Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M63/00—Other fuel-injection apparatus having pertinent characteristics not provided for in groups F02M39/00 - F02M57/00 or F02M67/00; Details, component parts, or accessories of fuel-injection apparatus, not provided for in, or of interest apart from, the apparatus of groups F02M39/00 - F02M61/00 or F02M67/00; Combination of fuel pump with other devices, e.g. lubricating oil pump
  • F02M63/02—Fuel-injection apparatus having several injectors fed by a common pumping element, or having several pumping elements feeding a common injector; Fuel-injection apparatus having provisions for cutting-out pumps, pumping elements, or injectors; Fuel-injection apparatus having provisions for variably interconnecting pumping elements and injectors alternatively
  • F02M63/0205—Fuel-injection apparatus having several injectors fed by a common pumping element, or having several pumping elements feeding a common injector; Fuel-injection apparatus having provisions for cutting-out pumps, pumping elements, or injectors; Fuel-injection apparatus having provisions for variably interconnecting pumping elements and injectors alternatively for cutting-out pumps or injectors in case of abnormal operation of the engine or the injection apparatus, e.g. over-speed, break-down of fuel pumps or injectors ; for cutting-out pumps for stopping the engine
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M59/00—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps
  • F02M59/02—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps of reciprocating-piston or reciprocating-cylinder type
  • F02M59/10—Pumps specially adapted for fuel-injection and not provided for in groups F02M39/00 -F02M57/00, e.g. rotary cylinder-block type of pumps of reciprocating-piston or reciprocating-cylinder type characterised by the piston-drive
  • F02M59/102—Mechanical drive, e.g. tappets or cams
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B9/00—Piston machines or pumps characterised by the driving or driven means to or from their working members
  • F04B9/02—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical
  • F04B9/04—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical the means being cams, eccentrics or pin-and-slot mechanisms
  • F04B9/042—Piston machines or pumps characterised by the driving or driven means to or from their working members the means being mechanical the means being cams, eccentrics or pin-and-slot mechanisms the means being cams

Definitions

• the invention relates to a common rail fuel system for supplying high pressure fuel to an internal combustion engine.
• the invention also relates to a pump for use in such a fuel system, and to a cam arrangement forming part of the fuel system.
• Fuel systems are known in which the pump assembly includes a plurality of in- line pumping elements, each of which is driven by means of an associated shoe and roller arrangement.
• the roller of each arrangement cooperates with an associated cam, each of which is mounted upon a common drive shaft (the pump drive shaft).
• the shoe is arranged to cooperate with the pumping element such that as the rollers ride over their respective cam surfaces, the shoes are driven to cause the plungers to reciprocate within plunger bores, thereby causing pressurisation of fuel within an associated pumping chamber.
• the pumping chambers communicate with a common rail resulting in the production of high pressure fuel pulses which are then supplied to a plurality of fuel injectors.
• the pump drive shaft would be need to be driven at 5/6 of engine speed to give five pumping pulses per revolution of the crank shaft, and for an eight cylinder engine the pump drive shaft would need to be driven at 8/6 of engine speed to give eight pumping pulses per revolution of the crank shaft.
• different gearing systems would need to be used with engines having different numbers of cylinders, despite the use of a common pump which is suitable for use in different engines.
• an engine fuel system having an engine drive shaft and a multiple number of engine cylinders, the fuel system comprising at least three pump units, being less in total number than the number of engine cylinders, wherein each pump unit has a plunger and an associated drive arrangement including a cam mounted upon a pump drive shaft that is common to the cams of the other pump units, wherein first, second and third ones of the cams are shaped to include at least one rising flank to enable a plunger pumping stroke and at least one falling flank to enable a plunger return stroke, wherein the first and second cams are of similar form and the third cam is of dissimilar form, with the cams being oriented relative to each other on the pump drive shaft such that the pumping strokes of the plungers are substantially equally spaced in time and so that during a substantially complete revolution of the pump drive shaft they provide a total number of pumping strokes equal to the number of engine cylinders, thereby to permit the pump drive shaft to be driven at the same speed as the engine drive
• the first embodiment of the present invention advantageously provides a fuel system which is suitable for use in a five cylinder engine without the need for dedicated or complex gearing between the pump drive shaft and the engine drive shaft, as the pump drive shaft may be run at the same speed as the engine drive shaft.
