JP6019754B2 - Urea water thawing device - Google Patents

Description

  The present invention relates to a urea water thawing device, and in particular, urea water thawing of an exhaust gas purification system having a selective reduction catalyst that selectively purifies nitrogen compounds (hereinafter referred to as NOx) in exhaust gas with ammonia generated from urea water. Relates to the device.

  As a NOx purification catalyst for purifying NOx in exhaust gas, selective catalytic reduction (hereinafter referred to as “Selective Catalytic Reduction”) that selectively reduces and purifies NOx in exhaust gas using ammonia generated by hydrolysis from urea water by exhaust heat. SCR). An exhaust gas purification system provided with such an SCR is described in Patent Document 1, for example.

  Since urea water freezes at about −10 ° C., it may not be possible to supply urea water to the SCR especially during cold weather. Therefore, in the system described in Patent Document 1, a part of the engine coolant circuit is introduced into the urea water tank, and the urea water frozen by the coolant heated by the engine is thawed.

JP 2006-125331 A

  By the way, in order to promote warm-up when starting the engine, it is necessary to raise the coolant temperature early. Therefore, in a general engine, during the warm-up operation, the cooling water temperature is effectively increased by bypassing the circulation path of the cooling water from the radiator. However, when the cooling water heated by the engine is used for thawing the frozen urea water as in the above-described conventional technology, it takes time to increase the cooling water temperature, and as a result, the engine warm-up performance may be lowered. is there.

  The present invention has been made in view of these points, and an object of the present invention is to provide a urea water thawing device that can efficiently thaw frozen urea water while preventing deterioration in engine warm-up performance. .

  In order to achieve the above object, a urea water thawing device of the present invention injects urea water stored in a urea water tank into an exhaust passage of an engine by an injector, and exhausts ammonia with ammonia generated from the injected urea water. A urea water thawing device for an exhaust gas purification system in which a selective reduction catalyst for selectively purifying nitrogen compounds is provided in an exhaust passage on the exhaust downstream side of the injector, the exhaust gas downstream of the selective reduction catalyst. A first heat exchange passage provided in the exhaust passage for exchanging heat between the exhaust flowing through the exhaust passage and a fluid to be circulated; and provided in at least a part of the urea water tank; A second heat exchange channel that exchanges heat between the urea water stored in the fluid and the fluid to be circulated, a fluid outlet of the first heat exchange channel, and a fluid in the second heat exchange channel First connecting the inlet A fluid channel, a second fluid channel connecting the fluid outlet of the second heat exchange channel and the fluid inlet of the first heat exchange channel, and the first fluid channel or It is provided with the pump which is provided in the 2nd fluid channel and pumps fluid.

  A branch exhaust passage formed by branching from an exhaust passage between the selective reduction catalyst and the first heat exchange passage; and a branch portion between the exhaust passage and the branch exhaust passage. A flow path switching valve for switching the flow path of the exhaust, wherein the flow path switching valve has a temperature of the fluid heated in the first heat exchange flow path equal to or lower than a first upper limit threshold value for preventing boiling of the fluid In this case, the exhaust passage is used as the exhaust passage provided with the first heat exchange passage, while the temperature of the fluid raised in temperature in the first heat exchange passage is the first upper limit threshold value. If higher, the exhaust flow path may be switched to the branch exhaust passage.

  The pump stops when the temperature of the fluid flowing into the second heat exchange flow path or the temperature of the urea water in the urea water tank is higher than a second upper limit threshold value for preventing the urea water from deteriorating. May be.

Further, the fluid is a cooling water of the engine, at least a portion of said second fluid flow path or may be formed in the cylinder block of the engine.

  Further, the first fluid flow path and the second fluid flow path positioned upstream of the cylinder block are connected to bypass the cooling water flow path from the second heat exchange flow path. And a bypass valve that switches the cooling water flow path to the second heat exchange flow path or the bypass flow path, and the bypass valve flows into the second heat exchange flow path When the temperature of the cooling water or the temperature of the urea water in the urea water tank becomes higher than the second upper limit threshold, the cooling water flow path may be switched to the bypass flow path.

