JP2012013060A - Scr system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SCR system that properly determines whether a tank heater valve can be restarted or not and can execute an unfreezing control of a urea water.SOLUTION: The SCR system includes: the unfreezing control part 1 that controls the opening and closing of the tank heater valve 124; a coil temperature estimation part 2 that estimates a coil temperature; a restart voltage threshold setting part 3 that sets a restart voltage threshold Vth for determining whether the tank heater valve 124 can be opened or not according to an estimated coil temperature presented by an accumulated value Σ; and an release allowing/prohibiting part 4 that allows the opening of the tank heater valve 124 when a battery voltage Va is the restart voltage threshold Vth or more, and that prohibits the opening the tank heater valve 124 when the battery voltage Va is the restart voltage threshold Vth or less.

Description

  The present invention relates to an SCR system that purifies exhaust gas by injecting urea water into exhaust gas of a diesel vehicle, and relates to an SCR system that can defrost urea water without hindering warming of an engine or heating of a passenger compartment.

  As an exhaust gas purification system for purifying NOx in exhaust gas of a diesel engine, an SCR system using an SCR (Selective Catalytic Reduction) device has been developed.

  This SCR system supplies urea water upstream of the exhaust gas of the SCR device, generates ammonia by the heat of the exhaust gas, and reduces and purifies NOx on the SCR catalyst by this ammonia (for example, patents) Reference 1).

JP 2000-303826 A

  Urea water freezes at -10 ° C. Since the outside air temperature is low in winter and cold regions, urea water may freeze when the engine is cold started. Urea water is injected into the exhaust pipe by an injector called a dosing valve, but it is injected when the urea water is frozen or in a sherbet shape even at one location in the urea water tank or between the urea water tank and the dosing valve. I can't.

  As a countermeasure, a tank heater is configured by inserting a cooling line for circulating engine cooling water into the urea tank. In the tank heater, the urea water can be thawed by heat exchange between the cooling water and the urea water. The cooling line is provided with a tank heater valve that switches whether to supply cooling water to the tank heater. By opening the tank heater valve as necessary, the tank heater can be operated to defrost the urea water, and the urea water in the urea water tank can be raised to the target temperature. This is called thawing control.

  By the way, the tank heater valve has a valve body, a coil, and a spring, and when the coil is energized, the valve body itself is moved by electromagnetic force or the plunger to which the valve body is attached is opened. The When the coil is de-energized, the valve element returns to its original position by the spring force, and the tank heater valve is shut off.

  The thawing control may be performed for several tens of minutes, sometimes exceeding 1 hour. As described above, when the thawing control is performed for a long time and the energization of the coil is maintained for a long time, the temperature of the coil rises, the electrical resistance of the coil rises, and the current hardly flows. Since the holding current for holding the tank heater valve in the open state is less than the current required to open the tank heater valve, the open state is maintained. However, once energization of the coil is stopped, when the coil is energized before the coil is cooled, if the battery voltage is low, sufficient current does not flow and the tank heater valve may not be opened. Here, the voltage required to open the tank heater valve from the shut-off state is referred to as a restart voltage.

  When opening the tank heater valve, for the purpose of monitoring the disconnection / short circuit of the wiring, for example, duty control (pulse width modulation drive; PWM) that opens for 4 minutes and shuts off for 1 minute at an interval of 5 minutes. (Also referred to as driving). If the coil is not cooled during the duty control cut-off period, the restart voltage remains high. If the vehicle electrical components (such as an air conditioner) are activated to increase the electrical load and the battery voltage is lower than the restart voltage, Even if the coil is energized at the next opening timing, the tank heater valve is not opened.

  Since the thawing control unit that controls opening / closing of the tank heater valve cannot recognize that the tank heater valve has not been opened, it continues to pass current through the coil. For this reason, the temperature of the coil further increases, the restart voltage rises, and the state where the tank heater valve is not opened continues.

