1. Technical Field
The present disclosure relates to a piston for a reciprocating-piston internal combustion engine.
2. Description of Related Art
Pistons for a reciprocating-piston internal combustion engine are known from the prior art, for example the laid-open specification DE 10 2014 010 106 A1. A piston of said type is normally arranged in a cylinder of a reciprocating-piston internal combustion engine. The piston has a piston barrel which is normally also referred to as “body” or “piston body”. In English, the piston barrel is referred to as “piston skirt”. Furthermore, the piston has a ring belt which adjoins the piston barrel in an axial direction of the piston and which has 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 main engine (bearings, piston group) and the drive power of the auxiliary assemblies. Here, approximately 30% of the total friction arises in the piston group, wherein the piston barrel accounts for approximately ⅔ of the friction of the piston group.
The piston barrel friction is influenced by various influential variables. For example, the piston barrel friction is dependent on the engine rotational speed, the engine load, the gap between cylinder liner and piston barrel, and the shape of the piston barrel.
The present disclosure is based on the realization that the piston barrel friction is furthermore dependent on the viscosity of the oil film between piston barrel and the cylinder liner of the cylinder. The viscosity is dependent on the oil type and the oil temperature.
One aspect of the present disclosure is to provide an improved piston for a reciprocating-piston internal combustion engine, by way of which disadvantages of conventional pistons can be avoided. It is a further aspect of the present disclosure to provide a piston for a reciprocating-piston internal combustion engine with which piston barrel friction can be reduced.
Advantageous aspects and uses of the present disclosure will be discussed in more detail in the following description, in part with reference to the figures.
According to the present disclosure, a piston for a reciprocating-piston internal combustion engine is provided which is guided in slidingly movable fashion in a cylinder liner of a cylinder of the internal combustion engine and which, in a manner known per se, comprises a piston head and a piston barrel. The piston barrel serves for the guidance of the piston in the cylinder liner. The piston barrel adjoins the ring belt in an axial direction of the piston. Here, the axial direction corresponds to the direction of movement of the piston in the cylinder. It has already been stated above that the piston barrel is also referred to as piston body. The piston head is also referred to as piston crown.
The piston head has an encircling ring belt with at least one ring groove for a piston ring and has, in the region of the ring groove, an encircling fluid duct. The fluid duct is normally, and also in this document, referred to as cooling duct. The cooling duct is designed to be flowed through by a lubricant, in particular oil, and serves for the cooling of the combustion chamber depression, which is also referred to as piston depression. Here, the combustion chamber depression, which is heated as a result of the combustion process, heats the lubricant. All aspects in this document in which oil is used as a highlighted lubricant example also apply to other lubricants.
On the piston head, there may be provided an inlet bore via which the lubricant can flow into the cooling duct. Furthermore, an outflow bore may be provided, for example so as to be offset through 180° in a circumferential direction with respect to the inlet bore, via which outflow bore lubricant can emerge from the cooling duct.
According to general aspects of the present disclosure, the cooling duct extends from the ring belt as far as a wall of the piston barrel. The cooling duct is thus arranged not only in the region of the ring belt or of the piston head but also extends further downward into the region of the piston barrel. Here, “downward” means away from the piston head in the direction of the crankshaft connecting rod, or in the direction of the piston pin.
A cooling duct which extends as far as a wall of the piston barrel offers the advantage that the lubricant which is heated in the cooling duct in the region of the ring belt is conducted through the cooling duct to the wall of the piston barrel, whereby an energy transfer for heating the piston barrel is made possible. The additional heating of the piston barrel that is achieved in this way increases the oil film temperature between piston barrel and cylinder liner of the cylinder, whereby a reduction of the piston barrel friction is achieved. The higher the temperature of the oil film between piston barrel and cylinder liner, the lower the piston barrel friction. In particular in operating modes with very high load, it is possible by way of the lower region of the cooling duct for the piston body temperature to be reduced, and in this way for thermal damage of the oil film between cylinder liner and piston body to be avoided. Correspondingly to this conventional designation of the fluid duct as a cooling duct, that section of said fluid duct which extends, according to the present disclosure, as far as the wall of the piston barrel is referred to as part of the cooling duct, even though said section serves for supplying the lubricant that is heated in the upper region of the cooling duct to the piston barrel and heating said piston barrel, and thus actually serves as a “heating duct”.
