Method and device for controlling restart of internal combustion engine

Abstract

Combustion operation of an internal combustion engine (2) a series hybrid vehicle is automatically stopped and automatically restarted according to a power generation request. It is determined whether or not a catalyst temperature at the time of a restart request is equal to or higher than a predetermined activation temperature (S1, S2). If the catalyst temperature is equal to or higher than the activation temperature, substantially simultaneously with a start of motoring of the internal combustion engine (S9), fuel injection and ignition are started (S8). If the catalyst temperature is lower than the activation temperature, a valve timing is changed (S3) and a throttle valve opening is increased (S4) so as to increase volumetric efficiency, and the motoring is started (S5). When an elapsed time t from the start of the motoring reaches a required delay time tD (S6, S7), fuel injection and ignition are started (S8).

Description

TECHNICAL FIELD

[0001] [0001. The present invention relates to restart control of an internal combustion engine whose combustion operation is automatically stopped and automatically restarted during vehicle operation.BACKGROUND ART

[0002] [0002. Patent Document 1 discloses a technique of starting fuel injection and ignition with a delay from a start of motoring (cranking) of an internal combustion engine at the time of a cold start of the internal combustion engine. By performing the motoring at a sufficient rotational speed before the start of the fuel injection and the ignition, a negative pressure is developed, and also an in-cylinder temperature is increased.

[0003] [0003. In the case of the internal combustion engine whose combustion operation is automatically stopped and automatically restarted during vehicle operation, however, there often arises a case where temperature of a catalyst in an exhaust system is an activation temperature or higher at the time of the automatic restart. When the catalyst temperature is the activation temperature or higher, an oxygen storage capacity of the catalyst is saturated by the air passing through the catalyst during the motoring without combustion, and consequently, the NOx purification performance immediately after the start of combustion is decreased.CITATION LIST PATENT DOCUMENT

[0004] [0004. Patent Document 1: Japanese Unexamined Patent Application Publication No. JPH09-170543SUMMARY OF THE INVENTION

[0005] [0005. The present invention is a method of controlling restart of an internal combustion engine whose combustion operation is automatically stopped and automatically restarted during vehicle operation, the method comprising: determining whether or not a catalyst temperature at a time of a restart request is equal to or higher than an activation temperature; if the catalyst temperature is equal to or higher than the activation temperature, substantially simultaneously with a start of motoring of the internal combustion engine, starting fuel injection and ignition; and if the catalyst temperature is lower than the activation temperature, after a delay period from the start of the motoring of the internal combustion engine, starting the fuel injection and the ignition.

[0006] [0006. When the catalyst temperature is equal to or higher than the activation temperature, substantially simultaneously with the start of the motoring, the fuel injection and the ignition are started, thereby avoiding saturation of an oxygen storage capacity of a catalyst due to air flowing through the catalyst in an active state, which in turn avoiding a decrease in the NOx purification performance immediately after the start of combustion.

[0007] [0007. On the other hand, when the catalyst temperature is lower than the activation temperature, by the motoring performed for the delay period, a negative pressure in an intake system is developed, and an in-cylinder temperature is increased. Therefore, emissions immediately after the start of combustion are improved.

[0008] [0008. As described above, according to the present invention, by varying the timing of starting the fuel injection and the ignition after the start of the motoring depending on whether or not the catalyst temperature is equal to or higher than the activation temperature, deterioration of emissions immediately after the restart is suppressed as a whole.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [0009. Fig. 1 is a diagram illustrating a configuration of a series hybrid vehicle to which restart control according to the present invention is applied. Fig. 2 is a diagram illustrating a configuration of an internal combustion engine. Fig. 3 is a flow chart showing a process flow at the time of restart according to an embodiment. Fig. 4 is a time chart showing operations at the time of restart. Fig. 5 is a flow chart showing a process flow at the time of restart according to a second embodiment. Fig. 6 is a time chart showing operations at the time of restart according to the second embodiment. EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0010] [0010. Fig. 1 schematically illustrates a configuration of a series hybrid vehicle as an example of a vehicle to which the present invention is applied. The series hybrid vehicle includes a power generation-purpose motor generator 1 that operates mainly as a generator, an internal combustion engine 2 that is used as a power generation-purpose internal combustion engine to drive the power generation-purpose motor generator 1 in response to a power request, a vehicle travel-purpose motor generator 4 that operates mainly as a motor and drives driving wheels 3, and a battery 5 that temporarily stores the generated power. Electric power obtained by driving the power generation-purpose motor generator 1 by the internal combustion engine 2 is stored in the battery 5 via an inverter device (not shown). The vehicle travel-purpose motor generator 4 is driven and controlled using the power of the battery 5. Electric power generated during regeneration of the vehicle travel-purpose motor generator 4 is also stored in the battery 5 via the inverter device (not shown).