  As a result, the thawing of urea water does not proceed, the state in which urea injection is impossible continues, exhaust gas cannot be purified, and finally an SCR system abnormality warning is issued.

  Therefore, a restart voltage threshold is set for the battery voltage, the restart voltage threshold is compared with the battery voltage, and the tank heater valve is allowed to open only when the battery voltage is equal to or higher than the restart voltage threshold. When the voltage is less than the restart voltage threshold, a measure to prohibit the opening of the tank heater valve can be considered.

  However, assuming that the coil temperature is high, if the restart voltage threshold is set too high, the battery voltage will restart even when the coil temperature is low and the actual restart voltage is lower than the battery voltage. If it is less than the voltage threshold, opening of the tank heater valve is prohibited.

  Conversely, if the restart voltage threshold is set too low, even if the coil temperature is high and the actual restart voltage is higher than the battery voltage, if the battery voltage is equal to or higher than the restart voltage threshold, The tank heater valve is allowed to open and the coil is energized.

  As described above, when a fixed restart voltage threshold value is set, it is not possible to cope with a restart voltage that varies depending on the coil temperature, and although it is possible to open, it is prohibited to open or not open. Although it is possible, opening is permitted, and the thawing control of urea water falls into trouble.

  Therefore, an object of the present invention is to provide an SCR system that solves the above-described problems and that can accurately determine whether or not a tank heater valve can be restarted and execute thawing control of urea water.

  In order to achieve the above object, the present invention provides a urea water tank for storing urea water to be injected into an exhaust pipe of an engine, a tank heater line inserted through the urea water tank, and an electromagnetic force of a coil. A tank heater valve that branches and distributes cooling water to the tank heater line, a thawing control unit that controls opening / closing of the tank heater valve, a coil temperature estimation unit that estimates the temperature of the coil, and an estimated coil temperature A restart voltage threshold setting unit for setting a restart voltage threshold for determining whether or not the tank heater valve can be opened; and when the battery voltage is equal to or higher than the restart voltage threshold, the tank heater valve is permitted to be opened. When the battery voltage is less than the restart voltage threshold value, an open permission / prohibition unit for prohibiting the opening of the tank heater valve is provided.

  The coil temperature estimation unit uses any one or more of an outside air temperature, a cooling water temperature, a vehicle speed, and a battery voltage as a parameter, refers to a coefficient of temperature increase of the coil set in advance according to the parameter as a parameter, While the tank heater valve is open, the increase coefficient is cumulatively added in increments of a predetermined time, and the temperature decrease coefficient of the coil set in advance according to the parameter is referred to by the parameter. While the heater valve is shut off, the temperature of the coil may be estimated by cumulative subtraction at predetermined time intervals.

  The restart voltage threshold value setting unit is based on a threshold value for high temperature, which is a voltage at which the tank heater valve can be opened regardless of the coil temperature, and a voltage at which the tank heater valve cannot be opened regardless of the coil temperature. The low temperature threshold candidate is set in advance, and when the estimated coil temperature is equal to or higher than the preset upper limit, the high temperature threshold candidate is set as the restart voltage threshold, and the estimated coil temperature is set to the preset lower limit. When the value is less than or equal to the value, the low temperature threshold candidate may be set as the restart voltage threshold.

  The present invention exhibits the following excellent effects.

  (1) The urea water thawing control can be executed by accurately determining whether or not the tank heater valve can be restarted.

