JP7743752B2 - Engine control device and control method - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Sales will begin at dealerships that handle Mazda vehicles in Europe on September 28, 2021.

The present invention relates to technology for controlling an engine equipped with intake and exhaust valves.

Deposits can form (become stuck) between the intake valve and the valve seat, or between the exhaust valve and the valve seat. Deposits can cause compression leaks, in which compressed air leaks from the combustion chamber through the intake or exhaust port. Compression leaks can cause poor ignition, in which the air-fuel mixture in the combustion chamber does not burn properly (or misfires).

An engine that incorporates the aforementioned measures to prevent deposit buildup is known as the one described in Patent Document 1 below. In this engine, the presence or absence of deposit buildup is determined during deceleration fuel cutoff, and if deposit buildup is determined, control is implemented such as increasing the opening of the intake shutter valve. Increasing the opening of the intake shutter valve has the effect of increasing the pressure in the combustion chamber, increasing the likelihood that deposits will be crushed (removed).

Patent No. 6531780

As mentioned above, in Patent Document 1, deposit buildup determination and countermeasure control are only performed during deceleration fuel cutoff. In other words, no special countermeasures are taken even if deposits buildup occurs during engine combustion operation, i.e., operation involving the combustion of the air-fuel mixture in the combustion chamber. This raises concerns that countermeasures for deposits may be delayed. In other words, even if deposits buildup during engine combustion operation, no countermeasures are taken until the operating mode subsequently transitions to deceleration fuel cutoff, meaning that compression leakage and misfires caused by the deposits may continue for some time. In particular, if deposits buildup when the engine is idling or at a low rotation speed close to idling, compression leakage and misfires may occur when the engine's rotational inertia is low, potentially causing the engine to stall (stalling).

It is therefore proposed that some kind of deposit control measures be taken even while the engine is in combustion operation. However, depending on the content of the measures, this may affect the engine's emissions performance or fuel economy, so it is desirable to take appropriate measures that take these effects into consideration.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide an engine control device that can quickly take measures against deposits while reducing the impact on emissions performance or fuel economy.

In order to solve the above-mentioned problem, one aspect of the present invention provides an engine control device that controls an engine having a combustion chamber, an intake passage connected to the combustion chamber via an intake port, an exhaust passage connected to the combustion chamber via an exhaust port, an intake valve and an exhaust valve that open and close the intake port and the exhaust port, and an EGR passage that connects the intake passage and the exhaust passage, and that includes a fuel injection valve that injects fuel into the combustion chamber, an EGR valve that can be opened and closed in the EGR passage, an accessory that receives driving force from the engine to perform work, and a rotation detection unit that detects the engine speed, which is the rotation speed of the output shaft of the engine. The engine is equipped with a compression leak detection unit that detects compression leaks, which are air leaks from the combustion chamber through the intake port or the exhaust port during the compression stroke, and a controller that controls the fuel injection valve, the EGR valve, and the accessories. When compression leaks are detected by the compression leak detection unit, the controller executes a first control that limits the operation of the accessories, and when, after the first control, it is confirmed that the engine speed detected by the rotation detection unit is equal to or lower than a predetermined threshold, the controller executes a second control that involves at least one of reducing the opening of the EGR valve and increasing the amount of fuel injected from the fuel injection valve.

Detecting compression leakage indicates a high possibility of deposits on the intake or exhaust valve seat. In this invention, accessory operation is first restricted in such cases, thereby reducing the reverse torque applied to the engine by the accessory and reducing engine rotational resistance (external load). Furthermore, accessory operation restriction can be achieved in a short time, allowing for responsive reduction in engine rotational resistance. Reducing rotational resistance makes it easier to maintain engine rotation, even if poor ignition of the mixture occurs due to deposit buildup (compression leakage). In other words, reducing rotational resistance in response to accessory operation restriction reduces the likelihood of the engine stalling (stalling) due to poor ignition.

However, if the above-mentioned misfire occurs when the engine speed is relatively low (in other words, when rotational inertia is low), there is a high possibility that engine rotation cannot be maintained (leading to a stall) simply by limiting the operation of the accessories. In contrast, with the present invention, when the engine speed after limiting the operation of the accessories is below a predetermined threshold, control is executed to reduce the opening of the EGR valve or to increase the fuel injection amount, thereby preventing the occurrence of a stall due to the above-mentioned circumstances. In other words, when the opening of the EGR valve is reduced, the proportion of EGR gas, which is an inert gas, in the combustion chamber decreases, improving the ignition ability of the mixture. Furthermore, when the fuel injection amount is increased, the ignition ability of the mixture also improves. This reduces the possibility of misfire when the engine speed is low, effectively preventing the occurrence of a stall.

Furthermore, in the present invention, the above-mentioned control of changing the EGR valve opening or fuel injection amount is not performed unless the engine speed falls below a threshold, thereby reducing the possibility of affecting emissions performance or fuel economy. Reducing the EGR valve opening raises the combustion temperature in the combustion chamber, increasing the amount of NOx produced. Furthermore, increasing the fuel injection amount reduces fuel economy. In contrast, in the present invention, even if compression leakage is detected, these measures are not taken until the engine speed falls below a threshold, thereby reducing the possibility of an increase in NOx production or a decrease in fuel economy. In particular, if compression leakage is detected when the engine speed exceeds a threshold and the operation of accessories is restricted in response, deposits may be removed while the engine speed is maintained, eliminating the compression leakage before the engine speed falls below the threshold. In such cases, changing the EGR valve opening or fuel injection amount to address deposits is unnecessary, thereby minimizing the impact on emissions performance or fuel economy. In this way, the present invention can prevent engine stalls due to deposit buildup while reducing the impact on engine emissions and fuel economy.

The auxiliary equipment may include a generator that generates electricity using driving force from the engine. In this case, the first control may include control to stop power generation by the generator or to reduce the amount of power generated.

This configuration allows the engine's rotational resistance to be reduced quickly and appropriately by stopping power generation or reducing the amount of power generated.

Preferably, the compression leakage detection unit detects the compression leakage based on a first time required for the engine to pass through a first crank angle range that is included in the compression stroke or that crosses over the compression top dead center, and a second time required for the engine to pass through a second crank angle range that is included in the expansion stroke immediately after the compression stroke and is more retarded than the first crank angle range.

This configuration makes it possible to accurately detect compression leaks by utilizing the fact that the relationship between the first time and the second time changes depending on whether or not there is a compression leak. In other words, when a compression leak occurs, the compression reaction force acting on the piston during the compression stroke decreases, reducing the amount of change in the piston's movement speed before and after passing top dead center, causing a change in the relationship between the first time and the second time. This configuration makes it possible to accurately detect compression leaks by utilizing this fact.

The engine may be an in-vehicle engine connected to the wheels via an automatic transmission that can automatically change the reduction ratio. In this case, if it is determined after the first control that compression leakage has occurred while the engine speed is higher than the threshold, the controller preferably executes third control that controls the automatic transmission to maintain the engine speed high.

With this configuration, the automatic transmission can be controlled to maintain high engine speeds while the vehicle is running, reducing the possibility of the engine stalling.

