JPH03290028A - Fuel injector for series two-stage supercharging diesel engine - Google Patents

Abstract

PURPOSE:To simplify a control circuit by turning on and off pilot injection in synchronization with the operation of an exhaust change-over valve wherein the operation regions of small and large turbo charges are changed over by opening and closing the exhaust change-over valve. CONSTITUTION:A series two-stage supercharging Diesel engine has large and small turbo chargers A, B disposed in series in the direction of gas flow. An exhaust change-over valve D is provided in an exhaust bypass path C bypassing the small turbo charger so that the operation regions of the small and large turbo chargers B, A are changed over by opening and closing the exhausted change-over valve D. Then, a fuel injector E is is constituted to perform pilot injection and provided with a pilot injection controlling means F for selectively performing the pilot injection according to the opening and closing operations of the exhaust change-over valve D. The pilot injection is controlled to be performed in closing the exhaust change-over valve D and stopped in opening the same.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection device for a two-stage in-line supercharged diesel engine.

[Prior art]

In-line two-stage supercharged diesel engine (for example, Japanese Patent Application Laid-Open No. 45-90
In No. 84, a large turbocharger and a small turbocharger are arranged in series in the gas flow direction, and an exhaust switching valve is provided in the exhaust bypass passage that bypasses the small turbocharger, and the exhaust switching valve is installed in the operating range of the small turbocharger. The valve is closed, and the exhaust switching valve is opened in the operating range of the large turbocharger. By performing two-stage supercharging, a supercharging effect can be obtained over a wide range from a low engine speed region to a high engine speed region.

In diesel engines, diesel knock is likely to occur due to low boost pressure when the engine is under light load. Day
It is known that pilot injection is performed to reduce cell knock. That is, diesel knock occurs due to ignition delay after injection, or by performing pilot injection before main injection, ignition delay can be eliminated and diesel knock can be prevented. Also, when the boost pressure increases when the engine is under high load, diesel knock becomes less likely to occur.
Pilot injection is stopped.

[Problem to be solved by the invention]

In conventional technology, whether or not to perform pilot injection is determined by detecting operating condition factors such as engine speed and load, and if it is determined to be in the pilot injection region, pilot injection is executed, and if it is determined not to be in the pilot injection region. If this happens, the pilot injection will be stopped. In this case, a control circuit is required to determine whether or not it is in the pilot injection region, which has the disadvantage of complicating the configuration.

In a two-stage supercharged diesel engine, this invention turns pilot injection ON and OFF in synchronization with the operation of an exhaust switching valve.
By performing FF, the control circuit can be simplified.

[Problem to be solved by the invention]

According to this invention, in FIG. 1, a large turbocharger A and a small turbocharger B are arranged in series in the gas flow direction, and an exhaust switching valve is provided in an exhaust bypass passage C that bypasses the small turbocharger, and an exhaust switching valve is provided. In an in-line two-stage supercharged diesel engine in which the operating range is switched between a small turbocharger B and a large turbocharger A by opening and closing the valve valve, the fuel injection device E is configured to be capable of pilot injection, and the exhaust switching valve Equipped with pilot injection control means F that selectively operates pilot injection according to the opening/closing operation of the exhaust switching valve, pilot injection is performed when the exhaust switching valve is closed, and pilot injection is stopped when the exhaust switching valve is opened. A fuel injection device for an in-line two-stage supercharged diesel engine is provided.

[Effect]

The exhaust switching valve is opened and closed depending on the engine operating conditions.
When the exhaust switching valve is closed, the small turbocharger B performs supercharging, and when the exhaust switching valve is open, the large turbocharger A performs supercharging.

The pilot injection control means F executes pilot injection by the fuel injection device E when the exhaust switching valve is closed, and stops the pilot injection by the fuel injection device when the exhaust switching valve is opened.