The cooling duct may extend as far as a wall, arranged below the ring belt, of the piston barrel. The cooling duct preferably extends as far as below the ring belt. The piston barrel may have a pin bore for receiving a piston pin. The cooling duct may be formed in encircling fashion in the region of the ring belt, that is to say the cooling duct extends in the circumferential direction of the piston, preferably in encircling fashion through 360°, such that the cooling duct runs in ring-shaped fashion in the ring belt. The lower part of the cooling duct, that is to say the part which extends from the cooling duct in the region of the ring belt as far as a wall of the piston barrel, preferably does not extend in encircling fashion through 360°.
In a particularly advantageous aspect, the cooling duct extends as far as a lower end region, which is averted from the ring belt, of the wall of the piston barrel, in order that, in this way, said cooling duct can heat the piston barrel over the entire axial length thereof. Alternatively, the cooling duct may extend along at least 50% of the axial length of the piston barrel, more preferably along at least ⅔ of the axial length or furthermore preferably at least along ⅘ of the axial length of the piston barrel.
It has already been mentioned above that the piston barrel has at least one pin bore for receiving a piston pin. In a further aspect, the cooling duct may extend in the axial direction of the piston as far as the level of the at least one pin bore. It is particularly advantageous if the cooling duct extends in the axial direction of the piston as far as a lower end of the pin bore. Here, the lower end of the pin bore is that end which faces toward a connecting rod which engages on the piston.
The cooling duct may be, in the region of the wall of the piston barrel, fluidically connected by way of at least one first passage opening to a cylinder liner for the piston. In other words, the piston barrel or the wall of the piston barrel has a passage opening, for example in the form of a passage bore, via which lubricant can pass from the cooling duct to the cylinder liner of the piston. In this way, hot lubricant that is heated in the upper region of the cooling duct can be conducted in the cooling duct directly to the piston barrel, such that the temperature of the piston barrel can be increased even more efficiently. In this way, it is consequently possible to achieve an even better reduction of the piston barrel friction. It is thus possible for heated lubricant to pass through the at least one first passage opening to the cylinder liner of the piston. The at least one first passage opening may be arranged in a middle region of the piston barrel, preferably in the middle of the height of the piston barrel, in the axial direction.
In an advantageous variant aspect, a rib is arranged in the cooling duct such that the oil flow to the cylinder liner is intensified. The rib will hereinafter be referred to as oil-catching rib. The expression “lubricant-catching rib” is to be regarded as synonymous for this. This may be realized in particular by virtue of the oil-catching rib being arranged in the cooling duct such that a part of the oil flung back and forth in the cooling duct as a result of the piston movement strikes the oil-catching rib or is caught on the oil-catching rib and is conducted by the oil-catching rib to the at least one first passage opening. The flinging of the lubricant back and forth in the cooling duct owing to the upward and downward movement of the piston is also referred to as “shaker motion”. The oil-catching rib is thus arranged in the region of the at least one first passage opening such that a part of the lubricant is caught on the oil-catching rib during the shaker motion and can then flow along the rib to the at least one first passage opening.
The rib may project from the wall of the piston barrel towards the piston interior from the wall of the piston barrel. The rib may also be in the form of a web or projection which projects from the wall of the piston barrel toward the piston interior proceeding from the wall of the piston barrel.
Here, the oil-catching rib may be arranged at the level of or directly adjacent to the at least one first passage opening. It is thus possible for oil that strikes the oil-catching rib to be conducted to the at least one first passage opening in an efficient manner.
In accordance with one aspect of the disclosure, the oil-catching rib is arranged such that a lower edge of the first passage opening is arranged so as to be downwardly offset in the axial direction with respect to a horizontal oil-intercepting or lubricant-intercepting surface of the oil-catching rib. This offers the advantage that, even in the case of a low oil level on the oil-catching rib, a large transition cross section to the first passage opening is already opened up. Here, the first passage opening is preferably in the form of a passage bore such that the passage bore extends on the inner side of the piston barrel into a region of the oil-catching rib and forms a duct-like recess there in the form of an open duct for receiving the intercepted oil or lubricant.