The automatic transmission may include a lock-up clutch that directly connects the engine output shaft to the wheels. In this case, the third control preferably includes at least one of control to expand the lock-up region, which is the range of engine speeds at which the lock-up clutch is engaged, to the low-speed side, and control to change the shift pattern so that the engine speed at which a downshift that increases the reduction ratio (downshift speed) is performed is higher.

If the shift pattern is changed to increase the downshift RPM, downshifts will occur earlier than usual, for example, when the vehicle is decelerating. This allows the reduction ratio to be increased before engine RPM drops sufficiently, and the increased reduction ratio can be used to raise engine RPM. Furthermore, if the lockup region is expanded to the low RPM side, the lockup state (a state in which the engine output shaft is directly connected to the wheels) will be maintained up to lower engine RPMs than usual, for example, when the vehicle is decelerating. This allows the engine output shaft to continue rotating in sync with the wheels, and the rotational energy of the wheels can be used to suppress a drop in engine RPM. In either case, engine RPM is maintained relatively high, reducing the possibility of stalling.

According to another aspect of the present invention, there is provided a method for controlling an engine including a combustion chamber, an intake passage connected to the combustion chamber via an intake port, an exhaust passage connected to the combustion chamber via an exhaust port, an intake valve and an exhaust valve for opening and closing the intake port and the exhaust port, an EGR passage connecting the intake passage and the exhaust passage, a fuel injection valve for injecting fuel into the combustion chamber, an EGR valve provided in the EGR passage so as to be able to open and close, an output shaft, and an accessory that performs work by receiving driving force from the output shaft , the method comprising the steps of: It includes a first step of detecting compression leakage, which is a phenomenon in which air leaks through the intake port or the exhaust port; a second step of restricting the operation of the auxiliary equipment if the compression leakage is detected in the first step; a third step of detecting the engine speed, which is the rotation speed of the output shaft, after the second step; and a fourth step of reducing the opening of the EGR valve and increasing the amount of fuel injected from the fuel injection valve if it is confirmed that the engine speed detected in the third step is below a predetermined threshold.

This control method invention can also achieve the same effects as the control device invention described above.

As described above, the engine control device and control method of the present invention enable rapid deposit countermeasures to be implemented while reducing the impact on emissions performance or fuel economy.

1 is a system diagram showing the overall configuration of an engine to which a control device according to an embodiment of the present invention is applied; FIG. 2 is a cross-sectional view showing details of an intake/exhaust valve and its valve operating mechanism. FIG. 2 is a plan view schematically showing the structure of a power transmission system between an engine and wheels. FIG. 2 is a functional block diagram showing a control system for an engine and an automatic transmission. 4 is a flowchart showing an example of countermeasure control against deposit adhesion to a valve seat portion. FIG. 10 is a diagram for explaining a method for calculating a compression state index value.

[Overall engine configuration]
1 is a system diagram showing the overall configuration of an engine to which a control device according to one embodiment of the present invention is applied. The engine 1 shown in this diagram is a four-stroke diesel engine mounted on a vehicle as a power source for driving the vehicle. The engine 1 includes an engine body 2, an intake passage 30 through which intake air introduced into the engine body 2 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 2 flows, an EGR device 50 that recirculates a portion of the exhaust gas flowing through the exhaust passage 40 back to the intake passage 30, and a supercharger 60 that supercharges the intake air flowing through the intake passage 30.

The engine body 2 is, for example, a multi-cylinder engine having multiple cylinders 2a aligned in a direction perpendicular to the plane of the paper in FIG. 1 (see also FIG. 3, described later). The engine body 2 includes a cylinder block 3, a cylinder head 4, and multiple pistons 5. The cylinders 2a are formed by the cylinder block 3 and the cylinder head 4. That is, multiple cylindrical spaces corresponding to the multiple cylinders 2a are formed inside the cylinder block 3, and the cylinder head 4 is attached to the upper surface of the cylinder block 3 so as to close off these cylindrical spaces from above. A piston 5 is housed in each cylinder 2a so that it can slide back and forth. Note that in this embodiment, the side from the cylinder block 3 toward the cylinder head 4 is referred to as the top, and the opposite is referred to as the bottom; however, this is for convenience of explanation and is not intended to limit the installation orientation of the engine body 2.

A combustion chamber C is formed above the piston 5 of each cylinder 2a. Each combustion chamber C is a space defined by the lower surface of the cylinder head 4, the side surface (cylinder liner) of the cylinder 2a, and the upper surface (crown surface) of the piston 5. The combustion chamber C is supplied with fuel injected from a fuel injection valve 9, which will be described later. The piston 5 receives the combustion energy of the fuel supplied to the combustion chamber C and reciprocates up and down. Note that, because the engine 1 of this embodiment is a diesel engine, fuel containing diesel is used as the fuel supplied to the combustion chamber C.

The crankshaft 7, which is the output shaft of the engine body 2, is located at the bottom of the cylinder block 3 (below the pistons 5). The crankshaft 7 is connected to the pistons 5 of each cylinder 2a via connecting rods 8, and rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 5.

A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3. The crank angle sensor SN1 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotation speed of the crankshaft 7. The water temperature sensor SN2 is a sensor that detects the temperature of the cooling water flowing inside the cylinder block 3 and cylinder head 4, i.e., the engine water temperature. The crank angle sensor SN1 corresponds to the "rotation detection unit" in this invention.

Fuel injection valves 9 are attached to the cylinder head 4. Each fuel injection valve 9 injects fuel into the combustion chamber C of each cylinder 2a, and one fuel injection valve 9 is provided for each cylinder 2a.

The fuel injection valve 9 is attached to the cylinder head 4 so that its tip is exposed to the combustion chamber C. The tip of this fuel injection valve 9 is formed with multiple nozzle holes (not shown) that serve as fuel outlets. The fuel injected from each nozzle hole is burned by self-ignition in the combustion chamber C, which is heated and pressurized by the compression action of the piston 5.

The cylinder head 4 is formed with intake ports 11 and exhaust ports 12. The intake ports 11 are ports that connect the combustion chambers C of each cylinder 2a to the intake passage 30. The exhaust ports 12 are ports that connect the combustion chambers C of each cylinder 2a to the exhaust passage 40. An intake valve 13 is provided in the intake ports 11 of each cylinder 2a, and an exhaust valve 14 is provided in the exhaust ports 12 of each cylinder 2a.

The cylinder head 4 is equipped with an intake valve train 15 and an exhaust valve train 16. The intake valve train 15 is a mechanism that drives the intake valves 13 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The exhaust valve train 16 is a mechanism that drives the exhaust valves 14 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The intake valves 13 periodically open and close the opening of the intake port 11 on the combustion chamber C side in response to the drive of the intake valve train 15. The exhaust valves 14 periodically open and close the opening of the exhaust port 12 on the combustion chamber C side in response to the drive of the exhaust valve train 16.

An alternator 18 is connected to the crankshaft 7 via a transmission member such as a belt. The alternator 18 is a generator that generates electricity using driving force from the crankshaft 7, and is a type of auxiliary equipment for the engine 1. The alternator 18 has a built-in regulator circuit (not shown) for adjusting the amount of electricity generated. The regulator circuit can adjust the amount of electricity generated depending on conditions such as the vehicle's electrical load and remaining battery charge.

