Engine start control device

Abstract

To provide a starting device of an engine capable of reducing torque of the starting device that is consumed to start the engine at the time of starting the engine.SOLUTION: A starting control device of an engine comprises stop position detection means of detecting a position of a piston 5 of each cylinder 2 when an engine is stopped, intake pressure detection means of detecting an intake pressure, which is a pressure in an intake passage 30, and a determination unit 203 that determines whether or not the position of the piston 5 of each cylinder 2 detected by the stop position detection means after the engine is stopped is within a predetermined target range X0. When it is determined that the position of the piston 5 of each cylinder 2 after the engine is stopped is not within the target range X0, and the intake pressure detected by the intake pressure detection means is lower than an atmospheric pressure, the engine is started by starting means M even when an engine starting condition is not satisfied.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a start control device provided in an engine having a starting means capable of forcibly starting the engine by rotating a crankshaft. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in vehicles equipped with an engine, the engine has been automatically stopped and then started using a starting device in order to improve fuel efficiency.

[0003] Here, it is desirable that the torque of the starting device used for starting the engine is small. For example, if the torque of the starting device is used for devices other than the engine, if the torque of the starting device used for starting the engine becomes large, it may affect the operation of the other devices, so it is desirable to reduce the torque.

[0004] In response to this, it has been studied to set the position of each cylinder (the position of the piston of each cylinder) when the engine is stopped to a position suitable for starting, that is, a position where the torque of the starting device consumed for starting the engine can be reduced. For example, in the engine of Patent Document 1, the following control is performed immediately before the engine is stopped. That is, after the intake of the stop-time expansion stroke cylinder (the final expansion cylinder in Patent Document 1), which is a cylinder that stops during the expansion stroke, is completed, the throttle valve opening is increased to control the intake amount of the stop-time compression stroke cylinder (the final compression cylinder in Patent Document 1), which is a cylinder that stops during the compression stroke. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-60827 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the engine of Patent Document 1, the increase in the intake amount of the compression stroke cylinder at the time of stopping suppresses the rise of the piston of the cylinder. Therefore, it is considered that the possibility that the stop position of the compression stroke cylinder at the time of stopping deviates from the desired position toward the top dead center side is low. However, due to the response delay of the throttle valve, the intake amount of the compression stroke cylinder at the time of stopping may not be increased sufficiently, and the possibility that the stop position of the compression stroke cylinder at the time of stopping deviates from the desired position is not zero. And, if the stop position of the compression stroke cylinder at the time of stopping, that is, the stop position of each cylinder of the engine, is not the desired position, the torque consumed by the starting device to start the engine becomes large as described above.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide an engine starting device that can reduce the torque of the starting device consumed to start the engine when starting the engine. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a start control device provided in an engine including a plurality of cylinders, a fuel supply means for supplying fuel to each cylinder, a piston provided in each cylinder so as to be able to reciprocate, a crankshaft that rotates in conjunction with the reciprocating movement of the piston, a starting means capable of forcibly starting the engine by rotating the crankshaft, and an intake passage through which intake air introduced into each cylinder flows, the start control device comprising: a stop position detection means for detecting a position of the piston of each cylinder when the engine is stopped; an intake pressure detection means for detecting an intake pressure which is a pressure in the intake passage; and a control means for controlling each part of the engine such as the fuel supply means and the starting means, the control means comprising: a stop control unit for stopping the supply of fuel to the cylinders by the fuel supply means to stop the engine when a predetermined engine stop condition is satisfied; a start control unit for starting the engine by the starting means when a predetermined engine start condition is satisfied after the engine is stopped; and a determination unit for determining whether or not the position of the piston of each cylinder detected by the stop position detection means is within a predetermined target range after the engine is stopped. ,beforeThe determination unit determines that the position of the piston of each cylinder is not within the target range. In this case, the start control unit The intake pressure detected by the intake pressure detection means is the atmospheric pressure. When the pressure is lower than the predetermined pressure and equal to or higher than the predetermined judgment pressure, The engine is started by the starting means even when the engine start condition is not satisfied. when the intake pressure is less than the judgment pressure, the engine is started by the starting means in response to the establishment of the engine start condition, and the judgment pressure is set to a smaller value as the deviation amount of the position of the piston from the target range increases. It is characterized by:

[0009] When the engine is stopped, the pressure in the cylinder with the intake valve open is almost equal to the intake pressure. Therefore, when the intake pressure is low, the cylinder pressure and the intake amount of the cylinder that is stopped during the transition from the intake stroke to the compression stroke and whose intake valve is still open are low. As a result, when the intake pressure is low, the torque consumed by the starting device to push up the piston of the cylinder and start the engine is kept relatively small. However, even if the intake pressure is low immediately after the engine is stopped, if the engine is stopped for a long time, the intake pressure will increase due to air leaking into the intake passage, and the torque consumed by the starting device to start the engine will increase.

[0010] In contrast, in the present invention, if the position of the piston of each cylinder at the time of engine stop is out of the target range, the intake pressure is adjusted to the atmospheric pressure without waiting for the engine start condition to be satisfied. When the intake pressure is lower than the reference pressure and is equal to or higher than the reference pressure, The engine is started by the starting device while the intake pressure is relatively low. In other words, in the present invention, when the torque of the starting device used to start the engine is likely to be large due to the position of the pistons of each cylinder being out of the target range when the engine is stopped, the engine is started before this torque becomes even larger with an increase in intake pressure. Therefore, according to the present invention, the torque of the starting device used to start the engine can be kept small.

[0011] Also, When the determining unit determines that the position of the piston of each cylinder is not within the target range, and the intake pressure detected by the intake pressure detecting means is less than a predetermined determination pressure that is lower than atmospheric pressure, the start control unit determines that the engine start condition is satisfied. I like it The engine is started by the starting means. do.

