DE1476393A1 - Liquid-cooled piston - Google Patents

Description

Maschinenfabrik Augsburg-Nürnberg, public limited company

Augsburg H76393

Stadtbachstrasse 7

P.B. 2336

Liquid-cooled flask

The invention relates to a liquid-cooled piston in particular. for internal combustion engines whose bottom is cooled by spraying and in which the coolant in crosshead engines is unimpeded runs freely through the piston rod or in the case of plungers into the crankcase.

In modern internal combustion engines of high power this results inevitably an increased thermal stress on the working piston, so that the heat introduced into the piston crown even with good Thermal conductivity of the piston material to the coolant can no longer be easily dissipated.

A basic distinction is made between cooling the piston with water and lubricating oil. The 7 / water cooling is - as a result of the much lower viscosity of the coolant and thus better heat transfer - significantly more effective than oil cooling, but it requires it as a result of the necessary separation of supply and discharge to the piston (trombones) from the machine room a significantly higher construction effort.

Various embodiments are known for oil cooling. In the case of light metal pistons, for example, cooling coils have been cast into the piston, preferably in the area of the piston rings, to which the coolant is fed through bores in the drive rod and in the piston pin, while the process

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- P.B. 2336

H76393

■ takes place freely in the crankcase. With this cooling, however, " The piston crown and piston crown continue to be exposed to the high temperatures.

To prevent this and to have a better cooling effect the piston has already been injected from below, i.e. from the drive rod. Such a localized one However, cooling is only suitable for pistons of small dimensions, but not for larger pistons sufficient.

In addition, attempts have been made to use such spray cooling due to the additional arrangement of rooms that are only partially filled with coolant, in which the coolant flows back and forth could splash, improve.

It is also known to cool the piston by forcing the coolant flow, wherein to improve the Heat transfer in pistons has also been proposed, to build in the piston cavities Pührungsflachen so are designed that between the same and the wall to be cooled only a small space for the flow of the coolant remains. The cooling chambers of the piston are completely filled with cooling liquid. By such internals the manufacture of the pistons is made more difficult and In addition, their weight increases unnecessarily, and it is also difficult to get the coolant into the outermost corners of the cooling space .bring to.

There are also known pistons in the annular cavity delimited by the piston head and the piston wall several nozzles open, which in one deviating from the radial Direction are arranged and wherein the coolant · in the cavity a rotating movement around the piston axis by the coolant emerging from the nozzles. Here, too, the coolant completely fills the cooling space

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the end. The heat dissipation is due to the moderate speed limited in particular near the wall.

With the growing specific performance, it continues however, all these are sufficient for increased heat incidence in the flask Measures for adequate cooling of the piston crown are not sufficient. In particular, it can be seen, for example, in the case of highly loaded pistons that the cooling oil on the underside of the piston crown becomes lacquered and coked, which makes the cooling worse and worse over time will.

These disadvantages can occur in the case of a piston whose base is molded on is cooled, can be avoided according to the invention that in the vicinity of the piston head a plurality of against the Narrow bores (nozzles) directed towards the bottom surface on the cold room side for the passage of the coolant supplied under high pressure is provided. With this measure, the entire underside of the piston crown can be covered by the spray jets, because the coolant hits the ground at high speed and spreads over a limited area Distributed like a film, namely as long as the kinetic energy stored in the beam is present. By a multitude of incident rays, the effective area of which is defined by the Liquid pressure and the nozzle size can be determined, the cooling effect can be precisely adapted locally to the respective requirements by the liquid film adhering to the piston crown being continuously smashed by the impinging jet and thus heat is drawn from the wall during the entire work cycle. It is known that the heat transfer is high Measure directly from the speed of the coolant the wall surface (boundary layer) depends. The effect of the present invention is best understood from an estimation the speeds of the coolant on the surface to be cooled. In the case of a piston with forced circulation of the coolant it becomes difficult to control flow velocities in spite of internals to guide the oil of more than 2 to 3 m / s,

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SAD

P.B. 2536

because otherwise the amount of oil to be pumped through and the performance of the Oil pumps get too high. With spray cooling, the jets hit at least 10 times the speed on the wall surface. Starting from the point of impact it takes the speed of the spreading oil film in radial direction Direction abι but if the points of impact are sufficiently close to one another, Nevertheless, it is possible to achieve a significantly higher speed over the entire oil-wetted area than with a forced circulation. Another advantage of the cooling according to the invention is the effective 'Applicable- ^ ability even at low speeds, where a pure splash cooling is relatively ineffective.