The intake passage 30 is a tubular member for introducing intake air into the combustion chamber C of each cylinder 2a. The intake passage 30 has an intake manifold 30a and a surge tank 30b in its downstream section near the engine body 2. The surge tank 30b is a tank that provides an expanded space for equalizing the amount of intake air introduced to each cylinder 2a. The intake manifold 30a includes multiple branch pipes that connect the surge tank 30b to the intake ports 11 of each cylinder 2a. The section of the intake passage 30 upstream of the surge tank 30b is formed as a single pipe.

An air cleaner 31, an intercooler 32, and an intake shutter valve 33 are provided in the intake passage 30 upstream of the surge tank 30b. The air cleaner 31 is a filter that removes foreign matter from the intake air. The intercooler 32 is a heat exchanger that cools the intake air compressed by the supercharger 60. The intake shutter valve 33 is an electrically operated butterfly valve that is installed in the intake passage 30 and can be opened and closed to throttle the flow rate of the intake air. The air cleaner 31, intercooler 32, and intake shutter valve 33 are arranged in this order from the upstream side furthest from the engine main body 2.

An air flow sensor SN3 and an intake pressure sensor SN4 are attached to the intake passage 30. The air flow sensor SN3 is a sensor that detects the flow rate of intake air introduced into the engine body 2, and is located downstream of the air cleaner 31 in the intake passage 30. The intake pressure sensor SN4 is a sensor that detects the pressure of the intake air introduced into the engine body 2, and is located in the surge tank 30b.

The exhaust passage 40 is a tubular member for discharging exhaust gases discharged from the combustion chambers C of each cylinder 2a to the outside. The exhaust passage 40 has an exhaust manifold 40a in its upstream section, close to the engine body 2. Although not shown in detail, the exhaust manifold 40a includes multiple branch pipes that communicate with the exhaust ports 12 of each cylinder 2a, and an exhaust manifold where these branch pipes converge. The section of the exhaust passage 40 downstream of the exhaust manifold 40a (exhaust manifold) is formed as a single pipe.

A catalytic converter 41 is provided downstream of the exhaust manifold 40a in the exhaust passage 40. The catalytic converter 41 contains an oxidation catalyst 41a that oxidizes and neutralizes CO and HC in the exhaust gas, and a DPF (diesel particulate filter) 41b that captures particulate matter contained in the exhaust gas.

The supercharger 60 is a so-called two-stage supercharger, and is equipped with a first supercharger 61 and a second supercharger 62 arranged in series.

The first supercharger 61 is a turbocharger including a first compressor 61a arranged in the intake passage 30 and a first turbine 61b coaxially connected to the first compressor 61a and arranged in the exhaust passage 40. The first compressor 61a is arranged in a portion of the intake passage 30 between the air cleaner 31 and the intercooler 32. The first turbine 61b is arranged in a portion of the exhaust passage 40 upstream of the catalytic converter 41.

Similarly, the second supercharger 62 is a turbocharger including a second compressor 62a disposed in the intake passage 30 and a second turbine 62b coaxially connected to the second compressor 62a and disposed in the exhaust passage 40. The second compressor 62a is disposed downstream of the first compressor 61a in the intake passage 30, i.e., between the first compressor 61a and the intercooler 32. The second turbine 62b is disposed upstream of the first turbine 61b in the exhaust passage 40.

The first supercharger 61 is a turbocharger that is larger than the second supercharger 62. That is, the first compressor 61a and the first turbine 61b are larger in size than the second compressor 62a and the second turbine 62b.

An intake bypass passage 63 is connected to the intake passage 30. The intake bypass passage 63 is a passage for bypassing the second compressor 62a. An electrically operated bypass valve 63a is provided in the intake bypass passage 63 so that it can be opened and closed.

A first exhaust bypass passage 64 and a second exhaust bypass passage 65 are connected to the exhaust passage 40. The first exhaust bypass passage 64 is a passage for bypassing the first turbine 61b, and the second exhaust bypass passage 65 is a passage for bypassing the second turbine 62b. An electrically operated wastegate valve 64a is provided in the first exhaust bypass passage 64 so that it can be opened and closed. An electrically operated regulator valve 65a is provided in the second exhaust bypass passage 65 so that it can be opened and closed.

When supercharging is performed by the first supercharger 61, the wastegate valve 64a is closed. This allows exhaust gas discharged from the engine body 2 to be introduced into the first turbine 61b, which is rotated and driven by the exhaust gas. The first compressor 61a rotates in conjunction with the first turbine 61b, compressing the intake air downstream. In other words, the first supercharger 61 achieves supercharging by compressing the intake air in the intake passage 30 and sending it to the engine body 2.

When supercharging is performed by the second supercharger 62, the regulator valve 65a and bypass valve 63a are closed. As a result, exhaust gas discharged from the engine body 2 is introduced into the second turbine 62b, which is rotated and driven by the exhaust gas. The second compressor 62a rotates in conjunction with the second turbine 62b, compressing the intake air downstream. In other words, the second supercharger 62 achieves supercharging by compressing the intake air in the intake passage 30 and sending it to the engine body 2.

The EGR device 50 includes an EGR passage 51, an EGR cooler 52, and an EGR valve 53. The EGR passage 51 is a passage for recirculating exhaust gas from the exhaust passage 40 to the intake passage 30, and connects the exhaust passage 40 and the intake passage 30 to each other. Specifically, the EGR passage 51 connects a portion of the exhaust passage 40 upstream of the second turbine 62b with a portion of the intake passage 30 between the intake shutter valve 33 and the surge tank 30b. The EGR cooler 52 is a heat exchanger that cools the exhaust gas, i.e., EGR gas, recirculated to the intake passage 30 through the EGR passage 51. The EGR valve 53 is an electrically operated valve provided in the EGR passage 51 to adjust the amount of exhaust gas recirculated, i.e., the EGR amount. The EGR valve 53 is located downstream of the EGR cooler 52 in the EGR passage 51 (closer to the intake passage 30).

[Details of intake and exhaust valves]
2 is a cross-sectional view showing the intake and exhaust valves 13, 14 and their valve operating mechanisms 15, 16 of the engine body 2 in detail. As shown in this figure, the intake valve 13 has a stem portion 13a and an umbrella portion 13b. The stem portion 13a is a vertically long, cylindrical member that is supported by the cylinder head 4 so as to be slidable in the axial direction (vertical direction). The umbrella portion 13b is a disk-shaped member that can close the opening of the intake port 11 on the combustion chamber C side, and is formed so that its diameter expands from the lower end of the stem portion 13a.

Similarly, the exhaust valve 14 has a stem portion 14a and an umbrella portion 14b. The stem portion 14a is a vertically long, cylindrical member that is supported by the cylinder head 4 so that it can slide axially (vertically). The umbrella portion 14b is a disk-shaped member that can close the opening of the exhaust port 12 on the combustion chamber C side, and is formed so that its diameter expands from the lower end of the stem portion 14a.

