TECHNICAL FIELD

The present invention relates to an internal combustion engine. The present invention further relates to a method for controlling an internal combustion engine. According to further aspects, the invention relates to a computer program for performing a method for controlling an internal combustion engine, as well as a computer program product for performing a method for controlling an internal combustion engine. BACKGROUND

A piston of a four-stroke internal combustion engine, ICE, performs four strokes, an intake stroke, a compression stroke, a power stroke, and an exhaust stroke in a cylinder of the ICE. A conventional four-stroke ICE has the same geometrical compression ratio and expansion ratio, i.e. the compression stroke has the same length as the power stroke. The working medium is compressed during the compression stroke from bottom dead centre, BDC, of the piston to top dead centre, TDC, of the piston. A certain amount of energy is added around the TDC as the working medium combusts. Thereafter the working medium is expanded during the power stroke. Since the working principle of the conventional ICE involves the same geometrical compression ratio and expansion ratio, there is a lot of power still remaining in the cylinder when the piston reaches the BDC. This is an intrinsic characteristic of the conventional ICE. The power remaining in the cylinder at high load corresponds to approximately 30 % of the brake power and can theoretically be extracted in e.g. a turbine connected to an exhaust arrangement of the cylinder. The brake power of an ICE is the power available at an output shaft/crankshaft of the ICE.

The exhaust arrangement of the ICE has to be opened before the piston reaches its BDC during the power stroke. Otherwise, if the exhaust arrangement would open later, e.g., when the piston reaches the BDC, the internal pressure from the exhaust gas (working medium) inside the cylinder would impede the movement of the piston towards the TDC during the exhaust stroke. Accordingly, available engine power would be reduced.

The exhaust arrangement of a conventional four-stroke ICE comprises at least one poppet valve. A poppet valve is a robust and durable solution able to withstand a cylinder pressure of 25 MPa and a cylinder gas temperature of more than 2000 K while remaining gas tight. However, a poppet valve controlled by a camshaft has a drawback in that it is at rest when it starts to open, which entails a slow initial opening speed of the poppet valve. Thus, the poppet valve throttles an outflow of exhaust gas through the exhaust arrangement. At least a first amount of exhaust gas within the cylinder flows past the poppet valve as it opens up and is throttled before the poppet valve provides a large opening for passage of the exhaust gas. This reduces the available energy in the exhaust gas in a non-reversible process. Expressed differently, a poppet valve produces a large percentage of irreversible pressure loss due to throttling of the exhaust gas as they pass the poppet valve.

As indicated above, an ICE may comprise a turbine for utilising exhaust gas pressure to drive a turbine wheel of the turbine. From the discussion above it follows that low exhaust gas pressure loss in a flow path from the cylinder to a turbine is problematic to achieve.

US 3961484 discloses an ICE. The ICE utilises a power recovery turbine operated by the exhaust gases from the engine cylinders by dimensioning the stacks connecting the exhaust valve flow areas to the turbine such that each stack has a cross-sectional flow area less than the cross-sectional flow area of the exhaust valve when fully opened. While there results a slight increase in frictional losses in the stack and pumping losses to the piston, such losses are allegedly made up by decreases in throttling losses across the exhaust valve flow area during the valve opening process. However, there still remains the throttling problem associated with the poppet valve proving a slow increase in exhaust valve flow area inherent with a poppet valve.

US 4535592 discloses a turbo compound ICE having conventional reciprocally movable pistons, cylinders, manifolds, fuel-oxygen admixing apparatus or fuel injection, firing apparatus or compression ignition. The ICE comprises respective nozzle means for conveying the exhaust gas from the respective cylinders to one or more turbines. The nozzle means have its inlet and discharge ends connected, respectively, with the respective boundary walls of respective combustion chambers or cylinders and with the inlet to a turbine. A quick opening valve admits exhaust gas from the respective cylinder to the nozzle means. Thus, an efficient use of exhaust gas by a turbine employed with the engine is provided. A poppet valve may open at a later stage during an exhaust stroke after most of the useful exhaust gas energy is expended through the quick opening valve and the nozzle.

One problem with the quick opening valve is that it is difficult to provide a seal with the quick opening valve, which seal is able to withstand the high temperature and pressure inside the respective cylinder. DE 102010008264 discloses an exhaust gas turbocharged low-displacement internal combustion engine. The small size reduces fuel consumption while turbo charging counteracts reduction in performance. In a low-displacement internal combustion engine, especially at low speeds, where the exhaust gas flow is low, only a small amount energy is available for driving the turbocharger. Accordingly, such internal combustion engines provide low torque at low speeds. DE 102010008264 suggests that the exhaust pipes lead via a shut-off device to the exhaust gas turbine of the turbocharger. The shut-off device is controlled such that a respective exhaust pipe is blocked when the exhaust valve of the respective cylinder opens. As a result of the shut-off of the exhaust pipe upstream of the shut-off device an exhaust gas, pressure is built up, e.g. up to 10 bar. Consequently, when the shut-off device opens, a pressure pulse is directed to the exhaust gas turbine. The pressure pulse causes an effective drive of the turbine and thus, allows effective charging.

Accordingly, a higher charging pressure is achieved at low engine speeds, which may be beneficial in a low-displacement internal combustion engine. However, the build-up of a high pressure in the exhaust pipe upstream of the shut-off device comes at a cost. Instead of traveling unimpededly upwardly in the relevant cylinder bore with an open exhaust valve, the piston meets resistance form the closed shut-off device and the resulting pressure build-up. Thus, more energy is required to move the piston upwardly in the cylinder bore.

