JPS6287609A - Direct-injection type diesel engine - Google Patents

Abstract

PURPOSE:To suppress occurrence of smoke and obtain a high output by arranging the single-hole nozzle of a fuel injection valve on the periphery of one side of a combustion chamber and directing this single-hole nozzle to the periphery of the other side of the combustion chamber. CONSTITUTION:A recessed groove 4a is formed at the top of a piston 4, and a combustion chamber 5 is formed in this recessed groove 4a. A fuel injection valve 8 has a single-hole nozzle 25, and this single-hole nozzle 25 is arranged on the periphery of one side of the combustion chamber 5. This single-hole nozzle 25 is directed to the periphery of the other side of the combustion chamber 5, and this single-hole nozzle 25 is arranged so that the injected fuel F passes the side of the center G of the combustion chamber. The fuel injection rate from the fuel injection valve 8 is first increased then decreased. Accordingly, occurrence of smoke is suppressed and a high output can be obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a direct injection diesel engine.

[Prior Art] Some of the diesel engines commonly used at present have fuel injection valves with multiple nozzle holes, while others have fuel injection valves with a single nozzle hole.

However, when a fuel injection valve is equipped with a large number of nozzle holes, fuel accumulates in the injection nozzle sac volume, and this accumulated fuel generates unburned hydrocarbons, or oxidation combustion occurs at multiple points simultaneously. This causes problems such as combustion noise and increased NOx. On the other hand, if the fuel injection valve has a single nozzle hole, these problems can be avoided, but smoke increases due to insufficient fuel dispersion and mixing, and in high load ranges There is a problem in that the fuel consumption rate worsens and the swirl needs to be strengthened, resulting in a shortage of intake air in the high speed range, making it impossible to obtain a sufficiently high output.

On the other hand, a diesel engine is known in which the fuel injection is divided into multiple times and the interval between each injection is controlled depending on the operating state of the engine (see Japanese Patent Laid-Open No. 17250/1983). By dividing the fuel injection into a plurality of times in this way, the air utilization rate can be increased and the mixing of the injected fuel and air can be promoted.

゛ [Problems to be solved by the invention] However, if the fuel injection is simply divided in this way, the injected fuel will be injected into the same area of the combustion chamber, so the sprays will overlap each other and smoke will occur, and the air utilization will be reduced. In order to increase the efficiency, the swirl must be made stronger, which causes a problem in that the amount of intake air is insufficient and high output cannot be obtained.

[Means for solving problems]

In order to solve the above problems, the present invention provides a direct injection diesel engine in which a groove is formed at the top of the piston and a combustion chamber is formed within the groove. For example, a single-hole nozzle is placed at the periphery of the combustion chamber, and the single-hole nozzle is placed so that the injected fuel passes to the side of the center of the combustion chamber, and the single-hole nozzle is placed so that the injected fuel passes to the side of the center of the combustion chamber. The injection rate is initially high and then lowered.

〔Example〕

Referring to Figures 1 to 4, 1 is the engine body, 2 is the cylinder block, 3 is the cylinder head,
4 is a piston, 5 is a combustion chamber 5, 6 is an intake valve, 7 is an exhaust valve, 8 is a fuel injection valve arranged in the combustion chamber 5, and 9 is an intake manifold. A groove 4a is formed at the top of the piston 4, and a combustion chamber 5 is formed within this groove 4a. The fuel injection valve 8 has a single nozzle hole, that is, a single-hole nozzle 25, as will be described later, and the single-hole nozzle 25 is arranged around one side of the combustion chamber 5. , 0 single-hole nozzles 71 and 25 are directed toward the other side periphery of the combustion chamber 5, and the single-hole nozzles 25 at j7 are oriented so that the injection fuel rod iF is on the side of the combustion chamber center G, as shown in FIG. It is arranged so that it passes through the direction.

