INTERNAL COMBUSTION ENGINE WITH A HYDRAULICALLY VARIABLE GAS EXCHANGE VALVE TRAIN

Abstract

A hydraulically variable gas exchange valve train for an internal combustion engine is proposed that includes a hydraulic housing with a pressure chamber, a pressure relief chamber, and a vent duct. The vent duct is connected hydraulically on a housing inner side via a restriction to the pressure relief chamber, and opens on the housing outer side below the pressure relief chamber with regard to a direction of gravity. The vent duct opens into a hydraulic reservoir, wherein the vent duct opening lies below a normal level of the hydraulic reservoir with regard to the direction of gravity.

Claims

1. An internal combustion engine having a hydraulically variable gas exchange valve train, which comprises: a hydraulic housing having: a pressure chamber, a pressure relief chamber, and, a vent duct, and, the pressure chamber, the pressure relief chamber and the vent duct connected to one another hydraulically, a master piston, guided within the hydraulic housing, the master piston driven on a housing outer side by a cam and defining the pressure chamber on a housing inner side, a slave piston, guided within the hydraulic housing, the slave piston driving a gas exchange valve on the housing outer side and defining the pressure chamber on the housing inner side, and, a hydraulic valve, which, in a closed state, interrupts a hydraulic connection between the pressure relief chamber and the pressure chamber, and, the vent duct is connected hydraulically on the housing inner side via a restriction to the pressure relief chamber, and opens on the housing outer side below the pressure relief chamber in relation to a direction of gravity, wherein the vent duct opens into a hydraulic reservoir, and a vent duct opening is below a normal hydraulic fluid level of the hydraulic reservoir in relation to the direction of gravity.

2. The internal combustion engine as claimed in claim 1, wherein when the gas exchange valve is closed, the vent duct opening is below a boundary of the pressure chamber defined by the slave piston in relation to the direction of gravity.

3. The internal combustion engine as claimed in claim 1, wherein the vent duct opening is always below a hydraulic fluid level of the hydraulic reservoir in relation to the direction of gravity.

4. The internal combustion engine as claimed in claim 1, wherein the vent duct has a circular first tube section having an inside diameter of at least 6 mm.

5. The internal combustion engine as claimed in claim 4, wherein the vent duct opening is formed by a circular second tube section adjoined to the circular first tube section, the circular second tube section having a tube outside diameter that is less than a tube outside diameter of the circular first tube section.

6. The internal combustion engine as claimed in claim 4, wherein the circular first tube section is part of a vent tube secured in the hydraulic housing.

7. The internal combustion engine as claimed in claim 6, wherein the vent tube is screwed into the hydraulic housing.

8. The internal combustion engine as claimed in claim 1, wherein the hydraulic reservoir is formed by a hollow in a cylinder head of an internal combustion engine, the hollow being closed in the direction of gravity and configured to collect hydraulic fluid during operation of the internal combustion engine.

9. A hydraulically variable gas exchange valve train configured for an internal combustion engine, the valve train comprising: a hydraulic housing having: a pressure chamber; a pressure relief chamber; and, a vent duct connected hydraulically on a housing inner side via a restriction to the pressure relief chamber; and, the pressure chamber, pressure relief chamber, and vent duct connected to one another hydraulically; a master piston guided within the hydraulic housing, the master piston defining the pressure chamber on the housing inner side and configured to be driven on a housing outer side by a cam; a slave piston guided within the hydraulic housing, the slave piston defining the pressure chamber on the housing inner side and configured to drive a gas exchange valve on the housing outer side; and, a hydraulic valve capable of hydraulically connecting or hydraulically disconnecting the pressure relief chamber and the pressure chamber; and, the vent duct opens into a hydraulic reservoir on the housing outer side below the pressure relief chamber in relation to a direction of gravity; and, a vent duct opening is below a normal hydraulic fluid level of the hydraulic reservoir in relation to the direction of gravity.

10. The hydraulically variable gas exchange valve train of claim 9, wherein the hydraulic valve is configured to allow hydraulic fluid flow: i) from the pressure relief chamber to the pressure chamber; and, ii) from the pressure chamber to the pressure relief chamber.

11. The hydraulically variable gas exchange valve train of claim 9, wherein the vent duct includes a vent tube of uniform diameter, the vent tube having an opening that extends within the hydraulic reservoir.

12. The hydraulically variable gas exchange valve train of claim 9, wherein the vent duct includes a first section and a second section.

13. The hydraulically variable gas exchange valve train of claim 12, wherein the first section is a circular first section and the second section is a circular second section.