[0012] That is When the intake pressure is sufficiently low, i.e., below the threshold pressure, and the torque of the starting device used to start the engine is sufficiently low, the engine is started in response to the establishment of the engine start condition. Therefore, the torque of the starting device used to start the engine is kept low, and the engine stop time is secured, thereby preventing the fuel economy from deteriorating.

[0013] Moreover, The greater the deviation of the piston position from the target range, the greater the judgment pressure but Set to a small value will be done.

[0014] That is The greater the deviation of the piston position of each cylinder from the target range when the engine is stopped, the greater the torque of the starting device for starting the engine is, so the lower the judgment pressure is set, and the engine is started in a state of a lower intake pressure. This makes it possible to more reliably reduce the torque of the starting device used for starting the engine. Effect of the Invention

[0015] As described above, according to the engine start control device of the present invention, the torque of the starter consumed for starting the engine can be reduced. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a vehicle equipped with an engine to which a starting control device according to an embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a schematic configuration diagram of the engine. [Diagram 3] FIG. 2 is a schematic cross-sectional view of an engine body. [Figure 4] FIG. 2 is a diagram showing the strokes performed in each cylinder of the engine. [Diagram 5] FIG. 2 is a block diagram showing a control system of the engine. [Figure 6]4 is a graph showing the relationship between a cylinder stop position and a motor torque required for starting the engine. [Figure 7] FIG. 4 is a diagram showing a target range of a cylinder stop position. [Figure 8] 5 is a flowchart showing a specific procedure for stop position control. [Figure 9] FIG. 4 is a diagram showing a range of cylinder stop positions that must be avoided; [Figure 10] 4 is a flowchart showing a specific procedure for start timing adjustment control. [Figure 11] 4 is a graph showing the relationship between intake manifold pressure and starting torque for each cylinder stop position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (1) Overall structure 1 is a schematic diagram of a vehicle 100 equipped with an engine E to which an engine start control device according to an embodiment of the present invention is applied. In this embodiment, the vehicle 100 is a hybrid vehicle equipped with the engine E and a motor M as a drive source for the vehicle 100 (wheels 101). The motor M corresponds to the "starting means" in the claims.

[0018] As shown in FIG. 1, in addition to wheels 101, an engine E, and a motor M, a vehicle 100 is equipped with a clutch 102 that disconnectably connects the output shaft of the engine E and the rotating shaft of the motor M, a battery 103 that exchanges power with the motor M, a transmission 104 connected to the motor M, a drive shaft 106 connected to the wheels 101, and a power transmission device 105 that includes a differential gear, etc. and connects the transmission 104 and the drive shaft 106.

[0019] (Engine configuration) 2 is a schematic diagram of the engine E. The engine E includes an engine body 1, an intake passage 30 through which intake air introduced into the engine body 1 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 1 flows, and an EGR device 44 that recirculates EGR gas, which is a part of the exhaust gas flowing through the exhaust passage 40, to the intake passage 30. The engine E also includes a turbocharger 46, a turbine 48 provided in the exhaust passage 40, and a compressor 47 provided in the intake passage 30 and rotated by the turbine 48. The engine E of this embodiment is a four-stroke diesel engine, and is driven by receiving a supply of fuel mainly composed of diesel.

[0020] The engine body 1 has a cylinder block 3 in which cylinders 2 are formed, and a cylinder head 4 that covers the cylinder block 3.

[0021] Fig. 3 is a schematic cross-sectional view of the engine body 1. As shown in Fig. 3, the engine E of this embodiment is an in-line six-cylinder engine, and the engine body 1 (more specifically, a cylinder block 3) is formed with six cylinders 2 arranged in a row (first cylinder 2A, second cylinder 2B, third cylinder 2C, fourth cylinder 2D, fifth cylinder 2E, and sixth cylinder 2F, in that order from one side along the arrangement direction of the cylinders 2).

[0022] A piston 5 is housed in each cylinder 2 so that it can slide back and forth. A combustion chamber 6 is defined above the piston 5 in each cylinder 2. Each piston 5 is connected to a crankshaft 7 via a connecting rod 8. In response to the reciprocating motion of each piston 5, the crankshaft 7 rotates around its central axis.

[0023] An injector 15 that injects fuel into the cylinder 2 (combustion chamber 6) is attached to the cylinder head 4, one for each cylinder 2. The piston 5 reciprocates as the mixture of supplied fuel and air burns in the combustion chamber 6 and is pushed down by the expansion force caused by the combustion. The injector 15 corresponds to the "fuel supply means" in the claims.

[0024] The cylinder head 4 is provided with intake ports 9 for introducing intake air into each cylinder 2 (combustion chamber 6), intake valves 11 for opening and closing the intake ports 9, exhaust ports 10 for guiding exhaust gas generated in each cylinder 2 (combustion chamber 6), and exhaust valves 12 for opening and closing the exhaust ports 10, each for each cylinder 2. The engine body 1 is of a four-valve type, with two intake valves and two exhaust valves, and each cylinder 2 is provided with two intake ports 9 and two exhaust ports 10, as well as two intake valves 11 and two exhaust valves 12.

[0025] FIG. 4 is a diagram showing the strokes performed in each cylinder 2. As described above, engine E is a four-stroke engine. Thus, in each cylinder 2, intake stroke → compression stroke → expansion stroke → exhaust stroke are performed consecutively in this order. Engine E is also an in-line six-cylinder engine. Thus, pistons 5 provided in each cylinder 2A to 2F reciprocate with a phase difference of 120° CA (120 degrees in crank angle), and combustion occurs in the following order every 120° CA: first cylinder 2A → fifth cylinder 2E → third cylinder 2C → sixth cylinder 2F → second cylinder 2B → fourth cylinder 2D.

[0026] In this specification, the intake, compression, expansion, and exhaust strokes refer to one combustion cycle, i.e., the period during which the crankshaft 7 rotates twice (360° CA), divided into four equal crank angles, during which intake, compression, expansion, and exhaust are primarily performed, respectively.

