Diesel engine with exhaust gas recirculation device and coolant supply device

Abstract

Diesel engine (10), comprising: an EGR line (G3) configured to recirculate a portion of exhaust gas expelled from an engine body (11) as a combustion gas to the engine body (11); an EGR cooler (16) which is provided in the EGR line (G3) and is configured to cool exhaust gas by means of a coolant; a coolant supply device configured to supply coolant to the EGR cooler (16); and a control device (30) configured to activate the coolant supply device, characterized by the fact that the coolant supply device comprises a coolant tank (31) configured to store coolant, a coolant supply line (W11,W12) configured to supply coolant in the coolant tank (31) to the EGR cooler (16), and a coolant pump (33) provided in the coolant supply line (W11,W12), and the control device (30) is configured to activate the coolant pump (33) when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than a preset prescribed temperature.

Description

[0001] The present invention relates to a diesel engine equipped with an exhaust gas recirculation device and a coolant supply device.

[0002] To reduce nitrogen oxides (NOx) in the exhaust gas, exhaust gas recirculation (EGR) is used. In EGR, a portion of the exhaust gas expelled from the combustion chamber of a diesel engine into an exhaust pipe is diverted into an exhaust gas recirculation line, mixed with combustion air to form a combustion gas, and then returned to the combustion chamber. This reduces the oxygen concentration of the combustion gas, lowers the combustion temperature by slowing down the combustion process (the reaction between fuel and oxygen), and reduces the amount of NOx produced.

[0003] Since a portion of the exhaust gas is mixed with the combustion air, in EGR (Exhaust Gas Recirculation) the exhaust gas is mixed with the combustion air after cooling in an EGR cooler to prevent a decrease in intake boost efficiency. In this case, the EGR cooler generally uses engine coolant to cool the exhaust gas. An example of such an exhaust gas recirculation device is disclosed in JP 2000-130 266 A, which is described below.

[0004] The exhaust gas emitted by a diesel engine contains particulate matter (PM), specifically soot, which is produced from incompletely combusted fuel. When the EGR cooler cools the exhaust gas with engine coolant, this causes the soot in the exhaust gas to adhere to a heat transfer tube and be deposited, thus reducing the cooling efficiency.

[0005] From WO 2016 / 103 393 A1, a diesel engine of this type is known with exhaust gas recirculation (EGR) and an EGR cooler provided in an EGR line. The EGR cooler can also be cooled by supplying cooling water from the engine block's water jacket.

[0006] From US patent 2011 / 0 107 983 A1, a cooling system for an internal combustion engine is known that has a bypass line which is hydraulically connected in parallel to an (external) radiator between the radiator's supply and return lines, i.e., the standard lines of the engine cooling circuit, and in which the EGR cooler and a coolant pump are located. A control device activates the coolant pump during an engine warm-up phase to return the coolant discharged from the radiator directly to the radiator's inlet via the bypass line, thus providing enhanced cooling to the EGR cooler.

[0007] The present invention solves the problems described above and aims to provide a diesel engine in which a reduction in performance due to deposits on an EGR cooler is suppressed.

[0008] To achieve the above-described objective, a diesel engine of the present invention includes the features of claim 1.

[0009] Accordingly, coolant is supplied to the EGR cooler by activating the coolant supply device when the engine is running and its temperature is equal to or below a specified temperature. Since the exhaust gas contains water vapor, soot adhering to the outer surface of the heat transfer tube that forms the EGR cooler also contains water vapor. When the heat transfer tube is cooled by a low-temperature coolant, the soot adhering to the tube is cooled, causing the water vapor within it to condense. As the condensate forms within the soot, its volume expands, and the layer of soot adhering to the heat transfer tube becomes more easily removable, as it is lifted away by the condensate.Here, when the exhaust gas comes into contact with the soot deposit layer on the heat transfer pipe, the detachment of the soot deposit layer is facilitated by the pressure of the exhaust gas, and the soot is removed by being detached from the outer surface of the heat transfer pipe. This suppresses the power loss caused by deposits on the EGR cooler.

[0010] In the diesel engine of the present invention, an EGR valve is preferably provided in the EGR line, and the control device is preferably configured to activate the coolant supply device when the EGR valve is open, when the engine body is in operation and the temperature of the engine body is equal to or below the prescribed temperature.

[0011] Accordingly, coolant is supplied to the EGR cooler when the EGR valve is open, when the engine is running, and when the engine temperature is equal to or below the specified temperature. Since the exhaust gas comes into contact with the soot deposit layer in a state where the soot adhering to the heat transfer tube has cooled and is more easily detached, the pressure of the exhaust gas allows the soot to be removed by detaching it from the outer surface of the heat transfer tube at an early stage.

