Abstract:
A supercharged internal combustion engine system wherein during periods of high power demand the weight of combustion chamber charge is increased by cooling a portion of intake air in a turboexpander using high-pressure air from a storage tank. In addition to increasing engine output power, cold air intake also reduces engine pre-ignition (knocking) thereby reducing emissions. Mechanical energy produced during expansion of high-pressure air may be used to operate a turbocompressor, which compresses intake air and further increases charge weight. Effective supercharging is achieved even at low engine speeds. One of the objects of the invention is to obtain more power from small displacement ICE and thus providing automotive vehicles with sufficient acceleration in addition to good fuel economy. Another object of the invention is to enhance turbocharged engines and reduce their response lag. Air storage tank may be recharged using energy recovered during vehicle deceleration.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional patent application U.S. Ser. No. 61/124,090, filed on Apr. 14, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to supercharged internal combustion engines and, more particularly, to superchargers capable of fast response to engine demand and delivering boost independent of engine speed. 
       BACKGROUND OF THE INVENTION 
       [0003]    Supercharging of Internal Combustion Engines: One of the long-term goals of the automotive manufacturers is to reduce fuel consumption and emissions of modern automotive vehicles powered by internal combustion engines (ICE) while increasing engine efficiency. One approach to reaching this goal is reducing the ICE displacement. However, downsized engines having reduced swept volume typically exhibit insufficient power and torque when operating with normal aspiration. Performance of downsized engines may be recovered by supercharging. It is well known in the art that ICE power output increases with increased weight of air ingested into engine cylinders and available for combustion. Weight of intake air ingested into engine cylinders can be increased by either (1) increasing the pressure of intake air beyond what can be accomplished by natural aspiration or by (2) reducing the temperature of intake air or by (3) a combination of (1) and (2). A supercharged ICE, therefore, receives combustion air with higher density than a naturally aspirated ICE. As a result, supercharging allows generating increased power from an engine of a given displacement or, generating a given power output from an engine of smaller size, weight, cost, and emissions. In addition, reduced charge temperature is known to reduce ICE emissions by decreasing charge pre-ignition also known as knocking. 
         [0004]    One commonly used type of a supercharger is the exhaust-gas turbocharger which typically includes a turbine and a centrifugal compressor on a common shaft. The turbine is rotated by exhaust gases from the engine and spins the compressor. The compressor receives intake air, compresses it, and supplies it to ICE combustion chamber(s). Turbochargers provide the advantages of relatively smooth transition from natural aspiration to supercharged operation while utilizing some of the residual energy of hot exhaust gas, which would otherwise be largely wasted. The compression of intake air increases its temperature and thus undesirably limits its density. The challenges of constructing a turbocharged ICE include: 1) reducing as much as possible the response time lag and 2) reducing the temperature of air delivered to ICE. Information relevant to attempts to overcome these challenges and the disadvantages of such attempts are described below. 
         [0005]    A turbocharged ICE is susceptible to a slow response time known as the “turbo lag” which is caused by the low pressure and low quantity of exhaust gases that are available to operate the turbine at low engine speeds. This translates to insufficient quantity of intake air delivered to the engine and results in insufficient torque at low engine speeds. The turbo-lag problem may be corrected in-part by the use of a variable nozzle turbine, which alters the cross-sectional area through which the exhaust gas flows in accordance with engine speed. However, this approach provides only a partial solution, adds complexity and cost, and reduces reliability. Another approach to reducing the turbo lag may use one or more jets of air injected onto the compressor wheel of a turbocharger as disclosed, for example, by Williams et al. in U.S. Pat. No. 3,190,068. Such air jets may be directed generally onto the vanes of the compressor wheel so as to transfer a part of their momentum to the wheel and thus accelerate the rotational speed of the compressor. Air injected in this manner becomes a part of the intake air ingested by the engine. 
         [0006]    Recently, an electrically-assisted turbocharger (also known as the “e-turbo”) has been proposed to remedy the turbo lag. Since the e-turbo makes supercharging independent of engine speed, it promises to virtually eliminate the turbo lag. Generally, in the e-turbo, electric power drawn from vehicle electric system (e.g., battery) is provided to an electric motor which spins a turbo-compressor. There are two different types of e-turbo known. The first type is formed by directly coupling an electric motor to the shaft of a conventional exhaust turbocharger, as disclosed, for example, by Kawamura in U.S. Pat. No. 4,958,497. A drawback of this approach is that during acceleration of the e-turbo to operational speed the electric motor has to overcome the compound inertia of both the turbo-compressor and the exhaust turbine while additionally being exposed to very high temperatures. The second type of e-turbo is formed by coupling an electric motor to a turbocompressor, as disclosed, for example, by Woolenberger et al., in U.S. Pat. No. 6,079,211. This type of an e-turbo can be used in series or in parallel with a conventional turbocharger to reduce the turbocharging lag and to increase torque at low ICE speeds, such as disclosed, for example, by Hoecker et al., in U.S. Pat. No. 6,889,503. However, both e-turbo approaches face the challenge of attaining the extremely fast startup and acceleration to reach operating speeds of 50,000 to 70,000 revolutions per minute (rpm) in less than one second. To meet this challenge may require ultrahigh power electronics and electric power source combined with sophisticated computer control. In particular, according to an article authored by Thomas Kattwinkel et al. entitled “Mechatronic Solution for Electronic Turbocharger” SAE paper number 2003-01-0712 published by the Society of Automotive Engineers, Inc., Warrendale, Pa., the e-turbo electric demand may not be satisfactorily met with the standard 12 volt automotive battery system. 
