JP2009097345A - Engine starting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly start the engine rotation by improving the starting property in the case of restart of an engine by temporary inversion operation of the engine by combustion by igniting a stoppage compression stroke cylinder, and then by normal operation by combustion by igniting the stoppage expansion stroke cylinder compressed thereby. <P>SOLUTION: During the inversion operation of an engine 1, a stoppage expansion stroke cylinder 12B is compressed sufficiently by controlling the close time IVC of an intake valve 19 relatively to the advance angle side (SD1). At the same time, it is controlled relatively to the retard angle side after the normal operation (SD3, SD5) so that the effective compression rate of the stoppage compression stroke cylinder 12A and a stoppage intake stroke cylinder 12C is lowered. When the stoppage intake stroke cylinder 12C exceeds TDC, the intake valve close time IVC is shifted to the advance angle side (SD7) so as to quickly start the engine rotation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine starting device that automatically starts an engine that has been automatically stopped at an idle time or the like in response to a restart request, and more particularly to control of the operation timing of an intake valve at the time of starting.

2. Description of the Related Art Conventionally, an engine control system (idle stop system) is known in which an engine is automatically stopped during idling for the purpose of reducing fuel consumption and suppressing CO ₂ emission. In such a system, the engine must be started immediately in response to an engine restart request such as a start operation. However, in a general starting method in which the engine is started through cranking by the starting motor, the starting time is short. There is a tendency that it becomes a little longer, and there is also a problem that the noise accompanying cranking makes the driver feel uncomfortable.

  In this regard, the inventors of the present application ignited and combusted a cylinder stopped in the compression stroke (hereinafter also referred to as a compression stroke cylinder at the time of stopping. Thus, there is proposed a method (hereinafter also referred to as reverse combustion start) in which the engine is rotated forward and restarted by itself by igniting and burning after compressing the expansion stroke cylinder at the time of stop by this reverse rotation operation.

For example, in the one described in Patent Document 1, when the engine is operated in reverse as described above, the closing timing of the intake valve is retarded by a predetermined crank angle or more than BDC before switching from reverse to forward rotation. The intake valve is surely opened so that fresh air is introduced into the compression stroke cylinder when stopped. In this way, after the stop-time compression stroke cylinder shifts to the expansion stroke as the engine rotates forward, it can be ignited and burned again, thereby improving engine startability.
JP 2007-92719 A

  By the way, in the reverse combustion start as described above, it is important to sufficiently compress the stop-time expansion stroke cylinder in which the first combustion for engine forward rotation is performed by the reverse rotation operation. In order to take in fresh air into the cylinder during the compression stroke when the combustion is performed for reverse operation, the intake valve closing timing is controlled to be considerably retarded, and the valve is opened relatively early during reverse operation. As a result, the stroke of the reverse rotation operation becomes insufficient, and the expansion stroke cylinder at the time of stop may not be sufficiently compressed.

  In addition, as the engine rotates forward, the cylinder that was in the intake stroke at the time of stopping (the intake stroke cylinder at the time of stop) shifts to the compression stroke and reaches the top dead center following the compression stroke cylinder at the time of stop. Since the air in the cylinder is warmed by heat radiation from the cylinder wall surface during idling stop, the compression reaction force is increased and there is a possibility that the engine rotation is greatly reduced.

  In view of these points, an object of the present invention is to control the operation timing of the intake valve at the time of restart in an engine starter that automatically stops the engine when idling or the like and then restarts automatically. The idea is to improve the startability and to make the engine start up smoothly.

  In order to achieve the above object, in the present invention, during the engine reverse operation at the time of restart, the closing timing of the intake valve is controlled to be relatively advanced so that the expansion stroke cylinder at the time of stop can be sufficiently compressed. On the other hand, after the forward rotation, the compression reaction force of the cylinder is reduced by controlling to a relatively retarded angle side.

  More specifically, according to the first aspect of the present invention, when a predetermined restart condition is satisfied after the engine is automatically stopped, the engine is temporarily operated in reverse by igniting and burning the compression stroke cylinder of the stopped engine. It is assumed that the engine starter is configured to ignite and burn the expansion stroke cylinder to be compressed thereby to automatically restart and automatically restart the engine. Intake valve control for controlling the closing timing of the intake valve at least in the compression stroke cylinder at the time of stop relatively to the advance side during the reverse operation of the engine and to the relatively retard side after the forward rotation Means shall be provided.

  With the above configuration, when the engine is automatically restarted, first, a cylinder stopped in the compression stroke (stopped compression stroke cylinder) is ignited, and the air-fuel mixture in the cylinder burns, whereby the engine The cylinder that has stopped in the expansion stroke is compressed by this, and the cylinder that is stopped in the expansion stroke (stop expansion cylinder) is compressed. At this time, at least the closing timing of the intake valve in the stop compression stroke cylinder is By being controlled relatively forward, the intake valve remains relatively close to the bottom dead center during reverse rotation in the cylinder, ensuring a reverse operation stroke and expansion during stop. The stroke cylinder can be sufficiently compressed.

  By igniting and burning the air-fuel mixture in the stop expansion stroke cylinder in a sufficiently compressed state, a large starting torque to the normal rotation side can be given to the engine. When the engine switches to normal rotation, the compression stroke cylinder at the time of stop is compressed accordingly. At this time, the closing timing of the intake valve is controlled to be relatively retarded. Since the effective compression ratio is reduced and the compression reaction force is reduced, it is advantageous for starting up the engine rotation.

  Preferably, a piston position detecting means for detecting a stop position of the piston in the expansion stroke cylinder at the time of stop is provided, and the advancement timing of the intake valve closing timing during the reverse rotation operation of the engine according to the detected piston stop position. Is adjusted (Claim 2).

  That is, even if the intake valve closing timing is advanced in order to ensure the reverse operation stroke of the engine as described above, the intake air is taken in at the end of the reverse operation, that is, before and after switching from the reverse operation to the normal operation. If the valve is not opened, the burned gas cannot be discharged from the compression stroke cylinder at the stop time, and the compression reaction force of the compression stroke cylinder at the stop time becomes excessive after the forward rotation.

