Exhaust valve control device for engine

Abstract

To enable prompt temperature rise of a catalyst device without deteriorating combustion stability.SOLUTION: An exhaust valve control device for an engine 1 includes: a variable exhaust valve device (exhaust VVL 19, exhaust S-VT 18) that changes at least valve opening timing of an exhaust valve 12; a catalyst device 31 that purifies exhaust gas; and a control device 100 that executes temperature rise control for raising a temperature of the catalyst device when the catalyst device is inactive after start of the engine. In the temperature rise control, the control device delays the valve opening timing of the exhaust valve to a crank angle after a bottom dead center 50deg. in an exhaust stroke.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed herein relates to an exhaust valve control device for an engine. [Background technology]

[0002] Patent Document 1 describes a conventional internal combustion engine. This internal combustion engine executes rapid catalyst warm-up control, which rapidly warms up the catalyst during cold start of the internal combustion engine to activate the catalyst. Specifically, the internal combustion engine retards the exhaust valve closing timing during the rapid catalyst warm-up control. Retarding the exhaust valve closing timing creates an overlap period during which both the intake valve and the exhaust valve are open, and the combustion speed is slowed by increasing the internal EGR, causing the temperature of the exhaust gas to rise. The catalyst is heated by the high-temperature exhaust gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-37907 Summary of the Invention [Problem to be solved by the invention]

[0004] A known example of temperature control for raising the temperature of an inactive catalytic device is to retard the ignition timing, thereby delaying the center of combustion to the latter half of the expansion stroke, reducing the work done in the expansion stroke and increasing internal energy, thereby supplying high-temperature exhaust gas to the catalytic device. In the conventional internal combustion engine described in Patent Document 1, the center of combustion is retarded by slowing the combustion speed, so one of the goals is to reduce the work done in the expansion stroke.

[0005] However, temperature rise control, which reduces the work done during the expansion stroke and increases the internal energy, slows combustion because combustion begins under conditions where the pressure inside the cylinder is significantly reduced. This has the disadvantage of reducing combustion stability during temperature rise control. Furthermore, for example, when the outside air temperature is extremely low, it is difficult to sufficiently raise the temperature of the exhaust gas supplied to the catalytic converter, even if the ignition timing is retarded. Temperature rise control, which reduces the work done during the expansion stroke and increases the internal energy, also has the problem of delayed activation of the catalytic converter in extremely low-temperature environments.

[0006] Furthermore, in the conventional catalyst rapid warm-up control described in Patent Document 1, if the exhaust valve closing timing is significantly delayed to increase the exhaust gas temperature, the overlap period becomes too long, resulting in excessive internal EGR. Excessive internal EGR reduces combustion stability during catalyst rapid warm-up control.

[0007] The technology disclosed herein enables the catalyst device to heat up quickly without reducing combustion stability. [Means for solving the problem]

[0008] The technology disclosed herein relates to an engine exhaust valve control device. The engine exhaust valve control device includes: a variable exhaust valve device that changes at least the opening timing of the exhaust valve; a catalytic converter located in an exhaust passage of the engine and purifying exhaust gas; a control device that executes temperature rise control to increase the temperature of the catalytic converter when the catalytic converter is inactive after the engine is started, In the temperature increase control, the control device delays the opening timing of the exhaust valve to a crank angle of 50 degrees or more after bottom dead center of the exhaust stroke.

[0009] In the temperature rise control that promotes the activation of an inactive catalytic converter, the opening timing of the exhaust valve is set to a crank angle of 50 degrees or more after bottom dead center of the exhaust stroke. After the piston reaches bottom dead center of the exhaust stroke, it rises with the exhaust valve closed, recompressing the gas in the engine's combustion chamber. The gas, now hotter as a result of recompression, is supplied to the catalytic converter when the exhaust valve opens. The catalytic converter is heated by the high-temperature exhaust gas.

[0010] This device's temperature rise control involves having the piston do normal work during the expansion stroke, and then converting some of the piston work into exhaust energy during the exhaust stroke, thereby raising the temperature of the exhaust gas supplied to the catalytic converter. Unlike conventional temperature rise control, this system does not require combustion that reduces work during the expansion stroke and increases internal energy, making it possible to advance the combustion center of gravity more than conventional temperature rise control. As a result, the deterioration of combustion stability during temperature rise control is suppressed.

[0011] Furthermore, in conventional temperature rise control, the center of combustion is relatively retarded, which tends to increase emissions, specifically the amount of NOx (nitrogen oxides), HC (hydrocarbons), and CO (carbon monoxide).In contrast, the temperature rise control of the above device relatively advances the center of combustion, which can reduce emissions.

[0012] Temperature rise control is generally performed immediately after a cold start of the engine while the vehicle in which the engine is installed remains stationary. Because no driving torque is required of the engine, the torque required of the engine during temperature rise control is small. During temperature rise control, the required engine torque is met even if part of the piston work in the exhaust stroke is converted into exhaust energy.

[0013] In the temperature increase control, the control device may delay the opening timing of the exhaust valve to a crank angle of 70 degrees or more after bottom dead center of the exhaust stroke.

[0014] If the exhaust valve opening timing is further delayed beyond 70 degrees after bottom dead center on the exhaust stroke, the piston work converted into exhaust energy during the exhaust stroke increases. Retarding the exhaust valve opening timing is advantageous for raising the temperature of the exhaust gas supplied to the catalytic converter. As mentioned above, because the engine's required torque is small, the required engine torque can be met even if the exhaust valve opening timing is delayed to a crank angle of 70 degrees or more after bottom dead center on the exhaust stroke.

[0015] The retard limit of the exhaust valve opening timing may be set based on the required torque of the engine. When the required torque of the engine is relatively high, the exhaust valve opening timing may be set relatively to the advance side, and when the required torque of the engine is relatively low, the exhaust valve opening timing may be set relatively to the retard side.

