U.S. patent application number 10/139056 was filed with the patent office on 2003-04-24 for turbocharger with wastegate.
Invention is credited to Day, Andrew P., McEwen, James Alexander.
Application Number | 20030074898 10/139056 |
Document ID | / |
Family ID | 9914553 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030074898 |
Kind Code |
A1 |
McEwen, James Alexander ; et
al. |
April 24, 2003 |
Turbocharger with wastegate
Abstract
This invention relates to an actuator assembly for a
turbocharger pressure control valve assembly and a method of
assembling a pressure control assembly of a turbocharger. The
assembly comprises an actuator coupled to an actuator rod which in
use is coupled to the valve assembly to control the position
thereof. The actuator rod comprises an elongate member at least a
portion of which is flexible. The actuator rod may be a resilient
member which may be substantially straight when unstressed. In use
the actuator rod may extend in a substantially straight line
between the actuator and the valve assembly.
Inventors: |
McEwen, James Alexander;
(Brighouse, GB) ; Day, Andrew P.; (Huddersfield,
GB) |
Correspondence
Address: |
Gary M. Gron
Law Offices
60701 Cummins Inc.
P.O. Box 3005
Columbus
IN
47202-3005
US
|
Family ID: |
9914553 |
Appl. No.: |
10/139056 |
Filed: |
May 3, 2002 |
Current U.S.
Class: |
60/602 |
Current CPC
Class: |
F02B 37/025 20130101;
F15B 15/10 20130101; F02B 37/186 20130101; F02B 39/00 20130101;
Y02T 10/12 20130101 |
Class at
Publication: |
60/602 |
International
Class: |
F02D 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2001 |
GB |
0111681.3 |
Claims
Having thus described the invention, what is novel and desired to
be secrued by Letters Patent of the United States is:
1. An actuator assembly for a turbocharger pressure control valve
assembly, the actuator assembly comprising an actuator coupled to
an actuator rod which in use is coupled to the valve assembly to
control the position thereof, wherein the actuator rod comprises an
elongate member at least a portion of which is flexible.
2. An actuator assembly according to claim 1, wherein the actuator
rod is a resilient member.
3. An actuator assembly according to claim 2, wherein the actuator
rod is substantially straight when unstressed.
4. An actuator assembly according to claim 1, wherein in use the
actuator rod extends in a substantially straight line between the
actuator and the valve assembly.
5. An actuator assembly according to claim 1, wherein the actuator
rod comprises a sleeveless cable.
6. An actuator assembly according to claim 5, wherein the actuator
rod comprises a multi-strand cable.
7. An actuator assembly according to claim 1, wherein the actuator
is a pneumatic actuator.
8. An actuator assembly according to claim 7, wherein the pneumatic
actuator comprises a spring loaded diaphragm or sliding seal housed
within a pressure chamber, said diaphragm or seal being attached to
a first end of the actuator rod.
9. An actuator assembly according to claim 8, wherein said pressure
chamber is provided with a guide formation adapted to direct force
exerted by the actuator rod on the diaphragm/sliding seal along the
direction of movement thereof.
10. An actuator assembly according to claim 9, wherein said guide
comprises a boss surrounding an opening through which the actuator
rod extends into the pressure chamber.
11. An actuator assembly according to claim 10, wherein the
actuator comprises a sliding seal mounted within said pressure
chamber, and said sliding seal is provided with guide means to
resist any forces tending to pull the sliding seal of its intended
direction of movement.
12. A turbocharger comprising a compressor driven by an exhaust gas
turbine wheel, said turbine wheel being rotatable within a housing
having an inlet for exhaust gas and an outlet downstream of said
turbine wheel, said turbine housing having a passageway that
extends from said inlet to said outlet, thus bypassing said turbine
wheel, said turbocharger further comprising a valve assembly
displaceable between a position blocking flow through said bypass
passageway and another position permitting flow, an actuator, and
an actuator rod connected between said actuator and said valve
assembly to displace said valve assembly, said actuator rod being
elongate and at least a portion of said actuator rod being
flexible.
13. A turbocharger according to claim 13, wherein the end of the
actuating rod remote from said actuator is secured to a lever arm
extending from the valve assembly by way of which the valve is
operated.
