GB2559178A

GB2559178A - A method of accelerating warming of a vehicle engine following ignition

Info

Publication number: GB2559178A
Application number: GB1701469.7A
Authority: GB
Inventors: Agurto Goya Alan
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-01-30
Filing date: 2017-01-30
Publication date: 2018-08-01
Anticipated expiration: 2037-01-30
Also published as: GB2559178B; GB201701469D0

Abstract

A method of accelerating warming of components of a vehicle (10, Fig. 1) following engine ignition, the vehicle (10, Fig. 1) comprising an engine 12, an energy recovery system 16, and a coolant circuit 31 that delivers coolant fluid to the energy recovery system 16 for transfer of thermal energy to the coolant fluid, and to each component; the method comprising operating the energy recovery system 16 in a low recovery mode, in which the amount of thermal energy that is converted in to work is reduced relative to a normal recovery mode, during a warm-up period each component, corresponding to a time period during which 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 coolant fluid in the coolant circuit 31. The energy recovery system may comprise a turbine 21 and compressor 22 that are coupled.

Description

(71) Applicant(s):

Jaguar Land Rover Limited (Incorporated in the United Kingdom)

Abbey Road, Whitley, Coventry, Warwickshire, CV3 4LF, United Kingdom (72) Inventor(s):

Alan Agurto Goya (56) Documents Cited:

EP 1522685 A1 WO 2014/049412 A1

WO 2016/028548 A1 US 20110232301 A1 (58) Field of Search:

INT CL B60H, F01N, F01P, F02B, F02D, F02G, F02N, F28D

Other: WPI, EPODOC (74) Agent and/or Address for Service:

Jaguar Land Rover

Patents Department W/1/073, Abbey Road, Whitley, COVENTRY, CV3 4LF, United Kingdom (54) Title of the Invention: A method of accelerating warming of a vehicle engine following ignition Abstract Title: A Method of Accelerating Warming of a Vehicle Engine Following Ignition (57) A method of accelerating warming of components of a vehicle (10, Fig. 1) following engine ignition, the vehicle (10, Fig. 1) comprising an engine 12, an energy recovery system 16, and a coolant circuit 31 that delivers coolant fluid to the energy recovery system 16 for transfer of thermal energy to the coolant fluid, and to each component; the method comprising operating the energy recovery system 16 in a low recovery mode, in which the amount of thermal energy that is converted in to work is reduced relative to a normal recovery mode, during a warm-up period each component, corresponding to a time period during which 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 coolant fluid in the coolant circuit 31. The energy recovery system may comprise a turbine 21 and compressor 22 that are coupled.

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A Method of Accelerating Warming of a Vehicle Engine Following Ignition

TECHNICAL FIELD

The present disclosure relates to a method of accelerating warming of a vehicle engine following ignition. Aspects of the invention relate to a method of accelerating warming of one or more components of a vehicle following engine ignition, a controller, a computer program product, a non-transitory computer readable medium, a controller arranged to control an energy recovery system, and a vehicle.

BACKGROUND

At ignition, 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.

In this respect, 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. As 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.

Similarly, other vehicle components must warm to normal operating temperatures following ignition before operating efficiently. For example, in a hybrid vehicle comprising an electric drive system for operating the vehicle in an electric mode, 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.

In a further example, from a user’s perspective 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.

It is against this background that the present invention has been devised.

SUMMARY OF THE INVENTION

An 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.

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.

This manner of operation is the opposite of that adopted during normal operation, when the waste heat recovery system maximises the useful work obtained from thermal energy contained in the exhaust gas. However, the useful work sacrificed by the waste heat recovery system during the warm-up period is compensated for by the overall gain in vehicle efficiency that is achieved by reducing the duration of the warmup period, thereby achieving a net benefit.

It is noted that in known arrangements including a waste heat recovery system and an engine connected to a common coolant circuit, operating the waste heat recovery system inevitably transfers some heat energy to the coolant circuit and, in turn, the engine. Thus, waste heat recovery systems always contribute to warming of the engine during the warm-up period in such arrangements.

