DE4344137B4 - System for protecting a catalyst in the exhaust system of an internal combustion engine from overheating - Google Patents

Abstract

method for protecting a catalyst (118, 122) from overheating, in which a actual Catalyst temperature (TIst) can be determined, depending on the Operating state of the internal combustion engine (100) and / or environmental conditions and / or the change the actual Catalyst temperature (TIst) a maximum allowable catalyst temperature (TMax) is specifiable and dependent on the from the maximum allowable Catalyst temperature (TMax) and the actual catalyst temperature (TIst) measures (A, B, C, D) for cooling of the catalyst (118, 122) can be taken.

Description

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

to Conversion of contained in the exhaust gases of an internal combustion engine Pollutants in less harmful Substance is a catalyst in modern internal combustion engines in the exhaust system intended. When the temperature of the catalyst is above the minimum operating temperature the catalyst accelerates the chemical reactions between individual exhaust components, in particular such reactions, which translates into less harmful substances such as water and carbon dioxide lead. The catalyst is usually due to the exhaust gases of the internal combustion engine and by the exothermic reactions between individual components heated up this exhaust. For example, to the catalyst starting the internal combustion engine as quickly as possible to its operating temperature to heat up, a possible installation of the catalyst far upstream in the exhaust system, that is at a point where the exhaust gas temperature is very high. on the other hand it has to be sure that the maximum permissible Temperature of the catalyst is not exceeded because the catalyst otherwise damaged or even completely destroyed becomes. The risk of overrun the maximum allowed Catalyst temperature is but the greater, the further upstream of the catalyst installed in the exhaust system. The installation site must therefore usually with regard to a possible rapid heating of the catalyst and adequate protection before overtemperature be optimized. As in this optimization method the least favorable Case with regard to possible overshoot the maximum allowed Temperature must be taken into account, inevitably smears be made at the achievable heating time of the catalyst or it has to otherwise provisions to protect the catalyst from overheating to be hit.

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

In the DE 42 18 523 C1 a catalyst arrangement is described, which can be heated to an approximately constant temperature due to different ways to guide the exhaust gas. The plan is to split on two exhaust gas streams that emit different amounts of energy on their way to the catalyst. A relatively hot partial flow passes directly via a short and thin bypass line to the catalyst. The other, cooler partial flow is led to a silencer housing via a large main exhaust gas line, which has a large mass. In the muffler housing then the exhaust gas must first flow around the entire catalyst body before it can get into a flow opening, the exhaust loses more energy.

By the control of the partial flows by means of a flap, it is thus possible, the catalyst under all operating conditions at an optimal operating temperature to keep.

Of the Invention is based on the object, the catalyst in the exhaust system to optimally protect an internal combustion engine.

These The object is achieved by those in claim 1 and those described below advantageous embodiments and developments solved.

Advantages of invention

The Invention has the advantage that it provides optimum protection of the catalyst offers in the exhaust system of an internal combustion engine and still a very short heating of the catalyst is possible.

In the protection system according to the invention, depending on the operating state of the internal combustion engine and / or environmental conditions, a maximum permissible catalyst temperature can be predetermined and an actual catalyst temperature can be determined. Depending on the maximum allowable catalyst temperature and the actual catalyst temperature, measures may be taken to cool the catalyst. This has the advantage that both the actual state of the catalyst and the effectiveness of any measures to be taken are taken into account and thus a very reliable and efficient protection system is available. Depending on the cooling requirements of the catalytic converter and the cooling potential of the individual measures, it is decided which measure is used. Thus, the catalyst temperature is controlled by the staggered measures. A control of the measures used is possible by the achieved catalyst temperature and, if necessary, comparison with reference values or comparison of the effects of the individual measures on the catalyst temperature. The inventive system thus diagnoses the effectiveness of a individual measures.

If a first predefinable threshold for the difference from the maximum permissible Catalyst temperature and the actual catalyst temperature will be the first measures for the cooling of the Catalyst hit.

Especially It is advantageous to specify further threshold values for the difference and falling below the other thresholds successively more activities for cooling of the catalyst.

The maximum permissible Catalyst temperature becomes dependent of the expected energy flow of Internal combustion engine and / or determined by the existing cooling potential, the by at least one of the operating parameters or environmental parameters outside temperature, Vehicle speed, engine speed, octane number the fuel or operating condition of a device for regulation of the drive slip is characterized. Furthermore, in strong Gradients of the actual Catalyst temperature another value for the maximum allowable catalyst temperature be given - in particular a smaller value with increasing catalyst temperature. In order to become the measures initiated earlier with increasing catalyst temperature and thus becomes the thermal dead time of the entire system even under dynamic operating conditions compensated.

