JP4720779B2 - Exhaust temperature reduction control device and method - Google Patents

Description

  The present invention relates to a technical field of an exhaust temperature reduction control device and method for reducing the temperature of exhaust gas discharged from, for example, an internal combustion engine of a vehicle.

  As this type of exhaust temperature reduction control device, there is one that reduces the temperature of exhaust gas by using an exhaust gas recirculation (EGR) system that recirculates the exhaust gas of the internal combustion engine to the intake side again.

  For example, Patent Document 1 discloses a technique of detecting the temperature of a catalyst provided in an exhaust path and increasing the EGR amount when the detected temperature exceeds a start temperature.

  Patent Document 2 discloses a technique for reducing the temperature of exhaust gas by enriching the air-fuel ratio when the temperature of the catalyst cannot be sufficiently reduced by the above-described EGR system.

JP-A-7-83034 JP-A-4-298666

  However, for example, a continuously variable transmission (CVT) vehicle such as a hybrid vehicle travels with a high engine load even at low and medium speeds for the purpose of improving fuel efficiency. The pressure is small. For this reason, when the EGR amount is increased to reduce the exhaust gas temperature, there is a technical problem that it is difficult to cause the increased EGR to flow into the intake pipe.

  The present invention has been made in view of the above-described problems, for example, and provides an exhaust temperature reduction control device and method that can effectively reduce the exhaust temperature by increasing the EGR amount. Let it be an issue.

In order to solve the above problems, an exhaust temperature reduction control device of the present invention includes a rotation speed changing means capable of changing the rotation speed of an internal combustion engine, and an exhaust gas recirculation means capable of recirculating the exhaust gas of the internal combustion engine to the intake side. A temperature detecting means for detecting the temperature on the exhaust side of the internal combustion engine; a fuel increasing means capable of increasing the amount of fuel supplied to the internal combustion engine and enriching the air-fuel ratio; and increasing the rotational speed of the internal combustion engine. In addition, control of the rotation speed changing means and control of the exhaust gas recirculation means so as to increase the amount of exhaust gas recirculated, and fuel efficiency deterioration caused by operation of the fuel increase means The fuel consumption deterioration rate comparison means for comparing the deterioration rate with each other when the temperature is lowered by the second predetermined temperature, and when the detected temperature exceeds the first predetermined temperature, the fuel consumption rate deterioration ratio In comparison by means, and control means for controlling the while deterioration rate of the fuel consumption is low.

  According to the exhaust temperature reduction control apparatus of the present invention, the temperature on the exhaust side of the internal combustion engine is first detected by the temperature detection means during the operation. The "exhaust side temperature" here means the temperature of an arbitrary portion or member that constitutes or is attached to the exhaust path of the internal combustion engine or the temperature of the gas in the exhaust path, etc. It means the temperature related to a predetermined location, member or medium on the exhaust side that is the target of temperature detection.

  When the temperature on the exhaust side is detected, it is determined whether or not the temperature exceeds the first predetermined temperature. The “first predetermined temperature” here is a reference value for determining whether to increase the rotational speed of the internal combustion engine, and typically has a margin for the heat-resistant temperature of members provided in the exhaust path. It is a given temperature. When the detected temperature exceeds the first predetermined temperature, the rotational speed of the internal combustion engine is increased by the rotational speed changing means. Further, the amount of exhaust gas (hereinafter referred to as “EGR” as appropriate) recirculated to the intake side is increased by the exhaust gas recirculation means.

  As the rotational speed of the internal combustion engine increases, the pressure in the intake pipe of the internal combustion engine decreases. For this reason, EGR comes to flow into the intake pipe more smoothly. Accordingly, it is possible to increase the amount of EGR, increase the EGR introduction rate (that is, the ratio of EGR in the air-fuel mixture used for combustion of the internal combustion engine), and reduce the exhaust temperature. By reducing the exhaust temperature, it is possible to prevent, for example, a failure or deterioration of a member provided in the exhaust path due to the heat of the exhaust.

