JP2006112272A - Intake air temperature control system for internal combustion engine - Google Patents

Abstract

An intake air temperature control system capable of more simply and more accurately controlling an intake air temperature in an internal combustion engine including an exhaust gas recirculation device.
In an intake air temperature control system for an internal combustion engine, an exhaust gas recirculation device for recirculating a part of exhaust gas to an intake system, and a temperature detection in a combustion chamber for detecting or estimating a temperature in a combustion chamber of the internal combustion engine at a predetermined timing. Detected by a temperature adjusting device that adjusts at least one of the temperature of the fresh air flowing through the intake system of the internal combustion engine and the temperature of the recirculated exhaust gas flowing through the exhaust gas recirculation device, or Control means for controlling the fresh air temperature and the recirculated exhaust gas temperature to the respective target temperatures via the temperature adjusting device based on the estimated temperature in the combustion chamber.
[Selection] Figure 2

Description

  The present invention relates to an intake air temperature control system for controlling intake air temperature in an internal combustion engine including an exhaust gas recirculation device.

  The exhaust state of the internal combustion engine is closely related to the combustion temperature of the fuel mixture in the combustion chamber, and the combustion temperature is strongly influenced by the intake air temperature. Therefore, in order to more precisely control the operating state of the internal combustion engine, the various operating parameters (for example, fuel injection timing, injection pressure, EGR valve opening, throttle valve opening, etc.) are the same. Even if the intake air temperature (fresh air temperature and recirculation exhaust gas temperature) is different, the NOx generation amount and the HC and CO emission amounts change. Therefore, it is necessary to consider the intake air temperature in order to properly control the exhaust state.

Therefore, in an internal combustion engine equipped with an exhaust gas recirculation device (EGR device), if there is a deviation between the intake air temperature, which is a predetermined reference, and the current reference temperature, the deviation may occur. In the case of estimation, by controlling the amount of heat exchange in the heat exchange device (EGR cooler) in the exhaust gas recirculation device, the intake air finally flowing into the cylinder (the mixture of fresh air and recirculated exhaust gas) ) Has been disclosed (for example, see Patent Document 1). By this technique, the influence on the combustion temperature due to the deviation of the intake air temperature can be suppressed.
JP 2004-44484 A Japanese Patent Laid-Open No. 11-200955

  The intake air temperature in the internal combustion engine is an important parameter for controlling the combustion state. In particular, when the internal combustion engine includes an exhaust gas recirculation device, the intake air temperature is determined by the mixing ratio of fresh air and the recirculated exhaust gas, and the respective temperatures. Here, when the intake air temperature is precisely controlled based on a predetermined reference value, it is necessary to accurately grasp the surrounding environment where the internal combustion engine is placed, such as the outside air temperature. This is because the relationship between the reference value and the ambient temperature of the internal combustion engine causes a shift in the relationship between the intake air temperature required for the internal combustion engine and the reference value.

  For this reason, when the intake air temperature is precisely controlled based on the reference value, it is necessary to create a control map for intake air temperature control by assuming the surrounding environment of a plurality of internal combustion engines in advance. There is a risk that man-hours will increase.

  In view of the above problems, an object of the present invention is to provide an intake air temperature control system that enables simpler and more precise control of intake air temperature in an internal combustion engine including an exhaust gas recirculation device.

  In order to solve the above-described problems, the present invention focuses on the temperature in the combustion chamber of the internal combustion engine, particularly the temperature in the combustion chamber at a predetermined time that greatly affects the combustion state. That is, the intake air temperature is controlled not directly based on the ambient environment of the internal combustion engine but directly on the temperature in the combustion chamber, particularly on the combustion chamber temperature at a predetermined time that greatly affects the combustion state, thereby controlling the intake air temperature more precisely. And make it more concise.

