DE102017202409B4 - UREA WATER INJECTION CONTROL DEVICE - Google Patents

Abstract

A urea water injection control device (30) for supplying urea water stored in a urea water tank (14) into an exhaust passage (13) of an internal combustion engine (11) for reducing nitrogen oxides contained in an exhaust gas of the internal combustion engine (11) by a reduction catalyst (17), wherein the urea water injection control device (30) includes an injector (18) provided in the exhaust passage (13) for injecting the urea water and a urea water pump (15) provided in a urea water passage (19) that controls the urea water tank (14) and the injector (18) for supplying the urea water from the urea water tank (14) to the injector (18), the urea water injection control device (30) comprising: an engine state acquiring part (32) for acquiring a driving state of an engine (21 ), which drives the urea water pump (15);a reverse driving part (33) for driving the motor (21) in a reverse direction opposite to a forward direction of supplying urea water to the injector (18) to supply the urea water in the urea water passage (19) return to the urea water tank (14); anda return checking part (34) for checking whether return of urea water from the urea water channel (19) to the urea water tank (14) has been completed based on the driving state of the engine (21) obtained by the engine state obtaining part (32), in a state, in which the motor (21) is driven by the reverse driving part (33), wherein when the motor state obtaining part (32) determines that the motor (21) is operating stably, the motor state obtaining part (32) takes the driving state of the motor (21) at that time as one obtains a stable driving state, and the return checking part (34) sets a setting value based on the stable driving state and determines whether the return of the urea water from the urea water channel (19) to the urea water tank (14) has been completed based on the driving state of the engine (21), which is obtained by the engine state obtaining part (32), and the setting value.

Description

The present invention relates to a urea water injection control device.

A urea SCR system (SCR corresponds to selective catalytic reduction) conventionally uses urea as an aftertreatment for cleaning exhaust gas from an internal combustion engine. In the urea SCR system, nitrogen oxides (NOx) included in the exhaust are reduced by adding urea to the exhaust. The urea used in the urea SCR system is supplied as the urea water. The urea water stored in a urea water tank is supplied to an injector through a urea water passage and is injected by the injector into the exhaust gas flowing in an exhaust passage. The urea water is delivered to the injector by a urea water pump. The urea water occasionally deposits the urea dissolved as a crystal when the urea water freezes due to falling ambient temperature or when a concentration of the urea water changes due to evaporation of water. Deposited solid urea occasionally causes clogging of the injector or the urea water channel.

JP 2009 - 2 260 A proposes to return urea water remaining in a urea water channel to a urea water tank by driving a urea water pump in a reverse direction opposite to a forward direction for supplying the urea water. A period for driving the urea water pump in the reverse direction is set according to an environment of the urea water SCR system such as an air temperature and an atmospheric pressure. For this reason, when a sensor for detecting air temperature or atmospheric pressure has an individual difference or aging deterioration, a period for driving the urea water pump in the reverse direction has a larger error. If the period for driving the urea water pump in the reverse direction is set to be shorter than required, the urea water remaining in the urea water passage is not sufficiently returned. If the period for driving the urea water pump in the reverse direction is set longer than required, the urea water pump is continuously driven even after completing the return of the urea water from the urea water channel. As a result, electrical energy is consumed unnecessarily.

It will also refer to the JP 2001 - 132 655 A referred to, which was determined to be the state of the art.

It is therefore an object of the present invention to provide a urea water injection control device that checks whether return of urea water from a urea water channel has been completed and reduces unnecessary power consumption of a urea water pump after completion of urea water return while avoiding remaining of the urea water in the urea water channel.

The task is solved by the features of independent claim 1. Advantageous refinements can be found in the dependent claims.

According to the present invention, a urea water injection control device for an exhaust gas purification system is provided. The urea water injection control device supplies urea water stored in a urea water tank into an exhaust passage of an internal combustion engine for reducing nitrogen oxides contained in an exhaust of the internal combustion engine through a reduction catalyst. The urea water injection control device further controls an injector provided in the exhaust passage for injecting the urea water and a urea water pump provided in a urea water passage connecting the urea water tank and the injector for supplying the urea water from the urea water tank to the injector.

• 1 ist ein Blockschaltbild, das eine Harnstoffwasserinjektionssteuervorrichtung gemäß einer ersten Ausführungsform der vorliegenden Erfindung darstellt;
• 2 ist ein schematisches Diagramm, das ein Abgasreinigungssystem einschließlich der Harnstoffwasserinjektionssteuervorrichtung gemäß der ersten Ausführungsform darstellt;
• 3 ist ein Ablaufdiagramm, das eine Hauptroutine, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß der ersten Ausführungsform darstellt;
• 4 ist ein Ablaufdiagramm, das eine Harnstoffwasserrückbringungsabschlussüberprüfungsverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß der ersten Ausführungsform darstellt;
• 5 ist ein Zeitdiagramm, das eine Motorrotationsänderung bezüglich Zeit in der Harnstoffwasserinjektionssteuervorrichtung gemäß der ersten Ausführungsform darstellt;
• 6 ist ein Ablaufdiagramm, das eine Motorstoppverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß der ersten Ausführungsform darstellt;
• 7 ist ein Ablaufdiagramm, das die Motorstoppverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß der ersten Ausführungsform darstellt;
• 8 ist ein Ablaufdiagramm, das eine Harnstoffwasserrückbringungsabschlussüberprüfungsverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß einem ersten Beispiel zur Erläuterung der Erfindung darstellt;
• 9 ist ein Zeitdiagramm, das eine Motorrotationsänderung bezüglich Zeit in der Harnstoffwasserinjektionssteuervorrichtung gemäß dem ersten Beispiel zur Erläuterung der Erfindung darstellt;
• 10 ist ein Ablaufdiagramm, das eine Harnstoffwasserrückbringungsabschlussüberprüfungsverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß einer zweiten Ausführungsform darstellt;
• 11 ist ein Zeitdiagramm, das eine Motorrotationsänderung bezüglich Zeit in der Harnstoffwasserinjektionssteuervorrichtung gemäß der zweiten Ausführungsform darstellt;
• 12 ist ein Ablaufdiagramm, das eine Harnstoffwasserrückbringungsabschlussüberprüfungsverarbeitung, die durch die Harnstoffwasserinjektionssteuervorrichtung ausgeführt wird, gemäß einem zweiten Beispiel zur Erläuterung der Erfindung darstellt; und
• 13 ist ein Zeitdiagramm, das eine Motorrotationsänderung bezüglich Zeit in der Harnstoffwasserinjektionssteuervorrichtung gemäß dem zweiten Beispiel zur Erläuterung der Erfindung darstellt.

