Patent Publication Number: US-6217299-B1

Title: Integrated pump and tappet unit for a fuel feeding system

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an integrated pump and tappet unit for a fuel feeding system of an internal combustion engine. 
     Large diesel engines refer here to such engines that are applicable for instance for main propulsion engines or auxiliary engines for ships or for power plants for production of heat and/or electricity. 
     In order to accomplish fuel injection under high pressure into a cylinder of an engine a high pressure pump is needed as well as phasing of the operation of the pump according to the operating cycle of the cylinder, which can be accomplished by means of a tappet member controlled by a cam shaft or the like member of the engine. In so-called common pressure or common rail systems and their applications this kind of phasing is not necessary, but nevertheless the operation of the pump may be controlled by means of corresponding members. In accordance with known techniques the pump and the tappet are arranged to be entirely separate units. In this case a separate lubrication is arranged for the pump, whereby fuel, especially heavy oil utilized in modern engines, cannot enter the tappet unit, in which it could be mixed with the lubrication oil. The pump and tappet then each need, however, a body of their own, which increases the manufacturing costs and requires more space. 
     It is further known to connect the pump and the tappet to each other, which makes the construction simpler and decreases the manufacturing costs. However, in known solutions in which the pump and tappet are connected together, mixing of the fuel with the lubrication oil is possible, as a consequence of which the quality of the lubrication oil decreases and affects the whole circulation of lubricant. This may result in the pump and the tappet becoming stuck and may even result in damage of various kinds to the bearings, including the crank shaft bearings. 
     SUMMARY OF THE INVENTION 
     An aim of the invention is to provide an improved pump and tappet unit, with which the advantages of integration can be achieved but from which the drawbacks of the known solutions can be eliminated. A further aim is to create a solution which is applicable to high pressure feeding of fuel and which may easily be connected as part of a fuel feeding system in which a pressure accumulator unit common to at least two cylinders of an engine is utilized and in which the fuel is first pumped under low pressure from a fuel tank into the system. 
     In accordance with the invention the pump and tappet body comprises a one-piece casting and the tappet member and the piston member are connected to each other by means of a tappet arm which passes sealingly through a flange member fixed to the body so that entry of fuel from the fuel chamber to the side of the tappet member is prevented. When the members required for both the pumping and tappet functions are arranged inside of such a one-piece pump and tappet body, a simple and cost effective solution can be accomplished. 
     A one-piece casting, as opposed to an assembly of multiple pieces, is essentially homogeneous. Use of a one-piece casting for the pump and tappet body is advantageous because the one-piece casting is simple and inexpensive to construct and manufacture, and avoids certain disadvantages associated with manufacturing the body from multiple pieces, such as the presence of joints through which fuel can leak and the cost of assembly. 
     The flange member is with advantage provided with a duct for leading lubrication oil into a lubricator groove abutting the tappet arm. By further providing the flange member with a sealing ring, which is located between the lubricator groove and the fuel chamber, mixing of fuel and lubrication oil, with harmful results for the operation of the unit, can effectively be prevented. The body may further include a chamber located between the flange member and the piston member for collecting possible fuel leaked from the fuel chamber. When the collecting chamber is provided with a drain duct the space above the flange member remains de-pressurized, which is advantageous for the sealing arrangement in the flange member and hereby assists in fulfilling the aims of the invention. 
     The fuel chamber is with advantage connected through a non-return valve to a low pressure fuel line included in the fuel feeding system for leading fuel from a fuel tank into the fuel chamber. In addition the low pressure fuel line is provided with a control valve upstream of the non-return valve. In this way, the arrangement according to the invention can with advantage form a part of a fuel feeding system, in which the feeding of fuel from a fuel tank into the cylinders of an engine occurs through both a low pressure part and a high pressure part of the feeding system. 
     The body with advantage includes a pipe element or structure, through which the low pressure fuel line is led, and has ducts for connecting the pipe element with the fuel chamber. In addition the pipe elements of the bodies of successive pump and tappet units are connected to each other for providing a common low pressure fuel line. By leading the fuel further through a constant pressure valve of the like back into the fuel tank, the uniform low pressure fuel feeding line can be arranged to form a closed loop. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention is described, by way of example, with reference to the attached drawings, in which 
     FIG. 1 shows an embodiment of a pump and tappet unit according to the invention in section and the tappet in its lower position, 
     FIG. 2 shows the embodiment of FIG. 1 with the tappet in its upper position, 
     FIG. 3 shows a sectional view taken along the line III—III of the embodiment of FIG. 1 slightly modified, and 
     FIG. 4 illustrates several units according to the invention being arranged to be part of a low pressure fuel line of a fuel feeding system of an engine. 
    
