Method and apparatus for controlling catalyst warm-up operation

Abstract

To make three of generation of negative pressure for a brake booster, ignition timing retard for warming up a catalyst, and securing of torque for maintaining idle operation coexist to the maximum.SOLUTION: An engine required torque to be generated for maintaining an idle operation is calculated (S1), a net target air amount required for the engine required torque is calculated when an ignition timing is MBT (S2), a required ignition timing retard amount required for warming up a three way catalytic converter is determined (S3), a retard target air amount required for realizing the engine required torque under an ignition timing according to the required ignition timing retard amount is calculated (S4, S5), and an upper limit differential pressure securing target air amount required for securing a negative pressure is calculated (S6). The retard target air amount and the differential pressure securing target air amount are compared with each other (S7), and when the retard target air amount is equal to or less than the differential pressure securing target air amount, the throttle valve is controlled according to the retard target air amount, and the ignition timing retard according to the required ignition timing retard amount is performed (S8 to 10).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and a control device for controlling catalyst warm-up operation in which an idling operation is performed with ignition timing retarded in order to warm up an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine. [Background technology]

[0002] In a spark ignition internal combustion engine equipped with an exhaust purification catalyst, a catalyst warm-up operation is generally performed with ignition timing retardation to warm up the exhaust purification catalyst when transitioning from cold start to idle operation.Patent Document 1 describes that ignition timing is retarded when the catalyst is not yet warmed up, and intake air amount increase / decrease control and ignition timing advance / retard control are combined to maintain the actual engine speed at a target idle speed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-180184 Summary of the Invention [Problem to be solved by the invention]

[0004] Vacuum-type brake boosters are known as one of the components of vehicle brake systems, and in many cases, the intake vacuum generated in the intake system of an internal combustion engine is used as the vacuum source for the vacuum-type brake booster. In such a configuration, it is necessary to achieve a high level of vacuum generation to prevent insufficient vacuum in the vacuum-type brake booster, retard the ignition timing for catalyst warm-up, and ensure torque for maintaining stable idling. Patent Document 1 does not disclose anything about vacuum generation. [Means for solving the problem]

[0005] The present invention is a catalyst warm-up operation control method for performing idling operation accompanied by ignition timing retardation in order to warm up an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, comprising: A torque that should be generated by the internal combustion engine to maintain idle operation is calculated as an engine required torque; Calculating the intake air amount required for the engine required torque when the ignition timing is MBT as a net target air amount; determining a required ignition timing retard amount necessary for warming up the exhaust purification catalyst; calculating an intake air amount required to realize the required engine torque under an ignition timing according to the required ignition timing retard amount as a retard target air amount; an upper limit of the intake air amount required to ensure negative pressure downstream of the air amount control device in the intake passage is calculated as a target air amount for ensuring differential pressure; The retard target air amount is compared with the differential pressure ensuring target air amount, and if the retard target air amount is equal to or less than the differential pressure ensuring target air amount, the air amount control device is controlled in accordance with the retard target air amount, and the ignition timing is retarded in accordance with the required ignition timing retard amount.

[0006] Because ignition timing retardation reduces the torque of the internal combustion engine, the target air retard amount required to achieve the required engine torque under the required ignition timing retard amount is greater than the net target air amount when the ignition timing is MBT. If the target air retard amount is equal to or less than the target air amount required to ensure negative pressure, the air amount control device is controlled according to this target air retard amount, and at the same time, the ignition timing is retarded according to the required ignition timing retard amount. In other words, it is possible to obtain a sufficient level of negative pressure while ensuring the required engine torque required to maintain idle operation, and to retard the ignition timing according to the required ignition timing retard amount. [Effects of the Invention]

[0007] According to this invention, it is possible to achieve a high level of coexistence of the three elements of generating a sufficient level of negative pressure, retarding the ignition timing to warm up the catalyst, and ensuring torque to maintain stable idle operation. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram showing the configuration of an internal combustion engine that performs catalyst warm-up control according to an embodiment; [Figure 2] 4 is a flowchart showing a process flow of catalyst warm-up control in one embodiment. [Figure 3] 10 is a flowchart showing a process for correcting the target idle rotation speed when the retard target air amount exceeds the target air amount for ensuring differential pressure. [Figure 4] 10 is a flowchart showing a process for correcting the target idle rotation speed when the net target air amount exceeds the target air amount for ensuring differential pressure. [Figure 5] FIG. 10 is a characteristic diagram showing an example of efficiency vs. retard angle characteristic. [Figure 6] 10 is an explanatory diagram showing a comparison of air amounts such as a net target air amount and a retarded target air amount and ignition timing settings, with the horizontal axis representing axial torque. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an internal combustion engine 1 of one embodiment to which the present invention is applied. The internal combustion engine 1 of the one embodiment is a four-stroke spark-ignition internal combustion engine (a so-called gasoline engine) used to drive a vehicle, and each cylinder is provided with an intake valve 2, an exhaust valve 3, and an ignition plug 4. The illustrated example is configured as a direct injection type engine, and a fuel injection valve 5 that injects fuel into the cylinder is disposed, for example, on the intake valve 2 side. Note that the engine may also be configured as a port injection type in which fuel is injected toward an intake port 6.

