ENERGY RECOVERY DEVICE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is being filed on June 10, 2016 as a PCT International Patent Application and claims the benefit of U.S. Patent Application Serial No. 62/174,250, filed on June 11, 2015, the disclosure of which is incorporated herein by reference in its entirety.

GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with government support under Contract No. DE- EE0005650 awarded by the National Energy Technology Laboratory funded by the Office of Energy Efficiency & Renewable Energy of the United States Department of Energy. The government has certain rights in the invention.

TECHNICAL FIELD

[0003] The present disclosure relates to a volumetric fluid expander used for power generation.

BACKGROUND

[0004] Volumetric expanders can be utilized to recover waste heat from a power plant, such as an internal combustion engine. In one application, waste heat from a power plant is recovered by expanding the exhaust gases from the power plant through the expander. In such instances, the expander housing and its rotors are directly exposed to significant heat from the exhaust gases as well as particulate matter present in the exhaust.

SUMMARY

[0005] An expander and engine start-up control method is disclosed including the steps of: providing an internal combustion engine which generates an exhaust flow stream and an expander which receives the exhaust flow stream to generate useful work; detecting that the internal combustion engine has been started; supplying a torque command of zero to a motor/generator to cause rotors within the expander to be held in a static fixed position; sensing a temperature of a housing of the expander; changing the torque command target value for the motor/generator once the expander housing temperature sensor indicates that the housing has reached a predetermined temperature. This approach allows the expander components to thermally heat soak to minimize operating clearances and maximize efficiency.

[0006] The expander and engine start-up control method can also include the steps of: providing an internal combustion engine which generates an exhaust flow stream and an expander which receives the exhaust flow stream to generate useful work; detecting that the internal combustion engine has been started; and causing rotors within the expander to be held in a static fixed position upon detecting that the internal combustion engine has been started for a first time period.

[0007] An expander and engine start-up control method is disclosed including the steps of: providing an internal combustion engine which generates an exhaust flow stream and an expander which receives the exhaust flow stream to generate useful work; detecting that the internal combustion engine has been started; supplying a non-zero torque command to a motor/generator to cause rotors within the expander to rotate; changing the torque command value and/or discontinuing power to the motor/generator once the rotors have been sensed to be rotating or after a predetermined period of time has been reached. This method ensures that a rotor that may have become bound due to condensation or soot buildup will be actively unbound by activation of the motor/generator which prevents excessive backpressure on the engine exhaust caused by bound rotors.

[0008] An expander and engine shut-down control method is disclosed including the steps of: providing an internal combustion engine which generates an exhaust flow stream and an expander which receives the exhaust flow stream to generate useful work; detecting that the internal combustion engine has been shut down; supplying a torque command of zero to the motor/generator to cause rotors within the expander to be held in a static fixed position; changing the target torque command and/or discontinuing power to the motor/generator once the expander housing temperature sensor indicates that the housing has reached a predetermined temperature or after a predetermined period of time has been reached. This step can also be implemented after the inlet pressure of the expander is within a certain pressure of the expander outlet pressure, for example within 5kPa. This method prevents an increase in operating clearances as the expander components expand in response to temperature at different rates. [0009] A power generation and recovery system is also disclosed that includes an internal combustion engine which generates an exhaust flow stream and an expander having a pair of rotors which receives the exhaust flow stream to generate useful work. The system can also include an electronic controller adapted to detect when the internal combustion engine has been started and adapted to cause the rotors within the expander to be held in a static fixed position upon detecting that the internal combustion engine has been started for a first time period.

DRAWINGS

[0010] Figure 1 is a schematic for an expander and engine start-up control strategy using a fluid expander in accordance with the principles of this disclosure.

[0011] Figure 2 is a schematic for an expander and engine shut down control strategy in accordance with the principles of this disclosure.

[0012] Figure 3 is a schematic for an expander and engine start-up control strategy using a fluid expander in accordance with the principles of this disclosure.

[0013] Figure 4 is a schematic showing an expander and vehicle for which the control strategies of Figures 1 to 3 may be used.

[0014] Figure 5 is a schematic cross-sectional view of the expander shown in Figure 4.

[0015] Figure 6 is a schematic see-through perspective view of the expander shown in Figure 4.

[0016] Figure 7 is a schematic perspective view of a packaged expander and motor/generator shown in Figure 4.

[0017] Figure 8 is a schematic cross-sectional view of the packaged expander and motor/generator shown in Figure 7.