14. A turbocharger according to claim 13, wherein said end of the
actuator rod is secured to said lever arm such that there is no
relative movement between the rod and lever arm at the point of
connection.
15. A turbocharger according to claim 14, wherein the actuator rod
is clamped, crimped welded or bonded to said lever arm which is
adapted accordingly.
16. A turbocharger, according to claim 15, wherein the actuator rod
comprises an elongate flexible member.
17. A turbocharger, according to claim 16, wherein the actuator rod
comprises a multi-strand cable.
18. A method of assembling a pressure control assembly of a
turbocharger, the turbocharger comprising a turbine housing and a
compressor, the pressure control assembly comprising a valve
assembly mounted within the turbine housing, a pneumatic actuator
mounted to the turbocharger to receive pressurised air from the
compressor or an external air supply, a flexible actuator rod
extending from the pneumatic actuator, and a lever arm extending
from the valve assembly and the turbine housing and linking the
actuator rod to the valve assembly, the method comprising:
assembling the valve assembly and lever arm on the turbine housing;
assembling the pneumatic actuator and actuator rod as a
sub-assembly; mounting the pneumatic actuator/actuating rod
sub-assembly to the turbocharger; and securing the end of the
actuator rod remote from the pneumatic actuator to the lever
arm.
19. A method according to claim 18, wherein the actuator rod is
secured to the lever arm by one of clamping, crimping, welding or
bonding.
20. A method according to claim 19, wherein prior to securing the
actuator rod to the lever arm, the valve assembly is held in a
closed position by appropriate clamping of the lever arm and said
pneumatic actuator is pressurised to a predetermined pressure,
thereby to determine the minimum pressure at which said valve will
in use begin to open.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a turbocharger incorporating a
wastegate and wastegate actuator, and in particular relates to the
manner in which the actuator is connected to the wastegate.
BACKGROUND OF THE INVENTION
[0002] Turbochargers are well known devices for supplying air to
the intake of an internal combustion engine at pressures above
atmospheric (boost pressures). A conventional turbocharger
essentially comprises an exhaust gas driven turbine wheel mounted
on a rotatable shaft within a turbine housing. For instance, in a
centripetal turbine the turbine housing defines an annular inlet
passageway around the turbine wheel and a generally cylindrical
axial outlet passageway extending from the turbine wheel. Rotation
of the turbine wheel rotates a compressor wheel mounted on the
other end of the shaft within a compressor housing. The compressor
wheel delivers compressed air to the intake manifold of the engine,
thereby increasing engine power.
[0003] Turbochargers incorporating wastegates are also well known.
A wastegated turbocharger has a bypass passageway between the
exhaust inlet and exhaust outlet portions of the turbine housing to
enable control of the turbocharger boost pressure. A wastegate
valve is located in the passageway and is controlled to open the
passageway when the pressure level of the boost air increases to a
predetermined level, thus allowing some of the exhaust gas to
bypass the turbine wheel preventing the boost pressure from rising
further. The wastegate valve is generally actuated by a pneumatic
actuator operated by boost air pressure delivered by the compressor
wheel. The position of the wastegate valve, and thus the amount of
exhaust gas permitted to bypass the turbine wheel, is thus
controlled in direct response to variations in the boost
pressure.
[0004] A conventional pneumatic actuator comprises a spring loaded
diaphragm or sliding seal housed within a canister (referred to as
the wastegate actuator can) which is mounted to the compressor
housing. The diaphragm seal acts on a connecting rod which actuates
the wastegate valve assembly which is mounted in the turbine
housing.
[0005] The actuator can is connected to the compressor outlet via a
hose to deliver boost air to the can which acts on the diaphragm
(or sliding seal) to oppose the spring bias. The spring is
selected, and the actuator and wastegate valve initially set, so
that under low boost conditions the wastegate valve remains closed.
However, when the boost pressure reaches a predetermined maximum
the diaphragm seal is moved against the action of the spring and
operates to open the wastegate valve (via the connecting actuator
rod) thereby allowing some exhaust gas to bypass the turbine
wheel.
