KR0180545B1 - Fuel system for double engine fuel diesel engine - Google Patents

Abstract

Each engine cylinder includes one or more sets of injectors 1, 2 for injecting fuel gas and pilot oil into the cylinder. One injector 2 serves to inject the pilot oil and the second injector 1 serves to supply gas when the valve is opened by the control oil pressure in the conduit 6. If the pressure relief valve 18 installed in the conduit is closed, the pressure will only achieve the value required to open the gas valve. A piston affected by the pilot oil pressure in the conduit 7 loads the valve 18 in the closed position against the spring force. If the valve is in the closed position, the control oil pressure will actuate the valve member toward the closed position so that the continuous closing of the valve is independent of the pilot oil pressure. The relief valve 18 will also limit the maximum pressure in the control oil conduit 6.

Description

Fuel system for double fuel diesel engine

1 is a schematic representation of the main components of a fuel system according to the present invention for a single set of dual fuel injectors.

2 is a longitudinal sectional view of a relief valve of a system with a valve housing and a valve member.

3 is an enlarged cross-sectional view of the housing of FIG. 2 as viewed from the valve member.

4 is a side view of the actuating piston.

5 and 6 are enlarged side and cross-sectional views of the valve member of FIG.

7 is an enlarged cross-sectional view of the valve seat for a valve of FIG.

8 is a cross-sectional view of the sliding bushing coupled to the valve seat.

9 is a graph of possible pressure courses in an oil conduit connected to a valve member.

* Explanation of symbols for main parts of the drawings

1: injector 2: injector

7: pilot oil conduit 36: piston

40: valve member 45: spring

53: valve seat 60: intermediate duct

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates generally to dual fuel diesel engines driven by gas as primary fuel and pilot oil as auxiliary tackifier, wherein each cylinder connected to at least one control oil conduit is a gas injection injection valve, Pilot oil suction conduit with injector valve for ignition oil injection, pressure relief valve installed in control oil conduit with valve member actuated towards closed position by pressure in pilot oil suction conduit The valve member is in the open position during the compression stroke of each engine cycle and opens the first drain duct in the control oil conduit if the pressure in the pilot oil conduit is lower than the open pressure of the pilot oil injector valve. .

In order to set a satisfactory ignition of fuel injected into the engine cylinder to the dual fuel engine at the desired moment for the purpose of optimizing the operating cycle of the process, the fuel system of the engine is for example a gas oil which acts to initiate combustion in the cylinder. Or an amount of easily ignitable pilot oil, such as diesel oil, to be injected into the cylinder before or at the same time as each gas injection.

If the pilot oil injection is not achieved, the amount of gas injected into the cylinder is automatically ignited late during the operation of the engine piston, or after flowing out of the cylinder or during mixing with the hot exhaust gas from the remaining cylinder in the exhaust system. It is almost certain that for example it is ignited by sparks from another cylinder.

In some cases, the gas has to be exploded and entails engine damage, which poses a great risk, so it should include a gas exhaust system and possibly a turbocharger associated with it.

In the fuel system described in Japanese Patent Application No. 179765/86 of the applicants, the pressure relief valve ensures that only gas is injected into a cylinder, which is usually provided with pilot oil to be pre-injected.

If no pilot oil pressure is generated under normal engine operation or if the pressure value required to open the oil valve in the injector is not achieved, the pressure relief valve will not close and the control oil will then pass continuously through the valve and into the injector. Leak through the first drain duct of the valve. Thus, by keeping the gas valve in the injector closed, the possibility of a failure of pilot oil injection into a cylinder will be immediately detected and it is ensured that the gas injection through the actual injector during the same operating cycle is prevented in advance. In view of the fact that the injector of the residual engine cylinder is not affected by the pressure release in the control oil conduit, the engine can generally continue to operate while, on the other hand, if the cause of the failure of pilot oil injection is eliminated or extinguished itself, Automatically resume operation.

Pilot oil pressure can be achieved by a cam-operated dose pump, just before the injection moment, the pressure rises rapidly from the low main pump pressure to the pressure necessary to open the oil valve in the injector. Due to the fact that the pilot oil is only used as an ignition aid, the injection of the pilot oil is set to occur only at the start of the engine piston's operating stroke, so that the pilot oil pressure is higher than the main pump pressure but not sufficient to open the oil valve. To the level.

