EP1338790A1 - Noise optimized apparatus for injecting fuel - Google Patents

Abstract

Pump/nozzle system has a high pressure chamber (25) which is impinged upon via a pump piston (3), and a storage piston (23) held within a storage chamber (24) and impinged upon via a pressure spring arranged in a spring-holding chamber (42). A non-return throttle element (35) arranged between the high pressure chamber and the storage chamber delays the pressure drop in the storage chamber. Preferred Features: The non-return throttle element is a non-return throttle valve or non-return valve.

Description

Technical field

In systems for injecting fuel into the combustion chamber of internal combustion engines are used in high pressure pumps and in the respective versions of Injectors, nozzle holder combinations or pump-nozzle systems, partial bodies, such as. B. Switching valves, injectors, moved. A volume is displaced by their movement. The displaced volume is replenished on the suction side. For the necessary Volume flow, an adjustment of the pressures and cross sections is required. is if the supply of fuel is insufficient, the pressure on the suction side drops. If the vapor pressure of the fluid to be pumped falls below, it breaks off the liquid column and the formation of cavitation bubbles. With recompression of the fluid above the vapor pressure results from the collapse of the vapor bubbles a sound.

State of the art

Pump and nozzle systems (UI = and Unit Injector) are used today on self-igniting internal combustion engines generated mechanically-hydraulically controlled pre-injection phases, on the one hand to reduce combustion noise and on the other hand to minimize pollutants contribute. A distinction can be made between four operating states in pump-nozzle systems. A pump piston is moved upwards via a return spring. The under Constant pressure fuel flows from the low pressure part of the fuel supply via the engine block integrated inlet bores and the inlet channel in the Solenoid valve space. The solenoid valve is open. Passed through a connecting hole the fuel in the high pressure space.

When the drive cam rotates, the pump piston moves down. The Solenoid valve remains in its open position and the fuel is through the Pump piston via the inlet channel back into the low-pressure part of the fuel supply pressed.

In a third phase of the injection process, an actuator becomes one by the control unit controlled at a certain time so that the actuator is pulled into a seat and the Connection between high pressure chamber and low pressure part is closed. This time is also referred to as "electrical start of spraying". The high fuel pressure in the High-pressure space rises continuously due to the movement of the pump piston, causing there is also an increasing pressure at the injection nozzle. Upon reaching one Nozzle opening pressure increases the nozzle needle, causing fuel in the Combustion chamber is injected. This time is also called the "actual start of spraying" or also referred to as the start of funding. Due to the high delivery rate of the pump piston the pressure continues to rise during the entire injection process. In one final operating state, the actuator is switched off again, after which the actuator after a short delay and opens the connection between the high pressure room and low pressure part is released again. As an actuator come z. B. solenoid valves or piezo actuators.

The peak pressure is reached in this transition phase. After that, the pressure breaks a lot quickly together. The injection nozzle closes when the pressure falls below the nozzle closing pressure and ends the injection process. The rest, from the pump element to the apex The fuel delivered by the drive cam is fed into the low-pressure section via the return channel pressed.

Single pump systems, like the one just described, are intrinsically safe. H. in the unlikely An error can only occur as an uncontrolled injection give: If the solenoid valve remains open, it cannot be injected because the Fuel flows back into the low pressure part and pressure cannot build up. Since the The high-pressure chamber is filled exclusively via the actuator When the actuator remains closed, no fuel can enter the high-pressure chamber. In this case too, it is possible to inject at most once. Pump-nozzle systems (Unit Injectors) are usually installed in the cylinder head and are high Exposed to temperatures. To keep the temperatures in the Unit Injector (UI) as low as possible to keep, the components of the unit injector are cooled in the control by fuel, which in turn flows back into the low pressure part of the fuel injection system.

The total pressure p _{tot of} a flowing medium is composed of a static pressure component p _stat and a dynamic pressure component p _dyn . If you see pressure drops, such as. B. generated by friction, the resulting total pressure is constant. In contrast, the kinetic pressure is proportional to the square of the flow velocity according to the following relationship: p dyn = ρ 2 ν 2

If the fuel in the pump of the unit injector system is strongly accelerated, it drops the static pressure. The steam pressure can fall below, so that Adjust cavitation symptoms.

