Internal combustion engine

An internal combustion engine includes an internal combustion engine body including an intake valve and an exhaust valve, and a controller configured or programmed to perform a control to set a rotational speed of the internal combustion engine body to a predetermined rotational speed based on an environmental temperature at a time of starting the internal combustion engine body, and perform a control to drive the internal combustion engine body at the set predetermined rotational speed during a time period until when fuel is supplied to a combustion chamber of the internal combustion engine body and first ignition is performed.

TECHNICAL FIELD

The present invention relates to an internal combustion engine, and more particularly, it relates to an internal combustion engine including a controller configured or programmed to perform a control to warm a combustion chamber before the first ignition.

BACKGROUND ART

In general, an internal combustion engine including a controller configured or programmed to perform a control to warm a combustion chamber before the first ignition is known. Such an internal combustion engine is disclosed in Japanese Patent Laid-Open No. 2009-299538, for example.

Japanese Patent Laid-Open No. 2009-299538 discloses an engine including a control device configured or programmed to perform a control to warm a combustion chamber before the first ignition by motoring, and a variable valve timing mechanism. The control device is configured or programmed to uniformly set the closing timing of an intake valve to be more advanced than the reference timing (during steady operation) by the variable valve timing mechanism at the time of motoring. Thus, the engine closes the intake valve early on the bottom dead center side and retains a large amount of intake air in a cylinder so as to compress the intake air and raise the temperature in the cylinder. When the temperature in the cylinder rises, a fuel is effectively atomized, and thus an exhaust gas immediately after the first explosion is reduced.

PRIOR ART

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, in the engine disclosed in Japanese Patent Laid-Open No. 2009-299538, at the time of motoring, the closing timing of the intake valve is uniformly set to be more advanced than the reference timing (during steady operation), and it is difficult to perform an appropriate control to reduce the exhaust gas according to the environmental temperature of the engine. That is, in the engine described in Patent Document 1, the variable valve timing mechanism is not controlled in consideration of the environmental temperature such as cold start.

The present invention has been proposed in order to solve the aforementioned problem, and an object of the present invention is to provide an internal combustion engine capable of performing an appropriate control to reduce an exhaust gas according to the environmental temperature of the internal combustion engine.

Means for Solving the Problem

In order to attain the aforementioned object, an internal combustion engine according to an aspect of the present invention includes an internal combustion engine body including an intake valve and an exhaust valve, and a controller configured or programmed to perform a control to set a rotational speed of the internal combustion engine body to a predetermined rotational speed based on an environmental temperature at a time of starting the internal combustion engine body, and perform a control to drive the internal combustion engine body at the set predetermined rotational speed during a time period until when fuel is supplied to a combustion chamber of the internal combustion engine body and first ignition is performed.

As described above, the internal combustion engine according to this aspect of the present invention includes the controller configured or programmed to perform a control to set the rotational speed of the internal combustion engine body to the predetermined rotational speed based on the environmental temperature at the time of starting the internal combustion engine body, and perform a control to drive the internal combustion engine body at the set predetermined rotational speed during the time period until when the fuel is supplied to the combustion chamber of the internal combustion engine body and the first ignition is performed. Accordingly, for example, when the environmental temperature is low (in the case of cold start), it is possible to effectively warm the inside of the combustion chamber due to friction between a cylinder and a piston and inertia supercharging when the rotational speed of the internal combustion engine body is set to be particularly high, and thus an appropriate control to reduce an exhaust gas can be performed according to the environmental temperature of the internal combustion engine. When the inside of the combustion chamber is warmed, atomization of the fuel is promoted, and the exhaust gas generated at the time of the first ignition can be reduced.

The aforementioned internal combustion engine according to this aspect preferably further includes a variable valve mechanism configured to adjust an opening-closing timing of the intake valve under control of the controller, and the controller is preferably configured or programmed to perform a timing control to set a closing timing of the intake valve based on the predetermined rotational speed such that a largest amount of outside air is introduced.

According to this structure, the (largest amount of) outside air can be effectively introduced into the combustion chamber in consideration of inertia supercharging based on the rotational speed of the internal combustion engine body and intake pulsation, for example. Consequently, the pressure in the combustion chamber is effectively increased such that the inside of the combustion chamber can be effectively warmed, and thus a more appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the internal combustion engine.

