US20080216779A1

US20080216779A1 - Apparatus for and Method of Controlling a Starting Operation to Restart an Engine

Info

Publication number: US20080216779A1
Application number: US12/044,610
Authority: US
Inventors: Satoru Watanabe; Hiromasa Kubo; Minoru Ohsuga; Toru Kitayama
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2007-03-08
Filing date: 2008-03-07
Publication date: 2008-09-11
Also published as: JP2008223499A; JP4755128B2; KR100935708B1; KR20080082550A; CN101260837A; DE102008013114A1

Abstract

In an engine provided with a variable valve mechanism which varies an operating angle of an intake valve and a lift amount thereof, when an engine operation is automatically stopped after the establishment of an idling stop condition, the operating angle of the intake valve and the lift amount thereof are varied to be smaller, so that a load of the variable valve mechanism at an engine operation restarting time is low. Then, when the engine operation restarting is requested, a first explosion pressure is obtained by performing fuel injection and ignition on a cylinder stopped in an expansion stroke, so that the engine operation is started. Further, after a first intake stroke, the operating angle of the intake valve and the lift amount thereof are increased.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an apparatus for and a method of controlling a starting operation to restart an engine of which the operation is stopped. More particularly, the present invention relates to a technology for restarting an engine provided with a variable valve mechanism for varying opening characteristics of an engine valve, by igniting fuel in a combustion chamber of the engine in a state where the operation of the engine is stopped.
2. Description of the Related Art
Japanese Laid-open (Kokai) Patent Application Publication No. 2005-030236 discloses a vehicular control apparatus for automatically stopping an operation of an engine if a condition for automatically stopping the engine operation is established during idling of the engine, and for igniting fuel in a combustion chamber of the engine to restart the engine operation when a restarting condition of the engine is satisfied after the automatic stopping of the engine.
In case where the engine operation is restarted in a manner as described above, employing no starter motor, it is possible to raise a rate of success in restarting of an engine by increasing, as much as possible, a torque allowance which is a difference between a torque necessary for starting a rotating motion of a crankshaft and a torque generated by the engine.
Therefore, with a conventional technology, an effort has been made for increasing the torque generation from an engine by, for example, enhancing the combustion performance of the engine. However, it has developed that only enhancement of the combustion performance of an engine is unable to constantly achieve a high success rate in the starting of an engine.
On the other hand, as a method of increasing the afore-mentioned torque allowance, there has been proposed a method of lowering engine friction to thereby reduce the torque necessary for starting the rotating motion of a crankshaft. Nevertheless, there has been hitherto proposed no measure that can achieve such an effective lowering of engine friction as is able to contribute greatly to a rise in the rate of success in restating of the engine.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to raise a success rate in restarting of an engine operation through a reduction in a torque necessary for driving a rotating motion of a crankshaft by lowering an engine friction, with an engine provided with a variable valve mechanism, which is provided for varying the opening characteristics of an engine valve.
In order to achieve the above object, the present invention provides such a novel technical concept that, when a fuel existing in a combustion chamber of an engine is ignited for restarting an engine operation during stopping of the engine operation, a forcible reduction of a load that is applied by a variable valve mechanism is encouraged.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating a general construction of an engine embodying the present invention;

FIG. 2 is a perspective view illustrating a variable valve lift mechanism according to an embodiment of the present invention;

FIG. 3 is a side view, in part cross-section, of the variable valve lift mechanism according to the embodiment of the present invention;

FIG. 4 is a diagram illustrating a variable valve timing mechanism according to the embodiment of the present invention;

FIG. 5 is a flowchart illustrating a controlling process for an automatic stopping of an engine operation according to the embodiment of the present invention;

FIG. 6 is a graphical view illustrating a correlation between an operating angle of an intake valve and a lift amount thereof, and a starting torque for a crankshaft, according to the embodiment of the present invention;

FIG. 7 is a flowchart illustrating a controlling of an operation for restarting an engine after the engine operation is automatically stopped, according to the embodiment of the present invention;

FIG. 8 is a time chart illustrating a fuel injection timing, an ignition timing and an intake stroke at a time of restarting the operation of the engine according to the embodiment of the present invention; and,

