Plain bearing with lubricant channel and at least three axial sliding positions

Description

[0001] The invention relates to a plain bearing which can be used in particular in a valve train of an internal combustion engine, wherein a bearing piece of the plain bearing, which can in particular be designed as a cam piece of the valve train, is rotatably and axially displaceably mounted within a bearing opening of a bearing housing. The axial displaceability serves to bring different cam lobes of the cam piece into operative connection with a gas exchange valve of the internal combustion engine, as required, thereby changing the actuation of the gas exchange valve during operation of the internal combustion engine. In order to minimize friction between the bearing housing and the bearing piece, a lubricant channel is integrated into the bearing housing, via which lubricant can be supplied to the contact gap formed between the bearing housing and the bearing piece.

[0002] A corresponding valve train is known from DE 10 2017 203 869 A1. In this valve train, the cam piece can be positioned in two axial sliding positions relative to the bearing housing that accommodates it. The lubricant channel formed in the bearing housing runs radially and, with respect to the axial extent (along the rotational axis), is located centrally in the inner bearing surface of the bearing housing intended for contact with the cam piece.

[0003] A similar valve train is also known from DE 10 2017 205 463 A1, wherein in this valve train lubricant channels are integrated into the cam piece for supplying lubricant to the contact gap of a plain bearing formed by a cam piece and a bearing housing.

[0004] A valve train in which three-stage movable cam pieces of a camshaft are mounted in plain bearings and in which the radius of the outer bearing surfaces of the cam pieces is larger than the largest radius of three different cam lobes is known from DE 10 2017 210 661 A1.

[0005] DE 10 2007 027 979 B4 discloses a plain bearing according to the preamble of patent claim 1.

[0006] The object of the invention was to provide a plain bearing which is advantageously suitable for a rotatable and at least three-stage axially displaceable bearing of a cam piece in a bearing housing of a valve train of an internal combustion engine.

[0007] This object is achieved with a plain bearing according to patent claim 1. A valve train with such a plain bearing and an internal combustion engine with a corresponding valve train are the subject matter of patent claims 8 and 10. Advantageous embodiments of the plain bearing, the valve train, and the internal combustion engine are the subject matter of the further patent claims and / or emerge from the following description of the invention.

[0008] According to the invention, a plain bearing is provided which has at least one bearing housing and a bearing piece which is mounted rotatably and axially displaceably (in each case with respect to a relative axis of rotation) within a bearing opening of the bearing housing, wherein the bearing piece forms an outer bearing surface which contacts an inner bearing surface of the bearing housing, forming a contact gap. A first lubricant channel and a second lubricant channel are integrated into the bearing housing or the bearing piece, which are provided for supplying lubricant to the contact gap, wherein these lubricant channels open into the inner bearing surface of the bearing housing or into the outer bearing surface of the bearing piece at an axial distance from one another, and wherein the supply of lubricant via the first lubricant channel and the second lubricant channel can be influenced by means of a distribution device.

[0009] The axial displaceability of the bearing piece relative to the bearing housing is provided according to the invention such that the outer bearing surface of the bearing piece or the inner bearing surface of the bearing housing covers (at least largely, preferably completely) the openings of the first lubricant channel and the second lubricant channel in a first sliding position. In this first sliding position, the distribution device preferably supplies lubricant to the contact gap via both the first lubricant channel and the second lubricant channel.

[0010] In a second sliding position, the outer bearing surface of the bearing piece or the inner bearing surface of the bearing housing covers the opening of the first lubricant channel (at least largely, preferably completely) and exposes the opening of the second lubricant channel (at least largely, preferably completely) (i.e., at least largely does not cover the opening of the second lubricant channel). In this second sliding position, the distribution device preferably supplies lubricant to the contact gap exclusively via the first lubricant channel (i.e., not also via the second lubricant channel).

