HYDRAULIC CAMSHAFT ADJUSTER, AND METHOD FOR OPERATING THE HYDRAULIC CAMSHAFT ADJUSTER

Abstract

A hydraulic camshaft adjuster adjusts the control time of gas exchange of an internal combustion engine. A reservoir for storing pressure medium is formed on a cover of the hydraulic camshaft adjuster. An overflow opening of the cover is dimensioned such that a volume of pressure medium remains in the reservoir when the hydraulic camshaft adjuster is stationary. This ensures that pressure medium is supplied to the return valve of a central locking mechanism when the engine is running.

Claims

1. A hydraulic camshaft adjuster for adjusting the control times of gas exchange valves of an internal combustion engine, the hydraulic camshaft adjuster comprising: a stator which can be rotated in synchrony with a crankshaft of the internal combustion engine a rotor arranged so as be rotatable relative to the stator and which can rotate in synchrony with a camshaft; and a mid-position locking mechanism for locking the rotor in a middle position; wherein several webs are provided on the stator and which divide an annular chamber between the stator and the rotor into a plurality of pressure chambers; the rotor comprises a rotor hub and a plurality of vanes which extend radially outwardly from the rotor hub and divide the pressure chambers into two groups of working chambers, wherein the groups have different action directions and can be loaded by a pressure medium flowing respectively into and out of a pressure medium circuit; the hydraulic camshaft adjuster is partially closed on an end face by at least one cover; a reservoir for storing pressure medium is formed in one of the at least one cover; the at least one cover comprises defines an overflow opening through which the pressure medium can emerge in the axial direction from the hydraulic camshaft adjuster; the reservoir is dimensioned relative to the overflow opening such that, when the hydraulic camshaft adjuster is at a standstill, a pressure medium sump remains which, on start-up of the hydraulic camshaft adjuster, ensures the supply of pressure medium to check valves of the mid-position locking mechanism; and the check valves for supplying pressure medium to the mid-position locking mechanism are arranged on a first pitch circle diameter, and check valves for supplying pressure medium to the working chambers are arranged on a second pitch circle diameter less than the first pitch circle diameter.

2. The hydraulic camshaft adjuster as claimed in claim 1, wherein the at least one cover on which the reservoir for storing the pressure medium is formed, is free from dead volumes.

3. The hydraulic camshaft adjuster as claimed in claim 1, wherein the at least one cover comprises by a locking cover and a reservoir cover, wherein the reservoir is formed on the reservoir cover.

4. The hydraulic camshaft adjuster as claimed in claim 1, wherein a blocking element is formed on one of the at least one covers and blocks the inflow of pressure medium into a dead volume.

5. The hydraulic camshaft adjuster as claimed in claim 4, wherein a pocket is formed on the reservoir cover.

6. The hydraulic camshaft adjuster as claimed in claim 5, wherein the blocking element eliminates an inflow of pressure medium into the pocket.

7. The hydraulic camshaft adjuster as claimed in claim 4, wherein the dead volume is formed by an opening for access to check valves or as a recess for a screw connection.

8. The hydraulic camshaft adjuster as claimed in that claim 1, wherein on one of the at least one covers, the reservoir has a geometry deviating from a cylindrical form in order to reduce a dead volume which retains pressure medium that cannot be used for oil supply to the mid-position locking mechanism in the start-up phase.

9. A method for operating a hydraulic camshaft adjuster as claimed in claim 1, wherein when the internal combustion engine stops, the pressure medium collects in the reservoir, and when the internal combustion engine restarts, the pressure medium is flung out of the reservoir by centrifugal force onto an outer, substantially annular starting volume, wherein the check valves for supplying the mid-position locking mechanism are arranged in a region of the hydraulic camshaft adjuster which is covered by the substantially annular starting volume.

10. A hydraulic camshaft adjuster comprising: a stator having a plurality of inwardly projecting webs; a rotor having a plurality of outwardly projecting vanes interspersed with the inwardly projecting webs to define two groups of working chambers; a locking cover fixed to the stator and including a locking mechanism; and a reservoir cover fixed to the stator and defining an annular reservoir; a plurality of first check valves for supplying pressure medium from the reservoir to the working chambers, the first check valves located a first distance from an axis of rotation; and a second check valve for supplying pressure medium from the reservoir to the locking mechanism, the second check valve located a second distance greater than the first distance from the axis of rotation.

11. The hydraulic camshaft adjuster of claim 10 wherein the locking mechanism is a mid-position locking mechanism.

12. The hydraulic camshaft adjuster of claim 10 wherein: the reservoir cover defines an overflow opening; the reservoir opening is dimensioned such that a volume of pressure medium remains in the reservoir when the stator is stationary; and the volume is sufficient to supply the second check valve when the stator rotates.

