Engine device

Abstract

To suppress deterioration of emission after restoration from fuel cut of an engine.SOLUTION: An engine device comprises: an engine; a purification catalyst attached to an exhaust pipe of the engine; and a control device that controls the engine based on a required equivalence ratio. The control device executes post-restoration rich control of setting the required equivalence ratio to a first value larger than a value 1 when an oxygen storage amount of the purification catalyst is equal to or larger than a first storage amount threshold value after the engine is restored from fuel cut, and setting the required equivalence ratio to a second value smaller than the first value and larger than the value 1 when the oxygen storage amount is less than the first storage amount threshold value.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an engine device.

Background Art

[0002] Conventionally, as this type of engine device, in a device including an engine and a purification catalyst attached to an exhaust pipe of the engine, after the return from fuel cut of the engine, a post-return rich control for setting the required air-fuel ratio of the exhaust gas flowing into the purification catalyst to rich is executed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described engine device, after the return from fuel cut of the engine, if the required air-fuel ratio is uniformly made relatively small (the required equivalence ratio is made relatively large) as the post-return rich control, when the oxygen storage amount of the purification catalyst is not so large, the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe to the outside air increases, and emissions may deteriorate.

[0005] The main object of the engine device of the present invention is to suppress the deterioration of emissions after the return from fuel cut of the engine.

Means for Solving the Problems

[0006] The engine device of the present invention has taken the following means to achieve the above-described main object.

[0007] The engine device of the present invention includes an engine and A purification catalyst attached to an exhaust pipe of the engine, A control device that controls the engine based on a required equivalence ratio, An engine device comprising: After the return from fuel cut of the engine, when the oxygen storage amount of the purification catalyst is equal to or greater than a first storage amount threshold value, the control device sets a first value greater than 1 for the required equivalence ratio, and when the oxygen storage amount is less than the first storage amount threshold value, the control device sets a second value smaller than the first value and greater than 1 for the required equivalence ratio, and executes post-return rich control. This is the gist.

[0008] In the engine device of the present invention, after the return from fuel cut of the engine, when the oxygen storage amount of the purification catalyst is equal to or greater than a first storage amount threshold value, a first value greater than 1 is set for the required equivalence ratio, and when the oxygen storage amount is less than the first storage amount threshold value, a second value smaller than the first value and greater than 1 is set for the required equivalence ratio, and post-return rich control is executed. Thereby, after the return from fuel cut of the engine, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe to the outside air, and to suppress deterioration of emissions.

[0009] In the engine device of the present invention, as the post-return rich control, when the number of fuel injection times performed in any cylinder after the return from fuel cut is less than a number threshold value and the oxygen storage amount of the purification catalyst is equal to or greater than a first storage amount threshold value, the control device sets the first value for the required equivalence ratio, and when the oxygen storage amount is less than the first storage amount threshold value and when the number of injection times is equal to or greater than the number threshold value, the control device may set the second value for the required equivalence ratio.

[0010] In the engine device of the present invention, a rear air-fuel ratio sensor attached downstream of the purification catalyst in the exhaust pipe is further provided. When the rear air-fuel ratio sensor is activated, the control device determines that the air-fuel ratio condition where the rear air-fuel ratio detected by the rear air-fuel ratio sensor is equal to or less than the air-fuel ratio threshold value or the storage amount condition where the oxygen storage amount is equal to or less than the second storage amount threshold value which is less than the first storage amount threshold value is satisfied, and ends the rich control after return. When the rear air-fuel ratio sensor is not activated, the control device may end the rich control after return when the storage amount condition is satisfied. In this way, it is possible to more appropriately determine whether to end the rich control after return according to whether the rear air-fuel ratio sensor is activated or not.

[0011] In this case, the control device estimates the oxygen storage amount based on the front air-fuel ratio upstream of the purification catalyst in the exhaust pipe and the intake air amount, and the second storage amount threshold value may be set to a larger value when the rear air-fuel ratio sensor is not activated than when the rear air-fuel ratio sensor is activated. In this way, it is possible to more appropriately determine whether to end the rich control after return when the rear air-fuel ratio sensor is not activated.

[0012] In the engine device of the present invention, when the execution condition of the feedback control for making the difference between the equivalence ratio and the target equivalence ratio based on the required equivalence ratio small is satisfied, the control device controls the engine based on the target equivalence ratio and the feedback value obtained by the feedback control. When the execution condition of the feedback control is not satisfied, the control device controls the engine based on the target equivalence ratio. As the post-return rich control, when there is no setting history in which a third value smaller than the second value and larger than value 1 is set for the required equivalence ratio while the execution condition of the feedback control is not satisfied, the control device may set the first value or the second value for the required equivalence ratio. When the execution condition of the feedback control is satisfied, and when the execution condition of the feedback control is not satisfied and there is the setting history, the control device may set the third value for the required equivalence ratio. By doing so, it is possible to prevent the required equivalence ratio from being changed from the third value to the first value or the second value during the post-return rich control.

