JP2013160151A - Control device for compressed self ignition engine with turbosupercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compressed self ignition engine 1 with a first turbosupercharger (a small-size turbosupercharger 62) and a second turbosupercharger (a large-size turbosupercharger 61) in which ignitability is reliably secured after end of deceleration when fuel cut is set to be performed in an operational area of the second turbosupercharger.SOLUTION: A controller (PCM 10) allows at least a first turbosupercharger to operate when an operational condition of an engine is in a first area in a low rotation side, and allows only a second turbosupercharger to operate by fully opening a flow control valve (a regulating valve 64a) when the operational condition of the engine is in a second area in a high rotation side. The controller also allows the first turbosupercharger to operate by setting opening of the flow control valve to be in a close side when an operational area of the engine is in the second area to operate only the second turbosupercharger at deceleration of a vehicle when the fuel cut is set to be performed.

Description

  The technology disclosed herein relates to a control device for a compression self-ignition engine with a turbocharger.

  In a diesel engine that combusts fuel supplied into a cylinder by compression self-ignition, Patent Document 1 describes a technique for increasing the amount of heat generated by pre-stage combustion by increasing the pilot injection amount before the engine is warmed up. Yes. As a result, the temperature state in the cylinder when the fuel by main injection is ignited increases to substantially the same temperature as after the completion of warm-up, and the ignitability of the fuel before warm-up of the engine is improved.

JP-A-11-93735

  By the way, when the vehicle is decelerated with a fuel cut, the temperature in the cylinder gradually decreases due to the fact that combustion is not performed during the deceleration. For example, there is a problem that the ignitability of the fuel deteriorates at the time of reacceleration after completion of deceleration.

  This deterioration in ignitability is particularly noticeable during deceleration when the engine operating state is in the high rotation side operating region, because the actual time for changing the crank angle is shortened because the engine speed is relatively high. It is. That is, even if fuel is previously injected by pilot injection as described in Patent Document 1, the pre-stage combustion becomes unstable due to a short reaction time, and the temperature and pressure in the cylinder increase due to the pre-stage combustion. Is difficult to obtain. As a result, the ignitability of the fuel injected by the main injection is deteriorated particularly after the end of deceleration in the high rotation side operation region. In addition, when the engine is operating at a high speed and in a low load operating region, the amount of fuel injection is reduced, so that the pre-stage combustion by pilot injection becomes further unstable, and the temperature and pressure in the cylinder due to the pre-stage combustion become unstable. The rise will become more difficult to obtain.

  Such an operation region on the high rotation side includes a small turbocharger and a large turbocharger, and is configured to switch between operation and non-operation of the small turbocharger according to the engine speed. Further, in the diesel engine with a two-stage turbocharger, this corresponds to a region in which the small turbocharger is deactivated and only the large turbocharger is activated. For this reason, since only the large turbocharger operates during deceleration and during re-acceleration after completion of deceleration, almost no supercharging pressure is obtained during deceleration, and the pressure in the cylinder gradually decreases. At the time of reacceleration after the end of deceleration, the rise of the supercharging pressure becomes slow, and as a result of the delay in the pressure increase in the cylinder, the ignitability of the fuel is further deteriorated.

  Also, for example, specific environmental conditions such as extremely low outside air or high altitude, specific operating conditions such as low engine water temperature or low oil temperature, or these specific environmental conditions and specific operation Under the condition where the conditions overlap, the compression end temperature and the compression end pressure in the cylinder are lowered, which is disadvantageous for the ignitability of the fuel. Under these specific conditions, it becomes more difficult to ensure the ignitability of the fuel after the end of deceleration in the high speed side operation region (in other words, the operation region of the large turbocharger).

  In addition, in a compression self-ignition engine in which the geometric compression ratio is set to a relatively low compression ratio, for example, less than 16, in order to improve exhaust emission performance and fuel consumption, the geometric compression ratio is low. This also makes it difficult to ensure the ignitability of the fuel, since the compression end temperature and the compression end pressure are lowered.

  The technology disclosed herein has been made in view of such a point, and an object of the technology is to provide a first turbocharger and a second turbocharger having two turbines arranged in series in an exhaust passage. An object of the present invention is to reliably ensure the ignitability after the end of deceleration set to perform fuel cut in the operating region of the second turbocharger in the compression self-ignition engine with a machine.

  A control device for a turbocharger-equipped compression self-ignition engine disclosed herein is configured to inject a fuel into the cylinder, and a compression self-ignition engine configured to self-ignite the fuel supplied into the cylinder. A first turbocharger having a fuel injection valve, a first turbine disposed in an exhaust passage of the compression self-ignition engine, and configured to supercharge intake air supplied to the cylinder; and the exhaust A second turbocharger having a second turbine disposed downstream of the first turbine in the passage and configured to supercharge intake air supplied to the cylinder; and the first turbine A flow rate adjusting valve arranged in a bypass path for bypassing and configured to control the operation of the first turbocharger by adjusting the opening thereof; at least the fuel injection valve; and the flow rate Through the control of Seiben and a controller configured to operate the compression ignition engine.

  Then, when the operating state of the compression self-ignition engine is in a preset low-rotation side first region, the controller performs at least the first turbo excess by adjusting the opening of the flow rate adjustment valve. When the turbocharger is operated and when it is in the second region on the high speed side having a higher rotational speed than the first region, only the second turbocharger is operated by fully opening the flow rate adjusting valve. The controller also closes the opening of the flow rate adjustment valve when the operating range of the compression self-ignition engine is in the second range and the vehicle is set to perform fuel cut when the vehicle is decelerated. By setting to, the first turbocharger is operated.

