GB2533157A

GB2533157A - Thermal energy management system and method

Info

Publication number: GB2533157A
Application number: GB1422145.1A
Authority: GB
Inventors: Matthew Rutledge John; David Blundell Guy
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2014-12-12
Filing date: 2014-12-12
Publication date: 2016-06-15
Anticipated expiration: 2034-12-12
Also published as: GB2533157B

Abstract

This disclosure is directed to a thermal energy management system and a method for managing thermal energy for exhaust gases, and in particular to a thermal energy management system and method for turbocharged internal combustion engines. The disclosure provides a thermal energy management system 10 for an internal combustion engine 11 having a crankshaft 25. The thermal energy management system 10 comprises: a turbocharger comprising a compressor 14 and a turbine 17 mounted on a common turboshaft 18 ; a flywheel 31 ; a first clutch 32 to couple the flywheel 31) to the turbo shaft 18; a second clutch 34 to couple the flywheel 31 to the crankshaft 25; and a first transmission 33 to determine a gear ratio between the flywheel 31 and the turbocharger shaft 18. The turbocharger may be of fixed or variable geometry (VGT) and the first transmission 33 may be a continuously variable transmission (CVT).

Description

THERMAL ENERGY MANAGEMENT SYSTEM AND METHOD

Technical Field

This disclosure is directed to a thermal energy

management system and a method for managing thermal energy for exhaust gases, and in particular to a thermal energy management system and method for turbocharged internal combustion engines.

Background

Turbochargers are typically used with internal combustion engines, such as diesel engines, in order to maximise the power available therefrom. Other benefits of turbocharged engines include greater fuel efficiency and lower emissions relative to a naturally aspirated engine of similar power. Turbochargers typically have a turbine to extract power from the engine exhaust gases. The turbine drives a compressor that compresses the gas (typically air) to be delivered to the engine intake. The resulting increased air density within the cylinders may allow for more fuel to be injected into the cylinders and effectively combusted, thereby increasing the engine work output.

A turbocharger may employ a fixed geometry turbine, which may be designed to operate at a maximum efficiency condition. Alternatively, the turbine may be a variable geometry turbine, which may include a variable geometry mechanism that can be altered to regulate the flow of exhaust gas into the turbine. -2 -

A common problem associated with turbocharged engines is that the power, fuel efficiency, and emissions-control performance may be reduced during transient conditions. Transient conditions may occur, for example, under a rapidly increasing or decreasing engine load. Under a rapidly increasing engine load, a turbocharger compressor may require increased torque in order to deliver an increased air flow, but such increased torque may not be available if a turbine driving the compressor is not fully spun-up. This may result in a power lag until the intake air flow increases to the requisite level.

Exhaust gases generated by an internal combustion engine, such as a diesel engine, may contain particles and gases that are preferably reduced or removed from the exhaust gas stream before it is released into the atmosphere. These particles and gases may be removed from the exhaust gas stream by an aftertreatment system, which may include a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and/or a selective catalytic reduction (SCR) module. For example, the exhaust gases may contain hydrocarbons and carbon monoxide, which may be converted into carbon dioxide and water by a DOC. The exhaust gases may contain diesel particulate matter or soot, which may be removed by a DPF. The exhaust gases may also contain nitrous oxides (N0x), which may be converted into less harmful emissions, such as nitrogen and water, by an SCR module. The components of an aftertreatment system may require an elevated temperature in order to operate effectively. -3 -

WO-A-2006/115596 discloses a method for operating a turbocharged internal combustion engine having an aftertreatment device, wherein the turbocharger comprises a variable-geometry-turbine. The temperature of the exhaust gas delivered to the after-treatment device is substantially matched to a predetermined target temperature by controlling a variable-geometry mechanism of the turbine to control the amount of power extracted by the turbine. The boost pressure is substantially matched to a predetermined target boost 10 pressure by either inputting mechanical power into or extracting mechanical power from the turbocharger, as required, using a power addition/extraction device, such as a motor/generator, coupled to the turbocharger.

