KR20070041399A - Piston for the crosshead engine - Google Patents

Abstract

A piston top (2) received in an upper flange (9) of the piston rod (1), the piston top having a piston head (3) connected to a rotating piston skirt (4), the piston head having central cooling Covering the seal (8), the cooling chamber is allowed to enter the coolant through a supply conduit (10) arranged on the piston rod (1), the coolant is returned to the radially outside the supply conduit (10) pipe (11) In crosshead engines, in particular pistons for two-stroke large diesels, which can be guided through, the cooling chambers 8 are provided in the cooling chamber 8 in which the center is raised at the upper end of the piston rod 1 even when the piston head 3 is raised upward. Arrangement of the insert body 17 can achieve a good cooling effect, in which the insert body supports the nozzle 21 facing the inner surface opposite the piston head 3 and communicating with the feed conduit 10. With an annular chamber 22 And, the annular chamber form the coolant collecting chamber.

Piston rod, upper piston, piston skirt, piston head, cooling chamber, supply conduit, return pipe, insert body, nozzle, annular chamber, coolant collection chamber.

Description

Pistons for crosshead engines {PISTON FOR THE CROSSHEAD ENGINE}

1 shows a radially cut piston in accordance with the present invention without coolant.

FIG. 2 shows what happens when the piston of FIG. 1 with coolant reaches a bottom dead center. FIG.

FIG. 3 shows what happens when the piston of FIG. 1 with coolant reaches a top dead center. FIG.

Explanation of symbols on the main parts of the drawings

1: piston rod 2: upper piston

3: piston head 4: piston skirt

5: lower piston 6: flange

7: frame 8: cooling chamber

9: tappet 10: supply conduit

11: return pipe 12: pipe

13: cooling hole 14: connecting hole

15: ring channel 16: perforated hole

17: insert body 18: ring tappet

19: bore 20: distributor chamber

21: nozzle 22: annular chamber

23: drain conduit 24: seal

DE 199 62 325 C2

DE 198 15 919 B4

EP 07 47 591 B1

The present invention relates to a piston for a crosshead engine, in particular a two-stroke large diesel, comprising a piston top received in an upper region of the piston rod, the piston top having an upper piston head connected to the piston skirt, the piston head being centered. Covering the cooling chamber, the cooling chamber is capable of introducing coolant through a supply conduit arranged in the piston rod, and the coolant can be led through a return pipe disposed radially outside the supply conduit.

Devices of this kind are described in DE 199 62 325 C2. In this well known arrangement, a coolant jet emerges from the upper end of the feed conduit formed by the central bore of the piston rod, and the coolant jet stem appears in the middle region of the inner surface of the piston head. Here the piston head is recessed in the center. Thus the contour of the upper boundary of the cooling chamber rises out of the radius in the middle. At this time, the coolant encountered in the center of the piston head is equally divided outside the radius when the upward movement of the piston is delayed to cool the entire piston head.

However, pistons with a raised piston head are also well known, for example, as DE 198 15 919 B4 shows. Since the central part of the piston head is raised, here the contour of the cooling chamber upper boundary is inclined radially outward. At this time, as long as the cooling is carried out in the same manner as above, the coolant is not evenly distributed out of the radius when the upward movement of the piston is delayed, but collects in the central region of the dome formed by the raised piston head. In this case, therefore, there is a risk that the radially outer regions of the piston head will not cool reliably.

EP 07 47 591 B1 shows a piston with a cooling chamber located below the piston head, where the upper boundary of the cooling chamber is likewise raised in the center, ie in the shape of a dome. The piston head covering the cooling chamber here has cooling holes distributed on the surface and starting from the cooling chamber and tilted at an angle to the piston axis. An insert body provided in the cooling chamber borders the distributor chamber through the supply conduit and supports nozzles branching from the distributor chamber and projecting into respective corresponding cooling holes, the nozzles respectively cooling holes arranged therein. Inject inside. In this case, during the downward movement of the piston, the coolant is pushed into the cooling hole and forms a lining which is actually fixed there, where the spray stem released by the nozzle cannot be braked by the lining, which is undesirable for cooling action. There is a disadvantage. Apart from this, here the nozzles are not arranged coaxially with respect to the bore axis but are inclined at an opposite angle, which impedes cooling of the bottom of the bore, as the spray stems emitted from the nozzles hit the sidewalls of the bore, respectively placed. I can receive it.

