JP2004301082A - Engine starting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reverse an engine a little in restarting the engine before combustion in a cylinder in an expansion stroke to ensure an effective stroke of an piston, particularly, in reverse rotation, and thereby to reduce compression resistance in a starting period thereafter. <P>SOLUTION: An engine starting system has an intake valve closing timing variable means 13 for varying closing timing of an intake valve, and an ECU 30 for performing a start control. In restarting the engine, the ECU 30 controls to perform combustion of a cylinder in a compression stroke to operate the engine in a reverse rotation direction, before controlling to perform combustion of the cylinder in the expansion stroke and to rotate the engine in a normal direction and then to start the engine. Particularly, the ECU controls to advance intake valve closing timing when the engine is operated in the reverse rotation direction at initial starting, and controls the intake valve closing timing to retard from a top dead center by a predetermined angle in the starting period thereafter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an engine starting device that automatically stops an engine once at the time of idling and then automatically restarts the engine after that.
[0002]
[Prior art]
In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, the engine is automatically stopped once at idle, and then automatically restarted when restart conditions such as starting operation are satisfied. Engine starters have been developed.
[0003]
In this way, when the engine is automatically restarted after the engine is stopped, it is required that the engine be started immediately in response to a start operation or the like. Therefore, the engine is started via cranking in which the engine output shaft is driven by a starting motor. The conventional general starting method which requires a considerable time to complete the starting is not preferable.
[0004]
Therefore, it is desirable that fuel be supplied to a specific cylinder of the stopped engine to cause ignition and combustion, and that the engine be started immediately with the energy. In this case, if the fuel is supplied to the cylinder in the expansion stroke and the combustion is performed while the engine is stopped, the energy of the combustion can be applied in the normal rotation direction of the engine. However, when the engine is operating, combustion is performed after the combustion chamber is in a high compression state, so that a large amount of energy is obtained.However, when the engine is stopped, air leaks from the cylinder in the expansion stroke and the pressure in the combustion chamber increases. Therefore, even if fuel is supplied into the combustion chamber at the low pressure to perform combustion, sufficient energy required for starting is often not obtained.
[0005]
As a countermeasure against such a problem, in a multi-cylinder engine, when the engine is stopped, the first combustion is performed on a cylinder in a compression stroke to push down a piston of the cylinder to a position before a bottom dead center, and the cylinder is in an expansion stroke. After the cylinder piston approaches the top dead center to increase the in-cylinder pressure of the cylinder, fuel is injected into the cylinder in the expansion stroke to ignite and burn, and thus the engine rotates in the normal direction. There has also been proposed a device devised so as to increase the combustion energy acting on the fuel cell (for example, see Patent Document 1).
[0006]
[Patent Document 1]
WO 01/81759 pamphlet [0007]
[Problems to be solved by the invention]
By the way, in the case of the starting device as disclosed in Patent Document 1, when the engine is reversed by pushing down the piston of the cylinder by the combustion in the compression stroke at the initial stage of the start, the piston of the cylinder reaches a position close to the bottom dead center. It is desirable that the compression stroke of the cylinder during the expansion stroke can be increased by securing the effective stroke of the cylinder. However, in general, the closing timing of the intake valve of the engine is set to a somewhat retarded side (compression stroke side) from the bottom dead center. Therefore, when the piston of the cylinder in the compression stroke moves to the bottom dead center due to the operation in the reverse direction of the engine, when the cylinder moves to the advanced side from the closing timing of the intake valve, the intake valve opens and the combustion pressure increases. Will not work effectively. This limits the effective stroke of the piston. There is room for improvement in this regard.
[0008]
Also, during the start-up period in which the engine is driven in the normal rotation direction and the rotation speed is gradually increased after such an engine reverse rotation operation, the compression pressure is relatively high because it is difficult to overcome the compression top dead center if the compression pressure is high. It is preferable to keep it low, and there is still room for improvement in this respect.
[0009]
SUMMARY OF THE INVENTION In view of the above circumstances, the present invention secures an effective stroke when the piston of the cylinder is depressed by combustion in the compression stroke cylinder at the initial stage of engine start, and can sufficiently increase the compression pressure of the cylinder in the expansion stroke. In addition, the present invention provides an engine starting device capable of reducing the compression pressure during the subsequent engine starting period, thereby improving the startability.
[0010]
[Means for Solving the Problems]
According to the present invention, when a restart condition is satisfied after the engine is stopped, the engine is operated in a reverse direction by a predetermined amount by supplying fuel to a cylinder in a compression stroke when the engine is stopped, and performing ignition and combustion. In an engine starter for increasing the in-cylinder pressure of a cylinder that can be in an expansion stroke when the engine is stopped, and then performing combustion in the cylinder that can be in the expansion stroke, the engine is rotated in a forward direction and restarted. An intake valve closing timing variable unit that can change a closing timing of the engine; and a control unit that controls fuel injection, ignition timing control, and control of the intake valve closing timing variable unit when the engine is restarted. During the start-up period from the start of the engine restart to the transition to the normal control, the air drawn into the cylinder is blown back to the intake port side and the effective expansion ratio is reduced. The intake valve closing timing is set to be later than the top dead center by a predetermined amount so as to lower the effective compression ratio, and control is performed so as to advance the intake valve closing timing when the engine is operated in the reverse rotation direction at the beginning of startup. is there.
