U.S. patent application number 13/175875 was filed with the patent office on 2012-01-26 for roots supercharger with a shunt pulsation trap.
Invention is credited to Paul Xiubao Huang, Sean William Yonkers.
Application Number | 20120020824 13/175875 |
Document ID | / |
Family ID | 45493780 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120020824 |
Kind Code |
A1 |
Huang; Paul Xiubao ; et
al. |
January 26, 2012 |
ROOTS SUPERCHARGER WITH A SHUNT PULSATION TRAP
Abstract
A shunt pulsation trap for a Roots supercharger reduces
pulsation, NVH and improves efficiency without significantly
increasing overall size of the supercharger. Generally, a Roots
supercharger with the shunt pulsation trap has a pair of
interconnected and synchronized parallel multi-helical-lobe rotors
housed in a transfer chamber with the same number of lobes for
propelling flow from a suction port to a discharge port of the
transfer chamber without internal compression. The shunt pulsation
trap comprises an inner casing as an integral part of the transfer
chamber, and an outer casing oversized surrounding the inner
casing, therein housed various pulsation dampening means or
pulsation energy recovery means or pulsation containment means, at
least one injection port (trap inlet) branching off from the
transfer chamber into the pulsation trap chamber and a feedback
region (trap outlet) communicating with the supercharger outlet
pressure.
Inventors: |
Huang; Paul Xiubao;
(Fayetteville, GA) ; Yonkers; Sean William;
(Peachtree City, GA) |
Family ID: |
45493780 |
Appl. No.: |
13/175875 |
Filed: |
July 3, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61366140 |
Jul 20, 2010 |
|
|
|
Current U.S.
Class: |
418/157 |
Current CPC
Class: |
F01C 21/10 20130101;
F04C 29/0035 20130101; F04C 18/16 20130101; F01C 1/086
20130101 |
Class at
Publication: |
418/157 |
International
Class: |
F01C 21/00 20060101
F01C021/00 |
Claims
1. A Roots supercharger with a shunt pulsation trap apparatus,
comprising: a. a housing structure having an inner casing with a
flow suction port, a flow discharge port and a transfer chamber
there-between, and at least one injection port located at least one
lobe span away from said flow suction port communicating with said
transfer chamber and at least one feedback region communicating
with said flow discharge port, and an outer casing enclosing said
inner casing; b. two parallel multi-helical-lobe rotors having same
number of lobes and rotatably mounted on two parallel rotor shafts
respectively inside said inner casing and interconnected through a
set of timing gears to rotate in synchronization for propelling
flow from said suction port to said discharge port: c. a shunt
pulsation trap apparatus comprising said inner casing as an
integral part of said transfer chamber, and said outer casing
oversized surrounding said inner casing, therein housed various
pulsation dampening means or pulsation energy recovery means or
pulsation containment means, at least one trap inlet (said
injection port) branching off from said transfer chamber into said
pulsation trap and at least one trap outlet (said feedback region)
communicating with said supercharger discharge port; d. whereby
said Roots supercharger is capable of achieving high pulsation and
NVH reduction at source and improving supercharger efficiency while
being kept light in mass, compact in size and suitable for both
mobile and stationary applications at the same time.
2. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said multi-helical-lobe rotor is of
twisted shape in its axial direction and having at least three or
more lobes per rotor.
3. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said injection port (trap inlet) is at
least one lobe span away from said supercharger suction opening and
has a converging cross-sectional shape or a converging-diverging
cross-sectional (De Laval nozzle) shape in feedback flow
direction.
4. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means
comprises at least one layer of perforated plate or acoustical
absorption materials or other similar types for turning pulsation
into heat.
5. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means
comprises at least one layer of perforated plate on which there is
at least one synchronized valve that is closed and opened as said
each lobe passes said trap inlet.
6. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means
comprises at least one Helmholtz resonator.
7. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means
comprises at least one Helmholtz resonator in parallel with at
least one layer of perforated plate or acoustical absorption
materials or other similar types for turning pulsation into
heat.
8. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means
comprises at least one Helmholtz resonator in parallel with at
least one synchronized valve that is closed and opened as each said
lobe passes said trap inlet.
9. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means and said
energy recovery means comprise at least a diaphragm or a piston or
other similar types in parallel with at least one layer of
perforated plate or acoustical absorption materials or other
similar types for partially turning pulsation into heat and
partially absorbing pulsation energy and turning that energy into
pumping air from said trap outlet through said perforated plate
into said trap.
10. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means and
energy recovery means comprise at least a diaphragm or a piston or
other similar types in parallel with an opening for absorbing
pulsation energy and turning that energy into pumping air from said
trap outlet through said opening into said trap.
11. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means and
energy recovery means comprise at least a diaphragm or a piston or
other similar types synchronized with at least one valve for
absorbing pulsation energy and turning that energy into pumping air
from said trap outlet through said valve into said trap.
12. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means and
energy recovery means comprise at least a diaphragm or a piston or
other similar types synchronized with at least one valve for
absorbing pulsation energy and turning that energy into driving an
externally connected load.
13. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation dampening means and
energy recovery means comprise at least a diaphragm or a piston or
other similar types synchronized with at least two valves, one at
trap inlet, the other at trap outlet, for absorbing pulsation
energy and turning that energy into driving an externally connected
load.
14. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation trap further comprises
at least one perforated plate located at said suction port or at
least one perforated plate located at said discharge port or both
either before or alternatively after said trap outlet
15. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation containment means
comprises at least one control valve located at said trap
outlet.
16. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 1, wherein said pulsation containment means
comprises at least one layer of perforated plate or acoustical
absorption materials or other similar types for turning pulsation
into heat, in series with at least one control valve located at
said trap outlet.
17. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 15 or 16, wherein said control valve in said
pulsation containment means is a one way valve, like a reed
valve.
18. The Roots supercharger with shunt pulsation trap apparatus as
claimed in claim 15 or 16, wherein said control valve in said
pulsation containment means is a rotary valve that is timed to
close and open as each said lobe passes said trap inlet.
19. The perforated plate as claimed in claim 14 has holes with a
cross-sectional shape of either constant area or converging shape
or a converging-diverging (De Laval nozzle) shape in flow
direction.
Description
CLAIM OF PRIORITY
[0001] This application claims priority to Provisional U.S. patent
application entitled ROOTS SUPERCHARGER WITH A SHUNT PULSATION
TRAP, filed Jul. 20, 2010, having application No. 61/366,140, the
disclosure of which is hereby incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the field of
rotary blowers or compressors used in automotive supercharging
applications, and more particularly relates to a double rotor
helical shaped multi-lobe type commonly known as Roots blowers or
superchargers (other often used names are rotary PDs, rotary lobe
or rotary piston types), and more specifically relates to a shunt
pulsation trap for reducing pulsations and induced vibration, noise
and harshness (NVH) from such superchargers for internal combustion
engines.
[0004] 2. Description of the Prior Art
[0005] Ever since German engineer Gottlieb Daimler filed the first
patent in late 19.sup.th century, the Roots supercharger has been
most widely used in supercharging automotive engines until
turbocharging took its place. However, they are still popular for
all kinds of 2-stroke and 4-stroke cycle engines either gasoline or
diesel.
[0006] It has long been known that Roots blower or supercharger
possesses a unique capability for generating adequate discharge
pressures over a wide speed range. This unique variable pressure
adaptability is attributed better to a wave Roots compression
theory postulated by this author. Inside a Roots blower or a
supercharger, air is not compressed "by a rapid backflow without
internal compression" as the conventional Roots principle has been
believed, but instead it is compressed by a series of pressure
waves or shock waves generated by a sudden opening of lobes to the
supercharger discharge pressure. The wave theory is based on a well
studied physical phenomenon as occurs in a shock tube (invented in
1899) where a diaphragm separating a region of high-pressure gas
from a region of low-pressure gas inside a closed tube. As shown in
FIG. 1a-1b, when the diaphragm is suddenly broke open, a series of
expansion waves is generated propagating from the low-pressure to
the high-pressure region at a speed of sound, and simultaneously a
series of pressure waves which quickly coalesces into a shockwave
is propagating from the high-pressure to the low-pressure region at
a speed faster than the speed of sound. An interface, also referred
to as the contact surface that separates low and high pressure
gases, follows at a lower velocity after the shock wave. Further
compression is achieved by the reflected shock wave at the end wall
of the low pressure region to the level very close to the final
equilibrium pressure.
[0007] To understand the Roots compression principle in light of
the shock tube theory, let's review a cycle of a classical Roots
supercharger as illustrated from FIGS. 2a to 2e by following one
flow cell in a typical three-lobe configuration. In FIGS. 2a, low
pressure air first enters the spaces between lobes of a pair of
rotors axially as they are open to inlet during their outward
rotation from inlet to outlet. At lobe position shown in FIG. 2b,
the air becomes trapped between two lobes and supercharger inner
casing as it is transported from inlet to outlet. Then the trapped
air is suddenly opened to higher pressure of the outlet as shown in
FIG. 2c.
[0008] According to the conventional theory, a backflow would rush
in compressing the air inside the cell at this point as shown in
FIG. 2c. Since it is almost instantaneous and there is no volume
change taking place, the compression is regarded as an iso-choric
process (constant volume). After the compression, the rotors
continue to move against this full pressure difference until lobes
from two rotors meet again, meshing out the compressed air to
outlet chamber and return to inlet suction position to start the
next cycle, as shown in FIG. 2d.
[0009] However, according to the shock tube theory, the lobe
opening phase as shown in FIG. 2c resembling the diaphragm bursting
of a shock tube as shown in FIG. 1b would generate a series of
compression waves or a shock wave. The wave front sweeps through
the low pressure air and compresses it at the same time at a speed
faster than the speed of sound. This results in an almost
instantaneous wave compression well before the induced flow
interface (backflow as in conventional theory) could arrive because
wave travels much faster than the fluid, as illustrated by the wave
propagation in FIG. 2e. In this view, the pressure waves or shock
waves are the primary driver for the Roots compression while the
backflow is simply an induced flow behind the shockwave after
compression takes place.