Valve seats 11a and 12a are attached to the cylinder head 4. The valve seat 11a is a ring-shaped member attached to the opening of the intake port 11 on the combustion chamber C side, and comes into tight contact with the periphery of the head portion 13b of the intake valve 13 when the valve is closed. The valve seat 12a is a ring-shaped member attached to the opening of the exhaust port 12 on the combustion chamber C side, and comes into tight contact with the periphery of the head portion 14b of the exhaust valve 14 when the valve is closed.

The intake valve mechanism 15 includes a camshaft 21, a swing arm 23, and a valve spring 25. The camshaft 21 is a rotatable shaft connected to the crankshaft 7 via a transmission member such as a timing chain. Specifically, the camshaft 21 includes a shaft portion 21a extending in the direction in which the cylinders 2a are aligned (a direction perpendicular to the plane of the paper in Figure 2) and multiple cam portions 21b provided on the shaft portion 21a at positions corresponding to the intake valves 13 of each cylinder 2a. The swing arm 23 is swingably supported below the cam portions 21b of each cylinder 2a. The valve spring 25 is attached to the cylinder head 4 in a state that biases the intake valves 13 in a closing direction (upward). As the camshaft 21 rotates, the intake valves 13 periodically open due to downward pressure transmitted from the cam portions 21b via the swing arm 23. On the other hand, when this pressing force is not acting, the intake valve 13 is maintained in a closed state in which the head portion 13b is in close contact with the valve seat 11a due to the upward biasing force of the valve spring 25.

Similarly, the exhaust valve mechanism 16 includes a camshaft 22, a swing arm 24, and a valve spring 26. The camshaft 22 is a rotatable shaft connected to the crankshaft 7 via the transmission member. Specifically, the camshaft 22 includes a shaft portion 22a extending in the direction in which the cylinders 2a are aligned (a direction perpendicular to the plane of FIG. 2 ) and multiple cam portions 22b provided on the shaft portion 22a at positions corresponding to the exhaust valves 14 of each cylinder 2a. The swing arm 24 is swingably supported below the cam portions 22b of each cylinder 2a. The valve spring 26 is attached to the cylinder head 4 in a state that biases the exhaust valves 14 in a closing direction (upward). As the camshaft 22 rotates, the exhaust valves 14 periodically open due to downward pressure transmitted from the cam portion 22b via the swing arm 24. On the other hand, when this pressing force is not acting, the exhaust valve 14 is maintained in a closed state in which the head portion 14b is in close contact with the valve seat 12a due to the upward biasing force of the valve spring 26.

[Power system]
FIG. 3 is a plan view schematically showing the structure of a power transmission system that transmits the output of the engine 1 to the wheels W1 of the vehicle. The vehicle in this example is a front-engine, rear-wheel-drive (FR) vehicle. Therefore, in FIG. 3, the wheels W1 are rear wheels, and the engine body 2 is located in an engine compartment at the front of the vehicle. Note that FIG. 3 shows an in-line four-cylinder engine body 2 having four cylinders 2a arranged in a row, but the number and arrangement of the cylinders 2a can be changed as appropriate.

As shown in FIG. 3, the power transmission system of the vehicle in this embodiment includes an automatic transmission 101 connected to the engine main body 2, a propeller shaft 102 extending rearward from the automatic transmission 101, a differential 103 connected to the rear end of the propeller shaft 102, and a pair of drive shafts 104 extending left and right from the differential 103. A wheel W1 is attached to each end of each drive shaft 104 in the vehicle width direction. The output rotation of the engine main body 2 is changed in speed by the automatic transmission 101 and then input to the differential 103 via the propeller shaft 102. The rotation input to the differential 103 is transmitted to each wheel W1 via the left and right drive shafts 104.

The automatic transmission 101 includes a torque converter 110 and a transmission body 120. The torque converter 110 is a fluid clutch that transmits the output rotation of the engine body 2, i.e., the rotation of the crankshaft 7, to the transmission body 120 via an actuating fluid (ATF). The transmission body 120 is a device that transmits the rotation input from the torque converter 110 to the wheels W1 while changing the speed.

The torque converter 110 incorporates a pump impeller 111 that rotates integrally with the crankshaft 7 of the engine main body 2, a turbine runner 112 that faces the pump impeller 111, and a stator 113 that is positioned between the pump impeller 111 and the turbine runner 112. The rotation of the pump impeller 111 is transmitted to the turbine runner 112 via the working fluid in the torque converter 110. The rotation of the turbine runner 112 is input to the transmission main body 120 via the turbine shaft 114.

A lock-up clutch 115 is provided inside the torque converter 110. The lock-up clutch 115 is a clutch that connects and disconnects the crankshaft 7 of the engine main body 2 and the turbine runner 112. When the lock-up clutch 115 is engaged to connect the crankshaft 7 and the turbine runner 112, the crankshaft 7 and the turbine shaft 114 (the input shaft of the transmission main body 120) are mechanically connected without the intervention of a fluid, and the rotation of the crankshaft 7 is transmitted directly to the wheel W1. In other words, the lock-up clutch 115 is a clutch that directly connects the output shaft (crankshaft 7) of the engine 1 and the wheel W1.

Engaging the lock-up clutch 115 improves power transmission efficiency. However, if the lock-up clutch 115 is engaged when the engine speed or vehicle speed is low, vibrations from the engine 1 are more likely to be transmitted to the vehicle. For this reason, the lock-up clutch 115 is engaged under specified conditions except when the engine speed or vehicle speed is low, and is released (disengaged) when the engine speed or vehicle speed is low.

The transmission main body 120 incorporates a multi-stage transmission mechanism 121 capable of achieving multiple gear stages with different reduction ratios. The transmission mechanism 121 includes a gear mechanism 122 that combines multiple planetary gear sets, multiple frictional engagement elements (not shown) including clutches and brakes that are engaged or disengaged to switch the power transmission path through the gear mechanism 122, and a hydraulic control valve 123 (Figure 4) consisting of a solenoid valve or the like that controls the hydraulic pressure supplied to each frictional engagement element to switch its engagement/disengagement. The hydraulic control valve 123 engages or disengages the appropriate frictional engagement elements, thereby achieving the desired gear stage in the transmission mechanism 121 according to the vehicle speed, etc. The output rotation of the torque converter 110, i.e., the rotation of the turbine shaft 114, is transmitted to the propeller shaft 102 (and ultimately the wheels W1) after being shifted at a reduction ratio corresponding to the gear stage of the transmission mechanism 121.

[Control system]
4 is a functional block diagram showing a control system for the engine 1 and automatic transmission 101. The PCM 70 shown in this diagram is a microprocessor for overall control of the engine 1 and automatic transmission 101, and is composed of a well-known CPU, ROM, RAM, etc. The PCM 70 corresponds to the "controller" in the present invention.

Detection information from various sensors is input to the PCM70. For example, the PCM70 is electrically connected to the crank angle sensor SN1, water temperature sensor SN2, air flow sensor SN3, and intake pressure sensor SN4 mentioned above. Information detected by each of these sensors (i.e., information such as crank angle, engine speed, engine water temperature, intake air flow rate, and intake pressure) is sequentially input to the PCM70.

