JP4935094B2 - Two-stage turbocharging system for diesel engines - Google Patents

Description

The present invention relates to a two-stage turbocharging system for a diesel engine equipped with a high-pressure stage turbocharger and a low-pressure stage turbocharger.

  Regarding the supercharging of an internal combustion engine, a wastegate turbocharger, a variable capacity turbocharger, and the like have been developed for the purpose of expanding an operation range of an exhaust turbocharger. However, the relationship between the engine speed, torque and exhaust gas flow rate is as shown in FIG. 8, and it is intended to obtain a high pressure ratio (high supercharging pressure) in a wide range of rotation of the internal combustion engine with one supercharger. In this case, the operating efficiency is lowered due to the characteristics of the turbocharger, and surge is likely to occur, so that the range of the operating flow rate is reduced.

For this reason, a two-stage supercharging system aimed at increasing the supercharging pressure by improving the multistage boosting and the supercharger operating efficiency is used. In this two-stage supercharging system , two superchargers are arranged in series in two stages, and the intake air is boosted in two stages, a low pressure stage and a high pressure stage, to reduce the rising pressure ratio in each single stage. As a result, the operating efficiency is improved.

One of the two-stage supercharging systems is a sequential type two-stage supercharging system . In this system, as shown in FIG. 1, two turbochargers 5 and 6 having greatly different capacities are arranged in series, and an appropriate supercharger 5 and 6 can be selected according to the operating state of the internal combustion engine 1. By providing the bypasses 6a and 6d , the working area of the supercharging system 10 is expanded.

In this two-stage supercharging system 10, as shown in FIG. 9, during low-speed to medium-speed rotation, supercharging is performed using a small-capacity high-pressure turbocharger 6 without using the low-pressure turbocharger 5. It was carried out, whereas, when in the high-speed rotation and high load region, by using the low-pressure stage turbocharger 5 of large capacity adapted to the operating region, a single stage supercharging system with equal or supercharging the prior art Do.

In this system 10, the capacity of the low-pressure stage turbocharger 5 and that of the high-pressure stage turbocharger 6 are greatly different, so that the series type two-stage supercharging system can perform supercharging even in an operation region where supercharging is difficult. Can be paid.

  In this system 10, when the high-pressure turbine 6 having a small capacity is operated in the full-load operation state, the exhaust pressure is increased. Therefore, depending on the operation state, the entire amount of exhaust gas may be bypassed by the high-pressure turbine 6 t and the low pressure. It is necessary to flow to the stage turbine 5t. Therefore, the low-pressure stage turbocharger 5 and the high-pressure stage turbocharger 6 are switched and used according to the operating state.

  In this system 10, in the low speed / low load operation, the high pressure turbocharger 6 with a small flow rate is used to achieve high supercharging and high EGR rate, low NOx and low soot combustion, and small inertia. Because it becomes a high-speed turbine, the turbo lag during acceleration is eliminated and drivability is improved. In high-speed / high-load operation, switching to a low-pressure turbo is used to avoid deteriorating engine performance.

  However, when the operating state of the internal combustion engine is in the low speed rotation region, it is necessary to send the entire amount of exhaust gas to the high pressure turbine 6 in order to obtain the required supercharging pressure, and in the middle speed rotation region. Since supercharging is performed using both the low-pressure stage turbocharger 5 and the high-pressure stage turbocharger 6, it is necessary to accurately control the exhaust gas flow rate sent to both the high-pressure stage and low-pressure stage turbines.

  Therefore, in this system 10, a high-pressure stage exhaust bypass passage 6d provided with a bypass valve 6e for flow control is provided. The bypass valve 6e has a flow rate characteristic that allows the entire amount of exhaust gas to flow without causing an increase in exhaust pressure in an operating state where the exhaust gas flow rate is large, while the exhaust gas flow rate is small to medium. In such an operating state, it is required that the flow of exhaust gas from the high-pressure turbine 6t can be controlled.

However, in the prior art, the turbocharger switching control in the two-stage supercharging system is performed by map control or boost control.