  Here, since the first turbine is disposed on the upstream side in the exhaust passage and the second turbine is disposed on the downstream side in the exhaust passage, the first turbocharger having the first turbine can operate even at a low exhaust flow rate. The second turbocharger corresponding to the small turbocharger and having the second turbine corresponds to a large turbocharger that is highly efficient at a high exhaust flow rate.

  According to this configuration, since the combustion is not performed during the deceleration of the vehicle set to perform the fuel cut, the temperature in the cylinder gradually decreases. Therefore, after the deceleration of the vehicle accompanied by the fuel cut is finished, the ignitability of the fuel is deteriorated due to the low in-cylinder temperature. Further, when the deceleration of the vehicle accompanied by the fuel cut is performed in the operation region (that is, the second region) in which only the second turbocharger is operated, the second turbocharger is substantially operated during the deceleration. It becomes inactive and almost no supercharging pressure is obtained by the second turbocharger, and the pressure in the cylinder gradually decreases. At the same time, after the deceleration is finished, for example, when reacceleration is attempted by depressing the accelerator pedal, only the second turbocharger is operated, so that the boost pressure rises slowly and the pressure in the cylinder is increased. However, it will not increase easily. This is also disadvantageous for the ignitability of the fuel and also reduces the acceleration performance.

  On the other hand, in the above configuration, the controller performs the fuel cut when the operation region of the compression self-ignition engine is in the second region on the high speed side that operates only the second turbocharger. When the vehicle is decelerated, the flow adjustment valve is set to the closed side so that the bypass path is closed, so that the first turbocharger can be operated even in the operating region of the second turbocharger. Operate.

  As a result, the temperature in the cylinder gradually decreases during deceleration, and after the deceleration ends, the operation of the first turbocharger continues even if the temperature in the cylinder is relatively low. As compared with the case where the second turbocharger is operated, the pressure drop in the cylinder is suppressed. As a result, the ignitability of the fuel after completion of deceleration is ensured by compensating for the temperature drop in the cylinder.

  In addition, it is preferable that the first turbocharger is continuously operated during re-acceleration after completion of deceleration. By doing so, the supercharging pressure rises quickly, so that the pressure in the cylinder becomes sufficiently high, and the ignition performance of the fuel is ensured more reliably, and the acceleration performance is also improved.

  In the operation map of the first and second turbochargers determined by the rotational speed and torque of the compression self-ignition engine, at least the first region for operating the first turbocharger, and the second turbocharger A switching line that is a boundary with the second region for operating only the supercharger is set, and the controller adjusts the opening of the flow rate adjusting valve according to the operation map, and the controller also Under a specific condition in which at least one of the compression end temperature and the compression end pressure in the cylinder is equal to or lower than a predetermined value, the first region is expanded to the high rotation side by changing the switching line to the high rotation side. In addition, the switching line may be changed so that the first region expands toward the high rotation side as the load decreases.

  Here, as “a specific condition in which at least one of the compression end temperature and the compression end pressure in the cylinder is a predetermined value or less”, specifically, the outside air temperature is a predetermined temperature (for example, 0 ° C. or less), Specific environmental conditions including high altitude (for example, 2000 m or more), engine water temperature is a predetermined temperature or lower (for example, 60 ° C. or lower), and oil temperature is a predetermined temperature or lower (for example, 50 ° C. or lower). Specific operating conditions to include, and combinations of these specific environmental conditions and specific operating conditions can be illustrated.

  According to this configuration, under a specific condition in which the ignitability of the fuel is reduced, the switching region in the operation map of the first and second turbochargers is changed to expand the first region to the high rotation side. Prior to the change of the switching line, the operation region, which was the second region in which only the second turbocharger is operated, becomes the first region in which the first turbocharger is operated. In this region, the first turbocharger is operated. The machine comes to work. Therefore, if the flow rate adjustment valve is controlled according to the operation map with the changed switching line, it is set so that the fuel cut is performed even when the operation state of the compression self-ignition engine is in the high rotation region. When the vehicle decelerates, not the second turbocharger but the first turbocharger operates. As a result, the pressure drop in the cylinder during deceleration can be suppressed, and the ignitability of the fuel after the deceleration can be reliably ensured. Further, since the engine speed gradually decreases during deceleration, the engine operating state is within the first region in which the first turbocharger operates even after the deceleration ends. Therefore, the operation of the first turbocharger continues after the deceleration ends, and for example, the supercharging pressure at the time of reacceleration rises quickly. This improves acceleration performance.

  In addition, since the switching line is changed so that the first region expands toward the high rotation side as the load is low, the ignitability is likely to be further deteriorated when the fuel injection amount is relatively small, and the rotation speed is high. The low load operation region is the first region. For this reason, as a result of the operation of the first turbocharger in this operating region, the ignitability of the fuel after the end of deceleration is reliably ensured, and a quick rise of the supercharging pressure at the time of reacceleration is obtained. It is done.

  The controller controls the fuel injection valve so that a shaft torque of the compression self-ignition engine becomes a predetermined value or less during deceleration of the vehicle set to perform the fuel cut under the specific condition. It is also possible to inject a small amount of fuel and burn the minute fuel.

  Here, “small amount of fuel” means that the amount of fuel injected into the cylinder is equal to or greater than the amount that the fuel is ignited and burned, and the shaft torque is less than a predetermined value, in other words, less than the mechanical resistance of the engine. It is to set below the amount that does not occur. The minute amount of fuel can be changed by various factors such as fuel injection timing. For example, when the fuel injection timing is set to a late timing after the compression top dead center, combustion occurs in the expansion stroke even if the fuel injection amount is relatively large, and thus the generated shaft torque becomes small. Therefore, it is possible to set a relatively small amount of “slightly small amount”. Moreover, since it is possible to control the ignitability of the fuel by dividing and injecting the fuel, the injection amount can also be changed by this.

