JP2009174364A - Engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce or eliminate turbo lag in a lean burn engine, for example an engine provided with a sequential turbocharger. <P>SOLUTION: This engine control device includes a plurality of exhaust pipes introducing exhaust gas from each of a plurality of cylinder groups in parallel and keeping mutual communication by communication pipes, a plurality of turbines arranged in each of the plurality of exhaust pipes and having different capacities, a change over means changing over an exhaust passage comprising the plurality of exhaust pipes and communication pipes to lead exhaust gas form the plurality of cylinder groups to at least one of the plurality of turbines, and a control means controlling the change over means according to an operation zone to which an operation point provided by target revolution speed of the engine and target torque. When both turbo zones touch a large turbo zone at a high revolution speed side or a high torque side in the operation zone, a small turbo zone is at least partially put in a touching range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technical field of an engine control device for controlling a lean burn engine including, for example, a sequential turbocharger.

  When the engine is in a predetermined operating state, the air-fuel ratio is controlled to a target value (for example, 22) on the lean side of the fuel (that is, lean side) rather than the stoichiometric air-fuel ratio (for example, 14.7). Lean burn engines that improve the performance are known.

  However, in such a lean fuel, there is a problem that the conventional three-way catalyst device cannot sufficiently purify nitrogen oxides (NOx) in the exhaust gas.

  Thus, so-called NOx catalysts are known. The NOx catalyst adsorbs NOx in the exhaust in an oxygen-rich state (that is, an oxidizing atmosphere) formed by lean air-fuel ratio control, and then a hydrocarbon HC excess state (that is, formed by rich air-fuel ratio control) In the reducing atmosphere), the adsorbed NOx is reduced.

  By the way, this NOx catalyst has another problem of sulfur poisoning. That is, if sulfur S, its compound SOx, or the like adheres to the portion that adsorbs NOx, the NOx adsorption capacity is reduced.

  Therefore, Patent Document 2 discloses bank control that attempts to recover from sulfur poisoning by utilizing the property that sulfur S or the like is desorbed from the NOx catalyst under a predetermined high temperature state (for example, 650 ° C. or higher). Proposed. According to this bank control, the air-fuel ratio of the mixed gas used for combustion is allocated to a predetermined value on the rich side or lean side for each cylinder, whereby unburned gas is appropriately supplied to the NOx catalyst, and is included in the unburned gas. The unburned hydrocarbon and residual oxygen are combusted, and the NOx catalyst is heated to a predetermined high temperature state (for example, 650 ° C. or higher), so that sulfur S and the like are desorbed.

  Here, when the lean burn engine includes a sequential turbocharger composed of large and small turbochargers arranged in parallel, a bank control region (see FIG. 5 (a)), not only one of the large and small turbochargers is activated, but also activates both turbochargers. Note that an operation region in which only the small turbocharger is operated is referred to as a “small turbo region”, and an operation region in which only the large turbocharger is operated is appropriately referred to as a “large turbo region”.

  However, when the operating point is switched from the bank control region to the high turbo region on the high speed or high torque side, that is, the operation of both large and small turbochargers is switched to the operation of only the large turbocharger. The following problems can occur. That is, until just before switching to the large turbo range, the exhaust energy is distributed in both large and small, so the exhaust energy necessary to output the desired boost pressure alone is accumulated in the large turbocharger. Not. For this reason, when transitioning from the bank control region to the high turbo region on the high speed or high torque side, it takes a certain amount of time to reach the exhaust energy required for the large turbocharger, and the torque rises. Delays can cause turbo lag and torque shocks.

  As a technology for preventing the occurrence of this type of turbo lag and torque shock, for example, Patent Document 1 discloses that when switching from supercharging operation of only one large or small turbocharger to supercharging operation of both turbochargers. A technique has been proposed in which the air-fuel ratio is corrected to the lean side, thereby reducing the amount of heat of vaporization accompanying fuel vaporization to compensate for the decrease in exhaust temperature.

