Engine equipment

Abstract

To suppress the worsening of emission.SOLUTION: A control device sets a control center air-fuel ratio using a first setting method in a time before predetermined conditions are established, and sets the control center air-fuel ratio using a second setting method in a time after the predetermined conditions are established. In each of the first setting method and the second setting method, the control center air-fuel ratio is set so that a difference between a target rear air-fuel ratio and a rear air-fuel ratio is cancelled. In the first setting method, a variation per unit time of the control center air-fuel ratio is allowed to be greater than in the second setting method. The predetermined conditions include difference conditions that a difference between the control center air-fuel ratio set using the first setting method and a storage value for the control center air-fuel ratio set using the second setting method in the past or predetermined air-fuel ratio is equal to or smaller than a predetermined difference.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to engine systems. [Background technology]

[0002] Conventionally, an engine apparatus of this type has been proposed that includes a catalyst provided in the engine's exhaust system to purify exhaust gases, and an air-fuel ratio sensor that detects the air-fuel ratio of exhaust gases midway through or downstream of the catalyst in the exhaust system (see, for example, Patent Document 1). In this engine apparatus, when predetermined feedback control conditions are met, a control input including an integral term is calculated for feedback control so that the output value of the air-fuel ratio sensor becomes a target value. Furthermore, during feedback control, when predetermined conditions are met that estimate that the air-fuel ratio of exhaust gases upstream of the catalyst is well reflected in the air-fuel ratio of exhaust gases midway through or downstream of the catalyst, the integral term calculated just before the feedback control ends is updated and stored as the initial value of the integral term for the next feedback control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-26431 Summary of the Invention [Problem to be solved by the invention]

[0004] An engine system has also been developed that controls the engine so as to cancel the difference between the output value of a front air-fuel ratio sensor, which detects the air-fuel ratio of exhaust gas upstream of the exhaust catalyst, and a target front air-fuel ratio based on a control center air-fuel ratio. In such engine systems, when the engine coolant temperature is low and combustion in the combustion chamber is difficult to stabilize, the concentration of high molecular weight hydrocarbons in the exhaust gas from the combustion chamber tends to increase. Because high molecular weight hydrocarbons have a slower diffusion rate than low molecular weight hydrocarbons and carbon monoxide, when the concentration of high molecular weight hydrocarbons is high, the output value of the front air-fuel ratio sensor tends to be leaner than the actual value. Therefore, if the control center air-fuel ratio is set using the same method when the coolant temperature is low as when the coolant temperature is relatively high, the actual air-fuel ratio of the exhaust gas upstream and downstream of the exhaust catalyst may be disturbed, potentially resulting in poor emissions.

[0005] The engine device of the present disclosure has a primary objective of suppressing deterioration of emissions. [Means for solving the problem]

[0006] The engine device of the present disclosure employs the following measures to achieve the above-mentioned main object.

[0007] [1] The engine device of the present disclosure is The engine and a purification device attached to an exhaust system of the engine and having a catalyst for purifying exhaust gas; a front air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas upstream of the purification device in the exhaust system as a front air-fuel ratio; a rear air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas downstream of the purification device in the exhaust system as a rear air-fuel ratio; a control device that controls the engine so that a difference between a target front air-fuel ratio based on a control center air-fuel ratio and the front air-fuel ratio is canceled out; An engine device comprising: the control device sets the control center air-fuel ratio by a first setting method before a predetermined condition is satisfied, and sets the control center air-fuel ratio by a second setting method after the predetermined condition is satisfied; the first setting method and the second setting method are setting methods for setting the control center air-fuel ratio so that a difference between a target rear air-fuel ratio and the rear air-fuel ratio is canceled out, the first setting method is a setting method that allows a larger amount of change per unit time of the control center air-fuel ratio than the second setting method, the predetermined condition includes a difference condition in which a difference between the control center air-fuel ratio set by the first setting method and a stored value of the control center air-fuel ratio previously set by the second setting method or a predetermined air-fuel ratio is equal to or smaller than a predetermined difference. The gist of this is as follows.

