Internal combustion engine

Abstract

The invention relates to an internal combustion engine comprising a crankshaft, one or more cylinders including a cylinder head, a piston, a combustion chamber, one or more intake valves, one or more exhaust valves, an intake system configured for feeding intake air to the engine, an exhaust system configured for conveying exhaust gas away from the engine, a pressure charging system connected to the intake system and an exhaust gas recirculation (EGR) system arranged to feed branched off exhaust gas from the exhaust system to the intake system via an EGR conduit wherein: —the internal combustion engine includes a valve actuation device configured to allow for late or early closing of the intake valves in accordance with late or early Miller-type valve timing, and wherein—the EGR system includes a gas feeding device configured to feed exhaust gas through the EGR conduit in modes of operation wherein the pressure in the intake system exceeds the pressure in the exhaust system. Additionally, a method of improving efficiency of an internal combustion engine is described.

Claims

1. A method of improving efficiency of an internal combustion engine wherein the internal combustion engine comprises a crankshaft, one or more cylinders including a cylinder head, a piston, a combustion chamber, intake valves operated in accordance with late and/or early Miller-type valve timing, exhaust valves, an intake system configured for feeding intake air to the internal combustion engine, an exhaust system configured for conveying exhaust gas away from the internal combustion engine, an exhaust gas recirculation (EGR) system including a gas feeding device connected to an EGR drive unit and being configured to feed exhaust gas branched off from the exhaust system through an EGR conduit and into the intake system and a pressure charging system connected to the intake system, wherein the gas feeding device is a displacement pump and wherein the displacement pump is arranged in the EGR conduit between the exhaust system and the intake system, characterized in that the method includes the steps of: operating the internal combustion engine under such conditions that a pressure in the intake system exceeds or is substantially similar to a pressure in the exhaust system, and operating the gas feeding device to pressurise and thereby supply the branched off exhaust gas to the intake system, or operating the internal combustion engine under such conditions that the pressure in the exhaust system is higher than the pressure in the intake system, configuring the EGR system and/or the EGR drive unit to be driven by the gas feeding device so as to generate a power output, operating the engine so as to drive the gas feeding device by means of exhaust gas flowing from the exhaust system to the intake system and thereby operate the gas feeding device in an energy recovery mode where the EGR drive unit generates the power output, wherein the method includes: in operating conditions wherein the pressure in the exhaust system is lower than the pressure in the intake system, or in operating conditions wherein a turbine of the pressure charging system operates below desired speed, operating the EGR system in an at least partially reversed mode such that the gas feeding device supplies pressure to the pressure charging system, and operating a re-directing system configured to re-direct flow of exhaust gas from the gas feeding device to the turbine by operating valves in the re-directing system to close the EGR feed flow and opening any valves to the pressure charging system.

2. The method according to claim 1, wherein the method of operating the internal combustion engine under such conditions that the pressure in the exhaust system is higher than the pressure in the intake system includes the step of: conveying the power output to an energy reservoir such as a battery or a capacitor or conveying the power output to the internal combustion engine.

3. An internal combustion engine comprising a crankshaft, one or more cylinders including a cylinder head, a piston, a combustion chamber, one or more intake valves operated in accordance with late and/or early Miller-type valve timing, one or more exhaust valves, an intake system configured for feeding intake air to the engine, an exhaust system configured for conveying exhaust gas away from the engine, an exhaust gas recirculation (EGR) system including a gas feeding device connected to an EGR drive unit and being configured to feed exhaust gas branched off from the exhaust system through an EGR conduit and into the intake system and a pressure charging system connected to the intake system, wherein the gas feeding device is a displacement pump and wherein the displacement pump is arranged in the EGR conduit between the exhaust system and the intake system, wherein the internal combustion engine is configured to execute the method according to claim 1.

4. A non-transitory computer readable medium storing a computer program comprising program code for performing the method according to claim 1 when said program is run on a computer.

