DE4344137A1 - System for protecting catalytic converter of IC engine - Google Patents

Abstract

A system for protecting the catalytic converter (118,122) of an IC engine (100) against excess temperature determines an instantaneous actual temperature (T1st) for the converter (118,122) using the sensors (116,120,124) which in conjunction with the further sensors (106,110,130,114,132) registering the engine parameters and in accord with the prevailing environmental conditions enables a maximum permissible converter temperature (Tmax) to be established by the controller (136). By examining the difference (dT) between (Tmax) and (T1st) and comparing the result with a series of benchmarks (ABCD) which represent increasingly intensive levels of exhaust cooling a suitably protective level is identified for action.

Description

The invention relates to a system for protecting a catalyst in the Exhaust system of an internal combustion engine before overtemperature according to the Preamble of claim 1.

To convert the contained in the exhaust gases of an internal combustion engine pollutants in less harmful substances is in modern Internal combustion engines provided a catalyst in the exhaust system. If the temperature of the catalyst above the minimum operating temperature the catalyst accelerates the chemical reactions between individual exhaust gas components, in particular those Reactions that lead to a conversion into less harmful substances such as for example, water and carbon dioxide. The catalyst will usually through the exhaust gases of the internal combustion engine and through the exothermic reactions between individual components of these exhaust gases heated up. For example, after starting the catalyst Internal combustion engine as quickly as possible to its operating temperature to heat up, the catalyst can be installed as far as possible upstream in the exhaust system, i.e. at a point where the exhaust gas temperature is very high. On the other hand, however, represents that the maximum allowable temperature of the catalyst not exceeded, otherwise the catalytic converter will be damaged or  is completely destroyed. The risk of exceeding the maximum permissible catalyst temperature is the greater, the further upstream the catalyst is installed in the exhaust system. The installation The location must therefore be as fast as possible Heating of the catalyst and adequate protection against over temperature can be optimized. Since in this optimization process the worst case with regard to a possible exceeding of the maximum permissible temperature must be taken into account inevitably cuts in the attainable heating time of the Kataly sators or other arrangements must be made Protection of the catalyst against overtemperature.

State of the art

There are already individual methods and devices for protecting the Catalyst known. From DE 23 40 541 A1, for example known in operations in the internal combustion engine that lead to an unzu casual temperature increase in the exhaust system or in the catalytic converter lead, the fuel metering or the supply of air / force partially interrupt the mixture of substances.

The invention has for its object the catalyst in the exhaust gas system to optimally protect an internal combustion engine.

This object is by claim 1 and the following be solved advantageous refinements and developments.

Advantages of the invention

The invention has the advantage that it provides optimal protection of the Offers catalyst in the exhaust system of an internal combustion engine and nevertheless a very short heating-up time of the catalyst is possible.  

In the protection system according to the invention depends on the operating state the internal combustion engine and / or environmental conditions a maxi times allowable catalyst temperature and it is a deed neuter catalyst temperature can be determined. Depending on the maxi times the permissible catalyst temperature and the actual catalyst measures to cool the catalyst can be taken be opened. This has the advantage that both the actual Zu level of the catalyst as well as the effectiveness of possibly meeting the measures are taken into account and thus a very reliable and efficient protection system is available. Depending on the cooling requirement of the catalyst and according to the cooling potential of the individual measures decided which measure to use. With that the Catalyst temperature regulated by the staggered measures. Egg ne control of the measures used is achieved by the Catalyst temperature and, if necessary, comparison with reference values or Comparison of the effects of the individual measures on the catalytic converter gate temperature possible. The system according to the invention is diagnosed thus the effectiveness of the individual measures independently.

If a first predefinable threshold value for the difference from the maximum permissible catalyst temperature and the actual kata If the temperature falls below the lysator temperature, the first measures are taken Cooling of the catalyst hit.

It is particularly advantageous to set further threshold values for the difference to be specified and if the further threshold values are undershot, successively Siv to take further measures to cool the catalyst.

The maximum permissible catalyst temperature depends on the he Waiting energy flow of the internal combustion engine and / or from the existing NEN cooling potential determined by at least one of the operating Characteristics or environmental characteristics outside temperature, vehicle ge speed, speed of the internal combustion engine, octane number of the  Fuel or operating condition of a device for controlling the Traction slip is characterized. Furthermore, with strong Gradient of the actual catalyst temperature another value be specified for the maximum permissible catalyst temperature - in particular a smaller value with increasing catalyst temperature door. The measures are taken when the catalyst temperature rises initiated earlier and thus the thermal dead time of the Ge entire system also compensated for under dynamic operating conditions.

The actual catalyst temperature is measured or from the Heating current from a heated exhaust gas probe or from the upstream of the Kata measured exhaust gas temperature or using a Model determined from operating parameters of the internal combustion engine.

