A HIGH PRESSURE FUEL CONNECTION ARRANGEMENT TO AN INJECTOR HOLDER IN A COMMON RAIL SYSTEM

Technical field

The invention relates to a high pressure fuel connection arrangement to an injector holder in a common rail system for a large internal combustion engine according to the preamble of claim 1.

Background art

In this specification the term "large internal combustion engine" refers to such engines that are used, for example, as main propulsion engines or auxiliary engines in ships or in power plants for the production of heat and/or electricity.

In a known arrangement a pipe for feeding high pressure fuel from a common rail system into an injector is directly connected with threads to the injector holder. It has turned out this is an unreliable solution since due to the rather limited length of the thread engagement the pipe has limited strain which may result in insufficient retaining force for sealing the high pressure common rail system at 1800 bar or more. Also provision of threads to the rather narrow wall section of the injector holder is not easy and may result in shortened lifecycle of the components.

An object of the invention is to provide a new connection arrangement, which solves the above mentioned and other problems of the prior art. It is also an object of the invention to provide a reliable connection arrangement with uncomplicated construction. A further object is to provide an arrangement which makes it possible to handle and control leakage draining out from the outside of the injector holder and, thus, to enable controlling the condition of the injection equipment.

Disclosure of the invention

The objects of the invention can be met substantially as is disclosed in claim 1 , the other claims presenting more details of different features of the invention.

In accordance with the invention the arrangement includes fixing means ar- ranged in threaded connection with a first part of a chamber in the cylinder head for fixing the second pipe means tightly to the injector holder, the fixing means exerting the fixing force through an enlarged part with suitable counter surface arranged in the second pipe means. Said chamber is arranged in communication with the injector holder through a second part of the chamber, the second pipe means being at least of substantial length spaced apart from said chamber between the fixing means and the injector holder.

Hereby direct connection of the pipe means by threads to the injection holder can be dispensed with allowing for sufficient tightening of the pipe means to the injector holder to comply with different operating conditions and fuels to be util- ised in the engine. Since the chamber is in communication with the injector holder independent on the supply of the high pressure fuel through the pipe means it can with advantage be utilised for collecting leakage from the outside of the injector holder.

The length of the second pipe means between the fixing means and the injector holder and the diameter of the chamber are selected so as to allow slight bending of the second pipe means located therein under certain strain caused by the fixing means. The use of pipe means with a long loaded length provides a better retained strain when pipe working lengths change due to thermal loading changes.

In case there is a risk of excessive bending of the second pipe means the second pipe means may be provided with a supporting element for supporting it to the cylinder head along the second part of the chamber.

In practice the length of the second pipe means between the enlarged part and the second end is with advantage from about 10 to 20 times the diameter thereof. The diameter of the chamber is respectively about 40% - 100% larger

than the second pipe means located therein. By these dimensions it is easier to handle variations in the strain of the pipe means resulting from different operating conditions of the engine.

When the chamber is arranged to collect so called dirty leakage draining from the external surface of the injector holder this chamber is practically pressure- less since the question is only about a sealing mixture dribble. Notwithstanding, the cylinder head is in this case with advantage provided with a duct or the like for leading the collected leakage away from the chamber and the cylinder head. This allows for control of the volume of the leakage and detection of any larger leakages.

In a favourable embodiment the first part of the chamber is with advantage bounded by the cylinder head, the fixing means and the second pipe means including the enlarged part thereof. The diameter of the first part of the chamber is with advantage substantially larger than the diameter of the second part of the chamber and includes substantial free space for collecting said leakage.

The fixing means is preferably a sleeve formed bolt element through which the second pipe means is fitted. Thus it can easily be tightened by means of ordinary tools and it is in no direct connection with the high pressure fuel supplied through the pipe means.