FIG. 9 is a time chart illustrating behavior of an engine rotation number at the time of restarting the engine operation according to the embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram illustrating a systematic construction of an engine for vehicle according to an embodiment of the present invention.
Referring to FIG. 1, an engine 101 is a typical internal combustion engine to which the present invention may be applied and comprised of a V-type six-cylinder engine provided with right and left banks, and the same is an engine in which fuel is directly injected into each cylinder to be ignited by an ignition plug.
In an intake pipe 102 of engine 101, there is disposed an electronically controlled throttle 104.
Air having passed though electronically controlled throttle 104 is distributed to each bank and thereafter, is further distributed to each of cylinders in each of the banks.
In each cylinder, suction of the air takes place into a combustion chamber 106 via an intake valve 105.
The gas having combusted in combustion chamber 106 in each cylinder is discharged from combustion chamber 106 via an exhaust valve 107 and thereafter, flows together through each bank, to be purified by a front catalytic converter 108 a, 108 b and a rear catalytic converter 109 a, 109 b, which are disposed in each bank.
The flows of the exhaust gas from each bank after being purified by rear catalytic converter 109 a, 109 b enter together in a common exhaust passage to thereby flow into a muffler 103, and is thereafter discharged from muffler 103 into the atmosphere.
Exhaust valve 107 is driven by a cam axially supported on an exhaust camshaft 110, to open or close under a fixed lift amount, a fixed operating angle and a fixed valve timing.
On the other hand, a lift amount of intake valve 105, an operating angle thereof and a valve timing thereof on respective banks are variably controlled by variable valve lift mechanisms 112 a, 112 b and variable valve timing mechanisms 113 a, 113 b, which constitute variable valve mechanisms disposed in respective banks.
Each of variable valve lift mechanisms 112 a, 112 b is a mechanism which continuously varies the lift amount of intake valve 105 and the operating angle thereof.
Further, each of variable valve timing mechanisms 113 a, 113 b is a mechanism which continuously varies a phase of the center of the operating angle of intake valve 105 by changing a rotating phase of an intake camshaft 3 relative to a crankshaft.
An electronic control unit (ECU) 114 incorporating therein a microcomputer, sets a target intake air amount and a target intake negative pressure according to engine operating conditions, and controls electronically controlled throttle 104, variable valve lift mechanisms 112 a and 112 b, and variable valve timing mechanisms 113 a and 113 b, based on the set target intake air amount and the set target intake negative pressure.
Engine control unit 114 receives signals from various sensors, such as an air flow sensor 115 for detecting an amount of intake air flow of engine 101, an accelerator sensor 116 for detecting a depression amount of an accelerator pedal, a crank angle sensor 117 for detecting a rotating angle of the crankshaft, a throttle sensor 118 for detecting an opening TVO of electronically controlled throttle 104, a water temperature sensor 119 for detecting a temperature of the cooling water of engine 101, an air- fuel ratio sensor 111 a, 111 b disposed in each bank for detecting an air-fuel ratio based on oxygen concentration in the exhaust gas, a brake switch 120 which is turned ON when a foot brake of a vehicle is operated, a vehicle speed sensor 121 for detecting a vehicle speed.
Further, a fuel injection valve 131 is disposed for directly injecting fuel into combustion chamber 106 in a cylinder bore of each cylinder on each bank. Furthermore, an ignition plug 122 is disposed on a top portion of each combustion chamber 106.
Next, there will be described the structure of each of variable valve lift mechanisms 112 a, 112 b, and the structure of each of variable valve timing mechanisms 113 a, 113 b, with reference to FIGS. 2 through 4.
In engine 101, a pair of intake valves 105, 105 is disposed for each cylinder on each bank, and above intake valves 105, 105, an intake camshaft 3 which is driven for rotation by the crankshaft of engine 101 is rotatably supported so as to extend in a direction along a cylinder train.
Swing cams 4, each of which is in contact with a valve lifter 2 a of each intake valve 105 for causing intake valve 105 to open or close, are mounted by fitting on an outer surface of intake camshaft 3, so as to be relatively rotatable with respect to intake camshaft 3.
Between intake camshaft 3 and swing cams 4, variable valve lift mechanism 112 a or 112 b which continuously varies the operating angle of intake valves 105 as well as the lift amount thereof, is disposed.
Further, on one end portion of intake camshaft 3 on each bank, there is disposed variable valve timing mechanism 113 a or 113 b which changes the rotating phase of intake camshaft 3 relative to the crankshaft to continuously vary the phase of the center of the operating angle of each intake valve 105.
As shown in FIGS. 2 and 3, each of variable valve lift mechanisms 112 a, 112 b includes: a drive cam 11 of circular shape which is fixedly and eccentrically mounted on intake camshaft 3; a link 12 of ring shape which is fitted to an outer surface of drive cam 11 to be rotatable relative to drive cam 11; a control shaft 13 which extends in a direction of the cylinder train to be in approximately parallel with intake camshaft 3; a control cam 14 of circular shape which is fixedly and eccentrically mounted on control shaft 13; a locker arm 15 which is fitted onto an outer surface of control cam 14 to be rotatable relative to control cam 14, and has one end thereof connected to a tip end of link 12 of ring shape; and a link 16 of rod shape which is disposed to be connected to the other end of locker arm 15 and to swing cam 4.
