JP2011007131A - Exhaust gas recirculation control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation control device accurately determining drop of cooling performances of a cooling device cooling recirculation exhaust gas recirculated from an exhaust gas channel to an intake air channel.SOLUTION: The exhaust gas recirculation control device detects EGR gas quantity and cooling water quantity by calculating from a physical model (S400). When the EGR gas quantity is higher than a prescribed quantity and absolute values of change quantities of the EGR gas quantity and the cooling water quantity are smaller than prescribed values respectively (S404:Yes), the exhaust gas recirculation control device detects actual cooling efficiency of an EGR cooler as a cooling performance detection value (S408) and calculates a cooling performance threshold C based on the EGR gas quantity and the cooling water quantity detected in S400 for comparing with the cooling performance detection value (S410). When cooling efficiency which is the cooling performance detection value is lower than the cooling performance threshold C (S412: Yes), the exhaust gas recirculation control device determines that cooling performances of the EGR cooler 22 drop (S414).

Description

  The present invention is applied to an exhaust gas recirculation system that cools a recirculated exhaust gas that is recirculated from an exhaust flow path to an intake flow path through a recirculation flow path with a cooling device that is installed in the recirculation flow path. The present invention relates to an exhaust gas recirculation control device that determines a decrease in the exhaust gas.

  Conventionally, an exhaust gas recirculation (EGR) system that recirculates exhaust gas from an exhaust flow path of an internal combustion engine to an intake flow path suppresses combustion in a cylinder of the internal combustion engine and reduces NOx emissions. It has been known.

  The recirculated exhaust gas (also referred to as EGR gas) recirculated from the exhaust side to the intake side through the recirculation flow path connecting the exhaust flow path and the intake flow path is cooled by an EGR cooler (see, for example, Patent Document 1). ). By lowering the temperature of the EGR gas with the EGR cooler, the combustion temperature in the cylinder is lowered to further suppress combustion, and if the amount of EGR gas is the same, a larger amount of exhaust gas is sucked from the exhaust side. Can be refluxed to the side.

By the way, if the particulates in the EGR gas adhere to and accumulate on the cooling fins of the EGR cooler when passing through the EGR cooler, the cooling performance of the EGR cooler deteriorates.
Therefore, in Patent Document 1, the temperature difference of the EGR gas between the inlet and the outlet of the EGR cooler, or the temperature difference of the cooling water between the inlet and the outlet of the cooling water passage for flowing the cooling water to the EGR cooler, that is, the EGR cooler is the EGR gas. The temperature difference of the EGR cooler, which indicates how much the EGR gas temperature has decreased or how much the temperature of the cooling water has increased due to cooling, and whether the cooling performance of the EGR cooler has decreased A deviation from a reference temperature difference, which is a threshold for determining whether or not, is obtained. When this deviation is larger than the standard deviation, it is determined that the cooling performance of the EGR cooler has deteriorated. In Patent Document 1, the reference temperature difference is obtained from the engine speed and the fuel injection amount.

JP 2006-300026 A

  By the way, the temperature difference of the EGR gas between the inlet and the outlet of the EGR cooler or the temperature difference of the cooling water varies depending not only on the cooling performance of the EGR cooler itself but also on the amount of EGR gas or cooling water passing through the EGR cooler.

  For example, when the amount of EGR gas is large, the temperature of the EGR gas is less likely to decrease than when the amount of EGR gas is small, so the temperature difference between the EGR gas at the inlet and the outlet of the EGR cooler is small. Also, when the amount of cooling water is small, the temperature of the EGR gas is less likely to decrease than when the amount of cooling water is large, so the temperature difference between the EGR gas at the inlet and the outlet of the EGR cooler is small.

  Thus, not only the cooling performance of the EGR cooler itself, but also the temperature difference of the EGR gas or the cooling water between the inlet and outlet of the EGR cooler, which varies depending on the amount of EGR gas or the amount of cooling water, the engine speed and the fuel. If the deterioration of the cooling performance of the EGR cooler is determined by comparing the reference temperature difference set based on the injection amount, is the cooling performance of the EGR cooler actually reduced due to changes over time such as particulate accumulation? Therefore, it cannot be distinguished whether it is lowered due to a change in the EGR gas amount or the cooling water amount. Therefore, there is a risk of erroneously determining the cause of the decrease in the cooling performance of the EGR cooler.

  The present invention has been made to solve the above problem, and an exhaust gas recirculation control for accurately determining a decrease in cooling performance of a cooling device that cools a recirculated exhaust gas recirculated from an exhaust flow path to an intake flow path. An object is to provide an apparatus.

  According to the first to seventh aspects of the present invention, the cooling performance detecting means detects the cooling performance of the cooling device that cools the recirculated exhaust gas, and the correlation value detecting means is a cooling performance correlation value that correlates with the cooling performance of the cooling device. And the threshold value calculation means calculates the cooling performance threshold value based on the cooling performance correlation value detected by the correlation value detection means. Then, the cooling performance determination unit determines a decrease in cooling performance based on the cooling performance detection value detected by the cooling performance detection unit and the cooling performance threshold.

