Engine control device

Abstract

To provide an engine control device capable of suppressing deterioration of deceleration feeling while preventing excessive temperature rise of a catalyst device.SOLUTION: When the accelerator opening degree decreases to less than a predetermined accelerator determination opening degree, execute a fuel cut for stopping fuel injection by the fuel supply device 11, and when the fuel cut is executed, execute intake air amount increase control for controlling the intake air amount adjusting device 22 such that the intake air amount is larger when the catalyst temperature specified by the catalyst temperature specifying device is high than when the catalyst temperature is low; When it is detected by the brake operation state detection device that the brake is operated during execution of the intake air amount increase control, the intake air amount adjustment device is controlled so that the intake air amount is larger than that when it is detected that the brake is not operated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A catalytic converter installed in the engine's exhaust passage to purify exhaust gas deteriorates when exposed to high temperatures. Therefore, in order to maintain good engine exhaust gas performance, it is necessary to prevent the catalytic converter from becoming excessively hot.

[0003] Patent document 1 discloses an engine that, in order to prevent the catalytic converter from overheating, increases the amount of air drawn into the combustion chamber during fuel cutoff (fuel cut), which stops the fuel supply to the combustion chamber, and introduces a large amount of air into the exhaust passage and ultimately the catalytic converter, thereby cooling the catalytic converter with that air. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-132185 Summary of the Invention [Problem to be solved by the invention]

[0005] Fuel cut is mainly implemented when the driver wants to decelerate the vehicle. On the other hand, if the amount of air drawn into the combustion chamber during fuel cut is increased, the pumping loss is reduced, and the rate at which the engine speed and, therefore, the vehicle speed decrease is slowed. Therefore, a configuration that simply increases the amount of air drawn into the combustion chamber during fuel cut, as in Patent Document 1, has the problem of worsening the feeling of deceleration.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide an engine control device that can prevent an excessive rise in temperature of a catalyst device while suppressing a deterioration in the deceleration feeling. [Means for solving the problem]

[0007] The engine control device according to the present invention is an engine control device provided in a vehicle equipped with a brake device for braking wheels and an accelerator pedal for adjusting vehicle speed, and includes an engine body having a combustion chamber formed therein, an exhaust passage and an intake passage respectively connected to the engine body, a fuel supply device for supplying fuel to the combustion chamber, an intake amount adjustment device for adjusting the intake amount which is the amount of air taken into the combustion chamber, a catalytic device provided in the exhaust passage for purifying exhaust gas, a catalyst temperature specifying device for specifying the catalyst temperature which is the temperature of the catalytic device, an accelerator opening detection device for detecting an accelerator opening which is the opening of the accelerator pedal, a brake operation state detection device for detecting the operation state of the brake device, and a control circuit for controlling the fuel supply device and the intake amount adjustment device. and a control unit, wherein the control unit performs a fuel cut to stop fuel injection by the fuel supply device when the accelerator opening detected by the accelerator opening detection device is less than a predetermined accelerator judgment opening, and when the fuel cut is performed and the catalyst temperature identified by the catalyst temperature identification device is high, the control unit performs intake amount increase control to control the intake amount adjustment device so that the intake amount is larger than when the catalyst temperature is low, and when the intake amount increase control is performed and the brake operation state detection device detects that the brake device is operating, the control unit controls the intake amount adjustment device so that the intake amount is larger than when it is detected that the brake device is not operating (Claim 1).

[0008] In this invention, when the catalyst temperature is high, the intake air volume, i.e., the amount of air introduced into the combustion chamber and the exhaust passage, is increased during fuel cut, allowing the catalyst device to be cooled by a large amount of air during the fuel cut.

[0009] Furthermore, when a fuel cut is performed, the intake air volume is increased when the brake device is activated compared to when it is deactivated. Therefore, when the braking force of the brake device is sufficient to decelerate the vehicle and a deceleration feeling is ensured, the increased air volume can promote a decrease in the temperature of the catalytic converter. On the other hand, when the deceleration feeling is not ensured by the brake device, the intake air volume is relatively reduced, which increases pumping loss and ensures a deceleration feeling. Therefore, according to the present invention, it is possible to prevent the catalytic converter from overheating while suppressing a deterioration in the deceleration feeling.

[0010] In the above configuration, preferably, the control unit performs the intake air amount increase control when the gear stage of the multi-speed transmission mounted on the vehicle is a high-speed stage equal to or higher than a predetermined judgment gear stage, and prohibits the intake air amount increase control when the gear stage is a low-speed stage lower than the judgment gear stage (Claim 2).

[0011] When a fuel cut accompanied by intake air amount increase control ends and fuel supply is resumed, the amount of air in the combustion chamber is likely to increase significantly. Here, fluctuations in engine torque have a greater impact on the wheels when the transmission is in a low gear than when it is in a high gear. Therefore, if intake air amount increase control is performed when the transmission is in a low gear (below the threshold gear), a relatively large torque shock may occur due to the increase in engine torque when fuel supply is resumed. In contrast, with the above configuration, intake air amount increase control is performed when the transmission is in a high gear and prohibited when the transmission is in a low gear. This avoids a large torque shock while ensuring an opportunity to perform intake air amount increase control, i.e., an opportunity to cool the catalytic converter.

