JP7433713B2 - Internal combustion engine control device - Google Patents

Description

The present invention relates to a control device for controlling an internal combustion engine mounted on a vehicle.

In recent years, hybrid vehicles equipped with two types of power sources, an electric motor and an internal combustion engine, have become popular to a certain extent. A series type hybrid vehicle (for example, refer to the following patent document) generates electricity by driving a power generation motor generator with an internal combustion engine, and stores the generated electricity in a power storage device, such as a lithium ion secondary battery or a nickel metal hydride secondary battery. It is stored in a battery and/or a capacitor such as the like, and is supplied to a motor generator for driving. Then, the driving motor generator rotates the drive wheels of the vehicle to drive the vehicle.

Not only the power generation motor generator but also the driving motor generator can generate power by regenerative braking, and the generated power can be stored in the power storage device. If the power storage device has already stored electric charge to its full capacity, the electric power obtained through regenerative braking is purposely supplied to the power generation motor generator, which operates as an electric motor to perform motoring that rotates and drives the internal combustion engine. This consumes excess electricity.

In a hybrid vehicle, it is possible to drive the vehicle using the rotational driving force output from the driving motor generator without performing firing in which the internal combustion engine burns fuel to generate rotational driving force. Therefore, even when the vehicle is in operation, the internal combustion engine may continue to stop rotating.

When the amount of charge stored in the power storage device decreases or when the required output for the motor generator for driving is large, the internal combustion engine is started and the rotational driving force output by the internal combustion engine is used to drive the motor generator for power generation, thereby generating electricity. to charge the power storage device or increase the power supplied to the driving motor generator.

In a series type hybrid vehicle, the power generation motor generator also serves to motor (or crank) the internal combustion engine in preparation for starting the stopped internal combustion engine. During motoring, the necessary power is supplied from the power storage device.

While the internal combustion engine is not firing, the three-way catalyst for exhaust purification installed in the exhaust passage is cooled and its temperature gradually decreases. When the catalyst becomes significantly low temperature, it becomes deactivated (inactivated), and the efficiency of purifying harmful substances contained in the combustion gas deteriorates.

Therefore, while the internal combustion engine is stopped, the current temperature of the catalyst is estimated or actually measured, and if the current temperature falls below a threshold, the internal combustion engine is restarted, firing is resumed, and the catalyst is kept warm. There is.

In conventional control, the threshold value to which the current temperature of the catalyst should be compared was set uniformly, regardless of the age of the vehicle, mileage, etc. However, the performance of the catalyst deteriorates over time, and the catalyst temperature required to exhibit the necessary purification ability also fluctuates (rises). If the threshold value is set relatively low considering a new catalyst or a catalyst that has not deteriorated over time, it will not be possible to restart the internal combustion engine in time if the catalyst deteriorates over time, that is, the catalyst will not be able to purify harmful substances. The internal combustion engine is started after the efficiency has clearly deteriorated, and there is a concern that the amount of harmful substances emitted will increase.

On the other hand, if the threshold value is set relatively high with an aged catalyst in mind, the internal combustion engine may restart too quickly if the catalyst has not deteriorated over time, in other words, the purification efficiency of the catalyst may not be maintained sufficiently. This causes the internal combustion engine to be started unnecessarily even when the engine is running, resulting in wasteful fuel consumption.

JP 2019-131035 Publication

An objective of the present invention is to maintain high emission performance over a long period of time while suppressing an increase in fuel consumption.

The present invention provides a control device for controlling an internal combustion engine installed in a vehicle , which measures or estimates the current temperature of an exhaust purification catalyst installed in an exhaust passage of the internal combustion engine when the internal combustion engine is operating. and permitting the operation of the internal combustion engine to be stopped on the condition that the current temperature of the catalyst exceeds the upper limit threshold, and also measuring or estimating the current temperature of the catalyst when the operation of the internal combustion engine is stopped. , the internal combustion engine is started on the condition that the current temperature of the catalyst falls below the lower limit threshold, and immediately after starting the stopped internal combustion engine, the air-fuel ratio of the gas flowing into the catalyst increases or decreases. , the length of the period until the amplitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage decreases below a predetermined value, or the amplitude of the output signal of the air-fuel ratio sensor decreases below a predetermined value. measuring or estimating the temperature of the catalyst when the air-fuel ratio sensor It is assumed that the higher the temperature of the catalyst when the amplitude of the output signal of is reduced below a predetermined value, the greater the degree of deterioration of the catalyst. If the amplitude of is larger than a predetermined value, the control device for the internal combustion engine is configured to thereafter raise the upper limit threshold higher than before or raise the lower limit threshold higher than before .

