Turbocharger control actuator

A control actuator for a turbocharger comprises a diaphragm-displaced actuator rod projecting outwardly from an actuator housing through a spring-biased retainer which sealably permits axial and angular rod movement for variably positioning a turbocharger wastegate valve.

BACKGROUND OF THE INVENTION 
This invention relates to turbochargers and control devices therefor. More 
specifically, this invention relates to an improved pressure-responsive 
actuator for controlling the operation of the turbocharger. 
Turbochargers are well known in the prior art, and typically comprise a 
turbine for driving a compressor to supply relatively high pressure charge 
air to a combustion engine. The turbine is rotatably driven by exhaust 
gases from the engine, and in turn rotatably drives a compressor for 
compressing charge air supplied to the engine. An inherent design problem 
with turbochargers, however, is that the rotational speed of the turbine 
and compressor increases as the speed and/or load of the engine increases. 
At relatively high operating engine speeds or loads, it is possible for 
the turbine and compressor to be driven at speeds above critical design 
limits, or for the compressor to supply charge air to the engine at boost 
pressures higher than the engine can withstand. 
A wide variety of control devices for turbochargers have been developed to 
limit the rotational speed of the turbocharger compressor, and thereby to 
control the boost pressure level of the charge air supplied by the 
compressor. Such devices may be mounted either on the compressor or the 
turbine, and commonly includes blow-off or pop-off valves, turbine bypass 
or wastegate valves, compressor inlet control valves, and the like. These 
valve devices are generally similar to each other in principle in that 
each comprises a valve responsive to a predetermined pressure level or 
pressure differential to restrict the availability of gases for driving 
the turbine, or for supply to the engine by the compressor. For example, a 
turbine wastegate valve operates to close a flow path bypassing the 
turbine, and may be opened by a pressure-responsive valve actuator to 
allow a portion of the engine exhaust gases to bypass the turbine to 
atmosphere. In this manner, the turbine is rotatably driven by a 
relatively reduced mass flow of exhaust gases to limit the rotational 
speed of the turbine, and thereby also to limit and control the rotational 
speed and resultant boost pressure of charge air supplied by the 
compressor. 
Pressure responsive valve actuators typically comprise an actuator housing 
including a diaphragm dividing the housing into a pair of separate 
pressure chambers. Inlet ports couple the two pressure chambers to 
different sources of pressure and/or vacuum to subject the diaphragm to a 
prescribed pressure differential. Changes in the pressure differential, 
such as may occur during increases or decreases in engine speed or load, 
cause displacement of the diaphragm which in turn displaces an actuator 
rod connected thereto. The rod projects out of the housing, and is 
connected to an appropriate valve assembly on the turbocharger for 
positioning a valve to control turbocharger operation. 
In practice, one major consideration in the design of pressure-responsive 
valve actuators is to provide an adequate seal allowing passage of the 
actuator rod through the actuator housing without significant gas leakage. 
This is particularly important wherein the pressure sources coupled to the 
actuator housing comprise gaseous air-fuel mixtures, or wherein the 
actuator housing is mounted in close association to hot engine components 
or the turbine of the turbocharger. In this regard, prior art seals which 
have satisfactory prevented gas leakage typically have restricted 
displacement of the actuator rod to axial motion only. This type of seal 
finds its primary application wherein the actuator rod comprises a valve 
stem connected directly to or formed integrally with a valve head, and 
wherein axial rod motion is sufficient to properly position the valve 
head. See, for example, U.S. Pat. Nos. 3,035,408; 3,091,077; 3,104,520; 
3,195,805; 3,196,606; 3,270,495; 3,389,553; 4,005,578; 4,005,579; and 
4,019,323; all of which relate to valve actuators with valve stems or rods 
limited to axial motion. However, it is sometimes desirable to use other 
types of valve structures, such as a relatively inexpensive butterfly 
valve or the like positionally adjusted by means of a crank arm. With 
these alternate valve structures, at least some arcuate motion of the 
actuator rod is required for adjusting the position of the valve. However, 
with prior art devices wherein the actuator rod is constrained for axial 
movement only, relatively complex and multiple-link mechanical couplings 
have been required between the rod and the valve structure for 
accommodating the desired arcuate movement. See, for example, U.S. Pat. 
