DIESEL ENGINE FUEL INJECTION PUMP WHICH PISTONS ARE SEALED WITH ALL METAL SEAL RINGS

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CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to the Korea Patent Application No. 10-2006-0031762, filed Apr. 7, 2006, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The presently claimed invention relates generally to diesel engines, diesel engine fuel injection pumps, and related mechanical parts. More specifically, the presently claimed invention relates to the sealing of the mechanical parts including the engine pistons.

BACKGROUND

Traditionally, the piston of a diesel engine fuel injection pump does not have any sealing device. The sealing of the pistons is achieved by the viscosity of the diesel fuel combining with the minimal clearance between the piston and the cylinder bore internal wall with precision in the order of a few microns. Technological advances make it possible for high-pressure fuel injection system with Common Rail Direct Injection (CRDI) to be used in diesel engines.

While older fuel injection systems have an average pressure of 300 bar. Newer systems that use CRDI can create a pressure that is near 3,000 bar, that is 3,000 times higher pressure than atmospheric pressure, for better combustion of finer fuel droplets injected under extremely high pressure. Thus, the combustion condition of the diesel engine has drastically improved. The near perfect combustion, that creates almost no toxic exhaust, is achieved by injecting exceedingly fine fuel droplets under extremely high pressure in the split injecting system in combination with the multiple fuel injections instead of a single one during each combustion cycle.

Diesel engines apparently become far better after the introduction of CRDI system, but because of the absence of sealing means on the pistons of the fuel injection pumps, fuel saving is still not practically achievable.

When a diesel engine fuel injection pump operates under very high pressure reaching 3,000 bar, the diameter of the piston is necessary to be as small as possible since the total load on the piston reaches above one metric ton under such high pressure. For example when the piston diameter is 7 mm, the total load on the 7 mm piston becomes 1,154 kg under the internal pressure of 3,000 bar. Using three pistons of 7 mm cross sectional diameter in a pump, the total load on the shaft, as transferred from the pistons, becomes 3,462 kg. The rated load then becomes 5,293 kg when a 50% safety factor is accounted for. This requires excessively large diameter shaft and drive bearings in the pump.

The fuel pump of a plain 3,000 cc passenger car diesel engine should pump fuel at 300 cc/min to run the car at the speed of 60 km/hour. With a cylinder bore of a 7 mm cross sectional diameter and 0.385 square cm cross sectional area, a three-piston pump, in which the pumping stroke is 7 mm, could pump 0.81 cc per rotation of the pump shaft. The pump shaft rotates at 370 rpm to pump 300 cc/min. When the cylinder bore of the fuel injection pump has a cross sectional diameter of 7 mm, the outer diameter of the piston cannot exceed 6.98 mm, which is 0.02 mm smaller in diameter than that of the cylinder bore. The cross sectional area of the piston is then equal to 0.382 square cm. Thus, the clearance between the cylinder bore and the piston has an area of 0.003 square cm. This area is 0.8% of the cylinder bore cross sectional area. In other words, there is a minimum of 0.8% of internal leak between the cylinder bore and the piston under atmospheric pressure even the pump is in idle. When the pump is running and a 3,000 bar internal pressure is being applied, the internal leak can reach above 60% of total pumping capacity of the pump, which means nearly 60% of fuel pumping energy is lost by internal leaking Furthermore, the internal leaking rate grows rapidly during the life of the pump. It is because the clearance between the cylinder bore and the piston generates vibrations of the piston in the bore during the combustion cycles, and the vibrations widen the clearance over time, so increases the internal leaking over time.

A typical fuel injection pumping system includes a pressure accumulator for storing pressurized fuel in the accumulator for maintaining a constant pressure with as little pressure fluctuation as possible for uniform combustion and minimum engine vibration. The fuel injection pump must pump at least 40% more fuel than the engine burning capacity in order to be able to store excessive pressurized fuel in the accumulator. Because of the internal leaking which grows over time, eventually the fuel injection pump cannot pump enough extra fuel for the accumulation of pressurized fuel in the accumulator under the condition which the engine keeps running for a long period of time without idling. The fuel supply to the engine from the fuel pump becomes less than the fuel needed for combustion to maintain speed. At this point, the replacement of the fuel injection pump is needed. Usually this occurs once every year on average. Therefore, this is a general desire in the art of diesel engine technology to find a better fuel injection pump, particularly a better fuel injection pump that does not wear out frequently.

