JP2009097346A - Control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively raise temperature of an exhaust gas flowing in an exhaust gas post-treatment device of a diesel engine including a plurality of cylinder groups without requiring a complicated control. <P>SOLUTION: Cylinders are distinguished by an individual bank exhaust temperature control routine (S11) when exhaust gas temperature control conditions are satisfied. Control with a normal fuel injection quantity is executed (S12) if it is a bank B2 the distance of which to a catalytic converter is long, and control increasing fuel injection quantity is executed (S13) if it is a bank B1 the distance of which to the catalytic converter is short. A fuel injection quantity is increased by changing a main injection and a post injection to a cylinder on the bank B1 side. Exhaust gas temperature is raised by increasing an injection time of the post injection near a bottom dead center while preventing torque fluctuation when the post injection is changed. The catalytic converter is quickly activated thereby, and a PM filter is quickly regenerated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine having a plurality of cylinder groups.

  Generally, in an engine having a plurality of cylinder groups such as a horizontally opposed type and a V type, exhaust gas is supplied to an exhaust aftertreatment device such as a catalytic converter by collecting exhaust passages for each cylinder group into one. However, the pipe length from the exhaust passage to the catalytic converter is different for each cylinder group due to the outfitting of the engine room.

  For this reason, in the group of cylinders having a long pipe line to the catalytic converter, exhaust heat is released to the pipe wall, resulting in a decrease in the temperature of the exhaust gas flowing into the catalytic converter from the gathering portion. There is a possibility that it takes time to activate the catalytic converter or that the activity of the catalytic converter cannot be maintained if the low load operation is continued. As countermeasures, there are methods such as improving the heat insulation performance of the exhaust pipe and increasing the amount of noble metal supported by the catalytic converter.

  In order to cope with this, Patent Document 1 discloses that the first exhaust passage connected to the first cylinder group and the second exhaust passage connected to the second cylinder group are second to the crankshaft axis. In an engine that is connected to the collective exhaust passage at a position deviated toward the exhaust passage side and includes a catalytic converter in the collective exhaust passage, the temperature of the exhaust gas exhausted from the first cylinder group is exhausted from the second cylinder group. Technology is disclosed that secures the exhaust gas temperature necessary to enhance the activation of the catalytic converter by controlling the combustion state of the engine so as to be higher than the temperature of the exhaust gas to be generated.

Further, in Patent Document 2, in an engine in which exhaust pipes having different lengths up to the catalytic converter are connected to at least two cylinder groups, exhaust gas discharged from one of the two cylinder groups is discharged from the other. A technique is disclosed in which the temperature is made higher than the exhaust gas and the outputs of the two cylinder groups are made uniform.
JP 59-200010 A JP 9-317506 A

  The technologies disclosed in Patent Document 1 and Patent Document 2 are both for the spark ignition type engine such as a gasoline engine, and the exhaust temperature is reduced by delaying the ignition timing and the opening timing of the exhaust valve. To raise. For this reason, in a diesel engine having a plurality of cylinder groups, it is difficult to apply when trying to cope with a decrease in exhaust temperature caused by the distance of the exhaust passage to the catalytic converter being different for each cylinder group. .

  Moreover, in the technique disclosed in Patent Document 1, the temperature of the catalytic converter is increased by increasing the temperature of the exhaust gas discharged from the cylinder group having a long distance to the catalytic converter, and the exhaust gas temperature at the exhaust port is increased. However, the amount of heat released to the exhaust pipe also increases, which is not efficient for improving the temperature of the exhaust gas flowing into the catalytic converter.

  Further, in the technique disclosed in Patent Document 2, the exhaust temperature is increased by increasing the opening timing of the exhaust valve, which requires a variable valve timing mechanism or the like, and the control is complicated. Instead, it becomes a factor of cost increase.

  The present invention has been made in view of the above circumstances, and can effectively increase the temperature of exhaust gas flowing into the exhaust aftertreatment device of a diesel engine having a plurality of cylinder groups without requiring complicated control. An object of the present invention is to provide an engine control device.