  Therefore, as the piston stop position of the expansion stroke cylinder at the stop is relatively closer to the top dead center, the advance angle of the intake valve closing timing during the reverse rotation operation of the engine is increased, and the piston stop position is relatively bottom dead. If it is close to the point, the advance angle of the intake valve closing timing is reduced. In this way, the intake valve is more reliably opened before switching from the reverse operation to the forward rotation while ensuring a sufficient stroke until the intake valve opens during the reverse operation in the compression stroke cylinder at the stop. Fuel gas can be discharged.

  Then, after the engine switches to normal rotation, if the compression stroke cylinder at the time of stop exceeds the compression top dead center and shifts to the expansion stroke, the cylinder that was in the intake stroke at the time of stop will shift to the compression stroke. As described above, the air in the cylinder is warmed during the automatic stop of the engine and is in a high temperature state, and if it is left as it is, the compression reaction force becomes considerably large and self-ignition tends to occur.

  Therefore, it is preferable that the intake valve closing timing is relatively retarded until the stop-time intake stroke cylinder that has shifted to the compression stroke due to the forward rotation of the engine as described above reaches the compression top dead center. (Claim 3), and in this way, the effective compression ratio is reduced in the intake stroke during the stop as in the compression stroke cylinder during the stop, and the compression reaction force is increased. This can be suppressed, and is advantageous for smoothly starting up the engine rotation, and suppresses the increase in temperature and pressure during the compression stroke, thereby suppressing the occurrence of self-ignition.

  If the stop-time intake stroke cylinder that has shifted to the compression stroke reaches the compression top dead center, the intake valve closing timing of each cylinder is changed to a relatively advanced angle side, and then the engine rotation The speed is maintained until it reaches a predetermined idle speed (Claim 4). If the closing timing of the intake valve is changed to the relatively advanced side in this way, the charging efficiency of the intake air becomes high, and the engine speed rises quickly due to the increase in the starting torque.

  Furthermore, if the engine speed that has risen so far reaches the idle speed, this time, the closing timing of the intake valve is changed to the relatively retarded side, and the intake charge efficiency of the cylinder is reduced, thereby reducing the engine Suppression is suppressed (claim 5). In this way, the engine does not blow up significantly as in a general starter start, and the driver can be prevented from feeling uncomfortable during the automatic start.

  As described above, according to the engine starter according to the present invention, the engine is once reversely operated by the combustion of the stop-time compression stroke cylinder, thereby compressing the stop-time expansion stroke cylinder and burning it. When securing the starting torque of the engine, during the reverse operation, the intake valve closing timing is controlled to be relatively advanced so that the stop expansion stroke cylinder can be sufficiently compressed. After the forward rotation, the effective compression ratio of the cylinder is reduced by controlling this to the retarded angle side, so that sufficient starting torque can be obtained by the combustion of the expansion stroke cylinder at the stop, and the cylinder after the start of the forward rotation The engine reaction can be started up smoothly by reducing the compression reaction force.

In particular, if the advance angle of the intake valve closing timing during engine reverse rotation operation is adjusted according to the piston stop position in the stop expansion stroke cylinder, the stop expansion stroke cylinder regardless of variations in the piston stop position Can be sufficiently compressed, and when the engine switches to normal rotation, the burned gas can be more reliably discharged from the compression stroke cylinder when stopped, which is also advantageous for smoothly starting the engine rotation. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

(Outline of engine control system)
FIG. 1 shows an embodiment of an engine control system E including an engine starter according to the present invention. The system E includes an engine 1 and an ECU 2 (engine controller) for controlling the engine 1. The engine 1 includes a cylinder head 10 and a cylinder block 11 and is provided with four cylinders 12A to 12D as shown in FIG. As shown in FIG. 1, pistons 13 connected to the crankshaft 3 are fitted in the cylinders 12A to 12D, respectively, so that the cylinders 12A to 12D are disposed above the pistons 13 in the cylinders 12A to 12D. A combustion chamber 14 is formed.

  Here, in general, in a multi-cylinder four-cycle engine, each cylinder performs a combustion cycle composed of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of a cylinder engine, when referred to as the first cylinder 12A, the second cylinder 12B, the third cylinder 12C, and the fourth cylinder 12D from one end in the cylinder row direction, the first cylinder (# 1), the third cylinder (# 3), Combustion is performed with a phase difference of 180 degrees in crank angle in the order of the fourth cylinder (# 4) and the second cylinder (# 2).

  A spark plug 15 for igniting and burning the air-fuel mixture in the combustion chamber 14 is provided at the top of each combustion chamber 14 of each of the cylinders 12A to 12D. An electrode is disposed so as to face the combustion chamber 14. A fuel injection valve 16 for directly injecting fuel into the combustion chamber 14 is provided on the side of the combustion chamber 14 (right side in FIG. 1). The fuel injection valve 16 is an ignition plug. Fuel is injected toward the vicinity of the 15 electrodes. The fuel injection valve 16 is opened for a time corresponding to the pulse width by the input of a pulse signal from the ECU 2, and an amount of fuel corresponding to the valve opening time is injected into each cylinder 12A to 12D.

  The cylinder head 10 is provided with an intake port 17 and an exhaust port 18 so as to open to the ceiling of the combustion chamber 14 of each of the cylinders 12A to 12D. A valve 19 and an exhaust valve 20 are respectively provided. The intake port 17 and the exhaust port 18 respectively extend obliquely upward away from the combustion chamber 14, open on the intake side and exhaust side sidewalls of the cylinder head 10, and communicate with the intake passage 21 and the exhaust passage 22. Yes.

  The intake valve 19 and the exhaust valve 20 are each driven by a valve operating mechanism having a camshaft (not shown), and as described above, the cylinders 12A to 12D perform a combustion cycle with a predetermined phase difference. Basic opening / closing operation timings of the intake / exhaust valves 19 and 20 for each cylinder 12 are set. In addition, in this embodiment, a phase variable mechanism 23 (variable valve timing, hereinafter also referred to as VVT) capable of continuously changing the phase with respect to the rotation of the crankshaft 3 within a predetermined angle range is attached to the camshaft on the intake side. It has been.

  As an example, although not shown, the VVT 23 is incorporated between the front end portion of the intake side camshaft and the sprocket around which the cam chain is wound, and the sprocket and camshaft are driven by the driving force of the electromagnetic actuator. It is a known electromagnetic drive type that causes a phase difference between them. Such an electromagnetically driven VVT can be operated when the engine 1 is started unlike a hydraulic type, and also operates very quickly, so that the response delay is small.