[0012] In the above configuration, preferably, when the intake amount increase control is performed, the control unit controls the intake amount adjustment device so that the intake amount decreases as the gear stage of the transmission installed in the vehicle decreases (Claim 3).

[0013] With this configuration, the increase in engine torque when fuel supply is resumed after fuel cut accompanied by intake air amount increase control ends is suppressed to a smaller extent the lower the gear, preventing a large torque shock when the gear is low and enhancing the cooling effect of the catalytic converter when the gear is high.

[0014] In the above configuration, preferably, when the fuel cut is not being performed and the catalyst temperature is high, the control unit limits the intake air amount to a predetermined upper limit intake air amount or less by the intake air amount adjusting device (claim 4).

[0015] According to this configuration, when fuel cut is not being performed and the catalyst temperature is high, the intake air volume is prevented from exceeding the upper intake air volume limit, thereby minimizing the combustion energy generated in the combustion chamber. This prevents the catalyst temperature from becoming excessively high. However, increasing the number of times the intake air volume is restricted increases the number of times engine output is restricted, which may result in a deterioration in vehicle drivability. In contrast, in the present invention, as described above, the catalyst device is cooled when fuel cut is being performed, thereby reducing the number of times the catalyst temperature becomes high when fuel cut is not being performed. Therefore, it is possible to prevent the catalyst temperature from rising excessively while suppressing a deterioration in drivability.

[0016] In the above configuration, the intake amount adjusting device may be a throttle valve provided in the intake passage for opening and closing the intake passage (claim 5). [Effects of the Invention]

[0017] As described above, the engine control device of the present invention can prevent the catalyst device from overheating and suppress deterioration of the deceleration feeling. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a control block of the engine system. [Figure 3] 10 is a flowchart showing a procedure for setting a catalyst protection flag. [Figure 4] 4 is a flowchart showing the contents of control performed by the PCM. [Figure 5] 4 is a graph showing the relationship between the gear position and the brake opening degree and the target throttle opening degree. [Figure 6] 10 is a flowchart showing the details of throttle control during non-FC. [Figure 7] 4 is a time chart showing the time changes of each parameter during fuel cut. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Overall configuration of the engine system) FIG. 1 is a schematic diagram showing a preferred embodiment of an engine system E to which an engine control device according to the present invention is applied. The engine system E includes an engine body 1 that is driven by a supply of fuel, and an intake passage 20 and an exhaust passage 30 connected to the engine body 1. The intake passage 20 is a passage through which intake air, which is air introduced into the engine body 1, flows. The exhaust passage 30 is a passage through which exhaust gas discharged from the engine body 1 flows. The engine system E is installed in a vehicle such as an automobile as a power source for driving the vehicle.

[0020] The engine body 1 is a multi-cylinder engine having a plurality of cylinders 2A (only one of which is shown in FIG. 1). In this embodiment, the engine body 1 is a four-cylinder in-line engine, with the four cylinders 2A aligned in a direction perpendicular to the plane of the paper in FIG. 1. The engine body 1 includes a cylinder block 2 having the plurality of cylinders 2A formed therein, a cylinder head 3 attached to the upper surface of the cylinder block 2 so as to close the upper end openings of each cylinder 2A, and a plurality of pistons 4 housed in each cylinder 2A so as to be able to slide back and forth.

[0021] A combustion chamber 5 is defined above the piston 4 of each cylinder 2A. As will be described later, fuel is supplied to the combustion chamber 5. The mixture of the supplied fuel and air is burned in the combustion chamber 5, and the expansion force caused by the combustion causes the piston 4 to reciprocate up and down.

[0022] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 of each cylinder 2A via connecting rods. The crankshaft 13 rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4.

[0023] A vehicle equipped with the engine system E is equipped with a multi-speed transmission as the transmission 60. The transmission 60 is also an automatic transmission, and the transmission 60 and the crankshaft 13 are connected via a torque converter and the like. The output of the engine body 1 is transmitted to the wheels 70 via the crankshaft 13, the torque converter, the transmission 60 and the like. In this embodiment, the transmission 60 is a six-speed multi-speed transmission, and realizes six forward gears with different gear ratios.

[0024] A crank angle sensor SN1 is attached to the cylinder block 2. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 13, and the engine speed, which is the rotation speed of the crankshaft 13.

[0025] An intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5 are formed in the cylinder head 3 for each cylinder 2A. The cylinder head 3 is also equipped with an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber 5 side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber 5 side, for each cylinder 2A.

[0026] The cylinder head 3 is fitted with one injector 11 for each cylinder 2A that supplies fuel into the combustion chamber 5. The engine body 1 is a gasoline engine, and the injector 11 injects fuel, including gasoline, into the combustion chamber 5. The injector 11 injects fuel into the combustion chamber 5. The injector 11 is a side-injection fuel injection valve, and its tip faces the combustion chamber 5 from the inner circumferential surface of the combustion chamber 5. The cylinder head 3 is fitted with one spark plug 10 for each cylinder 2A that ignites the fuel-air mixture in the combustion chamber 5. The spark plug 10 is arranged so that its tip, including the spark plug, faces the inside of the combustion chamber 5 from near the center of the ceiling surface of the combustion chamber 5. The injector 11 corresponds to the "fuel supply device" of the present invention.