The invention is very flexible and universally applicable, because one Numerous options for specifying the maximum permissible kata lysator temperature, to determine the actual catalyst temperature and for cooling the catalyst is provided.

drawing

The invention is based on the Darge in the drawing presented embodiments explained.

Show it

Fig. 1 shows an internal combustion engine with a catalyst and other components that are important for the invention and

Fig. 2 is a flow chart of the method according to the invention.

Description of the embodiments

In Fig. 1, an internal combustion engine 100 and some components that are important in connection with the invention are shown schematically. The internal combustion engine 100 is supplied via an intake tract 102 to the air / fuel mixture and the exhaust gases are discharged into an exhaust duct 104 . In the intake tract 102 - seen in the flow direction of the intake air - an air flow meter or air flow meter 106 , for example a hot-wire air flow meter, a throttle valve 108 with a sensor 110 for detecting the opening angle of the throttle valve 108 and at least one injection nozzle 112 are attached. An exhaust gas probe 114 , a temperature sensor 116 , a pre-catalytic converter 118 with a temperature sensor 120 and a main catalytic converter 122 with a temperature sensor 124 are arranged in the exhaust gas duct 104 , as seen in the flow direction of the exhaust gas. To the pre-catalyst 118 around a bypass channel leads 126, that is, the bypass passage 126 connects the area of the exhaust duct 104 upstream of the primary catalytic converter 118 to the area of the exhaust passage 104 downstream of the primary catalytic converter 118th In the bypass channel 126 , a shut-off valve 128 is arranged, with which the bypass channel 126 can be completely or partially closed.

A speed sensor 130 and a temperature sensor 132 are attached to the internal combustion engine 100 . Furthermore, the internal combustion engine 100 has, for example, four spark plugs 134 for igniting the air / fuel mixture in the cylinders. The output signals of the air flow meter or air mass meter 106 , the sensor 110 for detecting the opening angle of the throttle valve 108 , the exhaust gas probe 114 , the temperature sensors 116 , 120 and 124 , the speed sensor 130 and the temperature sensor 132 are fed to a central control device 136 via corresponding connecting lines. The control unit 136 evaluates the sensor signals and controls the injection nozzle or injectors 112 , the spark plugs 134 and the shut-off valve 128 via further connecting lines.

All of the components shown in FIG. 1 are not absolutely necessary for carrying out the method according to the invention. Which components are required depends on the embodiment of the inven tion. For example, the bypass channel 126 with the shut-off valve 128 is not absolutely necessary to carry out the method according to the invention. If these components are present, however, they can advantageously be included in the process according to the invention. Even the pre-catalyst 118 is dispensable since the invention can be used both to protect pre-catalysts and to protect main catalysts. The use of the invention to protect the main catalytic converter 122 is particularly recommended when there is no pre-catalytic converter 118 . Because it makes in principle no difference whether the invention is used to protect the primary catalytic converter 118 or to protect the main catalyst 122 is below no longer lyst between Vorkata 118 and main catalyst 122 distinguished and generally speaking instead of catalyst, unless it specific things are addressed for the pre-catalyst 118 or the main catalyst 122 .

Essentially, the cooling potential is determined in the invention from the operating state of the internal combustion engine 100 and the ambient conditions, which is currently available for cooling the catalytic converter. Depending on the cooling potential, a maximum permissible catalyst temperature TMax is specified. The higher the cooling potential, the higher TMax will be. Furthermore, the actual catalyst temperature T actual is determined. Depending on how close TIst is to TMax, different measures are taken to cool the catalytic converter. If TIst is so far from TKat that there is no danger to the catalyst, no measures are taken for cooling. Details of the sequence of the method according to the invention and of the measures used for cooling the catalyst are shown in FIG. 2 and described in the associated text.

Figure 2 shows a flow diagram of the invention. In a first step 200, the cooling potential present under the current operating and ambient conditions is determined and a maximum permissible catalyst temperature TMax is specified as a function thereof. The cooling potential indicates whether a strong or only a weak cooling effect can be achieved. For example, a higher cooling effect can be achieved at a low outside temperature than at a high outside temperature. Consequently, a higher value for TMax is specified at a low outside temperature than at a high outside temperature. Likewise, the vehicle speed can influence the cooling potential and thus TMax, since at a high vehicle speed a stronger air flow is available to cool the catalytic converter than at a low vehicle speed. Furthermore, the speed of the internal combustion engine can be taken into account when specifying TMax, since the heating power of the exhaust gases is low at a low speed and a higher value for TMax can therefore be specified. The octane number of the fuel used can also be taken into account, since if the octane number is high, interventions to reduce knocking are generally less necessary, and therefore the exhaust gas temperature is lower and consequently a higher value for TMax is permissible. If a traction control system is available and no measures to reduce traction slip are currently active, a higher value for TMax can also be specified.

