JP6960241B2 - Cooling control device and cooling control method for reducing agent injection valve - Google Patents

Description

The present invention relates to a cooling control device and a cooling control method for a reducing agent injection valve that injects urea water into an exhaust pipe of an internal combustion engine.

Particulate matter (hereinafter, also referred to as “PM (Particulate matter)”) and NO _X (nitrogen oxide) may be contained in the exhaust of an internal combustion engine such as a diesel engine. In order to remove PM in the exhaust, the exhaust passage is provided with a particulate filter that collects particulate matter. In order to remove _{NO X} in the exhaust gas, a urea SCR (Selective Catalytic Reduction) system including a reduction catalyst that reduces and purifies _{NO X is provided.} The urea SCR system decomposes _{NO X} by reacting _{ammonia produced from the urea water with NO X} in the exhaust gas using urea water as a reducing agent.

Urea water is supplied into the exhaust passage by a reducing agent injection valve provided in the exhaust pipe on the upstream side of the reduction catalyst. When the reducing agent injection valve is exposed to high-temperature exhaust gas, it may be damaged by heat such as melting of the electromagnetic coil which is an actuator. On the other hand, in order to keep the temperature of the urea addition valve (reducing agent injection valve) exposed to high temperature exhaust below the upper limit temperature in the temperature compensation range, the target instantaneous supply amount is added and urea water is injected to reduce the temperature. A technique for cooling an agent injection valve is disclosed.

Japanese Unexamined Patent Publication No. 2017-14912

In the exhaust gas purification device described in Patent Document 1, the amount of heat given to the reducing agent injection valve from the exhaust increases as the flow rate of the exhaust gas discharged from the internal combustion engine increases or the temperature of the exhaust gas increases. , The target instantaneous supply amount is set according to the accelerator operation amount and the engine rotation speed (internal combustion engine rotation speed). However, when the particulate filter is provided on the upstream side of the mounting position of the reducing agent injection valve in the exhaust passage, the particulate filter can also be a heat source. Specifically, when the amount of PM collected by the particulate filter increases, regeneration control for burning the collected PM is executed. When the PM is burned, not only the temperature of the exhaust gas rises, but also the amount of gas flowing through the mounting position of the reducing agent injection valve increases due to the generation of combustion gas. Therefore, it cannot be said that it is sufficient to perform injection for cooling the reducing agent injection valve according to the flow rate and temperature of the exhaust gas discharged from the internal combustion engine.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the amount of heat generated by using a particulate filter as a heat source in addition to the amount of heat of exhaust discharged from an internal combustion engine. It is an object of the present invention to provide a cooling control device for a reducing agent injection valve and a cooling control method capable of executing cooling control of the agent injection valve.

_{In order to solve the above problems, according to a certain viewpoint of the present invention, NO X} in the exhaust gas is reduced and purified on the downstream side of the particulate filter that collects the particulate matter in the exhaust gas of the internal combustion engine. In the cooling control device for cooling the reducing agent injection valve provided in the exhaust pipe on the upstream side of the reduction catalyst, the state value according to the amount of heat received from the exhaust to the reducing agent injection valve and the reduction from the reducing agent injection valve. The tip temperature estimation unit that estimates the tip temperature of the reducing agent injection valve based on the state value according to the amount of heat released to the agent, and the injection amount of the reducing agent that is injected from the reducing agent injection valve when the tip temperature exceeds the threshold. The state value according to the amount of heat received includes at least the value of the exhaust flow rate, and the tip temperature estimation unit is the exhaust gas discharged from the internal combustion engine during the regeneration of the particulate filter. Provided is a cooling control device for a reducing agent injection valve, which estimates the tip temperature by increasing and correcting the flow rate according to the generation of combustion gas due to the regeneration of the particulate filter.

_{Further, in order to solve the above problems, according to another viewpoint of the present invention, NO X} on the downstream side of the particulate filter that collects particulate matter in the exhaust gas of the internal combustion engine and in the exhaust gas is reduced. In the cooling control method for cooling the reducing agent injection valve provided in the exhaust pipe on the upstream side of the reducing agent to be purified, the state value according to the amount of heat received from the exhaust to the reducing agent injection valve and the reducing agent injection. The step of estimating the tip temperature of the reducing agent injection valve based on the state value according to the amount of heat released from the valve to the reducing agent, and the injection amount of the reducing agent injected from the reducing agent injection valve when the tip temperature exceeds the threshold value. The state value according to the amount of heat received from the exhaust to the reducing agent injection valve includes at least the value of the exhaust flow rate, and the exhaust flow rate discharged from the internal combustion engine during regeneration of the particulate filter. Is provided, a cooling control method for a reducing agent injection valve is provided, in which the tip temperature is estimated by increasing and compensating according to the generation of combustion gas due to the regeneration of the particulate filter.

