WO2014064484A1

WO2014064484A1 - Vehicle comprising a rankine system

Info

Publication number: WO2014064484A1
Application number: PCT/IB2012/002684
Authority: WO
Inventors: Nicolas Espinosa; Jean Baptiste MALEGUE; Lionel Simon
Original assignee: Renault Trucks
Priority date: 2012-10-23
Filing date: 2012-10-23
Publication date: 2014-05-01

Abstract

The vehicle (1) comprises: - a chassis (2) having an average plane (P) which is substantially horizontal when the vehicle is on a substantially horizontal ground; - an internal combustion engine (4) and an exhaust line (12) collecting exhaust gases from said engine; - a Rankine system (13), comprising a tank (15) for a working fluid, said working fluid flowing in a loop and being successively evaporated in a heat exchanger (16) by heat exchange with the exhaust gases, expanded in an expander (17), condensed in a condenser (18) and compressed in a pump (19). With respect to a direction (Z) that is substantially orthogonal to the chassis average plane (P), the condenser (18) is installed higher than the tank (15), and the tank (15) is installed higher than the pump (19).

Description

VEHICLE COMPRISING A RA KINE SYSTEM

Field of the invention The present invention relates to a vehicle comprising a Rankine system.

Technological background For many years, attempts have been made to improve the efficiency of internal combustion engines of vehicles, which has a direct impact on fuel consumption.

For this purpose, it has long been proposed to provide vehicles with an engine arrangement equipped with a waste heat recovery system, i.e. a system making use of the thermal energy which is contained in hot exhaust gases or in other engine fluids and which would otherwise be lost.

One example of a waste heat recovery system is a Rankine system, which comprises a circuit in which a working fluid flows in a closed loop and undergoes successive processes according to the Rankine thermodynamic cycle:

- the working fluid, which is a liquid at this stage, is pumped, i.e. compressed, from low to high pressure;

- the high pressure working liquid is evaporated into a working gas by the heat source, for example by the exhaust gases;

- the working gas is expanded in an expander;

- finally, the working gas is condensed in a condenser.

As a result, at least part of the thermal energy of the heat source used to evaporate the working fluid is recovered in the expander under the form mechanical energy. It is conventional to transform that mechanical energy into electricity thanks to a generator driven by the expander, but it is also known to mechanically connect an output shaft of the expander to the driveline of the vehicle so that the energy recovered in the expander is re-used directly in mechanical form to assist in propelling the vehicle.

However, in practice, the implementation of a Rankine system on a vehicle presents a number of problems. For example, it was found that various problems could arise during the Rankine system operation, and more precisely during the starting of the system, due to a non-optimal arrangement of the various components. In particular, the pump may not start properly, and/or some working fluid can be trapped in specific places of the system, thereby impacting the correct operation of the system.

It therefore appears that vehicles comprising a Rankine system are not fully satisfactory and could be improved. Summary

It is an object of the present invention to provide an improved vehicle comprising a Rankine system which can overcome some drawbacks of the prior art, especially in view of Improving the operation of the Rankine system during the start and in steady state.

According to the invention such a vehicle comprises:

- a chassis having an average plane which is substantially horizontal when the vehicle is on a substantially horizontal ground;

- an internal combustion engine installed on the chassis and an exhaust line capable of collecting exhaust gases from said engine;

- a Rankine system comprising a tank for a working fluid, and designed to carry said working fluid in a loop, in which said working fluid can be successively evaporated in a heat exchanger by heat exchange with the exhaust gases, expanded in an expander, condensed in a condenser and compressed in a pump.

Moreover, with respect to a direction that is substantially orthogonal to the chassis average plane, the condenser is installed on the vehicle higher than the tank, and the tank is installed on the vehicle higher than the pump.

Positioning the tank higher than the pump ensures than enough working fluid is provided to the pump when said pump is started, for an effective pump priming.