  In this way, since the gas amount of the recirculated exhaust gas (EGR gas) that is closely correlated with the cooling performance of the cooling device is detected as the cooling performance correlation value, the cooling performance threshold value according to the increase or decrease of the gas amount that is the cooling performance correlation value Can be calculated.

  As a result, the cooling performance threshold value can be calculated in consideration of the change in the cooling performance of the cooling device due to the increase or decrease of the gas amount, so that the cooling performance of the cooling device due to the increase or decrease of the gas amount based on the detected cooling performance value and the cooling performance threshold value. It is possible to determine a decrease in the cooling performance of the cooling device in a state in which the change is excluded. As a result, it is possible to determine with high accuracy without erroneously determining a decrease in the cooling performance of the cooling device itself due to a change over time or the like.

  According to the second aspect of the present invention, the cooling performance detecting means is based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side, and the water temperature of the cooling water flowing through the cooling device. The cooling efficiency is detected as a cooling performance detection value.

The cooling efficiency can be detected from, for example, the following expression based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side, and the temperature of the cooling water flowing through the cooling device.
Cooling efficiency = (exhaust upstream temperature−exhaust downstream temperature) / (exhaust upstream temperature−water temperature) (1)
Thereby, based on the exhaust upstream temperature of the cooling device, the exhaust downstream temperature, and the water temperature of the cooling water flowing through the cooling device, the cooling efficiency can be detected with high accuracy as the cooling performance detection value.

Here, the cooling efficiency detected from the equation (1) as the cooling performance detection value decreases as the gas amount increases and the cooling device becomes difficult to cool the recirculated exhaust gas.
Therefore, according to the invention described in claim 2, the threshold value calculation means decreases the cooling performance threshold value as the gas amount increases. Thus, the detected cooling performance value detected with high accuracy and the increase in the gas amount. Based on the cooling performance threshold value considering the cooling efficiency that becomes smaller, it is possible to determine the deterioration of the cooling performance of the cooling device with high accuracy.

  According to the invention described in claim 3, the cooling performance detecting means detects the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature of the cooling device as the cooling performance detection value, and the threshold value calculating means is configured to increase the gas amount. Accordingly, the cooling performance threshold value is reduced.

  Here, the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature of the cooling device represents a decrease amount indicating how many times the temperature of the recirculated exhaust gas is cooled by the cooling device as a cooling performance detection value. The temperature difference between the exhaust upstream temperature and the exhaust downstream temperature becomes smaller as the gas amount increases.

  Thus, based on the cooling performance detection value represented by the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature of the cooling device, and the cooling performance threshold value considering the temperature difference that decreases as the gas amount increases, the cooling of the cooling device Degradation of performance can be determined with high accuracy.

  According to the fourth aspect of the present invention, the cooling performance detecting means detects the exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value, and the threshold value calculating means is the cooling performance threshold value as the gas amount increases. Increase

  Here, the exhaust downstream temperature of the cooling device represents how many times the recirculated exhaust gas has been cooled by the cooling device as a cooling performance detection value. The exhaust downstream temperature increases as the amount of gas increases and the cooling device becomes difficult to cool the recirculated exhaust gas. In other words, the cooling performance threshold value calculated based on the exhaust downstream temperature increases as the gas amount increases.

  In this way, the deterioration of the cooling performance of the cooling device can be accurately determined based on the cooling performance detection value represented by the exhaust downstream temperature of the cooling device and the cooling performance threshold considering the exhaust downstream temperature that increases as the gas amount increases. Can be judged.

  According to the fifth aspect of the present invention, the cooling performance determination means satisfies at least one of the conditions when the absolute value of the change amount of the gas amount is smaller than the predetermined value and when the gas amount is larger than the predetermined amount. When it is done, the cooling performance deterioration judgment is performed.

  When the absolute value of the change amount of the gas amount is smaller than the predetermined value, the variation in the cooling performance of the cooling device is small. In addition, when the gas amount is larger than the predetermined amount, the variation in cooling performance caused by, for example, the change in the flow rate of the recirculated exhaust gas flowing through the cooling device is smaller than when the gas amount is less than the predetermined amount.

  Therefore, when the absolute value of the change amount of the gas amount is smaller than the predetermined value and when at least one of the conditions when the gas amount is larger than the predetermined amount is satisfied, the cooling performance of the cooling device is highly accurate. Can be judged.

  According to the sixth aspect of the present invention, the correlation value detecting means further detects the amount of cooling water flowing through the cooling device as the cooling performance correlation value, and the threshold value calculating means is configured such that the correlation value detecting means uses the cooling performance correlation value as the cooling performance correlation value. A cooling performance threshold value is calculated based on the detected gas amount and cooling water amount.