As shown in FIG. 1, the fuel injection valve 8 is attached to the shilling head 3 at an angle, so that the fuel injected from the hole nozzle 25 is injected from above the periphery of the combustion chamber 5 into other parts of the combustion chamber 5. It will be injected downward at the side periphery. As shown in FIGS. 1 and 4, the fuel injection valve 8 is connected to a fuel pressure accumulation pipe 11 common to each cylinder via a fuel supply pipe 10.
connected to.

The fuel accumulator pipe 11 has a pressure accumulator chamber 12 with a constant volume inside thereof, and the fuel in this pressure accumulator chamber 12 is supplied to the fuel injection valve 8 via the fuel supply pipe 10. On the other hand, the pressure accumulation chamber 12 is connected to a discharge port of a fuel supply pump 14 via a fuel supply pipe 13. A suction port of the fuel supply pump 14 is connected to a discharge port of a fuel pump 15, and a suction port of the fuel pump 15 is connected to a fuel reservoir tank 16. Further, the discharge port of the fuel supply pump 14 is connected to the suction side of the fuel supply pump 14 via a fuel return conduit 17, and a relief valve 18 that opens at a constant pressure is disposed within the fuel return conduit 17. Therefore, the fuel pressure in the pressure accumulation chamber 12 is maintained constant by the relief valve 18. The fuel pump 15 is provided to feed the fuel in the fuel reservoir tank 16 into the fuel supply pump 14. There is no need to specifically provide the pump 15. On the other hand, the fuel supply pump 14 is provided to discharge high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulator 12. Ru.

FIG. 5 shows a side sectional view of the fuel injection valve 8. Referring to FIG. 5, 20 is the fuel injection valve body, 21 is the nozzle, 22
23 is a spacer, 23 is a nozzle holder for fixing the nozzle 21 and spacer 22 to the fuel injection valve body 20, and 24 is a nozzle holder.
2 shows a fuel inlet, and 25 shows a single-hole nozzle formed at the tip of the nozzle 21, respectively. The fuel injection valve main body 20, the spacer 22, and the nozzle 21 each have controls arranged in series with each other. ′
! A-rond 26, pressure bottle 27 and needle 28 are slidably inserted. control! -] A fuel chamber 29 is formed above the fuel inlet 26, and this fuel chamber 29 is connected to the fuel inlet 24.
and is connected to a pressure accumulation chamber 12 (FIG. 2) via a fuel supply pipe 10. Therefore, the fuel pressure in the pressure accumulation chamber 12 is applied to the fuel chamber 29, and the fuel pressure in the fuel chamber 29 acts on the -h plane of the control rod 26. The needle 28 has a conical pressure receiving surface 30, and a needle pressurizing chamber 31 is formed around this pressure receiving surface 3C. The needle pressurizing chamber 31 is connected to the fuel chamber 29 via a fuel passage 32 on the one hand, and an annular fuel passage 3 formed in the hollow part of the needle 28 on the other hand.
3 to the single-hole nozzle 25. A compression spring 34 is inserted into the fuel injection valve main body 20 to urge the pressure bottle 27 downward, and the needle 28 is inserted into the compression spring 34.
4 is pressed downward. The control iron 26 has a pressure receiving surface 35 having a conical shape in its middle part, and this pressure receiving surface 35
A control rod pressurization chamber 36 is formed around the control rod. Pressurized chamber 3
6 communicates with a cylinder 37 formed within the fuel injection valve body 20, and a hydraulic piston 38 is slidably inserted into the cylinder 37.

An O-ring 39 is attached to this hydraulic piston 38.