Summary

According to a first aspect of the present disclosure there is provided a thermal energy management system for an internal combustion engine having a crankshaft, comprising: a turbocharger comprising a compressor and a turbine mounted on a common turboshaft; a flywheel; a first clutch operable to couple the flywheel to the turboshaft; a second clutch operable to couple the flywheel to the crankshaft; and a first transmission operable to determine a gear ratio between the flywheel and the turboshaft.

According to a second aspect of the present disclosure there is provided a method of managing thermal energy in exhaust gases exiting an exhaust manifold of an internal combustion engine, the internal combustion engine comprising a turbocharger comprising a compressor and a turbine mounted on a common turboshaft, the method comprising the steps of: -4 -in a first mode, coupling a flywheel to the turboshaft such that the turboshaft delivers kinetic energy to the flywheel; in a second mode, uncoupling the flywheel from the turboshaft and coupling the flywheel to a crankshaft of the engine such that the flywheel delivers kinetic energy to the crankshaft; and in a third mode, uncoupling the flywheel from the crankshaft and coupling the flywheel to the turboshaft such that the flywheel delivers kinetic energy to the turboshaft.

Brief Description of the Drawings

Figure 1 is a schematic of an internal combustion engine having a thermal energy management system according 15 to the present disclosure; Figure 2 is a schematic of the thermal energy management system of Figure 1 in a first operating mode; Figure 3 is a schematic of the thermal energy management system of Figure 1 in a second operating mode; and Figure 4 is a schematic of the thermal energy management system of Figure 1 in a third operating mode.

Detailed Description

Figure 1 illustrates a thermal energy management system 10 for an engine 11. The engine 11 may be an internal combustion engine such as a compression-ignition or spark-ignition engine. The engine 11 may generally comprise a -5 -fluid intake arrangement, such as an intake manifold 12, for directing intake fluid to a plurality of cylinders 21 and a plurality of pistons (not shown) located in the cylinders 21 for providing power to a crankshaft 25 via cranks (not shown). A throttle valve (not shown) may be provided in the fluid intake arrangement for controlling the flow rate of intake fluid into the cylinders 21. Fuel, such as diesel, petrol, or natural gas, may be selectively provided to the cylinders 21, either directly injected into the cylinders 21 or by some other means, via one or more fuel injectors (not shown). The fuel may combust with the intake fluid and drive the pistons, thereby rotating the crankshaft 25 and providing an engine 11 output torque and power. Exhaust gases may be produced by the combustion process, which may be directed from the cylinders 21 out of the engine 11 via an exhaust manifold 13.

The arrangement may enable the intake of the engine 11 to be boosted via a compressor 14. The compressor 14 may typically include a compressor wheel (not shown) having blades, mounted on a turboshaft 18 in a known manner. When the compressor 14 is not operable (i.e. being driven), the blades of the compressor 14 may be stationary such that intake fluid flows through the gaps between them, or they may rotate under the reaction force from the intake gas flow only. Alternatively, a compressor bypass (not shown) may be provided, and the intake fluid may be substantially directed via the compressor bypass when the compressor 14 is not in operation.

The compressor 14 may be fluidly connected to an inlet 22, for the ingress of intake fluid, which may typically be -6 -ambient air (or, less typically, an air-fuel mix). The compressor 14 may further be fluidly connected to the intake manifold 12 by first and second intake conduits 15 and 16. A cooler 19 may be disposed between the first and second intake conduits 15 and 16, tc cool the compressed air prior to its ingress into the engine 11. The cooler 19 may be any suitable type of cooler known in the art, for example an air-to-air charge cooler. An inlet throttle (not shown) may be provided between the cooler 19 and the intake manifold 12.

The compressor 14 may be mechanically coupled to a turbine 17 via the turboshaft 18. The turbine 17 may typically include a turbine wheel (not shown) having blades, mounted on the turboshaft 18. The turbine 17 may be a fixed-geometry turbine having an inlet (not shown) which is optimised for predetermined conditions. Alternatively, the turbine 17 may be a variable-geometry turbine having a variable geometry mechanism (not shown) to regulate the flow of exhaust into the turbine 17. Together, the compressor 14 and turbine 17 form a turbocharger.

