CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is being filed on December 2, 2016 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Serial No. 62/262,707, filed on December 3, 2015, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to organic Rankine cycle systems. More

particularly, a Roots-type expander that does not require a dedicated lubrication circuit or source for gear case components.

BACKGROUND

[0003] The Rankine cycle is a power generation cycle that converts thermal energy to mechanical work. The Rankine cycle is typically used in heat engines, and accomplishes the above conversion by bringing a working substance from a higher temperature state to a lower temperature state. The classical Rankine cycle is the fundamental thermodynamic process underlying the operation of a steam engine.

[0004] The Rankine cycle typically employs individual subsystems, such as a condenser, a fluid pump, a heat exchanger such as a boiler, and an expander turbine. The pump is frequently used to pressurize the working fluid that is received from the condenser as a liquid rather than a gas. The pressurized liquid from the pump is heated at the heat exchanger and used to drive the expander so as to convert thermal energy into mechanical work. Upon exiting the expander, the working fluid returns to the condenser where any remaining vapor is condensed. Thereafter, the condensed working fluid returns to the pump and the cycle is repeated.

[0005] A variation of the classical Rankine cycle is the Organic Rankine cycle (ORC), which is named for its use of an organic, high molecular mass fluid, with a liquid-vapor phase change, or boiling point, occurring at a lower temperature than the water-steam phase change. As such, in place of water and steam of the classical Rankine cycle, the working fluid in the ORC may be a solvent, such as n-pentane, toluene, or ethanol. The ORC working fluid allows Rankine cycle heat recovery from lower temperature sources such as biomass combustion, industrial waste heat, geothermal heat, solar ponds, etc. The low-temperature heat may then be converted into useful work, which may in turn be converted into electricity.

[0006] Further development in such Rankine cycle systems is desired.

SUMMARY

[0007] A heat recovery system is disclosed in which a working fluid (e.g. ethanol) is simultaneously utilized as a heat transfer medium and as a source of lubrication and cooling for gears, seals, and bearings within the expander. A small amount of mass flow of the working fluid, in its liquid state, can be diverted from a working fluid pump and into gear cases of the expander to be used as a cooling mechanism for the gears, lubricate the mesh between them, and lubricate the bearings and seals throughout the expander. Such a system eliminates the need for a dedicated lubrication circuit in which a substance other than the working fluid is used to lubricate the gears and bearings throughout the expander. It also eliminates organic Rankine cycle (ORC) architectures that utilize a percentage of oil in the working fluid. In such systems, the oil/working fluid travels through the entire system or is separated by an oil/working fluid separator. The oil-free expander minimizes parasitic losses, reduces complexity of assembly, increases reliability, and reduces part count. By utilizing the working fluid as lubrication the risk of cross contamination between the oil in the gear cavities and the working fluid is completely eliminated.

Preventing potential contamination of engine oil and fouling of heat exchangers (e.g. evaporators, condenser, and/or recuperator). The life and quality of the working fluid is also preserved.

[0008] A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 schematically depicts a vehicle including a Rankine cycle system in accordance with the principles of the present disclosure.

[0010] FIG. 2 is a schematic example of the system shown in FIG. 1. [0011] FIG. 3 is a schematic depiction of a Rankine cycle system employing a Rankine cycle working circuit and a lubrication circuit having features that are examples of inventive aspects in accordance with the principles of the present disclosure;

[0012] FIG. 4 shows an example fluid expander usable in the systems shown in FIGS. 1-3.

[0013] FIG. 5 is a cross-sectional schematic view of a single stage Roots-style expander suitable for use in extracting mechanical energy from the system of FIG. 1;

[0014] FIG. 6 is a schematic depiction of the Roots-style expander of FIG. 5;

[0015] FIG. 7 is a cross-sectional view showing timing gears of the Roots-style expander of FIG. 5; and

[0016] FIG. 8 is a diagram depicting the Rankine cycle employed by the system shown in FIGS. 1-3.

