JP5957995B2 - Engine start control device - Google Patents

Description

  The present invention is provided in a reciprocating engine that takes out the energy of combustion gas generated by combustion of air-fuel mixture in a combustion chamber as a reciprocating motion of a piston, and automatically stops the engine when a predetermined automatic stop condition is satisfied. Then, the present invention relates to an engine start control device for automatically starting the engine when a predetermined restart condition is satisfied.

  In recent years, there has been a demand for further improving the fuel efficiency of an in-vehicle engine mounted on a vehicle such as an automobile. As a countermeasure, a so-called idle stop function that automatically stops or starts the engine under a predetermined condition. The engine which added is increasing. In such an engine with an idling stop function, it is required to start the engine quickly and reliably at the time of automatic start for restarting the engine once stopped.

  For example, in Patent Document 1 below, the amount of air in the cylinder is optimized by adjusting the intake air flow rate during the automatic stop operation of the engine, and the ignitability of the air-fuel mixture when automatic start is started is improved. Has been done.

JP 2004-124753 A

  When the ignitability at the time of automatic start is improved by optimizing the air amount as in Patent Document 1, the speed and reliability of automatic start can be improved. However, if only the combustion under favorable conditions is performed at the time of automatic engine start, there is a risk that the engine speed will rise more than necessary, and depending on the timing when the driver of the vehicle depresses the accelerator pedal. Shows a behavior that the vehicle suddenly jumps out, and the passenger may feel uncomfortable.

  In order to prevent the above situation, it is only necessary to perform unfavorable combustion during the automatic start of the engine, but at this time, if the wall surface temperature of the combustion chamber is low, it is difficult for the fuel to vaporize. There is a risk of destabilization (in some cases misfire). Of course, if the engine is automatically stopped only when the wall temperature of the combustion chamber is high (automatic stop is not permitted at low temperatures), there is no risk of instability of combustion as described above. There will be fewer opportunities to stop and a sufficient fuel efficiency improvement effect will not be obtained.

  For such a problem, if the wall surface temperature can be raised quickly during the automatic engine start, even if the automatic start is started from a state where the wall temperature of the combustion chamber is low, the combustion does not become unstable. If necessary, unfavorable combustion can be performed, and engine blow-up can be suppressed.

  The present invention has been made in view of the above circumstances, and provides an engine start control device capable of quickly raising the wall surface temperature of a combustion chamber when restarting an automatically stopped engine. The purpose is to do.

In order to solve the above-described problems, the present invention is provided in a reciprocating vehicle-mounted engine that extracts the energy of combustion gas generated by combustion of an air-fuel mixture in a combustion chamber as a reciprocating motion of a piston, and has a predetermined automatic stop condition. Is an engine start control device that automatically stops the engine when a predetermined restart condition is satisfied, and then automatically starts the engine when a predetermined restart condition is satisfied. Detection means for detecting a related predetermined temperature, and valve control means capable of variably controlling at least one of the closing timing of the intake valve and the opening timing of the exhaust valve of the engine, the valve control means, when the engine automatic start of the detected temperature is low a low temperature than a predetermined value by the detection means, at least in all the cylinders of the engine Together by the effective expansion ratio of the engine to the point of finished on engine complete explosion combustion controls the intake and exhaust valves to be lower than the effective compression ratio times, after the engine has reached a complete explosion enable effective expansion ratio It is characterized by being higher than the compression ratio (claim 1).

According to the present invention, since the valve timing is controlled so that the effective expansion ratio of the engine is lower than the effective compression ratio at the time of automatic engine start in a low temperature state, of the energy of the combustion gas generated in the combustion chamber The rate of conversion into work that pushes down the piston decreases (in other words, cooling loss increases), and the temperature of the combustion gas during the expansion stroke can be maintained at a relatively high value. As a result, the wall surface temperature of the combustion chamber can be quickly raised. For example, even if bad combustion is performed in order to suppress the blow-up after the engine is completely exploded, the combustion may become extremely unstable. In addition, misfires can be reliably prevented.
In particular, in the present invention, the effective expansion ratio is made lower than the effective compression ratio as described above until the engine reaches the complete explosion, and the effective expansion ratio is made higher than the effective compression ratio after reaching the complete explosion. Until the complete explosion of the engine, the engine can be warmed up by lowering the effective expansion ratio, and after the complete explosion, the effective expansion ratio can be returned to the original to perform combustion with high thermal efficiency.

In the present invention, preferably, the valve control means advances the opening time of the exhaust valve with respect to the bottom dead center at the time of automatic engine start in the low temperature state and until the time of engine complete explosion . The effective expansion ratio is made lower than the effective compression ratio (claim 2).

  According to this configuration, it is possible to appropriately create a state in which the effective expansion ratio is lower than the effective compression ratio by reducing the effective expansion ratio by advancing the opening timing of the exhaust valve.

The engine can be a spark ignition engine having an ignition plug that ignites an air-fuel mixture in a combustion chamber. In such a spark ignition type engine, more preferably, when the vehicle has not been requested to start after the engine has completely exhausted after the start of the automatic start, the ignition timing of the spark plug is set to It is set later than the ignition timing set at the start ( claim 3 ).

  According to this configuration, an excessive increase in the rotational speed after the complete explosion of the engine (engine blow-up) is suppressed by the ignition timing retard. For example, after a short time after the complete explosion of the engine, Even when there is a request to start the vehicle, the vehicle does not jump out suddenly, and the safety and riding comfort of the vehicle can be improved.