The urea water injection control device includes an engine state obtaining part, a reverse driving part, and a return checking part. The engine state obtaining part acquires a driving state of a motor that drives the urea water pump. The reverse driving part drives the motor in a reverse direction opposite to a forward direction of supplying urea water to the injector to return the urea water in the urea water passage to the urea water tank. The return checking part checks whether return of urea water from the urea water channel to the urea water tank has been completed based on the driving state of the engine obtained by the engine state obtaining part in a state in which the engine is driven by the reverse driving part.

• 1 is a block diagram illustrating a urea water injection control device according to a first embodiment of the present invention;
• 2 Fig. 10 is a schematic diagram illustrating an exhaust gas purification system including the urea water injection control device according to the first embodiment;
• 3 Fig. 10 is a flowchart illustrating a main routine executed by the urea water injection control device according to the first embodiment;
• 4 Fig. 10 is a flowchart illustrating urea water return completion verification processing executed by the urea water injection control device according to the first embodiment;
• 5 Fig. 10 is a timing chart illustrating an engine rotation change with respect to time in the urea water injection control device according to the first embodiment;
• 6 Fig. 10 is a flowchart illustrating engine stop processing executed by the urea water injection control device according to the first embodiment;
• 7 Fig. 10 is a flowchart illustrating the engine stop processing executed by the urea water injection control device according to the first embodiment;
• 8th Fig. 10 is a flowchart illustrating urea water return completion verification processing executed by the urea water injection control device according to a first example for explaining the invention;
• 9 Fig. 10 is a timing chart showing an engine rotation change with respect to time in the urea water injection control device according to the first example for explaining the invention;
• 10 Fig. 10 is a flowchart illustrating urea water return completion verification processing executed by the urea water injection control device according to a second embodiment;
• 11 Fig. 10 is a timing chart illustrating an engine rotation change with respect to time in the urea water injection control device according to the second embodiment;
• 12 Fig. 10 is a flowchart illustrating urea water return completion verification processing executed by the urea water injection control device according to a second example for explaining the invention; and
• 13 Fig. 10 is a timing chart showing a motor rotation change with respect to time in the urea water injection control device according to the second example for explaining the invention.

A urea water injection control device will be described below with reference to several embodiments shown in the drawings. In the following embodiments, like structural parts are denoted by like reference numerals for ease of description.

(First embodiment)

According to 1 A urea water control device (simply referred to as a control device) 30 is provided in an exhaust gas purification system 10, as shown in FIG 2 is shown. As in 2 As shown, the exhaust gas purification system 10 is configured as an SCR system that supplies urea water in exhaust gas emitted from an internal combustion engine 11 mounted in a vehicle and reduces nitrogen oxides contained in the exhaust gas. The exhaust gas of the internal combustion engine 11 is emitted into the atmosphere through an exhaust duct 13 formed by an exhaust pipe member 12. The internal combustion engine 11 can be a diesel engine. The exhaust gas purification system 10 is not limited to the diesel engine, but may be implemented in a gasoline engine or a gas turbine engine. The internal combustion engine 11 is not limited to being mounted in the vehicle, but may be mounted on a power generation unit, for example.

The exhaust gas purification system 10 includes a urea water tank 14, a urea water pump 15, a urea water passage part 16, a reduction catalyst 17 and an injector 18. The urea water tank 14 stores urea water, which is a water solution of urea. The urea water pump 15 discharges the urea water stored in the urea water tank 14 into the urea water channel 19 formed in the urea water channel part 16. The reduction catalyst 17 is provided in the exhaust duct 13 formed by the exhaust pipe member 12. The injector 18 is connected to the urea water tank 14 through the urea water channel 19. The urea water discharged from the urea water pump 15 is supplied to the injector 18 through the urea water passage 19. The injector 18 is provided in the exhaust pipe element 12. The injector 18 protrudes in the exhaust duct 13 through the exhaust pipe element 12. An upper end of the injector 18 is exposed in the exhaust duct 13. The urea water supplied to the injector 18 is injected into the exhaust gas flowing in the exhaust passage 13. The exhaust gas emitted from the internal combustion engine 11 and the urea water injected from the injector 18 are mixed in the exhaust passage 13 and flow into the reduction catalyst 17. Nitrogen oxide contained in the exhaust gas is produced by chemical reaction the urea that is in the urine Substance water is contained in the reduction catalyst 17.

The urea water pump 15, which supplies the urea from the urea water tank 14 to the injector 18, is operated by a motor 21. The motor 21 drives the urea water pump 15 in a forward direction or reverse direction by changing a direction of a power supply or a pattern of a power supply from a battery 22. When the urea water pump 15 is driven in the forward direction by the motor 21, the urea water stored in the urea water tank 14 is supplied to the injector 18. When the urea water pump 15 is driven by the motor 21 in the reverse direction opposite to the forward direction, the urea water in the urea water passage 19 connected to the injector 18 is returned to the urea water tank 14.

