JP5589987B2 - Exhaust temperature control device - Google Patents

Description

  The present invention relates to an exhaust temperature control device that controls the temperature of exhaust gas from an internal combustion engine.

  Conventionally, there has been known an exhaust purification system in which a catalyst device for purifying a specific substance (for example, hydrocarbon, nitrogen oxide, etc.) contained in exhaust gas of an internal combustion engine (hereinafter also referred to as an engine) is provided on an exhaust passage. It has been. For example, Patent Document 1 discloses an exhaust emission control device that includes a NOx storage catalyst (also referred to as a NOx trap catalyst or a NOx storage reduction catalyst) that processes nitrogen oxide (hereinafter referred to as NOx), which is one of specific substances. Have been described. The NOx storage catalyst stores NOx under a lean atmosphere and reduces the NOx stored under a rich atmosphere to perform an exhaust purification process.

  Patent Document 2 describes a storage catalyst (HC trap catalyst) formed by combining a three-way catalyst with a storage material (HC adsorbent) that adsorbs or desorbs hydrocarbons discharged from an internal combustion engine. . In this technology, hydrocarbons are adsorbed (trapped) when the catalyst temperature of the storage catalyst is relatively low, and the hydrocarbons are desorbed and oxidized when the catalyst temperature is relatively high, thereby purifying the exhaust. ing.

  As described above, in the exhaust purification process using the catalyst device on the exhaust passage, the chemical reaction on the catalyst proceeds in accordance with the atmosphere (oxygen concentration, oxidation, concentration of reducing components) in the vicinity of the catalyst and the catalyst temperature. Therefore, it is required to appropriately control both the exhaust air-fuel ratio and the exhaust temperature.

JP 2010-24957 A JP-A-2005-240726

  However, in the conventional exhaust purification system, since the control of the exhaust air-fuel ratio and the control of the exhaust temperature influence each other, there is a problem that it is difficult to appropriately control both of them.

  For example, regarding the control of the exhaust air-fuel ratio, as a typical technique for making the air-fuel ratio rich (that is, reducing the air-fuel ratio), it is conceivable to increase the fuel injection amount. However, since the amount of heat generated in the cylinder increases as the amount of fuel increases, the exhaust temperature may rise to a desired temperature or higher. Although there are technologies that significantly delay the timing of fuel injection so that fuel does not burn in the cylinder and technologies that add fuel into the exhaust passage, these technologies allow unburned fuel to react on the catalyst. This produces a reducing atmosphere, and there are restrictions on the catalyst temperature as in the case of the cylinder, and the response is poor.

  On the other hand, it is theoretically possible to make the air-fuel ratio rich by reducing the amount of air supplied into the cylinder. However, in this case, since the engine output decreases, it cannot be carried out depending on the driving state of the vehicle and the load condition. Further, if the air amount is excessively reduced, smoke is generated. Therefore, there is a limit to adjusting the air-fuel ratio by changing the air amount.

  As described above, there is a correlation between the exhaust temperature and the amount of fuel. If the amount of fuel increases, the amount of heat received from the fuel increases and the exhaust temperature rises.If the amount of fuel is small, the amount of heat decreases accordingly. The temperature drops. Due to the presence of such a correlation, it is not possible to freely change only one of the exhaust air-fuel ratio and the exhaust temperature, which means that both the exhaust air-fuel ratio and the exhaust temperature are controlled to be in an appropriate state. There is a fact that it is difficult.

The present invention has been devised in view of such problems, and an object thereof is to provide an exhaust temperature control device that can control the exhaust temperature of an internal combustion engine without being restricted by an air-fuel ratio.
The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

(1) An exhaust temperature control device disclosed herein includes a fresh air amount control means for controlling a fresh air amount supplied into a cylinder of an internal combustion engine, and a recirculation passage that communicates an exhaust passage and an intake passage of the internal combustion engine. Recirculation gas amount control means for controlling the recirculation gas amount flowing through Furthermore, a fuel injection valve that injects fuel into the cylinder of the internal combustion engine, and a fuel injection that controls the amount of additional fuel injected from the fuel injection valve to reduce the exhaust gas flowing through the exhaust passage to a desired air-fuel ratio Control means.
The fresh air amount control means holds the fresh air amount supplied to the intake passage at a constant amount, and the recirculation gas amount control means holds the fresh air amount at a constant amount by the fresh air amount control means. In such a state, the flow rate control is performed to increase the recirculation gas amount according to the increase in the additional fuel amount controlled by the fuel injection control means , and the temperature of the exhaust gas that rises as the additional fuel amount increases. Is reduced by increasing the amount of the recirculated gas, and the temperature of the exhaust gas when the exhaust gas reaches the desired air-fuel ratio is made lower than a predetermined limit temperature .