Also in the engine of the present invention, in its forced starting, it is possible to control the intake and exhaust valves to always be higher than the effective expansion ratio effective compression ratio (claim 4).

  When the engine is forcibly started, there is no problem even if the engine blows up and combustion can always be performed in good condition, so that the combustion becomes extremely unstable even if the wall temperature of the combustion chamber is not raised rapidly. There is no. Under such circumstances, the effective expansion ratio can always be set higher than the effective compression ratio when the engine is forcibly started unlike the automatic start.

  As described above, according to the engine start control device of the present invention, when the automatically stopped engine is restarted, the wall surface temperature of the combustion chamber can be quickly raised, and the stability of combustion is improved. Can do.

1 is a diagram illustrating an overall configuration of an engine to which a start control device according to an embodiment of the present invention is applied. It is a top view of the engine. It is a flowchart which shows the specific procedure of the automatic stop control which stops the said engine automatically. It is a figure which illustrates the state of each cylinder in the time of the said automatic stop control being complete | finished. It is a flowchart which shows the specific procedure of the automatic start control which starts the said engine automatically. It is explanatory drawing which shows the relationship between the effective expansion ratio at the normal time, and an effective compression ratio. It is explanatory drawing which shows the relationship between the effective expansion ratio set at the time of the engine automatic start in a low temperature state, and an effective compression ratio. It is explanatory drawing for showing that lowering | hanging an effective expansion ratio leads to the raise of in-cylinder temperature.

(1) Overall Configuration of Engine FIGS. 1 and 2 are diagrams showing the overall configuration of an engine to which a start control device according to an embodiment of the present invention is applied. The engine shown in the figure is a reciprocating four-cycle gasoline engine mounted on a vehicle as a driving power source. The engine body 1 of this engine is of a so-called in-line 4-cylinder type, and includes a cylinder head 11 having four cylinders 12A to 12D arranged in a row, a cylinder head 10 provided on the upper surface of the cylinder block 11, Each of the cylinders 12A to 12D has a piston 13 inserted in a reciprocating manner.

  The piston 13 is connected to the crankshaft 3 via a connecting rod (not shown), and the crankshaft 3 rotates around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 13. .

  A combustion chamber 14 is formed above the piston 13, and fuel mainly composed of gasoline is supplied to the combustion chamber 14 by injection from an injector 16 described later. And the air-fuel mixture of the injected fuel and air burns in the combustion chamber 14, so that the piston 13 pushed down by the expansion force due to the combustion reciprocates in the vertical direction.

  The cylinder head 10 is provided with one set of spark plugs 15 and injectors 16 for each cylinder.

  The injector 16 is provided so as to face the combustion chamber 14 from the side of the intake side, and injects fuel (fuel mainly composed of gasoline) supplied from a fuel supply pipe (not shown) from the tip. Specifically, the injector 16 has a built-in needle valve and a solenoid (both not shown), and the needle valve is driven in the opening direction as the solenoid is energized, so that an amount corresponding to the valve opening time is obtained. The fuel is injected from the tip of the injector 16 toward the vicinity of the electrode of the spark plug 15.

  The spark plug 15 is provided so as to face the combustion chamber 14 from above, and discharges a spark from the electrode at the tip in response to power supply from an ignition circuit (not shown). Here, in the four-cycle four-cylinder engine as in this embodiment, the piston 13 provided in each of the cylinders 12A to 12D moves up and down with a phase difference of 180 ° (180 ° CA) in crank angle. For this reason, the timing of ignition by the ignition plug 15 of each cylinder 12A to 12D is set to a timing shifted in phase by 180 ° CA. Specifically, if the cylinder numbers of the cylinders 12A, 12B, 12C, and 12D are 1, 2, 3, and 4, respectively, the first cylinder 12A → the third cylinder 12C → the fourth cylinder 12D → the second cylinder In the order of 12B, ignition is performed at a timing shifted by 180 ° CA, and combustion is performed in this order. For this reason, for example, if the first cylinder 12A is in the expansion stroke, the third cylinder 12C, the fourth cylinder 12D, and the second cylinder 12B are in the compression stroke, the intake stroke, and the exhaust stroke, respectively.

  The cylinder head 10 is provided with an intake port 17 and an exhaust port 18 that open to the combustion chambers 14 of the cylinders 12A to 12D, and an intake valve 19 and an exhaust valve 20 that open and close the ports 17 and 18, respectively. The intake valve 19 and the exhaust valve 20 are driven to open and close in conjunction with the rotation of the crankshaft 3 by valve mechanisms 30 and 31 including a pair of camshafts and the like disposed in the cylinder head 10.

  A VVT 32 is incorporated in the valve operating mechanism 31 for the exhaust valve 20. The VVT 32 is called a variable valve timing mechanism, and is a variable mechanism for variably setting the operation timing of the exhaust valve 20. The VVT 32 employed in this embodiment is an electromagnetic VVT provided with an electric actuator capable of changing the rotational phase of the camshaft. The opening timing (opening start timing) of the exhaust valve 20 according to the driving of the actuator. ) And the closing time can be changed at the same time, and such a change operation can be performed even when the engine is stopped.

  A water jacket (not shown) through which cooling water flows is provided inside the cylinder block 11 and the cylinder head 10, and a water temperature sensor SW1 for detecting the temperature of the cooling water in the water jacket (in the present invention). Corresponding to such detection means) is provided in the cylinder block 11.

