Technical field

This invention relates to a hydraulic tappet.

More specifically, this invention relates to a hydraulic tappet comprising a bridge for actuating valves.

The expression hydraulic tappet normally means a tappet equipped with a hydraulic telescopic device, connected to the lubricating circuit of the motor, which, with its travel, is able to automatically recover the clearance existing between the tappet and the valves actuated by it.

The above-mentioned clearance is to be considered the result of multiple components such as, for example, machining tolerances, thermal expansion and wear of parts after their normal use.

Background art

In the distribution systems, which control through the valves the fluid flow into and out from the cylinders of the internal combustion engine, prior art teaches the use of plungers mounted on rockers or on bridges to reduce the clearance between the valves and the components designed for their actuation.

It is basically plungers integrated in telescopic hydraulic means.

These hydraulic telescopic elements of known type are in the form of an assembled cartridge which comprises an outer jacket and an inner plunger engaged slidably with each other.

There is also a valve unit integral n movement with the plunger.

These prior art solutions, even though operatively effective, have been seen to not be free from drawbacks.

Especially in the assembly on a bridge, as a result of the dimensional limitations imposed by this architecture, these prior art solutions do not allow an easy installation, also requiring an increase in size of the bridge itself.

Moreover, the sliding between the jacket and the plunger, which must occur substantially in a sealed fashion, requires the production of a coupling between the two with extremely fine tolerances, thus implying high costs for making these elements.

This drawback is also found with telescopic elements of the type not with a cartridge, where a sliding surface is formed directly in the bridge body as described in US patent 8210144.

Disclosure of the invention

The aim of this invention is provide a hydraulic tappet which is able to overcome the drawbacks of the prior art and which is at same time inexpensive to make, practical to operate and simple to install.

Brief description of the drawings

The technical features of the invention, with reference to the above aims, are clearly described in the appended claims and its advantages are more apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate preferred, non-limiting example embodiments of it, and in which:

- Figure 1 is a schematic side elevation view, with some parts in cross- section and others cut away, of a preferred embodiment of the hinge according to this invention;

- Figure 2 shows a scaled-up detail of the tappet of Figure 1 .

Detailed description of preferred embodiments of the invention

As illustrated in the accompanying drawings, the reference numeral 1 denotes their its entirety parts of a hydraulic tappet for an internal combustion engine (not illustrated), made in accordance with this invention.

The tappet 1 comprises a bridge 2 configured for controlling the movement of two valves, not illustrated, the bridge 2 being actuated in known manner by a rocker, also not illustrated.

The bridge 2 has a central portion 2c and two side arms 2a, 2b extending on both sides from the central portion 2c and designed to engage with respective rods, not illustrated, of respective valves.

More in detail, the above-mentioned and not illustrated valves engage in respective holes 3 made in the respective lower faces of the two arms 2a, 2b of the bridge 2.

With reference to Figures 1 and 2, the bridge 2 has, at its above- mentioned central portion 2c, a blind cylindrical cavity 4 having an inner wall 4a, a bottom wall 4f and an upper outlet 5.

The cylindrical cavity 4 has a central axis A.

The hydraulic tappet 1 comprises a device 6 for recovering the clearance between the tappet and the valves (one or more), not illustrated, actuated by it.

As clearly illustrated in the accompanying drawings, inside the above- mentioned through cavity 4 is housed the device 6 for recovering the clearance between the tappet and one or more valves, not illustrated, actuated by it.

The device 6 for recovering the clearance comprises a plunger 7 slidably engaged inside the above-mentioned cavity 4 and emerging from it partially at the relative upper outlet 5.

The plunger 7 comprises a central body 8 and an upper cover 9.

Inside the main body 8 of the plunger 7, in a suitable recess, is formed a space defining an oil storage tank 10.

The tank 10 is advantageously cylindrical in shape.

The tank 10 is covered by the above-mentioned cover 9 applied at the top, towards the outside.

Advantageously, the cover 9 is fixed to the central body 8 by the interposition of an elastic ring 9a occupying at least partly two circumferential hollows made respectively on the cover 9 and on the body 8 and facing each other.

The upper cover 9 is designed to engage, with known methods and not illustrated nor further described hereafter, with other tappet elements 1 , such as a rocker, for example by a pushing element of the so-called bell- bottom type.

The cover 9 advantageously has a diameter greater than the diameter of the above-mentioned upper outlet 5 of the cylindrical cavity 4, to limit with a shape impediment the stroke of the plunger 7 inside the cylindrical cavity 4.

