JP2018127920A - Control device for internal combustion engine - Google Patents

Abstract

[PROBLEMS] To estimate the coolant temperature of an EGR cooler with high accuracy and control the coolant flow to the EGR cooler even when EGR gas flows through the EGR passage and when fresh air flows backward. When the flow direction of the gas passing through the EGR passage is a forward flow from the exhaust passage side to the intake passage side, the water temperature of the cooling water flowing through the EGR cooler is estimated based on the cooling performance of the EGR gas. The On the other hand, when the flow direction of the gas passing through the EGR passage is reverse from the intake passage side to the exhaust passage side, the coolant temperature is estimated based on the fresh air cooling performance. When the estimated coolant temperature is lower than the reference value, the valve of the coolant channel connected to the EGR cooler is closed, and the coolant flow to the EGR cooler is shut off. [Selection] Figure 3

Description

  The present invention relates to a control device for an internal combustion engine including an EGR device, and more particularly to a control device for an internal combustion engine having a structure in which fresh air can flow backward from an intake passage to an EGR passage.

  Patent Document 1 discloses a technique related to control of an internal combustion engine provided with an EGR device that recirculates a part of exhaust gas to an intake passage through an EGR passage.

JP 2012-041904 A

  In an internal combustion engine equipped with an EGR device, fresh air may flow backward from the intake passage to the EGR passage due to the relationship between the pressure in the intake passage and the pressure in the exhaust passage. However, the cooling performance differs between EGR gas and fresh air. For this reason, when the amount of water flow to the EGR cooler is controlled in the same way during the forward flow in which the EGR gas flows through the EGR passage and in the reverse flow in which the fresh air flows, generation of condensed water due to overcooling of the EGR gas, Boiling of cooling water can occur due to shortage.

  In order to avoid this, it is conceivable to estimate the coolant temperature of the EGR cooler and control the flow of water to the EGR cooler according to the estimated water temperature. In this regard, Patent Document 1 discloses a method for estimating the cooling water temperature of the EGR cooler. However, the estimation of the cooling water temperature in Patent Document 1 is based on the premise that the EGR gas flows in the forward flow, that is, the EGR passage, and does not take into consideration that the fresh air is in the reverse flow. As described above, since the cooling performance for cooling water differs between EGR gas and fresh air, the cooling water temperature estimation method of Patent Document 1 on the premise of EGR gas circulation assumes that the cooling water of the EGR cooler during reverse flow is used. It is difficult to estimate the water temperature with high accuracy.

  Further, Patent Document 1 discloses that the water flow to the EGR cooler is controlled based on the estimated coolant temperature. However, in the configuration of Patent Document 1, the water flow to the EGR cooler is unnecessary. The water pump is stopped. However, since the supply of engine cooling water is also stopped by stopping the water pump, it is not possible to stop water flow to the EGR cooler after the engine warm-up is completed.

  The present invention has been made to solve the above-described problems. In an internal combustion engine having a structure in which fresh air can flow backward from the intake passage to the EGR passage, the cooling of the EGR cooler can be performed even in the case of fresh air backward flow. An object of the present invention is to provide an improved control device for an internal combustion engine capable of estimating the water temperature of water with high accuracy and controlling the flow of the cooling water to the EGR cooler according to the water temperature of the cooling water.

  In order to achieve the above object, a control apparatus for an internal combustion engine of the present invention has the following configuration. That is, the control device for an internal combustion engine includes an EGR device, a cooling water passage connected to the EGR cooler, and a control device. The EGR device includes an EGR passage connecting the exhaust passage and the intake passage, an EGR valve installed in the EGR passage, and an EGR cooler installed in the EGR passage. The cooling water flow path is connected to the EGR cooler and introduces cooling water into the EGR cooler. A valve for opening and closing the cooling water channel is installed in the cooling water channel. The control device is connected to the actuator of the valve and controls the introduction of the cooling water to the EGR cooler by controlling the opening and closing of the valve.

