Method and device for controlling restart of internal combustion engine

Abstract

An internal combustion engine (2) of a tandem hybrid vehicle performs automatic stop and automatic restart of combustion operation in response to a power generation request. When a restart request is requested, it is determined whether the catalyst temperature is greater than or equal to the activation temperature (S1, S2), and if the catalyst temperature is greater than or equal to the activation temperature, fuel injection and ignition (S8) are started substantially simultaneously with motor drive start (S9) of the internal combustion engine. If the temperature is lower than the activation temperature, the valve timing is changed (S3) and the throttle valve opening degree is increased (S4) so that the volumetric efficiency is increased, and motor driving is started (S5). When the elapsed time t from the start of motor driving reaches the required delay time tD (S6, S7), fuel injection and ignition are started (S8).

Description

Technical Field

[0001] This invention relates to a restart control in an internal combustion engine that automatically stops and restarts combustion operation during vehicle operation. Background Technology

[0002] Patent Document 1 discloses a technique in which fuel injection and ignition are delayed from the start of the internal combustion engine's motor drive (crankshaft rotation) during a cold start. By operating the motor at a sufficient speed before fuel injection and ignition begin, a negative pressure is created, and the cylinder temperature rises.

[0003] However, for internal combustion engines that automatically stop and restart during vehicle operation, the catalyst temperature in the exhaust system may be greater than or equal to the activation temperature during automatic restart. Thus, when the catalyst temperature is above or equal to the activation temperature, the oxygen storage capacity of the catalyst will become saturated as air flows through it without combustion driven by the electric motor, leading to a decrease in NOx purification performance at the start of combustion.

[0004] Patent Document 1: Japanese Patent Application Publication No. 9-170543 Summary of the Invention

[0005] This invention relates to a restart control method for an internal combustion engine that automatically stops and restarts combustion during vehicle operation. When a restart request is requested, it is determined whether the catalyst temperature is greater than or equal to the activation temperature. If the temperature is greater than or equal to the activation temperature, then fuel injection and ignition begin substantially simultaneously with the start of the internal combustion engine's electric motor drive. If the temperature is below the activation temperature, fuel injection and ignition will begin after a delay period is given, following the start of the internal combustion engine's electric motor drive.

[0006] At temperatures above or equal to the activation temperature, fuel injection and ignition are initiated substantially simultaneously with the start of motor drive, thereby avoiding saturation of oxygen storage capacity caused by air flowing through the activated catalyst, and thus preventing a decrease in NOx purification performance at the beginning of combustion.

[0007] On the other hand, when the temperature is below the activation temperature, the motor drive during the delay period enables the formation of negative pressure in the intake system and the rise of the cylinder temperature, thereby improving emissions after the start of combustion.

[0008] Thus, according to the present invention, by differentiating the timing of initial fuel injection and ignition after the start of motor drive based on whether the catalyst temperature is greater than or equal to the activation temperature, the overall emissions degradation after restarting is suppressed. Attached Figure Description

[0009] Figure 1 This is a structural illustration of a series hybrid vehicle that utilizes the restart control method described in this invention.

[0010] Figure 2 This is a structural diagram illustrating an internal combustion engine.

[0011] Figure 3 This is a flowchart illustrating the process of restarting in one embodiment.

[0012] Figure 4 It is a timing diagram representing the actions during a restart.

[0013] Figure 5 This is a flowchart illustrating the process of restarting in the second embodiment.

[0014] Figure 6 This is a timing diagram illustrating the operation of the second embodiment. Detailed Implementation

[0015] Figure 1 The structure of a series hybrid vehicle, as an example of a vehicle to which the present invention is applied, is schematically shown. The series hybrid vehicle is configured to include: a generator 1, which primarily functions as a generator; an internal combustion engine 2, which serves as a generator-generating internal combustion engine to drive the generator 1 upon power request; a driving generator 4, which primarily functions as an electric motor to drive drive wheels 3; and a battery 5, which temporarily stores the generated electricity. The electricity obtained by driving the generator 1 through the internal combustion engine 2 is stored in the battery 5 via an inverter device (not shown). The driving generator 4 uses the electricity from the battery 5 for drive control. The electricity generated by the driving generator 4 during regeneration is also stored in the battery 5 via an inverter device (not shown).