The vehicle is also equipped with an accelerator sensor SN5 and a vehicle speed sensor SN6. The accelerator sensor SN5 is a sensor that detects the degree of depression of the accelerator pedal operated by the driver of the vehicle, i.e., the accelerator opening degree. The vehicle speed sensor SN6 is a sensor that detects the traveling speed of the vehicle, i.e., the vehicle speed. The detection information from these accelerator sensor SN5 and vehicle speed sensor SN6 is also input sequentially to the PCM 70.

The PCM 70 controls each part of the engine 1 and automatic transmission 101 based on the input information from each of the sensors SN1 to SN6. That is, the PCM 70 is electrically connected to the fuel injection valve 9, alternator 18, intake shutter valve 33, EGR valve 53, bypass valve 63a, wastegate valve 64a, and regulator valve 65a, as well as to the lock-up clutch 115 and hydraulic control valve 123 of the automatic transmission 101. The PCM 70 outputs control signals to these devices that are generated based on the input information from each of the sensors SN1 to SN6.

[Countermeasures against deposit adhesion]
Deposits (foreign matter) may adhere to the valve seat of the intake valve 13 or the exhaust valve 14. For example, deposits adhering to the inner wall of the intake passage 30 may accidentally break off and flow downstream, becoming lodged between the head portion 13b of the intake valve 13 and the valve seat 11a. Alternatively, deposits flowing into the combustion chamber C may become lodged between the head portion 14b of the exhaust valve 14 and the valve seat 12a. Such deposit adhesion (lodging) to the valve seat can lead to compression leakage, a phenomenon in which compressed air leaks from the combustion chamber C through the intake port 11 or the exhaust port 12 during the compression stroke. When compression leakage occurs, the fuel-air mixture injected into the combustion chamber C is prone to improper combustion (or misfire), resulting in poor ignition. Therefore, in this embodiment, as a countermeasure against deposit adhesion to the valve seat, the PCM 70 executes control as shown in FIG. 5 . Details of this control are described below.

Figure 5 is a flowchart showing the details of the control executed by the PCM 70 while the engine 1 is running and the crankshaft 7 is rotating. When this control starts, the PCM 70 reads the information output from each of the sensors SN1 to SN6 (step S1).

Next, the PCM 70 calculates a compression state index value V, which is an index value representing the compression state of cylinder 2a (step S2). Specifically, the PCM 70 calculates the compression state index value V as the ratio (T1/T2) of the first time T1 to the second time T2 shown in FIG. 6. The first time T1 is the time required to pass through a first crank angle range ΔC1 that spans from the compression stroke to the expansion stroke, and the second time T2 is the time required to pass through a second crank angle range ΔC2 that is included in the expansion stroke immediately following the compression stroke. The PCM 70 calculates the compression state index value V (= T1/T2), which is the value obtained by dividing the former by the latter, for each combustion cycle of each cylinder 2a. The compression state index value V can be calculated based on input information from the crank angle sensor SN1.

More specifically, the first crank angle range ΔC1 is set to a predetermined angle range that includes compression top dead center (TDC), which is the boundary between the compression stroke and the expansion stroke. The second crank angle range ΔC2 is set to a predetermined angle range that is retarded from the first crank angle range ΔC1 and included in the expansion stroke. Furthermore, the first crank angle range ΔC1 and the second crank angle range ΔC2 are set to have the same width (e.g., a width of 30° CA) on Figure 6. Here, the movement speed of the piston 5 through the second crank angle range ΔC2 is faster than the movement speed of the piston 5 through the first crank angle range ΔC1. This is because the compression reaction force acting on the piston 5 is maximized at compression top dead center and because an expansion force acts to accelerate the piston 5 during the expansion stroke. Furthermore, the fact that the passage speed through the second crank angle range ΔC2 is faster than the passage speed through the first crank angle range ΔC1 as described above means that the second time T2, which is the passage time through the second crank angle range ΔC2, is shorter than the first time T1, which is the passage time through the first crank angle range ΔC1. Therefore, the compression state index value V, calculated as T1/T2 as described above, is usually calculated as a value significantly greater than 1.

However, if compressed air is leaking from combustion chamber C through intake port 11 or exhaust port 12 during the compression stroke, i.e., if compression leakage is occurring, the compression reaction force acting on piston 5 during the compression stroke will be smaller, and the difference between first time T1 and second time T2 will decrease. This means that the compression state index value V (= T1/T2), which is the ratio between the two, will approach 1. In other words, compression state index value V is a parameter that varies depending on the presence or absence of compression leakage. PCM 70 estimates the compression state (presence or absence of compression leakage) of each cylinder 2a by calculating compression state index value V, which has these properties, for each combustion cycle of each cylinder 2a.

In this way, in this embodiment, the compression state index value V, which is a parameter for compression leakage detection, is calculated by the PCM 70 based on input information from the crank angle sensor SN1. Therefore, the combination of the crank angle sensor SN1 and the PCM 70 corresponds to the "compression leakage detection unit" in the present invention.

After calculating the compression state index value V in step S2, the PCM 70 determines whether deposits have formed on the valve seat portion based on the calculated compression state index value V (step S3). Specifically, for each combustion cycle of each cylinder 2a, the PCM 70 compares the compression state index value V with a predetermined threshold value Vx to determine whether the former is lower than the latter, i.e., whether V<Vx holds. If V<Vx, i.e., the compression state index value V is lower than the threshold value Vx, occurs for a predetermined number of consecutive cycles n1 for the same cylinder 2a, the PCM 70 determines that deposits have formed on the valve seat portion (between the intake valve 13 and valve seat 11a or between the exhaust valve 14 and valve seat 12a) of that cylinder 2a. Note that the number of consecutive cycles n1 here may be set to, for example, "2."

The threshold value Vx used in the determination in step S3 is determined from the average value of the compression state index values V for all cylinders 2a calculated one cycle prior. If the compression state index value V for a specific cylinder 2a is smaller than this threshold value Vx, it means that there is a high possibility that compression leakage is occurring in that specific cylinder 2a, that is, there is a high possibility that compressed air is leaking from the combustion chamber C due to deposits on the valve seat portion of that specific cylinder 2a. Therefore, if the above-mentioned condition of V<Vx occurs for the same cylinder 2a for n1 consecutive cycles, the PCM 70 determines that deposits have formed in that cylinder 2a.

If the determination in step S3 is NO, that is, if it is confirmed that no deposits have adhered to the valve seats of any of the cylinders 2a, the PCM 70 executes normal engine control (step S13). Note that, because no deposit countermeasures are required in this case, the controls corresponding to steps S8, S9, S11, and S12, described below, are not executed.