Contact name and additional fuel, means fuel is further injected after the main injection for obtaining power, the additional fuel is used for the purpose of the temperature of the object and the exhaust to reduce the air fuel ratio of the exhaust gas to a high temperature It is done. Further, the flow control and is that of control of the fresh air amount to change the recirculated gas amount while being held in a fixed amount. When the additional fuel amount is increased by the fuel injection control means, it is preferable to increase the recirculation gas amount by the recirculation gas amount control means, and to decrease the recirculation gas amount when the additional fuel amount is decreased.

(2 ) It is preferable that the recirculation gas amount control means sets the recirculation gas amount to zero at the start of injection of the additional fuel by the fuel injection control means.
(3) said equipped with an exhaust temperature detection means for detecting the temperature of the exhaust gas flowing through the exhaust passage of the internal combustion engine, the recirculation gas amount control means, the temperature of the detected exhaust by the exhaust temperature detecting means the temperature limit It is preferable to increase the amount of the reflux gas when the value reaches.

( 4 ) The fresh air amount control means includes the intake passage upstream of the connection portion between the intake passage and the return passage, and the exhaust gas downstream of the connection portion between the exhaust passage and the return passage. It is preferable that the supercharger is capable of adjusting the supercharging flow rate provided across the passage.
( 5 ) It is preferable that the fresh air amount control means is a throttle valve provided in the intake passage upstream of the connection portion between the intake passage and the return passage.

  According to the exhaust gas temperature control device of the present invention, the recirculation passage is opened while the fresh air amount is kept constant (the fuel amount is a predetermined amount corresponding to the required air-fuel ratio) by the recirculation gas amount control means. Since the flow rate control is performed to change the amount of the recirculated gas that has been circulated and the temperature has decreased, the exhaust temperature of the internal combustion engine can be controlled. That is, the exhaust temperature can be controlled without being restricted by the air-fuel ratio (in other words, independent of the air-fuel ratio).

1 is an overall configuration diagram of an exhaust temperature control device according to an embodiment. It is a graph explaining the exhaust gas temperature control by the exhaust gas temperature control apparatus which concerns on one Embodiment, (a) is the relationship between recirculation gas amount and an air fuel ratio, (b) is the relationship between recirculation gas amount and intake manifold pressure, (c ) Shows the relationship between the amount of recirculated gas and the amount of fresh air, and (d) shows the change in exhaust temperature obtained when controlled to the relationship shown in FIG. It is a graph explaining the air-fuel ratio control using the exhaust gas temperature control apparatus which concerns on one Embodiment, (a) is a post injection amount, (b) is a recirculation | reflux gas amount, (c) shows the change of exhaust temperature. It is a flowchart explaining the control procedure of the exhaust temperature control apparatus which concerns on one Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described in the following embodiment.

[1. Device configuration]
As shown in FIG. 1, the exhaust temperature control device of the present embodiment is applied to an engine (internal combustion engine) 10 having an exhaust purification device 23. Here, the engine 10 is a direct injection diesel engine, and a fuel injection valve 11 is provided in each cylinder of the engine 10. Each fuel injector 11 is supplied with pressurized fuel from a common rail 12. The fuel injection valve 11 injects this high-pressure fuel into the cylinder. Further, the engine 10 is provided with an engine speed sensor 27, and the engine speed detected by the engine speed sensor 27 is transmitted to the ECU 1 described later.

  An intake manifold (hereinafter abbreviated as “intake manifold”) 13 is mounted on the intake side of the engine 10. The intake manifold 13 is connected to an intake passage 14 through which air (fresh air) supplied from the outside of the vehicle flows and a recirculation passage 24 through which air (exhaust) discharged from the cylinder recirculates. In the intake passage 14, from the upstream side, an air filter 15 that removes dust and dirt in the air, a compressor 16a of a supercharger 16 that compresses fresh air, an intercooler 17 that cools the compressed air, and an intake air A throttle valve 18 for adjusting the amount of fresh air flowing through the passage 14 is provided.

  An exhaust manifold (hereinafter abbreviated as “exhaust manifold”) 19 is attached to the exhaust side of the engine 10. The exhaust manifold 19 is connected to an exhaust passage 20 and a return passage 24 for guiding exhaust to the outside of the vehicle and exhausting it. From the upstream side, the exhaust passage 20 is supplied with an air-fuel ratio sensor 21 for detecting the air-fuel ratio of the exhaust flowing through the exhaust passage 20, an exhaust temperature sensor 22 for detecting the temperature of the exhaust, the turbine 16b of the supercharger 16, and the exhaust. An exhaust purification device 23 for purification is provided.

