JP6573225B2 - Automatic engine stop control device - Google Patents

Description

  The present invention relates to an engine automatic stop control device, and in particular, an engine including an SCR catalyst for reducing and purifying NOx provided in an exhaust passage of an engine, and a urea supply device for supplying urea water to the SCR catalyst. The present invention relates to an automatic stop control device.

  Conventionally, in order to prevent air pollution, diesel vehicles reduce and purify NOx (nitrogen oxides) in exhaust gas discharged from the engine, and suppress NOx from being discharged into the atmosphere. . Specifically, the exhaust system of the engine is provided with an SCR catalyst (Selective Catalytic Reduction) and a urea supply device that supplies urea water to the SCR catalyst. The urea supply device supplies urea water to the exhaust system, and is hydrolyzed by the heat of the exhaust gas and adsorbs ammonia to the SCR catalyst. Ammonia adsorbed on the SCR catalyst reduces and purifies NOx and suppresses NOx from being discharged into the atmosphere.

  Here, when the engine is restarted after the engine is stopped, the exhaust gas is not flowing into the exhaust system or the exhaust gas is at a low temperature, so that ammonia is adsorbed to the SCR catalyst even if urea water is supplied to the exhaust system. I can't. For this reason, at the time of restart, the SCR catalyst may not be able to reduce and purify NOx. Therefore, in Patent Document 1, when the driver operates the vehicle to stop, if the ammonia adsorption amount of the SCR catalyst is smaller than the target adsorption amount, the engine is not stopped and the idle state is continued and urea water is supplied. This increases the ammonia adsorption amount of the SCR catalyst.

  On the other hand, there is known an automatic engine stop control, so-called idle stop control, in which the engine is automatically stopped when the driver depresses the brake pedal after stopping and the engine is automatically restarted when the accelerator pedal is depressed. By this idle stop control, it is possible to suppress fuel consumption and exhaust gas emission when the vehicle is stopped.

JP 2009-197728 A

  However, during the idle stop control, the engine is automatically stopped and the exhaust gas does not flow to the exhaust system. Therefore, even if urea water is supplied to the exhaust system, ammonia cannot be adsorbed on the SCR catalyst. That is, if the ammonia adsorption amount of the SCR catalyst is insufficient during idle stop control, the SCR catalyst may not be able to reduce and purify NOx when the engine is restarted.

  Accordingly, an object of the present invention is to provide an automatic engine stop control device in which the SCR catalyst can reduce and purify NOx when the engine is restarted when automatic engine stop control is performed.

In order to solve the above-mentioned problem, an automatic stop control device for an engine comprising: an SCR catalyst for reducing and purifying NOx provided in an exhaust passage of the engine; and a urea supply device for supplying urea water to the SCR catalyst. An engine automatic stop control means for executing engine automatic stop control for automatically stopping the engine when a predetermined start condition is satisfied and restarting the engine when a predetermined restart condition is satisfied; And a urea supply control means for controlling the supply of the engine, and when a predetermined condition for reducing the NOx purification performance of the SCR catalyst is satisfied, the engine automatic stop control means prohibits the execution of the engine automatic stop control and working together to continue the urea supply control means have lines supplying the urea water by the urea supply device, NOx purification performance of the SCR catalyst is decreased The constant condition is that the temperature of the SCR catalyst is lower than the set temperature, and the urea supply control means determines that the SCR catalyst is controlled by the urea supply device when the temperature of the SCR catalyst is equal to or higher than the decomposition temperature at which urea can be hydrolyzed to ammonia. Urea water is supplied to the catalyst, and the set temperature is set to the decomposition temperature .

In the present invention configured as described above, when a predetermined condition for reducing the NOx purification performance of the SCR catalyst is satisfied, the operation of the engine is continued and urea water is supplied to the SCR catalyst. The amount of adsorption can be increased. Therefore, even when the engine automatic stop control is performed, the SCR catalyst can reduce and purify NOx when the engine is restarted.
Further, since the urea water is supplied while prohibiting the execution of the engine automatic stop control based on the temperature of the SCR catalyst, the ammonia adsorption amount can be increased when the temperature of the SCR catalyst is lower than the set temperature. . Further, when the temperature of the SCR catalyst is lower than the decomposition temperature capable of being hydrolyzed to ammonia, the ammonia adsorption amount can be increased.