[0027] The intake passage 20 is connected to the cylinder head 3 so as to communicate with the intake port 6 of each cylinder 2A. In the intake passage 20, an air cleaner 21, a throttle valve 22, and a surge tank 23 are arranged in this order from the upstream side in the flow direction of intake air.

[0028] The air cleaner 21 is a filter that removes foreign matter from the intake air. The throttle valve 22 is a valve that opens and closes the intake passage 20. The amount of intake air flowing through the intake passage 20, and therefore the amount of air drawn into the combustion chamber 5, is changed depending on the opening of the throttle valve 22. The surge tank 23 is a tank that provides space for evenly distributing the intake air to each cylinder 2A. The throttle valve 22 corresponds to the "intake air amount adjustment device" of the present invention.

[0029] An air flow sensor SN2, an intake air temperature sensor SN3, and an intake air pressure sensor SN4 are arranged in the intake passage 20. The air flow sensor SN2 detects the intake air volume, which is the amount of air taken into each combustion chamber 5 through the intake passage 20. The intake air temperature sensor SN3 detects the intake air temperature, which is the temperature of the air flowing through the intake passage 20. The intake air pressure sensor SN4 detects the intake air pressure, which is the pressure inside the intake passage 20. The air flow sensor SN2 and the intake air temperature sensor SN3 are arranged near the air cleaner 21 and detect the flow rate and temperature of air passing through the intake passage 20 near the air cleaner 21, respectively. The intake air pressure sensor SN4 is arranged in the surge tank 23 and detects the pressure inside the surge tank 23.

[0030] The exhaust passage 30 is connected to the cylinder head 3 so as to communicate with the exhaust ports 7 of each cylinder 2A. A catalytic device 31 is disposed in the exhaust passage 30. The catalytic device 31 includes a catalyst and is a device that purifies exhaust gas by utilizing the action of the catalyst.

[0031] The catalytic device 31 incorporates a three-way catalyst. As a result, when the air-fuel ratio of the exhaust gas is at or near the stoichiometric air-fuel ratio, the catalytic device 31 oxidizes HC (hydrocarbons) and CO (carbon monoxide) while reducing NOx (nitrogen oxides). Here, the three-way catalyst has the property of storing oxygen. Therefore, when the exhaust gas contains a large amount of oxygen, the catalytic device 31 stores the oxygen. When the amount of stored oxygen is large, the catalytic device 31 is unable to sufficiently reduce NOx.

[0032] A front O2 sensor SN5 and a rear O2 sensor SN6 are disposed in the exhaust passage 30. The front O2 sensor SN5 is attached to a portion of the exhaust passage 30 upstream of the catalytic converter 31 (in the direction of exhaust gas flow) and detects the oxygen concentration and air-fuel ratio of the exhaust gas passing through this portion. The rear O2 sensor SN6 is attached to a portion of the exhaust passage 30 downstream of the catalytic converter 31 (in the direction of exhaust gas flow) and detects the air-fuel ratio of the exhaust gas passing through this portion. The front O2 sensor SN5 is a so-called linear O2 sensor that outputs a voltage proportional to the oxygen concentration and air-fuel ratio of the exhaust gas. On the other hand, the rear O2 sensor SN6 is a so-called λ sensor that determines whether the exhaust gas has an air-fuel ratio close to the stoichiometric air-fuel ratio, is richer than the stoichiometric air-fuel ratio, or is leaner than the stoichiometric air-fuel ratio.

[0033] In this embodiment, the exhaust passage 30 is a so-called 4-2-1 type exhaust passage. That is, the exhaust passage 30 is configured such that four exhaust passages extending from the engine body 1 converge into two passages, which then converge into one downstream (in the direction of exhaust gas flow). The catalytic device 31, front O2 sensor SN5, and rear O2 sensor SN6 are all located downstream of the point where the exhaust passages converge into one passage.

[0034] The engine system E is provided with an EGR device 40. The EGR device 40 includes an EGR passage 41. The EGR passage 41 is a passage that connects the exhaust passage 30 and the intake passage 20 and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage 20. The EGR passage 41 connects a portion of the exhaust passage 30 downstream of the catalytic device 31 (in the flow direction of the exhaust gas) with a portion of the intake passage 20 between the throttle valve 22 and the surge tank 23.

[0035] An EGR cooler 42 and an EGR valve 43 are provided in the EGR passage 41. The EGR cooler 42 cools the EGR gas flowing through the EGR passage 41 by heat exchange. The EGR valve 43 is a valve that opens and closes the EGR passage 41. The amount of EGR gas recirculated to the intake passage 20 is changed depending on the opening degree of the EGR valve 43. The EGR valve 43 is provided in the EGR passage 41 closer to the intake passage 20 than the EGR cooler 42.

[0036] (Control system) FIG. 2 is a functional block diagram showing the control system of the engine system E. The PCM 100 shown in this diagram is a device that is mounted on a vehicle and provides overall control of the engine system E. The PCM 100 is composed of a microcomputer that includes a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The PCM 100 corresponds to the "control unit" in this invention.