[0011] In a third sliding position, the outer bearing surface of the bearing piece or the inner bearing surface of the bearing housing exposes the opening of the first lubricant channel (at least largely, preferably completely) and covers (at least largely, preferably completely) the opening of the second lubricant channel. In this third sliding position, the distribution device preferably supplies lubricant to the contact gap exclusively via the second lubricant channel (i.e., not also via the first lubricant channel).

[0012] The distribution device of a plain bearing according to the invention is designed such that a preferably spherical valve body is arranged in each of the lubricant channels, which closes the respective lubricant channel and thereby prevents lubricant from being discharged from this lubricant channel if the associated orifice is not covered or exposed and consequently the orifice is arranged outside the contact gap. On the other hand, the valve body opens the respective lubricant channel and thereby enables lubricant to be supplied to the contact gap via this lubricant channel if the associated orifice is covered. This makes it possible to achieve, in a particularly simple design, that lubricant only emerges from the respective orifice if it is also located in the region of the contact gap as a result of an overlap.

[0013] Preferably, it can then also be provided that the valve body, when closing the associated lubricant channel, protrudes from the outlet opening of this lubricant channel. This allows automatic opening and closing of the lubricant channels as a result of an axial displacement of the bearing piece relative to the bearing housing. A valve body, which protrudes from the associated outlet opening when there is no overlap, is pressed into the associated lubricant channel when the overlap of this outlet opening is achieved by a relative displacement between the bearing housing and the bearing piece.

[0014] A plain bearing according to the invention enables an advantageous supply of lubricant to the contact gap in at least three sliding positions, which is particularly true when, as is preferably provided, the outer bearing surface of the bearing piece and the inner bearing surface of the bearing ring only partially overlap each other in the second sliding position and / or in the third sliding position. This makes it possible to design both the outer bearing surface of the bearing piece and the inner bearing surface of the bearing housing with a relatively small extension in the axial direction (with respect to the relative axis of rotation), whereby the installation space required for integrating such a plain bearing into, for example, a valve train according to the invention for an internal combustion engine is relatively low.

[0015] Such a valve train comprises at least one camshaft mounted in a plain bearing according to the invention, wherein the camshaft is designed as a cam piece or comprises at least one such cam piece, and wherein this cam piece is the bearing piece of the plain bearing. Furthermore, the valve train comprises at least three cam lobes arranged axially offset from one another, wherein at least two, preferably all three, cam lobes are different. These cam lobes can alternatively be brought into operative connection with a gas exchange valve of an internal combustion engine according to the invention by a corresponding axial displacement of the cam piece, whereby they actuate the gas exchange valve with different valve lift profiles. The gas exchange valve is assigned to a combustion chamber of the internal combustion engine in order to control the introduction of fresh gas into this combustion chamber or the discharge of exhaust gas from this combustion chamber.For moving the cam piece, an internal combustion engine according to the invention also comprises an adjusting device.

[0016] According to a preferred embodiment of a valve train according to the invention, the cam piece can be sleeve-shaped and mounted on a base shaft of the camshaft in a rotationally fixed and axially displaceable manner. This avoids having to axially displace the entire camshaft in order to alternately engage the cam lobes with the gas exchange valve.

[0017] According to a preferred embodiment of a plain bearing according to the invention, the first lubricant channel and the second lubricant channel can be formed integrally in at least one section, and thus, for example, they only divide into separate lubricant channels shortly before the orifices. This allows for a relatively simple integration of the lubricant channels into the bearing housing or the bearing piece.

[0018] In an embodiment of a plain bearing according to the invention, in which the bearing piece as a cam piece has at least three axially offset cam lobes, it can further preferably be provided that the radius of the outer bearing surface of the bearing piece is larger than the largest radius of the cam lobes. This enables advantageous assembly of such a plain bearing and in particular of a valve train of an internal combustion engine comprising such a plain bearing. In addition, this can result in a particularly compact design of the plain bearing with regard to its extension in the axial direction, in particular in combination with the likewise preferred embodiment according to which the outer bearing surface of the bearing piece and the inner bearing surface of the bearing housing only partially overlap in the second sliding position and / or in the third sliding position.The inner bearing surface of the bearing housing can then project beyond the outer bearing surface of the bearing piece or the cam piece in the axial direction without causing a collision with a cam lobe, preferably arranged directly axially adjacent to the outer bearing surface. Accordingly, it can also be provided that in the second and / or third sliding position, at least one cam lobe is arranged at least partially within the bearing opening.

