EGR device

Abstract

To properly clean an EGR cooler using an inexpensive configuration.SOLUTION: An EGR device is configured to extract a portion of exhaust gas from an engine exhaust pipe 55 via an EGR pipe 44B and recirculate it to an intake pipe 56 as recirculation gas. The EGR device is equipped with an exhaust throttle valve 47 that narrows the flow of exhaust gas downstream of the position where recirculation gas is extracted in the exhaust pipe 55, and is equipped with a control device that, when a condition is established in which there is concern about the accumulation of soot compounds in an EGR cooler 57 and EGR valve 43 midway through the EGR pipe 44B, executes a cleaning mode of opening the EGR valve 43 to a specified opening degree and narrowing the exhaust throttle valve 47 to forcibly increase the flow rate and flow velocity of the recirculation gas.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] This invention relates to an EGR device.

Background Art

[0002] A configuration is adopted in which condensate generated in the EGR cooler is collected, and the EGR cooler is washed with the collected condensate (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described technology, a container device for collecting condensate is required. Further, since the condensate may be dirty, the cleaning of the EGR cooler is not properly performed.

[0005] An object of the present invention is to provide an EGR device that solves the above-described problems.

Means for Solving the Problems

[0006] The above object of the present invention is achieved by the following configuration.

[0007] That is, in the invention described in claim 1, it is an EGR device configured to extract a part of the exhaust gas from the exhaust pipe (55) of the engine through the EGR pipe (44B) and recirculate it as the recirculation gas to the intake pipe (56). The EGR device is provided with an exhaust throttle valve (47) that restricts the flow of the exhaust gas on the downstream side of the extraction position of the recirculation gas in the exhaust pipe (55). When conditions that raise concerns about the deposition of soot compounds on the EGR cooler (57) and the EGR valve (43) in the middle of the EGR pipe (44B) are satisfied, the EGR valve (43) is opened to a specified opening degree and the exhaust throttle valve (47) is throttled to forcibly increase the flow rate and flow velocity of the recirculation gas. The EGR device is characterized by including a control device that executes a cleaning mode.

[0008] In the invention described in claim 2, the EGR pipe (44B) and the air compressor (77) are connected by a cleaning pipe (78), a cleaning valve (79) is provided at the outlet portion (78a) of the cleaning pipe (78), and when conditions that raise concerns about the deposition of soot compounds on the EGR cooler (57) and the EGR valve (43) in the middle of the EGR pipe (44B) are satisfied, the EGR valve (43) is opened to a specified opening degree and the exhaust throttle valve (47) is throttled. The cleaning valve (79) is opened to send compressed air from the air compressor (77) into the EGR pipe (44B), and the EGR device according to claim 1 is characterized by including a control device that executes a cleaning mode to forcibly increase the flow rate and flow velocity of the recirculation gas.

[0009] In the invention described in claim 3, a flow meter (72) is provided on the downstream side of the EGR cooler (57). When the flow meter (72) detects a value below a specified flow rate after the cleaning mode is executed, the EGR device according to claim 1 or 2 is characterized by including a control device that gives an alarm.

Advantages of the Invention

[0010] Since the present invention is configured as described above, in the invention of claim 1, the EGR cooler (57) can be appropriately cleaned at low cost by control using an existing device.

[0011] In the invention according to claim 2, compressed air from the air compressor (77) is added to clean the EGR cooler (57), so the cleaning ability is improved.

[0012] In the invention according to claim 3, when the flow meter (72) detects a value below the specified flow rate after the cleaning mode is executed, an alarm is notified, so that malfunctions in cleaning can be quickly recognized.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

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Figure 9

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Figure 13

Embodiments for Carrying Out the Invention

[0014] The best mode for carrying out the present invention will be described.

[0015] Figure 1 is an overall configuration diagram of a common rail fuel injection device. The common rail fuel injection device is applicable to, for example, a multi-cylinder diesel engine, but it may also be a gasoline engine. And the common rail fuel injection device is composed of a common rail 1 for storing high-pressure fuel corresponding to the injection pressure, a pressure sensor 2 attached to the common rail 1, a high-pressure pump 4 for pumping up the fuel drawn from the fuel tank 3 and pressurizing it to pump it into the common rail 1, a fuel injection nozzle 6 for injecting the high-pressure fuel stored in the common rail 1 into the cylinder 5 of the engine E, a control device (ECU), etc. for controlling the operations of the high-pressure pump 4, the fuel injection nozzle 6, etc. ECU is an abbreviation for Engine Control Unit.