  Note that the above-described control of the rotation speed changing means and the exhaust gas recirculation means may be performed at the same time or may be performed at the same time. That is, if the control is performed so that the EGR flows into the intake pipe at the timing when the pressure of the intake pipe becomes negative due to the increase in the rotation speed, the above-described effect can be obtained.

  In the present invention, in particular, in an internal combustion engine provided in a vehicle that travels with a high load even at low and medium speed rotation, such as a hybrid vehicle or other CVT vehicle, the intake pipe negative pressure of the internal combustion engine is small. This is effective when the EGR introduction rate cannot be increased sufficiently.

  As described above, according to the exhaust gas temperature reduction control apparatus of the present invention, by increasing the rotational speed of the internal combustion engine, the amount of EGR is increased while decreasing or decreasing the pressure of the intake pipe. It is possible to effectively increase the EGR introduction rate and reliably reduce the exhaust temperature.

  In one aspect of the exhaust temperature reduction control apparatus of the present invention, the temperature detection means detects the temperature of a catalyst provided in the exhaust path of the internal combustion engine.

  According to this aspect, the temperature of the catalyst provided in the exhaust path of the internal combustion engine is detected by the temperature detection means. The catalyst is provided for purifying harmful substances in the exhaust such as CO, HC and NOx, and is exposed to the exhaust in the exhaust path. For this reason, for example, when the internal combustion engine is operated at a high load, the catalyst is exposed to extremely high temperature exhaust gas, which may cause the temperature to rise abnormally and rapidly deteriorate.

  However, in this embodiment, in particular, when the temperature of the catalyst detected by the temperature detecting means exceeds a temperature at which the catalyst deteriorates (that is, the first predetermined temperature), the rotational speed changing means and the exhaust gas recirculation. The exhaust gas temperature can be reduced by controlling the means. Thereby, it can prevent that the temperature of a catalyst becomes abnormally high. Therefore, it is possible to prevent rapid deterioration of the catalyst.

  In another aspect of the exhaust temperature reduction control apparatus of the present invention, the rotational speed changing means changes the rotational speed of the internal combustion engine while maintaining the output of the internal combustion engine.

  According to this aspect, the rotational speed of the internal combustion engine is changed while maintaining the output of the internal combustion engine. Here, since the output of the internal combustion engine depends on the product of the rotational speed and the torque, for example, when increasing the rotational speed, the output is maintained by decreasing the torque.

  By operating in this way, the rotational speed can be changed without changing the work amount of the internal combustion engine. Therefore, for example, in an internal combustion engine provided in an automobile, the rotation speed can be changed without affecting the vehicle speed.

  In another aspect of the exhaust temperature reduction control apparatus of the present invention, the fuel supplied to the internal combustion engine is increased to control the fuel increase means capable of enriching the air-fuel ratio, the rotational speed changing means, and the exhaust gas recirculation means. The control means further comprises a fuel consumption deterioration rate comparing means for comparing the fuel consumption deterioration rate by the fuel increasing means by the operation of the fuel increasing means when the temperature is lowered by a second predetermined temperature. Is capable of controlling the fuel increasing means to operate, and performs one control in which the deterioration rate of the fuel consumption is low in the comparison by the fuel consumption rate deterioration comparison means.

  According to this aspect, the fuel increase means and the fuel consumption deterioration rate comparison means are further provided, and the fuel consumption deterioration rate comparison means controls the rotational speed changing means and the exhaust gas recirculation means (hereinafter referred to as “first control” as appropriate). The fuel consumption deterioration rate due to the fuel increase means is compared with the fuel consumption deterioration rate due to the control of the fuel increasing means (hereinafter referred to as “second control” as appropriate). In this comparison, each of the first and second controls compares the fuel consumption deterioration rate when the temperature detected by the temperature detecting means is lowered by the second predetermined temperature. The “second predetermined temperature” here is a reference value when comparing the fuel consumption deterioration rates of the first and second controls. Typically, the detected temperature is provided in the exhaust path. The temperature is such that a margin is given to the temperature that is equal to or lower than the heat resistance temperature of the member.