On the other hand, a drive device 40 for driving the hydraulic piston 38 is attached to the fuel injection valve body 20. This drive device 40 includes a casing 41 fixed to the fuel injection valve main body 20.
and a piezoelectric element 42 inserted between a hydraulic piston 38 and a casing 40. This piezoelectric element 42 has a laminated structure in which a large number of thin plate-like piezoelectric elements are laminated, and when a voltage is applied to this piezoelectric element 42, the piezoelectric element 42 causes distortion in the longitudinal direction due to an electrostrictive effect. That is, it extends in the longitudinal direction. This amount of elongation is, for example, 5
Although it is a small amount of about 0 μm, the response is extremely good,
The response time from applying voltage to stretching is 80μSe
It is about C. When the voltage application is stopped, the piezoelectric element 42 immediately contracts. As shown in FIG. 5, a disc spring 43 is inserted between the hydraulic piston 38 and the fuel injection valve main body 20, and the spring force of the disc spring 43 causes the hydraulic piston to
8 is pressed toward the piezoelectric element 42.

As shown in FIG. 6, a fuel passage 4 is provided within the hydraulic piston 38.
4 is formed, and a check valve 45 is inserted into this fuel passage 44. Fuel is circulated between the casing 41 and the piezoelectric element 42 by a device (not shown) in order to cool the piezoelectric element 42, and when the fuel in the control rod pressurizing chamber 36 leaks, the fuel in the casing 41 flows into the fuel passage 44. and is supplied into the control rond pressurizing chamber 36 via the check valve 45.

When the fuel in the control rod pressurizing chamber 36 is not pressurized, the needle 28 receives a downward force acting on the upper surface of the control rod 26, a downward force due to the compression spring 34, and a downward force acting on the needle 28. An upward force acting on the pressure receiving surface 30 is applied. At this time, the diameter of the control rod 26, the spring force of the compression spring 34, and the area of the pressure receiving surface 30 of the needle 28 are set so that the sum of the downward forces is slightly larger than the upward forces. Therefore, a downward force is acting on the normal needle 28, and thus the normal needle 28 is connected to the single hole nozzle 2.
5 are closed. Next, when a voltage is applied to the piezoelectric element 42, the piezoelectric element 42 expands, causing the hydraulic piston 38 to move to the left, and as a result, the pressure in the control rond pressurizing chamber 36 increases. At this time, since an upward force acts on the pressure receiving surface 35 of the control rod 26, the control rod 26
, and thus the needle 28 rises, so that fuel is injected from the single-hole nozzle 25. As mentioned above, the response time at this time is about 80 μSec, which is quite fast.

On the other hand, when the voltage application to the piezoelectric element 42 is stopped, the piezoelectric element 42 contracts, and as a result, the fuel pressure in the control rod pressurizing chamber 36 decreases, so that the control rod 2
6 and needle 28 are lowered to stop fuel injection. The response at this time is also extremely fast, about 80 μsec.

As described above, when the fuel in the control rod pressurizing chamber 36 is not pressurized, the sum of the downward forces acting on the needle 28 is slightly larger than the upward force (so that the control rod 26 The diameter, the spring force of the compression spring 34, and the area of the pressure receiving surface 30 of the needle 28 are determined.Therefore, by applying a small upward force to the pressure receiving surface 35 of the control rod 26, the needle 28 can be raised. The fuel pressure in the control rod pressurizing chamber 36 that needs to be increased in order to raise the needle 28 is small, and thus the electric power that needs to be applied to the piezoelectric element 42 is also small.

Referring again to FIG. 4, an electronic control unit 50 for controlling the fuel injection valve 8 is provided.

This electronic control unit 50 consists of a digital computer, and is connected to the R
It includes an OM (read-on memory) 52, a RAM (random access memory) 53, a CPU (microprocessor) 54, and an input board 56.

As shown in FIG. 4, a pair of disks 60 and 61 are attached to the engine crankshaft, and a pair of crank angle sensors 62 and 63 are arranged opposite the toothed outer peripheral surfaces of these disks 60 and 61. . On the other hand, the crank angle sensor 62 generates an output pulse indicating that the No. 1 cylinder is at the intake top dead center.
It is possible to determine which cylinder's fuel injection valve 8 is to be operated from the two output pulses. The other crank angle sensor 63 generates an output pulse every time the crankshaft rotates by a certain angle, so the engine speed can be calculated from the output pulse of the crank angle sensor 63.

