Technical field

This invention relates to a hydraulic tappet.

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.

More specifically, this invention relates to a hydraulic tappet for internal combustion engines comprising a rocker arm supporting a plunger designed to actuate a valve. 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 the rockers to reduce the clearance between the rockers themselves and the valves.

It is basically plungers integrated in telescopic hydraulic means.

The patent documents US 5,622, 147 and US 5,758,613 show two examples of these hydraulic telescopic elements.

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 rocker, as a result of the dimensional limitations imposed by this architecture, these prior art solutions do not allow the making of large high pressure chambers, this implying the reaching of very high pressures with the same force transmitted to the valves.

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.

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 top plan view of a preferred embodiment of the hydraulic tappet made according to this invention;

- Figure 2 is a cross-sectional view of the hydraulic tappet of Figure 1 , according to the plane through the line ll-ll of Figure 1 ;

- Figure 2a is an enlarged view, with some parts cut away in order to better illustrate others, of a detail of Figure 2;

- Figures 3 and 4 are enlarged views of two respective details of the tappet of Figure 2;

- Figures 5 and 6 are respective cross-sectional views, with some parts cut away, of a variant embodiment of the tappet of the preceding drawings, in two different operating configurations.

Detailed description of preferred embodiments of the invention

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

The hydraulic tappet 1 comprises a rocker 2 and a device 3 for recovering the clearance between the tappet and one or more valves, not illustrated, actuated by it.

The rocker 2 has a central hole 4 designed to house a shaft, not illustrated, for oscillation of the rocker 2 about a respective axis A1 of oscillation.

The rocker 2 has a first arm B1 and a second arm B2 positioned, respectively, on opposite sides relative to the central hole 4.

The first arm B1 is designed to support a follower element, not illustrated, configured for engaging, in known manner, with a cam, which is also not illustrated, in a cam-follower mechanism.

The second arm B2 has, at a distal end relative to the central hole 4, a through cavity 5 extending with axial symmetry.

The through cavity 5 extending with axial symmetry has a central axis A2 skew relative to the above-mentioned axis A1 of oscillation of the rocker. As illustrated in Figure 2a, the through cavity 5 has an inner wall 5a, a lower outlet 6 and an upper outlet 7, the latter being longitudinally opposite each other.

The lower outlet 6 of the cavity 5 advantageously has a smaller diameter than that of the upper mouth 7.

At the upper outlet 7 the inner wall 5a has a threaded portion F.

As clearly illustrated in Figures 2, 5 and 6, inside the above-mentioned through cavity 5 is housed the device 3 for recovering the clearance between the tappet and one or more valves, not illustrated, actuated by it.

The device 3 for recovering the clearance comprises a plunger 8 slidably engaged inside the above-mentioned cavity 5 and emerging from it partially at the relative lower outlet 6.

As illustrated in Figures 2 and 5, the portion of the plunger 8 emerging from the lower outlet 6 of the cavity 5 supports an articulated member 9 for pushing the one or more valves, not illustrated, of the internal combustion engine.

As illustrated in Figure 2, the above-mentioned pushing element 9 is advantageously configured, in known manner, in a bell-bottom fashion, and connected to the plunger 8 by means of an articulated ball joint S. The device 3 for recovering the clearance comprises, in the proximity of the above-mentioned upper mouth 7 of the cavity 5, a check valve unit 10 for adjusting a flow of oil circulating inside the above-mentioned cavity 5, a plunger 8 and a first helical spring M1 interposed between the above- mentioned valve unit 10 and the plunger 8.

The valve unit 10 comprises a main body 1 1 having cylindrical dimensions which is located inside the cavity 5 closing the upper mouth 7.

The main body 1 1 has an outer threaded wall 1 1 a and is designed to engage by screwing with the above-mentioned threaded portion F of the wall 5a inside the cavity 5.

According to alternative embodiments of the invention, not illustrated, the main body 1 1 is fixed inside the cavity 5 by friction connection through forced insertion (also known as pressing).

In the preferred embodiment illustrated in Figure 1 , on the upper annular face of the main body 1 1 there are two holes 12, which are diametrically opposite each other, designed to define respective gripping points of a tool for clamping the main body 1 1 .

On the other hand, according to the variant embodiment illustrated in Figures 5 and 6, the main body 1 1 protrudes above the cavity 5 so as to allow the screwing of a ring nut 13 for clamping on the relative outer threaded wall 1 1 a.

