VCR connecting rod

Abstract

The invention relates to a VCR connecting rod (10) for setting different compression ratios, comprising a switching valve, which is designed such that in a first switching position, a first support cylinder (20) of the support cylinders is supplied with hydraulic fluid for switching the connecting rod, while a second support cylinder (21) is emptied. At least after the second support cylinder (21) is emptied, the second support cylinder (21) is decoupled from the supply of hydraulic fluid and / or from the first support cylinder (20), so that no fluid can flow into the second support cylinder (21).

Description

Technical Field

[0001] The present invention relates to a VCR connecting rod, ie a connecting rod for "variable compression ratio", and to an internal combustion engine having the VCR connecting rod. Background Art

[0002] When designing internal combustion engines, it has been recognized that it can be meaningful to change the compression ratio during operation. The compression ratio is the ratio between the minimum volume and the maximum volume of the combustion chamber, which is related to the piston position. For this purpose, it is known that the effective length of the connecting rod can be designed variably. This occurs in the following way: for example, the bearing device of the piston in the connecting rod is provided with an eccentric, so that the connecting rod length and thus the compression ratio are variable via a change in the angular position of the eccentric. The setting is achieved via a support cylinder that is alternately filled or emptied of hydraulic fluid and is coupled to the eccentric. The hydraulic fluid is supplied to the connecting rod via a distribution system located in the crankshaft and its crank pin. However, in a preferred embodiment, the setting of the eccentric is less achieved by the hydraulic pressure in the support cylinder. More precisely, for each combustion cycle, a load is repeatedly generated that acts on the connecting rod, that is, the so-called "force on the gas power side" is generated on the gas power side GKS due to combustion and the so-called "force on the mass power side" is generated on the mass power side MKS due to inertia. These forces cause the adjustment of the eccentric, and the pressure in the hydraulic fluid in the support cylinder is formed so that the correspondingly set eccentricity is maintained. Summary of the invention

[0003] However, the hydraulic system thus produced has a certain elasticity, which cannot be completely avoided. That is, if, for example, the support cylinder on the GKS is completely filled and the support cylinder on the MKS is completely emptied, the gas power on the GKS causes a certain adjustment of the eccentric, which in the case of the other support cylinder MKS generates a negative pressure and thus sucks in some hydraulic fluid there, which must be discharged again in the next phase of the combustion cycle. The object of the present invention is to improve the hydraulic system so that the rigidity is increased and it is avoided that the support cylinder is filled to a certain extent in the described manner when it should originally remain empty. The individual components of the VCR switching, namely mainly the eccentric and the support cylinder, (as long as switching is not required) move as little relative to each other as possible in relation to the combustion cycle, because wear is generated thereby. That is, if at least one support cylinder is slightly filled in relation to the combustion cycle, then this repeated slight movement is further coupled to the other components mentioned due to the mechanical coupling. The corresponding micro-movements can lead to micro-friction. Micro-friction, i.e. repeated movements with very low amplitudes, is then problematic because the micro-friction causes the lubricant to leave the friction area and thus the required lubricant wetting of the surface is impaired.

[0004] This object is achieved by a VCR connecting rod for setting different compression ratios of an internal combustion engine.Preferred developments are described in this document.

[0005] A VCR connecting rod for setting different compression ratios of an internal combustion engine comprises a supply of hydraulic fluid via a crank pin of a crankshaft. For switching the eccentric of the VCR connecting rod, two supporting cylinders coupled to the eccentric are provided, wherein the switching valve is set up so that in a first switching position, the first of the supporting cylinders is supplied with hydraulic fluid for switching the connecting rod, while the second supporting cylinder is emptied. At least after the second supporting cylinder is emptied, the second supporting cylinder is decoupled from the supply of hydraulic fluid and / or from the first supporting cylinder, so that no hydraulic fluid can flow into the second supporting cylinder. The expression "at least" mentioned above preferably includes that during the switching of the first switching position (i.e. during the emptying of the second supporting cylinder), in some embodiments, in the case of the second supporting cylinder, there can be a connection to the supply of hydraulic fluid either via the crank pin or via the supply of the first supporting cylinder. Connection means a fluid connection or fluid communication. However, since the second supporting cylinder is emptied during this time period, no fluid flows into the second supporting cylinder via the connection. In addition, this means in particular that the decoupling occurs in the state in which the switching mentioned has been completed. The above-mentioned decoupling preferably takes place both with respect to the first support cylinder and with respect to the supply of fresh fluid (ie during the filling of the second support cylinder).

