Title: Gas exchange valve mechanism for an internal combustion engine
Abstract: A gas exchange valve device for an internal combustion engine is provided with a hydraulic apparatus which includes a fluid circuit and at least one pressure reservoir connected to the fluid circuit and containing piston prestressed by a device, and also includes a controllable actuating device. A gas exchange valve is also provided, whose valve element is acted on by the actuating device. In order to achieve a simpler design of the gas exchange valve device the pressure reservoir is disposed so that in an approximately unpressurized state of the pressure reservoir, its piston at least indirectly locks the valve element of the gas exchange valve in an essentially closed position.
Patent Number: 6,848,400 Issued on 02/01/2005 to Gaessler, et al.
| Inventors:
|
Gaessler; Hermann (Vaihingen, DE);
Diehl; Udo (Stuttgart, DE);
Mischker; Karsten (Leonberg, DE);
Walter; Rainer (Pleidelsheim, DE);
Schiemann; Juergen (Markgroeningen, DE);
Grosse; Christian (Kornwestheim, DE);
Beuche; Volker (Stuttgart, DE);
Reimer; Stefan (Markgroeningen, DE)
|
| Assignee:
|
Robert Bosch GmbH (Stuttgart, DE)
|
| Appl. No.:
|
258215 |
| Filed:
|
February 10, 2003 |
| PCT Filed:
|
February 14, 2002
|
| PCT NO:
|
PCT/DE02/00522
|
| 371 Date:
|
February 10, 2003
|
| 102(e) Date:
|
February 10, 2003
|
| PCT PUB.NO.:
|
WO02/06679 |
| PCT PUB. Date:
|
August 29, 2002 |
Foreign Application Priority Data
| Feb 19, 2001[DE] | 101 07 698 |
| Current U.S. Class: |
123/90.12; 123/90.15 |
| Intern'l Class: |
F01L 009/02 |
| Field of Search: |
123/90.12,90.13,90.15
|
References Cited [Referenced By]
U.S. Patent Documents
| 6223846 | May., 2001 | Schechter | 180/165.
|
| 6308690 | Oct., 2001 | Sturman | 123/508.
|
| 6321703 | Nov., 2001 | Diehl et al. | 123/90.
|
| Foreign Patent Documents |
| 37 39 891 | Jun., 1989 | DE.
| |
| 198 26 047 | Dec., 1999 | DE.
| |
| 199 35 871 | Feb., 2001 | DE.
| |
Primary Examiner: Denion; Thomas
Assistant Examiner: Eshete; Zelalem
Attorney, Agent or Firm: Greigg; Ronald E.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a 35 USC 371 application of PCT/DE 02/00522, filed on
Feb. 14, 2002.
Claims
We claim:
1. In a gas exchange valve device (10) for an internal combustion engine
(12), in particular of a motor vehicle, having a hydraulic apparatus (15),
which includes a fluid circuit (38, 42, 46, 54) and at least one pressure
reservoir (62, 72) connected to the fluid circuit (38, 42, 46, 54) and
containing a piston (66, 76) prestressed by device (68, 84), and also
includes a controllable actuating device (16), and having a gas exchange
valve (12) whose valve element (26) is acted on by the actuating device
(16), the improvement wherein the pressure reservoir (72) is disposed so
that in an approximately unpressurized state of the pressure reservoir
(72), its piston (76) at least indirectly locks the valve element (26) of
the gas exchange valve (12) in an essentially closed position, and that
the pressure reservoir is embodied so that in the event of a decrease of
the hydraulic pressure in the fluid circuit, the pressure reservoir can
supply a sufficient fluid volume so that the actuating device can move the
valve element of the gas exchange valve into an essentially closed
position.
2. The gas exchange valve device (10) according to claim 1 wherein, in the
approximately unpressurized state of the pressure reservoir (72), the
piston (76) of the pressure reservoir (72) acts at least indirectly on a
valve shaft (24) of the valve element (26) of the gas exchange valve (12).