  However, in Patent Document 1, bank control specific to the lean burn engine as described above is not assumed. That is, in the lean burn engine, no special consideration is given when switching from the operation of both large and small turbochargers to the operation of only the large turbocharger. In this case, in particular, since the exhaust energy is distributed to both large and small turbochargers, turbo lag and torque shock may occur after switching.

JP 7-217476 A JP-A-8-189388

  The present invention has been made in view of the above-described problems, for example, in a configuration in which large and small turbochargers are arranged in parallel in the intake and exhaust systems of a lean burn engine equipped with a NOx catalyst. It is an object to provide an engine control device capable of reducing or eliminating shock.

  An engine control apparatus according to the present invention is an engine control apparatus for controlling a lean burn engine in order to solve the above-described problem, and guides exhaust from each of a plurality of cylinder groups in parallel and communicates with each other by a communication pipe. At least one of the plurality of exhaust pipes that communicates with each other, a plurality of turbines that are disposed in each of the plurality of exhaust pipes and have different capacities, and exhaust from the plurality of cylinder groups. Switching means for switching the exhaust passage composed of the plurality of exhaust pipes and the communication pipe, the target engine speed of the engine, and the operating region to which the operating point defined by the target torque belongs, Control means for controlling the switching means, and in the operating region, exhaust is guided only to a small turbine having a relatively small capacity among the plurality of turbines. The small turbo region, the large turbo region in which exhaust gas is guided only to a large turbine having a capacity larger than that of the small turbine, and both turbo regions in which exhaust gas is guided to both the small turbine and the large turbine. In the region, when the two turbo regions are in contact with the large turbo region on the high rotation speed side or the high torque side, the small turbo region is interposed at least partially in the contact range.

  In this configuration, the lean burn engine burns fuel under the condition that the air-fuel ratio is always lean (ie, excess air) for the purpose of improving fuel efficiency, and is temporarily stoichiometric (ie, stoichiometric air-fuel ratio) to rich. An engine that burns under conditions (ie, excess fuel). A lean burn engine typically includes a NOx catalyst in its exhaust pipe in addition to a three-way catalyst. The NOx catalyst is a catalyst that effectively purifies nitrogen oxides (that is, NOx) contained in the exhaust gas in which oxygen coexists. For example, a lean storage reduction type NOx to which a storage material that stores NOx in a lean atmosphere is added. It is a catalyst.

  The cylinder group is preferably composed of a plurality of cylinders whose operation phases are separated as much as possible in order to avoid interference of exhaust. Exhaust gas from a plurality of cylinders constituting one cylinder group is collected by a manifold, and is led to the outside of the vehicle in parallel with other exhaust pipes by one exhaust pipe corresponding to the one cylinder group. However, the exhaust pipes communicate with each other through a communication pipe. Therefore, the exhaust from one cylinder group can be selectively guided to another exhaust pipe by the switching means described later.

  The plurality of turbines are disposed in each of the plurality of exhaust pipes. As described above, since the plurality of exhaust pipes are arranged in parallel, it can be said that the plurality of turbines are arranged in parallel. Each turbine is paired with a compressor disposed in the intake pipe and functions as a turbocharger. These turbines have different capacities. That is, the flow rate or flow rate of the exhaust gas to be sprayed is different. The turbine capacities may be structurally different in advance, or may be different afterwards by using a so-called variable capacity turbocharger.

  The exhaust passage is composed of a plurality of exhaust pipes and communication pipes, and other pipes through which the exhaust can pass, and indicates the pipe through which the exhaust passes.

  The switching means is composed of, for example, one or a plurality of switching valves provided in a plurality of exhaust pipes and communication pipes, and by switching these open / closed states, it is switched whether or not exhaust gas is allowed to pass through, Switch the exhaust passage. Thereby, the exhaust from the plurality of cylinder groups can be guided to at least one of the plurality of turbines.

  The control means is, for example, an electronic control unit, and defines an operation point based on signals from various sensors and a target engine speed and target torque set based on a predetermined map, and the operation to which the operation point belongs. The switching means is controlled according to the area.

