EP3502453B1 - Piston for a reciprocating piston combustion engine - Google Patents

Description

The invention relates to a piston for a reciprocating internal combustion engine.

From the prior art, for example from the laid-open specification DE 10 2014 010 106 A1 , pistons for a reciprocating internal combustion engine are known. Such a piston is usually arranged in a cylinder of a reciprocating internal combustion engine. The piston has a piston skirt, which is usually also referred to as a "skirt" or "piston skirt". In English, the piston skirt is called the "piston skirt". In addition, the piston has a ring belt adjoining the piston skirt in the axial direction of the piston, with at least one ring groove for a piston ring. The ring belt is part of the piston head.

The friction of an internal combustion engine is made up of the friction of the basic engine (bearing, piston group) and the drive power of the auxiliary units. The piston group accounts for about 30% of the total friction, with the piston skirt causing about 2/3 of the friction of the piston group.

The piston skirt friction is influenced by various influencing factors. For example, the piston skirt friction depends on the engine speed, the engine load, the gap between the liner and the piston skirt and the shape of the piston skirt.

From the EP 3 208 453 A1 a piston is known which has a circumferential cooling channel in the area of the ring belt 6 which extends from the ring belt in the axial direction along an inner surface of the wall of the piston skirt. As a result, an oil film temperature of the oil film in the cylinder liner between the piston skirt and cylinder can be increased in order to reduce the piston skirt friction. When the piston moves back and forth, lubricant heated in the upper section of the cooling channel also reaches the inner surface of the wall of the piston skirt in order to enable an energy transfer for heating the piston skirt GB493126 A and US 2013/206084 A1 reveal further pistons.

It is an object of the invention to provide an improved piston for a reciprocating piston internal combustion engine with which the disadvantages of conventional pistons can be avoided. The object of the invention is in particular to provide a piston for to provide a reciprocating internal combustion engine with which piston skirt friction can be reduced.

These objects are achieved by a piston for a reciprocating internal combustion engine with the features of the independent claim. Advantageous embodiments and applications of the invention are the subject matter of the dependent claims and are explained in more detail in the following description with partial reference to the figures. According to the invention, a piston for a reciprocating piston internal combustion engine is provided, which is slidably guided in a liner of a cylinder of the internal combustion engine and comprises, in a manner known per se, a piston head and a piston skirt. The piston skirt is used to guide the piston in the cylinder barrel. The piston skirt adjoins the ring belt in the axial direction of the piston. The axial direction corresponds to the direction of movement of the piston in the cylinder. It was already stated above that the piston skirt is also referred to as the piston skirt. The piston head is also known as the piston crown. The piston head has a circumferential ring belt with at least one ring groove for a piston ring.

The piston has a fluid channel, having an upper section arranged in the area of the ring belt and a lower section starting from the upper section and extending along an inner surface of the wall of the piston skirt, in particular such that when the piston moves back and forth in the upper section Of the fluid channel heated lubricant also reaches the inner surface of the wall of the piston skirt and is guided through this in order to enable an energy transfer for heating the piston skirt.

In this document, the fluid channel is referred to as a cooling channel and is also referred to as a first cooling channel, for better differentiation from a second cooling channel, which will be described below.

The upper section of the cooling channel can be formed circumferentially in the ring belt. The first cooling channel is designed to be filled with a medium, for example with a cooling fluid, e.g. B. a cooling liquid or sodium, which has a melting point of about 98 ° C, or a lubricant, especially oil, to be filled. The upper section is used to cool the combustion bowl, which is also known as the piston bowl. The combustion bowl heated by the combustion process heats the medium, e.g. B. that Lubricant. The first cooling channel is not only arranged in the area of the ring belt or the piston head, but also extends down into the area of the piston skirt, so that cooling fluid is guided along at least a partial area of the inner wall of the piston skirt. "Down" here means away from the piston head in the direction of the crankshaft connecting rod or in the direction of the piston pin. This cooling channel, which extends to the wall of the piston skirt, offers the advantage that the cooling fluid heated in the cooling channel in the area of the ring belt is guided in the lower section along the inner surface of the wall of the piston skirt, which enables energy to be transferred to heat the piston skirt. The lower section preferably runs parallel to the axial direction. The additional heating of the piston skirt achieved in this way increases the oil film temperature between the piston skirt and the cylinder liner, thereby reducing the piston skirt friction. The capacity of the lower section of the first cooling channel running in the area of the piston skirt can be at least 30% of the capacity of the upper section running in the area of the ring belt. The capacity of the lower section is preferably at least as large as the capacity of the upper section.