3. The gas exchange valve device (10) according to claim 1 wherein a
contact surface (87) at least indirectly connected to the piston (76) of
the pressure reservoir (72) and a contact surface (25) at least indirectly
connected to the valve element (26) of the gas exchange valve (12)
cooperate in a frictionally engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
4. The gas exchange valve device (10) according to claim 2 wherein a
contact surface (87) at least indirectly connected to the piston (76) of
the pressure reservoir (72) and a contact surface (25) at least indirectly
connected to the valve element (26) of the gas exchange valve (12)
cooperate in a frictionally engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
5. The gas exchange valve device according to claim 3 wherein the contact
surface at least indirectly connected to the piston (76) of the pressure
reservoir (72) and/or the contact surface at least indirectly connected to
the valve element (26) of the gas exchange valve (12) are embodied in the
form of a friction surface or surfaces (25, 87).
6. The gas exchange valve device according to claim 4 wherein the contact
surface at least indirectly connected to the piston (76) of the pressure
reservoir (72) and/or the contact surface at least indirectly connected to
the valve element (26) of the gas exchange valve (12) are embodied in the
form of a friction surface or surfaces (25, 87).
7. The gas exchange valve device according to claim 1 wherein the contact
surface (87) at least indirectly connected to the piston (76) of the
pressure reservoir (72) and/or the contact surface (25) at least
indirectly connected to the valve element (26) of the gas exchange valve
(12) cooperate in a positively engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
8. The gas exchange valve device according to claim 2 wherein the contact
surface (87) at least indirectly connected to the piston (76) of the
pressure reservoir (72) and/or the contact surface (25) at least
indirectly connected to the valve element (26) of the gas exchange valve
(12) cooperate in a positively engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
9. The gas exchange valve device according to claim 3 wherein the contact
surface (87) at least indirectly connected to the piston (76) of the
pressure reservoir (72) and/or the contact surface (25) at least
indirectly connected to the valve element (26) of the gas exchange valve
(12) cooperate in a positively engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
10. The gas exchange valve device according to claim 4 wherein the contact
surface (87) at least indirectly connected to the piston (76) of the
pressure reservoir (72) and/or the contact surface (25) at least
indirectly connected to the valve element (26) of the gas exchange valve
(12) cooperate in a positively engaging fashion in the approximately
unpressurized state of the pressure reservoir (72).
11. The gas exchange valve device according to claim 7 wherein a recess
(25) is provided in the valve shaft (24) of the valve element (26) of the
gas exchange valve (12) and an engaging section (87) is at least
indirectly connected to the piston (76) and engages in the recess (25) in
the approximately unpressurized state of the pressure reservoir (72).
12. The gas exchange valve device according to claim 2 wherein a recess
(25) is provided in the valve shaft (24) of the valve element (26) of the
gas exchange valve (12) and an engaging section (87) is at least
indirectly connected to the piston (76) and engages in the recess (25) in
the approximately unpressurized state of the pressure reservoir (72).
13. The gas exchange valve device according to claim 3 wherein a recess
(25) is provided in the valve shaft (24) of the valve element (26) of the
gas exchange valve (12) and an engaging section (87) is at least
indirectly connected to the piston (76) and engages in the recess (25) in
the approximately unpressurized state of the pressure reservoir (72).
14. The gas exchange valve device according to claim 5 wherein a recess
(25) is provided in the valve shaft (24) of the valve element (26) of the
gas exchange valve (12) and an engaging section (87) is at least
indirectly connected to the piston (76) and engages in the recess (25) in
the approximately unpressurized state of the pressure reservoir (72).
15. The gas exchange valve device according to claim 7 wherein a recess
(25)is provided in the valve shaft (24) of the valve element (26) of the
gas exchange valve (12) and an engaging section (87) is at least
indirectly connected to the piston (76) and engages in the recess (25) in
the approximately unpressurized state of the pressure reservoir (72).
16. The gas exchange valve device according to claim 7 wherein the recess
(25) is disposed so that the gas exchange valve (12) is locked in a
slightly open position in the approximately unpressurized state of the
pressure reservoir (72).
17. The gas exchange valve device according to claim 1 wherein the piston
(76) of the pressure reservoir (72) is connected to locking rod (86),
which acts on the valve element (26) of the gas exchange valve (12) in the
approximately unpressurized state of the gas exchange valve (12).
18. The gas exchange valve device according to claim 4 wherein the piston
(76) of the pressure reservoir (72) is connected to locking rod (86),
which acts on the valve element (26) of the gas exchange valve (12) in the
approximately unpressurized state of the gas exchange valve (12).