5. A vehicle comprising an internal combustion engine according to claim 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

(2) In the drawings:

(3) FIG. 1 is a schematic drawing showing a truck with an internal combustion engine according the first aspect of the invention;

(4) FIG. 2 is a schematic drawing showing, in a sectional view, a part of an internal combustion engine;

(5) FIG. 3A is a schematic drawing showing elements of an internal combustion engine according to one example embodiment of the invention;

(6) FIG. 3B is a schematic drawing showing the elements of an internal combustion engine according to FIG. 3A, however including additional features;

(7) FIG. 3C schematically shows a further example embodiment of the internal combustion engine according to FIG. 3B, however in an at least partially reversed drive mode;

(8) FIG. 3D schematically shows a further example embodiment of an internal combustion engine with a low-pressure EGR system;

(9) FIG. 4 is a schematic drawing showing intake valve opening and closure relative to CAD (Crank Angle Degree) for late and early Miller cycle operation;

(10) FIG. 5 is a graphical representation of the pressure conditions in an exhaust system, an intake system and in the gas feeding device;

(11) FIG. 6A is a flowchart illustrating a method of improving efficiency of an internal combustion engine according to one example embodiment of the present invention;

(12) FIGS. 6B-6F are flowcharts illustrating methods of improving efficiency of an internal combustion engine according to further example embodiments of the present invention;

(13) FIG. 7A is a flowchart illustrating a first mode of operation of a method of improving efficiency of an internal combustion engine in accordance with the second aspect of the present invention, and

(14) FIG. 7B is a flowchart illustrating a second mode of operation of a method of improving efficiency of an internal combustion engine in accordance with the second aspect of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

(15) It is to be understood, that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize, that many changes and modifications may be made within the scope of the appended claims.

(16) FIG. 1 is a schematic drawing showing a truck 200 with an internal combustion engine according to an aspect of the present invention.

(17) FIG. 2 is a schematic drawing showing, in a sectional cut-out view, a part of an internal combustion engine. In particular, the drawing shows the essential parts of a cylinder 101 of an embodiment of an internal combustion engine 100.

(18) The internal combustion engine 100 may include one or more cylinders 101, and the cylinders 101 may be arranged in any configuration such in in-line, in a V, in flat/boxer configuration etc.

(19) As can be seen in FIG. 2, each cylinder 1 includes a cylinder head 2, a piston 3 configured for reciprocating towards and away from the cylinder head 2 and a combustion chamber 1a located between the piston 3 and the cylinder head 2. Each cylinder 1 moreover includes one or more intake valves 4 arranged in association with the combustion chamber 1a and one or more exhaust valves 5 arranged in association with the combustion chamber 1a.

(20) An intake system 6 for feeding intake air to the engine 100 is provided in connection with the intake valves 4, and an exhaust system 7 for conveying exhaust gas away from the engine 100 is provided in connection with the exhaust valves 5.

(21) The intake valves 4 control inflow of intake air from the intake system 6 to the cylinder 1, and the exhaust valves 5 control exhaust of exhaust gas to the exhaust system 7 from the cylinder 1.

(22) As shown in FIG. 2, the engine 100 may include a valve actuation device 8 configured for opening and closing the intake valve 4. The valve actuation device 8 may be configured for, or controlled to, allowing for late or early closing of the intake valve 4 according to the Miller-type valve timing principles. Similarly, the engine 100 may include a valve actuation device 9 configured for, or controlled to, opening and closing, or even late or early opening and closing, of the exhaust valve 5.

(23) One or more of the valve actuating devices 8, 9 may be controlled to open or close the intake and exhaust valves 4, 5 according to predetermined and/or dynamic timing schedules; including early and late Miller-type valve timing. This will be explained further in the below.

(24) In one embodiment, one valve actuation device 8, 9, operates one intake/exhaust valve 4, 5.

(25) FIG. 3A schematically shows an internal combustion engine 100 according to one example embodiment of the invention. The engine 100 is an in-line six cylinder engine and the engine 100 includes the components shown in FIG. 2.

