JP2007107525A - Piston for cross-head engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly reliably cool a piston crown, in a piston provided with the piston crown having a rising center or with a cooling chamber formed to have a dome shape. <P>SOLUTION: This piston is used in particular for a large two-cycle diesel engine and is provided with a piston upper part (2) mounted to an upper flange (9) of a piston rod (1). The piston upper part (2) is provided with the piston crown (3) connected to a piston skirt (4) annularly surrounding the periphery, and the piston crown (3) covers the central cooling chamber (8). In this chamber (8), coolant can be injected via a supply line (10) arranged inside the piston rod (1), and can be carried away via a return line (11) provided outside in the radial direction of the line (10). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston for a crosshead engine, particularly for a two-cycle large diesel engine, comprising a piston upper part attached to the upper end of a piston rod, the piston upper part being a piston surrounding the periphery of the piston. An upper piston crown leading to the skirt is provided, which covers the central cooling chamber, into which coolant can be injected via a supply line arranged in the piston rod. The coolant is carried away via a return line provided outside the supply line in the radial direction.

  Such a structure is known from US Pat. In this known structure, a coolant jet exits from the upper end of the supply line formed by the central bore of the piston rod, and this coolant jet is injected into the middle region inside the piston crown. The piston crown is recessed at the center. Therefore, the contour of the upper partition of the cooling chamber becomes higher from the center toward the outside in the radial direction. At this time, since the coolant injected to the center of the piston crown is distributed outward in the radial direction when the upward movement of the piston is decelerated, the entire piston crown is cooled.

  A piston having a piston crown with a raised center is also known, and is described in Patent Document 2, for example. Since the center of the piston crown is raised, the contour of the upper partition of the cooling chamber is lowered outward in the radial direction. When cooling in the same manner as described above, the coolant is not distributed radially outward when the piston's upward movement is decelerated, but rather at the center of the dome formed by the raised piston crown in the center. Accumulate in the area. However, in this case, there is a risk that the outer region cannot be reliably cooled in the radial direction of the piston crown.

Patent Document 3 describes a piston having a cooling chamber under a piston crown, and the upper partition of the cooling chamber is also raised at the center and is formed in a dome shape. Here, a cooling bore is provided in the piston crown that covers the cooling chamber, but this cooling bore is distributed over the entire surface of the piston crown, and exits from the cooling chamber and is inclined with respect to the piston shaft. A plug is provided in the cooling chamber, which partitions the distributor chamber connected to the supply line, and this plug is equipped with a nozzle that exits from here and leads to each assigned cooling bore. Coolant is injected from the nozzles to the assigned cooling bores. The disadvantage here is that during the downward movement of the piston, the coolant enters the cooling bore and stays there, forming a substantially filled liquid, which is injected from the nozzle. The jet is braked, and the jet is not sufficiently injected, which adversely affects the cooling action. Apart from that, here the nozzles are not arranged coaxially with the bore axis, but are tilted towards the bore axis, so that the jets coming out here are injected into the side walls of the respective assigned bores, so that the bore bottom Adversely affects cooling.
German Patent Invention No. 199 62 325 German Patent Application Publication No. 198 15 919 European Patent No. 07 47 591

  Therefore, an object of the present invention is to improve the above-described configuration by a simple and low-cost method, and to increase the cooling of the piston crown even in a piston having a piston crown or a dome-shaped cooling chamber raised at the center. It is to be able to do it with reliability.

  According to the present invention, according to the present invention, a plug placed in a cooling chamber with a raised center is arranged at the upper end of the piston rod, and this plug is provided with a nozzle that is directed to the inside of the piston crown and communicates with the supply line. This can be solved by surrounding the plug with a ring-shaped space constituting the coolant recovery space.

  The nozzle assigned to each one zone inside the piston crown to be cooled can sufficiently inject coolant onto the entire inner surface of the piston crown. The jet injected onto the inner surface of the piston crown is powerful in a suitable manner, so that the remaining film of coolant from the previous injection is removed and the new coolant can fully contact the inner surface of the piston crown to be cooled. Thus, the cooling capacity of the coolant is fully utilized. The jet injected on the inner surface of the piston crown forms a cooling bale that extends radially with respect to the jet axis, and this cooling bale contacts the zone boundary of the adjacent cooling bale, resulting in turbulent coolant flow. This turbulent flow causes a large heat transfer, so that the cooling effect is higher than in the case of laminar flow. The coolant that flows down the surface that is sprayed by the nozzle is collected in the collection space that surrounds the plug, but because of the inertial force, it is blown upward each time the piston ascends in the top dead center area and decelerates. In addition, the piston crown is injected and thereby the piston crown is additionally cooled.

  Preferred configurations and higher-level developments of the higher-level means can be seen from the dependent claims.