• the fuel system may be used with a ten cylinder engine. This represents a significant cost saving and provides a system which can be standardised for a wide range of vehicles.
• first, second and third cams are shaped to include at least one rising flank to enable a plunger pumping stroke of an associated plunger and at least one falling flank to enable a plunger return stroke, the first and second cams being of similar form or shape and the third cam being of dissimilar form or shape, and wherein the first, second and third cams are oriented relative to each other on the pump drive shaft such that the pumping strokes of the plungers are substantially equally spaced in time and so that during a substantially complete revolution of an associated pump drive shaft provide a total number of pumping strokes equal to the number of engine cylinders.
• the pump drive shaft of the pump can therefore be driven at the same speed as the engine drive shaft, or at an integer multiple of the speed of the engine drive shaft.
• Changing the cam arrangement of the pump thus enables the pump to be adapted for use in engines having different numbers of engine cylinders without having to change and/or provide additional gearing between the engine drive shaft and the pump drive shaft.
• the first, second and third cams may, in one embodiment, be formed integrally with the pump drive shaft, so that the interchangeable cam arrangement includes an integral arrangement of the pump shaft and one or more cams.
• one or more of the cams may be formed as a separate part and may be machined such that it forms an interference fit with the pump drive shaft.
• At least one of the cams is shaped to delay onset of a return stroke of its associated plunger to define a dwell period. At least one of the return strokes is delayed so that the return strokes of that particular pump for a complete rotation of the pump drive shaft are not equally spaced in time. By delaying the onset of a return stroke in this way the plunger therefore dwells for a period of time at the top of its stroke, before the return stroke commences.
• the first and second cams are formed or shaped such that upon substantially a complete revolution of the pump drive shaft, in use, the first and second plungers each perform two return strokes, two pumping strokes and a dwell period, and the third cam is shaped such that a third plunger performs one pumping stroke and one return stroke and a dwell period, and wherein the first, second and third cams are oriented relative to one another such that five substantially equally spaced pumping strokes are performed during each complete revolution of the pump drive shaft.
• the cams are formed such that the dwell periods occur when the plungers are at their innermost positions in their respective bores, prior to the commencement of a return (or filling) stroke.
• the cams may be formed such that the dwell periods occur prior to the commencement of a pumping stroke, when the plungers are at their outermost positions in their respective bores.
• References to a complete revolution of the pump drive shaft are intended to mean a substantially 360 degree revolution of the pump drive shaft.
• the first and second cams may be profiled such that, in use, the associated dwell period is arranged to continue for approximately 72 degrees of rotation of the pump drive shaft, and the third cam may be profiled such that the associated dwell period is arranged to continue for approximately 216 degrees of rotation of the pump drive shaft.
• each pumping stroke is arranged to continue for approximately 72 degrees of rotation of the pump drive shaft, and each return stroke is also arranged to continue for approximately 72 degrees of rotation of the pump drive shaft.
• the pump of the system preferably includes, in one embodiment, a drive arrangement for each plunger having a roller which is cooperable with an associated cam to drive a shoe.
• the system is particularly applicable for use in a diesel internal combustion engine, and for delivering fuel at high pressures (150 to 2000 bar) to an accumulator volume, for example a common rail of the fuel system.
• a pump for use in the fuel system of the first aspect of the invention, the pump including the at least three pump units thereof.
