JP2010007648A - Diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently regenerate a diesel particulate filter in a post-treatment device provided in an exhaust path of exhaust gas. <P>SOLUTION: An EGR circuit 44 connects the downstream side of an exhaust gas post-treatment device 46 to the upstream side of an air intake turbine 36 of a turbocharger TB. A diesel engine has an engine control unit 100 which performs the control of fully closing an EGR valve 43 and throttles a throttle valve 47 to regenerate the diesel particulate filter 46b when a pressure sensor 52 provided at the upstream side of a diesel particulate filter 46b detects pressure equal to or higher than a predetermined value; and stops the regeneration of the diesel particulate filter 46b when a temperature sensor 53 provided at the downstream side of the diesel particulate filter 46b detects the temperature equal to or higher than the predetermined value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a diesel engine equipped with an aftertreatment device for treating exhaust gas and EGR.

A technique for reducing a part of the exhaust gas after passing through the aftertreatment device to the intake side of the engine is disclosed. However, when the post-processing device is forcibly regenerated, there is no disclosure of a control technique that associates this forcible regeneration with the EGR reduction rate (see, for example, Patent Document 1).
JP 2007-315372 A

    In the technology as described above, since the control technology related to the EGR reduction rate is not disclosed when the processing device is forcibly regenerated, there is a drawback in that regeneration of the post-processing device and EGR reduction are not performed with high accuracy. is there.

  The subject of this invention is providing the diesel engine which eliminates the above malfunctions.

The above object of the present invention is achieved by the following configuration.
That is, in the first aspect of the present invention, the supercharger (TB), the EGR circuit (44) for reducing a part of the exhaust gas to the intake system, and the lower side of the exhaust turbine (45) of the supercharger (TB). In the diesel engine provided with an exhaust gas aftertreatment device (46) having a diesel particulate filter (46b) for collecting at least particulate matter (PM) in the exhaust gas on the side, the EGR circuit (44) includes the exhaust gas A pressure sensor provided on the upstream side of the diesel particulate filter (46b) is configured to connect the downstream side of the gas aftertreatment device (46) and the upstream side of the intake turbine (36) of the supercharger (TB). When 52) detects a pressure equal to or higher than a predetermined value, the EGR valve (43) is fully closed and the throttle valve (47) is throttled to set the diesel particulate filter (46b). When the temperature sensor (53) provided on the downstream side of the diesel particulate filter (46b) detects a temperature equal to or higher than a predetermined value, control is performed to stop regeneration of the diesel particulate filter (46b). The diesel engine is characterized in that an engine control unit (100) is provided.

    According to the operation of the first aspect, the burned exhaust gas exits from the cylinder, and part of the exhaust gas is reduced from the EGR circuit (44) to the intake system in the middle of the combustion. The EGR gas flowing in the EGR circuit (44) is reduced from the downstream side of the diesel particulate filter (46b) to the upstream side of the intake turbine (35) of the supercharger (TB).

    The diesel particulate filter (46b) that constitutes a part of the aftertreatment device (46) collects the particulate matter (PM) in the exhaust gas, but if the low load state continues for a long time, the particulate matter (PM) Will become clogged up. The clogged state is measured by the pressure sensor (52), and when the pressure exceeds a predetermined level, the EGR valve (43) is fully closed and the throttle valve 47 on the lower side of the post-processing device (46) is also throttled. Then, since the exhaust gas temperature rises, (PM) is burned out by the high-temperature exhaust gas, and the diesel particulate filter (46b) is regenerated.

    During regeneration of such a diesel particulate filter (46b), if the temperature sensor (53) on the downstream side of the diesel particulate filter (46b) detects a high temperature equal to or higher than a predetermined value, the diesel particulate filter (46b) Stop playback.

  In the invention according to claim 2, the EGR cooler (57) is provided in the EGR circuit (44), and the intercooler (37) is disposed downstream of the intake turbine (36) of the supercharger (TB). The diesel engine according to claim 1, wherein the diesel engine is characterized in that

  The action of claim 2 is the action of claim 1, and the gas passing through the EGR circuit (44) is cooled by the EGR cooler (57). Further, the intake air from the atmosphere and the EGR gas are merged, supercharged by the intake turbine (36), and cooled by the intercooler (37).