[0016] In addition, the retard limit of the exhaust valve opening timing may be set within a range in which the temperature of the exhaust gas supplied to the catalytic converter does not become too high. If the exhaust valve opening timing is retarded, the temperature of the exhaust gas also increases, but exhaust gas with an excessively high temperature may cause damage to the catalytic converter. The exhaust valve opening timing may be retarded within a range in which the catalytic converter is not damaged.

[0017] The engine exhaust valve control device further includes a spark plug that ignites an air-fuel mixture in a combustion chamber of the engine, In the temperature increase control, the control device may set the ignition timing of the spark plug so that the center of combustion is in the first half of the expansion stroke.

[0018] Here, the first half of the expansion stroke may be the first half when the expansion stroke is divided into two equal parts: the first half (0-90 degrees aTDC) and the second half (90-180 degrees aTDC). If the center of combustion is in the first half of the expansion stroke, high combustion stability can be ensured. Furthermore, the amount of emissions does not increase.

[0019] the variable exhaust valve device changes the opening timing of the exhaust valve by changing the lift amount of the exhaust valve, The control device may delay the opening timing of the exhaust valve in the temperature rise control compared to the opening timing of the exhaust valve in the non-temperature rise control, and may set the closing timing of the exhaust valve to the same timing as the closing timing of the exhaust valve in the non-temperature rise control.

[0020] If the exhaust valve closing timing is fixed and the exhaust valve lift amount is reduced, the exhaust valve open period will be shortened, and the exhaust valve open timing will be retarded, and if the exhaust valve lift amount is increased, the exhaust valve open period will be lengthened, and the exhaust valve open timing will be advanced.

[0021] Because the exhaust valve closing timing is the same during temperature rise control and non-temperature rise control, the period during which the exhaust valve is open during the intake stroke during temperature rise control is not prolonged. This prevents an increase in internal EGR and reduces a decrease in combustion stability during temperature rise control.

[0022] the variable exhaust valve device changes the opening and closing timing of the exhaust valve without changing the lift amount of the exhaust valve, The control device may delay both the opening and closing timings of the exhaust valve in the temperature increase control compared to the opening and closing timings of the exhaust valve in the non-temperature increase control.

[0023] The exhaust valve opening timing can also be changed by a so-called S-VT (Sequential-Valve Timing) mechanism, which may be, for example, a mechanism that continuously changes the rotational phase of the camshaft relative to the crankshaft within a predetermined angle range.

[0024] The control device may determine the amount of retardation of the opening timing of the exhaust valve in the temperature increase control within a range in which a predetermined level of combustion stability or higher is ensured.

[0025] When the exhaust valve closing timing is retarded in conjunction with the retardation of the exhaust valve opening timing, if the valve closing timing is retarded significantly, there is a risk of a deterioration in combustion stability. By determining the amount of retardation of the exhaust valve opening timing within a range that ensures a predetermined level of combustion stability, the deterioration of combustion stability during temperature rise control is suppressed.

[0026] The control device may be configured to switch the opening timing of the exhaust valve from a retarded timing to the opening timing of the exhaust valve in the non-temperature rise control upon termination of the temperature rise control after the temperature of the catalytic device reaches an activation temperature.

[0027] If the exhaust valve opening timing is kept retarded until the temperature of the catalyst device reaches the activation temperature, high-temperature exhaust gas is supplied to the catalyst device during temperature rise control. Supplying high-temperature exhaust gas to the catalyst device during temperature rise control is advantageous in that it quickly increases the temperature of the catalyst device and shortens the period of temperature rise control.

[0028] The control device may, during the temperature rise control, advance the opening timing of the exhaust valve from a retarded timing toward the opening timing of the exhaust valve in the non-temperature rise control as the temperature of the catalytic device rises.

[0029] Advancement of the exhaust valve opening timing can increase engine torque. Advancement of the exhaust valve opening timing in accordance with the rise in catalyst temperature during temperature rise control is advantageous for ensuring the torque required to drive engine accessories, for example, during temperature rise control.

[0030] The engine exhaust valve control device disclosed herein comprises: a variable exhaust valve device that changes at least the opening timing of the exhaust valve; a catalytic converter located in an exhaust passage of the engine and purifying exhaust gas; a control device that executes temperature rise control to increase the temperature of the catalytic converter when the catalytic converter is inactive after the engine is started, the control device delays the opening timing of the exhaust valve to a point after the bottom dead center of the exhaust stroke during the temperature rise control, and advances the opening timing of the exhaust valve relative to that during the temperature rise control during the non-temperature rise control in which the catalytic device is activated, The control device closes the exhaust valve at the same timing during the temperature increase control and the temperature non-rise control.

[0031] As with the previous system, this system's temperature control involves allowing the piston to do its normal work during the expansion stroke, then converting part of the piston's work into exhaust energy during the exhaust stroke, thereby raising the temperature of the exhaust gas supplied to the catalytic converter, allowing the combustion center to be advanced more than with conventional temperature control. As a result, the deterioration of combustion stability during temperature control is suppressed, and emissions can be reduced.

