JP2009133290A - Reducing agent pump control device and reducing agent discharging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducing agent pump control device which can control impeller lock. <P>SOLUTION: The control device is provided with a pump case and an impeller. A pump chamber is formed in the pump case, and the impeller arranged in the pump chamber is rotary-driven by an electric motor part. The control device is applied to a urea water pump used for discharging urea water which reduces nitrogen oxides contained in the exhaust from an engine. The control device is provided with an ECU (control means) and judgment means (S40, S50). The ECU controls the operation of the electric motor part, and the judgment means (S40, S50) judge whether or not the pump-stop state where reduction is not necessary is a long-term stop state where the pump-stop state has been continuing for a predetermined period of time or more. When it is judged by the judgment means (S40, S50) that the pump-stop state is a long-term stop state, the ECU exercises fixation-prevention control by which the electric motor part is operated so that the impeller is temporarily rotary-driven. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reducing agent pump control device and a reducing agent discharge system for reducing nitrogen oxides contained in exhaust gas of an internal combustion engine.

  In recent years, selective catalytic reduction (SCR) type urea SCR systems that reduce NOx (nitrogen oxides) in exhaust gas are being developed in internal combustion engines (particularly diesel engines) applied to automobiles and the like. Some have been put to practical use.

  In this urea SCR system, a selective reduction type NOx purification catalyst (SCR catalyst) is provided in an exhaust pipe of an internal combustion engine, and urea water (urea aqueous solution) as a reducing agent is added to the exhaust pipe upstream thereof. A water addition valve is provided. In such a system, urea water is added to the exhaust pipe by the urea water addition valve, whereby urea water is supplied to the NOx purification catalyst together with the exhaust gas, and the exhaust gas is purified by a NOx reduction reaction on the NOx purification catalyst. The At the time of NOx reduction, ammonia (NH3) is generated by hydrolyzing urea water with exhaust heat, and NOx is selectively reduced by NOx even in an environment with a high oxygen concentration by ammonia in the NOx purification catalyst. Purification will be performed.

Moreover, such a urea SCR system includes a urea water pump that pumps urea water stored in a tank to a urea water addition valve, and the pump includes a pump case that forms a pump chamber therein, a pump chamber And an impeller that is rotationally driven by an electric motor (see, for example, Patent Document 1).
Japanese translation of PCT publication No. 2004-510093

  However, if the pump chamber is not filled for a long time without being filled with urea water (reducing agent aqueous solution), the water component of the urea water adhering to the inner surface of the pump case or the impeller surface evaporates. The urea component (reducing agent component) of the urea water is deposited. Then, the precipitated urea component fixes the impeller to the inner surface of the pump case, and an impeller lock that makes the impeller unable to rotate may occur. In particular, when the impeller is made of resin, if the drive current is supplied to the electric motor in a state where the impeller is locked, the impeller may be damaged.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a reducing agent pump control device in which impeller lock is suppressed.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

In invention of Claim 1,
A reducing agent for discharging a reducing agent aqueous solution for reducing nitrogen oxides contained in exhaust gas of an internal combustion engine, including a pump case that forms a pump chamber therein, and an impeller that is disposed in the pump chamber and is driven to rotate by an electric motor. Applied to the pump,
Control means for controlling the operation of the electric motor, and determination means for determining whether or not the pump stop state that does not require reduction is a long-term stop state that continues for a predetermined time or more,
The control means performs sticking prevention control for operating the electric motor to temporarily rotate the impeller when the determination means determines that the long-term stop state has occurred.

  According to this, when the pump stop state that does not require reduction continues for a predetermined time or more, the impeller is temporarily driven to rotate, so that even if the reducing agent component (for example, urea component) is deposited, the impeller is completely fixed. If the predetermined time is set so that the rotational drive is performed before the reduction, the reducing agent component deposited on the impeller surface can be peeled off. Alternatively, if the predetermined time is set so that the rotation drive is performed before the reducing agent component is deposited, the impeller can be prevented from sticking. Therefore, impeller lock can be suppressed.

  In the invention according to claim 2, the reducing agent pump is disposed in a tank for storing the reducing agent aqueous solution, and the sticking prevention control is such that the water level in the tank is equal to or lower than a preset threshold value. It is characterized by being executed on the condition. As described above, in the in-tank system in which the reducing agent pump is arranged in the tank, if there is a sufficient amount of the reducing agent aqueous solution in the tank, the reducing agent aqueous solution (for example, urea water) is present in the pump chamber even when the pump is not operated. Will be full. Therefore, since the reducing agent component does not precipitate even in the long-term stopped state, no impeller lock occurs.