13. The hydraulic camshaft adapter of claim 12 wherein the reservoir cover is free from dead volumes.

14. The hydraulic camshaft adapter of claim 12 further comprising a blocking element configured to block inflow of pressure medium into a dead volume of the reservoir cover.

15. The hydraulic camshaft adapter of claim 12 wherein the reservoir cover includes a pocket to accommodate a check valve or a screw connection.

16. The hydraulic camshaft adapter of claim 15 further comprising a blocking element configured to block inflow of pressure into the pocket.

17. A hydraulic camshaft adjuster comprising: a stator having a plurality of inwardly projecting webs; a rotor having a plurality of outwardly projecting vanes interspersed with the inwardly projecting webs to define two groups of working chambers; a locking cover fixed to the stator and including a locking mechanism; and a reservoir cover fixed to the stator and defining an annular reservoir; and a first check valve for supplying pressure medium from the reservoir to the locking mechanism, the first check valve located a first distance from the axis of rotation; wherein the reservoir cover defines an overflow opening; the reservoir opening is dimensioned such that a volume of pressure medium remains in the reservoir when the stator is stationary; and the volume is sufficient to supply the first check valve when the stator rotates.

18. The hydraulic camshaft adjuster of claim 17 wherein the locking mechanism is a mid-position locking mechanism.

19. The hydraulic camshaft adjuster of claim 18 further comprising a plurality of second check valves for supplying pressure medium from the reservoir to the working chambers, the second check valves located a second distance, less than the first distance, from an axis of rotation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The hydraulic camshaft adjuster and corresponding method is now explained in more detail below with reference to preferred exemplary embodiments and the associated drawings. The same components or components with the same function are designated by the same reference signs. The drawings show:

[0021] FIG. 1 an exemplary embodiment of a hydraulic camshaft adjuster in a sectional depiction;

[0022] FIG. 2 a three-dimensional depiction of a cover of a hydraulic camshaft adjuster, and the distribution of pressure medium in various operating states;

[0023] FIG. 3 a sectional depiction through a hydraulic camshaft adjuster and the pressure medium sump with the internal combustion engine switched off;

[0024] FIG. 4 a further sectional depiction through a hydraulic camshaft adjuster and the pressure medium distribution after a start-up of the internal combustion engine;

[0025] FIG. 5 a further sectional depiction through a hydraulic camshaft adjuster to illustrate a dead volume; and

[0026] FIG. 6 a further sectional depiction through a hydraulic camshaft adjuster.

DETAILED DESCRIPTION

[0027] FIG. 1 shows an exemplary embodiment of a hydraulic camshaft adjuster 1 for adjusting the valve control times of an internal combustion engine. The hydraulic camshaft adjuster 1 shown diagrammatically in FIG. 1 is configured as a vane cell adjuster in the known fashion, and comprises a stator 2 which can be driven by a crankshaft (not shown) of an internal combustion engine, and a rotor 3 which can be connected rotationally fixedly to a camshaft (also not shown). The rotor 3 has a rotor hub 4 from which several vanes 5 extend in the radial direction. In the depiction shown, the hydraulic camshaft adjuster 1 is shown in a sectional view through the stator 2 and the rotor 3. The stator 2 has a plurality of webs 6 which divide an annular chamber between the stator 2 and rotor 3 into several pressure chambers 8. The pressure chambers 8 are divided by the vanes 5 of the rotor 3 into two groups of working chambers 9, 10 with different action directions. Sealing elements 7 are provided at the tips of the vanes 5 to prevent overflow from one working chamber 9, 10 into the respective other working chamber 9, 10. The hydraulic camshaft adjuster 1 has a mid-position locking mechanism 11 which comprises a locking pin 13 for locking the rotor 3 relative to the stator 2 in a locking guide 12 fixed to the stator. The stator 2 is delimited on its first end face 20 by a locking cover 17 and a reservoir cover 18, and on its second end face 21 by a sealing cover 33, each of which is connected rotationally fixedly to the stator 2. The locking guide 12 may be arranged both in the stator 2 itself and also in one of the covers 17, 18 connected rotationally fixedly to the stator 2, in particular in the locking cover 17.

[0028] In principle, the rotary angle of the camshaft relative to the crankshaft in normal operation of the hydraulic camshaft adjuster 1 is adjusted in that the first group of working chambers 9 is loaded with a pressure medium 19, thereby increasing their volume, while simultaneously pressure medium 19 is displaced from a second group of working chambers 10, thereby reducing their volume. The working chambers 9 whose volume is increased in groups during this adjustment movement are designated, working chambers 9 with one action direction, while the working chambers 10 whose volume is simultaneously reduced are designated working chambers 10 with the opposite action direction. The volume increase of the working chambers 9 means that the rotor 3 is twisted in the advance direction relative to the stator 2. The corresponding supply of pressure medium to the working chambers 9, 10 takes place by a pressure medium pump 15 which conveys pressure medium 19 from a storage container 16 into the working chambers 9, 10 of the hydraulic camshaft adjuster 1.