SUMMARY

It is an objective of the presently claimed invention to provide a design of a diesel engine fuel injection pump that can produce high pressure, has minimal internal leakage that will not grow substantially over time, better durability, and relatively low manufacturing complexity. It is a further objective of the presently claimed invention to provide such design with the use of all-metal-seal rings.

In accordance to various embodiments of the presently claimed invention, all-metal-seal rings are used for the sealing of the piston and the cylinder bore of a diesel engine fuel injection pump. The diesel engine fuel injection pump equipped with one or more all-metal-seal rings on the pistons can produce absolute zero internal leakage even at very low speed such as 20 rpm.

A cylinder bore of a fuel injection pump having a 18 mm cross sectional diameter has a the cross section area of 2.55 square cm. When the one or more all-metal-seal rings are fitted on the piston, the outer diameter of the piston plus all-metal-seal rings becomes exactly same as that of the cylinder bore and both cross sectional areas are also the same, leaving zero leakage area.

If the fuel injection pump has three pistons and if the piston stroke is 18 mm, which is same to the cross sectional diameter of the piston, the displacement of the pump per rotation of shaft is 13.77 cc, so the shaft rotational speed required to pump fuel at 300 cc/min is 21.8 rpm.

This low speed pumping is practical only when zero internal leakage is guaranteed; otherwise there will be near 100% internal leakage at the pressure of 3,000 bar because the pistons cannot create the sealing function from the viscosity of the diesel fuel at such a low speed.

However, low shaft rotational speed is possible in the engine fuel injection pump equipped with all-metal-seal rings on the pistons because the zero-leakage sealing relies not the viscosity of the diesel fuel but on the all-metal-seal rings. Operating the engine fuel injection pump at low speed prolongs the life of the pump and ensures the constant high performance of the pump throughout its life, and in turn dampens the diesel engine's vibrations, providing a quieter and comfortable car ride.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail hereinafter with reference to the drawings, in which:

FIG. 1 shows the cross-sectional view of an embodiment of a diesel engine fuel injection pump equipped with all-metal-seal rings on the pistons in accordance to the presently claimed invention.

DETAILED DESCRIPTION

In the following description, designs of an engine fuel injection pump equipped with all-metal-seal rings on the pistons are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

Referring to FIG. 1. An embodiment of a diesel engine fuel injection pump equipped with all-metal-seal rings on the pistons comprises: a pump drive shaft 31 and an eccentric cam 30, wherein the pump drive shaft 31 and the eccentric cam 30 are made into a single piece and is assembled into a pump body 16. A three-rod-piston-drive cam 28 is assembled on to the eccentric cam 30, backed up by a bearing 29. Each of the three cylinder heads 17 comprises a discharge valve 22, a discharge port 26, and a pump piston 19 inserted in a cylinder bore. The cylinder heads 17 is attached to the pump body 16 and are positioned evenly around the circular pump body. The cylinder heads 17 are further fastened to the pump body 16 by tie bolts 18.

Rotation of the pump drive shaft 31 rotates the eccentric cam 30 and together creates a reciprocal motion on the piston drive cam 28. The piston drive cam 28 pushes up each of the pump pistons 19 into its respective cylinder bore. The pump piston 19 then is returned by the force of a return spring 21. The reciprocation of pump piston 19 created by the piston drive cam 28 creates the pumping force, suction force, and compression force. The action of a suction valve 23 and the discharge valve 22 during the reciprocation of the pump piston 19 causes liquid fuel to flow into pump body 16 through the inlet port 24 and hole 25 inside of the pump piston 19.

In the prior art, internal leakage is unavoidable as it is created by the clearance between each of the pump pistons 19 and its respective cylinder bore. The diesel engine fuel injection pump as shown in FIG. 1, however, has each of the pump pistons 19 fitted with an all-metal-seal ring 20. The pump pistons 19 fitted with an all-metal-seal ring 20 completely eliminates the space between itself and the internal wall of the cylinder bore.