On the other hand, if step S3 returns YES and a deposit is found on the valve seat of any cylinder 2a, i.e., if a deposit is found between the intake valve 13 (or exhaust valve 14) and the valve seat 11a (or 12a) of that cylinder 2a, the PCM 70 determines whether the engine 1 is undergoing deceleration fuel cut (step S4). Deceleration fuel cut is an operating mode in which fuel injection from the fuel injection valve 9 is stopped during vehicle deceleration; in other words, an operating mode in which rotation of the wheels W1 is used to maintain rotation of the crankshaft 7. Such deceleration fuel cut is permitted, for example, when the accelerator pedal is zero (the accelerator pedal is not depressed), the vehicle speed is higher than a predetermined reference speed, and the engine speed is higher than a predetermined reference speed. The PCM 70 determines whether the conditions for permitting deceleration fuel cutoff are met based on input information from the crank angle sensor SN1, accelerator sensor SN5, and vehicle speed sensor SN6, and if the conditions are met, executes deceleration fuel cutoff.

If step S4 returns YES, confirming that deceleration fuel cut is being performed, the PCM 70 changes the opening of the intake shutter valve 33 to a value greater than normal (step S5). That is, during deceleration fuel cut, the opening of the intake shutter valve 33 is normally set to a relatively small value for purposes such as engine braking. In contrast, in step S5, the intake shutter valve 33 is controlled so that its opening is increased to a value greater than the normal opening during deceleration fuel cut. This is to increase the in-cylinder pressure, which is the internal pressure of cylinder 2a (combustion chamber C), and increase the likelihood that deposits adhering to the valve seat will be crushed.

On the other hand, if step S4 returns NO and it is confirmed that deceleration fuel cut is not being performed, that is, if it is confirmed that operation involving combustion of the air-fuel mixture (combustion operation) is being performed, the PCM 70 determines whether the alternator 18 is operating (step S6). That is, the PCM 70 checks the power generation status of the alternator 18, and if a predetermined amount or more of power is being generated, it determines that the alternator 18 is operating.

If step S6 returns YES and it is confirmed that the alternator 18 is operating, the PCM 70 stops the operation of the alternator 18 (step S7). That is, the PCM 70 controls the regulator circuit within the alternator 18 so that power generation by the alternator 18 stops (the amount of power generated becomes essentially zero). This reduces the counter torque acting on the crankshaft 7 from the alternator 18, thereby reducing the rotational resistance (external load) of the crankshaft 7. Note that stopping the alternator 18 in step S7 is skipped if step S6 returns NO (i.e., if the alternator 18 is not operating).

Next, the PCM 70 prohibits engine 1 from idling (step S8). Idle stop is a control that automatically stops engine 1 when certain idle stop conditions are met, such as when the vehicle speed is zero and the accelerator pedal position is zero. In step S8, the PCM 70 turns on the idle stop prohibition flag so that engine 1 will not automatically stop even if the idle stop conditions are met. This is to prevent engine 1 restart failures due to deposit buildup.

Next, the PCM 70 changes the idle speed of the engine 1 to a value higher than normal (step S9). This increase in idle speed increases the rotational inertia of the engine 1 during idle operation. This makes it less likely for the engine to stall even when the engine is switched to idle operation with deposits still present.

Next, the PCM 70 determines whether the engine speed is equal to or lower than a predetermined threshold value Nx based on input information from the crank angle sensor SN1 (step S10). The threshold value Nx is set to an appropriate value higher than the idle speed after the increase in step S9. For example, the threshold value Nx can be set to approximately 1200 rpm.

If step S10 returns YES and the engine speed is confirmed to be equal to or lower than the threshold value Nx, the PCM 70 changes the opening of the EGR valve 53 to a value smaller than normal (step S11). That is, during combustion operation of the engine 1, the opening of the EGR valve 53 is normally controlled so that an appropriate amount of EGR gas is introduced into the combustion chamber C of each cylinder 2a, depending on the operating conditions, for purposes such as reducing the amount of NOx produced by combustion. In contrast, in step S11, the EGR valve 53 is controlled so that the opening of the EGR valve 53 is reduced to a value smaller than the normal opening determined depending on the operating conditions. The reduced opening of the EGR valve 53 may be set to an appropriate value within a range in which the amount of EGR gas recirculated is reduced compared to normal. It is also possible to reduce the opening of the EGR valve 53 to a value equivalent to a fully closed position, at which the recirculation of EGR gas is essentially stopped.

Next, the PCM 70 changes the amount of fuel injected by the fuel injector 9 to a value greater than normal (step S12). That is, during combustion operation of the engine 1, the fuel injector 9 of each cylinder 2a is normally controlled so that an appropriate amount of fuel commensurate with the required torque of the engine 1, which is determined by factors such as the accelerator pedal position and vehicle speed, is supplied to the combustion chamber C of each cylinder 2a. In contrast, in step S12, the fuel injector 9 is controlled so that more fuel is injected than the normal injection amount determined based on the required torque. Note that this increased injection control should be performed at least on the fuel injector 9 of the cylinder 2a for which deposits were confirmed in the determination of step S3, but it is also possible to increase the injection amount of the fuel injector 9 of all cylinders 2a.

Next, we will explain the control when the determination in step S10 is NO, i.e., when the engine speed is greater than the threshold value Nx. In this case, the PCM 70 determines whether deposits continue to accumulate (step S14). Specifically, the PCM 70 determines whether the compression state index value V is less than the threshold value Vx (V<Vx) for a predetermined number of consecutive cycles n2 for the cylinder 2a for which deposits were determined to exist in step S3. If the V<Vx state occurs for n2 consecutive cycles after the deposit determination, this means that compression leakage has occurred for n1+n2 consecutive cycles for the same cylinder 2a, indicating a high probability that the deposits have not yet been removed. Note that the number of consecutive cycles n2 here is preferably greater than the number of consecutive cycles n1 used in the determination in step S3 (determining whether deposits exist). For example, the number of consecutive cycles n2 can be set to "5."

If step S14 returns NO, confirming that deposits are not continuing to build up, the PCM 70 executes normal shift control for the automatic transmission 101 (step S17). Note that, because no deposit countermeasures are required in this case, the controls corresponding to steps S15 and S16, described below, are not executed.

On the other hand, if step S14 returns YES, confirming that deposits continue to adhere, the PCM 70 changes the shift pattern of the automatic transmission 101 so that downshifts to lower gears (i.e., increase the reduction ratio) occur earlier (step S15). In other words, the PCM 70 changes the shift pattern so that the downshift speed, which is the engine speed at which downshifts occur during deceleration, is higher than usual. This causes downshifts associated with deceleration to occur earlier than usual.

Next, the PCM 70 changes the lockup release speed so that the lockup region, which is the range of engine speeds at which the lockup clutch 115 is engaged, expands toward lower speeds (step S16). That is, the PCM 70 changes the lockup release speed, which is the engine speed at which the lockup clutch 115 is released during deceleration, to a value lower than normal. This expands the lockup region toward lower speeds, and the lockup state is maintained down to engine speeds lower than normal.

In the flowchart of FIG. 5 described above, the control of step S7 corresponds to the "first control" in the present invention, the controls of steps S11 and S12 correspond to the "second control" in the present invention, and the controls of steps S15 and S16 correspond to the "third control" in the present invention. Alternatively, the determination of step S3 corresponds to the "first step" in the present invention, the control of step S7 corresponds to the "second step" in the present invention, the determination of step S10 corresponds to the "third step" in the present invention, and the controls of steps S11 and S12 correspond to the "fourth step" in the present invention.