[0006] In conventional arrangements the wastegate valve is mounted
on a valve stem which extends through the turbine housing and which
is rotated to open and close the valve. Rotation of the valve stem
is achieved by the reciprocal motion of the actuator rod via a
lever arm which links the end of the actuator rod to the valve
stem. To accommodate the motion of the actuator rod there is a
pivotable joint between the lever arm and the actuator rod, the
opposite end of the actuator lever being secured (typically by
welding) to the end of the valve stem. For accurate operation of
the actuator it is also important that the diaphragm seal maintains
alignment within the canister, and thus that the rod maintains its
alignment along the axis of the actuator can. It is therefore known
to design the pivotal joint between the actuator rod and the lever
arm to allow a slight amount of movement along the axis of the
actuator lever to limit the tendency of the actuator rod to pulled
off-line as it reciprocates.
[0007] The "lift off point", i.e. that pressure at which the
wastegate valve begins to open, is critical to operation of the
wastegate and therefore must be very carefully set when the
actuator and wastegate are assembled to the turbocharger. The
precise actuator can pressure at which the diaphragm begins to move
is dependent upon the preload of the spring used. Unfortunately,
because tolerances to which springs can practically be manufactured
mean that there can be variations in spring rate from one spring to
the next, it is necessary to set the lift off point of each
turbocharger individually.
[0008] One method of carrying out the initial set up of the
conventional actuator assembly described above, is a process known
as "weld to set". The actuator can, actuating rod and actuator
lever are pre-assembled, and mounted to the turbocharger. The
wastegate valve is then clamped shut from within the turbine
housing and the actuator can is pressurised to the desired lift off
pressure. With the diaphragm, actuator rod and valve thus held in
their respective relative positions immediately prior to lift off,
the end of the actuator lever welded to the valve stem.
Accordingly, any increase in the pressure supplied to the actuator
above the predetermined lift off pressure will cause the valve to
open.
[0009] A known alternative to the above is to use an adjustable
length actuator rod, typically comprising a threaded rod and rod
end. The set point is achieved by adjusting the length of the rod,
either by turning the rod end or a nut captured in the rod end
assembly.
[0010] European patent publication number 0 976 919 discloses a
two-part actuator rod which overcomes many of the disadvantages of
the conventional actuator rod described above. The two parts of the
rod are connected via a spherical joint located towards the
wastegate end of the rod which allows rotational freedom between
the end of the rod connected to the actuator and the end of the rod
connected to the actuator lever. This arrangement greatly
simplifies initial set up by obviating the need to pre-assemble the
lever to the actuator rod (the lever instead being pre-assembled to
the wastegate valve stem) or the need to provide an adjustable
length rod. However, both of the above actuator assemblies suffer
the disadvantage that the respective pivotable joints add to the
component cost and provide a site for wear to occur.
OBJECT OF THE INVENTION
[0011] Accordingly, it is an object of the present invention to
provide an actuating assembly for a turbocharger wastegate which
overcomes problems associated with conventional arrangements
discussed above. In particular it is an object of the present
invention to provide an improved actuator rod.
SUMMARY OF THE INVENTION
[0012] According to a first aspect of the present invention there
is provided an actuator assembly for a turbocharger pressure
control valve assembly, the actuator assembly comprising an
actuator coupled to an actuator rod which in use is coupled to the
valve assembly to control the position thereof, wherein the
actuator rod comprises an elongate member at least a portion of
which is flexible.
[0013] According to a second aspect of the present invention there
is provided a turbocharger including a pressure control assembly
comprising an actuator, a valve assembly, and an actuating rod
connected between the actuator and the valve assembly, the actuator
controlling operation of the valve assembly via the actuator rod,
wherein the actuator rod comprises an elongate member at least a
portion of which is flexible.
[0014] Preferably the actuator rod comprises a multi-strand cable
e.g. a steel cable.
[0015] The provision of a flexible actuator rod offers a number of
advantages over conventional rigid actuator rods as is discussed in
more detail in the following description. It is to be understood
that the degree of flexibility could vary from one embodiment of
the invention to another. Preferably the rod is sufficiently
flexible to flex under normal operating conditions as it moves to
actuate the valve assembly, but not, for instance, to flex
significantly under force of gravity if held at one end only. The
rod need not be flexible along its entire length although preferred
embodiments are flexible at least along a substantial portion of
the length of the rod.
