EP1297249B1 - Method for operating an internal combustion engine in particular in a motor vehicle - Google Patents

Description

State of the art

The invention is based on a method for operating an internal combustion engine, in particular of a motor vehicle, in the fuel in a lean mode and in a rich mode injected into a combustion chamber and between the two modes is switched. The invention also relates to a corresponding internal combustion engine and a control unit for such an internal combustion engine.

In diesel, as well as in gasoline internal combustion engines, it is known, a NOx storage catalyst for reducing the Use pollutant emissions. For the operation of the NOx storage catalytic converter it is necessary that Internal combustion engine from lean mode to fat Switch operating mode. In this fat mode is regenerates the NOx storage catalyst. After Carrying out the regeneration becomes the internal combustion engine switched back to the lean mode again.

When switching between the lean and the fat Operating mode must be ensured in particular no switchover or the like. arises. The the Internal combustion engine supplied air mass, as well as the Internal combustion engine injected fuel quantity must therefore when switching between the two modes of operation be influenced, in particular that of the Internal combustion engine generated torque no peaks or Jumps or the like. having.

Purpose and advantages of the invention

The object of the invention is a method for operating an internal combustion engine, in particular of a motor vehicle to create a switch between the fat ones Mode and lean mode without any Switching pressure or the like is possible.

This task is used in a method of the beginning mentioned type according to the invention achieved in that a Air mass and an injection quantity for lean operation constantly be determined that from the air mass and out the injection amount is a lambda for lean operation is constantly determined that one of the lambda for the Lean operation deviating Lambda for the rich mode and for which transitions are given there, and that a desired air mass for the rich mode and for the Transitions there from the Lambda for lean operation and from the lambda for the rich mode and for the Transitions there is determined.

The control and / or regulation of the internal combustion engine during Transition from lean to fat mode, as well in the fat mode itself, is thus on the Basis of injection quantity and air mass performed, the ansich for the lean mode are provided. From this air mass and injection quantity for lean operation is a lambda for the leaner Operating mode calculated. This lambda comes with a lambda linked to the desired lambda for transition into the rich operating mode or for the rich operating mode as represents such. From this link of the calculated Lambdas for the lean mode as well as the desired Lambdas for the rich mode or for the transition There, the target air mass is then determined in which the Internal combustion engine during transition to rich mode or in the rich operating mode itself is supplied. It It is understood that in determining the desired air mass also other operating variables of the internal combustion engine play a role.

Overall, the inventive control and / or Control is an air-guided system. It is located on the Basis of lambda for lean operation in dependence from the desired lambda for the rich mode or for the transition there calculates the target air mass, the the internal combustion engine to be supplied. The Internal combustion engine is thus in the first step with the help a change in the air mass towards the fat Operating mode influenced.

It is understood that corresponding also for a Switching the engine from the rich Operating mode in the lean mode applies.

It is essential that in the inventive control and / or regulation a jump in the desired air mass harmless remains. The actual air mass and thus also the nominal injection quantity and that generated by the internal combustion engine Torque is jump-free. Any tips or Jumps of the generated by the internal combustion engine Torques are safely avoided in this way.

It is particularly advantageous if the lambda for the Lean operation in an efficiency for lean operation and the Lambda for the fat mode in an efficiency be converted for the fat mode when the Efficiency for lean operation with the air mass for the Meager operation is multiplied, and if that Multiplication result by the efficiency for the is divided into rich operating mode.

This represents a particularly simple and effective way and Way in which the lambda for lean operation with the given lambda for the rich mode and for the Transitions can be linked there. It is essential doing that the two lambdas each in one Efficiency to be converted. This transformation allows easy linking of the respective sizes and the calculation of the desired air mass according to the invention it.

In an advantageous embodiment of the invention, in the measured or simulated an actual air mass or is modeled, is a setpoint for the lambda in the fat mode and for the transitions there in Dependence on the air mass and the injection quantity for determines the lean operation, and it becomes a target injection quantity for the fat mode and for the Transitions there from the actual air mass and the setpoint determined for the lambda.