The turbine 17 may be fluidly coupled to the exhaust manifold 13 by a first exhaust conduit 20. Exhaust gases exiting the exhaust manifold 13 through the first exhaust conduit 20 may be directed to drive the turbine 17. A wastegate (not shown) may be provided in the first exhaust conduit 20 so that some or all of the exhaust gases leaving the exhaust manifold 13 may he directed to bypass the turbine 17 when reduced torque is desired. -7 -

An exhaust gas recirculation (EGR) system (not shown) may be provided to optionally recirculate a portion of the exhaust gases back to the cylinders 21. The FOR system may be a high pressure system, which may route exhaust gases upstream of the turbine 17 to the intake manifold 12. Alternatively, the EGR system. may be a low pressure system, which may route exhaust gases downstream of the turbine 17 to upstream of the compressor 14. The exhaust gases in the EGR system may be cooled via a heat exchanger (not shown).

After passing through the turbine 17, the exhaust gases may pass through a second exhaust conduit 23 to an aftertreatment system 30. The aftertreatment system 30 may receive and treat the exhaust gases to remove pollutants, before releasing the exhaust gases to the atmosphere through an exhaust pipe 24.

The aftertreatment system 30 may comprise a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and/or a selective catalytic reduction (SCR) module, as is known in the art. The aftertreatment system 30 may operate effectively at certain temperatures, the efficiency of the exhaust gas treatment being cptimised when the exhaust gas temperature is within a predetermined optimal temperature range having lower and upper limits of temperature, which may vary according to the type of aftertreatment system 30. The lower and upper limits of temperature may be obtained from the manufacturer of the aftertreatment system 30, or may be determined by the skilled person from the components used in the aftertreatment system 30. -8 -

Typically, a DOC may be disposed upstream of any other components in the aftertreatment system 30. The DOC may comprise at least one catalyst for oxidising pollutants, such as carbon monoxide and hydrocarbons, and/or for assisting the elimination of other pollutants, such as NON. The catalyst may be a noble metal (such as palladium or platinum) or a base metal oxide (such as aluminium oxide). These materials may cause the oxidation of hydrocarbons and carbon monoxide present in the exhaust gases to carbon dioxide and water. The catalyst may be coated over a honeycomb structure or formed on the surface of ceramic pellets.

The DOC may have a lower temperature limit at which the catalyst starts to operate effectively and an upper temperature limit which may be the temperature at which the catalyst is damaged by heat exposure or stops catalysing effectively. A suitable lower temperature limit may be in the region of 180°C and a suitable upper temperature limit may be in the region of 550°C for a compression-ignition engine running on diesel fuel.

A DPF may be present in the aftertreatment system 30 in addition to, or instead of, the DOC. If the aftertreatment system 30 comprises a DOC, a DPF, and an SCR module, the DPF is typically provided downstream of the DOC and upstream of the SCR module. The DPF may be of any suitable form known in the art, for example a ceramic honeycomb, an alumina coated wire mesh, or a ceramic foam.

For DPFs, there is usually no lower temperature limit for filtration (capturing soct) but there is typically one -9 -for regeneration (the removal of soot). The lower temperature limit for regeneration may depend on what type of regeneration is being used. The DPF may be passively regenerative, in which nitrogen dioxide is used to oxidise the filtered particulate material from the filter when the exhaust gas temperature is within a predetermined temperature range. The lower temperature limit for passive regeneration may be in the region of 250-300°C. A regenerative filter may comprise a catalyst to allow such ignition to occur at a lower temperature. Alternatively, the filter may be actively regenerated by actively raising the temperature of the exhaust gas adjacent to the filter to the ignition temperature required to achieve oxygen-soot oxidation, such that the soot may be burned off with oxygen.

