JPH086638B2 - Oil-cooled multi-part plunger piston for internal combustion engines - Google Patents

Description

FIELD OF THE INVENTION The present invention comprises a piston lower part and a piston upper part consisting of a piston bottom and an outer wall with a piston ring fitted in a ring groove. Through a piston pin that is supported in a bearing hole that extends through
It is pivotally attached to a connecting rod connected to the crankshaft of an internal combustion engine, and the upper piston part is supported by a ring-shaped supporting collar integrally formed on the upper part of the lower piston part with a contact surface that forms a step from the piston bottom. The piston lower part via a cylindrical centering surface, and is centered by the centering surface provided on the piston lower part and connected to the piston lower part by a plurality of screws. Similar to the lower part of the piston, a protrusion penetrated by a central cooling oil outflow hole coaxial to the longitudinal axis of the piston is arranged, and this protrusion at the upper edge shows the cooling oil filling state in the internal cooling chamber. The cooling chamber is limited in the lower part by a recess in the lower part of the piston extending between the support collar and the outer surface of the projection and in the upper part the piston. It is restricted by a recess in the upper part and is connected to the outer cooling chamber via an oblique communication hole in the upper part of the piston, which cooling chamber extends both in the upper part of the piston and in the lower part of the piston. Oil-cooled plunger pistons.

PRIOR ART Such an oil-cooled plunger piston is known from DE-A-1526598. Such pistons are less suitable for overcoming high ignition pressures. Because, the degree of deformation of the lower part of the piston under the action of ignition pressure is relatively large,
This is because the piston bites. This deformation of the lower part of the piston results from the fact that the upper part of the piston is supported there, i.e. via the ring-shaped support collar and additionally the outer wall of the upper part of the piston. In this case, the supporting collar and the outer wall of the piston upper part are supported on the lower part of the piston by suitable contact surfaces. Since the upper piston part is supported by the lower piston part via two ring-shaped contact surfaces, it is practically impossible to load both contact surfaces with a defined force. This is because one or the other of the two contact surfaces is loaded with great force due to manufacturing errors that cannot be avoided.
Since the upper part of the piston itself is composed of thin walls at many points, the degree to which the upper part of the piston deforms due to combustion temperature and ignition pressure is not negligible, and finally the outer wall surface of the piston upper part and the cylinder hole wall A relatively large amount of play is required between and. However, the disadvantage that the lower part of the piston deforms can be dealt with by configuring the lower part of the piston by providing an elliptic cylinder of appropriate size and swelling so that the deformation due to the action of ignition pressure can be absorbed. . However, the deformation that occurs in the lower portion of the piston configured in this way adversely affects the consumption of lubricating oil. This is because the outer peripheral surface of the lower portion of the piston has a non-circular shape, and it is considered that a large amount of lubricating oil is required at a specific portion of the cylinder hole wall. This problem has been taken into account in the known pistons to which the present invention is directed by providing a plurality of oil scraping rings, but the function of these oil scraping rings has been empirically shown to be high wear. Therefore, it is not fully exerted. Moreover, the oil scraping ring cannot scrape the lubricating oil to a sufficiently desired film thickness at a portion where there is too much lubricating oil. Further, the type of guiding the cooling oil from the outside to the inside, which is adopted in such a known piston, has been proved to be uneconomical. This is because in this case, a piston pin having a complicated structure is necessary to supply the cooling oil. Piston pins pierced by such lateral and vertical holes are only suitable for overcoming average ignition pressures from low ignition pressures due to their low bearing capacity.

Further, according to West German Patent No. 2821176,
Oil-cooled plunger pistons for combustion engines are known in which the lower part of the piston is made of a light metal and the upper part of the piston is made of a metal having a low heat transfer coefficient but a high heat resistance, for example steel.

The problem to be solved by the invention is to improve a plunge piston of the type mentioned at the beginning such that the plunge piston is economical to manufacture and transmits an ignition pressure of 125 to 160 bar. The shape of the plunger piston changes slightly due to this ignition pressure, especially the piston ring part in the upper part of the piston maintains the cylindrical shape, and the lower range of the lower part of the piston is the upper range. The ovalization is substantially avoided with respect to the above, and a better attraction of the cooling oil is obtained in the manufactured plunger piston, in particular with regard to the reduction of the amount of oil used.