  Therefore, according to the invention described in claim 2, in which the sticking prevention control is executed on the condition that the water level in the tank is equal to or lower than a preset threshold value, in the case of a long-term stop state, unnecessary electric drive is performed. The operation of the motor can be prohibited, and useless power consumption by the electric motor can be avoided.

  In the invention according to claim 3, the pump case is formed with a suction port for introducing the reducing agent aqueous solution in the tank into the pump chamber, and the threshold is set to the height of the suction port. It is characterized by that. If the reducing agent aqueous solution is present up to the water level of the suction port, the reducing agent aqueous solution at the suction port is sucked up by the surface tension to the clearance (pump chamber) between the pump case and the impeller. Therefore, since the pump chamber is filled with the reducing agent aqueous solution, the reducing agent component does not precipitate even when the pump chamber is stopped for a long time. Therefore, prohibiting unnecessary operation of the electric motor can be suitably realized.

  According to a fourth aspect of the present invention, the pump stop state that does not require reduction is a state in which the operation of the internal combustion engine is stopped. Incidentally, another example of the pump stop state that does not require reduction is a low-load operation state such as an idling operation of the internal combustion engine.

  According to a fifth aspect of the present invention, there is provided estimation means for estimating the degree of adhesion of the pump case and the impeller, and the predetermined time used by the determination means is variably set so as to be shorter as the estimated degree of adhesion is larger. It is characterized by that. Therefore, when the degree of sticking is large, the impeller is driven more frequently, and thus the certainty of peeling the deposited reducing agent component from the impeller surface can be improved. On the other hand, when the degree of fixation is small, the impeller is driven less frequently, so that it is possible to reduce power consumption by the electric motor while peeling the deposited reducing agent component from the impeller surface.

  According to a sixth aspect of the invention, there is provided estimation means for estimating the degree of adhesion of the pump case and the impeller, and the operation time of the electric motor in the adhesion prevention control is increased as the estimated degree of adhesion increases. It is characterized by variable setting. For this reason, when the degree of fixation is large, the impeller rotational drive time becomes long, so that the certainty of peeling the deposited reducing agent component from the impeller surface can be improved. On the other hand, when the degree of sticking is small, the impeller rotational drive time is shortened, so that it is possible to reduce power consumption by the electric motor while peeling off the deposited reducing agent component from the impeller surface.

  According to a seventh aspect of the invention, there is provided back electromotive force detection means for detecting back electromotive force generated by inertial rotation of the impeller immediately after stopping the drive current to the electric motor, and the estimation means comprises the back electromotive force detection means. The sticking degree is estimated based on the magnitude of the counter electromotive force detected by the electromotive force detecting means.

  The inventor has found that there is a correlation between the magnitude of the back electromotive force and the degree of fixation. That is, since the rotation speed of the impeller when the drive current is flowing becomes slower as the degree of fixation increases, the inertial rotation speed immediately after the drive current is stopped becomes slower, and as a result, the counter electromotive force becomes smaller. Therefore, according to the seventh aspect of the present invention that estimates the sticking degree based on the magnitude of the back electromotive force, it is possible to easily estimate the sticking degree with high accuracy.

  The invention according to claim 8 is characterized in that the estimating means estimates the degree of adhesion based on at least one of a temperature of the reducing agent aqueous solution, an outside air temperature, and an operating time of the internal combustion engine.

  Furthermore, the present inventor has found that the temperature of the reducing agent aqueous solution, the outside air temperature, the operation time of the internal combustion engine, and the degree of fixation are correlated. That is, if the temperature of the reducing agent aqueous solution and the outside air temperature are high, evaporation of the water component in the reducing agent aqueous solution is promoted, so that precipitation of the reducing agent component is promoted, and as a result, the degree of fixation increases. Further, if the operating time of the internal combustion engine is long, the temperature of the exhaust gas and the exhaust pipe of the internal combustion engine becomes high, so that the temperature of the portion that discharges the reducing agent aqueous solution (for example, the reducing agent aqueous solution addition valve) becomes high. Therefore, the temperature of the reducing agent aqueous solution also increases and the degree of fixation increases as described above. Therefore, according to the invention of claim 8, wherein the sticking degree is estimated based on at least one of the temperature of the reducing agent aqueous solution, the outside air temperature, and the operation time of the internal combustion engine, it is easy to accurately estimate the sticking degree. it can.

  The invention according to claim 9 is characterized in that the determination means repeatedly executes the determination as to whether or not the pump stop state continues for a predetermined time or more even after the sticking prevention control is executed. According to this, as long as the pump stop state continues, the reducing agent pump operates intermittently, so that the reliability of avoiding impeller sticking can be improved.