  As shown in FIG. 2, the downstream side of the intake passage 21 is an independent branch intake passage 21a for each of the cylinders 12A to 12D, and the upstream end of each branch intake passage 21a communicates with the surge tank 21b. The intake passage 21 upstream of the surge tank 21b is a common intake passage 21c common to the cylinders 12A to 12D. An electric throttle valve 24 for adjusting the passage cross-sectional area to restrict the intake flow is disposed. It is driven by an electric motor 24a. Further, as shown only in FIG. 2, an air flow sensor 25 for detecting the intake air amount and an intake pressure sensor 26 for detecting the intake air pressure are arranged on the upstream side and the downstream side of the throttle valve 24, respectively. ing. In this embodiment, a passage that bypasses the throttle valve 24 is not provided, and the intake air flow rate during idle operation is adjusted by the throttle opening.

  Further, the engine 1 of this embodiment is provided with a starter motor 27. The starter motor 27 is well known in the art, and although not shown in detail, a pinion gear is provided at the tip of an output shaft that can advance and retreat in the axial direction. When the engine 1 is started, the pinion gear is engaged with a ring gear on the outer periphery of the flywheel. The crankshaft 3 is forcibly rotated (cranking) via the flywheel.

  The engine 1 is provided with an alternator 28 that is drivingly connected to the crankshaft 3 by a belt or the like. Although not shown in detail, the alternator 28 includes a regulator circuit 28a that changes the output voltage by controlling the current of the field coil and thereby adjusts the amount of power generation. The control command (for example, voltage) is input, so that the amount of power generation is basically controlled in accordance with the electrical load of the vehicle electrical components and the in-vehicle battery voltage.

  Further, the engine 1 is provided with two crank angle sensors 30 and 31 for detecting the rotation angle of the crankshaft 3. The ECU 2 mainly determines the engine rotation speed based on a signal from one crank angle sensor 30. As will be described in detail later, the rotation direction and the rotation angle of the crankshaft 3 are detected by the crank angle signals output from the two crank angle sensors 30 and 31 that are out of phase with each other.

  Reference numeral 32 shown in FIG. 1 is a cam angle sensor that detects a specific rotational position of the intake camshaft and outputs it as a cylinder identification signal. Reference numeral 33 denotes an accelerator pedal operation amount (accelerator opening by the driver). It is an accelerator opening degree sensor for detecting a degree).

  The ECU 2 receives signals from the sensors 25, 26, 30 to 33, outputs control signals for the injection amount and the injection timing to the fuel injection valve 16, and sets the ignition timing for the ignition device 29 of the spark plug 15. And a throttle opening degree control signal is output to the motor 24a of the throttle valve 24. As will be described in detail below, the ECU 2 automatically stops the engine by stopping the fuel supply to each of the cylinders 12A to 12D when a predetermined engine stop condition is satisfied at the time of idling. The engine 1 is automatically restarted if a predetermined restart condition is established by an operator's operation or the like.

  That is, when the engine 1 is restarted, the engine 1 is basically started only with its own power without borrowing the power of the starter motor 27. In this embodiment, as schematically shown in FIG. First, the first combustion is performed in the cylinder 12 in which the piston 13 is stopped in the middle of the compression stroke (# 1 cylinder 12A in the example of the drawing, hereinafter also referred to as the compression stroke cylinder at the time of stop), and the piston 13 By pushing down, the crankshaft 3 is slightly rotated reversely ((a) in the same figure), so that the cylinder 12 in the expansion stroke (# 2 cylinder 12B in the example shown in the figure) is referred to as the expansion stroke cylinder at the time of stop. And the air-fuel mixture in the cylinder 12B is compressed ((b) in the figure). Then, by igniting and burning the air-fuel mixture in the expansion stroke cylinder 12B that has been compressed and thus increased in temperature and pressure, a torque in the forward rotation direction is given to the crankshaft 3, and the engine 1 is Let it start.

  In order to start the engine 1 only with its own force in this way, the torque in the forward rotation direction as much as possible is given to the crankshaft 3 by the combustion of the expansion stroke cylinder 12B at the time of stop, and thereby (c) in FIG. As shown in FIG. 6, the cylinder 12A that reaches compression top dead center (hereinafter abbreviated as TDC) must overcome the compression reaction force (compression pressure) and exceed TDC. Therefore, in order to start the engine 1 reliably, it is necessary to ensure sufficient air for combustion in the stop-time expansion stroke cylinder 12B.

  Specifically, if the piston stop position of the expansion stroke cylinder 12B during the stop is closer to the BDC than the upper limit position (for example, about ATDC 95 to 100 ° CA) slightly lower than the bottom dead center (BDC) from the center of the stroke, combustion occurs. However, the closer to the BDC, the closer the piston 13 approaches TDC in the compression stroke cylinder 12A at the time of stop, so this time it is necessary for combustion for the reverse operation of the engine 1 It will not be possible to secure the correct air. Therefore, the lower limit of the piston stop position in the expansion stroke cylinder 12B at the time of stop is, for example, about ATDC 120 to 125 ° CA, and a range R between them is suitable for the reverse combustion start (see FIG. 6).

  Therefore, in this embodiment, when the engine 1 is automatically stopped during idling, the fuel supply is stopped at a rotational speed slightly higher than the idling rotational speed, and the throttle valve 24 is opened for a predetermined period thereafter. By closing at an appropriate timing, the required amount of air is sucked into the stop expansion stroke cylinder 12B and the stop compression stroke cylinder 12A, respectively, so that the air amount of the expansion stroke cylinder 12B becomes slightly larger than that of the compression stroke cylinder 12A. I have to. By doing so, the piston 13 of the expansion stroke cylinder 12B stops within the range R due to the balance of the compression pressure of the air in the two cylinders 12A and 12B.

(Engine automatic stop)
Next, the outline of the engine stop control will be described based on the flowchart of FIG. This flow starts at a predetermined timing during engine operation, and in step SA1, the flow waits until a predetermined automatic stop condition is satisfied. For example, if the vehicle speed is lower than a predetermined speed, the brake operation is continued for a predetermined time, the engine water temperature is within a predetermined range, and there is no particular inconvenience for stopping the engine 1, the engine automatic stop condition Is determined to have been established.

