Method and apparatus for controlling start of internal combustion engine

Abstract

To start combustion operation of an internal combustion engine at proper timing when a catalyst becomes an active state, in a device for performing preheating by current-carrying to an EHC before starting the internal combustion engine.SOLUTION: When a start request of the engine is generated, energization of the EHC is started (time t1). When it is estimated that the temperature of the EHC approaches the activation temperature from the resistance value of the EHC (time t2), motoring of the internal-combustion engine is started by power running of a motor generator for power generation. Since air flows through the EHC due to motoring, the upstream air-fuel ratio sensor shows an output corresponding to the oxygen concentration of air. When the EHC is activated, the oxygen concentration indicated by the downstream air-fuel ratio sensor decreases due to the oxygen storage capacity and the catalytic action. Based on the decrease in the concentration of oxygen, it is determined that the catalytic converter has been activated (time t3), the combustion operation of the engine is started, and the energization of the EHC is terminated.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a startup control technology for an internal combustion engine, which includes an electrically heated catalyst in an exhaust passage, energizing the electrically heated catalyst to preheat it before starting the internal combustion engine, and starting the internal combustion engine in an activated catalyst state. [Background technology]

[0002] Electrically heated catalysts (EHCs) are known as catalysts used in the exhaust systems of internal combustion engines. These catalysts can be heated by passing current through them, thereby accelerating catalytic activation. By starting to pass current through the electrically heated catalyst before the engine starts, the catalyst can be preheated, reducing emissions immediately after the engine starts.

[0003] The temperature of an electrically heated catalyst, which rises as current is passed through the electrically heated catalyst, is generally estimated using the characteristic that resistance changes with temperature.

[0004] Patent document 1 discloses that the supply of electricity to an electrically heated catalyst is started at the same time as the start of combustion operation of the internal combustion engine, and when the inversion period ratio, which is the ratio between the inversion period of the upstream O2 sensor and the inversion period of the downstream O2 sensor under air-fuel ratio feedback control, becomes equal to or less than a predetermined value, the catalyst is deemed to be activated and the supply of electricity to the electrically heated catalyst is terminated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-28252 Summary of the Invention [Problem to be solved by the invention]

[0006] In the method of estimating the temperature from the change in the resistance value of the electrically heated catalyst, the temperature-resistance characteristics change relatively significantly due to individual differences, deterioration, etc., so it is difficult to start the internal combustion engine at the appropriate timing when the catalyst has truly reached an activated state through preheating. In other words, it is easy for the start of the internal combustion engine to be unnecessarily delayed or for emissions to worsen due to an excessively early start.

[0007] The technology of Patent Document 1 is based on the premise that the internal combustion engine is in combustion operation, and cannot be applied to preheating before starting. [Means for solving the problem]

[0008] The present invention provides a startup control method for an internal combustion engine, which includes providing an electrically heated catalyst in an exhaust passage, energizing the electrically heated catalyst to preheat it before starting the internal combustion engine, and starting the internal combustion engine in an activated catalyst state, comprising: supplying a gas containing oxygen to the electrically heated catalyst when it is estimated that the catalyst temperature has approached an activation temperature after the start of energization of the electrically heated catalyst; While the gas is flowing, the oxygen concentration is detected on both the upstream and downstream sides of the electrically heated catalyst. When the oxygen concentration on the downstream side becomes lower than the oxygen concentration on the upstream side, it is assumed that the catalyst has reached an activated state, and the internal combustion engine starts combustion operation. [Effects of the Invention]