[0018] Figure 9 is a perspective view of the expander shown in Figure 7. DETAILED DESCRIPTION

[0019] With reference to Figures 1-3, strategies start-up and shut-down strategies for an expander utilized in conjunction with a power plant, such as an internal combustion engine, are disclosed. The disclosed strategies are suitable for a wide range of expander and system configurations. For example, the disclosed strategies may be utilized with the expander and system configurations shown and described in Patent Cooperation Treaty (PCT) International Publication Number WO 2014/144701 and in United States Patent Application Publication US 2014/0260245, the entireties of which are incorporated herein by reference.

Volumetric Energy Recovery Device (Expander)

[0020] In general, the volumetric energy recovery device or expander 20 relies upon the kinetic energy and static pressure of a working fluid to rotate an output shaft 38. The expander 20 may be an energy recovery device 20 wherein the working fluid 12-1 is the direct engine exhaust from the engine. In such instances, device 20 may be referred to as an expander or expander, as so presented in the following paragraphs.

[0021] The expander 20 has a housing 22 with a fluid inlet 24 and a fluid outlet 26 through which the working fluid 12-1 undergoes a pressure drop to transfer energy to the output shaft 38. The output shaft 38 is driven by synchronously connected first and second interleaved counter-rotating rotors 30, 32 which are disposed in a cavity 28 of the housing 22. Each of the rotors 30, 32 has lobes that are twisted or helically disposed along the length of the rotors 30, 32. Upon rotation of the rotors 30, 32, the lobes at least partially seal the working fluid 12-1 against an interior side of the housing at which point expansion of the working fluid 12-1 only occurs to the extent allowed by leakage which represents and inefficiency in the system. In contrast to some expanders that change the volume of the working fluid when the fluid is sealed, the volume defined between the lobes and the interior side of the housing 22 of device 20 is constant as the working fluid 12-1 traverses the length of the rotors 30, 32. Accordingly, the expander 20 may be referred to as a "volumetric device" as the sealed or partially sealed working fluid volume does not change.

[0022] The expander 20 is shown in detail in Figures 5 and 6. In the particular embodiment shown at Figures 5 and 6, the expander 20 inlets and outlets are configured for use with a relatively low pressure working fluid, such as exhaust from an internal combustion engine or fuel cell. However, the following description is generally applicable for use with any type of a working fluid. The expander 20 includes a housing 22. As shown in Figure 5, the housing 22 includes an inlet port 24 configured to admit relatively high-pressure working fluid 12-1 from the heat exchanger 18 (shown in Figure 12). The housing 22 also includes an outlet port 26 configured to discharge working fluid 12-2 to the condenser 14 (shown in Figure 12). It is noted that the working fluid discharging from the outlet 26 is at a relatively higher pressure than the pressure of the working fluid at the condenser 14.

[0023] As additionally shown in Figure 6, each rotor 30, 32 has four lobes, 30-1, 30-2, 30-3, and 30-4 in the case of the rotor 30, and 32-1, 32-2, 32-3, and 32-4 in the case of the rotor 32. Although four lobes are shown for each rotor 30 and 32, each of the two rotors may have any number of lobes that is equal to or greater than two, as long as the number of lobes is the same for both rotors. Accordingly, when one lobe of the rotor 30, such as the lobe 30-1 is leading with respect to the inlet port 24, a lobe of the rotor 32, such as the lobe 30-2, is trailing with respect to the inlet port 24, and, therefore with respect to a stream of the high-pressure working fluid 12-1.

[0024] As shown, the first and second rotors 30 and 32 are fixed to respective rotor shafts, the first rotor being fixed to an output shaft 38 and the second rotor being fixed to a shaft 40. Each of the rotor shafts 38, 40 is mounted for rotation on a set of bearings (not shown) about an axis XI, X2, respectively. It is noted that axes XI and X2 are generally parallel to each other. The first and second rotors 30 and 32 are interleaved and continuously meshed for unitary rotation with each other. With renewed reference to Figure 5, the expander 20 also includes meshed timing gears 42 and 44, wherein the timing gear 42 is fixed for rotation with the rotor 30, while the timing gear 44 is fixed for rotation with the rotor 32. The timing gears 42, 44 are configured to retain specified position of the rotors 30, 32 and prevent contact between the rotors during operation of the expander 20.

