BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention pertains to a plug assembly to maintain and eliminate a fluid pressure in an accumulator tank, according to the preamble of claim 1.

It is common, particularly in heavy goods vehicles, to use a fuel system in the form of a Common Rail System. In a Common Rail System a high pressure pump is used to create a very high pressure in a liquid fuel in an accumulator tank (Common Rail). The fuel pressure in the accumulator tank may be in the range of 2,000 bar. During the operation of a combustion engine, fuel is led from the accumulator tank, via individual high pressure conduits, to injection elements that inject the pressurised fuel into the combustion engine's respective cylinders.

In connection with troubleshooting such fuel systems, one or more high pressure conduits may be loosened from their connecting sections in the accumulator tank, following which plugs are applied to the exposed sections. The vehicle's starting engine is used to operate both a feed pump and the high pressure pump, so that fuel is led to the accumulator tank with a fuel pressure as high as the fuel pressure during the operation of the combustion engine. On occasions when all the connecting sections are equipped with plugs, any leakage in component parts, such as the high pressure pump or an overpressure valve in the accumulator tank, may be detected. On other occasions, all connecting parts except one may be equipped with plugs to detect a potential leakage in an individual injection element. During troubleshooting work, the fuel pressure in the accumulator tank may need to be built up and eliminated several times. The fuel pressure in the accumulator tank is usually eliminated by releasing one of the plugs. Since the fuel has a very high pressure in the accumulator tank, as a rule, some of the fuel spurts out at a very high speed. This entails a risk of injury to e.g. the fingers and eyes of persons carrying out the troubleshooting. The fact that fuel spurts out uncontrollably into the environment is also unsuitable. Alternatively, the fuel pressure in an accumulator tank may be led down into one of the combustion engine's cylinders. This alternative, however, entails a risk of dilution of the engine oil.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a plug assembly, which facilitates elimination of the fuel pressure in an accumulator tank, without any risk of personal injury. Another objective is to provide a robust and fail-safe plug assembly with a small number of component parts.

This objective is achieved with the plug assembly of the type specified at the beginning, which is characterised by the features specified in the characterising portion of claim 1. In addition to the parts found in a conventional plug, the plug assembly comprises a moveably arranged locking body and a manoeuvring device, with which the locking body obtains a movement between a closed position in which it blocks an opening in a connecting section, and an open position in which the opening is exposed. The plug assembly also comprises a sleeve-shaped device with an internal space, and a flow passage that connects the fluid in the accumulator tank with the internal space of the sleeve-shaped device, at times when the locking body is in the open position. When the fluid pressure in the accumulator tank is to be eliminated, the locking body is brought into the open position with the help of the manoeuvring device. Thus, the pressurised fluid in the accumulator tank gains access to an extra volume for expansion. Since fluids are nearly incompressible, a pressurised fluid may obtain a considerable pressure decrease when it gains access to a relatively small extra volume. In this case, the fluid expands in the flow channel and in the internal space of the sleeve-shaped device. The fluid will thus not come into contact with the person who handles the plug assembly. Thus, when the pressure in the accumulator tank is eliminated with the help of the plug assembly, the risk of personal injuries is nearly nil. The plug assembly thus comprises a fastening device, a locking body, a manoeuvring device and a sleeve-shaped device. The plug assembly thus contains relatively few parts and thus has a robust construction. According to one embodiment of the present invention, said flow passage is adapted to throttle the pressurised fluid, which is led from the accumulator tank to the internal space. Suitably, the flow channel comprises a number of narrow and curved passages, where the pressure of the fluid is successively decreased as it is led from the accumulator tank to the internal space. With the help of such a flow channel, the expansion of the fluid is relatively slow and it thus has a relatively low speed when it reaches the internal space. According to one embodiment of the present invention, the sleeve-shaped device comprises a passage, connecting the internal space directly or indirectly with air at the surrounding pressure. Thus, the fluid in the accumulator tank may expand to the pressure of the surrounding environment. In this case, the fluid's overpressure in the accumulator tank may be entirely eliminated. The passage may be a relatively small hole or another form of opening, connecting the internal space with the surrounding air.

According to one embodiment of the present invention, the manoeuvring device comprises a bolt between the sleeve-shaped device and the fastening device, so that the sleeve- shaped device is in direct or indirect contact with a contact surface of the locking body, so that a screw movement of the sleeve-shaped device in relation to the fastening device results in a movement of the locking body between the closed position and the open position. The sleeve-shaped device may comprise a contact surface, which is in contact with a contact surface of the locking body. In this case, the sleeve- shaped device is thus used both to receive the expanded fluid in the internal space and to move the locking body between the closed position and the open position. The manoeuvring device may comprise a pressure unit, which is arranged between the sleeve- shaped device and the locking body, so that it transmits the movement of the sleeve-shaped device to the locking body. In this case the movement of the sleeve- shaped device is transmitted to a movement of the locking body via a separate intermediate device.

