GB2564524A

GB2564524A - A method of controlling a waste heat recovery system

Info

Publication number: GB2564524A
Application number: GB1807385.8A
Authority: GB
Inventors: Agurto Goya Alan
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2017-05-16
Filing date: 2018-05-04
Publication date: 2019-01-16
Anticipated expiration: 2038-05-04
Also published as: GB201807385D0; GB201707829D0; GB2564524B

Abstract

A method of controlling a Rankine cycle Waste Heat Recovery (WHR) system 14 of a vehicle 1 comprises receiving driving data comprising route data indicative of characteristics of a route along which the vehicle 1 is expected to travel. The driving data is analysed to predict properties (temperature and flow rate) of the exhaust gas from the internal combustion engine 2 while the vehicle 1 travels along the route; and the waste heat recovery system 14 is controlled based on the predicted properties of the exhaust gas. The control may determine operation of the pump or another part of the heat engine. The route date may include road gradient or trajectory, a junction or speed restriction, or meteorological conditions such as headwind. By predicting future properties of the exhaust gas, the waste heat recovery system can be controlled more efficiently.

Description

A Method of Controlling a Waste Heat Recovery System

TECHNICAL FIELD

The present disclosure relates to a method for controlling a waste heat recovery system and particularly, but not exclusively, to a method for controlling a Rankine cycle engine in a vehicle. Aspects of the invention relate to a method, to a controller, to a computer program product, to a non-transitory computer-readable medium and to a vehicle.

BACKGROUND

As is well-known, internal combustion engines (ICEs) typically convert only around a third of the energy released by combustion of fuel into mechanical work. The majority of the remaining energy is lost to the environment as heat, in particular through exhaust gasses expelled from the ICE.

Various waste heat recovery (WHR) systems are known for recovering thermal energy contained in exhaust gasses. Such systems are typically disposed upstream of catalytic converters within a vehicle exhaust system, and include, for example, exhaust driven turbochargers. However, the amount of thermal energy that may be recovered by a WHR system positioned upstream of a catalytic converter is limited, as the exhaust gasses must remain sufficiently warm for effective operation of the catalytic converter. Accordingly, opportunities exist for further heat energy recovery downstream of the catalytic converter.

In this respect, Rankine cycle engines have shown effective capability, in a lab setting, for recovering heat energy from exhaust gasses downstream of a catalytic converter during sustained engine loads.

Known Rankine cycle engines use a heat exchanger to transfer thermal energy from exhaust gasses to a working fluid, such as ethanol, to vaporise the working fluid. Gaseous working fluid then passes through an expander, such as a turbine, to drive an electrical generator, with the resulting electrical energy being stored in a vehicle battery or used to power electrical systems directly.

The working fluid then enters a condenser that is coupled to a heat sink such as a vehicle coolant circuit, to remove thermal energy from the working fluid so that it reverts to a liquid state before returning to the heat exchanger. A Rankine cycle engine can therefore be regarded as a complex, non-linear multiple-input multiple-output (ΜΙΜΟ) system involving two phase transitions that must be carefully managed for optimised operation.

The work that can be recovered by a Rankine cycle engine is a function of both the temperature and the pressure of the working fluid downstream of the heat exchanger, with pressure having the greater influence. Each of these parameters can be adjusted within a working range that reflects the physical constraints of the system. For example, the maximum working fluid temperature is limited by the capacity of the vehicle coolant circuit, which must not be overloaded.

In broad terms, the temperature of the working fluid can be manipulated by varying the rate at which the fluid is pumped through the heat exchanger, whereas the fluid pressure can be manipulated through control of the turbine. For example, reducing the flow rate of working fluid into the heat exchanger allows more time for heat to transfer from exhaust gas to the working fluid as it passes through, thereby producing a higher exit temperature for the working fluid. In parallel, the resistance of the turbine may be increased, for example by controlling the generator torque, to raise back pressure in the system.

It is clear that neither of the above mechanisms for adjusting the parameters of the working fluid can achieve instantaneous changes. Instead, respective time constants are defined for the Rankine cycle engine that govern the rate at which the temperature and pressure of the working fluid - and, in turn, the rate at which energy is recovered at the turbine - may be changed. These time constants can be significant in practice, for example of the order of a few seconds.

If the Rankine cycle engine were operating under steady state conditions, the time constants associated with varying the properties of the working fluid would not present a particular problem, as the system could operate at an optimum point after an initial settling period.

However, in practice a vehicle faces transient loads, for example during urban driving characterised by low speed driving with frequent changes in engine load, leading to a correspondingly intermittent supply of thermal energy through the exhaust gasses. The thermal inertial of the Rankine cycle engine makes it difficult to respond to such changes. For example, conventional PID controllers have been found to be incapable of maximising energy recovery under such conditions.

At the extreme, at low engine load the exhaust gasses may not be warm enough for the working fluid to vaporise in the heat exchanger, especially if the working fluid flow rate is too high and/or the inlet temperature of the working fluid is too low. As liquid working fluid cannot drive the turbine, in such circumstances the turbine must be bypassed and no energy can be recovered. Indeed, at such times the Rankine cycle engine will actually represent a further load on the ICE and thus increase fuel consumption temporarily. This operating state must therefore be avoided whenever possible.

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

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a method of controlling a waste heat recovery system of a vehicle. The waste heat recovery system is configured to recover thermal energy from exhaust gas expelled from an internal combustion engine of the vehicle. The method comprises: receiving driving data comprising route data, the route data being indicative of characteristics of a route along which the vehicle is expected to travel; analysing the driving data to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route; and controlling the waste heat recovery system based on the predicted properties of the exhaust gas. The waste heat recovery system comprises a Rankine cycle engine, comprising: a heat exchanger configured to transfer heat energy from the exhaust gas expelled from the internal combustion engine to a working fluid; a pump configured to urge working fluid into the heat exchanger; and a heat engine configured to convert thermal energy contained in working fluid exiting the first heat exchanger into mechanical work. Controlling the waste heat recovery system based on the predicted properties of the exhaust gas comprises operating the pump to manipulate a temperature of working fluid exiting the heat exchanger and/or operating the heat engine to manipulate a pressure of working fluid exiting the heat exchanger.

By controlling the waste heat recovery system based on predicted properties of the exhaust gas, advantageously transient changes in those properties can be taken into account. This enhances control of the system compared with a more conventional approach in which the system is controlled based purely on the instantaneous state of the vehicle.

