DE102004030301A1 - Operation of internal combustion engine comprises estimating future catalyst temperature from present and past engine parameter values and cooling catalyst if estimated temperature exceeds threshold value - Google Patents

Abstract

Operating an internal combustion engine with a catalytic converter comprises determining the values of a set of engine parameters affecting the catalyst temperature, estimating the catalyst temperature at a future time from the parameter values at the present and at least one previous time, and cooling the catalyst if the estimated temperature exceeds a threshold value. An independent claim is also included for an internal combustion engine control device (unspecified) adapted to carry out the above process.

Description

The The present invention relates to an operating method for an internal combustion engine with catalytic converter and a control device for carrying out such a method.

Out EP-A-0 231 611 discloses an operating method for an internal combustion engine. with the help of an empirically determined model the temperature the catalytic converter based on operating parameters of the engine, namely the air mass flow and the air-fuel ratio, is calculated and, if the calculation shows that the catalyst is a critical temperature reached, is intervened in the operation of the internal combustion engine regulatory, to prevent a further increase in temperature. In Scripture while there is talk of a "prediction" of the catalyst temperature, however, the prediction is always based on current values of the considered ones Operating parameters of the engine. That is, the time horizon of the prediction is the time span for a temperature compensation between the catalyst flowing through, among the considered current Operating parameters generated exhaust stream and the material of the catalyst is required. If the "prediction" shows that the Temperature of the catalyst over a critical value rises, then at the time this result is obtained, either the actual temperature of the catalyst already at the critical value, or at least by a corresponding one Control of the internal combustion engine created all conditions so that the catalyst temperature will inevitably reach the critical value shortly becomes. This forces a critical temperature to be chosen as the critical value below the temperature at which damage or accelerated aging of the catalyst actually starts, because only so can be guaranteed be avoided that a catalyst damaging overheating actually.

In In practice, it has proved necessary between one with the conventional one Method calculated temperature of the catalyst and a temperature in the case of damage of the catalyst due to overheating enters a safety distance of up to 30 K. this leads to to significant consumption disadvantages. If it were possible, the catalyst immediately operate below the temperature at which the damage starts, so could the fuel consumption of the internal combustion engine in comparison to a 30 K lower catalyst temperature by this safety margin reduce by about 2%.

It There is therefore a need for an operating method for an internal combustion engine and a controller to carry it out, that allow, the mentioned Safety distance between a critical temperature of the catalyst in the action to prevent overheating of the catalyst must be taken, and the temperature at the damage begins to diminish.

The Task is solved by an operating method with the features of claim 1 and a control unit according to claim 9.

The inventive method comprises as a method step the detection of a set of the tempera ture of the catalytic converter influencing operating parameters the engine. Which parameters are these depends on one for the calculation the catalyst temperature used mathematical model. In the already mentioned in the EP-A-0 231 611 used Model, these parameters are the air mass flow and the air-fuel ratio; it however, is easily conceivable, the calculation being based on other with these correlated parameters. Of course, besides Air mass flow and air-fuel ratio also additional Parameters such as the ambient temperature of the catalyst and the internal combustion engine, a measured at the internal combustion engine itself Temperature, the difference between current and optimal ignition timing, the torque reserve etc. taken into account become.

Based of the set of parameter values thus detected and at least one to an earlier At the time the set of values of the same parameter becomes the Temperature of the catalyst at a future time predicted.

one According to the first embodiment of the method, this is done by a trend of these values of each individual parameter assessed and the value of the parameter on the future Time is extrapolated.

that is, if e.g. due to an acceleration process, the air mass flow increases, so this is a comparison of the present and a past Detected air mass flow value, and a future mass air flow value is assuming a continuation of the perceived evolution predicts.

On the basis of the thus forecast future parameter values, a prognosis of the catalyst temperature is made at the future time. In this case, the mathematical model used to estimate the future catalyst temperature from the future parameter values may be an already known model, which is conventionally used to calculate the catalyst temperature from current operating parameter values.

one According to a second embodiment of the method, the prognosis takes place instead of moving from the current Time and the at least one earlier time recorded parameter values in each case the catalyst temperature at the respective times estimated and the apparent trend of the temperature in the future is extrapolated.

If the thus predicted temperature of the catalyst Exceeds limit, become action for cooling hit the catalyst. That is, set the measures for cooling already at a time when the predicted catalyst temperature not yet reached. Therefore, it is possible to set the limit higher as with conventional Method. There as well the time when the catalyst temperature reaches the limit, further in the future than at a current operating parameter value based Temperature calculation, stands for activities for cooling the catalyst has more time available, allowing for the cooling of the Catalyst possibly necessary intervention in the operation of the internal combustion engine can be less violent.

