Patent Publication Number: US-2013239568-A1

Title: Turbo Assist

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Patent Application No. 61/611,809, entitled “Turbo Assist,” filed Mar. 16, 2012, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to electric machines and turbochargers, and more particularly, to electric machines for operating in connection with turbochargers on internal combustion engines. 
     BACKGROUND 
     A turbocharger or exhaust driven supercharger is a device, driven at least partially off the combustion exhaust of an internal combustion engine, that boosts the pressure and throughput of combustion air into the engine. The turbocharger has a compressor, typically a centrifugal compressor, for compressing the combustion air. The compressor resides on a common shaft with a turbine, typically a radial or axial turbine, for receiving the combustion exhaust and driving the compressor via the common shaft. The compressor, turbine and shaft define the rotating assembly of the turbocharger.  FIG. 1  shows a typical turbocharged engine arrangement having a reciprocating internal combustion engine  12  with an exhaust manifold  14  and a turbocharger  16  coupled to receive exhaust from the manifold  14 . The exhaust passes through the turbine of the turbocharger  16  and out an exhaust conduit  18 . A wastegate valve  20  upstream of the turbocharger  16  can be selectively operated (e.g., by an engine control unit, ECU) to partially bypass the turbocharger  16 , directing some of the exhaust directly into the exhaust conduit  18 , thereby controlling the amount of exhaust going to the turbocharger. The exhaust that passes through the turbine of the turbocharger  16  drives the compressor to compress ambient air received at the turbocharger  16  and output the compressed air through an intake conduit  22  into the intake of the engine  12 . The compressed air and fuel are combusted in the engine  12  to produce kinetic energy, typically in the form of rotating movement of an output shaft. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic flow diagram of a prior art internal combustion engine system having a turbocharger. 
         FIG. 2A  is a schematic illustration of a side cross-sectional view of an example electric machine connected to a compressor and turbine. 
         FIG. 2B  is a schematic illustration of a side cross-sectional view of another example electric machine connected to a compressor and turbine. 
         FIG. 3A  is a graphical comparison of performance characteristics for a compressor with and without motor assistance. 
         FIG. 3B  is another graphical comparison of performance characteristics of a compressor with and without motor assistance. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A turbocharger system on an engine can include an electric machine coupled to the rotating assembly of the turbocharger. The electric machine can assist driving the compressor to create higher supercharging pressure for engine operation, without having to rely on a supply of exhaust from the engine. The electric machine can also be used to recover energy from the engine, output by the engine in the form of excess exhaust. The energy recovered by the electric machine can be stored and used in powering the electric machine and/or can supplement other systems, including supplementing power to a power distribution grid. Other uses than those identified above for this power can be envisioned based on the specific application of the engine. 
       FIG. 2A  is a schematic illustration of a side cross-sectional view of an example turbocharger system  200  with an electric machine  202 . The electric machine  202  is coupled to the shaft  204  that carries the compressor  206  and the turbine (not shown) to rotate within a housing assembly  214 . The shaft  204  is supported by one or more bearings  205  intermediate the compressor  206  and turbine. The housing assembly  214  has a compressor inlet  216  that couples to an air intake portion  218  of the engine. The electric machine  202  resides in the compressor inlet  216  within the housing assembly  214  (as shown in  FIG. 2A ) or in a separate housing attached to the housing assembly  214  (not shown). 
     The electric machine  202  includes a rotor  208  and a stator  210 . The rotor  208  is configured to rotate within the stator  210 , as described in more detail below. In certain instances, the electric machine  202  is a permanent magnet, synchronous, multiphase alternating current (A/C) motor/generator, where the magnetic field of the rotor  208  is generated entirely or in part by one or more permanent magnets. To this end, in  FIG. 2A , the rotor  208  is shown with a plurality of permanent magnets  220  rigidly affixed to a cylindrical rotor shaft  222  using a non-magnetic sleeve  224 . The rotor  208  is coupled to the shaft  204  so that rotation of the rotor  208  causes rotation of the compressor  206  and vice versa. In certain instances, the rotor  208  is directly coupled to the shaft  204  with no intermediate components (e.g., no couplings, gearbox, clutches, coupling and/or other components) or only rigid intermediate components.  FIG. 2A  shows a bolt-on arrangement with a bolt that extends through the rotor  208 , and threadingly engages the shaft  204 , clamping the rotor  208  abutting an end of the shaft  204 . In other instances, the rotor  208  can be coupled to the shaft  204  using clutches, a gearbox with fixed or multiple gear ratios, a flexible or rigid coupling and/or in another manner. In certain instances, the manner of coupling the rotor  208  to the shaft  204  is configured to be selectively engaged or disengaged, for example, to enable the rotor  208  to be disengaged when not needed or desired.  FIG. 2A  shows the rotor  208  cantilevered off the end of the shaft  204 , and no additional bearings (beyond the bearings  205 ) are needed to support the rotor  208 . In other instances, additional bearings may be provided, for example, at the end of the rotor  208  opposite the coupling to the shaft  204 . Such additional bearings can be mechanical bearings and/or magnetic bearings. 