DETAILED DESCRIPTION

[0017] Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures.

[0018] The present disclosure relates generally to a Rankine cycle system (e.g., an organic Rankine cycle system) that utilizes heat from a heat source to generate useful work. In one example, the heat source is waste heat from a device such as a prime mover (e.g., an internal combustion engine such as a diesel engine or spark ignition engine, a fuel cell, etc.). In one example, a mechanical device, such as a rotary expander, is used to extract mechanical energy from the Rankine cycle system. In one example, the Rankine cycle system is an organic Rankine cycle system that heats and vaporizes the Rankine cycle working fluid (e.g., a solvent such as ethanol, n-pentane, toluene or other solvents) to temperatures that can equal or exceed 250 degrees Celsius (C).

[0019] Such high temperatures can deteriorate the lubricating oil used to lubricate moving components (e.g., bearings, gears, etc.) of mechanical devices (e.g., rotary expanders) used to extract energy from the Rankine cycle circuit. In this regard, with respect to flowable lubricating oils, it is desirable to use a lubrication cooling circuit that maintains the lubricant at acceptable temperatures. Grease typically is not effective because the solvent forming the Rankine cycle working fluid can cause de-greasing. Furthermore, grease will deteriorate at high temperatures. Lubricating oils can present issues when ineffective sealing (e.g., at mechanical components such as expanders, pumps or other components with moving parts that require lubrication) allows such oils to mix with the Rankine cycle working fluid. For example, lubricant within the Rankine cycle working fluid can be detrimental to the evaporation process by fouling the evaporator coils.

[0020] Aspects of the present disclosure relate to a closed-loop organic Rankine cycle system including a Rankine cycle working circuit and a lubrication circuit. In the examples shown herein, the working and lubrication circuits use the same working fluid. As such, in certain examples, the Rankine cycle working circuit and the lubrication circuit share a common hydraulic pump. In certain examples, the lubricant and the Rankine cycle working fluid mix downstream of an expander upstream from a low pressure side of the pump. In certain examples, the lubrication circuit is a cooling circuit wherein relatively cool lubricant is used to lubricate components (e.g. bearings, timing gears, etc.) of a mechanical expander that extracts energy/work from the Rankine cycle working circuit.

[0021] Referring to FIG. 1, an example system is shown in which a vehicle 300 is powered by a power plant 116. The power plant 116 can be, for example, an internal combustion engine, a fuel cell, a diesel engine and/or or a spark ignition engine. The vehicle 300 can include a torque transfer arrangement 302 (e.g., a drive train, drive shaft, transmission, differential, etc.) for transferring torque from the engine crankshaft to one or more axles 304 of the vehicle 300. The axles 304 can be coupled to wheels 308, or to tracks or other structures adapted to contact the ground. The system can additionally include an organic Rankine cycle system 100. The organic Rankine cycle system 100 is configured to convert heat energy from a heat source, such as an engine 116, into mechanical energy. In such examples, the organic Rankine cycle system 100 and the engine 116 are carried with a vehicle chassis/frame 306 (shown schematically).

[0022] Referring to FIG. 2, an example power plant 116 and organic Rankine cycle system 100 are shown in further detail. The organic Rankine cycle system 100 is configured to cycle a Rankine cycle working fluid (e.g., a solvent such as ethanol, n- pentane, toluene or other solvents) repeatedly through a closed-loop organic Rankine cycle. As depicted at FIG. 2, the organic Rankine cycle system 100 includes a Rankine cycle working circuit 100 having a condensing zone 104, a heating zone 106, and a mechanical energy extracting zone 108. In the example shown, the condensing zone 104 includes a condenser 170, the heating zone 106 includes a heat exchanger that transfers heat from the power plant 116 to the working fluid, and the mechanical energy extracting zone 108 includes an expander. A hydraulic pump 110 is used to move the working fluid through the Rankine cycle circuit 100. The energy extracting zone 108 can include an output shaft 400 that is connected to a drive component 305 of the power plant (e.g. a pulley associated with the front end accessory drive via a belt). Still referring to FIG. 2, a control valve(s) 155 can be provided to control the flow rate and/or proportion of working fluid flowing to the energy extracting zone and to the heating zone 106. In some instances, it is desirable to maintain operation of the lubrication circuit when flow through the work circuit is not desired.