[0009] According to the present invention, it is possible to correctly determine whether the catalyst is active before the internal combustion engine starts combustion operation, and to start the internal combustion engine combustion operation at an appropriate timing, thereby achieving reduction in emissions through catalytic action from an early stage. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of the configuration of a series hybrid vehicle. [Figure 2] FIG. 1 is an explanatory diagram illustrating the configuration of an intake system and an exhaust system of an internal combustion engine. [Figure 3] 4 is a time chart showing the operation of the first embodiment. [Figure 4] 6 is a time chart showing the operation of the second embodiment. [Figure 5] 10 is a time chart showing the operation of the third embodiment. [Figure 6] FIG. 4 is a characteristic diagram showing the relationship between the temperature and resistance value of an electrically heated catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic configuration of a series hybrid vehicle as an example of a vehicle to which the present invention can be applied. The series hybrid vehicle includes a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 used as a power-generating internal combustion engine that drives the power-generating motor-generator 1 in response to a power demand, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that stores the generated power. The power obtained by the internal combustion engine 2 driving the power-generating motor-generator 1 is stored in the battery 5 via an inverter device (not shown). The traction motor-generator 4 is driven and controlled using the power from the battery 5. The power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0012] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. Information such as the accelerator pedal position and vehicle speed (not shown) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. Such a series hybrid vehicle has two driving modes: an EV mode in which the vehicle runs on power from the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of the internal combustion engine 2. Even if the SOC is above the lower limit, the internal combustion engine 2 is driven and the vehicle runs in the HEV mode when the required driving force of the vehicle is relatively large. Therefore, the internal combustion engine 2 repeatedly performs combustion operation and stops of combustion operation while the main switch of the vehicle is on.

[0013] 2 shows the configuration of the intake system and exhaust system of the internal combustion engine 2. The internal combustion engine 2 of one embodiment is a four-stroke spark-ignition gasoline engine equipped with a turbocharger 13 as a supercharger, and is, for example, a so-called direct injection type internal combustion engine in which a fuel injection valve injects fuel directly into the cylinder. It may also be a port injection type.

[0014] A compressor 15 of a turbocharger 13 is disposed in the intake passage 12 of the internal combustion engine 2, and an electronically controlled throttle valve 21 that controls the amount of intake air is disposed downstream of the compressor 15. A water-cooled intercooler 22, for example, that cools the supercharged intake air is disposed between the compressor 15 and the throttle valve 21. An air cleaner 28 is disposed upstream of the compressor 15, and a vacuum generating valve 27 that generates the vacuum required for exhaust gas recirculation is disposed between the compressor 15 and the air cleaner 28. The throttle valve 21 and the vacuum generating valve 27 are both butterfly valves with circular valve bodies, and the opening degrees of each are controlled by the engine controller 8.

[0015] An exhaust turbine 14 of a turbocharger 13 is disposed in an exhaust passage 11 of the internal combustion engine 2. Downstream of the exhaust turbine 14, an electrically heated catalyst (hereinafter referred to as EHC) 17, which serves as an upstream catalytic converter using, for example, a three-way catalyst, and a downstream catalytic converter 18 using, for example, a three-way catalyst, are disposed. The EHC 17 of the embodiment is a porous monolithic ceramic carrier formed using a conductive ceramic material such as SiC, coated with a three-way catalyst. The monolithic carrier itself generates heat when energized. A heater separate from the monolithic carrier may also be provided. An exhaust silencer 19 is disposed downstream of the downstream catalytic converter 18 in the exhaust passage 11, and the exhaust passage 11 is opened to the outside via the exhaust silencer 19. An upstream air-fuel ratio sensor 31 is disposed at the inlet side of the EHC 17 in the exhaust passage 11, and a downstream air-fuel ratio sensor 32 is disposed at the outlet side.

[0016] An exhaust gas recirculation passage 24 for recirculating a portion of the exhaust gas to the intake system is provided between the exhaust passage 11 and the intake passage 12. A base end 24a of the exhaust gas recirculation passage 24 branches off from the exhaust passage 11 downstream of the exhaust turbine 14, more specifically, between the EHC 17 and the downstream catalytic converter 18. A tip end 24b is connected to the intake passage 12 at a position upstream of the compressor 15. The exhaust gas recirculation passage 24 includes, for example, a water-cooled EGR gas cooler 26 for cooling the recirculated exhaust gas, and an EGR valve 25 whose opening is variably controlled by the engine controller 8.