  Further, the exhaust purification system includes a urea water pump that pumps urea water from the urea water tank to the injector, and the second heat exchange channel is connected to the urea water tank and the urea water pump. May be introduced.

  The pump may be an electric pump.

  According to the urea water thawing device of the present invention, it is possible to efficiently thaw frozen urea water while preventing a decrease in engine warm-up performance.

It is a typical whole block diagram which shows the urea water thawing | decompression apparatus which concerns on 1st embodiment of this invention. In the first embodiment of the present invention, (a) is a diagram for explaining an exhaust passage when the exhaust passage switching valve is turned on, and (b) is an exhaust when the exhaust passage switching valve is turned off. It is a figure explaining a flow path. It is a flowchart which shows the control content which concerns on 1st embodiment of this invention. It is a typical whole block diagram which shows the urea water thawing | decompression apparatus which concerns on 2nd embodiment of this invention. In 2nd embodiment of this invention, (a) is a figure explaining a cooling water flow path when a bypass valve is closed, (b) is a figure explaining a cooling water flow path when a bypass valve is opened. (C) is a figure explaining a cooling water flow path when a thermostat is opened. It is a flowchart which shows the control content which concerns on 2nd embodiment of this invention.

  Hereinafter, each embodiment of the urea water thawing device according to the present invention will be described with reference to the drawings. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[First embodiment]
First, based on FIG. 1, it demonstrates from the whole structure of the exhaust gas purification system to which 20A of urea water defrosting apparatuses of 1st embodiment are applied.

  An exhaust purification system according to the present embodiment includes an oxidation catalyst (Diesel Oxidation Catalyst: hereinafter referred to as DOC) 12 provided in an exhaust passage 11 of a diesel engine (hereinafter simply referred to as an engine) 10, and an exhaust downstream of the DOC 12. A diesel particulate filter (hereinafter referred to as DPF) 13 provided in the passage 11, an SCR 14 provided in the exhaust passage 11 downstream of the DPF 13, and urea water in the exhaust passage 11 A urea water injector 15 for injecting urea water, a urea water tank 16 for storing urea water, and a supply module 17 for supplying the urea water in the urea water tank 16 to the urea water injector 15.

DOC12 generates the NO ₂ to oxidize NO in the exhaust, to NO in the exhaust to increase the proportion of NO _2, functions to raise the denitration efficiency by SCR 14.

  The DPF 13 collects particulate matter (hereinafter referred to as PM) in the exhaust gas, and when the collected amount of PM exceeds a predetermined amount, regeneration that accumulates and removes the accumulated PM is performed. The regeneration of the DPF 13 is performed by supplying unburned fuel to the DOC 12 on the upstream side of the exhaust by post-injection and increasing the exhaust temperature by heat due to oxidation.

  The SCR 14 adsorbs ammonia generated from urea water sprayed in the exhaust passage 11 by the urea water injector 15 and reduces and purifies NOx from the exhaust gas passing through the adsorbed ammonia.

  The urea water injector 15 is provided in the exhaust passage 11 located between the DPF 13 and the SCR 14. The urea water injector 15 is connected to the urea water tank 16 through a supply line 19.

The supply module 17 includes a urea water pump 17a that pumps the urea water and a urea water temperature sensor 18 that detects the temperature of the supply module 17 (the temperature of the urea water in the supply line 19). The urea water temperature T _UR detected by urea water temperature sensor 18 is electrically connected to an electronic control unit (hereinafter, ECU hereinafter) is output to the 40.

  Next, a detailed configuration of the urea water thawing system 20A of the present embodiment will be described. The urea water thawing system 20A includes a heat exchange exhaust passage 11a, a branch exhaust passage 11b, an exhaust passage switching valve 21, a waste heat recovery heat exchange passage 22, and a urea water thawing heat exchange passage 23. The upstream fluid passage 24, the downstream fluid passage 25, the electric pump 26, the fluid temperature sensor 27, and the ECU 40 are provided.

  In the present embodiment, the waste heat recovery heat exchange channel 22 corresponds to the first heat exchange channel of the present invention, and the urea water thawing heat exchange channel 23 corresponds to the second heat exchange channel of the present invention. Corresponds to the road. The upstream fluid channel 24 corresponds to the first fluid channel of the present invention, and the downstream fluid channel 25 corresponds to the second fluid channel of the present invention.