[0013] In this case, when the predetermined request is not being made, the control device sets the required equivalence ratio to the target equivalence ratio. When the predetermined request is being made, the control device sets the larger of the required equivalence ratio and the second required equivalence ratio based on the predetermined request to the target equivalence ratio. The execution condition of the feedback control may include the condition that the predetermined request is not being made. Further, when the end condition of the post-return rich control is satisfied, the control device may reduce the required equivalence ratio from its value at that time.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0015] Next, the mode for carrying out the present invention will be described using examples.

Examples

[0016] FIG. 1 is a configuration diagram showing an outline of the configuration of an automobile 10 including an engine device 11 as an embodiment of the present invention. As shown in the figure, the automobile 10 of the embodiment includes an engine 12, a starter (not shown) for cranking the engine 12, a transmission TM that transmits the power from the engine 12 to a drive shaft DS connected to drive wheels DW via a differential gear DF, and an electronic control unit 50 as a control device for controlling the engine 12, the starter, and the transmission TM. As the engine device 11 of the embodiment, mainly, the engine 12 and the electronic control unit 50 correspond.

[0017] The engine 12 is configured as a multi-cylinder internal combustion engine that outputs power through four strokes of intake, compression, expansion (explosive combustion), and exhaust using, for example, gasoline or diesel fuel. This engine 12 has an in-cylinder injection valve 26 that injects fuel into the cylinder and a spark plug 30. The engine 12 inhales the air cleaned by the air cleaner 22 into the intake pipe 23, passes it through the throttle valve 24, and further inhales it into the combustion chamber 29 through the intake valve 28. Also, fuel is injected from the in-cylinder injection valve 26 during the intake stroke and the compression stroke. Then, it is explosively combusted by an electric spark from the spark plug 30, and the reciprocating motion of the piston 32 pushed down by the energy of the explosive combustion is converted into the rotational motion of the crankshaft 14. The exhaust discharged from the combustion chamber 29 to the exhaust pipe 34 through the exhaust valve 33 is discharged to the outside air through the purification device 35. The purification device 35 has a purification catalyst (three-way catalyst) 35a that purifies harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

[0018] The electronic control unit 50 includes a microcomputer having a CPU 51, a ROM 52, a RAM 53, a flash memory 54, input / output ports, communication ports, and the like. Signals from various sensors are input to the electronic control unit 50 via the input ports. Examples of the signals input to the electronic control unit 50 include the crank angle θcr from the crank position sensor 14a that detects the rotational position of the crankshaft 14 of the engine 12, and the coolant temperature Tw from the water temperature sensor 15 that detects the temperature of the coolant of the engine 12. Also included are the cam angles θci and θco from the cam position sensor 16 that detects the rotational position of the intake camshaft that opens and closes the intake valve 28 and the rotational position of the exhaust camshaft that opens and closes the exhaust valve 33. Further examples include the throttle opening TH from the throttle position sensor 24a that detects the position (opening degree) of the throttle valve 24, the intake air amount Qa from the air flow meter 23a attached upstream of the throttle valve 24 in the intake pipe 23, and the intake air temperature Ta from the temperature sensor 23t attached upstream of the throttle valve 24 in the intake pipe 23. Also included are the front air-fuel ratio AFf from the front air-fuel ratio sensor 37 attached upstream of the purification device 35 in the exhaust pipe 34 and the rear air-fuel ratio AFr from the rear air-fuel ratio sensor 38 attached downstream of the purification device 35 in the exhaust pipe 34. Additionally, the rotational speed of the input shaft of the transmission TM from the rotational speed sensor attached to the input shaft of the transmission TM and the rotational speed of the output shaft of the transmission TM from the rotational speed sensor attached to the output shaft of the transmission TM can be mentioned. Also included are the ignition signal IG from the ignition switch 60 and the shift position SP from the shift position sensor 62 that detects the operating position of the shift lever 61. Further examples include the accelerator opening Acc from the accelerator pedal position sensor 64 that detects the depression amount of the accelerator pedal 63, the brake pedal position BP from the brake pedal position sensor 66 that detects the depression amount of the brake pedal 65, and the vehicle speed V from the vehicle speed sensor 67.

[0019] From the electronic control unit 50, various control signals are output via the output ports. Examples of the signals output from the electronic control unit 50 include a control signal to the throttle valve 24 of the engine 12, a control signal to the in-cylinder injection valve 26, and a control signal to the spark plug 30. Also, a control signal to a starter (not shown) and a control signal to the transmission TM can be included.