Control shaft 13 is rotatably driven by an actuator 17 such as an electric motor, via a gear train 18 to be rotated within a predetermined angular range.
According to the above-mentioned configuration, when intake camshaft 3 rotates in association with the crankshaft, ring shaped link 12 performs an approximately translational motion via drive cam 17, and also, locker arm 15 swings about the center axis of control cam 14 while causing swing cams 4 to swing via rod shaped link 16, so that intake valves 105 are driven to open or close.
Further, when control shaft 13 is changed in its rotating angle, the axle center of control cam 14, which is the swing center of locker arm 15, is changed in its position, and as a result, the orientation of each swing cam 4 is changed.
Hence, the operating angle of each intake valve 105 and the lift amount thereof are continuously varied while the phase of the center of the operating angle of each intake valve 105 being approximately fixed.
Incidentally, it may be possible to use variable valve lift mechanism 112 a or 112 b having a different type of characteristics, in which when the valve operating angle and the valve lift amount of intake valve 105 are varied, a variation in the phase of the center of the valve operating angle per se simultaneously takes place.
FIG. 4 shows each of variable valve timing mechanisms 113 a, 113 b.
Each of variable valve timing mechanisms 113 a, 113 b is fixed to a sprocket 25, which is rotated in synchronism with the crankshaft, and includes: a first rotator 21 which is rotated together with sprocket 25; a second rotator 22 which is fixed to the one end of intake camshaft 3 by means of a bolt 22 a, to be rotated together with intake camshaft 3; and an intermediate gear 23 of cylindrical shape which is engaged, via helical splines 26, with an inner peripheral face of first rotator 21 and with an outer peripheral face of second rotator 22.
Intermediate gear 23 is connected to a drum 27 via a thread screw 28, and a torsion spring 29 is disposed between drum 27 and intermediate gear 23.
Intermediate gear 23 is urged by torsion spring 29 in a direction for causing a change in the valve timing to be retarded (in the left direction in FIG. 4), and when a voltage is applied to an electromagnetic retarder 24 for generating a magnetic force, intermediate gear 23 is moved in a direction for causing a change in the valve timing to be advanced (in the right direction in FIG. 4), via the motion of drum 27 and thread screw 28.
A relative phase between rotators 21 and 22 is changed according to an axial position of intermediate gear 23, so that the rotating phase of intake camshaft 3 relative to the crankshaft is changed, and the phase of the center of the operating angle of intake valve 105 is continuously varied.
Actuator 17 comprised of e.g., an electric motor and electromagnetic retarder 24 are controlled to be driven by control signals transmitted from electronic control unit 114.
Electronic control unit 114 capable of setting a target angle of control shaft 13 performs a feedback control of an amount of operation of actuator 17 so that an actual angle of control shaft 13 detected by an angle sensor 32 approaches the set target angle.
Further, electronic control unit 114 detects the rotating phase of intake camshaft 3 relative to the crankshaft based on a signal from a cam sensor 31 which outputs the signal at a reference angle position of intake camshaft 3, and a signal from crank angle sensor 117 to thereby perform a feedback control of an amount of operation of electromagnetic retarder 24, so that the detected result approaches a target rotating phase.
Furthermore, electronic control unit 114 has an Idle-Stop-Start control function for automatically stopping an operation of engine 101 when an automatic operation stop condition is established during an idling state of engine 101, and for automatically restarting the operation of engine 101 when an operation restarting condition is established after the operation of engine 101 has been automatically stopped.
By the above-described Idle-Stop-Start control function of the electronic control unit 114, the operation of engine 101 is automatically stopped, for example, in a state of waiting for the signal change at a traffic intersection, to thereby intentionally aim a reduction in fuel consumption as well as exhaust emission.
For restarting the operation of engine 101 by the Idle-Stop-Start control function, it is required that restarting of the operation of engine 101 occurs promptly in response to a starting operation performed by a driver. For this purpose, in place of the restarting by employing a starter motor, the operation of engine 101 is started by igniting the fuel in the combustion chamber in a state where the operation of engine 101 is stopped, as described later.
A flowchart of FIG. 5 illustrates the details of the Idle-Stop-Start control processed by electronic control unit 114.
In step S201, judgment is made as to whether or not a condition for automatically stopping the operation of engine 101 is established.
Here, when the following conditions (1) through (5) are all established, it is judged that the condition for automatically stopping the operation of engine 101 is established.