[0006] The above-described decoupling has the following advantages: Firstly, the evacuated chamber is also decoupled from the connecting rod bearing, so that pressure fluctuations cannot be communicated there. In particular, it is ensured that even in a state in which hydraulic fluid is not supposed to flow into one of the support cylinders, a corresponding fluid flow does not occur. This is not excluded in the prior art. This results in no disruptive pressure excitations occurring and in greater operational safety.

[0007] In the case of a VCR connecting rod, at least in the emptied position, at least one (and preferably both) support cylinders can be ventilated and / or vented. The terms ventilation and venting refer in particular to the creation of an at least partially open or openable passage from the pressure chamber of the support cylinder to the surroundings of the connecting rod. Ventilation and venting can preferably be achieved via a single common passage for ventilation and venting. This makes it possible that in the event of pressure fluctuations or negative pressure, no hydraulic fluid is sucked in, primarily in the emptied support cylinder. Instead, air can be sucked in. However, since air has a much lower viscosity, it can be discharged again more easily (compared to oil).

[0008] The inventive problem is solved equivalently by the two methods described above. In one of the methods, on the hydraulic side, the decoupling prevents hydraulic fluid from flowing into the emptied support cylinder(s), while in the other method it is ensured that air can flow into the support cylinder(s) instead of the hydraulic fluid. In other words, it is advantageous if air is located in the region instead of the hydraulic fluid, since the air can be discharged again more easily. The two methods can be combined.

[0009] It is particularly advantageous if the volumes of the first and second support cylinders are of equal size and, depending on the position of the switching valve, the total volume is conveyed from the first support cylinder into the second support cylinder or vice versa during the switching. The fluid volume is preferably guided via a non-return valve. It is particularly advantageous if the non-return valve is formed by a movable switching element of the switching valve or is accommodated there. Fluid volumes of different sizes can be achieved by different cross-sectional areas of the support cylinders. Alternatively or additionally, this is possible by varying the movement path of the lever arm, i.e. the support cylinder / piston pair. In this way, a system that is as closed as possible is produced and essentially only sealing losses have to be provided via the supply.

[0010] Alternatively, the first and second support cylinders can have fluid volumes of different sizes, and for the fluid, when filling the smaller support cylinder, an outflow for the fluid to leave the VCR connecting rod can be provided. Figure 2 ) is known that excess hydraulic fluid can be discharged into the connecting rod bearing on the crankshaft side. However, this is preferably prevented by the non-return valve 16, since pressure fluctuations in the fluid can affect the connecting rod bearing. Instead, the discharge of the hydraulic fluid for use and the delivery of the replenishing hydraulic fluid usually does not require any special effort. The outflow of oil from the support cylinder to be emptied into the crankcase or the controlled outflow downwards brings the advantages of a constant hydraulic resistance, a better partition design and a higher switching speed.

[0011] In particular, the first and second work cylinders can optionally exchange functions or act doubly in the second switching position of the switching valve. Accordingly, the system is then identical for the two work cylinders in terms of switching system.

[0012] In a further alternative, the first and second support cylinders can have fluid volumes of different sizes and during the filling of the larger support cylinder, an outflow of the fluid of the smaller support cylinder out of the VCR connecting rod can be provided. In this way, in the event of a pressure drop in the emptied support cylinder, a vacuum can be prevented from forming in the emptied support cylinder, which could lead to cavitation. In other words, it can be advantageous if during the filling of the larger support cylinder, an outflow of the fluid of the smaller support cylinder out of the VCR connecting rod is possible and / or if in the emptied state of the smaller support cylinder, a fluid discharge of the hydraulic fluid from the support cylinder to the surroundings is produced (for example via a switching valve). This discharge has the effect that an underpressure or even a negative pressure at the outlet of the smaller support cylinder can be prevented.