The lower temperature limit for active regeneration may be in the region of 500-600°C. Typically, for active regeneration, the DPF temperature is raised by injecting fuel upstream of the DPF rather than relying on the engine exhaust temperature.

The upper temperature limit for the DPF may be a function of soot loading (and, to a smaller extent, of exhaust volume flow rate). If the DPF is heavily loaded with soot (due to failed or missed regenerations previously), then there may be a risk that at high temperature too much soot will burn off at once, causing the DPF to melt. The risk may be increased if the exhaust flow is low (reducing the amount of heat carried away in the exhaust stream).

An SCR module may be present in the aftertreatment system 30 in addition to, or instead of, the DOC and/or the DPF. If the aftertreatment system 30 comprises a DOC, a DPF, -10 -and an SCR module, the SCR module is typically provided downstream of the other components. The SCR module may comprise a reductant injector located upstream of a catalyst. The reductant injector may inject a liquid or gaseous reductant into the stream of exhaust gases entering the SCR module. The high temperature of the exhaust gases may cause the reductant to evaporate, and the resulting combination of gases may contact the catalyst. In the presence of the catalyst, the reductant may react with the NO in the exhaust gases to form nitrogen, water, and carbon dioxide, which may pass to the atmosphere via the exhaust pipe 24. In a particular embcdiment, the SCR module may be a urea SCR module in which the reductant is aqueous ammonia. The catalyst may comprise zeclites, vanadium, or the like.

The SCR module may have two lower temperature limits. The first lower temperature limit may be the lowest temperature for catalyst activity, i.e. the lowest temperature at which NOx may be reduced to nitrogen across the catalyst. This may depend on the type of SCR catalyst, but is generally 250-300°C tc achieve a useful level of NOx conversion (i.e. at the point at which 80% of the NO can be reduced). The second lower temperature limit may be the limit for dosing of the reductant. For example, in the case of a water/urea solution system, there is a risk of formation of deposits at low temperatures (such as ammonium hydrogen sulphate). Other types of dosing system may have other constraints at low temperature. Generally, the dosing of reductant solution is limited at exhaust temperatures below 200-220°C due to the risks of deposit formation. Rapid warmup of exhaust gases on engine start-up may be desirable for two reasons: first, the hotter the catalyst, the more efficient the reduction of NON; and second, the sooner the minimum dosing temperature is reached, the sooner urea may be added to the catalyst to reduce the NOx.

There may also be two upper limits on SCR temperature, which may depend on the catalyst formulation. The first upper limit may be the deactivation temperature, above which the catalyst may either deactivate or may produce harmful emissions. This first upper limit may be in the region of 600°C. The aftertreatment system 30 may be designed to avoid breaching the first upper temperature limit. The second upper temperature limit may be lower than the first upper temperature limit. The second upper temperature limit may be in the region of 300°C, and may be a performance limit relating to an upper temperature beyond which the volume of urea that can be stored on the catalyst may reduce; this limits the NO conversion efficiency as, beyond this temperature, it may not possible to dose as much urea without unreacted ammonia release (known as ammonia 'slip') out of the SCR module.

At least one temperature sensor (not shown) may be provided to determine the temperature of the exhaust gases prior to entering, and/or at various stages in, the aftertreatment system 30. One or more of the following temperature sensors may be provided in an aftertreatment system 30 having a DOC, a DPF, and/or an SCR module: an 'engine out' temperature sensor in the second exhaust conduit 23 (used to determine when the DOC is hot enough to inject fuel thereon to enable active DPF regeneration, and to determine when the 'engine out' NOx sensor can be turned on); a 'DOC out' temperature sensor between the DOC and the -12 -DPF (used to measure the temperature change resulting from any fuel burned on the DOC to enable active DPF regeneration, and to monitor the 'DPF in' temperature); and/or an 'SCR in' temperature sensor between the DPF and the SCR module (used to determine when the SCR should be dosed).

