Hydraulic valve lash adjuster with idle stroke function for a valve train of an internal combustion engine

Abstract

A hydraulic valve lash adjuster with idle stroke function for a valve train of an internal combustion engine, said hydraulic valve lash adjuster comprising a piston (2, 2′, 2″) that is guided for displacement in a piston housing (4) and elastically supported against said housing (4), said piston (2, 2′, 2″) comprising a low pressure chamber (3) that communicates via an axial opening (7) in a piston bottom (8) with a high pressure chamber (5) defined by the piston housing (4) and the piston (2, 2′, 2″), and further comprising a control valve (9, 9′, 9″, 9′″) acting between said pressure chambers (3, 5), said control valve (9, 9′, 9″, 9′″) comprising a valve closing body (10, 10′, 10″) that can be brought to bear sealingly against a valve seat (15, 15′) that surrounds the axial opening (7) on a piston body undersurface (18) and is received in an element (12, 12′) that limits a closing body stroke (17), and said control valve (9, 9′, 9″, 9′″) further comprising a control valve spring (11) that loads the valve closing body (10, 10′, 10″) with a spring force in opening direction, and an idle stroke being produced during a collapsing movement between the piston (2, 2′, 2″) and the piston housing (4) during which said valve closing body (10, 10′, 10″) is hydraulically loaded in closing direction against the action of the control valve spring (11) by a pressure build-up in the high pressure chamber (5), whereby a retarded pressure build-up can be obtained through a flow control device (23, 23′) arranged on a high pressure chamber-side and comprising a flow control element (24, 24′) and a medium pressure chamber (19) that extends between the flow control element (24, 24′) and the axial opening (7) of the piston (2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, shows a portion of an RSHVA comprising a flow control device, in a longitudinal section, in an open position of the control valve,

FIG. 1 a, a piston of the RSHVA of FIG. 1, as a detail,

FIG. 1 b, a disk-shaped flow control element of the RSHVA of FIG. 1, as an enlarged detail,

FIG. 1 c, a closing body cap of the RSHVA of FIG. 1, as an enlarged detail,

FIG. 1 d, a needle-shaped valve closing body of the RSHVA of FIG. 1, as an enlarged detail,

FIG. 2, a second form of embodiment of the RSHVA in a longitudinal section in an open position of the control valve, with a modified valve spring mounting,

FIG. 2 a, a piston of the RSHVA of FIG. 2, as a detail,

FIG. 2 b, a needle-shaped valve closing body of the RSHVA of FIG. 2, as an enlarged detail,

FIG. 3, a third form of embodiment of the RSHVA in a longitudinal section in an open position of the control valve, with a ball-shaped valve closing body,

FIG. 3 a, the form of embodiment of the RSHVA of FIG. 3 in a closed position of the control valve,

FIG. 3 b, a piston of the RSHVA of FIG. 3, as a detail,

FIG. 3 c, a closing body cap of the RSHVA of FIG. 3, and

FIG. 4, a fourth form of embodiment of the RSHVA in a longitudinal section in an open position of the control valve, with a pot-like flow control element.

DETAILED DESCRIPTION OF THE DRAWINGS

The RSHVA shown in FIG. 1 is advantageously configured as a hydraulic tappet 1 (roller tappet, cup tappet etc.) of a valve train of an internal combustion engine in an automotive vehicle. The structure and mode of functioning of such hydraulic valve lash adjusters having a control valve spring with an opening function are known, per se, particularly also from the aforesaid publications. By way of example, reference is made here to WO 2006 010 413 A1. According to the invention, the tappet 1 additionally comprises a flow control device 23.

In the tappet 1, a cylindrical piston 2 is guided with sealing clearance for axial displacement in a piston housing 4. A low pressure chamber 3 serving as an oil reservoir is configured within the piston 2 and can be supplied with control oil or engine oil through an oil supply, not illustrated. The piston 2 and the housing 4 define a high pressure chamber 5. For adjusting a valve lash, the axial length of the high pressure chamber 5 can be varied by a piston spring 6 that is configured as a coiled compression spring through which the piston 2 and the housing 4 are elastically supported on each other. Said pressure chambers 3 and 5 are connected through an axial opening 7 in the form of a piston bore in a piston bottom 8.