  This operating region includes a small turbo region, a large turbo region, and both turbo regions. Here, in the small turbo region, exhaust is guided only to a small turbine having a relatively small capacity among a plurality of turbines. In the large turbo region, exhaust is guided only to a large turbine having a larger capacity than a small turbine. In both turbo regions, exhaust is directed to both small and large turbines. However, the small turbo region may include not only a mode in which 100% exhaust gas is guided to the small turbine but also a mode in which a small amount of exhaust gas is guided to other turbines. The same applies to the large turbo region.

  In the operation region, when both turbo regions are in contact with the large turbo region on the high rotation speed side or the high torque side, the small turbo region is interposed at least partially in the contact region. Note that “at least partially” means that both turbo regions do not need to intervene the small turbo region over the entire range where the high turbo speed side or the high torque side contacts the large turbo region. is there. That is, in the operation region, both the turbo region, the small turbo region, and the large turbo region basically exist in this order toward the high rotation speed side or the high torque side. This is to allow the case where no turbo region is interposed.

  According to this configuration, when the operating point transitions from both turbo regions to the large turbo region on the high speed side or the high torque side, the small turbo region is not directly transitioned to the large turbo region. Transition to the large turbo region indirectly via Then, since the capacity of the small turbine is smaller than the capacity of the large turbine, the time required for the supercharging to start up is shortened in the small turbo region that passes through. As a result, turbo lag and torque shock can be reduced or eliminated as compared with the case of direct transition to the large turbo region.

  In one aspect of the engine control apparatus according to the present invention, the two turbo regions are bank control regions, and in the bank control region, the first cylinder in which the air-fuel ratio is controlled to be lean among the plurality of cylinder groups. Bank control wherein the exhaust passage is switched so that exhaust from a group is introduced into one of the plurality of turbines and exhaust from a second cylinder group whose air-fuel ratio is controlled to other than lean is introduced into the other Is performed by the control means.

  According to this configuration, since the bank control is performed in both turbo regions, the unburned gas is burned in the sulfur-poisoned NOx catalyst to form a predetermined high-temperature state (for example, 650 ° C. or more), and thus the poisoning recovery can be performed. It becomes possible. Then, when the operating point subsequently transitions to the high turbo region on the high speed side or the high torque side, turbo lag and torque shock can be reduced or eliminated as compared to the case of transitioning directly to the large turbo region.

  In another aspect of the engine control apparatus according to the present invention, in the operation region, the large turbo region is in contact with the small turbo region on the high rotation speed side or the high torque side, and both the turbo regions are in the small region. It straddles the boundary between the turbo region and the large turbo region.

  According to this configuration, both turbo regions are in contact with the large turbo region on the high rotation speed side or the high torque side. Therefore, as described above, turbo lag and torque shock can be similarly reduced or eliminated if the small turbo region is interposed at least partially in the contact area.

  In another aspect of the engine control apparatus according to the present invention, the engine control device further includes an intake pressure detection unit that detects an intake pressure in an intake pipe in which a plurality of compressors that are a pair of the plurality of turbines is disposed, In the interposed small turbo region, when the detected intake pressure exceeds a predetermined pressure threshold, the switching means is controlled so as to transition to the large turbo region.

  In this configuration, the predetermined pressure threshold is a value that is specified in advance by experience, experiment, or simulation as a pressure that indicates the rise of supercharging by a small turbine, and is a value that takes into account the margin to the specified pressure. Also good. In addition, “when the intake pressure exceeds a predetermined pressure threshold” includes “when the intake pressure exceeds a predetermined pressure threshold” or “when the intake pressure exceeds a predetermined pressure threshold”. included.

  According to this configuration, since the small turbo region is interposed, turbo lag and torque shock can be reduced or eliminated, and in addition, after confirming the start of supercharging by the small turbine, it is possible to transition to the large turbo region at an appropriate timing. .

  The operation and other advantages of the present invention will become apparent from the best mode for carrying out the invention described below.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as the best mode for carrying out the invention.

  FIG. 1 is a schematic top view of an engine and a control device thereof according to the embodiment. As shown in FIG. 1, the engine is, for example, a lean burn engine having four cylinders, and four cylinders 12 a, 12 b, 12 c, and 12 d are provided in the cylinder block 10.

