GB2141512A

GB2141512A - A self-adjusting hydraulic tappet

Info

Publication number: GB2141512A
Application number: GB08406723A
Authority: GB
Inventors: Roberto Barabino; Franco Colanzi
Original assignee: RIV SKF Officine di Villar Perosa SpA; RIV Officine di Villar Perosa SpA
Current assignee: SKF Industrie SpA
Priority date: 1983-04-01
Filing date: 1984-03-15
Publication date: 1984-12-19
Also published as: FR2543614A3; FR2543614B3; GB2141512B; DE8408525U1; IT8353149V0; GB8406723D0; JPS59160803U

Abstract

A self-adjusting hydraulic tappet for the control of a valve in an internal combustion engine is described, comprising a cup-shape body 6 provided with a bottom wall 8 which contacts a cam 9 and a side wall 7 which slides in a corresponding seat in the crankcase of the said engine, the said side and bottom walls 7, 8 defining an internal cavity 10 within the said cup-shape body 6; the tappet includes a closure element in the form of a disc 13 disposed within the said cavity 10 of the cup-shape body 6 in such a way that the said closure element 13 defines a first chamber 14 with the said bottom wall 8 and a first part of the said side wall 7, and a piston element 15 of cylindrical form disposed above the said closure element 13 and slidable within the said cavity 10, the said piston element 15 defining a second chamber 16 with the said closure element 13 and with the other part of the said side wall 7, and valve means 25 disposed on the said closure element 13 operable to put a source of fluid 28 under pressure into communication with the said second chamber 16. <IMAGE>

Description

SPECIFICATION A self-adjusting hydraulic tappet for a heat engine, in particular one in which the valves are controlled via rockers The present invention relates to a self-adjusting hydraulic tappet intended for an internal combustion engine, in paticular an engine of the type in which the valves are operated by a cam shaft and a transmission including rockers.

In such an arrangement, as is known, the transmission of drive from each cam to the associated valve is obtained by means of a transmission system including a push-rod which is operated by the cam, and a reciprocating rocker operated, in turn, by the pushrod. In such a construction an arrangement the tappet is usually disposed between the cam and the lower end of the said push-rod.

As is known, the members which control the opening and closing of the valves are subjected to wear inasmuch as they slide under pressure over one another, and in particular the part of the tappet which is in contact with the cam and which is more easily worn than this, is worn away during operation, thus producing gaps which prevent the complete opening of the valve. Periodically, therefore, it is necessary to obtain a correct adjustment; moreover, the play between the cam and the valve vaies in different operating conditions of the engine, this play depending on the thermal expansion of the members of the drive train interposed between the cam and the valve.

There are, however, mechanisms, usually situated on the tappet, which adjust the play in a continuous and automatic manner as soon as it occurs. There are known tappets intended to be utilised in drive trains of the type first described, wherein the cam shaft is disposed lateraliy of the cylinders, in which the compensation for play is effected by hyrdraulic means. These comprise a substantially cup-shape body provided with a bottom wall which contacts an associated cam and a side wall which can slide in a corresponding seat in the engine crankcase, and a movable element which is slidable within the said cupshape body and against which the said pushrod engages.Within the s aid movable element there is defined a first chamber which is in communication with a source of fluid under pressure via suitable ducts formed in the walls of the element and of the cup-shape body, whilst a second chamber is defined between this movable element and the cup-shape body itself. The two said chambers are in communication with one another by means of a hole formed in the movable element and passage through it is controlled by valve means normally constituted by a small disc or a ball, normally held by the action of a spring against a suitable valve seat. This spring is normally supported by a bush on which a second spring acts, which is interposed between the bottom wall of the cup-shape body and the said movable element.

The oil under pressure is supplied to the first chamber and from it, through the valve means, enters into the second; when the force exerted by the cam acts on the tappet the pressure of the oil contained in the second chamber increases thereby pressing the valve shutter of the valve means against the associated valve seat in such a way as to prevent the passage of oil from the second chamber to the first. Tappets such as those described above have various disadvantages. First of all, they are constructionally very complex and therefore expensive because of the large number of members of which they are composed and because of the numerous grinding operations which are necessary to impart the necessary surface finish to the surfaces of these members to obtain correct operation.

Further, they are not very reliable; in fact, the said springs, being cyclically deformed, are subjected to fatiguing stresses which can bring about breakage thereof.

The object of the present invention is to provide an hydraulic tappet of the type described with a very simple structure and a reliable operation, which will therefore be free from the disadvantages first mentioned.