  If it is determined in step SA1 that the automatic stop condition is satisfied (YES), the process proceeds to step SA2 to start engine speed adjustment control. For example, the reduction state of the engine rotational speed Ne is monitored based on a signal from the crank angle sensor 30, and the degree of decrease in the engine rotational speed is adjusted by changing the power generation amount of the alternator 28 in accordance with this. Is.

  That is, when the engine 1 is stopped, the engine speed when the cylinders 12A to 12D pass through the TDC sequentially (hereinafter also referred to as the TDC rotation speed) in the process of gradually decreasing the rotation speed, and the engine stop. It is known that there is a clear correlation with the piston stop position of the cylinder 12 that is in the expansion stroke later. Therefore, the TDC rotational speed is detected, and the amount of power generated by the alternator 28 is controlled in accordance with the detected value, so that the engine rotation drop is adjusted, and the piston 13 of the cylinder 12 in the expansion stroke at the time of stopping is operated. Stop within the range R suitable for the restart.

  Specifically, first, the fuel injection amount and the like are controlled so that the engine rotational speed Ne becomes a predetermined rotational speed N1 (for example, 760 rpm), and the process proceeds to step SA3, where the engine rotational speed Ne is the predetermined rotational speed. Wait until N1 or higher. If this rotational speed is N1 or higher, the routine proceeds to step SA4, fuel injection to each cylinder 12A-12D is stopped (fuel cut), and the routine proceeds to step SA5.

  In step SA5, the throttle valve 24 is opened so as to have a preset opening, and the amount of intake air to each of the cylinders 12A to 12D is increased so that sufficient scavenging is performed. In step SA6, the system waits until the engine speed Ne becomes a predetermined speed N2 or less. This rotational speed N2 is for closing the throttle valve 24 at a timing such that the intake amount to the stop expansion stroke cylinder 12B is larger than that of the stop compression stroke cylinder 12A in consideration of the intake transport delay. For example, a range of about 500 to 600 rpm may be set.

  Then, it waits until the engine rotational speed Ne becomes equal to or lower than the predetermined rotational speed N2, and adjusts the reduced state of the engine rotational speed Ne by the control of the alternator 28 and the like as described above. That is, if the decrease in engine rotation is too slow, the power generation amount of the alternator 28 is increased so that the load on the engine 1 increases. On the other hand, if the degree of decrease in engine rotation is too rapid, the power generation amount is decreased so that the load on the engine 1 is decreased. Decrease.

  Then, by adjusting the degree of decrease in the engine speed Ne after the fuel cut by controlling the alternator 28, the trajectory of the engine speed Ne that gradually decreases while repeating up and down in a short cycle is gradually corrected. The state can be converged to an appropriate state by the last TDC before completion of the stop at the latest.

  If the engine rotational speed Ne becomes equal to or lower than the predetermined rotational speed N2 (YES in step SA6), the process proceeds to step SA7 to close the throttle valve 24, but thereafter, the control of the alternator 28 as described above continues. In step SA8, it is determined whether or not the engine 1 has passed the last TDC, that is, whether or not it is immediately before the engine 1 is stopped. This determination can be determined to be YES when the TDC rotational speed is equal to or lower than a predetermined position, for example.

  After passing through the last TDC, the engine 1 stops after rotating (swinging) several times in the forward and reverse directions by the compression reaction force of the two cylinders 12 and 12 in the compression stroke and the expansion stroke, respectively. Will do. Therefore, if it is determined to be YES immediately before the stop, the process proceeds to step SA9 to end the engine rotation speed adjustment control, and the process proceeds to step SA10 to stop the engine 1 based on the signals from the crank angle sensors 30, 31 (completely (Stop) is confirmed, and the piston stop position of the expansion stroke cylinder 12B is detected by a subroutine (see FIG. 5) described later, and this is stored in the memory to complete the engine stop control (end).

  That is, as described above, the crankshaft 3 rotates several times in both forward and reverse directions just before the engine 1 is stopped. Therefore, the piston stop position cannot be detected only by counting the signal from the crank angle sensor 30. Therefore, in this embodiment, the rotation direction and the rotation angle of the crankshaft 3 are detected as follows based on the crank angle signals output from the two crank angle sensors 30 and 31 and shifted from each other. A crank angle with respect to TDC or BDC of each cylinder 12A to 12D, that is, a piston stop position is detected.

-Detection of piston stop position-
Specifically, FIG. 5A is a flowchart showing a subroutine for detecting the stop position of the piston 13. In step SB1 after the start, each output signal from the first and second crank angle sensors 30, 31 is shown. Based on CA1 and CA2, whether the second crank angle signal CA2 is Low or High when the first crank angle signal CA1 rises, or the second crank angle signal CA2 when the first crank angle signal CA1 falls. Is High or Low.

  That is, during forward rotation of the engine, the second crank angle signal CA2 has a phase delay of about a half pulse width with respect to the first crank angle signal CA1, as shown in FIG. The second crank angle signal CA2 becomes Low when rising, and the second crank angle signal CA2 becomes High when the first crank angle signal CA1 falls. On the other hand, at the time of reverse rotation, the phase of the second crank angle signal CA2 advances by about a half pulse width with respect to the first crank angle signal CA1, as shown in FIG. The second crank angle signal CA2 becomes High when the first crank angle signal CA1 rises, and the second crank angle signal CA2 becomes Low when the first crank signals CA1 fall.

  That is, it is possible to determine whether the engine 1 is rotating forward or reverse depending on whether the phase relationship between the crank angle signals CA1 and CA2 is as shown in FIG. If it is determined in step SB1 that the engine 1 is in the forward rotation state (YES), the process proceeds to step SB2 and the count number of the CA counter for measuring the crank angle change in the forward rotation direction of the engine 1 is increased. If it is determined that the vehicle is in the reverse rotation state (NO), the process proceeds to step SB3, the count number of the CA counter is decreased, and then the process returns.

  Then, the rotation angle of the crankshaft 3 can be obtained by counting the number of rising or falling edges of the crank angle signals CA1 and CA2 by the CA counter. This is because the rise and fall of the first crank angle signal CA1 and the second crank angle signal CA2 are caused by rotation of the crankshaft 3 every predetermined angle (in this embodiment, the interval between the rise and fall is approximately 10 degrees). This is because it occurs every time.