[0023] Referring to FIGS. 3 and 4, more detailed schematics of the system 300 are shown. FIG. 3 shows a complete system while FIG. 4 shows an example expander layout useable in the system of FIG. 3.

[0024] Referring to FIG. 3, it can be seen that the pump 110 includes a low pressure side 112 in fluid communication with the condensing zone 104, via a reservoir 160, and a high pressure side 114 in fluid communication with the heating zone 106. The mechanical energy extracting zone 108 has an inlet side 117 in fluid communication with the heating zone 106 and an outlet side 118 in fluid communication with the condensing zone 104.

[0025] The Rankine cycle system 100 also includes a lubrication circuit 113 for cycling/circulating and cooling the working fluid portion that is used to lubricate moving parts associated with a mechanical component (e.g., a rotary expander) of the mechanical energy extracting zone 108. The Rankine cycle working circuit 102 and the lubrication circuit 113 include a shared segment 115 in which the Rankine cycle working fluid from both circuits is transported. The Rankine cycle working circuit 102 and the lubrication circuit 113 are co-extensive along the shared segment 115 which feeds into the inlet 172 of a condenser 170. The condensed fluid is delivered from an outlet 174 of the condenser 170 to an inlet 162 of a fluid reservoir 160. It is beneficial to deliver the working fluid from the lubrication circuit 113 to the condenser 170 so that heat absorbed by the working fluid from the lubricated components (e.g. gears, bushings, bearings, etc.) can be dissipated. This reduces the condenser loading and the amount of required heat rejection.

[0026] As shown, the pump 110 is positioned in fluid communication with the fluid reservoir 160 such that the working fluid flows from an outlet 164 of the reservoir 160 and through the pump 110 from the low pressure side 112 to the high pressure side 114. The pump 110 provides positive pressure for cycling flow through both the Rankine cycle working circuit 102 and the lubrication circuit 113. As shown at Figure 2, the shared segment 115 terminates at control valve assembly 153, which includes a single three-way control valve 155. Figure 3 shows an alternative configuration in which the control valve assembly 153 includes two two-way control valves 155, wherein the shared segment 115 terminates at the valves 155. The control valve(s) 155 controls the flow and/or proportion of working fluid delivered to the Rankine cycle working circuit 102 and the lubrication circuit 113 and can be electronically controlled by a controller 500 associated with the power plant 116.

[0027] The Rankine cycle working circuit 102 includes a non-shared segment 121 that extends from the control valve 155 (upper valve on Figure 3), through the heating zone 106, and the mechanical energy extracting zone 108. The lubrication circuit 113 includes a non-shared segment 123 that extends from the control valve 155 (lower valve on Figure 3) and through the mechanical energy extracting zone 108. At the mechanical energy extracting zone 108, the lubricant can flow through lubricant containing structures 125 such as bearings, bearing chambers, and gear chambers of a rotary mechanical expander 127. From the lubricant containment structures 125 (125a, 125b, 125c, 125d) of the mechanical energy extracting zone 108, the lubricant can flow to the primary mixing location 111 via segment 129. With this configuration, the working fluid entering the expander 127 via the lubrication circuit 113 enters the lubricant containing structures 125 in a liquid state where it can act as a lubricant while the working fluid entering the expander 127 via the work circuit is superheated or at least a two-phase fluid such that the expander 127 can extract energy from the expander 127.

