Patent Application
20070227516
The present invention generally relates to superchargers. More particularly, the invention concerns a centrifugal supercharger.
Superchargers have become pervasive in automobiles, boats, aircraft, and commercial stationary engines as the need to maximize power output has increased due to the use of smaller engines. Centrifugal superchargers employ a high-speed impeller to develop their boost pressure. Although such high-speed machinery places extreme demands on the associated drive machinery, e.g., bearings, seals, shafts, housing components, and the like, centrifugal compressors benefit from very high thermodynamic efficiencies, resulting in optimum engine outputs.
Most centrifugal superchargers employ some sort of speed increasing mechanism to provide the rotation speed for the centrifugal compressor portion of the device to work. This mechanism, which is usually comprised of two parallel shafts with either a belt or gear system connecting them, requires matching cylindrical bores for the shafts and bearings. In the current art, a minimum of two bearing bores and two locating pin bores are machined in each part that comprise the supercharger case and cover, and the two are assembled like two halves of a clam shell, e.g. the separating plane of the individual case components is orthogonal to both shafts. This process requires eight (8) precision boring operations. A significant problem exists in manufacturing the very precise bores of the case components. For example, the accuracy needed to obtain the desired relationship between the two shafts requires true position and parallelism tolerances of 0.0005 inches. These extremely tight tolerances challenge the capabilities of even the newest and best state-of-the-art computer-controlled machining centers. Manufacturing these assemblies requires expensive and time-consuming set-up, machining, measuring and matching procedures. Even with very careful manufacturing procedures, a significant component rejection rate exists, due to parts that do not meet the strict tolerance requirements.
In view of the above, there exists a need for an efficient supercharger that is easy to manufacture and service.
The present invention provides a very efficient supercharger that is easy to manufacture and service.
One feature of the present invention comprises a supercharger that has a case, or housing that is split into a primary section and a removable section. This two-piece housing greatly enhances and simplifies the ability to attain the required precision manufacturing tolerances.
Another feature of the present invention comprises a sleeve, or intermediate member disposed substantially around a shaft located within the supercharger housing. The intermediate member may be used on the driveshaft, the impeller shaft, or may be used on both shafts. Between the intermediate member and the shaft are bearing assemblies that allow the shafts to rotate. One feature of the intermediate member is that it has a coefficient of thermal expansion (CTE) that is substantially similar to the CTE of the bearing assemblies.
Yet another feature of the present invention comprises a disengagement device located between the supercharger impeller and the engine, or motor that drives the supercharger. The disengagement device allows selective disengagement of the impeller from the engine.
A further feature of the present invention comprises an impeller shaft support designed to reduce mechanical stress and associated rotodynamic instabilities.
Yet another feature of the present invention comprises a supercharger impeller having at least three sets of blades. A first set of primary blades has a first height and a set of secondary, or splitter blades have a second, shorter height. A third set of splitter blades has a third height that is less than the height of the second set of splitter blades.
Another feature of the present invention comprises a supercharger having a modular compressor housing. The modular compressor housing includes two or more modular components. In one embodiment, the compressor housing includes a main housing and a shroud. In other embodiments, the compressor housing includes a main housing, a shroud and a diffuser.
These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout.
It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims.
In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. As used herein, the “present invention” refers to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the “present invention” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s).
Referring to
Referring to
Driveshaft 12 is mechanically coupled to impeller shaft 20 such that rotation of the driveshaft imparts rotation on the impeller shaft 20, thereby causing rotation of impeller 22. The mechanical coupling between the input drive and impeller shafts includes a drive gear 30 disposed about driveshaft 12 and an impeller gear (not shown) disposed about impeller shaft 20. In a preferred embodiment, the drive gear 30 has a larger circumference than the impeller gear, thereby causing the impeller gear to rotate faster than the drive gear 30.
As shown in
The impeller gear (not shown) is coupled to impeller shaft 20 such that the rotation of impeller gear imparts rotation to the impeller shaft and impeller 22. Drive gear 30 is connected to driveshaft 12 such that the rotation of drive gear 30 imparts rotation to the impeller shaft 20.