  Since the present invention is configured as described above, in the invention according to the first aspect, regeneration and stoppage of the diesel particulate filter (46b) are appropriately performed. Further, since the EGR gas is reduced after passing through the diesel particulate filter (46b), the influence of the particulate matter (PM) on the combustion can be reduced.

  In the invention described in claim 2, in addition to the effect of claim 1, since it is cooled by both the EGR cooler (57) and the intercooler (37), the NOx reduction effect is increased.

The best mode for carrying out the present invention will be described.
FIG. 1 is an overall configuration diagram of a pressure accumulation type fuel injection device. The accumulator fuel injection device is applied to, for example, a multi-cylinder diesel engine, but may be a gasoline engine. The accumulator fuel injection device pressurizes the common rail 1 accumulating high-pressure fuel corresponding to the injection pressure, the pressure sensor 2 attached to the common rail 1, and the fuel pumped up from the fuel tank 3, and pumps the fuel to the common rail 1. A high-pressure pump 4, a fuel injection nozzle 6 for injecting high-pressure fuel accumulated in the common rail 1 into the cylinder 5 of the engine E, a control device (ECU) for controlling the operation of the high-pressure pump 4 and the fuel injection nozzle 6 Consists of ECU is an abbreviation for engine control unit.

Thus, the common rail 1 injects fuel to each cylinder 5 of the engine E, and makes the fuel supply a required pressure.
The fuel in the fuel tank 3 is sucked into the high-pressure pump 4 driven by the engine E through the fuel filter 7 through the suction passage, and the high-pressure fuel pressurized by the high-pressure pump 4 is guided to the common rail 1 through the discharge passage 8. Stored.

    The high-pressure fuel in the common rail 1 is supplied to the fuel injection nozzles 6 for the number of cylinders through the high-pressure fuel supply passages 9, and the fuel injection nozzles 6 are operated to the respective cylinders based on commands from the ECU 100. The surplus fuel (return fuel) from each fuel injection nozzle 6 is guided to a common return passage 10 by each return passage 10 and returned to the fuel tank 3 by this return passage 10.

    In addition, a pressure control valve 11 is provided in the high-pressure pump 4 to control the fuel pressure (common rail pressure) in the common rail 1. The pressure control valve 11 is connected to the fuel tank 3 from the high-pressure pump 4 by a duty signal from the ECU 100. The flow area of the return passage 10 for surplus fuel to the fuel is adjusted, whereby the amount of fuel discharged to the common rail 1 side can be adjusted to control the common rail pressure.

    Specifically, the target common rail pressure is set according to the engine operating conditions, and the common rail pressure is feedback-controlled through the pressure control valve 11 so that the common rail pressure detected by the rail pressure sensor 2 matches the target common rail pressure. It is configured.

    As shown in FIG. 2, the ECU 100 of the diesel engine E having the common rail 1 in the work vehicle (agricultural work machine) has three types of modes, a travel mode A, a normal work mode B, and a heavy work mode C in relation to the rotational speed and the output torque. The configuration has a control mode.

    The traveling mode A is droop control in which the output also varies with the variation of the engine speed. It is used when traveling without farming. For example, when the traveling speed is reduced or stopped by applying a brake, the engine speed decreases with an increase in the traveling load, so that the traveling speed can be safely reduced or stopped.

    The normal work mode B is isochronous control in which the engine speed is constant and the output is changed according to the load even when the load varies. It is used for normal farm work. For example, if it is a tractor, it is when the cultivated land is hard during plowing work and resistance is applied to the plowing blade. Is the time.

    In the heavy work mode C, in addition to the isochronous control in which the engine speed is constant and the output is changed according to the load even when the load fluctuates in the same manner as the normal work mode B, the engine speed is increased when the load is close to the limit. This is a control with heavy load control that increases In particular, it is used when farming near the load limit. For example, when plowing with a tractor, the engine output increases beyond the normal limit even when encountering hard cultivated land, so work can be performed efficiently without interruption. .

