JP2011026988A - Exhaust pipe direct fuel injection system, internal combustion engine and control method of exhaust pipe direct fuel injection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust pipe direct fuel injection system capable of grasping the state of fuel injection into an exhaust pipe and leading a fuel flow rate to an appropriate value, an internal combustion engine and a control method of the exhaust pipe direct fuel injection system. <P>SOLUTION: First and second vessels 21a, 21b different in capacity are provided in series at a fuel supply pipe 18b connecting a supply pump 17 and an injector 19 for injecting fuel into an exhaust pipe 9. The second vessel 21b contains a fuel pressure sensor 22b. A control unit 20 measures a change in a fluctuation width of fuel pressure or in a frequency of fuel pressure based on the fluctuation information of fuel pressure in the second vessel 21b which is detected by the fuel pressure sensor 22b, measures a flow rate of fuel injected into the exhaust pipe 9 based on the measured change, and corrects the flow rate of fuel injected into the exhaust pipe 9 based on the measured value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control method for an exhaust pipe direct fuel injection system, an internal combustion engine, and an exhaust pipe direct fuel injection system. More specifically, the present invention can grasp the state of fuel injection into the exhaust pipe and appropriately adjust the fuel flow rate. The present invention relates to an exhaust pipe direct fuel injection system, an internal combustion engine, and a control method for an exhaust pipe direct fuel injection system.

  In recent years, from the viewpoint of air environment conservation, automobiles that use diesel oil or gasoline as fuel have improved the exhaust gas purification action by using an LNT (Lean NOx Traps) catalyst in the aftertreatment device installed in the exhaust pipe. . This is because the LNT catalyst supports alkali metal or alkaline earth metal together with noble metal, oxidizes nitric oxide (NO) in a lean state and adsorbs on the catalyst as nitrate, and purifies nitrogen oxide (NOx) in a reducing atmosphere. This is because it has an excellent effect of being able to.

  When this LNT catalyst is used, a NOx adsorption reaction on the LNT catalyst is required during the NOx purification, and in order to maintain the reaction, fuel is periodically injected and supplied into the exhaust gas. The reduction reaction at is promoted.

  In addition, in order to avoid the problem that the NOx adsorption amount decreases due to sulfur in the fuel and the purification rate decreases, the sulfur removal treatment is performed, but the temperature increase and heat treatment necessary for the sulfur removal are also performed in the fuel. Is injected into exhaust gas and supplied.

  By the way, when fuel is supplied into the exhaust pipe, an injector is used to inject the fuel into the exhaust pipe at a pressure higher than that of the exhaust gas. However, the fuel lubrication action is used for the injector injection mechanism parts to ensure stable operation. In order to do this, a cooling structure with water circulation is provided.

  However, when the fuel is intermittently injected from the injector, if a part of the fuel remains at the tip of the injector and is exposed to high-temperature exhaust gas, the carbon in the fuel remaining inside the injector is the main component. Will be produced. In some cases, the solid matter acts to hinder the injection and inhibits fuel supply into the exhaust pipe (see, for example, Patent Documents 1 and 2).

  In addition, in the LNT catalyst, in the sulfur desorption process that requires a reducing atmosphere that lowers the oxygen concentration after periodically raising the catalyst temperature, fuel supply into the exhaust pipe is hindered and the amount of injected fuel is reduced. In such a case, it is difficult to ensure the necessary temperature and excess air ratio (λ). As a result, there is a problem that the sulfur removal treatment becomes insufficient and the NOx purification performance is lowered.

  Further, in feedback (hereinafter referred to as F / B) control in which the catalyst temperature is estimated from the exhaust injection amount set on the control map, when the actual injection amount or catalyst temperature is not subject to F / B control, the exhaust pipe When the injection amount is too small, there is a problem that the actual catalyst temperature is insufficiently raised, the desulfurization process becomes poor, and the performance deteriorates.

  In addition, when there is a variation in the injection amount for each injector that injects fuel into the exhaust pipe, and the change in the injection amount with respect to the pressure is also different individually, the difference in the injection characteristics due to these injectors may cause insufficient sulfur removal. is there. For example, when the amount of injected fuel is large, it becomes a mixed state exceeding an appropriate ratio with oxygen in the exhaust gas, oxygen shortage occurs, and the temperature does not rise to the temperature required for sulfur treatment, so sulfur removal becomes insufficient and NOx purification As the performance deteriorates, white smoke may be generated if the fuel is discharged without being oxidized on the catalyst. On the other hand, when the amount of injected fuel is small, there is a possibility that λ required for the reducing atmosphere generation process at the time of the sulfur desorption process does not become 1 or less or the air-fuel ratio rich state becomes shallow. Although it is possible to sort the injectors within a certain characteristic range as a countermeasure, there is a problem that if the standard value is reduced, the cost increases and the merchantability is reduced.

