Catalyst warm-up control method and catalyst warm-up control device for internal combustion engine

Abstract

An internal combustion engine (1) mounted on a series hybrid vehicle for power generation has an upstream catalyst converter (8) and a downstream catalyst converter (9) in an exhaust system. If the temperature of the upstream catalyst converter (8) is less than or equal to a threshold value at the start of the internal combustion engine (1), low-speed / low-load operation is performed so that the ignition timing is greatly retarded. If it is determined that the upstream catalyst converter (8) is warmed up based on the amount of heat input, the operation is switched to an operation at a rotational speed and load at which the ignition timing is near the MBT point and is set to be near the optimum fuel consumption point. Until it is determined that the catalyst of the downstream catalyst converter (9) is warmed up, the operation of the internal combustion engine (1) is continued regardless of a request for power generation. If it is determined that the downstream catalyst converter (9) is warmed up based on the amount of heat input, the stop of the internal combustion engine (1) is permitted.

Description

TECHNICAL FIELD

[0001] The present application relates to catalyst warm-up control after start of an internal combustion engine in a series hybrid vehicle. BACKGROUND

[0002] Patent Document 1 discloses a technique in which, as catalyst warm-up control of an internal combustion engine of a hybrid vehicle in which both the internal combustion engine and a motor generator are provided as travel drive sources, the operating conditions such as the load of the internal combustion engine are made different in warm-up operation of a first catalyst located on the upstream side of an exhaust system and in warm-up operation of a second catalyst located on the downstream side.

[0003] However, in this prior art, a structure is formed in which, if the requested output of the internal combustion engine decreases according to the vehicle travel state, the internal combustion engine is stopped even if the catalyst warm-up is not complete. Therefore, exhaust purification of the internal combustion engine is not necessarily sufficiently achieved.

[0004] Patent Document 2 is also structured such that the internal combustion engine is stopped when the requested output of the internal combustion engine decreases during catalyst warm-up operation. Furthermore, Patent Document 2 describes, as a non-preferred example, an example in which the operation of the internal combustion engine is continued until the catalyst warm-up is complete, but only one catalyst corresponding to the upstream catalyst is disclosed, and multiple catalysts are not considered.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-112962

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-120853 SUMMARY

[0007] Regarding the catalyst warm-up control of the present application, in an internal combustion engine mounted in a series hybrid vehicle for power generation and started / stopped according to a power generation request from the vehicle side,

[0008] After start of the internal combustion engine, the catalyst warm-up states of a first catalyst located on the upstream side and a second catalyst located on the downstream side of the exhaust system are detected or estimated respectively,

[0009] Until it is determined that the warm-up of the two catalysts is complete, the operation of the internal combustion engine is continued regardless of the power generation request.

[0010] The internal combustion engine is continued to operate like this until the warm-up of the second catalyst is complete, and therefore the exhaust performance of the internal combustion engine becomes good. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a system configuration diagram of an internal combustion engine that represents one embodiment of the present application.

[0012] Figure 2 This is a flowchart showing catalyst warm-up control after the internal combustion engine is started.

[0013] Figure 3 This is the functional module diagram of the same catalyst warm-up control.

[0014] Figure 4 This is a time chart showing an example of catalyst warm-up control. DETAILED DESCRIPTION

[0015] Hereinafter, one embodiment of the present invention will be described in detail based on the accompanying drawings. Figure 1 The following shows the system configuration of an internal combustion engine 1, which is one embodiment of the present invention. This internal combustion engine 1 is used for power generation and is installed in a series hybrid vehicle. A series hybrid vehicle is a hybrid vehicle in which a generator driven by the internal combustion engine generates electricity, and the generated electricity drives an electric motor for travel. Specifically, the series hybrid vehicle comprises: a generator-type electric generator that primarily functions as a generator; an internal combustion engine 1 that functions as a generator-type internal combustion engine and drives the generator-type electric generator in response to power demand; a motor-type electric generator that primarily functions as a motor to drive the drive wheels; a battery that temporarily stores the generated electricity; and an inverter device that converts power between the battery and each motor-type electric generator.

[0016] like Figure 1 As shown, an internal combustion engine 1 of one embodiment is a four-stroke spark-ignition gasoline internal combustion engine equipped with a turbocharger 2. An exhaust turbine 3 of the turbocharger 2 is disposed in an exhaust passage 7 of the internal combustion engine 1. Downstream of the exhaust turbine 3, an upstream catalytic converter 8 and a downstream catalytic converter 9, each utilizing, for example, a three-way catalyst, are disposed in sequence. Typically, the upstream catalytic converter 8 is mounted at the outlet of the exhaust turbine 3 within the engine compartment, while the downstream catalytic converter 9 is disposed under the vehicle floor. Further downstream, an exhaust muffler 11 is disposed in the exhaust passage 7, opening the exhaust passage 7 to the exterior.

