can then be activated in this operating range.

This results in a simple implementation in existing monitoring systems.

If excessive torque (TQI) is also detected in this operating state, emergency running reactions are activated which, with limited functionality, allow the vehicle to continue to the workshop for troubleshooting. This ensures high availability of the vehicle even in the event of an excessive torque error.

The invention is explained in more detail below with reference to the drawing. Show it:

FIG. 1 shows a schematic illustration of an internal combustion engine with direct injection, in which the method according to the invention is used and

Figure 2 is a flowchart for monitoring and controlling the internal combustion engine

FIG. 1 shows a roughly schematic representation of an internal combustion engine with direct Benzm injection, which depends on gig of operating parameters both with a homogeneous mixture (homogeneous with an air ratio λ = l or homogeneous λ> l), as well as with stratified charge λ »l can be operated. For reasons of clarity, only those parts are shown which are necessary for understanding the invention. In particular, only one cylinder of a multi-cylinder internal combustion engine with direct injection is shown.

Reference number 10 denotes a piston which delimits a combustion chamber 12 in a cylinder 11. An intake duct 13 opens into the combustion chamber 12, through which the combustion air flows into the combustion chamber 12, controlled by an inlet valve 14. Controlled by an exhaust valve 15, an exhaust duct 16 branches off from the combustion chamber 12, in the further course of which an oxygen sensor in the form of a broadband (linear) lambda probe 17 and a NOx storage catalytic converter 18 are arranged.

With the signal from the lambda probe 17, the air ratio is regulated in accordance with the setpoint values in the various operating ranges of the internal combustion engine. This function is performed by a lambda control device known per se, which is preferably integrated in a control device 21 of the internal combustion engine.

To control the fuel / air mixture of the internal combustion engine in the optimal lambda window during stoichiometric operation, the signal from an oxygen sensor 32 arranged after the NOx storage catalytic converter 18 is required as a guide probe. A binary lambda probe (2-point lambda probe) based on zirconium oxide Zr02 is preferably used as the oxygen sensor 32 and has a step characteristic with regard to its output signal with a lambda value λ = 1. This probe signal of the lambda probe 32 arranged after the NOx storage catalytic converter 18 is also used to control the storage regeneration and to adapt model variables such as the oxygen or NOx Storage capacity used. As an alternative to the oxygen sensor 32 serving as a guide probe, a NOx sensor can also be used.

The temperature of the NOx storage catalytic converter 18, which is required for the consumption and emission-optimal control of the exhaust gas aftertreatment system, is calculated using a temperature model from the sensor signal of a temperature sensor 33. Based on this measurement signal, catalyst heating and catalyst protection measures are also initiated. As an alternative to this, the temperature of the NOx storage catalytic converter 18 can also be measured directly by arranging a temperature sensor directly in the housing thereof.

The NOx storage catalytic converter is used to comply with the required exhaust gas limit values in operating areas with lean combustion. Due to its coating, it adsorbs the NOx compounds generated in the exhaust gas during lean combustion.

An exhaust gas recirculation device is provided in order to reduce the NOx emissions of the internal combustion engine that occur especially in internal combustion engines with direct injection and stratified charge operation. By adding exhaust gas to the fresh air drawn in, the peak combustion temperature is reduced, which reduces the temperature-dependent nitrogen oxide emission. To return a defined partial flow of the exhaust gas, an exhaust gas recirculation line 19 branches off from the exhaust gas duct 16 in the flow direction of the exhaust gas, in front of the NOx storage catalytic converter 18

Throttle valve 20 mouths in the intake duct 13. The amount of the recirculated exhaust gas is adjusted by changing the duty cycle of a signal output by the control device 21 for a controllable valve 22, generally referred to as an exhaust gas recirculation valve. The fresh air necessary for combustion in the cylinder 11 flows through an air filter (not shown) and an air mass meter 23 into the intake tract 13 to the throttle valve 20. This throttle valve 20 is an electric motor-controlled throttle element (E-gas system), the opening cross section of which in addition to actuation by the driver (driver's request), it can also be set independently of this via signals from control device 21. For example, this can reduce disturbing load change reactions of the vehicle when accelerating and decelerating, as well as torque jumps during the transition from operation with a homogeneous mixture to operation with stratified charge and unrestricted air flow. At the same time, a signal for the position of the throttle valve 20 is output to the control device 21 for monitoring.