In the aforementioned structure in which the timing control is performed, the controller is preferably configured or programmed to continue the timing control until a first cycle in which the fuel is supplied to the combustion chamber and the first ignition is performed, and to control the variable valve mechanism to restore a valve timing of the intake valve to that during steady operation in second and subsequent cycles.

In the second and subsequent cycles, the intake amount is increased due to the influence of recirculation of an EGR gas, for example, as compared with the first cycle, and thus it is necessary to set the valve timing to the predetermined valve timing. Therefore, with the structure described above, the timing control can be continued for a longer time as compared with a case in which the timing control is finished only at the initial stage of a period before the first ignition, and thus the inside of the combustion chamber can be more effectively warmed. Consequently, a more appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the internal combustion engine.

The aforementioned internal combustion engine according to this aspect preferably further includes a variable valve mechanism configured to adjust an opening-closing timing of the intake valve under control of the controller, and the controller is preferably configured or programmed to close the intake valve on a retardation angle side of an intermediate phase between a bottom dead center and a top dead center while a piston moves from the bottom dead center to the top dead center during the time period until when the fuel is supplied to the combustion chamber and the first ignition is performed.

According to this structure, a gas in the cylinder, the temperature of which has risen due to the friction between the piston and the cylinder, for example, can be blown back to the intake pipe side for a relatively long time during movement of the piston from the bottom dead center to the top dead center. That is, the high-temperature gas can be blown back to the intake pipe side for a time longer than at least half of the time required for the piston to move from the bottom dead center to the top dead center. Consequently, atomization of the fuel can be effectively promoted, and thus unburned fuel can be reduced while the exhaust gas can be reduced. Thus, the fuel injection amount at the time of cold start can also be reduced. The exhaust gas can be reduced, and thus the amount of precious metal used as a catalyst may be reduced.

In this case, the controller is preferably configured or programmed to close the intake valve at the top dead center or in a vicinity of the top dead center during the time period until when the fuel is supplied to the combustion chamber and the first ignition is performed.

According to this structure, the high-temperature gas in the cylinder can be blown back to the intake pipe side for a longer time while the piston moves from the bottom dead center to the top dead center. Consequently, atomization of the fuel can be promoted more effectively.

In the aforementioned internal combustion engine according to this aspect, the controller is preferably configured or programmed to supply the fuel to the combustion chamber and perform the first ignition at a timing at which a temperature in the combustion chamber exceeds a predetermined set temperature based on an estimation logic for estimating the temperature in the combustion chamber.

According to this structure, the estimation logic is used such that the controller does not need to perform a calculation to determine the timing for the first ignition, and thus the control load on the controller can be reduced.

In this case, the estimation logic preferably includes a map showing a relationship between the temperature in the combustion chamber and driving duration of the internal combustion engine body at the predetermined rotational speed.

According to this structure, with the map showing the relationship between the temperature in the combustion chamber and the driving duration (motoring duration) of the internal combustion engine body at the predetermined rotational speed, the timing for the first ignition can be easily determined without performing a complex calculation.

The aforementioned internal combustion engine according to this aspect preferably further includes a temperature sensor to measure a temperature in an intake pipe, and the controller is preferably configured or programmed to supply the fuel to the combustion chamber and perform the first ignition at a timing at which the temperature measured by the temperature sensor exceeds a predetermined set temperature.

According to this structure, the timing at which the fuel is supplied to the combustion chamber and the first ignition is performed can be accurately determined with the temperature sensor.

In the aforementioned internal combustion engine according to this aspect, the environmental temperature preferably includes at least one of a temperature of outside air around the internal combustion engine body or a temperature of cooling water of the internal combustion engine body.

According to this structure, a control to warm the inside of the combustion chamber can be performed before the first ignition with a temperature sensor that measures the temperature of the outside air around the internal combustion engine body or a temperature sensor that measures the temperature of the cooling water of the internal combustion engine body, which is generally provided in an internal combustion engine.

The aforementioned internal combustion engine according to this aspect preferably further includes a hybrid drive motor to drive a piston, and the controller is preferably configured or programmed to set the rotational speed of the internal combustion engine body to the predetermined rotational speed based on the environmental temperature at the time of starting the internal combustion engine body, and to control the hybrid drive motor to drive the internal combustion engine body at the set predetermined rotational speed during the time period until when the fuel is supplied to the combustion chamber and the first ignition is performed.

According to this structure, motoring is performed by the hybrid drive motor such that an appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the internal combustion engine.