[0016] As described above, the common rail 1 injects fuel into each cylinder 5 of the engine E and sets the pressure to the required pressure for fuel supply.

[0017] The fuel in the fuel tank 3 is sucked into the high-pressure pump 4 driven by the engine E through the suction passage via the fuel filter 7, and the high-pressure fuel pressurized by this high-pressure pump 4 is guided to the common rail 1 through the discharge passage 8 and stored.

[0018] The high-pressure fuel in the common rail 1 is supplied to the fuel injection nozzles 6 for the number of cylinders through each high-pressure fuel supply passage 9. Based on the command from the ECU100, the fuel injection nozzles 6 operate in each cylinder, and the high-pressure fuel is injected and supplied into each cylinder chamber 5 of the engine E. The surplus fuel (return fuel) at each fuel injection nozzle 6 is guided to the common return passage 10 through each return passage 10 and returned to the fuel tank 3 through this return passage 10.

[0019] Also, 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. This pressure control valve 11 adjusts the flow area of the return passage 10 for the surplus fuel from the high-pressure pump 4 to the fuel tank 3 by means of a duty signal from the ECU100, and thereby can control the common rail pressure by adjusting the fuel discharge amount to the common rail 1 side.

[0020] Specifically, a target common rail pressure is set according to engine operating conditions, and the common rail pressure is feedback-controlled via a pressure control valve 11 so that the common rail pressure detected by the rail pressure sensor 2 matches the target common rail pressure.

[0021] 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) is configured to have three control modes: a traveling mode A, a normal work mode B, and a heavy work mode C in the relationship between the rotational speed and the output torque. The ECU 100 is connected to the control device 200 on the vehicle side.

[0022] The traveling mode A is a droop control in which the output also varies with the fluctuation of the engine rotational speed. It is used when moving without performing agricultural work. For example, when braking to decelerate or stop the traveling speed, the engine rotational speed decreases with the increase of this traveling load, so the deceleration or stop of the traveling speed can be performed safely.

[0023] The normal work mode B is an isochronous control in which the engine rotational speed is constant and the output is changed according to the load even when the load varies. It is used when performing normal agricultural work. For example, in the case of a tractor, it is when the cultivated land is hard and resistance is applied to the tillage blade during tillage work, and in the case of a combine, it is when the amount of harvested crops is large and the load increases during harvesting work, that is, when the output varies and the rotational speed is maintained.

[0024] The heavy work mode C is a control that adds a heavy load control in which the rotational speed is increased and the output is increased when approaching the load limit in addition to the isochronous control in which the engine rotational speed is constant and the output is changed according to the load even when the load varies, similar to the normal work mode B. In particular, it is used when performing agricultural work near the load limit. For example, when a tractor is performing tillage work, especially when encountering hard cultivated land, the engine output increases beyond the normal limit, so the work can be carried out without interruption and efficient work becomes possible.

[0025] These working modes A, B, and C are configured to be switched by operating a working mode switch capable of switching between the respective working modes A, B, and C, or by shifting the travel speed lever of an agricultural vehicle (such as a tractor, combine harvester, rice transplanter, etc.), or by turning on and off a working clutch (a rotary part in the case of a tractor, a cutting part and a threshing part in the case of a combine harvester), etc.

[0026] In the diesel engine E, by performing pilot injection in which a small amount of fuel is injected pulsatively prior to the main injection, the ignition delay is shortened, the knocking sound peculiar to the diesel engine E is reduced, and the noise can be reduced.

[0027] This pilot injection was limited to one or two times before the main injection, but by using the accumulator type fuel injection device of the common rail 1, the state of the pilot injection can be changed according to the situation of the engine E, and the reduction of noise and the generation of white smoke or black smoke due to incomplete combustion can be suppressed. Also, by performing pilot injection in which a small amount of fuel is injected pulsatively prior to the main injection, the amount of nitrogen oxides in the exhaust gas is reduced.