Means for Solving the Problems An object of the present invention is to configure a piston upper part consisting of an outer wall having a piston bottom and a piston ring fitted in a ring groove, and a piston lower part, and a piston lower part. Through a piston pin that is supported in a bearing hole that extends laterally through the connecting rod that is connected to the crankshaft of the internal combustion engine, and the piston upper part is a contact surface that forms a step from the piston bottom. , Supported on the end face of a ring-shaped support collar integrally formed on the upper part of the piston lower part and connected to the support flange by a plurality of fastening screws, and coaxial with the piston lower part on the longitudinal axis of the piston. A cooling oil outflow hole is arranged, and this cooling oil outflow hole is opened to an inner cooling chamber connected to an outer cooling chamber arranged on the opposite side of the supporting collar by a communication hole, In an oil-cooled plunger piston of the type in which the cooling chamber on the side extends to both the upper part and the lower part of the piston, (a) the upper part of the piston is almost solid and only within the range of the outer cooling chamber. As a plate with a blind hole, it is integrally manufactured from spheroidal graphite cast iron or steel material, while the lower part of the piston is almost closed except for the cooling oil outflow hole on the upper surface facing the upper part of the piston. In other places, it is made of solid and integrally and is manufactured by pressure casting from aluminum or aluminum alloy or by hot pressing the material. (B) The upper part of the piston is only in the deflection neutral zone. It is supported by the ring-shaped contact surface on the support collar of the lower part of the piston. -Shaped oil receiving recess, which is lowered almost to the plane of the connecting rod head, and which is relatively thin on the outer side in the radial direction and which is not affected by ignition pressure during engine operation. And is solved by the fact that this outer wall part is separated from the outer wall of the upper piston part by a ring gap. Advantageous embodiments of the invention are described in the dependent claims.

Advantages of the Invention The upper part of the piston is made of spheroidal graphite cast iron or steel material in the form of a very solid plate, whereas the lower part of the piston is made by pressure casting from aluminum or by hot pressing the material. This allows the plunger piston to be manufactured relatively economically. However, due to the structural features imparted to it, the plunger piston is able to withstand the high loads exerted on it during operation, despite the fact that the lower part of the piston is made of aluminum. This is because both the upper piston part and the lower piston part independently form a rigid block, and the upper piston part is supported by the lower piston part in a special manner. That is, the piston upper part is so arranged that the ignition pressure acting on the piston upper part is transmitted in good form to the piston lower part and from there to the crankshaft via the piston and the connecting rod connected thereto. Supported by. That is, the ignition pressure is directly guided to the connecting rod head, and the outer peripheral portion of the lower portion of the piston does not actually receive this ignition pressure and is not deformed. Due to the fact that the cooling oil is attracted in the manner according to the invention, a very good cooling action is achieved in the plunger piston. By virtue of the advantageous distribution of the communication holes between the inner and outer cooling chambers, in particular by virtue of the fact that the communication holes have different spacings of suitable size, size and inclination. The non-uniform temperature distribution acting on the upper part of the piston is controlled so as to avoid non-uniform radial deformation of the piston bottom. This, combined with the fact that the upper piston part is supported in the region of the deflection neutral zone, maintains the outer wall of the upper piston part in a substantially cylindrical shape under the action of thermal and mechanical loads. Contribute for. Furthermore, the fact that the outer wall of the upper piston part does not come into contact with the upper range of the lower part of the piston on account of the gap provided by the invention, makes it difficult for the lower part of the piston to move from the upper part of the piston to the upper range of the lower part of the piston. The acting force is not transmitted. The lower part of the piston thus maintains the given shape for good operating values.

The invention will now be described with reference to the drawings: In the drawings, corresponding parts or the same parts of each illustrated plunger piston are given the same reference numerals.