As already mentioned, the inventive Control and / or regulation an air-guided system. The desired air mass according to the invention as a function of determined the respective desired lambda. In the above development of the invention, the actual air mass, So the actual of the internal combustion engine supplied air mass measured. It is also possible the actual air mass from other operating variables of To simulate or model internal combustion engine. These Actual air mass changes according to the changes the target air mass..A change in the actual air mass has According to the invention, a change in the desired injection quantity result. This means that the target injection quantity ultimately adapted to the desired air mass. All in all thus always a desired air mass and a target injection quantity generated on the one hand by the desired Lambda depend on the other hand always on each other are coordinated.

By changing the target injection quantity in Dependence on the actual air mass and thus in Depending on the target air mass is thus the completed air-guided system according to the invention. There the desired injection quantity and the actual air mass always Ensuring that there is no coordination Cracks or tips or the like. that of the internal combustion engine generated torque can arise.

It is particularly advantageous if the desired value for the Lambda in rich mode and for transitions there from a target efficiency for the fat Operating mode and for the transitions there is determined and if the target efficiency by dividing from the actual air mass by the said multiplication result is determined.

This represents a particularly simple and effective way and Way, with which the target injection quantity are calculated can. It is essential, in turn, that a transformation from an efficiency to a lambda is performed. Furthermore, it is important that the from the Air mass and the injection quantity for lean operation resulting multiplication result also at the Determination of the desired injection quantity according to the invention is used. In this way, even at the target injection quantity ensures that when switching between the operating modes no jump in the target injection quantity arises.

In an advantageous embodiment of the invention is the conversion of a lambda into an associated one Efficiency or vice versa by means of a reference characteristic and by means of additive and / or multiplicative Corrections performed. This way, on the one hand achieved that conversion between a lambda and an efficiency or vice versa with a possible low computational effort can be made. On the other hand, this ensures that Changes of the internal combustion engine with the help of corrected for additive and / or multiplicative adaptation can be.

In a further advantageous embodiment of the Invention, in which the injection with one in the Combustion chamber fuel to be injected in two or more Part injections will be injected, the Start of injection or the start of control and / or the Injection duration or the activation duration of Partial injections depending on the operating mode and / or depending on operating variables of Internal combustion engine determined differently. That's it particularly advantageous if for the start of injection and / or the injection duration when switching between the Operating modes a hysteresis is taken into account.

These measures make it particularly easy possible, the inventive method for operating a Apply engine to engines that have two or three more partial injections per fuel injection carry out. This is especially true for diesel engines the case. Likewise this can especially in internal combustion engines with direct injection come into use.

Of particular importance is the realization of the inventive method in the form of a Computer program for a control unit of the Internal combustion engine is provided. The computer program is executable on a computer of the controller and the Execution of the method according to the invention suitable. In In this case, therefore, the invention by the Computer program realized, so this Computer program in the same way represents the invention like the method that the Computer program is suitable. The computer program can preferably stored on a flash memory. As a computer, a microprocessor may be provided. The Control unit in which the computer program is included is in particular for controlling and / or regulating a Plurality of Betriebsgrößen.der internal combustion engine intended.

Other features, uses and benefits of Invention will become apparent from the following description of embodiments of the invention shown in FIGS the drawing are shown. All form described or illustrated features alone or in any combination the subject of the invention, regardless of their summary in the Claims or their dependency as well as independently from their formulation or presentation in the description or, in the drawing.

Embodiments of the invention

FIG. 1

shows a schematic block diagram of a Embodiment of an inventive Method for operating an internal combustion engine in particular of a motor vehicle,

FIGS. 2a and 2b

show schematic block diagrams of Embodiments for converting a Efficiency according to lambda and vice versa,

FIG. 3

shows a schematic block diagram of a Embodiment for use different maps for the drive time a main injection,

FIG. 4

shows a schematic block diagram of a Embodiment for the inclusion of a Hysteresis at injection of fuel in the internal combustion engine, and

FIG. 5

shows a schematic diagram for the Connection between an efficiency and Lambda when using a hysteresis.

The following method for control and / or regulation an internal combustion engine is based on a diesel engine described. It is, however, on it noted that the method described in adapted manner also in a gasoline internal combustion engine can be used. Especially It is possible, the described method in a Use internal combustion engine with direct injection.