  The heat exchange exhaust passage 11a is formed in the exhaust passage 11 on the exhaust downstream side of the SCR 14 and a silencer (not shown). In the heat exchange exhaust passage 11a, a waste heat recovery heat exchange passage 22 described later in detail is interposed.

  The branch exhaust passage 11 b is formed by branching from the exhaust passage 11 located between the SCR 14 and the waste heat recovery heat exchange passage 22. In the present embodiment, the branch exhaust passage 11b and the heat exchange exhaust passage 11a also function as a tail pipe that discharges the exhaust to the outside.

  The exhaust flow path switching valve 21 is, for example, a known butterfly valve, and is provided at a branch portion between the heat exchange exhaust passage 11a and the branch exhaust passage 11b. When the exhaust flow path switching valve 21 is turned on in response to an instruction signal input from the ECU 40, the upstream end of the branch exhaust passage 11b is closed. That is, the exhaust gas from the SCR 14 flows into the heat exchange exhaust passage 11a and is released to the outside air (see FIG. 2A). On the other hand, when the exhaust flow path switching valve 21 is turned OFF in response to an instruction signal input from the ECU 40, the upstream end of the heat exchange exhaust passage 11a is closed. That is, the exhaust gas from the SCR 14 flows into the branch exhaust passage 11b and is released to the outside air (see FIG. 2B).

  The waste heat recovery heat exchange flow path 22 exchanges heat between the fluid flowing through the flow path and the exhaust flowing through the heat exchange exhaust passage 11a, and meanders in the heat exchange exhaust passage 11a. Is formed. In the present embodiment, the waste heat recovery heat exchange flow path 22 is provided on the exhaust downstream side of the SCR 14, so that the SCR 14 becomes lower than the catalyst activation temperature due to a decrease in exhaust temperature due to waste heat recovery. Can be prevented.

  The heat exchange flow path for thawing urea water exchanges heat between the fluid flowing through the flow path and the urea water in the urea water tank 16 and the supply module 17 in order to thaw the frozen urea water. Do. For this reason, the urea water thawing heat exchange flow path 23 is introduced into the urea water tank 16 and introduced into the supply module 17 along the supply line 19.

  The upstream fluid flow path 24 allows the fluid heated by heat exchange with the exhaust gas in the waste heat recovery heat exchange path 22 to flow into the urea water thawing heat exchange path 23. Therefore, the upstream fluid passage 24 is connected at its upstream end to the fluid outlet portion of the waste heat recovery heat exchange passage 22 and at the downstream end thereof as the fluid of the urea water thawing heat exchange passage 23. Connected to the entrance.

  The downstream fluid flow path 25 allows the fluid cooled by heat exchange with the urea water in the urea water thawing heat exchange flow path 23 to flow into the waste heat recovery heat exchange flow path 22. For this reason, the downstream end fluid passage 25 has an upstream end connected to the fluid outlet of the urea water thawing heat exchange passage 23 and a downstream end connected to the fluid in the waste heat recovery heat exchange passage 22. Connected to the entrance.

  The electric pump 26 pumps fluid and is provided in the upstream fluid flow path 24. The driving of the electric pump 26 is controlled according to an instruction signal input from the ECU 40. When the electric pump 26 is driven, the fluid to be pumped is a fluid composed of the waste heat recovery heat exchange channel 22, the upstream fluid channel 24, the urea water thawing heat exchange channel 23, and the downstream fluid channel 25. Cycle through the circuit. The electric pump 26 may be provided in the downstream fluid flow path 25.

The fluid temperature sensor 27 detects the temperature of the fluid heated by heat exchange with the exhaust, and is provided in the upstream fluid flow path 24 adjacent to the fluid outlet portion of the waste heat recovery heat exchange flow path 22. ing. The fluid temperature T _WA detected by the fluid temperature sensor 27 is input to the electrically connected ECU 40.

  The ECU 40 performs various controls such as fuel injection of the engine 10 and urea water injection by the urea water injector 15, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, output signals of various sensors are input to the ECU 40.