The actual Catalyst temperature is measured or from the heating of a heated exhaust gas probe or measured from the upstream of the catalyst Exhaust temperature determined or using a model of operating characteristics of Internal combustion engine determined.

The Invention is very flexible and unviversell applicable, as a Variety of possibilities to specify the maximum allowable Catalyst temperature, to determine the actual catalyst temperature and for cooling the catalyst is provided.

drawing

The Invention will be described below with reference to the drawing Embodiments explained.

It demonstrate

1 an internal combustion engine with a catalyst and other components that are important to the invention and

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

description the embodiments

In 1 are an internal combustion engine 100 and some components that are important in the context of the invention, shown schematically. The internal combustion engine 100 is via an intake system 102 Supplied air / fuel mixture and the exhaust gases are in an exhaust duct 104 issued. In the intake tract 102 are - seen in the direction of flow of the intake air - an air flow meter or air mass meter 106 For example, a hot wire air mass meter, a throttle 108 with a sensor 110 for detecting the opening angle of the throttle valve 108 and at least one injector 112 appropriate. In the exhaust duct 104 are - seen in the direction of the exhaust gas - an exhaust gas probe 114 , a temperature sensor 116 , a precatalyst 118 with a temperature sensor 120 and a main catalyst 122 with a temperature sensor 124 arranged. To the pre-catalyst 118 A bypass channel leads around 126 that is the bypass channel 126 connects the area of the exhaust duct 104 upstream of the precatalyst 118 with the area of the exhaust duct 104 downstream of the precatalyst 118 , In the bypass channel 126 is a shut-off valve 128 arranged with which the bypass channel 126 can be completely or partially closed.

At the internal combustion engine 100 are a speed sensor 130 and a temperature sensor 132 appropriate. Furthermore, the internal combustion engine has 100 For example, four spark plugs 134 to ignite 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 become a central control unit 136 supplied via corresponding connecting lines. The control unit 136 evaluates the sensor signals and controls the injection nozzle or injection nozzles via further connecting lines 112 , the spark plugs 134 and the shut-off valve 128 at.

For carrying out the method according to the invention are not necessarily all in 1 required components required. Which components are needed depends on the embodiment of the invention. For example, the bypass channel 126 with the shut-off valve 128 not absolutely necessary for carrying out the method according to the invention. However, if these components are present, they can be advantageously included in the process of the invention. Even the pre-catalyst 118 is dispensable, since the invention can be used both for the protection of precatalysts and for the protection of main catalysts. The use of the invention to protect the main catalyst 122 especially recommended if no pre-catalyst 118 is available. Since it makes no difference in principle, whether the invention for the protection of the precatalyst 118 or for the protection of the main catalyst 122 is used in the following, no longer between pre-catalyst 118 and main catalyst 122 instead of talking about catalyst, unless it is for the precatalyst 118 or the main catalyst 122 specific things addressed.

In essence, in the invention from the operating condition of the internal combustion engine 100 and the ambient conditions determines the cooling potential that is currently available for cooling the catalyst. Depending on the cooling potential, a maximum permissible catalyst temperature TMax is specified. The higher the cooling potential, the higher will be TMax. Furthermore, the actual catalyst temperature TIst is determined. Depending on how close TIst is to TMax, different measures are taken to cool the catalyst. If TIst is so far away from TKat that there is no danger to the catalyst, no cooling measures will be taken. Details of the course of the process according to the invention and the measures used for cooling the catalyst are shown in FIG 2 presented and described in the accompanying text.

2 shows a flow chart of the invention. In a first step 200 the cooling potential present under the current operating and environmental conditions is determined and a maximum permissible catalyst temperature TMax is specified as a function of this. 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 with a low outside temperature than with a high outside temperature. Consequently, at a low outside temperature, a larger value for TMax is given than at a high outside temperature. Likewise, the vehicle speed may affect the cooling potential, and thus TMax, because at high vehicle speed, a greater flow of air is available to cool the catalyst than at low vehicle speed. Furthermore, the speed of the engine can be taken into account in the specification of TMax, since at a low speed, the heating power of the exhaust gases is low and thus a higher value for TMax can be specified. Also, the octane rating of the fuel used can be taken into account, since with a high octane number, fewer interventions are usually required to reduce knocking and thus the exhaust gas temperature is lower, and consequently a higher value of TMax is allowed. If traction control is present and there are currently no measures to reduce traction, a higher value for TMax may also be specified.