To reduce the pollutant emissions of a diesel engine is a NOx storage catalyst intended. This NOx storage catalyst is provided, the internal combustion engine alternately in one lean and operate a fat mode. In the become the lean mode nitrogen oxides received by the NOx storage catalyst and cached. The NOx storage catalyst is with loaded with nitrogen oxides. Before the NOx storage catalytic converter completely with the nitrogen oxides is laden, the internal combustion engine is in a fat Switched operating mode. In this fat mode get unburned hydrocarbons as well Carbon monoxide and hydrogen to the NOx storage catalyst. The in the NOx storage catalyst stored nitrogen oxides then react with the Hydrocarbons, carbon monoxide and hydrogen and then can u.a. as carbon dioxide and water to the Atmosphere are delivered. The fat mode of operation Internal combustion engine is maintained until the NOx storage catalytic converter again as completely as possible Nitrogen oxides is discharged. This unloading of Nitrogen oxides is also called regenerating the NOx storage catalyst designated.

For the above described operation of Internal combustion engine, it is thus necessary between lean mode and rich mode and to switch. For these switching operations may in particular, no momentum jump occur.

FIG. 1 shows a control with which it is possible to switch over between a lean and a rich operating mode, without a torque jump occurring in the process. Starting point of the control of Figure 1 is a predetermined injection amount M _{E, lean} for lean operation and a predetermined air mass M _{L, lean} also for lean operation. These two quantities M _{E, lean} and M _{L, lean} are provided by a general control and / or regulation of the internal combustion engine. If the internal combustion engine has, for example, an exhaust gas recirculation, then said quantity M _{L, lean, is} usually generated by a regulation for this exhaust gas recirculation. The size M _{E, lean} usually corresponds to the propulsion request of the driver or the torque to be generated.

As a further input variable in the figure 1, an actual air mass M _{L, is} present, which is measured by means of an air mass sensor. It is possible that the signal of the air mass sensor is corrected by means of further measured variables. The switchover between the lean and the rich operating mode takes place with the aid of a predefinable lambda value λ _between which, as has been explained, can be changed in particular as a function of the loading of the NOx storage catalytic converter to a rich lambda value or a lean lambda value.

The injection quantity M _{E, lean} is multiplied by a fixed factor 14.5 for diesel fuel, and then divided by the air mass M _{L, lean} . The result of this division is then a lambda value λ _lean for lean operation. This lambda value λ _lean is permanently generated from the two quantities M _{E, lean} and M _{L, lean} , irrespective of whether the internal combustion engine is in a lean or a rich operating mode.

As will be explained with reference to FIGS. 2a and 2b, the lambda value λ _{lean is converted} in a block 10 into an efficiency η _lean for the lean operation. This efficiency η _lean is then multiplicatively linked to the air mass M _{L, lean} . The result of this multiplication is indicated by the reference numeral A in FIG.

The specifiable lambda value λ _between is converted by a block 11 into an efficiency η _between . This conversion will be explained in connection with FIGS. 2a and 2b.

The above multiplication result A is divided by the efficiency η _between . The result of this division represents a desired air mass M _{L, soll} is. This target air mass M _L, is an output signal of the controller of Figure 1. The target air mass M _{L, should} be used, for example., The opening angle of a Throttle to influence, with the air that is supplied to the internal combustion engine, for example. Via an intake manifold, can be changed.

The target air mass M _{L, is to} represent the target value, ie the desired, the internal combustion engine to be supplied air mass. As already mentioned, the actual air supplied to the internal combustion engine mass is measured by means of an air mass sensor. The measurement signal is then - as already explained - the actual air mass M _{L, is} .

The aforementioned multiplication result A is divided according to FIG. 1 by the actual air mass M _{L, is} . The result of the division represents a desired efficiency η _soll . This target efficiency η _soll is converted by a block 12 into a desired lambda value λ _soll . This conversion will be explained with reference to FIGS. 2a and 2b.

Lambda setpoint λ _soll is multiplied by a fixed factor of 14.5 for diesel fuel. After that, the actual air mass M _{L, is divided} by the multiplied by 14.5 lambda setpoint λ _soll . The division result is a target injection quantity M _{E, soll} .

The target injection quantity M _{E, is to} provide an output signal of the controller of Figure 1. With the reference injection amount M _{E should,} may, for example, an injection valve of the internal combustion engine are controlled, with which the target injection quantity M _{E, to} the combustion chamber the internal combustion engine is injected.