14. The hydraulically variable gas exchange valve train of claim 13, wherein a first inner diameter of the first section is larger than a second inner diameter of the second section.

15. The hydraulically variable gas exchange valve train of claim 14, wherein the first inner diameter is at least 8 mm.

16. The hydraulically variable gas exchange valve train of claim 14, wherein the second inner diameter is about 4 mm.

17. The hydraulically variable gas exchange valve train of claim 9, wherein the vent duct is formed by a bleed tube secured in the hydraulic housing.

18. The hydraulically variable gas exchange valve train of claim 17, wherein the bleed tube is screwed into the hydraulic housing.

19. The hydraulically variable gas exchange valve train of claim 17, wherein the bleed tube includes a first section and a second section.

20. A hydraulically variable gas exchange valve train configured for an internal combustion engine, the valve train comprising: a hydraulic housing having: a pressure chamber; a pressure relief chamber; and, a vent duct connected hydraulically on a housing inner side via a restriction to the pressure relief chamber; and, the pressure chamber, pressure relief chamber, and vent duct connected to one another hydraulically; a master piston guided within the hydraulic housing, the master piston defining the pressure chamber on the housing inner side and configured to be driven on a housing outer side by a cam; a slave piston guided within the hydraulic housing, the slave piston defining the pressure chamber on the housing inner side and configured to drive a gas exchange valve on the housing outer side; and, a hydraulic valve capable of hydraulically connecting or hydraulically disconnecting the pressure relief chamber and the pressure chamber; and, the vent duct opens into a hydraulic reservoir on the housing outer side below the pressure relief chamber in relation to a direction of gravity; and, a vent duct opening is below a boundary of the pressure chamber defined by the slave piston.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Further features of this disclosure will be found in the following description and in the drawings, in which three illustrative embodiments of the disclosure are illustrated schematically. Unless stated otherwise, identical or functionally identical features or components are provided with identical reference signs here. In the drawings:

[0015] FIG. 1a shows the first illustrative embodiment with a vent duct of stepped diameter;

[0016] FIG. 1b shows the duct opening and the hydraulic reservoir of the first illustrative embodiment in an enlarged detail;

[0017] FIG. 2 shows the second illustrative embodiment with a relatively low-lying hydraulic reservoir;

[0018] FIG. 3 shows the third illustrative embodiment with a duct opening which dips permanently into the hydraulic reservoir.

DETAILED DESCRIPTION

[0019] FIG. 1a shows schematically the section of the internal combustion engine which is essential to the understanding of this disclosure, having a hydraulically variable gas exchange valve train. It illustrates a cylinder head 1 having two gas exchange valves 2 of the same type per cylinder and associated cams 3 of a camshaft, the valves being subject to a spring force in the closing direction. The variability of the gas exchange valve train is produced in a known manner by means of a hydraulic unit arranged between the cams 3 and the gas exchange valves 2. This unit comprises a hydraulic housing 4, which is secured in the cylinder head 1 and in which one pressure chamber 5 and one pressure relief chamber 6 are formed and one master piston 7 is guided for each cylinder, said piston being driven on the housing outer side by the cam 3 and defining the pressure chamber 5 on the housing inner side. Two slave pistons 8 per cylinder are furthermore guided in the hydraulic housing 4, said pistons driving the gas exchange valves 2 on the housing outer side and defining the common pressure chamber 5 on the housing inner side. An electromagnetic hydraulic valve 9, in the present case a normally open 2/2-way valve, interrupts the hydraulic connection between the pressure relief chamber 6 and the pressure chamber 5 in the closed state. In the open state of the hydraulic valve 9, some of the hydraulic fluid displaced by the master piston 7 can flow off into the pressure relief chamber 6 without participating in the actuation of the slave piston 8 and of the associated gas exchange valve 2. A piston-type pressure accumulator 10 for receiving the displaced hydraulic fluid is connected to each pressure relief chamber 6. The pressure relief chambers 6 are connected via a hydraulic connection (not shown) on the hydraulic housing 4 to the hydraulic circuit, i.e. the oil circuit of the internal combustion engine.

[0020] The operation of the hydraulic gas exchange valve train, which is known per se, can be summarized in that the pressure chamber 5 between the master piston 7 and the slave piston 8 acts as a hydraulic linkage. Here, the hydraulic fluid, which is displaced by the master piston 7 proportionally to the lift of the cam 3neglecting leaksis divided in accordance with the opening time and the opening duration of the hydraulic valve 9 into a first partial volume, which acts on the slave piston 8, and a second partial volume, which flows off into the pressure relief chamber 6, including the piston-type pressure accumulator 10. This enables fully variable setting of the stroke transmission of the master piston 7 to the slave piston 8 and consequently not only of the timings but also of the lift height of the gas exchange valves 2.