[0020] The electronic control unit 50 calculates the engine speed Ne of the engine 12 based on the crank angle θcr from the crank position sensor 14a. Also, the electronic control unit 50 calculates the load factor KL of the engine 12 (the ratio of the volume of air actually inhaled in one cycle to the stroke volume per cycle of the engine 12) based on the intake air amount Qa from the air flow meter 23a and the engine speed Ne of the engine 12. Further, the electronic control unit 50 estimates the temperature Tc of the purification catalyst 35a of the purification device 35 based on the coolant temperature Tw from the water temperature sensor 15, the engine speed Ne of the engine 12, and the load factor KL. In addition, the electronic control unit 50 calculates the equivalence ratio φ by dividing the front air-fuel ratio AFf from the front air-fuel ratio sensor 37 by the stoichiometric air-fuel ratio AFth. Also, the electronic control unit 50 estimates the oxygen storage amount OS of the purification catalyst 35a of the purification device 35 based on the front air-fuel ratio AFf from the front air-fuel ratio sensor 37 and the intake air amount Qa from the air flow meter 23a.

[0021] In the automobile 10 of the embodiment configured in this way, the electronic control unit 50 sets the target gear stage Gs* of the transmission TM based on the accelerator opening Acc and the vehicle speed V, and controls the transmission TM so that the gear stage Gs of the transmission TM becomes the target gear stage Gs*. Also, based on the accelerator opening Acc, the vehicle speed V, and the gear stage Gs of the transmission TM, the target torque Te* of the engine 12 is set, and based on the target torque Te* of the engine 12, the target load factor KL* is set, and intake air amount control, fuel injection control, ignition control, etc. of the engine 12 are performed so that the engine 12 is operated at the target load factor KL*.

[0022] Also, in the motor vehicle 10 of the embodiment, during driving, when the accelerator is turned off during the operation of the engine 12 and the fuel cut condition of the engine 12 is satisfied, the electronic control unit 50 executes fuel cut of the engine 12 (interrupts fuel injection control and ignition control), and when the accelerator is turned on during the fuel cut of the engine 12 and the return condition of the engine 12 is satisfied, the electronic control unit 50 returns the engine 12 from fuel cut (restarts fuel injection control and ignition control).

[0023] Here, intake air amount control, fuel injection control, and ignition control will be described. In intake air amount control, the electronic control unit 50 sets a target air amount Qa* based on the target load ratio KL* of the engine 12, sets a target opening degree TH* of the throttle valve 24 so that the intake air amount Qa becomes the target air amount Qa*, and controls the throttle valve 24 using the set target opening degree TH*. In ignition control, the electronic control unit 50 sets a target ignition timing Ti* of the spark plug 30 based on the rotational speed Ne and the load ratio KL of the engine 12, and controls the spark plug 30 using the set target ignition timing Ti*.

[0024] In fuel injection control, when the execution condition of feedback control for making the difference between the equivalence ratio φ and the target equivalence ratio φ* small is satisfied, as shown in Equation (1), the electronic control unit 50 multiplies the base injection amount Qfb by the target equivalence ratio φ* and the feedback correction coefficient kfb calculated by feedback control to set the target injection amount Qf* of the in-cylinder injection valve 26, and controls the in-cylinder injection valve 26 using the set target injection amount Qf*. On the other hand, when the execution condition of feedback control is not satisfied, as shown in Equation (2), the electronic control unit 50 multiplies the base injection amount Qfb by the target equivalence ratio φ* to set the target injection amount Qf*, and controls the in-cylinder injection valve 26 using the set target injection amount Qf*.

[0025] Qf* = Qfb × φ* × kfb (1) Qf* = Qfb × φ* (2)

[0026] Here, as the execution condition of the feedback control, it is possible to use the condition that the combustion of the engine 12 is stable and the output-related rich demand is not being made. The output-related rich demand is made, for example, when the target load factor KL* is equal to or greater than the threshold value KLref.

[0027] The base injection amount Qfb can be calculated, for example, by multiplying the unit injection amount (the injection amount per 1% of the load factor KL) Qfpu by the load factor KL. The target equivalence ratio φ* is set to the required equivalence ratio φra when the output-related rich demand is not being made, and the larger of the required equivalence ratios φra and φrb is set when the output-related rich demand is being made. The required equivalence ratio φra is set as follows. In normal control, when the rear air-fuel ratio sensor 38 is activated (able to detect the rear air-fuel ratio AFr), based on the rear air-fuel ratio AFr, values greater than 1 (rich-side values) and values less than 1 (lean-side values) are alternately set for the required equivalence ratio φra, and when the rear air-fuel ratio sensor 38 is not activated (not able to detect the rear air-fuel ratio AFr), the value 1 is set. Also, after the return from fuel cut, after performing the post-return rich control of setting a value somewhat greater than 1 for the required equivalence ratio φra for a certain period, the required equivalence ratio φra is gradually decreased to approach the value 1 through the gradual decrease control by rate processing, and then the normal control is shifted to. The required equivalence ratio φrb is the required equivalence ratio based on the output-related rich demand, and may be set to increase as the target load factor KL* increases, or may be set to a uniform value.