The control illustrated in FIG. 1 and explained above is guided by air. This means that first the target air mass M _{L, should be} calculated from the input variables of the controller. This target air mass M _{L, should} , as has been explained, the actual air mass M _{L, is} the result. From this measured actual air mass M _{L, is} then the target injection quantity M _{E, should be} calculated.

If the internal combustion engine is in the lean operating mode, then the lambda value λ _between the lambda value λ corresponds to _lean for lean operation. As a result, the target air mass M _L, equal to the air mass M _{L, is lean} for lean operation. Also, the target injection quantity M _{E, should} equal to the injection amount M _{E, lean} for the lean operation. In this lean mode of operation, the control of FIG. 1 therefore has no change in the two input variables M _{E, lean} and M _{L, lean} .

If it is now necessary to switch to regeneration of the NOx storage catalytic converter in a rich operating mode, the lambda value λ is changed _between in the direction of a rich lambda value. The lambda value λ _between is thus reduced, for example, in the direction of the value 0.95.

This has the consequence that on the intervention of the efficiency η _between the target air mass M _{L, should} be changed. Due to the desired rich mode, the target air mass M _{L, should be} reduced.

As a result, the actual air mass M _{L, is} also smaller. According to the control of FIG. 1, this then also means that the desired injection quantity M _{E, is to be} increased.

Overall, this is achieved by the fact that Air / fuel ratio towards a fat Mode, ie to a fuel surplus changed.

If the regeneration of the NOx storage catalytic converter is completed, then it is possible to revert to the lean operating mode of the internal combustion engine. This is achieved by increasing the lambda value λ _between leaning back towards the lambda value λ _lean for the lean operation. This then has the consequence that the target air mass M _{L, should be} greater and the target injection quantity M _{E, should} be smaller at the same time. The air / fuel ratio of the internal combustion engine is thus changed toward a lean mode.

As soon as the lambda value λ _between the lambda value λ has again reached _lean for the lean operation, the already explained equilibrium sets in again, in which the desired air mass M _{L, soll} the air mass M _{L, lean} for the lean operation and the target injection quantity M _{E, is} the injection quantity M _{E, lean} for the lean operation corresponds.

In the control of Figure 1 is in the blocks 10 and 11th a lambda value is converted into an efficiency. By doing Block 12 conversely becomes an efficiency in one Lambda value converted. In FIGS. 2a and 2b shown how these conversions are performed can.

FIG. 2 a shows an efficiency η as an input variable and a lambda value λ as the output variable. Furthermore, the speed n of the internal combustion engine and the injection quantity M _{E, lean} for the lean operation of the internal combustion engine is specified. These two latter operating variables of the internal combustion engine are supplied to a total of four maps. Depending on these operating variables, the values of y _off , y _mul , x _off and x _{mul are} generated by the four maps. The value y _off is subtracted from the efficiency η. The resulting difference is divided by the value y _mul . The division result is fed to a reference characteristic curve 24 for the conversion of the efficiency into the lambda value. From the output signal of the reference characteristic 24, the value x _{off is} subtracted. The subtraction result is divided by the value x _mul . The lambda value λ is then available as the result of the division.

With the help of the maps 20, 21, 22, 23 it is thus possible, a correction of the reference characteristic 24th make. The maps 20, 22 each serve an additive correction, while the maps 21, 23 cause a multiplicative correction.

In FIG. 2b, a conversion of a lambda value λ in an efficiency η in a correspondingly reverse manner carried out. Again, there are four maps 25, 26, 27, 28 present, with which a reference characteristic 29 for the Conversion of a Lambda value into an efficiency can be corrected. Again, this is a correction the reference characteristic 29 in additive and multiplicative Way possible.

The map 25 is identical to the map 23. The same applies to the other maps 26, 27, 28th or 22, 21, 20. The characteristic curve 29 is the inverse function the characteristic 24.

As has already been explained, the setpoint injection quantity M _{E, ought} to be used in FIG. 1 to control an injection valve of the internal combustion engine. With this injector then the said target injection quantity M _{E, is} to be injected into the combustion chamber of the internal combustion engine. In diesel internal combustion engines, it is advantageous to divide the injection of the fuel into the combustion chamber of the internal combustion engine into two partial injections. Thus, a pilot injection quantity M _{E, VE is} injected as part of a pilot injection and a main injection quantity M _{E, HE} in the context of a main injection into the combustion chamber of the internal combustion engine. The pre-injection amount M _{E, VE} and the main injection amount M _{E, HE} together then give the target injection quantity M _{E, soll} .