  Furthermore, the control device of the present invention is configured as follows. That is, when the flow direction of the gas passing through the EGR passage is the forward flow from the exhaust passage side to the intake passage side, the coolant temperature is estimated based on the cooling performance of the EGR gas. On the other hand, when the flow direction of the gas passing through the EGR passage is reverse from the intake passage side to the exhaust passage side, the coolant temperature is estimated based on the fresh air cooling performance. When the estimated coolant temperature is lower than the reference value, the valve is closed to interrupt the coolant flow to the EGR cooler.

  According to the present invention, when the EGR gas flows through the EGR passage in the forward flow, the coolant temperature is estimated based on the cooling performance of the EGR gas, and when the fresh air flows in the reverse flow, the cooling is performed based on the cooling performance of the new air. The water temperature is estimated. Therefore, the coolant temperature can be estimated with higher accuracy, and the introduction of the coolant to the EGR cooler can be controlled accordingly. Therefore, generation of condensed water due to overcooling and boiling of cooling water can be prevented more reliably.

It is a figure which shows typically the system configuration | structure of the internal combustion engine to which the control apparatus of embodiment of this invention is applied. It is a figure which shows typically the structure of the engine cooling system of the internal combustion engine of embodiment. It is a flowchart for demonstrating the routine of control which the control apparatus of embodiment performs. It is a figure for demonstrating the relationship between the differential pressure | voltage of intake pressure and exhaust pressure, and the gas flow rate of an EGR channel | path. It is a flowchart for demonstrating the subroutine of EGR / C water temperature estimation performed in step S140 of the routine of FIG. It is a flowchart for demonstrating the subroutine of EGR / C water temperature estimation performed in step S240 of the routine of FIG. It is a figure for demonstrating the relationship between a gas flow rate and hA. It is a figure for demonstrating the determination of the water flow stoppage possibility to the EGR cooler 36 in the control of embodiment, and the determination result. It is a flowchart for demonstrating the example of the other control routine which the control apparatus of embodiment performs. It is a timing chart for explaining other examples of control of an embodiment.

1. Overall Configuration of System FIG. 1 is a diagram schematically showing a system configuration of an internal combustion engine to which a control device according to an embodiment of the present invention is applied. The internal combustion engine includes an engine body 4 configured as a spark ignition engine. An intake passage 6 for sucking air from the outside is connected to the intake port of the engine body 4. In the intake passage 6, an air cleaner 12, a compressor 20 a, an intercooler 14, and a throttle 16 are arranged in this order from the upstream toward the engine body 4.

  An exhaust passage 8 for discharging exhaust gas to the outside is connected to the exhaust port of the engine body 4. In the exhaust passage 8, a turbine 20 b, an S / C catalyst 24, and a U / F catalyst 26 that constitute the turbocharger 20 together with the compressor 20 a are arranged in this order from the engine body 4 toward the downstream.

  The internal combustion engine includes an EGR device 30 that recirculates part of the exhaust gas from the exhaust passage 8 to the intake passage 6. The EGR device 30 includes an EGR passage 32, an EGR cooler 36, and an EGR valve 38. The EGR passage 32 connects the exhaust passage 8 downstream of the S / C catalyst 24 and upstream of the U / F catalyst 26 and the intake passage 6 downstream of the throttle 16. The EGR cooler 36 is provided in the EGR passage 32, and the EGR valve 38 is provided in the EGR passage 32 downstream of the EGR cooler 36 in the direction of EGR gas flow (forward flow direction).