(26) FIG. 3A further shows, that the intake system 6 is provided in connection with the intake valves 4, and that the exhaust system 7 is provided in connection with the exhaust valves 5.

(27) An EGR system 102 is provided between the exhaust system 7 and the intake system 6. The EGR system includes a gas feeding device 15, or EGR pump 15, and an EGR conduit 110 allowing for fluid communication between the exhaust system 7 and the intake system 6. The gas feeding device 15 is operative to feed and/or control flow of exhaust gas from the exhaust system 7 via the EGR conduit 110 to the intake system 6.

(28) The gas feeding device 15 may be driven by an EGR drive unit 22 as discussed below with reference to FIG. 3B.

(29) The engine 100 further includes a pressure charging system 12 connected to the intake system 6, for, in certain operating conditions of the engine 100, pressurising the intake air to a pressure above the pressure in exhaust system 7. In FIG. 3A the pressure charging system 12 is a turbocharger comprising a turbine 11 and a compressor 12b. The turbine 11 is operative to drive the compressor 12b via a shaft.

(30) The EGR system 102 is a high pressure EGR system where exhaust gas is branched off from the flow of exhaust gas upstream the turbine 11.

(31) The compressor 12b is arranged to pressurise air in the intake system 6 dependent on operating conditions of the engine 100 and, when required, provide a positive pressure differential, or pressure differential, between the intake system 6 and the exhaust system while operating with late or early Miller-type valve timing, such that the pressure in the intake system 6 exceeds the pressure in the exhaust system 7.

(32) A so called wastegate may be provided to divert exhaust gas away from the turbine 11 in order to regulate turbine speed as discussed below with reference to FIG. 3B.

(33) The pressurised intake air may be cooled in a cooler such as a charge air cooler, or intercooler, as discussed below with reference to FIG. 3B.

(34) During operation of the engine 100, a portion of the exhaust gas is branched off from the flow of exhaust gas flowing in exhaust system 7, upstream the turbine 11, to the EGR system 102. The remaining exhaust gas is conveyed to the turbine 11 of the turbocharger.

(35) The exhaust gas branched off from the stream of exhaust gas is, via EGR conduit 110, led to the gas feeding device 15 and, in certain operating conditions, the gas feeding device 15 pressurises the exhaust gas to a pressure level at least corresponding to the absolute pressure level in the intake system 6; this in order to allow for flow of exhaust gas from the exhaust system 7 to the inlet system 6 irrespective of the pressure differential between the exhaust system 7 and the intake system 6.

(36) Flow of gas in the EGR conduits 110 may be controlled by one or more EGR valves 10 as discussed below with reference to FIG. 3B.

(37) It should be noted that conveyance of EGR gas be facilitated by an EGR piping system including one or more EGR conduits 110. The EGR conduits 110 may be made from any suitable material and in any size and geometry.

(38) FIG. 3B schematically shows an internal combustion engine 100 according to one example embodiment of the invention. The engine 100 includes the components shown in FIGS. 2 and 3A however with additional features.

(39) The exhaust system 7 is in this embodiment separated into two sections; one section for cylinders 1, 2 and 3 and one section for cylinders 4, 5 and 6; as counted from the left hand side of the drawing. The two sections of the exhaust system 7 may convey exhaust gas through an EGR valve 10 arranged to ensure that a part of the exhaust gas is branched off from the exhaust system 7 and further to control the volume of exhaust gas returned to the intake system 6 as EGR. The remaining exhaust gas is further conveyed to the turbine part 11 of the turbocharger.

(40) A wastegate system 103 may be provided to divert exhaust gas away from the turbine 11 in order to regulate turbine speed. The wastegate system 103 includes a valve 13 operative to bypass excess pressure, or excess flow of exhaust gas, around the turbine 11 in order to regulate maximum boost pressure delivered by the pressure charging system 12.

(41) The pressurised intake air may be cooled in a cooler 18 such as a charge air cooler or intercooler. The cooler 18 increases the efficiency of the pressure charging system by reducing, or removing a part of, induction air heat and compression heat added to the compressed intake air by the pressure charging system 12. By this, volume density of the intake air is increased.

