JP4798099B2 - Control device for internal combustion engine - Google Patents

Description

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

  Conventionally, in an internal combustion engine such as a diesel engine, exhaust gas recirculation (EGR: Exhaust Gas) that suppresses the generation of NOx by returning a part of the exhaust gas from the exhaust passage to the intake passage and lowering the combustion temperature in the engine. A device is known. The EGR device is provided with an EGR cooler to lower the temperature of exhaust gas (EGR gas) returned to the intake passage. When the EGR device cools the temperature of the EGR gas, the combustion temperature in the engine can be lowered and the generation of NOx can be suppressed.

  Patent Document 1 below describes an exhaust purification device for an internal combustion engine that suppresses emission reduction by controlling the intake air amount and EGR amount with respect to the EGR cooler cooling efficiency. Patent Document 2 describes an EGR gas temperature estimation device that estimates EGR cooler cooling efficiency from EGR cooler upstream / downstream temperatures and cooling water temperature. Patent Document 3 describes an exhaust purification device for an internal combustion engine in which the combustion temperature is reduced by retarding the fuel injection timing.

JP 2002-129996 A JP 2004-156457 A JP 2003-293810 A

  However, as EGR gas returns to the intake passage as the operation time of the internal combustion engine elapses, deposits such as HC and soluble organic components (SOF) adhere to the heat exchange portion of the EGR cooler, thereby cooling the EGR cooler. Performance (heat exchange rate) decreases. As a result, the EGR cooler has a problem that the emission deteriorates due to aging. Patent Documents 1 to 3 do not discuss any point of preventing emission deterioration due to aging deterioration of the EGR cooler.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can prevent deterioration of emissions due to aging deterioration of an EGR cooler.

In one aspect of the present invention, a fuel injection unit that injects fuel into an internal combustion engine, an EGR passage that recirculates EGR gas that is part of exhaust gas from an exhaust passage to an intake passage, and an EGR passage attached to the EGR passage a control apparatus for an internal combustion engine having an EGR cooler, based on the heat exchange efficiency of the EGR cooler, a control means for correcting retarding the fuel injection timing of said fuel injection means, wherein, prior Symbol The retardation correction amount is increased as the heat exchange efficiency of the EGR cooler becomes lower.

The control device for an internal combustion engine includes fuel injection means, an EGR passage, an EGR cooler, and control means. The fuel injection means is, for example, a fuel injection valve, and injects fuel into the internal combustion engine. The EGR passage recirculates EGR gas that is part of the exhaust gas from the exhaust passage to the intake passage. An EGR cooler is attached to the EGR passage. The control means is, for example, an ECU (Electronic Control Unit), and retards the fuel injection timing of the fuel injection means based on the heat exchange efficiency of the EGR cooler. The retardation correction amount is obtained, for example, from a map with the heat exchange efficiency of the EGR cooler. Thus, by correcting the delay of the fuel injection timing, the ignition delay is shortened, so that the combustion temperature can be lowered and the generation of NOx can be reduced. Further, in a state where the heat exchange efficiency of the EGR cooler is relatively high, the EGR gas is cooled by the EGR cooler, so that the combustion temperature in the internal combustion engine can be lowered and the generation of NOx can be suppressed, and the heat of the EGR cooler can be suppressed. In a state where the exchange efficiency is relatively low, the generation of NOx can be suppressed by correcting the delay of the fuel injection timing and lowering the combustion temperature in the engine 10.

In another aspect of the control apparatus for an internal combustion engine, the retardation correction amount is a correction amount that can retard the fuel injection timing without misfiring.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[Configuration of internal combustion engine]
First, the configuration of the control device for an internal combustion engine according to the present embodiment will be described. FIG. 1 is a block diagram showing a schematic configuration of a control device 100 for an internal combustion engine according to the present embodiment. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals.

  In FIG. 1, a control device 100 for an internal combustion engine includes an in-line four-cylinder diesel engine as an internal combustion engine (engine) 10. Each cylinder of the engine 10 is connected to an intake manifold 11 and an exhaust manifold 12. The engine 10 includes a fuel injection valve 15 provided in each cylinder, and a common rail 14 that supplies high-pressure fuel to each fuel injection valve 15. The common rail is in a high-pressure state by a fuel pump (not shown). Supplied. Each fuel injection valve 15 has its fuel injection amount and injection timing controlled by a control signal S1 from the ECU 7.