  First, map control will be described. In this map control, referring to map data indicating the valve opening degree of the bypass valve based on the engine speed and the fuel injection amount as shown in FIG. The valve opening is calculated, and the turbocharger is switched by controlling the valve opening.

  In the case of this map control, the bypass valve is controlled according to the map data created in the steady test regardless of the operation of the turbocharger. Therefore, between the high-pressure stage turbocharger and the low-pressure stage turbocharger usage area. Due to the turbo lag during the transition, there is a problem that a difference occurs between the map data and the actual exhaust gas flow rate, resulting in a decrease in boost pressure or the like. That is, because the exhaust gas flow rate is different even at the same engine speed and fuel injection amount due to the turbo lag at the time of transition, the operating state of the turbo differs.

  This is shown in FIG. FIG. 11 shows a case where acceleration is started by depressing the accelerator from a constant speed to increase the fuel injection amount Qf. As the fuel injection amount Qf increases, the engine speed Ne increases and boost (supercharging pressure) Pg2 (B) increases. In the case of this map control, when the engine speed Ne1 is reached, the control of the bypass valve is started, and when it is Ne2, the bypass valve is fully opened (100%).

  During this transition, boost Pg2 (B) does not become as high as boost Pg1 during steady operation due to the turbo lag. As described above, when the bypass valve is opened and closed in a state where the turbo efficiency is lowered, as in the steady state, the rotation of the high-pressure stage turbocharger suddenly falls, and thus a phenomenon occurs in which the boost Pg2 (B) falls. Vg1 indicates the exhaust gas flow rate during steady operation, and Vg2 indicates the exhaust gas flow rate during transition. Spv represents a bypass valve control signal.

Next, boost control will be described. In this boost control, the intake air amount of the engine is detected, and when it is in the low intake air amount region, the exhaust switching valve is forcibly opened, that is, the intake air. If the pressure difference between the upstream and downstream of the exhaust gas switching valve is eliminated by switching the turbocharger based on the amount, the fluttering force of the exhaust gas switching valve will no longer act on the exhaust gas switching valve. There has been proposed a control method for an engine with a supercharger that can prevent chatter noise from occurring (see, for example, Patent Document 1).

In addition, by switching the turbocharger based on the intake air pressure at the outlet of the high-pressure compressor, it is possible to obtain an intake manifold pressure that increases as the engine speed increases, and the exhaust switching valve is switched from closed to open. There has been proposed a supercharging pressure control device for a two-stage supercharged internal combustion engine capable of obtaining a smooth torque change even when there is an increase in torque due to a decrease in exhaust pressure (see, for example, Patent Document 2). .)

However, when switching the turbocharger based on these intake air amounts or intake air pressures, the exhaust gas flow rate is the only intake air amount or air pressure that affects the actual behavior of the turbocharger. However, there is still a problem that a turbo lag or the like occurs at the time of switching.

Further, since the gasoline engine is operated by controlling the air-fuel ratio (A / F) so as to be constant at 14 to 15, the exhaust gas flow rate can be easily estimated from the intake air flow rate. Since the intake air amount and the fuel injection amount are controlled independently, there is a problem that it is difficult to accurately estimate the exhaust gas flow rate only from the intake air amount.
JP-A-3-213620 Japanese Patent Laid-Open No. 4-17725

The present invention has been made to solve the above-described problems, and its object is to consider turbo characteristics in a sequential type two-stage supercharging system including a high-pressure stage turbocharger and a low-pressure stage turbocharger. Te, based on exhaust gas flow rate, by performing the switching control of the high-pressure stage turbocharger and Teidan圧turbocharger, even in the transition period, blanking - possible to control the supercharging pressure smoothly without sagging strike It is to provide a two-stage supercharging system for a diesel engine capable of achieving the above.