However, in known arrangements the 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. In contrast, 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. In such arrangements, 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.

If the vehicle is a hybrid vehicle comprising an electric drive system for operating in an electric mode, the one or more components to be warmed may comprise an electric component associated with the electric drive system. In this case, 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.

Alternatively, or in addition, 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.

It is noted that 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.

In some embodiments, the method comprises transferring thermal energy from exhaust gas expelled from the engine to the coolant circuit using a heat exchanger. In such embodiments, 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.

In embodiments including an electromagnetic coupling module to couple a turbine to a compressor, operating the energy recovery system in a low recovery mode may comprise operating the electromagnetic coupling module to supply torque to the turbine. Alternatively, or in addition, 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. In such embodiments, 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.

When a heat exchanger is present, the method may comprise heating coolant fluid in the coolant circuit using an electrically-driven heater attached to or integrated with the heat exchanger.

In any embodiment involving a heat exchanger as described above, the method may comprising operating the energy recovery system according to an inverse Brayton cycle. In other embodiments, 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.

In another aspect, 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.

Another aspect of the invention provides 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.

In some embodiments, 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.

Where the energy recovery system comprises a turbine and a 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.

In one embodiment in which the energy recovery system comprises a turbine, a compressor and an arrangement of valves and 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. In this embodiment the first valve and the second valve are operable to allow exhaust gas to bypass the turbine via the conduit. Optionally, in this same embodiment, 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.

In an alternative embodiment in which the energy recovery system comprises a turbine, a compressor and an arrangement of valves and conduits, 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. In this embodiment the first valve and the second valve are operable to allow exhaust gas to bypass the compressor via the conduit.

In a further embodiment in which 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. In this embodiment, the first valve and the second valve are operable to allow exhaust gas to bypass the turbine via the conduit. Optionally, in this same embodiment, 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.

In embodiments of the invention in which an arrangement of valves and conduits facilitate it, operating the energy recovery system in a low recovery mode may comprise bypassing the turbine and, alternatively or additionally, bypassing the compressor.

In embodiments of the invention in which an arrangement of valves and conduits facilitate it, 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. Alternatively or additionally, 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.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

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 internal combustion engine, exhaust system and waste heat recovery system of Figure 1 according to one embodiment of the invention;

Figure 3 is a temperature-entropy diagram for a driving cycle of the internal combustion engine and waste heat recovery system depicted in Figure 2;

Figure 4 is a schematic longitudinal cross-sectional view of an electromagnetic coupling module of the waste heat recovery system of Figure 2;

Figure 5 corresponds to Figure 4 but shows a schematic transverse crosssectional view of the electromagnetic coupling module;

Figure 6 illustrates schematically the electromagnetic coupling module further including a power electronics module and a battery;

Figure 7 is a flow diagram showing a method of operating the waste heat recovery system of Figure 2;

Figure 8 illustrates schematically the internal combustion engine, exhaust system and waste heat recovery system of Figure 1 according to another embodiment of the invention; and

Figure 9 illustrates schematically a cabin warming system suitable for use with embodiments of the invention.

DETAILED DESCRIPTION

A specific embodiment of the invention will now be described in which numerous specific features will be discussed in detail in order to provide a thorough understanding of the inventive concept as defined in the claims. However, it will be apparent to the skilled person that the invention may be put into effect without the specific details and that in some instances, well known methods, techniques and structures have not been described in detail in order not to obscure the invention unnecessarily.

To place the embodiments of the invention in a suitable context, reference will firstly be made to Figure 1, which schematically illustrates a vehicle 10 including, at least, an internal combustion engine 12, an exhaust system 14 and a waste heat recovery system 16. The waste heat recovery system 16 is configured to extract work from hot exhaust gas expelled by the internal combustion engine 12.

As is conventional, the vehicle 10 also includes a cabin 17 within which the driver and other occupants are accommodated.

Noting that it is not possible to convert all of the heat contained in exhaust gas into useful work, waste heat recovery systems such as that represented in Figure 1 typically include a heat exchanger that removes residual heat energy from the exhaust gases once a maximum amount of work has been extracted. Such 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 12.