[0021] The pressure relief chambers 6 are connected to a common vent duct 11 in the hydraulic housing 4, which is hydraulically connected on the housing inner side, via restrictions 12, to the respective pressure relief chamber 6 and opens on the housing outer side into a hydraulic reservoir 13 in the interior of the cylinder head 1. The restrictions 12 are geodetically above the pressure relief chambers 6, that is to say in relation to the direction, symbolized by the arrow, of gravity g, and the hydraulic reservoir 13 is geodetically below the pressure relief chambers 6. The duct opening 14 of the vent duct 11 is geodetically not only below the level 15 of the hydraulic reservoir 13 but also below the boundary 16 of the pressure chamber 5 defined by the slave pistons 8 when said pistons are fully retracted into the hydraulic housing 4 with the gas exchange valves 2 closed. The hydraulic reservoir 13, which is unpressurized relative to the internal pressure of the cylinder head 1, is formed by a hollow 17 in the cylinder head 1 (see FIG. 1b), which is closed in the direction of gravity and in which hydraulic fluid collects during the operation of the internal combustion engine.

[0022] The vent duct 11 is formed on the housing outer side by a vent tube 18 screwed firmly and sealingly into the hydraulic housing 4. This tube has a circular first tube section 19, the tube inside diameter of which is between 8 mm and 9 mm. The first tube section 19 merges at a diameter step 20 into a circular second tube section 21 with a tube inside diameter of about 4 mm. The tube outside diameter of the second tube section 21 is correspondingly small and dimensioned in such a way that the second tube section 21 can be introduced into the hollow 17 without collisions when the hydraulic unit is installed in the cylinder head 1.

[0023] FIG. 1a shows the vented filling level of the hydraulic system shortly after the internal combustion engine is switched off. Here, the level 15 of the hydraulic reservoir 13 is the initially defined normal level. The detail in FIG. 1b shows the filling level of the hydraulic system at a significantly later time, at which the hydraulic fluid has cooled fully and the volume thereof has shrunk accordingly. The vacuum which forms with the decrease in volume in the hydraulic chambers has the effect that additional hydraulic fluid is sucked out of the hydraulic reservoir 13 into the pressure relief chambers 6. This induction of additional fluid without air bubbles ends when the level 15 of the hydraulic reservoir 13 falls geodetically below the duct opening 14. After this, pressure compensation between the pressure relief chambers 6 and the environment of the hydraulic housing 4 is accomplished by back suction of air bubbles 22. The tube inside diameter of the first tube section 19, which is significantly larger than the size of the air bubbles, enables the air bubbles 22 to migrate upward through the oil column situated therein, wherein the oil column closes again after the air bubbles 22 have passed through. This maintains a vacuum, which inhibits hydraulic leakage into the cylinder head 1 through the guide clearance between the slave pistons 8 and the hydraulic housing 4 and thusin addition to the volume compensation from the hydraulic reservoir 13delays the critical emptying of the pressure chamber 5.

[0024] In the second illustrative embodiment, which is illustrated in FIG. 2, the hydraulic reservoir 13 is geodetically significantly lower than in the first illustrative embodiment. The higher oil column between the boundary 16 and the level 15 of the hydraulic reservoir 13 causes an increased vacuum in the hydraulic system in favor of further reduced leakage of the pressure chambers 5 through the guide clearance around the slave pistons 8. In this embodiment, the vent duct 11 is formed by a vent tube 18 of uniform diameter, wherein the tube inside diameter is of such large dimensions in this case too that the air bubbles 22 rising therein can pass through the oil column standing in the vent tube 18.

[0025] The third illustrative embodiment in FIG. 3 has a hydraulic reservoir 13, the volume of which is so large that the duct opening 14 is always geodetically below the level 15 of the hydraulic reservoir 13.

LIST OF REFERENCE CHARACTERS

[0026] 1 cylinder head [0027] 2 gas exchange valve [0028] 3 cam [0029] 4 hydraulic housing [0030] 5 pressure chamber [0031] 6 pressure relief chamber [0032] 7 master piston [0033] 8 slave piston [0034] 9 hydraulic valve [0035] 10 piston-type pressure accumulator [0036] 11 vent duct [0037] 12 restriction [0038] 13 hydraulic reservoir [0039] 14 duct opening [0040] 15 level [0041] 16 boundary [0042] 17 hollow [0043] 18 vent tube [0044] 19 first tube section [0045] 20 diameter step [0046] 21 second tube section [0047] 22 air bubble