[0008] In the engine device of the present disclosure, the control device sets the control center air-fuel ratio using a first setting method before a predetermined condition is met, and sets the control center air-fuel ratio using a second setting method after the predetermined condition is met. The first and second setting methods are setting methods for setting the control center air-fuel ratio so as to cancel out the difference between the target rear air-fuel ratio and the rear air-fuel ratio. The first setting method is a setting method that allows a larger amount of change in the control center air-fuel ratio per unit time than the second setting method. The predetermined condition includes a difference condition in which the difference between the control center air-fuel ratio set using the first setting method and a stored value of the control center air-fuel ratio or a predetermined air-fuel ratio previously set using the second setting method is equal to or less than a predetermined difference. By defining the first setting method in this manner, it is possible to suppress fluctuations in the actual front air-fuel ratio and the rear air-fuel ratio, and to suppress deterioration of emissions, even before the predetermined condition is met. Furthermore, by setting the predetermined conditions in this manner, it is possible to suppress a sudden change in the control center air-fuel ratio before and after the predetermined conditions are met, thereby suppressing the actual front air-fuel ratio and rear air-fuel ratio from being disturbed, and suppressing the deterioration of emissions.

[0009] [2] In the engine device of the present disclosure (the engine device described in [1] above), the predetermined condition may include, in addition to the difference condition, a water temperature condition in which the engine cooling water temperature is equal to or higher than a predetermined water temperature.

[0010] [3] In the engine device of the present disclosure (the engine device described in [1] or [2] above), the first setting method may be a setting method for setting the control center air-fuel ratio using feedback control with a proportional term and an integral term based on the difference between the target rear air-fuel ratio and the rear air-fuel ratio, and the second setting method may be a setting method for setting the control center air-fuel ratio using feedback control with the integral term based on the difference between the target rear air-fuel ratio and the rear air-fuel ratio.

[0011] [4] In the engine device of the present disclosure (the engine device described in any one of [1] to [3] above), the first setting method may set the control center air-fuel ratio at shorter intervals than the second setting method. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an automobile 10 equipped with an engine device 11. FIG. [Figure 2] 6 is a flowchart showing an example of a setting processing routine executed by an electronic control unit 70. [Figure 3] 10 is a time chart showing an example of the coolant temperature Tw of the engine 12, the total hydrocarbon concentration, the rear air-fuel ratio AF2, the control center air-fuel ratio AFc, the method for setting the control center air-fuel ratio AFc, the target front air-fuel ratio AF1*, and the difference ΔAFc. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic diagram of an automobile 10 equipped with an engine device 11 according to the present embodiment. As shown in the figure, the automobile 10 includes an engine 12, a starter (not shown) for cranking the engine 12, a transmission TM for varying the speed of power from the engine 12 and transmitting it to the drive wheels DW, and an electronic control unit 70 as a control device for controlling the engine 12, the starter, and the transmission TM.

[0014] The engine 12 is configured as a multiple-cylinder internal combustion engine that uses fuel such as gasoline or diesel to output power through four strokes: intake, compression, expansion (explosive combustion), and exhaust. The engine 12 has an in-cylinder injection valve 26 that injects fuel into a combustion chamber 29, and an ignition plug 30. The in-cylinder injection valve 26 is located approximately in the center of the top of the combustion chamber 29 and injects fuel in the form of a spray. The ignition plug 30 is located near the in-cylinder injection valve 26 so that it can ignite the fuel sprayed in the form of a spray from the in-cylinder injection valve 26.