[0012] In the diesel engine of the present invention, the coolant supply device comprises a coolant tank configured for storing coolant, a coolant supply line to the EGR cooler in the coolant tank, and a coolant pump provided in the coolant supply line, and the control device activates the coolant pump when the engine body is in operation and the temperature of the engine body is equal to or below the prescribed temperature.

[0013] Accordingly, by equipping the EGR cooler with a cooling system using a coolant supply line and a coolant pump in addition to the water jacket for cooling the engine body, the cooling system of the EGR cooler can be activated when needed, which ensures a greater degree of freedom in the implementation of the cleaning treatment of the EGR cooler.

[0014] In the diesel engine of the present invention, the control device preferably activates the coolant supply device when the operating time of the engine body exceeds a preset prescribed operating time and when the engine body is in operation and the temperature of the engine body is equal to or below the prescribed temperature.

[0015] Therefore, if the engine block's operating time exceeds the prescribed operating time, coolant is diverted to the EGR cooler, removing soot adhering to the heat transfer pipe. This allows the EGR cooler to be cleaned only when necessary, thus maintaining the engine block's cooling capacity.

[0016] In the diesel engine of the present invention, the control device preferably activates the coolant supply device when the opening time of the EGR valve exceeds a preset prescribed opening time and when the engine body is in operation and the temperature of the engine body is equal to or below the prescribed temperature.

[0017] If the EGR valve's opening time exceeds the prescribed time, coolant is fed to the EGR cooler, removing soot adhering to the heat transfer pipe. This allows the EGR cooler to be cleaned only when necessary, thus maintaining the engine's cooling capacity.

[0018] In the diesel engine of the present invention, the control device preferably activates the coolant supply device when the temperature of the exhaust gas expelled from the EGR cooler reaches or exceeds a preset prescribed temperature and when the engine body is in operation and the temperature of the engine body is equal to or below the prescribed temperature.

[0019] Therefore, coolant is supplied to the EGR cooler and soot adhering to the heat transfer pipe is removed, based on the understanding that the cooling capacity of the EGR cooler decreases when the temperature of the exhaust gas expelled from the EGR cooler reaches or exceeds the prescribed temperature. This allows the EGR cooler cleaning treatment to be performed only when necessary, thus maintaining the cooling capacity of the engine block.

[0020] According to the diesel engine of the present invention, a decrease in performance due to deposits on an EGR cooler can be suppressed. Fig. Figure 1 is a schematic configuration diagram representing a diesel engine according to a first example. Fig. Figure 2 is a flowchart illustrating a cleaning procedure for an EGR cooler. Fig. Figure 3 is a schematic configuration diagram representing a diesel engine according to a second example. Fig. Figure 4 is a schematic configuration diagram representing a diesel engine according to one embodiment.

[0021] Preferred embodiments of a diesel engine according to the present invention are now described in detail with reference to the attached drawings. It should be noted that the present invention is not limited to these embodiments and that, where several embodiments and examples exist, the invention is intended to include a configuration that combines these embodiments and examples.

[0022] Fig. Figure 1 is a schematic configuration diagram representing a diesel engine according to the first example, which is not according to the invention but serves to illustrate features of the invention.

[0023] As in Fig. As shown in Figure 1, in a diesel engine 10 of the first example, a cylinder head is mounted on a cylinder block to form an engine body 11. The engine body 11 is provided with a plurality of cylinder bores 12 (four in the present example). A piston 13 is mounted in each of the cylinder bores 12 so that it can move up and down via a cylinder liner (not shown). Although not shown in the figure, the engine body 11 has a lower section that rotatably supports a crankshaft. Each piston 13 is connected to the crankshaft via a connecting rod.

[0024] The engine body 11 is provided with an air supply distributor 14 via an inlet port (not shown) and with an exhaust manifold 15 via an outlet port (not shown). An inlet valve and an exhaust valve are arranged at the inlet and outlet ports, respectively. The inlet and exhaust valves are capable of opening and closing the inlet and outlet ports by being actuated by an inlet cam and an exhaust cam of an inlet camshaft and an exhaust cam, respectively (not shown). The engine body 11 is also provided with a fuel injector (not shown), which is capable of injecting high-pressure fuel into a combustion chamber.

[0025] Accordingly, the diesel engine 10 is configured to perform four strokes (intake stroke, compression stroke, expansion stroke, and exhaust stroke) during two rotations of the crankshaft. In this process, the intake camshaft and the exhaust camshaft each complete exactly one rotation, and the intake and exhaust valves open and close the intake and exhaust ports, respectively. Then, when air is supplied to the individual combustion chambers in the engine block 11 from an air distributor 14 via the individual intake ports, the air is compressed by the upward movement of the individual pistons 13. When the high-pressure fuel is injected into the combustion chamber from the individual fuel injectors, the high-pressure fuel ignites spontaneously and burns. The resulting combustion gas is then expelled from each exhaust port to the exhaust manifold 15 as exhaust gas.