     The stator  210  includes a winding  226  that can carry electrical current and either generate an electromagnetic field to drive the rotor  208  to rotate or, when the rotor  208  is rotated by the shaft  204 , receive an induced current (i.e., generate electrical power). The stator  210  is contained (at least partially, or as shown in  FIG. 2A , wholly) in an electric machine housing  228 . In certain instances, the housing  228  includes cooling passages that receive a flow of a cooling fluid, thus enabling the housing  228  to operate as a cooling jacket to the remainder of the motor generator  202 . 
     Although described herein as a permanent magnet AC electric machine  202 , the electric machine  202  can take other forms, AC or DC, with or without permanent magnets, and/or other variations. 
     The electric machine  202  is electrically coupled to a power electronics module  230 . In certain instances, the power electronics module  230 , as will be discussed in more detail below, is bidirectional and conditions the electrical power to and from the electric machine  202  to specified parameters (e.g., specified voltage and/or frequency). In other instances, the power electronics module  230  is unidirectional. To enable driving the electric machine  202 , the power electronics module  230  can include a variable frequency drive. The power electronics module  230  is coupled to a controller  232  that operates in controlling the electric machine  202  and/or the power electronics  230 . For example, the controller  232  can control the power electronics module  230  to control the rate at which the electric machine  202  rotates when operating as a motor, as well as change the electric machine  202  between motoring and generating. The controller  232  can be separate from the engine&#39;s engine control unit (ECU) and communicate with the ECU and/or the controller  232  can be integrated with the engine&#39;s ECU. 
     The electric machine  202  is carried in the turbocharger system housing assembly  214 . In certain instances, as shown in  FIG. 2A , the housing assembly  214  can contact and seal around the perimeter of the electric machine housing  228 . Such contact facilitates conductive heat transfer between the electric machine  202  and the housing assembly  214  for cooling the electric machine  202 . Additionally, if sealed, all airflow en route to the compressor  206  (designated by the arrows labeled “Air”) must pass through the electric machine  202 , thus cooling the electric machine  202 . In certain instances, air can flow through an air gap between the rotor  208  and stator  210 , through passages in the stator  210  itself and/or through other passages through the electric machine  202 . In other instances, a gap and/or passages can be provided around the exterior of the electric machine  202  so that air en route to the compressor  206  flows around and cools the exterior of the electric machine  202 . Suction created by operation of the compressor  206  can aid in drawing air through and/or around the electric machine  202 . In certain instances, the conductive and/or convective cooling described above is enough to omit additional cooling mechanisms, including externally sourced coolant flow through the electric machine housing  228 . 
     Although shown in  FIG. 2A  as being substantially cylindrical, the electric machine  202  can conform to the curvature of a bell-shaped intake housing  238  into the compressor  206 . For example, while the rotor  208  and stator  210  of the electric machine  202  remain substantially cylindrical, all or a portion of the outer diameter of electric machine outer housing  234  can correspond to and match, entirely or substantially, the inner diameter of the bell-shaped intake  238 . Further, the housing  234  can include azimuthally spaced apart fins  236  that extend into contact with the interior surface of the bell-shaped intake  238  and the stator  210 . Like the housing  228  of  FIG. 2A , the fins  236  conductively heat transfer between the electric machine  202  and the exterior parts of the turbocharger (here, the bell-shaped intake  238 ), but also allow air to pass over the exterior of the stator  210  to the compressor  206  in the spaces between the fins  236  for additional convective cooling. In certain instances, the upstream end turns of the windings  226  can be shaped to mimic the curvature of the bell-shaped intake  238 , having the same or a similar radius of curvature as the curvature of the intake  238 . Such a curved shape end turns lessens the resistance to air flowing through the electric machine  202  over end turns that are not so curved. 
