Field of the invention

The present invention relates to a vehicle internal combustion engine arrangement, and more specifically to such an arrangement comprising a waste heat recovery system.

Technological background

For many years, attempts have been made to improve the efficiency of internal combustion engines, 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 circuit.

In such a circuit, a 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 or compressed from low to high pressure;

- the high pressure working liquid is evaporated into a gas by a hot engine fluid flowing in another circuit of the engine arrangement;

- the working gas is expanded in an expander;

- finally, the working gas is condensed.

As a result, at least part of the thermal energy of the hot fluid used to evaporate the Rankine 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.

However, in many applications, the electricity produced with this system may exceed the electrical needs of the vehicle and, consequently, may not be fully used. On the other hand, using the energy recovered by this system in the form of mechanical energy, for example by connecting the expander to the driveline of the vehicle, may involve the implementation of additional complex systems, which would make the arrangement more complex, would require space and ultimately bring weight and cost.

It therefore appears that engine arrangements comprising a waste heat recovery system which have been proposed for vehicles are not fully satisfactory and can be improved. Summary

It is an object of the present invention to provide an improved vehicle internal combustion engine arrangement which can overcome the above mentioned drawbacks.

More specifically, an object of the present invention is to provide an internal combustion engine arrangement for a vehicle, comprising a waste heat recovery system which can allow better use of the energy recovered from the exhaust gases.

According to the invention, such an internal combustion engine arrangement comprises:

- an internal combustion engine, an intake line capable of carrying intake gases towards the engine and an exhaust line capable of collecting exhaust gases from said engine;

- a waste heat recovery system carrying a working fluid in a loop, in which said working fluid is successively compressed, heated in a heat exchanger by means of at least one engine fluid, and expanded in a first expander;

- a first compressor located in said intake line and mechanically connected to the first expander of the waste heat recovery system.

Thus, in an internal combustion engine arrangement according to the invention, the thermal energy of at least one engine fluid, such as exhaust gases, EGR gases, engine cooling fluid, lubrication fluid, charged intake gases, etc. , is converted by the waste heat recovery system into mechanical energy by the expander and is transferred in mechanical form from the expander of said waste heat recovery system towards a compressor provided in the intake line. The recovered energy is used to compress intake gases to be delivered to the engine intake - in addition to or in place of the compressor of a turbocharger or of a supercharger - in order to improve the engine efficiency. Thereby, at least part of the energy of the waste heat recovery system is recovered on the engine pistons due to lower pumping losses.

Consequently, at least part of the energy needed for compressing intake gases is recovered by means of the waste heat recovery system without needing an intermediate form of energy transfer other than the mechanical energy transfer from the expander to the compressor.

Another advantage of the invention is that it does not require expensive or complex implementations to connect the expander of the waste heat recovery system to the first compressor.

Brief description of the drawings

The following detailed description of several embodiments 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 embodiments disclosed.

Figures 1 to 6 are schematic drawings of an engine arrangement according to several embodiments of the invention.

Detailed description The vehicle internal combustion engine arrangement 1 according to the invention comprises an internal combustion engine 2, typically a reciprocating piston engine which can be a diesel engine or a spark ignition engine. The invention relates in particular, but not exclusively, to heavy trucks.

Intake gases are carried towards the engine 2 by an intake line 3, while an exhaust line 4 is provided for collecting exhaust gases from said engine 2 and for directing them towards various devices before they are released into the atmosphere.

The engine arrangement 1 also comprises a waste heat recovery system 5 carrying a working fluid in a loop.

In the illustrated embodiments, the waste heat recovery system 5 is of the Rankine type, where the working fluid is carried in a closed loop, with a condenser for condensing the working fluid between the expander and the compressor. However, other types of waste heat recovery system are possible, such as, for example, systems of the Stirling type. It is also possible to implement the invention, including all variants herein described, with a Brayton type waste heat recovery system where the working fluid, usually air, is carried in an open loop. In a Brayton type system, air can be discharged to the atmosphere after being expanded while fresh air is absorbed by the compressor. In all cases, the working fluid for the heat recovery system does not circulate through the internal combustion engine.

In the embodiment shown in the figures, the waste heat recovery system 5 comprises a heat exchanger 6 in which the working fluid can be heated by heat transfer from at least one hot heat engine fluid. For example, the working fluid can be directly heated by exhaust gases passing through the heat exchanger 6. This heat exchanger 6 can comprise a boiler in which the fluid flowing in the system 5 is evaporated by the hot exhaust gases.