MODES FOR CARRYING OUT THE INVENTION

Embodiments embodying the present invention are hereinafter described on the basis of the drawings.

First Embodiment

The structure of an engine1(an example of an internal combustion engine) according to a first embodiment is now described with reference toFIGS. 1 to 6.

As shown inFIG. 1, the engine1according to the first embodiment is incorporated in a hybrid vehicle10.

The engine1includes an engine body2(an example of an internal combustion engine body), a variable valve mechanism3(seeFIG. 2), an intake pipe4a(seeFIG. 2) connected to the upstream side of the engine body2, an exhaust pipe4bconnected to the downstream side of the engine body2, an electric motor5(an example of a hybrid drive motor) used for motoring, and an engine control unit (ECU)6(an example of a controller).

As shown inFIG. 2, the engine body2includes a cylinder block21and a cylinder head22attached to an upper portion of the cylinder block21. The cylinder block21includes a cylinder24in which a combustion chamber23is provided inside. A crankshaft (not shown) is provided in the engine body2. Furthermore, the engine body2includes an intake valve26aand an exhaust valve26b. The engine1opens and closes the intake valve26aand the exhaust valve26bat predetermined valve timings by rotating camshafts25aand25bby the power of the crankshaft.

The cylinder block21includes a water jacket27that circulates cooling water W to cool the engine1. The water jacket27is arranged adjacent to the combustion chamber23. At the time of motoring, the temperature of the engine1(the combustion chamber23and the cylinder24) rises due to friction between a piston P and the cylinder24and the compression of air in the cylinder24(combustion chamber23). Therefore, at the time of motoring, the cooling water W takes heat from the engine1, the temperature of which has risen, such that the temperature of the cooling water W also rises.

The variable valve mechanism3is configured to adjust the opening-closing timings of the intake valve26aand the exhaust valve26bof the combustion chamber23. Specifically, the variable valve mechanism3is configured to independently shift rotation of the camshafts25aand25bin a retard or advance direction in order to shift the opening-closing timings of the intake valve26aand the exhaust valve26b. The variable valve mechanism3is installed on a timing chain (not shown), and continuously changes the opening-closing timing of the intake valve26a(exhaust valve26b) while maintaining the cam phases and lift amount profiles. Therefore, the angular width of the valve opening period of the intake valve26a(exhaust valve26b) does not change. The variable valve mechanism3is an electric mechanism that can operate even before the engine is started.

That is, the variable valve mechanism3is configured to advance or retard both the opening timing (hereinafter referred to as the IVO (intake valve open)) and the closing timing (hereinafter referred to as the IVC (intake valve close)) of the intake valve26a.

The variable valve mechanism3is also configured to advance or retard both the opening timing (hereinafter referred to as the EVO (exhaust valve open)) and the closing timing (hereinafter referred to as the EVC (exhaust valve close)) of the exhaust valve26b. The variable valve mechanism3is configured to be driven under control of the ECU6.

The intake pipe4ais configured to supply intake air to the combustion chamber23via the intake valve26a. The exhaust pipe4bis configured to discharge exhaust air (exhaust gas) discharged from the combustion chamber23to the outside (atmosphere) via the exhaust valve26b. The exhaust pipe4bis provided with a catalyst C and a muffler F arranged on the downstream side of the catalyst C.

The intake pipe4aand the exhaust pipe4bare each provided with an EGR pipe4cto recirculate an EGR gas (exhaust gas). The EGR pipe4cis provided with an EGR valve (not shown) to open and close the EGR pipe4cand an EGR gas cooler (not shown) to cool the EGR gas. An injector (not shown) that injects a fuel into an intake passage is provided in the intake pipe4a(on the upstream side of the intake valve26a).

The electric motor5is configured to drive the engine body2at a predetermined rotational speed (set rotational speed) at the time of motoring. The predetermined rotational speed (set rotational speed) is not a constant rotational speed, but a rotational speed that is reset each time motoring is performed. The set predetermined rotational speed (set rotational speed) does not vary during the course of one motoring operation. The electric motor5is configured to be driven under control of the ECU6.

Structure of ECU

The ECU6is configured or programmed to control each portion of the engine1. The ECU6is configured or programmed to control the electric motor5and the variable valve mechanism3to effectively warm the engine body2(the inside of the cylinder24and the inside of the combustion chamber23) at the time of motoring. Thus, the ECU6effectively raises a pressure inside the cylinder24(inside the combustion chamber23) to promote atomization of the fuel at the time of the first explosion (when the fuel is supplied to the combustion chamber23and ignited for the first time) and reduce the exhaust gas immediately after the explosion.

