JP7234964B2 - Control device for internal combustion engine - Google Patents

Description

The present invention relates to a control device for an internal combustion engine.

An internal combustion engine described in Patent Document 1 includes an EGR passage, an EGR valve, and an EGR cooler. The EGR passage connects the exhaust passage and the intake passage. An EGR valve and an EGR cooler are provided in the EGR passage. The EGR valve adjusts the amount of EGR gas flowing through the EGR passage. The EGR cooler cools the EGR gas flowing through the EGR passage.

JP 2003-336549 A

The cooling performance of the EGR cooler may deteriorate due to deposits and the like generated by cooling the EGR gas flowing through the EGR cooler. When the cooling performance of the EGR cooler deteriorates, even if the amount of EGR gas introduced into the EGR cooler is the same, the EGR cooler may not be able to sufficiently cool the EGR gas. In this case, the temperature of the EGR gas introduced into the intake passage through the EGR passage may rise excessively. For example, if a part of the intake passage is made of resin, the introduction of EGR gas having a temperature higher than the endurable temperature of the resin may deform the resin.

A control device for an internal combustion engine for solving the above problems is a control device for an internal combustion engine, wherein the internal combustion engine includes an EGR passage connecting an exhaust passage and an intake passage, and an EGR passage provided in the EGR passage. and a water-cooled EGR cooler provided in the EGR passage for cooling the EGR gas flowing through the EGR passage, wherein the control device controls the EGR a temperature calculation unit that calculates the temperature of EGR gas flowing through a portion of the passage on the intake passage side of the EGR cooler based on the operating state of the internal combustion engine; a temperature detecting portion for detecting the temperature of EGR gas flowing through the EGR passage, a temperature acquiring portion for acquiring the temperature of EGR gas flowing through the portion of the EGR passage closer to the exhaust passage than the EGR cooler, and the temperature calculating portion. A decrease amount calculation unit that calculates the amount of decrease in the cooling performance of the EGR cooler based on the calculated value of and the detected value of the temperature detection unit, the temperature and supply amount of the cooling water supplied to the EGR cooler, and the decrease amount and an upper limit heat exchange amount calculation unit that calculates an upper limit heat exchange amount that is the maximum amount of heat that the EGR cooler can heat exchange based on a predetermined regulation of the temperature of the EGR gas acquired by the temperature acquisition unit an upper limit gas amount calculation unit that calculates an upper limit gas amount, which is a maximum flow rate of EGR gas that can be cooled by the EGR cooler, based on the upper limit heat exchange amount; a control unit for controlling the opening of the EGR valve so as not to exceed the upper limit gas amount.

Hereinafter, regarding the temperature of the EGR gas flowing through the portion of the EGR passage on the intake passage side of the EGR cooler, the reference temperature is the temperature before the cooling performance of the EGR cooler declines, and the actual temperature is the temperature detected by the temperature detection unit. It says. Further, the temperature of the EGR gas flowing through the portion of the EGR passage closer to the exhaust passage than the EGR cooler is referred to as the pre-cooling temperature.

When the cooling performance of the EGR cooler has not deteriorated, the actual temperature matches the reference temperature. When the cooling performance of the EGR cooler deteriorates, the actual temperature rises with respect to the reference temperature. This amount of increase increases as the cooling performance of the EGR cooler decreases. Therefore, the amount of decrease in the cooling performance of the EGR cooler can be calculated by the amount-of-decrease calculator based on the reference temperature and the actual temperature. Note that the reference temperature can be calculated by the temperature calculating unit based on the operating state of the internal combustion engine by previously determining the relationship between the reference temperature and the operating state of the internal combustion engine through experiments or the like. The actual temperature can be detected by the temperature detector. The pre-cooling temperature can be obtained by the temperature obtaining unit by calculating based on the operating state of the internal combustion state, or by detecting the temperature of the EGR gas flowing through the portion of the EGR passage closer to the exhaust passage than the EGR cooler. .

The cooling performance of the EGR cooler when the cooling performance is not degraded can be determined based on the temperature and supply amount of the cooling water supplied to the EGR cooler. Therefore, based on the cooling performance of the EGR cooler and the amount of decrease in the cooling performance of the EGR cooler, the upper limit heat exchange amount, which is the maximum amount of heat that can actually be exchanged by the EGR cooler with decreased cooling performance, is calculated. can be calculated by the department.

The actual temperature increases as the upper limit heat exchange amount decreases. Also, the actual temperature increases as the flow rate of the EGR gas that has passed through the EGR cooler increases. Furthermore, the higher the pre-cooling temperature, the higher the actual temperature. Therefore, the upper limit gas amount, which is the maximum flow rate of EGR gas that can cool the actual temperature to the specified temperature, can be calculated by the upper limit gas amount calculator based on the pre-cooling temperature and the upper limit heat exchange amount.