A diesel engine two-stage turbocharging system for achieving the above-described object includes a low-pressure stage compressor of a low-pressure stage turbocharger and a high-pressure stage compressor of a high-pressure stage turbocharger in order from the upstream side of the intake passage of the diesel engine. And a high-pressure stage intake bypass passage for bypassing the high-pressure stage compressor, and a high-pressure stage turbine of the high-pressure stage turbocharger and a low-pressure stage turbine of the low-pressure stage turbocharger in order from the upstream side of the exhaust passage. In a two-stage turbocharging system for a diesel engine having a high-pressure stage exhaust bypass passage for bypassing a stage turbine, an intake air intake amount grasping means for obtaining an intake air amount, a fuel injection amount grasping means for obtaining a fuel injection amount, An exhaust gas flow rate calculation method for obtaining an exhaust gas flow rate based on the intake air amount and the fuel injection amount When provided with an exhaust gas flow amount control means for controlling the inflow of exhaust gas flowing into the high pressure stage exhaust bypass passage, based on the capacity of the exhaust gas flow rate and the high-pressure stage turbocharger and the low-pressure stage turbocharger, the In the control of the exhaust gas inflow control means, when the fuel injection amount is increased and the exhaust gas flow rate is gradually increased, the exhaust gas flow rate becomes the first exhaust gas flow rate which is the maximum value of the capacity of the high pressure turbine. From time to time, the inflow amount of the exhaust gas flowing into the high-pressure stage exhaust bypass passage is gradually increased until the second exhaust gas flow rate set by the capacity ratio of the high-pressure stage turbocharger and the low-pressure stage turbocharger is reached. The inflow amount of the exhaust gas is maximized when the second exhaust gas flow rate is reached.

According to this configuration, since the exhaust gas flow rate is calculated from the intake air amount and the fuel injection amount, and the turbocharger switching control is performed based on the exhaust gas flow rate, problems such as a decrease in boost due to the turbo lag are prevented. In the transition period, the boost pressure can be controlled smoothly without a drop in boost.
In addition, according to this configuration, the inflow amount of exhaust gas is controlled according to the relationship between the exhaust gas flow rate and the capacity of the turbocharger, in other words, adjustment control of the valve opening degree of the bypass valve is performed. It becomes possible.

Further, in the two-stage supercharging system for the diesel engine, the exhaust gas flow rate calculation means calculates an exhaust gas mass flow rate as the exhaust gas flow rate, and the exhaust gas inflow amount control means calculates the high pressure based on the exhaust gas mass flow rate. The exhaust gas inflow amount to the stage exhaust bypass passage is controlled. The exhaust gas mass flow rate represents the amount of exhaust gas by mass.

  With this configuration, since the exhaust gas mass flow rate can be calculated as the sum of the intake air amount (mass) and the fuel injection amount (mass), the control can be performed based on the exhaust gas mass flow rate that is easy to calculate, resulting in relatively simple control. In addition, when using this mass flow rate, it uses on the assumption that the density of exhaust gas is almost decided by rotation-load.

Alternatively, in the two-stage turbocharging system for a diesel engine, the exhaust gas density calculating means for obtaining the exhaust gas density is provided, and the exhaust gas flow rate calculating means includes the intake air amount, the fuel injection amount, and the exhaust gas flow rate as the exhaust gas flow rate. An exhaust gas volume flow rate is calculated from the exhaust gas density, and the exhaust gas inflow rate control means is configured to control the inflow amount of exhaust gas to the high-pressure stage exhaust bypass flow path based on the exhaust gas volume flow rate. The exhaust gas volume flow rate represents the amount of exhaust gas in volume.

  With this configuration, the sum of the intake air amount (mass) and the fuel injection amount (mass) can be controlled based on the exhaust gas volume flow rate obtained by dividing by the exhaust gas density that is a function of the exhaust gas temperature. Actually, the turbo performance changes with the volume flow rate, and the work is taken out according to the volume of the fluid that has passed through the turbo. Therefore, the volume flow rate is usually used to represent the operating state of the turbo. Since the volume changes when the temperature changes even with the same mass, the density is corrected from the exhaust gas temperature. Thereby, the control accuracy can be increased as compared with the case of controlling by the exhaust gas mass flow rate.