SUMMARY

It would be advantageous to achieve an internal combustion engine, ICE, overcoming, or at least alleviating, at least some of the above mentioned drawbacks. In particular, it would be desirable to enable low throttling losses in a flow of exhaust gas from a cylinder of the ICE in order to be able to utilise a large portion of remaining energy in the exhaust gases in a turbine connected to an exhaust opening of the ICE. To better address one or more of these concerns, an ICE, a vehicle, and a method for controlling an ICE, having the features defined in the independent claims is provided. According to an aspect of the invention, there is provided an internal combustion engine; ICE, comprising a crankshaft, at least one cylinder arrangement, and a turbine. The at least one cylinder arrangement forms a combustion chamber, and comprises a cylinder bore, a piston arranged to reciprocate in the cylinder bore between a top dead centre, TDC, and a bottom dead centre, BDC, an exhaust valve, and an exhaust opening arranged at an inner delimiting surface of the combustion chamber, the exhaust valve comprising a valve head configured to seal against a valve seat of the exhaust opening. An exhaust conduit extends from the exhaust opening to an inlet of the turbine. The internal combustion engine comprises a second valve arranged in the exhaust conduit, the second valve being configured to close and open the exhaust conduit, wherein the second valve is opened after the exhaust valve has started to open. The second valve has a faster valve area opening speed than the exhaust valve, wherein the second valve starts to open within a range of 10 - 90 degrees crankshaft angle after the exhaust valve has started to open.

Since the ICE comprises a second valve arranged in the exhaust conduit, the second valve being configured to close and open the exhaust conduit, and being opened after the exhaust valve has started to open, within a range of 10 - 90 degrees crankshaft angle after the exhaust valve has started to open, the pressure between the cylinder bore and the exhaust conduit upstream of the second valve is equalised, at least to a certain degree before the second valve opens. Moreover, since the second valve has a faster valve area opening speed than the exhaust valve, the exhaust gases are subjected to less throttling as they pass the second valve to the turbine than when they passed the exhaust valve. Thus, a relatively high percentage of the available energy from the exhaust gases may be recovered in the turbine connected to the exhaust conduit. As a result, the above-mentioned object is achieved.

More specifically, as the exhaust valve opens before the second valve, the pressure in a first portion of the exhaust conduit up to the closed second valve gradually increases, preferably until the pressure between the cylinder bore and the first portion of the exhaust conduit has been substantially equalised. Thus, exhaust gas flow across the exhaust valve during the initial phase of opening the exhaust valve can take place while the turbine is isolated from communicating with the exhaust valve by the second valve. Once the second valve starts to open, the exhaust valve will have been opened to such a degree that the exhaust gases flow substantially unimpeded through the exhaust opening. Since the second valve has a faster valve area opening speed than the exhaust valve, the exhaust gases reach the turbine with less throttling than if there were no second valve and the exhaust opening would

communicate directly via the exhaust conduit with the turbine.

Thus, the exhaust valve may be configured to withstand the high pressures and

temperatures during combustion within the cylinder bore, while the second valve is arranged protected from the high pressures and temperatures in the exhaust conduit, and thus, does not have to be configured for withstanding the same high pressures and temperatures.

Instead, the second valve may be configured for fast opening in order to provide a low loss transfer of the exhaust gases to the turbine. The exhaust gases present in the cylinder, at the end of the power stroke and the beginning of the exhaust stroke, will be available for extraction of the remaining energy therein with much lower irreversible losses than has been possible in connection with an ICE wherein the exhaust gases have been throttle across an exhaust valve when passing directly through an exhaust conduit to a turbine. Thus, in an ICE according to the present invention, recovery of energy from the exhaust gases in the turbine arranged downstream of the exhaust valve may be improved. This efficient transfer of the exhaust gases from the cylinder to the turbine is achieved by the fast opening second valve, which considerably reduces the irreversible throttling losses typically occurring across the exhaust valves of an ICE wherein the exhaust valves communicate directly with the turbine.

Accordingly, the invention provides for an increased utilisation of the energy available in the cylinder at the end of the power stroke. The invention entails the possibility to increase recovery of energy from the exhaust gases compared to an ICE that would otherwise have been wasted in a non-reversible throttling process across the exhaust valve.

This increased recovered energy may be used to:

Increase the work transferred from the turbine to a centrifugal compressor in order to improve the positive pumping work during induction, i.e. increased Open Cycle Efficiency, OCE, or increase relative air/fuel ratio, λ, i.e. increased Closed Cycle

Efficiency, CCE.

Drive a specific turbine that delivers power to an electrical motor/generator unit, MGU attached to a shaft of the turbine, or to the crankshaft of the ICE, i.e. turbo

compounding, or to auxiliary devices of e.g. a relevant vehicle.

A number of the above mentioned alternatives for utilising the increased recovered energy may be employed simultaneously, e.g. the combination of turbo charging along with turbo compounding (electrical or mechanical), implemented with the use of a turbine. Furthermore, the negative piston pumping work during the exhaust stroke will be eliminated or at least significantly reduced, resulting in increased OCE. In summary, the present invention will result in an increase in Brake Thermal Efficiency, BTE, compared to an ICE wherein the exhaust valves communicate directly with the turbine via the exhaust conduit.

The ICE may be a four-stroke ICE, or a two-stroke ICE. The ICE may comprise more than one cylinder arrangement, each cylinder arrangement forming a combustion chamber and comprising a cylinder bore, a piston arranged to reciprocate in the cylinder bore, a connecting rod connecting the piston with a crankshaft, and an exhaust valve for outflow of exhaust gas from the cylinder bore. The ICE may comprise more than one turbine, such as e.g. two turbines, or one turbine for each cylinder arrangement of the ICE. In case of two turbines, the exhaust valves of a number of cylinder arrangements may be connected to one turbine, and the exhaust valves of the remaining cylinder arrangements may be connected to the other turbine. The turbine may for instance form part of a turbocharger, the ICE may be a turbo compound engine, to which the turbine may be connected via the crankshaft, or the turbine may drive an electric generator.