[0027] Specifically, the intake stroke in this specification does not refer to the period from when the intake valve 11 actually starts opening to when it closes, but refers to the period when the piston 5 is located between the exhaust top dead center TDCe and the intake bottom dead center BDCi. The compression stroke refers to the period when the piston 5 is located between the intake bottom dead center BDCi and the compression top dead center TDCc. The expansion stroke refers to the period when the piston 5 is located between the compression top dead center TDCc and the expansion bottom dead center BDCe. The exhaust stroke refers to the period when the piston 5 is located between the expansion bottom dead center BDCe and the exhaust top dead center TDCe.

[0028] Note that compression top dead center TDCc is the uppermost position (closest to the cylinder head 4) of the reciprocating range of the piston 5, and is the position that the piston 5 reaches after the intake valve 11 closes and before the exhaust valve 12 opens. Expansion bottom dead center BDCe, exhaust top dead center TDCe, and intake bottom dead center BDCi are positions of the piston 5 when the crankshaft 7 rotates forward by 180° CA, 360° CA, and 540° CA, respectively, from a state in which the piston 5 is at compression top dead center TDCc. In the following description, the position of the piston 5 is appropriately described as the position of the cylinder 2.

[0029] The intake valves 11 of each cylinder 2 are driven by a valve train 13 including an intake camshaft arranged in the cylinder head 4. The valve train 13 for the intake valves 11 incorporates an intake S-VT 13a that can change the opening and closing timing of each intake valve 11 collectively. Similarly, the exhaust valves 12 of each cylinder 2 are driven by a valve train 14 including an exhaust camshaft arranged in the cylinder head 4. The valve train 14 for the exhaust valves 12 also incorporates an exhaust S-VT 13a that can change the opening and closing timing of each exhaust valve 12 collectively. The intake S-VT 13a (exhaust S-VT 14a) is a so-called phase-type variable mechanism, which changes the valve opening timing IVO (EVO) and valve closing timing IVC (EVC) of each intake valve 11 (each exhaust valve 12) simultaneously and by the same amount.

[0030] The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. The intake passage 30 is provided with an air cleaner 31, a compressor 47, a throttle valve 32, an intercooler 33, and a surge tank 34 in this order from the upstream side. The compressor 47 is rotationally driven by the turbine 48 as described above, and compresses (supercharges) the air passing through the compressor 47. The air compressed by the compressor 47 and cooled by the intercooler 33 is introduced into the cylinder 2 (combustion chamber 6). The throttle valve 32 is a valve that can open and close the intake passage 30. The amount of air flowing through the intake passage 30, and therefore the amount of intake air introduced into the cylinder 2 (combustion chamber 6), is changed according to the opening degree of the throttle valve 32.

[0031] The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. The exhaust passage 40 is provided with, in this order from the upstream side, a turbine 48 and an exhaust purification device 41 for purifying the exhaust gas. The exhaust purification device 41 incorporates a three-way catalyst 42 and a DPF (diesel particulate filter) 43. The turbine 48 rotates by receiving energy from the exhaust gas flowing through the exhaust passage 40, and the compressor 47 rotates in conjunction with this.

[0032] The EGR device 44 includes an EGR passage 44A that connects the exhaust passage 40 and the intake passage 30, and an EGR valve 45 provided in the EGR passage 44A. The EGR passage 44A connects a portion of the exhaust passage 40 upstream of the turbine 48 to a portion of the intake passage 30 between the intercooler 33 and the surge tank 34. The EGR valve 45 is a valve that can open and close the EGR passage 44A. The amount of EGR gas recirculated to the intake passage 30, and therefore the amount of EGR gas introduced into the cylinder 2 (combustion chamber 6), is changed according to the opening degree of the EGR valve 45. An EGR cooler (not shown) that cools the exhaust gas (EGR gas) recirculated from the exhaust passage 40 to the intake passage 30 by heat exchange is disposed in the EGR passage 44A.

[0033] (2) Control system Fig. 5 is a block diagram showing a control system of the vehicle 100. The controller 200 shown in Fig. 5 is a microprocessor for comprehensively controlling the motor M, the engine E, etc., and is composed of a well-known CPU, ROM, RAM, etc. The controller 200 corresponds to the "control means" in the claims.

[0034] The controller 200 receives detection signals from various sensors provided on the vehicle 100 .

[0035] Specifically, the cylinder block 3 of the engine E is provided with a crank angle sensor SN1 for detecting the rotation angle of the crankshaft 7, i.e., the engine speed. The cylinder head 4 of the engine E is provided with a cam angle sensor SN2 for detecting the angle of an intake cam included in the intake valve mechanism 13. The controller 200 determines which cylinder is in which stroke based on the detection signal of the cam angle sensor SN2 and the detection signal of the crank angle sensor SN1. The intake passage 30 of the engine E is provided in a portion downstream of the throttle valve 32 with an intake manifold pressure sensor SN3 for detecting the pressure of the intake air passing through this portion. Hereinafter, the pressure of the intake air passing through the portion downstream of the throttle valve 32 of the intake passage 30 is referred to as the intake manifold pressure. In addition, the intake air referred to in this specification refers to the gas introduced into the cylinder 2 (combustion chamber 6), and refers to the gas including the EGR gas and the air when EGR gas is introduced into the cylinder 2 in addition to the air. An exhaust O2 sensor S is provided in the exhaust passage 40 of the engine E to detect the exhaust O2 concentration, which is the concentration of oxygen contained in the exhaust gas passing through the exhaust passage 40. N4 is provided. The exhaust O2 sensor SN4 is disposed between the turbine 48 and the exhaust purification device 41. The vehicle 100 is also provided with a motor rotation speed sensor SN5 for detecting the rotation speed of the motor M, an accelerator opening sensor SN6 for detecting the accelerator opening, which is the opening of the accelerator pedal operated by the driver who drives the vehicle 100, a vehicle speed sensor SN7 for detecting the vehicle speed, and an atmospheric pressure sensor SN8 for detecting the atmospheric pressure. Information detected by these sensors SN1 to SN7 is sequentially input to the controller 200. Here, the above-mentioned intake manifold pressure sensor SN3 corresponds to the "intake pressure detection means" in the claims, and the above-mentioned intake manifold pressure, that is, the pressure of the intake air passing through the portion of the intake passage 50 of the engine E downstream of the throttle valve 32 corresponds to the "intake pressure" in the claims.

