JP2019002315A - Reducing agent feeding device - Google Patents

Abstract

A reducing agent supply device capable of preventing erroneous detection of a reducing agent sensor is provided. A reducing agent supply device is provided for reducing agent tanks for storing a reducing agent used as a reducing agent for reducing and purifying NOx in exhaust gas of an internal combustion engine, and for exhaust gas passing through an exhaust passage of the internal combustion engine. A reducing agent supply path for supplying the reducing agent to the reducing agent injector that injects the reducing agent, and an opening at the downstream end located in the reducing agent tank, and the reducing agent remaining in the reducing agent supply path is removed from the reducing agent tank. A reducing agent recovery path that is returned to the opening, a reducing filter that is provided in the vicinity of the opening, returns to the reducing agent tank through the reducing agent recovery path, and a separation filter that separates air contained in the reducing agent. . [Selection] Figure 2

Description

  The present invention relates to a reducing agent supply apparatus.

  Selective catalytic reduction that reduces NOx to nitrogen and water using urea water as a reducing agent as an exhaust gas purification system for purifying NOx in exhaust gas of diesel engines mounted on vehicles such as trucks and buses (SCR: Selective Catalytic Reduction) system has been developed (see, for example, Patent Document 1).

  The SCR system supplies urea water stored in a urea water tank to an exhaust pipe upstream of the SCR device, hydrolyzes urea with heat of exhaust gas or a catalyst in the SCR device, and generates ammonia. NOx is reduced by the catalyst in the apparatus. An appropriate amount of urea water is injected by, for example, a urea water injector provided in the exhaust pipe.

  The urea water is supplied to the urea water injector by a supply module including a supply pump and a urea water pressure sensor. The supply module is connected to the urea water tank through the suction line, and the urea water sucked up from the urea water tank through the suction line is supplied to the urea water injector through the pressure feed line connecting the supply module and the urea water injector. . The opening and closing of the urea water injector is controlled by a DCU (Dosing Control Unit) according to the detection value of a NOx sensor provided upstream and / or downstream of the SCR device.

  After stopping the engine (key-off) and stopping the injection of urea water, surplus urea water remaining in the pumping line is returned from the pumping line to the urea water tank by the return line.

JP 2000-303826 A

  However, when the excess urea water remaining in the pumping line is returned to the urea water tank, the urea water is bubbled by being depressurized. That is, a large amount of bubbles are formed in the urea water returned to the urea water tank.

  For this reason, there is a problem that a large amount of formed bubbles may interfere with detection of the urea water sensor provided in the urea water tank, and may cause erroneous detection of the urea water sensor. If erroneous detection of the urea water sensor occurs, an appropriate amount of urea water cannot be supplied to the urea water injector, and consequently the purification process of NOx in the exhaust gas is hindered.

  The objective of this invention is providing the reducing agent supply apparatus which can prevent the misdetection of a reducing agent sensor.

The reducing agent supply apparatus according to the present invention is:
A reducing agent tank for storing a reducing agent used as a reducing agent for reducing and purifying NOx in exhaust gas of an internal combustion engine;
A reducing agent supply path for supplying the reducing agent to a reducing agent injector that injects the reducing agent into exhaust gas passing through an exhaust passage of the internal combustion engine;
A reducing agent recovery path having an opening at a downstream end located in the reducing agent tank and returning the reducing agent remaining in the reducing agent supply path to the reducing agent tank;
A separation filter that is provided in the vicinity of the opening and separates the reducing agent that passes through the reducing agent recovery path and is returned to the reducing agent tank and the air contained in the reducing agent;
Is provided.

  According to the present invention, erroneous detection of the reducing agent sensor can be prevented.

It is a figure which shows an example of a structure of the SCR system in this Embodiment. It is a figure which shows an example of a structure in the urea water tank in this Embodiment. It is a figure which shows the modification of the structure in the urea water tank in this Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of the SCR system 100 in the present embodiment. An SCR device 11 is connected to an exhaust pipe 10 of a diesel engine mounted on a vehicle such as a truck or a bus. A urea water injector 12 that injects urea water U is provided upstream of the SCR device 11, and a NOx sensor 13 is provided upstream and downstream of the SCR device 11.

