JP2722621B2 - Unit injector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a unit injector.

[Conventional technology]

The unit injector is usually a plunger driven by an engine, a fuel pressurized chamber filled with fuel and pressurized by the plunger, and a fuel pressure in response to the fuel pressure in the fuel pressurized chamber. A needle that opens when the pressure exceeds the pressure, a fuel overflow passage that overflows fuel in the fuel pressurization chamber, and an overflow valve that is driven by the actuator and disposed in the fuel overflow passage. Fuel injection is performed when the flow valve is closed.

By the way, in such a unit injector, the needle is usually kept in a closed state by a spring force, and the needle is lifted by applying a high fuel pressure to a conical needle pressure receiving surface formed on the outer peripheral surface of the needle to raise the fuel. An injection is performed. Next, when the overflow valve is opened and the fuel pressure in the fuel pressurizing chamber is rapidly decreased, the fuel pressure acting on the needle pressure receiving surface is also rapidly decreased at the same time, so that the needle moves in the valve closing direction by the spring force. To close the nozzle opening. However, when the fuel pressure in the fuel pressurizing chamber is suddenly reduced in this way, the entire high-pressure fuel filled around the needle between the nozzle orifice from the needle pressure receiving surface moves toward the fuel pressurizing chamber, and as a result, The pressure around the needle near the nozzle opening temporarily drops to a much lower pressure, for example, below atmospheric pressure. However, when the pressure around the needle near the nozzle opening becomes a considerably low pressure as described above, many small bubbles are generated around the needle near the nozzle opening. Therefore, when the needle is opened next time, the fuel containing these bubbles is ejected first, which causes a problem that the rising of the fuel injection rate is deteriorated.

In addition, the response of the needle is not so good due to its own inertia and friction with the surroundings. Therefore, even if the fuel pressure acting on the needle pressure receiving surface drops rapidly, the needle does not close the nozzle port immediately, and After a while, the needle closes the nozzle port. Therefore, if the fuel pressure acting on the needle pressure receiving surface drops rapidly and becomes lower than the pressure in the combustion chamber, the combustion gas in the combustion chamber flows around the needle through the nozzle port before the needle closes. Is generated.

In order to avoid such a problem, when the overflow valve is opened in order to stop the fuel injection, the overflow action of the fuel is suppressed to suppress the decrease in the fuel pressure in the fuel pressurizing chamber. It will be good. Therefore, when the overflow control valve is closed, the unit pressure in which the fuel pressure in the fuel pressurized chamber acts in the valve opening direction of the overflow valve and the overflow valve is always urged in the valve closing direction by a spring. It is publicly known.
187965). In this unit injector, the fuel in the fuel pressurization chamber is maintained at a certain pressure or higher by the spring force of a spring that biases the overflow valve. As a result, since the fuel pressure around the needle does not decrease so much, generation of many small bubbles around the needle is prevented, and combustion gas in the combustion chamber is prevented from flowing around the needle.

[Problems to be solved by the invention]

However, in this unit injector, the spring force of the spring for biasing the overflow valve cannot be adjusted from the outside, and thus, after the unit injector is assembled, the opening pressure of the overflow valve is reduced to the normal opening pressure. There is a problem that it cannot be adjusted accurately.

[Means for solving the problem]

According to the present invention, in order to solve the above problems, a plunger driven by an engine, a fuel pressurized chamber filled with fuel and pressurized by the plunger, and responsive to fuel pressure in the fuel pressurized chamber are provided. A needle that opens when the fuel pressure exceeds a predetermined pressure, a fuel overflow passage that overflows fuel in the fuel pressurization chamber, and an overflow that is driven by an actuator and disposed in the fuel overflow passage. And a flow valve,
When the overflow valve is closed, the fuel pressure in the fuel pressurization chamber acts in a direction to open the overflow valve, and when the overflow valve is held closed by the actuator, the fuel is injected. Is performed, the overflow valve is normally biased in the valve closing direction by a spring, and a spring force adjusting screw capable of adjusting the spring force of the spring from the outside of the unit injector housing is attached to the unit injector housing. I have.

[Action]

When the closing action of the overflow valve by the actuator to stop the fuel injection is released, the overflow valve opens, and the fuel pressure in the fuel pressurization chamber decreases. When the fuel pressure in the fuel pressurizing chamber decreases, the overflow valve is closed by the spring force, and the fuel pressure in the fuel pressurizing chamber is maintained at a certain pressure determined by the spring force.

