DK201100649A - Device for scraping off a rod and reciprocating piston engine provided with such a device - Google Patents

Abstract

In a device for scraping off a circumferential surface, wetted with a fluid, of a rod which is movable in an axial direction, comprising at least two scraper lamellas (23a, b) of equal shape which are mutually offset relative to each other in axial direction and having radial variability, and which, with a radial protrusion, are received on a common holder ring (21) which is provided with radial inner open annular grooves for the said lamellas (23a, b) and has likewise radial variability, and which, due to a spring arrangement associated with its radial outer surface, can be reduced in size in a radial direction an optimal scraping effect of ali scraper lamellas (23a, b) of a common holder ring (21) can be attained in that at least the rear lamella (23a) in the moving direction of the rod (11) is radially resilientiy supported relative to the groove bottom of the associated annular groove.

Description

MAN DIESEL & TURBO,

Branch of MAN DIESEL & TURBO SE, Germany

Device for scraping off a rod and reciprocating piston engine provided with such a device

The invention relates to a device for scraping off a circumferential surface wetted with a fluid, of a rod which is movable in an axial direction through an opening of said device comprising at least two scraper lamellae being of equal shape; being mutually offset relative to each other in axial direction; and respectively being split to allow for individual radial variability; and with a radial protrusion being received on a common holder ring which is provided with radial inner open annular grooves for said lamellas and has similar radial variability due to a split design, thus in radial direction allowing spring-biased adaptation to the area circumscribed by said holder ring due to a spring arrangement associated with the radial outer surface of said holder ring.

The invention further relates to a cross head reciprocating piston engine especially in the form of a large sized two stroke uniflow internal combustion engine, provided with such a device.

In the known arrangements of this type the scraping lamellas are radially stiffly supported on the associated groove bottom, so that they have the same fixed internal diameter coacting with the rod. The fluid film in the gap between the rod and a scraper lamella scraping off the rod generates hydrodynamic supporting forces which are balanced by the spring forces acting on the holder ring. The radial position of the holder ring and herewith the size of the gap between the rod and its lamella is defined therefore by the leading scraper lamella of a set, first coacting with a given rod area for the actual direction of rod movement being substantially axial, although components from rotation can be compressed in the rod movement pattern. By the active scraper lamella the fluid film thickness is reduced to half. This renders it uncertain for the next lamella to effectively reach the fluid film for further scraping off. The negative result is poor scraping off fluid so that a comparatively thick fluid film remains on the rod. If the rod is scraped off, a piston rod of a crosshead motor cylinder cylinder lube oil polluted by combustion residues comes into contact with the piston rod in the area above the crankcase. The above result leads to the disadvantage that the piston rod moving up and down can feed comparatively much cylinder lube oil and combustion residues from above to the crankcase which will lead to a pollution of the system oil contained in the crankcase so that this system oil which must be clean enough for bearing lubrication and hydraulics needs frequent filtration.

Starting from this point of view it is the object of the invention to ensure that each scraper lamella of a common holder ring has an optimal scraping effect.

According to the present invention, this object is attained in that at least the rear lamella or at least one leading lamella, respectively, as seen in the moving direction of the rod is radially resiliently supported relative to the groove bottom of the associated annular groove.

With these measures the disadvantages of the known arrangements can be avoided. The resilient support makes the respective lamella individually variable in the radial direction, so it will be adjusted by the radially acting forces. Dependent on the resiliency of its support relative to the groove bottom the respective lamella is more or less thrown back into the associated groove, so that the next lamella not thrown back can become effective. Since the film thickness is reduced to half by each effective lamella the invention leads to a high reduction of the film thickness which ensures in connection with a crosshead motor a strong separation of cylinder lube oil from above and system oil from below and therefore minimizes the need for filtration of the system oil which need a high cleanness. A further advantage of the invention is that also chemical contamination of the delicate system oil from the often chemically aggressive brought-down fluid from the cylinder environment is reduced, thereby reducing the requirement for system oil replacement as such e.g. bearing-attacking chemical contamination cannot be filtered away. A still further advantage of the invention is that the lamella's flexible support also enables simple wear compensation. in the following further advantageous developments and preferred embodiments of the superposed idea are recited.