Specifically, in the first embodiment, the ECU6performs a control to set the rotational speed of the engine body2to a predetermined rotational speed based on the environmental temperature at the time of starting the engine body2. Then, the ECU6controls the electric motor5to drive the engine body2at the set predetermined rotational speed (set rotational speed) during a time period until when the fuel is supplied to the combustion chamber23of the engine body2and the first ignition is performed.

The ECU6is configured or programmed to set the predetermined rotational speed (set rotational speed) to be lower as the environmental temperature becomes higher, and set the predetermined rotational speed (set rotational speed) to be higher as the environmental temperature becomes lower.

The environmental temperature refers to the temperature of the cooling water W that flows through the water jacket27of the engine body2. The engine body2includes a temperature sensor S1to measure the environmental temperature (the temperature of the cooling water W). The ECU6is configured or programmed to acquire information on the environmental temperature (the temperature of the cooling water W) from the temperature sensor S1before starting motoring.

For example, as shown inFIG. 3, when the environmental temperature is T1 [° C.], the ECU6sets the rotational speed (set rotational speed) of the engine body2at the time of motoring to R1 [rpm].

When the environmental temperature is T2 [° C.] higher than T1 [° C.], the ECU6sets the rotational speed (set rotational speed) of the engine body2at the time of motoring to R2 [rpm] smaller than R1 [rpm] (T1<T2 and R1>R2).

When the environmental temperature is T3 [° C.] higher than T2 [° C.], the ECU6sets the rotational speed (set rotational speed) of the engine body2at the time of motoring to R3 [rpm] smaller than R2 [rpm] (T2<T3 and R2>R3). As the rotational speed decreases, the noise vibration (NV) of the engine1can be reduced.

As an example, the rotational speed of the engine body2at the time of motoring is set within a range of about 1000 [rpm] or more and about 4000 [rpm] or less.

As shown inFIG. 4, the ECU6is configured or programmed to perform a timing control to set the timing at which the variable valve mechanism3closes the intake valve26ato be closer to the retardation angle side as setting the predetermined rotational speed (set rotational speed) to be higher. The timing control refers to a control to set the closing timing of the intake valve26asuch that the largest amount of outside air can be introduced into the combustion chamber23. In the timing control, the closing timing of the intake valve26ais set to be at least on the advance angle side of an intermediate phase α between a bottom dead center and a top dead center during movement of the piston P from the bottom dead center to the top dead center (seeFIG. 5).

For example, when setting the rotational speed (set rotational speed) of the engine body2to R1 [rpm] based on the environmental temperature of T1 [° C.], the ECU6sets the timing (IVC) of closing the intake valve26ato a11 [degree]. In the following, setting for motoring in which the rotational speed is R1 and the IVC is a11 [degree] is defined as the first motoring setting.

When setting the rotational speed (set rotational speed) of the engine body2to R2 [rpm] based on the environmental temperature of T2 [° C.] higher than T1 [° C.], the ECU6sets the timing (IVC) of closing the intake valve26ato a21 [degree] on the advance angle side of a11 [degree]. In the following, setting for motoring in which the rotational speed is R2 [rpm] and the IVC is a21 [degree] is defined as the second motoring setting.

When setting the rotational speed (set rotational speed) of the engine body2to R3 [rpm] based on the environmental temperature of T3 [° C.] higher than T2 [° C.], the ECU6sets the timing (IVC) of closing the intake valve26ato a31 [degree] on the advance angle side of a21 [degree]. In the following, setting for motoring in which the rotational speed is R3 [rpm] and the IVC is a31 [degree] is defined as the third motoring setting.

As shown inFIG. 5, the EVC and EVO are set to the same angle regardless of the motoring setting. InFIG. 5, the EVC is indicated by a41 [degree], and the EVO is indicated by a42 [degree]. Furthermore, the IVO in the first motoring setting is indicated by a12 [degree]. The IVO in the second motoring setting is indicated by a22 [degree]. The IVO in the third motoring setting is indicated by a32 [degree].