         [0007]    In summary, prior art does not teach a supercharged ICE system that is effective during the conditions of high torque and low engine speed, has a fast response, is simple, economical, and can be easily retrofitted onto existing ICE, does not require exotic electric motors and power supply, avoids exposing electrical components to high temperatures, and reduces susceptibility to charge pre-ignition. Furthermore, the prior art does not teach an ICE where intake air is mixed with cold air from a turboexpander. Moreover, prior art does not teach an ICE supercharged by an a turbocompressor operated by a turboexpander expanding high-pressure air, wherein compressed intake air produced by the turbocompressor is cooled by the cold air produced by the turboexpander. It is against this background that the significant improvements and advancements of the present invention have taken place. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a supercharged ICE system wherein the supercharger assembly comprises a turboexpander expanding high-pressure air that supplies cold, dense air to ICE combustion chamber. Intake of dense air increases the weight of ICE charge and thus enables increase of ICE output power. The supercharger assembly may also include an ejector pump operated by cold air from the turboexpander. The nozzle pumps intake air thereby increasing its density both by compression and by cooling. The supercharger assembly may also include a turbocompressor for feeding compressed air into the ICE intake. The turbocompressor is operated by the energy extracted by the turboexpander from expanding high-pressure air. The supercharged ICE system may further include means for regulating the flow and/or pressure of high-pressure air fed to the turboexpander and thereby regulating the supercharging action. In addition, the supercharged ICE system may include means for sensing ICE power demand and appropriately controlling the operation of the turboexpander and of the turbocompressor pump (if used) to supercharge the ICE in response to demand. 
         [0009]    Turboexpanders are well known devices in the art of cryogenics where they are used to refrigerate gas for production of cryogenic liquids. See, for example, “Turboexpanders and Process Applications,” by H. P. Bloch and C. Soares, Gulf Professional Publishing of Butterworth-Heinemann, Woburn, Mass., 2001. The turboexpander comprises an expansion turbine that converts pressure energy of a gas into mechanical work as the gas expands though the turbine. More specifically, expansion of high-pressure gas in the turboexpander spins the turbine to very high rotational speeds. The gas is substantially cooled as a part of the expansion process. The turboexpansion process is nearly isentropic with the efficiency often exceeding 90%. Depending on the application, the mechanical energy generated by the turboexpander may be dumped into a brake such as a fluid brake (e.g., oil brake) or it may be used to operate a turbocompressor. Assemblies having a turboexpander and turbocompressor on the same shaft are known in the art of cryogenic refrigeration. In a turboexpander/turbocompressor, mechanical energy generated by turboexpansion of a first stream of gas is transferred from the turbine via the common shaft to a compressor wheel of the turbocompressor that compresses a second stream of gas. 
         [0010]    In one embodiment of the present invention a supercharger assembly comprises a turboexpander expanding high-pressure air from a high-pressure air source and discharging expanded cold air stream into ICE intake passage. Cold air may be discharged through a nozzle producing a high-velocity flow which entrains intake air from other intake air sources and pumps it into ICE intake. Cold air from the turboexpander may be mixed with intake air from other sources such as ambient air, engine-driven supercharger, exhaust gas turbocharger, or electric turbocharger. The resulting intake air mixture is colder and denser. Flow of intake air from other sources may be regulated by a valve. The supercharged ICE system may also include a compressor and an air tank for providing high-pressure air to the turboexpander. The compressor may be driven by the ICE output shaft, vehicle drive train, an electric motor, or by other suitable means. Mechanical energy produced by the expansion of high-pressure air in the turboexpander may be dissipated in a brake. 
         [0011]    In another embodiment of the invention a supercharger assembly comprises a turboexpander expanding high-pressure air and providing expanded cold air into ICE intake while also operating a turbocompressor to pump intake air into the ICE intake. Cold air from the turboexpander is mixed with the pumped (compressed) air from the turbocompressor and cools it before feeding the mixture to the ICE intake. In yet another embodiment, a bypass duct is used to reduce flow path resistance of the turbocompressor during natural ICE aspiration. 
         [0012]    Accordingly, it is an object of the present invention to provide a supercharged ICE system capable of generating a high volume flow of intake air at high density especially during the conditions of high torque demand and relatively low engine speeds. The supercharged ICE system of the present invention is simple, lightweight, and inexpensive to manufacture which makes it suitable for large volume production of automotive vehicles. 
         [0013]    It is another object of the invention to provide a supercharger assembly having a fast response to demand conditions. 
         [0014]    It is yet another object of the invention to provide a supercharger assembly that is compact and easily integrable into an ICE system. 
         [0015]    It is yet another object of the invention to provide a supercharger assembly that is simple, robust, and economical. 
         [0016]    It is yet another object of the invention to provide a supercharger assembly that can be easily retrofitted onto existing ICE. 
         [0017]    It is still another object of the invention to cool ICE intake air compressed by a turbocharger or an engine driven supercharger. 
         [0018]    It is still another object of the invention to obtain more power from a small displacement ICE and thus providing automotive vehicle equipped with such an ICE with sufficient acceleration in addition to good fuel economy. 
         [0019]    It is a further object of the invention to provide a booster stage for a conventional supercharger (engine-driven supercharger or exhaust gas turbocharger) and thus improve ICE performance at low rpm while also reducing response time. 
         [0020]    It is still further object of the invention to provide a supercharger that can be used with hybrid vehicles to boost the power of the ICE and thus giving the hybrid vehicle more power to accelerate and ascend grade. 