[0028] Figure 3 shows a side view of a work vehicle (tractor) equipped with a diesel engine having a common rail 1 as described above, and Figure 4 shows a plan view thereof. The plan view shows a state in which the cabin 14 shown in Figure 3 is omitted.

[0029] The tractor is provided with front wheels 12, 12 and rear wheels 13, 13 at the front and rear of the body, and is configured to appropriately reduce the rotational power of the engine E mounted at the front of the body by a transmission in a transmission case T and transmit it to these front wheels 12, 12 and rear wheels 13, 13.

[0030] At the center of the vehicle body and on the handle post 15 inside the cabin 14, a steering wheel 16 is supported, and a seat 17 is provided behind it. Below the steering wheel 16, a forward and reverse lever 18 for switching the traveling direction of the vehicle body in the front-rear direction is provided. When this forward and reverse lever 18 is moved forward, the vehicle body moves forward, and when it is moved rearward, the vehicle body moves backward.

[0031] Also, on the opposite side of the forward and reverse lever 18 across the handle post 15, an accelerator lever 25 for adjusting the engine speed is provided. Also, at the right corner of the step floor 19, an accelerator pedal 23 for adjusting the engine speed in the same way, and left and right brake pedals 24L, 24R for operating the brakes on 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.

[0032] Also, the main transmission lever 26 is at the left front part of the seat 17, and a sub-transmission lever 27 that can select any one of low speed, medium speed, high speed, and neutral is behind it. Further, a PTO transmission lever 28 is provided on its right side. Further, on the right side of the seat 17, a position lever 29 for setting the height of the working machine 21 (such as a rotary tiller), an automatic tilling depth lever 30 for automatically setting the tilling depth of the field, an upper lift switch 31 and a lower lift switch 32 for the working machine 21 are arranged behind these levers. Further, an automatic leveling switch 33 and a backup switch 34 for the working machine 21 are arranged behind them. The backup switch 34 automatically raises the working machine 21 when the vehicle body is moving backward. The working machine 21 is configured to be connected to the rear of the vehicle body by a link 22. The tractor drives the working machine 21 and makes the vehicle body travel to perform operations such as tilling in the field. 21a is a hydraulic cylinder for raising and lowering the working machine 21.

[0033] Figure 5 is a schematic diagram of intake and exhaust into cylinder 5 of the engine, and is an embodiment of a four-cycle diesel engine. The air supercharged by the intake turbine 36 of the supercharger TB passes from the air cleaner 35 through the intake turbine 36 and the intercooler 37 and is sent into cylinder 5 from the intake manifold 38. 39 is the intake valve, and 40 is the piston. 48 is a cam that opens and closes the intake and exhaust valves 39 and 41 via the rocker arm 49.

[0034] The exhaust gas burned in cylinder 5 passes from the exhaust valve 41 through the exhaust manifold 42, and then is discharged by driving the supercharger TB with the exhaust turbine 45 of the supercharger TB.

[0035] This diesel engine has an EGR (Exhaust Gas Recirculation) circuit 44 for mixing a part of the exhaust gas into the intake side. By mixing a part of the exhaust gas into the intake side in the EGR circuit, the amount of oxygen (O2) is reduced, and the generation of nitrogen oxides Nox is reduced. However, if the EGR rate rises too much, conversely the amount of oxygen becomes less and incomplete combustion occurs, so 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 the exhaust pipe 55 on the downstream side of the post-treatment device 46 described later and the intake pipe 56 on the upstream side of the intake turbine 36 of the supercharger TB. Also, an EGR cooler 57 is provided in the middle of the EGR circuit 44. The reduction amount of the exhaust gas into cylinder 5 changes according to the opening and closing of this EGR valve 43.

[0036] The exhaust gas after passing through the exhaust turbine 45 passes through the post-treatment device 46 and is discharged into the atmosphere from the muffler 50. The post-treatment device 46 is composed of an oxidation catalyst (DOC) 46a and a diesel particulate filter (DPF) 46b.

