JP7582007B2 - Engine stop position control device - Google Patents

Description

The present invention relates to a stop position control device that is installed in an engine that has a starting means that can forcibly start the engine by rotating the crankshaft.

Conventionally, in vehicles equipped with an engine, the engine has been automatically stopped and then forcibly started using a starting means in order to improve fuel efficiency.

In a multi-cylinder engine, the torque required of the starting means to start the engine varies depending on the position of each cylinder (the piston position of each cylinder) when the engine is stopped, so it is necessary to set the position of each cylinder to a position suitable for starting when the engine is stopped.

In response to this, for example, the engine of Patent Document 1 performs the following control immediately before the engine is stopped. In other words, 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 increase 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.

JP 2013-60827 A

In the engine of Patent Document 1, the increase in the intake air amount of the stopped compression stroke cylinder suppresses the rise of the piston of that cylinder. This prevents the stop position of the stopped compression stroke cylinder from shifting toward the top dead center side from the desired position. However, when the throttle valve opening is increased, the amount of air in the stopped compression stroke cylinder and the intake passage increases. As a result, the oxygen concentration in the intake air amount of each cylinder when the engine starts increases, which makes it easier for the amount of NOx generated immediately after the engine starts.

The present invention was made in consideration of the above circumstances, and aims to provide an engine stop position control device that can control the position of each cylinder when the engine is stopped to a position suitable for starting, while preventing an increase in the amount of NOx generated immediately after the engine is started.

In order to solve the above problems, the present invention provides a stop position control device provided in an engine having a plurality of cylinders, a fuel supply means for supplying fuel to each cylinder, a piston provided in each cylinder so as to be capable of reciprocating, 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, an intake passage through which intake air introduced into each cylinder flows, and an exhaust passage through which exhaust gas discharged from each cylinder flows, the stop position control device including a throttle valve provided in the intake passage and opening and closing the intake passage, an EGR passage that connects the intake passage downstream of the throttle valve to the exhaust passage and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage, an EGR valve that opens and closes the EGR passage, and controls each part of the engine including the fuel supply means, the throttle valve, and the EGR valve to start the fuel supply when a predetermined engine stop condition is established. and a control means for performing a fuel cut to stop the fuel supply to the cylinder by the fuel cut means. The control means predicts the stop position of a stop-time compression stroke cylinder, which is a cylinder that stops during the compression stroke after the fuel cut is performed, and if the predicted stop position of the stop-time compression stroke cylinder is on the top dead center side of a predetermined target range, performs a valve opening increase control to increase the opening of the throttle valve or the EGR valve during the intake stroke immediately before the stop of the stop-time compression stroke cylinder. If a first condition is satisfied that the oxygen concentration in the intake passage is less than a predetermined reference concentration, the control means performs the control to increase the opening of the throttle valve as the valve opening increase control, and if a second condition is satisfied that the oxygen concentration in the intake passage is equal to or greater than the reference concentration, the control means performs the control to increase the opening of the EGR valve as the valve opening increase control (claim 1).

According to the present invention, when the stopping position of the stopped compression stroke cylinder is predicted to be closer to the top dead center than the target range, the opening of the throttle valve or EGR valve is increased during the intake stroke immediately before the stopped compression stroke cylinder is stopped, increasing the amount of air or EGR gas introduced into the stopped compression stroke cylinder, thereby increasing the intake amount of the cylinder. Therefore, the rise of the piston of the stopped compression stroke cylinder is suppressed, and the stopping position of the cylinder is less likely to deviate from the target range to the top dead center side, that is, the stopping position of the cylinder is less likely to deviate from the range suitable for starting.

Moreover, in the present invention, when the oxygen concentration in the intake passage is equal to or higher than a predetermined reference concentration, the opening of the EGR valve is increased, and the intake volume is increased by increasing the EGR gas. EGR gas is a gas that is recirculated from the exhaust passage to the intake passage, and since it contains burnt gas, its oxygen concentration is low. Therefore, even if the amount of EGR gas is increased, the increase in oxygen concentration in the stopped compression stroke cylinder and other cylinders whose intake valves are open is suppressed. Therefore, according to the present invention, while reducing the possibility that the cylinder stop position deviates from the target range as described above, it is possible to suppress the further increase in oxygen concentration in each cylinder when the oxygen concentration in the intake passage is equal to or higher than a predetermined reference concentration, and the associated increase in the amount of NOx generated at engine start.