  The ECU 40 includes an electric pump drive control unit 41 and a switching valve control unit 42 as some functional elements. In the present embodiment, these functional elements are described as being included in the ECU 40, which is an integral piece of hardware. However, any one of these functional elements may be provided in separate hardware.

The electric pump drive control unit 41 controls the driving of the electric pump 26 according to the fluid temperature T _WA detected by the fluid temperature sensor 27 (or the urea water temperature T _UR detected by the urea water temperature sensor 18). More specifically, the ECU 40 stores a temperature (for example, 30 ° C. since the performance of urea water deteriorates at about 60 ° C.) that prevents deterioration of the urea water as the urea water temperature upper limit threshold T _LIM1 .

When the fluid temperature T _WA input from the fluid temperature sensor 27 (or the urea water temperature T _UR input from the urea water temperature sensor 18) is equal to or lower than the urea water temperature upper limit threshold T _{LIM1, the} electric pump drive control unit 41 A drive instruction signal is input to the electric pump 26. On the other hand, when the fluid temperature T _WA input from the fluid temperature sensor 27 (or the urea water temperature T _UR input from the urea water temperature sensor 18) exceeds the urea water temperature upper limit threshold T _LIM1 , the electric pump drive control unit 41 A stop instruction signal is input to the electric pump 26.

The switching valve control unit 42 controls the exhaust flow path switching valve 21 according to the fluid temperature T _WA detected by the fluid temperature sensor 27. More specifically, the ECU 40 stores a temperature (for example, 80 ° C.) that prevents boiling of the fluid as the fluid temperature upper limit threshold T _LIM2 . Switching valve control unit 42, the fluid temperature T _WA inputted from the fluid temperature sensor 27 when following this fluid temperature upper threshold T _LIM2 inputs an instruction signal to the ON exhaust flow switching valve 21. That is, the upstream end of the branch exhaust passage 11b is closed, and the exhaust flows into the heat exchange exhaust passage 11a (see FIG. 2A).

On the other hand, the fluid temperature T _WA inputted from the fluid temperature sensor 27 is more than the fluid temperature upper threshold T _LIM2, switching valve control unit 42 inputs an instruction signal to the OFF exhaust flow switching valve 21. That is, the upstream end of the heat exchange exhaust passage 11a is closed, and the exhaust flows into the branch exhaust passage 11b (see FIG. 2B).

  Next, based on FIG. 3, the control flow by the urea water thawing system 20A of the present embodiment will be described. This control starts simultaneously with the start of the engine 10 (key switch ON of the ignition switch).

  In step (hereinafter, “step” is simply referred to as “S”) 100, the drive instruction signal is input from the electric pump drive control unit 41 to the electric pump 26, and at the same time, the exhaust flow path switching valve 21 is turned on from the switching valve control unit 42. An instruction signal is input. That is, the temperature of the fluid is raised by heat exchange with the exhaust gas in the waste heat recovery heat exchange channel 22, and the heated fluid passes through the upstream side fluid channel 24 and the heat exchange channel 23 for thawing urea water. And the thawing of urea water is started.

Thereafter, when the urea water is thawed, in S110, the fluid temperature T _WA inputted from the fluid temperature sensor 27 (or the urea water temperature T _UR inputted from the urea water temperature sensor 18) is changed to the urea water temperature upper limit threshold T _LIM1. It is determined whether or not When the fluid temperature T _WA (or urea water temperature T _UR ) is equal to or lower than the urea water temperature upper threshold T _{LIM1, the process returns to} S100, while the fluid temperature T _WA (or urea water temperature T _UR ) is the urea water temperature upper threshold. If T _LIM1 is exceeded, the process proceeds to S120.

In S120, upon receiving the fluid temperature T _WA has reached the urea water temperature upper threshold T _LIM1, stop instruction signal to the electric pump 26 is inputted from the electric pump operation control unit 41.

In S130, whether the fluid temperature T _WA inputted from the fluid temperature sensor 27 has reached the fluid temperature upper threshold T _LIM2 is determined. If the fluid temperature T _WA exceeds the fluid temperature upper threshold T _LIM2, the control of the exhaust flow path switching valve 21 is input an instruction signal to OFF from the switching valve control unit 42 in S140 is returned.