It is a principal part block diagram of the SCR system which shows one Embodiment of this invention. 1 is a configuration diagram showing in detail an SCR system showing an embodiment of the present invention. It is an input-output block diagram of the SCR system of FIG. (A) is a transition diagram for determining whether to permit or prohibit valve opening in the present invention, (b) is a transition diagram for estimated coil temperature in the present invention, and (c) is a transition diagram for cumulative values and valve control regions. It is a flowchart which shows the process sequence in this invention.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIGS. 1 and 2, an SCR system 100 according to the present invention is inserted into a urea water tank 105 that stores urea water for injection into an exhaust pipe 102 of a diesel engine E, and a urea water tank 105. The tank heater line 124 is opened by an electromagnetic force of a coil (not shown) and a tank heater valve 124 for branching and distributing engine cooling water to the tank heater line 131, and the tank heater valve 124 is controlled to be opened / closed. Decompression control unit 1, coil temperature estimation unit 2 for estimating the coil temperature, and restart voltage threshold Vth for determining whether or not the tank heater valve 124 can be opened according to the estimated coil temperature represented by the cumulative value Σ When the battery voltage Va is equal to or higher than the restart voltage threshold Vth, the tank heater valve 12 Allow open, when the battery voltage Va is less than the restart voltage threshold Vth, are those having an open enabling and disabling unit 4 to prohibit the opening of the tank heater valve 124.

  In the present embodiment, the coil temperature estimation unit 2 uses any one or more of the outside air temperature, the cooling water temperature, the vehicle speed, and the battery voltage as a parameter, and a coil temperature increase coefficient α set in advance according to the parameter as a parameter. The temperature increase coefficient α is cumulatively added at predetermined time intervals while the tank heater valve 124 is opened, and the coil temperature decrease coefficient β set in advance according to the parameter is referred to by the parameter. While the tank heater valve 124 is shut off, the temperature of the coil is estimated by cumulatively subtracting the temperature decrease coefficient β every predetermined time. That is, the cumulative value Σ of the temperature increase coefficient α and the temperature decrease coefficient β is the estimated coil temperature.

  The temperature increase coefficient α and temperature decrease coefficient β depend on coil environmental conditions such as outside air temperature, cooling water temperature, vehicle speed, battery voltage, etc. In addition to setting, correction values are set in a one-dimensional map that is referenced by vehicle speed and a one-dimensional map that is referenced by battery voltage, and a reference value that is referenced by outside temperature and cooling water temperature is referenced by vehicle speed and battery voltage. It can be obtained by correcting the value.

  The temperature increase coefficient α corresponds to the amount of heat stored in the coil per unit time due to heat generated by energization and heat radiation to the outside air / cooling water, and represents the ease of increasing the coil temperature (ease of heating). Therefore, the temperature increase coefficient α is a small value when the outside air temperature is low, and the temperature increase coefficient α is a large value when the outside air temperature is high. When the cooling water temperature is low, the temperature increase coefficient α is a small value, and when the cooling water temperature is high, the temperature increase coefficient α is a large value. When the vehicle speed is high, the temperature increase coefficient α is a small value, and when the vehicle speed is low, the temperature increase coefficient α is a large value. When the battery voltage is low, the temperature increase coefficient α is a small value, and when the battery voltage is high, the temperature increase coefficient α is a large value.

  The temperature decrease coefficient β corresponds to the amount of heat emitted from the coil per unit time due to heat radiation to the outside air / cooling water, and represents the ease with which the coil temperature decreases (ease of cooling). The temperature decrease coefficient β is preferably set to a negative value and accumulated by an addition process common to the temperature increase coefficient α.

  Further, in the present embodiment, the restart voltage threshold value setting unit 3 includes the high temperature threshold candidate VH composed of a voltage capable of opening the tank heater valve 124 regardless of the coil temperature, and the tank heater valve 124 regardless of the coil temperature. Is set in advance, and when the estimated coil temperature represented by the cumulative value Σ is equal to or higher than a preset upper limit value ΣH, the high temperature threshold candidate VH Is set to the restart voltage threshold value Vth, and when the estimated coil temperature represented by the cumulative value Σ is equal to or lower than a preset lower limit value ΣL, the low temperature threshold candidate VL is set to the restart voltage threshold value Vth. Yes.

  Specifically, as shown in FIG. 2, the SCR system 100 includes a SCR device 103 provided in the exhaust pipe 102 of the engine E, and a dosing that injects urea water upstream of the SCR device 103 (upstream side of exhaust gas). A valve (urea injector, dosing module) 104, a urea tank 105 for storing urea water, a supply module 106 for supplying urea water stored in the urea tank 105 to the dosing valve 104, a dosing valve 104 and a supply module 106 A DCU (Dosing Control Unit) 126 for controlling the above is mainly provided.