  In this way, the amount of gas and cooling water that closely correlate with the cooling performance of the cooling device are detected as the cooling performance correlation value, so the cooling performance threshold is calculated according to the increase and decrease of the gas amount and cooling water amount that are the cooling performance correlation value. it can.

  As a result, the cooling performance threshold value can be calculated in consideration of the change in cooling performance of the cooling device due to the increase and decrease in the gas amount and the cooling water amount. It is possible to determine a decrease in the cooling performance of the cooling device in a state in which the change in the cooling performance of the cooling device due to is excluded. As a result, it is possible to determine with high accuracy a decrease in the cooling performance of the cooling device itself due to changes over time.

  According to the seventh aspect of the present invention, the cooling performance determining means determines the amount of change in the amount of cooling water when the absolute value of the amount of change in gas amount is smaller than a predetermined value, as well as when the gas amount is larger than a predetermined amount. When at least one of the conditions when the absolute value is smaller than the predetermined value is satisfied, the cooling performance deterioration determination is performed.

  When the absolute value of the change amount of the gas amount is smaller than the predetermined value, the variation in the cooling performance of the cooling device is small. In addition, when the gas amount is larger than the predetermined amount, the variation in cooling performance caused by, for example, the change in the flow rate of the recirculated exhaust gas flowing through the cooling device is smaller than when the gas amount is less than the predetermined amount. Further, when the absolute value of the change amount of the cooling water amount is smaller than the predetermined value, the variation in the cooling performance of the cooling device is small.

  Therefore, at least one of the case where the absolute value of the change amount of the gas amount is smaller than the predetermined value, the case where the gas amount is larger than the predetermined amount, and the case where the absolute value of the change amount of the cooling water amount is smaller than the predetermined value. When the condition is satisfied, the cooling performance of the cooling device can be determined with high accuracy.

  According to the invention described in claim 8, the cooling performance detecting means detects the cooling performance of the cooling device that cools the recirculated exhaust gas, and the correlation value detecting means cools the cooling performance as a cooling performance correlation value that correlates with the cooling performance of the cooling device. The amount of water is detected, and the threshold value calculation means calculates a cooling performance threshold value based on the cooling performance correlation value detected by the correlation value detection means. Then, the cooling performance determination unit determines a decrease in cooling performance based on the cooling performance detection value detected by the cooling performance detection unit and the cooling performance threshold.

In this way, the amount of cooling water closely correlated with the cooling performance of the cooling device is detected as the cooling performance correlation value, so the cooling performance threshold value can be calculated according to the increase or decrease of the cooling water amount that is the cooling performance correlation value.
As a result, the cooling performance threshold value can be calculated in consideration of the change in the cooling performance of the cooling device due to the increase or decrease of the cooling water amount. It is possible to determine a decrease in the cooling performance of the cooling device in a state in which the change is excluded. As a result, it is possible to determine with high accuracy a decrease in the cooling performance of the cooling device itself due to changes over time.

  According to the ninth aspect of the invention, the cooling performance detecting means is based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side of the cooling device, and the water temperature of the cooling water flowing through the cooling device. The cooling efficiency of the cooling device is detected as a cooling performance detection value.

  As described above, the cooling efficiency can be detected from Equation (1) based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side, and the temperature of the cooling water flowing through the cooling device. Thereby, based on the exhaust upstream temperature of the cooling device, the exhaust downstream temperature, and the water temperature of the cooling water flowing through the cooling device, the cooling efficiency can be detected with high accuracy as the cooling performance detection value.

Here, the cooling efficiency detected from the expression (1) as the cooling performance detection value increases as the amount of cooling water increases and the cooling device easily cools the recirculated exhaust gas.
Therefore, according to the invention described in claim 9, the threshold value calculation means increases the cooling performance threshold value as the cooling water amount increases. Thus, the cooling performance detection value detected with high accuracy and the increase in the cooling water amount are increased. Therefore, it is possible to determine with high accuracy a decrease in the cooling performance of the cooling device on the basis of the cooling performance threshold in consideration of the cooling efficiency that becomes larger.

According to the invention of claim 10, the cooling performance detecting means detects a temperature difference between the exhaust upstream temperature on the exhaust upstream side of the cooling device and the exhaust downstream temperature on the exhaust downstream side of the cooling device as a cooling performance detection value, The threshold value calculation means increases the cooling performance threshold value as the cooling water amount increases.
Here, the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature of the cooling device represents a decrease amount indicating how many times the temperature of the recirculated exhaust gas is cooled by the cooling device as a cooling performance detection value. Then, the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature increases as the cooling water amount increases.

  Thus, based on the cooling performance detection value represented by the temperature difference between the exhaust upstream temperature and the exhaust downstream temperature of the cooling device and the cooling performance threshold considering the temperature difference that increases as the amount of cooling water increases, the cooling of the cooling device Degradation of performance can be determined with high accuracy.