Embodiments of the invention take advantage of this arrangement, by recognising that heat transferred to the coolant circuit in the heat exchanger of the waste heat recovery system 16 can then in turn be transferred to the engine 12, and thereby contribute to warming of the engine 12. Moreover, the waste heat recovery system 16 can be operated to enhance heat transfer to the coolant through the heat exchanger during an engine warm-up period by operating the system 16 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.

In hybrid vehicles comprising an electric drive system for operating in an electric mode, 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 12. Therefore, in such arrangements transferring additional thermal energy to the coolant circuit from a waste heat recovery system 16 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.

Furthermore, 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. In this example, the warm-up period includes the time during which the cabin temperature rises to a desired level.

It should therefore be appreciated that 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.

Since all of the above examples relate to vehicle components that are attached to a common coolant circuit, transferring additional thermal energy to the coolant circuit from a waste heat recovery system will accelerate warming of all of those components simultaneously. For example, using this general approach the warm-up times for a vehicle engine, an electric drive system and a cabin warming system can all be reduced together.

For simplicity, in the embodiments of the invention described below the component to be warmed is the vehicle engine. However, the skilled reader will understand that these embodiments can also be applied directly to warming of other vehicle components, such as those listed above.

Various types of waste heat recovery systems may be used for this purpose, including thermoelectric modules, Otto Cycles, Rankine Cycles, Brayton Cycles or Inverse Brayton Cycles. Some specific implementations of the last of these are described below to illustrate how the inventive concept might be put into practice, and the skilled reader would understand that the principles outlined below could be applied to any type of waste heat recovery system that ejects heat to a coolant fluid to accelerate engine warm-up and thereby obtain the associated benefits.

It is noted that a separate heat exchanger may not be required if the waste heat recovery system includes an integral heat exchanging facility. For example, 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.

Such waste heat recovery systems are already present in the vehicle 10 and act during normal operation of the engine 12 to raise overall efficiency by recovering thermal energy from exhaust gas. Accordingly, using a waste heat recovery system 16 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 12, as described above.

Moving on to Figure 2, the exhaust system 14 and the waste heat recovery system 16 are shown in more detail. To provide a complete description of the apparatus used in this embodiment for the skilled person, the principles of operating the waste heat recovery system 16 for its primary purpose of recovering useful work are described before moving on to consider how the apparatus may be used in a low recovery mode to minimise the extraction of work and, in turn, accelerate warming of the engine 12 during the warm-up period.

In the embodiment shown in Figure 2, the exhaust system 14 includes a conventional turbocharging system comprising an exhaust-driven primary turbine 15 that is mechanically coupled to a primary compressor 17 that is used to raise the pressure of air at an intake 19 to the engine 12, to improve engine performance.

The waste heat recovery system 16 is disposed downstream of the primary turbine 15 and is used to recover further thermal energy from the exhaust gas. As noted above, in this example the waste heat recovery system 16 operates an Inverse Brayton Cycle to extract work from the recovered thermal energy.

Accordingly, the waste heat recovery system 16 comprises a secondary turbine 21 for extracting work from the exhaust gas exiting the primary turbine 15, which is still relatively hot. The waste heat recovery system 16 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 circuit 31 that also supplies coolant fluid to the engine 12. The engine 12 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 12.

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.

In this embodiment, the electromagnetic coupling module 20 is a magnetic gearbox, as described in more detail later with reference to Figures 4 and 5. 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 which 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.

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.

As shall be described in more detail later, 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. In this operating mode, 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 12 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 31 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 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. Specifically, 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, and 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 16 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 16 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.