[0037] The PCM 100 is electrically connected to a crank angle sensor SN1, an air flow sensor SN2, an intake air temperature sensor SN3, an intake air pressure sensor SN4, a front O2 sensor SN5, and a rear O2 sensor SN6. Information detected by each of the sensors SN1 to SN6 is sequentially input to the PCM 100.

[0038] A vehicle equipped with the engine system E is equipped with an accelerator pedal 91 that is depressed by the driver, and an accelerator sensor SN7. The accelerator pedal 91 is an operating device for changing and adjusting the output of the engine main body 1 and, ultimately, the vehicle speed. The accelerator sensor SN7 detects the amount of depression of the accelerator pedal 91, i.e., the accelerator opening, which is the opening degree of the accelerator pedal 91. The accelerator opening is a parameter that is 0 (%) when the accelerator pedal 91 is not depressed and 100 (%) when the accelerator pedal 91 is at its maximum depression amount. The accelerator sensor SN7 corresponds to the "accelerator opening detection device" of the present invention.

[0039] The vehicle is equipped with a brake device 81, a brake pedal 82, and a brake sensor SN8. The brake device 81 is a device that applies braking force to the wheels 70 to brake the wheels 70. The brake pedal 82 is an operating device that switches between driving and stopping the brake device 81 and increases or decreases the braking force that the brake device 81 applies to the wheels 70. The brake pedal 82 is operated by depressing it. The brake sensor SN8 detects the amount of depression of the brake pedal 82, i.e., the brake opening, which is the opening degree of the brake pedal 82, and the operating state of the brake device 81. The brake opening is a parameter that is 0 (%) when the brake pedal 82 is not depressed and is 100 (%) when the depression amount of the brake pedal 82 is maximum. The brake sensor SN8 corresponds to the "brake operation state detection device" of the present invention.

[0040] The vehicle is equipped with a vehicle speed sensor SN9 for detecting vehicle speed. The vehicle is provided with a start switch SW1 that is operated by the driver to start the engine main body 1. When a predetermined operation is performed on the start switch SW1, the switch turns to IG_ON, power is supplied to each part of the engine system E, and the engine main body 1 becomes startable. Furthermore, when a predetermined operation is performed on the start switch SW1 while the switch is in the IG_ON state, the switch turns to IG_OFF, power supply to each part of the engine system E is stopped, and the engine main body 1 becomes unable to start.

[0041] The PCM 100 sequentially receives information detected by the accelerator sensor SN7 and the brake sensor SN8, and a signal from the start switch SW1.

[0042] The PCM 100 controls each part of the engine system E while making various determinations and calculations based on input information from the sensors SN1 to SN9 and the start switch SW1. The PCM 100 is electrically connected to the spark plug 10, the injector 11, the throttle valve 22, the EGR valve 43, etc., and outputs control signals to these devices based on the results of the calculations.

[0043] (Fuel cut and basic control during fuel cut) When a fuel cut condition is met—engine speed is higher than a predetermined idle speed and accelerator opening is equal to or smaller than a predetermined accelerator determination opening—the PCM 100 stops driving the injectors 11 of each cylinder 2A to stop fuel injection into each combustion chamber 5. The accelerator determination opening is set to 0 (zero), i.e., a nearly fully closed position, and fuel cut is essentially performed when the accelerator pedal 91 is not depressed (accelerator-off). During fuel cut, except when the intake amount increase control described below is being performed, the PCM 100 controls the throttle opening to a predetermined normal FC opening. The normal FC opening is 0 (zero), i.e., a nearly fully closed position, and is preset to a smaller (closer) position than the throttle opening achieved when fuel cut is not being performed. Furthermore, during fuel cut, except when the EGR valve malfunction diagnosis described below is being performed, the PCM 100 fully closes the EGR valve 43.

[0044] (Catalyst protection control) Next, the catalyst protection control performed by the PCM 100 to prevent the catalyst device 31 from overheating will be described.

[0045] (Catalyst temperature conditions) 3 is a flowchart showing the procedure for calculating the catalyst protection flag. Catalyst protection control is performed when the catalyst temperature, which is the temperature of the catalytic converter 31, is high. Specifically, catalyst protection control is performed when the catalyst temperature is equal to or higher than a first judgment temperature, and when the catalyst temperature has reached or exceeded the first judgment temperature but has not yet fallen below a second judgment temperature. The catalyst protection flag is a flag that indicates whether the conditions for performing this catalyst protection control are met.

[0046] Steps S51 to S56 shown in FIG. 3 are repeatedly performed at predetermined intervals while IG_ON is on. First, the PCM 100 reads various information including the detected values ​​of sensors SN1 to SN9 (step S51). In step S51, the PCM 100 reads at least the intake air amount detected by the air flow sensor SN2, the engine speed detected by the crank angle sensor SN1, and the intake air temperature detected by the intake air temperature sensor SN3. Next, the PCM 100 estimates the catalyst temperature, which is the temperature of the catalytic converter 31 (step S52). Specifically, the PCM 100 estimates the temperature of the exhaust gas based on the intake air amount, the engine speed, the intake air temperature, the amount of fuel injected from the injector 11, and the like, and estimates the catalyst temperature based on the estimated exhaust gas temperature. In this embodiment, the PCM 100 determines the catalyst temperature in this way, and the PCM 100 corresponds to a "catalyst temperature determining device" in addition to the "control device" of the present invention.