  In the present invention, it is preferable that the predetermined condition under which the NOx purification performance of the SCR catalyst is reduced is when the ammonia adsorption amount adsorbed on the SCR catalyst is smaller than the set adsorption amount. In the present invention configured as described above, since the urea water is supplied by prohibiting the execution of the engine automatic stop control based on the ammonia adsorption amount, the ammonia adsorption amount when the ammonia adsorption amount of the SCR catalyst is insufficient. Can be increased.

  In the present invention, preferably, the urea supply control means supplies urea water to the SCR catalyst by the urea supply device until the ammonia adsorption amount of the SCR catalyst reaches the target adsorption amount, and the set adsorption amount is set to the target adsorption amount. Has been. In the present invention configured as described above, the ammonia adsorption amount of the SCR catalyst can be reliably increased to the target adsorption amount.

  In the present invention, preferably, the urea supply control means sets the target adsorption amount according to the temperature of the SCR catalyst. In the present invention configured as described above, since the target adsorption amount is set according to the temperature, an appropriate amount of urea water according to the temperature can be supplied.

  According to the engine automatic stop control device of the present invention, when engine automatic stop control is performed, the SCR catalyst can reduce and purify NOx when the engine is restarted.

1 is a schematic configuration diagram of an engine to which an engine automatic stop control device according to an embodiment of the present invention is applied. 1 is a block diagram showing an engine automatic stop control device according to an embodiment of the present invention. FIG. It is a flowchart which shows the control flow performed by the engine automatic stop control apparatus by embodiment of this invention. FIG. 4 is a flowchart showing a specific procedure for calculating the temperature, the ammonia adsorption amount, the target adsorption amount, and the urea water injection amount of the SCR catalyst read in S1 of FIG. It is a graph which shows the relationship between the temperature of a SCR catalyst, the upper limit adsorption amount of ammonia, and a target adsorption amount.

Hereinafter, an automatic engine stop control device 70 according to an embodiment of the present invention will be described with reference to the drawings.
First, a schematic configuration of an engine provided with an engine automatic stop control device 70 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an engine provided with an engine automatic stop control device 70 according to an embodiment of the present invention.

  As shown in FIG. 1, an engine 1 includes a cylinder 2 that forms a combustion chamber 2a, a piston 4 that reciprocates within the cylinder 2, a connecting rod 6 that has one end connected to the piston 4, and the connecting rod. 6 and a crankshaft 8 to which the other end is connected. The engine 1 further includes a crank angle sensor 9 that detects the rotation angle and the rotation speed of the crankshaft 8, and a fuel supply device 10 that supplies fuel to the combustion chamber 2a. The engine 1 is a so-called diesel engine that is spontaneously ignited by injecting fuel containing light oil as a main component into a fuel chamber that has been compressed to a high temperature by the action of a piston.

  The fuel supply device 10 includes a fuel tank 40 that stores fuel, a low-pressure fuel pump 42 that pumps fuel in the fuel tank 40, a high-pressure fuel pump 44 that pressurizes fuel pumped from the low-pressure fuel pump 42, and a high-pressure A fuel pressure sensor 46 that detects the pressure of the fuel pressurized by the fuel pump 44 and an injector 48 that is a fuel injection valve that injects the fuel pressurized by the high-pressure fuel pump 44 into the combustion chamber 2a. .

  The intake system that supplies air to the combustion chamber 2 a is provided with an air cleaner 12 that purifies the intake air and an intake passage 13 that extends from the air cleaner 12 to the intake port 20. In the intake passage 13, an intake air temperature / flow rate sensor 14 for detecting the temperature and flow rate of air taken in through the air cleaner 12, a throttle valve 16 for changing the intake air amount, and an opening degree of the throttle valve 16 are detected. And a throttle valve sensor 18 is provided. The air sucked through these intake systems flows into the combustion chamber 2a through the intake port 20 communicating with the intake opening of the combustion chamber 2a and the intake valve 22 that opens and closes the intake opening.