In the exhaust pipe 102 of the engine E, a DOC (Diesel Oxidation Catalyst) 107, a DPF (Diesel Particulate Filter) 108, and an SCR device 103 are sequentially arranged from the upstream side to the downstream side of the exhaust gas. The DOC 107 is for oxidizing NO in the exhaust gas exhausted from the engine E into NO ₂ and controlling the ratio of NO and NO ₂ in the exhaust gas to increase the denitration efficiency in the SCR device 103. The DPF 108 is for collecting PM (Particulate Matter) in the exhaust gas.

  A dosing valve 104 is provided in the exhaust pipe 102 on the upstream side of the SCR device 103. The dosing valve 104 has a structure in which an injection hole is provided in a cylinder filled with high-pressure urea water, and a valve body that closes the injection hole is attached to the plunger, and the valve is pulled up by energizing the coil to raise the plunger. The body is separated from the nozzle and the urea water is injected. When energization of the coil is stopped, the plunger is pulled down by the internal spring force and the valve body closes the injection port, so that the urea water injection is stopped.

  The exhaust pipe 102 on the upstream side of the dosing valve 104 is provided with an exhaust temperature sensor 109 that measures the temperature of the exhaust gas at the inlet of the SCR device 103 (SCR inlet temperature). An upstream NOx sensor 110 that detects the NOx concentration on the upstream side of the SCR device 103 is provided upstream of the SCR device 103 (here, upstream of the exhaust temperature sensor 109), and downstream of the SCR device 103. Is provided with a downstream NOx sensor 111 for detecting the NOx concentration downstream of the SCR device 103.

  The supply module 106 includes an SM pump 112 that pumps urea water, an SM temperature sensor 113 that measures the temperature of the supply module 106 (the temperature of urea water flowing through the supply module 106), and the pressure of urea water in the supply module 106 ( The urea water pressure sensor 114 for measuring the pressure on the discharge side of the SM pump 112 and the urea water flow path are switched to supply urea water from the urea tank 105 to the dosing valve 104 or within the dosing valve 104. And a reverting valve 115 for switching whether to return the urea water to the urea tank 105. Here, the urea water from the urea tank 105 is supplied to the dosing valve 104 when the reverting valve 115 is OFF, and the urea water in the dosing valve 104 is supplied to the urea tank 105 when the reverting valve 115 is ON. I tried to return it.

  When the reverting valve 115 is switched to supply urea water to the dosing valve 104, the supply module 106 uses the SM pump 112 to supply the urea water in the urea tank 105 to a liquid supply line (suction line) 116. And the excess urea water is returned to the urea tank 105 through a recovery line (back line) 118.

  The urea tank 105 is provided with an SCR sensor 119. The SCR sensor 119 includes a level sensor 120 that measures the level (level) of urea water in the urea tank 105, a temperature sensor 121 that measures the temperature of urea water in the urea tank 105, and a sensor in the urea tank 105. And a quality sensor 122 for measuring the quality of the urea water. The quality sensor 122 detects the quality of the urea water in the urea tank 105 by detecting, for example, the concentration of urea water and whether or not a different mixture is mixed in the urea water from the propagation speed and electrical conductivity of the ultrasonic waves. To do.

  A tank heater line 131 branched from a cooling line 123 for circulating cooling water for cooling the engine E is connected to the urea tank 105 and the supply module 106. The tank heater line 131 passes through the urea tank 105 and exchanges heat between the cooling water flowing from the cooling line 123 and the urea water in the urea tank 105. The tank heater line 131 passes through the supply module 106 and exchanges heat between the cooling water flowing from the cooling line 123 and the urea water in the supply module 106.

