JP2015203347A - Control device of exhaust purification system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an exhaust purification system which achieves both failure avoidance of a urea water pump and improvement in start-up performance by changing start-up torque of a motor in accordance with a condition.SOLUTION: A torque changing section 34 controls torque generated by a motor 16 in a manner that changes first torque which is usual start-up torque to second torque which is lower than the first torque when freezing of urea water is considered in a previous start-up condition. That is, the motor 16 is started up with the second torque lower than the first torque when a urea water thawing process is performed in the last start-up of the motor 16 and thereby preventing the motor 16 and a urea water pump 15 driven thereby from excessive force. In contrast, the torque changing section 34 sets the torque applied to the motor 16 at the usual first torque when the urea water thawing process taking into consideration the freezing of the urea water is not performed in the last start-up and thereby enabling the motor 16 to achieve a target rotation speed in a short period of time.

Description

  The present invention relates to an exhaust purification system control device that purifies exhaust gas from an internal combustion engine.

  Conventionally, a urea SCR (Selective Catalytic Reduction) system using urea as post-processing for purifying exhaust gas of an internal combustion engine is known. In the urea SCR system, nitrogen oxide (NOx) contained in the exhaust is reduced by adding urea to the exhaust. Here, urea is added to the exhaust gas as urea water as an aqueous solution. The urea water stored in the urea water tank is pressurized by the urea water pump and supplied to the injector via the urea water passage (Patent Document 1).

  The urea water pump that pressurizes the urea water is driven by a motor such as a brushless motor. When starting from a stopped state, this motor generates a torque larger than that in a steady rotational state in order to converge to a target rotational speed. However, urea water used for the urea SCR system may freeze in a cold region. If the motor is started in such a state where the urea water is frozen or the urea water is not sufficiently thawed, there is a possibility that the urea water pump may be broken due to the starting torque generated by the motor. On the other hand, if the torque generated at the start of the motor is reduced in order to avoid the failure of the urea water pump, the start-up at the normal start time when the urea water is not frozen and the convergence to the steady rotational speed will deteriorate. There's a problem.

JP 2008-157218 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an exhaust purification system that achieves both avoidance of failure of the urea water pump and improvement of startability by changing the starting torque of the motor according to conditions. .

  In the present invention, the torque changing means changes the starting torque of the motor according to the previous starting condition of the motor. The previous start condition of the motor is acquired at the previous start of the motor and stored in the storage means. The torque changing means acquires the previous start condition stored in the storage means. This previous start condition includes a start condition indicating whether or not the process was executed at the previous motor start, such as the presence or absence of thawing process of urea water or the case where the motor is returned from the stop due to overcurrent. It is out. The torque changing means changes the torque at the start of the current motor with reference to the previous start condition acquired from the storage means. Thereby, the torque changing means limits the torque applied to the motor when freezing of the urea water is considered in the previous start condition. On the other hand, the torque changing means does not limit the torque applied to the motor when freezing of the urea water is not considered in the previous start condition. Therefore, it is possible to achieve both the avoidance of the failure of the urea water pump due to the excessive torque being applied and the improvement of the startability by the torque without the limitation being applied.

According to a third aspect of the present invention, the torque changing means changes the starting torque of the motor according to the voltage of the power source. Therefore, the starting torque of the motor is stabilized according to the voltage of the power source. Therefore, the starting torque of the motor can be precisely controlled.
In the invention according to claim 4, the torque changing means changes the starting torque according to the temperature of the urea water when the previous starting condition is not stored. Therefore, the starting torque of the motor is set according to the latest urea water temperature even when the previous starting condition is not stored in the storage means. This avoids forcibly starting the motor when the urea water is frozen. Therefore, it is possible to avoid the failure of the urea water pump due to excessive torque being applied.