Both phenomena can occur during the movement of the accumulator piston. The accumulator piston movement leads to compression of the fuel in the spring holder. So that increases the back pressure of the injection nozzle, which leads to the end of the pre-injection phase. additionally becomes the second opening pressure by the compression for the subsequent injection elevated. Quick opening is necessary to ensure good emission results of the accumulator piston is essential. The quick opening is not critical from an acoustic point of view, since the suction side is connected to the element space in the same There is still high pressure at the time. When moving the accumulator piston backwards, it must Pour the displaced volume into the spring holder. The inflow takes place either via a connection to the return - or a connection to the inlet circuit. The fuel passes through a throttle, the cross section of which has a certain value. If the throttle is enlarged, a residual pressure dependent on the flow cross section can be obtained hold. If the displaced volume flow is greater than the volume added, then the pressure in the spring holder drops. When the pressure in the spring holder drops, the If the vapor pressure falls below this, cavitation can occur.

When the accumulator piston moves back at the end of the injection process, the Liquid column above the storage piston moves in the direction of the element space. To this The point in time in the element space is already close to the vapor pressure, which means a rapid backflow can take place. The high flow rate can lead to a If the vapor pressure falls below this, cavitation phenomena appear again have as a consequence.

EP 0 404 916 B1 relates to a fuel injection nozzle. The fuel injector, in particular designed as a pump nozzle comprises a nozzle needle is acted upon by a spring in the closing direction. At the fuel injector a pressure chamber in front of the seat of the nozzle needle with one of a spring-loaded escape piston limited storage space. The escape piston (= storage piston) forms a sealing seat with its accumulator piston liner. The storage space is located from the pressure chamber after this sealing seat. The one cylindrical guide part having the storage piston is at its end facing away from the storage space Pressure is applied to a damping space that can be filled with fuel and has one Cone on that in a damping space delimiting and having an opening Plate immersed. The cylindrical guide part of the accumulator piston has a ratio diameter / Height from 1: 0.1 to 1: 0, 4, with the pin of the storage piston one variable cross-section, which dips into the boundary plate and the accumulator piston a guide extension with grooves on its side facing the storage space having.

Presentation of the invention

According to the proposed solution, the storage piston return movement can be delayed can be achieved without, on the other hand, the accumulator piston opening movement within a pump-nozzle system (UI - Unit Injector) significantly. For this purpose, a backflow throttle valve in the area of the high-pressure connection of the storage space to be ordered.

The backflow throttle valve is permeable when viewed in the opening direction of the accumulator piston, so that the pre-injection controlled by hydraulic means is not impaired is. At the end of the main injection, the high pressure drops in the entire high pressure volume so far that the closing pressure level of the accumulator piston is reached. When reached the closing pressure of the accumulator piston begins. When in use a backflow throttle valve is between the pressure on the accumulator piston side the backflow throttle and the pressure on the high pressure side a pressure difference a, which causes the backflow throttle to close. In this case, the pressure can be reduced delayed only take place via the throttle point itself, so that the return movement is strong is slowed down.

By designing the seat cross-section, the stroke, the throttle cross-section or Spring adaptation of the return flow throttle element can cause the storage piston return movement, d. H. the component movement relevant for the cavitation phenomena is delayed so far that fuel runs into the interior of the spring holder without cavitation, so that there is no noise.

Instead of a backflow throttle valve, a check valve can also be used in the unit injector system be used. At the end of the injection, the pressure on the High pressure side, whereupon the check valve closes. The pressure in the memory remains at a level so that the accumulator piston remains in its open position. manufacturing and tolerance-related leaks in the storage piston guide cause a slow The pressure drops until the closing pressure of the accumulator falls below and the The storage piston closes slowly.

The pressure always remains above during the refilling of the spring holder cavity of steam pressure, cavitation phenomena can be avoided, which is advantageous on the noise development of such a pump-injector system effect.

drawing

The invention is described in more detail below with reference to the drawing.

