JP2019078189A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

To suppress an increase in cost caused by adopting a configuration for preventing urea precipitation.SOLUTION: An urea water injection valve 31 for injecting urea water is provided upstream of a selective reduction catalyst 33 in an exhaust pipe 15. An urea water tank 34 and urea water piping 36 serving as a supply route of the urea water to the urea water injection valve 31 include a tank inner heater 38 and a piping heater 39, respectively. When a temperature of urea water supplied to the urea water injection valve 31 is equal to or lower than a prescribed temperature that is predetermined as a temperature that may cause freezing of urea water, an electronic control unit 40 performs ON control of the tank inner heater 38 and the piping heater 39. When an inner wall surface temperature at an urea water collision position in the exhaust pipe 15 is within a precipitation temperature zone predetermined as a temperature zone enabling precipitation of urea on an inner wall surface of the exhaust pipe 15, the electronic control unit 40 performs the ON control of the tank inner heater 38 and the piping heater 39.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system of an internal combustion engine.

  The exhaust gas purification apparatus of Patent Document 1 includes a selective reduction catalyst provided in an exhaust pipe of an internal combustion engine, and a urea water injection valve for adding urea water upstream of the selective reduction catalyst in the exhaust pipe. Moreover, the exhaust gas purification apparatus of patent document 1 is provided with the electrothermal heater in the outer periphery of the exhaust pipe. The electric heater is located at a location corresponding to the location to which the urea added from the urea water injection valve adheres in the extending direction of the exhaust pipe. In the exhaust gas purification apparatus of Patent Document 1, when the electric heater is energized, the portion of the exhaust pipe where the electric heater is provided is heated. Along with this, the urea deposited on the inner wall of the exhaust pipe is melted or pyrolyzed and removed from the inner wall of the exhaust pipe, and new precipitation of urea is suppressed.

JP 2005-214175 A

  In the exhaust gas purification apparatus of Patent Document 1, in order to remove the urea deposited on the inner wall of the exhaust pipe or to suppress the deposition of urea, it is necessary to separately provide an electric heater in the exhaust pipe. Therefore, it contributes to an increase in the cost of the exhaust gas purification apparatus, such as an increase in the number of parts and an increase in the number of assembling steps.

  In order to solve the above problems, the present invention provides a selective reduction catalyst provided in an exhaust pipe of an internal combustion engine, a urea water injection valve for injecting urea water upstream of the selective reduction catalyst in the exhaust pipe, and An electromagnetic heater provided in a supply path of urea water to the urea water injection valve and heating urea water supplied to the urea water injection valve, and a temperature of the urea water supplied to the urea water injection valve are the urea And a heater control unit that turns on the electromagnetic heater when the temperature is lower than or equal to a predetermined temperature determined as a temperature at which water may freeze. As a temperature zone where the inner wall surface temperature of the urea water collision position where the urea water injected from the urea water injection valve collides is a temperature zone higher than the specified temperature and urea may be deposited on the inner wall surface of the exhaust pipe Predetermined deposition If in degrees band turns on controlling the electromagnetic heater.

  According to the above configuration, the temperature of the aqueous urea solution rises under the situation where urea may precipitate on the inner wall surface of the exhaust pipe. Then, if the temperature of the aqueous urea solution rises, when the aqueous urea solution adheres to the inner wall surface of the exhaust pipe, the amount of heat transferred from the inner wall surface to the aqueous urea solution can be reduced. As a result, it is possible to suppress that the temperature of the inner wall surface of the exhaust pipe is lowered due to the adhesion of the urea water, and it becomes easy to maintain the inner wall surface temperature of the exhaust pipe higher than the deposition temperature zone. Therefore, precipitation of urea on the inner wall surface of the exhaust pipe can be suppressed. Moreover, the heating of the above-mentioned urea water is realized by the electromagnetic heater for freeze protection of urea water. Therefore, it is not necessary to separately provide an electromagnetic heater only to suppress the deposition of urea, and the cost increase of the exhaust purification system can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of an internal combustion engine. Explanatory drawing which shows the precipitation temperature zone of urea. The flowchart which shows the on-off control processing of an electromagnetic heater.