JP 2008-297799 A JP 2009-30509 A

  An object of the present invention is to understand the state of fuel injection into an exhaust pipe, and to guide the fuel flow rate to an appropriate value. Fuel direct injection system in an exhaust pipe, internal combustion engine, and fuel direct injection system in an exhaust pipe It is to provide a control method.

  In order to achieve the above object, an exhaust pipe direct fuel injection system of the present invention is an exhaust pipe direct fuel injection system having a fuel injection device for injecting fuel supplied from a fuel supply pump into the exhaust pipe. A first container and a second container having a smaller capacity than the first container are provided in series in a fuel supply path connecting the fuel injection device and the fuel injection device, and a fuel pressure sensor is provided in the second container, and the fuel pressure sensor Is used to detect a change in the fuel pressure in the second container, measure the flow rate of the fuel injected into the exhaust pipe based on the detection information, and determine the amount of fuel injected into the exhaust pipe based on the measured value. Control means for correcting the flow rate is provided.

  In the above-described exhaust pipe direct fuel injection system, a change in fuel pressure fluctuation range or frequency change is measured as a change in fuel pressure in the second container detected by the fuel pressure sensor.

  In order to achieve the above object, an internal combustion engine of the present invention comprises the above-described exhaust pipe direct fuel injection system.

  In addition, a control method for a direct fuel injection system in an exhaust pipe according to the present invention for achieving the above object is a method for controlling a direct fuel injection system in an exhaust pipe having a fuel injection device for injecting fuel supplied from a fuel supply pump into the exhaust pipe. In the control method, a first container and a second container having a smaller capacity than the first container are provided in series in a fuel supply path connecting the fuel supply pump and the fuel injection device, and a fuel pressure is applied to the second container. A sensor is provided, the fuel pressure sensor detects a change in the fuel pressure in the second container, the flow rate of the fuel injected into the exhaust pipe is measured based on the detection information, and the flow rate is measured based on the measured value. Control for correcting the flow rate of the fuel injected into the exhaust pipe is performed.

  Further, the above-described control method of the direct fuel injection system in the exhaust pipe measures the change in the fluctuation range of the fuel pressure or the change in the frequency as the fluctuation of the fuel pressure in the second container detected by the fuel pressure sensor. It is.

  Further, in the above-described control method for the direct fuel injection system in the exhaust pipe, when the flow rate of the fuel is corrected, the measured value of the flow rate of the fuel injected into the exhaust pipe is less than a preset required flow value of the fuel. Is modified to increase the flow rate of fuel injected into the exhaust pipe and to increase the amount of fuel injection requested next time, and the measured value of the flow rate of fuel injected into the exhaust pipe is set to a predetermined fuel requirement. When the flow rate is larger than the flow rate value, the fuel injection into the exhaust pipe is stopped or the flow rate of the fuel injected into the exhaust pipe is reduced, and the next fuel injection request amount is corrected.

  According to the present invention, a change in fuel pressure is detected by a fuel pressure sensor provided in a small one of two large and small containers provided in series in a fuel supply path from a fuel supply pump to an exhaust pipe, and the detection is performed. Since the flow rate of the fuel injected into the exhaust pipe is measured based on the information and the flow rate of the fuel injected into the exhaust pipe is corrected based on the measured value, the actual fuel injection amount can be measured. The state of fuel injection into the exhaust pipe can be grasped, and the fuel flow rate can be led to an appropriate value.

  For this reason, it is possible to correct variations in the amount of fuel injected into the exhaust pipe due to individual differences in injectors that inject fuel into the exhaust pipe. Further, by adding the measured value of the fuel flow rate into the exhaust pipe to the correction item of the F / B control, the flow rate of the fuel injected into the exhaust pipe can be set to an optimum value according to the situation. Further, it is possible to detect defects such as stop of fuel injection into the exhaust pipe and a decrease in the injection amount due to clogging of an injector that injects fuel into the exhaust pipe. For this reason, it is possible to warn of the occurrence of defects.