[0013] Alternatively, in another alternative, the first and second support cylinders can have fluid volumes of different sizes, and during the filling of the larger support cylinder it can be provided structurally that no passage for the fluid of the smaller support cylinder to flow out of the VCR connecting rod occurs. This can avoid losses of hydraulic fluid from the VCR connecting rod, which are unnecessary in this case, since the hydraulic fluid volume of the smaller support cylinder can be completely accommodated by the larger support cylinder. This also means that only when filling the smaller support cylinder does a continuous oil loss occur via the downward control into the engine interior, thus reducing oil consumption and increasing the operating safety of the connecting rod bearing.

[0014] In all variants, at least one of the support cylinders comprises a ventilation and / or exhaust duct 22 from its pressure chamber to the surroundings of the VCR connecting rod 10. Preferably, no mechanism for opening and closing the ventilation and exhaust duct as a function of the operating state can be provided. In other words: the duct remains open at all times or in all switching states. If a sufficiently small cross section is selected, it can be prevented that an extremely large amount of hydraulic fluid is present on the cross section, but a sufficiently effective air exchange is still possible. The ventilation and exhaust duct can also be arranged adjacent to the pressure chamber. The ventilation and exhaust duct preferably leads directly to the outside of the VCR connecting rod. Preferably, the ventilation and exhaust duct is not guided via a switching valve.

[0015] Alternatively, at least one of the support cylinders can also comprise a ventilation and / or exhaust duct from its pressure chamber to the surroundings of the VCR connecting rod and can be provided with a switchable sealing mechanism for opening and / or closing the ventilation and / or exhaust duct 23 as a function of the pressure, for example the pressure acting on the connecting rod. The ventilation and / or exhaust duct mentioned above is preferably a direct duct, for example a bore, which is led through the wall of the support cylinder. And / or the ventilation and / or exhaust duct mentioned starts, for example, with a bore in the pressure chamber of the support cylinder.

[0016] An internal combustion engine can comprise at least one combustion chamber according to the reciprocating piston principle, and a corresponding VCR connecting rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is described below by way of example based on preferred embodiments. The accompanying drawings show:

[0018] Figure 1 A cross section through the VCR connecting rod 10 is shown,

[0019] Figure 2 A hydraulic schematic diagram of a VCR connecting rod according to the prior art is shown,

[0020] Figure 3 and 4 A first variant of the VCR linkage according to the invention is shown in correspondingly different switching positions,

[0021] Figure 5 and 6 A second variant of the VCR linkage according to the invention is shown in correspondingly different switching positions,

[0022] Figure 7 and 8 shows the variation of the second variant of the VCR linkage in correspondingly different switching positions, and

[0023] Fig. 9 and 10 A section through one of the support cylinders is shown in each case to illustrate the exhaust opening. DETAILED DESCRIPTION

[0024] exist Figure 1 , a section through a VCR connecting rod 10, i.e. a connecting rod for changing the compression ratio, is shown. In the upper region, an eccentric 40 is shown, which supports a bolt 41, which in turn serves to support and guide a piston of an internal combustion engine in which the VCR connecting rod 10 is installed. In the lower region (not shown), a support for the crank pin 12 is provided (see FIG. 1 ). Figure 2 ), the VCR connecting rod is supported and guided via the support device and is supplied with hydraulic fluid. The inlet into the connecting rod 10 is also referred to as the supply part 15 in the following. A switching switch (not shown) is provided on the lower part of the VCR connecting rod 10, which is located on the outside at the side, and the switching switch can be put into different positions by contact with a guide plate arranged in the engine compartment. The switching switch causes the switching valve 30 to switch into two different positions, the circuit diagram of which is shown in Figures 3 to 8 A channel leads from the switching valve 30 to the support cylinders 20 and 21, which are coupled to the eccentric 40. Depending on the pressure prevailing in the support cylinders 20, 21, the force acting on the piston can move the eccentric 40 into different positions.