  The exhaust system for discharging air from the combustion chamber 2a includes an exhaust port 24 communicating with the exhaust opening of the combustion chamber 2a, an exhaust valve 26 for opening and closing the exhaust opening, and an exhaust passage 30 extending from the exhaust port 24 to the outside of the vehicle. And are provided. The exhaust path 30 collects the oxidation catalyst 31 that oxidizes CO and HC in the gas (exhaust gas) exhausted through the exhaust path 30 to detoxify, and soot (soot) in the exhaust gas. DPF (Diesel particulate filter) 32, an SCR catalyst 33, and a slip catalyst 34 that oxidizes ammonia that has not been used in the SCR catalyst 33 and has flowed downstream. Exhaust gas generated in the combustion chamber 2a flows into the exhaust passage 30 from the exhaust port 24, passes through various catalysts, and is discharged outside the vehicle.

  The SCR (Selective Catalytic Reduction) catalyst 33 is a catalyst that reduces and purifies NOx contained in exhaust gas and renders it harmless (converts it into N2 and H2O). The SCR catalyst 33 adsorbs ammonia and reduces and purifies NOx in the exhaust gas when the exhaust gas passes through. Specifically, the SCR catalyst 33 converts NOx in the exhaust gas into N2 or H2O by a chemical reaction using ammonia as a reducing agent.

  In the exhaust passage 30 between the DPF 32 and the SCR catalyst 33, a urea supply device 35 that supplies urea water toward the exhaust passage 30, and the urea water is uniformly dispersed in the cross section of the exhaust passage 30 and is downstream. A mixing plate 36 for flowing to the side is provided.

  The urea supply device 35 is connected to a tank 37 for storing urea water, a supply pipe 38 for supplying the stored urea water, and a downstream end of the supply pipe 38 to inject the urea water into the exhaust passage 30. A urea injector 39 is provided. The urea injector 39 is an injection valve that injects or stops urea water based on a signal from the engine control unit 72. The urea supply device 35 is configured to inject urea water from the urea injector 39 when the temperature Ts of the SCR catalyst 33 is equal to or higher than the decomposition temperature at which urea can be hydrolyzed into ammonia.

  Further, in the exhaust passage 30 between the DPF 32 and the SCR catalyst 33, a NOx concentration sensor 78 that is provided upstream of the urea injector 39 and detects the NOx concentration of the exhaust gas passing through the exhaust passage 30, and the mixing plate 36. And an exhaust gas temperature sensor 79 for detecting the temperature of exhaust gas passing through the exhaust passage 30 is provided.

  Next, an engine automatic stop control device 70 according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing an engine automatic stop control device 70 according to an embodiment of the present invention.

  As shown in FIG. 2, the engine automatic stop control device 70 according to the present embodiment includes various sensors, an engine control unit 72 that controls the engine 1 and the urea supply device 35 based on detection signals of the various sensors, and an engine control unit. The intake valve 22, the exhaust valve 26, the injector 48, and the urea supply device 35 that are actuated based on a request signal from 72 are provided. The various sensors are a vehicle speed sensor 73 for detecting the vehicle speed (the absolute speed of the vehicle), an accelerator sensor 74 for detecting the on / off state of the accelerator pedal, a brake sensor 76 for detecting the on / off state of the brake pedal, and a NOx concentration sensor 78. The exhaust temperature sensor 79 and the intake air temperature / flow rate sensor 14.

  The engine control unit 72 is an ECU (Electronic Control Unit) that integrates, calculates, and stores signals from each device and performs request processing on each device. The engine control unit 72 includes an input interface circuit for inputting signals from various sensors, an output interface circuit for outputting a request signal to each device, a CPU for processing the input signals, a memory, and operating these It is comprised from the program (it is not shown above) for making it do. The engine control unit 72 functions as the engine automatic stop control unit 80 and the urea supply control unit 82 of the present invention.

