Note: Descriptions are shown in the official language in which they were submitted.
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VARIABLE GEOMETRY TURBOCHARGER
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates generally to the field of turbochargers having
variable turbine inlet geometries. More particularly, the present invention
provides a simplified structural arrangement for positioning multiple
aerodynamic vanes in the inlet nozzle of the turbine housing and an integrated
actuator for control of the vane position.
Descrintion of the Related Art:
In a turbocharger it is often desirable to control the flow of
exhaust gas into the turbine to improve the efficiency or operational range.
Various configurations of variable nozzles have been employed to control the
exhaust gas flow. Multiple pivoting vanes annularly positioned around the
turbine inlet and commonly controlled to alter the throat area of the passages
between the vanes is an approach which has been successfully used in prior
turbochargers. Various approaches to this method for implementing a variable
nozzle are disclosed in US Patent numbers 4,679,984 to Swihart et al. entitled
"Actuation System for Variable Nozzle Turbine" and 4,804,316 to Fleury
entitled "Suspension for the Pivoting Vane Actuation Mechanism of a
Variable Nozzle Turbocharger" having a common assignee with the present
application.
In more detail, US 4,679,984 discloses a turbocharger having a variable
nozzle vane assembly. A plurality of pivotable vanes are mounted between the
turbocharger backplate and unison ring on one side, and an annular side wall
independent of the turbine housing, on the other side. Each vane inicudes a
drive
pin which pivots the vane in response to rotational movement of the unison
ring.
In order to achieve this, the unison ring has a plurality of slots on its
inner radial
surface, each slot receiving a vane drive pin.
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While multiple vane variable nozzle turbochargers have significantly
increased the overall efficiency and capability of turbochargers, the
complexity of support and actuation structures for the vanes have increased
manufacturing costs and occasionally created maintenance issues. It is
therefore desirable to reduce the complexity and parts count of variable
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nozzle structural arrangements and improve the actuation systems to increase
reliability and reduce manufacturing cost for turbochargers employing them.
SUMMARY OF THE INVENTION
A variable geometry turbocharger employing the present invention
includes a turbine housing having a standard inlet for exhaust gas and an
outlet
to the exhaust system of the engine. A volute is connected to the inlet and an
integral outer nozzle wall is incorporated in the turbine housing casting
adjacent the volute. A center housing is attached to the turbine housing . A
center bore in the center housing carries a bearing assembly. A compressor
housing having an air inlet and a compressed air outlet is attached to the
center
housing.
A turbine wheel is carried within the turbine housing and attached to a
shaft extending through the center housing, supported by the bearing
assembly. The shaft attached to a compressor impeller carried within the
compressor housing.
A plurality of vanes having rotation posts extending from a first -
surface substantially parallel to the outer nozzle wall provide the variable
nozzle. The posts are received in circumferentially spaced apertures in the
outer nozzle wall. The vanes further have actuation tabs extending from the
opposite surface of the vanes. A unison ring is engaged between the center
housing and the vanes and has a plurality of profiled slots equal in number to
the vanes. The slots are oriented obliquely to a circumference of the unison
ring and receive the tabs. The profiled surfaces of the slots engage the
substantially flat sides of the tabs on different surfaces during the
translation to
provide optimum control and wear reduction.
Actuation of the unison ring is accomplished by a radial slot and a
crank shaft having a pin engaging the radial slot. The crank shaft is movable
continuously from a first position to a second position, causing the pin to
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translate in the radial slot and impart force perpendicular to the radial slot
to
urge rotational motion of the unison ring. The rotational motion of the unison
ring causes the tabs to traverse the actuation slots from a first end of the
slots
to a second end of the slots. The oblique orientation of the slots causes a
continuously variable rotation of the vanes from a first open position to a
second closed position.
An integral hydraulic actuator provides the actuation mechanism for
the crank shaft. Mounted in a boss in the center housing, the actuator uses a
piston and piston rod attached by a rack and pinion to the crank shaft for
position control of the vanes. Hydraulic pressure to operate the piston is
provided by a solenoid operated multiport valve with direct feedback through
a cam mounted on the crank shaft adjacent the pinion gear.