As described above, according to the present invention, it is possible to execute the cooling control of the reducing agent injection valve in consideration of the amount of heat generated by the particulate filter as a heat source in addition to the amount of heat of the exhaust gas discharged from the internal combustion engine.

It is a schematic diagram which shows the structural example of the exhaust gas purification system to which the cooling control device of the reducing agent injection valve which concerns on embodiment of this invention is applied. It is a block diagram which shows the structural example of the cooling control device of the reducing agent injection valve which concerns on the same embodiment. It is a flowchart which shows the example of the cooling control method of the reducing agent injection valve which concerns on the same embodiment. It is explanatory drawing which shows an example of the method of estimating the tip temperature of a reducing agent injection valve.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

<1. Overall configuration of vehicle exhaust purification system>
A configuration example of an exhaust gas purification system mounted on a vehicle to which the vehicle control device according to the present embodiment can be applied will be described. FIG. 1 is a schematic view showing a configuration example of the exhaust gas purification system 10.

The exhaust purification system 10 is provided in the exhaust system of the internal combustion engine 5 represented by a diesel engine or a gasoline engine. In this embodiment, an example in which the internal combustion engine 5 is a diesel engine will be described. The exhaust purification system 10 includes an oxidation catalyst 19 arranged in an exhaust pipe 11 of an internal combustion engine 5, a particulate filter 17, a reduction catalyst 13, and an ammonia slip catalyst 15. The oxidation catalyst 19, the particulate filter 17, the reduction catalyst 13, and the ammonia slip catalyst 15 are arranged in the exhaust pipe 11 in this order from the upstream side of the exhaust flow. The exhaust purification system 10 includes a reducing agent supply device 30 that supplies urea water into the exhaust pipe 11 upstream of the reduction catalyst 13.

The oxidation catalyst 19 is a catalyst that oxidizes unburned hydrocarbons (HC: Hydrogen), nitric oxide (NO), and the like contained in the exhaust gas. The particulate filter 17 is a filter that collects PM in the exhaust gas. The PM collected by the particulate filter 17 is burned by the regeneration control executed at an appropriate time. In the regeneration control, for example, the unburned HC contained in the exhaust of the internal combustion engine 5 is increased, and the exhaust temperature is raised by the heat of oxidation generated when the HC is oxidized by the oxidation catalyst 19, and is captured by the particulate filter 17. The collected PM is burned. The method of regenerating the particulate filter 17 is not limited to the above example.

The reduction catalyst 13 is a catalyst that reduces _{NO X} contained in the exhaust gas of the internal combustion engine 5. _{The reduction catalyst 13 adsorbs ammonia (NH 3} ) generated from urea water supplied by the reducing agent supply device 30, and causes a reduction reaction between _{NO X} and NH ₃ in the exhaust flowing into the reduction catalyst 13. NO _X is decomposed into water (H ₂ O) and nitrogen (N _2). The reduction catalyst 13 has a characteristic that the adsorbable amount of _{NH 3 decreases as the catalyst temperature increases.} The reduction catalyst 13 has a characteristic that the reduction efficiency of _{NO X} increases as the amount of _{NH 3 adsorbed increases.}

The ammonia slip catalyst 15 is a catalyst that decomposes _{NH 3 contained in the exhaust gas.} The ammonia slip catalyst 15 oxidizes and decomposes _{NH 3} that has flowed out (ammonia slip) to the downstream side of the reduction catalyst 13 to suppress the release _{of NH 3 into the atmosphere.}

The reducing agent supply device 30 includes a reducing agent injection valve 31 fixed to an exhaust pipe 11 upstream of the reducing catalyst 13 and a pump 41 for pumping urea water. The drive of the pump 41 and the reducing agent injection valve 31 is controlled by the reducing agent injection control device 100. As the urea water, for example, urea water having the lowest freezing temperature and a concentration of about 32.5% is used. Urea water is stored in the storage tank 50. The storage tank 50 is provided with a tank temperature sensor 51 that detects the temperature of urea water. The signal output from the tank temperature sensor 51 is transmitted to the reducing agent injection control device 100. The amount of urea water supplied is _{set based on the concentration of NO X} contained in the exhaust gas, the temperature of the reduction catalyst 13, the _{amount of NH 3} adsorbed by the reduction catalyst 13, and the amount of NO _{X adsorbed to the downstream side of the reduction catalyst 13.} Alternatively, _{the outflow of NH 3} is controlled so as not to exceed the permissible value.