• Figure 1 is a sectional side view of a known fuel pump which is suitable for use with the cam arrangement of the present invention
• Figure 2 shows a cam arrangement forming part of the fuel pump in Figure 1 , for use in a six cylinder engine, for example;
• Figure 3 shows the profiles of the surfaces of the identical first and second cams of the cam arrangement of Figure 2;
• Figure 4 is a graph showing plunger lift for the fuel pump of Figure 1 incorporating the cam arrangement of Figure 2;
• Figure 5 shows a cam arrangement of the present invention, which may be used in the fuel pump of Figure 1 in a five cylinder engine;
• Figure 6 shows the profile of the surfaces of first and second identical cams of the cam arrangement of Figure 5;
• Figure 7 shows the profile of the surface of a third, dissimilar cam of the cam arrangement of Figure 5.
• Figure 8 is a graph showing plunger lift for the fuel pump of Figure 1 incorporating the cam arrangement of Figure 5.
• a fuel pump 10 of generally known type which forms part of a fuel injection system of a diesel engine and which may be adapted in accordance with the present invention.
• the fuel pump 10 includes three pump assemblies 12a, 12b, 12c which are arranged to supply fuel at high pressure to a common rail or accumulator volume (not shown) of the fuel injection system.
• Each pump assembly 12a, 12b, 12c includes a respective pumping element or plunger 14a, 14b, 14c which is moveable within a plunger bore 32a,32b,32c provided in a first pump housing 16 to cause pressurisation of fuel within an associated pumping chamber 18a, 18b, 18c.
• each pump assembly 12a, 12b, 12c is substantially identical to the others, only the structure and operation of the first pump assembly 12a will be described in detail.
• the plunger 14a of the first pump assembly 12a is driven though a pumping cycle by means of a drive arrangement.
• the drive arrangement includes a shoe 20a which is cooperable with a base end of the first plunger 14a, and a roller 22a which cooperates with a surface of a first cam 24a mounted upon a pump drive shaft 26 that is common to each pump assembly 12a, 12b, 12c.
• the pump drive shaft 26 extends through a second pump housing 27 and is driven, in use, so that the roller 22a rides over the cam surface and drives the shoe 20a and plunger 14a to reduce the volume of the pumping chamber 18a (i.e. the plunger 14a is driven inwardly within its plunger bore 32a).
• Each plunger 14a, 14b, 14c has an associated return spring 28a,28b,28c which serves to urge its respective plunger outwardly from its 32a,32b,32c bore to increase the volume of the pumping chamber 18a, 18b, 18c.
• the second pump housing 27 is secured to an intermediate housing 25 mounted upon the first pump housing 16.
• the intermediate housing 25 is shaped to define a chamber (not shown) through which a lower portion of the plunger 14a extends. This chamber is partially filled with engine oil which serves to lubricate the shoe and roller arrangement 20a, 22a so as to improve durability.
• each pump assembly 12a,12b,12c includes a respective shoe and roller arrangement which is driven by an associated shaft mounted cam 24a,24b,24c.
• the cams 24a,24b,24c are axially spaced along the pump drive shaft 26 and arranged such that the pumping plungers 14a, 14b, 14c reciprocate within their respective bores 32a,32b,32c as the pump drive shaft 26 is rotated at a speed associated with the engine.
• fuel is supplied by means of a transfer pump 38 to an inlet metering valve (not shown).
• the inlet metering valve is arranged to vary the rate of flow of fuel into the pumping chambers 18a,18b,18c through an inlet passage 19 via an inlet check valve arrangement (also not shown).
• the transfer pump 38 typically takes the form of a conventional vane pump mounted upon the pump drive shaft 26 at a rear end of the second pump housing 27.
• Each pump assembly 12a, 12b, 12c is also provided with an outlet delivery valve arrangement to control fuel flow between the pumping chambers 18a, 18b, 18c and a high pressure supply passage (not visible in Figure 1) to the common rail.
• the pumping cycle through which the first pumping plunger 14a is driven, in use includes a pumping stroke and a return stroke.
• the pumping plunger 14a adopts its innermost (i.e. uppermost in Figure 1) position within its plunger bore 32a, and fuel pressure within the pumping chamber 18a is high due to the pressurisation which has been caused during the pumping stroke.