BRIEF DESCRIPTION OF THE DRAWINGS
The details and features of the present invention will be more clearly
understood with respect to the detailed description and drawings in whichr
Fig. 1 is an exploded view of an embodiment of a turbocharger employing the
present invention;
Fig. 2 is a side section elevation showing the turbine housing, center housing
2o and compressor back plate with the turbine shaft wheel assembly and
compressor impeller as supported by the bearing system;
Fig. 3 is an end section elevation through the center housing showing an
embodiment of an integral actuation valve arrangement according to the
invention;
Fig. 4 is a partial view of an alternate embodiment of the valve piston
arrangment;
Fig. 5a is a view along line G-G of Fig. 3 and with Figs. 5b-c provides
section
views of the crank shaft assembly extending from the actuation valve to the
unison ring engaging the nozzle vanes;
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Figs 6 a-e are end views of the unison ring and nozzle vanes demonstrating the
variable vane positions and the actuation structural arrangement;
Fig. 7 is a reverse end view of an alternative embodiment of the unison ring
showing a blind relief design for pressure compensation;
Fig. 8 is a schematic side view of the unison ring of Fig. 7 and vanes as
mounted in the turbine housing to demonstrate the pressure compensation for
vane tolerance control; and
Figs. 9a-e are schematic side views of the actuation valve porting and piston
structure for control of the vane position.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, the embodiment of the invention shown in
Fig. 1 includes a compressor housing 10 which is connected to a backplate 12
using two or more clamps 14 secured by bolts 16. The backplate is attached to
a center housing 18 with multiple bolts 20 and a seal ring 22. A turbine
housing 24 is connected to the center housing using multiple clamps 26
secured by bolts 28. A turbine wheel and shaft assembly 30 is carried within
the turbine housing. Exhaust gas or other high energy gas supplying the
turbocharger enters the turbine housing through inlet 32 and is distributed
through the volute in the turbine housing for substantially radial entry into
the
turbine wheel through a circumferential nozzle entry 34.
Multiple vanes 36 are mounted to a nozzle wall 38 machined into the
turbine housing using posts 40 extending from the vanes for rotational
engagement within holes 42 in the nozzle wall. Actuation tabs 44 extend from
the vanes to be engaged by slots 46 in unison ring 48 which acts as the second
nozzle wall. The configuration of the tabs, slots and unison ring will be
explained in greater detail subsequently. An actuator crank 50 terminates at a
first end in a lever arm 52 carrying a pin 54 to engage'elliptical slot 56 in
the
unison ring for rotation of the ring as will be later explained. The crank
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extends into a boss 58 in the center housing casting through a bushing 60 and
a gear 62 which is secured to the crank by a pin 64 and is received into an
end
bearing 66 which mates with aperture 68 in the crank boss. An 0-ring 70
seals the end bearing and a snap ring 72 secures the end bearing into the
aperture 68.
A bearing system having two journal bearings 74 and a bearing spacer
76 support the shaft wheel assembly in the center housing center bore 78. The
shaft further extends through a thrust collar 80 which engages a thrust
bearing
82 carried between the center housing and compressor back plate. A piston
lo ring 84 seals the thrust collar with the shaft bore in the back plate. The
stack
up of the shaft wheel assembly within the turbine housing, center housing and
back plate is best seen in Fig. 2. The unison ring and vanes are not shown for
clarity. The compressor impeller 86 is attached to the shaft wheel assembly.
Referring again to Fig. 1, the integrated actuator for the turbocharger
is housed in an actuator boss 82 in the casting of the center housing 18. A
solenoid valve 84 is mounted in an aperture at one end of the boss while the
actuating components are mounted in a second aperture at the opposite end of
the boss. The actuating components include a piston 86 that incorporates a
rod 88 having a rack gear 90 engaging the gear 62 mounted on the crank shaft
50. A ring seal 92 surrounds the piston circumference sealing the piston in
the
bore of the actuator boss. Additional ring seals 94 and 96 seal the piston rod
to a rod bore of smaller diameter than the piston bore. The piston bore is
sealed with a piston end 98 held in the bore with a snap ring 100. A bolt 102
is inserted into a threaded hole in the piston end for use in manipulating the
piston end. An additional ring seal 104 seals the piston end to the bore.
Alternatively, a freeze plug 106 is employed as a replacement for the piston
end. The solenoid valve is secured to the boss with a bracket 108 held by a
bolt 110. Bore plugs 112 and 114 seal the blind ends of actuation passages in
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the actuator boss while steel balls 116 are employed to seal other actuation
passages, described in greater detail subsequently.
Fig. 2 is a side sectional elevation of the turbocharger showing the
assembled turbine housing, center housing and compressor back plate with the
turbine shaft wheel assembly and compressor impeller supported by the
bearing assembly.
Fig. 3 is an end sectional view through the actuator boss and assembled
actuator components. Fig. 4 shows the alternative freeze plug arrangement for
sealing the piston bore.
As best seen in Fig. 2, the center housing includes a main casting
portion and a turbine housing back plate 120 for attachment of the center
housing to the turbine housing using bolts, as previously described. Fig. 5a
is
a sectional view showing the crank shaft assembly with the gear 62 bushing 60
mounted in the main casting portion of the center housing with the crank shaft
extending across the air gap between the main casting portion and the turbine
housing back plate and into an aperture in the back plate. Fig. 5b shows the
details of the crank shaft sealing arrangement in the back plate aperture. A
first metalic ring seal 122 having a first diameter is employed to seal an
inner
diameter of the aperture 124, while a second metalic ring seal 126 is employed
in combination with the first seal to seal a second larger diameter 128 of the
aperture. This arrangement allows continued sealing during uneven thermal
expansion of the main casting portion and the back plate during operation.