The ECU6is configured or programmed to supply the fuel to the chamber23and perform the first ignition at the timing at which the in-cylinder temperature (estimated environmental temperature) exceeds a predetermined set temperature (ignition start temperature T10 [° C.]) based on an estimation logic for estimating the temperature in the combustion chamber23. That is, the ECU6is configured or programmed to perform a control to end the motoring based on the estimation logic. Note that the predetermined set temperature (ignition start temperature T10 [° C.]) in the cylinder estimated by the estimation logic is a predetermined temperature at which it is estimated that the fuel is appropriately atomized and the exhaust gas can be reduced after the first explosion. The set temperature (ignition start temperature T10 [° C.]) is a temperature common to each of the first to third motoring settings.

As shown inFIG. 6, the estimation logic is a map M showing the relationship between the environmental temperature (in-cylinder temperature) and the driving duration (motoring duration) of the engine body2at the predetermined rotational speed.

InFIG. 6, the motoring duration for reaching the ignition start temperature T10 [° C.] in each motoring setting is shown to be substantially the same, but the motoring duration for reaching the ignition start temperature T10 [° C.] in each motoring setting may be different from each other.

The ECU6is configured or programmed to continue the timing control until the first cycle in which the fuel is supplied to the combustion chamber23and the first ignition is performed, and to control the variable valve mechanism3to restore the valve timing of the intake valve26ato that during steady operation in the second and subsequent cycles. In the second and subsequent cycles, the EGR gas (exhaust gas) is recirculated from the exhaust pipe4bto the intake pipe4avia the EGR pipe4c.

Control Flow at Time of Motoring by ECU

A control flow at the time of motoring by the ECU6is now described with reference toFIGS. 2 to 6.

First, the ECU6acquires the information on the environmental temperature (the temperature of the cooling water W) from the temperature sensor S1(seeFIG. 2) provided in the engine body2at the time of starting the engine body2. Then, the ECU6sets the rotational speed of the engine body2to the predetermined rotational speed based on the acquired environmental temperature.

Furthermore, the ECU6performs a control (timing control) to adjust the timing at which the variable valve mechanism3closes the intake valve26aaccording to the predetermined rotational speed (set rotational speed).

Next, the ECU6controls the electric motor5to drive the engine body2at the predetermined rotational speed (set rotational speed). Then, the ECU6supplies the fuel to the combustion chamber23and performs the first ignition at the timing at which the temperature (environmental temperature (in-cylinder temperature)) in the combustion chamber23exceeds the predetermined set temperature (ignition start temperature) based on the estimation logic (map M) for estimating the temperature (environmental temperature (in-cylinder temperature)) in the combustion chamber23.

Note that the ECU6continues the timing control until the first cycle in which the fuel is supplied to the combustion chamber23and the first ignition is performed, and in the second and subsequent cycles, the ECU6controls the variable valve mechanism3to restore the valve timing of the intake valve26ato that during steady operation.

Advantageous Effects of First Embodiment

According to the first embodiment, the following advantageous effects are achieved.

According to the first embodiment, as described above, the engine1includes the ECU6configured or programmed to perform a control to set the rotational speed of the engine body2to the predetermined rotational speed based on the environmental temperature at the time of starting the engine body2, and perform a control to drive the engine body2at the set predetermined rotational speed during the time period until when the fuel is supplied to the combustion chamber23of the engine body2and the first ignition is performed.

Accordingly, for example, when the environmental temperature is low (in the case of cold start), it is possible to effectively warm the inside of the combustion chamber23due to the friction between the cylinder24and the piston P and inertia supercharging when the rotational speed of the engine body2is set to be particularly high, and thus an appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the engine1. When the inside of the combustion chamber23is warmed, atomization of the fuel is promoted, and the exhaust gas generated at the time of the first ignition can be reduced.

According to the first embodiment, as described above, the engine1further includes the variable valve mechanism3capable of adjusting the opening-closing timing of the intake valve26aunder control of the ECU6, and the ECU6is configured or programmed to perform the timing control to set the closing timing of the intake valve26abased on the predetermined rotational speed such that the largest amount of outside air can be introduced. Accordingly, the (largest amount of) outside air can be effectively introduced into the combustion chamber23in consideration of inertia supercharging and intake pulsation based on the rotational speed of the engine body2, for example. Consequently, the pressure in the cylinder24is effectively increased such that the inside of the combustion chamber23can be effectively warmed, and thus a more appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the engine1. From the viewpoint of inertia supercharging, when the closing timing (IVC) of the intake valve26ais closer to the retardation angle side as the rotational speed of the engine1increases, the intake amount increases. However, considering intake pulsation (air resistance), the inertia supercharging effect becomes large when the rotational speed of the engine1is medium (about 3000 rpm to about 4000 rpm), and the inertia supercharging effect becomes small when the rotational speed of the engine1is high. Therefore, when the engine1is rotating at high speed, the intake amount may be larger on the advance angle side.