  The engine control unit 72 (engine automatic stop control means 80) automatically stops the engine 1 when a predetermined start condition (for example, the vehicle is stopped and the brake pedal is on) is satisfied, and a predetermined restart condition (for example, an accelerator pedal). Is established), automatic engine stop control for restarting the engine 1, so-called idle stop control is executed. The engine control unit 72 (urea supply control means 82) executes urea supply control in which urea water is supplied into the exhaust passage 30 by operating the urea supply device 35 and ammonia is adsorbed on the SCR catalyst 33. The engine control unit 72 determines the temperature Ts of the SCR catalyst 33 and the ammonia adsorption amount based on data detected from the NOx concentration sensor 78, the exhaust temperature sensor 79, the intake air temperature / flow rate sensor 14, and the outside air temperature sensor (not shown). Qc, target adsorption amount Qa of ammonia, and urea water injection amount U are calculated. The engine control unit 72 injects urea water from the urea injector 39 at the timing when the predetermined condition is satisfied and the urea water injection amount U.

  Next, a control flow by the automatic engine stop control device 70 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing a control flow executed by the engine automatic stop control device 70 according to the embodiment of the present invention. In FIG. 3, S indicates each step.

  First, as shown in FIG. 3, in S1, the engine control unit 72 determines that the current vehicle speed, the on / off state of the accelerator pedal and the brake pedal, the temperature Ts of the SCR catalyst 33, the ammonia adsorption amount Qc, the target adsorption amount Qa, Various data of the urea water injection amount U are read in a timely manner. Specific procedures for calculating the temperature Ts, the ammonia adsorption amount Qc, the target adsorption amount Qa, and the urea water injection amount U will be described later.

  Next, in S2, the engine control unit 72 determines whether a start condition for engine automatic stop control is satisfied based on the current vehicle speed and the on / off state of the brake pedal. Here, the start condition is set as to whether the vehicle is stopped (0 km / h) and the brake pedal is in an on state. Instead of this, the start condition of the engine automatic stop control may be set, for example, whether or not the current vehicle speed is 12 km / h or less and the accelerator pedal is in an off state.

  When the vehicle is running or stopped but the brake pedal is in an off state (S2; No), the engine control unit 72 continues the normal operation mode (S3), and the engine according to the driving operation of the driver. 1 and the urea supply device 35 are controlled.

  If the vehicle is stopped and the brake pedal is on (S2; Yes), the vehicle is expected to be in a stopped state, and the process proceeds to S5. In S5, the engine control unit 72 determines whether or not the current temperature Ts of the SCR catalyst 33 is lower than the set temperature (first predetermined condition). The set temperature is stored in advance in the engine control unit 72, and is set to a decomposition temperature at which urea can be hydrolyzed to ammonia. The decomposition temperature here is about 180 ° C., and is set to a value obtained by adding a margin of about 10 ° C. to the decomposition temperature (about 170 ° C.) at which urea starts hydrolysis into ammonia. If the temperature is lower than the decomposition temperature, ammonia is not adsorbed and there is a high possibility that the NOx purification performance of the SCR catalyst 33 is lowered. Therefore, whether the NOx purification performance of the SCR catalyst 33 is lowered by setting the set temperature to the decomposition temperature. Can be determined.

  In S5, when the temperature of the SCR catalyst 33 is equal to or higher than the set temperature (S5; No), since the NOx purification performance of the SCR catalyst 33 is in a sufficient state, the engine control unit 72 executes engine automatic stop control ( At the same time as S7), the urea supply device 35 is stopped (S8). Specifically, the engine control unit 72 automatically stops the engine 1 by stopping fuel injection from the injector 48 into the combustion chamber 2a (fuel cut). At the same time, the engine control unit 72 closes the urea injector 39 to stop the supply of urea water into the exhaust passage 30.

  In S5, when the temperature Ts of the SCR catalyst 33 is lower than the set temperature (S5; Yes), there is a high possibility that the NOx purification performance of the SCR catalyst 33 is deteriorated, and the process proceeds to S6. In S6, the engine control unit 72 determines whether or not the current ammonia adsorption amount Qc of the SCR catalyst 33 is smaller than the set adsorption amount (second predetermined condition). Here, the set adsorption amount is set to a target adsorption amount Qa (about 1 g) which is an ammonia adsorption amount that allows the SCR catalyst 33 to reduce and purify NOx in the exhaust gas passing through the exhaust passage 30. Thereby, it is possible to determine whether or not an amount of ammonia capable of reducing and purifying NOx is adsorbed by the SCR catalyst 33.