Next the here described operating and environmental characteristics can also the change of this Characteristics TMax influence. For example, would with fast falling speed a higher value for TMax is given are considered as slowly decreasing speed or increasing speed.

After in step 200 given the maximum allowable catalyst temperature TMax under the given conditions, a step follows 202 in which the actual catalyst temperature TIst is determined. This can be done by a direct measurement with the temperature sensors 120 respectively. 124 respectively. Furthermore TIst can also be determined from the exhaust gas temperature immediately in front of the catalyst, wherein the exhaust gas temperature with the temperature sensor 116 is detected. The exhaust gas temperature can also be measured with the help of the exhaust gas sensor 114 be determined, 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 into which, for example, the operating parameters speed and load are received.

At step 202 closes a step 204 in which the difference dT is formed from the maximum allowable catalyst temperature TMax and the actual catalyst temperature TIst. It follows a step 206 in which is queried, whether in step 204 determined temperature difference dT is smaller than a predetermined threshold S1. If so, cooling of the catalyst is required to prevent the maximum allowable catalyst temperature TMax from being exceeded. Consequently, if the query of the step is true, it concludes 206 a step 208 in which one or more measures for the cooling of the catalyst are carried out, which are referred to below as measures A. If the invention for the protection of the precatalyst 118 is inserted and a bypass channel 126 exists, measures A may be that in the bypass channel 126 arranged shut-off valve 128 to open and thus the exhaust gases around the pre-catalyst 118 around pass. This will be the precatalyst 118 cooled, more precisely, it cools due to the reduced heat output or the temperature increase is at least slowed down.

Furthermore, as part of the measures A, a cooling of the catalyst can be achieved in that the wind on the exhaust pipes before the catalyst and / or the catalyst itself is deflected that any existing insulating the exhaust pipes are opened, that in a double-walled exhaust system, the gap is traversed with air or that the active length of the exhaust duct 104 is extended upstream of the catalyst by connecting a portion, wherein the additional portion is preferably in the driving wind range.

All activities A have the advantage that they do not lead to a loss of comfort and that the Pollutant emission is not or only slightly increased. However, they are each associated with a certain effort, so that in the Rule of the measures A only those are realized, which at the respective Internal combustion engine type are already provided for other reasons or can be realized with reasonable effort.

Is the query of the step 206 not satisfied, in other words, if the temperature difference dT is greater than the threshold S1, it follows step 206 a step 210 at. In step 210 If necessary, the measures A are deactivated, that is, if the measures A in a previous run of the flowchart in step 208 have been activated, they will step in the current pass 210 deactivated again. With the step 210 the flowchart is over and can start again.

The described functional unit of the flowchart consisting of a comparison of the temperature difference dT with a threshold value (step 206 ) and activating (step 208 ) or deactivate (step 210 ) of measures for cooling the catalyst depending on whether the temperature difference dT is smaller or larger than the threshold, is a total of four times, but with different thresholds and different measures. The thresholds S1, S2, S3 and S4 are used for the comparisons and, depending on the result of the comparisons, measures A, B, C and D can be activated or deactivated to cool the catalytic converter. The threshold values S1, S2, S3 and S4 are staggered according to urgency, ie they decrease in this order.

For example, if the threshold value S1 is undershot, cooling of the catalytic converter is only advisable, but it is urgently necessary if the threshold value S4 is undershot. When the threshold value S1 is reached, the actual value TIst of the catalyst temperature is still relatively far away from the maximum permissible catalyst temperature TMax. By contrast, when the threshold value S4 is reached, the actual value TIst of the catalyst temperature is already very close to the maximum allowable catalyst temperature TMax, so that a slight increase in the actual value TIst of the catalyst temperature would already lead to exceeding the maximum permissible catalyst temperature TMax. Accordingly, increases in the possibly to be activated measures A, B, C and D for cooling the catalyst, the Prirität the cooling effect compared to the ride comfort, fuel consumption and emission behavior, ie it is more and more emphasis on the cooling effect and a worse ride comfort or a higher fuel consumption and a poorer emissions behavior accepted. In particular, the flow chart is after step 208 as follows:
It follows in step 212 a query whether the temperature difference dT is smaller than the threshold value S2. If this is the case, follow step 212 a step 214 at. In step 214 the measures B are activated to cool the catalyst. The measures B serve to reduce the engine filling. This can be done by a Saugrohrverstellung, which leads to a lower charge of the internal combustion engine 100 leads, or by a camshaft adjustment, which also leads to a lower charge. Is the query of the step 212 not fulfilled, then one step closes 216 in which the measures B are deactivated if necessary. With step 216 the flowchart is finished and can be re-entered at step 200 kick off.