  A tank heater valve (coolant valve) 124 for switching whether or not to supply cooling water to the urea tank 105 and the supply module 106 is provided at a connection point between the cooling line 123 and the tank heater line 131. Although the cooling line 123 is also connected to the dosing valve 104, the dosing valve 104 is configured to be supplied with cooling water regardless of whether the tank heater valve 124 is opened or closed. 2, the tank heater line 131 and the cooling line 123 are arranged along the liquid feed line 116, the pressure feed line 117, and the recovery line 118 through which the urea water passes. .

  FIG. 3 shows an input / output configuration diagram of the DCU 126.

  As shown in FIG. 3, the DCU 126 includes an upstream NOx sensor 110, a downstream NOx sensor 111, an SCR sensor 119 (level sensor 120, temperature sensor 121, quality sensor 122), exhaust temperature sensor 109, and SM of the supply module 106. The temperature sensor 113, the urea water pressure sensor 114, and an input signal line from an ECM (Engine Control Module) 125 that controls the engine E are connected. From the ECM 125, signals of outside air temperature, cooling water temperature, and engine parameters (engine speed, etc.) are input.

  The DCU 126 also has output signal lines to the tank heater valve 124, the SM pump 112 and the reverting valve 115 of the supply module 106, the dosing valve 104, the heater of the upstream NOx sensor 110, and the heater of the downstream NOx sensor 111. Connected. Note that the input / output of signals between the DCU 126 and each member may be input / output via individual signal lines or input / output via a CAN (Controller Area Network).

  The DCU 126 estimates the amount of NOx in the exhaust gas based on the engine parameter signal from the ECM 125 and the exhaust gas temperature from the exhaust temperature sensor 109, and based on the estimated amount of NOx in the exhaust gas. When the urea water amount to be injected from the dosing valve 104 is determined and further injected with the urea water amount determined by the dosing valve 104, the dosing valve 104 is controlled based on the detected value of the upstream NOx sensor 110, The amount of urea water injected from the dosing valve 104 is adjusted.

  FIG. 4A is a determination transition diagram of valve opening permission / prohibition in the present invention, where the horizontal axis represents time and the vertical axis represents battery voltage. In the present invention, the restart voltage threshold Vth is set to either the high temperature threshold candidate VH or the low temperature threshold candidate VL.

  The high temperature threshold candidate VH is a voltage at which the tank heater valve 124 can be opened regardless of the coil temperature, that is, a high voltage at which the tank heater valve 124 can be opened even when the coil temperature is high and current does not easily flow through the coil. is there. The high temperature threshold candidate VH is set to a voltage higher than the standard battery voltage, for example.

  The low temperature threshold candidate VL is a voltage at which the tank heater valve 124 cannot be opened regardless of the coil temperature, that is, the tank heater valve 124 cannot be opened even when the coil temperature is low and current easily flows through the coil. Voltage. The low temperature threshold candidate VL is set, for example, to the minimum operation guarantee voltage of the coil.

  FIG. 4B is a transition diagram of the estimated coil temperature in the present invention, in which the horizontal axis represents time, and the vertical axis represents the estimated coil temperature. FIG. 4C is a transition diagram of the cumulative value and the valve control region, where the horizontal axis represents time and the vertical axis represents the cumulative value. In the present invention, an upper limit value ΣH and a lower limit value ΣL are set in advance for the accumulated value.

  The upper limit value ΣH is set to a temperature at which the tank heater valve 124 cannot be opened when the battery voltage is lower than the high temperature threshold candidate VH because the coil temperature is high. The lower limit value ΣL is set to a temperature at which the tank heater valve 124 can be opened as long as the coil temperature is sufficiently low and the battery voltage exceeds the low temperature threshold candidate VL.

  Hereinafter, the operation of the SCR system 100 of the present invention will be described with reference to FIGS. 4 (a) to 4 (c).