[0047] Next, the PCM 100 determines whether the catalyst temperature estimated in step S52 is equal to or higher than a first judgment temperature (step S53). The first judgment temperature is set in advance and stored in the PCM 100. The first judgment temperature is set to, for example, about 900°C. If the determination in step S53 is YES, meaning that the catalyst temperature is equal to or higher than the first judgment temperature, the PCM 100 sets a catalyst protection flag to 1 (step S54).

[0048] On the other hand, if the determination in step S53 is NO and the catalyst temperature is less than the first judgment temperature, the PCM 100 determines whether the conditions that the catalyst protection flag is 1 and the catalyst temperature is less than the second judgment temperature are met (step S55). If the determination in step S55 is NO and the catalyst protection flag is 0 or the catalyst temperature is equal to or greater than the second judgment temperature, the PCM 100 ends the process (returning to step S51). That is, the PCM 100 maintains the value of the catalyst protection flag at its current value. On the other hand, if the determination in step S55 is YES, the catalyst protection flag is 1, and the catalyst temperature is less than the second judgment temperature, that is, if the catalyst temperature becomes equal to or greater than the first judgment temperature and the catalyst protection flag is set to 1, and then the catalyst temperature drops to less than the second judgment temperature, the PCM 100 sets the catalyst protection flag to 0 (step S56) and ends the process (returning to step S51).

[0049] In this way, the catalyst protection flag is set to 1 when the catalyst temperature is equal to or higher than the first judgment temperature, or when the catalyst temperature has reached or exceeded the first judgment temperature but has not yet dropped below the second judgment temperature, and the conditions for implementing catalyst protection control are met. In other cases, when the conditions for implementing catalyst protection control are not met, the flag is set to 0. The catalyst protection flag is set to 0 when IG_OFF is selected.

[0050] (Fuel cut control) Fig. 4 is a flowchart showing control mainly performed during fuel cut by the PCM 100. Step S61 and subsequent steps shown in Fig. 4 are repeatedly performed at predetermined intervals while IG_ON.

[0051] First, the PCM 100 reads various information including the detected values ​​of the sensors SN1 to SN9 (step S61). In step S61, the PCM 100 reads at least the engine speed detected by the crank angle sensor SN1, the accelerator opening detected by the accelerator sensor SN7, the brake opening detected by the brake sensor SN8, and the vehicle speed detected by the vehicle speed sensor SN9.

[0052] Next, the PCM 100 determines whether or not a fuel cut is in progress (step S62). Specifically, the PCM 100 determines whether or not the above-described fuel cut condition is met and the fuel injection of the injectors 11 of all the cylinders 2A has stopped.

[0053] If the determination in step S62 is NO, meaning that fuel cut is not being performed, the PCM 100 performs non-FC throttle control (step S100). Non-FC throttle control is control of the throttle valve 22 that is performed during normal operation when fuel cut is not being performed. Non-FC throttle control will be described later. After performing step S100, the PCM 100 ends the process (returns to step S61).

[0054] If the determination in step S62 is YES and fuel cut is in progress, the PCM 100 determines whether the catalyst protection flag is 1 (step S63). In step S63, the determination is made using the catalyst protection flag that is calculated separately based on the catalyst temperature as described above.

[0055] If the determination in step S63 is NO and the catalyst protection flag is 0, the PCM 100 proceeds to step S66. In step S66, the PCM 100 sets the normal FC opening to the target throttle opening, which is the target value of the throttle opening. As described above, the normal FC opening is preset to an opening close to fully closed. After step S66, the PCM 100 proceeds to step S67.

[0056] If the determination in step S63 is YES and the catalyst protection flag is 1, the PCM 100 determines whether the gear is a higher gear than the determination gear (step S64). In this embodiment, the determination gear is set to 5th gear, and the PCM 100 determines whether the current gear is 5th gear or 6th gear. The PCM 100 identifies the current gear based on the current vehicle speed and engine speed, and uses this to make the determination in step S64.

[0057] If the determination in step S64 is NO and the gear is not a high gear, that is, if the gear is one of first to fourth gears, the PCM 100 proceeds to step S66, sets the normal FC opening to the target throttle opening, and then proceeds to step S67. On the other hand, if the determination in step S64 is YES and the gear is a high gear, the PCM 100 proceeds to step S65, and performs intake amount increase control, which is one type of catalyst protection control.

[0058] The intake air amount increase control is a control for increasing the intake air amount, which is the amount of air taken into the combustion chamber 5. In step S65, the PCM 100 sets the target throttle opening to an opening that is larger (more open) than the normal FC opening. In steps S69 and S71, which will be described later, the throttle valve 22 is opened and closed so as to achieve the target throttle opening. Therefore, when the intake air amount increase control is performed, the intake air amount is increased compared to when the intake air amount increase control is not performed (when step S66 is performed).

[0059] In step S65, the PCM 100 sets the target throttle opening based on the brake opening and the gear position within a range that is greater than the normal FC opening.