According to the above configuration, the opening degree of the EGR valve is controlled by the controller so that the flow rate of the EGR gas introduced into the EGR cooler does not exceed the upper limit gas amount. As a result, even if the cooling performance of the EGR cooler is degraded, it is possible to prevent the temperature of the EGR gas introduced into the intake passage through the EGR passage from excessively rising above the specified temperature.

1 is a schematic configuration diagram of an internal combustion engine and a control device for the internal combustion engine; FIG. FIG. 4 is an explanatory diagram showing the exhaust temperature according to the engine speed and the engine load factor; 4 is a flowchart showing EGR control; 4 is a flowchart showing EGR control;

An embodiment of a control device for an internal combustion engine will be described below with reference to FIGS. 1 to 4. FIG. First, a schematic configuration of the vehicle 100 will be described.
As shown in FIG. 1, a vehicle 100 has an internal combustion engine 10 . The internal combustion engine 10 includes cylinders 11 , pistons 12 , connecting rods 13 , crankshafts 14 , intake passages 16 and exhaust passages 17 .

In the cylinder 11, a mixture of fuel and intake air is combusted. Although a plurality of cylinders 11 are provided, only one is shown in FIG. The piston 12 is housed inside the cylinder 11 so as to be able to reciprocate. Crankshaft 14 is connected to piston 12 via connecting rod 13 .

The intake passage 16 is connected to the cylinder 11 . The intake passage 16 introduces intake air into the cylinder 11 from the outside of the internal combustion engine 10 . The intake passage 16 includes a surge tank 16A that suppresses intake pulsation and the like. The material of the portion constituting the surge tank 16A is a synthetic resin. The exhaust passage 17 is connected to the cylinder 11 . The exhaust passage 17 discharges the exhaust from the cylinder 11 to the outside of the internal combustion engine 10 .

The internal combustion engine 10 has a throttle valve 22 , a first fuel injection valve 26 , a second fuel injection valve 27 , a catalyst 24 , a water pump 31 , a turbocharger 40 and a supply passage 61 . The turbocharger 40 has a compressor 41 , a shaft 42 and a turbine 43 . The compressor 41 is attached to a portion of the intake passage 16 upstream of the surge tank 16A. The turbine 43 is attached to the exhaust passage 17 . Turbine 43 is connected to compressor 41 via shaft 42 . When the turbine 43 rotates due to the flow of exhaust gas, the compressor 41 rotates integrally with the turbine 43 to supercharge the intake air.

The throttle valve 22 is attached to a portion of the intake passage 16 downstream of the compressor 41 and upstream of the surge tank 16A. The throttle valve 22 adjusts the amount of intake air that flows through the intake passage 16 per unit time.

The first fuel injection valve 26 is attached to a portion of the intake passage 16 downstream of the surge tank 16A. The first fuel injection valve 26 injects fuel supplied from a fuel tank (not shown) into the intake passage 16 . The second fuel injection valve 27 is attached to the cylinder 11 . The second fuel injection valve 27 injects fuel supplied from a fuel tank (not shown) into the cylinder 11 . The catalyst 24 is attached to a portion of the exhaust passage 17 downstream of the turbine 43 . The catalyst 24 purifies the exhaust flowing through the exhaust passage 17 .

The water pump 31 supplies cooling water to each part of the internal combustion engine 10 through the supply passage 61 . Water pump 31 is connected to crankshaft 14 . The water pump 31 is a so-called mechanical water pump driven by the driving force of the crankshaft 14 . The water pump 31 discharges more cooling water per unit time as the rotational speed of the crankshaft 14 increases.

The internal combustion engine 10 has an EGR passage 51 , an EGR valve 52 and an EGR cooler 53 . The EGR passage 51 connects a portion of the exhaust passage 17 upstream of the turbine 43 and the surge tank 16A in the intake passage 16 . The EGR passage 51 recirculates exhaust gas flowing through the exhaust passage 17 to the intake passage 16 as EGR gas.

The EGR valve 52 is attached in the middle of the EGR passage 51 . The EGR valve 52 adjusts the amount of EGR gas that flows per unit time from the exhaust passage 17 side to the intake passage 16 side in the EGR passage 51 .

The EGR cooler 53 is attached closer to the intake passage 16 than the EGR valve 52 in the EGR passage 51 . Cooling water is supplied to the EGR cooler 53 through a supply passage 61 . The EGR cooler 53 is a water-cooled intercooler. The EGR cooler 53 cools the EGR gas flowing inside the EGR cooler 53 by heat exchange with cooling water.

