JP4137831B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust purification device for an engine (hereinafter referred to as “exhaust purification device”) that uses a liquid reducing agent to reduce and remove nitrogen oxide (NOx) in exhaust gas, and in particular, the liquid reducing agent is frozen. The present invention also relates to a technology that enables the supply of the engine quickly after the engine is started.

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device disclosed in Japanese Patent Laid-Open No. 2002-4840 (Patent Document 1) has been proposed.
Such an exhaust purification device arranges a NOx reduction catalyst in the exhaust passage of the engine, and injects and supplies the reducing agent stored in the tank upstream of the exhaust of the NOx reduction catalyst, thereby reducing NOx and reducing agent in the exhaust. A catalytic reduction reaction is performed to purify NOx into harmless components.

For the reduction reaction, ammonia having good reactivity with NOx is used. Ammonia is obtained by heating the solid urea stored in the tank to a liquid state, supplying it into the exhaust, and hydrolyzing it using exhaust heat and water vapor in the exhaust.
Furthermore, in order to accurately supply a necessary amount of urea into the exhaust gas, a liquid reducing agent such as an aqueous urea solution may be used instead of using solid urea. In this case, since the liquid reducing agent may freeze in the tank when it is cold, a heater is provided in the tank to heat the frozen liquid reducing agent during engine operation.
Japanese Patent Laid-Open No. 2002-4840

However, even if the heater is provided in the tank as described above, since the capacity of the tank is large, it takes time until the frozen liquid reducing agent is thawed. Therefore, after the engine is started, too late supply of the liquid reducing agent to the exhaust gas, NOx is a risk would Tsu such is sufficiently reduced and removed kuna from the exhaust.
Therefore, in view of the conventional problems as described above, the present invention comprises two tanks, a main tank and a sub-tank having a smaller capacity than the main tank, so that the liquid reducing agent in the sub-tank is electrically discharged after the engine is started. An object of the present invention is to provide an exhaust purification device that can be supplied quickly after starting the engine even if the liquid reducing agent is frozen by heating with a heater.

For this reason, the invention according to claim 1 is an exhaust emission control device for an engine, comprising a reduction catalyst disposed in an engine exhaust passage for reducing and purifying nitrogen oxides using a liquid reducing agent, and a liquid reducing agent. A main tank for storing, a sub-tank having a capacity smaller than that of the main tank and storing the liquid reducing agent supplied from the main tank; and a reducing agent for supplying the liquid reducing agent stored in the sub-tank to the reduction catalyst Supply means, heating means for heating the liquid reducing agent stored in the main tank by a heat medium having the engine as a heat source, and an electric heater for heating the liquid reducing agent stored in the sub tank. The sub-tank is formed of a member having excellent thermal conductivity, and has an inner wall formed in a substantially tapered shape whose diameter expands downward, and the electric heater , Characterized in that it is disposed below the sub-tank.

According to a second aspect of the invention, said sub-tank, the so liquid reducing agent flows from the main tank, you being disposed below the main tank.

According to a third aspect of the present invention, a vent pipe for introducing air into the sub tank is provided.
According to a fourth aspect of the present invention, there is provided heating means for heating the vent pipe.
According to a fifth aspect of the present invention, there is provided heat insulating means for suppressing heat dissipation from the sub tank to the outside air.

The invention according to claim 6 is engine operation detecting means for detecting whether or not the engine is operating, wall surface temperature detecting means for detecting the temperature of the wall surface of the sub tank, and the engine is operating. And an operation control means for operating the electric heater when the temperature of the wall surface of the sub tank is equal to or lower than a predetermined value.
According to a seventh aspect of the present invention, after the operation of the reducing agent temperature detecting means for detecting the temperature of the liquid reducing agent in the main tank and the electric heater, the temperature of the liquid reducing agent in the main tank is higher than a predetermined value. And a first stop control means for stopping the operation of the electric heater.

The invention described in claim 8 is characterized in that it comprises second stop control means for stopping the operation of the electric heater after a predetermined time has elapsed since the operation of the electric heater.
The invention according to claim 9 is characterized in that a concentration sensor for detecting the concentration of the liquid reducing agent is attached to the sub tank.

According to the first aspect of the present invention, the liquid reducing agent stored in the main tank is heated by the heat medium having the engine as a heat source by the heating means. Further, the liquid reducing agent stored in the sub tank is heated by the electric heater. Since the sub tank has a smaller capacity than the main tank, even if the liquid reducing agent in the sub tank is frozen, it is immediately thawed. Thereby, a liquid reducing agent can be supplied rapidly.
Further, the sub tank is formed of a member having excellent heat conductivity, and an electric heater is provided below the sub tank, so that the liquid can be efficiently heated from the surroundings while convection of the liquid reducing agent in the sub tank.
Further, since the inner wall of the sub tank is formed in a substantially tapered shape that expands downward, the liquid reducing agent that has been frozen and adhered to the inner wall is easily peeled off and is not caught on the inner wall. Fall to the bottom of the. And since it heats with the electric heater provided in the lower part of the sub tank, the liquid reducing agent in a sub tank can be thawed efficiently.