[0028] Next, the operation of the motor vehicle 10 of the thus configured embodiment will be described, particularly the setting process of the required equivalence ratio φra during fuel cut of the engine 12 and after the return from fuel cut. FIG. 2 is a flowchart showing an example of a processing routine executed by the electronic control unit 50. This routine is executed when the fuel cut condition of the engine 12 is satisfied and the fuel cut of the engine 12 is started. In the description of this routine, for simplicity, the case where no output-related rich request is made, that is, the case where the required equivalence ratio φra is set to the target equivalence ratio φ*, will be described.

[0029] When the processing routine in FIG. 2 is executed, the electronic control unit 50 first compares the oxygen storage amount OS of the purification catalyst 35a of the purification device 35 with a threshold value OSref1 (step S100). Here, the oxygen storage amount OS is estimated based on the front air-fuel ratio AFf from the front air-fuel ratio sensor 37 and the intake air amount Qa. The threshold value OSref1 is used to determine whether the oxygen storage amount OS of the purification catalyst 35a is relatively large.

[0030] When the oxygen storage amount OS of the purification catalyst 35a is equal to or greater than the threshold value OSref1 in step S100, a value φ1 greater than 1 is set for the required equivalence ratio φra (step S110). On the other hand, when the oxygen storage amount OS of the purification catalyst 35a is less than the threshold value OSref1, a value φ2 that is less than φ1 and greater than 1 is set for the required equivalence ratio φra (step S120). Subsequently, it is determined whether the return condition of the engine 12 is satisfied (step S130). When it is determined that the return condition of the engine 12 is not satisfied, the process returns to step S100. In this way, it waits for the return condition of the engine 12 to be satisfied.

[0031] When it is determined in step S130 that the return condition of the engine 12 is satisfied, post-return rich control is started (step S140), and it is determined whether or not the execution condition of feedback control is satisfied (step S150). When it is determined that the execution condition of feedback control is not satisfied, the injection number Nf is compared with the threshold value Nfref (step S160), and the oxygen storage amount OS of the purification catalyst 35a is compared with the above-described threshold value OSref1 (step S170). Here, the injection number Nf is set to the value 0 as the initial value during fuel cut of the engine 12, and is incremented each time fuel injection is performed from the in-cylinder injection valve 26 in any cylinder after returning from fuel cut. As the threshold value Nfref, for example, the number of cylinders of the engine 12 or twice that number can be used.

[0032] When the injection number Nf is less than the threshold value Nfref in step S160 and the oxygen storage amount OS of the purification catalyst 35a is greater than or equal to the threshold value OSref1 in step S170, the value φ1 is set for the required equivalence ratio φra (step S180). When the oxygen storage amount OS of the purification catalyst 35a is less than the threshold value OSref1 in step S170, the value φ2 is set for the required equivalence ratio φra (step S180). The required equivalence ratio φra set in this way is set to the target equivalence ratio φ* as described above and is used for setting the target injection amount Qf*. When the injection number Nf is less than the threshold value Nfref, if the value φ1 is uniformly set for the required equivalence ratio φra, when the oxygen storage amount OS is less than the threshold value OSref1 (when it is not so much), the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air increases, and emissions may deteriorate. On the other hand, in the embodiment, when the injection number Nf is less than the threshold value Nfref and the oxygen storage amount OS is less than the threshold value OSref1, by setting a value φ2 smaller than the value φ1 for the required equivalence ratio φra, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air and suppress deterioration of emissions. Note that when fuel cut is performed only for a short time, the event that the oxygen storage amount OS is less than the threshold value OSref1 when the injection number Nf is less than the threshold value Nfref is likely to occur.

[0033] When the injection count Nf is equal to or greater than the threshold value Nfref in step S160, the value φ2 is set for the required equivalence ratio φra (step S190). Further, when it is determined in step S150 that the execution condition for feedback control is satisfied, a value φ3 that is smaller than the value φ2 and greater than the value 1 is set for the required equivalence ratio φra (step S200).

[0034] After thus setting the required equivalence ratio φra in any of steps S180, S190, and S200, it is determined whether the rear air-fuel ratio sensor 38 is activated (able to detect the rear air-fuel ratio AFr) (step S210). When it is determined that the rear air-fuel ratio sensor 38 is activated, a value OS1 that is less than the above-described threshold value OSref1 is set for the threshold value OSref2 (step S220), the rear air-fuel ratio AFr detected by the rear air-fuel ratio sensor 38 is compared with the threshold value AFrref (step S240), and the oxygen storage amount OS is compared with a threshold value OSref2 that is less than the threshold value OSref1 (step S250). Here, the threshold value AFrref and the threshold value OSref2 are used for determining whether to end the rich control after the return. When the rear air-fuel ratio AFr is greater than the threshold value AFrref in step S240 and the oxygen storage amount OS is greater than the threshold value OSref2 in step S250, the process returns to step S150. In this case, the rich control after the return is continued.