Hereinafter, an embodiment of an internal combustion engine 10 to which the exhaust gas purification apparatus of the present invention is applied will be described. First, a schematic configuration of the internal combustion engine 10 will be described.
As shown in FIG. 1, an internal combustion engine 10 is provided with an intake pipe 11 for introducing intake air (external air) from the outside. At a downstream end of the intake pipe 11, an intake manifold 12 for distributing intake air from the intake pipe 11 to a plurality of (four in this embodiment) cylinders 13 is connected. The intake manifold 12 is divided into four branch pipes on the downstream side, and the downstream end of each branch pipe is connected to each cylinder 13. An exhaust manifold 14 for discharging exhaust gas from the inside of each cylinder 13 is connected to each cylinder 13. The exhaust manifold 14 is divided into four branch pipes on the upstream side, and the upstream end of each branch pipe is connected to each cylinder 13. The downstream side of the exhaust manifold 14 is gathered into one, and the downstream end of the exhaust manifold 14 is connected to the exhaust pipe 15.

  The intake pipe 11 is provided with an air flow meter 21 for detecting an intake flow rate GA flowing through the inside of the intake pipe 11. Further, on the downstream side of the air flow meter 21 in the intake pipe 11, a throttle valve 22 for adjusting an intake flow rate GA supplied into each cylinder 13 is provided. The throttle valve 22 adjusts the intake flow rate GA supplied into each cylinder 13 by adjusting the valve opening degree.

  The exhaust pipe 15 is provided with an oxidation catalyst 23 for oxidizing hydrocarbons (HC) in the exhaust gas. The oxidation catalyst 23 is obtained by supporting activated alumina on the surface of a carrier, and oxidizes hydrocarbons to water and carbon dioxide. A particle filter 24 is provided downstream of the oxidation catalyst 23 in the exhaust pipe 15. The particle filter 24 is made of porous ceramic and collects particulate matter (PM) having a predetermined particle diameter or more. Further, on the surface of the particle filter 24, a catalyst for promoting the oxidation of the particulate matter is supported.

  An exhaust temperature sensor 26 for detecting an exhaust temperature TH downstream of the particle filter 24 is provided downstream of the particle filter 24 in the exhaust pipe 15. Unburned fuel that has not been burned in each cylinder 13 travels along the flow of exhaust and reaches the oxidation catalyst 23. The unburned fuel is oxidized in the oxidation catalyst 23, and the temperature of the exhaust gas is increased accordingly. Then, the exhaust gas heated by the oxidation catalyst 23 reaches the particle filter 24, whereby the particulate matter collected by the particle filter 24 is burned and the particle filter 24 is regenerated.

  A urea water injection valve 31 for injecting urea water into the exhaust pipe 15 is provided downstream of the exhaust temperature sensor 26 in the exhaust pipe 15. The urea water injection valve 31 is a normally closed solenoid valve, and is opened when it is energized to inject urea water into the exhaust pipe 15. A dispersion plate 32 is disposed downstream of the urea water injection valve 31 in the exhaust pipe 15. The dispersion plate 32 promotes atomization of the urea water by dispersing the urea water injected from the urea water injection valve 31. The urea contained in the urea water injected from the urea water injection valve 31 is heated by the exhaust gas to be hydrolyzed to generate ammonia gas.

  The selective reduction catalyst 33 (SCR catalyst) is provided downstream of the dispersion plate 32 in the exhaust pipe 15. The selective reduction catalyst 33 reduces nitrogen oxides (NOx) contained in the exhaust gas to nitrogen and water, using ammonia gas derived from urea water injected from the urea water injection valve 31 as a reducing agent. A downstream side of the selective reduction catalyst 33 in the exhaust pipe 15 is connected to a muffler or the like (not shown).