A suitable control unit (not shown) may be provided to monitor the data received from the one or more sensors and to operate the various components of the aftertreatment system 30 accordingly. In an arrangement comprising only one of the aforementioned temperature sensors, the control unit may be programmed to utilise the temperature data retrieved from that sensor to infer the other relevant temperatures using known algorithms. Additionally, the control unit may use the outputs from the one or more sensors, singly or in combination, as inputs for other functions including, but not limited to, performance and condition monitoring, hardware protection, and performance optimisation.

The thermal energy management system 10 may be disposed between the turbine 17 and a crankshaft 25 of the engine 11. In one configuration, the turbine 17 may be mechanically coupled to the crankshaft 25 via a flywheel 31. This may be achieved via the turboshaft 18 running through the turbine 17. A first clutch 32, which may be a friction-disc clutch, may be disposed between the flywheel 31 and the turboshaft 18. A first transmission 33 Pay be disposed between the first clutch 32 and the flywheel 31. The first transmission 33 may be employed to allow the differential speeds between the flywheel 31 and the turboshaft 18 to be managed. Alternatively, the first transmission 33 may be disposed -13 -between the turboshaft le and the first clutch 32. The first transmission 33 may be a continuously variable transmission (CVT), which may be of any suitable type known in the art. A second clutch 34, which may be a friction-disc clutch, may be disposed between the flywheel 31 and the crankshaft 25, and a second transmission 35 may be disposed between the second clutch 34 and the crankshaft 25. Alternatively, the second transmission 35 may be disposed between the flywheel 31 and the second clutch 34. The second transmission 35 may, for example, be a CVT or a fixed speed ratio transmission, which may be of any suitable type known in the art. Various mechanical couplings 36 may be used to connect the elements of the thermal energy management system 10. The control unit (not shown) may be operable to control the various components of the thermal energy management system 10.

Some known engine systems comprise multiple turbochargers (not shown), and therefore more than one turbine 17. In such an engine system, the thermal energy management system 10 may be associated with any one of the turbines. For example, in a twin turbocharger system, having a low pressure turbine and a high pressure turbine, the thermal energy management system 10 may be associated with either of the low pressure or high pressure turbines.

Furthermore, the thermal energy management system 10 may be associated with a turbocharger in series or in parallel with a known mechanically or electrically driven supercharger.

Industrial Applicability

The thermal energy management system 10 has industrial applicability in the field of engines, in particular -14 -internal combustion engines, and may be used on a variety of different internal combustion engines, such as diesel engines. The thermal energy management system 10 is particularly suited to be applied to boosted engines 11, such as engines including turbochargers, having an aftertreatment system 30.

In use, ambient air may enter the inlet 22 and be directed to the compressor 14, which may be driven by the turbine 17 via the turboshaft 18. The compressor 14 may compress the ambient air, which may then pass through the first intake conduit 15 to ccoler 19, before passing through the second intake conduit 16 to the intake manifold 12 of the engine 11. In the cylinders 21 of the engine 11, the compressed air may be mixed with fuel injected by the fuel injector (not shown). The mixture may combust to produce work on the crankshaft 25. The exhaust gases which result from combustion may leave the engine 11 via the exhaust manifold 13 and pass via the first exhaust conduit 20 to the turbine 17. As the exhaust gases pass through the turbine 17, they may drive the turbine 17, which may cause the turboshaft 18 (and, hence, the compressor 14) to rotate. After exiting the turbine 17, the exhaust gases may pass to the aftertreatment system 30, before being directed to the atmosphere via the exhaust pipe 24.

The thermal energy management system 10 may operate in one of three modes of operation. Selection of the three modes of operation may be governed by the control unit (not shown).