(1) A vehicle speed is at 0 km/h.
(2) The engine rotation number (rpm) is equal to or less than a given reference rotation number.
(3) Accelerator opening is closed to the full.
(4) A brake switch 120 is turned ON.
(5) The cooling water temperature is equal to or higher than a given reference temperature.

For the above automatic operation stop condition, it is supposed that the operation of engine 101 is automatically stopped when a vehicle halts and waits for the signal change at a traffic intersection in a state where engine 101 is completely warmed-up. However, it is noted that the automatic operation stop condition is not limited to the above.
If the automatic operation stop condition is not established, the present controlling routine is terminated without proceeding to the succeeding steps, and engine 101 continues to be operated.
On the other hand, if the automatic operation stop condition is established, the intake air amount of engine 101 and opening characteristics of intake valve 105 are controlled, before the operation of engine 101 is stopped.
Firstly, in step S202, electronically controlled throttle 104 is closed to an opening thereof at which the intake air amount required for idling is obtained.
In next step S203, each of variable valve lift mechanisms 112 a, 112 b is controlled so that the operating angle of intake valve 105 and the lift amount thereof are at the maximum, and also, each of variable valve timing mechanisms 113 a, 113 b is controlled so that the phase of the center of the operating angle of intake valve 105 is retarded to the most.
At this stage, it is to be understood that in a normal operation time, the intake air amount of engine 101 is controlled by varying the opening characteristics of respective intake valves 105 by variable valve lift mechanisms 112 a, 112 b and variable valve timing mechanisms 113 a, 113 b, and the intake negative pressure is controlled by changing the throttle opening by electronically controlled throttle 104.
To the contrary, the process in steps 8202 and S203 is executed by switching to a state where the intake air amount and the intake negative pressure are controlled by electronically controlled throttle 104. Namely, by the process in step S202, variable valve lift mechanisms 112 a, 112 b and variable valve timing mechanisms 113 a, 113 b are controlled so that the intake air amount is at the maximum, but by the process in step S203, the opening of electronically controlled throttle 104 is made smaller so that the intake air amount is controlled to become that at an idling time.
In step 8204, the fuel injection by fuel injection valve 131 is stopped and also the ignition by ignition plug 122 is stopped, so that the operation of engine 101 is stopped.
In step S205, the opening of electronically controlled throttle 104, which has been made smaller so that the intake air amount of engine 101 is controlled to be that at the idling time, is opened to the full while engine 101 is inertially rotating.
Since the fuel injection and the ignition are stopped before electronically controlled throttle 104 is opened to the full, torque of engine 101 does not increase.
When the opening of electronically controlled throttle 104 is opened to the full during engine 101 is inertially rotated after the fuel injection and the ignition are stopped, since variable valve lift mechanisms 112 a, 112 b and variable valve timing mechanisms 113 a, 113 b are controlled so that the intake air amount reaches the maximum, engine 101 sucks therein a lot of air.
Then, when engine 101 sucks therein a large amount of intake air, a large amount of compression work takes place in each cylinder, and therefore, one cylinder among six cylinders is permitted to stop its piston motion at an approximately fixed position thereof during an expansion stroke. It is to be noted that in the one cylinder in which the piston motion is stopped during the expansion stroke, confinement of the intake air within the cylinder occurs.
As described later, when the operation of engine 101 should be restarted, the fuel is injected to the cylinder in which the piston motion is stopped during the expansion stroke so as to cause ignition and thus, the crankshaft starts to be rotated by an explosion pressure at that time. Accordingly, in order to restart the operation of engine 101, it is necessary to stop one cylinder among six cylinders during the expansion stroke.
Here, if a load applied while engine 101 is inertially rotating is rather small, a braking force due to the compression work is weakened resulting in that a piston is stopped at relatively retarded timing during the expansion stroke. Then, when the motion of piston in the above-mentioned one cylinder is stopped at the retarded timing during the expansion stroke thereof, a rotating force derived from the combustion in the one cylinder must be reduced, and as a result, restarting performance is degraded.
Therefore, an increase in the intake air amount while engine 101 is inertially rotating is intended, so that one cylinder among six cylinders is stopped in its piston motion at a position advanced as much as possible during the expansion stroke.
In step S206, judgment is made based on the signal from crank angle sensor 117 as to whether or not the rotation of engine 101 is completely stopped.
If the rotation of engine 101 is completely stopped, the routine proceeds to step S207.
In step S207, for the purpose of restarting of engine 101, electronically controlled throttle 104 is closed to come to the opening thereof at which the intake air amount at the time of idling operation of the engine is obtained, and also, the operating angle of intake valve 105 and the lift amount thereof controlled by variable valve lift mechanism 112 a or 112 b are controlled to become target values suitable for automatic starting of an engine, i.e., engine 101.
The target values for the automatic starting of the engine are set to be smaller than those at the time of starting by employing the starter motor and also to be smaller than those required for continuing the operation to restart engine 101. As a result, a load applied by variable valve lift mechanisms 112 a, 112 b, in other words, a load due to driving of intake valves 105 to open, at the time of automatic starting of the engine, can be greatly lessened.