     The turbine of the turbocharger system  200  is coupled to receive combustion exhaust from combustion of fuel and air within the internal combustion engine via the engine&#39;s exhaust manifold. The engine can be a reciprocating internal combustion engine powered by heavy fuel oil, diesel, gasoline, natural gas and/or other fuel. In other instances, the engine could be another type of engine. For example, the engine could be a non-piston type engine, such as a Wankel rotary engine and/or other type of engine. The exhaust output from the engine passes through the turbine and drives the turbine to rotate, and in turn, rotate the compressor  206 . As the compressor  206  rotates, it draws in air from the intake portion  218 , compresses the air and outputs that compressed air to the engine for use in combusting fuel. The amount of exhaust available to drive the turbine and, thus the compressor  206 , is dependent on engine operation. For example, the engine produces more exhaust under high load and/or at high operational speeds, and less exhaust under low load and/or at low operational speeds. Greater amounts of exhaust typically enable driving the compressor  206  to rotate more quickly. The flow and pressure of air output by the compressor  206 , in turn, is dependent on the speed at which the compressor  206  rotates and the efficiency of the compressor at the rotational speed. Therefore, the flow and pressure output from the compressor  206 , to the extent the compressor  206  is driven by the turbine, is tied to the engine operating conditions. 
     At some engine operating conditions, the engine does not produce enough exhaust to rotate the compressor  206  at a rate that produces a desired or specified flow and pressure of air to the engine and/or a desired or specified compressor efficiency. The electric machine  202  can be used to electro assist operation of the turbocharger, i.e., drive the electric machine  202  to assist the turbine in rotating the shaft  204  and/or brake the shaft  204  with the electric machine  202  to achieve the desired or specified engine operating efficiency and/or desired or specified compressor efficiency. For example, at a given engine operating condition, the available exhaust alone may not be enough to rotate the compressor  206  fast enough to achieve a desired or specified (e.g., maximum) engine efficiency. The electric machine  202  may be powered to assist the turbine in rotating the compressor  206  faster, and fast enough to achieve the desired or specified engine efficiency at the given operating condition. In another example, at a given engine operating condition, the available exhaust alone may operate the compressor  206  in stall. Power can be supplied to the electric machine  202  or the electric machine  202  operated to generate power to brake the rotating compressor  206  to a rotational rate that produces stable pressure generation. In yet another example, power can be supplied to the electric machine  202  to assist or brake rotation of the compressor  206  to maintain the compressor at a desired or specified (e.g., maximum) compressor efficiency over different exhaust production of the engine and/or different ambient conditions. By assisting or braking the rotation of the compressor  206  using the electric machine  202 , the engine and/or the compressor  206  can be maintained at desired or specified operational efficiencies regardless of the exhaust produced by the engine and ambient conditions. In instances where an auxiliary blower is provided to supply additional compressed air to the engine (beyond what the turbocharger would normally), the electric machine  202  can operate the compressor  206  to supplement the operation of the auxiliary blower or can enable omitting the auxiliary blower. 
     Some engines with turbochargers are optimized to run for extended periods of time at a specified steady state engine operating conditions. When the engine operation departs from the specified, optimum steady state engine operating conditions, the efficiency of the engine operation drops and in some cases, drops substantially. Some examples of engines optimized to run for extended periods of time at specified steady state operating conditions include engines used for marine propulsion, engines used for generating power in rail applications, stationary engines such as used for running generators, pumps or compressors, and/or other engines. By assisting or braking the rotation of the compressor  206  using the electric machine  202 , the amount of air supplied by the turbocharger system  200  can be adjusted based on engine requirements, rather than based on available exhaust for operating the turbine, to improve (and sometimes maximize) engine operating efficiency at operating conditions different from the specified, optimum steady state engine operating conditions. For example, in the context of a marine propulsion engine, the turbocharger system  200  described above would allow the vessel to cruise at differing speeds above and below the cruising speed associated with the specified, optimum steady state engine operating conditions while still maintaining a high engine operating efficiency. One measure of engine operating efficiency is fuel efficiency. Operating the turbocharger system  200  as described above can improve fuel efficiency of the engine operation across multiple operating conditions of the engine above and below the specified, optimum engine operating conditions. In improving fuel efficiency, emissions can also be decreased. 
     During transient operation, the exhaust to the turbocharger system  200  lags, in time, the engine loading and speed events that cause the engine to generate exhaust. This lag, together with a lag resulting from accelerating the inertial mass of the rotating assembly, delays the operation of the compressor  206  in generating a desired or specified flow and pressure of air to the engine. Power can be supplied to the electric machine  202  to assist in accelerating the compressor  206  and/or brake the compressor  206  more quickly and independently from the exhaust production to reduce lag. 
     At startup, power can be supplied to the electric machine  202  to turn the compressor  206  to supply compressed air to the engine to facilitate start-up, even though little or no exhaust is being produced. In instances where a supplemental start-up booster compressor is used to facilitate engine start-up, the electric machine  202  rotating the compressor  206  can supplement, and in some instances, supplant the supplemental start-up booster. 