As the pump 41, for example, an electric diaphragm pump or an electric gear pump is used. In the present embodiment, the reducing agent supply device 30 includes a pressure sensor 43 for detecting the pressure of urea water supplied from the pump 41 to the reducing agent injection valve 31. The signal output from the pressure sensor 43 is transmitted to the reducing agent injection control device 100. The reducing agent injection control device 100 feedback-controls the output of the pump 41 based on the sensor signal of the pressure sensor 43 so that the pressure of the urea water supplied to the reducing agent injection valve 31 is maintained at a predetermined target value. ..

As the reducing agent injection valve 31, for example, an electromagnetically driven reducing agent injection valve whose opening and closing can be switched by turning on / off the energization is used. The electromagnetically driven reducing agent injection valve 31 includes an electromagnetic coil as an actuator, and the piston moves to open the valve when the electromagnetic coil is energized. In the present embodiment, the pressure of the urea water supplied to the reducing agent injection valve 31 is controlled to be a predetermined target value, and the reducing agent injection control device 100 injects the urea water according to the indicated injection amount of the urea water. Control the time.

The exhaust gas purification system 10 includes an exhaust temperature sensor 21, a differential pressure sensor 27, and a downstream NO _X concentration sensor 23. The exhaust temperature sensor 21 is provided in the exhaust pipe 11 upstream of the reduction catalyst 13 and detects the exhaust temperature. The differential pressure sensor 27 detects the pressure difference between the upstream and downstream of the particulate filter 17. The downstream NO _X concentration sensor 23 is provided in the exhaust pipe 11 downstream of the reduction catalyst 13, and mainly _{detects the NO X} concentration on the downstream side of the reduction catalyst 13 (downstream NO _X concentration). The signals output from these sensors are transmitted to the reducing agent injection control device 100.

<2. Configuration example of cooling control device>
Next, a configuration example of the reducing agent injection control device 100 according to the present embodiment will be described. In the present embodiment, the reducing agent injection control device 100 functions as a cooling control device for the reducing agent injection valve 31. FIG. 2 is a block diagram for explaining a configuration example of the reducing agent injection control device 100 according to the present embodiment.

The reducing agent injection control device 100 is configured to include a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), an electric circuit, and the like, and various functions are realized by the processor executing a computer program. It is a device. A part or all of the reducing agent injection control device 100 may be composed of, for example, a microcomputer, a microprocessor unit, or the like, or may be composed of an updatable device such as firmware. It may be a program module or the like executed by a command from a CPU or the like.

The reducing agent injection control device 100 includes a cooling injection control unit 112, a tip temperature estimation unit 114, an injection amount calculation unit 118, an injection valve drive control unit 120, a pump drive control unit 122, and a storage unit 124. .. The reducing agent injection control device 100 includes a sensor signal S_tg of the exhaust temperature sensor 21, a sensor signal S_dp of the differential pressure sensor 27, a sensor signal S_nd of the downstream NO _X concentration sensor 23, a sensor signal S_tu of the tank temperature sensor 51, and a pressure sensor. Acquires 43 sensor signals S_pu. The reducing agent injection control device 100 can acquire information on the operating state of the internal combustion engine 5 such as the rotation speed Ne of the internal combustion engine 5 and the fuel injection amount Q via a communication means such as CAN (Controller Area Network). ing.

(2-1. Memory unit)
The storage unit 124 has one or more storage elements such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The storage unit 124 stores a computer program executed by the processor, control parameters used in the calculation, a calculation result by the processor, an acquired sensor value, and the like. The storage unit 124 may be another storage device such as an HDD (Hard Disk Drive) or a storage device.

(2-2. Pump drive control unit)
The pump drive control unit 122 is composed of a processor and an electric circuit, and controls the drive of the pump 41. In the present embodiment, the pump drive control unit 122 feedback-controls the output of the pump 41 based on the difference between the pressure Pu of urea water detected by the pressure sensor 43 and the preset target pressure. As a result, the pressure Pu of the urea water supplied to the reducing agent injection valve 31 is maintained at a value near the target pressure.