The term, valve area opening speed, relates to the speed at which a valve opens, i.e. the change of opening area of a valve per time unit, e.g. m ² /second. The valve area opening speed may be linear, or non-linear, e.g. increasing. The second valve having a faster valve area opening speed than the exhaust valve means that the second valve has a faster valve area opening speed at the instance when the second valve starts to open than the opening speed of the exhaust valve when it starts to open. In this manner throttling losses across the second valve are lower compared to throttling losses across the exhaust valve, if the exhaust valve would be directly connected to a turbine as in a prior art ICE.

The combustion chamber is arranged inside the cylinder arrangement, above the piston.

Intake air enters the combustion chamber through an intake arrangement of the cylinder arrangement during the intake stroke of the piston. The intake air may be compressed by a turbocharger. The internal combustion engine may be e.g. a compression ignition (CI) engine, such as a diesel type engine, or a spark ignition engine, such as an Otto type engine and comprises in the latter case a sparkplug or similar device in the cylinder arrangement.

Fuel may be injected into the combustion chamber during part of the compression stroke or intake stroke of the piston, or may be entrained with the intake air. The fuel may ignite near the TDC between the compression stroke and the power stroke of the piston.

According to embodiments, the at least one cylinder arrangement forms a combustion chamber, wherein the cylinder arrangement has a maximum volume, V MAX, between a bottom dead centre, BDC, of the piston and an upper inner delimiting surface of the combustion chamber. The second valve may be arranged at a position in the exhaust conduit within a range of 1 % - 25 % of the maximum volume, V _M AX, downstream of the exhaust opening, or within a range of 1 % - 1 5 % of the maximum volume, VMAX, downstream of the exhaust opening. In this manner, a volume of a first portion of the exhaust conduit, between the exhaust valve and the second valve, may have a volume, which permits pressure

equalisation, at least to a large extent, between the combustion chamber and the first portion of the exhaust conduit, before the second valve starts to open. The second valve being arranged at a position in the exhaust conduit expressed in a defined volume, means that the defined volume, in this case defined in percent of the maximum volume of the combustion chamber, is provided in the exhaust conduit between the exhaust opening and the second valve.

According to embodiments, the second valve may comprise a valve body, the valve body may have a flow passing positional range, in which a flow of exhaust gas passes the second valve, and a zero-flow positional range, in which the exhaust conduit is closed at the second valve, and wherein the valve body is configured to be set into motion before the valve body reaches the flow passing positional range. In this manner, the second valve may provide a fast valve area opening speed. In comparison with a poppet valve, which has to be accelerated from a rest position when it is opened, the valve body being in motion may provide a faster valve area opening speed. According to a further aspect of the invention, there is provided a vehicle comprising an internal combustion engine according to any one of aspects and/or embodiments discussed herein.

According to a further aspect of the invention, there is provided a method for controlling an internal combustion engine, the internal combustion engine comprising at least one cylinder arrangement, a crankshaft, and a turbine. The at least one cylinder arrangement forms a combustion chamber, and comprises a cylinder bore, a piston arranged to reciprocate in the cylinder bore between a top dead centre and a bottom dead centre, a connecting rod connecting the piston with the crankshaft, an exhaust valve and an exhaust opening arranged at an inner delimiting surface of the combustion chamber, the exhaust valve comprising a valve head configured to seal against a valve seat of the exhaust opening. An exhaust conduit extends from the exhaust opening to an inlet of the turbine. The internal combustion engine comprises a second valve arranged in the exhaust conduit, the second valve being configured to close and open the exhaust conduit. The method comprises, in sequence, steps of:

- opening the exhaust valve,

- turning the crankshaft a predetermined crankshaft angle within a range of 10 - 90 degrees, and thereafter

- opening the second valve at a faster valve area opening speed than the exhaust valve.

Further features of, and advantages with, the invention will become apparent when studying the appended claims and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and/or embodiments of the invention, including its particular features and advantages, will be readily understood from the example embodiments discussed in the following detailed description and the accompanying drawings, in which:

Fig. 1 schematically illustrates an internal combustion engine, ICE, according to

embodiments,

Fig. 2 schematically illustrates a cylinder arrangement of an ICE 2,

Figs. 3a - 3c schematically illustrate cross-sections through a second valve according to embodiments,

Figs. 4a - 4e illustrate alternative embodiments of a second valve,

Figs. 5 and 6 illustrate embodiments of ICE:s with more than one cylinder arrangement, Fig. 7 shows a schematic example of a turbine map of a turbine, and

Fig. 8 illustrates a method for controlling an ICE.

Fig. 9 schematically illustrates the opening and closing of an exhaust valve and a second valve.

DETAILED DESCRIPTION

Aspects and/or embodiments of the invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 schematically illustrates an internal combustion engine, ICE, 2 according to embodiments. In these embodiments, the ICE 2 is a four-stroke ICE. The ICE 2 comprises at least one cylinder arrangement 4, a crankshaft 20, and a turbine 8. Fig. 1 also schematically illustrates a vehicle 1 comprising an internal combustion engine 2 according to any one aspect and/or embodiment disclosed herein. The vehicle 1 may be e.g. a heavy vehicle such as a truck or a bus.