• the outlet valve arrangement is closed due to the equalisation of fuel pressures in the pumping chamber 18a and the common rail.
• the pumping plunger 14a Upon commencement of its return stroke, the pumping plunger 14a is initially allowed to retract from its bore 32a due to decompression within the pumping chamber 18a and retraction of the shoe 20a under the force of the return spring 28a as the roller 22a rides over the surface of the first cam 24a.
• the roller 22a is urged in an upward direction.
• the roller 22a follows the surface of the first cam 24a, causing the shoe 20a to be urged in an upwards direction and hence the pumping plunger 14a to be driven inwardly within its plunger bore 32a.
• Fuel within the pumping chamber 18a is unable to flow past the closed delivery valve due to high fuel pressure within the rail, and hence fuel pressure within the pumping chamber 18a starts to increase.
• fuel within the pumping chamber 18a is pressurised to a sufficiently high level to cause the outlet delivery valve to open, thereby permitting pressurised fuel to flow from the pumping chamber 18a into the common rail.
• the outlet delivery valve is caused to close due to high pressure fuel within the rail, thus holding fuel pressure within the rail at a high level.
• the plunger 14a is urged outwardly from its bore 32a by a force due to the return spring 28a (acting in combination with residual fuel pressure within the pumping chamber 18a), to commence the next filling phase.
• FIGS 2 and 3 show the cams 24a, 24b, 24c of the pump in Figure 1 in further detail, the cams 24a, 24b, 24 collectively being referred to as a cam arrangement 100.
• Each cam includes two generally circular end regions in the form of a nose 50 and a base 52, a first generally flat side 54 and a second generally flat side 56.
• the nose and base portions 50, 52 of the cam are substantially identical.
• Each cam 24a, 24b, 24c is symmetrical about a minor diameter X-X, which extends between the first and the second flattened sides 54, 56, and about a major diameter Y-Y, which extends from the nose 50 to the base 52 of each cam.
• each cam 24a, 24b, 24c having two rising flanks and two falling flanks so that the plungers 14a, 14b, 14c associated with each cam 24a, 24b, 24c perform two pumping strokes (one corresponding to or being enabled by the first rising flank and the other corresponding to or being enabled by the second rising flank) and two return strokes during a pumping cycle comprising one revolution of the pump drive shaft 26.
• the cams 24a, 24b, 24c are oriented at angularly offset positions of 60 degrees with respect to one another, so that the cam arrangement 100 produces six equally spaced pumping pulses per revolution of the pump drive shaft 26.
• the cam arrangement 100 is therefore suitable for use, in particular, with a six cylinder engine.
• the profiles of the cam surfaces will now be described in further detail with reference to Figure 3.
• the surfaces of the cams 24a, 24b, 24c comprise (starting from the centre of the first flattened side 54) a first bottom dwell portion 58, a first rising flank portion 60, a first top dwell portion 62, a first falling flank portion 64, a second bottom dwell portion 66, a second rising flank portion 68, a second top dwell portion 78, and lastly a second falling flank portion 72.
• the dwell portions 58, 62, 66 and 78 are so-named because as the rollers 22a, 22b, 22c travel over these regions of their associated cam surface the associated plunger 14a, 14b, 14c is caused to 'dwell' or 'pause' for a while, not moving inwardly or outwardly from the plunger bore but maintaining a substantially constant position.
• each of the first, second and third pumping plungers 14a, 14b, 14c performs the following sequence of events in response to respective rollers 22a, 22b, 22c following the cam profiles: a first pumping stroke, a first top dwell, a first return stroke, a first bottom dwell, a second pumping stroke, a second top dwell, a second return stroke, and a second bottom dwell.
• the dwell portions are shaped to define dwell periods of relatively short duration, although it is also possible to shape the surfaces of the cams 24a, 24b, 24c to provide no short dwells at all.
• the roller 22a of the first pump unit is in contact with the first bottom dwell portion of the first cam 24a and the first plunger 14a is at its outermost position within its bore 32a (i.e. at the bottom of its stroke).