  Therefore, by providing the internal combustion engine with the above-described fuel injection system directly in the exhaust pipe, the adsorption reaction of NOx on the LNT catalyst in the exhaust pipe can be improved, and the sulfur desorption process can be improved. For this reason, since the purification performance of NOx on the LNT catalyst can be improved, purification of exhaust gas can be promoted.

It is a block diagram of the internal combustion engine of embodiment of this invention. It is an expanded sectional view of the fuel flow measurement unit of the internal combustion engine of FIG. FIG. 3 is a graph showing measurement results of fuel pressure fluctuations in a large and small capacity container provided in a fuel supply path of the direct fuel injection system for an exhaust pipe of the internal combustion engine of FIG. 1. FIG. 3 is a graph showing measurement results of fuel pressure fluctuations in a large and small capacity container provided in a fuel supply path of the direct fuel injection system for an exhaust pipe of the internal combustion engine of FIG. 1. FIG. 2 is a graph showing the influence of fuel pressure on the fluctuation range of fuel pressure in a small-capacity container provided in the fuel supply path of the direct injection fuel direct injection system of the internal combustion engine of FIG. 1. It is a figure which shows the control flow of the fuel direct injection system in the exhaust pipe of the internal combustion engine of FIG. It is a figure which shows the control flow of the fuel direct injection system in the exhaust pipe of the internal combustion engine of FIG. FIG. 2 is a graph showing the result of measuring the variation in the frequency of fuel pressure in a small capacity container provided in the fuel supply path of the direct fuel injection system in the exhaust pipe of the internal combustion engine of FIG. 1. FIG. 2 is a graph showing a relationship between a frequency of fuel pressure and an output voltage in a small-capacity container provided in a fuel supply path of the direct injection fuel direct injection system of the internal combustion engine of FIG. 1.

  Hereinafter, a control method for an exhaust pipe direct fuel injection system, an internal combustion engine, and an exhaust pipe direct fuel injection system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The internal combustion engine of the first embodiment shown in FIG. 1 is, for example, a common rail type diesel engine (hereinafter simply referred to as an engine) 1 and is mounted on an automobile such as a truck. The engine 1 expands the piston in the cylinder 3 by expansion based on self-ignition that occurs when fuel is supplied to air that has been compressed and heated to high temperature in the combustion chamber of the cylinder 3 of the engine body (internal combustion engine body) 2. It has a configuration for extruding. In addition, this invention is not limited to a diesel engine, It can also apply to a gasoline engine etc.

  First, the intake / exhaust system of the engine 1 will be described. An intake manifold 4 is connected to each inlet of the plurality of cylinders 3 of the engine body 2. An intake pipe 5 a is connected to the intake manifold 4.

  An exhaust manifold 6 is connected to the outlet of each of the plurality of cylinders 3. An intake pipe 5 a is connected to the exhaust manifold 6 via an EGR (Exhaust Gas Recirculation) system 7. The EGR system 7 is an exhaust gas recirculation system, and includes an EGR pipe 7a, an EGR cooler 7b, and an EGR valve 7c.

  The exhaust manifold 6 is connected to the turbine inlet of the supercharger 8. The supercharger 8 has a turbine and a compressor (compressor) formed integrally with each other. The intake pipe 5a is connected to the outlet of the compressor of the supercharger 8 through the intake pipe 5b. Thereby, when the turbine of the supercharger 8 is rotated by the force of the exhaust gas, the compressor is driven in conjunction with this, and the intake gas compressed by the drive of the compressor is sent into the cylinder 3 of the engine body 2. ing.

  An exhaust pipe 9 is connected to the turbine outlet of the supercharger 8. A post-processing device 10 is connected to a midway position of the exhaust pipe 9. For example, a NOx purification catalyst unit that reduces nitrogen oxides (NOx) and a filter that collects and removes PM (Particulate Matter) are connected in series to the aftertreatment device 10 in order along the flow direction of exhaust gas. Has been. For example, a NOx storage reduction catalyst (Lean NOx Trap: hereinafter abbreviated as LNT catalyst) is used in the NOx purification catalyst section. The LNT catalyst is a catalyst capable of purifying NOx in a reducing atmosphere by supporting an alkali metal or alkaline earth metal together with a noble metal, oxidizing nitric oxide (NO) in a lean state, and adsorbing it as a nitrate on the catalyst. is there. In the exhaust pipe 9, a temperature sensor 11 that detects the temperature of the exhaust gas is installed in a stage preceding the aftertreatment device 10.