For example, the method of the invention may predict and adapt to a drop in temperature and flow rate of exhaust gas arising from the vehicle coming to rest, allowing the waste heat recovery system to continue to recover energy while the vehicle is stationary. In contrast, a conventional control approach based solely on vehicle state often cannot cope with step changes in exhaust properties and may have to cease energy recovery temporarily at such times.

The method may comprise operating the pump to maintain the temperature of working fluid exiting the heat exchanger above a value. This value may be a vaporisation temperature of the working fluid. Operating the pump may comprise reducing the flow rate of working fluid at an output of the pump which is in communication with an input of the heat exchanger.

The method may further comprise operating the heat engine to maintain the pressure of working fluid exiting the heat exchanger above a value. This may comprise restricting the amount of mechanical work converted by the heat engine.

The method may comprise optimising control of the waste heat recovery system using an optimisation algorithm. The optimisation algorithm may be based on model predictive control and may comprise a genetic algorithm, for example.

The route data may be indicative of a layout of a road defining the route along which the vehicle is expected to travel. For example, the route data may be indicative of at least one of the following characteristics of the road: a gradient of the road; a change in trajectory of the road, for example due to a bend in the road; a junction; and a speed restriction.

The route data is optionally indicative of meteorological conditions on the route along which the vehicle is expected to travel. For example, the route data may be indicative of a headwind incident on the vehicle. Precipitation and ambient temperature and pressure may also be indicated, for example.

At least some of the route data may be received from at least one of the following: a mapping system; a navigational system, for example an onboard GNSS system; a radar system; a camera system or a parking assistance system.

The driving data may comprise vehicle data, the vehicle data being indicative of one or more vehicle operating parameters. For example, the one or more vehicle operating parameters may comprise at least one of the group comprising: vehicle velocity; a currently-selected gear; an accelerator pedal position; a selected operating mode; a state of one or more auxiliary electrical systems; a state-of-charge of a vehicle battery; a quantity of fuel held in a fuel tank of the vehicle; and a braking state. In such embodiments, at least some of the driving data may be received from vehicle sensors.

Analysing the driving data may comprise supplying the driving data as an input to a vehicle model that simulates vehicle operation to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route.

The predicted properties of the exhaust gas may comprise a flow rate of the exhaust gas and/or a temperature of the exhaust gas. Together, these properties provide an indication of the energy content of the exhaust gas, which represents the potential energy recovery possible for the waste heat recovery system.

In some embodiments, the waste heat recovery system comprises a Rankine cycle engine, comprising: a heat exchanger configured to transfer heat energy from the exhaust gas expelled from the internal combustion engine to a working fluid; a pump configured to urge working fluid into the heat exchanger; and a heat engine configured to convert thermal energy contained in working fluid exiting the first heat exchanger into mechanical work.

In such embodiments, controlling the waste heat recovery system based on the predicted properties of the exhaust gas comprises controlling operation of at least one of the pump and the heat engine. For example, the method may comprise operating the pump to manipulate a temperature of working fluid exiting the heat exchanger. Alternatively, or in addition, the method may comprise operating the heat engine to manipulate a pressure of working fluid exiting the heat exchanger. In turn, manipulating the temperature and pressure of the working fluid that exits the heat exchanger dictates the rate at which mechanical work is generated by the heat engine, with pressure tending to have the greater influence.

Another aspect of the invention provides a controller configured to implement the method of the above aspect to control a waste heat recovery system of a vehicle.

Further aspects provide a computer program product comprising computer readable code for controlling a computing device to perform the method of the above aspect to control a waste heat recovery system of a vehicle, and a non-transitory computer readable medium comprising such a computer program product.

Yet another aspect provides a controller configured to control a waste heat recovery system of a vehicle, the waste heat recovery system being configured to recover thermal energy from exhaust gas expelled from an internal combustion engine of the vehicle. The controller comprises: an input configured to receive driving data comprising route data, the route data being indicative of characteristics of a route along which the vehicle is expected to travel; a processing module configured to analyse the driving data to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route; and a control module configured to control the waste heat recovery system based on the predicted properties of the exhaust gas. The waste heat recovery system comprises a Rankine cycle engine, comprising: a heat exchanger configured to transfer heat energy from the exhaust gas expelled from the internal combustion engine to a working fluid; a pump configured to urge working fluid into the heat exchanger; and a heat engine configured to convert thermal energy contained in working fluid exiting the first heat exchanger into mechanical work. The control module is configured to control the waste heat recovery system based on the predicted properties of the exhaust gas comprises the control module being configured to operate the pump to manipulate a temperature of working fluid exiting the heat exchanger and/or operate the heat engine to manipulate a pressure of working fluid exiting the heat exchanger.

The input for receiving driving data may comprise an electronic processor having an electrical input for receiving said driving data, and an electronic memory device electrically coupled to the electronic processor and having instructions stored therein.

The processing module may be configured to access the memory device and execute the instructions stored therein such that it is operable to analyse the driving data to predict properties of the exhaust gas expelled from the internal combustion engine.

In another aspect, the invention extends to a vehicle comprising: an internal combustion engine; a waste heat recovery system configured to recover thermal energy from exhaust gas expelled from the internal combustion engine; and the controller of the above aspect for controlling the waste heat recovery system.

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 like features are assigned like reference numerals, and in which:

Figure 1 is a schematic drawing of a vehicle including a waste heat recovery system that is suitable for use with embodiments of the invention;

Figure 2 schematically shows the waste heat recovery system of Figure 1 in more detail;

Figure 3 is a block diagram representing a known control architecture for the waste heat recovery system of Figure 1;

Figure 4 is a block diagram representing a control architecture according to an embodiment of the invention for the waste heat recovery system of Figure 1;

Figure 5 is a detail view of a vehicle model of the control architecture of Figure 4;

Figure 6 is a set of graphs showing a range of vehicle operating parameters over a simulated driving cycle;

Figure 7 is a further set of graphs showing a range of vehicle operating parameters over a further simulated driving cycle;

Figure 8 is a further set of graphs showing a range of vehicle operating parameters over a further simulated driving cycle;

Figures 9 to 10 show a series of plots representing an incremental process for determining a control input for the waste heat recovery system of Figure 1 based on predicted exhaust properties output by the vehicle model of Figures 4 and 5; and

Figure 11 is a flow diagram representing a process according to an embodiment of the invention for controlling the waste heat recovery system of Figure 1.

DETAILED DESCRIPTION

In general terms, embodiments of the invention make use of modelling techniques in combination with data relating to a vehicle’s driving environment to predict future engine load. Based on the predicted engine load, a waste heat recovery system such as an organic Rankine cycle engine can then be operated in a manner that anticipates transient loads and thereby increases energy recovery relative to a system that is controlled directly from instantaneous operating conditions.