[0028] In certain examples, Rankine cycle working fluid can leak past the shaft seals of expander 127 into the lubricant containment structures 125. However, as the lubricant and the working fluid are the same working fluid, the leakage of Rankine cycle working fluid into the lubrication circuit 113 at the mechanical expander 127 does not pose any issue for the system. Likewise, some of the Rankine cycle working fluid may migrate through seals in the expander 127 such that segment 131 carries a mixture of lubricant and Rankine cycle working fluid. Thus, special sealing used to absolutely prevent leakage is not needed thereby reducing the quantity and/or expense of the seals in the system.

Accordingly, reliability is increased while risk is reduced. [0029] Pressure from the pump 110 drives flow of the Rankine cycle working fluid through the non-shared segment 121 and also drives flow of lubricant through the nonshared segment 123. The mechanical expander 127 can include one or more rotor chambers 128 (128a, 128b, 128c) containing one or more rotors. In use, the heated Rankine cycle working fluid from the heating zone 106 flows through the rotor chambers 128 of the mechanical expander 127 causing rotation of the rotors such that useful work is extracted from the Rankine cycle circuit 102. For example, work can be extracted via an output shaft 400. At the rotary mechanical expander 127, some Rankine cycle working fluid may flow across seals from rotor chamber 128 to the lubricant containment structures 125. Thus, in some examples, a mixture of Rankine cycle working fluid and lubricant (which are the same type of fluid) flows from the lubricant containment structures 125 through segment 129 to the primary mixing location 111. At the primary mixing zone 111, primary mixing between the lubricant and the Rankine cycle working fluid occurs. The mixed lubricant and Rankine cycle working fluid then flows from the mechanical primary mixing zone 111 through the condensing zone 104 and then to the reservoir where the mixture is stored. The combined working fluid flows through the pump 110 and back to the control valve(s) 155.

[0030] By configuring the system 100 to mix the Rankine cycle working fluid and the lubricant upstream of the condenser 170, separate outlet pipes for each chamber 128 do not need to be tied together and routed to feed into the pump 110. Rather, the lubricant outlet ports simply need to be routed to the nearby expander outlet. This results in fewer leak paths and simplified packaging. Moreover, it is fully ensured that any working fluid that enters in the lubrication chambers 125 through the seals (e.g. dynamic shaft seals or turbo rings) is easily drained and returned back to the liquid state since both segments 129 and 131 feed into the condenser 170 after being mixed together at the primary mixing location 111.

[0031] In the depicted example, the Rankine cycle system 100 is configured to recapture waste energy from a prime mover, such as an engine 116 (e.g., an internal combustion engine such as a diesel or spark ignition engine or a fuel cell), by drawing waste heat from the engine (e.g., by drawing heat from the engine exhaust such as from a main exhaust line and/or from exhaust in an exhaust gas recirculation line). As depicted at FIG. 1, the heating zone 106 of the organic Rankine cycle system 100 includes at least one heat exchanger 150 for drawing waste heat from the engine 116. The heat exchanger 150 transfers heat from the engine 116 to the Rankine cycle working fluid of the Rankine cycle circuit 102 as the working fluid passes through the heating zone 106 thereby heating and evaporating the working fluid. In certain examples, the working fluid is super-heated. In other examples, the working fluid is not super-heated.

Mechanical Energy Extraction/Recovery Device

[0032] As described above, the organic Rankine cycle system 100 of FIGS. 1-3 includes a mechanical energy extraction zone 108 including at least one mechanical device (e.g., a reaction turbine, a piston engine, a scroll expander, a screw-type expander, a Roots expanders, etc.) capable of outputting mechanical energy from the Rankine cycle working circuit 102. In certain examples, the mechanical device relies upon the kinetic energy, temperature/heat and pressure of the working fluid to rotate the output shaft 400 (see FIG. 2). Where the mechanical device is used in an expansion application, such as with a Rankine cycle, energy is extracted from the working fluid via fluid expansion. In such instances, the mechanical device may be referred to as an expander or expansion device. However, it is to be understood that the mechanical device is not limited to applications where a working fluid is expanded across the device. In certain examples, the mechanical device includes one or more rotary elements (e.g., turbines, blades, rotors, etc.) that are rotated by the working fluid of the Rankine cycle so as to drive rotation of the output shaft 400 of the mechanical device. In certain examples, the output shaft 400 can be coupled to an alternator used to generate electricity, used to power active components, or used to charge a battery suitable for providing electrical power on demand. In other examples, the output shaft 400 can be coupled to a hydraulic pump used to generate hydraulic pressure, used to power active hydraulic components, or used to charge a hydraulic accumulator suitable for providing hydraulic pressure on demand. In still other examples, the output shaft 400 can be mechanically coupled (e.g., by gears, belts, chains or other structures) to other active components or back to a prime mover that is the source of waste heat for the Rankine cycle system.

