Hydraulic valve lash adjuster for a valve train of an internal combustion engine

Abstract

A hydraulic valve lash adjuster for a valve train of an internal combustion engine, for example for an automotive vehicle, said hydraulic valve lash adjuster comprising a piston (2) that is guided for displacement in a piston housing (4) and elastically supported against said housing, said piston (2) comprising a low pressure chamber (3) that communicates via an axial opening (26) in a piston bottom (19) with a high pressure chamber (5) defined by the piston housing (4) and the piston (2), and further comprising a control valve (6) acting between said pressure chambers (3, 5), said control valve (6) comprising a valve closing body (7) that can be brought to bear sealingly against a valve seat (24) that surrounds the axial opening (26) on a piston body undersurface (28) and is received in a closing body cap (9) whose cap bottom (21) acts as a stroke limitation of the valve closing body (7), and said control valve (6) further comprising a control valve spring (8) that loads the valve closing body (7) in opening direction, and, during a collapsing movement between the piston (2) and the piston housing (4), said valve closing body (7) being hydraulically loadable in closing direction against the biasing force of the control valve spring (8) by a pressure build-up in the high pressure chamber (5).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described more closely in the following with reference to one example of embodiment illustrated in the appended drawings.

FIG. 1 shows a longitudinal section of a portion of an RSHVA comprising a control valve of the invention shown in open position, and

FIG. 2 shows a longitudinal section of a valve closing body of the RSHVA of FIG. 1 on an enlarged scale.

DETAILED DESCRIPTION OF THE DRAWINGS

The RSHVA shown in FIG. 1 is advantageously configured as a hydraulic tappet 1, for example a cup tappet or a roller tappet of a valve train of an internal combustion engine in an automotive vehicle.

The tappet 1 comprises a cylindrical piston 2 that is guided for axial displacement with a sealing clearance in a piston housing 4. A cylindrical recess in the interior of the piston 2 forms a low pressure chamber or oil reservoir 3 that is supplied with control oil through a feed arrangement, not illustrated. A central piston bore 26 arranged in a front end piston bottom 19 of the piston 2 connects the low pressure chamber 3 to a high pressure chamber 5 that is defined by the piston bottom 19 and the housing 4. The axial opening 26 can be loaded by a control valve 6 that controls a control oil exchange between the two pressure chambers 3 and 5.

The control valve 6 comprises a valve closing body 7 configured according to the invention, a control valve spring 8 configured as a coiled compression spring and a closing body cap 9. The control valve spring 8 is supported in direction of the low pressure chamber 3 on a support surface 27 of the piston bore 26 and biases the valve closing body 7 with a spring force in opening direction, i.e. towards the high pressure chamber 5.

For more clarity, FIG. 2 shows an enlarged representation of the valve closing body 7. This is configured as a cylindrical sealing piston that comprises a plate-like sealing surface 10 on its valve seat-side end. On its valve-distal end, the closing body 7 has a flat configuration in a central region 11. The central region 11 is surrounded by a circumferential chamfer that forms a surface of application 12 for the control oil. The invention further provides a dirt-collecting device 13 that is advantageously configured as a cylindrical, valve seat-side central bore in the valve closing body 7 with a bottom-side sink 14 and collects and stores any pollutants flushed in through the oil reservoir 3.

The closing body cap 9 comprises a collar-shaped cap flange 15 with which it is advantageously retained by a clamp joint on the undersurface 28 of the piston bottom 19 in a circular recess 16 that tapers slightly towards the front end of the piston bottom 19. A piston spring 20 configured as a coiled compression spring is supported between the cap flange 15 of the closing body cap 9 and a housing bottom 18 of the housing 4.

The valve closing body 7 is guided with a radial guide clearance in the closing body cap 9 that is filled by the closing body 7 with the exception of a region 17 remaining free due to the chamfer 12 for oil reception and a small volume left free in the region of the cap flange 15. A free space volume of the high pressure chamber 5 is accordingly reduced by the space volume occupied by the closing body 7. Through a cap oil passage 23, for example, in the form of one or more slot-like openings in the side wall region of the closing body cap 9, the oil-receiving region 17 can be fed with control oil from the outer part of the high pressure chamber 5, mainly for the hydrostatic loading of the surface of application 12.