A Possibility, to cool the catalyst is that supplied to the internal combustion engine To be greased mixture, i. the air-fuel ratio on to set a value lower than that originally forecast for the future time.

As a general rule and independent of the kind considered Operating parameters can be provided that a predicted Operating parameters change is locked so that it can not be executed when detected that will make her overreach the limit value of the catalyst temperature would result.

The easiest way a forecast of future Values of operating parameters is a linear extrapolation of the present and a past value of a parameter. Depending on the available processing power of the operating procedure exporting ECU but are also more elaborate Forecasting methods such as extrapolation of a higher order or a regression calculation possible, each taking the consideration require parameter values at several past times. Also heuristic methods, in particular fuzzy logic methods, come as a forecasting process into consideration.

A different possibility The forecast is based on the current and past values of the Parameter to assess whether the load of the internal combustion engine and so that the temperature of the catalyst increases, and, if an increase the value of at least one parameter is determined to be the future one Estimated time is added by adding a for these parameters given increments to the current value this parameter. It is assumed that the parameter is defined so that its increase causes an increase in the catalyst temperature leads. A restriction in terms of the nature of the parameters is not associated with it, since each parameter, its increase to a decrease in the catalyst temperature leads, can be converted by sign reversal into a parameter, which grows with the catalyst temperature.

Both approaches described above, linear or other extrapolation and addition of a fixed increment be combined in an operating procedure by: they can be applied to different parameters.

Around can additionally increase the reliability of the process be provided that after the future parameter values have been estimated are the development of the relevant parameters monitored will and a change this parameter over the predicted values that are not known a priori Catalyst temperature lead could, is locked.

Further Features and advantages of the invention will become apparent from the following Description of exemplary embodiments with reference to the attached Characters. Show it:

1 a schematic representation of an internal combustion engine with downstream catalytic converter, to which the present invention is applicable;

2 a flowchart of a first embodiment of the operating method according to the invention;

3 a first modification of the method 2 ;

4 a second modification of the method 2 ; and

5 a flow chart of a second off design of the operating method according to the invention;

In the 1 is with 1 denotes a single combustion chamber of an internal combustion engine such as an Otto engine. At the combustion chamber 1 are at least one inlet valve 2 for fresh air, at least one outlet valve 3 for exhaust gas and a fuel injection valve 4 arranged, which fuel directly into the combustion chamber 1 atomized. In an inlet valve 2 upstream suction line 5 is one by a servomotor 6 adjustable throttle 7 arranged. Between the throttle 7 and the inlet valve 2 There is a (not shown) distributor, are supplied via the other, not shown in the figure combustion chambers with fresh air.

An air mass sensor 8th is in the intake pipe 5 in front of the throttle 7 arranged. Alternatively or additionally, for estimating the air flow rate of the internal combustion engine, a pressure sensor in the intake line could be used 5 downstream of the throttle 7 be arranged.

One from the exhaust valve 3 outgoing exhaust pipe runs to a catalytic converter 9 ,

A control unit 10 the internal combustion engine installed in a motor vehicle is equipped with an accelerator pedal 11 connected to detect a load request of the driver and on the basis of this load request, that of the sensor 8th detected mass air flow, one of a speed sensor 12 on a crankshaft 13 the engine detected speed and possibly other factors influencing the position of the throttle 7 and those from the injector 4 to specify the amount of fuel to be injected. The control unit 10 is in a known and not explained in more detail here way as a microcontroller with a CPU, a read only memory for storing an operating program and various required for the operation of the CPU characteristics and other parameters, a memory for variables used by the CPU and various input-output interfaces for the communication with the various sensors, the servomotor 6 and the injection valve 4 built up. The method according to the invention is part of the operating program of the control unit 10 implemented.

A first embodiment of the method is based on the flowchart of 2 explained. In the 2 shown method steps are repeated at times t _n-1 , t _n , t _{n + 1} , .... For the description, it is assumed that the instant t _n corresponds to the present.

In step S1, values P _i (t _n ) of a set {P _i } of operating parameters of the internal combustion engine are measured. These operating parameters include those of the air mass sensor 8th detected air flow rate of the internal combustion engine and the air-fuel ratio λ, with the aid of a λ-probe 14 be detected directly in the exhaust pipe or may be specified by the engine control in so-called pre-controlled operation. Alternatively, other parameter combinations could be detected, which are in a known relationship with the mentioned, for example, the pressure in the intake manifold and / or the opening angle of the throttle valve and the sensor 12 detected speed, which allow a conclusion on the gas flow rate of the internal combustion engine, the flow rate of the injection valve 4 from which, together with the gas flow rate, adjusted by the λ-control, the air-fuel ratio can be estimated, etc ..

