|Title of Invention
A POSITIVE DISPLACEMENT SUPERCHARGER AND A METHOD OF PRODUCING A HOUSING OF THE SUPERCHARGER
|A positive displacement supercharger includes a housing defining a rotor cavity with a pair of positive displacement rotors operative to carry air axially from an inlet end to an outlet in the cavity wall near an outlet end of the cavity. The outlet communicates with an outlet plenum partially defined by the cavity wall. The cavity wall includes a stiff portion defining a plurality of lightening recesses, such as a waffle pattern, limiting distortion of the wall by pulsations in the plenum. The recesses may be time and cost efficiently converted to Helmholtz tuners by covering the recesses with a cover plate, which may be perforated to include at least one tuning opening (perforation) into each tuning chamber (recess) and forming tuning volumes of the tuning chambers and their associated tuning openings effective to attenuate selected frequencies of pulsations in the plenum and thereby reduce undesired noise emanating from the air system of the supercharger.
SUPERCHARGER WITH HOUSING
INTERNAL NOISE ATTENUATION
 This invention relates to positive displacement compressors or
superchargers, such as roots type or screw compressors utilized for
automotive engine superchargers and other purposes.
BACKGROUND OF THE INVENTION
 It is known in the art to utilize positive displacement
compressors having lobed rotors for supercharging internal combustion
engines and for providing compressed air for other purposes. Such a
compressor used as an automotive supercharger may include a housing
having a rotor cavity in which a pair of parallel rotors having interleaved
lobes rotate to effect compression of air discharged through an opening in the
cavity wall near an outlet end of the housing. The rotors may be belt driven
by the engine through a pulley connected directly, or through a gear train, to
the pair of rotors. A closure may be mounted on the housing to contain the
compressed air before discharging it air through the housing or otherwise to
the engine air intake and associated cylinders.
 Between the housing and the closure, an outlet plenum is
formed which receives the compressed air from the rotors through an outlet
near an outlet end of the cavity. The plenum is subject to pulsations created
by the pumping action of the rotors. Accordingly, the outlet side of the
housing wall is desirably stiffened by providing a cross-ribbed pattern or grid
similar to a waffle. The ribs provide a stiffened portion to reduce flexing of
the rotor wall. The waffle pattern results in a plurality of lightening recesses
in the wall to reduce its mass and the weight of the housing.
 The pulsations created in the plenum react with the air
induction system of the engine, particularly within the rotor housing and
plenum, to cause vibrations of the structure that result in undesired noise of
various frequencies, which it is desired to minimize.
SUMMARY OF THE INVENTION
 Attenuation of high frequency noises in engine induction
systems, especially with superchargers, is sometimes provided by adding
quarter wave tuners or Helmholtz tuners. Higher frequency Helmholtz
tuners are very small and any significant attenuation requires a number of
small tuning volumes. These tuning volumes require space in the induction
system as well as added materials to create the tuning volumes and connect
them in the system.
 In accordance with the invention, a plurality of internal
Helmholtz tuners are provided near the source of the pulsations in the
supercharger outlet plenum. A perforated plate or similar cover is mounted
over the waffle pattern of recesses formed in an outer surface of the cavity
wall. The plate acts to restrict access to the recesses and to form a number
of Helmholtz tuners. These include tuning chambers formed by the recesses
and connected with the plenum by passages formed by the perforations in the
cover plate. The tuners provide spring mass systems in which the mass of
air in the inlet opening of each tuner vibrates against the volume of air within
the associated tuning chamber, which acts as a pneumatic spring to provide
attenuation of one or more specific frequencies within the outlet plenum
depending upon the specific tuning frequencies of the various tuners formed
within the rotor housing.
 The invention provides an efficient and low cost means for
attenuating noise creating pulsations using pre-existing or modified waffle
pattern recesses to form tuning chambers by the addition of a suitable
perforated cover plate.