[0010] From the above Roots cycle analysis, it should be noted that
energy transfers directly between two fluids by waves without using
mechanical components like pistons or vaned impellers. Their major
benefits are their potentials to generate large pressure changes in
short time or small distance in an efficiency equivalent to those
of dry screw compressors of the present times. Moreover, there is
no over-compression or under-compression as in the case of
conventional positive displacement compressors with a
pre-determined pressure ratio, a unique ability to adapt to varying
pressure demands. This makes Roots supercharger ideal for variable
pressure applications such as in automotive supercharging at
different speeds or different pressure boosting levels while
maintaining a good efficiency throughout the process. Since the
compression is achieved through faster moving waves or shock waves
without hardware or the associated inertial, Roots supercharger can
be build very small in size and simple in structure without
complicated geometry or rotor contours.
[0011] Despite the above mentioned generally attractive features
for Roots potentials, several challenges have impeded their
extensive commercial applications. Among them, the number one issue
is pulsation control. According to the wave Roots theory, when
pressure waves or shockwaves are generated on low pressure side
compressing the air inside the lobe cell, a series of expansions
waves are generated simultaneously on high pressure side. Those
large amplitude expansion waves combined with the reflected
pressure wave or shockwaves from the lobe cells, if not blocked or
treated, could travel downstream, creating huge pressure and flow
pulsations and induced vibrations that could destroy downstream
components, or generate noises as high as 170 dB for high pressure
applications. Therefore, a large sized pulsation dampener, either
in the form of a plenum or a reactive type, is usually required at
the discharge stream of a Roots supercharger to dampen the air
borne pulsations. It is generally very effective in pulsation
control but requires large size to be effective, not suitable for
mobile applications such as automobiles and trucks. At the same
time, discharge dampeners used today could create high pressure
losses that contribute to poor supercharger efficiency. For this
reason, Roots superchargers are often cited with high pulsation,
noise and low efficiencies, all of which prevent it from a wider
use in spite of its unique merits due to wave compression.
[0012] Various attempts have been made to reduce Roots pulsations
throughout years, but only limited successes have been achieved.
The main reason for this failure is believed to be lacking an
adequate Roots compression mechanism that could point to the root
cause of pulsations. Traditionally, Roots compression has been
regarded as a backflow mechanism instead of the wave mechanism as
described above. Based on the conventional backflow principle which
attributes sudden backflow as the cause of discharge pressure
pulsations, most of the efforts have been focused on controlling
this backflow. Among the methods, a flow feedback principle is most
widely used, for example, as first disclosed in U.S. Pat. No.
4,215,977 to Weatherston, and later in U.S. Pat. No. 4,768,934 to
Soeters (Eaton), U.S. Pat. No. 6,589,034 to Vorwerk (Ford) and U.S.
Pat. No. 6,874,486 to Prior (GM). The idea is to feed back a
portion of the outlet air through an injection port to the transfer
chamber prior to discharging to the outlet, thereby gradually
increasing the air pressure inside the cell and lengthening the
pressure equalizing time, hence reducing discharge pressure spikes
compared with a sudden opening at discharge. However, its
effectiveness for pulsation attenuation is limited because it fails
to recognize that the waves, not fluid flow, are the primary cause
of the air-borne pulsations. In view of the wave compression
theory, having a flow back earlier could reduce pulsations by
elongating releasing time to discharge pressure. However, it failed
to recognize hence attenuate the simultaneously generated expansion
waves at the injection port that eventually travel down-stream
unblocked, causing high pulsations. Moreover, the prior art failed
to address the high flow losses associated with the high induced
jet velocity through the injection port, resulting in a low
supercharger efficiency that hampers it from being used more widely
to more energy sensitive applications.
[0013] Since the amplitude of pressure pulsation in a supercharger
is typically much higher than the upper limit of 140 dB set in
classical acoustics, the small disturbance assumption or the
resulting linear theory is inadequate to predict its behavior.
Instead, the following rules can be used for large disturbances
when the SPL is beyond 140 dB. These rules are based on the above
discussed Shock Tube theory and can be used to judge the source of
gas pulsation and quantitatively predict its amplitude and travel
directions. In principle, these rules are applicable to the
discharge process of any positive displacement fluid machines such
as internal combustion engines, expanders and pneumatic motors, or
compressors or pumps. [0014] 1. Rule I: For two closed compartments
(either moving or stationery) with different pressure levels
p.sub.3 and p.sub.1 (FIG. 1a), there will be no pulsation generated
if the two compartments are kept isolated with each other [0015] 2.