  The cylinder block 11 is provided with a crank angle sensor SW2 for detecting the rotation angle and rotation speed of the crankshaft 3. The crank angle sensor SW2 outputs a pulse signal according to the rotation of the crank plate 34 that rotates integrally with the crankshaft 3, and based on this pulse signal, the rotation angle (crank angle) of the crankshaft 3 and The rotational speed (engine rotational speed) is detected.

  On the other hand, the cylinder head 10 is provided with a cam angle sensor SW3 for outputting cylinder discrimination information. That is, the cam angle sensor SW3 outputs a pulse signal according to the passage of the teeth of the signal plate that rotates integrally with the camshaft. Based on this signal and the pulse signal from the crank angle sensor SW2, Which cylinder is in which stroke is determined.

  An intake passage 21 and an exhaust passage 22 are connected to the intake port 17 and the exhaust port 18 of the cylinders 12A to 12D, respectively. That is, intake air (fresh air) from the outside is introduced into the combustion chambers 14 of the respective cylinders 12A to 12D through the intake passage 21, and exhaust gas (combustion gas) generated in the combustion chambers 14 is introduced into the exhaust passage 29. It is designed to be discharged to the outside.

  Of the intake passage 21, a range from the engine body 1 to the upstream side by a predetermined distance is a branch passage portion 21a branched for each of the cylinders 12A to 12D, and an upstream end of each branch passage portion 21a is a surge tank 21b. It is connected to the. A common passage portion 21c including a single passage is provided on the upstream side of the surge tank 21b.

  The common passage portion 21c is provided with a throttle valve 24 that can be opened and closed, and the amount of air (intake flow rate) flowing into each of the cylinders 12A to 12D is adjusted according to the opening degree of the throttle valve 24. It has become. The throttle valve 24 employed in this embodiment is an electric type driven by an electric actuator. Such an electric throttle valve 24 is basically opened and closed in conjunction with the opening degree of an accelerator pedal 40, which will be described later. In some cases, the electric throttle valve 24 is driven to open and close without being linked to the accelerator pedal 40. There is also.

  An air flow sensor SW4 for detecting the intake flow rate is provided in the common passage portion 21c upstream of the throttle valve 24.

  An alternator 28 is connected to the crankshaft 3 via a belt or the like. This alternator 28 incorporates a regulator circuit for adjusting the amount of power generation by controlling the current of the field coil (not shown), and the target value of power generation (target power generation) determined from the electric load of the vehicle, the remaining battery capacity, etc. Based on the current), the driving force is obtained from the crankshaft 3 to generate power.

  The cylinder block 11 is provided with a starter motor 36 for starting the engine. The starter motor 36 has a motor body 36a and a pinion gear 36b that is rotationally driven by the motor body 36a. The pinion gear 36b meshes with the ring gear 35 connected to one end of the crankshaft 3 so as to be detachable. When the starter motor 36 is used to start the engine, the pinion gear 36b moves to a predetermined meshing position and meshes with the ring gear 35, and the rotational force of the pinion gear 36b is transmitted to the ring gear 35. As a result, the crankshaft 3 is driven to rotate.

(2) Control system The engine configured as described above is centrally controlled by an ECU (engine control unit) 50 shown in FIG. As is well known, the ECU 50 is composed of a microprocessor having a CPU, a memory, a counter timer group, an interface, and a bus for connecting them together. Such an ECU 50, for example, during the normal operation of the engine, controls the fuel injection operation of the injector 16, the ignition operation of the spark plug 15, the opening / closing operation of the throttle valve 24, etc. In addition to basic functions such as control based on various conditions such as required torque) and rotation speed, the engine is automatically stopped or started under a predetermined condition as a so-called idle stop function. It also has a function to make it. That is, the engine of this embodiment is an engine with an idle stop function.

  Various information is input to the ECU 50 from various sensors. That is, the ECU 50 is electrically connected to the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, and the airflow sensor SW4 provided in each part of the engine, and input signals from these sensors SW1 to SW4. Based on the above, various information such as engine coolant temperature, crank angle, rotational speed, cylinder discrimination information, intake air flow rate, and the like are acquired.

  The ECU 50 also receives information from various sensors (SW5 to SW9) provided in the vehicle. That is, the vehicle includes an accelerator opening sensor SW5 for detecting the opening degree of the accelerator pedal 40 that is depressed by the driver, and a brake sensor for detecting ON / OFF of the brake pedal 41 (presence of braking). SW6, a vehicle speed sensor SW7 for detecting the traveling speed (vehicle speed) of the vehicle, a battery sensor SW8 for detecting the remaining capacity of the battery (not shown), and a room temperature sensor SW9 for detecting the temperature in the vehicle interior And are provided. Based on the input signals from these sensors SW5 to SW9, the ECU 50 acquires information such as the accelerator opening, the presence / absence of the brake, the vehicle speed, the remaining battery capacity, and the vehicle interior temperature.

  More specific functions of the ECU 50 will be described. The ECU 50 functionally includes an operating state determination unit 51, a combustion control unit 52, a starter control unit 53, and a valve control unit 54.