[0026] In the engine housing 11, an air supply line G1 is connected to the air supply distributor 14, and an exhaust line G2 is connected to the exhaust manifold 15. An EGR line G3 has one end section connected to the exhaust line G2 and the other end section connected to the air supply line G1. This EGR line G3 is configured to introduce a portion of the exhaust gas into the air supply line G1 and is equipped with an EGR cooler 16 and an EGR valve 17.

[0027] The engine housing 11 is provided with a water jacket 21 in which the coolant is circulated for cooling. The water jacket 21 is connected to a radiator 22 via a coolant inlet line (coolant cooling line) W1 and a coolant outlet line (coolant cooling line) W2. The coolant inlet line W1 is equipped with a coolant circulation pump 23. Additionally, the coolant inlet line W1 and the coolant outlet line W2 are connected to each other via a bypass line W3, and a three-way thermostatic valve 24 is provided at a connection point between the coolant outlet line W2 and the bypass line W3.

[0028] An exhaust gas cooling line W4 is configured to introduce coolant from the water jacket 21 into the EGR cooler 16, thereby cooling the exhaust gas. One end section of the exhaust gas cooling line W4 is connected to the water jacket 21, and its other end section is connected to the coolant outlet line W2 at a position closer to the side of the water jacket 21 (engine body 11) than the thermostat three-way valve 24. The exhaust gas cooling line W4 is equipped with an electrically driven coolant pump 25.

[0029] A control unit 30 is capable of controlling the opening and closing of the EGR valve 17 and the activation and deactivation of the coolant pump 25. The engine housing 11 is also equipped with a temperature sensor 26, which is configured to measure the temperature of the coolant in the water jacket 21. The temperature sensor 26 outputs a measurement result to the control unit 30. It should be noted that the coolant circulation pump 23 is located in and operated within the engine housing 11 to be synchronized with the engine housing 11, and the coolant circulation rate increases as the engine speed increases. Furthermore, the three-way thermostatic valve 24 opens and closes according to the coolant temperature, and if the coolant is, for example, in a low-temperature range (e.g.,When the coolant is in a high temperature range (e.g. 80 °C or lower), the coolant inlet line W1 is closed, allowing the coolant outlet line W2 and the bypass line W3 to communicate with each other, and when the coolant is in a high temperature range (e.g. 80 °C or higher), the bypass line W3 is closed, allowing the coolant outlet line W2 and the radiator 22 or the coolant inlet line W1, which is downstream of the radiator 22, to communicate with each other.

[0030] Furthermore, the EGR cooler 16 comprises a large number of heat transfer tubes arranged in a hollow housing. The exhaust gas line G2 is connected to the housing, and the exhaust gas cooling line W4 is also connected to the heat transfer tubes. This directs the exhaust gas from the exhaust gas line G2 into the housing, supplying the coolant to the heat transfer tubes. Heat exchange then occurs between the exhaust gas in the housing and the coolant in each of the heat transfer tubes, with the exhaust gas being cooled by the coolant. Since the exhaust gas contains particulate matter (PM), soot can adhere to and deposit on the outer surface of each of the heat transfer tubes, reducing the efficiency of the heat exchange between the exhaust gas and the coolant and preventing the exhaust gas from being cooled sufficiently.

[0031] Therefore, in the present example, the EGR cooler 16 is configured to be regenerated by the supply of coolant at a temperature equal to or below a specified temperature when the engine block 11 is in operation. This removes soot adhering to and deposited on the outer surface of the heat transfer tube. Since the exhaust gas contains water vapor, water vapor is trapped in the soot adhering to the outer surface of the heat transfer tube. Therefore, by flowing coolant at a specified temperature (preferably 40 °C or lower) into the heat transfer tube, the soot adhering to its outer surface is cooled by the heat transfer tube, and the water vapor within it condenses into water.Since water vapor expands in volume when it condenses into water, the soot deposit layer adhering to the heat transfer pipe is more likely to be dislodged by the condensate generated within it. When the exhaust gas comes into contact with the soot deposit layer on the heat transfer pipe in this state, the pressure exerted by the exhaust gas facilitates the detachment of the soot deposit layer, and the soot is removed by being detached from the outer surface of the heat transfer pipe.

[0032] In the diesel engine 10 of the present example, the control unit 30 activates the coolant supply device when the engine block 11 is running and the temperature of the engine block 11, i.e., the temperature of the coolant in the water jacket 21, is equal to or below a prescribed temperature, in order to supply the coolant to the EGR cooler 16 at a low temperature. The soot deposit layer adhering to the outer surface of each of the heat transfer tubes inside the EGR cooler 16 is then cooled and removed.