As will apparent in further examples, and whatever the type of waste heat recovery system is used, other engine fluids could be used to heat the working fluid, including EGR gases, which are a portion of the exhaust gases, engine cooling fluid, lubrication fluid, charged intake gases, etc.... In such a case, the heat exchanger would be located on a line carrying the relevant fluid. The system could in fact comprise several heat exchangers in which the working fluid would be heated either by the same engine fluid, or by different engine fluids. Those several heat exchangers would typically be arranged in series in the waste heat recovery loop, but could also be arranged in parallel.

Downstream from the heat exchanger 6, the gas flows through a first expander 7. The first expander 7 can be a turbine, a piston machine, a scroll expander, a screw expander, etc. , all of which are capable of recovering the energy of the heated and pressurized gas and of transforming it into mechanical energy.

In a Rankine type circuit, downstream from the first expander 7, the gas, which has been expanded, and thereby cooled, can flow towards a condenser 8 in which it becomes a liquid again. Downstream from the condenser 8, the fluid - as a liquid - will be compressed before entering the heat exchanger 6, for example by means of a pump or compressor 9. In the pump 9, the fluid is pumped and compressed from low to high pressure, and then directed towards the heat exchanger 6 again. The Rankine system could be more elaborated and could for example comprise an additional heat exchanger in which the working fluid coming out of the pump is preheated by working fluid coming out of the expander.

According to the invention, there is provided a first compressor 10 located in the intake line 3 and mechanically connected to the first expander 7 of the waste heat recovery system 5. The first compressor 10 compresses at least part of the intake gases which are to be delivered to the engine intake.

The mechanical connection between the first expander of the waste heat recovery system and the first compressor can be direct, with both elements rotating at the same speed on a common shaft, or could include a mechanical transmission, for example including a belt and pulley transmission, a gearing transmission, etc.... Such a transmission could allow the first expander 7 and the first compressor to be physically spaced apart on the vehicle. Such a mechanical transmission could also include a speed reduction or multiplication system, a gearbox, a hydraulic coupler, a continuously variable ratio transmission, etc., so as to allow each of them to operate in their respective optimum speed range.

The engine arrangement may comprise a second compressor in the intake line for compressing at least part of the intake gases which are to be delivered to the engine intake. Such compressor can be part of a turbocharger, thereby driven by a turbine located on the exhaust line 4, or part of a supercharger, thereby driven mechanically by the engine 2.

In an implementation of the invention, the first compressor 10 is located in a first branch 3a of the intake line 3. The intake line 3 further comprises a second branch 3b, with said first and second branches 3a, 3b of the intake line 3 merging upstream from the engine 2, and for example upstream from a charge air cooler 11. The engine arrangement 1 may further comprise a turbocharger 2 including a second expander 3, such as a turbine, which is driven by the exhaust gases flowing towards the atmosphere. The second expander 13 is located in the exhaust line 4. Furthermore, the turbocharger 12 includes a second compressor 14 which is mechanically connected to the second expander 13 and located in the second branch 3b of the intake line 3, in order to compress air before it enters the engine 2. In this embodiment, the two compressors are arranged in parallel in the intake line. Thus, the first compressor 10 works in parallel with the second compressor 14 of the turbocharger 12, in order to feed the engine 2 with pressurized intake gases.

In such a case, a valve could be provided on the first branch 3a of the intake line, or at the junction point between the first branch 3a and the second branch 3b. Such a valve could include a simple check valve, or a three way valve. Such a valve could be used to inhibit compressed gases provided by the second compressor from flowing into the first branch 3a when the pressure delivered by the second compressor 14 would exceed the pressure delivered by the first compressor. Such would be the case when the Rankine system would be shut down, for example for lack of available cooling power at the condenser 8.

Alternatively, the two compressors could be arranged in series such that the engine intake gases are first compressed by one of the compressors to a first pressure level, and then compressed by the other compressor to a higher pressure level. In such a case, it can be advantageous to arrange the first compressor, driven by the expander of waste heat recovery system, upstream of the second compressor in the intake line. The intake line can then have only one branch. In a series arrangement, it can be advantageous to provide a bypass line for either one or both of the compressors so that the intake gases can by-pass the given compressor.

The series or parallel arrangements are also both applicable if the second compressor is part of a supercharger.

In both the case of a parallel arrangement and of a series arrangement of the two compressors, the two compressors can be used simultaneously, alternatively, or independently one from the other depending on the operating conditions of the engine arrangement. When not used, the given compressor is preferably by-passed or its branch of the intake is preferably shut-off in the case of a parallel arrangement.