[0033] In one example, the mechanical device used at the mechanical energy extracting zone 108 can include a Roots-style rotary device referred to herein as a Roots-style expander. Patent Cooperation Treaty patent application publication WO 2014/117159 discloses multi-stage expanders suitable for such use herein. The entirety of WO Ί59 is incorporated by reference herein. The pressure at the inlet side of the device is greater than the pressure at the outlet side of the device. The pressure drop between the inlet and outlet drives rotation within the device. Typically, except for decompression related to fluid leakage and device inefficiencies, expansion/decompression does not occur within the device itself, but instead occurs as the working fluid exits the device at the outlet. The device can be referred to a volumetric device since the device has a fixed displacement for each rotation of a rotor within the device.

[0034] As shown at FIGS. 3 and 4, the extraction device 127 includes a first stage 180, a second stage 182, and a third stage 184, wherein working fluid enters the inlet 117, then passes through the rotors of the first stage 180, then passes through the rotors of the second stage 182, and then passes through the rotors of the third stage 184 before existing through outlet 118. As there are gear sets and bearing points at the ends of each stage 180, 182, 184, lubrication containment chambers or structures 125a, 125b, 125c, and 125d are provided and placed in fluid communication with a lubrication fluid. The expander 127 shown at FIG. 3 includes a singular lubrication inlet 190 while the expander schematic 127 shows individual inlets into each of the lubrication chambers or structures. Any combination of internal and/or external lubrication circuits may be utilized without departing from the concepts presented herein. Where reference is made to specific lubrication circuit routing configurations, those references are made with respect to FIG. 3.

[0035] In one example, the chambers 125a - 125d are placed in fluid communication with each other via a fluid delivery circuit 192 including internal and/or external branch lines, for example, branch line 192a, 192b, 192c, 192d, 192e, and 192f (FIG. 3). To ensure that the appropriate lubricant flow reaches each of the chambers 125a - 125d, flow control orifices may be provided in one or more of the individual branch lines 192a - 192e (FIG. 3) or the branch lines shown at FIG. 4. After passing through the chambers 125a - 125d, the lubricant can be discharged through outlets in the device 127, for example, outlets 194, 196, and 198 (FIG. 3). As shown, outlets 194, 196, and 198 are placed in fluid

communication with branch line 129. As outlets 194 - 198 are in close proximity to outlet 118, very little piping is required to reconnect the respective lines at primary mixing location 111. As stated previously, this approach minimizes costs and results in a more compact construction. [0036] FIGS. 5-7 depict a generic, single stage Roots-style expander 200 also suitable for use at the mechanical energy extraction zone 108 of the Rankine cycle system 100.

Expander 200 relies on the same general operating principles as extraction device 127 and the descriptions of each are therefore largely applicable for the other. The expander 200 includes a housing 202 having an inlet 204 and an outlet 206. In use, the inlet 204 is in fluid communication with the heating zone 106 of the Rankine cycle system 100 and the outlet 206 is in fluid communication with the condensing zone 104 of the Rankine cycle system 100.

