JP2010138823A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce initial cost and running cost while securing antifreezing performance of liquid reductant and its precursor. <P>SOLUTION: This exhaust emission control device includes a NOx reducing catalyst 20 using ammonia produced from urea water solution for reducing and eliminating NOx in exhaust gas, an injection nozzle 18 for injecting and supplying the urea water solution into the upstream side of the exhaust gas, a reductant tank 28 for storing the urea water solution, and a supply module 24 for sucking the liquid reductant or its precursor stored therein and forcibly feeding it to the injection nozzle 18. In the state that a suction tube for sucking the urea water solution from the reductant tank 28 passes through one side face wall of the reductant tank 28, the supply module 24 is mounted directly on one side face of the reductant tank 28. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device that uses a liquid reducing agent or a precursor thereof to reduce and purify nitrogen oxides (NOx) in exhaust gas.

As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device described in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed. This exhaust purification apparatus injects and supplies a liquid reducing agent or a precursor thereof according to the engine operating state to the exhaust upstream of the NOx reduction catalyst disposed in the exhaust pipe, and the NOx and reducing agent in the exhaust by the NOx reduction catalyst And NOx is purified to harmless components by a selective reduction reaction. Further, in a cold region, the liquid reducing agent or its precursor may freeze, so that engine cooling water is circulated through the reducing agent tank, and a pipe with an electric heater is employed in the reducing agent supply system.
JP 2000-27627 A

  However, in the conventionally proposed technology, the piping with an electric heater is expensive and the electric power for driving the heater is indispensable, so an increase in initial cost and running cost is inevitable.

  Therefore, in view of the conventional problems as described above, the present invention reexamines the mounting structure of the supply module that sucks and pumps the liquid reducing agent or its precursor from the reducing agent tank, thereby An object of the present invention is to provide an exhaust emission control device that reduces initial costs and running costs while ensuring anti-freezing performance.

  Therefore, in the present invention, a reduction catalyst that is disposed in the engine exhaust pipe and reduces and purifies nitrogen oxides in exhaust using a reducing agent, and a liquid reducing agent or a precursor thereof is injected upstream of the reduction catalyst exhaust. An injection nozzle for supplying, a reducing agent tank for storing the liquid reducing agent or its precursor, and a supply module for sucking the liquid reducing agent or its precursor stored in the reducing agent tank and pumping it to the injection nozzle. In the constructed exhaust purification apparatus, the supply module is directly attached to one side surface of the reducing agent tank in a state where the suction tube for sucking the liquid reducing agent or its precursor penetrates one side wall of the reducing agent tank.

  According to the present invention, since the supply module is directly attached to one side surface of the reducing agent tank with the suction tube penetrating the one side wall of the reducing agent tank, the piping connecting the reducing agent tank and the supply module. Is no longer necessary. For this reason, the piping with an electric heater which connects a reducing agent tank and a supply module becomes unnecessary, and an initial cost and a running cost can be reduced. Further, since the suction tube is not exposed to the outside air, the liquid reducing agent or its precursor existing in the suction tube is difficult to freeze, and the antifreezing performance of the liquid reducing agent or its precursor can be ensured.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the overall configuration of an exhaust emission control device that selectively reduces and purifies NOx contained in engine exhaust using an aqueous urea solution that is a precursor of a liquid reducing agent.

A nitrogen oxidation catalyst 16 that oxidizes nitrogen monoxide (NO) into nitrogen dioxide (NO ₂ ) and an aqueous urea solution are injected along the exhaust circulation direction into the exhaust pipe 14 connected to the exhaust manifold 12 of the engine 10. An injection nozzle 18 to be supplied, a NOx reduction catalyst 20 that reduces and purifies NOx using ammonia generated from an aqueous urea solution, and an ammonia oxidation catalyst 22 that oxidizes ammonia that has passed through the NOx reduction catalyst 20 are in this order. Arranged. Further, the injection nozzle 18 is supplied with a reducing agent via a supply module 24 having a built-in electric pump for sucking and feeding a urea aqueous solution and a dosing module 26 having a flow rate control valve for controlling an injection supply flow rate of the urea aqueous solution. The urea aqueous solution stored in the tank 28 is supplied. Further, in order to prevent the urea aqueous solution from freezing by circulating the engine cooling water to the reducing agent tank 28, an inlet 28A and an outlet 28B of the engine cooling water are respectively formed on the upper surface thereof, and a heat exchanger made of a pipe material is formed here. 28C is connected.

  The supply module 24 and the dosing module 26 are electronically controlled by a dosing control unit (hereinafter referred to as “dosing ECU”) 30 having a built-in computer in order to supply an aqueous urea solution corresponding to the engine operating state from the reducing agent tank 28 to the injection nozzle 18. Is done. The dosing ECU 30 receives an exhaust gas temperature signal from an exhaust gas temperature sensor 32 attached to the exhaust pipe 14 positioned between the nitrogen oxidation catalyst 16 and the injection nozzle 18 and controls the engine 10 electronically. An engine speed signal and a fuel injection amount signal are input from a unit (hereinafter referred to as “engine ECU”) 34. Then, the dosing ECU 30 calculates the urea aqueous solution addition flow rate according to the exhaust temperature, the engine rotation speed, and the fuel injection amount in accordance with a control program stored in a ROM (Read Only Memory) or the like, and supplies based on the calculation result. The electric pump of the module 24 and the flow control valve of the dosing module 26 are controlled. The dosing ECU 30 may be built in the supply module 24.