[0017] 1 receives detection signals from a variety of sensors, not shown in detail, directly or via other controllers, such as an air flow meter that detects the amount of intake air, the above-mentioned air-fuel ratio sensors 31 and 32 that detect the exhaust air-fuel ratio, a crank angle sensor that detects the engine speed, a water temperature sensor that detects the coolant temperature, a boost pressure sensor that detects the boost pressure, an accelerator position sensor that detects the amount of depression of the accelerator pedal, an atmospheric pressure sensor that detects the atmospheric pressure, an outside air temperature sensor, etc. Based on these detection signals and requests from the other controllers, the engine controller 8 optimally controls the fuel injection amount and injection timing, ignition timing, the opening of the throttle valve 21, the boost pressure, the EGR rate, the opening of the vacuum generating valve 27, etc.

[0018] 3 is a time chart illustrating the operation of the first embodiment. From top to bottom, the chart shows (a) EHC current supply power, (b) EHC temperature, (c) EHC resistance value, (d) rotation speed of the internal combustion engine 2, (e) output of the air-fuel ratio sensor (particularly the downstream air-fuel ratio sensor 32), more specifically the oxygen concentration based on the air-fuel ratio sensor output, and (f) air-fuel ratio. The dashed line in column (e) indicates the oxygen concentration detected by the upstream air-fuel ratio sensor 31.

[0019] In this example, a request to start the internal combustion engine 2 is made at time t1 due to, for example, a drop in the SOC of the battery 5, and the EHC 17 begins to be energized. Thereafter, at time t2, it is estimated that the temperature of the EHC 17 has approached its activation temperature, and motoring of the internal combustion engine 2 is initiated by powering the power-generator motor-generator 1 to allow air to flow through the EHC 17. In the illustrated example, it is estimated that the temperature of the EHC 17 has approached its activation temperature when its resistance value falls below a predetermined resistance value. There is a correlation between the temperature and resistance value of the EHC 17, as shown in FIG. 6, and it is possible to estimate the temperature of the EHC 17 based on the resistance value. However, as shown by the dashed line in FIG. 6, the temperature-resistance characteristic varies due to individual differences and deterioration, making it impossible to precisely determine whether the EHC 17 has reached its activation state.

[0020] Because air flows through the EHC 17 when the internal combustion engine 2 is motoring, the upstream air-fuel ratio sensor 31 outputs an output that generally corresponds to the oxygen concentration of the air. The output of the downstream air-fuel ratio sensor 32 is also not significantly different from that of the upstream air-fuel ratio sensor 31 when the EHC 17 is inactive. Because the EHC 17 continues to be energized after time t2, the EHC 17 eventually becomes activated. As this catalyst becomes active, oxygen is stored in the EHC 17 due to the oxygen storage capacity of the three-way catalyst, and oxygen is consumed by catalytic action, resulting in a decrease in the oxygen concentration output by the downstream air-fuel ratio sensor 32. Based on this decrease in oxygen concentration, it is determined that the catalyst has become activated at time t3. This causes the internal combustion engine 2 to start combustion operation, and the energization of the EHC 17 ends.

[0021] In one example, the catalyst is determined to have reached an activated state when the oxygen concentration of the downstream air-fuel ratio sensor 32 becomes lower than the oxygen concentration of the upstream air-fuel ratio sensor 31. In another example, the integral of the difference between the oxygen concentration of the upstream air-fuel ratio sensor 31 and the oxygen concentration of the downstream air-fuel ratio sensor 32 is calculated, and the catalyst is determined to have reached an activated state when this integral value reaches a predetermined value. In yet another example, assuming that the gas introduced into the exhaust system by motoring is air, the catalyst is determined to have reached an activated state when the oxygen concentration of the downstream air-fuel ratio sensor 32 becomes a predetermined oxygen concentration or lower.

[0022] In addition, if the oxygen concentration of the downstream air-fuel ratio sensor 32 becomes lower than the oxygen concentration of the upstream air-fuel ratio sensor 31 at time t2 or before time t2, the internal combustion engine 2 may be started to operate in combustion mode, assuming that the catalyst is already in an activated state.