Advantageously, with reference to Figures 5 and 6, the ring nut 13 is defined by a locknut.

According to further alternative embodiments, not illustrated, the ring nut has an external thread designed to engage by screwing with the threaded portion F of the wall 5a of the cylindrical cavity 5.

Inside the main body 1 1 there is a space defining an oil storage tank 14. The tank 14 is advantageously cylindrical in shape.

The tank 14 is covered by a specific cover 15 applied at the top, towards the outside.

In the preferred embodiments illustrated in the accompanying drawings, the cover 15 has the shape of a dome.

In its lower part axially opposite the cover 15, a housing 16 is made on the main body 1 1 for a ball 17 for retaining the oil.

The ball 17 is retained inside the housing 16 by a containment cage 16a of substantially known type.

The valve unit 10 comprises a second helical spring M2 positioned at least partly inside the housing 16 and designed to apply a relative elastic action against the ball 17, for pushing the latter away from the tank.

As illustrated in the accompanying drawings and in detail in Figure 4, the plunger 8 has a lower portion 8a (with reference to the relative configuration with respect to the rocker 2) with an approximately hemispherical shape, to engage with the above-mentioned articulated pushing element 9 of the one or more or valves, not illustrated, of the internal combustion engine.

The plunger 8 has an upper end portion 8b with diametric dimensions greater than the lower portion 8a.

The plunger 8 also has an intermediate portion 8c interposed between the above-mentioned upper 8a and lower 8b portions.

The intermediate 8c portion slidably engages with the lower outlet 6 of the cavity 5.

The intermediate portion 8c has diametric dimensions less than the upper portion 8b. At the relative above-mentioned upper portion 8b the plunger 8 supports an annular sealing element 18 mounted on it externally and designed to guarantee the dynamic seal between the plunger 8 and the inside wall 5a of the cavity 5 during the sliding of the plunger 8 along the axis A2.

As illustrated in Figures 2, 5 and 6 with reference to both the embodiments of this invention, inside the through cavity 5 the plunger 8 is positioned with the elative upper portion 8b facing the main body 1 1 of the valve unit 10.

The plunger 8, at the relative above-mentioned upper portion 8b, has inside it a cavity 19 for housing and guiding the above-mentioned first helical spring M1 , the housing cavity 19 being shaped in the form of a cylindrical crown.

In detail, the above-mentioned housing cavity 19, in the shape of a cylindrical crown, is delimited, in the respective internal diameter, by a cylindrical pin 20 coaxial with the plunger 8.

Advantageously, the cylindrical pin 20 is returned inside a hole 21 made in the plunger 8.

Advantageously, the cylindrical pin 20 is made of plastic material.

More specifically, the plunger 8 and the main body 1 1 of the valve unit are mechanically separate, and physically separated along the direction of the axis A2.

In other words, between the plunger 8 and the main body 1 1 is defined a high pressure chamber 22, the chamber 22 having a variable volume as a function of the sliding of the plunger 8.

The chamber 22 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.

The above-mentioned high pressure chamber 22 has the shape of a disc. With reference to Figures 2, 5 and 6, the disc-shaped chamber 22 has diameter substantially equal to that of the plunger 8 at its above- mentioned upper end portion 8b facing the valve unit 10. The variability of the volume of the high pressure chamber 22, consequent to the sliding of the plunger along the cavity 5 according to the direction of the axis A2, advantageously allows, in a substantially known manner, the recovery of any clearance existing between the tappet 1 and the valves, not illustrated, of the internal combustion engine.

Between the tank 14 and the high pressure chamber 22 there is a connecting conduit 23 configured to place them in fluid communication with each other.

The above-mentioned ball 17 is located along the above-mentioned connecting conduit 23 and is designed to obstruct it, under certain operating conditions, that is to say, when the pressure of the oil in the chamber 22 becomes such as to exceed the opposing elastic action exerted on the ball 17 by the second helical spring M2.

In other words, the ball 17 is designed to close the connecting conduit 23 when the pressure in the high pressure chamber 22 is greater than that existing in the tank 14, the second spring helical M2 performing basically the function of preventing unwanted blockages of the ball 17 in its cavity

16.

The spring M2 is designed to keep the ball 17 in a position such as not to obstruct the channel 23 when the pressure in the tank 14 is greater than or equal to the pressure in the high pressure cavity 22.

The check valve unit 10 is of the type normally open.

The spring M2 is configured in such a way as to delay the closing of the check valve unit 10, to allow the plunger 8 to move along the cavity 5 to compensate for any wear and thermal expansion.