In the open state of the valve shown in FIG. 1, the valve closing body 7 is pressed by the biased control valve spring 8 against a cap bottom 21 of the closing body cap 9, so that the central region 11 of the valve closing body 7 bears flatly with mating contact against the cap bottom 21. The cap bottom 21 acts a stroke limitation for the closing body 7 in the opening direction of the control valve 6. In this way, the width of an opening gap 22 and thus a closing body stroke of the control valve 6 is defined. This position corresponds to a camshaft position in the cam base circle phase.

Upon a loading through a cam lobe of a cam of the rotating camshaft of the internal combustion engine, the piston 2 and the housing 4 are pushed together, so that the RSHVA tappet 1 at first produces an idle stroke during which oil flows through the opening gap 22 and the piston bore 26 into the low pressure chamber 3. At the same time, an increasing hydraulic pressure is built up in the high pressure chamber 5, and this pressure loads the valve closing body 7, more precisely, its surface of application 12, substantially hydrostatically and brings the closing body 7 to bear, against the action of the control valve spring 8, against a flat sealing surface 25 of a valve seat 24 corresponding to the plate-like sealing surface 10 of the closing body 7, so that the control valve 6 closes. Subsequently, further mechanical loading through the cam is transmitted through the now incompressible high pressure chamber 5 to the gas exchange valve to be actuated, and this opens.

With the further rotation of the camshaft, the cam returns relative to the tappet 1 into the cam base circle so that the gas exchange valve closes. The piston spring 20 presses the piston 2 and the housing 4 so far apart that no more lash exists between the tappet 1 and the camshaft, more precisely, the cam. During this time, the pressure in the high pressure chamber 5 falls and the control valve 6 opens, so that control oil can flow into the high pressure chamber 5.

Claims

1. A hydraulic valve lash adjuster 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 a closing body cap whose cap bottom acts as a stroke limitation of the valve closing body, and said control valve further comprising a control valve spring that loads the valve closing body in opening direction, and, during a collapsing movement between the piston and the piston housing, said valve closing body being hydraulically loadable in closing direction against the biasing force of the control valve spring by a pressure build-up in the high pressure chamber, wherein the valve closing body is configured as a needle-shaped, elongate sealing piston whose valve seat-proximate end comprises a plate-shaped sealing surface that cooperates with a correspondingly configured sealing surface of the valve seat and whose valve seat-distal end comprises a surface of application for hydraulic loading, and the valve closing body substantially fills a space volume of the closing body cap surrounding the valve closing body.

2. A hydraulic valve lash adjuster of claim 1, wherein the valve closing body is guided in the closing body cap with a guide clearance.

3. A hydraulic valve lash adjuster of claim 1, wherein a guide means is arranged or configured on the valve closing body and/or the closing body cap.

4. A hydraulic valve lash adjuster of claim 3, wherein the guide means acts as a anti-tilt device and/or a centering means and/or an anti-rotation device of the valve closing body.

5. A hydraulic valve lash adjuster of claim 1, wherein at least a central region of the valve seat-distal, cap bottom-side end of the valve closing body has a shape mating the cap bottom.

6. A hydraulic valve lash adjuster of claim 1, wherein the surface of application is configured as a circumferential chamfer on the valve seat-distal end of the valve closing body and can be hydraulically loaded through an oil passage in the valve body cap.

7. A hydraulic valve lash adjuster of claim 1, wherein a dirt-collecting device is configured in the valve closing body.

8. A hydraulic valve lash adjuster of claim 7, wherein the dirt-collecting device is configured in the valve closing body as a recess that is arranged coaxially to the axial opening and is open on the valve seat-proximate end of the valve closing body.

9. A hydraulic valve lash adjuster of claim 8, wherein the recess is configured as a cylindrical collecting pocket.

10. A hydraulic valve lash adjuster of claim 8, wherein the recess comprises a bottom-side sink.