CN110199096B

CN110199096B - Length-adjustable connecting rod having a cylinder-piston unit with a plurality of piston seals

Info

Publication number: CN110199096B
Application number: CN201780068188.5A
Authority: CN
Inventors: 佐尔坦·里巴; 凯·阿伦斯; 马丁·博登施泰纳; 斯特芬·拉茨; 马尔特·黑勒
Original assignee: AVL List GmbH; Iwis Motorsystem GmbH and Co KG
Current assignee: AVL List GmbH; Iwis Motorsystem GmbH and Co KG
Priority date: 2016-11-03
Filing date: 2017-11-03
Publication date: 2022-04-01
Anticipated expiration: 2037-11-03
Also published as: CN110199096A; DE102016120967A1; AT519305B1; WO2018083256A1; AT519305A3; AT519305A2

Abstract

The invention relates to a length-adjustable connecting rod for an internal combustion engine, having a first connecting rod part, a second connecting rod part and at least one cylinder-piston unit for adjusting the first connecting rod part relative to the second connecting rod part, wherein the cylinder-piston unit comprises a cylinder bore, an adjusting piston arranged in the cylinder bore in a longitudinally movable manner, at least one pressure chamber arranged in the cylinder bore, and a sealing device arranged between an outer wall of the adjusting piston and an inner wall of the cylinder bore. The sealing arrangement here comprises at least two piston seals which are arranged in separate grooves formed on the outer device wall of the adjusting piston and are in sliding contact with the inner device wall of the cylinder bore. The invention further relates to an internal combustion engine having such a length-adjustable connecting rod, and to the use of a cylinder-piston unit for a length-adjustable connecting rod of an internal combustion engine.

Description

Length-adjustable connecting rod having a cylinder-piston unit with a plurality of piston seals

Technical Field

The invention relates to a length-adjustable connecting rod for an internal combustion engine, having a first connecting rod part, a second connecting rod part and at least one cylinder-piston unit for adjusting the first connecting rod part relative to the second connecting rod part, wherein the cylinder-piston unit comprises a cylinder bore, an adjusting piston arranged in the cylinder bore in a longitudinally movable manner, at least one pressure chamber arranged in the cylinder bore, and a sealing device arranged between an outer wall of the adjusting piston and an inner wall of the cylinder bore. The invention further relates to an internal combustion engine having such a length-adjustable connecting rod and to the use of a length-adjustable connecting rod for an internal combustion engine for a cylinder-piston unit.

Background

The thermal efficiency of internal combustion engines, in particular gasoline engines, depends on the compression ratio epsilon, i.e. the ratio of the total volume before compression to the extruded volume (epsilon-is the (stroke volume V)_h+ squeeze volume V_c) Extruded volume V_c). As the compression ratio is raised, the heat efficiency increases. The thermal efficiency is decreasing in relation to the increase in the compression ratio, but of course still appears relatively strong in the range of values common today.

In practice, the compression ratio cannot be arbitrarily increased, since an excessively high compression ratio would lead to an accidental self-ignition of the combustion mixture due to the increase in pressure and temperature. This premature combustion not only leads to unstable operation and the occurrence of so-called knocking in gasoline engines, but may also lead to damage to the engine components. In the partial load range, the risk of self-ignition is low, which is related to the operating point of the engine in addition to the influence of ambient temperature and pressure. Therefore, a higher compression ratio can be achieved in the partial load range. Therefore, in the development of modern internal combustion engines, efforts are made to match the compression ratio to the operating points of the engine.

In order to achieve Variable Compression Ratios (VCRs), different solutions exist with which to change the position of the stroke journal of the crankshaft or of the piston pin of the engine piston or to change the effective length of the connecting rod. Here, solutions for adjusting the component continuously and discontinuously, respectively, exist. Continuous control enables CO to be achieved on the basis of a compression ratio that can be adjusted for each operating point₂Optimal reduction of emissions and oil consumption. Rather, the discontinuous adjustment enables structural and operational advantages to be achieved with two stages of end stops designed for the adjustment movement, and nevertheless enables fuel consumption and CO to be achieved in comparison with conventional crank drives₂Significant savings in emissions.

Document US 2,217,721 has described an internal combustion engine with a connecting rod of adjustable length having two rod parts which are telescopically movable relative to each other and which together form a high-pressure chamber. In order to fill and drain the high-pressure chamber with engine oil and thus to vary the length of the connecting rod, a hydraulic control mechanism is provided with a control valve having a spring-biased closure element which can be moved into an open position by the pressure of the engine oil.

EP 1426584 a1 shows a discontinuous adjustment of the compression ratio for an internal combustion engine, wherein an eccentric connected to a gudgeon pin enables the adjustment of the compression ratio. The fixing of the eccentric in one or the other end position of the pivot range is achieved here by means of a mechanical locking. DE 102005055199 a1 likewise discloses a mode of operation of a variable-length connecting rod, with which different compression ratios can be achieved. This embodiment is also realized here by an eccentric in the small connecting rod eye, which is fixed in its position by two hydraulic cylinders with variable resistance.

WO 2013/092364 a1 describes a length-adjustable connecting rod for an internal combustion engine, which has two rod parts which are telescopically movable relative to one another, wherein one rod part constitutes a cylinder and the second rod part constitutes a length-adjustable piston element. A high-pressure chamber is formed between the control piston of the first rod part and the cylinder of the second rod part, which high-pressure chamber is supplied with engine oil via a hydraulic control mechanism having an oil channel and a valve associated with the oil pressure. A similar length-adjustable connecting rod for an internal combustion engine with telescopically movable rod parts is shown in WO 2015/055582 a 2.