  Next, the fuel supply system of the engine 1 will be described. Each cylinder 3 of the engine body 2 is provided with an electromagnetic injector 15 that directly injects fuel into the combustion chamber. Each injector 15 is connected to a supply pump (fuel pump) 17 via a common rail 16. A fuel tank (not shown) is connected to the supply pump 17 through a fuel supply pipe 18a. The arrow F1 indicates the direction in which the fuel flows in the fuel supply pipe 18a.

  The engine 1 of the first embodiment has an exhaust pipe direct fuel injection system that directly injects fuel into the exhaust pipe 9 at a constant pressure. The exhaust pipe direct fuel injection system includes a fuel supply pipe 18 b, an injector (fuel injection device) 19, a control unit 20, and a fuel flow rate measurement unit (hereinafter simply referred to as a measurement unit) 21.

  The injector 19 is a device that directly injects fuel into the exhaust pipe 9, and is installed in the exhaust pipe 9 at a stage preceding the aftertreatment device 10. A common rail 16 is connected to the injector 19 through a fuel supply pipe 18 b, and fuel is supplied from the common rail 16.

  A control unit (control means) 20 is electrically connected to the injector 19 and its operation is controlled. This control unit 20 has a function of intermittently supplying fuel into the exhaust pipe 9 by controlling the operation of the injector 19 and controlling the flow rate and injection timing of the fuel.

  The control unit 20 is electrically connected to the measurement unit 21 and measures the flow rate of the fuel injected into the exhaust pipe 9 based on the detection information relating to the change in fuel pressure transmitted from the measurement unit 21. The flow rate of the fuel injected into the exhaust pipe 9 can be corrected based on the measured value.

  The measurement unit 21 has a detection unit for detecting information related to fluctuations in fuel pressure necessary for measuring the amount of fuel injected into the exhaust pipe 9, and is located in the middle of the fuel supply pipe 18b. Is installed. The measurement unit 21 transmits information on the detected fuel pressure fluctuation to the control unit 20.

  Next, an enlarged sectional view of an example of the measurement unit 21 is shown in FIG. The arrow F2 indicates the direction of fuel flow.

  The measurement unit 21 includes a first container 21a and a second container 21b having different large and small capacities. That is, a relatively large-capacity first container 21a and a relatively small-capacity second container 21b are sequentially connected in series along the fuel flow direction F2 to the fuel supply pipe 18b. The first container 21a is formed, for example, with a capacity 5 to 10 times, preferably 10 times that of the second container 21b.

  Each of the first container 21a and the second container 21b is provided with fuel pressure sensors (hereinafter simply referred to as sensors) 22a and 22b. The pressure sensor 22a is a sensor for detecting the fuel pressure in the first container 21a, and is installed on the upper part of the first container 21a with the sensor surface in contact with the fuel.

  The pressure sensor 22b is a sensor for detecting the fuel pressure in the second container 21b, and is installed at the bottom of the second container 21b with its sensor surface in contact with the fuel. The pressure sensors 22 a and 22 b are electrically connected to the control unit 20, convert the fuel pressure information in the container detected by each into an electrical signal and transmit it to the control unit 20.

  Here, when the fuel pressurized at a constant pressure is injected and supplied into the exhaust pipe 9 through the injector 19, the fuel volume is reduced in the first container 21a and the second container 21b, and the supply pump 17 is supplied. The fuel pressure fluctuates due to the pressurized supply by. The magnitude of the variation in the fuel pressure varies depending on the flow rate of the fuel injected into the exhaust pipe 9 through the injector 19 in addition to the volume of the container for detecting the fuel pressure and the magnitude of the fuel pressurization pressure.

Therefore, in the exhaust pipe direct fuel injection system of the first embodiment, the volume of the second container 21b having a small capacity of the measurement unit 21 is set to an appropriate value (for example, about 5 to 10 cm ³ , preferably 10 cm ³ ). Then, the fuel pressure in the second container 21b is changed according to the flow rate of the fuel injected into the exhaust pipe 9 through the injector 19, and this is detected by the pressure sensor 22b. The control unit 20 measures the change in the fluctuation range of the fuel pressure based on the information on the fuel pressure detected by the pressure sensor 22b, and the actual fuel injection amount (injected into the exhaust pipe 9 based on the measurement result) Measure the fuel flow rate. And based on the measurement result, it correct | amends so that the fuel injection quantity to the exhaust pipe 9 may enter into an appropriate range.