[0035] When it is determined in step S210 that the rear air-fuel ratio sensor 38 is not activated, a threshold value OS2 that is less than the threshold value OSref1 and greater than the value OS1 is set for the threshold value OSref2 (step S230), and the oxygen storage amount OS is compared with the threshold value OSref2 (step S250). Then, when the oxygen storage amount OS is greater than the threshold value OSref2, the process returns to step S150. In this case, the rich control after the return is continued.

[0036] In this way, the processes of steps S150 to S250 are repeatedly executed. When it is determined in step S210 that the rear air-fuel ratio AFr is activated, when the rear air-fuel ratio AFr is equal to or less than the threshold value AFrref in step S240 or when the oxygen storage amount OS is equal to or less than the threshold value OSref2 in step S250, the rich control after return is terminated (step S260), the gradual reduction control is executed (step S760), and this routine is terminated. Further, when it is determined in step S210 that the rear air-fuel ratio AFr is not activated, when the oxygen storage amount OS is equal to or less than the threshold value OSref2 in step S250, the rich control after return is terminated (step S260), the gradual reduction control is executed (step S760), and this routine is terminated. When the gradual reduction control is terminated in this way, the normal control is started.

[0037] Generally, since the detection accuracy of the rear air-fuel ratio AFr is higher than the estimation accuracy of the oxygen storage amount OS, when the rear air-fuel ratio AFr can be detected, it is preferable to determine whether to end the rich control after return using the rear air-fuel ratio AFr. However, when the rear air-fuel ratio sensor 38 is not activated, the rear air-fuel ratio AFr cannot be detected, so it is necessary to determine the end of the rich control after return by other methods. Based on this, in the embodiment, when the rear air-fuel ratio sensor 38 is activated, it is determined whether to end the rich control after return using the rear air-fuel ratio AFr and the oxygen storage amount OS, and when the rear air-fuel ratio sensor 38 is not activated, it is determined whether to end the rich control after return using the oxygen storage amount OS. In this way, it is possible to determine whether to end the rich control after return according to whether the rear air-fuel ratio sensor 38 is activated. Moreover, the inventors confirmed through analysis and experiments that during the rich control after return, the oxygen storage amount OS (estimated value) is less likely to decrease compared to the actual oxygen storage amount OSas. Therefore, when the rear air-fuel ratio sensor 38 is not activated, by making the threshold OSref2 larger (set as value OS2) than when the rear air-fuel ratio sensor 38 is activated, compared with the case where the threshold OSref2 is the same as when the rear air-fuel ratio sensor 38 is activated (set as value OS1), the end determination of the rich control after return can be made more appropriately. In the embodiment, when the rear air-fuel ratio sensor 38 is activated, the determination using the rear air-fuel ratio AFr is given priority over the determination using the oxygen storage amount OS (to suppress the interference of the determination using the oxygen storage amount OS), so the threshold OSref2 is set as the value OS1.

[0038] FIG. 3 and FIG. 4 are time charts respectively showing an example of the state of the presence or absence of fuel cut of the engine 12, the establishment of the execution conditions of the feedback control, the oxygen storage amount OS (estimated value) and the actual oxygen storage amount OSac, the required equivalence ratio φra, and the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air. The following will be described in order.

[0039] The time chart of FIG. 3 will be described. In FIG. 3, for the oxygen storage amount OS, the actual oxygen storage amount OSac, the required equivalence ratio φra, and the amount of hydrocarbons in the exhaust gas, the solid line indicates the example, and the dashed-dotted line indicates the first comparative example. The first comparative example is different from the example in that when the fuel cut of the engine 12 is in progress or when the fuel cut is resumed and the injection number Nf is less than the threshold value Nfref, the value φ1 is uniformly set for the required equivalence ratio φra (excluding the processes of steps S100, S120, and S170 from the processing routine of FIG. 2).

[0040] In the time chart of FIG. 3, in the example and the first comparative example, when the engine 12 resumes from the fuel cut (time t11), the required equivalence ratio φra is held at the value φ1. When the injection number Nf reaches the threshold value Nfref or more, the required equivalence ratio φra is changed to the value φ2. When the execution condition of the feedback control is satisfied (time t12), the feedback control is started and the required equivalence ratio φra is changed to the value φ3. Thereafter, in the first comparative example, when the fuel cut of the engine 12 is started (time t13), the value φ1 is set for the required equivalence ratio φra regardless of the oxygen storage amount OS. When the fuel cut is resumed (time t14), the required equivalence ratio φra is held at the value φ1. In the example of FIG. 3, at this time, the required equivalence ratio φra is made relatively large in a state where the actual oxygen storage amount OSac is not so large, and the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air increases. On the other hand, in the example, when the fuel cut of the engine 12 is started (time t13), when the oxygen storage amount OS is less than the threshold value OSref1, the value φ2 is set for the required equivalence ratio φra. When the fuel cut is resumed (time t14), the required equivalence ratio φra is held at the value φ2. Thereby, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air and suppress deterioration of emissions.

