JPH0672580B2 - Fuel injection device for diesel engine - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a fuel injection device for a diesel engine,
In particular, the present invention relates to a fuel injection device for a diesel engine suitable for use in a diesel engine for automobiles and capable of improving output performance and improving fuel efficiency over the entire rotation range of the engine.

[Prior art]

As a fuel injection pump for supplying fuel to a diesel engine, especially a diesel engine for automobiles, the fuel injection rate is controlled according to the engine operating state.
A so-called variable injection rate type fuel injection pump is known. This is, for example, as shown in Japanese Utility Model Publication No. 56-127360.
The fuel pressure is controlled by injecting the fuel in synchronization with the engine rotation and changing the volume of a plunger chamber formed at the tip of the plunger to pressurize the fuel to a pressure suitable for the injection and the plunger chamber. For controlling the period, it is provided with an injection period control mechanism including an accumulator piston, and by changing the volume of the plunger chamber by the accumulator piston, the fuel pressure is controlled to control the injection period. It is designed to be optimized. According to such a variable injection rate type fuel injection pump, as shown by the circles in FIG. 1 (during low speed rotation) and FIG. 2 (during high speed rotation), the black circles are also shown in FIG. 1 and FIG. Although the injection period becomes longer and both the diesel smoke and the fuel consumption rate become smaller than those of the fixed injection rate type fuel injection pump which does not have the injection period control mechanism shown in (4), it is still not sufficient. This is because it is possible to adapt the injection period by using a variable-injection-rate fuel injection pump, but this lowers the injection rate, hinders atomization of the injected fuel, and provides a sufficient injection period compatibility. It is because the effect is not obtained. On the other hand, as a fuel injection valve for injecting the fuel pressurized in the plunger chamber of the fuel injection pump into the engine combustion chamber, a so-called two-stage injection type that reduces the initial injection rate and enables two-stage injection Fuel injection valves are known. this is,
For example, actual development 57-107967, actual public 54-3224, actual public 53-
52987, Japanese Patent Publication No. 47-46807, Japanese Patent Publication No. 47-47046, etc., a plurality of springs for setting the valve opening pressure of the nozzle are provided.
In the initial stage of injection with a small fuel pressure, the first spring restrains the lift of the needle to perform a small amount of initial injection, and in the latter stage of the injection when the fuel pressure is sufficiently high, the needle is resisted against the second spring. Is sufficiently lifted to perform a large amount of main injection, thereby promoting atomization of the injected fuel. However, when this two-stage injection type fuel injection valve is used in combination with a fixed injection rate type fuel injection pump,
As indicated by the broken line B in FIG. 3 (at full load), there was a problem that the injection period was insufficiently adapted and the effect of atomization could not be fully exhibited. In FIG. 3, the alternate long and short dash line A
Shows an injection period when a conventional one-stage injection type fuel injection valve and a fixed injection rate type fuel injection pump are used in combination.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, solves the drawbacks of the conventional variable injection rate fuel injection pump and the conventional two-stage injection fuel injection valve, and improves the output performance over the entire rotation range. It is also an object of the present invention to provide a fuel injection device for a diesel engine that can improve fuel efficiency.

[Constitution of the invention]

The present invention, in a fuel injection device for a diesel engine, changes the volume of a plunger for sucking fuel in synchronization with engine rotation and pressurizing it to a pressure suitable for injection, and a plunger chamber formed at the tip of the plunger. In addition to including an accumulator piston for making the back pressure of the accumulator piston smaller in the engine low speed rotation range than in the engine high speed rotation range, the stroke of the accumulator piston is controlled, A variable-injection-rate fuel injection pump including an injection period control mechanism for making the pressure increase of the fuel pressurized in the plunger chamber in the engine low-speed range slower than in the engine high-speed range, and the fuel injection pump. In order to inject the fuel pressurized in the plunger chamber into the engine combustion chamber, the fuel pressure is small at the beginning of injection. And a two-stage injection type fuel injection valve that performs a large amount of main injection in the latter stage of injection when the fuel pressure is sufficiently high, and the injection rate of the injection rate variable fuel injection pump is reduced. Is compensated by the two-stage injection type fuel injection valve, and incompatibility of the injection period of the two-stage injection type fuel injection valve is compensated by the injection rate variable fuel pump. The above object is achieved. In addition, the embodiment of the present invention sets the injection period in the low speed rotation range of the fuel injection pump to 20 to 25 ° CA and the injection period in the high speed rotation range to 30 to 35 ° CA, so that it is optimal for the number of revolutions. The injection period is obtained. Furthermore, in another embodiment of the present invention, an optimal two-stage injection is performed by setting the injection initial set pressure in the fuel injection valve to 15 kg / cm ² G and the late injection set pressure to 200 kg / cm ² G. It is the one.