It shows:

Figure 1

the general structure of a pump injector system for fuel supply the combustion chambers of a self-igniting internal combustion engine,

Figure 1a

an enlarged view of the flow connection between the storage space and cavity of the spring holder according to the prior art Figure 1,

Figure 2

the one arranged between the accumulator piston space and the spring holder cavity Backflow throttle unit to delay the closing movement of the accumulator piston,

Figure 3

the accumulator piston in its closed position,

Figure 4

opening the sealing seat of the accumulator piston when it reaches its opening pressure and

Figure 5

the sealing of a cavity in the injector by a sealing seat end face opposite the accumulator piston.

variants

Figure 1 shows the general structure of a pump-nozzle system for fuel supply of combustion chambers of self-igniting internal combustion engines.

In the pump-nozzle system shown in Figure 1, a pump piston 3 is movable is accommodated in a pump body 4, actuated via a ball pin 1. The ball stud 1 in turn is actuated via a rocker arm 28 which is arranged in a tiltable manner one of its ends is provided with a roller body which is rotatable at the end of the rocker arm is stored. The roller body rolls on a cam of a drive camshaft 27. The deflection of the rocker arm 28 about its axis of rotation depends on the shape of the Cam top, which in the illustration according to Figure 1 eccentric to the axis of rotation of the Drive camshaft 27 runs.

The pump piston 3 of the pump body 4 of the pump-nozzle system is by a return spring 2 acted on the one hand on a flat surface of the pump body 4 and on the other hand is supported on a cover-like support element, which is in the upper region of the pump piston 3 movable in the pump body 4 is arranged.

An actuator is arranged on the side of the pump body 4, which is the embodiment shown in FIG includes a solenoid 10. The solenoid 10 of the actuator acts an armature 9, which in turn acts on a solenoid valve needle. The anchor 9 of the Actuator is acted upon by a compensating spring 7. Reference number 6 is the magnetic core referred to, which encloses the solenoid 10 of the actuator.

Below the actuator, a fuel return 11 is shown, via which from the pump-nozzle system outflowing, excess fuel in a no further in Figure 1 low pressure range shown, e.g. B. flow back the tank of a motor vehicle can. The pump-nozzle system is in the fastening area on the cylinder head of the internal combustion engine sealed by sealing elements 12. Within the unit injector system are formed in the wall inlet holes 13 through which fuel a low-pressure fuel supply V, a valve chamber one here as a solenoid valve trained actuator flows to the element space 25. Because of the pressures fuel is passed through the pump body 4 for cooling the actuator and arrives via a bore system formed in the pump body 4 into one through two sealing rings 12 limited space from where it is via the fuel return identified by reference numeral 11 is dissipated. Via the fuel return in the unit injector according to the leakage fuel in the pump piston 3 can be derived from the illustration in FIG. 1 become; there is also a separation by means of throttle points formed in the return system of steam bubbles possible.

Reference number 14 designates a hydraulic stop which functions as a damper. A nozzle needle 18 extends partially below the hydraulic stop is enclosed by an integrated injector body 20. The nozzle needle 18 is seated in its front area facing the combustion chamber 17 within a needle seat 15. By means of a clamping nut 19 are the pump-nozzle system and the nozzle needle 18 partially enclosing integrated injection nozzle 20 connected to each other; below the clamping nut 19, a sealing washer 16 is arranged around the combustion chamber 17 Self-igniting internal combustion engine against the cylinder head of the internal combustion engine seal. The cylinder head of the self-igniting internal combustion engine is designated by reference numeral 21.

There is a cavity within the pump-nozzle system as shown in FIG. 1 a spring holder 42 is provided which, for. B. designed as a coil spring compression spring 22 records. The lower end of the compression spring 22 is supported on a disk-shaped one Use in the cavity of the spring holder 42 and applied to its opposite End of a storage piston 23. The storage piston 23, for example formed in two parts, comprising a peg-shaped element and a disc, is inside of the pump-nozzle system 1 enclosed by a storage space 24. The disc can be formed as a separate, separate component. The storage space 24 of the Storage piston 23 and the cavity of the spring holder 42 are over a in Figure 1a enlarged opening 31 shown in fluid communication with each other.