(2-3. Injection amount calculation unit)
The injection amount calculation unit 118 is composed of a processor and an electric circuit, and calculates the indicated injection amount Q_urea of urea water. The indicated injection amount Q_urea of the urea aqueous solution is the amount _{of NH 3} required to purify _{the NO X in the exhaust gas discharged from the internal combustion engine 5, and the amount of NH 3 in} excess or deficiency with respect to _{the target NH 3} adsorption amount of the reduction catalyst 13. It is set according to the sum of. _{The amount of NH 3} required to purify _{NO X} in the exhaust gas can be calculated based _{on the NO X} flow rate on the upstream side of the reduction catalyst 13. _{The NO X} flow rate on the upstream side of the reduction catalyst 13 can be obtained by multiplying _{the NO X} concentration NO _X _us in the exhaust gas calculated based on the operating state of the internal combustion engine 5 by the exhaust gas flow rate F_gas. The injection amount calculation unit 118 obtains the NO _X flow rate per unit time corresponding to one injection cycle, and calculates the _{NH 3} amount required to purify _{the NO X} in the exhaust gas for each injection cycle.

NH ₃ amount of excess or deficiency with respect to the target adsorbed NH ₃ amount can be calculated by subtracting the current adsorbed NH ₃ amount from the target NH ₃ adsorption amount of the reduction catalyst 13. The target NH ₃ adsorption amount can be calculated based on the catalyst temperature T_cat and the exhaust flow rate F_gas. The current NH ₃ adsorption amount is, for example, continuously used for purifying _{NO X and the NH 3} amount (positive value) corresponding to the indicated injection amount Q_urea of urea water continuously from the time when the _{NH 3 adsorption amount is zero when not in use.} It can be calculated by continuing to integrate the amount of NH _{3 (negative value).} When the indicated injection amount Q_urea of urea water is increased for cooling the reducing agent injection valve 31, NH ₃ (negative value) flowing out to the downstream side of the reduction catalyst 13 may be added. _{Since the adsorbable amount of NH 3} in the reduction catalyst 13 changes according to the catalyst temperature T_cat, the excess or deficiency of the NH _{3 amount with respect to the target NH 3} adsorption amount can be either positive or negative.

Injection amount calculation unit 118, the amount of the NH ₃ amount and the target NH ₃ NH ₃ amount capable of producing urea water combined with NH ₃ amount of excess or deficiency relative adsorbed amount needed to purify NO _X in the exhaust gas Is set as the indicated injection amount Q_urea of one injection cycle.

(2-4. Injection valve drive control unit)
The injection valve drive control unit 120 is composed of a processor and an electric circuit, and controls the drive of the reducing agent injection valve 31. The injection valve drive control unit 120 controls the energization of the reducing agent injection valve 31 based on the indicated injection amount Q_urea calculated by the injection amount calculation unit 118. In the present embodiment, the pressure Pu of the urea water supplied to the reducing agent injection valve 31 is maintained at a value near the target pressure, and the injection valve drive control unit 120 injects the reducing agent according to the indicated injection amount Q_urea. The drive duty ratio of the valve 31 is set to control the energization of the reducing agent injection valve 31. Specifically, the injection valve drive control unit 120 sets the drive duty ratio, which is the ratio of the energization time to the total time, for each injection cycle in which the injection start time is set in advance at predetermined time intervals, and energizes. Take control.

(2-5. Tip temperature estimation unit)
The tip temperature estimation unit 114 is a reducing agent injection valve based on a state value according to the amount of heat received from the exhaust to the reducing agent injection valve 31 and a state value according to the amount of heat radiated from the reducing agent injection valve 31 to urea water. The tip temperature T_tip of 31 is estimated. In the present embodiment, the tip temperature estimation unit 114 estimates the temperature T_coil of the electromagnetic coil portion of the reducing agent injection valve 31, and receives heat from the exhaust to the reducing agent injection valve 31 with respect to the temperature T_coil of the electromagnetic coil portion. The tip temperature T_tip is calculated by adding the rising temperature T1 and subtracting the temperature T2 that falls due to heat dissipation from the reducing agent injection valve 31 to the urea water.

The temperature T_coil of the electromagnetic coil portion is based on the power supply voltage V of the reducing agent injection valve 31, the resistance value R of the current supply circuit to the reducing agent injection valve 31, and the supply current value I to the reducing agent injection valve 31. Can be estimated. The temperature T1 that rises due to heat reception from the exhaust to the reducing agent injection valve 31 can be calculated based on the exhaust flow rate F_gas and the exhaust temperature T_gas, which are state values according to the amount of heat received. The temperature T2, which decreases due to heat radiation from the reducing agent injection valve 31 to urea water, can be calculated based on the indicated injection amount Q_urea of urea water and the temperature T_urea, which are state values according to the heat radiation amount.