  And in the comparison mentioned above, exhaust temperature is reduced by performing one control by which the fuel consumption deterioration rate was made low. That is, when the fuel consumption deterioration rate is lower in the first control, the control of the rotational speed of the internal combustion engine and the amount of exhaust gas to be recirculated as described above is performed, and the fuel consumption deterioration rate is lower in the second control. In this case, the air-fuel ratio is enriched by the fuel increasing means.

  The fuel consumption deterioration rate by each of the first and second controls varies depending on various conditions such as the rotational speed and torque of the internal combustion engine when starting the control, for example. Deterioration can be reduced. It should be noted that the fuel consumption deterioration rate by each of the first and second controls may be calculated at the time of comparison, or can be derived relatively easily by preparing a table or the like in advance.

  As described above, the exhaust temperature reduction control device according to this aspect further includes the fuel increase means for reducing the exhaust temperature, and uses the first and second controls depending on the situation, thereby improving the fuel efficiency. Deterioration can be reduced.

  In an aspect further comprising the fuel increase means and the fuel consumption deterioration rate comparison means described above, the control means is configured such that, in the fuel consumption deterioration rate comparison means, a difference between the fuel consumption deterioration rates compared with each other is within a predetermined range. In this case, the rotation speed increasing means and the exhaust gas recirculation means may be controlled.

With this configuration, when the difference between the deterioration rates of the fuel consumption in each of the first and second controls is within a predetermined range, the first control (that is, the increase and resumption of the rotational speed of the internal combustion engine) is performed. Increase in the amount of exhaust gas circulated). Here, the “predetermined range” is a value serving as a reference for determining which of the first control and the second control is performed. The predetermined range can be arbitrarily set, for example, a value of about 5% is set.

  In the second control, since the air-fuel ratio is enriched, not only the fuel consumption is deteriorated but also the CO contained in the exhaust gas is increased. For this reason, when the difference between the fuel consumption deterioration rates of the first and second controls is 5%, it is considered that there is almost no difference in the fuel consumption deterioration, and the first control without increasing CO is preferentially performed. To do. Thereby, it is possible to prevent deterioration of exhaust emission.

Alternatively, in an aspect further comprising a fuel increase means and a fuel consumption deterioration rate comparison means, the temperature detection means, when the control means controls the rotation speed increase means and the exhaust gas recirculation means, the control means performs the control. after the control of the rotational speed increase hand Dan及 beauty said exhaust gas recirculation means is performed, and detects the temperature again, the control unit, when the detected again temperature exceeds the first predetermined temperature The fuel increasing means may be controlled.

  If comprised in this way, after 1st control is performed, the temperature on an exhaust side will be detected again by a temperature detection means. Then, when the temperature detected again exceeds the first predetermined temperature, the second control is performed.

  The effect of reducing the exhaust temperature by the first control is finite because, for example, the amount of EGR that can be used is limited. Therefore, even after the first control is performed, the exhaust side temperature may exceed the first predetermined temperature. If the second control is performed in such a case, the exhaust temperature can be further reduced. Therefore, the exhaust temperature can be surely set to the first predetermined temperature or lower.

  In another aspect of the exhaust gas temperature reduction control apparatus of the present invention, the exhaust gas temperature reduction control device further includes a cooling water temperature detecting means for detecting a temperature of the cooling water of the internal combustion engine, wherein the control means has a third temperature of the detected cooling water. When the temperature exceeds a predetermined temperature, the rotation speed increasing means and the exhaust gas recirculation means are not controlled.

According to this aspect, the temperature of the cooling water for the internal combustion engine is detected by the cooling water temperature detecting means. Then, when the detected temperature of the cooling water exceeds the third predetermined temperature, the first control is not performed.
Here, the “third predetermined temperature” is a reference value for determining whether or not to increase the EGR. For example, if the temperature is exceeded, the cooling of the internal combustion engine by the cooling water cannot catch up. The temperature is such that a margin is provided for the temperature at which the internal combustion engine overheats.