  The recirculation passage 24 is a so-called exhaust gas recirculation (EGR) passage in which an upstream end is connected to the exhaust manifold 19 and a downstream end is connected to the intake manifold 13 to communicate the intake side and the exhaust side. That is, the recirculation passage 24 is a passage for using the exhaust gas by returning it to the intake system again and circulating it. Here, the recirculation passage 24 is connected so as to communicate the intake manifold 13 and the exhaust manifold 19, but may be configured to communicate the intake passage 14 and the exhaust passage 20.

  A reflux gas amount control valve (reflux gas amount control means) 25 for adjusting the flow rate of exhaust gas (hereinafter referred to as reflux gas) flowing through the reflux passage 24 is provided on the downstream side in the reflux passage 24. The opening degree of the recirculation gas amount control valve 25 is controlled by a recirculation gas amount control unit 3 of the ECU 1 described later to adjust the recirculation gas amount. A recirculation gas cooler 26 is interposed in the recirculation passage 24 to cool high-temperature exhaust gas (reflux gas) flowing from the exhaust manifold 19 to the recirculation passage 24. The recirculation passage 24 is usually disposed outside the engine room and has a certain length. Therefore, if the recirculation gas flows through the recirculation passage 24, it is naturally radiated. Therefore, even if the recirculation gas cooler 26 is not interposed, the temperature of the recirculation gas decreases.

  With such a configuration, the high-temperature exhaust discharged from the cylinder of the engine 10 is exhausted from the exhaust manifold 19 through the exhaust passage 20 and discharged to the outside, and through the return passage 24 and through the return passage 24 and the return gas cooler 26. Then, the refrigerant is separated into a reflux gas that is cooled and led to the intake manifold 13 and flows out. Further, fresh air that is supplied from the outside of the vehicle and flows through the intake passage 14 and recirculation gas that flows through the recirculation passage 24 and whose flow rate is controlled by the recirculation gas amount control valve 25 flow into the intake manifold 13.

  The supercharger (fresh air amount control means) 16 includes an intake passage 14 upstream of a connection portion between the intake system (intake manifold 13 here) and the return passage 24, an exhaust system (here exhaust manifold 19), and a return passage. 24 is disposed across the exhaust passage 20 on the downstream side of the connecting portion with the connecting portion 24. The turbine 16 b provided in the exhaust passage 20 rotates at a high speed by the energy (kinetic energy and thermal energy) of the exhaust gas flowing through the exhaust passage 20. The compressor 16a provided in the intake passage 14 coaxially with the turbine 16b is driven by utilizing the rotation of the turbine 16b to compress the intake air and send the compressed air downstream (that is, supercharge). In the present embodiment, the supercharger 16 is configured as a variable capacity turbo (hereinafter referred to as VG turbo) 16 that can adjust the amount of air to be compressed (supercharge flow rate).

  The VG turbo 16 can change the supercharging efficiency of the compressor 16a by changing the opening area of the turbine blade of the turbine 16b. That is, the compressor 16a is controlled by changing the rotational speed of the turbine 16b, and the amount of air to be supercharged (fresh air amount) is controlled. In general, the VG turbo 16 is controlled so that the opening area of the turbine blade changes according to the rotational speed of the engine 10. That is, when the engine 10 is running at a high speed, the turbine 16b rotates at a sufficient speed because the exhaust flow rate is large and the flow rate is fast. Therefore, at the time of high rotation, the opening area of the turbine blade is increased to increase the supercharging efficiency. On the contrary, when the engine 10 is running at a low speed, the exhaust flow rate is small and the flow rate is slow. Therefore, the opening area of the turbine blade is reduced to accelerate the exhaust flow rate, and the turbine 16b is rotated at a high speed to increase the supercharging efficiency.

In the present embodiment, the VG turbo 16 is configured to be able to change the supercharging efficiency regardless of the engine speed. In other words, the VG turbo 16 is configured as a new air amount control means for adjusting the amount of air (new air amount) compressed by the compressor 16a by controlling the turbine 16b by a new air amount control unit 2 of the ECU 1 described later. .
The throttle valve (fresh air amount control means) 18 is provided on the downstream side of the VG turbo 16 and upstream of the intake manifold 13 and adjusts the amount of fresh air flowing through the intake passage 14 according to the valve opening. The valve opening degree is controlled by the new air amount control unit 2 of the ECU 1.