〔Example〕

FIG. 2 shows an embodiment of the invention, l.

is the main body of the diesel engine, which includes an intake pipe 12 and an exhaust pipe 1.
4 is connected. A large turbocharger 17 and a small turbocharger 18 are arranged in series. The large turbocharger 17 includes a compressor 2°, a turbine 22,
It is composed of a rotating shaft 24. small turbocharger 1
8 is a compressor 26, a turbine 28, and a rotating shaft 25
It consists of A compressor 2o of a large turbocharger 17 is installed in the intake pipe 12 in the flow direction of intake air.
, the compressor 26 of the small turbocharger 18, and the intercooler 29 downstream thereof. In the exhaust pipe, the turbine 28 of the small turbocharger 18 and the turbine 22 of the large turbocharger 17 are arranged in this order in the flow direction of exhaust gas.

A first exhaust bypass passage 30 is connected to the exhaust pipe by bypassing the turbine of the large turbocharger 17, and a wastegate valve 3, which is a butterfly valve, is connected to the first exhaust bypass passage 30.
2 is placed. The wastegate valve 32 is connected to a diaphragm actuator 34 and the diaphragm 3
4a is connected to the bypass valve 32. Bypass valve 32 is normally biased to close by spring 34b, but the negative pressure applied to diaphragm 34a causes wastegate valve 32 to open against spring 34b.

A second exhaust bypass passage 36 is provided to bypass the turbine 28 of the small turbocharger 18, and an exhaust switching valve 38 as a butterfly valve is provided in the second bypass passage 36. The exhaust switching valve 38 is connected to its actuator 40, and the actuator 40 is configured as a two-stage diaphragm mechanism.

As described later, this actuator 40 closes the exhaust switching valve 38 until the large turbocharger 17 exerts its full supercharging capacity, and switches the exhaust switching valve 38 when the large turbocharger 17 reaches its full supercharging capacity. It has the property of causing the valve 38 to open rapidly. The exhaust switching valve 40 includes diaphragms 40a, 40b and springs 40c, 406, one diaphragm 40a is connected to the exhaust switching valve 40 via a rod 40e, and the other diaphragm 40b is connected to a rod 40f. diaphragm 40
A step-like opening characteristic of the exhaust switching valve 38 can be obtained by applying supercharging pressure to a or by applying supercharging pressure to the diaphragm 40b. That is, when supercharging pressure is applied to the diaphragm 40b, the exhaust switching valve 38 is opened against the force of the spring 40c and the combined force of the spring 40d, so that the valve is opened slowly. When supercharging pressure acts on the diaphragm 40a, the exhaust switching valve 38 is opened against only the force of the spring 40c, so that the valve operation is quick during that time.

An intake bypass passage 44 that bypasses the compressor 26 of the small turbocharger 18 is provided, and an intake bypass valve 46 is disposed in the intake bypass passage 44. The intake bypass valve 46 is connected to a diaphragm actuator 48, and the operation of the intake bypass valve 46 is controlled by the pressure applied to the diaphragm 48a. This intake bypass valve 46 closes the intake bypass passage 44 in the operating range of the small turbocharger 8 before the startup of the large turbocharger 17 is completed, but after the startup is completed, the supercharging pressure acts on the diaphragm 48a from below. , intake bypass valve 46
The valve is opened.

In this invention, an exhaust gas recirculation (EGR) device is provided, and the EGRg device has an exhaust gas recirculation passage (EGR passage) 50.
and an exhaust gas recirculation control valve (EGR) on the EGR passage 50.
valve) 52, and the EGR valve 52 has a diaphragm 5.
2a and a valve body 52b, and the opening and closing of the valve body 52b is controlled according to the pressure applied to the diaphragm 52a.

A three-way solenoid valve (VSm54) is provided to control the pressure on the actuator 34 of the wastegate valve 34. The position is switched between the position 56 upstream of 29 where supercharging pressure is introduced.When atmospheric pressure is introduced, the spring 3
4b drives the wastegate valve 32 to close;
When supercharging pressure is introduced, the waste gate valve 32 is opened against the spring 34b.