The piston bore 7 can be loaded by a control valve 9 that is arranged coaxially under the piston bore 7 on a piston bottom undersurface 18 of the piston bottom 8. The control valve 9 can be actuated through an alternating high pressure build-up and a pressure equalization between the pressure chambers 3 and 5 as a function of a cyclic cam loading of the tappet 1 during the routine operation of the valve train.

The control valve 9 comprises a valve closing body 10, illustrated separately in FIG. 1d, a control valve spring 11 configured as a coiled compression spring and a closing body cap 12 fixed on the piston bottom undersurface 18 and represented in FIG. 1c in which the closing body 10 is received and whose bottom 16 serves as a stroke limitation for the closing body 10. The construction and the fixing of such a closing body cap on a piston bottom are described, in particular, in the Applicant's DE 10 2004 018 386 A1.

The valve closing body 10 is advantageously configured as an elongate, cylindrical body, a so-called valve needle, with a plate-shaped sealing surface 13 that corresponds to a planar sealing surface 14 of a valve seat 15 surrounding the piston bore 7.

The control valve spring 11 is arranged partially submerged in a central recess 29 of the closing body 10 and is supported between a bottom 33 of the recess 29 and an edge 32 of the axial opening 7, so that in the open state of the valve shown in FIG. 1, the closing body 10 is pressed by a biasing spring force of the control valve spring 11 against the stroke-limiting bottom 16 of the closing body cap 12. In this way, an opening gap corresponding to a closing body stroke 17 is rendered free between the closing body 10 and the valve seat 15 and enables an oil flow between the pressure chambers 3 and 5. To enable a more effective transfer of control oil through the piston bore 7 via the coils of the control valve spring 11 in the open state of the control valve 9, the recess 29 in the closing body 10 may comprise an additional lateral protrusion 31, not specified further.

FIG. 1 a shows the piston 2 of the RSHVA in a separate representation in which two cylindrical recesses 19 and 20 that are configured on the piston bottom undersurface 18 as a stepped continuation of the piston bore 7 can be seen, the diameter of the upper recess 19 being smaller than that of the lower bore 20 but larger than the diameter of the piston bore 7. The closing body cap 12 with its advantageously resilient configuration can be clipped with the help of a collar-like cap flange 21 configured on the closing body cap 12 into the lower recess 20 that is slightly tapered inwards. The piston spring 6 is supported between the cap flange 21 and a bottom 22 of the piston housing 4, so that the closing body cap 12 is additionally fixed on the piston bottom undersurface 18.

The upper, valve seat-proximate recess 19 functions as a medium pressure chamber and constitutes, according to the invention, in operative connection with a flow control element 24, the flow control device 23. The flow control element 24 shown in FIG. 1b is advantageously configured as a disk out of sheet steel. The flow control disk 24 comprises apertures 25 configured as bores. Further, a central bore 26 of the flow control disk 24 serves to receive the closing body 10 with a radial guide clearance.

The flow control disk 24 is fixed to the cap flange 21 on the step of the recess 19. It can also be fixed separately firmly to this step. Through the flow control disk 24, the recess 19 functions as a medium pressure chamber because, due to the apertures 25, the hydraulic pressure build-up is comparatively retarded. The degree of retardation can be determined by the size, geometry and number of bores 25 as also by their positioning relative to one or more recesses 27 of the closing body cap 12 already at the designing stage.