  In order to simplify the explanation, it is assumed that the opening control (actually PWM drive) of the tank heater valve 124 is started and continued from the left end of FIGS. 4 (a) to 4 (c). The valve control area is an ON area (basically, the opening of the tank heater valve 124 is permitted; however, it is not always permitted), and the restart voltage threshold Vth is set to the low temperature threshold candidate VL. It is assumed that it is set.

  The coil temperature estimation unit 2 estimates the coil temperature from the accumulation of the opening time and shut-off time of the tank heater valve 124. Specifically, the coil temperature estimation unit 2 obtains the temperature increase coefficient α by referring to the map based on the outside air temperature, the cooling water temperature, the vehicle speed, and the battery voltage, and cumulatively adds them in increments of a predetermined time. Therefore, the cumulative value Σ increases as shown in FIG. That is, the estimated coil temperature increases as shown in FIG. Note that, in actuality, PWM driving is performed, and the temperature decrease coefficient β is cumulatively subtracted during the PWM driving interruption period, but the vertical fluctuation of the cumulative value Σ due to this is omitted.

  The restart voltage threshold value setting unit 3 sets a restart voltage threshold value Vth for determining whether or not the tank heater valve 124 can be opened according to the estimated coil temperature represented by the cumulative value Σ. Until the cumulative value Σ reaches the upper limit value ΣH, the restart voltage threshold Vth remains the low temperature threshold candidate VL. During this period, the valve control area is maintained in the ON area as shown in FIG.

  When the cumulative value Σ is equal to or higher than the upper limit value ΣH, the restart voltage threshold setting unit 3 sets the high temperature threshold candidate VH to the restart voltage threshold Vth. At the same time, the valve control region is switched to the OFF region (basically a region where the opening of the tank heater valve 124 is prohibited; however, it is not always prohibited).

  The open permission / prohibition unit 4 permits the opening of the tank heater valve 124 when the battery voltage Va is equal to or higher than the restart voltage threshold Vth, and the tank heater valve 124 when the battery voltage Va is lower than the restart voltage threshold Vth. Is prohibited. Therefore, when the valve control region is the ON region, opening is permitted if the battery voltage Va is equal to or higher than the low temperature threshold candidate VL as shown in FIG. However, if the battery voltage Va is equal to or lower than the low temperature threshold candidate VL, the tank heater valve 124 is prohibited from being opened even if the valve control region is the ON region. On the other hand, when the valve control region is the OFF region, the opening is prohibited when the battery voltage Va is less than the high temperature threshold candidate VH. However, if the battery voltage Va is equal to or higher than the high temperature threshold candidate VH, the opening of the tank heater valve 124 is permitted even if the valve control region is the OFF region.

  When the valve control region becomes the OFF region, the opening of the tank heater valve 124 is basically prohibited, so that the coil is hardly energized and the coil temperature decreases. In agreement with this, in the coil temperature estimation part 2, the cumulative value Σ decreases. The restart voltage threshold setting unit 3 sets the low temperature threshold candidate VL to the restart voltage threshold Vth when the accumulated value Σ is equal to or lower than the lower limit value ΣL. At the same time, the valve control area is switched to the ON area.

  Next, a processing procedure in the present invention will be described.

  It is assumed that when the vehicle is key-on, the cumulative value Σ = 0, the valve control region = ON region, and the restart voltage threshold Vth = low temperature threshold candidate VL are preset.

  As shown in FIG. 5, in step S51, the coil temperature estimation unit 2 determines whether or not the current valve control region is the ON region. If the current valve control region is the ON region, the determination is YES and the process proceeds to step S52a. If the current valve control region is the OFF region, the determination is NO and the process proceeds to step S52b.

  In step S52a, the coil temperature estimation unit 2 determines whether the coil is energized. If the PWM drive is in the open period, the coil is energized, so the determination is YES and the process proceeds to step S53a. If the PWM drive is in the cutoff period or is continuously shut off, the coil is not energized. It becomes NO and progresses to step S54a.