[0033] When the EGR valve 17 provided in the EGR line G3 is open, the soot deposit layer on the heat transfer pipe, which is easier to remove after cooling, comes into contact with the exhaust gas at this time, which facilitates the removal by the pressure of the exhaust gas and the removal from the outer surface of the heat transfer pipe.

[0034] In the present example, the coolant stored in the water jacket 21 is used as the coolant, and an exhaust gas cooling line W4, configured to supply the coolant from the water jacket 21 to the EGR cooler 16, and the coolant pump 25 provided in the exhaust gas cooling line W4 are used as the coolant supply device. The control device 30 then activates the coolant pump 25 when the engine block 11 is running and the temperature of the coolant in the water jacket 21 is equal to or below a specified temperature.

[0035] The control of a cleaning process for the EGR cooler 16 in the diesel engine 10 of the first example is described in detail below. Fig. Figure 2 is a flowchart illustrating the cleaning process of the EGR cooler.

[0036] As in Fig. 1 and Fig. As shown in Figure 2, in step S11, the controller 30 determines whether the engine body 11 is running. The operation of the engine body 11 can be determined, for example, by whether the engine speed exceeds 0. If it is determined here that the engine body 11 is not running (No), the processing terminates this routine without implementing anything. If, on the other hand, it is determined that the engine body 11 is running (Yes), the controller 30 determines in step S12 whether the EGR valve 17 is open. Since the controller 30 performs an opening / closing control of the EGR valve 17 according to the operating state of the engine body 11, the opening state of the EGR valve 17 can be determined by a control signal from it. If it is determined here that the EGR valve 17 is not open (No), the processing terminates this routine without implementing anything.

[0037] If, however, it is determined that the EGR valve 17 is open (Yes), the controller 30 determines in step S13 whether the coolant temperature in the water jacket 21 is equal to or below a specified temperature. The controller 30 uses an input value from the temperature sensor 26 to determine whether the coolant temperature is equal to or below the specified temperature. If it is determined that the coolant temperature is higher than the specified temperature (No), the processing terminates the routine without implementing anything. If, however, it is determined that the coolant temperature is equal to or below the specified temperature (Yes), the controller 30 activates the coolant pump 25 in step S14.

[0038] When the coolant pump 25 is activated, the coolant from the water jacket 21 is supplied to the EGR cooler 16 via the exhaust gas cooling line W4 at a low temperature, i.e., a temperature equal to or below the prescribed temperature. The soot deposit layer adhering to the heat transfer tube in the EGR cooler 16 then detaches more easily due to cooling by the coolant, as the water vapor in the coolant condenses into water, and the expansion of the condensate lifts the soot deposit layer. The more easily detached soot deposit layer is then removed from the outer surface of the heat transfer tube by the exhaust gas flowing in the EGR cooler 16.

[0039] It should be noted that the coolant circulation pump 23 is operated in the engine block 11, so that the coolant from the water jacket 21 is supplied to the EGR cooler 16 via the exhaust gas cooling line W4. However, the coolant circulation pump 23 operates according to the rotational speed of the engine block 11, and when the rotational speed of the engine block 11 is low, the coolant circulation rate is also low. Furthermore, the coolant circulation pump 23 does not supply the coolant from the water jacket 21 via the exhaust gas cooling line W4 directly to the EGR cooler 16, making it difficult to adequately cool the heat transfer line of the EGR cooler 16.

[0040] In the present example, the coolant is forcibly directed from the exhaust gas cooling line W4 to the EGR cooler 16 at low temperatures by activating the coolant pump 25 provided in the exhaust gas cooling line W4, thereby actively cooling and removing the soot deposit layer adhering to the heat transfer pipe of the EGR cooler 16.

[0041] In step S15, it is then determined whether a prescribed time period has elapsed since the activation of the coolant pump 25. This prescribed time is the period during which the soot deposit layer adhering to the heat transfer tube detaches after the heat transfer tube of the EGR cooler 16 has been cooled by the coolant in a low-temperature state, and this prescribed time is determined based on tests. If it is determined here that a prescribed time period has not elapsed since the activation of the coolant pump 25 (No), this process continues. If, however, it is determined that a prescribed time period has elapsed since the activation of the coolant pump 25 (Yes), in step S16 the operation of the coolant pump 25 is stopped and the cleaning treatment of the EGR cooler 16 is terminated.