In a further particularly advantageous variant, at least one second passage opening may be provided in the cooling duct in the region of the wall of the piston barrel, by way of which second passage opening the cooling duct is fluidically connected to the cylinder liner. The at least one first passage opening and the at least one second passage opening are arranged in each case on opposite sides of the oil-catching rib in the axial direction of the piston. This offers the advantage that lubricant which is caught on the oil-catching rib during the upward movement of the piston and lubricant which is caught on the oil-catching rib during the downward movement of the piston can pass to the running surface of the piston. It is thus possible, during the shaker motion of the lubricant, for lubricant which is caught on the top side of the oil-catching rib to pass to the running surface through those passage openings which are arranged adjacent to the top side of the oil-catching rib, whereas lubricant which is caught on the bottom side of the oil-catching rib during the downward movement of the piston can pass to the running surface through those passage openings which are arranged adjacent to the oil-catching rib below the latter in the axial direction.
In this further variant, the oil-catching rib is thus arranged between the at least one first passage opening and the at least one second passage opening, preferably in each case directly adjacent and/or next to the at least one first passage opening and the at least one second passage opening. It is preferable for multiple such first and/or second passage openings to be arranged so as to be distributed in the circumferential direction, preferably along a circular line, in order to increase the heat transfer from the cooling duct to the cylinder liner.
The oil-catching rib may be formed in encircling fashion in the circumferential direction of the piston on that wall of the piston barrel which adjoins the cooling duct. Here, the circumferential direction lies in a plane perpendicular to the axial direction of the piston.
Furthermore, the oil-catching rib may have a first section, which runs in encircling fashion on the wall of the piston barrel and which extends in a radial direction of the piston, and a second section, which extends in the axial direction of the piston, wherein the second section is arranged at that end region of the first section which is averted from the wall of the piston barrel. This makes it possible for lubricant that is flung back and forth to be caught in a particularly effective manner and for the caught lubricant to be supplied to the respective passage opening in the piston barrel. Here, the radial direction is perpendicular to the axial direction.
Here, a further advantageous possibility for the realization according to the present disclosure of an oil-catching rib provides that the second section of the oil-catching rib extends in the axial direction both in the direction of the piston head and in the opposite direction, that is to say in the direction of the crankshaft. This design variant is particularly advantageous if it is the intention for lubricant to be caught, and supplied to a passage opening, both in part during the upward movement and in part during the downward movement of the piston.
In a further aspect of the disclosure, the wall of the piston barrel may have a profiling on a side facing toward the cooling duct, wherein the profiling is preferably formed by a channel structure. The profiling increases the surface area of the wall of the cooling duct on the side of the piston barrel, whereby the heat transfer to the piston barrel is increased by way of the lubricant that is caught on the profiling.
In a further aspect of the disclosure, the piston barrel may have, on its outer surface, a depression which surrounds an end region, that is to say the end region adjoining the cylinder liner of the piston, of the at least one first passage bore. The outer surface of the piston barrel is to be understood to mean that surface of the piston barrel which faces toward the cylinder liner. The depression may be in the form of a groove or channel. The depression may in particular be in the form of a wide shallow channel. This also reduces the fluid shear surfaces.
A corresponding depression may also be provided for the at least one second passage opening. The depression improves the distribution of lubricant, which emerges from the end region of the at least one first passage opening and/or of the at least one second passage opening, between cylinder liner and piston barrel.
In a further advantageous aspect of the disclosure, a further passage opening, in particular a passage bore, may be provided, said further passage opening being provided on a wall, situated opposite the piston barrel, of the cooling duct. Said passage opening will hereinafter also be referred to as lubricant return bore. The lubricant can flow back to the piston interior through said lubricant return bore. Said lubricant return bore is preferably positioned such that an oil level advantageous for temperature transport is set in the cooling duct, which may be realized for example by adaptation of the spacing of the lubricant return bore from the lower end of the cooling duct.
Here, said passage opening is arranged, in the axial direction of the piston, so as to be spaced apart from the lower end of the cooling duct and below the at least one first passage opening. The lower end of the cooling duct is that end which is furthest removed from the piston head. The lubricant return bore is thus arranged on that side of the cooling duct which faces toward the inner side of the piston.
Here, it may be advantageous if the lubricant return bore runs obliquely downward from the wall of the cooling duct to a piston interior space, because this is advantageous from a production aspect, because in this case, no angle head drill is required.