[Operation of the invention]

The injection rate of the fuel injected into the engine combustion chamber, that is, the fuel injection amount per unit time (unit crank angle) depends on the injection pipe pressure and the needle lift amount. Further, in the fuel injection control of the diesel engine, the injection rate and the injection pressure must be appropriately controlled with time according to the crank angle. For example, the start of fuel injection from a fuel injection valve used in a diesel engine depends on the relationship between the valve opening pressure of the fuel injection valve and the injection pipe internal pressure of the fuel to be pumped. By controlling the pressure characteristic with respect to the crank angle, the injection timing must be controlled appropriately. Further, for example, from the viewpoint of atomizing the fuel injected into the engine fuel chamber, the injection rate and injection pressure must be controlled appropriately. The injection rate variable type fuel injection pump used in the present invention is
It includes a plunger for absorbing fuel in synchronization with engine rotation and pressurizing it to a pressure suitable for injection, and an accumulator piston for changing the volume of the plunger chamber formed at the tip of the plunger. Further, the back pressure of the accumulator piston is made smaller in the engine low-speed rotation range than in the engine high-speed rotation range to control the stroke of the accumulator piston and pressurize in the plunger chamber in the engine low-speed rotation range. It includes an injection period control mechanism for slowing the increase in the pressure of the fuel to be injected than in the engine high speed rotation range. As described above, the variable injection rate fuel injection pump of the present invention realizes the control of the injection period according to the engine rotation speed by controlling the pressure increase characteristic with respect to the crank angle. That is, the valve opening period of the fuel injection valve is controlled by controlling the pressure increase characteristic. On the other hand, the two-stage injection type fuel injection valve used in the present invention is
A small amount of initial injection is performed in the initial stage of injection with a low fuel pressure, and a large amount of main injection is performed in the latter stage of injection with a sufficiently high fuel pressure. In the two-stage injection type fuel injection valve, as described above, such initial injection and main injection are more suitable for combustion in the engine fuel chamber, etc.
The atomization of injected fuel can be promoted. However, although the injection rate variable fuel injection pump can control the injection period as described above, it has found a problem that the injection rate is lowered and atomization of the injected fuel is hindered. On the other hand, when the two-stage injection type fuel injection valve is combined with a conventional fixed injection rate type fuel injection pump, the injection period becomes incompatible, and atomization of the injected fuel is hindered. I will end up. In the present invention, by combining the variable injection rate type fuel injection pump and the two-stage injection type fuel injection valve, an effect that cannot be expected by those skilled in the art has been found. That is, by combining these, naturally, while applying the two-stage injection type fuel injection valve, optimal injection time control according to the engine speed is performed by the injection rate variable fuel injection pump. It can be realized. Further, the inventors have found an unexpected and excellent effect of improving atomization of the fuel injected into the engine combustion chamber, in addition to the effect naturally conceivable as described above. That is, the variable injection rate fuel injection pump has a time-dependent pressure characteristic according to the crank angle. Further, the two-stage injection type fuel injection valve has two stages of valve opening pressure, and the characteristics of the injection pipe internal pressure and the needle lift amount are unique. In the present invention, the fuel injection pump of the variable injection rate type and the two-stage injection type fuel injection valve are combined to atomize the fuel injected into the engine combustion chamber. It is a thing. Therefore, in the present invention, since the variable injection rate type fuel injection pump and the two-stage injection type fuel injection valve are used in combination, the effect of adapting the injection period by the variable injection rate type fuel injection pump is obtained. Not only appears sufficiently, but the effect of atomizing the fuel by the two-stage injection type fuel injection valve is synergized, and as shown by the crosses in FIGS. 1 and 2 above, the diesel smoke and the fuel consumption rate are significantly increased. Can be lowered. or,
As indicated by the solid line C in FIG. 3 above, the injection period can be sufficiently adapted.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. In this embodiment, as shown in FIG. 4, a plunger 12 for sucking fuel in synchronization with the rotation of the engine 10 and pressurizing it with a pressure suitable for injection, and a plunger chamber 14 formed at the tip of the plunger 12 are shown. Injection period control mechanism for controlling the fuel pressure and controlling the injection period by changing the volume of