19. The gas exchange valve device according to claim 11 wherein the piston
(76) of the pressure reservoir (72) is connected to locking rod (86),
which acts on the valve element (26) of the gas exchange valve (12) in the
approximately unpressurized state of the gas exchange valve (12).
20. The gas exchange valve device according to claim 16 wherein the piston
(76) of the pressure reservoir (72) is connected to locking rod (86),
which acts on the valve element (26) of the gas exchange valve (12) in the
approximately unpressurized state of the gas exchange valve (12).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The current invention relates to a gas exchange valve device for an
internal combustion engine, in particular of a motor vehicle, having a
hydraulic apparatus, which includes a fluid circuit and at least one
pressure reservoir connected to the fluid circuit and containing a piston
prestressed by a device, and also includes a controllable actuating
device, and having a gas exchange valve whose valve element is acted on by
the actuating device.
2. Description of the Prior Art
A gas exchange valve device of the above kind is known from DE 198 26 047
A1. Such a gas exchange valve device is used when the internal combustion
engine has no camshaft. An engine of this kind has the advantage that the
control times for the inlet and outlet valves are independent of the
position of the piston of the respective cylinder. Depending on the
operating state of the engine, for example at a high speed, and depending
on the torque desired by the driver, valve opening and closing times can
be achieved, which permit an operation of the engine that is particularly
optimized in terms of emissions and consumption.
The known hydraulic apparatus functions with a hydraulic circuit, which is
supplied from a hydraulic reservoir by means of a high-pressure hydraulic
pump. The actuating device has a hydraulic piston, which can be acted on
in both movement directions and is connected to the valve shaft of the
valve element of a gas exchange valve. By means of 2/2-on/off valves, one
of the two chambers of a hydraulic cylinder can be acted on with a higher
pressure, which leads to a corresponding movement of the piston and
therefore of the valve element in the engine block.
The hydraulic circuit is connected to a hydraulic pressure reservoir, which
is embodied as a spring-loaded piston reservoir and is used to damp
oscillations in the hydraulic system. Furthermore, a similarly embodied
emergency pressure reservoir is connected to one of the two chambers of
the hydraulic cylinder, and in the event of a decrease of the pressure in
the hydraulic line, supplies enough pressure and fluid volume so that the
valve can be moved into its closed neutral position. The two pressure
reservoirs function with different pressure levels, which are set by the
differing rigidities of their restoring springs.
When there is a slight leakage in hydraulic circuit, if the engine to be
supplied is turned off for a long period of time, then it is possible for
both of the pressure reservoirs to empty out completely, which results in
a complete pressure relief of the hydraulic circuit. In order to be able
to keep the valve element of the gas exchange valve in the closed position
even in this instance, the known gas exchange valve device is provided
with an emergency closing spring, which pushes the piston of the actuating
device and therefore also the valve element into the closed position in
the absence of hydraulic pressure.
This assures that when the engine is restarted, the valve element does not
protrude into the combustion chamber in such a way that it can collide,
for example with other valve elements or even with the piston of the
engine that is moving in the combustion chamber. The disadvantage of such
an emergency closing spring, however, is that it is provided solely for
this one special purpose and has no function otherwise. In addition,
integrating the emergency closing spring into the gas exchange valve
device can be problematic due to lack of available space. Finally, the
emergency closing spring increases the hydraulic pressure required to open
the valve element of the gas exchange valve since its closing force must
also be overcome. Therefore, a higher hydraulic pressure and consequently
a higher energy consumption are required in order to open the gas exchange
valve during normal operation.
The object of the current invention, therefore, is to modify a gas exchange
valve device of the type mentioned at the beginning in such a way that it
can be produced more simply and inexpensively and can be operated with the
lowest possible energy costs.
This object is attained in a gas exchange valve device of the type
mentioned at the beginning in that the pressure reservoir is disposed so
that in an approximately unpressurized state of the pressure reservoir,
its piston at least indirectly locks the valve element of the gas exchange
valve in an essentially closed position.