The internal combustion engine 10 has an airflow meter 71 , a water temperature sensor 72 , a crank angle sensor 73 and an EGR gas temperature sensor 74 . The airflow meter 71 is attached to a portion of the intake passage 16 upstream of the compressor 41 . The airflow meter 71 detects an intake air amount GA, which is the amount of intake air flowing through the intake passage 16 per unit time.

A water temperature sensor 72 detects a water temperature WH, which is the temperature of cooling water flowing through the supply passage 61 . The crank angle sensor 73 is attached near the crankshaft 14 . A crank angle sensor 73 detects a crank angle SC, which is the rotation angle of the crankshaft 14 .

The EGR gas temperature sensor 74 is attached to a portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 . The EGR gas temperature sensor 74 detects an EGR gas temperature TE, which is the temperature of EGR gas flowing through the EGR passage 51 .

Vehicle 100 includes a control device 80 . A signal indicating the amount of intake air GA is input from the airflow meter 71 to the controller 80 . A signal indicating the water temperature WH is input from the water temperature sensor 72 to the control device 80 . A signal indicating the crank angle SC is input from the crank angle sensor 73 to the controller 80 . A signal indicating the EGR gas temperature TE is input from the EGR gas temperature sensor 74 to the controller 80 .

The control device 80 calculates an engine speed NE, which is the number of revolutions of the crankshaft 14 per unit time, based on the crank angle SC. The control device 80 calculates the engine load factor KL based on the engine speed NE and the intake air amount GA. Here, the engine load factor KL is the ratio of the current amount of air flowing into the cylinder to the amount of air flowing into the cylinder when the internal combustion engine 10 is in steady operation with the throttle valve 22 fully open at the current engine speed NE. represent. The cylinder inflow air amount is the amount of intake air that flows into each cylinder 11 during the intake stroke.

The control device 80 includes a control section 81 . The control unit 81 executes various engine controls such as opening degree control of the throttle valve 22 and fuel injection control of the first fuel injection valve 26 and the second fuel injection valve 27 . Specifically, the control unit 81 selects three operating regions based on the engine speed NE and the engine load factor KL. The control unit 81 stores an operating range selection map showing the operating range to be selected in association with the engine speed NE and the engine load factor KL. As shown in FIG. 2, in the operating region selection map, the fuel efficiency priority region A1 is selected when the engine speed NE is less than a predetermined value and the engine load factor KL is less than a predetermined value. Further, in the operating range selection map, the catalyst priority range A2 is selected when the engine speed NE is less than a predetermined value and the engine load factor KL is greater than or equal to a predetermined value. In the operating range selection map, the stoichiometric air-fuel ratio priority range A3 is selected when the engine speed NE is greater than or equal to a predetermined value and the engine load factor KL is greater than or equal to a predetermined value. Here, the fuel efficiency priority range A1 is an operating range in which suppression of fuel consumption in the internal combustion engine 10 is prioritized. Further, the catalyst priority region A2 is an operating region in which priority is given to suppressing the temperature of the exhaust gas flowing through the catalyst 24 from becoming excessively high. The stoichiometric air-fuel ratio priority region A3 is an operating region in which priority is given to bringing the combustion of fuel in the cylinder 11 closer to the combustion at the stoichiometric air-fuel ratio.

The control unit 81 controls the opening of the throttle valve 22 by outputting a control signal S1 to the throttle valve 22 based on the engine speed NE, the engine load factor KL, and the operating region. The controller 81 then adjusts the amount of intake air flowing through the intake passage 16 per unit time through the throttle valve 22 . Further, the control unit 81 controls the fuel injection of the first fuel injection valve 26 by outputting a control signal S2 to the first fuel injection valve 26 based on the engine speed NE, the engine load factor KL, and the operating region. Execute. The control unit 81 executes fuel injection control of the second fuel injection valve 27 by outputting a control signal S3 to the second fuel injection valve 27 based on the engine speed NE, the engine load factor KL, and the operating region. .

The control unit 81 executes EGR valve control for controlling the opening degree of the EGR valve 52 . The control unit 81 calculates a target EGR rate X, which is a target value of the EGR rate, based on the engine speed NE, the engine load factor KL, and the operating region. Here, the EGR rate is the ratio between the amount of EGR gas recirculated to the intake passage 16 and the intake air amount GA, which is the amount of intake air flowing through the intake passage 16 . Based on the target EGR rate X and the intake air amount GA, the control unit 81 also calculates a base EGR gas amount Y, which is a reference value for the amount of EGR gas flowing through the EGR passage 51 per unit time. Then, the control unit 81 calculates a target EGR gas amount Z, which is a target value for the amount of EGR gas flowing through the EGR passage 51 per unit time, based on the base EGR gas amount Y and an upper limit gas amount M2, which will be described later. The control unit 81 outputs a control signal S4 to the EGR valve 52 based on the target EGR gas amount Z. As shown in FIG. The control unit 81 controls the opening of the EGR valve 52 to adjust the amount of EGR gas, which is the amount of EGR gas flowing through the EGR passage 51 per unit time.