According to the present invention there is provided a self-adjusting hydraulic tappet for the control of a valve of an internal combustion engine in which this valve is operated by a cam shaft through a transmission mechanism which includes at least one member which contacts the tappet, the said tappet including a cup-shape body provided with a bottom wall for contacting the said cam and a side wall slidable in a corresponding guide in the crankcase of the said engine, the said side and bottom walls defining a cavity within the said cup-shape body, characterised by the fact that it includes a closure element in the form of a disc disposed within the said cavity of the cup-shape body in such a way that the said closure element defines a first chamber with the said bottom wall and a first part of the said side wail, and a piston element of cylindrical form disposed above the said closure element and slidable within the said cavity, the said piston element defining a second chamber with the said closure element and the other part of the said side wall and being provided with a seat able to constitute an abutment for an end of the said member, and valve means disposed on the said closure element operable to put a source of fluid under pressure into communication with the said second chamber for supplying fluid to the interior thereof to press the said piston against the end of the said member.

For a better understanding of the present invention various embodiments thereof will now be described, by way of example, with reference to the attached drawings, in which: Figure 1 is a diagram of the valve control mechanism of an internal combustion engine of which the tappet of the invention forms part; Figure 2 is an axial section through a first embodiment of the tappet of the invention; Figure 3 is an axial section through a second embodiment of the tappet of the invention; and Figure 4 is an axial section through a third embodiment of the tappet of the invention.

The valve control mechanism on which the tappet of the invention can be utilised may be of the type including a rocker 1 and in which the cam-shaft 2 is disposed to one side of the longitudinal axis of the cylinders 3. When such a constructional arrangement is adopted, each valve 4, which can be mounted in the cylinder head as has been shown in Figure 1, or may be a side valve, is operated by a transmission including the tappet 5 which directly contacts the cam 2 and a push-rod 5a one end of which abuts against the tappet itself whilst the other engages one arm of the rocker 1; the valve 4 is normally held in the closed position by a helical spring 4a.

The tappet 5 of the invention comprises a substantially cup-shape body 6 having a substantially cylindrical side wall 7 and a bottom wall 8 which can contact the surface of a cam 9. The said side and bottom walls define a cavity 10 within the cup-shape body 6, which is of substantially cylindrical form.

The tappet further includes a closure element in the form of a disc 1 3 disposed within the cavity 10 in such a way that this element defines with the bottom wall 8, and with the bottom part of the side wall 7 of the cupshape body 6 a first chamber 14; the tappet then includes a piston element 1 5 of substantially cylindrical form disposed above the closure element 1 3 and which is slidable within the cavity 10; this piston element 1 5 defines, with the closure element 1 3 and with the upper part of the side wall 7 of the cup-shape body 6 a second chamber 76.The piston element 1 5 is provided with a seat 1 7 of substantially concave form which can constitute an abutment for an end 1 8 of the pushrod 5a.

Finally, the tappet of the invention includes valve means, generally indicated 25, disposed within the closure element 1 3 and operable to put a source of fluid under pressure into communication with the second chamber 1 6 in such a way as to supply the fluid itself to the interior thereof in a manner which will be explained, to press the piston element 1 5 against the end 18 of the push-rod 5a. The cupshape body 6 is then provided with a substantially annular shoulder 26 which constitutes an abutment for the closure element 1 3 as can be seen clearly in Figure 2, and a hole 27 formed in its side wall 6, which can put the first chamber 1 4 into communication with a further duct 28, in turning communicating with a source of fluid under pressure.

In the embodiments of Figures 2 and 3 the closure element 1 3 is traversed by an axial hole 29 which can put the first chamber 14 into communication with the second chamber 16, and the flow of fluid through this hole is controlled by valve means 25; these latter may include a conical seat 32 for a ball 33 as has been shown in the embodiment of Figure 2, or else a flat seat 34 for a small disc 35 as has been shown in the embodiment of Figure 3. Conveniently, a suitable stop member 36 of annular form provided with suitable arms is inserted in a corresponding annular groove formed above the ball 33 or the disc 35 for the purpose of limiting the upward displacement of these members.

In the embodiment of Figure 4, the com munication between the source of fluid under pressure and the second chamber 1 6 takes place via a hole 40 formed in the part of the side wall 7 of the cup-shape body 6 which surrounds the closure element 13, a radial hole 41 and an axial hole 42 formed in the closure element 1 3. The valve means 25 include a conical seat 43 for a corresponding ball 44 pressed against the seat itself by a helical spring 45.

