DE10016123C2 - Method for heating an exhaust gas catalytic converter for an internal combustion engine - Google Patents

Description

The invention relates to a method for heating an Ab gas catalyst for an internal combustion engine according to Claim 1.

The pollutant emission of an internal combustion engine can be through catalytic after-treatment with the help of a three-way ka talysators in connection with a lambda control device reduce effectively. An important requirement for this is however, that next to the lambda sensor of the control device the catalytic converter also reaches its operating temperature Has. Below this temperature, at the typical force vehicle catalytic converters approx. 300 ° C, the exhaust gas catalytic converter is un effective to little effective and the reaction takes place only with un enough small conversion rates (<< 10%) instead. To a ensure that the light-off temperature is reached quickly and thus pollutant emissions during the cold start phase the internal combustion engine, in which within the first 10-15 70 to 90% of the total pollutants of HC and CO emissions are reduced, however, are various known heating strategies.

Rapid warming of the catalytic converter can also by retarding the ignition angle, increasing the idle speed speed, mixture thinning, mixture enrichment in connection with secondary air injection into the exhaust system of the internal combustion engine machine done.

To quickly get the catalytic converter up to its operating temperature To heat up, measures are currently being taken that a deterioration in the efficiency of the combustion process and thus lead to an increase in exhaust gas temperature. additionally will increase the idle speed of the internal combustion engine  made to increase the exhaust gas mass flow pass. Both measures are with a higher fuel consumption related. In addition, if the intervention is too strong the uneven running of the internal combustion engine in the course of the combustion. Both the increase in idle speed and the increase in Uneven running deteriorates the comfort of a vehicle.

DE 43 34 771 C1 is a motor vehicle electrical type lay in an electrical machine with an electrical system generator known function in a first mode of operation as a board mains generator can be operated, a controller for setting of the excitation current for the electrical machine, and one electrical consumers with comparatively high performance needs, for example a heater for an exhaust gas talysator. The system also sees a switch through which an output of the electrical machine is optional se with an on-board power supply line or with the consumption cher is connectable, and a control unit for control of controller and switch either in the first or one second mode, so that the electrical machine with the Vehicle electrical system is connected and the controller operates adjusts to an electrical system voltage or the electrical Ma is connected to the consumer and the controller Operating voltage adjusted to a higher setpoint. Next these two functions are preferably a third function provided as a starter motor for the electrical machine. Such a motor vehicle electrical system is used in motor vehicles.

The invention has for its object a method admit with the exhaust gas catalytic converter of an internal combustion engine ne can be heated effectively.

This object is achieved by the features of claim 1 solved. Advantageous further developments are in the dependent claims Chen specified. The invention is based on the idea of  Crankshaft starter generator supports the heating use measures for the catalytic converter.

Shortly after the engine starts, it contributes the low intake manifold pressure only a little to the total torque of the Systems at. The torque of the internal combustion engine is now increases and at the same time the torque of the crankshaft Starter generator reduced to the same extent. For heating the Exhaust catalytic converter becomes the indicated torque of the combustion engine increased beyond its torque loss, so that the crankshaft starter generator has a negative torque (Generator operation) must generate the required clutch to maintain the moment.

Simply by increasing the torque of the internal combustion engine increases the exhaust gas temperature and the exhaust gas mass flow rate, which already faster heating of the catalytic converter tors is achieved. In addition, the Internal combustion engine the measures mentioned for heating the Exhaust gas catalytic converter can be used better because the combustion engine runs more stable at higher loads and thus stronger  Interventions in the burning process are possible without the To significantly increase uneven running of the internal combustion engine.

One such, under the crankshaft starter generator supported exhaust gas catalyst heating measure has the advantage that an improvement in consumption through less effectiveness degree deterioration of the overall system can be achieved, because part of the crankshaft starter generator too much generated energy is stored in the vehicle battery and the electrical energy consumption by the start is thereby balanced.

It is also a comfort improvement through a higher barrel rest of the engine, and an improvement the heating effectiveness of the known heating measures.

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

Fig. 1 is a block diagram of an internal combustion engine with egg ner exhaust gas aftertreatment system, in which the dung OF INVENTION modern method is applied,

Fig. 2 is a flowchart for a supported by the crankshaft starter-catalyst heaters and

Fig. 3 shows the time courses of selected parameters of the internal combustion engine before, during and after the catalyst heating.

In Fig. 1, an internal combustion engine with an associated gas aftertreatment system is shown very simply in the form of a block diagram. Only those components are shown which are necessary for an understanding of the invention. In particular, the representation of the fuel circuit has been omitted.

The internal combustion engine 10 is supplied with the air necessary for combustion via an intake duct 11 . An air mass meter 12 , a throttle valve block 13 and, in accordance with the number of cylinders, a set of injection valves 15 , only one of which is shown, are provided in the intake duct 11 in the flow direction of the intake air. However, the method according to the invention can also be used in a system which has only one injection valve for all cylinders (central injection system, single point injection system) or in which the fuel is injected directly into the cylinders of the internal combustion engine or in a multi-cylinder internal combustion engine ( direct injection).