  Under certain conditions where the ignitability of the fuel is low, the vehicle is decelerated by continuing to inject and burn a small amount of fuel without performing fuel cut even during deceleration with fuel cut set. A decrease in the temperature in the cylinder is suppressed without impairing. As a result, the ignitability of the fuel is more reliably ensured in combination with the pressure increase in the cylinder due to the operation of the first turbocharger after deceleration, for example, at the time of reacceleration.

  The controller includes a main injection that performs fuel injection near a compression top dead center in order to perform main combustion mainly including diffusion combustion by controlling the fuel injection valve, and a pre-stage combustion before the compression top dead center. It is good also as performing the front | former stage injection which performs at least 1 time of fuel injection at the timing before the said compression top dead center so that may generate | occur | produce.

  Producing the pre-stage combustion by performing the pre-stage injection before the main injection is advantageous for increasing the compression end temperature and the compression end pressure in the cylinder, and sufficiently ensures the ignitability of the fuel injected by the main injection. .

  On the other hand, as described above, in the operating region on the high rotation side, the ignitability of the fuel injected by the pre-stage injection decreases and the pre-stage combustion becomes unstable, resulting in an increase in the temperature and pressure in the cylinder due to the pre-stage combustion. However, since the pressure in the cylinder is increased by the operation of the first turbocharger in the above configuration, it is possible to reliably ensure the ignitability of the fuel after the deceleration with the fuel cut is completed. .

  The compression self-ignition engine may have a geometric compression ratio set to less than 16. A low compression ratio engine is advantageous in improving fuel consumption and exhaust emission performance, but has a relatively low compression end temperature and compression end pressure, which is disadvantageous for fuel ignitability. For this reason, in the region on the high rotation side where the second turbocharger is operated, the fuel ignitability is likely to deteriorate after completion of deceleration accompanied by fuel cut. Since the reduction of the pressure in the cylinder is suppressed by operating the machine, it is possible to reliably ensure the ignitability after the end of deceleration even for a low compression ratio engine.

  As described above, according to the control device for the compression self-ignition engine with a turbocharger, the fuel cut in the second region on the high rotation side set so that only the second turbocharger operates is performed. At the time of deceleration accompanying this, by operating the first turbocharger, the pressure in the cylinder after completion of deceleration is maintained as high as possible, so that the ignitability of the injected fuel can be reliably ensured.

It is the schematic which shows the structure of a diesel engine. It is a block diagram concerning control of a diesel engine. It is a figure which shows an example of the operation | movement map of a 2 stage turbocharger. (A) An example of the fuel injection aspect which an injector performs, (b) An example of the time change of the heat release rate accompanying it. It is a contour figure about the index of ignitability on a temperature-pressure plane using cylinder temperature and cylinder pressure as parameters. (A) accelerator opening, (b) fuel injection amount, (c) regulating valve opening, (d) supercharging pressure, (e) in-cylinder temperature, in an example of an operation pattern including acceleration, deceleration and reacceleration, It is an example of the time chart which concerns on the change of.

  Hereinafter, the diesel engine which concerns on embodiment is demonstrated based on drawing. The following description of the preferred embodiment is merely exemplary in nature. 1 and 2 show a schematic configuration of an engine (engine body) 1 according to the embodiment. The engine 1 is a diesel engine that is mounted on a vehicle and is supplied with fuel mainly composed of light oil.

  The engine 1 includes a cylinder block 11 provided with a plurality of cylinders 11a (only one is shown), a cylinder head 12 provided on the cylinder block 11, and a lower side of the cylinder block 11, and is lubricated. And an oil pan 13 in which oil is stored. In each cylinder 11a of the engine 1, a piston 14 is fitted and removably fitted. A top surface of the piston 14 is formed with a cavity defining a reentrant combustion chamber 14a. The piston 14 is connected to the crankshaft 15 via a connecting rod 14b.

  In the cylinder head 12, an intake port 16 and an exhaust port 17 are formed for each cylinder 11a, and an intake valve 21 and an exhaust valve that open and close the opening of the intake port 16 and the exhaust port 17 on the combustion chamber 14a side. 22 are arranged respectively.

  In the valve systems that drive these intake and exhaust valves 21 and 22, respectively, a hydraulically operated variable mechanism that switches the operation mode of the exhaust valve 22 between a normal mode and a special mode on the exhaust valve side (see FIG. 2 below). VVM (Variable Valve Motion). Although detailed illustration of the configuration of the VVM 71 is omitted, two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and the first cam A lost motion mechanism that selectively transmits the operating state of one of the first and second cams to the exhaust valve 22 is configured to transmit the operating state of the first cam to the exhaust valve 22. In some cases, the exhaust valve 22 operates in a normal mode that is opened only once during the exhaust stroke, whereas when the operating state of the second cam is transmitted to the exhaust valve 22, the exhaust valve 22 is in the exhaust stroke. It operates in a special mode in which the valve is opened twice, and so-called exhaust is opened twice.

  Switching between the normal mode and the special mode of the VVM 71 is performed by hydraulic pressure supplied from an engine-driven hydraulic pump (not shown), and the special mode is used in the control related to the internal EGR. In order to enable switching between the normal mode and the special mode, an electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed. The execution of the internal EGR is not limited to the double opening of the exhaust. For example, the internal EGR control may be performed by opening the intake valve 21 twice, or by opening the intake twice. An internal EGR control may be performed in which the burned gas remains by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed in the intake stroke. The internal EGR control by the VVM 71 is performed mainly when the engine 1 with low fuel ignitability is cold.