From the viewpoint of efficiently sealing the supply of high pressure fuel through the pipe means the contact surface of the fixing means is cone formed and its counter surface in the enlarged part is either ball formed or cone formed. Correspondingly, the head of the second end of the second pipe means is preferably ball shaped and its counter surface in the injector holder is cone formed. Ball shape of the head of the second end of the second pipe means is ideal to comply with possible misalignments as the pipe means bends on the assembly into the cylinder head.

Brief Description of Drawings

In the following the invention will be described with reference to the accompanying schematic drawing, the only figure of which illustrates an embodiment of the arrangement according to the invention as a sectional view.

Detailed Description of Drawings

In the drawing the reference numeral 1 indicates a cylinder head of an internal combustion engine supporting an injector holder 2 by means of which high pressure fuel is injected into a cylinder of the engine in a way known as such (not shown). High pressure fuel provided by a common rail system (not shown) is delivered through a first pipe means 3 into the cylinder head 2 and a second pipe means 4 is provided for supplying the high pressure fuel further within the cylinder head 1 into the injector holder 2. A first end 4a of the second pipe means 4 is tightly connected with the first pipe means 3. Any suitable fixing means 10, for example a sleeve with threaded connection with the pipe end 4a, may be provided for securing the tight connection between the first and the second pipe means 3 and 4. The second end 4b of the second pipe means 4 is in direct connection with the injector holder 2 by means of mutual contact surfaces 4e and 2a respectively. The surface 2a may be cone formed and the surface 4e is preferably ball shaped for providing a reliable and tight engagement.

The cylinder head 1 is provided with a chamber 5,6 which is in communication with the clearance 11 between the cylinder head 1 and the injector holder 2 and locating a substantial part of the second pipe means 4. The arrangement includes further a fixing means 7, for instance a sleeve or the like bolt element, through which the second pipe means 4 is led and which is engaged by threads 8 with a first part 5 of the chamber 5,6 in the cylinder head 2. The second pipe means 4 is provided with an enlarged part 4c with a counter surface 4d arranged in cooperation with the surface 7a in the fixing means 7. These surfaces 4d and 7a can be cone formed. Alternatively, in analogy with the surface 4e the surface 4d may with advantage be also ball formed so as to better comply with possible bending of the second pipe means as discussed below. Hereby the pipe means 4 can be tightly sealed to the counter surface 7a of the fixing means

7 more close to the first end 4a of the second pipe means 4. The enlarged part 4c need not be an integral part of the second pipe means 4 but if desired it may also be implemented as a separate threaded connection sleeve for instance.

As can be seen from the figure the part of the second pipe means 4 between the enlarged part and the injector holder 2 is of substantial length especially in view of its diameter. The advantage of this kind of layout of the second pipe means 4 within the second part of the chamber 6 is the long strain length which enables retention of load despite fuel temperature operation extremes of 4O ⁰ C up to 15O ⁰ C with heavy fuel oil. If needed a second part 6 of the chamber 5,6 allows some bending of the second pipe means 4 so that sufficient retention of load can be maintained under different conditions. On the other hand this part of the second pipe means 4 may be provided with some guidance to provide limits to a bending of this kind. In the figure this is only schematically indicated by means of a supporting element 13. Naturally such a supporting element should be designed to allow leakage through it so as to allow collecting leakage through the chamber parts 5 and 6 as described below. For this aim and in view of said bending the second part 6 is with advantage of smaller diameter than the first part 5 of the chamber 5,6.

As apparent from the figure the first part 5 of the chamber 5,6 is through the second part 6 of the chamber 5,6 in communication with the clearance 11 in which a sealing mixture dribble drains out from the injector holder to the external surface thereof. Therefore these chamber parts 5 and 6 may with advantage be utilised for collecting this so called dirty leakage, which can be led away from the cylinder head 1 by means of a duct 12. This leakage may then be followed and a sudden and sufficient increase may be detected possibly indicating a large leakage to be taken care of to avoid any damage of the equipment.

It is clear that the invention is not limited to the examples mentioned above but it can be implemented in many other different embodiments within the scope of the inventive idea and the attached claims.