[0060] Specifically, in step S65, the PCM 100 sets the target throttle opening so that the target throttle opening when the brake opening is equal to or greater than a predetermined brake pedal determination opening is greater than the target throttle opening when the brake opening is less than the brake pedal determination opening. The brake pedal determination opening is set to a value close to 0 (zero) and is the boundary between operation and non-operation of the brake device 81. As a result, when the brake opening is equal to or greater than the brake pedal determination opening, the brake device 81 operates to apply braking force to the wheels 70. On the other hand, when the brake opening is less than the brake pedal determination opening, the brake device 81 does not operate and does not apply braking force to the wheels 70.

[0061] Furthermore, in step S65, the PCM 100 sets the target throttle opening so that the higher the gear, the greater the opening. In this embodiment, the PCM 100 sets the target throttle opening so that the target throttle opening when the gear is in sixth gear is greater than the target throttle opening when the gear is in fifth gear. The target throttle opening is set so that it is greater when the brake opening is equal to or greater than the brake pedal determination opening with the same gear, than when it is less than the brake pedal determination opening, and so that it is greater when the gear is in a higher gear than when the brake opening is the same with the same brake opening.

[0062] The setting of the target throttle opening in step S65 uses the gear position calculated based on the engine speed and vehicle speed, the brake opening detected by the brake sensor SN8, and the brake pedal determination opening that is set in advance and stored in the PCM 100. In this embodiment, as shown in Fig. 5, the target throttle opening (D1) when the gear position is fifth speed and the brake opening is less than the brake pedal determination opening, the target throttle opening (D2) when the gear position is fifth speed and the brake opening is equal to or greater than the brake pedal determination opening, the target throttle opening (D3) when the gear position is sixth speed and the brake opening is less than the brake pedal determination opening, and the target throttle opening (D4) when the gear position is sixth speed and the brake opening is equal to or greater than the brake pedal determination opening are all set in advance to be larger than the normal FC opening and to have the above-mentioned relationship, and are stored in the PCM 100. The PCM 100 extracts a value that matches the current conditions from these four stored openings (D1, D2, D3, D4) and sets it as the target throttle opening.

[0063] In step S67, the PCM 100 opens and closes the throttle valve 22 so that the opening of the throttle valve 22 becomes the target throttle opening set in step S65 or step S66. For example, the PCM 100 identifies the current opening of the throttle valve 22 based on the drive current of the throttle valve 22, the output of a throttle valve opening sensor capable of detecting the opening of the throttle valve 22, etc., and drives the throttle valve 22 based on the current opening of the throttle valve 22 and the target throttle opening. After step S67, the PCM 100 ends the process (returns to step S61).

[0064] As described above, during fuel cut (determination in step S62 is YES), when the catalyst protection flag is 1 (determination in step S63 is YES) and the gear is a high gear (determination in step S64 is YES), intake amount increase control is implemented and the throttle opening is set to an opening greater than the normal FC opening. This increases the intake amount more than when the catalyst protection flag is 0 (determination in step S63 is NO) or the gear is a low gear (determination in step S64 is NO). Furthermore, when the intake amount increase control is implemented, the throttle opening is larger when the brake device 81 is activated than when it is not activated, thereby increasing the intake amount, and the higher the gear is, the larger the throttle opening is, thereby increasing the intake amount.

[0065] (Throttle control when not in FC mode) Next, the non-FC throttle control in step S100 will be described with reference to the flowchart in FIG.

[0066] When non-FC throttle control is started, the PCM 100 first calculates a target torque, which is a target value of the engine torque (step S101). The PCM 100 calculates the target torque based on the accelerator opening detected by the accelerator sensor SN7, the vehicle speed detected by the vehicle speed sensor SN9, etc.

[0067] Next, the PCM 100 sets a target intake air amount, which is a target value of the intake air amount (step S102). The PCM 100 sets the target intake air amount based on the target torque, the engine speed detected by the crank angle sensor SN1, and the like.

[0068] Next, the PCM 100 determines whether the catalyst protection flag is 1 (step S103). If the determination in step S103 is YES and the catalyst protection flag is 1, the PCM 100 determines whether the target intake air amount set in step S102 is greater than the upper limit intake air amount (step S104). The upper limit intake air amount is set in advance and stored in the PCM 100. If the determination in step S104 is YES and the target intake air amount is greater than the upper limit intake air amount, the PCM 100 resets the target intake air amount to the upper limit intake air amount (step S105). That is, the target intake air amount is changed from the value set in step S102 to the upper limit intake air amount. After step S105, the PCM 100 proceeds to step S106.

[0069] On the other hand, if the judgment in step S103 is NO and the catalyst protection flag is 0, or if the target intake air volume set in step S102 is equal to or less than the upper limit intake air volume, PCM100 proceeds to step S106 without performing step S105, i.e., while maintaining the target intake air volume at the value set in step S102.

[0070] In step S106, the PCM 100 opens and closes the throttle valve 22 so as to achieve the target intake air amount set in step S102 or the target intake air amount reset to the upper limit intake air amount in step S105. When step S106 is performed, the non-FC throttle control ends.

[0071] As described above, when fuel cut is not being performed and the catalyst protection flag is 1, the PCM 100 performs control to limit the target intake air amount, and therefore the intake air amount, to an upper limit intake air amount or less, as one of catalyst protection controls.

