Method and device for controlling restart of internal combustion engine
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2023-08-24
- Publication Date
- 2026-06-11
Abstract
Description
Method and device for controlling restart of internal combustion engine
[0001] The present invention relates to restart control in an internal combustion engine in which combustion operation is automatically stopped and automatically restarted while a vehicle is in operation.
[0002] Patent Document 1 discloses a technique for starting fuel injection and ignition after a delay from the start of motoring (cranking) of an internal combustion engine during a cold start of the engine. By motoring at a sufficient rotational speed before the start of fuel injection and ignition, negative pressure develops and the temperature inside the cylinder increases.
[0003] However, in an internal combustion engine in which combustion operation is automatically stopped and automatically restarted while the vehicle is in operation, the temperature of the exhaust system catalyst may often be above its activation temperature during automatic restart. When the catalyst temperature is above its activation temperature, the oxygen storage capacity of the catalyst is saturated by air passing through the catalyst during motoring without combustion, and the NOx purification performance immediately after combustion starts decreases.
[0004] Japanese Patent Application Publication No. 9-170543
[0005] This invention is a restart control method for an internal combustion engine in which combustion operation is automatically stopped and automatically restarted while the vehicle is in operation, and determines whether the catalyst temperature is equal to or higher than an activation temperature when a restart request is made, and if it is equal to or higher than the activation temperature, starts fuel injection and ignition substantially simultaneously with the start of motoring of the internal combustion engine, and if it is below the activation temperature, starts fuel injection and ignition after a delay period has been given after the start of motoring of the internal combustion engine.
[0006] When the temperature is above the activation temperature, fuel injection and ignition are started substantially simultaneously with the start of motoring, thereby avoiding saturation of oxygen storage capacity due to air flowing through an activated catalyst and thus a decline in NOx purification performance immediately after combustion begins.
[0007] On the other hand, if the temperature is below the activation temperature, motoring during the delay period will develop negative pressure in the intake system and increase the temperature inside the cylinder, improving emissions immediately after the start of combustion.
[0008] Thus, according to the present invention, by varying the timing for starting fuel injection and ignition after motoring begins depending on whether the catalyst temperature is above the activation temperature, overall deterioration of emissions immediately after restart is suppressed.
[0009] 1 is a diagram illustrating the configuration of a series hybrid vehicle to which the restart control according to the present invention is applied; 2 is a diagram illustrating the configuration of an internal combustion engine; 3 is a flowchart illustrating the flow of processing at the time of restart according to one embodiment; 4 is a time chart illustrating operation at the time of restart according to a second embodiment; and 5 is a time chart illustrating operation of the second embodiment.
[0010] 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 power demands, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 that temporarily stores the generated power. Electric 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. Electric power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).
[0011] The operation of motor generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. 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 motor generators 1 and 4, an engine controller 8 that controls internal combustion engine 2, and a battery controller 9 that manages battery 5. Information such as the accelerator pedal position and vehicle speed (not shown) is input to controller 6. Battery controller 9 also calculates the SOC of battery 5 based on the voltage and current of battery 5. Basically, a decrease in SOC requests engine controller 8 to start internal combustion engine 2. Such a series hybrid vehicle has two driving modes: an EV mode in which the vehicle runs on power from battery 5 without combustion operation of internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of internal combustion engine 2.
[0012] In other words, the internal combustion engine 2 is not constantly in combustion operation while the vehicle is running with the main switch of the vehicle on, but is repeatedly automatically stopped and automatically restarted in response to a request for power generation. During automatic restart, the internal combustion engine 2 is motored by the power generation motor generator 1 mechanically connected to the crankshaft of the internal combustion engine 2.
[0013] 2 shows the system configuration of the internal combustion engine 2. This internal combustion engine 2 is, for example, a four-stroke, spark-ignition internal combustion engine equipped with a turbocharger 12. A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on the ceiling wall of each cylinder 13, and an ignition plug 16 is arranged in the center surrounded by these intake valves 14 and exhaust valves 15. A fuel injection valve 17 that supplies fuel into the cylinder 13 is provided below the intake valve 14. The ignition timing of the spark plug 16 and the injection timing and injection amount of fuel by the fuel injection valve 17 are controlled by an engine controller 8.
[0014] The intake valve 14 is also equipped with a variable valve timing mechanism 18 that can change the valve timing, i.e., the opening and closing timing. This variable valve timing mechanism 18 may be of any type, but for example, a mechanism that retards the phase of the camshaft relative to the phase of the crankshaft can be used.