  The cylinder head 12 is provided with an injector 18 for injecting fuel, and a glow plug 19 for warming the intake air in each cylinder 11a to improve the ignitability of the fuel when the engine 1 is cold. The injector 18 is arranged so that its fuel injection port faces the combustion chamber 14a from the ceiling surface of the combustion chamber 14a. Basically, fuel is directly supplied to the combustion chamber 14a near the top dead center of the compression stroke. The injection is supplied.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 11a. On the other hand, an exhaust passage 40 for discharging burned gas (that is, exhaust gas) from the combustion chamber 14a of each cylinder 11a is connected to the other side of the engine 1. In the intake passage 30 and the exhaust passage 40, as will be described in detail later, a large turbocharger 61 and a small turbocharger 62 for supercharging intake air are disposed.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. On the other hand, a surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 is an independent passage branched for each cylinder 11a, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 11a.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, compressors 61a and 62a of large and small turbochargers 61 and 62, and an intercooler 35 that cools the air compressed by the compressors 61a and 62a, A throttle valve 36 is provided for adjusting the amount of intake air into the combustion chamber 14a of each cylinder 11a. The throttle valve 36 is basically fully opened, but is fully closed when the engine 1 is stopped so that no shock is generated.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 11a and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. Yes.

  On the downstream side of the exhaust manifold in the exhaust passage 40, the turbine 62b of the small turbocharger 62, the turbine 61b of the large turbocharger 61, and exhaust for purifying harmful components in the exhaust gas in order from the upstream side. A purification device 41 and a silencer 42 are provided.

The exhaust purification device 41 includes an oxidation catalyst 41a and a diesel particulate filter (hereinafter referred to as a filter) 41b, which are arranged in this order from the upstream side. The oxidation catalyst 41a and the filter 41b are accommodated in one case. The oxidation catalyst 41a has an oxidation catalyst carrying platinum or platinum added with palladium or the like, and promotes a reaction in which CO and HC in the exhaust gas are oxidized to produce CO ₂ and H ₂ O. Is. The filter 41b collects particulates such as soot contained in the exhaust gas of the engine 1. The filter 41b may be coated with an oxidation catalyst. As will be described later, the engine 1 greatly reduces or eliminates the production of RawNOx by reducing the compression ratio, and omits a catalyst for NOx treatment.

  A portion of the intake passage 30 between the surge tank 33 and the throttle valve 36 (that is, a portion on the downstream side of the small compressor 62a of the small turbocharger 62), the exhaust manifold and the small turbocharger in the exhaust passage 40. The portion between the turbocharger 62 and the small turbine 62 b (that is, the upstream portion of the small turbocharger 62 from the small turbine 62 b) is an exhaust gas recirculation for recirculating a part of the exhaust gas to the intake passage 30. They are connected by a passage 51. The exhaust gas recirculation passage 51 is provided with an exhaust gas recirculation valve 51a for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and an EGR cooler 52 for cooling the exhaust gas with engine cooling water. Yes.

  The large turbocharger 61 has a large compressor 61 a disposed in the intake passage 30 and a large turbine 61 b disposed in the exhaust passage 40. The large compressor 61 a is disposed between the air cleaner 31 and the intercooler 35 in the intake passage 30. On the other hand, the large turbine 61b is disposed between the exhaust manifold and the oxidation catalyst 41a in the exhaust passage 40.

  The small turbocharger 62 has a small compressor 62 a disposed in the intake passage 30 and a small turbine 62 b disposed in the exhaust passage 40. The small compressor 62 a is disposed on the downstream side of the large compressor 61 a in the intake passage 30. On the other hand, the small turbine 62 b is disposed on the upstream side of the large turbine 61 b in the exhaust passage 40.

  That is, in the intake passage 30, a large compressor 61a and a small compressor 62a are arranged in series from the upstream side, and in the exhaust passage 40, a small turbine 62b and a large turbine 61b are arranged in series from the upstream side. Has been. The large and small turbines 61b and 62b are rotated by the exhaust gas flow, and the large and small turbines 61a and 62a connected to the large and small turbines 61b and 62b are rotated by the rotation of the large and small turbines 61b and 62b, respectively. Each operates.

  The small turbocharger 62 is relatively small, and the large turbocharger 61 is relatively large. That is, the large turbine 61 b of the large turbocharger 61 has a larger inertia than the small turbine 62 b of the small turbocharger 62.

  A small intake bypass passage 63 that bypasses the small compressor 62 a is connected to the intake passage 30. The small intake bypass passage 63 is provided with a small intake bypass valve 63 a for adjusting the amount of air flowing to the small intake bypass passage 63. The small intake bypass valve 63a is configured to be in a fully closed state (that is, normally closed) when no power is supplied.

  On the other hand, the exhaust passage 40 is connected to a small exhaust bypass passage 64 that bypasses the small turbine 62b and a large exhaust bypass passage 65 that bypasses the large turbine 61b. The small exhaust bypass passage 64 is provided with a regulating valve 64a for adjusting the exhaust amount flowing to the small exhaust bypass passage 64, and the large exhaust bypass passage 65 has an exhaust amount flowing to the large exhaust bypass passage 65. A wastegate valve 65a for adjusting the pressure is provided. Both the regulating valve 64a and the waste gate valve 65a are configured to be in a fully open state (that is, normally open) when no power is supplied.

  The large turbocharger 61 and the small turbocharger 62 are integrated into a single unit including the intake passage 30 and the exhaust passage 40 in which the large turbocharger 61 and the small turbocharger 62 are arranged, thereby forming a supercharger unit 60. doing. The supercharger unit 60 is attached to the engine 1.