One embodiment of the all-metal-seal ring is the coiled felt seal (CFS). One exemplary embodiment of CFS is the helical spring tube type dynamic rotary seal. It is described in the Korea Patent Application No. 10-2006-0031762. Excerpts of its English translation are presented in the Appendix A of the present document.

The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalence.

APPENDIX A

Helical spring tube type dynamic rotary seal constructed with C-type partial rings, which are joined by dovetail joint method

Brief Description of Drawings

FIG. 2: Partial ring which could be press stamped out of thin metal sheet, that having male and female dovetail joint shape on two ends to make the joints be strong when progressively joined.

FIG. 3: Two partial rings are overlapped to insert male dovetail of first partial ring into female dovetail of next partial ring for progressive joining to construct helical wound tube.

FIG. 4: Blank of the tubular shape seal of this invention, which is metal strap wound helical tube.

FIG. 5: Partially cutaway view of completed dynamic seal of this invention which is completed by grinding the inside and outside diameter of the blank to have proper function in the seal.

FIG. 6: A partial ring with assisting imaginary parts to explain the dynamic rotary seal principle with this invention.

FIG. 7: Half cutaway view of example of completed dynamic rotary seal using this invention.

Explanation of Numbered Parts in the Drawings FIGS. 2-7

1—A partial ring stamped out of thin metal sheet.

2—Male end of dovetail joint on C-type partial ring.

3—Female end of dovetail joint on C-type partial ring.

4—Dovetail Joint line, which is the result of dovetail joining of C-type partial rings.

5—Helical spring tube constructed by progressive joining of number of C-type partial rings along the helical track.

6—Shaft free circle that made slightly bigger diameter than the shaft diameter to keep it away from shaft all the time.

7—Shaft contact circle that made slightly smaller than shaft diameter to make it keep contact with shaft all the time.

8—Housing contact circle that made slightly bigger than inside diameter of the housing to make it keep contact with housing all the time.

9—Housing free circle that made slightly smaller than inside diameter of the housing to keep it away from the housing all the time.

10—Hosing seal layer whose outside diameter is housing contact circle and inside diameter is shaft free circle.

11—Displacement absorption layer whose outside diameter is housing free circle and inside diameter is shaft free circle.

12—Shaft seal layer whose outside diameter is housing free circle and inside diameter is shaft contact circle.

13—Shaft.

14—Arrow to indicate the shaft rotating direction.

15—Arrow to indicate the spreading direction of shaft seal ring when the ring spreads.

16—An imaginary pin which blocks rotating of shaft seal ring.

17—Housing.

18—Inside diameter of the housing.

19—Snap ring that inserted in snap ring groove to the hold holding ring.

20—Holding ring that holds the seal ring assembly.

21—Compression ring that pushes source rings of seal ring assembly to keep all the rings in seal ring assembly be tightly contacted one another to block leak between rings.

22—Compression spring to provide compression force of compression ring.

23—Outside diameter of the rotating shaft.

24—Completed seal assembly.

25—Snap ring groove.

Detailed Description

Category of this invention falls in the dynamic blocking technology of the leak that inevitably arising between stationary housing and rotating shaft when pressure rises in the rotary compression system.

The dynamic rotary seal used on screw type compression system is called “mechanical seal”. A mechanical seal is composed of six parts in minimum, which are the stator block, rotor block, stator disk, rotor disk, rotor disk spring and rotor block disk seal. The entire seal function fails if any one of these parts fails. The stator disk and the rotor disk are the parts that perform the actual sealing function by contacting rubbing rotating under pressure. Those two parts must have not only high wear resistance but also low friction. They must be able to dissipate heat in possible highest speed. Surface area can be adjusted for less contacting area for less friction heat but the less area results faster wear out. High wear resistant materials have high friction but low friction material having low wear resistance. If they are made with high wear resistant material for long life the friction heat could affect the quality of the media in contact, in some cases even bring fire.

Two contacting faces in mechanical seal are under pressure and constantly rubbing so they are wearing in all instance even submicron unit range but that submicron wear clearance always causes whole seal failure when the submicron wear is not compensated in every instance along with wear out.