  In S6, when the ammonia adsorption amount Qc of the SCR catalyst 33 is equal to or larger than the set amount (S6; No), the NOx purification performance of the SCR catalyst 33 is in a sufficient state, so the engine control unit 72 performs the engine automatic stop control. At the same time as the execution (S7), the urea supply device 35 is stopped (S8).

  In S6, when the ammonia adsorption amount Qc of the SCR catalyst 33 is lower than the set adsorption amount (S6; Yes), since the ammonia adsorption amount Qc is insufficient with respect to the target adsorption amount Qa, the process proceeds to S9. In S9, the engine control unit 72 performs the engine automatic stop control because the NOx purification performance of the SCR catalyst 33 is deteriorated (the ammonia adsorption amount of the SCR catalyst 33 is insufficient). It is prohibited (S9). As a result, the engine 1 continues the idling state and allows the high-temperature exhaust gas corresponding to the load of the engine 1 to pass through the exhaust path 30.

  Next, in S10, the temperature Ts of the SCR catalyst 33 has reached the decomposition temperature or higher due to the heat of the exhaust gas, and the engine control unit 72 operates the urea supply device 35 to execute urea supply control. Specifically, the engine control unit 72 opens the urea injector 39 to inject the urea water stored in the tank 37 into the exhaust passage 30. At that time, the amount injected from the urea injector 39 is set to the urea water injection amount U read in S1.

  In S11, when it is detected by various sensors that the ammonia adsorption amount Qc of the SCR catalyst 33 has reached the target adsorption amount Qa, the engine control unit 72 ends the supply of urea water and executes engine automatic stop control. Thereafter, the control flow described above is repeatedly executed.

  FIG. 4 is a flowchart showing a specific procedure for calculating the temperature Ts, the ammonia adsorption amount Qc, the target adsorption amount Qa, and the urea water injection amount U of the SCR catalyst read in S1 of FIG. 3, and FIG. It is a graph which shows the relationship between temperature Ts of this, upper limit adsorption amount Qx of ammonia, and target adsorption amount Qa. A specific procedure for calculating the temperature Ts, the ammonia adsorption amount Qc, and the urea water injection amount U of the SCR catalyst read in S1 of FIG. 3 will be described. In FIG. 4, S indicates each step.

  As shown in FIG. 4, first, in S <b> 21, the engine control unit 72 estimates the temperature Ts of the SCR catalyst 33. The temperature Ts of the SCR catalyst 33 is, for example, the temperature of the carrier of the SCR catalyst 33 and the bed temperature.

  Specifically, in S21, the engine control unit 72 first calculates the amount of heat input to the SCR catalyst 33 based on the temperature of the exhaust gas detected by the exhaust temperature sensor 79 and the flow rate of the exhaust gas. The exhaust gas flow rate is estimated from the intake air flow rate detected by the intake air temperature / flow rate sensor 14, the opening of an EGR valve (not shown), and the like. Next, the engine control unit 72 calculates the amount of heat released from the SCR catalyst 33 based on the vehicle speed detected by the vehicle speed sensor 73 and the outside air temperature detected by the outside air temperature sensor (not shown). The temperature Ts of the SCR catalyst 33 is calculated based on the amount of heat input and the amount of heat released and the heat capacity of the SCR catalyst 33 stored in advance. The higher the vehicle speed, the lower the temperature Ts because heat dissipation is promoted, and the lower the vehicle speed, the higher the temperature Ts.

  Next, in S22, the engine control unit 72 determines a target adsorption amount Qa of ammonia to be adsorbed by the SCR catalyst 33 based on the temperature Ts. Specifically, the engine control unit 72 stores in advance a map (FIG. 5) that defines the relationship between the temperature Ts of the SCR catalyst 33 and the target adsorption amount Qa, and the target corresponding to the temperature Ts based on this map. The adsorption amount Qa is determined.