[0016] The operation of electric 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 consists of multiple controllers connected to each other in a communicable manner, including electric motor controller 7 which controls electric generators 1 and 4, engine controller 8 which controls internal combustion engine 2, and battery controller 9 which manages battery 5. Information such as accelerator pedal opening (not shown) or vehicle speed is input to controller 6. In addition, battery controller 9 calculates the state of charge (SOC) of battery 5 based on the voltage and current of battery 5. Basically, based on the decrease in SOC, it requests engine controller 8 to start internal combustion engine 2. As operating modes of such a series hybrid vehicle, there are EV mode, which operates without combustion of internal combustion engine 2 and runs on electricity from battery 5, and HEV mode, which operates while generating electricity through combustion of internal combustion engine 2.

[0017] That is, the internal combustion engine 2 does not always burn and run when the vehicle's main switch is turned on, but rather repeatedly stops and restarts automatically according to power generation requests. During automatic restarts, the internal combustion engine 2 is driven by the electric motor 1, which is mechanically connected to the crankshaft of the internal combustion engine 2.

[0018] Figure 2 The system structure of the internal combustion engine 2 is shown. This internal combustion engine 2 is, for example, a four-stroke spark-ignition internal combustion engine with a turbocharger 12. A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on the top wall of each cylinder 13, and a spark plug 16 is arranged in the center surrounded by these intake valves 14 and exhaust valves 15. A fuel injection valve 17, which supplies fuel to the cylinder 13, is located below the intake valves 14. The ignition timing of the spark plug 16 and the timing and amount of fuel injection achieved by the fuel injection valve 17 are controlled by the engine controller 8.

[0019] In addition, the intake valve 14 has a variable valve timing mechanism 18 that can change the valve timing, i.e., the opening and closing times. The variable valve timing mechanism 18 can be any type of mechanism, but it can be a mechanism that delays the phase of the camshaft relative to the phase of the crankshaft.

[0020] The intake passage 21 has an intake manifold 21a. An electronically controlled throttle valve 22, whose opening is controlled according to a control signal from the engine controller 8, is located upstream of the intake manifold 21a. The compressor 12a of the turbocharger 12 is located upstream of the throttle valve 22. An air flow meter 24 for detecting the amount of intake air and an air filter 25 are located upstream of the compressor 12a. An intercooler 26, such as a water-cooled one, is provided between the compressor 12a and the throttle valve 22 to cool the intake air, which becomes hot and high-pressure. A recirculation valve 27 is provided to connect the injection side and the intake side of the compressor 12a.

[0021] In the exhaust passage 30, there is a turbine 12b containing a turbocharger 12. Downstream of the turbine 12b, a pre-catalytic converter 31 and a main catalytic converter 32, each composed of a three-way catalytic converter, are disposed. The pre-catalytic converter 31 is located at the outlet of the turbine 12b, and the main catalytic converter 32 is located in the vehicle chassis. Upstream of the exhaust passage 30 from the turbine 12b, an air-fuel ratio sensor 33 is disposed to detect the air-fuel ratio. The turbine 12b has an exhaust gas bypass valve 34, which controls the boost pressure by allowing a portion of the exhaust gas to bypass the boost pressure. The exhaust gas bypass valve 34 may be, for example, an electrically operated type whose opening is controlled by the engine controller 8.

[0022] Additionally, there is an exhaust return passage 35 that allows a portion of the exhaust gas to flow back from the exhaust passage 30 to the intake passage 21. In this exhaust return passage 35, for example, a water-cooled EGR gas cooler 37 and an EGR valve 38 are provided.