  Next, the function and effect of the urea water thawing device 20A according to this embodiment will be described.

  In a cold district or the like, if the engine 10 is stopped for a predetermined period, the urea water in the urea water tank 16 or the supply module 17 may freeze. Therefore, the conventional urea water thawing device thaws the frozen urea water using the cooling water heated by the engine, but the heat of the cooling water is taken away by this thawing, and the warm-up performance of the engine is reduced. There was a possibility of making it.

  On the other hand, in the urea water thawing device 20A of this embodiment, a fluid circuit separate from the cooling water circuit of the engine 10 is provided, and the urea water tank 16 and the supply are made using exhaust heat discharged from the engine 10. The urea water in the module 17 is thawed.

  Therefore, according to the urea water thawing device 20A of the present embodiment, the frozen urea water can be effectively thawed without reducing the warm-up performance of the engine 10.

  Further, in the urea water thawing device 20A of the present embodiment, the driving of the electric pump 26 is stopped when the temperature of the fluid that performs heat exchange exceeds the upper limit temperature that prevents deterioration of the urea water.

  Therefore, according to the urea water thawing device 20A of the present embodiment, it is possible to effectively prevent the urea water from being heated and deteriorated more than necessary.

  Further, in the urea water thawing device 20A of the present embodiment, the waste heat recovery heat exchange channel 22 that performs heat exchange between the exhaust and the fluid is provided on the exhaust downstream side of the SCR 14.

  Therefore, according to the urea water thawing device 20A of the present embodiment, the exhaust gas (NOx emission) is effectively deteriorated by avoiding that the SCR 14 is lower than the catalyst activation temperature due to a decrease in the exhaust temperature due to waste heat recovery. Can be prevented.

[Second Embodiment]
Hereinafter, based on FIGS. 4-6, the urea water thawing | decompression apparatus 20B which concerns on 2nd embodiment of this invention is demonstrated. In the second embodiment of the present invention, a fluid for thawing urea water is used as cooling water for the engine 10, and further, warming up of the engine 10 is promoted by cooling water whose temperature is raised by waste heat recovery. Constituent elements having the same functions as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 4, the urea water thawing device 20 </ b> B according to the present embodiment includes a heat exchange exhaust passage 11 a, a branch exhaust passage 11 b, an exhaust passage switching valve 21, and a waste heat recovery heat exchange passage 22. , The urea water thawing heat exchange flow path 23, the upstream cooling water flow path 30, the connection cooling water flow path 31, the cylinder block internal flow path 32, the water pump 33, the downstream cooling water flow path 34, and the bypass A flow path 35, a bypass valve 36, a radiator flow path 37, a cooling water temperature sensor 38, and an ECU 40 are provided.

  The upstream side cooling water flow path 30 causes the cooling water heated by heat exchange with the exhaust gas in the waste heat recovery heat exchange flow path 22 to flow into the urea water thawing heat exchange flow path 23. Therefore, the upstream side cooling water passage 30 is connected at its upstream end to the cooling water outlet portion of the waste heat recovery heat exchange passage 22 and at the downstream end of the urea water thawing heat exchange passage 23. Connected to the cooling water inlet.

  The cooling water flow path 31 for connection allows the cooling water that has flowed through the heat exchange flow path 23 for thawing urea water to flow into the flow path 32 in the cylinder block. For this reason, the cooling water flow path 31 for connection is connected to the cooling water outlet part of the heat exchange flow path 23 for thawing urea water, and the downstream end part is connected to the cooling water inlet of the flow path 32 in the cylinder block. Connected to the department.

  The in-cylinder block flow path 32 circulates the cooling water flowing from the connection cooling water flow path 31 through a water jacket (not shown), and is formed in the cylinder block of the engine 10.

The water pump 33 pumps and supplies cooling water, and is provided adjacent to the cooling water inlet of the in-cylinder block flow path 32. The water pump 33 is driven by power transmitted from a crankshaft (not shown) of the engine 10.

  The downstream cooling water flow path 34 causes the cooling water that has flowed through the cylinder block flow path 32 to flow into the waste heat recovery heat exchange flow path 22. For this reason, the downstream side cooling water flow path 34 is connected at its upstream end to the cooling water outlet part of the in-cylinder block flow path 32 and at the downstream end thereof is the cooling water inlet of the heat exchange path 22 for waste heat recovery. Connected to the department.