  The SCR device 11 is generated by hydrolyzing urea water injected from a urea water injector 12 (also referred to as a dosing valve, corresponding to the reducing agent injector of the present invention) at a high temperature of exhaust gas or by a catalyst in the SCR device 11. The exhaust gas is purified by reducing the NOx into nitrogen gas and water vapor by the catalyst in the SCR device 11 using the ammonia. The NOx sensor 13 downstream of the SCR device 11 detects NOx in the exhaust gas after processing by the SCR device 11, monitors that the NOx value in the exhaust gas downstream of the SCR device 11 is steady, and sends it to the DCU 14. Send measurement values.

  The NOx sensor 13 has been described as being disposed upstream and downstream of the SCR device 11, but is not necessarily disposed both upstream and downstream, and is disposed upstream and / or downstream of the SCR device 11. Just do it.

  The detection value of the NOx sensor 13 is input to a DCU (Dosing Control Unit) 14. The DCU 14 performs opening / closing control of the urea water injector 12 according to the detection value of the NOx sensor 13. Although not shown, the DCU 14 performs the following operations when the CPU reads and executes a predetermined program from the memory, for example.

  The DCU 14 controls the urea water injector 12 according to the detection value from the NOx sensor 13 upstream of the SCR device 11. Specifically, the DCU 14 calculates the amount and timing of injecting the urea water U from the urea water injector 12, drives the supply pump 18 to increase the urea water U to a specified pressure, and opens and closes the urea water injector 12. The amount of urea water U calculated at the calculated timing is injected.

  The urea water U injected from the urea water injector 12 is stored in a urea water tank 15 (corresponding to the reducing agent tank of the present invention). When the urea water injector 12 is in the open state, the urea water U is sucked into the supply pump 18 of the supply module 17 from the suction line 16 and is pumped through the pressure feed line 20 (corresponding to the “reducing agent supply path” of the present invention). 12 is pumped. At this time, foreign matters in the urea water are removed through the filter 19. Further, after the diesel engine is stopped and the urea water injection from the urea water injector 12 is stopped (when the urea water injector 12 is in the closed state), the excess urea water U remaining in the pumping line 20 is filtered by the filter 19. Is returned to the urea water tank 15 by a return line 21 (also referred to as a reflux pipe, corresponding to the “reducing agent recovery path” of the present invention).

  An ultrasonic or optical urea water sensor 22 (corresponding to the reducing agent sensor of the present invention) is provided in the urea water tank 15. The urea water sensor 22 detects the level and quality (for example, temperature or urea concentration) of the urea water U in the urea water tank 15 and transmits it to the DCU 14. For example, when the level of the urea water U in the urea water tank 15 is detected by the urea water sensor 22, the remaining amount of the urea water U is detected from the level of the urea water U detected by the urea water sensor 22, and the urea water U As a guide for replenishment.

  By the way, when the excess urea water U remaining in the pumping line 20 is returned to the urea water tank 15, the urea water U is bubbled by being depressurized. That is, a large amount of bubbles (air) are formed in the urea water U returned to the urea water tank 15.

  For this reason, the large amount of bubbles formed may interfere with the detection of the urea water sensor 22 provided in the urea water tank 15 and may cause erroneous detection of the urea water sensor 22. If erroneous detection of the urea water sensor 22 occurs, an appropriate amount of urea water U cannot be supplied to the urea water injector 12, and this will hinder the purification process of NOx in the exhaust gas.

  Therefore, in the present embodiment, the separation filter 30 (see FIG. 2) that separates the urea water U that passes through the return line 21 and is returned to the urea water tank 15 and the air contained in the urea water U is used as the urea. It is provided in the water tank 15.

  FIG. 2 is a diagram illustrating an example of the configuration in the urea water tank 15. As shown in FIG. 2, the urea water U stored in the urea water tank 15 is sucked into the supply pump 18 of the supply module 17 from the suction line 16 when urea water is injected. On the other hand, after the urea water injection from the urea water injector 12 is stopped, surplus urea water U remaining in the pumping line 20 is returned from the pumping line 20 to the urea water tank 15 by the return line 21.