As shown in FIG. 8, an intake stroke during which each intake valve 105 is driven at the above-mentioned target values for the automatic starting of the engine is set only for first one cylinder among six cylinders, and the combustion in this first one cylinder occurs at the fourth combustion among the combustions of the six cylinders. By controlling the operating angle of intake valve 105 and the lift amount thereof to come to the target values for the automatic starting of the engine, the intake air amount of each cylinder is greatly reduced, and accordingly, there is a possibility that the torque is not sufficiently generated during the fourth combustion. However, if the sufficient torque can be generated in the succeeding combustions, engine 101 can be successfully restarted.
On the other hand, at the time of starting the engine, a work for opening intake valves 105 must be performed by a first explosion pressure. Thus, if a load for driving the opening of intake valves 105 during a first intake stroke is high, an increase in the crankshaft rotation by the first explosion pressure is inhibited so that the starting performance of the engine is greatly lowered.
Accordingly, in the first intake stroke at the time of executing the automatic starting of the engine, it is desirable to avoid such a situation that consumption of a large part of energy by the first explosion occurs for driving the opening of intake valves 105 rather than for sucking the air of which the amount is enough for generating a torque. Therefore, by decreasing the load for driving the opening of intake valves 105 in the first intake stroke, the automatic starting of the engine can be achieved at a high rate of success.
Thus, the values that are certainly smaller than the values required for continuing the starting of the engine, are set to become the target values for the automatic starting of the engine, and the target values for the automatic starting of the engine may be set at the minimum valve operating angle and the minimum valve lift amount in variable valve lift mechanisms 112 a, 112 b, and further, the above-mentioned minimum valve operating angle and minimum valve lift amount may be zero, respectively.
However, in case of an engine having lesser number cylinders such as a four-cylinder engine, of which combustion interval is longer than that of the six-cylinder engine, a variation of the rotating speed thereof may become large unless the combustion for generating torque is performed sequentially from the beginning of the starting of the engine and as a result, the starting performance of the engine must be degraded. Therefore, in such a case, taking into account a rise in the rotation by the first explosion pressure, the afore-described target values for the automatic starting of the engine are set so that a substantial amount of air suctioned during the first intake stroke can be ensured.
In the above automatic starting of the engine, since the crankshaft starts to rotate by virtue of the fuel combustion in the combustion chamber, if the torque allowance is made larger by increasing the rotational energy obtained by the first combustion or by lowering the friction which consumes this rotational energy, engine 101 can be restarted by the automatic starting of the engine at a high probability.
Therefore, in order to perform the automatic starting of the engine in a state where the operating angle of intake valve 105 and the lift amount thereof are set smaller values, respectively, and the load of variable valve lift mechanisms 112 a, 112 b is lessened, the valve operating angle and the valve lift amount are forcibly set in advance, at the time of stopping of the engine, to become smaller than those in the starting of the engine by employing the starter motor.
Each of variable valve lift mechanisms 112 a, 112 b transmits a driving force from the crankshaft to valve lifter 2 a of each intake valve 105 by means of a complex mechanism. Therefore, as shown in FIG. 6, in the case of a standard valve operating angle and a standard valve lift amount, a starting torque necessary for driving the crankshaft at the time of the automatic starting of the engine becomes significantly larger than that necessary for directly driving the operation of intake valves 105 by the cams axially supported by the camshaft.
However, as shown in FIG. 6, by significantly decreasing the valve operating angle and the valve lift amount, it is possible to reduce the starting torque for the crankshaft to become lower than that necessary for directly driving intake valves 105 by the cam axially supported by the camshaft.
Then, if the automatic starting of the engine is executed in the state where the starting torque for driving the crankshaft is intentionally reduced, it is possible to start the engine rotation in good response as soon as the first combustion occurs, and therefore an improvement of the success rate in the automatic starting of the engine can be achieved.
In step S208, the cylinder in which the expansion stroke of its piston is stopped is stored as a specific cylinder on which the fuel injection and the ignition are firstly performed at the time of restarting the engine.
Incidentally, during a time period in which engine 101 is stopped by the automatic stopping operation, each of variable valve lift mechanisms 112 a, 112 b is kept to maintain a state where the valve operating angle and the valve lift amount are set at the target values for the automatic starting of the engine, and is ready for a subsequent restarting of the engine.
Next, there will be described a controlling processed for an automatic starting of the engine from the above automatic stopping state of the engine with reference to the flowchart of FIG. 7.
In step S301, judgment is made as to whether or not a condition for the starting of the engine is established.
That is to say, it is judged that the condition for the starting of the engine is established, if any one of the following conditions (1) through (4) is satisfied.

