Information
-
Patent Grant
-
6553950
-
Patent Number
6,553,950
-
Date Filed
Friday, March 22, 200222 years ago
-
Date Issued
Tuesday, April 29, 200321 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 9012
- 123 9013
- 123 9015
- 123 9016
- 123 9048
- 123 9055
- 123 198 F
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International Classifications
-
Abstract
In an internal-combustion engine with a hydraulic system for variable operation of the valves, the piston for operating each valve includes an auxiliary hydraulic tappet.
Description
BACKGROUND OF THE INVENTION
The present invention relates to internal-combustion engines of the type comprising:
at least one induction valve and at least one exhaust valve for each cylinder, each valve being provided with respective elastic means that bring back the valve into the closed position to control communication between the respective induction and exhaust ducts and the combustion chamber;
a camshaft for operating the induction and exhaust valves of the cylinders of the engine by means of respective tappets;
in which at least one of said tappets controls the respective induction or exhaust valve against the action of said elastic return means via the interposition of hydraulic means including a hydraulic chamber containing fluid under pressure;
said hydraulic chamber containing fluid under pressure being connectable, via a solenoid valve, to an outlet channel for decoupling the valve from the respective tappet and causing fast closing of the valve under the action of respective elastic return means;
said hydraulic means further comprising a piston associated to the stem of the valve and slidably mounted in a guide bushing, said piston being set facing a variable-volume chamber defined by the piston inside the guide bushing, said variable-volume chamber being in communication with the hydraulic chamber containing fluid under pressure by means of an end aperture of said guide bushing, said piston having an end appendage designed to be inserted into said end aperture during the final stretch of the closing stroke of the valve in order to restrict the communication port between said variable-volume chamber and said hydraulic chamber containing fluid under pressure, so as to slow down the stroke of the valve in the proximity of its closing.
An engine of the type referred to above is, for example, described and illustrated in the European patent applications Nos. EP-A-0 803 642 and EP-A-1 091 097 filed by the present applicant.
Studies and tests carried out by the present applicant have shown that some problems may arise during operation, and in particular noise on account of the play that may arise between the various parts both as a result of the constructional tolerances and on account of wear. In particular, it has emerged that in the course of operation of the engine, the ring which functions as a seat for the engine valve and which is received into a cavity of the engine cylinder head may undergo displacements of one or two tenths of a millimeter following upon the continuous impact of the head of the valve against the ring. So far this problem has been solved by using pads for compensating the play.
SUMMARY OF THE INVENTION
The purpose of the present invention is to overcome the above-mentioned problems.
With a view to achieving this purpose, the subject of the invention is an engine having all the characteristics referred to at the beginning of the present description and characterized moreover in that set between the stem of the valve and the aforesaid piston for actuating the valve is an auxiliary hydraulic tappet.
In the practical implementation, the aforesaid auxiliary hydraulic tappet comprises an auxiliary piston which is slidably mounted in the body of the actuating piston, has one end set inside the actuating piston and set facing a chamber within the actuating piston, the said chamber being in communication with the chamber containing fluid under pressure of the system for controlling the valves, and one end set outside the actuating piston, which is in contact with the end of the valve stem, elastic means being provided for bringing back said auxiliary piston into an end-of-stroke position in the direction of the valve stem.
Inside the aforesaid chamber made within the actuating piston, a non-return valve is set which enables passage of fluid under pressure coming from the hydraulic pressure chamber inside the chamber of the auxiliary hydraulic tappet.
As emerges clearly from the foregoing description, in the engine according to the invention, the stem of the valve is not rigidly connected to the actuating piston, given that set between them is the aforesaid auxiliary hydraulic tappet, which is thus able to recover all the possible play that may arise as a result of the fabrication tolerances or wear of the parts.
The arrangement according to the invention may be adopted both for the induction valves and for the exhaust valves, but is particularly useful in the case of the exhaust valves, in that the problems referred to above tend to occur more easily for this type of valve.