[0025] The output shaft 38 is rotated by the working fluid 12 as the working fluid undergoes expansion from the relatively high-pressure working fluid 12-1 to the relatively low-pressure working fluid 12-2. As may additionally be seen in both Figures 5 and 6, the output shaft 38 extends beyond the boundary of the housing 22. Accordingly, the output shaft 38 is configured to capture the work or power generated by the expander 20 during the expansion of the working fluid 12 that takes place in the rotor cavity 28 between the inlet port 24 and the outlet port 26 and transfer such work as output torque from the expander 20. Although the output shaft 38 is shown as being operatively connected to the first rotor 30, in the alternative the output shaft 38 may be operatively connected to the second rotor 32.

Drive System

[0026] In one example, the expander 20 can be interfaced with a motor/generator 70 and utilized in a vehicle 50 having an internal combustion engine 52, as shown at Figure 4. The variable drive system 19 can also be interfaced with an engine or power plant 52 and a motor/generator 70, as described in US 2014/0260245. Alternatively, the variable drive system 19 can be interfaced with a supercharger and a motor/generator, as described in WO 2014/144701.

[0027] In the configuration shown, all recaptured waste heat power from the expander is transferred to the motor/generator 70. A load storage device 60 may be provided to store the work generated by the expander 20 which may be accumulated for subsequent release on demand. In the example, shown, the load storage device 60 is a battery which stores electrical energy from the motor/generator 70. Accordingly, the motor/generator 70 may draw power from the load storage device 60 to drive the expander 20.

[0028] With reference to Figures 4 and 7-9, it can be seen that the expander shaft 38 is directly coupled to a shaft 71 of the motor/generator 70 through a splined connection. Other connection types may be used. To provide a packaged unit, an adapter plate 21 may be utilized such that the motor/generator 70 and the expander 20 can be bolted together. In some examples, the motor/generator 70 and expander 50 are coupled together via other means, for example, via gears or belts.

System Control and Operation

[0029] The system shown in Figure 4 may be operated through a control system. Such a system is presented at Figure 4 which shows an electronic controller 500. The electronic controller 500 is schematically shown as including a processor 500A and a non-transient storage medium or memory 500B, such as RAM, a flash drive or a hard drive. Memory 500B is for storing executable code, the operating parameters, and the input from the operator user interface 500D, while processor 500A is for executing the code. The electronic controller is also shown as including a transmitting/receiving port 500C, such as a vehicle CAN bus. A user interface 500D may also be provided to activate and deactivate the system, allow a user to manipulate certain settings or inputs to the controller 500, and to view information about the system operation.

[0030] The electronic controller 500 typically includes at least some form of memory 500B. 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 includes computer readable storage media and computer readable communication media.

[0031] 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.

[0032] 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.

[0033] Electronic controller 500 is also shown as having a number of inputs/outputs that may be used for implementing desired operational modes of the system 10. For example, electronic controller 500 provides outputs for commanding an expander bypass valve 202 and for controlling the variable drive system 19 (e.g. activating and deactivating motor/generator 70). Referring to Figure 4, an exhaust line 54 having an exhaust bypass line 54a and valve 202 are provided to allow exhaust gases to be diverted around the energy recovery device 20, when desired. Likewise, electronic controller 500 receives inputs for the control of the system 10, for example an input from pressure sensor 206 and/or 209 upstream of the expansion device 20, an input from pressure sensor 208 downstream of the expansion device, an input from temperature sensor 209 indicating the expander housing temperature, and various other inputs via the vehicle CAN bus. It is also noted that the above described components of controller 500 may simply be implemented as part of the primary vehicle operating system controller and is not necessarily a separate controller.

Start-up and Shut-down Control Strategies

[0034] Referring to Figure 1, an expander and engine and start-up control strategy 1000 is disclosed which can be implemented by the electronic controller 500. The control strategy 1000 allows the expander X to thermally soak without rotation of the rotors to minimize coating abrasion due to the changes in clearances between the expander housing and the rotors disposed within the housing. As the exhaust gases from the internal combustion engine are generally at a much higher temperature than the ambient air, it is possible that the expander rotors will expand at a greater rate than that of the housing when first exposed to the exhaust gases. Where small clearances exist, excessive abrasion between the rotors and housing can occur until the housing and rotors reach operating temperature. To minimize abrasion during this transitory period, the control strategy 1000 functions to prevent the rotors from rotating in a fixed position (i.e. zero speed condition) until the expander has reached its steady state operating temperature.