(1) Brake switch 120 is turned OFF.
(2) The accelerator opening is not yet closed to the full,
(3) The continuation time for which the state of stopping of the engine operation continues has exceeded a reference time period.
(4) A battery voltage is equal to or less than a reference voltage.

At this stage, it should, however, be understood that the condition for the starting of the engine is not limited to the above-listed items.
If the condition for the starting of the engine is satisfied, the routine proceeds to step S302 where the fuel is injected to the cylinder stopped in the expansion stroke, which has been stored in step S208, and immediately thereafter, the operation for ignition is executed.
In V-type six-cylinder engine 101, as shown in FIG. 8 for example, if it is assumed that the cylinder stopped in the expansion stroke is the sixth cylinder on the left bank, the fuel of a previously determined amount is injected from fuel injection valve 131 into the combustion chamber of the sixth cylinder in response to a request for the starting of the engine, and also, spark ignition is performed by ignition plug 122 of the sixth cylinder so that the previously injected fuel is ignited for combustion.
Then, in the sixth cylinder, the piston is moved down by the explosion pressure due to the fuel combustion, and the crankshaft starts to rotate and therefore, the starting of engine 101 is commenced.
When the sixth cylinder is in the expansion stroke, the third cylinder on the right bank is in the intake stroke during which intake valves 106 are opened. However, since the operating angle of intake valves 105 and the lift amount thereof controlled by variable valve lift mechanisms 112 a, 112 b on both banks, are controlled to be set at the target values for the automatic starting of the engine, the load required for driving the opening of intake valves 105 of the third cylinder is suppressed to be smaller.
Therefore, the starting torque necessary for starting the rotation of the crankshaft by means of the first explosion pressure in the sixth cylinder becomes smaller, and a rise in the rotating speed of the crankshaft can takes place in good response to the first explosion. As a result, it is possible to improve the rate of success in the automatic starting of the engine (refer to FIG. 9).
In next step S303, the fuel injection and the ignition are performed on a cylinder which has been stopped in the compression stroke thereof.
In engine 101, the ignition is performed in succession in the order of the first cylinder→the second cylinder→the third cylinder→the fourth cylinder→the fifth cylinder→the sixth cylinder, and therefore, it can easily confirm that which one of the cylinders has been stopped in the compression stroke based on this ignition order and the stored data of cylinder which is stopped in the expansion stroke.
In the example shown in FIG. 8, the first cylinder on the right bank is the cylinder which has been stopped in the compression stroke, and accordingly, after the fuel is injected to the sixth cylinder for ignition, the fuel is injected to the first cylinder for ignition thereof, to thereby cause the explosion combustion in the first cylinder subsequently after the explosion combustion in the sixth cylinder, so that the crankshaft which has started to rotate by the explosion pressure in the sixth cylinder continues the rotation thereof and the rotating speed of the crankshaft is further increased.
After the fuel injection and the ignition on the cylinder which has bee stopped in the compression stroke, the fuel injection and the ignition are performed according to the prescribed ignition order.
Incidentally, the timing for performing the fuel injection in the automatic starting of the engine is determined to be in the intake stroke.
In step S304, judgment is made as to whether or not it is a timing for starting a control which is executed for variably incrementing the valve operating angle and the valve lift amount which are controlled by variable valve lift mechanism 112 (112 a or 112 b) on the bank to which the cylinder stopped in the expansion stroke belongs, from the target values for the automatic starting of the engine.
The operation angle of intake valves 105 and the lift amount thereof are forcibly lessened in order to reduce a load expended for driving the opening of intake valves 105 in the first intake stroke. However, in such a case, since the amount of intake air is reduced, the sufficient torque cannot be obtained. Therefore, if the amount of intake air is also small in the next intake stroke, a reduction in the engine rotating speed takes place.
Therefore, for the second intake stroke from a start of the automatic starting of the engine, it is necessary to set a larger valve operating angle and a larger valve lift amount than the respective target values for the automatic starting of the engine, so that the necessary and sufficient amount of suction of the intake air can be achieved.
Accordingly, taking a response delay of variable valve lift mechanisms 112 into consideration, a point of time previous by a response delay time to a starting time of the second intake stroke is set as the start timing of controlling for variably incrementing the valve operating angle and the valve lift amount from the target values for the automatic starting of the engine.
However, at this stage, the above-mentioned start timing of controlling can be set at a point of time when the cylinder stopped in the compression stroke reaches the top dead center when the operation of the engine is automatically stopped, by which the operating angle of intake valves 105 and the lift amount thereof are increased after the first work to do the compression stroke is finished.
If the variable increment of the valve operating angle and the valve lift amount are started from the point of time when the cylinder stopped in the compression stroke reaches the top dead center, it is possible to prevent an occurrence of such an unpleasant state that the load expended for driving the opening of intake valves 105 increases during the first compression work and as a result, the rise in the engine rotating speed becomes dull.
If a determination is made that the time started from the automatic starting is at the starting timing of controlling, the routine proceeds to step S305, to start the controlling for variably incrementing the valve operating angle and the valve lift amount controlled by variable valve lift mechanism 112 (112 a or 112 b) on the bank to which the cylinder stopped in the expansion stroke belongs, from the target values for the automatic starting of the engine toward values required for continuing the operation for the starting of the engine.
In step S306, judgment is made as to whether or not a certain delay period has elapsed since commencement of the controlling process of step S305.
The above-mentioned certain delay period may be set at a fixed period of time, but is preferably set at such a period of time in which the rotation of an engine only for one stroke takes place.
Then, when judgment is made that the above-described delay period has elapsed, the routine proceeds to step S307, to start the control of variably incrementing the valve operating angle and the valve lift amount controlled by variable valve lift mechanism 112 on the bank to which the cylinder stopped in the expansion stroke does not belong, from the target values for the automatic starting of the engine toward the values required for continuing the starting of the engine.
In the above-described automatic starting of the engine, the operating angle of intake valves 105 and the lift amount thereof in the first intake stroke after commencement of the starting of the engine operation are forcibly made smaller, so that the starting torque for the crankshaft is reduced to thereby enhance the starting performance. However, from the second intake stroke, it is necessary to increase the valve operating angle and the valve lift amount so that the intake air amount capable of continuing the starting of the engine can be obtained.