The exhaust gas purification system 10 described above is controlled by the control device 30. As in 1 As shown, the control device 30 includes a microcomputer 31 constituted by a CPU, a ROM and a RAM, and controls the exhaust gas purification system 10 by executing computer programs stored in the ROM. The control device 30 realizes an engine state acquisition part 32, a reverse drive part 33, a return check part 34 and an engine stop part 35 by software by executing the computer programs by the microcomputer 31. The engine state acquisition part 32, the reverse drive part 33, the return check part 34 and the engine stop part 35 may be implemented by hardware or an Combination of software and hardware can be realized.

The engine state acquiring part 32 acquires a driving state of the engine 21 that drives the urea water pump 15. Specifically, the motor state obtaining part 32 obtains a torque and/or a rotational speed and/or a current of the motor 21. The motor 21 is controlled to maintain its torque or its rotational speed at a constant value. The motor state acquisition unit 32 acquires the rotation speed of the motor 21 as the driving state when the motor 21 is controlled to maintain its torque at the constant value. The motor state acquiring part 32 acquires the current supplied to the motor 21 as the driving state when the motor 21 is controlled to maintain its rotation speed at the constant value. The motor state acquiring part 32 directly acquires the rotation speed of the motor 21 from, for example, a rotation speed sensor provided on the motor 21. The motor state obtaining part 32 can indirectly obtain the rotation speed of the motor 21 from a control pattern of the current or voltage provided to the motor 21.

The reverse driving part 33 drives the motor 21 that drives the urea water pump 15 in the reverse direction. As described above, when the urea water stored in the urea water tank 14 is supplied to the injector 18, the urea water pump 15 and the motor 21 for driving the urea water pump 15 are driven to rotate in the forward direction. The reverse driving part 33 drives the motor 21 to rotate in the reverse direction opposite to the forward direction by changing the direction or pattern of power supply from the battery 22 to the motor 21. The urea water pump 15 is thus driven to rotate in the reverse direction opposite to the direction at the time of urea water supply. Accordingly, the urea water remaining in the urea water passage 19 is returned to the urea water tank 14 by the urea water pump 15 rotating in the reverse direction.

The return checking part 34 checks whether the return of urea water from the urea water channel 19 to the urea water tank 14 has been completed. Specifically, the return checking part 34 acquires the driving state of the motor 21 from the motor state obtaining unit 32 when the motor 21 rotates backward through the reverse driving part 33. The return checking part 34 checks whether the urea water return has been completed based on the acquired driving state of the engine 21.

In the first embodiment, the return checking part 34 checks whether the return of the urea water has been completed based on the rotation speed of the motor 21. The reverse driving part 33 controls the motor 21 rotating in the reverse direction to maintain its torque at the constant torque value. At this time, the motor state acquiring part 32 acquires, as the driving state of the motor 21, the rotation speed Rc of the motor 21 rotating in the reverse direction. The return checking part 34 determines that the return of the urea water from the urea water passage 19 to the urea water tank 14 has been completed when the rotation speed Rc of the engine 21 obtained by the engine condition obtaining part 32 increases to be equal to or greater than an increased rotational speed Rt. When the urea water remains in the urea water passage 19, the motor 21, which rotates in the reverse direction for returning the urea water, is burdened by the urea water remaining in the urea water passage 19. When the return of urea water is completed, the load of the urea water acting on the engine 21 is reduced. Accordingly, the rotation speed Rc of the motor 21, which is controlled to maintain its torque at the constant torque value, temporarily increases at the time of completion of the urea water. The rotation speed Rc of the motor 21 thus changes with the load, which changes according to the amount of remaining urea water. The return checking part 6 determines a change time of the rotation speed Rc of the motor 21 as a time of completion of return of the urea water.

The engine stopping part 35 stops the engine 21 when the return checking part 34 determines that the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed. That is, the motor stop part 35 stops the operation of the motor 21 when the return of urea water has been completed. Since the driving of the motor 21 is stopped after the completion of returning the urea water, unnecessary energy consumption is reduced. When the return checking part 34 determines that the return of urea water has been completed, the engine stopping part 35 stops the engine 21 immediately or after a predetermined time period D.

Processing of the control device 30 according to the first embodiment will be described below.

(main routine)

As in 3 As shown, the control device 30 performs two main processing. The controller 30 first checks whether the return of urea water has been completed at step S11 when it is time to return the urea water. The controller 30 then controls stopping of the engine 21 at S12 when the return of urea water has been completed.

(return completion verification)

Processing for return completion verification in the first embodiment is described with reference to 4 and a timing diagram of 5 described. The controller 30 starts returning the urea water from the urea water passage 19 to the urea water tank 14 at S101. The controller 30 drives the urea water pump 15 through the motor 21 at a time T11 of 5 and brings the urea water remaining in the urea water passage 19 back to the urea water tank 14. At this time, the reverse driving part 33 drives the motor 21 in the reverse direction.

When the motor 21 is driven at S101, the motor state obtaining part 32 checks whether the motor 21 operates stably at S102. That is, the engine state obtaining part 32 checks whether the engine 21 is running after starting the engine 21 as shown in 5 is shown is in a stable operating state in which the rotation speed is constant. The engine 21 reaches a stable operating state after an acceleration period between the start time T11 and a time T12. The engine state acquiring part 32 acquires the rotation speed of the engine 21 in a continuation period between the time T12 and a time T13 5 and checks whether the motor 21 is in the stable rotation state. In this case, the motor 21 is controlled by the reverse driving part 33 to maintain the constant torque.

When the motor 21 is in the stable operating state (S102: YES), the motor state obtaining part 32 acquires the rotation speed of the motor 21 at that time as a stable rotation speed Rs at S103. If the motor 21 is not in the stable operating state (S102: NO), returns the engine state acquisition part 32 returns its processing to S102 and waits until the engine 21 operates stably.