    These work modes A, B, and C are operations of a work mode changeover switch that can switch between the work modes A, B, and C, or a shift operation of a traveling speed change lever of a farm vehicle (tractor, combine, rice transplanter, etc.) Alternatively, it is configured to be switched by an on / off operation or the like of a work clutch (rotary if it is a tractor, and mowing part or threshing part if it is a combine).

    In diesel engine E, pilot injection that injects a small amount of fuel in a pulse manner prior to main injection makes it possible to shorten the ignition delay, reduce the knocking noise peculiar to diesel engine E, and reduce noise It has a simple structure.

    This pilot injection is performed only once or twice before the main injection. By using the accumulator fuel injection device of the common rail 1, pilot injection is performed according to the situation of the engine E. Thus, it becomes possible to reduce the noise and the generation of white smoke or black smoke due to incomplete combustion. Further, by performing pilot injection in which a small amount of fuel is pulse-injected prior to main injection, the amount of nitrogen oxides in the exhaust gas is reduced.

  FIG. 3 shows a side view of a tractor equipped with a diesel engine having the common rail 1 as described above, and FIG. 4 shows a plan view thereof. In the plan view, the cabin 14 shown in FIG. 3 is omitted.

  The tractor includes front wheels 12 and 12 and rear wheels 13 and 13 at the front and rear portions of the fuselage, and the rotational power of the engine E mounted on the front portion of the fuselage is appropriately decelerated by a transmission in the transmission case T so that the front wheels 12 , 12 and the rear wheels 13, 13.

  A steering handle 16 is supported on the handle post 15 in the cabin 14 at the center of the body, and a seat 17 is provided behind the steering handle 16. A forward / reverse lever 18 is provided below the steering handle 16 to switch the advancing direction of the aircraft to the front / rear direction. When the forward / reverse lever 18 is moved to the front side, the aircraft moves forward, and when it is moved backward, the aircraft moves backward.

    An accelerator lever 25 for adjusting the engine speed is provided on the opposite side of the forward / reverse lever 18 with the handle post 15 in between, and an accelerator for similarly adjusting the engine speed is provided at the right corner of the step floor 19. The pedal 23 and left and right brake pedals 24L, 24R for operating the left and right rear wheels 13, 13 are provided. A clutch pedal 20 is provided at the left corner of the step floor 19.

  The main transmission lever 26 is located at the left front portion of the seat 17, the auxiliary transmission lever 27 capable of selecting any of the low speed, medium speed, high speed and neutral positions is located behind the main transmission lever 26, and further on the right side thereof is the PTO transmission lever 28. Is provided. Further, on the right side of the seat 17, a position lever 29 for setting the height of the working machine 21 (rotary or the like), an automatic tilling lever 30 for automatically setting the tilling depth of the field, and the working machine 21 after these levers. The right-up switch 31 and the right-down switch 32 are arranged, and then the automatic horizontal switch 33 and the backup switch 34 of the work machine 21 are arranged. The backup switch 34 automatically raises the work machine 21 when the machine moves backward. The work machine 21 has a configuration in which a link 22 is connected to the rear of the machine body. The tractor performs work such as tillage in the field by driving the work machine 21 and running the machine body. 21a is a hydraulic cylinder which raises and lowers the working machine 21.

  FIG. 5 is a schematic diagram of intake and exhaust into the cylinder 5 of the engine, which is an embodiment of a four-cycle diesel engine. The air supercharged by the intake turbine 36 of the supercharger TB passes through the intake turbine 36 and the intercooler 37 from the air cleaner 35 and is sent from the intake manifold 38 into the cylinder 5. Reference numeral 39 is an intake valve, and 40 is a piston. A cam 48 opens and closes the intake and exhaust valves 39 and 41 via a rocker arm 49.