The block diagram which shows the control apparatus of the exhaust gas purification system by 1st Embodiment. The schematic diagram which shows the exhaust gas purification system by 1st Embodiment Schematic which shows the electrical structure of the motor of the exhaust gas purification system by 1st Embodiment. Schematic which shows the flow of a process by the control apparatus of the exhaust gas purification system by 1st Embodiment. Schematic showing timing chart in low torque start Schematic showing timing chart in high torque start Schematic which shows the flow of a process by the control apparatus of the exhaust gas purification system by 2nd Embodiment.

Hereinafter, a control device for an exhaust gas purification system according to a plurality of embodiments will be described with reference to the drawings. Note that, in a plurality of embodiments, substantially the same components are denoted by the same reference numerals, and description thereof is omitted.
(First embodiment)
An exhaust purification system 10 shown in FIG. 2 constitutes an SCR system in which urea water is added to exhaust discharged from an internal combustion engine 11 mounted on a vehicle, for example, to reduce NOx contained in the exhaust. Exhaust gas from the internal combustion engine 11 is released to the atmosphere via an exhaust passage 13 formed by the exhaust pipe member 12. The internal combustion engine 11 is a diesel engine, for example. The exhaust purification system 10 may be applied not only to a diesel engine but also to a gasoline engine or a gas turbine engine. Further, the exhaust purification system 10 is not limited to the on-board internal combustion engine 11, but may be applied to a stationary internal combustion engine 11 such as a power generation unit, for example.

  The exhaust purification system 10 includes a urea water tank 14, a urea water pump 15, a motor 16, a urea water passage portion 17, and a reduction catalyst 18. The urea water tank 14 stores an aqueous solution of urea that is urea water. The urea water pump 15 is accommodated in the urea water tank 14. The motor 16 drives the urea water pump 15. The urea water pump 15 is driven by supplying electric power to the motor 16, pressurizes the urea water sucked from the urea water tank 14, and discharges it to the urea water passage portion 17. The urea water passage portion 17 forms a urea water passage 19. The reduction catalyst 18 is provided in the exhaust passage 13 formed by the exhaust pipe member 12.

  The exhaust purification system 10 includes an injector 21 in addition to the above. The urea water passage 19 is connected to the injector 21 at the end opposite to the urea water pump 15. The urea water discharged from the urea water pump 15 is supplied to the injector 21 via the urea water passage 19. The injector 21 is provided on the exhaust pipe member 12. The injector 21 penetrates the exhaust pipe member 12 and has a tip exposed to the exhaust passage 13. The urea water supplied to the injector 21 is injected into the exhaust gas flowing through the exhaust passage 13. Exhaust gas discharged from the internal combustion engine 11 and urea water injected from the injector 21 are mixed in the exhaust passage 13 and flow into the reduction catalyst 18. NOx contained in the exhaust is reduced by a chemical reaction with urea contained in the urea water in the reduction catalyst 18.

  The above-described exhaust purification system 10 is controlled by the control device 30. As shown in FIG. 1, the control device 30 includes a control unit 31, a storage unit 32, a temperature sensor 33, a torque change unit 34, and a freezing determination unit 35. The control unit 31 includes a microcomputer having a CPU, a ROM, and a RAM, and controls the exhaust purification system 10 by a computer program stored in the ROM. The storage unit 32 is configured by a non-volatile medium such as a flash memory. The storage unit 32 may be shared with the ROM and RAM of the control unit 31. The storage unit 32 stores the previous start condition. The previous start condition is the previous start condition of the motor 16 when the motor 16 is started, that is, the previous start condition of the motor 16. Specifically, the previous start condition includes the following conditions.

(1) Overcurrent return: Whether or not the previous start of the motor 16 is a return from a stop associated with the supply of overcurrent. (2) Freezing and thawing processing: The previous start of the motor 16 performs thawing of urea water. The temperature sensor 33 corresponds to a temperature detection unit and detects the temperature of the urea water stored in the urea water tank 14. The temperature sensor 33 outputs the detected temperature of the urea water to the control unit 31 as an electrical signal. The control device 30 is connected to a battery 36 as a power source, the motor 16 and the injector 21. Thereby, the control apparatus 30 controls the drive of the motor 16 and the injector 21 by controlling the electric power supplied from the battery 36.