[0011]
According to the present invention, when the engine is restarted, first, combustion is performed in the cylinder in the compression stroke, so that the engine reverses to a certain extent, whereby the piston of the cylinder, which can be in the expansion stroke, rises and the in-cylinder pressure increases. Thereafter, the combustion is performed in the cylinder, so that the combustion pressure in the cylinder is increased, and the combustion pressure effectively acts on the piston, so that a driving force in the engine normal rotation direction is obtained.
[0012]
In this case, the intake valve closing timing is advanced at the time of engine reverse rotation operation at the beginning of the start, so that the intake valve is prevented from opening when the piston approaches the bottom dead center of the cylinder in the compression stroke, and the piston effective stroke is prevented. Therefore, the in-cylinder pressure of the cylinder which may be in the expansion stroke is sufficiently increased. Then, during the subsequent start period, the intake valve closing timing is delayed, so that the compression resistance in the cylinder which is in the compression stroke during the start period is reduced.
[0013]
By these actions, the startability is enhanced.
[0014]
In the present invention, it is preferable that the control means delays the closing timing of the intake valve when the operation of the engine changes from the operation in the reverse direction to the operation in the normal direction. By doing so, the compression resistance at the time of forward rotation is reduced at an early stage, and the startability is further improved.
[0015]
Further, the engine includes a piston position detecting means for detecting a piston position when the engine is stopped, and the control means includes a cylinder which is in a compression stroke when the piston position of the cylinder in an expansion stroke is within a predetermined appropriate range when the engine is stopped. When the engine is operated in the reverse direction by a predetermined amount by the combustion of the cylinder and then the combustion is performed in the cylinder in the expansion stroke, and the piston position is within a certain range near the top dead center in the appropriate range. Further, it is preferable that the intake valve closing timing at the beginning of the start is advanced.
[0016]
With this configuration, when the piston position in the expansion stroke is within a certain range near the top dead center of the appropriate range, the engine is operated in the reverse direction by the combustion in the cylinder in the compression stroke, and at that time, Although the piston of the cylinder in the compression stroke is pushed down from a position near the bottom dead center, the effective stroke of the piston is secured as much as possible in this case.
[0017]
Further, the fuel supply amount may be controlled such that the air-fuel ratio of the combustion for the reverse rotation at the initial stage of the start of the cylinder in the compression stroke when the engine is stopped is a lean air-fuel ratio larger than the stoichiometric air-fuel ratio.
[0018]
In particular, a piston position detecting means for detecting a piston position when the engine is stopped is provided, and the control means is configured such that when the engine is stopped, the piston position of the cylinder in the expansion stroke is within an intermediate range of three equal strokes, and When the engine is closer to the top dead center than 行 of the stroke, the intake valve closing timing is advanced, and when the engine is stopped, the air-fuel ratio of the combustion in the cylinder in the compression stroke for reversing the initial stage of starting is calculated as the stoichiometric air-fuel ratio. The air-fuel ratio is set to be larger than the above, and fuel is supplied to the cylinder after the initial combustion, and the combustion is performed again when the cylinder moves to the expansion stroke beyond the compression top dead center. Is preferred.
[0019]
In this way, when the piston position of the cylinder in the expansion stroke is near the top dead center within the middle range of the stroke, that is, when the piston position of the cylinder in the compression stroke is near the bottom dead center, the cylinder in the compression stroke Due to the relatively large amount of air in the piston, the piston can be moved to near the bottom dead center even when burning with a lean air-fuel ratio, and the piston effective stroke is advanced by advancing the intake valve closing timing. Is secured. Then, by setting the air-fuel ratio of the combustion at the initial stage of combustion in the cylinder in the compression stroke to be lean, surplus air is left, and when the cylinder shifts to the expansion stroke, combustion can be performed again. Startability is further enhanced.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
1 and 2 show a schematic configuration of an engine according to an embodiment of the present invention. In these figures, the engine main body is constituted by a cylinder head 1 and a cylinder block 2, has a plurality of cylinders, and has four cylinders 3A to 3D in the illustrated embodiment. A piston 4 is fitted into each of the cylinders 3A to 3D, and a combustion chamber 5 is formed above the piston 4. The piston 4 is connected to a crankshaft 6 via a connecting rod.
[0022]
A spark plug 7 is provided at the top of the combustion chamber 5 of each of the cylinders 3A to 3D, and the tip of the plug faces the combustion chamber 5.
[0023]
Further, a fuel injection valve 8 for directly injecting fuel into the combustion chamber 5 is provided on a side portion of the combustion chamber 5. The fuel injection valve 8 has a built-in needle valve and a solenoid (not shown). When a pulse signal is input, the fuel injection valve 8 is driven and opened for a time corresponding to the pulse width at the pulse input time. Is configured to inject an amount of fuel according to the following. The injection direction of the fuel injection valve 8 is set so as to inject fuel toward the vicinity of the ignition plug 7. Fuel is supplied to the fuel injection valve 8 via a fuel supply passage or the like by a fuel pump (not shown), and a fuel supply system is provided so as to provide a fuel pressure higher than the pressure in the combustion chamber during the compression stroke. Is configured.