The device 6 for recovery of the clearance comprises, supported by the central body 8 of the plunger 7, the check valve means 1 1 for adjusting a flow of oil circulating inside the cavity 4.

The device 6 for recovery comprises a first helical spring M1 interposed between the bottom wall 4f of the cylindrical cavity 4 and the central body 8 of the plunger 7.

The first spring M1 is designed to oppose the movement of the plunger 7 inside the cylindrical cavity 4 towards the relative bottom wall 4f.

At the above-mentioned 4f bottom wall of the cylindrical cavity 4 there is, for the hydraulic tappet 1 , a high pressure chamber 12, which has a variable volume as a function of the sliding of the cylindrical plunger 7 inside the cavity 4.

The chamber 12 is defined by high pressure since the oil in it reaches maximum pressure values due to the compression action to which it is subjected in use.

Inside the central body 8 of the plunger 7 there is also formed a connecting conduit 13 configured to place the tank 10 in fluid communication with the above-mentioned high pressure chamber 12.

The above-mentioned valve means 1 1 comprise a ball 14 for retaining the oil interposed between the oil storage tank 10 and the high pressure chamber 12, the ball 14 being designed to close the connecting conduit 13 preventing the circulation of oil inside it.

The ball 14 is housed inside a respective housing 15 made in the central body 8 of the plunger 7.

The tappet 1 also comprises, positioned below the above-mentioned housing 15 a plate 16 for containing the ball 14 inside the housing 15. The valve means 1 1 also comprise a second spring M2 interposed between the connecting conduit 13 and the ball 14, the second spring M2 acting on the ball 14, on the opposite side to the plate 16, to keep it normally moved away from the conduit 13 at least until the pressure of the oil inside the high pressure chamber 12 reaches a predetermined value such as to overcome the force applied by the second spring M2.

In other words, the second helical spring M2 is designed to apply a relative elastic action against the ball 14, for pushing the latter away from the tank 10.

The second spring M2 is housed inside a bushing 17 facing above the oil storage tank 10, the bushing 17 forming, with a respective central hole, the above-mentioned connecting conduit 13.

More in detail, with reference to Figure 2, the ball 14 is designed to obstruct the conduit 13 preventing the passage of oil from the high pressure chamber 12 towards the storage tank 10.

As illustrated in detail in Figure 2, the plunger 7 has a bottom portion 7a with a smaller diametric size, that is to say, less than the remaining upper portion which slidably engages on the inner cylindrical wall 4a of the cavity 4.

At the relative above-mentioned lower portion 7a the plunger 7 houses and supports an annular sealing element 18 mounted on it externally and designed to guarantee the dynamic seal between the plunger 7 and the inner wall 4a of the cavity 4 during the sliding of the plunger 7 along the cavity 4.

Between the lower portion 7a and annular unit 18 there is an annular gap 12a inside of which the oil present in the high pressure chamber 12 flows. Advantageously, the annular sealing unit 18 is of the self-energising type. As described in more detail below, the oil inside the high pressure chamber 12 flows inside the gap 12a and applies on the annular sealing unit 18 a radial force towards the outside, pushing it against the inner wall 4a of the cavity 4. As shown in Figure 2, the containment plate 16 is advantageously shaped in the form of a cup and has a circumferential edge 19 configured to move towards the underside of the above- mentioned annular sealing element 18 with a relative upper face 19a.

Again with reference to Figure 2, the above-mentioned first spring M1 has a relative upper end, consisting basically of a first coil, located in contact with a lower face 19b of the circumferential edge 19.

In use, the variability of the volume of the high pressure chamber 12, consequent to the sliding of the plunger 7 along the cavity 4 according to the direction of the axis A, advantageously allows the recovery of any clearance existing between the tappet 1 and the valves, not illustrated, of the internal combustion engine.

As mentioned, between the oil storage tank 10 and the high pressure chamber 12 there is a connecting conduit 13, configured to place them in fluid communication with each other.

The above-mentioned ball 14 is located along the above-mentioned connecting conduit 13 and is designed to obstruct it, under certain operating conditions, that is to say, when the pressure of the oil in the chamber 12 becomes such as to exceed the opposing elastic action exerted on the ball 14 by the second helical spring M2.