[0011] [0011. Operation of the motor generators 1 and 4, charge and discharge of the battery 5, and operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is configured by a plurality of controllers connected to each other so as to be able to communicate with each other, such as a motor controller 7 for controlling the motor generators 1 and 4, an engine controller 8 for controlling the internal combustion engine 2, and a battery controller 9 for managing the battery 5. The controller 6 inputs information such as an opening degree of an accelerator pedal (not shown) and a vehicle speed. The battery controller 9 determines an SOC of the battery 5 on the basis of voltage and current of the battery 5. Basically, based on decrease in this SOC, the engine controller 8 is required to start the internal combustion engine 2. As operating modes of such series hybrid vehicle, they are an EV mode in which the vehicle travels by power of the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle travels while generating power by combustion operation of the internal combustion engine 2.

[0012] [0012. That is, the combustion operation of the internal combustion engine 2 is not constantly performed during vehicle operation in which a main switch of the vehicle is on, but automatic stop and automatic restart of the internal combustion engine 2 are repeated according to a power generation request. When performing the automatic restart, motoring of the internal combustion engine 2 is performed by power running of the power generation-purpose motor generator 1 mechanically connected to a crankshaft of the internal combustion engine 2.

[0013] [0013. Fig. 2 illustrates a system configuration of the internal combustion engine 2. This internal combustion engine 2 is, for instance, a four-stroke cycle spark ignition internal combustion engine having a turbocharger 12. A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on a ceiling wall surface of each cylinder 13 of the internal combustion engine 2, and an ignition plug 16 is disposed at a center portion 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 valves 14. An ignition timing of the ignition plug 16, and a fuel injection timing and a fuel injection amount by the fuel injection valve 17 are controlled by the engine controller 8.

[0014] [0014. The intake valve 14 is provided with a variable valve timing mechanism 18 that can change a valve timing, i.e. an opening timing and a closing timing of the intake valve 14. As the variable valve timing mechanism 18, any type of variable valve timing mechanism can be used. For instance, a mechanism in which a phase of a camshaft is retarded or advanced relative to a phase of a crankshaft could be used.

[0015] [0015. In an intake passage 21, an intake collector 21a is provided, and at an upstream side with respect to this intake collector 21a, an electronically controlled throttle valve 22 whose opening is controlled by a control signal from the engine controller 8 is provided. A compressor 12a of the turbocharger 12 is located at an upstream side of the throttle valve 22, and an air flow meter 24 for detecting an amount of intake air and an air cleaner 25 are disposed at an upstream side with respect to the compressor 12a. Between the compressor 12a and the throttle valve 22, in order to cool high-temperature and high-pressure intake air, for instance, a water-cooled intercooler 26 is provided. Furthermore, a recirculation valve 27 is provided so as to connect a discharge side and a suction side of the compressor 12a.

[0016] [0016. In an exhaust passage 30, a turbine 12b of the turbocharger 12 is located, and at a downstream side of this turbine 12b, a pre-catalyst device 31 and a main catalyst device 32, each of which is made up of a three-way catalyst, are disposed. The pre-catalyst device 31 is disposed at an outlet of the turbine 12b, and the main catalyst device 32 is disposed under a floor of the vehicle. An air-fuel ratio sensor 33 for detecting an air-fuel ratio is disposed at an upstream side with respect to the turbine 12b in the exhaust passage 30. The turbine 12b is provided with a waste gate valve 34 that bypasses a part of an exhaust gas in accordance with a boost pressure in order to control the boost pressure. As the waste gate valve 34, for instance, an electrically operated valve whose opening is controlled by the engine controller 8 is used.