Nos. 2,356,124; 2,374,708; and 3,096,614. 
Some attempts in the prior art have been made to provide a relatively 
inexpensive seal for sealing passage of the actuator rod through a 
turbocharger actuator housing, while at the same time allowing for at 
least some arcuate actuator rod movement. However, these prior art designs 
have related to various flexible or elastomeric seal arrangements, or 
alternately, to the use of seals formed from relatively exotic materials. 
See, for example, U.S. patent application Ser. No. 843,392 assigned to the 
same assignee herein. However, these prior art seals allowing angular 
movement of the actuator rod have not proven totally satisfactory for long 
life operation in the high temperature, vibratory environment of 
turbochargers. 
The present invention overcomes the problems and disadvantages of the prior 
art by providing an improved turbocharger control actuator having an 
actuator rod projecting outwardly from an actuator housing, and including 
improved means for sealing passage of the actuator rod through the housing 
to allow axial and angular movement of the actuator rod with respect to 
the housing. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a turbocharger control actuator comprises 
an actuator housing with an internal diaphragm dividing the housing into a 
pair of separate pressure chambers. The diaphragm is connected to an 
actuator rod projecting through one of the chambers and outwardly from the 
housing for connection to a turbocharger control valve, such as a turbine 
wastegate valve. The diaphragm and the rod displace in response to 
variations in pressure differential applied to the diaphragm via ports 
opening into the pressure chambers for connection of said chambers to a 
selected pair of pressure sources. 
An annular retainer is received about the actuator rod, and coacts with the 
housing and the rod for sealing passage of the rod through an opening 
formed in the actuator housing. More specifically, the retainer includes a 
cylindrical portion having an annular bushing secured therein which 
slidably and sealingly receives the actuator rod. The retainer cylindrical 
portion blends into a spherical or bulbular-shaped sealing seat disposed 
within the rod opening formed in the actuator housing and sealingly seated 
upon a matingly configured lip formed in said housing. The spherical seat 
expands radially outwardly within the housing to define a base plate for 
supporting the lower end of a spring compressively received between the 
base plate and the diaphragm. 
In operation, the spring biases the diaphragm so as to prevent actuator rod 
movement until the pressure differential applied to the diaphragm exceeds 
a predetermined threshold. The spring also urges the spherical sealing 
seat of the retainer into sealing engagement with the housing lip to 
prevent leakage of gases out of the actuator housing. Importantly, the rod 
is sealingly movable axially with respect to the bushing, and the retainer 
sealing seat is pivotal with respect to the housing lip whereby the 
sealing seat and lip together form a gimbal to accommodate angular 
deviation of the actuator rod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A control actuator 10 of this invention is shown in FIG. 1 mounted on a 
turbocharged combustion engine 12. The engine 12 is generally conventional 
in form, and may comprise any of a wide variety of combustion engines such 
as a reciprocating engine of the type used for automotive vehicles having 
a driven crankshaft 14 for power output. Intake charge air for the engine 
12 is supplied through an intake manifold 16 from a compressor 18 of a 
turbocharger 20. The compressor 18 draws ambient air through an inlet 22, 
and compresses the air for supply to the engine. Exhaust gases expelled by 
the engine are drivingly coupled to a turbine 24 of the turbocharger 20 
via an exhaust manifold 26, and are discharged from the turbine 24 through 
an exhaust conduit 28. In operation, the engine exhaust gases rotatably 
drive the turbine 24 which, in turn, drives the compressor 18 via a shaft 
(not shown) carried in an interconnecting center housing 30. 
In many turbocharged engines, it is possible for the turbocharger 20 to 
operate at rotational speeds higher than the turbocharger mechanical 
components can withstand, or to supply compressed charge air to the engine 
at boost pressures higher than the engine can withstand. Specifically, at 
relatively high operating speeds or loads, the mass flow rate of exhaust 
gases is sufficient to drive the turbine 24 at a rotational speed 
exceeding turbocharger or engine critical design limits. To prevent damage 
to the system, as well as to provide system control, control means are 
provided for preventing the rotational speed of the turbine and the 
compressor from exceeding a predetermined level, and thereby limit or 
control the compressor boost pressure. 