[0037] The expander housing 202 defines an internal cavity 208 (i.e., a rotor chamber) that provides fluid communication between the inlet 204 and the outlet 206. The internal cavity 208 is formed by first and second parallel rotor bores 210 defined by cylindrical bore -defining surfaces 222. The expander 200 also includes first and second rotors 212 respectively mounted in the first and second rotor bores 210. Each of the rotors 212 includes a plurality of lobes 214 mounted on a shaft 216. The shafts 216 are parallel to one another and are rotatably mounted relative to the expander housing 202 by bearings 217. The shafts 216 are free to rotate relative to the housing 202 about parallel axes of rotation 213. The lobes 214 of the first and second rotors 212 intermesh/interleave with one another. Intermeshing timing gears 218 are provided on the shafts 216 so as to synchronize the rotation of the first and second rotors 212 such that the lobes 214 of the first and second rotors 212 do not contact one another in use. In certain examples, the lobes 214 can be twisted or helically disposed along the lengths of the shafts 216. The rotors 212 define fluid transfer volumes 219 between the lobes 214. The lobes 214 can include outer tips 220 that pass in close proximity to the bore-defining surfaces 222 of the housing 202 as the rotors 212 rotate about their respective axes 213. In certain

embodiments, the outer tips 220 do not contact the bore-defining surfaces 222.

[0038] In use of the expander 200, working fluid (e.g., vaporized working fluid or two- phase working fluid) from the heating zone 106 enters the expander housing 202 through the inlet 204. Upon passing through the inlet 204, the vaporized working fluid enters one of the fluid transfer volumes 219 defined between the lobes 214 of one of the rotors 212. The pressure differential across the expander 200 causes the working fluid to turn the rotor 212 about its axis of rotation 213 such that the fluid transfer volume 219 containing the vaporized working fluid moves circumferentially around the bore-defining surface 222 from the inlet 204 to the outlet 206. As the rotors 212 are rotated by the working fluid, mechanical energy is transferred out from the expander 200 through the output shaft 400 which coincides with one of the shafts 216. The output shaft 400 (FIG. 3) extends outwardly beyond an outer boundary of the expander housing 202 so as to be accessible for transferring torque/energy from the expander 200.

[0039] It will be appreciated that working fluid from the inlet 204 enters the internal cavity 208 of the housing 202 at a central region CR of the internal cavity 208 that is between parallel planes P, which include the axes 213 and which extend between inlet and outlet sides of the expander housing 202. The working fluid from the inlet 204 enters fluid transfer volumes 219 of the rotors 212 at the central region CR and causes the rotors 212 to rotate in opposite directions about their respective axes 213. The rotors 212 are rotated about their respective axes 213 such that the fluid transfer volumes 219 containing the working fluid move away from the central region CR along their respective

circumferential bore-defining surface 222 of the housing 202 to outer regions OR (i.e., regions outside the planes P) of the internal cavity 208 as indicated by arrows 230 (see FIG. 4). The rotors 212 continue to rotate about their respective axes 213 thereby moving the fluid transfer volumes 219 from the outer regions OR back to the central region CR adjacent the outlet 206 as indicated by arrows 232. The working fluid from the fluid transfer volumes 219 exits the expander housing 202 through the outlet 206 as indicated by arrows 234.

[0040] The intermeshing gears 218 and bearings 217 can be positioned within a lubrication chamber 402 containing lubricant for lubricating the gears 218 and the bearings 217.

Lubricant Containing Structures

[0041] Referring to FIG. 4, lubricant containing structures 125a-125d that are generally analogous to the lubrication chamber 402 are shown. Each of the lubricant containing structures 125a-125d is shown as at least containing bearings 217 while structures 125b- 125d also show pairs of timing gears 218. Structures 125b-125d additionally show drive gears 215 that allow for the rotors of one stage to drive the rotors of the adjacent stage. Many other configurations of gear and bearing arrangements are possible. The lubricant containing structures may also be referred to as gear cases. [0042] During operation, the temperature in the rotor cavity can be as high as 300°C to 350°C and thus bearings and timing gears in the expander 127 are exposed to relatively high temperatures. The high temperature can deteriorate lubricating fluid for the bearings and timing gears and reduce the life of the bearings, seals, and timing gears. To prevent this from occurring, the lubrication circuit 113 can be used to circulate working fluid as a lubricant through the lubrication chamber 402 so the lubricant is exposed to the high temperatures for only a limited amount of time.

