Control device for engine

Abstract

To provide a control device for an engine capable of preventing hunting in control and appropriately operating the engine when executing temperature rise processing (regeneration processing) of a filter for collecting PMs.SOLUTION: In a control device for an engine that performs one-cylinder fuel cut to raise a temperature of a filter for collecting PMs in exhaust gas and burns the PMs accumulated in the filter, a target temperature b of exhaust gas entering the filter is set on the basis of an accumulation amount of the PMs, a target equivalence ratio p relative to a combustion cylinder is set on the basis of a difference between an actual temperature a and the target temperature b of exhaust gas before execution of the one-cylinder fuel cut to execute specific cylinder fuel cut, and the equivalence ratio p is corrected so that an actual temperature c of the exhaust gas during execution of the specific cylinder fuel cut follows the target temperature b (Steps S7, S8).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device for an engine (internal combustion engine), and more particularly to a control device for an engine capable of suspending the fuel supply of only one or some of the cylinders during the operation of an engine having a plurality of cylinders.

Background Art

[0002] In internal combustion engines such as gasoline engines and diesel engines, a temperature increase treatment (or regeneration treatment) for regenerating a filter that collects PM (Particulate Matter) is performed. The temperature increase treatment is, for example, controlling the air-fuel ratio of one cylinder among a plurality of cylinders to be rich (less than the theoretical air-fuel ratio) and the air-fuel ratio of the other cylinders to be lean (equal to or greater than the theoretical air-fuel ratio), or performing a fuel cut (one-cylinder fuel cut, specific cylinder fuel cut, or partial cylinder fuel cut) that suspends the fuel supply of only one or some of the plurality of cylinders, thereby increasing the temperature of the filter and the catalyst. By performing such a one-cylinder fuel cut or specific cylinder fuel cut, the cylinder to be combusted is set in a rich state with a large amount of fuel, and fresh air, that is, oxygen before combustion, is sent from the cylinder where the fuel cut is performed to the filter. Thereby, a so-called afterburning phenomenon is induced to increase the temperature of the filter, and the PM deposited on the filter can be combusted and removed. That is, the regeneration of the filter can be promoted.

[0003] When performing a temperature increase process by such a single-cylinder fuel cut or a specific cylinder fuel cut, a control device for an internal combustion engine is described in Patent Document 1 for the purpose of suppressing overheating caused by an inflow of unburned fuel more than expected into a catalyst. The control device for the internal combustion engine described in this Patent Document 1 executes a rich combustion process as a temperature increase process for burning and removing PM collected by a GPF (Gasoline Particulate Filter) for regeneration. In the rich combustion process, the fuel supply to some of the plurality of cylinders of the engine is stopped. At the same time, the target equivalence ratio (target value of the equivalence ratio) of the combustion cylinders is set to be richer than the stoichiometric air-fuel ratio for the combustion cylinders where the air-fuel mixture is burned, and fuel injection is performed.

[0004] Further, Patent Document 2 describes a control device for an internal combustion engine for the purpose of aborting the regeneration process of a GPF before the temperature of the GPF becomes excessively high. The control device for the internal combustion engine described in this Patent Document 2 stops the combustion control of some cylinders and executes a regeneration process in which the air-fuel ratio of the air-fuel mixture in the remaining cylinders is made richer than the stoichiometric air-fuel ratio when the amount of PM collected by the GPF increases. At that time, the temperature of the GPF and the amount of PM collected by the GPF are acquired each time, and an allowable value is set according to the temperature (estimated temperature) of the GPF and the amount of PM (deposition amount) during the execution of the regeneration process. Then, when the amount of air flowing into the GPF exceeds the allowable value during a predetermined period, the regeneration process is aborted.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the control device for an internal combustion engine described in Patent Document 1 and Patent Document 2 mentioned above, when performing a temperature increase process (or a regeneration process), based on the amount of PM deposition in the GPF and the estimated temperature of the GPF, the target equivalence ratio of the injection amount for the combustion cylinder is determined. In particular, since the estimated temperature of the GPF is used as input information for setting the target equivalence ratio, it is impossible to distinguish the difference between the state of the GPF and the actual temperature before the start of the temperature increase process as described above. Therefore, there is a risk that the target temperature of the GPF that should originally be maintained will be changed. When the target temperature of the GPF in the temperature increase process changes, the target equivalence ratio for the combustion cylinder also fluctuates, and as a result, control hunting occurs when the engine is operated.