Usefully each lamella of the holder ring can be radially resiliently supported. This ensures that in the case of a reciprocating rod the rod is scraped off during each stroke and fro or up and down respectively with the same effect.

Advantageously a resilient support of a lamella in the associated annular groove can be achieved by a flexible padding inlay preferably having a profile like a so-called O-ring. This leads to a very simple embodiment low in price. Also a simple possibility for retrofit is given. Of course a separate flexible padding inlay in a said groove can also have other suited section profile / shape, even hollow, to allow compression for more or less lamella radial movement, preferably in combination with a suitably selected polymer material with elastic properties.

According to another advantageous measure for resiliently supporting a lamella in the associated annular groove, the lamella on its radial outer surface can be provided with a layer of elastic material of a suitably compressible structure or profiling. Such a layer may preferably be integral with the associated lamella, e.g. by some vulcanizing process, which reduces the number of parts and enables a simple assembly.

Practically the holder ring can contain two scraper lamellae. This ensures a statically defined support of the holder ring against the rod by means of both lamellae so that a balanced wear will occur. A further practical measure may be that the holder ring is provided with at least one discharge outlet mouth in the area between the two scraper lamellas. This ensures a safe drain of the scraped off and collected fluid so that a pressure build up within the room between the lamellae is avoided.

Additionally or alternatively, the holder ring can have at least one frontal (axial) side, preferably both frontal sides, provided with at least one respective discharge groove, so that also a sure drain is achieved of the fluid stemmed in front of the rear lamella (ie of the fluid hindered passage between the rod surface and the lamella first scraping a given rod area in the actual substantially axial direction of rod movement). This can simplify the job of the associated lamella.

Practically each discharge outlet and / or discharge groove can communicate with a drain line which can be connected with an annular ring groove provided in an annular housing for reception of the associated holder ring.

According to a further preferred embodiment the holder ring and the lamella can be circumferentially segmented into sets of more pieces so that mounting around the rod is possible even if the rod is kept in place in an associated machine.

Practically at least the segments of the holder ring can be provided on both ends with one another overlapping tongues whereby the area of the overlapping tongues is advantageously sealed outwardly by a cover element arranged on the radially outer surface of the holder ring. By these measures a leak off scraped of fluid can be avoided.

For generating the radially inwardly directed forces for engaging the scraper lamellas with the rod the holder ring is biased by a spring toward smaller diameter. For receiving an annular spring the holder ring can advantageously be provided with a radially outward open annular groove. A further practical measure may be that at least one element of the device is provided with at least one tag, preferably of the RFID type, comprising stored data to unambiguously define said element or device. This can simplify the assembly and / or servicing of the device according to the present invention.

The following preferred working example of the invention is described by means of the drawings, wherein

Fig. 1 shows a vertical cross section of a big sized diesel engine of the crosshead type,

Fig. 2 shows an enlarged view of the lower area of the scavenge chamber of the arrangement according to Fig. 1,

Fig 3 shows a scraping device of the present design with two scraper lamellas having the same fixed internal diameter,

Fig. 4 shows a scraping device according to the present invention,

Fig5 shows a top view of a segmented holder ring,

Fig. 6 shows a side view of the holder ring according to Fig. 5,

Fig. 7 shows an example for outwardly sealing the segmented holder ring. A diesel engine as represented in FIG. 1 can be used for driving maritime objects or large sized power plants or the like. Such internal combustion engine being used as an example for scoped reciprocating piston engines of cross-head type. The basic structure and mode of operation of such reciprocating engines are known and are therefore described in the following only as long as it is necessary in order to understand the present invention.

The engine shown in FIG. 1 contains in its lower part a crankcase 1 while a crankshaft 2 is borne by so called main bearings. On the upside of the crankcase 1 a row of cylinders 3 is arranged. Each cylinder 3 contains a cylinder liner 4 while a piston 5 is arranged which is movable down and up. The piston 5 functions as the lower movable delimitation of a combustion chamber 6 inside the liner 4. The cylinder liner 4 is supported on the surrounding housing of a scavenge chamber 7 which can be charged with scavenge air or gas.