[0035] In a first step 1002, the system detects that the power plant, which may be a gasoline or diesel internal combustion engine, is in an operating state. This can be accomplished through communication with the vehicle CAN/BUS system. In a second step 1004, the system supplies power to the motor/generator to hold the rotors in a fixed, static position by supplying sufficient power to counteract the rotational force on the rotors provided by the exhaust gases passing by the rotors. This mode of operation can be implemented by placing the motor in a "zero torque" mode of operation which is available in certain motor control packages. During this step, some of the exhaust gases from the engine can be bypassed around the expander with the bypass valve or other means to prevent undue backpressure, if desired. [0036] In a step 1006, which occurs concurrently with step 1004, the temperature of the expander housing is sensed. In addition to, or as an alternative, a timer can also be initiated once power is supplied to the motor/generator or when the engine is detected to have been started. In a step 1008, the torque command target value for the

motor/generator is changed or power is discontinued when the sensed temperature at the expander housing reaches a predetermined temperature correlating to the normal expander operating condition. Once power to the motor/generator is discontinued, the expander rotors are able to rotate as the exhaust gases pass through the expander in a normal mode of operation such that work is transferred from the expander to the motor/generator and stored in the energy storage device or otherwise utilized. If desired, the timer can be used instead of or in conjunction with the housing temperature sensor to deactivate the motor/generator after a predetermined period of time. Proxies for determining that the expander has reached its normal operating temperature may be used as well, for example algorithms based on other sensors in the system may be utilized. In one example, a clutch or brake can be used to prevent the rotors from operating in addition to or instead of utilizing a motor/generator.

[0037] Referring to Figure 2, an expander and engine shut-down control strategy 1100 is shown, which can be implemented by the electronic controller 500. The control strategy 1100 allows the expander rotors to be stopped quickly after the engine shuts down such to prevent the above noted excessive abrasion issues from arising from an expander housing that is contracting at a faster rate than the rotors once cooling begins with exhaust gases no longer flowing through the expander.

[0038] In a step 1102 of the control strategy 1100, the engine is detected to be shut down after being in an operating state. In a step 1104, the motor/generator is activated to supply power to the expander to hold the rotors in the fixed position by supplying sufficient power to counteract the rotational force on the rotors provided by the gradually reducing exhaust gas flow passing by the rotors. In one example, this is accomplished by placing the motor in the "zero torque" mode of operation. A brake or clutch, alone or in combination with the motor/generator can be also used to stop rotation of the rotors at step 1104. In a step 1106, the torque command target value is changed and/or power to the motor/generator is discontinued. Step 1106 can be implemented after any of a variety of conditions has been met. For example, step 1106 can occur once the expander housing temperature sensor has reached a predetermined temperature, when a timer has reached a predetermined value, and/or when the rotors have reached a zero speed condition. This step can also be implemented after the inlet pressure of the expander is within a certain pressure of the expander outlet pressure, for example when sensor 206 or 209 reads within about 5kPa of sensor 208.

[0039] Referring to Figure 3, a second expander and engine start-up control strategy 1200 is shown, which can be implemented by the electronic controller 500. The control strategy 1200 allows the expander to be initially activated by supplying power to the motor/generator to rotate the rotors upon engine start-up. In some applications, it is possible that soot will build up on the expander rotors and/or the interior of the expander housing over time which can eventually cause the rotors to bind. Condensation can also build up within the expander and can also cause binding when temperatures drop sufficiently to cause freezing. When binding occurs, the torque to overcome the binding can be excessive in some cases causing undesired engine droop, degradation in engine performance, and damage to the expander and/or other engine components. In the case of direct waste heat applications in which engine exhaust flows through the expander, this binding can also be very detrimental to engine performance and can lead to severe damage since the locked expander will significantly increase the back pressure on the engine until the rotors can freely rotate.

[0040] In a step 1202 of the control strategy 1200, the system detects that the power plant, which may be a gasoline or diesel internal combustion engine, is in an operating state. In a second step 1204, the motor/generator is activated to supply power to the expander to cause the rotors to rotate in the same direction as they rotate during normal operation. This can be accomplished by supplying a non-zero torque command target value to the motor/generator. The torque supplied at step 1204 is sufficient to break the rotors free of any binding. In a step 1206, the torque command target value is changed and/or power to the motor/generator is discontinued when the rotors have been determined to be in a rotating condition, thus indicating that the rotors can freely rotate. If the rotors do not rotate after supplying power to the motor/generator, an alert can be sent to the vehicle communication system, the exhaust gases can be bypassed around the expander, and/or the engine can be shut down at a step 1208.