[0017] The turbocharger 2 includes a bypass passage 4a for connecting the outlet side and the inlet side of the exhaust turbine 3 in order to control the boost pressure, and an electric wastegate valve 4 for opening and closing the bypass passage 4a.

[0018] The intake passage 14 of the internal combustion engine 1 is provided with the above-described compressor 6 of the turbocharger 2, and on a more downstream side than the compressor 6, an electronically controlled throttle valve 15 that controls the amount of intake air is provided. The throttle valve 15 is located at the inlet portion of a manifold portion 16, and on a more downstream side than the manifold portion 16, the intake passage 14 branches for each cylinder as an intake runner. An intercooler 17 that cools the supercharged intake air, for example, a water-cooled type, is provided between the upstream side of the manifold portion 16, that is, between the compressor 6. In addition, the manifold portion 16 is provided with a pressure sensor 18 that detects the intake air pressure (supercharging pressure) in the manifold portion 16.

[0019] Further, in the present application, the internal combustion engine 1 can be a naturally aspirated mechanism that does not have a supercharger.

[0020] An air cleaner 23 is provided at the most upstream portion of the above-described intake passage 14, and on the downstream side of the air cleaner 23, an air flow meter 24 that detects the amount of intake air is provided.

[0021] Between the above-described exhaust passage 7 and the above-described intake passage 14, an exhaust recirculation passage 26 for recirculating a portion of the exhaust gas to the intake system is provided. One end of the exhaust recirculation passage 26, which is the upstream end, branches from the downstream side of the upstream side catalyst converter 8 of the exhaust passage 7. Further, the other end, which is the downstream end, is connected to the intake passage 14 at a position on the upstream side of the compressor 6. In the middle of the above-described exhaust recirculation passage 26, an exhaust recirculation control valve 27 that variably controls the opening degree according to the operating conditions is interposed, and on a position more on the exhaust passage 7 side than the exhaust recirculation control valve 27, an EGR gas cooler 28 that cools the recirculated exhaust gas is provided.

[0022] An air-fuel ratio sensor 31 is provided on the inlet side of the above-described upstream side catalyst converter 8, and an oxygen sensor 32 is provided on the inlet side of the above-described downstream side catalyst converter 9. An exhaust gas temperature sensor 33 is provided on the outlet side of the downstream side catalyst converter 9.

[0023] The above-described internal combustion engine 1 is comprehensively controlled by an engine controller 12. In addition to the above-described air flow meter 24, pressure sensor 18, and the like, detection signals of various sensors such as a crank angle sensor 34 for detecting the engine rotational speed, a water temperature sensor 35 for detecting the cooling water temperature, an accelerator opening sensor 36 for detecting the depression amount of an accelerator pedal operated by the driver, and the like are input to the engine controller 12. The engine controller 12 controls the fuel injection amount from a fuel injection valve 37, the injection timing, the ignition timing of a spark plug 38, the opening of the throttle valve 15, the opening of the exhaust bypass valve 4, the opening of the exhaust gas recirculation control valve 27, and the like to be optimum based on the above-described detection signals. In addition, although not illustrated in detail, the internal combustion engine 1 of the embodiment has an intake side variable valve timing mechanism that changes the valve timing of an intake valve 41 and an exhaust side variable valve timing mechanism that changes the valve timing of an exhaust valve 42, and the engine controller 12 also appropriately controls the above-described variable valve timing mechanisms.

[0024] Further, at the time of cold start of the internal combustion engine 1, the engine controller 12 executes prescribed catalyst warm-up control in order to activate the catalyst converters 8, 9 early.

[0025] Figure 2 The flowchart shown in FIG. 6 represents the processing flow of the catalyst warm-up control performed by the engine controller 12. This Figure 2 The flow is started in conjunction with the start of the internal combustion engine 1. Further, after the vehicle is started, a request for power generation is generated so that the internal combustion engine 1 is started. First, in step 1, it is determined whether or not the upstream catalyst converter 8 is greater than or equal to the catalyst activation temperature at the time of start of the internal combustion engine 1. This is determined by comparing the catalyst temperature estimated based on the information of the catalyst temperature at the time of end of the last trip (i.e., at the time of cut-off, which is found from the detected temperature of the exhaust temperature sensor 33), and the elapsed time from the end of the last trip, with a prescribed threshold value (corresponding to the catalyst activation temperature). If the upstream catalyst converter 8 reaches the activation temperature, the processing after step 4 described later is immediately entered.