[0036] The controller 200 executes various judgments and calculations based on input information from each sensor to control each part of the engine E, such as the intake S-VT 13a, exhaust S-VT 14a, injector 15, throttle valve 32, and EGR valve 45, as well as the motor M and clutch 102. The controller 200 functionally includes a stop control unit 201 that performs engine stop control (to be described later) to automatically stop the engine E, a start control unit 202 that performs engine start control and start timing adjustment control (to be described later) to start the engine E, and a judgment unit 203 that judges whether a cylinder stop position (to be described later) is within a target range X0 (to be described later).

[0037] In this embodiment, the intake valve 11 is configured to always close on the retarded side of the intake bottom dead center BDCi while the engine E is running, and the controller 200 controls the intake S-VT 13a to achieve this.

[0038] In addition, in this embodiment, the basic driving mode of the vehicle 100 is set to an EV mode in which the wheels 101 are driven only by the motor M, and is switched to an engine drive mode in which the engine E is driven only when the output of the motor M alone is insufficient, and the controller 200 switches the driving mode based on the vehicle speed, etc.

[0039] Specifically, the controller 200 judges whether an engine start condition, which is a condition for starting the engine E, is satisfied, and whether an engine stop condition, which is a condition for stopping the engine E, is satisfied, based on the running state of the vehicle 100 and the operation state of the accelerator pedal. For example, the controller 200 judges that the engine start condition is satisfied when the vehicle speed is equal to or higher than a predetermined engine start speed and the accelerator pedal opening is equal to or higher than a predetermined engine start opening while the engine E is stopped. The controller 200 also judges that the engine stop condition is satisfied when the vehicle speed is lower than a predetermined engine stop speed or the accelerator pedal opening is lower than a predetermined engine stop opening while the engine E is running. The controller 200 sequentially judges whether each of the above conditions is satisfied, based on the detection results of the vehicle speed sensor SN7 and the accelerator pedal opening sensor SN6, etc.

[0040] The controller 200 (start control section 202) performs engine start control to start the engine E when engine start conditions are met. In the engine start control, the controller 200 first shifts the clutch 102 from a released state to an engaged state. When the clutch 102 is in an engaged state, the output of the motor M is transmitted to the engine E. As a result, the engine E is forcibly rotated by the motor M. That is, cranking of the engine E is started. When cranking is started, the controller 200 then injects the first fuel from the injector 15 during the compression stroke into the cylinder 2 that has been stopped near the intake bottom dead center BDCi, and causes the fuel to self-ignite and burn. Thereafter, the control shifts to normal engine control, and the controller 200 sequentially injects fuel from the injector 15 into each cylinder 2. Here, as described above, the clutch 102 is in an engaged state. As a result, the driving force of the engine E is transmitted to the wheels 101 via the motor M, the transmission 104, and the like.

[0041] Moreover, when the controller 200 (stop control unit 201) determines that the engine stop condition is satisfied, it performs engine stop control to stop the engine E. In the engine stop control, the controller 200 first performs a fuel cut to stop the fuel supply from the injector 15 to each cylinder 2. By stopping the fuel supply, the engine speed decreases and the engine stops. Here, if the engine speed decreases, there is a risk that the engine body 1 and the engine mount supporting it will resonate with each other, and the vibration of the engine body 1 will increase. Therefore, as the engine stop control, the controller 200 performs a control to fully close the throttle valve 32. That is, by fully closing the throttle valve 32, the engine speed is reduced early, and thus the period during which the engine speed becomes the resonant speed is shortened. Specifically, after the fuel cut is performed, the controller 200 closes the throttle valve 32 toward full closure when the engine speed becomes equal to or lower than a predetermined throttle closing speed N1. Furthermore, when the engine stop condition is met and the engine E stops (the rotation speed of the engine E becomes 0), the controller 200 switches the clutch 102 from the engaged state to the released state.

[0042] (Engine stop position control) Next, a description will be given of the stop position control that is performed by the controller 200 after the engine stop control is performed. The stop position control is a control for setting the position of each cylinder 2 (piston 5 of each cylinder 2) within a predetermined target range when the engine E is stopped.

[0043] In the following description, the time when the engine E is stopped, specifically, when the engine speed is 0 and the engine E is completely stopped, is simply referred to as the time when the engine is stopped. Also, the position of each cylinder 2 (piston 5 of each cylinder 2) when the engine is stopped is referred to as the cylinder stop position.

[0044] In this specification, a cylinder whose stroke is the compression stroke when the engine is stopped (when the engine E is completely stopped) and whose piston 5 is located in the range from the compression top dead center (TDCc) to 120° CA before the compression top dead center (BTDCc) is referred to as a "stop-time compression stroke cylinder." Also, a cylinder whose combustion order is one before the stop-time compression stroke cylinder, whose stroke is the expansion stroke when the engine is stopped (when the engine E is completely stopped) and whose piston 5 is located in the range from the compression top dead center (TDCc) to 120° CA after the compression top dead center (ATDCc) is referred to as a "stop-time expansion stroke cylinder." In addition, a cylinder whose combustion order is one after the compression stroke cylinder at engine stop, whose stroke when the engine is stopped (when the engine E is completely stopped) is the intake stroke or compression stroke, and whose piston 5 position is in the range from 60° CA before intake bottom dead center (BBDCi) to 60° CA after intake bottom dead center (ABDCi) is called a compression transition cylinder at engine stop.