Further, the tip temperature estimation unit 114 estimates the tip temperature T_tip by increasing at least one of the exhaust flow rate F_gas and the exhaust temperature T_gas, which are state values according to the amount of heat received, during the regeneration of the particulate filter 17. Since the PM collected in the particulate filter 17 burns during the regeneration of the particulate filter 17, the exhaust temperature on the downstream side of the particulate filter 17 is higher than that in the case where the regeneration control of the particulate filter 17 is not performed. T_gas rises. Further, since combustion gas is generated by combustion of PM during regeneration of the particulate filter 17, the exhaust flow rate F_gas on the downstream side of the particulate filter 17 increases as compared with the case where the regeneration control of the particulate filter 17 is not performed. do.

Therefore, the tip temperature estimation unit 114 estimates the tip temperature T_tip in consideration of the influence of the amount of heat generated from the particulate filter 17 as a heat source during the regeneration of the particulate filter 17, so that the exhaust flow rate F_gas or the exhaust can be exhausted. Increase and correct at least one of the temperatures T_gas. For example, the tip temperature estimation unit 114 may add the flow rate F_gas_reg of the combustion gas generated by the combustion of PM to the exhaust flow rate F_gas. Further, the tip temperature estimation unit 114 may add the rising temperature T_reg due to the combustion of PM to the exhaust temperature T_gas. The rise temperature T_reg in this case may include not only the rise in the exhaust temperature T_gas but also the rise in the temperature considering the amount of heat transferred from the particulate filter 17 to the reducing agent injection valve 31 via the exhaust pipe 11. ..

(2-6. Cooling injection control unit)
The cooling injection control unit 112 increases the injection amount of urea water injected from the reducing agent injection valve 31 when the tip temperature T_tip estimated by the tip temperature estimation unit 114 exceeds the threshold value T_tip0. For example, the cooling injection control unit 112 executes a control for increasing urea water (hereinafter, also referred to as “cooling control”), so that the injection amount calculation unit 118 performs a predetermined amount with respect to the calculated indicated injection amount Q_urea. Is added or a predetermined coefficient is multiplied, and the indicated injection amount Q_urea is increased and corrected. As a result, the amount of heat radiated from the reducing agent injection valve 31 to the urea water is increased, and the cooling efficiency of the reducing agent injection valve 31 is improved.

<3. Operation example of reducing agent injection control device>
Next, an operation example of the reducing agent injection control device 100 as the cooling control device for the reducing agent injection valve according to the present embodiment will be described. FIG. 3 is a flowchart showing an example of the cooling injection control process by the reducing agent injection control device 100.

First, the cooling injection control unit 112 of the reducing agent injection control device 100 determines whether or not the particulate filter 17 is being regenerated (step S11). The discrimination method is not particularly limited. For example, when a flag indicating that the regeneration control of the particulate filter 17 is being executed is set or an execution signal is input, the cooling injection control unit 112 determines that the particulate filter 17 is being regenerated. You may.

When the particulate filter 17 is being regenerated (S11 / Yes), the tip temperature estimation unit 114 of the reducing agent injection control device 100 calculates a correction amount used for estimating the tip temperature T_tip of the reducing agent injection valve 31 (step). S13). For example, the tip temperature estimation unit 114 calculates the exhaust flow rate F_gas_reg and the rise temperature T_reg used for the increase correction. On the other hand, when the particulate filter 17 is not being regenerated (S11 / No), the tip temperature estimation unit 114 sets the correction amount used for estimating the tip temperature T_tip of the reducing agent injection valve 31 to zero (step S15). The tip temperature estimation unit 114 estimates the tip temperature T_tip after setting the correction amount in step S13 or step S15 (step S17).

FIG. 4 is an explanatory diagram showing an example of arithmetic processing for estimating the tip temperature T_tip. In the example of the tip temperature T_tip estimation method shown in FIG. 4, the temperature T1 at which the reducing agent injection valve 31 receives heat from the exhaust or the exhaust pipe and rises is added to the temperature T_coil of the electromagnetic coil of the reducing agent injection valve 31. At the same time, the tip temperature T_tip is calculated based on the value obtained by subtracting the temperature T2 that decreases due to the injection of urea water.

