Connecting rod for a variable compression internal combustion engine

A connecting rod for a variable compression internal combustion engine, the connecting rod including an eccentrical element adjust arrangement for adjusting an effective connecting rod length, wherein an adjustment travel of the eccentrical element adjustment arrangement is adjustable by a switch valve, and wherein a valve housing of the switch valve is axially secured in a borehole of the connecting rod.

RELATED APPLICATIONS

This application claims priority from German patent applications DE 10 2018 107 668.1 filed on Mar. 29, 2018, and DE 10 2018 124 464.9, filed on Oct. 4, 2018, both of which are incorporated in their entirety by this reference.

FIELD OF THE INVENTION

The invention relates to a connecting rod for a variable compression internal combustion engine and to the variable compression internal combustion engine with the connecting rod.

BACKGROUND OF THE INVENTION

In internal combustion engines a high compression ratio has a positive effect upon an efficiency of the internal combustion engine. Compression ratio is typically defined as a ratio of an entire cylinder cavity before compression to a remaining cylinder cavity after compression. In internal combustion engines with external ignition, in particular gasoline engines that have a fixed compression ratio, the compression ratio, however, may only be selected high enough so that a so-called “knocking” of the internal combustion engine is prevented during full load operations. However, for much more prevalent partial load operations of the internal combustion engine, thus for a lower cylinder charge the compression ratio can be selected at a higher level without “knocking” occurring. The important partial load operations of an internal combustion engine can be improved when the compression ratio is variably adjustable. In order to adjust the compression ratio systems with variable connecting rod length are known which actuate an eccentrical element adjustment arrangement of a connecting rod by hydraulic switch valves.

A generic switch valve can be derived e.g. from DE 10 2012 112 461 A1. The switch valve is configured as a cartridge solution. This has the advantage that the switch valve can be checked for leak tightness independently from the connecting rod arrangement into which the switch valve is installed. The switch valve is pressed into the connecting rod body.

BRIEF SUMMARY OF THE INVENTION

Thus, it is an object of the invention to provide an improved cost effective connecting rod for a variable compression internal combustion engine wherein the connecting rod can be reliably produced.

It is another object of the invention to provide a variable compression internal combustion engine with the connecting rod.

The objects are achieved according to an aspect of the invention by the features of the independent claims.

Advantageous embodiments and advantages of the invention can be derived from the dependent claims, the description and the drawing figures.

A connecting rod is proposed for a variable compression internal combustion engine, the connecting rod including an eccentrical element adjustment arrangement for adjusting an effective connective rod length, wherein an adjustment travel of the eccentrical element adjustment arrangement is adjustable by a switch valve. Thus, a valve housing of the switch valve is axially secured in a bore hole of the connecting rod.

The connecting rod includes a connecting rod body and a connecting rod cover arranged at the connecting rod body wherein the connecting rod body and the connecting rod cover envelop a crank bearing eye. A connecting rod bearing eye with the eccentrical element adjustment arrangement is arranged at the opposite end of the connecting rod body. A connecting rod length is a distance of a center axis of the crank bearing eye from a center axis of the connecting rod bearing eye.

It is advantageous for an engineering design implementation of the hydraulic diagram of a connecting rod for a variable compression internal combustion engine to arrange switch valves in the connecting rod body. Typically pressed interconnections are used where valves with a cylindrical external geometry e.g. turn components are pressed into bore holes transversal to a connecting rod center plane. In order to deal with the high loads of the connecting rod the valves have to be positioned so that the bore holes are only exposed to minimum loads which can lead to an oval deformation which however can occur during engine operations. On the one hand side strong deformations lead to leakage when the pressed interconnections are weak and thus reduce the axial retaining force of the pressed interconnection so that the valve can exit from the bore hole in the axial direction. On the other hand side a pressed interconnection can only have an oversize that is permissible based on the structural mechanics of the connecting rod and of the valve due to assembly tensions. Furthermore the valves can rotate axially when the pressed interconnections are weak and do not have enough friction. The orientation of the switch valve in the bore hole can be essential for the function of the valve e.g. when the capture device of the valve is not arranged in the valve axis. This yields a goal conflict for the compressed interconnection configuration: sufficient axial retaining force, position fixation and little leakage versus an impermissibly high assembly tension superimposed by operating tensions.