Accordingly, the present invention provides an intake air temperature control system for an internal combustion engine, and an exhaust gas recirculation device that recirculates a part of the exhaust gas discharged from the internal combustion engine to the intake system, and a temperature in the combustion chamber of the internal combustion engine at a predetermined time. And a temperature adjustment device for adjusting at least one of a temperature of fresh air flowing through the intake system of the internal combustion engine and a temperature of recirculated exhaust gas flowing through the exhaust gas recirculation device And the fresh air temperature and the recirculated exhaust gas temperature are controlled to the respective target temperatures via the temperature adjusting device based on the temperature in the combustion chamber detected or estimated by the combustion chamber temperature detecting means. Control means.

  Since the internal combustion engine is provided with an exhaust gas recirculation device, the intake air flowing into the cylinder of the internal combustion engine is composed of fresh air from the outside of the internal combustion engine and recirculation exhaust gas from the exhaust gas recirculation device. Therefore, the intake air temperature in the internal combustion engine is determined by the fresh air temperature, the recirculation exhaust temperature, the mixing ratio of both, and the like. Of course, there may be cases where the intake air is only fresh air or only recirculated exhaust.

  Here, the feature of the intake air temperature control system for the internal combustion engine is that the intake air temperature is adjusted based on the temperature in the combustion chamber detected or estimated by the combustion chamber temperature detection means, not the surrounding environment of the internal combustion engine. It is a point. By controlling the intake air temperature based on the temperature in the combustion chamber at a predetermined time that is directly attributable to the combustion state, the combustion state in the combustion chamber is controlled regardless of the ambient environment that is an external factor other than the operating parameters of the internal combustion engine. It is possible to control the intake air temperature as precisely as possible to achieve the target state. In other words, it is possible to control the intake air temperature more simply and more precisely by directly relating the combustion chamber temperature and the intake air temperature in terms of control. The temperature in the combustion chamber detected and estimated by the combustion chamber temperature detection means is the temperature in the combustion chamber at a predetermined time. This predetermined time is a time having a strong relationship with the combustion state in the combustion chamber, for example, a time of compression top dead center when the temperature in the combustion chamber is greatly increased.

  In addition, the intake air temperature is adjusted via a temperature adjusting device. This temperature adjusting device adjusts the temperature of at least one of fresh air and recirculated exhaust gas to each target temperature. Is that the temperature of fresh air and recirculated exhaust gas is adjusted based on the temperature detected by the combustion chamber temperature detecting means. Note that the target temperature here means that when fresh air and recirculated exhaust gas are mixed to become intake air, the intake air temperature corresponds to the target combustion state reached by the combustion performed in the combustion chamber, This is the temperature of the circulating exhaust. Accordingly, the temperatures of the fresh air and the recirculated exhaust are raised and lowered as needed by the temperature adjusting device.

  Further, the internal combustion engine has a variable compression ratio mechanism that can change the compression ratio to an arbitrary compression ratio, depending on the operating state (engine load, engine speed, etc.) of the internal combustion engine. Even in the case where the compression ratio is changed by the variable compression ratio mechanism, the intake air temperature is controlled based on the temperature in the combustion chamber at a predetermined timing in the above intake temperature control system. Regardless of the compression ratio, the intake air temperature corresponding to the target state of the combustion state performed in the combustion chamber can be controlled more simply and more precisely.

  Here, in the intake air temperature control system for an internal combustion engine, the temperature adjustment device adjusts the fresh air temperature by exchanging heat with fresh air flowing through the intake system of the internal combustion engine. Alternatively, it may be a recirculation exhaust heat exchange device that adjusts the recirculation exhaust temperature by exchanging heat with the recirculation exhaust flowing through the exhaust recirculation device. That is, the temperature of fresh air and recirculated exhaust gas is adjusted by a so-called heat exchanger.

  Further, in the intake air temperature control system for an internal combustion engine described above, when the internal combustion engine further includes a supercharger that supercharges fresh air, the fresh air temperature is controlled by the control means via the temperature adjustment device. Alternatively, when the recirculation exhaust temperature is raised, the supercharging pressure by the supercharger may be raised.