If it is determined that the catalyst is deteriorating, it may be possible to output a message to that effect.

According to the present invention, it is possible to maintain high emission performance over a long period of time while suppressing an increase in fuel consumption of an internal combustion engine mounted on a vehicle as much as possible.

1 is a diagram showing a schematic configuration of a series-type hybrid vehicle and a control device according to an embodiment of the present invention. FIG. 3 is a diagram showing an outline of an internal combustion engine installed in the hybrid vehicle of the embodiment. FIG. 3 is a flowchart showing an example of a procedure of processing executed by the control device for an internal combustion engine according to the embodiment according to a program. FIG. 3 is a timing diagram illustrating changes in air-fuel ratios upstream and downstream of the catalyst immediately after starting the internal combustion engine of the embodiment.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of the main systems of a hybrid vehicle in this embodiment. This hybrid vehicle includes an internal combustion engine 1, a power generation motor generator 2 that is driven by the internal combustion engine 1 to generate electricity, a power storage device 3 that stores the power generated by the power generation motor generator 2, and the power generation motor generator 2 and/or the power generation motor generator 2. Alternatively, it includes a driving motor generator 4 that receives power from the power storage device 3 and drives the drive wheels 62 of the vehicle.

The hybrid vehicle of this embodiment is a series hybrid electric vehicle that uses the internal combustion engine 1 only for power generation, and the drive wheels 62 of the vehicle are exclusively supplied with driving force for running from the running motor generator 4. The internal combustion engine 1 and the driving wheels 62 are mechanically separated, and originally no rotational torque is transmitted between them. That is, the internal combustion engine 1 can rotate completely independently of the driving motor generator 4 and the drive wheels 62, and can also stop completely independently. Therefore, even when the vehicle is in operation with the ignition switch (power switch or ignition key) turned ON and the vehicle is ready to run when the driver depresses the accelerator pedal, the power storage device 3 is not fully charged. In a situation where electric charges are stored and the brake booster 15 stores sufficient negative pressure, the internal combustion engine 1 may not be operated with fuel combustion.

A crankshaft, which is a rotating shaft of the internal combustion engine 1, is mechanically connected to a rotating shaft of a power generation motor generator 2 via a gear mechanism. Then, by inputting the rotational torque output by the internal combustion engine 1 to the power generation motor generator 2, the power generation motor generator 2 generates power. The generated electric power is charged to the power storage device 3 and/or supplied to the motor generator 4 for driving. The power generation motor generator 2 also functions as a motoring electric motor that generates rotational torque to rotationally drive the crankshaft of the internal combustion engine 1. For example, the power generation motor generator 2 performs motoring (cranking) in preparation for starting the stopped internal combustion engine 1.

The driving motor generator 4 generates driving force for driving the vehicle, and inputs the driving force to the driving wheels 62 via the reduction gear 61. Further, the driving motor generator 4 generates electricity by being rotated by the driving wheels 62, and recovers the kinetic energy of the vehicle as electrical energy. The electric power generated by this regenerative braking charges the power storage device 3.

However, if the power storage device 3 has already been charged to its full capacity and it is difficult to charge it further, the electric power regenerated by the driving motor generator 4 may be supplied to the power generating motor generator 2 to generate electricity. The motor generator 2 is operated as an electric motor to rotationally drive the internal combustion engine 1. This allows excess power to be used up while maintaining the vehicle's braking performance. Furthermore, at this time, since the rotation of the internal combustion engine 1 is maintained, a fuel cut in which the fuel supply to the cylinders 11 of the internal combustion engine 1 is temporarily stopped can be executed.

The generator inverter 21 converts AC power generated by the power generation motor generator 2 into DC power. Then, the DC power is input to the power storage device 3 or the drive inverter 41. Furthermore, when operating the power generation motor generator 2 as an electric motor, the generator inverter 21 converts the DC power supplied from the power storage device 3 and/or the drive inverter 41 into AC power, and then converts the power generation motor generator 2 into AC power. Enter.