The diesel engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. This PCM 10 constitutes a controller. As shown in FIG. 2, the PCM 10 includes a water temperature sensor SW1 that detects the temperature of the engine cooling water, a supercharging pressure sensor SW2 that is attached to the surge tank 33 and detects the pressure of the air supplied to the combustion chamber 14a, An intake air temperature sensor SW3 that detects the temperature of the intake air, a crank angle sensor SW4 that detects the rotation angle of the crankshaft 15, and an accelerator opening sensor that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle. Detection signals of SW5, an O ₂ sensor SW6 for detecting the oxygen concentration in the exhaust gas, and an exhaust pressure sensor SW7 for detecting the exhaust pressure upstream of the small turbine 62b are input, and various detection signals are generated based on these detection signals. The state of the engine 1 and the vehicle is determined by performing calculations, and the injector 18 and the glow plug 19 are correspondingly determined. , Control signals are output to the VVM 71 of the valve operating system and the actuators of the various valves 36 and 51a.

  The PCM 10 controls the operation of the large and small turbochargers 61 and 62 when the engine is operating. Specifically, the PCM 10 controls the openings of the small intake bypass valve 63a, the regulator valve 64a, and the wastegate valve 65a to the openings set according to the operating state of the engine 1, respectively. Specifically, as shown in an example of the operation map in FIG. 3, the PCM 10 does not fully open the small intake bypass valve 63a and the regulating valve 64a in the first region (A) on the lower rotation side than the switching line indicated by the solid line. When the waste gate valve 65a is fully closed, only the small turbocharger 62 or both the large and small turbochargers 61 and 62 are operated. On the other hand, in the second region (B) on the high rotation side with respect to the switching line indicated by the solid line, the small turbocharger 62 becomes exhaust resistance, so the small intake bypass valve 63a and the regulating valve 64a are fully opened, and the waist By opening the gate valve 65a close to a fully closed state, the small turbocharger 62 is bypassed and only the large turbocharger 61 is operated. The waste gate valve 65a is set slightly open to prevent the large turbocharger 61 from over-rotating.

  Thus, the engine 1 is configured to have a relatively low compression ratio with a geometric compression ratio of 12 or more and less than 16 (for example, 14), thereby improving exhaust emission performance and thermal efficiency. It is trying to improve.

(Outline of engine combustion control)
The basic control of the engine 1 by the PCM 10 mainly determines a target torque (in other words, a target load) based on the accelerator opening, and the fuel injection amount and injection timing corresponding to the target torque are determined by the injector 18. This is realized by operation control. The target torque is set so as to increase as the accelerator opening increases and the engine speed increases, and the fuel injection amount is set based on the target torque and the engine speed. The injection amount is set to increase as the target torque increases and as the engine speed increases. Further, the recirculation ratio of the exhaust gas into the cylinder 11a is controlled by controlling the opening degree of the throttle valve 36 and the exhaust gas recirculation valve 51a (that is, external EGR control) or by controlling the VVM 71 (that is, internal EGR control). .

  FIG. 4 shows an example of a fuel injection mode when the operating state of the engine 1 is in a specific operating region (see FIG. 4A) and an example of the heat generation rate associated therewith (see FIG. 4B). Is shown. As will be described later, this specific operation region includes a relatively high rotation region in which the large turbocharger 61 is operated and a region where the load on the engine 1 is relatively low.

  As shown in FIG. 5A, the injector 18 performs three pre-injections (pre-stage injections) at a relatively short time interval at a timing relatively close to the compression top dead center during the compression stroke. Then, the main injection is executed once near the compression top dead center. That is, a total of four fuel injections are executed. The three pre-injections cause pre-combustion (corresponding to pre-stage combustion) having a sufficient heat generation rate so that the peak of the heat generation rate occurs at a predetermined time before compression top dead center. In other words, pre-combustion occurs before the start of main combustion, thereby increasing the temperature and pressure in the cylinder 11a at the time of starting main injection. This improves the ignitability of the fuel injected by the main injection and shortens the ignition delay time τmain. As shown in the figure, the main injection starts injection at a predetermined timing before the compression top dead center or at the compression top dead center, but because the ignition delay time τmain is short, the main combustion associated with the main injection is Starts near compression top dead center. This can be advantageous for improving thermal efficiency and thus fuel economy. Moreover, the said combustion makes the raise of the heat release rate of subsequent main combustion slow. This can be advantageous in reducing combustion noise and improving NVH performance. That is, the pre-injection and the accompanying pre-combustion can improve the controllability of the main combustion to generate the main combustion at a desired timing, thereby realizing improvement in fuel consumption and NVH performance.

  Here, the start timing of the pre-injection is set to a timing at which the fuel injected from the injector 18 falls within the cavity of the piston 14 (in other words, the combustion chamber 14a). Therefore, the start timing of the pre-injection cannot be greatly advanced, and the start timing is set to about 20 ° CA before compression top dead center at the maximum.

  Further, the PCM 10 further sets the target boost pressure according to the operating state of the engine 1 in a steady state, and adjusts the opening degree of the regulating valve 64a and the wastegate valve 65a so that the target boost pressure is achieved. At the same time, supercharging pressure feedback control is performed to control opening and closing of the small intake bypass valve 63a.

(Turbocharger operation map change control)
As described above, the engine 1 is set to a relatively low compression ratio with a geometric compression ratio of less than 16. Here, FIG. 5 shows a contour diagram of the ignitability index on the temperature-pressure plane using the in-cylinder temperature and the in-cylinder pressure as parameters. The ignitability index here is, for example, an ignition delay time from the start of fuel injection to the start of combustion. As indicated by white arrows in the figure, the higher the in-cylinder temperature and the higher the in-cylinder pressure, the better the ignitability. The engine 1 having a relatively low geometric compression ratio has a lower compression end temperature and a lower compression end pressure, and therefore is relatively in the lower left in FIG.