Advantageously, the tank 14 is formed integrated in the valve unit 10.

This feature allows a modular and rapid assembly of the hydraulic tappet 1 .

More specifically, according to the preferred embodiments illustrated, the tank 14 is formed integrated in the main body 1 1 of the valve unit 10.

In use, during the normal operation of the internal combustion engine in which the tappet 1 is integrated, oil is fed into the high pressure chamber 22; following this flow of oil, the plunger 8 is pushed to move away from the valve unit 10 until annulling any clearances existing between the rocker and the other components of the internal combustion engine (valves, cams) with which it operates in conjunction.

Figures 5 and 6 illustrate, relative to the second embodiment of the tappet 1 equipped with clamping ring nut 13, two different positions adopted by the main body 1 1 of the valve unit 10.

In particular, Figure 5 shows a condition of maximum screwing of the body 1 1 whilst Figure 6 shows a condition of only partial screwing of the body 1 1 .

In short, the position of the main body 1 1 inside the cavity 5 can be adjusted through different degrees of screwing.

The possibility of varying the relative position of the body 1 1 of the valve unit in the through cavity 5 makes it possible, advantageously, on the one hand, to be able to adapt the tappet 1 to internal combustion engines characterised by different clearances and, on the other hand, to be able in any case to minimise the volume of the high pressure chamber 22.

Different clearances translate, in effect, into different excursions required for the plunger 8 for their compensation and, if the average clearance present in an internal combustion engine for automobiles with average engine sizes is typically about 2.5 mm, the clearance normally present in large diesel engines for lorries is much higher.

With regard to the size of the high pressure chamber, minimising its volume means guaranteeing greater rigidity to the system in its entirety, taking into account the inevitable presence of air in the oil contained inside it (at least in certain operating phases of the motor) and the consequent compressibility.

In other words, the smaller the volume of the high pressure chamber the smaller is the risk of triggering compressive phenomena of the elastic type.

For this purpose, that is to say, limiting the volume of oil inside the chamber 22, a contribution is also provided by the cylindrical pin 20, having, on the one hand, the function of guiding the first spring M1 during the movements of the plunger 8 and, on the other hand, the purpose of occupying the space inside the spring M1 , preventing that this is occupied by an equivalent volume of oil.

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 8 is slidable directly on the through cavity 5 made on the rocker, 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 5a of the cavity 5 as the sliding surface of the plunger 8, 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 5a of the cavity 5 is not even necessary, because the unit 18 can compensate for any imprecisions in the coupling with the plunger 8. The making of the through cavity 5 is therefore particularly inexpensive, as it is performed by boring fully in the rocker 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.

Another advantage resulting from this invention is due to the limitation of the number of components of the tappet: sliding the plunger 8 directly on the inner wall 5a of the cavity 5 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 22 which may in fact extending diametrically to the inner wall 5a of the cavity 5. A greater surface of the high pressure chamber 22 implies small pressures on the components with the same force.

In other words, since the surface of the high pressure chamber 22 is greater, the force transmitted by the rocker 2 to the valves will result in less pressure inside the chamber 22.

A direct consequence of this circumstance is less stress on the components, such as, for example, the valve unit 10 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 rocker on which the clearance recovery device is installed, with consequent reduction in weight and cost of the rocker, which may also be more easily integrated in an existing system.

Moreover, advantageously, with the hydraulic tappet according to the invention, the main body 1 1 of the valve unit is stationary relative to the rocker 2 which it supports, thus guaranteeing a greater overall rigidity of the system.

A further advantage results from the construction of the intermediate portion 8c of the plunger 8 with diametric dimensions less than the upper portion 8b. This configuration allows, in effect, a smaller overall size of the rocker 2 at the lower outlet 6 whilst guaranteeing a considerable diametric size of the high pressure chamber 22. In this way, that is to say, with a large chamber 22, it is possible, with the same force acting on the plunger 8, to lower the pressure value reached inside it, thereby limiting the general mechanical stress of the system.

Yet another advantage, again relative to limiting the number of components of the tappet, is due to the possibility of assembling the same in a modular fashion: inside the cavity 5 there are in fact basically inserted only two components, that is to say, the valve unit 10 and the plunger 8. The ease of assembly of the tappet according to the invention is also due to the fact that the valve unit 10 is physically separate from the plunger 8. Moreover, the valve unit 10 is pre-assembled and advantageously its operation may also be tested before being mounted inside a specific tappet.