  The control device 30 implements the torque changing unit 34 and the freezing determination unit 35 in software by executing a computer program. The torque changing unit 34 and the freeze determining unit 35 may be realized by hardware, or may be realized by cooperation of software and hardware. The torque changing unit 34 changes the torque when the motor 16 is started, that is, the starting torque. Specifically, the torque changing unit 34 changes the starting torque of the motor 16 according to the previous starting condition stored in the storage unit 32. The torque changing unit 34 starts the motor 16 with a preset first torque when “overcurrent return” is stored as the previous start condition. On the other hand, the torque changing unit 34 starts the motor 16 with the preset second torque when “freezing and thawing processing” is stored as the previous start condition.

  When “overcurrent return” is stored as the previous start condition, the motor 16 is started normally at the time of the previous start. Therefore, the torque changing unit 34 sets the starting torque of the motor 16 to the same first torque as that of the normal starting. As a result, the motor 16 is supplied with a current corresponding to the first torque, and quickly rises to a steady rotational speed. On the other hand, when “freezing and thawing processing” is stored as the previous start condition, urea water may be frozen at the previous start. For this reason, if the motor 16 is started with the same starting torque as usual, the urea water pump 15 or the motor 16 may be damaged by the frozen urea water. Therefore, the torque changing unit 34 sets the starting torque of the motor 16 to a second torque smaller than the first torque, so that the motor 16 is supplied with a current corresponding to the second torque smaller than the first torque. The rotational speed increases more slowly than the start by the first torque. As a result, an excessive force is not applied to the urea water pump 15 and the motor 16, and the failure of the urea water pump 15 and the motor 16 is reduced.

  The freezing determination unit 35 determines whether or not the urea water stored in the urea water tank 14 is frozen. The freezing determination unit 35 determines whether the urea water is frozen based on the temperature of the urea water detected by the temperature sensor 33. Urea water is an aqueous solution of urea, and freezes when it falls below a specific melting point. Therefore, the freezing determination unit 35 determines that the urea water stored in the urea water tank 14 is frozen when the temperature of the urea water detected by the temperature sensor 33 falls below the temperature at which freezing is expected. Further, the freezing determination unit 35 may be configured not only to detect the temperature of the urea water directly by the temperature sensor 33 to determine freezing but also to indirectly determine freezing. The freezing determination unit 35 determines whether urea water is frozen based on, for example, the outside air temperature detected by an outside air temperature sensor that detects the outside air temperature, or the cooling water temperature detected by the water temperature sensor that detects the temperature of the cooling water of the internal combustion engine 11. May be judged. Furthermore, the freezing determination unit 35 may be configured to determine the presence or absence of freezing based on an image of the urea water tank 14 as well as the temperature. When the freezing determination unit 35 determines that the urea water is frozen, the control unit 31 executes a “freezing and thawing process” for thawing the frozen urea water. This “freezing and thawing process” is performed, for example, by heating the urea water in the urea water tank 14 using a heater provided in the urea water tank 14. In addition, the “freezing and thawing process” may be configured not only to heat the urea water with a heater but also to supply the motor 16 with power that does not generate rotational torque and to heat the urea water by the heat generated by the coil of the motor 16. Good.

