Note: Descriptions are shown in the official language in which they were submitted.
6~
1 AN IMPROVED VARIABLE FLOW TURBINE
Field of the Invention
This invention relates to an improved variable flow turbine
and more particularly to an improved variable flow turbine for a
turbocharger which can be mounted on an internal combustion
engine.
Background of the Invention
Currently, there are two general types of radial in~low
turbines which are utilized in turbochargers. One type is known
as a fixed geometry turbine which is configured such that the
shape and area of the fluid passage(s), which extends from the
fluid inlet to the turbine rotor, can not be physically
changed. An example o a fixed geometry turbine is described in
U.S. Patent 3,664,761, issued to Zastrow in 1972. The second
type of turbine is known as a variable flow turbine, one design
of which is configured to have radially positioned inner and
outer fluid passages with a valve positioned across one of the
passages to regulate the fluid flow therethrough. By regulating
the size of the opening to the one passage by moving the valve,
one can vary the cross-sectional area of the fluid flow path and
thereby compensate for variations in the fluid ~low rate and
pressure caused by operating an engine at different speeds and
loads. An example of a variable flow turbine is described in
U.S. Patent 4,177,00~, issued to Nancarrow in 1979. In the
Nancarrow patent, the turbine has a straight fluid inlet portion
which leads into a scroll-shaped portion. Both the fluid inlet
portion and the scroll-shaped portion are divided into a pair of
flow paths. Each of the flow paths are further divided in the
scroll-shaped portion only into primary and secondary flow paths
by a wall formed integral with the housing. In addition, a
valve is disposed at the fluid inlet across the secondary flow
path which may be rotated to direct the flow away from the wall
to regulate the fluid flow.
Of the two types of turbines, engines usiny the fi~ed
geometry turbine are less efficient. This is because in
turbocharged engines with a fixed geometry turbine, the turbine
is matched to the compressor which is normally configured for
maximum efficiency ~hen the engine is at its peak torque.
Consequently, the engine cannot operate at optimum e~ficiency at
rated speed and load because the efficient operating flow ~ange
'~'.~`'
~2~
1 of the compressor is less than that required by the engine. A
variable flow turbine, on the other hand, can increase the
engine's rated point efficiency by using compressors with high
efficiency at rated speed and load and lower efficiency when the
engine is at peak torque. This is possible because the power o~
the variable flow turbine can be increased at peak torque to
compensate for the lower efficiency of the compressor. Also,
engines with variable flow turbines are more efficient at less
than maximum speeds and loads where maximum charge air pressure
is not needed. In these situations, the variable flow turbines
can increase the turbine flow area to reduce the exhaust
manifold pressure.
Currently, there is a need to develop a turbocharger with a
variable flow turbine which is highly efficient throughout the
operating range of the engine. Now, an improved variable flow
turbine has been invented which can meet these requirements.
Summary of the_Invention
Briefly, this invention relates to an improved variable flow
turbine which can be used in a turbocharger to improve the
efficiency of an engine. The turbine has a housing constructed
of a curved section and a volute section. The curved section
contains a fluid inlet at one end and is joined at the opposite
end to the volute section. Located within the volute section is
a turbine rotor having a fluid outlet which is coaxially aligned
with the axis o~ the volute section. This rotor i5 rotated by
the exhaust gases from the engine's manifold which enter the
turbine through the fluid inlet The turbine also has a control
valve positioned at the fluid inlet and a divider wall which
extends inwardly from the control valve into both sections of
the housing. The divider wall is constructed so as to divide
the housing into radially inner and outer fluid passages. In
particular~ the passages within the volu~e section are divided
so as to have a constantly decreasing cross-sectional area as
they approach the turbine rotor. The control valve is employed
to regulate flow through the înner passage and by regulating its
position the momentum of the exhaust gases can be varied. The
curved section extends downstream of the control valve to
minimize throttling losses. In addition, by rotating the
control valve toward the divider wall to partially or fully
block the inner fluid passage, the velocity of the exhaust gases
- 2 -
~2~
1 increase as they are routed onto the blades of the turbine
rotor. The ability of the turbine to vary the momentum of the
flowing exhaust gases through the curved section by means of the
control valve improves the e~ficiency of the turbine for a
predetermine~ torque curve throughout a desired engine operating
range.
The general object of this invention is to provide an
improved variable flow turbine which can be used in a
turbocharger to increase the power output of an internal
combustion engine. A more specific object of this invention is
to provide an improved variable flow turbine which can
adjustably increase the velocity of an incoming fluid ~low to
increase the power output of the turbine.
Another object of this invention is to provide an improved
variable flow turbine for a turbocharger which utilizes a
control valve upstream of a curved section which is rotatable
such that incoming exhaust gas is efficiently directed onto the
periphery of the turbine rotor.