  The driving state determination unit 51 sequentially determines the states of the engine and the vehicle based on signals from input elements including the sensors SW1 to SW9. In particular, in the present embodiment, the operating state determination unit 51 has a function of determining whether or not an automatic stop condition that is a condition for automatically stopping the engine is satisfied, and a condition for restarting the automatically stopped engine. It has a function to determine whether or not the restart condition is satisfied.

  The combustion control unit 52 drives the injector 16, the spark plug 15, and the throttle valve 24 to appropriately adjust the fuel injection amount, the injection timing, the ignition timing, and the throttle opening, and each cylinder 12A of the engine. It controls the combustion of the air-fuel mixture performed at ~ 12D.

  The starter control unit 53 executes control for driving the starter motor 36 to temporarily forcibly rotate the engine when the engine is started. Note that in an engine with an idle stop function as in this embodiment, an engine start (hereinafter referred to as “engine start such as this”) that is started when a passenger performs a predetermined operation (for example, key operation or button operation). There are two types of start patterns: “forced start” and engine start that is started when the restart condition is satisfied after the engine is automatically stopped (hereinafter, such engine start is referred to as “automatic start”). is there. The starter control unit 53 drives the starter motor 36 to apply a rotational force to the engine in both cases of forced start and automatic start.

  The valve control unit 54 variably controls the operation timing of the exhaust valve 20 by driving the VVT 32. In the present embodiment, the valve control unit 54 and the VVT 32 constitute the valve control means according to the present invention.

(3) Automatic Stop Control Next, the contents of the automatic engine stop control executed by the ECU 50 will be described with reference to the flowchart of FIG. When the process shown in the flowchart of FIG. 3 is started, the ECU 50 executes control for reading various sensor values (step S1). Specifically, the detection signals from the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, the airflow sensor SW4, the accelerator opening sensor SW5, the brake sensor SW6, the vehicle speed sensor SW7, the battery sensor SW8, and the room temperature sensor SW9, respectively. Based on these signals, various information such as engine coolant temperature, crank angle, rotation speed, cylinder discrimination information, intake air flow rate, accelerator opening, presence / absence of brake, vehicle speed, remaining battery capacity, vehicle interior temperature, etc. To get.

  Next, the ECU 50 determines whether or not an automatic engine stop condition is satisfied based on the information acquired in step S1 (step S2). For example, the vehicle is in a stopped state, the opening degree of the accelerator pedal 40 is zero (accelerator OFF), the brake pedal 41 is depressed more than a predetermined depression force (brake ON), and the engine coolant temperature is It is above a predetermined value (that is, warm-up has progressed to some extent), the remaining capacity of the battery is above a predetermined value, and the load on the air conditioner (the difference between the cabin temperature and the set temperature of the air conditioner) is relatively small It is determined that the automatic stop condition is satisfied when all of the plurality of requirements such as the above are met. As for the requirement that the vehicle is in a stopped state, it is not always necessary to make a complete stop (vehicle speed = 0 km / h), and the vehicle stops when the vehicle speed falls below a predetermined low vehicle speed (for example, 3 km / less). You may determine with being in a state.

  When it is determined YES in step S2 and it is confirmed that the automatic stop condition is satisfied, the ECU 50 determines the opening of the throttle valve 24 in advance from the opening (several percent) set during idle operation. The control to increase to a predetermined opening degree (for example, 20 to 30%) is executed (step S3). Here, the reason why the throttle valve 24 is opened is to increase the amount of air introduced into each of the cylinders 12A to 12D during the automatic stop of the engine and promote scavenging of the residual gas.

  Next, the ECU 50 executes a fuel cut that stops the supply of fuel from the injector 16 (step S4). That is, when the opening operation of the throttle valve 24 is finished, the target injection amount that is the amount of fuel to be injected from the injectors 16 of the cylinders 12A to 12D is set to zero, and the fuel injection from all the injectors 16 is stopped. By doing so, a fuel cut is executed.

  Even if the supply of the engine is stopped by the fuel cut, the engine temporarily rotates by inertia. The ECU 50 determines whether or not the engine rotational speed has become equal to or lower than a predetermined reference speed N1 during the inertia rotation (step S5). If it is determined YES in this case and it is confirmed that the engine will be completely stopped soon, the ECU 50 drives the throttle valve 24 in the closing direction, and its opening degree is fully closed (0%) or close to low. Control to set the opening is executed (step S6). Here, the reason why the throttle valve 24 is closed is to suppress vibrations and the like generated when the engine is completely stopped.

  Next, the ECU 50 determines whether or not the engine has completely stopped (that is, whether or not the rotational speed has reached 0 rpm) based on the rotational speed of the engine (step S7). And when it determines with YES here and it is confirmed that the engine has stopped completely, automatic stop control is complete | finished.

  FIG. 4 illustrates a state of each cylinder 12A to 12D of the engine after the automatic stop control as described above is completed. In the example of this figure, the first cylinder 12A stops in the expansion stroke, the second cylinder 12B stops in the exhaust stroke, the third cylinder 12C stops in the compression stroke, and the fourth cylinder 12D stops in the intake stroke. Yes. In the following, a cylinder stopped in the XX stroke by the automatic stop control may be referred to as a “stopped XX stroke cylinder”. For example, the cylinder 12A stopped in the expansion stroke is referred to as “stop expansion stroke cylinder 12A”, the cylinder 12B stopped in the exhaust stroke is referred to as “stop exhaust stroke cylinder 12B”, and the cylinder stopped in the compression stroke. 12C is referred to as “stopped compression stroke cylinder 12C”, and the stopped cylinder 12D stopped in the intake stroke is referred to as “stopped intake stroke cylinder 12D”.