  As shown in FIG. 2, the supply module 24 has a suction tube 24 </ b> A for sucking urea aqueous solution from the reducing agent tank 28 passing through one side (back) wall of the reducing agent tank 28. It is attached. Here, as shown in FIG. 3, the tip of the suction tube 24 </ b> A is capable of sucking the urea aqueous solution without trouble even when the remaining amount of the urea aqueous solution stored in the reducing agent tank 28 is small. It is desirable to bend toward the bottom surface (the same applies hereinafter). Further, the suction tube 24A is shown in FIGS. 2 and 3 in order to exchange heat with the engine cooling water flowing through the heat exchanger 28C and to be thawed in a short time when the urea aqueous solution existing in the suction tube 24A is frozen. In addition, it is desirable that at least a part thereof be joined to the heat exchanger 28C.

In such an exhaust purification device, the urea aqueous solution injected and supplied from the injection nozzle 18 into the exhaust pipe 14 is hydrolyzed by the exhaust heat and the water vapor in the exhaust and converted into ammonia. This ammonia is selectively reduced with NOx in the exhaust gas in the NOx reduction catalyst 20 and purified to harmless water (H ₂ O) and nitrogen (N ₂ ). At this time, in order to improve the NOx purification efficiency by the NOx reduction catalyst 20, NO is oxidized to NO ₂ by the nitrogen oxidation catalyst 16, and the ratio of NO to NO ₂ in the exhaust gas is improved to be suitable for the reduction reaction. The Further, ammonia that has passed through the NOx reduction catalyst 20 is oxidized by the ammonia oxidation catalyst 22 disposed downstream of the exhaust gas, so that ammonia is suppressed from being released into the atmosphere as it is.

  Since the supply module 24 is directly attached to one side surface of the reducing agent tank 28 with the suction tube 24 </ b> A penetrating the one side wall of the reducing agent tank 28, piping connecting the reducing agent tank 28 and the supply module 24. Is no longer necessary. For this reason, the piping with an electric heater which connects the reducing agent tank 28 and the supply module 24 becomes unnecessary, and the initial cost and the running cost can be reduced. Further, since the suction tube 24A is not exposed to the outside air, the urea aqueous solution present in the suction tube 24A is difficult to freeze, and the antifreezing performance of the urea aqueous solution can be ensured.

FIG. 4 shows details of a tank mounting structure in which a reducing agent tank 28 is mounted on the side surface of the vehicle body frame on the premise of a moving vehicle.
A reducing agent tank 28 is attached to the lateral side surface of the side rail 36 constituting the body frame via a bracket 38. Since there are few auxiliary machines between the left and right side rails 36 and below the pair of left and right side rails 36 compared to the outside of the vehicle width, there is a relatively large space. For this reason, the lower part of one side located inside the vehicle width of the reducing agent tank 28 is bulged to the inside through the lower side of the side rail 36, and the supply module 24 is directly attached to the bulged portion. Other configurations are the same as those shown in FIGS. 1 to 3, so refer to the description thereof. In this way, the capacity of the reducing agent tank 28 can be increased while ensuring the antifreezing performance of the urea aqueous solution and reducing the initial cost and running cost.

  The present invention is not limited to an exhaust gas purification device that uses an aqueous urea solution, but can also be applied to an aqueous ammonia solution, a gas oil mainly composed of hydrocarbons, gasoline, kerosene, or the like as a liquid reducing agent or a precursor thereof. It is.

1 is an overall configuration diagram of an exhaust emission control device embodying the present invention. Sectional view showing details of supply module mounting structure Partial sectional view showing the detailed structure of the suction hose and heat exchanger Sectional view showing details of tank mounting structure based on moving vehicle

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 14 Exhaust pipe 18 Injection nozzle 20 NOx reduction catalyst 24 Supply module 24A Suction tube 28 Reductant tank 28A Cooling water inlet 28B Cooling water outlet 28C Heat exchanger 36 Side rail

Claims (4)

A reduction catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides in exhaust using a reducing agent;
An injection nozzle for injecting and supplying a liquid reducing agent or a precursor thereof upstream of the exhaust of the reduction catalyst;
A reducing agent tank for storing the liquid reducing agent or a precursor thereof;
A supply module that sucks the liquid reducing agent stored in the reducing agent tank or a precursor thereof and pumps it to the injection nozzle;
Comprising
The supply module is directly attached to one side of the reducing agent tank in a state where a suction tube for sucking the liquid reducing agent or its precursor from the reducing agent tank penetrates one side wall of the reducing agent tank. Exhaust gas purification device.   The reducing agent tank is attached to the side surface of the side rail that constitutes the vehicle body frame on the outer side of the vehicle width, and the lower part of one side located inside the vehicle width bulges to the inside of the side rail through the lower side of the side rail. 2. The exhaust emission control device according to claim 1, wherein a supply module is directly attached to the bulging portion.   The exhaust purification device according to claim 1 or 2, wherein a tip portion of the suction tube is bent toward a bottom surface of the reducing agent tank.   At least a part of the suction tube is joined to a heat exchanger that heats the liquid reducing agent or its precursor by circulating engine cooling water inside the reducing agent tank. Item 4. The exhaust emission control device according to any one of Items 3 to 3.

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