[0010] An electronically controlled throttle valve 10, whose opening is controlled by a control signal from an engine controller 9, is disposed upstream of a collector section 8 in an intake passage 7 connected to the intake port 6 of each cylinder, as an air amount control device. An air flow meter 11 that detects the amount of intake air is disposed upstream of the throttle valve 10, and an air cleaner 12 is disposed further upstream. The vehicle brake device (not shown) is equipped with a vacuum-type brake booster, and vacuum (so-called intake vacuum) taken from a position downstream of the throttle valve 10 in the intake passage 7, for example from the collector section 8, is supplied to the vacuum-type brake booster as a vacuum source via a vacuum passage.

[0011] The exhaust ports 13 of each cylinder are joined together to form a single exhaust passage 14, which is provided with an exhaust purification catalyst for purifying the exhaust, such as a three-way catalyst 15. The three-way catalyst 15 is, for example, a monolithic ceramic catalyst in which a catalyst layer containing catalytic metal is coated on the surface of a monolithic ceramic body having fine passages formed therein. The three-way catalyst 15 may also be configured to further include a downstream catalyst (a so-called underfloor catalyst) arranged in series.

[0012] An upstream air-fuel ratio sensor 19 for detecting the air-fuel ratio of exhaust gas discharged from the internal combustion engine 1 is disposed on the inlet side of the three-way catalyst 15 in the exhaust passage 14, i.e., on the upstream side of the three-way catalyst 15. This upstream air-fuel ratio sensor 19 is a so-called wide-range air-fuel ratio sensor that obtains an output corresponding to the exhaust air-fuel ratio. Furthermore, a downstream air-fuel ratio sensor 20 is disposed on the outlet side or downstream side of the three-way catalyst 15, that detects the air-fuel ratio of exhaust gas flowing out from the three-way catalyst 15. Like the upstream air-fuel ratio sensor 19, the downstream air-fuel ratio sensor 20 is a wide-range air-fuel ratio sensor that obtains an output corresponding to the exhaust air-fuel ratio. Note that the air-fuel ratio sensors 19, 20 may be so-called O2 sensors.

[0013] Detection signals from the air-fuel ratio sensors 19, 20 and the air flow meter 11 are input to the engine controller 9. Further detection signals from a number of sensors, such as a crank angle sensor 21 for detecting the engine speed, a water temperature sensor 22 for detecting the coolant temperature, an accelerator position sensor 23 for detecting the depression amount of the accelerator pedal operated by the driver, and an atmospheric pressure sensor 24 for detecting the atmospheric pressure, are input to the engine controller 9. Based on these input signals, the engine controller 9 optimally controls the amount and timing of fuel injection by the fuel injection valve 5, the ignition timing by the spark plug 4, the opening of the throttle valve 10, etc.

[0014] As one of various controls of the internal combustion engine 1, the engine controller 9 performs a catalyst warm-up operation with ignition timing retardation to warm up the three-way catalyst 15 during idling operation after a cold start of the internal combustion engine 1. The catalyst warm-up operation starts immediately after cranking of the internal combustion engine 1 ends and the engine transitions to self-sustaining operation, and ends when the warm-up of the three-way catalyst 15 is complete (for example, when the catalyst temperature estimated from the input heat amount reaches a predetermined temperature). The catalyst warm-up operation also ends when the vehicle starts moving, that is, when the engine transitions to non-idling operation. During this catalyst warm-up operation, three things are simultaneously taken into consideration: early warm-up of the three-way catalyst 15, maintenance of stable idling operation, and ensuring vacuum for the vacuum-pressure brake booster.

[0015] 2 is a flowchart showing the process flow of catalyst warm-up control according to one embodiment, which is executed during idle operation after a cold start. The routine shown in this flowchart is repeatedly executed by the engine controller 9. During idle operation, idle speed control is executed by another routine (not shown). In idle speed control, the actual speed of the internal combustion engine 1 is detected by the crank angle sensor 21, and an appropriate feedback control is used to increase or decrease, for example, the intake air amount or the engine torque requirement so that the actual speed converges to a target idle speed.