  According to the two-stage turbocharging system of a diesel engine according to the present invention, boost switching is reduced even in a transient state by performing turbocharger switching control using the exhaust gas flow rate as an index in consideration of the characteristics of the turbocharger. Therefore, the supercharging pressure can be controlled smoothly.

Hereinafter, a two-stage turbocharging system for a diesel engine according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, in the two-stage supercharging system 10, the low-pressure stage compressor 5 c of the low-pressure stage turbocharger 5 and the high-pressure stage compressor of the high-pressure stage turbocharger 6 are sequentially arranged from the upstream side of the intake passage 3 of the diesel engine 1. 6c, and a high-pressure stage turbine 6t of the high-pressure stage turbocharger 6 and a low-pressure stage turbine 5t of the low-pressure stage turbocharger 5 are provided in this order from the upstream side of the exhaust passage 4.

  The low-pressure stage turbocharger 5 is provided with a low-pressure stage exhaust bypass passage 5a for bypassing the low-pressure stage turbine 5t. The low-pressure stage exhaust bypass passage 5a has a waste gate for controlling the flow rate of exhaust gas flowing therethrough. Install the valve 5b. The waste gate valve 5b is opened, closed, or adjusted in valve opening by an actuator 5d that operates with the supercharging pressure from the supercharging pressure supply pipe 14. By this adjustment, the turbocharger 5 can be prevented from being damaged by over-rotation of the turbocharger 5, and the boost pressure can be kept constant.

  In the intake system, the high-pressure stage turbocharger 6 is provided with a high-pressure stage intake bypass flow path 6a that bypasses the high-pressure stage compressor 6c, and the high-pressure stage intake bypass flow path 6a and the intake flow path 3 are joined to each other. Is equipped with a high-pressure stage intake bypass valve (three-way valve in FIG. 1) 6b for controlling the amount of flowing gas. An intercooler 7 is provided in the intake passage 3 between the high-pressure stage intake bypass valve 6b and the intake manifold 3a to cool the compressed intake air whose temperature has risen.

  Further, in the exhaust system, a high-pressure stage exhaust bypass passage 6d for bypassing the high-pressure turbine 6t is provided, and the high-pressure stage exhaust bypass passage 6d has a high-pressure stage exhaust bypass valve 6e for controlling the flow rate of the flowing exhaust gas. Install. The high-pressure stage exhaust bypass valve 6e is opened, closed, or adjusted in valve opening by an actuator 6f controlled by a 2-way valve 6g. The actuator 6f operates with the supercharging pressure from the supercharging pressure supply pipe 14, but the two-way valve 6g performs valve opening, valve closing, and adjustment of the valve opening.

  And regarding EGR, the EGR flow path 11 provided with the EGR cooler 12 and the EGR valve 13 is provided by connecting the exhaust manifold 4a and the intake manifold 3a. By this EGR flow path 11, EGR gas Ge is introduced from the exhaust manifold 4 a to the intake manifold 3 a via the EGR cooler 12 and the EGR valve 13.

Further, the two-stage turbocharging system 10 of the diesel engine 1 includes an intake air amount grasping means, a fuel injection grasping means, an exhaust gas density calculating means, an exhaust gas flow rate calculating means, and an exhaust gas inflow amount control means, although not shown. To do.

  This intake air amount grasping means is means for obtaining the intake air amount Qaw, and is obtained from the measured data of MAF (mass air flow sensor) and the map data of the target intake air amount based on the engine speed and torque (load). The intake air amount Qaw is obtained from the target intake air amount. The fuel injection grasping means is a means for obtaining the fuel injection amount Qfv, and is obtained from the target fuel injection amount, but may be a method for obtaining the actual fuel injection amount.

  The exhaust gas density calculating means obtains the exhaust gas density ρg based on the exhaust gas temperature measured by the exhaust gas temperature sensor or the exhaust gas temperature Tg calculated from the exhaust gas temperature map data based on the engine speed and torque. From the data of the exhaust gas density ρg based on the exhaust gas temperature Tg, the exhaust gas density ρg with respect to the current exhaust gas temperature Tg is obtained. The exhaust gas flow rate calculation means is a means for obtaining the exhaust gas flow rate Vg2 based on the intake air amount Qaw and the fuel injection amount Qfv.