• the roller 22b of the second pump unit is in contact with the first falling flank portion 64 of the second cam 24b
• the roller 22c of the third pump unit is in contact with the first rising flank portion 60 of the third cam 24c.
• the roller 22a travels up the rising flank portion 60 of the first cam 24a. This causes the first plunger 14a to be raised within its bore 32a and the first pumping stroke to be commenced.
• the first plunger 14a will be at its innermost position within its bore 32a with the roller 22a engaged with the nose 50 of the first cam 24a.
• the first plunger 14a dwells at the top dwell portion 62 top of its stroke for a short period of time.
• the roller 22a travels from the nose 50 of the cam down the first falling flank portion 64. During this period the first plunger 14a is lowered in its bore 32a as it performs its first return stroke.
• the plunger 14a reaches the bottom of its stroke at 180 degrees, whereupon it dwells for a short period of time at the second bottom dwell portion 66.
• the first cam 24a causes the first pumping plunger 14a to move up within its bore 32a, thereby performing the second pumping stroke as the roller 22a travels from the centre 56 of the second side to the base of the first cam 24a (along the second rising flank portion 68).
• the first plunger 14a is raised to its innermost position in its bore (at 270 degrees) where it dwells briefly at the second top dwell portion 78.
• the first plunger 14a then completes its second return stroke as the cam shaft rotates from 270 to 360 degrees, the roller 22a traversing the second falling flank portion 72 of the first cam 24a to return to the first bottom dwell portion 58.
• the second 14b and third 14c plungers complete the same series of pumping events as the first plunger 14a, but with events out of phase with one another by 120 degrees. Due to the plungers being offset from one another by 60 degrees, the pumping events of the second pumping plunger 14b follow those of the first plunger 14a by substantially 60 degrees, and those of the third plunger 14c follow those of the second plunger 14b by substantially 60 degrees.
• the first plunger 14a is at the top of its stroke at 30 degrees from reference position A
• the second plunger 14b is at the top of its stroke at 90 degrees
• the third plunger 14c is at the top of its stroke at 150 degrees
• the first plunger 14a is at the top of its stroke again at 180 degrees, and so on.
• the cam arrangement 100 of Figures 2 and 3 may also be used in a 12 cylinder engine by running the pump drive shaft 26 at twice the speed of the crank shaft.
• the pump drive shaft 26 may, in theory, be run at any integer multiple speed of the engine drive shaft to provide an equal number of pumping strokes to the number of engine cylinders, with the pumping strokes being equally spaced in time.
• the number of engine cylinders is not an integer multiple of the number of plungers of the pump (e.g. three).
• the invention sets out to address this problem, and does so by providing a cam arrangement having three cams, but one of which is of different form to the other two, and providing the cams at selected angular positions on the drive shaft 26 to be able to drive the shaft 26 at engine speed (or at an integer multiple of engine speed), whilst providing the required number of pumping strokes per cycle to match the number of engine cylinders.
• FIG. 5 there is shown a cam arrangement 101 of an embodiment of the present invention which is suitable use with a fuel pump 10 of the type shown in Figure 1 and which replaces the cam arrangement 100 shown in Figures 2 and 3.
• the cam arrangement 101 comprises first, second and third cams 24a, 24b, 24c, which are arranged on the pump drive shaft 26 at axially spaced locations and oriented about the drive shaft at angularly offset positions.
• the pump includes the cam arrangement 101 of Figure 5
• the pump is suitable, in particular, for use in a five cylinder engine.
• first 24a and second 24b cams of the cam arrangement 101 are of substantially identical form, and are similar in shape to conventional cams which comprise (in cross-section) a generally base-like section of part-circular form having a cam nose.
• each of the first and second cams 24a, 24b has a base section 52 of substantially part-circular form having a radius R, the base section 52 being spaced apart from an opposite dominant cam nose 50 of substantially part-circular form and having a radius r (where R>r) by pinched (or concave) first and second sides, 54 and 56 respectively.