As best seen in
One feature of this aspect of the invention is that the demanding manufacturing tolerances for the gear housing 26 are much easier to achieve, thereby increasing manufacturability, and decreasing waste generated by parts that are out-of-tolerance. In addition, the number of precision machining operations required to manufacture the gear housing 26 can be significantly reduced, e.g., from 8 individual boring operations to two. Advantageously, this reduces manufacturing costs. In addition, this invention feature adds rigidity to the supercharger 10, and maximizes the manufacturing precision, thereby resulting in improved alignments between gears and shafts for smoother, quieter operation, simplified manufacturing processes, and reduced overall manufacturing costs.
Again referring to
Some centrifugal superchargers employ the existing lubrication system of the host engine for the supercharger lubrication. However, there exist several advantages of having a self-contained supercharger lubrication system, wherein the supercharger's lubricating fluid is separate from the engine's lubricating fluid. One advantage of a self-contained lubrication system is simplification and ease of installation. Some existing supercharger self-contained lubrication systems utilize a splash system wherein one or more gears are dipped into an oil bath. However, these designs suffer from the disadvantage that built-up heat cannot be discharged.
Referring again to
Some superchargers provide an air-assist approach to augmenting lubricating oil circulation within the supercharger gearcase. Generally, the air assist approach results in an air-oil mist lubrication, which aids in achieving reliable operation and the minimization of bearing assembly failure.
In one embodiment of the present invention, the supercharger 10 preferably includes an air assist approach, wherein compressed air from the supercharger 10 is introduced into the lubricating oil by use of a mixing air-assist nozzle assembly (not shown). Such an air-assist assembly may be similar to one described in U.S. Pat. No. 6,293,263. In operation, engine oil, under pressure, mixes with supercharger discharge air, also under pressure, and introduces an air-oil lubricating mist into the supercharger. The lubricating mist is preferably directed towards the supercharger 10 internal gear, shaft, and bearing components.
One advantage of using an oil/air mist is that the oil can be readily sprayed onto the gears and bearings, thereby maximizing gear and bearing life. Further, the pressurized air atomizes the oil and improves distribution and also assists in driving the oil out of the gear housing 26 after use (and into the lubrication reservoir 28), thereby minimizing the oil cycle time in the gear housing 26, and providing improved lubrication and cooling of the gears and bearings.
Referring to
Referring now to FIGS. 3A-D, the precision bearing fit and alignment required for high-speed supercharger operation is often difficult to maintain. One problem stems from the intrinsic difference in the coefficient of thermal expansion (CTE) between the bearing assemblies, which are typically ferrous-based, and the gear housing, which is usually made of aluminum. For example, the CTE for aluminum is relatively high (0.00001244 unit length change, per degree Fahrenheit) when compared to ferrous materials such as cast iron (0.00000655), carbon steel (0.00000533), and 440C stainless steel (0.0000056). Most bearing assemblies, such as those used by the present invention, are comprised of steel or ceramic (Silicon Nitride) rolling elements, retained in angular position and alignment by a cage, and interposed between inner and outer steel races. Typical material of the steel races would be SAE52100 ferrous-based steel, although other ferrous-based materials may be used including 440C, and martensitic Chromium steels with homogeneous carbonitride microstructure.
As shown in FIGS. 3A-D, according to another aspect of the present invention, an intermediate member, sheath, or sleeve 60 is disposed around the impeller shaft bearing assemblies 40a, 40b. Sleeve 60 preferably comprises a ferrous-based material having a CTE that is substantially similar to the CTE of the bearing assemblies 40a, 40b. According to some embodiments, the CTE of the sleeve preferably includes a CTE that may range between about 0.000004 and about 0.000007 in/in-° F. (i.e., 4.0×10−6, and 7.0×10−6 in/in-° F.). Suitable ferrous-based materials for the sleeve 60 include, but are not limited to, grade G2 gray iron, DURA-BAR®, free-machining steels such as 12L14, and all other ferrous-based materials having a CTE that is substantially similar to the CTE of the bearing assemblies 40a, 40b (DURA-BAR is a registered trademark of Wells Manuf. Co. of Skokie, Ill.).