In addition, when the oxygen concentration is below the reference concentration, the throttle valve opening is increased to increase the amount of intake air by increasing the amount of air. Therefore, when the oxygen concentration is below the reference concentration, the oxygen concentration in each cylinder can be prevented from becoming excessively low, ensuring the combustibility of the mixture when the engine is started, and achieving a good start.

In the above configuration, preferably, when the first condition is satisfied, the control means changes the opening of the throttle valve based on the predicted stop position of the stop-time compression stroke cylinder (claim 2).

With this configuration, the amount of air introduced into the cylinder during the compression stroke at the time of stopping is adjusted based on the stopping position of the cylinder, so that the stopping position of the cylinder can be more reliably kept within the target range.

In the above configuration, preferably, when the second condition is satisfied, the control means changes the opening of the EGR valve based on the predicted stop position of the stop-time compression stroke cylinder (claim 3).

With this configuration, the amount of EGR gas introduced into the cylinder is adjusted based on the stop position of the compression stroke cylinder when stopped, so the stop position of the cylinder can be more reliably kept within the target range.

In the above configuration, preferably, the engine is equipped with a turbocharger including a turbine provided in the exhaust passage and a compressor provided in the intake passage, and the EGR passage is connected to the exhaust passage upstream of the turbine (claim 4).

In this configuration, the length of the EGR passage is shorter than if the EGR passage were connected to the exhaust passage downstream of the turbine. Therefore, EGR gas can be introduced into the intake passage and cylinders soon after the EGR valve is opened. Therefore, when the second condition is met, the amount of EGR gas introduced into the compression stroke cylinder at the time of stop, i.e., the amount of intake air, can be reliably increased before the engine comes to a complete stop, and the stop position of the compression stroke cylinder at the time of stop can be more reliably kept within the target range.

As described above, the engine stop position control device of the present invention can control the position of each cylinder when the engine is stopped to a position suitable for starting, while preventing an increase in the amount of NOx generated immediately after the engine is started.

1 is a schematic configuration diagram of a vehicle equipped with an engine to which a stop position control device according to an embodiment of the present invention is applied; FIG. 2 is a schematic configuration diagram of the engine. FIG. 2 is a schematic cross-sectional view of an engine body. FIG. 2 is a diagram showing the strokes performed in each cylinder of the engine. FIG. 2 is a block diagram showing a control system of the engine. 4 is a graph showing the relationship between a cylinder stop position and a motor torque required for starting the engine. FIG. 4 is a diagram showing a target range of a cylinder stop position. 5 is a flowchart showing a specific procedure for stop position control. FIG. 4 is a diagram showing a range of cylinder stop positions that must be avoided; 5 is a time chart showing the time changes of each parameter when the stop position control is performed in a state where the intake manifold _O2 concentration is less than a reference concentration. 4 is a time chart showing the time changes of each parameter when the stop position control is performed in a state where the intake manifold _O2 concentration is equal to or higher than a reference concentration. 13 is a diagram showing a cylinder stop position when intake valve retard control is not performed. FIG.

(1) Overall Configuration Fig. 1 is a schematic diagram of a vehicle 100 equipped with an engine E to which an engine stop position 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.

As shown in FIG. 1, in addition to wheels 101, an engine E, and a motor M, a vehicle 100 includes a clutch 102 that connects the output shaft of the engine E to the rotating shaft of the motor M in a disconnectable manner, 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 and the like and connects the transmission 104 to the drive shaft 106.

(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 a supply of fuel mainly composed of diesel.

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

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

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.

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 fuel and air supplied to it 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.

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 exhausting 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 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.

Figure 4 shows the strokes performed in each cylinder 2. As mentioned above, engine E is a four-stroke engine. Thus, in each cylinder 2, the 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, the 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 every 120°CA in the following order: first cylinder 2A → fifth cylinder 2E → third cylinder 2C → sixth cylinder 2F → second cylinder 2B → fourth cylinder 2D.

Here, the intake, compression, expansion, and exhaust strokes referred to in this specification refer to the periods obtained by dividing one combustion cycle, i.e. the period during which the crankshaft 7 rotates twice (360° CA), into four equal crank angles, during which intake, compression, expansion, and exhaust are primarily performed, respectively.

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.

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

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 all at once. 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 14a that can change the opening and closing timing of each exhaust valve 12 all at once. The intake S-VT 13a (exhaust S-VT 14a) is a so-called phase-type variable mechanism that changes the valve opening start timing IVO (EVO) and valve closing timing IVC (EVC) of each intake valve 11 (each exhaust valve 12) simultaneously and by the same amount.