  Further, the exhaust gas inflow control means is a means for controlling the inflow amount Qb of the exhaust gas flowing into the high-pressure stage exhaust bypass passage 6e based on the calculated exhaust gas flow rate Vg2, and controls the high-pressure stage exhaust bypass valve 6e. A bypass valve control mechanism (actuator 6f, 2-way valve 6g) and a bypass valve control device for controlling the bypass valve control mechanism.

  These intake air amount grasping means, fuel injection amount grasping means, exhaust gas flow rate calculating means and other computing means and bypass valve control device are incorporated in an engine control device called an engine control unit (ECU) for controlling the diesel engine 1. It is.

The exhaust gas inflow control means of the present invention closes the high pressure exhaust bypass valve 6e of the high pressure exhaust bypass passage 6d when the engine 1 is operating at a low speed and a low load, and at an intermediate speed and a medium load, The bypass valve 6e is gradually opened, and control is performed to fully open the bypass valve 6e at high speed and high load.

FIG. 2 schematically shows the exhaust gas flow rate with respect to the engine speed and torque indicating the operating state of the engine. As shown in FIG. 2, when the exhaust gas flow rate is low at low speed and low load, the high pressure stage turbocharger 6 is in the high pressure stage operation region. When the exhaust gas flow rate is high at high speed and high load, the low pressure stage turbocharger 5 It becomes a low-pressure stage operation area.

As shown in FIG. 2, a bypass valve opening control region (hatched portion) at medium speed / medium load is provided in a portion where the high pressure stage operation region shifts to the low pressure stage operation region. In this bypass valve opening control region, as shown in FIG. 3, the high-pressure stage exhaust bypass valve 6e is gradually opened as the exhaust gas flow rate increases, and the high-pressure stage turbo is used using the high-pressure stage exhaust bypass passage 6d. The operation region of the charger 6 gradually shifts to the operation region of the low-pressure turbocharger 5.

  In the present invention, as shown in FIG. 2, the bypass valve opening between the high-pressure stage operating region where only the high-pressure stage turbocharge 6 operates and the low-pressure stage operating region where only the low-pressure stage turbocharger 5 operates. By switching the turbochargers 5 and 6 in the control region, the valve opening degree of the high-pressure stage exhaust bypass valve 6e is controlled based on the exhaust gas flow rate Vg2, as shown in FIG. That is, when the exhaust gas flow rate Vg2 becomes the first exhaust gas flow rate Q1, the valve opening degree starts to increase from 0%, and when the exhaust gas flow rate Vg2 becomes the second exhaust gas flow rate Q2, the maximum valve opening degree (100%). After that, that is, when the exhaust gas flow rate Vg2 is Q2 or more, the maximum valve opening (100%) is maintained.

  The first exhaust gas flow rate Q1 is the maximum value of the capacity of the high-pressure stage turbine 6t, and when the exhaust gas flow rate Vg2 becomes the first exhaust gas flow rate Q1, the valve opening degree starts to increase from 0%, The inflow amount Qb of the exhaust gas into the bypass channel 6d starts to increase.

  The second exhaust gas flow rate Q2 is a value set according to the capacity ratio of the high-pressure stage turbocharger 6 and the low-pressure stage turbocharger 5. When the second exhaust gas flow rate Q2 is reached, the valve opening is 100%, The amount Qb of exhaust gas flowing into the stage exhaust bypass passage 6d is maximized.

  That is, in the control of the exhaust gas inflow control means, when the exhaust gas flow rate Vg2 becomes the first exhaust gas flow rate Q1, which is the maximum value of the capacity of the high pressure stage turbine 6t, the exhaust gas flows into the high pressure stage exhaust bypass passage 6e. The amount Qb starts to increase, and the exhaust gas inflow amount Qb is maximized when the second exhaust gas flow rate Q2 set by the capacity ratio of the high-pressure stage turbocharger 6 and the low-pressure stage turbocharger 5 is reached.

