WO2018138314A1 - Système de récupération de chaleur - Google Patents

Système de récupération de chaleur Download PDF

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Publication number
WO2018138314A1
WO2018138314A1 PCT/EP2018/052086 EP2018052086W WO2018138314A1 WO 2018138314 A1 WO2018138314 A1 WO 2018138314A1 EP 2018052086 W EP2018052086 W EP 2018052086W WO 2018138314 A1 WO2018138314 A1 WO 2018138314A1
Authority
WO
WIPO (PCT)
Prior art keywords
turbine
compressor
recovery system
engine
exhaust gas
Prior art date
Application number
PCT/EP2018/052086
Other languages
English (en)
Inventor
Paul Chandler
Alan GOYA
Original Assignee
Jaguar Land Rover Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB1701470.5A external-priority patent/GB2559179B/en
Priority claimed from GB1701467.1A external-priority patent/GB2559176B/en
Priority claimed from GB1701469.7A external-priority patent/GB2559178B/en
Application filed by Jaguar Land Rover Limited filed Critical Jaguar Land Rover Limited
Publication of WO2018138314A1 publication Critical patent/WO2018138314A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/02—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using heat
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/02—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using heat
    • F01N5/025—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using heat the device being thermoelectric generators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/04—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using kinetic energy
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/02—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
    • F01N2900/1404—Exhaust gas temperature
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present disclosure relates to a waste heat recovery system and methods for controlling the same and particularly, but not exclusively, to a waste heat recovery system for an engine exhaust system. Aspects of the invention relate to a waste heat recovery system, a method of recovering energy from hot exhaust gases, a method of controlling a waste heat recovery system and to a vehicle.
  • Turbomachinery is commonly used to recover heat energy by expanding hot exhaust gas through a turbine to extract work.
  • waste heat recovery with conventional turbomachinery is optimised to operate in a narrow range. This means that in light-duty automotive vehicles, for example, where the engine is subject to a wide range of loads, the turbomachinery often operates outside its optimum range and therefore inefficiently.
  • the components of a vehicle are typically at or near ambient temperature if the engine has not operated recently. From that initial condition, the engine temperature gradually rises until it reaches an equilibrium defining a normal operational temperature. The time over which the engine temperature rises defines an engine warm-up period, during which the engine operates less efficiently than it does when at its normal operational temperature, primarily due to increased frictional losses.
  • lubricating oils used to reduce frictional resistance between moving engine components are selected according to their properties - in particular, viscosity - when at their normal operating temperature.
  • the viscosity of a fluid tends to decrease as temperature rises, the viscosity of the lubricating oils is therefore higher than required for optimised operation during the warm-up period, when the temperature of the lubricating oils is below their normal operating temperature, thus leading to increased fuel consumption.
  • other vehicle components must warm to normal operating temperatures following ignition before operating efficiently.
  • components of the electric drive system such as a battery may need to reach a threshold temperature before they can operate sufficiently effectively for the vehicle to switch to the electric mode.
  • the cabin temperature may need to rise to a comfortable level following engine ignition if the ambient temperature is low. It is therefore desirable to minimise the length of such warm-up periods to maximise the proportion of time for which the engine and other vehicle components operate at their normal operational temperatures.
  • Various approaches have been proposed to accelerate engine warming following ignition. These typically include dedicated components within the vehicle to transfer additional heat energy to the engine during the warm-up period. For example, a heat exchanger may be added between a vehicle exhaust system and a vehicle coolant circuit to transfer heat from exhaust gas to coolant fluid entering the engine, thereby returning to the engine heat expelled through the exhaust gas and thus reducing the duration of the warm-up period. In such approaches a valve must be included to enable the heat exchanger to be bypassed once the engine reaches its operational temperature, so that the engine does not overheat.
  • a drawback with this known approach is that the dedicated heat exchanger that is used to heat the engine during the warm-up period operates only for a short time after each ignition, and is therefore idle for a large proportion of the time for which the engine is active. Since such apparatus adds significant weight to the vehicle and reduces the space available for other components, the low usage factor is undesirable.
  • the present invention has been devised to mitigate or overcome at least some of the above-mentioned problems.
  • a waste heat recovery system for an exhaust system of an engine configured to be controlled by an energy management system.
  • the waste heat recovery system comprises an inlet for receiving hot exhaust gases from the engine exhaust system, a turbine shaft carrying a turbine for extracting work from the hot exhaust gases and producing cool exhaust gases at a turbine outlet.
  • the turbine is configured to expand the hot exhaust gases to a sub-atmospheric pressure.
  • a compressor shaft carries a compressor to purge the cool exhaust gases to the atmosphere and the turbine shaft and compressor shaft are coupled by an electromagnetic coupling module for converting the extracted work into electricity.
  • the electromagnetic coupling module includes a magnetic gear assembly configured to provide a variable speed ratio between the compressor shaft and the turbine shaft.
  • the waste heat recovery system further comprises a heat exchanger configured to receive exhaust gases from the turbine outlet and deliver exhaust gases to a compressor inlet and a thermoelectric generator configured to convert thermal energy from the heat exchanger into electricity.
  • the magnetic gear assembly allows the compressor and turbine to be optimised and operated independently from each other, thus increasing the efficiency of the waste heat recovery system. Furthermore, the magnetic gearing reduces the effects of noise, vibration and harshness within the turbomachinery and reduces mechanical losses within the system.
  • the thermoelectric generator provides the advantage of increased system efficiency as it maximises the heat recovered within the system.
  • the energy management system controls the waste heat recovery system, which helps to ensure that the waste heat recovery system operates as efficiently as possible.
  • the waste heat recovery system comprises a bypass valve fitted across one or more of the turbine, the compressor and the heat exchanger, where the or each bypass valve is operable to divert exhaust gases around the respective component across which it is fitted.
  • the energy management system is configured to control one or each of the bypass valves based on the load under which the engine is operating.
  • the compressor is configured to raise the pressure of the cold exhaust gases to approximately atmospheric pressure. This ensures that the cold exhaust gases are purged to the atmosphere.
  • the magnetic gear assembly comprises a stationary member comprising a set of electromagnets, in which case the compressor shaft carries a first magnetic arrangement, a second moveable member carries a second magnetic arrangement and the turbine shaft carries a set of core members arranged to modulate a magnetic field between the compressor shaft and the second moveable member.
  • the second moveable member is magnetically coupled to the turbine shaft to define the speed ratio therebetween, and the electromagnets are operable to influence the magnetic coupling, thereby to vary the speed ratio.
  • the electromagnets are operable to control the rotation of the second moveable member so as to vary the speed ratio between the compressor shaft and the turbine shaft.
  • a drive current applied to the electromagnets is configurable to operate the electromagnetic coupling module in a power-assist mode.
  • the waste heat recovery system comprises a control module for receiving at least one engine operating condition, and the control module is configured to control the speed ratio of the magnetic gear assembly in response to the at least one engine operating condition.
  • the engine operating condition is at least one of: exhaust gas mass flow, manifold pressure, power recovered through the turbine or a power demanded by the compressor.
  • the waste heat recovery system comprises a battery configured to store the electricity generated by the electromagnetic coupling module and the thermoelectric generator.
  • a method of recovering waste heat energy from an exhaust system of an engine comprising a turbine and a compressor, the turbine and compressor being coupled by an electromagnetic coupling module for converting the extracted work into electricity.
  • the electromagnetic coupling module includes a magnetic gear assembly configured to provide a variable speed ratio between the turbine and the compressor.
  • the method comprises: receiving hot exhaust gases from the engine exhaust system, expanding the hot exhaust gases to a sub-atmospheric pressure through the turbine and producing cool exhaust gases at a turbine outlet, passing the cool exhaust gases through a heat exchanger to remove thermal energy within the exhaust gases and using the thermal energy removed by the heat exchanger to generate electricity in a thermoelectric generator and purging the cool exhaust gases to the atmosphere via the compressor and controlling the variable speed ratio between the turbine and the compressor.
  • the hot exhaust gases received from the engine exhaust system are only expanded through the turbine and the cool exhaust gases produced at the turbine outlet are only passed through the heat exchanger if there is enough thermal energy to extract work in an efficient manner using both the turbine and the thermoelectric generator. This is explained in further detail below.
  • the method comprises operating one or more bypass valves fitted across one or more of the turbine, the compressor and the heat exchanger to divert exhaust gases around the respective component across which it is fitted.
  • the method comprises operating the one or more bypass valves in dependence upon the load under which the engine is operating.
  • the method in a low load operating condition of the engine, comprises operating at least one bypass valve fitted across at least one of the turbine, the compressor or the heat exchanger so that flow is diverted around at least one of the turbine, the compressor or the heat exchanger.
  • the method in a high load operating condition of the engine, comprises operating at least one bypass valve fitted across at least one of the turbine, the compressor or the heat exchanger so that flow is diverted through at least one of the turbine, the compressor or the heat exchanger.
  • the invention provides a method of controlling an energy recovery system for an engine exhaust system of a vehicle.
  • the energy recovery system comprises a turbine for generating torque and a compressor, the turbine and the compressor being coupled by an electromagnetic coupling module that transmits torque from the turbine to the compressor.
  • the method comprises operating the electromagnet coupling module in one of an assist mode or a generator mode depending on the overall fuel efficiency of the vehicle when the electromagnet coupling module is operating in each of these modes.
  • the energy recovery system comprises a turbine for generating torque and a compressor, the turbine and the compressor being coupled by an electromagnetic coupling module that transmits torque from the turbine to the compressor.
  • the method comprises receiving at least one signal indicative of a property of exhaust gas flowing through the engine exhaust system, and determining, based on the or each signal indicative of a property of the exhaust gas, respective overall fuel efficiencies for the vehicle if the electromagnetic coupling module is operated in each of the following operating modes: (i) an assist mode, in which torque is generated from electrical energy input to the electromagnetic coupling module, which torque is transmitted to the compressor in addition to the torque transmitted to the compressor from the turbine; and (ii) a generator mode, in which electrical energy is generated from some of the torque transmitted from the turbine.