  The intake air is guided to the inlets of the small compressor 31C of the small turbocharger 31 and the large compressor 32C of the large turbocharger 32 provided in the pipe line of the intake pipe 38. The intake air pressurized by the small compressor 31C and the large compressor 32C is cooled by an intercooler (not shown), and is supplied to the cylinders 12a to 12d via the throttle valve 40 and the intake manifold 42. The small compressor 31C and the large compressor 32C may be driven by the small turbine 31T and the large turbine 32T, respectively, and may be provided in series in the pipe line of the intake pipe 38 or may be provided in parallel.

  The electronic control unit 46 includes an arithmetic processing unit and a memory, and provides control signals for an input port to which signals from various sensors indicating the operating state of the engine are supplied, and for the throttle valve 40 and the variable valve gear 44. An output port for output is provided. The various sensors include, for example, a throttle valve position sensor that detects the opening (position) of the throttle valve 40, an intake pressure sensor 381 that detects intake pressure upstream of the throttle valve 40, and a driver's depression of an accelerator pedal. An accelerator sensor 382 that detects the amount, a vehicle speed sensor 383 that detects the vehicle speed of the vehicle on which the engine is mounted, a rotation speed sensor and a rotation angle sensor that detect the rotation speed and rotation angle of the crankshaft 13, and the like. Here, the combination of the target engine speed and target torque is also referred to as the engine operating point. The electronic control unit 46 basically sets the operating point according to a predetermined map, giving priority to the engine operating efficiency.

  The order of ignition in each cylinder is adjusted so that the intake stroke, the compression stroke, the combustion / expansion stroke, and the exhaust stroke do not overlap each other as much as possible in order to smoothly rotate the shared crankshaft 13. In particular, the ignition order is, for example, 12a-12c-12d-12b so that the force applied to the crankshaft 13 from each cylinder is dispersed. At this time, when exhaust from each cylinder is collected together by the manifold and sent to the turbine, in order to avoid interference of exhaust from each cylinder, the first of the cylinders 12a and 12d whose operation phases are farthest from each other is provided. Exhaust gas from the cylinder group is collected by the exhaust sub-manifold 201 and introduced into the small turbine 31T of the small turbocharger 31 provided in the pipe line via the exhaust pipe 211 communicating with the downstream end thereof. On the other hand, the exhaust from the second cylinder group consisting of cylinders 12b and 12c, which are also the most distant from each other in operating phase, is collected by the exhaust sub-manifold 202, and the pipeline is connected via the exhaust pipe 212 communicating with the downstream end thereof. Is introduced into a large turbine 32T of a large turbocharger 32 provided in Hydrocarbons (HC) contained in the exhaust from each of the small turbine 31T and the large turbine 32T are purified by pre-catalysts 231 and 232 made of a three-way catalyst. The exhaust gas after purification is collected by the exhaust pipe 24 at a later stage, and the remaining nitrogen oxides (hereinafter referred to as NOx) are purified by the NOx catalyst 26. Thereafter, the exhaust is discharged to the atmosphere through a silencer (not shown).

  Here, the control valve used for the exhaust passage switching control will be described with reference to FIGS. 2 to 5 in addition to FIG. Here, FIG. 2 is a schematic plan view showing an open / close state of each control valve for introducing the exhaust gas only to the small turbine 31T in the engine control apparatus according to the embodiment. FIG. 3 is a schematic plan view showing an open / close state of each control valve for introducing exhaust gas only to the large turbine 32T in the engine control apparatus according to the embodiment. FIG. 4 is a schematic plan view showing an open / close state of each control valve for introducing exhaust gas into both the small turbine 31T and the large turbine 32T in the engine control apparatus according to the embodiment. For the exhaust passage switching control, the exhaust pipe 211 and the exhaust pipe 212 are connected by an exhaust communication pipe 213 upstream of each of the small turbine 31T and the large turbine 32T. And the 1st control valve 221 is provided in the pipe line of the exhaust pipe 211 between the connection part with the exhaust communication pipe 213, and the small turbine 31T. The second control valve 222 is provided between the connection portion with the exhaust communication pipe 213 and the large turbine 32T in the pipe line of the exhaust pipe 212. A communication control valve 223 is provided in the pipe line of the exhaust communication pipe 213.