[0045] FIG. 6 is a graph showing the relationship between the cylinder stop position and the minimum torque of the motor M required to start the engine E after it has stopped at this cylinder stop position (hereinafter, referred to as starting torque, as appropriate). The horizontal axis of FIG. 6 also shows the positions of the compression stroke cylinder at the stop, the compression transition cylinder at the stop, and the expansion stroke cylinder at the stop. FIG. 7 is a diagram showing the target range of the cylinder stop position and the corresponding stop positions of the compression stroke cylinder at the stop, the compression transition cylinder at the stop, and the expansion stroke cylinder at the stop. In FIG. 7, the top point of the circle is the top dead center (TDC), the bottom point is the bottom dead center (BDC), and the position of each cylinder 2 (the position of the piston 5 of each cylinder 2) is shown so that the position of the piston 5 becomes more retarded as it moves clockwise.

[0046] As shown in FIG. 6, the starting torque varies depending on the cylinder stop position. The starting torque is minimum when the cylinder stop position is 7This is the position shown by the solid line in FIG. 1, where the stop-time compression stroke cylinder is at 60° CA before compression top dead center (BTDCc), the stop-time expansion stroke cylinder is at 60° CA after compression top dead center (ATDCc), and the stop-time compression transition cylinder is at intake bottom dead center (BDCi). In other words, the starting torque is minimum when the pistons 5 of the stop-time compression stroke cylinder and the stop-time expansion stroke cylinder are at the same position relative to top dead center. Hereinafter, the cylinder stop position at which the starting torque is minimum is referred to as the optimal position P0.

[0047] The target range of the cylinder stop position is a position where the starting torque is equal to or less than a predetermined reference torque T1 when the intake manifold pressure is atmospheric pressure, and is set in a range from a first position P1 on the advanced side of the optimal position P0 to a second position P2 on the retarded side of the optimal position P0. The reference torque T1 is set to a value between the maximum and minimum values ​​of the starting torque. Correspondingly, the first position P1 is set to a position where the position of the compression stroke cylinder at the time of stopping is 75° CA before the compression top dead center (BTDCc), the position of the compression transition cylinder at the time of stopping is 15° CA before the intake bottom dead center (BBDCi), and the position of the expansion stroke cylinder at the time of stopping is 45° CA after the compression top dead center (ATDCc). In addition, the second position P2 is set to a position where the position of the compression stroke cylinder at the time of stopping is 40° CA before compression top dead center (BTDCc), the position of the compression transition cylinder at the time of stopping is 20° CA after intake bottom dead center (ABDCi), and the position of the expansion stroke cylinder at the time of stopping is 80° CA after compression top dead center (ATDCc).

[0048] The controller 200 performs stop position control when the cylinder stop position is outside the target range X0. Lead angle The intake retard control prevents the cylinder stop position from falling outside the target range X0. Retard and a throttle opening increase control to prevent the throttle opening from shifting to the "increasing throttle opening" side.

[0049] A specific procedure for the stop position control will be described with reference to the flowchart of Fig. 8. Step S1 in the flowchart of Fig. 8 is carried out after the engine stop control has been carried out.

[0050] In step S1, the controller 200 determines whether the engine speed has fallen below the reference speed N2. The controller 200 makes this determination based on the detection result of the crank angle sensor SN1. The reference speed N2 is preset and stored in the controller 200. If the determination in step S1 is NO and the controller 200 determines that the engine speed is equal to or higher than the reference speed N2, the controller 200 repeats step S1 and waits for the engine speed to fall below the reference speed N2. On the other hand, if the determination in step S1 is YES and the controller 200 determines that the engine speed has fallen below the reference speed N2, the controller 200 proceeds to step S2.

[0051] In step S2, the controller 200 retards the phase of the intake valve 11 by the intake S-VT 13a, and retards the intake valve closing timing IVC, which is the closing timing of the intake valve 11, to a first reference timing (intake retard control). The first reference timing is set in advance and stored in the controller 200. The first reference timing is set to a timing that is more retarded than the intake valve closing timing IVC immediately after the engine stop control is performed (immediately after the control for fully closing the throttle valve 32 is performed) and more advanced than a second reference timing, which will be described later.

[0052] Next, in step S3, the controller 200 predicts the engine stop time when the engine E stops and the cylinder stop position, i.e., the position of each piston 5 when the engine E stops. The controller 200 predicts the above time and position based on the detection value of the intake manifold pressure sensor SN3, the detection value of the crank angle sensor SN1, the detection value of the cam angle sensor SN2, etc. After step S3, the process proceeds to step S4.

[0053] In step S4, the controller 200 determines whether the engine will stop after passing the second compression top dead center based on the prediction result in step S3. Specifically, in step S4, the controller 200 determines whether two cylinders will pass the compression top dead center (TDCc) from the current time until the engine stops.

[0054] If the determination in step S4 is NO, that is, if it is determined that the engine E will not be stopped until the timing after the second compression top dead center from the current time point, the controller 200 returns to step S3. The system continues to predict the engine stop timing and cylinder stop position.

[0055] On the other hand, if the determination in step S4 is YES and it is determined that the engine will stop after passing the second compression top dead center, the controller 200 proceeds to step S5. In step S5, the controller 200 determines whether the cylinder stop position predicted in step S3 (hereinafter referred to as the predicted cylinder stop position) is included in the avoidance required range X1. As shown in FIG. 9, the avoidance required range X1 is a range on the retard side of the target range X0, and is a range from a state in which the piston 5 of the stopped compression stroke cylinder is at the most retarded position of the target range X0 (40° CA before compression top dead center (BTDCc) corresponding to the second position P2) to a state in which the piston 5 of the stopped compression stroke cylinder is at compression top dead center (TDCc). In other words, in step S5, it is determined whether the predicted stop position of the stopped compression stroke cylinder is closer to top dead center (compression top dead center TDCc) than the target range.