The techniques that are used to predict forthcoming transient loads are considered in more detail later. First, a vehicle 1 that is suitable for use in embodiments of the invention is described with reference to Figure 1, to provide context for the invention.

The vehicle 1 shown in Figure 1 is a hybrid vehicle, although it is noted that embodiments of the invention are applicable to any type of vehicle.

In Figure 1, dashed lines illustrate communication pathways between vehicle systems and directional arrows represent the reuse of exhaust gas energy by each system in the vehicle 1.

The vehicle 1 includes an ICE 2 and an electric motor 4, each of which can provide propulsive power for the vehicle 1. The electric motor 4 can be driven by a battery 6, through an inverter (not shown), under the control of an electronic control unit (ECU) 8. In this manner, the electric motor 4 can provide propulsive power for the vehicle 1 alongside, or separately to, the ICE 2. For example, the ICE 2 and the electric motor 4 may be arranged in a parallel hybrid powertrain layout, which allows either simultaneous or separated power transmission from the ICE 2 and the electric motor 4 to road wheels of the vehicle 1.

The vehicle 1 further includes an exhaust system 10 that evacuates exhaust gasses from combustion chambers of the ICE 2 to the atmosphere. The exhaust system contains a catalytic converter 12, which converts pollutants within the exhaust gasses into more innocuous substances.

In the example shown in Figure 1, a WHR system 14 is positioned downstream of the catalytic converter 12. The WHR system 14 operates under the control of the ECU 8 to extract heat energy from the exhaust gasses, as they pass therethrough, and convert that heat energy into electrical energy that may be stored in the battery 6 or used directly to power the electric motor 4.

In the downstream position shown in Figure 1, the exhaust gasses have no subsequent use after exiting the WHR system 14 and so can be reduced to a minimum temperature by the WHR system 14, in turn maximising potential energy recovery.

In this instance, the electrical power demand at the WHR system 14 is determined by an energy management strategy, operated by the ECU 8, which optimises the contributions of propulsive power from the ICE 2 and the electric motor 4 to satisfy the thrust demand with minimal fuel consumption. In other variations, the power demand may depend on the power consumption of other electrical systems of the vehicle 1.

Figure 2 illustrates an embodiment of the WHR system 14 in more detail. The WHR system 14 includes a first heat exchange means in the form of a heat exchanger 16 that is configured to transfer heat energy from exhaust gasses in the exhaust system 10 to a working fluid within the WHR system 14, such as ethanol, to vaporise the working fluid.

The WHR system 14 further includes a heat engine in the form of a turbine 18 that expands vaporised working fluid received from the heat exchanger 16 to drive an electrical generator 20. In other embodiments the heat engine may take various other forms, including that of a reciprocating piston engine, and it may power a mechanical device, such as a flywheel or gearbox, as opposed to the electric generator 20. A second heat exchange means in the form of a condenser 22 is disposed downstream of the turbine 18 to condense the working fluid before it returns to the heat exchanger 16. The condenser 22 comprises a reservoir for collecting liquefied working fluid, and is connected to a heat sink in the form of a coolant circuit 24, to which heat energy is transferred from the working fluid.

In this embodiment, the coolant circuit 24 corresponds to a main vehicle coolant circuit that also delivers coolant fluid to the ICE 2. The engine coolant circuit 24 circulates an engine coolant fluid through the ICE 2 of the vehicle 1, a cooler 26 such as a conventional radiator, a coolant pump 28 and the condenser 22 of the WHR system 14. A pressure charging means in the form of a pump 30 is provided to pressurise the working fluid and generate circulatory flow within the WHR system 14.

The working fluid must be in gaseous form downstream of the heat exchanger 16 for it to be expanded by the turbine 18 to produce work and thereby recover energy. If the working fluid is not vaporised in the heat exchanger 16, for example because the energy flux through the exhaust system is insufficient during periods of idling, the working fluid must therefore be diverted around the turbine 18.

For this reason the WHR system 14 shown in Figure 2 also includes a bypass route around the turbine 18 in the form of a first bypass duct 32. A first valve 34, which is a three-way valve in this embodiment, is provided at a point at which the first bypass duct 32 intersects a flow path between the heat exchanger 16 and the turbine 18, to control flow of working fluid into the first bypass duct 32 and the turbine 18.

The WHR system 14 includes another bypass route, defined by a second bypass duct 36, which enables exhaust gas expelled from the ICE 2 to bypass the heat exchanger 16. A three-way second valve 38 is positioned at a point at which the second bypass duct 36 intersects a flow path between the ICE 2 and the heat exchanger 16, to control flow of exhaust gas into the bypass duct 36 and the heat exchanger 16.

Bypassing the heat exchanger 16 may be useful for controlling back pressure in the exhaust system 10, for example, or to protect components of the WHR system 14 at times when the temperature of exhaust gas entering the heat exchanger 16 is very high. The second bypass duct 36 also provides an auxiliary means of regulating the temperature of the working fluid in the WHR system 14 alongside control of the pump 30, in that controlling the second valve 38 to divert exhaust gas into the second bypass duct acts to reduce heat transfer into the heat exchanger 16, in turn lowering the temperature of working fluid exiting the heat exchanger 16.

The first and second valves 34, 38 are controlled by the ECU 8 and may be operated in dependence upon feedback measurements from various sensors (not shown). For example, the sensors include pressure, temperature, and volumetric flow rate sensors, used to measure the properties of the working fluid and/or exhaust gasses at various points in the circuit. The measured parameters are used to inform the ECU 8, which controls the system operation in response. The ECU 8 can control the first and second valves 34, 38, the pump 30, the condenser 22 and the heat exchanger 16 to match the exhaust load and meet the instantaneous power demand.

The skilled reader will appreciate that the components of the WHR system 14 described thus far correspond to the fundamental elements of an organic Rankine cycle engine, in which the heat exchanger 16 acts as a heat source and the condenser 22 acts as a heat sink.

The flow of working fluid during operation of the WHR system 14 will now be described in detail below.

In use, working fluid is collected, in a condensed form, in the reservoir of the condenser 22. The working fluid is drawn from the reservoir by the action of the pump 30 under the control of the ECU 8, which can adjust the flow rate in accordance with the predicted future engine load, for example, as shall be discussed later.

The working fluid passes downstream of the pump 30 in a pressure charged state and enters the heat exchanger 16. The working fluid flows through the heat exchanger 16 and exchanges heat with a counter-current flow of exhaust gas received from the ICE 2. As already noted, the exhaust gasses have already passed through the one or more catalytic converters 12 and thus the heat extracted at the heat exchanger 16 can be maximised without risking compromising operation of downstream components.