[0042] It should be noted that in the preceding description, when the engine block 11 is in operation and the temperature of the coolant in the water jacket 21 is equal to or below a prescribed temperature, the coolant pump 25 is activated, the low-temperature coolant is supplied to the EGR cooler 16, and the soot adhering to the heat transfer tube is cooled and removed. However, if the temperature of the coolant in the water jacket 21 is equal to or below the prescribed temperature, the low-temperature coolant does not always need to be supplied to the EGR cooler 16. In other words, this cleaning control is only carried out if a prescribed amount of soot adhering to the heat transfer tube significantly reduces the cooling capacity.

[0043] For example, the coolant supply device is activated when the engine block 11 is in operation and its temperature is equal to or below a prescribed temperature, and when the operating time of the engine block 11 after a cleaning cycle exceeds a preset prescribed operating time. In this case, the prescribed operating time is the time required until a significantly reduced cooling capacity occurs because the soot in the EGR cooler 16 adheres to the heat transfer tube, and this time can be preset based on testing.

[0044] Furthermore, the coolant supply device is activated when the engine block 11 is in operation and its temperature is equal to or below a prescribed temperature, and when the opening time of the EGR valve 17 exceeds a preset prescribed opening time after the cleaning control has been performed. In this case, the prescribed opening time is the time required until a significantly reduced cooling capacity occurs due to the soot adhering to the heat transfer tube in the EGR cooler 16 during the time the EGR valve 17 is open, and this time can be preset based on testing.

[0045] Furthermore, the coolant supply device is activated when the engine block 11 is in operation and the temperature of the engine block 11 is equal to or below a prescribed temperature, and when the temperature of the exhaust gas expelled from the EGR cooler 16 reaches or exceeds a preset prescribed temperature after the cleaning control has been carried out. In this case, the prescribed temperature is an exhaust gas temperature at which soot adheres to the heat transfer tube in the EGR cooler 16, which significantly reduces the cooling capacity, and this temperature can be preset based on tests.

[0046] In this way, the diesel engine of the first example comprises the EGR line G3, which is configured to recirculate a portion of the exhaust gas expelled from an engine body 11 back to the engine body 11 as combustion gas; the EGR cooler 16, which is provided in the EGR line G3 and configured to cool an exhaust gas by means of coolant; a coolant supply device, which is configured to supply coolant to the EGR cooler 16; and the control device 30, which is configured to activate the coolant supply device when the engine body 11 is in operation and the temperature of the engine body 11 is equal to or below a preset prescribed temperature.

[0047] Accordingly, coolant is supplied to the EGR cooler 16 when the engine block 11 is in operation and its temperature is equal to or below a specified temperature. When the heat transfer tube of the EGR cooler 16 is cooled by a low-temperature coolant, the soot adhering to the heat transfer tube is cooled, and the water vapor in it is converted into condensation. As the condensation forms within the soot, its volume expands, and the soot deposit layer adhering to the heat transfer tube is more easily detached by the lifting action of the condensation. When the exhaust gas comes into contact with the soot deposit layer on the heat transfer tube, the detachment of the soot deposit layer is facilitated by the pressure of the exhaust gas, and the soot is removed by being detached from the outer surface of the heat transfer tube.This can suppress the performance loss caused by the deposit on the EGR cooler 16.

[0048] In the diesel engine of the first example, the EGR valve 17 is located in the EGR line G3, and the control device 30 is configured to activate the coolant supply device when the EGR valve 17 is open, when the engine block 11 is running, and when the engine block 11 temperature is equal to or below the prescribed temperature. Since the exhaust gas thus comes into contact with the soot deposit layer in a state where the soot adhering to the heat transfer tube is cooled and more easily detached, the contact pressure of the exhaust gas enables the soot to be removed from the outer surface of the heat transfer tube at an early stage.

[0049] In the diesel engine of the first example, the coolant supply device comprises the exhaust gas cooling line W4, which is configured to supply coolant from the water jacket 21 of the engine block 11 to the EGR cooler 16, and the coolant pump 25 provided in the exhaust gas cooling line W4. The control device 30 activates the coolant pump 25 when the engine block 11 is in operation and the temperature of the coolant in the water jacket 21 is equal to or below a prescribed temperature. Accordingly, the coolant in the water jacket 21 is forcibly supplied from the exhaust gas cooling line W4 to the EGR cooler 16 by the coolant pump 25, so that the adhering soot can be removed at an early stage by appropriate cooling of the heat transfer tube.

[0050] In the diesel engine of the first example, the control device 30 supplies coolant to the EGR cooler 16 based on the assumption that soot adheres to the heat transfer tube and that the cooling capacity of the EGR cooler 16 decreases when the operating time of the engine block 11 exceeds a preset prescribed operating time, or when the opening time of the EGR valve 17 exceeds the preset prescribed opening time, or when the temperature of the exhaust gas expelled from the EGR cooler 16 reaches or exceeds a preset prescribed temperature. Accordingly, it is possible to perform the cleaning process in the EGR cooler 16 only when necessary, thereby reducing the use of coolant in the water jacket 21 and maintaining the cooling capacity of the engine block 11.