[0023] In addition to the detection signals from the air flow meter 24 and the air-fuel ratio sensor 33, the engine controller 8 also receives detection signals from a group of sensors, including a crankshaft angle sensor 41 for detecting engine speed, a coolant temperature sensor 42 for detecting coolant temperature, catalyst temperature sensors 43 and 44 for detecting catalyst temperatures in the pre-catalytic converter 31 and the main catalytic converter 32 respectively, an atmospheric pressure sensor 45 for detecting atmospheric pressure, an ambient temperature sensor 46 for detecting ambient temperature, and a boost pressure sensor 47 for detecting boost pressure. Based on these detection signals or requests from other controllers 7 and 9, the engine controller 8 optimizes the fuel injection quantity and timing, ignition timing, throttle valve opening 22, and boost pressure.

[0024] Furthermore, the catalyst temperature sensors 43 and 44 can also be sensors that indirectly determine the catalyst temperature based on the preceding and following gas temperatures, rather than directly detecting the catalyst carrier temperature. In this case, after the combustion operation of the internal combustion engine 2 automatically stops, the current catalyst temperature is estimated sequentially based on various temperature conditions.

[0025] Basically, when the SOC of battery 5 drops to a predetermined starting SOC value, the internal combustion engine 2 starts, and after the SOC reaches a sufficient level, the internal combustion engine 2 stops. Furthermore, in one embodiment, when the requested power exceeds the power available from battery 5, such as when the vehicle is requested to accelerate rapidly while driving in EV mode, the internal combustion engine 2 also restarts to generate electricity. Therefore, the automatic restarting and automatic stopping of the internal combustion engine 2 is repeated relatively frequently.

[0026] Next, refer to Figure 3 The flowchart illustrates the control during the automatic restart of the internal combustion engine 2, a key component of the present invention. Furthermore, Figure 3 The process shown in the flowchart is repeatedly executed in the engine controller 8 when the combustion operation of the internal combustion engine 2 stops.

[0027] Initially, in step 1, it is determined whether there is a restart request for the internal combustion engine 2 based on the SOC of the battery 5. If there is no restart request, the processing flow ends. If there is a restart request, the process proceeds to step 2, where it is determined whether the catalyst temperature Tc at this time is greater than or equal to the predetermined activation temperature Tc0. As the catalyst temperature Tc, in one example, the temperature of the pre-catalytic converter 31 detected by the catalyst temperature sensor 43 can be used as a representative, but the temperature of the main catalytic converter 32 can also be used as a representative catalyst temperature Tc.

[0028] If the catalyst temperature Tc is lower than the activation temperature Tc0, there is no effect on the oxygen storage capacity of the catalyst due to airflow. Therefore, from step 2 to step 3 and subsequent steps, the aim is to achieve an in-cylinder temperature rise and negative pressure formation driven by the electric motor. First, in step 3, the variable valve timing mechanism 18 of the intake valve 14 is controlled so that the volumetric efficiency during electric motor drive is relatively higher than the volumetric efficiency during restart when the activation temperature Tc0 is greater than or equal to. In one embodiment, for the basic valve timing setting (valve timing setting during normal operation and restart when the activation temperature Tc0 is greater than or equal to), in order to improve fuel economy, it is a so-called delayed closing valve timing setting in which the intake valve closing time IVC is significantly delayed relative to the bottom dead center. In contrast, during restart when the activation temperature Tc0 is lower than the activation temperature Tc0, the valve timing is set such that the intake valve closing time IVC is relatively close to the bottom dead center in order to improve volumetric efficiency. Then, in step 4, similarly, to improve volumetric efficiency, the opening (TVO) of the throttle valve 22 is increased and corrected compared to the opening at restart when the activation temperature is greater than or equal to the activation temperature. Then, in step 5, the motor drive of the generator 1 for power generation is started. For example, the motor drive is performed at a specified speed of approximately 1000 to 1500 rpm. Driven by this motor, the cylinder temperature rises, creating negative pressure within the intake system.

[0029] In step 6, the required delay time tD (in other words, the motor drive time before fuel injection and ignition begins) is calculated based on the ambient temperature To and the coolant temperature Tw. The lower the ambient temperature, the longer the required delay time tD; similarly, the lower the coolant temperature, the longer the required delay time tD. For example, the delay time tD can be calculated using a graph that sets the ambient temperature To and the coolant temperature Tw as parameters.