  For example, the EGR may be configured to be cooled by cooling water of an internal combustion engine. In such a case, if the amount of EGR is increased, the temperature of the cooling water increases and the effect of cooling the internal combustion engine decreases.

  In this embodiment, in particular, when the temperature of the cooling water exceeds the third predetermined temperature, the first control is not performed, so the amount of EGR does not increase. For this reason, in order to reduce exhaust temperature, the temperature of cooling water does not rise. Therefore, it is possible to prevent an excessive load from being applied to the cooling water and the internal combustion engine from overheating.

  In addition, if it is an aspect further provided with the fuel increasing means described above, the exhaust temperature can be reduced by performing the second control even when the temperature of the cooling water exceeds the third predetermined temperature. is there.

For exhaust gas temperature reduction control method of the present invention is to solve the problems described above, changeable rotational speed changing means the rotational speed, increasing to air recirculation possible exhaust gas recirculation means and the fuel supplying exhaust to the intake side In the internal combustion engine provided with the fuel increasing means capable of enriching the engine, a member temperature detecting step for detecting the temperature on the exhaust side of the internal combustion engine, and the control of the rotational speed changing means so as to increase the rotational speed of the internal combustion engine And the deterioration rate of fuel consumption by controlling the exhaust gas recirculation means so as to increase the amount of exhaust gas that is recirculated, and the deterioration rate of fuel consumption due to the operation of the fuel increase means. comparison of respectively the fuel economy rate comparison step of comparing with each other in the case where the second to the predetermined temperature drop, the detected if the temperature exceeds a first predetermined temperature, the fuel consumption deterioration comparison step Oite, and a control step of performing deterioration rate is low and has been one control of the fuel consumption.

  According to the exhaust temperature reduction control method according to the present invention, as in the case of the exhaust temperature reduction control device of the present invention described above, the pressure of the intake pipe is decreased by increasing the rotational speed of the internal combustion engine or Since the amount of EGR is increased while decreasing, it is possible to effectively increase the EGR introduction rate and reliably reduce the exhaust temperature.

  In the exhaust temperature reduction control method of the present invention, various aspects similar to the various aspects of the exhaust temperature reduction control apparatus of the present invention described above can be employed.

  The operation and other advantages of the present invention will become apparent from the best mode for carrying out the invention described below.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
First, the configuration of an engine that is an example of the “internal combustion engine” of the present invention to which the exhaust temperature reduction control device according to the first embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of the engine.

  In FIG. 1, an engine 200 causes an air-fuel mixture to explode in a cylinder 201 by a spark plug 202 and converts a reciprocating motion of a piston 203 generated according to an explosive force into a rotational motion of a crankshaft 205 via a connection rod 204. It is configured to be able to. The engine 200 is mounted on, for example, a vehicle or a hybrid vehicle on which an electric motor is mounted together with the engine 200, and generates power by burning gasoline or alcohol fuel.

  When the fuel in the cylinder 201 is burned, the air sucked from the outside passes through the intake pipe 206 and is mixed with the fuel injected from the injector 207 to become an air-fuel mixture. Fuel is supplied to the injector 207 from the fuel tank 223 via the filter 224. The fuel tank 223 is provided with a fuel sensor 225 for detecting the remaining amount of fuel.

  The communication state of the intake pipe 206 and the cylinder 201 is controlled by opening and closing the intake valve 208. The air-fuel mixture combusted in the cylinder 201 becomes exhaust gas, and is exhausted through the exhaust pipe 210 through the exhaust valve 209 that opens and closes in conjunction with the opening and closing of the intake valve 208.

  An air cleaner 211 is disposed upstream of the intake pipe 206 to purify air sucked from outside. An air flow meter 212 is disposed on the downstream side (cylinder side) of the air cleaner 211. The air flow meter 212 has a form called a hot wire type, and is configured to be able to directly measure the mass flow rate of the inhaled air. The intake pipe 206 is further provided with an intake air temperature sensor 213 for detecting the temperature of the intake air.

