[0001] The present invention refers to an internal combustion engine having a hydraulic
tappet able to prevent any air bubbles which may be present in oil arriving from a
lubricating circuit and made to circulate in an outer reservoir, from reaching an
inner reservoir and possibly the high pressure chamber, since gases tend to exert
an unsteadying or prejudicial effect on the supply of oil to the inner reservoir and
thence to the high pressure chamber, and therefore also on the compensation of play
in the tappet, particularly when the internal combustion engine is restarted after
a period of rest.
[0002] Hydraulic tappets basically comprise a first element, or outer part engaging a driving
cam, an outer reservoir where the oil is first collected, and a second element, or
inner part, telescopically moving inside the first element and in contact with the
stem of one of the valves of the internal combustion engine. An inner reservoir and
a high pressure chamber of variable capacity are formed by the telescopic sliding
of the second element within the first element, such high pressure chamber communicating
with the inner reservoir by means of a check or ball-valve. The invention is conceived
for generally overhead cam drives, where bubbles tend to rise to the parts in the
region driven by the cam.
[0003] One of the drawbacks of this type of tappet is the fact that the oil reaching first
the outer reservoir and then the inner reservoir and the high pressure chamber may
contain air bubbles so that there is less oil than needed in the high pressure chamber
especially when the engine is restarted and therefore play of the tappet cannot be
fully adjusted.
[0004] In order to minimise the drawback of gas, e.g. air bubbles in the oil reaching the
high pressure chamber, provision is made in prior proposals for a duct drawing in
oil from the bottom of the outer reservoir where there is minimum or no air since
air tends to rise. Such a duct is usually complicated and costly to make, but the
invention aims at improving this kind of duct. In order to overcome these drawbacks,
the present invention, in a first embodiment, features an inclined duct extending
from the outside of the inner wall of the outer reservoir towards the inside, and
also extending in an upwards direction to a higher point in the inner reservoir, obtained
by mechanical working on the known inner annular collar provided in the outer part
to separate the outer reservoir from the inner reservoir. This can be obtained by
boring a hole in an element projecting from the collar, e.g. using a drill which is
introduced from the bottom of the outer part, such introduction being enabled by the
fact that the channel forming the outer labyrinth-shaped reservoir is open at the
bottom for the mechanical working and is only closed later, after such duct has been
made, by addition of an annular base.
[0005] According to another embodiment of the present invention, the duct provided in the
collar which is positioned between the labyrinth and the receiving seat for the inner
reservoir is obtained by making suitable grooves and rebates, for instance by milling,
in said inner collar. There is thus provided an L-shaped channel, being a closed portion
in the form of a right-angle in co-operation with an insert able to close the bottom
of the reservoir as in the first embodiment of the invention, wherein a vertical cylindrical
element of the insert fits into the receiving cavity for the telescopically moving
inner part and thus can form a vertical guiding wall for the inner part which slides
inside the outer one. The vertical cylindrical element thus performs two important
functions.
[0006] The present invention will now be described in detail with reference to the attached
drawings wherein:
Figs 1 and 2 show respectively a vertical cross-section and an underneath plan view
of the outer part of the tappet, according to a first embodiment of the invention;
and
Figs 3 and 4 show a vertical cross-section and an underneath plan view of a second
embodiment of the invention.
[0007] There is known a hydraulic tappet comprising an inner part and an outer part. Between
these parts there are defined an outer reservoir, an inner reservoir and a high pressure
chamber, respectively. The oil from the lubrication circuit enters the outer reservoir
via an inlet and then moves into the inner reservoir flowing through suitable openings.
Subsequently, the oil moves into the high pressure chamber as the result of the relative
movement of the telescopically moving parts.
[0008] The oil flowing from the lubrication circuit to the outer reservoir tends to contain
air bubbles which would prejudice the compensating function of the tappet if the bubbles
flowed into the inner reservoir and thence into the high pressure chamber. In order
to avoid this drawback, the oil in the outer reservoir is transferred to the inner
one via a duct which preferably draws it directly from the bottom of the outer reservoir.
Since any air bubbles in the oil tend to rise upwards in the outer reservoir, the
duct inlet will contain reduced or no air contact. However, this concept has been
difficult to put into practice, and the present invention aims to practise it in an
easy and economical way.