  By the above subroutine, even when the crankshaft 3 rotates in the forward and reverse directions as described above when the engine 1 is automatically stopped, the crank angle is accurately detected regardless of this, and the piston stop position is specified. Can do. Therefore, this subroutine constitutes the piston position detection unit 2a (piston position detection means) of the ECU 2 that detects the stop position of the piston 13 in the expansion stroke cylinder 12B when the engine 1 is stopped.

  According to the automatic stop control of the engine 1 as described above, the throttle valve 24 is opened for the first predetermined period at the time of fuel cut at idling, and the cylinders 12 and 12 that respectively become the expansion stroke and the intake stroke after the stop are respectively required. A range R suitable for restarting the piston 13 in the expansion stroke cylinder 12 after the engine is stopped by adjusting the degree of decrease in the engine rotation speed by controlling the alternator 28 and the like so that a large amount of air is sucked. (See FIG. 6).

  Further, as described above, when the throttle valve 24 is opened for a predetermined period in the engine stop operation period, almost all the burned gas in each of the cylinders 12A to 12D is scavenged out of the cylinder and filled with fresh air. Become. However, after the engine 1 is stopped, the air pressure leaks immediately even in the expansion stroke cylinder 12 and the compression stroke cylinder 12 in which the intake and exhaust valves 19 and 20 are closed, so that each of the cylinders 12A to 12D has a piston. There is a state where fresh air (air) at approximately atmospheric pressure exists in the volume corresponding to the stop position.

(Reverse combustion start)
Next, restart of the engine 1 automatically stopped as described above will be described in detail with reference to FIGS. FIG. 6 is a schematic diagram showing the reverse operation of the stop-time compression stroke cylinder 12A and the stop-time expansion stroke cylinder 12B, and FIG. 7 is a flowchart showing the combustion control procedure at the start. FIG. 8 is a flowchart showing the procedure of the VVT control. FIG. 9 shows the in-cylinder pressure and engine of each cylinder 12A-12D by fuel injection and ignition for each cylinder 12A-12D at the time of reverse combustion start. It is the time chart which showed a mode that a rotational speed changed with the change of the closing timing IVC of the intake valve 19 at that time.

  The engine start control of this embodiment is to start the engine 1 by itself as described above. For this purpose, the engine 1 is reversed a little by first burning the compression stroke cylinder 12A (# 1 cylinder) at the time of stop. The engine is operated (FIG. 3 (a)), thereby compressing the inside of the stop stroke cylinder 12B (# 2 cylinder), and then igniting and burning (FIG. 3 (b)). Thus, by compressing the expansion stroke cylinder 12B at the time of stop, the combustion pressure becomes high, the effective stroke becomes long, and a large starting torque can be obtained.

  On the other hand, when the compression stroke cylinder 12A at the time of stop is first burned, the burned gas is filled in the cylinder 12A. Therefore, after the engine 1 starts normal rotation, the cylinder 12A When TDC (first TDC at start-up) is reached (FIG. 3 (c)), there is a possibility that the compression reaction force will increase and the engine rotation will drop more or even exceed TDC. is there.

  Therefore, in this embodiment, the VVT 23 is operated at the time of starting, and the opening / closing operation timing of the intake valve 19 is finely changed as follows, so that the reverse rotation is ensured while ensuring the stroke until the intake valve 19 opens during the reverse rotation operation. At the end of the operation, immediately before switching to normal rotation, the intake valve 19 is opened so that the burned gas is discharged from the cylinder 12A.

  Specifically, first, as shown in FIG. 6, the piston 13 of the expansion stroke cylinder 12B at the time of stop is positioned within a range R suitable for reverse combustion start by the above-described stop control. It is inevitable that the stop position varies in the vicinity of either the side or the BDC side. When the piston stop position is in the vicinity of the upper limit of the range R (for example, about ATDC 95 ° CA) as shown in FIG. 9A, the intake valve 19 is provided at the end of the reverse rotation stroke (indicated by an arrow in the figure). Is required to set the closing timing IVC to about ABDC 40 ° CA, for example.

  On the other hand, as shown in FIG. 5B, if the piston stop position is near the lower limit of the range R (about ATDC 120 ° CA), that is, close to the BDC, the closing timing IVC of the intake valve 19 is accordingly retarded. (In the example shown in the figure, it is necessary to set to about ABCDC 60 ° CA). From this, at the time of reverse rotation operation of the engine 1, the closing timing IVC of the intake valve 19 is controlled in the range of, for example, ABDC 40 to 60 ° CA as described above according to the piston stop position of the stop expansion stroke cylinder 12B. I have to.

-Procedure for combustion control-
Next, with regard to a specific control procedure at the time of starting, first, a fuel injection and ignition, that is, a combustion control procedure will be described based on a flowchart of FIG. This flow starts after the engine 1 is automatically stopped as described above, and it is determined in step SC1 whether or not a predetermined engine restart condition is satisfied. The restart conditions are when the brake is released to start from a stopped state, when an accelerator operation is performed, when the engine is required to operate the air conditioner, etc. If such a condition is not satisfied, the process waits until the condition is satisfied. If the restart condition is satisfied (YES in step SC1), the process proceeds to step SC2.

  In step SC2, it is determined whether to perform the reverse combustion start as described above or the starter motor 27. For example, based on the piston stop position of the stop-time expansion stroke cylinder 12B detected by the above-described subroutine (see FIG. 5), if it is within the range R suitable for the reverse combustion start, it is determined YES and the process proceeds to step SC3. On the other hand, if not (NO) starter start is selected. A description of the specific procedure for starting the starter will be omitted.

  In step SC3, the air amount in the stop compression stroke cylinder 12A and the stop expansion stroke cylinder 12B is calculated based on the piston stop position, and in the subsequent step SC4, for example, the stoichiometric air-fuel ratio, etc. A fuel injection amount that achieves a predetermined air-fuel ratio is calculated, and fuel is injected into the stop-time compression stroke cylinder 12A. The predetermined air-fuel ratio is obtained from a map set in advance in association with the piston stop position when the engine is stopped.