In the drawing is an embodiment of the invention and although shown for the piston of an engine with a cross head. Show it"

Fig. 1 is a longitudinal section through the invention Pistons

FIG. 2 shows a section along line II II of FIG. 1; FIG. 3 shows a detail.

The piston consists in a known way of several parts namely) borrowed the piston crown with the piston crown 1 and the skirt 2 to which the piston rod 3 is connected by screws 4, while the crown is attached to the drive rod by studs 5 will. The piston is cooled by a coolant, which flows through a large number of nozzle-like bores 6, leaks under pressure, each of which has an area of approximately 30

- Recorded 60 cm of the floor. The bores 6, 7 are annular Inserts 8, 9 attached, one 8 of which extends near the piston skirt, while the other 9 in the extension of the piston rod bore is arranged. The holes themselves are alternating in pairs on the circumference and below arranged inclined to one another at an acute angle. In order to prevent the individual beams from interfering with each other, and the oil film spreading on the piston

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To give a preferred direction, the holes 6 are expedient arranged somewhat inclined in the circumferential direction, as can be seen from FIG. Between the holes are each radial incisions 10 in the inserts 8, 9 to allow the coolant to flow back slightly to the drain hole 11 in the piston rod to ensure. The coolant is also supplied through the piston rod, through the outer annular space 12, the bore 13 into the space 14 and via the nozzles 6, 7 to the piston crown. The coolant supply is much more restricted than the drain to prevent the piston from moving fills with liquid. During half a revolution, i.e. when the upward acceleration force is the force of gravity predominates, the liquid is on the one to be cooled Piston crown so that the heat from the piston crown or the adhering boundary layer migrates into the liquid. At after With the acceleration force directed downwards, on the other hand, only a thin film sticks to the floor, which quickly increases the temperature of the wall and would therefore no longer cool if the film was not broken up by the liquid emerging from the nozzles and constantly renewed. During the downward acceleration force, part of the liquid filling is thrown out by the piston rod, the rest Partly pressed into the cavities below the spray nozzles, so the nozzles must protrude above the liquid level i.e. higher than the lower edge of the drainage slots The liquid level is indicated at 15 in FIG. 1. Of course, the liquid pressure in the nozzles is at least to be kept as high as the acceleration pressure counteracting the spraying *

As can be seen from Fig. 1, by a number below Different angles directed bores of the entire area to be cooled of the piston can be detected. Each of these on the Rays hitting the ground spreads according to the inherent energy in a thin film, whereby the liquid drips off at the contact borders with the neighboring film.

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In this way, the entire surface can be covered with a layer of cooling liquid be coated, which is constantly renewed and causes a good cooling of the piston.

The invention applies primarily to the coolant lubricating oil, but is not limited thereto.

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Claims (6)

P.B. 2336 - 7 -. Claims:. 1Λ Lüesigkeiirsgekühlter piston jr-iit & / for internal combustion ^s - "'machines, the bottom of which is cooled by spraying and in which the coolant runs essentially unhindered, characterized in that in the height of the piston head a large number of bores (nozzles) for the passage of the coolant supplied under high pressure is provided, which are directed at an obtuse angle against the floor surface to be cooled, so that the entire floor surface is wetted directly by the impinging liquid jets. 2. Piston according to claim 1, characterized in that the Boh- i'n itt iffrfn / Stanchions are provided on annular inserts, with / between the individual bores or groups of bores incisions are provided for the coolant return. 3 * piston according to claim 1, characterized in that the one annular insert extends in the vicinity of the piston skirt, while the other is arranged in the extension of the piston rod bore. Jf 4 · Piston according to claim 1, characterized in that the Form inserts with the piston crown. 5. Piston according to claim 1, characterized in that the Bores are alternately arranged in pairs in the radial plane and each at an acute angle to one another get lost. BAD ORIGINAL 9098 17/0617 P.B. 2336 H76393 6. Piston according to claim 1, characterized in that the bores are inclined in the Ünfangsrichtung so that the film produced by the liquid jets spreads preferentially in a certain direction. 9 0 3817/0617