In order to deal with conflicting requirements very tight tolerance ranges can be selected for the pressed interconnections, however, fabrications cost increases considerably through this measure so that high volume production is not economical anymore.

Therefore the valve housing of the switch valve is provided axially secured in the bore hole of the connecting rod body. Thus, the valve housing cannot get loose and cannot slide or rotate from its predetermined position in the connecting rod body.

This way the upper limit of the pressed interconnection of the valve housing in the connecting rod body can be adapted to the maximum permissible mounting tensions and the lower limit can be moved towards an economical fabrication. The risk of axially moving or rotating the switch valve in the connecting rod during engine operations can be advantageously reduced by the described face side axial safety of the valve housing in the connecting rod.

A simple axial safety can be provided by a weld seam or weld spots between the valve housing and the connecting rod body or connecting rod cover. By the same token a glue or a face coating, e.g. lacquer can be used as a safety.

According to an advantageous embodiment the connecting rod can have one or plural axial bore holes whose protrusions are deformed into one or plural face recesses of the valve housing to provide axial safety for the switch valve. This variant uses a recessed bore hole in the connecting rod and a milled cut out in the valve on the face side. The recessed bore holes provide centering for a forming tool e.g. with a hard ball head which presses the protrusion of the recessed bore holes into the milled cut out of the valves in order to axially secure and fixate the valve against rotation. By the same token a recessed bore hole can be associated with several milled cut outs of different valves. Thus the axial safety can be selected independently from the valve position in the connecting rod. By the same token plural milled cut outs or forming processes can be used.

Recessed bore holes which are arranged in the connecting rod close enough to the bore hole in the connecting rod to receive the switch valve can have a sufficiently thin wall thickness towards the bore hole to form the protrusion so that the material of these protrusions can be displaced towards the bore hole by mechanical pressure. When the valve housing has face recesses at this location the material of the protrusions can be pushed into these recesses. Thus, an interlocking is provided between the connecting rod body or the connecting rod cover and the valve housing. This way the valve housing is secured in the bore hole against axial movement. When the recesses in the valve housing are not circumferential but arranged along a limited angular range the valve housing and thus the switch valve can also be secured against rotation in the bore hole.

According to an advantageous embodiment of the connecting rod the valve housing can have axial bore holes that are recessed wherein protrusions of the recessed bore holes are deformed into one or plural face side recesses of the connecting rod in order to secure the switch valve in the axial direction. The recessed bore holes can also be arranged in the valve and the face side cut outs can be arranged in the connecting rod body. This facilitates axially securing the valve housing in the bore hole of the connecting rod when the material of the protrusions is displaced.

According to an advantageous embodiment of the connecting rod the protrusions of the recessed bore holes can be pressed into the recesses by a forming tool. The material of the protrusions can be pressed into the recesses by a mechanical pressure that can be generated e.g. by a forming tool. Thus, the desired teething between the connecting rod body and the connecting rod cover and the valve housing can be achieved in a suitable manner.

According to an advantageously embodiment of the connecting rod balls can be pressed in to the recessed bore holes, which presses the protrusions into the recesses. Pressing a ball into the recessed bore hole is one variant of this technical solution. When pressing the ball into the recessed bore hole the protrusion is deformed far enough so that an axial safety and a rotation safety is provided, but the ball is also prevented from disengaging. Thus, the desired teething can be achieved between the connecting rod body or the connecting rod cover or the valve housing in a suitable manner. In a similar manner also cone shaped or frustum shaped elements can be pressed into the recessed bore holes in order to achieve the desired effect.

According to an advantageous embodiment of the connecting rod the recesses can be provided as a bevel that is circumferentially arranged on an outer edge of the valve housing. A simple embodiment of the recesses of the valve housing can be configured in a form of a bevel that is circumferentially arranged on an outer edge of the valve housing. This helps to achieve an axial safety of the valve housing in the bore hole of the connecting rod. When the material of the protrusions is pressed with a suitable pressure into the bevel and against the valve housing, then a safety against rotation of the valve housing can be achieved in the bore hole.

According to an advantageous embodiment of the connecting rod, the valve housing can have an axial protrusion at least at one face, wherein the protrusion is fixed with a retaining ring in order to secure the switch valve axially. Another variant of the face side axial safety is used for protruding valves that are fixed by retaining rings with respect to their axial position. Also DIN-standard components can be used as retaining rings. The retaining ring can be fixed by a fit, a weld, in a groove, a thread or a similar fixing option at the valve.