[0015] The intake passage 21 has an intake collector 21a, and upstream of this intake collector 21a is provided an electronically controlled throttle valve 22 whose opening is controlled by a control signal from the engine controller 8. The compressor 12a of the turbocharger 12 is located upstream of the throttle valve 22, and an air flow meter 24 that detects the amount of intake air and an air cleaner 25 are located upstream of the compressor 12a. A water-cooled intercooler 26, for example, is provided between the compressor 12a and the throttle valve 22 to cool the high-temperature, high-pressure intake air. A recirculation valve 27 is also provided to communicate the discharge side and intake side of the compressor 12a.
[0016] The turbine 12b of the turbocharger 12 is located in the exhaust passage 30, and a pre-catalyst device 31 and a main catalytic device 32, each consisting of a three-way catalyst, are disposed downstream of the turbine 12b. The pre-catalyst device 31 is located at the outlet of the turbine 12b, and the main catalytic device 32 is located under the floor of the vehicle. An air-fuel ratio sensor 33 that detects the air-fuel ratio is disposed upstream of the turbine 12b in the exhaust passage 30. The turbine 12b is equipped with a wastegate valve 34 that bypasses a portion of the exhaust gas in accordance with the boost pressure in order to control the boost pressure. The wastegate valve 34 is, for example, an electrically operated valve whose opening is controlled by the engine controller 8.
[0017] The engine is also provided with an exhaust gas recirculation passage 35 that recirculates a portion of the exhaust gas from the exhaust passage 30 to the intake passage 21, and this exhaust gas recirculation passage 35 is provided with, for example, a water-cooled EGR gas cooler 37 and an EGR valve 38.
[0018] In addition to the air flow meter 24 and air-fuel ratio sensor 33, the engine controller 8 receives detection signals from various sensors, such as a crank angle sensor 41 for detecting engine speed, a water temperature sensor 42 for detecting coolant temperature, catalyst temperature sensors 43 and 44 for detecting catalyst temperatures of the pre-catalyst device 31 and the main catalyst device 32, an atmospheric pressure sensor 45 for detecting atmospheric pressure, an outside air temperature sensor 46 for detecting outside air temperature, and a boost pressure sensor 47 for detecting boost pressure. Based on these detection signals and requests from the other controllers 7 and 9, the engine controller 8 optimally controls the fuel injection amount and injection timing, ignition timing, throttle valve 22 opening, boost pressure, etc.
[0019] The catalyst temperature sensors 43, 44 may be configured to indirectly determine the catalyst temperature from the gas temperatures before and after the catalyst, instead of directly detecting the catalyst carrier temperature. In this case, after the combustion operation of the internal combustion engine 2 is automatically stopped, the current catalyst temperature is successively estimated from various temperature conditions, etc.
[0020] Basically, the internal combustion engine 2 is started when the SOC of the battery 5 drops to a predetermined start-up SOC value, and is stopped when the SOC reaches a sufficient level. Furthermore, in one embodiment, when the required power exceeds the power that can be supplied from the battery 5, such as when sudden acceleration of the vehicle is required while traveling in EV mode, the internal combustion engine 2 is restarted and power is generated. Therefore, the internal combustion engine 2 is automatically restarted and stopped relatively frequently.
[0021] Next, control for automatically restarting the internal combustion engine 2, which is a main part of the present invention, will be described with reference to the flowchart of Figure 3. The process shown in the flowchart of Figure 3 is repeatedly executed by the engine controller 8 while the combustion operation of the internal combustion engine 2 is stopped.
[0022] First, in step 1, it is determined whether a restart request for the internal combustion engine 2 has been made based on the SOC of the battery 5, etc. If there is no restart request, the routine ends. If there is a restart request, the routine proceeds to step 2, where it is determined whether the catalyst temperature Tc at that time is equal to or higher than a predetermined activation temperature Tc0. As an example, the temperature of the pre-catalyst device 31 detected by the catalyst temperature sensor 43 can be used as a representative catalyst temperature Tc, but the temperature of the main catalyst device 32 may also be used as a representative catalyst temperature Tc.
[0023] If the catalyst temperature Tc is below the activation temperature Tc0, the flow of air does not affect the oxygen storage capacity of the catalyst. Therefore, the process proceeds from step 2 to step 3 and beyond, where motoring is used to increase the in-cylinder temperature and develop negative pressure. First, in step 3, the variable valve timing mechanism 18 of the intake valve 14 is controlled so that the volumetric efficiency during motoring is relatively higher than the volumetric efficiency during restart at the activation temperature Tc0 or higher. In one embodiment, the basic valve timing setting (the valve timing setting during normal operation and during restart at the activation temperature Tc0 or higher) is a so-called delayed valve timing setting in which the intake valve closing timing IVC is relatively delayed from bottom dead center to improve fuel economy. In contrast, during restart at temperatures below the activation temperature Tc0, the intake valve closing timing IVC is set relatively closer to bottom dead center to increase the volumetric efficiency. Furthermore, in step 4, the throttle valve 22 opening TVO is increased compared to the opening during restart at the activation temperature or higher, in order to similarly increase the volumetric efficiency. Then, in step 5, motoring is started using the power-generating motor-generator 1. For example, motoring is performed at a predetermined rotation speed of about 1000 to 1500 rpm. This motoring increases the temperature inside the cylinder, and negative pressure develops in the intake system.