[0041] The time chart of FIG. 4 will be described. FIG. 4 illustrates the state when the rear air-fuel ratio sensor 38 is not activated. In FIG. 4, regarding the oxygen storage amount OS, the actual oxygen storage amount OSac, the required equivalence ratio φra, and the amount of hydrocarbons in the exhaust gas, the solid line indicates the example, and the dashed-dotted line indicates the second comparative example. The second comparative example is different from the example in that the value OS1 is uniformly set to the threshold value OSref2 (the process of step S230 in the processing routine of FIG. 2 is replaced with the same process as step S220).

[0042] In the time chart of FIG. 4, in the example and the second comparative example, up to time t14, it is the same as the example of FIG. 3. Then, when returning from fuel cut (time t14), as rich control after return, the required equivalence ratio φra is held at the value φ2, and when the execution condition of feedback control is satisfied (time t15), the feedback control is started and the required equivalence ratio φra is changed to the value φ3. After that, in the second comparative example, when the oxygen storage amount OS reaches a value equal to or less than the value OS1 (time t17), the rich control after return is terminated, and as deceleration control, the required equivalence ratio φra is gradually decreased. In the example of FIG. 4, at this time, the rich control after return is terminated after the actual oxygen storage amount OSac becomes sufficiently small, and the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air increases. On the other hand, in the example, when the oxygen storage amount OS reaches a value equal to or less than the value OS2, which is larger than the value OS1 (time t16), the rich control after return is terminated, and as deceleration control, the required equivalence ratio φra is gradually decreased. Thereby, since the rich control after return can be terminated before the actual oxygen storage amount OSac becomes sufficiently small, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air and suppress deterioration of emissions.

[0043] In the engine device 11 mounted on the automobile 10 of the embodiment described above, after the return from the fuel cut of the engine 12, when the oxygen storage amount OS is equal to or greater than the threshold value OSref1, the value φ1 is set for the required equivalence ratio φra, and when the oxygen storage amount OS is less than the threshold value OSref1, the value φ2 smaller than the value φ1 is set for the required equivalence ratio φra. Thereby, it is possible to suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air and suppress the deterioration of emissions.

[0044] In the engine device 11 mounted on the automobile 10 of the embodiment, it is assumed that the electronic control unit 50 executes the processing routine of FIG. 2. However, the electronic control unit 50 may execute the processing routine of FIG. 5 instead. The processing routine of FIG. 5 is the same as the processing routine of FIG. 2 except that the processing of step S152 is added. Therefore, the same step numbers are assigned to the same processes as those of the processing routine of FIG. 2 in the processing routine of FIG. 5, and detailed description thereof is omitted. In the description of this routine, the case where an output-related rich request is made is considered.

[0045] In the processing routine of FIG. 5, when the electronic control unit 50 determines in step S150 that the execution condition of the feedback control is not satisfied, it determines whether there is a setting history in which the value φ3 is set for the required equivalence ratio φra (step S152). This setting history is reset during fuel cut of the engine 12. When it is determined that there is no such setting history, the value φ1 or the value φ2 is set for the required equivalence ratio φra (steps S180 and S190), and the processing after step S210 is executed. On the other hand, when it is determined that there is such a setting history, the value φ3 is set for the required equivalence ratio φra (step S200), and the processing after step S210 is executed. As a result, when the rich control after return is being executed (the processing of steps S150 to S250 is repeatedly executed), after the value φ3 is set for the required equivalence ratio φra, even if an output-related rich request is made and the execution condition of the feedback control is not satisfied, the required equivalence ratio φra is maintained at the value φ3 without increasing it (changing it to the value φ1 or the value φ2). As a result, when the rich control after return is terminated and the deceleration control is then executed, the required equivalence ratio φra can be decreased from the value φ3 instead of from the values φ1 or φ2. Therefore, it is possible to suppress an increase in the time until the required equivalence ratio φra (target equivalence ratio φ*) reaches the value 1, suppress an increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air, and suppress deterioration of emissions.