A three-way solenoid valve (VSV2) 58 is provided to control the diaphragm pressure of the actuator 40 of the exhaust switching valve 38.
The position of the outlet 60 at which the supercharging pressure is introduced is switched. Furthermore, the pressure at the outlet 60 of the compressor 26 of the small turbocharger is constantly introduced into the diaphragm 40b.

Two three-way solenoid valves 64, 66 are provided for pressure control to the actuator 48 of the intake bypass valve 47. A three-way solenoid valve (VSV3) 64 is provided above the diaphragm 48a of the actuator 48 of the intake bypass valve 46 for pressure control;
The position is switched between a position where atmospheric pressure is introduced to the upper side of the compressor and a position where supercharging pressure from the compressor outlet 60 of the small turbocharger 18 is introduced. In addition, 3-way solenoid valve (VSV4) 6'
Reference numeral 6 is provided to control the pressure below the diaphragm 48a of the actuator 48 of the intake bypass valve 46. It changes depending on the position at which the supercharging pressure of the compressor outlet 60 of the turbocharger 26 is introduced.

3-way solenoid valve (VSV5) 704i Provided to control the operation of the EGR valve 52, this solenoid valve 70 is connected to the diaphragm 5
The position is switched between a position where atmospheric pressure is introduced into 2a and a position where negative pressure from the negative pressure pump 67 is introduced.

A control circuit 72 is provided for supercharging control in the present invention, and is connected to each solenoid valve 54 (VSVI), 58 (VSV2), 6
4 (VSV3), 66 (VSV4), 70 (VSV
5) Perform the drive. The control circuit 72 is connected to 14 various sensors to execute control according to the present invention. Mass, large turbocharger 17 compressor 20
A first pressure sensor 78 is provided to detect the outlet pressure P of the compressor 26 of the small turbocharger 18, and a second pressure sensor 80 is provided to detect the outlet pressure P2 of the compressor 26 of the small turbocharger 18.

A fuel injection device 82 is provided in each cylinder (four cylinders in this embodiment). Each fuel injection device 2 is a unit injector in this embodiment, and is a type of fuel injection device driven directly by the camshaft of the engine. FIG. 3 schematically shows the configuration of a unit injector, in which a tappet 84 drives a plunger 85 downward against a spring 86 by a cam (not shown) on the camshaft of the engine.

The pressure chamber 88 below the plunger 85 communicates with the needle 92 through a passage 90, and when the hydraulic pressure from the pressure chamber 88 acts on the needle 88, the needle 88 is opened.

The overflow valve 94 terminates fuel injection by releasing the pressure in the pressure chamber 88 at an arbitrary time, and controls pilot injection and fuel injection amount. A hydraulic chamber 96 is formed at one end of the overflow valve 94, and this hydraulic chamber 96 communicates with an actuator 98 made of a laminated piezoelectric element. When the actuator 98 is energized, its piezoelectric element expands, and the piston 98A is driven downward against the spring 99.
The pressure in the hydraulic chamber 96 increases and the overflow valve 94 is closed.

When the overflow valve 94 is closed, the pressure in the pressure chamber 88 causes the needle 92 to open. Fuel from the fuel tank 100 is supplied to the passage 104 and the actuator 98 via the fuel supply pump 102.
is introduced into the hydraulic chamber 88 through a space 106 around it and a passage 108 .

When the actuator 98 is energized, the overflow valve 84 closes the passage 110 from the pressure chamber 88 as described above, but when the actuator 98 is de-energized, the piezoelectric element contracts to its original thickness, so the pressure chamber 96 is closed. The pressure decreases, and the overflow valve 94 is driven away from the valve seat 114 by the urging force of the spring 112, and the pressure in the pressure chamber 88 is reduced to the valve seat 11.
4. Central passage 94A1 hole 94B of overflow valve 94, passage 12
0 to the fuel tank 100. Therefore, the needle 92 is closed and fuel injection is stopped. In FIG. 2, control circuit 72 generates a fuel injection control signal to fuel injector 82. In FIG.