[Action and effect]
As described above, in this embodiment, it is determined whether or not a deposit has formed on the valve seat portion based on the presence or absence of compression leakage estimated from the compression state index value V, and if the presence of a deposit is confirmed, control is executed (S7) to stop power generation by the alternator 18. Furthermore, if it is confirmed after power generation is stopped that the engine speed is equal to or lower than the threshold value Nx, control is executed (S11) to reduce the opening of the EGR valve 53 and control is executed (S12) to increase the amount of fuel injected from the fuel injection valve 9. This configuration has the advantage of being able to quickly address the formation of deposits while reducing the impact on emissions performance or fuel economy.

In other words, in this embodiment, power generation by the alternator 18 is stopped in response to confirmation of deposit buildup, thereby reducing the reverse torque applied from the alternator 18 to the engine body 2 (crankshaft 7) and reducing the rotational resistance (external load) of the engine body 2. Furthermore, because power generation by the alternator 18 can be stopped (the amount of power generated can be changed) in a short time, the rotational resistance of the engine body 2 can be reduced responsively. When rotational resistance is reduced, it becomes easier to maintain rotation of the crankshaft 7 even if poor ignition of the mixture occurs due to deposit buildup (compression leakage). In other words, reducing rotational resistance in response to power generation stoppage reduces the possibility of the engine 1 stalling (stalling) due to poor ignition.

However, if the above-mentioned misfire occurs when the engine speed is relatively low (in other words, when rotational inertia is low), there is a high possibility that stopping the alternator 18 alone will not be enough to maintain rotation of the crankshaft 7 (leading to an engine stall). In contrast, in this embodiment, when the engine speed after stopping power generation is equal to or lower than the threshold value Nx, control is executed to reduce the opening of the EGR valve 53 and increase the fuel injection amount, thereby preventing engine stalls due to the above-mentioned circumstances. In other words, reducing the opening of the EGR valve 53 reduces the proportion of EGR gas, which is an inert gas, in the combustion chamber C, thereby improving the ignitability of the mixture. Furthermore, increasing the fuel injection amount also improves the ignitability of the mixture. The combination of these effects sufficiently reduces the possibility of misfire when the engine speed is low, thereby effectively preventing engine stalls.

Furthermore, in this embodiment, the above-described control for changing the opening of the EGR valve 53 and the fuel injection amount is not performed unless the engine speed falls below the threshold Nx, thereby reducing the possibility of affecting emissions performance and fuel economy. That is, reducing the opening of the EGR valve 53 raises the combustion temperature in the combustion chamber C, which has the effect of increasing the amount of NOx generated. Furthermore, increasing the fuel injection amount has the effect of reducing fuel economy. In contrast, in this embodiment, even if deposit formation (compression leakage) is confirmed, the opening of the EGR valve 53 is not reduced until the engine speed falls below the threshold Nx, thereby reducing the possibility of an increase in NOx generation due to this reduction in opening. Similarly, even if deposit formation is confirmed, the fuel injection amount is not increased until the engine speed falls below the threshold Nx, thereby reducing the possibility of a decrease in fuel economy due to this increase in injection amount. In particular, if deposits are detected when the engine speed exceeds the threshold Nx and power generation by the alternator 18 is stopped in response, the deposits may be removed while the engine speed is maintained, potentially eliminating the compression leak before the speed drops below the threshold Nx. In such a case, there is no need to change the opening of the EGR valve 53 or the fuel injection amount to address the deposits, minimizing the impact on emissions performance and fuel economy. In this way, this embodiment can prevent engine stalls due to deposit buildup while mitigating the impact on the emissions performance and fuel economy of the engine 1.

In this embodiment, the compression state index value V is calculated as the ratio (T1/T2) of the first time T1 required to pass through the first crank angle range ΔC1 that spans the compression top dead center and the second time T2 required to pass through the second crank angle range ΔC2 included in the expansion stroke. By comparing the compression state index value V with a threshold value Vx, the occurrence of compression leakage and, ultimately, the formation of deposits on the valve seat can be accurately estimated. In other words, when compression leakage occurs, the compression reaction force acting on the piston 5 during the compression stroke decreases, thereby reducing the amount of change in the movement speed of the piston 5 before and after passing the compression top dead center. This means that the difference between the first time T1 and the second time T2 decreases; in other words, the ratio (T1/T2) of the first time T1 and the second time T2 decreases. Therefore, according to this embodiment, in which the ratio between the first time T1 and the second time T2 is calculated as the compression state index value V, compression leakage (and therefore deposit formation) can be estimated with high accuracy based on the size of the compression state index value V.

In addition, in this embodiment, if it is confirmed that deposits continue to adhere while the engine speed is greater than the threshold value Nx after the alternator 18 has stopped generating electricity (continued compression leakage), the shift pattern is changed so that the engine speed at which a downshift to increase the reduction ratio is performed (downshift speed) is higher than normal (S15), and the range of engine speeds at which the lock-up clutch 115 is engaged (lock-up region) is expanded to the lower speed side (S16). With this configuration, the engine speed can be maintained high while the vehicle is running, reducing the possibility of the engine stalling.

In other words, in this embodiment, the shift pattern is changed to increase the downshift rotational speed, so that downshifts occur earlier than usual when the vehicle is decelerating, for example. This allows the reduction ratio to be increased before the engine rotational speed drops sufficiently, and the increased reduction ratio can be used to raise the engine rotational speed. Furthermore, because the lockup region is expanded to the low rotational speed side, the lockup state (a state in which the crankshaft 7 and the wheel W1 are directly coupled) is maintained up to lower engine rotational speeds than usual, for example, when the vehicle is decelerating. This allows the crankshaft 7 to maintain a state in which it rotates in synchronization with the wheel W1, and the rotational energy of the wheel W1 can be used to suppress a drop in engine rotational speed. In this way, in this embodiment, the automatic transmission 101 is controlled to maintain a relatively high engine rotational speed, further reducing the possibility of the engine stalling.

Furthermore, maintaining a high engine speed as described above means that the engine speed is less likely to drop below the threshold value Nx. This reduces the likelihood that the above-mentioned control of changing the opening of the EGR valve 53 and the fuel injection amount will be required, further reducing the impact on the emissions performance and fuel economy of the engine 1.

[Modification]
In the above embodiment, when deposits (compression leakage) are found on the bubble seat portion, power generation by the alternator 18 is stopped. However, instead of this control, control may be performed to reduce the amount of power generated while continuing power generation by the alternator 18. In other words, the countermeasure against deposits using the alternator 18 is sufficient as long as it limits the operation of the alternator 18 so as to reduce the rotational resistance of the engine body 2 (crankshaft 7), and it is not necessary to stop power generation itself.

Furthermore, the control that is first performed when deposits build up, i.e., the first control in this invention, can be any control that restricts the operation of an accessory that receives driving force from the engine 1 to perform work, and is not limited to the alternator 18. For example, the accessory whose operation is restricted could be an air conditioning compressor driven by the crankshaft 7 of the engine 1. The air conditioning compressor is a compressor that pumps refrigerant used in an air conditioning system installed in a vehicle. In this case, the first control can be control to stop the air conditioning compressor from pumping refrigerant, or control to reduce the amount of refrigerant pumped. In either case, it is possible to reduce the rotational resistance of the engine main body 2 caused by the operation of the air conditioning compressor, thereby preventing the engine from stalling.