  According to the eleventh aspect of the invention, the cooling performance detecting means detects the exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value, and the threshold value calculating means is the cooling performance threshold value as the amount of cooling water increases. Make it smaller.

  Here, the exhaust downstream temperature of the cooling device represents how many times the recirculated exhaust gas has been cooled by the cooling device as a cooling performance detection value. The exhaust downstream temperature becomes lower as the amount of cooling water increases and the recirculated exhaust gas becomes easier to cool the cooling device. In other words, the cooling performance threshold value calculated based on the exhaust downstream temperature decreases as the cooling water amount increases.

  Thus, based on the cooling performance detection value represented by the exhaust downstream temperature of the cooling device and the cooling performance threshold considering the exhaust downstream temperature that becomes lower as the amount of cooling water increases, the deterioration of the cooling performance of the cooling device can be accurately performed. Can be judged.

According to the twelfth aspect of the present invention, when the absolute value of the amount of change in the cooling water amount is smaller than a predetermined value, the cooling performance determination unit performs the cooling performance determination.
When the absolute value of the change amount of the cooling water amount is small, the variation in the cooling performance of the cooling device is small. Therefore, when the absolute value of the change amount of the cooling water amount is smaller than the predetermined value, the cooling performance of the cooling device can be determined with high accuracy.

  The functions of the plurality of means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. The functions of the plurality of means are not limited to those realized by hardware resources that are physically independent of each other.

The block diagram which shows the exhaust gas recirculation system to which this embodiment is applied. (A) is a map for obtaining a reference threshold value for cooling performance from the engine speed and the fuel injection amount, (B) is a characteristic diagram for obtaining a correction coefficient for correcting the reference threshold value according to the EGR gas amount, and (C) is a cooling water amount. The characteristic view which calculates | requires the correction coefficient which correct | amends a reference | standard threshold value according to. The flowchart which shows the fall determination routine of cooling performance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust gas recirculation (EGR) system to which an ECU (Electronic Control Unit) 60 is applied as an exhaust gas recirculation control device according to an embodiment of the present invention.

(EGR system 20)
The fuel injected from the fuel injection valve 4 burns in an internal combustion engine (hereinafter also referred to as “engine”) 2, and exhaust gas is discharged from the engine 2 to the exhaust passage 210. The EGR system 20 is a system that recirculates exhaust gas discharged from the engine 2 to the exhaust flow path 210 from the exhaust flow path 210 to the intake flow path 200 through the recirculation flow path 220. The engine 2 is, for example, a 4-cylinder diesel engine.

  Foreign matter is removed from the intake air drawn into the intake flow path 200 by the air cleaner 10, and the intake air amount is detected by the air flow meter 12. The air flow meter 12 is installed on the intake upstream side of the position where the recirculation flow path 220 is connected to the intake flow path 200. That is, the intake air amount detected by the air flow meter 12 is the intake air upstream side of the position where the recirculated exhaust gas (EGR gas) is recirculated from the exhaust side to the intake side.

  The flow rate of the intake air from which foreign matter has been removed by the air cleaner 10 is adjusted by the throttle valve 14. The throttle valve 14 is throttled to allow more EGR gas to enter in the light load region, but is maintained in a fully open state in the high load region in order to increase the intake amount and reduce pumping loss. The intake air that has passed through the throttle valve 14 is drawn into each cylinder of the engine 2.

  The EGR system 20 includes a reflux flow path 220, an EGR cooler 22, an EGR valve 24, an ECU 60, and the like. The EGR cooler 22 and the EGR valve 24 are installed in the reflux flow path 220 in this order from the exhaust side.

  The recirculation flow path 220 connects the intake flow path 200 and the exhaust flow path 210, and exhaust gas is recirculated from the exhaust side to the intake side through the recirculation flow path 220. The recirculation flow path 220 connects an exhaust flow path 210 on the exhaust upstream side of the DPF (Diesel Particulate filter) 40 and an intake flow path 200 on the intake downstream side of the throttle valve 14.

  The EGR cooler 22 is formed, for example, in a laminated structure in which thin plates extending from the exhaust upstream side toward the downstream side are laminated at a predetermined interval. Between the thin plates, layers in which cooling water flows and layers in which wavy fins are installed are alternately formed. The layer in which the fins are installed forms a cooling channel. The EGR cooler 22 cools the EGR gas with the cooling water flowing through the cooling flow path. The cooling water supplied to the EGR cooler 22 is cooled by a vehicle radiator or the like. The cooling water is supplied to the EGR cooler 22 by a mechanical pump driven by engine torque in synchronization with the rotation of the engine 2.

  The EGR valve 24 is an electromagnetic valve whose opening degree is controlled by the duty ratio or the amount of supplied power. By controlling the opening degree of the EGR valve 24, the amount of EGR gas that is the amount of exhaust gas recirculated through the recirculation flow path 220 from the exhaust side to the intake side is adjusted.