Further parameters which may belong to the set {P _i } are, for example, the temperature of the wall of the combustion chamber 1 and / or the coolant or oil temperature, which have an influence on the temperature of the exhaust gas fed to the catalyst, or the ambient temperature, which is the heat losses of the catalyst 9 affected. The position of the accelerator pedal 1 itself can be counted to the parameter set {P _i }, but it does not have, since its influence on the catalyst temperature indirectly, via the control unit 10 depending on the accelerator pedal position influenced operating parameters such as throttle position, air flow rate, etc. is detected.

Also, the time derivatives of the parameters mentioned above as belonging to the set {P _i } may themselves belong to the parameter set; their consideration makes it possible to base the catalyst temperature forecast not only on the currently measurable values of the individual parameters, but also on the values which they are likely to assume in the near future.

In step S2, the controller calculates 10 from the parameter values P _i (t _n ) thus acquired and the parameter values P _i (t _n-1 ) acquired at the previous time t _n-1 and in each case the difference Δ _{n, i} = P _i (t _n ) -P _i (tn _-1 ). It then stores the new set of parameter values P _i (t _n ) in step S3, overwriting the oldest stored set. In the exemplary embodiment considered here, only one set of parameter values is stored in each case, ie the parameter values P _i (t _n-1 ) are overwritten.

In step S4, for the future time t _{n + 1,} parameter values P * _i (t _{n + 1} ) are predicted by adding the difference Δ _{n, i} to the current parameter values P _i (t _n )

In step S5, the controller calculates 10 a predicted catalyst temperature T * (t _{n + 1} ) based on the predicted parameter values P * _i (t _{n + 1} ).

In step S6 it is checked whether the predicted for the time t _{n + 1} temperature T * (t _{n + 1} ) exceeds a maximum permissible for the continuous operation of the catalyst temperature T _C. If not, then the operating parameter values P * _i (t _{n + 1} ) based on the prediction of step S5 are straightforward and the engine can be operated with these parameter values. In this case, the method immediately jumps to the driving of the internal combustion engine in step S10. If the verification shows that the predicted temperature is higher than the temperature T _C , then there are measures to protect the catalyst 9 required before overheating. For this purpose, the control unit checks 10 first in step S7, whether the current operating conditions correspond to rich combustion or stoichiometric to lean combustion. In the former case (λ <1), the mixture must be further enriched to protect the catalyst; accordingly, in step S8, the air-fuel ratio of the engine is decreased.

If In step S7, lean combustion is detected is oxygen stored in the catalyst, and a sudden enrichment of the mixture would become its quick implementation and thus to a further increase in temperature to lead. In this case, the load of the internal combustion engine must be reduced become.

It follows the control of the motor (S10), each by the step S8 or S9 corrected values of the throttle position or the Air flow rate and / or the injection quantity.

In a first modification of the method of 2 is the step S4 of 2 by the step S4 'of 3 replaced. Instead of adding to the present value P _i (t _n ) only the change Δ _{n, i} calculated in step S2, this change is previously multiplied by a factor a which is greater than 1 in step S4 '. This can be understood as the introduction a safety margin taking into account that the change in the parameter P _i could be stronger in the future than in the past, or as the forecast for a time t _n + a δ, where δ = t _{n + 1} - t _n , ie a time farther in the future than t _{n + 1} The probability of exceeding the limit value T _{C is} predicted in the method according to FIG 3 bigger than the one after 2 That is, the prognosis is more uncertain, but an impending exceedance of the critical temperature T _C is detected sooner, and the changes of the load or the air-fuel ratio required to prevent the overshoot can be made smaller than in the case of FIG 2 , This results in highly dynamic operation of the engine automatically increased safety distance to the limit temperature T _C , while stationary operation can be driven very close to the limit temperature T _C and thus fuel-saving.

It is obvious that there are a number of other methods with which predicted operating parameter values P * _i (t _{n + 1} ) can be calculated. Thus, for example, a linear compensation function can be calculated by linear regression on the basis of current and several past measured values of the relevant operating parameters, and the value of this compensation function at time t _{n + 1} can be used as the forecast value.

Another modification of step S4 is in 4 shown. Here S4a is judged for the parameter P _i in only step, whether the sign of its change Δ _{n is i} such that the modification results in an increase in the catalyst temperature. If not, the change is disregarded: the current value P _i (t _n ) is also assumed as the forecast value for the time t _{n + 1} in step S 4 b. However, if the change .DELTA.n _{, i} leads to an increase in the temperature, then in step S4c the predicted value P * _i (t _{n + 1} ) is the sum of the current parameter value P _i (t _n ) and one predetermined for this parameter Increment Incr _i assumed. A value which corresponds to the maximum possible rise of the parameter P _i from the time t _n to the time t _{n + 1} is expediently used as the increment Incr _i . Such a maximally possible increase may, for example, result for the mass air flow as a parameter from the fact that the possible acceleration of the vehicle in which the internal combustion engine is installed and with it the increase of the crankshaft speed or of the air mass flow is limited by the ratio of available power of the engine Internal combustion engine for vehicle mass. For a parameter such as the air-fuel ratio, a maximum increment in that from the controller 10 be established.