  • the method further comprises comparing the respective fuel efficiencies for the assist mode and the generator mode to determine the operating mode that provides the highest overall fuel efficiency for the vehicle, and operating the electromagnetic coupling module in the operating mode that provides the highest overall fuel efficiency for the vehicle.
  • operating the electromagnetic coupling module in the assist mode increases the torque available for the compressor above that produced by the turbine. This in turn reduces the amount of torque that the turbine must produce to drive the compressor at a nominal level, thereby reducing the back-pressure created by the turbine within the exhaust system. Therefore, when the exhaust gas contains insufficient thermal energy for the energy recovery system to operate effectively, operating in the assist mode minimises the impact of the energy recovery system on the overall performance of the vehicle to which the exhaust system belongs.
  • the assist mode may be of particular benefit in arrangements in which the energy recovery system is used with a turbocharged engine, such that there is a further turbine upstream of the turbine of the energy recovery unit.
  • the signals indicative of exhaust gas flow rate and temperature may comprise direct measurements of those properties of the exhaust gas, or alternatively the signals may relate to an engine speed and/or load, which are indirectly indicative of the temperature and flow rate of exhaust exiting the engine.
  • the electromagnetic coupling module optionally comprises a magnetic gearbox having a first moveable member coupled to the turbine, a second moveable member coupled to the compressor, and a set of electromagnets that are arranged to influence coupling between the first and second moveable members.
  • operating in the assist mode may comprise operating the electromagnetic coupling module to convert electrical energy into torque by supplying an electrical current to the electromagnets to create a rotating magnetic field that imparts torque on the second moveable member.
  • the rotating magnetic field generated by the electromagnets may impart torque on the second moveable member through a third moveable member of the magnetic gearbox.
  • operating the electromagnetic coupling module to generate electrical energy from some of the torque transmitted from the turbine may comprise controlling an electrical current induced in the electromagnets by rotation of the first and second moveable members.
  • the electromagnetic coupling module may comprise an electric motor that is coupled to the compressor and an electric generator that is coupled to the turbine, in which case the method may comprise electrically coupling the turbine and the compressor.
  • the electromagnetic coupling module may be configured to provide a variable speed ratio between the turbine and the compressor, in which case the method may comprise controlling the speed ratio to drive the compressor at a minimum speed required to raise the pressure of the exhaust gas to atmospheric pressure.
  • the method may comprise supplying electrical energy to the electromagnetic coupling module from a battery when operating in the assist mode.
  • the method may also comprise determining an optimum energy input to the electromagnetic coupling module to maximise fuel efficiency in the assist mode.
  • the method may comprise determining the overall fuel efficiency for the vehicle if the energy recovery system is deactivated, and deactivating the energy recovery system in the event that the respective fuel efficiencies for the assist mode and the generator mode are lower than the fuel efficiency if the energy recovery system is deactivated.
  • Deactivating the energy recovery system may entail ceasing supplying exhaust gas to the energy recovery system, for example by directing exhaust gas into a bypass route around the energy recovery system.
  • the at least one signal indicative of a property of exhaust gas flowing through the engine exhaust system may comprise one or more of: a signal indicative of a flow rate of exhaust gas through the engine exhaust system; and a signal indicative of a temperature of exhaust gas flowing through the engine exhaust system.
  • the energy recovery system comprises a turbine for generating torque and a compressor, the turbine and the compressor being coupled by an electromagnetic coupling module that transmits torque from the turbine to the compressor.
  • the controller comprises an input arranged to receive a signal indicative of a flow rate of exhaust gas through the engine exhaust system and a signal indicative of a temperature of exhaust gas flowing through the engine exhaust system.
  • the controller further comprises a processor arranged to determine, based on the flow rate and the temperature of the exhaust gas, respective overall fuel efficiencies for the vehicle if the electromagnetic coupling module is operated in each of the following operating modes: (i) an assist mode, in which torque is generated from electrical energy input to the electromagnetic coupling module, which torque is transmitted to the compressor in addition to the torque transmitted to the compressor from the turbine; and (ii) a generator mode, in which electrical energy is generated from some of the torque transmitted from the turbine.
  • the processor is further arranged to compare the respective fuel efficiencies for the assist mode and the generator mode to determine the operating mode that provides the highest overall fuel efficiency for the vehicle.
  • the controller also comprises a control module arranged to operate the electromagnetic coupling module in the operating mode that provides the highest overall fuel efficiency for the vehicle.
  • the processor may have an electrical input for receiving said signals indicative of a flow rate and a temperature of exhaust gas through the engine exhaust system.
  • the controller may further comprise an electronic memory device electrically coupled to the processor and having instructions stored therein.
  • the processor may be configured to access the memory device and execute the instructions stored therein such that it is operable to determine the respective overall fuel efficiencies for the vehicle if the electromagnetic coupling module is operated in each of the operating modes.
  • the energy recovery system comprises a turbine that is arranged to generate torque from a flow of exhaust gas, a compressor, and an electromagnetic coupling module that couples the turbine to the compressor to transmit torque from the turbine to the compressor.
  • the electromagnetic coupling module is operable in each of the following operating modes: (i) an assist mode, in which torque is generated from electrical energy input to the electromagnetic coupling module, which torque is transmitted to the compressor in addition to the torque transmitted to the compressor from the turbine; and (ii) a generator mode, in which electrical energy is generated from some of the torque transmitted from the turbine.
  • the invention extends to a vehicle comprising an engine exhaust system and the energy recovery system of the above aspect.
  • Another aspect of the invention provides a method of accelerating warming of one or more components of a vehicle following engine ignition.
  • the vehicle comprises an engine, an energy recovery system for recovering thermal energy from exhaust gas expelled from the engine and for converting thermal energy recovered from exhaust gas expelled from the engine in to work, and a coolant circuit that delivers coolant fluid to the energy recovery system, for transfer of thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid, and delivers coolant fluid to the or each component.
  • the method comprises operating the energy recovery system in a low recovery mode, in which the amount of thermal energy that is converted in to work by the energy recovery system is reduced relative to a normal recovery mode, during a warm-up period to enhance a rate of transfer of thermal energy from the exhaust gas to coolant fluid in the coolant circuit.
  • waste heat recovery system By making use of the waste heat recovery system to accelerate warming of the component during the warm-up period, redundancy of vehicle components is reduced compared with the prior art approaches described above, since the waste heat recovery system is typically used at all times while the engine is active. Specifically, the system is used for accelerating warming of the vehicle component during the warm-up period, and is used for recovering useful work from thermal energy contained in the exhaust gas at all other times when the engine is active.
  • Operating the waste heat recovery system in the low recovery mode entails minimising, or at least reducing, the thermal energy that is recovered by the system from the exhaust gas and converted into useful work. This enhances, and optionally maximises, the rate of transfer of thermal energy from the exhaust gas to coolant fluid in the coolant circuit.
  • waste heat recovery system is operated to maximise the useful work extracted from the exhaust gas at all times, which in turn minimises any incidental heating of the engine during the warm-up period.
  • embodiments of the invention take the opposite approach of reducing work extraction, and in turn enhancing warming of the engine, during the warm-up period.
  • the one or more components to be warmed may comprise the engine itself.
  • the warm-up period includes a period during which the engine temperature rises to a normal operating temperature at which the engine operates most efficiently.
  • the one or more components to be warmed may comprise an electric component associated with the electric drive system.
  • the warm-up period includes a period during which the components of the electric drive system warm to a threshold temperature at which the electric drive system can operate the vehicle in an electric mode.
  • the one or more components to be warmed may comprise a component of a cabin heating system of the vehicle, in which case the warm-up period may include a period during which a cabin of the vehicle warms to a desired temperature.
  • the method of the invention can be used to warm several vehicle components simultaneously, including the vehicle engine, components of an electric drive system, and components of a cabin warming system, for example.
  • the method may comprise monitoring the temperature of the or each component to determine when the or each component is operating in the warm-up period.
  • the method comprises transferring thermal energy from exhaust gas expelled from the engine to the coolant circuit using a heat exchanger.
  • the energy recovery system optionally comprises a turbine configured to receive exhaust gas expelled from the engine and deliver expanded exhaust gas to the heat exchanger, and a compressor configured to compress exhaust gas exiting the heat exchanger.
  • the turbine is coupled to the compressor, for example by an electromagnetic coupling module.
  • the electromagnetic coupling module may comprise a magnetic gearbox.
  • operating the energy recovery system in a low recovery mode may comprise operating the electromagnetic coupling module to supply torque to the turbine.
  • operating the energy recovery system in a low recovery mode may comprise operating the electromagnetic coupling module so that no torque is transferred between the turbine and the compressor.
  • Operating the energy recovery system in a low recovery mode may comprise bypassing the turbine.
  • the method may further comprise directing exhaust gas through the compressor before entering the heat exchanger, or alternatively operating the energy recovery system in a low recovery mode may comprise bypassing the compressor.
  • the method may comprise heating coolant fluid in the coolant circuit using an electrically-driven heater attached to or integrated with the heat exchanger.
  • the method may comprising operating the energy recovery system according to an inverse Brayton cycle.
  • the energy recovery system may be operated according to any of: an Otto cycle; a Rankine cycle; or a Brayton cycle. If the energy recovery system comprises a thermoelectric generator, the method may comprise operating the thermoelectric generator to convert electrical energy into thermal energy that is transferred to the coolant circuit.
  • the method optionally comprises receiving a signal indicative of engine ignition, and selecting the low recovery mode for the energy recovery system on receipt of the signal indicative of engine ignition.
  • the invention also extends to a controller configured to implement the method of the above aspect, to a computer program product comprising computer readable code for controlling a computing device to perform the method of the above aspect, and to a non-transitory computer readable medium comprising such a computer program product.
  • a controller arranged to control an energy recovery system for recovering thermal energy from exhaust gas expelled from an engine of a vehicle, and for converting thermal energy recovered from the exhaust gas in to work, to accelerate warming of one or more components of the vehicle following engine ignition.
  • the vehicle comprises a coolant circuit that delivers coolant fluid to the energy recovery system, for transfer of thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid, and delivers coolant fluid to the or each component.
  • the controller comprises an input arranged to receive at least one signal indicative of a temperature of a component to be warmed.