The exhaust gas combusted in the cylinder 5 passes through the exhaust manifold 42 from the exhaust valve 41 and is then discharged by driving the supercharger TB with the exhaust turbine 45 of the supercharger TB.
This diesel engine has an EGR (exhaust gas recirculation device) circuit 44 for mixing a part of the exhaust gas into the intake side. In the EGR circuit, a part of the exhaust gas is mixed into the intake side to reduce the amount of oxygen (O2), thereby reducing the generation of nitrogen oxide Nox. However, if the EGR rate increases too much, the amount of oxygen decreases and incomplete combustion occurs. Therefore, it is necessary to adjust the EGR rate according to the combustion state. This adjustment is performed by the EGR valve 43. The EGR circuit 44 connects between an exhaust pipe 55 on the downstream side of a post-processing device 46 described later and an intake pipe 56 on the upstream side of the intake turbine 36 of the supercharger TB. In addition, an EGR cooler 57 is provided in the middle of the EGR circuit 44. The amount of exhaust gas reduced into the cylinder 5 varies depending on how the EGR valve 43 is opened and closed.

  The exhaust gas that has passed through the exhaust turbine 45 passes through the aftertreatment device 46 and is discharged from the muffler 50 into the atmosphere. The post-processing device 46 includes an oxidation catalyst (DOC) 46a and a diesel particulate filter (DPF) 46b.

    The oxidation catalyst (DOC) burns the incombustible material chamber, and the diesel particulate filter (DPF) is for collecting the granulated material chamber (PM). The EGR valve 43 and the throttle valve 47 are controlled by the ECU 100. The post-processing device 46 may be composed of only a diesel particulate filter (DPF) 46b. If an oxidation catalyst (DOC) is provided, the non-combustible material burns, resulting in cleaner exhaust gas.

  When the state of the exhaust gas is low (low load) continues for a long time, the DPF 46b has a concern that PM will accumulate and the capacity may be reduced. Therefore, a throttle valve 47 is provided on the lower side of the post-processing device 46, and when the throttle valve 47 is throttled, the pressure in the DPF 46b is kept high, so the temperature also rises. This makes it possible to regenerate the DPF 46b due to the influence of a high temperature. That is, when exhaust gas having a high temperature passes through the DPF 46b, the DPF 46b is regenerated by burning off the PM present in the DPF 46b.

  In the DPF regeneration operation for regenerating the DPF 46b, both the EGR valve 43 and the throttle valve 47 are throttled. Then, the gas temperature in the DPF 46b is raised together with the retard (retard) of the fuel injection timing so that the DPF 46b starts to be regenerated. This eliminates the need for fuel after-injection (in order to increase the exhaust gas temperature) or reduces the number of after-injections, so that the amount of fuel consumption can be suppressed and the environment is good.

  As a condition for performing such a DPF regeneration operation, a pressure sensor 52 is provided on the upper side of the post-processing device 46, and when the value of the pressure sensor 52 exceeds a predetermined value, PM accumulates in the DPF 46b. Therefore, the DPF regeneration operation is performed.

  Further, if the state in which the DPF regeneration operation is started continues for a long time, the DPF 46b is damaged due to an overheating state. Therefore, a temperature sensor 53 is provided on the lower side of the post-processing device 46, and when the value of the temperature sensor 53 exceeds a predetermined value, the DPF regeneration operation is stopped and the normal operation is resumed.

  In normal operation, the EGR valve 43 and the throttle valve 47 are simultaneously controlled to appropriately control the EGR amount. In particular, by having the throttle valve 47, the gas temperature in the DPF 46b can be kept high.

  With the configuration as described above, an intake throttle is not required. In other words, since the intake side pressure is high in an engine with a supercharger, an exhaust throttle valve or an intake throttle is required to secure the amount of EGR gas, and control in conjunction with the EGR valve is required, but such a system is unnecessary. It becomes.

  Further, since the exhaust gas downstream of the DPF 46b is taken out, it is possible to prevent the performance deterioration caused by the dirt of the supercharger TB. And since EGR gas is cooled by the EGR cooler 57, an effect becomes large with respect to NOx reduction.

  As described above, in the DPF forced regeneration mode in which the regeneration operation of the DPF is performed, the exhaust throttle valve 47 is throttled and the EGR valve 43 is fully closed by ON-OFF control. Therefore, NO is increased because the exhaust gas is not reduced, and this NO is converted to NO2 by the oxidation catalyst (DOC) 46a, and regeneration of the DPF 46b is promoted.