SUMMARY OF THE INVENTION
The invention is based on the fact that the pressure reservoir is embodied
so that in the event of a decrease of the hydraulic pressure in the fluid
circuit, the pressure reservoir can always supply a sufficient fluid
volume so that the actuating device can move the valve element of the gas
exchange valve into an essentially closed position. In order to supply
this fluid volume, the piston of the pressure reservoir moves toward its
unpressurized neutral position due to its initial stress. It reaches this
position when the fluid circuit and therefore also the pressure reservoir
are essentially unpressurized.
According to the invention, this movement of the valve element of the
pressure reservoir is also used for the locking process of the valve
element: namely, the pressure reservoir is disposed so that its piston
releases the valve element of the gas exchange valve when the fluid
circuit exerts pressure on the piston and pushes it out of its neutral
position. In such an operating state, in which the fluid circuit and
consequently also the pressure reservoir are pressurized, the valve
element can move freely and as a result, the engine can also be operated
in a normal fashion.
By contrast, if the pressure in the fluid circuit falls to a value below
the normal operating pressure, then the spring action on the piston pushes
the hydraulic fluid out of the pressure reservoir and the actuating device
closes the valve element of the gas exchange valve. According to the
invention, however, the pressure reservoir is disposed so that when the
piston reaches its unpressurized neutral position and consequently no
fluid volume can be supplied from the pressure reservoir in order to close
the valve element or keep it in its closed position, the piston locks the
valve element of the gas exchange valve in this essentially closed
position.
With the gas exchange valve device according to the invention, an emergency
closing spring is no longer required since the piston of the pressure
reservoir performs the function of locking the valve element of the gas
exchange valve in an essentially closed position in the event of a
pressure loss. The gas exchange valve device according to the invention
can consequently be produced more simply and inexpensively. Moreover, less
hydraulic pressure is required to move the valve element into an open
position since no forces other inertial forces of the valve element need
be overcome.
Advantageous modifications of the invention are also disclosed.
A first modification discloses that the piston of the pressure reservoir
acts at least indirectly on a valve shaft of the valve element of the gas
exchange valve in the approximately unpressurized state of the pressure
reservoir. The valve shaft of the valve element generally has a certain
length, which allows the pressure reservoir to be positioned with
relatively little trouble so that its piston can act on the valve shaft.
However, it is also, for example, conceivable for the piston of the
pressure reservoir to act directly on the actuating device and e.g. for it
to lock the piston of the hydraulic cylinder in a particular position
there.
In this case, it is particularly preferable for a contact surface at least
indirectly connected to the piston of the pressure reservoir and a contact
surface at least indirectly connected to the valve element of the gas
exchange valve to cooperate with frictional engagement in the
approximately unpressurized state of the pressure reservoir. In general,
only very slight forces are required to lock the valve element of the gas
exchange valve in position. Depending on the installation position of the
engine and of the gas exchange valve, it is only necessary to prevent the
valve element of the gas exchange valve from moving out of the closed
position into the open position merely by means of its own weight. This
prevention is possible by means of a simple frictional engagement. An
engagement of this kind can be very simply and inexpensively produced.
It is possible for the contact surface at least indirectly connected to the
piston of the pressure reservoir and/or the contact surface at least
indirectly connected to the valve element of the gas exchange valve to be
embodied in the form of a friction surface or surfaces. This allows the
frictional engagement and consequently the possible holding force to be
improved in a simple manner.
Furthermore, the contact surface at least indirectly connected to the
piston of the pressure reservoir can cooperate in a positively engaging
manner with the contact surface at least indirectly connected to the valve
element of the gas exchange valve in the approximately unpressurized state
of the pressure reservoir. This embodiment is possible alternatively to or
in addition to the frictional engagement mentioned above. A positive
engagement permits an even more reliable locking of the valve element in
the desired position.
In one such particularly preferred modification of the gas exchange valve
according to the invention, the valve shaft of the valve element of the
gas exchange valve is provided with a recess in which an engaging section
at least indirectly connected to the piston of the pressure reservoir
engages in the approximately unpressurized state of the pressure
reservoir. Such a positive engagement can be easily and inexpensively
achieved. Naturally, it is also conceivable for the reverse to be true,
namely, that a recess in a part connected to the piston moves onto a
protrusion provided on the valve shaft of the valve element. It should
also be noted at this point that it is equally possible for there to be a
positively engaging connection with the actuating device, which actuates
the valve element.