  An intake passage 20 connected to the intake manifold 11 cools an air flow meter 21 that measures the amount of air flowing into the engine 10 (fresh air amount), a throttle valve 22, a compressor 23a of a turbocharger 23, and intake air. An intercooler 24 is provided. A turbine 23 b of the turbocharger 23 and a catalyst 30 are provided in the exhaust passage 25 connected to the exhaust manifold 12. The catalyst 30 is, for example, a NOx storage reduction catalyst that processes NOx.

  In the control device 100 for the internal combustion engine, an EGR passage 31 that connects the exhaust passage 25 and the intake passage 20 is provided. The EGR passage 31 functions as an EGR device. Specifically, the EGR passage 31 connects the upstream position of the turbine 23 b in the exhaust passage 25 and the downstream position of the compressor 23 a in the intake passage 20. Therefore, part of the exhaust gas (EGR gas) returns from the upstream position of the turbine 23 b in the exhaust passage 25 to the downstream position of the intercooler 24 in the intake passage 20 via the EGR passage 31.

  The EGR passage 31 is provided with an EGR cooler 32 and an EGR valve 33. The EGR cooler 32 has a heat exchanging portion in which cooling water is circulated outside the EGR passage 31, and cools the EGR gas by exchanging heat between the EGR gas and the cooling water in the heat exchanging portion. . When the EGR gas cooled by the EGR cooler 32 is mixed with the inflow air of the intake passage, the combustion temperature in the engine 10 is lowered, and the generation of NOx is reduced. The EGR valve 33 is for adjusting the flow rate of the EGR gas flowing through the EGR passage 31, and its opening degree is controlled by a control signal S <b> 2 from the ECU 7.

  The ECU (Electronic Control Unit) 7 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown). ECU20 acquires a detection signal from the various sensors with which the control apparatus 100 of the internal combustion engine was equipped, and controls the engine 10 based on this. In the control apparatus for an internal combustion engine according to the present embodiment, the ECU 7 corrects the delay of the fuel injection timing of the fuel injection valve 15 based on the heat exchange efficiency of the EGR cooler 32 (hereinafter referred to as “EGR cooler efficiency”). . Therefore, the ECU 7 functions as a control unit in the present invention.

(Control method for internal combustion engine)
Next, the internal combustion engine control method according to this embodiment will be specifically described.

  When the EGR cooler 32 is attached, heat exchange between the EGR gas and the cooling water is actively performed, so that the EGR gas can be sufficiently cooled, and the intake air temperature in the intake manifold 11 decreases. Therefore, the combustion temperature in the engine 10 is lowered, and the generation of NOx can be sufficiently suppressed.

  However, as the operating time of the engine 10 elapses, deposits such as HC and SOF adhere to the heat exchanging portion of the EGR cooler 32 while the EGR gas returns to the intake passage, so that the EGR gas, the cooling water, The heat exchange efficiency during the period decreases, and the EGR cooler 32 deteriorates over time. If the EGR cooler deteriorates over time, the EGR gas cannot be sufficiently cooled, and the intake air temperature in the intake manifold 11 rises. Thereby, the combustion temperature in the engine 10 rises. When the combustion temperature in the engine 10 rises, it becomes strong against misfire and HC and CO can be reduced, but it becomes difficult to sufficiently suppress the generation of NOx.

  Therefore, in the control device for an internal combustion engine according to the present embodiment, the ECU 7 corrects the delay of the fuel injection timing of the fuel injection valve 15 based on the EGR cooler efficiency of the EGR cooler 32. By correcting the delay of the fuel injection timing, the ignition delay is shortened, so that the combustion temperature can be lowered and the generation of NOx can be reduced. The details will be described below.

  FIG. 2 is a graph showing the relationship between the EGR cooler efficiency and the retardation correction amount of the fuel injection timing. Specifically, the retardation correction amount shown in the graph of FIG. 2 indicates a correction amount capable of retarding the fuel injection timing. Therefore, if the fuel injection timing is retarded larger than the retard correction amount shown in the graph of FIG. As can be seen from the graph of FIG. 2, the higher the EGR cooler efficiency, the lower the intake air temperature in the intake manifold 11, so the correction amount that can be retarded becomes smaller. On the other hand, the lower the EGR cooler efficiency, Since the intake air temperature in the manifold 11 rises, the correction amount that can be retarded increases.