According to an advantageous embodiment of the connecting rod, the valve housing can have an axial shoulder on a first face and an axial protrusion on a second face, wherein the protrusion is fixed by a retaining ring in order to axially secure the switch valve. Thus, the valve can also be alternatively provided with an axial shoulder at a face, wherein the axial shoulder contacts the connecting rod body or the connecting rod cover and a retaining ring at the axial protrusion of the second face which functions as a reaction bearing on the other face of the connecting rod in order to fix the valve housing. The retaining ring can be fixed at the valve by a fit, by a weld, in a groove, by a thread or a similar fixing option at the valve.

According to an advantageous embodiment of the connecting rod, the retaining ring can be attached at the protrusion by a press fit, by a welded joint or by a thread. The retaining ring can be advantageously fixed at the valve by a fit, a weld, in a groove, a thread or a similar fixing option.

According to an advantageous embodiment of the connecting rod, the retaining ring can include at least one rotation safety. In order to provide an additional rotation safety, the retaining ring can be secured against rotation, e.g., as a ring with retaining lobes that interlock in a counterpiece or interlock on both sides.

According to an advantageous embodiment of the connecting rod, the rotation safety can include at least one lobe that protrudes radially outward from the retaining ring and that is fixed at the connecting rod, in particular at the connecting rod cover. In particular the lobe can be bonded together with the connecting rod, e.g., welded together.

According to an advantageous embodiment of the connecting rod, the lobe can engage a recess of the connecting rod. Advantageously the lobe can interlock in a recess of the connecting rod. Thus, it can be advantageously provided that the retaining ring can be disengaged again, e.g., when the switch valve is to be replaced.

According to an advantageous embodiment of the connecting rod, the valve housing can have an axial protrusion at least on one face, wherein the protrusion is deformed after mounting the valve housing in order to axially secure the switch valve. Thus, an axial safety can be facilitated without additional components. Advantageously the valve housing is heat-treated in the portion of the protrusion before the deforming process.

According to an advantageous embodiment of the connecting rod, at least one center punch can be provided on at least one face of the valve housing in order to provide axial safety for the switch valve which displaces material of the valve housing into a borehole gap between the valve housing and the connecting rod. Through material deformation, the switch valve can be secured against an axial movement and against rotation. This can be achieved on the one hand side by putting a center punch into the face of the valve housing wherein the center punch deforms material in a radially outward direction towards the connecting rod body or connecting rod cover.

According to an advantageous embodiment of the connecting rod, at least one center punch can be arranged on at least one face of the connecting rod in order to provide axial safety for the switch valve so that material of the connecting rod is displaced into the borehole gap between the valve housing and the connecting rod. Alternatively the axial safety of the switch valve can also be provided by putting a center punch into the face of the connecting rod, wherein material is deformed in a radially inward direction towards the valve housing.

According to an advantageous embodiment of the connecting rod, at least one safety element can be arranged in the borehole gap between the valve housing and the connecting rod in order to provide axial safety for the switch valve. Using a retaining element, e.g., a fitted key, a cone, a wedge, is another option wherein the retaining element can be configured as a DIN-standard component and is driven on a face side between the valve and the borehole into the borehole gap. The retaining element can be additionally welded, glued or fixed in a similar manner. A combination of using a retaining ring and providing axial safety with the retaining element is providing axial safety by retaining pins. Thus, at least one pin can be pressed, welded, glued or joined otherwise into the borehole gap or a pocket between the connecting rod body and the valve housing on each face of the valve housing.

According to another aspect of the invention, an internal combustion engine with at least one connecting rod is proposed. Thus, a connecting of the type described supra can be advantageously used in order to implement an eccentrical element adjustment arrangement and an advantageous combustion process in order to reduce fuel burn of the internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

In the drawing figures identical or like components are designated with identical reference numerals. The drawing figures merely illustrate exemplary embodiments and do not limit the spirit and scope of the invention.

FIGS. 1 and 2illustrate a connecting rod1according to the invention for a variable compression internal combustion engine whereinFIG. 1illustrates a side view of the connecting rod1andFIG. 2illustrates a blown-up sectional view through the connecting rod10. The connecting rod1includes a connecting rod cover2and an adjustable eccentrical element adjustment arrangement6with an eccentrical element4that is arranged at least in sections in a connecting rod bearing eye3. A crank-bearing eye5is arranged at the opposite end of the connecting rod body2wherein the crank-bearing eye is closed by the connecting rod cover10. The eccentrical element adjustment arrangement6is used for adjusting an effective connecting rod length. The connecting rod length is a distance of a center axis of the crank-bearing eye5from a center axis of the connecting rod bearing eye3.