The higher the temperature of the oil film between the piston skirt and the liner, the lower the piston skirt friction. Corresponding to this usual designation of the fluid channel as a cooling channel, the lower section of this fluid channel extending according to the invention to the wall of the piston skirt is also referred to as part of the cooling channel, although this section serves to supply the lubricant heated in the upper area of the cooling channel to the piston skirt and to heat it , and thus actually serves as a "heat channel".

The first cooling channel is characterized in that it is closed and permanently filled with a medium, in particular a cooling fluid. In other words, the degree of filling of the cooling channel with cooling fluid is constant, that is to say, the amount of cooling fluid in the first cooling channel is preferably introduced into the piston for a lifetime and does not change. The first cooling channel thus has no inlet and no outlet via which cooling fluid can enter or exit during operation of the piston. An inlet can only be provided for the first filling of the first cooling channel, which, however, is closed after filling, e.g. B. by welding or closing with a plug or a screw cap. In contrast, the amount of medium in the first cooling channel does not change to conventional cooling channels with spray oil filling, in which the degree of filling fluctuates depending on the engine speed and the oil pressure at the oil spray nozzle. This can reduce the amount of piston cooling oil required. Furthermore, the optimal cooling in the oil channel is ensured, since the filling level of the first cooling channel remains constant. In combination with the above-described configuration of the first cooling channel with an upper and a lower section, an optimal distribution of the heat from the upper region of the piston to the piston rings and the piston skirt takes place.

A particular advantage of the closed first cooling channel is that the temperature of the cooling fluid in the first cooling channel increases more than in the case of an open cooling channel. This increases the temperature of the piston skirt significantly, which significantly increases the heat flow from the piston to the liner.

The state of the art in internal combustion engines is that the oil spray nozzles are switched off when idling and at low loads. Due to the increased heat flow from the piston to the liner, the area in which the vehicle is driven without oil spray nozzles can be significantly enlarged.

Another advantage is that if the first cooling channel is suitably designed (capacity, length, etc.), the oil spray nozzles can be completely dispensed with. In this case, there is also no load-dependent heat input into the engine oil. This means that there is no need to install an oil cooler, as the interaction of the oil with the engine is sufficient for cooling.

According to the invention, the piston has a further fluid channel which, in contrast to the first fluid channel, is, however, designed to be open. This further fluid channel is referred to below as the second cooling channel. The second cooling channel is not fluidly connected to the first cooling channel. The second cooling channel is designed so that a lubricant, in particular oil, can flow through it. All statements in this document in which oil is used as a highlighted lubricant example also apply to other lubricants.

The provision of the second fluid channel is particularly advantageous in engines with a very high specific power in order to increase the cooling power in the ring belt by combining the first cooling channel with a closed cooling channel and the second open cooling channel.

The open second cooling channel thus serves as an additionally usable cooling channel, which is supplied with lubricant when required.

The second cooling channel can for example be arranged in the piston head, in particular below the piston bowl. The second cooling channel is used for additional cooling of the combustion bowl.

The second cooling channel can have at least one inlet opening through which the lubricant can flow into the second cooling channel, and can furthermore have at least one outlet opening through which the lubricant can exit from the second cooling channel. The inlet opening can be arranged in the area of the piston interior on the underside of the piston head. This is advantageous for filling the second cooling channel with spray oil with an oil spray nozzle. The inlet opening can be designed as an inlet bore. Accordingly, the outlet opening can be designed as a drain hole.