One particular arrangement would provide a first compressor arranged in parallel with a second compressor being part of a supercharger, each in a separate parallel branch of the intake line, with an additional compressor being part of a turbocharger and being located in the intake line downstream of the junction point of the two branches. Besides, the engine arrangement 1 can comprise an exhaust after treatment system 16 located in the exhaust line 4 and including several units in order to reduce air pollution and meet legal requirements.

The units can comprise:

- a diesel oxidation catalyst (not shown)

- a diesel particulate filter 17, which is intended to remove un- burnt particles contained in the exhaust gases;

- and/or a selective catalyst reduction device 18 which is used to treat nitrogen oxides (NOx) contained in the exhaust gases by converting them into water and nitrogen, which are both non toxic substances.

According to a first embodiment of the invention, shown in figure 1 , the heat exchanger 6 of the waste heat recovery system 5 can be located in the exhaust line 4. In other words, the working fluid flowing in the waste heat recovery system 5 is heated by the exhaust gases flowing in the exhaust line 4 towards the atmosphere.

In this embodiment, the second expander 13 of the turbocharger 12 can be located in the exhaust line 4 upstream from the heat exchanger 6.

Besides, at least one unit of the exhaust after treatment system 16 can be located upstream from the heat exchanger 6 of the waste heat recovery system 5.

For example, all units of the exhaust after treatment system 16 can be located upstream from the heat exchanger 6, preferably downstream from the second expander 13. Alternatively, the exhaust line 4 could successively comprise, from the engine 2 towards the atmosphere: the second expander 13 of the turbocharger 12, a diesel particulate filter 17, the heat exchanger 6 of the waste heat recovery system 5, and a selective catalyst reduction device 18.

According to a second embodiment of the invention, shown in figure 2, the heat exchanger 6 of the waste heat recovery system 5 can be located in an EGR line 20 capable of rerouting a portion of the exhaust gases into the intake line 3.

An EGR (exhaust gas recirculation) system is conventionally used to meet the regulations concerning the upper limit of NOx (nitrogen oxide and nitrogen dioxide) emissions in internal combustion engines. To that end, a portion of the exhaust gases is made to recirculate back to the engine cylinders, through the EGR line 20 which terminates in the intake line. This results in lowering the combustion temperatures and, as a consequence, limits NOx generation as NOx is generated by oxygen and high temperature.

Additionally, by providing an optional EGR cooler 21 on the EGR line 20, the EGR gases may be cooled before there are reintroduced into the engine 2, in addition to the cooling effect obtained for the EGR gases in the heater 6, which further reduces NOx emissions as this allows the introduction into the cylinders of a greater mass of exhaust gases. The EGR cooler 21 for example uses the engine coolant but could also be air cooled.

Furthermore, an EGR valve 22 is preferably provided in the EGR line, typically downstream from the EGR cooler 21. The aperture rate of said EGR valve 22 is typically controlled according to the engine operating conditions to allow an appropriate amount of exhaust gases to flow in the EGR line 20 and to be rerouted towards the engine 2.

In the illustrated embodiment, the inlet of the EGR line 20 is connected to the exhaust line 4 upstream from the expander 13 of the turbocharger 12, and the outlet of the EGR line 20 is connected to the intake line 3 downstream from the second compressor 14 of the turbocharger, but other implementations are possible.

The second embodiment takes advantage of the significant amount of energy which is included in EGR gases, which have a high temperature, and makes it possible to recover at least part of said energy.

In figure 3 is represented a variant of the embodiment of figure 1. The main difference is that the output of the first compressor 0 is connected to the intake line 3 by a branch line 3a which joins the intake line 3 at a junction point J upstream of the second compressor 14, rather than downstream. In this example, the intake line has a parallel intake branch 3c upstream of junction point J through which the second compressor 14 can suck fresh air at ambient pressure. A valve, for example a check valve 30, can be installed in the parallel intake branch 3c to prevent reverse flow in that branch, especially preventing any substantial leak towards ambient of pressurized air delivered by the first compressor at junction point J. In this embodiment, the first and the second compressors are arranged in series. More particularly, the first compressor is the low pressure compressor and the second compressor is the high pressure compressor, but the second compressor can also draw fresh air directly from the exterior when the first compressor is not able to deliver pressurized air. In figure 4 is represented a variant of the embodiment of figure 3, where no fresh air can be delivered directly to the second compressor because of the absence of a parallel intake branch as in embodiment of Figure 3. In this embodiment, the first and the second compressors are arranged in series. More particularly, the first compressor is the low pressure compressor and the second compressor is the high pressure compressor. On the other hand, the system is shown as being fitted with a by-pass line 32, preferably equipped with a suitable by-pass valve 34, to by-pass the second compressor 14, so that pressurized air delivered by the first compressor 10 can, in certain operating conditions, be directed directly to the engine 2 without going through the second compressor 14.