The internal combustion engine in the present embodiment has an engine cooling system 50. FIG. 2 is a diagram schematically showing the configuration of the engine cooling system. As shown in FIG. 2, the engine cooling system 50
It has the 1st cooling water flow path 52 and the 2nd cooling water flow path 53 through which cooling water distribute | circulates. The first cooling water channel 52 is connected to the cooling water outlet of the engine body 4, and the second cooling water channel 53 is connected to the cooling water inlet of the engine body 4. Cooling water is supplied to and discharged from both the cylinder block and the cylinder head of the engine body 4 by the first cooling water channel 52 and the second cooling water channel 53. A water pump (WP) 54 for circulating cooling water to the engine cooling system 50 is installed in the second cooling water flow path 53.

  The engine cooling system 50 further includes a first branch channel 55 and a second branch channel 56 arranged in parallel with each other so as to connect the first coolant channel 52 and the second coolant channel 53. And a bypass channel 57. One end of the first branch channel 55 is connected to the first cooling water channel 52, and the other end is connected to the second cooling water channel 53. The first branch passage 55 is provided with an EGR cooler 36 and a shutoff valve 64 that opens and closes the first branch passage 55. In a state where the shutoff valve 64 is open, the cooling water flows from the first cooling water channel 52 into the first branch channel 55 and is supplied to the EGR cooler 36. By closing the shutoff valve 64, the inflow of cooling water to the EGR cooler 36 is shut off.

  One end of the second branch flow path 56 is connected to the first cooling water flow path 52, and the other end is connected to the second cooling water flow path 53. A radiator 66 is installed in the second branch channel 56. A thermostat 68 is installed at the connecting portion between the second branch flow path 56 and the second cooling water flow path 53. The thermostat 68 adjusts the amount of cooling water flowing from the first cooling water channel 52 into the second branch channel 56, that is, the amount of cooling water introduced into the radiator 66.

  An end portion of the first cooling water channel 52 communicates with one end of the bypass channel 57, and an end portion of the second cooling water channel 53 communicates with the other end of the bypass channel 57. By the bypass flow path 57, the EGR cooler 36 and the radiator 66 are bypassed, and the cooling water flows.

  In the system shown in FIG. 1, an intake side temperature sensor 41 for measuring the temperature of intake air and an intake side pressure sensor 42 for measuring the pressure of intake air are in the vicinity of the connection portion between the intake passage 6 and the EGR passage 32. Is installed. An exhaust side temperature sensor 44 for measuring the exhaust temperature and an exhaust side pressure sensor 45 for measuring the exhaust pressure are installed in the vicinity of the connection portion between the exhaust passage 8 and the EGR passage 32. As shown in FIG. 2, an engine outlet water temperature sensor 46 for measuring the outlet water temperature of the cooling water is installed at the outlet of the engine body 4.

  The system of FIG. 1 includes a control device 40. Various sensors for measuring the state quantity of the internal combustion engine, including the intake side temperature sensor 41, the intake side pressure sensor 42, the exhaust side temperature sensor 44, the exhaust side pressure sensor 45, and the engine outlet water temperature sensor 46 are the control device 40. It is connected to the. The control device 40 controls the operation of the internal combustion engine by operating various devices and actuators included in the internal combustion engine based on information obtained by these sensors. The control device 40 is an ECU (Electronic Control Unit) having at least one CPU, at least one ROM, and at least one RAM. However, the control apparatus 40 may be comprised from several ECU. In the control device 40, various functions related to engine control are realized by loading a program stored in the ROM into the RAM and executing it by the CPU.

2. Control by the Control Device In the internal combustion engine having the EGR device 30 configured as shown in FIG. 1, fresh air flows backward from the intake passage 6 to the EGR passage 32 due to the relationship between the pressure in the intake passage 6 and the pressure in the exhaust passage 8. It can happen. The cooling performance, that is, the amount of heat exchanged with the cooling water in the EGR cooler 36 differs between the EGR gas and the fresh air. Therefore, the control device 40 determines whether the gas flowing through the EGR passage 32 is EGR gas or fresh air, and accordingly, the coolant temperature in the EGR cooler 36 (hereinafter referred to as “EGR / C water temperature”). (Also called). Furthermore, by controlling the opening and closing of the shutoff valve 64 according to the estimated EGR / C water temperature, the flow of cooling water into / off the EGR cooler 36 is controlled, thereby generating and cooling the condensed water in the EGR cooler 36. Prevent boiling of water.