[0030] In step 7, it is determined whether the elapsed time t from the start of motor drive has reached a value greater than or equal to the delay time tD. After the elapsed time t reaches the delay time tD, the process proceeds from step 7 to step 8, where fuel injection and ignition begin. Thus, the combustion operation of the internal combustion engine 2 begins. If the internal combustion engine 2 completes its start-up (complete explosion) and becomes independently operating, the generator 1, whose speed is controlled, quickly switches to regenerative power generation mode.

[0031] Thus, when the catalyst temperature Tc at the time of restart request is lower than the activation temperature Tc0, fuel injection and ignition begin after the electric motor drive during the delay time tD. The negative pressure created in the intake system by the electric motor drive increases the cylinder temperature, thereby improving fuel atomization and vaporization, and reducing emissions (e.g., HC or CO) at the start of combustion. Furthermore, by changing valve timing and increasing the throttle valve opening TVO during electric motor drive, the amount of air drawn into the cylinder increases in each cycle, effectively raising the cylinder temperature. Additionally, by taking into account the ambient temperature To and coolant temperature Tw when setting the delay time tD, good performance is achieved even when the ambient temperature To or coolant temperature Tw is low.

[0032] In addition, the delay time tD varies depending on temperature conditions or motor drive speed, and is for example, about 1 second.

[0033] In step 2, if it is determined that the catalyst temperature Tc is greater than or equal to the activation temperature Tc0, the process proceeds from step 2 to step 9, where the motor drive of the generator 1 for power generation is initiated. Furthermore, substantially simultaneously with the start of the motor drive, fuel injection and ignition begin in step 8.

[0034] Thus, when the catalyst temperature Tc is greater than or equal to the activation temperature Tc0, fuel injection and ignition begin rapidly. Consequently, driven by an electric motor without combustion, oxygen-containing air does not flow into the catalytic converters 31 and 32 in large quantities. This avoids saturation of the catalyst's oxygen storage capacity, thereby preventing a deterioration in NOx levels immediately after startup.

[0035] Figure 4 This is a timing diagram illustrating the restart process when the catalyst temperature Tc is lower than the activation temperature Tc0 at the time of the restart request. It contrasts the changes in (a) catalyst temperature Tc and ambient temperature To, (b) coolant temperature Tw, (c) internal combustion engine speed Ne, (d) intake valve closing timing IVC, (e) throttle valve opening TVO, (f) elapsed time t, and (g) injection start indicator. In this example, a restart request occurs at time t1, when the catalyst temperature Tc is lower than the activation temperature Tc0. At time t1, the motor drive begins, and substantially simultaneously, the intake valve closing timing IVC is changed and the throttle valve opening TVO is increased. Then, at time t2, after a predetermined delay time tD from time t1, fuel injection and ignition begin. Furthermore, after startup, the intake valve closing timing IVC and throttle valve opening TVO return to their normal states.

[0036] Next, refer to Figure 5 Flowchart and Figure 6The timing diagram illustrates the restart process in the second embodiment. In the second embodiment, instead of specifying the delay period by the elapsed time t as in the previous embodiment, the delay period is specified by the cylinder temperature Tic during motor drive.

[0037] Figure 5 The flowchart shown is basically the same as Figure 3 The flowchart shown is the same. If the catalyst temperature Tc is greater than or equal to the activation temperature Tc0 when the restart request is made (step 1), then fuel injection and ignition (step 8) will start substantially simultaneously after the motor drive starts (step 9).

[0038] If the catalyst temperature Tc is less than the activation temperature Tc0, the valve timing is changed in such a way that the intake valve closing time IVC is close to the bottom dead center (step 3), and the throttle valve opening TVO is increased and corrected (step 4), and the motor drive is started (step 5).

[0039] In the second embodiment, the process proceeds from step 5 to step 11, where the cylinder temperature Tic, which gradually increases due to motor drive, is estimated. For example, an initial cylinder temperature Tic is estimated based on the ambient air temperature To and the coolant temperature Tw. The temperature rise during each cycle (or each minute unit of time) driven by the motor is accumulated, thereby progressively estimating the cylinder temperature Tic. Then, in step 12, it is determined whether the estimated cylinder temperature Tic becomes greater than or equal to a predetermined threshold temperature Tic0. The estimation of the cylinder temperature Tic is repeated until the threshold temperature Tic0 is reached.