According to WO 2015/055582 a2, the compression ratio in an internal combustion engine should be adjusted by the connecting rod length. The connecting rod length influences the compression volume in the combustion chamber, wherein the stroke volume is predetermined by the positioning of the crankshaft journal and the cylinder bore. Thus, a short connecting rod will result in a lower compression ratio than a long connecting rod if the other geometrical dimensions of, for example, the piston, the cylinder head, the crankshaft, the valve control, etc., are the same. In the known length-adjustable connecting rods, the connecting rod length is hydraulically varied between two positions. The entire connecting rod is designed in multiple parts, wherein the length change is effected by a telescopic mechanism which can be adjusted by means of a double-acting hydraulic cylinder. A small connecting rod eye, which is usually used to accommodate a piston pin, is connected to the piston rod (telescopic rod section). The associated adjusting piston is guided in a cylinder, which is arranged in a connecting rod part with a large connecting rod eye, which is usually used to accommodate a crankshaft journal, in an axially displaceable manner. The adjusting piston divides the cylinder into two pressure chambers, an upper and a lower pressure chamber. The two pressure chambers are supplied with engine oil via a hydraulic control, wherein the supply of engine oil to the pressure chambers is effected via the lubrication of the connecting rod bearings. For this purpose, an oil feed-through is required from the crankshaft journal via a connecting rod bearing to the connecting rod and there via the check valve of the actuating mechanism to the pressure chamber.

If the connecting rod is in a long orientation, there is no engine oil in the upper pressure chamber. While the lower pressure chamber is completely filled with engine oil. During operation, the connecting rod is alternately pulled and squeezed due to gas and inertial forces. In the long setting of the connecting rod, the tensile force is absorbed by mechanical contact with the upper stop of the adjusting piston. Therefore, the link length does not change. The active pressing force is transmitted via the piston surface to the lower pressure chamber filled with oil. The oil pressure rises because the check valve of this chamber prevents the oil from flowing back, wherein very high dynamic pressures, which are significantly higher than 1000bar, may occur in the lower pressure chamber. The link length does not change. The connecting rod is hydraulically blocked by a system pressure in this direction.

In the short position of the link, the relationship is shifted. The lower pressure chamber is empty and the upper pressure chamber is filled with engine oil. The pulling force causes the pressure in the upper pressure chamber to rise. The pushing force is taken up by a mechanical stop.

The length of the connecting rod can be adjusted in two stages by evacuating one of the two pressure chambers. For this purpose, one of the two check valves in the inlet is bridged or opened by the regulating device in each case by the associated return channel. The return ducts allow the engine oil to drain into the crankcase independently of the pressure difference between the pressure chamber and the supply device. Each check valve loses its function accordingly. Both return channels are opened and closed by means of a control valve, wherein always exactly one return channel is open and the other return channel is closed. The actuator for switching the two return channels is here actuated, for example hydraulically, by the supply pressure.

The installation space for such a connecting rod is limited both axially and radially. The installation space is limited in the direction of the crankshaft by the bearing width and the counterweight distance. In the axial direction, there is only a construction space between the small connecting rod eye for supporting the piston pin and the large connecting rod eye for supporting the crankshaft journal and a possible adjustment stroke of the connecting rod.

In internal combustion engines the forces transmitted by the connecting rod are relatively large, and therefore the pressure in the pressure chamber of the cylinder-piston unit can also be considerable. In view of the high internal pressures in such cylinder-piston units, the fatigue strength of the materials used is problematic, while the design of the components is also problematic with regard to the small installation space.

A further aspect of a length-adjustable connecting rod with a cylinder-piston unit for use in an internal combustion engine is that the hydraulic adjusting mechanism is usually supplied with engine oil of the internal combustion engine, the viscosity of which engine oil decreases not only with decreasing operating temperature but also with increasing operating time and is also entrained in the adjusting mechanism of the connecting rod with respect to harmful particles. In addition to soot particles that arise from their combustion in the engine, casting residual particles or chips from engine manufacture and processing are also transported via the engine oil. The actuating structure of the length-adjustable connecting rod must maintain the operability permanently, irrespective of the reduction in the viscosity of the engine oil and the particles transported by the engine oil into the actuating mechanism.

In view of the extreme pressure differences of significantly more than 1,000bar in the pressure space of the cylinder-piston unit for a length-adjustable connecting rod and the influence of the force transmission via the connecting rod to the crankshaft on the power output of the internal combustion engine, contact-type sealing devices or structurally designed seals are used in conventional length-adjustable connecting rods. Leakage from the respectively blocked pressure chamber will lead to the retraction of the adjusting piston into the respective pressure chamber, whereby the amount of work is consumed in response to the force acting on the adjusting piston and the displacement of the adjusting piston, which will result in a power loss of the internal combustion engine. This power loss is subtracted from the improved thermal efficiency of the internal combustion engine caused by the variable compression ratio, corresponding to the respective design of the cylinder-piston unit. In conventional length-adjustable connecting rods with cylinder-piston units, simple gap seals are usually used as sealing means. The gap seal has a certain leakage due to the design structure, compared to a contact seal that prevents leakage as a touch type sealing device. The advantages of the clearance seal are: the number of components is reduced, so that the assembly is easy and the installation space of the cylinder-piston unit is reduced. Accordingly, the leakage inherent in the system in the gap seal causes heating of the system in addition to power loss. A contact seal (for example a piston or rod seal which may be arranged between the movable components of the cylinder-piston unit) can almost completely prevent leakage of engine oil from the pressure chamber and avoid corresponding power losses. However, contact seals are very sensitive to soot particles and swarf in the engine oil, which can lead to significant damage to the surfaces of the seal and ultimately to failure or failure of the seal. This risk increases with higher system pressures, since particles from the engine oil are transported to an elevated degree between the piston periphery and the cylinder wall and are embedded there at the sealing surfaces.

