JP2020060160A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device of an internal combustion engine which can perform suction return control capable of making compatible both a suction return (collection) of a sufficient quantity of urea water for the prevention of a malfunction of a gear pump, and the suppression of the dryness of a gear in the gear pump.SOLUTION: An exhaust emission control device of an internal combustion engine comprises a selective reduction-type NOx catalyst 12, a reductant supply device 20 for supplying urea water into an exhaust passage 10 on the upstream side of the catalyst, and a control device 30 for controlling the reductant supply device 20. The reductant supply device 20 includes a urea water tank 24, a urea water addition valve 22, a urea water flow passage 26, and a gear pump 28 which can forwardly and reversely rotate. The control device 30 performs suction return control by reversely rotating the gear pump 28 at a stop of an engine, stops the reverse rotation when a variation of a rotation number of the gear pump 28 is detected during the execution of the reverse rotation, and after a stop of the reverse rotation, forwardly rotates the gear pump 28 by a prescribed minute rotation amount.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine that includes a selective reduction NOx catalyst and a reducing agent supply device that supplies a reducing agent for NOx to the NOx catalyst.

  For example, Patent Document 1 discloses an exhaust emission control device for an internal combustion engine that includes a NOx selective reduction catalyst and a reducing agent supply device that supplies a reducing agent (ammonia) for NOx to the NOx catalyst. This reducing agent supply device includes a urea water tank, an injector (urea water addition valve) that adds urea water, a pipe (urea water flow path) that connects the urea water tank and the urea water addition valve, and the urea water is pressure-fed. It is equipped with a pump.

  In the above exhaust gas purification device, after the engine is stopped, the pump is rotated in the reverse direction to collect the urea water remaining in the urea water supply system including the urea water addition valve and the urea water flow path in the urea water tank. Water recovery processing (suck back control) is executed. This urea water recovery process is executed such that a predetermined amount of urea water remains in the urea water supply system. This predetermined value is determined in consideration of the total volume in the urea water supply system and the increase in the volume of the residual urea water due to expansion due to freezing.

JP, 2005-078643, A JP, 2016-098648, A

  A part that may be damaged due to freezing of the urea water, such as a pump internal pressure sensor, may be incorporated inside the urea water pump. For this reason, in order to prevent a malfunction of the pump due to the damage of the component due to the freeze expansion of the urea water, it is necessary to sufficiently suck the urea water back to the position of such component. On the other hand, when the pump is a gear pump, it is desirable that the suck-back control be performed in consideration of suppressing drying of gears in the gear pump.

  The present invention has been made in view of the above-described problems, and is a suction-back that can achieve both suction-back (recovery) of urea water in an amount sufficient to prevent malfunction of the gear pump and suppression of drying of gears in the gear pump. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine, which is capable of executing control.

An exhaust gas purification apparatus for an internal combustion engine according to the present invention is arranged in an exhaust passage of an internal combustion engine, and uses a selective reducing NOx catalyst that reduces NOx in exhaust gas by using NH ₃ as a reducing agent, and the selective reducing NOx catalyst. A reducing agent supply device that supplies urea water into the exhaust passage on the upstream side,
A control device that controls the reducing agent supply device.
The reducing agent supply device includes a urea water tank that stores the urea water, a urea water addition valve that adds the urea water to the exhaust passage, and a urea water flow that connects the urea water addition valve and the urea water tank. And a gear pump capable of forward and reverse rotation, and forwardly rotating to pump the urea water from the urea water tank to the urea water addition valve.
When the engine is stopped, the control device sucks back the urea water addition valve, the urea water flow passage, and the gear pump so that the urea water remaining in the gear pump moves to the urea water tank. The control is performed, and when the rotation speed fluctuation of the gear pump is detected during the execution of the reverse rotation, the reverse rotation is stopped, and after the reverse rotation is stopped, the gear pump is normally rotated by a predetermined minute rotation amount. Let