The tip temperature estimation unit 114 calculates the temperature T1 that rises due to the amount of heat received by the reducing agent injection valve 31 from the exhaust or the exhaust pipe, based on the exhaust temperature T_gas and the exhaust flow rate F_gas, which are the state values of the amount of heat received. In this embodiment, the exhaust temperature T_gas is detected by the exhaust temperature sensor 21. Further, the exhaust flow rate F_gas is estimated based on the operating state of the internal combustion engine 5. The tip temperature estimation unit 114 has a preset heat transfer coefficient from the exhaust or exhaust pipe 11 to the reducing agent injection valve 31, or a coefficient related to a delay time from the measurement time of the exhaust temperature T_gas or the exhaust flow rate F_gas. At least one coefficient may be used to calculate the temperature T_tip that rises due to heat reception based on the exhaust temperature T_gas and the exhaust flow rate F_gas.

Further, the tip temperature estimation unit 114 may use the regeneration control execution signal S_reg, the pressure difference dP_dpf between the upstream and downstream of the particulate filter 17, or the upstream and downstream of the particulate filter 17 during regeneration of the particulate filter 17. The correction amount of the state value according to the heat receiving amount is calculated based on at least one information of the temperature difference dT_dpf. In the present embodiment, the pressure difference dP_dpf can be detected by the differential pressure sensor 27. The exhaust temperature T_gas on the downstream side can be detected by the exhaust temperature sensor 21. The exhaust temperature T_gas on the upstream side can be estimated based on the operating state of the internal combustion engine 5.

The correction amount may be at least one of, for example, the flow rate F_reg of the combustion gas generated by the combustion of PM added to the exhaust flow rate F_gas, or the rising temperature T_reg caused by the combustion of PM. The combustion gas flow rate F_reg is used as a correction amount to be added to the exhaust gas flow rate F_gas. The rising temperature T_reg is used as a correction amount to be added to the temperature according to the amount of heat received by the reducing agent injection valve 31 from the exhaust gas or the exhaust pipe. In step S15 of the flowchart shown in FIG. 3, these correction amounts are set to zero.

For example, the correction amount when the particulate filter 17 is not being reproduced may be zero, and the correction amount when the reproduction control execution signal S_reg of the particulate filter 17 is input may be a constant. For example, when the regeneration control execution signal S_reg of the particulate filter 17 is input, the exhaust flow rate F_gas used for calculating the temperature T1 according to the amount of heat received by the reducing agent injection valve 31 from the exhaust or the exhaust pipe is a constant amount. It may be augmented and corrected. Alternatively, when the regeneration control execution signal S_reg of the particulate filter 17 is input, the temperature corresponding to the amount of heat that can be received by the reducing agent injection valve 31 calculated based on the exhaust flow rate F_gas and the exhaust temperature T_gas increases by a certain amount. It may be corrected. In this case, the correction amount (constant) may be set based on a value acquired in advance by actual measurement or simulation.

Alternatively, the correction amount during regeneration of the particulate filter 17 may be set based on the pressure difference dP_dpf between the upstream and downstream of the particulate filter 17 and the temperature difference dT_dpf between the upstream and downstream of the particulate filter 17. During the regeneration of the particulate filter 17, the pressure difference dP_dpf becomes smaller as the combustion of PM progresses. Therefore, the flow rate F_reg and the rising temperature T_reg of the combustion gas can be estimated based on the amount of decrease in the pressure difference dP_dpf. Further, during the regeneration of the particulate filter 17, the exhaust temperature T_gas on the downstream side of the particulate filter 17 rises due to the combustion of PM, and the temperature difference dT_dpf between the upstream and the downstream becomes large. Therefore, the flow rate F_reg of the combustion gas and the rising temperature T_reg can be estimated based on the change in the temperature difference dT_dpf. For example, the tip temperature estimation unit 114 refers to the characteristic line or map information showing the relationship between the pressure difference dP_dpf, the temperature difference dT_dpf, the flow rate F_reg of the combustion gas, and the rising temperature T_reg stored in the storage unit 124 in advance. , The correction amount of the state value may be obtained.