These crank angle sensors 62 and 63 are connected to the input boat 5.
Connected to 5. Further, a load sensor 65 is attached to the accelerator pedal 64, which generates an output voltage proportional to the amount of depression of the accelerator pedal 64.

This load sensor 65 is connected to the input port 55 via an AD converter 66. On the other hand, the output port 56 is connected to a drive circuit 70 for driving and controlling the piezoelectric element 42 of each fuel injection valve 8 .

FIG. 7 shows a circuit diagram of a drive circuit 70 for driving and controlling the piezoelectric element 42. In addition, in FIG. 7, the piezoelectric elements 42 of each fuel injection valve 8 are respectively 42a and 42.
b, 42c, and 42d. In FIG. 7, each terminal 71a, 71b, 71c, 71d is a terminal for applying a voltage to the corresponding piezoelectric element 42a, 42b, 42c, 42d, and each piezoelectric element 42
Other terminals a, 42b, 42c, 42d? 2a,
72b, 72c, and 72d are grounded. In addition, in FIG. 7, SI to S4 are switching elements on the charging side,
S, -S3 are switching elements on the discharge side, and these switching elements $1-3ll7 are, for example, thyristors. Also, L is the coil on the charging side, L,
~L4 is the coil on the discharge side, C0 is the capacitor, ■. indicates a DC power supply, T indicates a transistor, and COM indicates a comparator. The collector of the transistor T is connected to the power supply v0,
The emitter of the transistor T is connected to each thyristor S, ~S4 via a coil L0. Also, the transistor T
The emitter of is grounded via capacitor C0. The base of the transistor T is connected to the comparator CO via the resistor R.
Connected to the output terminal of M.

The inverting input terminal of the comparator COM is connected between the emitter of the transistor T and the capacitor C0, and the non-inverting input terminal of the comparator COM is connected to the drive circuit 73.

Gate Gl ""'OB of each thyristor S I-S s
and the input terminal O of the drive circuit 73 is connected to the electronic control unit 5.
0 output port 56. The drive circuit 73 generates an output voltage according to the output signal output to the output port 56, and this output voltage is applied to the non-inverting input terminal of the comparator COM.

Next, basic fuel injection control of the fuel injection valve 8 will be explained with reference to the time chart shown in FIG. In addition,
In Fig. 8, CG is the injection start signal inputted by the gate G of the charging side thyristors 31 to S4, ~G44, and DG is the injection stop signal inputted to the gate of the discharging side thyristor S, ~Ss. , 0 is the output voltage of the drive circuit 73 that determines the needle lift bit of the fuel injector 8, C is the amount of charge stored in the capacitor c0, L is the lift amount of the needle 28 (Fig. 5), and R is the fuel injection rate. 7 or less,
In order to make the explanation easier to understand, only the case where the piezoelectric element 42a is controlled will be explained.

Before the injection start signal CG is generated, an amount of charge determined by the output voltage of the drive circuit 73 is stored in the capacitor C0, as will be described later. Next, when the injection start signal CG is input to the gate G, the thyristor S1 is temporarily turned on. At this time, since the capacitor C0 and the coil L0 constitute a resonant circuit, the voltage applied to the piezoelectric element 42a is boosted, and the charge stored in the capacitor Co is supplied to the piezoelectric element 42a, so that the piezoelectric element 42a It will be charged. The amount of charge at this time is capacitor C
It is proportional to the amount of charge stored at zero. On the other hand, since the amount of elongation of the piezoelectric element 42a is proportional to the amount of charge to the piezoelectric element 42a, the amount of elongation of the piezoelectric element 42a is proportional to the amount of charge stored in the capacitor C0. On the other hand, the fifth
As can be seen from the figure, the amount of displacement of the hydraulic piston 38 is proportional to the amount of extension of the piezoelectric element 42a.
Since the amount of lift of the needle 28 is proportional to the amount of displacement of the hydraulic piston 38, the amount of lift of the needle 28 is proportional to the amount of extension of the piezoelectric element 42a. As a result, the amount of lift of the needle 28 is proportional to the amount of charge stored in the capacitor C6.