[0009] According to one form of embodiment of the invention (Figs 1 and 2), the outer part
10 of the hydraulic tappet consists of a monoblock provided with an inwardly and upwardly
extending inlet duct 12 through which the oil from the lubrication circuit of the
internal combustion engine enters. The oil then arrives in the upper region of an
outer reservoir 14 and flows through a minimum of 180° along a circular path 16 formed
between an outer wall 18 and an inner collar 20 which are integral with the outer
part monobloc, and reaches a position on the right hand side as viewed, which side
is indicated at 22 in Figs 1 and 2. In a position opposite that of the oil inlet duct
12, the collar 20 provides an abutment 24, which is drilled or other mechanically
worked to obtain an upwardly and inwardly inclined duct 26. This working is made possible
by the fact that the bottom of the outer annular reservoir comprises an insert 28
consisting of an annular diaphragm which is not present for the working, being mounted
only after the inclined duct 26 has been formed. Therefore, before positioning insert
28, it has been made possible for the tip of a drill to be inserted from below in
the appropriately inclined direction of the axis 30 of duct 26, in order to enable
production of such duct by boring or drilling in an easy and economical way. As shown
in Fig 1, the inlet of duct 26 is in the lower part of the outer chamber portion 22
and the outlet of duct 26 is located in the upper part of a cavity 32 destined to
receive the parts intended to form the inner reservoir and the high pressure chamber
and intended also to engage the valve stem in a manner compensated for lost motion.
By this means, duct 26 enables oil to be drawn in with minimum or zero air bubbles
even after long standing before a start-up of the engine. After the inclined duct
26 has been formed, the bottom of the outer reservoir is closed by insert of said
annular diaphragm 28, which is made in any suitable material. The inner cylindrical
surfaces 36 and 34 of collar 20 define respectively a receiving cavity and a guide
for the known telescopically moving parts (not shown) of the hydraulic tappet which
form the inner reservoir and the high pressure chamber in known manner.
[0010] According to the second embodiment of the invention (Figs 3 and 4) which aims also
to achieve the same result, e.g. reduce (air) bubbles reaching the inner reservoir,
the function of oil conveying duct 26 of the first embodiment is provided by formation
by mechanical working for example by milling, of a vertical groove 38 in the wall
of a collar 20 likewise formed as a monobloc with outer part 20 and outer wall 18
and inlet channel 12, said collar 20 generally dividing outer and inner reservoirs
14 and 32. The collar 20 separates an outer reservoir labyrinth 22 from a cavity which
receives the telescoping part forming the abutment with the valve stem, the inner
reservoir and the high pressure chamber. A radial groove 40 is provided e.g. milled
in the lower edge of the collar 20. The grooves 38 and 40 generally perpendicular
to each other, together with a preferably metal insert 42 which consists of an upper
and axially extending cylindrical sleeve 44 and an annular and radially extending
lower flange 46, form a duct, which has a closed portion in the general form of a
right- angle, i.e. shaped as a "L", which duct communicates with and draws oil from
the bottom of the outer reservoir. The external periphery of the flange 46 is suitably
secured to the internal vertical surface 48 of the outer wall 18 of the outer part
10, whereas the external surface of the sleeve 44 fits snugly into the internal bore
or cavity formed on the internal surface of collar 20. Therefore, the inner surface
of sleeve 44 acts as a guide for the usual telescopically moving parts of the hydraulic
tappet.
1. An oil tappet comprising an outer part (10) for contact with a driving cam, and
an inner part for contact with the stem of a valve of an internal combustion engine,
said inner part arranged to slide inside the outer part, the two parts together forming
an outer reservoir (14,16,22), a circular passage (16) extending for at least 180°,
an inner reservoir and a high pressure chamber which can communicate with the inner
reservoir via a check valve, characterised in that the outer part (10) of the tappet
is integrated as a monobloc with an inner annular collar (20) and an outer wall (18),
said inner annular collar (20) being generally concentric with the outer wall (18),
the base of the outer reservoir (14,16,22) is provided by an insert (28 or 42) and
the communication between the said passage (16) of the outer reservoir and the inner
reservoir is from an area (22) of the outer reservoir diametrically opposite the oil
inlet (12) of the outer reservoir (14), which is achieved by a region (26; 38,40)
of mechanical working on said inner annular collar (20).
2. A tappet according to Claim 1, characterised in that the base of the outer reservoir
(14,16,22) comprises an annular diaphragm secured to the inner surface of the outer
wall (18) of the outer part (10), and the communication between the outer and the
inner reservoir is made via a duct (26) provided by an oblique channel (26) in the
annular collar (20), this channel (26) extending inwardly and upwardly from a low
position in the outer reservoir at the circumferential location where there is an
abutment (24), the preparation of such channel being carried out before the annular
diaphragm (28) is mounted.
3. A tappet according to Claim 1, characterised in that the base of the outer reservoir
comprises an annular flange (46) of an insert (42) of which a cylindrical sleeve (44)
projects from the annular flange (46), said sleeve (44) acting as a guide for the
telescopically moving parts of the hydraulic tappet, the inner surface of the internal
collar (20) of the outer part (10) being provided with an upwardly extending groove
(38), and the lower outer edge of said collar (20) being provided with a horizontal
generally radial groove (40), whereby such grooves together with the vertical cylindrical
sleeve (44) and with the annular flange (46) of the metal insert (42) form the communication
from the base of the outer reservoir to preferably a higher point of the receiving
cavity for the parts forming the inner reservoir and the high pressure chamber, such
communication thereby being a duct of generally right-angled or L-shaped form.