-15 -The first mode of operation is illustrated in Figure 2. In the first mode of operation, the first clutch 32 may be engaged and the second clutch 34 may be disengaged. Thus the flywheel 31 may be mechanically coupled to the turboshaft 18 of the turbine 17, and the flywheel 31 may be uncoupled from the crankshaft 25. As such, torque may be transferred from the turboshaft 18 to the flywheel 31, using an appropriate gear ratio in the first transmission 33 (as depicted by the arrows 40 in Figure 2). Thus power may be extracted from the turbine 17 to spin-up the flywheel 31. As a result, the turbine 17 may be slowed, which may increase the back pressure of the exhaust gases in the first exhaust conduit 20. Consequently, the temperature of the exhaust gases in the first exhaust conduit 20, which pass through the turbine 17 to the aftertreatment system 30, may be Increased. The slower turbine 17 will also lead to lower compressor 14 speeds, which may reduce the engine air flow. This may result in a lower engine air:fuel ratio, which may also act to Increase the temperature cf the exhaust gases. The power harvested from the turbine 17 may be stored in the flywheel 31, in the form of kinetic energy, for later use.

This first mode of operation may be employed when the exhaust gases are below a 'predetermined threshold temperature' required for efficient operation of the aftertreatment system 30, which may occur, for example, during start-up of the engine 11. The temperature of the exhaust gases may be detected by the relevant temperature sensor (not shown) or computed by the control unit (not shown) based on the temperature data available. The predetermined threshold temperature may be the lower temperature limit of any of the components of the -16 -aftertreatment system 30, namely the DOC, the DPF, and/or the SCR module. In particular, the predetermined threshold temperature may be the lower temperature limit of the SCR module, typically the lowest temperature for catalyst activity. The first mode of operation may be employed until one of the following two conditions is met: the temperature of the exhaust gases reaches the predetermined threshold temperature; or the flywheel 31 reaches its maximum speed (i.e. when the kinetic energy store is full).

The second mode of operation is illustrated in Figure 3. In the second mode of operation, the first clutch 32 may be disengaged and the second clutch 34 may be engaged. Thus the flywheel 31 may be mechanically uncoupled from the turboshaft 18 of the turbine 17, and the flywheel 31 may be coupled to the crankshaft 25. As such, torque may be transferred from the flywheel 31 to the crankshaft 25, via the second transmission 35 (as depicted by the arrows 41 in Figure 3). Thus power may be extracted from the flywheel 31 and transmitted to the crankshaft 25. Consequently, a portion of the power requirement by the engine 11 may be met by the energy stored in the flywheel 31, and therefore a smaller work output may be required by the engine 11 to achieve the same net power at the crankshaft 25. The reduced work requirement from the engine 11 may result in reduced engine fuel consumption.

This second mode of operation may be employed when the exhaust gases are at the predetermined threshold temperature, and when it may be desirable to feed additional power to the crankshaft 25. For example, flywheel 31 power may be fed to the crankshaft 25 during engine acceleration, -17 -in order to increase the rate of engine load acceptance/ (and hence acceleration), which may result in a better transient response. However, in such situations it is preferable to first feed power to the turboshaft 18 (as per the third mode, described below), which may have a greater effect on the transient response. Alternatively, under steady state operating conditions (when the engine 11 is at the desired speed and load), once the turbocharger has reached its desired operating condition, then any excess power in the flywheel 31 can be fed to the crankshaft 25 in order to assist with meeting the engine load and to reduce fuel consumption. However, there may be times under steady state operating conditions when the benefit from feeding flywheel 31 power to the turboshaft 18 may outweigh the benefits of sending it to the crankshaft 25, for example if the reduction in engine pumping losses from turbo assist outweighs the reduction in engine load from direct crank assist; these would be cases when the air system is near its limits.

The third mode of operation is illustrated in Figure 4. In the third mode of operation, the first clutch 32 may be engaged and the second clutch 34 may be disengaged. Thus the flywheel 31 may be mechanically coupled to the turboshaft 18 of turbine 17, and the flywheel 31 may be uncoupled from the crankshaft 25. In this mode, torque may be transferred from the flywheel 31 to the turboshaft 18, using an appropriate gear ratio for the first transmission 33 (as depicted by the arrows 42 in Figure 4). Thus power may be extracted from the flywheel 31 and transmitted to the turboshaft 18. The additional torque provided to turboshaft 18 by the flywheel 31 may cause the turboshaft 18 to accelerate.