The at least one cylinder arrangement 4 forms a combustion chamber 23, and comprises a cylinder bore 12, a piston 10, an exhaust arrangement 14, an inlet arrangement 16, and a fuel injection arrangement 18, and/or an ignition device. The piston 10 is arranged to reciprocate in the cylinder bore 12 between a top dead centre, TDC, and a bottom dead centre, BDC. In Fig. 1 , the piston 10 is illustrated with continuous lines at BDC, and with dashed lines at TDC. The cylinder arrangement 4 has a maximum volume, V _M AX, between the BDC of the piston 10 and an upper inner delimiting surface 24 of the combustion chamber 23. The combustion chamber 23 is formed above the piston 10 inside the cylinder arrangement 4. A connecting rod 22 connects the piston 10 with the crankshaft 20. The cylinder arrangement 4 has a total swept volume, V _s , in the cylinder bore 12 between the BDC and the TDC of the piston 10. The cylinder arrangement 4 has a compression ratio, ε. VMAX may be expressed as:

The exhaust arrangement 14 comprises an exhaust valve and an exhaust opening as will be discussed below with reference to Fig. 2. The exhaust arrangement 14 is arranged for outflow of exhaust gases from the cylinder bore 12 to the turbine 8. An exhaust conduit 6 extends from the exhaust opening to an inlet 29 of the turbine 8. The ICE 2 comprises a second valve 40 arranged in the exhaust conduit 6. The exhaust arrangement 14 is configured to open and close an exhaust flow area, ACYL, of the exhaust opening during an exhaust sequence of the piston reciprocation. The exhaust sequence may start before the piston 10 reaches its BDC during the power stroke and ends around the TDC of the piston between the exhaust stroke and the intake stroke.

The turbine 8 has an inlet 29 and comprises a turbine wheel 27.

Fig. 2 schematically illustrates the at least one cylinder arrangement 4 of the ICE 2 of Fig. 1 . In particular, the exhaust arrangement 14 is shown in more detail. The exhaust arrangement 14 comprises an exhaust valve 26 and an exhaust opening 28. The exhaust gases escape from the combustion chamber 23 through the exhaust opening 28 as soon as the exhaust valve 26 starts to open. The exhaust conduit 6 extends from the exhaust opening 28 to the inlet 29 of the turbine 8. The exhaust valve 26 comprising a valve head 30 configured to seal against a valve seat 32 extending around the exhaust opening 28. The valve seat 32 may be provided in the cylinder arrangement 4 e.g. at the upper inner delimiting surface 24 of the combustion chamber 23. The exhaust valve 26 may be a poppet valve as known in the art. In such manner, there is provided a robust and durable solution able to withstand a cylinder pressure of up to 25 MPa or more, and a cylinder gas temperature of more than 2000 K while providing a gas tight sealing of the exhaust opening 28 during the combustion stroke.

The ICE 2 may comprise a camshaft 25 for controlling movement of the exhaust valve 26, and opening and closing of the exhaust valve 26. The camshaft 25 comprises a lobe 34 configured to cause a motion of the valve head 30 for opening and closing the exhaust opening 28. As the camshaft 25 rotates, the end portion 36 of the exhaust valve 26 follows the lobe 34, causing the motion of the valve head 30. The exhaust valve 26 may be biased towards its closed position, as known in the art, e.g. by means of a spring (not shown). In embodiments, wherein the ICE 2 is a four-stroke ICE, the inlet arrangement 16 may comprise an inlet valve 42, movements of which are controlled by a camshaft 44 in a similar manner to the exhaust valve 26, as shown in Fig. 2. In embodiments, wherein the ICE 2 is a two-stroke ICE, there may instead be provided an inlet port in the cylinder bore 12, as is known in the art. The inlet valve 42, or the intake port, is separate from the exhaust valve 26. That is, intake gas flows through the intake valve 42, or the intake port, directly into the cylinder bore 12, and does not pass the exhaust valve 26, and the exhaust gases flow directly from the cylinder bore 12 through the exhaust valve 26, and do not pass the intake valve 42 or intake port.

The ICE 2 comprises a second valve 40 arranged in the exhaust conduit 6. The second valve 40 is configured to close and open the exhaust conduit 6. The second valve 40 is opened after the exhaust valve 26 has started to open, within a range of 10 - 90 degrees crankshaft angle after the exhaust valve has started to open. The second valve 40 has a faster valve area opening speed than the exhaust valve 26. In this manner, the exhaust gases are subjected to low throttling as they pass the second valve 40 compared to when they pass an exhaust valve in an ordinary ICE without the second valve in the exhaust conduit. Less throttling means that more energy is available for recovery from the exhaust gases in the turbine 8 connected to the exhaust conduit 6.

When the exhaust valve 26 starts to open, a pressure in a first portion 60 of the exhaust conduit 6, from the outlet opening 28 to the second valve 40, gradually increases before the second valve 40 starts to open. Suitably, the pressure in the cylinder bore 12 and the first portion 60 of the exhaust conduit 6 is substantially the same before the second valve 40 starts to open. Since the second valve 40 is closed while the exhaust valve 26 starts to open, flow of exhaust gases across the exhaust valve 26 during the initial phase of opening the exhaust valve 26 will not affect the transfer of exhaust gases to the turbine 8. The faster valve area opening speed of the second valve 40 than of the exhaust valve 26, ensures efficient transfer of the exhaust gases to the turbine 8 through a second portion 62 of the exhaust conduit 6. The second portion 62 of the exhaust conduit extends from the second valve 26 to the inlet 29 of the turbine 8.