In the example shown in FIG. 8, the cylinder which is firstly in the intake stroke after commencement of the starting of the engine operation is the third cylinder on the right bank, and from the view point that the driving to open intake valves 105 in the large valve operating angle and the large lift amount is avoided in the first expansion stroke, it is necessary to reduce the operating angle of intake valve 105 and the lift amount thereof in the first intake stroke of the third cylinder.
However, for the fourth cylinder which is secondly in the intake stroke, it is necessary to ensure the intake air amount at which the engine operation can be continued, rather than lessening the load expended for driving the opening of intake valves 105. From this point, with the left bank, the control for variably incrementing the valve operating angle and the valve lift amount may be started immediately after commencement of the starting of the engine operation.
However, if actuator 17 is operated before the first top dead center in order to increase the valve operating angle and the valve lift amount with the left bank, the crankshaft starts to rotate due to the first explosion combustion, to produce resistance against engine 101 in which the intake air amount in the first cylinder is being compressed, so that a rise in the engine rotating speed becomes dull.
Accordingly, it is preferable that the timing to start the controlling for variably incrementing the valve operating angle and the valve lift amount on the left bank comes after the top dead center of the first cylinder at the earliest. More preferably, the timing to start the controlling for variably incrementing the valve operating angle and the valve lift amount on the left bank comes at a more delayed time after the top dead center, and therefore, is set at the most delayed time at which the valve operating angle and the valve lift amount in the intake stroke of the fourth cylinder can be increased.
To be specific, for example, a point of time that comes earlier by a response lag time than the opening timing of intake valves 105 at the valve operating angle after the controlling operation for incrementing is set as the start timing of controlling for variably incrementing the valve operating angle and the valve lift amount in the intake stroke of the fourth cylinder.
Incidentally, the start timing of controlling for variably incrementing the valve operating angle and the valve lift amount in the left bank can be set based on an angle from termination of the intake stroke of the third cylinder.
Further, if the control for incrementing the valve operating angle and the valve lift amount on the right bank is started simultaneously with the controlling for incrementing the valve operating angle and the valve lift amount on the left bank, the valve operating angle and the valve lift amount in the previous intake stroke of the third cylinder are incremented to be overlapped with the incremented valve operating angle and the incremented valve lift amount in the second intake stroke of the fourth cylinder, so that a large load for driving the opening of intake valves 105 is additionally expended at an initial period of the automatic starting of the engine.
Therefore, the controlling for variably incrementing the valve operating angle and the valve lift amount on the right bank is started with a time difference from the starting time of the controlling on the left bank. If this time difference corresponds to a time for one stroke, it is possible to avoid the increment of the valve operating angle and the valve lift amount at least in the first intake stroke of the third cylinder, so that the first intake stroke of the third cylinder is executed in a state where the valve operating angle and the valve lift amount are small.
Namely, for the intake stroke on the right bank, the first intake stroke is executed in the state where the valve operating angle and the valve lift amount are small, and the valve operating angle and the valve lift amount are incremented to the values by which the starting of the engine operation can be continued from the next intake stroke.
However, in the case where the load by operating actuator 17 is negligibly smaller compared to the load for driving the opening of intake valves 105, the controlling for variably incrementing the valve operating angle and the valve lift amount on the bank to which the cylinder stopped in the expansion stroke belongs can be started with the start of the automatic starting of the engine, and the valve operating angle and the valve lift amount on the other bank can be started after the first intake stroke in the other bank is terminated.
Further, the control start timing for variably incrementing the valve operating angle and the valve lift amount can be determined based on a judgment of completion of the starting of engine 101. For example, it is possible that at a point of time when it is judged that the engine rotating speed or an acceleration for speeding up of the engine rotation exceeds a reference value, it is judged that the starting of the engine is completed, and the control for variably incrementing the valve operating angle and the valve lift amount is started for variable valve lift mechanism 112 on the bank to which the cylinder to be next in the intake stroke or for two variable valve lift mechanisms 112 a, 112 b at the same time.
In this case, the control start timing at step S304 is the point of time when it is judged that the engine rotating speed or the acceleration for speeding up the engine rotation exceeds the reference value.
Further, in the case where there is disposed a variable valve lift mechanism which varies an operating angle of exhaust valves 107 and a lift amount thereof together with variable valve lift mechanism 112 which varies the operating angle of intake valves 105 and the lift amount thereof, it is possible that the operating angle of exhaust valves 107 and the lift amount thereof as well as those of intake valves 106 are forcibly set to be small at the automatic starting of the engine, and the operating angle of intake valves 105 and the lift amount thereof start to be incremented with a time difference between those of exhaust valves 107.
Further, the variable valve mechanism is not limited to the above-described variable valve lift mechanism 112, and for example, may be a variable valve mechanism which varies opening characteristics of engine valve by switching a three-dimensional cam or a plurality of cams. Therefore, the present invention is widely applicable to an engine provided with a variable valve mechanism which varies an operating angle and/or a lift amount of an engine valve.
Furthermore, in an electromagnetic drive valve which drives to open or close an engine valve using an electromagnet, it is possible to reduce a load of the electromagnetic drive valve to thereby enhance the rate of success in the automatic starting of an engine, by forcibly decreasing the valve operating angle at the automatic starting of the engine.
Still further, it is possible to judge, based on the engine rotating speed, the acceleration for increasing the engine rotating speed or the like after the automatic starting of an engine, as to whether the automatic starting of the engine is succeeded or failed, and when the automatic starting of the engine is failed, the starter motor is automatically driven to thereby restart the engine operation.
Moreover, engine 101 is not limited to the V-type engine, and may be a horizontally-opposed engine or an in-line engine.
The entire contents of Japanese Patent Application No. 2007-058958 filed on Mar. 8, 2007 a priority of which is claimed, are incorporated herein by reference.
While only selected embodiment has been chosen to illustrate and describe the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims.
Furthermore, the foregoing description of the embodiment according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Claims