According to a further aspect, a capacity of the first cooling channel can be greater than a capacity of the second cooling channel.

The first cooling channel extends as far as a wall of the piston skirt arranged below the ring belt. The first cooling channel preferably extends at least to below the ring belt. The piston skirt can have a pin eye for receiving a piston pin. The first cooling channel can be designed circumferentially in the area of the ring part, d. That is, the cooling channel extends in the circumferential direction of the piston, preferably around 360 °, so that the cooling channel runs in a ring shape in the ring belt. Preferably the lower part of the first cooling channel, i. H. that part which, starting from the upper section of the first cooling channel in the area of the ring belt as far as a wall of the piston skirt, does not extend around 360 °.

According to a particularly advantageous embodiment, the first cooling channel extends along the inner surface of the wall of the piston skirt to a lower end region of the wall of the piston skirt facing away from the ring belt, in order to be able to heat the piston skirt over its entire axial length. Alternatively, the cooling channel can extend along at least 50% of the axial length of the piston skirt along the inner surface of the wall of the piston skirt, more preferably along at least 2/3 of the axial length or further preferably along at least 4/5 of the axial length of the piston skirt. The lower section of the cooling channel runs parallel to the axial direction and is delimited on the outside by the inner surface of the wall of the piston skirt.

It was already mentioned above that the piston skirt has at least one pin eye for receiving a piston pin. According to a further embodiment, the cooling channel can extend in the axial direction of the piston up to the level of the at least one bolt eye along the inner surface of the wall of the piston skirt. It is particularly advantageous if the cooling channel extends in the axial direction of the piston as far as a lower end of the bolt eye. Here, the lower end of the bolt eye is that which faces a connecting rod engaging the piston.

According to a further preferred embodiment, the wall of the piston skirt can have a profile on a side facing the first cooling channel, the profile preferably being formed by a groove structure. The profiling increases the surface area of the wall of the cooling channel on the side of the piston skirt, as a result of which the heat transfer to the piston skirt is increased by the lubricant that adheres to the profiling.

According to a further advantageous embodiment, a wall section of the first cooling channel, which connects an upper area of the first cooling channel, which is designed circumferentially in the area of the ring belt, with a lower area of the cooling channel, which adjoins the wall of the piston skirt, is designed such that the lubricant is thrown against the wall of the piston skirt. This part of the wall of the cooling channel is referred to below as the transition wall section. For example, the transition wall section of the cooling channel is designed in such a way that it has a section which runs obliquely downwards towards the piston skirt, on which in the lower region of the cooling channel there is a wall of the cooling channel that runs more steeply downwards in comparison and is arranged opposite the piston skirt, connects. The section of the transition wall section running obliquely downward can, for example, have the shape of a lateral surface of a truncated cone. In this embodiment, the lubricant is thrown particularly efficiently against the wall of the piston skirt when shaking, so that the heat transfer is improved.

According to a further aspect, an arrangement (device) is provided with a piston which comprises both the first cooling channel and the second cooling channel, as described above. The arrangement or device further comprises an oil spray nozzle which is provided for supplying the piston with lubricant and is arranged such that a piston interior and an inlet opening of the second cooling channel can be sprayed with lubricant from the lubricant pump. The arrangement or device further comprises a control device of the oil spray nozzle, which is designed to selectively switch the lubricant pump on or off as a function of an operating parameter of an internal combustion engine, from which the current engine load can be derived.

For example, the control device can be designed to operate the reciprocating internal combustion engine in wide partial load ranges without spray cooling and to switch on the oil spray nozzles only at operating points close to full load.