According to one embodiment of the present invention, the sleeve-shaped device comprises a grip section for a tool, with which the sleeve- shaped device is given a turning movement in relation to the fastening device. In order to ensure that the locking body blocks the connecting section's opening in a required manner, it is suitable to provide a turning movement of the sleeve-shaped device with a relatively large torque. For this reason, it is suitable to use a tool for this purpose.

According to one embodiment of the present invention, the locking body comprises a conically shaped section, adapted to block the connecting section's opening in the closed position. With a conically shaped section, the lock element may provide a good sealing of the connecting section's opening. The connecting section's opening is advantageously designed with a similar conical section, so that a relatively large contact area is obtained between the locking body and the connection section in the closed position.

According to one embodiment of the present invention, the sleeve-shaped device comprises a fastening section for a hose, adapted to lead away fluid collected in the expansion space. Thus, the fluid may easily be led to a container or similar collection vessel. The hose may advantageously be used to maintain the surrounding pressure in the internal space. Alternatively, the internal space may be emptied of fluid without a hose. In this case, the plug assembly may be released from the accumulator tank, following which the internal space may be emptied of fluid. According to one embodiment of the present invention, the fastening device comprises a surface adapted to bring the locking body to the open position when the fastening device is applied to the connecting section. Thus, the locking body is moved along to a suitable open position in relation to the connecting section's opening by the fastening device. The fastening device advantageously comprises a threaded section, with which it is releasably connected to a threaded section in the connecting section. Thus, the fastening device may be screwed onto the connecting section during an application process of the plug assembly. The fastening device may comprise a grip section for a tool. Thus, the fastening device may easily be screwed onto a connecting section of the accumulator tank. The tool may also be used to keep the fastening device in a specific position when the sleeve-shaped device is turned in relation to the fastening device.

According to one embodiment of the present invention, the plug assembly is adapted to be applied to a connecting section of an accumulator tank in the form of a so-called common rail, which contains fuel with a high pressure. Such fuel systems are used in particular in heavy goods vehicles. In such a fuel system, a very high fuel pressure is created in the accumulator tank. When troubleshooting such systems, a pressure may be created inside the accumulator tank, which is as high as during operation of the combustion engine. When troubleshooting a Common Rail System, at least one plug assembly according to the present invention is used, in order to close a connecting section of the accumulator tank (Common Rail). In order to close other connecting sections in the accumulator tank, conventional plugs may be used. When the fluid pressure in the accumulator tank is to be eliminated, the manoeuvring device brings the locking body into the open position. Thus, the opening in the connecting section is exposed, so that the pressurised fuel in the accumulator tank may expand, via the flow passage, out into the internal space of the sleeve-shaped device. In connection with this, the fuel in the accumulator tank obtains a reduced pressure.

The objective mentioned in the introduction is also achieved with the method according to claim 13. BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of a preferred embodiment of the invention with reference to the enclosed drawings, in which: Fig. 1 shows a fuel system in the form of a common rail system,

Fig. 2 shows a part of the common rail system with a plug assembly according to the present invention,

Fig. 3 shows the plug assembly in Fig. 2 in an open position and

Fig. 4 shows the plug assembly in Fig. 2 in a closed position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 shows a fuel system in the form of a so-called Common Rail System for injection of fuel into a combustion engine, which in this case is exemplified as a diesel engine 1. The fuel system and the diesel engine 1 are advantageously assembled in a heavy goods vehicle. The fuel system comprises a fuel tank 2 with a fuel conduit 3 to lead diesel oil from the fuel tank 2 to the diesel engine 1. During operation, a feed pump 6 sucks diesel oil from the fuel tank 2 to a first filter house 5. In the first filter house 5, a coarse filtering of the diesel oil takes place. Any water and large particles in the diesel oil are separated here. After the coarse filtering in the first filter house 5, the diesel oil is sufficiently free of contaminants to ensure that the feed pump 6 is not damaged. The diesel oil is subsequently led to a second filter house 7. In the second filter house 7, the diesel oil is finely filtered. The finely filtered diesel oil is led from the second filter house 7 to a high pressure pump 8. The diesel oil is now entirely free of contaminants, which may otherwise damage the high pressure pump 8 and other components on the fuel system's high pressure side.