 These and other features and advantages of the invention will
be more fully understood from the following description of certain specific
embodiments of the invention taken together with the accompanying
DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a pictorial view of an engine supercharger assembly
according to the invention;
 FIG 2 is a partial cross-sectional view showing a rotor and
drive assembly mounted within the supercharger of FIG. 1;
 FIG. 3 is an isometric view of the housing for the
supercharger of FIG. 1;
 FIG. 4 is an exploded view of the housing and plate assembly
of FIG. 3; and
 FIG. 5 is an enlarged view of a single tuning volume forming
a Helmholtz resonator in one of the waffle pattern recesses of the housing of
DESCRIPTION OF AN EXEMPLARY EMBODIMENT
 Referring now to the drawings in detail, numeral 10 generally
indicates a positive displacement compressor or supercharger for use with a
V-type internal combustion engine. Supercharger 10 includes a rotor
housing 12 containing a drive and rotor assembly 14 and mounting an upper
housing closure 16. The rotor assembly is belt driven through a pulley 18
connected to a rotor drive shaft 20 extending from a gear case 22 of the
drive and rotor assembly 14.
 Figure 2 illustrates the drive and rotor assembly 14, which
includes the gear case 22 carrying a gear train 24 and bearings 26 which
drive and support a pair of oppositely rotating drive and driven rotors 27,
29. The rotors are of the helical Roots type having, respectively, interleaved
clockwise and counterclockwise helical lobes 28, 30. These co-act to form
rotor chambers 31 that carry charging air from an inlet end 32 toward an
outlet end 34 of the housing. Alternatively, screw type helical rotors could
be used in the supercharger.
 Figures 3 and 4 illustrate assembly and exploded views
respectively of the rotor housing 12. Housing 12 includes a pair of outer
sidewalls 36 and an inlet end wall 38. An internal rotor cavity 40 is defined
by a cavity wall 42. An outlet opening 44 extends through the wall 42,
which communicates the rotor cavity 40 with an outlet plenum 46 extending
along an outer side 48 of the cavity wall 42 under the closure 16.
 As shown in the exploded view of FIG. 4, a central part of the
wall outer side 48 is formed as a stiff portion 50 defined by a pattern of
cross ribs 52 which form a plurality of elongated recesses 54. The recesses
are closed by restriction means in the form of a cover plate 56, which
includes a plurality of perforations 58, at least one connected with each
recess. The recesses form tuning chambers 60, which join with the
perforations 58 acting as tuning openings to form Helmholtz tuners 62.
 One exemplary Helmholtz tuner is shown by FIG. 5 as the
tuning volumes shown in positive space of an associated tuning chamber 60
and its tuning opening 58 shown as a protrusion. The protrusion represents
the volume occupied, by the mass of air present in the tuning opening 58 at
any time. The comparative volume of the tuning chamber is shown by the
larger mass 60 acting as a spring, while the air mass in tuning opening 58
acts as a mass in the mass/spring tuner.
 The Helmholtz tuners may be designed or adjusted to
attenuate the same or different resonant frequencies of pulsations by varying
the volumes of the recesses or varying the thickness of the cover plate or the
diameters of the holes or perforations 58. In addition, more than one
perforation could be connected with a single chamber in order to obtain a
different frequency range. The tuners 62 could be designed for attenuating a
single frequency or could be individually tuned to more than one frequency
in order to obtain a desirable tuning result for the interior of the plenum and
the resulting reduction of pulsations therein.
 In operation, air pulsations created in the outlet plenum 46
may be attenuated, at least in part, by one or more Helmholtz tuners formed
by the combined waffle pattern with its associated cover plate 56. The tuners
provide opposing frequency pulsations that attenuate the pulsations of air
within the plenum near their source and thus reduce the noise caused by
pulsations within the plenum.
 The invention takes advantage of a stiffening pattern, such as
a waffle pattern, which may be already formed within the outer side of the
rotor cavity wall in order to stiffen it against reaction to pulsations. The
pattern is converted to Helmholtz tuners by merely placing restriction means,
such as a cover or plate, over the waffle pattern and providing the necessary
size and number of tuning openings in the form of perforations through the
cover or plate to obtain the desired frequency attenuation. The assembly is
thus economically efficient, in that it uses an already existing structural
element of the housing in order to form the tuning chambers with a minimum
of increased weight and cost.