[0019] The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawings. The drawings show, in simplified form: Fig. 1: an internal combustion engine with an internal combustion engine according to the invention in a plan view; Fig. 2: the internal combustion engine in a longitudinal section; Fig. 3: a section of the valve train of the internal combustion engine in a first sliding position of the associated cam piece; Fig. 4: the section of the valve train in a second sliding position of the cam piece; and Fig. 5: the section of the valve train in a third sliding position of the cam piece.

[0020] In the Fig. 1 An internal combustion engine is shown. The internal combustion engine can, for example, power a motor vehicle (not shown).

[0021] The internal combustion engine includes the in further details also in the Fig. 2illustrated internal combustion engine 1. The internal combustion engine 1 forms a plurality of (here: four) cylinder openings 4 in a combination of cylinder crankcase 2 and cylinder head housing 3. The cylinder openings 4 are connected on the inlet side to an intake manifold 5 of a fresh gas line 6 and on the outlet side to an exhaust manifold 7 of an exhaust line 8 of the internal combustion engine. In a known manner, fresh gas (essentially air) is burned with fuel in combustion chambers 9, which are delimited by the cylinder openings 4 together with the pistons 10 guided therein and the cylinder head housing 3. For this purpose, the fuel can be injected directly into the combustion chambers 9 by means of fuel injectors 11. The exhaust gas produced during the combustion of the fuel-fresh gas mixture is discharged via the exhaust line 8.

[0022] The supply of fresh gas into the combustion chambers 9 and the removal of exhaust gas from the combustion chambers 9 is controlled by four gas exchange valves 12, 13, namely two inlet valves 12 and two outlet valves 13, per combustion chamber 9, which are controlled by a Fig. 1 not shown valve train of the combustion engine 1. The valve train comprises, according to the Fig. 2a crankshaft 14 forming crankpins 15, wherein the crankpins 15 are connected to the pistons 10 via connecting rods 16. This converts linear movements of the pistons 10 into a rotation of the crankshaft 14, wherein the rotation of the crankshaft 14 in turn causes a periodic change in the direction of the linear movements of the pistons 10. The rotation of the crankshaft 14 is also transmitted via a timing gear, for example a toothed belt drive 17, to two camshafts 18, each of which actuates two gas exchange valves 12, 13 per combustion chamber 9 via, for example, rocker arms or finger levers (not shown).

[0023] The internal combustion engine further comprises an exhaust gas turbocharger. This has an exhaust gas turbine 19 integrated into the exhaust system 8 and a fresh gas compressor 20 integrated into the fresh gas system 6. An impeller of the exhaust gas turbine 19, driven in rotation by the exhaust gas flow, drives an impeller of the compressor 20 via a shaft 21. The resulting rotation of the impeller of the compressor 20 compresses the fresh gas passed through it. A wastegate 22 can be used to limit the boost pressure by diverting a portion of the exhaust gas flow past the exhaust gas turbine 19 when the internal combustion engine 1 is operating at high speed and / or under load. Furthermore, an exhaust gas aftertreatment device 23 is integrated into the exhaust system 8.