[0056] If the determination in step S5 is YES and it is determined that the predicted cylinder stop position is included in the avoidance range X1 (if it is determined that the predicted stop position of the compression stroke cylinder at the time of stopping is on the top dead center side of the target range X0), then in step S6, the controller 200 increases the opening of the throttle valve 32. In this embodiment, the controller 200 increases the opening of the throttle valve 32 so that the increase in the opening of the throttle valve 32 increases as the deviation of the predicted cylinder stop position from the target range X0 (second position P2) increases (throttle opening increase control). Step S 6 After that, the process proceeds to step S7. On the other hand, if the determination in step S5 is NO, that is, if it is determined that the predicted cylinder stop position is not included in the avoidance-required range X1, the controller 200 proceeds to step S7.

[0057] In step S7, the controller 200 performs control to retard the phase of the intake valve 11 by the intake S-VT 13a to retard the intake valve closing timing IVC to the second reference timing (intake retard control). When the intake valve closing timing IVC reaches the second reference timing, the controller 200 ends the process (stop position control). The second reference timing is set in advance and stored in the controller 200. For example, the second reference timing is set to the most retarded timing among the timings that the intake valve closing timing IVC can take. Note that, although step S7 is performed after step S5 in the flowchart of FIG. 8, step S5 and step S7 are performed almost simultaneously, and the controller 200 performs step S7 immediately after the determination in step S4 is YES and it is determined that the engine will stop after passing the second compression top dead center.

[0058] By carrying out the above-described intake retard control, the possibility that the cylinder stop position will be on the advanced side of the target range X0 becomes low.

[0059] Specifically, while the engine is running, the intake valve closing timing IVC is retarded from the intake bottom dead center BDCi. Therefore, if the phase of the intake valve 11 is retarded immediately after it is determined that the engine E will stop after passing the second compression top dead center, the retard amount of the intake valve closing timing IVC from the intake bottom dead center BDCi increases, and the amount of intake air blowing back from the cylinder 2 (combustion chamber 6) to the intake port 9 increases. After the above determination is made, that is, immediately before the engine stops, the intake stroke of the stop-time compression stroke is performed later than the intake stroke of the stop-time expansion stroke cylinder. Therefore, if the phase of the intake valve 11 is retarded as described above, the amount of intake air blowing back from the cylinder 2 of the stop-time compression stroke cylinder to the intake port 9 increases, and the intake amount of the stop-time compression stroke cylinder is prevented from becoming excessive relative to the intake amount of the stop-time expansion stroke cylinder. Therefore, there is a low possibility that the intake volume of the stopped compression stroke cylinder will be excessively large compared to the intake volume of the stopped expansion stroke cylinder, thereby suppressing the rise of the piston 5 of the stopped compression stroke cylinder, and there is a low possibility that the stopped compression stroke cylinder will be located on the bottom dead center side of the target range X0, i.e., the cylinder stop position will be on the advanced side of the target range X0.

[0060] In addition, by implementing the throttle opening increase control, the cylinder stop position is set to a position outside the target range X0. This reduces the possibility of the timing becoming retarded.

[0061] Specifically, if the opening of the throttle valve 32 is increased immediately after it is determined that the engine E will stop after passing the second compression top dead center, the intake amount of the stop-time compression stroke cylinder, which performs the intake stroke later than the stop-time expansion stroke cylinder immediately before the engine stops, increases. As a result, if the opening of the throttle valve 32 is increased as described above when it is determined that the predicted cylinder stop position is included in the avoidance required range X1 (when it is determined that the predicted stop position of the stop-time compression stroke cylinder is on the top dead center side of the target range X0), the increase in the intake amount of the stop-time compression stroke cylinder suppresses the rise of the piston 5 of the cylinder, and the stop-time compression stroke cylinder is less likely to be on the top dead center side of the target range X0, that is, the cylinder stop position is less likely to be within the avoidance required range X1, which is retarded from the target range X0.

[0062] (Start timing adjustment control) As described above, by implementing the stop position control including the intake retard control and the throttle opening increase control, the possibility that the cylinder stop position will deviate from the target range X0 is reduced. However, depending on the drive delay caused by the deterioration of the intake S-VT 13a, the variation in the sliding resistance of the piston 5 caused by the deterioration of the engine E, etc., the cylinder stop position may deviate from the target range X0 even if the stop position control is implemented.

[0063] Therefore, the controller 200 (start control section 202) performs the start timing adjustment control described below so that the starting torque can be kept low even if the cylinder stop position is out of the target range X0. Figure 10 is a flowchart showing the procedure of the start timing adjustment control. Step S20 in Figure 10 is started when the engine E comes to a complete stop.

[0064] In step S20, the controller 200 detects the cylinder stop position. The controller 200 calculates the current cylinder stop position based on the detection results of the crank angle sensor SN1 and the cam angle sensor SN2. In this manner, in this embodiment, the cylinder stop position, i.e., the position of the piston 5 of each cylinder 2 when the engine is stopped, is detected based on the detection results of the crank angle sensor SN1 and the cam angle sensor SN2, and these sensors SN1 and SN2 correspond to the "stop position detection means" in the claims.

[0065] In step S21, the controller 200 determines whether or not the engine start condition is not satisfied. The controller 200 makes this determination based on the detection values ​​of the vehicle speed sensor SN7, the accelerator opening sensor SN6, and the like.

[0066] If the determination in step S21 is NO and it is determined that the engine start condition is satisfied, the controller 200 performs step S 26 The engine E is started by the motor M.

[0067] On the other hand, if the determination in step S21 is YES, that is, if it is determined that the engine start condition is not satisfied, the controller 200 proceeds to step S22. In step S22, the controller 200 (determination unit 203) determines whether or not the cylinder stop position calculated in step S20 is outside the target range X0.

[0068] If the determination in step S22 is NO and the cylinder stop position is within the target range X0, the controller 200 maintains the stop of the engine E and returns to step S21.