[0037] The oxidation catalyst (DOC) combusts the non-combustible chamber, and the diesel particulate filter (DPF) is for collecting particulate matter (PM). The EGR valve 43 and the throttle valve 47 are configured to be controlled by the ECU 100. The aftertreatment device 46 may be composed only of the diesel particulate filter (DPF) 46b. When an oxidation catalyst (DOC) is provided, the non-combustible substances burn, resulting in cleaner exhaust gas.

[0038] When the state of low exhaust gas temperature (low load) continues for a long time in the DPF 46b, PM accumulates, and there is concern about a decrease in performance. Therefore, a throttle valve 47 is provided on the downstream side of the aftertreatment device 46. When this throttle valve 47 is throttled, the pressure inside the DPF 46b is kept high, so the temperature also rises. As a result, due to the influence of the high temperature, the DPF 46b can be regenerated. That is, when high-temperature exhaust gas passes through the DPF 46b, the PM existing inside the DPF 46b is burned off, and the DPF 46b is regenerated.

[0039] As the DPF regeneration operation for regenerating the DPF 46b, both the EGR valve 43 and the throttle valve 47 are throttled. Then, in combination with the retard (retarded angle) of the fuel injection timing, the gas temperature inside the DPF 46b is raised so that the DPF 46b enters the regeneration process. As a result, after-injection of fuel (to raise the exhaust gas temperature) becomes unnecessary, or the number of after-injections can be reduced, so the fuel consumption can be suppressed, which is also good for the environment.

[0040] As conditions for performing such a DPF regeneration operation, a pressure sensor 52 is provided on the upstream side of the aftertreatment device 46, and a pressure sensor 53 is also provided on the downstream side of the aftertreatment device 46. When this pressure difference becomes equal to or greater than a predetermined value, PM has accumulated in the DPF 46b and is in a state of acting as a resistance, so the DPF regeneration operation is performed. Also, a configuration may be adopted in which a pressure sensor 58 is provided between the DOC 46a and the DPF 46b instead of the pressure sensor 52.

[0041] Also, if the state of entering the DPF regeneration operation continues for a long time, it will enter a heat generation state and the DPF 46b will be damaged. Therefore, a temperature sensor 59 is provided on the downstream side of the post-treatment device 46, and when the value of this temperature sensor 59 exceeds a predetermined value, the DPF regeneration operation is stopped and the operation returns to normal operation.

[0042] During 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 inside the DPF 46b can be kept high.

[0043] With the above-described configuration, the intake throttle becomes unnecessary. That is, in a supercharged engine, since the intake pressure is high, an exhaust throttle valve or an intake throttle is provided to ensure the EGR gas amount, and control linked to the EGR valve is required, but such a system becomes unnecessary.

[0044] Also, in order to extract the exhaust gas downstream of the DPF 46b, it is possible to prevent performance deterioration due to contamination of the supercharger TB. And since the EGR gas is cooled by the EGR cooler 57, the effect on NOx reduction becomes greater.

[0045] As described above, in the DPF forced regeneration mode for performing the DPF regeneration operation, the exhaust throttle valve 47 is throttled and the EGR valve 43 is configured to be fully closed by ON-OFF control. Therefore, since the reduction of the exhaust gas is not performed, NO increases, and this NO is converted to NO2 by the oxidation catalyst (DOC) 46a, and the regeneration of the DPF 46b is promoted.

[0046] Also, during the forced regeneration of the DPF 46b, when the engine speed shifts to low idle, the EGR valve 43 is fully opened. Since a temperature sensor 59 is provided on the downstream side of the DPF 46b, it may be added as a condition that the detection value by this temperature sensor 59 has risen above a predetermined value.

[0047] When performing forced regeneration of the DPF 46b by closing the throttle valve 47, the engine speed was set to a low speed to increase the supplied oxygen amount, and the temperature was easily increased by the decrease in the exhaust gas flow rate. However, when the engine speed was changed to low idle or near it during regeneration, due to the increase in the supplied oxygen amount and the decrease in the flow rate, the soot burned rapidly. As a result, the temperature may rise rapidly and the DPF 46b may be damaged. Therefore, it is necessary to control the soot so that the maximum temperature does not exceed the allowable temperature.