For the definition of the above-mentioned pilot injection and main injection, the respective start of activation or injection start and the respective activation duration or injection duration are decisive. The distribution of the target injection quantity M _{E, is} to the pilot injection and the main injection, as well as the determination of the respective control start and the respective control duration of the pilot injection and the main injection are dependent on a plurality of operating variables of the internal combustion engine. It is possible that under certain conditions, for example. In a lean mode of the internal combustion engine, no pre-injection is no longer available. It is also possible that, for example, in a rich operating mode of the internal combustion engine, the time interval between the pilot injection and the main injection is substantially increased.

One reason for these measures is the fact that in internal combustion engines with a pressure accumulator, the so-called rail pressure p _Rail , with which the fuel is supplied to the injection valves, is influenced by the successive pilot injection and main injection. In particular, it is possible that the pre-injection creates a vibration in the pressure chamber in which the fuel is made available for injection via the injection valves. The main injection then depends on this vibration of the rail pressure p _Rail , as a time shift of the main injection with respect to the pilot injection leads directly to a change in the present during the main injection rail pressure p _Rail .

FIG. 3 shows by way of example a possibility with which the activation duration AD _HE for the main injection can be determined as a function of the operating state of the internal combustion engine. For this determination of the control duration AD _HE for the main injection, the injection quantity M _{E, HE} for the main injection and the rail pressure p _{Rail are} specified as input variables. These input variables are fed to three characteristic diagrams 30, 31, 32.

With the map 30, a drive duration AD _{HE is} output for the main injection, in which no pilot injection is present. With the map 31, a drive duration AD _{HE is} output for the main injection, in which a pre-injection is present. And finally, the map 32 outputs a drive time AD _HE for the main injection provided for the rich mode of the internal combustion engine.

With the aid of a changeover 33, one of the three maps 30, 31, 32 is selected as a function of a signal B. About the changeover 33, the respective output signal of the selected map 30, 31, 32 is then passed as the drive time AD _HE . The signal B is a status signal which, for example, is predetermined as a function of the operating mode of the internal combustion engine. Likewise, the signal B can be predefined as a function of further operating variables of the internal combustion engine.

The possibility of switching between different maps described by way of example in FIG. 3 based on the drive duration AD _HE for the main injection can be applied in a corresponding manner to the start of the main injection, the drive duration for the pilot injection, and the start of the pilot injection.

As a further measure, it is possible to transition between lean mode and rich mode as well conversely, the transition between the rich mode and the lean mode by means of a hysteresis make.

FIG. 4 shows by way of example a possibility with which such a hysteresis can be realized on the basis of the activation start AB _{VE of} the pilot injection. Thus, a map 40 is provided, which are fed as input signals, the rotational speed n of the internal combustion engine and the injection quantity M _{E, lean} for the lean operation of the internal combustion engine. As an output signal, the map 40 generates a delta value ΔAB _VE for the start of the pilot injection.

Furthermore, the desired lambda value λ _{soll is} supplied to a hysteresis characteristic 41. If the lambda setpoint is in a rich range, the hysteresis curve 41 produces the value 1 as the output signal. If, however, the lambda setpoint λ _soll is in a lean range, the output value of the hysteresis curve 41 is 0.

This output value of the hysteresis characteristic 41 is multiplicatively linked to the delta value ΔAB _VE for the start of the pilot injection. This means that this delta value ΔAB _{VE is} completely passed on in a rich region of the internal combustion engine, but is completely suppressed in a lean region of the internal combustion engine.

Thereafter, the multiplication result generated in the described manner is additively linked to the drive start AB _{VE, lean} for the pre-injection in a lean mode. The result of this addition is then the control start AB _VE for the pre-injection, which ultimately determines the point in time at which the injection valve is opened for the purpose of pre-injection.

Overall, therefore, in FIG. 4, in a lean operating mode, the predetermined actuation start AB _{VE, lean, is} not changed, since the output signal of the hysteresis curve 41 is equal to zero. In contrast, in a rich operating mode of the internal combustion engine, the control start AB _{VE, lean is changed} by the delta value ΔAB _VE . This means that the control start of the pilot injection is changed to an earlier point in time in the aforementioned rich operating mode of the internal combustion engine.