[0025] Figure 2 The hydraulic sketch of the prior art shows an embodiment of the present invention. In the switching position of the switching valve 30 shown here, the hydraulic fluid can reach the VCR connecting rod 10 via the crankshaft (not shown) and its crank pin 12 via the supply part 15. The switching valve 30 is according to Figure 2 is switched so that hydraulic fluid cannot flow out of the support cylinder 21. When pressure acts on the support cylinder 20, hydraulic fluid is pressed out of it and at the same time its piston moves downwards, which is caused by the mechanical coupling via the eccentric 40: the piston of the support cylinder 21 is lifted and hydraulic fluid flows into the support cylinder 21 via the switching valve 30 and the non-return valve 21a. This process ends when the support cylinder 20 is completely emptied or the support cylinder 21 is completely filled. In this way, the eccentric 40 has already reached one of its end positions. When the switching valve 30 is switched, this process takes place in a mirrored manner.

[0026] If pressure is applied to the completely filled support cylinder after reaching the end position, the support cylinder (contrary to its purpose) can move in slightly due to the elasticity of the entire system. Accordingly, the support cylinder 20 is slightly lifted and slightly filled. At the next force change to the load acting on the support cylinder 20, the fluid is discharged again. Therefore, there is always a certain movement in the components, which causes wear and is correspondingly intended to be reduced or prevented by the present invention.

[0027] The following Figures 3 to 8 The embodiments of the invention have in common that the emptied support cylinder (respectively 20 or 21) cannot be filled without changing the position of the switching valve 30. No flow of hydraulic fluid from other sections of the VCR connecting rod 10 into the support cylinder occurs. Generally speaking, it is advantageous that if the first support cylinder is in the emptying condition (without switching of the switching valve 30), no hydraulic fluid can flow from the other support cylinder, i.e. the second support cylinder, into the first support cylinder. It can also be applicable that if the first support cylinder is in the emptying condition (without switching of the switching valve 30), no hydraulic fluid can flow into the first support cylinder via the supply 15.

[0028] exist Figure 3In the view of , the VCR connecting rod 10 can be supplied with hydraulic fluid from the supply part 15 via the non-return valve 16. The non-return valve 16 ensures that pressure fluctuations in the VCR connecting rod 10 are not transmitted to the support device of the VCR connecting rod 10 with the crank pin 12. Via the switching valve 30, the fluid pressure is conducted to the support cylinder 21, which then moves out when there is no corresponding counterpressure on it. Although there is a connection from the support cylinder 21 to the support cylinder 20 via the valve 30, the non-return valve 31 contained in the switching valve 30 ensures that no fluid can flow in this direction. More precisely, the task of the non-return valve 31 is that at the point in time when the switching valve 30 has just been switched and the hydraulic fluid is still contained in the support cylinder 20, this hydraulic fluid can flow into the support cylinder 21 and thus cause a switching of the eccentric position. Figure 3 and Figure 4 In the embodiment of the invention, the volumes of the support cylinders 20 and 21 are of equal size. This means that the hydraulic fluid can be completely accommodated by the other support cylinder in each case and ideally can work without fluid losses, which means that it is not necessary to replenish the hydraulic fluid via the supply 15. However, since hydraulic fluid losses always occur, for example through leaks, the supply 15 is always required. When the switching valve 30 is switched into its second position, the filling conditions are precisely reversed, so that the support cylinder 21 is emptied and the support cylinder 20 is filled, as in Figure 4 This design results in the desired decoupling of the emptied support cylinder.