Furthermore, as the lift amount of the needle 28 increases, the amount of fuel injected from the single hole nozzle 25 per unit time increases.
Therefore, the greater the needle lift amount on the second day, the greater the fuel injection rate.

Therefore, the fuel injection rate is proportional to the amount of charge stored in the capacitor C0.

Next, when the injection stop signal DGI is input to the gate Gs, the thyristor S5 is temporarily turned on. At this time, the back electromotive force caused by the coil L1 causes the piezoelectric element 42a to
A negative voltage is applied to the piezoelectric element 42a, and as a result, the piezoelectric element 42a
Since the charge is immediately discharged, the piezoelectric element 42a immediately contracts and fuel injection is stopped. On the other hand, the drive circuit 7 uses the fall of the injection start signal CG+ as a trigger.
The output voltage of No. 3 is changed. Injection start signal CG,
When input to the gate GI, the terminal voltage of the capacitor C0 decreases, so the output voltage of the comparator COM becomes high level, and as a result, the transistor T is turned on and the capacitor C0 is gradually charged. Then capacitor C
When the terminal voltage of 0 exceeds the output voltage of the drive circuit 73, the output voltage of the comparator COM becomes a low level. As a result, transistor T is turned off and charging of capacitor C0 is stopped. Then, the injection start signal CG is activated again.
However, since the amount of charge in the capacitor C0 immediately before the injection start signal CGt is generated is greater than the amount of charge in the capacitor C0 immediately before the injection start signal CGI is generated, the injection start signal CGz is input to the gate GI. When this occurs, the lift IL of the needle 28 increases, and therefore the fuel injection rate R also increases. As can be seen from the above explanation, injection can be started at any time by the injection start signal and injection stop signal input to each gate G+ to G8, and the injection period can be freely determined.
The fuel injection rate R can be freely controlled by changing the lift amount of the needle 28 depending on the output voltage.

Next, the fuel injection method according to the present invention will be explained based on the flowchart shown in FIG. Note that the injection control shown in FIG. 9 is executed at every predetermined crank angle. Referring to FIG. 9, first, in step 100, the output signal of the crank angle sensor 63 representing the engine speed NE and the output signal of the load sensor 65 representing the engine load are taken in. Next, in step 101, the pre-injection timing TI, the pre-injection period 4, the pre-injection needle lift tVl, the post-injection timing T2, the post-injection period L2, and the post-injection needle lift ffi v z are determined. These T1. L.I.

V + , T z , L 2 and V2 are engine speed N
is previously stored in ROM 52 as a function of E and load. Then in step 102 these T +
, L 1. Vl.

Data representing T z, L z, and V z is written to the output port 56, and fuel injection is performed based on this data. FIG. 10 shows an example of fuel injection. In Fig. 10, the vertical axis shows the fuel injection rate R, and the horizontal axis shows the crank angle θ.
shows. As shown in FIG. 10, in the present invention, 2
The injection is divided into three times, and the fuel injection rate R of the first injection A is
It can be seen that the fuel injection rate B is higher than the fuel injection rate B of the post-injection B. That is, in the present invention, fuel is first injected from the single-hole nozzle 25 of the fuel injection valve 8 at a high fuel injection rate, and then fuel is injected at a low fuel injection rate.

Next, the injection timing and fuel injection rate of the pre-injection A and the post-injection B will be explained with reference to FIG.

FIG. 11 (al indicates where pre-injection A was performed).

In the pre-injection A, the needle lift amount is large, and therefore the fuel injection rate is high, so the penetration force of the injected fuel is large.