[0024] In step 6, the required delay time tD (in other words, the motoring time before fuel injection and ignition start) is calculated based on the outside air temperature To and the coolant temperature Tw at that time. The required delay time tD becomes longer the lower the outside air temperature, and similarly, the required delay time tD becomes longer the lower the coolant temperature. For example, the delay time tD is calculated using a map that uses the outside air temperature To and the coolant temperature Tw as parameters.
[0025] In step 7, it is determined whether the elapsed time t from the start of motoring is equal to or greater than the delay time tD. When the elapsed time t reaches the delay time tD, the process proceeds from step 7 to step 8, where fuel injection and ignition are initiated. This initiates combustion operation of the internal combustion engine 2. When the internal combustion engine 2 has fully exploded and is operating autonomously, the power-generating motor-generator 1, which is under speed control, quickly transitions to regeneration, i.e., power generation mode.
[0026] Thus, if the catalyst temperature Tc at the time of the restart request is below the activation temperature Tc0, fuel injection and ignition are initiated after motoring for the delay time tD. Motoring develops negative pressure in the intake system and raises the in-cylinder temperature, improving atomization and vaporization of the injected fuel and improving emissions (e.g., HC and CO) immediately after the start of combustion. Furthermore, by changing the valve timing and increasing the throttle valve opening TVO during motoring, the amount of air drawn into the cylinder per cycle increases, effectively raising the in-cylinder temperature. Furthermore, because the delay time tD is set taking into account the outside air temperature To and the coolant temperature Tw, good operation is achieved even when the outside air temperature To and the coolant temperature Tw are low.
[0027] The delay time tD varies depending on the temperature conditions, motoring rotation speed, etc., but is, for example, about one second.
[0028] If it is determined in step 2 that the catalyst temperature Tc is equal to or higher than the activation temperature Tc0, the process proceeds from step 2 to step 9, where motoring is started using the power-generating motor-generator 1. Then, substantially simultaneously with the start of motoring, fuel injection and ignition are started in step 8.
[0029] In this way, when the catalyst temperature Tc is equal to or higher than the activation temperature Tc0, fuel injection and ignition are initiated quickly, so that motoring without combustion does not cause a large amount of oxygen-containing air to flow into the catalytic converters 31 and 32. This prevents the oxygen storage capacity of the catalyst from becoming saturated, and thus prevents a deterioration in NOx emissions immediately after startup.
[0030] FIG. 4 is a time chart illustrating the restart operation when the catalyst temperature Tc at the time of a restart request is less than the activation temperature Tc0. It compares changes in (a) catalyst temperature Tc and ambient temperature To, (b) coolant temperature Tw, (c) engine speed Ne, (d) intake valve closing timing IVC, (e) throttle valve opening TVO, (f) elapsed time t, and (g) injection start flag. In this example, a restart request is made at time t1, when the catalyst temperature Tc is less than the activation temperature Tc0. At time t1, motoring begins, and substantially simultaneously, the intake valve closing timing IVC is changed and the throttle valve opening TVO is increased. Then, at time t2, a predetermined delay time tD after time t1, fuel injection and ignition begin. After the restart, the intake valve closing timing IVC and throttle valve opening TVO return to their normal states.
[0031] Next, the restart process of the second embodiment will be described with reference to the flowchart of Figure 5 and the time chart of Figure 6. In the second embodiment, instead of defining the delay period by the elapsed time t as in the above embodiment, the delay period is defined by the in-cylinder temperature Tic during motoring.
[0032] The flowchart shown in FIG. 5 is basically the same as the flowchart shown in FIG. 3, and if the catalyst temperature Tc is equal to or higher than the activation temperature Tc0 when a restart is requested (step 1), fuel injection and ignition are started (step 8) substantially simultaneously after motoring begins (step 9).
[0033] If the catalyst temperature Tc is less than the activation temperature Tc0, the valve timing is changed so that the intake valve closing timing IVC approaches bottom dead center (step 3), and the throttle valve opening TVO is increased (step 4), and motoring is started (step 5).