[0048] For this purpose, when the temperature sensor 59 exceeds a predetermined value, it is configured to increase the engine speed to the medium speed range. As a result, the flow rate of the exhaust gas increases, so the maximum temperature decreases, and damage to the DPF 46b can be prevented. Also, when controlling the value of the predetermined value of the temperature sensor 59 near the limit value, the regeneration of the DPF 46b can be performed efficiently.

[0049] When increasing the engine speed to the medium speed range, it may be configured to first increase to the maximum speed and then decelerate to the medium speed range. As a result, since the exhaust gas flows at the maximum speed once, it is possible to prevent the DPF 46b from being heated by preheating or the like and exceeding the threshold temperature.

[0050] Also, during forced regeneration of the DPF 46b, when shifting the engine speed to low idle as described above, the post-injection is interrupted, then the engine speed is increased to the maximum speed, and the post-injection is resumed at the stage of shifting to the medium speed range. As a result, a rapid increase in the exhaust gas temperature can be suppressed, and damage to the DPF 46b can be prevented.

[0051] When the differential pressure across the DPF46b becomes equal to or greater than a predetermined value, after work, the driver can select the regeneration mode of the DPF46b with the selection switch 67, and the DPF46b will be automatically regenerated. After the regeneration of the DPF46b, the engine will be automatically stopped. The differential pressure across the DPF46b is monitored by the pressure sensors 58 and 53. If the differential pressure across the DPF46b immediately before engine stop is equal to or greater than the predetermined value, it will be notified by a warning lamp or an alarm, and the driver will operate a switch (not shown) to perform the regeneration of the DPF46b by himself.

[0052] And even when the engine key is in the off position, by selecting the regeneration mode, the engine will maintain rotation in the idling state and execute the regeneration of the DPF46b. When the differential pressure across the DPF46b becomes equal to or less than the predetermined value, the engine will be automatically stopped.

[0053] As a result, even after the work is completed, the DPF46b can be automatically regenerated and the engine can be stopped, so that the driver can leave the machine and perform other work.

[0054] When performing the regeneration of the DPF46b, as shown in FIG. 5, the air on the intake side may be configured to be sent from the pipeline 61 to the upstream side of the DPF46b. That is, when performing the regeneration of the DPF46b, the valve 60 may be opened to send the air on the intake side upstream of the supercharger TB with a large amount of oxygen to the upstream side of the DPF46b. As a result, the regeneration efficiency will be improved.

[0055] Also, the temperature of the DPF46b is monitored by the temperature sensors 62 and 59, and the temperature rise during regeneration may be confirmed in three steps. First, throttle the intake air (not shown) and confirm the temperature rise in this throttled state of the intake air. Next, perform the first post-injection to confirm the temperature rise. At this point, if the temperature before and after the DPF46b has not reached 250 degrees, perform the second post-injection, but no further temperature rise can be expected, so the regeneration will be interrupted once. Of course, if it is 250 degrees or more, perform the second post-injection to perform the regeneration of the DPF46b.

[0056] As shown in FIG. 5, an air-fuel ratio sensor 63 is provided on the downstream side of the DPF 46b. When performing post-injection to regenerate the DPF 46b, if the fuel injection amount becomes too large, the fuel consumption deteriorates, and if it is too small, the temperature does not rise and regeneration cannot be performed. Therefore, a configuration is adopted in which the value of the air-fuel ratio sensor 63 is fed back to the ECU 100 to determine the injection amount. As a result, appropriate fuel consumption is achieved and regeneration of the DPF 46b becomes possible. Further, instead of the air-fuel ratio sensor 63, the pressure value in the intake manifold may be configured to be fed back.

[0057] When performing regeneration of the DPF 46b as described above, in the case of a multi-cylinder engine, the combustion of some cylinders may be configured to be stopped. In this way, by stopping the combustion of some cylinders, even if the engine friction is the same, the load per cylinder may be increased to raise the exhaust temperature.

[0058] In the EGR valve 43, soot and HC adhere and integrate with moisture such as condensation to form a viscous liquid. In such a state, the EGR valve 43 operates, but when the engine is stopped and the engine cools, the viscous liquid may solidify, and when the engine is restarted, the EGR valve 43 may not move. In order to solve such a problem, the EGR valve 43 is provided with a cleaning function. That is, by forcibly operating the EGR valve 43 during after-run after the engine is stopped to remove the viscous liquid, the EGR valve 43 does not solidify even when the engine cools.