The liner 4 extends with its lower portion into the scavenge chamber 7 and ends with clearance above the chamber bottom 8. In the area of the lower end of the liner 4 inlet ports 9 are provided. The inlet ports 9 are passed by the piston 5 when it is moved down and up whereby a communication between the scavenge chamber 7 and the combustion chamber 6 is opened and closed.

The piston 5 is connected to an associated crosshead 10 by a piston rod 11 arranged along the axis of the cylinder liner 4 and the piston 5. The crosshead 10 is positioned within the crankcase 1 and is designed as a sledge moving up and down and guided by associated guides 12 parallel to the axis of the piston 5 and piston rod 11. The crosshead 10 contains a crosshead pin 13 fixed to the piston rod 11. On this pin 13 a connection rod 14 is borne which connects the crosshead 10 with the crankshaft 2. The scavenge chamber bottom 8 rests on the crankcase ceiling 1. The piston rod 11 passes through the wall arrangement built by the scavenge chamber bottom 8 and the crankcase ceiling, whereby the piston rod 11 penetrates an associated seal packing 15 provided in the scavenge chamber bottom 8.

The cylinder liner is supplied with suitable lubrication oil (in the application named as cylinder oil) which together with combustion residues can drip down to the scavenge chamber bottom 8 as far as it is not burned. For disposing this dripping down fluid a drain 16 communicating with the bottom area of the scavenge chamber 7 is provided. The chamber bottom 8 can be inclined towards the drain 16 and / or provided with a ring channel surrounding the seal packing 15 and communicating with the drain 16. Also, exhaust gas containing further combustion residues can enter the scavenge chamber 7 when the inlet ports 9 are opened during the downstroke of the piston 5.

In the crankcase 1 oil of high cleanliness is present (in the application named as system oil) which oil is used for lubrication of the bearings as well as for hydraulic purposes. For filtering this oil a filtering station (not shown) is provided. To prevent pollution of the system oil by cylinder oil the crankcase 1 must be separated from the scavenge chamber 7. For these purposes the seal packing 15 is provided which can be designed as a stuffing box.

The said stuffing box has, as is best shown in Fig.2, an annular housing 17. This housing 17 is arranged in a surrounding socket 18 of the scavenge chamber bottom 8 which socket defines a hole for passing through of the piston rod 11. The housing 17 is provided with radial inner open annular grooves. Each of these grooves has an associated ring arrangement. These ring arrangements are partly designed as scraper rings 19 and partly as sealing rings 20. Practically the scraper rings 19 can be positioned above the sealing rings 20.

The object of the sealing rings 20 is to overcome the pressure difference between the pressure in the scavenge box 8 (about 5 bar) and the pressure in the crankcase 1 (about 1 bar) while the object of the scraper rings 19 is to reduce the oil film on the outer surface of the piston rod 11. In this connection, one must consider that the piston rod 11 above the seal packing 15 comes into contact with cylinder oil which is deposited on its outer surface in the form of a more or less thick oil film.

As can be seen from Figs. 3 and 4 each scraper ring 19 comprises a holder ring 21 seated in the associated annular groove 22 of the housing 17 and a set of more than one uniform scraper lamellas 23a, b seated in associated annular grooves of the holder ring 21. In the present embodiment of two scraper lamellas 23a, b are provided per holder ring 21. Thereby either scraper lamella 23a, b will function as the first or last with respect to the moving direction D of the reciprocating piston rod 11. Naturally also a set with more than two scraper lamellas can be provided on a common holder ring. The equally shaped scraper lamellas 23a, b are axially mutually offset against each other and are radially protruding over the radially inner surface of the associated holder ring 21 so that scraper edges are generated.

The holder ring 21 and the scraper lamellas 23a, b have radial variability and the holder ring 21 is spring-biased by a surrounding ring shaped spring 24 toward a smaller diameter for engaging the scraper lamellas 23a, b with the piston rod 11. The ring shaped spring 24 is placed in an outer open annular groove 25 of the holder ring 21. The thickness of the oil film 26 deposited on the outer surface of the piston rod 11 should be reduced by the scraper lamellas 23a, b.