When the intake air temperature is controlled by the control means via the temperature adjusting device, the intake air density changes.
That is, when the intake air temperature rises, the intake air density decreases, and as a result, the intake air amount decreases. Therefore, when the intake air temperature rises, that is, when the fresh air temperature or the recirculation exhaust gas temperature rises, the intake pressure that decreases as the temperature rises is increased by increasing the supercharging pressure by the supercharger. Thus, it is possible to secure the necessary intake air amount in the combustion chamber and suppress the deterioration of the emission.

  In an intake air temperature control system for an internal combustion engine having an exhaust gas recirculation device, the intake air temperature can be controlled more simply and more precisely.

  Here, an embodiment of an intake air temperature control system for an internal combustion engine according to the present invention will be described based on the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a compression ignition internal combustion engine (hereinafter simply referred to as “internal combustion engine”) 1 to which an intake air temperature control system according to the present invention is applied and a control system thereof. The internal combustion engine 1 is a compression ignition type internal combustion engine having four cylinders 2. Further, a fuel injection valve 3 for directly injecting fuel into the combustion chamber of the cylinder 2 is provided. The fuel injection valve 3 is connected to a pressure accumulating chamber 4 that stores fuel pressurized to a predetermined pressure. An intake branch pipe 7 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 7 is connected to a combustion chamber via an intake port. Similarly, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 is connected to a combustion chamber via an exhaust port. Here, the intake port and the exhaust port are provided with an intake valve and an exhaust valve, respectively.

  The intake branch pipe 7 is connected to the intake pipe 8. An air flow meter 9 for detecting the amount of intake air flowing through the intake pipe 8 is provided upstream of the intake pipe 8, and an intake throttle valve 10 for adjusting the flow rate of intake air flowing through the intake pipe 8 is provided further downstream thereof. It has been. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10.

  The intake pipe 8 on the downstream side of the intake throttle valve 10 is provided with a compressor side of a supercharger 16 that operates using exhaust energy as a drive source, and the exhaust branch pipe 12 is provided with a turbine side of the supercharger 16. . The supercharger 16 is a so-called variable capacity supercharger. The supercharger 16 has a movable nozzle vane therein, and the supercharging pressure by the supercharger 16 is controlled by adjusting the opening degree of the nozzle vane. . The intake pipe 8 downstream of the supercharger 16 is provided with an intercooler 15 for cooling the intake air that has been pressurized by the supercharger 16 and has reached a high temperature. The intercooler 15 is a heat exchange device to which cooling water for cooling is supplied and the cooling capacity of the intercooler 15 is controlled by adjusting the supply amount.

  Further, the turbine side of the supercharger 16 is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected to a muffler downstream. In the middle of the exhaust pipe 13, a NOx catalyst 14 of a so-called storage reduction type NOx catalyst is provided.

  Further, the internal combustion engine 1 is provided with an EGR device 21. The EGR device 21 recirculates a part of the exhaust gas flowing through the exhaust branch pipe 12 to the intake branch pipe 7. The EGR device 21 includes an EGR passage 22 extending from the exhaust branch pipe 12 (upstream side) to the intake branch pipe 7 (downstream side), and an EGR for cooling EGR gas provided in order from the upstream side on the EGR passage 22. A cooler 23 and an EGR valve 24 for adjusting the flow rate of EGR gas are included. The EGR cooler 23 is a heat exchange device to which cooling water for cooling is supplied and the supply capacity of the EGR cooler 23 is adjusted to control the cooling capacity of the EGR cooler 23.

  The internal combustion engine 1 is also provided with an electronic control unit (hereinafter referred to as “ECU”) 20 for controlling the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, and the like for storing various programs and maps to be described later, and controls the operating conditions of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request. Unit.

  Here, the fuel injection valve 3 performs an opening / closing operation by a control signal from the ECU 20. That is, according to a command from the ECU 20, the fuel injection timing and the fuel injection amount from the fuel injection valve 3 are controlled for each injection valve in accordance with the operation state such as the engine load and engine speed of the internal combustion engine 1. Further, the opening degree of the EGR valve 24, the cooling water supply amount to the intercooler 15, the cooling water supply amount to the EGR cooler 23, the nozzle vane opening degree of the supercharger 16, and the like are also controlled in accordance with commands from the ECU 20.