(42) The exhaust gas branched off from the exhaust system 7 may be conveyed, possibly via an EGR valve 10 and/or an EGR cooler 14, to the gas feeding device 15 for pressurisation to a pressure level at least corresponding to the pressure in the intake system 6.

(43) In operating conditions wherein the pressure in the exhaust system 7 is sufficiently high, pressurisation by means the gas feeding device 15 may be unnecessary—and the gas feeding device 15 may be bypassed via a bypass conduit 17. A bypass valve 16 may be provided for controlling the flow in the bypass conduit 17. In FIG. 3B, the bypass valve 16 is arranged in the bypass flow line 17. Alternatively, or additionally, the gas feeding device 15 may in such conditions also operate freely with the flow of EGR gas.

(44) Separation of the exhaust systems 7 according to the embodiment shown in FIG. 3B allows for preservation of pressure pulses in the exhaust system 7. One benefit of this configuration is that the preserved pressure pulses are conveyed to the turbine 11, thereby propelling the turbine 11 also in operating conditions resulting in low or insufficient pressure in the exhaust system 7 to propel the turbine 11. Additionally, a non-separated exhaust system, as shown in FIG. 3A, provides higher exhaust backpressure and thus lower volumetric efficiency and increased residuals in the cylinder 1.

(45) The EGR valve 10 may be configured for branching off exhaust gas from one, both or multiple exhaust systems; hence the EGR valve 10 may constitute a multi-function or dual valve. In some embodiments, the EGR valve 10 may be configured for branching off exhaust gas from only one section of the exhaust system 7. This may, however, skew the engine operation and result in unevenly distribution of exhaust gas between the cylinders 1.

(46) According to one example embodiment, the gas feeding device 15 may constitute a displacement type pump connected to an EGR drive unit 22. The EGR drive unit 22 may be configured to drive the gas feeding device 15 in a feed mode to feed exhaust gas into the intake system 6.

(47) The EGR drive unit 22 may furthermore be configured to generate power output in a compound mode of operation (driven mode); i.e. in an energy recovery mode of operation. The compound mode is applicable, or available, when the engine operating conditions result in higher pressure in the exhaust system 7 than in the intake system 6; i.e. in a negative differential between exhaust system 7 and intake system 6. When the engine is operating in such condition, natural flow of exhaust gas from the exhaust system 7 to the intake system 6 may take place while driving the gas feeding device 15 and the EGR drive unit 22—and thus allow for operation in compound mode.

(48) The EGR drive unit 22 may, as an example, constitute an electrical motor capable of operating as a generator in a reversed drive mode. Alternatively, the EGR drive unit may constitute a mechanical drive such as a belt, chain or gear drive or a hydraulic or pneumatic drive.

(49) According to one example embodiment shown in FIG. 3B, an energy reservoir 23, such as a battery or a capacitor, is connected to the EGR drive unit 22, for storing energy in compound mode.

(50) The EGR drive unit 22 may furthermore be configured to drive the gas feeding device 15 in reverse to provide pressure towards the turbine 11 in order to spin up the compressor 12b. In this manner, it is possible to improve low end performance of the engine 100. Reverse mode may be applied irrespective of the differential pressure between the exhaust system 7 and the intake system 6.

(51) FIG. 3C schematically shows an embodiment of an engine 100 according to FIG. 3B, however with additional features and configured for reverse drive mode of the EGR system 102.

(52) In FIG. 3C the EGR system 102 is provided with a gas re-directing system 24 configured to re-direct the flow from the gas feeding device 15 from its normal feed direction via the re-directing system 24 to the turbine 11. The flow direction is controlled through (re-directing) valves 25 configured for closing the EGR feed flow while opening for flow to the pressure charging system 12.

(53) The re-direction system 24 may include conduits interconnecting the valves 25, so that the flow from the gas feeding device 15 may be re-directed from its normal route and through the piping to the turbine 11. The valves 25 may be connected to a control unit 26, or ECU, configured to control opening and closing of the valves 25 dependent on drive mode.