Fig. 9 schematically illustrates the opening and closing of the exhaust valve 26 and the second valve 40. One full four-stroke cycle of a four-stroke ICE 2 is indicated along the axis in Fig. 9. The exhaust valve 26 and the second valve 40 are opened and closed with the same frequency, i.e. the exhaust and second valves 40, 26, open the same number of times during operation of the ICE 2. However, they may remain open during time periods of different lengths. For instance, since the exhaust valve 26 opens before the second valve 40, the exhaust valve 26 may remain open for a longer period of time than the second valve 40 in order to permit all exhaust gases to escape from the combustion chamber 23. This is shown with full lines in Fig. 9. The second valve 40 may close at the same time as the exhaust valve 26, as shown with the full lines in Fig. 9. Alternatively, the second valve 40 may close later than the exhaust valve 26, as shown with the broken line in Fig. 9. Naturally, when the exhaust valve 26 starts to open again the second valve 40 must be closed.

According to some embodiments, the second valve 40 may have a valve area opening speed >0,75 m ² /sec. In this manner, a faster opening of the second valve 40 may be provided than by the exhaust valve 26, and efficient recovery of energy from the exhaust gases in the turbine 8 arranged downstream of the second valve 20 may be achieved. The valve area opening speed may vary during the opening of the second valve 40. For instance, the valve area opening speed may increase during the opening of the second valve 40.

Now referring to Figs. 1 and 2, the second valve 40 may be arranged at a position in the exhaust conduit 6 within a range of 1 % - 25 % of the maximum volume, VMAX, downstream of the exhaust opening 28, preferably within a range of 1 % - 1 5 % of the maximum volume, VMAX, downstream of the exhaust opening 28. That is, the first portion 60 of the exhaust conduit 6 has a volume within a range of 1 % - 25 % of the maximum volume, VMAX, or according to alternative embodiments, within a range of 1 % - 1 5 % of the maximum volume, VMAX. Thus, the volume of the first portion 60 of the exhaust conduit 6 has a volume in relation to V MAX, which permits pressure equalisation, at least to a large extent, between the combustion chamber 23 and the first portion 60 of the exhaust conduit 6, before the second valve 40 starts to open. Put differently, the second valve 40 is opened when pressure equalization between the cylinder bore and the first portion 60 of the exhaust conduit 6 has occurred to a substantial degree. Moreover, the second valve 40 is opened when the exhaust valve 26 has exposed sufficient area to not produce a palpable throttling of the exhaust gases when second valve 40 is opened

The second valve 40 starts to open within a range of 1 0 - 90 degrees crankshaft angle after the exhaust valve 26 has started to open, preferably within a range of 1 0 - 40 degrees crankshaft angle after the exhaust valve 26 has started to open, or within a range of 30 - 40 degrees crankshaft angle after the exhaust valve 26 has started to open. In this manner, pressure equalisation, at least to a large extent, between the combustion chamber 23 and the first portion 60 of the exhaust conduit 6, before the second valve 40 starts to open is permitted. Suitably, the second valve 40 is not opened later than 1 0 degrees crankshaft angle after BDC.

As mentioned above, the at least one cylinder arrangement 4 forms a combustion chamber 23, and the cylinder arrangement 4 has a maximum volume, V MAX, between a bottom dead centre, BDC, of the piston 10 and an upper inner delimiting surface 24 of the combustion chamber 23. According to embodiments, the inlet 29 of the turbine 8 has a turbine inlet area, A™, wherein the exhaust conduit 6 has an exhaust conduit volume, VEXH , extending from the exhaust opening 28 to the turbine inlet area, A™, and wherein the exhaust conduit volume, V EXH≤ 0.5 times the maximum volume, VMAX. In this manner, the exhaust conduit 6 may have a volume suitable for transferring the exhaust gases efficiently to the turbine 8. More specifically, with the above mentioned volume of the first portion 60 of the exhaust conduit 6, the second portion 62 of the exhaust conduit 62 accordingly, having a volume within a range of 75 % - 99 % of VMAX, the second portion 62 has a volume suitable for transferring the exhaust gases efficiently from the second valve 40 to the turbine 8, and thus, for efficiently driving the turbine 8.

The turbine wheel inlet area, A™, is provided at an opening of a housing of the turbine where the exhaust gases are admitted to the turbine wheel 27. The turbine wheel inlet area, A™, may suitably be the nozzle throat area of the turbine 8. The nozzle throat area may also be referred to as turbine house throat area, turbine house critical area, or similar and may often be specified for a specific turbine. In case the nozzle throat is not specified for a specific turbine, and/or the position of the nozzle throat area is not specified, the turbine wheel inlet area, A™, extends perpendicularly to a flow direction of the exhaust gases. In embodiments of turbines where the exhaust conduit extends along a portion of the turbine wheel e.g. in a volute, such as e.g. in a twin scroll turbocharger, the turbine wheel inlet area, A™, is defined at the section of the exhaust conduit where the turbine wheel is first exposed to the exhaust gases emanating from the relevant cylinder arrangement. As mentioned above, the exhaust arrangement 14 is configured to open and close an exhaust flow area, A _C YL, of the exhaust opening 28 during an exhaust sequence. The exhaust conduit 6 connects the exhaust opening 28 with the turbine 8. The exhaust conduit 6 has an exhaust conduit volume, V _E XH . In Fig. 1 the exhaust conduit volume, V EXH , is illustrated as a box. In practice, the exhaust conduit 6 extends between the exhaust flow area, ACYL, and the turbine wheel inlet area, A™, on both sides of the second valve 40. Accordingly, the exhaust conduit volume, VEXH is formed by the volume of the exhaust conduit between the exhaust flow area, ACYL, of the exhaust opening 28 and the turbine wheel inlet area, A™.