[0032] Furthermore, during temperature rise control, the exhaust valve closing timing is the same as during non-temperature rise control, which prevents an increase in internal EGR during temperature rise control, thereby also preventing a decrease in combustion stability during temperature rise control. [Effects of the Invention]

[0033] According to the engine exhaust valve control device, the temperature of the catalyst device can be raised quickly without deteriorating the combustion stability. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 shows the engine. [Figure 2] FIG. 2 is a block diagram of the engine system. [Figure 3] FIG. 3 shows pv diagrams and lift curves of the intake valve and exhaust valve for each of the temperature increase control and non-temperature increase control. [Figure 4] FIG. 4 shows the changes in the in-cylinder pressure and the heat release rate with respect to the progression of the crank angle in both the conventional AWS and the new temperature rise control. [Figure 5]FIG. 5 shows the exhaust temperature and combustion stability in the conventional AWS and the new temperature rise control. [Figure 6] FIG. 6 shows the maximum in-cylinder temperature and NOx concentration in the conventional AWS and the new temperature rise control. [Figure 7] FIG. 7 shows the HC concentration and the CO concentration in the conventional AWS and the new temperature rise control. [Figure 8] FIG. 8 shows the changes in HC concentration and CO concentration that occur when the opening timing of the exhaust valve is changed. [Figure 9] FIG. 9 is a flowchart showing the procedure of the temperature increase control. [Figure 10] FIG. 10 shows the lift curve of the exhaust valve in the temperature rise control according to the modified example. [Figure 11] FIG. 11 is a flowchart showing a control procedure for temperature increase control according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an engine exhaust valve control device will be described below with reference to the drawings. The engine exhaust valve control device described here is an example.

[0036] (Engine configuration) FIG. 1 shows an engine 1. FIG. 2 is a block diagram of an engine system including the engine 1. The engine 1 is installed in an automobile. The engine 1 is a driving source for running the automobile. The engine 1 is operated by receiving a supply of fuel containing, for example, gasoline.

[0037] The engine 1 includes an engine body 1a having a plurality of cylinders 2. The engine body 1a has a plurality of cylinders 2. The plurality of cylinders 2 are arranged in a line, for example, in a direction perpendicular to the plane of the paper in FIG.

[0038] The engine body 1a has a cylinder block 3 in which cylinders 2 are formed, and a cylinder head 4 located on the cylinder block 3. Pistons 5 are fitted into the cylinders 2 so that they can reciprocate. The pistons 5 are connected to a crankshaft via connecting rods 8. A combustion chamber 6 is formed by the cylinders 2, the cylinder head 4, and the pistons 5. As the pistons 5 reciprocate, the engine 1 repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

[0039] The cylinder head 4 has an intake port 9 and an exhaust port 10. The intake port 9 is connected to an intake passage 20. The intake port 9 is a port for introducing gas supplied from the intake passage 20 into the cylinder 2. The exhaust port 10 is connected to an exhaust passage 30. The exhaust port 10 is a port for guiding exhaust gas from the cylinder 2 to the exhaust passage 30.

[0040] The engine 1 has an intake valve 11 and an exhaust valve 12. The intake valve 11 opens and closes an intake port 9. The exhaust valve 12 opens and closes an exhaust port 10.

[0041] The engine 1 has an intake valve train mechanism. The intake valve train mechanism drives the intake valve 11. The intake valve train mechanism of this embodiment includes an intake S-VT 17. The intake S-VT 17 continuously changes the rotational phase of the intake camshaft relative to the crankshaft within a predetermined angle range. The opening and closing timings of the intake valve 11 are continuously advanced or retarded while maintaining a constant opening period of the intake valve 11.

[0042] The engine 1 has an exhaust valve train mechanism. The exhaust valve train mechanism drives the exhaust valve 12. In this embodiment, the exhaust valve train mechanism includes an exhaust S-VT 18. The exhaust S-VT 18 continuously changes the rotational phase of the exhaust camshaft relative to the crankshaft within a predetermined angle range. The exhaust S-VT 18 continuously changes the opening and closing timings of the exhaust valve 12 to the advance or retard side while maintaining a constant exhaust valve opening period.

[0043] The exhaust valve train also includes an exhaust VVL (Variable Valve Lift). The exhaust VVL 19 switches the cam that opens and closes the exhaust valve 12 between a first cam and a second cam. The first cam is a cam that provides a relatively large lift amount for the exhaust valve 12. As shown by the dashed line in the lower diagram of FIG. 3, the first cam can open the exhaust valve 12 throughout the entire exhaust stroke. The second cam is a cam that provides a relatively small lift amount for the exhaust valve 12. As shown by the solid line in the lower diagram of FIG. 3, the second cam can open the exhaust valve 12 for part of the exhaust stroke. In other words, the exhaust VVL 19 can switch the opening timing of the exhaust valve 12 between an advanced opening timing and a retarded opening timing without changing the closing timing of the exhaust valve 12.

[0044] As described above, the intake passage 20 is connected to the intake port 9. An air cleaner 21 is disposed at the upstream end of the intake passage 20. The air cleaner 21 filters fresh air. Air that passes through the air cleaner 21 is supplied to the cylinders 2 via the intake passage 20 and the intake port 9. A surge tank 25 is disposed downstream of the intake passage 20. The portion of the intake passage 20 downstream of the surge tank 25 is an intake manifold. The intake manifold distributes air to multiple cylinders 2.

[0045] The air flow sensor SN2 is located downstream of the air cleaner 21 in the intake passage 20. The air flow sensor SN2 outputs a signal corresponding to the air flow rate in the intake passage 20.

[0046] A throttle valve 22 is positioned in the intake passage 20 between the air cleaner 21 and the surge tank 25. The throttle valve 22 changes the size of the cross-sectional area of ​​the intake passage 20 through which air passes.

[0047] As described above, the exhaust passage 30 is connected to the exhaust port 10. The upstream end of the exhaust passage 30 is an exhaust manifold. The exhaust manifold collects exhaust gases from multiple cylinders 2. The exhaust gases discharged from the cylinders 2 flow through the exhaust passage 30.

[0048] A catalytic device 31 is located in the exhaust passage 30. The catalytic device 31 purifies the exhaust gas discharged from the cylinder 2. The catalytic device 31 includes, for example, a three-way catalyst. The three-way catalyst oxidizes HC and CO and reduces NOx, thereby removing emissions contained in the exhaust gas. However, the catalytic device 31 is not limited to a three-way catalyst.