(54) FIG. 3C further shows that the control unit 26 may be operative to control various devices in the engine 100. The control unit 26 may be configured for obtaining various input signals from a plurality of not shown sensors. Control of the devices may depend on operating conditions and performed in response to software stored in a memory held in the control unit. As an example, the control unit may be operative to control opening and closing of the intake valves 4 via the valve actuating members 8, the gas feeding device and turbocharger; in dependence with operating conditions, user input and drive mode including e.g. feed mode, compound mode and reversed, or at least partially reversed, mode etc.

(55) In FIG. 3C the control unit 26 is, as shown, operative to control the pressure charging system 12, the valve 13 in the wastegate system 103, the EGR valve 10, the EGR drive unit 22, the valve actuating members 8, 9, the bypass valve 16, the valves 25 in the re-directing system 24 etc.

(56) It should be noted, that the control unit 26 may be operative to control one or more devices as required and dependent on the chosen embodiment of the present invention. The control unit 26 may be operative to communicate with additional controllers and communication gateways etc.

(57) FIG. 3C moreover shows, that the EGR system 102 may be connected to an EGR valve arranged in the exhaust gas system 7 upstream turbine 11; hence a high-pressure EGR system 102 is shown.

(58) FIG. 3D schematically shows a further example embodiment of an engine 100 with a low-pressure EGR system 102.

(59) In FIG. 3D it is shown, that the EGR system 102 is connected to an outlet 27 arranged on the turbine 11, and that a low pressure EGR valve 10b is arranged to control EGR flow to the gas feeding device 15.

(60) In additional and not shown embodiments of the present invention, exhaust gas for the EGR system 102 may be branched off downstream the turbine 11 including from a section of the exhaust gas treatment systems.

(61) FIG. 4 schematically shows the principles of late and early Miller-type valve timing for one cylinder 1 according to the present invention.

(62) The upper diagram 104 represents opening and closing profiles of an intake valve.

(63) The lower diagram 105 represent the piston stroke between top dead centre (TDC) at 360 CAD (Crank Angle Degree starting from 0 degree at commence of the expansion stroke) and the bottom dead centre (BDC) at 540 CAD.

(64) The solid line 106, in the upper diagram, represents late Miller-type valve timing. As can be seen, in late Miller-type valve timing, the intake valve opens at approximately 360 CAD and closes at approximately 550 CAD, i.e. after the BDC at 540 CAD; thereby representing late valve closure.

(65) The broken line 107, in the upper diagram, represents early Miller-type valve timing. As can be seen, the intake valve opens at approximately 360 CAD and closes at approximately 530 CAD, i.e. before BDC at 540 CAD; thereby representing an early valve closure.

(66) It should be noted, that FIG. 4 only shows one example of late and early Miller-type valve timing. Depending on different operating conditions, different timing for opening and closing of the inlet valve may be applied without departing from the scope of the present invention.

(67) According to one example embodiment of the invention, late Miller-type valve timing may be applied by closing the intake valve in the range of 540 CAD to 680 CAD, preferably 540 CAD to 640 CAD, more preferred in the range of 540 CAD to 600 CAD and most preferred in the range of 540 CAD to 580 CAD. The selection of the desired range will depend on operating conditions, where the abovementioned ranges have shown desirable results.

(68) According to one example embodiment of the invention, early Miller-type valve timing may be applied by closing the intake valve in the range of 500 CAD to 540 CAD, preferably in the range of 520 CAD to 540 CAD and most preferred in the range of 530 CAD to 540 CAD. The selection of the desired range will depend on operating conditions, where the above-mentioned ranges have shown desirable results.

(69) There are different valve actuation systems available, including valve actuation devices 8, that allows for early and/or late Miller-type valve timing. The actuation systems may be fixed valve actuation systems or variable valve actuation systems. A valve actuation system per se is known in the art and any suitable valve actuation system can be used for late and early Miller-type valve timing in the context of the present invention.