  A tenth aspect of the present invention includes a pump case that forms a pump chamber therein, and an impeller that is disposed in the pump chamber and is driven to rotate by an electric motor, and reduces nitrogen oxides contained in the exhaust gas of the internal combustion engine. A reducing agent discharge system comprising: a reducing agent pump that discharges a reducing agent aqueous solution; and the reducing agent pump control device. According to this reducing agent discharge system, the above-described various effects can be similarly exhibited.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
The reducing agent pump control device according to the present embodiment is applied to a urea water pump that discharges a urea aqueous solution (hereinafter simply referred to as urea water) using urea as a reducing agent, and is discharged from the urea water pump. Urea water is pressurized and sent to the injection valve. The injection valve is arranged to inject urea water into the exhaust flow in the exhaust passage of a diesel engine (hereinafter referred to as an engine) as an internal combustion engine.

  FIG. 1 is an overall configuration diagram showing the overall configuration of the urea SCR system in the present embodiment. This overall configuration diagram shows an exhaust emission control device for purifying exhaust gas discharged from an engine of an automobile (not shown). The configuration of the exhaust purification device is roughly classified into an exhaust system component, a urea water supply system component, and a control system component.

  The constituent parts of the exhaust system are arranged in order from the exhaust upstream side, DPF1 (Diesel Particulate Filter), exhaust pipe 2 (upstream exhaust passage of the catalyst), catalyst 3, and exhaust pipe 4 (downstream exhaust of the catalyst) Passage). The DPF 1 is a continuously regenerating PM removal filter that collects PM (Particulate Matter, particulate matter) in exhaust gas, and repeatedly collects and removes the collected PM by, for example, post injection after main fuel injection ( This is equivalent to the regeneration process of the PM removal filter). Further, the DPF 1 carries a platinum-based oxidation catalyst (not shown) and can remove HC and CO together with a soluble organic component (SOF) which is one of the PM components.

The catalyst 3 is a part that promotes a reduction reaction of NOx and purifies exhaust gas.
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 12H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)
Such a reaction is promoted to reduce NOx in the exhaust. In these reactions, an aqueous solution (hereinafter referred to as urea water) containing ammonia (NH 3) serving as a NOx reducing agent is mixed with exhaust gas and supplied to the catalyst 3. Specifically, urea water is injected and supplied by an injection valve, which will be described later, toward the exhaust gas flowing through the exhaust pipe 2 on the upstream side of the catalyst 3.

  The components of the urea water supply system include a urea water supply unit 5, an injection valve 6, a delivery pipe 7, and the like. The urea water supply unit 5 includes a urea water tank 8, a urea water pump 9 (reducing agent pump), and the like. I have. 1 shows a state in which the urea water tank 8 is mounted on the vehicle, and the vertical direction of the urea water tank 8 and the urea water pump 9 is in the direction shown in FIG. 1 when mounted on the vehicle. Yes.

  The urea water in the urea water tank 8 is sucked into the urea water pump 9 through the filter 9a and is sent under pressure. Thereafter, the discharge pressure is adjusted by the regulator 9 b and then supplied to the injection valve 6 through the delivery pipe 7. The injection port formed at the tip of the injection valve 6 is constituted by one injection port or an assembly (group injection holes) of a number of fine injection holes. When the needle valve that opens and closes the injection port is opened by an electromagnetic actuator, the urea water supplied to the injection valve 6 is atomized and injected into the exhaust pipe 2. When the supply pressure from the urea water pump 9 exceeds the set value of the regulator 9b, the urea water in the delivery pipe 7 is returned to the urea water tank 8 by the regulator 9b.

  The urea water tank 8 is constituted by a sealed container with a liquid supply cap, and urea water having a predetermined concentration is stored therein. A urea water pump 9 is provided in the urea water tank 8 so as to be immersed in the urea water. The urea water pump 9 constitutes an in-tank type pressure feed pump and an ECU 10 (control means). This is an electric pump that is driven to rotate by a drive signal from the motor. The detailed configuration of the urea water pump 9 will be described later in detail with reference to FIG.

  The components of the control system include an ECU 10 (electronic control unit), a crank angle sensor 11, an accelerator operation amount sensor 12, an exhaust sensor 13, a water level sensor 14, a pressure sensor 15, and the like. The ECU 10 includes a well-known microcomputer, receives detection values from various sensors 11, 12, 13, 14, and 15, and based on these detection values, various types such as the urea water pump 9 and the injection valve 6 are provided. Controls the drive amount of the actuator.

  The crank angle sensor 11 detects the rotational speed of the crankshaft (engine rotational speed) by detecting the rotational angle of the crankshaft (output shaft). The accelerator operation amount sensor 12 detects the required engine load by detecting the operation amount of the accelerator pedal by the driver. The exhaust sensor 13 is provided in the exhaust pipe 4 on the downstream side of the catalyst 3, and both the NOx sensor and the exhaust temperature sensor are built in, and the amount of NOx in the exhaust (as a result, the NOx purification rate by the catalyst 3) and the exhaust Detect temperature. The water level sensor 14 is provided in the urea water tank 8 and detects the water level of the urea water in the urea water tank 8. The pressure sensor 15 is provided in the middle of the delivery pipe 7 and is configured to detect the supply pressure of urea water to the injection valve 6.