[0029] exist Figures 5 to 8 Two embodiments are shown in which one of the support cylinders has a larger cross-section. This is the support cylinder 20 on the gas power side (= GKS), on which the combustion force acts via the (combustion chamber) piston and which can be constructed to be correspondingly enlarged in some embodiments. Since the volumes of the two support cylinders 20 and 21 are different at this time, an excess of hydraulic fluid will occur when filling the other support cylinder, i.e. the support cylinder 21 on the mass force side (= MBS). This fluid is output from the VCR connecting rod 10 to the interior of the engine via the outflow section 50. Therefore, when filling the GKS support cylinder 20, fresh hydraulic fluid is delivered via the supply section 15 because the amount of the MKS support cylinder 21 is insufficient. Figure 5 and 6 In this embodiment, the hydraulic circuit diagram corresponds to a large extent to Figure 3 and 4 implementation method, but in which Figure 5, it is shown that during the outflow from the GKS support cylinder 20 into the MKS support cylinder 21, the volume flow can also be discharged to the surroundings via the switching valve 30. In order to ensure that an unnecessary amount of hydraulic fluid does not flow out, the outflow 50 is provided with an outflow throttle 51 which limits the flow. In another switching position of the switching valve 30, the MKS support cylinder 21 is emptied and its hydraulic fluid preferably flows into the GKS support cylinder 20. In addition, an outflow to the surroundings is possible, but it is minimized by the outflow throttle 51. This embodiment can be preferably selected when it is to be ensured that the hydraulic flow is optimized with regard to avoiding cavitation. That is to say, if in Figure 6 If a force is applied to the GKS support cylinder 20 in the switching state of the MKS support cylinder 21, the MKS support cylinder 21 (described above) will be slightly lifted due to its elasticity. This will lead to negative pressure in its cylinder volume or in the delivery line and to the formation of vacuum bubbles, which can lead to material damage when they collapse in the form of cavitation. This can be avoided by opening the channel to the outside of the VCR connecting rod 10. This path runs through the switching valve 30 and the outflow throttle valve 51.

[0030] exist Figure 7 and Figure 8 In the two switching positions, another variant is shown, wherein according to Figure 8 The only difference is that in the evacuated state of the MKS support cylinder 21, there is no connection to the outside of the VCR valve. In this case, preferably ventilation and exhaust can be used, which will be explained below and can also be used in the above-mentioned embodiment.

[0031] to this end, Fig. 9 and 10 The piston of one of the support cylinders is shown in FIG. Figure 1 , wherein the features mentioned here can be used in both support cylinders 20, 21. The piston shown (without reference numerals) comprises a seal 25, which causes a seal relative to the cylinder. The hole is designed as a ventilation and exhaust section 22, so that it leads from the fluid space to a point outside the pressure from the seal 25 in the piston. The tolerance of the hole is very narrow and can have a diameter of, for example, 0.1 mm or 0.2 mm. Due to the different flow resistances, only a small amount of hydraulic fluid but significantly more air can pass through the hole. In the case of a negative pressure that has been formed as described above, air can enter the hydraulic volume of the support cylinder from the engine interior through the ventilation and exhaust section 22, thereby reducing the cavitation tendency. If the support cylinder is loaded with pressure, the ventilation and exhaust section 22 serves as an exhaust section. The ventilation and exhaust section 22 also has the general task of preventing a permanent air volume from accumulating in the support cylinder, because the accumulated air is discharged via the ventilation and exhaust section. Accordingly, the exhaust hole can preferably branch out from the fluid space at a point located vertically above. And in Fig.10An alternative to the venting is shown in FIG. A bore 23 provided in the piston opens into a gas collecting chamber 24 which is delimited by a section of the connecting rod 26 of the support cylinder. When the support cylinder is loaded with pressure, the fitting / seal between the connecting rod 26 and the piston closes the outlet. Due to the play in the bearing of the connecting rod 26 in the piston, the gas discharge is possible when the connecting rod 26 is unloaded. When the connecting rod 26 is loaded with pressure as described above, the gas collecting chamber 24 is slowly filled with gas flowing through the narrow bore 23 and, due to the compressibility, accumulates significantly in the gas collecting chamber 24 until the pressure in the connecting rod 26 drops and the gas can flow out.

[0032] Figures 3 to 8 The embodiments of the present invention are relatively similar, and the relevant differences have been mentioned in detail in the description. This means that for the sake of brevity, the explanations mentioned only in one of the embodiments can be directly applied to the other embodiments, unless these explanations are obviously contradictory thereto. The reference numerals are used uniformly on the corresponding embodiments, as long as the corresponding components basically realize the corresponding same functions.

[0033] Reference numerals list

[0034] 10 VCR connecting rod

[0035] 12 Crank pin

[0036] 15 Supply Department

[0037] 16 Check valve

[0038] 20 (Gas power side) support cylinder (also a larger support cylinder)

[0039] 21 (Mass force side) support cylinder (also a smaller support cylinder)

[0040] 20a, 21a Check valve

[0041] 22 and 23 are ventilation and exhaust parts respectively.