[0034] In the second embodiment, the process proceeds from step 5 to step 11, where the in-cylinder temperature Tic, which increases due to motoring, is estimated. For example, the initial in-cylinder temperature Tic is estimated based on the outside air temperature To and the coolant temperature Tw, and the in-cylinder temperature Tic is successively estimated by accumulating the temperature increase for each cycle (or each small unit time) due to motoring. Then, in step 12, it is determined whether this estimated in-cylinder temperature Tic is equal to or greater than a predetermined threshold temperature Tic0. Estimation of the in-cylinder temperature Tic is repeated until the threshold temperature Tic0 is reached.
[0035] When the estimated in-cylinder temperature Tic reaches the threshold temperature Tic0, the process proceeds from step 12 to step 8, where fuel injection and ignition are started.
[0036] The time chart of Figure 6 is basically the same as the time chart of Figure 4, but column (f) shows changes in in-cylinder temperature Tic instead of elapsed time t. At time t1, motoring begins, and essentially simultaneously, the intake valve closing timing IVC is changed and the throttle valve opening TVO is increased. Then, at time t12, when the estimated in-cylinder temperature Tic increases from time t1 and reaches a predetermined threshold temperature Tic0, fuel injection and ignition begin.
[0037] Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, an example in which the present invention is applied to an internal combustion engine for generating electricity in a series hybrid vehicle has been described, but the present invention can also be applied to internal combustion engines in other types of hybrid vehicles, or to internal combustion engines that serve as a driving source for vehicles that do not have a motor (for example, internal combustion engines with an idling stop function).
[0038] Furthermore, the variable valve timing mechanism may be provided on both the intake valve and the exhaust valve, or the variable valve timing mechanism may be provided only on the exhaust valve side.
Claims
1. A spark-ignition internal combustion engine for power generation that drives a generator in a series hybrid vehicle that is propelled by motor output, and a restart control method for an internal combustion engine in which the combustion operation is automatically stopped and automatically restarted while the vehicle is in operation, When a restart request is made, it is determined whether the catalyst temperature is above the activation temperature. If the temperature is above the activation temperature, fuel injection and ignition are initiated substantially simultaneously with the start of motoring of the internal combustion engine by the powering of the above-mentioned generator. If the temperature is below the activation temperature, the internal combustion engine is motored by the generator at a rotational speed of 1000 to 1500 rpm to raise the in-cylinder temperature, and fuel injection and ignition are started after a delay period has elapsed, which is set to allow at least 15 rotations of motoring to occur from the start of motoring of the internal combustion engine. A method for controlling the restart of an internal combustion engine.
2. The above delay period ends when the elapsed time from the start of motoring reaches a predetermined time. A method for controlling the restart of an internal combustion engine according to claim 1.
3. The above delay period is determined by estimating the in-cylinder temperature rising due to motoring, and ends when this estimated in-cylinder temperature reaches a predetermined temperature. A method for controlling the restart of an internal combustion engine according to claim 1.
4. The lower the outside temperature, the longer the above delay period should be set. A method for controlling the restart of an internal combustion engine according to claim 1.
5. The lower the coolant temperature of the internal combustion engine, the longer the above delay period should be set. A method for controlling the restart of an internal combustion engine according to claim 1.
6. The valve timing of at least one of the intake and exhaust valves is corrected so that, when the temperature is below the activation temperature, the volumetric efficiency during motoring is higher than when the temperature is above the activation temperature. A method for controlling the restart of an internal combustion engine according to claim 1.
7. When the temperature is below the activation temperature, the throttle valve opening is increased to compensate so that the volumetric efficiency during motoring is higher than when the temperature is above the activation temperature. A method for controlling the restart of an internal combustion engine according to claim 1.
8. (delete)
9. In a series hybrid vehicle that runs on motor output, a spark-ignition internal combustion engine for power generation drives the generator, A catalytic converter for exhaust gas purification is installed in the exhaust passage of this internal combustion engine, A controller that automatically stops and restarts the combustion operation of the internal combustion engine while the vehicle is in operation, Equipped with, The above controller is When a restart request is made, it is determined whether the catalyst temperature is above the activation temperature. If the temperature is above the activation temperature, fuel injection and ignition are initiated substantially simultaneously with the start of motoring of the internal combustion engine by the powering of the above-mentioned generator. If the temperature is below the activation temperature, the internal combustion engine is motored by the generator at a rotational speed of 1000 to 1500 rpm to raise the in-cylinder temperature, and fuel injection and ignition are started after a delay period has elapsed, which is set to allow at least 15 rotations of motoring to occur from the start of motoring of the internal combustion engine. A restart control device for internal combustion engines.