The control device 80 includes a temperature calculator 82 . The temperature calculator 82 calculates an estimated downstream temperature Tout1, which is an estimated value of the temperature of EGR gas flowing through a portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 . Here, the temperature calculator 82 stores an estimated temperature map in which the estimated downstream temperature Tout1 is associated with the operating state of the internal combustion engine 10 at the time of manufacture when the cooling performance of the EGR cooler 53 has not deteriorated. The estimated temperature map is a map representing the estimated downstream temperature Tout1 in association with the engine speed NE, the engine load factor KL, and the target EGR rate. It should be noted that the estimated temperature map can be obtained by performing experiments or the like in advance. A temperature calculation unit 82 refers to the estimated temperature map and calculates an estimated downstream temperature Tout1 based on the engine speed NE, the engine load factor KL, and the target EGR rate. The estimated downstream temperature Tout1 calculated by the temperature calculator 82 increases as the engine speed NE increases. The estimated downstream temperature Tout1 calculated by the temperature calculator 82 increases as the engine load factor KL increases. The estimated downstream temperature Tout1 calculated by the temperature calculator 82 is higher as the target EGR rate is higher.

The control device 80 has a temperature detector 83 . The temperature detection unit 83 acquires the EGR gas temperature TE detected by the EGR gas temperature sensor 74 as a detected downstream temperature Tout2, which is the temperature of the EGR gas in the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53. . Therefore, the temperature detection unit 83 detects the detected downstream temperature Tout2 through the EGR gas temperature sensor 74 .

The control device 80 includes a decrease amount calculator 84 . The decrease amount calculator 84 calculates the performance decrease amount ΔQ of the EGR cooler 53 based on the estimated downstream temperature Tout1 and the detected downstream temperature Tout2. Here, in the EGR cooler 53, deposits are generated as the EGR gas flowing through the EGR cooler 53 is cooled. If such deposits adhere to the inside of the EGR cooler 53, the cooling performance of the EGR cooler 53 will deteriorate. The performance decrease amount ΔQ represents the decrease amount of the cooling performance of the EGR cooler 53 whose cooling performance is decreased as described above.

The control device 80 includes a temperature acquisition section 85 . The temperature acquisition unit 85 calculates an estimated exhaust temperature Tin, which is an estimated value of the temperature of EGR gas flowing through a portion of the EGR passage 51 closer to the exhaust passage 17 than the EGR cooler 53 . Here, as indicated by the dashed line in FIG. 2, the temperature of the exhaust gas discharged from the cylinder 11 into the exhaust passage 17 increases as the engine speed NE increases and as the engine load factor KL increases. The temperature acquisition unit 85 stores an estimated exhaust gas temperature map representing the estimated exhaust gas temperature Tin in association with the engine speed NE and the engine load factor KL. Then, the temperature acquisition unit 85 refers to the estimated exhaust temperature map and calculates the estimated exhaust temperature Tin based on the engine speed NE and the engine load factor KL.

The control device 80 includes an upper limit heat exchange amount calculator 86 . The upper limit heat exchange amount calculator 86 calculates the upper limit heat exchange amount Q2max of the EGR cooler 53 based on the water temperature WH, the engine speed NE, and the performance decrease amount ΔQ. Here, the upper limit heat exchange amount Q2max of the EGR cooler 53 is the maximum amount of heat that the current EGR cooler 53 can exchange per unit time.

The control device 80 includes an upper limit gas amount calculator 87 . The upper limit gas amount calculator 87 calculates the upper limit gas amount M2 based on the upper limit heat exchange amount Q2max. Here, the upper limit gas amount M2 is the maximum amount of EGR gas that can cool the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the exhaust passage 17 than the EGR cooler 53 to a predetermined specified temperature Tout3. It is the flow rate per unit time. Also, the specified temperature Tout3 is set as a temperature lower than the durable temperature of the synthetic resin surge tank 16A.

Note that the control device 80 can be configured as a circuit including one or more processors that execute various processes according to a computer program (software). Note that the control device 80 is configured as a circuit including one or more dedicated hardware circuits, such as an application specific integrated circuit (ASIC), or a combination thereof, which executes at least part of the various types of processing. may The processor includes a CPU and memory such as RAM and ROM. The memory stores program code or instructions configured to cause the CPU to perform processes. Memory or computer-readable media includes any media that can be accessed by a general purpose or special purpose computer.

Next, the EGR control executed by the control device 80 will be described with reference to FIGS. 3 and 4. FIG. The control device 80 repeatedly executes EGR control from when the control device 80 starts operating to when it ends its operation.