[0016] According to a third aspect of the present invention there
is provided a method of assembling a pressure control assembly of a
turbocharger, the turbocharger comprising a turbine housing and a
compressor, the pressure control assembly comprising a valve
assembly mounted within the turbine housing, a pneumatic actuator
mounted to the turbocharger to receive pressurised air from the
compressor or an external air supply, a flexible actuator rod
extending from the pneumatic actuator, and a lever arm extending
from the valve assembly and the turbine housing and linking the
actuator rod to the valve assembly, the method comprising:
[0017] assembling the valve assembly and lever arm on the turbine
housing;
[0018] assembling the pneumatic actuator and actuator rod as a
sub-assembly;
[0019] mounting the pneumatic actuator/actuating rod sub-assembly
to the turbocharger; and
[0020] securing the end of the actuator rod remote from the
pneumatic actuator to the lever arm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Specific embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0022] FIG. 1 is an axial cross-section through a conventional
turbocharger illustrating the major components of a
turbocharger;
[0023] FIG. 2 illustrates details of a conventional turbocharger
wastegate valve and actuator assembly;
[0024] FIG. 3 is a perspective view of a wastegate valve actuator
assembly in accordance with an embodiment of the present
invention;
[0025] FIG. 4 shows a detail of the actuator assembly of FIG.
3;
[0026] FIG. 5 is a further perspective view of the actuator
assembly of FIG. 3, looking in the direction of arrow A on FIG. 3
and with part of the actuator can cut away to reveal internal
detail; and
[0027] FIG. 6 shows internal details of the actuator can of FIGS. 4
and 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Referring first to FIG. 1, this illustrates the basic
components of a conventional centripetal type turbocharger. The
turbocharger comprises a turbine 1 joined to a compressor 2 via a
central bearing housing 3. The turbine 1 comprises a turbine
housing 4 which houses a turbine wheel 5. Similarly, the compressor
2 comprises a compressor housing 6 which houses a compressor wheel
7. The turbine wheel 5 and compressor wheel 7 are mounted on
opposite ends of a common shaft 8 which is supported on bearing
assemblies 9 within the bearing housing 3.
[0029] The turbine housing 4 is provided with an exhaust gas inlet
10 and an exhaust gas outlet 11. The inlet 10 directs incoming
exhaust gas to an annular inlet chamber 12 which forms a volute
surrounding the turbine wheel 5. The exhaust gas flows through the
turbine and into the outlet 11 via a circular outlet opening which
is coaxial with the turbine wheel 5.
[0030] Referring now to FIG. 2, this illustrates components of a
conventional prior art wastegate valve and actuator assembly which
is not visible from FIG. 1. The turbine housing 4 is provided with
a bypass passageway (not shown) which communicates between the
exhaust inlet 10 and the exhaust outlet 11 bypassing the turbine
wheel 5. The bypass passageway communicates with the exhaust inlet
10 via a circular opening (not shown) which is opened and closed by
a valve member 13a of a wastegate valve 13 provided for controlling
the flow therethrough. In FIG. 2 the part of the turbine housing 4
defining the inlet 10 is shown partially cut away to reveal details
of the wastegate valve 13 which is operated by rotation of a valve
stem 14 which extends through a bush 14a in the turbine housing
5.
[0031] Rotation of the valve stem 14, and thus actuation of the
wastegate valve 13, is achieved by an actuator assembly mounted on
the outside of the turbocharger and comprising a spring loaded
pneumatic actuator 15 which is linked to the valve stem 14 via a
connecting rod 16 and actuating lever 17. The actuator can 15
receives compressed air from the outlet of the compressor 2 and
thus is conventionally mounted to the outside of the compressor
housing 6 by an appropriate bracket (not shown). Details of an
appropriate mounting arrangement are omitted from FIG. 2 for
simplicity but may be entirely conventional.
