JP2015081544A - Reductant supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove precipitates deposited at a downstream side of an addition valve in an addition direction for adding a reductant without deteriorating the fuel economy of an internal combustion engine.SOLUTION: An addition valve 1 of a reductant supply device is arranged at an upstream side of a NOx purification catalyst in an exhaust passage 2 of an internal combustion engine, and adds urea water to the exhaust passage 2 in a state that the urea water is atomized by valve-opening drive by an electronic control device 6. The electronic control device 6 performs removal control for removing precipitates deposited at a downstream side of the addition valve 1 in the addition direction as follows. That is, the addition valve 1 is brought into a valve-opened state under a situation that the pressure of the urea water supplied to the addition valve 1 is lowered compared with the case that the addition of the urea water from the addition valve 1 is performed. When the addition valve 1 is brought into the valve-opened state under such a situation, the urea water flows out of the addition valve 1 as indicated by an arrow Y, and the precipitates are dissolved by the urea water and removed. Here, fuel in the internal combustion engine is not used for the removal of the precipitates at this time.

Description

  The present invention relates to a reducing agent supply apparatus.

  As an exhaust gas purification device for an internal combustion engine, a device that reduces and purifies NOx in exhaust gas by the NOx purification catalyst by adding a reducing agent upstream of a selective reduction type NOx purification catalyst provided in an exhaust passage. Are known. In such an exhaust purification device, in order to realize the addition of the reducing agent upstream of the NOx purification catalyst in the exhaust passage, a reduction valve equipped with an addition valve that receives the reducing agent and adds the reducing agent to the exhaust passage. An agent supply device is provided.

  By the way, because the reducing agent is added from the addition valve in a state where the exhaust temperature is low, deposits due to the reducing agent may accumulate downstream in the addition direction of the addition valve in the exhaust passage. Patent Document 1 describes performing removal control for removing the precipitate. In this removal control, the temperature of the exhaust gas flowing through the exhaust passage is raised using the fuel of the internal combustion engine, and thereby the deposit deposited downstream in the addition direction of the addition valve is dissolved and removed.

JP 2010-150979 A

  In the removal control of Patent Document 1, since the fuel of the internal combustion engine is used to raise the temperature of the exhaust gas in order to remove the deposit, it is inevitable that the fuel consumption of the internal combustion engine is deteriorated by that amount.

  The objective of this invention is providing the reducing agent supply apparatus which can remove the deposit deposited downstream of the addition direction of the addition valve for adding a reducing agent, without deteriorating the fuel consumption of an internal combustion engine.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A reducing agent supply device that solves the above-described problem includes an addition valve that receives the supply of the reducing agent and adds the reducing agent for exhaust purification to the exhaust passage of the internal combustion engine, and is deposited downstream in the addition direction of the addition valve. Removal control for removing precipitates by the reducing agent is performed as follows. That is, the addition valve is opened in a state where the pressure of the reducing agent supplied to the addition valve is lower than when the reducing agent is added from the addition valve for exhaust gas purification. . In such removal control, the addition valve is opened under a situation where the pressure of the reducing agent supplied to the addition valve is lower than when the reducing agent is added from the addition valve for exhaust purification. Therefore, the atomized reducing agent is not added from the addition valve, and the reducing agent flows out from the addition valve. The reducing agent flowing out from the addition valve in this way dissolves and removes the deposit deposited downstream in the addition direction of the addition valve. Further, when the deposit is removed in this way, the fuel of the internal combustion engine is not used for the removal, so that the fuel consumption of the internal combustion engine is not deteriorated by the amount of the fuel.

1 is a schematic diagram showing an entire reducing agent supply apparatus.

Hereinafter, an embodiment of a reducing agent supply apparatus will be described with reference to FIG.
As shown in FIG. 1, the addition valve 1 of the reducing agent supply device is provided upstream of the selective reduction type NOx purification catalyst in the exhaust passage 2 of the internal combustion engine. The addition valve 1 is connected to a tank 4 through a pipe 3, and a pump 5 is provided in the middle of the pipe 3. The reducing agent supply device includes an electronic control device 6 that controls the driving of the addition valve 1 and the pump 5. Through the driving of the pump 5 by the electronic control unit 6, the urea water in the tank 4 is supplied to the addition valve 1 through the pipe 3. The addition valve 1 is supplied with urea water in a pressurized state through the drive of the pump 5, and is added to the exhaust passage 2 as indicated by a broken line in a state where the urea water is atomized through the valve opening drive by the electronic control device 6. To do. The mist-like urea water added to the exhaust passage 2 is hydrolyzed by exhaust heat to become ammonia. This ammonia is supplied as a reducing agent to the NOx purification catalyst.

  By the way, when urea water is added from the addition valve 1 under a condition where the exhaust temperature is low, there is a possibility that precipitates such as urea are deposited downstream of the addition valve 1 in the addition direction in the exhaust passage 2 as indicated by a two-dot chain line. There is. In such a state where the deposit is accumulated, the precipitate inhibits the diffusion of the urea water added from the addition valve 1, so that it is inevitable that the urea water becomes difficult to atomize. And if the urea water added from the addition valve 1 becomes difficult to atomize, hydrolysis by the exhaust heat of the urea water becomes difficult to proceed, and NOx reduction by the NOx purification catalyst using ammonia generated by the hydrolysis is efficient. It is not often done. As a result, the NOx purification rate in the exhaust gas at the NOx purification catalyst may be reduced.