  Hereinafter, specific control will be described with reference to FIGS. FIG. 3 is a flowchart for illustrating a control routine executed by control device 40 in the present embodiment. The routine of FIG. 3 is a routine that is repeatedly executed every predetermined control time Δt during operation of the internal combustion engine. In the routine of FIG. 3, first, in step S102, it is determined whether or not the execution of this routine is the first execution after the internal combustion engine with the IG switch turned on.

  If it is determined in step S102 that it is the first execution, next, initial setting is executed in step S110. In the initial setting, the EGR / CTw (t) at the current time t is set to the engine outlet water temperature Twm (t) measured by the engine outlet water temperature sensor 46.

If it is determined in step S102 that the execution is not the first time, or after the initial setting is executed in step S110, it is next determined in step S120 whether or not a fresh air backflow condition is satisfied. Here, the fresh air reverse flow condition is a condition that is satisfied when the direction of gas flow in the EGR passage 32 is a reverse flow from the intake passage 6 side toward the exhaust passage 8 side. More specifically, the following equation (1) is set as the fresh air backflow condition.
Differential pressure ΔP (t) = Pg1 (t) −Pg2 (t)> 0 (1)
In equation (1), Pg1 (t) is the intake pressure Pg1 (t) [kPa] measured based on the output of the intake side pressure sensor 42 measured at time t, and Pg2 (t) is the exhaust at time t. This is the exhaust pressure measured based on the output of the side pressure sensor 45. That is, the fresh air backflow condition in step S120 is that the intake pressure Pg1 (t) is higher than the exhaust pressure Pg2 (t) at time t.

  If it is determined in step S120 that the fresh air backflow condition is satisfied, next, the fresh air passage flow rate is estimated in step S130. On the other hand, if it is determined in step S120 that the fresh air backflow condition is not satisfied, then in step S230, estimation of the EGR gas passage flow rate is executed. The fresh air passage flow rate or the EGR gas passage flow rate is calculated as a gas flow rate Gg (t) passing through the EGR cooler 36 at time (t) according to a map having the differential pressure ΔP as an axis.

  FIG. 4 is a diagram for explaining the relationship between the differential pressure ΔP and the gas flow rate Gg. As shown in FIG. 4, within a range where the pressure difference between the intake pressure Pg1 and the exhaust pressure Pg2 (that is, | ΔP |) is small to some extent, the gas flow rate Gg increases as the differential pressure ΔP increases. When the pressure difference between Pg1 and the exhaust pressure Pg2 increases, the gas flow rate Gg is generally stabilized at a constant amount.

  In the present embodiment, a map that defines the correlation between the differential pressure ΔP and the gas flow rate Gg shown in FIG. 4 is created in advance based on actual measurement values and stored in the control device 40. Different maps are prepared depending on whether the gas flow rate Gg (t) estimated here is fresh air or EGR gas. In the processing of step S130 or step S230, the gas flow rate Gg (which is an estimated value of the fresh air passage flow rate or the EGR gas passage flow rate according to the differential pressure ΔP (t) at time (t) according to the map in each case. t) is calculated.

  Note that different maps are used for fresh air and EGR gas because the flow direction differs between fresh air and EGR gas, so the per-gas per change to the EGR cooler 36 changes, and the flow rate is constant. This is because the pressure loss changes. At the same flow rate, it is considered that the pressure loss of fresh air is larger than the pressure loss of EGR gas.

  In step S130, after the gas flow rate Gg (t), which is an estimated value of the fresh air passage flow rate, is calculated, next, in step S140, the EGR / C water temperature is estimated in consideration of the influence of fresh air. . On the other hand, after the gas flow rate Gg (t), which is an estimated value of the EGR gas passage flow rate, is calculated in step S230, next, in step S240, the EGR / C water temperature is estimated in consideration of the influence of the EGR gas. Is done.