  As shown in FIG. 2, when the first control valve 221 is opened, the second control valve 222 is closed, and the communication control valve 223 is opened, both the exhaust from the first cylinder group and the exhaust from the second cylinder group are detected. It is introduced only into the small turbine 31T.

  As shown in FIG. 3, when the first control valve 221 is closed, the second control valve 222 is opened, and the communication control valve 223 is opened, both the exhaust from the first cylinder group and the exhaust from the second cylinder group are detected. It is introduced only into the large turbine 32T.

  As shown in FIG. 4, when the first control valve 221 and the second control valve 222 are both opened and the communication control valve 223 is closed, the exhaust from the first cylinder group and the exhaust from the second cylinder group are respectively small turbines. 31T and the large turbine 32T.

  The opening / closing control of the first control valve 221, the second control valve 222, and the communication control valve 223 is performed by the electronic control unit 46 according to the operating point in the engine operating region shown in FIG. FIG. 5 is a map showing the operating range of the engine according to the embodiment by a combination of the target engine speed and the target torque.

  First, a comparative example and its problem will be described with reference to FIG. FIG. 5A shows the small turbo region, the large turbo region, and the bank control region, which are operating regions of the engine, with the upper limit being the WOT torque, that is, the torque when the throttle valve 40 is fully opened. Generally, the low rotation speed / low load area is a small turbo area and the high rotation speed / high torque area is a large turbo area so that supercharging can be performed with high efficiency over a wide operation area. The bank control area spans the boundary between the small turbo area and the large turbo area. In the bank control region, when the air-fuel ratio of the first cylinder group is controlled to be lean, for example, to make the temperature of the NOx catalyst 26 a desorption temperature such as sulfur S, the air-fuel ratio of the second cylinder group becomes rich. The exhaust from each cylinder group is controlled and introduced into each of the small turbine 31T and the large turbine 32T. Here, as indicated by the thick arrows in FIG. 5A, when the operating point is switched from the bank control region to the high turbo region on the high speed or high torque side, as pointed out in the background art described above, Appropriate time is required to reach the exhaust energy required for supercharging by the large turbocharger 32, and the increase in torque is delayed, which may cause turbo lag and torque shock.

  In contrast, in the present embodiment, as shown in FIG. 5B, an extended small turbo region is provided between the bank control region and the large turbo region. The exhaust flow rate sufficient to output the desired supercharging pressure by the small turbocharger 31 alone is smaller than that by the large turbocharger 32 alone. Therefore, if the exhaust flow rate does not change, the time required to reach an exhaust flow rate sufficient to output a desired supercharging pressure is shorter than that of the large turbocharger 32 alone. As a result, the rise of supercharging is accelerated and the turbo lag is reduced. Specific control at this time will be described with reference to FIG. Here, FIG. 6 is a flowchart showing control by the engine control apparatus according to the embodiment.

  As shown in FIG. 6, first, it is determined whether or not a bank control execution condition is satisfied (step S1). Here, the bank control execution condition is determined, for example, whether or not a predetermined time has elapsed from the previous bank control execution timing and the NOx catalyst 26 is assumed to be again poisoned with sulfur.

  Here, when it is determined that the execution condition of the bank control is not satisfied (step S1: No), the bank control is not executed, so that the operation point is not switched from the bank control area to the large turbo area. Therefore, this control is finished.

  On the other hand, when it is determined that the bank control execution condition is satisfied (step S1: Yes), it is then determined whether or not the operating point of the engine is in the bank control region (step S2).

  Here, when it is determined that the operation point of the engine is in the bank control region (step S2: Yes), in order to introduce exhaust into both the small turbine 31T and the large turbine 32T, as shown in FIG. Both the first control valve 221 and the second control valve 222 are opened, and the communication control valve 223 is closed (step S3).

  On the other hand, when it is determined that the operating point of the engine is not in the bank control region (step S2: No), it is determined whether or not the engine is in the small turbo region (step S4).