〔Example〕

Referring to FIG. 1, FIG. 2, FIG. 4 and FIG.
1 is a housing body of the unit injector, 2 is a nozzle having a nozzle port 3 formed at the tip thereof, 4 is a spacer,
Reference numeral 5 denotes a sleeve, and reference numeral 6 denotes a nozzle holder for fastening the nozzle 2, the spacer 4, and the sleeve 5 to the housing body 1, respectively. A needle 7 for controlling opening and closing of the nozzle port 3 is slidably inserted into the nozzle 2, and the top of the needle 7 is connected to a spring retainer 9 via a pressure pin 8. The spring retainer 9 is constantly pressed downward by the compression spring 10, and this pressing force is transmitted to the needle 7 via the pressing pin 8. Therefore, the needle 7 is normally urged by the compression spring 10 in the valve closing direction.

On the other hand, a plunger hole 11 is formed coaxially with the needle 7 in the housing body 1, and a plunger 12 is slidably inserted into the plunger hole 11. The upper end of the plunger 12 is connected to a tappet 13, which is constantly urged upward by a compression spring 14. This tappet
13 is moved up and down by a cam (not shown) driven by the engine, whereby the plunger 12 is moved up and down in the plunger hole 11. On the other hand, a fuel pressurizing chamber 15 defined by a lower end portion 12a of the plunger 12 is formed in the plunger hole 11 below the plunger 12. This fuel pressurization chamber
Numeral 15 is connected to a needle pressurizing chamber 18 through a rod-shaped filter 16 and a fuel passage 17 (FIG. 5).
Is the nozzle port 3 through the annular fuel passage 19 around the needle 7
Linked to On the inner wall surface of the plunger hole 11, there is formed a fuel supply port 20 which opens into the fuel pressurizing chamber 15 when the plunger 12 is at the upper position, as shown in FIG. 2-3k in fuel pressurization chamber 15
Fuel at a feed pressure of about g / cm ² is supplied. The fuel supply port 20 is, for example, a fuel tank (not shown) via a fuel discharge passage 20a extending in a direction perpendicular to the fuel supply port 20 and a relief valve (not shown) having a valve opening pressure of about ² to 3 kg / cm ^2. Connected to. Further, as shown in FIG. 4, a fuel port 21 which is inevitably formed for drilling the fuel supply port 20 is formed on the side opposite to the fuel supply port 20 with respect to the plunger hole 11. The outer end of 21 is closed by blind plug 22. This fuel port 21 is a fuel supply port
It extends coaxially with 20 and opens into the plunger hole 11. A circumferential groove 23 extending from the fuel supply port 20 to the fuel port 21 is formed on the inner wall surface of the plunger hole 11. Therefore, the plunger 12 is lowered and the plunger 12 is moved to the fuel supply port 20.
And the fuel supply port 20 when the fuel port 21 is closed
And the fuel port 21 are communicated with each other through a circumferential groove 23, so that the fuel pressure in the fuel port 21 is
The same feed pressure as in 20 is maintained. On the other hand, a circumferential groove 26 is formed on the outer peripheral surface of the plunger 12 slightly above the lower end surface 12a of the plunger, and the circumferential groove 26 is provided with a fuel through a fuel release hole 27 formed in the plunger 12. Pressurizing chamber
It is made to communicate within 15.

On the other hand, a sliding hole 30 extending in the lateral direction is formed in the housing body 1 near the side in the plunger hole 11.
Accordingly, the sliding hole 30 is formed such that its axis is parallel to the straight line substantially perpendicular to the common axis of the plunger 12 and the needle 7 with a space therebetween. An overflow valve 31 is slidably inserted into the sliding hole 30. As shown in FIGS. 1 and 2, the sliding hole 30 is composed of a small-diameter hole 32 and a large-diameter hole 33 coaxially arranged with each other. A part 34 is formed. On the other hand, a conical hole 35 is formed coaxially with the small-diameter hole 32 in the housing body 1 on the side opposite to the large-diameter hole 33 with respect to the small-diameter hole 32, and a valve seat having a conical outer peripheral surface is formed in the conical hole 35. The member 36 is fitted. The valve seat member 36 is fixed in the conical hole 35 by a nut 37 screwed to the housing body 1. A groove 39 is formed on the end surface 38 of the valve seat member 36 facing the small diameter hole 32, and the groove 39
A substantially conical valve seat portion 40 is formed on the inner peripheral surface of the valve seat. On the other hand, one end of the overflow valve 31 projects into the concave groove 39, and an outer peripheral portion 41 of one end of the overflow valve 31 is seated on the conical valve seat portion 40.