  • the controller further comprises a processing module configured to determine, based on the or each signal received at the input, that the vehicle is operating in a warm-up period, corresponding to a time period during which the or each component warms to a normal operating temperature following ignition, and to generate control signals to operate the energy recovery system in a low recovery mode, in which the amount of thermal energy that is converted in to work by the energy recovery system is reduced relative to a normal recovery mode, during the warm-up period to increase a rate of transfer of thermal energy recovered from the exhaust gas to coolant fluid in the coolant circuit.
  • the controller also comprises an output configured to transmit the control signals to the energy recovery system.
  • a further aspect of the invention provides a vehicle comprising an engine, an energy recovery system for recovering thermal energy from exhaust gas expelled from the engine and for converting thermal energy recovered from exhaust gas expelled from the engine in to work, a coolant circuit that delivers coolant fluid to the energy recovery system, for transfer of thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid, and to one or more components of the vehicle, and the controller of either of the above aspects.
  • Another aspect of the invention provides an energy recovery system for recovering thermal energy from exhaust gas expelled from an engine of a vehicle and for converting thermal energy recovered from exhaust gas expelled from the engine in to work
  • the vehicle comprising a coolant circuit for delivering coolant fluid to the energy recovery system, for transfer of thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid, and for delivering coolant fluid to one or more components of the vehicle, wherein the energy recovery system is configured to be operated in a low recovery mode, in which the amount of thermal energy that is converted in to work by the energy recovery system is reduced relative to a normal recovery mode, during a warm-up period of the or each component, corresponding to a time period during which the or each component warms to a normal operating temperature following ignition, to increase a rate of transfer of thermal energy recovered from the exhaust gas to the coolant fluid in the coolant circuit.
  • the energy recovery system optionally comprises a turbine configured to receive exhaust gas expelled from the engine and deliver expanded exhaust gas to a heat exchanger, and a compressor configured to compress exhaust gas exiting the heat exchanger.
  • the turbine is coupled to the compressor, for example by an electromagnetic coupling module.
  • the electromagnetic coupling module may comprise a magnetic gearbox.
  • operating the energy recovery system in a low recovery mode may comprise operating the electromagnetic coupling module to supply torque to the turbine.
  • operating the energy recovery system in a low recovery mode may comprise operating the electromagnetic coupling module so that no torque is transferred between the turbine and the compressor.
  • the system may additionally comprise an arrangement of valves connected by suitable fluid conduits to create respective bypass routes around the turbine and the compressor, so that these elements of the energy recovery system may be bypassed through appropriate control of the valves to divert the exhaust gas into the conduits.
  • a first valve may be disposed upstream of the turbine, a second valve may be disposed downstream of the turbine and a conduit may connect the first valve and the second valve.
  • the first valve and the second valve are operable to allow exhaust gas to bypass the turbine via the conduit.
  • the energy recovery system may comprise a third valve disposed upstream of the compressor, a fourth valve disposed downstream of the compressor and a conduit connecting the third valve and the fourth valve, wherein the third valve and the fourth valve are operable to allow exhaust gas to bypass the compressor via the conduit.
  • a first valve may be disposed upstream of the compressor, a second valve may be disposed downstream of the compressor and a conduit may connect the first valve and the second valve.
  • the first valve and the second valve are operable to allow exhaust gas to bypass the compressor via the conduit.
  • the energy recovery system comprises a turbine, a compressor, a heat exchanger and an arrangement of valves and conduits
  • the energy recovery system may comprise a first valve disposed upstream of the turbine, a second valve disposed upstream of the compressor and a conduit connecting the first valve and the second valve.
  • the first valve and the second valve are operable to allow exhaust gas to bypass the turbine via the conduit.
  • the energy recovery system may comprise a third valve disposed downstream of the compressor and a conduit connecting the third valve and the second valve, the third valve and the second valve being operable to allow exhaust gas to pass from downstream of the compressor to the heat exchanger via the conduit, a fourth valve disposed downstream of the turbine and a conduit connecting the fourth valve and the third valve, the fourth valve and the third valve being operable to allow exhaust gas to pass from the heat exchanger to the atmosphere.
  • operating the energy recovery system in a low recovery mode may comprise bypassing the turbine and, alternatively or additionally, bypassing the compressor.
  • operating the energy recovery system may comprise directing exhaust gas through the compressor before entering the heat exchanger.
  • the energy recovery system may comprise an electrically-driven heater attached to or integrated with the heat exchanger for heating coolant fluid in the coolant circuit.
  • the energy recovery system may comprise a thermoelectric generator for converting electrical energy into thermal energy that is transferred to the coolant circuit.
  • a further aspect of the invention provides a vehicle comprising an engine, an energy recovery system as described above and a coolant circuit that delivers coolant fluid to the energy recovery system, for transfer of thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid, and delivers coolant fluid to one or more components of the vehicle.
  • aspects of the invention provide a vehicle comprising the waste heat recovery system, the energy recovery system or the controller of the above aspects. Further aspects of the invention provide an energy management system configured to carry out the methods of the above.
  • the invention also extends to a computer program product comprising computer readable code for controlling a computing device to perform a method according to any of the above aspects, and a non-transitory computer readable medium comprising such a computer program product.
  • Figure 1 illustrates schematically a vehicle comprising an internal combustion engine, an exhaust system and a waste heat recovery system
  • Figure 2 illustrates schematically the waste heat recovery system in Figure 1 further including an electromagnetic coupling module and a thermoelectric generator;
  • Figure 3 illustrates schematically the internal combustion engine, exhaust system and waste heat recovery system of Figure 1 ;
  • Figure 4 illustrates a temperature - entropy diagram for a driving cycle of the internal combustion engine and waste heat recovery system depicted in Figure 3;
  • Figure 5 is a schematic longitudinal cross-sectional view of an electromagnetic coupling module of the waste heat recovery system of Figure 2;
  • Figure 6 corresponds to Figure 4 but shows a schematic transverse cross- sectional view of the electromagnetic coupling module
  • Figure 7 illustrates schematically the waste heat recovery system of Figure 1 , an Energy Management System and a battery for the waste heat recovery system;
  • Figure 8 illustrates schematically the electromagnetic coupling module in Figure
  • Figure 9 illustrates schematically the internal combustion engine, exhaust system and waste heat recovery system of Figure 1 according to another embodiment of the invention.
  • Figure 10 is a further temperature - entropy diagram for a driving cycle of the internal combustion engine and waste heat recovery system depicted in Figure
  • Figure 1 1 is a flow diagram showing a method of operating the waste heat recovery system of Figure 2;
  • Figure 12 illustrates schematically the internal combustion engine, exhaust system and waste heat recovery system of Figure 1 according to another embodiment of the invention
  • Figure 13 is a flow diagram showing a method of operating the waste heat recovery system of Figure 2;
  • Figure 14 illustrates schematically the internal combustion engine, exhaust system and waste heat recovery system of Figure 1 according to another embodiment of the invention.
  • Figure 15 illustrates schematically a cabin warming system suitable for embodiments of the invention.
  • Figure 1 illustrates schematically a vehicle 10 including, at least, an internal combustion engine 16, an exhaust system 14 and a waste heat recovery system 12a in accordance with one possible embodiment of the invention.
  • the vehicle 10 also includes a cabin 17 within which the driver and other occupants are accommodated.
  • the waste heat recovery system 12a is a system for extracting work from hot exhaust gases produced by the internal combustion engine 16.
  • the waste heat recovery system 12a comprises a turbine 21 for extracting work from the hot exhaust gases within the exhaust system 14, a compressor 22 to purge cooled exhaust gases back to the atmosphere and a heat exchanger 23 for rejecting any remaining heat to a thermoelectric generator 28.
  • the turbine 21 , compressor 22 and heat exchanger 23 are each fitted with a bypass valve 29a, 29b, 29c, respectively, which is operable so as to allow the exhaust gases to bypass the respective component of the waste heat recovery system 12a.
  • the turbine 21 and compressor 22 are electromagnetically coupled through an electromagnetic coupling module 20.
  • the electromagnetic coupling module 20 disconnects mechanically the turbine 21 and compressor 22 and offers a variable magnetic gearing between the turbomachines.
  • the variable magnetic gearing reduces the effects of noise, vibration and harshness within the turbomachinery and reduces mechanical losses within the system.
  • the turbine 21 is mounted to an input shaft 24 which provides a mechanical input to the electromagnetic coupling module 20.
  • the turbine 21 is configured to receive hot exhaust gases from the exhaust system 14, to expand the hot exhaust gases in order to extract mechanical work and to output cool, relatively low pressure exhaust gases through a turbine outlet 26.
  • the heat exchanger 23 is located between the turbine outlet 26 and an inlet 27 to the compressor 22.
  • the heat exchanger 23 is configured to receive the cool exhaust gases from the turbine outlet 26, and to remove any remaining thermal energy from within the exhaust gases to a cooling medium.
  • the heat exchanger 23 removes the thermal energy from the exhaust gases by means of a liquid coolant that is circulated through the heat exchanger.
  • the heat exchanger 23 is configured to reject any remaining heat in the exhaust gases to the thermoelectric generator 28, to increase the density of the exhaust gases and to lower the back pressure on the turbine. Cooling the exhaust gases increases the density of the exhaust gases which in turn lowers the temperature, viscosity and velocity of the fluid.
  • the thermoelectric generator 28 is configured to convert thermal energy captured by the heat exchanger 23 into electricity.
  • the electricity captured by the thermoelectric generator 28 is passed through a DC to DC voltage convertor (not shown) before being stored within a battery (not shown).
  • the compressor 22 is mounted to an output shaft 25 from the electromagnetic coupling module 20.
  • the output shaft 25 provides a torque that drives the compressor 22.
  • the compressor 22 is configured to receive cold, low pressure exhaust gases that are output from the heat exchanger 23, to raise the pressure of the low pressure exhaust gases to atmospheric pressure and to purge the exhaust gases to the atmosphere.
  • the electromagnetic coupling module 20 is coupled to the turbine 21 via the input shaft 24 and provides a mechanical output to the compressor 22 via the output shaft 25.
  • Figure 3 illustrates schematically the configuration of the internal combustion engine 16 and the waste heat recovery system 12a together with an exhaust system 14.