  After the urea water is recovered to the position of the gear pump by the suction-back control, the air sucked from the urea water addition valve reaches the gear of the gear pump. As a result, the load on the gear pump decreases, and the pump rotation speed fluctuates. According to the present invention, the suction back (reverse rotation) is stopped when the fluctuation of the pump rotation speed is detected during the reverse rotation of the gear pump for sucking back the urea water. Therefore, the urea water can be collected up to a portion near the gear of the gear pump (that is, in an amount sufficient to prevent malfunction of the gear pump). Then, according to the present invention, after the reverse rotation of the gear pump is stopped, the operation of normally rotating the gear pump by a predetermined minute rotation amount is executed. This can prevent the gears from drying. As described above, according to the present invention, it is possible to execute the suck-back control that makes it possible to both suck back (recover) urea water in an amount sufficient to prevent malfunctions of the gear pump and suppress drying of the gear in the gear pump. .

It is a figure for explaining an example of composition of an exhaust gas purification device of an internal-combustion engine concerning an embodiment of the invention. It is a schematic diagram showing an example of the internal structure of the urea water pump (gear pump) shown in FIG. It is a figure for demonstrating the determination method of the timing which stops the reverse rotation of the urea water pump in the suction back control which concerns on embodiment of this invention. It is a flow chart which shows a routine of processing concerning suck back control concerning an embodiment of the invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the embodiments described below, when the number of each element, the number, the amount, the range, etc. is referred to, the number referred to unless otherwise specified or the principle is clearly specified. However, the present invention is not limited to this. Further, the structures, steps, and the like described in the embodiments below are not necessarily essential to the present invention, unless otherwise specified or clearly specified in principle.

1. System Configuration Example of Exhaust Gas Purification Device FIG. 1 is a diagram for explaining a configuration example of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention. The system shown in FIG. 1 is applied to an internal combustion engine (a diesel engine as an example). A selective reduction type NOx catalyst (SCR (Selective Catalytic Reduction) catalyst) 12 is arranged in an exhaust passage 10 of the internal combustion engine.

A urea water addition valve 22 of the reducing agent supply device 20 is installed in the exhaust passage 10 on the upstream side of the SCR catalyst 12. The urea water addition valve 22 adds (injects) urea water that is a precursor of ammonia (NH ₃ ) into the exhaust passage 10. The urea water injected from the urea water addition valve 22 into the exhaust passage 10 is hydrolyzed to NH ₃ and supplied to the SCR catalyst 12. The SCR catalyst 12 reduces the nitrogen oxides (NOx) in the exhaust gas by using the supplied urea water-derived NH ₃ as a reducing agent.

  As shown in FIG. 1, the reducing agent supply device 20 includes a urea water addition valve 22 and a urea water tank 24, a urea water flow path 26, and a urea water pump 28 as main components. The urea water tank 24 stores urea water. The urea water flow path 26 connects the urea water addition valve 22 and the urea water tank 24. In the example shown in FIG. 1, the urea water pump 28 is arranged at the end of the urea water flow path 26 on the urea water tank 24 side, and most of it is located in the urea water tank 24.

  FIG. 2 is a schematic diagram showing an example of the internal structure of the urea water pump 28 shown in FIG. The urea water pump 28 is a gear pump that utilizes a pair of gears 28a and 28b for pumping urea water as shown in FIG. The urea water pump 28 is, for example, an electric type, and is configured to be rotatable in forward and reverse directions. Further, the urea water pump 28 has a pump rotation speed sensor 28c for detecting the pump rotation speed and a pump internal pressure sensor 28d for detecting the discharge pressure thereof. The pump internal pressure sensor 28d in the example shown in FIG. 2 is located upstream of the pair of gears 28a and 28b in the flow direction of the urea water during execution of the suck-back control described later.

  The system shown in FIG. 1 further includes a control device 30. The control device 30 is a DCU (Dosing Control Unit) that controls the reducing agent supply device 20 (the urea water addition valve 22 and the urea water pump 28). The control device 30 is electrically connected to various sensors that detect various information necessary for controlling the reducing agent supply device 20, such as the pump rotation speed sensor 28c and the pump internal pressure sensor 28d. The control device 30 has a processor and a memory. The memory stores programs and maps necessary for controlling the reducing agent supply device 20. Further, various information is input to the control device 30 from the various sensors described above. The processor determines the operation amount of each actuator (the urea water addition valve 22 and the urea water pump 28) by reading the program from the memory and executing the program while utilizing these pieces of information.