  FIG. 5 is a flowchart for explaining the EGR / C water temperature estimation subroutine executed in step S140, and FIG. 6 is a flowchart for explaining the EGR / C water temperature estimation subroutine executed in step S240. is there. The routines of FIGS. 5 and 6 use different maps and calculation methods depending on whether the gas is fresh air or EGR gas, but the processing flow is the same, so the following description will be given collectively. To do.

  In the routine of FIG. 5 (or FIG. 6), it is first determined in step S141 (or S241) whether or not the shutoff valve 64 is open. If it is determined in step S141 (or S241) that the shutoff valve 64 is open, the process proceeds to step S142 (or S242). In the state where the shutoff valve 64 is opened, the cooling water is introduced into the EGR cooler 36. Accordingly, in step S142 (or S242), the EGR / C water temperature Tw (t + Δt) at time (t + Δt) is set to the engine outlet water temperature Twm (t) at time t.

On the other hand, if it is determined in step S141 (or S241) that the shutoff valve 64 is not open, the process proceeds to step S143 (or S243). In step S143, hA [W / K] at the time of fresh air backflow is calculated. In step S243, hA [W / K] at the time of EGR gas introduction, that is, in the forward flow is calculated. Here, h is a heat transfer coefficient [W / m ² · K], and A is an area [m ² ]. hA is calculated according to a map with the gas flow rate Gg as an axis. The hA has a different value depending on whether the inflowing gas is fresh air or EGR gas. Hereinafter, calculation of hA will be described.

  FIG. 7 is a diagram for explaining the relationship between the gas flow rate Gg [g / s] and hA [W / K]. In FIG. 7, the line A indicates a reverse flow, that is, a case where fresh air flows in the EGR passage 32, and a line B indicates a forward flow, that is, a case where EGR gas flows in the EGR passage 32. As shown in FIG. 7, the gas flow rates Gg and hA have a relationship in which hA increases as the gas flow rate increases.

  In the present embodiment, a map that defines the correlation between the gas flow rate Gg and hA as shown in FIG. 7 is created in advance based on the actual measurement values and stored in the control device 40. However, since the correlation between the gas flow rate and hA is different between the case where the gas flow rate Gg (t) is the fresh air flow rate and the case where the gas flow rate is the EGR gas flow rate, different maps are prepared. In the process of step S143 (or S243) described above, hA [W / K] corresponding to the gas flow rate Gg (t) at time (t) is calculated according to the map in each case.

The reason why different maps are prepared for fresh air and EGR gas is because the correlation is different as described above, and there are the following two reasons. One reason is that the flow direction is different between fresh air and EGR gas, and therefore the per-gas per change with respect to the cooling core of the EGR cooler 36 changes, so that the rate of change of hA [W / K] with respect to the gas flow rate Gg is different. The other is that the gas composition is different between EGR gas and fresh air, and the value of the heat transfer coefficient h [W / m ² · K] is also different.

  Next, in step S144 (or S244), the gas temperature of the EGR cooler 36 is calculated. More specifically, in step S144, the gas temperature Tg (t) of the EGR cooler 36 during reverse flow is set to the intake air temperature Tg1 (t) measured according to the output of the intake side temperature sensor 41. In step S244, the gas temperature Tg (t) of the EGR cooler 36 during forward flow is set to the exhaust gas temperature Tg2 (t) measured according to the output of the exhaust gas temperature sensor 44.