  The urea water injection valve 31 receives supply of urea water from a urea water tank 34 mounted on the vehicle. The urea water tank 34 is configured to be able to store a fixed amount of urea water. In the urea aqueous solution tank 34, a feed pump 35 which pumps up and pressure-feeds the urea aqueous solution in the urea aqueous solution tank 34 is provided. A urea water pipe 36 connecting the feed pump 35 and the urea water injection valve 31 is connected to the feed pump 35. The urea water pumped by the feed pump 35 is supplied to the urea water injection valve 31 via the urea water pipe 36. In this embodiment, the urea aqueous solution tank 34, the feed pump 35, and the urea aqueous solution piping 36 correspond to a supply route of urea aqueous solution to the urea aqueous solution injection valve 31.

  An in-tank temperature sensor 37 is provided in the urea aqueous tank 34 to detect the temperature of the urea aqueous solution stored in the urea aqueous tank 34 as an in-tank temperature TT. Further, in the urea water tank 34, an in-tank heater 38 for heating the urea water stored in the urea water tank 34 is provided. The in-tank heater 38 is an electromagnetic heater, and when the electric power is supplied to the in-tank heater 38, the in-tank heater 38 generates heat to heat the urea water. Further, inside the urea water pipe 36, a pipe heater 39 for heating the urea water pipe 36 is provided. The pipe heater 39 is an electromagnetic heater, and generates heat when electric power is supplied to the pipe heater 39 to heat the urea water pipe 36 and the urea water flowing therethrough. In FIG. 1, a piping heater 39 is illustrated outside the urea water piping 36 for convenience of illustration. In this embodiment, the in-tank heater 38 and the pipe heater 39 correspond to an electromagnetic heater that heats the urea water supplied to the urea water injection valve 31.

  The internal combustion engine 10 configured as described above is controlled by an electronic control unit 40 (ECU). The electronic control unit 40 includes an operation unit that executes various programs (applications), a non-volatile storage unit in which various programs are stored, a volatile memory in which data is temporarily stored when executing a program, etc. Computer with

  A signal indicating the intake flow rate GA is input to the electronic control unit 40 from the air flow meter 21. Further, the electronic control unit 40 receives a signal indicating the exhaust temperature TH from the exhaust temperature sensor 26 and a signal indicating the tank internal temperature TT from the tank internal temperature sensor 37. Various other signals indicating the operating state of the internal combustion engine 10 are also input to the electronic control unit 40.

  The electronic control unit 40 outputs, to the urea water injection valve 31, an operation signal MSr for controlling the injection of urea water from the urea water injection valve 31. The electronic control unit 40 controls the open period of the urea water injection valve 31 based on the detection value of a NOx sensor (not shown) provided in the exhaust pipe 15 and the like. For example, when the NOx concentration detected by the NOx sensor is high, control is performed so that the urea valve injection period of the urea water injection valve 31 is long and a large amount of urea water is injected.

  The electronic control unit 40 outputs an operation signal MSh for controlling the in-tank heater 38 and the pipe heater 39 to the in-tank heater 38 and the pipe heater 39. That is, the electronic control unit 40 functions as a heater control unit that performs on / off control of the in-tank heater 38 and the pipe heater 39. Since the same operation signal MSh is input to the in-tank heater 38 and the pipe heater 39, the in-tank heater 38 and the pipe heater 39 are simultaneously turned on and off.

  The electronic control unit 40 turns on the in-tank heater 38 and the piping heater 39 when there is a possibility that the urea water supplied to the urea water injection valve 31 is frozen. Specifically, when the in-tank temperature TT detected by the in-tank temperature sensor 37 is equal to or lower than a predetermined temperature Tf predetermined as a temperature at which the urea water may freeze, the electronic control unit 40 The on-tank heater 38 and the piping heater 39 are on-controlled. Further, when the in-tank temperature TT detected by the in-tank temperature sensor 37 exceeds the specified temperature Tf, the electronic control unit 40 turns off the in-tank heater 38 and the pipe heater 39. The specified temperature Tf is, for example, zero degrees Celsius to several degrees Celsius.