  • the waste heat recovery system 12a operates an Inverted Brayton Cycle and the internal combustion engine operates an Otto Cycle.
  • the temperature - entropy diagram 40 corresponding to the thermodynamic processes is shown in Figure 4.
  • the subscript "s” denotes the ideal state at the end of each process wherein the state has the same entropy value as the beginning of the process thus denoting an ideal isentropic process.
  • the ideal Otto cycle consists of four branches, namely: an isentropic compression process from state 1 to state 2 S , a constant volume heat addition process (combustion) from state 2 S to state 3, an isentropic expansion process from state 3 to state 4 S , and a constant volume heat rejection process from state 4s to state 1 .
  • the gas still carries a large amount of thermal energy making it inefficient to simply reject the heat to the atmosphere.
  • the thermal energy stored within the gas at state 4 is passed through an Inverted Brayton Cycle as part of a waste heat recovery process in order to increase the thermal energy extracted from the gases. This offers the advantage of increasing the overall thermal efficiency of the vehicle 10 and reducing the vehicle's emissions.
  • the gases at state 4 are over-expanded through the turbine 21 to state 5 where the gas is at a sub-atmospheric pressure.
  • the gases are then passed through the heat exchanger 23 to extract any remaining thermal energy within the gases.
  • the thermal energy extracted by the heat exchanger 23 is captured by the thermoelectric generator 28 and converted into electricity.
  • the cold exhaust gases are output from the heat exchanger 23 in state 6.
  • the cool, low pressure exhaust gas is then passed through the compressor 22 in order to raise the pressure of the gases to atmospheric pressure at state 7, prior to being purged to the atmosphere at state 1 .
  • the cool, low pressure gas is passed through more than one compressor in order to pressurise the gas in a number of stages.
  • FIG. 5 schematically depicts a longitudinal-sectional view of the electromagnetic coupling module 20 of the waste heat recovery system 12a.
  • the electromagnetic coupling module 20 comprises a magnetic gear assembly arranged to couple the input shaft 24 and the output shaft 25 magnetically.
  • the turbine 21 is attached to the input shaft 24 and the compressor 22 is attached to the output shaft 25, as described previously.
  • the output shaft 25 is attached to a tubular inner rotor 50 arranged to rotate with the output shaft 25.
  • the inner rotor 50 carries a set of permanent magnets 53, which are equally sized and evenly distributed around the inner rotor 50.
  • the permanent magnets 53 are orientated such that the source and sinks of the magnetic flux are aligned at their radially inner and outer ends, and with alternating polarity around the circumference.
  • the input shaft 24 is attached to a tubular intermediate rotor 52 that surrounds the inner rotor 50.
  • the intermediate rotor 52 is arranged to rotate with the input shaft 24.
  • the intermediate rotor 52 includes a series of core members 52a (shown in Figure 6), which hereafter will be referred to as pole-pieces.
  • the pole pieces 52a are made from a ferromagnetic material and are equally sized and evenly distributed around the circumference of the intermediate rotor 52, separated by air or by a non-magnetic material.
  • the intermediate rotor 52 is surrounded by an outer rotor 54 comprising a plurality of magnets in the form of a set of equally sized permanent magnets 62 evenly distributed around the outer rotor 54.
  • the permanent magnets 62 are orientated such that the poles face radially inwards and outwards with alternating polarity.
  • the stator 56 Surrounding the outer rotor 54 is an outer casing, a part of which acts as a stator 56.
  • the stator 56 has a set of electromagnets 58 disposed around its inner circumference.
  • the electromagnets 58 are of equal size to one another, and are equidistantly spaced around the stator 56.
  • the electromagnets 58 each comprise a coil of wire disposed around a ferromagnetic core, such that magnetic poles are formed when the wire is energised. The orientation of the magnetic poles is dependent on the direction of the current flowing through the coil.
  • a voltage may be applied, for example from a battery.
  • the electromagnets 58 are all connected together in series and the alternating polarity is provided for by appropriate connection of the coils of the respective electromagnets.
  • a single length of wire may be used to form the coils of all the electromagnets 58, with the coils of neighbouring electromagnets 58 being wound in opposite senses.
  • the inner rotor 50, the intermediate rotor 52, the outer rotor 54 and the stator 56 are each separated by air gaps, and disposed in concentric relation.
  • the electromagnetic coupling module 20 of the waste heat recovery system 12a is depicted in cross-section.
  • the electromagnetic coupling module 20 comprises the inner rotor 50, the intermediate rotor 52, the outer rotor 54 and the stator 56.
  • the outer rotor 54 includes an inner set of permanent magnets 60 which cooperate with the magnets on the inner rotor 50 to provide a magnetic gearing, and an outer set of permanent magnets 62 which cooperate with the electromagnets 58 on the stator 56 to form an e-machine.
  • the current flowing in the coils of the electromagnets 58 can be varied to control the driving torque applied to the outer rotor 54 by the outer set of permanent magnets 62. This enables the speed of rotation of the outer rotor 54 to be controlled, and hence the speed ratio of the magnetic gear to be varied and controlled.
  • the inner rotor 50 comprises twenty-four permanent magnets, or twelve pole-pairs, arranged to produce a spatially varying magnetic field.
  • the intermediate rotor 52 carries core members in the form of sixteen pole-pieces and the outer rotor 54 carries two sets of permanent magnets 53.
  • the outer set of magnets 62 comprises six permanent magnets, or three pole-pairs and the inner set 60 comprises eight permanent magnets, or four pole pairs, with each set arranged to produce a spatially varying field.
  • the outer set 62 of magnets has a different number of poles to the inner set 60 of magnets. It is an advantage of this embodiment that the gear and the electric motor can be tuned independently of each other by varying the number of permanent magnets in each set.
  • the magnetic gear assembly uses known principles to create a three-way gear ratio between the inner, intermediate and outer rotors 50, 52, 54, in a manner analogous to an epicyclic gearbox.
  • the inner set 60 of permanent magnets attached to the outer rotor 54 create a first magnetic field
  • the permanent magnets 53 of the inner rotor 50 generate a second magnetic field.
  • the first and second magnetic fields extend radially toward one another across the intermediate rotor 52.
  • the pole pieces 52a pass through and interact with the first and second magnetic fields in such a way that rotation of the intermediate rotor 52 induces rotation of the inner and outer rotors 50, 54.
  • the induced rotation of the inner rotor 50 differs from the speed of rotation of the intermediate rotor 52, defining a gear ratio between the intermediate rotor 52 and the inner rotor 50.
  • the outer rotor 54 rotates at a speed that is different to the inner and intermediate rotors, 50, 52, and hence a three-way gear ratio is defined.
  • the pole pieces 52a modulate the first and second magnetic fields as they pass through them, such that a first modulated field is created between the intermediate rotor 52 and the inner rotor 50, and a second modulated field is created between the intermediate rotor 52 and the outer rotor 54. Since the pole pieces 52a rotate, the spatial distributions of the first and second modulated fields are not fixed; the first modulated field rotates at a speed which is governed by the relative sizes of the pole pieces 52a and the inner set 60 of permanent magnets of the outer rotor 54, along with the speed of rotation of the intermediate rotor 52 relative to the first magnetic field. Correspondingly, the rotation of the second modulated field is dictated by the relative speeds of the inner and intermediate rotors 50, 52.
  • the second magnetic field couples to the first modulated field, such that the inner rotor 50 is rotated at the same speed as the first modulated field. Accordingly, the inner rotor 50 is magnetically coupled to the intermediate rotor 52, so that torque is transferred between the intermediate rotor 52 and the inner rotor 50. Similarly, the first magnetic field couples to the second modulated field to transfer torque between the intermediate and outer rotors 52, 54.
  • the inner rotor 50 rotates at a speed that is determined in part by the rotational speed of the intermediate rotor 52 relative to the outer rotor 54. Therefore, for a given rotational speed of the intermediate rotor 52, the speed at which the inner rotor 50 moves may be varied by energising the electromagnets 58 of the stator 56 to create a third magnetic field that drives rotation of the outer rotor 54, in a similar manner to a conventional electric motor. In this way, the gear ratio between the inner and intermediate rotors 50, 52 can be controlled.
  • the electromagnets 58 are wired in series, with the coils arranged such that when a current is applied the electromagnets 58 have alternating polarity.
  • each electromagnet 58 has an electromagnet 58 of opposite polarity on either side.
  • the orientation of the polarity of the electromagnets 58 is determined by the direction of the current flowing through them. Therefore, an alternating current can be applied to the electromagnets 58 in order to alternate the direction of the polarity of each electromagnet 58, and effectively rotate the third magnetic field.
  • the outer set 62 of magnets of the outer rotor 54 couples to the third magnetic field, and so the outer rotor 54 rotates at the same speed as the third magnetic field.
  • the rotational speed of the inner rotor 50 is dependent on the relative rotational speeds of the intermediate and outer rotors 52, 54. So, the rotational speed of the inner rotor 50 can be controlled by controlling the rotational speed of the outer rotor 54.
  • the electromagnets 58 are operable to control the gear ratio. Therefore, the speed of the output shaft 25 that drives the compressor 22 can be controlled to a desired level for a range of input shaft speeds through appropriate control of the gear ratio.
  • the three-way gear ratio persists and so the outer rotor 54 continues to rotate, albeit passively.
  • rotation of the outer set 62 of magnets of the outer rotor 54 induces an alternating current in the electromagnets 58 of the stator 56, the current having a frequency that is proportional to the speed of rotation of the outer rotor 54.
  • the electrical energy contained in the induced current can be stored by a vehicle battery, such that the electromagnetic coupling module 20 acts as a generator, defining the generator mode. Once the induced current is established, it can be controlled so as to impart a load on the outer rotor 54 and therefore regain control of the gear ratio. This enables the speed of the inner rotor 50 to be optimised when operating in a generator mode.
  • the electromagnetic coupling module 20 therefore acts as a power split device, in that energy recovered from the exhaust gas by the turbine 21 and supplied to the intermediate rotor 52 can be divided between the compressor 22, which is driven by the inner rotor 50, and the vehicle battery. Typically, once the compressor 22 is driven at an optimum rate, all surplus power is diverted to the vehicle battery for maximised efficiency.