         [0021]    These and other objects of the present invention will become apparent upon a reading of the following specification and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic view of a supercharged ICE system in accordance with one preferred embodiment of the subject invention. 
           [0023]      FIG. 2  is a schematic view of a supercharged ICE system in accordance with another preferred embodiment of the subject invention. 
           [0024]      FIG. 3  is a schematic view of a supercharged ICE system in accordance with yet another preferred embodiment of the subject invention. 
           [0025]      FIG. 4  is a schematic view of a two-stage configuration of the turboexpander/turbocharger assemblies. 
           [0026]      FIG. 5  is a flow chart showing preferred control routine for operations of an electronic control unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Selected embodiments of the present invention will now be explained with reference to drawings. In the drawings, identical components are provided with identical reference symbols. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are merely exemplary in nature and are in no way intended to limit the invention, its application, or uses. 
         [0028]    Referring to  FIG. 1 , there is shown a supercharged internal combustion engine (ICE) system  10  in accordance with a first embodiment of the subject invention. The ICE system  10  comprises an ICE  20  and a supercharger assembly  100 . The ICE  20  has at least one combustion chamber  34  fluidly coupled to an intake passage  22  and to an exhaust passage  24 . The type of ICE  20  can be either a compression ignition (diesel), a fuel injected spark ignition, carbureted spark ignition, or homogeneous charge compression ignition (HCCI) also known as controlled auto-ignition (CAI). Furthermore, the ICE  20  may also include an output shaft  28  and a torque sensor  30  for sensing ICE output torque. When the ICE system  10  is installed in an automotive vehicle, the output shaft  28  may provide power to a transmission  74 , which in turn, may spin a drive shaft  48  to operate vehicle wheels  64  via differential  82  and axle  52  as is commonly practiced in the art. The supercharger assembly  100  may comprise an intake duct  126 , a turboexpander assembly  120 , a high-pressure air supply line  138 , control valve  132 , pressure regulator  130 , interconnecting lines  136  and  137 , and air feed line  148 . In addition, the supercharger assembly  100  may also include a compressor  164 , compressor inlet line  176 , aftercooler  178 , check valve  180 , air tank  160 , and interconnecting lines  172 ,  176 ,  184 , and  186 . 
         [0029]    The intake duct  126  has an upstream end  108  fluidly connected to a source of intake air and a downstream end  110  fluidly connected to the intake passage  22 . Suitable sources of intake air include 1) atmospheric air which may be provided at near ambient pressure and 2) output air from a supercharger (such as engine-driven supercharger, exhaust gas turbocharger, or an electric turbocharger) which may be preferably provided at a pressure higher than ambient atmospheric pressure. The upstream end  108  may be equipped with a pressure sensor  156  and a temperature sensor  158 . The downstream end  110  may be equipped with a pressure sensor  154  and a temperature sensor  151 . The intake duct  126  may also include a valve  168  to regulate air flow therethrough. The valve  168  may be installed upstream of the location where the air feed line  148  is fluidly connected to the intake air duct  126 . Suitable valve  168  includes an automatic check valve permitting a intake air flow from the upstream end  108  to the downstream end  110  of duct  126  but restricting the flow in the opposite direction. An example of such an automatic check valve may be a flapper style check valve. Another suitable valve  168  may be an actuated valve, which in an open position offers low resistance to intake air flow. Such a valve may be a butterfly-type valve. A suitable actuator may be a stepping motor, which allows precise control over valve position. 
         [0030]    The compressor  164  can be of any suitable type including piston, vane, scroll, diaphragm, and screw type (also known as Lysholm) and it may have one or more stages to obtain a desired level of compression. Suction port of the compressor  164  is fluidly coupled by the inlet line  176  to the intake duct  126  and it is adapted for drawing a portion of intake air therefrom. The compressor  164  is preferably driven mechanically, hydraulically or by other suitable means from the output shaft  28  of the ICE  20  or from the vehicle drive shaft  48 . Suitable mechanical means may include 1) direct coupling and/or 2) a system of belt and pulleys. Suitable mechanical means may comprise a clutch  157  that allows engaging the compressor  164  in accordance with predetermined conditions as it will be described below. Clutch  157  may be controlled mechanically, electrically, pneumatically, hydraulically, or by other suitable means. Preferably, the drive of the compressor  164  has a variable speed capability to allow the compressor  164  to operate at a controlled speed and substantially independent from the speed of the output shaft  28  and the drive shaft  48 . This approach allows the compressor  164  to deliver large quantities of air even the output shaft  28  and the drive shaft  48  operate at low speeds. The compressor  164  may be engaged, for example, during vehicle deceleration to a stop and recover a significant portion of vehicle&#39;s kinetic energy event at relatively slow vehicle motion. For example, suitable hydraulic means may drive the compressor  164  from the vehicle drive shaft  48  using a hydraulic pump and motor assembly with variable speed capability. Alternatively, the compressor  164  may be driven by an electric motor. Discharge port of the compressor  164  is fluidly coupled to the air tank  160  via the aftercooler  178 , check valve  180  and interconnecting lines  172 ,  184  and  186 . 