[0042] 24 Gas Collection Chamber

[0043] 25 Seals

[0044] 26 Connecting rod of support cylinder

[0045] 30 Switching valve

[0046] 31, 32 Check valve

[0047] 40 Eccentric wheel

[0048] 41 Hole for piston support

[0049] 50 outflow part

[0050] 51 Outflow throttle valve

Claims

1. A VCR connecting rod (10) for setting different compression ratios of an internal combustion engine, wherein the VCR connecting rod (10) comprises a supply (15) for hydraulic fluid via a crank pin (12) of a crankshaft, and for switching an eccentric wheel (40) of the VCR connecting rod (10) a first and a second support cylinder (20, 21) coupled to the eccentric wheel (40) are provided, The switching valve (30) is designed such that, in a first switching position, the first support cylinder (20) is supplied with hydraulic fluid for switching the VCR connecting rod, while the second support cylinder (21) is emptied. It is characterized in that At least after the second support cylinder (21) has been emptied, the second support cylinder (21) is decoupled from a hydraulic fluid supply and / or from the first support cylinder (20) so that no hydraulic fluid can flow into the second support cylinder (21).

2. A VCR connecting rod (10) for setting different compression ratios of an internal combustion engine, wherein the VCR connecting rod (10) comprises a supply (15) for hydraulic fluid via a crank pin (12) of a crankshaft, and for switching an eccentric (40) of the VCR connecting rod (10) two first and second support cylinders (20, 21) coupled to the eccentric (40) are provided, The switching valve (30) is designed such that, in a first switching position, the first support cylinder (20) is supplied with hydraulic fluid for switching the VCR connecting rod, while the second support cylinder (21) is emptied. It is characterized in that A ventilation and / or exhaust (22, 23) is provided for the second support cylinder (21), at least in the evacuated position.

3. A VCR connecting rod (10) according to claim 1 or 2, wherein the fluid volumes required for respectively filling the first and second support cylinders (20, 21) are of equal size and the fluid volumes are conveyed from the first support cylinder (20) into the second support cylinder (21) or vice versa depending on the position of the switching valve (30) and the fluid volumes are guided along the non-return valves (31, 32).

4. The VCR connecting rod (10) according to claim 3, wherein the nonreturn valve (31, 32) is formed by a movable switching element of the switching valve (30) or is contained in the switching valve (30).

5. The VCR connecting rod (10) of claim 1 or 2, wherein the first and second support cylinders (20, 21) have fluid volumes of different sizes, and for the hydraulic fluid, an outflow portion is provided for the fluid to leave the VCR connecting rod (10) when filling the smaller support cylinder.

6. The VCR connecting rod (10) according to claim 1 or 2, wherein in a second switching position of the switching valve (30), the first and second support cylinders (20, 21) exchange functions.

7. The VCR connecting rod (10) according to claim 1 or 2, wherein the first and second support cylinders (20, 21) have fluid volumes of different sizes, and during filling of the larger support cylinder, there is no structural provision for the fluid of the smaller support cylinder to flow out of the VCR connecting rod (10) via an outflow portion provided for this purpose.

8. The VCR connecting rod (10) according to claim 1 or 2, wherein the first and second support cylinders (20, 21) have fluid volumes of different sizes and during filling of the larger support cylinder, the fluid of the smaller support cylinder can flow out of the VCR connecting rod (10) via an outflow (50) provided for this purpose.

9. The VCR connecting rod (10) according to claim 1 or 2, characterized in that: At least one of the first and second support cylinders comprises a ventilation and / or exhaust passage (22) from its pressure chamber to the surroundings of the VCR connecting rod (10), and no mechanism is provided for opening and closing the ventilation and exhaust passage in dependence on the operating state.

10. The VCR connecting rod (10) according to claim 1 or 2, characterized in that: At least one of the first and second support cylinders comprises a ventilation and / or exhaust passage (23) from its pressure chamber to the surroundings of the VCR connecting rod (10) and is provided with a sealing mechanism for opening and / or closing the ventilation and / or exhaust passage (23) according to the pressure acting on the VCR connecting rod.

11. An internal combustion engine according to the reciprocating piston principle having at least one combustion chamber, the internal combustion engine having a VCR connecting rod (10) according to any one of the preceding claims.

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