[0043] Because the lubricant used in the system 100 is the same as the working fluid being used for expansion through the expander 127, some modifications to the bearings, drive gears, timing gears and/or other components requiring lubrication can be beneficial to proper system operation. For example, bearings 217 can be provided as journal type bearings or bushings can be used wherein the liquid working fluid (e.g. ethanol) is used as a film lubricant, as bushings which do not require lubrication, or as ball bearings using the liquid working fluid (e.g. ethanol) as lubrication.

[0044] Additionally, sealing between the lubrication containing structures and the rotor cavities can be enhanced to minimize stage-to- stage leaks and maximize shaft output torque. For example, dynamic shaft seals (lip seals), face seals (ceramic material or one such that can survive operating temps, 300C+ and surface velocities), and/or labyrinth seals to relieve pressure on the dynamic and face seals may be utilized. Such

configurations can minimize drag and frictional losses in the system.

[0045] The working fluid lubricant of the lubrication circuit 113 is cooled by the Rankine cycle working fluid as both fluids pass through the condenser 170. Inside the condenser 170, the combined working fluid condenses and cools as it undergoes a phase change within the condensing zone 104. It is also possible to combine the lubrication circuit 113 into the Rankine cycle working fluid circuit 102 after the Rankine cycle working fluid has been passed through the condenser 170. In such a case, the condensed Rankine cycle working fluid is then able to absorb heat from the working fluid that is used as a lubricant. It will be appreciated that the lubrication chamber 402 is one example of a lubricant containment structure 125 and that other lubricant containing structures 125 (e.g., other lubricant chambers) can also be provided as part of the lubrication circuit 113. Rankine Cycle Operation

[0046] FIG. 8 shows a general diagram depicting a representative Rankine cycle applicable to the system 100, as described with respect to FIGS. 1-3. The diagram depicts different stages of the Rankine cycle showing temperature in Celsius plotted against entropy "S", wherein entropy is defined as energy in kilojoules divided by temperature in Kelvin and further divided by a kilogram of mass (kJ/kg*K). The Rankine cycle shown in FIG. 8 is specifically a closed-loop Organic Rankine Cycle (ORC) that may use an organic, high molecular mass working fluid with a liquid-vapor phase change or boiling point occurring at a lower temperature than the water-steam phase change of the classical Rankine cycle. Accordingly, in the system 100, the working fluid may be a solvent, such as ethanol, n-pentane or toluene.

[0047] In the diagram of FIG. 2, the term "Q" represents the heat flow to or from the system 100, and is typically expressed in energy per unit time. The term "W" represents mechanical power consumed by or provided to the system 100, and is also typically expressed in energy per unit time. As may be additionally seen from FIG. 2, there are four distinct processes or stages 142-1, 142-2, 142-3, and 142-4 in the ORC. During stage 142- 1, the Rankine cycle working fluid in the form of a partial or wet vapor enters and passes through at least one condenser 170 at the condensing zone 104, in which the Rankine cycle working fluid is condensed at a constant temperature to become a saturated liquid. Following stage 142-1, the Rankine cycle working fluid is pumped from low to high pressure by the pump 106 during the stage 142-2. During stage 142-2, the Rankine cycle working fluid is in a liquid state.