Although piston-stroke machines are well known in many technical fields and reciprocating piston engines are constantly being optimized, improved and further developed in the field of the automotive industry, the sealing conditions in cylinder-piston units of connecting rods of adjustable length, despite extensive development and research, are still unsatisfactory, in particular in terms of the necessary service life of the connecting rod of adjustable length relative to the total operating time of the internal combustion engine. In comparison to conventional reciprocating piston engines, the contact-type piston seals in the cylinder-piston units of the connecting rods with adjustable length are subject to considerable temperature loads due to extremely high pressures and changing force directions and contamination of the engine oil with soot particles and chips, in addition to wear due to mechanical contact. This leads to rapid wear of the piston seal and formation of grooves in the wall of the cylinder-piston unit and ultimately to failure of the sealing arrangement and loss of power to the internal combustion engine. Accordingly, in recent developments, the length-adjustable connecting rod preferably uses a gap seal, which at least achieves the advantage of a smaller number of components for a smaller installation space. Functionally, however, such gap seals are subject to considerable wear in the cylinder-piston unit of the connecting rod whose length can be adjusted, since the gap between the cylinder and the adjusting piston must be selected to be relatively small in order to achieve a sealing effect sufficient for extreme pressure differences. Whether a non-contacting gap seal or a contacting seal is used as the sealing means of the cylinder-piston unit, the high system pressure in the cylinder-piston unit will cause soot particles and chips from the engine oil to penetrate between the cylinder wall and the piston periphery side and get stuck between the seal surfaces, which can lead to severe damage at the surfaces and ultimately to wear and failure of the cylinder-piston unit.

Disclosure of Invention

The object of the present invention is therefore to provide a length-adjustable connecting rod having a cylinder-piston unit and an improved sealing arrangement which, despite a high pressure difference and a small installation space, enables an improved permanent sealing effect.

This object is achieved according to the invention in that the sealing arrangement comprises at least two piston seals, wherein each piston seal is arranged in a separate groove surrounding the outer device wall of the adjusting piston and is in sliding contact with the inner device wall of the cylinder bore. The provision of at least two piston seals reduces the pressure drop which, due to the extremely high system pressure, has to be absorbed via each individual piston seal therein and accordingly reduces the risk of entrainment of particles from the engine oil and subsequently avoids damage to the seal surfaces due to particles. Furthermore, the gradual reduction of the high system pressure in the cylinder-piston unit enables the use of simpler and less expensive piston seals having a flatter design, which can be used in the less available installation space of the cylinder-piston unit even without structural pressing measures being designed. In order to reliably build up the pressure, the piston seals are each arranged in separate grooves running around the outer wall of the control piston, which grooves not only ensure the sealing of the piston seals against the control piston, but also enable reliable positioning of the piston seals with little effort despite the high system pressure and relative movement with respect to the inner wall of the cylinder bore. In order to increase the positive effect of the stepwise reduction of the pressure and to limit the pressure drop acting on the individual piston seals, the sealing arrangement comprises 3, preferably at least 4 piston seals.

In general, the adjusting piston and the cylinder bore of the cylinder-piston unit are designed rotationally symmetrically, but are not limited to this geometry. The length-adjustable connecting rod according to the invention also comprises an elliptical, polygonal or other cross-sectional shape of the adjusting piston and of the cylinder bore of the cylinder-piston unit.

Preferably, the piston seal of the sealing device is configured as a double-acting piston seal. This not only facilitates the alternating relative movement between the control piston and the cylinder bore and also avoids adverse effects on the sealing effect, but also enables a double-sided action of the cylinder-piston unit. A suitable embodiment of the piston seal is provided here: the double-acting piston seal is of two-part design, wherein the two-part piston seal has a positioning ring and a sliding ring, preferably made of plastic. The positioning ring, usually a dimensionally stable O-ring, enables a reliable arrangement of the piston seal in the pretensioning relative to the circumferential groove in the outer wall of the adjusting piston. Accordingly, a sliding ring, preferably made of a low-friction plastic material, having a rectangular body and a sealing lip arranged centrally in the direction of the inner wall of the cylinder bore, makes it possible to achieve a good seal with high pressure resistance and a good low-friction sliding capability with respect to the inner wall of the cylinder bore.

A meaningful design rule is: the sealing device comprises a wiper, wherein the wiper is arranged on the end of the outer device wall of the adjusting piston facing the pressure chamber. The wiper arranged between the pressure chamber filled with engine oil and the first piston seal in the direction of the pressure chamber prevents or reduces the entrainment of soot particles and chips from the engine oil into the gap between the control piston and the cylinder bore and ultimately between the piston seal and the inner wall of the cylinder bore. The risk of wear, damage and failure of the sealing arrangement is thereby reduced and the service life of the cylinder-piston unit is therefore ultimately significantly increased.

Particular embodiments provide for: the control piston of the cylinder-piston unit is designed as a control piston which acts on both sides, wherein the control piston, which is arranged in the cylinder bore so as to be movable in the longitudinal direction, forms a first pressure chamber and a second pressure chamber for receiving engine oil and is each delimited on one side. A bilaterally acting control piston makes it possible to control the stroke of the piston rod with the respective cylinder-piston unit in the direction of a greater compression ratio and in the direction of a smaller compression ratio. Thus, this different regulating piston from DE 102005055199 a1 is used for the bidirectional regulation of the piston stroke or compression ratio. Expediently, a stepped piston can be used, by means of whose larger end face the connecting rod is pushed into its extended position under corresponding pressure loading. Due to the main force relationships in internal combustion engines, it is generally sufficient for the smaller end faces to be used for adjustment in the opposite direction. The adjusting piston can have a wiper at the end of the outer wall facing the first pressure chamber and the second pressure chamber.

