TECHNICAL FIELD

The present disclosure relates to a control device, an exhaust gas purification system including the control device, and a control method of an engine for executing, in the engine including a DOC and a DPF in an exhaust passage, a forced regeneration process of removing PM deposited on the DPF by increasing a temperature of the DPF.

BACKGROUND

An engine (diesel engine) may be equipped with an exhaust gas purification device which includes a diesel oxidation catalyst (DOC) disposed in an exhaust passage of the engine and a diesel particulate filter (DPF) disposed downstream of the DOC in the exhaust passage to collect particulate matters (PM), such as soot, contained in an exhaust gas (see Patent Document 1, 2).

If the PM collected by the DPF is deposited and clogs the DPF, PM-collecting performance may be declined, or an exhaust pressure (a pressure of the exhaust passage) may be increased, deteriorating fuel efficiency. Thus, the forced regeneration process of removing the PM deposited on the DPF is executed every time a PM deposition amount reaches a predetermined amount, or an engine operation time elapses a certain period of time.

Forced regeneration (automatic regeneration) of the DPF is executed by forcibly increasing an inlet temperature of the DPF. In general, the inlet temperature of the DPF is forcibly increased by supplying a non-combusted fuel to an exhaust gas treatment device by late-post injection, which is to inject a fuel after a main-combustion injection timing, and oxidizing the non-combusted fuel with the diesel oxidization catalyst (DOC) to generate heat, after the inlet temperature of the DOC is increased to a predetermined temperature (about 250° C.) at which the DOC is active.

In order to increase the inlet temperature of the DOC to the above-described predetermined temperature, reducing (decreasing) the opening degree of an intake throttle valve disposed in an intake passage of the engine, or adjusting an injection amount or an injection timing of the non-combusted fuel in early-post injection executed after the main-combustion injection timing and before the late-post injection timing are performed widely. It is possible to increase the inlet temperature of the DOC to the above-described predetermined temperature by reducing the opening degree of the exhaust throttle valve disposed in the exhaust passage of the engine. However, this method has not conventionally been adopted very much.

CITATION LIST

Patent Literature

Patent Document 1: JP2003-206724A

Patent Document 2: JP2004-353529A

SUMMARY

Technical Problem

The following problems can be given as a reason why the temperature increase method of reducing the opening degree of the exhaust throttle valve has not been adopted. Since the intake throttle valve is disposed in the intake passage for sending air (combustion gas) to the engine, a usage environment thereof is stable. By contrast, since the exhaust throttle valve is disposed in the exhaust passage for flowing the exhaust gas discharged from the engine, a usage environment thereof is unstable. More specifically, an operation failure and a decrease in responsiveness, which are caused by fixation of the exhaust throttle valve due to, for example, non-combusted fuel (HC) and particulate matters (PM) contained in the exhaust gas discharged from the engine, become problems, respectively. For example, if an actual opening degree of the exhaust throttle valve is less than an instructed opening degree instructed by the control device due to the operation failure by the fixation, the exhaust throttle valve is narrowed more than expected, which may decrease the amount of air supplied to the engine and the amount of the exhaust gas discharged from the engine, may increase the temperature and the pressure of the exhaust gas flowing through the exhaust passage. Moreover, since the exhaust throttle valve is narrowed more than expected, the temperature and the pressure of the exhaust gas flowing through the exhaust passage may also be increased by abnormal combustion of a residual fuel remaining in the combustion chamber. Then, if the temperature of the exhaust gas flowing through the exhaust passage is increased more than expected, a failure in engine and thermal deterioration of the oxidation catalyst of the DOC may be caused.

In view of the above issues, an object of at least one embodiment of the present invention is to provide a control device capable of preventing abnormal increases in temperature and pressure of the exhaust gas in the exhaust passage of the engine, during control of reducing the opening degree of the exhaust throttle valve.

Solution to Problem

(1) A control device according to at least one embodiment of the present invention is a control device configured to be able to execute, in an engine which includes a DOC disposed in an exhaust passage of the above-described engine, a DPF disposed downstream of the above-described DOC in the above-described exhaust passage, and a temperature increase unit for increasing a temperature of each of the above-described DOC and the above-described DPF, a forced regeneration process of removing PM deposited on the above-described DPF by increasing the temperature of the above-described DPF. The above-described forced regeneration process includes a first temperature increase process of controlling the above-described temperature increase unit such that the temperature of the above-described DOC is increased to a first temperature, and a second temperature increase process of controlling the above-described temperature increase unit such that the temperature of the above-described DPF is increased to a second temperature which is higher than the above-described first temperature after completion of the above-described first temperature increase process. The above-described temperature increase unit includes an exhaust throttle valve disposed in the above-described exhaust passage. The above-described control device includes a valve opening/closing operation execution part configured to cause the above-described exhaust throttle valve to execute a valve opening/closing operation of increasing an opening degree of the above-described exhaust throttle valve to be greater than a predetermined opening degree for a predetermined time, when the above-described forced regeneration process is switched from the above-described first temperature increase process to the above-described second temperature increase process.