As shown in FIGS. 3A-D, the sleeve 60 includes an opening 62 for gear engagement. Additionally, the sleeve 60 includes a lubrication conduit 64 in fluid communication with a lubrication oil supply conduit 51, and lubrication apertures 65 in fluid communication with lubrication conduit 64. Lubricating oil may then drain back to reservoir 28 via drain port 66, which is aligned to be in communication with port 54 (shown in
According to some embodiments, the intermediate member, or sleeve 60 is pressed or shrink-fitted into the gear housing 26. In other embodiments, sleeve 60 may be installed with a clearance fit into housing 26, and retained thereto by a fastener, or other suitable device.
Referring now to
In a preferred embodiment, lubricating oil, supplied under pressure via conduit 51, which is in communication with conduit 63, is forced into annular gap 67 and creates a hydrostatic supporting force, which reacts to gear loads during supercharger 10 operation. Advantageously, this hydrostatic load supporting mechanism also promotes vibration damping characteristics, resulting in quieter operation of the supercharger 10.
One feature of the sleeve 60 is that it maintains the bearing assemblies 40a, 40b securely in the gear housing 26 during a range of supercharger 10 operating temperatures. More importantly, the fit between bearing races 40a, 40b and sleeve 60 are maintained regardless of operating temperature. This is achievable because the CTE's of the sleeve 60 and the bearing assemblies 40a, 40b are substantially matched, thereby expanding and contracting in unison. This feature is especially beneficial to the high-speed impeller shaft 20 bearings 40a, 40b, which may operate at speeds exceeding 60,000 RPM. It will be appreciated that a sleeve(s) 60 may also be placed around the driveshaft bearing assemblies 38a, 38b.
Referring now to
Referring to FIGS. 4C-D, superchargers can experience very fast drive- and impeller shaft acceleration rates. The acceleration rates are amplified by the step-up ratio between the driveshaft 12 and the impeller shaft 20, which is typically in the range of 3:1 to 5:1 (i.e., 3 to 1 and 5 to 1). That is, the impeller shaft 20 may rotate five times faster than the driveshaft 12. High acceleration and deceleration forces, generally caused by “blipping” the engine, can stress the impeller shaft 20 and its related components, and cause de-stabilizing effects of bearings 40a, 40b, sufficient to cause catastrophic failure. However, the most severe stresses and bearing instabilities generally occur during the transition from very high to relatively slow impeller shaft 20 rotational speeds. An extreme example would be a very rapid rotational acceleration immediately followed by a very rapid deceleration. Such an acceleration rate with the peak point of destabilization is depicted in
Again referring to
As shown in
By way of example, a FORMSPRAG® sprag clutch (part number CL42875) can be used as the clutch in the present invention (FORMSPRAG is a registered trademark of Dana Corporation of Toledo, Ohio). Of course, other types of clutches, including, but not limited to roller clutches, spring clutches, centrifugal clutches, friction clutches, non-friction clutches, mechanical clutches, pneumatic clutches, hydraulic clutches, electrical clutches, diaphragm clutches and hysteresis clutches, can be employed without departing from the scope of the present invention. It will be appreciated that the disengagement device 70 may be located anywhere between the engine 14 and the impeller 22. For example, the disengagement device 70 may be located between the driveshaft 12 and the impeller shaft 20, or between the impeller shaft 20 and the impeller 22.
According to other embodiments, the disengagement device 70 may comprise a speed-sensitive engagement mechanism such as a traditional centrifugal clutch. Alternatively, the disengagement device 70 may comprise both a speed-sensitive engagement feature and an overrunning or disengaging feature. Advantageously, the speed-sensitive engagement feature permits the supercharger 10 to be substantially disengaged from the engine 14 during very low speed operation and engine idle, when supercharger 10 noise maybe objectionable.