[0015] In the engine 12, air purified by an air cleaner 22 is drawn into an intake pipe 23, passes through a throttle valve 24 and a surge tank 25, and is further drawn into a combustion chamber 29 via an intake valve 28. Fuel is injected from an in-cylinder injection valve 26 during the intake stroke or compression stroke and ignited by a spark plug 30, causing the air-fuel mixture to explode and burn. The reciprocating motion of a piston 32, which is pushed down within the cylinder by the energy of the explosive combustion, is converted into the rotational motion of the crankshaft 14. Exhaust gas discharged from the combustion chamber 29 into an exhaust pipe 34 via an exhaust valve 33 is then discharged into the outside air via a purification device 35. The purification device 35 has a catalyst (three-way catalyst) 35a that purifies harmful components in the exhaust, such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

[0016] The electronic control unit 70 includes a microcomputer having a CPU, ROM, RAM, flash memory, input / output ports, and communication ports. The electronic control unit 70 receives signals from various sensors via the input ports. For example, the electronic control unit 70 receives a crank angle θcr from a crank position sensor 14a that detects the rotational position of the crankshaft 14 of the engine 12 and a coolant temperature Tw from a water temperature sensor 15 that detects the temperature of the coolant in the engine 12. The electronic control unit 70 also receives cam angles θci and θco from a cam position sensor 16 that detects the rotational position of an intake camshaft that opens and closes the intake valve 28 and an exhaust camshaft that opens and closes the exhaust valve 33. The electronic control unit 70 also receives an intake air volume Qa from an air flow meter 23a installed upstream of the throttle valve 24 in the intake pipe 23 and an intake air temperature Ta from a temperature sensor 23t installed upstream of the throttle valve 24 in the intake pipe 23. The electronic control unit 70 also receives as inputs a throttle opening TH from a throttle position sensor 24a that detects the position (opening) of the throttle valve 24, and a surge pressure Ps from a pressure sensor 25a attached to the surge tank 25. The electronic control unit 70 also receives as inputs a front air-fuel ratio AF1 from a front air-fuel ratio sensor 37 that is attached to the exhaust pipe 34 upstream of the purification device 35 and detects the air-fuel ratio of the exhaust, and a rear air-fuel ratio AF2 from a rear air-fuel ratio sensor 38 that is attached to the exhaust pipe 34 downstream of the purification device 35 and detects the air-fuel ratio of the exhaust. The electronic control unit 70 also receives as inputs a rotation speed Nin from a rotation speed sensor attached to the input shaft of the transmission TM and a rotation speed Nout from a rotation speed sensor attached to the output shaft of the transmission TM. The electronic control unit 70 also receives an ignition signal IG from an ignition switch 80 and a shift position SP from a shift position sensor 82 that detects the operating position of a shift lever 81. The electronic control unit 70 also receives inputs of an accelerator opening Acc from an accelerator pedal position sensor 84 that detects the amount of depression of an accelerator pedal 83, a brake pedal position BP from a brake pedal position sensor 86 that detects the amount of depression of a brake pedal 85, and a vehicle speed V from a vehicle speed sensor 87.

[0017] The electronic control unit 70 outputs various control signals via output ports. For example, the electronic control unit 70 outputs control signals to the throttle valve 24, the in-cylinder injection valve 26, and the spark plug 30 of the engine 12. The electronic control unit 70 also outputs control signals to a starter (not shown) and a transmission TM.

[0018] The electronic control unit 70 calculates the rotation speed Ne of the engine 12 based on the crank angle θcr from the crank position sensor 14a. The electronic control unit 70 calculates the load factor KL of the engine 12 based on the intake air amount Qa from the air flow meter 23a and the rotation speed Ne of the engine 12. The load factor KL is defined as the ratio of the volume of air actually taken in per cycle to the stroke volume per cycle of the engine 12. The electronic control unit 70 estimates the temperature Tc of the catalyst 35a of the purification device 35 based on the coolant temperature Tw from the water temperature sensor 15, the rotation speed Ne of the engine 12, and the load factor KL. The electronic control unit 70 estimates the oxygen storage capacity OS of the catalyst 35a based on the front air-fuel ratio AF1 from the front air-fuel ratio sensor 37, the rear air-fuel ratio AF2 from the rear air-fuel ratio sensor 38, and the intake air amount Qa.