BRIEF DESCRIPTION OF THE DRAWINGS
Further characteristics and advantages of the present invention will emerge from the ensuing description, with reference to the attached drawings, which are provided purely by way of non-limiting examples, and in which:
FIG. 1
is a cross-sectional view of the cylinder head of an internal-combustion engine according to the embodiment known from the European patent application EP-A-0 803 642 filed by the present applicant;
FIG. 2
is a cross-sectional view at an enlarged scale of a detail of
FIG. 1
;
FIG. 3
is a cross-sectional view at an enlarged scale of a detail of the engine according to the invention; and
FIG. 4
is a view at an even more enlarged scale of a detail of FIG.
3
.
DETAILED DESCRIPTION OF THE INVENTION
With reference to
FIGS. 1 and 2
, the internal combustion engine described in the prior European patent application No. EP-A-0 803 642, as well as in EP-A-1 091 097, filed by the present applicant is a multi-cylinder engine, for example, an engine with five cylinders set in line, comprising a cylindrical head
1
.
The head
1
comprises, for each cylinder, a cavity
2
formed in the base surface
3
of the head
1
, the said cavity
2
defining the combustion chamber into which two induction ducts
4
,
5
and two exhaust ducts
6
give out. Communication of the two induction ducts
4
,
5
with the combustion chamber
2
is controlled by two induction valves
7
of the traditional poppet or mushroom type, each comprising a stem
8
slidably mounted in the body of the head
1
. Each valve
7
is brought back to the closing position by springs
9
set between an inner surface of the head
1
and an end cup
10
of the valve. Opening of the induction valves
7
is controlled, in the way that will be described in what follows, by a camshaft
11
which is slidably mounted about an axis
12
within supports of the head
1
and which comprises a plurality of cams
14
for operating the valves.
Each cam
14
for operating an induction valve
7
cooperates with the cap
15
of a tappet
16
slidably mounted along an axis
17
, which in the case illustrated is directed substantially at 90° with respect to the axis of the valve
7
(the tappet may also be mounted so that it is aligned, as will be illustrated with reference to FIG.
3
), within a bushing
18
carried by a body
19
of a pre-assembled subassembly
20
that incorporates all the electrical and hydraulic devices associated to operation of the induction valves, according to what is illustrated in detail in what follows. The tappet
16
is able to transmit a thrust to the stem
8
of the valve
7
so as to cause opening of the latter against the action of the elastic means
9
via fluid under pressure (typically oil coming from the engine-lubrication circuit) present in a chamber C and a piston
21
slidably mounted in a cylindrical body constituted by a bushing
22
, which is also carried by the body
19
of the subassembly
20
. Again according to the known solution illustrated in
FIG. 1
, the chamber C containing fluid under pressure associated to each induction valve
7
can be set in communication with an outlet channel
23
via a solenoid valve
24
. The solenoid valve
24
, which may be of any known type suitable for the function illustrated herein, is controlled by electronic control means, designated as a whole by
25
, according to the signals S indicating operating parameters of the engine, such as the position of the accelerator and the engine r.p.m. When the solenoid valve
24
is opened, the chamber C enters into communication with the channel
23
, so that the fluid under pressure present in the chamber C flows into said channel, and a decoupling of the tappet
16
of the respective induction valve
7
is obtained, the said induction valve
7
then returning rapidly into its closed position under the action of the return spring
9
. By controlling the communication between the chamber C and the outlet channel
23
, it is therefore possible to vary the opening time and opening stroke of each induction valve
7
as desired.
The outlet channels
23
of the various solenoid valves
24
all open out into one and the same longitudinal channel
26
, which communicates with one or more pressure accumulators
27
, only one of which can be seen in FIG.
1
. All the tappets
16
with the associated bushings
18
, the pistons
21
with the associated bushings
22
, and the solenoid valves
24
and the corresponding channels
23
,
26
are carried and made in the aforesaid body
19
of the pre-assembled subassembly
20
, to the advantage of speed and ease of assembly of the engine.
The exhaust valves
80
associated to each cylinder are controlled, in the embodiment illustrated in
FIG. 1
, in a traditional way by a camshaft
28
by means of respective tappets
29
.
FIG. 2
illustrates, at an enlarged scale, the body
19
of the pre-assembled subassembly.
FIG. 2
illustrates in detail the makeup of the piston
21
. In a way of itself known, the piston
21
has a tubular body slidably mounted inside the bushing
22
and defining, within said bushing, a variable-volume chamber
34
, which communicates with the chamber C containing fluid under pressure by means of an end central aperture
35
made in the bushing
22
.
In the case of the known solution illustrated in
FIG. 2
, the opposite end of the piston
21
is drive-fitted on an end portion
36
of a stem
37
associated to the stem
8
of the valve
7
. During normal operation, when the cam
14
governs opening of the valve
7
it causes the displacement of the tappet
16
, so bringing about a transfer of fluid under pressure from the chamber C to the chamber
34
and the consequent opening of the valve
7
against the action of the spring
9
. The chamber C communicates with an annular chamber
70
by means of radial holes
71
made in the bushing
18
. The annular chamber
70
communicates with the cylinders associated to the two valves
7
. According to the prior art, fast closing of the valve may be obtained by emptying the chamber C of oil under pressure by means of opening of the solenoid valve
24
. In this case, the valve
7
quickly returns to its closing position under the action of the spring
9
. To prevent any excessively violent impact of the valve
7
against the seat, when the valve
7
is just about to reach its closing position it is slowed down. This result is obtained, again according to the prior art, by hydraulic braking means, which consist of an end central appendage
38
provided on the tubular piston
21
and designed to insert into an aperture in the bottom wall of the bushing
22
during the final stretch of the closing stroke of the valve. During the closing stroke, the piston
21
is displaced upwards (with reference to FIG.
3
), and the variable-volume chamber
34
reduces in volume, so that the oil under pressure is pushed in the direction of the chamber C. When the end appendage
38
of the piston
21
enters the end aperture of the bushing
22
, the return of oil under pressure from the chamber
34
to the chamber C takes place, in the case of the prior art, through the small gaps (not visible in the drawing), caused by the play, which are present between the appendage
38
and the wall of the aperture
35
. The outflow of oil is thus considerably slowed down, and consequently the stroke of the valve is also slowed down. Again according to the prior art, also associated to the cylinder
21
is a non-return valve which comprises a spherical open-close element
39
pushed inside the tubular body of the piston
21
by a spring
40
towards a position in which it obstructs an end central hole
41
of the piston
21
which extends starting from the inner cavity of the piston
21
until it comes out onto the end facing the chamber C. The inner chamber of the piston
21
moreover communicates with side passages
42
that come out onto the end annular surface of the piston
21
, the said surface surrounding the appendage
38
and being set facing the chamber
34
. As has already been said, the structure described above is also known.
Operation of the spherical open-close element
39
is described in what follows. During the closing stroke of the valve
7
, the spherical open-close element
39
is kept in its closing position by the spring
40
and by the pressure of the oil in the chamber
34
. When the chamber C is emptied of oil under pressure by opening of the solenoid valve
20
, the valve
7
quickly returns to its closing position under the action of the spring
9
, except for the fact that it is slowed down immediately prior to closing as a result of the engagement of the appendage
38
in the aperture
35
, so as to prevent any violent impact of the valve against its seat. When the valve is instead opened, to enable a fast transmission of the pressure exerted by the cam
14
via the tappet
16
to the piston
21
, the spherical open-close element
39
is displaced into the open position against the action of the spring
40
as a result of the thrust exerted by the fluid under pressure coming from the chamber C. Opening of the spherical open-close element
39
causes the pressure to be communicated, via the hole
41
and the side holes
42
, directly to the end annular surface of the piston
21
that is set facing the chamber
34
, so as to be able to exert a high force on the piston
21
even when the appendage
38
is still within the aperture
35
.
As already mentioned at the beginning of the present description, the drawback that occurs in the known solution described above lies in the fact that play may be set up between the various parts of the device both on account of the fabrication tolerances and as a result of wear, in particular in the area corresponding to the rings W (FIG.
1
), which function as seats for the heads of the valve, the said heads moving backwards by one or two tenths of a millimeter into their respective seats as a result of the continuous impact of the valves. In the known solutions, this leads to the need to use pads for regulating the play, with all the problems that this solution entails in terms of waste of time and complications.
In order to overcome the above problem, the device for actuating the valve is modified as illustrated in
FIGS. 3 and 4
.
FIG. 3
illustrates a simplified version of the valve-control system, in which the axis of the tappet
16
is aligned with the axis of the stem
8
of the valve (not illustrated in FIG.