Still another object of this invention is to provide an
improved variable flow turbine which permits the use of a more
efficient compressor at rated engine speed to increase engine
efficiency.
A further object of this invention is to provide an improved
variable flow turbine which enables an engine to produce a
higher low speed torque.
Still further, an object of this invention is to provide an
improved variable ~low turbine which will produce higher engine
ef~iciency at all engine speeds and loads.
Still further, an objec~ of this invention is to provide an
improved variable flow turbine which will improve the transient
response of an engine.
Other objects and advantages of the present invention will
become more apparent to those skilled in the a~t in view of the
following description and the accompanying drawings.
Brief Description of the Drawin~s
Fig. 1 is a side view of an improved variable flow turbine.
Fig. 2 is a cross-sectional view of Fig. 1 showing the
improved variable ~low turbineO
Fig. 3 is a partial sectional view taken along the line 3--3
of Fig. 1 including an attached connecting shaft and
~?64~
Compressor .
Fig. 4 is a view of the fluid inlet into the variable flow
turbine taken along the line 4--4 of Fig. 2.
Fig. 5 is an alternative embodiment of a fluid inlet to a
turbine having a control valve positioned across the inner
passage.
~ ig. ~ is a view taken along the line 6--6 of Fig. 5 showing
an axially divided turbine housing.
Fig. 7 is a sectional view taken along the line 7--7 of
Fig. 5 showing a rotary control valve.
Detailed Description of the Preferred Embodiments
Referring now to the drawings, particularly ~ig. 3, a
tur~ocharger 10 is shown having an improved var;able flow
turbine 11. The turbine 11, which is connected to a compressor
12, has a housing 13, see Figs. 1 and 2, constructed of a curved
section 14 and a volute section 16. The curved section 14 is an
arcuately-shaped member which is adapted to be attached at a
first flanged end 18 by bolts (not shown) inserted through bolt
holes 20, see Fig. 4, to the exhaust manifold of an internal
combustion engine. The curved section 14 has an angular span of
at least 30 degrees, preferably 30 to 180 degrees and more
preferably about 45 to 90 degrees. The curved section 14 has an
inlet 22 formed at the flanged end 18 and joins the volute
section 16 at an opposite end 24. The volute ~ection 16 has an
angular span of at least 270 degrees and preferably about 360
degrees. The arc for the volute section 16 is formed about an
axis which extends perpendicular into the paper as viewed in
Fig. 1. A connecting shaft 26 rotatably joins the turbine
housing 13 to the compressor 12 and rotates about the axis of
the volute section. The connecting shaft 26 carries a turbine
rotor 28 and a compressor wheel 30 at its opposite ends. The
turbine rotor 28, which is enclosed in the turbine housing 13,
has a plurality of circumferentially spaced blades 34 which
extend outward from the central axis in a radial fashion~ The
particular shape and configuration of the blades 34 can vary as
is well known to those skilled in the turbine art. The turbine
housing 13 also has an outlet 32 as shown in Fig. 3. As the
exhaust gases of an engine are directed into the turbine 11,
they cause the turbine rotor 28 to rotate. As the turbine rotor
28 revolves, it causes the compressor wheel 30 to do likewise
-- 4
~6~
1 via the connecting shaft 26. The compressor wheel 30 in turn
supplies relatively high pressure charge air to the engine.
Positioned close to the fluid inlet 22 is a control valve 36
for controlling gas flow into the turbine housing 13. The
control valve 36, preferably a rotary valve, is fitted to the
inner surface of the curved section 14. The control valve 36
has a valve insert 40 which is movable between open and closed
positions to regulate gas flow through the variable flow turbine
11. In the open position, see Fig. 2, the valve insert 40 is
arranged flush with the inner surface of the curved section 14
and permits the exhaust gases to flow through the entire curved
section 14. In the closed position, indicated by the dotted
line in Fig. 2, the valve insert 40 restricts the flow path of
the gases through the curved section 14. The control valve 36
is operated by a control mechanism 42 via pin 43 and linkage
44. The control mechanism 42 can be pivotally attached at one
end 46 to a fixed support 48 so that linear movement of the
linkage 44 will cause rotational movement of the control valve
36. It should be noted that the control mechanism 42 can be
manually or automaticall~ operated as is well known to those
skilled in the art. The control mechanism 42 can also be
adapted for substantially any linear or non-linear response to
variations of engine parameters, such as: engine operating
speed, engine load, intake manifold pressure, engine emissions,
smoke density of the exhaust gas leaving the engine and entering
the atmosphere, temperature of the exhaust gas, or a combination
thereof. In addition, the control mechanism 42 can be adapted
to parameters, such as the speed of the turbine rotor 28 and
throttle position.