The illustrated oil-cooled plunger piston comprises a lower piston portion generally designated 1 and an upper piston portion generally designated 2. The solid, solid piston upper part 2 comprises a piston bottom 3 and a cylindrical outer surface 5 and an outer wall 4 having a plurality of ring grooves in which the piston rings 6 are fitted. The outer wall 4 of the piston upper part 2 is a thick wall part 7 connecting to the piston bottom 3.
And a thin wall portion 9 connected to the lower edge 8 of the wall portion 7. Starting from the lower edge 8, on the thick wall portion 7 of the outer wall 4, there is a cylindrical centering surface 11 arranged coaxially to the piston longitudinal axis and a contact surface 12 perpendicular to the piston longitudinal axis. And are formed. The upper part 2 of the piston is connected to the lower part 1 of the piston via the contact surface 12 of the piston.
And is supported on the outer end surface 13 of a ring-shaped support collar 14 arranged above the lower piston part 1. The centering of the piston upper part 2 with respect to the piston lower part 1 is effected by means of a flat cylindrical centering surface 11. The centering surface 11 surrounds a cylindrical centering surface 15 formed outside the support collar 14. Code 16
Shows a relatively solid retaining head which forms the upper end of the lower piston part 1. The upper piston part 2 is fixed to the lower piston part 1 with four clamping screws 17. The length and arrangement relationship of these tightening screws are shown in FIGS. 5 and 6.

Reference numeral 18 designates a piston pin which is secured axially by two safety rings 20 in a bearing hole 19 which extends laterally through the lower piston part 1. This piston pin 18
A bearing sleeve 21 is fixed on the upper part. The position of this bearing sleeve is fixed in the inner chamber 24 of the lower piston part 1 between the surfaces 22, 23 parallel to the longitudinal axis of the piston. Via the piston pin 18 and the bearing sleeve 21 above it, the plunger piston is connected to a connecting rod 25 and a connecting rod head 26 which are connected to the crankshaft of an internal combustion engine (not shown).
Is pivotally connected in the range of. In this case, this connection extends laterally through the connecting rod head 26 and encloses the bearing sleeve 21.
Through 27.

Reference numeral 28 designates a protrusion 28 arranged above the holding head 16. The protrusion 28 is integrally formed with the lower portion 1 of the piston as a whole. The projection 28 is pierced by a central cooling oil outlet hole 29 which is arranged coaxially with the longitudinal axis of the piston. The cooling oil outflow hole 29 further penetrates the holding head 16 and opens into the inner chamber 24 of the piston lower portion 1. The cooling oil outflow hole 29 is formed as a hole provided in the lower piston portion 1 which is enlarged in a conical shape or a trumpet shape in the cooling oil inflow range as in the embodiment of FIGS. 1, 2 and 3. be able to. The conical or trumpet-like enlargement ensures a good deflection of the cooling oil flow exiting the connecting rod. As an alternative to this arrangement, the cooling oil outlet hole 29 can also be constituted by a through hole in the cooling oil guide sleeve 30, as in the embodiment shown in FIGS. 3 and 4. . The cooling oil guide sleeve 30 is inserted into a receiving hole 31 penetrating the holding head 16 provided with a protrusion 28, and is elastically supported by the connecting rod head 26 in a sliding contact at the lower expanding portion. The protrusion 28 projects into the inner cooling chamber indicated generally by the reference numeral 33, where the upper edge 32 limits the cooling oil filling state. The inner cooling chamber 33 extends in the lower region between the support collar 14 and the upper protrusion 28 of the holding head 16 in a ring shape. The inner cooling chamber 33 is limited in the upper region by a recess in the upper part of the piston. The inner cooling chamber 33 is an oblique communication hole formed in the upper portion 2 of the piston.
It is connected via 34 to an outer cooling chamber, indicated generally by the reference numeral 35. The outer cooling chamber is formed in both the piston upper part 2 and the piston lower part 1 and extends around the holding head 16 in the piston lower part 1.

The solid piston upper part 2 is made in one piece and from spheroidal graphite cast iron or steel material. The lower piston part 1, on the other hand, is likewise integral, but is produced by pressure casting from aluminum or an aluminum alloy or by hot pressing the material. As long as the undercut is unavoidable, this undercut will be cut later. Piston lower part 1
Since the lower part 1 of the piston has a significantly larger bearing capacity than the lower part of the piston made only by casting, the lower part 1 of the piston receives and transmits a large force. Become suitable to do.