  In such an engine 1, the temperature and pressure in the cylinder 18 a are further increased under the condition that the outside air temperature is a low outside air temperature of 0 ° C. or lower and the specific environmental condition such as a high altitude of 2000 m or higher. The fuel ignitability is further disadvantageous. Further, for example, the temperature in the cylinder 18a is lowered even under operating conditions of the engine 1 such that the water temperature of the engine 1 is 60 ° C. or lower or the oil temperature is 50 ° C. or lower. descend. When such specific environmental conditions overlap with specific operating conditions, the ignitability is further deteriorated.

  Under such conditions, when the vehicle is decelerated with a fuel cut, the temperature in the cylinder 11a gradually decreases during the deceleration due to the stop of combustion, so that the fuel supply is restored at the time of re-acceleration after the deceleration, for example. However, there is a possibility of misfire due to deterioration of ignitability.

  In particular, when the operating state of the engine 1 is in a region on the high rotation side, the actual time with respect to the change in the crank angle is short because the rotational speed of the engine 1 is relatively high, and a sufficient fuel reaction time cannot be ensured. As described above, since the start timing of the pre-injection cannot be greatly advanced, the reaction time of the fuel injected by the pre-injection becomes shorter as the rotational speed of the engine 1 becomes higher. As a result, the ignitability of the fuel is lowered and pre-combustion becomes unstable. This may lead to a situation where the temperature and pressure (compression end temperature and compression end pressure) in the cylinder 11a at the time of main injection are not sufficiently increased, and the ignitability of the fuel injected by the main injection is also deteriorated. Will end up.

  Further, in a region on the high rotation side and in a region where the load is lower, the total amount of fuel to be injected decreases, so the amount of injection by pre-injection also decreases, and pre-combustion becomes increasingly unstable. This leads to further deterioration in the ignitability of the fuel injected by the main injection.

  Therefore, the temperature in the cylinder 11a decreases at the time of deceleration accompanied by a fuel cut when the operating state of the engine 1 is in the high-rotation side and low-load operating region under the specific environmental conditions and specific operating conditions described above. As a result, the ignitability after the end of the deceleration is extremely deteriorated. Moreover, since this operation region corresponds to the second region (B) in which the large turbocharger 61 operates as shown in FIG. 3, almost no supercharging pressure is obtained during deceleration, and the inside of the cylinder 11a The pressure of the water gradually decreases. This is also a factor that deteriorates the ignitability after the end of deceleration, and only the large turbocharger 61 operates even if the accelerator pedal is depressed and reacceleration is attempted after the end of the deceleration. Therefore, the rise of the supercharging pressure is bad and the pressure in the cylinder 11a does not increase easily. As a result, the ignitability is not very good and the acceleration performance is also lowered.

  Therefore, in this engine system, when both the specific environmental condition and the specific operation condition described above are satisfied, the switching line in the operation map of the two-stage turbocharger shown in FIG. 3 is changed. As a result, when the operating state of the engine 1 is in the high rotation side region, the small turbocharger 62 is activated during deceleration accompanied by fuel cut, and the pressure in the cylinder 11a is reduced during deceleration. Is suppressed, and deterioration of ignitability after completion of deceleration is avoided.

  Specifically, when a predetermined precondition is satisfied, the PCM 10 changes the switching line in the operation map from a solid line to a broken line as shown in FIG. This predetermined precondition includes both the environmental conditions and the operating conditions described above. Specifically, the outside air temperature is a predetermined temperature or lower (for example, 0 ° C. or lower) and a high altitude of a predetermined level or higher (for example, 2000 m or higher). (The environmental conditions), the water temperature of the engine 1 is not higher than a predetermined temperature (for example, 60 ° C. or lower), and the oil temperature is not higher than the predetermined temperature (for example, 50 ° C. or lower). Operating conditions). It is determined that the precondition is satisfied when all of these are satisfied, and that the precondition is not satisfied otherwise. Note that it may be determined that the precondition is satisfied when at least one of the above-described environmental conditions and at least one of the above-described operating conditions are satisfied.

  In the changed switching line indicated by the broken line, the first region (A) in which the small turbocharger 62 operates is expanded to the high rotation side as compared with the normal switching line indicated by the solid line. That is, when the precondition is satisfied, the switching line is changed to the high rotation side.

  The switching line after the change is not the one in which the switching line before the change is moved in parallel to the high rotation side. The first region (A) in which the small turbocharger 62 operates is on the low load side. Compared to the high load side, it is set so as to spread widely on the high rotation side. As a result, as described above, the high-revolution side and low-load operation region where ignitability is likely to deteriorate is the second region (B) in which the large turbocharger 61 operates in the normal operation map. As a result, the operating region is included in the first region (A) in which the small turbocharger 62 operates in accordance with the change of the switching line.

  Next, acceleration, deceleration and re-acceleration of the vehicle when the operating state of the engine 1 is in the low load region on the high rotation side as shown by (1) to (6) in the operation map of FIG. The change of various parameters in the operation pattern including will be described with reference to FIG. FIG. 6 shows changes in various parameters when the switching line in the operation map of FIG. 3 is changed to a switching line indicated by a broken line, and when the switching line remains a switching line indicated by a solid line, in other words The change of the parameter in the conventional control is indicated by a broken line.

  First, the process from the state (1) to the state (2) corresponds to the acceleration state of the vehicle in the first region (A) in which the small turbocharger 62 operates. During acceleration of the vehicle, the accelerator opening gradually increases as shown in FIG. 6 (a), and accordingly, the fuel injection amount gradually increases as shown in FIG. 6 (b). As a result, the rotational speed and load of the engine 1 gradually increase.