  The second exhaust gas flow rate Q2 is a value determined by the characteristics of the two turbochargers 5 and 6, and is determined by the characteristics of supercharging and exhaust pressure and the characteristics of exhaust gas. This is where the efficiency of the turbocharger 5 has increased.

In the first embodiment, the exhaust gas flow rate Vg2 is calculated as follows: {intake air amount (mass) Qaw (g / cyc) + fuel injection amount Qfv (mm ³ / cyc) × The exhaust gas mass Qgc (g / min) per cycle per cylinder is calculated from the fuel density ρf (g / mm ³ )} (Qgc = Qaw + Qfv × ρf), and the number of cylinders Nc and engine speed Ne ( rpm) / 2 to calculate the exhaust gas mass flow rate Vg2w (g / min) (Vg2w = Qgc × Nc × Ne / 2). This exhaust gas mass flow rate Vg2w is defined as an exhaust gas flow rate Vg2 (Vg2 = Vg2w).

  That is, the exhaust gas flow rate calculation means calculates the exhaust gas mass flow rate Vg2w as the exhaust gas flow rate Vg2. Then, the exhaust gas inflow amount control means controls the inflow amount Qb of the exhaust gas to the high-pressure stage exhaust bypass passage 6d based on the exhaust gas mass flow rate Vg2w.

In the second embodiment, the exhaust gas flow rate Vg2 is calculated as follows: {intake air amount (mass) Qaw (g / cyc) + fuel injection amount Qfv (mm ³ / cyc) × From the fuel density ρf (g / mm ³ )}, an exhaust gas mass Qgc (g / cyc) per cycle of one cylinder is calculated (Qgc = Qaw + Qfv × ρf), and the cylinder number Nc and the engine speed Ne ( rpm) / 2 to calculate the exhaust gas mass flow rate Vg2w (g / min) (Vg2w = Qgc × Nc × Ne / 2). The exhaust gas mass flow rate Vg2w (g / min) is divided by the exhaust gas density ρg (g / mm ³ ) as a function of the exhaust gas temperature (° C.) to calculate the exhaust gas volume flow rate Vg2v (mm ³ / min) (Vg2v = Vg2w / ρg), this is the exhaust gas flow rate Vg2 (Vg2 = Vg2v). The exhaust gas density (g / mm ³ ) ρg is stored as predetermined data based on the exhaust gas temperature (° C.).

  Since the turbo performance actually changes depending on the volume flow rate of the exhaust gas, it is preferable to control the turbo in terms of the exhaust gas volume flow rate Vg2v instead of the exhaust gas mass flow rate Vg2w.

  That is, the exhaust gas flow rate calculation means calculates the exhaust gas volume flow rate Vg2v from the intake air amount Qaw, the fuel injection amount Qfw, and the exhaust gas density ρg as the exhaust gas flow rate Vg2, and the exhaust gas inflow rate control means calculates the high pressure based on the exhaust gas volume flow rate Vg2v. The amount Qb of exhaust gas flowing into the stage exhaust bypass passage 6d is controlled.

  Control of the high-pressure stage exhaust bypass valve 6e based on the exhaust gas flow rate Vg2 is performed based on, for example, a control flow as shown in FIG. The control flow in FIG. 6 is illustrated as a control flow that is repeatedly called when the high-pressure stage exhaust bypass valve 6e is controlled.

  When this control flow starts, in step S11, the intake air amount Qaw measured by the MAF and the fuel injection amount Qfv used for fuel injection are read. When the exhaust gas volume flow rate Vg2v is used as the exhaust gas flow rate Vg2, the exhaust gas temperature Tg is also read. If there is no exhaust gas temperature sensor, the exhaust gas temperature Tg is estimated from the map data indicating the exhaust gas temperature based on the engine rotation speed and load from the engine rotation speed and load at that time.