In other words, one of the contacting disk, rotating disk, must move toward the mating disk, the stationary disk, to compensate wear. This means the rotating disk must travel axial direction toward the stationary disk on the rotating block while the rotating block is rotating. Rotating disk must be able to slide on the rotating block to constantly move toward the stationary disk. Thus there is another place to block leak between rotating disk and rotating block.

The axial direction movement of the rotating disk on the rotating block by wear out of disk is very little distance, within few mm in a year, so the sealing between rotating disk and rotating block could be satisfied by simple rubber O-ring for cheaper model and by metal bellows for higher performance. In short the real problem in rotary dynamic seal in prior art is in the sealing between rotating disk and rotor block, not only in contacting disks.

A rubber O-ring inserted between rotating disk and rotor block shall be burnt in high temperature media and shall be extruded under high pressure media and be attacked in the corrosive media but there are no ways to omit it.

Metal bellows are more expensive, sometimes three times of the whole mechanical seal, and the metal bellows makes complicate structure which hinders thin compact design that is very important in precision machines.

The ultimate target is to produce single piece rotary dynamic seal which is compact, higher sealing performance, cheaper and lower maintenance while the rotary dynamic sealing system of prior art which generally called mechanical seal having so many parts are inevitably inter related, complicate structure, expensive in production cost, higher maintenance cost and shorter life.

FIG. 2 shows the C-shaped partial ring (1) which is the basic source ring of this invention. Partial ring (1) must be stamped out by press or fabricated by contour cutting process such as laser cutting or wire cutting from sheet stock to have two faces of partial ring (1) in perfect parallel. C-shaped partial ring (1) is a ring that made to have a part of the ring cut away so as to make the partial rings be progressively joined by the male dovetail( 2) and female dovetail (3) made on two ends of the partial ring (1). The value of the cut away angle should be determined accordingly along with diameter.

FIG. 3 shows the method of progressive joining of two partial rings (1) by the male dovetail (2) of first partial ring (1) and female dovetail (3) of next partial ring (1).

FIG. 4 shows the completed helical spring tube (5) by progressive joining of partial rings (1) and those dovetail joint line (4) must be permanently set by welding or brazing after joining The starting point shows the male dovetail (2) and the ending point shows female dovetail (3) on completed helical spring tube (5). As the helical spring tube (5) is constructed by the progressive joining of the partial rings (1) the dovetail joint line(4) shall be distributed on the tube surface on shifted point as much as the cutaway angle of the partial ring (1) so the dovetail joint line (4) will be adequately distributed on tube surface evading weak joint points be overlapped.

FIG. 5 shows the partial cutaway view of seal assembly (24) which is completed sealing ring of this invention. The seal assembly (24) is completed by grinding of inner diameter and outer diameter by making 4 different diameters, two on inside and two on outside of the helical spring tube (5). The smaller diameter of the inside diameter of seal assembly (24) is called shaft contacting circle (7) which is made about 0.5% smaller than the outside diameter of the shaft (23) so as to tightly contact with shaft (13) all the time when the shaft (13) is inserted inside of the seal assembly (24). The larger diameter of the inside diameter of seal assembly (24) is called shaft free circle (6) which made little larger than the outside diameter of the shaft (23) so as to prevent shaft free circle (6) from contacting outside diameter of the shaft (23) at anytime. The larger diameter of the outside diameter of seal assembly (24) is called housing contact circle (8) which is made about 0.5% larger than the inside diameter of the housing (18) so as to keep the housing contact circle (8) tightly contact all the time with inside diameter of the housing (18) when the seal assembly (24) is assembled inside of the housing (17). The smaller diameter of the outside diameter of the seal assembly (24) is called housing free circle (9) which made little smaller than the inside diameter of the housing (18) to prevent the housing free circle (9) from contacting the inside diameter of the housing (18) at anytime. The purpose of making these 4 different diameter circle is to build three different functioned layers in the seal assembly (24). The first layer is called housing seal layer (10), which is the stacking of the housing seal rings whose outside diameter is housing contact circle (8) and inside diameter is shaft free circle (6). The function of the housing seal layer is blocking the leak between inside diameter of the housing (18) and seal assembly (24) and the number of the rings to construct layer for optimum sealing performance shall be determined by designer according to different sizes. The second layer is called shaft seal layer (12) which is the stacking of the shaft seal rings whose outside diameter is housing free circle (9) and inside diameter is shaft contact circle (7). The function of the shaft seal layer is blocking the leak between outside diameter of the shaft (23) and seal assembly (24) and the number of the rings to construct layer for optimum sealing performance shall be determined by designer according to different sizes. The third layer is called displacement absorption layer (11) which is stacking of the suspended rings whose outside diameter is housing free circle (9) and the inside diameter is shaft free circle (6). The displacement absorption layer (11) is built between the housing seal layer (10) and the shaft seal layer (12) to absorb eccentric vibration of the shaft and also absorbs the dimensional change of the whole system by wearing along with use.

