Abstract:
A multi-chamber positive displacement pump comprises a unitary housing in which is formed a plurality of cylinders. A pumping plunger is slidably mounted in each cylinder to define a pumping chamber. Means are provided for reciprocating the pumping plungers in order cyclically to vary the volume of the pumping chambers to effect delivery of a pumped fluid from the pumping chambers. A delivery passage is connected to each of the pumping chambers to receive pumped fluid therefrom, the delivery passage comprising at least one gallery formed in the unitary housing and open to an end face of the housing and passageways which extend through the unitary housing from the galleries to the pumping chambers. The galleries are closed by an end plate which is secured to the unitary housing. Feed passages and working fluid passages may likewise be defined by combination of galleries in the end face and passageways in the unitary housing. Preferably, all the galleries are in the same end face and are closed by a common end plate which acts as a mounting plate for the pump.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a multi-chamber positive displacement pump, and in the preferred embodiment of the invention provides a positive displacement pump suitable for delivering high pressure fuel to the fuel injection system of an internal combustion engine. It is to be understood, however, that the invention is not limited to this application and may be utilised in a wide range of multi-chamber positive displacement pumps. 
     2. State of the Art 
     Common rail fuel injection systems for internal combustion engines require the provision of a high pressure pump for supplying fuel at high pressure to the common rail or to an accumulator associated therewith. Such pumps must typically operate at pressures up to 1600 bar, and may in the future need to operate at pressures in excess of 2000 bar, and must accordingly be of the positive displacement type. In order to utilise common rail fuel injection technology in mass produced automobile engines the required fuel pump must be effective at delivering the required fuel volume and pressure, but must in addition be highly reliable, compact, and economical to manufacture. The requirements for compact and economical design are particularly difficult to meet in a pump which is required to deliver fuel reliably over many years at the pressures required by common rail fuel injection systems. 
     Whilst it is generally recognised that reducing the number of individual components in a particular assembly leads to an increase in reliability and a reduction in manufacturing costs, this general desideratum is often at variance with requirements for a compact design and is particularly difficult to achieve in a relatively complex mechanism such as a multi-chamber positive displacement pump. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a multi-chamber positive displacement pump in which the number of individual components is reduced as compared with prior art pumps without significant sacrifice in terms of reliability or compactness of design. 
     According to one aspect of the present invention there is provided a multi-chamber positive displacement pump comprising: a unitary housing in which is formed a plurality of cylinders; a pumping plunger slidably mounted in each cylinder to define a pumping chamber; means for reciprocating the pumping plungers in order cyclically to vary the volume of the pumping chambers to effect delivery of a pumped fluid from the pumping chambers; and a delivery passage connected to each of the pumping chambers to receive pumped fluid therefrom, the delivery passage comprising at least one gallery formed in the unitary housing and open to an end face of the housing and passageways which extend through the unitary housing from the gallery to the pumping chambers, the gallery being closed by an end plate which is secured to the unitary housing. 
     The use of a unitary housing which defines both the pumping chambers and the delivery passageway in association with an end plate which closes the galleries which form part of the delivery passages reduces to a minimum the number of components necessary for the body of the pump and minimises the number of high pressure seals required within the pump. The reduction in the number of components required and the resultant reduction in the number of seals which must be effected significantly reduces the production costs of the pump and improves the reliability thereof. In the preferred embodiment of the invention these improvements are achieved without any sacrifice in the overall size of the pump, as compared with comparable pumps having a larger number of individual components. 
     In the preferred embodiment of the invention the passageways in the unitary housing which form part of the delivery passage are formed by drillings which are machined from the galleries. The galleries can be formed in an end face of the housing by any convenient means, for example when the housing is forged or cast or as a subsequent machining operation, and can be formed to facilitate drilling of the passageways as required. In the preferred embodiment of the invention, in which the pump has three pumping chambers, it is preferred to provide three galleries each close to an associated pumping chamber. A delivery valve is located in a bore which connects each gallery to its associated pumping chamber and passageways associated with two of the galleries connect those galleries to the third gallery. Preferably, an outlet passage extends though the unitary housing from the third gallery to the exterior of the pump. 
     Preferably, the feed passages which are required to feed fluid which is to be pumped to the pumping chambers are also formed by way of galleries in an end face of the unitary housing and passageways formed in the unitary housing. The end face in which the feed galleries are formed can conveniently be the same end face as that in which the delivery galleries are formed whereby the end plate can be used to close both the delivery galleries and the feed galleries. In the case of a pump in which hydraulic pressure is used to effect movement of the pumping plungers in the feed direction, the working fluid passages which are used to supply working fluid to the pumping plunger return pistons are also formed by way of galleries in an end face of the unitary housing and passageways formed within the unitary housing. Again, the end face in which the working fluid galleries are formed is preferably the same end face as that in which the delivery galleries are formed, and the end plate is used to close the working fluid galleries. 