(4) Automatic Start Control Next, specific contents of the engine automatic start control executed by the ECU 50 will be described with reference to the flowchart of FIG. When the processing shown in the flowchart of FIG. 5 starts, the ECU 50 reads various sensor values (step S11), and determines whether or not the engine restart condition is satisfied based on the values (step S12). . For example, the brake pedal 41 has been released, the accelerator pedal 40 has been depressed, the engine coolant temperature has fallen below a predetermined value, the amount of decrease in the remaining battery capacity has exceeded an allowable value, The stop time (elapsed time after automatic stop) exceeded the upper limit time, the necessity of air conditioner operation occurred (that is, the difference between the cabin temperature and the set temperature of the air conditioner exceeded the allowable value), etc. When at least one of the requirements is satisfied, it is determined that the restart condition is satisfied.

  Next, the ECU 50 determines whether or not the engine coolant temperature detected by the water temperature sensor SW1 is lower than a predetermined value Tx (step S13).

  When it is determined YES in step S13 and it is confirmed that the engine coolant temperature is lower than the predetermined value Tx, the ECU 50 determines the valve timing that is the operation timing of at least one of the intake and exhaust valves 19 and 20 as the engine effective Control for setting the timing at which the expansion ratio becomes lower than the effective compression ratio is executed (step S14). Specifically, in this embodiment, by driving the VVT 32 provided in the valve operating mechanism 31 for the exhaust valve 20, the opening timing of the exhaust valve 20, which is the timing when the exhaust valve 20 starts to open, is advanced, The effective expansion ratio of the engine is lowered and the value is set to a value lower than the effective compression ratio. Here, the “effective compression ratio” refers to the volume of the combustion chamber 14 defined by the piston 13 located at the top dead center and the piston at the time when the intake valve 19 is closed (that is, the substantial compression start time). The ratio with the volume of the combustion chamber 14 divided by 13 is said. The “effective expansion ratio” means the volume of the combustion chamber 14 defined by the piston 13 located at the top dead center, and the piston 13 at the time when the exhaust valve 20 is opened (that is, the substantial exhaust start time). The ratio to the volume of the combustion chamber 14 partitioned by.

  FIGS. 6 and 7 are diagrams showing how the relationship between the effective compression ratio and the effective expansion ratio of the engine changes before and after step S14 (control to advance the opening timing of the exhaust valve 20). It is. In the figure, TDC represents top dead center, IVC represents closing timing of intake valve 19, EVO represents opening timing of exhaust valve 20, and BDC represents bottom dead center.

  First, at the normal time when the control of step S14 is not performed, as shown in FIG. 6, the closing timing (IVC) of the intake valve 19 is at a top dead center (TDC) than the opening timing (EVO) of the exhaust valve 20. It is set on the near side. Thus, the combustion chamber volume V0 at TDC and the combustion chamber volume V2 at EVO are larger than the effective compression ratio, which is the ratio (V1 / V0) between the combustion chamber volume V0 at TDC and the combustion chamber volume V1 at IVC. The effective expansion ratio, which is the ratio (V2 / V0), is set higher. This is because the effective compression ratio cannot be made very high for reasons such as wanting to avoid abnormal combustion. On the other hand, when the effective expansion ratio is as high as possible, the period during which the expansion energy of the combustion gas pushes down the piston 13 becomes longer. This is because the thermal efficiency is increased.

  On the other hand, when the control of step S14 is performed and the opening timing (EVO) of the exhaust valve 20 is advanced, the opening timing (EVO) of the exhaust valve 20 is closed as shown in FIG. It moves to the side closer to the top dead center (TDC) than the timing (IVC), so that the effective expansion ratio (= V2 ′ / V0) becomes lower than the effective compression ratio (= V1 / V0). This is a measure for rapidly increasing the wall surface temperature of the combustion chamber 14 as will be described in detail later.

  After changing the valve timing so that the effective compression ratio> the effective expansion ratio as described above, the ECU 50 executes control for driving the starter motor 36 (step S15). Thereby, a rotational force is applied to the crankshaft 3 of the engine, and the engine starts to rotate.

  Next, the ECU 50 sequentially executes control for burning the fuel injected from the injector 16 by ignition of the spark plug 15 for each of the cylinders 12A to 12D (step S16).

  Specifically, in the control in step S16, first, fuel is injected from the injector 16 into the combustion chamber 14 of the stop-time expansion stroke cylinder 12A shown in FIG. The mixture of fuel and air injected into the expansion stroke cylinder 12A at the time of stop ignites and burns. Subsequently, fuel is injected from the injector 16 into the compression stroke cylinder 12C at the time of stop, and after waiting for the piston 13 of the cylinder 12C to reach the vicinity of the top dead center (compression top dead center), the ignition is performed. When the plug 15 is ignited, the fuel / air mixture injected into the stop-time compression stroke cylinder 12C burns during the expansion stroke after the ignition. Further thereafter, fuel injection and ignition are performed in the order of the stop-time intake stroke cylinder 12D and the stop-time exhaust stroke cylinder 12B in this order, and combustion is continued. At this time, the opening degree of the throttle valve 24 is set to a predetermined opening degree that is higher than the fully closed state (0%).