  The electronic control unit 40 detects the inner wall surface temperature of the urea water collision position where the urea water injected from the urea water injection valve 31 collides among the inner wall surfaces of the exhaust pipe 15 even if the tank temperature TT exceeds the specified temperature Tf. In the case where the estimated temperature Te of is the predetermined deposition temperature zone, the in-tank heater 38 and the piping heater 39 are on-controlled. In the present embodiment, the urea water collision position in the exhaust pipe 15 is the downstream side of the urea water injection valve 31 in the exhaust pipe 15 and the upstream side of the dispersion plate 32.

  Here, as shown in FIG. 2, when the temperature of the urea water collision position of the exhaust pipe 15 is low, even if the urea water collides with and adheres to the inner wall surface of the exhaust pipe 15, the water of the urea water evaporates It is difficult to precipitate solid urea. In addition, urea in urea water is less susceptible to heat-induced alteration and hard to solidify. Therefore, when the temperature of the urea water collision position is low, the amount of urea deposited on the inner wall surface of the exhaust pipe 15 per predetermined urea water injection amount is small.

  When the temperature of the urea water collision position of the exhaust pipe 15 is medium, when the urea water collides with and adheres to the inner wall surface of the exhaust pipe 15, the water of the urea water evaporates to precipitate solid urea. In addition, urea in urea water is degraded by heat and solidifies with the precipitated solid urea. Therefore, when the temperature of the urea water collision position of the exhaust pipe 15 is medium, the amount of deposited urea on the inner wall surface of the exhaust pipe 15 per predetermined amount of urea water injection increases accordingly.

  On the other hand, when the temperature of the urea water collision position of the exhaust pipe 15 is high, even if solid urea precipitates on the inner wall surface of the exhaust pipe 15 or solidified urea solidifies, the solid urea melts and becomes exhaust It can be removed by riding, or it can be vaporized or decomposed by the heat of the exhaust. Therefore, when the temperature of the urea water collision position of the exhaust pipe 15 is high, the amount of urea deposition on the inner wall surface of the exhaust pipe 15 per predetermined urea water injection amount decreases.

  Therefore, in the present embodiment, one point in the temperature zone where the amount of deposited urea increases as the temperature of the urea water collision position of the exhaust pipe 15 increases becomes the first temperature Tx1, and the temperature of the urea water collision position of the exhaust pipe 15 The second temperature Tx2 is a point in the temperature zone in which the amount of deposited urea decreases as the value of f increases. Then, a temperature range between the first temperature Tx1 and the second temperature Tx2 is used as a urea deposition temperature range.

  The first temperature Tx1 and the second temperature Tx2 are determined in advance by performing tests and simulations. For example, the first temperature Tx1 is approximately 100 ° C. to 125 ° C., and the second temperature Tx2 is approximately 275 ° C. to 300 ° C. Therefore, the urea deposition temperature zone defined by the first temperature Tx1 and the second temperature Tx2 is a temperature zone sufficiently higher than the predetermined temperature Tf which is predetermined as the temperature at which the urea water may freeze. .

  Next, the on / off control processing of the piping heater 39 based on the temperature of the urea water collision position of the exhaust pipe 15 by the electronic control unit 40 will be described according to FIG. Note that this control process is repeatedly performed at predetermined control cycles while the internal combustion engine 10 is being driven.

  As shown in FIG. 3, when the on / off control process of the pipe heater 39 based on the temperature of the urea water collision position of the exhaust pipe 15 is executed, the electronic control unit 40 (heater control unit) executes the process of step S11. . In step S11, the electronic control unit 40 calculates an estimated temperature Te which is an estimated value of the inner wall surface temperature of the urea water collision position in the exhaust pipe 15. Specifically, the electronic control unit 40 controls the exhaust temperature TH detected by the exhaust temperature sensor 26, the intake flow rate GA detected by the air flow meter 21, the injection amount of urea water injected from the urea water injection valve 31, urea water injection Based on the urea water temperature Tu that is the temperature of the urea water injected from the valve 31, the estimated temperature Te of the urea water collision position is calculated. When calculating the estimated temperature Te, the electronic control unit 40 calculates the estimated temperature Te to a value closer to the exhaust temperature TH as the intake flow rate GA detected by the air flow meter 21 increases. Further, the electronic control unit 40 calculates the estimated temperature Te to a value lower than the exhaust temperature TH as the injection amount of urea water injected from the urea water injection valve 31 increases and as the urea water temperature Tu decreases.