[0049] An exhaust temperature sensor SN3 is located upstream of the catalytic converter 31. The exhaust temperature sensor SN3 outputs a signal corresponding to the temperature of the exhaust gases supplied to the catalytic converter 31. An EM sensor SN4 is located downstream of the catalytic converter 31. The EM sensor SN4 outputs a signal related to the emissions in the exhaust gases that have passed through the catalytic converter 31.

[0050] The engine 1 has an EGR passage 41. The EGR passage 41 connects a portion of the exhaust passage 30 upstream of the catalytic device 31 with the surge tank 25 in the intake passage 20. A portion of the exhaust gas passes through the EGR passage 41 and recirculates as EGR gas from the exhaust passage 30 to the intake passage 20. An EGR cooler 43 is located in the EGR passage 41. The EGR cooler 43 cools the EGR gas flowing through the EGR passage 41.

[0051] The engine 1 has an EGR valve 42. The EGR valve 42 adjusts the size of the cross-sectional area of ​​the EGR passage 41.

[0052] The engine 1 has a spark plug 13. The spark plug 13 is attached to the cylinder head 4 for each cylinder 2. The spark plug 13 forcibly ignites the air-fuel mixture in the combustion chamber 6. The ignition timing of the spark plug 13 is specified by a control device 100, which will be described later. Note that the engine 1 may have two spark plugs 13 for each cylinder 2.

[0053] The engine 1 has an injector 14. The injector 14 is attached to the cylinder head 4 for each cylinder 2. The injector 14 injects fuel into the combustion chamber 6 at a predetermined timing.

[0054] As shown in FIG. 2, the engine system includes a control device 100. The control device 100 controls the operation of the engine 1. The control device 100 is a control unit based on a well-known microcomputer. The control device 100 includes a CPU 101, a memory 102, and an input / output bus 103. The CPU 101 is a central processing unit that executes computer programs. These computer programs include basic control programs such as an OS and application programs that are run on the OS and implement specific functions. The memory 102 stores various computer programs or data used when the computer programs are executed. This computer program is a control program for controlling the engine 1, such as a control program that executes the control procedure shown in FIG. 9 or 11. The memory 102 includes a processing area that the CPU 101 uses when performing a series of processes. The input / output bus 103 inputs and outputs electrical signals to and from the control device 100.

[0055] The control device 100 is electrically connected to the air flow sensor SN2, exhaust temperature sensor SN3, and EM sensor SN4. The air flow sensor SN2, exhaust temperature sensor SN3, and EM sensor SN4 output signals to the control device 100. The control device 100 is also electrically connected to a crank angle sensor SN1, an accelerator opening sensor SN5, and a water temperature sensor SN6. The crank angle sensor SN1 is attached to the cylinder block 3 and outputs a signal corresponding to the rotation of the crankshaft to the control device 100. The accelerator opening sensor SN5 is attached to the accelerator pedal mechanism and outputs a signal corresponding to the depression amount of the accelerator pedal to the control device 100. The water temperature sensor SN6 is attached to the engine main body 1a and outputs a signal corresponding to the temperature of the coolant for the engine 1 to the control device 100. The control device 100 receives signals from these sensors SN1-SN6.

[0056] The control device 100 determines the state of the engine 1 based on signals from the sensors SN1-SN6, and outputs control signals to the spark plug 13, the injector 14, the intake S-VT 17, the exhaust S-VT 18, the exhaust VVL 19, the throttle valve 22, and the EGR valve 42. The control device 100 controls the operation of the engine 1 by outputting control signals to each device.

[0057] A starter motor 51 is also electrically connected to the control device 100. The starter motor 51 cranks the engine body 1a. The control device 100 outputs a control signal to the starter motor 51 when the engine body 1a starts.

[0058] (Catalyst device temperature rise control) When the temperature of the catalytic converter 31 is low and the catalytic converter 31 is inactive, the engine system executes temperature rise control to quickly raise the temperature of the catalytic converter 31. The temperature rise control is executed immediately after a cold start of the engine 1. If the catalytic converter 31 becomes active through the temperature rise control, the catalytic converter 31 purifies the exhaust gas and suppresses the emission of emissions. The temperature rise control of the catalytic converter 31 executed immediately after a cold start of the engine 1 is called an AWS (Accelerated Warm-up System).

[0059] Conventional AWS heats the catalytic converter 31 by reducing the work done during the expansion stroke and increasing the internal energy. In other words, the ignition timing is set late, for example, after 45 degrees after top dead center, and combustion is performed so that the center of gravity of combustion is later than the latter half of the expansion stroke. This causes high-temperature exhaust gas to be supplied to the catalytic converter 31, heating the catalytic converter 31. However, this combustion, which reduces the work done during the expansion stroke and increases the internal energy, begins under conditions where the in-cylinder pressure has dropped significantly, resulting in slow combustion. Conventional AWSs have the disadvantage of being prone to reduced combustion stability.

[0060] Furthermore, when the outside air temperature is extremely low, it is difficult to sufficiently increase the temperature of the exhaust gas supplied to the catalytic converter 31 even if the ignition timing is delayed.

[0061] The temperature rise control of the catalytic converter 31 in this engine system does not increase internal energy by reducing the work done during the expansion stroke, but rather increases the temperature of the exhaust gas supplied to the catalytic converter 31 by converting part of the piston work done during the exhaust stroke into exhaust energy.

[0062] FIG. 3 shows the lift curve (lower diagram) and pv diagram (upper diagram) of the exhaust valve 12 for temperature rise control and non-temperature rise control, respectively. The solid line in the lower diagram of FIG. 3 shows the lift curve of the exhaust valve 12 for temperature rise control. The dashed line in the lower diagram of FIG. 3 shows the lift curve of the exhaust valve 12 for non-temperature rise control. The solid line in the upper diagram of FIG. 3 is the pv diagram for temperature rise control, and the dashed line in the upper diagram of FIG. 3 is the pv diagram for non-temperature rise control. The dashed line in the lower diagram of FIG. 3 shows the lift curve of the intake valve 11.