-18 -This third mode of operation may be employed when the exhaust gases are at or above the predetermined threshold temperature, either to increase the transient response of 5 the engine 11 or to reduce engine fuel consumption.

Under certain circumstances, such as during acceleration (during which the engine 11 accepts load), the amount of intake air available from the compressor 14 may be inadequate. In such situations, by accelerating the turboshaft 18 using the third mode of operation, the compressor 14 may achieve a faster boost rise rate. This may allow more fuel to be combusted at an earlier stage during the engine acceleration or load acceptance, which may lead to faster engine acceleration or load acceptance, and hence an increased transient response.

During steady state operation, when additional boost may not be required, the additional torque provided to the 20 turboshaft 18 may allow a given turbine 17 speed to be maintained with reduced turbine 17 torque from the exhaust gases; hence the required exhaust expansion (pressure drop) across the turbine 17 may be reduced. This may mean that a portion of the exhaust gases may be bypassed around the turbine 17 via a wastegate (not shown), or that, in the case of a variable geometry turbine, the variable geometry vanes (not shown) may be more open. The reduced expansion ratio may lead to a lower pressure in the exhaust manifold 13. However, the intake manifold 12 pressure may be maintained (since the total torque in the turboshaft 18, and hence compressor 14 power, is unaltered), so the pressure differential (exhaust manifold 13 pressure minus intake -19 -manifold 12 pressure) across the engine 11 may be reduced. This may lead to reduced engine 11 pumping work (the net work the engine 11 needs to do on the exhaust stroke to force the exhaust out of the cylinder), which may reduce the engine 11 fuel consumption (as the engine 11 has to do less indicated work to achieved the same net power at the crankshaft 25).

The thermal energy management system 10 may additionally operate in one of a further three modes of operation (fourth, fifth, and sixth modes). Selection of the further three modes of operation may be governed by the control unit (not shown).

In the fourth mode of operation, both the first clutch 32 and the second clutch 34 pay be disengaged, with the flywheel 31 turning. Thus the turning flywheel 31 may be mechanically uncoupled from both the turboshaft 18 and the crankshaft 25. The fourth mode of operation may be employed to store the kinetic energy in the flywheel 31 until it is needed.

In the fifth mode of operation, the first clutch 32 may be disengaged and the second clutch 34 may be engaged. Thus the flywheel 31 may be mechanically uncoupled from the turboshaft 18, and the flywheel 31 may be coupled to the crankshaft 25. In this mode, torque may be transferred from the crankshaft 25 to the flywheel 31, via the second transmission 35. Thus power may be extracted from the crankshaft 25 and transmitted to the flywheel 31.

-20 -The fifth mode of operation may be employed when the flywheel 31 is initially stationary. In such a situation, it may be more appropriate to start the flywheel 31 from the crankshaft 25 than from the turboshaft 18, due to a smaller speed differential between the crankshaft 25 and the stationary flywheel 31 (than between the turboshaft 18 and the stationary flywheel 31). Additionally, the larger inertia of the crankshaft 25 (relative to the turboshaft 18) may be better able to absorb any shock form starting the flywheel 31.

The fifth mode may also be employed to maintain a predetermined minimum flywheel 31 speed and flywheel 31 energy store. By maintaining a minimum flywheel 31 speed, the fifth mode may obviate the need to strain the first clutch 32 and first transmission 33 when spinning up the flywheel 31 from a very slow or zero speed. By maintaining a minimum flywheel 31 energy store, the fifth mode may enable the second and third modes of operation, and hence their transient response benefit, to be utilised at any time during the running of the engine 11, and not only after initial engine 11 starting and warming (after which the first mode of operation may not be used).