[0024]
Further, an intake port 9 and an exhaust port 10 are opened to the combustion chamber 5 of each of the cylinders 3A to 3D, and an intake valve 11 and an exhaust valve 12 are provided in these ports 9, 10. The intake valve 11 and the exhaust valve 12 are driven by a valve operating mechanism. The opening / closing timing of the intake / exhaust valves 11 and 12 of each cylinder is set so that each cylinder performs a combustion cycle with a predetermined phase difference as described in detail later.
[0025]
Further, the intake valve 11 is provided with intake valve closing timing varying means 13 which can change the closing timing. The intake valve closing timing varying means 13 can switch the valve lift characteristic of the intake valve between three types, a normal characteristic V1, a late closing characteristic V2, and an early closing characteristic V3, as shown in FIG. 3, for example. The normal characteristic V1 is set so that the intake valve closing timing is slightly later than the bottom dead center and is a timing suitable for increasing the charging efficiency during the normal operation. The late closing characteristic V2 is obtained by delaying the closing timing as compared with the normal characteristic V1, and the air sucked into the cylinder is blown back to the intake port side so that the effective compression ratio becomes lower than the effective expansion ratio. The valve closing timing is set a predetermined amount later than the top dead center. Further, the early closing characteristic V3 is one in which the closing timing is earlier than that of the normal characteristic V1, and is set so that the intake valve 11 closes at approximately the bottom dead center.
[0026]
Although the specific structure of the intake valve closing timing varying means 13 is not limited in the present invention, for example, a first valve operating cam providing a normal characteristic V1, a second valve operating cam providing a late closing characteristic V2, an early closing characteristic A third valve cam that provides V3 is provided on the camshaft, and the intake valve 11 is selectively opened and closed by any one of the valve cams between the valve cam and the intake valve 11. As described above, a switching mechanism that is operated by hydraulic pressure or the like to switch the connection between the valve operating cam and the intake valve may be provided. Alternatively, the intake valve may be operated by an electromagnetic valve mechanism including a pair of electromagnets for opening and closing the valve, and the opening / closing timing of the intake valve may be changed by controlling energization of these electromagnets. You may do so.
[0027]
Returning to FIG. 1, an intake passage 15 and an exhaust passage 16 are connected to the intake port 9 and the exhaust port 10, respectively. The intake passage 15 is provided with a throttle valve for adjusting the amount of intake air. In this embodiment, a throttle valve 17 is provided in the branch intake passage 15a close to the intake port 9 in order to increase the responsiveness of the control of the amount of intake air. Is provided. That is, the intake passage 15 has a branch intake passage 15a for each cylinder downstream of the surge tank 15b, and the downstream end of each branch intake passage 15a communicates with the intake port 9 of each cylinder. A throttle valve 17 composed of a multiple rotary valve for adjusting the throttle of each branch intake passage 15a at the same time is disposed near the downstream end. The throttle valve 17 is driven by an actuator 18.
[0028]
An air flow sensor 20 for detecting the amount of intake air is provided in the common intake passage 15c upstream of the surge tank 15b in the intake passage 15. The crankshaft 6 is provided with a crank angle sensor for detecting a rotation angle thereof. In the present embodiment, as described later in detail, the crankshaft 6 outputs crank angle signals that are out of phase by a certain amount. Two crank angle sensors 21 and 22 are provided. Further, there is provided a cylinder identification sensor 23 which can provide a cylinder identification signal by detecting a specific crank angle of the engine. In addition, a water temperature sensor 24 for detecting a temperature of engine cooling water, an accelerator opening sensor 25 for detecting an accelerator opening (accelerator operation amount), and the like are provided as detection elements necessary for controlling the engine. .
[0029]
Numeral 30 denotes an ECU (engine control unit) as a control means, which receives signals from the sensors 20 to 25, outputs a signal for controlling the fuel injection amount and the injection timing to the fuel injection valve 8, and It outputs an ignition timing control signal to the device and a control signal to the valve drive changing means 13. Further, a signal for controlling the throttle opening is output to the actuator 18 of the throttle valve 17. Further, a signal for controlling the driving of the starter (starting motor) 31 is output when necessary.
[0030]
Then, when a predetermined engine stop condition is satisfied during idling, the engine is automatically stopped by stopping fuel supply or the like, and the engine is automatically restarted when a subsequent engine restart condition is satisfied. When the stop position of the piston is within a specific range when the engine is restarted, first, when the engine is stopped, fuel is supplied to a cylinder in a compression stroke to cause ignition and combustion to operate the engine in a predetermined amount in the reverse direction. After that, the combustion is performed in the cylinder in the expansion stroke, whereby the engine is rotated in the normal direction and started. In addition, as control of the intake valve closing timing varying means 13, the intake valve 11 is set to the early closing characteristic V3 (see FIG. 3) at the time of engine reverse rotation operation at the beginning of the start, and the intake valve 11 is late closed characteristic V2 during the subsequent starting period. (See FIG. 3).