As shown in FIG. 1, one such control means comprises a wastegate valve 
assembly 32 mounted on the turbine 24, and including a pivot pin 34 
extending outwardly from the turbine 24 and connected to a crank arm 36. 
Movement of the crank arm 36 through an arcuate path illustrated by arrow 
35 with respect to the axis of the pivot pin 34 serves to move an 
internally mounted wastegate valve (not shown), such as a butterfly or 
flap valve, to open and close a turbine bypass passage (also not shown). 
More specifically, the wastegate valve is disposed along an internal 
bypass passage communicating directly between the exhaust manifold 26 and 
the exhaust conduit 28 so that a portion of the engine exhaust gases 
bypasses the rotating turbine when the valve is opened consequently to 
control turbocharger rotational speed and boost. Importantly, the specific 
construction of the turbine 24 including the valve assembly 32 and the 
bypass passage is generally well known in the art, and thereby is not 
shown or described in detail. However, for a specific example of a 
representative turbocharger including the turbine, valve assembly, and 
bypass passage, see U.S. Pat. No. 4,120,156, assigned to the assignee of 
the present application and incorporated by reference herein. 
The control actuator 10 of this invention is shown in more detail in FIGS. 
2 and 3. As shown, the actuator 10 comprises a generally cylindrical metal 
housing 38 formed from complementary upper and lower halves 40 and 42, 
respectively. The housing halves 40 and 42 are each generally circular in 
cross section, and include radially outwardly extending flanges 44 and 46, 
respectively. A circular diaphragm 48 formed from a suitable flexible 
elastomeric or rubber-based material extends across the housing 38 to 
divide the housing into two separate chambers 50 and 52. The periphery of 
the diaphragm is received between the flanges 44 and 46, and is secured in 
place as by means of the lower flange 46 rolled over the upper outer edge 
of the upper flange 44. 
The diaphragm 48 comprises a performed or convoluted diaphragm carried upon 
a piston member 54 positioned within the lower chamber 52 of the actuator 
housing. As shown, the piston member 54 has a diameter less than that of 
the housing 38 and the diaphragm 48 so as not to interfere with movement 
of the diaphragm in response to relative pressures in the chambers 50 and 
52. The diaphragm is biased upwardly as illustrated in FIG. 2 by a spring 
78, the function of which will be described hereafter in more detail. 
Alternately, if desired, the diaphragm may be conventionally secured to 
the piston member as by means of opposed retainer plates (not shown) for 
stiffening the central portion of the diaphragm and for connection to said 
piston member. 
An actuator rod 58 is suitably connected as by welding to the lower face of 
the piston member 54, as viewed in FIG. 2. The actuator rod 58 extends 
downwardly from the piston member 54 through the chamber 52, and outwardly 
from the housing 38 through an opening 39. The lower end of the rod 58 
extends further through an opening 41 in a bracket 64 provided for 
connection of the actuator 10 to the turbocharger 20 by bolts 66 (FIG. 1). 
The lowermost end of the rod 58 is threadably received in a rod extension 
68 which in turn is pivotally connected to the end of the valve assembly 
crank arm 36 by a pin 70. Accordingly, pressure responsive movement of the 
diaphragm 48 within the housing 38 displaces the rod 58 to swing the crank 
arm 36 about the axis of the pin 34, and thereby opens or closes the 
control valve (not shown) within the turbine 24. Importantly, the crank 
arm 36 swings through the arcuate path illustrated by arrow 35 in FIG. 1, 
whereby the actuator rod 58 must be free to move axially and slightly 
angularly with respect to the housing 38 as indicated by arrow 85 in FIG. 
2. Of course, suitable alternate connecting schemes for connecting the 
actuator rod 58 to the valve assembly 32 may be employed, if desired. 