(70) Late Miller-type valve timing keeps the intake valve open longer than the “optimum” at BDC for a traditional four-stroke engine (Otto or Diesel), and thereby increases volumetric efficiency. The effect of this is that the charge gases, i.e. intake air and EGR, are pushed back into the intake system by the piston; hence in effect acting as a pressure charging system to increase the intake system pressure. This increases pumping work, but it also adds thermal transfer in cylinder and intake ports.

(71) Early Miller-type valve timing, intake valve closes before the BDC and has the advantage of less losses than late Miller. Both early and late Miller have the advantage of increased efficiency of the engine by offering the same effective compression ratio and a larger expansion ratio.

(72) FIG. 5 is a graphical representation of the pressure conditions in an exhaust system, an intake system and in the gas feeding device.

(73) The chart 108 shows effective torque load by the gas feeding device 15 (feed mode) as a function of CAD.

(74) The chart 109 shows pressure levels P.sub.before gas feeding device 15 (P_b_pump in chart) and P.sub.after gas feeding device (P_a_pump in chart)

(75) A pressurised intake system may, as mentioned above, include a cooler 18 such as an intercooler. Typically, during flow through the cooler, a few kPa of charge pressure is lost, meaning that the boost pressure in the intake system 6 will be slightly lower than the boost pressure just downstream the compressor 12b. The gas feeding device 15 works, in feed mode, towards the intake system 6, meaning that the pressure at the outlet of the gas feeding device 15 will be substantially equivalent to the boost pressure in the intake system; however, here as well, with a small pressure drop caused mainly by the EGR valve, if present, and any EGR cooler 14. This means that the intake pressure of the gas feeding device 15 is slightly lower than the exhaust manifold pressure; typically a few kPa. The pressure drops are flow dependant, so for very low flows, the pressure drops are basically none. The gas feeding device 15 basically needs to have the same pressure ratio as present over the engine, but with the pressure drop in the EGR cooler+EGR valve+piping added:
ΔP gas feeding device=(P Intake System−P Exhaust System)+ΔP EGR system

(76) The gas feeding device 15 may, as mentioned, be any type of pump capable of feeding or pumping gas. If the gas feeding device 15 constitutes a displacement pump, it will add or receive work only when there is a pressure difference across the pump. This is due to the fact, that the displacement pump has no internal compression.

(77) The preferred type of displacement pump is a Roots pump (blower), which has a continuous flow compared to intermittent flow. This means that the flow is not interrupted and flows continuously into the intake system 6 of the engine 100.

(78) As the gas feeding device 15 is performing work only when there is a higher pressure on the outlet than on the intake side, work is carried out by the gas feeding device 15 when needed only. Similarly, when an exhaust pressure pulse reaches the intake of the gas feeding device 15, no pump work is needed. During such scenarios, exhaust gas is merely transported by the gas feeding device 15 to its outlet without adding work or compressing gas. In addition to this, it is possible to extract energy from the gas feeding device when the pressure ratio is negative. This has been explained in greater detail with reference to FIGS. 3B and 3C.

(79) Turning again to FIG. 5, the various states of operation of the gas feeding device 15 is schematically shown as a result of a control function measuring pressure and possibly further input parameters (engine speed, load etc.) in the engine 100 for the purpose of determining the state of operation. The pressure levels (and possibly further parameters) are measured and supplied to the control unit 26 (FIG. 3D), which, based on the measurements, determines the mode of operation for the gas feeding device 15. As mentioned above, the modes of operation may be EGR feeding or EGR compounding, i.e. energy recovery. In the latter case the energy recovered may be transferred back to the engine or be stored in an energy storage for later use.

(80) FIG. 6A schematically illustrates the main steps of operating the internal combustion engine according to the present invention. The steps are described with reference to the internal combustion engine as described with reference to FIGS. 1-5. The steps are: step S1: branching off a part of the exhaust gas stream from the exhaust system 7 to be returned to the intake system 6 via the EGR system 102, step S2: delivering the branched off exhaust gas stream to the intake system 6, step S3: pressurising the intake system 6 via the pressure charging system 12 to a level above the exhaust gas pressure, step S4: opening the intake valve 4 of the cylinder 1 and maintaining the intake valve 4 open for late or early closing of the intake valve 4.