         [0031]    The aftercooler  178  may be of the same general type used in conventional compressed air systems to remove the heat of compression from the air downstream of a compressor. The aftercooler  178  may be cooled by ambient air or by ICE coolant or other suitable means. The check valve  180  prevents a backflow of high-pressure air from the air tank  160  into the compressor  164  when the compressor is not operating. Line  184  may also include a water separator to remove water condensate from cooled air flow. The design and the choice of materials for the air tank  160  are preferably selected to reduce the likelihood of tank rupture in case of vehicle collision and/or fire. In this respect a plurality of smaller interconnected tanks may be preferable to a single large tank. The air tank  160  may also include a pressure sensor and a temperature sensor that may be used together to determine the amount of air stored. In addition, the air tank  160  may contain an automatic drain valve for automatic expulsion of water condensate that has formed inside the tank. 
         [0032]    The pressure regulator  130  is fluidly connected to the air tank  160  by means of the high-pressure line  138 . Preferably, the pressure regulator  130  is remotely controllable in a manner that allows remotely controlling the pressure level in line  137 . Suitable pressure regulators that are remotely controllable either electrically, pneumatically, hydraulically, or mechanically have been disclosed in prior art and are available commercially. The control valve  132  is fluidly connected to the pressure regulator  130  by means of line  136  and to the inlet port of the turboexpander  144  of the turboexpander assembly  120  by means of line  137 . The control valve  132  may be of on/off type preferably having a very low flow impedance. Alternatively, the control valve  132  may be adapted for substantially smooth regulation of flow of high-pressure air in which case the pressure regulator  130  may become unnecessary. 
         [0033]    The turboexpander assembly  120  comprises a turboexpander  144  and a brake  158 . The turboexpander  144  includes a turbine wheel  134 . The turbine wheel  134  and the brake  158  are mounted on a common shaft  166 . The inlet port of turboexpander  144  is fluidly connected to the air tank  160  via pressure regulator  130 , valve  132 , and interconnecting lines  136 ,  137 , and  138 . The outlet port of the turboexpander  144  is fluidly connected to the air feed line  148  which is terminated inside the intake duct  126  with a nozzle  140 . The nozzle  140  is oriented toward the downstream end  110  of the duct  126 . The purpose of the nozzle is to direct cold air generated by the turboexpander assembly  120  generally in the direction of the downstream end  110  of the intake duct  126 . One nozzle or several nozzles working in parallel may be used. Suitable nozzle types include a simple orifice, a subsonic nozzle, a sonic nozzle, supersonic nozzle, converging-diverging nozzle, and a lobed nozzle. Lobed nozzles are known to have improved characteristics for mixing of the surrounding air with the high velocity jet the produce. An engine throttle, if used, may be located in the intake duct  126 . 
         [0034]    The ICE system  10  preferably includes an electronic control unit (ECU)  194 . Suitable ECU may comprise a central processing unit, a read-only memory, random access memory, input and output ports, and the like. The ECU  194  may be configured to receive signals from sensors in the ICE system  10 , to determine whether certain predetermined conditions exist based on the measured parameters. 
         [0035]    During normal operation of the supercharged ICE system  10 , the compressor  164  is caused to maintain air pressure in tank  160  within predetermined limits. In particular, the compressor  164  draws air (preferably free of dust and solid particulates ) from the intake duct  126  through the inlet line  176  and compresses it to a desired pressure. Preferred compressor output pressure is between 100 and 300 psi. As an alternative, the compressor  164  may draw filtered air from ambient atmosphere. Output of the compressor  164  is fed through line  172  into the aftercooler  178  where the heat of compression is largely removed, and through line  184 , check valve  180  and line  186  into the tank  160 . The air tank  160  may be equipped with a pressure switch having one higher setting and one lower setting. The pressure switch may be wired to the controls of the compressor  164  (and/or to the clutch  157 , if used) so that the compressor  164  maintains the pressure in the air tank  160  between predetermined limits. Alternatively, the compressor  164  may be equipped with an unloader valve which automatically relieves the compressor of the pumping load when air tank  160  is charged to a predetermined pressure value. Preferably, the compressor  164  is engaged in a smooth and/or gradual manner to avoid imposing abrupt load on its source of motive power. In particular, to avoid excessive power drain on the ICE or the vehicle power train, operation of the compressor may be prohibited or restricted during periods of high power demand. Alternatively, operation of the compressor may be allowed only when the ICE output torque is less than a predetermined ICE output torque value. If the compressor  164  is operated from the output shaft  28  or the vehicle drive shaft  48 , operation of the compressor  164  may be allowed only when the torque in the output shaft  28  or the vehicle drive shaft  48  is less than a predetermined shaft torque value. If the compressor  164  is operated from the output shaft  28  or the vehicle drive shaft  48  using a variable speed drive, such a variable speed drive is preferably arranged to operate the compressor  164  at a speed substantially independent of the speed of the output shaft  28  or the vehicle drive shaft  48 . In particular, constant speed of compressor  164  is preferably maintained during at least a portion of time during which the vehicle decelerates. This approach permits efficient use of vehicle&#39;s kinetic energy to operate the compressor  164 . 
         [0036]    When the ICE  20  operates without the aid of the supercharger  100 , the control valve  132  is closed. Intake air stream  150  preferably free of dust and solid particulates may enter the upstream end  108  of intake duct  126  and it may exit through the downstream end  110  into the intake passage  22  of ICE  10  without a significant temperature change. The compressor  164  may be operated concurrently, as necessary to maintain pressure inside the tank  160  within predetermined limits. 