     In a particularly preferred embodiment of the invention delivery galleries, feed galleries and working fluid galleries are all formed in the same end face of the unitary housing and a common end place is used to close all the galleries. 
     In a particularly preferred embodiment of the invention the unitary housing defines a central chamber which houses the cam or crank mechanism used for driving the pumping plungers. In this case, an aperture is provided in the unitary housing extending from the exterior thereof to the central chamber at a point diametrically opposite each of the cylinders. The aperture may be used to gain machining access for the purposes and machining the cylinders and any bores required to house tappet gear or return pistons associated with the pumping plungers. After manufacture, the apertures are preferably closed by a plug. Under these circumstances, the feed passageways and/or the working fluid passageways can extend via the aperture. In the preferred embodiment, the working fluid passageways extend via the apertures and the closure plugs used to close the apertures after manufacture incorporate a peripheral groove to provide communication through the aperture between different parts of the working fluid passageways. 
     It will be appreciated that the effective closing of the delivery galleries is of critical importance. Given the very high pressures present in the delivery galleries it is difficult to provide conventional elastomeric seals which will be effective to give the required sealing. Accordingly, in the preferred embodiment of the invention the delivery galleries are sealed at the end plate by means of deformable hard material seals which, during assembly of the pump, are squeezed between the end plate and the unitary housing. By way of example, the hard material may be soft iron. In order to exert the clamping force necessary to deform the soft iron into sealing engagement with the unitary housing the screws used to secure the end plate to the unitary housing are preferably positioned adjacent each delivery gallery. Preferably, each delivery gallery has associated therewith at least two screws to produce the required clamping force. 
     The pressures present in the feed galleries and working fluid galleries are very substantially lower than those associated with the delivery galleries and accordingly the feed galleries and working fluid galleries can be sealed at the end plate by means of an appropriate elastomeric seal. In the preferred embodiment of the invention, a single elastomeric seal component effects sealing of all the feed galleries and all the working fluid galleries. 
     In the preferred embodiment of the invention a hydraulic piston arrangement is used to effect each return (fill) stroke of each pumping plunger. To this end, the tappet associated with each pumping plunger works in a cylinder machined in the unitary housing. Because of the unitary nature of the housing and the fact that both the tappet cylinder and the pumping cylinder can be machined simultaneously (or at least during the same automated machining sequence) means that there is no danger of misalignment of each pumping cylinder and its associated tappet cylinder. This means that arrangements for compensating for misalignment (such as are, for example, described in out co-pending European Patent Appliance EP-A-0972936) are not required in the case of the preferred embodiment of the present invention and a relatively simple connection between each pumping plunger and its associated tappet is all that is required. Because of this, if required, means can be provided for preventing rotation of the tappets about that their longitudinal axes. These means may, for example, be formed by a ridge in the interior space of each tappet which engages a slot formed in the unitary housing. The required ridge can, for example, be formed easily if the tappets are of sintered construction. 
     The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying Drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section on the line I—I of FIG. 2 showing a preferred embodiment of multi-chamber positive displacement pump according to the present invention; 
     FIG. 2 is a cross-section on the line II—II of FIG. 1; 
     FIG. 3 is a view of the end face of the housing of the pump of FIGS. 1 and 2; 
     FIG. 4 is a view of the face of the end plate of the pump of FIGS. 1 and 2 which mates with the end face of the pump housing; 
     FIG. 5 is a perspective ghost view of the housing of the pump of FIGS. 1 and 2, with the various internal passageways and galleries of the housing shown; 
     FIG. 6 illustrates in detail the tappet assembly associated with one of the pumping plungers of the pump of FIGS. 1 and 2; and 
     FIG. 7 is a cross-section on the line VII—VII of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, the illustrated pump  1  comprises a unitary housing  2  of, for example, steel. The housing comprises a forging or casting which has been machined to provide various apertures, passageways and galleries. The end face  3  (FIG. 3) of the housing is flat and mates, in use, with an end plate  4  which is secured to the unitary housing by suitable bolts or screws which engage threaded holes  5  formed in the unitary housing  2 . 
     Conveniently, the end plate  4  may be used to mount the pump on the cylinder block of its associated engine. To this end, the end plate is formed with lugs  44  having fixing holes  45 . To the extent that different engines will require different fixing hole arrangements these can readily be accommodated by using different end plates. 