The recess can be disposed so that the gas exchange valve is locked in a
slightly open position in the approximately unpressurized state of the
pressure reservoir. This has the advantage of facilitating the starting of
the internal combustion engine. The reason for this is that the starter of
the engine only has to overcome the inertial moments of the moving parts
and does not have to perform any secondary work since the compression work
required for the pressure buildup in the hydraulic circuit only has to be
exerted when the engine is operating. Naturally it should be noted that
the position of the valve element in which the locking takes place is
selected so that there is no danger of the valve element either colliding
with the piston moving in the combustion chamber of the engine or
colliding with the valve elements of other gas exchange valves.
One simple possibility for using the movement of the piston to lock the
valve element in place is comprised in that the piston of the pressure
reservoir is connected to a locking rod, which acts on the valve element
of the gas exchange valve in the approximately unpressurized state of the
gas exchange valve.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention will be explained in detail below in
conjunction with the accompanying drawings, in which:
FIG. 1 shows a schematic representation of a first exemplary embodiment of
a gas exchange valve device of an internal combustion engine;
FIG. 2 shows a partial section through a region of the gas exchange valve
device from FIG. 1, with a valve element and a pressure reservoir; and
FIG. 3 shows a partial section through a valve element and a pressure
reservoir of a second exemplary embodiment of a gas exchange valve device
of an internal combustion engine.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
In FIG. 1, a gas exchange valve device is labeled as a whole with the
reference numeral 10. It includes a gas exchange valve, which in this
instance is embodied as an inlet valve 12 of an internal combustion engine
14.
A hydraulic cylinder 16 actuates the inlet valve 12. This cylinder includes
a housing 18 in which a piston 20 is guided in a sliding faction by means
of a piston rod 22. The piston rod 22 passes through the housing 18 and is
connected to a valve shaft 24, which in turn has a disk-shaped valve
element 26 formed onto it. A region of the surface of the valve shaft 24
is embodied as a friction surface 25 (see FIG. 2). When the inlet valve 12
is closed, the valve element 26 rests tightly against a valve seat 28 in
the upper region of a combustion chamber 30 of the internal combustion
engine 14.
The gas exchange valve device 10 also has a reservoir 34 from which
hydraulic fluid is supplied by a high-pressure pump 36 into a
high-pressure hydraulic line 38. Downstream of a check valve 40, the
high-pressure hydraulic line 38 splits into a branch 42, which feeds
directly into a lower working chamber 44 of the hydraulic cylinder 16 in
FIG. 1 (the terms "above" and "below" in this description only refer to
the depiction in the figures; naturally the parts of the gas exchange
device 10 can be installed in any arbitrary position). Another branch 46
of the high-pressure hydraulic line 38 leads to a 2/2-on/off valve 48,
which a spring 50 presses into its closed position in the currentless
state. Downstream of the 2/2-on/oft valve 48, the branch 46 of the
high-pressure hydraulic line 38 leads to an upper working chamber 52 of
the hydraulic cylinder 16 in FIG. 1. From there, a high-pressure hydraulic
line 54 leads back to the reservoir 34 by means of an additional 2/2-on
off valve 56 and a check valve 58. The 2/2-on/off valve 56 is open in the
currentless state.
A branch line 60, which is connected to a pressure reservoir 62, is also
connected to the point at which the high-pressure hydraulic line 38 splits
into the branch 42 and the branch 46. The pressure reservoir 62 has a
housing 64 that contains a mobile piston 66. A spring 68 acts on the
piston 66 toward the end of the pressure reservoir 62, which is connected
to the branch line 60. The rigidity and spring path of the spring 68 are
selected so that the pressure reservoir 62 can function as an oscillation
damper for pressure fluctuations occurring in the hydraulic lines 38, 42,
46, and 54.
The housing 18 of the hydraulic cylinder 16 has a housing 70 of another
pressure reservoir 72 formed onto it. FIG. 2 shows the embodiment of this
additional pressure reservoir 72 in detail.
The housing 70 contains a cavity 74, which contains a mobile piston 76. The
outer circumference surface of the piston 76 is sealed in relation to the
inner wall of the cavity 74 by means of a sealing ring 78, which rests in
an annular groove 80 in the outer circumference surface of the piston 76.