[0032] The actuator 15 comprises a diaphragm or sliding valve (e.g.
piston), not shown, mounted within a cylindrical canister (the
actuator can) 18 on one end of the actuator rod 16. The actuator
rod 16 extends from the front of the actuator can 15 towards the
turbine housing 4 and wastegate valve 13. In FIG. 2 the actuator
can is shown cut away to reveal detail of a coil spring 19 mounted
coaxially around the actuator rod 16 and acting between the
diaphragm/sliding seal (not shown) and the front end of the
actuator can 18. The coil spring 19 thus biases the actuator rod
towards the rear of the actuator can 18.
[0033] The actuator rod connects the diaphragm/seal of the actuator
15 to the wastegate valve 13 via the lever arm 17. The end of the
actuator rod 16 is connected to the actuator lever 17 via a pivotal
connection 20 to allow relative movement between the two whereas
the lever 17 is fixed to the valve stem 14, typically by welding as
mentioned above.
[0034] In use, the wastegate valve 13 will in low boost conditions
be held closed by the action of the spring 19. However, once the
pressure in the compressor outlet reaches a predetermined limit,
the pressurised air transmitted to the actuator 15 forces the
diaphragm/seal to move against the action of the spring 19 thereby
opening the wastegate valve 13 to allow inlet exhaust gas to bypass
the turbine. In this way, the maximum boost pressure produced by
the turbocharger can be controlled and limited.
[0035] In the illustrated example, the actuator rod 16 is of
adjustable length. That is, the actuator rod 16 has two portions
which can be moved relative to each other by rotation of an
adjusting nut 16a to lengthen or shorten the rod. This allows the
length of the rod to be adjusted at initial set up to ensure that
at the "lift off" pressure, i.e. that pressure at which the valve
begins to open, the actuator rod 16 is properly aligned with the
axis of the actuator 15 (provided the actuator can is itself
correctly mounted to the compressor).
[0036] FIGS. 3 to 6 illustrate an embodiment of an actuator
assembly in accordance with the present invention which overcomes a
number of disadvantages of the conventional arrangement described
above. Essentially, the actuator assembly comprises a pneumatic
actuator 21 an actuator rod 22 and an actuating lever 23. The
actuator 21 may be entirely conventional and may be mounted to the
compressor housing in a conventional way so as to receive air from
the compressor outlet via an inlet pipe 21a. The fundamental
differences between the actuator assembly of the invention and the
conventional system described above lie in the nature of the
actuating rod 22 and its manner of connection to the suitably
modified lever 23.
[0037] In accordance with the invention, the actuating rod 22 is
flexible, comprising in this embodiment a multi-strand steel cable.
The actuator end of the rod 22 is secured within one end of a steel
sheath 24 (for instance by crimping) the other end of which is
secured to a piston rod 25 (again by crimping or welding etc). The
piston rod 25 supports a piston 26 which is slidable along the axis
of the actuating can 27. A coil spring 28 is mounted between the
piston 26 and the front end of the actuating can 27 to bias the
piston 26, and thus actuator rod 24, towards the rear of the
actuator can 27 thereby holding the valve assembly in a closed
position. The actuator is provided with an actuator rod guide 29 in
the form of a cylindrical boss which receives the end of the sleeve
24 which extends into the actuator can 27. This ensures that the
actuator rod is effectively orientated along the axis of the
actuator can 27 at its point of entry into the actuator. This helps
ensure that the force exerted on the piston rod 25, and thus piston
26, by the tension in the actuator rod 22 acts along the axis of
the actuator can 27, i.e. in the direction of movement of the
piston 26, even if the actuator is misaligned with the actuating
lever 23. An additional guide 30 surrounds the piston 26 to further
prevent the piston being pulled off-axis as it moves within the
actuator can 27.
[0038] The opposite end of the actuator rod 22 is secured to the
lever 23 which is formed as a clamp. Pressure is applied to the end
of the actuator rod 22 to hold it firmly in position by tightening
a clamping nut 24. The lever 23 further defines an aperture 25
enabling connection of the lever arm to the wastegate valve stem,
for instance by the conventional method of welding the lever to the
valve stem 14.