    
     DETAILED DESCRIPTION 
     In the drawing  1  indicates a pump and tappet body, which is mounted on an engine, for instance on its so-called console support (not shown more closely), by means of screw bolts  22 . The pump and tappet body  1  encloses a tappet member  2  movable in the body  1  against the force of a spring  6  and to which a roll follower  4  is journalled by means of a stub shaft  3 . Reciprocating movement of the tappet member  2  is controlled in known manner through the roll follower  4  cooperating with a cam race  5 , which is included in a cam of a cam shaft of the engine (not shown). 
     Attached to the tappet member  2  there is a tappet arm  7 , at one end of which a piston member  8  is connected to be movable against the force of a spring  9 . A cover element  10 , including a cylindrical part defining a fuel chamber  11 , is fixed to the body  1  by means of screw bolts  27  so that the cylindrical part is within the body  1 . The fuel chamber  11  is arranged in cooperation with the piston member  8  so that the piston member  8  pumps fuel in a way shown in FIGS. 1 and 2 from the chamber  11  through a non-return valve  15  and a duct  16  either directly or through a pressure accumulator into one or more cylinders of the engine (not shown; regarding the pressure accumulator arrangement reference is made to patent application Ser. No. 09/314,640 the entire disclosure of which is hereby incorporated by reference herein). On the other hand fuel is led into the chamber  11  from a low pressure fuel line of the engine (cf. FIGS. 3 and 4) through a duct  12 , a control valve  13  and a non-return valve  14 . By means of the control valve  13  the amount of fuel to be fed into the chamber  11  can be controlled and, when needed, the feeding may temporarily be entirely cut off. A cylinder-like lower part  10   a  of the cover element is so designed that it keeps the spring  9  at its proper position. 
     A separate flange member  17 , through which the tappet arm  7  is led, is fixed to the body  1  by means of screws  35 . The flange member  17  is provided with one or more lubricator ducts  18 , which connect a ring-like lubricator groove  21  to a lubricator groove  19  encircling the tappet arm  7 . In addition the flange member  17  is provided with a sealing ring  20  providing a seal between the flange member and the tappet arm  7 . An additional sealing ring provides a seal between the flange member and the body  1 . Fuel and/or lubricant possibly accumulating in a chamber  28  located above the flange member  17  are led away through a drain duct  29  (FIG.  3 ). By means of these arrangements it is possible to minimize the fuel being mixed with the lubricant. 
     With reference specifically to FIGS. 3 and 4 the body  1  includes a pipe element  1   a,  a duct  23  of which is part of a fuel line  32  of a fuel feeding system of the engine. In addition the fuel feeding system comprises a low pressure pump  31 , which pumps fuel from a fuel tank  30  to the pump and tappet units (for a matter of simplicity FIG. 4 shows only the bodies  1 ), pipes  33  connecting these units to one another through the pipe elements  1   a  and a constant pressure valve or a throttle valve  34 , through which the fuel line  32  is led back into the fuel tank  30 . 
     As is apparent from FIG. 3, in each pump and tappet unit the fuel is led from the duct  23  in the pipe element  1   a  onward through ducts  24 ,  25  and  26  into the duct  12 , schematically shown in FIGS. 1 and 2, which leads the fuel into the fuel chamber  11  of the pump. Integration of the pipe element  1   a  and the separate fuel ducts and lubricator ducts with the body  1  to be manufactured as a one-piece casting makes the construction simpler and thereby requires less space and costs. 
     In the embodiment of FIG. 3 the tappet arm  7  connecting the tappet member  2  to the piston member  8  is somewhat differently designed. The tappet arm  7  may be composed of two separate pieces which, however, form one functional entity due to the spring  9 . 
     The invention is not restricted to the embodiments shown but several modifications are feasible within the scope of the attached claims.