In a tappet 1′ shown in FIG. 2, comprising a control valve 9″, a stepped, cylindrical widening 28 of the axial opening 7 is configured in the piston bottom 8 of a piston 2′ (FIG. 2a). The widening 28 corresponds to a recess 29′ of a closing body 10′ (FIG. 2b), the control valve spring 11 being submerged on both sides in these recesses 28 and 29′ while being supported between an axial edge 34 of the widening 28 and a bottom 33′ of the closing body recess 29′.

FIG. 3 shows a further form of embodiment of a tappet 1″ comprising a control valve 9″ and a piston 2″ (FIG. 3b) in which, in place of the valve needle 10, 10′, a control valve ball 10″ constitutes the valve closing body. The control valve is shown in an open state in FIG. 3 and in a closed state in FIG. 3a. The control valve ball 10″ corresponds to a ball valve seat 15′ and is received in a closing body cap 12′ (FIG. 3c) of comparatively small axial design length. A cap bottom 16′ of the closing body cap 12′ is arched inwards. By pressing the advantageously plastically deformable arching further inwards in axial direction, a closing body stroke of the control valve ball 10″ can be reset.

The control valve spring 11 is supported in opening direction between the control valve ball 10″ and a stepped widening 30 of the piston bore 7. A lateral protrusion 31′ can be additionally configured within the piston bore 7 at the level of the control valve spring 11. The medium pressure chamber 19 of the flow guide device 23 comprises a different remaining free space volume corresponding to the different closing body geometry (FIG. 3, FIG. 3a).

Finally, FIG. 4 shows a fourth form of embodiment with a tappet 1′″, a control valve 9′″ and a flow control device 23′ in which a flow control element 24′ has a pot-shaped configuration. The control valve ball 10″ is received in the pot 24′ so that this assumes the stroke limitation function of the conventional closing body cap. The piston 2′ corresponds to the form of embodiment of FIG. 3.

A central bore 26′ arranged in a bottom 35 of the pot 24′ has a diameter that is smaller than the diameter of the control valve ball 10″. Oil transfer is effected through the apertures 25 in the radial portion of the flow control element 24′ when the ball 10″ is bearing against central bore 26′. When the ball 10″ lifts off the central bore 26′ upon a hydraulic loading, this central bore 26′ is unblocked and made available, in addition to the apertures 25, for the pressure build-up in the medium pressure chamber 19.

The known mode of the functioning of an RSHVA is supplemented with an additional control mechanism, the inventive flow control device 23, 23′:

The open position of the valve in which the closing body 10, 10′, 10″ bears against its stroke limitation corresponds to a camshaft position in the cam base circle of a camshaft rotating in the valve train. Upon a subsequent excursion of a cam lobe, the tappet 1, 1′, 1″ is compressed, so that a pressure build-up is initiated in the high pressure chamber 5. This results in a hydraulic loading of the closing body 10, 10′, 10″ that leads to a flow of control oil from the high pressure chamber 5 in the direction of the low pressure chamber 3. Till the resulting hydraulic force on the closing body becomes high enough to overcome the biasing force of the control valve spring 11, so that the closing body 10, 10′, 10″ lifts off its stroke limitation, that is to say, off the cap bottom 16, 16′ or the pot bottom 35, and comes to bear sealingly against the valve seat 15, 15′, the tappet 1, 1′, 1″ produces an idle stroke through its axial collapsing movement, i. e. it compensates its axial loading.

A pressure differential thus produced in closing direction is controlled by the inventive flow control device 23, 23′. Above the flow control element 24, 24′, a comparatively medium pressure is at first built up in the medium pressure chamber 19 because the flow control element 24, 24′ blocks or weakens a build-up of high pressure like in the rest of the high pressure chamber 5. Due to the apertures 25, the high pressure build-up is retarded because the volume flow or the flow cross-section is reduced compared to an unobstructed oil flow. Accordingly, as a result, the point of time of closing of the control valve 9, 9′, 9″, 9′″ is deferred and the magnitude of the idle stroke is changed. The adjustment or configuration of the apertures 25, if need be, adapted to further parameters like closing body stroke 17, biasing force of the control valve spring 11 and configuration of the recesses 27 in the closing body cap 12, 12′, thus enables a setting of a desired idle stroke.