When the stable rotation speed Rs is obtained, the return checking part 34 sets the increased rotation speed Rt at S104. The return checking part 34 sets the increased rotation speed Rt based on the stable rotation speed Rs obtained at S103. When the urea water is returned from the urea water passage 19, the rotation speed of the motor 21 varies with parameters such as temperature, which changes a physical property of the urea water. For this reason, the stable rotation speed Rs obtained at S103 varies each time the urea water is returned. The return checking part 34 acquires the rotation speed Rs each time the urea water is returned, and sets the increased rotation speed Rt based on the acquired stable rotation speed Rs. In this case, the increased rotation speed Rt is set, which is, for example, meh is ten percent higher than the rotation speed Rs. The increase rate of the increased rotation speed Rt with respect to the stable rotation speed Rs can be arbitrarily set according to the configuration of the exhaust gas purification system 10.

After setting the increased rotation speed Rt at S104, the return checking part acquires the rotation speed Rc of the motor 21 at S105. That is, the return checking part 34 obtains the last rotation speed of the motor 21 as the rotation speed Rc. The return checking part 34 checks at S106 whether the rotation speed Rc obtained at S105 is equal to or greater than the increased rotation speed Rt. That is, the return checking part 34 checks whether the last rotation speed Rc of the motor 21 is equal to or greater than the increased rotation speed Rt.

When the rotation speed Rc is equal to or greater than the increased rotation speed Rt (S106: YES), the return checking part 34 determines at S107 that the return of the urea water has been completed. That is, when the last rotation speed Rc of the motor 21 is equal to or greater than the increased rotation speed Rt, the return checking part 34 determines that the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed. Under the condition that the motor 21 is controlled to maintain its torque at the constant torque value, the load acting on the motor 21 decreases because the urea water decreases in accordance with the amount of the urea water remaining in the urea water passage 19. For this reason, at a time T14 decreases from 5 , at which the urea water remaining in the urea water channel 19 decreases, the rotation speed Rc of the motor 21 increases continuously. At a time T15 at which the return of the urea water of the urea water passage 19 has been completed, the rotation speed Rc of the motor 21 increases to the increased rotation speed or more. The return checking part 34 determines that the return of urea water of the urea water passage 19 has been completed at time T15 at which the rotation speed Rc of the motor 21 increases to the increased rotation speed Rt or more. The controller 30 returns its processing to S11 of the main routine shown in 3 is shown. If the rotation speed Rc is smaller than the increased rotation speed Rt (S106: NO), the return checking part 34 returns its processing to S105. That is, the return checking part 34 continues to monitor the rotation speed Rc of the motor 21 from time T13 at which the rotation speed Rc is smaller than the increased rotation speed Rt to time T14.

(engine stop control)

Coming back to S11 the in 3 In the main routine shown, starting from checking the completion of urea water return, the engine stopping part 35 controls the engine 21 to stop. The engine 21 is stopped immediately after it is determined that the urea water return is completed at S107 or after a predetermined delay period D from the determination of the urea water return completion. When the engine 21 is stopped immediately after the determination of the urea water return completion, the engine stopping part 35 controls the engine 21 at S111 as shown in 6 is shown to stop after processing following determination of urea water return completion at S107 to S11 from 3 returns. The motor 21 that drives the urea water pump 15 is thus stopped immediately after the completion of returning urea water from the urea water channel 19 to the urea water tank 14. That is, the engine 21 is at time T15 5 stopped.

In the other case, where the engine 21 is stopped after the predetermined delay period D from the completion of returning urea water, the engine stopping part 35 sets a time count Tc at S121 as in 7 is set to 0 after processing following the determination of completion of urea water return at S107 to S11 from 3 returns. That is, the engine stop part 35 sets the time count Tc, which is a time count of a timer provided in the control device 30, to 0. The engine stop part 35 then increments the time count Tc at S122 after starting the measurement of the time count Tc at S121.

After incrementing the time count Tc at S122, the engine stopping part 35 checks at S123 whether the time count Tc is equal to or greater than the predetermined delay period D. That is, the engine stop part 35 checks whether the time count Tc, whose count was started at S122, has reached the delay period D. If the time count Tc is equal to or larger than the predetermined delay period D (S123: YES), the engine stopping part 35 controls the engine to stop at S124. If the time count Tc is smaller than the predetermined delay period D (S123: NO), the processing of the engine stop part 35 returns to S122 and waits until the time count Tc reaches the predetermined delay period D. Thus, the motor 21 driving the urea water pump 15 is stopped after the predetermined delay period D based on the determination of completion of the urea water return from the urea water passage 19 to the urea water tank 14. That is, even when the rotation speed Rc of the motor 21 reaches the increased rotation speed Rt at time T15, the motor 21 continues its operation until time T16, which is later than time T15 by the predetermined delay period D. The motor 21 is therefore stopped after time T16.

In the first embodiment described above, the return checking part 34 checks whether the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed based on the driving state of the engine 21 obtained by the engine state obtaining part 32 when the engine 21 is driven by the reverse driving part 33 is driven backwards. The motor 21 that drives the urea water pump 15 changes its driving state according to the presence and absence of the urea water in the urea water passage 19. The return checking part 34 therefore checks whether the return of urea water has been completed based on the change in the driving state of the motor 21 caused by the engine state acquisition part 32 is acquired. Thus, the return checking part 34 checks whether the return of urea water has been completed without the influence of changes in the external environment such as atmospheric pressure and temperature and errors of sensors of this external environment. That is, the return checking part 34 checks whether the return of urea water has been completed based on the driving state of the engine 21. It is thus possible to eliminate the urea water remaining in the urea water passage 19 and unnecessary consumption of energy used to drive the urea water pump15 after completion of the urea water return.