In order to ensure ignition of the gas, the injection of the gas into the engine cylinder must be initiated before all the injected pilot oil has combusted and must continue to be injected when the pilot oil pressure drops to a medium level. The valve member of the pressure relief valve is thus preceded by a cylindrical slide provided at both ends with a coaxial axial shoulder formed as a needle valve in cooperation with a valve seat surrounding the duct leading the pilot oil conduit and the control oil conduit respectively. According to the technology. When the pilot oil pressure is high enough to ensure oil injection, the pilot oil exerts a force on the shoulder in communication with the ignition oil conduit that is strong enough to push the valve member to the closed position by overcoming the spring resistance. The opposite shoulder shuts off the drain duct in the control oil conduit. At the same time the shoulder is opened and the pilot oil is passed by the associated valve seat so that the pilot oil pressure is transferred into the space around the shoulder to act on the overall cross-sectional area of the slide. Due to the fact that the pilot oil pressure in the closed position of the valve member affects an area significantly greater than the counter shoulder affected by the control oil pressure, a medium level of pilot oil pressure is required to actually keep the valve member in the closed position. Becomes high enough.

Except for the valve seat and the drain ducts of the control oil, the associated shoulders are extremely heavily loaded for a short period of time during each engine cycle, as soon as the valve closes, the high pilot oil pressure may cause rapid valve corrosion. This is because it acts on the overall cross-sectional area.

At the intermediate level, the pilot oil pressure does not exhibit a constant value, but the pressure fluctuates around the decreasing average pressure towards the end of the operating stroke of the engine piston. Such a change in pressure results in the generation of undesirable pressure fluctuations by opening and closing the valve several times in a continuous sequence before the pilot oil pressure drops sufficiently to allow the valve to remain in the permanently open position.

Another drawback of the preceding fuel system is that closing of the valve member entails significant volume expansion of the duct in communication with the pilot oil intake conduit leading to a drop in pilot oil pressure that is disadvantageous for uniform ignition of the pilot oil.

The specification of US-A-2 518 400 relates to a pressure relief valve for a dual fuel diesel engine, the valve member of which connects the control oil pressure conduit to the drain duct in the open position and the gas suction in the closed position. Connect the conduit to the hydraulic piston to open the valve. The valve member is biased toward the closing direction through the piston by the initial pump pressure which is mainly constant during normal operation of the engine and which is supplied to the intake conduit of the pilot oil pump. As long as the minimum prime pump pressure is supplied to the oil intake conduit, the relief valve is closed, which means that the relief valve maintains gas intake open even though no pilot oil is injected into the engine cylinder.

It is an object of the present invention to ameliorate the above mentioned drawbacks. Another object of the present invention is to obtain accurate control of the control oil pressure as well as the most uniform pressure course in the control and pilot oil conduits.

It is another object of the present invention to provide a reliable corrosion resistant pressure relief valve.

For this purpose, the above-described fuel system according to the present invention is characterized in that the valve member is operated by pilot oil pressure through a piston, and by the control oil pressure when the valve member is in the closed position and shuts off the first drain duct. It is operated towards a closed position.

Due to the fact that the control oil pressure acts to push the closed valve member toward the closed position, the pilot oil pressure is used to increase the control oil pressure to a pressure level sufficient to overcome the force of the spring acting in the open direction on the valve member. Used only for the initial closing, the control valve remains closed by the control oil pressure until the control oil supplied to the control oil conduit is adequate for the load of the engine and stopped at the operating stroke of the engine piston at which gas injection is terminated. maintain.

The use of a piston to transfer the pressure effect of the pilot oil to the valve member results in a correct actuation valve and also because it only requires the pilot oil pressure necessary to initiate gas injection to ensure the operation of the pressure relief valve. Was done.

In a preferred embodiment with a slide-in valve member having a coaxial shoulder designed as a needle valve that interacts with a valve seat surrounding the first drain duct at one end, the slide is disposed in the compression chamber and axially from the shoulder. A spaced apart facing first piston surface, the intermediate duct extending through the slide connecting the compression chamber and the first drain duct when the shoulder contacts the valve seat in the closed position of the valve member, the piston being the axis of the slide It is characterized in that it has a second piston that is stably fixed to the bore in the directional alignment and is axially spaced from the shoulder and is faced by the pilot oil pressure. For proper dimensioning of the area of the first and second valve surfaces, the shoulder and valve seat will be subjected to a low load during operation, in which an upward pressure acting in the open direction on the shoulder acts in the closed direction on the first piston surface. This corresponds to a similar upward pressure. This embodiment is structurally simple and all the oil filling chambers in the valve are always in excellent flow connection with the control oil conduit or with the lateral drains open under low pressure, thereby providing a quick setting of the valve according to the pilot and control oil pressures prepared at any time. setting so that the oil in the chamber is not exhausted at all through a flow restricting slot opening, such as a closed valve seat.