  In order to achieve the above object, a control device for a diesel engine according to the present invention has a plurality of cylinder groups, and joins exhaust branch pipes connected to each cylinder group at positions offset with respect to the axis of the crankshaft. In a diesel engine that is connected to one common exhaust pipe and an exhaust aftertreatment device is provided in the common exhaust pipe, a control condition for increasing the temperature of the exhaust gas flowing into the exhaust aftertreatment device is satisfied The fuel injection amount for the cylinder group communicating with the exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device is increased, and the exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device is increased. And a control unit for controlling the temperature of the exhaust gas flowing through the exhaust gas to be higher than the temperature of the exhaust gas flowing through the other exhaust branch pipes.

  ADVANTAGE OF THE INVENTION According to this invention, the temperature of the exhaust_gas | exhaustion which flows into the exhaust gas aftertreatment apparatus of the diesel engine which has a some cylinder group can be raised effectively, without requiring complicated control.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 relate to a first embodiment of the present invention, FIG. 1 is a schematic configuration diagram of an engine system, FIG. 2 is a flowchart showing a main routine of exhaust temperature control, and FIG. 3 is an exhaust temperature control routine for each bank. FIG. 4 is an explanatory diagram of an increase in fuel injection amount, FIG. 5 is a flowchart of an exhaust temperature control routine for each bank with a fuel injection timing retard, and FIG. 6 is an explanatory diagram showing a fuel injection timing retard.

  In FIG. 1, reference numeral 1 denotes a diesel engine having a plurality of cylinder groups such as a horizontally opposed type or a V type (hereinafter simply referred to as “engine”), and in the present embodiment, a horizontally opposed type engine. . In this engine 1, a cylinder block is divided into two cylinder groups of left and right banks B1 and B2 with a crankshaft 2 as a center, and an intake manifold communicating with an intake port of each cylinder is connected to each cylinder head of each bank B1 and B2. 2a and 2b are attached.

  The intake manifolds 2a and 2b of each bank are communicated with a common intake pipe via an intake chamber 3, and an injector 4 is disposed for each cylinder immediately upstream of the intake port of each cylinder. In the present embodiment, the injector 4 is an electromagnetic valve that intermittently opens and closes the nozzle hole at the tip by a drive signal. The injector 4 is supplied from a fuel supply system such as a high pressure pump (not shown) or a common rail for fuel stock pressure. Fuel is injected into the combustion chamber of each cylinder at a predetermined injection timing.

  Exhaust manifolds (exhaust branch pipes) 5a and 5b communicating with the exhaust ports of the cylinders are attached to the cylinder heads of the banks B1 and B2 of the engine 1, respectively. The exhaust manifolds 5a and 5b of each bank are merged at a position offset to the bank B1 side with respect to the axis of the crankshaft 2 for reasons of equipment in the engine room, and communicated with a common exhaust pipe 6.

  A turbocharger 7 is interposed in the common exhaust pipe 6 offset to the bank B1 side, and a catalytic converter 8 as an exhaust aftertreatment device is interposed downstream of the turbocharger 7. . The catalytic converter 8 includes, for example, a pre-stage catalyst such as an oxidation catalyst on the upstream side and a PM filter that filters and collects particulate matter (PM) on the downstream side.

  The engine 1 described above is controlled by an electronic control unit (ECU) 50 as a control unit that is configured around a microcomputer. The ECU 50 includes a crank angle sensor 9 that detects the rotational position of the crankshaft 2 and an accelerator opening sensor 10 that detects the accelerator opening, and various other sensors and switches that detect the operating state of the engine 1. Various actuators including the injector 4 are connected to the output side.

  The ECU 50 processes signals from sensors in accordance with a control program stored in the memory to detect an engine operating state, and controls energization control of a glow plug (not shown), fuel injection control via the injector 4, and the like. Perform engine control. In this engine control, the cylinder in the bank B1 close to the catalytic converter 8 immediately after starting or in an operating state where low-load operation continues or in a periodic regeneration control operation for regenerating the PM filter of the catalytic converter 8 Is controlled so as to be higher than the temperature of the exhaust gas from the cylinder of the bank B 2 far from the catalytic converter 8.