[0039] Provision of a flexible actuator rod in accordance with the
invention is based on the realisation that the actuator rod is in
fact always in tension since the wastegate valve is always biased
towards an open position against the action of the actuator spring
by the gas pressure within the exhaust gas inlet. Thus, when moving
the valve from a closed to an open position it is not actually
necessary to push the valve open (as with the action of a
conventional rigid actuator rod) but rather simply to allow the
valve to open under the pressure of the exhaust inlet gas. Adoption
of a flexible actuator rod therefore has no detrimental effect on
the basic operation of the actuator assembly and instead provides a
number of benefits over conventional rigid actuating rods.
[0040] The ability of the actuator rod to flex obviates the need to
provide a pivotal connection between the actuator rod and the
actuating lever as with the conventional arrangement described
above, or to provide a spherical joint as with the actuator rod
described in European patent publication number 0 976 919 (as
mentioned above). This reduces the number of components needed in
manufacture of the actuating assembly and removes the pivotal
joints which can wear during use.
[0041] The need for an adjustable length actuator rod is also
obviated since the effective length of the rod (i.e. the length of
the rod extending between actuating the lever and the actuator) is
determined at set up.
[0042] The flexible nature of the actuator rod allows for a certain
degree of missalignment between the actuator 15 and the wastegate
valve assembly without exerting significant off-axis force on the
actuator diaphragm/sliding seal etc. This further reduces the cost
and complexity of manufacture by increasing manufacturing
tolerances of the various components and simplifying assembly.
[0043] A further significant advantage of a flexible actuating rod
is that it can provide a degree of damping between the wastegate
valve assembly and the actuator. In the particular embodiment
described in which the actuator rod is a multi-strand cable, energy
is dissipated through friction as strands of the cable rub together
as the cable flexes. This damps the vibration caused by fluttering
of the wastegate valve as the pressure within the exhaust gas inlet
which fluctuates is a recognised problem of conventional wastegate
actuator assemblies.
[0044] It will be appreciated that many modifications may be made
to the embodiment of the invention described above. For instance,
the actuator rod end may be connected to the actuating lever by any
appropriate means and not just by clamping as illustrated.
Preferred means allow the effective length of the actuator rod to
be determined at initial set up and include alternatives such as
welding (or otherwise bonding) or crimping. The actuator lever
itself can be of any desired configuration suitable for the chosen
connection method and the location of the valve assembly.
[0045] The actuator rod itself need not be a multi-strand steel
cable. Multi-strand cables are preferred because of the improved
damping offered by interaction of the cable strands. However, other
cable materials may be employed including other metals and
synthetic materials including plastics fibres. The cable may for
instance be a composite of fibres of different materials.
[0046] As mentioned above, the actuator rod need not be a cable but
could comprise an essentially single piece rod but having the
required flexibility. Such a rod may have the dimensions of a
conventional rod but be fabricated from material with the required
inherent flexibility. Alternatively, a suitable rod can be
manufactured from a conventional material, such as steel, but made
thinner than a conventional rod to again provide the required
flexibility. The appropriately skilled person will appreciate the
many possible variations.
[0047] Moreover, the rod need not be flexible along its entire
length. For instance a rod comprising one or more flexible portions
joined to one or more rigid sections could be used. An essentially
single piece flexible rod, possibly with connecting end pieces
(such as the sleeve 24 of the illustrated example), is however
preferred for mechanical simplicity.
[0048] As mentioned above, the actuator may be entirely
conventional. However, in the illustrated embodiment the actuator
is modified by the provision of the actuator rod guide 29 and
piston guide 30. It will be appreciated that the exact form of
these guides may vary considerably. Furthermore one or both of
these guides could be omitted, particularly if steps are taken to
ensure the actuator is correctly aligned with the actuator lever as
with conventional assemblies. In addition, whereas in the
illustrated example the actuator rod 22 is connected to the piston
26 via a piston rod 25 it will be appreciated that the actuator rod
22 could extend through the sleeve 24 and be connected directly to
the piston. Indeed, the sleeve 24 could be omitted entirely.
[0049] Again, it will be appreciated that many modifications could
be made to the detailed design of the actuator can. For instance,
the sliding piston actuator could be replaced by a diaphragm
actuator. Other possible modifications will be readily apparent to
the appropriately skilled person.
* * * * *