[0019] In the automobile 10 of this embodiment, the electronic control unit 70 sets a target gear Gs* of the transmission TM based on the accelerator pedal position Acc and the vehicle speed V, and controls the transmission TM so that the gear Gs of the transmission TM becomes the target gear Gs*. The electronic control unit 70 also sets a required load factor KL* of the engine 12 based on the accelerator pedal position Acc, the vehicle speed V, and the gear Gs of the transmission TM, and performs intake air amount control, fuel injection control, and ignition control of the engine 12 based on the set required load factor KL*.

[0020] In intake air amount control, the electronic control unit 70 sets a target air amount Qa* based on the required load factor KL*, sets a target opening 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 TH*. In ignition control, the electronic control unit 70 sets a target ignition timing Ti* of the spark plug 30 based on the engine speed Ne and the load factor KL of the engine 12, and controls the spark plug 30 using the set target ignition timing Ti*.

[0021] In fuel injection control, the electronic control unit 70 sets a basic injection amount Qfbs of the direct injection valve 26 based on the load factor KL, and also sets a target front air-fuel ratio AF1*. The setting of the target front air-fuel ratio AF1* will be described later. Next, as shown in equation (1), the electronic control unit 70 calculates a feedback value AFfb0 through feedback control to cancel out the difference between the target front air-fuel ratio AF1* and the front air-fuel ratio AF1, and calculates a feedback correction coefficient Kfb by adding a value of 1 to the calculated feedback value AFfb0. In equation (1), "kp0" is the gain of the proportional term, and "ki0" is the gain of the integral term. Then, the electronic control unit 70 multiplies the base injection amount Qfbs by the feedback correction coefficient Kfb to calculate a target injection amount Qf* of the direct injection valve 26, and controls the direct injection valve 26 using the calculated target injection amount Qf*.

[0022] AFfb0=kp0·(AF1-AF1*)+ki0·∫(AF1-AF1*)dt (1)

[0023] Here, the setting of the target front air-fuel ratio AF1* will be described. The electronic control unit 70 sets the target front air-fuel ratio AF1* based on the control center air-fuel ratio AFc. The control center air-fuel ratio AFc is set by a setting processing routine, which will be described later. For example, when the target front air-fuel ratio AF1* is set to a value (AFc+εL) leaner than the control center air-fuel ratio AFc by a predetermined amount εL, if the amount of change in the oxygen storage amount OS of the catalyst 35a reaches or exceeds a threshold value OS1, the target front air-fuel ratio AF1* is switched to a value (AFc-εR) richer than the control center air-fuel ratio AFc by a predetermined amount εR. Also, when the target front air-fuel ratio AF1* is set to a value (AFc-εR), if the amount of change in the oxygen storage amount OS of the catalyst 35a reaches or exceeds a threshold value OS2, the target front air-fuel ratio AF1* is switched to a value (AFc+εL). The predetermined amounts εL and εR may be the same or different. Also, the threshold values OS1 and OS2 may be the same or different. In the first iteration of repeatedly setting the target front air-fuel ratio AF1*, the target front air-fuel ratio AF1* may be set to either the value (AFc+εL) or the value (AFc−εR).

[0024] Next, the operation of the engine device 11 mounted on the automobile 10 of this embodiment, in particular the process of setting the control center air-fuel ratio AFc in fuel injection control of the engine 12, will be described. Figure 2 is a flowchart showing an example of a setting process routine executed by the electronic control unit 70. This routine is repeatedly executed while the engine 12 is operating.

[0025] 2 is executed, the electronic control unit 70 first checks the value of flag F (step S100). Flag F indicates whether or not the warm-up of the engine 12 has been completed. Flag F is initially set to a value of 0 when the engine 12 starts operating, and is then switched to a value of 1 in step S180 when both warm-up completion conditions (the water temperature condition in step S120 and the difference condition in step S150) are met.