[0007] This invention was conceived by focusing on the above technical problems, and an object thereof is to provide a control device for an engine that can appropriately perform a temperature increase process or a regeneration process of a filter that collects PM, and can prevent control hunting and operate the engine appropriately.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention provides a control device for an engine that has a plurality of cylinders and burns particulate matter (PM) deposited on a filter by raising the temperature of the filter that collects the particulate matter in the exhaust gas by performing a specific cylinder fuel cut (or partial cylinder fuel cut) in which the fuel supply to one or a part of the plurality of cylinders is suspended during operation. The control device includes a control unit that controls the engine and performs the specific cylinder fuel cut. The control unit sets a target temperature of the exhaust gas flowing into the filter based on the deposition amount of the particulate matter deposited on the filter, and when performing the specific cylinder fuel cut, sets a target equivalence ratio (target value of the equivalence ratio) for a combustion cylinder that supplies fuel among the plurality of cylinders based on the difference between the actual temperature of the exhaust gas before performing the specific cylinder fuel cut and the target temperature, controls the fuel supply amount to the combustion cylinder so as to achieve the target equivalence ratio, performs the specific cylinder fuel cut, and corrects the target equivalence ratio so that the actual temperature during the execution of the specific cylinder fuel cut follows the target temperature.

Effect of the Invention

[0009] In the engine control device of the present invention, by performing a specific cylinder fuel cut, the filter and the catalyst are brought to a high temperature state, and the particulate matter deposited on the filter is burned and removed. That is, the filter is regenerated. When performing such a specific cylinder fuel cut, the target temperature of the exhaust gas (the target value of the incoming gas temperature) is set based on the deposition amount of the particulate matter deposited on the filter. For example, the target temperature of the exhaust gas is determined for each deposition amount of the particulate matter in the form of a map, and the target temperature of the exhaust gas is calculated based on such a map. That is, in the engine control device of the present invention, the target temperature of the exhaust gas is set without using the estimated temperature of the filter as in the prior art. Further, in the engine control device of the present invention, when performing a specific cylinder fuel cut, based on the difference between the actual temperature of the exhaust gas before the execution of the specific cylinder fuel cut and the target temperature of the exhaust gas, the target equivalence ratio for the combustion cylinder when performing the specific cylinder fuel cut is set. And in the engine control device of the present invention, after starting the specific cylinder fuel cut, the above target equivalence ratio is corrected so as to reduce the difference between the actual temperature of the exhaust gas during the execution of the specific cylinder fuel cut and the target temperature of the exhaust gas. That is, based on the difference between the actual temperature and the target temperature of the exhaust gas, the specific cylinder fuel cut of the engine is feedback controlled. Thus, in the engine control device of the present invention, without using the estimated temperature of the filter, instead, using the actual temperature of the exhaust gas, the temperature increase and regeneration of the filter by the above specific cylinder fuel cut are performed. Therefore, it is possible to avoid inappropriate changes in the control target value due to the inability to distinguish the state of the filter and the difference in the actual temperature. That is, it is possible to prevent hunting of the control by keeping the control target value (the target temperature of the exhaust gas) constant.

[0010] Therefore, according to the engine control device of the present invention, it is possible to appropriately perform the temperature increase process or the regeneration process of the filter that collects PM by performing a specific cylinder fuel cut, and to prevent hunting of the control and appropriately operate the engine.

Brief Description of the Drawings

[0011]

Figure 1

Embodiment for Carrying Out the Invention

[0012] Embodiments of the present invention will be described with reference to the drawings. Note that the embodiments shown below are merely examples of the case where the present invention is embodied, and do not limit the present invention.

[0013] The engine to be controlled in the embodiment of the present invention is, for example, an internal combustion engine such as a gasoline engine or a diesel engine mounted on a vehicle as a driving force source, and is configured such that the output adjustment and operating states such as starting and stopping are electrically controlled. For example, the opening degree of the throttle valve, the fuel supply amount or injection amount, the execution and stop of ignition, and the ignition timing are electrically controlled. Alternatively, the fuel injection timing is electrically controlled.