Next, in step S145 (or S245), the heat quantity Q [W] is calculated. The amount of heat Q [W] is calculated using hA calculated in step S143 (or S243), gas temperature Tg (t) calculated in step S144 (or S244), and EGR / C water temperature Tw (t). Is calculated according to the following equation (2). The EGR / C water temperature Tw (t) used in equation (2) is the EGR / C water temperature calculated and stored in step S142 (or S242) or S146 (or S246) when this routine was executed last time. This corresponds to the previous value of Tw (t + Δt).
Q = hA × (Tg (t) −Tw (t)) (2)

  Next, in step S146 (or S246), the EGR / C water temperature Tw (t + Δt) when the shutoff valve 64 is closed is estimated. The EGR / C water temperature Tw (t + Δt) is calculated by adding ΔTw (t + Δt) to the previous value Tw (t + Δt) of the EGR / C water temperature Tw (that is, Tw (t + Δt) = Tw (t) + ΔTw ( t + Δt)).

Here, ΔTw (t + Δt) is expressed by the following equation (3) using the heat quantity Q [W] calculated in step S145 (or S245), the control time Δt, and the specific heat capacity C [J / K]. Calculated.
Tw (t + Δt) = Q × Δt / C (3)
Note that the specific heat capacity C [J / K] in the equation (3) is a value determined based on a prior measurement result and stored in the control device 40.

Note that when the shutoff valve 64 is open, the cooling water is flowing into the EGR cooler 36. Therefore, in step S142 (or S242), the EGR / C water temperature Tw (t + Δt) is the time t before Δt. Is set to the engine outlet water temperature Twm (t). However, instead of this processing, the EGR / C water temperature Tw (t + Δt) may be set in consideration of heat transfer by the following equation (4).
Tw (t + Δt) = Twm (t) + ΔTw (4)

In Expression (4), ΔTw is a temperature difference caused by heat transfer between the cooling water and fresh air in the EGR cooler 36. The calculation of ΔTw may be the same method as in steps S143 to S146 (or S243 to S246). However, as a map for calculating hA in step S143 (or S243), the gas flow rate Gg (fresh air passage flow rate or EGR gas passage flow rate) of the EGR cooler 36 and the cooling water flow rate [L / min] of the EGR cooler 36 are axised. The difference is that a three-dimensional map is used.

  After the process of step S142 (or S242) or step S146 (or S246), the process by the current subroutine is terminated, and the process returns to the control routine of FIG. In step S150 of FIG. 3, it is determined whether or not the water flow to the EGR cooler 36 can be stopped. In step S150, it is determined whether or not the water flow can be stopped based on whether or not the EGR / C water temperature Tw (t + Δt) calculated in step S140 (or S240) is lower than a reference value described later.

  If it is determined in step S150 that the water flow can be stopped, the shutoff valve 64 is closed in step S160, the inflow of the cooling water to the EGR cooler 36 is shut off, and the current process ends. On the other hand, if it is determined in step S150 that the water flow cannot be stopped, the shutoff valve 64 is opened and the cooling water flows into the EGR cooler 36, and the current process ends.

  FIG. 8 is a diagram for explaining the determination of whether or not to stop water flow to the EGR cooler 36 and the determination result, which are executed in steps S150 to S170. As shown in FIG. 8, when EGR gas is introduced, that is, when the EGR valve 38 is open, the reference value for determining whether or not the water flow can be stopped is a determination value for whether or not countermeasures against condensed water are necessary. It becomes the criteria for countermeasures against condensed water.

  That is, when the EGR / C water temperature Tw (t + Δt) calculated in step S140 or S240 is lower than the condensed water countermeasure criteria, there is a possibility that condensed water is generated due to the introduction of EGR. In this case, it is determined in step S150 that the water flow can be stopped, and the shutoff valve 64 is closed. However, when the water temperature is less than about 60 [° C.], EGR is not usually introduced to prevent the generation of condensed water. Therefore, it is unlikely that the EGR / C water temperature Tw (t + Δt) will be less than the aggregate water countermeasure criteria when the EGR introduction is actually executed.

  If EGR gas is introduced and the EGR / C water temperature Tw (t + Δt) is equal to or higher than the condensed water countermeasure criteria, it is determined in step S150 that the water flow stop is impossible, and the shutoff valve 64 is opened.