The above-described influencing of the control start AB _{VE of} the pilot injection can be applied in a corresponding manner also to the start of control of the main injection and to the activation duration of the pilot and / or the Haupteirispritzung.

If a hysteresis is used, as an example explained in connection with Figure 4, it can be advantageous or even necessary that even with the Conversions of the blocks 10, 11, 12 of Figure 1 a Hysteresis is applied. Such hysteresis is illustrated by way of example in FIG. When the hysteresis 5 in the blocks 10, 11, 12 of Figure 1 to Application comes, then it is convenient or even required if the additive and multiplicative Corrections of the reference characteristics 24 and 29 of the figures 2a and 2b are performed in sections, namely each separately for the two branches in FIG. 5 illustrated hysteresis.

Claims (10)

1. Method for operating an internal combustion engine, in particular of a motor vehicle, in which fuel is injected into a combustion chamber in a lean operating mode and in a rich operating mode, and in which the engine is switched between the two operating modes, characterized in that an air mass (M_L,lean) and an injection quantity (M_E,lean) for the lean-burn mode are continually determined, in that a lambda (λ_lean) for the lean-burn mode is continually determined from the air mass and the injection quantity, in that a lambda (λ_inter) for the rich operating mode and for the transitions to it, the said lambda differing from the lambda for the lean-burn mode, is predetermined, and in that a desired air mass (M_L,des) for the rich operating mode and for the transitions to it is determined from the lambda for the lean-burn mode and from the lambda for the rich operating mode and for the transitions to it.
2. Method according to Claim 1, characterized in that the lambda for the lean-burn mode is converted into an efficiency for the lean-burn mode, and the lambda for the rich operating mode and for the transitions to it is converted into an efficiency for the rich operating mode and the transitions to it, in that the efficiency for the lean-burn mode is multiplied by the air mass for the lean-burn mode, and in that the multiplication result is divided by the efficiency for the rich operating mode and for the transitions to it.
3. Method according to Claim 1 or 2, in which an actual air mass is measured or simulated or modelled, which is characterized in that a desired value for the lambda in the rich operating mode and for the transitions to it is determined as a function of the actual air mass and the injection quantity for the lean-burn mode, and in that a desired injection quantity for the rich operating mode and for the transitions to it is determined from the actual air mass and the desired value for the lambda.
4. Method according to Claims 2 and 3, characterized in that the desired value for the lambda in the rich operating mode and for the transitions to it is determined from a desired efficiency for the rich operating mode and for the transitions to it, and in that the desired efficiency is determined by dividing the actual air mass by the said multiplication result.
5. Method according to one of the preceding claims, characterized in that the conversion of a lambda into an associated efficiency or vice versa is carried out by means of a reference characteristic curve and by means of additive and/or multiplicative corrections.
6. Method according to one of the preceding claims, in which the fuel which is to be injected into the combustion chamber by an injection is injected in two or more sub-injections, characterized in that the start of actuation and/or the duration of actuation of the sub-injections is determined differently as a function of the operating mode and/or as a function of operating variables of the internal combustion engine.
7. Method according to Claim 6, characterized in that a hysteresis is taken into account for the start of actuation and/or the duration of actuation when switching between the operating modes.
8. Computer program characterized in that it carries out a method according to one of Claims 1 to 7 when it is implemented on a control unit.
9. Computer program according to Claim 8, characterized in that it is stored on a memory, in particular on a flash memory.
10. Control unit for an internal combustion engine, in particular of a motor vehicle, in which, in the internal combustion engine, the fuel can be injected into a combustion chamber in a lean operating mode and in a rich operating mode, and in which the engine can be switched between the two operating modes, characterized in that an air mass (M_L,lean) and an injection quantity (M_E,lean) for the lean-burn mode can be continually determined by the control unit, in that a lambda (λ_lean) for the lean-burn mode can be continually determined from the air mass and the injection quantity, in that a lambda (λ_inter) for the rich operating mode and for the transitions to it, which deviates from the lambda for the lean-burn mode, can be predetermined, and in that a desired air mass (M_L,des) for the rich operating mode and for the transitions to it can be determined from the lambda for the lean-burn mode and from the lambda for the rich operating mode and for the transitions to it.

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