2. Control of the reducing agent supply device The control of the reducing agent supply device 20 by the control device 30 includes urea water injection amount control using the urea water addition valve 22. During execution of the urea water injection amount control, the urea water pump 28 rotates forward to pump the urea water from the urea water tank 24 to the urea water addition valve 22. Then, the urea water addition valve 22 injects the urea water in an amount corresponding to the required urea water injection amount based on, for example, the concentration of NOx discharged from the cylinder of the internal combustion engine and the target NOx purification rate according to the engine operating conditions. .

2-1. Basic operation and problem of suck back control The control of the reducing agent supply device 20 by the control device 30 further includes the following "suck back control". The suck-back control is executed when the engine is stopped in order to prevent damage to the urea water addition valve 22, the urea water flow path 26, and the urea water pump 28 due to freezing of the remaining urea water in the parts. . During the execution of the suck-back control, the urea water pump 28 is rotated in the reverse direction so that the urea water remaining in the above-mentioned portion moves to the urea water tank 24. Note that the urea water addition valve 22 is opened during the execution of the suck-back control.

  Here, inside the urea water pump 28, there are built-in parts such as a pump internal pressure sensor 28d that may be damaged due to freezing of the urea water. Therefore, in order to prevent the malfunction of the urea water pump 28 due to the damage of the component due to the freezing and expansion of the urea water, it is necessary to sufficiently suck the urea water back to the position of such component.

  On the other hand, the following points must be taken into consideration when executing the suck back control. That is, since the gas is sucked from the urea water addition valve 22 when the urea water is sucked back, the gears 28a and 28b may be dried if the sucking back is excessive. When the gears 28a and 28b are dry, the pump efficiency is lowered (so-called air bite occurs) when the urea water pump 28 is subsequently operated, as compared with the case where the gears 28a and 28b are wet. As a result, it takes time to fill the urea water.

2-2. Characteristic part of suck-back control according to the embodiment In view of the above-mentioned problems, the suck-back (recovery) of urea water in an amount sufficient to prevent malfunction of the urea water pump 28 (gear pump) and the gear 28a in the urea water pump 28, In order to achieve both the suppression of drying of 28b, the suck back control of the present embodiment is executed as follows.

  FIG. 3 is a diagram for explaining a method of determining the timing for stopping the reverse rotation of the urea water pump 28 in the suckback control according to the embodiment of the present invention. The suck-back control is executed while controlling the rotation speed of the urea water pump 28 to a predetermined suck-back rotation speed. Therefore, when the suck-back control is started, the pump rotation speed increases toward the suck-back rotation speed as the suck-back time elapses, as shown in FIG. After that, when the air sucked from the urea water addition valve 22 reaches the gears 28a and 28b after the pump rotation speed reaches the suction back rotation speed, the pump rotation speed fluctuates as shown in FIG. More specifically, when the air reaches the gears 28a, 28b, the pump load decreases. As a result, the pump rotation speed instantly increases.

  Therefore, in the present embodiment, in order to detect the above-described fluctuations in the pump rotation speed, it is determined whether or not the amount of change in the pump rotation speed is equal to or greater than a predetermined threshold value during the execution of the suction back control. When this determination is satisfied, it is determined that the air has reached the gears 28a and 28b, and the reverse rotation (suck back) of the urea water pump 28 is stopped.

  Then, in the suck-back control of the present embodiment, after the reverse rotation is stopped by the above method, the operation of rotating the urea water pump 28 forward by a predetermined minute rotation amount is executed. More specifically, this minute rotation amount is a value required to wet the gears 28a and 28b, and is determined in advance by experiments or the like.

2-3. Process of Control Device FIG. 4 is a flowchart showing a routine of a process relating to suck-back control according to the embodiment of the present invention. It is assumed that this routine is started when the engine is stopped (more specifically, when the ignition switch of the vehicle equipped with the internal combustion engine including the exhaust emission control device of the present embodiment is turned off).