  Specifically, the ECU 10 calculates the urea water injection amount from the injection valve 6 based on the engine rotation speed detected by the crank angle sensor 11 and the accelerator operation amount detected by the accelerator operation amount sensor 12. And it controls so that a drive current may be output to the solenoid valve which carries out valve opening operation of the injection valve 6 so that it may become the calculated injection amount. Further, the injection amount calculated as described above is feedback-corrected so that the NOx amount detected by the exhaust sensor 13 becomes a desired amount. Further, the ECU 10 controls the driving of the urea water pump 9 based on the detection values of the water level sensor 14 and the pressure sensor 15 (details will be described later).

  In the urea SCR system having the above-described configuration according to the present embodiment, the urea water in the urea water tank 8 is pumped to the injection valve 6 through the delivery pipe 7 by driving the urea water pump 9 during engine operation. Urea water is added and supplied into the exhaust pipe 2. Then, urea water is supplied to the SCR catalyst 3 together with the exhaust gas in the exhaust pipe 2, and the exhaust gas is purified by performing a NOx reduction reaction in the SCR catalyst 3.

When reducing NOx, for example,
(NH2) 2CO + H2O → 2NH3 + CO2 (Formula 4)
By such a reaction, urea water is hydrolyzed by exhaust heat. As a result, ammonia (NH3) is generated, and this ammonia is added to the NOx in the exhaust gas selectively adsorbed by the SCR catalyst 3. Then, a reduction reaction based on the ammonia (the above reaction formulas (Formula 1) to (Formula 3)) is performed on the catalyst 3, whereby NOx is reduced and purified.

  Next, the single-piece | unit structure of the urea water pump 9 is demonstrated in detail using FIGS.

  As shown in FIG. 2, the urea water pump 9 includes a pump unit 18 having a mechanism unit that pumps urea water, and an electric motor unit 19 that generates a driving force that drives the mechanism unit to pump urea solution. I have. The pump unit 18 is a vortex pump including a pump case and an impeller 22. The pump case joins two members of the upper case 20 and the lower case 21, and forms a space as a pump chamber arranged inside the mating surface to be joined so that a section screen that divides the chamber faces. . An impeller 22 as a rotating member whose relative position with respect to this space is defined is rotatably accommodated.

  FIG. 3 is a perspective view showing the impeller 22 alone, and the impeller 22 formed in a disk shape is provided with a plurality of blade grooves 22a in the rotation direction, and an annular outer periphery on the outer side in the rotation radial direction of the blade grooves 22a. A portion 22b is formed. 4 is an enlarged view of FIG. 2, and C-shaped pump passages 23 are formed in portions of the upper case 20 and the lower case 21 facing the blade grooves 22a. The arrow Y in FIG. 4 shows the flow of urea water when the impeller 22 is rotated, and the urea water in the pump chamber flows out to the pump passage 23 from the outer side in the radial direction of the blade groove 22a in the front in the rotational direction. To do. And the urea water which flowed out in this way flows in into the rotation diameter direction inner side of the blade groove | channel 22a of a rotation direction back.

  By repeating such outflow and inflow of urea water a number of times between the blade grooves 22 a, the urea water in the pump chamber becomes a swirling flow and is pressurized in both pump passages 23. The urea water sucked from the suction port 24 provided in the lower case 21 is boosted in the pump passage 23 by the rotation operation of the impeller 22 and is pumped to the electric motor unit 19 described later.

  Each part of the pump unit 18 and the electric motor unit 19 through which the urea water is circulated and exposed to the urea water is formed of a urea-resistant constituent material (corrosion-resistant constituent material) having corrosion resistance and oxidation resistance to the urea water. Has been. A urea-resistant component (corrosion-resistant component) is exposed to urea water to form a passive film on the surface exposed to urea water, and the metal oxide and urea water contained in the inner layer combine to passivate. It is formed of a passive film regenerating material that regenerates the film. The upper case 20 and the lower case 21 are made of metal, for example, austenitic stainless steel as a passive film regenerating material, and are formed using SUS304 classified by JIS classification. The impeller 22 is formed of a resin (for example, a phenol resin).

  The electric motor unit 19 is a brushless motor including a stator core 25, a rotor 26, a rotating shaft 27, a bobbin 28, a coil 29, and the like, and functions to generate a driving force that is energized to pump urea water. The stator core 25 is configured by arranging six cores in the circumferential direction. The ECU 10 switches the magnetic poles formed on the inner peripheral surface of each core facing the rotor 26 by controlling energization to the coil 29 according to the rotational position of the rotor 26. The coil 29 is supplied with power from a terminal 43 connected by a connector.