  Exhaust temperature sensors 30 and 32 are installed in the recirculation flow path 220 on the exhaust upstream side and the exhaust downstream side of the EGR cooler 22, respectively. An intake pressure sensor 34 and an intake air temperature sensor 36 are installed in the intake flow path 200 on the intake downstream side of the connection portion between the intake flow path 200 and the return flow path 220.

  The DPF 40 is installed on the exhaust downstream side of the connection portion between the exhaust passage 210 and the reflux passage 220. The DPF 40 is formed of a honeycomb structure in which an oxidation catalyst such as platinum is supported on a porous ceramic. The inlet side and the outlet side of the flow path formed in the exhaust flow direction of the honeycomb structure of the DPF 40 are alternately sealed. Particulates, which are harmful components in the exhaust gas, flow in from the flow path in which the inlet side is not sealed and the outlet side is sealed, and pass through the partition walls of the honeycomb structure forming the flow path. It is collected in the pores. Then, the exhaust gas flows out from the flow path in which the inlet side is sealed and the outlet side is not sealed.

  The ECU 60 is mainly configured by a microcomputer having a CPU, a RAM, a ROM, a flash memory, a communication interface and the like (not shown). The ECU 60 controls the engine operating state by the CPU executing a control program stored in a storage device such as a ROM or a flash memory of the ECU 60.

  The ECU 60 outputs the air flow meter 12, the exhaust temperature sensors 30, 32, the intake pressure sensor 34, the intake air temperature sensor 36, the water temperature sensor 50, the engine speed (NE) sensor 52, the accelerator opening sensor 54, and other various sensors. The engine operating state is acquired from the signal. The ECU 60 controls the injection timing and the injection amount of the fuel injection valve 4 based on the acquired engine operating state. The ECU 60 also includes main injection that generates the main torque of the engine based on the engine operating state, and performs multi-stage injection such as pilot injection before the main injection and post injection after the main injection.

  The pilot injection is performed so that air and a small amount of fuel are mixed in advance before ignition by the main injection. The post-injection is performed to inject a minute amount of fuel and burn the particulates collected by the DPF 40.

Further, the ECU 60 adjusts the amount of EGR gas that recirculates from the exhaust side to the intake side by controlling the opening degree of the EGR valve 24.
(Cooling performance degradation of EGR cooler 22)
Since the exhaust gas in the exhaust passage 210 is recirculated to the intake passage 200 through the EGR cooler 22, particulates in the exhaust gas may adhere to cooling fins or the like of the EGR cooler 22. When particulates adhere to and accumulate on the EGR cooler 22, heat exchange between the EGR gas flowing through the EGR cooler 22 and the cooling water is hindered, and the cooling efficiency of the EGR cooler 22 decreases. The cooling efficiency as the cooling performance detection value of the EGR cooler 22 is calculated and detected by the equation (1) as described above, for example.

  In equation (1), the exhaust upstream temperature, the exhaust downstream temperature, and the water temperature are detected from the output signals of the exhaust temperature sensor 30, the exhaust temperature sensor 32, and the water temperature sensor 50, respectively. The denominator of the formula (1) indicates a decrease temperature when the EGR gas is cooled to the maximum water temperature, and the numerator indicates the decrease temperature at which the EGR gas is actually cooled by the EGR cooler 22. That is, the cooling efficiency of the formula (1) represents the ratio of the actual cooling performance to the maximum cooling performance. Thus, the actual cooling performance of the EGR cooler 22 can be detected with high accuracy by calculating the cooling efficiency of the EGR cooler 22 from the equation (1).

  Here, the cooling efficiency of the EGR gas not only changes due to changes over time, such as adhesion of particulates, but also changes depending on the amount of EGR gas flowing through the EGR cooler 22 and the amount of cooling water.

  For example, when the amount of EGR gas is large, the temperature of the EGR gas is less likely to decrease than when the amount of EGR gas is small, and therefore the temperature difference between the EGR gas at the inlet and the outlet of the EGR cooler 22 is small. In addition, when the amount of cooling water is small, the temperature of the EGR gas is less likely to decrease than when the amount of cooling water is large, so the temperature difference between the EGR gas at the inlet and the outlet of the EGR cooler 22 is small. That is, the EGR gas amount and the cooling water amount are cooling performance correlation values that are closely correlated with the cooling performance of the EGR cooler 22.

  Here, the EGR gas amount and the cooling water amount can be estimated from the engine speed and the fuel injection amount. As described above, since the EGR gas amount and the cooling water amount are closely correlated with the cooling performance of the EGR cooler 22, the engine speed and the fuel injection amount are based on the EGR gas amount and the cooling water amount. As shown in FIG. 2A, a reference threshold value C0 that represents a cooling efficiency that serves as a reference when it is determined that the cooling performance of the EGR cooler 22 is deteriorated can be calculated.