According to the second aspect of the present invention, since the liquid reducing agent flows from the main tank to the sub tank, it is not necessary to newly provide a device for supplying the liquid reducing agent from the main tank to the sub tank, and an increase in cost can be suppressed. The

According to the invention described in claim 3 , even if the inflow path of the liquid reducing agent from the main tank to the sub tank is blocked, the air passes through the vent pipe and flows into the sub tank. Thereby, the liquid reducing agent in a sub tank can be discharged | emitted smoothly.
According to invention of Claim 4 , even if a liquid reducing agent freezes in a vent pipe, since it can be thawed immediately, obstruction | occlusion of a vent pipe can be suppressed.

According to the fifth aspect of the present invention, heat radiation from the sub tank to the outside air is suppressed, and the liquid reducing agent in the sub tank can be efficiently heated by the electric heater.
According to the sixth aspect of the present invention, when the engine is in operation and the liquid reducing agent in the sub tank is frozen, the electric heater is automatically operated, and the supply shortage of the liquid reducing agent can be suppressed.

According to the seventh aspect of the invention, since the operation of the electric heater is stopped when the liquid reducing agent can be supplied from the main tank, the consumption of electric power used by the electric heater can be suppressed.
According to the invention described in claim 8 , the operation of the electric heater is stopped after a predetermined time has elapsed since the operation of the electric heater. At this time, the consumption of electric power used by the electric heater can be suppressed by setting the predetermined time to the time until the liquid reductant in the frozen sub tank is thawed by the electric heater.

According to the ninth aspect of the present invention, even if the liquid reducing agent is frozen, the concentration can be detected in a short time after the engine is started.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of an exhaust emission control device for an engine according to the present invention.
An exhaust pipe 2 that is an exhaust passage of the engine 1 is provided with a NOx reduction catalyst 3 that reduces and purifies NOx. An injection nozzle 4 for injecting and supplying urea aqueous solution as a liquid reducing agent into the exhaust pipe 2 is disposed upstream of the NOx reduction catalyst 3. The liquid reducing agent may be an aqueous ammonia solution in addition to the aqueous urea solution.

  An aqueous urea solution stored in the tank 6 is supplied to the injection nozzle 4 together with compressed air by a reducing agent supply device 5. Further, in order to control the flow rate of the urea aqueous solution supplied to the NOx reduction catalyst 3 according to the engine operating state, an injection controller 7 incorporating a computer is provided. The injection controller 7 controls the reducing agent supply device 5 according to the engine operating state, that is, the engine rotation speed and the fuel injection amount input via a CAN (Controller Area Network).

As illustrated in FIG. 2, the tank 6 includes a main tank 10 and a sub tank 11 having a smaller capacity than the main tank 10.
The main tank 10 and the sub tank 11 are connected in communication so that the urea aqueous solution in the main tank 10 flows into the sub tank 11. The aqueous urea solution in the sub tank 11 is supplied to the reducing agent supply device 5 through the pipe 12.

The main tank 10 is provided with a heat exchanger 13 (heating means) that heats the urea aqueous solution in the main tank 10 by circulating the cooling water of the engine 1 through a pipe provided therein. The main tank 10 is provided with a reducing agent temperature sensor 14 for detecting the temperature of the urea aqueous solution in the main tank 10.
On the other hand, in the sub tank 11, when the urea aqueous solution in the tank 6 is frozen, the urea aqueous solution in the main tank 10 is thawed by heating by the heat exchanger 13 after the engine 1 is started, and the reducing agent supply device 5 The amount of urea aqueous solution necessary for reducing and purifying NOx in the exhaust gas can be stored before the urea aqueous solution can be supplied to the exhaust gas. The inner wall 11a of the sub tank 11 is formed in a substantially tapered shape that increases in diameter downward. An electric heater 15 for heating the urea aqueous solution in the sub tank 11 is provided below the sub tank 11. The periphery of the sub tank 11 is covered with a heat insulating material 16 so as to suppress heat radiation from the sub tank 11 to the outside air.