Furthermore, positioning the condenser higher than the tank allows the working fluid located in the condenser to naturally return to the tank, and thus to be provided to the pump when said pump is started. Indeed, when the Rankine system is not in use, the working fluid tends to condense in the condenser, insofar as it is the coolest place of the circuit. Therefore, thanks to the invention, the working fluid that would tend to accumulate in the condenser can flow towards the pump by gravity, which is favourable especially for stat-up phases. Therefore, the invention is particularly critical for a Rankine system installed on a vehicle since the system will experience frequent stop and start phases, connected to the vehicle operation which is by nature much subject to repeated start and stop cycles.

In concrete terms, the direction that is substantially orthogonal to the chassis average plane is substantially vertical when the vehicle is on a substantially horizontal ground.

In practice, the various components of the Rankine system are not necessarily arranged in alignment along said direction, i.e. not necessarily located directly one above the others. According to the invention, the projection of said components on said direction are arranged at the above mentioned respective heights, i.e. the condenser projection is higher than the tank projection, and the tank projection is higher than the pump projection on said direction.

Besides, these components can be arranged on the vehicle chassis far away from one another, provided the requirements on the respective heights are met. For example, the condenser may be located at the front part of the vehicle while the pump is located at the rear part of the vehicle.

The term "vehicle" embraces all types of vehicles, including industrial vehicles, trucks, construction equipment machines such as excavators, loaders, haulers, compactors etc.

These and other features and advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as a non-limiting example, an embodiment of a vehicle according to the invention.

Brief description of the drawings

The following detailed description of an embodiment of the invention is better understood when read in conjunction with the appended drawings, it being however understood that the invention is not limited to the specific embodiment disclosed.

Figure 1 is a schematic representation of a vehicle comprising a Rankine system according to an embodiment the invention; Figures 2 and 3 are views of an embodiment of the Rankine system of Figure 1 , respectively in perspective and in side view;

Figure 4 is a perspective view of the Rankine system of Figure 2 installed on a vehicle chassis.

Detailed description

As this is schematically and partially illustrated in Figure 1 , a vehicle 1 , such as a truck, comprises a chassis 2 which has an average plane P which is substantially horizontal when the vehicle 1 is on a substantially horizontal ground. As shown in Figure 4, the chassis 2 can typically comprise two lateral beams 3 extending longitudinally and connected by transverse bars (not shown).

The direction that is substantially orthogonal to the chassis average plane is defined as "Z", bearing in mind that said direction Z is not necessarily vertical, depending on whether the vehicle 1 is on a substantially horizontal ground or not.

The vehicle 1 further comprises an internal combustion engine 4 installed on the chassis 2. The engine 4 is able to drive the drive wheels 5 of the vehicle 1 , which partly support the chassis 2, through a driveline 6. The driveline 6 can include mainly a clutch 7, a gearbox 8, a propulsion shaft 9, and at least one drive axle comprising for example a differential 10 and a drive shaft 11 for each of a left and of a right drive wheel 5.

An exhaust line 12 is provided for collecting the exhaust gases from the engine 4, i.e. the gases which result from the combustion in the engine.

The vehicle 1 is also equipped with a Rankine system 13. The system 13 is preferably installed on the chassis 2. The Rankine system 13 comprises a circuit 14 forming a loop and including a tank 15 for a working fluid. In said circuit 14, the working fluid is successively evaporated in a heat exchanger 6 by heat exchange with the exhaust gases flowing in the exhaust line 12, expanded in an expander 17, condensed in a condenser 18, and compressed in a pump 19. The engine exhaust gases could be exhaust gases circulating in a recirculation circuit for being fed to the engine intake. Other heated engine fluids could also be used as heat source for the Rankine system. The Rankine system could have several heat exchangers where the working fluid would be heated successively by several different engine heated fluids.

More specifically, the vehicle 1 can comprise an exhaust directional valve 20 located in the exhaust line 12 and capable of directing part of the exhaust gases towards the heat exchanger 16, which here is an evaporator. The rest of the exhaust gases continue in the exhaust line without flowing through the heat exchanger 16. Owing to the high temperature of the exhaust gases which flow in the heat exchanger 16, the working fluid is evaporated into a gas.