According to the first embodiment, as described above, the ECU6is configured or programmed to continue the timing control until the first cycle in which the fuel is supplied to the combustion chamber23and the first ignition is performed, and to control the variable valve mechanism3to restore the valve timing of the intake valve26ato that during steady operation in the second and subsequent cycles (ignition control). In the second and subsequent cycles, the intake amount is increased due to the influence of recirculation of the EGR gas, for example, as compared with the first cycle, and thus it is necessary to set the valve timing to the predetermined valve timing. Therefore, with the structure described above, the timing control can be continued for a longer time as compared with a case in which the timing control is finished only at the initial stage of a period before the first ignition, and thus the inside of the combustion chamber23can be more effectively warmed. Consequently, a more appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the engine1.

According to the first embodiment, as described above, the ECU6is configured or programmed to supply the fuel to the combustion chamber23and perform the first ignition at the timing at which the temperature in the combustion chamber23exceeds the predetermined set temperature based on the estimation logic for estimating the temperature in the combustion chamber23. Accordingly, the estimation logic is used such that the ECU6does not need to perform a calculation to determine the timing for the first ignition, and thus the control load on the ECU6can be reduced.

According to the first embodiment, as described above, the estimation logic includes the map M showing the relationship between the temperature in the combustion chamber23and the driving duration of the engine body2at the predetermined rotational speed. Accordingly, with the map M showing the relationship between the temperature in the combustion chamber23and the driving duration (motoring duration) of the engine body2at the predetermined rotational speed, the timing for the first ignition can be easily determined without performing a complex calculation.

According to the first embodiment, as described above, the engine1further includes the electric motor5to drive the piston P, and the ECU6is configured or programmed to set the rotational speed of the engine body2to the predetermined rotational speed based on the environmental temperature at the time of starting the engine body2, and to control the electric motor5to drive the engine body2at the set predetermined rotational speed during the time period until when the fuel is supplied to the combustion chamber23and the first ignition is performed. Accordingly, motoring is performed by the electric motor5such that an appropriate control to reduce the exhaust gas can be performed according to the environmental temperature of the engine1.

Second Embodiment

A second embodiment of the present invention is now described with reference toFIGS. 1 and 7 to 9. In this second embodiment, an example in which the timing at which an ECU206(an example of a controller) closes an intake valve26ais further retarded from the timing (seeFIG. 5) according to the first embodiment without performing a timing control (an example in which a super retardation angle control is performed) is described, unlike the first embodiment in which the timing control is performed by the ECU6. The same or similar structures as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

An engine201(an example of an internal combustion engine) according to the second embodiment shown inFIG. 7includes the ECU206configured or programmed to perform the super retardation angle control to set the closing timing of the intake valve26ato be on the retardation angle side. Furthermore, the engine201includes a temperature sensor S2to measure the temperature of gas in an intake pipe4a. The temperature sensor S2is provided on the downstream side of a throttle valve (not shown).

The super retardation angle control refers to controlling a variable valve mechanism3by the ECU206to set the relative rotation phase of the intake valve26ato be on the retardation angle side so as to reach a phase in which the engine201cannot be started and the engine201cannot operate autonomously even when a fuel is injected into the engine201and ignited.

Specifically, as shown inFIG. 8, the ECU206is configured or programmed to close the intake valve26a(set the IVC to a52 [degree]) on the retardation angle side of an intermediate phase α between a bottom dead center and a top dead center while a piston P moves from the bottom dead center to the top dead center during a time period until when the fuel is supplied to a combustion chamber23and the first ignition is performed. More specifically, the ECU206is configured or programmed to close the intake valve26aat the top dead center (or in the vicinity of the top dead center) during the time period until when the fuel is supplied to the combustion chamber23and the first ignition is performed.

As an example, when the IVC is set to a52 [degree], the IVO is set to a51 [degree] on the retardation angle side of an intermediate phase β between the top dead center and the bottom dead center during movement of the piston P from the top dead center to the bottom dead center.