[0026] When the electronic control unit 70 determines in step S100 that the flag F is set to 0, it inputs the coolant temperature Tw from the water temperature sensor 15 (step S110) and determines whether a water temperature condition exists in which the coolant temperature Tw is equal to or greater than the threshold value Twth (step S120). Here, the water temperature condition is one of the warm-up completion conditions. Although details will be described later, before the warm-up completion condition exists, the control center air-fuel ratio AFc is set by a first setting method (step S170). After the warm-up completion condition exists, the control center air-fuel ratio AFc is set by a second setting method (step S200). The first and second setting methods are setting methods for setting the control center air-fuel ratio AFc so that the difference between the target rear air-fuel ratio AF2* and the rear air-fuel ratio AF2 is canceled out. The first setting method is a setting method that allows the rate of change (amount of change per unit time) dAFc of the control center air-fuel ratio AFc to be larger than the second setting method. The first setting method and the second setting method will be described in detail later.

[0027] When the electronic control unit 70 determines in step S120 that the coolant temperature Tw is less than the threshold value Twth and the water temperature condition is not satisfied, it waits for a first time to elapse since the previous setting of the control center air-fuel ratio AFc (step S160), sets the control center air-fuel ratio AFc using a first setting method (step S170), and ends this routine. The first time may be a fixed time, or may be, for example, a time corresponding to 0.5 or 1 cycle when the target front air-fuel ratio AF1* is alternately switched between rich and lean with respect to the control center air-fuel ratio AFc. Note that, when this routine is executed for the first time, it is immediately determined in step S160 that the first time has elapsed.

[0028] When the electronic control unit 70 determines in step S120 that the coolant temperature Tw is equal to or higher than the threshold value Twth and that the water temperature condition is met, it inputs the stored value AFcm stored in the flash memory (step S130). Here, the stored value AFcm is the latest value of the control center air-fuel ratio AFc previously set using the second setting method. For example, the stored value AFcm is set to the control center air-fuel ratio AFc last set after the warm-up completion condition of the engine 12 was met during the previous trip.

[0029] Next, the electronic control unit 70 calculates the difference ΔAFc between the control center air-fuel ratio (previous AFc) set the previous time this routine was executed and the stored value AFcm (step S140), and determines whether or not a difference condition is established in which the calculated difference ΔAFc is equal to or less than a threshold value ΔAFcth (step S150). Here, the difference condition is one of the warm-up completion conditions, similar to the water temperature condition.

[0030] When the electronic control unit 70 determines in step S150 that the difference ΔAFc is greater than the threshold value ΔAFcth and the difference condition is not satisfied, it waits until a first time has elapsed since the control center air-fuel ratio AFc was last set (step S160), sets the control center air-fuel ratio AFc using a first setting method (step S170), and ends this routine.

[0031] When the electronic control unit 70 determines in step S150 that the difference ΔAFc is equal to or less than the threshold value ΔAFcth and that the difference condition is satisfied, it determines that the warm-up completion condition is satisfied and switches the flag Fc from 0 to 1 (step S180). Next, the electronic control unit 70 waits for a second time, which is longer than the first time, to elapse since the previous setting of the control center air-fuel ratio AFc (step S190), sets the control center air-fuel ratio AFc using a second setting method (step S200), and updates the stored value AFcm by setting the set control center air-fuel ratio AFc to the stored value AFcm (step S210), and then ends this routine. The second time may be a fixed time, or may be, for example, a time corresponding to two or three cycles when the target front air-fuel ratio AF1* is alternately switched between rich and lean with respect to the control center air-fuel ratio AFc.

[0032] When flag F is set to the value 1 in this way, the electronic control unit 70 determines in step S100 that flag F is set to the value 1 the next time this routine is executed, and executes the processing from step S190 onwards.