[0048] From stage 142-2 the Rankine cycle working fluid is transferred to stage 142-3. During stage 142-3, the pressurized Rankine cycle working fluid enters and passes through the heat exchanger 150 where it is heated at constant pressure by an external heat source to become a vapor or a two-phase fluid, (i.e., liquid together with vapor). During stage 142- 4, the Rankine cycle working fluid, in the form of a fully vaporized fluid or a two-phase fluid (e.g. a partial vapor state), passes through the mechanical energy extracting zone 108, thereby generating useful work or power. The working fluid may expand at the outlet of the mechanical energy extracting zone 108 thereby decreasing the temperature and pressure of the working fluid such that some additional condensation of the working fluid may occur. Following stage 142-4, the working fluid is returned to the condensing zone 104, at which point the cycle completes and will typically restart at stage 142-1.

[0049] It is noted that the shape of the diagram shown in FIG. 8 will change from what is shown due to the use of the working fluid for the lubricant. As the ratio of working fluid used as a lubricant in comparison to that used for expansion is relatively small, a relatively small shift of the depiction is expected to occur.

The Electronic Control System

[0050] The system 100 can operate in various modes. For example, a start-up mode can be implemented in which the valve 155 associated with the work circuit 121 is held closed while the valve 155 associated with the lubrication circuit 113 is held open to flood the lubrication structures or gear cases with liquid working fluid. The start-up mode can be followed by a normal running mode, wherein the valve associated with the work circuit 121 is opened. This operation protects the expander from being caused to rotate by the working fluid when the amount of liquid fluid in the gear cases may not be present for sufficient lubrication.

[0051] In one configuration, the flow rate into the gear cases or lubrication structures 125a, 125b, 125c, 125d via control valve 155 can be dictated by the operating speed (i.e. rotational speed of the rotors) of the expander and/or by gear case temperature via one or more input sensors 502 in direct communication with controller 500 or received from another source, such as the vehicle CAN bus. For example, the valve 155 could open to a certain degree based on an expander speed and/or temperature setpoint. The temperature could be a measured temperature of the working fluid in the gear case or lubrication structures or could be a temperature of the gear case or lubrication structure housing. In one example, up to and including a preset expander rotor rotational speed, the inlet valves (e.g. valve 155) to the gear cases are closed and no fluid is introduced to the gear cases. Above the preset expander rotor rotational speed, the mass flow rate of the working fluid being introduced into the lubricant cavities is proportional to the expander speed to minimize parasitic losses and maximize power generation. In some applications, a suitable rotational speed is 100 revolutions per minute (RPM). Other values may be used in certain applications, such as 200 RPM. Once above the preset rotational speed, the operation of the lubricant valve 155 can be a function of the expander rotational speed such that the lubricant valve 155 is open to a greater degree at relatively higher speeds and is open to a lesser degree at relatively lower speeds. In one implementation, the operation of the lubricant valve 155 can be further controlled such that if the temperature at of the leaving working fluid lubricant (or chamber) reaches greater than a maximum threshold value, the mass flow will be increased by further or fully opening the lubricant valve 155 and overriding all other controls until temperature is reduced below the maximum threshold value. In one example, the maximum threshold value is 120 degrees Celsius.

[0052] Referring to Figure 3 the electronic controller 500 is schematically shown as including a processor 500A and a non-transient storage medium or memory 500B.

Memory 500B is for storing executable code, the operating parameters, and the input from various inputs while processor 500A is for executing the code. Examples of memory 500B include computer readable media. Computer readable media includes any available media that can be accessed by the processor 500A. By way of example, computer readable media include computer readable storage media and computer readable communication media.

[0053] Computer readable storage media includes volatile and nonvolatile, removable and non-removable media implemented in any device configured to store information such as computer readable instructions, data structures, program modules or other data. Computer readable storage media includes, but is not limited to, random access memory, read only memory, electrically erasable programmable read only memory, flash memory or other memory technology, compact disc read only memory, digital versatile disks or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by the processor 500A.

[0054] Computer readable communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term "modulated data signal" refers to a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, computer readable communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency, infrared, and other wireless media. Combinations of any of the above are also included within the scope of computer readable media. [0055] From the forgoing detailed description, it will be evident that modifications and variations can be made without departing from the spirit and scope of the disclosure.