According to a further aspect, a reciprocating piston internal combustion engine is provided, comprising a piston which comprises the first cooling channel, but not an open second cooling channel, as described above. According to this aspect, the reciprocating internal combustion engine cannot have an oil spray nozzle for supplying the piston with lubricant and / or no oil cooler for cooling the lubricant for the reciprocating internal combustion engine, so that the heat exchange of the medium in the closed first cooling channel with the internal combustion engine is sufficient for cooling.

Furthermore, a motor vehicle is provided with a piston as described in this document. The motor vehicle can be a utility vehicle, for example a truck or bus.

• Figur 1 einen Teilschnitt eines Kolbens gemäß eines Beispiels;
  und
• Figur 2 einen Teilschnitt eines Kolbens gemäß einer ersten Ausführungsform.

The preferred embodiments and features of the invention described above can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the accompanying drawings. Show it:

• Figure 1 a partial section of a piston according to an example;
  and
• Figure 2 a partial section of a piston according to a first embodiment.

Identical or functionally equivalent elements are denoted by the same reference symbols in all figures and in some cases are not described separately.

Figure 1 shows a partial section of an example. The piston 10 comprises a piston head 5 which has a circumferential ring belt 6. The ring belt 6 comprises several ring grooves 6a for a piston ring. In the axial direction A, the piston skirt 1 adjoins the ring belt 6 downwards, which, in contrast to the ring belt 6, does not is carried out completely circumferentially. The piston 10 is therefore not designed as a full skirt piston. The piston skirt 1 is slidingly mounted in the cylinder liner, a wall 10 of the piston skirt sliding back and forth along the liner when the piston moves. The piston 10 is mounted in a corresponding cylinder (not shown) of a cylinder piston housing (not shown) of a reciprocating internal combustion engine. The piston skirt 1 has at least one pin eye 8 for receiving a piston pin. A connecting rod (not shown) mounted on the crankshaft is articulated to the piston 10 via such a piston pin in order to convert the translational movements of the piston 10 in the cylinder into rotational movements of the crankshaft about its axis of rotation as a result of this articulated coupling.

" aufweist. Der Kolben 10 umfasst ferner einen ersten Kühlkanal 2, mit einem im Bereich der Ringpartie 6 angeordneten oberen Abschnitt 3 und einen vom oberen Abschnitt ausgehenden, sich entlang einer Innenfläche 12 der Wandung 11 des Kolbenhemds 1 erstreckenden unteren Abschnitt 4. Der untere Abschnitt 4, der sich im Bereich des Kolbenhemds 1 befindet, grenzt an die Wandung 10 des Kolbenhemds 1 an und ist entlang dieser geführt. Im Gegensatz zum oberen Abschnitt 3 des Kühlkanals 2, der um 360° umlaufend ausgeführt ist, ist der untere Abschnitt 4 des Kühlkanals 2 nicht vollständig umlaufend ausgeführt, bedingt durch die nicht vollständig umlaufend ausgeführte Lauffläche des Kolbens 10.The piston 10 also has a piston bowl 7, also referred to as a combustion chamber bowl. The piston bowl 7 is designed as a so-called omega bowl. This means that the piston bowl 7 has a cross section which is at least essentially the shape of a "

The piston 10 further comprises a first cooling channel 2, with an upper section 3 arranged in the area of the ring belt 6 and a lower section 4 starting from the upper section and extending along an inner surface 12 of the wall 11 of the piston skirt 1. The lower section 4, which is located in the area of the piston skirt 1, adjoins and is guided along the wall 10 of the piston skirt 1. In contrast to the upper section 3 of the cooling channel 2, which is designed to run around 360 °, the lower section 4 of the The cooling channel 2 is not completely circumferential, due to the running surface of the piston 10 which is not completely circumferential.

In the example shown, the lower region of the section 4 of the cooling channel 2 extends in the axial direction A of the piston to the lower end 8 of the bolt eye or essentially almost along the entire axial length of the piston skirt 1. Both the upper section 3 and the lower Section 4 of the cooling channel 2 extend circumferentially along the outer wall of the piston 10.