[0029] A reservoir 14 for storing pressure medium 19 is formed on the rotor 3, on the stator 2 and/or on one of the covers 17, 18 of the hydraulic camshaft adjuster 1. The reservoir 14 is hydraulically connected to the working chambers 9, 10 and allows pressure medium 19 to flow into the working chambers 9, 10 if the pressure medium pump 15 cannot convey sufficient pressure medium 22 and a vacuum is created in one of the working chambers 9, 10. FIG. 1 shows a hydraulic camshaft adjuster 1 in which the reservoir is formed in the webs 6 of the stator 2, wherein the webs 6 may come into active connection with the working chambers 9, 10 of the hydraulic camshaft adjuster 1 via check valves 27, 28.

[0030] FIG. 6 shows a further section through a hydraulic camshaft adjuster 1. The hydraulic connection of the reservoir 14 to the working chambers 9, 10 of the hydraulic camshaft adjuster 1 can be seen. The locking cover 17 is here arranged between the first end face 20 of the stator 2 and the reservoir cover 18. Check valves 27 for supplying the working chambers 9, 10 for the smart phasing function of the hydraulic camshaft adjuster 1, and check valves 28 for supplying the supporting chambers 24, are formed in the locking cover 17. Oil is supplied to the working chambers 9, 10 in normal operation by the pressure medium pump 15 through a central valve (not shown) and corresponding supply bores 37, 38 in the rotor 3. Since the check valves 28 for the support chambers 24 lie on a larger pitch circle diameter 30 than the check valves 27 for the smart phasing function, it is guaranteed that the support function has priority over the adjustment function on start-up of the internal combustion engine.

[0031] FIG. 2 shows a three-dimensional depiction of a cover 17, 18 of a hydraulic camshaft adjuster 1 and the distribution of pressure medium in different operating states. The cover 17, 18 is rotationally fixedly attached to an end face 20, 21 of the hydraulic camshaft adjuster 1 and forms a reservoir 14 for storing pressure medium 19. When the internal combustion engine is at a standstill and the hydraulic camshaft adjuster 1 is also at a standstill, a partial quantity of the pressure medium 19 present in the reservoir 14, in particular the oil of the internal combustion engine, flows out of the reservoir 14 via the overflow opening 23, so that after a short time, a pressure medium sump 25 is formed which extends up to the lower edge of the overflow opening 23. On subsequent start-up of the internal combustion engine 1, the hydraulic camshaft adjuster is set in rotation by the crankshaft of the internal combustion engine so that the pressure medium 19 is displaced outwardly by the centrifugal force and bears on the wall of the cover 18 along a substantially annular portion. The pressure medium volume during start-up 35 corresponds to the pressure medium volume of the pressure medium sump 25. On further operation of the hydraulic camshaft adjuster 1, the reservoir 14 is filled further, whereby the annular portion widens and the reservoir 14 is filled from the outside towards the inside, until the additional pressure medium emerges again through the overflow opening 23 when the reservoir 14 is completely filled. The pressure medium volume increases to the pressure medium volume 34 shown in FIG. 2 for continuous engine operation.

[0032] FIG. 3 shows a section through a hydraulic camshaft adjuster 1. It is evident that the check valves 28 for the mid-position locking mechanism 11 lie on a first pitch circle diameter 30, and the check valves 27 for the smart phasing function lie on a second pitch circle diameter 29 with a smaller diameter. Access points to the working chambers 9, 10 for the locking mechanism also lie on the first pitch circle diameter DA and are covered by the check valves 28. When the internal combustion engine has stopped, the pressure medium sump 25 (shown in FIG. 3) forms in the reservoir 14 of the cover 17, 18. FIG. 3 also shows the locking pins 13 and locking guide 12 of the mid-position locking mechanism 11.

[0033] FIG. 4 shows a further section through a hydraulic camshaft adjuster 1, wherein the hydraulic camshaft adjuster 1 rotates at the rotation speed of the camshaft, i.e. at half the rotation speed of the crankshaft, after a start-up of the internal combustion engine. The pressure medium 19 is pressed radially outward under centrifugal force to an edge of the cover 17, 18 so that an annular volume 35 in the cover is covered with pressure medium 19, the volume of which substantially corresponds to the pressure medium volume of the pressure medium sump 25. The access points to the support chambers 24 for the locking mechanism 11 are here covered by pressure medium 19, so that the support chambers 24 cannot draw in air. In this way, the rotor 3 of the hydraulic camshaft adjuster 1 can be supported against the alternating moments of the camshaft and move into the middle locking position.