[0069] On the other hand, if the determination in step S22 is YES and the cylinder stop position is outside the target range X0, the controller 200 proceeds to step S23. In step S23, the controller 200 determines whether the intake manifold pressure is less than the atmospheric pressure, that is, whether the intake manifold pressure is a negative pressure. The controller 200 makes this determination based on the detection results of the atmospheric pressure sensor SN8 and the intake manifold pressure sensor SN3. Note that even after the engine E is stopped, the detection results of the atmospheric pressure sensor SN8 and the intake manifold pressure sensor SN3 are sequentially input to the controller 200, and the determination in step S23 is made based on the atmospheric pressure and the intake manifold pressure detected when step S23 is performed.

[0070] If the determination in step S23 is NO, that is, the intake manifold pressure is equal to or higher than the atmospheric pressure and is not a negative pressure, the controller 200 maintains the stop of the engine E and returns to step S21.

[0071] On the other hand, if the determination in step S23 is YES, meaning that the intake manifold pressure is less than atmospheric pressure, that is, a negative pressure, the controller 200 proceeds to step S24. In step S24, the controller 200 sets a determination pressure to be used in the next step S25.

[0072] The judgment pressure is the intake manifold pressure that is the criterion for determining whether or not to start the engine E. The starting torque changes depending on the cylinder stop position as described above, but also changes depending on the intake manifold pressure. Specifically, when starting the engine E, the motor M raises each piston 5 of the stop-time compression stroke cylinder and the stop-time compression transition cylinder while compressing the intake air in these cylinders 2 (combustion chambers 6). As a result, the torque of the motor M consumed for starting the engine E, i.e., the starting torque, is reduced when the amount of intake air in each cylinder 2 of the stop-time compression stroke cylinder and the stop-time compression transition cylinder is smaller. Here, the stop-time compression transition cylinder is a cylinder whose stop position is in the range from 60° CA before the intake bottom dead center (BBDCi) to 60° CA after the intake bottom dead center (ABDCi), and the intake valve 11 is still open when the engine is stopped. In other words, the intake valve 11 is controlled so that the intake valve 11 of the stop-time compression transition cylinder is in an open state when the engine is stopped. In this embodiment, the intake valve closing timing IVC is retarded immediately before the engine is stopped by implementing the intake retard control, so that the intake valve 11 of the stop-time compression transition cylinder is in an open state when the engine is stopped. In this way, the intake valve 11 is stopped in an open state, so the intake amount of the stop-time compression transition cylinder is reduced as the intake manifold pressure is lower. In other words, with the intake valve 11 open, the pressure in the cylinder 2 of the stop-time compression transition cylinder is almost the same as the intake manifold pressure, and low intake manifold pressure means that the pressure in the cylinder 2 of the stop-time compression transition cylinder is low and the intake amount is small. Therefore, even if the cylinder stop position is the same, the lower the intake manifold pressure, the smaller the starting torque becomes.

[0073] Fig. 11 is a graph showing the relationship between intake manifold pressure and starting torque for each cylinder stop position. Fig. 11 shows the above relationship for the optimum position P0, the first and second positions P1 and P2, the third position P3 shown in Fig. 6 which is a position shifted from the target range X0, the fourth position P4 shown in Fig. 6 which is a position which is shifted from the target range X0 more than the third position P3, and the fifth position P5 shown in Fig. 6 which is a position which is shifted from the target range X0 more than the fourth position P4. Note that Pa in Fig. 11 indicates atmospheric pressure.

[0074] As shown in FIG. 11, the higher the intake manifold pressure is, the greater the starting torque becomes, regardless of the cylinder stop position. Also, regardless of the intake manifold pressure, the greater the deviation of the cylinder stop position from the optimal position P0, the greater the starting torque becomes. Also, if the cylinder stop position is located outside the target range X0, the greater the deviation of the cylinder stop position from the target range X0, the greater the starting torque becomes. And, if the cylinder stop position is located outside the target range X0, the greater the deviation of the cylinder stop position from the target range X0, the greater the intake manifold pressure at which the starting torque becomes the reference torque T1. Low become.

[0075] In this embodiment, the judgment pressure is set to the intake manifold pressure at which the starting torque at the current cylinder stop position becomes the above-mentioned reference torque T1. As described above, the greater the deviation of the cylinder stop position from the target range X0, the greater the intake manifold pressure at which the starting torque becomes the reference torque T1. Low Thus, in step S24, the controller 200 sets the judgment pressure to a larger value as the deviation amount of the cylinder stop position detected in step S20 from the target range X0 increases. small Set the value.

[0076] In this embodiment, the intake manifold pressure when the starting torque becomes the reference torque T1 is preset for each cylinder stop position and stored in a map. For example, in Fig. 11, the judgment pressure when the current cylinder stop position is the third position P3 is set to the pressure indicated by Pim3, the judgment pressure when the current cylinder stop position is the fourth position P4 is set to the pressure indicated by Pim4, and the judgment pressure when the current cylinder stop position is the fifth position P5 is set to the pressure indicated by Pim5, and these are stored in the controller 200. The controller 200 extracts the intake manifold pressure corresponding to the cylinder stop position detected in step S20 from this map and sets it as the judgment pressure.

[0077] After step S24, the process proceeds to step S25. In step S25, the controller 200 determines whether the intake manifold pressure is equal to or higher than the determination pressure set in step S24. The determination in step S25 is made based on the detection result of the intake manifold pressure sensor SN3 when step S25 is performed.

[0078] If the determination in step S25 is NO, that is, the intake manifold pressure is less than the determination pressure, the controller 200 maintains the stop of the engine E and returns to step S20.

[0079] On the other hand, if the determination in step S25 is YES and the intake manifold pressure is equal to or higher than the determination pressure, the controller 200 26 The engine E is started by the motor M.