The pump piston 3, which can be moved up and down in the vertical direction via the rocker arm 28 acts on a high-pressure chamber 25 within the pump-nozzle system, which is also called Element space is called. Below the disk-shaped delimiting the high-pressure chamber 25 The component branches off from a high-pressure inlet to the nozzle chamber, which is the nozzle needle 18 acted on the cylinder head end of the pump-nozzle system. from The fuel, which is under high pressure, flows into the nozzle chamber via an annular gap Direction of the needle seat 15, from where it is in an upward movement of the nozzle needle 18th within a pilot injection and a main injection into the combustion chamber 17 of the self-igniting internal combustion engine is injected.

For the sake of completeness it should be mentioned that with reference numeral 26 a solenoid valve spring is referred to, which acts on the solenoid valve needle 8 in the reset direction.

Figure 1a is an enlarged view of the area of the pump-nozzle system according to Figure 1 can be seen in which the opening 31 between the storage space and the cavity of the spring holder is shown on an enlarged scale.

As can be seen from the illustration in FIG. 1a, the storage piston 23 enclosed by the storage space 24 and is from the high pressure side through from High-pressure space 25 (also element space) emerging, under high pressure Fueled. By the downward movement of an end face 29 of the accumulator piston 23 when it is subjected to high pressure via the high-pressure chamber 25, the fuel compressed in the cavity of the spring holder 42. This increases the back pressure the injector, thereby bringing about an end to a pre-injection phase. To qualitatively Ensuring high-quality emission results is a quick opening of the storage piston 23 required. When the storage piston 23 is opened quickly, the Suction side of the accumulator piston 23 with the high-pressure chamber 25 (also element chamber) in Connection. At this time, there is 25 inside the high-pressure space (also element space) High pressure on.

When the storage piston 23 moves back, the displaced volume must be in the Follow the cavity of the spring holder 42. This can be done via a connection on Return or at the inlet circuit. Is the displaced fuel volume larger than that the quantity conveyed, the pressure in the cavity of the spring holder 42 drops the steam pressure leads to cavitation. Furthermore, the Return movement of the storage piston 23 at the end of an injection process the liquid column above the accumulator piston 23 in the direction of the high-pressure chamber 25 (also element chamber) emotional. At this point the pressure is inside the high pressure room 25 already close to the vapor pressure, which results in a rapid backflow. The high flow velocity during this backflow process leads to the value falling below of the vapor pressure and can in turn follow cavitation phenomena pull yourself.

Figure 2 is schematically a between the storage space and cavity of the spring holder Backflow throttle element to delay the movement of the accumulator piston remove.

Figure 2 shows, reproduced in a highly simplified manner, a backflow throttle valve 35, which between the storage space 24 of the storage piston 23 and the element space 25 of the Pen holder is arranged. By means of the backflow throttle valve 35 it is possible to to slow down the return movement of the accumulator piston 23 without the opening movement, which should be largely unhindered, the storage piston 23 essential to change. The backflow throttle valve 35, which in the illustration according to FIG. 2 is shown schematically, comprises a valve body 37 which by means of a spring element 36 is acted upon and a permanently acting throttle point 44, via which the storage space 24 of the storage piston 23 and the element space 25 with each other in Are in fluid communication.

After the pressure difference between the element space 25 and the storage space 24 of the accumulator piston 23 has brought the backflow throttle valve 35 to build the pressure in the storage space 24 slowly decreases in the direction of the element space 25. Due to the slow degradation, the movement of the storage piston 23 within the Storage space 24 slows down so that fuel, e.g. from the inlet holes 13 in can flow in the cavity 42 within the spring holder B quickly enough so that there the vapor pressure is not undercut. Can the pressure there be above the vapor pressure cavitation does not occur, so that cavitation-free operation occurs can be achieved.

The backflow throttle valve 35 allows an unimpeded opening movement of the storage piston 23 in the storage space 24, since the backflow throttle valve 35 in the second Direction 40 is permeable. After the end of the injection, the high pressure drops overall High pressure volume, d. H. within the element space 25 so far that the Closing pressure of the accumulator piston 23 is reached and its closing movement begins. Due to a pressure difference between the pressure on the accumulator side End of the backflow throttle valve 35 and the pressure on the high pressure side of the backflow throttle valve 35, d. H. on the side facing the element space 25 that closes Backflow throttle valve 35.