The operation of the tappet described is as follows.

When it is in a rest condition, illustrated in Figures 2,3 and 4, there is no fluid in the second chamber 1 6 (or it is at atmospheric pressure) and therefore the piston element 1 5 is in its lowermost end-of-stroke position in which at least part of its surface is in contact with the upper surface of the closure element 1 3. As soon as the engine starts to operate oil under pressure arrives at the duct 28 and from this passes through the hole 27 into the first chamber 14.The oil under pressure causes separation of the ball 32 or the disc 35 from its associated seat and enters into the second chamber 16: the quantity of oil which enters into this chamber is that necessary to space the piston element 1 5 axially from the closure element 1 3 sufficient to eliminate play from the transmission between the cam 9 and the push-rod 5a.

During the opening phase of the valve, because of the force applied to the tappet by the cam 9 the pressure within the second chamber 1 6 increases with the consequence that the ball 33 or the disc 35 is pressed against the associated seat preventing the escape of oil from the chamber. In this phase, thereffore, the oil contained in the chamber generates a hydraulic bearing operable to maintain the two cupshape bodies in their correct relative axial positions.

The operation of the embodiment of the tappet shown in Figure 4 is similar to that of the two previous embodiments; in that the oil coming from the duct 28 arrives directly in the chamber 1 6 without traversing a previous chamber (the first chamber 14) which was present in the previously described embodiments.

It has been found that with the tappet described play in the transmission between the cam and the valve is completely eliminated and impacts resulting from the presence of such play are completely suppressed. The time required for such play to be compensated is very short and the second chamber 1 6 fills completely even with very low oil pressures such as those which obtain when the engine is idling. These favourable results are due to the improved sealing action formed between the interception members, and to the absence of springs which require not inconsiderable forces for the opening of the members themselves, and to the minimal influence exerted by inertia effects.

It is evident, then, that the structure of the described tappet is very simple, it being constituted by very few members all of very simple form. Because of this structure the operation of the tappet is also reliable, and since there are no members which are resiliently deformed during operation there is no possibility of breakage due to fatigue.

It is apparent that the tappet described can be utilised with a transmission mechanism between valve and cam different from that described, in which the push-rod 5a is omitted; in this case the rocker 1 or other member of the transmission can directly contact the tappet 5.

Claims

1. A self-adjusting hydraulic tappet for the control of a valve of an internal combustion engine in which the valve is operated by a cam shaft through a transmission mechanism which includes at least one member which contacts the tappet, the said tappet including a cup-shape body provided with a bottom wall for contacting the cam and a side wall slidable in a corresponding guide in the engine crank case, the said side and bottom walls defining a cavity within the said cup-shape body, characterised by the fact that it includes a closure element in the form of a disc disposed within the said cavity of the cup-shape body in such a way that the said closure element defines a first chamber with the said bottom wall and a first part of the said side wall, and a piston element of cylindrical form disposed above the said closure element and slidable within the said cavity, the said piston element defining a second chamber with the said closure element and the other part of the said side wall and being provided with a seat capable of constituting an abutment for one end of the said member, and valve means disposed on the said closure element operable to put a source of fluid under pressure into communication with the said second chamber for supplying the said fluid to the interior thereof tc press the said piston against the end of the said member.

2. A tappet according to Claim 2, characterised by the fact that the said cup-shape body is provided with shoulder means constituting an abutment for the said closure element.

3. A tappet according to Claim 1 or Claim 2, characterised by the fact that at least one hole is formed in the said first part of the said side wall of the said cup-shape body, in communication with the said source of fluid under pressure for supplying oil under pressure to the said first chamber, the said valve means being operable to put the said first and second chambers in communication with one another.

4. A tappet according to Claim 1 or Claim 2, characterised by the fact that there is formed a first hole in the part of the said side wall of the said cup-shape body which surrounds the said disc element, in communication with the said source of fluid under pressure, and there being formed a second radial hole in the said closure element in communication with the s aid first hole, the said valve means being operable to put the said second hole into communication with the said second chamber.

5. A tappet according to Claim 4, characterised by the fact that the said valve means include a ball movable in a seat having an axis substantially coincident with the axis of the said second radial hole, the said ball being biased by a spring.

6. A self-adjusting hydraulic tappet for control of a valve in an internal combustion engine, substantially as described and ill us- trated in the attached drawings.