• the first and second cams 24a, 24b therefore each have one rising flank and one falling flank on one cam side 54 and another rising flank and another falling flank on the other cam side 56.
• the first rising flank corresponds to, or enables, a first pumping stroke and the second rising flank corresponds to, or enables, a second pumping stroke.
• each of the associated plungers 14a, 14b is driven to perform two pumping strokes and two return strokes with each pumping cycle comprising one complete or full 360 degree revolution of the pump drive shaft 26 (when performing a pumping stroke, the roller 22a,22b rides up a rising flank of the associated cam 24a,24b as it rotates, and during a return stroke the roller rides down a falling flank).
• the first and second 24a,24b cams are also profiled such that at the end of one of the plunger pumping strokes, but before the onset of the next return stroke, the roller 22a,22b dwells for a relatively long period of time at the peak of one of the rising flanks (referred to as long top dwell).
• the cams 24a,24b may be profiled such that between one of the plunger pumping strokes and the following return stroke, the roller 22a,22b dwells for a short period of time at the peak of one of the rising flanks (referred to as short top dwell).
• a period of short bottom dwell may also be provided so that, at the end of the return stroke, the roller 22a,22b dwells for a short period of time before commencing the following pumping stroke.
• each of the cams 24a, 24b includes a first rising flank portion 60, a first short top dwell portion 62, a first falling flank portion 64, a first short bottom dwell portion 66, a second rising flank portion 68, a long top dwell portion 70, a second falling flank portion 72, and a second short bottom dwell portion 58.
• the first pumping plunger 14a performs the following sequence of events in response to the roller 22a following the cam surface: a first pumping stroke over 60, a first short top dwell period over 62, a first return stroke over 64, a first short bottom dwell period over 66, a second pumping stroke over 68, a long top dwell period over 70, a second return stroke over 72, and a second short bottom dwell period over 58.
• the second pumping plunger 14b performs an identical sequence of events to the first pumping plunger 14a, except that the second plunger events follow those of the first plunger by about 72 degrees, as will be explained in more detail below.
• the third pumping plunger 14c Upon a complete 360 degree revolution of the drift shaft 26, the third pumping plunger 14c performs the following sequence of events in response to the third roller 22c following the profile of the third cam surface: a long dwell period over 76, a return stroke over (or enabled by) the falling flank 64, a short bottom dwell period over 66, and a pumping stroke over (or enabled by) the rising flank 60.
• the third cam surface may be profiled such that no short bottom dwell period is provided.
• the first, second and third cams 24a, 24b, 24c are mounted upon the pump drive shaft 26 such that the noses 50 of the first and second cams 24a, 24b and the concave relief portion 74 of the third cam 24c are angularly offset by substantially 72 degrees.
• the first roller 22a rides up the first rising flank 60 of the first cam 24a so that the first plunger 14a is raised within its bore 32a and the pumping stroke is commenced. While this is occurring, the second roller 22b rides down the second falling flank portion 72 of the second cam 24b thereby causing the second pumping plunger 14b to be lowered in its bore 32b (i.e. during the return stroke).
• the third roller 22c meanwhile is maintained in contact with the generally part-circular dwell portion 76 of the third cam 24c so that the third plunger 14c remains at its innermost position within its bore 32c.
• the first plunger 14a dwells briefly at the end of its first pumping stroke
• the second plunger 14b dwells briefly at the end of its return stroke
• the third plunger 14c remains at the top of its stroke.
• the first roller 22a traverses from the first short top dwell portion 62 of the first cam 24a to the first falling flank portion 64, thereby causing the first plunger 14a to be lowered in its bore 32a.
• the second roller 22b rides up the first rising flank portion 60 towards the second cam nose 50.
• the third roller 22c is maintained in contact with the circular dwell portion 76 of the third cam 24c and so the third plunger 14c dwells at the end of its pumping stroke.
• the first plunger 14a dwells briefly at the end of its return stroke
• the second plunger 14b dwells brief at the end of its pumping stroke
• the third plunger 14c remains innermost in its bore 32c at the end of its pumping stroke.