  The rotor 26 has a rotating shaft 27 and a permanent magnet 31 and is rotatably installed on the inner periphery of the stator core 25. One end portion of the rotating shaft 27 is rotatably supported by the bearing portion 32, and the other end portion is rotatably supported by the bearing portion 33. The rotary shaft 27 is positioned in the axial direction by pressing one end portion of the rotary shaft 27 against the pin portion 35.

  The permanent magnet 31 is a plastic magnet formed into a cylindrical shape by kneading magnetic powder into a thermoplastic resin material such as PPS, and is directly formed on the outer periphery of the rotating shaft 27 by injection molding or the like. The permanent magnet 31 forms eight magnetic pole portions in the rotation direction. These magnetic pole portions are magnetized so as to form different magnetic poles alternately in the rotational direction on the outer peripheral surface facing the stator core 30.

  The housing 36 serves as both the housing of the pump unit 18 and the electric motor unit 19. The housing 36 is made of metal, and is formed by caulking the lower case 21 and the end cover 37 at both ends in the axial direction. The upper case 20 is abutted against the step 36 a of the housing 36 in the axial direction. Thereby, the upper case 20 is positioned in the axial direction. The above-described bearing portion 32 is fixed to the center portion of the upper case 20 by press-fitting. The lower case 21 is fixed by caulking at one end side of the housing 36. Due to the axial force generated by the caulking, the upper case 20 and the stepped portion 36a and the lower surface 21 and the upper case 20 are pressed against each other in the axial direction. Secure and seal with urea water.

  The urea water pressure-fed to the electric motor unit 19 side is sent out in the order of the flow path 38 and the discharge path 39 between the stator core 25 and the rotor 26, and is supplied from the discharge port 40 to the injection valve 6 side. The discharge port 40 of the discharge passage 39 that opens to the outside from the end cover 37 is formed eccentrically with respect to the bearing portion 33.

  The coil 29 described above is resin-molded with an insulating resin material 45, and the insulating resin material 45 is integrally formed with an end cover 37 that covers the end of the stator core 25 opposite to the pump portion 18. The end cover 37 is configured by integrally forming a bearing portion 33 that supports the rotary shaft 27, a support portion of the terminal 43, and the discharge port 40 with an insulating resin material 45.

  A check valve 47 and a spring 48 are accommodated in the discharge port 40 formed by the end cover 37. When the urea water boosted by the pump unit 18 reaches a predetermined pressure or higher, the check valve 47 lifts against the load of the spring 48 and the urea water is discharged from the discharge port 40 to the injection valve 6 side. The check valve 47 is provided so as to prevent a back flow of urea water discharged from the urea water pump 9.

  By the way, when the water level of the urea water stored in the urea water tank 8 is lower than the lower end position of the suction port 24 provided in the lower case 21 (the height shown by the one-dot chain line W in FIGS. 1 and 2). The urea water in the pump such as the discharge passage 39, the flow passage 38, and the pump chamber stops the rotation of the impeller 22 and simultaneously flows out from the suction port 24 to the urea water tank 8. When the urea water pump 9 is not operated for a long time without the urea water being filled in the pump chamber in this way, the upper and lower surfaces 22c and 22d (see FIG. 3) of the impeller 22 and the pump case 20 are left. , 21, the urea component of the urea water is deposited as the aqueous component of the urea water evaporates.

  When the urea component is deposited as described above at the clearances CL1, CL2 (see FIG. 4) between the pump cases 20, 21 and the impeller 22, the precipitated urea component fixes the impeller 22 to the inner surfaces of the pump cases 20, 21. Therefore, there is a concern about the impeller lock that makes the impeller 22 unrotatable. In particular, when the impeller 22 is made of resin as in the present embodiment, the impeller 22 may be damaged if power is supplied to the coil 29 of the electric motor unit 19 in a state where the impeller is locked. In order to eliminate the concern about such impeller lock, in this embodiment, sticking prevention control described below is performed.

  FIG. 5 is a flowchart showing the processing contents of the sticking prevention control executed by the microcomputer of the ECU 10. The series of processing shown in FIG. 5 is triggered by the engine being stopped by turning off the ignition switch. The microcomputer shown in FIG. 5 is forcibly terminated when the microcomputer of the ECU 10 is repeatedly executed every time (for example, the calculation cycle performed by the CPU described above) and the ignition switch is turned on or the engine is started.