  A throttle valve 214 that adjusts the amount of intake air into the cylinder 201 is disposed downstream of the air flow meter 212 in the intake pipe 206. A throttle position sensor 215 is electrically connected to the throttle valve 214, and its opening degree can be detected. Further, an accelerator position sensor 216 that detects the amount of depression of the accelerator pedal 226 by the driver and a throttle valve motor 217 that drives the throttle valve 214 are also provided around the throttle valve 214.

  A crank position sensor 218 that detects the rotational position of the crankshaft 205 is provided in the vicinity of the crankshaft 205. The crank position sensor 218 is configured to be able to acquire the position of the piston 203 inside the cylinder 201 and the rotational speed of the engine 200 based on the rotation state of the crankshaft 205. A knock sensor 219 capable of measuring the knock strength of the engine 200 is disposed in the cylinder block that houses the cylinder 201.

  A three-way catalyst 222 which is an example of the “catalyst” of the present invention is installed in the exhaust pipe 210. The three-way catalyst 222 is a catalyst capable of purifying CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) discharged from the engine 200, respectively. The three-way catalyst 222 is adjacent to a catalyst temperature sensor 231 that is an example of the “temperature detection means” of the present invention, and detects the temperature of the three-way catalyst 222.

  The intake pipe 206 and the exhaust pipe 210 are communicated with each other by an EGR passage 228. The EGR passage 228 is provided with an EGR control valve 227 for controlling the amount of EGR introduced from the exhaust pipe 210 to the intake pipe 206 by opening and closing, and an EGR cooler 229 for cooling the EGR. An EGR device 230 which is an example of “exhaust gas recirculation means” is configured.

  The ECU (Electronic Control Unit) 100 is an example of the “control means” in the present invention, and is an electronic control unit that controls the overall operation of the engine system.

  Next, the operation and effect of the exhaust temperature reduction control apparatus according to the present embodiment will be described with reference to FIGS. 2 and 3 in addition to FIG. FIG. 2 is a flowchart showing the operation of the exhaust temperature reduction control apparatus according to the first embodiment, and FIG. 3 is a graph showing the control of the rotational speed of the engine.

  In FIG. 2, when the exhaust temperature reduction control apparatus according to the present embodiment is operating, the temperature of the three-way catalyst 222 is first detected by the catalyst temperature sensor 231, and the detected temperature is an example of the “first predetermined temperature” in the present invention. It is determined whether or not the threshold value T1 is exceeded (step S1). If the detected temperature exceeds the threshold value T1 (step S1: YES), the process proceeds to step 2. If the detected temperature does not exceed the threshold value T1 (step S1: NO), it is determined that the exhaust temperature need not be reduced, and the process ends.

  When the temperature of the three-way catalyst 222 exceeds the threshold value T1, the ECU 100 calculates an EGR introduction rate for setting the temperature of the three-way catalyst 222 to be equal to or lower than the threshold value T1 (step S2). That is, how much EGR should be increased is calculated.

  Subsequently, the ECU 100 calculates an engine rotation speed for realizing the EGR introduction rate calculated in step S2 (step S3). That is, the engine speed is calculated to obtain the intake pipe negative pressure that allows the increased EGR to flow smoothly.

  After calculating the EGR introduction rate and the engine speed, the actually calculated values are applied. First, the engine speed is increased to the value calculated in step S3 (step S4). As a result, the pressure in the intake pipe 206 decreases. Below, the control at the time of increasing an engine speed is demonstrated in detail.

  In FIG. 3, the engine 200 before controlling the rotational speed according to the present embodiment is operating on the power operating line. In addition, the state before control is represented as points A, C, and E in the graph. Here, when the engine speed is controlled, the control is performed while maintaining the output of the engine 200 (that is, on an equal power line indicated by a chain line in the graph). More specifically, the engine rotational speed is increased and the engine torque is decreased. Thus, the operation is changed to point B when operating at point A, similarly to point D when operating at point C, and to operation at point F when operating at point E.