The drive inverter 41 converts the DC power supplied from the power storage device 3 and/or the generator inverter 21 into AC power, and inputs the AC power to the driving motor generator 4 . Furthermore, the drive inverter 41 converts the AC power generated by the driving motor generator 4 into DC power when performing regenerative braking of the vehicle, and inputs the DC power to the power storage device 3 or the generator inverter 21 . The generator inverter 21 and the drive inverter 41 form part of a PCU (Power Control Unit).

Power storage device 3 is a battery, a capacitor, or the like. The battery is a high voltage secondary battery with high energy density, such as a lithium ion secondary battery or a nickel hydride secondary battery. The power storage device 3 charges and stores electric power generated by each of the power generation motor generator 2 and the traveling motor generator 4. In addition, the power storage device 3 discharges electric power for operating each of the power generation motor generator 2 and the traveling motor generator 4 as electric motors, and supplies necessary electric power to these motor generators 2 and 4.

FIG. 2 shows an outline of the internal combustion engine 1 installed in the hybrid vehicle of this embodiment. The internal combustion engine 1 is a spark ignition four-stroke engine, and includes a plurality of cylinders 11 (for example, three cylinders, one of which is shown in FIG. 1). An injector 111 is provided near the intake port of each cylinder 11 to inject fuel toward the intake port. Furthermore, a spark plug 112 is attached to the ceiling of the combustion chamber of each cylinder 11. The spark plug 112 causes a spark discharge between a center electrode and a ground electrode upon application of an induced voltage generated in an ignition coil.

The intake passage 13 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 11. On the intake passage 13, an air cleaner 131, an electronic throttle valve 132, a surge tank 133, and an intake manifold 134 are arranged in this order from upstream. The air cleaner 131 is located at the most upstream position in the intake passage 13, that is, at the intake port that takes in air. The intake port opens at the front of the vehicle to take in cold air and improve the charging efficiency of the internal combustion engine.

The exhaust passage 14 for discharging exhaust gas guides exhaust gas generated as a result of burning fuel within the cylinders 11 from the exhaust port of each cylinder 11 to the outside. An exhaust manifold 142 and a three-way catalyst 141 for purifying exhaust gas are arranged on the exhaust passage 14. Upstream and downstream of the catalyst 41 in the exhaust passage 4, air-fuel ratio sensors 143 and 144 are installed to detect the air-fuel ratio of gas flowing through the exhaust passage 4. The air-fuel ratio sensors 143 and 144 may each be an O ₂ sensor that has an output characteristic that is non-linear with respect to the air-fuel ratio of exhaust gas, or a linear A/F sensor that has an output characteristic that is proportional to the air-fuel ratio of exhaust gas. There may be. The output characteristics of the _O2 sensor, which outputs a voltage signal according to the oxygen concentration in exhaust gas, is that in a certain range (window) near the stoichiometric air-fuel ratio, the rate of change in output relative to the air-fuel ratio shows a large and steep slope; In a lean region where the air-fuel ratio is large, the fuel asymptotically approaches a lower saturation value, and in a rich region where the air-fuel ratio is small, it asymptotically approaches a higher saturation value, forming a so-called Z characteristic curve.

The external EGR (Exhaust Gas Recirculation) device 12 includes an external EGR passage 121 that communicates the exhaust passage 14 and the intake passage 13, an EGR cooler 122 provided on the EGR passage 121, and an EGR passage 121 that opens and closes the EGR passage 121. The EGR valve 123 controls the flow rate of EGR gas flowing through the EGR valve 123. The entrance of the EGR passage 121 is connected to a predetermined location downstream of the catalyst 141 in the exhaust passage 14 . The outlet of the EGR passage 121 is connected to a predetermined location downstream of the throttle valve 132 in the intake passage 13, particularly to the surge tank 133.

The internal combustion engine 1 is equipped with a brake booster 15 for reducing the operating force required when braking the vehicle, that is, the force required to press the brake pedal. In this field, the brake booster 15 introduces negative intake pressure from the downstream side of the throttle valve 132 in the intake passage 13 (or the surge tank 133), and uses the negative pressure to boost the force applied to the brake pedal. It is widely known. The brake booster 15 has a constant pressure chamber (negative pressure chamber) that stores negative pressure and a variable pressure chamber (atmospheric pressure chamber) to which atmospheric pressure is applied, and the constant pressure chamber is connected to the intake passage 13 via a negative pressure pipe 151. ing. Negative pressure conduit 151 guides intake negative pressure downstream of throttle valve 132 to the constant pressure chamber. A check valve 152 is provided on the negative pressure conduit 151 to keep the negative pressure within the constant pressure chamber and prevent positive pressure from being applied to the constant pressure chamber.