Further, in the first embodiment, the return checking part 34 determines that the return of urea water of the urea water passage 19 to the urea water tank 14 is completed when the rotation speed Rc of the motor 21 reaches the increased rotation speed Rt in the state where the torque of the motor 21 is controlled to be constant. In the state where the motor 21 driving the urea water pump 15 is controlled to maintain the constant torque, the rotation speed Rc of the motor 21 varies according to the urea water remaining in the urea water passage 19. When the return of urea water is completed, the load acting on the motor 21 decreases and the rotation speed Rc of the motor 21 increases. When the rotation speed Rc of the motor 21 increases and reaches the increased rotation speed Rt, the return checking part 34 determines that the return of urea water has been completed. The return checking part 34 is thus able to determine the completion of the urea water return based on the rotation speed Rc of the motor 21. Accordingly, it is possible to eliminate urea water remaining in the urea water channel 19.

Further, in the first embodiment, when the return checking part 34 determines that the return of urea water has been completed, the engine stopping part 35 stops the engine 21 immediately or after the predetermined delay period D. In the case where the engine 21 is stopped immediately following the determination that the urea water return has been completed, driving of the urea water pump 15 is reduced after the completion of the urea water return. As a result, unnecessary energy consumption is reduced.

In the other case, where the engine 21 is stopped after the predetermined delay period D based on the determination of the completion of urea water return by the return checking part 34, the return of urea water is promoted more securely. The urea water pump 15 is positioned near the urea water tank 14 or at a location in the urea water channel 19 and spaced from the urea water tank 14. In this configuration, if the engine 21 is stopped immediately after the rotation speed Rc of the engine 21 reaches the increased rotation speed Rt, the urea water is likely to partially remain in the urea water passage 19. For example, if the urea water channel 19 is long or branched, it may not be possible to return all the urea water to the urea water tank 14 at the time of stopping the engine 21. By continuing to drive the motor 21 over the predetermined delay period D even after the determination of completion of the urea water return, urea water remaining in the urea water passage 19 is safely returned to the urea water tank 14. The predetermined delay period D may be set according to a shape of the urea water passage 19. The urea water channel 19 changes shape during the operation of the control device 30 does not. The predetermined delay period D is set specifically for the exhaust gas purification system 10 to which the control device 30 is implemented, so that the urea water is surely returned in accordance with the characteristic of the urea water passage 19. Since the continued driving or extended driving of the motor 21 during the predetermined delay period D is necessary to return the urea water remaining in the urea water passage 19, the continued driving is not unnecessary. Accordingly, it is possible to prevent urea water from remaining in the urea water passage 19 and reduce unnecessary energy consumption in driving the urea water pump 15 after completion of the urea water return.

(First example to explain the invention)

The control device 30 according to a first example for explaining the invention will be described next. The control device 30 according to the first example for explaining the invention is configured similarly to the first embodiment. However, in the first example for explaining the invention, the return verification part 34 carries out the urea water return completion verification processing slightly differently than that of the first embodiment. In the first example for explaining the invention, the return checking part 34 checks whether the return of urea water has been completed based on the rotation speed of the motor 21. The reverse driving part 33 controls the torque of the motor 21 rotating in the reverse direction to the constant torque. In this control, the motor state acquiring part 32 acquires the rotation speed Rc of the motor 21 rotating in the reverse direction as the driving state of the motor 21. When the rotation speed Rc of the motor 21 acquired by the motor state acquiring part 32 is the increased rotation speed Rt during a predetermined period If the continuation period reaches or exceeds Tt or longer, the return checking part 34 determines that the return of urea water from the urea water channel 19 to the urea water tank 14 has been completed. Similar to the first embodiment, the load acting on the motor 21 varies according to the urea water remaining in the urea water passage 19. For this reason, the rotation speed of the motor 21 increases with a decrease in the urea water to be returned. When the period of continuation of the rotation speed Rc exceeding the increased rotation speed Rt reaches the predetermined continuation period Tt, the return checking part 34 determines that this time is the time of completion of the urea water return. The predetermined continuation period Tt is arbitrarily set according to the characteristics of the engine 21.

Verification processing of a urea water recovery completion in the first example for explaining the invention will be explained with reference to a 8th flowchart shown and an in 9 time diagram shown. Same processing and operations as those of the first embodiment will not be described.

The controller 30 starts returning the urea water from the urea water channel 19 to the urea water tank 14 at S210. The controller 30 drives the urea water pump 15 through the motor 21 at a time T21 of 9 and brings the urea water remaining in the urea water passage 19 back to the urea water tank 14. At this time, the reverse driving part 33 drives the motor 21 in the reverse direction. When the motor 21 is driven at S201, the motor state obtaining part 32 checks whether the motor 21 operates stably at S202. If the motor 21 is in the stable operation state (S202: YES), the motor state obtaining part 32 acquires the rotation speed of the motor 21 in a period between time T22 and time T23 in FIG: 9 as the stable rotation speed Rs at S203. If the motor 21 is not in the stable state Operation state (S202: NO), the processing of the engine state obtaining part 32 returns to S202 and waits until the engine 21 operates stably.

When the stable rotation speed Rs is obtained, the return checking part 34 sets the increased rotation speed Rt at S204. The return checking part 34 sets the increased rotation speed Rt based on the stable rotation speed Rs obtained at S203. The increased rotation speed Rt can be arbitrarily set according to the configuration of the exhaust gas purification system 10 and the like. After setting the increased rotation speed Rt at S204, the return checking part 34 sets a time count Tm to 0 at S204. That is, the return checking part 34 sets the time count, which is a count of a timer provided in the control device 30, to 0.

After setting the time count Tm to 0 at S205, the return checking part 34 acquires the rotation speed Rc of the motor 21 at S206. The rotation speed Rc of the motor is the last rotation speed of the motor 21. The return checking part 34 checks at S204 whether the rota obtained at S206 tion speed Rc is equal to or greater than the increased rotation speed Rt. At a time T24 in 9 , at which the urea water remaining in the urea water passage 19 is reduced, the rotation speed Rc of the motor 21 increases continuously. At a time T25 in 9 , at which the return of the urea water from the urea water passage 19 has been completed, the rotation speed Rc of the motor 21 increases to the increased rotation speed Rt or more.