  • the thermoelectric generator 28 is a solid state device that converts thermal energy into electricity.
  • the thermoelectric generator 28 is made of N type and P type semiconductor materials which are sandwiched between a hot side and a cold side. When a temperature gradient is applied to the thermoelectric generator 28, across the hot side and the cold side, a voltage is generated.
  • the hot side of the thermoelectric generator 28 is mounted to the heat exchanger 23 and the cold side is exposed to the ambient air. The magnitude of the generated voltage is proportional to the temperature gradient applied to the thermoelectric generator.
  • the cold side of the thermoelectric generator can be cooled further by the use of, for example, a heat sink, coolant or the like. Cooling the cold side is desirable as it increases the temperature gradient across the thermoelectric generator as a whole which increases the amount of electricity the thermoelectric generator can produce.
  • Thermoelectric generators are often mounted directly to hot exhaust pipes within modern day vehicles in order to help increase overall vehicle efficiency.
  • engine exhaust gas is passed through the exhaust system 14 into the waste heat recovery system 12a to be expanded through the turbine 21 .
  • the turbine 21 uses this expansion to generate torque, which is transmitted through the input shaft 24 to the intermediate rotor 52 of the variable magnetic gear.
  • the torque is further transmitted, at a desired speed ratio, through the inner rotor 50 and the output shaft 25, to the compressor 22.
  • This causes the compressor 22 to rotate at a speed determined by the speed of the turbine 21 and the gear ratio of the variable magnetic gear. In this way, the speed at which the compressor 22 rotates is dissociated from the input speed of the turbine 21 .
  • the rotation of the turbine 21 causes the rotation of the compressor 22 by virtue of the interaction between the inner 50, intermediate 52 and outer 54 rotors of the variable magnetic gear as described above, with the outer rotor 54 forming a speed ratio control rotor.
  • the intermediate pole-piece carrying rotor 52 is attached to the input shaft 24 and therefore to the turbine 21 .
  • the turbine 21 which may be subjected to very high exhaust gas temperatures, is isolated from the magnetic elements of the variable magnetic gear. This avoids excessive heating of the inner rotor magnets, which reduces any impact that high temperatures within the assembly may have on the operational efficiency and durability of the variable magnetic gear.
  • the waste heat recovery system 12a is controlled by an Energy Management System 70 forming part of an engine control module (not shown) as shown in Figure 7.
  • the Energy Management System 70 determines how much thermal energy is contained within the exhaust gases based on the engine's load conditions and thus determines how best to maximise the energy extraction from the exhaust gases.
  • the energy of the exhaust gases depends on the exhaust flow rate and the temperature of the exhaust gases. These parameters can be estimated by monitoring the engine load conditions.
  • the Energy Management System 70 operates the bypass valves 29a, 29b, 29c based on the engine load, thus diverting the exhaust gases around the turbine 21 , compressor 22 and heat exchanger 23 accordingly so as to extract heat from the exhaust gases in the most efficient manner.
  • the energy extracted from the hot exhaust gases is then supplied to a battery 72 of the vehicle 10 in the form of electricity.
  • Three example operating conditions are outlined below. In high load conditions there is typically a large amount of thermal energy stored within the exhaust gases that can be captured by the waste heat recovery system 12a. In these conditions there is enough thermal energy to extract work in an efficient manner using both the turbine 21 and the thermoelectric generator 28.
  • the Energy Management System 70 determines this and therefore closes all the bypass valves 29a, 29b, 29c, thus forcing the exhaust gases through the turbine 21 , the heat exchanger 28 and the compressor 22 allowing electricity to be generated by both the electrical motor generator and thermoelectric generator.
  • This operational mode is known as full waste heat recovery mode.
  • the Energy Management System 70 determines that operating the turbine 21 and compressor 22 would be inefficient and as a result opens the bypass valves 29a, 29b across the turbine 21 and the compressor 22, thus forcing the exhaust gases only through the heat exchanger 23.
  • the thermoelectric generator 28 is the sole waste heat recovery component in operation. This operating mode is known as partial waste heat recovery mode. Operating the turbine 21 and compressor 22 in this scenario would otherwise reduce the overall system efficiency as there is not enough thermal energy within the exhaust gases to expand through a turbine, and hence the Energy Management System opens the bypass valves 29a, 29b. In this scenario, expanding the exhaust gases through the turbine would be inefficient and create a back pressure which would result in the engine operating at a reduced efficiency.
  • the Energy Management System 70 determines that there is not enough thermal energy within the exhaust gases to efficiently extract work and as a result opens all the bypass valves 29a, 29b, 29c, diverting all of the exhaust gases around the components 21 , 22, 23.
  • This operating mode is known as a bypass mode. In this situation no waste heat is recovered from the exhaust gases. This situation typically arises when there is a relatively low amount of thermal energy within the exhaust gases, for example, when the engine is idling or under the low load conditions. Operating the waste heat recovery system 12a in these conditions is detrimental to the overall vehicle 10 efficiency.
  • the electricity generated by the waste heat recovery system 12a is stored within the battery 72 and the electricity is then used within the vehicle 10, for example to drive an electric motor within a hybrid powertrain.
  • the electricity generated by the electrical motor-generator is passed through an AC to DC voltage converter 74 prior to being stored within the battery 72 whilst the electricity generated via the thermoelectric generator 28 is passed through a DC to DC voltage convertor 76 prior to being stored in the battery 72.
  • Power can also be directed from the battery 72 to the electrical-motor generator in certain operational conditions. This can occur when there is not enough thermal energy within the exhaust gases to drive the compressor 22 as well as the turbine 21 .
  • the variable magnetic gear ratio is controlled by an engine control module 78 as shown in Figure 8.
  • the engine control module 78 comprises the energy management system 70 and a controller for controlling the variable magnetic gear within the electromagnetic coupling module 20 to ensure that both the turbine 21 and compressor 22 are operating in an efficient manner.
  • the engine control module 78 sets the turbine's 21 operating conditions as to maximise the power extraction from the hot exhaust gases and sets the compressor 22 to operate in such a way as to minimise power consumption. This in turn maximises the net power recovery from the hot exhaust gases via the waste heat recovery system 12a.
  • the engine control module 78 sets the variable magnetic gear to an optimum gear ratio based on, at least one of the following operating conditions: mass flow, power recovery by turbine or power demand by the compressor.
  • the variable magnetic gear gives the advantage of allowing the optimisation of the turbine 21 and compressor 22 individually across a wide range of operating conditions.
  • Torque is applied to the intermediate rotor 52 by the rotation of the turbine 21 .
  • the pole pieces mounted to the intermediate rotor 52 interact with the permanent magnets 53 mounted to the inner rotor 50 which in turn applies a torque to the inner rotor 50 and thus the compressor 22.
  • the magnetic flux of the internal rotor 50 interacts with the permanent magnets 53 mounted to the outer rotor 54 which induces a flux and thus a current into the windings of the e-machine.
  • the torque which must be applied to the outer rotor 54, by the e-machine is governed by the required speed ratio as defined by the engine control module 78, as well as the torque on the turbine 21 . In turn, the torque on the turbine 21 is governed by the engine speed and load.
  • the control module 78 directs power from the electromagnets 58 to a battery 72, such that the e-machine acts as a generator.
  • both the inner rotor 50 and the outer rotor 54 are driven passively by the intermediate rotor 52, and the movement of the outer rotor 54 induces a current in the electromagnets 58 which is fed back to a battery 72 via a power electronic module 79 as shown by Figure 8.
  • the AC to DC converter 74 rectifies the AC signal output from the e-machine to a DC signal which is in turn stored within the battery 72.
  • Figure 9 shows the exhaust system 14 in combination with a different embodiment of a waste heat recovery system 12b.
  • the exhaust system 14 includes a conventional turbocharging system comprising an exhaust-driven primary turbine 15 that is mechanically coupled to a primary compressor 13 that is used to raise the pressure of air at an intake 19 to the engine 16, to improve engine performance.
  • the waste heat recovery system 12b is disposed downstream of the primary turbine 15 and is used to recover further thermal energy from the exhaust gas.
  • the waste heat recovery system 12b operates an Inverse Brayton Cycle to extract work from the recovered thermal energy.
  • the waste heat recovery system 12b comprises a secondary turbine 21 for extracting work from the exhaust gas exiting the primary turbine 15, which is still relatively hot.
  • the secondary turbine of Figure 9 therefore corresponds to the turbine of Figure 2.
  • the waste heat recovery system 12b further includes a secondary compressor 22 to purge cooled exhaust gas back to the atmosphere and a heat exchanger 23 for rejecting any remaining heat to a coolant that also supplies coolant fluid to the engine 16.
  • the secondary compressor of Figure 9 therefore corresponds to the compressor of Figure 2.
  • the heat exchanger 23 of Figure 9 does not include a thermoelectric generator such as that of the Figure 2 embodiment.
  • the engine 16 is situated downstream of the heat exchanger 23 on the coolant circuit, such that heat transferred to the coolant fluid by the heat exchanger 23 is in turn carried to the engine 16.
  • the secondary turbine 21 and secondary compressor 22 are electromagnetically coupled through an electromagnetic coupling module 20, which mechanically disconnects the secondary turbine 21 and the secondary compressor 22 by providing a variable effective gear ratio between the two.
  • the electromagnetic coupling module 20 typically utilises non-contacting elements, and so reduces the effects of noise, vibration and harshness within the turbomachinery and reduces mechanical losses within the system.
  • the electromagnetic coupling module 20 is the same magnetic gearbox as that used in the Figure 2 embodiment, which was described earlier with reference to Figures 5 and 6.
  • the skilled person will appreciate that other forms of electromagnetic coupling module 20 may be used, such as a pair of electric machines operating in tandem.
  • the secondary turbine 21 is mounted to an input shaft 24 that provides a mechanical input to the electromagnetic coupling module 20.
  • the electromagnetic coupling module 20 supplies torque to the secondary compressor 22 through an output shaft 25.