[0033] Here, the setting method (first setting method or second setting method) of the control center air-fuel ratio AFc and the setting interval (first time or second time) of the control center air-fuel ratio AF will be described. In the first setting method or second setting method, the control center air-fuel ratio AFc is set to the sum of the basic air-fuel ratio AFbs, the operating condition correction value AFad, and the feedback correction values AFfb1 and AFfb2. As the basic air-fuel ratio AFbs, for example, the stoichiometric air-fuel ratio (14.6) is used. The operating condition correction value AFad is set based on the rotation speed Ne and the load factor KL of the engine 12, etc. As shown in equations (2) and (3), values calculated by feedback control to cancel out the difference between the target rear air-fuel ratio AF2* and the rear air-fuel ratio AF2 are set to. As the target rear air-fuel ratio AF2*, for example, the stoichiometric air-fuel ratio is used. In equations (2) and (3), "kp1" is the gain of the proportional term, and "ki1" and "ki2" are the gains of the integral terms. The gains ki1 and ki2 may be the same value, or the gain ki1 may be a value greater than the gain ki2.

[0034] AFfb1=kp1·(AF2-AF2*)+ki1·∫(AF2-AF2*)dt (2) AFfb2=ki2·∫(AF2-AF2*)dt (3)

[0035] The feedback correction value AFfb1 is calculated using feedback control with a proportional term and an integral term, while the feedback correction value AFfb2 is calculated using only the integral term without using the proportional term, so the feedback correction value AFfb1 is more likely to change quickly than the feedback correction value AFfb2. Also, the first time (the set interval when the control center air-fuel ratio AFc is set by the first setting method) is set to a shorter time than the second time (the set interval when the control center air-fuel ratio AFc is set by the second setting method). For these reasons, the control center air-fuel ratio AFc set by the first setting method is more likely to change quickly than the control center air-fuel ratio AFc set by the second setting method. This is done for the following reasons.

[0036] When the coolant temperature Tw is low and combustion in the combustion chamber 29 is not stable, the concentration of high molecular weight hydrocarbons (e.g., C3H8) in the exhaust gas from the combustion chamber 29 tends to be high. Furthermore, the front air-fuel ratio sensor 37 is generally designed based on the diffusion speed of relatively low molecular weight molecules such as carbon monoxide (CO). High molecular weight hydrocarbons have a larger molecular weight and a slower diffusion speed than low molecular weight hydrocarbons (e.g., C2H4) and carbon monoxide. For these reasons, when the coolant temperature Tw is low, the front air-fuel ratio AF1 detected by the front air-fuel ratio sensor 37 tends to deviate leaner than the actual front air-fuel ratio AF1act. The inventors confirmed this through experiments, analysis, etc. Therefore, if the control center air-fuel ratio AFc is set by the second setting method when the coolant temperature Tw is low, as is the case when the coolant temperature Tw is high, the change in the control center air-fuel ratio AFc is slow, and the target front air-fuel ratio AF1* and the target injection amount Qf* based on the control center air-fuel ratio AFc may deviate relatively significantly from their ideal values, causing the actual front air-fuel ratio AF1act and the rear air-fuel ratio AF2act to be disturbed, resulting in a deterioration in emissions. In light of the above, in this embodiment, the control center air-fuel ratio AFc set by the first setting method is designed to change more quickly than the control center air-fuel ratio AFc set by the second setting method. This makes it possible to prevent the actual front air-fuel ratio AF1act and the rear air-fuel ratio AF2act from being disturbed and to prevent emissions from being deteriorated before the warm-up of the engine 12 is complete.