  That is, the exhaust manifolds 5a and 5b have different exhaust passage pipe lengths to the collecting section, and the exhaust passage pipe length and the pipe volume to the catalytic converter 8 are more on the bank B2 side than on the bank B1 side. Therefore, even if the exhaust temperature on the bank B2 side is raised, the amount of heat released to the pipe wall increases, which is efficient in raising the temperature of the exhaust gas flowing into the catalytic converter 8. I can't say that. Therefore, the loss due to heat dissipation is controlled by controlling the temperature of the exhaust gas from the bank B1 side, which is relatively short in the length of the exhaust passage to the catalytic converter 8, to be higher than the temperature of the exhaust gas from the bank B2 side. Can be suppressed to improve the heat energy transfer efficiency, and the catalytic converter 8 can be efficiently heated.

  The control for increasing the exhaust gas temperature on the bank B1 side is performed based on the fuel injection amount control for each bank, and the fuel injection amount for the cylinders in the bank B1 is increased more than the fuel injection amount for the cylinders in the bank B2. Then, the exhaust temperature on the bank B1 side close to the catalytic converter 8 is raised. In addition to this fuel injection amount control for each bank, the delay control of the fuel injection timing is additionally performed to correct the torque variation between cylinders due to the difference in the fuel injection amount for each bank. can do.

  Next, the exhaust gas temperature control by the ECU 50 will be described with reference to the flowcharts shown in FIGS.

  The flowchart in FIG. 2 shows a main routine for exhaust gas temperature control. First, in the first step S1, it is determined whether or not an exhaust gas temperature control condition for the catalytic converter 8 is satisfied. The exhaust temperature control condition is determined on the condition that the catalyst inactivation of the catalytic converter 8 or the regeneration operation of the PM filter is performed when the engine is started or when the load is low.

  Whether the catalytic converter is activated is determined, for example, as catalyst inactive when it is within a set time after the engine is started, or when it is in an operating state in which low load operation such as idle operation continues for a set time or longer. The exhaust temperature control condition is satisfied. Further, the exhaust gas temperature control condition for PM filter regeneration is that the exhaust temperature must be increased for PM filter regeneration in all cylinders, the exhaust temperature is low, the extremely low load region where regeneration cannot be performed, or the need for regeneration The exhaust temperature control condition is satisfied when it is an operation region excluding a high load region where there is no exhaust gas and a predetermined regeneration cycle is reached.

  In step S1, when the exhaust temperature control condition is not satisfied, the routine proceeds from step S1 to step S2, and normal control is executed. In this normal control, a fuel injection amount necessary for starting and a fuel injection amount capable of maintaining idle rotation are ensured, and a necessary fuel amount is increased during the regeneration operation of the PM filter.

  On the other hand, if the exhaust temperature control condition is satisfied in step S1, the process proceeds from step S1 to step S3, and the bank-specific exhaust temperature control routine shown in FIG. 3 is executed. Then, the exhaust temperature on the bank B1 side where the distance and volume of the exhaust passage to the catalytic converter 8 are relatively small is set higher than the exhaust temperature on the bank B2 side where the distance and volume of the exhaust passage to the catalytic converter 8 is relatively large. Control to be higher.

  The bank-specific exhaust temperature control routine of FIG. 3 will be described. In the exhaust temperature control routine for each bank, in the first step S11, cylinder discrimination is performed based on the signal from the crank angle sensor 9, and it is determined whether the current fuel injection target cylinder is the bank B1 or B2. As a result, if the current fuel injection target cylinder is a cylinder in bank B2, control is performed with a normal fuel injection amount in step S12, and if it is a cylinder in bank B1, the fuel injection amount is determined in step S13. Control to increase the amount.