1. An apparatus for controlling a starting operation of an engine provided with a variable valve mechanism capable of varying opening characteristics of an engine valve, comprising:

a starting device configured to execute ignition of fuel existing in a combustion chamber of the engine in a state where an engine operation is stopped, to thereby start the engine operation; and

a load controlling device configured to forcibly reduce a load expended by the variable valve mechanism at a moment of starting of the engine operation by the starting device.

2. The apparatus according to claim 1, wherein the load controlling device continues to hold a state where the load by the variable valve mechanism is forcibly reduced for one stroke of the engine.

3. The apparatus according to claim 1, wherein the load controlling device continues to hold a state where the load by the variable valve mechanism is forcibly reduced up to a top dead center of compression stroke at the first time.

4. The apparatus according to claim 1, wherein the load controlling device continues to hold a state where the load by the variable valve mechanism is forcibly reduced until judgment is made that a starting of the engine operation is completed.

5. The apparatus according to claim 1, wherein the load controlling device forcibly controls the opening characteristics such that a load expended for driving an opening of the engine valve is small, to forcibly reduce the load by the variable valve mechanism.

6. The apparatus according to claim 5, wherein the load controlling device forcibly controls the opening characteristics such that the load expended for driving the opening of the engine valve is small, when the engine operation is stopped.

7. The apparatus according to claim 1, wherein the variable valve mechanism is comprised of a mechanism that is capable of varying a lift amount of the engine valve, and

the load controlling device forcibly reduces the valve lift amount, to forcibly reduce the load by the variable valve mechanism.

8. The apparatus according to claim 1i wherein the variable valve mechanism is comprised of a mechanism that is capable of varying an operating angle of the engine valve, and

the load controlling device forcibly reduces the valve operating angle, to forcibly reduce the load by the variable valve mechanism.

9. The apparatus according to claim 1, wherein

the variable valve mechanism is comprised of a plurality of identical variable valve mechanisms arranged to be independent from each other, and

the load controlling device controls the plurality of independent variable valve mechanisms, respectively, to vary the opening characteristics of the engine valves with a time difference between the plurality of independent variable valve mechanisms, to forcibly reduce the loads by the variable valve mechanisms.

10. The apparatus according to claim 9, wherein the engine is provided with two banks, each including the variable valve mechanism, and

the load controlling device is configured to control the variable valve mechanism on each of the two banks to vary the opening characteristics with a time difference between the variable valve mechanisms on the two banks.

11. The apparatus according to claim 9, wherein the load controlling device controls the plurality of independent variable valve mechanisms to vary the opening characteristics in which the loads expended for driving openings of respective of the engine valves are, respectively, small to those in which the loads expended for driving the openings of the respective engine valves are, respectively, large, with a time difference between the plurality of independent variable valve mechanisms.

12. A method of controlling a starting operation of an engine provided with a variable valve mechanism capable of varying opening characteristics of an engine valve, comprising the steps of:

judging as to whether or not there is an issuance of a request for starting the engine;

igniting fuel existing in a combustion chamber of the engine, when there is the issuance of the request for starting the engine, in a state where an engine operation is being stopped, to thereby restart the engine operation; and

forcibly reducing a load expended by the variable valve mechanism at a moment of starting of the engine operation.

13. The method according to claim 12, wherein the step of forcibly reducing the load by the variable valve mechanism comprises the steps of:

judging as to whether or not there has been an elapse of a period of time for one stroke of the engine from commencement of the starting of the engine operation; and

forcibly reducing the load by the variable valve mechanism during a time duration until elapsing of the said period of time has elapsed.

14. The method according to claim 12, wherein the step of forcibly reducing the load expended by the variable valve mechanism comprises the steps of:

judging as to whether or not there has been an elapse of a period of time from the starting of the engine operation to arriving at the compression top dead center at a first time; and

forcibly reducing the load by the variable valve mechanism during a time duration until elapsing of the said period of time.

15. The method according to claim 12, wherein the step of forcibly reducing the load by the variable valve mechanism comprises the steps of:

judging as to whether or not the starting of the engine operation has completed; and

forcibly reducing the load by the variable valve mechanism during a time duration until it is judged that the starting of the engine operation is completed.

16. The method according to claim 12, wherein the step of forcibly reducing the load by the variable valve mechanism comprises the steps of:

judging as to whether or not the engine operation is stopped; and

controlling the variable valve mechanism, when it is judged that the engine operation is stopped, toward the destination that the engine valve has the opening characteristics in which the load for driving an opening of the engine valve is small.

17. The method according to claim 12, wherein the variable valve mechanism is comprised of a plurality of identical variable valve mechanisms, each being independent from one another, and

the step of forcibly reducing the load by the variable valve mechanism comprises the steps of:

allowing some of the plurality of variable valve mechanisms to perform a variation of the opening characteristics of the engine valve;

judging as to whether or not there is an elapse of a given delay time from the variation of the opening characteristics of the engine;

urging, after judgment of the elapse of the delay time, the other variable valve mechanisms except for the some of the plurality of variable valve mechanisms that have not yet performed variation of the opening characteristics, to vary the opening characteristics of the engine valve.

18. The method according to claim 17, wherein the engine is provided with first and second banks, each including the variable valve mechanism, and

the step of allowing the some of the plurality of variable valve mechanisms to vary the opening characteristics of the engine valve, controls the variable valve mechanism on the first bank to vary the opening characteristics of the engine valve, and

the step of allowing, after the elapse of the given delay time, the other variable valve mechanisms to vary the opening characteristics, allows the variable valve mechanism on the second bank to vary the opening characteristics of the engine valve.

19. The method according to claim 17, wherein the stop of allowing the some of the variable valve mechanisms to vary the opening characteristics of the engine valve and the step of allowing, after the elapse of the given delay time, the other variable valve mechanisms to vary the opening characteristics of the engine valve, allow the plurality of variable valve mechanisms to vary the opening characteristics such a manner that loads for driving opening of the engine valves are changed from a small load state to a large load state, respectively.

20. An apparatus for controlling a starting operation of an engine provided with a variable valve mechanism capable of varying opening characteristics of an engine valve, comprising:

operation starting means for igniting fuel existing in a combustion chamber of the engine in a state where an engine operation is stopped, to thereby start the engine operation; and

load-controlling means for forcibly reducing a load expended by the variable valve mechanism at a moment of starting the engine operation by the operation starting means.