[0059] As shown in FIG. 5, in order to control the DPF 46b and the engine, conventionally, a pre-temperature sensor 62 is provided on the inlet side of the DPF 46b, and a post-temperature sensor 59 is provided at the outlet of the DPF 46b. The intake throttle valve 70 is a valve that adjusts the amount of air flowing toward the intake manifold 38.

[0060] The flowchart of FIG. 6 shows the relationship between the exhaust temperature and the intake throttle valve. When the value of the pre-temperature sensor 62 provided at the inlet of the DPF 46b becomes equal to or lower than a predetermined temperature, the regeneration ability of the DPF 46b decreases, so the regeneration frequency of the DPF 46b increases.

[0061] Therefore, when the value of the pre-temperature sensor 62 becomes equal to or lower than a predetermined temperature, control is performed to close the intake throttle valve 70. Specifically, it is configured to close the intake throttle valve 70 from 10% to 30%. Alternatively, it may be configured to gradually close until the regeneration ability of the DPF 46b is restored. In this case, it is until the combustion begins to be affected. As a result, the DPF 46b can be regenerated to some extent even during normal operation, so the frequency of forced regeneration of the DPF 46b by interrupting the work running can be reduced.

[0062] The flowchart of FIG. 7 shows the relationship between the fuel injection amount and the intake throttle valve. When a sudden load acts on the vehicle body and the fuel injection amount increases, the value of the pre-temperature sensor 62 provided at the inlet of the DPF 46b decreases. Therefore, control is performed to close the intake throttle valve 70. In this case, it is until the combustion begins to be affected. As a result, the DPF 46b can be regenerated to some extent even during normal operation, so the frequency of forced regeneration of the DPF 46b by interrupting the work running can be reduced.

[0063] Instead of the fuel injection amount, control may be performed to close the intake throttle valve 70 according to the operation amount of the accelerator.

[0064] The flowchart of FIG. 8 shows the relationship between the state of the work implement 21 and the intake throttle valve. When the work implement 21 is lowered to perform work, the load increases, so the fuel injection is increased. When the fuel injection amount increases, the value of the pre-temperature sensor 62 provided at the inlet of the DPF 46b becomes lower. Therefore, control is performed to close the intake throttle valve 70. In this case, it is assumed until the combustion begins to be affected. As a result, since the DPF 46b can be regenerated to some extent even during normal operation, the frequency of forced regeneration of the DPF 46b by interrupting the work running can be reduced. As shown in FIG. 3, in this embodiment, it is a work implement of a tractor, but it may also be work of other work vehicles. For example, the intake throttle valve 70 may be controlled to close according to the entry of the threshing device of a combine. Also, in a lawn mower such as a mower, when the lawn mowing lever is in the engaged state, the intake throttle valve 70 may be controlled to close.

[0065] FIG. 9 explains the EGR circuit 44A that reduces a part of the exhaust gas after passing through the supercharger TB to the intake side. The exhaust gas after passing through the EGR valve 43 is cooled by the EGR cooler 57 and reduced to the intake side, but the situation of PM deposited in the EGR cooler 57 is difficult to grasp. Therefore, a flow meter 72 is provided on the downstream side of the EGR cooler 57, and the ECU 100 stores the values of the flow meter 72 for a plurality of opening degrees of the EGR valve 43 when the EGR cooler 57 is in a new state. Since PM accumulates in the EGR cooler 57 over time, even if the opening degree of the EGR valve 43 is the same, the value of the flow meter 72 decreases (threshold value or difference). This state is a condition in which there is concern about the deposition of soot compounds.

[0066] Therefore, the configuration is such that the opening degree of the EGR valve 43 is changed so as to be in a state before the value of the flow meter 72 decreases.

[0067] As a result, an appropriate amount of exhaust gas can be reduced to the intake side, so that deterioration of the NOx concentration can be prevented.