  The bypass flow path 35 diverts the cooling water from the urea water thawing heat exchange flow path 23, and connects the upstream side cooling water flow path 30 and the connection cooling water flow path 31.

  The bypass valve 36 is provided in the bypass flow path 35 and selectively switches the flow path of the cooling water. The opening and closing of the bypass valve 36 is controlled in accordance with an instruction signal input from the electrically connected ECU 40. When the bypass valve 36 is closed, the cooling water flows into the urea water thawing heat exchange flow path 23 (see FIG. 5A), while when the bypass valve 36 is opened, the cooling water flows into the bypass flow path 35. It flows in (see FIG. 5B).

The radiator flow path 37 allows cooling water to flow into the radiator 39 that exchanges heat between the cooling water and the outside air, and connects the downstream side of the connection cooling water flow path 31 and the upstream side of the downstream cooling water flow path 34. To do. A known thermostat 50 is provided at a branch portion between the radiator flow path 37 and the downstream cooling water flow path 34. When the cooling water temperature exceeds 87 ° C., the thermostat 50 causes the cooling water to flow through the radiator flow path 37 . That is, the cooling water circulates in the cooling water circuit constituted by the cylinder block inner passage 32 and the radiator passage 37 (see FIG. 5C).

The cooling water temperature sensor 38 detects the temperature of the cooling water heated by the heat exchange with the exhaust gas, and is provided in the upstream cooling water passage 30 adjacent to the cooling water outlet portion of the heat exchange passage 22 for waste heat recovery. Is provided. The coolant temperature T _CO detected by the coolant temperature sensor 38 is inputted to the electrically connected ECU 40.

  The ECU 40 includes a bypass valve control unit 43 and a switching valve control unit 42 as some functional elements.

The bypass valve control unit 43 controls the bypass valve 36 according to the cooling water temperature T _CO detected by the cooling water temperature sensor 38 (or the urea water temperature T _UR detected by the urea water temperature sensor 18). More specifically, the ECU 40 stores a temperature (for example, 30 ° C.) for preventing deterioration of the urea water as the urea water temperature upper limit threshold T _LIM1 .

When the coolant temperature T _CO input from the coolant temperature sensor 38 (or the urea solution temperature T _UR input from the urea solution temperature sensor 18) is equal to or lower than the urea solution temperature upper limit threshold T _{LIM1, the} bypass valve control unit 43 A valve closing instruction signal is input to the bypass valve 36. That is, the cooling water heated in the waste heat recovery heat exchange flow path 22 flows into the urea water thawing heat exchange flow path 23 (see FIG. 5A).

On the other hand, when the cooling water temperature T _CO input from the cooling water temperature sensor 38 (or the urea water temperature T _UR input from the urea water temperature sensor 18) exceeds the urea water temperature upper limit threshold T _LIM1 , the bypass valve control unit 43 A valve opening instruction signal is input to the bypass valve 36. That is, the cooling water heated in the waste heat recovery heat exchange channel 22 flows into the bypass channel 35 and bypasses the urea water thawing heat exchange channel 23 (see FIG. 5B).

Switching valve control unit 42, depending on the coolant temperature T _CO detected by the coolant temperature sensor 38, and controls the exhaust flow switching valve 21. More specifically, the ECU 40 stores a temperature (for example, 80 ° C.) that prevents boiling of the cooling water as the cooling water temperature upper limit threshold T _LIM3 . Switching valve control unit 42, the cooling water temperature T _CO input from coolant temperature sensor 38 when the cooling water temperature upper threshold T _{LIM 3} below, inputs an instruction signal for turning ON the exhaust flow switching valve 21. On the other hand, the cooling water temperature T _CO input from coolant temperature sensor 38 is more than the cooling water temperature upper threshold T _{LIM 3,} the switching valve control unit 42 inputs an instruction signal to the OFF exhaust flow switching valve 21.

  Next, based on FIG. 6, the control flow by the urea water defrosting system 20B of this embodiment is demonstrated. This control starts simultaneously with the start of the engine 10 (ignition switch key switch ON).