Further embodiments provide for: the adjusting piston has a piston rod on a second end side delimiting the second pressure chamber, which piston rod extends through a rod bore of the cylinder-piston unit, wherein at least two rod seals are provided, each of which is arranged in a circumferential groove in the rod bore and is in sliding contact with the piston rod. The two individual rod bores, which are reliably arranged in the individual circumferential grooves in the rod bores, also make it possible to relieve high system pressures in the region of the piston rod in a multi-stage manner, and accordingly use a simply designed and more inexpensively manufactured rod seal. Here, the rod seal is in sliding contact with the piston rod for a reliable sealing function and for a movability of the piston rod relative to the rod bore. It is expedient to provide a rod wiper, wherein the rod wiper is arranged on the end of the rod bore facing the second pressure chamber. The rod wiper thus prevents soot particles and chips from the engine oil from being introduced between the piston rod and the rod bore and thus prevents wear, damage and ultimately failure of the sealing arrangement between the piston rod and the rod bore of the cylinder-piston unit.

For a simple construction of the length-adjustable connecting rod, the first connecting rod part can be connected to the adjusting piston of the cylinder-piston unit, while the second connecting rod part has the cylinder bore of the cylinder-piston unit.

The invention further relates to the use of a sealing arrangement for a length-adjustable connecting rod of an internal combustion engine for a cylinder-piston unit having a first connecting rod part and a second connecting rod part which can be adjusted by means of a cylinder-piston unit in order to move the first connecting rod part relative to the second connecting rod part, the cylinder-piston unit comprising a cylinder bore, an adjusting piston which is arranged in the cylinder bore in a longitudinally movable manner, at least one pressure chamber which is arranged in the cylinder bore, and a sealing arrangement which is arranged between an outer wall of the adjusting piston and an inner wall of the cylinder bore, wherein the sealing arrangement comprises at least two piston seals, each piston seal being arranged in a separate groove which is surrounded on the outer wall of the adjusting piston and being in sliding contact with the inner wall of the cylinder bore. Despite the extremely high system pressures and the relatively small overall dimensions of the cylinder-piston unit, the use of a plurality of piston seals in the cylinder-piston unit of the length-adjustable connecting rod still enables good sealing of the pressure chamber and, via a gradual reduction of the high system pressures, enables the use of piston seals having small dimensions. The cylinder-piston unit is actuated by gas and inertial forces of the internal combustion engine acting on the rod part, and the positioning of the rod part is locked by the engine oil present in the at least one pressure chamber.

In a further aspect, the invention relates to an internal combustion engine having at least one reciprocating piston, at least one compression ratio adjustable in a cylinder, and at least one length-adjustable connecting rod according to the above-described embodiments connected to the reciprocating piston. Preferably, but not necessarily, all reciprocating pistons of the internal combustion engine are equipped with such a connecting rod of adjustable length. The fuel savings of such an internal combustion engine can be considerable and up to 20% when the compression ratio is adjusted accordingly depending on the respective operating state. Suitably, the cylinder-piston unit of the length-adjustable connecting rod may be coupled to an engine oil hydraulic installation of the internal combustion engine. The pressure prevailing in the engine oil circuit can thus be used to adjust and lock the adjusting piston in the cylinder bore of the cylinder-piston unit. Furthermore, the adjusting mechanism of the length-adjustable connecting rod can be actuated by means of the pressurized engine oil.

Further modifications provide for: the system pressure of the engine oil in the pressure chamber of the cylinder-piston unit is between 1000bar and 3000bar, preferably between 2000bar and 3000 bar. Limiting the system pressure enables a reliable structural design of the inner diameter of the cylinder bore and the wall thickness of the cylinder, and thus of the length-adjustable connecting rod according to the invention.

According to a development of the invention, a timing drive can be provided, which has at least one timing chain, a tensioning and/or guide rail, and/or a chain tensioner, which connects the crankshaft with at least one camshaft of the internal combustion engine. The timing mechanism is important in this respect, since it can have a significant effect on the dynamic load of the internal combustion engine and thus on the length-adjustable connecting rod. The timing mechanism is preferably designed such that no excessively high dynamic forces are introduced via the timing mechanism. Alternatively, such a timing gear can also be designed with a spur gear toothing or a drive belt, for example a toothed belt, which is pretensioned by means of a tensioning device with a tensioning roller.

Drawings

Embodiments are explained in more detail below with reference to the drawings. Wherein:

fig. 1 shows a schematic cross section of an internal combustion engine;

FIG. 2 shows a schematic view of the length adjustable linkage of FIG. 1 in a partially cut-away illustration;

FIG. 3 shows a cross-sectional view of an embodiment of an adjusting piston of the cylinder-piston unit of FIG. 2;

fig. 4 shows a sectional view of a further embodiment of the adjusting piston of the cylinder-piston unit of fig. 2.