  As described above, by increasing the rotation speed while maintaining the output of the engine 200, for example, when the engine 200 is mounted on a vehicle or the like, the rotation speed is increased without affecting the vehicle speed. Is possible. Moreover, the effect of stabilizing the combustion of the engine 200 can be obtained by performing control that reduces the engine torque. For this reason, the amount of EGR that can be introduced without causing deterioration of combustion also increases.

  Returning to FIG. 2, after increasing the engine speed, the EGR control valve 227 is controlled to increase the EGR introduction rate to the value calculated in step S2 (step S5). The increased EGR is smoothly introduced because the pressure in the intake pipe 206 is reduced due to the increase in the rotational speed. Therefore, the effect of reducing the exhaust temperature by increasing the EGR can be obtained with certainty.

  As explained above, according to the exhaust gas temperature reduction control apparatus according to the first embodiment, by increasing the engine speed before increasing the EGR, the EGR introduction rate can be effectively increased and ensured. An effect of reducing the exhaust temperature can be obtained.

<Second Embodiment>
Next, an exhaust temperature reduction control apparatus according to the second embodiment will be described with reference to FIGS. 4 to 6 in addition to FIG. The second embodiment is different from the first embodiment described above in that the air-fuel ratio can be enriched, and the other configurations and operations are generally the same. Therefore, in the second embodiment, points different from the first embodiment will be described in detail, and descriptions of other configurations and operations will be omitted as appropriate.

  First, the configuration of the engine 200 to which the exhaust temperature reduction control device according to the second embodiment is applied will be described with reference to FIG. 1 again.

  In FIG. 1, the ECU 100 is configured to increase the fuel injection amount and to enrich the air-fuel ratio by controlling an injector 207 which is an example of the “fuel increase means” of the present invention. An air-fuel ratio sensor 221 is disposed upstream of the three-way catalyst 222 in the exhaust pipe 210 and detects the air-fuel ratio of the engine 200 from the exhaust gas discharged from the exhaust pipe 210.

  Further, the ECU 100 operates as an example of the “fuel consumption deterioration rate comparison means” of the present invention, and the fuel consumption deterioration rate when the air-fuel ratio is enriched as described above, the increase in the rotational speed of the engine 200 described in the first embodiment, and The fuel consumption deterioration rate when the EGR introduction rate is increased is calculated and compared with each other.

  In the second embodiment, the EGR cooler 229 is configured to cool the EGR using the cooling water of the engine 200. In the water jacket in the cylinder block, a water temperature sensor 220 which is an example of the “cooling water temperature detecting means” of the present invention is disposed.

  Next, the operation and effect of the exhaust temperature reduction control apparatus according to the second embodiment will be described with reference to FIGS. 4 to 6 in addition to FIG. FIG. 4 is a flowchart showing the operation of the exhaust temperature reduction control apparatus according to the second embodiment. FIG. 5 is a graph showing the engine speed control together with the fuel increase amount, and FIG. 6 is a graph showing the engine speed control together with the fuel consumption.

  In FIG. 4, when the operation of the exhaust temperature reduction control apparatus according to the second embodiment starts, it is first determined whether or not the temperature of the three-way catalyst 222 exceeds the threshold value T1 as in the first embodiment (step). S1). Next, the temperature of the cooling water of the engine 200 is detected by the water temperature sensor 220, and it is determined whether or not the temperature of the cooling water exceeds a threshold value T2, which is an example of the “third predetermined temperature” of the present invention ( Step S6). When the temperature of the cooling water exceeds the threshold value T2 (step S6: YES), the process proceeds to step S7-2, and then the process of step S9 is performed. That is, in this case, the EGR introduction rate is not increased. Therefore, it is possible to prevent the cooling water from becoming higher temperature for cooling the EGR, and the engine 200 can be prevented from overheating. Step S7-2 is the same process as step S7. Steps S7 and S9 will be described later in detail. When the temperature of the cooling water does not exceed the threshold value T2 (step S6: NO), the processes of steps S2 and S3 described in the first embodiment are performed. Here, the EGR introduction rate and the engine rotation speed are calculated so that the temperature of the three-way catalyst 222 is reduced by the target value T3 which is an example of the “second predetermined temperature” of the present invention.