  Next, the ECU 50 determines whether or not the engine has completely exploded, that is, whether or not combustion has been performed once in all the cylinders 12A to 12D of the engine (step S17). And when it determines with YES here and complete explosion of an engine is confirmed, driving the VVT32, the opening timing of the exhaust valve 20 is set so that the effective expansion ratio of the engine becomes higher than the effective compression ratio. Control to return to the timing is executed (step S18). In other words, the opening timing (EVO) of the exhaust valve 20 that has been accelerated by the control in step S14 is delayed again and away from the top dead center (TDC), thereby opening the exhaust valve 20 as shown in FIG. The timing (EVO) is moved closer to the bottom dead center (BDC) than the closing timing (IVC) of the intake valve 19, thereby setting the effective expansion ratio (V2 / V0) higher than the effective compression ratio (V1 / V0). .

  Next, the ECU 50 determines whether or not the accelerator pedal 40 is depressed, that is, whether or not there is a request to start the vehicle (step S24). Here, if the restart condition established in step S12 is established when the accelerator pedal 40 is depressed, or otherwise, the accelerator pedal 40 is depressed in the middle of the complete explosion. In the case where it is determined, of course, the determination in step 24 is YES. Then, the ECU 50 shifts to normal operation, and executes normal combustion control in which an amount of fuel corresponding to the opening of the accelerator pedal 40 (accelerator opening) is injected from the injector 16 to ignite the air-fuel mixture (step) S26).

  On the other hand, when it is determined NO in step S24 and it is confirmed that the accelerator is OFF (the vehicle has not been requested to start), the ECU 50 blows the air-fuel mixture to ignite and burn by ignition at a later timing than usual. Rising suppression control is executed (step S25). That is, the ignition timing of the spark plug 15 is normally set to MBT, which is the timing at which the torque is most close to the compression top dead center, or the vicinity thereof, but in the blow-up suppression control in step S25, the ignition timing is Set significantly slower than. This is to prevent the engine speed from temporarily rising excessively. For example, if the ignition timing immediately after the engine reaches the complete explosion is set near MTB, the momentum of the rotation at the time of the complete explosion of the engine will remain, causing a phenomenon that the engine speed temporarily rises. However, when the ignition timing after the engine complete explosion is retarded as in step S25 above, the engine torque temporarily decreases, so the rotational speed after the engine complete explosion is stabilized and the engine blows up. Is suppressed.

  Note that the ignition retard (blasting suppression control) in step S25 is executed for, for example, several combustions, and thereafter, the routine proceeds to normal operation (step S26).

  Next, a description will be given of the control performed when it is determined NO in step S13, that is, when the engine coolant temperature is equal to or higher than a predetermined value Tx. In this case, the ECU 50 sets the opening timing of the exhaust valve 20 to a normal timing, that is, a timing at which the effective expansion ratio of the engine is higher than the effective compression ratio (see FIG. 6). Then, the starter motor 36 is driven to forcibly rotate the engine (step S21), and fuel injection and ignition are sequentially performed on the cylinders 12A to 12D to burn the air-fuel mixture (step S22).

  Next, the ECU 50 confirms that the engine has completely exploded (combustion is performed once in all of the cylinders 12A to 12D) (step S23), and determines whether or not the accelerator is ON (step S24). Depending on the result, the blow-up suppression control with retarded ignition timing is executed and then the normal operation is started (steps S25 and S26), or the normal operation is immediately started (step S26).

(5) Control during forced engine start Next, when the engine is forcibly started, that is, when the occupant who has boarded the vehicle performs a predetermined operation (key operation or button operation) for starting the engine. The start will be briefly described.

  When the engine is forcibly started, in general, after the engine is forcibly rotated by one or more rotations by the starter motor 36, fuel injection and ignition are sequentially performed on each of the cylinders 12A to 12D to start the engine vigorously. As described above, the forced rotation of one or more rotations (rotation by the starter motor 36) is required until the first ignition (combustion). The forced start of the engine is a state where the system is once shut down and the cylinder discrimination information becomes invalid. This is because at least one rotation of the engine is required to newly perform cylinder discrimination.

  In the forced start of the engine as described above, the opening timing of the exhaust valve 20 is set to the normal timing shown in FIG. 6, that is, the timing at which the effective expansion ratio becomes higher than the effective compression ratio. Further, the ignition timing of the spark plug 15 is not intentionally delayed as in the case of automatic starting (step S25 in FIG. 5), and combustion by ignition at a timing relatively close to MBT is continuously executed. Is done.

(6) Operation, etc. As described above, the engine shown in the present embodiment is a reciprocating gasoline engine with a so-called idle stop function that automatically stops and starts the engine under a predetermined condition. (Spark ignition engine). When the engine is automatically started to restart the engine that has been automatically stopped, it is checked whether or not the engine coolant temperature is lower than a predetermined value Tx (step S13). The opening timing (opening start timing) of the exhaust valve 20 is advanced from the bottom dead center so that the ratio becomes lower than the effective compression ratio (step S14). According to such a configuration, the wall surface temperature of the combustion chamber 14 can be quickly increased even in the engine automatic start in a low temperature state where the cooling water temperature of the engine is low, and the combustion stability can be improved. There is.