When the brake pedal is not operated by the driver, the constant pressure chamber and variable pressure chamber communicate with each other, and the variable pressure chamber is isolated from atmospheric pressure. When the brake pedal is operated, the constant pressure chamber and the variable pressure chamber are cut off, and the atmosphere is introduced into the variable pressure chamber. As a result, the pressure difference between the constant pressure chamber and the variable pressure chamber becomes a control pressure that doubles the force applied to the brake pedal. The brake pedal force amplified by the brake booster 15 is converted into hydraulic pressure in the master cylinder 16 . The master cylinder pressure output by the master cylinder 16, that is, the pressure of the brake fluid discharged by the master cylinder 16, is transmitted to a brake device such as a brake caliper or a wheel cylinder via a hydraulic pressure circuit, and is used to brake the vehicle by the brake device. used.

An ECU (Electronic Control Unit) 0, which is a control device that controls the internal combustion engine 1, the power generation motor generator 2, the power storage device 3, the inverters 21 and 41, and the driving motor generator 4, includes a processor, memory, input interface, output interface, etc. It is a microcomputer system with The ECU0 includes a plurality of ECUs, namely an EFI (Electronic Fuel Injection) ECU01 that controls the internal combustion engine 1, a generator ECU02 that controls the power generation motor generator 2 and the generator inverter 21, and a BMS (Battery Management) that controls the power storage device 3. The system) ECU 03, the drive machine ECU 04 that controls the driving motor generator 4 and the drive machine inverter 41, etc., and the HV (Hybrid Vehicle) ECU, which is the upper controller that controls these, are connected to the CAN (Controller Area Network), etc. They are connected to each other so that they can communicate with each other via telecommunication lines.

For the ECU 0, a vehicle speed signal a is output from a vehicle speed sensor that detects the actual vehicle speed, and a crank angle signal b is output from a crank angle sensor that detects the rotation angle and engine speed of the crankshaft of the internal combustion engine 1. , an accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal by the driver as the accelerator opening (so to speak, the driving force that the driver requests for the vehicle), and the intake passage 13 (in particular, An intake temperature/intake pressure signal d output from a temperature/pressure sensor that detects the intake air temperature and intake pressure in the surge tank 133), a cooling water temperature signal output from a water temperature sensor that detects the temperature of the cooling water of the internal combustion engine 1. e, a signal f output from a sensor that detects the amount of charge stored in the power storage device 3 (or SOC (State of Charge)), particularly a sensor that detects the terminal current and/or voltage of the battery 3, and the outside temperature. an outside temperature signal g outputted from an outside temperature sensor that detects the outside temperature, a signal h outputted from a sensor that detects the applied current and/or applied voltage to the power generation motor generator 2, and the air-fuel ratio of the exhaust gas upstream of the catalyst 141. A signal m output from an air-fuel ratio sensor 143 that detects the air-fuel ratio, a signal n output from an air-fuel ratio sensor 144 that detects the air-fuel ratio of exhaust gas downstream of the catalyst 141, and the like are input.

ECU0 senses the accelerator opening degree operated by the driver, the shift position, that is, the position of the shift lever (selector lever), the ON/OFF status of the switch operated by the driver, and the current state of the vehicle, which are sensed through various sensors. The driving motor generator 4 outputs an output depending on the vehicle speed, the slope of the road surface, the amount of charge stored in the power storage device 3, the magnitude of the negative pressure stored in the brake booster 15, the power generated by the power generation motor generator 2, etc. The rotation torque output by the internal combustion engine 1, the electric power generated by the power generation motor generator 2, or the rotation torque output by the power generation motor generator 2 are controlled to increase or decrease.

In principle, if the power storage device 3 currently stores sufficient charge and the output required for the driving motor generator 4 is small, the fuel supply to the internal combustion engine 1 is cut off and the internal combustion engine 1 is operated. do not. On the other hand, if the amount of charge stored in the power storage device 3 decreases or if the output required from the driving motor generator 4 is large, the internal combustion engine 1 is started and fuel is supplied to the cylinder 11. The internal combustion engine 1 drives the generator motor generator 2 with the rotational torque output from the internal combustion engine 1 to generate electricity to charge the power storage device 3 or increase the electric power supplied to the driving motor generator 4. do.