  First, in step S10, the detection value of the water level sensor 14 is acquired, and it is determined whether or not the acquired detection value (water level) is smaller than a preset threshold value. The threshold value is set at the lower end position W of the suction port 24 of the urea water pump 9. If it is determined that the water level of the urea water stored in the urea water tank 8 is equal to or higher than the threshold value W (S20: NO), the process proceeds to step S30, and the process of FIG. To do. Note that the operation of the urea water pump 9 is stopped when the processing of FIG. 5 is started.

  When it is determined that the water level of the urea water is lower than the threshold value W (S20: YES), counting is started in step S40 (determination means) and the time measurement process is executed. In a subsequent step S50 (determination means), it is determined whether or not the count value is larger than a threshold value. That is, it is determined whether or not the operation stop state of the urea water pump 9 is a long-term stop state that continues for a predetermined time C or longer. If it is determined that the count value does not exceed the threshold value (S50: NO), the process returns to step S40, and an increment process for increasing the count value is performed in step S40.

  If it is determined that the count value exceeds the threshold value for a long-term stop state (S50: YES), a drive current is supplied from the ECU 10 to the terminal 43 so as to temporarily rotate the impeller 22 to drive the electric motor unit. 19 is activated. At this time, the rotation speed of the impeller 22 may be less than one rotation, and for example, it may be rotated only a few radians.

  FIG. 6 exemplifies one aspect of the sticking prevention control by the process of FIG. 5, and shows a change in the drive voltage applied to the electric motor unit 19. If the engine is stopped by turning off the ignition switch in a state where the water level of the urea water is lower than the threshold value W, the count is started at that time. When the predetermined time C0 elapses, a driving voltage having a pulse width of the motor operating time Δt0 is applied to perform the first impeller rotation driving. Thereafter, when the predetermined time C1 further elapses, a pulse driving voltage having a width of the motor operating time Δt1 is applied to perform the second impeller rotation driving.

  Then, unless the urea water tank 8 is replenished with urea water and the water level becomes W or higher or the engine is not started, the impeller rotation drive in step S60 is repeatedly performed. However, if the voltage of the in-vehicle battery BAT (see FIG. 1) serving as a power supply source to the electric motor unit 19 is lower than a preset set value, the battery BAT is considered to be in an insufficiently charged state, You may make it prohibit the impeller rotational drive by step S60.

  The count value (predetermined time C) is set on the order of several hours, and the drive current supply time (motor operating time Δt) is set to less than 1 second. Therefore, the impeller 22 is intermittently operated for several seconds every several hours. In the present embodiment, the predetermined time C and the motor operation time Δt each time are set to the same value.

  As described above, according to the present embodiment, the following effects can be obtained.

  (1) In a state where the water level of the urea water is lower than the threshold value W, the impeller 22 is intermittently operated by the sticking prevention control every time the predetermined time C0, C2, C3 elapses after the engine is stopped. Even if the urea component is deposited in the clearances CL1 and CL2 with the impeller 22, the reducing agent component can be peeled off at an early stage of deposition. Further, since the operation of the impeller 22 related to the sticking prevention control causes a small amount of remaining urea water in the urea water tank 8 to flow into the clearances CL1 and CL2, the urea is discharged during a predetermined time C until the next impeller operation. The amount of precipitation of components can be reduced. Therefore, it is possible to avoid impeller lock due to the precipitated urea component fixing the impeller 22 to the inner surfaces of the pump cases 20 and 21.

  (2) In the present embodiment, the threshold value W is set at the lower end position of the suction port 24 of the urea water pump 9. And if it is the water level more than this lower end position W, the urea water of the urea water tank 8 will be sucked up by surface tension to clearance CL1, CL2 of the impeller 22, and the pump chamber will be in the state filled with urea aqueous solution, The urea component does not precipitate even in the long-term stop state. Therefore, unnecessary operation of the electric motor unit 19 is prohibited, and useless power consumption of the battery BAT can be avoided.

(Second Embodiment)
In the first embodiment, the predetermined time C and the motor operating time Δt are fixed and set. In the present embodiment, the degree of adhesion between the pump cases 20 and 21 and the impeller 22 is estimated and estimated. The predetermined time C and the motor operation time Δt are variably set according to the degree of fixation. Hereinafter, the procedure for estimating the sticking degree and variable setting will be described with reference to FIG.

  Of the processing steps in FIG. 7, the processing from step S10 to S60 is the same as the processing steps S10 to S60 in FIG. Then, after rotating the impeller 22 in step S60, the current value I flowing in the power supply line to the urea water pump 9 is acquired in step S70 (estimating means). The current value I is detected by the ammeter 10a shown in FIG. 10, and is the peak value of the counter electromotive force generated by the inertial rotation of the impeller 22 immediately after the drive current to the electric motor unit 19 is stopped. is there. Specifically, the current value I acquired in step S70 is a peak value within a predetermined time immediately after the current value once becomes zero after the pulse drive voltage applied to the electric motor unit 19 is turned off. Yes (see the lower part of FIG. 8).