5 shows a flowchart of a second embodiment of the method. As in the case of 2 The steps of this method are cyclically at times t _n-1, t _n, t _{n + 1,} ... are repeated, it being assumed for the description that the time t _n the presence corresponds.

Step S1 is identical to the step of FIG 2 and will not be described again. From the parameter values P _i (t _n ) measured in step S 1 for the instant t _n, the temperature T (t _n ) of the catalyst at the present time t _{n is} calculated in step S 2 ''. In step S3 '' the difference Δ _n between the current temperature T (t _n ) and the temperature T (t _n-1 ) stored during the previous iteration is calculated at time t ( _n-1 ). In step S4 ", the current temperature T (t _n ) is stored for use in the upcoming iteration. The for the time t _{n + 1} to be forecasted temperature T * (t _{n + 1)} in step _n S5 '' by simple extrapolation of the observed development trend of the temperature, by adding of Δ to T (t _n) is obtained. The subsequent steps S6 to S10 are again with those of the method of 2 identical and will not be explained again.

The computational effort is significantly smaller in this method than in the method of 2 because only a single value, the temperature, and not all parameters P _i need to be extrapolated. If the temperature is a monotonous function of the individual parameters P _i , however, this does not involve a significant loss of forecast reliability.

1

combustion chamber

2

intake valve

3

outlet valve

4

Fuel injection valve

5

suction

6

servomotor

7

throttle

8th

Air mass sensor

9

catalytic converter

10

control unit

11

accelerator

12

Speed sensor

13

crankshaft

14

λ-probe

Claims (9)

Operating method for an internal combustion engine with catalytic converter ( 9 ), comprising the steps of a) detecting values of a set of the temperature of the catalytic converter ( 9 ) influencing operating parameters (P _i (t _n )) of the internal combustion engine (S1); b) estimating the temperature (T * (t _{n + 1} )) of the catalytic converter ( 9 ) at a future time (t _{n + 1} ) on the basis of the values (P _i (t _n ), P _i (t _n-1 )) of the parameters at the present (t _n ) and at least one past time (t _n-1 ) (S4; S4 ';S4a-S4c); c) if the temperature (T * (t _{n + 1} )) estimated in step b) exceeds a limit value, cooling (S7-S10) of the exhaust gas catalytic converter ( 9 ). Operating method according to claim 1, wherein step b) comprises the following substeps: b1) estimating the values (P * _i (t _{n + 1} )) of the parameters of the set at the future time (t _{n + 1} ) on the basis of the values (P _i (t _n ), P _i (t _n-1 )) of the parameters at the present (t _n ) and at least one past time (t _n-1 ) (S4; S4 ';S4a-S4c); b2) estimating the temperature (T * (t _{n + 1} )) of the catalytic converter ( 9 ) at the future time based on the parameter values (S5) estimated in step b1). Operating method according to claim 1, in which step b) comprises the following sub-steps: b1 ') estimating the temperatures (T (t _n ), T (t _n-1 )) of the catalytic converter ( 9 ) at the present (t _n ) and at least one past time (t _n-1 ); b2 ') estimating the temperature (T * (t _{n + 1} )) of the catalytic converter ( 9 ) at the future time (t _{n + 1} ) based on the estimated temperatures in step b1 ') (S5''). Operating method according to one of claims 1 to 3, wherein for cooling the catalytic converter ( 9 ) the mixture supplied to the internal combustion engine is enriched (S8). Operating method according to one of claims 1 to 3, wherein for cooling the catalytic converter ( 9 ) the load of the internal combustion engine is reduced below a value corresponding to a current accelerator pedal position (S9). Operating method according to one of the preceding claims, in in step b) the future Value of at least one parameter from its current value and its value is linearly extrapolated to the one past time becomes. Operating method according to one of the preceding claims, in which it is judged in step b) on the basis of the current and past values of one of the parameters whether the change of the parameter leads to an increase of the temperature of the catalytic converter ( 9 ) (S4a) and that, if determined, the value of the parameter in question is estimated at the future time by adding (S4c) a given increment (Incr _i ) to the current value of the parameter (P _i (t _n )) , Operating method according to one of the preceding claims, in the speed of the set of parameters, the mass air flow, and / or the Air-fuel ratio belongs / belong to the internal combustion engine. control unit for one Internal combustion engine that is set up, the method after a of the preceding claims perform.