The upper part of the sub tank 11 is connected to the upper part of the main tank 10 through a vent pipe 17. The ventilation pipe 17 is covered with a heat insulating material 18 at least around the portion below the maximum liquid level of the main tank 10.
The sub tank 11 is provided with a wall surface temperature sensor 19 for detecting the temperature of the wall surface. Further, the sub tank 11 is provided with a concentration sensor 20 for detecting the concentration of the urea aqueous solution therein. The concentration of the aqueous urea solution detected by the concentration sensor 20 is output to the injection controller 7 and is used, for example, for operation control of the reducing agent supply device 5.

A controller 21 that inputs the temperature of the aqueous urea solution from the reducing agent temperature sensor 14, the temperature of the wall surface from the wall surface temperature sensor 19, and the operating state of the engine 1 via the CAN, and controls the operation of the electric heater 15. Is provided.
Here, the control procedure of the electric heater 15 in the controller 21 in the embodiment of the exhaust gas purification apparatus of the present invention will be described with reference to FIG. First, the controller 21 is supplied with power by turning on a power switch such as a key switch and starts control. The control according to the flowchart shown in the figure is repeatedly performed at predetermined time intervals.

First, in step 1 (denoted as S1 in the figure, the same applies hereinafter), it is determined from the operating state of the engine 1 input via the CAN whether or not the engine 1 is in operation. If it is in operation, go to step 2. If not, go to END. Note that the processing in step 1 corresponds to engine operation detection means.
In step 2, the wall surface temperature Ta is input from the wall surface temperature sensor 19, and it is determined whether or not it is equal to or less than a predetermined value T1. When the wall surface temperature Ta is equal to or lower than the predetermined value T1, the process proceeds to step 3. When the value is higher than the predetermined value T1, the process proceeds to END. The predetermined value T1 may be set slightly higher than the freezing temperature of the urea aqueous solution.

In step 3, the operation of the electric heater 15 is started. In addition, the process of steps 1-3 corresponds to an operation control means.
In step 4, the temperature Tb of urea water is input from the reducing agent temperature sensor 14, and it is determined whether or not it is higher than a predetermined value T1. When the temperature Tb of the urea water is higher than the predetermined value T1, the process proceeds to step 5. When the temperature Tb of the urea water is equal to or lower than the predetermined value T1, step 4 is repeated.

In step 5, the operation of the electric heater 15 is stopped. Then, the process proceeds to END. The processes in steps 4 and 5 correspond to the first stop control means.
According to the above configuration, the exhaust of the engine 1 passes through the exhaust pipe 2 and is guided to the NOx reduction catalyst 3. At this time, the injection controller 7 controls the operation of the reducing agent supply device 5 based on the rotational speed of the engine 1 and the fuel injection amount, so that the urea aqueous solution in an amount suitable for the engine operating state is injected together with the compressed air into the injection nozzle 4 To the exhaust pipe 2 upstream of the NOx reduction catalyst 3. The aqueous urea solution injected and supplied into the exhaust pipe 2 is hydrolyzed by the exhaust heat and the water vapor in the exhaust to produce ammonia. The produced ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 3 to be purified into water and harmless gas.

  Since the main tank 10 is provided with the heat exchanger 13 using the cooling water of the engine 1, the urea water solution in the main tank 10 is heated by the cooling water when the engine 1 is operated. Further, the sub-tank 11 is provided with an electric heater 15, and when the engine 1 is operated, the electric heater 15 is operated when the wall surface temperature of the sub-tank 11 is equal to or lower than a predetermined value T 1. The aqueous solution is heated by the electric heater 15. At this time, the sub-tank 11 has a capacity enough to store a necessary amount of urea aqueous solution from when the engine 1 is started until the urea aqueous solution can be supplied from the main tank 10. The aqueous urea solution is immediately thawed, and the aqueous urea solution can be quickly injected into the exhaust pipe 2. Thereby, insufficient supply of the urea aqueous solution into the exhaust pipe 2 can be suppressed.

  Since the heat insulating material 16 is provided around the sub tank 11, heat radiation from the sub tank 11 to the outside air is suppressed, and the urea aqueous solution in the sub tank 11 can be efficiently heated by the electric heater 15. In addition, the sub tank 11 is formed of a member having excellent thermal conductivity, and the electric heater 15 is provided in the lower part thereof, so that the urea aqueous solution in the sub tank 1 can be efficiently heated from the surroundings while convection is performed. . Furthermore, since the inner wall 11a of the sub tank 11 is formed in a substantially tapered shape that expands downward, the urea aqueous solution that freezes and adheres to the inner wall 11a is easily peeled off and is caught on the inner wall 11a. It falls to the lower part of the sub tank 11 without. And since it heats with the electric heater 15 provided in the lower part of the sub tank 11, the urea aqueous solution in the sub tank 11 is thawed efficiently.