  The reason for detecting the pressure of the small-capacity second container 21b is that the large-capacity first container 21a has a large volume, so the change in pressure is small even if the flow rate changes, whereas the small-capacity second container 21b. This is because the volume is small in 21b, so that the change in pressure is large when the flow rate is changed (the fuel pressure changes within a detectable high pressure range). Since this pressure width changes also with the value which pressurizes a fuel according to an engine speed, this value is acquired from the fuel pressure value detected with the pressure sensor 22a of the large capacity | capacitance 1st container 21a. The fuel pressure value from the pressure sensor 22a of the large-capacity first container 21a has been verified from the experimental results by the present inventor to have very little influence due to the fuel injection to the exhaust pipe 9.

  Here, it is considered that the fluctuation of the fuel pressure in the first and second containers 21a and 21b depends on the volume of fuel injected into the exhaust pipe 9. The following formulas (1) -a, (1) -b, formulas (2) -a, (2) -b represent the supply pump at the same time as the fuel volumes in the first and second containers 21a, 21b change, respectively. 17 shows that the fuel pressure (fuel flow rate) changes depending on the volume because the fuel volume in the first and second containers 21a and 21b changes.

  First, consider when fuel is decreasing. That is, the fuel flows into the first and second containers 21a and 21b in a pressurized state. Consider a case where the fuel in the first and second containers 21a and 21b is decreased by an injection amount into the exhaust pipe 9 under intermittent flow.

First container 21a:
Pa1 × Va = Pa1 ′ × (Va−ΔV0)
Pa1 ′ = (Va × Pa1) / (Va−ΔV0) (1) −a

  Va: volume of first container 21a, Pa1: pressure value of pressurized fuel measured in first container 21a before fuel injection into exhaust pipe 9, Pa1 ': after fuel injection into exhaust pipe 9 The pressure value of the pressurized fuel measured in the first container 21a, ΔV0: a fuel volume that decreases in the fuel supply pipe 18b due to fuel injection into the exhaust pipe 9.

Second container 21b:
Pb1 × Vb = Pb1 ′ × (Vb−ΔV0)
Pb1 ′ = (Vb × Pb1) / (Vb−ΔV0) (1) −b

  Vb: volume of the second container 21b, Pb1: pressure value of pressurized fuel measured in the second container 21b before fuel injection into the exhaust pipe 9, Pb1 ′: after fuel injection into the exhaust pipe 9 Is the pressure value of the pressurized fuel measured in the second container 21b.

  Next, let us consider the recovery of the fuel condition. That is, after the fuel injection to the exhaust pipe 9 is completed, the pressure that is quickly restored returns to the pre-injection state in the first and second containers 21a and 21b, and the fuel flows into the first and second containers 21a and 21b with a delay. Consider the case of returning to the amount of.

First container 21a:
Pa2 ′ × Va = Pa2 × (Va−ΔV1)
Pa2 ′ = ((Va−ΔV1) × Pa2) / Va (2) −a

  Pa2: pressure value of fuel recovered in the first container 21a after fuel injection into the exhaust pipe 9, Pa2 ′: after insufficient fuel is supplied due to fuel injection into the exhaust pipe 9 in the first container 21a The pressure value of ΔV1: the volume of fuel that is reduced by the injection of fuel into the exhaust pipe 9 and supplied into the first container 21a.

Second container 21b:
Pb2 ′ × Vb = Pb2 × (Vb−ΔV1)
Pb2 ′ = ((Vb−ΔV1) × Pb2) / Vb (2) −b

  Pb2: pressure value of fuel recovered in the second container 21b after fuel injection into the exhaust pipe 9, Pb2 ′: after supply of insufficient fuel due to fuel injection into the exhaust pipe 9 in the second container 21b Pressure value.

  Next, FIGS. 3 to 5 show calculation results of pressure fluctuations by the direct fuel injection system in the exhaust pipe of the first embodiment. For example, the volume ratio (= large capacity / small capacity) of the first container 21a and the second container 21b is 10, and the volume of the small container 2b is 10 cc.

  FIG. 3 shows the results of measuring fuel pressure fluctuations in the first and second containers 21a and 21b at an engine speed of 1000 rpm and FIG. 4 at an engine speed of 2000 rpm, respectively. It can be seen that the variation in the fuel pressure in the small-capacity second container 21b is greater than the variation in the fuel pressure in the large-capacity first container 21a.