     In certain instances, a controller  232  can include a control algorithm for controlling the turbocharger system  200  to supply air to the engine based on engine demands, for example, to achieve a desired or specified engine operation (e.g., maximum efficiency), regardless of the exhaust available to operate the turbocharger system  200 . The controller  232  can include a number of inputs, including one or more engine operating parameters (e.g., engine speed, throttle position, engine load, compressor speed and/or other operating parameters). The control algorithm can cover start-up, transient operation and/or steady state operation. The controller  232  can be pre-programmed with a map of compressor  206  operation to engine operating condition and/or the controller  206  can adaptively derive the operation of the compressor  206  based on engine operating conditions. The controller  232  can be coupled to the power electronics  230  to operate the power electronics  230  in operating the electric machine  202 . 
     In certain instances, the electric machine  202  can be powered by excess exhaust to generate power. For example, at some engine operating conditions, typically high load and high speed, the amount of exhaust available to drive the compressor  206  is more than is needed to operate the engine at the operating conditions. As mentioned above, this excess exhaust is normally vented by a wastegate valve (e.g., wastegate valve  20  of  FIG. 1 ). However, rather than venting the excess exhaust, the excess exhaust can be maintained passing through and powering the turbine to rotate the compressor  206 . The electric machine  202  is operated as a generator to brake the compressor  206  and generate electrical power. In certain instances, the power can be provided to bidirectional power electronics  230  and conditioned for storage and later use in powering the electric machine  202 . Alternately or additionally, the power can be used for powering other components of the engine and/or a larger system, and can be supplied to a power grid or stored. The power output by the electric machine  202  can be used to supplement or replace other generators (e.g., on-board generators of a vehicle, such as a ship or boat, rail car, airplane and/or road going vehicle). The electric power generated by the electric machine  202  may be of a certain phase, frequency, voltage and be AC or DC, depending on the configuration and operating speed of the electric machine  202 . The power electronics  230  can reconfigure one or more of the phase, frequency, and/or voltage of the electric power to a desired or specified phase, frequency, and/or voltage, for example, to match the power carried on the grid or bus or other specified characteristics. In certain instances the power electronics  230  includes an inverter and/or rectifier for converting from AC to DC or DC to AC depending on the configuration of the electric machine  202  and the desired output from the power electronics  230 . For example, the power electronics  230  may be used to output 3-phase 60 Hz AC power output at a voltage of about 400 VAC to about 480 VAC, preferably about 460 VAC. Other settings, including other phases, frequencies, and voltages, AC or DC are within the concepts described herein. 
       FIGS. 3A and 3B  are graphical comparisons of example performance characteristics for a compressor with and without electric machine assistance. As can be seen from the graphs, the engine operation efficiency can be improved over the entire operating range. In the example, powering the electric machine to drive the compressor is able to improve efficiency at 0.6 load (Case 1) and at 0.45 load (Case 2) as compared to without the electro assist of the electric machine. 
     As discussed above, in certain aspects, the turbocharger system can be operated to decrease fuel consumption and emissions across multiple operating conditions of the engine above and below the engine&#39;s optimum engine operating conditions. For example, the engine can be operated at part load, yet with higher fuel efficiency and lower emissions that it would have with a conventional turbocharger. 
     In certain aspects, the turbocharger system can be controlled to control back pressure of the engine. For example, the turbocharger system can be operated to reduce back pressure of the engine. Reducing back pressure helps with a cleaner scavenge cycle in a two stroke engine. 
     In certain aspects, the turbocharger system can supplement or eliminsate the need for auxiliary blowers or compressors that supply air to the engine, including auxiliary blowers used to supplement turbocharger operation and/or start-up booster compressors used to facilitate engine start-up. 
     In certain aspects, the electric machine can be provided without any bearings, making it easier to incorporate an electric machine to an existing turbocharger design and making the system lower cost than if a bearing were provided in the electric machine. Furthermore, the electric machine efficiency can be higher because there are no bearing frictional losses. 
     In certain aspects, the electric machine enables rotating the rotating assembly of the turbocharger system so that it can be balanced without having to remove the turbocharger system from the engine. Further, rotating the rotating assembly when the engine is not in use can clean the compressor and/or turbine blades, and can pressurize the engine to clean deposits from inside the engine. Even during operation, the rotating speed of the turbocharger system can be controlled to promote cleaning the compressor and/or turbine blades. Also, motoring the rotating assembly can smooth out cyclical operating speeds that fatigue the compressor and turbine, and therefore, reduce fatigue stresses. 
     In certain aspects, the electric machine can be cooled without any active cooling, only by the intake air flowing through and/or around the electric machine and the conductive heat transfer with the housing of the turbocharger system. In certain aspects, additional liquid cooling can be provided in the housing of the electric machine. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.