In normal operation when the engine 12 is at its operational temperature, reducing the pressure of the exhaust gas to below atmospheric pressure in the secondary turbine 21 maximises the amount of work that can be extracted, and also minimises the amount of residual thermal energy that must be extracted by the heat exchanger 23. In this way, the waste heat recovery system 16 operates an Inverse Brayton Cycle and so optimises heat recovery from the exhaust gas, as now explained in more detail with reference to Figure 3, which shows a plot of temperature against entropy at various numbered stages of the arrangement of Figure 2. Each stage corresponds to a respective state of an air/fuel mixture moving through the engine 12 and the exhaust system 14, and the locations within the physical apparatus to which the numbered stages relate are indicated with corresponding numbers in Figure 2.

It is noted that in embodiments of the invention the waste heat recovery system 16 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 12 will in turn be warmed more quickly. However, to provide a thorough understanding of the waste heat recovery system 16 for the skilled person, the principles of its normal operation are first described, with reference to Figure 3.

In Figure 3, 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 3, namely a transition from state 1 to state 2, corresponds to compression of air supplied to the engine intake 19 by the primary compressor 17.

Next, an Otto cycle begins as the compressed air enters the engine 12 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 5_S, and a constant volume heat rejection process from state 5_S to state 2.

However, at state 5 the gas still carries a large amount of thermal energy, making it inefficient to simply reject the heat to the atmosphere. So, 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 17, thereby using some of the waste heat energy to increase engine performance and thus improve efficiency.

Then, as already noted, 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 16. 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.

In the Inverted Brayton Cycle, 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. In some embodiments of the invention 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.

Figure 4 schematically depicts a longitudinal-sectional view of the electromagnetic coupling module 20 of the waste heat recovery system 16. The electromagnetic coupling module 20 comprises a magnetic gear assembly arranged to couple the input shaft 24 and the output shaft 25 magnetically. The secondary turbine 21 is attached to the input shaft 24 and the secondary 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 sources 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 5), 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, which in turn is surrounded by 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. To energise the electromagnets 58, a voltage may be applied, for example from the vehicle battery 29. In this example, the electromagnets 58 are all connected together in series and alternating polarity is provided for by appropriate connection of the coils of the respective electromagnets 58. For example, 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.

As seen more clearly in Figure 5, the outer rotor 54 includes an inner set of permanent magnets 60 which cooperate with the permanent magnets 53 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 53, or twelve pole-pairs, arranged to produce a spatially varying magnetic field. The intermediate rotor 52 carries 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. In this embodiment, 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.

In use, 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, and 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. As the input shaft 24 drives rotation of 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. Similarly, 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.

In more detail, 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.

As noted above, the inner rotor 50 rotates at a speed which 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.

As noted above, the electromagnets 58 are wired in series, with the coils arranged such that when a current is applied the electromagnets 58 have alternating polarity. Therefore, 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. As noted above, 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.

In this way, the electromagnets 58 are operable to control the gear ratio. Therefore, the speed of the output shaft 25 that drives the secondary compressor 22 can be controlled to a desired level for a range of input shaft speeds through appropriate control of the gear ratio.

In addition to controlling the gear ratio by adjusting the frequency of the drive current supplied to the electromagnets 58, it is also possible to assist the secondary turbine 21 with driving the secondary compressor 22 by injecting extra electrical energy into the electromagnetic coupling module 20 in the form of an increase in the magnitude of the current delivered to the electromagnets 58. As the skilled person understands, a higher current generates a stronger electromagnetic field around the electromagnets 58, which increases the torque imparted to the outer rotor 54. This in turn reduces the torque that must be transmitted to the intermediate rotor 52 to produce a given inner rotor 50 speed. This manner of operation defines the power-assist mode referred to above.

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 12. 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.

Conversely, if the drive current to the electromagnets 58 is removed, the three-way gear ratio persists and so the outer rotor 54 continues to rotate, albeit passively. In this situation, 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 the vehicle battery 29, 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 by the power electronic module 28 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 secondary turbine 21 and supplied to the intermediate rotor 52 can be divided between the secondary compressor 22, which is driven by the inner rotor 50, and the vehicle battery 29. Typically, once the secondary compressor 22 is driven at an optimum rate, all surplus power is diverted to the vehicle battery 29 for maximised efficiency.

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. In 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.