In view of these problems, the object of the present invention is to simplify the apparatus of the kind mentioned at the outset so as to reliably perform cooling of the piston head, even in the case of a piston having a centrally raised piston head or a dome-shaped cooling chamber. It is also offered at a low cost.

The object of the invention is that the insert body, which is installed in the cooling chamber in which the center part is raised, is arranged at the upper end of the piston rod, the insert body faces the inner surface opposite the piston head and supports the nozzle communicating with the supply conduit and is surrounded by the annular chamber, The annular chamber is achieved by forming a coolant collection chamber.

The nozzles respectively corresponding to the piston head inner surface area to be cooled can concentrate the entry of coolant throughout the inner surface of the piston head. The spray stem striking the inner surface of the piston head is preferably strong enough that the coolant film formed by the first entering coolant remaining on the inner surface is removed and the fresh coolant can be in intensive contact with the inner surface of the piston head to be cooled. Therefore, the cooling capacity of the coolant is fully utilized. The spray stem striking the inner surface of the piston head forms a cooling membrane that extends radially about the spray stem axis at the inner surface, which impinges on the adjacent cooling membrane at the boundary of the zone. The result is a turbulent flow in the coolant which leads to active heat transfer, thus increasing the cooling effect compared to laminar disturbance. Coolant flowing from the surface entering by the nozzle collects in the collection chamber surrounding the insert body and is driven upward in the top dead center region due to the effective inertia force whenever the upward movement of the piston is delayed. Thus, additional air supply and concomitant cooling of the piston head is achieved.

Preferred and improved forms of the measures are set out in the dependent claims.

As such, it may be desirable for the inner surface of the piston head to be entered by the nozzles to be smooth and undivided. In such a case, it helps the formation of the cooling film which extends in the radial direction and together with the generation of turbulence in the coolant.

In another preferred solution of the invention, the number of nozzles arranged per unit area of the piston head inner surface is chosen according to the heat load in each case. Therefore, more nozzles may be arranged in regions with a relatively high heat load, for example, a region having a relatively low heat load. It is thus advantageously possible to balance a relatively large local temperature difference.

In another refinement of the solutions, the axis of the nozzle may extend substantially perpendicular to the surface respectively corresponding to the piston head inner surface. This helps to evenly expand the cooling membrane in the radial direction and also to the reliable entry of the entire piston head inner surface.

Preferably, the spacing between the nozzle and the corresponding inner surface of the piston head is 4 to 7 times the nozzle diameter. In this case, it is possible to form a reliable jet cone, which further aids in the formation of a radially diffused cooling film.

According to another refinement of the solutions, the piston skirt can have cooling holes parallel to the axis, the cooling holes being able to enter the coolant through connecting holes starting from the coolant collection chamber and obliquely upwards. The collection chamber surrounding the insert body is preferably capable of further entering the coolant at the upper boundary of the cooling chamber, as well as allowing for reliable entry of the coolant into the cooling holes even though the cooling chamber upper boundary extends inclined towards the edges. The coolant may then flow through the return pipe.

Other preferred and improved forms of the above solutions are set forth in the remaining dependent claims, and can be more fully understood from the following description of the embodiments based on the drawings.

The main field of application of the present invention is a two-stroke large diesel engine with a crosshead structure used in ship driving and the like. The structure and mode of operation of these engines are well known.