A temperature sensor 24 detects the temperature of the intake air in the intake duct 13 of the internal combustion engine and emits a corresponding signal to the control device 21. In a preferred embodiment, the temperature sensor 24 can be integrated in the air mass meter 23.

A spark plug 25 and an injection valve 26 protrude into the combustion chamber 12, through which the fuel is injected against the compression pressure in the combustion chamber 12. The demand and provision of the fuel for this injection valve 26 is carried out by a known fuel supply system for gasoline direct injection, of which only a high-pressure accumulator 27 is shown from the associated fuel circuit, to which the individual injection valves are connected.

A temperature sensor 28 detects a signal corresponding to the temperature of the internal combustion engine, for example by measuring the coolant temperature. The speed N of the internal combustion engine is detected with the aid of a markings on the crankshaft or a sensor 29 which scans the sensor wheel connected to it. Both signals are used by the control direction 21 for further processing, inter alia for controlling the internal combustion engine with respect to the control strategy to be chosen — homogeneous mixture or stratified mixture.

Further control parameters that are required for operating the internal combustion engine, such as, for example, accelerator pedal position, signals from knock sensors, battery voltage, driving dynamics requirements, etc., are also supplied to the control device 21 and are generally identified in the figure by the reference symbol 30. The above-mentioned parameters are used in the control device 21 by processing stored control routines, among other things. the load state of the internal combustion engine is recognized, the raw NOx emission of the internal combustion engine and the degree of loading of the NOx storage catalytic converter are determined. The parameters are also processed and processed in such a way that, in certain operating states of the internal combustion engine, i.a. a switchover from operation with a homogeneous mixture to operation with stratified charging and vice versa can be carried out and / or a recirculation of exhaust gas can be initiated.

In addition, a block 31 for torque determination and torque monitoring is provided in the control device 21, the function of which will be explained in more detail.

Furthermore, the control device 21 is connected to a storage device 34 in which, among other things, Various threshold values TQI_SW1, TQI_SW2, and at least one map KF1 are stored, the respective meaning of which is explained in more detail with reference to the description of the following figure.

FIG. 2 shows the process for monitoring and controlling the internal combustion engine when an impermissibly high torque occurs in the form of a flowchart which is only shown schematically. Depending on whether the internal combustion engine is operated with a stratified air-fuel mixture (air ratio λ »l, left branch in FIG. 2) or with a homogeneous air-fuel mixture (air ratio λ> l, right branch in FIG. 2) different monitoring mechanisms for the torque of the internal combustion engine are activated.

When the internal combustion engine is operated with a homogeneously lean air / fuel mixture, the torque of the internal combustion engine determined at lambda λ = l operation is corrected with an efficiency which is dependent on lambda. Since the optimal ignition angle when operating the internal combustion engine with an air ratio λ> l, e.g. λ = l ... l, 4 deviates from that with λ = l operation, an additional correction is carried out. For this purpose, the actual lambda value determined by the lambda probe 17 (FIG. 1) is used.

In operation with a stratified air-fuel mixture (λ »l), the torque delivered by the internal combustion engine is almost exclusively dependent on its speed and the fuel mass. For this reason, the torque can be determined in this operating mode via a map KF1, which is spanned over the speed and the fuel mass. The fuel mass supplied to the cylinders of the internal combustion engine can be estimated as a function of the signal from the lambda probe 17, as specified, for example, in W099 / 18343.

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

The first threshold value TQI_SW1 is determined by tests on a test bench, by driving tests or by simulation and is stored in the memory 34. If the current torque TQI is less than the first threshold value TQI_SW1, the process jumps back either to method step S1 when the internal combustion engine is operating with a stratified air-fuel mixture (λ »l) (dashed line), or to the method step S3, when the internal combustion engine is in operation with a homogeneous air-fuel mixture (λ> l).

In the flowchart shown in FIG. 2, the threshold value SW1 applies to the current torque TQI of the internal combustion engine, regardless of whether the operation with a stratified air-fuel mixture (λ »l) or the operation with a homogeneous air-fuel mixture (λ > l) is activated. However, it is also possible to provide two threshold values different in height depending on the two operating modes of the internal combustion engine.