According to the invention, the first cooling channel 2 is closed and permanently filled with a medium 15, ie the amount of the medium 15 (eg lubricant, cooling fluid) in the first cooling channel is constant and does not change. The first cooling channel 2 thus has no inlet and no outlet via which cooling fluid could enter or exit during operation of the piston. An inlet can only be provided for the first filling of the first cooling channel, the after filling, however, is closed, e.g. B. by welding or closing with a plug or a screw cap.

The example of Figure 1 has the advantage that the medium 15, which cools the piston head 5 in the upper region 3 of the cooling channel 2 and is heated in the process, is thrown back and forth between a bottom dead center and an upper dead center in the cooling channel 2 by the reciprocating movement of the piston ( "Shaken"), so that the medium 15 heated in the upper cooling channel region 3 also reaches the inner surface of the wall 10 of the piston skirt 1 and thus heats it. By heating the wall 10 of the piston skirt, the oil film which is located between the outside 13 of the piston skirt and the cylinder liner is also heated, whereby its friction effect is reduced. As a result, an effective reduction in piston skirt friction can be achieved. The wall of the lower section 4 of the first cooling channel 2, which is located opposite the wall 10 of the piston skirt, is designated by the reference numeral 14.

Compared to an open cooling channel, with the closed cooling channel 2 the medium in the cooling channel 2 is heated to a greater extent and the heat flow from the piston to the liner is significantly increased as a result, since the temperature of the piston skirt increases significantly.

In Figure 1 it can also be seen that the transition between the upper area 3 of the cooling channel 2 and the lower area 4 of the cooling channel 2 is designed such that the medium is guided along a transition wall section 9 of the cooling channel 2. The transition wall section 9 is arranged on the side of the cooling channel 2 facing the inside of the piston and connects the upper area 3 of the cooling channel to the lower area 4 of the cooling channel. The transition wall section 9 runs straight downwards, with a strong downward curvature or also an edge being formed at the end of the transition wall section 9 at the transition to the lower wall section 4 of the cooling channel. The oil flowing along the transition wall section 9 is thrown at this bend like a jump against the inner surface 11 of the wall 10 of the piston skirt 1, so that an effective wetting of the wall 10 of the piston skirt with lubricant is made possible.

In Figure 2 a first embodiment of the piston 20 is shown. Here, components with the same reference symbols correspond to the components of FIG Figure 2 and are not described separately.

The peculiarity of the embodiment of the Figure 2 lies in the fact that, in addition to the closed cooling channel 2, a second cooling channel 22 is provided, which, in contrast to the first cooling channel 2, is, however, open. The second cooling channel 22 is not fluidly connected to the first cooling channel. The second cooling channel 22 is arranged here, for example, below the piston recess 7 and extends only in the piston head 5. The second cooling channel 22 has an inlet bore 21 through which the lubricant can flow into the second cooling channel. The second cooling channel 22 also has one or more outlet openings, via which lubricant can exit again from the second cooling channel 22. According to the exemplary embodiment, the inlet bore 21 is arranged in the area of the piston interior on the underside of the piston head 5. An oil spray nozzle 23 is arranged below the piston skirt 1 in such a way that lubricant 24 emerging from the oil spray nozzle 23 is sprayed onto the inlet bore 21.

The provision of the second fluid channel is particularly advantageous in engines with a very high specific power in order to increase the cooling power in the ring belt by combining the first cooling channel with a closed cooling channel and the second open cooling channel. The open second cooling channel can thus serve as an optionally additionally usable cooling channel, which is supplied with lubricant when required.

Although the invention has been described with reference to particular exemplary embodiments, it will be apparent to a person skilled in the art that various changes can be made and equivalents used as replacements without departing from the scope of the invention. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it encompass all embodiments that fall within the scope of the appended claims.