High-performance superchargers (such as for competitive drag racing applications) require high rotational speeds that create high air-flow and pressure ratios, thereby creating significant rotordynamic problems and challenges. One such problem is the inherent lack of stiffness at the impeller-to-impeller shaft shoulder connection point. In a typical supercharger, the impeller abuts against a spacer, which in turn abuts against a shoulder on the impeller shaft. The diameter of the impeller shaft shoulder is normally only slightly larger than the diameter of the impeller shaft, thereby resulting in a relatively low bending stiffness in the region between the impeller and the adjacent support bearing. Low stiffness in this region may result in impeller shaft bending at rotational speeds that are within the range of the supercharger's high-speed operation, giving rise to rotordynamic critical speeds, identified by dynamic instabilities and/or excessive vibration. Excessive impeller shaft bending and associated dynamic instabilities frequently results in the impeller contacting the compressor housing, causing catastrophic failure of the impeller.
Referring to
As best seen in FIG. SA, transition section 20c preferably comprises a curvilinear taper providing a gradual transition between the first and second impeller shaft sections. In the illustrated embodiment, transition section 20c is substantially concave. However, as would be understood to those of ordinary skill in the art, transition section 20c may also be substantially convex or substantially straight, without departing from the scope of the present invention. Advantageously, the transition section 20c is configured to significantly reduce impeller shaft stress at critical rotational speeds. More particularly, the tubular spacer 84 allows the transition section 20c to be shaped in a preferred configuration, e.g., a fillet with generous radius, thereby dramatically increasing the fatigue resistance of the impeller shaft 20. This is because the transition section 20c can be shaped to minimize localized stresses, thereby eliminating or minimizing the formation of fatigue cracks.
Referring now to FIG. SB, other advantages of replaceable shaft-bearing cartridge 68 become apparent. In this preferred embodiment, bearings 40a, 40b are of the angular contact type, and are mounted as duplex tandem pairs, known in the art as “DT”, with the pairs, in turn mounted “back-to-back” to each other. Bearings 40a are firmly retained to impeller shaft 20 proximal section 20b by retaining washer 86 and threaded fastener 87, which engages a mating threaded receptacle in proximal section 20b. Bearings 40b are retained by spacers 84, 82, impeller 22, washer 88 and impeller fastener 89, which engages a mating threaded portion of distal section 20a. Preferably, a static preload force should be applied in order to maintain stability of 40a, 40b. Preload is provided by spring elements 83, which generate a preload force against retainers 85. In this preferred embodiment, the preload force may range from about 50 lbf to about 400 lbf.
Alternative embodiments are also possible, and these are described and incorporated herein as within the scope of the present invention. In one such embodiment, angular contact bearings 40a, 40b may be configured as rigidly preloaded duplex sets, and mounted either back- to-back (known in the art as “DB”) or face-to-face (known in the art as “DF”). Advantageously, the clamping forces acting on bearings 40a, 40b inner races are developed by threaded fastener 87 and impeller fastener 89, which in turn enable the rigid preloading of bearings 40a, 40b.
Referring now to
On one hand, it is desirable to have a low blade count at the impeller inlet to decrease aerodynamic blockage and increase airflow. On the other hand, in order to increase impeller efficiency, a high blade count is preferred further along the airflow passageway (especially near the impeller outlet). Such a design allows the specific impeller work (e.g., total work per unit blade) to be reduced, thereby reducing blade loading effects to more efficient levels.
Referring to
As depicted in
Specifically, in a preferred embodiment (as shown in
One feature of this aspect of the invention is that the relatively low blade count within inlet region 90 induces a low density air flow that minimizes aerodynamic blockage. Conversely, the relatively high blade count within outlet region 96 provides excellent aerodynamic performance by minimizing blade loading.
Referring now to
As shown in
As shown in a preferred embodiment of
Referring to
Thus, it is seen that a centrifugal supercharger is provided. One skilled in the art will appreciate that the present invention can be practiced by other than the above-described embodiments, which are presented in this description for purposes of illustration and not of limitation. The description and examples set forth in this specification and associated drawings only set forth preferred embodiment(s) of the present invention. The specification and drawings are not intended to limit the exclusionary scope of this patent document. Many designs other than the above-described embodiments will fall within the literal and/or legal scope of the following claims, and the present invention is limited only by the claims that follow. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well.
This is a continuation application of co-pending U.S. application Ser. No. 10/698,192 filed Oct. 31, 2003 entitled “Supercharger.”
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10698192 | Oct 2003 | US |
| Child | 11470114 | Sep 2006 | US |