The piston shown in FIG. 1 is connected with a crosshead (not shown in detail) via a piston rod 1. The piston comprises a piston top 2 having a piston head 3 on the combustion chamber side and a piston skirt 4 for receiving the outer edge of the piston head 3, the piston bottom being provided with a piston bottom 5. The piston top 2 is received on a flange 6 provided in the upper end region of the piston rod 1. The rotary piston skirt 4 also has a radially inward rotating frame 7 lying on the flange 6 with the sealing means 24 in an in-line arrangement, the frame With the piston head 3 borders the central cooling chamber 8 of the piston top 2, which is arranged in the piston head 3. The piston rod comprises a tappet 9 protruding above the flange 6, which tappet engages the cooling chamber 8 and forms the lower termination of the cooling chamber.

The piston head 3 having approximately the same thickness in the region of the cooling chamber 8 rises in the center portion, resulting in a dome shape. This also applies to the upper boundary of the cooling chamber 8 formed by the inner surface of the piston head 3.

Coolant can enter the cooling chamber 8. The piston rod 1 also has a supply conduit 10 arranged in the cooling chamber 8 and capable of entering coolant, and a return pipe 11 arranged outside the supply conduit. The feed conduit 10 is formed by a pipe 12 inserted into the central bore of the piston rod 1, which is surrounded by a ring channel forming the return pipe 11. The coolant supplied to the supply conduit 10 may be placed under a certain pressure. There is no pressure in the return pipe 11.

In the outer region of the piston skirt 4 there is provided a cooling hole 13 which is evenly distributed on the circumference and mainly parallel to the axis, the cooling holes being each capable of entering the coolant through corresponding connection holes 14. It is connected to the cooling chamber (8). At least one connecting hole 14 is arranged for each cooling hole 13. Cooling holes 13 parallel to the axis branch from the ring channel 15 which connects the cooling holes and is closed down by the piston bottom 5, the ring channel being through holes 16 in the flange 6. Through the return pipe (11). The through hole 16 is arranged slightly above the bottom of the ring channel 15.

The insert body 17 which is installed in the cooling chamber 8 is mounted on the upper end of the piston rod 1, that is, on the upper end of the tappet 9 of the piston rod 1 bounding the lower part of the cooling chamber 8, The insert body closes the ring channel forming the return pipe 11 with a ring tappet 18 which engages the ring channel and includes a supply conduit 10 in the central bore 19 of the ring tappet. 12) is engaged. The bore 19 communicates with the dispenser chamber 20 provided in the insert body 17, and a nozzle 21 arranged on the insert body 17 is connected with the dispenser chamber, and the nozzle into the cooling chamber 8. Extrude The nozzle 21 can be easily formed as a pipe section received on the insert body 17.

The end of the pipe section forming the nozzle 21 faces the inner surface of the piston head, ie towards the upper boundary of the cooling chamber 8, wherein the nozzle axes are each substantially perpendicular to the corresponding impingement surface. The spacing of the nozzles 21 with respect to the corresponding collision surface respectively amounts to 20 mm to 30 mm. This is generally four to seven times the nozzle diameter, ie the inner diameter of the pipe section forming the nozzle 21.

The diameter of the insert body 17 is smaller than the inner width of the cooling chamber 8. In this way, an annular chamber 22 is created which surrounds the insert body 17. The annular chamber acts as a collection chamber for the coolant flowing out of the walls of the cooling chamber 8. The connecting holes 14 branch off from the annular chamber 22 and face up obliquely from the annular chamber. In order to be able to empty the annular chamber 22 completely, the annular chamber branches to the bottom level and is connected with the return pipe 11 via a drain conduit 23 having a relatively small cross section. The cross section of the drain conduit 23 can be very small such that relatively large short-circuit flow does not occur on the drain conduit during normal operation, and thus no serious loss of coolant occurs. This requires that the annular chamber 22 can be emptied within an hour for engines that have been stationed for a relatively long time. Therefore, an inner width of the drain conduit of 4 mm to 7 mm is sufficient. These measures ensure that the piston top 2 can be dismantled during maintenance work without removing the coolant from the annular chamber 22.