If the current torque TQI exceeds the first threshold value TQI_SW1, the system immediately switches to homogeneous operation with an air ratio λ = 1 and the torque monitoring method for homogeneous operation λ = 1 is activated (method step S4). The torque of the internal combustion engine in this operating case is determined from operationally relevant variables for homogeneous operation at λ = l, in particular from the air mass flow LMM determined by the air mass meter 23 (FIG. 1), as is already the case at the beginning mentioned international patent application W099 / 183443. The determination of the current torque and the monitoring, i.e. the comparison with the threshold values takes place in block 31 of control device 21.

The current torque TQI determined in a known manner is then compared in a method step S5 with a maximum torque (second threshold value SW2) desired by the driver of the vehicle driven by the internal combustion engine. The second threshold is also TQI SW2 determined by tests on a test stand, by driving tests or by simulation and is stored in the memory 34. The quantity-controlled operation of the internal combustion engine (homogeneous operation λ = 1) is maintained when the current torque TQI is below the second threshold value TQI_SW2. This query is on hold. There is no switching to stratified charge mode λ >> l or m homogeneous mode λ> l, even if no error occurs in homogeneous mode λ = l, ie the second threshold value TQI_SW2 is never reached. The switching process is therefore irreversible for the current driving cycle.

If the query in method step S5 delivers a positive result, ie if the torque TQI exceeds the second threshold value TQI_SW2, it is ensured by initiating emergency running 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, by switching off the electric gas throttle valve, or the speed is limited by suppressing the injection for a specific number of cylinders. As an emergency operation function, in addition to interventions in the filling or in the fuel supply, interventions in the ignition can also take place, which on the one hand limit the torque or the acceleration, but on the other hand allow the vehicle to continue to the next workshop.

Alternatively, the predetermined condition for an emergency operation (query in method step S 5) can also be designed such that the difference between the current torque and the permissible maximum value is integrated for a predetermined period of time, starting at a point in time at which the current value becomes greater than the maximum value of the torque. The condition is met if the integral is larger than another threshold value. The condition can also be designed in any other way. In the flow chart of Figure 2, the method erfindungssgemä- SSE the example of the torque control has been explained, but Moreover, it is also possible not the torque itself, but to attract a proportional torque magnitude manufacturing ^•. For example, in the case of operation the

Internal combustion engine with stratified charge, the fuel mass flow supplied to the internal combustion engine can be used in an advantageous manner.

Claims

claims

1. A method for monitoring an internal combustion engine, which is operated depending on operating parameters either with a homogeneous air-fuel mixture or with a high excess of air to form a stratified air-fuel mixture, characterized in that

-While the internal combustion engine is operating with a stratified air-fuel mixture with an air ratio λ >> l or during operation with a homogeneous air-fuel mixture with an air ratio λ> l, the current value of that indicated by the internal combustion engine is constant Torque (TQI) or a value proportional to the torque (TQI) is determined,

- the current values of the torque (TQI) or the quantity proportional to the torque (TQI) are compared with a first threshold value (TQI_SW1) and - if the first threshold value (TQI_SW1) is exceeded, the internal combustion engine is operated with homogeneous air -

Fuel mixture with an air ratio λ = l is switched.

2. The method according to claim 1, characterized in that -in operation of the internal combustion engine with homogeneous air-

Fuel mixture with an air ratio λ = l the current values of the torque (TQI) or the quantity proportional to the torque (TQI) are continuously determined,

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

and if the second threshold value (TQI_SW2) is exceeded, emergency operation measures are initiated for the vehicle driven by the internal combustion engine.

3. The method according to claim 1, characterized in that the following measures can be carried out individually or in combination for emergency operation:

- De-energizing an E-gas throttle valve (20)., - Suppression of the injection for individual cylinders of the internal combustion engine, - Ignition intervention.

4. The method according to claim 1 and 2, characterized in that the threshold values (TQI_SW1, TQI_SW2) are determined experimentally and are stored in a memory (31) of a control device (21) controlling the internal combustion engine.

5. The method according to claim 1 and 2, characterized in that for the threshold values (TQI_SW1, TQI_SW2) applies:

TQI_SW1> TQI_SW2

6. The method according to claim 1 or 2, characterized in that when operating the internal combustion engine with stratified

Air-fuel mixture with an air ratio λ >> l is used as the torque proportional quantity of the fuel mass flow (KST) supplied to the internal combustion engine.