The high pressure pump 8 is adapted to pressurise the diesel oil, so that it is fed with a very high pressure into an accumulator tank 9 in the form of a so-called Common Rail. The high pressure in the accumulator tank 9 constitutes a driving source to facilitate an injection of the diesel oil into the diesel engine's 1 respective cylinders with a high pressure. The accumulator tank 9 comprises several connecting sections 10 for connection of high pressure conduits 13. The high pressure conduits 13 lead fuel from the accumulator tank 9 to injection elements 12, which inject diesel oil into the diesel engine's 1 cylinders with a high pressure. The accumulator tank 9 comprises an overpressure valve 11, which opens if the pressure in the accumulator tank exceeds a highest acceptable pressure. A return conduit 14 returns excess diesel oil, which has not been injected by the injection elements 12, to the fuel tank 2. The return conduit 14 also returns diesel oil from the accumulator tank 9 to the fuel tank 2 at times when the over pressure valve 11 opens.

Fig. 2 shows the accumulator tank 9 at a time when troubleshooting is carried out by the fuel system. All high pressure conduits 13 have here been disconnected from the accumulator tank's 9 connecting sections 10. One of the connecting sections 10 has been sealed with a plug assembly 16 according to the present invention. Other connecting sections 10 have been sealed with plugs 15 of a conventional type. During troubleshooting, a start engine in the vehicle may be activated to operate the feed pump 6 and the high pressure pump 8, so that a high fuel pressure is created in the accumulator tank 9. In this case, no injection elements 12 are connected to the accumulator tank 9. Here, it is possible to control any potential leakages from components such as the over pressure valve 11 and the high pressure pump 8. When this is done, one high pressure conduit 13 and one injection element 12 at a time may be connected to the accumulator tank 9. Thus, the leakage from individual injecting elements 12 may be tested. Other types of troubleshooting may obviously also be carried out when a high pressure prevails in the accumulator tank 9. When the fuel pressure in the accumulator tank 9 is to be eliminated, the plug assembly 16 is used. It is, however, possible to eliminate the pressure in the accumulator tank 9 by releasing one of the conventional plugs 15. Since the fuel pressure in the accumulator tank 9 is very high, there is a risk of personal injuries if the pressure is eliminated with the help of one of the conventional plugs 15.

The plug assembly 16 is shown in more detail in Fig. 3 and 4. The plug assembly 16 comprises a fastening device 18, with which it may be fastened on a connecting section 10 of the accumulator tank 9. The fastening device 18 is equipped with a centrally arranged through-hole. The fastening device 18 comprises an internally threaded section 18a, with which it is screwed onto an external threaded section 10a of the connecting section 10. The plug assembly 16 comprises a locking body 19, which is mainly arranged inside the central through-hole of the fastening device 18. The locking body 19 is shiftably arranged between a closed position, in which it blocks an opening 10b in the connecting section, and an open position in which it exposes the opening 10b. The locking body 19 comprises a conically shaped section 19a, with which it blocks the opening 10b of the connecting section in the closed position. The locking body 19 comprises a contact surface 19c. The fastening device 18 comprises a contact surface 18c, which is adapted to come into contact with the contact surface 19c and move along the locking body 19 when the fastening device 18 is screwed onto the connecting section 10.

The plug assembly comprises a sleeve-shaped device 20, comprising a through-hole extending from a first end to a second end. The through-hole has a variable diameter in different parts of the sleeve- shaped device 20. In a part of said hole, located at the first end of the sleeve-shaped device 20, the fastening device 18 and the locking body 19 are received. The sleeve-shaped device 20 comprises, in another part of said hole, an expansion space 20a. Said hole forms, at the other end of the sleeve-shaped device 20, a relatively narrow passage 20c which connects the expansion space 20a with the pressure of the surrounding environment. Thus, the surrounding pressure is maintained inside the expansion space 20a. Said hole comprises, in a part of the sleeve-shaped device 20, an internal threaded section 20b which is connected with an external threaded section 18b of the fastening device 18. The threaded sections 18b, 20b form a bolt between the sleeve- shaped device 20 and the fastening device 18. When the sleeve-shaped device 20 carries out a screw movement, it is shifted in an axial direction in relation to the fastening device 18. The sleeve- shaped device 20 comprises a grip section 20e for a tool, with which the sleeve- shaped device 20 is given said screw movement in relation to the fastening device 18. The grip section 20e may have externally flat-lined sections, so that it may be turned with a wrench or a similar tool. The sleeve-shaped device 20 also comprises a fastening section 20f for a hose 17. With the help of the hose 17, fuel collected in the internal space 20a may be led away to a container or similar for collection of diesel oil.