By acting on the exhaust directional valve, it is possible to control the amount of gases directed to the heat exchanger and to by-pass partly or totally the heat exchanger 16 for limiting the amount of heat that is provided to the Rankine system 13. Such strategy may be used especially when the cooling capacity of the vehicle 1 is not high enough to cool the working fluid in the condenser 18, or when, to match the required cooling capacity, it would be necessary to actuate an engine driven or electrically driven fan.

The line 21 of circuit 14 which connects the heat exchanger 16 and the expander 17 can include a valve 22 capable of directing all or part of the working fluid flow in a by-pass line 23 of the expander 17, typically for the starting or shut down phases of the Rankine system 13. The expander may be a Pelton turbine, but other types of expanders can be used, such as a centrifugal turbine, a screw expander, a piston expander, etc...

Downstream from the expander 17, the gas is condensed in the condenser 18. The condenser 18 can be arranged at the front part of the vehicle 1 , so that the working fluid can be condensed by heat exchange with ambient air moving through the condenser due to the vehicle motion.

Alternatively, as depicted in the figures, the condenser 18 can be designed to condense the working fluid by heat exchange with the engine cooling fluid, or another relatively low temperature circuit. In this embodiment, the condenser 18 is thus an indirect condenser arranged on a portion of the engine cooling circuit 24. The working fluid can be ethanol, while the engine cooling fluid can be a mixture of water and glycol. Nevertheless, other working fluids could be used, for example water, a refrigerant fluid such as rf245fa, etc... Also, other engine cooling fluids could be used

This embodiment is advantageous in that it does not require the condenser 18 to be arranged at the front part of the vehicle 1 , where only limited space is generally available. Moreover, such an arrangement does not require long pipes in the working fluid circuit 14 between the front part of the vehicle 1 and the other components of the Rankine system 13, which can be located at the median or even the rear part of the vehicle 1 , since the condenser 18 can be located closer to these other components. Furthermore, condensing the working fluid with this implementation may allow reducing the size of the condenser since the cooling agent is a liquid rather than air.

Besides, this can improve the Rankine system efficiency and avoid the necessity to deactivate it. Indeed, in some operating conditions, the cold provided by ambient air moving through a condenser located at the front part of the vehicle is not enough to cool and condensate the working fluid. This can typically happen at high loads, and/or when outside air temperature is fairly high. In this case, in order to prevent the working fluid from overheating or from reaching too high pressure levels, or to prevent the activation of the vehicle fan in order to provide additional cold to the condenser, which would have negative consequences on the overall energy consumption of the vehicle, the Rankine system can need to be deactivated. This drawback can be avoided or at least minimized with the illustrated arrangement of the condenser 18 making use of the engine cooling fluid.

Another advantage of this embodiment is that it allows minimizing the amount of working fluid, and makes the starting phases of the Rankine system 13 easier, in particular because cavitation problems are avoided.

The condensed working fluid then flows to the tank 15. In certain systems, and typically depending on the type of working fluid used, the Rankine system 13 may further comprise a sub-cooler 25 which is located upstream from the pump 19. The sub-cooler 25, preferably located downstream from the tank 15, can be air-cooled and can in that case include a sub-cooler fan 26. Such a sub-cooler 25 makes it possible to lower the working fluid temperature by around 2-3°C, which may further limit the risk of cavitation at the pump inlet.

Finally, the pump 19, which may be driven by an electric motor 27, pumps the working fluid, which is a liquid at this stage, from low to high pressure before it enters the heat exchanger 16.

According to a possible implementation of the vehicle 1 , the expander can have an output shaft 28 which can be mechanically connected to the engine crankshaft or to the driveline. More precisely, although it could be connected to any part of the driveline, the output shaft may advantageously be connected to the drive wheels differential 10. More specifically, the vehicle 1 can comprise a viscous coupling unit 29, such as a hydrodynamic torque converter, which connects mechanically the drive wheels differential 10 and the expander shaft 28, in order to transfer torque from the expander to the driveline while allowing different speed ratios between the two. Also, especially in the case of a high-speed expander such as a pelton turbine or a centrifugal turbine, a speed reducing transmission can be interposed between the expander and the driveline, preferably between the expander and the viscous coupling unit if such unit is provided.