  In the routine shown in FIG. 4, the control device 30 first starts sucking back urea water (reverse rotation of the urea water pump 28) in step S100. After that, the process proceeds to step S102.

  In step S102, the control device 30 determines whether or not the pump rotation speed has changed. Specifically, the pump rotation speed sensor 28c is used to determine whether or not the amount of change in the pump rotation speed is equal to or greater than a predetermined threshold. It should be noted that the determination as to whether or not the pump rotation speed has changed in step S102 may be made based on whether or not the pump rotation speed is equal to or greater than a predetermined threshold value, instead of the amount of change in the pump rotation speed.

  If the determination result of step S102 is negative, the process returns to step S100. On the other hand, if this determination result is affirmative, that is, if the fluctuation in the pump rotation speed is detected, the process proceeds to step S104.

  In step S104, the control device 30 stops sucking back the urea water (reverse rotation of the pump). After that, the process proceeds to step S106.

  In step S106, the control device 30 rotates the urea water pump 28 in the forward direction by the minute rotation amount described above. Then, this routine is ended.

3. Effect According to the suck-back control of the present embodiment described above, when a change in the pump rotational speed is detected after starting the suck-back of urea water (reverse rotation of the pump), the suck-back (reverse rotation of the pump) is stopped ( End). As a result, the urea water can be collected up to the parts near the gears 28a and 28b of the urea water pump 28 (that is, in an amount sufficient to prevent the trouble of the urea water pump 28 (gear pump)). In addition, it is also possible to control the amount of sucking back by the reverse rotation of the pump for sucking back by managing the pump reverse rotation time. However, with such a method, it is difficult to accurately control the suck-back amount when the variation in pump efficiency is taken into consideration. On the other hand, according to the method of the present embodiment, fluctuations in the pump rotational speed that are instantaneously obtained when air reaches the gears 28a and 28b (that is, when urea water can be collected near the gears 28a and 28b). Reverse rotation is stopped by using. As a result, the sucking back amount can be controlled more accurately and stably so that the urea water is collected near the gears 28a and 28b.

  Then, according to the suck-back control of the present embodiment, after the reverse rotation of the pump is stopped, the operation of rotating the urea water pump 28 in the normal direction by the minute rotation amount is executed. This can prevent the gears 28a and 28b from drying. Therefore, during the subsequent operation of the urea water pump 28, it is possible to suppress a temporary decrease in the pumping capacity of the urea water pump 28 due to air trapping, and thus it is possible to suppress the time required to fill the urea water.

10 Exhaust passage 12 Selective reduction type NOx catalyst (SCR catalyst)
20 Reducing Agent Supply Device 22 Urea Water Addition Valve 24 Urea Water Tank 26 Urea Water Flow Path 28 Urea Water Pump (Gear Pump)
28a, 28b Gear 28c Pump speed sensor 28d Pump internal pressure sensor 30 Control device

Claims (1)

A selective reduction type NOx catalyst which is arranged in an exhaust passage of an internal combustion engine and uses NH ₃ as a reducing agent to reduce NOx in exhaust gas;
A reducing agent supply device for supplying urea water into the exhaust passage on the upstream side of the selective reduction type NOx catalyst;
A control device for controlling the reducing agent supply device,
Equipped with
The reducing agent supply device,
A urea water tank for storing the urea water,
A urea water addition valve for adding the urea water to the exhaust passage,
A urea water flow path connecting the urea water addition valve and the urea water tank,
A forward and reverse rotation is possible, and a gear pump that pressure-feeds the urea water from the urea water tank to the urea water addition valve by forward rotation,
Including,
The control device is
When the engine is stopped, the urea water addition valve, the urea water flow path and the urea water remaining in the gear pump perform sucking back control for performing reverse rotation of the gear pump so as to move to the urea water tank,
When the rotation speed fluctuation of the gear pump is detected during execution of the reverse rotation, the reverse rotation is stopped, and
An exhaust emission control device for an internal combustion engine, characterized in that, after stopping the reverse rotation, the gear pump is normally rotated by a predetermined minute rotation amount.

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