  • the electromagnetic coupling module 20 When the electromagnetic coupling module 20 is driven by the secondary turbine 21 it can operate in a generator mode to generate electrical energy in the form of an alternating current. This current is fed to a power electronic module 28 that converts the alternating current into a direct current that is suitable to supply a vehicle battery 29. Thus, thermal energy extracted from the exhaust gas by the secondary turbine 21 is converted into electrical energy, which can be stored in the vehicle battery 29 for later use.
  • the electrical coupling module 20 is also operable in reverse in a power-assist mode to provide additional torque to the output shaft 25 to drive the secondary compressor 22.
  • the power electronic module 28 acts to convert a DC output from the battery 29 into an AC drive signal for the electromagnetic coupling module 20.
  • the secondary turbine 21 is configured to receive hot exhaust gas from the exhaust system 14, to expand the hot exhaust gas to extract mechanical work and to output cooled exhaust gas below atmospheric pressure through a turbine outlet 26.
  • the heat exchanger 23 is located between the secondary turbine 21 and the secondary compressor 22 and so receives the cooled exhaust gas from the turbine outlet 26 during normal operation when the engine 16 is at its operational temperature.
  • the heat exchanger 23 is configured to transfer any residual thermal energy within the exhaust gas to a cooling medium, for example a liquid coolant that is circulated around the coolant circuit and through the heat exchanger 23. By cooling the exhaust gas further, the heat exchanger 23 increases its density and lowers the back pressure on the secondary turbine 21 .
  • the secondary compressor 22 comprises an inlet 27 that is configured to receive cold, low pressure exhaust gas exiting the heat exchanger 23.
  • the secondary compressor 22 raises the pressure of the exhaust gas to atmospheric pressure and then purges the exhaust gas to the atmosphere.
  • the exhaust system 14 also includes a bypass route 30 that enables exhaust gas to be diverted around the waste heat recovery system 12b in certain operating conditions, in particular when there is so little energy contained in the exhaust gas that conversion losses dominate when operating the waste heat recovery system 12b.
  • a bypass route 30 that enables exhaust gas to be diverted around the waste heat recovery system 12b in certain operating conditions, in particular when there is so little energy contained in the exhaust gas that conversion losses dominate when operating the waste heat recovery system 12b.
  • Another scenario in which the bypass route 30 may be used is when the restriction presented to the exhaust gas by the heat exchanger 23 is so large as to cause significant pumping losses in the engine 16.
  • a valve 32 is disposed between the primary and secondary turbines 15, 21 and is operable to direct exhaust gas either into the waste heat recovery system 12b or into the bypass route 30.
  • the waste heat recovery system 12b is operated in the opposite manner, to maximise the residual heat in the exhaust gas that is then transferred to the coolant circuit 31 in the heat exchanger 23 so that the engine 16 will in turn be warmed more quickly.
  • the principles of its normal operation are first described, with reference to Figure 10.
  • the subscript "s" denotes the ideal state at the end of each process wherein the state has the same entropy value as the beginning of the process, thus denoting an ideal isentropic process.
  • the first transition between states shown in Figure 10, namely a transition from state 1 to state 2, corresponds to compression of air supplied to the engine intake 19 by the primary compressor 13.
  • an Otto cycle begins as the compressed air enters the engine 16 and is mixed with fuel.
  • An ideal Otto cycle consists of four branches, namely: an isentropic compression process from state 2 to state 3 S , a constant volume heat addition process (combustion) from state 3 S to state 4, an isentropic expansion process from state 4 to state 5s, and a constant volume heat rejection process from state 5 S to state 2.
  • the gas still carries a large amount of thermal energy, making it inefficient to simply reject the heat to the atmosphere.
  • the primary turbine 15 expands the hot exhaust gas to extract energy that is used to generate electrical energy and to drive the primary compressor 13, thereby using some of the waste heat energy to increase engine performance and thus improve efficiency.
  • the remaining thermal energy stored within the gas at state 6 undergoes an Inverted Brayton Cycle as the gas passes through the waste heat recovery system 12b. This enables further thermal energy to be extracted from the gas and so increases the overall thermal efficiency of the vehicle 10 whilst reducing emissions.
  • the gas at state 6 is over-expanded through the secondary turbine 21 to state 7 where the gas is at a sub-atmospheric pressure.
  • the gas then passes through the heat exchanger 23 to remove any remaining thermal energy within the gas.
  • Cold exhaust gas is output from the heat exchanger 23 in state 8.
  • the cool, low pressure gas is then delivered to the secondary compressor 22 to raise the pressure of the gas to atmospheric pressure at state 9, prior to being purged to the atmosphere and thus completing the cycle.
  • the cool, low pressure gas is expanded through a series of secondary compressors, and the skilled person will appreciate that the principle remains the same.
  • the gear ratio of the electromagnetic coupling module 20 of the waste heat recovery system 12b of Figure 9 is controlled by the engine control module 78 introduced earlier with reference to Figure 8.
  • the engine control module 78 controls the electromagnetic coupling module 20 to ensure that both the secondary turbine 21 and secondary compressor 22 are operating in an efficient manner, whilst maximising electrical energy generated and returned to the vehicle battery 29 under high load conditions.
  • the engine control module 78 sets the secondary turbine's 21 operating conditions to maximise power extraction from the hot exhaust gas, and sets the secondary compressor 22 to operate in such a way as to minimise power consumption. This in turn maximises the net power recovery from the hot exhaust gas via the waste heat recovery system 12b.
  • the engine control module 78 sets the variable magnetic gear to an optimum gear ratio based on at least one of the following operating conditions: exhaust gas mass flow, power recovery by the secondary turbine 21 or power demand by the secondary compressor 22.
  • the engine control module 78 comprises a set of inputs that are arranged to receive signals indicative of each of these vehicle operating parameters.
  • the engine control module 78 includes an input that receives a measurement of exhaust gas flow rate that is derived from a sensor disposed within the exhaust system 14.
  • variable magnetic gear of this embodiment gives the advantage of allowing individual optimisation of the secondary turbine 21 and secondary compressor 22 across a wide range of operating conditions.
  • the electromagnetic coupling module 20 can operate in one of two modes: an assist mode (or power-assist mode); and a generator mode.
  • the generator mode is useful during normal operation when there is a high flow of hot exhaust gas to the secondary turbine, and therefore a significant amount of waste heat energy available for recovery.
  • the power-assist mode is useful where the exhaust gas flow is at a low level and so the energy that can practically be recovered from it is less than is required to drive the waste heat recovery system 12b to reduce the back pressure on the exhaust system.
  • the exhaust system 14 includes a bypass route 30 that enables the waste heat recovery system 12b to be bypassed altogether.
  • Figure 1 1 shows a process 80 performed by the engine control module 78 to determine the mode of operation adopted by the exhaust system 14 and the electromagnetic control module 20 at any given moment.
  • the engine control module 20 makes a decision on the basis of all data received at its inputs, but in the simplified process 80 shown in Figure 1 1 the operating mode is selected with reference only to the mass flow rate and the temperature of exhaust gas in the exhaust system 14. It is noted that both the temperature and the mass flow rate of the exhaust gas must be known to determine the rate at which thermal energy can be recovered by the waste heat recovery system 12b, in turn enabling an assessment of the best mode in which to operate the electromagnetic coupling module 20. Indeed, the temperature and mass flow rate of the exhaust gas are also used to determine whether to operate the electromagnetic coupling module 20 at all, or if the bypass mode should be used instead.
  • the process 80 begins when the engine control module 78 receives at step 81 data relating to the mass flow rate and the temperature of exhaust gas through the exhaust system 14.
  • the point at which the mass flow rate and the temperature of the exhaust gas are measured is typically upstream of the primary turbine 15 and downstream of a catalytic converter (not shown).
  • one of the three above operating modes must be selected, namely the bypass mode, the generator mode, or the power assist mode.
  • the objective of the process 80 is therefore to determine whether switching to either of the two modes not currently selected would provide an improvement in engine efficiency.
  • the engine efficiency for the present operating condition can be determined through measurements of various vehicle operating parameters.
  • the potential engine efficiency in the other two modes is modelled using the principles outlined below.
  • the engine control module 78 uses, as required, the temperature and mass flow rate data to determine at step 82 the overall fuel efficiency if the exhaust system 14 is operated in the bypass mode, if the electromagnetic coupling module 20 is operated in the generator mode, and if the electromagnetic coupling module 20 is operated in the power-assist mode, taking into account the consumption of electrical power by the electromagnetic coupling module 20 in the latter case.
  • the engine control module 78 first determines the waste exhaust energy available according to the present vehicle running condition.
  • the values for temperature and mass flow rate used in the above equation may be influenced by the operating mode that the vehicle 10 is using when the calculation is performed.
  • the engine control module 78 uses virtual models to adjust the estimation of the waste heat that would be available in each operating mode under the present operating conditions as required.
  • the available waste energy is used to determine the potential engine efficiency if the electromagnetic coupling module 20 operates in the generator mode, in which a portion of the available waste exhaust energy is recovered and the efficiency of the engine is increased as shown in Figure 10.
  • the engine control module 78 models the scenario in which the electromagnetic coupling module 20 acts as motor in the power-assist mode to consume energy from a source such as a battery or a mechanical energy storage means, and the upstream turbo is over-expanded, thereby increasing the efficiency of the engine as in Figure 10.
  • the amount of energy consumed by the electromagnetic coupling module 20 while in the power-assist mode may be variable, in which case an optimum amount of energy to use to drive the electromagnetic coupling module 20 as a motor is calculated.
  • the resulting engine efficiency at this optimum power level is then used as the basis for the comparison with the engine efficiency in the other operating modes, to determine the appropriate mode to select. If the bypass mode is not selected, this too is modelled by the engine control module 78 to determine the overall efficiency if the waste heat recovery system 12b were to be deactivated by directing exhaust gas into the bypass route 30.
  • the engine control module 78 compares the three efficiencies that it has calculated, and determines at step 83 which operating mode offers the highest overall fuel efficiency.
  • a high efficiency for the generator mode typically indicates that the engine 16 is operating at high load and thus there is significant thermal energy to be recovered from the exhaust gas.
  • the engine control module 78 determines at step 83 that the electromagnetic coupling module 20 should be operated in its generator mode to convert surplus thermal energy into electrical energy. The appropriate operating mode is then selected at step 84.