  As described above, the injection amount of urea water injected from the urea water injection valve 31 is calculated based on the detection value or the like of a NOx sensor (not shown) provided in the exhaust pipe 15. Further, the urea water temperature Tu is handled as the same temperature as the in-tank temperature TT detected by the in-tank temperature sensor 37 when the in-tank heater 38 and the pipe heater 39 are turned off. Further, when the in-tank heater 38 and the pipe heater 39 are turned on, the urea water temperature Tu adds the heating portion of the urea water by the pipe heater 39 to the in-tank temperature TT detected by the in-tank temperature sensor 37. It is treated as an estimated value. That is, when the in-tank heater 38 and the pipe heater 39 are turned on, the urea water temperature Tu is slightly higher than the in-tank temperature TT. When the calculation of the estimated temperature Te is completed, the process of the electronic control unit 40 proceeds to step S12.

  In step S12, the electronic control unit 40 determines whether the estimated temperature Te of the urea water collision position calculated in step S11 is within the urea deposition temperature zone. That is, the electronic control unit 40 determines whether the estimated temperature Te is equal to or higher than the first temperature Tx1 and equal to or lower than the second temperature Tx2. If the estimated temperature Te is less than the first temperature Tx1 or exceeds the second temperature Tx2 (NO in step S12), the process of the electronic control unit 40 proceeds to step S15. If the estimated temperature Te is within the urea deposition temperature zone (YES in step S12), the process of the electronic control unit 40 proceeds to step S13.

  In step S13, the electronic control unit 40 determines whether the urea water temperature Tu injected from the urea water injection valve 31 is equal to or less than a predetermined upper limit temperature Tmax. The upper limit temperature Tmax is set to, for example, about 90 ° C. in order to prevent urea water from boiling in the urea water pipe 36 and the urea water injection valve 31 and generating vapor. If the urea water temperature Tu exceeds the upper limit temperature Tmax (NO in step S13), the process of the electronic control unit 40 proceeds to step S15. If the urea water temperature Tu is less than or equal to the upper limit temperature Tmax (YES in step S13), the process of the electronic control unit 40 proceeds to step S14.

  In step S14, the electronic control unit 40 turns on the in-tank heater 38 and the pipe heater 39. When the in-tank heater 38 and the pipe heater 39 have already been turned on, the on state is maintained. Thereafter, the series of control ends, and the process from step S11 is repeated in the next control cycle.

  On the other hand, when the processing of the electronic control unit 40 shifts to step S15 without satisfying the conditions in step S12 and step S13, the electronic control unit 40 performs off control of the in-tank heater 38 and the piping heater 39. If the in-tank heater 38 and the pipe heater 39 have already been turned off, the off state is maintained. Thereafter, the series of control ends, and the process from step S11 is repeated in the next control cycle.

Next, the operation and effects of the above embodiment will be described.
In the above embodiment, when the temperature of the inner wall surface of the exhaust pipe 15 exceeds the second temperature Tx2, urea is less likely to precipitate on the inner wall surface of the exhaust pipe 15, and even if urea is precipitated, the urea melts. It is then removed by the exhaust, or it is vaporized or pyrolyzed by the heat of the exhaust. Therefore, when the temperature of the inner wall surface of the exhaust pipe 15 is equal to or higher than the second temperature Tx2, the deposition amount of urea on the inner wall surface of the exhaust pipe 15 is limited to a certain amount.

  Here, when the urea water injected from the urea water injection valve 31 collides and adheres to the inner wall surface of the exhaust pipe 15, the heat of the inner wall surface of the exhaust pipe 15 is transmitted to the urea water, and the inner wall surface of the exhaust pipe 15 Is cooled. Therefore, at the urea water collision position where the urea water injected from the urea water injection valve 31 collides among the inner wall surfaces of the exhaust pipe 15, the temperature of the inner wall surface tends to be equal to or lower than the second temperature Tx2 It is easy to deposit. For example, the dispersion plate 32 in the exhaust pipe 15 is configured such that urea water is properly dispersed in a state in which the exhaust pipe 15 is not deposited with urea. Therefore, if an excessive amount of urea is deposited at the urea water collision position in the exhaust pipe 15 and the flow of the exhaust is disturbed, the urea water may not be dispersed properly.