[0023] 4 shows a time chart of a second embodiment in which the EHC 17 starts to be energized when the main switch (Ready SW) of the vehicle is turned on. In this second embodiment, the air-fuel ratio is enriched when the combustion operation of the internal combustion engine 2 is stopped, and the amount of oxygen storage in the EHC 17 is kept low.

[0024] From top to bottom, the diagram shows (g) the on / off state of the main switch (Ready SW), (h) the engine operation request flag, (i) the combustion operation permission flag, (a) the EHC current supply power, (b) the EHC temperature, (c) the EHC resistance value, (d) the rotation speed of the internal combustion engine 2, (e) the output of the air-fuel ratio sensor (particularly the downstream air-fuel ratio sensor 32), more specifically the oxygen concentration based on the air-fuel ratio sensor output, and (f) the air-fuel ratio.

[0025] In this example, the main switch is turned off at time t11, stopping combustion operation, and enriching the air-fuel ratio at that time. At time t12, the internal combustion engine 2 is stopped, and the vehicle is also stopped. The enrichment of the air-fuel ratio just before stopping reduces the oxygen storage amount in the EHC 17. Thereafter, at time t13, the main switch is turned on to resume driving, and the EHC 17 begins to be energized. At time t14, the resistance value of the EHC 17 falls below a predetermined resistance value, which indicates that its temperature is approaching the activation temperature. The engine operation request flag is turned on, and motoring of the internal combustion engine 2 is started by powering the power-generating motor-generator 1 described above.

[0026] As in the first embodiment described above, the oxygen concentration output by the downstream air-fuel ratio sensor 32 decreases as the catalyst of the EHC 17 becomes active. Based on this decrease in oxygen concentration, it is determined that the catalyst has become active at time t15. This causes the combustion operation of the internal combustion engine 2 to start, and the energization of the EHC 17 to end. Immediately after the start of the combustion operation, the air-fuel ratio is enriched to offset the oxygen supplied by motoring.

[0027] In this second embodiment, when the combustion operation of the internal combustion engine 2 is stopped, the amount of oxygen stored in the EHC 17 is reduced by enriching the air-fuel ratio, so that it is possible to reliably obtain a decrease in the oxygen concentration of the downstream air-fuel ratio sensor 32 due to catalytic activation.

[0028] 5 shows a time chart of a third embodiment in which the EHC 17 is energized when the engine operation request flag is turned on. In this third embodiment, similar to the second embodiment, the air-fuel ratio is enriched when the combustion operation of the internal combustion engine 2 is stopped, and the oxygen storage amount of the EHC 17 is kept low.

[0029] As in FIG. 4, from top to bottom, the diagram shows (g) on / off of the main switch (Ready SW), (h) engine operation request flag, (i) combustion operation permission flag, (a) EHC current supply power, (b) EHC temperature, (c) EHC resistance value, (d) rotation speed of the internal combustion engine 2, (e) output of the air-fuel ratio sensor (particularly the downstream air-fuel ratio sensor 32), more specifically the oxygen concentration based on the air-fuel ratio sensor output, and (f) air-fuel ratio.

[0030] In this example, the main switch is turned off at time t21, stopping combustion operation, and enriching the air-fuel ratio at that time. At time t22, the internal combustion engine 2 is stopped, and the vehicle is also stopped. The enrichment of the air-fuel ratio just before stopping reduces the oxygen storage amount in the EHC 17. Thereafter, at time t23, the main switch is turned on to resume driving. Thereafter, at time t24, when the engine operation request flag is turned on, energization of the EHC 17 begins. At time t25, the resistance value of the EHC 17 falls below a predetermined resistance value, and it is estimated that its temperature has approached the activation temperature, and motoring of the internal combustion engine 2 by powering the power-generating motor-generator 1 begins.

[0031] As in the first embodiment described above, the oxygen concentration output by the downstream air-fuel ratio sensor 32 decreases as the catalyst of the EHC 17 becomes active. Based on this decrease in oxygen concentration, it is determined that the catalyst has become active at time t26. As a result, the combustion operation of the internal combustion engine 2 starts, and the energization of the EHC 17 ends. Immediately after the start of the combustion operation, the air-fuel ratio is enriched to offset the oxygen supplied by motoring.