In the known arrangements according to FIG. 3 the scraper lamella 23a, b are radially stiffly seated in the associated grooves of the holder ring 21. The first scraper lamella 23a, this is the rear lamella in the moving direction D of the piston rod 11, scrapes off a certain layer of cylinder oil whereby the thickness of the oil film 26 is reduced to half as indicated by d1 and d2. In the gap between the scraping off lamella 23a and the outer surface of the piston rod 11 a hydrodynamic pressure is generated which is balancing the inwardly directed spring forces of ring shaped spring 24. According to the radial position of the holder ring 21 and herewith the radial position of each further lamella, here the second scraper lamella 23b, is defined by the radial position of the first scraper lamella 23a. If the scraper lamellas 23a, b have the same shape and therefore the same diameter and if by means of the first scraper lamella 23a the oil film thickness is reduced to half it occurs that the next lamella, here the second scraper lamella 23b is distanced from the surface of the remaining oil film and therefore does not have any scraping effect.

This negative result is overcome according to the present invention by radially resiliently seating of at least the first scraper lamella 23a in the associated annular groove of the holder ring 21 as can be seen from FIG. 4. In the illustrated embodiment, both scraper lamellas 23a, b are resiliently seated in the associated grooves of the holder ring 21 by a flexible element 27 positioned between the groove bottom and the outer radial surface of the lamellas 23a, b. element 27 the associated lamella 23a, b is adjustable in the radial direction by the forces acting in the radial direction. Therefore each scraper lamella 23a, b can reach the oil film 26 whereby by each lamella 23a, b the thickness of the oil film 26 is reduced to approx.half as is indicated at d1, d2, d3 in Fig.4. The positive result is a stronger reduction in the thickness of the oil film 26 so that the amount of cylinder oil fed by the piston rod 11 from above the seal packing 15 to below into the crankcase 1 will be comparatively small and substantially reduced therefore costly adverse contamination of the system oil of the crankcase 1 by cylinder oil is substantially reduced.

For building a flexible element 27 mentioned above a flexible padding can be deposited in the associated annular groove of the holder ring 21 behind the associated scraper lamella 23a, b. This flexible padding can have a flexible cross section design and / or be made of a flexible material. Practically a so-called O-ring known for several purposes can be inserted. Of course a separate flexible padding inlay in a said groove can also have other suited section profile / shape, even hollow, to allow compression for more or less lamella radial movement, preferably in combination with a suitably selected polymer material with elastic properties. Alternatively or additionally it would also be possible to provide the outer circumference of the scraper lamellas 23a, b with an elastic layer consisting of flexible material and / or designed with a flexible cross section. In case of using rubber like material the said elastic layer can be vulcanized on. For other materials other uniting processes for integration with the lamella may be questioned for example crimping / elastic gripping, application of adhesive or the like.

To avoid a flood of oil in the scraping area the scraped off oil or oil mixture containing cylinder oil and combustion residues must be drained away from the scraping area. For this purpose the holder ring 21 is provided with at least one discharge outlet 28 mouthing in the area between the two scraper lamellas 23a, b. In the embodiment shown in Fig.4 the holder ring 21 is further provided at least at its front side adjacent the rear lamella 23a, preferably on both front sides, with at least one respective discharge groove 29. Naturally, more than one outlet and / or discharge grooves equally arranged over the circumference of the holder ring 21 can be provided. For draining away the collected oil the outlet (s) 28 as well as the discharge groove (s) 29 communicate with a drain line 30 shown in Fig.2 which can lead to an oil reservoir (not shown). The oil drained away by the discharge outlets 28 as well as grooves 29 gets into the associated annular groove 22 of the housing 17 and each such groove 22 of the housing 17 can be connected to the drain line 30 so that an unhindered and permanent flow path is given.

For enabling a simple mounting of a scraper ring 19 around the piston rod 11 held in place through the scavenge chamber bottom 8 or the crankcase ceiling the scraper ring 19 consisting of a holder ring 21 as well as the associated scraper lamellas 23a, b can be circumferentially segmented. According to the holder ring 21 and the scraper lamellas 23a, b consist of sets of more segment pieces. In the working example shown in FIG. 5 a three segment division is used. According to three segment pieces 19a, b, c or here respectively 120 ° each are provided. To avoid gaps between the several segment pieces 19a, b, c, build a straight channel for the scraped off oil at least the segment pieces of the holder ring 21 are provided, as shown in Fig. 6, on both ends with tongues 31 overlapping one another. Hereby the free passage through the double-angled channel of gap 32 is substantially reduced, especially when also the scraper blades are mounted for use.