The minimum valve seat load while maintaining correct valve action is due to another improvement of the preferred embodiment, in which the pressure in the pilot oil conduit preferably matches the region of the second piston surface and the spring characteristics. By closing when raised to the determined pressure obtained, the closing force exerted on the surface of the second piston by the determined pressure in the pilot oil conduit corresponds to the spring opening force when the slide is in the closed position.

If the fuel system is designed to set the upstream control oil pressure of the pressure relief valve to each injector before generating the pilot oil pressure on the same injector and control the ignition moment only by adjusting the pilot oil pump, the spring breakage prematurely causes the relief valve to fail. This will result in premature closure and premature gas injection. To avoid this drawback, one embodiment provides that a sliding bushing coaxial with the first drain duct and the slide in the terminal position blocks the second drain duct in communication with the control oil conduit, the sliding bushing and the slide being In between, it has a spring for biasing the slide towards the open position and biasing the sliding bushing towards the closed position. If the spring breaks, the sliding bushing will be spaced apart from the terminal position and the second drain duct will be peeled off, thus preventing the pressure rise in the control oil conduit and keeping the gas valve closed. Since the injection gas falls into the engine cylinder, the fault condition is quickly detected by the engine's motor system, so that the operator can change the spring.

In a preferred embodiment, in which an effective piston region is provided on the inner side of the sliding bush that operates in the opening direction of the bushing, the control oil pressure in the second drain duct acts on the region, and the overload of the valve member and the associated sheet The bushing is shut off in a simple manner with an inner rim shaped as a valve which interacts with the valve seat arranged coaxially with respect to the bushing on the slide of the second drain duct opposite the spring. Since the control oil pressure acting on the effective area of the sliding bushing exceeds the predetermined pressure level according to the spring biasing force, the discharge of the control oil is allowed.

Preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 shows a fuel gas injector 1 and a pilot oil injector 2 suitable for common mounting on a cylinder cover (not shown) of an engine cylinder, with the forefront of the injectors protruding into the combustion chamber of the cylinder. At the end, there are provided atomizers 3 and 4, each having nozzle holes (not shown) for injecting gas and pilot oil into the engine cylinder, respectively.

A gas inlet conduit 5 and a control oil inlet conduit 6 coming from a suitable source are provided on top of the injector 1, which acts to open the valve contained in the injector and the gas into the cylinder. It is controlled toward the closed position by controlling the injection of the spring and biased spring. A suction conduit 7 for ignition oil is shown on top of the ignition oil injector, which can be conducted through a spring biased valve to the associated nozzle hole in the atomizer 4.

If the engine is driven with a gas having a high heat value, the required gas spray area can be surely small enough that the gas and pilot oil injectors can be incorporated into a single injector. Embodiments of such injectors are described in detail in the applicant's Japanese Patent Application No. 179,766.

A cam 11 for operating the control oil pump 12 for supplying the pilot oil pump 10 with the cam 9 and the control oil to the injector 1 is shown in FIG. 1 on the control shaft of the engine. Fasten as indicated by). The pumps 10, 12, which can be in the form of so-called Bosch in a known manner, have a means for changing the amount supplied to the pump by the relative rotation of the piston and a means for changing the starting instant (feeding phase) of the lining and effective pump stroke. Equipped with. The pump 10 includes an inlet 13 in addition to the outlet of the pump connected to the conduit 7 through which the inlet 13 receives pilot oil from the prime pump and return conduit 14 to the suction side of the prime pump. do. In a similar manner, the pump 12 is connected to the return conduit 16 for the control oil source and the inlet 16 for the control oil, which can be a prime pump connected to the pilot oil pump.

Alternatively, a control valve actuated by the cam 11 can be used instead of the pump 12 so that a suitable high pressure can be supplied from a source for the control oil, the appropriate pressure being a gas valve or injector to achieve this purpose. It is a pressure that can be operated on the area of (1) to open the valve and to keep the valve open against the force from the associated closing spring.