  In the control apparatus for an internal combustion engine according to the present embodiment, for example, the ECU 7 stores in advance a relationship between the EGR cooler efficiency and the fuel injection timing retardation correction amount shown in the graph of FIG. 2 as a map, and based on the map The delay correction amount for the fuel injection timing is adjusted. Specifically, the ECU 7 increases the retard correction amount of the fuel injection timing when the EGR cooler efficiency decreases, and retards the retard correction amount of the fuel injection timing when the EGR cooler efficiency increases. Will be reduced. A method for estimating the EGR cooler efficiency will be described later in detail.

  According to the control device for an internal combustion engine, in a state where the EGR cooler efficiency is relatively high, the EGR gas is cooled by the EGR cooler 32, thereby reducing the combustion temperature in the engine 10 and suppressing the generation of NOx. In the state where the EGR cooler efficiency is relatively low, the fuel injection timing can be corrected to retard the combustion temperature in the engine 10 and the generation of NOx can be suppressed. By doing in this way, in the control device for an internal combustion engine according to the present embodiment, it is possible to sufficiently suppress the generation of NOx even if the EGR cooler deteriorates over time.

(EGR cooler efficiency estimation method)
Next, a method for estimating the EGR cooler efficiency will be described. As an estimation method of the EGR cooler efficiency, hereinafter, a method of estimating the EGR cooler efficiency based on the travel distance of the vehicle on which the engine 10 is mounted, and an EGR efficiency based on the integrated amount of the flow rate of the EGR gas passing through the EGR cooler 32 will be described. A method for estimating the EGR cooler efficiency based on the temperature at the inlet / outlet of the EGR gas of the EGR cooler 32 and the water temperature of the cooling water will be described.

  First, a method for estimating the EGR cooler efficiency based on the travel distance of the vehicle on which the engine 10 is mounted will be described with reference to FIG. A graph 41 indicated by a solid line in FIG. 3 is a graph showing the relationship between the travel distance of the vehicle and the EGR cooler efficiency. As shown in the graph 41 of FIG. 3, as the travel distance of the vehicle increases, the operation time of the engine 10 also increases. Therefore, the amount of deposit that accumulates in the heat exchange portion on the EGR cooler 32 increases, and the EGR cooler efficiency increases. Will decline. On the other hand, as the traveling distance of the vehicle becomes shorter, the operation time of the engine 10 also becomes shorter. Therefore, the amount of deposit accumulated in the heat exchange section on the EGR cooler 32 decreases, and the EGR cooler efficiency increases.

  However, as shown in the graph 41 of FIG. 3, the EGR cooler efficiency has a lower limit value CL, and does not decrease below the lower limit value CL when the travel distance is a certain distance or more. The reason is as follows. That is, when deposits adhere to and accumulate on the heat exchange part of the EGR cooler 32, the heat exchange efficiency between the EGR gas and the cooling water decreases, and the temperature of the EGR gas rises. However, when the amount of deposit deposited by adhering to the heat exchanging portion of the EGR cooler 32 exceeds a certain amount, a part of the deposit adhering to the heat exchanging portion is removed from the heat exchanging portion by the EGR gas whose temperature has increased. It is. When the travel distance is a certain distance or more, the amount of deposit adhering to the heat exchanging portion of the EGR cooler 32 and the amount of deposit deposited on the heat exchanging portion of the EGR cooler 32 are equal and an equilibrium state is obtained. Therefore, if the EGR cooler efficiency at this time is CL, the EGR cooler efficiency will not be lower than the lower limit value CL.

  In the control apparatus for an internal combustion engine according to the present embodiment, when the EGR cooler efficiency is estimated based on the travel distance of the vehicle on which the engine 10 is mounted, the ECU 7 travels the vehicle as indicated by a graph 41 in FIG. The relationship between the distance and the EGR cooler efficiency is stored in advance as a map, and the EGR cooler efficiency is estimated using the map based on the travel distance obtained from a detection signal such as a vehicle speed sensor (not shown). .

