turning to fig2 , a compressor 10 a and motor 11 a are coupled to a continuous variable transmission ( cvt ) 15 . the motor 11 a may or may not be hermetically sealed within a casing 14 a . thus , the design of fig2 is applicable to both hermetic and open systems . the cvt 15 eliminates the need for the costly combination of a gearbox 13 and vsd 12 of the prior art system shown in fig1 . further , the prior art system shown in fig1 can only be constructed economically as a hermetic system with a hermetic casing 14 and lower capacity motor 11 as vsds 12 are not readily available for larger motors 11 a , which can provide power exceeding 2000 hp or 1500 kw . systems requiring higher capacities require multiple compressors 10 , gear boxes 13 , motors 11 , vsds 12 and the costs associated therewith . of course , in addition to be suitable for higher capacities , the system illustrated in fig2 is also applicable to lower capacity systems . suitable designs for cvts 15 , 15 a , 15 b are illustrated in fig3 - 5 and include hydraulic or hydrostatic , hydro - mechanical and purely mechanical cvts . referring first to fig3 , a hydrostatic or hydraulic cvt 15 is illustrated whereby input power from the motor 11 a is delivered to a hydraulic pump 21 through an input shaft 18 . the motor 11 a may be operated at a constant speed . a continuous loop 45 connects the hydraulic pump 21 to a hydraulic motor 22 . the variable - displacement hydraulic pump 21 is used to vary the fluid flow into hydrostatic motor 22 . the rotational motion of the motor 11 a operates the hydrostatic pump 21 and the pump 21 converts the rotational motion into fluid flow through the loop 45 . then , with the hydrostatic motor 22 located on the driven side of loop 45 , the fluid flow is converted back into rotational motion of an output shaft 19 . the output shaft 19 is connected to an impeller 33 of the compressor 10 a . the compressor 10 a is part of a refrigerant cycle 60 which includes a condenser 52 that receives fluid from the compressor 10 a and delivers evaporated fluid to the evaporator 53 through a restriction orifice 55 and back into the compressor 10 a . a controller 50 is utilized to control the speeds of the hydraulic pump 21 and hydraulic motor 22 based on the “ leaving chilled water temperature ” at the evaporator 53 indicated at 54 in fig3 ( and fig4 - 5 ). while the disclosed systems 15 , 15 a , 15 b , 60 are particularly adaptable to large water chillers , other applications will be apparent to those skilled in the art the controller 50 will control the speed of the hydraulic pump 21 and hydraulic motor 22 in response to changes in the load to the refrigerant cycle 60 , as measured by the leaving chilled water temperature at 54 . thus , the leaving chilled water temperature at 54 are shown as input signals to the controller 50 in fig3 - 5 and the links between the controller 50 and the hydraulic pumps 21 , 21 a . hydraulic motors 22 , 22 a and pulley 41 are shown as output signals in fig3 - 5 . in fig4 , a hydrostatic cvt like the one shown at 15 in fig3 is combined with a planetary gear set 17 and appropriate clutches ( not shown ) to create a hybrid system referred to as a hydro - mechanical cvt 15 a . the hydro - mechanical cvt 15 a transfers power from the drive motor 11 a to the compressor 10 a in three different modes . at a low speed , power is transmitted hydraulically using the hydraulic pump 21 a and hydraulic motor 22 a ; at a high speed , power is transmitted mechanically by the drive motor 11 a through the gear set 17 ; between these extremes , the cvt 15 a uses both hydraulic and mechanical means to transfer power to the output shaft 19 a . the drive motor 11 a is connected to the planetary gear set 17 by the proximal drive shaft 18 a . the planetary gear set 17 divides the power delivered by the proximal drive shaft 18 a from the motor 11 a into two output power paths : one output power path passing to the distal output shaft 19 a through the ring gear 23 , planetary gear 30 , carrier 26 and sun gear 24 ; and the second output power