[0031]
In the present embodiment, as described above, the first combustion for the reverse rotation of the engine in the compression stroke when the engine is stopped and the combustion for the normal rotation of the cylinder in the expansion stroke when the engine is stopped are performed. Then, a first restart control mode in which the cylinder which was in the compression stroke when the engine was stopped and shifted to the expansion stroke performs re-combustion in the cylinder, and a second restart control in which the re-combustion is not performed And a third restart control mode in which the engine is started by combustion in an expansion stroke cylinder while assisting with a starter (starting motor) 31 without performing initial combustion in a cylinder in a compression stroke when the engine is stopped. The operation is selectively executed according to the stop position of the piston.
[0032]
Control of engine stop and restart by the ECU 30 will be described with reference to FIGS. In the following description, a cylinder in an intake stroke is referred to as an intake cylinder, a cylinder in a compression stroke is referred to as a compression cylinder, a cylinder in an expansion stroke is referred to as an expansion cylinder, and a cylinder in an exhaust stroke is referred to as an exhaust cylinder.
[0033]
The process shown in the flowchart of FIG. 4 starts from a state in which the engine is running, and the ECU 30 first determines whether or not an idle stop condition is satisfied in step S1. This determination is made based on the vehicle speed, the engine temperature (temperature of the engine cooling water), and the like. For example, the stopped state where the vehicle speed is 0 continues for a predetermined time or more, the engine temperature is within a predetermined range, and the engine is stopped. For example, when there is no particular inconvenience in performing the idle stop condition, the idle stop condition is satisfied.
[0034]
When the idle stop condition is satisfied, the fuel supply to each cylinder of the engine is stopped (step S2), then the throttle valve 17 is once opened to a predetermined opening (step S3), and then the engine speed is reduced to a predetermined speed or less. This state is maintained (step S4) until the rotation speed becomes equal to or lower than the predetermined rotation speed, and the throttle valve 17 is closed (step S5).
[0035]
Subsequently, it is determined in step S6 whether or not the engine has stopped. When the engine has stopped, the stop position is determined in step S7 based on the detection of the stop position of the piston by the stop position detection routine of FIG. It is determined whether it is within the range. In this case, in the expansion cylinder when the engine is stopped, the range of the piston stop position indicated by hatching in FIG. 5 is the range A, that is, the range corresponding to the middle stage of the expansion stroke (the middle range among the three equal parts). It is a predetermined range. If it is within the predetermined range A, it is determined in a step S8 whether or not the piston stop position is on the TDC (top dead center) side of the predetermined position (1/2 of the stroke) in the expansion cylinder when the engine is stopped. judge.
[0036]
Based on the determinations in steps S7 and S8, when it is confirmed that the stop position of the piston 4 is within the predetermined range A and is on the TDC side (within the range A1), the stop position shown in FIG. (1) When the routine (R1) of the restart control mode is executed and it is confirmed that the stop position of the piston 4 is within the predetermined range A and within the range A2 on the BDC side (bottom dead center side). Executes the second restart control mode routine (R2). When it is confirmed that the stop position of the piston 4 is outside the predetermined range A, the routine (R3) of the third restart control mode is executed.
[0037]
FIG. 6 shows a stop position detection routine. When this routine starts, the ECU 30 checks the first crank angle signal CA1 (the signal from the first crank angle sensor) and the second crank angle signal CA2 (the signal from the second crank angle sensor), and checks the first crank angle signal CA2. It is determined whether or not the second crank angle signal CA2 is Low when CA1 rises, or whether the second crank angle signal CA2 is High when the first crank angle signal CA1 falls. In short, it is determined whether the relationship between the phases of these signals CA1 and CA2 is as shown in FIG. 7A or FIG. 7B to determine whether the engine is rotating forward or backward. Is determined (step S11).
[0038]
That is, at the time of normal rotation of the engine, as shown in FIG. 7A, the second crank angle signal CA2 is generated with a phase delay of about a half pulse width with respect to the first crank angle signal CA1, so that the first crank angle signal CA1 is generated. At the rise of CA1, the second crank angle signal CA2 becomes Low, and at the fall of the first crank angle signal CA1, the second crank angle signal CA2 becomes High. On the other hand, at the time of reverse rotation of the engine, as shown in FIG. 7 (b), the second crank angle signal CA2 is generated with a phase advance of about half a pulse width with respect to the first crank angle signal CA1, so that when the engine rotates forward. Conversely, when the first crank angle signal CA1 rises, the second crank angle signal CA2 becomes High, and when the first crank angle signal CA1 falls, the second crank angle signal CA2 becomes Low. Therefore, if the determination in step S11 is YES, the CA counter for measuring the change in the crank angle in the normal rotation direction of the engine is increased (step S12), and if the determination in step S11 is NO, the CA counter is decreased. (Step S13). Then, when the engine is stopped, the stop position is obtained by checking the value of the CA counter (step S14).