Rule II: If the divider between high pressure p.sub.3 and low
pressure p.sub.1 is suddenly removed (FIG. 1b), it will trigger
pulsation generation at opening as a mixture of Pressure Waves (PW)
or a shock wave, Expansion Waves (EW) and an Induced Fluid Flow
(IFF) with magnitudes as follows:
[0015] PW=p.sub.2-p.sub.1 (1)
EW=p.sub.3-p.sub.2 (2)
IFF Velocity=(p.sub.2-p.sub.1/(d.sub.1.times.W) (3)
where d.sub.1 is the density of low pressure region and W the speed
of shock wave travelling into the low pressure region, and
p2=(p.sub.3.times.p.sub.1).sup.1/2 (4) [0016] 3. Rule III: the
generated Pressure Waves (PW) or shock wave travel at the shock
wave speed W to low pressure region while Expansion Waves (EW) move
at the speed of sound in a direction opposite to PW, while at the
same time both waves induce an unidirectional fluid flow (IFF)
moving in the same direction as the pressure waves (PW) Pay
attention to Rule #2 which gives the location of pulsation source
as place of sudden opening between p.sub.3 and p.sub.1. It also
indicates the sufficient conditions for gas pulsation generation as
existence of pressure difference and sudden opening. Because all PD
fluid machines convert energy between shaft and fluid by dividing
incoming continuous fluid stream into parcels of compartment size
for delivery to the discharge as indicated by its corresponding
cycle, there always exists a "sudden" opening at discharge to
return these discrete parcels of cavities back to a continuous
stream again. So the two sufficient conditions are automatically
satisfied at the moment of discharge opening if there is a pressure
difference existing between the cavity and outlet it is opened to.
The pulsation magnitude predicted by Rule #2 can be very high if
(p.sub.3-p.sub.1) is large enough for an un-throttled (or
infinitely fast) opening as in a shock tube. However, most PD type
fluid machines operate with finite discharge opening speed which
somehow throttles the induced fluid flow to a maximum sonic
velocity that takes places at a pressure ratio of 1.89, say for a
perfect gas with 1.4 specific heat ratio. In addition, a hardware
(like lobe or valve disk) induced flow pulsation co-exists with
pressure difference induced pulsation, but its magnitude is
typically much smaller for most existing fluid machinery, and is
roughly proportional to its equivalent velocity pressure.
[0017] It should be pointed out the drastic magnitude and behavior
difference between acoustic waves and pulsations discussed above.
First of all, the linear acoustics is limited to pressure
fluctuation level below 140 dB, equivalent to pressure level of
0.002 Bar or 0.03 psi. For fluid machinery, the measured pressure
fluctuation or pulsation is often in the range of 0.3-30 psi (or
even higher), equivalent to 160-200 dB. So pulsation pressures are
much higher and well beyond the pressure range intended in
classical acoustics. Physically, the acoustic waves are sound waves
travelling at the speed of sound with no macro fluid movement with
it while pulsations are a mixture of strong pressure and expansion
waves that also induce an equally strong macro fluid flow
travelling with speeds from a few centimeters per second up to 1.89
times of the speed of sound (Mach Number=1.89), for example. It is
this large pressure forces and induced high velocity fluid flow
that could directly damage a system and components on its
travelling path, in addition to exciting vibrations and noises.
With the above Pulsation Rules, it is hoped that more realistic
pulsation prediction is made possible so that the true nature of
pulsations can be realized, hence controlled.
[0018] Accordingly, it is always desirable to provide a new design
and construction of a Roots supercharger that is capable of
achieving high pulsation and NVH reduction at source and improving
supercharger efficiency without externally connected silencers
while being kept light in mass, compact in size and suitable for
high efficiency, high pressure ratio applications at the same
time.
SUMMARY OF THE INVENTION
[0019] Accordingly, it is an object of the present invention to
provide a Roots supercharger with a shunt pulsation trap in
parallel with the transfer chamber for trapping and attenuating
pulsations at source.
[0020] It is a further object of the present invention to provide a
Roots supercharger with a shunt pulsation trap as an integral part
of the supercharger casing that does not need an externally
connected pulsation dampener or silencer so that it remains light
in weight and compact in size with less noise radiation
surfaces.
[0021] It is a further object of the present invention to provide a
Roots supercharger with a shunt pulsation trap that emits pulsation
free gases downstream hence reduce fatigue failure of downstream
components.
[0022] It is a further object of the present invention to provide a
Roots supercharger with a shunt pulsation trap that is capable of
achieving all the above objectives in a wide range of engine
operating speeds and loads.