  The motor 16 described above has three terminals 41, 42, and 43 corresponding to the U phase, V phase, and W phase as shown in FIG. High side switching elements 51, 52, 53 are connected between the terminals 41, 42, 43 and the battery 36, respectively. The high-side switching elements 51, 52, and 53 are, for example, P-channel MOSFETs. Further, low-side switching elements 54, 55, and 56 are connected between the terminals 41, 42, and 43 and the ground potential (GND), respectively. The low side switching elements 54, 55, 56 are, for example, N-channel MOSFETs. The control unit 31 performs control so that the high-side switching elements 51, 52, and 53 and the low-side switching elements 54, 55, and 56 in a specific phase are not simultaneously turned on. The ON signal inputs of the high side switching elements 51, 52, 53 and the low side switching elements 54, 55, 56 are connected to the drive circuit 57. The drive circuit 57 receives the signal connected from the control unit 31 and the ON signals of the high-side switching elements 51, 52, 53 and the low-side switching elements 54, 55, 56, and drives each switching element. The position detection unit 58 includes, for example, an encoder and detects the position of a rotor (not shown) of the motor 16.

  The control unit 31 switches the energization pattern to each phase of the motor 16 based on the position of the rotor of the motor 16 detected by the position detection unit 58. Thereby, the motor 16 is rotationally driven. Further, in the case of the sensorless motor 16 in which the position detector 58 is not provided, the control unit 31 estimates the position of the motor 16 by monitoring the induced voltage generated in the phase that is not energized. In the case of the sensorless motor 16, no induced voltage is generated when the motor 16 is started, and the position cannot be detected. Therefore, when the sensorless motor 16 is started, the control unit 31 performs position fixing control for energizing in the direction of two specific patterns to fix the position of the rotor. The control unit 31 performs fixed drive control forcibly switching the energization pattern within a preset time following the rotor position fixing control. When the position by the induced voltage is detected by the fixed drive control, the control unit 31 shifts to the steady rotation control that continues the steady rotation. In the case of the present embodiment, the motor 16 is described as sensorless.

Next, the flow of processing by the control device 30 having the above configuration will be described with reference to FIG.
When it is time to start the motor 16, the torque changing unit 34 acquires the previous start condition from the storage unit 32 (S101). That is, the torque changing unit 34 acquires the previous start condition stored in the storage unit 32. Then, the torque changing unit 34 determines whether or not the acquired previous start condition is “freezing and thawing processing” (S102). That is, the torque changing unit 34 determines whether or not “freezing and thawing processing” is included as the previous start condition. When “freezing and thawing process” is included in the previous start condition, it means that the process for thawing the frozen urea water was performed prior to the start of the motor 16 when the motor 16 was started last time. To do.

The torque changing unit 34 starts the motor 16 with the second torque when the “freezing and thawing process” is included in the previous start condition (S102: Yes) (S103). On the other hand, when the “freezing and thawing process” is not included in the previous start condition (S102: No), the torque changing unit 34 starts the motor 16 with the first torque (S104). Therefore, when the “freezing and thawing process” is not included in the previous start condition, the motor 16 rises to the target rotation speed in a short period of time.
As described above, when the motor 16 is started, the torque changing unit 34 acquires the previous start condition, and sets the start torque for starting the motor 16 according to the acquired previous start condition.

Next, a timing chart for controlling the motor 16 will be described with reference to FIGS. 5 and 6.
In FIG. 5, the start of the process is t0. The freezing determination unit 35 executes “freezing and thawing processing” for thawing urea water from t0 to t1 when freezing of urea water is predicted. The torque changing unit 34 acquires the previous start condition at t2 after the “freezing and thawing process” is completed. In this case, since the “freeze-thaw process” is executed from t0 to t1, the previous start condition includes “freeze-thaw process”. Therefore, the torque changing unit 34 sets the second torque as the starting torque of the motor 16. Thereby, the control unit 31 outputs a low torque command value corresponding to the second torque as the torque command value output to the motor 16 at t3. The control unit 31 maintains this low torque command value until t5 when the fixed drive control ends after t4 when the position fixed control ends. From t3 to t4, the control unit 31 outputs a PWM signal having a preset duty ratio for position fixing control for fixing the position of the rotor of the motor 16. When the position fixing control is completed and the process shifts to the fixed driving control at t4, the control unit 31 outputs a PWM signal having a duty ratio corresponding to the low torque command value. At this time, the PWM signal is output as a duty ratio lower than that at the time of normal starting. As a result, the rotation speed of the motor 16 increases as time elapses from t4, and the increase in the rotation speed moderates as it approaches the target rotation speed. When the motor 16 reaches the target rotational speed at t5, the control unit 31 shifts to steady rotational speed control for maintaining the motor 16 at a steady rotational speed. The control unit 31 outputs a PWM signal with a constant duty ratio when in the steady rotation speed control. The control unit 31 sets the low torque command value to “0” when reaching a steady rotation speed and reaching a preset period, that is, t6 when the start period of the motor 16 has elapsed. The control unit 31 stops outputting the PWM signal at time t7 when the driving of the motor 16 is stopped. As a result, the motor 16 stops at a reduced rotational speed. These t3 to t7 correspond to low torque starting that starts the motor 16 with the second torque.