Here, the air-fuel ratio sensor 21 is provided in the exhaust passage 20 upstream of the turbine 16b, detects the air-fuel ratio (A / F) of the exhaust gas flowing through the exhaust passage 20, and transmits the detection result to the ECU 1. As a means for detecting the air-fuel ratio of the exhaust, an oxygen concentration sensor (O ₂ sensor) is provided instead of the air-fuel ratio sensor 21, and the detection result by the oxygen concentration sensor and the amount of fuel injected into the cylinder from the fuel injection valve 11 are provided. The air-fuel ratio may be calculated from the above.
Here, the exhaust temperature sensor (exhaust temperature detection means) 22 is provided in the exhaust passage 20 upstream of the turbine 16b, detects the temperature of the exhaust gas flowing through the exhaust passage 20, and transmits the detection result to the ECU 1.

  The exhaust purification device 23 is a device that is provided in the exhaust passage 20 on the downstream side of the turbine 16b and removes substances contained in the exhaust before discharging the exhaust to the outside. Exhaust gas discharged from an internal combustion engine such as a gasoline engine or a diesel engine contains particulate matter (hereinafter referred to as PM) and nitrogen oxide (hereinafter referred to as NOx). In order to remove these substances from the exhaust gas, the exhaust purification device 23 includes a particulate filter (hereinafter referred to as a filter), an oxidation catalyst, a NOx storage catalyst, and the like.

The filter collects PM in the exhaust gas and oxidizes and removes the collected PM. Oxidation catalyst produces NO ₂ as the oxidizing agent for burning the PM from the NO contained in the exhaust. The oxidation catalyst also has a function of raising the exhaust temperature when forcibly burning PM with a filter.

  The NOx storage catalyst is configured, for example, by supporting a noble metal such as platinum (Pt) or rhodium (Rh) and a NOx storage agent such as barium (Ba) or potassium (K). The NOx storage catalyst captures and stores NOx under a lean atmosphere (oxidizing atmosphere) in which the air-fuel ratio of the exhaust gas is large. Then, the NOx occluded in a rich atmosphere (reducing atmosphere) with a small exhaust air-fuel ratio is released and reduced by reacting with hydrocarbon (HC) or carbon monoxide (CO) as a reducing agent. In addition, since NOx purification performance falls by NOx adsorption catalyst by sulfur content (S) adsorption | suction, regular S reproduction | regeneration (namely, discharge | release of adsorption | suction S in a reducing atmosphere and moderate high-temperature state) is needed.

  Next, the configuration of the ECU 1 will be described. The ECU 1 inputs and outputs signals to and from a CPU that executes various arithmetic processes, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores calculation results and the like in the CPU, and the outside. A computer configured to include an input / output port or the like. As shown in FIG. 1, an air-fuel ratio sensor 21, an exhaust gas temperature sensor 22 and an engine speed sensor 27 are connected to the input side of the ECU 1, and the fuel injection valve 11 and VG turbo of each cylinder are connected to the output side of the ECU 1. 16 turbines 16b, a throttle valve 18 and a reflux gas amount control valve 25 are connected.

[2. Control configuration]
[2-1. Exhaust temperature control]
The ECU 1 has a functional element as the fresh air amount control unit 2, a functional element as the recirculation gas amount control unit 3, and a functional element as the fuel injection control unit 4. The exhaust temperature control apparatus controls the exhaust temperature by each control performed by the new air amount control unit 2 and the recirculation gas amount control unit 3. First, the contents of each control performed by the new air amount control unit 2 and the recirculation gas amount control unit 3 will be described, and then the exhaust temperature control by the new air amount control unit 2 and the recirculation gas amount control unit 3 will be described with reference to FIG. I will explain.

  The fresh air amount control unit (fresh air amount control means) 2 controls the opening area of the turbine blade of the turbine 16b and the opening degree of the throttle valve 18 to thereby respectively supply fresh air supplied from the outside of the vehicle to the intake passage 14. It controls the flow rate. In the present embodiment, the fresh air amount control unit 2 performs control to keep the fresh air amount supplied into the cylinder of the engine 10 at a constant amount. Hereinafter, this control is referred to as holding control.

  In this holding control, the fresh air amount control unit 2 controls the supercharging efficiency (supercharging flow rate) of the VG turbo 16 in accordance with the flow rate and flow velocity of the exhaust gas that changes depending on the number of revolutions of the engine 10, and the throttle valve 18 This is done by controlling the opening. The holding control can be performed by either one of the VG turbo 16 and the throttle valve 18.

  For example, when holding control is performed only with the throttle valve 18, the opening degree of the throttle valve 18 may be controlled so that the amount of fresh air supplied into the intake manifold 13 is controlled to be a constant amount. When holding control is performed, the supercharging efficiency of the VG turbo 16 is controlled in accordance with the flow rate of the exhaust gas, etc., and the amount of fresh air compressed by the compressor 16a and sent to the intake passage 14 is held at a constant amount. . At this time, a map obtained by mapping the relationship between the rotational speed of the engine 10 and the supercharging efficiency of the VG turbo 16 in advance is stored, and holding control is performed using the detection result of the engine rotational speed sensor 27. May be. Further, a flow rate sensor (not shown) may be provided in the intake passage 14 or the exhaust passage 20, and the holding control may be performed by controlling the VG turbo 16 using the value of the exhaust flow rate detected by the flow rate sensor.