  As shown in FIG. 5, the target adsorption amount Qa of ammonia varies according to the temperature Ts of the SCR catalyst 33. The target adsorption amount Qa is set to a value smaller than the upper limit adsorption amount Qx of ammonia. The upper limit adsorption amount Qx is the upper limit ammonia adsorption amount Qc that can be adsorbed by the SCR catalyst 33, and is a so-called saturated adsorption amount. The SCR catalyst 33 has a property that it becomes difficult to adsorb ammonia as its temperature increases. For this reason, the upper limit adsorption amount Qx decreases as the temperature Ts of the SCR catalyst 33 increases.

  Specifically, as shown in FIG. 5, the target adsorption amount Qa of ammonia is set according to the tendency of the upper limit adsorption amount Qx, and is set so as to decrease as the temperature Ts of the SCR catalyst 33 increases. In the range from the first predetermined temperature T1 to the second predetermined temperature T2, the target adsorption amount Qa is set to change depending on the temperature Ts. In the low temperature range where the temperature is equal to or lower than the first predetermined temperature T1, the target adsorption amount Qa is set to a constant value Q1 at which sufficient NOx purification performance can be obtained. Further, the target adsorption amount Qa is set to zero in the high temperature range where the temperature is equal to or higher than the second predetermined temperature T2.

  In S23, the engine control unit 72 estimates an ammonia adsorption amount Qc which is the amount of ammonia currently adsorbed on the SCR catalyst 33. Specifically, the ammonia adsorption amount Qc is calculated by subtracting the ammonia consumption amount at each time in the SCR catalyst 33 from the ammonia supply amount at each time point stored as a past history, and integrating this subtraction value. Is done.

  Next, in S <b> 24, the engine control unit 72 estimates an ammonia consumption amount W that is the amount of ammonia consumed in the SCR catalyst 33. Specifically, the engine control unit 72 calculates the amount of NOx flowing into the SCR catalyst 33 based on the NOx concentration in the exhaust gas and the flow rate of the exhaust gas. Based on the inflow amount of NOx and the ammonia consumption amount for NOx per unit of the SCR catalyst 33 stored in advance, the ammonia consumption amount W consumed for NOx reduction by the SCR catalyst 33 is calculated.

  In S25, the engine control unit 72 determines the urea water injection amount U to be injected from the urea injector 39. Specifically, the urea water injection amount U is a supply amount of ammonia necessary for increasing the ammonia adsorption amount Qc to the target adsorption amount Qa in the SCR catalyst 33. The urea water injection amount U is calculated by subtracting the ammonia adsorption amount Qc calculated in S23 from the ammonia target adsorption amount Qa determined in S22. The urea water injection amount U may be calculated based on the ammonia consumption amount W instead of this. This completes the specific procedure for calculating the temperature Ts of the SCR catalyst, the ammonia adsorption amount Qc, the target adsorption amount Qa, and the urea water injection amount U.

  The engine control unit 72 performs calculation according to the specific procedure described above in a timely manner, and stores various data of the SCR catalyst temperature Ts, the ammonia adsorption amount Qc, the target adsorption amount Qa, and the urea water injection amount U.

Next, the (action) effect of the engine automatic stop control device 70 according to this embodiment of the present invention will be described.
According to the engine automatic stop control device 70 of the present embodiment, when the first or second predetermined condition for reducing the NOx purification performance of the SCR catalyst 33 is satisfied, the engine control unit 72 (engine automatic stop control means). 80) prohibits the execution of the engine automatic stop control and continues the operation of the engine 1, and the engine control unit 72 (urea supply control means 82) performs urea supply control for supplying urea water to the urea supply device 35. Therefore, the ammonia adsorption amount Qc of the SCR catalyst 33 whose NOx purification performance is reduced can be increased. Therefore, even when the engine automatic stop control is performed, the SCR catalyst 33 can reduce and purify NOx when the engine is restarted.

Further, according to the present embodiment, the first predetermined condition is when the temperature Ts of the SCR catalyst 33 is lower than the set temperature. Therefore, when the temperature Ts of the SCR catalyst 33 is lower than the set temperature ( In the case of YES in S5, the execution of the engine automatic stop control is prohibited (S9), the engine 1 is kept in the idle state, the temperature Ts of the SCR catalyst 33 is increased to the decomposition temperature or more, and urea water is supplied to the SCR catalyst 33. Since it supplies (S10), the ammonia adsorption amount Qc can be increased.