[0017] [0017. Furthermore, an exhaust gas recirculation passage 35 that recirculates a part of the exhaust gas from the exhaust passage 30 to the intake passage 21 is provided. In this exhaust gas recirculation passage 35, for instance, a water-cooled EGR gas cooler 37 and an EGR valve 38 are provided.

[0018] [0018. The engine controller 8 inputs detection signals of sensors such as, in addition to the air flow meter 24 and the air-fuel ratio sensor 33, a crank angle sensor 41 for detecting an engine rotation speed, a water temperature sensor 42 for detecting a 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 a 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, the fuel injection timing, the ignition timing, the opening of the throttle valve 22, the boost pressure, etc.

[0019] [0019. Here, as the catalyst temperature sensors 43 and 44, instead of a sensor that directly detects a carrier temperature of the catalyst, a sensor that indirectly detects a catalyst temperature from gas temperatures etc. at front and rear sides of the sensor may be used. In this case, after the combustion operation of the internal combustion engine 2 is automatically stopped, a current catalyst temperature is sequentially estimated from various temperature conditions etc.

[0020] [0020. Basically, the internal combustion engine 2 is started when the SOC of the battery 5 deceases to a predetermined start SOC value, and the internal combustion engine 2 is stopped when the SOC reaches a sufficient level. Furthermore, in one embodiment, when required power exceeds the power that can be supplied from the battery 5, such as when the vehicle is required to suddenly accelerate during vehicle travel in EV mode, the internal combustion engine 2 is restarted, and power generation is performed. Therefore, automatic restart and automatic stop of the internal combustion engine 2 are repeated relatively frequently.

[0021] [0021. Next, control performed when automatically restarting the internal combustion engine 2, which is a main part of the present invention, will be described with reference to a flow chart of Fig. 3. A process shown in the flow chart of Fig. 3 is repeatedly executed by the engine controller 8 during stop of the combustion operation of the internal combustion engine 2.

[0022] [0022. First, in step 1, it is determined whether or not there is a restart request of the internal combustion engine 2 based on the SOC etc. of the battery 5. If there is no restart request, the routine ends. If the restart request has been made, the process proceeds to step 2, and it is determined whether or not a 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 could also be used as a representative catalyst temperature Tc.

[0023] [0023. If the catalyst temperature Tc is lower than the activation temperature Tc0, since there is no influence on the oxygen storage capacity of the catalyst due to the flow of air, the process proceeds from step 2 to step 3 and beyond, and by performing the motoring, rise in an in-cylinder temperature and development of a negative pressure are achieved. First, in step 3, the variable valve timing mechanism 18 of the intake valve 14 is controlled so that volumetric efficiency during the motoring is relatively higher than volumetric efficiency at the time of the restart at the activation temperature Tc0 or higher. In one embodiment, basic valve timing setting (valve timing setting in the normal operation and at the time of the restart at the activation temperature Tc0 or higher) is a so-called delayed closing valve timing setting in which an intake valve closing timing IVC is delayed relatively significantly from the bottom dead center in order to improve fuel efficiency. In contrast to this, valve timing at the time of the restart at the catalyst temperature lower than the activation temperature Tc0 is set so that the intake valve closing timing IVC is relatively close to the bottom dead center so as to increase the volumetric efficiency. Furthermore, in step 4, similarly, in order to increase the volumetric efficiency, an opening TVO of the throttle valve 22 is corrected and increased, as compared with an opening at the time of the restart at the activation temperature Tc0 or higher. Then, in step 5, motoring using the power generation-purpose motor generator 1 is started. For instance, motoring is performed at a predetermined rotational speed of about 1000 to 1500 rpm. With this motoring, the in-cylinder temperature is increased, and the negative pressure in the intake system is developed.