A fuel injection pump 11 of variable injection rate including 16 and the fuel pressurized in the plunger chamber 14 of the fuel injection pump 11 is injected into the engine combustion chamber 10A at the initial stage of low fuel pressure injection. Is composed of a two-stage injection type fuel injection valve 40 that performs a small amount of initial injection and performs a large amount of main injection in the latter stage of injection when the fuel pressure is sufficiently high. In the figure, 18 and 20 are rollers and a cam plate for axially reciprocating the plunger 12 in synchronism with engine rotation, and 22 is a control end of pumping of fuel pressurized in the plunger chamber 14. A spill ring 24 for cutting the fuel when the engine is stopped, a fuel cut solenoid 26 for cutting the fuel, and a fuel 26 pressurized in the plunger chamber 14 via a delivery valve 28 and a fuel injection pipe 30. Is a distribution passage for distributing to each cylinder. The injection period control mechanism 16 of the fuel injection pump 11 is, for example, as shown in detail in FIG. 5, a cylinder 32 arranged to pass through the plunger chamber 14, and a cylinder 32 slidably fitted in the cylinder 32. An accumulator piston 34 that allows the volume of the plunger chamber 14 to be variable, and the piston 34
14 A spring 36 for urging in the contracting direction and a stroke control mechanism 38 for controlling the stroke of the accumulator piston 34 according to the engine operating state. The stroke control mechanism 38 is, for example, a fuel injection pump.
The discharge pressure of a feed pump (not shown) built in 11 is used as the back pressure of the accumulator piston 34 and the back pressure chamber 34A.
And a first fuel passage 38A to be introduced into
And a second fuel passage 38C that guides the discharge pressure of the feed pump from the upstream side of the throttle 38B.
And a check valve 38D provided in the middle of the second fuel passage 38C for blocking the fuel flow of the accumulator piston 34 in the back pressure chamber 34A contracting direction. In this example, the discharge pressure of the feed pump is introduced into the back pressure chamber 34A via the second fuel passage 38C, and
When the accumulator piston 34 moves to the right in the figure,
Since the pressure of the back pressure chamber 34A is maintained by the action of the throttle 38B and the check valve 38D, the stroke of the accumulator piston 34 is determined by the discharge pressure of the feed pump, that is, the discharge pressure depending on the engine rotation speed. It will be controlled short when high and long when low. Therefore, when the engine speed is low, the injection period will be longer than in the conventional case. The injection period control mechanism 16 includes, for example, the fuel injection pump 11
The injection period in the low speed rotation range is 20 to 25 ° CA, and the injection period in the high speed rotation range is 30 to 35 ° CA. The fuel injection valve 40 is, for example, as shown in detail in FIG.
A nozzle holder 42 in which a fuel supply passage 42A communicating with a fuel storage chamber in the nozzle is formed, a nozzle 46 attached to the lower end of the nozzle holder 42 by a nozzle retainer 44, and a nozzle 46 incorporated in the nozzle 46 The non-shoulder shoulder abuts against the end surface 42B of the nozzle holder 42 so that the needle 47 is limited to a predetermined lift amount and the first needle formed in the nozzle holder 42.
The upper end of the partition wall 4 of the nozzle holder 42 is housed in the spring chamber 42C.
The first push rod which is in contact with 2D and whose lower end is connected to the needle 47
1st for setting the initial injection valve opening pressure, which contacts the spring bearing of 48
The main injection valve opening, in which the setting spring 50 and the second spring chamber 42E of the nozzle holder 42 have their upper ends abutted against the spring receiver of the screw plug 52 and their lower ends abutted against the upper spring receiver of the second push rod 53. A second setting spring 54 for setting pressure, and a shim 56 for adjusting the initial needle lift amount 1 corresponding to the distance between the upper end of the first push rod 48 and the lower end of the second push rod 53. Has been done. The relationship among the pressure in the injection pipe, the needle lift, and the injection rate in the fuel injection valve 40 is as shown in FIG. That is,
Initial injection valve opening pressure P ₁ (eg 150kg / cm ² G)
The needle 47 moves up against the first setting spring 50 when reaching, and stops rising once the upper end of the first push rod 48 contacts the lower end of the second push rod 53. Adjustment of the needle lift amount 1 at that time is performed by changing the thickness of the shim 56. At the time of this initial injection, the opening area of the needle valve seat is appropriately throttled, so that the injection rate can be suppressed to a small value as shown in FIG. 7C even if the pressure is slightly high. Next, the injection pipe pressure is the main injection valve opening pressure P ₂ (for example, 200 kg / cm
² G), the second set spring 54 is compressed this time, the total lift L is increased, and the main injection is performed until the pressure decreases to the valve closing pressure P ₃ . The elapsed time T for increasing the pressure from P _{1 to} P ₂ is
It is determined by adjusting the set load of the second setting spring 54. The operation will be described below. Plunger for fuel injection pump 11 synchronized with engine rotation
12 reciprocates in the left-right direction in FIG. 4, and along with this, the fuel whose injection period has been optimized by the injection period control mechanism 16 via the distribution passage 26 and the delivery valve 28 is the fuel injection pipe.