  Here, the exhaust temperature when the engine 1 is under high load and high speed is higher than the exhaust temperature when the engine 1 is under low load and low speed. Therefore, when the operating state of the engine 1 changes from low load low rotation to high load high rotation, the temperature of the EGR gas also increases. At this time, a part of the deposit adhering to the heat exchanging portion of the EGR cooler 32 is removed from the heat exchanging portion by the EGR gas whose temperature has risen, and the EGR cooler efficiency is increased. For example, as shown in the broken line graph 42 in FIG. 3, when the exhaust gas temperature increases due to traveling at a high speed during the travel distance L1, the efficiency of the EGR cooler increases.

  Therefore, if the ECU 7 determines that the exhaust temperature has risen based on a detection signal from a temperature sensor (not shown) attached to the exhaust passage 25, the ECU 7 calculates the vehicle travel distance indicated by the graph 41 in FIG. A correction is performed to increase the EGR cooler efficiency estimated using a map indicating the relationship with the EGR cooler efficiency by a correction amount corresponding to a travel distance when the exhaust temperature rises, for example, a travel distance when traveling at high speed. It is also good. By doing in this way, EGR efficiency can be estimated more correctly.

  Next, a method for estimating the EGR efficiency based on the integrated amount of the flow rate of the EGR gas passing through the EGR cooler 32 (hereinafter referred to as “cooler passing exhaust gas integrated amount”) will be described.

  The graph of FIG. 4 is a graph showing the relationship between the cooler passage exhaust gas integrated amount and the EGR cooler efficiency. As shown in the graph of FIG. 4, as the cumulative amount of exhaust gas passing through the cooler increases, the amount of deposit that accumulates in the heat exchange portion of the EGR cooler 32 increases, so the EGR cooler efficiency of the EGR cooler 32 decreases. On the other hand, as the cumulative amount of exhaust gas passing through the cooler decreases, the amount of deposit accumulated in the heat exchange portion of the EGR cooler 32 decreases, so that the EGR cooler efficiency of the EGR cooler 32 increases. However, the EGR cooler efficiency does not decrease when the accumulated amount of exhaust gas passing through the cooler exceeds a certain amount. This is because, as described above, if the cumulative amount of exhaust gas passing through the cooler is a certain amount or more, the amount of deposits adhering to the heat exchanging part of the EGR cooler 32 and the deposit accumulated in the heat exchanging part of the EGR cooler 32 are This is because the amount to be removed becomes equal and an equilibrium state is reached.

  In the control apparatus for an internal combustion engine according to the present embodiment, when estimating the EGR cooler efficiency based on the cooler passage exhaust gas integrated amount, the ECU 7, for example, the cooler passage exhaust gas integrated amount and EGR shown in the graph of FIG. The relationship with the cooler efficiency is stored in advance as a map, and the cooler passage exhaust gas integration is based on the cooler passage exhaust gas integration amount obtained from the detection signal from the A / F sensor (not shown) attached to the EGR passage 31. The EGR cooler efficiency is estimated using a map showing the relationship between the amount and the EGR cooler efficiency.

  Here, the EGR cooler efficiency estimated based on the integrated amount of exhaust gas passing through the cooler may be further corrected based on the temperature of the EGR gas. The EGR cooler efficiency has the following relationship with the temperature of the EGR gas. That is, when the temperature of the EGR gas rises to the first predetermined temperature or more, a part of the deposit attached to the heat exchange part of the EGR cooler 32 is easily detached, and the EGR cooler efficiency is increased. . This first predetermined temperature is approximately 350 ° C. On the other hand, when the temperature of the EGR gas is decreased to be equal to or lower than the second predetermined temperature, deposits in the EGR gas are likely to adhere to the heat exchange portion of the EGR cooler 32, and the EGR cooler efficiency is decreased. This second predetermined temperature is approximately 200 ° C. When the temperature of the EGR gas is a temperature between the first predetermined temperature and the second predetermined temperature, the EGR cooler efficiency is substantially constant.

