GB2068496A - I.C. engine valve clearance setting device - Google Patents

Abstract

The invention relates to a device for clearance setting in a valve control system of an internal combustion engine, in which the cam 1 acts in order to move the valve stem 2 by way of a bucket 10, there being mounted on the base of the bucket and coaxially thereto two elements 14, 18 interconnected by a screw coupling for setting the clearance. <IMAGE>

Description

SPECIFICATION Clearance setting device for the valve control system of an internal combustion engine This invention relates to a clearance setting device for the valve timing control system of an internal combustion engine, these valves being operated by a cam shaft by way of a bucket type tappet, the device being characterised by being an integral part of the bucket body.

With the bucket type tappet, the necessary clearance between the base contour of the cam and the valve stem is set in most cases by disposing a pad of gauged thickness either inside the bucket and between it and the valve stem, or on the outside of the bucket between -it and the cam.

With both systems, in order to carry out the setting, a set of pads of various thicknesses has to be available. Furthermore, the first method also requires the removal of the cam shaft.

To obviate these drawbacks, it has been proposed to use threaded pins screwed into the body of the bucket and engaging with the valve stem either by way of one of their ends if they are disposed coaxially to the bucket, or by a way of a longitudinal inclined surface which they are provided with if they are disposed substantially perpendicular to the bucket axis.

However, even these two methods are not free from drawbacks. In this respect, the first requires splitting of the cam and possibly also a bore between the two half cams to allow passage of the key with which the threaded pin is screwed in or out. The second has the merit that the pin is easily accessible through a bore provided in the side wall of the bucket, but its drawback is that the minimum clearance which can be set is that obtainable by means of one complete revolution of the pin, because the inclined surface must always be brought into contact with the valve stem, and thus only with a slightly inclined surface and consquently with a fairly long pin can a stepwise setting with very low steps be attained.

The object of the present invention is a clearance setting device which has the advantages of the threaded pin setting systems, but without the drawbacks of the first method, and with the advantage over the second method of allowing an extremely fine and precise setting which is very close to continuous setting, it being of the type comprising extremely low steps, so that the minimum clearance which can be set is very small.

This object is attained according to the invention by a clearance setting device for a valve cam control system of an internal combustion engine, of the type in which a cam moves a bucket slidable in its seat coaxially to the stem of a valve in order to move said stem in opposition to a spring, wherein the base of said bucket element comprises a seat in which a thrust member designed to act on the stem is guided so that it slides axially but is constrained to rotate, and into it there is screwed a threaded pin of a disc which rests on the bucket base in order to collaborate with the cam, resilient means keeping the disc adhering to the bucket.

The setting device is described in detail hereinafter with reference to one embodiment represented by way of non-limiting example on the accompanying drawing, in which the single figure represents a section through the setting device on a plane passing through the axis of the relative valve.

The reference numeral 1 indicates the cam of the control shaft for the valve, of which only the stem indicated by 2 is shown. The reference numeral 3 indicates the internal combustion engine head in which said valve is housed, and the reference numeral 4 indicates the seat of the bucket type tappet disposed between the cam 1 and the valve stem 2. The reference numerals 5 and 6 indicate the normal spiral return springs which urge the valve against its seat. The reference numerals 7, 8 indicate the half cones for fixing the upper spring support cap 9.

The bucket 10 of the valve control tappet has a perforated base 11 , and is provided with an inner annular wall 12 which is grooved longitudinally at 13.

The reference numeral 14 indicates a disc, of diameter not exceeding that of the bucket, disposed between the base wall 11 of the bucket 10 and the cam 1. The disc 14 is provided with a centering step 25 and at least one tooth 1 5-which engages with one of the longitudinal grooves 1 3 of the bucket 10. The disc 14 is also provided with a shank 16 threaded externally at 20 and disposed concentrically to the interior of the annular wall 12 of the bucket. The disc 14 is also provided on its periphery with a set of notches 17 to facilitate its gripping by the tool used to rotate it.