[0023] It is a further object of the present invention to provide a
Roots supercharger with a shunt pulsation trap that is capable of
achieving higher adiabatic efficiency in the range equivalent or
close to conventional turbocharger or dry screw supercharger, say
up to about 80%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Referring particularly to the drawings for the purpose of
illustration only and not limited for its alternative uses, there
is illustrated:
[0025] FIGS. 1a and 1b show the pressure and wave distribution of a
shock tube device before and after the diaphragm is broken;
[0026] FIG. 2a to 2d (PRIOR ART) show the Roots compression cycle
of a conventional Roots supercharger;
[0027] FIG. 2e shows the triggering mechanism for wave generation
of a conventional Roots supercharger;
[0028] FIG. 3a to 3d show the wave Roots compression cycle of the
present invention Roots supercharger with a shunt pulsation
trap:
[0029] FIG. 3e shows the triggering mechanism for wave generation
of the present invention Roots supercharger with a shunt pulsation
trap;
[0030] FIGS. 4a and 4b show a perspective and a cross-sectional
side view of a preferred embodiment of the shunt pulsation trap
also showing different shapes of injection port nozzle;
[0031] FIGS. 5a and 5b-c show a perspective and a cross-sectional
side view of an alternative embodiment of the shunt pulsation trap
with an additional wave reflector either after or before the
feedback port
[0032] FIG. 6 is a cross-sectional view of different shapes of a
wave reflector of the shunt pulsation trap;
[0033] FIG. 7 is a perspective view of another alternative
embodiment of the shunt pulsation trap with resonators;
[0034] FIGS. 8a, 8b and 8c show a perspective and cross-sectional
side views of another alternative embodiment of the shunt pulsation
trap with a diaphragm as a dampener and pump;
[0035] FIGS. 9a and 9b show a cross-sectional view of a rotary
valve and a reed valve in open and close positions;
[0036] FIGS. 10a, 10b and 10c show a perspective and
cross-sectional side views of yet another alternative embodiment of
the shunt pulsation trap with a piston as a dampener and pump;
[0037] FIGS. 11a, 11b and 11c show a perspective and
cross-sectional side views of yet another alternative embodiment of
the shunt pulsation trap with a diaphragm used as a dampener pump
to drive an external load;
[0038] FIGS. 12a and 12b show a perspective and cross-sectional
side views of yet another alternative embodiment of the shunt
pulsation trap with a valve at trap outlet.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0039] Although specific embodiments of the present invention will
now be described with reference to the drawings, it should be
understood that such embodiments are examples only and merely
illustrative of but a small number of the many possible specific
embodiments which can represent applications of the principles of
the present invention. Various changes and modifications obvious to
one skilled in the art to which the present invention pertains are
deemed to be within the spirit, scope and contemplation of the
present invention as further defined in the appended claims.
[0040] It should also be pointed out that though drawing
illustrations and description are devoted to a helical three-lobe
Roots supercharger in the present invention, the principle can be
applied to other types of rotary supercharger with different
numbers of lobes such as four-lobed, five-lobed or six lobed, etc.
as long as both rotors have the same number of lobes. The principle
can also be applied to either gas or liquid media, such as helical
lobe or helical gear pumps that are variations of helical Roots
superchargers for liquid and the later uses involute lobe shape to
allow the lobes function as gears with rolling interfacial contact.
In addition, helical lobe expanders are the above variations too
except being used to generate shaft power from a media pressure
drop.
[0041] As a brief introduction to the principle of the present
invention, FIGS. 3a to 3d show again a complete cycle of Roots
compression for a three-lobe Roots supercharger but with an
addition of a shunt (parallel) pulsation trap of the present
invention. In broad terms, pulsation traps are used to trap AND
attenuate pulsations from compressed air or gas in order to reduce
air borne pulsations discharged to atmosphere or downstream
applications. Discharge dampener is one type of pulsation trap
(traditional type) which is connected in series with the transfer
(compression) chamber and through which both fluid flow and
pulsation waves pass. The shunt pulsation trap is another type of
pulsation trap but connected in parallel with the transfer
(compression) chamber. As illustrated in FIGS. 3a and 3b, the
phases of flow suction and trapping are still the same as those
shown in FIGS. 2a and 2b. But during compression phase, instead of
waiting until opening at the outlet as conventional Roots
supercharger, the trapped flow cell is pre-opened to an injection
port (or trap inlet) that is at least one lobe span away from the
supercharger inlet port (For a three-lobe supercharger, it is 120
degrees, a four-lobe supercharger, 90 degrees). The injection port
is branched off from the transfer chamber into the pulsation trap
as a parallel chamber that is also communicating with the
supercharger outlet through a feedback region (trap outlet).
Between injection and feedback region and within pulsation trap,
there is various pulsation dampening means or pulsation energy
recovery means or both, to control pulsation energy before it
travels downstream. As shown in FIG. 3c or 3c, a series of waves is
generated as soon as the trapped air is opened to the trap inlet
due to a pressure difference between the pulsation trap (relates to
outlet pressure) and trapped air (relates to inlet pressure): The
generated pressure waves or shockwaves travel to low pressure side
compressing the air inside the cell, and at the same time, the
simultaneously generated expansion waves on high pressure side,
together with part of reflected shockwaves, are entering the
pulsation trap, and therein are being stopped and attenuated.
Because waves travel at a speed about 5-20 times faster than the
rotor tip speed, the attenuation is well under way even before the
lobe tip reaches the outlet, hence discharging a pulsation-treated
air. If the shunt chamber (pulsation trap) energy dissipating
volume and dampening resistance are specifically designed for
achieving optimum attenuation, the pulsation-treated air can be
almost pulse free. After the compression and pulsation attenuation
phase, the lobes of two rotors will engage, meshing out the
pulse-free compressed air to outlet and return to inlet suction
position to start next cycle, as shown in FIG. 3d.
[0042] The principal difference with the conventional Roots
supercharger is in the compression and dampening phase: instead of
waiting and delaying the compression and attenuation action until
the lobe tip reaches the outlet by using a serially-connected
dampener silencer, the shunt pulsation trap would start compression
and induce pulsations into the trap as soon as the trap inlet is
exposed to the trapped flow cell after it is sealed from the inlet.