In addition to the operating and environmental parameters described here, also change the change in these parameters TMax. For example With a rapidly falling speed, this would be a higher value for TMax be specified as with a slowly falling speed or with steep gender speed.  

After the maximum permissible catalytic converter temperature TMax has been specified in step 200, a step 202 follows in which the actual catalytic converter temperature T actual is determined. This can be done by a direct measurement with the temperature sensors 120 or 124 . Furthermore, TIst can also be determined from the exhaust gas temperature immediately upstream of the catalytic converter, the exhaust gas temperature being detected by the temperature sensor 116 . The exhaust gas temperature can also be determined with the aid of the exhaust gas sensor 114 , for example from the heating current which is required to keep the exhaust gas sensor at a predetermined temperature. Furthermore, the catalyst temperature can be determined with the aid of a model, which includes, for example, the operating parameters speed and load.

Step 202 is followed by step 204, in which the difference dT is formed from the maximum permissible catalyst temperature TMax and the actual catalyst temperature TIst. A step 206 follows, in which a query is made as to whether the temperature difference dT determined in step 204 is smaller than a predeterminable threshold value S1. If this is the case, cooling of the catalyst is required in order to prevent the maximum permissible catalyst temperature TMax from being exceeded. Consequently, if the query of step 206 applies, step 208 follows in which one or more measures for cooling the catalytic converter are carried out, which are referred to below as measure A. If the invention is used to protect the pre-catalytic converter 118 and a bypass duct 126 is present, the measures A may consist of opening the shut-off valve 128 in the bypass duct 126 and thus diverting the exhaust gases around the pre-catalytic converter 118 . As a result, the precatalyst 118 is cooled, more precisely, it cools down as a result of the reduced heating power or the temperature rise is at least slowed down.

Furthermore, within the framework of measures A, a cooling of the catalytic converter can be achieved in that the head wind is deflected onto the exhaust pipes in front of the catalytic converter and / or onto the catalytic converter itself, that any insulating shells of the exhaust pipes are opened, that in a double-walled exhaust system the space is flowed through with air or that the active length of the exhaust duct 104 upstream of the catalyst is extended by connecting a section, the additional section preferably being in the driving wind range.

All measures A have the advantage that they do not lead to a com cause continued loss and that the pollutant emission is not or only ge is slightly increased. However, they are each with a certainty sen effort associated so that usually depending on the measures A because only those are realized that are at the respective distillery engine type are already provided for other reasons or can be realized with reasonable effort.

If the query of step 206 is not fulfilled, in other words, if the temperature difference dT is greater than the threshold value S1, then Step 206 is followed by a step 210. In step 210 who which measures A may deactivate, that is, if the measures A in a previous pass of the flow chart in step 208 have been activated, they will be in the current run in step 210 deactivated again. With step 210, the run of the Flow chart ended and can start over.

The functional unit of the flow chart described consists of a comparison of the temperature difference dT with a threshold value (Step 206) and the activation (step 208) or deactivation (Step 210) dependent on measures for cooling the catalyst whether the temperature difference dT is smaller or larger than that Threshold, exists four times in total, but with below  different threshold values and different measures. For the The threshold values S1, S2, S3 and S4 are used for comparisons and depending on the results of the comparisons, measures A, B, C and D activated or deactivated to cool the catalyst. The Threshold values S1, S2, S3 and S4 are graded according to urgency, d. H. they decrease in that order.

For example, if the threshold S1 is undershot, it is cool development of the catalyst is only advisable, if the However, threshold S4 is urgently required. When you reach the Threshold S1 is the actual value T actual of the catalyst temperature relatively far from the maximum permissible catalyst temperature TMax away. When the threshold value S4 is reached, the actual value Tact is the catalyst temperature, on the other hand, is already very close to the maximum permissible catalyst temperature TMax, so that a low actual increase in the actual value T is the catalyst temperature to one Exceeding the maximum permissible catalyst temperature TMax would ren. The measure to be activated may increase accordingly men A, B, C and D to cool the catalyst the priority of Cooling effect compared to driving comfort, fuel consumption and the exhaust gas behavior, d. H. the cooling effect is becoming more and more important laid and a poorer driving comfort or a higher fuel consumption or poorer exhaust behavior. in the individually, the flow chart after step 208 continues as follows continue:

A query follows in step 212 as to whether the temperature difference dT is smaller than the threshold value S2. If this is the case, step 212 is followed by step 214. In step 214, measures B for cooling the catalyst are activated. The measures B serve to reduce the engine charge. This can be done by an intake manifold adjustment, which leads to a lower charge of the internal combustion engine 100 , or by a camshaft adjustment, which also leads to a lower charge. If the query from step 212 is not fulfilled, step 216 follows, in which measures B may be deactivated. The flow of the flow chart is ended at step 216 and can begin again at step 200.