As shown in FIGS. 2-4, sealing means is provided for sealing the passage of 
the rod 58 through the opening 39 in the housing 38, while at the same 
time allowing axial and angular movement of the rod with respect to the 
housing. As shown, the area of the housing 38 circumferentially 
surrounding the opening 39 is depressed downwardly to form a generally 
spherically-shaped lip 72. This lip 72 bearingly receives an annular 
retainer 74 concentrically carried about the rod 58. More specifically, 
the retainer 74 is formed from a suitable metal material to include a 
central generally spherical bulbular-shaped sealing seat 76 which matingly 
seats upon the lip 72 of the housing. This sealing seat 76 blends upwardly 
into a radially expanded base plate 77 with an outer upstanding rim 79 for 
receiving and retaining the lower end of the spring 78 compressively 
carried between the retainer 74 and the piston member 54. In operation, 
the spring 78 biases the diaphragm 48 as will be hereafter explained in 
more detail, and springably urges the spherical sealing seat 76 of the 
retainer 74 into pivotal sealing engagement with the housing lip 72. 
Conveniently, the spring 78 comprises a conical spring with its narrower 
end in bearing engagement with the base plate 77 to axially pre-load the 
retainer 74 without significant cocking or tilting with respect to the 
housing lip. Importantly, the base plate 77 of the retainer 74 is axially 
spaced a suitable distance from the lower extent of the housing 38, as 
indicated by arrow 80, to allow the retainer 74 to shift angularly with 
respect to the housing lip 72. With this construction, the retainer 74 and 
housing lip 72 together form a gimbal for accommodating angular deviation 
of the rod 58 while maintaining a relatively tight gas seal between the 
retainer and the lip. 
The spherical sealing seat 76 of the retainer 74 blends downwardly into a 
generally cylindrical portion 82 concentrically carried about the actuator 
rod 58. The cylindrical portion 82 internally carries an annular bushing 
84 of a suitable resinous material or the like which is received about the 
shaft 58 and configured to allow sealed axial motion of the shaft with 
respect thereto. The bushing 84 is held in position as by crimping 
indicated at 86 to prevent axial bushing displacement. Accordingly, in 
operation, sealed axial sliding motion of the rod 58 is allowed with 
respect to the bushing 84, and angular shifting say through an arc of 
about 10.degree. as indicated by arrow 85 is accommodated between the 
retainer sealing seat 76 and the housing lip 72. 
In operation, the diaphragm 48 is subjected to a predetermined pressure 
differential by means of hose fittings 67 and 69 suitably mounted on the 
housing 38 in alignment with a pair of ports 88 and 90 respectively 
opening into the chambers 50 and 52. In this manner, a first pressure from 
one source is applied to the chamber 50, and a second pressure from a 
second source (which may comprise a vacuum) is applied to the chamber 52 
whereby the diaphragm movably responds to variations in the pressure 
differential applied thereto. Importantly, this pressure differential must 
exceed a predetermined threshold as governed by the characteristics of the 
biasing spring 78 before diaphragm movement occurs. 
By way of a specific example in one application of the actuator 10, 
discharge pressure from the compressor 18 or engine intake manifold 
pressure is supplied to the upper chamber 50 via the fitting 67, and 
compressor inlet negative pressure is supplied to the lower chamber 52 via 
the fitting 69. In this manner, during engine operation, substantial 
positive pressure is applied to the chamber 50, whereas a subatmospheric 
pressure is applied to the chamber 52. When this pressure differential 
exceeds the predetermined threshold, the differential urges the diaphragm 
48 to shift downwardly and thereby axially displaces the piston member 54 
and the actuator rod 58. Any angular motion required to swing the crank 
arm 36 (FIG. 1) to open or close the control valve within the turbine 24 
is accommodated by pivot movement between the sealing seat 76 of the 
retainer 74 and the housing lip 72. Of course, during such pivoting or 
shifting motions, the spring 78 springably maintains the retainer 74 in 
sealing contact with the housing lip 72. 
The control actuator of this invention may include a wide variety of 
modifications and improvements within the scope of the invention. For 
example, the valve assembly 32 may comprise any of a wide variety of valve 
assemblies including wastegate, blow-off and pop-off valves or the like. 
Accordingly, no limitation on the invention set forth herein is intended 
except by way of the appended claims.