  In S <b> 200, the water pump 33 is driven by the start of the engine 10, and an instruction signal for turning on the exhaust flow path switching valve 21 is input from the switching valve control unit 42. That is, the temperature of the cooling water is raised by heat exchange with the exhaust gas in the waste heat recovery heat exchange flow path 22, and the raised temperature of the cooling water is passed through the upstream cooling water flow path 30 for the heat exchange flow for thawing urea water It flows into the channel 23 and the thawing of urea water is started.

Thereafter, when the urea water is thawed, in S210, the cooling water temperature T _WA inputted from the cooling water temperature sensor 38 (or the urea water temperature T _UR inputted from the urea water temperature sensor 18) is changed to the urea water temperature upper limit threshold T. _It is determined whether _LIM1 has been reached. When the cooling water temperature T _WA (or urea water temperature T _UR ) is equal to or lower than the urea water temperature upper limit threshold T _{LIM1, the process returns to} S200, while the cooling water temperature T _WA (or urea water temperature T _UR ) is the urea water temperature. If the upper limit threshold T _LIM1 is exceeded, the process proceeds to S220.

In S220, in response to the fact that the cooling water temperature T _CO reaches the urea water temperature upper threshold T _LIM1, the valve opening instruction signal is inputted from the bypass valve control unit 43 to the bypass valve 36. That is, the cooling water bypasses the urea water thawing heat exchange flow path 23.

In S230, the cooling water temperature T _CO input from coolant temperature sensor 38 whether or not reached in the cooling water temperature upper threshold T _{LIM 3} is determined. If the cooling water temperature T _CO is below the cooling water temperature upper threshold T _{LIM 3} is returned to S220 to continue the warming up of the engine 10. On the other hand, the cooling water temperature T _CO may exceed the cooling water temperature upper threshold T _{LIM 3} an instruction signal to turn OFF the exhaust passage switching valve 21 from the switching valve control unit 42 in S240 is input.

Further, in S250, in response to the cooling water temperature exceeding 87 ° C., the cooling water flow path is switched from the downstream cooling water flow path 34 to the radiator flow path 37 by the thermostat 50. That is, the flow path of the cooling water is switched to the cooling water circuit constituted by the in-cylinder block flow path 32 and the radiator flow path 37, and this control is returned.

  Next, the effect by the urea water thawing apparatus 20B of this embodiment is demonstrated. In addition, description is abbreviate | omitted about what has the same effect as 20 A of urea water thawing apparatuses of 1st embodiment.

  In the urea water thawing device 20B of the present embodiment, the cooling water heated by heat exchange with the exhaust gas in the waste heat recovery heat exchange channel 22 after the engine 10 is started is the urea water thawing heat exchange channel 23. And flows into the cylinder block flow path 32. When the thawing of urea water is completed, the cooling water flows through the bypass flow path 36 and bypasses the urea water thawing heat exchange flow path 23, and the heat exchange for waste heat recovery is completed until the warm-up of the engine 10 is completed. It flows into the cylinder block flow path 32 while being heated in the flow path 22. That is, even after the urea water is thawed with the cooling water heated by the waste heat recovery, the heating of the cooling water by the waste heat recovery is continued and the warm-up of the engine 10 is promoted.

  Therefore, according to the urea water thawing device 20B of the present embodiment, the frozen urea water can be effectively thawed while improving the warm-up performance of the engine 10.

  The present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the spirit of the present invention.

  For example, although the heat exchange exhaust passage 11a and the branch exhaust passage 11b have been described as being formed in the exhaust passage 11 on the exhaust downstream side of the silencer, they may be formed immediately downstream of the SCR 14, and the catalyst heater If provided, it may be formed on the exhaust upstream side of the SCR 14.

  Moreover, in 2nd embodiment, it is good also as a structure further equipped with the electric pump 26 in the upstream cooling water flow path 30. FIG. In this case, if the water pump 33 is an electromagnetic clutch type water pump and the driving thereof is stopped as necessary, the engine load during the warm-up operation can be effectively reduced.