[0014] Furthermore, the engine to be controlled in the embodiment of the present invention has a plurality of cylinders, and is configured to be capable of "specific cylinder fuel cut", "single-cylinder fuel cut", or "partial cylinder fuel cut", or "cylinder stop operation" in which the fuel supply to only one or some of the plurality of cylinders is suspended. As a specific example of the engine configuration, for example, an engine having four cylinders such as the "internal combustion engine 10" shown in "FIG. 1 of Patent Document 1" described above can be cited. And the engine control device in the embodiment of the present invention is provided with a control unit similar to the "control device 70" shown in "FIG. 1 of Patent Document 1". The control unit in the embodiment of the present invention controls the operating state of the engine and executes the above-described specific cylinder fuel cut.

[0015] As described above, in the conventional temperature increase process (or regeneration process) of the filter, since the estimated temperature of the filter is used, hunting of control may occur. Therefore, in the engine control device according to an embodiment of the present invention, while appropriately performing the temperature increase process or regeneration process of the filter by the above-described specific cylinder fuel cut (or single cylinder fuel cut), in order to prevent hunting of control, for example, it is configured to execute the control shown in the flowchart of FIG. 1 below.

[0016] In the flowchart of FIG. 1, first, in step S1, the actual temperature (GPF inlet gas temperature) a of the current exhaust gas before starting the single cylinder fuel cut (F / C) is acquired and confirmed.

[0017] In step S2, from the deposition amount (PM deposition amount) of particulate matter (PM) deposited on the filter (GPF), the target temperature (GPF inlet gas temperature target value) b of the exhaust gas is determined. For example, the target temperature b of the exhaust gas is determined for each deposition amount of PM in the form of a map, and based on such a map, the target temperature b of the exhaust gas is calculated.

[0018] In step S3, from the difference (difference between the actual value a and the target value b of the GPF inlet gas temperature) between the actual temperature a of the exhaust gas and the target temperature b of the exhaust gas, the equivalent ratio p necessary for raising the inlet gas temperature is determined. The equivalent ratio p is the control target value (target equivalent ratio) of the equivalent ratio for the combustion cylinder when performing the single cylinder fuel cut as the temperature increase process of the filter. By controlling the fuel supply amount to the combustion cylinder so as to be this equivalent ratio p, the single cylinder fuel cut (specific cylinder fuel cut) is executed. The equivalent ratio p in this step S3 is calculated as the feed forward (FF) term in the control arithmetic expression having the equivalent ratio p as the control target value.

[0019] In step S4, single-cylinder fuel cut is executed. Single-cylinder fuel cut is a control to suspend the fuel supply only to one cylinder of an engine having a plurality of cylinders, that is, to perform fuel cut. By executing this single-cylinder fuel cut, the cylinder to be combusted (combustion cylinder) becomes rich, that is, the air-fuel mixture supplied into the cylinder is in a state where the ratio of fuel is higher than the stoichiometric air-fuel ratio. At the same time, oxygen is sent from the cylinder where fuel cut is performed to a filter that collects PM. Thereby, in the exhaust system of the engine, unburned fuel and oxygen are reacted to induce a so-called afterburning phenomenon, and the temperature of the filter can be increased. By raising the temperature of the filter on which PM is deposited and burning the PM, the regeneration of the filter can be promoted.

[0020] Note that in the flowchart of FIG. 1, as the specific cylinder fuel cut, a control example of performing the temperature increase process or the regeneration process of the filter by the single-cylinder fuel cut as described above is shown. In the engine control device according to the embodiment of the present invention, not limited to a single cylinder, the temperature increase process or the regeneration process of the filter may be performed by a specific cylinder fuel cut (or partial cylinder fuel cut control) that performs fuel cut on a plurality of cylinders.

[0021] In step S5, the temperature c of the gas entering the GPF during the execution of the single-cylinder fuel cut, that is, the actual temperature c of the exhaust gas during the execution of the specific cylinder fuel cut is acquired and confirmed.