Detailed Description

Fig. 1 schematically shows an internal combustion engine (gasoline engine) 1. The internal combustion engine 1 has three cylinders 2.1, 2.2 and 2.3, in each of which a reciprocating piston 3.1, 3.2, 3.3 moves up and down, respectively. The internal combustion engine 1 furthermore comprises a crankshaft 4, which is rotatably mounted by means of crankshaft bearings 5.1-5.4. The crankshaft 4 is connected to the associated reciprocating pistons 3.1, 3.2 and 3.3 by connecting rods 6.1, 6.2 and 6.3, respectively. The crankshaft 4 has eccentrically arranged crankshaft journals 7.1, 7.2 and 7.3 for each connecting rod 6.1, 6.2 and 6.3. The large connecting rod eye 8.1, 8.2 and 8.3 is supported on the associated crankshaft journal 7.1, 7.2 and 7.3, respectively. The small connecting rod eyes 9.1, 9.2 and 9.3 are supported on the gudgeon pins 10.1, 10.2 and 10.3, respectively, and are thus pivotably connected to the associated reciprocating pistons 3.1, 3.2 and 3.3. The terms "small connecting rod eyes 9.1, 9.2 and 9.3" and "large connecting rod eyes 8.1, 8.2 and 8.3" do not mean absolute or relative size relationships, but merely serve to distinguish the components and associations of the internal combustion engine shown in fig. 1. Thus, the dimensions of the diameters of the small link eyes 9.1, 9.2 and 9.3 can be smaller, equal or larger than the dimensions of the diameters of the large link eyes 8.1, 8.2 and 8.3.

The crankshaft 4 is provided with a crankshaft sprocket 11 and is coupled with a camshaft sprocket 13 by means of a timing chain 12. The camshaft sprocket 13 drives the camshaft 14 with its associated cams for operating the intake and exhaust valves (not shown in detail) of each cylinder 2.1, 2.2 and 2.3. The slack side of the timing chain 12 is tensioned by means of a pivotably arranged tensioning rail 15, which is pressed onto the timing chain by means of a chain tensioner 16. The pulling side of the timing chain 12 may slide along the guide rail. The main functional modes of the timing mechanism, including fuel injection and ignition by means of an ignition coil, are not explained in detail and are assumed to be known. The eccentricity of the crankshaft journals 7.1, 7.2 and 7.3 definitively presets the stroke travel H_KEspecially when the crankshaft 4 is in the present case arranged exactly under the centre of the cylinders 2.1, 2.2 and 2.3. The reciprocating piston 3.1 is shown in its lowest position in fig. 1, while the reciprocating piston 3.2 is shown in its highest position. In the present case, the difference is the stroke travel H_K. Residual height H_C(see cylinder 2.2) the remaining pressing height in cylinder 2.2 is obtained. Combined with the diameter of the reciprocating piston 3.1, 3.2 or 3.3 or of the associated cylinder 2.1, 2.2 and 2.3, is moved by stroke H_KObtain the stroke volume V_hAnd from the remaining pressing height H_CCalculating the extrusion volume V_c. Of course, the extruded volume V_cDecisively in relation to the construction of the cylinder head. From these volumes V_hAnd V_cA compression ratio epsilon is obtained. In detail, the stroke volume V_hAnd an extrusion volume V_cIs divided by the extruded volume V_cThe compression ratio epsilon is calculated. Currently, a common epsilon value for gasoline engines is between 10 and 14.

In order to be able to adapt the compression ratio epsilon depending on the operating point (n, T, throttle position) of the internal combustion engine 1, the connecting rods 6.1, 6.2 and 6.3 are designed to be adjustable over their length according to the invention. Thus, it is possible to operate at a higher compression ratio in the partial load range than in the full load range.

Fig. 2 shows an exemplary length-adjustable connecting rod 6.1, which is of the same design as the connecting rods 6.2 and 6.3. Therefore, the description also applies accordingly. The connecting rod 6.1 has a connecting rod head 17.1 with the small connecting rod eye 9.1, a first connecting rod part 18.1 which is guided telescopically in a second connecting rod part 19.1. The relative movement of the first connecting rod part 18.1 in the longitudinal direction with respect to the second connecting rod part 19.1 takes place by means of a cylinder-piston unit 20.1, which has an adjusting piston 21.1 and a cylinder bore 22.1 and a sealing device 23.1 between the adjusting piston 21.1 and the cylinder bore 22.1. A lower bearing shell 19b.1 is arranged on the second connecting rod part 19.1, which together with the lower region of the second connecting rod part 19.1 encloses the large connecting rod eye 8.1. The lower bearing shell 19b.1 and the second connecting rod part 19.1 are connected to one another in the usual manner by means of fasteners. The lower end of the first connecting rod part 18.1 is connected to an adjusting piston 21.1, which is guided displaceably in a cylinder bore 22.1 of the second connecting rod part 19.1. At the upper end, the second link part 19.1 has a cap 19a.1 through which the first link part 18.1 is guided and sealed. Thus, the cap 19a.1 seals the cylinder bore 22.1 as a whole. The adjusting piston 21.1 is designed as a stepped piston. A first pressure chamber 24.1 with a circular cross section is formed below the adjusting piston 21.1, and a circular second pressure chamber 25.1 is formed above the adjusting piston 21.1. The adjusting piston 21.1 and the cylinder bore 22.1 are part of an adjusting mechanism for changing the length of the connecting rod. Also belonging to the adjusting mechanism is a hydraulic circuit 26.1, which will be described in more detail below, for the entry and exit of hydraulic fluid into and out of the pressure chambers 24.1 and 25.1, respectively, and thus for the fixing of the adjusting piston 21.1, which is actuated by means of a force acting on the connecting rod 6.1.

In the present exemplary embodiment, the section of the second connecting rod part 19.1 in the region of the pressure chambers 24.1 and 25.1 and the adjusting piston 21.1 is designed in a circular ring shape in cross section (in addition to the hydraulic fluid lines that may be present). Can imagineOther geometric dimensions. In this case, therefore, the associated outer radius r of the upper section of the second connecting rod part 19.1_aMinus the internal radius r of the bore 22.1_iTo obtain the wall thickness D_W. In this symmetrical embodiment, the wall thickness D_WIs of uniform thickness over the circumference of the second connecting rod part 19.1 and the stresses in the material of the second connecting rod part 19.1 are uniformly low, so that the maximum system pressure occurring in the connecting rod 6.1 remains within the manageable limits on the basis of the relatively large piston diameter for the adjusting piston 21.1.