[0068] Also, when the value of the flow meter 72 decreases by a predetermined ratio with respect to the target value, a configuration is adopted in which a notification is given to promote the removal of soot in the EGR cooler 57.

[0069] With only the configuration of changing the opening degree of the EGR valve 43 so as to be in the state before the value of the flow meter 72 decreases, it becomes impossible to cope. That is, it is necessary to actively remove the soot in the EGR cooler 57.

[0070] When the condition that deposition of soot compounds on the EGR cooler 57 and the EGR valve 43 in the middle of the EGR pipe 44B is suspected is satisfied, the ECU 100 has a cleaning mode in which the EGR valve 43 is opened to a specified opening degree and the exhaust throttle valve 47 is throttled to forcibly increase the flow rate and flow velocity of the recirculation gas.

[0071] By executing this cleaning mode, the inside of the EGR cooler 57 can be cheaply cleaned by control using the existing device.

[0072] Also, regarding the removal of soot in the EGR cooler 57, the scavenging valve 79 is operated to stop the inflow of gas from the supercharger TB, and the compressed air from the air compressor 77 is configured to be sent from the scavenging pipe 78 to the EGR circuit 44A. Further, the second valve 80 is operated so that the compressed air after passing through the EGR cooler 57 is discharged into the atmosphere from the second pipe 81.

[0073] Thereby, the soot in the EGR cooler 57 can be removed.

[0074] Also, the EGR pipe 44B and the air compressor 77 are connected by a scavenging pipe 78, and a scavenging valve 79 is provided at the outlet portion 78a of the scavenging pipe 78.

[0075] When the condition that deposition of soot compounds on the EGR cooler 57 and the EGR valve 43 in the middle of the EGR pipe 44B is suspected is satisfied, the EGR valve 43 is opened to a specified opening degree and the exhaust throttle valve 47 is throttled, and the scavenging valve 79 is opened to send the compressed air from the air compressor 77 into the EGR pipe 44B.

[0076] As a result, compressed air from the air compressor 77 is added to clean the EGR cooler 57, thereby improving the cleaning ability.

[0077] Also, a flow meter 72 is provided on the downstream side of the EGR cooler 57, and when the flow meter 72 detects a value below a specified flow rate after the execution of the cleaning mode, an alarm is notified.

[0078] As a result, malfunctions in cleaning can be quickly detected.

[0079] FIG. 10 shows a flowchart for confirming the regeneration state of the DPF 46b. Although the intake throttle valve 70 is not closed (fully open) and no post-injection of fuel is performed to increase the exhaust gas temperature, the exhaust gas temperature at the inlet side of the DPF 46b may become higher than a predetermined value. Such a phenomenon occurs in highlands where the air volume becomes thin, and in some situations, it may cause thermal damage to the engine. Therefore, the increase in the exhaust gas temperature is suppressed by increasing the rail pressure of the common rail 1.

[0080] As another problem in highlands where the air volume becomes thin, when the opening degree of the EGR valve 43 is not corrected in highlands, the NOx concentration increases. Also, the exhaust temperature increases. In highlands, it is necessary to expand the opening degree of the EGR valve 43 to eliminate the above-mentioned problem.

[0081] Therefore, the air volume is predicted by an atmospheric pressure sensor (not shown), and the opening degree of the EGR valve 43 is changed to an opening degree suitable for the predicted air volume, and the post-injection amount is also changed. Instead of the atmospheric pressure sensor, the air volume may be predicted from the altitude by GPS.

[0082] As described above, during the regeneration of the DPF46b, the intake throttle valve 70 is closed to a predetermined opening degree to increase the exhaust gas temperature and perform the regeneration of the DPF46b. However, if the intake throttle valve 70 is closed at a high speed so as to achieve the target air volume, the combustion becomes unstable due to the sudden decrease in the air volume, and THC (total hydrocarbon: the total value of methane and non-methane hydrocarbons) increases.

[0083] Therefore, as shown in FIG. 11, the configuration is such that the air volume is gradually reduced over X seconds from the start of regeneration. Thereby, the generation of THC (total hydrocarbon) can be suppressed.