Further, the tip temperature estimation unit 114 calculates the temperature T2 that is lowered by the injection of urea water based on the temperature Tu_tank of urea water, which is the state value of the amount of heat radiation, and the indicated injection amount Q_urea of urea water. In this embodiment, information on the energization time Ti_dos and the injection interval Int_dos of the reducing agent injection valve 31 is used as values according to the indicated injection amount Q_urea of urea water. In the present embodiment, the temperature Tu_tank of urea water is detected by the tank temperature sensor 51 provided in the storage tank 50. Further, the energizing time Ti_dos and the injection interval Int_dos of the reducing agent injection valve 31 are values set by the injection valve drive control unit 120. For example, the tip temperature estimation unit 114 subtracts the temperature Tu_tank of urea water from the value obtained by adding the temperature T1 to the temperature T_coil of the electromagnetic coil, multiplies it by the duty ratio coefficient according to the injection state of the reducing agent injection valve 31, and dissipates heat. Calculate the decreasing temperature T2. The larger the amount of urea water injected, the longer the energization time Ti_dos or the shorter the injection interval Int_dos, and the duty ratio coefficient is set to increase accordingly. Therefore, the larger the amount of urea water injected, the larger the temperature T2 that drops due to heat dissipation.

The tip temperature estimation unit 114 further adds the temperature T1 according to the amount of heat received from the exhaust or the exhaust pipe to the temperature T_coil of the electromagnetic coil, and subtracts the temperature T2 that decreases due to heat dissipation to urea water. The tip temperature T_tip may be calculated by multiplying by a coefficient related to the delay time of arithmetic processing.

Returning to FIG. 3, after the tip temperature T_tip is estimated in step S17, the cooling injection control unit 112 determines whether or not the tip temperature T_tip exceeds the threshold value T_thre (step S19). The threshold value T_thre is set to an appropriate value smaller than the heat-resistant temperature so as not to cause thermal damage to the reducing agent injection valve 31 in consideration of the heat-resistant temperature of the reducing agent injection valve 31. When the tip temperature T_tip is equal to or less than the threshold value T_thre (S21 / No), it is not necessary to execute the cooling injection of the reducing agent injection valve 31, so the reducing agent injection control device 100 returns to step S11 and repeats the process.

On the other hand, when the tip temperature T_tip exceeds the threshold value T_thre (S19 / Yes), the cooling injection control unit 112 executes the cooling injection of the reducing agent injection valve 31 (step S21). When executing the cooling injection of the reducing agent injection valve 31, the injection amount calculation unit 118 of the reducing agent injection control device 100 is excessive or insufficient with respect to the _{amount of NH 3} required to purify _{NO X} in the exhaust and the target amount of NH _{3 adsorbed.} adding a predetermined amount to an instruction injection amount Q_urea of NH ₃ amount and can generate NH ₃ amount of combined urea water, or, by multiplying a predetermined coefficient, to increase correction of the instructed injection amount Q_urea. For example, the injection amount calculation unit 118 may obtain the addition amount or coefficient of urea water according to the difference between the estimated tip temperature T_tip and the threshold value T_thre, and correct the indicated injection amount Q_urea. As a result, the amount of heat radiated from the reducing agent injection valve 31 to the urea water can be increased according to the amount of heat received by the reducing agent injection valve 31, and the reducing agent injection valve 31 can be appropriately cooled. Even when the amount of urea water injected is increased and NH ₃ flows out to _{the downstream side of the reduction catalyst 13, NH 3} is oxidized and decomposed by the ammonia slip catalyst 15.

As described above, the reducing agent injection control device 100 according to the present embodiment injects the reducing agent based on the flow rate F_reg of the combustion gas and the rising temperature T_reg, which increase due to the combustion of PM, during the regeneration of the particulate filter 17. Either the exhaust flow rate F_gas or the exhaust temperature T_gas, which is a state value according to the amount of heat received by the valve 31, is increased and corrected. As a result, the discrepancy between the actual tip temperature of the reducing agent injection valve 31 and the estimated tip temperature T_tip can be reduced. Therefore, it is possible to suppress thermal damage such as melting of the electromagnetic coil due to excessive temperature rise of the tip temperature, which may occur when the injection amount of urea water for cooling is suppressed by estimating the tip temperature T_tip to be low. can. Alternatively, an increase in the consumption of urea water that may occur when the indicated injection amount Q_urea of urea water is increased more than necessary in order to prevent thermal damage to the reducing agent injection valve 31, or NH _{3 to the downstream side of the reducing catalyst 13} The outflow can be suppressed.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

For example, in the above embodiment, it is determined whether or not the exhaust flow rate F_gas and the exhaust temperature T_gas are corrected depending on whether or not the particulate filter 17 is being regenerated, but the present invention is not limited to such an example. The period for correcting the exhaust flow rate F_gas and the period for correcting the exhaust temperature T_gas may be different. Specifically, when the regeneration control of the particulate filter 17 is completed, the increase in the exhaust flow rate F_gas is eliminated relatively quickly, while the increase in the exhaust temperature T_gas is eliminated over time. Therefore, the end time of the increase correction of the exhaust temperature T_gas may be delayed by a predetermined time from the end time of the regeneration control of the particulate filter 17. As a result, the estimation accuracy of the tip temperature T_tip of the reducing agent injection valve 31 can be further improved.