  In the next step S12, the exhaust gas flow rate Vg2 is calculated. As described above, the exhaust gas flow rate Vg2 is calculated from the intake air amount Qaw and the fuel injection amount Qfv read in step S11 in accordance with the exhaust gas flow rate calculation flow as shown in FIGS. When the exhaust gas volume flow rate Vg2v is used, the exhaust gas density ρg is calculated from the exhaust gas temperature Tg, and the exhaust gas mass flow rate Vg2w is divided by the exhaust gas density ρg to calculate the exhaust gas volume flow rate Vg2v.

  In the next step S13, the opening degree of the high-pressure stage exhaust bypass valve 6e is calculated from the calculated exhaust gas flow rate Vg2. In the next step S14, the valve opening degree of the high-pressure stage exhaust bypass valve 6e is controlled so as to be this valve opening degree. In the control of the valve opening, DUTY control is performed in simple control, but lift control of lift of the high-pressure stage exhaust bypass valve 6e is performed in more precise control. When this step S14 is completed, the process returns.

On the other hand, in the control of the high-pressure stage intake bypass valve 6b on the high-pressure stage compressor 6c side, the pressure difference between the intake passage 3 and the high-pressure stage intake bypass passage 6a is monitored, and the pressure of the high-pressure stage intake bypass passage 6a increases. In such a case, it is controlled to open, or automatically opened as an automatic valve. Further, when the high-pressure stage exhaust bypass valve 6e is almost fully opened, the work is stopped, so that the valve opening degree of the high-pressure stage exhaust bypass valve 6e is opened with a threshold value. In these cases, a corresponding map is created in advance, and control is performed based on the map.

  By following this control flow, the exhaust gas flow rate Vg2 is calculated, and the valve opening degree of the high pressure exhaust gas bypass valve 6e is controlled based on the exhaust gas flow rate Vg2, so that the high pressure exhaust gas bypass channel 6d is based on the exhaust gas flow rate Vg2. It is possible to control the inflow amount Qb of the exhaust gas to the.

  FIG. 7 shows the state of the exhaust gas flow rate (volume) Vg2 and boost Pg2 (A) when acceleration is started by depressing the accelerator from a constant speed and increasing the fuel injection amount Qf in this embodiment. Vg1 indicates the exhaust gas flow rate (volume) during steady operation, and Pg2 (B) indicates boost when the conventional map control is performed (same as Pg2 (B) in FIG. 11). Further, Ne represents the engine speed, Qf represents the fuel injection amount, and Spv represents a control signal for the high-pressure stage exhaust bypass valve 6e.

  According to FIG. 7, since the opening degree of the high-pressure stage exhaust bypass valve 6e is controlled in consideration of the behavior at the time of transition and the exhaust gas flow rate Vg2 flowing through the high-pressure stage turbocharger 6, as shown by the boost Pg1, It can be seen that the control can be performed smoothly without a drop like the boost Pg2 (B).

Therefore, according to the two-stage turbocharging system 10 of the diesel engine 1 configured as described above, the exhaust gas flow rate Vg2 is calculated from the intake air amount Qaw and the fuel injection amount Qfv, and the turbocharger 5, based on the exhaust gas flow rate Vg2. Since the switching control of 6 is performed, it is possible to prevent the occurrence of problems such as a decrease in boost due to the turbo lag, and it is possible to smoothly control the boost pressure without a drop in boost even during a transition.

It is a figure which shows the structure of the two-stage supercharging system of the diesel engine of embodiment which concerns on this invention. It is a figure which shows the relationship between the waste gas flow volume and the operation area | region of a turbocharger. It is a figure which shows the relationship between the exhaust gas flow rate in the two-stage supercharging system, and the valve opening degree of a high pressure stage exhaust bypass valve. It is a figure which shows the calculation flow of exhaust gas flow volume (mass). It is a figure which shows the calculation flow of exhaust gas flow volume (volume). It is a figure which shows the control flow of the two-stage supercharging system of the diesel engine of embodiment which concerns on this invention. It is a figure which shows the control and boost of an Example and a prior art example. It is a figure which shows the relationship between the driving | operation area | region (engine speed, torque) of an engine, and exhaust gas flow volume. It is a conceptual diagram which shows the operation area | region (engine speed, torque) of an engine, and the operation area | region of a high pressure stage turbocharger and a low pressure stage turbocharger. It is an example of the map data which shows the valve opening degree of a high pressure stage exhaust bypass valve based on an engine speed and fuel injection amount used by control of a prior art. It is a figure which shows the behavior at the time of the boost transient by the map control in a prior art.