In the query of step 218, which follows step 214, the temperature difference dT is compared with the threshold value S3. If dT is smaller than S3, step 220 follows in which measures C are activated. If, on the other hand, dT is greater than S3, step 218 is followed by step 222, in which measures C may be deactivated. The measures C include a drastic reduction in the engine charge by partially closing the throttle valve 108 . The flow of the flow chart is ended at step 222 and can begin again at step 200.

Step 220 is followed by step 224, in which the tempera door difference dT is compared with the threshold value S4. Is dT small ner than S4, step 224 is followed by step 226, in which measures D are activated. If dT is larger than S4, step 224 is followed by step 228, in which the measure men D may be deactivated. Measures D include a cool the catalyst by enriching the air / fuel mixture. The enrichment can be done in stages, if necessary. H. instead of one Several threshold values can be used against the threshold S4, which are each assigned a level of enrichment.

With both step 226 and step 228 is the pass of the flow chart ended and can begin again with step 200 nen.  

It is not essential to have four Kate as described above categories A, B, C and D of measures for cooling the catalyst watch. More or less can also be used. Next The measures described here do not necessarily have to be included in the combinations described here and the series described here sequence occur. It is essential for the invention that the maximum permissible catalyst temperature TMax depending on operating and Um conditions, the influence on the cooling possible of the catalyst have that the value TMax thus determined with the actual value TIst the catalyst temperature is compared and that different measures depending on the result of this comparison men can be used to cool the catalyst.

Claims (8)

1. System for protecting a catalyst ( 118 , 122 ) from overtemperature, characterized in that an actual catalyst temperature (Tact) can be determined, depending on the operating state of the internal combustion engine ( 100 ) and / or on ambient conditions and / or the change in the actual Catalyst temperature (TIst) a maximum permissible catalyst temperature (TMax) can be specified and, depending on the maximum permissible catalyst temperature (TMax) and the actual catalyst temperature (TIst), measures for cooling the catalyst ( 118 , 122 ) can be taken. 2. System according to claim 1, characterized in that a first threshold value (S1) for the difference (dT) from the maximum permissible catalyst temperature (TMax) and the actual catalyst temperature (TIst) can be predetermined and when the first threshold value (S1) is undershot first measures (A) for cooling the catalyst ( 118 , 122 ) are taken. 3. System according to claim 2, characterized in that further threshold values (S2, S3, S4) for the difference (dT) can be predetermined and, if the further threshold values (S2, S3, S4) are undershot, further measures (B, C, D ) to cool the catalyst ( 118 , 122 ). 4. System according to any one of the preceding claims, characterized indicates that the maximum permissible catalyst temperature (TMax) depending on the existing cooling potential and / or the change in cooling potentials and / or changing the actual catalyst temperature (Tact) is determined. 5. System according to claim 4, characterized in that the cooling potential by at least one of the operating parameters or environmental parameters external temperature, vehicle speed, speed of the internal combustion engine ( 100 ), octane number of the fuel or Betriebszu stood a device for controlling the traction slip is charac terized. 6. System according to any one of the preceding claims, characterized in that the actual catalyst temperature (TIst) is measured or determined from the exhaust gas temperature measured upstream of the catalyst ( 118 , 122 ) or with the aid of a model from operating parameters of the internal combustion engine ( 100 ) is determined. 7. System according to any one of the preceding claims, characterized in that for cooling the catalyst ( 118 , 122 ) at least egg ne of the measures

• Opening a shut-off valve ( 128 ) in a bypass channel ( 126 ) to the catalytic converter ( 122 ),
• - Redirecting the airstream to the exhaust duct ( 104 ) or the catalyst ( 118 , 122 ),
• - opening the insulating shells of the exhaust duct ( 104 ),
• - blowing air into the space between a double-walled exhaust duct ( 104 ),
• Increasing the active length of the exhaust gas duct ( 104 ) upstream of the catalytic converter ( 118 , 122 ),
• - Reduction of the air filling of the internal combustion engine ( 100 ) by adjusting the intake manifold or camshaft or reducing the opening angle of the throttle valve ( 108 ) or
• - Greasing of the air / fuel mixture is provided.

8. System according to any one of the preceding claims, characterized in that the measures for cooling the catalyst ( 118 , 122 ) can be subjected to a diagnosis by the values determined for the actual catalyst temperature (Tact) after initiation of the respective measures with reference values are compared or the values for the actual catalyst temperature (Tact) determined after the initiation of various measures are compared with one another.