  Subsequently, in step SC5, after elapse of a predetermined time set in consideration of the fuel vaporization time from the fuel injection to the stop-time compression stroke cylinder 12A, the spark plug 15 of the cylinder 12A is energized to ignite the mixture. To do. In step SC6, the piston 13 is activated depending on whether or not the edge of the signal from the crank angle sensors 30, 31 (rise or fall of the crank angle signal) is detected within a predetermined time after ignition. It is determined whether it has moved (determination based on detection of the crank angle signal is based on the above-described subroutine). If the piston 13 does not move, it may be ignited again.

  Subsequently, in step SC7, fuel is injected into the cylinder 12B so that the air / fuel ratio becomes a predetermined air-fuel ratio with respect to the air amount in the stop expansion stroke cylinder 12B calculated in step SC3. Also in this case, the air-fuel ratio is obtained from a map set in advance in association with the piston stop position or the like when the engine is stopped.

  In step SC8, the stop-time expansion stroke cylinder 12B is ignited and combusted after a predetermined time (ignition delay) has elapsed since the reverse rotation operation of the engine 1 was detected. During this ignition delay time, the piston 13 of the expansion stroke cylinder 12B at the time of stop is raised by the reverse rotation operation of the engine 1, the air-fuel mixture in the cylinder 12B is sufficiently compressed, and the piston 13 is almost stopped by the compression reaction force. This corresponds to the time until the operation, and is obtained from a map set in advance in association with the piston stop position or the like.

  If the air-fuel mixture sufficiently compressed in the stop expansion stroke cylinder 12B is ignited and combusted in this way, the engine 1 starts normal rotation with a sufficiently large torque and compresses the stop compression stroke cylinder 12A. To do. Then, over the TDC of this cylinder 12A, that is, the first TDC after the start of forward rotation, each of the cylinders 12A to 12D proceeds to the next stroke.

  Subsequently, in step SC9, after the intake stroke cylinder 12 (# 3 cylinder 12C in FIG. 3) at the time of stoppage is shifted to the compression stroke by the forward rotation operation of the engine 1 started as described above, The fuel is injected at a predetermined timing (for example, after the middle stage of the compression stroke). That is, the air in the intake stroke cylinder 12C at the time of stop is warmed by heat radiation from the cylinder wall surface while the engine 1 is stopped and is in a high temperature state. Where ignition is likely to occur, if the fuel is injected at an appropriate timing, the temperature and pressure in the cylinder 12C can be lowered by the latent heat of vaporization, the compression reaction force can be reduced, and the occurrence of self-ignition can be suppressed. Will also be possible.

  Then, in step SC10, it is determined whether or not the stop-time intake stroke cylinder 12C has exceeded TDC, and if it exceeds TDC and shifts to the expansion stroke (YES), in step SC11, the ignition plug 15 of the stop-time intake stroke cylinder 12C is applied. Energized to ignite the air-fuel mixture in the cylinder 12C. By igniting and burning after TDC in this way, torque in the reverse direction is not generated, which is advantageous in smoothly starting up the engine rotation.

  Then, in step SC12, the routine shifts to normal combustion control, and the stop exhaust stroke cylinder 12D that burns following the stop intake stroke cylinder 12C, the stop expansion stroke cylinder 12B that reaches the second combustion cycle at start, and the stop time. Normal fuel injection and ignition control are executed in the compression stroke cylinders 12A,. After the engine rotational speed reaches the idle rotational speed, the ignition timing of each of the cylinders 12A to 12D may be retarded until the intake negative pressure becomes sufficiently large so as to suppress a sudden increase in the engine. .

  In the flow of FIG. 7, when a predetermined restart condition is satisfied after the engine 1 is automatically stopped, the compression stroke cylinder 12A at the time of stop is ignited and burned to be temporarily reversely operated and compressed thereby. The start-up combustion control unit 2b of the ECU 2 is configured to cause the engine 1 to automatically restart by being ignited and combusted at the stop expansion stroke cylinder 12B.

-VVT control procedure-
Next, the flow of VVT control shown in FIG. 8 will be described. This flow starts when it is determined YES in step SC2 of the above-described combustion control flow (FIG. 7) and reverse combustion start is selected. First, in step SD1, the closing timing IVC of the intake valve 19 is controlled by the operation of the VVT 23 based on the piston stop position of the stop-time expansion stroke cylinder 12B detected by the above-described subroutine (see FIG. 5). As described above with reference to FIG. 6, this control is set in advance by experiments or the like so that the piston stop position is closer to the advance angle side as it is closer to TDC and is closer to the retard side as it is closer to BDC. This is done based on the map.

  Thus, by controlling the closing timing IVC of the intake valve 19 according to the piston stop position of the stop expansion stroke cylinder 12B, a sufficient stroke until the intake valve 19 is opened during the reverse rotation operation of the engine 1 is secured. However, at the end of the reverse rotation operation, immediately before switching to the normal rotation, the intake valve 19 can be opened to discharge the burned gas from the stop-time compression stroke cylinder 12A. In this way, a large starting torque to the forward rotation side can be obtained by sufficiently burning the expansion stroke cylinder 12 at the time of stop and burning it.

  Subsequently, in step SD2, it is determined whether or not the engine rotation has been reversed based on the signals from the crank angle sensors 30 and 31 (see the subroutine of FIG. 5 (a)) until the engine 1 changes from reverse operation to normal operation. Waits and starts normal rotation (determination is YES), the process proceeds to step SD3. Here, after operating the VVT 23 so that the closing timing IVC of the intake valve 19 is changed to the retard side, the operating state is fed back and retarded until the effective compression ratio becomes less than a predetermined value (step SD4), This state is maintained (step SD5).

  Thus, when the closing timing IVC of the intake valve 19 is controlled to be retarded compared to that during reverse rotation after the start of forward rotation, the closing timing of the intake valve 19 opened before the start of forward rotation is delayed in the stop-time compression stroke cylinder 12A. In addition, the burned gas is sufficiently discharged, and during that time, even if the piston 13 rises, the inside of the cylinder is not compressed, so that the effective compression ratio is reduced and the compression reaction force is also reduced. Therefore, the drop in engine rotation can be reduced, and the TDC (TDC first met at start-up) can be reliably overcome.