With the above configuration (1), the control device causes the exhaust throttle valve to execute the valve opening/closing operation of increasing the opening degree of the exhaust throttle valve to be greater than the predetermined opening degree for the predetermined time, when the forced regeneration process is switched from the first temperature increase process to the second temperature increase process. Executing the above-described valve opening/closing operation, the exhaust throttle valve can flow a non-combusted fuel and the PM deposited on the exhaust throttle valve downstream of the exhaust throttle valve in the exhaust passage. Reducing the non-combusted fuel and the PM deposited on the exhaust throttle valve, it is possible to prevent an operation failure caused by fixation of the exhaust throttle valve during the second temperature increase process. That is, it is possible to prevent an actual opening degree of the exhaust throttle valve from being less than an instructed opening degree instructed by the control device. Thus, since the actual opening degree of the exhaust throttle valve is equal to the instructed opening degree instructed by the control device, it is possible to set an appropriate flow rate of the exhaust gas flowing downstream of the exhaust throttle valve in the exhaust passage during the second temperature increase process. Thus, with the above configuration, it is possible to prevent abnormal increases in temperature and pressure of the exhaust gas in the exhaust passage of the engine, and to prevent a failure in the engine and thermal deterioration of an oxidation catalyst of the DOC, during control of reducing the opening degree of the exhaust throttle valve.

(2) In some embodiments, in the control device according to the above configuration (1), the above-described valve opening/closing operation execution part is configured to instruct the above-described exhaust throttle valve such that at least one of a speed at which the above-described exhaust throttle valve is opened or a speed at which the above-described exhaust throttle valve is closed in execution of the above-described valve opening/closing operation is not greater than a predetermined speed.

The amount of the exhaust gas flowing downstream of the exhaust throttle valve in the exhaust passage is rapidly increased/decreased, if the speed at which the exhaust throttle valve is opened and the speed at which the exhaust throttle valve is closed in execution of the valve opening/closing operation exceed the predetermined speed, increasing a possibility of occurrence of air flow noise (noise). With the above configuration (2), since at least one of the speed at which the exhaust throttle valve is opened or the speed at which the exhaust throttle valve is closed in execution of the valve opening/closing operation is not greater than the predetermined speed, it is possible to suppress occurrence of the air flow noise.

(3) In some embodiments, in the control device according to the above configuration (1) or (2), the above-described valve opening/closing operation execution part is configured to instruct the above-described exhaust throttle valve on an opening degree, which is less than a fully open opening degree, as an opening degree of the above-described exhaust throttle valve in execution of the above-described valve opening/closing operation.

If the opening degree of the exhaust throttle valve in execution of the valve opening/closing operation is fully open, the amount of the exhaust gas flowing downstream of the exhaust throttle valve in the exhaust passage is rapidly touched, which may result in the exhaust gas which is not purified by an exhaust gas purification device being discharged to the atmosphere. With the above configuration (3), since the opening degree of the exhaust throttle valve in execution of the valve opening/closing operation is less than the fully open opening degree, it is possible to suppress discharge of the exhaust gas, which is not purified by the exhaust gas purification device, to the atmosphere.

(4) In some embodiments, in the control device according to any one of the above configurations (1) to (3), the above-described valve opening/closing operation execution part is configured to cause the above-described exhaust throttle valve to execute the above-described valve opening/closing operation before late-post injection in the above-described second temperature increase process.

During execution of the late-post injection, the non-combusted fuel passes through the exhaust throttle valve having the decreased opening degree, which is likely to cause the operation failure due to fixation of the exhaust throttle valve. With the above configuration (4), executing the above-described valve opening/closing operation before the late-post injection in the second temperature increase process to reduce the non-combusted fuel and the PM deposited on the exhaust throttle valve, it is possible to prevent the operation failure caused by fixation of the exhaust throttle valve during the late-post injection.