[0032] In this third embodiment, when the combustion operation of the internal combustion engine 2 is stopped, the amount of oxygen stored in the EHC 17 is reduced by enriching the air-fuel ratio, so that it is possible to reliably obtain a decrease in the oxygen concentration of the downstream air-fuel ratio sensor 32 due to catalytic activation.

[0033] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, motoring is performed to supply gas containing oxygen. However, instead of motoring, air may be supplied upstream of the EHC 17 using a secondary air pump or the like. In addition, in the above embodiment, the approach to the activation temperature is estimated from the resistance value of the EHC 17. However, the approach to the activation temperature may be estimated based on the elapsed time since the start of power supply. Furthermore, while the above embodiment has been described using a series hybrid vehicle as an example, the present invention may also be applied to other types of hybrid vehicles and to the start of internal combustion engines other than hybrid vehicles. [Explanation of symbols]

[0034] 1...Power generating motor generator 2...Internal combustion engine 8...Engine controller 17…EHC 31...Upstream air-fuel ratio sensor 32...Downstream air-fuel ratio sensor

Claims

1. A start control method for an internal combustion engine, comprising: providing an electrically heated catalyst in an exhaust passage; energizing the electrically heated catalyst to preheat it before starting the internal combustion engine; and starting the internal combustion engine in a catalytically activated state, supplying a gas containing oxygen to the electrically heated catalyst when it is estimated that the catalyst temperature has approached an activation temperature after the start of energization of the electrically heated catalyst; While the gas is flowing, the oxygen concentration is detected on both the upstream and downstream sides of the electrically heated catalyst. When the oxygen concentration on the downstream side is lower than the oxygen concentration on the upstream side, the catalyst is deemed to have reached an activated state, and combustion operation of the internal combustion engine is started. A method for controlling the start of an internal combustion engine.

2. The electrically heated catalyst has a characteristic that its resistance value decreases as the temperature increases, After the start of energization of the electrically heated catalyst, when the resistance value decreases to a predetermined value, it is estimated that the catalyst temperature has approached the activation temperature.

2. The internal combustion engine start control method according to claim 1.

3. the internal combustion engine is an internal combustion engine that drives a generator in a hybrid vehicle, The gas is supplied to the electrically heated catalyst by Motoring is performed by powering the generator.

2. The internal combustion engine start control method according to claim 1.

4. The gas is supplied to the electrically heated catalyst by By supplying secondary air to the exhaust system, 2. The internal combustion engine start control method according to claim 1.

5. enriching the air-fuel ratio when the internal combustion engine is stopped; The oxygen storage capacity of the electrically heated catalyst is kept low.

2. The internal combustion engine start control method according to claim 1.

6. The catalyst is considered to have reached an active state when the oxygen concentration downstream is lower than the oxygen concentration upstream.

2. The internal combustion engine start control method according to claim 1.

7. The integral value of the difference between the oxygen concentration on the upstream side and the oxygen concentration on the downstream side is calculated, and when this integral value reaches a predetermined value, the catalyst is deemed to have reached an activated state.

2. The internal combustion engine start control method according to claim 1.

8. The gas is atmospheric air, When the downstream oxygen concentration is equal to or lower than a predetermined oxygen concentration, the catalyst is deemed to have reached an active state.

2. The internal combustion engine start control method according to claim 1.

9. A start control device for an internal combustion engine, which includes an electrically heated catalyst in an exhaust passage, and which preheats the electrically heated catalyst by energizing it before starting the internal combustion engine, and starts the internal combustion engine in an activated catalyst state, supplying a gas containing oxygen to the electrically heated catalyst when it is estimated that the catalyst temperature has approached an activation temperature after the start of energization of the electrically heated catalyst; While the gas is flowing, the oxygen concentration is detected on both the upstream and downstream sides of the electrically heated catalyst. When the oxygen concentration on the downstream side is lower than the oxygen concentration on the upstream side, the catalyst is deemed to have reached an activated state, and combustion operation of the internal combustion engine is started. A starting control device for an internal combustion engine.

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