Claims

1. A hydraulic valve lash adjuster with idle stroke function for a valve train of an internal combustion engine, said hydraulic valve lash adjuster comprising a piston that is guided for displacement in a piston housing and elastically supported against said housing, said piston comprising a low pressure chamber that communicates via an axial opening in a piston bottom with a high pressure chamber defined by the piston housing and the piston, and further comprising a control valve acting between said pressure chambers, said control valve comprising a valve closing body that can be brought to bear sealingly against a valve seat that surrounds the axial opening on a piston body undersurface and is received in an element that limits a closing body stroke, and said control valve further comprising a control valve spring that loads the valve closing body in opening direction, and an idle stroke being produced during an axial collapsing movement between the piston and the piston housing during which said valve closing body is hydraulically loaded in closing direction against the action of the control valve spring by a pressure build-up in the high pressure chamber, wherein a retarded pressure build-up can be obtained through a flow control device arranged on a high pressure chamber-side and comprising a flow control element and a medium pressure chamber that extends between the flow control element and the axial opening.

2. A hydraulic valve lash adjuster of claim 1, wherein the medium pressure chamber is arranged in a stepped recess on the piston bottom undersurface of the piston bottom.

3. A hydraulic valve lash adjuster of claim 1, wherein the flow control element is fixed on the piston bottom undersurface.

4. A hydraulic valve lash adjuster of claim 1, wherein the flow control element is configured as a disk.

5. A hydraulic valve lash adjuster of claim 4, wherein the flow control disk is fixed on the piston bottom undersurface by a cap flange of a closing body cap in which the valve closing body is received.

6. A hydraulic valve lash adjuster of claim 1, wherein, for adjusting the retarded pressure build-up, the flow control element element comprises at least one aperture.

7. A hydraulic valve adjuster of claim 6, wherein at least one aperture is configured as bores.

8. A hydraulic valve adjuster of claim 6, wherein at least one aperture comprises disk-spring-type flaps.

9. A hydraulic valve adjuster of claim 6, wherein at least one aperture comprises latch-type flaps.

10. A hydraulic valve lash adjuster of claim 6, wherein the pressure build-up can be adjusted by a positioning of the at least one aperture of the flow control element relative to one or more recesses of the closing body cap.

11. A hydraulic valve lash adjuster of claim 1, wherein the flow control disk comprises a central bore in which the valve closing body is guided with a guiding clearance.

12. A hydraulic valve lash adjuster of claim 1, wherein the valve closing body is configured as a needle-shaped sealing piston acting through a plate-shaped sealing surface.

13. A hydraulic valve lash adjuster of claim 12, wherein the control valve spring is arranged partially submerged in a central recess of the sealing piston, coaxially to the axial opening and supported between an edge of the axial opening and a bottom of the recess.

14. A hydraulic valve lash adjuster of claim 12, wherein approximately one half of a length of the control valve spring is submerged in a central recess of the sealing piston and another half of the length is submerged in a widening of the axial opening, and the control valve spring is supported between an edge of the widening of the axial opening and a bottom of the recess.

15. A hydraulic valve lash adjuster of claim 1, wherein the valve closing body is configured as a ball.

16. A hydraulic valve lash adjuster of claim 1, wherein the flow control element is configured as a pot comprising apertures, said pot receives the valve control body and acts, at the same time, as a stroke limitation of the valve closing body.

17. A hydraulic valve lash adjuster of claim 16, wherein the flow control pot comprises a central bore whose diameter is smaller than a diameter of the valve closing body.

18. A hydraulic valve lash adjuster of claim 1, wherein a configuration of the aperture or apertures of the flow control element and/or a spring force of the control valve spring and/or the closing body stroke of the valve closing body are matched to one another.

19. A hydraulic valve lash adjuster of claim 1, wherein the flow control element is made of any solid material.