[0024] The internal combustion engine also comprises an adjusting device 24, by means of which one of a total of three cam lobes 25 can be assigned to the intake valves 12 and / or the exhaust valves 13 as required. This adjusting device 24 can be controlled by a control device 26 and in the Fig. 2only indicated schematically. The function of the adjusting device 24 is based on the longitudinal axial displaceability of sleeve-shaped cam pieces 27, which are arranged in a rotationally fixed manner on a base shaft 28 via intermeshing longitudinal gears. The cam pieces 64 have three different cam lobes 25 for each of the intake valves 28 or exhaust valves 30 actuated by them, which cam lobes are alternatively brought into operative connection with the associated gas exchange valves 12, 13 depending on the respectively set axial sliding position of the cam pieces 27. The structure and mode of operation of the adjusting device 24 can correspond to one of those disclosed in DE 10 2017 203 869 A1, DE 10 2017 205 463 A1, and DE 10 2017 210 661 A1.

[0025] In addition to the base shaft 28 of the camshaft 18, the cam pieces 27 are each rotatably mounted in at least one plain bearing, wherein this mounting of the cam pieces 27 also ensures axial mobility, which makes it possible to adjust the various sliding positions of the cam pieces 27, in which the various cam lobes 25 are brought into operative connection with the respective associated gas exchange valve 12, 13.

[0026] The plain bearings provided for the mounting of the cam pieces 27 comprise, according to the Fig. 3 to 5each use a section of the cylinder head housing 3 as a bearing housing 29, which forms a cylindrical bearing opening 30 in which a cylindrical bearing section 31 of the respective cam piece 27 is arranged. The outer diameter of the bearing section 31 of the cam piece 27 is only slightly smaller than the inner diameter of the bearing opening 30 in order to achieve largely play-free but also jam-free relative mobility between the bearing housing 29 and the bearing section 31 of the cam piece 27. The wall of the bearing housing 29 delimiting the bearing opening 30 represents an inner bearing surface 32 of the bearing housing 29, and the outer surface of the bearing section 31 of the cam piece 27 represents an outer bearing surface 33 of the cam piece 27, with a contact gap 34 being formed between the overlapping area of ​​the inner bearing surface 32 and the outer bearing surface 33.

[0027] For each of the plain bearings provided for supporting a cam piece 27, two lubricant channels 35, 36 are integrated into the cylinder head housing 3 and thus into the bearing housing 29, which are connected to a common lubricant source (not shown). The lubricant channels 35, 36 of each plain bearing are initially integral, i.e., formed as a common channel section, and then separate into partial strands which, spaced apart axially (with respect to the rotational axis 37 of the camshaft 18 and thus also of the cam pieces 27), open into the inner bearing surface 32 of the respective bearing housing 29. By means of the lubricant channels 35, 36, a preferably liquid lubricant can be introduced into the contact gap 34 of each plain bearing in order to realize the lowest possible friction relative movement between the components of the plain bearing, i.e., between the cam pieces 27 and the cylinder head housing 3 of the internal combustion engine 1.

[0028] The Fig. 3 to 5 show different sliding positions of a plain bearing of the internal combustion engine 1, which is provided for supporting a cam piece 27, wherein in a first sliding position according to the Fig. 3the bearing section 31 of the cam piece 27 is positioned axially centrally within the bearing opening 30 of the bearing housing 29. The outer bearing surface 33 of the cam piece 27 covers the outlet openings 38 of both lubricant channels 35, 36 (completely), so that the contact gap 34 is also arranged in the region of both outlet openings 38. In this first sliding position, lubricant is supplied to the contact gap 34 via both lubricant channels 35, 36. This is ensured by a corresponding functional position of a distribution device of the plain bearing, which is formed by a spherical valve body 39 arranged within each of the lubricant channels 35, 36 and an associated valve seat 40 arranged in the region of the respective outlet opening 38.

[0029] If the outer bearing surface 33 of the cam piece 27 covers the opening 38 of a lubricant channel 35, 36, the valve body 39 arranged in this lubricant channel 35, 36 is lifted slightly from the corresponding valve seat 40. This lubricant channel 35, 36 is thus opened, so that lubricant can flow through the corresponding opening 38 into the contact gap 34 of the plain bearing. If, on the other hand, the outer bearing surface 33 of the cam piece 37 does not cover the opening 38 of a lubricant channel 35, 36 or exposes it, the valve body 39 arranged in this lubricant channel 35, 36 is pressed against the corresponding valve seat 40 at least by the pressure of the lubricant, and possibly also by the force of gravity acting on it, whereby the corresponding lubricant channel 35, 36 is closed.When the valve body 39 is pressed against the corresponding valve seat 40 in such a position, it projects far out of the corresponding orifice 38 that it is lifted off the valve seat by subsequent contact with the bearing section 31 of the cam piece 27 in order to open the corresponding lubricant channel 35, 36.