     The housing  2  defines a central chamber  6  which, in the assembled pump, houses the eccentric  7  of a crank shaft  8  which is mounted in the housing  2  and end plate  4  by means of respective bearings  9 , 10 . Three pumping cylinders  11  are formed in the unitary housing by machining via apertures  12  which extend from the exterior of the housing to the chamber  6 . 
     Each cylinder  11  has slidably mounted therein a pumping plunger  13  so that three pumping chambers  14  are formed. It will be noted that the pumping chambers  14  are formed entirely within the unitary housing  2  and the pumping plungers and only these two components are used to form and close the pumping chambers. 
     In order to effect the required movement of the pumping plungers  13  in the forward (delivery) direction, each pumping plunger  13  has secured thereto a tappet assembly  15  which includes a roller  16  rotatably mounted on a shaft secured to a tappet shell  17 . In use, as the crank shaft  8  is rotated, the pumping plungers  13  are successively moved from bottom dead centre to top dead centre to deliver pumped fluid from the pumping chambers  14 . In order to effect the return (fill) stroke of each pumping plunger  13 , a suitable working fluid, for example pressurised fuel, or pressurised lubricating oil from an engine lubrication system, is delivered to a working chamber  18  defined between each respective tappet shell  17  and the unitary housing  2 . The presence of pressurised fluid in the chambers  18  exerts a continuous radially inward force on the tappet shell  17 . This force is transmitted from the tappet shells  17  to the pump plungers  17  and is sufficient to effect the required return (fill) stroke of the pumping plungers. 
     In order to provide for operation in the pump described above three separate sets of passages are required, namely: a delivery passage for receiving pumped fluid from each of the pumping chambers and delivering such fluid to the pump outlet; a feed passage to take fluid to be pumped from the pump inlet to each of the pumping chambers; and a working fluid passage to provide working fluid to the chambers  18  to effect the return (fill) strokes of the pumping plungers. In the case of the preferred embodiment of the invention the various passages are provided by means of passageways and galleries formed in the unitary housing  2 , the galleries being closed by the end plate  4 . This arrangement gives rise to a particularly desirable configuration in which the number of seals required is small and the design is compact. 
     With further reference to FIGS. 3-5, and referring firstly to the delivery passage, this is formed by delivery galleries  19 ,  20  and  21 , a delivery passageway  22  which connects the delivery gallery  20  to the delivery gallery  19 , a delivery passageway  23  which connects the delivery gallery  21  to the delivery gallery  19 , and an outlet passage  24  which connects the delivery gallery  19  to an appropriate outlet fitting secured to the pump. The galleries  19 ,  20  and  21  are formed in the end face  3  of the unitary housing, for example by machining. The galleries can be easily formed to an optimum profile, for example the ends may be part-spherical to avoid stress concentrations and to provide optimum entry conditions for drilling the passageways  22 ,  23  and  24 . Each of the galleries  19 ,  20 ,  21  is connected directly to its associated pumping chamber  14  by means of a drilling  25  which houses a delivery valve  26 . The passageways  22 ,  23  and  24 , and the drillings  25  are all formed exclusively in the unitary housing. 
     In order to close the galleries  19 ,  20 ,  21  at the end face  3 , suitable seals (not shown), for example of soft iron, are provided in conforming slots  27  (FIG. 4) provided in the end plate  4 . The thickness of the seals is slightly greater than the depth of the slots, and the area of each slot is slightly larger than the area of its corresponding gallery so that the seals are squeezed firmly against the zone of the housing end face  3  surrounding the galleries as the end plate is bolted to the housing. It will be noted in this context that the fixing screws used to secure the end plate  4  of the housing  2  are located immediately adjacent the galleries with each gallery being located substantially between two screws. Accordingly, a massive clamping force is available to ensure an adequate high pressure seal. The high pressure seals effected at the galleries are the only high pressure seals required in the entire delivery passage network. 
     In a manner similar to that described above with reference to the delivery passage, the feed passage is provided by way of feed galleries  28 ,  29  and  30  provided in the end face  3  of the housing  2  and feed passageways  31 ,  32  and  33  formed in the housing. The feed passageway  31  extends through the housing from the feed gallery  28  to the feed gallery  30 ; the feed passageway  32  extends through the housing from the feed gallery  30  to the feed gallery  29 ; and the feed passageway  33  extends through the housing from the feed gallery  29  to the feed gallery  28 . It will be noted that each feed gallery  28 ,  29 ,  30  is accordingly connected to each of the adjacent feed galleries. This arrangement minimises back pressure as a result of flow resistance and inertia. Two parallel though unequal length paths are available from the metering valve to each feed gallery. Each feed gallery is connected to its associated pumping chamber  14  by a passage  34  which extends through the housing and enters its associated pumping chamber  14  at a point immediately radially outwardly of the position of the end face of the associated pumping plunger when the pumping plunger is at bottom dead centre. 