[0046] FIG. 6 is a time chart showing an example of the state of the presence or absence of fuel cut of the engine 12, the presence or absence of an output-related rich request, the establishment of the execution condition of the feedback control, the rear air-fuel ratio AFr, the required equivalence ratios φra and φrb, the target equivalence ratio φ*, the oxygen storage amount OS, and the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air. In the figure, for the rear air-fuel ratio AFr, the required equivalence ratio φra, the target equivalence ratio φ*, the oxygen storage amount OS, and the amount of hydrocarbons in the exhaust gas, the solid line indicates a modified example (when the processing routine of FIG. 5 is executed), and the alternate long and short dash line indicates an embodiment (when the processing routine of FIG. 2 is executed).

[0047] In the time chart of FIG. 6, in the modified example and the embodiment, when the engine 12 returns from fuel cut (time t21), the required equivalence ratio φra is held at the value φ1, and when the injection number Nf reaches the threshold value Nfref or more, the required equivalence ratio φra is changed to the value φ2. When the execution condition of the feedback control is satisfied (time t22), the feedback control is started and the required equivalence ratio φra is changed to the value φ3. During this period, the required equivalence ratio φra is set to the target equivalence ratio φ*. Thereafter, in the embodiment, when the output-related rich demand starts (time t23), the execution condition of the feedback control becomes non-satisfied, the feedback control is stopped, and the required equivalence ratio φra is changed to the value φ2. In the example of FIG. 6, at this time, since the required equivalence ratio φrb is larger than the required equivalence ratio φra, the required equivalence ratio φrb is set to the target equivalence ratio φ*. Then, when the rear air-fuel ratio AFr reaches the threshold value AFrref or less (time t24), the required equivalence ratio φra is gradually decreased from the value φ2, and when the output-related rich demand ends (time t25), the target equivalence ratio φ* is switched from the required equivalence ratio φrb to the required equivalence ratio φra. In the example of FIG. 6, since the time until the required equivalence ratio φra (target equivalence ratio φ*) reaches the value 1 is relatively long, the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air is large. On the other hand, in this modified example, even when the output-related rich demand starts (time t23) and the execution condition of the feedback control becomes non-satisfied, the required equivalence ratio φra is held at the value φ3. Then, when the rear air-fuel ratio AFr reaches the threshold value AFrref or less (time t24), the required equivalence ratio φra is gradually decreased from the value φ2, and when the output-related rich demand ends (time t25), the target equivalence ratio φ* is switched from the required equivalence ratio φrb to the required equivalence ratio φra. Thereby, compared with the embodiment, it is possible to suppress the increase in the time until the required equivalence ratio φra (target equivalence ratio φ*) reaches the value 1, suppress the increase in the amount of hydrocarbons in the exhaust gas discharged from the exhaust pipe 34 to the outside air, and suppress the deterioration of emissions.

[0048] In the engine device 11 mounted on the motor vehicle 10 of the embodiment, the execution condition of the feedback control is set to use the condition that the combustion of the engine 12 is stable and the output-related rich demand is not made. However, the execution condition of the feedback control may be set to use the condition that the combustion of the engine 12 is stable.

[0049] In the engine device 11 mounted on the motor vehicle 10 of the embodiment, when the rear air-fuel ratio sensor 38 is activated, the value OS1 is set to the threshold value OSref2, and when the rear air-fuel ratio sensor 38 is not activated, the value OS2 larger than the value OS1 is set to the threshold value OSref2. However, the value OS1 may be set to the threshold value OSref2 regardless of whether the rear air-fuel ratio sensor 38 is activated or not.

[0050] In the engine device 11 mounted on the motor vehicle 10 of the embodiment, when the rear air-fuel ratio sensor 38 is activated, it is determined whether to end the rich control after return using the rear air-fuel ratio AFr and the oxygen storage amount OS. However, at this time, it may be determined whether to end the rich control after return using only any one of the rear air-fuel ratio AFr and the oxygen storage amount OS. As described above, generally, since the detection accuracy of the rear air-fuel ratio AFr is higher than the estimation accuracy of the oxygen storage amount OS, in this case, it is preferable to use the rear air-fuel ratio AFr among the rear air-fuel ratio AFr and the oxygen storage amount OS.

[0051] In the engine device 11 mounted on the motor vehicle 10 of the embodiment, the engine 12 is provided with an in-cylinder injection valve 26 for injecting fuel into the cylinder. However, instead of or in addition to the in-cylinder injection valve 26, it may be provided with a port injection valve for injecting fuel into the intake port.

[0052] In the embodiment, it is configured as the engine device 11 mounted on the motor vehicle 10 that runs using the power from the engine 12. However, it may be configured as the engine device mounted on a hybrid vehicle equipped with a motor in addition to the engine.

[0053] An explanation will be given regarding the correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems. In the embodiment, the engine 12 corresponds to the "engine", the purification catalyst 35a corresponds to the "catalyst", and the electronic control unit 50 corresponds to the "control device".