The internal combustion engine 1 is started while the internal combustion engine 1 is not being operated by supplying fuel to the cylinders 11 of the internal combustion engine 1 and the driving motor generator 4 is driving the drive wheels 62 to drive the vehicle. In order to perform power generation by the power generation motor generator 2, first, the power generation motor generator 2 is operated as an electric motor, and motoring for starting the internal combustion engine 1 is performed. Then, after the crankshaft of the internal combustion engine 1 has rotated for a predetermined number of times or more or for a predetermined angle or more, and cylinder discrimination for learning the current stroke or piston position of each cylinder 11 of the internal combustion engine 1 has been completed, each cylinder of the internal combustion engine 1 Fuel is injected at an appropriate timing according to the stroke of the engine, and firing is started to ignite and burn the fuel at an appropriate timing. The rotation angle and rotation speed of the crankshaft of the internal combustion engine 1, that is, the engine rotation speed, can be detected (in the generator ECU 02) via a resolver attached to the power generation motor generator 2, and the crank angle and rotation speed attached to the internal combustion engine 1 can be detected. It can also be detected via a sensor (at the EFI ECU01).

The rotation of the internal combustion engine 1 is accelerated by motoring and firing, and when the rotation speed exceeds the start determination value, the internal combustion engine 1 starts and becomes autonomously rotating (the power generation motor generator 2 The engine speed is determined to be able to maintain an upward trend even after reducing the output of the engine), and the output of the power generation motor generator 2, which is operating as an electric motor, is reduced to 0 and motoring is terminated. .

After determining whether to start the internal combustion engine 1, the internal combustion engine 1 rotationally drives the power generation motor generator 2. Furthermore, the power generation motor generator 2 is operated as a generator, and the generated power is increased from zero.

Note that the EFI ECU01, which forms part of the ECU0, acquires various information a, b, c, d, e, f, g, h, m, and n necessary for operational control of the internal combustion engine 1 via an input interface. , learns the engine rotational speed and estimates the amount of air taken into the cylinder 11 (so to speak, engine load factor). Then, the required fuel injection amount commensurate with the intake air amount (necessary to achieve the target air-fuel ratio), fuel injection timing (including the number of fuel injections for one combustion), fuel injection pressure, and ignition timing (one time The operating parameters of the internal combustion engine 1, such as the number of ignitions for combustion), the required EGR rate (or EGR gas amount), etc., are determined. This EFI ECU01 outputs various control signals i, j, k, l corresponding to operating parameters to the igniter of the spark plug 112, the injector 111, the throttle valve 132, the EGR valve 123, etc. via the output interface.

When the operation of the internal combustion engine 1 is stopped, in other words, when the internal combustion engine 1 is not firing, the temperature of the catalyst 141 gradually decreases. The catalyst 141 becomes deactivated when the temperature becomes significantly low, and the efficiency of purifying harmful substances contained in the combustion gas deteriorates. As shown in FIG. 3, the ECU0 (or EFI ECU01) that controls the internal combustion engine 1 of this embodiment actually measures or estimates the current temperature of the catalyst 141 at any time while the operation of the internal combustion engine 1 is stopped (step S1). (Step S2), on the condition that the current temperature of the catalyst 141 has fallen below the lower limit threshold (Step S3), the amount of depression of the accelerator pedal by the driver, the amount of charge stored in the power storage device 3, and the amount of charge stored in the brake booster 15 are determined. Regardless of the negative pressure, etc., the internal combustion engine 1 is restarted and firing is resumed (step S4). As a result, the combustion gas generated by burning fuel flows into the catalyst 141 to raise the temperature of the catalyst 141, and keep the catalyst 141 warm to a state where it can exhibit the minimum necessary purification efficiency.

After that, if the current temperature of the catalyst 141 exceeds the upper limit threshold (step S5), the amount of depression of the accelerator pedal by the driver is large, the amount of charge stored in the power storage device 3 is decreased, or the brake booster 15 Firing of the internal combustion engine 1 is stopped (step S7) unless there is a situation where firing of the internal combustion engine 1 should be maintained (step S6), such as when the negative pressure stored in the internal combustion engine is decreasing. Naturally, the upper limit threshold referred to in step S5 is higher than the lower limit threshold referred to in step S3.