  Following the processing in steps S2 and S3, the amount of fuel increase in the case where the temperature of the three-way catalyst 222 is reduced by the target value T3 due to fuel increase is calculated (step S7). The amount of increase in fuel varies depending on the engine operating state. Hereinafter, the fuel increase amount will be described in detail.

  In FIG. 5, the fuel increase amount line represents the fuel increase amount when the exhaust temperature is reduced by a predetermined temperature, and the more the fuel increase amount line is located in the upper right of the graph (that is, the higher the engine speed and the engine torque). It shows that a lot of fuel is used. For this reason, when the engine 200 is operating at the point A, the fuel increase amount is smaller than when the engine 200 is operating at the point C, and when the engine 200 is operating at the point E. The amount of increase in fuel is greater than when operating in the state of point C.

  Returning to FIG. 4, when the fuel increase amount is calculated, the fuel consumption deterioration rate R1 when the EGR introduction rate and the engine speed are increased and the fuel consumption deterioration rate R2 when the fuel is increased are calculated, respectively. Comparison is made (step S8). The fuel consumption deterioration rate R2 depends on the fuel increase amount calculated in step S7. On the other hand, the fuel consumption deterioration rate R <b> 1 varies depending on the operating state of the engine 200. Hereinafter, the fuel consumption deterioration rate R1 will be described in detail.

  In FIG. 6, a fuel consumption operation line indicated by a dotted line is a line indicating a state where the fuel consumption is the best. A concentric equal fuel consumption line is shown along the fuel consumption operation line. The fuel consumption becomes worse as the distance from the fuel consumption operation line increases. That is, the fuel efficiency is not relatively deteriorated during the control from the point A to the point B, but the fuel efficiency is significantly deteriorated during the control from the point C to the point D and from the point E to the point F. It becomes.

  Returning to FIG. 4, when R1 exceeds R2 in the comparison of the fuel consumption deterioration rate described above (step S8: YES), the fuel injected from the injector 207 (see FIG. 1) is the amount calculated in step S7. The air / fuel ratio is enriched (step S9). As a result, the temperature of the exhaust gas is reduced and the process ends.

  On the other hand, when R1 is equal to or less than R2 (step S8: NO), the processing of steps S4 and S5 described in the first embodiment is performed, and the temperature of the exhaust is reduced. In step S8, if the difference between R1 and R2 is within a predetermined range (for example, within 5%), the process may proceed to step S4. By doing this, when the fuel consumption deterioration rate is about the same, it is possible to avoid an increase in fuel that increases the CO in the exhaust, and to prevent the exhaust emission from deteriorating. The predetermined range can be arbitrarily set based on, for example, the engine CO emission amount.

  When the exhaust gas temperature is reduced by the process of step S5, it is determined again whether or not the temperature of the three-way catalyst 222 exceeds the threshold value T1 (step S10). If the temperature of the three-way catalyst 222 does not exceed the threshold value T1 (step S10: NO), the process ends. If the temperature exceeds the threshold value T1 (step S10: YES), a new fuel increase amount is calculated. Then, the exhaust temperature is reduced due to the increase in fuel (step S11). As a result, even if the exhaust gas temperature cannot be sufficiently reduced by increasing the EGR introduction rate, the temperature of the three-way catalyst 222 can be reliably set to T1 or less.

  As described above, according to the exhaust temperature reduction control device according to the second embodiment, the exhaust temperature reduction control apparatus according to the second embodiment is configured so that the fuel can be increased in order to reduce the exhaust temperature. It is possible to reduce the deterioration of fuel consumption.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. Exhaust temperature reduction control accompanying such a change is possible. Devices and methods are also within the scope of the present invention.