FIG. 6 shows the principle of the sealing of this invention. Since those three different functioned layers are constructed on a single strand of metal strap any force put to any point of the seal assembly (24) is immediately affects to all over the seal assembly (24). When the seal assembly (24) is inserted inside of the housing (17) with force the seal assembly (24) is tightly caught inside of the housing (17) because the outmost diameter of the seal assembly (24) is the housing contact circle (8) which is 0.5% larger than the inside diameter of the housing (18). As the housing seal layer (10) is tightly caught to the housing (17) whole seal assembly (24) is caught in the housing (17) so is the shaft seal layer (12). The innermost diameter of the seal assembly (24) which is the inner diameter of the shaft seal layer (12) is shaft contact circle (7) which is made about 0.5% smaller than the outside diameter of the shaft (23) so if the shaft (13) is inserted into shaft seal layer (12) by force whole shaft seal layer (13) must be tightly stick to shaft (13). If the shaft (13) starts rotate the shaft seal layer (12) also starts to rotate together with shaft (13) but the housing seal layer (10) which is tightly caught inside of the housing (17) prevents the shaft seal layer (12) from rotating.

This condition is as same as the FIG. 6 that shows one partial ring of the shaft seal layer (12) is about to start rotate by the rotating force of the shaft (13), the stopping action of the housing seal layer (10) is shown by imaginary stop pin (16). The shaft contact circle(7) is holding shaft diameter (23) but the shaft (13) starts to rotate to arrow (14) direction while the stop pin (16) prevents the ring (12) from rotate, then the friction force between shaft contact circle(7) and shaft diameter (23) is converted to open the partial ring (12) to the arrow (15) direction. When the partial ring (12) opens by the force arrow (15) direction the contacts between the ring (12) and shaft (13) is broken, other words there remain no more contact in that instance. No more contact means no more friction force generates so opening of the ring (12) is ended and spring back to its original position. Back to its original position of the ring (12) means the contacting of the ring (12) and shaft (13) and next instance the friction force opens the ring (12) again. The opening between the ring (12) and the shaft (13) could be a millionths of a mm since the open is open no matter how small value was the opening which is enough distance to eliminate contacting. So the open and close of the ring (12) could arise million times in a second in other words the opening clearance also could be millionths of a mm through which nothing can be leak in a millionths of a second. This condition is as same as the static seal of plain rubber O-ring since the contacting of ring (12) and shaft (13) is virtually never broken during the rotating of the shaft (13). This status is a unique phenomenon arising between helical spring and rotating round bar inserted inside of the spring, the condition should be called contacting non contacting condition. This contacting non-contacting phenomenon is utilized on helical spring over running clutch from long time ago but utilizing this phenomenon on dynamic seal is the first on this invention.

FIG. 7 is the representative drawing which shows the cutout view of completed dynamic rotary seal using seal assembly (24). There must be some means to hold the seal assembly (24) inside the cylinder (17) including holding ring (20) and snap ring (19) which is inserted in the snap ring groove (25). The compression ring (21) also provided to push source rings together to block leak between source rings by the spring force of the compression springs (22) which inserted in the holes made on the compression ring (21).

DIESEL ENGINE FUEL INJECTION PUMP WHICH PISTONS ARE SEALED WITH ALL METAL SEAL RINGS

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