[0037] Next, the difference condition out of the warm-up completion conditions (water temperature condition and difference condition) will be described. Because the method for setting the control center air-fuel ratio AFc differs before and after the warm-up completion condition is met, if only the water temperature condition is used as the warm-up completion condition, the control center air-fuel ratio AFc may suddenly change before and after the warm-up completion condition is met, causing the actual front air-fuel ratio AF1act and rear air-fuel ratio AF2act to become unstable, resulting in a deterioration in emissions. In contrast, in this embodiment, the difference condition is used as one of the warm-up completion conditions, thereby preventing the control center air-fuel ratio AFc from suddenly changing before and after the warm-up completion condition is met, preventing the actual front air-fuel ratio AF1act and rear air-fuel ratio AF2act from becoming unstable, and preventing a deterioration in controllability of the engine 12. Note that the threshold value ΔAFcth used in the difference condition is preferably determined by experiment, analysis, machine learning, or the like as the upper limit of a difference range in which it can be determined that the concentration of high molecular weight hydrocarbons has become sufficiently low.

[0038] FIG. 3 is a time chart showing an example of the engine 12 coolant temperature Tw, total hydrocarbon concentration, rear air-fuel ratio AF2, control center air-fuel ratio AFc, setting method of control center air-fuel ratio AFc, target front air-fuel ratio AF1*, and difference ΔAFc. The total hydrocarbon concentration is the hydrocarbon concentration taking into account the carbon number of each molecule. As shown in the figure, when the coolant temperature Tw is low, the control center air-fuel ratio AFc is set using a first setting method, and the target front air-fuel ratio AF1* is set based on the set control center air-fuel ratio AFc. Then, as the coolant temperature Tw rises, the total hydrocarbon concentration decreases and the rear air-fuel ratio AF2 pulsates and approaches the target rear air-fuel ratio AF2* from the rich side, thereby decreasing the difference ΔAFc. Then, when the difference condition is met (time t11) and the water temperature condition is also met (time t12), it is determined that the warm-up completion condition is met, and the setting method of the control center air-fuel ratio AFc is changed from the first setting method to the second setting method. The order in which the difference condition and the water temperature condition are satisfied varies depending on the situation.

[0039] In the engine system 11 mounted on the automobile 10 of the present embodiment described above, the electronic control unit 70 sets the control center air-fuel ratio AFc using a first setting method before the warm-up completion condition (predetermined condition) is met, and sets the control center air-fuel ratio AFc using a second setting method after the warm-up completion condition is met. The first and second setting methods are setting methods for setting the control center air-fuel ratio AFc so that the difference between the target rear air-fuel ratio AF2* and the rear air-fuel ratio AF2 is canceled out. The first setting method is a setting method that allows the rate of change (amount of change per unit time) dAFc of the control center air-fuel ratio AFc to be larger than that of the second setting method. The warm-up completion condition includes a water temperature condition in which the coolant temperature Tw is equal to or higher than a threshold value Twth and a difference condition in which the difference ΔAFc is equal to or lower than a threshold value ΔAFcth. By defining the first setting method in this manner, it is possible to suppress the actual front air-fuel ratio AF1act and the rear air-fuel ratio AF2act from becoming unstable before the warm-up completion condition is met, and to suppress deterioration of controllability of the engine 12. Furthermore, by defining the warm-up completion condition in this manner, it is possible to suppress a sudden change in the control center air-fuel ratio AFc before and after the warm-up completion condition is met, thereby suppressing the actual front air-fuel ratio AF1act and the rear air-fuel ratio AF2act from becoming unstable, and to suppress deterioration of controllability of the engine 12.

[0040] In the above-described embodiment, the electronic control unit 70 calculates the difference ΔAFc between the control center air-fuel ratio (previous AFc) set the previous time the routine of Fig. 2 was executed and the stored value AFcm, using the routine of Fig. 2. However, instead of the stored value AFcm, a predetermined value, for example, the stoichiometric air-fuel ratio, may be used.

[0041] In the above-described embodiment, the water temperature condition and the difference condition are used as the warm-up completion condition, but it is also possible to use only the difference condition as the warm-up completion condition.

[0042] In the above-described embodiment, the first time period (the set interval when the control center air-fuel ratio AFc is set by the first setting method) is set shorter than the second time period (the set interval when the control center air-fuel ratio AFc is set by the second setting method). However, the two may be set to be the same.