When the rotation speed Rc is equal to or greater than the increased rotation speed Rt (S207: YES), the return checking part 34 increments the time count Tm at S208. That is, when the rotation speed Rc reaches the increased rotation speed Rt, the return checking part 34 starts measuring the timing. If the rotation speed Rc is smaller than the increased rotation speed Rt (S207: NO), the return checking part 34 returns its processing to S205.

After incrementing the time count Tm at S208, the return checking part 34 checks at S209 whether the time count Tm is equal to or greater than the predetermined continuation period Tt. That is, the return checking part 34 checks whether the time count Tm, whose count was started at S208, has reached time T36. When the time count Tm is equal to or larger than the predetermined continuation period Tt (S209: YES), the return checking part 34 controls the motor to stop at S210. The control device 30 returns its processing to S11 in FIG 3 main routine shown. Following the determination by the return checking part 34 at S210 that the return of urea water has been completed, the engine stopping part 35 stops the engine 21 immediately at time T26 or at a time T27 which is after the predetermined delay period D from the determination of the urea water return completion. If the time count Tm is smaller than the predetermined continuation period Tt (S209: NO), the return checking part 34 returns to S206. That is, the return checking part 34 continues to monitor the rotation speed Rc of the motor 21 until the time count reaches the predetermined continuation period Tt.

In the first example for explaining the invention, the return checking part 34 determines that the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed when the rotation speed Rc of the motor 21 continues to be equal to or greater than the increased rotation speed Rt during the predetermined continuation period Tt or is longer. If the urea water contains bubbles, the load of the motor 21 may vary with the amount of urea water remaining in the channel, and the rotation speed Rc of the motor 21 may temporarily increase above the increased rotation speed Rt. In this case, the return verification part 34 is likely to incorrectly determine the completion of the urea water return. The return checking part 34 therefore determines that the return of urea water has been completed when the rotation speed Rc of the motor 21 continues to be equal to or greater than the increased rotation speed Rt during or longer than the predetermined continuation period Tt. Accordingly, it is possible to safely prevent urea water from remaining in the urea water passage 19 and reduce unnecessary energy consumption in driving the urea water pump 15 after completion of the urea water return.

(Second Embodiment)

The control device 30 according to a second embodiment will be described next. The control device 30 according to the second embodiment is configured similarly to the first embodiment. However, in the second embodiment, the return verification part 34 executes the urea water return completion verification processing differently from that in the first embodiment.

In the second embodiment, the return checking part 34 checks whether the return of urea water has been completed based on a power provided to the motor 21. The reverse driving part 33 controls the motor 21 which rotates in the reverse direction to maintain a constant rotation speed. In this control, the motor state acquiring part 32 acquires the current Ic supplied to the motor 21 rotating in the reverse direction as the driving state of the motor 21. When the current Ic supplied to the motor 21 and acquired by the motor state acquiring part 32, decreases to a reduced current value It, the return checking part 34 determines that the return of urea water from the urea water channel 19 to the urea water tank 14 has been completed. The load acting on the motor 21 rotating in the reverse direction for returning the urea water varies according to the urea water remaining in the urea water passage 19. The load acting on the motor 21 from the urea water decreases as the return flow supply of urea water is completed. For this reason, the current Ic supplied to the motor 21 when the rotation speed is controlled to be constant temporarily decreases at the time of completion of urea water recycling. The current Ic provided to the motor 21 varies according to changes in load caused by remaining urea water.

Verification processing of a urea water return completion in the second embodiment is explained with reference to a in 10 flowchart shown and an in 11 time diagram shown. Same processing and operations as those of the above-described embodiment and example for explaining the invention will not be described. The controller 30 starts returning the urea water from the urea water passage 19 to the urea water tank 14 at S301. The controller 30 drives the urea water pump 15 through the motor 21 at a time T31 11 and returns the urea water remaining in the urea water channel 19 to the urea water tank 14. At this time, the reverse driving part 33 drives the motor 21 in the reverse direction.

When the motor 21 is driven at S301, the motor state obtaining part 32 checks whether the motor 21 operates stably at S302. If the motor 21 is in the stable operating state (S302: YES), the motor state obtaining part 32 acquires the current supplied to the motor 21 in a period between time T32 and time T33 at S303 11 is provided as the stable current value Is. If the motor 21 is not in the stable operation state (S302: NO), the motor state obtaining part 32 returns its processing to S302 and waits until the motor 21 operates stably.

When the stable current value Is is obtained, the return checking part 34 sets a reduced current value It at S304. The return checking part 34 sets the reduced current value It based on the stable current value Is obtained at S303. When the urea water is returned from the urea water channel 19, the current provided to the motor 21 varies with parameters such as temperature that change the property of urea water. The stable current Is obtained at S303 therefore varies each time the urea water is returned. For this reason, the return checking part 34 acquires the stable current value Is every time the urea water is returned and sets the reduced current value It based on the acquired stable current value Is. In the second embodiment, the reduced current value It is set to be smaller than the stable current value Is, for example, by several tens of percent of the stable current value Is. The decrease rate of the reduced current value It with respect to the stable current value Is may be arbitrarily set according to the configuration of the exhaust gas purification system 10 and the like.

After setting the reduced current value It at S304, the return checking part 34 obtains the current Ic provided to the motor 21 at S305. That is, the return checking part 34 acquires the last current provided to the motor 21 as the current Ic. The return checking part 34 checks at S306 whether the current Ic obtained at S305 is equal to or smaller than the reduced current value It. That is, the return checking part 34 checks whether the last current Ic supplied to the motor 21 is equal to or smaller than the reduced current value It.