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 that order from the upstream side. The compressor 47 is driven to rotate by the turbine 48 as described above, and compresses (supercharges) the air passing through the compressor 47. 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.

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 order from the upstream side, a turbine 48 and an exhaust purification device 41 for purifying the exhaust gas. The exhaust purification device 41 has a built-in 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.

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 the portion of the exhaust passage 40 upstream of the turbine 48 to the 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. In addition, 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 arranged in the EGR passage 44A.

(2) Control System Fig. 5 is a block diagram showing the 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.

Detection signals from various sensors installed in the vehicle 100 are input to the controller 200.

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 the 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 SN4 is provided in the exhaust passage 40 of the engine E to detect an exhaust _O2 concentration, which is the concentration of oxygen contained in the exhaust gas passing through the exhaust passage 40. 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 revolution speed sensor SN5 that detects the revolution speed of the motor M, an accelerator opening sensor SN6 that detects an accelerator opening, which is the opening of an accelerator pedal operated by a driver who drives the vehicle 100, a vehicle speed sensor SN7 that detects the vehicle speed, and the like. Information detected by these sensors SN1 to SN7 is sequentially input to the controller 200.

The controller 200 performs various judgments and calculations based on the input information from each sensor, and controls 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.

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.

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.

Specifically, the controller 200 determines 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 determines that the engine start condition is satisfied when the vehicle speed is equal to or greater than a predetermined engine start speed and the accelerator pedal opening is equal to or greater than a predetermined engine start opening while the engine E is stopped. The controller 200 also determines that the engine stop condition is satisfied when the vehicle speed is less than a predetermined engine stop speed or the accelerator pedal opening is less than a predetermined engine stop opening while the engine E is running. The controller 200 sequentially determines 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.

When the controller 200 determines that the engine start condition is satisfied, it performs engine start control to start the engine E. In the engine start control, the controller 200 first shifts the clutch 102 from the released state to the engaged state. When the clutch 102 is in the 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, the cranking of the engine E is started. When the cranking starts, the controller 200 then injects the first fuel from the injector 15 during the compression stroke into the cylinder 2 that was stopped near the intake bottom dead center BDCi, and causes it to self-ignite and burn. After that, the controller 200 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 the engaged state. As a result, the driving force of the engine E is transmitted to the wheels 101 via the motor M and the transmission 104, etc.

When the controller 200 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. When the fuel supply is stopped, the engine speed decreases and the engine stops. Here, if the engine speed decreases, the engine body 1 and the engine mount supporting it may resonate, increasing the vibration of the engine body 1. Therefore, as the engine stop control, the controller 200 performs a control to fully close the throttle valve 32. In other words, by fully closing the throttle valve 32, the engine speed is reduced early, thereby shortening the period during which the engine speed becomes the resonant speed. 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. In addition, when the engine stop condition is met and the engine E stops (the engine E rotation speed becomes 0), the controller 200 switches the clutch 102 from an engaged state to a released state.

(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, that is, after the fuel cut is performed and the throttle valve 32 is fully closed. The stop position control is a control for placing the position of each cylinder 2 (the piston 5 of each cylinder 2) within a predetermined target range when the engine E is stopped.

In the following, 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. In addition, 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.

In addition, in this specification, a cylinder whose stroke when the engine is stopped (when engine E is completely stopped) is the compression stroke 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 called a compression stroke cylinder at the time of stopping. Also, a cylinder whose combustion order is one before the compression stroke cylinder at the time of stopping, whose stroke when the engine is stopped (when engine E is completely stopped) is the expansion stroke 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 called an expansion stroke cylinder at the time of stopping. In addition, a cylinder whose combustion order is one after the stop-time compression stroke cylinder, 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 stop-time compression transition cylinder.

Figure 6 is a graph showing the relationship between the cylinder stop position and the minimum torque of the motor M required to subsequently start the engine E that has stopped at this cylinder stop position (hereinafter, appropriately, referred to as the starting torque). The horizontal axis of Figure 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. Figure 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 Figure 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.

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 as shown by the solid line in FIG. 6, 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 when the starting torque is minimum is referred to as the optimal position P0.

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, 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 stopped compression stroke cylinder is 40° CA before compression top dead center (BTDCc), the position of the stopped compression transition cylinder is 20° CA after intake bottom dead center (ABDCi), and the position of the stopped expansion stroke cylinder is 80° CA after compression top dead center (ATDCc).

As stop position control, the controller 200 performs intake retard control to prevent the cylinder stop position from being on the retard side of the target range X0, and valve opening increase control to prevent the cylinder stop position from being on the advance side of the target range X0.