  The purpose is that the inside of the piston crown receiving the injection from the nozzle is smooth and not divided. This is advantageous for the formation of radially expanding cooling veils and the generation of coolant turbulence.

  Another preferred method is to select the number of nozzles provided per unit area inside the piston crown in accordance with the respective heat load. For example, more nozzles are assigned to areas with a high heat load, such as an injection area, than areas with a low heat load. Thereby, a large local temperature difference can be smoothed out in a suitable manner.

  In another development of the superordinate method, it is possible for the axis of the nozzle to extend approximately perpendicular to each assigned surface inside the piston crown. This is advantageous for expanding the cooling bale uniformly in the radial direction, thereby reliably contacting the inner surface of the piston crown.

  The purpose of the distance between the nozzle and the assigned inner surface of the piston crown is 4-7 times the nozzle diameter. Thereby, the jet can be jetted with high reliability, which further helps to form a cooling bale that expands radially.

  According to another development of the superordinate method, the piston skirts that surround the circumference can be provided with cooling bores extending parallel to the axis, and these cooling bores are located above the coolant recovery space and Coolant can be supplied through a connecting bore towards the. Due to the recovery space surrounding the plug, not only is coolant injected into the upper compartment of the cooling chamber in a suitable manner, but also the upper compartment of the cooling chamber is lowered towards the edge. Regardless, the coolant can be reliably supplied to the cooling bore and this coolant can then be carried away via the return line.

  Further preferred embodiments and purposeful developments of the superordinate method are described in the remaining dependent claims and can be understood in more detail from the following description using the figures.

  The main field of application of the present invention is a crosshead type two-cycle large diesel engine used for driving a ship or the like. The structure and operating method of such an engine are well known.

  The piston shown in FIG. 1 is connected to a crosshead (not shown in detail) via a piston rod 1. The piston is provided with a piston upper part 2, which has a piston crown 3 facing the combustion chamber and a piston skirt 4 that surrounds the periphery annularly and supports the outer edge of the piston crown 3. The piston lower part 5 is attached to this piston skirt. The piston upper portion 2 is placed on a flange 6 provided in the upper end region of the piston rod 1. For this purpose, the piston skirt 4 that surrounds the periphery is provided with a web 7 that surrounds the periphery of the piston skirt 4 on the flange 6 via the intermediate connection of the seal 24 on the radially inner side. Together with the piston crown 3, a partition of the central cooling chamber 8 of the piston upper part 2 assigned to the piston crown 3 is formed. The piston rod includes a journal 9 that extends over the flange 6 and is fitted into the cooling chamber 8 to form its lower end.

  The piston crown 3 having substantially the same thickness in the region of the cooling chamber 8 has a dome shape because it is raised at the center. Therefore, the upper partition of the cooling chamber 8 formed inside the piston crown 3 has a similar shape.

  Coolant can be injected into the cooling chamber 8. For this purpose, the piston rod 1 is provided with a supply line 10 assigned to the cooling chamber 8 and capable of supplying coolant, and a return line 11 arranged outside the supply line. The supply line 10 is formed by a pipe 12 inserted into the central bore of the piston rod 1, and the periphery of this pipe is surrounded by a ring-shaped duct that forms a return line 11. A constant pressure can be applied to the coolant supplied to the supply line 10. No pressure is applied to the return line 11.

  The outer region of the piston skirt 4 is provided with cooling bores 13 distributed on its circumference, preferably parallel to the axis, which receive coolant via their respective connection bores 14. It is connected to the cooling chamber 8 to be injected. Each cooling bore 13 is assigned at least one connection bore 14. The cooling bores 13 parallel to the axis pass through the branch bores 16 extending radially in the flange 6 as they exit the ring duct 15 connecting the cooling bores and closed below by the piston lower part 5. The return line 11 is contacted. The branch bore 16 is disposed slightly above the bottom of the ring-shaped duct 15.

  A plug 17 installed in the cooling chamber 8 is placed on the upper end of the piston rod 1, that is, the journal 9 of the piston rod 1 that divides the cooling chamber 8 in this figure. A ring-shaped duct to be formed is closed by a ring journal 18 fitted in the ring-shaped duct, and a pipe 12 containing a supply line 10 is fitted in a central bore 19 of the ring journal. The bore 19 communicates with a distributor chamber 20 provided in the plug 17, and a nozzle 21 disposed in the plug 17 is connected to the distributor chamber, and these nozzles protrude into the cooling chamber 8. ing. The nozzle 21 can simply be configured as a pipe portion attached to the plug 17.