  Further, when the engine rotation shifts to low idle during the forced regeneration of the DPF 46b, the EGR valve 43 is fully opened. Since the temperature sensor 53 is provided on the downstream side of the DPF 46b, it may be added to the condition that the detection value by the temperature sensor 53 has risen to a predetermined value or more.

  58a, 58b, 58c and 58d shown in FIG. 6 are intake ports into the respective cylinders 5. In the embodiment, there are four cylinders. Reference numeral 38 denotes the intake manifold described with reference to FIG. In the configuration of FIG. 5 described above, the EGR circuit 44 is returned to the upstream side of the supercharger TB. However, in the configuration of FIG. 6, the reduction is made to each port 58a, 58b, 58c, 58d immediately before the cylinder chamber 5. Constitute. As a result, the difference in the EGR reduction rate between the cylinders can be prevented, the combustion is stabilized, and the amount of pollutants in the exhaust gas is reduced.

  In the configuration of FIG. 7, the solenoid valves 59 a, 59 b, 59 c, 59 d are provided between the ports 58 a, 58 b, 58 c, 58 d immediately before the cylinder chamber 5 and the EGR circuit 44. The electromagnetic valves 59a, 59b, 59c, and 59d are configured to open in accordance with the opening timing of the intake valve 39 on the intake side. Thereby, the reduction | restoration of EGR gas can be performed accurately.

Next, FIG. 8 will be described.
The EGR supercharger 65 is driven from the crankshaft 60 of the engine E via a belt 66, and the valve 64 is opened to accumulate gas in the EGR surge tank 61. Thus, by using the dedicated EGR supercharger 65, even when the intake pressure is larger than the exhaust pressure, a check valve is unnecessary and stable EGR reduction is possible.

    A pressure sensor 65 is provided in the EGR surge tank 61 so that the pressure is always constant. In the EGR surge tank 61, the EGR circuit 44, or the exhaust gas pipe 67, CO2 sensors 62a, 62b, and 62c are provided, respectively. Among these CO 2 sensors 62 a, 62 b and 62 c, the one that plays an important role is the CO 2 sensor 62 a in the EGR surge tank 61. That is, since the EGR gas is once accumulated in the EGR surge tank 61 and then reduced, a sudden change in the CO2 concentration in the reduced EGR gas can be prevented, and control is facilitated and combustion is stabilized. Further, when reducing EGR gas, linear control is performed by the EGR valve 63, so that EGR pulsation during reduction can be prevented and turbulence of intake air can be prevented.

    Further, the CO2 sensors 62b and 62c provided in the EGR circuit 44 and the exhaust gas pipe 67 are for making an appropriate CO2 concentration. That is, based on information from the CO2 sensors 62b and 62c, the fuel injection timing is changed, and the timing and injection amount of pre-injection, pilot injection, after-injection and the like are controlled. The CO2 sensor 62d on the intake side after the EGR gas is merged is for measuring and confirming the concentration of CO2 that is actually inhaled.

Next, FIG. 9 will be described.
A part of the sucked air is sent to the upstream side of the DPF 46b. Specifically, a part of the supercharged air after passing through the intake turbine 36 of the supercharger TB is sent via the bypass circuit 70. The bypass circuit 70 is provided with a valve 71. When the engine is in a light load state, the valve 71 is opened to send a part of the air to the upstream side of the DPF 46b. As a result, the DPF 46b can be regenerated even at a low load. In this embodiment, the inlet of the EGR circuit 44 is on the upstream side of the exhaust turbine 45 of the supercharger TB, and the reduction port is on the downstream side of the intake turbine 36 of the supercharger TB. Reference numeral 68 denotes an EGR valve. 69 is a throttle valve between the exhaust turbine 45 and the DPF 46b.

  When fuel at full load is injected while the supercharging pressure of the supercharger TB is low, the excess air ratio decreases and a large amount of black smoke is discharged. Therefore, it is a conventionally known technique to limit the fuel injection amount when the supercharging pressure decreases.

  However, when such control is performed, in the series of flows in which the tractor increases the rotation from the low idle rotation speed to the high idle rotation speed and then lowers the work implement 21 to start the operation, the supercharger TB is overcharged. Due to the delay in supply, the fuel injection amount is limited at the time of low supercharging pressure at the start of work, and there is a disadvantage that the output becomes insufficient and the engine speed drops.