  The opening degree of the regulating valve 64a shown in FIG. 6C is gradually opened from the fully closed state as the operating state of the engine 1 approaches the changed switching line indicated by the broken line in FIG. Thus, in the first region (A), the supercharging pressure shown in FIG. 6 (d) increases due to the operation of the small turbocharger 62 and the large turbocharger 61, respectively. As the supercharging pressure increases, the in-cylinder pressure shown in FIG. 6 (e) also increases.

  State (2) also corresponds to a state in which the operating state of engine 1 has reached the changed switching line indicated by the broken line, as shown in FIG. For this reason, in the state (2), the regulating valve 64a is fully opened (see FIG. 6C), whereby the operation of the small turbocharger 62 is stopped. In the conventional control, since the states (1) and (2) are included in the second region, the regulating valve 64a remains fully open.

  From the state (2) to the state (3), the large turbocharger 61 operates, in other words, the vehicle acceleration state in the second region (B) where the operation of the small turbocharger 62 is stopped. Correspondingly, as shown in FIGS. 6A and 6B, the increase in the accelerator opening and the increase in the fuel injection amount are each continued. On the other hand, as shown in FIG. 6C, the opening degree of the regulating valve 64a remains in the open state. Thus, at the time of acceleration in the second region (B) on the high rotation side, only the large turbocharger 61 operates. As a result, as shown in FIG. 6 (d), the supercharging pressure once rises again in the vicinity of the timing of the state (2) where the regulating valve 64a is fully opened, and then rises again. The pressure in the cylinder 11a also changes in the same manner as the supercharging pressure changes (see FIG. 6 (e)). Thus, the engine 1 has its rotational speed and load increased.

  The state (3) and the state (4) correspond to the timing when the accelerator opening is zero and the acceleration is finished and the deceleration is started, as shown in FIG. As shown by the broken line in FIG. 3, the operating state of the engine 1 is reduced to fall below the fuel cut line, and as shown in FIG. 6B, the fuel injection amount is set to zero. Thus, a deceleration state accompanied by a fuel cut is established.

  In the transition from the state (3) to the state (4), the operating state of the engine 1 crosses the changed switching line as shown in FIG. 3, and the small turbocharger 62 is operated. One area (A) is formed. Therefore, as shown in FIG. 6C, the regulating valve 64a that has been fully opened is closed again, whereby the small turbocharger 62 resumes operation.

  State (4) corresponds to a state in the second region (B) in which the small turbocharger 62 is not operated before the change of the switching line. Therefore, this control can be rephrased as control for operating the small turbocharger 62 during deceleration with fuel cut even in the second region (B) where the small turbocharger 62 is not operated. Is possible.

  The process from state (4) to state (5) corresponds to deceleration accompanied by a fuel cut. Accordingly, the accelerator opening and the fuel injection amount are maintained at zero as shown in FIGS. 6 (a) and 6 (b). As a result, the rotational speed of the engine 1 gradually decreases with a low load.

  During deceleration with this fuel cut, since it is in the first region (A), the regulating valve 64a is maintained in the closed state, and thereby the small turbocharger 62 is maintained in the operating state. In the conventional control indicated by the broken line in FIG. 6C, the regulating valve 64a is fully opened and the large turbocharger 61 can be operated, but the large turbocharger 61 is substantially not decelerated during fuel cut. Stopped. For this reason, as shown by the broken line in FIG. 6D, the supercharging pressure decreases as the rotational speed of the engine 1 gradually decreases, and as shown by the broken line in FIG. 6E, the cylinder 11a. While the internal pressure also gradually decreases, the small turbocharger 62 can keep the supercharging pressure high by its operation even during deceleration with fuel cut. Further, with the maintenance of the supercharging pressure, the pressure drop in the cylinder 11a is also suppressed (see FIG. 6 (e)). As a result, the ignitability of the fuel after the end of deceleration is ensured. The opening degree of the regulating valve 64a is basically fully closed as shown by a solid line in FIG. 6C, but as shown by a one-dot chain line, the exhaust gas is exhausted with a decrease in the rotational speed of the engine 1. In response to the decrease in the flow rate, the small turbocharger 62 may be set to an intermediate opening so as not to overspeed.

  State (5) corresponds to a state in which the deceleration is completed and the reacceleration is started by depressing the accelerator pedal again, as shown in FIG. 6 (a). Accordingly, as shown in FIG. 3, since the operating state of the engine 1 exceeds the fuel cut line, fuel injection is resumed (see FIG. 6B).

  The process from the state (5) to the state (6) corresponds to a re-acceleration state of the vehicle, and if the operating state of the engine 1 at this time is before switching, the small turbocharger 62 is deactivated. Within the second region (B), the switching line is changed to the switching line indicated by the broken line, and the first region (A) for operating the small turbocharger 62 is obtained. Therefore, re-acceleration on the higher rotation side than the state (1) is also performed while operating the small turbocharger 62. That is, as shown in FIGS. 5A and 5B, the fuel injection amount increases as the accelerator opening increases, and the rotational speed and load of the engine 1 gradually increase (see FIG. 3), and the regulating valve 64a. The opening of is gradually opened from fully closed.

  By operating the small turbocharger 62 at the time of re-acceleration in this way, as shown in FIG. 6 (d), the supercharging pressure that was maintained at a relatively high level at the end of deceleration is quickly raised. Along with this, the pressure in the cylinder 11a also increases rapidly as shown in FIG. 6 (e).