The valve block 17 is inserted into the suction conduits 6, 7 upstream of the injector so that the conduits extend through the block in a spaced apart relationship. The pressure relief valve 18 inserted in the block can keep the control oil conduit 6 open in connection with the drain conduit 19 connected to the control oil collection vessel 20 under substantially atmospheric pressure, for example control oil. Inlet 15 may be provided from the container. In engines with higher yields per cylinder, more sets of three injectors (1, 2) can be provided on the respective cylinder lids, all of which have the same valve block advantageously mounted on the sides of the engine cylinder lids. From 17 are provided parallel to the control oil and pilot oil.

The pressure relief valve 18 shown in FIG. 2 has a bolt 23 on a mounting flange 24 which has a valve housing 22 at one end and which can be fastened to a valve block 17 at the other end. It includes the valve body 21 is determined by. The peripheral groove 25 in the valve body communicates with the inlet conduit 6 for the control oil via a lateral bore (not shown), and preferably also through the various inlet bores 27 for the control oil via a variety of four radial bores. To pass.

The lateral bore (not shown) emanating from the pilot oil suction conduit 7 is released at the base of the valve receiving bore in the valve block, so that the instantaneous pilot oil pressure in the conduit 7 ensures good pressure communication with the lateral bore. It acts at the extreme end of the valve housing 22 in the region around the recess 28.

Since the interior of the valve housing 22 is connected to the drain duct 19 through various radially directed drain openings 29, a pressure of typically 10 bar or less can be supplied to the interior of the housing.

Two dowels 30 in which a valve housing 22, a valve body 21 and a flange 24 are disposed in the bore for the purpose of placing the bore 26 and the opening 29 directly opposite the associated bore in the valve block. 31) are mutually fixed with respect to rotation.

The gasket 32 inserted in the recess around the outside of the valve housing blocks the pilot oil pressure from dropping as the pilot oil passes through the drain conduit 19. Similarly, two gaskets 33 arranged laterally on both sides of the recess 25 and respectively inserted into respective recesses in the outer periphery of the valve body block the loss of indifferent control oil.

In the valve housing 22 and the valve body 21, a stepwise increasing diameter of the housing at the extremes of the casing increases to avoid unnecessary corrosion and loading of the gaskets 32 and 33 when assembling the relief valve, mounting and releasing it in the valve block. Provided backwards, the first gasket is simply inserted past a short valve distance with a full diameter corresponding to the gasket before being inserted into the groove, and secondly, during mounting the outer part of the groove is only released from the associated sealing surface in the valve block. Will be placed as short as possible.

The first central bore 34 (FIG. 3) provided axially from the transverse groove 28 toward the valve body in the end cross section of the valve housing 22 into the second central bore having a larger diameter than the first central bore. It is released into the extending compression chamber 35. The piston 36 illustrated in FIG. 4 has a cylindrical body 37 which is fluidly inserted into the first bore and which is axially replaceable. The body part is incorporated through a cylindrical main part 36 and a neck 38 having a large diameter which defines the movement of the piston towards the recess 28 in such a manner as to engage the proximal end of the pressure chamber.

The valve member 40 is axially replaceable under the control of an end shaped with a piston 41 having a first axial piston surface disposed in the pressure chamber 35 and fluidly inserted into the second bore. Do. The opposite end of the valve member is shaped as a coaxial conical shoulder 43 which is received in the valve housing 22 recess and also acts as a needle valve. The member 40 includes a protruding peripheral flange 44 that forms a guide for the compression spring 45 between the shoulder and the piston.

A cylindrical projection 46 (FIG. 7) in the center on the valve body comprises a first drain duct 47 coaxial with a second bore of the valve housing, the duct being a cone for the valve member shoulder 45. The suction duct is extended toward the cut sheet 48 to enter the recess of the valve housing.

The sliding bushing 49 shown in FIG. 8 is fluidly assembled to the slide surface 50 on the projection 46 acting as a slide guide and also at the end remote from the valve member, especially for the spring 45. It has a protrusion peripheral flange (51) constituting.