In these embodiments, the exhaust conduit 6 fluidly connects only the exhaust opening 28 with the inlet 29 of the turbine 8. That is, the exhaust conduit 6 forms a separate conduit extending between the exhaust flow area, ACYL, and the turbine wheel inlet area, A™. The separate conduit does not have any other inlets or outlets for exhaust gases. Thus, the turbine wheel inlet area, A™, is a dedicated inlet area of the turbine 8 for the particular exhaust flow area, ACYL, connected thereto via the exhaust conduit 6.

The turbine wheel 27 of the turbine 8 may be connected to an impeller (not shown) for compressing and transporting intake air to the inlet arrangement 16. According to some embodiments, the turbine wheel 27 may be an axial turbine wheel. A turbine 8 comprising an axial turbine wheel may provide low backpressure. However, according to alternative embodiments the turbine wheel may be a radial turbine wheel, which also may provide low backpressure.

According to some embodiments, the cylinder arrangement 4 may have a total swept volume, V _s , in the cylinder bore 12 between the bottom dead centre, BDC, and the top dead centre, TDC, of the piston 10, wherein 0.3 < V _s < 4 litres. Mentioned purely as an example, in the lower range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for a passenger car, and in the middle and higher range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for a heavy load vehicle such as e.g. a truck, a bus, or a construction vehicle. Also in the higher range of Vs, the cylinder arrangement 4 may form part of an internal combustion engine for e.g. a generator set (genset), for marine use, or for rail bound (train) use.

Figs. 3a - 3c schematically illustrate cross-sections through a second valve 40 according to embodiments arranged in an exhaust conduit 6. The exhaust conduit 6 and the second valve 40 illustrate an example of the exhaust conduit 6 and the second valve 40 of Figs. 1 and 2.

The second valve 40 comprises a valve body 64 arranged in a valve housing 66. The valve body 64 has a through opening 68. The valve body 64 is movable in the valve housing 66 such that the through opening 68 either provides fluid communication between the first portion 60 of the exhaust conduit 6 and the second portion 62 of the exhaust conduit 6 on both sides of the second valve 40, or the valve body 64 prevents fluid communication between the first portion 60 and the second portion 62 of the exhaust conduit 6. Put differently, the valve body 64 has a flow passing positional range, in which a flow of exhaust gas passes the second valve 40, and a zero-flow positional range, in which the exhaust conduit 6 is closed at the second valve 40. In Fig. 3a the valve body 64 is shown arranged within the zero-flow positional range. The zero-flow positional range encompasses all positions of the valve body 64, in which flow through the second valve 40 is prevented. In Fig. 3b the valve body 64 has reached the beginning of the flow passing positional range, i.e. just when the second valve 40 starts to open as the through opening 68 fluidly connects the first and second portions 60, 62 of the exhaust conduit 6. In Fig. 3c the valve body 64 is also shown in the flow passing positional range, the through opening 68 having reached a position, in which the second valve 40 is fully open. Accordingly, as long as the through opening 68 fluidly connects the first and second portions 60, 62 of the exhaust conduit 6, the valve body 64 is in the flow passing positional range.

As can be concluded from Fig. 3a, and that the valve body 64 is arranged with the through opening 68 at a distance from the exhaust conduit 6, the valve body 64 is configured to be set into motion before the valve body 64 reaches the flow passing positional range. This means that the valve body 64 may be accelerated while the valve body 64 is in the zero/flow positional range. Accordingly, when the valve body 64 reaches the flow passing positional range, the valve body 64 may have a considerable speed. Thus, the second valve may provide a fast valve area opening speed, in particular, in comparison with a valve, which has to be accelerated from a rest position when it is opened, such as e.g. a poppet valve. In an alternative embodiment, the valve body may be continuously in motion thus, avoiding the need to accelerate the valve body. Instead, the valve body may be moved at a speed providing a higher valve area opening speed than the exhaust valve. This may be achieved in the embodiments according to Figs. 4a - 4e, below.

Figs. 3a - 3c illustrate the operating principle of the second valve 40.

Figs. 3a - 3c also illustrate a second valve 40 according to embodiments wherein the valve body 64 is configured to reciprocate. That is, the valve body 64 is arranged to linearly move back and forth in the valve housing 66. As the valve body 64 reciprocates, it moves between the zero-flow positional range and the flow passing positional range.

Alternative embodiments of the second valve 40, providing a fast valve area opening speed, are schematically illustrated in Figs. 4a - 4e. In the Figs. 4a - 4e embodiments of the second valve 40 the valve body 64 is configured to rotate.

In the embodiments of Fig. 4a and 4b the valve body 64 is configured to rotate about a rotation axis 70 extending substantially perpendicularly to the exhaust conduit 6. That is, the rotation axis 70 extends substantially perpendicularly to the through opening 68. As the valve body 64 rotates about the rotation axis 70, the valve body 64 moves from the zero-flow positional range to the flow passing positional range. In Fig. 4a the valve body 64 is shown in the zero-flow positional range. As discussed above, the valve body 64 is configured to be set into motion before the valve body 64 reaches the flow passing positional range. In Fig. 4b the valve body 64 is shown in the flow passing positional range. The valve body 64 may rotate one or more revolutions as it is moved between the zero-flow positional range and the flow passing positional range. The valve body 64 may be continuously rotated. Alternatively, the valve body 64 may pivot back and forth as it is moved between the zero-flow positional range and the flow passing positional range.