  If the stop-time compression stroke cylinder 12A exceeds the TDC and shifts to the expansion stroke, the stop-time intake stroke cylinder 12C is now in the compression stroke. However, as described above, the air in the cylinder 12C flows from the cylinder wall surface. Since it is in a high temperature state due to heat dissipation, there is a concern that the engine rotation will drop due to the compression reaction force as it is, and it will be difficult to get over the TDC (second TDC at the start), and self-ignition There is also a fear.

  Therefore, as described in the above-described combustion control flow (FIG. 7), fuel is injected into the stop-time intake stroke cylinder 12C at an appropriate timing of the compression stroke, and the temperature and pressure are reduced by latent heat of vaporization. In step SD6, it is determined whether or not TDC has been exceeded. Until TDC is exceeded (determination is NO), the flow returns to step SD5 to hold the closing timing IVC of the intake valve 19 on the retard side. By doing this, the effective compression ratio also decreases in the intake stroke cylinder 12C at the time of stop, and the engine rotation can be started smoothly by suppressing the drop of the engine rotation due to the compression reaction force, and the occurrence of self-ignition is suppressed. it can.

  When the intake stroke cylinder 12 at the time of stoppage exceeds TDC and shifts to the expansion stroke (YES in step SD6), the routine proceeds to step SD7, where the closing timing IVC of the intake valve 19 is again controlled to the advance side. In this way, the intake charge efficiency of the stop exhaust stroke cylinder 12D that shifts to the compression stroke following the stop intake stroke cylinder 12C increases, and the torque due to the combustion increases, so that the engine speed rises quickly.

  While waiting for the engine speed Ne to reach the idling speed Nidle while prompting the engine speed to rise (NO in step SD8), the process proceeds to step SD9 if the idling speed Nidle is reached (YES), and the intake valve The closing timing IVC of 19 is again controlled to the retard side. That is, when the engine speed Ne reaches the idle speed Nidle, the charging efficiency of the cylinders 12A to 12D that reach the combustion cycle is lowered again, the torque due to the combustion is reduced, and the engine speed suddenly increases. Try to suppress.

  Subsequently, in step SD10, based on the signal from the intake pressure sensor 26, it is determined whether the pressure (intake negative pressure) in the intake passage 21 downstream of the throttle valve 24 is higher than a predetermined pressure. The predetermined pressure is such that if the intake pressure is lower (the negative pressure is larger) than that, the amount of intake charge to each of the cylinders 12A to 12D does not increase so much that the engine 1 does not increase greatly. Specifically, it is obtained by experiments or the like, and is set slightly higher than the intake pressure state during idling after the engine 1 is warmed up.

  Then, the system waits until the intake pressure becomes equal to or lower than the set value (determination is NO). During this period, that is, when air is sucked into each cylinder 12C, 12D,. Until it becomes below, the intake valve closing timing IVC is held on the retard side (step SD9). On the other hand, if the intake negative pressure becomes larger than a predetermined value (YES in SD10), the process proceeds to step SD11, and VVT control is performed. Also shifts to normal control and ends the start control (end).

  The flow of FIG. 8 shows that the closing timing IVC of the intake valve 19 at the start of reverse combustion of the engine 1 is relatively advanced during reverse operation, and relatively retarded after normal rotation. An intake valve control unit 2c of the ECU 2 to be controlled is configured. The intake valve control unit 2c changes the advance angle of the intake valve closing timing IVC during the reverse operation according to the piston stop position in the stop-time expansion stroke cylinder 12B.

  In addition, the intake valve control unit 2c of this embodiment is configured so that the intake valve closing timing IVC is relatively retarded until the stop-time intake stroke cylinder 12C that has shifted to the compression stroke as the engine 1 rotates forward reaches TDC. If it exceeds TDC, it is changed to a relatively advanced angle side, and then held until the engine rotation speed Ne reaches the idle rotation speed Nidle. Change to the corner side.

(Engine system operation)
Therefore, according to the engine system E (engine starter) of this embodiment, first, when the engine 1 automatically stops during idling, the burned gas of each of the cylinders 12A to 12D is scavenged by the stop control described above. In addition, the piston stop position of the cylinder 12B that becomes the expansion stroke after the engine is stopped can be set within a range R suitable for restart slightly closer to the BDC than the center of the stroke.

  When the engine 1 is restarted, the engine 1 is started by itself without using the starter motor 27 by the above-described start control (FIGS. 3, 7, 8, etc.). The time series will be described below with reference to FIG. 9. First, when there is a restart request while the engine 1 is stopped (time t0), the engine 1 is stopped in the compression stroke, as indicated by reference numeral a1 in FIG. When the fuel injection valve 16 of the # 1 cylinder 12A is operated to inject fuel and the mixture formed thereby is ignited by the spark plug 17 (a2) and combusted, as shown in FIG. When the crankshaft 3 starts the reverse rotation operation (time t1), the engine speed Ne temporarily becomes a negative value as shown in FIG.

  When the reverse rotation operation of the engine 1 is detected by signals from the crank angle sensors 30 and 31, the fuel injection valve 16 of the stop expansion stroke cylinder 12B (# 2 cylinder) is operated as shown in FIG. a3), an air-fuel mixture is formed in the cylinder 12B, and the air-fuel mixture is compressed by the upward movement of the piston 13 due to the reverse rotation operation. At this time, the intake valve closing timing IVC is controlled to be relatively advanced as shown in FIG. 5 (g), so that the reverse stroke becomes longer and the piston 13 of the expansion stroke cylinder 12B during the stop rises to the vicinity of TDC. Thus, the air-fuel mixture is sufficiently compressed.

  Then, when the rotation direction of the engine 1 is reversed from the reverse rotation to the normal rotation by the compression pressure, that is, in synchronization with the start of the normal rotation of the engine 1 as shown in FIGS. : Start of forward rotation) Ignition is performed as indicated by a4 in FIG. As a result, a large combustion pressure is generated, and the engine speed Ne increases (see FIG. (F)). Further, the intake valve 19 is opened at the end of the reverse rotation operation of the engine 1 so that the burned gas is discharged from the compression stroke cylinder 12A at the time of stop, and in synchronism with the start of forward rotation of the engine 1, as shown in FIG. On the other hand, the intake valve closing timing IVC is changed to the retard side and held.