When the overflow valve 31 is seated on the valve seat member 36, the overflow valve
An annular pressurized fuel introduction chamber 42 is formed between the outer peripheral surface of the groove 31, the inner wall surface of the concave groove 39, and the housing body 1. A fuel overflow chamber 43 is formed. On the other hand, in the large diameter hole 33 of the sliding hole 30, the second fuel overflow chamber is provided.
A first fuel overflow chamber 43 and a second fuel overflow chamber 44 are communicated with each other through a fuel passage formed in the overflow valve 31 via 45. The second fuel overflow chamber 44 is connected to, for example, a fuel tank (not shown) via a fuel discharge passage 47 as shown in FIG. Further, the first fuel overflow chamber 43 is connected to the needle back pressure chamber 24 that accommodates the compression spring 10 through the fuel passage 25.
Linked to

As shown in FIG. 5, a fuel overflow channel 49 extending upward from the fuel passage 17 and always opening to the pressurized fuel introduction chamber 42 is formed in the housing body 1. The fuel overflow channel 49 is always in communication with the fuel pressurizing chamber 15, and therefore, the pressurized fuel introducing chamber 42
Is always in communication with the fuel pressurization chamber 15.

On the other hand, as shown in FIG. 3, the tip of the overflow valve 31 is formed of two conical surfaces 41a and 41b having different cone apex angles, and a boundary 41c between these conical surfaces 41a and 41b is formed by a valve seat portion. Line contact with 40. Therefore, the fuel pressure in the pressurized fuel introduction chamber 42 acts on the conical surface 41a, and the overflow valve 31 is urged in the valve opening direction by the fuel pressure in the pressurized fuel introduction chamber 42.

As shown in FIGS. 1 and 2, a rod guide for guiding and supporting a rod 50 is provided at the outer end of the large diameter hole 33 of the slide hole 30.
The rod guide 51 has a rod hole 52 therein. The rod 50 has a hollow cylindrical small-diameter portion 53 slidably inserted into a rod hole 52, and a large-diameter portion 54 located in the large-diameter hole 33. Rod inside rod guide 51
An adjusting screw 28a protruding into the small diameter portion 53 of 50 is screwed, and between the rod 50 and the adjusting screw 28a, the overflow valve 31 is always urged together with the rod 50 toward the valve seat portion 40, i.e., the overflow valve A compression spring 28 for urging the valve 31 in the valve closing direction is inserted. The head of the adjusting screw 28a is exposed to the outside, so that the spring force of the compression spring 28 can be adjusted from the outside by the adjusting screw 28a.

A pressure control chamber 55 defined by the end surface of the small diameter portion 53 is formed at the end of the rod 50 opposite to the large diameter portion 54. An actuator 60 is disposed above the pressure control chamber 55.
As shown in FIGS. 1 and 2, the rod 50 has a hollow cylindrical shape, so that the mass of the rod 50 is considerably reduced.

Actuator as shown in FIGS. 1 and 6
An actuator housing 62 integrally formed with the housing body 1 and having a piston hole 61 formed therein,
A piston 63 slidably inserted into the piston hole 61,
An end plate 64 for covering the top of the actuator housing 62, an end plate holder 65 for fixing the end plate 64 to the top of the actuator housing 62, and a synthetic resin cap 66 for covering the upper end of the end plate 64 are provided. A piezo-electric element 67 in which a number of piezoelectric element plates are stacked is inserted between the piston 63 and the end plate 64, and a variable volume chamber 68 defined by the lower end surface of the piston 63 is formed in the piston hole 61 below the piston 63. Is done.
The variable volume chamber 68 communicates with the pressure control chamber 55 via the fuel passage 69. An annular cooling chamber 70 is formed between the piston 63 and the actuator housing 62, and a compression spring 71 that constantly urges the piston 63 upward is inserted into the cooling chamber 70. When charge is applied to the piezoelectric element 67, the piezoelectric element 67 expands in the axial direction, and as a result, the variable volume chamber 68
Volume is reduced. On the other hand, when the electric charge charged in the piezoelectric element 67 is discharged, the piezoelectric element 67 contracts in the axial direction, and as a result, the volume of the variable volume chamber 68 increases.