         [0037]    When the ICE  20  operates with the aid of the supercharger  100 , the pressure regulator  130  regulates high-pressure air it receives from the high-pressure supply line  138  and flows regulated high-pressure air at a predetermined pressure into the line  136 . The valve  132  and the lines  136 ,  137 , and  148  are preferably constructed to have a very low impedance to air flow. The control valve  132  is in an open position and allows the high-pressure air to flow through the line  137  to the inlet port of the turboexpander  144 . The high-pressure expends in the turboexpander  144 , spins the turbine wheel  134 , and cools down. Mechanical work extracted in the expansion process is transmitted from the turbine wheel  134  by the common shaft  166  to the brake  158 . The brake  158  may dissipate supplied work into suitable gas or liquid medium. Cold air exits the turboexpander  144  and it forms a cold air stream  174 . The cold air stream  174  is transported through the air feed line  148  to the nozzle  140  and it emerges therefrom as a stream  146 . Concurrently, intake air stream  150  preferably free of dust and particulates enters the upstream end  108  of duct  126 , it mixes with the stream  146 , thereby producing a mixed engine feed stream  128 . As a result, air density at the downstream end  110  of duct  126  is greater than air density at the upstream end  108 , and the air temperature at the at the downstream end  110  is lower than at the upstream end  108 . This means that the air density of the engine feed stream  128  is significantly greater than the density of the intake air stream  150 . The mass flow rate of intake air flowing the intake passage is thus significantly increased, thereby enabling the ICE to produce more power. This a potential for producing more power be utilized by concurrently increasing the fuel flow rate to an appropriate level. 
         [0038]    If the valve  168  is installed in the intake duct  126 , it may be used to regulate the flow of the intake air stream  150 . For example, the valve  168  may be in a closed position when the mass flow rate of high-pressure air fed to the inlet of turboexpander  144  exceeds a predetermined mass flow rate value. When the valve  168  may be in a closed position, all of the intake air for the ICE is provided by the turboexpander assembly  120 . In particular, the output flow of the turboexpander assembly  120  may be increased to boost the pressure in the intake passage  22  to a level beyond what may be possible with the valve  168  in an open position (or with the valve  168  not installed). This may yield a double benefit of supplying the ICE with intake air that is both cold air and at elevated pressure. If the valve  168  is employed to regulate the intake air flow, the rates of closing and opening the valve are preferably controlled so that the density of intake air in intake passage  22  is varied substantially smoothly and sudden surges or drops in ICE output power are avoided. It should be noted that the intake air stream  150  may originate from intake air sources including ambient atmosphere or a discharge flow from a supercharger. The latter may be an engine driven supercharger, a turbocharger, or electric turbocharger. Injection of cold air stream  174  into an output of such a supercharger may reduce the need for an intercooler which is normally used downstream of a supercharger. 
         [0039]    Under typical driving conditions the periods of high-power demand are relatively short and (depending on vehicle driving conditions) may occur on the average only about 10% of the vehicle operating time. This means that the supercharger  100  may operate in an intermittent mode, supercharging the ICE for about 10% of the vehicle operating time. This may leave on the average about 90% of the vehicle operating time available for recharging the supercharger tank  160 . 
         [0040]    At any time during the ICE operation, the ECU  194  may monitor one or more operating parameters of the ICE system  10  and regulates the mass flow rate of air through the vortex tube  120  by operatively controlling the pressure regulator  130  and the valve  132  according to predetermined conditions. Operating parameters monitored by the ECU may include engine rotational speed, engine output torque, fuel flow rate, vehicle speed, throttle opening, and position of accelerator pedal. Other useful parameters monitored by the ECU may include ambient air pressure and temperature, intake air mass flow rate, intake air pressure and temperature, detection values of pressure sensors  154  and  156 , and detection values of temperature sensors  151  and  158 . The torque value can be either directly measured (for example, the torque value can be the detection value from the torque sensor  30 ) or it can be inferred from other ICE parameters. In particular, it is well known that engine torque value can be estimated from one or more ICE parameters including intake air mass flow rate, spark timing, or combustion chamber pressure data as noted, for example, by T. Jaine et al. in “High-Frequency IMEP Estimation and Filtering for Torque-Based SI Engine Controls,” SAE paper number 2002-01-1276, published by the Society of Automotive Engineers, Inc., Warrendale, Pa. Alternatively to using an ECU with a central processing unit, various electrical, mechanical, electromechanical, hydraulic, and/or pneumatic control mechanisms may be used to operate the valve  132  and the pressure regulator  130  in response to predetermined conditions. It will be apparent to those skilled in the art from this disclosure that the precise structure and algorithms for the ECU can be any combination of hardware and software that will carry out the functions of the present invention. 
         [0041]    Referring now to  FIG. 2 , there is shown a supercharged ICE system  11  in accordance with another embodiment of the subject invention and having enhanced capability to provide dense air to the ICE  20 . The ICE system  11  comprises a supercharger assembly  101  which is similar to the supercharger assembly  100  except that the brake  158  in the supercharger assembly  100  is replaced by a turbocompressor  182  in the supercharger assembly  101 . The turbocompressor  182  is preferably of the radial type frequently used in turbochargers and it includes a compressor wheel  145  is mounted on a common shaft  166  with the turbine wheel  134  of turboexpander  144 . In particular, the turboexpander  144 , turbocompressor  182 , and the shaft  166  for a turboexpander/turbocompressor assembly  162 . The inlet of the turbocompressor  182  is fluidly connected to the intake duct  126   a  and arranged to receive intake air therethrough. The outlet of the turbocompressor  182  is fluidly connected via intake duct  126   b  to the intake passage  22  of the ICE  20 . Note that while the general configuration of the turboexpander/turbocompressor assembly  162  is similar to that of commonly used turbocharger, there are significant difference in its design and construction. In particular, the turboexpander/turbocompressor assembly  162  operates at near ambient or at subambient temperatures, which permits the use of common materials for construction. For example, the turbine wheel  134 , the compressor wheel  145 , and the housings of the turboexpander  144  and the turbocompressor  182  may be made of aluminum, graphite epoxy, fiberglass epoxy, or plastics. In addition, low friction bearings such magnetic bearing may be used to suspend the shaft  166 , which allows for a quick response to acceleration demands. This is in a sharp contrast to a turbocharger that is exposed to the high temperature exhaust gases, which in turn necessitates the use of exotic, costly, and difficult-to-machine high-temperature materials. 