  That is, in the above embodiment, the valve timing is controlled so that the effective expansion ratio of the engine is lower than the effective compression ratio at the time of automatic engine start in a low temperature state, so that the energy of the combustion gas generated in the combustion chamber 14 Of these, the rate of conversion into work that pushes down the piston 13 decreases (in other words, cooling loss increases), and the temperature of the combustion gas during the expansion stroke can be maintained at a relatively high value. As a result, the wall surface temperature of the combustion chamber 14 can be quickly raised. For example, even if the combustion is performed with the ignition timing deliberately delayed in order to suppress the blow-up after the complete explosion of the engine, the combustion is extremely poor. Without becoming stable, misfires can be reliably prevented.

  FIG. 8 is a diagram for explaining that a decrease in the effective expansion ratio is advantageous for increasing the wall surface temperature of the combustion chamber 14. In FIG. 8, lower waveforms IN and EX (or EX ′) indicate lift curves of the intake valve 19 and the exhaust valve 20, respectively, and an upper waveform Tc (or Tc ′) is in the combustion chamber 14. The change of the cylinder temperature which is gas temperature is shown. As shown in the waveform EX ′ in the lower part of the figure, when the effective expansion ratio is higher than the effective compression ratio, the opening timing of the exhaust valve 20 is set near the bottom dead center (BDC) (in FIG. The time point is EVO1). On the other hand, as shown in the upper part of FIG. 8, the in-cylinder temperature gradually decreases with a decrease in the piston 13 (expansion of the combustion chamber volume) after a significant increase due to combustion near the top dead center (TDC). However, when the opening timing of the exhaust valve 20 is set to EVO1 close to bottom dead center (BDC) as described above, the piston 13 is positioned at a position corresponding to this EVO1 as shown by the waveform Tc ′. Until then, the in-cylinder temperature continuously decreases.

  On the other hand, when the opening timing of the exhaust valve 20 is advanced in order to reduce the effective expansion ratio, the exhaust valve 20 has a considerable amount of time until the piston 13 reaches the bottom dead center (BDC) as shown by the waveform EX in the lower part of FIG. It starts to open from the front (in FIG. 8, the point in time is EVO2). At the time of this EVO2, the temperature and pressure of the combustion gas are maintained at a sufficiently high level. Therefore, when the exhaust valve 20 is opened in this state, the combustion gas in the combustion chamber 14 flows out to the exhaust port 18, The internal pressure of the combustion chamber 14 decreases. Then, the pressure difference between the inside and outside of the combustion chamber 14 sandwiching the piston 13 becomes small, and thereafter, the amount of work by which the combustion gas pushes down the piston 13 decreases. That is, since the amount of energy that the combustion gas has to turn to work that pushes down the piston 13 is reduced, the temperature of the combustion gas remains even after the opening timing EVO2 of the exhaust valve 20 as shown by the waveform Tc in the upper part of FIG. It remains high.

  As described above, when the opening timing of the exhaust valve 20 is advanced and the effective expansion ratio becomes lower than the effective compression ratio, the opening timing of the exhaust valve 20 is higher than when the effective expansion ratio is higher than the effective compression ratio. It can be understood that the temperature of the later combustion gas increases, so that the wall surface temperature of the combustion chamber 14 is likely to rise, and the warm-up of the engine is promoted.

  In the above embodiment, when the engine automatically starts in a low temperature state where the coolant temperature of the engine is lower than the predetermined value Tx, after the effective expansion ratio is once set lower than the effective compression ratio as described above, the engine completes explosion. After reaching, the opening timing of the exhaust valve 20 is again returned to the bottom dead center (BDC) side so that the effective expansion ratio is made higher than the effective compression ratio (step S18). According to such a configuration, in the process until the engine reaches the complete explosion, the engine is warmed up by the decrease in the effective expansion ratio, and after the engine reaches the complete explosion, the effective expansion ratio is It can return and can perform combustion with high thermal efficiency.

  Further, in the above embodiment, when the vehicle has not been requested to start after the engine has reached a complete explosion, the ignition timing of the spark plug 15 is set late (step S25). According to such a configuration, an excessive increase in rotational speed (engine blow-up) after the complete explosion of the engine is suppressed. For example, after the engine complete explosion, the vehicle starts after a short time. Even when there is a request (accelerator ON), the vehicle does not jump out suddenly, and the safety and riding comfort of the vehicle can be improved.

  Unlike the above-described automatic engine start, the valve is set so that the effective expansion ratio is always higher than the effective compression ratio when the engine is started by the occupant's operation (that is, the engine is forcibly started). Timing is controlled. This is preferable at the time of forced start of the engine, because it is not necessary to suppress the engine blow-up (rather, it is preferable that a certain degree of blow-up can be made to ensure that the occupant recognizes completion of engine start-up). This is because it is not necessary to intentionally delay the ignition timing after the complete explosion of the engine. That is, in the forced start of the engine, it is not necessary to worry about engine blow-up, and combustion can always be performed in good condition, so that combustion is extremely unstable even if the wall surface temperature of the combustion chamber 14 is not increased rapidly. It will not become. For this reason, when the engine is forcibly started, unlike the automatic start, the effective expansion ratio is not made lower than the effective compression ratio in order to promote engine warm-up. Is always set higher than the effective compression ratio.

(7) Modification In the above embodiment, the engine cooling water temperature is detected by the water temperature sensor SW1, and the effective expansion ratio of the engine is determined from the effective compression ratio when the engine is automatically started in a state where the cooling water temperature is lower than the predetermined value Tx. However, the temperature used as a criterion for determining whether or not to reduce the effective expansion ratio changes in proportion to the wall surface temperature of the combustion chamber 14 (that is, in proportion to the wall surface temperature). Temperature) and is not limited to the engine coolant temperature. For example, the wall surface temperature of the combustion chamber 14 may be directly detected, or the gas temperature in the combustion chamber 14 may be detected.