path that drives a hydraulic pump 21 a through the action of the spur gear 27 and input pump gear 32 . the pump 21 a , in turn , drives a hydrostatic or hydraulic motor 22 a via the loop 45 a . the hydraulic motor 22 a is linked or coupled to the output shaft 19 a via the gears shown at 31 , 28 . regarding the power path from the motor 11 a to the output shaft 19 , the proximal drive shaft 18 is connected to a ring gear 23 of the planetary gearset 17 . the ring gear 23 is coupled to a sun gear 24 by the planetary gear 30 and carrier 26 . the sun gear 24 is coupled to or connected to the output drive shaft 19 a . regarding the second mechanical power path to the pump 21 a , rotational power is delivered from the motor 11 a to the pump 21 a via the gears 27 , 32 . the hydraulic pump 21 a drives the hydraulic motor 22 a that may be geared to the output shaft 19 a through the hydraulic motor output shaft 29 , output gear 31 and the shaft gear 28 that is connected to the output shaft 19 a . the power that is delivered to the planetary gear set 17 is therefore split to drive the hydraulic pump 21 a and to drive the output shaft 19 a directly . if the hydraulic pump 21 a is at zero or its minimum displacement and the hydraulic motor 22 a is at its maximum displacement , the hydraulic pump 21 a will ‘ freewheel ’ and rotate without producing any flow or pressure to the hydraulic motor 22 a . as the hydraulic pump 21 a cannot put any reaction torque on the planetary gearset 17 when the hydraulic pump 21 a is at zero or its minimum displacement , there can be no torque ( and hence no power ) going to the output shaft 19 a from the hydraulic motor 22 a . all power to the output shaft 19 a is provided by the drive motor 11 a through the carrier 26 and sun gear 24 . in this scenario , the hydraulic pump 21 a is set at its minimum displacement in the hydraulic motor 22 a at its maximum displacement . the gear 31 spins at a high rotational velocity but the rotational velocity of the output shaft 19 a and compressor 10 a is dictated by the drive motor 11 a . on the other hand , if a small amount of displacement is given to the hydraulic pump 21 a , the gear 27 will engage the gear 32 causing the pump 21 a to generate high pressure and a small flow rate to the hydraulic motor 22 a . this high pressure and small flow rate acts upon the hydraulic motor 22 a to produce high torque and low speed that is transmitted to the output die shaft 19 a via the gears 31 , 28 . the hydraulic pump 21 a under these conditions is also creating a reaction torque on the planetary gearset 17 which results in mechanical torque ( and hence power ) going directly to the output shaft 19 a through the ring gear 23 , carrier 26 and sun gear 24 , which combines with the power delivered from the hydraulic motor 22 a via the gears 31 , 28 . when the hydraulic pump 21 a is at its maximum displacement and the hydraulic motor 22 a is at its minimum displacement , the hydraulic motor 22 a cannot accept the flow rate from the hydraulic pump 21 a . this has the effect of locking the ring gear 23 to the planetary gear 30 , carrier 26 and sun gear 24 so the sun gear 24 ( and hence the output shaft 19 a ) rotates at its highest rotational velocity , and about 100 % of the power of the hydraulic pump 21 a is translated mechanically to the output shaft 19 a . the hydraulic motor 22 a is now freewheeling at zero displacement or torque to the output shaft 19 a . because all power from the hydraulic pump 21 a is now going to the output shaft 19 a mechanically via gears 23 , 30 , 26 , 24 , the cvt 15 a efficiency is very high when the hydraulic pump 21 a is operating at its maximum displacement . the cvt 15 a as illustrated in fig4 is ideal for large - scale centrifugal compressors 10 a because the power requirement increases with the cube of the impeller 33 speed , not linearly . as the cvt 15 a increases the impeller 33 speed within the compressor 10 a , additional power is fed mechanically to the output shaft 19 a and not hydraulically through the hydraulic motor 22 a of the cvt 