The specific steps of the stop position control will be described using the flowchart in Figure 8. Step S1 in the flowchart in Figure 8 is performed after engine stop control has been performed.

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 engine speed is determined to be equal to or greater than the reference speed N2, the controller 200 repeats step S1 to wait 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 engine speed is determined to be less than the reference speed N2, the controller 200 proceeds to step S2.

In step S2, the controller 200 retards the phase of the intake valve 11 by the intake S-VT 13a, retarding 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 to fully close the throttle valve 32 is performed) and more advanced than a second reference timing described later.

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.

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) between the current time and the time the engine stops.

If the determination in step S4 is NO, and it is determined that engine E will not stop at the timing two compression strokes after the current time, controller 200 returns to step S3 and continues predicting the engine stop timing and cylinder stop position.

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 set to 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.

If the determination in step S5 is YES and it is determined that the predicted cylinder stop position is within the avoidance range X1 (if it is determined that the predicted stop position of the compression stroke cylinder at the time of stopping is closer to the top dead center side than the target range X0), in step S6, the controller 200 sets the intake increase amount (valve opening increase control). As described below, if the determination in step S5 is YES, the intake amount of the compression stroke cylinder at the time of stopping is increased, and the above-mentioned intake increase amount is a target value for the increase in this intake amount.

The controller 200 sets the intake increase amount so that the greater the deviation of the predicted stop position of the piston 5 of the compression stroke cylinder at stop from the target range (the deviation from the second position P2, which is the most retarded side of the target range). After step S6, the process proceeds to step S7.

In step S7, the controller 200 judges whether the intake manifold _O2 concentration is equal to or higher than a predetermined reference concentration (valve opening degree increase control). The intake manifold _O2 concentration is the oxygen concentration of the gas in the intake passage 30 downstream of the throttle valve 32. The controller 200 makes this judgment based on the intake manifold O2 concentration when the judgment in step S4 is YES, that is, when it is judged that the engine E will stop after passing the second compression top dead center. In this embodiment, the controller 200 predicts the intake manifold _O2 concentration successively based on the detection value of the exhaust _O2 sensor SN4 while the engine is running, and makes the above judgment in step S7 using _this predicted value. The reference concentration is preset and stored in the controller 200. The reference concentration is set to a value slightly lower than the oxygen concentration in the atmosphere (for example, about 20%).

If the determination in step S7 is NO and the intake manifold _O2 concentration is less than the reference concentration, the process proceeds to step S8, where the controller 200 calculates a throttle opening increase amount, which is an increase amount of the opening of the throttle valve 32 (valve opening increase control). In other words, if the cylinder stop position is in the avoidance required range X1 and the intake manifold _O2 concentration is less than the reference concentration, the opening of the throttle valve 32 is increased (to the open side), and this increase amount of the opening is calculated in step S8. The controller 200 sets the throttle opening increase amount based on the intake increase amount set in step S6. The throttle opening increase amount is set to a larger value as the intake increase amount set in step S6 is larger. After step S8, the process proceeds to step S9.

In step S9, the controller 200 increases the opening of the throttle valve 32 by the throttle opening increase amount calculated in step S8 (valve opening increase control). After step S9, the process proceeds to step S12.

On the other hand, if the determination in step S7 is YES and the intake manifold _O2 concentration is equal to or higher than the reference concentration, the process proceeds to step S10, where the controller 200 calculates an EGR opening increase amount, which is an increase amount of the opening amount of the EGR valve 45 (valve opening increase control). In other words, if the cylinder stop position is in the avoidance required range X1 and the intake manifold _O2 concentration is equal to or higher than the reference concentration, the opening amount of the EGR valve 45 is increased (to the open side), and this increase amount of the opening amount is calculated in step S10. The controller 200 sets the EGR opening increase amount based on the intake increase amount set in step S6. The EGR opening increase amount is set to a larger value as the intake increase amount is larger.

After step S10, the process proceeds to step S11. In step S11, the controller 200 increases the opening of the EGR valve 45 by the amount of increase in the EGR opening calculated in step S10 (valve opening increase control). After step S11, the process proceeds to step S12. Note that when step S9 is performed to increase the opening of the throttle valve 32, the opening of the EGR valve 45 is not changed and is maintained at the opening when it is determined that the engine E will stop after passing the top dead center of the second compression stroke. Also, when step S11 is performed to increase the opening of the EGR valve 45, the opening of the throttle valve 32 is not changed and is maintained at the opening when it is determined that the engine E will stop after passing the top dead center of the second compression stroke.

Steps S5 to S11 are performed immediately after it is determined in step S4 that engine E will stop after passing second compression top dead center. The timing at which it is determined that engine E will stop after passing second compression top dead center is included in the period from when the stopped compression stroke cylinder is at exhaust top dead center TDCe just before the engine stops to when it is at 120° CA after exhaust top dead center TDCe, that is, the period during which the stopped compression stroke cylinder is in the intake stroke. Thus, the increase in the opening of the throttle valve 32 in step S9 or the increase in the opening of the EGR valve 45 in step S11 is performed during the intake stroke of the stopped compression stroke cylinder just before the engine stops.

In step S12, 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 preset 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 step S12 is performed almost simultaneously with the determination in step S4 becoming YES, and when it is determined that the engine E will stop after passing the second compression top dead center, the phase of the intake valve 11 is gradually retarded.

Here, the case where the judgment in step S5 is YES and the judgment in step S7 is NO corresponds to "if the first condition is met" and "when the first condition is met" in the claims, and the case where the judgment in step S5 is YES and the judgment in step S7 is YES corresponds to "if the second condition is met" and "when the second condition is met" in the claims.

10 and 11 are time charts showing the time change of each parameter when the above-mentioned stop position control is performed. In FIG. 10 and FIG. 11, from the top, the charts of the engine speed, the position of the piston 5 of the cylinder 2 in the compression stroke, the phase of the intake valve 11, the opening of the throttle valve 32, the opening of the EGR valve 45, the intake manifold _O2 concentration, and the intake manifold pressure are shown. FIG. 10 is a chart when it is determined that the predicted cylinder stop position is in the avoidance required range X1 (YES in step S5) and the intake manifold _O2 concentration is less than the reference concentration when it is determined that the engine E will stop after passing the second compression top dead center (NO in step S7). FIG. 11 is a chart when it is determined that the predicted cylinder stop position is in the avoidance required range X1 (YES in step S5) and the intake manifold _O2 concentration is equal to or greater than the reference concentration when it is determined that the engine E will stop after passing the second compression top dead center (YES in step S7). 10 and 11 show the changes in each parameter over time after fuel cut is performed.

As shown in Figures 10 and 11, after fuel cut is performed, the engine speed gradually decreases. In the example of Figures 10 and 11, the engine speed becomes equal to or lower than the throttle closing speed N1 at time t1. Accordingly, the throttle valve 32 starts to close at time t1, and then the throttle valve 32 is fully closed. Furthermore, when the engine speed becomes lower than the reference speed N2 at time t2 after the throttle valve 32 is closed, the phase of the intake valve 11 is retarded. In the example of Figures 10 and 11, the intake valve closing timing IVC reaches the first reference timing at time t3, and accordingly the retardation of the phase of the intake valve 11 is stopped, and the intake valve closing timing IVC is maintained at the first reference timing.

10 and 11, at time t4 after time t3, it is determined that the engine E will stop after passing the second compression top dead center. Specifically, in the example of FIG. 10 and FIG. 11, the engine E stops after the fourth cylinder 2D and the first cylinder 2A have exceeded the compression top dead center TDCc and before (without) the fifth cylinder 2E reaches the compression top dead center TDCc, and at time t4 immediately after the second cylinder 2B, which is one cylinder before the fourth cylinder 2D in the combustion order, has exceeded the compression top dead center TDCc, it is determined that the engine E will stop after passing the second compression top dead center. Note that in this example, the fifth cylinder 2E is the stop-time compression stroke cylinder.

When it is determined at time t4 that engine E will stop after passing top dead center of the second compression stroke, retarding of the phase of the intake valve 11, i.e., retarding of the intake valve closing timing IVC, is resumed immediately after time t4. In the example of Figures 10 and 11, the intake valve closing timing IVC reaches the second reference timing at time t6, and accordingly retarding of the phase of the intake valve 11 is stopped and the intake valve closing timing IVC is maintained at the second reference timing. Then, at time t7 after time t6, engine E comes to a complete stop.

Also, immediately after time t4, a determination is made as to whether the predicted cylinder stop position is in the avoidance required range X1. At this time, if it is determined that the predicted cylinder stop position is in the avoidance required range X1, a determination is made immediately thereafter as to whether the intake manifold _O2 concentration is less than the reference concentration. If the intake manifold _O2 concentration is less than the reference concentration when this determination is made, the opening degree of the EGR valve 45 is maintained at the opening degree before the above determination, i.e., before time t4, as shown in FIG. 10. In this embodiment, like the throttle valve 32, the EGR valve 45 is also closed at time t2 and is fully closed a while after time t2. Thus, the EGR valve 45 is maintained fully closed even after time t4. On the other hand, if the intake manifold _O2 concentration is less than the reference concentration, the opening degree of the throttle valve 32 is increased immediately after the above determination, i.e., immediately after time t4. Thereafter, at time t5, when the opening of the throttle valve 32 increases by the above-mentioned throttle opening increase amount, the increase in the opening of the throttle valve 32 is stopped and the opening of the throttle valve 32 is maintained at the increased opening.

In this way, when it is determined that the predicted cylinder stop position is in the avoidance range X1 and the intake manifold _O2 concentration is less than the reference concentration, the opening degree of the throttle valve 32 is increased immediately after time t4 when this determination is made, and as a result, the intake manifold _O2 concentration and the intake manifold pressure increase after time t4, as shown in FIG. 10.

On the other hand, even if it is determined that the predicted cylinder stop position is in the avoidance required range X1, if it is determined that the intake manifold _O2 concentration is equal to or higher than the reference concentration, the opening degree of the throttle valve 32 is maintained at the opening degree before time t4, i.e., fully closed, even after time t4 when this determination is made, as shown in Fig. 11. On the other hand, if the intake manifold _O2 concentration is equal to or higher than the reference concentration, the opening degree of the EGR valve 45 is increased immediately after time t4. Then, at time t5, when the opening degree of the EGR valve 45 is increased by the above-mentioned EGR opening increase amount, the increase in the opening degree of the EGR valve 45 is stopped, and the opening degree of the EGR valve 45 is maintained at the increased opening degree.

11, even when the opening of the EGR valve 45 is increased, the intake manifold pressure increases after time t4, similar to when the opening of the throttle valve 32 is increased. On the other hand, when the opening of the throttle valve 32 is increased as described above, the intake manifold _O2 concentration increases after time t4, whereas when the opening of the EGR valve 45 is increased, as shown in FIG 11, the intake manifold _O2 concentration hardly increases after time t4 and is substantially maintained at the concentration before time t4.

If it is determined at time t4 that the predicted cylinder stop position is not in the avoidance range X1, the openings of the throttle valve 32 and EGR valve 45 are maintained at the values they had before time t4 (in this embodiment, both are fully closed).

(Action, etc.)
As described above, in the above embodiment, when it is determined that the engine E will stop after the second compression top dead center, the intake retard control is performed to retard the phase of the intake valve 11. Therefore, it is possible to prevent the compression stroke cylinder at the time of stopping from shifting toward the bottom dead center side from the target range X0.

Specifically, as shown in FIG. 10 and FIG. 11, when the throttle valve 32 starts to close at time t2, the intake manifold pressure decreases. Even after the throttle valve 32 is fully closed, the intake manifold pressure decreases as the engine speed decreases. However, even if the opening degree of the throttle valve 32 and the EGR valve 45 is not increased, the intake manifold pressure gradually increases from a predetermined time just before the engine is stopped due to the decrease in the intake force of the engine body 1 and the leakage of intake air into the intake passage 30 from the periphery of the throttle valve 32, etc. Just before the engine is stopped, the intake stroke of the stop-time compression stroke cylinder is performed after the intake stroke of the stop-time expansion stroke cylinder. Therefore, if the intake valve closing timing IVC is maintained at a constant time in a state in which the intake manifold pressure just before the engine is stopped, the intake amount of the stop-time expansion stroke cylinder is likely to be greater than the intake amount of the stop-time expansion stroke cylinder as the intake manifold pressure increases. And the force applied from the intake to the piston 5 of the stop-time compression stroke cylinder is likely to be greater than the force applied from the intake to the piston 5 of the stop-time expansion stroke cylinder, so there is a risk that the stop position of the stop-time compression stroke cylinder will shift toward the bottom dead center from the target range X0. In other words, the cylinder stop position may shift toward the advance side from the target range X0 as shown by the solid line in FIG. 12.