Practically the area of the overlapping tongues can be blocked radially outward, so that the gap 32 cannot function as a disturbing leak channel compromising the drain mentioned above. For this purpose, as shown in Fig. 7, a cover element 33 covering the gap 32 on the outward side can be provided. The cover element 33 can be designed as a thin cover plate or band. In the embodiment shown in FIG. 7 the outer circumference of the holder ring 21 against the circular shape is flattened in the area of each division and therefore in the area of each gap 32, as is indicated by the flattened section 34. In this case the cover element 33 is so designed that its configuration corresponds to the ring part removed for getting the flattened section 34. Of course also the housing 17 may be of a split design to allow for removal / mounting while the piston rod is still connected both to the crosshead below and to the piston in the cylinder above.

In the working example described above in connection with a crosshead motor the scraped off fluid is cylinder lub oil and the rod concerned is a piston rod. But also other uses can come into question for example hydraulic cylinder piston aggregates. In the described working example, the seal packing 15 provided with one or more scraping devices should provide effective separation between the scavenge chamber 7 as well as the cylinder oil herein and the inside room of the crankcase 1 as well as the system oil herein. This separation work can be made easier if the blast generated during the start of the piston upstroke and passes the lower edge of the cylinder liner 4 and which is propelling a lot of cylinder oil probably polluted with combustion residues directly against the piston rod 11 , is diverted from a radial direction to at least mostly axial direction.

For this purpose, a skirt 35 resurrection from the scavenge chamber bottom 8 and surrounding the piston rod 11 can be provided, as shown in Fig 2. The skirt 35 shields the piston rod 11 against deposition of cylinder oil particles and combustion residues. In principle a simple tubular structure shielding the piston rod 11 can be sufficient. Preferably a funnel shaped or trumpet shaped upper rim can be provided. Practically the skirt 35, preferably also having a split design for placement around a mounted piston rod, may be attached to the upper flange of housing 17 or, as shown in FIG. 2, on the upper front end of the socket 18 enclosing the housing 17.

The experience has shown that it can also be usefull in the assembly as well as the maintenance aspect if at least one element of the scraping device according to the present invention is provided with at least one tag, preferably of the RFID type, containing stored data. to unambiguously authenticate the said element or device. Usefully the authenticating data can also comprise manufacturing, approval, historical and possible or planned future use of data or the like.

The above description of a preferred embodiment is not limiting the scope of the invention which is defined in the claims.

Claims (27)

1. A device for scraping off a circumferential surface wetted with a fluid, of a rod which in an axial direction is movable through an opening of said device comprising at least two scraper lamellas (23a, b) being of equal shape; being mutually offset relative to each other in axial direction; and respectively being split to allow for individual radial variability; and with a radial protrusion being received on a common holder ring (21) which is provided with radial inner open annular grooves for said lamellas (23a, b) and has likewise radial variability due to a split design, thus in radial direction allowing spring-biased adaption to the area circumscribed by said holder ring due to a spring arrangement associated with the radial outer surface of said holder ring, characterized in that at least the rear lamella (23a) as seen in the moving direction of the rod (11), is radially resiliently supported relative to the groove bottom of the associated annular groove.

2. A device for scraping off a circumferential surface wetted with a fluid, of a rod which in an axial directions is movable through an opening of said device comprising at least two scraper lamellas (23a, b) being of equal shape; being mutually offset relative to each other in axial direction; and respectively being split to allow for individual radial variability; and with a radial protrusion being received on a common holder ring (21) which is provided with radial inner open annular grooves for said lamellas (23a, b) and has likewise radial variability due to a split design, thus in radial direction allowing spring-biased adaption to the area circumscribed by said holder ring due to a spring arrangement associated with the radial outer surface of said holderring, characterized in that, at least one leading lamella (23b) as seen in the moving direction of the rod (11), is radially resiliently supported relative to the groove bottom of the associated annular groove.