  Specifically, the increase in the fuel injection amount is performed by changing the main injection or the post injection for the cylinder on the bank B1 side in the multistage injection of the fuel via the injector 4. For example, as shown in FIG. 4, when the multistage injection is a five-stage injection of pilot injection, pre-injection, main injection, after-injection, and post-injection, the injection time of post-injection near the bottom dead center that does not contribute to torque is set to By increasing, the exhaust temperature can be raised while preventing torque fluctuations, and the catalytic converter can be activated quickly even when the engine is started or when low-load operation continues.

  Further, during the regeneration operation of the PM filter, as is well known, by the post-injection near the bottom dead center, the gas containing the incomplete combustion component is intentionally discharged from the engine and burned (oxidized) by the preceding catalyst. The particulate matter collected in the PM filter by the generated heat is incinerated. Even in that case, it is possible to quickly regenerate the PM filter while minimizing deterioration in fuel consumption by effectively increasing the exhaust temperature by increasing the post injection time on only one bank B1 side. Become.

  On the other hand, when changing the main injection, the bank-specific exhaust temperature control routine of FIG. 5 is executed to increase the fuel injection amount and retard the injection timing. The bank-specific exhaust temperature control routine shown in FIG. 5 adds the step S14 of fuel injection timing retard to the bank-specific exhaust temperature control routine shown in FIG. If it is a cylinder, the fuel injection amount is increased in step S13, and the fuel injection timing is retarded in step S14.

  Specifically, as shown in FIG. 6, the time of main injection near the top dead center is extended, and the timing of the main injection is retarded to raise the exhaust temperature without breaking the torque balance. That is, if the main injection is extended only on one bank B1 side to increase the fuel injection amount, the torque of the cylinder on the one bank B1 side may increase and the torque balance with the cylinder on the other bank B2 may be lost. However, by retarding the main injection at the same time, the torque increase due to the fuel increase can be offset, and the exhaust temperature of one bank B1 can be raised while preventing torque variation.

  In this case, by combining the time extension of the main injection and the retard of the main injection timing with the time extension of the post injection, it is possible to minimize the fuel increase due to the main injection and reduce the influence of torque variation. is there.

  As described above, in the present embodiment, control is performed so that the exhaust temperature of the bank on the side where the length of the exhaust passage to the catalytic converter is short, the loss due to heat dissipation is suppressed, and the heat energy transfer efficiency is reduced. To improve. At that time, the exhaust temperature can be effectively increased only by increasing the fuel injection amount to the cylinder of the bank on the side where the pipe length of the exhaust passage to the catalytic converter is short, and the processing speed can be increased. Can do.

  Thereby, the catalytic converter at the time of start-up can be effectively promoted, and the activity of the catalytic converter can be maintained even when low load operation such as idling operation continues. Furthermore, even during a periodic regeneration operation for regenerating the PM filter, it is possible to promptly regenerate the PM filter by promoting incineration of the particulate matter collected in the PM filter.

  In particular, when the fuel injection amount is increased by increasing the post injection near the bottom dead center, the exhaust temperature can be raised without causing torque variation between banks, which is a simple control but has a great effect. Can be obtained. Even when the main injection near the top dead center is increased, by delaying the injection timing of the main injection, it is possible to prevent torque variation between banks in the same way, and to complicate the control unnecessarily. There is no invitation.

  Next, a second embodiment of the present invention will be described. 7 and 8 relate to a second embodiment of the present invention, FIG. 7 is a schematic configuration diagram of an engine system, and FIG. 8 is a flowchart of an exhaust temperature control routine for each bank.

  The second form retards the fuel increase and the injection timing of the bank B1 close to the catalytic converter 8 with respect to the first form described above, while restricting the intake amount of the bank B2 far from the catalytic converter 8.

  Generally, in a diesel engine, air is charged and compressed in a cylinder by supercharging or the like, and the fuel is ignited. Therefore, it can be said that the entire cylinder is lean combustion. Therefore, when the exhaust temperature control for each bank is performed, the exhaust air temperature can be raised without reducing the torque by limiting the excess air on the bank B2 side where the fuel injection amount increase (injection timing retard) is not performed. it can.