[0063] The opening timing of the exhaust valve 12 during temperature rise control is retarded relative to the opening timing of the exhaust valve 12 during non-temperature rise control. More specifically, the opening timing of the exhaust valve 12 is set to a crank angle of 50 degrees or more after bottom dead center of the exhaust stroke. The exhaust VVL 19 uses the second cam to open and close the exhaust valve 12, thereby reducing the lift of the exhaust valve 12 and retarding the opening timing of the exhaust valve 12 (see the hollow arrow in the lower diagram of Figure 3). The closing timing of the exhaust valve 12 during temperature rise control is the same as the opening timing of the exhaust valve 12 during non-temperature rise control. During temperature rise control, the exhaust valve 12 opens and closes only during a portion of the exhaust stroke.

[0064] Because the opening timing of the exhaust valve 12 is delayed after bottom dead center on the exhaust stroke, the piston performs normal work on the expansion stroke, and then on the exhaust stroke, the piston work corresponding to the hatched portion on the pv diagram in the upper diagram of Figure 3 is converted into exhaust energy. In other words, the gas temperature rises due to the recompression of the gas inside the cylinder 2, and after the exhaust valve 12 opens, high-temperature exhaust gas is supplied to the catalytic device 31.

[0065] Because temperature rise control is performed while the vehicle is stopped, no driving torque is required of the engine 1. During temperature rise control, the torque required of the engine 1 is small. During temperature rise control, even if part of the piston work in the exhaust stroke is converted into exhaust energy, the torque required of the engine 1 is met.

[0066] During non-temperature rise control, the exhaust VVL 19 uses the first cam to open and close the exhaust valve 12. The exhaust valve 12 opens before bottom dead center of the exhaust stroke, and the exhaust valve 12 is open for substantially the entire duration of the exhaust stroke.

[0067] Figure 4 shows the change in in-cylinder pressure (top graph) and the change in heat release rate (bottom graph) with respect to the progression of the crank angle for a conventional AWS and for the temperature rise control of this engine system. With a conventional AWS, ignition occurs, for example, during the second period of the expansion stroke (45-90 degrees after top dead center on the compression stroke), after which combustion begins. As shown by the dashed line in Figure 4, combustion begins under conditions where the in-cylinder pressure on the expansion stroke has dropped significantly, resulting in slow combustion and a longer combustion period. The center of gravity of combustion is, for example, in the second half of the expansion stroke (90-180 degrees after top dead center on the compression stroke).

[0068] The second half of the expansion stroke is the second half when the expansion stroke is divided into the first half (0-90 degrees after top dead center of the compression stroke) and the second half (90-180 degrees after top dead center of the compression stroke). The second period of the expansion stroke (45-90 degrees after top dead center of the compression stroke) is the second period when the expansion stroke is divided into four periods: the first period (0-45 degrees after top dead center of the compression stroke), the second period (45-90 degrees after top dead center of the compression stroke), the third period (90-135 degrees after top dead center of the compression stroke), and the fourth period (135-180 degrees after top dead center of the compression stroke).

[0069] The combustion center of gravity may be, for example, MFB50, which is the crank angle at which the mass fraction burned is 50%.

[0070] Unlike conventional AWS, the temperature rise control in this engine system does not require delaying the ignition timing to delay the center of combustion. With temperature rise control in this engine system, ignition occurs, for example, in the first period of the expansion stroke (0-45 degrees after top dead center on the compression stroke). As shown by the solid line in Figure 4, combustion begins before the pressure inside the cylinder drops significantly on the expansion stroke, making combustion relatively rapid and shortening the combustion period. The center of combustion is, for example, in the first half of the expansion stroke (0-90 degrees after top dead center on the compression stroke).

[0071] In conventional AWS, combustion occurs in the latter half of the expansion stroke, resulting in low combustion stability. In contrast, the temperature rise control in this engine system causes combustion to occur in the first half of the expansion stroke. The bottom diagram in Figure 5 compares the combustion stability of conventional AWS with that of temperature rise control in this engine system. With temperature rise control in this engine system, the center of combustion is relatively advanced, resulting in higher combustion stability than conventional AWS combustion.

[0072] The upper graph in Figure 5 compares the temperature of exhaust gas supplied to the catalytic converter 31 in the case of a conventional AWS with the temperature of exhaust gas obtained by temperature rise control in this engine system. With temperature rise control in this engine system, although the center of combustion is advanced, the exhaust gas temperature is increased by recompressing the exhaust gas during the exhaust stroke. Therefore, as shown in the upper graph in Figure 5, the temperature of exhaust gas obtained by temperature rise control in this engine system is higher than that obtained by a conventional AWS.

[0073] The temperature rise control in this engine system also suppresses emissions. The upper graph in Figure 6 compares the maximum in-cylinder temperature between a conventional AWS and the temperature rise control in this engine system. The lower graph in Figure 6 compares the NOx concentration between a conventional AWS and the temperature rise control in this engine system. The temperature rise control in this engine system reduces NOx more than the conventional AWS.

[0074] Conventional AWS combustion occurs in the latter half of the expansion stroke. The amount of downward movement of the piston 5 after combustion begins is relatively small. Because the expansion work associated with the downward movement of the piston 5 after combustion begins is small, the temperature inside the cylinder becomes higher. Because the temperature inside the cylinder is high, the concentration of NOx is relatively high.