In the sixth mode of operation, both the first clutch 32 and the second clutch 34 may be disengaged, with the flywheel 31 stationary. Thus the turning flywheel 31 may be mechanically uncoupled from both the turboshaft 18 and the crankshaft 25. The sixth mode of operation may be the default mode when the engine 11 is not running. The sixth mode may additionally be employed in a situation when all the stored energy in the flywheel 31 has been used and no -21 -suitable opportunity to recharge the flywheel 31 has been encountered. However, if the fifth mode of operation is being utilised to maintain a minimum flywheel 31 speed or a minimum flywheel 31 energy store, the sixth mode may be avoided when the engine 11 is running.

There are generally not specific cooling devices for aftertreatment systems. In cases of very high DPF soot loading, the engine 11 may derate (limit power) or shutdown to prevent the exhaust temperature elevating to an extent to cause all the soot to burn at once. The engine 11 and aftertreatment system 30 may be designed to stay within the temperature limits of the aftertreatment system 30.

Known turbocharged engines typically elevate engine exhaust temperature by one or more of the following methods: retarding combustion; reducing the air/fuel ratio; increasing back pressure in the exhaust gases via a back pressure valve; higher authority boost control; and additional combustion of fuel in the aftertreatment system. However, these methods may have associated disadvantages, such as increased fuel consumption. On the other hand, increasing exhaust temperature without a significant fuel consumption increase, in acccrdance with the present disclosure, may lead to reduced emissions and lower fuel consumption.

Claims

-22 -CLAIMS: 1. A thermal energy management system for an internal combustion engine having a crankshaft, comprising: a turbocharger comprising a compressor and a turbine mounted on a common turboshaft; a flywheel; a first clutch operable to couple the flywheel to the turboshaft; a second clutch operable to couple the flywheel to the crankshaft; and a first transmission operable to determine a gear ratio between the flywheel and the turboshaft.
2. A thermal energy management system according to claim 1, wherein the turbine is a fixed geometry turbine.
3. A thermal energy management system according to claim 1, wherein the turbine is a variable geometry turbine.
4. A thermal energy management system according to any one of the preceding claims, wherein the first transmission is a continuously variable transmission.
5. A thermal energy management system according to any one of the preceding claims, further comprising a second transmission operable to determine a gear ratio between the flywheel and the crankshaft.
6. An engine comprising a thermal energy management system according to any one of the preceding claims.

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7. A vehicle comprising an engine according to claim 6.
8. A method of managing thermal energy in exhaust gases exiting an exhaust manifold of an internal combustion engine, the internal combustion engine comprising a turbocharger comprising a coffpressor and a turbine mounted on a common turboshaft, the method comprising the steps of: in a first mode, coupling a flywheel to the turboshaft such that the turboshaft delivers kinetic energy to the 10 flywheel; in a second mode, uncoupling the flywheel from the turboshaft and coupling the flywheel to a crankshaft of the engine such that the flywheel delivers kinetic energy to the crankshaft; and in a third mode, uncoupling the flywheel from the crankshaft and coupling the flywheel to the turboshaft such that the flywheel delivers kinetic energy to the turboshaft.
9. A method of managing thermal energy according to claim 20 8, wherein the first mode is operated to slow exhaust gases passing through the turbine.
10. A method of managing thermal energy according to claim 8 or claim 9, wherein the first mode is implemented when a 25 temperature of exhaust gases is below a predetermined threshold temperature required by an aftertreatment system.
11. A method of managing thermal energy according to any one of claims 8 to 10, wherein the second mode or third mode 30 is implemented during engine acceleration.

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12. A method of managing thermal energy according to any one of claims 8 to 11, wherein the second or third mode is implemented during steady state operation.
13. A method of managing thermal energy according to any one of claims 8 to 12, wherein the second or third mode is implemented when a temperature of exhaust gases is above a predetermined threshold temperature required by an aftertreatment system.
14. A method of managing thermal energy according to any one of claims 8 to 13, further comprising the step of, in the first and third modes, using a transmission to adjust a gear ratio between the flywheel and the turboshaft.
15. A method of managing thermal energy according to claim 14, wherein the transmission is a continually variable transmission.