[0084] When the light load operation continues, the exhaust gas temperature decreases and soot with a large particle diameter accumulates in the DOC46a. Therefore, as shown in FIG. 12, a heating wire 73 is provided on the upstream side of the DOC46a, and when the ECU100 recognizes that the exhaust gas temperature is low, power is supplied to the heating wire 73 to burn the soot with a large diameter in front of the DOC46a. Thereby, clogging of the DOC46a can be prevented.

[0085] As the altitude increases, the air density of the atmosphere decreases. Due to this, the generation of white smoke and unburned fuel due to misfires during rapid acceleration and deceleration at high altitudes becomes likely. In order to solve this problem, according to the relationship between the air-fuel ratio sensor and the altitude, when the atmospheric pressure is low, the change amount of the speed during acceleration and deceleration is reduced to eliminate a sudden shortage of air volume.

[0086] Further, by closing the EGR valve 43 to increase the mass flow rate of air into the combustion chamber to increase the combustion efficiency, releasing the throttle of the waste gate (pressure limit) together with the measured air flow rate, performing fuel injection pressure and fuel injection amount limitation, adjusting the air-fuel ratio sensor to an appropriate value, installing the heating wire 73 in front of the DOC46a, and installing the heating wire 74 in front of the DPF46b, the generation of white smoke due to misfires and the generation of hydrocarbons, which are harmful substances to the atmosphere, can be suppressed.

[0087] In addition, by restricting the fuel injection amount and delaying the injection timing, proper combustion is achieved, reducing the deterioration of exhaust gas. At the same time, the fuel injection pressure is increased to make it easier to ignite even in a low air density environment.

[0088] Also, in order to prevent the deterioration of exhaust gas, in a high-altitude area with low atmospheric pressure (an area with low air density), output restriction is performed to suppress the emission of unburned fuel and white smoke.

[0089] Figure 13 shows the oil cooling configuration. The oil cooling is configured to attach an oil cooler to the engine side and cool it with a cooling fan. However, the oil cooler is expensive and may not fit within the engine room. Therefore, as shown in Figure 13, by arranging a cooling water pipe 76 in the oil pan 75, an oil cooling configuration is achieved. For the cooling water, by using a part of the cooling water after passing through the radiator, the oil can be cooled with a low-cost configuration.

Explanation of Symbols

[0090] 43 EGR valve 44B EGR pipe 47 Exhaust throttle valve 55 Exhaust pipe 56 Intake pipe 57 EGR cooler 72 Flow meter 77 Air compressor 78 Scavenging pipe 78a Outlet part of the scavenging pipe 79 Scavenging valve

Claims

1. An EGR device configured to extract a part of exhaust gas from an exhaust pipe (55) of an engine through an EGR pipe (44B) and recirculate it as recirculation gas to an intake pipe (56), the EGR device comprising an exhaust throttle valve (47) for narrowing the flow of exhaust gas downstream of the extraction position of the recirculation gas in the exhaust pipe (55), and a control device that, when a condition in which deposition of soot compounds on an EGR cooler (57) and an EGR valve (43) in the middle of the EGR pipe (44B) is a concern is satisfied, opens the EGR valve (43) to a specified opening degree and performs a throttling operation on the exhaust throttle valve (47) to forcibly increase the flow rate and flow velocity of the recirculation gas, thereby executing a cleaning mode.

2. The EGR pipe (44B) is connected to an air compressor (77) by a cleaning pipe (78), a cleaning valve (79) is provided at an outlet portion (78a) of the cleaning pipe (78), and when a condition in which deposition of soot compounds on an EGR cooler (57) and an EGR valve (43) in the middle of the EGR pipe (44B) is a concern is satisfied, the EGR valve (43) is opened to a specified opening degree, the exhaust throttle valve (47) is throttled, the cleaning valve (79) is opened, compressed air from the air compressor (77) is sent into the EGR pipe (44B), and a control device that executes a cleaning mode to forcibly increase the flow rate and flow velocity of the recirculation gas. The EGR device according to claim 1, characterized in that it is provided.

3. The EGR device according to claim 1 or 2, characterized in that a flow meter (72) is provided downstream of the EGR cooler (57), and when the flow meter (72) detects a value below a specified flow rate after the cleaning mode is executed, a control device for giving an alarm is provided.

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