[0075] As mentioned above, in contrast to conventional AWS, combustion during temperature rise control in this engine system occurs in the first half of the expansion stroke. The amount of downward movement of the piston 5 after combustion begins is greater than in conventional AWS. Because the amount of expansion work associated with the downward movement of the piston 5 is greater, the temperature inside the cylinder drops. Because the temperature inside the cylinder is low, the NOx concentration decreases during temperature rise control in this engine system.

[0076] The upper graph in Figure 7 compares the HC concentration between a conventional AWS and the temperature rise control in this engine system. The lower graph in Figure 7 compares the CO concentration between a conventional AWS and the temperature rise control in this engine system. The temperature rise control in this engine system reduces HC and CO more than the conventional AWS.

[0077] The upper graph in Figure 8 shows the change in HC concentration when the opening timing of the exhaust valve 12 is changed during temperature rise control in this engine system. Note that even if the opening timing of the exhaust valve 12 is changed, the fuel injection timing and ignition timing do not change. If the opening timing of the exhaust valve 12 is set to the expansion stroke, that is, if the opening timing is relatively advanced, the time for the combustion reaction in the cylinder 2 is shortened accordingly. As a result of the shorter reaction time, the HC concentration increases. As the opening timing of the exhaust valve 12 is delayed from the expansion stroke to the exhaust stroke, the reaction time increases, which causes the oxidation of HC to progress and the HC concentration to decrease (see arrow (1) in the upper graph in Figure 8).

[0078] Furthermore, if the opening timing of the exhaust valve 12 is delayed to 50 degrees or more after bottom dead center on the exhaust stroke, the gas inside the cylinder 2 is recompressed during the exhaust stroke, which promotes the oxidation of HC. As a result, the HC concentration is further reduced (see arrow (2) in the upper diagram of Figure 8). In other words, by delaying the opening timing of the exhaust valve 12 to a crank angle of 50 degrees or more after bottom dead center on the exhaust stroke during temperature rise control, the aforementioned improvement in combustion stability and reduction in NOx concentration are not only achieved, but the exceptional effect of further reducing the HC concentration is also achieved. The HC concentration during temperature rise control in this engine system is significantly lower than the HC concentration in the conventional AWS shown by the dashed line in the upper diagram of Figure 8.

[0079] The lower graph in Figure 8 shows the change in CO concentration when the opening timing of the exhaust valve 12 is changed during the temperature rise control of this engine system. As mentioned above, as the opening timing of the exhaust valve 12 is delayed from the expansion stroke to the exhaust stroke, the reaction time increases, which promotes CO oxidation and decreases the CO concentration (see arrow (3) in the lower graph in Figure 8). Note that if the opening timing of the exhaust valve 12 is delayed beyond 50 degrees after bottom dead center on the exhaust stroke, the gas in cylinder 2 is recompressed during the exhaust stroke, which promotes the oxidation of HC and generates CO, as described above. However, because the temperature required for the CO oxidation reaction is higher than the temperature required for the HC oxidation reaction, CO oxidation is not promoted as much. As a result, if the opening timing of the exhaust valve 12 is delayed beyond 50 degrees after bottom dead center on the exhaust stroke, the CO concentration increases slightly. However, as shown by arrow (4) in the lower graph in Figure 8, the CO concentration during the temperature rise control of this engine system is lower than the CO concentration with a conventional AWS.

[0080] As described above, the temperature rise control of this engine system involves having the piston do its normal work during the expansion stroke, and then converting part of the piston work into exhaust energy during the exhaust stroke to raise the temperature of the catalytic converter 31. This improves combustion stability and reduces emissions compared to conventional AWS, which reduces work during the expansion stroke and increases internal energy.

[0081] Furthermore, recompression of the gas after combustion in the cylinder 2 makes it possible to supply relatively hot exhaust gas to the catalytic converter 31 even when the outside air temperature is extremely low. Even in an extremely low temperature environment, the catalytic converter 31 is quickly activated.

[0082] Furthermore, because the opening timing of the exhaust valve 12 is retarded by changing the lift amount of the exhaust valve 12, the closing timing of the exhaust valve 12 becomes the same as during non-temperature rise control. Not retarding the closing timing of the exhaust valve 12 can prevent an increase in internal EGR during temperature rise control, which also prevents a decrease in combustion stability during temperature rise control.

[0083] (Control procedure for temperature rise control) Next, the control procedure for temperature rise control will be described with reference to the flowchart of Figure 9. In step S91, the engine system control device 100 determines whether the engine 1 has been started. Step S91 is repeated until the engine 1 has been started.

[0084] Once the engine 1 is started, in step S92, the control device 100 determines whether the catalytic converter 31 is inactive. The control device 100 may determine whether the catalytic converter 31 is inactive, for example, based on a signal from the water temperature sensor SN6. This is because, when the engine 1 is cold started, the temperature of the engine 1 coolant is low and the catalytic converter 31 is inactive. If the catalytic converter 31 is active, this flow ends.

[0085] If the catalytic converter 31 is inactive, the control device 100 executes temperature increase control of the catalytic converter 31. Specifically, in step S93, the control device 100 sets the opening timing of the exhaust valve 12 to 50 degrees after bottom dead center of the exhaust stroke. Specifically, the control device 100 instructs the exhaust VVL 19 to switch from the first cam to the second cam. If the lift amount of the exhaust valve 12 decreases due to the switch to the second cam, the opening timing of the exhaust valve 12 is retarded to 50 degrees after bottom dead center of the exhaust stroke.