  In FIG. 6, the start of the process is t10. In the case of the process shown in FIG. 6, it is assumed that the “freezing and thawing process” has not been executed prior to the previous start of the motor 16. The torque changing unit 34 acquires the previous start condition at t11 before starting the motor 16. In this case, the “freezing and thawing process” is not included in the previous start condition. Therefore, the torque changing unit 34 sets the first torque as the starting torque. Thereby, the control unit 31 outputs the high torque command value corresponding to the first torque as the torque command value output to the motor 16 at t12. The control unit 31 maintains this high torque command value until t14 when the fixed drive control ends after t13 when the position fixing control ends. At t12 to t13, the control unit 31 outputs a PWM signal having a duty ratio set in advance for position fixing control. When the position fixing control is completed and the process shifts to the fixed driving control at t13, the control unit 31 outputs a PWM signal having a duty ratio corresponding to the high torque command value. At this time, the PWM signal is output as a high duty ratio similar to that at the time of normal starting. Thereby, the rotation speed of the motor 16 increases toward the target rotation speed as time elapses from t13. When the motor is started with a high torque command value corresponding to the first torque, the duty ratio of the PWM signal is high as described above. Therefore, when the motor is started with the high torque command value, the motor 16 reaches the target rotational speed in a short period of time compared to when the motor 16 is started with the low torque command value. When the motor 16 reaches the target rotation speed at t14, the motor 16 shifts to steady rotation speed control. The control unit 31 outputs a PWM signal with a constant duty ratio when in the steady rotation speed control. The control unit 31 sets the high torque command value to “0” when reaching a steady rotation speed and reaching a preset period, that is, t15 when the start period of the motor 16 has elapsed. As a result, the motor 16 continues to rotate at a constant steady rotational speed. This t10 to t15 corresponds to high torque starting that starts the motor 16 with the first torque.

  As described above, in the first embodiment, the torque changing unit 34 changes the starting torque of the motor 16 according to the previous starting condition of the motor 16. The torque changing unit 34 refers to the previous start condition acquired from the storage unit 32 and changes the torque at the start of the current motor 16. Thereby, the torque change part 34 restrict | limits the torque which the motor 16 emits to the 2nd torque lower than the 1st torque which is a normal starting torque, when freezing of urea water is considered in the last starting condition. Therefore, when the urea water thawing process was performed at the previous start of the motor 16, the motor 16 is started with the second torque having a low torque. Thereby, an excessive force is not applied to the motor 16 and the urea water pump 15 driven thereby. On the other hand, the torque changing unit 34 sets the torque applied to the motor 16 to the normal first torque when the freezing and thawing process in consideration of the freezing of the urea water is not executed in the previous start condition. As a result, the motor 16 reaches the target rotational speed in a short period of time. Therefore, it is possible to achieve both avoidance of failure of the urea water pump 15 and improvement of startability.

(Second Embodiment)
The control device 30 of the exhaust purification system 10 according to the second embodiment will be described.
The control device 30 of the exhaust purification system 10 according to the second embodiment has the same configuration as that of the first embodiment, and the processing flow is different. A processing flow of the control device according to the second embodiment will be described with reference to FIG. The description of the same processing as that of the first embodiment is omitted.