  However, since the reference threshold value C0 is a value calculated from a map of the engine speed and the fuel injection amount, the actual EGR gas amount or the cooling water amount is calculated from a reference value estimated from the engine speed and the fuel injection amount. In the case of deviation, it is necessary to correct the reference threshold value C0 based on the actual EGR gas amount or the cooling water amount.

  Therefore, based on the characteristic diagrams of FIGS. 2B and 2C, the correction coefficient of the reference threshold C0 in the reference value of the EGR gas amount and the cooling water amount estimated from the engine speed and the fuel injection amount is set to 1. Then, correction coefficients k1 and k2 in the detected values of the actual EGR gas amount and the cooling water amount are calculated with respect to the estimated reference values of the EGR gas amount and the cooling water amount, respectively.

  As the amount of EGR gas increases, the cooling performance of the EGR cooler 22 decreases, so that the correction coefficient k1 decreases as shown in FIG. Further, since the cooling performance of the EGR cooler 22 increases as the amount of cooling water increases, the correction coefficient k2 increases as shown in FIG.

Thereby, the cooling performance threshold value C used as a reference | standard when determining with the cooling performance of the EGR cooler 22 falling can be calculated from following Formula (2).
C (cooling performance threshold) = C0 × k1 × k2 (2)
Then, the actual cooling efficiency of the EGR cooler 22 calculated from the equation (1) is compared with the cooling performance threshold value calculated from the equation (2), so that a decrease in the cooling performance of the EGR cooler 22 can be determined with high accuracy.

(Condition for cooling performance of EGR cooler 22)
When the absolute value of the change amount of the EGR gas amount is small, the change in the cooling performance of the EGR cooler 22 is also small. Further, when the absolute value of the change amount of the cooling water amount is small, the change in the cooling performance of the EGR cooler 22 is also small. Further, when the amount of EGR gas is large, even if the flow rate of the EGR gas flowing through the EGR cooler changes, the change in the cooling performance of the EGR cooler 22 is small. As described above, when the change in the cooling performance of the EGR cooler 22 is small, the actual cooling efficiency of the EGR cooler 22 and the cooling performance threshold value can be compared to determine a decrease in the cooling performance of the EGR cooler 22 with high accuracy. .

  Therefore, at least one of the case where the absolute value of the change amount of the EGR gas amount is smaller than the predetermined value, the case where the absolute value of the change amount of the cooling water amount is smaller than the predetermined value, and the case where the absolute value of the change amount of the cooling water amount is smaller than the predetermined value. When such a condition is satisfied, the determination of the cooling performance of the EGR cooler 22 is performed. It should be noted that it is more desirable to perform the determination of the cooling performance of the EGR cooler 22 when all the three conditions are satisfied.

(Detection of EGR gas amount and cooling water amount)
The intake air amount sucked into the engine 2 is the sum of the intake air amount detected by the air flow meter 12 and the EGR gas amount recirculated to the downstream side of the air flow meter 12. Therefore, the amount of EGR gas flowing through the recirculation flow path 220 can be detected by subtracting the intake air amount detected by the air flow meter 12 from the intake air amount sucked into the engine 2.

  The amount of intake air sucked into the engine 2 is based on a physical model such as a gas state equation based on the intake pressure, intake air temperature, and engine speed downstream of the connection between the intake passage 200 and the return passage 220. It can be calculated from The intake pressure and the intake temperature can be detected from the output signals of the intake pressure sensor 34 and the intake temperature sensor 36, respectively.

  Further, as described above, the cooling water is supplied to the EGR cooler 22 by a mechanical pump driven by engine torque. Therefore, the amount of cooling water flowing through the EGR cooler 22 can be detected by calculating from the physical model based on the engine speed detected from the output signal of the engine speed sensor 52. The amount of change in the EGR gas amount and the cooling water amount is calculated by differentiation.

(Cooling performance judgment routine)
FIG. 3 shows a routine for determining the cooling performance of the EGR cooler 22. The routine of FIG. 3 is always executed. In FIG. 3, “S” represents a step.

  In S400 of FIG. 3, the ECU 60 calculates and detects the EGR gas amount and the cooling water amount from the physical model as described above. In S402, the ECU 60 differentiates the EGR gas amount and the cooling water amount, respectively, to calculate an absolute value of the change amount of the EGR gas amount and the cooling water amount.

In S404, the ECU 60 determines whether or not the EGR gas amount is larger than a predetermined amount and the absolute values of the change amounts of the EGR gas amount and the cooling water amount are smaller than predetermined values.
If the EGR gas amount is less than or equal to the predetermined amount, or if either the absolute value of the change amount of the EGR gas amount or the cooling water amount is greater than or equal to the predetermined value (S404: No), the cooling performance of the EGR cooler 22 is highly accurate. The ECU 60 ends this routine.

  When the EGR gas amount is larger than the predetermined amount and the absolute values of the change amounts of the EGR gas amount and the cooling water amount are smaller than the predetermined values (S404: Yes), the ECU 60 reduces the cooling performance for the EGR cooler 22 in S406. Allow judgment.