The plug assembly 16 comprises a pressure device 21, which is arranged in an intermediate section of the through-hole of the sleeve-shaped device 20. The pressure device 21 comprises a first contact surface 21a, which is adapted to be in contact with a contact surface 20d of the sleeve-shaped device, and a second contact surface 21b, which is adapted to be in contact with a contact surface 19b of the locking body 19. Thus, the pressure device 21 may transmit a shifting movement of the sleeve-shaped device 20 to a similar shifting movement of the locking body 19. The locking body 19 may thus be shifted by the sleeve-shaped device 20 between an open position, in which the conical section 19a exposes the opening 10b to the connecting section 10, and a closed position, in which the conical section 19a seals the connecting section's opening 10b. At times when the connection section's opening 10b is exposed, a flow passage is created for diesel oil between the accumulator tank 9 and the internal space 20a in the sleeve-shaped device 20. The flow passage initially has a slot-shaped extension between an external surface of the locking body 19 and an internal surface of the fastening device 18. The flow passage subsequently has an extension along a slot- shaped space between an external surface of the pressure device 21 and an internal surface of the sleeve-shaped device 20. This flow passage is narrow and comprises curved sections, so that diesel oil led through the flow channel obtains a successively reduced pressure. A spacer 22 is placed around the connecting section 10. The spacer 22 defines a correct assembly position for the fastening device 18 on the connecting section 10.

The plug assembly 16 is applied on a connecting section 10 of the accumulator tank 9 when the accumulator tank 9 is empty. The plug assembly is applied on the accumulator tank 9 by screwing the fastening section 18 onto the fastening section via the threaded sections 10a, 18a. When the fastening section 18 is screwed onto the connecting section 10, the fastening section's connecting surface 18c comes into contact with the locking body's contact surface 19c. Thus, the fastening device 18 moves along the locking body 19 in the direction toward the connecting section's opening 10b when it is screwed onto the connecting section 10. When a front end surface of the fastening device 18 comes into contact with the spacer 22, it has reached a correct assembly position. In this position, the locking body's conically shaped section 19a is located at a relatively small distance from a corresponding conically shaped section, which defines the connecting section's opening 10b. The locking body 19 is here in an open position. Fig. 3 shows the locking body in the open position. The fastening device 18 may be screwed onto a connecting section 10 by hand, or with the help of a tool that is applied to the grip surface 18d.

Subsequently, a tool is applied on the grip surface 20e of the sleeve-shaped device. The tool turns the sleeve-shaped device 20, so that the threaded section 20b is given a screw movement in relation to the threaded section 18b of the fastening device. The sleeve- shaped device 20 thus obtains a movement to the left in relation to the fastening device and the connecting section 10. During this movement, the pressure device 21 is shifted by the sleeve- shaped device 20 via the abutting contact surfaces 20d, 21a. Via the abutting contact surfaces 19b, 21b, the pressure device in its turn moves along the locking body. The axial shifting movement of the sleeve-shaped device 20 is here transmitted to a corresponding axial shifting movement of the locking body 19 via the pressure device 21. The locking body's conical section 19a obtains contact relatively soon with the conical section, which defines the connecting section's opening 10b. With the help of the tool, the sleeve-shaped device 20 may obtain a torque, so that the locking body 19 is pressed with a relatively great force toward the conical section, defining the connecting section's opening 10b. The locking body 19 is now in a closed position, as shown in Fig. 4. When the locking body 19 is in the closed position, the vehicle's starting engine is activated, so that is operates the feed pump 6 and the high pressure pump 8. Thus an equally high pressure as during the operation of the combustion engine may be created in the accumulator tank 9. It is now possible to carry out a troubleshooting of different component parts in the fuel system. During different stages of the troubleshooting, or at least when the troubleshooting is completed, the fuel pressure in the accumulator tank 9 must be eliminated. In order to do so, a tool is applied on the grip surface 20e of the sleeve-shaped device. The tool turns, so that the sleeve-shaped device 20 is given a screw movement in relation to the fastening device 18 in a releasing direction, via the threaded sections 18b, 20b. Potentially, the fastening device 18 must be kept in its position with a tool applied to the grip surface 18d, in order for the sleeve-shaped device 20 to be given this movement. The fuel pressure in the accumulator tank is thus very high, and may be in the range of up to 3,000 bar. When the sleeve-shaped device 20 no longer retains the locking body 19 in the closed position, the locking body 19 is pressed backwards by the fuel pressure in the accumulator tank 9 to the open position, as shown in Fig. 3. In connection with this, pressurised fuel in the accumulator tank 9 is led to the expansion space 20a via the slot- shaped flow channel, which extends along the outside of the locking body 19 and the pressure device 21. Thus, the pressurised fuel may expand in the flow channel and in the internal space 20a, which results in the pressure in the accumulator tank 9 being reduced to the pressure of the surrounding environment. Since fluids are substantially incompressible, the internal space 20a may be made rather small. Only a small expansion space is required for a fluid, in order for the pressure of the fluid to be reduced radically. The fuel received in the internal space 20a may be led further in the hose 17 to the collecting container for the fuel. Thus no fuel is spilled. The invention is in no way limited to the embodiment described in the drawing, but may be varied freely within the framework of the claims.