  Here, when it is determined that the operating point of the engine is in the small turbo region (step S4: Yes), as shown in FIG. 2, the first control valve 221 is set to introduce the exhaust only to the small turbine 31T. Open, close the second control valve 222, and open the communication control valve 223 (step S5).

  On the other hand, when it is determined that the operating point of the engine is not in the small turbo region (step S4: No), it is assumed that the engine is in the remaining large turbo region. The fact that the operation point of the engine is in the large turbo region may be immediately after the operation point is switched from the bank control region to the large turbo region on the high rotation speed or high torque side. Then, the turbo lag and torque shock pointed out in the background art described above may occur. Therefore, it is determined whether or not the target rotational speed or the target torque is a value that is greater than or equal to the bank control region (step S6).

  Here, when it is determined that neither the target rotational speed nor the target torque is a value greater than or equal to the bank control region (step S6: No), there is a possibility that turbo lag or torque shock may occur even when switching to the large turbo region. Almost no. Therefore, in order to introduce the exhaust gas only to the large turbine 32T, as shown in FIG. 3, the first control valve 221 is closed, the second control valve 222 is opened, and the communication control valve 223 is opened (step S8).

  On the other hand, when it is determined that the target rotational speed or the target torque is a value that is greater than or equal to the bank control region (step S6: Yes), if the turbo lag or Torque shock can occur. Therefore, first, in order to introduce exhaust gas only to the small turbine 31T, as shown in FIG. 2, the first control valve 221 is opened, the second control valve 222 is closed, and the communication control valve 223 is opened (step S7). As a result, as compared with the case where the exhaust gas is introduced only into the small turbine 31T, the time until the exhaust gas flow rate sufficient to output the desired supercharging pressure is shortened. As a result, the rise of supercharging is accelerated and the turbo lag is reduced.

  Thereafter, the intake pressure upstream of the throttle valve 40 is detected by the intake pressure sensor 381, and it is determined whether or not the value is equal to or greater than a predetermined pressure threshold value indicating the rising of the supercharging of the small turbocharger 31 ( Step S9).

  Here, when it is determined that the upstream pressure of the throttle valve 40 is not equal to or higher than the predetermined pressure threshold value (step S9: No), the rise of supercharging is still insufficient and there is a possibility of turbo lag. Therefore, exhaust is continuously introduced only into the small turbine 31T (RETURN).

  On the other hand, when it is determined that the upstream pressure of the throttle valve 40 is equal to or higher than the predetermined pressure threshold (step S9: Yes), the rise of the supercharging is sufficient and the possibility of turbo lag is also eliminated. Therefore, in order to introduce the exhaust gas only to the large turbine 32T, as shown in FIG. 3, the first control valve 221 is closed, the second control valve 222 is opened, and the communication control valve 223 is opened (step S10).

  According to the embodiment described above, in the configuration in which the large and small turbochargers are arranged in parallel in the intake and exhaust systems of the lean burn engine including the NOx catalyst 26, the operation point is changed from the bank control region to the high rotational speed. Alternatively, it is possible to reduce or eliminate turbo lag and torque shock that may occur when switching to the large turbo region on the high torque side.

  In the above embodiment, the NOx catalyst 26 is an example of the “NOx catalyst” according to the present invention. The first cylinder group including the cylinders 12a and 12d and the second cylinder group including the cylinders 12b and 12c are examples of the “cylinder group” according to the present invention. The exhaust communication pipe 213 is an example of the “communication pipe” according to the present invention. The exhaust pipe 211 and the exhaust pipe 212 are examples of the “exhaust pipe” according to the present invention. The small turbine 31T and the large turbine 32T are examples of the “turbine” according to the present invention. The first control valve 221, the second control valve 222, and the communication control valve 223 are examples of the “switching unit” according to the present invention. The electronic control unit 46 is an example of the “control unit” according to the present invention. The small turbo region is an example of the “small turbo region” according to the present invention. The large turbo region is an example of the “large turbo region” according to the present invention. The bank control area is an example of “both turbo areas” according to the present invention. The small compressor 31C and the large compressor 32C are examples of the “compressor” according to the present invention. The intake pressure sensor 381 is an example embodiment that corresponds to the “intake pressure detection means” according to the present invention.