  The end of the pipe part forming the nozzle 21 is directed to the inside of the piston crown, that is, to the partition above the cooling chamber 8, and at this time, the nozzle axis is substantially perpendicular to the assigned injection surface. It is. The distance between the nozzle 21 and the assigned ejection surface is 20 to 30 mm. This distance is usually 4 to 7 times the nozzle diameter, i.e. the internal diameter of the pipe part forming the nozzle 21.

  The diameter of the plug 17 is smaller than the internal width of the cooling chamber 8. Therefore, a ring-shaped space 22 is generated around the plug 17. This ring-shaped space functions as a recovery space for recovering coolant that flows down from the wall of the cooling chamber 8. The connection bore 14 exits the ring-shaped space 22 and extends obliquely upward from here. In order to completely empty the ring-shaped space 22, this ring-shaped space is connected to the return line 11 by a drain line 23 having a relatively small cross section that exits from the same level as the bottom. By reducing the cross section of the drain line 23, it is possible to prevent a large bypass flow from occurring during normal operation, that is, not to cause a remarkable coolant loss. It is sufficient that the ring-shaped space 22 can be drained within a long time of, for example, one hour unit in a state where the engine is stopped. Therefore, the internal width of the drain line of 4 to 7 mm is quite sufficient. By the method described above, even if the piston upper part 2 is removed during maintenance work, the coolant can be reliably prevented from overflowing from the ring-shaped space 22.

  When the coolant is supplied to the supply line 10, the supply line injects a coolant jet indicated by an arrow in FIGS. 2 and 3 from the nozzle 21, and this coolant jet is inside the piston crown 3 on the opposite side. Reach the wall area of and cool this area. The nozzles 21 are then arranged such that each nozzle 21 injects into an assigned zone on the inner surface of the piston crown 3. At this time, the distribution of the nozzles 21 is selected so that the coolant is injected with high reliability over the entire inner surface of the piston crown 3. In order to make the temperature difference in the piston crown 3 as small as possible or prevent the temperature difference from occurring, the distribution of the nozzles 21 can be selected to allocate more nozzles 21 to the surface area with a high thermal load. Therefore, for example, the number of nozzles 21 can be assigned more to the region of the piston crown 3 to which the injected fuel is applied than to other regions of the same size.

  As already mentioned, the axis of the nozzle 21 is arranged at a substantially right angle, that is, at an angle of 90 ° ± 10 ° with respect to the injection surface of the inner surface of the assigned piston crown 3. The jet that has reached the inner surface of the piston crown 3 can remove the coolant film still remaining there, thereby making good contact with the surface to be cooled. The jet forms a cooling bale on this surface that spreads greatly in the radial direction. In order to help the cooling bale to expand uniformly in the radial direction, the inner surface of the piston crown 3 is as smooth and undivided as possible. A turbulent flow is generated where the cooling bales extending in the radial direction intersect, and this turbulent flow is useful for heat transfer from the piston crown 3 to the coolant and for a cooling effect. The same is true for the nozzle distance described above, which allows the jet to be efficiently conically shaped.

  As coolant, known methods use coolants in the form of water or preferably oil. The plug 17 including the nozzle 21 can prevent the coolant that has returned from the cooled surface from returning to the supply line 12. Therefore, new coolant is always prepared. The coolant that has returned from the cooled surface accumulates in a ring-shaped space 22 surrounding the plug 17, and this ring-shaped space thus forms a coolant recovery space.

  The coolant existing in the cooling chamber 8 is affected by the inertial force generated by the movement of the piston. Therefore, depending on the case, the inertial force acting upward or downward acts on the coolant, so that the relative movement of the coolant relative to the piston occurs when the piston changes direction or when the piston decelerates before changing direction. .

  When the piston descends, if it decelerates in the bottom dead center region, the coolant contained in the cooling chamber 8 is contained in the recovery space formed by the ring-shaped space 22 as shown by the dark color in FIG. Is pushed into. The coolant also collects at the bottom of the ring-shaped duct 15. The same is true for ascent as long as positive acceleration of the piston is taking place. The coolant pushed into the recovery space can be discharged through the connection bore 14. The connection bores 14 that exit from the recovery space and extend obliquely upward form substantially nozzles for generating coolant jets that respectively enter the assigned cooling bores 13 as indicated by arrows in FIG. . At this time, the connection bore 14 also reaches the opposite wall near the upper bore end of the assigned cooling bore 13, so that the axis of the connection bore and the generated coolant jet in this case also reach the upper end region of the cooling bore 13. Is arranged so that a good cooling effect can be achieved. Similarly, the coolant present in the cooling bore 14 also moves downwards during deceleration of the piston lifting movement, so that the ring-shaped duct 15 is filled with coolant up to the overflow edge of the bypass line 16.