[0026] In the case of less than the activation temperature, i.e., if the upstream catalyst converter 8 is in a cold state, from step 1, the processing proceeds to step 2, a large ignition timing lag for catalyst warm-up is performed, and the internal combustion engine 1 is operated at a low load and a low engine rotational speed. The exhaust temperature is raised due to the ignition timing lag, and the combustion center is on the lag side, thereby promoting the warm-up of the catalyst, particularly the upstream catalyst converter 8.

[0027] Next, in step 3, the warm-up state of the upstream side catalyst converter 8 is estimated. Specifically, the heat input to the upstream side catalyst converter 8 per cycle (in other words, the heat that flows out from the exhaust port and moves toward the upstream side catalyst converter 8) is calculated based on the rotational speed, load, ignition timing (retardation amount), valve timing of the intake valve 41 and exhaust valve 42, exhaust gas recirculation rate, fuel injection timing, combustion pressure, and the like of the internal combustion engine 1, and sequentially accumulated. Further, the input heat to the upstream side catalyst converter 8 is compared with a prescribed threshold value (Ql), and if it is greater than or equal to the threshold value (Ql), it is determined that the warm-up of the upstream side catalyst converter 8 is completed. Until the input heat reaches the prescribed threshold value (Ql), the process returns from step 3 to step 2, and the operation at a low speed / low load with a large ignition timing retardation is continued. Further, the determination of the completion of the warm-up in step 3 is repeated. During this period, even if there is no request for power generation indicated to the internal combustion engine 1, the internal combustion engine 1 does not stop but continues to operate. Further, as the threshold value (Ql) of the input heat in the determination in step 3, it can be set variably in accordance with the temperature of the upstream side catalyst converter 8 at the start calculated in step 1, or it can be set to be constant regardless of the temperature of the upstream side catalyst converter 8 at the start.

[0028] If it is determined that the warm-up of the upstream side catalyst converter 8 is completed, the process proceeds from step 3 to step 4, and the operation of the internal combustion engine 1 is continued with the ignition timing retardation and the relative increase in the rotational speed and load. In other words, the ignition timing is set to be near the MBT, and the rotational speed and load are set to be near the optimal fuel consumption point. That is, the operation of the internal combustion engine 1 is continued in order to avoid excessive deterioration of the fuel consumption and in order to warm up the catalyst of the downstream side catalyst converter 9. Further, in the case where the estimated temperature of the upstream side catalyst converter 8 at the start of the internal combustion engine 1 is greater than or equal to the threshold value, the operation in which the ignition timing in step 4 is set to be near the MBT point near the optimal fuel consumption point is started immediately.

[0029] In the next step 5, the warm-up state of the downstream-side catalyst converter 9 is estimated. Specifically, as in step 3, the heat input to the downstream-side catalyst converter 9 (in other words, the heat that flows out of the exhaust port and moves to the downstream-side catalyst converter 9 via the upstream-side catalyst converter 8) is calculated based on the rotational speed, load, ignition timing, valve timing of the intake valve 41 and exhaust valve 42, exhaust backflow rate, fuel injection timing, combustion pressure, and the like of the internal combustion engine 1, and sequentially accumulated. Further, the input heat to the downstream-side catalyst converter 9 is compared with a prescribed threshold value (Q2), and if it is greater than or equal to the threshold value (Q2), it is determined that the warm-up of the downstream-side catalyst converter 9 is complete. Until the input heat reaches the prescribed threshold value (Q2), the operation at the vicinity of the optimal fuel consumption point without the ignition timing lag is continued from step 5 back to step 4. Further, the determination of the warm-up completion of step 5 is repeated. During this period, even if there is no request for power generation indicated to the internal combustion engine 1, the internal combustion engine 1 does not stop and continues to operate. Further, as the threshold value (Q2) of the input heat in the determination of step 5, it can be variably set according to the temperature of the downstream-side catalyst converter 9 at the time of start (which can be estimated differently from the upstream-side catalyst converter 8, or which can be calculated from the estimated temperature of the upstream-side catalyst converter 8), or it can be set to be constant regardless of the temperature of the downstream-side catalyst converter 9 at the time of start.

[0030] If it is determined that the warm-up of the downstream-side catalyst converter 9 is complete, it proceeds from step 5 to step 6, and the stop of the internal combustion engine 1 corresponding to the request for power generation is permitted. Thus, in the absence of the request for power generation, the internal combustion engine 1 is stopped.