As shown in FIG. 3, when the EGR control is started, the control device 80 advances the process of step S11. In step S11, the control device 80 acquires the water temperature WH detected by the water temperature sensor 72 at the time of processing in step S11. Thereafter, control device 80 advances the process to step S12.

In step S12, the control device 80 determines whether or not the water temperature WH obtained in step S11 is within a predetermined range. Here, a specific example of the predetermined range is 86.degree. C. to 90.degree. In step S12, when the control device 80 determines that the water temperature WH acquired in step S11 is not within the predetermined range (S12: NO), the process proceeds to step S25. In step S12, when the control device 80 determines that the water temperature WH acquired in step S11 is within the predetermined range (S12: YES), the process proceeds to step S13.

In step S13, the control device 80 determines whether or not the clocked time indicating the time during which the water temperature WH has been determined to be within a predetermined range is being clocked. In step S13, when the control device 80 determines that time is being measured (S13: YES), the process proceeds to step S15. In step S13, when control device 80 determines that time is not being measured (S13: NO), the process proceeds to step S14.

In step S14, the control device 80 starts measuring the time for which the water temperature WH has been determined to be within a predetermined range. After that, the control device 80 advances the process to step S15.

In step S15, the control device 80 determines whether or not the clocked time is longer than or equal to a predetermined period of time. Here, a specific example of the predetermined period is ten and several seconds. In step S15, when the control device 80 determines that the measured time is not equal to or longer than the predetermined period (S15: NO), the process returns to step S11. In step S15, when the control device 80 determines that the clocked time is equal to or longer than the predetermined period of time (S15: YES), the process proceeds to step S21. In this case, the timer is reset.

In step S21, the temperature calculator 82 calculates the average value of the estimated downstream temperature Tout1 in a predetermined period as the estimated downstream temperature TAout1. After that, the process proceeds to step S22.

In step S22, the temperature detector 83 calculates the average value of the detected downstream temperature Tout2 in a predetermined period as the detected downstream temperature TAout2. After that, the process proceeds to step S23.

In step S23, the temperature acquisition unit 85 calculates the average value of the estimated exhaust gas temperature Tin over a predetermined period as the estimated exhaust gas temperature TAin. After that, the process proceeds to step S24.

In step S<b>24 , the decrease amount calculator 84 calculates a performance decrease amount ΔQ, which is the amount of decrease in the cooling performance of the EGR cooler 53 . Here, the amount of heat Q1 that can be heat-exchanged per unit time by the EGR cooler 53 at the time of manufacture, in which the cooling performance has not deteriorated, is represented by Equation (1).

Formula (1): Q1=M×C×(TAin−TAout1)
M: Amount of EGR gas flowing through the EGR passage 51 per unit time C: Specific heat of the EGR gas Further, the amount of heat Q2 that can be heat-exchanged per unit time by the EGR cooler 53 at the time of processing in step S24 is given by equation (2). expressed.

Formula (2): Q2=M×C×(TAin−TAout2)
Furthermore, the amount of performance decrease ΔQ, which is the amount of decrease in the cooling performance of the EGR cooler 53, is expressed by Equation (3).

Formula (3): ΔQ = Q1 - Q2 = M x C x (TAout2 - TAout1)
Therefore, the decrease amount calculation unit 84 calculates the performance decrease amount ΔQ by referring to Equation (3). Here, based on the target EGR gas amount Z at the time of processing in step S24, the reduction amount calculation unit 84 calculates the EGR gas amount, which is the amount of EGR gas flowing through the EGR passage 51 per unit time at the time of processing in step S24. Calculate M. Further, the decrease amount calculation unit 84 sets the specific heat C of the EGR gas to 1. Note that the decrease amount calculation unit 84 stores the calculated performance decrease amount ΔQ. After that, the decrease amount calculation unit 84 advances the process to step S31.

As described above, when the controller 80 determines in step S12 that the water temperature WH obtained in step S11 is not within the predetermined range (S12: NO), the process proceeds to step S25.

In step S25, the decrease amount calculation unit 84 sets the latest performance decrease amount ΔQ among the performance decrease amounts ΔQ stored in the decrease amount calculation unit 84 as the current performance decrease amount ΔQ. At the time of manufacture of the control device 80, "0" is stored as the performance degradation amount ΔQ. After that, the decrease amount calculation unit 84 advances the process to step S31.