  In S408, the ECU 60 calculates and detects the actual cooling efficiency of the EGR cooler 22 as a cooling performance detection value based on the equation (1). In step S410, the ECU 60 calculates the cooling performance threshold value C from the equation (2) based on the EGR gas amount and the cooling water amount detected in step S400 in order to compare with the cooling efficiency.

  In S412, the ECU 60 determines whether the detected cooling performance value is smaller than the cooling performance threshold value, that is, whether the cooling performance of the EGR cooler 22 is degraded. When the cooling performance detection value is equal to or greater than the cooling performance threshold value (S412: No), the ECU 60 determines that the cooling performance of the EGR cooler 22 has not deteriorated, and ends this routine.

  When the cooling performance detection value is smaller than the threshold value (S412: Yes), in S414, the ECU 60 determines that the cooling performance of the EGR cooler 22 is deteriorated, and ends this routine.

In the present embodiment, the engine 2 corresponds to the internal combustion engine of the present invention, the EGR cooler 22 corresponds to the cooling device of the present invention, and the ECU 60 corresponds to the exhaust gas recirculation control device of the present invention.
Also, S400 and S402 in FIG. 3 correspond to functions executed by the correlation value detecting means, S404, S406, S412, and S414 correspond to functions executed by the cooling performance determining means, and S408 is executed by the cooling performance detecting means. S410 corresponds to a function executed by the threshold value calculation means. The ECU 60 executes a process of S400 to S414 in FIG. 3 by a control program stored in a storage device such as a ROM or a flash memory, so that a cooling performance detecting unit, a correlation value detecting unit, a threshold calculating unit, and a cooling unit It functions as a performance judgment means.

  In the present embodiment described above, the cooling performance threshold value C is calculated by correcting the reference threshold value C0 calculated from the engine speed and the fuel injection amount based on the EGR gas amount and the cooling water amount. And the fall of the cooling performance of the EGR cooler 22 was determined by comparing the cooling efficiency representing the actual cooling performance of the EGR cooler 22 with the cooling performance threshold.

  As a result, in comparison with the case where the reference threshold value calculated from the engine speed and the fuel injection amount is compared with the cooling efficiency, the EGR gas is changed in consideration of the change in the cooling performance of the EGR cooler due to the change in the EGR gas amount and the cooling water amount. In the state where the change in the cooling performance of the EGR cooler due to the change in the amount and the amount of the cooling water is excluded, it is possible to determine the decrease in the cooling performance of the EGR cooler itself due to a change with time.

As a result, the deterioration of the cooling performance of the EGR cooler itself due to a change with time such as particulate deposition can be determined with high accuracy without erroneous determination.
[Other Embodiments]
In the above embodiment, the reference threshold value calculated from the engine speed and the fuel injection amount is corrected based on the EGR gas amount and the cooling water amount to calculate the cooling performance threshold value. On the other hand, the reference threshold value may be corrected based on only one of the EGR gas amount and the cooling water amount to calculate the cooling performance threshold value.

  Further, as the cooling performance detection value of the EGR cooler 22, instead of the cooling efficiency calculated from the equation (1), the EGR gas temperature (exhaust upstream temperature) on the exhaust upstream side of the EGR cooler 22 and the EGR gas temperature (exhaust upstream temperature) ( The temperature difference from the exhaust downstream temperature) or the EGR gas temperature on the exhaust downstream side may be detected as a cooling performance detection value of the EGR cooler 22 and compared with a corresponding cooling performance threshold.

Further, instead of the mechanical pump driven by the engine torque, the cooling water may be supplied to the EGR cooler 22 by an electric pump.
In addition, the EGR gas amount and the cooling water amount as the cooling performance correlation value may be directly detected by a flow rate sensor instead of being calculated from the physical model and detected.

  In the above embodiment, an example in which the present invention is applied to an EGR system of a diesel engine has been described. On the other hand, as long as the exhaust gas recirculated from the exhaust side to the intake side is cooled by the EGR cooler, the present invention is not limited to a diesel engine, but any EGR system for an internal combustion engine such as a direct injection type gasoline engine. Can be applied.

  In the above embodiment, the functions of the cooling performance detection means, the correlation value detection means, the threshold value calculation means, and the cooling performance determination means are realized by the ECU 60 whose functions are specified by the control program. On the other hand, at least a part of the functions executed by the ECU 60 may be realized by hardware whose functions are specified by the circuit configuration itself.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

2: diesel engine (internal combustion engine), 20: EGR (exhaust gas recirculation) system, 22: EGR cooler (cooling device), 24: EGR valve, 60: ECU (exhaust gas recirculation control device, cooling performance detecting means, correlation value) Detection means, threshold value calculation means, cooling performance determination means), 200: intake flow path, 210: exhaust flow path, 220: recirculation flow path

Claims (12)