[0016] First, in step 1, the torque that the internal combustion engine should generate to maintain idle operation is calculated as the engine required torque. This engine required torque is calculated by taking into account the load during idle operation (for example, the load due to the torque converter, etc.), various losses associated with idle operation, and the loads of various accessories driven by the internal combustion engine 1. The engine required torque also includes the increase / decrease in torque that is feedback controlled for the above-mentioned idle speed control.

[0017] In step 2, the amount of intake air required for the engine required torque when the ignition timing is MBT (in other words, basic ignition timing) is calculated as a net target air amount based on the engine required torque calculated in step 1. Note that, since the internal combustion engine 1, which is a spark ignition internal combustion engine, basically performs air-fuel ratio control with the stoichiometric air-fuel ratio as a target, an amount of fuel corresponding to the amount of intake air is supplied to the internal combustion engine 1, and therefore, basically, a torque corresponding to the amount of intake air is generated.

[0018] Next, in step 3, the required ignition timing retard amount required for warming up the three-way catalyst 15 is calculated. Here, the maximum ignition timing retard amount is set within constraints such as combustion noise and vibration so that catalyst warming is completed as quickly as possible. Note that whether catalyst warm-up operation is required (in other words, whether ignition timing retard is required) itself is determined based on the coolant temperature, catalyst temperature (estimated temperature), etc.

[0019] In step 4, torque efficiency is calculated, which is the ratio of torque under MBT to torque under ignition timing retarded according to the required ignition timing retard amount, based on the required ignition timing retard amount determined in step 3. In one embodiment, the correlation between torque efficiency and ignition timing retard amount is calculated in advance as an efficiency-retard amount characteristic, as shown in FIG. 5, and stored as a table in engine controller 9. Therefore, in step 4, torque efficiency for the required ignition timing retard amount is calculated by referring to this table. As shown in FIG. 5, the torque efficiency decreases as the ignition timing retard amount increases. In other words, the torque obtained with the same intake air amount (fuel amount) decreases. Although FIG. 5 shows only one characteristic, this characteristic varies slightly depending on the operating point (combination of engine speed and load) during idle operation, and in reality, a table is provided for each operating point. Note that instead of using a table, torque efficiency corresponding to the required ignition timing retard amount may be calculated using an arithmetic expression that approximates the characteristic shown in FIG. 5.

[0020] Using the torque efficiency thus determined, in the next step 5, the amount of intake air required to achieve the required engine torque at an ignition timing that matches the required ignition timing retard amount is calculated as the retard target air amount. Basically, the retard target air amount is calculated as "retard target air amount = net target air amount / torque efficiency." Because the torque efficiency when the ignition timing is retarded is less than 100%, the retard target air amount is greater than the net target air amount.

[0021] In the next step 6, the upper limit of the intake air amount required to ensure the negative pressure that serves as the negative pressure source for the vacuum-pressure brake booster is calculated as the target air amount for ensuring differential pressure. That is, the greater the opening of the throttle valve 10 and the greater the intake air amount, the lower the negative pressure, so a target air amount for ensuring differential pressure corresponding to the required level of negative pressure is determined. This target air amount for ensuring differential pressure is calculated based on the actual atmospheric pressure detected by the atmospheric pressure sensor 24. Corrections for other factors such as engine speed, compression ratio, water vapor partial pressure, and, if a variable valve mechanism is provided, the valve timing thereof, may also be added.

[0022] Next, proceeding to step 7, the magnitude of the retardation target air amount is compared with the differential pressure ensuring target air amount. If the retardation target air amount is equal to or less than the differential pressure ensuring target air amount, proceed to step 8, and the retardation target air amount is set as the final target air amount. Then, in step 9, the intake amount control device is controlled in accordance with the target air amount, i.e., the retardation target air amount. For example, the opening of the throttle valve 10 as the air amount control device is controlled in accordance with the retardation target air amount. Note that a valve provided in a bypass passage that bypasses the throttle valve 10 may also be used as the air amount control device. Also, in step 10, ignition timing is retarded in accordance with the required ignition timing retard amount. In other words, the final ignition timing is determined by adding the ignition timing retard amount to the MBT.