15 a . the supplemental use of mechanical power from the hydraulic pump 21 a through the gears 32 , 27 , 23 , 30 , 26 , 24 to the output shaft 19 a reduces power loss when the cvt 15 a is not operating at its fastest output speed , but the use of supplemental mechanical power also significantly reduces the size and power capacity requirements of the hydraulic circuit 21 a , 22 a , 45 a . for a 2000 hp (˜ 1500 kw ) compressor 10 a , the cvt 15 a needs a maximum of only about 200 hp (˜ 150 kw ) transmitted thru the hydraulic circuit 21 a , 22 a , 15 a . the cvt 15 a eliminates the need for varying the speed of the drive motor 11 a or utilizing a controller 50 to control the speed of the drive motor 11 a . the controller 50 may be used to adjust the displacements of the hydraulic pump 21 a and hydraulic motor 22 a in response to the leaving chilled water temperature measured at 54 on the leaving chilled water side in the evaporator 53 . instead , the drive motor 11 a may be operated at a constant speed . turning to fig5 the drive motor 11 a is connected to a pulley - based cvt 15 b by the drive shaft 18 b which is corrected to a variable - diameter pulley 41 . the pulley 41 includes a pair of opposing cones 44 , 45 . a belt 43 rides in the groove between the two cones 44 , 45 . v - belts are preferred if the belt is made of rubber although steel belts are becoming commonplace . when the two cones 44 , 45 of the pulley are spread apart , the effective pulley diameter increases , the belt 43 rides lower in the groove , and the radius of the belt loop going around the pulley gets smaller . when the cones 44 , 45 are pulled closer together , the effective pulley diameter decreases , the belt 42 rides higher in the groove , and the radius of the belt loop going around the pulley gets larger . the cvt 15 b of fig5 may use hydraulic pressure , centrifugal force spring tension to create the force necessary to adjust the pulley halves 44 , 45 . a controller 50 may be utilized to control the mechanism pulling the halves 44 , 45 apart and moving the halves 44 , 45 closer together . input to the controller 50 will again include the leaving chilled water temperature at 54 . in satisfaction of the above - described need , a large tonnage water chiller 60 is disclosed that comprises a drive motor 11 a connected to a shaft 18 . the drive shaft 18 is connected to a continuous variable transmission ( cvt ) 15 , 15 a , 15 b . the cvt 15 , 15 a , 15 b that is linked to a controller 50 . the controller 50 may controls the operation of the cvt 15 , 15 a , 15 b based on the leaving chilled water temperature at 54 . the output shaft 19 , 19 a , 19 b of the cvt 15 , 15 a , 15 b is linked to a refrigerant cycle 60 . the refrigerant cycle 60 includes the compressor 10 a , evaporator 53 , condenser 52 and metering orifice 55 . the controller 50 may control the flow of fluid through the refrigerant cycle 60 by controlling the speed of the hydraulic pump 21 , 21 a , hydraulic motor 22 , 22 a or spacing of the pulley halves 44 , 45 . in operation , the controller 50 may take an input signal from the leaving chilled water temperature at 54 ( i . e . and compares to a set point ). if the chilled water temperature leaving the chiller evaporator 53 is below the set point , then the output speed of the hydraulic pump 21 , 21 a is reduced by increasing the displacement of the hydraulic motor 22 , 22 a and reducing the hydraulic pump 21 , 21 a displacement . alternatively , the output of the variable diameter pulley 41 is reduced . if the leaving chilled water temperature at 54 is above be set point then the output speed of the hydraulic pump 21 , 21 a is increased by increasing the pump 21 , 21 a displacement and reducing the hydraulic motor 22 , 22 a displacement . alternatively , the output of the variable diameter pulley 41 is increased . while only certain embodiments have been set forth , alternatives and modifications will be apparent from the above description to those skilled in the art . these and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims .