Abstract:
A variable speed compressor system (A) incorporating an electric power generation capability by combining a variable-speed compressor assembly ( 70 ) with an electric motor assembly ( 50 ) via a drive subassembly ( 30 ) in a compact unit regulated by a control system ( 400 ). The control system ( 400 ) facilitates fully controllable boost-on-demand forced-air induction operation across an entire engine speed range, and offers intelligent electric power generation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 61/436,738 filed on Jan. 27, 2011, which is herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The invention is related generally to a variable speed compressor system, and in particular, to a variable speed compressor and alternator in a compact unit coupled to an engine, with a related control structure to provide fully controllable boost-on-demand supercharging operation across an entire engine speed range together with intelligent electric power generation. 
         [0004]    The increasing demand for fuel efficiency and emission reduction requires engines to provide higher output without increasing total piston displacement and weight. An effective way to achieve this goal is the use of forced air induction or compressor systems to boost the intake pressure. More air, and thus more fuel, can be added to each combustion cylinder within the engine. Consequently, more mechanical power is generated from each explosion in each cylinder. 
         [0005]    There are two major types of forced air induction or compressor systems. One is referred to as supercharger and the other is referred to as turbocharger. The difference between the two systems is their source of energy. Turbochargers are powered by the mass-flow of exhaust gases driving a turbine; superchargers are powered mechanically by belt or chain drives from the engine crankshaft. 
         [0006]    In general, superchargers offer performance and cost advantages over turbochargers. These advantages include no turbo lag and faster response, easy and inexpensive to install, and no introduction of a heat inertia effect in the exhaust system. This makes supercharger the most cost-effective way to increase engine power output. 
         [0007]    Conventional superchargers are driven by engine&#39;s crankshaft through a fixed gear ratio or speed ratio. The boost ratio increases with engine speed. At low engine speed, the boost ratio is low; the in-take mass flow is insufficient to provide desired engine torque. Therefore, there is a strong desire to develop a variable speed supercharger that is capable of delivering optimal boost ratios across the entire spectrum of engine speed, providing additional engine torque even at low engine speeds. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Briefly stated, the present disclosure provides a variable speed compressor system along with an associated control system and structure. The variable speed compressor system incorporates electric power generation and storage capability by combining the compressor with an alternator in a compact unit for connection to an external battery or other energy storage device. The control system and structure facilitates fully controllable boost-on-demand air compression operation across entire engine speed range and offers intelligent electric power generation, such as is required to maintain a battery&#39;s state of charging (SOC). 
         [0009]    In one embodiment of the present disclosure, a supercharger system of the present disclosure includes a three-shaft drive system, an electric machine, a supercharger compressor unit, and a controller that controls and operates the components of the supercharger system. The three-shaft drive system consists of an outer ring member, a sun member, at least one set of planetary members or clusters, and a carrier member. The three-shaft drive system serves as a power regulating device with its three shafts each connecting respectively to a drive pulley, the electric machine, and the compressor unit. 
         [0010]    The controller of the supercharger system of the present disclosure is configured to implement a control system capable of offering at least three operating modes by controlling the operational status of the electric machine to suit various performance needs. 
         [0011]    The first controlled mode of operation is the boosting mode, where the electric machine is controlled to rotate in an opposite direction relative to the direction of rotation of the drive pulley. The electric machine is in a motoring state, applying shaft torque in the same direction as the speed of rotation. The electric machine draws electric power from an external battery or energy storage system and delivers it to the three-shaft system providing drive power and shaft torque. The three-shaft drive system then combines the drive power with mechanical power from drive pulley and delivers the power to the supercharger compressor. In the boosting mode, the three-shaft drive system provides an increased speed ratio between the supercharger compressor and drive pulley. Therefore, even at relatively low engine speeds, the supercharger compressor is able to operate at a higher speed to provide high pressure forced air induction and to boost engine torque and power as required. 
         [0012]    The second controlled mode of operation is a neutral mode where the electric machine is controlled to be at rest (zero rotational speed), generating virtually no electric power. This mode is used when significant engine boosting or forced air induction is generally not required and/or the battery system is in its full state of charge. In the neutral mode, the compressor-to-pulley speed ratio is essentially the same as the base speed ratio of the three-shaft drive system. 
         [0013]    The third controlled mode is the charging mode, where the electric machine is controlled to rotate in the same rotational direction as the drive pulley. The electric machine is thus in the generating state, converting a portion of the mechanical power supplied from the drive pulley into electrical power to charge the battery system or provide power to another external energy storage device. In the charging mode, the three-shaft drive system provides a reduced compressor-to-pulley speed ratio, comparing with the base speed ratio of the drive system. In one example, the charging mode is used at vehicle high speed cruising, when engine speed is high and torque demand is relatively low. 
         [0014]    The three operating modes are realized under a so-called speed control logic by the control system where the control objective is to achieve a desired speed of the variable-speed compressor or electric machine by controlling the shaft torque of the electric machine through a torque-based control structure. The control structure comprises at least one feedback loop which compares the measured or estimated speed of the compressor shaft to a reference speed of the compressor shaft and generates a drive torque command for the electric machine. The feedback loop includes a PID control unit whose gains are determined by, among others, the rotational momentums of system components. The torque-based control structure may further include a feed-forward loop to improve controllability. The feed-forward loop generates a base drive torque command for the electric machine based on the operation status of the variable-speed compressor. Under the base torque command, the variable speed compressor is able to maintain substantial torque equilibrium among the three shafts in the three-shaft drive system under steady state conditions. 
         [0015]    The operation of the variable speed compressor may also be controlled under a torque control logic where the objective of the control structure is to achieve a desired torque level for the electric machine to generate electric power. 
         [0016]    The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the reading of the following description in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    In the accompanying drawings which form part of the specification: 
           [0018]      FIG. 1  is a schematic representation of a supercharger system of the present disclosure; 
           [0019]      FIG. 2  is an axial layout representation of a three-shaft drive subassembly; 
           [0020]      FIG. 3  is an exploded perspective sectional view of the three-shaft drive subassembly; 
           [0021]      FIG. 4  is a speed ladder diagram for the variable speed supercharger illustrating the relationship between the compressor, pulley, and electric machine; 
           [0022]      FIG. 5  is an axial layout representation of an alternate configuration for the three-shaft drive subassembly; 
           [0023]      FIG. 6  is a speed ladder diagram for the variable speed supercharger having the alternate configuration of  FIG. 5 , illustrating the relationship between the compressor, pulley, and electric machine; and 
           [0024]      FIG. 7  is a representation of the variable speed supercharger control structure of the present disclosure. 
       
    
    
       [0025]    Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale. 
         [0026]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. 
       DETAILED DESCRIPTION 
       [0027]    The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure. 
         [0028]    While the compressor system of the present disclosure is described below in the exemplary embodiment in the context of a variable speed supercharger, those of ordinary skill in the art will recognize that the control system and features of the present disclosure may be utilizes with other types of variable speed compressor systems, such as turbochargers or turbines, and that such systems are considered to be within the scope of the present disclosure. In addition, while the engine of the present disclosure is described below in the exemplary embodiments as being an internal combustion engine which directly receives the forced air induction from the compressor system, those of ordinary skill in the art will recognize that other types of engines or sources of driving power may be utilized, and that the forced air induction from the compressor system may be routed to the benefit of other systems or components besides the engine. 
         [0029]    Referring generally to (A) in  FIG. 1 , a variable speed compressor, such as a supercharger unit comprising a drive pulley subassembly  10 , a three-shaft drive subassembly  30 , an electric machine subassembly  50 , and a supercharger subassembly  70  is shown. The drive pulley subassembly  10  contains a drive pulley  1 , and a drive shaft  3  which is supported by a bearing assembly  5  on front casing  7 . 
         [0030]    The three-shaft drive subassembly  30  is a double-wedged traction drive unit (See:  FIG. 2  and  FIG. 3 ), comprising an outer ring  31 , a set of planet roller pairs  33  and  35 , a planet carrier  37 , and a sun shaft  39 . The outer ring  31  is operatively coupled to the drive shaft  3  through a drive plate  41  ( FIG. 1 ). The three-shaft drive subassembly  30  can take other forms, such as a conventional planetary gear drive or a planetary traction drive. 
         [0031]    The electric machine subassembly  50  contains a stator  51  and a rotor  53 . The rotor  53  is fixed onto the outer surface of a hollow shaft  43 , which in turn is supported through bearings  45  and  55  by case  59 . The hollow shaft  43  is connected to the planet carrier  37  of the three-shaft drive subassembly  30 . Electrical connections are provide for operatively coupling the electric machine subassembly  50  to an external energy delivery and storage system (not shown), such as a battery. 
         [0032]    The supercharger subassembly  70  is very similar to a variable-speed compressor commonly found in turbochargers. It includes a radial flow impeller  71  connected to the sun shaft  39  of the three-shaft drive system through a central shaft  138  which extends axially through the hollow shaft  43 , an air inlet port  73  and an air outlet volute  75 . The inlet port and outlet volute are integrated with a back case  77 . The central shaft  138  at its end closer to the impeller is supported by case  59  through a bearing  57 . As the impeller  71  spins at high speeds, air is drawn from the inlet port  73  and pushed out through the outlet volute  75  at increased pressure. Other types of supercharger compressors, such as scroll blower, screw blower, roots blower and vane blower, can also be used as the compressor subassembly of the current invention. 
         [0033]    Optionally, the variable speed supercharger unit may further include a brake unit  600  ( FIG. 7 ) to apply a stopping torque to the compressor and to prevent it from rotating when compressor&#39;s speed is too low or when it tends to rotate in an opposite direction. The brake unit  600  can be a frictional brake, a magnetic brake or even a one-way clutch. 
         [0034]    Referring again to  FIGS. 2 and 3 , the three-shaft drive subassembly  30  is a double-wedge traction drive which features sets of stepped planet rollers  33 ,  35  for high or low speed ratio. Each set of planet rollers  33 ,  35  are paired and uniquely arranged to facilitate torque actuated self-loading in both rotational directions. The double-wedge traction drive has one or more sets of planet roller pairs  38 , each comprising a first planet roller  35  and a second planet roller  33 , each having a large cylindrical surface and a small cylindrical surface. The small cylindrical surface of the first planet roller  35  is in frictional contact with the large cylindrical surface of the second planet roller  33 . The two planet rollers  33 ,  35  in a pair  38  are supported on a planet carrier  37  through bearings ( 33   c ,  35   c ) and pin shafts ( 33   b,    35   b ) on a pair of brackets  34  disposed at opposite axial ends of the pin shafts. 
         [0035]    The planet carrier is made of carrier base  37   a  and a carrier plate  37   b.  The carrier base has a set of bridges  37   c  for connecting with the carrier plate  37   b,  and a sleeve  37   d  for coupling with the hollow shaft  43  of the electric machine  50 . On both the carrier base  37   a  and the carrier plate  37   b  there are recesses  37   e  and  37   g  and studs  37   f  and  37   h.  The pair of brackets  34  are supported on the studs  37   f  and  37   h  (see  FIG. 3 ) of the planet carrier  37 . During operation, each pair of brackets  34 , along with the associated pair of planets  38  are free to rotate about the axis of the studs  37   f,    37   h.    
         [0036]    During operation, the large cylindrical surface of the first planet roller  35  in each pair of planets  38  is in frictional contact with a large cylindrical surface of the sun shaft  39  at the axial center of the three-shaft drive subassembly  30 . Correspondingly, the small cylindrical surface of the second planet roller  33  in each pair of planets  38  is in frictional contact with an inner cylindrical surface  32  of the outer ring  31 , which is segmented in an axial direction by a groove  32   a  to accommodate the large cylindrical surface of the second planet rollers. 
         [0037]    The base speed ratio of the traction drive shown in  FIG. 2  and  FIG. 3  is K=φ 1 φ 2 K 0 , where the ratio of the outer diameter of the large cylindrical surface to the small cylindrical surface of the first planet roller is φ 1 ; the ratio of the outer diameter of large cylindrical surface to the small cylindrical surface of the second planet roller is φ 2 ; and the ratio of the diameter of the inner cylindrical surface of the outer ring to the diameter of the outer cylindrical surface of sun shaft is K 0 . That is, 
         [0000]    
       
         
           
             
               
                 
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         [0038]    where: 
         [0039]    R p1     —     out =radius of the large cylindrical surface of the first planet roller; 
         [0040]    R p1     —     in =radius of the small cylindrical surface of the first planet roller; 
         [0041]    R p2     —     out =radius of the large cylindrical surface of the second planet roller; 
         [0042]    R p2     —     in =radius of the small cylindrical surface of the second planet roller; 
         [0043]    R r =radius of the inner cylindrical surface of the outer ring, 
         [0044]    R 2 =radius of the outer cylindrical surface of the sun shaft 
         [0045]    As can be seen, with stepped planet rollers, the base speed ratio of the traction drive is increased by a factor of φ=φ 1 φ 2 . 
         [0046]      FIG. 2  also depicts the torque actuated self-loading mechanism of the traction drive  30 . As the drive pulley  1  drives the outer ring  31  in the direction indicated by ω R , it turns the sun shaft  39  in the same direction as indicated by ω S . Now consider a pair  38  of planet rollers  33  and  35  in the traction drive assembly. The friction force exerting on the first planet roller  35  by the sun shaft  39  and the friction force exerting on the second planet roller  33  by the outer ring  31  forms a couple, which tends to rotate the planet roller pair  38  about the axis of the supporting studs  37   f  and  37   h,  between the sun shaft and the outer ring. Since the outermost distances between the large cylindrical surface of the first planet roller  35  and the small cylindrical surface of the second planet roller  33  is greater than an annular gap between the inner cylindrical surface of the outer ring  31  and the outer cylindrical surface of the sun shaft  39 , a wedge action is created. The wedge action produces a substantial normal contact load at the various frictional contacts. 
         [0047]    As seen in  FIG. 2 , the planet pairs  38  are arranged in two groups. Planet pairs in the same group are positioned anti-symmetrically about the axis of the sun shaft  39 . Planet pairs in adjacent group are positioned symmetrically. This allows the traction drive to operate in both rotational directions. 
         [0048]    When the outer ring  31  rotates clockwise, it drives the sun shaft  39  rotating in the same direction. The friction torque urges the planet pair  38  and the anti-symmetric planet  38   a  to pivot clockwise, wedging the planet pairs  38  and  38   a  between the outer ring  31  and the sun shaft outer circumference  39  to provide required normal contact load. 
         [0049]    When the outer ring  31  rotates counterclockwise, it also drives the sun shaft  39  in the same direction. The friction torque urges the planet pair  38   b  and its anti-symmetric planet pair  38   c  to rotate counterclockwise, wedging the said planet pairs between the outer ring  31  and the sun shaft  39  to provide required normal contact load. 
         [0050]    There are two wedge angles formed between the outer ring  31  and sun shaft  39 . The first wedge angle, denoted by α 1 , is formed for the second planet roller  33  between the outer ring  31  and the first planet roller  35 . The second wedge denoted by α 2 , is formed for the first planet roller  35  between the sun shaft  39  and the second planet roller  33 . To prevent excessive slippage at frictional contacts, the following geometrical conditions are required: 
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         [0051]    where μ is the maximum available friction coefficient at the frictional contact. 
         [0052]    The traction drive so constructed has three concentric rotating members: (1) the outer ring member  31 ; (2) the planet carrier member  37 ; and (3) the sun shaft member  39 . These three rotating members form the three-shaft drive system, having two degrees of freedom. The first shaft is the sun shaft member  39 , which is connected to impeller  71 . The second shaft is the outer ring member  31 , which is connected to the drive shaft  3 , and the third shaft is the planet carrier member  37  which is connected to the electric machine  50 . The speed of the impeller  71  is determined by the speed of drive pulley  1  and the speed of rotor  53  of the electric machine  50 . Thus, for a given drive pulley speed, which is proportional to engine speed, the speed of the impeller  71  can be adjusted by the electric machine  50  to meet boosting requirement.  FIG. 4  is a speed ladder diagram for the variable speed supercharger of the present invention which illustrates the speed relationship among the impeller  71 , the drive pulley  1 , and the electric machine rotor  53 . 
         [0053]    There are other ways to construct a double-wedge traction drive system  30  having three concentric rotating members.  FIG. 5  illustrates a layout diagram of an alternate double-wedge traction drive assembly  130 . The alternate configuration drive assembly  130  has an outer ring  31 , a set of paired planets  38 , a carrier (not shown) and a sun shaft  39  which are substantially similar to those found in the traction drive system  30 . The planet pair  38  includes a first stepped planet  35  having a large cylindrical surface and a small cylindrical surface, and a second stepped planet  33  having a large cylindrical surface and a small cylindrical surface. The small cylindrical surface of the first planet  35  is in frictional contact with the outer cylindrical surface of the sun shaft  39 , while the large cylindrical surface of the second planet  33  is in frictional contact with the inner cylindrical surface of the outer ring  31 . Between the first and second stepped planets  33 ,  35 , the large cylindrical surface of the first planet  35  is in friction contact with the small cylindrical surface of the second planet  33 . 
         [0054]    The base speed ratio of the traction drive shown in  FIG. 5  is K=K 0 /(φ 1 φ 2 ), where the ratio of the outer diameter of the large cylindrical surface to the small cylindrical surface of the first planet roller is φ 1 ; the ratio of the outer diameter of large cylindrical surface to the small cylindrical surface of the second planet roller is φ 2 ; and the ratio of the diameter of the inner cylindrical surface of the outer ring to the diameter of the outer cylindrical surface of sun shaft is K 0 . That is: 
         [0000]    
       
         
           
             
               
                 
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                   = 
                   
                     
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         [0055]    As one can see, with this arrangement, the base speed ratio of the traction drive is decreased by a factor of φ=φ 1 φ 2 . 
         [0056]    Similarly to that found in the prior embodiment, the planet pairs  38  in  FIG. 5  are arranged in groups. Planet pairs in a same group are arranged anti-symmetrically, while planet pairs  38  in adjacent group are symmetrically positioned to allow for bi-directional operation. 
         [0057]    Other connecting configurations of the three-shaft drive system  30  to the compressor subassembly  70 , the drive pulley  1 , and the electric machine  50  are possible. For example, the compressor subassembly  70  can be alternatively connected to the planet carrier  37  of the traction drive unit  30 ; the rotor of the electric machine can be alternatively connected to the sun shaft  39  of the traction drive unit; and the drive pulley  1  to the outer ring member  31  of the traction drive unit  30 . 
         [0058]    A speed diagram for the alternative configuration  130  of the traction drive unit of  FIG. 5  is depicted in  FIG. 6 . The common feature in the speed diagrams among various configurations is that the drive pulley  1  is connected to the second branch or the middle shaft, of the three shaft drive system  30 . 
         [0059]    The operation of the variable speed supercharger system is controlled by a torque-based control structure shown in  FIG. 7 . The control structure incorporates the variable speed supercharger  200 , a controller  400 , the engine  500 , and an engine electronic control unit  550 . The controller  400  further includes a PID control unit  410  and an optional feed forward control unit  420 . Input signals, such as the measured or estimated compressor speed, the reference compressor speed set point, engine speed, throttle position and other engine operation signals, are received by the controller  400 , which produces at least an output torque command to control the operation of the electric machine  50  in concert with engine operation. The controller  400  conditions and processes input signals. 
         [0060]    Specifically, the controller  400  compares a compressor speed signal to a set point, and produces a speed error signal if the speed of the compressor is not within a specified tolerance in reference with the set point. The speed error signal can be obtained simply as the differential between the measured speed signal and the reference set point. The PID control unit  410  receives the speed error signal as input and produces a torque adjustment signal by proportionally magnifying the error signal, integrating the error signal with respect to time or taking the time derivative of the speed error signal. The PID control unit  410  may have three separate and parallel paths, corresponding to proportional magnification, integration, and differentiation. The output signal of the PID control unit  410  combines signals from all three paths. 
         [0061]    Alternatively, controller  400  itself may produce the reference compressor speed set point based on engine operation signals, such as engine speed and throttle position. 
         [0062]    The optional feed-forward unit  420  receives input associated with the compressor operation status, and estimates a reference torque for the electric machine  50 . The reference torque is also known as the feed forward torque or the base torque. The operation status of compressor includes, but not limited to, compressor speed, compressor torque load and compressor power consumption. The reference torque is estimated under steady-state conditions such that by applying the reference torque to the electric machine, the three shaft system would achieve substantial torque equilibrium. The torque command for the electric machine  50  is then composed of the reference torque signal and the torque adjustment signal. 
         [0063]    For a connection configuration represented by  FIG. 4 , the reference torque is estimated as: 
         [0000]        T   ref     —     em =( K− 1)· T   cmp (ω cmp )   Eqn. (8)
 
         [0064]    where T cmp  is the compressor torque load which is a function of compressor speed ω cmp . K is the base speed ratio of the three-shaft drive system  30  (See:  FIG. 4 ). The total torque command for the electric machine  50  is: 
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         [0065]    where G P , G I , and G D  are gains of the PID control unit  410 , Δω is the speed error between the reference compressor speed (set point) ω cmp and the actual measured compressor speed ω act . 
         [0066]    For a connection configuration represented by  FIG. 6 , the reference torque is estimated as: 
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                     10 
                     ) 
                   
                 
               
             
           
         
       
     
         [0067]    The total torque command for the electric machine  50  is calculated using the same equation as Equation (9). 
         [0068]    To protect the electric machine  50  from being overloaded, the torque command T set     —     em  may be monitored and limited by a current saturation device (not shown) either inside or outside of said controller  400 . When a torque command exceeds the set limits, the signal is held at the set level until the torque command drop below or within the set level. 
         [0069]    The objective of the operation and control of the variable speed supercharger described so far is to control the speed of the compressor  71  or the electric machine  50  such that desired pressure ratio can be achieved. This control logic is referred to as the speed control logic. 
         [0070]    The controller  400  may be constructed to also provide a braking signal to a brake unit  600  based on engine operation status and on compressor operation status. When it deems that the compressor  71  ought to be stopped for safe or desired operation, a brake signal is issued. The brake unit  600  coupled to the variable speed supercharger unit  70  in turn applies a stopping torque to stop and hold the compressor  71 . Under such conditions, the speed of the compressor  71  is zero and is not really changeable to other speeds. The objective of the operation and control is therefore not to control compressor speed, rather to control the torque of the electric machine  50  to provide suitable charging conditions for an external battery system (not shown). When the shaft  38  of the compressor  71  is rotationally locked, the operation and control of the electric machine  50  is very similar to that of a conventional alternator. The controller is thus operated under so-called torque-control logic. 
         [0071]    When the shaft  138  of compressor  71  is locked, it is also possible to use the electric machine  50  to start the engine  500 , in this case the electric machine  50  functions as a conventional starter device. 
         [0072]    During the operation, speed-control logic and torque-control logic may be switched back and forth based on operation conditions. The two control logic may be handled by two separate control units within the controller  400  or by single unit in the controller  400 . 
         [0073]    Alternatively, the braking signal can be an input signal from the engine ECU  550 , and the controller  400  configured to switch back and forth between the speed-control logic and the torque-control logic based on a received braking signal. 
         [0074]    It is always desirable to restrict the power ratings of the electric machine  50 . Smaller electric machines not only reduces physical size but also reduced the cost for both electric machine itself and for its power electronic systems. To this end, it is recommended for connect configuration shown in  FIG. 4 , the following relationship be held: 
         [0000]    
       
         
           
             
               
                 
                   
                      
                     
                       
                         
                           ( 
                           
                             
                               
                                 
                                   K 
                                   p 
                                 
                                  
                                 K 
                               
                               SR 
                             
                             - 
                             1 
                           
                           ) 
                         
                         · 
                         
                           P 
                           cmp 
                         
                       
                       
                         P 
                         
                           cmp 
                            
                           
                               
                           
                            
                           _ 
                            
                           
                               
                           
                            
                           ma 
                            
                           
                               
                           
                            
                           x 
                         
                       
                     
                      
                   
                   ≤ 
                   1 
                 
               
               
                 
                   Eqn 
                   . 
                   
                       
                   
                    
                   
                     ( 
                     11 
                     ) 
                   
                 
               
             
           
         
       
     
         [0075]    where: 
         [0076]    K p  is rotational speed ratio of the speed of the drive pulley shaft  3  to speed of the engine crank shaft, K p =ω p /ω eng ; 
         [0077]    K is the base ratio of three-shaft drive system  30 ; 
         [0078]    SR is the speed ratio of the speed of the compressor shaft  138  to the speed of the engine crank shaft SR=ω cmp /ω eng ; 
         [0079]    P cmp  is the compressor power; 
         [0080]    P cmp     —     max  is the maximum power of compressor; 
         [0081]    ω p  denotes pulley shaft speed; 
         [0082]    ω cmp  denotes compressor speed; and 
         [0083]    ω eng  denotes engine speed. 
         [0084]    For connection configuration shown in  FIG. 6 , the following relationship is recommended: 
         [0000]    
       
         
           
             
               
                 
                   
                      
                     
                       
                         
                           [ 
                           
                             
                               
                                 ( 
                                 
                                   
                                     
                                       K 
                                       p 
                                     
                                      
                                     K 
                                   
                                   
                                     K 
                                     - 
                                     1 
                                   
                                 
                                 ) 
                               
                                
                               
                                 1 
                                 SR 
                               
                             
                             - 
                             1 
                           
                           ] 
                         
                         · 
                         
                           P 
                           cmp 
                         
                       
                       
                         P 
                         
                           cmp 
                            
                           
                               
                           
                            
                           _ 
                            
                           
                               
                           
                            
                           ma 
                            
                           
                               
                           
                            
                           x 
                         
                       
                     
                      
                   
                   ≤ 
                   1 
                 
               
               
                 
                   Eqn 
                   . 
                   
                       
                   
                    
                   
                     ( 
                     12 
                     ) 
                   
                 
               
             
           
         
       
     
         [0085]    The definitions of symbols in above equation are the same as in Equation (11). 
         [0086]    Other means of grouping and processing signals are possible, they should not be considered as deviation from the spirit of current invention. The present disclosure can be embodied in-part in the form of computer-implemented processes and apparatuses for practicing those processes or in the form of embedded systems. The present disclosure can also be embodied in-part in the form of computer program code containing instructions embodied in tangible media, such as solid-state memory devices, CD-ROMs, hard drives, or another computer readable storage medium, wherein, when the computer program code is loaded into, and executed by, an electronic device such as a computer, micro-processor or logic circuit, the device becomes an apparatus for practicing the present disclosure. 
         [0087]    The present disclosure can also be embodied in-part in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring, cabling, or busses, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the present disclosure. When implemented in a general-purpose microprocessor or an embedded system, the computer program code segments configure the microprocessor to create specific logic circuits and/or to provide output control signals. 
         [0088]    As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.