The reference numeral 1 8 indicates a thrust member in the form of a base cap disposed between the valve stem 2 and the shank 1 6 of the disc 14. The base cap 1 8 is provided with an annular projection 1 9 which is threaded internally at 21 and grooved externally at 22 to engage with the longitudinal grooving 1 3 of the bucket 10. The reference numeral 23 indicates a spring disposed between the base cap 1 8 and the base wall 11 of the bucket 10. Finally, the reference numeral 24 indicates recesses provided in the base part 11 of the bucket 10 for the insertion of a tool which enables the bucket to be moved downwards by urging it against the spring 23.

During the normal operation of the valve, the disc 14 and the base cap 18, which are screwed together, are prevented from unscrewing by the effect of the rotation of the valve 2 about its axis by virtue of the fact that both the base cap 1 8 and the disc 14 are constrained to rotate with the bucket 10 by way of the grooved connections 15-13 and 13-22.

In order to set the clearance between the cam 1 and valve stem 2, the bucket 10 is moved downwards against the action of the spring 23 by acting with a tool on the recesses 24 of its base wall 11. In this manner, the grooving 1 3 of the annular wall 12 of the bucket disengages from the tooth 1 5 of the disc 14, whereas it continues to remain engaged with the grooving 22 of the base cap 18, which thus remains at rest. The disc 14, thus released from the bucket 10, can be screwed in or out relative to the base cap 18, and thus moved axially in order to set the correct clearance between the base contour of the cam 1 and the disc 14 (and thus between the cam and valve stem).

The bucket 10 is then left free to return into contact with the disc 14 under the action of the spring 23, so that the nearest of the grooves 13 comes into engagement with the tooth 15 of the disc 14.

If the grooving 13 on the annular wall 12 is constructed in the form of very dense teeth, it is possible to obtain an extremely fine and precise setting very close to continuous setting, because the step between one position of the disc 14 and the next is very small. In this respect, the maximum difference between the required position and that effectively assumed by the disc 14 is at the most equal to the axial movement corresponding to a rotation equal to half the pitch of the teeth of the grooving 1 3.

The frontal coupling system between the disc 14 and the bucket 10 has been shown here as using for simplicity one end of the actual grooved seat in which the thrust element 1 8 slides.

However, any other known type of equivalent frontal coupling system can be used provided it prevents rotation of the disc 14 when it rests on the base of the bucket 10 by the action of the spring 23, the only constraint being that the angular pitch between the various coupling positions is such, according to the objects of the invention, as to correspond to a sufficiently small axial movement between the disc 14 and base cap 18.

Further modifications to the form of the parts can obviously be made to the device illustrated on the drawing and described heretofore by way of example, without leaving the scope of the present invention.

Claims (7)

1. A clearance setting device for a valve cam control system of an internal combustion engine, of the type in which a cam moves a bucket element slidable in its seat coaxially to the stem of a valve in order to move said stem in opposition to a spring, wherein the base of said bucket element comprises a seat in which a thrust member designed to act on the stem is guided so that it slides axially but is constrained to rotate, and into it there is screwed a threaded pin of a disc which rests on the bucket base in order to collaborate with the cam, resilient means keeping the disc adhering to the bucket.

2. A device as claimed in claim 1, wherein a frontal connection is provided between the disc and the bucket base, the connection being releasable by withdrawing the disc from the bucket base against said resilient means.

3. A device as claimed in claim 1, wherein the base of the bucket element extends on the valve side in the form of an annular appendix which constitutes said seat in which the thrust member is guided.

4. A device as claimed in claim 3, wherein said annular appendix is grooved longitudinally in order to engage with the outer surface of the thrust member, which is configured into a complementary manner.

5. A device as claimed in claim 4, wherein said disc comprises, coaxially to the pin, at least one radial tooth arranged to removably engage with one of the grooves of the grooved surface of the annular appendix when the disc rests on the base of the bucket element.

6. A device as claimed in claim 1, wherein said disc is provided on its periphery with a set of notches with which a tool used to rotate it can engage.

7. A device as claimed in claim 1, wherein the bucket element is provided on its periphery with a set of notches with which a tool used for urging it to withdraw from the disc can engage.