[0039]
FIG. 8 shows a routine of the first restart control mode executed when the determination in step S7 in the flowchart of FIG. 4 is YES. FIG. 9 shows the cycle and combustion operation of each cylinder when controlled by the first restart control mode. FIG. 9 shows the case of a four-cylinder four-cycle engine. 1 to NO. If it is called a four-cylinder, the cycle consisting of the intake, compression, expansion, and exhaust strokes is NO. One cylinder, NO. 3 cylinders, NO. 4 cylinder, NO. Since the two cylinders are sequentially executed with a phase difference of 180 ° in crank angle in the order of two cylinders, for example, as shown in FIG. If one cylinder is in the compression stroke, NO. The two cylinders are in the expansion stroke, NO. For the three cylinders, the intake stroke, NO. The four cylinders are in the exhaust stroke. The routine of FIG. 8 will be described with reference to FIG.
[0040]
In this routine, the ECU 30 first determines in step S21 whether a predetermined engine restart condition is satisfied, and waits if the engine restart condition is not satisfied.
[0041]
When an engine restart condition such as an accelerator operation for starting from a stopped state is performed or a battery voltage is reduced (when the determination in step S21 is YES), in step S22, the piston is turned off. Based on the stop position, the respective air amounts of the compression cylinder (NO. 1 cylinder in FIG. 9) and the expansion cylinder (NO. 2 cylinder in FIG. 9) are calculated. In other words, the combustion chamber volume of each cylinder is obtained from the stop position, and when the engine is stopped, the engine stops after a few revolutions after the fuel cut, so that each of the cylinders is filled with fresh air, In addition, since the in-cylinder pressure of each cylinder becomes substantially the atmospheric pressure while the engine is stopped, the amount of air can be obtained from the volume of the combustion chamber.
[0042]
Subsequently, in step S23, a fuel injection amount is determined so as to have a predetermined air-fuel ratio with respect to the calculated air amount of the compression cylinder, and fuel injection (F11 in FIG. 9) is performed on the cylinder with the calculated injection amount. In this case, the predetermined air-fuel ratio is set to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio so that surplus air remains after the first combustion in the cylinder. In step S24, a fuel injection amount is determined so that a predetermined air-fuel ratio (the stoichiometric air-fuel ratio or its vicinity) is obtained with respect to the calculated air amount of the expansion cylinder. F12) is performed.
[0043]
In step S25, the intake valve closing timing varying means 13 is controlled so that the intake valve 11 of the compression cylinder is closed early (early closing characteristic V3 in FIG. 3).
[0044]
Further, in step S26, after the time set in consideration of the fuel vaporization time has elapsed after the fuel injection of the compression cylinder, ignition is performed on the cylinder (I11 in FIG. 9). Thus, combustion is performed in the compression cylinder, and the piston of the cylinder is depressed by the combustion pressure to reverse the engine.
[0045]
Next, in step S27, it is determined whether or not the piston has moved based on whether or not an edge of the crank angle sensor (rising or falling of the crank angle signal) is detected within a predetermined time after ignition. If does not move, re-ignition is repeatedly performed on the compression stroke cylinder (step S28).
[0046]
When the edge of the crank angle sensor is detected, in step S29, ignition is performed for the expansion stroke after a predetermined delay time has elapsed after the edge detection. The delay time is obtained from a map (not shown) according to the stop position of the piston.
[0047]
In this way, in the first stroke until one of the cylinders reaches the top dead center after the start of the restart of the engine, ignition and combustion are performed in the compression cylinder, the engine reverses to a certain extent, and then ignition and combustion are performed in the expansion cylinder. Is performed and the engine rotates forward.
[0048]
Further, in step S30, the intake valve closing timing varying means 13 is controlled so that the intake valve 11 of the cylinder which is in the intake stroke during the engine start period is closed slowly (slow closing characteristic V2 in FIG. 3).
[0049]
Next, in step S31, when the predetermined crank angle is reached, fuel is injected again into the compression cylinder. In this case, the amount of air remaining in the compression cylinder is calculated, and the air-fuel ratio (the stoichiometric air-fuel ratio or slightly more than the stoichiometric air-fuel ratio) for the second fuel injection of the compression cylinder is set, and the fuel injection amount is calculated based on these. The fuel injection (F21) is performed on the compression cylinder with the injection amount. Then, in step S32, ignition (I21 in FIG. 9) is performed when the stop-time compression cylinder exceeds the top dead center. That is, in the second stroke in which the compression cylinder at the time of engine stop is the expansion stroke, recombustion is performed in this cylinder.
[0050]
Further, in step S33, fuel injection and ignition are sequentially performed on each cylinder while the intake valve is slowly closed until the start is completed. For example, the intake cylinder when the engine is stopped undergoes a compression stroke in the second stroke, but the fuel injection and ignition for this cylinder are controlled such that combustion is performed in this cylinder in the third stroke in which this cylinder shifts to the expansion stroke. Is done.
[0051]
When the start is completed, the process shifts to the normal control (step S34). As the normal control, the fuel injection amount, the injection timing and the ignition timing are controlled according to the operating state, and the intake valve closing timing is also controlled according to the operating state. It is closed slowly and has the normal characteristic V1 in FIG.