List of reference symbols

1

Piston skirt

2

First cooling channel

3

Upper section

4th

Lower section

5

Piston head

6th

Ring game

6a

Ring groove

7th

Piston recess

8th

Bolt eye

9

Transition wall section

10

piston

11

Wall of the piston skirt

12th

Inner surface of the wall of the piston skirt

13th

Outer surface of the piston skirt

14th

Wall

15th

Medium in the first cooling channel

20th

piston

21

Inlet opening, in particular inlet bore

22nd

Second cooling channel

23

Oil spray nozzle

24

Splashed lubricant

A.

Axial direction

Claims (11)

1. A piston (10; 20) for a reciprocating-piston internal combustion engine, comprising
   a piston crown (5), having an encircling ring section (6) with at least one ring groove for a piston ring;
   a piston skirt (1); and
   a first cooling channel (2), having an upper section (3) arranged in the region of the ring section (6) and a lower section (4) which proceeds from the upper section and which extends along an inner surface (12) of the wall (11) of the piston skirt (1);
   wherein the first cooling channel (2) is closed and is permanently filled with a medium (15); characterized by an open second cooling channel (22) .
2. The piston (20) according to Claim 1, characterized in that the second cooling channel (22) is arranged in the piston crown, in particular below the piston depression (7).
3. The piston (20) according to Claim 1 or 2, characterized in that the second cooling channel (22) has an inflow opening which is arranged in the region of the piston interior space at the underside of the piston crown.
4. The piston (20) according to any of the preceding claims, characterized in that a volume of the first cooling channel (2) is greater than a volume of the second cooling channel (22).
5. The piston according to any of the preceding claims, characterized in that the piston skirt (1) has at least one pin bore (8) for receiving a piston pin; and
   b1) in that the lower section (4) of the first cooling channel (2) extends in an axial direction of the piston along the inner surface of the wall (11) of the piston skirt (1) at least to the level of the at least one pin bore (8); and/or
   b2) in that the cooling channel extends in an axial direction of the piston along the inner surface of the wall (11) of the piston skirt (2) at least to a lower end of the pin bore (8).
6. The piston according to any of the preceding claims, characterized in that the first cooling channel (2) extends along the inner surface of the wall (11) of the piston skirt (2) along at least 2/3 of the axial length of the piston skirt, preferably to a lower end region (4), averted from the ring section (6), of the wall (11) of the piston skirt (1).
7. The piston according to any of the preceding claims, characterized in that the inner surface (12) of the wall (11) of the piston skirt (2) has a profiling (61), wherein the profiling (61) is formed preferably by a groove structure.
8. The piston according to any of the preceding claims, characterized in that

   a) a transition wall section of the first cooling channel (2) is provided,

   a1) which is arranged on the side of the first cooling channel (2) facing towards the piston inner side and

   a2) which connects the upper region (3) of the first cooling channel (2), which is of encircling form in the region of the ring section (6), to the lower region (4) of the first cooling channel (2) and

   a3) which has a section (9) running obliquely downwards towards the piston skirt (1), which section is adjoined in the lower region (4) of the first cooling channel (2) by a wall (14) of the first cooling channel (2), which wall runs more steeply downwards in relation to said section and is arranged opposite the piston skirt (1).
9. An arrangement, comprising

   a) a piston according to any of the preceding claims, and

   b) an oil spray nozzle which is provided for supplying lubricant to the piston and which is arranged such that a piston interior space and an inflow opening of the second cooling channel can be sprayed with lubricant by the lubricant pump, and

   c) a control device of the oil spray nozzle, wherein the control device is designed to selectively activate or deactivate the lubricant pump in a manner dependent on an operating parameter of an internal combustion engine, from which operating parameter the present engine load can be derived.
10. A reciprocating-piston internal combustion engine comprising a piston according to any of Claims 1 to 8, characterized in that the reciprocating-piston internal combustion engine has no oil spray nozzle for supplying lubricant to the piston and/or has no oil cooler for cooling the lubricant for the reciprocating-piston internal combustion engine.
11. A motor vehicle, in particular utility vehicle, having a piston according to any of Claims 1 to 8.

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