The heat exchanger 16 vaporises the working fluid by heating it to temperatures at and above the saturation temperature corresponding to the pressure of the working fluid. The ECU 8 operates the pump 30 to control the mass flow rate of working fluid and in turn manipulate the heat transfer at the heat exchanger 16. In this way, the pump 30 is operable to control the temperature of the working fluid.

If the pump 30 is controlled appropriately and sufficient thermal energy is present in the exhaust gas expelled from the ICE 2, the working fluid will be superheated in the heat exchanger 16 and therefore vaporised. Otherwise, the working fluid will exit the heat exchanger 16 still in liquid form.

Heated working fluid leaves the heat exchanger 16 and travels downstream towards the turbine 18.

If the working fluid is in a gaseous state, the first valve 34 is controlled to direct the working fluid into the turbine 18, where the working fluid is expanded to perform work on the electric generator 20, in turn generating electrical energy. The electrical energy is transferred according to the state of charge of the battery 6 and the power demand from the transmission system.

The working fluid cools significantly as it is expanded in the turbine 18, and its pressure may drop below atmospheric pressure. However, downstream of the turbine 18 the working fluid remains in a largely gaseous or vaporised state.

Alternatively, if the working fluid is not vaporised in the heat exchanger 16, for example because the pump 30 delivers working fluid to the heat exchanger 16 at a flow rate that is too high with respect to the thermal energy concurrently available from exhaust gas expelled from the ICE 2, the first valve 34 is controlled to direct the liquid working fluid exiting the heat exchanger 16 into the first bypass duct 32.

After passing through either the turbine 18 or the first bypass duct 32, working fluid travels onwards to the condenser 22 which is connected to the heat sink, namely the vehicle coolant circuit 24 in this embodiment. The working fluid passes through the condenser 22 and loses heat energy such that it condenses into a liquid and accumulates in the reservoir, thereby returning to its original condition.

Figures 4 and 5 represent elements of a control architecture that is incorporated into the ECU 8 to implement control of the WHR system 14 based on predicted engine load, and shall be described shortly.

First, by way of comparison Figure 3 shows a corresponding control architecture 40 for operating a Rankine cycle engine in the conventional manner based on present conditions as indicated by direct measurements.

Figure 3 shows an initial function, r(t), which represents the energy that is presently available from exhaust gas entering the heat exchanger 16 of the WHR system 14. Therefore, r(t) represents the maximum energy that can be recovered by the WHR system 14 at any given moment. R(t) may be derived using well-known principles from measurements of the exhaust gas mass flow rate and temperature, for example.

Function r(t) is received as an input to a conventional proportional-integral (PI) control algorithm 42, which uses the indicated energy available from exhaust gas alongside feedback data from the WHR system 14 to generate a control input for the WHR system 14, which is represented as function u(t). In particular, u(t) defines setpoints for the temperature and pressure of the working fluid of the WHR system 14 as it exits the heat exchanger 16.

As noted above, working fluid temperature in the WHR system 14 is adjusted using the pump 30, whereas working fluid pressure is manipulated through control of the turbine 18. Accordingly, the PI control algorithm 42 converts the temperature and pressure setpoints into operating parameters for the pump 30 and turbine 18 respectively.

Based on the indicated operating parameters, control commands are then generated for the pump 30 and for the turbine 18. These control commands are issued to the WHR system 14 to update its operation accordingly, which is reflected by the ‘WHR process’ block 44 in Figure 3.

Operation of the WHR system 14 produces an output energy recovery, namely the electrical power produced in the generator 20, which varies over time. This output is represented as y(t), and is the quantity that it is desirable to maximise.

Measurements are also gathered indicating the actual temperature and pressure of the working fluid exiting the heat exchanger 16. These measurements are used as feedback data for the PI control algorithm 42, which can refine the control input u(t) for the WHR system 14 accordingly using conventional feedback-loop control principles.

Thus, the conventional architecture 40 shown in Figure 3 implements control of the WHR system 14 based only upon instantaneous measurements of parameters of the exhaust gas entering the heat exchanger 16 and of the working fluid leaving the heat exchanger 16. The control architecture 40 can therefore only take a reactive approach to accommodating transient engine loads manifesting as step changes in the energy contained in the exhaust gas, and as already noted such an approach is limited in its effectiveness due to the inherent thermal inertia of the WHR system 14.

Moving on to Figure 4, a control architecture 50 according to an embodiment of the invention is shown in block diagram form to represent functional elements of the architecture 50. In this embodiment, the control architecture 50 is integrated with the ECU 8 of the vehicle 1, although in alternatives other control topologies are possible; for example, a dedicated controller for the WHR system 14 may be provided.

As in the conventional architecture of Figure 3, in the arrangement shown in Figure 4 the objective is to generate a control input u(t) for the WHR system 14 that dictates operation of components of the WHR system 14, in particular the turbine 18 and the pump 30 for control of the working fluid pressure and temperature respectively.

Indeed, the control input u(t) generated in the embodiment shown in Figure 4 may take the same form as that used in the conventional arrangement of Figure 3.

In this respect, the control input u(t) may take the form of a set of control commands, in which case the ECU 8 includes a control module configured to generate and issue the control commands.

Also similarly to the Figure 3 arrangement, operation of the WHR system 14 based on the control architecture 50 of Figure 4 is represented by a ‘WHR process’ block 44 that produces output recovered energy, which again is represented by the function y(t). In a further similarity, measurements of the temperature and pressure of working fluid exiting the heat exchanger 16 are used as feedback data in the control architecture 50 of Figure 4, as for the architecture of Figure 3.

However, a fundamental difference between the architectures shown in Figures 3 and 4 is that the architecture 50 of Figure 4 generates the control input u(t) for the WHR system 14 based not on direct measurements of the current vehicle state only, but on a predicted input, rp(t). The predicted input rp(t) represents the predicted properties of the exhaust gas over a time window defined ahead of the present moment during which the vehicle 1 is expected to traverse a particular route. In particular, the predicted properties of the exhaust gas include its temperature and mass flow rate. These properties in turn define the amount of energy that will be available for recovery by the WHR system 14.

By predicting the properties of exhaust gas over the forthcoming time window, the control architecture 50 can develop a control strategy that optimises operation of the WHR system 14 to account for changes in the energy available from the exhaust gas, and thereby maximise the average electrical power produced by the generator 20.