The throttle valve block 13 contains a throttle valve 14 and a throttle valve sensor, not shown, which emits a signal corresponding to the opening angle of the throttle valve 14 to a control device 21 . The Drosselklap pe 14 is, for example, an electric motor-controlled throttle element (E-gas), the opening cross section of which can be adjusted in addition to the operation by the driver (driver's request) depending on the operating range of the internal combustion engine via signals from the control device.

The air mass meter 12 serves as a load sensor in a so-called air mass-controlled control of the internal combustion engine. As an alternative to the air mass meter 12 , a pressure sensor 27 can also be used as the load sensor, which is arranged in a collector 26 of the intake tract of the internal combustion engine 10 (intake manifold pressure-controlled control of the internal combustion engine).

The internal combustion engine 10 is equipped with a crankshaft starter generator (KSG) 28 . The crankshaft starter generator 28 takes on the one hand the function of a conventional union starter (starter) and on the other hand the function of a separate alternator (generator) for charging the vehicle battery. Crankshaft starter generators are usually arranged between the internal combustion engine on the one hand and gearboxes or automatic gearboxes on the other hand coaxial with the cure, in direct connection or in connectable connection to this. Such a crankshaft starter generator is known, for example, from VDI reports number 14/15, 1998, B. Hoffmann, "Electrical energy for a 3-liter car", pages 39 to 53.

On the output side, the internal combustion engine 10 is connected to an exhaust gas duct 16 in which an exhaust gas catalytic converter 17 is arranged. This can be any type of exhaust gas analyzer, in particular a three-way catalytic converter or a NOx storage catalytic converter can be provided.

The sensor system for the exhaust gas aftertreatment includes, inter alia, an exhaust gas measuring sensor in the form of a lambda probe 18 arranged upstream of the exhaust gas catalytic converter 17 and an exhaust gas measuring sensor 19 arranged downstream of the exhaust gas catalytic converter 17 . With the signal from the lambda probe 18 , the mixture is regulated in accordance with the setpoint values. This function takes over a known Lambdaregelungseinrich device 20 , which is preferably integrated into a control device 21 which controls the operation of the internal combustion engine. Such electronic control devices 21 , which usually contain one or more microprocessors and which in addition to the fuel injection and the ignition control also take on a large number of other control and re gel tasks, are known per se, so that in the fol lowing only in connection with the Invention relevant structure and its operation is discussed. In particular, the control device 21 is connected to a storage device 22 , in which various characteristic fields and threshold values are stored, among other things.

The exhaust gas sensor 19 serves as a monitor probe for the lambda probe 18 arranged upstream of the exhaust gas catalytic converter 17 and can also be used to control and check the exhaust gas catalytic converter 17 .

A temperature sensor 29 upstream of the exhaust gas catalytic converter 17 detects the temperature of the exhaust gas. From this signal of the temperature sensor 29 , a criterion is derived in the control device 21 as to whether catalyst heating measures are necessary or not. This can be done, for example, using a known exhaust gas temperature model. The Temperatursen sensor 29 can also be installed directly in the monolith of the Abgaskata analyzer 17 . In this case, it immediately provides a value for the temperature of the catalytic converter 17th

The speed N of the internal combustion engine 10 is detected with the aid of a speed sensor 23 , the temperature of the internal combustion engine 10 is recorded via the temperature of the coolant TKW by means of a temperature sensor 25 . These signals are also fed to the control device 21 for further processing, such as the output signal MAF of the air mass meter 12 or, optionally, the output signal MAP of the intake manifold pressure sensor 27 and the signals of the two exhaust gas measuring sensors 18 , 19 .

To control and regulate the internal combustion engine 10 , the control device 21 is also connected via a data and control line 24 to further sensors and actuators (not explicitly shown).

The method for heating the exhaust gas catalytic converter is explained in more detail with the aid of the flow chart according to FIG. 2 and the time diagram according to FIG. 3.

At time t0 ( Fig. 3), the crankshaft starter generator 28 is energized, whereby the speed N of the internal combustion engine 10 increases very quickly from the initial value zero. By using a crankshaft starter generator as a starter for the internal combustion engine 10 , it is possible to drag the internal combustion engine 10 to a high speed (<800 1 / min) and when the intake manifold pressure falls below a predetermined threshold value, the fuel injection and the ignition to release (time t1 in Fig. 3). As a result, the cold start emissions of the internal combustion engine can be reduced. A conventional starter can also be used to start the internal combustion engine.

At time t1, internal combustion engine 10 has already reached its target speed N_SOLL, and in a first method step S1, a query is made as to whether measures for heating catalytic converter 17 are requested. Catalyst heating measures may not only be necessary after a cold start of the internal combustion engine 10 , but also during the operation of the internal combustion engine, situations can occur in which the exhaust gas temperature is so low that the exhaust gas catalytic converter 17 does not reach its temperature necessary for optimal conversion of the pollutants. This can be the case in particular when the internal combustion engine is operated at idle and the vehicle is running, for. B. is in a traffic jam.