  Therefore, the limit value of the fuel injection amount at the time of low supercharging is changed according to the load. Specifically, the position is changed at the position of the work machine 21. That is, when the position of the work implement 21 is close to the farm scene (descent), the limit value of the fuel injection amount is relaxed or the fuel injection amount is not limited. In this way, even when the turbocharger TB is at a low supercharging pressure, the limit value of the fuel injection amount is changed or released in a scene where a load is predicted to be applied to the engine or a scene immediately before the load is applied. By doing so, it becomes possible to prevent the engine speed from dropping.

    Also, even if the fuel injection amount limit value is loosened or released after the actual engine drop has started, it may not be in time and work efficiency will be reduced, but such problems can be prevented. Become.

    As a method for detecting the position of the work implement 21, the angle of the lift arm that supports the work implement 21 may be detected (detected by the lift arm angle sensor 22a in FIG. 3). You may comprise so that a raising / lowering position may be detected with a position sensor.

  FIG. 10 shows an engine performance curve. Limiting the maximum torque near the torque point where the NOx emission rate is bad with respect to the standard curve L1, increasing the common rail pressure in the rated high load range, and further injecting the pilot gas, but the exhaust gas deteriorates although the output is low It is configured to include a curve L2 of a mode with good fuel efficiency that is not allowed to occur. Specifically, since the fuel injection amount is large in the vicinity of the torque point, an engine equipped with a common rail is configured to suppress the increase in smoke and PM by increasing the rail pressure, but on the other hand, NOx becomes a heavy load. Therefore, by suppressing the maximum torque value, even if the rail pressure near the lower grade is increased, the overall NOx emission rate does not change and the fuel consumption rate near the rating is improved. Will be able to. Further, even if pilot injection is performed, smoke is not deteriorated due to an increase in rail pressure, fuel efficiency can be improved, and NOx can also be reduced. The standard curve L1 and the fuel consumption curve L2 are provided in the ECU 100 at the same time.

    It can be used for farm vehicles such as tractors and combiners as well as general vehicles.

Overall configuration diagram of accumulator fuel injection system Diagram showing the relationship between engine speed and output torque in control mode Left side view of tractor Top view of tractor Schematic diagram of intake and exhaust systems Schematic diagram of intake port Schematic diagram of intake port Schematic diagram of intake and exhaust systems Schematic diagram of intake and exhaust systems Diagram showing engine performance curve

Explanation of symbols

TB Supercharger PM Granulated material 36 Intake turbine 37 Intercooler 43 EGR valve 44 EGR circuit 45 Exhaust turbine 46 Exhaust gas aftertreatment device 46b Diesel particulate filter (DPF)
47 Throttle valve 52 Pressure sensor 53 Temperature sensor 57 EGR cooler 100 Engine control unit (ECU)

Claims (2)

  A supercharger (TB), an EGR circuit (44) for reducing a part of the exhaust gas to the intake system, and a granulated substance in the exhaust gas at least on the lower side of the exhaust turbine (45) of the supercharger (TB) In the diesel engine provided with the exhaust gas aftertreatment device (46) having a diesel particulate filter (46b) for collecting (PM), the EGR circuit (44) is located downstream of the exhaust gas aftertreatment device (46). Is connected to the upstream side of the intake turbine (36) of the turbocharger (TB), and the pressure sensor (52) provided on the upstream side of the diesel particulate filter (46b) detects a pressure greater than a predetermined value. Then, the EGR valve (43) is fully closed and the throttle valve (47) is throttled to regenerate the diesel particulate filter (46b). When the temperature sensor (53) provided on the downstream side of the particulate filter (46b) detects a temperature equal to or higher than a predetermined value, an engine control unit (100) that performs control to stop the regeneration of the diesel particulate filter (46b) is provided. Diesel engine characterized by providing.   The EGR circuit (44) is provided with an EGR cooler (57), and an intercooler (37) is disposed downstream of the intake turbine (36) of the supercharger (TB). Diesel engine.

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