         [0042]    The operation of the supercharged ICE system  11  is similar to that of the supercharged ICE system  10  except that the intake air provided to the ICE  20  is also compressed to a higher pressure. In particular, when the ICE  20  operates with the aid of the supercharger  101 , high-pressure air flows through the line  137  into the turboexpander  144 , expands therein, spins the turbine wheel  134 , and cools down. Cold expanded air exits the turboexpander  144  and it forms a cold air stream  174 . The cold air stream  174  is transported through the air feed line  148  to the nozzle  140  and it emerges therefrom as a stream  146  inside the intake duct  126   b.  Mechanical work generated by the turboexpander  144  from the expansion process is transmitted from the turbine wheel  134  by the common shaft  166  to the compressor wheel  145  of the turbocompressor  182  and spins it. Intake air stream  150  is drawn through the intake duct  126   a  into the turbocompressor  182 , is compressed therein, and fed into the intake duct  126   b  where it is mixed with the stream  146 , thereby producing a mixed engine feed stream  128 ′. Intake air may be significantly heated by the compression in the turbocompressor  182 . Hot compressed air provided by the turbocompressor  182  into the intake duct  126   b  is at least in part cooled by mixing with the stream  146  of cold air fed into the intake duct  126   b  from the turboexpander  144 . As a result, the net increase in temperature (if any) of intake air flowing through supercharger assembly  101  is very limited. This means that the supercharger assembly  101  may provide compressed intake air to the ICE  20  without a need for an intercooler. In particular, depending on the operating conditions of the supercharger assembly  101 , the temperature of the engine feed stream  128 ′ may be lower than, about same as, or higher than the temperature of the intake air stream  150 . Controllability over intake air temperature may be beneficial if the ICE  20  operates in the homogeneous charge compression ignition (HCCI) mode. 
         [0043]    Referring now to  FIG. 3 , there is shown a supercharged ICE system  12  in accordance with another embodiment of the subject invention and having reduced intake flow path resistance during natural aspiration of the ICE  20 . The ICE system  12  comprises a supercharger assembly  102 , which is similar to the supercharger assembly  101  except that it further includes a bypass duct  190  that fluidly connects the inlet and outlet of the turbocompressor  182 . The bypass duct  190  further includes a bypass valve  188  intended to prevent a back flow through the bypass duct. The bypass valve  188  may be formed as a check valve that closes automatically whenever the pressure at the downstream end  110  of the intake duct  126   b ′ exceeds the pressure at the upstream end  108  of the intake duct  126   a ′ by more than a predetermined pressure amount. Alternatively, the bypass valve  188  may an actuated valve of a suitable type (e.g., gate valve, poppet valve, damper valve, or a butterfly valve) operated by the ECU  194 . For example, the ECU  194  may close the bypass valve  188  whenever the speed of the turbocompressor  182  exceeds a predetermined speed value. Conversely, the ECU  194  may open the bypass valve  188  whenever the speed of the turbocompressor  182  is below a predetermined speed value. As another example, the bypass valve  188  may be arranged to be closed when the mass flow rate of high-pressure air fed into the inlet port of the turboexpander  144  is more than a predetermined mass flow rate value and to be open when the mass flow rate is less than a predetermined mass flow rate value. If the valve  188  is an actuated valve, its closing and opening rate may be coordinated with the speed of the turbocompressor  182  to produce a substantially smooth variation in air density at the ICE intake passage  22 . This approach avoids undesirably abrupt changes in supercharger output air density and consequential abrupt changes in ICE power output. Suitably accurate control of valve  188  can be accomplished, for example, by actuating the valve  188  by a stepping motor. 
         [0044]    During a naturally aspirated operation of the ICE  20 , the bypass valve  188  is in an open position and the control valve  132  is closed. The ICE draws the intake air stream  150  through the intake duct  126   a ′ and through the bypass duct  190  into the ICE intake passage  22 . Some portion of the intake air may also flow through the turbocompressor  182 . When the ICE  20  is supercharged by the supercharger assembly  102 , the bypass valve  188  is closed, the control valve  132  is open and the turboexpander/turbocompressor assembly  162  is operated. 
         [0045]    A compression ratio achievable in a single stage turbocompressor is typically less than 1.8. To obtain a higher compression ratio, several turbocompressors  182  may be staged in series.  FIG. 4  shows two turboexpander/turbocompressor assemblies  162   b  and  162   b  connected in series. In particular, the inlet of the turbocompressor  182   a  may be fluidly connected to a source of intake air via the intake duct  126   a,  and the outlet of the turbocompressor  182   b  may be fluidly coupled to an ICE intake via the intake duct  126   b.  The outlet of the turbocompressor  182   a  is fluidly connected to the inlet of the turbocompressor  182   a  via a coupling duct  126   c.  The inlets  137   a  and  137   b  of turboexpanders  144   a  and  144   b  respectively may be connected to either common or separate sources of high-pressure air. The outlet of turboexpanders  144   a  may be fluidly connected to the coupling duct  126   c.  The outlet of turboexpanders  144   b  may be fluidly connected to the intake duct  126   b.  In operation, flow of high-pressure air into turboexpanders  144   a  and  144   b  may be controlled by either a common valve  132  and pressure regulator  130 , or by separate valves and pressure regulator. 