At least one radial second drain duct 52 extending between the conical cut valve seat 53 and the slide surface 50 surrounding the base of the protrusion 46 extends from the suction duct 27. The sheet 53 interacts with the inner team 54 of the bushing 49 which acts as a valve member. A compression spring 45 biases the bushing toward the closed position and the valve member. The inner part of the sliding bushing is formed of three different cross sections, each having a separate diameter. The bushing that engages the slide surface 50 has an inner diameter Dg slightly smaller than the diameter Dv of the adjacent sheet 53, the middle portion being the largest to form a cavity like a pressure chamber opposite the drain duct. Having a diameter, the chamber has an axial extension that allows oil to flow into the cavity even when the bushing is moved away from the valve seat.

Due to the fact that the ratio of diameters (Dv / Dg) is greater than 1, the inner part of the bushing has a valve seat when the control oil pressure is high enough so that the opening force on the area 55 exceeds the closing force of the spring 45. The effective piston region 55 is shown in the open direction which acts to move the bushing away from it. The control oil subsequently flows through the valve seat 53 and into the drain conduit 19 via the main portion of the valve housing and opening 29. The outer diameter of the flange 51 may be along the inner diameter of the recess to form a narrow throttle slit between the diameters through which the control oil can pass through the path in the recess. The limit of the pressure drop on the valve seat of the throttle slit is prevented by a sudden pressure drop occurring in the control oil conduit 6 when the bushing valve is opened. It will be appreciated that the sliding bushing acts as a pressure relief valve and shuts off the first drain duct when the valve member is in the closed position. If the pump 12 is arranged to supply sufficient oil quantity and the recess is designed to have a uniformly increasing diameter in the region 56 (FIG. 1) just above the spring side of the flange 51 rather than a large diameter, Appropriate setting of oil pressure is achieved in the throttle slit, which is a spring closing force through which the control oil immediately after the initial movement of the bushing away from the sheet penetrates into the annular chamber between the valve body 21 and the flange 51 and The cam 11 is controlled by the influence on the entire end surface 58 of the flange by the pressure to move the bushing further away from the sheet resulting in a lower throttle resistance due to the larger diameter in the area 56. Set the equilibrium indicated by the constant control pressure in the gas injector and increase the pressure until the oil supply is reduced or shut off.

When the spring 45 ruptures, it becomes apparent that even minute control oil pressure pushes the bushing 49 away from the sheet 53.

The closing of the first drain duct 47 is achieved under the condition of raising the pilot oil pressure in the conduit 7, the pressure on the second piston surface 59 consisting of the open end surface of the piston 37 engaging the recess. The silver piston 36 is increased to a value that exerts a closing force on the valve member 40 exceeding the spring force so that the piston and the body are projected until the valve surface of the shoulder 43 contacts the sheet 48. It is moved toward 46. Since the relative volume change in the system is small due to the piston having a short path and the second piston surface with a short area, the closing of the valve involves minimal interference in the ignition oil system.

The control oil supply is initiated without any risk of too early gas injection before the ignition oil pressure is raised to the injection pressure, which means that when the valve member is in the open position the control oil is only the first drain duct 47 and the drain conduit ( Because it leaks only through 19). As soon as the shoulder 43 engages the first drain duct 47, the pressure chamber 35 is connected to the control oil suction duct 27 via a continuous intermediate duct 60 in the center of the valve member. With respect to the mechanical strength of the shoulder, the intermediate duct of the portion extending through the shoulder may have a reduced diameter. The transverse spline 61 in the first piston surface intersects the intermediate duct and establishes a communication relationship between the chamber 35 and the intermediate duct regardless of whether the piston head 39 is firmly in contact with the valve member.

By setting the control oil pressure in the suction channel 27, the control oil generates a similar pressure that applies a closing force to the first piston surface 42 sufficient to hold the valve member in the closed position by a constant control oil supply. Will flow into the chamber 35. Once the control oil pressure is set, the function of the relief valve will be independent of the pilot oil pressure.

In the graph illustrated extremely simply in FIG. 9, the ordinate indicates the control oil pressure in bars and the abscissa indicates the angle of rotation of the crankshaft at intervals between the indications of the crankshaft angle of 10 °. The curve illustrated by the dashed line indicates the ignition oil pressure in front of the oil injector valve, which is evident from the example section of a complete operating cycle in which the ignition oil pressure is set just before the operating piston passing through the top dead center position as the operation cycle begins. At an ignition oil pressure of about 250 bar, the increase in pressure indicates a start of ignition oil injection, after which the valve member is immediately displaced to the closed position. The ignition oil injection continues until the actuation piston starts the actuation stroke.