Further, since the controller 21 controls the operation of the electric heater 15 to stop when the temperature of the aqueous urea solution in the main tank 10 becomes higher than the predetermined value T1, it is possible to supply the aqueous urea solution from the main tank 10. At that time, the operation of the electric heater 15 stops. Thereby, consumption of the electric power used with the electric heater 15 can be suppressed.
Since the upper part of the sub tank 11 is connected to the upper part of the main tank 10 through the vent pipe 17, the inlet of the urea aqueous solution from the main tank 10 to the sub tank 11 is blocked by the frozen urea aqueous solution in the main tank 10. Even if it is, air passes through the ventilation pipe 17 from the upper part of the main tank 10 and flows into the sub tank 11. Thereby, the urea aqueous solution in the sub tank 11 can be discharged | emitted smoothly. Furthermore, since the periphery of the vent pipe 17 is covered with the heat insulating material 18, it is possible to prevent the vent pipe 17 from being blocked by freezing of the urea aqueous solution therein.

Further, since the concentration sensor 20 is provided in the sub tank 11, even if the urea aqueous solution is frozen, the concentration can be detected in a short time after the engine is started.
Note that the controller 21 of the present embodiment controls the operation of the electric heater 15 to stop when the temperature of the aqueous urea solution in the main tank 10 is higher than the predetermined value T1, but the predetermined value after the electric heater 15 is activated. The operation of the electric heater 15 may be stopped after the time T2 has elapsed. The predetermined time T <b> 2 may be set to a time until the total amount of the urea aqueous solution in the frozen sub tank 11 is thawed by the electric heater 15. This process by the controller 21 corresponds to a second stop control means.

Further, the upper end of the vent pipe 17 may be extended upward from the maximum liquid level of the main tank 10 to be opened.
Further, an electric heater for heating the vent pipe 17 may be provided. Thereby, even if urea aqueous solution freezes in the ventilation pipe 17, it can be thawed immediately.

Configuration diagram of engine exhaust gas purification apparatus of the present invention Structural diagram of the tank The flowchart which shows the control procedure in the controller same as the above

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust pipe 3 NOx reduction catalyst 5 Reducing agent supply apparatus 10 Main tank 11 Sub tank 11a Inner wall 13 Heat exchanger 14 Reducing agent temperature sensor 15 Electric heater 16 Heat insulating material 17 Ventilation pipe 19 Wall surface temperature sensor 20 Concentration sensor 21 Controller

Claims (9)

A reduction catalyst disposed in the engine exhaust passage for reducing and purifying nitrogen oxides using a liquid reducing agent;
A main tank for storing the liquid reducing agent;
A sub-tank having a smaller capacity than the main tank and storing the liquid reducing agent supplied from the main tank;
Reducing agent supply means for supplying the liquid reducing agent stored in the sub-tank to the reduction catalyst;
Heating means for heating the liquid reducing agent stored in the main tank by a heat medium having the engine as a heat source;
An electric heater for heating the liquid reducing agent stored in the sub tank;
It is configured to include a,
The sub-tank is formed of a member having excellent thermal conductivity, and has a substantially tapered shape in which the inner wall expands downward.
The electric heater, the disposed under the sub-tank, engine exhaust purification device you wherein a.   2. The engine exhaust gas purification apparatus according to claim 1, wherein the sub tank is disposed below the main tank so that a liquid reducing agent flows from the main tank. 3. The engine exhaust gas purification apparatus according to claim 1 or 2 , further comprising a vent pipe for introducing air into the sub tank. The engine exhaust gas purification apparatus according to claim 3 , further comprising heating means for heating the vent pipe. The engine exhaust gas purification apparatus according to any one of claims 1 to 4 , further comprising heat insulating means for suppressing heat radiation from the sub tank to the outside air. Engine operation detecting means for detecting whether or not the engine is operating;
Wall surface temperature detecting means for detecting the temperature of the wall surface of the sub tank;
An operation control means for operating the electric heater when the engine is operating and the temperature of the wall surface of the sub tank is equal to or lower than a predetermined value;
The exhaust emission control device for an engine according to any one of claims 1 to 5 , further comprising: Reducing agent temperature detecting means for detecting the temperature of the liquid reducing agent in the main tank;
First stop control means for stopping the operation of the electric heater when the temperature of the liquid reducing agent in the main tank becomes higher than a predetermined value after the operation of the electric heater;
The exhaust emission control device for an engine according to claim 6 . 7. The engine exhaust gas purification apparatus according to claim 6 , further comprising second stop control means for stopping the operation of the electric heater after a predetermined time has elapsed since the operation of the electric heater. The engine exhaust gas purification apparatus according to any one of claims 1 to 8 , wherein a concentration sensor for detecting a concentration of the liquid reducing agent is attached to the sub tank.

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