[0072] (effect, etc.) FIG. 7 is a time chart that schematically shows the time variation (solid lines) of each parameter according to the above embodiment when fuel cut is initiated with the catalyst temperature at or above the first judgment temperature. FIG. 7 also shows an example in which the vehicle is being driven in a high-speed gear position. From top to bottom, FIG. 7 shows charts of the catalyst protection flag, fuel cut flag, brake opening, throttle opening, intake air amount, and catalyst temperature. The fuel cut flag is set to 1 when fuel cut is implemented and to 0 otherwise. In the chart of throttle opening, intake air amount, and catalyst temperature in FIG. 7, the dotted lines represent the throttle opening and intake air amount according to a comparative example, and indicate the throttle opening and intake air amount when the throttle opening after fuel cut is set to the opening when the catalyst flag is 0, i.e., the normal FC opening.

[0073] In the example of FIG. 7, fuel cut is initiated at time t1 with the catalyst protection flag set to 1 because the catalyst temperature is higher than the first judgment temperature. In the above embodiment, when fuel cut is initiated, the throttle opening is controlled to be larger (more open) than the normal FC opening. This opening is referred to as the first opening below and in FIG. 7. As described above, the throttle opening at this time is set based on the gear position and the brake opening. By controlling the throttle opening to the first opening, which is larger than the normal FC opening, in the above embodiment, the amount of intake air during fuel cut, and therefore the amount of air flowing into the catalytic converter 31, is greater than in the comparative example. Therefore, in the above embodiment, the catalytic converter 31 is cooled more by the larger amount of air, and the catalyst temperature decreases more quickly after fuel cut is initiated than in the comparative example in which the throttle opening is set to the normal FC opening.

[0074] In the example of FIG. 7, the brake opening is 0 (zero) until time t2, and the brake device 81 is inactive. On the other hand, after time t2, the brake pedal 82 is depressed, and the brake opening becomes equal to or greater than the brake pedal determination opening, and the brake device 81 is activated. As the brake device 81 switches from its inactive state to its active state, at time t2, the target throttle opening is set to an opening greater than the first opening (hereinafter and in FIG. 6, this opening is referred to as the second opening). Accordingly, after time t2, the throttle valve 22 is controlled to open to the second opening. As the throttle valve 22 is controlled to open, the intake amount increases after time t2. As a result, in the above embodiment, cooling of the catalytic device 31 is promoted after time t2, and the catalyst temperature decreases more rapidly.

[0075] As described above, in the above embodiment, when the catalyst protection flag is 1 and the catalyst temperature is high, the throttle opening and therefore the intake air amount during fuel cut are made larger than when the catalyst protection flag is 0 and the catalyst temperature is low. Therefore, according to the above embodiment, the timing of fuel cut can be used to cool the high-temperature catalytic device 31 with a large amount of air, thereby enabling the temperature to be reduced quickly. As described above, when the catalyst flag is 1 and the catalyst temperature is high, this means that the catalyst temperature is equal to or higher than the first judgment temperature, or that the catalyst temperature has once reached or exceeded the first judgment temperature but has not yet fallen below the second judgment temperature. When the catalyst flag is 0 and the catalyst temperature is low, this means that the catalyst temperature is lower than the second judgment temperature, or that the catalyst temperature has reached or exceeded the second judgment temperature but has not yet reached the first judgment temperature.

[0076] Here, if the intake air volume is simply increased during a fuel cut, the pumping loss will be reduced, which may slow the rate at which the engine speed decreases and worsen the feeling of deceleration. In contrast, in the above embodiment, when the brake device 81 is not activated, the throttle opening is reduced and the increase in the intake air volume is kept small. Therefore, when the brake device 81 is not activated and the brake device 81 does not provide a feeling of deceleration, it is possible to avoid the pumping loss from becoming excessively small and prevent a worsening of the feeling of deceleration. On the other hand, when the brake device 81 is activated and the brake device 81 can provide a feeling of deceleration, the throttle opening is increased and the intake air volume is increased sufficiently, so that the catalytic converter 31 can be reliably cooled by a large amount of air.

[0077] Furthermore, if the intake air amount is increased during a fuel cut, the amount of air in the combustion chamber 5 is likely to increase significantly when fuel is restored due to the large amount of air in the combustion chamber 5. Here, when the transmission 60 is in a low gear, fluctuations in engine torque have a greater impact on the wheels 70 than when the transmission 60 is in a high gear. Therefore, if intake air amount increase control is performed when the transmission 60 is in a low gear, a relatively large torque shock may occur due to the increase in engine torque when fuel is restored. In contrast, in the above embodiment, intake air amount increase control is performed only when the transmission 60 is in a high gear. In other words, intake air amount increase control is prohibited when the transmission 60 is in a low gear. Therefore, according to the above embodiment, the catalytic converter 31 can be cooled while taking advantage of the high gear to avoid a large torque shock that would occur when intake air amount increase control is performed. In other words, the catalytic converter 31 can be protected while improving the ride comfort of the vehicle.

[0078] Furthermore, in the above embodiment, the higher the gear, the larger the throttle opening, which increases the intake air volume. In other words, the lower the gear, the smaller the throttle opening, which reduces the increase in intake air volume. This prevents a large torque shock when the gear is low, and improves the cooling effect of the catalytic converter when the gear is high.