  FIG. 5 shows the influence of the fuel pressure on the fluctuation range of the fuel pressure in the second container 21b. It can be seen that depending on the fuel pressure in the second container 21b, the width of the pressure value that varies as the fuel flows changes.

  Next, a control method of the exhaust pipe direct fuel injection system of the first embodiment will be described with reference to FIGS. 6 and 7 show a control flow of the exhaust pipe direct fuel injection system.

  First, the value of the fuel pressure generated by pressurizing the fuel by the supply pump 17 is detected by an electric signal from the pressure sensor 22a of the large capacity first container 21a (detection of fuel pressure).

  Next, in accordance with an instruction for fuel injection into the exhaust pipe 9, fuel is injected from the injector 19 into the exhaust pipe 9 through the common rail 16 and the fuel supply pipe 18b. At this time, when a certain amount of fuel passes through the first and second containers 21a and 21b having different large and small capacities provided in the fuel supply pipe 18b, the fluctuation range of the fuel pressure in each container changes according to the container capacity. To do.

  Here, the control unit 20 estimates the flow rate of the fuel injected into the exhaust pipe 9 based on the fuel pressure information detected by the pressure sensor 22b of the small-capacity second container 21b and converted into an electric signal ( measure. Subsequently, as shown in step 100A of FIG. 6, the control unit 20 compares the measured fuel flow rate Qe1 with the required value Q + α preset in the control unit 20, and the measured fuel flow rate Qe1 is If it is less than the required value Q + α, the fuel injection into the exhaust pipe 9 is stopped as shown in Step 101A of FIG. 6, and then the exhaust pipe 9 in the exhaust injection time map is shown in Step 102A of FIG. The fuel injection time is increased to increase the fuel flow rate, and at the same time, as shown in step 103A of FIG.

  On the other hand, the control unit 20 compares the measured fuel flow rate Qe2 with the required value Q + α preset in the control unit 20 as shown in Step 100B of FIG. 7, and the measured fuel flow rate Qe2 is requested. If the value is larger than the value Q + α, the fuel injection into the exhaust pipe 9 is stopped as shown in step 101B of FIG. 7, and then the exhaust pipe 9 in the exhaust injection time map is shown in step 102B of FIG. The fuel injection time is reduced to reduce the fuel flow rate, and as shown in step 103B of FIG.

  The fuel injection request amount is corrected with respect to a map based on the engine speed and the fuel injection amount into the combustion chamber of the engine body 2.

  According to the exhaust pipe direct fuel injection system of the first embodiment as described above, the actual injection amount of the fuel supplied into the exhaust pipe 9 can be measured, so that the fuel is injected into the exhaust pipe 9. The fuel flow rate can be led to an appropriate value.

  For this reason, it is possible to correct variations in the amount of fuel injected into the exhaust pipe 9 due to individual differences in the injectors 19 that inject fuel into the exhaust pipe 9. Further, by adding the measured value of the fuel flow rate into the exhaust pipe 9 to the correction item of the F / B control, the flow rate of the fuel injected into the exhaust pipe 9 can be set to an optimum value according to the situation. . Further, it is possible to detect defects such as stoppage of fuel injection into the exhaust pipe 9 and a decrease in the injection amount due to clogging of the injector 19 that injects fuel into the exhaust pipe 9. For this reason, it is possible to warn of the occurrence of defects.

  Therefore, by providing the engine 1 with the above-described exhaust pipe direct fuel injection system, the NOx adsorption reaction on the LNT catalyst in the exhaust pipe 9 can be improved, and the sulfur desorption treatment performance can be improved. it can. For this reason, since the reduction reaction (purification performance) of NOx on the LNT catalyst can be improved, purification of exhaust gas can be promoted.

  Further, it is not necessary to reduce the standard value of the injector 19 that injects fuel into the exhaust pipe 9, so that the cost is not increased and the merchantability is not deteriorated.

Further, when calculating the fuel injection amount in the exhaust pipe based on the air-fuel ratio detected by the air-fuel ratio sensor, the calculation is made with the same fuel injection amount with the oxygen (O ₂ ) concentration in the intake air or exhaust gas. Although it varies depending on (O), such a case can be avoided in the case of the present embodiment.