In the following, the hydraulic circuit 26.1 used in the connecting rod 6.1 will be explained in more detail with reference to fig. 2. The adjusting piston 21.1 of the cylinder-piston unit 20.1 is designed as a stepped piston. A stepped piston is generally understood to be a double-acting piston with differently sized active surfaces. The first end side 27.1 is of circular design and is assigned to the first pressure chamber 24.1. The second end side 28.1 is designed in a circular ring shape and is associated with the second pressure chamber 25.1. The hydraulic circuit 26.1 runs on engine oil. For this purpose, the oil supply channel 29.1 is connected to the large rod eye 8.1, so that the engine oil can be supplied to the hydraulic circuit 26.1 or, if necessary, can flow out of it. The oil feed channel 29.1 is provided with a return throttle 30.1 with a check valve and a throttle in parallel therewith. From the return throttle 30.1 the engine oil reaches the control valve 32.1 via the channel 31.1. The control valve 32.1 comprises a control piston 32a.1, which is displaceably guided against a pressure spring 32 b.1.

The return channel 40.1 leads from the first pressure chamber 24.1 to the control valve 32.1. An oil channel 42.1, which can be blocked by the check valve 41.1, is likewise connected to the control valve 32.1 and leads to the first pressure chamber 24.1. The first return channel 40.1 is closed in the position of the control piston 32a.1 shown in fig. 2. The oil from the first pressure chamber 24.1 does not escape from the closed non-return valve 41.1. The adjusting piston 21.1 travels or is in the upper position of the final displacement and is hydraulically blocked there. The connecting rod 6.1 is thus in its longer position. The return line 43.1 leads from the second pressure chamber 25.1 to the control valve 32.1. In the position of the control valve 32.1 shown in fig. 2, oil from the second pressure chamber 25.1 can flow into the crankcase via the return line 43.1 and the control valve 32.1 and the outlet 44.1. A further non-return valve 46.1 is arranged in the oil channel 45.1, which likewise leads from the second pressure chamber 25.1 to the control valve 32.1.

However, if the pressure of the engine oil now flowing into the hydraulic circuit 26.1 is increased via the oil pump of the internal combustion engine, it occurs that the servo piston 32a.1 in the control valve 32.1 moves against the force of the pressure spring 32 b.1. Thereby, the first return channel 40.1 is opened and engine oil can flow out of the first pressure chamber 24.1 via the channel 31.1 and the return throttle 30.1. Thereby, the regulating piston 21.1 is lowered. At the same time, the return line 43.1 is closed and the second pressure chamber 25.1 is filled with engine oil via the oil channel 45.1 and the check valve 46.1. As soon as the adjusting piston 21.1 abuts against the lower stop, the adjusting piston 21.1 is hydraulically locked in this position as long as sufficient pressure is present at the control valve 32.1, and the connecting rod 6.1 assumes its short position. This moved-in position is advantageous at full load, while the moved-out position according to fig. 2 is advantageous for partial and low load operation. In respect of further functions and functional aspects, reference is additionally made to WO 2015/055582 a2, which describes in detail the adjusting mechanism shown here and alternatives thereto, which can likewise be used.

Fig. 3 shows a sectional view of the cylinder-piston unit 20.1 of the length-adjustable connecting rod 6.1 of fig. 2 with a two-stage adjusting piston 21.1, which is movable in a longitudinally movable manner in the cylinder bore 22.1. The sealing arrangement 23.1 provided between the inner wall 38.1 of the cylinder bore 22.1 and the outer wall 39.1 of the control piston 21.1 comprises two piston seals 33.1, which are each arranged in a separate, circumferential piston groove 34.1 in the outer wall 39.1 of the control piston 21.1. The piston seal 33.1, which is fixed in its position on the control piston 21.1 and is sealed off from the outer container wall 39.1 of the control piston 21.1, is in sliding contact with the inner container wall 38.1 of the cylinder bore 22.1. Accordingly, the piston seal 33.1 seals the first pressure chamber 24.1 and prevents the engine oil from passing through the first pressure chamber 24.1 via the gap between the outer wall 39.1 of the control piston 21.1 and the inner wall 38.1 of the cylinder bore 22.1. The piston seal 33.1 can be sealed in the direction of the first pressure chamber 24.1 and in the direction of the second pressure chamber 25.1 as a double-acting piston seal 33.1, corresponding to the positioning of the double-acting adjusting piston 21.1. The piston seal 33.1 is formed on both sides with a positioning ring which is arranged in the piston groove 34.1 with a preload and which ensures a reliable seal, and with a sliding ring made of a low-friction plastic material which, despite the sliding contact with the inner wall 38.1 of the cylinder bore 22.1 with sealing lips which act in both directions, nevertheless enables a good seal with respect to the inner wall 38.1.

In the extended position of the length-adjustable connecting rod 6.1 shown in fig. 2 and 3, a very high system pressure of significantly more than 1000bar prevails in the first pressure space 24.1 during the compression and combustion phase of the first cylinder 2.1 of the internal combustion engine 1. As a result of the use of a plurality of piston seals 33.1, a pressure reduction is achieved in the sealing arrangement 23.1 between the first pressure chamber 24.1 and the second pressure chamber 25.1, which is at atmospheric pressure in the removed position of the connecting rod 6.1, in a number of steps corresponding to the number of piston seals 33.1. The reduction of the pressure acting on the individual piston seals 33.1 enables the use of piston seals 33.1 with a reduced pressure-carrying capacity relative to high system pressures.