[0079] In addition, in the above embodiment, when the catalyst protection flag is 1 and the catalyst temperature is high, the intake air amount is prevented from exceeding the upper intake air amount while fuel cut is not being performed, and the combustion energy generated in the combustion chamber is kept low. This makes it possible to more reliably prevent the catalyst temperature from becoming excessively high.

[0080] However, if the number of opportunities to restrict the intake air amount increases, the number of opportunities to restrict engine output also increases, which may result in a deterioration in vehicle drivability. In contrast, in the above embodiment, the catalytic converter 31 is cooled when a fuel cut is performed to prevent the temperature from rising excessively. This reduces the opportunities for the catalyst temperature to become high when a fuel cut is not performed, thereby suppressing a deterioration in vehicle drivability.

[0081] (Variation) In the above embodiment, when the intake air amount increasing control is performed and when the control for limiting the intake air amount to equal to or less than the upper limit intake air amount is performed, the intake air amount is increased or decreased by increasing or decreasing the opening degree of the throttle valve 22. However, the device for increasing or decreasing the intake air amount is not limited to the throttle valve 22. For example, a variable valve mechanism capable of changing the opening and closing timing of the intake valve 8 may be provided in the device that drives the intake valve 8, and the intake air amount may be increased or decreased by changing the opening and closing timing of the intake valve 8.

[0082] In the above embodiment, the catalyst protection control (intake air amount increase control and control to limit the intake air amount to below the upper limit intake air amount) is described as being performed when the catalyst temperature is above the first judgment temperature, and when the catalyst temperature has become above the first judgment temperature but has not yet dropped below the second judgment temperature. However, the condition of when the catalyst temperature has become above the first judgment temperature but has not yet dropped below the second judgment temperature may be excluded from the conditions for performing catalyst protection control.

[0083] In the above embodiment, the case where the intake amount increase control is performed only when the gear is in a high gear has been described, but regardless of whether the gear is in a high gear or a low gear, the intake amount increase control may be performed when fuel is being cut and the catalyst protection flag is 1. Furthermore, when the intake amount increase control is performed, the target throttle opening may be set regardless of the gear.

[0084] In the above embodiment, the catalytic device 31 includes a three-way catalyst as a catalyst, but the catalyst included in the catalytic device 31 is not limited to this. Also, in the above embodiment, the injector 11 is a side injection type, but the injection type of the injector 11 is not limited to this. Also, in the above embodiment, the fuel is injected directly into the combustion chamber 5, but the fuel injection form is not limited to this. Also, the specific structure of the engine body 1, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0085] 1 Engine body 5 Combustion chamber 11 Injector (fuel supply device) 22 Throttle valve (intake volume control device) 30 Exhaust passage 31 Catalytic converter 60 Transmission 81 Brake equipment 100 PCM (control unit) SN7 Accelerator sensor (accelerator opening detection device) SN8 Brake sensor (brake operation status detection device)

Claims

1. An engine control device provided in a vehicle having a brake device for braking wheels and an accelerator pedal for adjusting vehicle speed, an engine body in which a combustion chamber is formed; an exhaust passage and an intake passage, each connected to the engine body; a fuel supply device for supplying fuel to the combustion chamber; an intake air amount adjusting device that adjusts an intake air amount, which is the amount of air taken into the combustion chamber; a catalytic converter provided in the exhaust passage for purifying exhaust gas; a catalyst temperature specifying device for specifying a catalyst temperature, which is the temperature of the catalyst device; an accelerator opening detection device that detects an accelerator opening, which is the opening of the accelerator pedal; a brake operation state detection device that detects the operation state of the brake device; a control unit for controlling the fuel supply device and the intake air amount adjustment device, The control unit a fuel cut is performed to stop fuel injection by the fuel supply device when the accelerator opening detected by the accelerator opening detection device is less than a predetermined accelerator judgment opening; When the catalyst temperature specified by the catalyst temperature specifying device is high during the fuel cut, an intake amount increase control is performed to control the intake air amount adjustment device so that the intake amount is larger than when the catalyst temperature is low, An engine control device characterized in that, when the intake air amount increase control is being implemented, if the brake operation state detection device detects that the brake device is operating, the intake air amount adjustment device is controlled so that the intake air amount is greater than when it is detected that the brake device is not operating.

2. 2. The engine control device according to claim 1, The control unit performs the intake air amount increase control when the gear stage of a multi-speed transmission mounted on the vehicle is a high-speed stage equal to or higher than a predetermined judgment gear stage, and prohibits the intake air amount increase control when the gear stage is a low-speed stage below the judgment gear stage.

3. 2. The engine control device according to claim 1, The control unit controls the intake amount adjustment device so that the intake amount decreases as the gear stage of the transmission installed in the vehicle decreases when the intake amount increase control is performed.

4. 2. The engine control device according to claim 1, The control unit is configured to limit the intake air amount to a predetermined upper limit intake air amount or less by the intake air amount adjusting device when the catalyst temperature is high and the fuel cut is not being performed.

5. The engine control device according to any one of claims 1 to 4, 10. An engine control device, wherein the intake amount adjusting device is a throttle valve provided in the intake passage for opening and closing the intake passage.

Images