  The recirculation gas amount control unit (recirculation gas amount control means) 3 controls the flow rate of the recirculation gas flowing through the recirculation passage 24 by controlling the opening degree of the recirculation gas amount control valve 25. The recirculation gas amount control unit 3 performs control to change the recirculation gas amount when the holding control by the new air amount control unit 2 is being performed. That is, the control by the recirculation gas amount control unit 3 is performed together with the holding control by the new air amount control unit 2. Hereinafter, this control is referred to as flow rate control.

FIG. 2 is a graph for explaining the exhaust gas temperature control. As shown in FIG. 2A, the fresh air amount control unit 2 sets the fresh air amount when the recirculation gas amount is zero as Q _N0 . The pressure in the intake manifold 13 at this time (hereinafter referred to as intake manifold pressure) is P ₀ as shown in FIG. 2B, and the air-fuel ratio is A / F ₀ as shown in FIG. 2C. The exhaust temperature is T ₀ as shown in FIG. The fresh air amount control unit 2 performs holding control for holding the fresh air amount at a constant amount Q _N0 . Here, since the fresh air amount is held at a constant amount Q _N0 , when the amount of fuel injected from the fuel injection valve 11 into the cylinder is constant, the air-fuel ratio A / F of the exhaust flowing into the exhaust passage is the recirculation gas Regardless of the amount, the air-fuel ratio A / F ₀ remains constant.

As shown in FIG. 2A, the recirculation gas amount control unit 3 gradually increases the recirculation gas amount from zero when the holding control by the new air amount control unit 2 is being performed. As a result, the recirculation gas flows into the intake manifold 13 in addition to the fresh air, so that the intake manifold pressure gradually increases from P _{0 as} shown in FIG. Further, the fresh air and the recirculated gas that have flowed into the intake manifold 13 are supplied as air-fuel mixture into the cylinder and burned. At this time, although the engine combustion is slightly affected by the inert gas (H ₂ O, CO ₂ ) and residual oxygen in the reflux gas, since a predetermined amount of fresh air is maintained, a significant deterioration in combustion is unlikely to occur. . The reflux gas is cooled by the reflux passage 24 and the reflux gas cooler 26. Therefore, as shown in FIG. 2 (d), the exhaust gas temperature is increased by the effect that the total amount of fluid for diluting the engine waste heat increases as the amount of the recirculated gas increases and that the recirculated gas is cooled. The temperature gradually decreases from the temperature T ₀ when the amount of reflux gas is zero.

  As described above, the exhaust temperature is lowered by increasing only the amount of the recirculated gas in the state where the retention control is performed by the fresh air amount control unit 2 (the fresh air amount is maintained at a constant amount). On the other hand, the exhaust gas temperature is increased by reducing the amount of the recirculated gas while keeping the fresh air amount at a constant amount. In other words, by controlling the fresh air amount and the recirculated gas amount at the same time, only the exhaust temperature changes.

[2-2. Air-fuel ratio control]
Next, air-fuel ratio control using the above exhaust gas temperature control device will be described. Here, an example in which the exhaust gas temperature control is combined with the air-fuel ratio control in the exhaust gas purification device 23 shown in FIG. 1 will be described.

  As shown in FIG. 1, the fuel injection control unit (fuel injection control means) 4 controls the amount of fuel injected by the fuel injection valve 11 and the injection timing. In the present embodiment, the fuel injection control unit 4 performs the so-called post injection after the main injection for obtaining power (torque). This post-injection is to inject further fuel after the main injection (that is, additional injection). The fuel injected later (hereinafter referred to as additional fuel) is combusted in the engine 10, but Since the ratio of power becomes smaller than that of injection, it is used for the purpose of reducing the air-fuel ratio of exhaust and for raising the temperature of exhaust, apart from the purpose of obtaining desired power. This post-injection is used in the exhaust purification process using the NOx storage catalyst.

  In the exhaust purification process using the NOx storage catalyst, air-fuel ratio control is important. This is because it is necessary to increase the air-fuel ratio in order to store NOx in the catalyst, and it is necessary to decrease the air-fuel ratio in order to reduce the stored NOx. The fuel injection control unit 4 controls the fuel amount (additional fuel amount) of post injection and performs air-fuel ratio control. That is, when the air-fuel ratio is decreased, the additional fuel amount is increased, and when the air-fuel ratio is increased, the additional fuel amount is decreased.