[0024] [0024. In step 6, based on an outside air temperature To and a coolant temperature Tw at that time, a required delay time tD (in other words, a motoring time before the start of fuel injection and ignition) is calculated. The lower the outside air temperature, the longer the required delay time tD. Similarly, the lower the coolant temperature, the longer the required delay time tD. For instance, the delay time tD is calculated using a map having the outside air temperature To and the coolant temperature Tw as parameters.

[0025] [0025. In step 7, it is determined whether or not an elapsed time t from the start of the motoring is equal to or greater than the delay time tD. If the elapsed time t reaches the delay time tD, the process proceeds from step 7 to step 8, and fuel injection and ignition are started. This causes the internal combustion engine 2 to start combustion operation. When the internal combustion engine 2 reaches a complete combustion state and enters self-sustaining operation, the power generation-purpose motor generator 1, which has been subjected to rotation control, quickly shifts to a regenerative mode, i.e. a power generation mode.

[0026] [0026. As described above, when the catalyst temperature Tc at the time of the restart request is lower than the activation temperature Tc0, the motoring is performed for the delay time tD, and then the fuel injection and the ignition are started. The motoring causes the negative pressure in the intake system to develop, and causes the in-cylinder temperature to increase, which bring about good atomization and good vaporization of the injected fuel, thereby improving emissions (for example, HC and CO) immediately after the start of combustion. In addition, during the motoring, by changing the valve timing and increasing the throttle valve opening TVO, an amount of air taken into the cylinder in each cycle increases, and the in-cylinder temperature is effectively increased accordingly. Furthermore, since the delay time tD is set in consideration of the outside air temperature To and the coolant temperature Tw, even when the outside air temperature To and the coolant temperature Tw are low, a good effect can be obtained.

[0027] [0027. The delay time tD varies depending on the temperature conditions, a motoring rotational speed, etc., but it is, for instance, about one second.

[0028] [0028. In step 2, if it is determined that the catalyst temperature Tc is equal to or higher than the activation temperature Tc0, the process proceeds from step 2 to step 9, and motoring using the power generation-purpose motor generator 1 is started. Then, substantially simultaneously with the start of the motoring, fuel injection and ignition are started in step 8.

[0029] [0029. In this manner, when the catalyst temperature Tc is equal to or higher than the activation temperature Tc0, the fuel injection and the ignition are initiated promptly. Therefore, a large amount of oxygen-containing air does not flow into the catalytic devices 31 and 32 due to the motoring without combustion. This makes it possible to avoid saturation of the oxygen storage capacity of the catalyst, and thus to avoid deterioration of NOx immediately after the start.

[0030] [0030. Fig. 4 is a time chart illustrating operations at the time of the restart when the catalyst temperature Tc at the time of the restart request is lower than the activation temperature Tc0, and shows changes in (a) the catalyst temperature Tc and the outside air temperature To, (b) the coolant temperature Tw, (c) an engine rotation speed Ne, (d) the intake valve closing timing IVC, (e) the throttle valve opening TVO, (f) the elapsed time t, and (g) an injection start flag. In this example, the restart request is made at time t1, and the catalyst temperature Tc at that time is lower than the activation temperature Tc0. At time t1, motoring is started, and substantially simultaneously with the start of the motoring, the intake valve closing timing IVC is changed, and the throttle valve opening TVO is increased. Then, at time t2 when the predetermined delay time tD has elapsed from time t1, fuel injection and ignition are started. After the start, the intake valve closing timing IVC and the throttle valve opening TVO are returned to their respective normal states.

[0031] [0031. Next, a process at the time of restart according to a second embodiment will be described with reference to a flow chart in Fig. 5 and a time chart in Fig. 6. In the second embodiment, instead of defining a delay period by the elapsed time t as in the above embodiment, the delay period is defined by an in-cylinder temperature Tic during motoring.

[0032] [0032. The flow chart in Fig. 5 is basically the same as the flow chart shown in Fig. 3. If the catalyst temperature Tc at the time of the restart request (step 1) is equal to or higher than the activation temperature Tc0, after start of motoring (step 9), substantially simultaneously with the start of the motoring, fuel injection and ignition are started (step 8).

[0033] [0033. If the catalyst temperature Tc is lower than the activation temperature Tc0, valve timing is changed so that the intake valve closing timing IVC gets close to the bottom dead center (step 3), and the throttle valve opening TVO is corrected and increased (step 4), then motoring is started (step 5).