[0080] In this manner, in this embodiment, if the cylinder stop position deviates from the target range X0 due to the implementation of the start timing adjustment control (the determination in step S22 is YES), even if the engine start condition is not satisfied (the determination in step S21 is YES), if the intake manifold pressure is less than atmospheric pressure (the determination in step S23 is YES) and is equal to or greater than the determination pressure (the determination in step S25 is YES), engine E will be started.

[0081] (effect, etc.) As described above, in the above embodiment, by implementing the above-mentioned start timing adjustment control after the engine is stopped, it is possible to prevent the torque of the motor M consumed in starting the engine E from becoming excessive while suppressing deterioration of the fuel efficiency performance of the engine E.

[0082] Specifically, when the engine E stops, air leaks from around the throttle valve 32 into the intake passage 30. Therefore, even if the intake manifold pressure is less than atmospheric pressure immediately after the engine stops, the intake manifold pressure gradually increases to atmospheric pressure as the engine E stops for a long time. When the intake manifold pressure is equal to or greater than atmospheric pressure, the starting torque is larger than when the intake manifold pressure is less than atmospheric pressure. For this reason, if the engine E is started simply when the engine start condition is satisfied without carrying out the above-mentioned start timing adjustment control, the engine E must be started when the intake manifold pressure is at atmospheric pressure when the engine E is stopped for a long time. If the cylinder stop position deviates from the target range X0 at this time, the starting torque, which is increased due to this deviation, becomes even larger when the intake manifold pressure is at atmospheric pressure.

[0083] In contrast, in the above embodiment, when the cylinder stop position deviates from the target range X0 and the intake manifold pressure is lower than atmospheric pressure, the engine E is started without waiting for the engine start condition to be satisfied. Therefore, even if the starting torque becomes large due to the cylinder stop position deviating from the target range X0, it is possible to prevent the torque from increasing further.

[0084] In the above embodiment, when the cylinder stop position is deviated from the target range X0, even if the intake manifold pressure is lower than the atmospheric pressure, the intake manifold pressure is lower than the judgment pressure which is lower than the atmospheric pressure. When the engine start condition is satisfied, engine E is started in response to the satisfaction of the engine start condition. In other words, when the cylinder stop position deviates from the target range X0 and the intake manifold pressure immediately after the engine is stopped is less than the judgment pressure, engine E is started when the intake manifold pressure rises to the judgment pressure or when the engine start condition is satisfied. Therefore, when the engine start condition is not satisfied, even if the intake manifold pressure has not risen to the judgment pressure and the starting torque can be suppressed to less than the reference torque T1, i.e., the allowable torque, starting of engine E can be avoided, and the stop time of engine E can be secured to suppress deterioration of fuel efficiency.

[0085] In particular, in the above embodiment, the determination pressure is changed according to the cylinder stop position, so that the stop time of the engine E can be secured while reliably suppressing the starting torque to a level close to an allowable torque.

[0086] (Modification) In the above embodiment, the case has been described where the stop position control is performed to bring the cylinder stop position into the target range X0 before the engine is stopped, but this stop position control may be omitted.

[0087] In the above embodiment, the determination pressure is changed depending on the cylinder stop position. However, the determination pressure may be set to a constant pressure regardless of the cylinder stop position.

[0088] In the above embodiment, in the case where the cylinder stop position deviates from the target range X0 and the intake manifold pressure is less than the judgment pressure even if it is less than the atmospheric pressure, the engine E is started when the intake manifold pressure rises to the judgment pressure or when the engine start condition is satisfied, but the control of waiting for the intake manifold pressure to rise to the judgment pressure may be omitted. In other words, regardless of whether the intake manifold pressure is less than the judgment pressure, the engine E may be started when the cylinder stop position deviates from the target range X0 and the condition that the intake manifold pressure is less than the atmospheric pressure is satisfied.

[0089] In the above embodiment, the engine E is a six-cylinder engine having six cylinders 2, but the number of cylinders of the engine E is not limited to this and may be four, for example. [Explanation of symbols]

[0090] 1 Engine body 2-cylinder 5 Piston 7 Crankshaft 15 Injector (fuel supply means) 30 Intake passage 32 Throttle valve 200 Controller (control means) 201 Stop control section 202 Starting control section 203 Judgment section E-Engine M Motor (starting means) SN1 Crank angle sensor (stop position detection means) SN2 Cam angle sensor (stop position detection means) SN3 Intake manifold pressure sensor (intake pressure detection means) SN8 Barometric Pressure Sensor

Claims

[Claim 1] A start control device provided in an engine having a plurality of cylinders, a fuel supply means for supplying fuel to each cylinder, a piston reciprocatingly provided in each cylinder, a crankshaft that rotates in conjunction with the reciprocating movement of the piston, a starting means for forcibly starting the engine by rotating the crankshaft, and an intake passage through which intake air introduced into each cylinder flows, a stop position detection means for detecting a position of a piston in each cylinder when the engine is stopped; an intake pressure detection means for detecting an intake pressure, which is a pressure in the intake passage; a control means for controlling each part of the engine such as the fuel supply means and the starting means, The control means a stop control unit that stops the supply of fuel to the cylinders by the fuel supply means when a predetermined engine stop condition is satisfied, thereby stopping the engine; a start control unit that starts the engine by the starting means when a predetermined engine start condition is satisfied after the engine is stopped; a determination unit that determines whether or not the position of the piston of each cylinder detected by the stop position detection means is within a predetermined target range after the engine is stopped, When the determination unit determines that the position of the piston of each cylinder is not within the target range, the start control unit starts the engine by the starting unit even when the engine start condition is not satisfied when the intake pressure detected by the intake pressure detection means is lower than atmospheric pressure and equal to or higher than a predetermined determination pressure, and starts the engine by the starting unit when the engine start condition is satisfied when the intake pressure is less than the determination pressure, 2. An engine start control device comprising: a start control unit for controlling an engine start control operation, the start control unit being operable to control a start control pressure of the engine;

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