  Here, as described above, there is a correlation between the magnitude of the back electromotive force and the magnitude of the sticking degree, and the back electromotive force decreases as the sticking degree increases. Therefore, in the subsequent step S80 (estimating means), when it is determined that the current value I acquired in step S70 has fallen below the target value Ith (threshold value) (S80: YES), it is estimated that the degree of fixation is large. In S90, the threshold value is changed to shorten the threshold value used in step S50 by a predetermined time. Thereby, since the interval of the intermittent operation of the impeller 22 by the sticking prevention control is shortened, the certainty of peeling the precipitated urea component from the surface of the impeller 22 can be improved.

  On the other hand, when the degree of adhesion is small and it is determined that I ≧ Ith in step S80 (S80: NO), the interval becomes longer, so that the electric motor portion is removed while peeling the precipitated urea component from the surface of the impeller 22. The power consumption by 19 can be reduced. In step S90 according to the present embodiment, the interval (predetermined time C) is made variable by variably setting the threshold used in step S50. However, in step S90, the motor operating time Δt may be variably set. Good. That is, when it is determined in step S80 that I <Ith (S80: YES), the pulse width (motor operating time Δt) of the drive voltage applied to the electric motor unit 19 is increased by a predetermined time in step S60. Thus, the motor operating time Δt is set and changed.

  FIG. 8 exemplifies one aspect of the sticking prevention control by the process of FIG. 7, and shows a change in the drive voltage applied to the electric motor unit 19. When the ignition switch is turned off and the engine is stopped while the water level of the urea water is lower than the threshold value W, the count is started at that time. When the predetermined time C0 has elapsed, a driving voltage having a pulse width of the motor operating time Δt0 is applied, and the first impeller rotation driving is performed in step S60. At this time, if it is determined that I <Ith in the next step S80 (S80: YES), it is estimated that the degree of fixation is large, and the next predetermined time C1 is shorter than the previous predetermined time C0. The setting is changed.

(Third embodiment)
In estimating the degree of sticking of the impeller 22, in the second embodiment, the impeller 22 is estimated based on the peak value of the counter electromotive force generated by the inertial rotation of the impeller 22 immediately after the drive current to the electric motor unit 19 is stopped. Yes. On the other hand, in the present embodiment, the sticking degree is estimated based on at least one of the temperature TN of the urea water in the urea water tank 8, the outside air temperature TA, and the engine operating time. As shown in FIG. 10, the urea water temperature TN is detected by the urea water temperature sensor 17 installed in the urea water tank 8, the outside air temperature TA is detected by the outside air temperature sensor 16, and the operating time of the engine is the ECU 10. It is measured by. Further, the operation time is the engine operation time from the IG on operation time point to the IG off operation time point immediately before the IG off operation and the processing of FIG. 7 are executed.

  Here, as described above, there is a correlation between the urea water temperature TN, the outside air temperature TA, the engine operation time, and the degree of fixation, and if the urea water temperature TN and the outside air temperature TA are high, the water component of the urea water Since evaporation is accelerated, the precipitation rate of the urea component is increased (see FIG. 9). Further, if the engine operating time is long, the temperature of the exhaust pipe 2 becomes high, so that the temperature of the injection valve 6 attached to the exhaust pipe 2 becomes high. Moreover, the temperature of the engine cooling water circulating through the injection valve 6 in order to cool the injection valve 6 also increases. Therefore, since the temperature of the urea water is also increased, the precipitation rate of the urea component is increased (see FIG. 9).

  Therefore, in this embodiment, instead of the estimation process in step S80 of FIG. 7, it is estimated that the degree of fixation is large when at least one of the urea water temperature TN and the outside air temperature TA exceeds the threshold value. Alternatively, it is estimated that the degree of sticking is large when the engine operating time exceeds a threshold value. If it is estimated that the degree of fixation is large, the same processing as step S90 in FIG. 7 is executed. Thereby, the effect similar to the said 2nd Embodiment is show | played.

(Other embodiments)
The above embodiments may be implemented with the following modifications. Further, the present invention is not limited to the description of the above embodiment, and the characteristic structures of the embodiments may be arbitrarily combined.

  In each of the above embodiments, the pump control device according to the present invention is applied to the in-tank system in which the urea water pump 9 is disposed in the urea water tank 8, but in-line in which the urea water pump 9 is disposed in the delivery pipe 7. The pump control device of the present invention may be applied to the system. In this case, regardless of the level of the urea water stored in the urea water tank 8, when the operation of the urea water pump 9 is stopped, the urea water in the urea water pump 9 (particularly in the pump chamber) flows into the urea water tank 8. To do. Therefore, it is desirable to abolish the processing of steps S20 and S30 in FIG. 5 and intermittently operate the impeller 22 after the engine is stopped regardless of the water level of the urea water. Incidentally, in the in-tank method, the processing in steps S20 and S30 may be abolished.