  When the EGR gas is not introduced, that is, when the EGR valve 38 is closed, the reference value for determining whether or not the water flow can be stopped is a boiling avoidance criterion that is a determination value of whether or not to boil the cooling water. Become.

  That is, when the calculated EGR / C water temperature Tw (t + Δt) is lower than the boiling avoidance criteria, it is determined that there is no possibility of boiling of the cooling water in the EGR cooler 36. In this case, it is determined in step S150 that water flow can be stopped, and the shutoff valve 64 is closed. On the other hand, if the EGR / C water temperature Tw (t + Δt) is equal to or higher than the boiling avoidance criteria, there is a possibility of boiling, so it is determined in step S150 that the water flow cannot be stopped, and the shutoff valve 64 is opened.

  The condensed water countermeasure criteria are smaller than the boiling avoidance criteria. The presence / absence of introduction of EGR gas is derived according to a map determined by, for example, the engine speed, load, etc. of the internal combustion engine. The map is created by matching in advance.

  As described above, in the present embodiment, the EGR / C water temperature is estimated separately for the forward flow when the EGR gas flows into the EGR passage 32 and the reverse flow when the fresh air flows. Therefore, the EGR / C water temperature can be estimated with high accuracy. Since the flow of the cooling water to the EGR cooler 36 is controlled according to the estimated EGR / C water temperature, the generation of condensed water and the occurrence of boiling can be reliably avoided.

3. Other Control Examples By the way, in the above control, there is a possibility that the estimated value of the EGR / C water temperature greatly deviates from the actual value with the lapse of time due to the accumulation of estimation errors. If the difference between the estimated value and the actual value becomes large, as a result, it is not correctly determined whether or not to stop the water flow to the EGR cooler 36 in step S150, and there is a possibility that the generation of condensed water or the boiling of the cooling water may occur.

  On the other hand, according to the following other control examples, when the EGR cooler has been stopped for a long time, a control that temporarily executes water flow to the EGR cooler 36 and resets the accumulated error is considered. It is done.

  FIG. 9 is a flowchart for explaining an example of another control routine executed by the control device. The routine of FIG. 9 is executed in place of the routine of FIG. 3 and is the same as the routine of FIG. 3 except that the processing of steps S300, S310, S320, S330, S340, and S350 is included. is there.

  In the routine of FIG. 9, if it is determined in step S100 that the control is the first control after the IG switch is turned on, Ctime is reset in step S300 and Ctime = 0. Ctime is a counter that counts an elapsed time after the shutoff valve 64 is closed after Ctime is reset to zero. Thereafter, in step S110, initial setting is executed.

  Further, after the estimated value of the EGR / C water temperature is calculated in step S140 or S240, next, Ctime is counted up in step S310, Ctime is finally reset to 0, and then the shutoff valve 64 is closed. It is updated to the elapsed time from the time it was spoken to the present. Next, in step S150, it is determined whether or not water flow to the EGR cooler 36 can be stopped.

  If it is determined in step S150 that it is not possible to stop water flow, the shutoff valve 64 is opened, and the process proceeds to step S350, where Ctime is reset. Thereafter, in step S170, the shutoff valve 64 is set to open, and water is passed to the EGR cooler 36.

  If it is determined in step S150 that the water flow can be stopped, it is determined in step S320 whether Ctime is smaller than the upper limit of the stop time. The upper limit of the stop time is a time threshold for determining that the deviation between the estimated value EGR / C water temperature Tw (t + Δt) and the actual value exceeds the allowable range, and is determined in advance based on the actually measured value. This is the stored value. In step S320, it is determined that the difference between the estimated value of the EGR / C water temperature and the actual value is not large by determining that Ctime, that is, the elapsed time after closing of the shutoff valve 64 is smaller than the upper limit value of the stop time. The Accordingly, the process proceeds to step S160, the shutoff valve 64 is set to be closed, and the flow of the cooling water to the EGR cooler 36 is shut off.