Extending inwardly from the control valve 36 into both
sections o~ the turbine housing 13 is a divider wall 50. The
divider wall 50 tapers to a tip 52 which is located
approximately tangential to the outer circumference of the
turbine rotor 28. This divider wall 50 is an arcuately-shaped
member which is integral with the turbine housing 13 and serves
to divide the turbine housing 13 into an inner or secondary
fl~id passage 54 and an outer or primary fluid passage 5S.
Preferably7 the area of the outer fluid passage 56 is larger
than the area of the inner fluid passage 54 and more preferably,
the area of the outer fluid passage 56 is approximately three
-- 5 --
1 times the area of the inner fluid passage 5~. When the area of
the inner and outer fluid passages 54 and 56 are approximately
in a 1 to 3 size relationship, respectively, the outer fluid
passage 56 will intersect approximately three times as much of
the periphery of the turbi.ne rotor 28 as the .inner fluid passage
54. In addition to ~he size difference of the fluid passages 54
and 56, the divider wall 50 cooperates with an inner surface 58
of the volute section 16, see Fig. 2, to provide a decreasing
cross-sectional area of the outer fluid passage 56. Preferably,
the cross-sectional area of both of the fluid passages 54 and 56
throughout the curved and the volute sections 1~ and 16,
respectively, will be constantly decreasing. This feature
provides a relatively uniform velocity of the exhaust gases onto
the turbine blades 34. Rotation of the control valve 36 from
the open position to a partially closed position, directs the
exhaust gases outward towards the divider wall 50 and thereby
increases the velocity of the exhaust gases flowing in both the
inner and outer passages 54 and 56, respectively. This
increased velocity combined with the increased mass average
radius of curvature of the flowing exhaust gases will increase
the power output of the turbine 11.
Further rotation of the control valve 36 to the fully closed
position, indicated by the dotted line in Fig. 2, directs all of
the flowing exhaust gases through the outer passage 56~ This
further increases both the velocity and the mass average radius
of curvature of the flowing exhaust gases and maximiæes the
power output of the turbine 11.
~ he curved section 14 combines with an inner surface 58 oE
the volute section 16 to form a tongue 60 having a tip 62. The
tip 62 is located at the opposite end 24 of the curved section
14 and is in close proximity to the circumference of the turbine
rotor 28, preferably tangential to the outer periphery of the
turbine rotor 28. The tongue tip 62 is located at an angular
span of about 90 degrees from the tip 52 of the divider wall 50
so as to expose about 75 percent of the peripheral area of the
turbine rotor 28 to the outer fluid passage 56. The tip 62 and
the inner surface 58 control the exhaust gases flowing between
the outer periphery of the turbine rotor 28 and the tongue 60.
The tip 62 also controls clockwise flow of the exhaus~ gases
-- 6 --
1 which could cause a pulsating ef~ect to be imparted to the
turbine rotor 28.
Turning now ~o Figs. 5-7, an alternative embodiment for a
variable flow turbine is shown having a control valve 64
positioned across ~he inner fluid passage 54. The control valve
64, having a valve insert 67, is rotatable within the curved
section 14 on seals 65, by a control linkage 66, see Fig. 7. As
the control valve 64 rotates, the valve insert 67 is movable
between open and closed positions. In the open position, as
shown in Fig. 5, the valve insert 67 is arranged flush with an
inner surface of the curved section 14 and permits the exhaust
gases to flow through both the inner and outer fluid passages 54
and 56. By rotating the valve insert 67 to~lard a divider wall
51 to a partially closed position, a portion of the inner
passage 54 is blocked. In the fully closed position, indicated
by the dotted line in Fig. 5, the valve insert 67 blocks the
exhaust gases from flowing through the inner fluid passage 54.
This permits both an increase in the gas velocity and an
increase in the mass average radius of curvature of the flowing
exhaust gases, thereby increasing the power output of the
turbine 11. The alternative embodiment also shows an axial
divider wall 68, see Fig. 6 and 7, which is aligned
approximately perpendicular to the divider wall 51 and extends
inward from the fluid inlet 22 into both sections 14 and 16 of
the turbine housing 13. The axial divider wall 68 divides the
turbine housing 13 into a pair of axially separated fluid flow
paths 70 and 72, each of which contains inner and outer fluid
passages 54 and 56, respectively. Each of the flow paths 70 and
72 is aligned with a separate exhaust manifold pipe to prevent
mixing of pulsating exhaust gases prior to their impingement
onto the turbine blades 34.