The cavity 74 is sealed in relation to the outside by a cover 82. The
cover 82 is provided with a ventilation opening that is not shown in the
drawing. A helical spring 84 is clamped between the cover 82 and the
piston 76 and pushes the piston 76 to the left in FIG. 2.
The piston 76 has a locking rod 86 formed onto it, which in the
unpressurized state of the pressure reservoir 72 depicted in FIG. 2,
extends through an opening 88 into a working chamber 90. The valve shaft
24 of the valve element 26 of the inlet valve 12 also passes through the
working chamber 90, extending perpendicular to the longitudinal axis of
the piston 76 and the locking rod 86. Sealing rings 92 and 94 seal it in
relation to the working chamber 90. The axial end of the locking rod 86
oriented toward the valve shaft 24 is embodied as a friction surface. A
branch line 96 leads from the working chamber 90 to the lower working
chamber 44 of the hydraulic cylinder 16.
The helical spring 84 of the pressure reservoir 72 is less rigid and has a
longer spring path that the spring 68 of the pressure reservoir 62. By
contrast with the pressure reservoir 62, the pressure reservoir 72
therefore does not function as an oscillation damper, but as an emergency
pressure reservoir, which as explained in detail below, in the event of a
pressure drop in the hydraulic lines 38, 42, 46, and 54, supplies of fluid
volume that is sufficient to move the valve element 26 of the inlet valve
12 into its closed position.
The gas exchange valve device 10 shown in FIGS. 1 and 2 functions in the
following manner:
The high-pressure pump 36 delivers hydraulic fluid from the reservoir 34
into hydraulic line 38 and from there, via the branch line 42 into the
lower working chamber 44 of the hydraulic cylinder 16. If the on/off valve
48 is open and the on/off valve 56 is closed, then the upper working
chamber 52 of the hydraulic cylinder 60 is also pressurized by the
hydraulic fluid. Since the engagement surface in the axial direction is
greater on the top of the piston 20 than on the bottom, in this instance,
the piston 20 is pushed downward and the inlet valve 12 is opened.
If the on/off valve 48 is closed and the on/off valve 56 is open, then the
upper working chamber 52 is connected to the ambient pressure by means of
the branch line 54, as a result of which the piston 20 is moved upward
again and the inlet valve 12 is closed. In this manner, very rapid opening
and closing times of the inlet valve 12 can be achieved without requiring
a mechanical triggering of the inlet valve 12, for example by means of a
camshaft of the internal combustion engine 14.
During normal operation, when high-pressure pump 36 delivers fluid into the
high-pressure line 38, the pressure prevailing in the lower working
chamber 44 of the hydraulic cylinder 16 is transmitted into the cavity 74
of the pressure reservoir 72 by means of the branch line 96, the working
chamber 90, and the opening 88. The rigidity of the helical spring 84 is
selected so as to allow it to be compressed by the piston 76 in this
instance as a result of the pressure prevailing in the cavity 74 so that
the piston 76 moves toward the right into the position depicted with
dashed lines in FIG. 2.
In this position, the friction surface 87 of the locking rod 86 is spaced
distinctly apart from the friction surface 25 on the valve shaft 24.
Consequently, the valve shaft 74 can freely move the valve element 26 and
the piston 20 of the hydraulic cylinder 16 can freely move the piston rod
22. Since neither the piston 20 nor the valve element 26 is pressed into
the one or the other position by a spring, only a slight hydraulic force
is required to move the valve element 26.
If the pressure in the hydraulic lines 38, 42, 46, and 54 decreases, for
example because the internal combustion engine 14 has been turned off, the
high-pressure pump 36 is therefore no longer delivering, and there is a
leakage in the hydraulic circuit, then the pressure in the cavity 74 of
the pressure reservoir 72 also decreases as a result. With the decreasing
pressure, the helical spring 84 can push the piston 76 of the pressure
reservoir 72 toward the left in FIG. 2. The hydraulic fluid stored in the
cavity 74 is therefore displaced into the lower working chamber 44 by
means of the opening 88, the working chamber 90, and the branch line 96.
Once there, the incoming hydraulic fluid pushes the piston 20 of the
hydraulic cylinder 16 upward again.