The predicted input is derived from driving data, e(t), which is gathered from a range of sources including vehicle sensors, GNSS systems, map data held in a memory of the ECU 8, park-assist systems comprising ultrasonic sensors, radar systems and vehicle-mounted cameras. The skilled reader will appreciate that vehicles may be equipped with other suitable apparatus that can provide useful driving data.

The driving data e(t) comprises vehicle data and route data. The vehicle data represents current vehicle operating parameters, and the route data provides information related to characteristics of a foreseeable section of road or route that the vehicle 1 will traverse during the defined time window.

To indicate the current driving state, the vehicle data element of the driving data typically includes signals indicative of the vehicle velocity and a currently-selected gear. Other indications that may be useful in this respect include an accelerator pedal position, a selected operating mode, the states of auxiliary electrical systems, a state-of-charge of the vehicle battery 6, a quantity of fuel held in a fuel tank of the vehicle 1, and a braking state, to name just a few. For example, sophisticated mapping systems may be able to provide an indication of headwinds based on weather forecasts and a direction of travel of the vehicle 1.

Regarding the characteristics of the route ahead of the vehicle 1, the route data element of the driving data e(t) may comprise GNSS data in combination with map data, which may indicate forthcoming corners or gradients in the road that would entail a predictable change in vehicle load based on the present velocity of the vehicle. Similarly, the driving data e(t) may include images acquired by on-board cameras to provide corresponding indications of the road layout ahead, whilst also indicating other possible causes of changes to vehicle load, such as traffic conditions, obstacles in the road or wet or icy road surface conditions.

Further characteristics of the route along which the vehicle 1 is expected to travel that may be indicated by the route data include changes in speed limit and indicators of expected breaks in the journey such as the presence of a service station in the vicinity of the vehicle 1.

For example, if the vehicle 1 has been in motion for a period exceeding a threshold and satellite data identifies a nearby service station on or near the expected route, the ECU 8 may determine that there is a high likelihood that the vehicle 1 will stop for an extended period of time and thus prepare the WHR system accordingly. For example, it may be advantageous to fully charge the battery 6 by maximising energy recovery before the stop, so that the electric motor 4 can be used to accelerate the vehicle 1 to a desired speed when re-joining a motorway.

Similarly, it may be useful to use electric drive and discharge the battery 6 fully ahead of an anticipated long motorway segment, which will allow a full recharge of the battery 6 from waste heat recovery.

Similar principles can be applied if the fuel level is low and a nearby petrol station is identified, thereby indicating a likely stop.

The driving data e(t) therefore provides a means for predicting the behaviour of the vehicle 1 over the course of the time window, based on its present behaviour and state and factors that may provoke changes to that behaviour. In turn, the engine load and resulting exhaust gas properties over the same time window can be predicted.

An example of a system that can provide driving data such as described above is the ‘eHorizon’ system by Continental™.

The driving data e(t) is input to a vehicle model 52, which is a functional block defining a processing module within the ECU 8 that analyses the driving data e(t). Said analysis takes the form of simulating behaviour of vehicle systems based on the predicted vehicle behaviour as indicated by the driving data e(t), to determine the properties of exhaust gas entering the heat exchanger 16 and thereby generate the predicted input rp(t).

In other embodiments, the vehicle model 52 may be hosted by a separate control module that supplies predicted exhaust gas properties to the ECU 8. In such arrangements, the ECU 8 and the separate control module may be considered to form a control system for controlling the WHR system 14.

The vehicle model 52 is shown in more detail in Figure 5, which indicates that the driving data e(t) is processed in a series of stages 54 that progressively calculate the expected temperature and mass flow rate of exhaust gas into the heat exchanger 16.

The initial stages 54 of the model 52 make adjustments to the driving data, for example to crop it to a desired time window and to apply compensation factors to account for driving resistance arising from headwinds and road surface type.

Subsequent stages 54 of the model 52 represent respective aspects of vehicle operation. For example, the behaviour of the transmission based on the current gear and any expected gear changes based on the driving data e(t) is determined first, after which the engine output based on the selected gear and vehicle load can be determined with reference to engine maps held by the ECU 8, accounting also for the state of auxiliary systems that place additional load on the ICE 2.

Once the expected engine output is known, the influence of the engine cooling system 24 is taken into account to determine the temperature of exhaust gas leaving the ICE 2. Finally, the vehicle model 52 includes a simulation of the exhaust gas path, which is used to determine the reduction in temperature and pressure of the exhaust as it flows between the ICE 2 and the heat exchanger 16, thereby producing estimates for the temperature and mass flow rate of exhaust gas into the heat exchanger 16.

The vehicle model 52 then applies post-processing algorithms to the calculated measurements to give final predicted values for the mass flow rate and temperature of exhaust gas entering the heat exchanger 16. The vehicle model 52 also takes into account the power consumption of the ICE 2 and the WHR system 14 and determines the power required by the vehicle 1 accordingly.

It is noted that, in contrast to the arrangement shown in Figure 3 in which the input r(t) includes only the current value for the temperature and mass flow rate of exhaust gas, the predicted input rp(t) used in the embodiment of Figure 4 defines a set of values for these properties of the exhaust gas over the defined time window.

Returning to Figure 4, once the vehicle model 52 has generated predicted values for the mass flow rate and the temperature of exhaust gas that will flow into the heat exchanger 16 during the defined time window, these values are supplied to an optimiser 56 that is based on a prediction model that is able to process the series of values for the temperature and mass flow rate respectively. This enables the optimiser 56 to develop a control strategy that maximises energy recovery by the WHR system 14 in accordance with expected future events, and generate the control input u(t) based on this strategy to adjust operation of the WHR system 16 accordingly.

In contrast, a conventional PI control algorithm cannot process a series of values over a defined time window; it is only capable of handling current values for each variable representing the present vehicle state. A PI control algorithm therefore has no capacity to account for expected future events.

In this embodiment the optimiser 56 is based on model predictive control (MPC), which is well known for use in process industries but is relatively untested in the automotive sector.

In this embodiment, MPC is implemented using a genetic algorithm of a kind that will be familiar to the skilled person, which was selected based on the results of a benchmarking exercise. However, other optimisation algorithms may be used in alternative embodiments, dynamic programming for example.

To illustrate the impact of the optimiser 56 in control of the WHR system 14, Figure 6 shows three graphs 56, 58, 60 stacked vertically, each plotting models of different aspects of vehicle behaviour over a simulated time period during which the vehicle 1 is modelled as undertaking a typical driving cycle involving both urban and extra-urban driving.