  On the other hand, if it is determined in step S320 that Ctime is greater than or equal to the stop time upper limit value, then in step S330, it is determined whether or not Ctime is greater than a value obtained by adding the restart permission time to the stop time upper limit value. Is done. The resuming permission time is a time threshold for determining that the EGR / C water temperature is reset by passing water to the EGR cooler 36, and is a value determined and stored in advance based on the actual measurement value.

  If it is determined in step S330 that Ctime is equal to or less than the value obtained by adding the restart permission time to the stop time upper limit value, the process proceeds to step S170, and the shutoff valve 64 is opened. Thereby, the water flow to the EGR cooler 36 is started or continued. Thereafter, the current process is temporarily terminated.

  As described above, this routine is repeatedly executed at intervals of the control time Δt. When the control routine is repeated, if it is determined in step S330 that Ctime has exceeded the value obtained by adding the restart permission time to the stop time upper limit value, the process proceeds to step S340, where Ctime is reset. Next, it progresses to step S160 and the cutoff valve 64 is closed.

  FIG. 10 is a timing chart for explaining another control example of the embodiment. As shown in FIG. 10, according to the above control, the shutoff valve 64 is closed at time t <b> 1 when it is determined that the water flow to the EGR cooler 36 can be stopped. However, at time t2 when Ctime, which is the elapsed time after closing of the shutoff valve 64, exceeds the stop time upper limit value, the shutoff valve 64 is opened once.

  Thereafter, the accumulated error of the estimated value of the EGR / C water temperature is also reset at time t3 when Ctime, which is the elapsed time after closing of the shutoff valve 64, exceeds the value obtained by adding the restart permission time to the stop time upper limit value. It is thought that there is. Therefore, at time t3, the shutoff valve 64 is closed again, and water flow to the EGR cooler 36 is stopped. When the shut-off valve 64 is closed, Ctime is reset, and the elapsed time after closing the valve is newly counted.

  As described above, according to the control of another control example, since the difference between the estimated value of the EGR / C water temperature and the actual value can be reduced, it is possible to determine whether or not the water flow can be stopped with higher accuracy. Can be done with.

4 Engine body 6 Intake passage 8 Exhaust passage 12 Air cleaner 14 Intercooler 16 Throttle 20 Turbocharger 20a Compressor 20b Turbine 24 S / C catalyst 26 U / F catalyst 30 EGR device 32 EGR passage 36 EGR cooler 38 EGR valve 40 Control device 41 Intake side temperature sensor 42 Intake side pressure sensor 44 Exhaust side temperature sensor 46 Engine outlet water temperature sensor 50 Engine cooling system 52 First cooling water passage 53 Second cooling water passage 54 Water pump 55 First branch passage 56 Second branch flow Path 57 Bypass path 64 Shutoff valve 66 Radiator 68 Thermostat

Claims (1)

An EGR device comprising: an EGR passage connecting an exhaust passage and an intake passage; an EGR valve installed in the EGR passage; and an EGR cooler installed in the EGR passage;
A cooling water flow path connected to the EGR cooler and introducing cooling water to the EGR cooler;
A valve installed in the cooling water flow path to open and close the cooling water flow path;
A control device for controlling opening and closing of the valve to control introduction of cooling water to the EGR cooler;
With
The controller is
When the flow direction of the gas passing through the EGR passage is the forward flow from the exhaust passage side to the intake passage side, the cooling water temperature is estimated based on the cooling performance of the EGR gas,
When the flow direction of the gas passing through the EGR passage is a reverse flow from the intake passage side to the exhaust passage side, the coolant temperature is estimated based on the fresh air cooling performance,
When the estimated water temperature of the cooling water is lower than a reference value, the valve is closed to block the flow of the cooling water to the EGR cooler.
A control device for an internal combustion engine.

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