[0086] In step S94, the control device 100 reads signals from various sensors. In the following step S95, the control device 100 determines whether the inlet temperature of the catalytic converter 31 is equal to or higher than a reference value and whether the amount of emissions is equal to or lower than a reference value. If the inlet temperature of the catalytic converter 31 is not equal to or higher than the reference value, that is, if the temperature of the exhaust gas supplied to the catalytic converter 31 is lower than the reference value, or if the amount of emissions from the exhaust gas passing through the catalytic converter 31 is higher than the reference value, the engine system raises the temperature of the exhaust gas to activate the catalytic converter 31 earlier. In step S96, the control device 100 further delays the opening timing of the exhaust valve 12. Specifically, the control device 100 instructs the exhaust S-VT 18 to retard the opening timing of the exhaust valve 12. As described above, the exhaust S-VT 18 can continuously retard the opening and closing timing of the exhaust valve 12. If the opening timing of the exhaust valve 12 is retarded, the piston work is converted into exhaust energy, and the temperature of the exhaust gas supplied to the catalytic device 31 increases.

[0087] The opening timing of the exhaust valve 12 may be set to 70 degrees or later after bottom dead center of the exhaust stroke. The later the opening timing of the exhaust valve 12, the more advantageous it is for raising the temperature of the exhaust gas. Note that the amount of retardation of the opening timing of the exhaust valve 12 is limited to a range in which the exhaust gas temperature does not become too high and damage the catalytic converter 31.

[0088] During temperature rise control, the vehicle is stopped and no driving torque is required of the engine 1, so the torque required of the engine 1 is relatively low. However, in addition to the torque required for idling the engine 1, there are cases where torque for driving engine accessories, for example, for cabin air conditioning or power generation, is required of the engine 1. The amount of retardation of the opening timing of the exhaust valve 12 is limited within a range in which the required torque of the engine 1 can be satisfied.

[0089] Steps S94, S95, and S96 are repeated until the determination in step S95 is Yes. If the determination in step S95 is Yes, the catalytic converter 31 is activated, and therefore the control device 100 changes the opening timing of the exhaust valve 12 to the expansion stroke in step S97. Specifically, the control device 100 instructs the exhaust VVL 19 to switch from the second cam to the first cam. If the lift amount of the exhaust valve 12 increases due to the switch to the first cam, the opening timing of the exhaust valve 12 is advanced.

[0090] 9, in step S95, it is determined whether the catalytic converter 31 has been activated and the temperature rise control is then terminated. Alternatively, the control device 100 may terminate the temperature rise control when a predetermined time has elapsed since the start of the temperature rise control.

[0091] (Variation) In addition to using the exhaust VVL 19 to change the opening timing of the exhaust valve 12, the control device 100 may also use the exhaust S-VT 18 to change the opening timing of the exhaust valve 12 during temperature rise control. FIG. 10 shows the lift curves of the exhaust valve 12 during temperature rise control and non-temperature rise control when the exhaust S-VT 18 is used. The solid line in FIG. 10 shows the lift curve of the exhaust valve 12 during temperature rise control. The dashed line in FIG. 10 shows the lift curve of the exhaust valve 12 during non-temperature rise control. The exhaust S-VT 18 retards the opening timing of the exhaust valve 12 during temperature rise control (see the white arrow in FIG. 10). Note that the exhaust S-VT 18 does not change the opening period of the exhaust valve 12, and therefore retarding the opening timing of the exhaust valve 12 also retards the closing timing of the exhaust valve 12.

[0092] By retarding the opening timing of the exhaust valve 12, the piston performs normal work during the expansion stroke, and then part of the piston work is converted into exhaust energy during the exhaust stroke, allowing the engine system to supply high-temperature exhaust gas to the catalytic converter 31. This accelerates the temperature rise of the catalytic converter 31. Also, as mentioned above, because the center of gravity of combustion is not retarded, combustion stability is ensured and emissions are suppressed.

[0093] The temperature rise control may be performed according to the flowchart of Fig. 9. Alternatively, the temperature rise control may be performed according to the flowchart of Fig. 11, for example. In the control procedure of Fig. 11, in step S111, the engine system control device 100 determines whether the engine 1 has been started. Step S111 is repeated until the engine 1 has been started.

[0094] When the engine 1 is started, the control device 100 determines in step S112 whether the catalytic converter 31 is inactive, for example, based on the signal of the water temperature sensor SN6. If the catalytic converter 31 is active, this flow ends.

[0095] If the catalytic converter 31 is inactive, the control device 100 executes temperature increase control of the catalytic converter 31. Specifically, in step S113, the control device 100 uses the exhaust S-VT 18 to set the opening timing of the exhaust valve 12 to 50 degrees after the bottom dead center of the exhaust stroke.

[0096] In step S114, the control device 100 reads signals from various sensors, and in the following step S115, the control device 100 calculates the difference between the inlet temperature of the catalytic converter 31 and a reference value, and the difference between the amount of emissions emitted and the reference value. In the following step S116, the control device 100 sets the opening timing of the exhaust valve 12 according to the difference calculated in step S115. If the difference between the inlet temperature of the catalytic converter 31 and the reference value is large, that is, if the temperature of the exhaust gas supplied to the catalytic converter 31 is low, or if the difference between the amount of emissions emitted and the reference value is large, that is, if the activity of the catalytic converter 31 is low, the control device 100 delays the opening timing of the exhaust valve 12. This increases the temperature of the exhaust gas.

[0097] Here, if the opening timing of the exhaust valve 12 is retarded, the opening timing may be set to 70 degrees or later after bottom dead center of the exhaust stroke. As shown in Figure 10, if the opening timing of the exhaust valve 12 is retarded, the closing timing is also retarded. This increases the overlap between the opening period of the exhaust valve 12 and the opening period of the intake valve 11, increasing internal EGR. The amount of retardation of the opening timing of the exhaust valve 12 is limited to a range in which combustion stability does not decrease below the standard due to an increase in internal EGR.

[0098] In step S116, if the difference between the inlet temperature of the catalytic device 31 and the reference value is small, that is, if the temperature of the exhaust gas supplied to the catalytic device 31 is relatively high, or if the difference between the emission amount and the reference value is small, that is, if the activity of the catalytic device is high, the control device 100 advances the opening timing of the exhaust valve 12.