  Further, when estimating the degree of clogging of the fuel injection valve in the exhaust passage based on the pressure in the common rail and the fluctuation state of the engine rotational speed, the pressure detection unit in the common rail and the fuel injection valve in the exhaust pipe are It is far away and a time delay occurs, but in the case of the present embodiment, such a situation can be avoided.

  Next, an exhaust pipe direct fuel injection system according to a second embodiment of the present invention will be described.

  As described in the first embodiment, when the fuel is injected into the exhaust pipe 9 and the fuel having a constant flow rate passes through the first and second containers 21a and 21b having the large and small sizes, the first and second containers 21a and 21a, The fuel pressure of 21b fluctuates. At this time, the frequency of the fuel pressure in the first and second containers 21a and 21b (that is, the number of fluctuations of the fuel pressure per unit time) changes. This is the flow rate of the fuel supplied into the exhaust pipe 9. Proportional.

  Therefore, in the second embodiment, the volume of the small-capacity second container 21b of the measuring unit 21 is set to an appropriate value (same as in the first embodiment), and the inside of the exhaust pipe 9 is passed through the injector 19. The fuel pressure in the second container 21b is varied according to the flow rate of the fuel injected into the fuel, and this is detected by the pressure sensor 22b. Based on the fuel pressure information detected by the pressure sensor 22b, the control unit 20 measures a change in frequency as a change in fuel pressure, and the actual fuel injection amount injected into the exhaust pipe 9 based on the measurement result. (Fuel flow rate) is measured. And based on the measurement result, it correct | amends so that the fuel injection quantity to the exhaust pipe 9 may enter into an appropriate range. Other configurations of the direct fuel injection system in the exhaust pipe and the internal combustion engine and the control method of the direct fuel injection system in the exhaust pipe are the same as those in the first embodiment.

  Here, the time change of the fuel volume in the first and second containers 21a and 21b, that is, the change when depending on the fuel flow rate was examined. The pressure sampling time is, for example, 0.5 seconds.

When the volume of the second container 21b is 10 cm ³ , it is assumed that the increase in fuel pressure is given by the above equation (2) -a, and the fuel volume has increased from 936 kPa to 1170 kPa at 2000 rpm. Decreases from 10 cm ³ to 8 cm ³ by 2 cm ³ in 0.5 seconds, resulting in a flow rate of 4 cm ³ / sec. Consider the case where this flow rate is reduced to 2 cm ³ / sec. Although the pressure is reduced by 1 cm ^{3 in} 0.5 seconds, the pressure at this time is 1040 kPa, and after 0.5 seconds, the pressure decreases by 2 cm ³ to 1170 kPa.

Next, let us consider a case where the fuel pressure once decreases after returning to the initial pressure and the pressure is given by the above-described equation (2) -b. The pressure is dropped to 749kPa from 936kPa at 2000 rpm, a fuel flow rate at this time is 4 cm ³ / sec, the fuel in the second container 21b is decreased by 2 cm ³ from 10 cm ³ to 8 cm ³ to 0.5 seconds Yes. Consider a case where the fuel flow rate is reduced to 2 cm ³ / sec so that this is reduced by 1 cm ³ in 0.5 seconds. Although the pressure is reduced by 1 cm ^{3 in} 0.5 seconds, the pressure at this time is 842 kPa, and further decreases by 2 cm ³ after 0.5 seconds and reaches 749 kPa.

  It is assumed that the above phenomenon occurs in a state where the fuel pressure generated by the supply pump 17 maintains a constant pressure depending on the engine rotation. When the fuel flows through the small volume fuel pressure measuring unit (second container 21b) at a constant flow rate, the fuel pressure in the container rises to compensate for the fuel volume that has flowed out, and the fuel flows out to lower the increased pressure. Further, when the fuel flow continues, the fuel pressure in the container decreases due to the outflow of fuel. This phenomenon is repeated when the fuel flows for several seconds.

  Therefore, when the fuel is intermittently injected into the exhaust pipe 9 and the fuel is continuously injected for several seconds, the fuel pressure fluctuates in the first and second containers 21a and 21b. Apart from the width of the fluctuating pressure, if the fluctuating pressure cycle, that is, the frequency is counted, the fuel flow rate at that time can be estimated (measured).

Next, FIG. 8 and FIG. 9 show the calculation results of the pressure fluctuation by the exhaust pipe direct fuel injection system of the second embodiment. The volume of the second container 21b was 10 cm ³ .