As a result, the fuel spray collects at the periphery of the combustion chamber 5 on the opposite side from the single-hole nozzle 25. This fuel amount iA rides the swirl w4 and turns while expanding and losing. When this fuel spray A reaches the side substantially opposite to the single-hole nozzle 25 with respect to the center of the combustion chamber 5 as shown in FIG. 10, the post-injection B is performed. In the subsequent injection B, the needle lift amount is small, and therefore the fuel injection rate is low.

As a result, the injected fuel (, -) has a weak penetration force (thus, the fuel spray B is formed around the single hole).

Therefore, within the combustion chamber 5, the fuel spray A resulting from the pre-injection and the fuel spray resulting from the post-injection are spatially separated. The injection timing and fuel injection rate for pre-injection and post-injection are as follows:
- J-・Ral: Set so that fuel spray A and fuel spray B are spatially separated.

Next, as shown in Fig. 11(c), the pre-injected fuel is ignited and combusted)↓"・!7, and then Fig. 11(d)
), the fuel B caused by the post-injection G is ignited and combusted. Figure 12 shows the heat release rate. In Fig. 12, the broken line indicates the heat release rate in a conventional single-injection diesel engine, and a indicates the heat release rate due to pre-injection A.
b + indicates the heat release rate due to post-injection.

Therefore, in the present invention, the heat release rate is the sum of a and b, and is represented by curve C. In this way, in the present invention, combustion is performed in two stages with a time delay, so combustion is gentle,
In this way, the generation of combustion noise is suppressed.

〔Effect of the invention〕

Since the fuel spray caused by the pre-injection and the fuel spray caused by the post-injection are spatially separated fl, 'I), the air utilization rate is increased,
In this way, the generation of smoke can be suppressed. In addition, since combustion is carried out in two stages with a time delay, it is possible to suppress the generation of combustion noise.Also, since the peak temperature of combustion is reduced, the generation of NOx can be suppressed. can. In addition, the intake boat structure 1, which can generate a low swirl because it does not require a very strong swirl.
: It is possible to secure a high amount of intake air and obtain high output. Furthermore, since the fuel injection valve can be placed around the combustion chamber, there is no need to consider interference with the fuel injection valve when arranging the intake and exhaust valves.1 Therefore, the intake and exhaust valves can be placed in optimal positions. be able to.

[Brief explanation of drawings]

Figure 1 is a side sectional view of the diesel engine, Figure 2 is a plan view of the top surface of the piston, Figure 3 is a side sectional view taken along line m-1Il in Figure 1, and Figure 4 is the entire diesel engine. figure,
Fig. 5 is a side cross-sectional view of the fuel injection valve, Fig. 6 is a plan cross-sectional view of the hydraulic screw 1, Fig. 7 is a circuit diagram of the drive circuit for driving the piezoelectric element, and Fig. 8 is a side cross-sectional view of the fuel injection valve. FIG. 9 is a flowchart for carrying out the fuel injection method according to the present invention, FIG. 10 is a diagram showing the fuel injection rate, No. 11 is a diagram for explaining the fuel injection action, and No. 12 is a diagram for explaining the fuel injection action. figure!
, is a diagram showing the heat release rate. 4a...concave groove, 5...combustion chamber, 8...
Fuel injection valve, 25...single hole nozzle. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 e Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] In a direct injection diesel engine in which a groove is formed at the top of the piston and a combustion chamber is formed within the groove, a single hole nozzle of the fuel injection valve is arranged around one side of the combustion chamber, and the single hole nozzle of the fuel injection valve is arranged around one side of the combustion chamber. The nozzle is directed toward the periphery of the other side of the combustion chamber, and the single-hole nozzle is arranged so that the injected fuel passes to the side of the center of the combustion chamber, and the fuel injection rate from the fuel injection valve is initially high and then A direct-injection diesel engine designed to be lower.