[0099] 9, the opening timing of the exhaust valve 12 is maintained at a retarded timing until the temperature of the catalytic converter 31 reaches the activation temperature, and after the temperature of the catalytic converter 31 reaches the activation temperature, the opening timing of the exhaust valve 12 is switched from the retarded timing to the opening timing of the exhaust valve 12 in non-temperature rise control upon completion of the temperature rise control. In the flow of FIG. 11, during the temperature rise control, the opening timing of the exhaust valve 12 is advanced from the retarded timing to the opening timing of the exhaust valve 12 in non-temperature rise control as the temperature of the catalytic converter 31 rises.

[0100] In step S117, the control device 100 determines whether the inlet temperature of the catalytic converter 31 is equal to or higher than a reference value and whether the amount of exhaust gas emissions that has passed through the catalytic converter 31 is equal to or lower than a reference value. If the determination in step S117 is No, the control device 100 repeats steps S114, S115, S116, and S117 to continue the temperature rise control. If the determination in step S117 is Yes due to activation of the catalytic converter 31, the control device 100 changes the opening timing of the exhaust valve 12 to the expansion stroke in step S118 to end the temperature rise control. Specifically, the control device 100 instructs the exhaust S-VT 18 to advance the opening timing of the exhaust valve 12. Note that if the determination in step S117 is Yes as a result of adjusting the opening timing in step S116, the opening timing of the exhaust valve 12 may already be set to the expansion stroke.

[0101] As the temperature of the catalytic converter 31 rises, the opening timing of the exhaust valve 12 is advanced, thereby increasing the torque of the engine 1. This is advantageous for ensuring the torque required to drive engine accessories, for example, during temperature rise control.

[0102] 9, if the opening timing of the exhaust valve 12 is kept retarded until the temperature of the catalytic converter 31 reaches the activation temperature, relatively high-temperature exhaust gas continues to be supplied to the catalytic converter 31 during the temperature rise control, so the temperature of the catalytic converter 31 rises quickly. As a result, there is an advantage in that the period of temperature rise control is shortened.

[0103] 11, in step S117, it is determined whether the catalytic converter 31 has been activated and the temperature rise control is then terminated. Alternatively, the control device 100 may terminate the temperature rise control when a predetermined time has elapsed since the start of the temperature rise control.

[0104] The above-described embodiments may be combined with each other to the extent possible. [Explanation of symbols]

[0105] 1 engine 12 Exhaust valve 13 Spark plug 18 Exhaust S-VT (variable exhaust valve system) 19 Exhaust VVL (Variable Exhaust Valve System) 100 control device 30 Exhaust passage 31 Catalytic converter 6 Combustion chamber

Claims

1. a variable exhaust valve device that changes at least the opening timing of the exhaust valve; a catalytic converter located in an exhaust passage of the engine and purifying exhaust gas; a control device that executes temperature rise control to increase the temperature of the catalytic converter when the catalytic converter is inactive after the engine is started, In the temperature rise control, the control device retards the opening timing of the exhaust valve to a crank angle of 50 degrees or more after bottom dead center of the exhaust stroke.

2. 2. The engine exhaust valve control device according to claim 1, In the temperature rise control, the control device retards the opening timing of the exhaust valve to a crank angle of 70 degrees or more after bottom dead center of the exhaust stroke.

3. 2. The engine exhaust valve control device according to claim 1, The engine further includes a spark plug for igniting the air-fuel mixture in the combustion chamber. The control device sets the ignition timing of the spark plug so that the center of combustion is in the first half of the expansion stroke during the temperature rise control.

4. The engine exhaust valve control device according to any one of claims 1 to 3, the variable exhaust valve device changes the opening timing of the exhaust valve by changing the lift amount of the exhaust valve, The control device delays the opening timing of the exhaust valve in the temperature rise control compared to the opening timing of the exhaust valve in the non-temperature rise control, and closes the exhaust valve at the same time as the closing timing of the exhaust valve in the non-temperature rise control.

5. The engine exhaust valve control device according to any one of claims 1 to 3, the variable exhaust valve device changes the opening and closing timing of the exhaust valve without changing the lift amount of the exhaust valve, An exhaust valve control device for an engine, wherein the control device delays both the opening and closing timings of the exhaust valve during the temperature rise control compared to the opening and closing timings of the exhaust valve during non-temperature rise control.

6. 6. The engine exhaust valve control device according to claim 5, The control device determines an amount of retardation of the opening timing of the exhaust valve in the temperature rise control within a range in which a predetermined level of combustion stability or higher is ensured.

7. 2. The engine exhaust valve control device according to claim 1, The control device switches the opening timing of the exhaust valve from a retarded timing to the opening timing of the exhaust valve in the non-temperature rise control upon termination of the temperature rise control after the temperature of the catalytic device reaches an activation temperature.

8. 2. The engine exhaust valve control device according to claim 1, The control device advances the opening timing of the exhaust valve from a retarded timing toward the opening timing of the exhaust valve in the non-temperature rise control as the temperature of the catalytic converter rises during the temperature rise control.

9. a variable exhaust valve device that changes at least the opening timing of the exhaust valve; a catalytic converter located in an exhaust passage of the engine and purifying exhaust gas; a control device that executes temperature rise control to increase the temperature of the catalytic converter when the catalytic converter is inactive after the engine is started, the control device delays the opening timing of the exhaust valve to a point after the bottom dead center of the exhaust stroke during the temperature rise control, and advances the opening timing of the exhaust valve relative to that during the temperature rise control during the non-temperature rise control in which the catalytic device is active, The control device is configured to close the exhaust valve at the same timing during the temperature increase control and the temperature non-rise control.

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