When the super retardation angle control is performed, the engine206shown inFIG. 7is configured to blow back a gas in a cylinder24to the intake pipe4aside in substantially all of phases (time) from when the piston P reaches the bottom dead center to when the piston P reaches the top dead center in a state in which the intake valve26ais opened. At this time, the temperature of the gas in the cylinder24rises due to frictional heat generated by sliding of the piston P along the inner peripheral surface of the cylinder24, and the gas with increased temperature (high-temperature gas) is blown back from the inside of the cylinder24to the intake pipe4aside. Consequently, when the fuel is injected from an injector (not shown) that injects the fuel into an intake passage, the fuel can be effectively atomized.

The ECU206is configured or programmed to supply the fuel to the combustion chamber23and perform the first ignition by injecting the fuel from the injector at the timing at which the temperature measured by the temperature sensor S2exceeds a predetermined set temperature.

Control Process by ECU at Time of Starting Engine

A control process performed by the ECU206at the time of starting the engine is now described with reference toFIG. 9.

First, in step S1, the ECU206sets the rotational speed of an engine body2to a predetermined rotational speed based on an environmental temperature. This control is the same or similar as that of the first embodiment, and thus description thereof is omitted.

Next, in step S2, the ECU206determines whether or not cold start has been performed based on the environmental temperature acquired via a temperature sensor S1. For example, the ECU206determines whether or not cold start has been performed by determining whether the environmental temperature acquired via the temperature sensor S1is equal to, greater than, or less than a predetermined threshold temperature. When cold start has been performed, the process advances to step S3. When cold start has not been performed, the process advances to step S7.

Next, in step S3, the ECU206performs the super retardation angle control. That is, the ECU206sets the closing timing of the intake valve26ato the valve timing (very late valve closing timing shown inFIG. 8) at which the intake valve26ais closed at the top dead center (or in the vicinity of the top dead center).

Next, in step S4, the ECU206determines whether or not the closing timing of the intake valve26ahas been changed to the very late valve closing timing as set in step S3via the variable valve mechanism12. When the closing timing has been changed to the very late valve closing timing, the process advances to step S5. On the other hand, when the closing timing has not been changed to the very late valve closing timing, the operation in step S4is repeated. The determination by the ECU206in step S4is performed using a predetermined rotation angle sensor (not shown) provided in the variable valve mechanism12, for example. The same applies to step S8described below.

Next, in step S5, an electric motor5(seeFIG. 1) is driven by the ECU206to start motoring (driving of the piston P). Consequently, the temperature of the gas in the cylinder24starts to rise due to the frictional heat generated by sliding of the piston P along the inner peripheral surface of the cylinder24.

Next, in step S6, the ECU206determines whether or not the temperature of the gas measured by the temperature sensor S2(seeFIG. 7) exceeds the predetermined set temperature. When the temperature measured by the temperature sensor S2exceeds the predetermined set temperature, the process advances to step S7. On the other hand, when the temperature measured by the temperature sensor S2does not exceed the predetermined set temperature, the operation in step S6is repeated.

Next, in step S7, the ECU206sets the opening-closing timing of the intake valve26ato the predetermined valve timing for ignition.

Next, in step S8, the ECU206determines whether or not the opening-closing timing of the intake valve26ahas been changed to the predetermined valve timing for igniting as set in step S7via the variable valve mechanism12. When the opening-closing timing of the intake valve26ahas been changed to the predetermined valve timing for ignition, the process advances to step S9. On the other hand, when the opening-closing timing of the intake valve26ahas not been changed to the predetermined valve timing for ignition, the operation in step S8is repeated.

Next, in step S9, the ECU206starts ignition of the engine201.

Advantageous Effects of Second Embodiment

According to the second embodiment, the following advantageous effects are achieved.

According to the second embodiment, as described above, the engine201includes the variable valve mechanism12capable of adjusting the opening-closing timing of the intake valve26aunder control of the ECU206, and the ECU206is configured or programmed to close the intake valve26aon the retardation angle side of the intermediate phase a between the bottom dead center and the top dead center while the piston P moves from the bottom dead center to the top dead center during the time period until when the fuel is supplied to the combustion chamber23and the first ignition is performed. Accordingly, the gas in the cylinder24, the temperature of which has risen due to the friction between the piston P and the cylinder24, for example, can be blown back to the intake pipe4aside for a relatively long time during movement of the piston P from the bottom dead center to the top dead center. That is, the high-temperature gas can be blown back to the intake pipe4aside for a time longer than at least half of the time required for the piston P to move from the bottom dead center to the top dead center. Consequently, atomization of the fuel can be effectively promoted, and thus unburned fuel can be reduced while an exhaust gas can be reduced. Thus, the fuel injection amount at the time of cold start can also be reduced. The exhaust gas can be reduced, and thus the amount of precious metal used as a catalyst may be reduced.