Further, in the above embodiment, the exhaust flow rate and the exhaust temperature are used as the state values according to the amount of heat received by the reducing agent injection valve 31, but the present invention is not limited to such an example. The tip temperature setting unit 114 may estimate the tip temperature T_tip of the reducing agent injection valve 31 using other state quantities.

Further, in the above embodiment, it is determined whether or not the particulate filter 17 is being reproduced based on the execution flag of the reproduction control of the particulate filter 17 or the execution instruction signal, but the present invention is not limited to such an example. For example, when the pressure difference dP_dpf between the upstream and downstream of the particulate filter 17 begins to decrease continuously, or when the temperature difference dT_dpf between the upstream and downstream of the particulate filter 17 continuously increases, the particulate filter It may be determined that the regeneration of the fill 17 has started.

5 Internal combustion engine 10 Exhaust purification system 11 Exhaust pipe 13 Reduction catalyst 15 Ammonia slip catalyst 17 Particulate filter 21 Exhaust temperature sensor 23 Downstream NO _X concentration sensor 27 Differential pressure sensor 30 Reduction agent supply device 31 Reduction agent injection valve 100 Reduction agent injection Control device (cooling control device)
112 Cooling injection control unit 114 Tip temperature estimation unit 118 Injection amount calculation unit 120 Injection valve drive control unit

Claims (5)

A reducing agent injection valve provided on the downstream side of the particulate filter that collects particulate matter in the exhaust gas of the internal combustion engine and on the upstream side of the reducing catalyst that reduces and purifies _{NO X in the exhaust gas.} In the cooling control device for cooling
The tip temperature of the reducing agent injection valve is estimated based on the state value according to the amount of heat received from the exhaust to the reducing agent injection valve and the state value according to the amount of heat radiated from the reducing agent injection valve to the reducing agent. Tip temperature estimation unit and
A cooling injection control unit that increases the injection amount of the reducing agent injected from the reducing agent injection valve when the tip temperature exceeds a threshold value is provided.
The state value according to the amount of heat received includes at least the value of the exhaust flow rate.
The tip temperature estimation unit estimates the tip temperature by increasing and correcting the exhaust gas discharged from the internal combustion engine during the regeneration of the particulate filter according to the generation of combustion gas due to the regeneration of the particulate filter. , Reducing agent injection valve cooling control device. The tip temperature estimation unit is a correction amount that increases the exhaust flow rate based on at least one of the pressure difference between the upstream and downstream of the particulate filter or the temperature difference between the upstream and downstream of the particulate filter. The cooling control device for the reducing agent injection valve according to claim 1. The cooling control device for a reducing agent injection valve according to claim 1, wherein the tip temperature estimation unit corrects the exhaust flow rate by a preset constant amount during regeneration of the particulate filter. The cooling control device for a reducing agent injection valve according to any one of claims 1 to 3, wherein the tip temperature estimation unit uses the injection amount and temperature of the reducing agent as state values according to the heat dissipation amount. A reducing agent injection valve provided on the downstream side of the particulate filter that collects particulate matter in the exhaust gas of the internal combustion engine and on the upstream side of the reducing catalyst that reduces and purifies _{NO X} in the exhaust gas. In the cooling control method for cooling
The tip temperature of the reducing agent injection valve is estimated based on the state value according to the amount of heat received from the exhaust to the reducing agent injection valve and the state value according to the amount of heat released from the reducing agent injection valve to the reducing agent. Steps to do and
A step of increasing the injection amount of the reducing agent injected from the reducing agent injection valve when the tip temperature exceeds a threshold value is provided.
The state value according to the amount of heat received from the exhaust to the reducing agent injection valve includes at least the value of the exhaust flow rate.
Cooling of the reducing agent injection valve that estimates the tip temperature by increasing and correcting the exhaust flow rate discharged from the internal combustion engine during the regeneration of the particulate filter according to the generation of combustion gas due to the regeneration of the particulate filter. Control method.

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