When using a backflow throttle valve 35 with a throttle point 44 remains Closing the closing element 37 only opens the throttle point 44, due to its design the pressure reduction can be influenced with regard to the flow cross section. By Delay in the pressure reduction in the direction of element space 25 becomes the movement of the storage piston 23 delays within the storage space 24. Because of the delayed expiration Return movement of the storage piston 23 results in a refilling of the cavity 42 of the spring holder B via inlet bores 13 such that none in this area Cavitation occurs because the pressure can be kept above the vapor pressure level.

By designing the seat cross section 38 on the backflow throttle valve 35, its stroke and by designing the throttle cross section of the throttle point 44 and the spring preload the movement of the storage piston 23 can be slowed down so far by the spring element 36 be avoiding the refilling of the cavity 42 of the spring holder of cavitation.

Figure 3 shows a storage piston in its closing position on the sealing seat.

It can be seen from the illustration in FIG. 3 that the accumulator piston 23 by one Stroke 41 has moved into its sealing seat 34 to the element space 25. The cavity 42 of the Spring holder B is connected via the opening 31 to part of the storage space 24. wherein an end face 29 on the underside of the storage piston 23 in the in FIG shown position by the stroke 41 is parked from the bottom of the storage space 24. In this position of the storage piston 23, it separates the element space 25 from the storage space 24th

Figure 4 shows the opening of the sealing seat on the accumulator piston when its opening pressure is reached. When the opening pressure level of the accumulator piston 23 is exceeded, it opens the sealing seat identified by reference numeral 34 on the top of the accumulator piston 23. The storage space 24 of the storage piston 23 is now opened over the Filled sealing seat 34 over the element space and the accumulator piston 23 moves in Direction to the cavity 42 of the spring holder B.

Figure 5 shows the sealing of the cavity of the spring holder B by a sealing seat opposite end face of the accumulator piston.

5 shows that the end face 29 of the accumulator piston 23 the opening 31, the storage space 24 and the cavity 42 of the spring holder B connects with each other. It can be seen from FIG. 5 that the storage piston 23 now the storage space 24, which in turn is connected to the element space 25 stands, seals against the cavity 42 of the spring holder B.

With regard to the design of the seat cross-section 38 of the backflow throttle valve 35 and the stroke 41 of the accumulator piston 23, these are to be designed such that the opening movement of the accumulator piston 23 proceeds almost unhindered in the phase shown in FIGS. 4 and 5. In the opening phase of the storage piston 23 in the direction designated by reference numeral 40 in FIG. 2, the storage space 24 is filled first and then the volume which results from the product of the storage piston end face 29 and the storage stroke path 41. Interpretation:

The calculation of the storage volume from the seat and the stroke depends on how the valve is designed, whether it is, for example, a conical seat or a ball seat deals, from which differing seat surface or average seat surface diameter can result.

It is advantageous to use the stroke of the backflow throttle valve 35 or an alternative Check valves should be as small as possible so that the entire opening cross-section can be reached after a short opening time.

With regard to the design of the spring element 36 of the backflow throttle valve 35 is The aim is to design the spring preload of the spring element 36 in such a way that the backflow throttle valve 35 held in a non-pressurized state in a defined preload position can be a quick as well as when closing the backflow throttle valve 35 Closing movement is supported.

The throttle cross section of the throttle point 44 formed on the backflow throttle valve 35 has the task of relieving pressure in the storage space 24 in the direction of the element space 25 to slow down so that there are no cavitation phenomena in the cavity 42 of the spring holder B. On the other hand, there is a pressure relief of the storage space 24 in the direction of the element space 25 can be realized sufficiently quickly, so that at the beginning of the next injection cycle the original pressure conditions, d. H. yourself Pressure equalization sets quickly enough.

In a further embodiment variant of the idea on which the invention is based a check valve can be used. The check valve, a z. B. spherical designed closing element 37, which by a spring element, preferably a coil spring 36 is acted upon, forms the limit shape of a backflow throttle element, in which the throttle is closed in the limit case. At the end of the injection Pressure in the high-pressure chamber 25 (also element chamber), which corresponds to the pump piston 3 whose stroke movement is subjected to high pressure. When closed Check valve, the pressure on the storage side 24 remains at such a high level, that the accumulator piston 23 remains in its open position. Due to leakage at the Accumulator piston guidance, which inevitably occurs due to production and tolerance, falls the pressure slowly decreases until the closing pressure of the accumulator falls below, and the accumulator piston 23 slowly begins its closing movement. Depending on the achievable pressure drop, due to a pressure reduction via the leakage gap, the pressure builds up in this way slowly that the refill of the spring holder 42 proceeds so that within the cavity of the spring holder 42, the pressure level is kept above the vapor pressure at all times can be, so that no cavitation phenomena within the cavity of the Spring holder 42 can occur and thus a significant improvement in noise Avoidance of vapor bubbles in the fuel can be achieved.