When the current Ic is equal to or smaller than the reduced current It (S306: YES), the return checking part 34 determines at S307 that the return of urea water has been completed. That is, when the last current Ic provided to the motor 21 is equal to or smaller than the reduced current value It, the return checking part 34 determines that the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed. The load acting on the motor 21 when the rotation speed is controlled to be constant varies with the amount of urea water remaining in the urea water passage 19. For this reason, when the urea water remaining in the urea water channel 19 at a time T34 of 11 is reduced, the current Ic provided to the motor 21 continuously decreases. When the return of urea water from the urea water channel 19 at a time T35 of 11 is completed, the current Ic provided to the motor 21 decreases to the reduced current value It or a smaller current value. The return checking part 34 therefore determines that the return of urea water from the urea water passage 19 has been completed at a time at time T35 at which the current Ic supplied to the motor 21 decreases to the reduced current value It or a smaller current value. The control device 30 thus returns its processing to S11 in 3 main routine shown. Following the determination of S307 that the return of urea water has been completed, the engine stopping part 35 stops the engine 21 immediately at time T35 or at a time 36 by the predetermined delay period D based on the determination the urea water return completion is later.

If the current Ic is determined to be larger than the reduced current value It (S306: NO), the return checking part 34 returns to step S305. That is, the return checking part 34 continues to monitor the current Ic provided to the motor 21 from time T33 at which the current Ic is larger than the reduced current value It to time T35.

In the second embodiment, the return checking part 34 determines that the return of urea water from the urea water passage 19 to the urea water tank 14 has been completed when the current Ic supplied to the motor 21 decreases to be smaller than the reduced current value It, in the state in which the motor 21 is controlled to maintain the constant rotation speed. The current Ic supplied to the motor 21 varies according to the amount of urea water remaining in the urea water passage 19 in the state where the rotation speed of the motor 21 for driving the urea water pump 15 is controlled to the constant rotation speed . When the return of urea water has been completed, the load acting on the motor 21 decreases and the current Ic supplied to the motor 21 decreases. The return checking part 34 therefore determines that the return of urea water has been completed when the current Ic supplied to the motor 21 decreases to the reduced current value It. Accordingly, it is possible to check whether the return of urea water has been completed based on the current Ic provided to the motor 21. Thus, it is possible to avoid remaining the urea water in the urea water channel 19.

(Second example to explain the invention)

The control device 30 according to a second example for explaining the invention will be described next. The control device 30 according to the second example for explaining the invention is configured similarly to the first embodiment.

However, in the second example for explaining the invention, the return verification part 34 executes the urea water return completion verification processing differently from that of the first embodiment. In the second example for explaining the invention, the return checking part 34 checks whether the return of urea water has been completed based on the power provided to the motor 21. The reverse driving part 33 controls the motor 21 which rotates in the reverse direction to maintain a constant rotation speed. In this control, the motor state obtaining part 32 acquires the current Ic provided to the motor 21 rotating in the reverse direction as the driving state of the motor 21. When the current Ic provided to the motor 21 and obtained by the motor state obtaining part 32 , decreases to be equal to or smaller than the reduced current value It, and continues for a predetermined continuation period Tt or longer, the return checking part 34 determines that the return of urea water from the urea water channel 19 to the urea water tank 14 has been completed. Similar to the first embodiment, the load acting on the motor 21 varies according to the urea water remaining in the urea water passage 19. Accordingly, the power provided to the motor 21 decreases when the return of urea water is completed. The return checking part 34 determines that the return of urea water has been completed when the current Ic supplied to the motor 21 continues to be smaller than the reduced current value It. This continuation period Tt is arbitrarily set, for example, according to an operation characteristic of the engine.

Verification processing of a urea water recovery completion in the second example for explaining the invention will be explained with reference to a 12 flowchart shown and an in 13 time diagram shown. Same processing and operations as those of the first embodiment will not be described.

The controller 30 starts returning the urea water from the urea water passage 19 to the urea water tank 14 at S401. The controller 30 drives the urea water pump 15 through the motor 21 at a time T41 of 13 and returns the urea water remaining in the urea water channel 19 to the urea water tank 14. At this time, the driving part 33 drives the motor 21 in the reverse direction.

When the motor 21 is driven at S401, the motor state obtaining part 32 checks whether the motor 21 operates stably at S402. If the motor 21 is in the stable operating state (S402: YES), the motor state obtaining part 32 acquires the current supplied to the motor 21 in a period between time T42 and time T43 at S403 13 is provided as the stable current value Is. If the motor 21 is not in the stable operating state (S402: NO), returns the engine state acquisition part 32 returns its processing to S402 and waits until the engine 21 operates stably.

When the stable current value Is is obtained, the return checking part 34 sets the reduced current value It at S404. The return checking part 34 sets the reduced current value It based on the stable current value Is obtained at S403. The reduced current value It may be arbitrarily set according to the configuration of the exhaust gas purification system 10 and the like. After setting the reduced current value It at S404, the return checking part 34 sets the time count Tm to 0 at S405. That is, the return checking part 34 sets the time count Tm, which is a time count of a timer provided in the control device 30, to 0.

After setting the time count Tm to 0 at S405, the return checking part 34 obtains the current Ic provided to the motor 21 at S406. The current Ic provided to the motor 21 is the last current value provided to the motor 21. The return checking part 34 checks at S407 whether the current value Ic obtained at S406 is equal to or smaller than the reduced current value It. At one time T44 in 13 , in which the urea water remaining in the urea water channel 19 is reduced, the current provided to the motor 21 continuously decreases. At one time T45 from 13 , at which the return of the urea water from the urea water passage 19 has been completed, the current Ic supplied to the motor 21 decreases to be equal to or smaller than the reduced current value It.

If the current Ic supplied to the motor 21 is equal to or smaller than the reduced current value It (S407: YES), the return checking part 34 increments the time count Tm at S408. That is, when the current Ic supplied to the motor 21 decreases to be equal to or smaller than the reduced current value It, the return checking part 34 starts measuring a timing. If the current Ic supplied to the motor 21 is larger than the reduced current value It (S407: NO), the return checking part 34 returns its processing to S405.