The flowcharts of FIGS. 4 and 5 explain the operation of control circuit 72. FIG. 4 shows a supercharging control routine, and in step 130, it is determined whether or not the compressor outlet pressure P2 of the small turbocharger 18>the compressor outlet pressure P1 of the large turbocharger 17 holds true. Figure 6 shows the relationship between engine speed NE and supercharging pressure (turbocharger outlet pressure) when the opening degree of the accelerator pedal is fixed constant. This is faster than the rise of the outlet pressure P1.

Therefore, in a state where the engine speed has not yet increased, P2>P holds true, and in step 132, the solenoid valve 5
4 (VSVI) is turned off, and the diaphragm 34a
Atmospheric pressure is introduced, and the wastegate valve 32 is closed by the spring 34b. In step 134, the solenoid valve 58 (VSV2> is OF) that controls the exhaust switching valve 40.
F is given. Therefore, atmospheric pressure acts on the diaphragm 40a of the actuator 40. On the other hand, diaphragm 40
Since the compressor outlet pressure of the small turbocharger 18 is always introduced into springs 40c and 4
The operation of the exhaust switching valve 38 is controlled by the compressor outlet pressure of the small turbocharger 18 opposing the spring force corresponding to the resultant force of 0d. That is, as long as the spring force is dominant over the supercharging pressure P2, the exhaust switching valve 38 remains fully closed, but at the rotation speed at which the supercharging pressure P2 reaches the predetermined value PSET (NE in FIG. 6). Until then, the exhaust switching valve 38 remains fully closed, and when P2-predetermined value PSP, T is reached, the exhaust switching valve 38 gradually opens against the closing biasing force that is the resultant force of the springs 40c and 40d. will be started. Regarding the operation of the intake bypass valve 46 at low engine speeds, in step 136 the solenoid valve 64 (VSV3) is set to O.
N and the compressor outlet pressure P of the turbocharger 18
2 acts on the upper side of the diaphragm 48a, the intake bypass valve 46 is closed. Further, in step 138, the solenoid valve 66 (VSV4) is turned off, so that the negative pressure from the negative pressure pump 67 acts on the lower side of the diaphragm 48a, so the diaphragm 48a is pulled downward, and the intake bypass valve 46 is closed. The force is increased to ensure that the valve closes reliably.

In the acceleration state, the engine speed NE increases to NH3, the rise of the compressor outlet pressure P1 of the large turbocharger 17 catches up with the compressor outlet pressure P2 of the small turbocharger 18, and P 2 = P.
+, proceeding from step 130 to step 140, the solenoid valve 54 (VSVI) is turned on, and the diaphragm 34
The supercharging pressure from position 56 is introduced to a, and the spring 34
The wastegate valve 32 is urged in the opening direction against the force b. In step 142, the operating solenoid valve 58 (VSV2) of the exhaust switching valve 38 is turned on. Therefore, since the supercharging pressure acts on the diaphragm 40a, the spring 40b does not participate in the force to close the exhaust switching valve 38 that opposes the supercharging pressure, and only the weak biasing force of the spring 40c participates in the closing force. Therefore, the actuator 40 opens the exhaust switching valve 38 all at once. In step 144, the solenoid valve 66 (VSV4) is turned off, so atmospheric pressure acts on the upper side of the diaphragm 48a, and in step 146, the solenoid valve 66 (VSV4) is turned on, and supercharging pressure acts on the lower side of the diaphragm 48b. Therefore, the diaphragm 48a is pressed upward, and the intake bypass valve 46 is opened all at once.

FIG. 5 is a flowchart illustrating how fuel injection is performed for one cylinder, and the fuel injection is controlled by controlling the energization of the piezoelectric actuator 98. For this reason, the control circuit 72 uses a thyristor (SCR).
It has a well-known charging and discharging control circuit using a switching unit (not shown)), and the charging pulse signal is SCR.
When the voltage is applied to the capacitor, the voltage charged in the capacitor is applied to the piezoelectric element, and the overflow valve 96 is closed. Further, when a discharge pulse signal is applied to the SCH, the voltage of the piezoelectric element is discharged, and the overflow valve is opened. The routine shown in FIG. 5 is executed at every predetermined crank angle (for example, every time the crankshaft rotates by 1° CA).