[0052]
The details of the routine of the second restart control mode (without reburning) executed when the determination in step S8 in the flowchart of FIG. 3 is NO are omitted, but the first restart control mode is omitted. In this routine, substantially the same processing as steps S21 to S24, S26 to S30, S33, and S34 is performed. However, in the process corresponding to step S23, the air-fuel ratio of the compression stroke cylinder obtained from the map according to the stop position of the piston becomes substantially the stoichiometric air-fuel ratio or richer than that.
[0053]
FIG. 10 shows a routine of the third restart control mode (motor assist) executed when the determination in step S7 in the flowchart of FIG. 4 is NO. In this routine, the ECU first determines in step S41 whether a predetermined engine restart condition is satisfied, and waits if the engine restart condition is not satisfied.
[0054]
When the engine restart condition is satisfied (when the determination in step S41 is YES), the drive of the starter 31 is started in step S42, and the air amounts of the compression cylinder and the expansion cylinder are calculated based on the piston stop positions in step S43. Then, in step S44, the fuel is injected so that the air-fuel ratio of each of the compression cylinder and the expansion cylinder is close to the stoichiometric air-fuel ratio. Then, in step S45, the ignition is performed on the cylinder after the time set in consideration of the fuel vaporization time has elapsed after the fuel injection of the expansion cylinder.
[0055]
Next, in step S46, ignition is performed on the compression cylinder when the predetermined crank angle is reached. Then, the drive of the starter 31 is stopped (step S47), and the process shifts to normal control (step S48).
[0056]
According to the above-described device of the present embodiment, the engine is automatically stopped when the engine is in a predetermined idle state that does not require the output of the engine and the engine stop condition is satisfied. When the engine stops, in the compression cylinder, as the piston approaches the top dead center, the air in the cylinder is compressed and pressure acts in a direction to push back the piston, whereby the engine reverses and the piston of the compression cylinder moves downward. When the piston is pushed back to the dead center side, the piston of the expansion cylinder moves to the top dead center side, whereby the air in the cylinder is compressed, and the pressure causes the piston of the expansion cylinder to be pushed back to the bottom dead center side. In this way, the piston is stopped after vibrating to some extent, and at this time, in the compression cylinder and the expansion cylinder, since the force of pushing back the piston closer to the top dead center is larger, the piston is stopped near the middle of the stroke. It is often a position.
[0057]
As described above, when the engine restart condition is satisfied after the engine is automatically stopped, the restart is performed. In this case, the piston position of the expansion cylinder at the time of the engine stop is set to a predetermined range A (near the middle of the stroke). 5), the engine is slightly reversed by ignition and combustion in the compression cylinder by executing the routine of the first restart control mode (FIG. 8) or the routine of the second restart control mode. Thereafter, the engine is driven in the normal rotation direction by ignition and combustion in the expansion cylinder.
[0058]
That is, according to the example shown in FIG. When ignition and combustion are performed after fuel injection into one cylinder, the piston of this cylinder is pushed down, and the engine reversely rotates, whereby the NO. In the two-cylinder, the piston approaches the top dead center, the air in the cylinder is compressed and the in-cylinder pressure increases, and ignition is performed in this state, and the fuel already injected into the cylinder burns. A relatively large combustion pressure acts on the piston of the expansion cylinder, and the driving force in the forward rotation direction of the engine is increased.
[0059]
By the way, if the intake valve 11 of the compression cylinder (NO. 1 cylinder) at the time of the engine stop is at the opening / closing timing of the normal characteristic (broken line in FIG. 9) at the time of the reverse rotation, the piston of the compression cylinder becomes the bottom dead center. When the intake valve 11 approaches the crank angle corresponding to the intake valve closing timing, the intake valve 11 is opened, the gas in the compression cylinder is discharged to the intake port side, and the combustion pressure acts on the piston. No longer. Therefore, the effective stroke of the piston of the compression cylinder is limited to a crank angle position corresponding to the closing timing of the intake valve 11, and therefore the compression of the expansion cylinder becomes insufficient.
[0060]
On the other hand, in the present embodiment, the closing timing of the intake valve 11 is advanced to near the bottom dead center in the early stage of the start and is closed early, so that the piston of the compression cylinder approaches the bottom dead center during the reverse rotation. Since the intake valve 11 does not open, the effective stroke of the piston of the compression cylinder is ensured, and the compression of the expansion cylinder is sufficiently performed. Then, the combustion is performed in the sufficiently compressed expansion cylinder to increase the combustion pressure, so that the driving force in the forward rotation direction of the engine is further increased.
[0061]
In addition, during the start period after the engine shifts from the reverse rotation to the forward rotation, the intake valve 11 is closed later than the normal characteristic, so that the engine passes through the compression top dead center of one of the cylinders during the start. Compression resistance is reduced.
[0062]
These operations will be described with reference to FIG. The figure shows the engine speed, the crank angle of the expansion cylinder (the cylinder that was in the expansion stroke when the engine was stopped), the cylinder pressure of the cylinder, the cylinder pressure of the compression cylinder (the cylinder that was in the compression stroke when the engine was stopped), and the intake air. A change in the in-cylinder pressure of a cylinder (a cylinder that was in an intake stroke when the engine was stopped) according to the passage of time from the start of the start is shown.