Here, considering the case of reducing the NOx storage catalyst, the fuel injection control unit 4 increases the amount of post-injection fuel (that is, the additional fuel amount, hereinafter also referred to as the post-injection amount) to reduce the exhaust gas. Although the air-fuel ratio is reduced, the exhaust temperature also increases due to the increase in the post injection amount. Exhaust system devices such as turbochargers and NOx storage catalysts have heat resistance that can withstand high-temperature exhaust, but a predetermined limit temperature (upper limit temperature) T _M is set in advance, so that the exhaust temperature is It is necessary to keep the temperature below the limit temperature. If began to decrease the air-fuel ratio by increasing the post injection amount, the exhaust temperature at a certain point reaches the limit temperature T _M, can not be increased any more post injection amount, to obtain the desired air-fuel ratio It is thought that it is not possible.

  At this time, exhaust temperature control by the exhaust temperature control device is performed separately from air-fuel ratio control by post injection. FIG. 3 shows a state in which exhaust gas temperature control is performed in conjunction with air-fuel ratio control. (A) is a change in the air-fuel ratio when the post injection amount is increased, and (b) is a recirculation for a change in the air-fuel ratio. A change in gas amount, (c) shows a change in exhaust temperature with respect to a change in air-fuel ratio. Each of FIGS. 3A to 3C includes three graphs (A, B, and C in the figure), and A, B, and C in the figure correspond to each other. In addition, here, it is assumed that the fresh air is retained, and although not shown in FIG. 3, the fresh air amount is controlled to be a certain amount for all of A, B, and C.

As shown in FIG. 3A, the air-fuel ratio when the post injection amount is zero is A / F ₀ . Further, the desired air-fuel ratio A / F _T fuel ratio necessary for performing the NOx reduction treatment. In order to obtain a desired air-fuel ratio A / F _T, gradually increasing the post injection amount as shown in FIG. 3 (a) (in the arrow A). When the post-injection amount is increased, the exhaust temperature also increases as shown in FIG. 3C (A in the figure). The exhaust temperature reaches the limit temperature T _M when the air-fuel ratio becomes A / F _1, and the post injection amount cannot be increased any more.

Therefore, as shown in FIG. 3B, when the air-fuel ratio becomes A / F ₁ , the amount of the reflux gas is increased (B in the figure). Note that the amount of the recirculated gas is controlled to zero during the period from the start of post injection (the air-fuel ratio is A / F ₀ ) until the air-fuel ratio becomes A / F ₁ (A in the figure). The increase of the recirculation gas amount, since the exhaust gas temperature is lower than the limit temperature T _M drops suddenly, it is possible to further increase the post-injection amount, the air-fuel ratio is closer to the desired air-fuel ratio A / F _T (FIG. Middle arrow B).

When the exhaust gas temperature reaches the limit temperature T _M again due to the increase in the post injection amount, the recirculation gas amount is further increased (C in the figure). As a result, the exhaust gas temperature decreases again, so that the post-injection amount is further increased to reduce the air-fuel ratio (arrow C in the figure). Thus, while increasing the post injection amount, the exhaust gas temperature is decreased, and the rising exhaust temperature is decreased by increasing the recirculation gas amount. Thus, to continue the post injection can be carried out, it is possible to obtain a desired air-fuel ratio A / F _T. In FIG. 3, the temperature of the exhaust when the desired air-fuel ratio A / _FT is reached is T _C which is _lower than the limit temperature T _M.

  By adjusting the recirculation gas amount and the post injection amount by this method, not only the temperature can be kept within the endurance limit (that is, not limited to the temperature limit control), but also the air-fuel ratio such as S regeneration of the NOx storage catalyst, etc. Both the catalyst temperature and the catalyst temperature can be brought into an appropriate state (that is, both the air-fuel ratio and the catalyst temperature can be controlled).

  The procedure of the exhaust gas temperature control shown in FIGS. 3A to 3C will be described with reference to the flowchart of FIG. The flowchart shown in FIG. 4 operates at a predetermined cycle (for example, a cycle of several [ms]). Each of the following steps is performed by each function (means) assigned to the hardware of the computer being operated by software (computer program).

  The exhaust temperature control apparatus starts the following control flow when it is desired to control the exhaust temperature. Here, a case will be described in which exhaust gas temperature control is performed together with air-fuel ratio control for reducing the NOx storage catalyst.