The plunger piston is designed for shaker cooling. In this case, the cooling oil is supplied to the plunger piston from the connecting rod 25. The connecting rod 25 has an internal passage through which cooling oil is introduced from a passage inside the crankshaft under pressure. In the drawing, among the passages inside the connecting rod, the ring passage around the supply hole 36 and the bearing sleeve 21.
Only 37 and the injection hole 38 in the connecting rod head 26 are shown. The injection hole 38 extends coaxially with the longitudinal axis of the connecting rod. The cooling oil injected in the form of a cooling oil flow from the injection hole 38 first reaches the cooling oil outflow hole 29, through which it passes through the inside cooling chamber 33.
Will be introduced to. From there, the cooling oil reaches the outer cooling chamber 35 through the communication hole 34 based on the piston movement during engine operation, and from there, through the outflow passage 39 arranged in the lower region of the cooling chamber 35, It is returned to the drive mechanism room.

The inner cooling chamber 33 is formed as a dome-shaped hollow chamber in the upper part. On the outside in the radial direction, this hollow chamber is formed by bending the inner wall 40 of the thick wall portion 7 of the outer wall 4 of the piston upper part 2 into a suitable shape and, subsequently to said inner wall 40, the inner surface 41 of the piston bottom 3. It is formed by an appropriate curve. A ridge 42 is provided coaxially with the longitudinal axis of the piston on the inner surface of the bottom of the piston, and this ridge 42 serves to favorably distribute the jetted cooling oil into the cooling chamber 33.

In the lower part, the inner cooling chamber 33 is limited by a ring-shaped recess 43 having a semicircular cross section. The wall 44 of the ring-shaped recess 43 is formed so as not to prevent the press tool from running after forming the recess.

The outer cooling chamber 35 is, in the region of the piston upper part 2, on the one hand a plurality of circumferentially distributed, slightly inclined with respect to the longitudinal axis of the piston from the lower edge 8 of the thick wall part 7 of the outer wall 4. It is formed by a blind hole 45 machined in this wall portion 7, and on the other hand by a ring-shaped chamber 46.
A bag hole 45 is opened in the ring-shaped chamber 46. Each bag hole
One of the communication holes 34 opens at 45. The communication hole 34 branches from the inner cooling chamber 33 in the range of the inner surface 40 of the thick wall portion 7 and opens obliquely upward near the end closed by the associated bag hole 45. The ring-shaped chamber 46 is radially outwardly by the inner surface 47 of the thin lower wall portion 9 of the outer wall 4 of the piston lower part 2, radially inwardly by the outer surface 48 of the support collar 14 and upwardly above the piston upper portion 2. It is limited by the lower edge 8 of the thick wall portion 7 of the outer wall 4 of the. Following the chamber 46 thus limited, the outer cooling chamber 35 faces downwards and is located in the lower piston part 1 as a ring-shaped oil receiving recess 49. The oil receiving recess 49 extends to the plane of the connecting rod head 26 and is limited radially outside by a thin walled outer wall portion 50 which is largely unaffected by ignition pressure during engine operation.

The reason why the thin outer wall portion 50 is not influenced by the ignition pressure is that the heights of the outer wall 4 of the piston upper portion 2 and the outer wall portion 50 of the piston lower portion 1 make the piston upper portion 2 and the piston lower portion 1 A ring gap 53 is selected to be formed between the flat lower edge 51 of the outer wall 4 of the upper piston portion 2 and the flat upper edge 52 of the outer wall portion 50 of the lower piston portion 1 after being joined together. Because. The piston upper part 2 is centered on the outside only via the ring-shaped centering surface 11 only against the piston lower part, and only on the ring-shaped contact surface 12 is supported on the piston lower part 1 and in its bending neutral zone. It is supported by the end face 13 of 14 and, furthermore, because of the ring gap 53, there is no coupling between the outer parts of the upper piston part 2 and the lower piston part 1, so that during engine operation Forces which adversely affect the shape of the outer wall part are not transmitted. In this case, no outer support is provided and the lower part 1 of the piston is satisfactorily cooled by the outer cooling chamber, so that the outer region of the plunger piston is heated only relatively slightly. This prevents the piston outer region from being subjected to different axial deformations under the influence of temperature. Moreover, in this case, the gap between the outer surface of the plunger piston formed by the outer surface 4 of the upper piston portion 2 and the outer surface 54 of the lower piston portion 1 can be made smaller than in conventional pistons. This has a favorable effect on the movement of the piston. This is because in this case the tilting of the piston remains limited to a small angle. This also results in a reduction in lubricating oil consumption.