The first rod part 18.1 comprises a piston rod 18a which extends in the direction of the axis of the first rod part 18.1 from the second end side 28.1 of the adjusting piston 23.1 in the direction of the small rod eye 9.1. As can be seen in fig. 3, the piston rod 18a.1 extends through a rod bore 36.1 in a cap 19a.1 of the second connecting rod part 19.1, which cap delimits the cylinder bore 22.1 in the direction of the small connecting rod eye 9.1. Two circumferential bore grooves 37.1 are provided in the shank bore 36.1 at a distance from one another, in each of which a shank seal 47.1 is arranged. The rod seal 47.1 is in this case seated in the bore groove 37.1 under pretensioning, in order to achieve the best possible sealing effect between the rod seal 47.1 and the rod bore 36.1. Similarly to the piston seal 33.1, the rod seal 47.1 can also be designed in two parts, with an outwardly arranged positioning ring and an internally arranged sliding ring made of plastic, which is in sliding contact with the piston rod 18a.1, in order to reliably seal the second pressure chamber 25.1 and to enable a gradual reduction of the system pressure in the second pressure chamber 25.1.

Fig. 4 shows a sectional view of a further embodiment of the adjusting piston 21.1 of the cylinder-piston unit 20.1 of the length-adjustable connecting rod 6.1 of fig. 2. The adjusting piston 21.1 is provided on its outer wall 39.1 with six piston grooves 34.1 arranged at a distance from one another, four piston seals 33.1 arranged at a distance from one another being arranged in the four central piston grooves 34.1. Since the piston seals 33.1 are each arranged in a separate piston groove 33.1 at a distance from one another, not only is a good sealing effect achieved between the piston seals 33.1 and the outer wall 39.1 of the cylinder bore 21.1, but in combination with the sliding contact between the piston seals 33.1 and the inner wall 38.1 of the cylinder bore 22.1, a progressive pressure reduction of the high system pressure in the first pressure chamber 24.1 or the second pressure chamber 25.1 is possible. The piston seals 33.1 with a medium maximum permissible pressure can also be used, since the pressure drop to be achieved by the respective piston seal 33.1 is reduced.

A wiper 48.1 is arranged in the piston groove 34.1 adjoining the first end side 27.1 and the second end side 28.1 on the outer device wall 39.1 of the control piston 21.1, which wiper prevents particles from the engine oil from penetrating into the gap 35.1 between the control piston 21.1 and the cylinder bore 22.1 when the control piston 21.1 moves in the cylinder bore 22.1. The engine oil scraper 48.1 is thereby reliably positioned in the piston groove 34.1 at the end of the outer wall 39.1 of the adjusting piston 21.1. In contrast to the gap seal, in this contact-type sealing device 23.1, the pressure drop is effected in stages via the piston seals 33.1, so that the wiper 48.1 is not sucked into the gap 35.1 during the movement of the adjusting piston 21.1.

Between the rod seal 47.1 in the bore groove 37.1 of the rod bore 36.1 and the second pressure chamber 25.1, a further wiper 48.1 is provided, which is likewise arranged in the bore groove 37.1 and prevents particles from the engine oil from penetrating between the rod bore 36.1 and the piston rod 18 a.1.

List of reference numerals

1 internal combustion engine

2.1, 2.2, 2.3 cylinders

3.1, 3.2, 3.3 reciprocating piston

4 crankshaft

Crankshaft bearing of 5.1, 5.2, 5.3, 5.4

6.1, 6.2, 6.3 connecting rod

7.1, 7.2, 7.3 crankshaft journal

8.1, 8.2, 8.3 big link eye

9.1, 9.2, 9.3 Small Link eye

10.1, 10.2, 10.3 piston pin

11 crankshaft sprocket

12 timing chain

13 camshaft sprocket

14 camshaft

15 tensioning rail

16 chain tensioner

17.1 connecting rod head

18.1 first Link portion

18a.1 piston rod

19.1 second Link part

19a.1 cover

19b.1 bearing housing

20.1 Cylinder-piston Unit

21.1 regulating piston

22.1 Cylinder bores

23.1 sealing device

24.1 first pressure Chamber

25.1 second pressure Chamber

26.1 Hydraulic Circuit

27.1 first end side

28.1 second end side

29.1 oil supply channel

30.1 reflux throttle valve

31.1 channels

32.1 control valve

32a.1 Servo piston

32b.1 compression spring

33.1 piston seal

34.1 piston groove

35.1 gap

36.1 rod hole

37.1 hole groove

38.1 inner vessel wall

39.1 outer vessel wall

40.1 Return channel

41.1 check valve

42.1 oil channel

43.1 Return line

44.1 outlet

45.1 oil passages

46.1 check valve

47.1 rod seal

48.1 oil wiper

D_WWall thickness

V_hVolume of stroke

V_cVolume of extrusion

H_CHeight of extrusion

H_KStroke

r_iInner diameter

r_aOutside diameter

Amount of S space

Compression ratio of epsilon

n number of revolutions

T temperature

Claims

1. A length-adjustable connecting rod (6.1) for an internal combustion engine (1), having: a first connecting rod section (18.1) and a second connecting rod section (19.1), the first connecting rod section (18.1) having a small connecting rod eye (9.1) for receiving a piston pin (10.1), and the second connecting rod section (19.1) having a large connecting rod eye (8.1) for receiving a crankshaft journal (7.1), wherein the first connecting rod section (18.1) is movable relative to the second connecting rod section (19.1) in order to adjust a distance between the large connecting rod eye (8.1) and the small connecting rod eye (9.1); at least one cylinder-piston unit (20.1) for adjusting the first connecting rod part (18.1) relative to the second connecting rod part (19.1), the cylinder-piston unit (20.1) comprising a cylinder bore (22.1), an adjusting piston (21.1) arranged in the cylinder bore (22.1) in a longitudinally movable manner, a first pressure chamber (24.1) provided in the cylinder bore (22.1) for receiving engine oil of the internal combustion engine, and a second pressure chamber (25.1) for receiving engine oil of the internal combustion engine, wherein the first pressure chamber (24.1) and the second pressure chamber (25.1) are each delimited on one side by the movable adjusting piston (21.1); a sealing device (23.1) arranged between an outer device wall (39.1) of the adjusting piston (21.1) and an inner device wall (38.1) of the cylinder bore (22.1),