It is noted that the current induced in the electromagnets 58 inherently creates a backelectromagnetic force on the outer rotor 54, which resists rotation of the rotor 54. At the same time, inertia of air in the exhaust system 14 resists rotation of the secondary turbine 21 and the compressor 22. Furthermore, the three-way gear ratio of the electromagnetic coupling module 20 persists at all times. Therefore, the turbine 21 and the compressor 22 do not truly freewheel in the decoupled mode, but instead rotate at respective speeds at which the forces that act to resist rotation of the elements of the electromagnetic coupling module 20 balance, within the constraints of the three-way gear ratio. However, for simplicity, the uncontrolled rotation of the secondary turbine 21 and the secondary compressor 22 in the decoupled mode shall be referred to as ‘freewheeling’.

It is noted that the electrical energy generated by the rotation of the outer rotor 54 in the decoupled mode is significantly lower than when the electromagnetic coupling module 20 operates in the generator mode. So, this mode of operation corresponds to a low recovery mode for the waste heat recovery system 16.

As the secondary turbine 21 and the secondary compressor 22 are allowed to freewheel, they present little resistance to the flow of exhaust gas through the exhaust system 14. The use of this operating mode in embodiments of the invention shall be described later.

Moving on to consider the waste heat recovery system 16 as a whole, in use, engine exhaust gas is passed through the exhaust system 14 into the waste heat recovery system 16 to be expanded through the secondary turbine 21. The secondary 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 secondary compressor 22. This causes the secondary compressor 22 to rotate at a speed determined by the speed of the secondary turbine 21 and the gear ratio of the variable magnetic gear.

In this way, the speed at which the secondary compressor 22 rotates is dissociated from the input speed of the secondary turbine 21. This ensures that the secondary compressor 22 rotates at an optimum speed for providing the required pressure increase for exhaust gas to be purged, without wasting energy by compressing the exhaust gas more than is required for purging. It also allows the secondary turbine 21 to rotate as fast as possible and thereby extract a maximum amount of energy from the exhaust gas.

It is an advantage of this example that the intermediate pole-piece carrying rotor 52 is attached to the input shaft 24 and therefore to the secondary turbine 21. In this way, the secondary 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 gear ratio of the electromagnetic coupling module 20 is controlled by an engine control module 74, as shown in Figure 6. The engine control module 74 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. In normal operation, the engine control module 74 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 16.

In contrast, during the engine warm-up period the engine control module 74 operates the waste heat recovery system in a low recovery mode to minimise power extraction from the exhaust gas, which in turn accelerates warming of the engine 12, as explained later.

The engine control module 74 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 or power demand by the secondary compressor. In this respect, the engine control module 74 comprises a set of inputs that are arranged to receive signals indicative of each of these vehicle operating parameters. For example, the engine control module 74 includes an input that receives a measurement of exhaust gas flow rate that is derived from a sensor disposed within the exhaust system 14.

The variable magnetic gear gives the advantage of allowing individual optimisation of the secondary turbine 21 and secondary compressor 22 across a wide range of operating conditions.

As noted above, the electromagnetic coupling module 20 can operate in one of three modes: an assist mode (or power-assist mode); a generator mode; and a decoupled 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. This typically occurs in high-load engine conditions, during which the gear ratio of the electromagnetic coupling module 20 is optimised to drive the secondary compressor 22 at a high efficiency point, while the remaining energy extracted from the exhaust gas is converted into electrical energy and returned to the vehicle battery 29. This maximises the electrical energy generated, whilst ensuring that the secondary compressor 22 provides an adequate pressure rise to purge the exhaust to atmosphere.

In the power-assist mode, electrical power is injected into the electromagnetic coupling module 20 to drive the inner rotor 50, and in turn the secondary compressor 22. Although this depletes the vehicle battery 29, it has been found that this approach provides an overall efficiency improvement in low-load engine conditions. This is because using electrical power to drive the secondary compressor 22 reduces the torque that is required from the secondary turbine 21, which therefore need not extract as much energy from the exhaust gas. This in turn reduces the pressure restriction caused by the secondary turbine 21, thereby minimising back-pressure on the primary turbine 15, which can therefore operate more effectively. This in turn increases the performance of the engine, to an extent that outweighs the energy consumption in the electromagnetic coupling module 20.