  In step S53a, the coil temperature estimation unit 2 obtains the temperature increase coefficient α by referring to the map using the outside air temperature, the cooling water temperature, the vehicle speed, and the battery voltage. On the other hand, in step S54a, the temperature decrease coefficient β1 is obtained by referring to the map based on the outside air temperature, the cooling water temperature, the vehicle speed, and the battery voltage. Here, the temperature decrease coefficient β1 is one of the temperature decrease coefficients β, and is set on the assumption that PWM drive is executed in the ON region.

  In step S55a, the coil temperature estimation unit 2 calculates a new cumulative value Σ by adding the temperature increase coefficient α or the temperature decrease coefficient β1 to the cumulative value Σ until just before.

  In step S56a, restart voltage threshold value setting unit 3 determines whether cumulative value Σ is equal to or greater than upper limit value ΣH. If the accumulated value Σ is less than the upper limit value ΣH, the determination becomes NO and the process proceeds to step S59. If the cumulative value Σ is equal to or greater than the upper limit value ΣH, the determination becomes YES and the process proceeds to step S57a.

  In step S57a, since the cumulative value Σ is equal to or greater than the upper limit value ΣH, the restart voltage threshold setting unit 3 substitutes the high temperature threshold candidate VH for the restart voltage threshold Vth, and in step S58a, the valve control region. To the OFF region.

  In step S59, the opening permission / prohibition unit 4 permits the opening of the tank heater valve 124 when the battery voltage Va is equal to or higher than the restart voltage threshold Vth, and when the battery voltage Va is lower than the restart voltage threshold Vth. The opening of the tank heater valve 124 is prohibited.

  The processing of steps S52b to S55b is substantially the same as the processing of steps S52a to S55a. If only the differences are described, the temperature decrease coefficient β2 is obtained from the map and used for the cumulative calculation. The temperature decrease coefficient β2 is one of the temperature decrease coefficients β, and is set on the assumption that the tank heater valve 124 is mainly shut off in the OFF region. It is assumed that temperature decrease coefficient β2 ≠ temperature decrease coefficient β1.

  In step S56b, restart voltage threshold value setting unit 3 determines whether cumulative value Σ is lower than or equal to lower limit value ΣL. If the cumulative value Σ exceeds the lower limit value ΣL, the determination is NO and the process proceeds to step S59. If the cumulative value Σ is equal to or lower than the lower limit value ΣL, the determination is YES and the process proceeds to step S57b.

  In step S57b, since the cumulative value Σ has become equal to or lower than the lower limit value ΣL, the restart voltage threshold setting unit 3 substitutes the low temperature threshold candidate VL for the restart voltage threshold Vth, and in step S58b, the valve control region To the ON area.

  The process of FIG. 5 is repeated every predetermined time. As a result, as described with reference to FIGS. 4A to 4C, when the cumulative value Σ (estimated coil temperature) gradually increases in the ON region and the cumulative value Σ reaches the upper limit value ΣH, the OFF region The cumulative value Σ gradually decreases. When the cumulative value Σ reaches the lower limit value ΣL, it returns to the ON region again. During this time, if the battery voltage Va is within the area labeled “open permitted” in FIG. 4A, the tank heater valve 124 is permitted to be opened, and if the battery voltage Va is within the area labeled “open prohibited”, the tank heater is opened. Opening of the valve 124 is prohibited.

  As described above, according to the SCR system 100 of the present invention, the coil temperature is estimated from the accumulation of the opening time and the shut-off time of the tank heater valve 124, and is regenerated according to the estimated coil temperature represented by the accumulated value Σ. Since the starting voltage threshold Vth is set, when the coil temperature is high and the restarting voltage is high, the restarting voltage threshold Vth to be compared with the battery voltage Va is set high, and a wide range of the battery voltage Va is set. Thus, the opening of the tank heater valve 124 is prohibited. On the other hand, when the coil temperature is low and the restart voltage is low, the restart voltage threshold Vth compared with the battery voltage Va is set low, and the tank heater valve 124 is allowed to open over a wide range of the battery voltage Va. The As a result, whether or not the tank heater valve 124 can be restarted is accurately determined, and the urea water thawing control can be executed reliably and more quickly.