As a supplement regarding the temperature of the catalyst 141, in a system in which a sensor for detecting the temperature of the catalyst 141 is installed, the ECU0 can directly measure the current temperature of the catalyst 141 by referring to the output signal of the temperature sensor. . In a system in which such a temperature sensor is not installed, the ECU0 estimates the current temperature of the catalyst 141 according to a known method. The temperature of the catalyst 141 when the internal combustion engine 1 is operating with firing is determined by the temperature flowing into the catalyst 141 according to the operating range of the internal combustion engine 1 [engine speed, throttle valve opening], air-fuel ratio, ignition timing, etc. It can be estimated based on the temperature of the exhaust gas, the outside temperature, the vehicle speed (the higher the vehicle speed, the more flow rate of the traveling air blown into the engine room, and the exhaust passage 14 is air-cooled). Further, the temperature of the catalyst 141 when the operation of the internal combustion engine 1 is stopped is the temperature of the catalyst 141 immediately before the operation of the internal combustion engine 1 is stopped, the length of the period during which the operation of the internal combustion engine 1 is stopped, It can be estimated based on outside temperature, vehicle speed, etc.

By the way, the performance of the catalyst 141 including its oxygen storage capacity deteriorates over time. Along with this, the temperature value of the catalyst 141 required to exhibit the minimum necessary purification efficiency also increases. The required temperature value is different between a new catalyst 141 or a catalyst 141 that has not deteriorated over time and a catalyst 141 that has deteriorated over time. Furthermore, the conditions under which the internal combustion engine 1 should be restarted in order to maintain the temperature and performance of the catalyst 141 are different.

Therefore, the ECU 0 of the present embodiment estimates the degree of deterioration of the catalyst 141 over time, and accordingly determines the temperature of the lower limit threshold value in step S3, which is a condition for restarting the internal combustion engine 1 that has stopped operating. and/or change the temperature of the upper limit threshold in step S5.

More specifically, as shown in FIG. 4, after the time t ₀ when the internal combustion engine 1 that had been stopped and firing is restarted, the air-fuel ratio of the combustion gas flowing into the catalyst 141, that is, the air-fuel ratio of the catalyst 141 The output signal m of the upstream air-fuel ratio sensor 143 oscillates up and down across the stoichiometric air-fuel ratio or a target air-fuel ratio in the vicinity thereof. Here, time t ₀ is when the ignition switch is turned from OFF to ON by the driver's hand to cold start the internal combustion engine 1, or when the internal combustion engine 1 is started after the internal combustion engine 1 has been stopped for a long period of time or more. 1 is started, the temperature of the catalyst 141 is at or near the outside temperature, the catalyst 141 is not activated, and the oxygen storage capacity of the catalyst 141 is low. Therefore, the air-fuel ratio of the gas flowing downstream from the catalyst 141, that is, the output signal n of the air-fuel ratio sensor 144 on the downstream side of the catalyst 141, also changes up and down in synchronization with the output signal m of the air-fuel ratio sensor 43 on the upstream side. It vibrates and its amplitude is large.

When a certain period of time has passed after restarting firing of the internal combustion engine 1, the catalyst 141 is heated by the combustion gas flowing into the catalyst 141 and its temperature rises, and the catalyst 141 is activated and the catalyst 141 is activated. Oxygen storage capacity increases. In other words, excess oxygen is stored when the air-fuel ratio of the gas flowing into the catalyst 141 is leaner than the target air-fuel ratio, and is stored when the air-fuel ratio of the gas flowing into the catalyst 141 is richer than the target air-fuel ratio. release the oxygen that was present. As a result, the air-fuel ratio amplitude of the gas flowing downstream from the catalyst 141 becomes clearly smaller.

In view of this, the ECU 0 determines the progress from the time t ₀ when the operation of the internal combustion engine 1 is restarted to the time t ₁ and t ₂ when the amplitude of the output signal n of the air-fuel ratio sensor 144 downstream of the catalyst 141 decreases to a predetermined value or less. By measuring the period, the degree of aging deterioration of the catalyst 141 is estimated. As shown by the solid line in FIG. 4, in the case of the catalyst 141 that has not deteriorated over time, the amplitude of the output signal n of the air-fuel ratio sensor 144 decreases to a predetermined value or less from the time t ₀ when the operation of the internal combustion engine 1 is resumed to the time t _{1 .} The elapsed period is short. On the other hand, as shown by the broken line in FIG. 4, in the aged catalyst 141, the amplitude of the output signal n of the air-fuel ratio sensor 144 decreases to a predetermined value or less from the time t ₀ when the operation of the internal combustion engine 1 is restarted. ₂ will take longer.