In the above embodiment, the compression state index value V representing the compression state of cylinder 2a was calculated as the ratio (T1/T2) of the first time T1 required to pass through the first crank angle range ΔC1 spanning the compression top dead center to the second time T2 required to pass through the second crank angle range ΔC2 included in the expansion stroke. However, the compression state index value V may be modified in various ways as long as it varies depending on the presence or absence of compression leakage. For example, the difference between the first time T1 and the second time T2 may be used as the compression state index value V. Furthermore, the first time T1 may be the time required to pass through a predetermined crank angle range that is more advanced than ΔC1 in FIG. 6 and is included in the compression stroke, and the second time T2 may be the time required to pass through a predetermined crank angle range that is more advanced or retarded than ΔC2 in FIG. 6 and is included in the expansion stroke. Furthermore, the average movement speed of the piston 5 may be calculated from the time required to pass through a specific crank angle range during each of the compression stroke and expansion stroke, and the ratio of these speeds may be used as the compression state index value V.

In the above embodiment, compression leakage is detected based on the above-mentioned compression state index value V calculated by the PCM 70 from the input information of the crank angle sensor SN1, but the means for detecting compression leakage is not limited to this. For example, an in-cylinder pressure sensor may be provided to detect the in-cylinder pressure, which is the internal pressure of cylinder 2a (combustion chamber C), and compression leakage may be detected based on the detected value of the in-cylinder pressure sensor. In this case, the in-cylinder pressure sensor corresponds to the "compression leakage detection unit" in this invention.

In the above embodiment, when the engine speed after deposit adhesion (compression leakage) is confirmed is equal to or lower than the threshold value Nx, control is performed to reduce the opening of the EGR valve 53 (S11) and control is performed to increase the amount of fuel injected from the fuel injection valve 9 (S12). However, it is not necessary to perform both of these two controls; only one of the controls may be performed. Even in this case, ignition performance can be improved and engine stalling can be suppressed.

In the above embodiment, even if the engine speed is greater than the threshold value Nx, if it is confirmed that deposits continue to adhere (that compression leakage is still occurring), control is executed to change the shift pattern so that the downshift speed is higher than normal (S15), and control is executed to lower the lockup release speed below normal (S16). However, it is not necessary to execute both of these two controls; only one of them may be executed. Even in this case, the engine speed can be maintained high and engine stalling can be suppressed.

In the above embodiment, if deposit adhesion (compression leakage) is detected during deceleration fuel cut, the opening of the intake shutter valve 33 is changed to a value greater than normal (step S5). However, in addition to or instead of this control, control may be executed to change the control pattern of the automatic transmission 101 so that the engine speed is maintained high (control similar to steps S15 and S16 described above).

In the above embodiment, an example was described in which the present invention was applied to a diesel engine that burns fuel containing diesel oil through self-ignition, but the engines to which the present invention can be applied are not limited to diesel engines. For example, the present invention can also be applied to spark-ignition engines equipped with accessories such as an alternator.

1: Engine C: Combustion chamber 7: Crankshaft (output shaft)
9: Fuel injection valve 18: Alternator (generator; auxiliary equipment)
11: Intake port 12: Exhaust port 13: Intake valve 14: Exhaust valve 30: Intake passage 40: Exhaust passage 50: EGR passage 53: EGR valve 70: PCM (controller, compression leak detector)
SN1: Crank angle sensor (rotation detection section, compression leak detection section)
101: Automatic transmission 115: Lock-up clutch

Claims (6)

A device for controlling an engine including a combustion chamber, an intake passage connected to the combustion chamber via an intake port, an exhaust passage connected to the combustion chamber via an exhaust port, an intake valve and an exhaust valve that open and close the intake port and the exhaust port, and an EGR passage that connects the intake passage and the exhaust passage,
a fuel injection valve that injects fuel into the combustion chamber;
an EGR valve provided in the EGR passage so as to be able to open and close;
an accessory that receives driving force from the engine and performs work;
a rotation detection unit that detects an engine rotation speed, which is the rotation speed of an output shaft of the engine;
a compression leakage detection unit that detects a compression leakage, which is a phenomenon in which air leaks from the combustion chamber through the intake port or the exhaust port during a compression stroke;
a controller for controlling the fuel injection valve, the EGR valve, and the auxiliary equipment,
The controller
When the compression leakage detection unit detects a compression leakage, a first control is executed to limit the operation of the auxiliary machine;
an engine control device that, after the first control, when it is confirmed that the engine speed detected by the rotation detection unit is equal to or lower than a predetermined threshold, executes a second control that involves at least one of reducing the opening of the EGR valve and increasing the amount of fuel injected from the fuel injection valve. 2. The engine control device according to claim 1,
The auxiliary machine includes a generator that generates electricity by receiving driving force from the engine,
An engine control device, wherein the first control includes control to stop power generation by the generator or to reduce the amount of power generation. 3. The engine control device according to claim 1,
The compression leakage detection unit detects the compression leakage based on a first time required for the engine to pass through a first crank angle range that is included in the compression stroke or that crosses over top dead center of compression, and a second time required for the engine to pass through a second crank angle range that is included in the expansion stroke immediately after the compression stroke and that is more retarded than the first crank angle range. The engine control device according to any one of claims 1 to 3,
the engine is an in-vehicle engine connected to wheels via an automatic transmission that can automatically change the reduction ratio,
An engine control device, wherein the controller executes third control to control the automatic transmission so that the engine speed is maintained high when it is confirmed after the first control that the compression leakage has occurred when the engine speed is greater than the threshold value. 5. The engine control device according to claim 4,
the automatic transmission includes a lock-up clutch that directly connects the output shaft of the engine to the wheels,
The third control is an engine control device that includes at least one of control to expand a lockup region, which is the range of engine speeds at which the lockup clutch is engaged, to the low speed side, and control to change the shift pattern so that the engine speed at which a downshift that increases the reduction ratio is performed is increased. A method for controlling an engine including a combustion chamber, an intake passage connected to the combustion chamber via an intake port, an exhaust passage connected to the combustion chamber via an exhaust port, an intake valve and an exhaust valve for opening and closing the intake port and the exhaust port, an EGR passage connecting the intake passage and the exhaust passage, a fuel injection valve for injecting fuel into the combustion chamber, an EGR valve provided in the EGR passage so as to be able to open and close, an output shaft, and an accessory that performs work by receiving driving force from the output shaft , the method comprising:
a first step of detecting a compression leak, which is a phenomenon in which air leaks from the combustion chamber through the intake port or the exhaust port during a compression stroke;
a second step of limiting operation of the accessory when the compression leakage is detected in the first step;
a third step of detecting an engine rotation speed, which is the rotation speed of the output shaft, after the second step;
a fourth step of performing at least one of reducing the opening of the EGR valve and increasing the amount of fuel injected from the fuel injection valve when it is confirmed that the engine speed detected in the third step is equal to or lower than a predetermined threshold.