[0063]
As shown in the figure, in the initial stage of the start, first, the in-cylinder pressure of the compression cylinder slightly increases due to combustion in the compression cylinder (part a), and the engine reverses, thereby compressing the inside of the expansion cylinder and increasing the pressure. (Part b). Subsequently, the in-cylinder pressure of the same cylinder rises due to combustion (part c), whereby the engine rotates forward. At this time, the expansion cylinder is sufficiently compressed by the early closing of the intake valve of the compression cylinder as described above. The in-cylinder pressure of the cylinder is increased, and the driving force in the normal rotation direction is increased.
[0064]
Next, when the compression cylinder shifts to the expansion stroke, the in-cylinder pressure increases by compression until the top dead center of the cylinder (d part), and after the top dead center, the in-cylinder pressure increases by combustion (e part). ).
[0065]
Next, when the intake cylinder shifts to the expansion stroke through the compression stroke, the in-cylinder pressure increases by compression until the top dead center of the cylinder (part f). In this case, an increase in the in-cylinder pressure due to the compression becomes a resistance to the engine rotation, and if the resistance is larger than the driving force, there is a possibility that the engine cannot be stopped without exceeding the top dead center of the cylinder. In this case, since the intake valve is closed late during the start period as described above, the increase in the in-cylinder pressure due to compression is smaller than in the case where the intake valve is not closed (broken line in the f section), thereby reducing the engine rotation. Therefore, it becomes easier to exceed the top dead center of this cylinder. If the cylinder exceeds the top dead center, the in-cylinder pressure greatly increases due to combustion (g portion), thereby increasing the driving force, and thus starting is achieved.
[0066]
If the piston position of the expansion cylinder when the engine is stopped is within the range A1 closer to the top dead center from the intermediate portion in the predetermined range A, the piston of the compression cylinder is closer to the bottom dead center. Since the torque required to move to the vicinity of the dead center decreases and the amount of air in the compression cylinder increases, the fuel injection amount is controlled so that the air-fuel ratio of the cylinder becomes lean. As a result, surplus air is left in the cylinder even after the initial combustion for the reverse rotation, so that fuel corresponding to the surplus air is injected, and when the cylinder shifts to the expansion stroke, re-combustion is performed, and startability is improved. Is enhanced.
[0067]
On the other hand, if the piston position of the expansion cylinder when the engine is stopped is in the range A2 closer to the bottom dead center than the intermediate portion in the predetermined range A, the piston of the compression cylinder is closer to the top dead center. Since relatively large torque is required to move to the vicinity of the dead center and the amount of air in the compression cylinder is relatively small, the fuel is set so that the air-fuel ratio of the cylinder is set to the stoichiometric air-fuel ratio or richer than this. The injection amount is controlled, and in this case, the above-described reburning is not performed.
[0068]
When the piston position of the expansion cylinder when the engine is stopped is in the range A2 close to the bottom dead center, the piston of the compression cylinder moves from the position close to the top dead center to the bottom dead center side, and the normal operation is performed. Since the movement stroke is secured even up to the position corresponding to the intake valve closing timing, it is not always necessary to advance the intake valve closing timing.
[0069]
Further, since the piston position when the engine is stopped often falls within the range A as described above, in most cases when the engine is restarted, it is better to control the first restart control mode or the second restart control mode. However, in rare cases, the piston position when the engine is stopped may deviate from the range A, and the piston position may be closer to the top dead center of the expansion cylinder (the lower dead center side of the exhaust cylinder) than the range A. If it is too close, it is not possible to take a sufficient amount of movement in the engine reverse direction, and the amount of air in the expansion cylinder is reduced, so that the torque obtained by combustion in the expansion cylinder is reduced. If it is too close to the bottom dead center side of the expansion cylinder (top dead center side of the exhaust cylinder), the amount of air in the exhaust cylinder will be small, so that sufficient torque for engine reversal will not be obtained. Restart according to the first restart control mode is difficult in these cases.
[0070]
Therefore, if the piston position when the engine is stopped deviates from the range A, the third restart control mode is executed and the starter assists the start.
[0071]
Note that the specific configuration of the device of the present invention is not limited to the above embodiment, but can be variously modified.
[0072]
For example, in the control shown in FIG. 8 and FIG. 9, when the engine shifts from the reverse operation to the forward operation in the initial stage of the start, the intake valve of the compression cylinder is changed to the late closing indicated by the dashed line in FIG. You may do so. With this configuration, the intake valve of the compression, which has been closed early to secure the piston effective stroke when the engine is operating in the reverse direction, is changed to be slowly closed when shifting to the operation in the normal direction. The compression resistance is reduced at an early stage, and the startability is further improved.
[0073]
Further, in the above-described embodiment, the combustion for driving the engine in the forward direction in the first stroke at the time of starting is performed in the expansion cylinder, but the movement of the piston is the same as that of the expansion cylinder in the intake cylinder. When the intake valve of the intake cylinder is closed, the cylinder becomes an expansion cylinder (it can be an expansion stroke), so that ignition and combustion can be performed in the intake cylinder that has been made into an expansion cylinder to apply a driving force in the engine normal rotation direction. .