[0030] In the first sliding position of a plain bearing provided for supporting a cam piece 27, a centrally arranged cam elevation 25 of the cam piece 27 is in operative connection with the associated gas exchange valve 12, 13 of the internal combustion engine 1.

[0031] The Fig. 4shows a second sliding position of a plain bearing provided for supporting a cam piece 27, in which the outer bearing surface 33 of the cam piece 27 covers the opening 38 of a first (35) of the lubricant channels 35, 36 and exposes the opening of the second lubricant channel 36. Lubricant is consequently only supplied to the contact gap 34 via the first lubricant channel 35. This prevents lubricant from escaping via the second lubricant channel 36, which would otherwise cause the lubricant to escape uncontrollably into the valve train and not into the contact gap 34, which in the second sliding position is not arranged in the region of the opening 38 of the second lubricant channel 36. In the second sliding position, a Fig. 3 to 5 right-hand cam lobe 25 of the cam piece 27 in operative connection with the associated gas exchange valve 12, 13 of the combustion engine 1.

[0032] The Fig. 5shows a third sliding position of a plain bearing provided for supporting a cam piece 27, in which the outer bearing surface 33 of the cam piece 27 covers the opening 38 of the second lubricant channel 36 and exposes the opening 38 of the first lubricant channel 35. Lubricant is then consequently supplied to the contact gap 34 only via the second lubricant channel 36. In the third sliding position, a Fig. 3 of the 5 left-hand cam lobe 25 in operative connection with the associated gas exchange valve 12, 13 of the combustion engine 1.

[0033] Both in the second sliding position according to the Fig. 4 as well as in the third sliding position according to the Fig. 5a section of the outer bearing surface 33 of the cam piece 27 is arranged outside the bearing opening 30 of the bearing housing 29, so that in these sliding positions the outer bearing surface 33 of the cam piece 27 and the inner bearing surface 32 of the bearing housing 29 only partially overlap. This is a consequence of the relatively small dimensions of the bearing housing 29 or the bearing opening 30 in the axial direction, which, however, has an advantageous effect with regard to the installation space requirement of the plain bearing when integrating it into the internal combustion engine 1 and in particular with regard to the minimum achievable distance between adjacent cylinder openings 4 from one another. This also leads to the fact that in the second sliding position according to the Fig. 4 a portion of one of the cam lobes 25 is arranged within the bearing opening 30 of the plain bearing.

[0034] In the Fig. 3 to 5It can also be seen that the radius of the cylindrical outer bearing surface 33 of the cam piece 27 is larger than the largest radius of the cam lobes 25, which enables advantageous assembly of the valve train of the internal combustion engine 1, since the respective cam piece 27, which is preferably formed in one piece, can be easily inserted into the associated bearing opening 30. List of reference symbols

[0035] 1 Combustion engine 2 Cylinder crankcase 3 Cylinder head housing 4 Cylinder opening 5 Intake manifold 6 Fresh gas line 7 Exhaust manifold 8 Exhaust line 9 Combustion chamber 10 Piston 11 Fuel injector 12 Gas exchange valve / intake valve 13 Gas exchange valve / exhaust valve 14 Crankshaft 15 Crankpin 16 Connecting rod 17 Toothed belt drive 18 Camshaft 19 Exhaust turbine 20 Fresh gas compressor 21 Shaft 22 Wastegate 23 Exhaust aftertreatment device 24 Adjustment device 25 Cam lift 26 Control device 27 Camshaft cam 28 Camshaft base shaft 29 Bearing housing 30 Bearing opening 31 Bearing section of the cam lobe 32 Inner bearing surface of the bearing housing 33 Outer bearing surface of the cam lobe 34Contact gap 35First lubricant channel 36Second lubricant channel 37Rotational axis of the camshaft / cam piece 38Orifice of a lubricant channel 39Valve body 40Valve seat