After incrementing the time count Tm at S408, the return checking part 34 checks at S409 whether the time count Tm is equal to or greater than the predetermined continuation period Tt. That is, the return checking part 34 checks whether the time count Tm started to count at S408 has reached the predetermined continuation period Tt, which is a time T46 of 13 corresponds. If the time count Tm is equal to or larger than the continuation period Tm (S409: YES), the return checking part 34 determines at S410 that the return of urea water has been completed. The control device 30 returns its processing to S11 in FIG 3 main routine shown. Following the determination by the return checking part 34 at S410 that the return of urea water has been completed, the engine stopping part 35 immediately stops the engine 21 at a time T46 or a time T47 by a predetermined delay period D later than the determination. If the time count Tm is smaller than the predetermined continuation period Tt (S409: NO), the return checking part 34 returns its processing to step S406. That is, the return checking part 34 continues to monitor the current Ic supplied to the motor 21 until the time count Tm reaches the predetermined continuation period Tt.

In the second example for explaining the invention, the return checking part 34 determines that the return of urea water from the urea water channel 19 to the urea water tank 14 has been completed when the current Ic provided to the motor 21 continues to be equal to or smaller than the reduced current value It during the predetermined continuation period Tt or longer. If the urea water contains bubbles, the load of the motor 21 may vary according to the amount of urea water remaining in the channel, and the current Ic provided to the motor 21 may temporarily become smaller than the predetermined current It. In this case, the return verification part 34 is likely to erroneously determine the completion of the urea water return. The return checking part 34 therefore determines that the return of urea water has been completed when the current Ic supplied to the motor 21 continues to be equal to or smaller than the reduced current value It for a predetermined continuation period Tt or longer. Accordingly, it is possible to safely prevent urea water from remaining in the urea water passage 19 and reduce unnecessary energy consumption in driving the urea water pump 15 after completion of the urea water return. The present invention is not limited to the above embodiments but may be implemented variously.

List of reference symbols:

10

Exhaust gas purification system

11

Internal combustion engine

12

Exhaust pipe element

13

exhaust duct

14

Urea water tank

15

Urea water pump

16

Urea water channel part

17

Reduction catalyst

18

injector

19

Urea water channel

21

engine

22

battery

30

Control device

31

Microcomputer

32

Engine condition acquisition part

33

Reverse drive part

34

Return verification part

35

Engine stop part

Claims (7)

A urea water injection control device (30) for supplying urea water stored in a urea water tank (14) into an exhaust passage (13) of an internal combustion engine (11) for reducing nitrogen oxides contained in an exhaust gas of the internal combustion engine (11) by a reduction catalyst (17), wherein the urea water injection control device (30) includes an injector (18) provided in the exhaust passage (13) for injecting the urea water and a urea water pump (15) provided in a urea water passage (19) that controls the urea water tank (14) and the injector (18) for supplying the urea water from the urea water tank (14) to the injector (18), the urea water injection control device (30) comprising: an engine state acquiring part (32) for acquiring a driving state of a motor (21) that drives the urea water pump (15); a reverse drive part (33) for driving the motor (21) in a reverse direction opposite to a forward direction of supplying urea water to the injector (18) to return the urea water in the urea water passage (19) to the urea water tank (14); and a return checking part (34) for checking whether return of urea water from the urea water channel (19) to the urea water tank (14) has been completed based on the driving state of the engine (21) obtained by the engine state obtaining part (32), in a state, in which the motor (21) is driven by the reverse drive part (33), wherein when the engine state acquiring part (32) determines that the engine (21) is operating stably, the engine state obtaining part (32) acquires the driving state of the engine (21) at that time as a stable driving state, and the return checking part (34) sets a setting value based on the stable driving state and determines whether the return of the urea water from the urea water channel (19) to the urea water tank (14) has been completed based on the driving state of the engine (21) determined by the engine state obtaining part (32) is obtained, and the determination value. Urea water injection control device according to Claim 1 , wherein: the return checking part (34) sets an increased rotation speed Rt as the setting value; and the return checking part (34) determines that the return of urea water from the urea water channel (19) to the urea water tank (14) has been completed when a rotation speed Rc of the motor (21) increases to be equal to or greater than the increased rotation speed Rt, in a state in which the motor (21) is controlled to maintain a constant torque. Urea water injection control device according to Claim 1 , wherein: the return checking part (34) sets an increased rotation speed Rt as the setting value; and the return checking part (34) determines that the return of urea water from the urea water channel (19) to the urea water tank (14) has been completed when a rotation speed Rc of the motor (21) increases to be equal to or greater than a predetermined continuation period Tt increased rotation speed Rt, in a state in which the motor (21) is controlled to maintain a constant torque. Urea water injection control device according to Claim 1 , wherein: the return checking part (34) sets a reduced current value Ic as the setting value; and the return checking part (34) determines that the return of urea water from the urea water channel (19) to the urea water tank (14) has been completed when a current Ic supplied to the motor (21) decreases to be equal to or less than the reduced one Current value It to be in a state in which the Motor (21) is controlled to maintain a constant rotation speed. Urea water injection control device according to Claim 1 , wherein: the return checking part (34) sets a reduced current value Ic as the setting value; and the return checking part (34) determines that the return of urea water from the urea water channel (19) to the urea water tank (14) has been completed when a current Ic provided to the motor (21) decreases for longer than a predetermined continuation period Tt to be equal to or smaller than the reduced current value It in a state in which the motor (21) is controlled to maintain a constant rotation speed. Urea water injection control device according to one of Claims 1 until 5 , further comprising: an engine stop part (35) for stopping the engine (21) immediately following a determination of the return checking part (34) indicating that the return of the urea water from the urea water channel (19) to the urea water tank (14) has been completed. Urea water injection control device according to one of Claims 1 until 5 , further comprising: an engine stop part (35) for stopping the engine (21) after a predetermined delay period following a determination of the return checking part (34) indicating that the return of urea water from the urea water channel (19) to the urea water tank (14) is completed became.

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