A rotation of the adjustable eccentrical element adjustment arrangement6is initiated by an impact of mass and load forces of the internal combustion engine wherein the mass and load forces impact the eccentrical element adjustment arrangement6during an operating stroke of the internal combustion engine. Effective directions of forces that impact the eccentrical element adjustment arrangement6change continuously during an operating stroke. The rotating movement or adjustment movement is supported by pistons that are integrated in the connecting rod1and that are loaded with a hydraulic fluid, in particular motor oil. The pistons thus prevent a resetting of the eccentrical element adjustment arrangement6due to varying force effective directions of forces that impact the eccentrical element adjustment arrangement6.

The pistons are operatively connected on both sides with a lever9of the eccentrical element adjustment arrangement6by eccentrical element rods7,8. The pistons are movably arranged in hydraulic chambers and loaded with hydraulic fluid through non-illustrated hydraulic fluid conduits through non-visible check valves. The check valves thus prevent a flowback of the hydraulic fluid from the hydraulic chambers back into the hydraulic fluid conduits and facilitate a pulling of hydraulic fluid into the hydraulic chambers. The hydraulic fluid conduits that are connected with the hydraulic chambers cooperate with a switch valve11at least partially.

The switch valve11which represents an enlarged detail in the sectional plane E-E includes a capture element13that is arranged in a valve housing12and which is moveable in an axial direction into a first switching position or a second switching position and interlockable by a spring loaded interlocking element in the first switching position or the second switching position.

In order to implement the hydraulic diagram of the connecting rod1in an engineering design, it is necessary to introduce a switch valve1into the connecting rod body2or the connecting rod cover10. A viable option is using pressed interconnections where switch valves11with a circular outer geometry (turned components) are pressed into boreholes23transversal to a center plane of the connecting rod. In order to bear the high loads of the connecting rod1the switch valves11have to be positioned so that the boreholes23are exposed to minimum loads from engine operations that can cause an oval deformation. On the one hand side strong deformations lead to leakage of weak pressed interconnections and reduce the axial retaining force of the pressed interconnection so that the switch valve11can move axially out of the borehole23. On the other hand side, the pressed interconnection can only be configured with an oversize that is permitted by the structural mechanics of the connecting rod1and of the switch valve11due to tensions caused by an assembly process. Additionally, the switch valves11can rotate axially when weak pressed interconnections are used that have an amount of friction that is too low. An orientation of the switch valve11in the borehole23can be important for example when the capture element is introduced into the switch valve remote from an axis. This causes a conflict in the design of the pressed interconnection, namely between sufficient axial retaining force, position fixing and low leakage versus an impermissibly high assembly tension that is superimposed by operating tensions.

In order to satisfy these conflicting requirements, very tight tolerance ranges can be selected for the pressed interconnections. However, fabrication cost increases significantly for these measures which renders them less attractive for applications with high volume production.

According to the invention, the valve housing12of the switch valve11is axially secured in a borehole23of the connecting rod1.

As evident in particular from the top view inFIG. 3and the corresponding sectional view inFIG. 4, the connecting rod1or the connecting rod cover10can have one or plural axial recessed boreholes14according to an embodiment wherein protrusions15of the axial recessed boreholes14that are oriented towards the valve housing12are deformed into one or plural face recesses16of the valve housing12to provide axial safety for the switch valve11. Alternatively, it is also possible to provide the axial recessed boreholes14in the valve housing12and to provide the recesses16in the connecting rod.

The protrusions15of the recessed boreholes14are pressed into the recesses16using a forming tool. Thus, the recessed boreholes14are used for centering the forming tool, e.g., for a hard ballhead which deforms the protrusions15and presses them into the recesses16, so that the valve housing12is secured axially in the borehole of the connecting rod1and secured against rotation.

A non-illustrated embodiment provides that balls are pressed into the recessed boreholes14of the connecting rod1so that the protrusions15are pressed into the recesses16.