As shown in FIG. 6, the housing body 1 has a check valve.
72 is inserted. The check valve 72 includes a ball 74 for controlling the opening and closing of the valve port 73, a rod 75 for regulating the lift of the ball 74, and a compression spring 76 for constantly pressing the ball 74 and the rod 75 downward. Thus, valve port 73 is normally closed by ball 74. The valve port 73 of the check valve 72 is connected to, for example, a low-pressure fuel pump (not shown) through a fuel inflow passage 77, and low-pressure fuel of ^{2 to 3} kg / cm ² is supplied from the fuel inflow passage 77. The check valve 72 can only flow toward the variable volume chamber 68, so that when the fuel pressure in the variable volume chamber 68 falls below 2-3 kg / cm ² , the fuel is Replenished within 68. Therefore, the inside of the variable volume chamber 68 is always filled with the fuel. On the other hand, as shown in FIG. 6, the lower end of the cooling chamber 70 is connected to a low-pressure fuel pump (not shown) through a fuel inflow passage 78, for example.
Low-pressure fuel of 3 kg / cm ² is supplied from the fuel inflow passage 78 into the cooling chamber 70. The piezo element 67 is cooled by this fuel. As shown in FIG. 4, the lower end of the cooling chamber 70 is connected to the fuel supply port 20 through a fuel outflow passage 79. A check valve 80 that can only flow is arranged. This check valve 80 is a ball that controls the opening and closing of the valve port 81.
82, a rod 83 for regulating the lift of the ball 82, and a compression spring 84 for constantly pressing the ball 82 and the rod 83 upward. After the fuel in the cooling chamber 70 cools the piezoelectric element 67, the fuel is supplied to the fuel supply port 20 through the fuel outflow passage 79.
Supplied to

As described above, the fuel flows into the cooling chamber through the fuel inflow passage 78.
The fuel is supplied into the fuel supply port 20 through the fuel outflow passage 79 and the check valve 80 after cooling the piezoelectric element 67. When the plunger 12 is in the upper position as shown in FIG.
The fuel is supplied into the fuel pressurizing chamber 15 from the fuel pressurizing chamber 15, and at this time, the inside of the fuel pressurizing chamber 15 and the
The pressure is as low as g / cm ² . At this time, the piezoelectric element 67 is in the maximum contraction position, and
The fuel pressure in the pressure control chamber 68 and the pressure in the pressure control chamber 55 is also as low as about ² to 3 kg / cm ² .

Further, at this time, the overflow valve 31 is biased on the valve seat portion 40 by the spring force of the compression spring 28, that is, the overflow valve 31 is closed.

Next, when the plunger 12 is lowered, the fuel supply port 20 and the fuel port 21 are closed by the plunger 12, so that the fuel pressure in the fuel pressurizing chamber 15 and the pressurized fuel introducing chamber 42 starts to increase. Next, the plunger 12 further descends, and when the fuel pressure in the pressurized fuel introduction chamber 42 increases, the overflow valve 31 opens, causing the fuel to overflow. At this time, pressurized fuel introduction chamber
The fuel pressure in 42, that is, the fuel pressure in the fuel pressurizing chamber 15, is a compression spring.
The opening pressure of the overflow valve 31 determined by 28 is maintained. In addition,
The valve opening pressure of the overflow valve 31 is set higher than the pressure in a combustion chamber (not shown).

Next, when electric charge is charged in the piezoelectric element 67 to start fuel injection, the piezoelectric element 67 extends in the axial direction, and as a result, the piston 63 descends, so that the variable volume chamber 68
And the fuel pressure in the pressure control chamber 55 sharply rises. When the fuel pressure in the pressure control chamber 55 rises, the rod 50 moves to the left in FIGS. 1 and 2, and accordingly the overflow valve 31 also moves to the left. Is the valve seat part 40
And the overflow valve 31 is closed. When the overflow valve 31 is closed, the fuel pressure in the fuel pressurizing chamber 15 rapidly rises due to the downward movement of the plunger 12, and the fuel pressure in the fuel pressurizing chamber 15 becomes a predetermined pressure, for example, 1500 kg / cm ^2. When the pressure exceeds the predetermined pressure, the needle 7 opens and fuel is injected from the nozzle port 3.

Next, the electric charge charged to the piezoelectric element 67 is discharged to stop the fuel injection.
67 contracts. As a result, since the piston 63 is raised by the spring force of the compression spring 71, the fuel pressure in the variable volume chamber 68 and the pressure control chamber 55 decreases. When the fuel pressure in the pressure control chamber 55 decreases, the rod 50 and the overflow fluid 31 immediately move to the right in FIGS. 1 and 2 due to the fuel pressure acting on the conical surface 41a of the overflow valve 31. The spilled fluid 31 is immediately opened when the valve 31 is separated from the valve seat portion 40. Overflow valve 31
When the valve opens, the high-pressure fuel in the fuel pressurizing chamber 15
The fuel is injected into the first fuel overflow chamber 43 through the pressurized fuel introduction chamber 49 and the pressurized fuel introduction chamber 42.