In step S31, the upper limit heat exchange amount calculator 86 calculates a reference heat exchange amount Q1max based on the water temperature WH and the engine speed NE. Here, the reference heat exchange amount Q1max is determined by the temperature and amount of cooling water supplied to the EGR cooler 53 at the time of processing in step S31. It is the maximum amount of heat that can be heat exchanged. The upper limit heat exchange amount calculator 86 stores a reference heat exchange amount map in which the reference heat exchange amount Q1max is associated with the operating state of the internal combustion engine 10 at the time of manufacture when the cooling performance of the EGR cooler 53 has not deteriorated. there is The reference heat exchange amount map is a map representing the reference heat exchange amount Q1max in association with the water temperature WH and the engine speed NE. Note that the reference heat exchange amount map can be obtained by performing experiments or the like in advance. The lower the water temperature WH, the lower the temperature of the cooling water supplied to the EGR cooler 53, which makes it easier for the EGR cooler 53 to cool the EGR gas. That is, the water temperature WH indicates the temperature of cooling water supplied to the EGR cooler 53 . In addition, as the engine speed NE increases, the amount of cooling water supplied to the EGR cooler 53 increases, and the EGR gas is easily cooled by the EGR cooler 53 . That is, the engine speed NE indicates the amount of cooling water supplied to the EGR cooler 53 . The upper limit heat exchange amount calculator 86 refers to the reference heat exchange amount map and calculates a reference heat exchange amount Q1max based on the water temperature WH and the engine speed NE. After that, the upper limit heat exchange amount calculation unit 86 advances the process to step S32.

In step S32, the upper limit heat exchange amount calculator 86 calculates the upper limit heat exchange amount Q2max of the EGR cooler 53 based on the reference heat exchange amount Q1max and the performance deterioration amount ΔQ. Here, the upper limit heat exchange amount Q2max is represented by Equation (4).

Equation (4): Q2max=Q1max-ΔQ
Therefore, the upper limit heat exchange amount calculation unit 86 calculates the upper limit heat exchange amount Q2max of the EGR cooler 53 with reference to Equation (4). After that, the upper limit heat exchange amount calculation unit 86 advances the process to step S33.

In step S33, the upper limit gas amount calculation unit 87 calculates the upper limit gas amount M2 for cooling the estimated exhaust gas temperature TAin acquired by the temperature acquisition unit 85 to a predetermined specified temperature Tout3. Here, the upper limit heat exchange amount Q2max of the EGR cooler 53 is represented by Equation (5).

Equation (5): Q2max = M2 x C x (TAin-Tout3)
Further, the upper limit gas amount M2 is represented by the formula (6) by converting the above formulas (4) and (5).

Formula (6): M2=Q2max/(C×(TAin−Tout3))
Therefore, the upper limit gas amount calculator 87 calculates the upper limit gas amount M2 based on the upper limit heat exchange amount Q2max, the specific heat C, the estimated exhaust gas temperature TAin, and the specified temperature Tout3 with reference to the above equation (6). Thereafter, the upper limit gas amount calculator 87 advances the process to step S41.

In step S41, the control unit 81 determines whether or not the base EGR gas amount Y is greater than the upper limit gas amount M2. In step S41, when the control unit 81 determines that the base EGR gas amount Y is equal to or less than the upper limit gas amount M2 (S41: NO), the process proceeds to step S81. On the other hand, in step S41, when the control unit 81 determines that the base EGR gas amount Y is larger than the upper limit gas amount M2 (S41: YES), the process proceeds to step S42.

In step S42, the control unit 81 determines whether or not fuel increase control is necessary. Here, the fuel increase control means that the fuel injection amount from the second fuel injection valve 27 is corrected to increase the heat of vaporization of the fuel, thereby increasing the temperature of the exhaust gas discharged from the cylinder 11 to the exhaust passage 17 and the catalyst. 24 is a control that suppresses the temperature from rising excessively. In step S42, when the control unit 81 determines that the fuel amount increase control is not necessary (S42: NO), the process proceeds to step S61. On the other hand, in step S42, when the control unit 81 determines that the fuel amount increase control is necessary (S42: YES), the process proceeds to step S51.

In step S51, the controller 81 executes fuel increase control. After that, the control unit 81 advances the process to step S52. In step S52, the control unit 81 sets the target EGR gas amount Z to "0". In this case, since the target EGR gas amount Z is "0" and the EGR gas is not introduced into the intake passage 16, the fuel increase control is executed. An excessive rise in the temperature or the temperature of the catalyst 24 is suppressed. After that, the control unit 81 terminates the current EGR control.

As described above, when a negative determination is made in step S42, the process proceeds to step S61. In step S61, the control unit 81 determines whether or not it is the fuel efficiency priority area A1. In step S61, when the control unit 81 determines that the fuel consumption priority area is not A1 (S61: NO), the process proceeds to step S71. On the other hand, in step S61, when the control unit 81 determines that it is the fuel consumption priority area A1 (S61: YES), the process proceeds to step S62.