The uppermost graph 60 plots the velocity of the vehicle 1 during the simulated driving cycle, which exhibits frequent changes within a range of 0 km/h to approximately 130 km/h. Two periods in which the vehicle 1 is stationary are of particular interest, as vehicle stops present a particular challenge to conventional control implementations. These appear at around 1000 seconds and 1450 seconds respectively in the example shown in Figure 6.

The middle graph 58 shows two plots of the pressure of working fluid entering the turbine 18 of the WHR system 14: one, shown as a dashed line, for a scenario in which a setpoint for the temperature of the working fluid was fixed at 300°C; and another, shown as a solid line, for a scenario where a setpoint for the working fluid temperature was adjusted by the optimiser 56 of the control architecture 50 of Figure 4.

The lowermost graph 60 shows two plots corresponding to those of the middle graph 58, but representing the temperature of the working fluid entering the turbine 18 instead of the pressure. A warm-up period 62 for the WHR system 14 is evident up to 600 seconds into the driving cycle, before which the temperature and pressure plots remain low for both scenarios. This reflects the fact that the WHR system 14 is not activated until the ICE 2 has had time to warm to its operational temperature so that exhaust gas entering the heat exchanger 16 contains sufficient energy to vaporise the working fluid of the WHR system 14 and support stable operation of the WHR system 14. Once activated, the pump 30 is operated to restrict working fluid flow, to achieve boiling conditions in the heat exchanger 16 as quickly as possible.

Following this, for both scenarios the temperature and pressure of the working fluid rise as the WHR system 14 begins to recover energy. It is notable that although all of the temperature and pressure plots fluctuate, the plots corresponding to the scenario where the temperature setpoint was constant exhibit significantly more fluctuation than the corresponding plots for the optimised system, which are much more stable in comparison.

As noted above, the periods during which the vehicle 1 was stationary are of particular interest because they illustrate one of the main advantages of the optimised approach, namely the ability to cope with step changes in exhaust gas energy resulting from idling of the ICE 2 when the vehicle 1 stops moving.

The plots corresponding to the fixed temperature setpoint approach plummet each time the vehicle 1 stops. This indicates that the system is unable to cope with the step changes in exhaust energy flux, and as a result the working fluid is not vaporised during those periods. In turn, the WHR system 14 reverts to its warm-up state and so the turbine 18 must be bypassed temporarily, meaning that no energy is recovered while the vehicle 1 is stationary for that scenario.

In contrast, for the optimised approach the temperature and pressure of the working fluid remain much closer to their respective long-term average values during the periods when the vehicle 1 is stationary. Therefore, the WHR system 14 continues to recover energy during those periods, because the working fluid temperature remains high enough to indicate that it is vaporised downstream of the heat exchanger 16. This is because the optimiser 56 anticipates that the vehicle 1 is going to come to rest based on the predicted input, and adjusts the control input to the WHR system 14 accordingly.

In this example, the changes made by the optimiser 56 manifest as holding of pressure of the working fluid before and after the vehicle 1 stops on each occasion, which is achieved through appropriate control of the turbine 18. As controlling the turbine 18 to restrict flow of working fluid, and thereby raise or hold its pressure, decreases the power produced by the generator, this strategy entails a short-term reduction in energy recovery prior to a vehicle stop. However, the ability to continue recovering energy while the vehicle 1 is stationary and avoid reverting to the warm-up state provides an overall improvement in efficiency over the course of the driving cycle.

In general terms, during normal operation while the ICE 2 is not idling, the optimiser 56 acts to minimise the temperature of the working fluid as it exits the heat exchanger 16, whilst ensuring that the temperature remains sufficiently high for the working fluid to be vaporised. This in turn maximises the energy that can be recovered, because a lower temperature entails a higher flow rate of working fluid through the turbine 18, which in turn increases the electrical power produced by the generator 20.

However, ahead of a vehicle stop event, a temperature setpoint is raised to combat the cooling effect that would otherwise arise as a result of the diminished exhaust gas temperature and flow rate. Since raising the temperature setpoint manifests in controlling the pump 30 to produce a lower flow rate of working fluid through the heat exchanger 16, a drop in exhaust gas energy flux has less of an impact than it would if the working fluid flow rate were high.

Whenever making adjustments, the optimiser 56 acts to account for the respective time constants associated with the temperature and the pressure of the working fluid, and thereby enables these parameters to be controlled more effectively against transient loads. In practice, this is achieved by adjusting setpoints for these parameters in a dynamic manner in accordance with the predicted exhaust properties.

Although raising the temperature and pressure of the working fluid in this way temporarily compromises energy recovery, by enabling the WHR system 14 to continue to recover energy during periods of engine idling the optimised approach provides a net gain in energy recovery over the course of the driving cycle shown in Figure 6.

In the example shown in Figure 6, it was found that the optimized approach provided a 3.1% improvement in overall fuel consumption compared to an equivalent vehicle that does not include the WHR system 14. In contrast, the approach in which the temperature setpoint was fixed provided a 2.3% improvement in fuel consumption. Thus, the optimiser 56 creates a significant improvement in overall efficiency relative to the conventional control approach. A further example of how the invention can optimise waste heat recovery is illustrated in Figure 7, which shows four graphs 63, 64, 65, 66. As with Figure 6, each graph plots a model of a different aspect of vehicle behaviour over a simulated time period during which the vehicle 1 is modelled as undertaking a typical driving cycle.

Graph 63 plots the velocity of the vehicle 1 during the simulated driving cycle. Two time periods of the drive cycle, labelled ti to t2 and t3 to t4 in figure 7, will be discussed further below.

Graph 64 shows two plots of the pressure of working fluid entering the turbine 18 of the WHR system 14: one, shown as a solid line, for a scenario in which a setpoint for the pressure of the working fluid is generated according to a conventional control architecture such as that shown in Figure 3; and another, shown as a dashed line, for a scenario where a setpoint for the working fluid pressure was adjusted by the optimiser 56 of the control architecture 50 of Figure 4.

Similarly, graph 65 shows two plots of the temperature of the working fluid entering the turbine 18 of the WHR system 14: one, shown as a solid line, for a scenario in which a setpoint for the temperature of the working fluid is generated according to the conventional control architecture; and another, shown as a dashed line, for a scenario where a setpoint for the working fluid temperature was adjusted by the optimiser 56.

Graph 66 shows plots showing the power output of the generator 20, i.e. the energy produced by the generator 20, over the simulated time period for each of: the setpoints generated according to the conventional architecture, and the setpoints adjusted by the optimiser 56.