10 Engine 11 Exhaust passage 11a Exhaust passage for heat exchange 11b Branch exhaust passage 14 SCR (selective reduction catalyst)
DESCRIPTION OF SYMBOLS 15 Urea water injector 16 Urea water tank 21 Exhaust flow path switching valve 22 Heat exchange flow path for waste heat recovery (1st heat exchange flow path)
23 Heat exchange channel for thawing urea water (second heat exchange channel)
24 Upstream fluid flow path (first fluid flow path)
25 Downstream fluid channel (second fluid channel)
26 Electric pump 40 ECU

Claims (6)

A selective reduction catalyst for injecting urea water stored in a urea water tank into an exhaust passage of an engine by an injector and selectively purifying nitrogen compounds in the exhaust with ammonia generated from the injected urea water. A urea water thawing device for an exhaust purification system provided in an exhaust passage on the exhaust downstream side,
A first heat exchange flow path that is provided in an exhaust passage downstream of the selective reduction catalyst and performs heat exchange between the exhaust flowing through the exhaust passage and the fluid to be circulated;
A second heat exchange flow path that is provided in at least a part of the urea water tank and exchanges heat between the urea water stored in the urea water tank and the fluid to be circulated;
A first fluid channel connecting a fluid outlet of the first heat exchange channel and a fluid inlet of the second heat exchange channel;
A second fluid channel connecting the fluid outlet part of the second heat exchange channel and the fluid inlet part of the first heat exchange channel;
Comprising a pump for pumping fluid disposed in front Stories second fluid flow path, and
The fluid is cooling water of the engine;
The second fluid flow path is connected to a cooling water flow path connected to the cooling water outlet of the second heat exchange flow path, and to an engine cylinder connected to the cooling water outlet of the connection cooling water flow path. Cylinder block flow path formed in the block, and downstream cooling connected to the cooling water outlet of the first heat exchange flow path and connected to the cooling water outlet of the flow path of the cylinder block A water flow path,
The discharge side of the pump is provided at the cooling water inlet of the flow path in the cylinder block,
A radiator flow path for connecting the downstream side of the cooling water flow path for connection and the upstream side of the downstream cooling water flow path and for allowing cooling water to flow into the radiator;
A thermostat is provided at a branch portion between the radiator flow path and the downstream-side cooling water flow path. The thermostat allows the cooling water to pass through the first heat exchange flow path until engine warm-up is completed. A urea water thawing device , wherein the cooling water from the cylinder block passage is caused to flow to a second fluid passage downstream of the thermostat so as to be heated . A branched exhaust passage formed by branching from an exhaust passage between the selective reduction catalyst and the first heat exchange passage;
A flow path switching valve provided at a branch portion between the exhaust passage and the branch exhaust passage to switch an exhaust flow path,
When the temperature of the fluid raised in temperature in the first heat exchange channel is equal to or lower than a first upper threshold value that prevents boiling of the fluid, the channel switching valve causes the exhaust channel to pass through the first heat exchange. When the temperature of the fluid raised in temperature in the first heat exchange flow path becomes higher than the first upper limit threshold, the exhaust flow path is changed to the branch exhaust passage. The urea water thawing device according to claim 1 to be switched.   The pump is stopped when the temperature of the fluid flowing into the second heat exchange channel or the temperature of the urea water in the urea water tank is higher than a second upper limit threshold value for preventing the urea water from deteriorating. The urea water thawing device according to claim 1 or 2. A bypass that connects the first fluid flow path and the second fluid flow path positioned upstream of the cylinder block to bypass the cooling water flow path from the second heat exchange flow path. A flow path;
A bypass valve that switches the cooling water flow path to the second heat exchange flow path or the bypass flow path, and
When the temperature of the cooling water flowing into the second heat exchange channel or the temperature of the urea water in the urea water tank becomes higher than the second upper limit threshold, the bypass valve The urea water thawing device according to claim 3 , wherein the urea water thawing device is switched to the bypass flow path. The exhaust purification system includes a urea water pump that pumps urea water from the urea water tank to the injector;
The urea water thawing device according to any one of claims 1 to 4 , wherein the second heat exchange channel is introduced into the urea water tank and the urea water pump. The pump, urea water decompression device according to any one of claims 1-5 which is electrically driven pump.