In another non-illustrated embodiment, the recesses16can be provided as a circumferential bevel on an outer edge30of the valve housing12. Also this configuration provides an axial safety and a rotation safety of the valve housing12in the connecting rod1when the protrusions15of the recessed boreholes14are pressed firmly enough.

According to another embodiment which is illustrated in a topview inFIG. 5and illustrated in the respective sectional view inFIG. 6, the switch valve11can have an axial stop configured as a shoulder17on a first face20, wherein the shoulder contacts the connecting rod1and contacts the connecting rod cover10in the embodiment illustrated inFIGS. 5 and 6. The valve housing12has an axial protrusion18on a second face21wherein the axial protrusion18is fixed by a retaining ring19in order to axially secure the switch valve11.

The retaining ring19can be pressed onto the protrusion18, welded down, or attached by a thread. Other attachment options are also conceivable according to the invention. According to a non-illustrated embodiment, the retaining ring19can engage a groove of the valve housing12and can be fixed therein.

In another non-illustrated embodiment, the valve housing12can also be configured without the shoulder17. When the retaining ring19that is arranged at the protrusion18is fixed at the valve housing12and at the connecting rod body2or the connecting rod cover10, e.g., welded down, this also facilitates an axial safety and a rotation safety of the valve housing12in the connecting rod1.

According to another non-illustrated embodiment, the protrusion18of the valve housing12can be deformed in order to provide an axial safety for the switch valve11. Thus, the valve housing12is heat treated in the portion of the protrusion18after assembly in the connecting rod1in order to be able to perform the deforming process of the protrusion18at the second face21.

The heat treatment is performed, e.g., by annealing the material, e.g., by a laser process or by inductive heating. A penetration depth of the heat treatment can be advantageously selected so that only the protrusion18is heat treated. Deforming the protrusion18is advantageously performed by a flanging method.

As illustrated in the isometric view ofFIG. 7, the retaining ring19can include an additional rotation safety26. For example, retaining lobes25are conceivable that engage corresponding recesses in the connecting rod1. The rotation safety26can include at least one lobe25that protrudes in a radial direction from the retaining ring19outward and that is fixed at the connecting rod1, in particular at the connecting rod cover10. The embodiment inFIG. 7includes two opposite radially outward protruding lobes25. The lobes25can engage corresponding recesses of the connecting rod1and can thus provide an effective rotation safety26.

FIG. 8illustrates a schematic top view of a switch valve11with center punches22on a face20,21of the valve housing12that is installed into the connecting rod1according toFIG. 1according another embodiment of the invention. Through the center punches22material of the valve housing12is displaced into a borehole gap27between the valve housing12and the connecting rod1by a forming tool in order to provide axial safety for the switch valve11. The arrow directions24inFIG. 8illustrate the deforming directions of the displaced material. The material is displaced away from the center punch22in a radially outward direction into the borehole gap27so that the valve housing12is effectively fixed in the borehole gap of the connecting rod cover10and thus axially secured and secured against rotation. The faces20,21of the valve housing12terminate with the faces28,29of the connecting rod cover10.

FIG. 9illustrates an alternative embodiment of a switch valve11with center punches22in the connecting rod cover10. In this case the material of the connecting rod cover10is displaced in a radially inward direction into the borehole gap27according to the illustrated deformation direction24in order to provide axial safety for the switch valve11.

As variants for axial safety and/or rotation safety, other embodiments are conceivable. A simple axial safety can also be provided by a weld seam or by spot welds. By the same token, a glue or a face coating (lacquer) can be used as a safety against a dropout or rotation of the valve housing12in the connecting rod1.

Another option is using a safety element31, e.g., a fit key, a cone, or a wedge, which can be configured, e.g., as a DIN-standard component and that can be driven on a face side between the valve housing12and the borehole. The standard component can be additionally welded, glued or joined in a similar manner.

FIG. 10illustrates a switch valve11with safety elements31of this type that is installed in a connecting rod1according toFIG. 1according to another embodiment of the invention in a schematic topview. In this embodiment at least one safety element, inFIG. 10three safety elements31, are arranged in the borehole gap27between the valve housing12and the connecting rod1in order to provide axial safety of the switch valve11.

A combination of using a retaining ring19and an axial safety through the safety element31is the axial safety by pins. Thus, at least one pin is pressed, welded, glued or joined in another way per side in a pocket in the connecting rod body or the connecting rod cover and the valve housing12.