It is the schematic which shows the structure of an engine. It is a flowchart which shows operation | movement of the exhaust temperature reduction control apparatus which concerns on 1st Embodiment. It is a graph which shows control of the rotational speed of an engine. It is a flowchart which shows operation | movement of the exhaust temperature reduction control apparatus which concerns on 2nd Embodiment. It is a graph which shows control of the rotational speed of an engine with a fuel increase amount. It is a graph which shows control of the rotational speed of an engine with a fuel consumption.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... ECU, 200 ... Engine, 206 ... Intake pipe, 210 ... Exhaust pipe, 220 ... Water temperature sensor, 221 ... Air-fuel ratio sensor, 222 ... Three-way catalyst, 230 ... EGR device, 231 ... Catalyst temperature sensor

Claims (7)

Rotation speed changing means capable of changing the rotation speed of the internal combustion engine;
Exhaust gas recirculation means capable of recirculating the exhaust gas of the internal combustion engine to the intake side;
Temperature detecting means for detecting the temperature on the exhaust side of the internal combustion engine;
Fuel increasing means capable of increasing the amount of fuel supplied to the internal combustion engine and enriching the air-fuel ratio;
The rate of deterioration of fuel consumption by controlling the rotation speed changing means so as to increase the rotation speed of the internal combustion engine and controlling the exhaust gas recirculation means so as to increase the amount of exhaust gas that is recirculated. And a fuel consumption deterioration rate comparison means for comparing the fuel consumption deterioration rate due to the operation of the fuel increasing means with each other when the temperature is lowered by a second predetermined temperature, respectively.
When the detected temperature exceeds a first predetermined temperature, the comparison by the fuel consumption worse comparing means, characterized in that it comprises a control means for performing the deterioration rate is low and has been one control of the fuel Exhaust temperature reduction control device.   The exhaust temperature reduction control device according to claim 1, wherein the temperature detection means detects a temperature of a catalyst provided in an exhaust path of the internal combustion engine.   The exhaust temperature reduction control device according to claim 1 or 2, wherein the rotation speed changing means changes the rotation speed of the internal combustion engine while maintaining the output of the internal combustion engine. The control means controls the rotation speed increasing means and the exhaust gas recirculation means when the fuel efficiency deterioration rate comparison means determines that the difference between the fuel efficiency deterioration rates compared with each other is within a predetermined range. The exhaust gas temperature reduction control device according to any one of claims 1 to 3, wherein: Said temperature detecting means, when the control of the rotation speed increasing means and said exhaust gas recirculation means by said control means has been performed, control lines of the rotational speed increase hand Dan及 beauty said exhaust gas recirculation means by said control means The temperature is detected again,
The said control means controls the said fuel increase means, when the temperature detected again exceeds the said 1st predetermined temperature. The fuel increase means as described in any one of Claim 1 to 4 characterized by the above-mentioned. Exhaust temperature reduction control device. Further comprising cooling water temperature detecting means for detecting the temperature of the cooling water of the internal combustion engine,
The control means does not control the rotation speed increasing means and the exhaust gas recirculation means when the detected temperature of the cooling water exceeds a third predetermined temperature. exhaust temperature reduction control apparatus according to any one of 5. Changeable rotational speed changing means the rotational speed, the internal combustion engine having a enrichment possible fuel increase means the increase was air recirculation possible exhaust gas recirculation means and the fuel supplied to the intake side of the exhaust,
A member temperature detecting step for detecting the temperature on the exhaust side of the internal combustion engine;
The rate of deterioration of fuel consumption by controlling the rotation speed changing means so as to increase the rotation speed of the internal combustion engine and controlling the exhaust gas recirculation means so as to increase the amount of exhaust gas that is recirculated. And a fuel consumption deterioration rate comparison step in which the fuel consumption deterioration rate due to the operation of the fuel increasing means is compared with each other when the temperature is lowered by the second predetermined temperature, respectively.
A control step of performing one control when the detected temperature is higher than a first predetermined temperature and the deterioration rate of the fuel consumption is low in the comparison in the deterioration rate comparison step of the fuel consumption rate. Exhaust temperature reduction control method.

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