It then dampens the pulsations within the trap simultaneously as
the cell flow is being compressed before reaching the outlet. In
this process, the flow cell being compressed and pulsations being
attenuated are happening in parallel with each other instead of in
series as in the conventional Roots supercharger. Or in another
word, compression and pulsation dampening are conducted at the same
time (hence the name parallel or shunt), not one after the other
(in series).
[0043] There are several advantages associated with the parallel
pulsation trap compared with the traditional serially connected
dampener silencer. First of all, pulsating wave attenuation is
separated from the main cell flow so that an effective attenuation
will not affect the main flow cell, resulting in both higher
compression efficiency and attenuation efficiency. In a traditional
serially connected silencer, both pulsating waves and fluid flow
travel together through the dampening elements inside the silencer
where a better attenuation always comes at a cost of higher static
pressure drop. So a compromise is often made in order to reduce
pressure loss by sacrificing the degree of pulsation dampening or
use a very large volume silencer in a serial setup.
[0044] Secondly, the parallel pulsation trap attenuates pulsation
much closer to the pulsation source than a serial one and is
capable of using a more effective pulsation dampening means without
affecting main flow efficiency. It can be built as an integral part
and conforming shape of the supercharger casing with a much smaller
size and footprint; hence less weight and cost. By replacing the
traditional serially connected silencer with an integral paralleled
pulsation trap, it will be light in weight and compact in size
which also reduces noise radiation surfaces and is more suitable
for mobile applications.
[0045] Moreover, the pulsation trap is so constructed that its
inner casing is an integral part of the outer casing of the
transfer chamber, and the outer casing are oversized surrounding
the inner casing, resulting in a double-walled structure enclosing
the noise source deeply inside the core with much less noise
radiation surface area. The casings could be made from a casting
that would be more wave absorptive, thicker and more rigid than a
conventional sheet-metal silencer casing, hence less noise
radiation.
[0046] With an integral pulsation trap, the supercharger outer
casing would be structurally more rigid and resistant to stress or
thermal related deformations. At the same time, the double-wall
casing tends to have a more uniform temperature distribution inside
the pulsation trap so that the traditional "banana shaped" casing
distortion would be kept to minimum, thus reducing internal
clearances and leakages, resulting in higher supercharger
efficiency.
[0047] Referring to FIGS. 4a-4b, there are shown a typical
arrangement of a preferred embodiment of a Roots supercharger 10
with a shunt pulsation trap apparatus 50. Typically, the Roots
supercharger 10 has two parallel rotors 12 mounted on two rotor
shafts respectively (not shown), where rotor shaft driven by an
external rotational driving mechanism (not shown) and through a set
of timing gears (not shown) drives the rotors 12 in synchronization
without touching each other for propelling flow from an axial
suction port 36 through a transfer chamber 37 to a discharge port
38 of the supercharger 10. The Roots supercharger 10 also has an
inner casing 20 as an integral part of the transfer chamber 37,
wherein the rotor shafts are mounted on an internal bearing support
structure (not shown). The casing structure further includes an
outer casing 28 with a space maintained between the inner casing 20
and the outer casing 28 forming the pulsation trap chamber 51.
[0048] As an important novel and unique feature of the present
invention, a shunt pulsation trap apparatus 50 is conformingly
surrounding the Roots supercharger 10 of the conventional design
shown in FIG. 2e, and its cross-section is illustrated in FIG. 3e
and FIG. 4b. In the embodiment illustrated, the shunt pulsation
trap apparatus 50 is further comprised of an injection port (trap
inlet) 41 branching off from the transfer chamber 37 into the
pulsation trap chamber 51 and a feedback region (trap outlet) 48
communicating with the supercharger outlet 38, therein housed
pulsation dampening means 43 or pulsation energy recovery means
(not shown). As lobe tip passes over the trap inlet 41 as shown for
the right rotor in FIG. 3e, a series of pressure waves are
generated at trap inlet 41 going into the transfer chamber 37
inducing a feedback flow 53. Simultaneously a series of expansion
waves are generated at trap inlet 41, but travelling in a direction
opposite to the feedback flow, that is: from trap inlet 41, going
through dampener 43 before reaching trap outlet 48 and supercharger
outlet 38. In FIGS. 4a-4b, the large arrows show the direction of
rotation and internal cell flow as propelled by the rotors 12 from
the suction port 36 to the discharge port 38 of the supercharger
10, while feedback flow 53 as indicated by the small arrows goes
from the feedback region (trap outlet) 48 through the dampener 43
into the pulsation trap chamber 51, then converging to the
injection port (trap inlet) 41 and releasing into the transfer
chamber 37 when lobe tip is opened up and becoming the compression
chamber 39.
[0049] When a Roots supercharger 10 is equipped with the shunt
pulsation trap apparatus 50 of the present invention, there exist
both a reduction in pulsation discharged from Roots supercharger to
supercharger downstream flow as well as an improvement in internal
flow field (hence its adiabatic efficiency) so that it is compactly
suitable for mobile applications, and efficiently suitable for
applications typically reserved for conventional turbochargers or
dry screw superchargers.