Explanation of symbols

1 Diesel engine
2 Engine body
3 Intake channel
4 Exhaust flow path
5 Low-pressure stage turbocharger
5a Low-pressure stage exhaust bypass flow path
5b Westgate valve
5c Low pressure compressor
5t low pressure stage turbine
6 High-pressure turbocharger
6a High-pressure stage intake bypass passage
6b High-pressure stage intake bypass valve
6c High pressure compressor
6d High-pressure stage exhaust bypass flow path
6e High-pressure stage exhaust bypass valve
6f Actuator
6g 2-way valve
6t high pressure turbine
10 Two-stage supercharging system
A Inhalation
G exhaust gas
Ge EGR gas
Nc Number of cylinders
Ne engine speed
Qaw Intake air volume (mass)
Qgc Mass of exhaust gas per cycle of one cylinder
Qfv Fuel injection amount (volume)
Vg2 exhaust gas flow rate
Vg2w Exhaust gas mass flow rate
Vg2v exhaust gas volume flow
ρf Fuel density
ρg exhaust gas density

Claims (3)

A low-pressure stage compressor of the low-pressure stage turbocharger and a high-pressure stage compressor of the high-pressure stage turbocharger are provided in order from the upstream side of the intake passage of the diesel engine, and the high-pressure stage turbine of the high-pressure stage turbocharger in order from the upstream side of the exhaust passage. A two-stage diesel engine having a low-pressure stage turbine for the low-pressure stage turbocharger, and having a high-pressure stage intake bypass path for bypassing the high-pressure stage compressor and a high-pressure stage exhaust bypass path for bypassing the high-pressure stage turbine In the supercharging system,
An intake air intake amount grasping means for obtaining an intake air amount; a fuel injection amount grasping means for obtaining a fuel injection amount; an exhaust gas flow rate calculating means for obtaining an exhaust gas flow rate based on the intake air amount and the fuel injection amount ; An exhaust gas inflow amount control means for controlling an inflow amount of exhaust gas flowing into the high pressure stage exhaust bypass passage based on the capacity of the high pressure stage turbocharger and the low pressure stage turbocharger ;
In the control of the exhaust gas inflow control means, when the fuel injection amount is increased and the exhaust gas flow rate is gradually increased, the exhaust gas flow rate becomes the first exhaust gas flow rate that is the maximum value of the capacity of the high-pressure turbine. Until the second exhaust gas flow rate set by the capacity ratio between the high-pressure stage turbocharger and the low-pressure stage turbocharger is reached, the inflow amount of the exhaust gas flowing into the high-pressure stage exhaust bypass passage is gradually increased. A two-stage turbocharging system for a diesel engine, wherein the exhaust gas flow rate is maximized when the second exhaust gas flow rate is reached.   The exhaust gas flow rate calculating means calculates an exhaust gas mass flow rate as the exhaust gas flow rate, and the exhaust gas inflow amount control means controls the exhaust gas inflow amount to the high-pressure stage exhaust bypass flow path based on the exhaust gas mass flow rate. The two-stage turbocharging system for a diesel engine according to claim 1, wherein   Exhaust gas density calculating means for obtaining an exhaust gas density is provided, and the exhaust gas flow rate calculating means calculates an exhaust gas volume flow rate from the intake air amount, the fuel injection amount, and the exhaust gas density as the exhaust gas flow rate, and controls the exhaust gas inflow amount control. The two-stage turbocharging system for a diesel engine according to claim 1, wherein the means controls the amount of exhaust gas flowing into the high-pressure stage exhaust bypass passage based on the exhaust gas volume flow rate.

Images