Claims

1. Sliding bearing comprising a bearing housing (29) and a bearing piece mounted within a bearing opening (30) of the bearing housing (29), which bearing piece forms an outer bearing surface (33) which contacts an inner bearing surface (32) of the bearing housing (29) to form a contact gap (34), a first lubricant channel (35) and a second lubricant channel (36) for supplying lubricant to the contact gap (34) being integrated into the bearing housing (29) or into the bearing piece, which lubricant channels open into the inner bearing surface (32) or the outer bearing surface (33) at an axial distance from one another, a supply of lubricant via the first lubricant channel (35) and the second lubricant channel (36) being able to be influenced by means of a distribution device, and the axial displaceability of the bearing piece relative to the bearing housing (29) being such that the outer bearing surface (33) of the bearing piece or the inner bearing surface (22) of the bearing housing (29) - overlaps the mouth openings (38) of the first lubricant channel (35) and the second lubricant channel (36) in a first sliding position of the sliding bearing, and - overlaps the mouth opening (38) of the first lubricant channel (35) and exposes the mouth opening (38) of the second lubricant channel (36) in a second sliding position of the sliding bearing and - exposes the mouth opening (38) of the first lubricant channel (35) and overlaps the mouth opening (38) of the second lubricant channel (36) in a third sliding position of the sliding bearing, characterized in that the bearing piece is mounted rotatably and axially displaceably within the bearing opening (30) and a valve body (39) is arranged in each of the lubricant channels (35, 36), which closes the relevant lubricant channel (35, 36) when the associated mouth opening (38) is exposed and which opens the relevant lubricant channel (35, 36) when the associated mouth opening (38) is overlapped.

2. Sliding bearing according to claim 1, characterized in that in the second sliding position and / or in the third sliding position of the sliding bearing, the outer bearing surface (33) of the bearing piece and the inner bearing surface (32) of the bearing housing (29) only partially overlap.

3. Sliding bearing according to either of the preceding claims, characterized in that the valve body (39), when it closes the associated lubricant channel (35, 36), protrudes from the mouth opening (38) of this lubricant channel (35, 36).

4. Sliding bearing according to any of the preceding claims, characterized in that the first lubricant channel (35) and the second lubricant channel (36) are integrally formed in at least one portion.

5. Sliding bearing according to any of the preceding claims, characterized in that the bearing piece is designed as a cam piece (27) and has at least three cam elevations (25) arranged axially offset from one another.

6. Sliding bearing according to claim 5, characterized in that the radius of the outer bearing surface (33) of the cam piece (27) is larger than the largest radius of the cam elevations (25).

7. Sliding bearing according to either claim 5 or claim 6, characterized in that in the second and / or third sliding position, at least one cam elevation (25) is arranged at least partially within the bearing opening (30).

8. Valve train for an internal combustion engine (1) characterized by a camshaft (18) which is mounted by means of at least one sliding bearing according to any of claims 5 to 7 and which forms or comprises the cam piece (27).

9. Valve train according to claim 8, characterized in that the cam piece (27) is sleeve-shaped and is mounted on a main shaft (28) of the camshaft (18) for conjoint rotation and so as to be axially displaceable.

10. Internal combustion engine (1) having at least one combustion chamber (9), at least one gas exchange valve (12, 13) associated with the combustion chamber (9), a valve drive according to either claim 8 or claim 9 for operating the gas exchange valve (12, 13), and an adjusting device (24) by means of which the cam piece (27) can be axially displaced such that the cam elevations (25) can alternatively be brought into operative connection with the gas exchange valve (12, 13).