As shown in FIG. 4, in step S <b> 10, the exhaust temperature T is detected by the exhaust temperature sensor 22. This temperature information is transmitted to the ECU 1, the detected exhaust temperature T in step S20 whether higher than a predetermined limit temperature T _M is determined. If the exhaust gas temperature has not reached the limit temperature T _M, the process proceeds from NO route to step S30, it increases the post injection quantity by the fuel injection control unit 4. Since the air-fuel ratio decreases due to the increase in the post injection amount, the air-fuel ratio sensor 21 detects the air-fuel ratio A / F in step S50. In step S60, the air-fuel ratio A / F detected whether reaches a desired air-fuel ratio A / F _T is determined. If reaches a desired air-fuel ratio A / F _T and the flow ends, and returns it does not reach the desired air-fuel ratio A / F _T, repeating the steps from step S10.

On the other hand, if the detected exhaust gas temperature reaches the limit temperature T _M in step S20, the post injection amount cannot be increased as it is, so in step S40, the recirculation gas amount control unit 3 sets the recirculation gas amount. increase. The exhaust gas temperature decreases as the amount of the recirculated gas increases. In steps S50 and S60, the air-fuel ratio A / F is determined. With such a control flow, a graph of temperature change as shown in FIG.

[3. effect]
Therefore, according to this exhaust gas temperature control device, the recirculation gas amount control unit 3 circulates the recirculation passage 24 in a state where the fresh air amount is kept constant (the fuel amount is a predetermined amount corresponding to the required air-fuel ratio). Thus, since the flow rate control for changing (increasing or decreasing) the amount of the recirculated gas whose temperature has decreased is performed, the exhaust temperature of the engine 10 can be controlled (reduced or increased). That is, only the exhaust temperature can be controlled without being restricted by the air-fuel ratio (in other words, independent of the air-fuel ratio).

  Further, when the exhaust gas temperature control is performed together with the air-fuel ratio control by the fuel injection control unit 4, the air-fuel ratio is controlled by the post-injection amount (additional fuel amount). Since it can be controlled by the control unit 2 and the recirculation gas amount control unit 3, the air-fuel ratio control can be performed while keeping the temperature of the exhaust gas within an appropriate temperature range. In other words, since only the exhaust temperature can be freely controlled, a desired air-fuel ratio can be obtained with certainty.

  In addition, since the amount of recirculated gas is increased as the post injection amount increases, the exhaust temperature can be lowered if the exhaust temperature increases due to the increase of the post injection amount. Thereby, the additional fuel for obtaining a desired air fuel ratio can be injected. That is, a desired air-fuel ratio can be obtained while preventing an excessive increase in the exhaust gas temperature.

  In addition, the amount of recirculation gas controlled by the recirculation gas amount control unit 3 is set to zero at the start of post injection, and is increased as the post injection amount increases. The amount and the swing width) can be increased. Thereby, the variation | change_quantity of exhaust temperature can be maximized.

Further, when the exhaust temperature reaches a predetermined limit temperature T _M , the recirculation gas amount is increased to lower the exhaust temperature, so that the exhaust temperature can be surely kept within a predetermined range, and the exhaust temperature is excessively increased. Therefore, it is possible to prevent a decrease in exhaust efficiency or failure of the exhaust gas purification device or the like. Further, since the amount of the recirculated gas is controlled using the exhaust gas temperature detected by the exhaust gas temperature sensor 22, the control configuration is simple.
Further, when maintaining a constant amount while supercharging fresh air with the VG turbo 16, a large amount of fresh air can be supplied to the intake passage 14, and the exhaust temperature is controlled independently while increasing the thermal efficiency of the engine 10. be able to.

Further, when the amount of fresh air is kept constant by adjusting the opening of the throttle valve 18, the device configuration is simple, the device can be downsized, and the cost can be reduced.
When the fresh air amount is kept constant using the VG turbo 16 and the throttle valve 18, fine adjustment is made by the throttle valve 18 while supercharging the VG turbo 16 to increase the fresh air amount. This ensures that the amount of fresh air is constant.

[4. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above embodiment, as shown in FIG. 3B, the amount of the recirculated gas is increased after the exhaust temperature reaches the limit temperature (in other words, the amount of the recirculated gas is increased stepwise). However, the increase in the amount of the recirculated gas may be continuously performed after the start of the post injection rather than after the exhaust gas temperature reaches the limit temperature. Thereby, exhaust temperature can be raised gently.

Further, since the temperature of the reflux gas decreases only by flowing through the reflux passage 24, the reflux gas cooler 26 may not be interposed in the reflux passage 24.
Further, means for detecting the air-fuel ratio (exhaust concentration) of the exhaust such as the air-fuel ratio sensor 21 is not essential, and it may be estimated by calculation from the fuel injection amount and the air amount.