  Further, the crank position sensor 30 is electrically connected to the ECU 20. The ECU 20 receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 1, and the engine rotational speed of the internal combustion engine 1 and the piston position in each cylinder 2. Etc. are detected. Further, an in-cylinder pressure sensor 31 that detects the pressure in the combustion chamber of the cylinder 2 is provided and is electrically connected to the ECU 20. Thereby, ECU20 detects the pressure in a combustion chamber. In FIG. 1, the in-cylinder pressure sensor 31 is attached to only one cylinder for convenience of display. The air flow meter 9 is also electrically connected to the ECU 20 to detect the amount of fresh air flowing into the combustion chamber.

  In the internal combustion engine 1 configured as shown in FIG. 1, the ECU 20 adjusts the intake air temperature that greatly affects the combustion state in the combustion chamber of the cylinder 2 in accordance with the flow of intake air temperature control shown in FIG. Note that the intake air temperature control in this embodiment is a routine that is repeatedly executed by the ECU 20 at a constant cycle.

  In S101, the combustion chamber temperature Tc at the time of compression top dead center of the cylinder 2 is estimated. Specifically, the total amount of the fresh air amount detected by the air flow meter 9 and the recirculated exhaust amount flowing into the intake branch pipe 7 estimated from the opening degree of the EGR valve 24 and the in-cylinder pressure sensor 31 are detected. The combustion chamber temperature Tc at the compression top dead center is calculated from the pressure in the cylinder at the compression top dead center. Whether or not the compression top dead center has been reached is determined based on a signal from the crank position sensor 30. The process of S101 by the ECU 20 corresponds to the combustion chamber temperature detecting means of the intake air temperature control system according to the present invention. When the process of S101 ends, the process proceeds to S102.

  In S102, the amount of cooling water supplied to the intercooler 15 and the amount of cooling water supplied to the EGR cooler 23 are adjusted based on the combustion chamber temperature Tc estimated in S101. Specifically, each cooling water amount to the intercooler 15 and the EGR cooler 23 is determined according to the control map shown in FIG. When the internal combustion engine 1 is working on different engine loads, the control map indicates the combustion chamber temperature Tc, the amount of cooling water supplied to the intercooler 15 that is a suitable intake air temperature, and EGR. The relationship with the amount of rejected water supplied to the cooler 23 is obtained in advance through experiments or the like and is mapped. That is, the combustion state in the internal combustion engine 1 is greatly influenced by the temperature Tc in the combustion chamber, and the combustion chamber temperature Tc and the intake air temperature are determined in view of the close relationship between the combustion chamber temperature Tc and the intake air temperature. The relationship between the air temperature and the recirculation exhaust temperature is uniquely mapped.

The control map of FIG. 3 shows only the relationship between the combustion chamber temperature Tc and the amount of cooling water supplied to the intercooler 15 and the EGR cooler 23. However, the constant intercooler cooling water amounts WICn and EGR cooler cooling are shown. When the water amount WECn is determined, the opening degree of the EGR valve 24 is also determined. That is, the mixing ratio of fresh air and recirculated exhaust is also determined. By the process of S102, the intake air temperature supplied to the combustion chamber of the cylinder 2 is directly determined based on the combustion chamber temperature Tc. The process of S102 by the ECU 20 corresponds to the control means of the intake air temperature control system according to the present invention. When the process of S102 ends, the process proceeds to S103.

  In S103, the supercharging pressure is adjusted by adjusting the opening degree of the nozzle vane of the supercharger 16. As a result, since the intake air temperature is adjusted in S102, the density of the intake air changes. As a result, there is a case where the intake amount required in the combustion state in the internal combustion engine cannot be sufficiently supplied, or the intake amount is excessively large. For example, if the amount of cooling water supplied to the intercooler 15 or the EGR cooler 23 is adjusted to be small in S102, the intake air temperature rises. As a result, the density of the intake air is reduced. In such a case, the supercharging pressure by the supercharger 16 is increased and the intake air amount finally flowing into the cylinder 2 is set as a target amount. After the process of S103 is completed, this control is terminated.