Recovering the energy from the expander 17 mechanically may be more advantageous than recovering said energy electrically, insofar as the amount of electricity so produced often exceeds the vehicle needs and therefore cannot be fully used, which is not satisfactory. Moreover, mechanically connecting the expander shaft 28 to the drive wheels differential 10 is one of the best options, since it makes it possible to directly provide additional torque with a satisfactory yield and since it is of greater flexibility in application.

Cardan joints or universal joints 30 are preferably interposed between the viscous coupling unit 29 and the drive wheels differential 10, to provide an adaptation means between the viscous coupling unit 29, which is preferably installed on the chassis 2, and the drive wheels differential 10, which is arranged on the vehicle drive axle and which therefore moves relative to the chassis due to the axle suspensions. Such joints are further advantageous in that they have very low mechanical losses.

Therefore, such an engine arrangement is simple in terms of coupling and efficiency.

According to an aspect of the invention, the various components of the Rankine system 13 are arranged in a certain spatial relationship with respect to the direction Z that is substantially orthogonal to the chassis average plane P.

Thus, as schematically illustrated in Figure 1 , the condenser 18 is installed on the chassis 2 at a location which is higher than that of the tank 15, and the tank 15 is installed on the chassis 2 at a location higher than that of the pump 19. Of course, due to installation constraints, it may be that the lowest point of the condenser is located slightly lower than the highest point of tank, and/or that the lowest point of the tank is located slightly lower than the highest point of pump, but, in all cases, the components shall be arranged such that most of the liquid, i.e. preferably more than 80%, contained in the higher component will flow to lower component under the mere action of gravity.

This makes it possible to ensure the pump 19 can properly start, even if some working fluid can stay in the condenser 18 when the Rankine system 13 is not in operation.

Typically, the condenser 18 may have a condenser inlet 181 and a condenser outlet 182, as shown on Figures 2 and 3.

Similarly, the tank 15 may have a tank inlet 151 , which in the example shown is on a top region of the tank 15, and a tank outlet, which is not visible on the figures but which is advantageously located in a bottom region of the tank. It is to be noted that the tank could be fillet with a joint inlet/outlet port, which would then preferably be located in a bottom region of the tank.

The pump 19 has a pump inlet 191.

With such a set-up, the various components of the Rankine system are preferably spatially located in such a way that, with respect to the direction Z that is substantially orthogonal to the chassis average plane P, the condenser outlet 182 is located higher than the tank inlet 151 and the tank outlet is located higher than the pump inlet 91.

In such a way, it is possible to route the connection pipes between the condenser and the tank, and between the tank and the pump, such that they exhibit a downward slope in such a way that, under the mere action of gravity, most or all of the fluid which condenses in the condenser flows to the tank and such that the tank provides a flow of liquid to the inlet pump. This ensures that best start-up conditions for the Rankine system.

Most preferably, the condenser outlet 82 is located, with respect to the direction Z that is substantially orthogonal to the chassis average plane P, at a low point with respect to an internal volume of the condenser in which the working fluid circulates. Thereby, virtually all of the liquid contained in the condenser 18 will tend to flow towards the tank 15 and the pump 19.

If a sub-cooler 25 is provided in the Rankine system 13, then said sub-cooler is preferably installed on the chassis 2 at a location whose position along direction Z is between that of the tank 15 and that of the pump 19. Such a location is preferred in order to ensure that the sub-cooler remains filled with liquid to ensure proper start of the pump by minimizing the risk of pump cavitation.

In the preferred embodiment shown on Figures 2 to 4, the sub- cooler 25 has a sub-cooler inlet 251 and a sub-cooler outlet 252, and in that, with respect to the direction Z that is substantially orthogonal to the chassis average plane P, the sub-cooler inlet 251 is located below the tank outlet and the sub-cooler outlet 252 is located above the pump inlet 191.