In step 160, it is determined whether the crank angle is at a predetermined crank angle position in one cycle of the engine. This crank angle position serves as a reference position for controlling the timing of fuel injection. If it is determined at step 160 that the position is the reference position, the process proceeds to step 162, where the position detection counter C is cleared; if it is not the reference position, the process proceeds to step 164, where the counter C is incremented. That is, from the value of the counter C, it is possible to know where the cylinder is located in the engine l cycle. In step 166, it is determined whether the exhaust switching valve 38 is closed.

The exhaust switching valve 38 is opened and closed by the solenoid valve 58 (VSV2).
This can be determined by the signal status (ON or F).

When it is determined that the exhaust switching valve 38 is closed, the process proceeds from step 166 to step 168, where it is determined whether C<C. In step 170, it is determined whether or not it is CTCI. No at step 160 and N at step 170.

When , C=C, and the timing of C=C is the crank angle position slightly before the plunger 85 starts descending (the point just before the plunger 85 starts effective compression).
It is set so that The process then proceeds to step 172, where a pulse signal is applied to the charging control SCR, so that a high voltage is applied to the actuator 98, and the pressure chamber 96 is
is pressurized and the overflow valve 94 seats on the valve seat 114. C=
The timing of C is set so that the crank angle position is a little before the plunger 85 starts descending, so after a while, the plunger 85 starts descending.
Since the pressure in the pressure chamber 88 increases, fuel injection (pilot injection) is performed as shown in FIG. 7 (N).

When C≧01, the process proceeds to step 174, where it is determined whether c<c2. In step 176, it is determined whether c>c2. No in step 174; N in step 174;

In this case, C=C2, and the process proceeds to step 178, where a pulse signal is applied to the discharge control SCR, so that the high voltage applied to the actuator 98 is released and the actuator 98 is discharged. Therefore, the piezoelectric element contracts, the pressure chamber 96 is depressurized, and the overflow valve 94 is separated from the valve seat 114. Therefore, the pressure in the pressure chamber 88 decreases and the nozzle 92 is closed, indicating the end of the pilot injection (0 in FIG. 7). The interval between cl and 02 is set so that an appropriate pilot injection amount can be obtained.

When C≧C2 in step 176, the process proceeds to step 180, where it is determined whether C(C3).In step 182, C
>C3. If No in step 180 and NO in step 182, C=C, and the process goes to step 172 again, where a pulse signal is applied to the charging control SCR, so a high voltage is applied to the actuator 98,
Pressure chamber 96 is pressurized and overflow valve 94 seats on valve seat 114 . The timing of C=C is the start of main injection m.

When C≧C8, the process advances from step 182 to step 184, where it is determined whether C<C4. In step 186, it is determined whether C>C<. If No in step 184 and No in step 186, C=C4, and the process returns to step 178, where a pulse signal is applied to the discharge control SCH, so that the high voltage applied to the actuator 98 is released and discharged. Therefore, the piezoelectric element contracts,
Pressure chamber 96 is depressurized and overflow valve 94 is spaced apart from valve seat 114. Therefore, the pressure in the pressure chamber 88 decreases and the nozzle 92 is closed, indicating the end of the main injection. C3
The interval between C2 and C2 is appropriately set so as to obtain a fuel injection amount suitable for the operation, including the pilot injection.

When it is determined in step 166 that the exhaust switching valve 38 is open, the process proceeds to step 180, and step 168-1
Since the pilot injection routine of 76 is not passed, the pilot injection l is not performed. Therefore, when the exhaust gas switching valve 38 is opened, only the main injection m (FIG. 7(N)) is executed.