Fig. 4c shows a cross-section along the exhaust conduit 6, while Figs. 4d and 4e show cross-sections perpendicularly to the exhaust conduit 6 through the second valve 40. In the embodiments of Figs. 4c - 4e the valve body 64 is configured to rotate about a rotational axis 72 extending substantially in parallel with the exhaust conduit 6. That is, the rotation axis 70 extends substantially in line with the through opening 68. As the valve body 64 rotates about the rotational axis 72, the valve body 64 moves from the zero-flow positional range to the flow passing positional range. In Fig. 4d the valve body 64 is shown in the zero-flow positional range. As discussed above, the valve body 64 is configured to be set into motion before the valve body 64 reaches the flow passing positional range. In Figs. 4c and e the valve body 64 is shown in the flow passing positional range. The valve body 64 may rotate one or more revolutions as it is moved between the zero-flow positional range and the flow passing positional range. The valve body 64 may be continuously rotated. Alternatively, the valve body 64 may pivot back and forth as it is moved between the zero-flow positional range and the flow passing positional range.

In the embodiments of Figs. 3a - 4e, the through hole 68 has been illustrated to have the same diameter as the exhaust conduit 6. In alternative embodiments, the through hole 68 may have a diameter larger than the exhaust conduit 6.

According to alternative embodiments, the valve body 64 need not be provided with a through hole. For instance, the valve body may be provided with a recess instead of the through hole. A further alternative may be that the valve body blocks the exhaust conduit in the zero-flow positional range, and is at least partially removed from the exhaust conduit in the flow passing positional range. According to some embodiments, the movement of the valve body 64 may be controlled by a mechanical link to e.g. the crankshaft or a camshaft of the ICE, such as by cogwheels, a chain, a belt, or a rocker mechanism. Such a mechanical link is arranged to time the opening and closing of the second valve with the strokes of the piston in the cylinder bore and such that the second valve opens after the exhaust valve. A Geneva drive, also referred to as Maltese Cross mechanism, may be form part of the mechanical link.

In the embodiments of Fig. 2 the movement of the second valve 40, i.e. the valve body of the second valve 40 are controlled by a control unit 54 and an electric motor 50. The control unit 54 controls the electric motor 50 to move the valve body of the second valve 40 between the zero-flow positional range and the flow passing positional range. The control unit 54 establishes a rotational position of the crankshaft 20 utilising a sensor 52 connected to the control unit 54. Thus, the control unit 54 is able to time the opening and closing of the second valve 40 with e.g. the exhaust valve 26. The control unit 54 may be configured to provide different timings for opening and/or closing the second valve 40 based e.g. on rotational speed of the crankshaft 20, the current load on the ICE 2, and/or operating conditions of the ICE 2 or of a vehicle 1 in which the ICE 2 is mounted. The electric motor 50 may be directly connected with the valve body of the second valve 40, or via gears or other mechanism, such as a Geneva drive. The control unit 54 may comprise a calculation unit which may take the form of substantially any suitable type of processor circuit or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The herein utilised expression calculation unit may represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The control system may comprise a memory unit. The calculation unit is connected to the memory unit, which may provide the calculation unit with, for example, stored programme code and/or stored data which the calculation unit needs to enable it to do calculations. The calculation unit may also be adapted to storing partial or final results of calculations in the memory unit. The memory unit may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis. The control unit 54 may be configured to control further functions of the ICE 2, and may for instance form part of an engine control system of the ICE 2. The control unit 54 may communicate with e.g. the electric motor 50 and/or the sensor 52 via one or more communication buses. Figs. 5 and 6 illustrate embodiments of the ICE 2, wherein more than one cylinder arrangement may connect to a turbine 8.

Fig. 5 illustrates embodiments wherein two cylinder arrangements 4 are connected to a turbine 8 via one turbine wheel inlet area, A™, i.e. the two cylinder arrangements 4 share the same turbine wheel inlet area, A™. Accordingly, the exhaust conduit branches 6', 6" from the exhaust port arrangements 14 of the two cylinder arrangements 4 are connected to form a common exhaust conduit 6 leading to the turbine 8 and the turbine wheel inlet area, A™. Since there exists a certain degree of crossflow between the two exhaust conduit branches 6', 6" as exhaust gases flow from one of the cylinder arrangements 4 to the turbine wheel inlet area, A™, the above discussed criteria: V EXH≤ 0.5 * VMAX may be valid for the collective exhaust conduit volume, VEXH . More specifically, the collective exhaust conduit volume, VEXH , is formed by the volume from A _C YL of one exhaust valve 26 in a first of the exhaust conduit branches 6', 6" and from the second valve 40 in a second of the exhaust conduit branches 6', 6" to A™ of the turbine 8. Namely, when exhaust gases from the cylinder arrangement 4 connected to the first exhaust conduit branch 6' are conducted to the turbine wheel inlet area, A™, the second valve 40 in the second exhaust conduit branch 6" suitably, is closed, and vice versa.

Fig. 6 illustrates embodiments wherein two cylinder arrangements 4 are connected to a turbine 8 via two separate exhaust conduits 6, each leading to one turbine wheel inlet area, A™. The turbine wheel inlet areas, A™, are positioned such that they may be considered to be connect to the turbine 8 at one position of the turbine 8. Accordingly, in these

embodiments, the turbine 8 is a multi-entry turbine comprising at least one further inlet 29', in addition to the inlet 29. That is, the further inlet 29' is separate from the inlet 29. The crossflow between two turbine wheel inlet areas, A™, in these embodiments is negligible. Accordingly, for each of the exhaust conduits 6 the above discussed criteria: V _E XH≤ 0.5 * VMAX may be valid.

In general, volumes of connections to/from the exhaust conduits 6 are not considered to form part of the exhaust conduit volume, V EXH , if such connections have a cross-sectional area below a limit value. According to embodiments, the exhaust conduit volume, VEXH , may exclude all volumes connected to the exhaust conduit via a connection having a total connection cross-section area, AGON ,≤ 0.022 times the maximum volume, VMAX, i.e. AGON≤ 0.022 * VMAX. With such a small cross-sectional area, AGON, any crossflow of exhaust gases through a connection is negligible. It may be noted that the factor 0.022 includes a conversion from volume to area, and has in this case the unit m ^~1 .