[0050] The theory of operation underlying the shunt pulsation trap
apparatus 50 of the present invention is as follows. As illustrated
in FIG. 3a to FIG. 3e and also refer to FIG. 4a to 4b, phases of
flow suction and flow transfer are still the same as those shown in
FIGS. 2a and 2b of a conventional Roots supercharger. But during
compression phase, instead of waiting to be opened to supercharger
outlet 38 as the conventional Roots supercharger does, the trapped
flow cell inside the transfer chamber 37 is pre-opened to the
injection port (or trap inlet) 41 that is at least one lobe span
away from the inlet port 36 opening (For a three-lobe supercharger,
it is 120 degrees; a four-lobe, 90 degrees). As shown in FIG. 3e, a
series of pressure waves or shock waves are produced due to a
pressure difference between the pulsation trap chamber 51 (close to
outlet pressure) and transfer chamber 37 (close to inlet pressure).
The pressure waves traveling into the transfer chamber 37 (now
becoming compression chamber 39) compress the trapped air inside,
but at the same time, the accompanying expansion waves and a small
portion of reflected pressure waves or shock waves enter the
pulsation trap chamber 51, and therein are being stopped and
attenuated by dampening means 43. Because waves travel at a speed
about 5-20 times faster than the rotor 12 tip speed, the
compression and attenuation are well under way even before the lobe
tip reaches the supercharger outlet opening 38, hence discharging a
pulsation-free or pulsation-reduced air. If pulsation trap volume
and dampening resistance are specifically selected for achieving
optimum attenuation, the pulsation reduction can be quite
significant so that traditional externally connected outlet
pulsation dampener or silencer is not needed anymore thus saving
space and weight and suitable for mobile applications.
[0051] Moreover, the hot feedback flow 53 sandwiched between the
cored and integrated inner casing 20 and outer casing 28 acts like
a water jacket in a piston cylinder of an internal combustion
engine, tending to equalize temperature difference between the cool
inlet port 36 and hot outlet port 38. This would lead to less
thermal distortion of the inner casing 20, which in turn would
decrease the internal end clearance and tip clearance. In addition,
by getting rid of the serially connected silencer, the associated
discharge dampening losses are eliminated for the main cell flow At
the trap inlet 41, the induced injection flow could be "choked" as
pressure ratio across reaches 1.89, seriously limiting injection
flow capacity and creating pressure losses. So using a flow nozzle
63 or de Laval nozzle 65, as shown in FIG. 4b, would improve
injection flow rate, injection time and flow efficiency compared to
a traditional orifice shape so that supercharger overall adiabatic
efficiency is greatly increased, hence suitable for applications
typically reserved for turbochargers or dry screw
superchargers.
[0052] FIG. 5 shows a typical arrangement of an alternative
embodiment of the Roots supercharger 10 with a shunt pulsation trap
apparatus 60. In this embodiment, a perforated plate 49 acting as a
wave reflector and an additional dampener is added to the preferred
embodiment as an additional means of the pulsation tarp 60.
[0053] FIG. 5b and FIG. 5c show wave reflector 49 is located either
before or after feedback region (trap exit) 48 respectively. In
theory, a wave reflector is a device that would reflect waves while
let fluid go through without too much pressure losses. In this
embodiment, the leftover pulsations either from the compression
chamber 39 or coming out of pulsation trap outlet 48 or both could
be further contained and prevented from traveling downstream
causing vibrations and noises, thus capable of achieving more
reductions in pulsation and noise but with additional cost of the
perforated plate and some associated losses. With the feedback flow
53 going through the pulsation trap 51, the main discharge cell
flow is unidirectional through the discharge wave reflector 49 as
shown in FIG. 5b without flow reversing losses and the associated
dampening losses are greatly reduced too by using perforated holes
with shape of either a flow nozzle 63 or de Laval nozzle 65 as
shown in FIG. 6, thus improving discharge flow efficiency compared
to a traditional Roots supercharger.
[0054] FIG. 7 shows a typical arrangement of yet another
alternative embodiment of the Roots supercharger 10 with a shunt
pulsation trap apparatus 70. In this embodiment, Helmholtz
resonators 71 are used as an alternative pulsation eliminating
means supplementing the pulsation trap 70. In theory, Helmholtz
resonators could reduce specific undesirable frequency pulsations
by tuning to the problem frequency thereby eliminating it. Since
the Roots supercharger generates a specific single frequency
pulsation when running at fixed speed and a Helmholtz resonator
could be tuned to that specific frequency for elimination. In this
embodiment, the pulsations generated at trap inlet 41 would be
treated by Helmholtz resonator 71 located close to trap inlet 41
and in parallel with dampener 43. It could also be used alone or in
multiple numbers or different sizes.