  In order to cope with such a situation, the electronic control unit 6 performs removal control for removing precipitates such as urea deposited downstream in the addition direction of the addition valve 1 as follows. That is, the addition valve 1 is opened under a situation in which the pressure of the urea water supplied to the addition valve 1 is lower than when urea water is added from the addition valve 1 for exhaust gas purification. State. Specifically, the addition valve 1 is left open for a longer time than when adding urea water for exhaust purification. Such removal control may be executed in a situation where it is determined that the precipitate has accumulated downstream in the addition direction of the addition valve 1.

Next, the operation of the reducing agent supply device will be described.
The electronic control unit 6 determines whether or not it is possible to determine that precipitates such as urea have accumulated downstream in the addition direction of the addition valve 1.

  As such a situation, for example, a situation in which the concentration of NOx in the exhaust gas downstream of the NOx purification catalyst in the exhaust passage 2 of the internal combustion engine is equal to or higher than a determination level can be given. This is because, when deposits are deposited downstream of the addition valve 1 in the addition direction, the NOx purification rate in the exhaust gas at the NOx purification catalyst is lowered for the reason described above, and thereby NOx in the exhaust gas downstream of the NOx purification catalyst. It is because the density | concentration of becomes high. Regarding the NOx concentration in the exhaust gas downstream of the NOx purification catalyst, a NOx sensor for detecting NOx in the exhaust gas is provided downstream of the NOx purification catalyst in the exhaust passage 2, and based on the detection signal from the NOx sensor. It is possible to ask.

  Further, as a situation where it can be determined that deposits of urea or the like have accumulated downstream in the addition direction of the addition valve 1, when the amount of increase in the cumulative operation time of the internal combustion engine reaches a predetermined value that causes the deposits to deposit, The situation can also be raised. Furthermore, as a situation where it can be judged that precipitates such as urea have accumulated downstream in the addition direction of the addition valve 1, a situation can be given in which the pressure upstream of the addition valve 1 in the exhaust passage 2 is equal to or higher than a judgment value. . This is because if the deposit accumulates downstream in the addition direction of the addition valve 1 in the exhaust passage 2, it becomes difficult for the exhaust to flow through the exhaust passage 2 due to the deposited deposit. This is because the pressure increases. The pressure upstream of the addition valve 1 in the exhaust passage 2 can be obtained based on a detection signal from the pressure sensor provided in the exhaust passage 2 upstream of the addition valve 1.

  The electronic control device 6 executes the above-described removal control when it can be determined that precipitates such as urea have accumulated downstream in the addition direction of the addition valve 1. In this removal control, by maintaining the addition valve 1 in the open state, the urea water flows from the addition valve 1 to the exhaust passage 2 and the pressure of the urea water supplied to the addition valve 1 gradually decreases. The situation becomes lower than when urea water is added from the addition valve 1 for exhaust purification. When the addition valve 1 is maintained in the open state under such circumstances, the atomized urea water is not added from the addition valve 1 and the urea water is indicated by an arrow Y in the figure. Will begin to flow out. In this way, the urea water flowing out from the addition valve 1 dissolves and removes the deposit (two-dot chain line in the figure) deposited downstream in the addition direction of the addition valve 1. Further, when the deposit is removed in this way, the fuel of the internal combustion engine is not used for the removal, so that the fuel consumption of the internal combustion engine is not deteriorated by the amount of the fuel.

According to the embodiment described in detail above, the following effects can be obtained.
(1) Precipitates such as urea accumulated downstream in the addition direction of the addition valve 1 for adding urea water to the exhaust passage 2 can be removed without deteriorating the fuel consumption of the internal combustion engine.

In addition, the said embodiment can also be changed as follows, for example.
In the removal control, the discharge flow rate of the pump 5 may be made lower than when urea water is added from the addition valve 1 for exhaust purification. In this case, the addition valve 1 is opened under a situation in which the pressure of the urea water supplied to the addition valve 1 is lower than when urea water is added from the addition valve 1 for exhaust gas purification. When the valve state is set, the situation can be caused more quickly.

  In addition, about the fall of the discharge flow rate of the said pump 5, you may reduce the discharge flow rate to a value larger than "0" by the rotational speed fall of the pump 5, or to "0" by the drive stop of the pump 5 It may be lowered.

  -Although urea water (ammonia) was illustrated as a reducing agent added from the addition valve 1, other reducing agents can also be used.

  DESCRIPTION OF SYMBOLS 1 ... Addition valve, 2 ... Exhaust passage, 3 ... Piping, 4 ... Tank, 5 ... Pump, 6 ... Electronic control unit.

Claims (1)

An addition valve for adding the reducing agent for purifying exhaust gas to the exhaust passage of the internal combustion engine in response to the supply of the reducing agent, and removal for removing deposits due to the reducing agent accumulated downstream in the addition direction of the addition valve In the reducing agent supply device that performs control,
The removal control is performed under the condition that the pressure of the reducing agent supplied to the addition valve is lower than when the reducing agent is added from the addition valve for exhaust gas purification. A reducing agent supply device characterized in that it is performed by opening the valve.