In Fig. 6 two example connections 7 with total minimum connection cross-section areas, AGON, have been indicated. Mentioned purely as an example, such connections 7 may form part of an exhaust gas recirculation (EGR) system, or may connect to sensors, etc. For a particular turbine, turbine rig test results are plotted in a turbine map. Based on such turbine maps a suitable turbine may be selected for a particular type of ICE. In one type of turbine map, a number of turbine speed lines may be plotted against a corrected flow and pressure ratios over the turbine. Such turbine speed lines may represent e.g. so-called reduced turbine rotational speeds, RPM _RE D. The corrected flow may be represented e.g. by a reduced mass flow, m' RED■ The standards SAE J 1 826 and SAE J922 relate to test procedures, nomenclature and terminology of turbochargers, and are incorporated herein by reference for further details of turbine maps and parameters related to turbochargers.

m' RED = m' ^* (T) ^1/2 / P , wherein m' is an actual mass flow rate through the turbine wheel, T is the exhaust gas temperature before the turbine wheel, and P is the exhaust gas pressure before the turbine wheel. In Fig. 7 a schematic example of a turbine map of turbine, such as a turbocharger is illustrated.

For a relevant turbine a normalised effective flow area, γ, may be defined as γ = A _T URB/V _M AX . Thus, the turbine wheel inlet area, A™, may be defined in relation to the maximum volume, VMAX, of the cylinder arrangement. Namely, ATURB = (ATIN/ATOT) ^* m' RED * (R/(K(2/(K + 1 ) ^X ))) ^1/2 , wherein X = (κ + 1 )/(κ -1 ). As mentioned above, A™, is the turbine wheel inlet area connected to the exhaust flow area, A _C YL, of a cylinder arrangement. The turbine may have more than one inlet area. Accordingly, Ατοτ is a total inlet area of the turbine, i.e. A™ and any additional turbine wheel inlet areas, ATINX, etc. (Ατοτ = A™ + ATINX + . . .) . R is the specific gas constant. An example value of R may be 287. κ = C _p / C _v , where C _p is the specific heat capacity at constant pressure of the exhaust gases and C _v is the specific heat capacity of the exhaust gases at constant volume. An example value of κ may be 1 .4 at a temperature of 293 K. ATURB may be obtained at a reduced mass flow, m' RED , of the turbine at e.g. 2.5 - 3.5 pressure ratio between an inlet side and an outlet side of the turbine and at a tip speed of e.g. 450 m/s of the turbine wheel. ATURB for a particular turbine may be obtained e.g. by extracting the reduced mass flow, m' RED , from a relevant turbine map for a turbine speed corresponding to the relevant tip speed at the relevant pressure ratio, and calculating ATURB with relevant data for the turbine and its operating conditions. Thereafter, γ may be calculated. According to embodiments herein γ > 0.22 m ^~1 .

According to some embodiments, the turbine 8 has a normalised effective flow area, γ, defined as γ = A _T URB/VMAX , wherein γ > 0.22 m ^~1 , wherein

ATURB = (Α™/Ατοτ) ^* m' _R ED ^* (R/(K(2/(K +1 ) ^x ))) ^1/2 , wherein X = (κ + 1 )/(κ -1 ), wherein Α _ΤΟ τ is a total inlet area of the turbine (8), and wherein ATURB is obtained at a reduced mass flow, m' RED , of the turbine 8 at 2.5 - 3.5 pressure ratio between an inlet side and an outlet side of the turbine 8 and at a tip speed of 450 m/s of the turbine wheel (27).

In such a turbine 8, energy from the exhaust gases passing the fast opening second valve 40 may be utilised. Accordingly, a low pressure drop may be provided as the second exhaust valve 40 opens and the exhaust gases are transferred through the second portion of the exhaust conduit 6 to the turbine 8, and the a large portion of the energy in the exhaust gases may be transformed into useful work as the exhaust gases expand over the turbine wheel of the turbine 8.

Fig. 8 illustrates a method 100 for controlling an ICE. The ICE may be an ICE 2 according to any aspect and/or embodiment discussed herein. Reference is therefore made to the above- discussed embodiments. The method 100 comprises, in sequence, steps of:

- opening 102 the exhaust valve 16,

- turning 104 the crankshaft 20 a predetermined crankshaft angle within a range of 10 - 90 degrees, and thereafter

- opening 106 the second valve 40 at a faster valve area opening speed than the exhaust valve 26.

In this manner, the pressure in the combustion chamber 23 and the exhaust conduit 6 upstream of the second valve 40 may be equalised, before the second valve 40 is opened at the fast valve area opening speed a predetermined crankshaft angle after the exhaust valve 26. According to a further aspect there is provided a computer program for performing a method for controlling an ICE 2 comprising instructions, which, when the program is executed by a computer, cause the computer to carry out the method 100 according to any aspect and/or embodiment discussed herein. The computer may for instance form a central processing unit of the control unit 54 discussed above.

According to a further aspect there is provided a computer-readable storage medium comprising instructions, which, when executed by a computer, cause the computer to carry out the method 100 according to any aspect and/or embodiment discussed herein. Again, the computer may be a central processing unit of the control unit 54 discussed above.

It is to be understood that the foregoing is illustrative of various example embodiments and that the invention is defined only by the appended claims. A person skilled in the art will realize that the example embodiments may be modified, and that different features of the example embodiments may be combined to create embodiments other than those described herein, without departing from the scope of the invention, as defined by the appended claims.