  In this respect, in the above embodiment, when the estimated temperature Te at the urea water collision position of the exhaust pipe 15 is equal to or higher than the first temperature Tx1 and equal to or lower than the second temperature Tx2 defined as the urea deposition temperature zone, The urea water injected from the water injection valve 31 is heated. When the temperature of the urea water rises, when the urea water adheres to the inner wall surface of the exhaust pipe 15, the amount of heat transferred from the inner wall surface to the urea water can be reduced. As a result, the temperature of the inner wall surface of the exhaust pipe 15 can be suppressed from being lowered due to the adhesion of urea water, and the temperature of the inner wall surface of the urea water collision position in the exhaust pipe 15 is higher than the deposition temperature zone. It becomes easy to maintain. Therefore, precipitation of urea on the inner wall surface of the exhaust pipe 15 can be suppressed.

  Moreover, in the above embodiment, the heating of the urea water for suppressing the precipitation of urea is realized by the in-tank heater 38 and the piping heater 39 for preventing the freezing of the urea water. The heater for preventing the urea water from freezing is generally mounted in the internal combustion engine 10 provided with the selective reduction catalyst 33. Therefore, it is not necessary to separately provide a new electromagnetic heater only to suppress the deposition of urea, and the cost increase of the exhaust gas purification apparatus can be minimized.

  Further, in the present embodiment, when the estimated temperature Te at the urea water collision position of the exhaust pipe 15 is within the urea deposition temperature zone, not only the in-tank heater 38 but also the piping heater 39 is on-controlled. Since the amount of urea water in the urea water pipe 36 is smaller than the amount of urea water stored in the urea water tank 34, the supply to the urea water injection valve 31 is performed by turning on the pipe heater 39. The temperature of the aqueous urea solution can be raised quickly.

  Furthermore, in the present embodiment, when the urea water temperature Tu of the urea water injected from the urea water injection valve 31 exceeds the upper limit temperature Tmax (for example, 90 ° C.), the in-tank heater 38 and the piping heater 39 are turned off. Does not heat the urea solution any further. Therefore, it is unlikely that the urea water boils in the urea water pipe 36 to generate vapor, and urea can not be properly injected from the urea water injection valve 31.

The above embodiment can be modified as follows. Moreover, it is also possible to apply a combination of a plurality of modifications as needed.
The overall configuration of the internal combustion engine 10 of the above embodiment is merely an example. For example, although four are illustrated as the number of cylinders 13 in the above embodiment, the number of cylinders 13 does not matter.

  -In addition to each composition illustrated by the above-mentioned embodiment, internal-combustion engine 10 may be provided with an EGR passage which recirculates a part of exhaust to intake pipe 11. Also, for example, the internal combustion engine 10 may be provided with a turbocharger that uses the flow of exhaust to compress intake air. Furthermore, a fuel addition valve may be provided upstream of the oxidation catalyst 23 in the exhaust pipe 15, and fuel may be added from the fuel addition valve when the particulate filter 24 is regenerated.

  In the exhaust pipe 15, another catalyst or the like may be provided instead of or in addition to the oxidation catalyst 23 and the particle filter 24. In addition, although one example of the number of selective reduction catalysts is shown, a second selective reduction catalyst may be provided downstream of the selective reduction catalyst 33.

  The heater may be attached to the outer circumferential surface of the exhaust pipe 15 instead of providing the pipe heater 39 inside the exhaust pipe 15. In this case, the urea water in the exhaust pipe 15 is heated via the exhaust pipe 15.

  In addition to the in-tank heater 38 and the pipe heater 39, an electromagnetic heater may be provided at another location. For example, the feed pump 35 may incorporate an electromagnetic heater. In addition, since the feed pump 35 constitutes a part of the supply path of urea water to the urea water injection valve 31, the electromagnetic heater built in the feed pump 35 is also an electromagnetic heater provided in the supply path. It is.