[0031] Further, after the warm-up of the catalyst converters 8, 9 is temporarily complete, the operation of the internal combustion engine 1 is appropriately controlled in such a way that the catalyst temperature is not lower than the active temperature.

[0032] Thus, in this embodiment, until the warm-up of both the upstream-side catalyst converter 8 and the downstream-side catalyst converter 9 is complete after the initial start of the internal combustion engine 1, the operation of the internal combustion engine 1 is continued regardless of the request for power generation. Therefore, the exhaust purification performance based on the upstream-side catalyst converter 8 and the downstream-side catalyst converter 9 can be reliably obtained.

[0033] Further, until the upstream side catalyst converter 8 is warmed up, the operation at a low speed / low load with a large ignition timing lag is performed, so the upstream side catalyst converter 8 is activated early, and deterioration of the exhaust performance during the period until the upstream side catalyst converter 8 is activated is minimized. Further, after the upstream side catalyst converter 8 is warmed up, the operation at the optimum fuel consumption point near the normal ignition timing near the MBT point is performed, so deterioration of the fuel consumption can be suppressed, and activation of the downstream side catalyst converter 9 is achieved.

[0034] Figure 3 The above catalyst warm-up control is expressed in a module diagram, and the contents of the control are not changed from those of the flowchart of Figure 2 The information of the catalyst temperature of the upstream side catalyst converter 8 at the end of the last trip (at the time of the cut-off) shown in module Bl (which depends on the detected temperature of the exhaust temperature sensor 33), and the elapsed time from the end of the last trip are input to module B2, in which the catalyst temperature of the upstream side catalyst converter 8 at the start of the engine 1 is calculated. In module B3, the calculated catalyst temperature of the upstream side catalyst converter 8 is compared with the threshold value (standard) set in module B4, and warm-up determination is performed. If not warmed up, the low speed / low load operation with the ignition timing lag is performed in the aforementioned manner.

[0035] In module B5, the heat input to the upstream side catalyst converter 8 is calculated using various parameters (rotational speed, load, ignition timing (lag amount), valve timing, exhaust backflow rate, fuel injection timing, combustion pressure) input from module B6. In module B7, the calculated input heat is compared with the threshold value (standard) Ql set in module B8. If the threshold value Ql is reached, the operation is shifted to the rotational speed and load at the optimum fuel consumption point near the normal ignition timing near the MBT point in the aforementioned manner.

[0036] In module B9, the heat input to the downstream side catalyst converter 9 is calculated using various parameters (rotational speed, load, ignition timing, valve timing, exhaust backflow rate, fuel injection timing, combustion pressure) input from module B10. In module Bl l, the calculated input heat is compared with the threshold value (standard) Q2 set in module B12. If the threshold value Q2 is reached, the stop of the engine 1 is permitted in module B13.

[0037] Next, Figure 4This is a timing chart showing an example of the operation of various components and parameter changes in the catalyst warm-up control according to the above-described embodiment. The chart shows, in order from the top, (a) vehicle speed, (b) torque (load) of the internal combustion engine 1, (c) rotational speed of the internal combustion engine 1, (d) calculated heat input to the upstream catalytic converter 8, (e) temperature of the upstream catalytic converter 8, (f) ignition timing retard operation termination determination flag, (g) ignition timing retard operation request flag, (h) calculated heat input to the downstream catalytic converter 9, (i) stop prohibition request flag prohibiting stopping of the internal combustion engine 1, (j) ignition timing, and (k) changes in temperature of the downstream catalytic converter 9.

[0038] In this time chart, the vehicle enters the power-on state at time t1, and the ignition timing retardation operation request flag (g) turns on. After the vehicle starts at time t2, a power generation request is generated, causing the internal combustion engine 1 to start, and autonomous operation of the internal combustion engine 1 begins at time t3. At this time, a retardation operation for catalyst warming is performed, significantly retarding the ignition timing and setting the rotational speed and load to low levels, in accordance with the ignition timing retardation operation request flag (g). Furthermore, the slight decrease in temperature of the upstream catalytic converter 8 and the downstream catalytic converter 9 (shown in (a) and (k)) during the period from time t1 to time t3 is due to cooling due to the wind blowing from the vehicle.

[0039] During operation with retarded ignition timing, as shown in (d), the heat input to the upstream catalytic converter 8 increases, reaching a predetermined threshold value Q1 at time t4. Concomitantly, the ignition timing retarded operation request flag shown in (g) turns OFF, shifting to operation with ignition timing near the MBT point and near the optimal fuel efficiency point relatively on the high-speed, high-load side.