As mentioned above, the graphs of figure 7 show two time periods of interest; during the period ti to t2 the vehicle is accelerating, and during the period t3 to t4 the vehicle decelerates before coming to rest. Between t4 and ti the vehicle is at rest. As will be understood by the relevant skilled person, the period of acceleration between ti and t2 corresponds to a period during which the energy available in the exhaust gas exiting the ICE 2 for recovery by the waste heat recovery system 14 is higher than the energy available when the vehicle is at rest.

With the present technique, prior to the period of acceleration, between t3 and ti, the optimiser 56 outputs the set points for the working fluid pressure and temperature, such that the pressure and temperature are maintained above respective values. This is shown in graphs 64 and 65 of figure 7. These values are selected such that the working fluid is in a gaseous state at ti, and remains in a gaseous state between ti and t2. The working fluid can therefore be expanded by the turbine 18 to produce work throughout the entire period of acceleration. The energy available in the exhaust gas during the period of acceleration used to increase the pressure of the gaseous working fluid, which in turn increases the pressure differential across the turbine 18 and therefore the amount of energy generated by the generator 20.

As described earlier, maintaining the pressure of the working fluid entering the turbine 18 above a value is achieved through appropriate control of the turbine 18 to restrict flow of working fluid. Restricting the flow of working fluid through the turbine 18 will have the effect of reducing the rate at which the pressure of the working fluid upstream of the turbine 18 decreases compared to when the flow through the turbine 18 is unrestricted. This is demonstrated, for example, by the greater negative gradient of the solid line compared to the dashed line in graph 64 between t4 and ti. Restricting flow through the turbine may be achieved by any suitable means, for example by applying a negative torque to the shaft of the turbine 18 through mechanical braking means, or by increasing the load on the generator 20 through increasing electrical resistance.

Also as described earlier, maintaining the temperature of the working fluid above a value may entail controlling the pump 30 to produce a lower flow rate of working fluid through the heat exchanger 16. Lowering the flow rate of working fluid through the heat exchanger will increase the length of time over which heat transfer from the exhaust gas to the working fluid will take place, thereby increasing the temperature of the working fluid downstream of the heat exchanger 16.

In contrast, the solid lines of graphs 64 and 65 show the pressure and temperature of the working fluid falling below the respective values during the period in which the vehicle is at rest in the case of the conventional control architecture. As such, the working fluid is in a liquid state at ti and therefore cannot be passed through the turbine 18 to produce work. The energy in the exhaust gas during a first part of the period from ti to t2 must therefore be used to vaporise the working fluid, instead of being converted to electrical energy by the generator 20 as is the case with the present technique. Therefore, for the time period ti to t2, more energy is generated by the waste heat recovery system when the pressure and temperature set points are generated by the optimiser 56 when compared with set points generated by a conventional control architecture.

The pressure and temperature set points generated by the optimiser 56 may be selected from a predetermined map of the relationship between pressure and temperature for the gaseous phase of the particular fluid selected as the working fluid.

It can be seen from graph 66 that the power output of the generator 20 over the period t3 to t4 is actually higher when the working fluid pressure and temperature set points are generated by the conventional control architecture compared to when the set points are generated by the optimiser 56. This is because when the generator 20 is operated according to the optimiser set points during the period t3 to t4, it is operated at a reduced power output so as to maintain the pressure of the working fluid above a value as described above. As such, the waste heat recovery system 14 operated in accordance with the optimiser 56 acts to restrict the amount of energy generated during the time period t3 to t4 in favour of maintaining the pressure of the working fluid above a value so as to generate a greater amount of energy during the period of acceleration ti to t2. This has the advantage of increasing the net amount of energy generated over the simulated drive cycle. This is demonstrated by graph 66.

Another example of a method according to the invention is shown in figure 8. Figure 8 has a first graph 67a which plots the velocity of the vehicle 1 during a simulated driving cycle, and a corresponding second graph 67b showing two plots of the temperature of the working fluid entering the turbine 18 of the WHR system 14: a first plot 67c for a scenario in which a setpoint for the temperature of the working fluid is generated according to a conventional control architecture such as that shown in Figure 3; and a second plot 67d for a scenario where a setpoint for the working fluid temperature was adjusted by the optimiser 56 of the control architecture 50 of Figure 4.

Also shown in figure 8 are two sets of time periods: a first set of time periods 68 (illustrated by a solid line) in which the vehicle is decelerating and a second set of time periods 69 (illustrated by a dashed line) in which the vehicle is accelerating. It can be seen from the second plot 67d in the second graph 67b that the temperature of the working fluid is maintained above a value, in a similar manner to that described above with reference to figure 7, after a period of deceleration in anticipation of a period of acceleration. This ensures that the working fluid is in a gaseous state throughout the entire period of acceleration, again, in much the same way as described above, so as to maximise the amount of energy recovered by the waste heat recovery system.

Figures 9 to 11 illustrate the iterative, finite-horizon optimisation of the control of the WHR system 14 implemented by the optimiser 56.

Figure 9 includes: an upper plot 70 that represents the predicted input rp(t) over a time window A, spanning from ti to tn, which defines a finite future horizon for the optimiser 56; and a lower plot 72 representing the control input u(t) generated by the optimiser 56 based on the predicted input rp(t) for a shorter time period spanning from ti to t2.

The control input u(t) generated for the period between ti and t2 is determined to maximise the electrical power produced by the generator 20 of the WHR system 14 over the time window A.

Therefore, in accordance with the principles of MPC, the optimiser 56 generates a control input u(t) for a time period ahead of the present moment that is significantly shorter than the time window for which predicted data is available from the vehicle model 52. This minimises the impact of uncertainty in the predicted vehicle behaviour.

Figure 10 shows an upper plot 74 and a lower plot 76, which correspond to their counterparts in Figure 9, but relate to a subsequent step in the iteration of the MPC algorithm executed by the optimiser 56, in which the time window A has shifted to the left to commence at t2 and the control input u(t) is generated for a subsequent time period spanning from t2 to t3. In this case, the control input u(t) is generated based on the updated time window A, and the initial conditions at t2, namely the current state of the vehicle 1 and the WHR system 14. This illustrates how the optimiser 56 progresses the iteration over time.

This process is repeated over a series of further iterations, as represented in Figure 11, which shows a further pair of plots 78, 80 that trace the predicted vehicle behaviour and the corresponding control input u(t) over a longer period. It is clear from this representation that the control input u(t) fluctuates less than the predicted input r(t), which illustrates the capability of the optimiser 56 to maintain relatively steady control of the WHR system 14 even when the energy available from exhaust gas varies greatly.