[0043] In the above-described embodiment, the engine device 11 is mounted on an automobile 10 having an engine 12. However, the engine device may be mounted on a hybrid vehicle having a motor in addition to an engine.

[0044] The correspondence between the main elements of the embodiment and the main elements of the invention described in the "Means for Solving the Problems" section will be described below. In the embodiment, the engine 12 corresponds to the "engine," the purification device 35 having the catalyst 35a corresponds to the "purification device," the front air-fuel ratio sensor 37 corresponds to the "front air-fuel ratio sensor," the rear air-fuel ratio sensor 38 corresponds to the "rear air-fuel ratio sensor," and the electronic control unit 70 corresponds to the "control device."

[0045] The correspondence between the main elements of the embodiments and the main elements of the invention described in the "Means for Solving the Problem" section does not limit the elements of the invention described in the "Means for Solving the Problem" section, since the embodiments are examples for specifically explaining the mode for implementing the invention described in the "Means for Solving the Problem" section. In other words, the interpretation of the invention described in the "Means for Solving the Problem" section should be based on the description in that section, and the embodiments are merely specific examples of the invention described in the "Means for Solving the Problem" section.

[0046] The above describes embodiments for implementing the present disclosure, but the present disclosure is not limited to these embodiments and can, of course, be implemented in various forms within the scope that does not deviate from the gist of the present disclosure. [Industrial Applicability]

[0047] The present disclosure is applicable to the engine device manufacturing industry and the like. [Explanation of symbols]

[0048] 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, 25 surge tank, 25a pressure 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 catalyst, 37 front air-fuel ratio sensor, 38 rear air-fuel ratio sensor, 70 electronic control unit, 80 ignition switch, 81 shift lever, 82 shift position sensor, 83 accelerator pedal, 84 accelerator pedal position sensor, 85 brake pedal, 86 brake pedal position sensor, 87 vehicle speed sensor.

Claims

1. The engine and a purification device attached to an exhaust system of the engine and having a catalyst for purifying exhaust gas; a front air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas upstream of the purification device in the exhaust system as a front air-fuel ratio; a rear air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas downstream of the purification device in the exhaust system as a rear air-fuel ratio; a control device that controls the engine so that a difference between a target front air-fuel ratio based on a control center air-fuel ratio and the front air-fuel ratio is canceled out; An engine device comprising: the control device sets the control center air-fuel ratio by a first setting method before a predetermined condition is satisfied, and sets the control center air-fuel ratio by a second setting method after the predetermined condition is satisfied; the first setting method and the second setting method are setting methods for setting the control center air-fuel ratio so that a difference between a target rear air-fuel ratio and the rear air-fuel ratio is canceled out, the first setting method is a setting method that allows a larger amount of change per unit time of the control center air-fuel ratio than the second setting method, the predetermined condition includes a difference condition in which a difference between the control center air-fuel ratio set by the first setting method and a stored value of the control center air-fuel ratio previously set by the second setting method or a predetermined air-fuel ratio is equal to or smaller than a predetermined difference. Engine equipment.

2. 2. The engine device according to claim 1, The predetermined condition includes, in addition to the difference condition, a water temperature condition that a cooling water temperature of the engine is equal to or higher than a predetermined water temperature. Engine equipment.

3. 3. The engine device according to claim 1 or 2, the first setting method is a setting method for setting the control center air-fuel ratio using feedback control with a proportional term and an integral term based on a difference between the target rear air-fuel ratio and the rear air-fuel ratio, the second setting method is a setting method for setting the control center air-fuel ratio using the feedback control using the integral term based on a difference between the target rear air-fuel ratio and the rear air-fuel ratio, Engine equipment.

4. 3. The engine device according to claim 1 or 2, the first setting method sets the control center air-fuel ratio at shorter intervals than the second setting method; Engine equipment.

Images