  At that time, the intake valve closing timing IVC is retarded prior to the crankshaft 3 of the engine 1 that rotates in the forward direction, so that the intake valve 19 that is opened before the start of the normal rotation in the stop-time compression stroke cylinder 12A is closed. Will be delayed and burnt gas will be discharged sufficiently. Further, since the inside of the cylinder is not compressed until the intake valve 19 is closed, the effective compression ratio is reduced compared to the case where the retard is not retarded (shown by a broken line in the figure), and the increase in the in-cylinder pressure is suppressed. As a result, the engine 1 can surely exceed the first TDC (first TDC) that is first met at the time of starting (time t3), and the drop in engine rotation at that time is reduced (see FIG. (F)). ).

  FIG. 7 (c) shows the stop-time intake stroke cylinder 12C (# 3 cylinder) that has shifted to the compression stroke after the stop-time compression stroke cylinder 12A has exceeded the initial TDC at the start as described above. As shown, fuel is injected after the middle of the compression stroke (a5), and the inside of the cylinder 12C is cooled by the latent heat of vaporization. In addition, the intake valve closing timing IVC is held on the retarded side (see Fig. (G)), and the effective compression ratio is lowered, so the rise in temperature and pressure due to compression is suppressed, preventing the occurrence of self-ignition. In addition, the compression reaction force of the cylinder 12C is reduced, and the engine 1 can reliably exceed the second TDC at the time of start.

  Then, when the stopped intake stroke cylinder 12C that has shifted to the expansion stroke beyond the second TDC is ignited (a7) and combustion is performed, torque in the forward rotation direction is applied to the engine 1, and the diagram (f) ), The engine speed Ne increases. When the stop-time intake stroke cylinder 12C exceeds TDC (time t4), the closing timing IVC of the intake valve 19 is again controlled to the advance side as shown in FIG. Since the charging efficiency is increased, the torque due to the combustion increases, and the engine speed Ne quickly reaches the idle speed Nidle (650 rpm in this example) (time t5).

  When the idle rotational speed Nidle is reached, the closing timing IVC of the intake valve 19 is again controlled to the retard side (see FIG. 5 (g)), and the charging efficiency of each of the cylinders 12A to 12D decreases. An increase in torque due to combustion is suppressed, and a sudden increase in engine rotation is suppressed. Thus, the engine starts up smoothly and converges to the idle rotation speed, so that even when the engine 1 is automatically started, the driver does not feel uncomfortable.

  In the above-described embodiment, when the engine 1 once reversely started when the engine 1 starts reverse combustion, after the TDC (TDC of the intake stroke cylinder 12C at the time of stop) exceeding the second time after the start of the normal rotation is exceeded. The closing timing IVC of the intake valve 19 is controlled to the relatively retarded angle side, and is controlled to the advanced angle side after exceeding the TDC. However, the present invention is not limited to this, and the normal control is shifted to after the forward rotation. The intake valve closing timing IVC may be controlled to the retard side.

  Further, it is not necessary to change the intake valve closing timing IVC during the engine reverse rotation operation according to the piston stop position of the stop-time expansion stroke cylinder 12B, and it is also possible to control the intake valve closing timing IVC to a preset timing.

  Further, it is not necessary to control the intake valve closing timing IVC by the electromagnetically driven VVT 23 as in the above-described embodiment. For example, the individual intake valve 19 is driven by an electromagnetic actuator. The present invention can also be applied to an engine.

  The engine starter according to the present invention can restart the engine smoothly in an extremely short time by an original reverse combustion start method, and is useful in an idling stop system of an automobile.

1 is a schematic configuration diagram of an engine control system according to an embodiment of the present invention. It is a schematic diagram which shows the structure of the intake system of an engine. It is explanatory drawing which shows the mode of the reverse combustion start of an engine. It is a flowchart which shows the outline of the control procedure of an engine automatic stop. (a) is a piston position detection subroutine, and (b) and (c) are explanatory diagrams showing signals output from two crank angle sensors in accordance with normal rotation and reverse rotation of the engine, respectively. It is explanatory drawing which shows reverse rotation operation | movement of the compression stroke cylinder at the time of a stop, and an expansion stroke cylinder. It is a flowchart which shows the procedure of the combustion control at the time of reverse combustion start. It is a flowchart which shows the procedure of the same VVT control. 6 is a time chart showing changes in in-cylinder pressure and engine speed for each cylinder during reverse combustion start together with changes in intake valve closing timing.

Explanation of symbols

E Engine control system (engine starter)
1 Engine 2 ECU (Engine Controller)
2a Piston position detector (piston position detector)
2b Start-up combustion control unit 2c Start-up VVT control unit (intake valve control means)
12A to 12D Cylinder 13 Piston 19 Intake valve 23 VVT (Intake valve control means)
30, 31 Crank angle sensor (piston position detection means)

Claims (5)

After the engine is automatically stopped, when a predetermined restart condition is satisfied, the compression stroke cylinder of the stopped engine is ignited and burned to temporarily reverse the operation, thereby igniting the expansion stroke cylinder to be compressed. In the engine starting device that is normally rotated by being burned and automatically restarted,
An intake valve control means for controlling the closing timing of the intake valve at least in the compression stroke cylinder to a relatively advanced angle side during the reverse rotation operation of the engine and to a relatively retarded angle side after the forward rotation; An engine starting device. A piston position detecting means for detecting a stop position of the piston in the expansion stroke cylinder of the stopped engine;
The intake valve control means increases the advance angle of the intake valve closing timing during the reverse rotation operation of the engine as the detected piston stop position is relatively closer to the top dead center. The engine starting device as described.   The intake valve control means keeps the closing timing of the intake valve relatively retarded until the cylinder that has shifted from the intake stroke to the compression stroke with the forward rotation of the engine reaches the compression top dead center. The engine starting device according to claim 1 or 2, wherein   The intake valve control means changes the closing timing of the intake valve to a relatively advanced side when the cylinder that has shifted from the intake stroke to the compression stroke with the forward rotation of the engine reaches the compression top dead center. The engine starter according to claim 3, wherein the intake valve closing timing is maintained until the rotational speed reaches a predetermined idle rotational speed.   The engine starter according to claim 4, wherein the intake valve control means changes the closing timing of the intake valve to a relatively retarded angle side after the engine rotational speed reaches the idle rotational speed.

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