[0034] [0034. In the second embodiment, the process proceeds from step 5 to step 11, and the in-cylinder temperature Tic, which increases by the motoring, is estimated. For instance, an 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 sequentially estimated by accumulating temperature rise in each cycle (or each small unit time) by the motoring. Then, in step 12, it is determined whether or not this estimated in-cylinder temperature Tic is equal to or higher than a predetermined threshold temperature Tic0. The estimation of the in-cylinder temperature Tic is repeatedly performed until the estimated in-cylinder temperature Tic reaches the threshold temperature Tic0.

[0035] [0035. When the estimated in-cylinder temperature Tic reaches the threshold temperature Tic0, the process proceeds from step 12 to step 8, and fuel injection and ignition are started.

[0036] [0036. The time chart in Fig. 6 is basically the same as the time chart shown in Fig. 4, but in (f), instead of the elapsed time t, a change in the in-cylinder temperature Tic is shown. At time t1, motoring is started, and substantially simultaneously with the start of the motoring, 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, which increases from time t1, reaches the predetermined threshold temperature Tic0, fuel injection and ignition are started.

[0037] [0037. Although the invention has been described above by reference to the embodiments of the invention, the invention is not limited to the embodiments described above, and various modifications can be made. For instance, the above embodiments describe the example in which the present invention is applied to the power generation-purpose internal combustion engine of the series hybrid vehicle. However, the present invention can also be applied to an internal combustion engine of other type of hybrid vehicle, or an internal combustion engine (e.g. an internal combustion engine having an idling stop function) that serves as a travel driving source of the vehicle having no motor.

[0038] [0038. Furthermore, the variable valve timing mechanism could be provided on both of 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 method of controlling restart of an internal combustion engine whose combustion operation is automatically stopped and automatically restarted during vehicle operation, the method comprising: determining whether or not a catalyst temperature at a time of a restart request is equal to or higher than an activation temperature; if the catalyst temperature is equal to or higher than the activation temperature, substantially simultaneously with a start of motoring of the internal combustion engine, starting fuel injection and ignition; and if the catalyst temperature is lower than the activation temperature, after a delay period from the start of the motoring of the internal combustion engine, starting the fuel injection and the ignition.

2. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein the delay period ends when an elapsed time from the start of the motoring reaches a predetermined time.

3. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein an in-cylinder temperature that increases by the motoring is estimated, and the delay period ends when an estimated in-cylinder temperature reaches a predetermined temperature.

4. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein the lower the outside air temperature, the longer the delay period is set.

5. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein the lower the coolant temperature of the internal combustion engine, the longer the delay period is set.

6. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein when the catalyst temperature is lower than the activation temperature, a valve timing of at least one of an intake valve and an exhaust valve is corrected so that volumetric efficiency during the motoring is higher than volumetric efficiency when the catalyst temperature is equal to or higher than the activation temperature.

7. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein when the catalyst temperature is lower than the activation temperature, an opening of a throttle valve is corrected and increased so that volumetric efficiency during the motoring is higher than volumetric efficiency when the catalyst temperature is equal to or higher than the activation temperature.

8. The method of controlling restart of the internal combustion engine as claimed in claim 1, wherein the internal combustion engine is an internal combustion engine that drives a generator in a hybrid vehicle capable of travelling by a motor output, and the motoring is performed by power running of the generator.

9. A restart control device of an internal combustion engine comprising: an internal combustion engine having, in an exhaust passage, a catalyst for purifying exhaust gas; and a controller configured to automatically stop and automatically restart combustion operation of the internal combustion engine during vehicle operation, wherein the controller is further configured to: determine whether or not a catalyst temperature at a time of a restart request is equal to or higher than an activation temperature; if the catalyst temperature is equal to or higher than the activation temperature, substantially simultaneously with a start of motoring of the internal combustion engine, start fuel injection and ignition; and if the catalyst temperature is lower than the activation temperature, after a delay period from the start of the motoring of the internal combustion engine, start the fuel injection and the ignition.

Images