[0023] On the other hand, if the retard target air amount is greater than the differential pressure ensuring target air amount, the process proceeds to step 11, where the differential pressure ensuring target air amount is set as the final target air amount. Then, in step 12, the intake air amount control device is controlled in accordance with the target air amount, i.e., the differential pressure ensuring target air amount. For example, the opening of the throttle valve 10 as the air amount control device is controlled in accordance with the differential pressure ensuring target air amount. Also, in step 13, the maximum ignition timing retard amount that can achieve the engine required torque under the differential pressure ensuring target air amount is calculated, and the ignition timing is retarded in accordance with this possible ignition timing retard amount. For example, torque efficiency can be calculated as the ratio between the net target air amount and the differential pressure ensuring target air amount, and the possible ignition timing retard amount can be calculated from the correlation between torque efficiency and ignition timing retard amount shown in Figure 5.

[0024] This type of control allows the three objectives of generating a sufficient level of negative pressure, retarding the ignition timing to warm up the catalyst, and ensuring torque to maintain stable idle operation to the maximum extent possible.

[0025] FIG. 6 is an explanatory diagram showing the relationship between the various target air amounts and ignition timing settings (ignition timing retard amount). The horizontal axis represents the axial torque, which indicates the magnitude of the engine torque requirement (in other words, the net target air amount). The upper (a) column shows the net target air amount L1, the target air amount L2 for ensuring differential pressure, and the target air amount L3 for retard. The characteristic shown by the thick solid line L4 is the target air amount that is ultimately controlled by the air amount control device. The net target air amount L1 is shown as a straight line with an appropriate slope, while the target air amount L3 for retard is shown as a straight line with a steeper slope corresponding to the decrease in torque efficiency. The target air amount L2 for ensuring differential pressure is shown as a constant air amount. The lower (b) column shows the ignition timing setting, including MBT and the ignition timing ADV after retard. The distance from the MBT line to the ignition timing ADV corresponds to the ignition timing retard amount.

[0026] The section of FIG. 6 up to torque Te1 on the horizontal axis corresponds to the processing in steps 8 to 10 of the flowchart in FIG. 2. Here, the final target air amount L4 is in line with the retard target air amount L3. In this section, the required ignition timing retard amount, which is the maximum retard amount, can be obtained. Furthermore, since the target air amount L4 (retard target air amount L3) is smaller than the differential pressure ensuring target air amount L2 as shown in the figure, a sufficient level of negative pressure is ensured.

[0027] The section from torque Te1 to torque Te2 in FIG. 6 corresponds to the processing in steps 11 to 13 in the flowchart of FIG. 2. Here, the final target air amount L4 is in line with the target air amount L2 for ensuring differential pressure. Therefore, a sufficient level of negative pressure is generated. In this section, as shown in the figure, the maximum possible ignition timing retard amount is obtained.

[0028] The torque Te1 corresponds to the engine required torque at which the retard target air amount L3 is equal to the differential pressure ensuring target air amount L2.

[0029] Torque Te2 corresponds to the engine torque required when the net target air amount L1 is equal to the target air amount L2 for ensuring differential pressure. Although not shown in the flowchart of Figure 2, if the net target air amount L1 exceeds the target air amount L2 for ensuring differential pressure, the final target air amount L4 will be in line with the net target air amount L1. Then, the ignition timing becomes MBT.

[0030] Here, the air amount and ignition timing retardation limit based on the target air amount L2 for ensuring differential pressure in the range from torque Te1 to torque Te2 may be limited intermittently. For example, if the limit based on the target air amount L2 for ensuring differential pressure is released, control will be performed in accordance with the retard target air amount L3 and the required ignition timing retard amount, as in the range up to torque Te1. Negative pressure generation for the vacuum-type brake booster does not necessarily have to be performed continuously.

[0031] Next, a second embodiment will be described in which the idle speed is increased to make it more advantageous to retard the ignition timing in the range from torque Te1 to torque Te2. Fig. 3 is a flowchart showing the main part of the process for correcting the target idle speed, which is executed together with the process shown in the flowchart of Fig. 2.

[0032] In step 21, the retard target air amount is compared with the differential pressure ensuring target air amount, and if the retard target air amount is equal to or less than the differential pressure ensuring target air amount, the process proceeds to step 22, where the target idle speed remains the normal basic target idle speed. On the other hand, if the retard target air amount is greater than the differential pressure ensuring target air amount, the process proceeds to step 23, where the target idle speed is set to a high target idle speed that is higher than the basic target idle speed. Increasing the idle speed in this way increases the margin for ignition timing retard, and increases the amount of ignition timing retard that can be achieved in the range from torque Te1 to torque Te2 in FIG. 6.

[0033] Next, a third embodiment will be described in which the idle speed is increased in the same manner as in the second embodiment to favor negative pressure generation in the range where the torque is greater than the torque Te2. Fig. 4 is a flowchart showing the main part of the process for correcting the target idle speed, which is executed together with the process shown in the flowchart of Fig. 2.