(5) In some embodiments, the control device according to any one of the above configurations (1) to (4) further includes a feedforward opening degree acquisition part configured to be able to acquire a feedforward opening degree, which is the opening degree of the above-described exhaust throttle valve, based on information regarding an operational condition of the above-described engine, a feedback opening degree acquisition part configured to be able to acquire a feedback opening degree, which is the opening degree of the above-described exhaust throttle valve, based on a difference between a preset target temperature and a detected temperature acquired by an exhaust gas temperature detection device capable of detecting a temperature of an exhaust gas flowing through the above-described exhaust passage, and an instructed opening degree decision part configured to decide greater of the above-described feedforward opening degree, which is acquired by the above-described feedforward opening degree acquisition part, and the above-described feedback opening degree, which is acquired by the above-described feedback opening degree acquisition part, as an instructed opening degree to be instructed for the above-described exhaust throttle valve.

With the above configuration, since the greater of the above-described feedforward opening degree and the above-described feedback opening degree as the instructed opening degree of the exhaust throttle valve, it is possible to prevent a lack of the amount of air supplied to the engine and the amount of an exhaust gas discharged from the engine, and to suppress the high temperature of the exhaust gas flowing through the exhaust passage exceeding the target temperature. Thus, with the above configuration, it is possible to prevent the abnormal increases in temperature and pressure of the exhaust gas in the exhaust passage of the engine, and to prevent the failure in the engine and the thermal deterioration of the oxidation catalyst of the DOC, during control of reducing the opening degree of the exhaust throttle valve.

(6) In some embodiments, the control device according to the above configuration (5) further includes a control gain adjustment part configured to be able to adjust a control gain when the above-described feedback opening degree is calculated. The above-described control gain adjustment part is configured to adjust the above-described control gain such that the above-described recalculated feedback opening degree is greater than the above-described feedforward opening degree, if the above-described detected temperature exceeds the above-described target temperature, and the above-described feedback opening degree is not greater than the above-described feedforward opening degree.

With the above configuration (6), if the detected temperature exceeds the target temperature, the feedback opening degree is decided as the instructed opening degree of the exhaust throttle valve. At this time, if the feedback opening degree is not greater than the feedforward opening degree, the control gain adjustment part adjusts the control gain such that the recalculated feedback opening degree is greater than the feedforward opening degree. With the above configuration, if the detected temperature exceeds the target temperature, the opening degree is controlled with the recalculated feedback opening degree being decided as the instructed opening degree of the exhaust throttle valve. Thus, control of increasing the opening degree of the exhaust throttle valve, and decreasing the temperature and pressure of the exhaust gas flowing through the exhaust passage is performed quickly such that the detected temperature approaches the target temperature, making it possible to shorten a period in which the exhaust gas flowing through the exhaust passage has the high temperature exceeding the target temperature.

(7) In some embodiments, the control device according to the above configuration (5) or (6) further includes a control gain adjustment part configured to be able to adjust a control gain when the above-described feedback opening degree is calculated. The above-described control gain adjustment part is configured to adjust the above-described control gain such that the above-described recalculated feedback opening degree is less than the above-described feedforward opening degree, if the above-described detected temperature is not higher than the above-described target temperature, and the above-described feedforward opening degree is not greater than the above-described feedback opening degree.

With the above configuration (7), if the detected temperature is not higher than the target temperature, the feedforward opening degree is decided as the instructed opening degree of the exhaust throttle valve. At this time, if the feedforward opening degree is not greater than the feedback opening degree, the control gain adjustment part adjusts the control gain such that the recalculated feedback opening degree is less than the feedforward opening degree. With the above configuration, if the detected temperature is not higher than the target temperature, the opening degree is controlled with the feedforward opening degree being decided as the instructed opening degree of the exhaust throttle valve. Thus, since the opening degree of the exhaust throttle valve is controlled based on the information regarding the operational condition of the engine, it is possible to prevent the lack of the amount of the air supplied to the engine and the amount of the exhaust gas discharged from the engine.

(8) In some embodiments, in the control device according to the above configurations (5) to (7), the above-described information regarding the operational condition of the engine includes a rotation speed of the above-described engine and a fuel injection amount.

With the above configuration (8), since the information regarding the operational condition of the engine includes the engine rotation speed and the fuel injection amount, the feedforward opening degree acquisition part can acquire an appropriate feedforward opening degree on which the engine rotation speed and the fuel injection amount are reflected.

(9) An exhaust gas purification system according to at least one embodiment of the present invention includes the control device according to any one of the above configurations (1) to (8), the above-described DOC, the above-described DPF, and the above-described temperature increase unit including the above-described exhaust throttle valve.