  The return line 21 has an opening 21 a at the downstream end located in the urea water tank 15. A separation filter 30 is provided in the vicinity of the opening 21a. Specifically, the separation filter 30 has an elongated cylindrical shape that extends from the vicinity of the opening 21 a to above the liquid surface of the urea water U stored in the urea water tank 15 and covers the return line 21. The separation filter 30 is made of an alkali-resistant material (for example, ceramic) so that it can withstand urea water.

  Further, the outer peripheral wall of the separation filter 30 is formed in a porous shape having a large number of holes 32 (pores), and urea water U that passes through the return line 21 and is returned to the urea water tank 15 and the urea water. The air contained in U is separated and only the urea water U separated from the air is allowed to pass through. The average diameter of the holes 32 (pores) is, for example, 30 μm or less. On the other hand, the air separated from the urea water U moves toward the liquid level of the urea water U, and then escapes above the liquid level from the opening 30 a formed at the upper end of the separation filter 30.

  For this reason, bubbles are prevented from forming in the urea water U returned to the urea water tank 15, that is, the bubbles do not interfere with the detection of the urea water sensor 22. Can be prevented. The urea water tank 15, the pressure feed line 20, the return line 21, and the separation filter 30 correspond to the reducing agent supply device of the present invention.

  In the above embodiment, the separation filter 30 has been described with respect to an example in which the separation filter 30 extends from the vicinity of the opening 21a of the return line 21 to above the liquid level of the urea water U stored in the urea water tank 15. The present invention is not limited to this. For example, as shown in FIG. 3, the separation filter 30 extends from the vicinity of the opening 21 a of the return line 21 to below the level of the urea water U stored in the urea water tank 15, and You may have the cylinder shape to cover.

  In this case, an air passage 34 (for example, a hose) that allows the air separated by the separation filter 30 to escape above the surface of the urea water U is provided at the upper end of the separation filter 30. Therefore, the opening 30 a is not formed at the upper end of the separation filter 30. With this configuration, the air separated from the urea water U passes through the air passage 34 and moves toward the liquid surface of the urea water U, and then escapes from the open end of the air passage 34 above the liquid surface. . For this reason, bubbles are prevented from forming in the urea water U returned to the urea water tank 15, that is, the bubbles do not interfere with the detection of the urea water sensor 22. Can be prevented. Moreover, compared with the structure shown in FIG. 2, the manufacturing cost can be reduced by the amount that the length in the longitudinal direction of the separation filter 30 is shortened.

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

  The present invention is useful as a reducing agent supply device that can prevent erroneous detection of a reducing agent sensor.

10 exhaust pipe 11 SCR device 12 urea water injector (reducing agent injector)
13 NOx sensor 14 DCU
15 Urea water tank (reducing agent tank)
16 Suction line 17 Supply module 18 Supply pump 19 Filter 20 Pressure feed line 21 Return line 22 Urea water sensor (reducing agent sensor)
30 Separation filter 32 Hole 34 Air passage 100 SCR system

Claims (5)

A reducing agent tank for storing a reducing agent used as a reducing agent for reducing and purifying NOx in exhaust gas of an internal combustion engine;
A reducing agent supply path for supplying the reducing agent to a reducing agent injector that injects the reducing agent into exhaust gas passing through an exhaust passage of the internal combustion engine;
A reducing agent recovery path having an opening at a downstream end located in the reducing agent tank and returning the reducing agent remaining in the reducing agent supply path to the reducing agent tank;
A separation filter that is provided in the vicinity of the opening and separates the reducing agent that passes through the reducing agent recovery path and is returned to the reducing agent tank and the air contained in the reducing agent;
A reducing agent supply device comprising: The separation filter has a cylindrical shape extending from the vicinity of the opening to above the liquid surface of the reducing agent stored in the reducing agent tank and covering the reducing agent recovery path.
The reducing agent supply apparatus according to claim 1. The separation filter has a cylindrical shape extending from the vicinity of the opening to below the liquid surface of the reducing agent stored in the reducing agent tank and covering the reducing agent recovery path,
An air passage for allowing the air separated by the separation filter to escape above the liquid surface is provided in the separation filter;
The reducing agent supply apparatus according to claim 1. The separation filter is a material having alkali resistance,
The reducing agent supply apparatus of any one of Claims 1-3. The separation filter has pores through which only the reducing agent passes,
The average diameter of the pores is 30 μm or less.
The reducing agent supply apparatus of any one of Claims 1-4.

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