Figure 12 is a flow diagram showing a process 90 that summarises the above described procedure for controlling the WHR system 14 using a predictive model to account for expected future events. As already noted, in this embodiment the process 90 is performed by the ECU 8, although other control architectures may be implemented in other embodiments.

The process 90 begins with the ECU 8 receiving at step 92 driving data eft) that indicates a present driving state of the vehicle 1 along with details of a foreseeable section of road that the vehicle 1 is expected to traverse in a time window commencing from the present moment.

The driving data eft) is passed to the vehicle model 52, which processes the data to predict at step 94 properties of the exhaust gas entering the heat exchanger 16 of the WHR system 14 over the course of the time window, in particular the temperature of the exhaust gas and its mass flow rate.

The predicted exhaust gas properties are then passed to the optimiser 56, which implements MPC to generate a control input uft) for the WHR system 14 that defines a control strategy for the WHR system 14 based on the predicted exhaust gas properties.

Generating the control input uft) initially entails determining at step 96 setpoints for the temperature and pressure of the working fluid of the WHR system 14, which in turn dictates setpoints for the pump 30, the turbine 18, and other components of the WHR system 14.

Then, control commands are generated based on the setpoints, and issued at step 98 to the respective components of the WHR system 14 to implement the control strategy determined by the optimiser 56 to account for predicted changes in exhaust gas energy flux.

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, although the embodiments of the invention described above are applied to a WHR system comprising a Rankine cycle engine, in other embodiments predictive modelling techniques may be used to optimise operation of other types of WHR system.

Claims

1. A method of controlling a waste heat recovery system of a vehicle, the waste heat recovery system being configured to recover thermal energy from exhaust gas expelled from an internal combustion engine of the vehicle, the method comprising: receiving driving data comprising route data, the route data being indicative of characteristics of a route along which the vehicle is expected to travel; analysing the driving data to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route; and controlling the waste heat recovery system based on the predicted properties of the exhaust gas; wherein the waste heat recovery system comprises a Rankine cycle engine, comprising: a heat exchanger configured to transfer heat energy from the exhaust gas expelled from the internal combustion engine to a working fluid; a pump configured to urge working fluid into the heat exchanger; and a heat engine configured to convert thermal energy contained in working fluid exiting the first heat exchanger into mechanical work; and wherein controlling the waste heat recovery system based on the predicted properties of the exhaust gas comprises operating the pump to manipulate a temperature of working fluid exiting the heat exchanger and/or operating the heat engine to manipulate a pressure of working fluid exiting the heat exchanger.

2. The method of claim 1, comprising operating the pump to maintain the temperature of working fluid exiting the heat exchanger above a value.

3. The method of claim 2, wherein the value above which the temperature of working fluid exiting the heat exchanger is maintained is a vaporisation temperature of the working fluid.

4. The method of claim 2 or claim 3, wherein operating the pump comprises reducing the flow rate of working fluid at an output of the pump, said output being in communication with an input of the heat exchanger.

5. The method of any preceding claim, comprising operating the heat engine to maintain the pressure of working fluid exiting the heat exchanger above a value.

6. The method of claim 5, wherein operating the heat engine to maintain the pressure of working fluid exiting the heat exchanger above a value comprises restricting the amount of mechanical work converted by the heat engine.

7. The method of any preceding claim, comprising optimising control of the waste heat recovery system using an optimisation algorithm, wherein the optimisation algorithm comprises a genetic algorithm and/or wherein the optimisation algorithm is based on model predictive control.

8. The method of any preceding claim, wherein the route data is indicative of a layout of a road defining the route along which the vehicle is expected to travel.

9. The method of claim 8, wherein the route data is indicative of at least one of the following characteristics of the road: a gradient of the road; a change in trajectory of the road; a junction; and a speed restriction.

10. The method of any preceding claim, wherein the route data is indicative of meteorological conditions on the route along which the vehicle is expected to travel and wherein optionally the route data is indicative of a headwind incident on the vehicle.

11. The method of any preceding claim, wherein at least some of the route data is received from at least one of the following: a mapping system; a navigational system; a radar system; a camera system or a parking assistance system.

12. The method of any preceding claim, wherein the driving data comprises vehicle data, the vehicle data being indicative of one or more vehicle operating parameters.

13. The method of claim 12, wherein the one or more vehicle operating parameters comprise at least one of the group comprising: vehicle velocity; a currently- selected gear; an accelerator pedal position; a selected operating mode; a state of one or more auxiliary electrical systems; a state-of-charge of a vehicle battery; a quantity of fuel held in a fuel tank of the vehicle; and a braking state.

14. The method of any preceding claim, wherein analysing the driving data comprises supplying the driving data as an input to a vehicle model that simulates vehicle operation to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route.

15. The method of any preceding claim, wherein the predicted properties of the exhaust gas comprise a flow rate of the exhaust gas and/or a temperature of the exhaust gas.

16. A controller configured to implement the method of any preceding claim to control a waste heat recovery system of a vehicle.

17. A computer program product comprising computer readable code for controlling a computing device to perform a method according to any of claims 1 to 15 to control a waste heat recovery system of a vehicle.

18. A non-transitory computer readable medium comprising the computer program product of claim 17.

19. A controller configured to control a waste heat recovery system of a vehicle, the waste heat recovery system being configured to recover thermal energy from exhaust gas expelled from an internal combustion engine of the vehicle, the controller comprising: an input configured to receive driving data comprising route data, the route data being indicative of characteristics of a route along which the vehicle is expected to travel; a processing module configured to analyse the driving data to predict properties of the exhaust gas expelled from the internal combustion engine while the vehicle travels along the route; and a control module configured to control the waste heat recovery system based on the predicted properties of the exhaust gas; wherein the waste heat recovery system comprises a Rankine cycle engine, comprising: a heat exchanger configured to transfer heat energy from the exhaust gas expelled from the internal combustion engine to a working fluid; a pump configured to urge working fluid into the heat exchanger; and a heat engine configured to convert thermal energy contained in working fluid exiting the first heat exchanger into mechanical work; and wherein the control module being configured to control the waste heat recovery system based on the predicted properties of the exhaust gas comprises the control module being configured to operate the pump to manipulate a temperature of working fluid exiting the heat exchanger and/or operate the heat engine to manipulate a pressure of working fluid exiting the heat exchanger.

20. A vehicle comprising: an internal combustion engine; a waste heat recovery system configured to recover thermal energy from exhaust gas expelled from the internal combustion engine; and a controller according to claim 16 or claim 19 for controlling the waste heat recovery system.