In figure 5 is shown a variant of the embodiment of figure 2 where the waste heat recovery system 5 comprises two heat exchangers 6a, 6b in which the working fluid is heated by two different engine fluids. In this example, the two engine fluids are respectively the exhaust gas flowing in line 4 and the EGR gas flowing in line 20. In the shown embodiment, the two heat exchangers 6a and 6b are arranged in series. A preferred series arrangement is to have the working fluid flowing first in the heat exchanger 6b to be heated by the exhaust gases flowing in exhaust line 4 and subsequently in the heat exchanger 6a to be heated the EGR gases. Nevertheless, a parallel arrangement of the two heat exchangers 6a, 6b could also be possible.

In the above embodmients, the first compressor 10 is independent from any expander located in the exhaust line 4. That is to say, in particular, that said first compressor 10 is not driven by the second expander 13 of the turbocharger 12.

To the contrary, in the embodiment of the invention which is shown on Figure 6, the first compressor 10 is mechanically connected to the first expander 7 of the waste heat recovery system 5 and is also connected mechanically to a second expander 13 which is located in the exhaust line 4. The second expander 3 is thereby driven by the exhaust gases of the engine. The second expander can be a turbine. In this arrangement, the first compressor is thereby driven mechanically by both the first and second expanders thanks to energy provided by the working fluid of the waste heat recovery system and by the exhaust gases. In the shown embodiment, the first compressor 10, the first expander 7 and the second expander 13 are connected on a common shaft. In a non-shown variants, the three elements could be connected one to the other by a different mechanical system, for example with one or several pulley-type transmission so that at least one of the elements is not aligned with the others, and/or with a speed reducing or enhancing transmission to adjust the speed ratio between the elements. Also, in a further variant, the system could comprise a second compressor mechanically connected to the first and second expanders and connected to the first compressor, thereby all being driven simultaneously by the working fluid and by the exhaust gases. The first and second compressors could in such case be arranged each in one of two parallel branches of the intake line.

In the above mentioned embodiments, the energy recovered by the waste heat recovery system, i.e. the energy delivered by the expander, is entirely used for compressing intake air. Nevertheless, it can be provided that part of the energy recovered by the waste heat recovery system is used for different purposes, in addition to the compression of intake gases. Indeed, for some operating phases of the engine arrangement, there may not be a significant advantage in compressing the engine intake gases, or the available energy might exceed the need of energy for compressing the intake gases.

Therefore, in one variant, the engine arrangement can be equipped with an additional expander in the waste heat recovery system, this additional expander being for example mechanically connected to an electric generator. The additional expander and the first expander could be arranged in parallel in the waste heat recovery loop or in series, and could be operated either simultaneously, alternatively, or independently. With such an arrangement, the additional expander and the associated generator can be controlled to absorb any excess energy available from the working fluid in the waste heat recovery circuit and which cannot be efficiently used solely for compressing intake air through the first compressor.

In another variant, an electric machine can be mechanically connected to the first compressor and to the first expander. With such a machine being a generator, it can be controlled to absorb any excess energy available from the first expander and which cannot be efficiently used by the first compressor. When used as generator, the electric machine can also be used to limit the speed of the first compressor and of the first expander, for example if the current operating conditions in the waste heat recovery system would otherwise tend to drive them at an inadequate speed. If the electric machine can also be operated as a motor, it can be used to increase the speed of the first compressor, at least for a certain period of time, for example to deliver quickly an increased amount of pressurized air to the engine.

The variants relating to the use of an electric machine driven by the waste heat recovery system can be implemented with all previously described embodiments of the invention, especially regardless of the type of waste heat recovery system, of the respective arrangement of the first compressor and of a possible second compressors in the intake line, of the engine fluid used as a heat source in the waste heat recovery system, of the presence or not of an additional intake compressor, and of the presence or arrangement an exhaust after-treatment system.

More generally, a significant advantage of the invention is that it makes it possible to improve the engine efficiency by compressing intake air, by using the thermal energy that is contained in an engine fluid and that would otherwise be lost.

Such an improvement over the prior art can be achieved with a fairly low number of components and without the implementation of costly or complex elements.

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