[0040] During operation near the optimal fuel consumption point, as shown in (h), the heat input to the downstream catalytic converter 9 increases and reaches a predetermined threshold value Q2 at time t5. In conjunction with this, the stop prohibition request flag shown in (i) turns OFF. Figure 4 In the example, assuming the power generation request ends before time t5, if the stop prohibition request flag turns off at time t5, operation of internal combustion engine 1 ends (see (b) and (c)). After time t5, so-called EV driving using battery power is achieved. While the stop prohibition request flag is on, operation of internal combustion engine 1 does not stop regardless of the power generation request. That is, as previously described, operation of internal combustion engine 1 continues until both upstream catalytic converter 8 and downstream catalytic converter 9 are warmed up.

[0041] Here, as shown in (k), the temperature of the downstream-side catalyst converter 9 is also gradually increased until time t4. However, the cumulative calculation of the input heat to the downstream-side catalyst converter 9 is started from time t4. Thereby, the control becomes simple.

[0042] Further, in the example of the first embodiment, the period from time t3 to t4 corresponds to the first interval in the technical solution, and the period from time t4 to t5 corresponds to the second interval. Figure 4

[0043] The above has been described in detail for one embodiment of the present application, but the present application is not limited to the above-described embodiment, and various modifications can be made. For example, the temperature of the upstream-side catalyst converter 8, the downstream-side catalyst converter 9, and the estimation of the warm-up state can be performed in various methods, and can be a structure in which the detection is directly performed by a temperature sensor. In addition, even in a structure in which an intermediate catalyst converter is further provided between the upstream-side catalyst converter 8 and the downstream-side catalyst converter 9, the present application can be similarly applied.​

Claims

1. A catalyst warm-up control method for an internal combustion engine, wherein the internal combustion engine is mounted on a series hybrid vehicle for power generation and is started / stopped in response to a power generation request from the vehicle. After the internal combustion engine is started, the catalyst warm-up states of the first catalyst located relatively upstream and the second catalyst located relatively downstream in the exhaust system are detected or estimated. Until it is determined that the warm-up of the two catalysts is completed, the internal combustion engine is not stopped and the operation of the internal combustion engine is continued even if there is no power generation request. here, In a first section from engine startup to completion of warming up of the first catalyst, ignition timing retardation is performed for catalyst warming up, and in a second section from completion of warming up of the first catalyst to completion of warming up of the second catalyst, operation without ignition timing retardation is performed. The catalyst warm-up state of the second catalyst is estimated by calculating the amount of heat input to the second catalyst since the first catalyst warm-up completion is determined. When the amount of heat input reaches a predetermined second standard, the second catalyst warm-up completion is determined.

2. The catalyst warm-up control method for an internal combustion engine according to claim 1, wherein: In the second range, the internal combustion engine is operated at a load and engine speed near the optimum fuel consumption point, and in the first range, the internal combustion engine is operated at a load and engine speed relatively lower than those in the second range.

3. The catalyst warm-up control method for an internal combustion engine according to claim 1 or 2, wherein: The catalyst warm-up state of the first catalyst is estimated by calculating the amount of heat input to the first catalyst from the start of the internal combustion engine. When the amount of heat input reaches a predetermined level, it is determined that the warm-up of the first catalyst is complete.

4. The catalyst warm-up control method for an internal combustion engine according to claim 3, wherein: The initial temperature of the first catalyst at the time of startup of the internal combustion engine is detected or estimated, and the above-mentioned standard is set based on the initial temperature.

5. A catalyst warm-up control device for an internal combustion engine, the internal combustion engine having a first catalyst located relatively upstream and a second catalyst located relatively downstream in an exhaust system, the internal combustion engine being mounted on a series hybrid vehicle for power generation, wherein: The catalyst warm-up control device is configured to instruct the start / stop of the internal combustion engine based on a power generation request from the vehicle side, and to detect or estimate the catalyst warm-up status of the first catalyst and the second catalyst respectively until it is determined that the warm-up of the two catalysts is completed. Even if there is no power generation request, the internal combustion engine is not stopped and the operation of the internal combustion engine is continued. here, In a first section from engine startup to completion of warming up of the first catalyst, ignition timing retardation is performed for catalyst warming up, and in a second section from completion of warming up of the first catalyst to completion of warming up of the second catalyst, operation without ignition timing retardation is performed. The catalyst warm-up control device is further configured to calculate the amount of heat input to the second catalyst from the time when the first catalyst is judged to be warm-up completed as an estimation of the catalyst warm-up state of the second catalyst, and to judge that the second catalyst is warm-up completed when the input heat reaches a predetermined second standard.

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