         [0046]    There is a variety of processes the ECU  194  may employ for controlling the operation of the supercharger  100 . Preferably, the ECU repeatedly executes the control routine  900  represented by the flowchart shown in  FIG. 5 . After the control routine  900  is started and the ECU obtains detection values of various ICE system sensors to determine ICE state (step  912 ). Such sensors may include, but are not limited to ICE rotational speed, position of accelerator pedal, throttle opening, fuel flow rate, vehicle speed, ICE output torque, air velocity in the intake duct  126 , air pressure in line  137 , setting of the pressure regulator  130 , position of the control valve  132 , position of the valve  168  (if used), position of the bypass valve  188  (if used), rotational speed of the turboexpander  144 , detection values of pressure sensors  154  and  156 , detection values of temperature sensors  151  and  158 , air pressure and temperature in ICE intake passage  22 , and ambient air pressure, temperature, and humidity. Preferably, the ECU calculates the actual ICE power output (P A ) and the power output being demanded from the ICE (P D ) (step  914 ). Based on the obtained parameters the ECU may determine whether or not an ICE power deficit exists (step  916 ). This may be accomplished, for example, by comparing the values of the actual ICE power output P A  and the demanded ICE power output (power demand) P D . A power deficit may be established when, for example, the power demand P D  is greater than the actual ICE power output P A  by more than a predetermined amount x (namely, P D −P A &gt;x). 
         [0047]    If a power deficit exists, the ECU may then calculate the air density (ρ T,req ) at the downstream end  110  of the intake duct  126  (supercharger output air density) required to meet the power demand at optimum throttle opening (if throttle is used) and air-fuel ratio (step  918 ). If the ICE has an electronically controlled throttle, an optional next step (not shown) can include opening of the throttle by a predetermined amount. The ECU  194  then obtains actual intake air density measurement (ρ T ) by obtaining the detection value of the pressure sensor  154  and temperature sensor  151  (step  920 ). The values of the required air density ρ T,req  and the actual air density ρ T  are then compared (step  922 ). If the required density value ρ T,req  is greater than the actual density value ρ T  by more than a predetermined amount y (namely, ρ T,req −ρ T &gt;y), the ECU increases the mass flow rate dm N /dt of high-pressure air into the turboexpander  144  by a predetermined incremental amount Δ(dm N /dt) (step  924 ). This may be accomplished by increasing the output pressure of the pressure regulator  130  with the valve  132  in open position. The value of incremental amount Δ(dm N /dt) may be made generally proportional to the difference between the required and actual air densities at the downstream end  110  of the intake duct  126  (namely, Δ(dm N /dt)∝ρ T,req −ρ T ). If desired, the incremental amount Δ(dm N /dt) can be appropriately limited not to exceed a predetermined value, and such a value can be updated each time the routine of  FIG. 4  is executed. This approach can be used to avoid abrupt changes in supercharger output pressure and consequential surge in ICE output. Preferably, an increase in the supercharging action is performed so that ICE power is increased in a smooth fashion and with prompt response to demand. To assure proper air-fuel ratio, ECU may adjust fuel flow rate as appropriate to improve ICE performance (step  926 ) and the routine is ended. If the required density value ρ T,req  is not greater than the actual density value ρ T  by more than a predetermined amount y (namely, ρ T,req −ρ T ≦y) (step  922 ), no change to the supercharger condition is required. Then the ECU may adjust fuel flow rate as appropriate for improved ICE performance (step  926 ) and the routine is ended. 
         [0048]    If the ECU determines that a power deficit does not exist (step  916 ), the ECU may then evaluate whether a power excess exists (step  928 ). A power excess may be established when, for example, the demand power output P D  is smaller than the actual ICE power output P A  by more than a predetermined amount x (namely, P A −P D &gt;x). If a power excess exists, the ECU may then calculate the air density ρ T,req  at the downstream end  110  of the intake duct  126  required to meet the power demand at optimum throttle opening (if throttle is used) and air-fuel ratio (step  930 ). If the ICE has an electronically controlled throttle, an optional next step (not shown) can include closing of the throttle by a predetermined amount. The ECU then obtains actual supercharger output air density measurement ρ T  by obtaining the detection values of the pressure sensor  154  and temperature sensor  151  (step  932 ). The values of the required pressure ρ T,req  and the actual air density ρ T  at the downstream end  110  of the intake duct  126  are then compared (step  934 ). If the required density value ρ T,req  is smaller than the actual density value ρ T  by more than a predetermined amount y (namely, ρ T −ρ T,req &gt;y), the ECU may decrease the mass flow rate dm N /dt of high-pressure air into the turboexpander  144  by a predetermined incremental amount Δ(dm N /dt) (step  936 ). This may be accomplished by decreasing the output pressure of the pressure regulator  130  with the valve  132  in an open position or by closing the valve  132 . The value of incremental amount Δ(dm N /dt) can be made generally proportional to the difference between the actual and the required densities in the intake duct  126 , namely Δ(dm N /dt)∝ρ T −ρ T,req ). If desired, the incremental amount Δ(dm N /dt) can be appropriately limited not to exceed a predetermined value which can be updated each time the control routine  900  is executed. This approach may be used to avoid abrupt changes in air density in the intake passage  22  and the consequential abrupt change in the ICE output. Preferably, a reduction in supercharging action is performed so that ICE power is decreased in a smooth fashion and with prompt response to demand. To assure proper air-fuel ratio, ECU can adjust fuel flow rate as appropriate to improve ICE performance (step  926 ) and the routine is ended. If the actual air density value ρ T  is not greater than the required air density value ρ T,req  in the transition duct by more than a predetermined amount y (namely, ρ T −ρ T,req ≦y) (step  922 ), no change to the supercharger condition is required. Then, the ECU can adjust fuel flow rate as appropriate for improved ICE performance (step  926 ) and the routine is ended. 