In addition, the fact that the upper part of the piston is centered on the support collar 14 on the outside provides the following advantages during engine operation. Since the aluminum material from which the lower piston part 1 is made has a larger expansion coefficient than the material from which the upper piston part 2 is made, the support mechanism of the upper piston part 2 expands more than the upper piston part 2. To do. That is, when the piston is heated, the coupling between the piston upper portion 2 and the piston lower portion 1 becomes a power transmission coupling, and during engine operation, between the contact surface between the piston lower portion 1 and the piston upper portion 2. Relative motion actually does not occur.

Next, various structures by which the plunger piston of the present invention can be configured, that is, depending on what ignition pressure the plunger piston is loaded with, will be described.

Especially when the plunger piston has an extremely high ignition pressure, for example,
In order to be able to overcome the ignition pressure of 150 bar, the lower piston part 1 is additionally reinforced and is arranged in a ring-shaped recess 43, and a reinforcing rib 55 extends radially through this recess 43. It is advantageous to reinforce with. Such an arrangement is shown in the plunger piston of FIGS. 3 and 4.

In the case of a plunge piston according to the invention in which the plunge piston is used in an internal combustion engine in which it is only necessary to overcome the ignition pressure, for example of 120 bar, the outflow passage 39 diverging from the oil receiving recess 59 with respect to the longitudinal axis of the piston. Advantageously, it is formed by a hole 56 extending axially through the lower piston part 1. This is the case for the embodiment shown in FIGS. 3 and 4. A bore 56 is formed tangentially in a lubricating groove 57 which is formed in the lower piston part 1 so as to be partly arranged around the piston pin 18 and which receives the oil which lubricates the piston pin. Further, a small pipe 58 is inserted in the hole 56, and this small pipe 58 projects into the oil receiving recess 49 for a predetermined length, and maintains a predetermined cooling oil filling height in the oil receiving recess 49. are doing. This configuration is also provided in the embodiment of FIGS. 3 and 4.

According to features of the invention and combinations thereof, for example 160
The satisfactory functioning of the plunger piston is ensured even at relatively high ignition pressures, which even reach bar. Particularly, since the upper piston portion and the lower piston portion are solidly configured, and the upper piston portion is supported by the lower piston portion 2 in the bending neutral zone, the ignition pressure acting on the plunger piston during engine operation is as good as possible. Is introduced into the connecting rod 25 via the support collar 14 and the piston pin 18. Moreover, this introduction is done on the outer wall 4 of the piston upper part 2.
And the outer surface 54 of the lower piston part 1 is kept cylindrical and coaxial. In addition to the fact that the cooling oil is supplied in the manner according to the invention, a very strong cooling of the upper piston part is not only achieved, but also a strong piston in the upper part of the lower piston part adjacent to the upper piston part. Cooling is also guaranteed. The unfavorable influence of the heat generated during engine operation on the shape of the upper piston part 2 and the lower piston part 1 is thus largely avoided even by the induction type of the cooling medium in the plunger piston.

[Brief description of drawings]

The drawings show two embodiments of the invention, the first of which:
1 is a cross-sectional view of the plunger piston of the present invention taken at a right angle to the piston pin axis, FIG. 2 is a cross-sectional view of the plunger piston of FIG. 1 taken along the piston pin axis, and FIG. 3 is the present invention. Another cross-sectional view of another embodiment of the plunger piston of FIG.
4 is a sectional view of the plunger piston of FIG. 3 taken along the piston pin axis, FIG. 5 is a sectional view of the plunger piston of FIG. 1 taken along the line VV of FIG. 1, and FIG. Four
FIG. 6 is a sectional view of the plunger piston shown in FIG. 4 along line VI-VI in FIG. 4. 1 ... Piston lower part, 2 ... Piston upper part, 3 ...
Piston bottom, 4 ... Outer wall, 5 ... Outer surface, 6 ... Piston ring, 7 ... Wall part, 8 ... Lower edge, 9 ... Wall part, 10
…… Undercut, 11 …… Centering surface, 12 …… Contact surface, 13 …… End surface, 14 …… Supporting collar, 15 …… Centering surface, 16 …… Holding head, 17 …… Tightening screw, 18 …… Piston Pin, 19 ... Bearing hole, 20 ... Safety ring, 21 ...
Bearing sleeves, 22, 23 ... Surface, 24 ... Inner chamber, 25 ... Connecting rod, 26 ... Connecting rod head, 28 ... Projection, 29 ... Cooling oil outlet hole, 30 ... Cooling oil guide sleeve, 31 ... Receptive hole, 32 ...
… Upper edge, 33 …… Cooling chamber, 34 …… Communication hole, 35 …… Cooling chamber,
36 ... Supply hole, 37 ... Ring passage, 38 ... Jet hole, 39 ...
… Outflow passage, 40 …… Inner wall, 41 …… Inner surface, 42 …… Rise,
43 …… recess, 44 …… wall, 45 …… blind hole, 46 …… room, 47 ……
Inner surface, 48 ... Outer surface, 49 ... Oil receiving recess, 50 ... Outer wall portion, 51 ... Lower edge, 52 ... Upper edge, 53 ... Ring gap, 54 ...
… Outside, 55 …… Reinforcing ribs, 56 …… Hole, 57 …… Lubricant, 58
...... Small pipe