  When the piston decelerates as it approaches the top dead center while ascending, the coolant present in the ring-shaped space 22 ejects vigorously from here and is injected into the upper partition of the cooling chamber 8 on the opposite side. This has been described with reference to FIG. In this manner, as shown in the dark color in FIG. 3, the coolant is injected to the upper partition of the cooling chamber 8, thereby being additionally cooled. The coolant is also blown up in the cooling bore 13 and reaches the upper bore wall as shown by the dark colored surface in FIG. The coolant present in the connection bore 14 is pushed upward from the connection bore 14 by the upward force, thereby generating a powerful jet. At this time, the coolant existing in the cooling bore 13 and in the ring-shaped duct 15 connecting them is similarly ejected upward, thereby additionally cooling the end of the cooling bore 13 close to the combustion chamber. be able to. The upward force acting on the coolant is also acting when the piston is lowered as long as the piston is positively accelerating downward.

  Due to the redirection of the piston and the different accelerations, the coolant present in the cooling chamber 8 and the cooling bore 13 is constantly moving because it is vigorously moved up and down, as described here, so that it is cooled. The effect is strengthened. At the same time, this produces a certain pumping effect, whereby coolant is supplied from the ring-shaped space 22 to the cooling bore 13 via the connection bore 14, from which the ring-shaped duct 15 and the branch bore 16 are passed. To the return line 11. Therefore, the above-mentioned force is useful for performing coolant circulation with high reliability.

It is radial direction sectional drawing of the piston of this invention, and has shown the state which does not contain a coolant. It is sectional drawing which shows the place where the coolant has entered the structure of FIG. 1 and has reached the bottom dead center. It is sectional drawing which shows the place where the coolant has entered the structure of FIG. 1 and has reached the top dead center.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston rod 2 Piston upper part 3 Piston crown 4 Piston skirt 5 Piston lower part 6 Flange 7 Web 8 Cooling chamber 9 Journal 10 Supply line 11 Return line 12 Pipe 13 Cooling bore 14 Connection bore 15 Ring-shaped duct 16 Branch bore 17 Plug 18 Ring journal 19 Bore 20 Distributor chamber 21 Nozzle 22 Ring-shaped space 23 Drain line 24 Seal

Claims (12)

Piston for a crosshead engine, particularly a two-cycle large diesel engine, comprising a piston upper part (2) attached to the upper end of the piston rod (1), and the piston upper part is a piston skirt surrounding the periphery of the piston skirt A piston crown (3) connected to (4), which covers the central cooling chamber (8), which is connected to the central cooling chamber via a supply line (10) arranged in the piston rod. Coolant can be injected, this coolant can be carried away via a return line (11) provided radially outward of the supply line (10),
At the upper end of the piston rod (1), a plug (17) provided in the cooling chamber (8) raised at the center is arranged, and this plug communicates with the supply line (10). In the ring-shaped space (22), which is provided with a nozzle (21) assigned to one zone inside the cooling target of the piston crown (3), facing the inside of the piston crown (3) Piston characterized by being surrounded.   2. Piston according to claim 1, characterized in that nozzles (21) are assigned to all areas inside the piston crown (3).   3. The piston according to claim 1, wherein the number of nozzles (21) provided per unit area inside the piston crown (3) is selected according to the respective heat load. Piston characterized by being.   4. The piston according to claim 3, wherein the area of the piston crown (3) that receives the fuel injection during the injection has a higher nozzle density than the other areas.   The piston according to any one of claims 1 to 4, wherein the inside of the piston crown (3) that receives the injection from the nozzle (21) has a smooth and undivided surface. Piston.   6. The piston according to claim 1, wherein the axis of the nozzle (21) extends substantially perpendicular to the inner surface of the opposing piston crown (3). A characteristic piston.   7. Piston according to claim 6, characterized in that the axis of the nozzle (21) extends at an angle of 90 ° ± 10 ° with respect to the inner surface of the opposing piston crown (3). piston.   8. A piston according to any one of the preceding claims, wherein the nozzle (21) is separated from the inner surface of the opposing piston crown (3) by a distance of 4 to 7 times the diameter of the nozzle, respectively. Piston characterized by that.   9. Piston according to claim 8, characterized in that the distance between the nozzle (21) and the inner surface of the piston crown (3) facing each other is between 20 and 30 mm.   The piston according to any one of claims 1 to 9, wherein the piston skirt (4) surrounding the periphery of the piston is preferably provided with a piston bore (13) parallel to the axis. The piston bore is characterized in that coolant can be supplied through a connection bore (14) that goes out of the ring-shaped space (22) forming the coolant recovery space and goes obliquely upward. Piston to do.   Piston according to claim 10, characterized in that at least one connection bore (14) is assigned to each cooling bore (13).   12. Piston according to claim 10 or 11, wherein the cooling bore (13) is directed upward from one ring duct (15) connecting the cooling bores, the ring duct being a return line. A piston connected to (11).