  For this reason, as shown in FIG. 7, the engine 1A in the second embodiment is provided with a device for intake air amount control with respect to the engine 1 in the first embodiment. Explaining the difference from the engine 1 of the first embodiment, the engine 1A controls the intake air amount for each bank B1, B2 downstream of the intake chamber 3 where the intake manifolds 2a, 2b of each bank are gathered. Valves (SCV) 20a and 20b are interposed, respectively.

  Actuators 21a and 21b are connected to the SCVs 20a and 20b, respectively, and the openings of the SCVs 20a and 20b are controlled via the actuators 21a and 21b. These actuators 21a and 21b are driven and controlled by the ECU 50 (or an intake control unit connected to the ECU 50 via a communication line).

  The bank-specific exhaust temperature control in the second embodiment is executed according to the routine shown in the flowchart of FIG. In this routine, after the cylinder discrimination in the first step S21, for the cylinders in the bank B1, the fuel injection amount is increased and the fuel injection timing is retarded in steps S24 and S25 as in the first embodiment. On the other hand, for the cylinders in the bank B2, the injection at the normal fuel injection amount is performed in step S22. In step S23, the opening of the SCV 20b on the bank B2 side is narrowed, and the intake amount on the bank B2 side is reduced. Limit.

  In the second mode, by increasing the exhaust temperature on the bank B1 side close to the catalytic converter 8 by increasing the fuel injection amount (injection timing retard), and restricting the intake amount on the bank B2 side far from the catalytic converter 8, Since the exhaust gas temperature on the B2 side is raised, the temperature of the exhaust gas flowing into the catalytic converter 8 can be increased more effectively than in the first embodiment.

Schematic configuration diagram of an engine system according to the first embodiment of the present invention. Same as above, flowchart showing the main routine of exhaust temperature control Same as above, flowchart of bank-specific exhaust temperature control routine Same as above, explanatory diagram of fuel injection amount increase Same as above, flow chart of bank-specific exhaust temperature control routine with fuel injection timing retard Same as above, explanatory diagram showing fuel injection timing retard Schematic configuration diagram of an engine system according to a second embodiment of the present invention. Same as above, flowchart of bank-specific exhaust temperature control routine

Explanation of symbols

1 Diesel engine 2 Crankshaft 4 Injector 5a, 5b Exhaust manifold (exhaust branch pipe)
6 Exhaust pipe 8 Catalytic converter (exhaust aftertreatment device)
50 Electronic control unit (control unit)
B1, B2 bank (cylinder group)

Claims (4)

It has a plurality of cylinder groups, and the exhaust branch pipes connected to each cylinder group are joined at a position offset with respect to the axis of the crankshaft and connected to one common exhaust pipe. In a diesel engine equipped with an exhaust aftertreatment device,
When a control condition for increasing the temperature of the exhaust gas flowing into the exhaust aftertreatment device is satisfied, the fuel injection amount for the cylinder group communicating with the exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device is set. And a control unit that controls the exhaust gas flowing through the exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device to be higher than the temperature of the exhaust gas flowing through the other exhaust branch pipes. A control device for a diesel engine.   When the control condition is satisfied, the control unit performs post-injection near the bottom dead center in multi-stage injection for a cylinder group communicating with an exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device. The diesel engine control device according to claim 1, wherein the amount is increased.   When the control condition is satisfied, the control unit performs main injection near the top dead center in multistage injection for a cylinder group communicating with an exhaust branch pipe having a relatively short pipe length to the exhaust aftertreatment device. 2. The diesel engine control apparatus according to claim 1, wherein the injection timing of the main injection is retarded while the fuel injection amount is increased.   The said control part restrict | limits air quantity with respect to the cylinder group connected to said other exhaust branch pipe, when the said control conditions are satisfied, The Claim 1 characterized by the above-mentioned. Diesel engine control device.

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