Supplied to 30. This pressurized fuel is introduced into the fuel injection valve 40, and in the fuel injection valve 40, a small amount of initial injection is performed in the initial stage of injection with a low fuel pressure, and the latter stage of injection with a sufficiently high fuel pressure. A large amount of main injection is performed on. Therefore, as shown by the solid line C in FIG. 3 above, regardless of the engine speed, the injection period becomes longer and the optimization is achieved, and the increase in pressure by the fuel injection valve 40 results in fine particles. Since the effect of the conversion is added, the diesel smoke and the fuel consumption rate are significantly reduced as shown by the crosses in FIGS. 1 and 2 above. In the present embodiment, the injection period in the low speed rotation range of the fuel injection pump 11 is 20 to 25 ° CA, and the injection period in the high speed rotation range is 30 to 35 ° CA. The period is obtained. Also, the set pressure in the fuel injection valve 40 at the initial stage of injection is 150 kg / cm ² G, and the set pressure at the latter stage of injection is 200 k.
Since it is set to g / cm ² G, optimum two-stage injection characteristics can be obtained. The injection period of the fuel injection pump 11 and the set pressure of the fuel injection valve 40 are not limited to this. Further, in the present embodiment, a mechanical injection period control mechanism including the accumulator piston 34 as the fuel injection pump 11.
Since the one equipped with 16 is used, it is easy to control. It should be noted that FIG. 8 shows the plunger chamber of the pump with respect to the crank angle in the case where the fuel pressurized by a general fixed type pump is injected into the engine combustion chamber by the one-stage injection valve. It shows the pressure characteristic, the pressure characteristic in the injection pipe, the needle lift amount characteristic of the injection valve, and the injection rate characteristic of the fuel injected into the engine combustion chamber. Further, FIG. 9 is a graph showing the same characteristics when the fuel pressurized by the variable injection rate type pump is injected into the engine combustion chamber by the one-stage injection valve. FIG. 10 is a graph showing similar characteristics when a fixed pump and a two-stage injection valve are used. FIG. 11 shows the pressure characteristic of the plunger chamber and the inside of the injection pipe when the fuel is injected into the engine combustion chamber by the two-stage injection valve while pressurizing by the variable injection rate type pump to which the present invention is applied. It is a graph which shows a pressure characteristic, a needle lift amount characteristic, and an injection rate characteristic. All of FIGS. 8 to 11 are in the engine low speed rotation range. First, as shown in FIG. 8, the injection rate characteristic with respect to the crank angle in the case of using the fixed pump and the one-stage injection valve shows that the injection rate increases after the start of fuel injection, and then again. It has a very simple injection rate characteristic that the injection rate decreases and the injection ends. Further, as shown in FIG. 9, when the variable injection rate type pump and the one-stage type injection valve are used, as can be seen in comparison with FIG. It has been extended. However, as shown in the graph of FIG. 9, immediately after the injection, the pressure in the injection pipe is temporarily reduced. For this reason, the needle lift amount is also reduced, and the injection rate is also temporarily reduced. Therefore, during such a period of time when the pressure in the injection pipe is decreasing, atomization of the fuel injected into the engine combustion chamber is hindered. Next, as shown in FIG. 10, when a two-stage injection valve is used for a fixed pump, a small amount of initial injection is performed at the beginning of injection, and then a large amount of main injection stabilizes. Is being done. However, since the fixed pump is used, the injection period cannot be controlled according to the engine rotation speed, which causes a problem of incompatibility of the injection period. On the other hand, in the case to which the present invention is applied as shown in FIG. 11, a variable injection rate type pump is particularly used for the two-stage type injection valve, and the injection is performed according to the engine speed. The period is controlled. In FIG. 11, each characteristic of the one using the fixed type pump and the two-stage type injection valve is indicated by a broken line (the above-mentioned
Figure 10 shows the transcription), but compared to these, the injection period can be effectively extended in the low engine speed region. Further, as is clear by comparing the injection rate characteristics of FIG. 11 and the one using the variable injection rate pump for the one-stage injection valve of FIG.
In spite of using the variable injection rate type pump, in the present invention, the injection pipe pressure, the needle lift amount, and the injection rate do not temporarily decrease after the injection. in this way,
In the present invention, when the variable injection rate pump and the two-stage injection valve are used in combination, the injection period is controlled according to the engine speed and the two-stage injection of the initial injection and the main injection is performed. In addition to the effects that are naturally conceivable, it is possible to solve the problem that the injection rate variable pump has, such as a temporary decrease in the injection rate.