[0034] Since it is known from experience that situations occur in which the hydraulic camshaft adjuster 1 is no longer able to turn the rotor 3 into the middle locking position and lock the locking pins 13 in the locking guide 12 after the internal combustion engine has stopped, the possibility of adjustment from an arbitrary position into the middle locking position on engine start-up has been considered in the hydraulic camshaft adjuster 1. For this, the support chamber 24, which is preferred according to the desired/released adjustment direction, must be supplied with pressure medium 19 which can be drawn out of the reservoir 14 only via a check valve 28. Unfavorably, with the engine stopped, the pressure medium 19 stored in the reservoir 14 is limited by the overflow opening 23 to a magnet for controlling a central valve of the hydraulic camshaft adjuster 1. The remaining pressure medium 19 thus flows through the overflow opening 23 to a central magnet of the hydraulic camshaft adjuster 1. It cannot therefore be guaranteed that, when the hydraulic camshaft adjuster 1 is at a standstill, all bores and check valves 27, 28 are coated with pressure medium 19. In order to utilize the existing pressure medium volume 25, 35 optimally, it is advantageous to minimize the volume which cannot be drawn upor only drawn up while mixing with airby the check valves 28. This volume is designated a dead volume 22. Therefore in the exemplary embodiment depicted, pockets 32 are provided in the cover 17, 18. The pockets 32 are arranged at locations on the cover 17, 18 where for example screws protrude into the cover 17, 18. In addition, dead volumes 22 are formed on the hydraulic camshaft adjuster 1 in the region in which intake bores for the check valves 27, 28 are formed. The cover 17, 18, or the reservoir 14 delimited by the cover 17, 18, does not simply have a cylindrical form but deliberately deviates from this form. On operation following start-up, the reservoir 14 is filled with pressure medium via the central valve of the hydraulic camshaft adjuster 1 until the check valves 27 for supplying the working chambers 9, 10 for the smart phasing function are also covered by pressure medium and can therefore be activated. The reservoir 14 is here filled effectively from outside to inside, i.e. the pressure medium ring formed by centrifugal force becomes wider over the operating period until surplus pressure medium 19 can again flow out via the overflow opening 23 in the direction of the central magnet.

[0035] FIG. 5 shows a further section through a hydraulic camshaft adjuster 1. A dead volume 22 is formed on the hydraulic camshaft adjuster 1, which can retain pressure medium 19 that is not available at the edge of the cover 17, 18 under centrifugal forces on rotation of the hydraulic camshaft adjuster. In order to avoid this, a blocking element 31 may be provided on the cover 17, 18 which blocks an inflow of pressure medium 19 into a pocket 32 or at least partially fills such a pocket 32 in order to reduce the dead volume 22. This dead volume 22 could otherwise fill with pressure medium 19 on immersion into the pressure medium sump 25 or under the centrifugal force on start-up of the hydraulic camshaft adjuster 1, wherein the pressure medium 19 in the dead volume 22 is not then available to supply pressure medium to the working chambers 9, 10. To prevent this, the pocket 32 is formed on the cover 17, 18, whereby the reservoir 14 has a form deviating from a cylindrical form and blocks a hydraulic connection from the reservoir 14 to the dead volume 22.

[0036] In a hydraulic camshaft adjuster 1, it is therefore possible to turn the rotor 3 from an arbitrary starting position into the middle locking position and lock it there. The pressure medium supply of the hydraulic camshaft adjuster 1 is thus improved, in particular in the start-up phase of the hydraulic camshaft adjuster 1 following start-up of the internal combustion engine.

LIST OF REFERENCE SIGNS

[0037] 1 Hydraulic camshaft adjuster [0038] 2 Stator [0039] 3 Rotor [0040] 4 Rotor hub [0041] 5 Vane [0042] 6 Web [0043] 7 Annular chamber [0044] 8 Pressure chamber [0045] 9 Working chamber [0046] 10 Working chamber [0047] 11 Mid-position locking mechanism [0048] 12 Locking guide [0049] 13 Locking pin [0050] 14 Reservoir [0051] 15 Pressure medium pump [0052] 16 Storage container [0053] 17 Locking cover [0054] 18 Reservoir cover [0055] 19 Pressure medium [0056] 20 First end face [0057] 21 Second end face [0058] 22 Dead volume [0059] 23 Overflow opening [0060] 24 Support chamber [0061] 25 Pressure medium sump [0062] 26 Inlet bore [0063] 27 Check valve [0064] 28 Check valve [0065] 29 First pitch circle diameter [0066] 30 Second pitch circle diameter [0067] 31 Blocking element [0068] 32 Pocket [0069] 33 Sealing cover [0070] 34 Oil level in continuous engine operation [0071] 35 Oil level during start-up [0072] 36 Screw