[0040] When the estimated cylinder temperature Tic reaches the threshold temperature Tic0, proceed from step 12 to step 8 to start fuel injection and ignition.

[0041] Figure 6 The timing diagram is basically the same as Figure 4 The timing diagram shown is the same, but in column (f), the change in cylinder temperature Tic is shown instead of time t. At time t1, the motor drive begins, substantially simultaneously changing the intake valve closing timing IVC and increasing the throttle valve opening TVO. Furthermore, at time t12, when the estimated cylinder temperature Tic, which has been gradually increasing from time t1, reaches the predetermined threshold temperature Tic0, fuel injection and ignition begin.

[0042] The present invention has been described in detail above with respect to one embodiment, but the present invention is not limited to the above embodiment and various modifications can be made. For example, in the above embodiment, an example of applying the present invention to a generator internal combustion engine in a series hybrid vehicle has been described, but it can also be applied to internal combustion engines in other types of hybrid vehicles, or to internal combustion engines that serve as the driving source for vehicles without electric motors (e.g., internal combustion engines with idle stop function).

[0043] Alternatively, it can be a structure where both the intake valve and the exhaust valve have variable valve timing mechanisms, or it can be a structure where only the exhaust valve side has a variable valve timing mechanism.

Claims

1. A method for controlling the restart of an internal combustion engine, which automatically stops and restarts combustion during vehicle operation. In this method for controlling the restart of an internal combustion engine, When a restart request is requested, it is determined whether the catalyst temperature is greater than or equal to the activation temperature. If the temperature is greater than or equal to the activation temperature, then fuel injection and ignition begin substantially simultaneously with the start of the internal combustion engine's electric motor drive. If the temperature is below the activation temperature, fuel injection and ignition will begin after a delay period is given, following the start of the internal combustion engine's electric motor drive.

2. The restart control method for an internal combustion engine according to claim 1, wherein, The aforementioned delay period ends when the elapsed time since the start of motor drive reaches the specified time.

3. The restart control method for an internal combustion engine according to claim 1, wherein, The aforementioned delay period is used to estimate the cylinder temperature that rises due to the motor drive, and the delay ends when the estimated cylinder temperature reaches the specified temperature.

4. The restart control method for an internal combustion engine according to claim 1, wherein, The lower the outside temperature, the longer the above delay period will be set.

5. The restart control method for an internal combustion engine according to claim 1, wherein, The lower the cooling water temperature of the internal combustion engine, the longer the aforementioned delay period should be set.

6. The restart control method for an internal combustion engine according to claim 1, wherein, At temperatures below the activation temperature, the valve timing of at least one of the intake and exhaust valves is corrected to achieve higher volumetric efficiency when driven by the motor compared to conditions at or above the activation temperature.

7. The restart control method for an internal combustion engine according to claim 1, wherein, When the throttle valve opening is below the activation temperature, the adjustment is made to increase the volumetric efficiency of the motor drive compared to when the activation temperature is above or equal to the activation temperature.

8. The restart control method for an internal combustion engine according to claim 1, wherein, The aforementioned internal combustion engine is the one that drives the generator in hybrid vehicles that can operate via an electric motor. The aforementioned motor is driven by the power generated by the aforementioned generator.

9. A restart control device for an internal combustion engine, comprising: An internal combustion engine, which has a catalyst for exhaust purification in the exhaust passage; and The controller automatically stops and restarts the internal combustion engine during vehicle operation. When a restart request is received, the controller determines whether the catalyst temperature is greater than or equal to the activation temperature. If the temperature is greater than or equal to the activation temperature, then fuel injection and ignition begin substantially simultaneously with the start of the internal combustion engine's electric motor drive. If the temperature is below the activation temperature, fuel injection and ignition will begin after a delay period is given, following the start of the internal combustion engine's electric motor drive.

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