An exhaust flow path and an intake flow path of an internal combustion engine are connected by a recirculation flow path, and a recirculation exhaust gas recirculated from the exhaust flow path to the intake flow path through the recirculation flow path is installed in the recirculation flow path. In an exhaust gas recirculation control apparatus that is applied to an exhaust gas recirculation system that cools by a cooling device that determines a decrease in cooling performance of the cooling device
Cooling performance detecting means for detecting the cooling performance of the cooling device;
Correlation value detecting means for detecting the amount of the recirculated exhaust gas as a cooling performance correlation value correlated with the cooling performance;
Threshold calculation means for calculating a cooling performance threshold based on the cooling performance correlation value detected by the correlation value detection means;
Cooling performance determination means for determining a decrease in the cooling performance based on the cooling performance detection value detected by the cooling performance detection means and the cooling performance threshold value calculated by the threshold value calculation means;
An exhaust gas recirculation control device comprising: The cooling performance detection means is configured to determine the cooling efficiency of the cooling device based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side of the cooling device, and the temperature of the cooling water flowing through the cooling device. Is detected as the cooling performance detection value,
The threshold value calculation means decreases the cooling performance threshold value as the gas amount increases.
The exhaust gas recirculation control apparatus according to claim 1. The cooling performance detection means detects a temperature difference between an exhaust upstream temperature on the exhaust upstream side of the cooling device and an exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value,
The threshold value calculation means decreases the cooling performance threshold value as the gas amount increases.
The exhaust gas recirculation control apparatus according to claim 1. The cooling performance detection means detects the exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value,
The threshold value calculation means increases the cooling performance threshold value as the gas amount increases.
The exhaust gas recirculation control apparatus according to claim 1.   The cooling performance determining means determines the cooling performance when the absolute value of the change amount of the gas amount is smaller than a predetermined value and when at least one of the conditions when the gas amount is larger than the predetermined amount is satisfied. The exhaust gas recirculation control apparatus according to any one of claims 1 to 4, wherein a reduction determination is performed. The correlation value detecting means further detects the amount of cooling water flowing through the cooling device as the cooling performance correlation value,
The threshold value calculation means calculates the cooling performance threshold value based on the gas amount and the cooling water amount detected by the correlation value detection means as the cooling performance correlation value.
The exhaust gas recirculation control apparatus according to any one of claims 1 to 5, wherein   The cooling performance determination unit is configured to determine whether the absolute value of the change amount of the gas amount is smaller than a predetermined value, when the gas amount is larger than the predetermined amount, and when the absolute value of the change amount of the cooling water amount is larger than a predetermined value. The exhaust gas recirculation control apparatus according to claim 6, wherein the cooling performance reduction determination is performed when at least one of the conditions is satisfied. An exhaust flow path and an intake flow path of an internal combustion engine are connected by a recirculation flow path, and a recirculation exhaust gas recirculated from the exhaust flow path to the intake flow path through the recirculation flow path is installed in the recirculation flow path. In an exhaust gas recirculation control apparatus that is applied to an exhaust gas recirculation system that cools by a cooling device that determines a decrease in cooling performance of the cooling device
Cooling performance detecting means for detecting the cooling performance of the cooling device;
Correlation value detecting means for detecting a cooling water amount flowing through the cooling device as a cooling performance correlation value correlated with the cooling performance;
Threshold calculation means for calculating a cooling performance threshold based on the cooling performance correlation value detected by the correlation value detection means;
Cooling performance determination means for determining a decrease in the cooling performance based on the cooling performance detection value detected by the cooling performance detection means and the cooling performance threshold value calculated by the threshold value calculation means;
An exhaust gas recirculation control device comprising: The cooling performance detection means is configured to determine the cooling efficiency of the cooling device based on the exhaust upstream temperature on the exhaust upstream side of the cooling device, the exhaust downstream temperature on the exhaust downstream side of the cooling device, and the temperature of the cooling water flowing through the cooling device. Is detected as the cooling performance detection value,
The threshold value calculation means increases the cooling performance threshold value as the cooling water amount increases.
The exhaust gas recirculation control apparatus according to claim 7 or 8, wherein The cooling performance detection means detects a temperature difference between an exhaust upstream temperature on the exhaust upstream side of the cooling device and an exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value,
The threshold value calculation means increases the cooling performance threshold value as the cooling water amount increases.
The exhaust gas recirculation control apparatus according to claim 7 or 8, wherein The cooling performance detection means detects the exhaust downstream temperature on the exhaust downstream side of the cooling device as the cooling performance detection value,
The threshold value calculation means reduces the cooling performance threshold value as the cooling water amount increases.
The exhaust gas recirculation control apparatus according to claim 7 or 8, wherein   12. The cooling performance determination unit according to claim 7, wherein when the absolute value of the amount of change in the cooling water amount is smaller than a predetermined value, the cooling performance determination unit performs the cooling performance decrease determination. Exhaust gas recirculation control device.

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