In a further advantageous variant, a wall section of the cooling duct, which wall section connects an upper region of the cooling duct, which is formed in encircling fashion in the region of the ring belt, to a lower region of the cooling duct, which adjoins the wall of the piston barrel, is designed such that the lubricant is flung against the wall of the piston barrel. Said part of the wall of the cooling duct will hereinafter be referred to as transition wall section. The transition wall section is preferably designed so as to form a ski-jump-like structure. For example, the transition wall section of the cooling duct is designed so as to have a section which runs obliquely downward toward the piston barrel and which is adjoined, in the lower region of the cooling duct, by a wall of the cooling duct, which wall runs downward more steeply in relation to said section and is arranged so as to be situated opposite the piston barrel, wherein the transition region between the wall section of the cooling duct and the wall which runs downward more steeply in relation to said section forms an edge. The obliquely downwardly running section of the transition wall section may for example have the shape of a shell surface of a frustrum. In the case of this aspect, the lubricant is thus flung against the wall of the piston barrel in a particularly efficient manner during the shaker motion, such that the heat transfer is improved.
A further aspect of the present disclosure relates to an arrangement comprising a piston as described in this document. The arrangement furthermore comprises a volume-flow-regulated lubricant pump which is provided for the supply of a lubricant to the piston, and a control device of the lubricant pump, wherein the control device is designed such that, in a manner dependent on an operating parameter of an internal combustion engine, from which operating parameter the present engine load can be derived, said control device controls or regulates a lubricant volume flow for the supply of lubricant to the piston such that, in the presence of a first value of the operating parameter, which corresponds to a first engine load, a first volume flow is set, and in the presence of a second value of the operating parameter, which corresponds to a second engine load greater than the first engine load, a second volume flow is set which is greater than the first volume flow. In this way, the oil volume flow via the oil spray nozzle can be regulated such that an advantageous oil temperature is set at the cooling duct. In the presence of low engine load, therefore, a small volume flow of the lubricant is set, and in the presence of high engine load, therefore, a correspondingly large volume flow of the lubricant is set.
A further aspect of the present disclosure relates to a motor vehicle, in particular a utility vehicle, having a piston as disclosed in this document.
The above-described aspects and features of the present disclosure may be combined with one another in any desired manner. Further details and advantages of the present disclosure will be described below with reference to the appended drawings, in which:
Identical or functionally equivalent elements are denoted by the same reference designations throughout the figures, and in some cases, will not be described separately.
In
The cooling duct 2 therefore comprises an upper section 3, which is situated in the region of the ring belt 6, and a lower section 4, which is situated in the region of the piston barrel 1 and which adjoins a wall 10 of the piston barrel. By contrast to the upper section 3 of the cooling duct 2, which is designed so as to run in encircling fashion through 360°, the lower section 4 of the cooling duct 2 is not of fully encircling form, owing to the fact that the running surface of the piston 20 is not of fully encircling form.
In the exemplary aspect shown, the lower region of the section 4 of the cooling duct 2 extends in the axial direction A of the piston as far as the lower end 8 of the piston bore or substantially almost along the entire axial length of the piston barrel 1. Both the upper section 3 and the lower section 4 of the cooling duct 2 extend circumferentially along the outer wall of the piston 20. The aspect of
It can also be seen in
Here, components with identical reference designations correspond to the components of
The special feature of the aspect of
A further special feature lies in the design of the oil-catching rib 52. The oil-catching rib 52 in turn has a first section 54 which extends in the radial direction away from the inner side of the wall 10 of the piston barrel. However, on the distal end of the first section 54, there is now arranged a second section 53 which extends in the axial direction, which second section extends in the axial direction both upwardly and downwardly away from the first section 54. The oil-catching rib 52 of
A sixth aspect of a piston 70 is illustrated in
It is emphasized that the design variants shown in
Even though the present disclosure has been described with reference to particular exemplary aspects, it is self-evident to a person skilled in the art that numerous alterations may be made, and equivalents used as substitutes, without departing from the scope of the present disclosure. Furthermore, numerous modifications may be made without departing from the associated scope. Consequently, the present disclosure is not intended to be restricted to the exemplary aspects disclosed, but rather is intended to encompass all exemplary aspects which fall within the scope of the appended patent claims. In particular, the present disclosure also claims protection for the subject matter and the features of the subclaims independently of the claims referred back to.
Number | Date | Country | Kind |
---|---|---|---|
102016001926.3 | Feb 2016 | DE | national |