Next, when the fuel pressure in the pressurized fuel introduction chamber 42 decreases to the valve opening pressure of the overflow valve 31, the overflow valve 31 closes, and thus the fuel pressure in the fuel pressurization chamber 15 is reduced by the overflow valve 31. The valve opening pressure is maintained. By the way, as described above, the valve opening pressure of the overflow valve 31 is set higher than the pressure in the combustion chamber, so that the fuel pressure in the annular fuel passage 19 is higher than the pressure in the combustion chamber. Therefore, the combustion gas in the combustion chamber passes through the nozzle port 3 through the annular fuel passage.
It is prevented from flowing into 19. Further, when the overflow valve 31 is opened, the fuel in the annular fuel passage 19 moves toward the fuel pressurizing chamber 15 because the fuel pressure in the fuel pressurizing chamber 15 rapidly decreases. Since the fuel pressure in 15 decreases only to the opening pressure of the overflow valve 31, the pressure in the annular fuel passage 19 does not decrease so much, and the generation of minute bubbles is prevented.

When the overflow valve 31 is opened, the fuel pressure in the first fuel overflow chamber 43 increases, and this fuel pressure is applied to the needle back pressure chamber 24. As a result, since the needle 7 is rapidly closed, good fuel injection can be ensured.

On the other hand, when the piezoelectric element 67 is contracted to open the overflow valve 31 and the fuel pressure in the variable volume chamber 68 is reduced, the fuel pressure in the variable volume chamber 68 is reduced by the fuel When the fuel pressure becomes lower than the fuel pressure in the figure, low-pressure fuel is supplied into the variable volume chamber 68 via the check valve 72.

Next, when the plunger 12 is further lowered, the circumferential groove 26 formed on the outer peripheral surface of the plunger 12 communicates with the fuel supply port 20 and the fuel port 21. At this time, the fuel in the fuel pressurizing chamber 15 is supplied to the fuel supply port 20 and the fuel port 21 through the fuel escape hole 27 and the circumferential groove 26 formed in the plunger 12.
Is discharged into Next, the plunger 12 moves up, returns to the upper end position, and starts lowering again.

〔The invention's effect〕

When the fuel injection is stopped, the fuel pressure in the fuel pressurized chamber is rapidly reduced, but is reduced only to a certain constant pressure, so that the combustion gas can be prevented from flowing into the fuel passage around the needle. The generation of minute bubbles in the fuel passage can be prevented. Further, in the present invention, since the spring force of the spring for urging the overflow valve can be adjusted from the outside, the opening pressure of the overflow valve is accurately adjusted to the normal opening pressure after the unit injector is assembled. be able to.

[Brief description of the drawings]

FIG. 1 is a side sectional view of the unit injector taken along the line II of FIG. 5, FIG. 2 is an enlarged side sectional view of a part of FIG. 1, and FIG. FIG. 4 is an enlarged side sectional view taken along line IV-IV of FIG. 5, FIG.
1 is a side sectional view taken along line VV in FIG. 1, FIG. 6 is a side sectional view taken along line VI-VI in FIGS. 1 and 8, and FIG. FIG. 8 is a plan view, and FIG.
It is the plane sectional view seen along the VIII line. 3 ... Nozzle port, 7 ... Needle, 12 ... Plunger, 15 ... Fuel pressurizing chamber, 28 ... Compression spring, 31 ... Overflow valve.

Claims (1)

(57) [Claims] A plunger driven by an engine, a fuel pressurization chamber filled with fuel and pressurized by the plunger, and a fuel pressure which is responsive to a fuel pressure in the fuel pressurization chamber, is set to a predetermined pressure. A needle that opens when the pressure exceeds the pressure limit, a fuel overflow passage that overflows fuel in the fuel pressurization chamber, and an overflow valve that is driven by an actuator and disposed in the fuel overflow passage. When the overflow valve is closed, the fuel pressure in the fuel pressurizing chamber acts in a direction to open the overflow valve, and the overflow valve is kept closed by the actuator. In a unit injector where fuel injection is sometimes performed, the overflow valve is normally urged in a valve closing direction by a spring, and a spring force adjusting screw capable of adjusting the spring force of the spring from outside the unit injector housing is provided. C Unit injector attached to managing.