(81) According to one example embodiment of step S4, the step of late closing relates to keeping the intake valve open until the crankshaft 150 reaches the range of 540 CAD to 680 CAD, preferably the range of 540 CAD to 640 CAD and more preferred the range of 540 CAD to 600 CAD and most preferred the range of 540 CAD to 580 CAD.

(82) According to one example embodiment of step S4, the step of early closing relates to keeping the intake valve open the crankshaft 150 reaches the range of 500 CAD to 540 CAD, preferably the range of 520 CAD to 540 CAD and most preferred the range of 530 CAD to 540 CAD.

(83) FIG. 6B schematically shows an example embodiment of the method shown in FIG. 6A; however with the step of: step S5: prior to S2, pressurising the branched off part of the exhaust gas by operating the gas feeding device 15 in feed mode in dependence of operational parameters of the engine 100 as well as different modes of operation.

(84) FIG. 6C schematically shows an example embodiment of the method shown in FIG. 6A; however, in operating conditions wherein the exhaust gas pressure is higher than the intake pressure. The embodiment incudes the further step of: step S6: opening the bypass valve 16 thereby bypassing the gas feeding device when the exhaust gas pressure in the exhaust system 7 exceeds the pressure in the intake system 6.

(85) FIG. 6D schematically shows an example embodiment of the method shown in FIG. 6A with further steps of: step S7: setting the gas feeding device 15 in compound mode to generate power output when the exhaust gas pressure in the exhaust system 7 is higher than the pressure in the intake system 6 to drive the gas feeding device 15 and thereby the EGR drive unit 22. step S8: transmitting energy to an energy reservoir, e.g. a battery or a capacitor, connected to the EGR drive unit 22 or transferring energy to the engine 100.

(86) FIG. 6E schematically shows an example embodiment of the method according to the invention wherein the method is configured to provide pressure towards the pressure charging system 12.

(87) The method includes the steps of: step S9: setting the EGR drive unit 22 to drive the gas feeding device 15 to provide pressure towards the pressure charging system 12.

(88) In this embodiment, the gas feeding device 15 may draw supply gas from the intake system or from the exhaust system.

(89) FIG. 6F schematically shows an example embodiment of the method shown in FIG. 6A, alternative to the method shown in FIG. 6E, and with a further step of: step S10: controlling valves 25 in the re-directing system 24 to close EGR feed and opening the valve 25 controlling flow to the pressure charging system 12.

(90) FIGS. 7A and 7B schematically show flowcharts illustrating two modes of operation of an internal combustion engine 100 operated in accordance with the second aspect of the present invention. The second aspect of the present invention relates to a method of improving efficiency of an internal combustion engine.

(91) FIG. 7A is a flowchart illustrating the first mode of operation; the first mode includes the steps of: step S20a: operating the internal combustion engine 100 under such conditions that the pressure in the intake system 6 exceeds, or is substantially similar to, the pressure in the exhaust system 7, step S21a: operating the gas feeding device 15 to pressurise and thereby supply branched off exhaust gas to the intake system 6.

(92) FIG. 7B is a flowchart illustrating the second mode of operation; the second mode includes the steps of: step S20b: operating the internal combustion engine 100 under such conditions that the pressure in the exhaust system 7 is higher than the pressure in the intake system 6, and, step S21b: configuring the EGR system 102 and/or the EGR drive unit 22 to be driven by the gas feeding device 15 so as to generate a power output, step S22b: operating the engine 100 so as to drive the gas feeding device 15 by means of exhaust gas flowing from the exhaust system 7 to the intake system 6 and thereby operate the gas feeding device 15 in an energy recovery mode where the EGR drive unit 22 generates a power output.

(93) In some embodiments, the method according to the second aspect of the present invention may be configured for switching between the first and the second mode of operation.

(94) It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.