Front Page Continuation (72) Inventor Horst Lintner Federal Republic of Germany Fitzsyuyatzüer Renrensyutraße 19 (56) References JP 59-147849 (JP, A) Actual development S59-181248 (JP, U) Actual development A 51-79239 (JP, U) JP-B 56-33575 (JP, B2) JP-B 54-16975 (JP, Y2)

Claims (6)

[Claims] 1. A piston upper part consisting of an outer wall having a piston ring and a piston ring fitted in a ring groove, and a piston lower part, which are supported in a bearing hole penetrating laterally through the piston lower part. Is connected to the connecting rod connected to the crankshaft of the internal combustion engine via the piston pin, and the piston upper part is a contact surface forming a step from the piston bottom, and is integrally formed on the upper part of the piston lower part. Is supported on the end face of a ring-shaped supporting collar and is coupled to the supporting collar with a plurality of tightening screws, and a cooling oil outlet hole coaxial with the piston longitudinal axis is arranged in the lower portion of the piston. The cooling oil outflow hole opens into an inner cooling chamber connected to an outer cooling chamber arranged on the opposite side of the support collar by a communication hole, and the outer cooling chamber is connected to the piston upper portion and the piston. In an oil-cooled plunger piston of the type extending to both the lower part and (a) the piston upper part (2) is almost solid, and the blind hole (45) is formed only in the range of the outer cooling chamber (35). ) Is integrally manufactured from spheroidal graphite cast iron or steel material, while the lower piston part (1) is the upper piston part (2).
Has a substantially closed shape except for the cooling oil outlet hole (29) on the upper surface facing toward the other side, and is otherwise integrally formed integrally and is formed by pressure casting from aluminum or an aluminum alloy or by heating the material. (B) The upper part (2) of the piston is supported by the ring-shaped contact surface (12) on the supporting collar (14) of the lower part (1) of the piston only in the deflection neutral zone. (C) The outer cooling chamber (35) in the range of the piston lower part (1) is extended by the ring-shaped oil receiving recess (49), and this oil receiving recess (49) is almost connected to the connecting rod head ( 26)
Of the outer wall portion (50), which is radially outwardly relatively thin and is not affected by ignition pressure in engine operation, the outer wall portion (50) being defined by the ring gap (53). ) An oil-cooled multi-part plunger piston of an internal combustion engine, characterized in that it is separated from the outer wall (4) of the upper part of the piston. 2. A plurality of reinforcing ribs (55) radially extending through a ring-shaped recess (43) forming a lower portion of the inner cooling chamber (33) are arranged. The plunger piston according to the first item of the range. 3. An outflow passage (39) branching from the oil receiving recess (49) opens into an inner chamber (24) surrounding the connecting rod head (26) of the lower piston portion (1). Range 1st
Plunger piston described in paragraph. 4. An outflow passage (39) branching from the oil receiving recess (49) is formed by a hole (56) extending in the piston lower portion (1) axially parallel to the piston longitudinal axis.
The plunger piston according to claim 1. 5. A lubrication groove (57) in which a hole (56) is partly formed in the lower piston part (1) around the piston pin (18) and receives oil for lubricating the piston pin (18). The plunger piston according to claim 4, which intersects with the tangential direction. 6. A small pipe (58) which is inserted into the hole (56) by a predetermined length into the oil receiving recess (49) and serves for maintaining a predetermined cooling oil filling height therein. The plunger piston according to claim 5, wherein