• the first roller 22a travels along the second rising flank 68 of the first cam 24a and towards the base 52 thereof. This causes the first plunger 14a to move from its outermost to its innermost position within the bore 32a so as to perform a pumping stroke.
• the second roller 22b travels down the first falling flank portion 64 of the second cam 24b, thereby causing the second plunger 14b to move from its innermost to outermost position within its bore 32b to carry out a return stroke.
• the third roller 22c is again maintained in contact with the long dwell portion 76 of the third cam 24c and is thus kept at the top of its stroke.
• the second plunger 14b dwells briefly at the bottom of its stroke, while both the first and third plungers 14a, 14c remain innermost in their respective bores 32a,32c.
• the next period of the pumping cycle takes place between 216 and 287 degrees of revolution of the pump drive shaft 26.
• the first roller 22a is travelling along the base 52 of the first cam 24a which defines the long top dwell portion 70, thereby causing the first plunger 14a to dwell at the top of its stroke for the whole of this period.
• the second roller 22b travels along the second rising flank portion 68 of the second cam 24b thereby causing the second plunger 14b to rise from the bottom of its stroke to the top of its stroke and perform a second pumping stroke.
• the third roller 22c meanwhile rides to the centre of the concave relief portion 74 of the third cam 24c causing the third plunger 14c to be lowered from its innermost to its outermost position within its bore 32c to perform a return stroke.
• the third plunger 14c dwells briefly at the bottom of its stroke, while the first and second plungers 14a, 14b remain innermost in their respective bores 32a,32b.
• the first roller 22a travels along the second falling flank portion 72 causing the first plunger 14a to be lowered from its innermost to its outermost position within its bore 32a to carry out a second return stroke.
• the second roller 22b meanwhile travels along the long top dwell portion 70 of the second cam 24b, thereby causing it to dwell at the top of its stroke during this period.
• the third roller 22c travels from the centre of the concave relief portion 74 of the third cam 24c to move the third plunger 14c from the bottom of its stroke to the top of its stroke such that a pumping stroke is performed.
• first and second cams 24a, 24b of the cam arrangement 101 have been described as having short bottom dwell portions 66 and 58 and a short top dwell portion 62, and the third cam 24c has been described as having a short bottom dwell portion 66, it will be apparent to the skilled person that the first, second and third 24a, 24b, 24c cams may be profiled such that substantially no such short top and bottom dwell portions are provided. It is one feature of the cam arrangement 101 described previously that its implementation in a fuel pump of an engine having five (or ten) engine cylinders provides a regular spacing of pumping strokes per cycle to match the number of engine cylinders.
• the pump drive shaft 26 can therefore be driven at engine speed (for a five cylinder engine), or at an integer multiple of engine speed (for a ten cylinder engine), matching pumping frequency to fuel injection frequency without the requirement for dedicated or complex gearing between the engine shaft and the pump drive shaft 26. It is a further advantageous feature of the invention that it can be readily be incorporated into existing pump installations by replacing the existing pump drive shaft and cams to co-operate with the existing plungers of the pump. So, for example, for an engine manufacturer, an existing type of pump can be adapted or converted conveniently for use in another engine by selecting a cam arrangement in accordance with the present invention, that is appropriate to provide the required number of pumping strokes per cycle for the number of engine cylinders. For example, the cam arrangement 101 in Figures 5 is also particularly suitable for use in a ten cylinder engine by running the camshaft at twice the speed of the crank shaft, again without the need for complex gearing.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Fuel-Injection Apparatus (AREA)
• Reciprocating Pumps (AREA)

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• 2004
  • 2004-10-15 AT AT04768917T patent/ATE357589T1/de not_active IP Right Cessation
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  • 2004-10-15 DE DE602004005489T patent/DE602004005489T2/de not_active Expired - Lifetime
  • 2004-10-15 WO PCT/GB2004/004387 patent/WO2005038234A1/fr active IP Right Grant

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