  When it is time to start the motor 16, the torque changing unit 34 determines whether or not the previous start condition is stored in the storage unit 32 (S201). When the torque changing unit 34 determines that the previous start condition is stored (S201: Yes), the torque changing unit 34 performs the processing from S101 to S104 in the first embodiment (S202 to S205). On the other hand, when determining that the previous start condition is not stored in the storage unit 32 (S201: No), the torque changing unit 34 acquires the temperature of the urea water from the temperature sensor 33 (S206). That is, the torque changing unit 34 acquires the temperature of the urea water in the urea water tank 14 when the previous start condition is not stored in the storage unit 32. The torque changing unit 34 sets the starting torque of the motor 16 based on the acquired urea water temperature (S207). Then, the torque changing unit 34 starts the motor with the set starting torque (S208). That is, when the temperature of the acquired urea water is low and freezing is expected, the torque changing unit 34 sets the starting torque of the motor 16 to a low torque like the second torque. On the other hand, when the temperature of the acquired urea water is high and there is no risk of freezing, the torque changing unit 34 sets the starting torque of the motor 16 to a high torque as with the first torque.

  Thus, in 2nd Embodiment, the torque change part 34 changes start torque according to the temperature of urea water, when the last start condition is not memorize | stored. Therefore, the starting torque of the motor 16 is set according to the latest urea water temperature even when the previous starting condition is not stored in the storage unit 32. Thereby, forcible start-up of the motor 16 when the urea water is frozen is avoided. Therefore, failure of the urea water pump 15 due to excessive torque can be avoided.

(Other embodiments)
In the above-described embodiments, the torque changing unit 34 may change the starting torque of the motor 16 according to the voltage of the battery 36. Thus, by changing the starting torque according to the voltage of the battery 36, the starting torque of the motor 16 is stabilized according to the voltage of the battery 36. Therefore, the starting torque of the motor 16 can be precisely controlled.

  The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

  In the drawings, 10 is an exhaust purification system, 14 is a urea water tank, 15 is a urea water pump, 16 is a motor, 30 is a control device, 32 is a storage unit (storage means), 33 is a temperature sensor (temperature detection means), 34 Is a torque changing unit (torque changing means), 35 is a freezing determining part (freezing determining means), and 36 is a battery (power source).

Claims (5)

In the exhaust gas purification system (10) comprising a urea water pump (15) for discharging urea water stored in a urea water tank (14) and a motor (16) for driving the urea water pump (15), the exhaust gas A control device (30) for controlling the purification system (10),
When starting the motor (16), storage means (32) for storing conditions at the time of starting;
When starting the motor (16), the previous start condition of the motor (16) stored in the storage means is acquired as the previous start condition, and the motor ( 16) torque changing means (34) for changing the starting torque;
A control device comprising: Freezing judgment means (35) for judging whether or not the urea water stored in the urea water tank (14) is frozen,
The said torque change means (34) changes the starting torque of the said motor (16) using the presence or absence of freezing of the urea water judged in the said freezing judgment means (35) as said last starting condition. Control device.   The control device according to claim 1 or 2, wherein the torque changing means (34) corrects the starting torque in accordance with a voltage of a power source that supplies electric power to the motor (16). A temperature detecting means (33) for detecting the temperature of the urea water stored in the urea water tank (14);
The torque changing means (34) changes the starting torque based on the temperature of the urea water detected by the temperature detecting means (33) when the previous starting condition is not stored in the storage means (32). The control device according to any one of claims 1 to 3. The torque changing means (34)
When the previous start condition is a return from a state in which an overcurrent is supplied to the motor (16), the start torque is set to a first torque,
The control device according to any one of claims 1 to 4, wherein when the previous start condition is a state of thawing frozen urea water, the start torque is set to a second torque smaller than the first torque. .

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