According to the present embodiment, the engine control unit 72 (urea supply control means 82) causes the urea supply device 35 to perform the SCR catalyst when the temperature Ts of the SCR catalyst 33 is equal to or higher than the decomposition temperature at which urea can be hydrolyzed into ammonia. The urea water is supplied to 33, and the set temperature is set to the decomposition temperature at that time. According to the present embodiment as described above, when the decomposition temperature of the SCR catalyst 33 is lower than the decomposition temperature capable of being hydrolyzed to ammonia (YES in S5) , that is, there is a high possibility that the NOx purification performance is deteriorated. In this case, the execution of the engine automatic stop control is prohibited (S9), the engine 1 is kept in the idle state, the temperature Ts of the SCR catalyst 33 is increased to the decomposition temperature or more, and urea water is supplied to the SCR catalyst 33 (S10). The ammonia adsorption amount Qc can be increased.

  Further, according to the present embodiment, the second predetermined condition is when the ammonia adsorption amount Qc adsorbed on the SCR catalyst 33 is smaller than the set adsorption amount. Therefore, the ammonia adsorption amount Qc of the SCR catalyst 33 is When it is insufficient, that is, when the NOx purification performance is lowered, the ammonia adsorption amount Qc can be increased.

  According to this embodiment, the engine control unit 72 (urea supply control means 82) supplies urea water to the SCR catalyst 33 by the urea supply device 35 until the ammonia adsorption amount Qc of the SCR catalyst 33 reaches the target adsorption amount Qa. The set adsorption amount is set to the target adsorption amount Qa at that time. According to this embodiment, the ammonia adsorption amount Qc of the SCR catalyst 33 can be reliably increased to the target adsorption amount Qa where the NOx purification performance is sufficient.

  Further, according to the present embodiment, the engine control unit 72 (urea supply control means 82) sets the target adsorption amount Qa according to the temperature Ts of the SCR catalyst 33, so that an appropriate amount of urea according to the temperature Ts is set. Water can be supplied, and urea supply control can be completed in a short time.

DESCRIPTION OF SYMBOLS 1 Engine 30 Exhaust path 33 SCR catalyst 35 Urea supply apparatus 39 Urea injector 70 Engine automatic stop control apparatus 72 Engine control part 80 Engine automatic stop control means 82 Urea supply control means Qa Target adsorption amount Qc Ammonia adsorption amount Ts Temperature

Claims (4)

An engine automatic stop control device comprising: an SCR catalyst for reducing and purifying NOx provided in an exhaust passage of an engine; and a urea supply device for supplying urea water to the SCR catalyst,
An engine automatic stop control means for executing an engine automatic stop control for automatically stopping the engine when a predetermined start condition is satisfied and restarting the engine when a predetermined restart condition is satisfied;
Urea supply control means for controlling the supply of urea water by the urea supply device,
When a predetermined condition for reducing the NOx purification performance of the SCR catalyst is satisfied, the engine automatic stop control means prohibits the execution of the engine automatic stop control to continue the operation of the engine and the urea supply control. means have lines supplying the urea water by the urea supply device,
The predetermined condition for reducing the NOx purification performance of the SCR catalyst is when the temperature of the SCR catalyst is lower than a set temperature,
The urea feed control means, when the temperature of the SCR catalyst is urea hydrolysable decomposition temperature or more of the ammonia by the urea supply device supplies urea water into the SCR catalyst, the set temperature, the An automatic engine stop control device set to the decomposition temperature .   The engine automatic stop control device according to claim 1, wherein the predetermined condition for reducing the NOx purification performance of the SCR catalyst is when the ammonia adsorption amount adsorbed on the SCR catalyst is smaller than a set adsorption amount. The urea supply control means supplies urea water to the SCR catalyst by the urea supply device until the ammonia adsorption amount of the SCR catalyst reaches a target adsorption amount,
The engine automatic stop control device according to claim 2, wherein the set adsorption amount is set to the target adsorption amount.   The automatic stop control device for an engine according to claim 3, wherein the urea supply control means sets the target adsorption amount in accordance with the temperature of the SCR catalyst.

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