Therefore, the ECU0 determines that the longer the measured elapsed period, the more advanced the aged deterioration of the catalyst 141 is, and sets the temperature of the lower limit threshold value in step S3 to a higher value, and/or sets the temperature of the lower limit threshold value in step S5 to a higher value. The upper threshold temperature mentioned in 2. is set to a higher value.

The length of the elapsed period from the time t ₀ when the operation of the internal combustion engine 1 is restarted to the time t ₁ and t ₂ when the amplitude of the output signal n of the air-fuel ratio sensor 144 decreases below a predetermined value can be directly measured by a timer. can. However, regardless of the timer, the length of the elapsed period described above is determined based on the measured temperature or estimated temperature of the catalyst 41 at the times t ₁ and t ₂ when the amplitude of the output signal n of the air-fuel ratio sensor 144 is reduced to a predetermined value or less. It is also possible to measure indirectly. That is, it can be inferred that the higher the actually measured or estimated temperature of the catalyst 41 at times t ₁ and t ₂ is, the longer the elapsed period is.

Incidentally, if the air-fuel ratio of the gas flowing into the catalyst 141 is adjusted up and down after restarting the internal combustion engine 1, the temperature of the catalyst 141 can be raised more quickly by the reaction heat generated within the catalyst 141. . This contributes to further reduction of the amount of harmful substances discharged.

In this embodiment, an internal combustion engine 1 mounted on a vehicle is controlled, and after the stopped internal combustion engine 1 is started, the flow flows into the exhaust purifying catalyst 141 installed in the exhaust passage 14. While the air-fuel ratio of the gas is increasing or decreasing, the elapsed period until the amplitude of the output signal n of the air-fuel ratio sensor 144 installed downstream of the catalyst 141 in the exhaust passage 14 decreases to a predetermined value or less is measured, or The control device 0 for the internal combustion engine 1 measures or estimates the temperature of the catalyst 141 when the amplitude of the output signal n of the fuel ratio sensor 144 is reduced to a predetermined value or less, and estimates the degree of deterioration of the catalyst 141 based on the temperature. .

In addition, the control device 0 of the present embodiment determines the conditions for restarting the internal combustion engine 1 in order to maintain the temperature of the catalyst 41 when the operation of the internal combustion engine 1 is stopped, depending on the length of the period. change.

According to this embodiment, if the aging of the catalyst 141 has not progressed, the lower limit threshold and upper threshold described above become lower values, and the temperature and purification efficiency of the catalyst 141 are still maintained. It is possible to avoid restarting the internal combustion engine 1 sooner than necessary, and to stop the operation of the restarted internal combustion engine 1 at an early stage. This makes it possible to reduce wasteful fuel consumption.

If the catalyst 141 has deteriorated over time, the lower limit threshold and the upper threshold become higher values, and the internal combustion engine 1 can be restarted promptly before the temperature and purification efficiency of the catalyst 141 drop significantly. Furthermore, the operation of the restarted internal combustion engine 1 can be maintained without being stopped early. Thereby, the catalyst 141 can reliably oxidize/reduce the harmful substances and render them harmless, making it possible to suppress the discharge of harmful substances over a long period of time. In addition, for the purpose of improving the emissions of the internal combustion engine 1, there is no need to increase the amount of expensive precious metal used in the catalyst 141.

Note that the present invention is not limited to the embodiments detailed above. For example, when the current temperature of the catalyst 141 falls below the lower limit threshold (step S3), if the amplitude of the output signal n of the air-fuel ratio sensor 144 downstream of the catalyst 141 has already become larger than a predetermined value, the internal combustion engine 1 Since it is not in time to restart or restart the internal combustion engine 1, the lower limit threshold in step S3 and/or the upper threshold in step S5 will be raised higher to speed up the restart of the internal combustion engine 1. Also, it is preferable to extend the operating period of the internal combustion engine 1.