3. A device according claim 1 or 2, characterized in that each lamella (23a, b) of the holder ring (21) is resiliently supported.

4. A device according claim 1 or 2, characterized in that for resiliently supporting a lamella (23 a, b) at least a flexible padding (27) is seated on the bottom of the associated annular groove.

5. A device according claim 4, characterized in that the flexible padding (27) is built by a ring made of elastic material.

6. A device according claim 5, characterized in that the elastic ring is an O-ring.

7. A device according one of the preceding claims, characterized in that a resiliently supported scraper lamella (23a, b) at least on its radial outer surface is provided with a layer of elastic material of a suitable compressible structure or profilation.

8. A device according claim 6, characterized in that the elastic layer is vulcanzed on the radial outer circumferential surface of the scraper lamella (23a, b).

9. A device according one of the preceding claims, characterized in that each holder ring (21) has two scraper lamellas (23a, b).

10. A device according one of the preceding claims, characterized in that the holder ring (21) is provided with at least one discharge outlet (28) mouthing in the area between two scraper lamellas (23a, b).

11. A device according one of the preceding claims, characterized in that the holder ring (21) is provided in the area of at least one frontal (axial) side with at least one respective discharge groove (29).

12. A device according claim 11, characterized in that the holder ring (21) has discharge grooves (29) in the area of both frontal (axial) sides.

13. A device according claims 10-12, characterized in that each discharge outlet (28) and/or discharge groove (29) is communicating with a drain line (30).

14. A device according claim 13, characterized in that the holder ring (21) is arranged in an associated radial inner open ring groove (22) of an annular housing (17) and that the ring groove (22) is connected to the drain line (30).

15. A device according one of the preceding claims, characterized in that the holder ring (21) and the lamellas (23a, b) are circumferentially segmented in sets of more pieces (19a, b, c) whereby at least the pieces of the holder ring are provided on both ends with tongues (31) overlapping one another.

16. A device according claim 15, characterized in that the area of the overlapping tongues (31) is sealed by a cover element (33) arranged on the radially outer surface of the holder ring (21).

17. A device according claim 16, characterized in that the radially outer surface of the holder ring (21) has flattened sections (34) in the area of overlapping tongues (31) and that cover elements (33) corresponding with the ring parts removed for building the flattened sections (34) are provided.

18. A device according one of the preceding claims, characterized in that that the holder ring (31) is provided with a radially outward open annular groove (25) for receiving an annular spring (24) building the associated spring arrangement.

19. A device according one of the preceding claims, characterized by a majority of holder rings (31) contained in a common annular housing (17).

20. A device according claim 19, characterized in that that the common annular housing (17) being of a split design allowing positioning around the rod without passage of a said rod end.

21. A device according claim 1 or 2, characterized in that the scraped off fluid is cylinder lube oil.

22. A device according claim 21, characterized in that the rod is a piston rod (11) of a motor having a piston rod (11).

23. A device according one of the preceding claims, characterized in that at least one element of the device is provided with at least one tag comprising stored data to unambiguously define said element or device.

24. A device according claim 23, characterized in that the tag is of the RFID-type.

25. An engine of the crosshead type, especially a big sized reciprocating piston two stroke internal combustion engine, with a crankcase (1) and at least one cylinder (3) containing a cylinder liner (4) which extends in a surrounding scavenge chamber (7) and a piston (5) arranged in the cylinder (3), whereby the piston (5) is connected with an associated crosshead (10) arranged in the crankcase (1) by a piston rod (11) which penetrates a seal packing (15) which is arranged in the wall arrangement between the scavenge chamber (7) and the crankcase (1) characterized in that at least one said seal packing (15) comprises at least one device according one of the preceding claims.

26. An engine according claim 25, characterized in that for at least one piston rod (11) a skirt (35) is provided upstanding from the scavenge chamber bottom (8) and surrounding the associated piston rod (11) related to the at least one said seal packing (15)..

27. An engine according claims 26, characterized in that the skirt (35) is attached to an upper flange of the housing (17) of the seal packing (15) or the upper front end of a socket (18) enclosing the housing (17) of the seal packing (15).