  The heater 38 in the tank and the pipe heater 39 may be omitted. That is, at least one electromagnetic heater may be provided in the supply path of urea water to the urea water injection valve 31.

  The on-tank heater 38 and the pipe heater 39 may not be on / off controlled at the same time, and both may be on / off controlled separately. For example, when the estimated temperature Te of the urea water collision position in the exhaust pipe 15 is in the urea deposition temperature zone, only the piping heater 39 may be controlled to be on.

  -Although the urea water temperature Tu of the urea water injected from the urea water injection valve 31 was calculated based on the tank temperature TT in the said embodiment, the calculation aspect of the urea water temperature Tu is not restricted to this. For example, if a temperature sensor for detecting the temperature in the urea water pipe 36 is provided downstream of the pipe heater 39 in the urea water pipe 36, the detected temperature of the temperature sensor may be the urea water temperature Tu. If the urea water injection valve 31 has a built-in temperature sensor or a temperature sensor for detecting the temperature in the vicinity of the urea water injection valve 31 is provided, the temperatures detected by these temperature sensors are It may be

  The method of estimating the estimated temperature Te of the urea water collision position in the exhaust pipe 15 can be changed as appropriate. For example, some of the parameters for calculating the estimated temperature Te in the above embodiment may be omitted, or other parameters may be added. If at least the urea water temperature Tu is used as a parameter for calculating the estimated temperature Te, the technology relating to on / off control of the in-tank heater 38 and the piping heater 39 of the above embodiment can be applied.

  The process of determining whether the urea water temperature Tu is equal to or less than the upper limit temperature Tmax may be omitted. For example, the upper limit of the period in which the in-tank heater 38 and the pipe heater 39 are continuously on may be defined. Even with this configuration, boiling of urea water in the urea water pipe 36 can be suppressed. Furthermore, in the heating performance of the in-tank heater 38 and the pipe heater 39, if there is no possibility that the urea water boils in the urea water pipe 36, the in-tank heater 38 corresponding to the urea water temperature Tu and the continuous on period of each heater. And the off control of the piping heater 39 is unnecessary.

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Intake pipe, 12 ... Intake manifold, 13 ... Cylinder, 14 ... Exhaust manifold, 15 ... Exhaust pipe, 21 ... Air flow meter, 22 ... Throttle valve, 23 ... Oxidation catalyst, 24 ... Particle filter, 26 ... exhaust temperature sensor, 31 ... urea water injection valve, 32 ... dispersion plate, 33 ... selective reduction catalyst, 34 ... urea water tank, 35 ... feed pump, 36 ... urea water piping, 37 ... tank temperature sensor, 38 ... tank Internal heater, 39: Piping heater, 40: Electronic control unit, GA: Intake flow rate, TH: Exhaust temperature, TT: Tank temperature, Tf: Specified temperature, Te: Estimated temperature of inner wall temperature, Tu: Urea water temperature, Tx1 ... first temperature, Tx2 ... second temperature.

Claims (1)

A selective reduction catalyst provided in an exhaust pipe of an internal combustion engine,
A urea water injection valve for injecting urea water upstream of the selective reduction catalyst in the exhaust pipe;
An electromagnetic heater provided in a supply path of urea water to the urea water injection valve and heating urea water supplied to the urea water injection valve;
A heater control unit that turns on the electromagnetic heater when the temperature of urea water supplied to the urea water injection valve is equal to or lower than a predetermined temperature predetermined as a temperature at which the urea water may freeze Equipped with
The heater control unit is a temperature zone in which the inner wall surface temperature of the urea water collision position on the inner wall surface of the exhaust pipe where the urea water injected from the urea water injection valve collides is higher than the specified temperature. The exhaust gas control apparatus according to claim 1, wherein the electromagnetic heater is on-controlled when the temperature range is a temperature range that is predetermined as a temperature range that may precipitate on the inner wall surface of the exhaust pipe.