In step S62, the control unit 81 calculates the best fuel efficiency, which is the best fuel efficiency, among the fuel efficiency when it is assumed that the EGR gas amount is set between "0" and the upper limit gas amount M2. After that, the process proceeds to step S63. In step S63, the control unit 81 sets the EGR gas amount for the best fuel economy as the target EGR gas amount Z. After that, the control unit 81 terminates the current EGR control.

As described above, when a negative determination is made in step S61, the process proceeds to step S71. In step S71, the control unit 81 sets the target EGR gas amount Z to the upper limit gas amount M2. After that, the control unit 81 terminates the current EGR control.

As described above, when a negative determination is made in step S41, the process proceeds to step S81. In step S81, the control unit 81 sets the base EGR gas amount Y as the target EGR gas amount Z. As shown in FIG. After that, the control unit 81 terminates the current EGR control.

The operation of this embodiment will be described.
As described above, regarding the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53, the estimated downstream temperature TAout1 indicates the temperature before the cooling performance of the EGR cooler 53 declines. The downstream temperature TAout2 indicates the current actual temperature. The estimated exhaust temperature TAin indicates the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the exhaust passage 17 than the EGR cooler 53 . In this embodiment, the estimated downstream temperature TAout1 corresponds to the reference temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 . Also, the detected downstream temperature TAout2 corresponds to the actual temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 . Furthermore, the estimated exhaust temperature TAin corresponds to the pre-cooling temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the exhaust passage 17 than the EGR cooler 53 .

When the cooling performance of the EGR cooler 53 has not deteriorated, the estimated downstream temperature TAout1 matches the detected downstream temperature TAout2. When the cooling performance of the EGR cooler 53 deteriorates, the detected downstream temperature TAout2 increases with respect to the estimated downstream temperature TAout1. This amount of increase increases as the cooling performance of the EGR cooler 53 decreases. Therefore, the performance decrease amount ΔQ, which is the amount of decrease in the cooling performance of the EGR cooler 53, can be calculated by the decrease amount calculation unit 84 based on the estimated downstream temperature TAout1 and the detected downstream temperature TAout2. Specifically, the performance degradation amount ΔQ is represented by Equation (3).

Formula (3): ΔQ = Q1 - Q2 = M x C x (TAout2 - TAout1)
Note that the estimated downstream temperature TAout1 can be calculated by the temperature calculator 82 based on the operating state of the internal combustion engine 10 by previously obtaining the relationship between the estimated downstream temperature TAout1 and the operating state of the internal combustion engine 10 through experiments or the like. . Further, the detected downstream temperature TAout2 can be detected by the temperature detecting portion 83 through the EGR gas temperature sensor 74. As shown in FIG.

Further, the reference heat exchange amount Q1max indicating the cooling performance of the EGR cooler 53 at the time of manufacture, in which the cooling performance has not deteriorated, can be determined based on the water temperature WH and the engine speed NE. Then, based on the reference heat exchange amount Q1max and the performance degradation amount ΔQ, the upper limit heat exchange amount calculation unit 86 can calculate an upper limit heat exchange amount Q2max, which is the maximum amount of heat that can actually be exchanged by the EGR cooler 53 whose performance has deteriorated. .

Specifically, the upper limit heat exchange amount Q2max is represented by Equation (4).
Equation (4): Q2max=Q1max-ΔQ
Here, the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 increases as the upper limit heat exchange amount Q2max decreases. Further, the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 increases as the flow rate of the EGR gas passing through the EGR cooler 53 increases. Furthermore, the temperature of the EGR gas flowing through the portion of the EGR passage 51 closer to the intake passage 16 than the EGR cooler 53 increases as the estimated exhaust gas temperature TAin increases. Therefore, the upper limit gas amount M2, which is the maximum flow rate of EGR gas that can cool the temperature of the EGR gas flowing through the EGR passage 51 to the specified temperature Tout3, can be calculated based on the estimated exhaust temperature TAin and the specified temperature Tout3. Specifically, the upper limit gas amount M2 is represented by Equation (6).

Formula (6): M2=Q2max/(C×(TAin−Tout3))
Effects of the present embodiment will be described.
(1) The opening of the EGR valve 52 is controlled by the controller 81 so that the flow rate of the EGR gas introduced into the EGR cooler 53 does not exceed the upper limit gas amount M2. As a result, even if the cooling performance of the EGR cooler 53 deteriorates, it is possible to prevent the temperature of the EGR gas introduced into the intake passage 16 through the EGR passage 51 from exceeding the specified temperature Tout3 and excessively rising.

This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.
- In the above embodiment, the EGR control can be changed. For example, from the viewpoint of controlling the opening of the EGR valve 52 so that the EGR gas amount does not exceed the upper limit gas amount M2, it is only necessary to calculate the upper limit gas amount M2 that defines the upper limit of the target EGR gas amount Z. Therefore, the processing from step S41 to step S81 may be omitted.