【The invention's effect】

As described above, according to the present invention, it is possible to simultaneously optimize the injection period and atomize the spray. Therefore, it has an excellent effect that the output performance and the fuel efficiency performance of the entire engine rotation range can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a conventional example using a fuel injection pump of fixed injection rate type or variable injection rate type, and an injection period in a low speed rotation range, diesel smoke and fuel consumption in an embodiment of the present invention. FIG. 2 is a diagram showing a comparison of examples of the relationship between the fuel consumption rates, and FIG. 2 is a diagram showing a comparison of the examples of the relationship between the injection period and the diesel smoke and the fuel consumption rate in the high speed rotation region. An example of the relationship between the engine speed and the injection period in the embodiment of the present invention will be compared with a conventional example in which a one-stage injection type or two-stage injection type fuel injection valve and a fixed injection rate type fuel injection pump are combined. 4 is a sectional view showing the configuration of the embodiment of the fuel injection device for the diesel engine according to the present invention, and FIG. 5 is the injection period control of the fuel injection pump used in the embodiment. FIG. 6 is a sectional view showing the structure of the mechanism, and FIG. FIG. 7 is a sectional view showing the structure of the injection valve, FIG. 7 is a diagram showing an example of the relationship among the pressure in the injection pipe, the needle lift, and the injection rate in the fuel injection valve, and FIG. 8 is a general fixed pump. When the pressurized fuel is injected into the engine combustion chamber by the one-stage injection valve, the pressure characteristic of the plunger in the pump, the pressure characteristic in the injection pipe, and the needle lift of the injection valve with respect to the crank angle A graph showing the fuel injection rate characteristic of the fuel injected into the engine combustion chamber,
FIG. 9 is a graph showing similar characteristics when the fuel pressurized by the variable injection rate pump is injected into the engine combustion chamber by the single-stage injection valve, and FIG. 10 is a fixed pump. FIG. 11 is a graph showing similar characteristics when using a two-stage injection valve and a two-stage injection valve. It is a graph which shows the same characteristic at the time of making it inject fuel into. 10 ... Engine, 11 ... Fuel injection pump, 12 ... Plunger, 14 ... Plunger chamber, 16 ... Injection period control mechanism, 30 ... Fuel injection pipe, 32 ... Cylinder, 34 ... Akyumirator piston , 36 ... Spring, 38 ... Stroke control mechanism, 40 ... Fuel injection valve, 46 ... Nozzle, 47 ... Needle, 50 ... First setting spring, 54 ... Second setting spring.

Claims (3)

[Claims] 1. A plunger for sucking fuel in synchronism with engine rotation and pressurizing it to a pressure suitable for injection, and an accumulator piston for changing the volume of a plunger chamber formed at the tip of the plunger. In addition, the back pressure of the accumulator piston is made smaller in the engine low-speed rotation range than in the engine high-speed rotation range to control the stroke of the accumulator piston, and the plunger in the engine low-speed rotation range is controlled. A fuel injection pump of variable injection rate including an injection period control mechanism for making the pressure increase of the fuel pressurized in the chamber slower than the engine high speed rotation range, and the fuel in the plunger chamber of the fuel injection pump. In order to inject the fuel into the engine combustion chamber, a small amount of the initial injection is performed at the beginning of the injection with the low fuel pressure to ensure that the fuel pressure is sufficiently high. And a two-stage injection type fuel injection valve that performs a large amount of main injection in the latter stage of the injection, and the injection rate reduction of the injection rate variable fuel injection pump is performed by the two-stage injection type fuel injection valve. The fuel injection device for a diesel engine, wherein the fuel injection valve of the two-stage injection type is adapted to compensate for the incompatibility of the injection period by the fuel pump of the variable injection rate type. 2. The fuel injection pump has an injection period in the low speed rotation range of 20 to 25 ° CA and an injection period in the high speed rotation range of 30.
The fuel injection device for a diesel engine according to claim 1, wherein the fuel injection device is set at ˜35 ° CA. 3. The diesel engine according to claim 1, wherein the set pressure at the initial stage of injection in the fuel injection valve is 150 kg / cm ² G and the set pressure at the latter stage of injection is 200 kg / m ² G. Combustion injection device.