When the coolant enters the supply conduit 10, the coolant emerges from the nozzles 21 in the form of a coolant spray stem (indicated by arrows in FIGS. 2 and 3), the coolant spray stem being each of the inner surface of the piston head 3. Cool the piston head while facing the opposite wall area. The nozzles 21 are then arranged such that each nozzle 21 has an area corresponding to the inner surface of the piston head 3. In this case, the distribution of the nozzle 21 is selected such that the coolant enters the entire surface of the inner surface of the piston head 3 reliably. In order to limit or prevent the temperature difference in the piston head 3 as much as possible, the distribution of the nozzles 21 can be selected such that a relatively large number of nozzles 21 are arranged in a surface area with a relatively high temperature load. Thus, for example, in the region of the piston head 3 which collides upon injection of fuel, a larger number of nozzles 21 can be arranged than other regions of the same size.

As already mentioned, the axes of the nozzles 21 are arranged at almost right angles, ie at an angle of 90 degrees +/- 10 degrees, to the impingement surfaces respectively formed on the inner surface of the piston head 3. The spray stems striking the inner surface of the piston head 3 remove the coolant film still remaining on the inner surface and with it enter the surface to be cooled. The spray stems form a cooling film that extends radially on the surface to be cooled. In order to help the cooling membrane to spread evenly in the radial direction, the inner surface of the piston head 3 is as smooth and undivided as possible. Turbulence occurs where radially extending cooling membranes collide with each other, contributing to the cooling effect as well as to heat transfer from the piston head 3 to the coolant. The same applies to the nozzle spacing (mentioned above) which allows the formation of the desired atomizing cone.

As is well known, coolants in the form of water or mainly oils are used as coolants. The insert body 17 with the nozzle 21 prevents coolant returning from the surface to be cooled back into the supply conduit 12. This ensures that fresh coolant is always available. The coolant returning from the surface to be cooled collects in the annular chamber 22 surrounding the insert body 17, which thus forms the coolant collection chamber.

The coolant in the cooling chamber 8 is subject to the inertial forces that occur due to the movement of the piston. Thus, upward or downward inertial forces act on the coolant, and the inertial forces cause relative movement of the coolant relative to the piston at the time of the piston's redirection to prior to the redirection.

When the piston is stopped in the bottom dead center region on the return stroke, the coolant contained in the cooling chamber 8 is pushed into the collection chamber formed by the annular chamber 22 as indicated by the black face in FIG. Coolant also collects at the bottom of the ring channel 15. This also applies to the upstroke as long as the upward positive acceleration of the piston occurs here. The coolant that is pushed into the collection chamber can flow out through the connection hole 14. The connecting holes 14 which obliquely rise up from the collection chamber here actually form nozzles, with each having a spray of coolant spray stems entering the corresponding cooling holes 13 as indicated by the arrows in FIG. 2. The connection holes 14 in this case are arranged to face the wall opposite the coolant jetting stem which is generated near the shaft and the upper bore end of the corresponding cooling hole 13, so that the coolant in the upper region of the cooling hole 13 Not only movement but also a good cooling effect are obtained. The coolant remaining in the cooling hole 14 likewise moves downwards when the upward movement of the piston is delayed, so that the ring channel 15 is filled with the coolant until it reaches the overflow edge of the through hole 16.