According to the second embodiment, as described above, the ECU206is configured or programmed to close the intake valve26aat the top dead center or in the vicinity of the top dead center during the time period until when the fuel is supplied to the combustion chamber23and the first ignition is performed. Accordingly, the high-temperature gas in the cylinder24can be blown back to the intake pipe4aside for a longer time while the piston P moves from the bottom dead center to the top dead center. Consequently, atomization of the fuel can be promoted more effectively.

According to the second embodiment, as described above, the engine201includes the temperature sensor S2to measure the temperature in the intake pipe4a, and the ECU206is configured or programmed to supply the fuel to the combustion chamber23and perform the first ignition at the timing at which the temperature measured by the temperature sensor S2exceeds the predetermined set temperature. Accordingly, the timing at which the fuel is supplied to the combustion chamber23and the first ignition is performed can be accurately determined with the temperature sensor S2.

Modified Examples

For example, while the example in which the environmental temperature is set as the temperature of the engine cooling water has been shown in each of the aforementioned first and second embodiments, the present invention is not restricted to this. In the present invention, the environmental temperature may be set as the outside air temperature around the engine body, the intake temperature, or the temperature outside the vehicle (outside air temperature), for example.

While the example in which at the time of motoring, the ECU changes the valve timing of the intake valve to the timing different from that during normal steady operation (the timing control is performed) has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, for example, at the time of motoring, the valve timing of the intake valve may be set to the same timing as that during normal steady operation (the timing control may not be performed).

While the example in which the estimation logic is the map showing the relationship between the temperature in the combustion chamber and the driving duration of the engine body at the predetermined rotational speed has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, for example, the estimation logic may be a predetermined calculating formula for deriving the temperature in the combustion chamber from the driving duration of the engine body at the predetermined rotational speed.

While the example in which the timing for the first ignition is determined by the ECU based on the estimation logic has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, for example, the timing for the first ignition may be determined by the ECU based on the measurement result of a temperature sensor or the like capable of measuring the temperature in the combustion chamber instead of the estimation logic.

While the example in which as shown inFIG. 3, the rotational speed of the engine body is set with a non-linear (quadratic curve) relationship with the environmental temperature has been shown in each of the aforementioned first and second embodiments, the present invention is not restricted to this. In the present invention, for example, the rotational speed of the engine body may be set with a linear relationship with the environmental temperature.

While the example in which at the time of motoring by the electric motor, the predetermined control is performed by the ECU has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, at the time of cranking by a starter motor, the predetermined control may be performed by the ECU.

While the example in which the set temperature (ignition start temperature) is a temperature common to each of the first to third motoring settings has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, the set temperature (ignition start temperature) may be a temperature different from each other for the first to third motoring settings. For example, the set temperature (ignition start temperature) may be a temperature obtained by adding T [° C.] (20 [° C.], for example) to the environmental temperature at the start of motoring in each of the first to third motoring settings.

While the example in which the ECU is configured or programmed to set the closing timing of the intake valve to be closer to the retardation angle side as setting the predetermined rotational speed (set rotational speed) to be higher has been shown in the aforementioned first embodiment, the present invention is not restricted to this. In the present invention, the ECU may be configured or programmed to set the closing timing of the intake valve to be closer to the advance angle side as setting the predetermined rotational speed (set rotational speed) to be higher.

While the example in which the timing for the first ignition is determined based on the temperature sensor provided on the intake pipe has been shown in the aforementioned second embodiment, the present invention is not restricted to this. In the present invention, as in the first embodiment, the timing for the first ignition may be determined based on an estimation logic.

While the example in which the process operations performed by the controller are described using a flow in a flow-driven manner in which processes are performed in order along a process flow for the convenience of illustration in the aforementioned second embodiment, the present invention is not restricted to this. In the present invention, the process operations performed by the controller may be performed in an event-driven manner in which the processes are performed on an event basis. In this case, the process operations performed by the controller may be performed in a complete event-driven manner or in a combination of an event-driven manner and a flow-driven manner.

DESCRIPTION OF REFERENCE NUMERALS