[0074]
【The invention's effect】
As described above, according to the engine starter of the present invention, at the start of startup in which the operation in the engine reverse direction is performed by combustion in the cylinder in the compression stroke at startup, the intake valve closing timing is advanced, When the piston approaches the bottom dead center of the cylinder in the compression stroke, the intake valve is prevented from being opened, and the effective stroke of the piston is ensured. Therefore, the in-cylinder pressure of the cylinder, which can be the expansion stroke, is sufficiently increased, and the engine The driving force in the rolling direction is increased. Also, during the subsequent engine start period, the intake valve closing timing is set a predetermined amount later than the top dead center so that the air sucked into the cylinder is blown back to the intake port side and the effective compression ratio becomes lower than the effective expansion ratio. As a result, the compression resistance in the cylinder that is in the compression stroke during the starting period is reduced. These synergistic effects can greatly enhance the startability.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an engine provided with a starting device according to an embodiment of the present invention.
FIG. 2 is a schematic plan view of the engine.
FIG. 3 is an explanatory diagram showing valve lift characteristics of an intake valve.
FIG. 4 is a flowchart of control for stopping and restarting the engine by the control means.
FIG. 5 is an explanatory diagram showing setting of a range for selecting a restart control mode according to a piston position when the engine is stopped.
FIG. 6 is a flowchart showing a process for detecting a piston position when the engine is stopped.
7A and 7B show crank angle signals from two crank angle sensors, wherein FIG. 7A shows a signal at the time of forward rotation of the engine, and FIG. 7B shows a signal at the time of reverse rotation of the engine.
FIG. 8 is a flowchart showing a first restart control mode.
FIG. 9 is an explanatory diagram showing a cycle of each cylinder, fuel supply, ignition timing, and the like when the engine is restarted.
FIG. 10 is a flowchart illustrating a process of determining start assist execution.
FIG. 11 is a diagram showing changes in the engine speed, the crank angle of an expansion cylinder, the in-cylinder pressure of the same cylinder, the in-cylinder pressure of a compression cylinder, and the in-cylinder pressure of an intake cylinder as time elapses after the start of the engine restart. .
[Explanation of symbols]
3A to 3D Cylinder 4 Piston 5 Combustion chamber 7 Spark plug 8 Fuel injection valve 13 Intake valve closing timing variable means 30 ECU
31 Starter

Claims (5)

When the restart condition is satisfied after the engine is stopped, fuel is supplied to the cylinder in the compression stroke when the engine is stopped, and ignition and combustion are performed to operate the engine in a predetermined amount in the reverse direction, and the engine is expanded when the engine is stopped. An engine starting device that increases the in-cylinder pressure of a cylinder that can be a stroke and then performs combustion in the cylinder that can be an expansion stroke to rotate the engine in a forward direction and restart the engine.
Intake valve closing timing variable means for changing the closing timing of the intake valve;
Control means for controlling fuel injection at the time of engine restart, control of ignition timing, and control of the intake valve closing timing variable means,
The above-mentioned control means is arranged such that, during a start period from the start of the engine restart to the transition to the normal control, the air sucked into the cylinder is blown back to the intake port side so that the effective compression ratio becomes lower than the effective expansion ratio. An engine start device for setting the intake valve closing timing later than a top dead center by a predetermined amount, and controlling the intake valve closing timing to be advanced when the engine is operated in the reverse direction at the beginning of starting. 2. The engine starting device according to claim 1, wherein the control means retards the intake valve closing timing when the engine changes from a reverse operation to a forward operation. A piston position detecting means for detecting a piston position when the engine is stopped; wherein the control means controls the combustion in the cylinder in the compression stroke when the piston position of the cylinder in the expansion stroke is within a predetermined appropriate range when the engine is stopped. By operating the engine in the reverse direction by a predetermined amount to cause combustion in the cylinder in the expansion stroke, and when the piston position is within a certain range near the top dead center of the appropriate range, 3. The engine starting device according to claim 1, wherein an intake valve closing timing at an early stage of starting is advanced. The control means controls the fuel supply amount such that the air-fuel ratio of the combustion for the reverse rotation at the initial stage of the start of the cylinder in the compression stroke when the engine is stopped is a lean air-fuel ratio larger than the stoichiometric air-fuel ratio. The engine starting device according to claim 1. A piston position detecting means for detecting a piston position when the engine is stopped, wherein the control means is configured such that when the engine is stopped, the piston position of the cylinder in the expansion stroke is within an intermediate range of three equal strokes; When the engine is closer to the top dead center than 1/2, the intake valve closing timing is advanced, and the air-fuel ratio of combustion for the reverse rotation of the cylinder in the compression stroke when the engine is stopped is smaller than the stoichiometric air-fuel ratio. A large lean air-fuel ratio is set so that fuel is supplied to the cylinder after the initial combustion, and combustion is performed again when the cylinder moves to an expansion stroke beyond the compression top dead center. The engine starting device according to claim 1, wherein

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