The present invention can also be applied to controlling an internal combustion engine installed in a vehicle that is not a hybrid vehicle, particularly to changing the conditions for executing an idle stop. Specifically, while the internal combustion engine is being idle-stopped, the internal combustion engine is restarted on the condition that the current measured temperature or estimated temperature of the exhaust purification catalyst falls below the lower limit threshold. In this case, the lower limit threshold value is set as the period elapses after the stopped internal combustion engine is started until the amplitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst decreases below a predetermined value (or the air-fuel ratio The higher the measured temperature or estimated temperature of the catalyst when the amplitude of the output signal of the sensor is reduced below a predetermined value (in other words, the more deterioration of the catalyst progresses), the higher the temperature is raised. Alternatively, when performing control to permit idle stop of the internal combustion engine with the requirement that the current measured or estimated temperature of the catalyst exceeds the upper limit threshold, the upper threshold may be set as the catalyst deteriorates. Pull it up high.

In addition, if the elapsed period after starting the stopped internal combustion engine until the amplitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst decreases below the specified level is longer than specified (or if the amplitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst If the measured temperature or estimated temperature of the catalyst is higher than a predetermined value when the amplitude of the output signal decreases to a predetermined value or less), that is, if it is determined that the catalyst is deteriorating, the control device outputs a message to that effect. You can also do that. Specifically, a diagnosis code indicating that catalyst deterioration is progressing is written into memory, and the code is output in a way that visually or audibly appeals to the driver of the vehicle (e.g., a check engine lamp in the cockpit). It may be possible to do things like turn on the light, display it on the display, output a warning sound, etc.).

The results of estimating the degree of deterioration of the catalyst can be used to determine whether warm-up of the internal combustion engine is complete or incomplete, whether to permit or disallow driving driven by the electric motor (only) immediately after startup in a hybrid vehicle, and various other controls. It can be used for judgment.

In addition, the specific configuration and processing contents of each part can be variously modified without departing from the spirit of the present invention.

0...Control unit (ECU)
DESCRIPTION OF SYMBOLS 1...Internal combustion engine 11...Cylinder 111...Injector 112...Spark plug 14...Exhaust passage 141...Catalyst 143...Air-fuel ratio sensor on the upstream side of the catalyst 144...Air-fuel ratio sensor on the downstream side of the catalyst m...Air-fuel ratio on the upstream side of the catalyst Signal n...Air-fuel ratio signal on the downstream side of the catalyst

Claims (3)

A control device that controls an internal combustion engine installed in a vehicle,
When the internal combustion engine is operating, the current temperature of the exhaust purification catalyst installed in the exhaust passage of the internal combustion engine is measured or estimated, and the internal combustion engine permit the suspension of operation of
Further, when the operation of the internal combustion engine is stopped, the current temperature of the catalyst is measured or estimated, and the internal combustion engine is started on the condition that the current temperature of the catalyst falls below a lower limit threshold,
Immediately after starting the stopped internal combustion engine, while the air-fuel ratio of the gas flowing into the catalyst is increasing or decreasing, the amplitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage is reduced to a predetermined value or less. The amplitude of the output signal of the air-fuel ratio sensor is determined by measuring the length of the period until the amplitude of the output signal of the air-fuel ratio sensor reaches a predetermined value, or by measuring or estimating the temperature of the catalyst when the amplitude of the output signal of the air-fuel ratio sensor decreases to a predetermined value or less. It is assumed that the longer the period until the reduction is below, the greater the degree of deterioration of the catalyst, or the higher the temperature of the catalyst when the amplitude of the output signal of the air-fuel ratio sensor is reduced to below the predetermined value, the greater the degree of deterioration of the catalyst. Assuming that is large,
Further, if the amplitude of the output signal of the air-fuel ratio sensor immediately after starting the stopped internal combustion engine is larger than a predetermined value, then the upper limit threshold value is raised higher than before, or the lower limit value is increased. An internal combustion engine control device that raises the threshold higher than ever before . If the amplitude of the output signal of the air-fuel ratio sensor immediately after starting the stopped internal combustion engine is larger than a predetermined value, then the upper limit threshold is raised higher than before, and the lower limit threshold is raised to this value. 2. The control device for an internal combustion engine according to claim 1, wherein the internal combustion engine is raised to a higher level . 3. The control device for an internal combustion engine according to claim 1 , which outputs a message to that effect when it is determined that deterioration of the catalyst is progressing .

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