[0022] Next, in step S6, the target temperature b of the exhaust gas calculated in step S2 above and the actual temperature c of the exhaust gas acquired in step S5 above are compared, and it is determined whether the target temperature b of the exhaust gas is equal to or higher than the actual temperature c.

[0023] If it is determined as “Yes” in this step S6 because the target temperature b of the exhaust gas is equal to or higher than the actual temperature c, the process proceeds to step S7.

[0024] In step S7, the equivalence ratio p is increased. That is, the equivalence ratio p is corrected so that the actual temperature c of the exhaust gas during the execution of the specific cylinder fuel cut follows the target temperature b, or so that the difference between the actual temperature c of the exhaust gas and the target temperature b is reduced. The equivalence ratio p in this step S7 is calculated as a feedback (FB) term in the control arithmetic expression with the equivalence ratio p as the control target value.

[0025] On the other hand, if it is determined as “No” in the above step S6 because the target temperature b of the exhaust gas is less than the actual temperature c, the process proceeds to step S8.

[0026] In step S8, the equivalence ratio p is decreased. That is, the equivalence ratio p is corrected so that the actual temperature c of the exhaust gas during the execution of the specific cylinder fuel cut follows the target temperature b, or so that the difference between the actual temperature c of the exhaust gas and the target temperature b is reduced. The equivalence ratio p in this step S8 is calculated as a feedback (FB) term in the control arithmetic expression with the equivalence ratio p as the control target value.

[0027] Then, when the equivalence ratio p is corrected in the above step S7 or step S8, the process proceeds to step S9, and the combustion of PM is carried out. That is, based on the equivalence ratio p corrected in step S7 or step S8, the temperature increase process of the filter by the specific cylinder fuel cut is executed, and the PM deposited on the filter is combusted.

[0028] When the temperature increase process of the filter by the specific cylinder fuel cut is executed in the above step S9, the routine shown in this flowchart of FIG. 1 is temporarily terminated. Note that the routine shown in this flowchart of FIG. 1 is repeatedly executed while the engine is running. Therefore, when the PM is combusted by the process of step S9 and the PM deposition amount of the filter changes, the feedforward term in the control arithmetic expression with the above equivalence ratio p as the control target value is changed, and the routine shown in the flowchart of FIG. 1 is repeated.

[0029] As described above, in the engine control device according to the embodiment of the present invention, instead of using the estimated temperature of the filter as exemplified in the prior art, the actual temperature a of the exhaust gas is used to raise the temperature and regenerate the filter by the above-described one-cylinder fuel cut (specific cylinder fuel cut). Therefore, it is possible to avoid inappropriate changes in the control target value due to the inability to discriminate the state of the filter and the difference in the actual temperature. That is, the target temperature b of the exhaust gas can be kept constant as the control target value, and hunting of the control can be prevented.

[0030] Therefore, according to the engine control device in the embodiment of the present invention, by executing one-cylinder fuel cut or specific cylinder fuel cut of a plurality of cylinders, it is possible to appropriately perform the temperature raising process or the regeneration process of the filter that collects PM, prevent hunting of the control, and appropriately operate the engine.

Claims

【Claim 1】 An engine control device that has a plurality of cylinders and, by performing a specific cylinder fuel cut that suspends the fuel supply to only one or a part of the plurality of cylinders during operation, raises the temperature of a filter that collects particulate matter in exhaust gas and burns the particulate matter deposited on the filter, comprising: a control unit that controls the engine and performs the specific cylinder fuel cut; the control unit: sets a target temperature of the exhaust gas entering the filter based on the deposition amount of the particulate matter deposited on the filter; when performing the specific cylinder fuel cut, sets a target equivalence ratio for a combustion cylinder that supplies fuel among the plurality of cylinders based on the difference between the actual temperature of the exhaust gas before performing the specific cylinder fuel cut and the target temperature; controls the fuel supply amount to the combustion cylinder so as to achieve the target equivalence ratio and performs the specific cylinder fuel cut; corrects the target equivalence ratio so that the actual temperature during the execution of the specific cylinder fuel cut follows the target temperature An engine control device characterized by the above.

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