It should be remembered that when the engine 14 is turned off, the on/off
valve 56 is without current and open and the upper working chamber 52 of
the hydraulic cylinder 16 is therefore unpressurized. As a result, the
piston rod 22 and the valve shaft 24 move the valve element 26 up again
and press it against the valve seat 28; the work of the piston 76 of the
pressure reservoir 72 thus finally brings the valve element 26 into its
closed position.
When the pressure in the cavity 74 decreases to the ambient pressure, i.e.
the pressure reservoir 72 is unpressurized, the piston 76 reaches its
furthermost position toward the left, which is defined by virtue of the
fact that the friction surface on the end of the locking rod 86 oriented
away from the piston 76 presses against the friction surface 25 on the
valve shaft 24 of the valve element 26. The spring path of the helical
spring 84 is selected so that even in this position of the piston 76 of
the pressure reservoir 72, the helical spring 84 is not completely
relaxed; i.e. it still exerts a force on the piston 76.
The length of the locking rod 86 in turn is selected so that when its
friction surface 87 rests against the friction surface 25 of the valve
shaft 24, the piston 76 does not yet come into contact with the defining
wall of the cavity 74 on the left in FIG. 2. Therefore, the helical spring
84 finally presses the friction surface 87 of the locking rod 86 against
the friction surface 25 on the valve shaft 24 and thus produces a
frictional engagement between these two elements.
This frictional engagement prevents the valve shaft 24 from being able to
move in the axial direction. This in turn means that the valve element 26
is locked in the closed position. In the gas exchange valve device 10
shown in FIGS. 1 and 2, it is therefore assured that when the system is
unpressurized, the valve element 26 is locked in a position in which the
inlet valve 12 is closed. This locking in the gas exchange valve device 10
is achieved without additional components, e.g. an emergency closing
spring. The gas exchange valve device 10 can therefore be easily and
inexpensively produced. Moreover, the piston 20 of the hydraulic cylinder
16 is not prestressed, which results in the fact that during normal
operation of the gas exchange valve device 10, a comparatively low
hydraulic force is required to move the piston 20 of the hydraulic
cylinder 16.
The discussion will now center on FIG. 3, which depicts a region of a
second exemplary embodiment of a gas exchange valve device 10. Those parts
whose function is equivalent to elements shown in FIGS. 1 and 2 are
provided with the same reference numerals. They will not be discussed in
further detail.
By contrast with the exemplary embodiment shown in FIGS. 1 and 2, no
friction surface is provided on the valve shaft 24 shown in FIG. 3.
Instead, a circumferential, V-shaped annular groove 25 is let into the
valve shaft 24. Analogous to this, the end of the locking rod 86 oriented
toward the valve shaft 24 is also not provided with a friction surface,
but has a tip 87, whose edges have the same inclination as the V-shaped
annular groove in the valve shaft 24. When the pressure reservoir is
unpressurized, the tip 87 of the locking rod 86 engages in the annular
groove 25 in the valve shaft 24 and thereby locks the valve element 26 in
a definite position.
The axial position of the annular groove 25 in the valve shaft 24 is
selected so that when the tip 87 of the locking rod 86 engages in the
annular groove 25 in the valve shaft 24, the inlet valve 12 is not
completely closed, but is slightly open. This means that the valve element
26 is lifted up from the valve seat 28. In order to prevent the valve
element 26 from colliding with the piston (not shown) moving in the
combustion chamber 30 of the internal combustion engine 14 or colliding
with other valve elements, the annular groove 25 in the valve shaft 24 is
positioned so that the opening stroke h of the valve element 26 is
approximately 0.5 to 1.0 mm.
In an exemplary embodiment that is not shown, the gas exchange valve device
does not have a separate pressure reservoir for the oscillation damping.
Instead, the oscillation damping function is integrated into the pressure
reservoir that locks the valve element in place in the unpressurized
state. This is achieved by virtue of the fact that the prestressing device
contained in it functions in two stages: in a harder region of the
prestressing device, it performs the oscillation damping function, in a
softer region, it performs the emergency pressure function and the locking
function. This can be achieved, for example, by connecting two springs
with different rigidities in series with each other.
The foregoing relates to preferred exemplary embodiments of the invention,
it being understood that other variants and embodiments thereof are
possible within the spirit and scope of the invention, the latter being
defined by the appended claims.
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