  Therefore, in the control apparatus for an internal combustion engine according to the present embodiment, the EGR cooler efficiency estimated based on the accumulated amount of exhaust gas passing through the cooler may be corrected as follows. That is, the ECU 7 determines that the temperature of the EGR gas is equal to or higher than the first predetermined temperature based on the temperature of the EGR gas obtained from a detection signal from a temperature sensor (not shown) attached to the EGR passage 31. If it is determined, correction is performed to increase the EGR cooler efficiency estimated based on the accumulated amount of exhaust gas passing through the cooler, and if it is determined that the temperature of the EGR gas is equal to or lower than the second predetermined temperature, It is assumed that correction for reducing the EGR efficiency estimated based on the integrated amount of exhaust gas passing through the cooler is performed. By doing in this way, EGR efficiency can be estimated more correctly. Here, it is assumed that the first predetermined temperature and the second predetermined temperature are obtained in advance by experiments or the like and stored in the ECU 7. The correction value of the EGR cooler efficiency is obtained from, for example, a map with the temperature of the EGR gas. This map is obtained in advance by experiments or the like and is stored in the ECU 7.

  Next, a method for estimating the EGR efficiency based on the temperature at the EGR gas inlet / outlet of the EGR cooler 32 and the coolant temperature will be described.

  In the control device for an internal combustion engine according to the present embodiment, the ECU 7 controls the temperature at the inlet of the EGR cooler 32 into which EGR gas flows (inlet temperature), the temperature at the outlet of the EGR cooler 32 from which EGR gas flows out (outlet temperature), EGR. The EGR efficiency can also be estimated based on the coolant temperature in the heat exchange section of the cooler 32. Specifically, the ECU 7 obtains the inlet temperature and the outlet temperature from a detection signal from a temperature sensor (not shown) attached to the EGR passage 31, and is attached to the cooling water passage in the heat exchange part of the EGR cooler 32. The EGR cooler efficiency can be obtained by obtaining the coolant temperature from a detection signal from a water temperature sensor (not shown) and substituting the values of the inlet temperature, the outlet temperature, and the water temperature into the following equation (1). .

EGR cooler efficiency = (inlet temperature-outlet temperature) / (inlet temperature-water temperature) (1)
By using the method described above, the ECU 7 can estimate the EGR cooler efficiency. In the control apparatus for an internal combustion engine according to the present embodiment, the ECU 7 estimates the EGR cooler efficiency using the method described above, and based on the estimated EGR cooler efficiency, the EGR cooler efficiency shown in the graph of FIG. And a map indicating the relationship between the fuel injection timing retardation correction amount and the fuel injection timing retardation correction amount is obtained, and the fuel injection timing is adjusted by the obtained retardation correction amount. By doing in this way, in the control device for an internal combustion engine according to the present embodiment, it is possible to sufficiently suppress the generation of NOx even if the EGR cooler deteriorates over time.

[Modification]
In the control device for an internal combustion engine of the present embodiment, as shown in FIG. 1, the EGR passage 31 connects the upstream position of the turbine 23 b in the exhaust passage 25 and the downstream position of the compressor 23 a in the intake passage 20. The so-called high-pressure loop EGR device (HPL). However, the present invention is not limited to this, and instead, the EGR passage 31 connects the downstream position of the turbine 23b in the exhaust passage 25 and the upstream position of the compressor 23a in the intake passage 20 so-called low-pressure loop EGR device. It goes without saying that the present invention can be applied even if it is (LPL).

It is a block diagram which shows schematic structure of the control apparatus of the internal combustion engine which concerns on this embodiment. It is a graph which shows the relationship between EGR cooler efficiency and the amount of retardation correction of fuel injection timing. It is a graph which shows the relationship between the travel distance of a vehicle, and EGR cooler efficiency. It is a graph which shows the relationship between cooler passage exhaust gas integrated amount and EGR cooler efficiency.

Explanation of symbols

7 ECU
10 Internal combustion engine
17 Fuel addition valve 20 Intake passage 23 Turbocharger 25 Exhaust passage 30 DPF
31 EGR passage 32 EGR cooler 33 EGR valve

Claims (2)

An internal combustion engine having fuel injection means for injecting fuel to the internal combustion engine, an EGR passage for recirculating EGR gas that is part of exhaust gas from the exhaust passage to the intake passage, and an EGR cooler attached to the EGR passage A control device,
Based on the heat exchange efficiency of the EGR cooler, comprising a control means for correcting the retardation of the fuel injection timing of the fuel injection means,
Wherein, the lower the heat exchange efficiency of the previous SL EGR cooler, the control device for an internal combustion engine, characterized by increasing the retard correction amount.   The control apparatus for an internal combustion engine according to claim 1, wherein the retard correction amount is a correction amount capable of retarding the fuel injection timing without misfiring.

Images