  In the second and third embodiments, when it is determined that the degree of fixation is large (S80: YES), the threshold value is changed to shorten the threshold value used in step S50 by a predetermined time. The threshold value may be variably set linearly in accordance with the magnitude of the degree, that is, the magnitude of the current value I acquired in step S70. Alternatively, the motor operation time Δt may be variably set linearly.

The whole block diagram which shows the whole structure of the urea SCR system in 1st Embodiment of this invention. The detailed block diagram of the urea water pump shown in FIG. The perspective view which shows the single-piece | unit structure of the impeller shown in FIG. The enlarged view of FIG. The flowchart which shows the processing content of the sticking prevention control which ECU shown in FIG. 1 performs. The figure which illustrates one aspect | mode of the sticking prevention control by the process of FIG. 5, and shows the change of the drive voltage applied to an electric motor part. The flowchart which shows the processing content of the sticking prevention control in 2nd Embodiment of this invention. FIG. 8 is a diagram illustrating an aspect of sticking prevention control by the process of FIG. 7 and illustrating changes in drive voltage and detection current applied to the electric motor unit. The graph which shows the relationship between urea water temperature TN, external temperature TA, engine operation time, and the precipitation rate of a urea component. The whole block diagram which shows the whole structure of the urea SCR system in 2nd and 3rd embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... ECU (control means), 10a ... Back electromotive force detection means, 8 ... Urea water tank, 9 ... Urea water pump (reducing agent pump), 14 ... Water level sensor, 19 ... Electric motor part, 20 ... Upper case (pump Case), 21 ... Lower case (pump case), 22 ... Impeller, S40, S50 ... Determination means, S70, S80 ... Estimation means.

Claims (10)

A reducing agent for discharging a reducing agent aqueous solution for reducing nitrogen oxides contained in exhaust gas of an internal combustion engine, including a pump case that forms a pump chamber therein, and an impeller that is disposed in the pump chamber and is driven to rotate by an electric motor. Applied to the pump,
Control means for controlling the operation of the electric motor;
Determination means for determining whether or not the pump stop state that does not require reduction is a long-term stop state that continues for a predetermined time or more;
With
The control means performs a sticking prevention control for operating the electric motor to temporarily rotate the impeller when the determination means determines that the long-term stop state has occurred. Control device. The reducing agent pump is disposed in a tank that stores the reducing agent aqueous solution,
2. The reducing agent pump control device according to claim 1, wherein the sticking prevention control is executed on condition that a water level in the tank is equal to or lower than a preset threshold value. 2. The suction opening for introducing the reducing agent aqueous solution in the tank into the pump chamber is formed in the pump case, and the threshold is set to a height of the suction opening. Or the reducing agent pump control apparatus of 2.   The reducing agent pump control device according to any one of claims 1 to 3, wherein the pump stop state that does not require reduction is a state in which the operation of the internal combustion engine is stopped. Comprising estimation means for estimating the degree of fixation of the pump case and the impeller;
5. The reducing agent pump control device according to claim 1, wherein the predetermined time used by the determination unit is variably set so as to be shorter as the estimated degree of sticking is larger. Comprising estimation means for estimating the degree of fixation of the pump case and the impeller;
6. The reducing agent pump control according to claim 1, wherein the operation time of the electric motor in the sticking prevention control is variably set so as to increase as the estimated degree of sticking increases. apparatus. Comprising back electromotive force detection means for detecting back electromotive force generated by inertia rotation of the impeller immediately after stopping the drive current to the electric motor;
The reducing agent pump control device according to claim 5 or 6, wherein the estimation means estimates the degree of sticking based on the magnitude of the back electromotive force detected by the back electromotive force detection means.   The said estimation means estimates the said adhesion degree based on at least 1 of the temperature of the said reducing agent aqueous solution, external temperature, and the operation time of the said internal combustion engine, The any one of Claims 5-7 characterized by the above-mentioned. Reductant pump control device.   9. The determination unit according to claim 1, wherein the determination unit repeatedly executes the determination as to whether or not the pump stop state continues for a predetermined time or more even after the sticking prevention control is executed. The reducing agent pump control device according to one. A reducing agent for discharging a reducing agent aqueous solution for reducing nitrogen oxides contained in exhaust gas of an internal combustion engine, including a pump case that forms a pump chamber therein, and an impeller that is disposed in the pump chamber and is driven to rotate by an electric motor. A pump,
Reducing agent pump control device according to any one of claims 1 to 9,
A reducing agent discharge system comprising:

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