3
). In
FIGS. 3 and 4
the parts that are in common with
FIGS. 1 and 2
are designated by the same reference numbers.
As emerges clearly in particular from
FIG. 4
, the body
21
of the actuating piston carries an auxiliary piston
360
, which, unlike the stem
37
of
FIG. 2
, is not rigidly connected to the body
21
. The auxiliary piston
360
is slidably mounted inside the tubular body of the actuating piston
21
with the interposition of a gasket which functions as an end-of-stroke element
101
. The auxiliary piston
360
has one end set inside the actuating piston
21
and set facing a chamber under pressure
102
of an auxiliary hydraulic tappet
100
. The return spring
40
of the spherical open-close element
39
rests against the head of a T bushing
103
which is fixed against an inner shoulder of the piston
21
and which has an internal hole
104
that sets the chamber
102
in communication with the holes
42
, which in turn have the function of providing communication with the chamber C under pressure through the variable-volume chamber
34
. The aforesaid communication of the pressure chamber
102
of the auxiliary hydraulic tappet with the circuit of the oil under pressure is controlled by a non-return valve
105
, which, in the example illustrated, consists of a bushing made of metal material that carries, by means of radial diaphragms (not illustrated), a spherical open-close element
106
, which is elastically pushed into a position for closing a hole
107
made in the bottom wall of the bushing
105
. The spherical open-close element
106
enables passage of oil under pressure in the direction of the pressure chamber
102
while it is closing, so isolating said chamber, to prevent a flow in the opposite direction.
The auxiliary piston
360
has a cap-like end
360
a
set outside the actuating piston
21
, which is in contact with the upper end of the stem
8
of the valve. The auxiliary piston
360
is brought back into an end-of-stroke position, in the direction of the valve stem
8
, by a spring
108
set between the cap-like end
360
a
and the end of the piston
21
facing said cap-like end
360
a.
During operation, the chamber
102
fills up with oil under pressure and consequently ensures that the transmission chain made up of the piston
21
, the auxiliary piston
360
, and the valve stem
8
operates properly, i.e., without any play that might lead to operating defects and/or noise.
Of course, the conformation and arrangement of the auxiliary hydraulic tappet
105
may also be altogether different from the one illustrated in the drawings purely by way of example.
Claims
- 1. An internal-combustion engine comprising:at least one induction valve and at least one exhaust valve for each cylinder, each valve being provided with respective elastic means that brings back the valve into the closed position to control communication between a respective induction and exhaust ducts and a combustion chamber; a camshaft for operating the induction and exhaust valves of the cylinders of the engine by means of respective tappets, in which at least one of said tappets controls the respective induction or exhaust valve against the action of said elastic return means via the interposition of hydraulic means including a hydraulic chamber (C) containing fluid under pressure; said hydraulic chamber containing fluid under pressure being connectable, via a solenoid valve, to an outlet channel for decoupling the valve from the respective tappet and causing fast closing of the valve under the action of respective elastic return means; said hydraulic means further comprising an actuating piston associated to the stem of the valve and slidably mounted in a guide bushing, said piston being set facing a variable-volume chamber defined by the piston and the guide bushing, said variable-volume chamber being in communication with the hydraulic chamber (C) containing fluid under pressure by means of a communication port constituted by an end aperture of said guide bushing, said piston having an end appendage designed to be inserted into said end aperture during a final stretch of a closing stroke of the valve in order to restrict the communication port between said variable-volume chamber and said hydraulic chamber containing fluid under pressure, so as to slow down the stroke of the valve in proximity of its closing, wherein set between the valve stem and the aforesaid piston (21) for actuating the valve is an auxiliary hydraulic tappet, and wherein the aforesaid hydraulic tappet comprises an auxiliary piston slidably mounted inside the body of the actuating piston and having one end that is set inside the actuating piston and set facing a chamber within the actuating piston which is in communication with the hydraulic chamber containing fluid under pressure, and one end set outside the actuating piston, which is in contact with the end of the valve stem, elastic means being provided for bringing back said auxiliary piston into an end-of-stroke position in the direction of the valve stem.
Priority Claims (1)
Number |
Date |
Country |
Kind |
TO2001A000272 |
Mar 2001 |
IT |
|
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