Besides, the expander 17 can be installed on the chassis 2 higher than the tank 15, with respect to direction Z. As a result, if there is a leakage in the expander 17, the working fluid can be collected and directed to the tank 15 by gravity. If no condensation or leakage of working fluid occurs in the expander, then the position of said expander does not matter.

Preferably, the expander 17 has an expander outlet 172 which is located higher than the condenser inlet 181.

In the above, it is understood that when an outlet of a component is preferably located higher than the inlet of another component, the said inlet and said outlet can be at the same level or substantially at the same level, as the purpose of the such arrangement is that most of the working fluid in liquid phase which may be contained in the component located higher can flow by gravity to the component located lower.

In any case, a most preferred arrangement is to have the condenser 18 installed on the chassis 2 at a location which is strictly higher than that of the tank 15, and to have the tank 15 installed on the chassis 2 at a location strictly higher than that of the pump 19, such that all liquid contained in the condenser can flow to the tank and that all the liquid contained in the tank can flow to the pump by the mere action of gravity.

The various components of the Rankine system 13 can be installed on the vehicle at different places, possibly far from each other, provided their respective heights along direction Z are respected, as above mentioned.

Alternatively, according to an advantageous implementation of the invention, at least the tank 15, the expander 17 and the pump 19 of the Rankine system 13 can be fixed on a frame 32 capable of being removably installed on the chassis 2. These components are arranged on the frame 32 according to the above mentioned respective heights. In other words, instead of being installed independently of each other directly or indirectly on the chassis 2, said components can be mounted on one single frame 32, which may additionally form a kind of housing. Thus, these components are not installed directly on the chassis 2 but on the frame 32, said frame 32 being installed on the chassis 2. For example, as shown in figure 4, the frame 32 can be mounted on a lateral beam 3 of the chassis 2. In practice, the Rankine system 13 can be arranged at the rear part of the vehicle 1 , which is less complex than installing said system near the engine 4, where little space is available due to other existing systems (such as turbo- compressors, turbo compound arrangements, etc.)

With this implementation, the installation and maintenance of the Rankine system 13 are made much easier. The Rankine system 13 can thus be designed as an add-on system that can be retrofitted to conventional vehicles, especially that can be integrated in a long haul truck without requiring significant changes. Furthermore, the Rankine system 13 is more compact, partly because no long pipes are required for the working fluid circuit 14.

The frame 32 can comprise a structure of beams 33 forming a kind of housing and supporting various components of the Rankine system 13, as well as walls 34 closing some of the housing faces, for example the top face as shown in figure 4.

The heat exchanger 16, which is generally arranged on the exhaust line, can preferably be located outside the frame 32, in the sense that it is not fixed on the frame but for example directly or indirectly on a lateral beam 3. Nevertheless, the heat exchanger is preferably located in the vicinity of the frame, i.e. in the vicinity of the components which are fixed on the frame, as shown in figure 4. Therefore, in this implementation, the heat exchanger 16 is not necessarily removed from the vehicle 1 together with the other components of the Rankine system 13 which are installed on the frame 32 when the frame is removed from the vehicle.

As regards the condenser 18, it can be fixed on the frame 32, or it can be arranged outside the frame 32, in the sense that it is not fixed on the frame, but preferably in the vicinity of the frame.

According to another aspect of the invention, as illustrated in figure 1 , the vehicle 1 can further comprise a valve cooling circuit 40 carrying a valve cooling fluid for cooling the exhaust directional valve 20. Such a valve cooling circuit can be especially useful where the exhaust directional valve comprises an electronic control unit which is integrated in immediate vicinity with the valve mechanism itself, the latter being directly exposed to the heat of the exhaust gases. Indeed, the electronic control unit of such an exhaust directional valve 20 cannot withstand too high temperatures, for example temperatures higher than 150-200°C, and therefore it can need cooling insofar as the exhaust gases temperature can be as high as 400-600°C. Additionally or alternatively, the valve cooling circuit can be useful for cooling the valve mechanism itself, where excessive temperatures can affect the movements of mobile parts, the fluid tightness and the overall durability.