Operation
The improved variable flow turbine 11 operates on the
exhaust gases fro~ the engine's manifold which pass through the
flow passages 54 and 56 and impinge upon the blades 34 of the
t~rbine rotor 28. The turbine rotor 28 will be driven at a rate
of speed which is related to the velocity and mass flow of the
exhaust gases. Accordingly, the rotational speed of the turbine
rotor 28 is related to the engine operating conditions, such as
engine speed and load. Furthermore, the cross-sectional flow
4~
1 area and shape of the flow passages 54 and 56, as well as the
shape of the divider wall 50, affects the velocity of the
exhaust gases and thereby also affects the rotational speed of
the turbine rotor 28. By sizing the cross-sectional flow area
of the outer passage 56 to be approximately three times the
cross-sectional flow area of the inner passage 54 and by
ut;lizing the curved section 14 in front of the volute section
16, one can better control the velocity of the exhaust gases.
By closing the control valve 36. A high velocity gas flow
through the outer passage 56 can be obtained at relatively low
engine operating speeds. With the inner fluid passage 54
blocked, the entire gas flow must pass through the outer fluid
passage 56. This assures that there is sufficient gas velocity
to drive the turbine rotor 28 at a sufficient speed to cause the
compressor wheel 30 to increase the boost pressure to the
engine.
As the speed or load of the engine increases, the velocity
and mass flow of the exhaust gases will also increase. At some
upper point on the engine's torque curve, the velocity and mass
flow of the exhaust gases will turn the turbine rotor 28 so fast
that either a component of the turbocharger 10 could exceed
critical operational limits and fail or the turbocharger could
produce boost pressures that exceed engine operational limits.
Before either of these can occur, the control valve 36 is
rotated towards the open position to permit the incoming exhaust
gases to flow through both the inner and outer flow passages 54
and 56, respectively.
By partially closing the control valve 36, the gas flow is
moved further away from the central axis of the turbine rotor
28, thereby increasing the mass average radius of curvatureO
The velocity is also increased due to the decrease in the cross-
sectional area of the curved section 14. For each position of
the control valve 36, the gas velocity flowing perpendicular to
the radius of curvature immediately downstream of the control
valve 36 yields a certain angular momentum. By closing the
control valve 36, the mass average radius of curvature and
velocity of the flowing exhaust are increased and therefore the
angular momentum is increased. This increase in mass average
velocity is noticed downstream, at the periphery of the turbine
rotor 28, approximately in accordance with the formula:
1 K
c = _
where: c is the mass average velocity of the exhaust
gases;
K is a constant value determined by the values
of c and R immediately downstream of the
control valve, which will produce the desired
value of c at the periphery of the turbine
rotor; and
R is the mass average radius of curvature for
the flowing exhaust gases.
The above formula applies to all turbines having volute
sections wherein friction and compressibility are neglected.
By partially or fully closing the control valve 36, the
velocity of the exhaust gases impinging on the blades 34 of the
1~ turbine rotor 2~ is increased, which in turn increases the
energy transferred to the turbine rotor 28 in accordance with
the well known Euler turbine equation:
UlC~ U2Cu2
~0 H =
where: H is the energy transferred to the turbine
rotor per unit mass of exhaust gas;
Ul is the velocity of the turbine blades 34 at
the periphery of the turbine rotor 28;
Cul is the velocity of the exhaust gas
tangential to the periphery of the turbine
rotor 28;
Cu2 is the mass average~ tangential velocity of
the exhaust gas leaving the turbine rotor 28;
U2 is the velocity of the turbine blade 34 at
the mass average radius of the flowing
exhaust gas leaving the turbine rotor 28; and
gc is a gravitational constant.
Partially or fully closing the control valve 36 to increase
turbocharger speed increases the charge air flow to the engine.
This allows more fuel to be injected into the engine for hiaher
engine torque and improved transient response, without exceeding
exhaust gas smoke density limits. For engine loads below the
maximum torque curve, the control valve 36 can be modulated to
provide the optimum combination of air-fuel ratio and pressure
,, _ g _
l differential across the engine for maximum engine efficiency.
Likewise, by partially or fully opening the control valve 36 at
high engine speeds and loads, the cross-sectional flow area is
increased and the mass average, radius of curvature is decreased
to control the turbocharger speed and the boost pressure to the
engine.
It should be noted that the vaneless nozzle turbine of this
invention can handle flowing exhaust gases with velocities above
Mach I without encountering choking problems. This ability to
handle absolute velocities, which exceed supersonic velocities,
is not present in turbines using vanes.
While the invention has been described in conjunction with
two specific embodiments, it is to be understood that many
alternatives, modifications, and variations will be apparent to
those skilled in the art in light of the aforegoing
description. Accordingly, this invention is intended to embrace
all such alternatives, modifications, and variations which fall
within the spirit and scope of the appended claims.
- lO -