         [0049]    If the routine step  928  establishes that value of P D −P A  is less than or equal to predetermined value x, it means that the absolute value of P D −P A  is less than or equal to predetermined value x (namely, |P D −P A |≦x). In such a case, neither power deficit or power excess exist and the routine is ended. This conditions may correspond to an automotive vehicle cruising on a level road or an ICE operating in idle. To ensure that ICE system  10  promptly responds to demand, the control routine  900  may be executed at a rapid repetition rate, preferably 10 to 100 times per second. An analogous routine may be also used to control the superchargers  101  and  102  if the ICE systems  11  and  12 , respectively. 
         [0050]    Alternative control routine responding to torque demand rather than power demand may be also implemented. Such a routine may be identical to the routine  900  except that in steps  914 ,  916 , and  928 , the term “power” is replaced with the term “torque”. Suitable methods for determining demand torque value are known in the art and include determination of demand torque from position of vehicle acceleration pedal. See, for example, N. Heintz et al., in “An Approach to Torque-Based Engine Management Systems,” SAE paper number 2001-01-0269, published by the already noted Society of Automotive Engineers. Another alternative control routine may be used if the ICE system has means for measuring intake air mass flow. Such a routine may be identical to the routine  900  except that in steps  918 ,  920 ,  922 ,  930 ,  932  and  934 , the terms “ρ T,req ” and “ρ T ” are replaced respectively with the terms “dm T,req /dt” and “dm T /dt” where dm T,req /dt is the mass flow of air required to meet ICE output demand and dm T /dt is the actual mass flow of air measured flowing through the transition duct  124 . Another variant of the control routine  900  may omit steps  918 ,  920 ,  922 ,  930 ,  932 , and  934 . 
         [0051]    Alternative criteria for establishing power deficit and power excess conditions include: 1) Power deficit condition is established when engine rotational speed is less than predetermined engine rotational speed value and engine output torque is more than a predetermined engine output torque value. Accordingly, power excess condition is established when engine rotational speed is more than predetermined engine rotational speed value and engine output torque is less than a predetermined engine output torque value. 2) Power deficit condition is established when engine rotational speed is less than predetermined engine rotational speed value and engine fuel flow rate is more than a predetermined fuel flow rate value. Accordingly, power excess condition is established when engine rotational speed is more than predetermined engine rotational speed value and engine fuel flow rate is less than a predetermined fuel flow rate value. 3) Power deficit condition is established when the actual engine torque (measured or inferred) value is less than the demand torque value calculated from the position of accelerator pedal. Accordingly, power excess condition is established when the actual engine torque (measured or inferred) value is more than the demand torque value calculated from the position of accelerator pedal. 
         [0052]    It will be appreciated that the present invention can be implemented with a variety of ICE of either reciprocating type or rotary type. The ICE can have any number of combustion chambers. Features of the various embodiments can be combined in any manner. As already noted, the supercharger assembly  100  (and each of its embodiments  101  and  102 ) be also used with engine-driven superchargers, exhaust gas turbochargers, and electric turbochargers to augment their performance. One advantage of using the invention in a combination with an engine driven supercharger or a turbocharger is that the performance of the overall ICE system is improved since the supercharger assembly of the subject invention provides improved supercharging performance in conditions of high torque and low engine speeds (e.g., during automotive vehicle acceleration from a stopped condition), whereas the conventional supercharger provides improved supercharging performance in conditions of high torque and high engine speeds, especially when such conditions last for a longer period of time (e.g., during extended grade ascent or passing). 
         [0053]    When the invention is used to supercharge ICE in vehicles such as trucks, busses, earth moving equipment, and utility vehicles that already have an existing supply of high-pressure air, such an existing supply may be used to feed high-pressure air into the turboexpander  144 . High-pressure air for operation of the turboexpander  144  may be also conveniently generated in ICE cylinders during vehicle braking, as for example, disclosed by Larson et al. in U.S. Pat. No. 6,922,997. 
         [0054]    The term “intake air” used in this application should be give an broad interpretation so as to include presence of ICE fuel and ICE exhaust gases. Thus, intake air is essentially a mixture of nitrogen, oxygen, carbon dioxide, water vapor, and inert gases, and it may also include ICE fuel vapor, nitrogen oxides, and hydrocarbons. Such fuel vapor, nitrogen oxides, and hydrocarbons may become a part of the intake air as a result of exhaust gas recirculation in the ICE. In some embodiments of the invention the high pressure (i.e., compressed) air for operation of the turboexpander may be derived from the intake air, therefore, the composition of the compressed air may be essentially the same as that of the intake air. 
         [0055]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” and “includes” and/or “including” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0056]    The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
         [0057]    Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. In addition, the term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. 
         [0058]    While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the present invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the present invention as defined by the appended claims and their equivalents. Thus, the scope of the present invention is not limited to the disclosed embodiments.