The solid line graph shows that the pressure coarse in the control oil conduit 6 results in a low load on the engine, and the dashed-dotted line illustrates the pressure coarse when the engine is operating at near full load. It is apparent that the control oil pressure before closing the valve member is at a low level corresponding to the draining-off pressure in the drain opening 29. At a small angle of rotation of the crankshaft after closing of the relief valve, the control oil pressure rises constantly towards the opening pressure of the gas injector valve of about 400 bar and is prepared at a pressure of about 90 bar, the control oil pressure being the pilot oil in the valve. Proceed with the closing of the pressure. The control oil pressure is maintained to rise to a pressure of about 600 bar until the bushing is opened, such that the pressure is generally maintained until the cam 11 or pump 12 stops supplying the ignition oil at the crankshaft position under the engine load. Stays constant.

An example of a variant embodiment is that the piston 37 and the valve member 40 can be manufactured as one unit and the intermediate duct 60 is designed as a duct which is housed in the valve housing and the valve body and the connecting chamber 35. (27) can be inserted.

Claims (10)

In a fuel system for a dual fuel diesel engine driven by gas as main fuel and pilot oil as ignition aid, each cylinder comprises at least one control oil conduit leading to a gas injection injection valve (1). (6), a valve operated toward the closed position by the pressure in the pilot oil suction conduit 7 and the pilot oil suction conduit with the injector valve 2 for pilot oil injection, and the open position by the spring 45; It is connected to a pressure relief valve 40 having a member 40 and installed in a control oil conduit, wherein the valve member is in an open position during the compression stroke of each engine cycle, and the pressure in the pilot oil conduit is applied to the pilot oil injector valve 2. When the pressure is lower than the opening pressure of), the first drain duct 47 in the control oil conduit is opened, and the valve member 40 is operated by the pilot oil pressure through the piston 36. And the member (40) is in the closed position and is operated toward the closed position by the control oil pressure when blocking the first drain duct. 2. A slide according to claim 1, wherein the valve member has a coaxial axial shoulder 43, which is designed as a needle valve to interact with the valve seat 48 surrounding the first drain duct 47 at one end. slid), the slide comprising a first piston surface 42 spaced axially away from the shoulder and disposed in the pressure chamber 35, wherein the intermediate duct 60 extending through the slide is a shoulder 43 ) Contacts the valve seat in the closed position of the valve member to connect the pressure chamber to the first drain duct, and the piston 36 is stably fixed to the bore in the axially aligned state of the slide 40 and spaced apart from the shoulder. A fuel system, characterized in that it has a second piston surface (59) facing axially and affected by pilot oil pressure. 3. A fuel system according to claim 2, wherein the area of the second piston surface (59) is generally smaller than the area of the first piston surface (42). 4. The fuel system according to claim 3, wherein the piston (36) is integrally coaxial with the slide and the intermediate duct is a central bore (60) in the slide. 3. The fuel system according to claim 2, wherein the effective area of the first piston surface (42) is larger than the cross-sectional area of the first drain duct (47). 3. The valve according to claim 2, wherein the valve is closed when the pressure in the pilot oil conduit rises to the determined pressure, and the spring characteristic and the region of the second piston surface 59 are the pilot oil when the slide 40 is in the closed position. The fuel system, characterized in that the closing pressure exerted on the surface of the second piston by the determined pressure in the conduit (7) is adapted to each other so as to correspond to the opening force of the spring. 3. A sliding bushing (49) coaxial with the first drain duct (47) and the slide (40) at the terminal position blocks the second drain duct (52) in communication with the control oil conduit (6). Wherein the sliding bushing and the slide have a spring between them biasing the slide to the open position and biasing the sliding bushing to the closed position. 8. A fuel system according to claim 7, wherein an effective piston region (55) acting in the opening direction of the bushing is provided inside the sliding bushing, and control oil pressure in the second drain duct acts on the effective region. 9. The bushing according to claim 8, wherein the bushing is inwardly shaped as a valve which interacts with a valve seat (53) coaxially disposed with respect to a bushing on the shaft portion of the second drain duct (52) disposed opposite the spring (45). A fuel system having a rim (54). 9. The fuel system according to claim 8, wherein the lower shaft of the valve seat (53) of the bushing is provided with a road slit extending to the discharge opening (29) for the control oil.