When the piston in the upstroke is stopped when it approaches the top dead center, the coolant contained in the annular chamber 22 is discharged out of the cooling chamber and flows out toward the upper boundary opposite the cooling chamber 8. This is the basis of FIG. 3. In this way, at the upper boundary of the cooling chamber 8, further coolant entry and at the same time additional cooling are implied, as is also indicated by the black side in FIG. 3. As implied by the black side in FIG. 3, the coolant is also lifted up in the cooling holes 13 to hit the upper bore wall. The coolant contained in the connection hole 14 is pushed up from the connection hole 14 by upward force, thus creating a strong spray stem. At this time, the coolant included in the cooling holes 13 and the ring channel 15 connecting the cooling holes is likewise discharged upwards, so that the end region of the cooling hole 13 close to the combustion chamber is further cooled. The upward force acting on the coolant is also effective during the return stroke of the piston as long as the positive downward acceleration of the piston is achieved.

Because of the piston's motion switching and different accelerations, the coolant contained in the cooling chamber 8 and the cooling hole 13 is discharged up and down as described above and at the same time maintains movement. Therefore, the cooling effect is enhanced. At the same time, a certain pumping effect occurs, whereby the coolant is supplied from the annular chamber 22 to the cooling holes 13 through the connecting hole 4, from the ring channel 15 and the drilling hole from the cooling holes. It may flow past the 16 and into the return pipe 11. The above mentioned forces thus circulate the coolant reliably.

According to the piston of the present invention, even in the case of a piston having a centrally raised piston head or a cooling chamber formed in a dome shape, the device of the kind mentioned at the outset is reliably and at low cost to reliably cool the piston head. Produced.

Claims (12)

A piston top 2 received in an upper region of the piston rod 1, the piston top having a piston head 3 connected to a piston skirt 4, the piston head having a central cooling chamber 8. It is covered, the cooling chamber is allowed to enter the coolant through the supply conduit 10 arranged in the piston rod (1), the coolant to the return pipe (11) installed radially outside the supply conduit (10) In crosshead engines, in particular two-stroke large diesel pistons, An insert body 17 provided in the cooling chamber 8 in which the center part is raised in the upper end of the piston rod 1 is arrange | positioned, The said insert body communicates with the said supply conduit 10, and the said piston head ( 3, respectively, facing the inner surface opposite to and supporting the nozzle 21 corresponding to the inner surface area to be cooled of the piston head and surrounded by the annular chamber 22, wherein the annular chamber forms a coolant collection chamber. piston. The method of claim 1, Piston, characterized in that the nozzle (21) is arranged in all areas of the inner surface of the piston head (3). The method according to claim 1 or 2, A piston, characterized in that the number of the nozzles (21) arranged per unit area of the inner surface of the piston head (3) is selected according to the heat load in each case. The method of claim 3, A piston, which is characterized in that the nozzles are arranged more concentrated in the areas of the piston head (3) exposed to the fuel injected from the outside than in the other areas. The method according to any one of claims 1 to 4, Piston, characterized in that the inner surface of the piston head (3) to be sprayed by the nozzle (21) has a smooth, undivided surface. The method according to any one of claims 1 to 5, Piston, characterized in that the axis of the nozzles (21) extend generally at right angles to the opposite surface of the inner surface of the piston head (3). The method of claim 6, Piston, characterized in that the axis of the nozzles (21) extends below an angle of 90 degrees ± 10 degrees with respect to the surface opposite the inner surface of the piston head (3). The method according to any one of claims 1 to 7, Piston, characterized in that the nozzles (21) are spaced four to seven times the diameter with respect to the inner surface opposite each of the piston head (3). The method of claim 8, A piston, characterized in that the spacing the nozzle has with respect to the inner surface on each opposite side of the piston head (3) is 20 mm to 30 mm. The method according to any one of claims 1 to 9, The piston skirt 4 has cooling holes 13 that are generally parallel to the axis and from the annular chamber 22 forming the coolant collection chamber through the connecting holes 14 at an angle upwards into the cooling holes. Piston characterized in that the entry of the coolant. The method of claim 10, Piston, characterized in that at least one connecting hole (14) is arranged in each cooling hole (13). The method according to claim 10 or 11, wherein Said cooling holes (13) branch upwardly from a ring channel (15) connecting said cooling holes, said ring channel being connected to a return pipe (11).

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