[0034] In step 31, the net target air volume is compared with the differential pressure target air volume. If the net target air volume is equal to or less than the differential pressure target air volume, the process proceeds to step 32, where the target idle speed remains the normal basic target idle speed. On the other hand, if the net target air volume is greater than the differential pressure target air volume, the process proceeds to step 33, where the target idle speed is set to a high target idle speed higher than the basic target idle speed. Increasing the idle speed in this way reduces the amount of air in the cylinder per cycle, reducing absolute pressure. In other words, the vacuum increases. Note that increasing the idle speed slightly increases the opening of the air volume control device, i.e., the throttle valve 10. However, the effect of increasing the number of cycles per unit time is relatively large, resulting in a higher vacuum. Therefore, vacuum is generated in the section after torque Te2 in FIG. 6, which allows for ignition timing retardation.

[0035] The correction of the target idle speed in the third embodiment can be applied in combination with the correction of the target idle speed in the section from torque Te1 to torque Te2 in the second embodiment in Fig. 6. In this case, the specific value of the high target idle speed may be different for each, or may be the same target idle speed. [Explanation of symbols]

[0036] 1...Internal combustion engine 4...Spark plug 9...Engine controller 10...Throttle valve 15...Three-way catalyst 21...Crank angle sensor

Claims

1. A catalyst warm-up operation control method for performing idle operation accompanied by ignition timing retardation in order to warm up an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, comprising: A torque that should be generated by the internal combustion engine to maintain idle operation is calculated as an engine required torque; calculating a net target air amount required for the required engine torque when the ignition timing is MBT; determining a required ignition timing retard amount necessary for warming up the exhaust purification catalyst; calculating an intake air amount required to realize the required engine torque under an ignition timing according to the required ignition timing retard amount as a retard target air amount; an upper limit of the intake air amount required to ensure negative pressure downstream of the air amount control device in the intake passage is calculated as a target air amount for ensuring differential pressure; comparing the retardation target air amount with the differential pressure ensuring target air amount, and if the retardation target air amount is equal to or less than the differential pressure ensuring target air amount, controlling the air amount control device in accordance with the retardation target air amount and retarding the ignition timing in accordance with the required ignition timing retard amount; A method for controlling catalyst warm-up operation.

2. When the retard target air amount is larger than the differential pressure ensuring target air amount, the air amount control device is controlled in accordance with the differential pressure ensuring target air amount, and an ignition timing retard amount corresponding to the differential pressure ensuring target air amount is calculated and the ignition timing is retarded in accordance with this. The catalyst warm-up control method according to claim 1 .

3. When the retard target air amount is larger than the differential pressure ensuring target air amount, the target idle rotation speed is corrected to be higher. The catalyst warm-up control method according to claim 1 .

4. the net target air amount is compared with the target air amount for ensuring differential pressure, and when the net target air amount is greater than the target air amount for ensuring differential pressure, the target idle rotation speed is corrected to be higher; The catalyst warm-up control method according to claim 1 .

5. 3. The catalyst warm-up operation control method according to claim 2, wherein the air amount and the ignition timing retard are restricted intermittently based on the target air amount for ensuring differential pressure.

6. The target air amount to ensure the differential pressure is calculated taking into account the actual atmospheric pressure. The catalyst warm-up control method according to claim 1 .

7. A control device for catalyst warm-up operation that performs idling with ignition timing retardation in order to warm up an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, an ignition device that performs ignition timing retard; an air amount control device that adjusts the amount of intake air in the internal combustion engine; A controller; Equipped with The above controller is an engine required torque calculation unit that calculates a torque that should be generated by the internal combustion engine to maintain idle operation as an engine required torque; a net target air amount calculation unit that calculates an intake air amount required for the required engine torque when the ignition timing is MBT as a net target air amount; a required ignition timing calculation unit that determines a required ignition timing retard amount necessary for warming up the exhaust purification catalyst; a retardation target air amount calculation unit that calculates, as a retardation target air amount, an intake air amount required to achieve the required engine torque under an ignition timing according to the required ignition timing retard amount; a differential pressure ensuring target air amount calculation unit that calculates an upper limit of the intake air amount necessary to ensure negative pressure downstream of the air amount control device in the intake passage as a differential pressure ensuring target air amount; a control unit that compares the retardation target air amount with the differential pressure ensuring target air amount, and if the retardation target air amount is equal to or less than the differential pressure ensuring target air amount, controls the air amount control device in accordance with the retardation target air amount and retards the ignition timing in accordance with the required ignition timing retard amount; Equipped with A control device for catalyst warm-up operation.

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