[0051] Fig. Figure 3 is a schematic configuration diagram representing a diesel engine according to a second example, which is not according to the invention but serves to illustrate features of the invention. It should be noted that elements with the same functions as in the examples described above are provided with the same reference numerals, and a detailed description of these is omitted.

[0052] In the second example, as in Fig. Figure 3 shows the engine body 11 provided with the water jacket 21, which is connected to the radiator 22 via the coolant inlet line W1 and the coolant outlet line W2. The coolant circulation pump 23 is located in the coolant inlet line W1. One end section of the exhaust cooling line W4 is connected to the water jacket 21, and the other end section is connected to the coolant outlet line W2 at a position further towards the side of the water jacket 21 than the thermostat three-way valve 24. The flow control valve 27 is located in the coolant outlet line W2 at a position further towards the side of the water jacket 21 than a connecting section of the exhaust cooling line W4.

[0053] The control device 30 is capable of controlling the opening / closing process of the EGR valve 17 and setting the opening degree of the flow control valve 27. The engine housing 11 is also equipped with the temperature sensor 26, which is configured to measure the temperature of the coolant in the water jacket 21. The temperature sensor 26 outputs a measurement result to the control device 30.

[0054] In this example, the EGR cooler 16 is configured to be regenerated by supplying coolant at a temperature equal to or lower than a specified temperature when the engine block 11 is running. This regeneration removes soot that adheres to and is deposited on the outer surface of the heat transfer tube. The control unit 30 activates the coolant supply device when the engine block 11 is running and its temperature—that is, the temperature of the coolant in the water jacket 21—is equal to or lower than a specified temperature, in order to supply a low-temperature coolant to the EGR cooler 16. The soot deposit layer adhering to the outer surface of each of the heat transfer tubes inside the EGR cooler 16 is then cooled and removed.

[0055] In this example, the coolant stored in the water jacket 21 is used as the coolant, and an exhaust gas cooling line W4, configured to supply coolant from the water jacket 21 to the EGR cooler 16, and the flow control valve 27 provided in the coolant outlet line W2 are used as the coolant supply device. The control device 30 then reduces the opening degree of the flow control valve 27 when the engine body 11 is in operation and the temperature of the coolant in the water jacket 21 is equal to or lower than a specified temperature. As the opening degree of the flow control valve 27 decreases, the flow rate of the coolant flowing from the water jacket 21 through the coolant outlet line W2 to the cooler 22 decreases, and the flow rate of the coolant flowing from the water jacket 21 to the exhaust gas cooling line W4 increases.Therefore, the cooling capacity of each of the heat transfer tubes in the EGR cooler 16 increases, and the soot deposit layer adhering to the outer surface of the heat transfer tube is cooled to detach and removed.

[0056] The control device 30 adjusts the opening degree of the flow control valve 27 according to the temperature of the coolant supplied by the temperature sensor 26 and the rotational speed of the engine housing 11. The control device 30 increases the opening degree of the flow control valve 27 when the temperature of the coolant increases or the rotational speed of the engine housing 11 increases.

[0057] When the EGR valve 17 provided in the EGR line G3 is open, the soot deposit layer on the heat transfer pipe, which is easier to remove after cooling, comes into contact with the exhaust gas, which facilitates the removal by the pressure of the exhaust gas and the removal from the outer surface of the heat transfer pipe.

[0058] It should be noted that the control of a procedure for cleaning the EGR cooler 16 in the diesel engine 10 of the second example is essentially the same as that of the first example, and therefore descriptions of it are omitted.

[0059] Thus, in the diesel engine of the second example, the coolant inlet line W1 and the coolant outlet line W2, configured to cool the coolant of the water jacket 21 of the engine body 11 by means of a cooler 22 and a coolant circulation pump 23 provided in the coolant outlet line W2, are provided, and the exhaust gas cooling line W4, configured to supply the coolant of the water jacket 21 to the EGR cooler 16, and the flow control valve 27, provided in the coolant outlet line W2, are provided as a coolant supply device, and furthermore, the control device 30 reduces the opening degree of the flow control valve 27 when the engine body 11 is in operation and the temperature of the coolant of the water jacket 21 is equal to or lower than the prescribed temperature.

[0060] Accordingly, by reducing the opening degree of the flow control valve 27, the coolant of the water jacket 21 can be more easily directed from the exhaust gas cooling line W4 to the EGR cooler 16. Thus, the heat transfer pipe can be adequately cooled and the adhering soot removed at an early stage by simply using the flow control valve 27, thereby avoiding an increase in manufacturing costs.