FIG. 8 shows a comparison between the compressor outlet pressure P2 of the small turbocharger and the turbine inlet pressure P3 of the small turbocharger, and point A is the point where the exhaust switching valve 38 starts opening (step 130 in FIG. 4). (P2=P, ) and the exhaust pressure increases significantly after this point.

FIG. 9 shows the exhaust pressure/air supply ratio P3/P2, and this ratio increases at a point after the exhaust switching valve starts opening. 10 and 11 schematically show the ignition delay with respect to compressor outlet pressure P 2 and turbine inlet pressure P3, and P2. This shows that in the region where P3 is small, the ignition delay is large and pilot injection is necessary. On the contrary, P2. P
In the region where 3 is large, the ignition delay is small and pilot injection is not necessary.

When the exhaust switching valve is closed, the exhaust pressure/intake air ratio P 3 / P 2 is small and diesel knock is likely to occur, but with this invention, diesel knock can be suppressed by performing pilot injection when the exhaust switching valve is closed. . In addition, when the exhaust switching valve is open, the exhaust pressure/intake air ratio P3/P2 is large, making diesel knock less likely to occur, but in this invention, unnecessary pilot injection is prevented by stopping pilot injection when the exhaust switching valve is opened. This makes it possible to suppress the noise generated from the diesel engine.

〔Effect of the invention〕

In this invention, by switching the pilot injection ON and OFF in synchronization with the operation of the exhaust switching valve, it is possible to perform accurate fuel injection control after reliably knowing whether or not it is in the pilot injection range by a simple means. It is possible to improve combustibility and reduce noise.

[Brief explanation of drawings]

FIG. 1 is a functional configuration diagram of the present invention. FIG. 2 is a schematic overall configuration diagram of the diesel engine of the present invention. FIG. 3 is a schematic configuration diagram of a fuel injection device in the day cell engine of FIG. 2. 4 and 5 are flowcharts explaining the operation of the control circuit of FIG. 2. FIG. 6 is a characteristic diagram of supercharging pressure with respect to rotation speed by a two-stage supercharging device. FIG. 7 is a timing diagram illustrating the operation of the control circuit shown in FIG. 2. FIG. 8 is a diagram showing compressor outlet pressure P2 and Tahin inlet pressure P3 of a small turbocharger with respect to engine speed. Figure 9 shows the turn inlet pressure P versus the compressor outlet pressure P2 of the small turbocharger with respect to the engine speed.
The figure which shows the ratio of 3. FIG. 10 is a diagram showing ignition delay characteristics with respect to compressor outlet pressure P2 of a small turbocharger. Figure 11 shows the Tachin inlet pressure P of a small turbocharger.
FIG. 3 is a diagram showing ignition delay characteristics for No. 3; lO...Engine body, 12...Intake pipe, 14...
・Exhaust pipe, 17...Large turbocharger, 18...
・Small turbocharger, 30--First exhaust bypass passage, 32--Uniist gate 1~valve, 36--Second exhaust bypass passage, 38--Exhaust switching valve, 44--Intake bypass valve ,5
0...EGR passage, 50A...Exhaust gas outlet, 5
4, 58.64.66...Solenoid valve (VSV), 78,
80...Pressure sensor, 82...Fuel injection device.

Claims (1)

[Claims] A large turbocharger and a small turbocharger are arranged in series in the gas flow direction, an exhaust switching valve is provided in the exhaust bypass passage that bypasses the small turbocharger, and the small turbocharger and large turbocharger can be connected by opening and closing the exhaust switching valve. In the in-line two-stage supercharged diesel engine in which the operating range is switched between the fuel injection device and the fuel injection device, the fuel injection device is configured to be capable of pilot injection, and the fuel injection device includes pilot injection control means that selectively operates the pilot injection according to the opening/closing operation of the exhaust switching valve. A fuel injection device for a two-stage in-line supercharged diesel engine, comprising: a pilot injection is performed when an exhaust switching valve is closed, and a pilot injection is stopped when the exhaust switching valve is opened.