[0055] FIGS. 8-11 show some typical arrangements of yet another
alternative embodiment of the Roots supercharger 10 with a shunt
pulsation trap apparatus 80. In this embodiment, a diaphragm or a
piston 81 is used as an alternative pulsation dampening and energy
recovery (pumping) means for pulsation trap 80. FIG. 8a shows an
one-valve configuration, FIG. 8b a two-valve, and FIG. 8c a
configuration with a dampener in place of the one-valve. In FIG. 8,
the top view shows a charging (dampening) phase with only the trap
inlet 41 and valve 82 open to the transfer chamber 37 while the
trap outlet 48 and valve 83 are closed. In the same way, the bottom
view shows a discharging (pumping) phase with the trap inlet 41 and
valve 82 closed to the transfer chamber 37 while the trap outlet 48
and valve 83 open. The valves 82/83 used could be any types that
are capable of being controlled and timed in the fashion as
described above, and one example is given in FIG. 9 for a rotary
valve. In operation, as an example shown in FIG. 8b, a series of
waves are generated as soon as the lobe tip pass over the pulsation
trap inlet 41 during charging phase. The pressure waves would
travel into the transfer chamber 37 while the accompanying
expansion waves enter the pulsation trap chamber 51 in opposite
direction. Because of the pressure difference between the pulsation
trap chamber 51 (close to outlet pressure) and transfer chamber 37
(close to inlet pressure), the diaphragm 81 would be pulled towards
the trap inlet 41 by the pressure difference hence absorbing the
pulsation energy and storing it with the deformed diaphragm 81
(charged). At this time, the valve 83 located at the trap outlet 48
is closed, effectively scaling the waves within the pulsation trap
chamber 51. As the rotor moves further and pressure difference is
diminishing as shown in the bottom view of FIG. 8b, the diaphragm
81 would be pulled away from the trap inlet 41 by the stored spring
energy, resulting in a pumping action sucking air in from the now
opened valve 83, building up the pressure again in the pulsation
trap chamber 51 while trap inlet valve 82 is kept closed at this
time. By alternatively open and close valves 82 and 83 in a
synchronized way timed with the lobe and diaphragm positions, the
pulsation energy could be effectively absorbed and re-used to keep
the cycle going while the waves within the trap is kept contained
and attenuated, resulting in a pulse-free air with minimal energy
losses.
[0056] FIG. 10 is similar to FIG. 8 except using a piston instead
of a diaphragm.
[0057] FIG. 11 shows a typical arrangement of yet another
alternative embodiment of the Roots supercharger 10 with a shunt
pulsation trap apparatus 80a. In this embodiment, the diaphragm or
a piston 81 is used as an alternative pulsation dampening and
energy recovery (pumping) means for the pulsation trap 80a. In the
embodiment shown in FIG. 11b, the difference with embodiment shown
in FIG. 8 and FIG. 10 is that all or part of the pulsation energy
stored is used to drive an external load 89, say a cooling fan.
[0058] FIG. 12 shows a typical arrangement of yet another
alternative embodiment of the Roots supercharger 10 with a shunt
pulsation trap apparatus 80b. In this embodiment, a control valve
86 is used as pulsation containment means for pulsation trap 80b,
one on each side of discharge port 38. In addition, FIG. 12 shows a
configuration with an optional dampener 43 between trap inlet 41
and control valve 86 located at trap outlet 48. The principle of
the operation is taking advantages of the opposite travelling
direction of wave and flow inside the pulsation trap 80b. By using
a directional controlled valve 86, it would only allow flow in
while keeping the waves from going out of the trap in a timed
fashion. In FIG. 12b, the left rotor shows the wave containment
phase with the trap inlet 41 open to the compression chamber 39
while the trap outlet 48 is closed by valve 86. In the same way,
the right rotor shows a flow-in phase when the compression is
finished and the trap outlet 48 is opened through valve 86. The
valve 86 used could be any types that are capable of being flow
controlled like a reed valve or timed with lobe rotation in a
fashion as described above, and one example is given in FIG. 9a for
a rotary valve. In operation, as an example shown in FIGS. 12a and
12b, a series of waves are generated as soon as the lobe tip pass
over the pulsation trap inlet 41 during isolation phase. The
pressure waves would travel into the compression chamber 39 while
the accompanying expansion waves enter the pulsation trap chamber
51 in opposite direction. At this time, the valve 86 located at the
trap outlet 48 is closed, effectively sealing the waves within the
pulsation trap chamber 51 where it is being dampened by an optional
dampener 43 inside. As the rotor moves further and pressure
difference is diminishing, the valve 86 at trap outlet 48 is opened
allowing air in and building up pressure again in the pulsation
trap chamber 51. By alternatively open and close valve 86 in a
synchronized way timed with the lobe positions, the waves and
pulsation energy could be effectively contained within the trap,
resulting in a pulse-free air to the outlet.
[0059] It is apparent that there has been provided in accordance
with the present invention a Roots supercharger with a shunt
pulsation trap for effectively reducing the high pulsations caused
by wave compression without increasing overall size of the
supercharger. While the present invention has been described in
context of the specific embodiments thereof, other alternatives,
modifications, and variations will become apparent to those skilled
in the art having read the foregoing description. Accordingly, it
is intended to embrace those alternatives, modifications, and
variations as fall within the broad scope of the appended
claims.
* * * * *