Both versions, i. H. when using a backflow throttle valve as Backflow throttle element or when using a check valve as a backflow throttle element it is achievable that through the integration between the element space 25 and the storage space 24 of the storage piston 23 a delay of the reset movement of the storage piston 23 can be achieved. By reducing the speed of movement of the accumulator piston 23 within the pump-nozzle system can be Decrease in the pressure level within the pump-nozzle system in the cavity 42 of the spring holder B effectively prevent below the vapor pressure. Since with the invention proposed solution no vapor bubble formation, d. H. Cavitation within the cavity 42 of the spring holder B can occur, is a much quieter operation of the pump-nozzle system when using the solution proposed according to the invention possible in high speed ranges of the pump-nozzle system.

LIST OF REFERENCE NUMBERS

1

bowling pins

2

Return spring

3

pump pistons

4

pump body

5

plug

6

magnetic core

7

balancing spring

8th

Solenoid valve needle

9

anchor

10

solenoid

11

Fuel return (low pressure)

12

poetry

13

inlet bore

14

hydraulic stop (damper)

15

needle seat

16

sealing washer

17

combustion chamber

18

nozzle needle

19

locknut

20

integrated injector

21

cylinder head

22

Compression spring (nozzle)

23

accumulator piston

24

storage space

25

High pressure room (element room)

26

Solenoid valve spring

27

camshaft drive

28

rocker arm

29

Front side of the accumulator piston

30

Space below the accumulator piston

31

opening

32

Valve chamber inlet

33

High pressure inlet to the nozzle

34

sealing seat

35

Rückströmdrossel / valve

36

spring element

37

closing element

38

Seat

39

first direction RSD / RSV

40

second direction RSD / RSV

41

Stroke piston 23

42

Cavity pen holder

43

Sealing surface cavity

44

Throttling point reverse flow throttle valve 35

A

Fuel supply (low pressure)

B

penholder

Claims (9)

Pump-nozzle system for supplying the combustion chamber (17) of a self-igniting internal combustion engine with fuel, with a high-pressure chamber (25) which can be pressurized via a pump piston (3) and with a storage piston (23) accommodated within a storage chamber (24) a compression spring (22) arranged in a spring holder space (42) is acted on, characterized in that a return flow throttle element (35) is arranged between the element space (25) and the storage space (24) of the storage piston (23), which element reduces the pressure in the storage space ( 24) delayed. Pump-nozzle system according to claim 1, characterized in that the backflow throttle element (35) is designed as a backflow throttle valve. Pump-nozzle system according to claim 1, characterized in that the backflow throttle element (35) is designed as a check valve. Pump-nozzle system according to claim 1, characterized in that the backflow throttle element (35) is permeable in a second direction (40) corresponding to the opening direction of the storage piston (23). Pump-nozzle system according to claim 1, characterized in that the backflow throttle element (35) in a first direction (39) corresponding to the closing direction of a storage piston (23) reduces the closing speed of the storage piston (23). Pump-nozzle system according to claim 2, characterized in that when a pressure difference Δ _{P occurs} above the return flow throttle element (35) between the element space (25) and the storage space (24), the return flow throttle element (35) closes such that pressure reduction only still takes place via a throttle point (44) of the return flow throttle element (35). Pump-nozzle system according to claim 1, characterized in that a sealing seat (34) is formed on the storage piston (23) which opens or releases the element space (25) against the storage space (24). Pump-nozzle system according to claim 1, characterized in that an end face (29) closing an opening (31) of the cavity (42) is formed on the accumulator piston (23) on the side facing a cavity (42) of a spring holder (B) , Pump-nozzle system according to claim 1, characterized in that a peg is formed on the storage piston (23) and plunges into the opening (31) to the cavity (42).

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