[0061] Fig. Figure 4 is a schematic configuration diagram representing a diesel engine according to one embodiment of the invention. It should be noted that elements with the same functions as in the examples described above are designated with the same reference numerals, and a detailed description of these is omitted.

[0062] In this embodiment, as in Fig.As shown in Figure 4, the EGR cooler 16 is configured to be regenerated by supplying coolant at a temperature equal to or lower than a specified temperature when the engine block 11 is running. This regeneration removes soot that adheres to and is deposited on the outer surface of the heat transfer tube. The control unit 30 activates the coolant supply device when the engine block 11 is running and its temperature, i.e., the temperature of the coolant in the water jacket 21, is equal to or lower than a specified temperature, in order to supply a low-temperature coolant to the EGR cooler 16. The soot deposit layer adhering to the outer surface of each of the heat transfer tubes inside the EGR cooler 16 is then cooled and removed.

[0063] In the present embodiment, the coolant stored in the water jacket 21 is stored as intermediate water, and a cooling system is provided that is separate from the cooling system of the engine body 11. In particular, a coolant tank 31 is connected via the first coolant supply line W11 to the upstream side of the EGR cooler 16 in the exhaust gas cooling line W4, namely to the side of the water jacket 21. The first coolant supply line W11 is equipped with: the three-way selector valve 32 at a connection section with the exhaust gas cooling line W4; and a coolant pump 33. Additionally, the coolant tank 31 is connected via the second coolant supply line W12 to the downstream side of the EGR cooler 16 in the exhaust gas cooling line W4, namely to the side of the coolant outlet line W2. The second coolant supply line W12 is equipped with a three-way selector valve 34 at a connection section with the exhaust gas cooling line W4.

[0064] This means that the coolant tank 31, configured for storing the coolant, the first coolant supply line W11 and the second coolant supply line W12, configured for supplying the coolant from the coolant tank 31 to the EGR cooler 16, and the coolant pump 33 provided in the first coolant supply line W11 are used as a coolant supply device. The control unit 30 then activates the coolant pump 33 when the engine block 11 is running and the temperature of the coolant in the water jacket 21 is equal to or lower than a specified temperature.

[0065] In other words, the flow path on the water jacket side 21 of the exhaust gas cooling line W4 is first closed by the three-way selector valve 32, and the EGR cooler side 16 of the exhaust gas cooling line W4 and the first coolant supply line W11 are caused to communicate with each other. Furthermore, the flow path on the coolant outlet side W2 of the exhaust gas cooling line W4 is closed by the three-way selector valve 34, and the EGR cooler side 16 of the exhaust gas cooling line W4 and the second coolant supply line W12 are caused to communicate with each other. Next, the coolant pump 33 is activated. Then, the coolant in the coolant tank 31 is supplied by the three-way selector valve 34 to the EGR cooler 16 of the exhaust gas cooling line W4 via the second coolant supply line W12.In this process, the heat transfer pipe of the EGR cooler 16 is cooled by the coolant, and the soot deposit layer adhering to the outer surface of the heat transfer pipe is cooled and removed.

[0066] If the EGR valve 17 provided in the EGR line G3 is open, the soot deposit layer on the heat transfer pipe, which is more likely to be removed after cooling, comes into contact with the exhaust gas, which facilitates the removal by the pressure of the exhaust gas and the removal from the outer surface of the heat transfer pipe.

[0067] The cleaning treatment of the EGR cooler 16 of the present embodiment is preferably carried out during the regeneration of a diesel particulate filter (DPF). The diesel particulate filter is a device for collecting and removing particulate material and black smoke contained in the exhaust gas of the diesel engine 10. Furthermore, the diesel particulate filter causes trapped particulate material and black smoke to be subjected to combustion by increasing the temperature of the exhaust gas before the filter becomes clogged. At this point, the heat transfer tube is cooled by supplying the coolant to the EGR cooler 16, and the soot deposit layer adhering to the outer surface of the heat transfer tube is removed.

[0068] It should be noted that the control of the method for cleaning the EGR cooler 16 in the diesel engine 10 of the embodiment is essentially the same as that of the first example, and therefore descriptions thereof are omitted.

[0069] Thus, in the diesel engine of the embodiment, the coolant supply device consists of the coolant tank 31, which is configured to store coolant, the first coolant supply line W11 and the second coolant supply line W12, which are configured to supply the coolant from the coolant tank 31 to the EGR cooler 16, and the coolant pump 33 provided in the first coolant supply line W11, and the control device 30 activates the coolant pump 33 when the engine body 11 is in operation and the temperature of the coolant in the water jacket 21 is equal to or lower than a prescribed temperature.