  • the engine control module 78 determines at step 83 that the power-assist mode is the appropriate operating mode for the exhaust system 14 and the electromagnetic coupling module 20, and selects this mode at step 84.
  • the bypass mode is selected at step 84 by operating the valve 32 to divert exhaust gas into the bypass route 30.
  • the state of charge (SOC) of the vehicle battery 29 is also taken into account when determining the overall efficiency of the vehicle 10. If the battery SOC is at or near 100%, there can be no efficiency improvement by operating in the generator mode, as any electrical energy generated in the electromagnetic coupling module 20 cannot be stored and so will be wasted. Therefore, in this situation the engine control module 78 selects either the power-assist mode or the bypass mode. Conversely, if the SOC is very low, operating the electromagnetic coupling module 20 in the power-assist mode may not be viable. Alternatively, where the capacity of the battery 29 to power a range of systems is limited due to a low SOC, vehicle systems that would provide a greater efficiency improvement than the waste heat recovery system 12b are prioritised. In such situations the engine control module 78 selects between the generator mode and the bypass mode.
  • the process 80 iterates continuously each time fresh data is received at the inputs to the engine control module 78, so that the appropriate operating mode is selected for the exhaust system 14 and the electromagnetic coupling module 20 at all times.
  • the particular configuration of the electromagnetic coupling module described above is offered as an example only, and many other configurations are possible.
  • the electromagnets need not be wound in an alternating fashion, and may instead be wound in groups of two or three.
  • the electromagnets may all be wound in the same way but energised separately to create a rotating magnetic field.
  • a pair of electric machines may be used in the place of a variable magnetic gear.
  • the secondary turbine may drive a dedicated generator that powers the vehicle battery, which in turn powers a stand-alone electric motor that drives the secondary compressor.
  • the generator and motor can be operated in the generator and power-assist modes in the same way as the variable magnetic gear described above.
  • Waste heat recovery systems may equally be applied to naturally-aspirated engines in which no primary turbine is present. In such arrangements, the same operating modes and principles apply as for the above described example.
  • operation in the generator mode enables thermal energy to be recovered and stored as electrical energy for later use.
  • selecting the power-assist mode reduces the back pressure presented to the exhaust system by the turbine of the waste heat recovery system, and thus mitigates the effect of the presence of the waste heat recovery system at times when there is insufficient waste thermal energy to operate it effectively.
  • waste heat recovery systems such as those represented in Figures 1 , 2, 3 and 9 typically include a heat exchanger that removes residual heat energy from the exhaust gases once a maximum amount of work has been extracted.
  • heat exchangers require a supply of coolant, and so are typically connected to a vehicle coolant circuit that also supplies coolant fluid to the vehicle engine 16.
  • Embodiments of waste heat recovery systems 12c, 12d according to the invention that take advantage of this arrangement are now described. These embodiments recognise that heat transferred to the coolant circuit in the heat exchanger of the waste heat recovery system 12c, 12d can then in turn be transferred to the engine 16, and thereby contribute to warming of the engine 16. Moreover, the waste heat recovery system 12c, 12d can be operated to enhance heat transfer to the coolant through the heat exchanger during an engine warm-up period by operating the system 12c, 12d in a low recovery mode, in which the amount of thermal energy that is extracted from the exhaust gas before it reaches the heat exchanger is minimised. This alleviates the problems noted above by reducing the time during which the engine operates below its optimum temperature range. Moreover, the benefits gained from reducing the warm-up period have been found to outweigh the thermal energy recovery that is sacrificed during this time.
  • components of the electric drive system such as a battery and an electric motor are typically also cooled by the same coolant circuit that supplies coolant fluid to the engine 16. Therefore, in such arrangements transferring additional thermal energy to the coolant circuit from a waste heat recovery system 12c, 12d in turn accelerates warming of the components of the electric drive system. This can be used to reduce a warm-up time associated with the electric drive system, for example a time during which the electric components warm to a threshold temperature at which the vehicle 10 can operate in the electric mode.
  • auxiliary systems such as a climate control system or other cabin warming system also typically draw heat from the engine coolant circuit. So, transferring additional thermal energy to the coolant circuit from a waste heat recovery device can also enable accelerated warming of the vehicle cabin 17, therefore improving driver comfort.
  • the warm-up period includes the time during which the cabin temperature rises to a desired level.
  • embodiments of the invention can be used to accelerate warming of a variety of vehicle components, including components of an electric system in a hybrid vehicle, a cabin warming system, and the vehicle engine.
  • waste heat recovery system includes an integral heat exchanging facility.
  • a thermoelectric module is typically cooled directly by a coolant circuit, and so a separate heat exchanger may not be required where such a module is used as a waste heat recovery system.
  • waste heat recovery systems are already present in the vehicle 10 and act during normal operation of the engine 16 to raise overall efficiency by recovering thermal energy from exhaust gas. Accordingly, using a waste heat recovery system 12c, 12d in a manner that accelerates engine warming during the warm-up period provides the benefits associated with minimising the duration of the warm-up period, without the redundancy that is inherent in prior art approaches that use dedicated components for warming the engine 16, as described above.
  • Figure 12 shows an embodiment of a waste heat recovery system 12c that has been optimised for this purpose.
  • the arrangement shown in Figure 12 differs from that of Figure 9 only with respect to the arrangement of valves in the system to create bypass routes, and the inclusion of a heating element. Accordingly, only those elements are described below, and all other elements of the system should be assumed to be identical to the corresponding elements of the Figure 9 system.
  • the exhaust system 14 includes two pairs of four-way valves 30 connected by suitable fluid conduits 32, with each pair being disposed one to each side of a respective one of the secondary turbine 21 and the secondary compressor 22.
  • a first valve 30a disposed upstream of the secondary turbine 21 is connected to a second valve 30b disposed downstream of the secondary turbine 21
  • a third valve 30c placed upstream of the secondary compressor 22 is connected to a fourth valve 30d situated downstream of the secondary compressor 22.
  • This configuration creates respective bypass routes around the secondary turbine 21 and the secondary compressor 22, so that these elements of the waste heat recovery system 12c may be bypassed through appropriate control of the valves 30 to divert the exhaust gas into the conduits 32.
  • the bypass routes may be used during the warm-up period to accelerate engine warming, as shall be described later.
  • the waste heat recovery system 12c further comprises a heating element 34 that is coupled to the heat exchanger 23 and arranged to convert an electrical current supplied by the battery 29 into heat that is transferred to coolant fluid passing through the heat exchanger, as explained in more detail later.
  • the waste heat recovery system 12c shown in Figure 12 operates according to the same principles as the system of Figure 9, as already described with reference to Figure 10. Similarly, the system 12c of Figure 12 can be controlled by the engine control module 78 of Figure 8.
  • the engine control module 78 operates the waste heat recovery system 12c of Figure 12 in a low recovery mode to minimise power extraction from the exhaust gas, which in turn accelerates warming of the engine 16, as explained later.
  • Operating in the power-assist mode reduces the amount of thermal energy that is extracted from the exhaust gas, which in turn increases the thermal energy transferred to the coolant in the heat exchanger 23 and on to the engine 16. Therefore, operating in the power assist mode immediately following ignition is a strategy that can be used to accelerate engine warming, and so reduces the time over which the engine operates below its optimum temperature range.
  • Another operating mode is possible for the electromagnetic coupling module 20, in which the secondary turbine 21 and the secondary compressor 22 are decoupled by removing the drive current to the electromagnets 58 and simply storing the current induced in the electromagnets 58 by passive rotation of the outer rotor 54 in the battery 29.
  • this decoupled mode rotation of the outer rotor 54 is entirely uncontrolled, and so the secondary turbine 21 and the secondary compressor 22 are unloaded and are therefore able to freewheel to some extent.
  • the current induced in the electromagnets 58 inherently creates a back- electromagnetic force on the outer rotor 54, which resists rotation of the rotor 54.
  • the exhaust system 14 includes bypass routes that enable the secondary turbine 21 and the secondary compressor 22 to be bypassed altogether.
  • FIG. 13 shows a general process 85 that the engine control module 78 performs during an engine warm-up period to accelerate engine warming and therefore reach the normal operational temperature as quickly as possible.
  • the process 85 begins when the engine control module 78 receives at step 86 a signal that is indicative of engine ignition.
  • Such a signal may be, for example, a signal indicating the temperature of coolant fluid within the coolant circuit 31 .
  • a signal is typically only generated while the engine is active, and a low engine coolant temperature is generally indicative that the engine has recently been activated. So, such a signal may be considered indicative of engine ignition.
  • the engine control module 78 controls at step 87 the waste heat recovery system 12c so as to maximise the heat energy transferred to the coolant circuit 31 by the heat exchanger 23.
  • this involves operating the waste heat recovery system 12c in a low recovery mode to minimise the heat extracted from the exhaust gas before it reaches the heat exchanger 23, and various ways to achieve this are suggested below.
  • the engine control module 78 monitors at step 88 the engine temperature to see whether the normal operational temperature has been reached. This may entail receiving a signal indicative of engine temperature from a temperature sensor embedded in the engine 16, for example, or alternatively an indirect measurement of the engine temperature may be provided by a sensor positioned in the exhaust gas flow, for example. Alternatively, the engine control module 78 may allow a fixed time period for the engine 16 to warm-up, for example 200 seconds.
  • the engine control module 78 While the engine 16 is still warming, the engine control module 78 maintains the waste heat recovery system 12c in the low recovery mode that maximises heat transfer to the coolant circuit 31 . Once the engine warm-up period completes, the engine control module 78 selects at step 89 an appropriate normal operating mode for the waste heat recovery system 12c, which then commences normal energy recovery in the manner described above.
  • One of the ways in which the reduction in temperature of the exhaust gas before reaching the heat exchanger 23 can be minimised, thereby maximising heat transfer to the coolant circuit 31 and in turn the engine 16, is to operate the electromagnetic coupling module 20 in the decoupled mode. This means that the secondary turbine 21 and the secondary compressor 22 freewheel and thus present little resistance to the exhaust gas flow, which therefore substantially maintains its temperature until reaching the heat exchanger 23.