- For example, the temperature calculator 82 may omit the process of calculating the estimated downstream temperature TAout1, which is the average value of the estimated downstream temperature Tout1 in a predetermined period. Similarly, the temperature detector 83 may omit the process of calculating the estimated downstream temperature TAout1, which is the average value of the detected downstream temperatures Tout2 over a predetermined period. In this case, the decrease amount calculator 84 may calculate the performance decrease amount ΔQ based on the estimated downstream temperature Tout1 and the detected downstream temperature Tout2 instead of the estimated downstream temperature TAout1 and the detected downstream temperature TAout2.

・Similarly, the temperature acquisition unit 85 may omit the process of calculating the estimated exhaust gas temperature TAin, which is the average value of the estimated exhaust gas temperature Tin in a predetermined period. In this case, the upper limit gas amount calculator 87 may calculate the upper limit gas amount M2 using the estimated exhaust temperature Tin instead of the estimated exhaust temperature TAin.

- The predetermined range in step S12 can be changed.
- The predetermined period in step S15 can be changed.
- In the above-described embodiment, the specified temperature Tout3 may be appropriately changed according to the material of the intake passage 16, for example.

- In the above embodiment, the configuration of the control device 80 can be changed. For example, the control unit 81 does not need to select three operating regions. Then, the control unit 81 may control the opening degree of the EGR valve 52 so that the EGR gas amount does not exceed the upper limit gas amount M2 regardless of the operating range.

- In the above embodiment, the configuration of the internal combustion engine 10 can be changed. For example, the water pump 31 is not limited to a mechanical water pump, and may be an electric water pump driven by an electric motor. Note that when an electric water pump is employed, the upper limit heat exchange amount calculator 86 may calculate the supply amount of cooling water to be supplied to the EGR cooler 53 based on the rotation speed of the electric motor.

- For example, the internal combustion engine 10 may include a temperature sensor that detects the temperature of EGR gas flowing through a portion of the EGR passage 51 closer to the exhaust passage 17 than the EGR cooler 53 . Then, the temperature acquisition unit 85 may use the temperature detected by the temperature sensor instead of the estimated exhaust gas temperature Tin.

ΔQ Performance degradation amount M2 Upper limit gas amount Q1max Standard heat exchange amount Q2max Upper limit heat exchange amount TAin Estimated exhaust temperature TAout1 Estimated downstream temperature TAout2 Detected downstream temperature TE EGR gas temperature Tin Estimated exhaust temperature Tout3 Regulation Temperature WH Water temperature 10 Internal combustion engine 11 Cylinder 16 Intake passage 17 Exhaust passage 31 Water pump 51 EGR passage 52 EGR valve 53 EGR cooler 74 EGR gas temperature sensor 80 Control device 81 Control section 82 ... Temperature calculation part 83 ... Temperature detection part 84 ... Decrease amount calculation part 85 ... Temperature acquisition part 86 ... Upper limit heat exchange amount calculation part 87 ... Upper limit gas amount calculation part 100 ... Vehicle

Claims (1)

A control device for an internal combustion engine,
The internal combustion engine is
an EGR passage connecting the exhaust passage and the intake passage;
an EGR valve provided in the EGR passage for adjusting the amount of EGR gas flowing through the EGR passage;
a water-cooled EGR cooler provided in the EGR passage for cooling EGR gas flowing through the EGR passage,
The control device is
a temperature calculation unit that calculates the temperature of EGR gas flowing through a portion of the EGR passage closer to the intake passage than the EGR cooler, based on the operating state of the internal combustion engine;
a temperature detection unit that detects the temperature of EGR gas flowing through a portion of the EGR passage closer to the intake passage than the EGR cooler;
a temperature acquisition unit that acquires the temperature of EGR gas flowing through a portion of the EGR passage closer to the exhaust passage than the EGR cooler;
a decrease amount calculation unit that calculates a decrease amount of the cooling performance of the EGR cooler based on the calculated value of the temperature calculation unit and the detection value of the temperature detection unit;
an upper limit heat exchange amount calculation unit that calculates an upper limit heat exchange amount, which is the maximum amount of heat that can be exchanged by the EGR cooler, based on the temperature and supply amount of cooling water supplied to the EGR cooler and the decrease amount;
calculating an upper limit gas amount, which is a maximum flow rate of EGR gas that can be cooled by the EGR cooler, based on the upper limit heat exchange amount. an upper limit gas amount calculator;
A control device for an internal combustion engine, comprising a control unit that controls the opening degree of the EGR valve so that the amount of EGR gas flowing through the EGR passage does not exceed the upper limit gas amount.

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