  According to the SCR system 100 of the present invention, the coil temperature is estimated using the temperature increase coefficient α and the temperature decrease coefficient β (β1, β2) depending on the environmental conditions of the coil such as the outside air temperature, the cooling water temperature, the vehicle speed, and the battery voltage. Therefore, the coil temperature can be estimated more realistically. That is, the tank heater valve 124 connecting the cooling line 123 and the tank heater line 131 is exposed to the outside air. For this reason, for example, when the outside air temperature is very low, the coil temperature may rise gradually even if energization is continued for a long time. In this case, the restart voltage of the coil does not increase, and a state where the restart voltage does not exceed the minimum operation guarantee voltage of the coil is maintained. As the outside air temperature increases, the coil temperature tends to rise. Further, when the vehicle speed is high, the cooling effect by the outside air is enhanced, and the coil temperature is difficult to increase. On the other hand, when the vehicle speed is low, the cooling effect by the outside air is difficult to obtain and the coil temperature is likely to rise. Further, since the engine coolant passes through the tank heater valve 124, the coil is cooled by the engine coolant when the coil temperature is higher than the engine coolant temperature. Also, if the battery voltage is high, the current increases and the coil temperature tends to rise. If the battery voltage is low, the current decreases, and the coil temperature rises more slowly than when the battery voltage is high. Considering these environmental conditions, the coil temperature can be estimated more realistically.

  In the present embodiment, the restart voltage threshold Vth is selectively set to the high temperature threshold candidate VH and the low temperature threshold candidate VL. However, the restart voltage threshold Vth is more than 3 depending on the estimated coil temperature. A restart voltage threshold may be set for each stage.

DESCRIPTION OF SYMBOLS 1 Defrosting control part 2 Coil temperature estimation part 3 Restart voltage threshold value setting part 4 Opening permission / prohibition part 100 SCR system 105 Urea water tank 124 Tank heater valve 131 Tank heater line

Claims (3)

A urea water tank for storing urea water for injection into the exhaust pipe of the engine;
A tank heater line inserted through the urea water tank;
A tank heater valve that opens due to the electromagnetic force of the coil and branches and distributes cooling water to the tank heater line;
A thawing control unit for controlling opening / closing of the tank heater valve;
A coil temperature estimator for estimating the temperature of the coil;
A restart voltage threshold setting unit for setting a restart voltage threshold for determining whether or not the tank heater valve can be opened according to the estimated coil temperature;
When the battery voltage is equal to or higher than the restart voltage threshold, the opening of the tank heater valve is permitted, and when the battery voltage is less than the restart voltage threshold, an opening permission / prohibition unit for prohibiting the opening of the tank heater valve is provided. SCR system characterized by comprising. The restart voltage threshold setting unit includes:
Threshold candidate for high temperature consisting of a voltage capable of opening the tank heater valve regardless of the coil temperature,
A low temperature threshold candidate consisting of a voltage at which the tank heater valve cannot be opened regardless of the coil temperature is preset,
When the estimated coil temperature is equal to or higher than the preset upper limit, the high temperature threshold candidate is set as the restart voltage threshold,
The SCR system according to claim 1, wherein when the estimated coil temperature is equal to or lower than a preset lower limit, the low temperature threshold candidate is set as a restart voltage threshold. The coil temperature estimator is
One or more of the outside air temperature, cooling water temperature, vehicle speed, and battery voltage are used as parameters,
The coefficient of temperature rise of the coil set in advance according to the parameter is referred to by the parameter, and this temperature rise coefficient is cumulatively added at predetermined time intervals while the tank heater valve is open,
By referring to the parameter of the temperature drop of the coil set in advance according to the parameter, and subtracting this temperature drop coefficient in increments of a predetermined time while the tank heater valve is shut off,
The SCR system according to claim 1, wherein the temperature of the coil is estimated.

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