[0054] Note that the correspondence between the main elements of the embodiment and the main elements of the invention described in the column of means for solving the problems is an example for specifically explaining the form for implementing the invention described in the column of means for solving the problems in the embodiment, and thus does not limit the elements of the invention described in the column of means for solving the problems. That is, the interpretation of the invention described in the column of means for solving the problems should be made based on the description in that column, and the embodiment is merely a specific example of the invention described in the column of means for solving the problems.

[0055] As described above, the embodiments have been used to explain the forms for implementing the present invention. However, the present invention is not limited to such embodiments, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Industrial Applicability

[0056] The present invention can be used in the manufacturing industry of engine devices and the like.

Explanation of Reference Numerals

[0057] 10 Automobile, 11 Engine device, 12 Engine, 14 Crankshaft, 14a Crank position sensor, 15 Water temperature sensor, 16 Cam position sensor, 22 Air cleaner, 23 Intake pipe, 23a Air flow meter, 23t Temperature sensor, 24 Throttle valve, 24a Throttle position sensor, 26 In-cylinder injection valve, 28 Intake valve, 29 Combustion chamber, 30 Spark plug, 32 Piston, 33 Exhaust valve, 34 Exhaust pipe, 35 Purification device, 35a Purification catalyst, 37 Front air-fuel ratio sensor, 38 Rear air-fuel ratio sensor, 50 Electronic control unit, 51 CPU, 52 ROM, 53 RAM, 54 Flash memory, 60 Ignition switch, 61 Shift lever, 62 Shift position sensor, 63 Accelerator pedal, 64 Accelerator pedal position sensor, 65 Brake pedal, 66 Brake pedal position sensor, 67 Vehicle speed sensor, DF Differential gear, DS Drive shaft, DW Drive wheel, TM Transmission.

Claims

1. An engine, A purification catalyst attached to an exhaust pipe of the engine, A control device for controlling the engine based on a required equivalence ratio, An engine device comprising: After the return from fuel cut of the engine, when the oxygen storage amount of the purification catalyst is equal to or greater than a first storage amount threshold, the control device sets a first value greater than 1 to the required equivalence ratio, and when the oxygen storage amount is less than the first storage amount threshold, the control device sets a second value smaller than the first value and greater than 1 to the required equivalence ratio, and executes post-return rich control. The control device, as the post-return rich control, When the number of fuel injection times performed in any cylinder after the return from the fuel cut is less than a number threshold and the oxygen storage amount of the purification catalyst is equal to or greater than the first storage amount threshold, the control device sets the first value to the required equivalence ratio. When the oxygen storage amount is less than the first storage amount threshold and when the number of injection times is equal to or greater than the number threshold, the control device sets the second value to the required equivalence ratio. Engine device.

2. The engine device according to claim 1, Further comprising a rear air-fuel ratio sensor attached to a downstream side of the purification catalyst in the exhaust pipe, The control device, When the rear air-fuel ratio sensor is activated, when an air-fuel ratio condition that the rear air-fuel ratio detected by the rear air-fuel ratio sensor is equal to or less than an air-fuel ratio threshold or a storage amount condition that the oxygen storage amount is equal to or less than a second storage amount threshold smaller than the first storage amount threshold is satisfied, the control device terminates the post-return rich control. When the rear air-fuel ratio sensor is not activated, when the storage amount condition is satisfied, the control device terminates the post-return rich control. Engine device.

3. The engine device according to claim 2, The control device estimates the oxygen storage amount based on the front air-fuel ratio upstream of the purification catalyst in the exhaust pipe and the intake air amount. The second storage amount threshold value is set to a larger value when the rear air-fuel ratio sensor is not activated than when the rear air-fuel ratio sensor is activated. Engine device.

4. An engine device according to any one of claims 1 to 3, wherein the control device, when the execution condition of the feedback control for making the difference between the equivalence ratio and the target equivalence ratio based on the required equivalence ratio small is satisfied, controls the engine based on the target equivalence ratio and the feedback value obtained by the feedback control, and when the execution condition of the feedback control is not satisfied, controls the engine based on the target equivalence ratio, wherein the control device, as the rich control after return, when the execution condition of the feedback control is not satisfied and there is no setting history in which a third value smaller than the second value and larger than value 1 is set for the required equivalence ratio, sets the first value or the second value for the required equivalence ratio, and when the execution condition of the feedback control is satisfied and when the execution condition of the feedback control is not satisfied and there is the setting history, sets the third value for the required equivalence ratio. Engine device.

5. An engine device according to claim 4, wherein the control device, when no predetermined request is made, sets the required equivalence ratio to the target equivalence ratio, and when the predetermined request is made, sets the larger of the required equivalence ratio and the second required equivalence ratio based on the predetermined request to the target equivalence ratio, and the execution condition of the feedback control includes a condition that no predetermined request is made. Engine device.

6. The engine device according to claim 4 or 5, when the end condition of the rich control after the return is satisfied, the control device decreases the required equivalence ratio from its value at that time, Engine device.

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