  In the above-described embodiment, the description has been given using the four-cylinder engine, but the present invention is applicable to other multi-cylinder engines. Or although the above-mentioned embodiment demonstrated using the structure provided with one large and small turbocharger, this invention is applicable also to the structure provided with each two or more.

  That is, the present invention is not limited to the above-described embodiment, and can be appropriately changed within a scope not departing from the gist or philosophy of the invention that can be read from the claims and the entire specification. The control device is also included in the technical scope of the present invention.

It is a typical top view of the engine which concerns on embodiment, and its control apparatus. In the engine control device according to the embodiment, it is a schematic plan view showing the open / close state of each control valve for introducing exhaust only to the small turbine 31T. In the engine control device according to the embodiment, it is a schematic plan view showing the open / close state of each control valve for introducing exhaust gas only to the large turbine 32T. In the engine control device according to the embodiment, it is a schematic plan view showing the open / close state of each control valve for introducing exhaust into both the small turbine 31T and the large turbine 32T. It is a map which shows the driving | operation area | region of the engine which concerns on embodiment by the combination of the target engine speed and target torque of an engine. It is a flowchart which shows the control by the engine control apparatus which concerns on embodiment.

Explanation of symbols

  38 ... Intake pipe, 40 ... Throttle valve, 42 ... Intake manifold, 44 ... Variable valve operating device, 10 ... Cylinder block, 12a, 12b, 12c. 12d ... cylinder, 201 ... exhaust sub manifold, 202 ... exhaust sub manifold, 213 ... exhaust communication pipe, 221 ... first control valve, 222 ... second control valve, 223 ... communication control valve, 31 ... small turbocharger, 31T ... Small turbine, 31C ... small compressor, 32 ... large turbocharger, 32T ... large turbine, 32C ... large compressor, 231 ... pre-catalyst, 232 ... pre-catalyst, 24 ... exhaust pipe, 26 ... NOx catalyst

Claims (4)

An engine control device for controlling a lean burn engine,
A plurality of exhaust pipes that guide exhaust from each of the plurality of cylinder groups in parallel and communicate with each other by a communication pipe;
A plurality of turbines disposed in each of the plurality of exhaust pipes and having different capacities from each other;
Switching means for switching an exhaust passage composed of the plurality of exhaust pipes and the communication pipe so as to guide exhaust from the plurality of cylinder groups to at least one of the plurality of turbines;
Control means for controlling the switching means according to the target engine speed of the engine and the operating region to which the operating point defined by the target torque belongs,
The operating region includes a small turbo region in which exhaust is guided only to a small turbine having a relatively small capacity among the plurality of turbines, a large turbo region in which exhaust is guided only to a large turbine having a larger capacity than the small turbine, and the Comprising both turbo regions where exhaust is directed to both the small turbine and the large turbine,
In the operation region, when the two turbo regions are in contact with the large turbo region on the high rotation speed side or the high torque side, the small turbo region is interposed at least partially in the contact region. Engine control device. Both turbo areas are bank control areas,
In the bank control region, exhaust from the first cylinder group in which the air-fuel ratio is controlled to be lean among the plurality of cylinder groups is introduced into one of the turbines, and the air-fuel ratio is controlled to other than lean. 2. The engine control device according to claim 1, wherein the control unit performs bank control in which the exhaust passage is switched so that exhaust from the second cylinder group is introduced to the other. In the operating region,
The large turbo region is in contact with the small turbo region on the high speed side or the high torque side,
The engine control device according to claim 1, wherein the both turbo regions straddle a boundary between the small turbo region and the large turbo region. An intake pressure detecting means for detecting an intake pressure in an intake pipe in which a plurality of compressors that are paired with the plurality of turbines are disposed;
The control means controls the switching means so as to transition to the large turbo area when the detected intake pressure exceeds a predetermined pressure threshold in the interposed small turbo area. The engine control device according to any one of claims 1 to 3.

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