In other words, the ball 14 is designed to close the connecting conduit 13 when the pressure in the high pressure chamber 12 is greater than that existing in the tank 10, the second spring helical M2 performing basically the function of keeping the ball 14 in a position such as not to obstruct the conduit 13 when the pressure in the tank 10 is greater than or equal to the pressure in the high pressure chamber 12. The spring M2 is configured in such a way as to delay the closing of the check valve units 1 1 , to allow the plunger 7 to move along the cavity 4 to compensate for any wear and thermal expansion.

During the normal operation of the internal combustion engine in which the tappet 1 is integrated, oil is fed inside the high pressure chamber 12; following this oil flow, the chamber 12 increases its volume and the plunger 7 is pushed to move away from the bottom wall 4f of the cavity 4, facilitated also by the elastic action of the first spring M1 , until eliminating any clearances existing between the bridge 2 and the other elements of the internal combustion engine with which the bridge 2 operates in conjunction.

After eliminating these clearances, the pushing action exerted by the other elements, not illustrated, of the tappet 1 on the cover 9 determine a simultaneous pushing downwards on the plunger 7 which, if it were not for the closing of the conduit 13 by the ball 14, could lead to a lowering of the plunger. However, thanks to the closing of the connecting conduit 13 (due basically to the action of the fluid friction force on the ball 14 by the oil present in the housing 15), the pressure of the oil inside the chamber 12 increases rapidly until a stopping the relative movement between plunger 7 and bridge 2, thereby improving the effect of transmitting the thrust to the underlying valves.

At the same time, the oil inside the high pressure chamber 12 flows around the annular sealing unit 18, in particular inside the gap 12a, and acts on it by applying forces axially upwards and radially outwards, pushing it against the inner wall 4a of the cavity 4.

The closing action against the inner wall 4a, together with the closing of the conduit 13 described above prevents the flow of oil outside the high pressure chamber 12.

The invention described above achieves the preset aims and brings important advantages.

A first advantage provided by the tappet 1 according to this invention is due to the fact that the plunger 7 is slidable directly on the through cavity 4 made on the bridge, without requiring the presence of any containment jacket as in prior art solutions.

This circumstance, that is to say, the use of the inner wall 4a of the cavity 4 as the sliding surface of the plunger 7, is permitted by the adoption of the dynamic annular sealing unit 18, thanks to which this sliding occurs in a sealed fashion.

Moreover, thanks to the presence of the annular sealing unit 18, a particularly precise machining tolerance (which is costly to achieve) for the inner wall 4a of the cavity 4 is not even necessary, because the unit 18 can compensate for any imprecisions in the coupling with the plunger 7. The making of the through cavity 4 is therefore particularly inexpensive, as it is performed by boring fully in the central portion 2c of the bridge 2 and does not even require, as mentioned, a machining tolerance which is particularly precise, resulting in less costly machining that would be required in the absence of the annular sealing unit 18.

In this regard, the circumstance described constitutes a considerable advantage also due to the problems notoriously widespread in the trade. The extreme precision required in the couplings has in fact forced the manufacturers of the prior art devices to resort to the so-called "select fit" procedure which consists in measuring before assembly all the components produced, dividing them into tolerance classes (that is, groups with similar micrometric measurements), and then assembling the components selected from compatible tolerance classes.

This articulated process is overcome advantageously by the solution according to the invention.

Another advantage resulting from this invention is due to the limitation of the number of components of the tappet: sliding the plunger 7 directly on the inner wall 4a of the cavity 4 means that no additional jacket is in fact required.

The absence of the jacket results in a further advantage: a greater surface area of the high pressure chamber 12 which may in fact extending diametrically to the inner wall 4a of the cavity 4.

A greater surface of the high pressure chamber 12 implies small pressures on the components with the same force.

In other words, since the surface of the high pressure chamber 12 is greater, the force transmitted by the rocker 2 to the valves will result in less pressure inside the chamber 12.

A direct consequence of this circumstance is less stress on the components, such as, for example, the valve units 1 1 or the annular sealing unit 18 which will also be subjected to less wear.

From another viewpoint, the circumstance described above also makes it possible, with an equal surface area of the high pressure chamber, to have overall dimensions less than there would be with a hydraulic telescopic unit of known type with an assembled cartridge (due to the presence, precisely, of the jacket outside the plunger). This reduced size translates into a smaller dimension required for the bridge on which the clearance recovery device is installed, with consequent reduction in weight and cost of the bridge, which may also be more easily integrated in an existing system.