Preferably, said valve cooling circuit 40 is disjoined from the engine cooling circuit 24, i.e. has no common parts with the engine cooling circuit 24 where the valve cooling fluid would mix with the engine cooling fluid. By providing a valve cooling circuit 40 which is disjoined from the engine cooling circuit 24 it is possible to arrange said valve cooling circuit 40 at a distance from the engine 4. For example, the valve cooling circuit 40 can be installed close to the Rankine system 13, at a median or rear part of the vehicle 1 , and can more generally be used for fulfilling other functions related to the Rankine system 13. This further allows the Rankine system 13 to be separated from the engine arrangement.

The valve cooling circuit 40 can comprise a cooler 41 capable of cooling the valve cooling fluid. This can be necessary if said valve cooling fluid is distinct from the engine cooling fluid and therefore cannot be cooled by the radiator and fan of the engine cooling circuit 24.

According to an embodiment, said cooler 41 can further be a heat exchanger arranged in the Rankine system 13, between the pump 19 and the heat exchanger 16, in which there is heat exchange between the Rankine working fluid and the valve cooling fluid so as to pre-heat the working fluid before it enters the heat exchanger 16.

If the working fluid is so preheated, the heat exchanger 16 can be downsized, and therefore more easily installed in a limited place on the chassis 2.

The cooler 41 can be located either on the main line of the valve cooling circuit 40 or on a diversion line thereof.

Furthermore, the valve cooling fluid can further be used as the viscous fluid in the viscous coupling unit 29. Preferably, the valve cooling circuit 40 and the working fluid circuit 14 of the Rankine system 13 are separate circuits with respect to the fluids, in that the valve cooling fluid and the working fluid do not mix. The two fluids could be of similar composition, but are preferably of different composition. For example the valve cooling fluid can advantageously be oil.

According to the embodiment depicted in figure 1 , the valve cooling circuit 40 can be part of a fluid circuit 42 which further comprises a lubricating loop 46, for example in view of lubricating the expander 17 of the Rankine system 3. The valve cooling fluid is then used as a lubricant for the expander 17, and possibly for other components of the Rankine system. In this embodiment, the bearings of the expander 17 are therefore not lubricated by the working fluid, nor by the engine cooling fluid, but by the valve cooling fluid. In particular, the lubricating loop 46 is disjoined from the engine cooling circuit 24.

More specifically, the fluid circuit 42 can comprise on the one hand the valve cooling circuit 40 which may form a closed loop including the viscous coupling unit 29. In said valve cooling circuit 40, the valve cooling fluid flows successively through the exhaust directional valve 20, for example especially around the electronic control unit of said exhaust directional valve 20, the cooler 41 , a filter 43, a pump 44, and through the viscous coupling unit 29. The valve cooling circuit 40 can further include a valve actuation portion 45, the same fluid being further used to actuate the exhaust directional valve 20, when such valve is hydraulically actuated.

On the other hand, the fluid circuit 42 can comprise the lubricating loop 46. For example, the lubricating loop 46 branches from the valve cooling circuit 40 between the pump 44 and the viscous coupling unit 29 and returns to said valve cooling circuit 40 upstream from the cooler 41. With this arrangement, the valve cooling circuit 40 and the lubricating loop 46 substantially form two separate loops, even if they share some portions and components. Alternatively, the fluid circuit 42 may comprise one and a single loop in which the fluid flows successively through every component, the valve cooling circuit 40 and the lubricating loop 46 being coincident.

The above described design provides a fluid circuit 42 dedicated to the Rankine system 13 and separate from other circuits, in particular from the engine cooling circuit 24, and from the circuit 14 of the Rankine system 13. Thus, the Rankine system 13 can more easily be designed as an add-on system that can be retrofitted to conventional vehicles. Preferably, said fluid circuit 42 can be fixed on the frame 32.

The invention is of course not limited to the embodiment described above as an example, but encompasses all technical equivalents and alternatives of the means described as well as combinations thereof.