  Thus, at the time of deceleration accompanying fuel cut, the temperature in the cylinder 11a decreases, but by suppressing the decrease in the pressure in the cylinder 11a by the operation of the small turbocharger 62, the fuel after the end of the deceleration is reduced. Ignition can be ensured. This corresponds to shifting the state in the cylinder 11a to the right as much as possible in the contour diagram shown in FIG. That is, as indicated by (1) to (6) in FIG. 3, in the low load operation region on the high rotation side, the pre-stage combustion due to the pre-stage injection becomes unstable, and therefore the temperature in the cylinder 11a is caused by the pre-stage combustion. It is difficult to increase (and both pressures) (this corresponds to shifting the state in the cylinder 11a upward or diagonally upward to the right in FIG. 5). For this reason, increasing the pressure in the cylinder 11a by operating the small turbocharger 62 is effective in ensuring fuel ignitability by compensating for the temperature drop in the cylinder 11a.

  Further, at the time of re-acceleration after the end of deceleration, the supercharging pressure quickly rises due to the operation of the small turbocharger 62, so the pressure in the cylinder 11a also increases early, fuel ignitability is further improved and acceleration is accelerated. The performance is also good.

  Note that, during the deceleration from the state (4) to the state (5), the fuel may not be cut but may be injected from the injector 18 to burn it. By so doing, combustion continues even during deceleration, so that a decrease in temperature in the cylinder 18a is suppressed. As a result, the ignitability of the fuel after the end of deceleration is maintained better.

  Here, the amount of fuel to be injected in the minute injection control may be set as appropriate within the range where the fuel injected into the cylinder 11a ignites and burns and the shaft torque becomes a predetermined value or less. Note that the minute amount of fuel can be changed depending on various factors such as the fuel injection mode (that is, the difference between injection timing and batch injection or split injection). In addition, for example, a small amount of injection (pre-injection) is performed at a timing before compression top dead center, and a plurality of fuel injections (main injection) are performed at a timing after compression top dead center. Also good. Such a fuel injection mode is advantageous in suppressing the generation of torque while ensuring the ignitability of fuel.

  Further, in the above configuration, this control is applied when a specific environmental condition and a specific operation condition in which ignitability deteriorates, but the specific environmental condition and the operation condition are not satisfied. However, when the operating state of the engine 1 is in the second region on the high rotation side where the large turbocharger 61 operates, the small turbocharger 62 is operated at the time of deceleration accompanied by a fuel cut. May be.

1 Diesel engine (compression self-ignition engine)
10 PCM (controller)
11a Cylinder 18 injector (fuel injection valve)
40 Exhaust passage 61 Large turbocharger (second turbocharger)
61b Large turbine (second turbine)
62 Small turbocharger (1st turbocharger)
62b Small turbine (first turbine)
64 Small exhaust bypass passage (bypass)
64a Regulating valve (Flow control valve)

Claims (5)

A compression self-ignition engine configured to self-ignite the fuel supplied into the cylinder;
A fuel injection valve configured to inject fuel into the cylinder;
A first turbocharger having a first turbine disposed in an exhaust passage of the compression self-ignition engine and configured to supercharge intake air supplied to the cylinder;
A second turbocharger having a second turbine disposed downstream of the first turbine in the exhaust passage and configured to supercharge intake air supplied to the cylinder;
A flow rate adjusting valve that is disposed in a bypass passage that bypasses the first turbine and is configured to control the operation of the first turbocharger by adjusting the opening thereof;
A controller configured to operate the compression self-ignition engine through control of at least the fuel injection valve and the flow rate regulating valve;
The controller performs at least the first turbocharger by adjusting the opening of the flow rate adjusting valve when the operation state of the compression self-ignition engine is in a preset first region on the low rotation side. And when in the second region on the high rotation speed higher speed than the first region, by operating the flow rate adjusting valve fully, only the second turbocharger is operated,
The controller also sets the opening of the flow rate adjustment valve to the closed side when the operating region of the compression self-ignition engine is in the second region and the vehicle is set to perform fuel cut when the vehicle is decelerated. A control device for a turbocharger-equipped compression self-ignition engine that operates the first turbocharger by setting. In the control device for a compression self-ignition engine with a turbocharger according to claim 1,
In the operation map of the first and second turbochargers determined by the rotational speed and torque of the compression self-ignition engine, at least the first region for operating the first turbocharger, and the second turbocharger A switching line that is a boundary with the second region for operating only the supercharger is set,
The controller performs opening adjustment of the flow rate adjustment valve according to the operation map,
The controller may also change the first region by changing the switching line to a high rotation side under a specific condition in which at least one of the compression end temperature and the compression end pressure in the cylinder is equal to or lower than a predetermined value. Of the turbocharger-equipped compression self-ignition engine that changes the switching line so that the lower the load, the larger the first region. The control device for a compression self-ignition engine with a turbocharger according to claim 2,
The controller controls the fuel injection valve so that a shaft torque of the compression self-ignition engine becomes a predetermined value or less during deceleration of the vehicle set to perform the fuel cut under the specific condition. A control device for a turbocharger-equipped compression self-ignition engine that injects a minute amount of fuel and burns the minute amount of fuel. In the control apparatus of the compression self-ignition engine with a turbocharger according to any one of claims 1 to 3,
The controller includes a main injection that performs fuel injection near a compression top dead center in order to perform main combustion mainly including diffusion combustion by controlling the fuel injection valve, and a pre-stage combustion before the compression top dead center. A control device for a turbocharger-equipped compression self-ignition engine that performs at least one fuel injection at a timing prior to the compression top dead center so as to occur. In the control apparatus of the compression self-ignition engine with a turbocharger according to any one of claims 1 to 4,
The compression self-ignition engine is a control device for a compression self-ignition engine with a turbocharger, the geometric compression ratio of which is set to less than 16.

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