 If desired, the waffle pattern may be modified in order to
provide attenuation of additional or alternative frequencies without increasing
significantly the cost of the improved supercharger rotor housing 12. In
another variation, the tuning openings could be formed by tubes extending
through the cover plate to provide longer tuning volumes. Alternatively, if
the pattern allows, some or all of the tuning openings could extend around
the cover plate, such as through notches in or passages through the cavity
 While the invention has been described by reference to certain
preferred embodiments, it should be understood that numerous changes could
be made within the spirit and scope of the inventive concepts described.
Accordingly, it is intended that the invention not be limited to the disclosed
embodiments, but that it have the full scope permitted by the language of the
1. A positive displacement supercharger comprising:
a housing including a rotor cavity having a surrounding cavity wall;
a pair of positive displacement rotors oppositely rotatable in the rotor
cavity and having interleaved helical lobes forming rotor chambers operative to
carry air axially from an inlet at an inlet end of the cavity to an outlet near an outlet
end of the cavity;
the outlet defined by an opening through the cavity wall and
communicating the rotor chambers with an outlet plenum partially defined by an
outer side of the cavity wall and subject to pulsations in the air discharged to the
the cavity wall being stiffened within the plenum by a stiff portion
defining a plurality of lightening recesses opening into the plenum, the stiff portion
limiting distortion of the wall by pulsations in the plenum; and
restriction means partially covering the openings into the plenum of at
least some of the recesses and forming tuning chambers, the restriction means
including at least one tuning opening between each tuning chamber and the plenum
and forming tuning volumes effective to attenuate selected frequencies of pulsations
in the plenum and thereby reduce undesired noise emanating from the discharge air
of the supercharger.
2. A supercharger as in claim 1 wherein the restriction means includes
a cover over at least part of the stiff portion and blocking air flow to the tuning
chambers under the cover except through the tuning openings.
3. A supercharger as in claim 2 wherein the tuning openings extend
through the cover.
4. A supercharger as in claim 3 wherein the cover is a plate.
5. A supercharger as in claim 1 wherein the stiff portion is ribbed.
6. A supercharger as in claim 1 wherein the stiff portion is cross-
ribbed in a waffle pattern.
7. A supercharger as in claim 1 wherein the tuning volumes define
8. A supercharger as in claim 1 wherein the supercharger housing is
efficiently produced by:
providing a rotor housing for a positive displacement supercharger of a
design that includes a stiff wall portion forming a part of an outlet plenum and
including cross-ribbed stiffeners defining recesses arranged in a pattern; and
applying a perforated cover plate closing the openings of the recesses
into the plenum portion with the perforations in the plate communicating between
the recesses and the plenum portion and proportioned to form volumes effective to a
attenuate selected frequencies of pulsations in the plenum and thereby reduce
undesired noise emanating from discharge air of an associated supercharger.
A positive displacement supercharger includes a housing defining a
rotor cavity with a pair of positive displacement rotors operative to carry air axially
from an inlet end to an outlet in the cavity wall near an outlet end of the cavity.
The outlet communicates with an outlet plenum partially defined by the cavity wall.
The cavity wall includes a stiff portion defining a plurality of lightening recesses,
such as a waffle pattern, limiting distortion of the wall by pulsations in the plenum.
The recesses may be time and cost efficiently converted to Helmholtz tuners by
covering the recesses with a cover plate, which may be perforated to include at least
one tuning opening (perforation) into each tuning chamber (recess) and forming
tuning volumes of the tuning chambers and their associated tuning openings
effective to attenuate selected frequencies of pulsations in the plenum and thereby
reduce undesired noise emanating from the air system of the supercharger.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|GM GLOBAL TECHNOLOGY OPERATIONS, INC
|300 GM RENAISSANCE CENTER, DETROIT, MICHIGAN
|PCT International Classification Number
|F02B 33/36; F04C 18/16; F02B 33/00
|PCT International Application Number
|PCT International Filing date