Claims

1. A vehicle comprising:

a chassis (2) having an average plane (P) which is substantially horizontal when the vehicle (1) is on a substantially horizontal ground;

an internal combustion engine (4) installed on the chassis (2) and an exhaust line (12) capable of collecting exhaust gases from said engine;

a Rankine system (13) comprising a tank (15) for a working fluid, and designed to carry said working fluid in a loop, in which said working fluid can be successively evaporated in a heat exchanger (16) by heat exchange with the exhaust gases, expanded in an expander (17), condensed in a condenser ( 8) and compressed in a pump (19);

characterized in that, with respect to a direction (Z) that is substantially orthogonal to the chassis average plane (P), the condenser (18) is installed higher than the tank ( 5), and the tank (15) is installed higher than the pump (19).

2. The vehicle according to claim 1 , characterized in that the condenser has a condenser inlet and a condenser outlet, the tank has a tank inlet and a tank outlet, and the pump has a pump inlet, and in that, with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P), the condenser outlet is located higher than the tank inlet and the tank outlet is located higher than the pump inlet.

3. The vehicle according to claim 2, characterized in that the condenser outlet is located, with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P), at a low point with respect to an internal volume of the condenser in which the working fluid circulated.

4. The vehicle according to any one of claims 1 to 3, characterized in that the Rankine system (13) further comprises a sub-cooler (25) which is located upstream from the pump (19) and which is installed between the tank (15) and the pump (19) with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P).

5. The vehicle according to claim 4, characterized in that the sub- cooler has a sub-cooler inlet and a sub-cooler outlet, and in that, with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P), the sub-cooler inlet is located below the tank outlet and the sub-cooler outlet is located above the pump inlet.

6. The vehicle according to any one of claims 1 to 5, characterized in that the expander (17) is installed higher than the tank (15), with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P).

7. The vehicle according to claim 6, characterized in that the expander has an expander outlet, and in that, with respect to the direction (Z) that is substantially orthogonal to the chassis average plane (P), the expander outlet is located above the condenser inlet.

8. The vehicle according to any one of claims 1 to 7, characterized in that at least the tank (15), the expander (17) and the pump (19) of the Rankine system (13) are fixed on a frame (32) capable of being removably installed on the chassis (2).

9. The vehicle according to claim 8, characterized in that the heat exchanger (16) is not fixed on the frame (32), but is located in the vicinity thereof.

10. The vehicle according to any one of claims 8 or 9, characterized in that the condenser (18) is fixed on the frame (32), or is not fixed on the frame (32) but is located in the vicinity thereof.

11. The vehicle according to any preceding claim, characterized in that the condenser (18) is designed to condense the working fluid by heat exchange with an engine cooling fluid.

12. The vehicle according to any one of claims 1 to 10, characterized in that the condenser (18) is arranged at the front part of the vehicle (1), so that the working fluid can be condensed by heat exchange with ambient air moving through the condenser (18) due to the vehicle motion.

13. The vehicle according to any preceding claim, characterized in that the expander has an output shaft (28) which is mechanically connected to a driveline of the vehicle.

14. The vehicle according to claim 13, characterized in that it the expander output shaft (28) is mechanically connected to the driveline through a viscous coupling unit (29) comprising viscous fluid.

15. The vehicle according to any preceding claim, characterized in that it further comprises an exhaust directional valve (20) located in the exhaust line (12) and capable of directing part of the exhaust gases towards the heat exchanger (16), and a valve cooling circuit (40) carrying a valve cooling fluid for cooling said exhaust directional valve (20), said valve cooling circuit (40) being disjoined from an engine cooling circuit (24).

16. The vehicle according to claim 15, characterized in that the valve cooling circuit (40) comprises a cooler (41) capable of cooling the valve cooling fluid, said cooler (41) being further arranged in the Rankine system (13), between the pump (19) and the heat exchanger (16), so as to pre-heat the working fluid before it enters the heat exchanger (16) by heat exchange in the cooler (41) between the valve cooling fluid and the working fluid.

17. The vehicle according to claim 14 combined with any one of claims 15 or 16, characterized in that the valve cooling fluid is further used as the viscous fluid in the viscous coupling unit (29).

18. The vehicle according to any one of claims 15 to 17, characterized in that the valve cooling fluid is distinct from the working fluid.