On the other hand, by implementing the intake retard control and retarding the phase of the intake valve 11 immediately before the engine is stopped, the retard amount of the intake valve closing timing IVC of the stop-time compression stroke cylinder immediately before the engine is stopped relative to the intake bottom dead center BDCi can be made greater than the retard amount of the stop-time expansion stroke cylinder, and the amount of intake air blowback to the intake port 9 of the stop-time compression stroke cylinder immediately before the engine is stopped can be made greater than the amount of intake air blowback of the stop-time expansion stroke cylinder. This prevents the force applied from the intake air to the piston 5 of the stop-time compression stroke cylinder from becoming excessive relative to the force applied from the intake air to the piston 5 of the stop-time expansion stroke cylinder, and prevents the stop position of the stop-time compression stroke cylinder from shifting toward the bottom dead center side from the target range X0.

In addition, depending on the degree of engine speed reduction just before the engine is stopped and the magnitude of the sliding resistance of the piston, the stopping position of the compression stroke cylinder at the time of stopping may deviate from the target range X0 toward the top dead center side. In contrast, in the above embodiment, if the stopping position of the compression stroke cylinder at the time of stopping is predicted to be closer to the top dead center side than the target range X0, valve opening increase control is implemented to increase the opening of the throttle valve 32 or EGR valve 45 during the intake stroke of the compression stroke cylinder at the time of stopping just before the engine is stopped. Therefore, it is possible to prevent the stopping position of the compression stroke cylinder at the time of stopping from deviating from the target range X0 toward the top dead center side.

Specifically, when the opening of the throttle valve 32 is increased, the amount of air introduced into the cylinder 2 (combustion chamber 6) increases, and the intake amount increases. Also, when the opening of the EGR valve 45 is increased, the amount of EGR gas introduced into the cylinder 2 (combustion chamber 6) increases, and the intake amount increases. As described above, just before the engine stops, the intake stroke of the stop-time compression stroke cylinder is performed after the intake stroke of the stop-time expansion stroke cylinder. Therefore, if the valve opening increase control is performed to increase the opening of the throttle valve 32 or the EGR valve 45 when the stop-time compression stroke cylinder is in the intake stroke, the intake amount of the stop-time compression stroke cylinder can be made greater than the intake amount of the stop-time expansion stroke cylinder, and the force that the intake air imparts to the piston 5 of the stop-time compression stroke cylinder can be made greater than the force that the intake air imparts to the piston 5 of the stop-time expansion stroke cylinder. This prevents the stopping position of the compression stroke cylinder from shifting toward the top dead center from the target range X0.

In this way, according to the above embodiment, the stop position of the compression stroke cylinder at the time of stopping can be prevented from shifting toward the bottom dead center or top dead center from the target range X0. As a result, according to the above embodiment, the torque of the motor M consumed to start the engine can be more reliably reduced.

Moreover, in the above embodiment, when the intake manifold _O2 concentration, i.e., the oxygen concentration in the intake passage 30, is equal to or higher than the reference concentration, the control for increasing the opening of the EGR valve 45 is performed as the valve opening increase control, and the intake amount is increased by increasing the EGR gas. The EGR gas contains burnt gas and therefore has a low oxygen concentration. As a result, even if the intake amount is increased by increasing the EGR gas, the increase in the oxygen concentration in the intake passage 30 and the oxygen concentration in the cylinder 2 (combustion chamber 6) is suppressed. Therefore, according to the above embodiment, it is possible to prevent the stop position of the compression stroke cylinder at the time of stopping from shifting toward the top dead center side from the target range X0, while preventing the oxygen concentration in the intake passage 30 and the cylinder 2 (combustion chamber 6) from further increasing when the oxygen concentration in the intake passage 30 is equal to or higher than the reference concentration. Here, if the oxygen concentration in the intake passage 30 and the cylinder 2 (combustion chamber 6) is high immediately before the engine is stopped, this concentration is almost maintained even after the engine is stopped, so that the amount of NOx generated in the engine E increases the next time the engine E is started. Therefore, according to the above embodiment, it is possible to suppress an increase in the amount of NOx produced when the engine is started, while suppressing the stop position of the stop-time compression stroke cylinder from shifting toward the top dead center side from the target range X0.

In the above embodiment, when the intake manifold _O2 concentration, i.e., the oxygen concentration in the intake passage 30, is less than the reference concentration, control is performed to increase the opening of the throttle valve 32 as valve opening increase control, and the intake amount is increased by increasing the amount of air. Therefore, when the oxygen concentration in the intake passage 30 is relatively low, the oxygen concentration in the intake passage 30 and the cylinder 2 (combustion chamber 6) is prevented from becoming further lower. Therefore, while preventing the stop position of the stop-time compression stroke cylinder from shifting toward the top dead center side from the target range X0, the oxygen concentration in the cylinder 2 (combustion chamber 6) at the time of engine start can be secured, thereby improving the combustibility of the mixture at the time of engine start, and thus the startability.