In other words, 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 16 to reduce the back pressure on the exhaust system.

The power assist mode can also be useful for accelerating engine warming during the warm-up period, as already noted and as described in more detail below.

As the compressor 22 is driven, in part, by the electromagnetic coupling module 20 when in the power-assist mode, expansion of the exhaust gas through the turbine 21 is minimal, although typically the exhaust gas is still at or below atmospheric pressure at state 7. The reduced pressure drop in turn minimises the work required from the compressor 22 to raise the pressure of the exhaust gas back up to atmospheric pressure for purging, which further reduces overall energy consumption.

Aside from the three modes in which the electromagnetic coupling module 20 can be operated, as noted above the exhaust system 14 includes bypass routes that enable the secondary turbine 21 and the secondary compressor 22 to be bypassed altogether. This creates a fourth mode of operation for the exhaust system 14 as a whole, namely a bypass mode, in which the secondary turbine 21 and the secondary compressor 22 do not operate, and exhaust gas is instead delivered directly to the heat exchanger 23.

Having fully described the principles of operation of the waste heat recovery system 16 shown in Figure 2 during normal operation, various modes of operating the system according to embodiments of the invention to accelerate engine warming during the warm-up period following ignition shall now be described. The operating modes described below are all characterised as low recovery modes for the waste heat recovery system 16, in which recovery of useful work from the exhaust gas is minimised, in turn enhancing the rate at which heat energy is transferred to the coolant circuit 31 and, in turn, the engine 12.

Figure 7 shows a general process 80 that the engine control module 74 performs during an engine warm-up period to accelerate engine warming and therefore reach the normal operational temperature as quickly as possible. The process 80 begins when the engine control module 74 receives at step 82 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. Such 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.

On receiving the signal, the engine control module 74 controls at step 84 the waste heat recovery system 16 so as to maximise the heat energy transferred to the coolant circuit 31 by the heat exchanger 23. In general terms, this involves operating the waste heat recovery system 16 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.

It is noted again at this stage that although operating the waste heat recovery module 16 in this way sacrifices the opportunity to convert thermal energy contained in the exhaust gas to electrical energy - as would be the case during normal operation - it has been found that the efficiency gains achieved through reducing the warm-up period by accelerating engine warming outweigh the potential gains through converting thermal energy in the exhaust gas to electrical energy, and so embodiments of the invention provide a net benefit to vehicle operating efficiency.

During the warm-up period the engine control module 74 monitors at step 86 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 12, 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 74 may allow a fixed time period for the engine 12 to warm-up, for example 200 seconds.

While the engine 12 is still warming, the engine control module 74 maintains the waste heat recovery system 16 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 74 selects at step 88 an appropriate normal operating mode for the waste heat recovery system 16, 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 12, 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.

Noting that the freewheeling secondary turbine 21 and compressor 22 continue to present a small resistance to the exhaust gas flow, which will cause a slight reduction in the exhaust gas temperature, retention of thermal energy within the exhaust gas can be further improved by operating the waste heat recovery system 16 in the bypass mode to direct the exhaust gas into the bypass routes and thereby bypass the secondary turbine 21 and compressor 22. In this scenario, the exhaust gas temperature drop between leaving the engine 12 and entering the heat exchanger 23 is minimised.

The heating element 34 provides an auxiliary means for maximising heat transfer to the coolant circuit while the waste heat recovery system 16 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 12 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 8 shows an alternative embodiment of the waste heat recovery system 16 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.

During engine warm-up, the 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 12. Similarly to the heating element 34, the thermoelectric generator 36 therefore provides a means for accelerating engine warming during the warm-up period.

However, unlike the heating element 34, which becomes redundant once the engine 12 reaches its operational temperature, the 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 16 shown in Figure 8 includes the same four valves 30 that are present in the embodiment of Figure 2, 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.

Specifically, 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.