[0070] By equipping the EGR cooler 16 with the cooling system, which includes the first coolant supply line W11, the second coolant supply line W12 and the coolant pump 33 separately from the cooling system for the water jacket 21 for cooling the engine body 11, the cooling system of the EGR cooler 16 can therefore be activated when required, thus ensuring a greater degree of freedom for carrying out the cleaning treatment of the EGR cooler 16. List of reference symbols 10 diesel engine 11 Engine housing 16 EGR coolers 17 EGR valve 21 Water coat 22 coolers 23 Coolant circulation pump 24 Thermostatic three-way valve 25 Coolant pump (coolant supply device) 26 Temperature sensor 27 Flow control valve (coolant supply device) 30 Control device 31 Coolant tank (coolant supply device) 32, 34 Three-way selector valve 33 Coolant pump (coolant supply device) G1 Air supply line G2 Exhaust pipe G3 EGR line W1 Coolant inlet line (coolant cooling line) W2 Coolant outlet line (coolant cooling line) W3 Bypass Line W4 Exhaust gas cooling line (coolant supply device) W11 First coolant supply line (coolant supply device) W12 Second coolant supply line (coolant supply device)

Claims

[1] Diesel engine (10), comprising: an EGR line (G3) configured to recirculate a portion of exhaust gas expelled from an engine body (11) as a combustion gas to the engine body (11); an EGR cooler (16) which is provided in the EGR line (G3) and is configured to cool exhaust gas by means of a coolant; a coolant supply device configured to supply coolant to the EGR cooler (16); and a control device (30) configured to activate the coolant supply device, characterized by , that the coolant supply device comprises a coolant tank (31) configured to store coolant, a coolant supply line (W11,W12) configured to supply coolant in the coolant tank (31) to the EGR cooler (16), and a coolant pump (33) provided in the coolant supply line (W11,W12), and the control device (30) is configured to activate the coolant pump (33) when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than a preset prescribed temperature. [2] Diesel engine (10) according to claim 1, wherein an EGR valve (17) is provided in the EGR line (G3) and the control device (30) is configured to activate the coolant supply device when the EGR valve (17) is open when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than the prescribed temperature. [3] Diesel engine (10) according to claim 1 or 2, wherein the coolant tank (31) is connected via a first coolant supply line (W11) to an upstream side of the EGR cooler (16) in an exhaust gas cooling line (W4) which is configured to supply coolant from a water jacket (21) of the engine body (11) to the EGR cooler (16), to the side of the water jacket (21), the first coolant supply line (W11) is equipped with a first three-way selector valve (32) at a connecting section with the exhaust gas cooling line (W4) and the coolant pump (33), the coolant tank (31) is connected by a second coolant supply line (W12) to the downstream side of the EGR cooler (16) in the exhaust gas cooling line (W4) at one side of a coolant outlet line (W2) of a coolant cooling line configured to cool the coolant of the water jacket (21) of the engine body (11) with a cooler (22) and a coolant circulation pump (23) provided in the coolant cooling line, and the second coolant supply line (W12) is provided with a second three-way selector valve (34) at a connecting section with the exhaust gas cooling line (W4). [4] Diesel engine (10) according to claim 3, wherein the control device (30) is configured to first close a flow path of the exhaust gas cooling line (W4) on the side of the water jacket (21) through the first three-way selector valve (32) and to connect the EGR cooler side (16) of the exhaust gas cooling line (W4) and the first coolant supply line (W11) to each other, furthermore to close a flow path of the exhaust gas cooling line (W4) on the side of the coolant outlet line (W2) through the second three-way selector valve (34) and to connect the EGR cooler side (16) of the exhaust gas cooling line (W4) and the second coolant supply line (W12) to each other, and then to activate the coolant pump (33) to pump the coolant in the coolant tank (31) from the second three-way selector valve (34) to the EGR cooler (16) of the exhaust gas cooling line (W4) through the second coolant supply line. (W12) to supply and to cool a heat transfer pipe of the EGR cooler (16) by means of the coolant. [5] Diesel engine (10) according to any one of claims 1 to 4, wherein the control device (30) is configured to activate the coolant supply device when an operating time of the engine body (11) exceeds a preset prescribed operating time and when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than the prescribed temperature. [6] Diesel engine (10) according to claim 2, wherein the control device (30) is configured to activate the coolant supply device when an opening time of the EGR valve (17) exceeds a preset prescribed opening time and when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than the prescribed temperature. [7] Diesel engine (10) according to any one of claims 1 to 6, wherein the control device (30) is configured to activate the coolant supply device when the temperature of an exhaust gas expelled from the EGR cooler (16) reaches or exceeds a preset prescribed temperature and when the engine body (11) is in operation and the temperature of the engine body (11) is equal to or lower than the prescribed temperature.

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