     Working fluid, for example pressurised fuel or lubricating oil, is fed to the working chambers  18  via working fluid galleries  35 ,  36 , and  37  formed in the end face  3  of the housing  2  and by means of working fluid passageways  38 ,  39 ,  40 . The working fluid passageway  38  connects the working fluid gallery  35  to the working fluid gallery  36 ; the working fluid passageway  39  connects the working fluid gallery  35  to the working fluid gallery  37 ; and the working fluid passageway  40  connects the working fluid gallery  36  to the working fluid gallery  37  The working fluid passageways  38 ,  39 ,  40  are formed in the unitary housing  2  and extend via the apertures  12  which extend from the exterior of the body to the central chamber  6 . To this end, closure plugs  41  (FIG. 4) which close the apertures  12  are each formed with a peripheral groove  42  to give the necessary continuity to the working fluid passageways. It will be appreciated that the pressure present in the working fluid passageways is relatively small and, in any event, any small leakage of working fluid from the grooves  42  inwardly to the chamber  6  will assist in lubricating the crank shaft and tappet rollers. The plugs  41  are pressed into position and are self-sealing to the pump exterior. The working fluid passage arrangement described above provides working fluid passages of generous proportions which is desirable in preventing excessive pressure spikes due to flow accelerations and ensures that there are periods of each revolution when the pressure in the working fluid circuit is low enough to permit make up of leakage past the tappets from the inlet pressure. If necessary, a pressure accumulator is provided in the working fluid circuit and a non-return valve isolates the working fluid circuit from the source of working fluid when pressure in the working fluid passage exceeds the inlet pressure of the working fluid. 
     The feed galleries and working fluid galleries are sealed at the end plate  4  by means of an elastomeric seal. The arrangement of the galleries facilitates use of a single seal component to effect required sealing. The seal component may be an elastomeric seal of “O” cross-section in which case a groove  43  (FIG. 4) is formed in the end plate to house the required seal component. Alternative sealing arrangements for the feed galleries and working fluid galleries may be used. It will be noted in this context that the operating pressures within these galleries are relatively small and accordingly no great difficulty should be encountered in providing effective sealing. 
     It will be appreciated that in the above described pump the pumping cylinders  11  can be machined simultaneously with, or at least during the same machining operation as, the cylinders forming the working chambers  18 . Accordingly, there is no risk of either axial or angular misalignment of the pumping cylinders  11  with the associated cylinders in which the tappets  15  slide. For this reason, a relatively simple connection between the pumping plungers  13  and their associated tappet assemblies  15  is possible. This connection can be effective, for example, by way of a circlip. This is in contrast to the arrangement described in our U.K. patent application 9815272 where, because of possible misalignment between the cylinders in which the pumping plungers work and the cylinders in which the tappets work a relatively complicated connection between the pumping plungers and the tappets is required. As a result of the relatively simple connection arrangement required by the present invention, means may be provided, if desired, for preventing rotation of the tappets within their bores. During pumping action the tappet rollers align themselves to the cam face. However, at top and bottom of stroke the tendency of the rollers to align themselves with the cam is small and unwanted twisting of the tappets could occur. Also, because hydraulic force is used to maintain the tappet rollers in engagement with the cam there is the possibility on assembly or at start up that misalignment may occur. In a preferred embodiment of the present invention and as seen in FIGS. 6 and 7 each tappet shell  17  is formed with an inwardly extending ridge  53  which runs in a corresponding slot  54  formed in the spigot  55  which defines the cylinder  11 . The slot  54  may be formed easily by drilling subsequent to, but in the same machining operation as, the pumping cylinders and tappet cylinders are formed. 
     Conveniently, the ridge  53  can be formed when the tappet shell is moulded prior to sintering, if a sintering process is employed to produce the tappet blank. The ridge  53  can be machined to provide a seating for the plunger retaining circlip  56  or, in the alternative, may be used to align the gap in the circlip which would facilitate rotationally fixing the pumping plunger to the tappet shell, if this was required. 
     The working fluid may be fuel supplied to the positive displacement pump from a low pressure transfer pump or may be pressurised lubricating oil, for example from the engine lubrication system. In either event, a backleak connection may be provided to allow a circulation of working fluid to ensure that the working fluid does not become overheated. 
     If desired, tappet orientation may be effected by means of screwed-in plugs rather than the ridges described above.