  In the above embodiment, after the restart condition is established for the engine that has been automatically stopped, the engine coolant temperature is confirmed, and if necessary (when the water temperature <Tx), the VVT 32 is driven to drive the exhaust valve 20. The effective expansion ratio of the engine is reduced by advancing the opening timing of the engine, but the timing for driving the VVT 32 is not limited to this. For example, when the automatic stop condition is satisfied when the temperature related to the wall surface temperature of the combustion chamber 14 is relatively low, the VVT 32 is driven in advance and the effective expansion ratio is increased before the engine is completely stopped by the automatic stop control. It may be lowered. In this case, the VVT 32 does not necessarily need to use the electromagnetic VVT as in the above embodiment, and may be a hydraulic VVT using an oil pump driven by an engine as a hydraulic supply source. However, even if the hydraulic type VVT is a VVT that uses an oil pump driven by an electric motor as a hydraulic supply source, the VVT can be driven even after the engine is completely stopped. (The VVT is driven after the restart condition is satisfied after the engine is automatically stopped).

  In the above embodiment, a VVT of a type that changes the rotational phase of the camshaft is adopted as the VVT 32 for the exhaust valve 20 so that not only the opening timing of the exhaust valve 20 but also the closing timing is changed as the VVT 32 is driven. However, the VVT 32 only needs to change at least the opening timing of the exhaust valve 20, and may change only the opening timing while the closing timing of the exhaust valve 20 is fixed.

  In the above embodiment, in order to make the effective expansion ratio of the engine lower than the effective compression ratio, the opening timing of the exhaust valve 20 is advanced with respect to the bottom dead center (the timing when the exhaust valve 20 is moved further toward the advance side than the bottom dead center). However, the effective compression ratio> the effective expansion ratio only needs to be satisfied as a result, and the method therefor is not limited to advancement of the opening timing of the exhaust valve 20. For example, the effective compression ratio> the effective expansion ratio can also be realized by increasing the effective compression ratio by increasing the closing timing of the intake valve 19 (closer to the bottom dead center).

  In the above embodiment, a preferred embodiment of the present invention has been described by taking a spark ignition gasoline engine as an example. However, an engine to which the configuration of the present invention can be applied uses the energy of the combustion gas generated in the combustion chamber. If it is a reciprocating engine taken out as a reciprocating motion of a piston, the kind will not be ask | required in particular. For example, the configuration of the present invention can be suitably applied to a compression self-ignition engine represented by a diesel engine (an engine that burns light oil by self-ignition). Even in the case of a diesel engine, the situation that it is necessary to suppress the blow-up when the engine is automatically started is the same. For example, after the complete explosion of the engine, the fuel injection amount is suddenly reduced or the injection timing is temporarily set. Measures are taken to suppress engine blow-up, such as by slowing down the engine. According to the configuration of the present invention, since the warm-up is promoted at the start of the automatic start by setting the effective compression ratio> the effective expansion ratio, the blow-up suppression control as described above (the sudden decrease in the injection amount or the injection timing) Combustion is prevented from becoming extremely unstable when performing (retard).

1 Engine body 12A-12D
13 Piston 14 Combustion chamber 15 Spark plug 32 VVT (Valve control means)
54 Valve control unit (valve control means)
SW1 Water temperature sensor (detection means)
Tx (temperature) predetermined value

Claims (4)

Provided in a reciprocating in-vehicle engine that takes out the energy of combustion gas generated by combustion of the air-fuel mixture in the combustion chamber as a reciprocating motion of the piston, and automatically stops the engine when a predetermined automatic stop condition is satisfied, An engine start control device for automatically starting the engine when a predetermined restart condition is satisfied,
Detecting means for detecting a wall temperature of the combustion chamber of the engine or a predetermined temperature related thereto;
Valve control means capable of variably controlling at least one of the closing timing of the intake valve and the opening timing of the exhaust valve of the engine,
When the engine is automatically started in a low temperature state in which the temperature detected by the detection means is lower than a predetermined value, the valve control means is configured to perform engine combustion until the time when the engine has been completely burned at least once in all cylinders of the engine. Control of the intake and exhaust valves so that the effective expansion ratio is lower than the effective compression ratio, and after the engine reaches a complete explosion, the effective expansion ratio is made higher than the effective compression ratio. Control device. The engine start control device according to claim 1,
The valve control means sets the effective expansion ratio of the engine to the effective compression ratio by advancing the opening timing of the exhaust valve with respect to the bottom dead center at the time of automatic engine start in the low temperature state and until the time of complete engine explosion. An engine start control device characterized in that the engine start control device is lower. The engine start control device according to claim 1 or 2 ,
The engine is a spark ignition engine having a spark plug for igniting an air-fuel mixture in a combustion chamber,
After the engine has reached a complete explosion after the start of the automatic start, if there is no vehicle start request, the ignition timing of the spark plug is set later than the ignition timing set at the time of forced start of the engine. An engine start control device. The engine start control device according to any one of claims 1 to 3 ,
An engine start control device, wherein an intake / exhaust valve is controlled so that an effective expansion ratio is always higher than an effective compression ratio when the engine is forcibly started.

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