FIG. 8 shows the result of measuring the change in the frequency of the fuel pressure in the second container 21b when the engine speed is 2000 rpm. When the fuel flow rate is 4 cm ³ / sec, the frequency is 15 times (1 Hz) in 15 seconds, and when the fuel flow rate is 8 cm ³ / sec, the frequency is 7 times (about 0.5 Hz) in 15 seconds.

  FIG. 9 shows the relationship between the frequency of the fuel pressure and the output voltage of the pressure sensor 22b. At a certain frequency, the output voltage is saturated and becomes a constant value. Therefore, an appropriate gradient (output voltage / frequency value) is selected so that the frequency in the range A where the output voltage is not saturated is used and the frequency at which the output voltage is saturated is not used. The slope is adjusted as necessary.

  Also in the second embodiment, the same effect as that of the first embodiment can be obtained.

  The control method of the exhaust pipe direct fuel injection system, the internal combustion engine, and the exhaust pipe direct fuel injection system of the present invention includes a small container of two large and small containers provided in series in a fuel supply path from the fuel supply pump to the exhaust pipe. The fuel pressure sensor provided in the fuel pressure sensor detects fluctuations in the fuel pressure, measures the flow rate of the fuel injected into the exhaust pipe based on the detected information, and based on the measured value, the flow rate of the fuel injected into the exhaust pipe The fuel injection state into the exhaust pipe can be grasped and the fuel flow rate can be led to an appropriate value, so that the direct fuel injection system in the exhaust pipe of an automobile, the internal combustion engine, and the exhaust It can be used as a control method for a direct fuel injection system in a pipe.

1 Diesel engine (internal combustion engine)
2 Engine body (Internal combustion engine body)
6 Exhaust manifold 8 Supercharger 9 Exhaust pipe 10 Aftertreatment device 16 Common rail 17 Supply pump (fuel pump)
18a, 18b Fuel supply pipe 19 Injector (fuel injection device)
20 Control unit (control means)
21 Fuel flow rate measurement unit 21a First container 21b Second containers 22a, 22b Fuel pressure sensor

Claims (6)

In an exhaust pipe direct fuel injection system having a fuel injection device for injecting fuel supplied from a fuel supply pump into the exhaust pipe,
A fuel supply path connecting the fuel supply pump and the fuel injection device is provided with a first container and a second container having a smaller capacity than the first container in series, and a fuel pressure sensor is provided in the second container,
The fuel pressure sensor detects a change in the fuel pressure in the second container, measures the flow rate of the fuel injected into the exhaust pipe based on the detected information, and injects the fuel into the exhaust pipe based on the measured value. Exhaust pipe direct fuel injection system provided with control means for correcting the flow rate of the fuel to be discharged.   2. The direct fuel injection system in an exhaust pipe according to claim 1, wherein a change in a fluctuation range of fuel pressure or a change in frequency is measured as a change in fuel pressure in the second container detected by the fuel pressure sensor.   An internal combustion engine comprising the exhaust pipe direct fuel injection system according to claim 1 or 2. In a control method for an exhaust pipe direct fuel injection system having a fuel injection device for injecting fuel supplied from a fuel supply pump into the exhaust pipe,
A fuel supply path connecting the fuel supply pump and the fuel injection device is provided with a first container and a second container having a smaller capacity than the first container in series, and a fuel pressure sensor is provided in the second container,
The fuel pressure sensor detects a change in the fuel pressure in the second container, measures the flow rate of the fuel injected into the exhaust pipe based on the detected information, and injects the fuel into the exhaust pipe based on the measured value. For controlling a direct fuel injection system in an exhaust pipe for performing control for correcting the flow rate of the fuel to be discharged.   The control method for a direct fuel injection system in an exhaust pipe according to claim 4, wherein a change in a fluctuation range of fuel pressure or a change in frequency is measured as a change in fuel pressure in the second container detected by the fuel pressure sensor. In correcting the fuel flow rate,
When the measured value of the flow rate of the fuel injected into the exhaust pipe is smaller than a predetermined required flow rate value of the fuel, the flow rate of the fuel injected into the exhaust pipe is increased and the next required fuel injection amount is increased. To correct
When the measured value of the flow rate of the fuel injected into the exhaust pipe is larger than the predetermined required flow rate value of the fuel, the fuel flow into the exhaust pipe is stopped or the flow rate of the fuel injected into the exhaust pipe 6. The method for controlling an exhaust pipe direct fuel injection system according to claim 4 or 5, wherein the control is performed so that the required amount of fuel injection next time is reduced.

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