  According to this control, on the basis of the combustion chamber temperature Tc of the cylinder 2, the ECU 20 determines the intake air temperature via the intercooler 15 that is a fresh air temperature adjusting device and the EGR cooler 23 that is a recirculated exhaust gas temperature adjusting device. Control directly. Accordingly, it is possible to control the intake air temperature more simply and more precisely.

  In this control, the combustion chamber temperature Tc is estimated based on a signal from the cylinder pressure sensor 31 or the like. However, a temperature sensor for detecting the temperature in the combustion chamber is provided to directly detect the combustion chamber temperature Tc. May be. Further, it may be estimated from the temperature of the intake air flowing through the intake branch pipe 7 and the cooling water temperature of the internal combustion engine 1.

  Further, a heater for heating the intake air may be provided in the intake pipe 8 as a fresh air temperature adjustment device, and the intake air may be heated by energizing the heater to adjust the temperature. At this time, the control map corresponding to FIG. 3 with respect to the fresh air is a control map showing the relationship between the combustion chamber temperature Tc and the energization amount to the heater.

  Further, as a recirculation exhaust gas temperature adjusting device, a bypass passage may be provided in parallel with the EGR cooler 23, and an adjustment valve for adjusting the ratio of the exhaust amount flowing through the EGR cooler 23 and the exhaust amount flowing through the bypass passage may be provided. By adjusting the ratio by this adjusting valve, the temperature of the recirculated exhaust gas is adjusted. At this time, the control map corresponding to FIG. 3 regarding the recirculated exhaust gas is a control map showing the relationship between the combustion chamber temperature Tc and the ratio.

It is a figure showing the schematic structure of the compression ignition internal combustion engine to which the intake air temperature control system of the internal combustion engine which concerns on the Example of this invention is applied. It is a flowchart regarding the intake air temperature control in the intake air temperature control system of the internal combustion engine which concerns on the Example of this invention. It is a figure which shows the control map used by the intake air temperature control in the intake air temperature control system of the internal combustion engine which concerns on the Example of this invention.

Explanation of symbols

1. Compression compression internal combustion engine (internal combustion engine)
7 .... Intake branch pipe 8 .... Intake pipe 9 .... Air flow meter 12 .... Exhaust branch pipe 13 .... Exhaust pipe 15 .... Intercooler 16 .... Excess Feeder 20 ... ECU
21 ... EGR device 23 ... EGR cooler 24 ... EGR valve 31 ... In-cylinder pressure sensor

Claims (3)

An exhaust gas recirculation device that recirculates part of the exhaust gas discharged from the internal combustion engine to the intake system;
Combustion chamber temperature detection means for detecting or estimating the temperature in the combustion chamber of the internal combustion engine at a predetermined time;
A temperature adjusting device that adjusts at least one of the temperature of fresh air flowing through the intake system of the internal combustion engine and the temperature of recirculated exhaust gas flowing through the exhaust gas recirculation device;
Control means for controlling the fresh air temperature and the recirculated exhaust gas temperature to the respective target temperatures via the temperature adjusting device based on the temperature in the combustion chamber detected or estimated by the combustion chamber temperature detecting means. When,
An intake air temperature control system for an internal combustion engine, comprising:   The temperature adjusting device is a heat exchanger for fresh air that adjusts the fresh air temperature by exchanging heat with fresh air that flows through the intake system of the internal combustion engine, or recirculated exhaust gas and heat that flows through the exhaust gas recirculation device. 2. An intake air temperature control system for an internal combustion engine according to claim 1, wherein the recirculation exhaust heat exchange device adjusts the recirculation exhaust temperature by performing exchange. A supercharger for supercharging fresh air in the internal combustion engine;
3. The supercharging pressure by the supercharger is increased when the fresh air temperature or the recirculated exhaust gas temperature is increased by the control means via the temperature adjusting device. An intake air temperature control system for an internal combustion engine according to claim 1.

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