In addition, in the above embodiment, when the opening of the throttle valve 32 and the EGR valve 45 is increased, the intake increase amount is set based on the deviation amount of the predicted stop position of the compression stroke cylinder at the time of stopping from the target range X0, and the increase amount of the opening of the throttle valve 32 and the EGR valve 45 is set based on this intake increase amount. In other words, the increase amount of the opening of the throttle valve 32 and the EGR valve 45 is set based on the predicted stop position of the compression stroke cylinder at the time of stopping. Therefore, these openings can be reliably changed to an opening that can position the stop position of the compression stroke cylinder at the time of stopping within the target range X0, and the stop position can be more reliably positioned within the target range X0.

In addition, in the above embodiment, the EGR passage 44A is connected to the exhaust passage 40 upstream of the turbine 48. In other words, the EGR passage 44A is connected to the exhaust passage 40 so that the passage length of the EGR passage 44A is shorter than when the EGR passage 44A is connected to the exhaust passage 40 downstream of the turbine 48. Therefore, after the EGR valve 45 is opened, the EGR gas can be introduced into the intake passage 30 and the stop-time compression stroke cylinder early. Therefore, when it is determined that the predicted cylinder stop position is within the avoidance range X1 and the opening degree of the EGR valve 45 is increased, the amount of EGR gas introduced into the stop-time compression stroke cylinder can be reliably increased before the engine E completely stops, and the stop position of the cylinder can be more reliably within the target range X0.

(Modification)
In the above embodiment, the intake retard control for retarding the phase of the intake valve 11 immediately before the engine E is stopped is always performed, but the control may be performed only when a predetermined condition is satisfied, such as when the predicted cylinder stop position is on the retard side of the target range X0. Also, the intake retard control may be omitted.

In the above embodiment, the amount of increase in the opening of the throttle valve 32 and the EGR valve 45 in the valve opening increase control is set based on the predicted stop position of the compression stroke cylinder at the time of stopping. However, the amount of increase may be a constant amount regardless of the stop position.

In addition, in the above embodiment, the engine E is described as 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, etc.

Reference Signs List 1 engine body 2 cylinder 5 piston 7 crankshaft 11 intake valve 13a intake S-VT
15 Injector (fuel supply means)
30 Intake passage 32 Throttle valve 40 Exhaust passage 44A EGR passage 45 EGR valve 200 Controller (control means)
E engine M motor (starting means)

Claims (4)

A stop position 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, an intake passage through which intake air introduced into each cylinder flows, and an exhaust passage through which exhaust gas discharged from each cylinder flows,
a throttle valve disposed in the intake passage for opening and closing the intake passage;
an EGR passage that connects the intake passage downstream of the throttle valve with the exhaust passage and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage;
an EGR valve that opens and closes the EGR passage;
a control means for controlling each part of the engine including the fuel supply means, the throttle valve, and the EGR valve, and for executing a fuel cut to stop the supply of fuel into the cylinders by the fuel supply means when a predetermined engine stop condition is established,
the control means predicts a stop position of a stopped compression stroke cylinder, which is a cylinder that stops during a compression stroke after the fuel cut is performed, and when the predicted stop position of the stopped compression stroke cylinder is on the top dead center side of a predetermined target range, performs a valve opening increase control to increase an opening of the throttle valve or an opening of the EGR valve during an intake stroke immediately before the stop of the stopped compression stroke cylinder;
an intake passage having an oxygen concentration in the intake passage that is greater than a predetermined reference concentration, the control means increasing the opening of the throttle valve as the valve opening increase control when a first condition is satisfied, and increasing the opening of the EGR valve as the valve opening increase control when a second condition is satisfied, the oxygen concentration in the intake passage that is greater than or equal to the reference concentration. 2. The engine stop position control device according to claim 1,
2. An engine stop position control device comprising: a control means for changing an opening degree of the throttle valve based on a predicted stop position of the compression stroke cylinder at the time of stop when the first condition is satisfied. 3. The engine stop position control device according to claim 1,
When the second condition is satisfied, the control means changes an opening degree of the EGR valve based on the predicted stop position of the compression stroke cylinder at the time of stop. In the engine stop position control device according to any one of claims 1 to 3,
the engine includes a turbocharger including a turbine provided in the exhaust passage and a compressor provided in the intake passage,
13. An engine stop position control device, comprising: an exhaust gas recirculation (EGR) passage connected to an exhaust passage upstream of the turbine;

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