Fig. 5b demonstrates the configuration during operation, with the temperature
of the back plate exceed the main portion, with resulting greater expansion
while Fig. 5c, shows the arrangement with nominal tolerance at a common
temperature for the main casting portion and the back plate.
The nozzle vanes36 in the turbine inlet nozzle are operated by the
unison ring 48. Fig. 6a shows the unison ring engaged by the end pin 54 of
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the crank shaft 50 in a radial slot 130. Rotation of the crank shaft causes
the
offset end pin to traverse the radial slot resulting in rotation of the unison
ring.
The vanes, mounted for rotation on pins 40 which extend into receiving holes
42 in the nozzle wall of the turbine housing, have guide tabs 132 which are
received in the slots 46 in the unison ring. As the unison ring rotates, the
motion of the slots causes the tabs to traverse from one end of the slot to
the
other resulting in rotation of the vanes from a first fully open position,
through
a neutral position, shown in Fig. 6a, to a fully closed position. Fig. 6b
shows
in phantom the fully open, neutral and fully closed positions of the vanes
with
tab positioning in the slots. Fig. 6c is an enlarged view of the unison ring
slot
with the tab shown in multiple positions. The tab incorporates substantially
flat sides 134 and 136 which provide extended engagement of the slot wall by
the tab to reduce point wear on the tab. The profile of the slot, not purely
oval,
is predetermined to provide maximum engagement with the tab, while
engaging first side 134 of the tab at the open and closed end points with
maximum area and the second side 136 during the intermediate positioning of
the vanes.
For the embodiment shown in the drawings, Fig. 6d shows the fully
open and fully closed positions of the vanes. A 22 degree rotation of the
vanes
is provided.
In certain applications, pressure balancing of the mounting of the vanes
in the nozzle is desirable. Fig. 7 shows one embodiment of the unison ring 48
that incorporates blind slots 46 while providing a blind relief 138 on the
reverse side of the ring with pressure ports 140 machined into the relief.
Fig.
8 is a detail side section of the relieved unison ring engaging the vanes in
the
nozzle. For the arrangement shown, pressure of the exhaust gas entering the
nozzle pressurizes the relieved back portion 138 of the unison ring through
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gap 142 provided by tolerancing of the mounting channel 144 in the back plate
120, through ports 140. Alternatively, a feed hole 146 is provided through the
back plate into the unison ring mounting channel proximate the location of the
ports 144. Total pressure of the exhaust gas urges the unison ring against the
vanes, which are in turn urged against the nozzle surface 38 in the turbine
housing. Holes 42 receiving the vane pins 40 are provided with sufficient
depth to allow the vanes to be maintained in close contact with the nozzle
surface and unison ring for minimum vane leakage.
Actuation of the vanes is initiated by the solenoid valve 84 and
actuation components previously described. Figs. 9a through 9e show the
various states of the actuation piston 86 and its piston rod 88 driving gear
62
through rack 90. The solenoid valve is reacted by a spring 150 having a cap
152 engaging a cam 154 machined into the gear body. Various ports, as will
be described are then opened and closed, hydraulically positioning the piston
which, through the mechanical closed loop of the rack and gear provides
positive control on the position of the crank shaft and, therefore, the unison
ring.
The solenoid valve is a proportional servo 4-way hydraulic actuator
control valve. As shown in Fig. 9a, if no current is applied to the solenoid,
port A is open, port B (top of the piston) is connected to drain port D. As
shown in Fig. 9b, when oil pressure is applied from the engine on which the
turbocharger is mounted, oil pressure is directed through port A into the
bottom of the piston, placing the vanes in a fully open position. When current
is applied to the solenoid, port A is closed, port A (bottom of the piston) is
connected to drain, port B opens and oil pressure is directed to the top of
the
piston, moving the piston to the left starting to close the vanes.
Fig. 9c shows the condition of the actuation systems with a balanced
state low current in the solenoid. Port A is closed, poitt B is closed and the
vanes are positioned as a function of the applied current. If the current is
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increased, Fig. 9d shows that port B is opened directing oil pressure to the
top
of the piston. Port A is connected to the drain and the piston moves to the
left,
moving the vanes in the closed direction. After some finite time, the system
stabilizes in a balanced state with high current as shown in Fig. 5e with port
A
S closed, port B closed and the vanes positioned as a function of the applied
current. Full current applied to the solenoid results in port B being closed,
oil
pressure being directed to the top of the piston while port A is connect to
the
drain and the piston moves to the left until a full closed vane position is
achieved. Removing current from the solenoid returns the actuation system to
io the state shown in Fig. 9a with the vanes fully open.
Having now fully described the invention as required by the patent
statutes, those skilled in the art will be able to ascertain modifications and
alterations to the specific embodiments disclosed herein. Such modifications
and alterations are within the scope of the invention as defined in the
15 following claims.
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