The engine is not limited to a direct injection diesel engine, and may be a gasoline engine.
In the above embodiment, the case where the exhaust gas temperature is decreased has been described. However, when it is desired to increase the exhaust gas temperature, the control opposite to the above may be performed. That is, it is only necessary to reduce the amount of reducing gas when holding control for holding the fresh air amount at a constant amount is performed.

  Further, in the above embodiment, when the exhaust gas temperature increases as the post injection amount increases, the recirculation gas amount is increased to lower the exhaust gas temperature. However, the exhaust temperature does not increase regardless of the post injection amount. It can also be applied when it rises. Furthermore, the present exhaust temperature control device is not limited to the case where it is implemented together with the air-fuel ratio control of the reduction process by the NOx storage catalyst, but can be implemented if it is desired to control the exhaust temperature.

  In the above embodiment, the case where the upstream end of the recirculation passage 24 is connected to the exhaust manifold 19 and the downstream end is connected to the intake manifold 13 has been described. However, from the intake passage 14 and the exhaust purification device 23 upstream of the compressor 16a. Alternatively, it may be configured to communicate with the downstream exhaust passage 20 (configured as a so-called low pressure EGR system). In this case, since the pressure difference between the intake passage 14 and the exhaust passage 20 is low and the reflux gas does not flow easily, a throttle valve for adjusting the amount of the reflux gas is provided upstream of the connection portion between the reflux passage and the intake passage. It is preferable to provide a supercharging state adjusting means such as a supercharger or an electric turbo upstream of the throttle valve 18 in order to make the new air amount constant.

  In the low-pressure EGR system, a fresh air amount may be controlled to be constant by providing a valve other than the throttle valve 18 on the exhaust upstream side of the portion where the recirculation passage and the intake passage are connected.

1 ECU (electronic control unit)
2 New air volume control unit (new air volume control means)
3 Reflux gas amount control unit (Reflux gas amount control means)
4 Fuel injection control unit (fuel injection control means)
10 Engine (Internal combustion engine)
11 Fuel Injection Valve 12 Common Rail 13 Intake Manifold (Intake Manifold)
14 Intake passage 15 Air filter 16 Supercharger (VG turbo, new air volume control means)
16a Compressor 16b Turbine 17 Intercooler 18 Throttle valve (new air volume control means)
19 Exhaust manifold (exhaust manifold)
20 Exhaust passage 21 Air-fuel ratio sensor 22 Exhaust temperature sensor (exhaust temperature detection means)
23 Exhaust purification device 24 Recirculation passage 25 Recirculation gas amount control valve (recirculation gas amount control means)
26 Reflux gas cooler 27 Engine speed sensor

Claims (5)

New air amount control means for controlling the amount of fresh air supplied into the cylinder of the internal combustion engine;
Recirculation gas amount control means for controlling a recirculation gas amount flowing through a recirculation passage communicating the exhaust passage and the intake passage of the internal combustion engine;
A fuel injection valve for injecting fuel into the cylinder of the internal combustion engine;
Fuel injection control means for controlling the amount of additional fuel injected from the fuel injection valve to reduce the exhaust gas flowing through the exhaust passage to a desired air-fuel ratio ,
The fresh air amount control means holds the fresh air amount supplied to the intake passage at a constant amount;
The recirculation gas amount control means is adapted to increase the additional fuel amount controlled by the fuel injection control means in a state where the fresh air amount is maintained at a constant amount by the new air amount control means. Implement flow control to increase gas volume ,
The temperature of the exhaust gas that rises due to the increase in the additional fuel amount is reduced by the increase in the recirculation gas amount, and the temperature of the exhaust gas when the exhaust gas reaches the desired air-fuel ratio is less than a predetermined limit temperature. An exhaust temperature control device characterized by: The recirculated gas amount control means, the injection start time of the additional fuel by the fuel injection control means is characterized by zero the recirculated gas amount, exhaust gas temperature control device according to claim 1. Exhaust temperature detection means for detecting the temperature of the exhaust gas flowing through the exhaust passage of the internal combustion engine,
The recirculated gas amount control means, the temperature of the detected said exhaust by the exhaust temperature detecting means, characterized in that to increase the recirculated gas amount reaches the limit temperature, the exhaust gas temperature according to claim 1 or 2, wherein Control device. The fresh air amount control means is provided on the intake passage on the upstream side of the connection portion between the intake passage and the return passage, and on the exhaust passage on the downstream side of the connection portion between the exhaust passage and the return passage. The exhaust gas temperature control device according to any one of claims 1 to 3 , wherein the exhaust gas temperature control device is a supercharger capable of adjusting a supercharging flow rate interposed therebetween. Said fresh air amount control means, wherein said a throttle valve provided upstream the intake passage than the connection portion between the intake passage and the return passage, one of the claims 1-4 1 The exhaust gas temperature control device according to Item.

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