  • the heating element 34 provides an auxiliary means for maximising heat transfer to the coolant circuit while the waste heat recovery system 12c operates in a low recovery mode, through converting electrical energy supplied by the battery 29 to heat that is transferred to the coolant fluid in addition to heat transferred from the exhaust gas.
  • the heating element 34 therefore offers an independent means for adding heat to the coolant fluid before it reaches the engine 16 that can be used alongside either of the above approaches, or in isolation, thereby further reducing the duration of the warm-up period. It is noted that the specifications of the heating element 34 are defined so that its energy consumption when active is lower than the improvement in vehicle efficiency created by reducing the warm-up period.
  • Figure 14 shows an alternative embodiment of the waste heat recovery system 12d that has a modified bypass route and in which a thermoelectric generator 36 is coupled to the heat exchanger 23 instead of a heating element 34.
  • thermoelectric generator 36 can be operated in the same way as the heating element 34 to convert electrical energy supplied by the vehicle battery 29 to thermal energy that is transferred to the coolant circuit 31 and on to the engine 16. Similarly to the heating element 34, the thermoelectric generator 36 therefore provides a means for accelerating engine warming during the warm-up period.
  • thermoelectric generator 36 can be used during normal operation to convert some of the residual heat energy contained in the exhaust gas when it reaches the heat exchanger 23 into electrical energy that is stored in the battery 29, thereby providing a further improvement in vehicle efficiency.
  • the waste heat recovery system 12d shown in Figure 14 includes the same four valves 30 that are present in the embodiment of Figure 12, but the conduits 32 connecting those valves are arranged differently so that the direction in which exhaust gas flows through the heat exchanger 23 is reversed.
  • the first valve 30a disposed upstream of the secondary turbine 21 is connected to the third valve 30c disposed between the heat exchanger 23 and the secondary compressor 22, and the second valve 30b disposed downstream of the secondary turbine 21 is connected to the fourth valve 30d positioned between the secondary compressor 22 and an exit of the exhaust system 14.
  • the third valve 30c is also connected to the fourth valve 30d to complete the circuit, which is described below.
  • valve 30c could be dispensed with by connecting the first valve 30a directly to the fourth valve 30d instead of connecting the third valve 30c to the fourth valve 30d.
  • the skilled person will readily be able to conceive many further variations on this arrangement to achieve the same effect.
  • exhaust gas is directed around the secondary turbine 21 through the conduit 32 connecting the first and third valves 30a, 30c.
  • the third valve 30c then directs the exhaust gas into the secondary compressor 22 and on to the fourth valve 30d.
  • the electromagnetic coupling module 20 is operated in the power assist mode to drive the secondary compressor 22 so that the exhaust gas is compressed and pushed towards the fourth valve 30d.
  • the fourth valve 30d then directs the exhaust gas back to the third valve 30c, which in turn directs the exhaust gas into the heat exchanger 23.
  • Compressing the exhaust gas in the secondary compressor 22 raises its temperature, meaning that the exhaust gas enters the heat exchanger 23 at a higher temperature than that at which it left the engine 16. This in turn increases the temperature difference between the exhaust gas and the coolant fluid in the coolant circuit 31 , therefore increasing the heat transfer rate between the exhaust gas and the coolant circuit 31 in the heat exchanger 23. In this way, re-routing the exhaust flow as in the embodiment of Figure 14 further increases the rate at which heat is transferred to the engine 16, and so further reduces the duration of the warm-up period.
  • This embodiment also illustrates one way in which operating the electromagnetic coupling module 20 in the power assist mode can contribute to a low recovery mode for the waste heat recovery system 12d. After exiting the heat exchanger 23, the cooled exhaust gas is directed from the second valve 30b to the fourth valve 30d, and is then purged to atmosphere.
  • FIG 15 shows a cabin heating system 90 in schematic form.
  • the cabin heating system 90 includes a radiator 92 that receives hot coolant from the vehicle engine 16, the coolant being pumped through the coolant circuit 31 by a pump 94, and passing through a thermostat 96 before reaching the radiator 92.
  • a fan 98 blows air across the radiator 92 to cool the coolant. Coolant at reduced temperature then flows back to the engine 16.
  • the thermostat 96 is also connected to a cabin heat exchanger 100, so that some hot coolant can be diverted to the cabin heat exchanger 100.
  • An integral fan (not shown) then blows air across the heat exchanger, so that the air is warmed before flowing into the cabin 17, thus warming the cabin 17. Coolant at reduced temperature then flows back from the cabin heat exchanger 100 to the thermostat 96, to be added to the coolant that is supplied to the engine 16.
  • the waste heat recovery system 12d can aid warming of the cabin 17, in that the system 12d can add heat energy to the coolant in the coolant circuit 31 , which supplies the cabin heat exchanger 100, thus increasing the temperature of air entering the cabin 17 during the warm-up period and in turn warming the cabin 17 more rapidly than is usually possible.
  • the particular configuration of the electromagnetic coupling module described above is offered as an example only, and many other configurations are possible.
  • the electromagnets need not be wound in an alternating fashion, and may instead be wound in groups of two or three.
  • the electromagnets may all be wound in the same way but energised separately to create a rotating magnetic field.
  • a pair of electric machines may be used in the place of a variable magnetic gear.
  • the secondary turbine may drive a dedicated generator that powers the vehicle battery, which in turn powers a stand-alone electric motor that drives the secondary compressor.
  • the generator and motor can be operated in the generator and power-assist modes in the same way as the variable magnetic gear described above.
  • waste heat recovery system that transfers heat to a coolant fluid may be used according to the principles of the embodiments of the invention described above to accelerate warming of a vehicle engine.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engine Equipment That Uses Special Cycles (AREA)

Abstract

L'invention concerne un système de récupération de chaleur (12) pour un système d'échappement de moteur (14), le système de récupération de chaleur (12) étant commandé par un système de gestion d'énergie (70). Le système de récupération de chaleur (12) comporte un orifice d'entrée pour la réception des gaz d'échappement chauds provenant du système d'échappement de moteur (14) et un arbre de turbine (24) portant une turbine (21) pour l'extraction de travail à partir des gaz d'échappement chauds et la production de gaz d'échappement froids au niveau d'un orifice de sortie de turbine (26). La turbine (21) est configurée pour dilater les gaz d'échappement chauds jusqu'à une pression subatmosphérique. Un arbre de compresseur (25) porte un compresseur (22) pour purger les gaz d'échappement froids vers l'atmosphère. L'arbre de turbine (24) et l'arbre de compresseur (25) sont couplés par un module de couplage électromagnétique (20) pour la conversion du travail extrait en électricité, le module de couplage électromagnétique (20) comprenant un ensemble d'engrenage magnétique configuré pour fournir un rapport de vitesse variable entre l'arbre de compresseur (25) et l'arbre de turbine (24). Le système comporte en outre un échangeur de chaleur (23) situé entre l'orifice de sortie de turbine (26) et le compresseur (22) et un générateur thermoélectrique (28) configuré pour convertir l'énergie thermique provenant de l'échangeur de chaleur (23) en électricité.
PCT/EP2018/052086 2017-01-30 2018-01-29 Système de récupération de chaleur WO2018138314A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
GB1701470.5A GB2559179B (en) 2017-01-30 2017-01-30 Waste heat recovery using an inverted Brayton cycle
GB1701467.1A GB2559176B (en) 2017-01-30 2017-01-30 Method for controlling a power-assist waste heat recovery system
GB1701470.5 2017-01-30
GB1701467.1 2017-01-30
GB1701469.7 2017-01-30
GB1701469.7A GB2559178B (en) 2017-01-30 2017-01-30 A method of accelerating warming of a vehicle engine following ignition

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US20180334927A1 (en) * 2017-05-17 2018-11-22 Systematic Power Method and apparatus for utilizing the waste heat of combustion gases of an internal combustion engine
GB2587858A (en) * 2019-08-01 2021-04-14 Man Energy Solutions Se Arrangement for energy provision
WO2021234376A1 (fr) * 2020-05-19 2021-11-25 Oxford University Innovation Limited Échangeur de chaleur silencieux pour un échappement de moteur, et système d'échappement de moteur, et système de moteur

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US20110232301A1 (en) * 2010-03-29 2011-09-29 Gm Global Technology Operations, Inc. Method for thermoelectric energy conversion in an exhaust gas recirculation system
US20140033706A1 (en) * 2012-08-02 2014-02-06 Ferrari S.P.A. Turbocharger provided with an electrical machine for a supercharged internal combustion engine
US20140075970A1 (en) * 2010-06-02 2014-03-20 Dwayne M. Benson Integrated Power, Cooling, and Heating Device and Method Thereof
WO2016000016A1 (fr) * 2014-06-30 2016-01-07 Kerbs Autotech Pty Ltd Système de récupération d'énergie thermique de moteur à combustion interne

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US20110232301A1 (en) * 2010-03-29 2011-09-29 Gm Global Technology Operations, Inc. Method for thermoelectric energy conversion in an exhaust gas recirculation system
US20140075970A1 (en) * 2010-06-02 2014-03-20 Dwayne M. Benson Integrated Power, Cooling, and Heating Device and Method Thereof
US20140033706A1 (en) * 2012-08-02 2014-02-06 Ferrari S.P.A. Turbocharger provided with an electrical machine for a supercharged internal combustion engine
WO2016000016A1 (fr) * 2014-06-30 2016-01-07 Kerbs Autotech Pty Ltd Système de récupération d'énergie thermique de moteur à combustion interne

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180334927A1 (en) * 2017-05-17 2018-11-22 Systematic Power Method and apparatus for utilizing the waste heat of combustion gases of an internal combustion engine
US10830108B2 (en) * 2017-05-17 2020-11-10 Systematic Power Method and apparatus for utilizing the waste heat of combustion gases of an internal combustion engine
GB2587858A (en) * 2019-08-01 2021-04-14 Man Energy Solutions Se Arrangement for energy provision
GB2587858B (en) * 2019-08-01 2022-12-28 Man Energy Solutions Se Arrangement for energy provision
WO2021234376A1 (fr) * 2020-05-19 2021-11-25 Oxford University Innovation Limited Échangeur de chaleur silencieux pour un échappement de moteur, et système d'échappement de moteur, et système de moteur

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