It is noted that the third 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. Indeed, the skilled person will readily be able to conceive many further variations on this arrangement to achieve the same effect.

When the bypass mode is selected, 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 12. 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 8 further increases the rate at which heat is transferred to the engine 12, 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 16.

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.

For completeness, Figure 9 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 12, 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 12.

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 12.

As already noted, the waste heat recovery system 16 can aid warming of the cabin 17, in that the system 16 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.

Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

For example, the particular configuration of the electromagnetic coupling module described above is offered as an example only, and many other configurations are possible. For example, the electromagnets need not be wound in an alternating fashion, and may instead be wound in groups of two or three. Alternatively, the electromagnets may all be wound in the same way but energised separately to create a rotating magnetic field.

Moreover, as already mentioned a pair of electric machines may be used in the place of a variable magnetic gear. For example, 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. In such an arrangement, 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.

Indeed, embodiments of the invention are possible when a fixed coupling is used between the secondary turbine and the secondary compressor. For example, the bypass modes described above remain applicable with such apparatus.

It is also noted that the arrangement described above in which the engine includes a conventional turbocharging arrangement is used by way of example only. Waste heat recovery systems according to embodiments of the invention 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 examples.

Finally, and to reiterate, more generally any type of 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.

Claims

1. A method of accelerating warming of one or more components of a vehicle following engine ignition, the 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; 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 comprising 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 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.

2. The method of claim 1, wherein the one or more components to be warmed comprise the engine.

3. The method of any preceding claim, wherein the vehicle is a hybrid vehicle comprising an electric drive system for operating the vehicle in an electric mode, and wherein the one or more components to be warmed comprise an electric component associated with the electric drive system.

4. The method of any preceding claim, wherein the one or more components to be warmed comprise a component of a cabin heating system of the vehicle.

5. The method of any preceding claim, comprising monitoring the temperature of the or each component to determine when the or each component is operating in the warm-up period.

6. The method of any preceding claim, comprising transferring thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid in the coolant circuit using a heat exchanger.

7. The method of claim 6, wherein the energy recovery system 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 10 exchanger;

wherein the turbine is coupled to the compressor.

8. The method of claim 7, wherein the turbine is coupled to the compressor by an electromagnetic coupling module.

9. The method of claim 8, wherein operating the energy recovery system in the low recovery mode comprises operating the electromagnetic coupling module to supply torque to the turbine.

20 10. The method of claim 8 or claim 9, wherein operating the energy recovery system in the low recovery mode comprises operating the electromagnetic coupling module so that no torque is transferred between the turbine and the compressor.

25 11. The method of any of claims 8 to 10, wherein the electromagnetic coupling module comprises a magnetic gearbox.

12. The method of any of claims 7 to 11, wherein operating the energy recovery system in the low recovery mode comprises bypassing the turbine.

13. The method of claim 12, comprising directing exhaust gas through the compressor before entering the heat exchanger.

14. The method of any of claims 7 to 12, wherein operating the energy recovery system in the low recovery mode comprises bypassing the compressor.

15. The method of any of claims 7 to 14, comprising heating coolant fluid in the

5 coolant circuit using an electrically-driven heater attached to or integrated with the heat exchanger.

16. The method of any preceding claim, wherein the energy recovery system comprises a thermoelectric generator, and wherein the method comprises

10 operating the thermoelectric generator to convert electrical energy into thermal energy that is transferred to the coolant circuit.

17. The method of any preceding claim, comprising receiving a signal indicative of engine ignition, and selecting the low recovery mode for the energy recovery

15 system on receipt of the signal indicative of engine ignition.

18. The method of any preceding claim, comprising operating the energy recovery system according to an inverse Brayton cycle.

20 19. The method of any of claims 1 to 17, comprising operating the energy recovery system according to any of: an Otto cycle; a Rankine cycle; or a Brayton cycle.

20. A controller configured to implement the method of any preceding claim.

25

21. A computer program product comprising computer readable code for controlling a computing device to perform a method according to any of claims 1 to 19.

22. A non-transitory computer readable medium comprising the computer program

30 product of claim 21.