With the above configuration (9), since the control device causes the exhaust throttle valve to execute the valve opening/closing operation when the forced regeneration process is switched from the first temperature increase process to the second temperature increase process, the exhaust gas purification system can prevent the operation failure caused by fixation of the exhaust throttle valve during the second temperature increase process.

(10) A control method of an engine according to at least one embodiment of the present invention is a control method of an engine, which includes a DOC disposed in an exhaust passage of the above-described engine, a DPF disposed downstream of the above-described DOC in the above-described exhaust passage, and a temperature increase unit for increasing a temperature of each of the above-described DOC and the above-described DPF, for executing a forced regeneration process of removing PM deposited on the above-described DPF by increasing the temperature of the above-described DPF. The above-described forced regeneration process includes a first temperature increase process of controlling the above-described temperature increase unit such that the temperature of the above-described DOC is increased to a first temperature, and a second temperature increase process of controlling the above-described temperature increase unit such that the temperature of the above-described DPF is increased to a second temperature which is higher than the above-described first temperature after completion of the above-described first temperature increase process. The above-described temperature increase unit includes an exhaust throttle valve disposed in the above-described exhaust passage. The above-described control method of the engine includes a step of executing a valve opening/closing operation of increasing an opening degree of the above-described exhaust throttle valve to be greater than a predetermined opening degree for a predetermined time, when the above-described forced regeneration process is switched from the above-described first temperature increase process to the above-described second temperature increase process.

With the above method (10), the control method of the engine includes a step of executing the valve opening/closing operation of increasing the opening degree of the exhaust throttle valve to be greater than the predetermined opening degree for the predetermined time, when the forced regeneration process is switched from the first temperature increase process to the second temperature increase process. Executing the above-described valve opening/closing operation, the exhaust throttle valve can flow the non-combusted fuel and the PM deposited on the exhaust throttle valve downstream of the exhaust throttle valve in the exhaust passage. Reducing the non-combusted fuel and the PM deposited on the exhaust throttle valve, it is possible to prevent the operation failure caused by fixation of the exhaust throttle valve during the second temperature increase process. That is, it is possible to prevent the actual opening degree of the exhaust throttle valve from being less than the instructed opening degree instructed by the control device. Thus, since the actual opening degree of the exhaust throttle valve is equal to the instructed opening degree instructed by the control device, it is possible to set the appropriate flow rate of the exhaust gas flowing downstream of the exhaust throttle valve in the exhaust passage during the second temperature increase process. Thus, with the above method, it is possible to prevent the abnormal increases in temperature and pressure of the exhaust gas in the exhaust passage of the engine, and to prevent the failure in the engine and the thermal deterioration of the oxidation catalyst of the DOC, during control of reducing the opening degree of the exhaust throttle valve.

(11) In some embodiments, the control method of the engine according to the above method (10) further includes a feedforward opening degree acquisition step of acquiring a feedforward opening degree, which is the opening degree of the above-described exhaust throttle valve, based on information regarding an operational condition of the above-described engine, a feedback opening degree acquisition step of acquiring a feedback opening degree, which is the opening degree of the above-described exhaust throttle valve, based on a difference between a preset target temperature and a detected temperature acquired by an exhaust gas temperature detection device capable of detecting a temperature of an exhaust gas flowing through the above-described exhaust passage, and an instructed opening degree decision step of deciding greater of the above-described feedforward opening degree, which is acquired in the above-described feedforward opening degree acquisition step, and the above-described feedback opening degree, which is acquired in the above-described feedback opening degree acquisition step, as an instructed opening degree to be instructed for the above-described exhaust throttle valve.

With the above method (11), since the control method of the engine decides the greater of the feedforward opening degree, which is acquired based on the information regarding the operational condition of the engine, and the feedback opening degree, which is acquired based on the difference between the preset target temperature and the detected temperature of the exhaust gas flowing through the exhaust passage, as the instructed opening degree of the exhaust throttle valve, it is possible to prevent the lack of the amount of the air supplied to the engine and the amount of the exhaust gas discharged from the engine, and to suppress the high temperature of the exhaust gas flowing through the exhaust passage exceeding the target temperature. Thus, with the above method, it is possible to prevent the abnormal increases in temperature and pressure of the exhaust gas in the exhaust passage of the engine, and to prevent the failure in the engine and the thermal deterioration of the oxidation catalyst of the DOC, during control of reducing the opening degree of the exhaust throttle valve.

Advantageous Effects

According to at least one embodiment of the present invention, provided is a control device capable of preventing abnormal increases in temperature and pressure of an exhaust gas in an exhaust passage of an engine, during control of reducing the opening degree of an exhaust throttle valve.