If, after evaluating the signal delivered by the exhaust gas temperature sensor 29 , it is determined in method step S1 that no catalyst heating measures are requested, then in a method step S2, if the catalyst heating measures are still activated, these are deactivated and incorporated into a normal operating strategy of the internal combustion engine, ie in Conventional control routines that are adapted to the operating range of the internal combustion engine are switched over. If the internal combustion engine 10 is equipped with a crankshaft starter generator 28 which, among other things, offers the possibility of withdrawing or supplying energy to the crankshaft of the internal combustion engine and in this way reducing or increasing the speed, this can be used, for example To optimize switching operations, drive in a fuel-efficient manner or to monitor and charge the vehicle battery (method step S3).

If the query in method step S1 shows that the exhaust gas analyzer 17 has to be heated, known measures for heating the exhaust gas analyzer 17 are activated in a method step S4. For this purpose, e.g. B. individually or in combination, the following measures are taken:

• - adjustment of the ignition angle in the late direction,
• - increase in idle speed,
• - rich combustion mixture with secondary air injection,
• - electrical heating of the catalytic converter

Since the specified measures have certain limits, in particular, the ignition angle cannot be adjusted as far as desired be postponed late without the operability of the internal combustion engine affect machine, the idle speed increase leads to increased fuel consumption and electrical Heating the catalytic converter is a very high energy counter consumption that be the vehicle battery considerably loads, becomes a more effective heating of the exhaust gas data the crankshaft starter generator drawn.

Therefore, the torque MQ_BKM of the internal combustion engine 10 is increased in a method step S5, for. B. by opening the throttle valve 14 by means of a ramp function and at the same time the torque MQ_KGS of the crankshaft starter generator 28 is reduced to the same extent in order to obtain the required clutch torque.

If the internal combustion engine 10 is equipped with a torque-based control device, the degree of opening of the throttle valve is derived from a torque request.

In a method step S6, a query is made as to whether the torque MQ_KSG of the crankshaft starter generator 28 is less than or equal to zero, that is to say the crankshaft starter generator 28 delivers a negative torque and supplies current. (Time t2). By means of the crankshaft starter generator 28 , a braking torque is built up in generator operation, which counteracts the torque of the internal combustion engine 10 . The vehicle battery is charged by the crankshaft starter generator 28 .

If the torque MQ_KSG is still positive, a branch is made to method step S5, otherwise it is checked in a method step S7 whether the vehicle battery is already fully charged. If this is not yet the case, the torque MQ_BKM of the internal combustion engine 10 is increased to an applied value MQ_BKM_APPL in a method step S8 and the same value is set for the braking torque MQ_KGS (times t2 to t3). The value MQ_BKM_APPL is determined experimentally by tests and is stored in the storage device 22 . The positive torque of the internal combustion engine 10 must be compensated for by the negative torque (braking torque) of the crankshaft starter generator 28, the effective torque is just so high that the friction losses are covered and the idle speed or the required clutch torque can be maintained , The method then branches to step S1.

If the query in method step S7 delivers a positive result, that is to say the vehicle battery is already fully charged, the operation of the crankshaft starter generator 28 to support the heating of the exhaust gas catalytic converter 17 is no longer possible and in a method step S9 the torque MQ_BKM becomes the Internal combustion engine 10 reduced and the torque MQ_KSG reduced (time t3). The method then branches to step S1.

Claims (6)

1. Method for heating an exhaust gas catalytic converter ( 17 ) of an internal combustion engine ( 10 ) arranged in the exhaust gas duct ( 16 ) of an internal combustion engine ( 10 ), which internal combustion engine ( 10 ) has a crankshaft starter generator ( 28 ),
heating measures to increase the temperature of the exhaust gas catalytic converter being activated as required,
the indicated torque (MQ_BKM) of the internal combustion engine ( 10 ) is increased,
the torque (MQ_KSG) of the crankshaft starter generator ( 28 ) is reduced and the crankshaft starter generator ( 28 ) is controlled from engine operation to generator operation, so that the load on the internal combustion engine ( 10 ) is increased while the clutch torque remains the same. 2. The method according to claim 1, characterized in that the indicated torque (MQ_BKM) of the internal combustion engine ( 10 ) by opening a in the intake duct ( 11 ) of the internal combustion engine ( 10 ) arranged throttle valve ( 14 ). 3. The method according to claim 2, characterized in that the opening of the throttle valve ( 14 ) takes place continuously. 4. The method according to claim 2, characterized in that the opening of the throttle valve ( 14 ) takes place suddenly. 5. The method according to claim 1, characterized in that in generator operation (MQ_KSG <0) of the crankshaft starter generator ( 28 ) the torque of the internal combustion engine ( 10 ) is increased to an applied value (MQ_BKM_APPL) and that of the crankshaft starter Generator ( 28 ) built braking torque (MQ_KSG) has the same value, so that the required clutch torque ( 10 ) remains constant. 6. The method according to claim 5, characterized in that before the increase in the torque of the internal combustion engine ( 10 ) to the applied value (MQ_BKM_APPL) the state of charge of the vehicle battery is queried and when the vehicle battery is fully charged, the torque (TQ_BKM) of the internal combustion engine ( 10 ) reduced and the negative torque (TQ_KSG) of the crankshaft starter generator ( 28 ) is reduced.