In the query of the step 218 who is in step 214 connects, the temperature difference dT is compared with the threshold S3. If d7 is smaller than S3, then a step closes 220 in which the measures C are activated. If dT is greater than S3, then step 218 a step 222 on, in which the measures C are possibly deactivated. The measures C include a drastic reduction in engine filling, characterized in that the throttle 108 partially closed. With step 222 the flowchart is finished and can be re-entered at step 200 kick off.

At step 220 closes a step 224 in which the temperature difference dT is compared with the threshold value S4. If dT is smaller than S4, then close step 224 a step 226 in which the measures D are activated. If dT is greater than S4, then step 224 a step 228 in which the measures D may be deactivated. The measures D include cooling of the catalyst by enrichment of the air / fuel mixture. The enrichment can possibly take place in stages, ie instead of a single threshold value S4, several threshold values can be used, to which one level of enrichment is assigned.

Both with step 226 as well as with step 228 the flowchart has finished, and can be redone with step 200 kick off.

It is not essential, as described above four categories A, B, C and D measures for cooling to provide the catalyst. It can also be more or less be used. Continue to have not necessarily the here described measures in the combinations described here and the order described here occur. Essential for the invention is that the maximum permissible Catalyst temperature TMax dependent of operating and environmental conditions, the influence on the cooling options have the catalyst that the thus set value TMax with the actual value TIst of the catalyst temperature and that depends on the Result of this comparison different measures for the cooling of the Catalyst can be used.

Claims (8)

Process for protecting a catalyst ( 118 . 122 ) before overtemperature at which an actual catalyst temperature (TIst) can be determined, in which, depending on the operating state of the internal combustion engine ( 100 ) and / or ambient conditions and / or the change of the actual catalyst temperature (TIst) a maximum allowable catalyst temperature (TMax) can be specified and in which depending on the maximum allowable catalyst temperature (TMax) and the actual catalyst temperature (TIst) measures (A, B , C, D) for cooling the catalyst ( 118 . 122 ) can be taken. Method according to Claim 1, in which a first threshold value (S1) for the difference (dT) can be predetermined from the maximum permissible catalyst temperature (TMax) and the actual catalyst temperature (TIst) and at which first measures (below the first threshold value (S1) A) for cooling the catalyst ( 118 . 122 ) to be hit. Method according to Claim 2, in which further threshold values (S2, S3, S4) for the difference (dT) can be predetermined and for which further measures (B, C, D) are successively applied when the further threshold values (S2, S3, S4) are undershot Cooling of the catalyst ( 118 . 122 ) to be hit. Method according to one of the preceding claims, in the maximum allowable Catalyst temperature (TMax) dependent from the existing cooling potential and / or the change the cooling potential and / or the change the actual Catalyst temperature (TIst) is determined. Method according to Claim 4, in which the cooling potential is determined by at least one of the operating parameters or environmental parameters outside temperature, vehicle speed, rotational speed (n) of the internal combustion engine ( 100 ), Octane number of the fuel or operating state of a means for controlling the traction slip is characterized. Method according to one of the preceding claims, wherein the actual catalyst temperature (TIst) is measured or from the upstream of the catalyst ( 118 . 122 ) measured exhaust gas temperature is determined or determined using a model from operating characteristics of the internal combustion engine. Method according to one of the preceding claims, in which for cooling the catalyst ( 118 . 122 ) at least one of the measures (A, B, C, D) - opening a shut-off valve ( 128 ) in a bypass channel ( 126 ) to the catalyst ( 122 ), - diverting 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 of a double-walled exhaust gas duct ( 104 ), - increasing the active length of the exhaust duct ( 104 ) upstream of the catalyst ( 118 . 122 ), - Reduction of the air charge of the internal combustion engine ( 100 ) by Saugrohrverstellung or camshaft adjustment or reducing the opening angle of the throttle valve ( 108 ) or - enriching the air / fuel mixture is provided. Method according to one of the preceding claims, in which the measures (A, B, C, D) for cooling the catalyst ( 118 . 122 ) can be subjected to a diagnosis by comparing the values for the actual catalyst temperature (TIst) determined after initiation of the respective measures (A, B, C, D) with reference values or, after initiating various measures (A, B, C, D ) are compared with each other for the actual catalyst temperature (TIst).