23. 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 comprising 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 to be warmed, the controller comprising:

an input arranged to receive at least one signal indicative of a temperature of a component to be warmed;

a processing module configured to determine, based on the or each signal received at the input, that the component to be warmed 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 the coolant fluid in the coolant circuit; and an output configured to transmit the control signals to the energy recovery system.

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 delivers coolant fluid to one or more components of the vehicle; and the controller of claim 20 or claim 23.

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 of claim 25 comprising:

a turbine configured to receive exhaust gas expelled from the engine and deliver expanded exhaust gas to a heat exchanger for transferring thermal energy recovered from exhaust gas expelled from the engine to the coolant fluid in the coolant circuit; and a compressor configured to compress exhaust gas exiting the heat exchanger; wherein the turbine is coupled to the compressor.

The energy recovery system of claim 26, wherein the turbine is coupled to the compressor by an electromagnetic coupling module.

The energy recovery system of claim 27, wherein operating the energy recovery system in the low recovery mode comprises operating the electromagnetic coupling module to supply torque to the turbine.

The energy recovery system of claim 27 or claim 28, wherein operating the energy recovery system in the low recovery mode comprises operating the electromagnetic coupling module so that no torque is transferred between the turbine and the compressor.

30. The energy recovery system of any of claims 27 to 29, wherein the electromagnetic coupling module comprises a magnetic gearbox.

31. The energy recovery system of any of claims 26 to 30 comprising:

5 a first valve disposed upstream of the turbine;

a second valve disposed downstream of the turbine; and a conduit connecting the first valve and the second valve; wherein the first valve and the second valve are operable to allow exhaust gas to bypass the turbine via the conduit.

32. The energy recovery system of claim 31 comprising:

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 a fourth valve; wherein

15 the third valve and the fourth valve are operable to allow exhaust gas to bypass the compressor via the conduit.

33. The energy recovery system of any of claims 26 to 30 comprising:

a first valve disposed upstream of the compressor;

20 a second valve disposed downstream of the compressor; and a conduit connecting the first valve and the second valve; wherein the first valve and the second valve are operable to allow exhaust gas to bypass the compressor via the conduit.

25 34. The energy recovery system of any of claims 26 to 30 comprising:

a first valve disposed upstream of the turbine; a second valve disposed upstream of the compressor; a conduit connecting the first valve and the second valve; wherein the first valve and the second valve are operable to allow exhaust gas

30 to bypass the turbine via the conduit.

35. The energy recovery system of claim 34 comprising:

a third valve disposed downstream of the compressor; a conduit connecting the third valve and the second valve; wherein the third valve and the second valve are operable to allow exhaust gas to pass from downstream of the compressor to the heat exchanger via the conduit.

5

36. The energy recovery system of claim 35 comprising:

a fourth valve disposed downstream of the turbine;

a conduit connecting the fourth valve and the third valve; wherein the fourth valve and the third valve are operable to allow exhaust gas to pass from the heat exchanger to the atmosphere.

37. The energy recovery system of claim 31 or claim 32 or any of claims 34 to 36, wherein operating the energy recovery system in the low recovery mode comprises bypassing the turbine.

15

38. The energy recovery system of claim 35 or claim 36 or claim 37 when dependent on claim 35 or claim 36 comprising directing exhaust gas through the compressor before entering the heat exchanger.

39. The energy recovery system of claim 32 or claim 33, wherein operating the

20 energy recovery system in the low recovery mode comprises bypassing the compressor.

40. The energy recovery system of any of claims 26 to 39 comprising an electrically-driven heater attached to or integrated with the heat exchanger for

25 heating coolant fluid in the coolant circuit.

41. The energy recovery system of any of claims 25 to 40 comprising a thermoelectric generator for converting electrical energy into thermal energy that is transferred to the coolant circuit.

42. A vehicle comprising:

an engine;

the energy recovery system of any of claims 25 to 41; 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.

Intellectual

Property

Office

Application No: GB1701469.7 Examiner: Bryce D'Souza