wherein the sealing device (23.1) comprises at least two piston seals (33.1), wherein each piston seal (33.1) is arranged in a separate piston groove (34.1) which surrounds the outer device wall (39.1) of the adjusting piston (21.1) and is in sliding contact with the inner device wall (38.1) of the cylinder bore (22.1),

the sealing device is characterized in that the piston seal (33.1) of the sealing device (23.1) is designed as a double-acting piston seal (33.1) and is designed in two parts, the two-part piston seal (33.1) being a positioning ring and a sliding ring, respectively, and the piston seal (33.1) being capable of sealing in the direction of the first pressure chamber (24.1) and in the direction of the second pressure chamber (25.1) in accordance with the positioning of the double-acting adjusting piston (21.1).

2. Length adjustable connecting rod (6.1) according to claim 1,

characterized in that the sealing means (23.1) comprises at least three piston seals (33.1).

3. Length adjustable connecting rod (6.1) according to claim 1 or 2,

characterized in that the sealing device (23.1) comprises a wiper (48.1), wherein the wiper (48.1) is arranged on the end of the outer device wall (39.1) of the adjusting piston (21.1) facing the first pressure chamber (24.1).

4. Length adjustable connecting rod (6.1) according to claim 1 or 2,

the adjusting piston (21.1) of the cylinder-piston unit (20.1) is designed as a bilaterally active adjusting piston (21.1), wherein the adjusting piston (21.1) arranged in the cylinder bore (22.1) so as to be longitudinally movable forms a first pressure chamber (24.1) and a second pressure chamber (25.1) for receiving engine oil and is each delimited on one side.

5. Length adjustable connecting rod (6.1) according to claim 4,

characterized in that the adjusting piston (21.1) has a piston rod (18a.1) on a second end face (28.1) which delimits the second pressure chamber (25.1), said piston rod extending through a rod bore (36.1) of the cylinder-piston unit (20.1), wherein at least two rod seals (47.1) are provided, wherein each rod seal (47.1) is arranged in a circumferential groove (37.1) in the rod bore (36.1) and is in sliding contact with the piston rod (18 a.1).

6. Length adjustable connecting rod (6.1) according to claim 5,

characterized in that a scraper (48.1) is provided, wherein the scraper (48.1) is arranged on the end of the rod bore (36.1) facing the second pressure chamber (25.1).

7. Length adjustable connecting rod (6.1) according to claim 1 or 2,

characterized in that the first connecting rod part (18.1) is connected to an actuating piston (21.1) of the cylinder-piston unit (20.1) and the second connecting rod part (19.1) has a cylinder bore (22.1) of the cylinder-piston unit (20.1).

8. Length adjustable connecting rod (6.1) according to claim 1,

characterized in that the connecting rod (6.1) is used for a gasoline engine.

9. Length adjustable connecting rod (6.1) according to claim 1,

characterized in that the sliding ring is made of plastic.

10. Length adjustable connecting rod (6.1) according to claim 1,

characterized in that the sealing means (23.1) comprises at least four piston seals (33.1).

11. Use of a sealing device (23.1) for a length-adjustable connecting rod (6.1) of an internal combustion engine (1), having a first connecting rod part (18.1) and a second connecting rod part (19.1) which are adjustable by means of the cylinder-piston unit (20.1), in order to move the first connecting rod part (18.1) relative to the second connecting rod part (19.1), of a cylinder-piston unit (20.1), the cylinder-piston unit (20.1) comprising a cylinder bore (22.1), an adjusting piston (21.1) which is arranged in the cylinder bore (22.1) in a longitudinally movable manner, a first pressure chamber (24.1) which is arranged in the cylinder bore (22.1), a second pressure chamber (25.1) and a sealing device (23.1) which is arranged between an outer device wall (39.1) of the adjusting piston (21.1) and an inner device wall (38.1) of the cylinder (22.1),

12. The use according to claim 11, in which,

characterized in that the sliding ring is made of plastic.

13. An internal combustion engine (1) having: at least one reciprocating piston (3.1, 3.2, 3.3), at least one compression ratio adjustable in a cylinder (2.1, 2.2, 2.3) and at least one length-adjustable connecting rod (6.1, 6.2, 6.3) according to one of claims 1 to 10 connected to the reciprocating piston (3.1, 3.2, 3.3).

14. The internal combustion engine (1) according to claim 13,

characterized in that the cylinder-piston unit (20.1) of the length-adjustable connecting rod (6.1, 6.2, 6.3) is coupled to an engine oil hydraulic system of the internal combustion engine (1).

15. The internal combustion engine (1) according to claim 13 or 14,

characterized in that the system pressure of the engine oil in the first pressure chamber (24.1) of the cylinder-piston unit (20.1) is between 1000bar and 3000 bar.

16. The internal combustion engine (1) according to claim 13 or 14,

characterized in that a timing drive is provided, which has at least one timing chain (12), a tensioning and/or guiding rail (15), and/or a chain tensioner (16), which connects a crankshaft (4) with at least one camshaft (14) of the internal combustion engine (1).

17. The internal combustion engine (1) according to claim 13 or 14,

characterized in that the system pressure of the engine oil in the first pressure chamber (24.1) of the cylinder-piston unit (20.1) is between 2000bar and 2500 bar.